CC Training Course

8/3/2019 CC Training Course

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MITTAL STEEL HUNEDOARA

W e l c o m e

Caster Intermediate TrainingCourse

Caster Intermediate Training

Course


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Con t inuou s Ca s t ing Techn o l ogy

A Transformation Process through Heat ExchangeDynamics


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Mi s s i on

The Operators of Caster has tobe as the Plane Pilot , ensuring asuccess of take off is the same asensuring a good start casting.


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W or ld T r end Con t inuou s Ca s t ing


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Evo l u t ion o f W o r ld S t ee l P r oduc t i on


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H i s to r y o f C on t inuou s C a s t ing CC was a new technology adopted

since 50s

Main advantages over the traditionalsteel complexes on yield, cost and

quality Billet Industry was born in the 60s

under Minimill Concept ( Scrap-EAF-CC) in Germany by Gerry Heffemann

Continuously transform from low

quality product in to SBQ ( special barquality) up to High value grades


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F i r s t B i l le t Ca s t e r Inve n ted i n 18 85


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D i f f e r en t S y s t em s


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Ca s t e r T yp e s


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Mach in e Com p onen t sLadle

Mold

First Apron

Widrawal

Tundish


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Lad l eRegarding the ladle, it traditionally has beenemployed as a transfer vessel, moving heats of steelweighing 20 to 350 tonnes from the steelmakingfurnace to the continuous casting machine.However,increasingly the ladle is being used as areactor in ladle furnaces or ladle-treatmentstations,installed between the steelmaking furnaceand the caster.In transferring steel from the steelmaking furnace tothe caster, a major problem is oxygen absorptionfrom the air, furnace slag and the ladle refractorylining.


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Tund i s hThe functions of the tundish are manifold. However, key features of a well-designedtundish can be identified as follows:a) Inclusion float-out should be maximized.b) The residence time of steel flowing to each of the strands must be the same to

ensure uniformity of steel quality.c)The flow pattern in the tundish should permit much of the steel to move close tothe surface where inclusions floating out can be absorbed by the tundish slag.d) Dead volume should be minimized because it effectively reduces the residencetime of the steel.e) Turbulence from the incoming ladle stream should be isolated, particularly when

open-stream pouring from tundish to moldf) The depth of the tundish must be sufficient, in excess of about 500 mm, to preventvortexing at the nozzle wells, which can draw the slag lower down into the moldpool.


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Tund i s h T yp e s


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F eO + MnO VS Ba s i c it y


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To t a l Oxyge n a s F ( f lu x )


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Tund i s h W e i r s


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Tun d i s h Re f r a c t o ry


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N i tr o gen & Oxygen P i ck U p a t L ad le Cha nge


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F low Con t r o l


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H Typ e T und i sh


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Mo l d The mold is the heart of the caster; it is the primary

heat-extraction device whose functions are to extractsuperheat from the liquid steel, to grow a solid shell of

sufficient thickness, to contain the liquid pool below themold without breakouts and to support the shell during itsinitial growth.

The design and operation of the mold, which governs heatextraction, profoundly affects surface and internal quality.


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M o l d S c h e m eMolds are made ofCopper with alloys

Molds need

Phosporous and Silveralloy otherwise areproun for distortion

For cost benefit theyadding Chrome orZirconium which hadPhos alloys


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Mo l d Su m it omo /S l a b


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M echa n i c a l D is t o r t i o n o f t he M o l d In a Billet Mold the mechanical

distortion is very high at themeniscus level

However the highest heat

transfer is taking place at themeniscus due to pirolization ofoil lubrication which creates anHidrogen gas that reduces theair gap resistance to heat

transfer


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Hea t T r an s fe r Mold Heat Extraction in the

mold depends on temperature,steel composition and shellticknness.

To transfer heat in the mold itfaces several barriers , such as,cooper mold, water flow andair gap

84% of the resistance is taking

by air gap whereas the othersis only 16% that explains thecooper mold effectivenness


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Hea t F lu x Rem ova l a s F ( V c )


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Rea c t ion s t a k i ng p l a ce i n Mo l d s


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So l i d i f i c a t ion i n M o l d Depending on Carbon content

is the shell thickness at the exitof the Mold

Low Carbon steel will have 10mm only

HC Steel will have 18 mm only

Low Carbon steel are moreproun to BOs and casting

defects Therefore GOOD LUBRICATION

is a must!!


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So l i d i f i c a t ion S t r and


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How Os c i l l a t i o n Ma r k is f o rmed ? Oscillation Marks are formed due to negative strip time

moment

Negative strip is the time that the speed of the mold is

higher than the casting speed in the downwardsmovement.

By the effect of this moment is how the shell is growinggradually in combination with:

High heat transfer Good lubrication due to oil evaporation

Hidrogen atmosfere which helps in faster solidification


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Osc i l la t io n M a r k w i t h M o ld Movem en t


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Osc i l la t io n Ma r k F o rm a t ion


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B i l le t O s c i l l a t ion M a rk


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Resea r c h -Re comm ended Mo l d Cha r a c t e r is t ic s f o rB i l l e t Ca s t ing M ach i ne s Copper grade DHP, silver-bearing Cu, Cr-Zr

Taper Double or multiple

Minimum wall thickness (mm) 13 for smaller billets (i.e. 100150 mm sq.)

(from Ref. 30),

20 for larger billets (i.e., 200 mm sq.)

Inside corner radius (mm) 34

Meniscus level (mm) 100150

Water velocity (m/s) > 1011

Mold tube support Four sides near top or top/bottom

Negative-strip time (s) 0.120.15 (from Ref. 26)

Mold lead (mm) 34 Water quality, e.g. total hardness < 5 ppm, no deposits on mold tubes

Cooling water channel width (mm) 35

Measure internal mold dimensions Yes


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Cas t S t r u c tu r e - F a c t o r o f I n f l u ence a) superheat of the steel,

b) steel composition,

c) fluid flow in the liquid pool,

d) section size, and e) machine design (curved vs. straight machines)

Objective : Is to maximize an equiaxed structurewhich is more crack-resistant and promotesreduced macrosegregation.


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Co l um na r S t ru c t u r e ( M ac roe ch t )


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M echa n i c a l S t r e s s e s

Axial tensile stresses that are concentrated locally in theweak region of the shell such as oscillation marks causing

transverse depressions and transverse cracks

Sticking in the Mold due

to improper lubrication

Bad Oscillation condition

Excessive taperWorn out Mold


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Sp ray C oo l ing


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P r im a r y & Se cond a r y Coo l ing From the Mold up to Spray Zone is a radical change

Main Objective of Mold Cooling is the formation of uniformshell enough to contain liquid pool

Heat Extraction in the Mold accounts for 60% in the first100 mm

Heat Extraction in the spray zone is a function of Flow anPressure that should be strong enough to break the steam

layer at the billet surface Due to poor heat transfer of the steel the first zone is a

key for the billet geometry


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F r i c t ions i n t he M o l d p r i o r to BO


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How BO s t a r t h ap p en i ng ?


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6 S t ep s p r io r BO hap p en


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Hea t T r an s f e r Be f o r e BO


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Type s o f S t ic k e r BO s


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Op e ra t iv e I s s ue s NH


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Con t d


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Op e ra t ion I s s ue s , C I L


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Con t d


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Op e ra t ion I s s ue s C I L


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W ate r Qua l it y a t C I L


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Op e r a t iv e I s s ue s o n New G r ade s a t TR


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Op e ra t ion I s s ue s a t Ne wC as t le SA

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