steel mill internship report

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Introduction The Pakistan Steel Mills is the producer of long rolled steel products in Karachi, Sind, Pakistan. The Pakistan Steel Mill is the country's largest industrial undertaking having a production capacity of 1.1 million tons of steel. The enormous dimensions of the project can be visualized from the construction inputs which involved the use of 1.29 million cubic meters of concrete, 5.70 million cubic meters of earth work (second to Tarbela Dam), 330,000 tones of machinery, steel structures and electrical equipment. It’s unloading and conveyor system at Port Qasim is the third largest in the world and its industrial water reservoir with a capacity of 110 million gallons per day is the largest in Asia. A 2.5 km-long sea water channel connects the sea water circulation system to the plant site with a consumption of 216 million gallons of sea water per day.

History of Pakistan Steel Mills After independence in 1947, it did not take long for Pakistan to come to the realization that progressive industrial and economical development would be impossible without the possession of a self reliant iron and steel making plant. The dependence on imports would cause serious setbacks to the country along with an extortionately high import bill which would be impossible to support. In 1968, the Government of Pakistan decided that the Karachi Steel Project should be sponsored in the public sector, for which a separate Corporation, under the Companies Act, be formed. In pursuance of this decision, Pakistan Steel Mills Corporation Limited was incorporated as a private limited company to establish and run steel mills at Karachi. Pakistan Steel Mills Corporation concluded an agreement with V/o Tyaz Prom export of the USSR in January, 1969 for the preparation of a feasibility report for the establishment of a coastal-based integrated steel mill at Karachi.

Founders of Pakistan Steel Mills The real founders of Pakistan Steel Mills are Prof. Dr. Niaz Muhammad, Wahab siddiqui and Russian scientist Mikhail Koltokof. It was the hard work of Niaz Muhammad that thousands of scientists and technical staff got trained by him. His inspirations and innovations got him the highest award from President of Pakistan, and also from Government of USSR. The Government of Pakistan has given him Pride of Performance. He was also nominated for Nobel prizes

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Iron Making Department (IMD) Introduction Iron Making Plant comprises of many small and big working units, the biggest one is Blast Furnace unit. This unit consists of two Blast Furnaces (BF-1 & BF-2) and both are in operation since 31st August 1981 and 07th August 1984 respectively, Inner volume of each furnace is 1033 Cu.M and its working volume is 893 Cu.M. Whereas the daily production capacity is 1750 tons of Pig Iron per furnace. BF-1 had two notches:a) Iron notch and b) Slag notch. Both notches have been closed permanently and another iron notch has been prepared instead. Blast Furnace No.2 still has one iron notch and one slag notch but its slag notch is rarely operated. Each furnace has 14 tuyers through which hot blast is injected at high temperature (1100 - 1200 C). Raw Material is charged from the top of the furnace through charging system comprising of double bell charging system. Hearth of the furnace is lined with carbon blocks whereas the inner walls of the furnace are lined with refractory bricks with embedded plate coolers of different types. The hot air blast alongwith a calculated quantity of natural gas is fed into the furnace through tuyeres at high pressure (up to 2.5 atm.) and high temperature (1200 C). As soon as the blast rises up the furnace shaft, the raw material gains heat and coke starts burning which produces CO and Co2. These gases further react with different oxides of the raw material and reduce them into their elementary shape (Fe, Si Mn etc.), and different oxides (such as A12O3, CaO, MgO) are also formed. The mixture of Fe, Si, Mn and carbon is called pig iron whereas the mixture of A12, O3, SiO2, CaO, MgO, MnO and other oxides is called slag. Both the molten iron and slag are collected in the hearth of the furnace from where they are tapped after a scheduled period through iron notch altogether. Slag is separated from the iron in the main

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runner just before the skimmer box. The pig iron is collected in the iron ladles and slag is separately collected in slag pots.The working area around the furnace, where a network of iron and slag runners is laid down is called cast house. The heavy equipment installed in the cast house are:i. To open the tap hole. ii. To close the tap hole after the completion of the tapping. iii. An E.O.T Crane of 20T/5T capacity to shift the materials and equipments from bottom house and to clean and prepare the iron and slag runners. There are three hot blast stoves for each furnace. One stove is on blast at a time while the other two remain on heating regime. The stoves are lined with Dinas Silica bricks and chequered brick work. The stoves are heated with mixture of N.Gas and B.F.Gas. When the dome temperature reaches 1350 C, the stove is ready to provide the hot blast to the furnace.The gases in the furnace, after completing the chemical reaction, leave the furnace at the top. These gases carry fine particles of raw materials with them. These gases (called B.F. Gas) are brought down the furnace through pipes of bigger diameter (internally lined with refractory bricks) into a vessel called dust catcher. Due to sudden drop of pressure in the dust catcher, the dust particles settle down at the bottom of the dust catcher, and the semi-cleaned gas is transferred to gas cleaning plant for further purification. All the raw materials charged into the furnace are initially stored in separate bins, called burden bins. Iron ore and fluxes are supplied to burden bins by RMHD, and Coke and Sinter by CokeOven and Sintering Plant respectively. These materials are then sieved and weighed according to charging schedule and continually fed into the furnace.There are two pig casting machines in Iron Making Department. A pig casting machine consists of two metallic chains (conveyers) containing metallic moulds. The molten metal is poured into these moulds and due to their continuous forward movement the filled moulds travel ahead and empty moulds take their places. After covering 10-15 m distance, water is sprinkled over molten pigs and the outer surface gets harder. At the end of themachine, pigs are struck away by a metallic hammer and collected in a railway gandola placed underneath. PCM No. of Machines - 2 Pigs weight - 18 / 23 / 45 Kgs Capacity - 140,000 Tons/year

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Pouring time of 140 T ladle i) 45 Kg Pigs - 55-60 minutes ii) 23 Kg Pigs - 60-65 minutes iii) 18 Kg Pigs - 70-75 minutes

SLAG GRANULATION PLANT The slag produced in the blast furnace is separately collected in slag pots at the furnace. The slag pots are then transported to SGP by railway locomotive for slag granulation. The molten slag is poured on a huge trough at a point where a heavy jet of water granulates the slag and throw it away in the yard. This granulated slag is then collected and shifted to open yard directly on trucks for cement factory or other purposes.

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SLAG DUMP YARD All the molten slag is not possible to pour out, however, some slag still remains at the bottom of the pot. After granulation, the slag pot is transported to slag dump yard far away from the SGP. It is an elliptical open yard where railway track is laid down at a sufficient height. The slag pot is placed at one of the post and electrically tilted up to maximum. A metallic bob (attached with the excavator) strikes the bottom of the ladle and the residue falls down the ground. Now the ladle becomes completely empty. The slag ladle coming from slag dump yard on way to blast furnace isstationed for a while at slag ladle sprinkling unit where a cold solution of lime water is sprinkled in the ladle so that the slag could not stick to the inner walls of the ladle at the time of pouring slag into it.

CENTRAL AIR SUPPLY STATION This is the unit where two huge fans are installed to supply cool air to the control rooms and other operational units ofblast furnace where sensitive electrical and automation equipment are installed. The air is cooled by counter-flow of chilled water in pipes (at 8C) and passed through filters to make it clean and dust free.

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CENTRAL ASPAIRATION UNIT Due to fine particles in raw materials, a cloud of dust may appear during receiving these materials at burden bins. Therefore to keep the atmosphere clean and clear, a network of suction pipes is installed over conveyors and bins. These pipes suck the dust with the help of huge fans installed at central aspiration unit for this purpose. This dust or fine particles are collected in an electric filter from where the dust is supplied to sintering plant.

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Engineering Lab (ENGG. LAB) Introduction

Electric protective devices Equipment applied to electric power systems to detect abnormal and intolerable conditions and to initiate appropriate corrective actions. These devices include lightning arresters, surge protectors, fuses, and relays with associated circuit breakers, reclosers, and so forth. From time to time, disturbances in the normal operation of a power system occur. These may be caused by natural phenomena, such as lightning, wind, or snow; by falling objects such as trees; by animal contacts or chewing; by accidental means traceable to reckless drivers, inadvertent acts by plant maintenance personnel, or other acts of humans; or by conditions produced in the system itself, such as switching surges, load swings, or equipment failures. Protective devices must therefore be installed on power systems to ensure continuity of electrical service, to limit injury to people, and to limit damage to equipment when problem situations develop. Protective devices are applied commensurately with the degree of protection desired or felt necessary for the particular system.

Protective relays These are compact analog or digital networks, connected to various points of an electrical system, to detect abnormal conditions occurring within their assigned areas. They initiate disconnection of the trouble area by circuit breakers. These relays range from the simple overload unit on house circuit breakers to complex systems used to protect extrahigh-voltage power transmission lines. They operate on voltage, current, current direction, power factor, power, impedance, temperature. In all cases there must be a measurable difference between the normal or tolerable operation and the

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intolerable or unwanted condition. System faults for which the relays respond are generally short circuits between the phase conductors, or between the phases and grounds. Some relays operate on unbalances between the phases, such as an open or reversed phase. A fault in one part of the system affects all other parts. Therefore relays and fuses throughout the power system must be coordinated to ensure the best quality of service to the loads and to avoid operation in the nonfaulted areas unless the trouble is not adequately cleared in a specified time. See Fuse (electricity), Relay

Zone protection For the purpose of applying protection, the electric power system is divided into five major protection zones: generators; transformers; buses; transmission and distribution lines; and motors (see illustration). Each block represents a set of protective relays and associated equipment selected to initiate correction or isolation of that area for all anticipated intolerable conditions or trouble. The detection is done by protective relays with a circuit breaker used to physically disconnect the equipment. For other areas of protection See Grounding, Uninterruptible power system

Zones of protection on simple power system Fault detection Fault detection is accomplished by a number of techniques, including the detection of changes in electric current or voltage levels, power direction, ratio of voltage to current, temperature, and comparison of the electrical quantities flowing into a protected area with the quantities flowing out, also known as differential protection.

Differential protection This is the most fundamental and widely used protection technique. The system compares currents to detect faults in a protection zone. Current transformers on either side of the protection zone reduce the primary currents to small secondary values, which are the inputs to the relay. For load through the equipment or for faults outside of the protection zone, the secondary currents from the two transformers are essentially the same, and they are directed so that the current through the relay sums to essentially zero. However, for internal trouble, the secondary currents add up to flow through the relay.

Overcurrent protection

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This must be provided on all systems to prevent abnormally high currents from overheating and causing mechanical stress on equipment. Overcurrent in a power system usually indicates that current is being diverted from its normal path by a short circuit. In low-voltage, distribution-type circuits, such as those found in homes, adequate overcurrent protection can be provided by fuses that melt when current exceeds a predetermined value. Small thermal-type circuit breakers also provide overcurrent protection for this class of circuit. As the size of circuits and systems increases, the problems associated with interruption of large fault currents dictate the use of power circuit breakers. Normally these breakers are not equipped with elements to sense fault conditions, and therefore overcurrent relays are applied to measure the current continuously. When the current has reached a predetermined value, the relay contacts close. This actuates the trip circuit of a particular breaker, causing it to open and thus isolate the fault. See Circuit breaker

Distance protection Distance-type relays operate on the combination of reduced voltage and increased current occasioned by faults. They are widely applied for the protection of higher voltage lines. A major advantage is that the operating zone is determined by the line impedance and is almost completely independent of current magnitudes.

Overvoltage protection Lightning in the area near the power lines can cause very short-time overvoltages in the system and possible breakdown of the insulation. Protection for these surges consists of lightning arresters connected between the lines and ground. Normally the insulation through these arresters prevents current flow, but they momentarily pass current during the high-voltage transient to limit overvoltage. Overvoltage protection is seldom applied elsewhere except at the generators, where it is part of the voltage regulator and control system. In the distribution system, overvoltage relays are used to control taps of tap-changing transformers or to switch shunt capacitors on and off the circuits. See Lightning and surge protection

Undervoltage protection This must be provided on circuits supplying power to motor loads. Low-voltage conditions cause motors to draw excessive currents, which can damage the motors. If a

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low-voltage condition develops while the motor is running, the relay senses this condition and removes the motor from service.

Underfrequency protection A loss or deficiency in the generation supply, the transmission lines, or other components of the system, resulting primarily from faults, can leave the system with an excess of load. Solid-state and digital-type underfrequency relays are connected at various points in the system to detect this resulting decline in the normal system frequency. They operate to disconnect loads or to separate the system into areas so that the available generation equals the load until a balance is reestablished.

Reverse-current protection This is provided when a change in the normal direction of current indicates an abnormal condition in the system. In an ac circuit, reverse current implies a phase shift of the current of nearly 180° from normal. This is actually a change in direction of power flow and can be directed by ac directional relays.

Phase unbalance protection This protection is used on feeders supplying motors where there is a possibility of one phase opening as a result of a fuse failure or a connector failure. One type of relay compares the current in one phase against the currents in the other phases. When the unbalance becomes too great, the relay operates. Another type monitors the threephase bus voltages for unbalance. Reverse phases will operate this relay.

Reverse-phase-rotation protection Where direction of rotation is important, electric motors must be protected against phase reversal. A reverse-phase-rotation relay is applied to sense the phase rotation. This relay is a miniature three-phase motor with the same desired direction of rotation as the motor it is protecting. If the direction of rotation is correct, the relay will let the motor start. If incorrect, the sensing relay will prevent the motor starter from operating.

Thermal protection Motors and generators are particularly subject to overheating due to overloading and mechanical friction. Excessive temperatures lead to deterioration of insulation and

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increased losses within the machine. Temperature-sensitive elements, located inside the machine, form part of a bridge circuit used to supply current to a relay. When a predetermined temperature is reached, the relay operates, initiating opening of a circuit breaker or sounding of an alarm.

Earthing It is common knowledge that Earthing, and especially Bonding, plays a most dominating role when it comes to personnel Safety and prevention of Fire and Explosions. What is seldom appreciated is that EARTHING plays a fundamental role in preventing over-voltage conditions. Hence it impacts on the short and long term LIFE of electrical equipment, such as the motors, lights fittings, etc. and electronic systems. At the low cost of implementation there is no measure that is more cost-effective.

DIFFERENTIAL PROTECTION It is a very reliable method of protecting generators, transformers, buses, and transmission lines from the effects of internal faults.

Figure: Differential Protection of a Generator In a differential protection scheme in the above figure, currents on both sides of the equipment are compared. The figure shows the connection only for one phase, but a similar connection is usually used in each phase of the protected equipment. Under normal conditions, or for a fault outside of the protected zone, current I1 is equal to current I2 . Therefore the currents in the current transformers secondaries are also equal, i.e. i1 = i2 and no current flows through the current relay.

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If a fault develops inside of the protected zone, currents I1 and I2 are no longer equal, therefore i1 and i2 are not equal and there is a current flowing through the current relay.

Differential Protection of a Station Bus The principle of the differential protection of a station bus is the same as for generators. The sum of all currents entering and leaving the bus must be equal to zero under normal conditions or if the fault is outside of the protected zone. If there is a fault on the bus, there will be a net flow of current to the bus and the differential relay will operate.

Figure: Single Line Diagram of Bus Differential Protection Differential Protection of Three Phase Transformers Differential protection of three phase transformers must take into account the change in magnitude and phase angle of the transformed current. Transformers Connected Y-Y or Delta-Delta

In these two connections, the primary and secondary currents are in phase, but their magnitudes are different. The difference in the currentmagnitude must be balanced out by the current transformer ratios.

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Figure: Differential Protection for a Y-Y Connected Transformer. If the transformer ratio is

The secondary currents of the current transformers are

During normal operating conditions or when the fault is outside of the protection zone,

Therefore, the ratios of the current transformers on the two sides of the power transformer must be

.

.

Sometimes standard current transformers with the ratios that satisfy the above equation are not available. In that case auxiliary transformers between one of the current transformers and the relay are used.

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Transformers Connected Y-D or D -Y. The primary and secondary currents have different magnitudes and they also have 30° phase shift. Both, the magnitude and the phase shift must be balanced by appropriate ratio and connection of the current transformers. The phase shift on a Y-D bank is corrected by connecting the C.T.’s on the D in Y, and on the Y side in D.

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Cold Rolling Mill (C.R.M)

INTRODUCTION Cold rolling is a metalworking process in which metal is deformed by passing it through rollers at a temperature below its re crystallization temperature. Cold rolling increases the yield strength and hardness of a metal by introducing defects into the metal's crystal structure. These defects prevent further slip and can reduce the grain size of the metal. Cold rolling is a method of cold working a metal. When a metal is cold worked, microscopic defects are nucleated throughout the deformed area. These defects can be either point defects (a vacancy on the crystal lattice) or a line defect (an extra half plane of atoms jammed in a crystal). As defects accumulate through

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deformation, it becomes increasingly more difficult for slip, or the movement of defects, to occur. This results in a hardening of the metal.

If enough grains split apart, a grain may split into two or more grains in order to minimize the strain energy of the system. When large grains split into smaller grains, the alloy hardens as a result of the Hall-Petch relationship. If cold work is continued, the hardened metal may fracture. During cold rolling, metal absorbs a great deal of energy. Some of this energy is used to nucleate and move defects (and subsequently deform the metal). The remainder of the energy is released as heat.

While cold rolling increases the hardness and strength of a metal, it also results in a large decrease in ductility. Thus metals strengthened by cold rolling are more sensitive to the presence of cracks and are prone to brittle fracture. In C.R.M. we get input (feeding) from Hot Steel Making (H.S.M) unit. In C.R.M the sheet gets thinned forcefully.

The 1700 hot strip mill operates on slabs produced at the steel making plant. It produces hot rolled sheets, coils and strips suitable for ship building and the manufacture of pipes of small, medium and large diameter, bodies of cars, buses and other vehicles, railway wagons, transformers, boilers, big tanks, machinery and formed sections. The hot rolled sheets are also utilized for the production of cold rolled sheets. It has a designed capacity of 445,000 tons. The cold rolling mill is a cold reversible mill with 200,000 tons capacity, from which 10,000 tons are turned into cold formed sections. The cold rolling mill operates on hot rolled sheets and coils produced at the hot strip mill. Cold rolled sheets are used for the production of bicycles, steel fabrication, steel containers, drums, barrels, vehicle and bus bodies, steel furniture, machinery parts, products and appliances, oil and gas appliances etc. Cold rolled sheets are also used for the production of galvanized sheets, and black plates and tinplates. Galvanized sheets are used for containers, trunks, boxes, packets, steel shuttering, desert coolers, construction and roofing, ducting equipment, appliances, paneling, utensils, air-conditioners, water heaters and fresh water tanks.

Cold and hot-formed sections are used for steel fabrications, furniture, vehicle and bus bodies, building construction, miscellaneous machinery and equipment/parts, steel doors and windows. The combined slitting units and hot rolled coil conveyor section of the cold rolling mill and the combined shearing unit and profile bending units were put into operation. The operation of the

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main cold rolling mill units marked the completion of the first phase of a 1.1 million tons production of steel products.

The main products and specifications from the plant are as follows: Hot rolled sheets have coils of thickness 1.6-10mm and width 630-1500 mm, with a weight of 14.5 tons. Cold rolled sheets have thickness of 0.30-2.5 mm, width 600-1500mm and length 1-4 meters. The weight of the coils is between 14.5 tons and 90 tons. Galvanized sheets and coils have thickness 0.35-1.5 mm with width 700-1500 mm. The weight of the coils will vary between 6.5 tons and 100 tons.

The plant also produces formed angle sections with the following dimensions: between 80x80 mm and 150x150mm. The lengths available are up to 12 meters.

Semi-finished products such as blooms and slabs are reheated at high temperatures in the reheating furnaces to make the metal malleable and then rolled into finished products at the rolling mills. PSMC currently has a Billet Mill, a Hot Strip Mill and a Cold Rolling Mill.

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UNITS OF C.R.M:-

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C.P.U(CENTRALISED PROCESSING UNIT)

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REVERSIBLE ROLLING MILL

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ANNEALING UNIT

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TEMPER MILL UNIT

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SHEARING Unit

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SLITTING UNIT

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GALVANIZING UNIT

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COMBINE SHEARING AND SLITTING UNIT SECTION

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FORMING UNIT(PROFILE BENDING UNIT)

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1) C.P.U(CENTRALISED PROCESSING UNIT):A central processing unit (CPU) or processor is an electronic circuit that can execute computer programs. This term has been in use in the computer industry at least since the early 1960s (Week 1961). The form, design and implementation of CPUs have changed dramatically since the earliest examples, but their fundamental operation has remained much the same. Early CPUs were custom-designed as a part of a larger, sometimes one-of-a-kind, and computer. However, this costly method of designing custom CPUs for a particular application has largely given way to the development of mass-produced processors that are made for one or many purposes. This standardization trend generally began in the era of discrete transistor mainframes and minicomputers and has rapidly accelerated with the popularization of the integrated circuit (IC). The IC has allowed increasingly complex CPUs to be designed and manufactured to tolerances on the order of nanometers. Both the miniaturization and standardization of CPUs have increased the presence of these digital devices in modern life far beyond the limited application of dedicated computing machines. Modern microprocessors appear in everything from automobiles to cell phones and children's toys. Here the sheet gets cleaned and is also cut from sides.

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2) REVERSIBLE ROLLING MILL:Reversible cold rolling mill is that one stand of mill is laid out in the line, and strip will pass the mill reciprocally till termination product. This line is characteristic with low cost, small occupation and flexible production. Here sheet gets thinned.

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3) ANNEALING UNIT:It is a process of heat treatment by which glass and certain metals and alloys are rendered less brittle and more resistant to fracture. Annealing minimizes internal defects in the atomic structure of the material and leaves it free from internal stresses that might otherwise be present because of prior processing steps . Ferrous metals and glass are annealed by heating them to high temperatures and cooling them slowly; copper and silver, however, are best annealed by heating and cooling quickly, then immersing in water. Large masses of metal or glass are cooled within the heating furnace; sheets are usually annealed in a continuous-process furnace. They are carried on a moving table through a long chamber in which the temperature is carefully graded from initial heat just below the softening point to that of room temperature at the end. Annealing time, especially of glass, varies widely according to the thickness of the individual piece; window glass, for example, requires several hours; plate glass, several days; and glass mirrors for reflecting telescopes, several months. Annealing is required as an intermediate step in metal-forming processes such as wire drawing or brass stamping in order to restore the ductility of the metal lost because of work hardening during the forming operation The output from annealing unit goes into temper mill.

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4) TEMPER MILL UNIT:A temper mill is a steel sheet and/or steel plate processing line composed of a horizontal pass cold rolling mill stand, entry and exit conveyor tables and upstream and downstream equipment depending on the design and nature of the processing system. A typical type of temper mill installation includes entry equipment for staging and accepting hot rolled coils of steel which have been hot wound at the end of a hot strip mill or hot rolled plate mill. Also included in a typical temper mill installation are pinch rolls, a leveler (sometimes two levelers), and a shear for cutting the finished product to pre-determined lengths, a stacker for accumulating cut lengths of product into a bundle.

Sometimes a temper mill installation includes a re-coil line where the finished product is a coil instead of bundles of cut lengths of product. Maximum product flexibility capability could be attained if the installation was arranged to produce both coils and bundles of cut to length product.

The heart of the temper mill is the cold rolling mill stand which produces the temper pass. It will include electric powered drive motors and speed reduction gearing suited to the process desired. The design of the rolling mill can be a 2-high or 4-high (even 6-high in some cases). The mill stand can be work roll driven or back up roll driven. The mill can be designed with hydraulic work roll bending and/or back up roll bending. Installations typically have a single rolling mill stand, but may have two. Pinch rolls provide back tension for the pay off reel in the entry section and entry and exit tension for the temper pass. The primary purpose of a temper mill is to improve the surface finish on steel products

The process goal is physical property enhancement through cold forming of the steel product in the bite of the work rolls. The physical properties that are enhanced by the temper pass due to elongation of the product include: • Dimensional trueness and repeatability • Suppression of yield point elongation • Improved product surface finish • Improve product shape and flatness • Decrease coil memory

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• Increase product yield strength • Develop proper stiffness or temper

Typical elongation produced in the product is 0.5% to 2%. Product dimensions vary. Thicknesses include typical sheet metal gauges up to 3/4" thick plate. Widths vary from 36" to 125". The finish of the rolled product is controlled by using rolls having a variety of surface finishes designed to impart the desired finish to the product. Roll finishes range from ground and polished rolls to impart a bright finish, to shot-blasted or electric-discharged textured rolls that produce a dull, velvety finish on the steel surface.

Typical auxiliary equipment includes PLC based controls, overhead traveling cranes, roll changing equipment, roll grinding equipment, hydraulic power unit(s), bundle lifting devices, Coil handling devices, etc.

The output from temper unit goes into either sharing unit or slitting unit.

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5) SHEARING UNIT:Shearing is a process for cutting sheet metal to size out of a larger stock such as roll stock. Shears are used as the preliminary step in preparing stock for stamping processes, or smaller blanks for CNC presses. Material thickness ranges from 0.125 mm to 6.35 mm (0.005 to 0.250 in). The dimensional tolerance ranges from ±0.125 mm to ±1.5 mm (±0.005 to ±0.060 in). The shearing process produces a shear edge burr, which can be minimized to less than 10% of the material thickness. The burr is a function of clearance between the punch and the die (which is nominally designed to be the material thickness), and the sharpness of the punch and the die Material selected for shearing should be standard stock sizes to minimize the extra costs associated with special slitting. Burrs and hold down marks which are inevitable, should be considered in the design of the end product. Burrs should be kept away from handling areas, preferably folded away, or in some obscure area. The same can be done with hold down marks too.

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6) SLITTING UNIT:The slitting mill was a watermill for slitting bars of iron into rods. The rods then were passed to nailers who made the rods into nails, by giving them a point and head. The slitting mill was probably invented near Liege in what is now Belgium. The first slitting mill in England was built at Dart ford, Kent in 1590. This was followed by one on Kinnock Chase by about 1611, and then Hyde Mill in Kinder in 1627. Others followed in various parts of the England where iron was made. However there was a particular concentration of them on the River Stour between Stourbridge and Stourport, where they were conveniently placed to slit iron that was brought up (or down) the River Severn before it reached nailers in the Black Country. The slitting mill consisted of two pairs of rolls turned by water wheels. Mill bars were flat bars of iron about three inches wide and half an inch thick. A piece was cut off the end of the bar with shears powered by one of the water wheels and heated in a furnace. This was then passed between flat rolls which made it into a thick plate. It was then passed through the second rolls (known as cutters), which slit it into rods. The cutters had intersecting grooves, which sheared the iron lengthways.

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7) GALVANIZING UNIT:In this unit iron is painted with a suspension of zinc particles in an organic solvent, so that a zinc coating remains following evaporation of the solvent. The principal method of making steel resist corrosion is by alloying it with metal, zinc. When steel is submerged in melted zinc, the chemical reaction permanently bonds the zinc to the steel through galvanizing. Therefore, the zinc isn't exactly a sealer, like paint, because it doesn't just coat the steel; it actually permanently becomes a part of it. The zinc goes through a reaction with the iron molecules within the steel to form galvanized steel. The most external layer is all zinc, but successive layers are a mixture of zinc and iron, with an interior of pure steel. These multiple layers are responsible for the amazing property of the metal to withstand corrosion-inducing circumstances, such as saltwater or moisture. Zinc also protects the steel by acting as a "sacrificial layer." If, for some reason, rust does take hold on the surface of galvanized steel, the zinc will get corroded first. This allows the zinc that is spread over the breach or scratch to prevent rust from reaching the steel. The degree of galvanizing is usually represented as the zinc's weight per surface area rather than the thickness of the zinc, because this gives a better representation of how much metal has been applied. Steel often gets galvanized after individual parts have been formed, such as braces, nails, screws, beams, or studs. However, raw galvanized steel in sheets will withstand some bending and forming without flaking. Galvanized steel can be found almost everywhere. You might be living in a steel frame house. You are no doubt surrounded by steel parts in your car that allow it to emerge from rainstorms unscathed. Many people work in an office with metal roofing made of galvanized steel. Besides being inexpensive and effective, this metal is popular because it can be recycled and reused multiple times.

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8) COMBINE SHEARING AND SLITTING UNIT:Input from Hot Steel Making (H.S.M) also goes into this unit.

9) SECTION FORMING UNIT (PROFILE BENDING UNIT):Rolling is a fabricating process in which the metal, plastic, paper, glass, etc. is passed through a pair (or pairs) of rolls. There are two types of rolling process, flat and profile rolling. In flat rolling the final shape of the product is either classed as sheet (typically thickness less than 3 mm, also called "strip") or plate (typically thickness more than 3 mm). In profile rolling the final product may be a round rod or other shaped bar, such as a structural section (beam, channel, joist etc). Rolling is also classified according to the temperature of the metal rolled. If the temperature of the metal is above its re crystallization temperature, then the process is termed as hot rolling. If the temperature of the metal is below its re crystallization temperature, the process is termed as cold rolling. Another process also termed as 'hot bending' is induction bending, whereby the section is heated in small sections and dragged into a required radius. Heavy plates tend to be formed using a press process, which is termed forming, rather than rolling. Output from Combine Sharing and Slitting Unit go

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DIGRAMATIC EXPLANATION

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Steel Making Department (SMD)

Introduction Steelmaking is the second step in producing steel from iron ore. In this stage, impurities such as sulfur, phosphorus, and excess carbon are removed from the raw iron, and alloying elements such as manganese, nickel, chromium and vanadium are added to produce the exact steel required. Basic oxygen steelmaking is a method of primary steelmaking in which carbon-rich molten pig iron is made into steel. Blowing oxygen through molten pig iron lowers the carbon content of the alloy and changes it into low-carbon steel. The process is known as basic due to the pH of the refractory—calcium oxide and magnesium oxide—that line the vessel to withstand the high temperature of molten metal.

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The process was developed in 1948 by Robert Durer and commercialized in 1952–1953 by Austrian VOEST and ÖAMG. The LD converter, named after the Austrian towns Linz and Donawitz (a district of Leoben) is a refined version of the Bessemer converter where blowing of air is replaced with blowing oxygen. It reduced capital cost of the plants, time of smelting, and increased labor productivity. Between 1920 and 2000, labor requirements in the industry decreased by a factor of 1,000, from more than 3 worker-hours per ton to just 0.003. The vast majority of steel manufactured in the world is produced using the basic oxygen furnace; in 2000, it accounted for 60% of global steel output. Modern furnaces will take a charge of iron of up to 350 tons and convert it into steel in less than 40 minutes, compared to 10–12 hours in an open hearth furnace. Steel making department is one of the most important departments in whole steel mill. Because of this department it is called steel mill. Here iron is converted into steel. Steel making department converts pig iron into steel that is transferred from iron making department to SMD through locomotive railway in ladle. The pig iron in molten form is first transferred into mixer. Then from mixer it is transferred to converter where other raw materials are also transferred to converter. Then it is heated and after oxidation steel and slag becomes separate. Then they are taken out separately. After than steel is given several shapes as needed.

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Converter in Pakistan Steel Mill: The Steel Making Plant Complex has two Linz. Donawitz converters. Each converter has a capacity of 130 tons of steel for which there is one bloom caster and two slab casters. Molten metal from the blast furnace is taken to the steel making plant where further reduction of impurities is done in an oxygen furnace (Linz Donawitz converters). The crude steel in liquid form is taken in a ladle for further refining, where ferroalloys are added to the liquid steel.

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Casting Method: PSMC employs continuous casting technology to cast the liquid steel into semi-finished products (i.e. cast billets, blooms and slabs). Cast billets are sold without any further processing whereas blooms and the slabs are further processed at the Billet Mill and the Hot Strip Mill respectively. Bloom 260 x 260 mm sizes are used for making billets which are utilized for manufacturing various steel products. The slabs of 150-200 mm thickness and 700-1500 mm width sizes produced at the Steel Making Plant are fed to the hot strip mill where they are rolled into stripes, sheets and coils.

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Electronic lab

SMD has a separate lab to control and monitor whole process of steel making. Because movement of whole machine is controlled through electronics. This lab is also responsible to repair things. The electronic section deals with the solid state electronic devices on the plant. It is subdivided into four categories for convenience. a) b) c) d)

Analog lab Digital lab Misc.lab Electro drive lab

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a) ANALOG LAB This lab is responsible for the repair and maintenance of the analog devices of the plant such as regulated and un-regulated power supply, automatic summation sub-units etc This lab has following systems: a) Analog gauge system (AGS): interlink the primary and secondary devices. b) Face code converter system: generator, register, memory, 3 phase amplifier, comparator, counter, galvanic separator and transformer. c) Force measurement panel: shaper card, power supply. d) Selling: mechanical to electrical. e) Tension system card: sheet level and angle.

b) Digital lab: This lab is concerned with the digital equipments on the plant which includes the entire process computerized system. In this lab checking stands are available in order to check the digital cards that are used in the control rooms. This lab is mostly concerned with the following equipments: 1) 2) 3) 4) 5) 6) 7) 8)

A/D converter D/A converter ROM+RAM Microprocessor Phase code converter Timer Digital display Force analog lab(primary) a) Selcin (Mechanical to electrical) b) AGS (analog gauge control system) c) Checking stand(face code converter system) 9) 3 phase generator 10) Comparator 11) Galvanic separator

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12) Counter 13) Transformer 14) Memory

c) Misc.lab: This lab deals with the miscellaneous devices on the plant which includes: a) b) c) d) e)

Controllers Timer Relay Counter and converters Other miscellaneous devices etc

D) Electro-drive lab: It deals with all types of motors that are used on the plant. It also deals with the high power supply to this heavy machinery. It deals with the following equipments: a) b) c) d)

Thyristor Synchronous motors Asynchronous motors Dc motors

Any other equipment related to motors

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PLC in SMD: A programmable logic controller (PLC) or programmable controller is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or light fixtures. PLCs are used in many industries and machines. Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in batterybacked or non-volatile memory. A PLC is an example of a hard real time system since output results must be produced in response to input conditions within a bounded time, otherwise unintended operation will result. The functionality of the PLC has evolved over the years to include sequential relay control, motion control, process control, distributed control systems and networking. The data handling, storage, processing power and communication capabilities of some modern PLCs are approximately equivalent to desktop computers. PLC-like programming combined with remote I/O hardware, allow a general-purpose desktop computer to overlap some PLCs in certain applications. Regarding the practicality of these desktop computer based logic controllers, it is important to note that they have not been generally accepted in heavy industry because the desktop computers run on less stable operating systems than do PLCs, and because the desktop computer hardware is typically not designed to the same levels of tolerance to temperature, humidity, vibration, and longevity as the processors used in PLCs. In addition to the hardware limitations of desktop based logic, operating systems such as Windows do not lend themselves to deterministic logic execution, with the result that the logic may not always respond to changes in logic state or input status with the extreme consistency in timing as is expected from PLCs. Still, such desktop logic applications find use in less critical situations, such as laboratory automation and use in small facilities where the application is less demanding and critical, because they are generally much less expensive than PLCs. In more recent years, small products called PLRs (programmable logic relays), and also by similar names, have become more common and accepted. These are very much like PLCs, and are used in light industry where only a few points of I/O (i.e. a few signals coming in from the real world and a few going out) are involved, and low cost is desired. These small devices are typically made in a common physical size and shape by several manufacturers, and branded by the makers of larger PLCs to fill out their low end product range. Popular names include PICO Controller, NANO PLC, and other names implying very small controllers. Most of these have between 8 and 12 digital inputs, 4 and 8 digital outputs, and up to 2 analog inputs. Size is usually about 4" wide, 3" high, and 3" deep. Most such devices include a tiny postage stamp sized LCD screen for viewing simplified ladder logic (only a very small portion of the program being visible at a given time) and status of I/O points, and typically these screens are accompanied by a 4-way rocker push-button plus four more separate push-buttons, similar to the key buttons on a VCR

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remote control, and used to navigate and edit the logic. Most have a small plug for connecting via RS-232 or RS-485 to a personal computer so that programmers can use simple Windows applications for programming instead of being forced to use the tiny LCD and push-button set for this purpose. Unlike regular PLCs that are usually modular and greatly expandable, the PLRs are usually not modular or expandable, but their price can be two orders of magnitude less than a PLC and they still offer robust design and deterministic execution of the logic. In SMD two types of PLCs are used. Their names are as follows: 1) Siemens S5 2) Mitsubishi E100

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Siemens S5 The Simatic S5 PLC is an automation system based on Programmable Logic Controllers. It is manufactured and sold by Siemens AG. Such automation systems control process equipment and machinery used in manufacturing. This product line is considered obsolete, as the manufacturer has since replaced it with their newer Simatic S7 PLC. However, the S5 PLC still has a huge installation base in factories around the world. Most automation systems integrators still have the ability to provide support for the platform.

Hardware The S5 line comes in the 90U, 95U, 101U, 100U, 105, 115U, 135U, and 155U chassis styles. Higher the number, the more sophisticated and more expensive the system. Within each chassis style, several CPUs are available, with varying speed, memory, and capabilities. Some systems provide redundant CPU operation for ultra-high-reliability control, as used in pharmaceutical manufacturing, for example. Each chassis consists of a power supply, and a backplane with slots for the addition of various option boards. Available options include serial and Ethernet communications, digital input and output cards, analog signal processing boards, counter cards, and other specialized interface and function modules.

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Software The S5 product line is usually programmed with a PC based software programming tool called Step 5. Step 5 is used for programming, testing, and commissioning, and for documentation of programs for S5 PLCs. The original Step 5 versions ran on the CPM operating system. Later versions ran on MS-DOS, and then versions of Windows through Windows XP. The final version of Step 5 is version 7.2. No further development of this product line has occurred since that time, due to its announced obsolescence. In addition to Step5, Siemens offered a proprietary State logic programming package called Graph5. Graph5 is a sequential programming language intended for use on machines that normally run through a series of discrete steps. It simulates a State machine on the S5 platform. Several third-party programming environments have been released for the S5. Most closely emulate Step5, some adding macros and other minor enhancements, others functioning drastically differently than Step5. One allows Step5 programs to be cross-compiled to and from the C programming language and BASIC.

Structured programming STEP 5 allows the creation of structured or unstructured programming, from simple AND/OR operations up to complex subroutines. A STEP 5 program may, therefore, contain thousands of statements. To maintain maximum transparency, STEP 5 offers a number of structuring facilities:   

Block technique - A linear operation sequence is divided into sections and packed into individual blocks. Segments - Within blocks, fine structuring is possible by programming subtasks in individual segments. Comments - Both a complete program as well as individual blocks or segments and individual statements can be directly provided with comments.

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Methods of representation STEP 5 programs can be represented in three different ways:   

Statement List (STL) - The program consists of a sequence of mnemonic codes of the commands executed one after another by the PLC. Ladder Diagram (LAD) - Graphical representation of the automation task with symbols of the circuit diagram Function Block Diagram (FBD) - Graphical representation of the automation task with symbols to DIN 40700/ DIN 40719.

Absolute or symbolic designations can be used for operands with all three methods of representation. In LAD and FBD complex functions and function block calls can be entered via function keys. They are displayed on the screen as graphical symbols.

Blocks Five types of blocks are available:     

Organization blocks (OB) - for managing the control program Programming blocks (PB) - contain the control program structured according to functional or process-oriented characteristics Sequence blocks (SB) - for programming sequential controls Function blocks (FB) - contain frequently occurring and particularly complex program parts Data blocks (DB) - for storing data required for processing the control program.

Some S5 PLCs also have block types FX (Extended Function Blocks), and DX (Extended Data Blocks); these are not distinct block types, but rather are another set of available blocks due to the CPU having more memory and addressing space.

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Operations STEP 5 differentiates between three types of operations: 





Basic operations, (e.g. linking, saving, loading & transferring, counting, comparing, arithmetic operations, module operations) - These can be performed in all three representations. Supplementary operations and complex functions, (e.g. substitution statements, testing functions, word-by-word logic operations, decrement/increment and jump functions.) These can only be executed in STL. System operations (direct access the operating system) - These can only be executed in STL.

Additional functions       

Saving user-specific project settings Symbol editor Automatic generation and updating of cross-reference lists Comparison of user programs Transferring blocks to EPROM and EEPROM memory modules for programmable controllers Rewiring inputs, outputs, flags, timers and counters Testing and service functions for startup and maintenance

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Electrical section This section is responsible for entire electrical system in the plant. It make sure that the electrical equipments on the plant are maintained and working properly. It deals with all the electrical equipments ranging from low voltage as low voltage as low as 240 volts to very high voltage of 11 kV. This section is also responsible for the proper distribution of electricity to the entire plant. Electrical section has three main branches: a) Low voltage protection 240v-1000v b) High voltage protection 6.6kv-11kv c) Relay protection. The equipment with which the electrical section is concerned is: a) b) c) d) e)

Breakers. Transformer. Thyristors. Relays. Other related equipment.

All these devices or equipments are either of low voltage or high voltage

Relays: Relays are very important for protection and switching in an electrical system. And it is of vital concern in the electrical section. A relay is an electrical operated switch. Many relays use as electromagnet to operate switching mechanism mechanically, but other operating principles are also used. Relay are used where it is necessary to control a circuit by a low-power signal (wit complete electrical isolation between control and controlled circuits), or where several circuits be controlled by one signal. The first relay was used in long distance telegraph circuit repeating the signal coming in from one circuit and re-transmitting it to another. Relay was used extensively in telephone exchanges and early computers to perform logical operation. Types of relay used in Pakistan steel are: 1) Electronic relays. 2) Electromagnetic relays. a) Rota tic armature relay.

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b) Hinged armature relay c) Plunger or solenoid relay 3) Induction relay. 4) Thermal relay. 5) Buchholz relay. These entire relay are operated differently and are used according to needs, some are of high power and some are of low power.

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Instrumentation section This section deals with all types of primary instruments that are installed on the locations from where a parameter is to be measured. This section is responsible for the repair, maintenance of the instrument and manufacturing of new primary instruments. This section has following lab: a) b) c) d) e)

Pressure and flow lab. Temperature lab. X-ray lab Electric measuring instruments lab Pneumatics lab

a) Pressure and flow lab: This lab is concerned with the instruments that are used to measure the pressure and flow of fluids throughout the plant. Instruments used to measure pressure are called ―pressure gauges‖ or ―vacuum gauges‖ A ―manometer‖ could also be referring to a pressure measuring instrument, usually limits to measuring pressures near to atmospheric. The term manometer is often used to refer specially to liquid column hydrostatic instruments. ―Absolute pressure‖ is zero referenced against a perfect vacuum, so it is equal to gauge pressure plus atmospheric pressure. ―Gauge pressure‖ is zero referenced against ambient air pressure, so it is equal to absolute pressure minus atmospheric pressure. Negative signs are usually omitted. Differential pressure is the difference in pressure between two points.

Orifice plate: An orifice plate with a hole through it, placed in the flow, it constricts the flow and measuring the pressure differential across the constriction gives the flow rate. It is basically a crude form of venture meter, but with higher energy losses. There are three types of orifice:

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a) Concentric b) Eccentric c) Segmental

B) Temperature lab: This lab deals with the primary temperature indicating instruments. There are three types of temperature indication instruments used in Pakistan steel. 1) 2) 3)

Thermocouple RTD’S Optical pyrometer

1) Thermocouple: A thermocouple is a junction between two different metals that produces a voltage related to a temperature difference. Thermocouple is a widely used type of temperature sensor for measurement and control and can also be used to convert heat into electric power. They are intensive and interchangeable are supplied fitted with standard connectors and can measure a wide range of temperatures. The main limitation is accuracy: system error of less than one degree Celsius(c) can be difficult to achieve Type B, S, R and K thermocouples are used extensively in the steel and iron industries to monitor temperatures and chemistry though out the steel making process. Disposable, immiscible, type S thermocouples are regularly used in the electric arc furnace process to accurately measure the temperature of steel before tapping. The cooling curve of a small steel sample can be analyzed and used to estimate the carbon content of molten steel.

2) RTD’S: Resistance thermometers also called resistance temperature Detectors or resistive thermal device (RTD’S) are temperature sensor that exploits the predictable change in electrical resistance of some materials with changing temperature. As they are almost invariably made of platinum, they are often called platinum resistance thermometers

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(PRTs). They are slowly replacing the use of thermocouple in many industries application below 600 degree centigrade due to higher accuracy and repeatability

3) Optical pyrometer: A pyrometer is a non-contacting device that intercepts and measures thermal radiation, a process known as pyrometer. This device can be used to determine the temperature of an objects’ surface. The word pyrometer comes from the Greek word for fire ―pyre‖ and meter meaning to measure. Pyrometer was originally coined to denote a device capable of measuring temperatures of object above incandescence (i.e. object bright to the human eye) Temperature is the fundamental parameter in metallurgical furnace operation. Reliable and continuous measurement of the melt temperature is essential for effective control of the operation. Smelting rates can be maximized, slag can be produced at the optimum temperature, fuel consumption is minimized and refractory life may also be lengthened. Thermocouple was the traditional devices used for this purpose, but they are unsuitable for continuous measurement because they rapidly dissolve.

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Conclusion During course of my internship, I found that Pakistan Steel Mill was set up with an objective to achieve a self reliant and vibrant economy. Up to some extent it has been successful. But due to ugly response of Government of Pakistan it is now in worst condition of history. During my visits to different departments I found that staff is very devoted to their work, they love to spend time in mill, and they are good teachers as well. They explained everything with good standards’ learned a lot about industrial automation and instrumentation. These are core things for any electronic engineer. By doing internship for whole 1 month I gain a lot of confidence, learned that what professionalism is. During this period I have overcome my many week points and mistakes. Pakistan Steel has potential to provide a sound base for industrialization and can provide stimuli for setting up of downstream industries. It can also play a significant role in purgation of technology and acquisition of new technologies. It has also contributed billion of rupees to Gov. of Pakistan in past., but unfortunately this Biggest industrial unit of Pakistan is suffering from various problems like lack of strategic direction, weak financial position, due capital repair, lack cost control, corruption and in efficient use of resources. After overcoming of these problems, it can make its operation more efficient and once again become a solid bar. May ALLAH once again give power to raise Pakistan Steel Mill (AMEEN?)

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Suggestions 

Management must pay attention to the capital repair of plant which otherwise will

prove costly for organization

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Old conservative and costly employees should be replaced with young intelligent, qualified and cheap generation

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The person who are trained from abroad should not be allowed to take VRF

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Pakistan Steel should be free from politics

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Proper orientation should be given to the market and sales promotion activities

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There are always need to improve working condition and safety measures in the production unit

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Pakistan steel can increase its profitability and efficiency by promoting its downstream industries