Wheel Casting

Introduction

• IR mfgs. Cast Steel Bogies & wheels

– CASNUB bogies at CLW

– Cast wheels for Wagons & Coaches

• Rail Wheel Factory (RWF) at Bangalore

– Capacity 1.2 lac/ annum – prodn. 2lac/annum!

– TOT from Griffin of USA

• Rail Wheel plant (RWP) at Bela, Patna

– Capacity 1.0 lac/ anum – new set up

• Copy of RWF

• Demand of wheel > 3lacs/ annum 29/06/2015 2

Cast Steel Wheels

• Special Parabolic profile

• Very low P & S content

• Fine equiaxed grained structure

• High yield to tensile ratio resulting from

– Specially designed heat treatment process

• Round shaped non-metallic inclusions

• IR Specification R – 19 / 1993 Pt-III

– Both for Carriage & Wagon Wheels

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Cast Steel Wheels

• Metallurgically forging route better than

casting

• Special technique of controlled pressure

casting

– Equivalent to forging route, even better

• Cross dendritic structure

– Barrier to dislocation movement

• Stipulated Mech. properties are well met

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Cast Vs. Forged Wheels

• High rate of production with uniform Quality

• Eliminates machining, any plate design

• Internal defect position is known – So, very easy to ensure soundness

• Cleanliness by refining of steel in EAF

• Unique deoxidation ensures globulized alumina

– These helps in achieving K1C value

• High K1C value

– Resistance against catastrophic failure in service

Chemistry of Cast Wheel

Elements Wagon wheels (BOXN) Coaching Wheels

Carbon 0.57% to 0.67% 0.47% to 0.57%

Mn 0.6% to 0.8% 0.6% to 0.8%

Si 0.15% to 0.70% 0.15% to 0.70%

S 0.03% Max 0.03% Max

P 0.03% Max 0.03% Max

Cr 0.15% Max 0.15% Max

Mo 0.06% Max 0.06% Max

Ni 0.25% Max 0.25% Max

Cr + Mo +

Ni

0.40 Max 0.40 Max

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CASTING & HEAT TREATMENT

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Liq. Steel from EAF

• Mainly Railway scraps melted in EAF

• Chemistry adjusted to reqd. spec.

• Temperature raised to required level

– 16800C – 16900C for coaching wheel

– 16900C – 17000C for wagon wheel (BOXN)

• Tapped in preheated ladle

• Nominal capacity 20 MT

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Tapping from EAF

Mould Blank

Cope

Drag

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Wheel Casting

• Major slag is removed from the top of ladle

• Ladle placed in ‘JOHN MOHR’ Pit

• Al. star thrust into as final deoxidiser

• Sample taken for Chemical Analysis & H2

• Top cover with Silimenite tube sits on top

• Graphite Mould sits on the top of tube

• Pit pressurised by air to lift the liq. Metal

• Liq. Metal flow to the mould to fill cavity

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Wheel Casting Contd…

• Plunger brought down to seal the gating

• Mould placed on conveyor, next one in

• Stripping after pre-determined time

– to take away the Risers along with top

• Wheels placed on conveyor to tunnel

• Moulds go back for cleaning and recycling

• Sprue Wash, Stamping & Hub Cutting

Slag Off Station

Placing at John Mohr Pit

Cope & Drag Assembly

Mould Cavity Filling

Wheel Parting from Mould

Hot Wheel Kiln

Sprue Washing/Grinding

Hub Cutting

Heat Treatment

• Placed to Moving Bed Normalising

Furnace • 7000C→10000C→9600C→9600C→9600C

• Followed by Rim Quenching

• Water jet on rim for 4-5 min.

• Tempering in Draw fce. at 5000C for 2hrs

• Hub Quenching in 3 stages, 40 sec each

• Air cooling to RT

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Wheel Inspection

• Apex grinding

• Shot blasting to clean

• Hardness Testing

• Visual Inspection in normal light

• Magnaflux Test for surface & sub-surface

under UV light, mainly for cracks

• Wheels with removable defect sent for defect

removal through grinding & rechecking

Magnetic Particle Testing

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Wheel Inspection Contd…

• Automated Multi probe UT in Sprue area

• Final Hub boring

• Final shot blasting

• Warpage checking

• Final Dimensional checking

• Closure test, Mech. test & BHN mapping

• 1 in 500 for Coach wheels

– 1 in 1000 for BOXN wheels

Ultrasonic Testing

Wheel Routing

Defect Codification

• Codes for some common defects

10 - Cracks

12 - Ceramic, Metal refractory

13 - Slag

15 - Pinholes

16 - Ultrasonic

32 - Gouged hub bore

35 - Gouged riser

46 – Pock holes

51 - Lap

62 - Mould inclusions

10 - Crack

12 – Metal Refractory

13 – Slag Inclusion

15 - Pinhole

51 - Lap

32 – Gouged Bore

47 – Pocker Holes

62 – Mould inclusion

Defect Removal

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RWF & Wheel Production.

• Producing both BOXN & Carriage wheels

• Production target this year is 2 lacs

– Against rated capacity of 1.2 lacs

• Continuous three shift operation

• Looking forward for Loco wheel production

• Axle forging from bloom a parallel activity

• Final product: Wheel sets & loose wheels

• Total production connected by LAN

Refractory Management

Prologue

• IR uses different types of furnaces

– High temp EAF & Ladle for cast steel

– High temp Cupola for cast iron

– Medium Temp HT furnaces

– Low temp Tempering, Stress Relieving furnace

etc

• All these furnaces need different refractories

• In this section, EAF, Ladle, HT & Draw

furnace refractories are covered

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Introduction

• Refractory is the material which can retain

its strength at high temperature

• Both Graphite & Alumina are refractory,

but

– Thermal conductivity is widely different

– Those with low TC normally called refractory

• Used to conserve heat & protect shell

• Different type of refractories for different

furnace and different sections of a furnace 12/27/2014 42

43

Chararecteristics of Refractory

• For furnace application, materials that – Withstand high temperatures and sudden

changes

– Withstand action of molten slag, glass, hot gases etc

– Withstand load at service conditions

– Withstand abrasive forces

– Conserve heat

– Have low coefficient of thermal expansion

– Will not contaminate the load

are called refractories

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EAF REFRACTORIES

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Electric Arc Furnace

• Most versatile equipment for production

Steel

• With high power rating furnaces, the load

on refractories has gone up considerably

• Some developments reduced consumption

– Water cooled panel

• 85% of roof and 70% of side walls water cooled

– LF, EBT, DC furnace etc.

• In IR, only water cooled panels are used

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Structure of EAF

• A typical EAF has following basic areas

– Circular shallow bath with a dish shaped bottom

– Cylindrical side walls with slag door

– Dome shaped roof with circular openings for

electrodes, fume extraction etc.

– Tap hole

• Different service condition of various areas

– Requires different types of refractory materials

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Roof of EAF

• One of the most affected portion subjected to

all kind of stresses; thermal, chemical &

mechanical

– very high temperature often exceeding 1700°C

– Corrosive action of slag and metal oxides

• Specially iron oxide fumes which is deleterious

– mechanical stresses. Due to complicated design

• Spalling due to temp fluctuation

• Formation of low melting compounds

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Roof of EAF

• The problem has been tackled in two ways

– by improving the quality of refractories

– by changes in the design of laying

• Conventionally Silica Bricks

• Can not meet present day requirements

– High alumina materials (up to 95% Al2O3)

– castables with Cr oxide or pre-fabricated shapes

– Water cooled roofs

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Side wall of EAF

• Subjected to – Severe thermal shock

– corrosive slag action

– Mechanical abuse during charging etc.

• 3 different zones, Slag, Roof drip & Hot spot – Hot spots zones - most severe condition

• Exposed to very high arc temp as well as slag

• Reflected bath heat

• Mag-carb bricks with 10-15% carbon with water cooled panel

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Hearth of EAF

• Hearth or bottom - a receptacle of liquid metal and slag

• Has to withstand very arduous service condition – High temperature

– Thermal stress due to fluctuation in temp. before and after tapping

– Slag and metal corrosion

– Mechanical abuse during charging

– High structural stresses during tapping at maxm. tilt

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Hearth of EAF

• Divided into two sections

– Sub-hearth with few layers of high fired magnesite bricks along with a fire bricks lining against the shell

– Working hearth or bottom made by ramming dolomite or magnesite, known as DRM • Provides a monolithic, joint free surface

• Thickness around 250-300 mm

• Life 5000 - 10000 heats depends upon size of furnace and operating parameters.

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Hearth of EAF

• DRM with little water & MgSO4

• Ramming or vibration with a vibrator

• After around 50 heats, top layer scraped out

• Fresh layer of DRM rammed to replenish

• Heating up of cold furnace – Light wood & charcoal lit up to drive out water

– Light scrap/boring about 500kg and arcing to heat

– Normal charging & arcing at low rate

– Holding at 12000C for 30 min

– Slow heating to desired temp.

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Tap Hole & Launder

• High Alumina brick joined by Alumina mortar

• Top surface repaired by WRM occasionally

• Tap hole plug to block tap hole – A mound with fireclay and graphite in water

– Tap hole packed

– Top surface with fireclay paste

– During tapping, the mass speared open

– Sometimes early opening of hole and metal flowing

– Higher Graphite, easier to open

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LADLE REFRACTORIES

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Ladle & Refractory

• Ladle is a bucket shaped container, flat bottom – Refractory lined round steel container

– Carrying liq. Metal from furnace to pouring station

• In IR different refractories for ladle lining – High alumina (70% min) brick

– High Alumina mortar

– High heat duty safety layer

– WRM

– DRM

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Ladle Preparation

• 1st layer – High heat duty fireclay bricks to IS 8

• Then bottom layer of High Alumina brick

• Gaps packed with DRM, sealed with mortar

• Vertical wall built up with a gap, mortar joint

• Gap packed with DRM, burnt refractory etc.

• Built up to rim, keeping lip opening

• Finished with WRM paste

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Ladle Preheating Cycle

• Before use, a definite preheat cycle to follow

– Air dry for 24 hours

– Heat at a rate of 500C per hr. till 3500C

– Soak for 4 hrs.

– Heat at a rate of 500C per hr. till 12000C

– Soak for 4 hrs.

– Lower at 9000C and hold till called for tapping

• A well prepared ladle lasts around 24 heats

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Synchronising Tapping Cycle

• Tap to tap time of a fce. ideally 2½ hrs.

• Two fce. should run simultaneously – At a phase lag of 1¼ hrs

• Pouring time 1hr, manipulation 15 mins.

• When ladle is empty, next fce. ready for tap

• If not possible for any disruption – Drain the ladle, clean by oxygen blowing

– put at ladle pre-heater and maintain 9000C

• Never allow the temp. to come below 7500C

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NORMALISING & DRAW

FURNACE

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NF and DF Refractory

• NF is Rotating hearth type fce.

• Different zones temp. from 5000C to 10000C

• At low temp, 45% alumina brick

• At higher temp, 55% alumina brick

• Slow heat to 3500C, soak 3 hrs, raise to 9xx000C

• Once lighted, should not be put off!

• At bottom and pedestal, 55% alumina mortar

• DF is walking hook type fce. at 5000C

• Lined with 45% alumina brick

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TESTING OF REFRACTORIES

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Common Test Parameters

• Chemical composition – %age of Alumina, Magnesia, Silica, C, Cr-oxide

etc. as the case may be

– %age of Fe as FeO

– %age of Li, Na, K

• Bulk density – Amount of refractory material within a volume

(kg/m3)

– High bulk density means high volume stability, heat capacity and resistance

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Common Test Parameters

• Porosity

– Volume of open pores as % of total refractory

volume

– Low porosity = less penetration of molten material

• Cold crushing strength

– Resistance of refractory to crushing

• Permanent Linear Change(PLC)

– Permanent change in dimension after heating to

working temperature and cooling down

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Common Test Parameters

• Pyrometric Cone Equivalent (PCE) • Temperature at which a ‘test pyramid’ (cone) fails

to support its own weight

– Tested against std. pyramid

of oxides that melt at specific

temperatures

• Refractoriness under load (RUL) – Creep at high temperature

– Deformation of refractory material under stress at given time and temperature

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Electric Arc Furnace Operation

Introduction

• Steel is primarily produced from pig iron

• Pig iron is produced from various iron ores

– Oxides, Carbonates, Sulphides etc. of iron

– Mixed with coke (reducing agent & Fuel)

– Charged in Blast furnace

– Reduced to iron in liq. form

– Contains large amount of other elements like

Si, Mn, S, P, etc.

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Introduction

• Treated in various converters like O/H,

Bessemer, L/D, etc to controlled chemistry

– End product is steel – normally mild steel

– Rolled to plate, sheet, bar, beams, channels

etc. for different commercial use

• Known as Primary Steel Making

• Normally Heavy Industry like TISCO, SAIL

• One more process is DRI

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Secondary Steel Making

• For specific composition (Low alloy, High

alloy & sophisticated) steels

• Mild Steel scrap as Raw material

• Melting in Electric arc furnace (EAF)

– Different treatment & alloy addition to achieve

desired chemistry

– Tapped in ladle

– Cast to shape or Intermediates

– Further rolled or forged to shape 29/06/2015 68

Secondary Steel Making & IR

• Mfg. of Cast Steel Bogies & wheels

• CASNUB bogies at CLW

• Demand of wheel > 3lacs/ anum

– Rail Wheel Factory (RWF) at Bangalore

• Capacity 1.2 lac/ anum – prodn. 2lac/anum!

• TOT from Griffin of USA

– Rail Wheel plant (RWP) at Bela, Patna

• Capacity 1.0 lac/ anum – new set up

• Copy of RWF

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Cast Steel Wheels

• Special Parabolic profile

• Very low P & S content

• Fine equiaxed grained structure

• High yield to tensile ratio resulting from

– Specially designed heat treatment process

• Round shaped non-metallic inclusions

• IR Specification R – 19 / 1993 Pt-III

– Both for Carriage & Wagon Wheels

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EAF OPERATION

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Furnace Charge

• Graded Steel Scrap with low S & P

– Mostly from Rly. source

• Light scrap – 15 %

• Medium scrap – 35 %

• Heavy scrap – 60 %

• Flux

– Fresh Lime with 90% CaO Min.

• Carburising agent

– Graphite or Petroleum Coke with low S 29/06/2015 72

Charging Quantity & Sequence

• For about 20MT yield

– 22MT Scrap, 200Kg Coke & 1200Kg lime

• Pet coke and 80% of total lime to be

charged at the bottom

• Then light scrap

• Heavy scrap and foundry returns

• Light boring & turning

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Operation Sequence

• Lifting of Electrodes

• Opening of hood

• Charging of RM

• Closing the hood

• Lowering of Electrodes

• Start Arcing

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Operation Sequence

• Primary Melting through arcing

• Scrap cutting by blowing oxygen

• 1st sample around 15400C with 90% melt

• O2 lancing→2nd sample→Deslag→16200C

• Carbon blocking → RSM → Rabling

• 3rd sample→ Adjustment→ check samples

• Preheated ladle→ Alloy addition

• Melt temp. to17000C → Tapping to Ladle 29/06/2015 75

Operation Sequence

• Slag removal from top

• Taking to JMP

• Al. star addition

• Covering JMP & tube insertion

• Placing of Graphite Mould

• Pressure pouring

• Cope parting & wheel separation

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Metallurgical Aspects

• Initial arcing & scrap cutting

– 90% of scrap in molten pool

– Gen Chemistry; C>0.80%

• O2 lancing or ‘C Boiling’

– Bath mixing

– Removal of Hydrogen & Nitrogen

– C reduction

– Dephosphorisation

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Phosphorus Removal

• Conditions for dephosphorisation

– Low temperature

– Viscous slag

– Oxidizing condition

– High Basicity (more than 2.5)

• All conditions are met at this stage

• P forms P2O5 and goes out as gas

• C also forms oxides and move out

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Metallurgical Aspects

• 2nd sample to ensure C & P level

• Raising bath temperature

• C continues to loose due to dissolved O2

• Add Mn to stop loss; Carbon blocking

– Mn is stronger deoxidiser

• Al → Si → Mn → C

• Slag off and add fresh lime as RSM

– 200kg lime, 50kg graphite and 20kg FeSi

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Sulphur Removal

• Large reduction not practical in EAF

– Low S scrap, weeding axle box, rubber etc.

• Conditions for desulpherisation

– Reducing atmosphere

– High basicity preferably > 2.00

– High fluidity of slag.

– Intimate contact between slag & metal

– High temperature of the bath(preferably >

16500C)

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Sulphur Removal

• Addition of RSM at high temp.

– S removal conditions are met

• Sometimes little Fluospar addition

– Fluidity increases

– Restrictive, as corrosive to lining!

• FeSi , strong deoxidiser but restrictive

• Rabling to get fresh interface

• Formation of CaS & going to slag

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Final adjustments

• 3rd sample should ensure

– S & P within range

– C around 0.5%

• If not, charge Graphite powder

• Raise temp. to 17000C, take 2 samples

consecutively, bring preheated ladle

• Add calculated amt.(based on analysis) of

FeSi, FeMn & Graphite in the ladle,Tap

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Tapping or Pouring

• Final deoxidation should be in the ladle.

• Temp of pouring depends on the Carbon & other alloying elements in the steel.

• The size and geometry of casting also determines the temp of pouring.

• Pouring temp should be optimised in the lower side.

• Speed of pouring should be optimised on the higher side.

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Power Consumption

• Ideal consumption of power

– 462 KWH/MT (Ref. MSTS)

• Normally it should not exceed more

than 20% of the ideal Power.

• Practical power consumption is 650-700

KWH/MT for making medium carbon steel

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Optmising Power Consumption

• Top be loaded with turning & boring

• Will facilitate easy bore-in stage of electrodes

• Excess heavy scrap should not be charged at the bottom.

• This may cause damage to the bottom as well as will take more time to lift the material in melt down stage.

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Good Melting Practice

• Power consumption at various stage (PF=0.75)

– Bore-in 300 unit

– Melt down 396 unit

– Refining 066 unit

Total 762 unit

• Charge composition

– HMS 50%

– MMS 30%

– LMS, Turning & Boring 20%

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Good Melting Practice

• Avoid over heating of furnace

• Maintain ladle at > 9000C

• Specific pre-heating cycle of ladle

• Correct basicity of slag

• Pre-heated of Scrap & Ferro Alloys

• At least 20 point carbon boil is essential

• Clean steel can be produced in clean and healthy furnace