STEEL AUTHORITY OF INDIA LIMITED DURGAPUR STEEL PLANT A PROJECT REPORT CREATED BYSUPARNA DAS
A project report created bySuparna das
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Title: INDUSTRIAL TRAINING AT DURGAPUR
STEEL PLANT Name: SUPARNA DAS Dept: Applied Electronics & Instrumentation Engineering Roll No: 08/EIE/05 University Roll No: 08103005005 University Regd No: 081030110397 College: HALDIA INSTITUTE OF TECHNOLOGY
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Title: INDUSTRIAL TRAINING AT DURGAPUR
STEEL PLANT Name: SUPARNA DAS Dept: Applied Electronics & Instrumentation Engineering Roll No: 08/EIE/05 University Roll No: 08103005005 University Regd No: 081030110397 College: HALDIA INSTITUTE OF TECHNOLOGY
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ACKNOWLEDGEMENT
I owe a great many thanks to a great many people who helped and supported me during the project. My deepest thanks to Mr.Dilip Haldar, AGM AGM of traffic t raffic department at DSP who who helped me a lot lot during the project. I express my indebtedness to him who despite his palpable professional engagement and accountability, generously looked after the project p roject without whom this project might be a day dream. My deepest sense of gratitude to Mr.Arvind Pathak , safety engineer at DSP, Mr. M r. Tapas Karmakar, DGM of Instrumentation department at DSP, Mr. P.K.Biswas, P.K.Biswas, I/C at the Skelp mill for their support and guidance. I would would also like to thank Mr. P.K.Singh P.K.Singh ,who helped helped me to increase my knowledge about instrumentation of blast furnace.
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CONTENTS
SUMMARY««««««««««««««««««.5 The Chemistry of Steel««««««««««««««6 Process Flow Diagram««««««««««««««.7 Raw Materials«««««««««««««««««..8-11 Coke Ovens & Coal Chemicals««««««««««..11-12 Sinter Plant«««««««««««««««««.....13-15 Blast Furnace«««««««««««««««««..16-18 Steel Melting Shop«««««««««««««««..19-22 Blooming & Billet Mill«««««««««««««« Section Mill««««««««««««««««««« Skelp Mill««««««««««««««««««««. Merchant Mill««««««««««««««««««. Wheel & Axle Plant««««««««««««««««. Electrically Technical Laboratory««««««««««..
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SUMMARY Durgapur Steel Plant is an integrated steel plant that means it produces steel from iron ore to semi-finish product and to finished product.DSP is one of the modernized steel plant under SAIL. There is a little bit of SAIL in everybody¶s life. Steel is used to make fridges, washing machines, ovens and microwaves, sinks, radiators, any kind of vehicles and many more things. DSP was setup in 1954 and SAIL came in 1973. As we know steel is a very useful material in our daily life. Its price is less, it has good strength, it can be bent to form any kind of shape. Initially it¶s annual capacity was of one million tonne of crude steel per year, the capacity of DSP was later expanded to 1.6 million tonnes in the 70's. A massive modernization program was undertaken in the plant in early 90's, which, while bringing numerous technological developments in the plant, enhanced the capacity of the plant to 2.088 million tonnes of hot metal, 1.8 million tonnes crude steel and 1.586 million tonnes saleable steel.
Iron ore, coal and limestone are the three basic raw materials for the steel industry. Steel is an alloy of iron and about 2% or less carbon. Nothing in the steel plant get wasted. Even the slags, which come out during the processing is used as the raw material for the cement making factory.
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The Chemistry of Steel
Iron Ore + Limestone + Coke + Sinter
Blast Furnace
Liquid iron + S lag Additions + Refinin g
Liquid Steel
Slag which comes out during steel making is used to produce cement.
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Plain Rounds & Ribbed Rounds (TMT Bars) 7
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Steel Strip / Skelp
Angles, Channel, Joist
Raw Materials: Raw Material Handling Plant is the starting point of steel making process. The objective of RMHP is to receive, load, unload and places all the raw materials required for steel making i.e. Iron ore, Limestone, and Dolomite. Apart from this, RMHP also deals with Sinter mix preparation using state of the art automation system.
Iron ore, coal and limestone are the three basic raw materials for the steel industry. Durgapur Steel Plant draws its coal from the adjacent JhariaRanigunj coal belt. A good amount of prime coking coal, having fairly low ash content, is also imported. Bulk of iron ore lumps and fines come from the mines at Bolani in Orissa. Lime stone comes from a variety of sources: Birmitrapur (Orissa), Jaisalmer (Rajasthan).
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Major functions of RMHP : 1. Tippling of wagons. 2. Stacking and reclaiming of raw materials. 3. Crushing of flux and coke. 4. Sinter mix preparation. 5. Blend mix supply to sinter plant. 6. Iron ore lump screening. 7. Screened iron ore supply to blast furnace. 8. Limestone, dolomite & iron ore lump supply to BOF.
R AW AT E R I A L S H A N D L I N G AW M AT G: M H
To improve and ensure consistency in raw material quality, the facilities, which have been installed, are: y y
y y
y
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Beneficiation/washing facilities, both for lump ore and fines at Bolani Screening of lump iron ore inside the plant, Selective crushing of coal at Coal Handling Plant, Base blending facilities for Sinter Plant, Silo-cum- Blending bunkers
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As part of the modernisation programme, new raw material handling storage and blending facilities with selective crushing of coal have been installed in order to ensure consistency in raw material quality. The beneficiation/washing facilities, both for lump ore and fines at Bolani, have a capacity to process 3.44 million tonnes (wet basis) per annum so as to be capable of catering to the entire requirement of the plant after modernisation. Durgapur is the only steel plant in the country to have a coal washery at the plant site.
Coke Ovens & Coal Chemicals:
No of batteries No. of ovens per battery
-5½ - 78
The coke ovens and coal chemicals zone is divided into four basic sections namely coal preparation plant, coal carbonisation plant, coke handling plant and coal chemicals. Presently, DSP is operating only three batteries. The Blast Furnace grade coke produced in Coke Ovens is directly used in Blast Furnaces while the undersized coke is used for sinter making. The volatile matters, which emanate during the process of coke making subsequently produce a variety of by-products like naphthalene oil, heavy creosote oil, light oil, crude tar partially distilled tar, Ammonium Sulphate fertilizer in brand name ³Raja´, nitration grade benzene, nitration grade toluene, industrial grade toluene, light solvent naphtha etc.
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The coke oven gas is generally used in combination with the Blast Furnace gas and BOF gas as fuel and is carried through pipelines to the different areas of the plant. The adjoining Alloy Steels Plant under SAIL is also supplied with this fuel gas from DSP. Coal Handling sections also attached with Coal Washery where raw coal is washed to reduced its ash content before using it blend preparation. The main units of Coal Washery are Heavy Media Bath, BATAC jig, Spiral Washer, Thickener and Filter. Presently Coal Washery is not working. C oke
Oven Battery: There were 3 batteries of 78 ovens each and a half battery of 39 ovens. Capacity of each oven is 20 tonnes approx. on dry basis. The standard coking time is 18 to 20 hours. The flue temperature is 1230 ºC. Resulting Coke of size 20 to 80 mm sent to BF and undersize coke is sent to RMHP. There are 4 special cars in this section: (a) Charging car: Takes coal from service bunkers to individual ovens (b) Ram car: Pushes the coke out of individual ovens (c) Guide car: Guides the coke during pushing operation (d) Quenching car: Receives the hot coke for quenching
The Charging car used in coke oven battery at DSP is the modernized charging car. The entire process of charging is carried out from the control room inside the charging car. 11 | P a g e
Sinter Plant: Raw Sinter is a hard porous lump produced by controlled heating of a mixure of Iron ore fines, lime stone fines, dolomite fines, coke fines and other waste materials. Usage of sinter in Blast Furnace offers many advantages, like, utilization of Iron ore fines (which otherwise cannot be used directly in Blast Furnace as it will choke the furnace due to its fineness), reduction in coke rate etc. The process of sintering started in 1910 and flourished in different countries where there was coke shortage. Advantages of using sinter are: (a) To utilize all waste of fines nature like Mill scale, Ferro Scrap, LD slag. (b) To reduction in coke rate in Blast Furnace (c) To increase productivity of blast furnace (d) To provide smooth Gas Dynamics inside BF stack. (e) To utilize Iron Ore fines and Coke breeze. (f) Better Operation of Blast Furnaces as Sinter is engineered product. Plant capacity: 3.009MT/annum Machine capacity: Sinter Plant 1 - 2500 T/day (for each old m/c) X 2 nos Sinter Plant 2 - 5184T/day (for new machine) X 1 no
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Major equipments:
Material Flow Diagram:
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Sinter plant is a Heavy Power consuming plant and it consumes about 1/4th of the total power. yThere are four electrostatic precipitators in Sinter Plant 2 and two electrostatic precipitators in Sinter Plant 1 to control both fugitive and stack emission. Now target Sinter in Blast Furnace burden is 70 - 75%. y Various fractions of sinter are used as follows: y
+25mm and +6 to -16mm +16 to -25mm -6mm
Blast furnace Hearth layer Return fines re-circulated in sinter plant
Sinter is made firstly mixing limestone and iron ore, later the extra coke is added sideways. Through the rubber conveyor belt sinters of different sizes are separated. Two belts are separated in the two sides. One takes away the sinters to the storage and another one takes it directly to the blast furnace. When direct belt stops sinter is provided to the blast furnace from the storage by the indirect belt. PLC is used for temperature maintenance , flow measurement.
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Blast Furnaces:
Material Flow Diagram:
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Blast furnaces are referred to as the µmother unit¶ of an integrated steel plant. Iron ore as available in nature is basically an oxide. It is charged into a blast furnace either as lump ore or in the form of sinter and reduced to molten iron by the coke at temperatures ranging from 1, 200 ± 1, 400 degrees centigrade. The limestone, acting as flux, absorbs the impurities in the molten iron and goes out as slag. The major portion of liquid hot metal is transferred to steel melting shop for conversion to steel and the rest portion is cast into pig iron in pig casting machines. Blast furnace slag high in lime-content is used for cement making. There are four Blast Furnaces in DSP, named µKasturba¶, µKamala¶, µSarada¶, µDurga¶ out of which three are running except µKasturbaµ.The useful volume of two furnaces is 1,400 cubic meters each and that of the other one is 1,800 cubic meters. The furnaces are presently operating at a productivity level of 1.3-1.4 tonnes/cubic meter/day. The furnaces are equipped with sophisticated and modern computerised control system and are operated with high blast temperatures (1,100 degree centigrade) and high top pressure (0.7 Kg/ sq. cm). The cast houses are provided with facilities like twin tap holes, rocking runners etc. There are also two numbers of Slag Granulation Plants, which convert molten blast furnace slag into granulated forms for ready use in the cement industry. There are three pig casting machines, with a total capacity of 2,12,000 tonnes/year. IRON OXIDE(Fe 2O3 / Fe3O4)
Reducer (Coke)
Iron Metal With Other Elements + Impurities + Gas (C, Si, Mn, P, S) (Al2O3, SiO 2) HIGH MELTING POINT
Slag(Low Melting ) 16 | P a g e
Flux (CaO, MgO)
Based on temperature profile blast furnace can be divided into three distinct zones Upper Zone
In this Zone burden is rapidly heated from ambient temperature to about 9000C and the ascending gases form the middle zone cools down from about 9000C to 100-200 0C In this Zone hematite and magnetite are reduced to wustite by carbon monoxide. Middle Zone
In this zone reduction of wustite to iron by carbon monoxide takes place partly Very little heat exchange takes place in this zone as the thermal capacity of solid & gas remaining in this zone are almost equal. The temperature of this zone remains at about 900 ° -10000C In this Zone hematite and magnetite are reduced to wustite by carbon monoxide. Lower Zone
Gas cools down from about 2000 ° C (flame temperature) to about 900 ° C due to following physico-chemical processes occurring: ± Direct reduction of unreduced wustite ± Reduction of metalloids ± Carburization of iron ± Fusion of slag and metal (The temperature of the molten materials reaches 1400 ° - 14500C in this zone) Role Of Coke In Blast Furnace
Coke performs the role of providing heat 17 | P a g e
Additionally, it also provides permeability, for gases to pass through, especially in the lower part of the furnace Thus, Coke acts as a reducer, provides heat and imparts permeability to the furnace. Larger sized sinters are placed at the lower portion and smaller sized are kept at the upper portion to provide mechanical support. The arrangement is like this to provide following advantages: Fall through decrease High permeability Wastage Heat retain Mechanical support Buffer line
Hot molten metal is coming out through this channel in BF
Hot metal car (ladel) 18 | P a g e
bf charge distributer
Steel Melting Shop: Mixers - 2 x 1, 300 t Converters - 3 x 110 t (nominal heat size) Molten iron is further refined at the Steel Melting Shop (SMS) to produce steel, which is hard and malleable. At DSP, there are 3 converters (Basic Oxygen Furnace) of 110-130 tonnes each. The SMS also has a Vacuum Arc Degassing (VAD) unit for making special grades of steel. A major portion of the steel is routed through the Continuous Casting Plant. Another major portion of the steel is taken to the teeming bay, where it is top poured into 8 tonne ingot moulds for making ingot steel. A portion of highly controlled steel is cast at the Special Casting Bay into fluted ingots and special quality blooms. Fluted ingots are bottom poured and are used for making wheel steel for DSP¶s Wheel & Axle Plant. A portion of the liquid steel is also bottom poured to make axle ingots.
SMS or Steel Melting Shop is the section where hot metal from blast furnaces converted into steel.. This type of Basic Oxygen Furnace was first used successfully in the places called Linz and Donawitz in Austria. The shop was added during modernization of DSP and has a capacity of 1.876 million tones per annum. 19 | P a g e
SMS can be divided into 3 sections: (a) Basic oxygen Furnace (b) Continuous Casting Plant (c) New Lime Calcination Plant a) Basic Oxygen Furnace (BOF): Hot Metal coming out of the Blast Furnaces is collected in ladles which are transported through rail and is poured into mixers. There are two nos. of mixers which serve the purpose of storing as well as homogenization of temperature and composition of hot metal. Coke oven gas is used here to maintain the temperature at around 1260 ºC. The shop has three converters each having a capacity of 110-130T. The average life of a converter is around 1800 heats. Oxygen is blown at high pressure into the converter through a lance for steel making. The oxygen blowing rate through the lance is 415 Nm3/min. and the blowing pressure is
14.2 to 14.3 bar. The tap-to-tap time of BOF is approximately 57 minutes out of which oxygen blowing time is approximately 18 min. The gas obtained from BOF converter has a calorific value of 2100 Kcal/Nm3 and is used as fuel. The tapping temperature at Converter for CCP is 1700 ºC and top pouring temperature is 1640 ± 1650 ºC. BOF has an online process automation system. The system uses VAX/VMS system which works on the principle of virtual memory. The whole data acquisition system contains various levels where the higher level caters to the need of quick retrieval of data about operation parameters and other activities. b ) C ontinuous C asting
Plant ( CC P): DSP has two billet casting machines & one bloom casting machine. In Continuous Casting Process, ladle containing liquid steel is kept on an arm of a moving turret. The liquid steel is allowed to fall on tundish, which acts as a distributor of liquid steel into 6/4 moulds in billet/bloom casting machine. The moulds are made of Copper and iscooled by demineralised water.It is a primary cooling wherein liquid steel does not come in direct contact with water. The initial formation of billet is made inside the mould itself. Once the 20
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newly formed Billet/Bloom leaves the mould it is subjected to secondary cooling or direct cooling in next stages. The Billets/Bloom are drawn out with the help of Withdrawl unit. The Billets/Blooms are cut into required sizes with the 14 help of mechanical shear/gas cutting torch. The Billets/Blooms are subsequently evacuated and cooled in air and stacked for dispatch. The Continuous Casting Process is an energy efficient process with better yields. It converts liquid steel into billets/blooms directly and thereby saves substantial energy and process time. It also leads to better quality. There are two billet casters each with six strands capable of producing billets of sizes varying from 80mm 2 to 150mm2. Presently only 100 mm2 and 125mm2 billets are produced with the length of 9 meters. The average casting time is 85 mins. There is one Bloom Caster with 4 strands capable of producing blooms of size 160 mm x 210 mm, 160 mm x 230 mm, 200 mm x 200 mm, 150 mm x 300 mm, 150 mm x 350 mm with a cutting length of 3.4 to 10 mtrs. c) New Lime C alcination Plant (NLC P): This plant came up to cater to the need of BOF. The main function of this plant is to produce lime from naturally available limestone. Lime is mainly required for slag formation during the steel making process. Presently, Limestone from Jaisalmer is used as input material for the plant. There are three kilns (annular shaft type), each having a capacity 300T/day. The kilns are vertical cylindrical structure. Limestone, which is charged from the top, descends through the kiln, where it is subjected to controlled heating by two firing zones. Coke Oven gas at 5500mm water pressure is used as fuel for heating. Thus it operates in the temperature range of 1200-1250 ºC.
The calcination process is almost over as the charge reaches the bottom portion of lower combustion zone and the calcined lime is discharged into a silo by lime discharging device. NLCP has got bunkers and conveyors for storage, handling and supply of fluxes to the converter shop.
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In the SMS plant K-type thermocouple is used to measure the temperature of the liquid steel. There is O2 pipeline inside the SMS plant. Sometimes the flow is restricted by placing orifice plate inside the pipeline to create differential pressure. By pressure transmitter the differential pressure is measured. The pneumatic pipelines are connected to the MCR (main control room) where the pressure difference is displayed. Magnetic flowmeter and Ultrasonic flowmeter measures the flow in percentage. In the magnetic flowmeter the display was 63.5%. Ultrasonic flowmeter measures the flow of liquid by the ultrasonic ray. Gate valves are used in the pipeline to restrict the flow. When there is 4mA of current, the pressure is 3 Psi and the valve is about to close. When we pass 20mA of current, the pressure is 15 Psi and the valve is fully open. Thus the control valves are used in various places in the steel plant to control the flow of molten metal, air, gas and water through any pipeline.
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BLOOMING & BILLET MILL: Main objective of this mill is to produce square and rectangular section called blooms. The 8T ingots produced at the SMS, are first sent to the stripper bay. Thestripped ingots are reheated for hot rolling process to give them different sizes. Sections above 125x125, are called blooms while sections below 125x125mm are called billets. Some blooms go to section mills and rests go to billets mill. From Billet Mill slabs go to Skelp Mill. Material Flow Diagram:
Process: Soaking pit furnaces are used for reheating the ingots at 1280C. There are 20 soaking pit furnaces with capacity 110T. Fuel used is CO gas + B.F gas in the ratio of 1:4. The reheating time is usually 1.5 times the track time. After soaking the ingots are lifted by means of vertical ingot charger cranes for soaking. It is a two high reversible type mill driven by two nos 3000 HP 23 |
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DC motor at the mills speed of 0/40/60 rpm. Here 1200T shear is used to cut fish tail, and then the blooms are put in the bloom transfer bank. There is a two high reversible mill driven by 4500HP DC motor. The rolls are counter weight balanced and driven with a speed of 0/80/120 rpm. Pit Time: This is the amount of time the ingots have to be placed in the soaking pits. This is equal to 1.5 times the track time, which is around 3 to 4.5 hrs for hot ingots and around 12 hrs for cold ingots. No. of passes in 42´ mill: 13, in case of normal steel and 19, in case of special steel.
Major Equipments:
Soaking Pits: 20 in numbers and of 3 types 42´ Blooming Mill - 2 high reversing type with twin motor drive. Primary
Hot Bloom Shearing. 32´ Intermediate Mill - 2 high reversing mill driven by 4500 HP DC motor. . 700 T Shear Billet Mill: Blooms produced in Blooming Mill are further rolled into slabs and billets of various sizes. The capacity of Billet Mill is 0.957 tonne per annum.
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The products of this mill are 50 mm square to 125mm square Billets and 140 to 240 mm x 75/80 mm skelp slabs.
Major Equipments: Mill Train - Continuous morgan design with 8 strands Up and Down Cut Shear: - For emergency purpose Flying Shear - Shear a max. cross section of 130 square inch. Reheating Furnace: Under the modernization scheme, the Blooming Mill including socking pits are supposed to be phased out. At present a new reheating furnace had been installed and running. Feed materials for reheating furnace are the blooms for Bloom Caster. Then Blooms are heated up in the furnace and directly fed to the Billet Mills.
SECTION MILL: Blooms from blooming mill are taken and rolled in section mill to produce light and medium structural like joists, channels and Angles. The capacity of Section Mill is 0.212 million tone per annum . Material Flow Diagram:
Process: Blooms coming from Bloom Stock Bay are first reheated in Reheating Furnace upto a temperature of 1250 ºC. Then it goes to 26´ 2 High Roughing 25 |
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Mill strands through the roller table. After initial reduction in roughing mill the stocks are rolled in 24´ 3 High Intermediate Mill stands. Finally, bars leaving the intermediate mill, enters into the 24´ 2 High Finishing Mills stands by traveling along the roller tables.
angle
channels
joists
After this finishing work the bars are cut by hot saws and cooled on one of the three transfer banks. Finally the bars are stacked in the staking area prior to straightening. Before dispatch, the bars are inspected, tested for chemical analysis and straightened by the straightening machines.
Products: Joists Channels Angles 26 |
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200 x 100mm, 175 x 85mm, 150 x 75mm, 116 x 100mm 200 x 75mm, 175 x 75mm, 150 x 75mm, 125 x 65mm 150 x 150mm, 130 x 130mm, 110 x 110mm, 100 x 100mm
Major Equipments: Reheating
Furnace - 2 continuous end charge end discharge type. Roughing Mill stands - Rolls of 26´ diameter two-high reversing, closed top type. Intermediate Mill Stands - 2 stands of 24´ diameter three-high non reversing open top housing type. Finishing Mill Stands - 24´ diameter two-high non-reversing, open top housing type. Finishing End - 2 hot saws. Straightening Machine - 3 cold straightening machines.
SKELP MILL: Skelp Mill was not there at the initial phase of Durgapur Steel Plant. It came up during the expansion of plant to 1.6MTPA in late 60¶s. Skelp is a narrow section mostly used for the pipes and tubes manufacturing. The annual capacity of this mill is 0.25 million tone per annum. Material Flow Diagram:
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Process: Skelp mill receives slabs from billet mill by rail transfer bogies. The slabs are taken on to charging table from the bogie. The slabs are fed to a reheating furnace by a Ram charger. The furnace is of side charge and side discharging type. The furnace is fired by a mixture of coke oven and Blast Furnace gas in a ratio of 1:1. The furnace has a heating capacity of 60T/Hr. The slabs are sent to the mill section, which consists of 11 horizontal strands and 3 vertical strands. These are arranged as shown below: E1-H1-H2-H3-H4-H5-E3-H6-COBBLE SHEAR-LOOPING TROUGH-H7-H8H9-H10-H11
Where H refers to horizontal strands and E refers to vertical edge. The roughing mill constitutes strands from H1 to H6 while H7 to H 11 constitute the finishing mill.
After rolling, the Skelp or strip is coiled and the coil is dispatched to customers. Products: Steel Strip and Skelp from 147 to 252 mm in width and 2.5 to 4.5 mm thick . .
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Furnace gas mixing is controlled through Microprocessors. Microprocessors can be set at manual, automatic and cascade mode. Side by side air mixing with gas is also controlled by the microprocessors. Furnace is having two zonesHeating zone Soaking zone Heating zone temperature is maintained at 1080 ° C in running furnace whereas soaking zone temperature is 1280 ° C. All the valves inside the pipeline are controlled by the microprocessors only. Furnace pressure is also maintained through microprocessor.
Mill is having 11 stands, 6 in roughing mill and rest in the finishing mill. After the finishing stand there is a pinch roll followed by two pinch rolls along with vibrator. Total coil is accommodated in coil bed. Front end of the coil is fed manually into the pinch roll and after that it is clicked in coil run. This coil is pushed back to the coil conveyor. Coil is strapped for packaging and stacked in dispatch section as per quality and section. Skelp mill produces skelp in the range of 146-235 mm primarily for tubes and pipes making industry.
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Pyrometers are used to detect the temperature when the skelp mill is at running condition as it senses the temperature from a distance.
DPT-Differential Pressure Transmitter
In the air-pipeline venturimeters are used and in the gas pipeline orifice plates are used to create differential pressure.
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MERCHANT MILL: Merchant Mill takes billets of size 100 mm x 100 mm from CCP and produces plain round bars and ribbed TMT bars of various diameters. The capacity of Merchant Mill is 0.28 million tone per annum of plain round and thermo mechanically treated (TMT) ribbed bars of dia. 12, 14, 16, 18, 20, 22, 24 and 28 mm. Material Flow Diagram:
Process: Billets from CCP are fed to the side charging & discharging type reheating furnace through furnace bed and ram charger. After reheating of it is delivered to the pinch roll and then to Roughing, Intermediate and Finishing mills stands Reheating Furnace Billets Through Ram Charger Up Down Cut Pendulam Shear Intermediate Mill Roughing Mill Finishing Mill Thermax Process Automatic Bundling / Binding Machine Despatch Area Cooling Bed Rotary Shear Rotary Shear 19 consecutively. Roughing mill consists of 7 stands, Intermediate consists of four and the Finishing mill consists of 2 stands. In between 7th & 8th stand a crop cum cobble shear is placed, which is used for cutting the front end of each bar. After this the finished products are passed thru three Thermax carriages where TMT bars produced tempered by intense cooling. Finally rotary shear cuts the rods into required length to accommodate them at cooling bed. After cooling the bars 31
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are cut by the Bar Shear and sent to automatic bundling / binding machine, where bars are packed and bound into neat bundles and sent to the dispatch bay.
Major Equipments: Charging Bed Reheating furnaces - Two ±zone type arranged for charging and discharging Pendulum shear - To cut the front end of billets Mills - Continuous morgan design with 4 repeaters consists of 13 horizontal stands (Roughing stands 1-7, Intermediate stands 8-11, Finishing stands 12-13) Snap Shear ± two nos. Crop cum cobble shear - used for cutting the rolled stock in case cobble is formed. Thermax carriage - 3 in numbers, Spray water at high pressure on the rolled bars. Rotary shear & Bar Shear - To cut rods into predetermined lengths. Automatic Binding / Bundling Machines - packs and binds the bars into neat bundles. Cooling Bed
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The layout consultancy is either fully automatic or manual which is done as per the specifications given by the customer. It has a high speed & produces 8 mm to 40 mm tmt bars. The bars have high production guiding, cutting, cooling, coiling & finds application for handling equipment. The Automatic Cooling bed consists of two major units: y
Twin-channel Bar receiving Mechanism
y
Movable Rack Cooling Bed
The Twin-channel Bar receiving mechanism is used to collect the TMT bars leaving the Quenching boxes after being sheared by the Flying Shear in two strands. The twin-channel is made out of CI central box, water cooled to prevent warping during rolling, and C-type CI channels which are suspended from a longitudinal structural. The closed C-type channels ensure that the bars do not come out and maintain safety of the personnel. The opening and closing of these channels is by means of a cam-shaft and follower rollers. After collection of each bar, the bar is dropped onto a fixed CI Straightening rack mechanism one by one, from where it is carried ahead by the Movable rack mechanism. The Twin-channel mechanism is provided along the full length of the Cooling bed. In case of a 54 m long Cooling Bed, the twin-cannel size is also 55 m long. The mechanism is installed about 300 mm above the Straightening racks. The Twin-channel bar receiving mechanism comprise of the following: y y
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Twin water-cooled C-type channels with water cooling arrangement. Supporting arrangement for the twin-channel and drive system.
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y
y
Cam device for opening closing of the pipes. Hydraulic Drive for operation of the cams.
The purpose of the cooling bed of a movable rack design is to uniformly air-cool the TMT bars and transporting the same in a phased manner from the entry of the cooling bed to discharge side. The front end of the bars are also leveled at the discharge side and a fixed number of bars sent for final length cutting by cold shear and bundling. The Movable rack Cooling Bed will be of a walking beam design. The mechanism shall ensure that the bars are uniformly positioned over the toothed racks. The cooling bed is designed considering the smallest and the maximum size of the bars being rolled, delivered from the finishing mill stand of the mill, and the cooling time required for the various sizes of the bar Rack type cooling bed design depends on Bars cut previously to given lengths, to slow them down, to transport them crosswise over a cooling surface ensuring that the rolled bars in very wide range of lengths, are kept as straight as possible, to collect the bars at the end of the cooling surface to predetermined packs matched to the requirements of the cold shear, and to discharge finally same onto a roller table which conveys the bar packs to the cold shear. The Complete system consists of the following: C.I. Fixed Straightening Racks:
These are Cast Iron toothed blocks, which receive the bars from the Bar Receiving Twin - Channel Mechanism. These racks help to straighten the bars, which are at a temperature of about 600 oC. Movable Rack Mechanism
These are steel fabricated tooth racks which are mounted on Eccentric Rollers to enable them to move in the x and y axis. The Racks shall be profile cut to suit the smallest size of bar (8 mm) and also the max size (25 mm) bars. This mechanism collects the bars from the Fixed Straightening Racks and transfers them towards the delivery side of the Cooling Bed. Fixed Rack Mechanism
These are also fabricated toothed racks, which receive the bars from movable rack mechanism as the bars are transferred toward the delivery side of the Cooling Bed. 34 |
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Drive for Movable Rack Mechanism
The drive to the movable rack mechanism will be through two motors driving two parallel sets of drive shafts. Each motor will transmit drive through Two worm Reduction Gear drives. The shaft incorporates eccentrics, which provide the two-axis movement to the movable rack mechanism. Bar aligning Rollers
Chain driven profile cut rollers which are fitted at the end of the Racks but before the bars leaves the racks are driven by motors to align the bars front end before delivery to the Run-out roller table. Throw off device
At the end of the collecting grid the bars pack is transported on the Delivery roller table by means of throw off fingers. Run out Roller Table
Chain Driven roller table at the end of the cooling rack is provided to transport the pack of the bars to the cold shear. Process Equipment The brief equipment list is given below. The detailed equipment list, along with the complete ordering specifications, shall be supplied to the customer after placement of order. Equipment List Bar Receiving Twin Channel system: y
Supporting Structures.
y
CI Twin channel with water-cooling arrangement.
y
Hydraulic cylinders.
y
Cam drive shaft.
y
Hydraulic Power Pack.
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WHEEL & AXLE PLANT: Wheel and Axle plant is a pride unit of Durgapur Steel Plant. The main customer of wheel sets is Indian Railways. This was commissioned in 1962 with a capacity to produce 45000 wheels per year and subsequently raised to 80000 wheels per year. Wheels are produced by pressing and rolling while axles are produced by forging. Subsequently both are heat treated and machined. For the ease of production, wheel manufacturing section and axle manufacturing sections are located into two different bays. Set wheels and axles are finally meet in assembly section. The present capacity is as follows: Wheels: 40000 tonnes / annum Axles: 16000 tonnes / annum Input: 12 sided Fluted Ingot of diameter 16´ & 14´ for wheels and Sqare blooms from Blooming Mill for axles. Material Flow Diagram:
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Process: Wheel making : The 12 sided fluted ingots are inspected and cut into numbers of blocks. After physical inspection, blocks are heated in rotary hearth furnace for 6-8 hours to a temperature of 1300 ºC. The heated cheeses are descaled and fed to 63/12 MN Press for forging & punching.
After this, wheel blanks are heated in batch type reheating furnace to 1150 ºC. The wheel is then rolled in a computerized wheel mill, where wheels achieve profile & dimension. After rolling, the wheels are fed to a
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20MN Dishing press, where the web profile is achieved. The wheel is then feed to a marking press of 3MN where sl. No., year and cast no. are stamped on the back rim. The wheel is then subjected to heat treatment which includes quenching and tempering to give hard rim and tough core.This prevents high internal stress during cooling and prevents warping of wheels. Next comes the machining part, where rim face, boss face, rim blending, condemning glove, chucking glove are machined by means of CN machines. Finally, the wheels are subjected to various tests such as Ultrasonic Test, Magnetic particle Test and BHN which are RITES certified. Axle making : Square bloom made of killed steel is the raw material for axle. These blooms are heated for 6-8 hours in continuous pusher type furnaces after inspection. Blooms are forged in a 7 tonnes hand operated axle forging hammer. The process takes around 9-10 minutes and the finishing temperature is 850 ºC. The axles are then subjected to heat treatment. After heat treatment, axle is straightened in 150 ton horizontal straightening press. Then the axles are allowed to cool down in normal conditions. Axle ends are sawed and are rough turned, then finish turned. Ultrasonic test is performed for checking physical soundness of every axle. The axles are inspected for dimensional accuracy at every stage of the process and for surface & diameter defectsafter completion. Finally set wheels and axles go to assembly section. After assembly the set is checked for track gauge and after inspection it is despatched .
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