CHAPTER-1 INTRODUCTION As we see in the many industries that the movement of heavy equipment or metals sheet is very tedious task and a huge labours and a lot of time is required to move from one place to desire place. So it’s complicated, uneconomical and also risky .To overcome this problem a machine is used which is called CRANE. Crane is a mechanical device in which lever, pulley, rope, hook & engine are used like as hydraulic crane, electromagnetic crane etc. By the help of crane we can move heavy metals (mainly metal sheet) from one place to another place very easily, it reduce working time, force and money. it can be operated by a single person so its reduce the need of labours. An electromagnetic crane is a type of crane in which we are using an electromagnet (which is made up of soft iron core and a copper wire is wounded around its periphery) to lift the heavy metal (made up of ferrous metal) and thus the work piece is lifted and keep in desired place by electromagnetic crane.
1.1 MECHANISM OF ELECTROMAGNETIC CRANE The magnetic strength of an electromagnet depends on the number of turns or wire and the current through the wire, and the size of the iron core. This allows electromagnets to be made much larger and stronger than a natural magnet, such that they can pick up very large objects. Also, when you turn off the electricity to an electromagnet, the magnetism is also turned off. Thus, an electromagnet can be used to pick up a piece of iron and then drop it someplace else.
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(fig. 1.1 SIMPLE CRANE)
1.2 History of crane The first construction cranes were invented by the Ancient Greeks and were powered by men or beasts of burden, such as donkeys. Larger cranes were later developed, employing the use of human tread wheels, permitting the lifting of heavier weights.
(fig.1.2-frame of electromagnetic crane)
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1.3 Use of crane Cranes are commonly employed in the transport industry for the loading and unloading of freight, in the construction industry for the movement of materials and in the manufacturing industry for the assembling of heavy equipment. The first construction cranes were invented by the Ancient Greeks and were powered by men or beasts of burden, such as donkeys. These cranes were used for the construction of tall buildings. Larger cranes were later developed, employing the use of human treadwheels, permitting the lifting of heavier weights.
1.4 Evolution of crane The earliest cranes were constructed from wood, but cast iron and steel took over with the coming of the Industrial Revolution. For many centuries, power was supplied by the physical exertion of men or animals, although hoists in watermills and windmills could be driven by the harnessed natural power. The first 'mechanical' power was provided by steam engines, the earliest steam crane being introduced in the 18th or 19th century, with many remaining in use well into the late 20th century. Mini - cranes are also used for constructing high buildings, in order to facilitate constructions by reaching tight spaces. Finally, we can find larger floating cranes, generally used to build oil rigs and salvage sunken ships. we can find larger floating cranes, generally used to build oil rigs and salvage sunken ships. The article also covers lifting machines that do not strictly fit the above definition of a crane, but are generally known as cranes, such as stacker cranes and loader cranes. There are used motors to move the craned.
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(fig1.3 - side working of labours using electromagnetic crane )
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1.5 LITERATURE SERVEY Our group decided to visit an industry (N.E Railway Gorakhpur) and we saw the working of that industry .Iron is the main work piece of that industry. We saw that they were using crane to lift heavy work pieces .we were happy to see that the movement of work piece was going very easily with the help of crane but a situation came, when they were lifting a flat iron sheet . For lifting the flat iron sheet first of all they bound a rope around the metal sheet by the help of no. of labours, which was a tough task. Then they moved flat sheet from its place to desire place by the help of crane. It looked very tough, time taking, uneconomical and risky. After that we thought, we should talk to them about that problem. They told us it is risky but we have to do it. We also talked about the environment of industry, production, raw material and marketing etc. So, after the discussion with them we concluded that the main problem of that industry with labours is their machine i.e. crane.
1.6 PROBLEM IDENTIFICATION As discussed earlier that we had visited an industry and there were so many problems that we identified during visit (including talking with their people). So the main problem was lifting the flat metal sheet of ferrous metal and complex shape type work piece by simple crane.
1.7 ISSUE After visiting industry and when we were coming back to home, we realized the problem of that industry and the only issue of discussion among us was- how we can solve their problem.
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CHAPTER-2
2.1 STATEMENT OF THE PROBLEM
It is very tedious, uneconomical, risky, time consuming, unpleasant to lift a flat metal sheet and complex shape type work piece by conventional cranes (made up of hook).
2.2 FORMULATION OF THE PROBLEMS
Formula for solenoidI= v/r r=ρ(l/A) B=µNi/L
Formula for belt pulleyP= (t1-t2)V t1/t2= T1-mg=ma
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2.3 PRESENTATION OF THE PROBLEMS As the problems were discussed earlier that there is a need of bounding the crane with the help of ropes and chains etc. And it is tough, risky, time taking also. Here we are going to present these problems by the help of some photographs with their explanations-
(fig2.1 - flat metal sheets)
In the above figure we can see that flat heavy metal sheets are there in the industry which we have to lift by the help of simple cranes.
(Fig2.2- chain used to lift flat metal sheet in conventional crane) In this figure we can see the chain by which flat sheet metal will be bound. Its tensile strength and other mechanical properties are very high. We have to bind the flat metal sheet by this chain arrangement. In actual practice it is very risky, tough and time taking also. In next photo we shall tell that how the actual figure is shown (i.e. when flat sheet metal is bounded by the chain).
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(fig2.3 - adjusting the flat metal sheet By chain in hook)
So we can that how the flat sheets are bounded by the simple crane. After bounding the chain, we have to adjust the chain and rope in the hook of the crane.
2.4 SOLUTION APPROACH
(fig2.4 - magnetic field produced by bar magnet)
Magnetic field lines of a solenoid which are similar to a bar magnet as illustrated above with the iron filings A magnet (from Greek μαγνήτηςλίθος, "Magnesian stone") is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other magnetic materials and attracts or repels other magnets. A permanent magnet is one that stays magnetized, such as a magnet used to hold notes on a refrigerator door. Materials which can be magnetized, which are also the ones that are strongly attracted to a magnet, are called ferromagnetic. These include iron, nickel, cobalt, some rare earth metals and some of their alloys, and some naturally [8]
occurring minerals such as lodestone. The other type of magnet is an electromagnet, a coil of wire which acts as a magnet when an electric current passes through it, but stops being a magnet when the current stops. Often an electromagnet is wrapped around a core of ferromagnetic material like steel, which enhances the magnetic field produced by the coil. Permanent magnets are made from "hard" ferromagnetic materials which are designed to stay magnetized, while "soft" ferromagnetic materials like soft iron are attracted to a magnet but don't tend to stay magnetized. Although ferromagnetic materials are the only ones strongly enough attracted to a magnet to be commonly considered "magnetic", all other substances respond weakly to a magnetic field, by one of several other types of magnetism. Paramagnetic materials, such as aluminum and oxygen are weakly attracted to a magnet. Diamagnetic materials, such as carbon and water, which include all substances not having another type of magnetism, are weakly repelled by a magnet. The overall strength of a magnet is measured by its magnetic moment, while the local strength of the magnetism in a material is measured by its magnetization. Background on the physics of magnetism and magnet
(fig2.5 - magnet)
2.4.1 THE EFFECT OF MAGNETISMThe magnetic field (usually denoted B) is called a field (physics) because it has a value at every point in space. The magnetic field (at a given point) is specified by two properties: (1) its direction, which is along the orientation of a compass needle; and (2) its magnitude (also called strength), which is proportional to how strongly the compass needle orients along that direction. Direction and magnitude makes B a vector, so B is a vector field. (B can also depend on time.) In SI units the strength of the magnetic field is given in teslas. [9]
2.4.2 MAGNETIC MOMENT A magnet's magnetic moment (also called magnetic dipole moment, and usually denoted μ) is a vector that characterizes the magnet's overall magnetic properties. For a bar magnet, the direction of the magnetic moment points from the magnet's north pole to its south pole, and the magnitude relates to how strong and how far apart these poles are. In SI units the magnetic moment is specified in terms of A•m². A magnet both produces its own magnetic field and it responds to magnetic fields. The strength of the magnetic field it produces is at any given point proportional to the magnitude of its magnetic moment. In addition, when the magnet is put into an "external" magnetic field produced by a different source, it is subject to a torque tending to orient the magnetic moment parallel to the field. The amount of this torque is proportional both to the magnetic moment and the "external" field. A magnet may also be subject to a force driving it in one direction or another, according to the positions and orientations of the magnet and source. If the field is uniform in space the magnet is subject to no net force, although it is subject to a torque. A wire in the shape of a circle with area A and carrying current I is a magnet, with a magnetic moment of magnitude equal to IA.
2.4.3 MAGNETIZATION The magnetization of an object is the local value of its magnetic moment per unit volume, usually denoted M, with units A/m. It is a vector field, rather than just a vector (like the magnetic moment), because the different sections of a bar magnet generally are magnetized with different directions and strengths (for example, due to domains, see below). A good bar magnet may have a magnetic moment of magnitude 0.1 A•m² and a volume of 1 cm³, or 0.000001 m³, and therefore an average magnetization magnitude is 100,000 A/m. Iron can have a magnetization of around a million A/m. Such a large value explains why magnets are so effective at producing magnetic fields. Two models for magnets: magnetic poles and atomic currents See also: Magnetic moment # Examples of magnetic moments Magnetic pole model: Although for many purposes it is convenient to think of a magnet as having distinct north and south magnetic poles, the concept of poles should not be taken literally: it is merely a way of referring to the two different ends of a magnet. The magnet does not have distinct "north" or "south" particles on opposing sides. (No magnetic monopole has yet been observed.) If a bar magnet is broken in half, in an attempt to [10]
separate the north and south poles, the result will be two bar magnets, each of which has both a north and south pole. The magnetic pole approach is used by professional magneticians to design permanent magnets. In this approach, the pole surfaces of a permanent magnet are imagined to be covered with 'magnetic charge', little 'North pole' particles on the North Pole and 'South poles' on the south pole, that are the source of the magnetic field lines. If the magnetic pole distribution is known, then outside the magnet the pole model gives the magnetic field exactly. By simply supplementing the pole model field with a term proportional to the magnetization (see Units and Calculations, below) the magnetic field within the magnet is given exactly. This pole model is also called the "Gilbert model" of a magnetic dipole.[1] Griffiths suggests (p. 258): "My advice is to use the Gilbert model, if you like, to get an intuitive "feel" for a problem, but never rely on it for quantitative results." Ampère model: Another model is the "Ampère model", where all magnetization is due to the effect of microscopic, or atomic, circular "bound currents", also called "Ampèrian currents" throughout the material. For a uniformly magnetized bar magnet in the shape of a cylinder, the net effect of the microscopic bound currents is to make the magnet behave as if there is a macroscopic sheet of electric current flowing around the surface of the cylinder, with local flow direction normal to the cylinder axis. (Since scraping off the outer layer of a magnet will not destroy its magnetic field, it can be seen that this is just a model, and the tiny currents are actually distributed throughout the material). The right-hand rule due to Ampère tells which direction the current flows. The Ampere model gives the exact magnetic field both inside and outside the magnet. It is usually difficult to calculate the Amperian currents on the surface of a magnet, whereas it is often easier to find the effective poles for the same magnet.
2.4.4 POLE NAMING CONVENTIONS The north pole of the magnet is the pole which, when the magnet is freely suspended, points towards the Earth's magnetic north pole in northern Canada. Since opposite poles (north and south) attract whereas like poles (north and north, or south and south) repel, the Earth's present geographic north is thus actually its magnetic south. Confounding the situation further, the Earth's magnetic field has reversed itself many times in the distant past. In order to avoid this confusion, the terms positive and negative poles are sometimes used instead of north and south, respectively. As a practical matter, in order to tell which pole of a magnet is north and which is south, it is not necessary to use the earth's magnetic field at all. For example, one calibration method [11]
would be to compare it to an electromagnet, whose poles can be identified via the righthand rule. Descriptions of magnetic behaviors There are several types of magnetism, and all materials exhibit at least one of them. This section describes, qualitatively, the primary types of magnetic behavior that materials can show. The physics underlying each of these behaviors is described in the next section below, and can also be found in more detail in their respective articles. Ferromagnetic and ferrimagnetic materials are the ones normally thought of as 'magnetic'; they are attracted to a magnet strongly enough that the attraction can be felt. These materials are the only ones that can retain magnetization and become magnets; a common example is a traditional refrigerator magnet. Ferrimagnetic materials, which include ferrites and the oldest magnetic materials magnetite and lodestone, are similar to but weaker than ferromagnetics. The difference between ferro- and ferrimagnetic materials is related to their microscopic structure, as explained below. Paramagnetic substances such as platinum, aluminum, and oxygen are weakly attracted to a magnet. This effect is hundreds of thousands of times weaker than ferromagnetic materials attraction, so it can only be detected by using sensitive instruments, or using extremely strong magnets. Magnetic ferrofluids, although they are made of tiny ferromagnetic particles suspended in liquid, are sometimes considered paramagnetic since they can't be magnetized. Diamagnetic substances such as carbon, copper, water, and plastic are even more weakly repelled by a magnet. All substances not possessing one of the other types of magnetism are diamagnetic; this includes most substances. Although force on a diamagnetic object from an ordinary magnet is far too weak to be felt, using extremely strong superconducting magnets diamagnetic objects such as pieces of lead and even frogs can be levitated so they float in midair. Superconductors repel magnetic fields from their interior and are strongly diamagnetic. Magnetism, at its root, arises from two sources: Electric currents, or more generally moving electric charges, create magnetic fields (see Maxwell's Equations). Many particles have nonzero "intrinsic" (or "spin") magnetic moments. (Just as each particle, by its nature, has a certain mass and charge, each has a certain magnetic moment, possibly zero.) In magnetic materials, the most important sources of magnetization are, more specifically, the electrons' orbital angular motion around the nucleus, and the electrons' intrinsic magnetic moment (see Electron magnetic dipole moment). The other potential sources of magnetism are much less important: For example, the nuclear magnetic moments of the nuclei in the material are typically thousands of times smaller than the electrons' magnetic moments, so they are negligible in the context of the magnetization of materials. (Nuclear [12]
magnetic moments are important in other contexts, particularly in Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI).) Ordinarily, the countless electrons in a material are arranged such that their magnetic moments (both orbital and intrinsic) cancel out. This is due, to some extent, to electrons combining into pairs with opposite intrinsic magnetic moments (as a result of the Pauli exclusion principle; see Electron configuration), or combining into "filled subshells" with zero net orbital motion; in both cases, the electron arrangement is so as to exactly cancel the magnetic moments from each electron. Moreover, even when the electron configuration is such that there are unpaired electrons and/or non-filled subshells, it is often the case that the various electrons in the solid will contribute magnetic moments that point in different, random directions, so that the material will not be magnetic. However, sometimes (either spontaneously, or due to an applied external magnetic field) each of the electron magnetic moments will be, on average, lined up. Then the material can produce a net total magnetic field, which can potentially be quite strong. The magnetic behavior of a material depends on its structure (particularly its electron configuration, for the reasons mentioned above), and also on the temperature (at high temperatures, random thermal motion makes it more difficult for the electrons to maintain alignment).
2.4.5 PHYSICS OF PARAMAGNETISM In a paramagnetic material there are unpaired electrons, i.e. atomic or molecular orbitals with exactly one electron in them. While paired electrons are required by the Pauli exclusion principle to have their intrinsic ('spin') magnetic moments pointing in opposite directions, causing their magnetic fields to cancel out, an unpaired electron is free to align its magnetic moment in any direction. When an external magnetic field is applied, these magnetic moments will tend to align themselves in the same direction as the applied field, thus reinforcing it.
2.4.6 PHYSICS OF DIAMAGNETISM In a diamagnetic material, there are no unpaired electrons, so the intrinsic electron magnetic moments cannot produce any bulk effect. In these cases, the magnetization arises from the electrons' orbital motions, which can be understood classically as follows: When a material is put in a magnetic field, the electrons circling the nucleus will experience, in addition to their Coulomb attraction to the nucleus, a Lorentz force from the magnetic field. Depending on which direction the electron is orbiting, this force may increase the centripetal force on the electrons, pulling them in towards the nucleus, or it may decrease the force, pulling them away from the nucleus. This effect systematically [13]
increases the orbital magnetic moments that were aligned opposite the field, and decreases the ones aligned parallel to the field (in accordance with Lenz's law). This results in a small bulk magnetic moment, with an opposite direction to the applied field. Note that this description is meant only as an heuristic; a proper understanding requires a quantum-mechanical description. Note that all materials undergo this orbital response. However, in paramagnetic and ferromagnetic substances, the diamagnetic effect is overwhelmed by the much stronger effects caused by the unpaired electrons.
2.4.7 PHYSICS OF FERROMAGNETISM A ferromagnet, like a paramagnetic substance, has unpaired electrons. However, in addition to the electrons' intrinsic magnetic moments wanting to be parallel to an applied field, there is also in these materials a tendency for these magnetic moments to want to be parallel to each other. Thus, even when the applied field is removed, the electrons in the material can keep each other continually pointed in the same direction. Every ferromagnetic substance has its own individual temperature, called the Curie temperature, or Curie point, above which it loses its ferromagnetic properties. This is because the thermal tendency to disorder overwhelms the energy-lowering due to ferromagnetic order. Magnetic Domains
(Fig2.6-Magnetic domains in ferromagnetic material)
The magnetic moment of atoms in a ferromagnetic material cause them to behave something like tiny permanent magnets. They stick together and align themselves into small regions of more or less uniform alignment called magnetic domains or Weiss domains. Magnetic domains can be observed with a magnetic force microscope to reveal magnetic [14]
domain boundaries that resemble white lines in the sketch.There are many scientific experiments
that can physically show magnetic fields. (Fig. 2.7-Effect of a magnet on the domains)
When a domain contains too many molecules, it becomes unstable and divides into two domains aligned in opposite directions so that they stick together more stably as shown at the right. When exposed to a magnetic field, the domain boundaries move so that the domains aligned with the magnetic field grow and dominate the structure as shown at the left. When the magnetizing field is removed, the domains may not return to aunmagnetized state. This results in the ferromagnetic material being magnetized, forming a permanent magnet. When magnetized strongly enough that the prevailing domain overruns all others to result in only one single domain, the material is magnetically saturated. When a magnetized ferromagnetic material is heated to the Curie point temperature, the molecules are agitated to the point that the magnetic domains lose the organization and the magnetic properties they cause cease. When the material is cooled, this domain alignment structure spontaneously returns, in a manner roughly analogous to how a liquid can freeze into a crystalline solid.
2.4.8 MAGNETIC HYSTERESIS The lag or delay of a magnetic material known commonly as Magnetic Hysteresis, relates to the magnetization properties of a material by which it firstly becomes magnetized and then de-magnetized. We know that the magnetic flux generated by an electromagnetic coil is the amount of magnetic field or lines of force produced within a given area and that it is more commonly called "Flux Density". Given the symbol B with the unit of flux density being the Tesla,T. We also know from the previous tutorials that the magnetic strength of an electromagnet depends upon the number of turns of the coil, the current flowing through the coil or the [15]
type of core material being used, and if we increase either the current or the number of turns we can increase the magnetic field strength, symbol H. Previously, the relative permeability, symbol μr was defined as the product of the absolute permeability μ and the permeability of free space μo (a vacuum) and this was given as a constant. However, the relationship between the flux density, B and flux density, H can be defined by the fact that the relative permeability, μr is not a constant but a function of the magnetic field intensity thereby giving magnetic flux density as: B = μ H. Then the magnetic flux density in the material will be increased by a larger factor as a result of its relative permeability for the material compared to the magnetic flux density in vacuum, μoH and for an air-cored coil this relationship is given as:
So for ferromagnetic materials the ratio of flux density to field strength (B/H) is not constant but varies with flux density. However, for air cored coils or any non-magnetic medium core such as woods or plastics, this ratio can be considered as a constant and this constant is known as μo, the permeability of free space, (μo = 4.π.10-7 H/m). By plotting values of flux density, (B) against the field strength, (H) we can produce a set of curves called Magnetisation Curves, Magnetic Hysteresis Curves or more commonly B-H Curves for each type of core material used as shown below.
2.4.9 B-H CURVE
(Fig2.8-B-H Curve) [16]
The set of magnetization curves, M above represents an example of the relationship between B and H for soft-iron and steel cores but every type of core material will have its own set of magnetic hysteresis curves. You may notice that the flux density increases in proportion to the field strength until it reaches a certain value were it can not increase any more becoming almost level and constant as the field strength continues to increase. This is because there is a limit to the amount of flux density that can be generated by the core as all the domains in the iron are perfectly aligned. Any further increase will have no effect on the value of M, and the point on the graph where the flux density reaches its limit is called Magnetic Saturation also known as Saturation of the Core and in our simple example above the saturation point of the steel curve begins at about 3000 ampere-turns per metre. Saturation occurs because as we remember from the previous Magnetism tutorial which included Weber's theory, the random haphazard arrangement of the molecule structure within the core material changes as the tiny molecular magnets within the material become "lined-up". As the magnetic field strength, (H) increases these molecular magnets become more and more aligned until they reach perfect alignment producing maximum flux density and any increase in the magnetic field strength due to an increase in the electrical current flowing through the coil will have little or no effect.
2.4.10 RETENTIVITY
Lets assume that we have an electromagnetic coil with a high field strength due to the current flowing through it, and that the ferromagnetic core material has reached its saturation point, maximum flux density. If we now open a switch and remove the magnetising current flowing through the coil we would expect the magnetic field around the coil to disappear as the magnetic flux reduced to zero. However, the magnetic flux does not completely disappear as the electromagnetic core material still retains some of its magnetism even when the current has stopped flowing in the coil. This ability to retain some magnetism in the core after magnetisation has stopped is called Retentivity or Remanence while the amount of flux density still present in the core is called Residual Magnetism, BR . The reason for this that some of the tiny molecular magnets do not return to a completely random pattern and still point in the direction of the original magnetising field giving them a sort of "memory". Some ferromagnetic materials have a high retentivity (magnetically hard) making them excellent for producing permanent magnets. While other ferromagnetic materials have low retentivity (magnetically soft) making them ideal for use in electromagnets, solenoids or relays. One way to reduce the this residual flux density to zero is to reverse the direction of current flow through the coil making the value of H, the magnetic field strength negative and this is called a Coercive Force, HC .
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If this reverse current is increased further the flux density will also increase in the reverse direction until the ferromagnetic core reaches saturation again but in the reverse direction from before. Reducing the magnetising current, i once again to zero will produce a similar amount of residual magnetism but in the reverse direction. Then by constantly changing the direction of the magnetising current through the coil from a positive direction to a negative direction, as would be the case in an AC supply, a Magnetic Hysteresis loop of the ferromagnetic core can be produced.
2.4.11 MAGNETIC HYSTERESIS LOOP
(Fig. 2.9- Magnetic Hysteresis Loop)
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The Magnetic Hysteresis loop above, shows the behavior of a ferromagnetic core graphically as the relationship between B and H is non-linear. Starting with an unmagnetised core both B and H will be at zero, point 0 on the magnetisation curve. If the magnetisation current, i is increased in a positive direction to some value the magnetic field strength H increases linearly with i and the flux density B will also increase as shown by the curve from point 0 to point a as it heads towards saturation. Now if the magnetising current in the coil is reduced to zero the magnetic field around the core reduces to zero but the magnetic flux does not reach zero due to the residual magnetism present within the core and this is shown on the curve from point a to point b. To reduce the flux density at point b to zero we need to reverse the current flowing through the coil. The magnetising force which must be applied to null the residual flux density is called a "Coercive Force". This coercive force reverses the magnetic field re-arranging the molecular magnets until the core becomes unmagnetised at point c. An increase in the reverse current causes the core to be magnetised in the opposite direction and increasing this magnetisation current will cause the core to reach saturation but in the opposite direction, point d on the cure which is symmetrical to point b. If the magnetising current is reduced again to zero the residual magnetism present in the core will be equal to the previous value but in reverse at point e. Again reversing the magnetising current flowing through the coil this time into a positive direction will cause the magnetic flux to reach zero, point f on the curve and as before increasing the magnetisation current further in a positive direction will cause the core to reach saturation at point a. Then the B-H curve follows the path of a-b-c-d-e-f-a as the magnetising current flowing through the coil alternates between a positive and negative value such as the cycle of an AC voltage. This path is called a Magnetic Hysteresis Loop. The effect of magnetic hysteresis shows that the magnetisation process of a ferromagnetic core and therefore the flux density depends on which part of the curve the ferromagnetic core is magnetised on as this depends upon the circuits past history giving the core a form of "memory". Then ferromagnetic materials have memory because they remain magnetised after the external magnetic field has been removed. However, soft ferromagnetic materials such as iron or silicon steel have very narrow magnetic hysteresis loops resulting in very small amounts of residual magnetism making them ideal for use in relays, solenoids and transformers as they can be easily magnetised and demagnetised. Since a coercive force must be applied to overcome this residual magnetism, work must be done in closing the hysteresis loop with the energy being used being dissipated as heat in the magnetic material. This heat is known as hysteresis loss, the amount of loss depends on the material's value of coercive force. By adding addictive's to the iron metal such as silicon, materials with a very small coercive force can be made that have a very narrow hysteresis loop. Materials with narrow hysteresis loops are easily magnetised and demagnetised and known as soft magnetic materials.
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2.4.12 MAGNETIC HYSTERESIS LOOPFOR SOFT AND HARD MATERIALS
(Fig. 2.10- Magnetic hysteresis loop for soft and hard materials)
Magnetic Hysteresis results in the dissipation of wasted energy in the form of heat with the energy wasted being in proportion to the area of the magnetic hysteresis loop. Hysteresis losses will always be a problem in AC transformers where the current is constantly changing direction and thus the magnetic poles in the core will cause losses because they constantly reverse direction. Rotating coils in DC machines will also incur hysteresis losses as they are alternately passing north the south magnetic poles. As said previously, the shape of the hysteresis loop depends upon the nature of the iron or steel used and in the case of iron which is subjected to massive reversals of magnetism, for example transformer cores, it is important that the B-H hysteresis loop is as small as possible. [20]
In the next tutorial about Electromagnetism, we will look at Faraday's Law of Electromagnetic Induction and see that by moving a wire conductor within a stationary magnetic field it is possible to induce an electric current in the conductor producing a simple generator.
2.5 SOLENOID A solenoid (from the Frenchsolénoïde, derived in turn from the Greeksolen "pipe, channel" + combining form of Greek eidos "form, shape"[1]) is a coil wound into a tightly packed helix. The term was invented by André-Marie Ampère to designate a helical coil.[2] In physics, the term refers specifically to a long, thin loop of wire, often wrapped around a metallic core, which produces a uniform magnetic field in a volume of space (where some experiment might be carried out) when an electric current is passed through it. Solenoids are important because they can create controlled magnetic fields and can be used as electromagnets. In engineering, the term may also refer to a variety of transducer devices that convert energy into linear motion. The term is also often used to refer to a solenoid valve, which is an integrated device containing an electromechanical solenoid which actuates either a pneumatic or hydraulic valve, or a solenoid switch, which is a specific type of relay that internally uses an electromechanical solenoid to operate an electrical switch; for example, an automobile starter solenoid, or a linear solenoid, which is an electromechanical solenoid.
Inside
(Fig. 2.11-Flow of current inside solenoid)
A solenoid with 3 Amperian loops: a, b and c. In short: the magnetic field inside an infinitely long solenoid is homogeneous and its strength does not depend on the distance from the axis, nor on the solenoid cross-sectional area. [21]
This is a derivation of the magnetic flux density around a solenoid that is long enough so that fringe effects can be ignored. In the diagram to the right, we immediately know that the flux density vector points in the positive z direction inside the solenoid, and in the negative zdirection outside the solenoid. We see this by applying the right hand grip rule for the field around a wire. If we wrap our right hand around a wire with the thumb pointing in the direction of the current, the curl of the fingers shows how the field behaves. Since we are dealing with a long solenoid, all of the components of the magnetic field not pointing upwards cancel out by symmetry. Outside, a similar cancellation occurs, and the field is only pointing downwards. Now consider the imaginary loop c that is located inside the solenoid. By Ampère's law, we know that the line integral of B (the magnetic flux density vector) around this loop is zero, since it encloses no electrical currents (it can be also assumed that the circuital electric field passing through the loop is constant under such conditions: a constant or constantly changing current through the solenoid). We have shown above that the field is pointing upwards inside the solenoid, so the horizontal portions of loop c do not contribute anything to the integral. Thus the integral of the up side 1 is equal to the integral of the down side 2. Since we can arbitrarily change the dimensions of the loop and get the same result, the only physical explanation is that the integrands are actually equal, that is, the magnetic field inside the solenoid is radially uniform. Note, though, that nothing prohibits it from varying longitudinally, which in fact it does.
Outside:-
(Fig. 2.12- Flow of current outside solenoid)
Magnetic field created by a solenoid (cross-sectional view) described using field lines. A similar argument can be applied to the loop a to conclude that the field outside the solenoid is radially uniform or constant. This last result, which holds strictly true only near the centre of the solenoid where the field lines are parallel to its length, is important in as much as it shows that the flux density outside is practically zero since the radii of the field outside the solenoid will tend to infinity. An intuitive argument can also be used to show that the flux density outside the solenoid is actually zero. Magnetic field lines only exist as loops, they cannot diverge from or converge to a point like electric field lines can (see Gauss's law for magnetism). The magnetic field lines follow the longitudinal path of the solenoid inside, so they must go in the opposite direction outside of the solenoid so that the lines can form a loop. However, [22]
the volume outside the solenoid is much greater than the volume inside, so the density of magnetic field lines outside is greatly reduced. Now recall that the field outside is constant. In order for the total number of field lines to be conserved, the field outside must go to zero as the solenoid gets longer. Of course, if the solenoid is constructed as a wire spiral (as often done in practice), then it emanates an outside field the same way as a single wire, due to the current flowing overall down the length of the solenoid.
2.5.1 QUANTITATIVE DESCRIPTION Now we can consider the imaginary loop b. Take the line integral of B around the loop of height l. The horizontal components vanish, and the field outside is practically zero, so Ampère's Law gives us:
where
is the magnetic constant,
the number of turns, the current. From this we get:
This equation is for a solenoid with no core. The inclusion of a ferromagnetic core, such as iron, increases the magnitude of the magnetic flux density in the solenoid. This is expressed by the formula
whereμeff is the effective or apparent permeability of the core, which is a function of the geometric properties of the core and its relative permeability. This equation is often used incorrectly due to the lack of understanding of the difference between relative and effective permeability, which can in fact differ by many orders of magnitude. For an open magnetic structure, the relationship between the effective permeability and relative permeability is given as follows:
wherek is the demagnetisation factor of the core.
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2.5.2 ELECTROMECHANICAL SOLENOIDS
(Fig. 2.13- magnetic forces of lines in magnet)
A 1920 explanation of a commercial solenoid used as an electromechanical actuator Electromechanical solenoids consist of an electromagnetically inductive coil, wound around a movable steel or iron slug (termed the armature). The coil is shaped such that the armature can be moved in and out of the center, altering the coil's inductance and thereby becoming an electromagnet. The armature is used to provide a mechanical force to some mechanism (such as controlling a pneumatic valve). Although typically weak over anything but very short distances, solenoids may be controlled directly by a controller circuit, and thus have very low reaction times. The force applied to the armature is proportional to the change in inductance of the coil with respect to the change in position of the armature, and the current flowing through the coil (see Faraday's law of induction). The force applied to the armature will always move the armature in a direction that increases the coil's inductance. Electromechanical solenoids are commonly seen in electronic paintball markers, pinball machines, dot matrix printers and fuel injectors.
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2.5.3 ROTARY SOLENOID The rotary solenoid is an electromechanical device used to rotate a ratcheting mechanism when power is applied. These were used in the 1950s for rotary snap-switch automation in electromechanical controls. Repeated actuation of the rotary solenoid advances the snapswitch forward one position. Two rotary actuators on opposite ends of the rotary snapswitch shaft, can advance or reverse the switch position. The rotary solenoid has a similar appearance to a linear solenoid, except that the core is mounted in the center of a large flat disk, with two or three inclined grooves cut into the underside of the disk. These grooves align with slots on the solenoid body, with ball bearings in the grooves. When the solenoid is activated, the core is drawn into the coil, and the disk rotates on the ball bearings in the grooves as it moves towards the coil body. When power is removed, a spring on the disk rotates it back to its starting position, also pulling the core out of the coil. The rotary solenoid was invented in 1944 by George H. Leland, of Dayton, Ohio, to provide a more reliable and shock/vibration tolerant release mechanism for air-dropped bombs. Previously used linear (axial) solenoids were prone to inadvertent releases. U.S. Patent number 2,496,880 describes the electromagnet and inclined raceways that are the basis of the invention. Leland's engineer, Earl W. Kerman, was instrumental in developing a compatible bomb release shackle that incorporated the rotary solenoid. Bomb shackles of this type are found in a B-29 aircraft fuselage on display at the National Museum of the USAF in Dayton, Ohio. Solenoids of this variety continue to be used in countless modern applications, and are still manufactured under Leland's original brand "Ledex", now owned by Johnson Electric.
2.5.4 ROTARY VOICE CALL A rotary voice coil is a rotational version of a solenoid. Typically the fixed magnet is on the outside, and the coil part moves in an arc controlled by the current flow through the coils. Rotary voice coils are widely employed in devices such as disk drives.
2.5.5 PNEUMATIV SOLENOID VALVES A pneumatic solenoid valve is a switch for routing air to any pneumatic device, usually an actuator, allowing a relatively small signal to control a large device. It is also the interface between electronic controllers and pneumatic systems.
2.5.6 HYDRAULIC SOLENOID VALVES Hydraulic solenoid valves are in general similar to pneumatic solenoid valves except that they control the flow of hydraulic fluid (oil), often at around 3000 psi (210 bar, 21 M Pa, 21 MN/m²). Hydraulic machinery uses solenoids to control the flow of oil to rams or actuators. Solenoid-controlled valves are often used in irrigation systems, where a relatively weak solenoid opens and closes a small pilot valve, which in turn activates the main valve by [25]
applying fluid pressure to a piston or diaphragm that is mechanically coupled to the main valve. Solenoids are also in everyday household items such as washing machines to control the flow and amount of water into the drum. Transmission solenoids control fluid flow through an automatic transmission and are typically installed in the transmission valve body.
2.5.7 AUTOMOBILE STARTER SOLENOID In a car or truck, the starter solenoid is part of an automobile starting system. The starter solenoid receives a large electric current from the car battery and a small electric current from the ignition switch. When the ignition switch is turned on (i.e. when the key is turned to start the car), the small electric current forces the starter solenoid to close a pair of heavy contacts, thus relaying the large electric current to the starter motor. Starter solenoids can also be built into the starter itself, often visible on the outside of the starter. If a starter solenoid receives insufficient power from the battery, it will fail to start the motor and may produce a rapid 'clicking' or 'clacking' sound. This can be caused by a low or dead battery, by corroded or loose connections in the cable, or by a broken or damaged positive (red) cable from the battery. Any of these will result in some power to the solenoid, but not enough to hold the heavy contacts closed, so the starter motor itself never spins, and the engine doesn't start.
2.5.8 PERMANENT MAGNET A permanent magnet is an object made from a material that is magnetized and creates its own persistent magnetic field. An everyday example is a refrigerator magnet used to hold notes on a refrigerator door. Materials that can be magnetized, which are also the ones that are strongly attracted to a magnet, are called ferromagnetic (or ferrimagnetic). These include iron, nickel, cobalt, some alloys of rare earth metals, and some naturally occurring minerals such as lodestone. Although ferromagnetic (and ferrimagnetic) materials are the only ones attracted to a magnet strongly enough to be commonly considered magnetic, all other substances respond weakly to a magnetic field, by one of several other types of magnetism. Ferromagnetic materials can be divided into magnetically "soft" materials like annealediron, which can be magnetized but do not tend to stay magnetized, and magnetically "hard" materials, which do. Permanent magnets are made from "hard" ferromagnetic materials such as alnico and ferrite that are subjected to special processing in a powerful magnetic field during manufacture, to align their internal microcrystalline structure, making them very hard to demagnetize. To demagnetize a saturated magnet, a certain magnetic field must be applied, and this threshold depends on coercivity of the respective material. "Hard" materials have high coercivity, whereas "soft" materials have low coercivity.
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2.6 WHY NOT PERMANENT MAGNET? As the name indicates that it is a permanent magnet and the magnetic properties of the magnet remain every time with in it. So when we shall use the permanent magnet in our project, it will stick the work piece at first time but it will not leave that work piece during that time when we have need to leave the work piece in desired place. So we can not use permanent magnet here.
2.7 WHY ELECTROMAGNET? We can not use permanent magnet here due to disadvantages of it above explained. So, we have to use such a magnet that it can do our work properly and easily. Electromagnet is a type of magnet in which we can create magnet field any time whenever needed, so that it can hold the flat metal sheet very easily and it can leave it in a desired place properly. The main advantage of using this type of magnet is that we can change the strength, intensity, magnitude of magnetic field in the solenoid by changing the number of turns in the solenoid, so that it can hold the work piece according to the need.
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CHAPTER-3
3.1 FINDING RESULTS i. ii. iii. iv. v.
It is used to lift and carry the work piece scrap of metal which is made up of ferrous metal. It reduces the human’s effort. When we are using conventional crane there is a need of adjusting the flat metal sheet so that time there is a need of more human’s effort. So it can reduce it by do this above work properly and easily. It can reduce the number of labours in the industry. Once it is set up in the industry, there is reduction in those areas which affects the production rate. If we are using this crane than we can save more time as it can do work faster than other conventional cranes and we can increase our production rate.
3.2 IMPLEMENTATION Till now, we have identified, formulated, analyzed and got the solution of the problem which we got from our industrial visit as discussed earlier. After doing such work now we are going to implementing this analysis, solution in our working model.
CONSTRUCTION OF ELECTROMAGNETIC CRANE Our electromagnetic crane consists of number of components, they are as follows1. Base of the crane. 2. Two wheels. 3. 3 DC Motors 4. Two switches 5. 2 Batteries 6. 2 Pulleys 7. Belt-pulley arrangement 8. A wire rope 9. Frame 10. Solenoid 11. A wire 12. A roller support 13. A joystick
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3.3 BRIEF DESCRIPTION OF COMPONENTS Now we will briefly describe all above components here above listed one by one -
3.3.1 BASE – base is a main part of our electromagnetic crane, and all component of the crane are situated on the base. The mechanical properties of base (strength, toughness, hardness) should be high. 3.3.2 TWO WHEELS- these are situated under the base of the crane, they support all the weight of the crane. By the help of these crane these tyres crane goes to the desire direction. the properties of wheels of our electromagnetic crane is that they can rotate freely. 3.3.3 3DC MOTOR- two dc motors we are using in two wheels respectively by the help of which wheels can rotate freely in desire directionand the remaining one dc motor is used to drive belt pulley arrangement. Every motor has six basic parts -- axle, rotor, stator, commutator, field magnet(s), and brushes. In most common motors, the external magnetic field is produced by high-strength permanent magnets1.
(fig. 3.1- rotor and stator of DC Motor)
The stator is the stationary part of the motor -- this includes the motor casing, as well as two or more permanent magnet pole pieces. The rotor (together with the axle and attached commutator) rotate with respect to the stator. The rotor consists of windings (generally on a core), the windings being electrically connected to the commutator. The above diagram shows a common motor layout -- with the rotor inside the stator (field) magnets. The geometry of the brushes, commutator contacts, and rotor windings are such that when power is applied, the polarities of the energized winding and the stator magnet(s) are misaligned, and the rotor will rotate until it is almost aligned with the stator's field magnets. [29]
As the rotor reaches alignment, the brushes move to the next commutator contacts, and energize the next winding. Given our example two-pole motor, the rotation reverses the direction of current through the rotor winding, leading to a "flip" of the rotor's magnetic field, driving it to continue rotating. In real life, though, motors will always have more than two poles (three is a very common number). In particular, this avoids "dead spots" in the commutator. You can imagine how with our example two-pole motor, if the rotor is exactly at the middle of its rotation (perfectly aligned with the field magnets), it will get "stuck" there. Meanwhile, with a twopole motor, there is a moment where the commutator shorts out the power supply (i.e., both brushes touch both commutator contacts simultaneously). This would be bad for the power supply, waste energy, and damage motor components as well. Yet another disadvantage of such a simple motor is that it would exhibit a high amount of torque "ripple" (the amount of torque it could produce is cyclic with the position of the rotor). As each brush transitions from one commutator contact to the next, one coil's field will rapidly collapse, as the next coil's field will rapidly charge up (this occurs within a few microsecond). We'll see more
about the effects of this later, but
in the meantime we can
(fig. 3.2- windings of DC Motor) see that this is a direct result of the coil windings' series wiring: The use of an iron core armature (as in the Mabuchi, above) is quite common, and has a number of advantages. First off, the iron core provides a strong, rigid support for the windings -- a particularly important consideration for high-torque motors. The core also conducts heat away from the rotor windings, allowing the motor to be driven harder than might otherwise be the case. Iron core construction is also relatively inexpensive compared with other, But iron core construction also has several disadvantages. The iron armature has a relatively high inertia which limits motor acceleration. This construction also results in high winding inductances which limit brush and commutator life.
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In small motors, an alternative design is often used which features a 'coreless' armature winding. This design depends upon the coil wire itself for structural integrity. As a result, the armature is hollow, and the permanent magnet can be mounted inside the rotor coil. Coreless DC motors have much lower armature inductance than iron-core motors of comparable size, extending brush and commutator life.
(Fig.3.3- Coreless armature winding) The coreless design also allows manufacturers to build smaller motors; meanwhile, due to the lack of iron in their rotors, coreless motors are somewhat prone to overheating. As a result, this design is generally used just in small, low-power motors. BEAMers will most often see coreless motors in the form of pager motors.
(Fig.3.4- an electric motor that runs on direct current electricity) [31]
Brushed DC electric motor, an internally commutated electric motor designed to be run from a direct current power source Brushless DC motor, a synchronous electric motor which is powered by direct current electricity and has an electronically controlled commutation system, instead of a mechanical commutation system based on brushes .
3.3.4TWO SWITCHES- we are using two switches here to supply the current whenever needed .In electronics, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another. The most familiar form of switch is a manually operated electromechanical device with one or more sets of electrical contacts. Each set of contacts can be in one of two states: either 'closed' meaning the contacts are touching and electricity can flow between them, or 'open', meaning the contacts are separated and non-conducting.
A switch may be directly manipulated by a human as a control signal to a system, such as a computer keyboard button, or to control power flow in a circuit, such as a light switch. Automatically-operated switches can be used to control the motions of machines, for example, to indicate that a garage door has reached its full open position or that a machine tool is in a position to accept another work piece. Switches may be operated by process variables such as pressure, temperature, flow, current, voltage, and force, acting as sensors in a process and used to automatically control a system. For example, a thermostat is an automatically-operated switch used to control a heating process. A switch that is operated by another electrical circuit is called a relay. Large switches may be remotely operated by a motor drive mechanism. Some switches are used to isolate electric power from a system, providing a visible point of isolation that can be pad-locked if necessary to prevent accidental operation of a machine during maintenance, or to prevent electric shock.
(Fig. 3.5- switches)
3.3.4 TWO BATTERIS- By the help of battery supply of current go to the solenoid and one dc motor (which is connected to belt pulley arrangement).
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3.3.6 TWO PULLEEYS- there is one pulley is connected to dc motor with the belt to derive shaft on which one end of wire is fixed and other end of wire is hang on other pulley to lift and drop the load at desired placed.
3.3.7 BELT-PULLEY ARRANGEMENT- In this arrangement there is a belt and a two pulleys. One of them(driving pulley) is mounted on the DC motor shaft and another one (driven pulley) is mounted on the shaft . 3.3.8 A WIRE ROPE-We are using a wire rope by which solenoid is hang. 3.3.9 FRAME-A frame is situated on the base, maximum arrangements of our project is mounted on this frame. 3.3.10 SOLENOID-It is the main key element of the project. It is the one which will raise or leave the work piece. 3.3.11 A WIRE- A wire connects the battery (power source) to the solenoid. 3.3.12 A ROLLER SUPPORT- There is a roller support under the base which supports the crane from the front part. 3.3.13 A JOYSTICK- We are using a joystick to drive the crane in the desired direction. In this joystick there are two cells which are acting as a power source.
3.4 WORKING Working of electromagnetic crane is as followsAn electromagnetic crane has a very simple working. First of all, we shall take the crane in its desired position i.e. From where the scrap materials/flat sheets of ferrous material to be lifted . Now, we shall down the pulley near the metal sheet, after that operator will turn ON the switch so that the current will flow in coil wire around the iron core. By which there will generate a strong magnetic field which will pick up that ferrous metal sheet by force of attraction. After that we shall drive crane by the help of joystick at desire place by the operator (where ferrous metal sheet have to put down). And now, operator will turn OFF the switch and thus flow of current will stop and metal sheet will be put in desire place.
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CONCLUSION
As we have solved problem of flat metal sheet by the help of electromagnetic crane replacing with conventional crane. But there are still many problems existing in industry. We will have to reduce these problems, working methods which are risky and not suitable for employee’s point of view. As it reduces human effort, it works faster than other cranes and it is economical and it requires less floor area too; so it can be beneficial for industry.
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DIRECTION FOR FUTURE RESERCH
As we know that there is requirement of an operator to drive this crane. By the help of computer and computer programming languages etc, it is possible to make it automatic crane.
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REFERENCE
Lancaster, Lynne (1999), "Building Trajan's Column", American Journal of Archaeology 103 (3): 419–439, doi:10.2307/506969, JSTOR 506969 Matheus, Michael (2002), "Mittelalterliche Hafenkräne", in Lindgren, Uta, Europäische Technik im Mittelalter. 800 bis 1400. Tradition und Innovation (4th ed.), Berlin: Gebr. Mann Verlag, pp. 345–348, ISBN 3-7861-1748-9Matthies, Andrea (1992), "Medieval Treadwheels. Artists' Views of Building Construction", Technology and Culture.
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