MACHINE DESIGN REVIEWER (LECTURE) Machine Design, Engineering Materials, Machine Shop Practice, and Manufacturing Process Revision 0 2012
Prepared By: Agerico U. Llovido – PME
CONTENTS A. PRESSURE VESSELS B. SHAFTS C. KEYS D. COUPLINGS E. FLYWHEELS F. SCREW FASTENINGS G. POWER SCREWS H. SPRING I.
BELTS
J.
CHAINS
K. WIRE ROPES L. SPUR GEARS M. HELICAL GEARS N. BEVEL GEARS O. WORM GEARS P. BRAKES Q. CLUTCHES R. BEARINGS S. RIVETED JOINTS T. WELDED JOINTS U. ENGINEERING MATERIALS V. MACHINE SHOP PRACTICE W. MANUFACTURING PROCESS
A. PRESSURE VESSEL - LECTURE
1. Thin-wall Pressure Vessel Thin-wall pressure vessel – is one whose plate thickness is small compared to the diameter of the vessel. The ratio t/Di is equal to or less than 0.1. 1.1
Circumferential tensile stress The fluid force acting on a longitudinal section of unit length is equal to pd, and for equilibrium of forces may be equated to the resisting force equal to 2tσt, where σt represents the circumferential, hoop, or tangential stress.
σt =
1.2
pDi 2t
Longitudinal tensile stress The fluid force acting on a ring section is equal to 1/4πDi2p and for equilibrium of forces may be equated to the resisting force πdtσl, where sl represents the longitudinal stress.
σl =
pDi 4t
Where σt = circumferential stress, psi σl = longitudinal stress, psi p = internal pressure, psi Di = internal diameter, in. t = wall thickness, in
1
A. PRESSURE VESSEL - LECTURE The formula above is also applicable to thin-wall sphere. 1.3
Joint efficiency or relative strength Joint strength is the ration of minimum strength of joint to the strength of solid plate. Minimum strength of jo int η= Strength of solid plate Then considering joint efficiency, Circumferential tensile stress pD σt = i 2tη Longitudinal tensile stress pD σl = i 4t pD σl = i 4tη
1.4
Factor of safety Factor of safety on specified material strengths is taken as 5.
2. Thick-Wall Cylinder Thick-wall cylinder – is one whose plate thickness is large compared to the diameter of the vessel. The ratio t/Di is greater than 0.1. 2.1 Lame’s formula Tangential stress, σt.
σt =
pi ri2 − po ro2 + ri 2ro2 (pi − po ) r 2 ro2 − ri2
Radial stress, σr,
σr =
pi ri 2 − po ro2 − ri2 ro2 (pi − po ) r 2 ro2 − ri2
Where: ro = outer radius of cylinder, in. ri = inner radius of cylinder, in. pi, po = internal and external pressure, respectively, psi t = wall thickness, ro – ri σt = tangential stress, psi σr = radial stress, psi Maximum tangential stress at the inside.
σt =
(
)
pi ro2 + ri 2 − 2po ro2 ro2 − ri2 2
A. PRESSURE VESSEL - LECTURE Maximum tangential stress at the outside.
σt =
(
2pi ri2 − po ro2 + ri 2 ro2 − ri2
)
Maximum shear stress at the inside surface.
τ=
ro2 (pi − po ) ro2 − ri2
Tangential and radial stress with zero value for the external pressure.
σt =
pi ri 2 ro2 1 + ro2 − ri 2 r 2
σr =
pi ri2 ro2 1 − ro2 − ri 2 r 2
Maximum tangential and radial stress with zero value for the external pressure.
σ t (max ) =
(
pi ro2 − ri2 ro2 − ri2
)
σ r (max ) = −p i
3
A. PRESSURE VESSEL - LECTURE 2.2
Maximum-normal-stress theory
2.3
σ t + pi t = ri − 1 σ −p t i Maximum-shear theory σs t = ri − 1 σ −p s i
Usually, σ s = 2.4
σt
2 Maximum-strain theory Birnie’s equation for open-end cylinders
σ t + (1 − µ )pi t = ri − 1 σ − (1 + µ )p t i Clavarino’s equation for closed-end cylinders σ t + (1 − 2µ )pi − 1 t = ri σ − (1 + µ )p t i
Where µ= poisson’s ratio 2.5
Maximum energy of distortion theory (Octahedral shear stress theory)
σt t = ri − 1 σ − 3p i t 2.6
Longitudinal stress
σl =
pi ri2 − po ro2 ro2 − ri2
For zero value of external pressure
σl =
pi ri 2 ro2 − ri2 -
End
4
-
B. SHAFTS - LECTURE 1. Definition A shaft is a rotating machine element which is used to transmit power from one place to another. The power is delivered to the shaft by some tangential force and the resultant torque (or twisting moment) setup within the shaft permits the power to be transferred to various machines linked up to the shaft. 2. Types of shafts 2.1 Axle – is a stationary member carrying rotating wheels, pulleys, etc. 2.2 Transmission shafts – transmit power between the source and the absorbing power. 2.3 Machine shafts – a shaft which is an integral part of the machine itself. The crank shaft is an example of machine shaft. 2.4 LIneshaft, or mainshaft is one driven by a primemover. 2.5 Countershafts, jackshafts, or headshafts – are shafts intermediate between a line shaft and a driven machine. 2.6 Spindles – are short shafts on machines. 3. Stresses in Shafts 3.1 Shear stresses due to the transmission of torque (i.e. due to torsional load). 3.2 Bending stresses (tensile or compressive) due to the forces acting upon machine elements like gears, pulleys etc. as well as due to the weight of the shaft itself. 3.3 Stresses due to combined torsional and bending loads. 4. Design of shafts 4.1 Strength 4.1.1 Shafts subjected to twisting moment only. 4.1.2 Shafts subjected to bending moment only. 4.1.3 Shafts subjected to combined twisting and bending moments. 4.1.4 Shafts subjected to axial loads in addition to combined torsional and bending loads. 4.2 Rigidity 4.2.1 Torsional rigidity 4.2.2 Lateral rigidity
5. Shafts Subjected to Twisting Moment Only
T τ = J r Where
T = Twisting moment (or torque) acting upon the shaft, J = Polar moment of inertia of the shaft about the axis of rotation, τ = Torsional shear stress, and d r = ; where d is the diameter of the shaft. 2
1
B. SHAFTS - LECTURE For solid shaft:
J=
π
×d 4
32 Then
π
T=
×τ × d 3
16 For hollow shaft: J=
π
[(d )
4
o
32 Then
− (di )4
]
(d o )4 − (d i )4 T = ×τ 16 do 6. Shafts Subjected to Bending Moment Only
π
M σb = I y
M = Bending moment, I = Moment of inertia of cross-sectional area of the shaft about the axis of rotation, σ b = Bending stress, and y = Distance from neutral axis to the outer-most fibre.
Where
For round solid shaft, π d I = × d 4 and y = 64 2 Then
π
M=
×σ b × d 3
32 For hollow shaft: I=
π
64 Then M=
[(d )
4
o
− (d i )4
]
(d )4 − (d i )4 π ×σ b o 16 do
7. Shafts Subjected to Combined Twisting Moment and Bending Moment 7.1 Maximum shear theory or Guest’s theory. It is used for ductile materials such as mild steel. 7.2 Maximum normal stress theory or Rankine’s theory. It is used for brittle materials such as cast iron. Maximum Shear Stress Theory 1 (σ b )2 + 4τ 2 τ max = 2
2
B. SHAFTS - LECTURE 2
π 16
2
32M 16T 16 + 4 3 = 3 3 πd πd πd
1 τ max = 2
[ M +T ] 2
2
×τ max × d 3 = M 2 + T 2
The expression
M 2 + T 2 is known as equivalent twisting moment and is denoted by Te .
Maximum Normal Stress Theory 1 1 σ b (max ) = σ b + (σ b )2 + 4τ 2 2 2 2
1 32M 1 σ b (max ) = × 3 + 2 πd 2
32M 16T π d 3 + 4 π d 3
(
2
)
1 2 2 2 M + M + T π 1 × σ b(max ) × d 3 = M + M 2 + T 2 32 2 1 The expression M + M 2 + T 2 is known as equivalent bending moment and is denoted by Me . 2
σ b (max ) =
32 π d3
)
(
)
(
8. Shaft Subjected to Fluctuating Loads
Te =
(K mM )2 + (Kt T )2
1 Me = K m M + 2 Where
(K mM )2 + (K t T )2
K m = Combined shock and fatigue factor for bending, and K t = Combined shock and fatigue factor for torsion.
3
B. SHAFTS - LECTURE
From Design of Machine Elements by V.M. Faires K σ σ σ es = ns σ ms + fs as for torsion SF σ ys
σe =
Kσ σn σ m + f a for bending SF σy
Where σ is a symbol for stresses. SF = size factor or load factors Maximum Shear Theory 1 2 1 σ e σ es = + N σ n 0.5σ n
2
2
von Mises-Hencky theory of failure (Octahedral shear theory) 1 2 2 2 1 σ e σ es = + N σ n 0.577σ n 9. Shaft Subjected to Axial Load in addition to Combined Torsion and Bending Loads
Resultant Stress M⋅y F σ1 = + I A 10. Design of Shafts on the basis of Rigidity 10.1 Torsional rigidity T ⋅L θ= J ⋅G 10.2 Lateral rigidity From strength of materials
4
B. SHAFTS - LECTURE d 2y M = dx 2 EI 11. Shaft Design by PSME Code/Machinery’s Handbook Allowable stresses: 27.6 MPa (4000 psi) for main power-transmitting shafts. 41.5 MPa (6000 psi) for lineshafts carrying pulleys. 58.7 MPa (8500 psi) for small, short shafts, counter shafts, etc.
IP Units Torque 63,000P T= N Diameter of solid shaft 5.1T D=3
σs
D=3
321,000P Nσ s
SI Units Torque 9.55 ×10 6 P T= N 6 10 P T=
ω
Diameter of solid shaft 5.1T D=3
σs
D=3 D=3
11.1
48.7 ×106 P Nσ s 5.1×106 P
ωσ s For main power-transmitting shafts. D 3N in IP units 80 D 3N P= in SI units 1.755 ×106 Where P = power transmitted, hp or kW N = angular velocity of the shaft in revolutions per minute (rpm). D = diameter of the haft, in or mm. For lineshafts carrying pulleys. D 3N P= in IP units 53.5 P=
11.2
5
B. SHAFTS - LECTURE D 3N in SI units 1.1738 ×10 6 11.3 For small, short shafts. D 3N P= in IP units 38 D 3N P= in SI units 0.837 ×10 6 12. Shaft Design by Machinery’s Handbook 12.1 Torsional deflection According to some authorities, the allowable twist in steel transmission shafting should not exceed 0.08 degree per foot length of the shaft. The diameter D(in.) of a shaft that will permit a maximum angular deflection of 0.08 degree per foot of length for a given torque T (in-lb) or for a given horsepower P can be determined from the formulas: D = 0.294 T P D = 4. 6 4 N Using metric SI units and assuming an allowable twist in steel transmission shafting of 0.26 degree per meter length, D = 2.264 T P D = 125.74 N Another rule that has been generally used in mill practice limits the deflection to 1 degree in a length equal to 20 times the shaft diameter. For a given torque or horsepower, the diameter of a shaft having this maximum deflection is given by: D = 0.13 T P D = 4. 03 N 12.2 For steel line shafting, it is considered good practice to limit the linear deflection to a maximum of 0.010 inch per foot of length. The maximum distance in feet between bearings, for average conditions, in order to avoid excessive linear deflection, is determined by the formulas: P=
L = 8.953 D 2 for shafting subject to no bending action except its own weight L = 5.23 D 2 for shafting subject to bending action of pulleys, etc. in which D = diameter of shaft in inches and L = maximum distance between bearings in feet. Pulleys should be placed as close to the bearings as possible. - end -
6
C. KEYS - LECTURE
1. Definitions Key - is a piece of mild steel inserted between the shaft and hub of the pulley to connect these together in order to prevent relative motion between them. It is always inserted parallel to the axis of the shaft. Keyway - is a slot or recess in a shaft and hub of the pulley to accommodate a key. 2. Types of Keys Flat key – is rectangular in section with the smaller dimension placed in a radial direction and they may or may not be tapered.
Square key – is square in section and may or may not be tapered. Round key – is circular in section and fit into holes drilled partly in the shaft and partly in the hub.
Barth key – is a square key with bottom two corners bevelled. Gib-head key - is a square or flat and tapered key with a head at one end known as gib head. It is usually provided to facilitate the removal of key.
Saddle key – is tapered and are either hollow with a radius of curvature slightly smaller than the shaft radius, or flat in which case they are assembled on a flat on the shaft. It is used without keyway on the shaft. Flat saddle key – is a taper key which fits in a keyway in the hub and is flat on the shaft.
1
C. KEYS - LECTURE Hollow saddle key – is a taper key which fits in a keyway in the hub and the bottom of the key is shaped to fit the curved surface of the shaft.
Woodruff key – is a key which fits into a semi-cylindrical seat on the shaft.
Feather key – is a key that allows the hub to move along the shaft but prevents rotation on the shaft.
Kennedy key – is a tapered square key, with or without gib heads, assembled with the diagonal dimension virtually in a circumferential direction. It is also called tangential key.
2
C. KEYS - LECTURE Rollpin – is a key driven or pressed into a hole that is small enough to close the slit, assembled in radial direction.
Splines – is a key made integral with the shaft which fits in the keyways broached in the hub.
3. Shearing and Crushing of the key Torque transmitted by the shaft, FD T= 2 63,000hp T= in-lb n P T= 2π n
Shearing stress 2T F τ= = wLD wL Crushing (Compressive) stress 2T 2F σc = = tLD tL Where D = shaft diameter w = width of key t = thickness of key F = tangential force T = torque
3
C. KEYS - LECTURE 4. Proportions of key The usual proportions of the square key are D w =t = 4 Typical hub lengths fall between 1.25D and 2.4D. For the same material and w = t = D/4, σ c = 2τ , L = 1.1571D.
-
End -
4
D. COUPLINGS - LECTURE
1. Definition Shaft couplings are used in machinery for several purposes, the most common of which are the following: a. To provide for the connection of shafts of units that are manufactured separately such as a motor and generator and to provide for disconnection for repairs or alternations. b. To provide for misalignment of the shafts or to introduce mechanical flexibility. c. To reduce the transmission of shock loads from one shaft to another. d. To introduce protection against overloads. e. To alter the vibration characteristics of rotating units. Note : A coupling is termed as a device used to make permanent or semi-permanent connection where as a clutch permits rapid connection or disconnection at the will of the operator. 2. Types of Shaft Couplings 2.1 Rigid Couplings Rigid coupling – is used to connect two shafts which are perfectly aligned. 2.1.1 Flange coupling - usually applies to a coupling having two separate cast iron flanges. Each flange is mounted on the shaft end and keyed to it. The faces are turned up at right angle to the axis of the shaft. One of the flange has a projected portion and the other flange has a corresponding recess.
2.1.2
Compression coupling utilizes two split cones which are drawn together by the bolts in order to produce a wedging action which tightens the parts of the coupling and the shafts.
2.2 Flexible Couplings Flexible coupling – is used to connect two shafts having both lateral and angular misalignment. 2.2.1 Oldham coupling Oldham coupling – is used to join two shafts which have lateral mis-alignment. 1
D. COUPLINGS - LECTURE
2.2.2
Universal (or Hooke’s) Coupling Universal or Hooke’s coupling – is used to connect two shafts whose axes intersect at a small angle. The inclination of the two shafts may be constant, but in actual practice, it varies when the motion is transmitted from one shaft to another.
2.2.3
Other flexible couplings Chain coupling, flexible disk coupling, gear type coupling, etc.
2
D. COUPLINGS - LECTURE 3. Stresses in Flange Coupling
Torque P FD T= = 2π n 2 Where F = total transmitted load on bolts D = diameter of bolt circle d = bolt diameter t = thickness n1 = number of bolts Fb = Force per bolts
Fb =
F n1
Shear stress in bolts F 4F τ = b = b2 As π d Compressive stress F σc = b td -
End -
3
E. FLYWHEELS - LECTURE 1. Definition of Flywheel A flywheel used in machines serves as a reservoir which stores energy during the period when the supply of energy is more than the requirement and releases it during the period when the requirement of energy is more than supply. A flywheel is a rotating member that acts as a storage reservoir for energy when work is not “consumed” at as fast a rate as the power is supplied.
2. Kinetic Energy, KE KE =
Iω 2 mv s2 = 2 2
(
)
(
)
(
)
I ω12 − ω 22 mk 2 ω12 − ω 22 m v s21 − v s22 = = 2 2 2 Where: I = mk2 = moment of inertia m = mass of flywheel = W/g r = radius of gyration ω1 = maximum angular velocity, rad/sec = 2pn1/60 ω2 = minimum angular velocity, rad/sec = 2pn2/60 vs1 = maximum speed = πDn1 vs2 = minimum speed = πDn2 ∆KE =
3. Coefficient of fluctuation, Cf Maximum fluctuation of speed - the difference between the maximum and minimum speeds during a cycle. Coefficient of fluctuation of speed - the ratio of the maximum fluctuation of speed to the mean speed. ω − ω 2 n1 − n2 v s1 − v s 2 Cf = 1 = = ω n vs Cf =
2(ω1 − ω 2 ) 2(n1 − n2 ) 2(v s1 − v s 2 ) = = ω1 + ω 2 n1 + n2 v s1 + v s 2
1
E. FLYWHEELS - LECTURE
4. Weight of Flywheel, W Engineers frequently neglect the effect of the hub and arms. W = πDbtρ Where D = mean diameter b = width of flywheel t = thickness of flywheel ρ = density of flywheel = 72,00 kg/m3 for cast-iron = 7,860 kg/m3 for steel Also
W=
g∆KE C f v s2
5. Stress in flywheel
σ = ρ v s2 Rules of thumb from experience specify the conventional limits of operation; 6000 fpm for cast iron and 10,000 fpm for cast steel.
6. Energy required for punching a metal 1 1 1 1 ∆KE = Ft = τ u At = τ u (π dt )t = τ u (π d )t 2 2 2 2 2 Where F = force required to punch a metal τu = ultimate shearing stress t = thickness of metal plate d = diameter of hole 7. Equations from Dynamics
ω=
θ
t ω = 2π n
α=
ω 2 − ω1 t 1 2
θ = ω1t + α t 2 -
End -
2
F. SCREW FASTENINGS - LECTURE 1. Screw Fastenings Screw fastening – is composed by a bolt and nut. Screw thread - is formed by cutting a continuous helical groove on a cylindrical surface.
2. Definitions
Major diameter – is the largest diameter of an external or internal screw thread. The screw is specified by this diameter. It is also known as outside or nominal diameter. Minor diameter – is the smallest diameter of an external or internal screw thread. It is known as core or root diameter. Pitch diameter – is the diameter of an imaginary cylinder, on a cylindrical screw thread, the surface of which would pass through the thread at such points as to make equal the width thread and the width of the spaces between the threads. It is also called an effective diameter. It is the mean diameter of major and minor diameters. Pitch – is the distance from a point on one thread to the corresponding point on the next. This is measured in an axial direction between corresponding points in the same axial plane. 1 Pitch = No. of threads per unit length of screw Lead – is the distance between two corresponding points on the same helix. It may also be defined as the distance which a screw thread advances axially in one rotation of the nut. Lead is equal to the pitch in case of single start thread, it is twice the pitch in double start, thrice the pitch in triple start and so on. Crest – is the top surface of the thread. Root – is the bottom surface created by the two adjacent flanks of the thread. Depth of thread – is the perpendicular distance between the crest and root. Flank – it the surface joining the crest and root. Angle of thread – is the angle included by the flanks of the thread. Slope – it is half the pitch of the thread.
1
F. SCREW FASTENINGS - LECTURE 3. Forms of screw threads
British standard Whitworth (B.S.W.) thread .
Unified standard thread.
.
Square thread.
British association (B.A.) thread.
Acme thread.
American national standard thread.
2
F. SCREW FASTENINGS - LECTURE Knuckle thread.
Buttress thread.
4. Basic profile of the thread.
5. Design profile of the nut and bolt.
3
F. SCREW FASTENINGS - LECTURE
6. Common Types of Screw Fastening a. Through bolt – a cylindrical bar with threads for the nut at one end and head at the other end. b. Tap bolt – a bolt screwed into a tapped hole of one of the parts to be fastened without the nut. c. Studs - a round bar threaded at both ends. One end of the stud is screwed into a tapped hole of the parts to be fastened, while the other end receives a nut on it, d. Cap screws - are similar to tap bolts except that they are of small size and a variety of shapes of heads are available. e. Machine screws - are similar to cap screws with the head slotted for a screw driver. These are generally used with a nut. f. Set screws – are used to prevent relative motion between two parts that tend to slide over one another. g. Coupling bolt – is finished all over, usually having coarse threads. h. Carriage bolt – is distinguished by a short potion of the shank underneath the head being square or finned or ribbed. i. Stove bolt – is a cheap variety of bolt made in small sizes. j. U-bolts – are in the form of U and are used as holding clamps, as on an automobile spring. k. Plow bolts – are widely used on farm machinery. l. Track bolts – are used in railway track construction. m. Lag screw – is used to fasten machinery and equipment to a wooden base. 7. Locking Devices a. Jam nut or lock nut b. Castle nut c. Sawn d. Penn, ring or grooved nut e. Locking with pin f. Locking with plate g. Spring lock washer 8. Design Stress:
σd =
σy 6
3 D < in 4
(As )12
3 σ d = 0.4σ y D > in
4
Where σy = yield strength of material, ksi σd = design tensile strength, ksi As = stress area, in2 D = nominal diameter, in. 9. Tightening stress, initial tension & tightening torque Tightening stress when proof stress available. σ i = 0.9σ p . Where σ p = proof stress
4
F. SCREW FASTENINGS - LECTURE Tightening stress when no proof stress σ i = 0.85σ y Initial tension = Fi = σ i As Tightening Torque = T = 0.2DFi 10. Elastic considerations Equivalent area of connected parts π π Ac = De2 − D 2 4 4
De = (Nut or head width across flats) +
h 2
kb ∆Fb = Fe k b + kc AE kc = c c L AbE b kb = L Bolts: kb Fe Ft = Fi + kb + kc Ft As Tube or connected parts: kc Fe Fc = Fi − k b + kc
σt =
Fc Ac For zero stress in the tube k +k Fo = b c Fi kc
σc =
5
F. SCREW FASTENINGS - LECTURE
11. Working Strength of Bolts (Machinery’s Handbook) The following empirical formula was established for the working strength of bolts used for packed joints or joints where the elasticity of a gasket is greater than the elasticity of the studs or bolts. W = σ t 0.55D 2 − 0.25D lbs where W = working strength of bolt or permissible load, in pounds, after allowance is made for initial load due to tightening; σt = allowable working stress in tension, pounds per square inch; and D = nominal outside diameter of stud or bolt, inches.
(
)
12. Set Screw Diameter of setscrew, d = 0.125D Power transmitted by a single set-screw Dnd 2.3 P= 50 Torque transmitted by a single set-screw T = 1250Dd 2.3 Where: P = horsepower transmitted, hp6. T = torque, in-lb D = shaft diameter, in n = speed, rpm d = set-screw diameter
- end -
6
G. POWER SCREWS - LECTURE
1. Definition Power screws (Translation screws) – are used to move machine parts against resisting forces, for instance, in a screw-operated tensile-testing machine, jack, press, or lead screw of a lathe. 2. Types of Screw Threads used for Power Screws 2.1 Square threads.
From Faires, Black and Adams. 7 h= p 16 2.2 Acme or Trapezoidal threads.
From Faires, h = 0.5p
2.3 Buttress threads.
From Faires, h = 0.663p
1
G. POWER SCREWS - LECTURE 3. Pitch and Lead Axial pitch or pitch – is the distance, measured axially, from a point on on ethread to the corresponding point on an adjacent thread. Lead – is the distance that a thread advances in one turn; it is the distance the nut moves along the axis in one turn. Lead angle – is the angle between a tangent to the pitch helix and a plane normal to the axis of the screw.
Pitch Pc = P =
1 No. of threads per inch
Lead Angle Lead λ = tan−1 π Dm
1 (Size + Dr ) 2 Where Dm is the mean thread diameter Dm =
4. Torque to turn screw For square thread Torque required to turn the thread against the load WDm WDm (tan λ + tan β ) WDm (tan λ + f ) = T= tan(β + λ ) = 2 2(1 − tan β tan λ ) 2(1 − f tan λ ) Torque required to turn the thread with the load WDm WDm (tan β − tan λ ) WDm ( f − tan λ ) T= tan(β − λ ) = = 2 2(1 + tan β tan λ ) 2(1 + f tan λ ) Where f = tanβ = coefficient of friction and β = angle of friction For Acme thread Torque required to turn the thread against the load
2
G. POWER SCREWS - LECTURE T=
WDm (cos φ tan λ + tan β ) WDm (cosφ tan λ + f ) = 2(cos φ − tan β tan λ ) 2(cos φ − f tan λ )
φ = pressure angle ≈ 14.5o Torque required to overcome collar friction: f W (Ro + Ri ) Tc = c 2 5. Efficiency of a square-thread screw
e=
ideal effort actual effort
Efficiency of square thread considering only the screw friction. tan λ tan λ (1 − f tan λ ) e= = tan(β + λ ) tan λ + f Efficiency of square thread considering screw friction and collar friction tan λ tan λ (1 − f tan λ ) e= = tan(β + λ ) fD tan λ + f + c c (1 − f tan λ ) Dm
Where Dc = Ro + Ri Efficiency of acme thread considering screw friction and collar friction tan λ (cosφ − f tan λ ) e= fD tan λ cosφ + f cos φ + c c (cos φ − f tan λ ) Dm 6. Condition for self-locking screw The condition for self-locking of a square thread is that β must be greater than λ, or that tan β (the coefficient of friction) must be greater than tan λ (the tangent of the lead angle). Self-locking Screw, β > λ Torque to lower the load WDm T= tan(β − λ ) 2 -
End -
3
H. SPRING - LECTURE 1. Definition SPRING – is defined as an elastic body, whose function is to distort when loaded and to recover its original shape when the load is removed. 2. Application: 2.1 To cushion, absorb or control energy due to either shock or vibration as in car springs, railway buffers, air-craft landing gears, shock absorbers and vibration dampers. 2.2 To apply forces, as in brakes, clutches and spring-loaded valves. 2.3 To control motion by maintaining contact between two elements as in cams and followers. 2.4 To measure forces, as in spring balances and engine indicators. 2.5 To store energy, as in watches, toys, etc. 3. Types of Springs (According to shapes) 3.1 Helical springs – are made up of a wire coiled in the form of a helix and is primarily intended for compressive or tensile loads. The cross-section of the wire from which the spring is made may be circular, square or rectangular. Forms of helical springs. 3.1.1 Compression helical spring 3.1.2 Tension helical spring
Closely coiled – when the spring is coiled so close that the plane containing each turn is nearly at right angles to the axis of the helix and the wire is subjected to torsion. Helix angle is usually less than 10 degrees. Open coiled – is coiled in such a way that there is a gap between the two consecutive turns, as a result of which the helix angle is large.
3.2 Conical and volute springs – are used in special applications where a telescoping spring or a spring with a spring rate that increases with the load is desired. The conical spring is wound with a uniform pitch whereas the volute springs are wound in the form of paraboloid with constant pitch and lead angles.
1
H. SPRING - LECTURE
3.3
Torsional springs – are springs that may be of helical or spiral type. Helical type – may be used only in applications where the load tends to wing up the spring and are used in various electrical mechanisms. Spiral type – is used where the load tends to increase the number of coils and when made of flat strip are used in watches and clocks.
3.4 Laminated or leaf springs (flat spring or carriage spring) – consist of a number of flat plates (known as leaves) of varying lengths held together by means of clamps and bolts.
2
H. SPRING - LECTURE 3.5 Disc or Belleville springs – consist of a number of conical discs held together against slipping by a central bolt or tube. These springs are used in applications where high spring rates and compact spring units are required. 3.6
Special purpose springs – these springs are air or liquid springs, rubber springs, ring springs etc.
4. Material for Helical Springs The springs are mostly made from oil-tempered carbon steel wires containing 0.60 to 0.70 per cent carbon and 0.60 to 1.0 per cent manganese. Music wire is used for small springs. Non-ferrous materials like phosphor bronze, beryllium copper, monel metal, brass etc., may be used in special cases to increase fatigue resistance and corrosion resistance. The helical springs are either cold formed or hot formed depending upon the size of the wire. Wires of small sizes (less than 10 mm diameter) are usually wound cold whereas larger size wires are wound hot. The strength of the wires varies with size, smaller size wires have greater strength and less ductility, due to the greater degree of cold working.
Severe service – means rapid continuous loading where the rate of minimum to maximum load (or stress) is one-half or less, as in automotive valve springs. Average service – includes the same stress range as in severe service but with only intermittent operation, as in engine governor springs and automobile suspension springs. Light service – includes springs subjected to loads that are static or very infrequently varied, as in safety valve springs.
5. Terms use in Compression Springs 5.1 Solid length – is the product of total number of coils and the diameter of the wire. 5.2 Free length – is the length of the spring in the free or unloaded condition. It is equal to the solid length plus the maximum deflection or compression of the spring and the clearance between the adjacent coils (when fully compressed).
3
H. SPRING - LECTURE 5.3 Spring index – is defined as the ratio of the mean diameter of the coil to the diameter of the wire. Spring index, C = D d Where D = Mean diameter of the coil, and d = Diameter of the wire. 5.4 Spring rate (stiffness or spring constant or spring scale) – is defined as the load required per unit deflection of the spring. Spring rate, k = F δ Where F = Load,and δ = Deflection of the spring. 5.5 Pitch – is defined as the axial distance between adjacent coils in uncompressed state. 6. End Connections for Compression Helical Springs
Inactive coils – part of the coil which is in contact with the seat and does not contribute to spring action. Active turns – turns which impart spring action.
4
H. SPRING - LECTURE
7. End Connections for Tension Helical Springs
5
H. SPRING - LECTURE 8. Stresses in helical springs of circular wire Helical compression spring. D = Mean diameter of the spring coil, d = Diameter of the spring wire, n = Number of active coils, G = Modulus of rigidity for the spring material, F = Axial load on the spring, τ = Maximum shear stress induced in the wire, C = Spring index = D d , p = Pitch of the coils, and δ = Deflection of the spring, as a result of an axial load W .
A.M. Wahl Equation:
τ =K×
8F ⋅ D 8F ⋅ C =K× 3 πd π d2
Where K =
4C − 1 0.615 + = Wahl’s stress factor 4C − 4 C
K = K S KC Where
K S = Stress factor due to shear, and K C = Stress concentration factor due to curvature.
6
H. SPRING - LECTURE 9. Deflection of Helical Springs of Circular Wire
11. Bodies with velocity
Angular deflection D F × (π D ⋅ n ) T ⋅l 16F ⋅ D 2 ⋅ n 2 θ= = = π J⋅G G ⋅d 4 × d 4G 32 Axial deflection 16F ⋅ D 2 ⋅ n D 8F ⋅ D 3 ⋅ n 8F ⋅ C 3 ⋅ n δ= × = = 2 G ⋅d G ⋅d 4 G ⋅d4
W 2 1 1 v = mv 2 = Fδ 2g 2 2
Stiffness of the spring or spring rate F G ⋅d 4 G ⋅d = constant = = δ 8D 3 ⋅ n 8C 3n
12. Energy of a spring 1 E = kδ 2 2
10. Impact load on spring (Free fall)
13. Spring in Series
1 W (h + δ ) = Fδ 2
1 1 1 1 = + + +L k k1 k2 k3 14. Spring in Parallel
k = k1 + k2 + k3 + L
- end -
7
I. BELTS - LECTURE 1. Definition The belts are used to transmit power from one shaft to another by means of pulleys which rotate at the same speed or at different speeds. 2. Types of Belts
2.1 Flat belt - is mostly used in the factories and workshops, where a moderate amount of power is to be transmitted, from one pulley to another when the two pulleys are not more than 8 metres apart. 2.2 V- belt - is mostly used in the factories and workshops, where a great amount of power is to be transmitted, from one pulley to another, when the two pulleys are very near to each other. 2.3 Circular belt or rope - is mostly used in the factories and workshops, where a great amount of power is to be transmitted, from one pulley to another, when the two pulleys are more than 8 metres apart. 3. Material used for Belts 3.1 Leather Oak-tanned leather is a standard material for flat belts. Chrome leather may be used where a very pliable material is desired. 3.2 Cotton or fabric belts. Most of the fabric belts are made by folding canvass or cotton duck to three or more layers (depending upon the thickness desired) and stitching together. 3.2 Rubber belts. Rubber belts are made in layers (say 3 to 12), called plies, of canvas duck impregnated with rubber which is later vulcanized. 3.3 V-belts. V-belts are made of fabric and cords molded in rubber and are generally covered with fabric. 4. General Belt Equation F1 − Fc F = e fθ (neglecting centrifugal tension, 1 = e fθ ) F2 − Fc F2 e fθ − 1 F1 − F2 = (F1 − Fc ) fθ e
Fc =
12 ρbv s2 wv s2 = go go
1
I. BELTS - LECTURE F1 = σbt 12 ρv s2 e fθ − 1 fθ F1 − F2 = bt σ − e 32 . 2 Where: F1 = is the maximum tension or the force on the approaching belt, lb. F2 = is the force on the receding side, lb. Fc = is the load on the belt due to the centrifugal force. Lb σ = design stress,psi. ρ = density of belt, lb/cu. in. for design, use ρ = 0.035 for leather and ρ = 0.045 lb for flat tuber belting. vs = speed in fps. f = coefficient of friction. θ = angle of contact’
5. Net Belt Pull and Horsepower Equation Net Belt Pull – is the difference of the forces F1 – F2. Horsepower Equation: (F − F )v (F − F )v hp = 1 2 m = 1 2 s hp 33,000 550 hp =
Tn hp 63,000
Where: vm = speed in fpm. T = torque in in-lb n = speed in rpm 6. Coefficient of Friction For normal design conditions for flat belts use the following: Leather on iron or steel, f = 0.3 Leather on paper pulley, f = 0.5 7. Strength of Leather belts For normal goof operating conditions and pulley sizes larger than the minimum, a design stress of σ d = 400η Where η is the relative strength of joint. η = 1.0 when joined by cementing; 0.88 by wire lacing; 0.35 by metal hook. 8. Belt speed. Experience suggest that the most economical designs are obtained for a belt speed of 4000 to 4500 fpm, but of course, any particular application may require some other speed.
2
I. BELTS - LECTURE 9. Length of Belts 9.1 Open Belt Drive.
L ≈ 2C + 1.57(D2 + D1 ) +
(D2 − D1 )2
4C Where; C is the center distance, D2 is the diameter of the larger pulley, D1 is the diameter of the smaller pulley 9.2 Crossed Belt Drive
L ≈ 2C + 1.57(D2 + D1 ) +
(D2 + D1 )2 4C
Where; C is the center distance, D2 is the diameter of the larger pulley, D1 is the diameter of the smaller pulley 10. Angle of Contact. For an open belt, the angles of contact are R −r D − D1 θ = π ± 2 sin−1 ≈π ± 2 radians C C Use the plus sign for the larger pulley and the minus sign for the smaller pulley. For crossed belts, the angles of contact are the same on both pulleys. 3
I. BELTS - LECTURE θ = π + 2sin −1
R+r radians C
Where: R = the radius (D2 = diameter) of the larger pulley, r = the radius (D1 = diameter) of the smaller pulley, C = the distance between pulley centers, and θ = the angle of contact in radians. In general, design equation used the minimum value of fθ, which is the smaller pulley when the pulleys are of the same materials. 11. Initial Tension. Initial tension (Fo) is tension at rest. Taylor’s recommendation is 71 lb/in. of width. 2 Fo = F1 + F2
12. Grade of Belting 12.1 Light drives. These are used to transmit small powers at belt speeds up to about 10 m/s as in agricultural machines and small machine tools. 12.2 Medium drives. These are used to transmit medium powers at belt speeds over 10 m/s but up to 22 m/s, as in machine tools. 12.3 Heavy drives. These are used to transmit large powers at belt speeds above 22 m/s as in compressors and generators. 13. Rated Capacity of Leather Belts (ALBA Tables or Table 17.1 and Table 17.2 by V.M. Faires). hp = (hp in K , Table 4 )(bC mC p )(C f 1C f 2 K)
Which is the nominal horsepower that the belt is to transmit (or the nameplate horsepower for an electric motor),and b in. is the belt width Cm is the correction factor for the type of drive; except for electric motors, use Cm = 1; Cp is the correction factor for the size of the smallest pulley; the smaller the pulleys, the greater is the flexure Cf is the correction factor for the environmental conditions, and more than one of these factors may be apply; thus a vertical drive in a dusty atmosphere and subjected to shock loads would correspond to a total factor of Cf = (0.83)(0.74)(0.71). 14. Law of Belting. “The approaching side must approach the pulley in a direction perpendicular to the pulley’s axis.”
4
I. BELTS - LECTURE 15. V-Belts. V-belt is mostly used in factories and workshops where a great amount of power is to be transmitted from one pulley to another when the two pulleys are very near to each other. 16. Standard Multiple V-Belt Dimension
Section A - b x t = ½ x 5/16 in, Dmin = 3 in. Section B – b x t = 21/32 x 13/32 in, Dmin = 5.4 in. Section C – b x t = 7/8 x 17/32 in, Dmin = 9 in. Section D – b x t = 1 ¼ x ¾ in, Dmin = 13 in. Section E – b x t = 1 ½ x 29/32 in 17. Rated Capacity of V-belts 10 3 0.09 c v m2 v m − Rated hp = a − e K d D1 10 6 10 3 v m where a, c, and e are constant for a particular belt section, D1 is the pitch diameter of the smaller sheave, Kd is a small-diameter factor for the given velocity ratio (Table 17.4, Faires or Table 3.5.7, PSME Code 2008 pg. 23), and vm fpm is the belt speed. Factors a, c and e for use in the above formula. (X, Y, and Z in PSME Code 2008, pg. 24) Regular Quality Belts (Used by Black and Adams book). Section A, a = 1.945, b = 3.801, e = 0.0136 Section B, a = 3.434, b = 9.830, e = 0.0234 Section C, a = 6.372, b = 26.948, e = 0.0416 Section D, a = 13.616, b = 93.899, e = 0.0848 Section E, a = 19.914, b = 177.74, e = 0.1222
Premium Quality Belts (Used by V.M. Faires Book) Section A, a = 2.684, b = 5.826, e = 0.0136 Section B, a = 4.737, b = 13.962, e = 0.0234 Section C, a = 8.792, b = 38.819, e = 0.0416 Section D, a = 18.788, b = 137.70, e = 0.0848 Section E, a = 24.478, b = 263.04, e = 0.1222 5
I. BELTS - LECTURE 18. V-Flat drive A V-flat drive is one using a small sheave and a larger diameter flat pulley. 19. Design Horsepower, Adjusted Rated Horsepower and Number of Belts Design Hp = Nsf(transmitted hp) Adjusted rated hp = KθKL (rated hp). Design hp No. of belts = Adjusted rated hp Use the next larger whole number. Where, Kθ = arc-of-contact factor (Table 17.5, Faires or Table 3.8, PSME Code 2008 pg. 25). KL = length correction factor (Table 17.5, Faires or Table 3.5.7, PSME Code 2008 pg. 24). 20. Minimum Center Distance D + D2 C= 1 + D1 or C = D2 2 whichever is larger 21. Center Distance Unknown B = 4L – 6.28(D2 + D1), we get C=
B + B 2 − 32(D2 − D1 )2 16
End -
-
6
J. CHAINS - LECTURE 1. General The chains are made up of number of rigid links which are hinged together by pin joints in order to provide the necessary flexibility for wrapping round the driving and driven wheels. These wheels have projecting teeth of special profile and fit into the corresponding recesses in the links of the chain as shown in Figure 1. The toothed wheels are known as sprocket wheels or simply sprockets. The sprockets and the chain are thus constrained to move together without slipping and ensures perfect velocity ratio. These chains are used for transmission of power, when the distance between the centers of shafts is short. These chains have provision for efficient lubrication.
2. Types of Power Transmission Chains 2.1 Block or bush chain. This type of chain was used in the early stages of development in the power transmission.
2.2 Bush roller chain. This consists of outer plates or pin link plates, inner plates or roller link plates, pins, bushes and rollers. A pin passes through the bush which is secured in the holes of the roller between the two sides of the chain. The rollers are free to rotate on the bush which protects the sprocket wheel teeth against wear. The pins, bushes and rollers are made of alloy steel.
1
J. CHAINS - LECTURE
2.3 Silent chain. A silent chain (also known as inverted tooth chain) is designed to eliminate the evil effects caused by stretching and to produce noiseless running. When the chain stretches and the pitch of the chain increases, the links ride on the teeth of the sprocket wheel at a slightly increased radius. This automatically corrects the small change in the pitch..
2
J. CHAINS - LECTURE
3. Terms and Definition 3.1 Pitch of chain (P) It is the distance between the hinge centre of a link and the corresponding hinge centre of the adjacent link.
3.2 Pitch circle diameter of chain sprocket (D). It is the diameter of the circle on which the hinge centers of the chain lie, when the chain is wrapped round a sprocket. 4. Designation of Roller Chains Chain no. Pitch
25
35
41
40
50
60
80
100
120
140
160
180
200
240
¼
3/8
½
½
5/8
¾
1
1¼
1½
1¾
2
2¼
2½
3
3
J. CHAINS - LECTURE 5. Tabulated Horsepower Ratings for Roller Chain Drives Refer to PSME Code 2008,, Table 3.11, page 27 and other references. 6. Types of Lubrication. Type I – manual lubrication – oil is applied periodically with a brush or spout can, preferably at least once every 8 hours of operation, (vmax = 300 fpm). Type II – drip lubrication – oil drops are directed between the link plate edges from a drip lubricator, (vmax = 1300 fpm). Type III – bath or disc lubrication – with bath lubrication the lower strand of chain runs through a sump of oil in the drive housing. The oil level should reach the pitch line of the chain at its lowest point while operating. With disc lubrication, the chain operates above the oil level. The disc picks up oil from the sump and deposits it onto the chain, usually by means of trough. (vmax = 2300 fpm). Type IV – oil stream lubrication – the lubricant is usually supplied by a circulating pump capable of supplying each chain drive with a continuous stream of oil. 7. Pitch and Pitch Circle Diameter
180 P = D sin N t Where: D = Diameter of the pitch circle, P = Pitch, and Nt = Number of teeth on the sprocket.
8. Velocity and Velocity Ratio of Chain Drives The velocity ratio of a chain drive is given by n N mw = 1 = 2 n2 N1 where n1 = Speed of rotation of smaller sprocket in r.p.m., n2 = Speed of rotation of larger sprocket in r.p.m., N1 = Number of teeth on the smaller sprocket, and N2 = Number of teeth on the larger sprocket. The average velocity of the chain is given by π Dn PNt n vm = ≈ fpm 12 12 where D = Pitch circle diameter of the sprocket in inches, and P = Pitch of the chain in inches. 4
J. CHAINS - LECTURE PNt = circumference of the sprocket.
9. Length of Chain and Centre Distance
The center distance for chain drives may of course be relatively short, but a minimum wrap of 120o is desirable; this condition is inevitably met when mw < 3. An average good center distance would be D2 + D1/2, where D2 is the pitch diameter of the larger sprocket, D1 of the smaller. The approximate length of chain is N2 + N1 (N 2 − N1 )2 + pitches , 2 40C Where C is in pitches. The length should be an even number of pitches to avoid using an offset link. This is the usual matter of adjusting chain length, center distance, and sprocket sizes so that everything fits. L ≈ 2C +
10. Center Distance for Given Length in mm or inches. P C = 2L − N 2 − N1 + (2L − N 2 − N1 )2 − 0.810(N 2 − N1 )2 8 11. Number of Teeth on the Smaller or Driving Sprocket or Pinion For very low speeds, the recommended minimum number of teeth on the smaller sprocket is Nmin = 12; for low speeds, Nmin = 17; for moderate speeds, Nmin = 21; for high speeds, Nmin = 25; for speed increasing drives, Nmin = 23. With odd tooth numbers on the smaller sprocket and an even number of pitches in the chain, the frequency of contact between a particular tooth and a particular roller is a minimum, presumable better distributing the wear. 12. Maximum Pitch 2
900 3 p≤ n Where p is the pitch in inches and n is the speed of the small sprocket.
5
J. CHAINS - LECTURE 13. Recommended Lubricant Viscosities. Temperature, F 20 to 40 40 to 100 100 to 120 120 to 140
Viscosity SAE 20 SAE 30 SAE 40 SAE 50
14. Determining the Number of Strands 14.1 For a given transmitted power, get the design power by multiplying it by the service factor. 14.2 Find the horsepower rating per strand from tables. 14.3 Divide the design horsepower by the horsepower rating per strand to get the number of strands. Use a certain factor as a function of the number of strands if any from tables.
-
End
6
-
K. WIRE ROPES - LECTURE
1. Definitions. 1.1 Wire Ropes – are made from cold-drawn wires that are first wrapped into strands; the strands are then wrapped into helices about a core or central elements, which is usually hemp or pulp. 1.2 Regular Lay – in which the wires and strands are twisted in opposite directions. 1.3 Lang Lay – in which the wires and strands are twisted in the same direction. 1.4 Non-preformed – the wires and strands are bent into place, resulting in high stresses in straight, unloaded rope. 1.5 Preformed – the individual strands having been mechanically shaped ahead of time into the helical configuration they have in the rope. 2. Construction of wire ropes. The construction is indicated by two numbers, the first giving the number of strands, the second the number of wires in each strands. Example: 6 x 19 wire rope has 6 strands each with 19 wires.
2.1 6 x7 – being made of heavy wire, provides maximum resistance to abrasion and wear. Used for haulages, rigging, guard rails. 2.2 6 x 19 – being a compromise of flexibility and wear resistance, is one of the most popular types. Uses, including all various cross sections: scraper and shovel cables, draglines, logging ropes, haulage, hoists. 2.3 6 x 37 – is an extra-flexible rope and therefore useful where abrasion is not severe and where relatively sharp bends must be tolerated. Used for winch lines, hawsers, overhead cranes, and hoists. 3. Wire rope materials. 3.1 Mild plow steel (IPS) – which has an ultimate strength of between 180 and 210 ksi, the higher values applying to the smaller wires 3.2 Plow steel (PS) – which has an ultimate strength of between 210 and 280 ksi, the higher values applying to the smaller wires 3.3 Improved plow steel (IPS) – which has an ultimate strength of between 240 and 280 ksi, the higher values applying to the smaller wires. 3.4 Traction – which has an ultimate strength of between 180 and 190 ksi, the higher values applying to the smaller wires 3.5 Iron, with lower carbon (about 0.1%) content (σu < 100 ksi). 3.6 Very-high-strength (VHS) – which has an ultimate strength of between 280 and 340 ksi, for premium jobs, about 15% stronger in rope form than IPS. 3.7 Others such as galvanized wire ropes in various steel grades of steel, phosphor bronze, stainless steel. 1
K. WIRE ROPES - LECTURE 4. Stress in wire rope. ED σb = w Ds Where, E = modulus of elasticity (3 x 104 ksi for steel) Dw = approximate wire diameter, in Ds = sheave diameter, in 5. Equivalent bending load Fb = σ b Am Where, Am = cross-sectional area of metal in each rope, in2. 6. Extension of the wire rope FL δ= AmE r Where, F = load , lb L = length of rope, in Er = modulus of the rope, ksi or psi 7. Factor of safety, N (static) F −F N= u b Ft Where, Fu = breaking strength, lb Fb = equivalent bending load, lb Ft = tensile force in the rope, lb 8. Recommended Factor of Safety (Static) Guys – 3.5 Miscellaneous hoisting equipment – 5 Haulage ropes, cranes, and derricks – 6 Small hoists – 7 Hot ladle cranes – 8 9. Factor of safety, N (fatigue) D D (p σ u )σ u N= r s 2Ft Where, Dr = rope diameter, in 2
K. WIRE ROPES - LECTURE Ds = sheave diameter, in p = bearing pressure per square inch of projected area of the rope on the sheave. p/σu = values taken from Figure 17.30 (Faires).
10. Properties of wire rope. (Table AT 28, Faires). 10.1 6 x 7 Wire Rope Approximate weight of rope, w lb. per ft. = 1.52Dr2 Minimum sheave diameter, Ds in. = 42Dr Desirable sheave diameter, Ds in. = 72Dr Wire diameter, Dw ≈0.111Dr Cross-section of area of metal, Am, sq. in. ≈ 0.38Dr2 Modulus of elasticity of the rope, Er, psi ≈ 13 x 106 psi 10.2 6 x 19 Wire Rope Approximate weight of rope, w lb. per ft. ≈ 1.6Dr2 Approximate weight of rope, w lb. per ft. ≈ 1.76Dr2 (IWRC) Minimum sheave diameter, Ds in. = 30Dr Desirable sheave diameter, Ds in. = 45Dr Wire diameter, Dw ≈0.067Dr Cross-section of area of metal, Am, sq. in. ≈ 0.4Dr2 Modulus of elasticity of the rope, Er, psi ≈ 12 x 106 psi Estimate of the ultimate strength in terms of Dr. VHS, Fu ≈ 48Dr2 tons. IPS, Fu ≈ 42Dr2 tons. PS, Fu ≈ 36Dr2 tons. MPS, Fu ≈32Dr2 tons. IWRC – multiply the values given by 1.075. 10.3 6 x 37 Wire Rope Approximate weight of rope, w lb. per ft. ≈ 1.55Dr2 Approximate weight of rope, w lb. per ft. ≈ 1.71Dr2 (IWRC) Minimum sheave diameter, Ds in. = 18Dr Desirable sheave diameter, Ds in. = 27Dr Wire diameter, Dw ≈0.048Dr Cross-section of area of metal, Am, sq. in. ≈ 0.4Dr2 Modulus of elasticity of the rope, Er, psi ≈ 12 x 106 psi 10.4 6 x 19 Traction Steel - Fu = (0.87)(Fu for MPS).
3
K. WIRE ROPES - LECTURE 11. Traction Drives
Maximum value of the ratio of the forces (at the point of limiting friction), with negligible centrifugal effects. F1 = e fθ F2 Values of f: Iron or steel sheave: greasy rope, 0.07; wet rope, 0.085; dry rope, 0.12 Wood-lined sheave: greasy rope, 0.14; wet rope, 0.17; dry rope, 0.235 Rubber- or leather-lined sheave: greasy rope, 0.205; wet rope, 0.4; dry rope, 0.495
4
L. SPUR GEARS - LECTURE 1. Gears Gears – are machine elements that transmit motion by means of successively engaging teeth. The gear drive is therefore positive, which gives it an advantage in motion-transmission performance over friction drives such as friction wheels and belts. 2. Definitions Spur gears – are toothed wheels whose tooth elements are straight and parallel to the shaft axis; they are used to transmit motion and power between parallel shafts. Pitch circle - It is an imaginary circle which by pure rolling action, would give the same motion as the actual gear. Pitch circle diameter - It is the diameter of the pitch circle. The size of the gear is usually specified by the pitch circle diameter. It is also called as pitch diameter. Pitch point – It is the point of tangency of the pitch circles. Pitch surface – It is the surface of the rolling discs which the meshing gears have replaced at the pitch circle. Addendum – It is the radial distance between the pitch circle and the addendum circle. Dedendum – It is the radial distance from the pitch circle to the root circle, that is, to the bottom of the tooth space. Addendum circle – It is the circle that bounds at the outer ends of the teeth. It is also called outside circle. Outside diameter – is the diameter of addendum circle. Dedendum circle – It is the circle that bounds the bottoms of the teeth. It is also called root circle. Whole depth (Total depth) – It is the radial distance between the addendum and the dedendum circle of a gear. It is equal to the sum of the addendum and dedendum. Working depth – It is radial distance from the addendum circle to the clearance circle. It is equal to the sum of the addendum of the two meshing gears. Clearance – It is the radial distance between the working-depth circle and the root circle; it is the dedendum minus the mating addendum. Tooth thickness – It is the width of the tooth measured along the pitch circle. Tooth space – It is the width of space between the two adjacent teeth measured along the pitch circle. Backlash - It is the difference between the tooth space and the tooth thickness, as measured on the pitch circle. 1
L. SPUR GEARS - LECTURE Face of the tooth – It is surface of the tooth between the pitch cylinder and the addendum cylinder. Top land – It is the surface of the top of the tooth. Flank – is the surface of the tooth between the pitch and root cylinders. Face width – It is the length of teeth in an axial direction. Bottom land – is the surface of the bottom of the tooth space. Profile – It is the curve formed by the face and flank of the tooth. Fillet radius – It is the radius that connects the root circle to the profile of the tooth. Pinion – the smaller of two meshing gears. Gears – the larger of two meshing gears. Path of contact – It is the path traced by the point of contact of two teeth from the beginning to the end of engagement. Length of the path of contact – It is the length of the common normal cut-off by the addendum circles of the wheel and pinion. Arc of contact – It is the path traced by a point on the pitch circle from the beginning to the end of engagement of a given pair of teeth. Arc of approach – It is the portion of the path of contact from the beginning of the engagement to the pitch point. Arc of recess – It is the portion of the path of contact from the pitch point to the end of the engagement of a pair of teeth. Angle of action – is the angle through which the gear turns from the time a particular pair of teeth come into contact until they go out of contact. Arc of action – subtends the angle of action. Angle of approach – is the angle through which the gear turns from the time a particular pair of teeth come in to come into contact until they are in contact at the pitch point. Angle of recess – is the angle through which the gear turns from the time a given pair of teeth are in contact at the pitch point until they pass out of mesh. 2
L. SPUR GEARS - LECTURE
Velocity ratio, mw –is the angular velocity of the driver divided by the angular velocity of the driven gear. Gear ratio, mg – is the number of teeth in the gear divided by the number of teeth in the pinion. Contact ratio, mc – the ratio of the length of arc of contact to the circular pitch. Base circle – is the circle from which the involute is generated. Degree of involute – is used to define the base circle for a particular pitch circle. Pressure angle or angle of obliquity – It is the angle between the common normal to two gear teeth at the point of contact and the common tangent at the pitch point. It is usually denoted by φ. The standard pressure angles are 14 1/2° and 20°.
3. Pitch Pitch – is a measure of the spacing, and usually also of the size, of the tooth. Circular pitch, Pc – is the distance in inches measured along the pitch circle from a point on one tooth to the corresponding point on an adjacent tooth. πD Pc = Ng 3
L. SPUR GEARS - LECTURE Diametral pitch, Pd – is the ratio of the number of teeth per inch of pitch diameter. Ng Pd = D Module – It is the ratio of the pitch circle diameter in mm to the number of teeth. It is usually denoted by mo. D mo = Ng Conversion from circular to diametral pitch Pc Pd = π Where, Ng = number of teeth D =diameter of the pitch circle Base pitch, Pb – (involute gearing only) – is the distance in inches measured along the base circle from a point on one tooth to the corresponding point on the adjacent tooth. It is also the distance between parallel profiles on adjacent teeth measured along the generating line. π Db π D cosφ Pb = = = Pc osφ Ng Ng Where, Db = the diameter of the base circle. D = the pitch diameter. Pitch angle – is the angle subtended by an arc on the pitch circle equal in length to the circular pitch. 4. Center Distance 1 C = (Dp + Dg ) 2 Where, Dp = diameter of pinion Dg = diameter of gear 5. Pitch-line speed π Dp np π Dg ng vm = = 12 12 Where, np = speed of pinion, rpm ng = speed of gear, rpm Dp = diameter of pinion, in Dg = diameter of gear, in vm = pitch-line speed, fpm 4
L. SPUR GEARS - LECTURE
6. Speed and gear ratio.
Speed ratio = Gear ratio =
np ng
Np Ng
Where, Np = number of teeth in the pinion Ng = number of teeth in the gear 7. Gear Tooth Proportions Full Depth Involute System (14 ½ deg, 20 deg, and 25 deg) Item Formula Addendum, a 1/Pd = Pc/π Clearance (min.) 0.25/Pd (0.157/Pd min.) Dedendum, d 1.25/Pd (1.157/Pd min.) Working Depth 2/Pd Whole Depth 2.25/Pd (2.157/Pd min.) Outside Diameter D + 2a
Stub-tooth system Item Formula Working depth 1.6/Pd Addendum, a 0.8/Pd Dedendum, d 1/Pd = Pc/π Clearance (min.) 0.2/Pd Whole Depth 1.8/Pd Pressure angle 20o
8. Transmitted Load Transmitted load – is the average transmitted load on the teeth. 33,000hp Ft = in English units. vm
Or Ft =
Power Pitch − line speed
5
L. SPUR GEARS - LECTURE 9. Normal and Separating Load F Normal load = Fn = t cos φ Separating load = Fr = Ft tanφ Where φ = pressure angle. 10. Face width 2.5Pc < b < 4Pc or
8 12.5
11. Strength of Gear Teeth (Lewis Equation) σ bY Fs = K f Pd Where, σ = design stress or endurance strength, psi b = face width, in Y = Lewis form factor Pd = diametral pitch Kf = strength reduction factor 12. Dynamic Load as a function of velocity only (metal teeth) For commercially cut, vm ≤ 2000 fpm. 600 + v m Fd = Ft lb 600 For carefully cut, 1000 < vm < 4000 fpm. 1200 + v m Fd = Ft lb 1200 For precision cut, vm > 4000 fpm Fd =
78 + v m
Ft lb 78 If the speed is over 2000 fpm, carefully cut teeth should be used; if the speed is more than 4000 fpm, the teeth should generally be precision cut. Use the above equation if for horsepower less than 20 hp. Fs ≥ Fd 13. Buckingham’s Average Dynamic Load for metal. 0.05v m (bC + Ft ) Fd = Ft + lb 1 0.05v m + (bC + Ft ) 2 Where vm = is the pitch line speed, fpm 6
L. SPUR GEARS - LECTURE Ft = is the transmitted load, lb b = is the face width, in C = is a function of the amount of the effective error and of the elasticity of the gear materials. kE g E p C= Eg + E p k = 0.107e for 14 ½ deg full-depth teeth k = 0.111e for 20 deg full-depth teeth k = 0.115e for 20 deg stub teetj e = effective or composite tooth error. Eg and Ep = are the modulii of elasticity of the materials of the gear and pinion Use the above equation if for horsepower more than 20 hp. Fs ≥ Fd
14. Limiting Wear Load Fw = DpbQK g σ 2 sinφ 1 1 + K g = 1.4 E p E g 2Dg 2Ng 2 mg Q= = = Dg + Dp Ng + N p mg + 1 Where; σ = surface endurance strength, psi Dp = diameter of pinion, in b = face width, in Kg = is a material factor Fw ≥ Fd 15. Intermittent and Continuous service For intermittent service: Fs ≥ Fd For continuous service: Fs ≥ Fd and Fw ≥ Fd 16. Internal gear Center distance, C =
1 (Dg − Dp ) 2
Fw = DpbQK g
σ 2 sinφ 1 1 + K g = 1.4 E p E g 2Dg 2Ng 2 mg Q= = = Dg − Dp Ng − N p mg − 1
7
M. HELICAL GEARS - LECTURE 1.
Definitions Helical gears – are toothed wheels whose tooth elements are cut in the form of a helix about an axis of rotation and are used to connect parallel shafts. Herringbone gears – are double helical gears consisting of right-hand and left-hand helices to absorb the axial thrust within the gear and are used to connect parallel shafts. Crossed helical gears – helical gears mounted on non-parallel shafts.
2. Helix angle and face width
Helix angle, ψ – is the angle between a tangent to the pitch helix and an intersecting axial element of the pitch cylinder. Base helix angle, ψ b – is the angle between a tangent to the base helix and an element of the base cylinder (which contains the base circles). Face contact ratio – is the advance of the tooth in the line of face width divided by the circular pitch. Face width, b: b ≥ 2Pa, bmin = 1.15Pa Where Pa is the axial pitch. 3. Pitches The pitch of a helical gear is the pitch in the diametral (transverse) plane, Pc for circular pitch, Pd for diametral pitch. Normal circular pitch, Pcn – is the distance between the teeth measured on the pitch surface along a normal to the helix. π D cosψ P Nt Pcn = Pc cosψ = and Pdn = d = Nt cosψ D cosψ Where Pdn Is the normal diametral pitch and Nt is the number of teeth. Axial pitch, Pa – is the distance between corresponding points on adjacent teeth measured in an axial direction. P πD π Pa = c = = tanψ Nt tanψ Pd tanψ 4. Pressure angles (Relationship) tanφn = tanφ cosψ
Where: φn = pressure angle in the normal plane. 1
M. HELICAL GEARS - LECTURE φ = pressure angle in the diametral plane. ψ = helix angle
5. Dynamic load for helical gears (vm < 5000 fpm). Fd = Ft +
( ) + (F + Cb cos ψ )
0.05v m Ft + Cb cos 2 ψ 0.05v m
2
12
lb
t
Where symbols have the usual meaning. 6. Strength of helical teeth σ bY FS = lb K f Pdn Where symbols have the usual meaning. Y is chosen in accordance with the equivalent (also called formative or virtual) number of teeth Ne. N Ne = cos 3 ψ 7. Limiting wear load bD QK Fw = p 2 g lb cos ψ Where symbols have the usual meaning. Kg =
σ 2 sinφn 1 1. 4
E p
+
1 Eg
8. Axial load Fa = Ft tanψ 9. Crossed helical gears The shafts can be at any angle Σ, but 90o is the most common. For same hands, Σ = ψ 1 +ψ 2 For opposite hands, Σ = ψ 1 −ψ 2 And N1 =
π D1 cosψ 1 Pcn
, N2 =
π D2 cosψ 2 Pcn
, mw =
n1 ω1 N 2 D2 cosψ 2 = = = n2 ω 2 N1 D1 cosψ 1
o
For Σ = 90 . cosψ 2 = cos(90 −ψ 1 ) = sinψ 1 , cosψ 1 = cos(90 −ψ 2 ) = sinψ 2 Then mw =
ω1 D2 sinψ 1 D2 tanψ 1 D2 = = = ω 2 D1 cosψ 1 D1 D1 tanψ 2
10. Efficiency of crossed helical gears. For Σ = 90o. cos φn − f cotψ 1 e= cos φn + f tanψ 1 2
N. BEVEL GEARS - LECTURE 1. Definition. Bevel Gears – are used to connect intersecting shafts, usually but not necessarily at 90o. 2. Terms used in Bevel Gears
Pitch cone – It is a cone containing the pitch elements of the teeth. Cone center – It is the apex of the pitch cone. It may be defined as that point where the axes of two mating gears intersect each other. Pitch angle – It is the angle made by the pitch line with the axis of the shaft. Cone distance – It is the length of the pitch cone element. It is also called as a pitch cone radius. Addendum angle – It is the angle subtended by the addendum of the tooth at the cone centre. Dedendum angle – It is the angle subtended by the dedendum of the tooth at the cone centre. Face angle – It is the angle subtended by the face of the tooth at the cone center. The face angle is equal to the pitch angle plus addendum angle. Root angle – It is the angle subtended by the root of the tooth at the cone center. It is equal to the pitch angle minus dedendum angle. Back (or normal) cone – It is an imaginary cone, perpendicular to the pitch cone at the end of the tooth. 1
N. BEVEL GEARS - LECTURE
Back cone distance – It is the length of the back cone. It is also called back cone radius. Backing – It is the distance of the pitch point from the back of the boss, parallel to the pitch point of the gear. Crown height – It is the distance of the crown point from the cone centre, parallel to the axis of the gear. Mounting height – It is the distance of the back of the boss from the cone centre. Pitch diameter – It is the diameter of the largest pitch circle. Outside or addendum cone diameter – It is the maximum diameter of the teeth of the gear. It is equal to the diameter of the blank from which the gear can be cut. 3. Types of Bevel Gears Straight bevel gears – are whose tooth profiles consist of straight elements that converge to a point at the cone center. Spiral bevel gears – are those having curved oblique teeth on which contact begins gradually and continues smoothly from end to end. Zerol bevel gears – whose teeth are curved but lie in the same direction as the teeth of straight bevel gears. Hypoid gears – resembles spiral bevel gears except that the shaft axes are offset, not intersecting. Instead of pitch cone, the pitch surface is a hyperboloid. Miter gears – are pair of bevel gears of the same size that are on shafts intersecting at right angles. They are equal in pitch angle. Angular gears – are bevel gears mounted on intersecting shafts at angles of other than 90o. Crown gear s – are bevel gears in which the pitch angle is 90o; that is the pitch cone has become a plane. 4. Proportions for Bevel Gear The proportions for the bevel gears of gear ratio of 1 may be taken as follows: Addendum, a = 1/Pd Dedendum, d = 1.2/Pd Clearance = 0.2/Pd Working depth = 2/Pd Thickness of tooth = 1.5708/Pd 5. Pitch angle γ. 2
N. BEVEL GEARS - LECTURE The pitch angle γ is computed as follows (Σ = angle between shafts): Ng 1 tan γ p = Σ = 90o tan γ g = = mg mg Np Σ < 90o
tan γ g =
mg sin Σ sin Σ = N p Ng + cos Σ 1 + mg cos Σ
tan γ p =
1 mg
Where the pitch angle of the pinion γp is equal to Σ – γg; Np denotes the number of teeth on the pinion, Ng the number of teeth on the gear. 6. Addendum and dedendum angle. addendum Addendum angle, α = tan−1 cone distance
Dedendum angle,
δ = tan−1
dedendum cone distance
7. Strength of Straight Bevel-Gear Teeth (Kf negligible). b b2 1 − + 2 Pd L 3L When b ≤ L 3 Fs =
Fs =
σ Yb
σ Yb(L − b) Pd L
The value of Y is chosen in accordance with the equivalent (also called formative or virtual) number of teeth Ne. Equivalent number of teeth for the pinion. 2rpLPd Nep = 2rbPd = rg Equivalent number of teeth for the gear. 2rg LPd Neg = rp
(
Where, rb L = rp rg , L = rp2 + rg2
)
12
8. Dynamic Load for Generated Bevel Gears. Fd = (VF )N sf K mFt Where, Ft = 33,000 hp/vm = the transmitted load, lb vm = πDn = the pitch-line speed at the large end, fpm Km = load distribution factor Nsf = service factor VF = velocity factor For straight, 3
N. BEVEL GEARS - LECTURE 50 + v 1m2 50 For bevel, VF =
78 + v1m2 VF = 78
12
9. Rated Strength of Bevel Gears. σ bJ K l Fs = d Pd K s K t K r Where, Ks = size factor according to pitch Kl = life factor for strength Kt = temperature factor Kr = reliability factor J = geometry factor for strength σd = design flexural stress b = face width Pd = pitch at the large end 10. Rated Wear Load for Bevel Gears.
σ cd2 C l
2
Fw = Dp bI 2 C e K t C r Where, Dp = pitch diameter of the pinion b= face width σcd = design contact stress Cl = life factor for wear Cr = reliability factor for wear I = geometry factor for wear Ce = elastic coefficient given by 1.5 π C e2 = 2 1 − µ p E p + 1 − µ g2 E g
(
)
(
)
4
O. WORM GEARS - LECTURE 1. Definition. Worm gears – are widely used for transmitting power at high velocity ratios between non-intersecting shafts that are generally, but not necessarily, at right angles. 2. Terms used in Worm Gearing Axial pitch – It is also known as linear pitch of a worm. It is the distance measured axially (i.e. parallel to the axis of worm) from a point on one thread to the corresponding point on the adjacent thread on the worm. Lead – It is the linear distance through which a point on a thread moves ahead in one revolution of the worm. For single start threads, lead is equal to the axial pitch, but for multiple start threads, lead is equal to the product of axial pitch and number of starts. Lead angle – It is the angle between the tangent to the thread helix on the pitch cylinder and the plane normal to the axis of the worm. Tooth pressure angle – It is measured in a plane containing the axis of the worm and is equal to one-half the thread profile angle. Normal pitch – It is the distance measured along the normal to the threads between two corresponding points on two adjacent threads of the worm. Helix angle – It is the angle between the tangent to the thread helix on the pitch cylinder and the axis of the worm. Velocity ratio – It is the ratio of the speed of worm in r.p.m. to the speed of the worm gear in r.p.m. 3. Pitch and Lead
1
O. WORM GEARS - LECTURE Pa = Pc Pcn = Pa cos λ = Pc cos λ
tan λ =
Lead L = π Dw π Dw
λ +ψ w = 90o
λg +ψ = 90o If the shaft angle is 90o. λ = ψ , λg = ψ w L = Nt Pa
mw =
Ng Nt
=
Dg cos λ Dw sin λ
=
Dg Dw tan λ
Where Pa = axial pitch Pc = circular pitch Pcn = normal pitch λ = lead angle of the worm thread ψw = helix angle of the worm thread λg = lead angle of the gear ψ = helix angle of the gear Dw = diameter of the worm Dg = diameter of the gear L = lead Nt = number of threads (or starts) on the worm Ng = number of teeth on the gear mw = velocity ratio 4. Relation of normal and diametral pressure angle. tanφn = tanφ cos λ Where φ = diametral pressure angle φn = normal pressure angle 5. Strength of Worm-Gear Teeth. The Lewis equation without Kf is usually applied. σ Yb σ YbPcn Fs = = Pdn π 6. Dynamic Load for Worm Gears. 1200 + v mg Ft lb Fd = 1200 2
O. WORM GEARS - LECTURE Ft =
33,000hp v mg
Where, Ft – is the transmitted load, lb. hp – is the output power. vmg – is the pitch-line speed of the gear, fpm. 7. Wear Load for Worm Gears. Fw = Dg bK w Where, Dg – is the pitch diameter of gear, in b – is the effective face width, in Kw – is the material factor. 8. Efficiency of Worm Gearing. cos φn cos λ − f sin λ cos φ n − f tan λ e = tan λ = tan λ cos φ n sin λ + f cos λ cos φn tan λ + f
9. Coefficient of Friction for Worm Gearing (Bronze Gear). For 3 < vr < 70 fpm 0.155 f = 0.2 vr For 70 < vr < 3000 fpm 0.32 f = 0.36 vr Where, vr = rubbing speed. π Dw nw vr = 12 cos λ 10. Driving force on the worm gear. 33,000hp Ft = v mg 11. Driving force on the worm. cos φn sin λ + f cos λ Wt = Ft = cos φ n cos λ − f sin λ 12. Separating force between worm and gear. Ft sinφn Wt sinφ n S= = cos φ n cos λ − f sin λ cos φn sin λ − f cos λ
3
P. BRAKES - LECTURE 1. Definition. Brakes – are friction devices used to regulate the motion of bodies (slowing them down, holding their speed constant, holding them at rest, etc. Single block or shoe brake – consists of a block or shoe which is pressed against the rim of a revolving brake wheel drum. Double Block or Shoe Brake – consists of two brake blocks applied at the opposite ends of a diameter of the wheel which eliminate or reduces the unbalanced force on the shaft. Band brake – consists of a flexible band of leather, one or more ropes, or a steel lined with friction material, which embraces a part of the circumference of the drum. Simple band brake – in which one end of the band is attached to a fixed pin or fulcrum of the lever while the other end is attached to the lever at a distance from the fulcrum. Differential band brake – in which the tension in the band assists in applying the brake. 2. Types of Brakes The brakes, according to the means used for transforming the energy by the braking element, are classified as : 1. Hydraulic brakes e.g. pumps or hydrodynamic brake and fluid agitator, 2. Electric brakes e.g. generators and eddy current brakes, and 3. Mechanical brakes. The mechanical brakes, according to the direction of acting force, may be divided into the following two groups : a. Radial brakes. In these brakes, the force acting on the brake drum is in radial direction. The radial brakes may be sub-divided into external brakes and internal brakes. According to the shape of the friction element, these brakes may be block or shoe brakes and band brakes. b. Axial brakes. In these brakes, the force acting on the brake drum is in axial direction. The axial brakes may be disc brakes and cone brakes. The analysis of these brakes is similar to clutches.
3. Pivoted Block or Shoe Brake
1
P. BRAKES - LECTURE The braking torque for a pivoted block or shoe brake (i.e. when 2θ > 60°) is given by
D 4 sinθ T = fP 2 2θ + sin 2θ Tangential frictional force, 4 sinθ F = fP 2θ + sin 2θ From the equilibrium of forces A(a + b ) − Pb − Fc = 0 T=
f ′AD(a + b ) 2(b + f ′c )
Where, P = operating force on block in radial direction. D = diameter of wheel. T = torque on wheel. θ = one-half angle of contact surface of block b = width of wheel f = coefficient of friction for materials of block and wheel f’ = equivalent coefficient of friction p = pressure between block and wheel A = applied force to produce a particular braking force F.
4. Simple Band brake
ΣMo = F1 (0) + F2 a − A(a + b ) = 0
For clockwise rotation, F1 > F2. F1 = e fθ F2 Torque on the brake wheel D T = (F1 − F2 ) 2 Relation between the force on the operating lever and the torque on the brake wheel 2
P. BRAKES - LECTURE A=
2Ta D(a + b) e fθ − 1
(
)
For clockwise rotation, F2 > F1. Exchange location of F1 and F2 in the figure. 5. Differential Band Brake
Summation of moments equals to zero. A(a + b ) − aF2 + cF1 = 0
aF2 − cF1 a+b For clockwise rotation, F1 > F2. F1 = e fθ F2 A=
Then,
A=
F1 a −c a + b e fθ
3
Q. CLUTCHES - LECTURE 1. Definition. Clutch – is a machine member used to connect a driving shaft to a driven shaft so that the driven shaft may be started or stopped at will, without stopping the driving shaft. Clutch – is a friction devices used to connect shafts (speeding up the driven bodies to the same angular velocity as the driving shaft). 2. Types of clutches 2.1 Positive clutches – are used when a positive drive is required. Jaw clutch – permits one shaft to drive another through a direct contact of interlocking jaws. It consists of two halves, one of which is permanently fastened to driving shaft by a sunk key. The other half of the clutch is movable and it is free to slide axially on the driven shaft, but it is prevented from turning relatively to its shaft by means of feather key. 2.2 Friction clutches – has its principal application in the transmission of power of shafts and machines which must be started and stopped frequently. 3. Types of Friction Clutches 3.1 Disc or plate clutches (single disc or multiple disc clutch), Single disc or plate clutch – consists of a clutch plate whose both sides are faced with a frictional material.
Multiple disc clutch - may be used when a large torque is to be transmitted.
1
Q. CLUTCHES - LECTURE
3.2 Cone clutches, Cone clutches – consists of one pair of friction surface only. In a cone clutch, the driver is keyed to the driving shaft by a sunk key and has an inside conical surface or face which exactly fits into the outside conical surface of the driven.
3.3 Centrifugal clutches. Centrifugal clutches – are usually incorporated into the motor pulleys. It consists of a number of shoes on the inside of a rim of the pulley.
2
Q. CLUTCHES - LECTURE 4. Torque and Power 2π Tn Power = 60 Where T = is the torque transmitted, n =speed in rpm. For English units: Tn hp = 63,000 Where T = is torque transmitted in in-lb, n = speed in rpm. 5. Multiple Disc Clutch
For new clutches and rigid mountings (uniformly distributed pressure). Np f P D 3 − d 3 T= = N p f Prf 3 D2 − d 2 Friction radius 1 D3 − d 3 3 D2 − d 2 For worn clutch plates (uniform axial wear). Np f P T= (D + d ) = Np f Prf 4 Friction radius 1 rf = (D + d ) 4 Where, T = torque transmitted Np = number of pairs of mating friction surfaces = 1 for single disc cluth f = coefficient of friction D , d = outer and inner diameter rf = friction radius 6. Cone clutches Fig. 17-7 B and A f P(D + d ) f Pr f T= = 4 sinα sinα 1 rf = (D + d ) 4 rf =
3
R. BEARINGS - LECTURE 1. Definition. Bearing – a machine element which support another moving machine element. It permits a relative motion between the contact surfaces of the members, while carrying the load. 2. Classification of Bearings 2.1 Depending upon the direction of load to be supported 2.1.1 Radial bearings – where the load acts perpendicular to the direction of motion of the moving element. 2.1.2 Thrust bearings - where the load acts along the axis of rotation. 2.2 Depending upon the nature of contact. 2.2.1 Sliding contact bearings – where the sliding takes place along the surfaces of contact between the moving element and the fixed element. 2.2.2 Rolling contact bearings – where the steel balls or rollers are interposed between the moving and fixed elements. The balls offer rolling friction at two points for each ball or roller. 3. Common Types of Sliding Contact Bearings 3.1 Journal, or sleeve, bearing. Journal bearings – are used to furnish lateral support to rotating shafts. The journal is the part of the shaft that runs in the bushing or sleeve. 3.2 Full journal bearing. Full journal bearing –where the angle of contact of the bushing with the journal is 360o. 3.3 Partial journal bearing Partial journal bearing – where the angle of contact of bushing the journal is 180o or less, 120o being a common value. 3.4 Clearance bearing Clearance – refers to the thickness of the space allowed for the lubricant that separates the parts having relative motion. Clearance bearing – is one which the radius of the journal is less than the radius of the bushing. 3.5 Fitted bearing Fitted bearing – is one in which the radius of the journal and bushing are equal. 3.6 Thrust bearing Thrust bearing – a bearing designed to support an axial load. 3.6.1 Step bearing – in which the end of the shaft is in contact with a bearing surface. 3.6.2 Collar bearing – in which a collar is attached to or formed integral with the shaft. 3.6.3 Pivoted-segment bearing – was developed in order to provide a converging film in a thrust bearing. 4. Properties of Lubricants 4.1 Viscosity - is the measure of degree of fluidity of a liquid. It is a physical property by virtue of which an oil is able to form, retain and offer resistance to shearing a buffer film-under heat and pressure. The viscosity of the lubricant is measured by Saybolt universal viscometer. It determines the time required for a standard volume of oil at a certain temperature to flow under a certain head through a tube of standard diameter and length. The time so determined in seconds is the Saybolt universal viscosity. In order to convert Saybolt universal viscosity in seconds to absolute viscosity (centipoise), the following formula may be used: 1
R. BEARINGS - LECTURE 180 Z = SG 0.22 S − S Where Z = is the absolute viscosity at temperature t, centipoises S = Saybolt Universal viscosity, sec SG = specific gravity at temperature t Viscosity conversion: 6.9 x 106 centipoises = 1 reyn = 1 lb-sec/in2. 4.2 Specific gravity (SG) – this property has no relation to lubricating value but is useful in changing the kinematic viscosity to absolute viscosity. Mathematically Absolute viscosity in centipoises = SG x kinematic viscosity in centistokes SGt = SG60 − 0.00035(t − 60) Where: SGt = specific gravity at temperature t SG60 = specific gravity at temperature 60 F t = temperature of oil 4.3 Viscosity index – is used to denote the degree of variation of viscosity with temperature. 4.4 Flash point – is the lowest temperature at which an oil gives off sufficient vapor to support a momentary flash without actually setting fire to the oil when a flame is brought within 6 mm at the surface of the oil. 4.5 Fire point – is the temperature at which an oil gives off sufficient vapor to burn it continuously when ignited. 4.6 Pour point or freezing point – is the temperature at which oil will cease to flow when cooled. 5. Terms used in Hydrodynamic Journal Bearing Figure 11.6 (Faires) 5.1 Diametral clearance, cd - is the difference between the diameters of the bearing and the journal. 5.2 Radial clearance, cr – is the difference between the radii of the bearing and the journal. c cr = d 2 5.3 Diametral clearance ratio – is the ratio of the diametral clearance to the diameter of the journal. c c = d = r D r 5.4 Eccentricity, e – is the radial distance between the centre of the bearing and the displaced centre (O′) of the bearing under load. c e = d − ho = cr − ho 2 5.5 Minimum oil film thickness - is the minimum distance between the bearing and the journal, under complete lubrication condition. It is denoted by ho and occurs at the line of centres as shown in Fig. 26.7. Its value may be assumed as cd / 4. 2
R. BEARINGS - LECTURE 5.6 Attitude or eccentricity ratio, ε. It is the ratio of the eccentricity to the radial clearance. e c −h h 2h ε = = r o =1− o =1− o cr cr cr cd 5.7 Short and long bearing. If the ratio of the length to the diameter of the journal (i.e. L / d) is less than 1, then the bearing is said to be short bearing. On the other hand, if L / d is greater than 1, then the bearing is known as long bearing.
6. Dimensional Analysis
µn r ho = φ s cr p c r
2
= φ (S )
Coefficient of friction
µn r D r f = f = φ s cd cr p cr
2
= φ (S )
Where,
φ = is used to mean a function of ho = minimum fim thickness, in. cr = radial clearance, in. cd = diametral clearance, in.
µ = absolute viscosity, reyns or lb-sec/in2. ns = angular speed of the journal, rps r = journal radius, in. D = journal diameter, in. p = unit load or bearing pressure, psi = W / (LD) = W (2rL). L = bearing length, in. W = bearing load, lb. S = Sommerfield number or bearing characteristic number, dimensionless. S=
µns r
2
µns D
2
= p cr p cd
7. Petroff’s Equation.
T f = Fr =
µAv h
r=
µπDLvips cd 2
r=
4 µπ 2r 3Lns in − lb. cr
3
R. BEARINGS - LECTURE 8. Types of Rolling Contact Bearings 1. Ball Bearing 2. Roller Bearing The ball and roller bearings consist of an inner race which is mounted on the shaft or journal and an outer race which is carried by the housing or casing. 9. Types of Radial Ball Bearings Following are the various types of radial ball bearings: 1. Deep-groove ball bearing – is one in which the balls are assembled by the eccentric displacement of the inner ring. 2. Filling-slot type ball bearing – has slots or notches that permit the assembly of more balls, giving a bearing of larger radial load capacity. 3. Self-aligning ball bearing – compensate for angular misalignment that arise from shaft or foundation deflection or errors in mounting. 4. Angular-contact bearings – where the line through the areas carrying the load makes an angle with the plane of the face of the bearing. 5. Double-row ball bearings – are similar to single-row ball bearings, except that each rings has two grooves. 6. Cylindrical roller bearings – where the contact is a line instead of a point as in ball bearings, which results in a greater area carrying the load and hence, for a particular size, in a larger radial capacity. 7. Self-aligning roller bearings – with spherical rollers running in a double-grooved inner ring, have curved outer rings that look like the outer ring of a self-aligning ball bearing. 8. Needle bearings – cylindrical bearings made with relatively long bearings. 9. Tapered roller bearings – where the rolling elements are frustums of a cone. 10. Static Load Capacity
Fs = C s Nb Db 2 Where, Fs = basic static load rating, lb. Nb = number of balls or rollers. Db = ball diameter. in Cs = a proportionality constant dependent on the type of bearing and the materials. 11. Dynamic Load Capacity.
Fd = CNb 2 3 (Nr cosα )0.7 D1.8 lb Where, Fd = the dynamic capacity of the bearing. Nr = number of rows of balles C = a constant that varies with the type of ball bearing α = locates the plane of the resultant force. 4
R. BEARINGS - LECTURE 12. Equivalent Dynamic Load. Fe = C r Fx [Fz C r Fx ≤ Q] Or Fe = 0.56C r Fx + C t Fz [Fz C r Fx > Q] Where, Fx – is the radial load Fz – is the thrust load Cr – is a rotation factor (Cr = 1 for inner race rotating, Cr = 1.2 for outer race rotating). Ct – is a thrust factor. Q - is from Table 12.2 of Faires. 13. Basic Dynamic Load Rating. Fr = (B10 )1 3 Fe Where B10 mr is the desired number of revolution before 10% failures have occurred.
5
S. RIVETED JOINTS - LECTURE 1. Definition A rivet is a short cylindrical bar with a head integral to it. The cylindrical portion of the rivet is called shank or body and lower portion of shank is known as tail. The rivets are used to make permanent fastening between the plates such as in structural work, ship building, bridges, tanks and boiler shells. The riveted joints are widely used for joining light metals.
2. Types of Riveted Joints, depending upon the way in which the plates are connected. 2.1 Lap Joint - is that in which one plate overlaps the other and the two plates are then riveted together. 2.2 Butt joint - is that in which the main plates are kept in alignment butting (i.e. touching) each other and a cover plate (i.e. strap) is placed either on one side or on both sides of the main plates. The cover plate is then riveted together with the main plates. 2.2.1 Single strap butt joint - the edges of the main plates butt against each other and only one cover plate is placed on one side of the main plates and then riveted together. 2.2.2 Double strap butt joint, the edges of the main plates butt against each other and two cover plates are placed on both sides of the main plates and then riveted together. 3. Types of riveted , joints depending upon the number of rows of the rivets. 3.1 Single riveted joint is that in which there is a single row of rivets in a lap joint and there is a single row of rivets on each side in a butt joint. 3.2 Double riveted joint is that in which there are two rows of rivets in a lap joint and there are two rows of rivets on each side in a butt joint.
1
S. RIVETED JOINTS - LECTURE 4. Chain and Zigzag Riveted 4.1 Chain riveted - when the rivets in the various rows are opposite to each other. 4.2 Zig-zag riveted – when the rivets in the adjacent rows are staggered in such a way that every rivet is in the middle of the two rivets of the opposite row .
5. Important Terms Used in Riveted Joints 5.1 Pitch – is the distance from the centre of one rivet to the centre of the next rivet measured parallel to the seam, p. 5.2 Back pitch – is the perpendicular distance between the centre lines of the successive rows , pb. 5.3 Diagonal pitch- is the distance between the centres of the rivets in adjacent rows of zig-zag riveted joint, pd. 5.4 Margin or marginal pitch – is the distance between the centre of rivet hole to the nearest edge of the plate, m. 6. Failures of a Riveted Joint 6.1 Tearing of the plate at an edge.
2
S. RIVETED JOINTS - LECTURE 6.2 Tearing of the plate across a row of rivets.
Tearing resistance or pull required to tear off the plate per pitch length, Pt = Atσ t = (p − d )t σ t Where, p = Pitch of the rivets, d = Diameter of the rivet hole, t = Thickness of the plate, and σt = Permissible tensile stress for the plate material. 6.3 Shearing of the rivets.
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S. RIVETED JOINTS - LECTURE Shearing resistance or pull required to shear off the rivet per pitch length, Ps = n ×
π 4
× d 2 ×τ in single shear
Ps = n × 2 ×
π 4
× d 2 ×τ in double shear
Where, d = Diameter of the rivet hole, τ = Safe permissible shear stress for the rivet material, and n = Number of rivets per pitch length. 6.4 Crushing of the plate or rivets.
Crushing resistance or pull required to crush the rivet per pitch length, Pc = n × d × t × σ c 7. Efficiency of a Riveted Joint. The efficiency of a riveted joint is defined as the ratio of the strength of riveted joint to the strength of the unriveted or solid plate. Least of Pt , Ps and Pc η= p × t ×σ t Where, p = Pitch of the rivets, t = Thickness of the plate, and σt = Permissible tensile stress of the plate material.
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T. WELDED JOINTS - LECTURE 1. Definition. Welded joint – is a permanent joint which is obtained by the fusion of the edges of the two parts to be joined together, with or without the application of pressure and a filler material. Welding – is extensively used in fabrication as an alternative method for casting or forging and as a replacement for bolted and riveted joints. It is also used as a repair medium e.g. to reunite metal at a crack, to build up a small part that has broken off such as gear tooth or to repair a worn surface such as a bearing surface. 2. Welding Processes 2.1 Fusion Welding – where the parts to be jointed are held in position while the molten metal is supplied to the joint. The molten metal may come from the parts themselves (i.e. parent metal) or filler metals which normally have the composition of the parent metal. The joint surface become plastic or even molten because of the heat from the molten filler metal or other source. Thus, when the molten metal solidifies or fuses, the joint is formed. 2.1.1 Thermit Welding – where a mixture of iron oxide and aluminium called thermit is ignited and the iron oxide is reduced to molten iron. The molten iron is poured into a mould made around the joint and fuses with the parts to be welded. 2.1.2 Gas Welding – is made by applying the flame of an oxy-acetylene or hydrogen gas from a welding torch upon the surfaces of the prepared joint. The intense heat at the white cone of the flame heats up the local surfaces to fusion point while the operator manipulates a welding rod to supply the metal for the weld. A flux is being used to remove the slag. 2.1.3 Electric Arc Welding – where the work is prepared in the same manner as for gas welding. In this case the filler metal is supplied by metal welding electrode. The operator, with his eyes and face protected, strikes an arc by touching the work of base metal with the electrode. The base metal in the path of the arc stream is melted, forming a pool of molten metal, which seems to be forced out of the pool by the blast from the arc. A small depression is formed in the base metal and the molten metal is deposited around the edge of this depression, which is called the arc crater. The slag is brushed off after the joint has cooled. 2.1.3.1 Un-shielded arc welding - When a large electrode or filler rod is used for welding. 2.1.3.2 Shielded arc welding – the welding rods coated with solid material are used. 2.2 Forge Welding - the parts to be jointed are first heated to a proper temperature in a furnace or forge and then hammered. This method of welding is rarely used now-a-days. An electric-resistance welding is an example of forge welding. 3. Types of Welded Joints 3.1 Lap Joint Lap joint or the fillet joint – is obtained by overlapping the plates and then welding the edges of the plates. The cross-section of the fillet is approximately triangular.
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T. WELDED JOINTS - LECTURE
3.2 Butt Joint
4. Strength of Butt Joint, F F = σ t tL Where, L = length of weld t = plate thickness
5. Strength of Fillet Welds, F F = τ (2tL) = 2τ Lb cos 45o
Where b = leg dimension t = bcos45o
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T. WELDED JOINTS - LECTURE 6. Fillet Welds, Eccentric Loading Case 1
3Fa 3Fa 4.24Fa = 2 = 2 o tL bL cos 45 bL2 F F 0.707F τ= = = o 2tL 2Lb cos 45 Lb
σ=
τ max
2 σ = τ 2 + 2
12
F 2 3Fa 2 = + 2 2tL 2tL
12
Case 2
Fe =
Feρ ′ τ 1 Jc or τ 1 = ρ′ Jc
AL2 + Ar 2 12 Where, Jc = polar moment of inertia of a long slender area with respect to C. r = is the distance between the axis O of a weld line and the axis C. A = is the throat area = tL Jc =
τ2 =
F A
3
T. WELDED JOINTS - LECTURE By cosine law
τ max = (τ 12 + τ 22 + 2τ 1τ 2 cosθ )
12
7. Annular Fillet Weld in Bending
σ1 =
4M 4M 5.66M = = 2 o 2 π tD π b cos 45 D π bD 2
(
)
8. Other Types of Welds Corner joint – may have weld metal placed on either the inside, outside, or both. Edge joint – is made along the edges of two or more parallel, or nearly parallel, plates. Plug weld – is obtained when the holes are filled or partially filled by weld metal fusing with the second plate. Spot weld – are resistance welds, usually round, in the same form as the electrodes that press the sheets together; used on thin material only. Intermittent weld – consists of short lengths of welds with space between. Tack weld – is an intermittent weld, lightly done to hold members in position for assembly purposes or for the principal welding. 9. Other Definitions. 9.1 Arc Welding – is done either with a carbon electrode on steel (tungsten electrode on non-ferrous) or with a metal electrode. 9.2 Submerged arc welding – where the arc is covered with a welding composition, and bare electrode wire is fed automatically. 9.3 Atomic-hydrogen process – where the energy form the arc is used to break the hydrogen molecules into atoms rather than to melt the metal. 9.4 Fusion welds – because the metals are joined by fusion. 9.5 Resistance welding – depends upon the resistance to the flow of electricity at the points to be joined. 9.6 Spot welding – where two electrodes press the sheets of metal together, and at the spot where the pressure is exerted, the resistance to the flow of current causes a heating which, together with the pressure results in a weld. 9.7 Seam welding – a resistance welding process where two copper rollers are used as electrodes and if two sheets of metal are passed between the rollers, a seam is welded where the rollers press the sheets together. 4
T. WELDED JOINTS - LECTURE 9.8 Gas welding – where a hot flame and a metal rod are used. The oxyacetylene process uses acetylene burned in oxygen. 10. Code number of steel electrodes The steel electrodes have code numbers (by ASTM and AWS) such as E 6010, where the first two (or three) digits (60) indicate a minimum tensile strength (ksi) and the last two digits in effect specify other variables such as coating, current supply, position of the weld, etc.
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U. ENGINEERING MATERIALS - LECTURE 1. Materials in Manufacturing 1. Metals used in manufacturing are usually alloys, which are composed of two or more elements, with at least one being a metallic element. Two Basic Groups of Metals 1.1.1 Ferrous metals – are based on iron; the group includes steel and cast iron. 1.1.2 Steel – can be defined as an iron-carbon alloy containing 0.02% - 2.11% carbon. Its composition often includes other alloying elements as well, such as manganese, chromium, nickel, and molybdenum, to enhance the properties of the metal. 1.1.3 Cast-iron – is a n alloy of iron and carbon (2% - 4%) used in casting (primarily sand casting). Silicon is also present in the alloy (in amounts from 0.5% to 3%), and other elements are often added also, to obtain desirable properties in the cast part. 2. Nonferrous metals – include the other metallic elements and their alloys. The nonferrous metals include the pure metals and alloys of aluminum, copper, gold, magnesium, nickel, silver, tin, titanium, zinc, and other metals. 3. Ceramics - is defined as a compound containing metallic (or semimetallic) and nonmetallic elements. Typical nonmetallic elements are oxygen, nitrogen, and carbon. Examples are clay. Silica, alumina, silicon carbide, alumina, tungsten carbide, titanium carbide, titanium nitride, and boron nitride. 4. Polymer – is a compound formed of repeating structural units called mers, whose atoms share electrons to form very large molecule. Polymers usually consist of carbon plus one or more other elements such as hydrogen, nitrogen, oxygen, and chlorine. Three categories of Polymers. 4.1 Thermoplastic polymers – can be subjected to multiple heating and cooling cycles without substantially altering the molecular structure of the polymer. Common thermoplastics include polyethylene, polystyrene, polyvinylchloride, and nylon. 4.2 Thermosetting polymers – chemically transform (cure) into a rigid structure upon cooling from a heated plastic condition. Members of this type include phenollics, amino resins, and epoxies. 4.3 Elastomers – are polymers that exhibit significant elastic behavior. They include natural rubber, neoprene, silicone, and polyurethane. 5. Composites – is a material consisting of two or more phases that are processed separately and then bonded together to achieve properties superior to those of its constituents. 2. Definitions. Age hardening or precipitation hardening – occurs in some metals, notable certain stainless steel, aluminum, and copper alloys, at ambient temperature after solution heat treatment, the process being one of a constituent precipitating from a solid solution. Alloy – is a substance with metallic properties, composed of two or more elements of which at least one is a metal. Alloying elements in steel – are usually considered to be the metallic elements added for the purpose of modifying the properties. Anisotropy – is the characteristic of exhibiting different properties when tested in different directions (as tensile strength “with the grain” or “across the grain”. Brittleness – is a tendency to fracture without appreciable deformation. Charpy test – is one in which a specimen, supported at both ends as a simple beam, is broken by the impact of a falling pendulum. 1
U. ENGINEERING MATERIALS - LECTURE Cold shortness – is brittleness of metals at ordinary or low temperatures. Cold working – is the process of deforming a metal plastically at a temperature below the recrystallization temperature and at a rate to produce strain hardening. Damping capacity – is the ability of a material to absorb or damp vibrations, which is a process of absorbing kinetic energy of vibration owing to hysteresis. Decarburization – is a loss of carbon from the surface of steel, occurring during hot rolling, forging, and heat treating, when surrounding medium reacts with the carbon (as oxygen and carbon combining). Ductility – is that property that permits permanent deformation before fracture in tension. Ductile material – elongation greater than 5% in 2-in. gage. Brittle material – elongation less than 5% in 2-in. gage. Elasticity – is the ability of a material to be deformed and to return to the original shape. Stress is proportional to strain only during an elastic deformation. Embrittlement – involves the loss of ductility because of a physical or chemical change of the material. Free carbon – is that part of the carbon content of steel or iron that is in the form of graphite or temper carbon. Hard drawn – is a temper produced in a wire, rod, or tube by cold drawing. Homogeneous materials – have the same structure at all points. Isotropic materials – have the same properties in all directions. Izod test – is a test in which a specimen, supported at one end as a cantilever beam, is broken by the impact of a falling pendulum. Killed steel – is steel that has been deoxidized with a strong deoxidizing agent, such as silicon or aluminum, in order to eliminate a reaction between the carbon and oxygen during solidification. Machinability – is a material’s susceptibility to extreme deformation in rolling or hammering. Mechanical properties – are those that have to do with stress and strain. Percentage elongation – is the extension in the vicinity of the fracture of a tensile specimen, expressed as a percentage of the original gage length, as 20% in 2 in. Percentage reduction of area – is the smallest area at the point of rupture of a tensile specimen divided by the original area. Physical properties – exclude mechanical properties and are other physical properties such as density, conductivity, coefficient of thermal expansion.
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U. ENGINEERING MATERIALS - LECTURE Plasticity – is the ability of a metal to be deformed considerably without rupture. Poisson’s ratio – is the ratio of the lateral strain (contraction) to the longitudinal strain (extension) when the element is loaded with a longitudinal tensile force. Precipitation heat treatment – brings about the precipitation of a constituent from a supersaturated solid solution by holding the body at an elevated temperature, also called artificial aging. Aging – precipitation occurring a ambient temperature. Proof stress – is that stress which causes a specified permanent deformation of a material, usually 0.01% or less. Red shortness – is a brittleness in steel when it is red hot. Relaxation – associated with creep, is the decreasing stress at a constant strain; important for metals in hightemperature service. Residual stresses – are those not due to applied loads or temperature gradients. Rimmed steel – is incompletely deoxidized steel. Solution heat treatment – is the process of holding an alloy at a suitably high temperature long enough to permit one or more constituents to pass into solid solution and then cooling fast enough to hold the constituents as a supersaturated solution. Stiffness – is the ability to resist deformation. It is measured by the elasticity in the elastic range; the higher the modulus the stiffer is the material. Strain hardening – is increasing the hardness and strength by plastic deformation at temperature lower that the recrystallization range. Temper – is a condition produced in a non-ferrous metal by mechanical or thermal treatment; for example, annealed temper (soft), hard temper, spring temper. Toughness – is the capacity of material to withstand a shock load without breaking. ‘ Transverse strength – refers to the results of a transverse bend test, the specimen being mounted as a simple beam; also called rupture modulus. Work hardening – is the same as strain hardening. Wrought steel – is steel that has been hammered, rolled, or drawn in the process of manufacture; it may be plain carbon or alloy steel.. 3. Heat Treatment Terms. Heat treatment – is an operation or combination of operations involving the heating and cooling of metal or an alloy in the solid state for the purpose of altering the properties of materials. Aging (and age hardening) – is a change in a metal by which its structure recovers from an unstable or metastable condition that has been produced by quenching or cold working. 3
U. ENGINEERING MATERIALS - LECTURE Annealing – is a heating and slow cooling of a solid metal, usually done to soften it. Critical range – has the same meaning as transformation range. Drawing – is often used to mean tempering. Graphitizing and annealing process – causes the combined carbon to transform wholly or in part into graphitic or free carbon; it is applied to cast iron, sometimes to high-carbon steel. Hardening – is the heating of certain steels above the transformation range and then quenching, for the purpose of increasing the hardness. In general case, hardening is any process of increasing the hardness of a metal. Malleablizing – is an annealing process whereby combined carbon in white cast iron is transformed wholly or in part to temper carbomn. Normalizing – is the heating of an iron-base alloy to some 100 F above the transformation range with subsequent cooling to below that range in still air at room temperature. The purpose is to produce a uniform structure. Spheroidizing – is any heating and cooling of steel that produces a rounded or globular form of carbide. Stress relieving (thermal) – is the heating of a metal body to a suitable temperature (generally just below the transformation range for steel, say 1100 – 1200 F) and holding it at that temperature for a suitable time (1 to 3 hours for steel) for the purpose of reducing internal residual stresses. The internal stresses may be present because the body has been cast, quenched, normalized, machined, cold worked, or welded. Tempering – is a reheating of hardened or normalized steel to a temperature below the transformation range, followed by any desired rate of cooling. Transformation range (for ferrous metal) is the temperature interval during which austenite is formed during heating; it is also the temperature interval during which austenite disappears during cooling. 4. Hardness Hardness – is a measure of its resistance to indentation. Common Instruments – Brinell, Rockwel, Vickers, and Shore scleroscope. Brinell hardness number (BHN) – is determined by a standard pressure (3000 kg. standard, 500 kg. for soft metals) applied to a 10-mm ball which presses for 10 sec. or more on surface of the material being tested. The load in kilograms divided by the area of the surface of the indentation in square millimeters is the BHN. Ultimate tensile stress of steel is approximately 500 x BHN psi. Rockwell tester – is faster than the Brinell and widely used commercially, utilized several different indenters and, in effect measures the depth of the penetration by the indenter. Rockwell scales – Rockwell B, Rockwell C, Rockwell A, Rockwell D, and Rockwell A. Rockwell superficial tester – is a different machine used for a piece of material too thin for the standard tester. Rockwell Scales – Rockwell N and Rockwell T. 4
U. ENGINEERING MATERIALS - LECTURE Vickers tester – has a square-base, diamond pyramid indenter, and the VIckets number Is the load in kilograms divided by the impressed area in square millimeters. Shore scleroscope number – is obtained by letting a freely falling hammer with a diamond point strike the object to be tested and measuring the height of rebound. This height is the Shore number. 5. AISI and SAE Specification Numbers. The first digit (or the first two digits) of the number represents a type of steel, for example: 1XXX is a plain carbon steel. 11XX is a plain carbon steel with greater sulfur content for free-cutting. 2XXX is nickel steel. The last two digits in four-digit numbers invariably give the approximate or average carbon content in “points” or hundredths of percent. For example. SAE 1030 or AISI C1030 has about 0.30% carbon, spoken as 30 points of carbon (nominal). In the AISI system, prefixes have the following meanings: B – acid Bessemer steel; C – basic, open hearth carbon steel, D – acid open-hearth carbon steel, E – electric-furnace steel (usually alloy) Letter B or L in the middle of the number indicate that boron or lead, respectively, has been added; as 94 B 40 and 11 L 41. An H at the end indicates that material can be bought on hardenability specification, as 9840H. Steel Plain carbon Free cutting Manganese Boron Nickel Nickel-chromium Heat and corrosion resistant Molybdenum Molybdenum-chromium Molybdenum-chromium-nickel Molybdenum-nickel Molybdenum-chromium-nickel Molybdenum-nickel Chromium Heat and corrosion resistant Chromium-vanadium Nickel-chromium-molybdenum Silicon-manganese Nickel-chromium-molybdenum (except 92XX)
SAE 10XX 11XX 13XX 14XX 2XXX 3XXX 303XX 4XXX 41XX 43XX 46XX 47XX 48XX 5XXX 514XX and 515XX 6XXX 8XXX 92XX 9XXX
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U. ENGINEERING MATERIALS - LECTURE 6. Alloy Steel Wrought alloy steel – is steel that contains significant quantities of recognized alloying metals, the most common being aluminum, chromium, cobalt, copper, manganese, molybdenum, nickel, phosphorus, silicon, titanium, tungsten, and vanadium. Alloys – are used to improve the hardenability of steel, to reduce distortion from heat treatment, to increase toughness, ductility, and tensile strength, and to improve low-temperature or high-temperature properties. Classification of alloys. 1. Low-alloy structural steels (not heat treated). 2. Low-carbon alloy steels (0.10 – 0.25% C) 3. Medium-carbon alloy steels (0.25 – 0.50% C) 4. High-carbon alloy steels (0.50 – 0.70% C) 5. High alloy steels, such as stainless steels Uses of alloy steels. AISI 2330 – bolts, studs, tubing subjected to torsional stresses. AISI 2340 – quenched and tempered shafting, connecting rods, very highly stresses bolts, forgings. AISI 2350 – high-capacity gears, shafts, heavy duty machine parts. AISI 3130 – shafts, bolts, steering knuckles. AISI 3140 – aircraft- and truck-engine crankshafts, oil-well tool joints, spline shafts, axles, earth moving equipment. AISI 3150 – wear-resisting parts in excavating and farm machinery, gears, forgings. AISI 3240 – shafts, highly stresses pins and keys, gears. AISI 3300 series – for heavy parts requiring deep penetration of the heat treatment (hardenability) and high fatigue strength per unit weight. AISI 4063 – leaf and coil springs. AISI 4130, 4140 – automobile connecting rods and axles, aircraft parts and tubing. AISI 4640 – gears, splined shafts, hand tools, miscellaneous heavy duty machine parts. AISI 8630 – connecting rods, bolts, shapes; air hardens after welding. AISI 8640, 8740 – gears, propeller shafts, knuckles, shapes. 7. Hardenability Hardenability – is the capacity of steel to through-harden when cooled from above its transformation range. 8. Case Hardening Case Hardening of iron base alloys – is a process of surface hardening whereby the surface or case is substantially harder than the core or inside metal. Case hardening is done by carburizing, cyaniding, nitriding, carbonitriding, induction hardening, and flame hardening. 1. Carburizing – is a process of adding carbon to the surface steel by exposing it to hot carbonaceous solids, liquids, or gases – above the transformation temperature. 8.1.1 Pack (or box) carburizing – the part is heated in contact with solid carburizing compounds of various constituents, including charcoal, burned bone, charred leather, tar, and barium, sodium, and calcium carbonates, especially barium carbonate and charcoal. 8.1.2 Gas carburizing – the part is heated in carburizing gases, such as methane, ethane, propane, and CO. 8.1.3 Liquid carburizing – the part is immersed in a molten salt bath that imparts a case similar to that obtained with gas or pack carburizing except that the case is thinner. 2. Cyaniding – is accomplished by immersing the part in a hot (about 1550 F) liquid salt bath, sodium cyanide (NaCN) being a common medium in both processes. 6
U. ENGINEERING MATERIALS - LECTURE 3. Nitriding – the machined and heat-treated part is placed in a nitrogenous environment, commonly ammonia gas. 4. Carbonitriding – is a process of case hardening steel by the simultaneous absorption of carbon and nitrogen from a surrounding hot gaseous atmosphere, followed by either quenching or slow cooling, as required. 5. Induction Hardening – consist of heating a thin surface layer, preferably of annealed or normalized steel, above the transformation range by electrical induction and then cooling, as required, in water, oil, air, or gas. 6. Flame Hardening – is a process of heating the surface of an iron-base alloy, which is preferably annealed or normalized, and then quenching it. 9. Work Hardening Work hardening – is the result of a metal being stresses at some point into its plastic range, usually ordinary temperatures (certainly below recrystallization temperature). 10. Wrought Iron Wrought iron – is made by burning the carbon from molten iron and then putting the product through hammering and rolling operations. The product contains some 1-3% slag and less than 0.1% carbon. 11. Cast Iron Cast iron – includes white cast iron, malleable iron, and nodular cast iron, but when cast iron is used without a qualifying adjective, gray cast iron, spoken of as gray iron is meant. 12. Malleable Iron Malleable iron – is a heat treated white cast iron. Malleablizing – is an annealing heat treatment of the white cast iron, in which substantially all of the carbon is combined in the form of iron carbide, during which the white iron changes to ferrite and free (or temper) carbob. 13. Nodular Cast Iron Nodular cast iron (also called ductile iron) – has the castability, machinability, and wearability of gray iron, but higher strength and ductility. 14. Cast Steel Cast steel – where the combination of highest strength and highest ductility in a cast ferrous metal is obtained. 15. Stainless Steel Stainless steel – is relatively expensive, but where the environment is significantly corrosive or at high or quite low temperature, it provides an economical answer for many problems. Three Classes of Stainless Steel 1. Austenitic steels - 200 and 300 series – that includes 3.5 to 22% nickel for stabilizing of austenite. 2. Martensitic steels – usually with no nickel, but some types have 2.5% maximum. 3. Ferritic steels – no nickel, do not harden by quenching and tempering. Methods of Hardening 1. Cold working 2. Age hardening (precipitation hardening) 3. Quenching and tempering 16. Copper Alloys Copper – is one of the oldest known metals, it has been the base of many alloys, as well as being used in a relatively pure form. 7
U. ENGINEERING MATERIALS - LECTURE Brass – an alloy of copper and zinc. Bronze – an alloy of copper and tin. Manganese bronze – is a high-strength brass, the improved mechanical properties being obtained by including small amounts of aluminum, iron, manganese, and tin. Phosphor bronze – is a bronze, but the finished product may have only a trace of the phosphor that was added primarily to deoxidize the melt, a treatment that improves the mechanical properties. Uses of Copper Alloys. 1. Admiralty metal – condenser and other heat-exchanger tubes and plates. 2. Aluminum bronze – corrosion-resistant parts; marine pumps, shafts, valves; parts where high strength, toughness, wearability, low coefficient of friction, and damping are important, as some bearings, gears, worm wheels, cam rollers; also a decorative metal, as in statues and costume jewelry, 3. Beryllium copper (also called beryllium bronze) – parts where high formability, high yield, fatigue, and creep strengths, and also good corrosion resistance are advantageous; springs, bolts and screws, firing pins, dies, surgical instruments, spark resistant tools. 4. Cartridge brass – electrical parts, automotive radiator cores, pins, rivets, springs, ammunition components, tubes. 5. Manganese bronze – clutch disks, pump rods, shafts, valve stems, welding rod. 6. Naval brass – condenser plates, marine hardware, propeller shafts, piston rods, valve stems, welding rod, balls, buts, bolts, and rivets. 7. Phosphor bronze – bellows, diaphragms, clutch disks, cotter pins, lock washers, bushings, springs, wire, welding rod, chemical hardware, wire brushes. 8. Silicon bronze – hydraulic pressure lines, hardware, bolts, nuts, rivets, screws, electrical conduits, heatexchanger tubes, welding rod. 9. Yellow brass: electrical fixtures, plumbing, wire, pins, rivets, screws, springs, architectural grillwork, radiator cores. 17. Lead, Tin, and Miscellaneous Alloys. 1. Babbitt B23-46T, grade 8 – has a lead base and is suitable bearing material for light and moderate service in various machines. 2. Tin Babbitt B23-49, grade 1 – has a tin base and is a general purpose bearing material, also used for die-castings. 3. Hastelloy B – is an expensive alloy of nickel, molybdenum, and iron (5%) that is very useful in chemical industry because it resists certain corrosion admirably. 4. Monel – is primarily an alloy of nickel and copper (67 Ni, 30 Cu). It is used for nonmagnetic aircraft parts such as pump rods, springs, valve stems, shafts. 5. Zinc alloy – may be used for either die castings or sand castings for such articles as automotive parts, building hardware, padlocks, toys, and novelties. 18. High-Temperature Service. Superalloys or superstrength alloys – are some combination of nickel, cobalt, chromium, iron, molybdenum, tungsten, columbium, titanium, and aluminum, but never containing all of these. 19. Plastics Thermosetting – which undergo chemical change and harden on being heated, usually under pressure. Thermoplastic – which soften as the temperature rises and remain soft in the heated state.
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V. MACHINE SHOP PRACTICE - LECTURE 1. Definition. Machine shop practice – consists of certain mechanical principles that are a part of all machine shop work everywhere such as the principle of cutting tools, cutting speeds and feeds, actions of gears, screws, cams, etc., applied in the construction of certain machines and tools and in the various machine operations; that is the method of holding and doing work. Machine shop – is a room or space with sidings and roofs where metal parts are cut to size required and put together to form mechanical units or machine. 2. Machine Shop Equipment 2.1 Lathe – a metal turning machine tool in which the work, while revolving on a horizontal axis, is acted upon by a cutting tool which is made to move slowly (feed) in a direction more or less parallel to the axis of the work (longitudinal feed), or in the direction at right angles to the axis of the work (cross feed). 2.2 Drill or Drill Press – a machine tool used mainly for producing holes in metal. 2.3 Shaper – is used for finishing flat or partly curved surfaces of metal pieces few in number and not over 305 mm or 610 mm long. 2.4 Planer – a machine tool used in the production of flat surfaces on pieces too large or too heavy or cannot be held in a shaper. 2.5 Grinding machine – a machine tool in which an abrasive wheel is used as a cutting tool to obtain a very high degree of accuracy and a smooth finish on metal parts. 2.6 Vertical boring mill – a machine purposely designed for finishing holes, the work table revolves on a vertical axis and the cutting tool is arranged above the table and may be fed laterally or up or down in any position. 2.7 Horizontal boring mill – a machine for finishing holes where the cutting tool revolves on a horizontal axis. 2.8 Universal milling machine – a milling machine designed and constructed that the table may be swiveled to a considerable angle in a horizontal plane to permit the milling of spiral (twisted) grooves. 2.9 Plain milling machine – a machine very similar in appearance and construction to the universal milling machine, differing chiefly in that it lacks the swivel table construction. 2.10 Vertical-spindle milling machine – a machine used of any end-milling and face milling operation. 2.11 Metal-cutting band saws – a machine tool designed to cut everything all the time, because it employs an endless band with sharp teeth moving in one direction. 3. Special Tools and Machinery in a Machine Shop. 3.1 Turret Lathe – a production lathe primarily consist of multiple-station tool holders or turrets, in place of a lathe compound rest and tailstock. 3.2 Broaching machine – applied in machining holes or other internal surfaces and also to many flat or other external surfaces. Internal broaching is applied in forming either symmetrical or irregular holes, grooves, or slots in machine parts, especially when the size or shape of the opening, or its length in proportion to diameter or width, make other machining processes impracticable. Broaching originally was utilized for such work as cutting keyways, machining round holes into square, hexagonal, or other shapes, forming splined holes, and for a large variety of other internal operations. 3.3 Mechanical Presses – a machine tools which is driven by an electric motor or mechanical power source and is used in sheet metal work like punching, shearing, bending, drawing, and other sheet metal forming operations.
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V. MACHINE SHOP PRACTICE - LECTURE 3.4 Hydraulic Presses – a machine tools which consists of a ram which is being actuated by the pressure of a hydraulic fluid, which is used in various operations such as bending, drawing, forced fitting, or diassembling of parts. 4. Hack and Band Saws Band saw (for metal) – a machine tool which is used to cut metal parts by the use of an endless band with saw teeth moving around two pulleys. Power hacksaw – a machine tool which is used to cut metal parts of light, medium and large sections using a reciprocating hacksaw blade.
5. Cutting Time Cutting time =
Length of cut Cutting speed
For power hacksaw: Cutting speed = Strokes per min× Feed per stroke For band saw: Cutting speed = Cutting speed × No. of teeth per inch × Feed per tooth For drilling and power hacksaw: Cutting speed = Revolution per min× Feed per revolution
End -
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W. MANUFACTURING PROCESS - LECTURE PSME CODE 2008, CHAPTER 14 1. Definition Hobbing – a method of making molds for the plastics and die casting industries. Infiltration – the process of filling the pores of a sintered product with molten metal in order to decrease porosity or to improve physical properties. Interferometry – the science of measuring with light waves, measuring to the millionth part of an inch (approx. 25 mm). The small instrument is known as optical flats. Intraforming – a process in which metal is squeezed at a pressure of about 300 tons or less into a die or mandrel to produce an internal configuration. Ironing – a name given to an operation for sizing and thinning the walls of drawn cups. Metal spinning – the operation of shaping thin metal by pressing it against a form while rotating. Piercing – the method of cold working by compression. Powder metallurgy – the art of producing commercial products from metallic powders by pressure. Spinning – the operation of shaping thin metal by pressing it against a form while it is rotating. Swaging – a force in impact which causes the metal to flow in some predetermined shape according to the design of the dies. Toughening – a form of tempering used to enhance the toughness of a hardened steel where high hardness is not particularly needed in service. Ultrasonic Impact Grinding – a means of cutting shapes of all kinds by the rapid motion of abrasive particles. 2. Classification of Manufacturing Processes. 2.1 Processes used to change the shape of materials. 2.2 Processes used for machining parts to a fixed dimension. 2.3 Process for obtaining a surface finish. 2.4 Process used for joining parts of materials. 2.5 Processes used to change the physical properties. 3. Processes 3.1 Brazing – a group of welding operation in which a non-ferrous filler metal melts at a temperature below that of the metal joined but is heated above 425 C. 3.2 Blow Molding – is used primarily to produce thin-walled hollow containers from thermoplastic resin. 3.3 Cold drawing – is a common method for reducing the size of wire, bar, tubing, and other shapes and is a different operation than the drawing (or deep drawing) of sheet metal. 3.4 Electro-forming – is one of the special processes for forming metals. Parts are produced by electrolytic deposition of metal upon conductive removable mold or matrix. 3.5 Explosive-forming – an excellent method of utilizing energy at a high rate, since the gas pressure and rate of detonation can be carefully controlled. 3.6 Electroplating – is done on all the common metals and even on many metal after their surfaces have been prepared.
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W. MANUFACTURING PROCESS - LECTURE 3.7 Extrusion – is done intermittently by a plunger in a cylinder, but the common continuous method are the material drop from a hopper into a heated cylinder in which it is pushed along and out through the opening in the die by screw. 3.8 Forging 3.8.1 Hammer forging – a hot work piece is placed on an anvil and struck repeatedly by a hammer. 3.8.2 Drop forging – the operation of forming parts hot on drop hammer with impression or cavity dies. 3.8.3 Press forging – is done in presses rather than with hammer. 3.8.4 Upset forging – also called hot reading and machine forging, consist of applying lengthwise pressure to a hot bar held between grooved dies to enlarge some section or sections, usually the end. 3.8.5 Roll forging – where two rolls are arranged on parallel shafts for roll forging. These roll segments have one or more sets of grooves. A piece of stock is placed between the rolls, which in turn squeeze the stock in one set of grooves. 3.9 Galvanizing – a process by which zinc coating is applied to a wide variety of steel product to provide protection against protection. 3.9.1 Hot dip galvanizing – dipping or passing the steel product through a bath of molten zinc. 3.9.2 Cold electro galvanizing – process of providing any metal with zinc coating by means of an electric current. 3.10 Grinding, Polishing – a process of finishing various materials for either safety, operational, or aesthetic appearances. 3.11 Metallizing – where the equipment for metal spraying consist of a pistol-shaped spray gun through which the metal, in the form of wire is fed to a blowpipe flame which melt it, the molten metal thus produced being sprayed by a steam of compressed air surrounding the flame. 3.12 Magnetic Forming – is another example of the direct conversion of electrical energy into useful work. The process involved charging the voltage is supplied by a high voltage source into a bank of capacitors connected in parallel. 3.13 Plastic processes – the processes employed in plastic technology are compression moulding, transfer moulding, injection moulding, extrusion, calendaring, blow moulding, film forming, thermal forming, vacuum forming, laminating and resin technology processes. 3.14 Plasma-Arc – a gas is heated by a tungsten arc to such a high temperature that it becomes ionized and acts as a conductor of electricity. 3.15 Riveting – mechanical means of permanently fastening parts together to rivet two parts. 3.16 Sintering – application of heat, which must be kept at a temperature below the melting point of the metal powder, in the production of commercial products from metallic powders by pressure or atomic forces, and resulting in the bonding of fine particles together, thus improving the strength and other properties of the finished product. 3.17 Soldering – uniting of two pieces of metal by means of a different metal which is applied between the two in a molten state. 3.18 Thermo-forming – consist of heating a thermo-plastic sheet until it softens and then forcing it to conform to some mold either by differential air pressure or mechanical means, 3.19 Ultrasonic machining – a mechanical process was designed to effectively machine hard brittle materials. 3.20 Wire drawing – where wire is made by cold drawing hot rolled wire rod through one or more dies to decrease it size and increase the physical properties. 2
W. MANUFACTURING PROCESS - LECTURE 4. Welding and Metal Cutting 4.1 Gas Welding – the process in which gases are used in combination to obtain a hot flame. 4.2 Electric-Arc Welding – a process wherein the metal is heated to its liquid state and allowed to solidify thereby making the joint. 4.3 Atomic Hydrogen Welding – an arc struck between two tungsten electrodes into which a jet of hydrogen is directed. 4.4 Electro-beam Welding – a work pierce contained in an executed chamber is bombarded by a beam of electrons from an electron gun at voltages between 0.5 kV and 100 kV. The energy of the electrons is transformed into heat on striking the work piece. 4.5 Electro-slug Welding – the work piece are usually set vertically, with a gap between them and copper plates or shoes are placed one or both sides of the joint to form a bath at the bottom of which an arc is established under a flux between one or more continuously fed electrode wires and a metal plate. 4.6 Flash Welding (Butt Welding) – the two metal parts to be welded are connected to a low voltage high current source. 4.7 Friction Welding (Cold Welding) – a purely mechanical welding technique in which one component remains stationary while the other is rotated against it under pressure. 4.8 Laser Welding and Drilling – laser beams are used for these purposes in industrial application requiring exceptionally high precision. 4.9 Metal Spraying – wire or powder from the nozzle of a spraying gun is fused by a gas flame, arc or plasma-jet, and the molten particles are projected in the form of a spray by means of compressed air or gas. 4.10 Plasma-Arc Welding – the heat source is an arc formed at a relatively small orifice through which stream of air, argon, helium, nitrogen or mixture if these gases flow. 4.11 Resistance Welding – a high current at low voltage flows through two components from electrodes. 4.12 Spark Erosion Machining – the metal is removed from the piece to be machined by the action of electric discharges between the piece and an electrode immersed in electrolyte. 4.13 Stud Welding – an arc is struck between the components to be joined and raised the temperature of the ends of the components to melting point. 4.14 Thermit Welding – a mixture of aluminum powder and a metal oxide powder is ignited by a special powder in a crucible. 5. Common Weld Defects 5.1 Lack of Penetration – caused by the base metals did not reach fusion temperature, fast welding rate or too large an electrode used. 5.2 Weld Cracks – occur at the weld heat affected zone due to brittle weldment associated with stresses. 5.3 Pinholes – are small holes through the weldment normally caused by gas bubbles escaping through the molten weld metal while cooling. 5.4 Porosity – are gas bubbles or minute impurities trapped in the weldment normally due to dirty or moist electrode or contaminated base metals. 5.5 Inclusion – a common weld defect. Slags or foreign materials are trapped inside the weld metal. 5.6 Weld Undercuts – are cuts between the weld metal and the base metal normally due to excessive welding current.
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W. MANUFACTURING PROCESS - LECTURE 6. Destructive Testing Destructive testing - a process where materials can be randomly tested by actual destruction of a work piece for examination. 6.1 Tensile test – a test specimen is cut-out from the work piece and stretched to failure. 6.2 Bending test – a test specimen is cut-out from the work piece and bended 90 deg to 180 deg. 6.3 Sectioning – the weld joint is cut by hacksaw along the centerline of the weld to allow visual examination of the weld. 7. Non-Destructive Testing Non-Destructive Testing – a process wherein weld examination is done without destroying the material. 7.1 Dye Penetrant Examination – this determine surface cracks and porosities which may not be readily seen. 7.2 Hardness Testing – a method of determining the hardness of the weld more particularly the heat affected zone. 7.3 Magnetic Particle Testing – uses electrical current to create a magnetic field in a specimen with the magnetic particles (iron powders) indicating where the field is broken by discontinuities such as cracks in the material. 7.4 Radiographic Examination – employs radioactive isotopes such as Cobalt-60, Iridium-192, Thulium-170, or Cesium-137 and radiographic films. 7.5 X-ray Examination – essentially the same with radiographic examination except only on the source of radiation. This utilized electricity powered X-ray machine that generate ionizing radiation. 7.6 Ultrasonic Examination – utilizes ultrasounds that penetrate most common materials. The time of rebound of ultrasounds from the probe which is pressed on one side of the material to the other side or any discontinuity is converted to unit of linear measure. 8. Air Pollution Control Equipment for collecting particulate matter (smoke, dust, fumes, mists, etc.) 8.1 Inertial separators – used for collecting medium and coarse size particulates. 8.2 Centrifugal separators – where the tangential inflow tube or cyclone separators are normally suitable for medium size (15 to 40 microns) and coarse size particulates while the axial flow inversion type or multiple cyclone separators are effective in collecting particulates in the 5 to 15 microns range. 8.3 Rinsing or wet collection device – these devices include spray-type, cyclone type, orifice-type, mechanical venture-type, jet-type, and packed tower scrubbers. 8.4 Filtration devices – have a high collection efficiency for sub-micron size particulates. 8.5 Electrostatic precipitators – suitable for the collection of a wide variety of dust and fumes. 8.6 Gravitational precipitators – used as pre-cleaners to remove coarse and abrasive particulates to protect and augment the main dust collectors. 9. Air Pollution Control Equipment for the collection of a wide gaseous and vapor emission. 9.1 Adsorption equipment – the absorbent selectively capture or remove gases or liquids from dirty gas streams even at very small concentrations. 9.2 Absorption equipment – by using selective liquids solvents, one or more constituents of a gas stream can be removed or covered. 9.3 Afterburners – combustion converts the combustible constituents of a gas stream into carbon and water. 9.4 Vapor condensers – by extracting heat or increasing pressure, vapor condensation is achieved.
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W. MANUFACTURING PROCESS - LECTURE 10. Water Pollution 10.1 Pollution – is the downgrading of water quality by sewage or other wastes to the point where it unreasonably affects water use for domestic, industrial, agricultural, navigational or other beneficial uses. 10.2 Clarifying waste water – is the process of removing turbidity, sediment and floating materials. 10.3 Coagulation – is the gathering together of finely divided or colloidal suspended matter into the particles. 10.4 Flocculation – is the agglomeration of finely divided suspended matter and floc caused by gently stirring or agitating the waste water. 10.5 Floatation – is basically sedimentation in reverse to remove floatable materials and solids with a specific gravity so close to water that they settle very slowly or not at all. 10.6 Gravity separation – is used to remove liquid pollutants that are insoluble in water such as petroleum oils and the cutting and coolant coils used in metal-finishing operations. 10.7 Granular activated carbon - has long been used in filtering equipment to remove color and turbidity and improve the taste of water by removing residual chlorine. 10.8 Biological filters (Trickling filters) – are basically a pile of rocks over which a sewage or industrial waste slowly trickles. 10.9 Activated sludge – is the process by which masses on settle able solid formed by simply aerating waste water containing biologically degradable compounds in the presence of microbes. 10.10 Anaerobic digestion – is widely used to stabilize concentrated organic solids removed from settling tanks, biological filters and activated sludge plants. 11. Chemical Processes 11.1 Adsorption – using granulated activated carbon is a reliable and effective way of removing organic impurities found in most water supplies. 11.2 Coagulation – is the process of adding chemicals to waste water to produce a flocculent precipitate that will remove fine suspended matter and colloidal substances by adsorption or mechanical entrainment. 11.3 Dialysis – a practical toll for recovering chemical from process waste. 11.4 Electro dialysis – reduces the dissolved solids content of water. 11.5 Ion exchange – is a versatile process that keeps extending its range of service. In waste water treatment it is used to remove or recover anions and cations depending on whether or not they are valuable, undesirable or both. 11.6 Neutralization – is frequently needed to keep pH in the range of 6 to 8 required by most water quality criteria. 11.7 Oxidation reduction and precipitation system – are widely applied for the treatment of plating wastes. 11.8 Sludge handling and disposal – is a final step from waste water treatment plants. 11.9 Sludge concentrators – are mainly used to thicken sludge from secondary clarifiers or mixtures of sludge from both primary and secondary treatment units. 11.10 Digestion under anaerobic conditions – makes sludge solid easier to dewater and convert parts of the inorganic matter to gaseous end products. 11.11 Dewatering – is handled by drying beds, lagoons, filters, and centrifugal. 11.12 Vacuum filtration – is the most widely used method of mechanical sludge dewatering. 11.13 Gravity filters – consists of two cells operating at atmospheric pressure. These cells are formed by a finemesh nylon filter cloth continuously travelling over front and rear guide wheel. - End 5
