Wheel Shop Process PDF

8 Wheel Shop Scrap Scr Charging Melting Spectro-Analysis Controlled Cooling Mould Split Pouring in Hot Wheel Kiln Sprue Wash & Hub Cutting Heat Treatment Stamping Shot Blasting Apex Grinding Hub Cooling...

8 Wheel Shop Scrap Scr Charging Melting Spectro-Analysis Controlled Cooling Mould Split Pouring in Hot Wheel Kiln Sprue Wash & Hub Cutting Heat Treatment Stamping Shot Blasting Apex Grinding Hub Cooling & Cooling Magnaglo and Hardness testing Cope and Drag Ultrasound Testing grinding Inspection & Stock Shot Peening and Warpage Hub Boring  9 Wheel Shop The Wheel Shop is the first unit of RWF. The wheels enable the train to move along the rails of the track. On an average, a wheel weighs about 500 kgs. The RWF produces eight different types of wheels having different composition, requirements and dimensions. The wheel shop recycles metals from the scrap yard and adds required resources to obtain the right composition for producing wheels. Later the melt is used for moulding to obtain the basic geometry of wheel. It undergoes various machining, finishing processes and inspection tests to conform to customers’ requirements. The Wheel Shop comprises of mainly three divisions: 1) Melting 2) Moulding 3) Finishing (WFPS)  10 MELTING  Scrap conditioning : Scraps are the basic additions to manufacture the wheels. They may be:  Rejected wheels  Rejected axles  Used axles and worn out wheels  Chips formed during machining processes The scraps are divided into three types – machine chips, light metals and heavy metals. This sectioning is important because during the initial melting process in the electric arc furnace, the distribution of heat is not uniform. The bucket charging distribution is such that from bottom to top; heavy, light and machine chips. This arrangement will prevent major fire spewing, scrap bridging, and scrap collapse when the arc is setup.  11  Charging of scrap: It can be simply defined as addition of scrap along with materials such as lime stone, calcined lime and coke/graphite to the furnace. Brief procedure  The electrodes are raised and an electromagnet via an EOT (Electric Overhead Traveling) crane transfers machine chips and some lights scraps into the furnace.  Bucket charging of scraps in the required order is done. The bucket opens from the bottom. The heavier metals are on the top, then the light and the machine chips.  Charge approximately 9000 to 1200 kgs calcined lime and 200 to 250 kgs coke/graphite.  Melting of scrap: The furnace used for melting is an electric arc furnace. RWF wheel shop contains three electric arc furnaces named A, B and C. They operate the same way and only in C; its tap hole order differs from A and B. The capacity of each furnace is 20-23 Metric Tons.  12 The three electrode electric arc furnace heats charged material by means of an electric arc. It consists of a refractory-lined vessel (Alumina bricks), usually water-cooled in larger sizes, covered with a retractable roof, and through which one or more graphite electrodes enters the furnace. The furnace is primarily split into three sections:  The shell, which consists of the sidewalls and lower steel "bowl"  The hearth, which consists of the refractory that lines the lower bowl  The roof, which may be refractory-lined or water-cooled, and can be shaped as a section of a sphere, or as a frustum (conical section). The roof also supports the refractory delta in its center, through which one or more graphite electrodes enter. Brief procedure  The electrodes are lowered. On supplying the necessary current and voltage an arc is struck between the electrodes and the charge for 45 to 55 minutes.  The gap between the electrodes and the charge is maintained by regulating the movements of the electrodes so that the arc remains between them.  After 45 to 55 minutes oxygen lancing pipe is used for cutting of scrap through the slag door. The temperature during this procedure is 1650 to 1700 °C.  The slag is formed which floats on the surface of the melt. This prevents oxidation, refines the metal and protects the furnace roof from excessive heat.  Removal of slag: During the Oxygen lancing, slag is eliminated through the slag door. Brief procedure  Dolomite is spread over the cleaned slag door.  Remove full slag before the temperature is 1630 °C.  13  If it is sluggish, shovel in 55 to 65 kgs of Fluorspar on the slag.  Ferro-manganese is used for slag reducing at around 1650 °C and 150 kgs of slag reducing mixture is also used.  Spectro – analysis: The testing of sample that has to be further used or subjected for wheel manufacture is done at the spectro lab. The sample (solidified metal) for testing is obtained from the electric arc furnace to determine the composition of various metal constituents within the required range.  Carburisation/Decarburisation: A sample of melt is taken for testing a percentage composition of C (Carbon), Si (Silica) and Mn (Manganese). These may differ from the fixed required percentage. Addition of materials to bring the composition to the fixed percentages may either be done by carburization or decarburization. Brief procedure  CARBURISATION, if the carbon content is founded to be lesser, required amount of Graphite is added when the electrodes are just inside the bath at 1640 °C and the sample is taken.  DECARBURISATION, if the carbon content is more, slag coated Oxygen lancing pipe is introduced to reduce Carbon content; based/depending on carbon to be reduced Oxygen is supplied.  The controlling content for this process are Ferro-manganese, Silica-manganese and Ferro-silicon.  Mix the bath thoroughly. After 3-4 minutes of arcing, take another sample for testing.  Tapping: It is the process of pouring the melt from the furnace into the ladle (melt carrying container) by tilting the base of the furnace.  14 Brief procedure  The ladle is prepared for tapping process and brought to the furnace through EOT crane.  Add required amount of Ferro-silicon, Ferro-manganese or Silicon-manganese into the ladle after the ladle preparation.  The tapping temperature should be between 1660 °C to 1720 °C.  The base of the furnace is tilted and tapping of the metal starts.  The ladle is adjusted so that the metal stream falls at the center of the ladle and not on the side walls.  Tapping is completed within 3 to 4 minutes to avoid temperature loss.  After tapping, the ladle is carried to the JMP (John Mohr Pit).  15 For 20 MT of liquid metal Item to be added Elements to increase Quantity of Ferro Aim to achieve allow to add for increase of element Graphite powder Carbon 2kgs for 0.01% to 60-62 for Box-N incr. 50-52 BG coach 70-72 CH-36 Wheel Ferro-silicon Silicon 140 kgs without 50-55 drain metal. 130 kgs with drain metal. Ferro-Manganese Manganese(Normally 3 kgs for 0.01% to 70-75(ladle) in furnace) incr. 30-45(furnace) Silicon-Manganese Manganese 3 kgs for 0.01% to 70-75 incr. MOULDING ROOM  16  John Mohr Pit(JMP): After the melt is poured into the ladle, it is carried to the JMP. The wheel shop has two John Mohr pits. The main purpose of JMP is for temperature measurement and maintenance and finalizing the melt composition. Brief procedure  Wait till the temperature is lesser than 1610 °C.  When the temperature is around 1560 to 1610 °C, immerse the Aluminum stars. The Aluminum stars are used to prevent change in composition of the melt.  A sample is taken for testing, this acts as the final analysis for the required/fixed composition.  Ladle insulation material is sprinkled into the ladle to maintain temperature.  The ladle is taken for insertion of the ceramic pipe. *NOTE: The ceramic pouring tube is fixed on a cover and it takes around 1 day for preparation because it has to withstand high temperatures of the melt. This is done in a Pouring Tube Section. The roof is lifted and lowered 2 to 3 times for the pouring tube to get accustomed to the heat. This process prevents cracking of the pouring tube.  Casting process: The casting process uses controlled pressure pouring process through which the melt rises in the ceramic pipe and fills the cavity of the approximate desired shape. This technique contains cope and drag system. They are made up of Graphite material.  17 Brief procedure  The ladle containing the molten metal placed in JMP is brought into the place of pouring and Ladle Insulation Material powder is sprayed into molten metal to prevent temperature loss.  The cope and drag assembly is placed on the covering of the ladle which contains a center circular hole. This hole houses the ingate through which molten metal gets into the cope-drag assembly.  The liquid metal with high air pressure comes out of the ladle through the ingate. A sensor prevents overflow of melt i.e.; graphite stopper plunges the bottom of the drag and prevents the further flow of liquid metal from ladle into cavity. It also prevents the liquid metal flowing back to the ladle from the cavity.  An asbestos gasket is used as a sealant between drag and pouring tube to prevent bleeding of liquid metal and also airation. One gasket is used for each cast wheel.  Once the mould is prepared it is subjected to 9 to 10 minutes of solidification. Solidification may be defined as allowing the metal to cool and solidify.  After solidification, the cope and drag assembly is split and the cast wheel is obtained.  18  The cope is clamped and lifted gently. Sometimes, wheel sticks to the cope so the crane moves up and down over the drag controlled by the operator.  The wheel is placed in hot wheel kiln where it is subjected to controlled air cooling. The cycle time is 32 minutes and 33 wheels can be accommodated.  The cope and drag are sent back separately for cleaning and preparation. *NOTE: The pouring of each wheel takes about 80seconds. For one heat 32 to 33 wheels can be casted. And a cope-drag assembly can be used for 20 to 25 wheels. Once the metal is poured paddy husk is added to the assembly through riser holes to prevent sudden drop in temperature of molten metal which otherwise would produce cracks/flaws in the surface of wheels. The important parameters are pouring time, metal initial and final temperature, pouring rate splitting time, wheels offloaded and riser weight.  19  Sprue washing: In casting, a sprue is a channel or passage through which a molten material is introduced into a mould. It contains a little part of the runner and riser which is not removed during splitting. These must be removed before the further cleaning of the wheel takes place. Brief procedure  After the controlled air cooling, the wheel coming out of the kiln is at a temperature of about 400 to 500 °C.  After sprue washing, the wheels are stamped where the wheel and heat numbers are stamped using a stamping machine. This is called stamping.  Hub cutting: The center portion of the wheel where the axle fits in is called the hub. To produce this hub of required diameter, hub cutting is carried out. The mixture of oxygen and LPG gas flame coming out of the nozzle at high pressure and velocity is used for hub cutting. Brief procedure  The hole is initially cut for a diameter lesser than the required during this process using hub cutting machine.  The average hub diameter is 188mm for BOX-N.  The part of the stopper pipe inserted during casting remains inside the cast wheel after being cut at both the edges. This is called pilot hole.  The hole is initially cleaned using pneumatic air.  The gas flame is directed to the pilot hole and moved along the radius and finally moved in a circular shape.  20  A Go-No Go gauge is used for checking its correctness. If found right, reload otherwise reject the wheel. *NOTE: If the hub cutters are under breakdown, wait till the temperature is lesser than 265°C , load them into normalizing. The temperature for hub cutting is between 265-400°C. The quality parameters are dimensional range of hub cut, details of hub not fallen/ pilot hole block, non-conforming wheels, O2 + LPG.  Normalizing: Normalizing is defined as a heat treatment process to heat the metal above the critical temperature, holding for a period of time long enough for transformation to occur and air cooling. In general, it is to bring or return to a normal or standard condition or state. Normalizing helps to maintain proper grain size. Brief procedure:  The wheels after hub cutting are sent into the rotary hearth furnace for normalizing process.  The rotary hearth furnace used for normalizing has 7 zones. First three zones are called as heating zones where the outer layer of the wheel and a few inner layers get heated.  21  The next four zones are called soaking zones wherein the heat spreads uniformly including the core of the wheel.  The temperature maintained in the furnace is between 890 to 960 °C.  The fuel used in rotary hearth furnace is high speed diesel.  Each wheel remains in the furnace for a duration of 90 minutes and 45 wheels in 2rows can accommodated inside the furnace.  The outer and inner walls of the furnace remain stationary whereas the hearth inside rotates with the help of rack and pinion gear.  The temperature of the wheel coming out of the furnace is greater than 800 °C. *NOTE: The quality parameters are normalizing furnace zone temperature, heat and wheel number, time in and out of normalizing furnace. Specifications of blowers used for normalizing Direction Flow Rated De-rated Motor of static static discharge pressure pressure Combustion V belt 6000 CFM 1300mm 1070mm 75 HP; air blower driven; LTV WG WG 1450 RPM Combustion V belt 5701 CFM 1083mm 890mm 60 HP; air blower driven;RTV WG WG 1450 RPM Dilution air Direct 2500 CFM 240mm 195mm 7.5 HP blower driven;LTV WG WG 2 pole Automising Direct 1206 CFM 1088mm 895mm 15 HP air blower driven;RTV WG WG 2 pole Nose cooling Direct 3300 CFM 176mm 145mm 7.5 HP air blower driven;RTV WG WG 4 pole 3 Air blower, V belt 400m /min 650mm 535mm 100 HP induced driven, WG WG 4 pole draught direct driven; RTH  22  Quenching: It is a stage of material processing through which a metal is quickly brought down to lower temperature from a high temperature by rapid cooling. During the movement of the train the outer portion of the wheel called the rim is in contact with the rail and hence it is this portion that is subjected to more wear and tear. Therefore, to increase the hardness of the rim, rim quenching is performed. Water is the medium for quenching. Brief procedure  The wheels coming out from the normalizing furnace are subjected to rim quenching wherein high pressure jet of water with 2.5 to 3.5 kg/cm2 pressure is made to fall only on the rim portion of the wheel for about five minutes.  This increases the hardness of the rim portion up to a depth of 5 to 8mm.  The temperature of the water for rim quenching is 18 to 35 °C.  Tempering : Since the wheels are manufactured by casting process, there are chances of internal stresses being introduced in the interior of the wheel. These stresses are very dangerous and may also damage the wheel during working. In order to remove these stresses from the wheel, they are sent into the draw furnace where the wheel undergoes tempering process. Brief procedure  Each wheel once entered the draw furnace remains inside for around 2.5 hours.  The draw furnace in RWF is run using high speed diesel and has a capacity of 80 wheels.  23  Hub cooling: During the assembly of the wheels with axles there are chances of crack formation in the hub portion. Hence, this portion needs to be hardened. This hardening of the hub portion is done by quenching process. This stage contains a conveyor belt that’s consists 3 hub coolers. Brief procedure  The wheels coming out of draw furnace is subjected to hub cooling in three regions – upper, middle and the inner portion of the hub is cooled separately.  The time taken in each of the region is 45 seconds.  High jet of water having a pressure of 2.5 kg/cm2 is sprayed on the interior of the hub during this process.  The hub portion becomes harder hence reducing the chance of crack.  The wheel after hub quenching has a rough surface and is air- cooled. The wheels need not be air-cooled separately, they are sent into stack yard for cooling for about 60 minutes.  24 Wheel Final Process Shop The finishing in the wheel shop happens in the Wheel Final Process Shop (WFPS). The wheels stored in the stack yard have a rough uneven surface. These wheels need to be cleaned and finished before its usage. This cleaning, finishing, and certain test is conducted in this cleaning shop.  Apex grinding: Since the wheels are casted in cope and drag assembly, there is extra material along the parting line. To eliminate the extra material, apex grinding is performed.  Cleaning: The surface of the wheel may contain dirt, ashes and even dust particles formed during storing; also the wheels contain scales formed during heat treatment process. To remove the unwanted dust and obtain a clean surfaced wheel, cleaning is performed. Brief procedure  It contains three roto blasts through which high velocity starch are made to strike the surface of the wheel.  25  Due to the impact of these particles, the surface dust present on the wheels gets removed due to the abrasive action.  Hence the surface cleaned wheel is obtained after the cleaning process.  Magnaglo testing: This is a fluorescent magnetic particle inspection method. This test is conducted for detecting surface cracks. Brief procedure  The cleaned wheels enter a dark room. Magnaglo powder uses water as a suspension medium. This is poured on the wheel.  The black light (with wavelength of 365 nm) is switched on and the magnaglo fluoresces bright yellow-green. The operator checks for fine surface and sub-surface discontinuities. A crack can be detected when the magnetic particles accumulate around it and it glows bright.  The operator uses radium chalks to indicate cracks. Further on, these will be grinded.  Ultrasound testing: Ultrasound testing (UT) is a family of non-destructive testing techniques based on the propagation of ultrasonic waves in the object or material tested. This test is performed to detect interior defects/flaws. Brief procedure  The wheel is directed for ultrasound testing.  The wheel spins with its bottom in water. The sensors underwater emit a pulse waves with center frequencies ranging from 0.1 to 15 MHz  26  A probe sends a sound wave into a test material. There are two indications, one from the initial pulse of the probe, and the second due to the back wall echo.  A defect creates a third indication and simultaneously reduces the amplitude of the back wall indication.  The operator will indicate the flaw code and place.  The wheel undergoes Brinell hardness test and the values will be displayed on a digital screen.  Warpage testing: The wheels during casting and heat treatment process remains at high temperature. During this temperature there are chances of wheel undergoing little bending. But this bending of wheels above certain limits is undesirable for the working of the wheel. Warpaging is a process in which these bends are detected and if it exceeds the limit, they will be rejected. Brief procedure  Receive wheel for warpage measurement.  Pass wheel for warpage if warpage reading is lesser than 1.0mm for all wheels.  The warpaging includes the balancing of wheels from which the defects relating to the shape of the wheels can be detected.  If the detected defects in the shape like bending of wheels etc. are more than the limiting value, wheels are rejected.  SHOT PEENING: Shot peening is a cold working process used to produce a compressive residual stress layer and modify mechanical properties of metals and composites. It entails impacting a surface with shot with force sufficient to  27 create plastic deformation. This process uses steels shots for peening cast iron wheels of hardness 255 to 363 BHN. Brief procedure  Steel shots are made to strike on the wheel at high speeds.  In case there are any cracks, the steel shots strike the cracks at high velocities and fill the gap and help remove the defects.  Each wheel undergoes this process for 1 minute on an average.  Hub bore machining: This is a rough boring operation carried before it is sent to the assembly shop. During hub boring, the center hole generated is of a smaller diameter than required. The hole needs to be enlarged to fit in the axle. This is done by hub boring machining. Brief procedure  A square shaped carbide insert is used for boring.  A hole of 3mm lesser than the diameter of the axle wheel seat is produced during this process.  28 COPE AND DRAG PREPARATION IN MOULDING ROOM  Cleaning stage:  After splitting the cope and drag, they are sent separately for their preparation. The cope and drag are first sent to their respective tilting machines where loose particles of dust fall out as they rotate.  An operator uses compressed air at high pressure to blow out the remaining dust.  The receiving temperature for blowing compressed air is 245-325°C.  Cope baking: The cope is coated with resin and baked in an oven. After cope baking, the cope is cleaned by sand blasting.  Cope spraying:  Fused Silica Powder are mixed with additives of CMC and Veegum powder to prepare mould spray. This spray is used for coating the mould which serves as an emulsion stabilizer, suspending agent and binder.  Check adhesion with adhesion tester whose acceptable range is from 50-65 PSI.  There are three spray guns. The quantity for BOX-N that is used for each region is as follows: Plate – 185ml Hub – 125ml Rim – 170ml  Drag spraying:  A spray mixture tank is used for mixing the fused silica powder along with additives to prepare the mould spray.  29  When the temperature is above 245°C, the drag enters the spray room and the cooling fan is put on.  The baume value for spray quantity from the two spray guns range from 39 to 41. Spray tank pressure – 8 to 10 PSI Atomizing pressure – 40 to 65 PSI  The drag is later sent to the MHO (Mould Holding Oven) waiting for pouring.  Spray quantity for BOX-N Hub – 125 ml Plate – 175 ml Rim – 175 ml  Stopper fitting:  An operator assembles the parts of the stopper pipe before fixing it on to the cope.  When the cope is received, the operator checks for the spray pattern.  If satisfied the stopper pipe assembly fixes onto the cope.  In the end, the operator fixes the stapple to avoid any slipping of stopper pipe.  The cope is later sent to the oven to wait for pouring.