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PSM Internship

by asad-alamgir





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Internship Report PEOPLES STEEL MILLS LIMITED Prepared by: Names Roll Number Dawood College of Engineering & Technology Degree Awarding Institute, Karachi. DEPARTMENT OF METALLURGY & MATERIALS ENGINEERING (Final year students.) Table of Contents Dedication Acknowledgments Chapter#1 Chapter#2 Chapter#3 Chapter#4 Chapter#5 Chapter#6 Introduction Process Flow Diagram Melting Shop (M-Shop) Bar Rolling Mill (Q-Shop) Slab & Bloom Rolling Mill (N-Shop) Forging Shop (R1,R2 & R3 Shop) Chapter#1 INTRODUCTION Peoples Steel Mills Ltd, a world class alloy and special steel manufacturing plant located in Manghopir, Karachi Pakistan and spread over an area of 100 acres was set-up by the Government of Pakistan in 1975 with Japanese assistance. In order to keep pace with emerging technologies, the plant was upgraded in 1996 though a comprehensive balancing & modernization programs with the technical assistance of VAIS, INTECO and Bohler of Austria. The plant is now equipped with modern melting, refining, degassing, electro slag re-melting and necessary casting , rolling and forging facilities with an annual capacity of 70,000mt. Products quality is assured through modern material testing facilities and well trained staff The plant has the capability to produce steels according to all major international quality standards and to date has manufactured more than 300 steel grades. Peoples Steel enjoys the highest market share in the alloy and special steel market of Pakistan. A diversified base of more than 200 customers includes high profile illustrious end users in automotive, defense, machinery construction, special/high rise buildings, transportation and engineering sectors in Pakistan. Components manufactured from our steel are supplied by our customers to renowned European & Japanese automobile manufactures. In addition to manufacturing & supply of quality steels Peoples Steel is extending it’s expertise in the following fields:  Material Testing & Analyzing-Chemical, Mechanical, NDT, Metallographic, Failure Analysis.  Industrial Project & Services-Plant Fabrication & Installation.Seamless Pipe Manufacturing–Pipe/Tubes up to 300mm diameter are expected to be available in near future. Chapter#2 PROCESS FLOW Chapter#3 ELECTRIC ARC FURNACE The melting shop of PSM consists of following facilities:  Electric arc furnace.  Ladle furnaces  Ladle Vacuum Degassing Unit.  Electro Slag Re-melting furnace.  Continuous Casting Machine. The brief processing and configuration of above processing unites is as follows: 3.0 Electric Arc Furnace: In PSM there are two EAF in M- shop. The basic purpose of EAF is to melt the Steel Scrape and provide oxidizing environment to remove phosphorous contents (Dephosphorization).The electric arc furnace operates as a batch melting process producing batches of molten steel known "heats". 3.0.1 Operation of an Electric Arc Furnace: The electric arc furnace operating cycle is called the tap-to-tap cycle and is made up of the following operations:  Furnace charging;  Melting;  Basic slag formation;  Tapping the steel;  Killing of steel( Deoxidation).  Refractory lining maintenance. i. Furnace Charging: The first step in the production of any heat is to select the grade of steel to be made. Usually a schedule is developed prior to each production shift. Thus the melter will know in advance the schedule for his shift. The scrap yard operator will prepare buckets of scrap according to the needs of the melter. Preparation of the charge bucket is an important operation, not only to ensure proper melt-in chemistry but also to ensure good melting conditions. The scrap must be layered in the bucket Chapter#3 ELECTRIC ARC FURNACE according to size and density to promote the rapid formation of a liquid pool of steel in the hearth while providing protection for the sidewalls and roof from electric arc radiation. Following is the classification of Steel Scrap used:  Home Scrape/ Shop returns:  Ferritic Stainless Steel    Maragin Steel Tool Steel Special alloy steel  Purchased Scrape:  Heavy mill Scrap 1 & 2  Sheratted Scrape The total time of charging is 45min. In PSM Scrap yard there are 8 buckets of different size ranges. ii. Charge Melting:  The EAF has evolved into a highly efficient melting apparatus and modern designs are focused on maximizing the melting capacity of the EAF. Melting is accomplished by supplying energy to the furnace interior. This energy can be electrical or chemical.  Electrical energy is supplied via the graphite electrodes and is usually the largest contributor in melting operations. Initially, an intermediate voltage tap is selected until the electrodes bore into the scrap. Usually, light scrap is placed on top of the charge to accelerate bore-in. Approximately 15 % of the scrap is melted during the initial bore-in period. After a few minutes, the electrodes will have penetrated the scrap sufficiently so that a long arc (high voltage) tap can be used without fear of radiation damage to the roof. The long arc maximizes the transfer of power to the scrap and a liquid pool of metal will form in the furnace hearth At the start of melting the arc is erratic and unstable. Wide swings in current are observed accompanied by rapid movement of the electrodes. As the furnace atmosphere Chapter#3 ELECTRIC ARC FURNACE heats up the arc stabilizes and once the molten pool is formed, the arc becomes quite stable and the average power input increases.  Chemical energy is be supplied via several sources including oxy-fuel burners and oxygen lances. Oxy-fuel burners burn natural gas using oxygen or a blend of oxygen and air. Heat is transferred to the scrap by flame radiation and convection by the hot products of combustion. Heat is transferred within the scrap by conduction. Large pieces of scrap take longer to melt into the bath than smaller pieces. In some operations, oxygen is injected via a consumable pipe lance to "cut" the scrap. The oxygen reacts with the hot scrap and burns iron to produce intense heat for cutting the scrap.  Oxidation of C, P, Mn, Si, Al:Once a molten pool of steel is generated in the furnace, oxygen can be lanced directly into the bath. This oxygen will react with several components in the bath including, aluminum, silicon, manganese, phosphorus, carbon and iron. All of these reactions are exothermic (i.e. they generate heat) and supply additional energy to aid in the melting of the scrap.  Oxidizing slag formation: The metallic oxides that are formed will end up in the slag. Once enough scrap has been melted to accommodate the second charge, the charging process is repeated. Once the final scrap charge is melted, the furnace sidewalls are exposed to intense radiation from the arc. As a result, the voltage must be reduced. Alternatively, creation of a foamy slag will allow the arc to be buried and will protect the furnace shell. In addition, a greater amount of energy will be retained in the slag and is transferred to the bath resulting in greater energy efficiency.  Sampling and chemical analysis of the melt: Once the final scrap charge is fully melted, flat bath conditions are reached. At this point, a bath temperature and sample will be taken. The analysis of the bath chemistry will allow the melter to determine the amount of oxygen to be blown during refining.  De-slagging: When sufficient amount of phosphrous has been oxidized and gone in to slag the slage is removed. iii. Basic slag formation: Basic slag is then formed by addition of flux and blowing of oxygen. The purpose of this basic slage formation is that the furnace is taped at 17000C at this temperature Chapter#3 ELECTRIC ARC FURNACE P2O5 ,which has penetrated in to refractories and remaining in the melt, decomposes resulting in increase in percentage of Phosphorous. But due to the formation of basic slag this effect is prevented. iv. Tapping the steel: When steel has got aimed( average of upper and lower limits) composition and temperature Steel is tapped in preheated ladles by tilting slowly at an angle of 450. v. Killing of steel( Deoxidation): During the tapping the steel is killed by using deoxidizers. Which include Ferrosilicon, Ferromanganese, Ferrochrome, Aluminum & Silicomanganese. The addition of these oxidizing agents is based on the composition of melt and cost. The basic purpose of killing of steel is to maintain oxygen content from 100 ppm to 200 ppm. 3.0.2 Chemistry of process: At this stage excessive carbon, phosphorous, silicon and manganese oxidize. The process is similar to that in Basic Oxygen Furnace. Basic oxidizing slag composed of lime (CaO) and ion ore (FeO) is used during the oxidizing period. Gaseous oxygen is blown into the melt for additional oxidizing and to stabilize the arc. Iron oxide causes increase of Oxygen content in the molten steel according to the reaction: (square brackets [ ] - signify solution in steel, round brackets ( ) - in slag, curly brackets {} - in gas). (FeO) = [Fe] + [O] Oxygen dissolved in the melt oxidizes carbon, phosphorous, silicon and manganese: [C] [Si] [Mn] 2[P] + [O] + {O2} + 1/2{O2} + 5/2{O2} = {CO} = (SiO2) = (MnO) = (P2O5) Carbon monoxide partially burns in the atmosphere: Chapter#3 {CO} + {O2} ELECTRIC ARC FURNACE = {CO2} The formed oxides are absorbed by the slag. CO bubbles floating up through the melt result in refining of the steel from non-metallic inclusions and hydrogen removal. Gaseous products CO and CO2 are removed by the exhausting system. Oxidizing potential of the atmosphere is characterized by the post-combustion ratio: {CO2}/({CO2}+{CO}). The oxidizing slag enriched with phosphorous and other oxides formed during this period is removed from the furnace to a slag pot (de-slagging). 3.0.3 Refractory lining of an Electric Arc Furnace Refractory linings of Electric Arc Furnaces are made generally of resin-bonded magnesia-carbon bricks. Fused magnesite grains and flake graphite are used as raw materials. When the bricks are heated the bonding material is cocked and turns into a carbon network binding the refractory grains, preventing wetting by the slag and protecting the lining the from erosion and chemical attack of the molten metal and slag. During the process if rammed magnasite layer is eroded then process known as gunning is applied to protect the lining. 3.0.4 EAF Configuration: Following is the configuration of electric arc furnace of PSM: Furnace Capacity Electrode Consumption Power Oxygen Lance Pressure Carbon Electrode Diameter Furnace Efficiency Current Voltage Taping Time Flux addition Tapping temperature 16 tons 3 Kg/ton 5 MW 2 bar 12” 90% 13000 amp 400+ 2 hr 2.5% of charge 17000C Chapter#3 3.0.5 Addition: ELECTRIC ARC FURNACE Following are the formulas used to calculate the amount of alloy addition during the process: CHAPTER#3 LADLE FURNACE Ladle furnace refining is the secondary reefing process. The purposes of secondary refining are many:  Temperature homogenization and adjustment  Chemical adjustments for carbon, sulfur, phosphorus, oxygen  Precise alloying,  Inclusion control,  Degassing 3.1 Ladle Furnace In PSM there are two ladle furnaces in melting shop. In PSM the ladle furnace operation is used to perform desulfurization. It is possible to remove sulfur at EAF but the temperature of desulfurization is high enough that at this temperature phosphorus reverse reaction stars. Therefore desulfurization is performed at LF. To perform it a reducing slag is formed by the addition of CaO. The temperature of molten steel is rase using electric arc similar to EAF. A porous plug; at the bottom of ladle; is to provide nitrogen gas for stirring of the molten metal to promote homogenization. Nitrogen is purged at 2bar .The ladle roof is typically a watercooled design with a refractory center or delta section and is configured to coordinate with existing ladles such that the roof will completely cover the top portion of the ladle when in the operating (i.e. fully lowered) position. 3.1.1 Process Chemistry: The most popular method of desulfurization is removal of sulfur from molten steel to the basic reducing slag. Basic slag is a slag containing mainly basic oxides: CaO, MgO, MnO, FeO. A typical basic slag consists of 35-60% CaO + MgO, 10-25% FeO, 15-30% SiO2, 5-20% MnO. Transition of sulfur from steel to slag may be presented by the chemical equation: [S] + (CaO) = (CaS) + [O] 3.1.2 Alloy Addition: Following are the formulas used to calculate the amount of alloy addition during the process: CHAPTER#3 LADLE FURNACE 3.1.3 Ladle Furnace Configuration: Transformer Electrode Diameter Voltage Amperage Power Consumption Refining Time Heat capacity 5MVA 8 inches 80-130V 400-5000 Amp 2500 KWH 90 min 10-14 0C/100KWH CHAPTER#3 VACUUM LADLE DEGASSING 3.2 Vacuum Ladle Degassing: The Melting Shop of PSM is equipped with Vacuum Ladle Degassing Unit. It is the final treatment of molten steel before going to continuous casting unit. There are different methods of Vacuum Ladle Degassing of steel some of them are as follows:  Recirculation Degassing (RH)  Recirculation Degassing with oxygen top lance (RH-OB)  Ladle Degassing (VD, Tank Degassing)  Vacuum Oxygen Decarburization (VOD) Vacuum Ladle Degassing Unit in PSM is capable to perform two of the above vacuum degassing treatments, VD & VOD. 3.2.1 Process Chemistry:  Methods of vacuum ladled gassing utilize there action of deoxidation by carbon dissolved in steel according to the equation: [C] + [O] = {CO} where: [C] and [O] - carbon and oxygen dissolved in liquid steel; {CO} - gaseous carbon monoxide.  Vacuum treatment of molten steel decreases the partial pressure of CO, which results in shifting equilibrium of the reaction of carbon oxidation. Bubbles of carbon monoxide form in the liquid steel, float up and then they are removed by vacuum system.  In addition to de-oxidation vacuum treatment helps to remove Hydrogen dissolved in liquid steel. Hydrogen diffuses into the CO bubbles and the gas is then evacuated by the vacuum pump. Movement of the molten steel caused by CO bubbles also results in refining the steel from non-metallic inclusions, which agglomerate, float up and are absorbed by the slag. CO bubbles also favor the process of floating and removal of nitride inclusions and gaseous Nitrogen.  As a result of vacuum treatment the oxygen content of molten steel reduced to 5 to 10 ppm.Steels refined in vacuum are characterized by homogeneous structure, low content of non-metallic inclusions and low gas porosity. Vacuum degassing methods are used for manufacturing large steel ingots, rails, ball bearings and other highquality steels. CHAPTER#3 3.2.2 Process Detail: VACUUM LADLE DEGASSING The Vacuum Ladle Degassing Unit consist of following main parts:  Watering Plant( Vacuum Generator)  Vacuum Chamber(Pit Type)  Regulator( Monitor Vacuum)  Valves(Control Vacuum) 3.2.3 Vacuum Generation: Vacuum Ladle Degassing Unit maximum vacuum is achieved step wise, as follows: S.No 1. 2. 3. 4. Vacuum Pumps 2-Rotary Pump Ejector Pump E4 Ejector Pump E3 Ejector Pump E2 Vacuum Range(torr) 760-220 220-60 60-6 6-3.7 Time 10 min 3min 3min 10min Initially 2-rotary pumps generate vacuum up to 220 torr, then one rotary pump stops and the ejectors pumps are started according vacuum achieved. 3.2.4 Ladle Degassing Process(VD):  In order to perform Ladle Degassing, on ladle with molten steel, which is arrived from Ladle Furnace Unit, a ledle cover is placed. On this vacuum cover a Silicon O-ring is placed as vacuum seal and finally vacuum cover is placed.  The ladle is equipped with a porous refractory plug mounted in the ladle bottom which is made up of high alumina refractory. Through the plug argon is supplied during vacuum treatment. There is an addition hopper with vacuum lock on the chamber cover. The hopper is used for adding alloying elements and also for oxygen lancing in VOD treatment. CHAPTER#3 VACUUM LADLE DEGASSING  The reaction [C] + [O] = {CO} starting in the steel under vacuum conditions causes stirring, which is additionally intensified by argon blown through the bottom porous plug.Intensive stirring of the melt and the slag results in deep desulfurization of the steel. Desulfurizing slags possessing high sulfur solubility are used in this process. Argon and CO bubbles also favor the process of floating and removal of nitride inclusions and gaseous nitrogen.  Benefits of Ladle Degassing (VD, Tank Degassing): -Hydrogen removal (degassing); -Oxygen removal (deoxidation); -Deep sulfur removal (desulfurization); -Carbon removal (decarburization); -Precise alloying; -Non-metallic inclusions (oxides and nitrides) removal; -Temperature and chemical homogenizing. 3.2.5 Vacuum Oxygen Decarburization (VOD)  In this method a vacuum chamber is equipped with a vertical water cooled lance for blowing oxygen on the molten steel surface.  Vacuum Oxygen Decarburization (VOD) method is used for manufacturing Stainless steels. Oxidation of liquid steel components under vacuum differs from that at normal pressure: oxygen is consumed mainly by the reaction [C] + [O] = {CO} rather than by oxidation of chromium, which is the main constituentof stainless steels.  VOD process allows to decarburize the steel with minor chromium losses. Oxidation reactions have also heating effect therefore the treated metal may be heated to a required temperature without any additional energy source.  After having the decarburization (oxidation) stage completed deoxidizers are added to the steel in order to remove excessive oxygen. Then a Desulfurizing slag is CHAPTER#3 VACUUM LADLE DEGASSING added to the molten steel surface. Stirring of the melt and the slag caused by argon blown through the porous bottom plug results in deep desulfurization of the steel.  At the end of the oxygen blowing period, the basicity of the slag is 1.8–2.5. Combined with strong argon stirring, this slag provides effective sulfur removal.  Amount of Oxygen Blown=16(%C) + 8(%Si) + 6.2(%Al) + Total Tonnage of ladle.  Benefits of Vacuum Oxygen Decarburization (VOD): -Deep carbon removal (decarburization). Low-carbon (
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