melting practice & wheel casting gc-08

8/6/2019 Melting Practice & Wheel Casting GC-08

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SECONDARY STEEL MAKING

&WHEEL CASTING

G. CHOWDHURY Prof. (Met)


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STEEL MELTING PRACTICE

Electric steel making is a SECONDARY

STEEL Making process

High alloy & sophisticated steels are

made in electric arc furnace.

Both S & P can be controlled in this

process


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REFRACTORIES

Basic refractories are used.

Bottom is monolithic made of MagnesiteDry Ramming Mass (DRM).

Slag line is made of Mag-Carb. Brick.

Remaining portion is Magnesite brick.

Roof is high alumina brick.


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CHARGING SEQUENCE & ARCING

Pet coke and 50% of total lime to becharged at the bottom

Then light scrap

Heavy scrap and foundry returns

Light boring & turning

Closing the hood

Lowering of Electrodes

Start Arcing


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DESULPHERISATION

CONDITIONS FOR DESULPHERISATION

Reducing condition of bath.

Low basicity preferably 2.00 High fluidity of slag.

Intimate contact between slag & metal

High temperature of the bath(preferablygreater than 15500C)


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DEPHOSPHORISATION

CONDITIONS FOR DEPHOSPHORISATION

Low temperature

Viscous slag

Oxidizing condition

High Basicity (more than 2.5)


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PROCESS OF OXIDATION

After melting lance oxygen (Carbon boiling) May charge iron ore.

Keep the furnace door open for entry ofadequate air.

This is purification stage of steel.

Phosphorus is eliminated in this stage.

Gases like H2 & N2 are eliminated in thisstage.

Over oxidation is to be avoided.

All siliceous impurities are eliminated as slag.


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PROCESS OF REDUCTION

O2 potential in the bath is brought down

by adding reducing agents

Reducing agents are FeSi, FeMn, Al,SiMn etc.

Based on the steel to be manufactured

reducing agents are to be selected Sulpher is eliminated at this stage


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ALLOYING

Depending on the chemical composition of

steel, it is alloyed.

Alloying always to be made at thereducing state except Ni & V.

Best sequence of alloying is FeSi, FeMn,

FeCr & at the last Al.

Killing by Al to be avoided or else to be

minimised.


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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 alsodetermines 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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LADLE PREPARATION

Steel shell layered with Alumina brick (IS 8) High Alumina Ramming Mass at the bottom

Layer of High Alumina Brick at the bottom

Gaps are filled up by Ramming Mass Side wall also with High Alumina Brick

Gaps are filled up by High Alumina Mortar

Gap between IS-8 and High Alumina brickfilled with slurry of Burnt Magnesite bricks,Chips of other bricks, Ramming Mass etc.


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LADLE PREPARATION Contd.

The lip and edges are prepared by

Ramming Mass

Allowed to air dry for24 hours Subjected to curing cycle through specific

heating plan to 9000C over72 hours

Brought down to75

00

C Hold Ready Ladle preparation and heating cycle is very

important to get clean metal and long life


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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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POWER CONSUMPTION

TO REDUCE POWER CONSUMPTION

Top surface of the f/c should be loadedwith turning & boring

This will facilitate easy bore-in stage ofelectrodes

Excess heavy scrap should not becharged at the bottom.

This may cause damage to the bottom aswell as will take more time to lift thematerial 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

Over heating of furnace to be avoided Pre-heat ladle (5000C 7000C) before pouring

Specific pre-heating cycle of ladle is essential

Correct basicity of slag should be maintained

Correct tap positions during melting isessential

Pre-heated Ferro Alloys should be charged

At least 20 point carbon boil is essential

Ferro Alloys should be estimated based on thefurnace condition

Clean steel can be produced in clean andhealthy furnace


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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

Placed to Moving Bed NormalisingFurnace followed by Rim Quenching,Tempering and Hub Quenching


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WHEEL INSPECTION

After Hub quenching, cooled to RT Shot blasting to clean and impart

compressive stress

Visual Inspection in normal light Magnaflux Test for surface & sub-surface

under UV light

Wheels with removable defect sent for defectremoval through grinding & rechecking

Automated Multi probe UT in Sprue area


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WHEEL INSPECTION Contd

Hardness Testing

Final Hub boring

Final shot blasting Warpage checking

Final Dimensional checking

Other Mech. Testing one in each Heat Closure Test & Hardness mapping 1 in 500


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CAST WHEELS AT RWF

Wheels to RDSO Spec. No. R-19 Part-III/1993.

Producing both BOXN & Carriage wheels

Production target this year is 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


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CAST WHEELS AT RWF

Metallurgically forging route better than casting

Special technique of controlled pressure casting

Equivalent to forging route, even better

Cross dendritc structure barrier to dislocation

movement

Mechanical properties as stipulated are well met

High K1C value Resistance against catastrophic failure in service


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CAST Vs FORGED WHEELS

High rate of production

Machining of wheel is eliminated, any plate design

In casting internal defect position is known

So, very easy to ensure soundness Very uniform Quality

No non-uniform quality arising of non-uniform hotworking with wide difference of reduction ratio

Cleanliness is achieved by refining of steel in EAF One thin series of inclusion as per ASTM E-45

Unique deoxidation ensures globulized alumina

This helps in achieving K1C value of the steel


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melting practice & wheel casting gc-08

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