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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