TAPER PREDICTION IN SLAB AND THIN SLAB CASTING MOLDS

Transcription

1 TAPER PREDICTION IN SLAB AND THIN SLAB CASTING MOLDS Claudio Ojeda Department of Mechanical Engineering University of Illinois at Urbana-Champaign October 5, 22 University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda

2 Introduction Taper plays an important role to ensure good contact and heat exchange between mold wall and shell surface. Shell growth uniformity Problems Excessive taper causes: Narrow face wearing. Extra tensile stress causes transverse cracking. Buckling of the shell wide face, causes gutter and longitudinal cracks. Insufficient taper causes: Breakouts in the steel shell. Bulging below mold causing subsurface longitudinal cracks. University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 2

3 Objectives Calculate ideal taper including the effects of: Shell shrinkage Mold distortion Flux layer thickness Funnel extra length (thin slabs) Investigate the effect of heat flux profile on Ideal Taper in conventional and thin slabs as affected by Heat flux profile Casting speed Steel grade Powder type Mold length University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 3

4 Model description Finite difference heat transfer and solidification model (COND). 2D Finite element elastic-viscoplastic thermal-stress model (CON2D). D slice-domain representing the behavior of a longitudinal slice through the centerline of the shell moving down the mold. Heat flux boundary condition is applied in the shell surface. University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 4

5 Model description Shell surface q Constant u Along this edge y Solidifying Shell tt F Insulated x Liquid steel Narrow face liquid steel Shell Wide face University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 5

6 Definition of ideal taper Billet molds IT= Shell shrinkage(z) (Mold distortion(z) Mold distortion meniscus) Slab molds IT= Shell shrinkage(z) (Mold distortion(z) Mold distortion meniscus) (flux thickness(z) flux thickness meniscus) Thin slab molds IT= Shell shrinkage(z) (Mold distortion(z) Mold distortion meniscus) (flux thickness(z) flux thickness meniscus) (funnel extra length meniscus funnel extra length(z)) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 6

7 Billet Mold distortion Billet casting operating conditions conditions Samarasekera, Brimacombe, Ironmaking and Steel making, 982, 2 mm Vol. 9, Issue, pp -5 Mold geometry Slab width Slab thickness 2 mm Mold height mm Cu plate thickness.5 mm Copper properties Thermal conductivity 36 W m - K - Elastic modulus 7 Gpa Poisson ratio.343 Thermal expansion coefficient 6.* -6 K - Density 894 kg m -3 Operating conditions Pour temperature 54 C Water slot heat transfer coefficient 35 kw m -2 K - Water temperature, T w Ambient temperature Meniscus level (below top mold) 3 C 25 C mm University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 7 DISPLACEMENT (mm) %C,. m/min Total shell shrinkage strain Mold distortion Ideal Taper DISTANCE BELOW MENISCUS (mm)

8 Slab Mold distortion Mold distortion = Wide face expansion + Narrow face distortion Wide face expansion Transmitted by clamping forces Linearized temperatures of hot and cold plate faces x WF = α mold Narrow face distortion moldwidth Tcoldmen + Thotmen Tcold + T Linearized temperatures of hot and cold plate faces Water jacket stiffness hot x NF = 3 _ ( α hot α cold ) T hot T cold ( thot + tcold ) [ 2 Lx x ] t 2 cold K _ University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 8

9 Validation of Thin-slab mold distortion Thin Slab operating conditions Mold geometry Slab width Slab thickness Mold height Cu plate thickness Water slot depth shallow slots Water slot thickness Distance between most slots 26 mm 75 mm mm 6 mm 35 mm 5 mm 4.6 mm Copper properties Thermal conductivity 35 W m - K - Elastic modulus 5 Gpa Poisson ratio.34 Thermal expansion coefficient 7.7* -6 K - Density 896 kg m -3 Operating conditions Water slot heat transfer coefficient kw m -2 K - Water temperature, T w Ambient temperature Meniscus level (below top mold) 37.8 C 35 C mm Heat flux profile.. Joong Kil Park, Brian G. Thomas, Indira V. Samarasekera, and U. Sok Yoon, Metallurgical and Materials Transactions B, 22, vol. 33B, pp Joong Kil Park, Brian G. Thomas, Indira V. Samarasekera, and U. Sok Yoon, Metallurgical and Materials Transactions B, 22, vol. 33B, pp University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 9

10 Validation of Thin-slab Mold distortion Wide face temperature Wide face expansion TEMPERATURE (C) Tref meniscus Hot face temperature Cold face temperature Hot face linearized temperature Cold face linearized temperature y = -.269x y = -.495x Thot Tcold WIDE FACE EPANSION (mm) Wide face expansion from Cond results Wide face expansion from 3D simulation meniscus DISTANCE BELOW TOP OF MOLD (mm) DISTANCE FROM TOP OF MOLD (mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda

11 Validation conventional slab mold distortion Conventional Slab operating cond. Mold geometry Slab width 94 mm Slab thickness 22 mm Mold height 7 mm Cu plate thickness 6 mm Water slot depth shallow slots 25 mm Water slot thickness 5 mm Distance between most slots 35 mm Copper properties Thermal conductivity 374 W m - K - Elastic modulus 7 Gpa Poisson ratio.343 Thermal expansion coefficient 7.7* -6 K - Density 894 kg m -3 Operating conditions Water slot heat transfer coefficient 35 kw m -2 K - Water temperature, T w Ambient temperature Meniscus level (below top mold) 5 C 35 C 84 mm Heat flux profile (. ) q = z.<z<.84m q = z.84.84<z<.7m B.G.Thomas, G. Li, A. Moitra and D. Habing: ISS transactions, October 998, pp University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda

12 Validation conventional slab mold distortion Wide face temperature Narrow face temperature Hot face temperature Cold face temperature Linearized hot face temperature Linearized cold face temperature 25 Hot face temperature Cold face temperature Linearized hot face temperature Linearized cold face temperature TEMPERATURE (C) y = x Tref meniscus y = -.769x Thot Tcold TEMPERATURE (C) y = -.678x meniscus y = -.32x Thot Tcold DISTANCE BELOW TOP OF THE MOLD (mm) DISTANCE BELOW TOP OF THE MOLD (mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 2

13 Validation conventional slab mold distortion Wide face expansion + Narrow face distortion MOLD DISTORTION (mm) Narrow face distortion calculated in the 3D simulation Analitical calculation of the mold distortion meniscus DISTANCE BELOW TOP OF THE MOLD (mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 3

14 Shell shrinkage Heat flux profile Importance of changes in meniscus area Casting speed Increasing casting speed increases instantaneous and average heat flux but decreases time for shrinkage. Mold length For the same conditions higher mold length causes higher shrinkage Steel grade Differences between low, peritectic and high carbon content steels Mold Powder composition Differences in solidification temperature University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 4

15 Effect of heat flux profile Shell shrinkage controlled by heat flux profile. Higher heat flux causes more shrinkage. Shell shrinkage sensitive to minor changes specially near the meniscus. Mean heat flux determined with*: Q = G µ T.9 flow V.47 C.7 % C.52exp.27 Q G is the mean heat flux (MW/m 2 ), µ is the powder viscosity at 3 o C, (Pa-s), T flow is the melting temperature of the mold flux ( o C), V c is the casting speed (m/min), and %C is the carbon content 2 *C. Cicutti, M. Valdez and T. Perez, "Mould Thermal Evaluation in a Slab Continuous Casting Machine," 85th Steelmaking Conference, (Nashville, TE, USA), Iron and Steel Society, Inc. (USA), Vol. 85, 22, University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 5

16 Effect of heat flux 6 5 HEAT FLU (MW/m2) Higher Meniscus heat flux Higher mold exit heat flux Heat flux average =.466 MW/m2.8%C,.5 m/min SHELL SHRINKAGE (mm) Higher meniscus heat flux Higher mold exit heat flux Heat Flux Average=.466 MW/m2.8%C,.5 m/min DISTANCE BELOW MENISCUS (mm) DISTANCE BELOW MENISCUS (mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 6

17 Effect of casting speed Higher casting speed causes higher heat flux (more shrinkage) but less dwell time (less shrinkage). Net effect: less shrinkage 7 HEAT FLU (MW/m 2 ) High heat flux q=6.5(t+) -.5 SHELL SURFACE TEMPERATURE(C) Width: 2 mm.7%c, Flux E. m/min.5 m/min.9 m/min TIME BELOW MENISCUS (mm) DISTANCE-BELOW-MENISCUS(mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 7

18 Effect of casting speed SHELL THICKNESS (mm) Width: 2 mm.7%c, Flux E. m/min.5 m/min.9 m/min DISTANCE BELOW MENISCUS (mm) TOTAL SHELL SHRINKAGE STRAIN (%) Width: 2 mm.7%c, Flux E. m/min.5 m/min.9 m/min DISTANCE-BELOW-MENISCUS(mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 8

19 Effect of casting speed Effect of casting speed on Ideal taper IDEAL TAPER (%) Width: 2 mm.7%c, Flux E. m/min.5 m/min.9 m/min DISTANCE BELOW MENISCUS (mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 9

20 Effect of casting speed Peritectic steels High carbon steels IDEAL TAPER (%) % Carbon Content,.2 m/min Casting Speed.3 % Carbon Content,.5 m/min Casting Speed.6 % Carbon Content,.8 m/min Casting Speed.6 % Carbon Content,.5 m/min Casting Speed Width: 2 mm DISTANCE BELOW MENISCUS (mm) IDEAL TAPER (%) % Carbon Content,.2 m/min Casting Speed.27 % Carbon Content,.5 m/min Casting Speed.47 % Carbon Content,.4 m/min Casting Speed.47 % Carbon Content,.3 m/min Casting Speed Width: 2 mm DISTANCE BELOW MENISCUS (mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 2

21 Effect of casting speed Cases B B 2B 3B 4B 5B 6B 7B 8B 9B B B 2B Grade low carbon peritectic medium carbon medium carbon high carbon high carbon Tliquidus Carbon content.7%.8%.3%.6%.27%.47% %Mn, %Si.3%,.3%.42%,.%.57%,.22%.87%,.4%.75%,.22% %P, %S.%,.7%.7%,.7%.7%,.7%.7%,.5%.8%,.7% Powder type E (22) E (22) C (666) C (666) E(22) E (22) Viscosity (Pa-s) sol. Temp ( C ) Casting Speed (m/min) Tundish temp (C) Heat Flux (MW/m2) Heat Average (MW/m2) Surf Temp (exit (C) Shrinkage (mm) COND Shrinkage 5mm CON2D Shrinkage (mm) CON2D Taper (%/mold) CON2D Flux layer (mm) Mold distortion+expansion (mm) Ideal NF (mm) Ideal NF (%) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 2

22 Effect of casting speed Higher casting speed causes higher heat flux (more shrinkage) but less dwell time (less shrinkage). Measured data of heat flux* Net effect: no change in shrinkage HEAT FLU (MW/m 2 ) Flux E Slab width: mm Slab thickness: 2 mm Working mold length: 8 mm Pouring temperature: 567 o C.7%C,. m/min, avg q:.39 MW/m 2.7%C,.5 m/min, avg q:.6 MW/m 2.7%C,.9 m/min, avg q:.8 MW/m 2.8%C,.3 m/min, avg q:.48 MW/m 2.8%C,.45 m/min, avg q:.56 MW/m DISTANCE BELOW MENISCUS (mm) TEMPERATURE(C) Flux E,.7%C,. m/min Flux E,.7%C,.5 m/min Flux E,.7%C,.9 m/min Flux E,.8%C,.3 m/min Flux E,.8%C,.45 m/min DISTANCE-BELOW-MENISCUS(mm) TOTAL SHELL SHRINKAGE STRAIN (%) Flux E,.7,. m/min Flux E,.7,.5 m/min Flux E,.7,.9 m/min Flux E,.8,.3 m/min Flux E,.8,.45 m/min DISTANCE-BELOW-MENISCUS(mm) *C. Cicutti, M. Valdez and T. Perez, "Mould Thermal Evaluation in a Slab Continuous Casting Machine," 85th Steelmaking Conference, (Nashville, TE, USA), Iron and Steel Society, Inc. (USA), Vol. 85, 22, University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 22

23 Effect of mold length Mold length For the same conditions (including heat flux), shell shrinkage strains for different mold lengths can be approximated with the same curve Shell shrinkage for different mold lengths can be obtained truncating the curves at the desired working mold length University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 23

24 Effect of mold length HEAT FLU (MW/m 2 ) q=6.5(t+) TIME BELOW MENISCUS (s) TOTAL SHELL SHRINKAGE STRAIN (%) %C, Flux E. m/min.5 m/min.9 m/min DISTANCE-BELOW-MENISCUS(mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 24

25 Effect of steel grade Thermal Linear Expansion (m/m) Low carbon steels (>.8%C) Steel grade effect Low carbon steels (>.8%C) %C.44%C.%C.27%C.44%C Reference Temperature = Solidus Temperature ( o C) Higher plastic strain Higher thermal expansion Peritectic steels (.%) Deeper oscillation marks causes lower heat flux Higher thermal expansion Final result the smallest shell shrinkages High carbon steels (>.2%) Shallow oscillation marks Higher heat flux Small inelastic strain Thermal strain Heat flux and shell shrinkage similar to low carbon steels University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 25

26 Effect of steel grade HEAT FLU (MW/m2) Casting speed:.5 m/min.7%c, Flux E.8%C, Flux E.3%C, Flux C.6%C, Flux C.47%C, Flux E DISTANCE BELOW MENISCUS (mm) SHELL SURFACE TEMPERATURE (C) Casting speed:.5 m/min.7%c, Flux E.8%C, Flux E.3%C, Flux C.6%C, Flux C.47%C, Flux E DISTANCE-BELOW-MENISCUS(mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 26

27 Effect of steel grade SHELL THICKNESS (mm) Casting speed:.5 m/min 4.7%C, Flux E.8%C, Flux E 3.3%C, Flux C 2.6%C, Flux C.47%C, Flux E DISTANCE BELOW MENISCUS (mm) TOTAL SHELL SHRINKAGE STRAIN (%) Casting speed:.5 m/min.7%c, Flux E.8%C, Flux E.3%C, Flux C.6%C, Flux C.47%C, Flux E DISTANCE-BELOW-MENISCUS(mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 27

28 Effect of steel grade TOTAL SHELL SHRINKAGE STRAIN (%) Powder E, meniscus to mold exit Powder C, meniscus to mold exit Powder E, 5 mm to mold exit Powder C, 5 mm to mold exit CARBON CONTENT (%) IDEAL TAPER (%) Casting speed:.5 m/min.7 %C, Flux E.8 %C, Flux E.3 %C, Flux C.6 %C, Flux C.47 %C, Flux E DISTANCE BELOW MENISCUS (mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 28

29 Effect of steel grade Grade low carbon peritectic medium carbon medium carbon high carbon Tliquidus Carbon content.7%.8%.3%.6%.47% %Mn, %Si.3%,.3%.42%,.%.57%,.22%.87%,.4%.75%,.22% %P, %S.%,.7%.7%,.7%.7%,.7%.7%,.5%.8%,.7% Powder type E (22) E (22) C (666) C (666) E (22) viscosity (Pa-s) sol. Temp (C) Flux comsumption rate (kg/t) Solid flux velocity ratio (V/Vc) Oscilation mark depth (mm) Casting Speed (m/min) Tundish temp (C) Heat flux average (MW/m 2 ) Surf Temp (exit (C) Shrinkage (mm) COND Shrinkage 5mm CON2D Shrinkage (mm) CON2D Taper (%/mold) CON2D Flux layer (mm) Narrow face distortion (mm) Wide face expansion (mm) Ideal NF (mm) Ideal NF (%) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 29

30 Effect of mold flux composition Study of the effect of Powder composition in shell shrinkage Mold powder viscosity Slight changes in shell shrinkage Mold powder Solidification temperature Higher solidification temperature causes a lower heat flux and consequently lower shell shrinkage University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 3

31 Effect of mold flux composition TOTAL SHELL SHRINKAGE STRAIN (%) %C,.5 m/min Flux solidification temperature: 4 o C Flux solidification temperature: 2 o C Flux solidification temperature: 6 o C Flux solidification temperature: 25 o C DISTANCE-BELOW-MENISCUS(mm) IDEAL TAPER (%) Flux solidification temperature: 4 o C Flux solidification temperature: 2 o C Flux solidification temperature: 6 o C Flux solidification temperature: 25 o C.7%C,.5 m/min DISTANCE BELOW MENISCUS (mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 3

32 Effect of mold flux composition Grade low carbon Tliquidus 527 Carbon content.7% %Mn, %Si.3%,.3% %P, %S.%,.7% Powder type A (RB - B) C (666) D (55) E (22) viscosity (Pa-s) sol. Temp (C) Flux comsumption rate (kg/t) Solid flux velocity ratio (V/Vc) Oscillation mark depth (mm) Casting Speed (m/min) Tundish temp (C) Heat Flux average (MW/m 2 ) Surf Temp (exit (C) Shrinkage (mm) COND Shrinkage 5 mm CON2D Shrinkage (mm) CON2D Taper (%/mold) CON2D Flux layer (mm) Narrow face distortion (mm) Wide face expansion (mm) Ideal NF (mm) Ideal NF (%) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 32

33 Conclusions More taper is needed near the top of the mold to compensate the more shrinkage of the steel shell. As casting speed increases, shrinkage decreases. Shell shrinkage depends mainly of the heat flux profile which depends of the casting speed and interface conditions. Peritectic steels generally requires smaller taper (due to the lower heat flux caused by bigger oscillation marks). Mold powders with higher solidification temperatures require less taper (due to lower heat flux). University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 33

34 Extra length in Funnel In thin slab casting there is a taper induced by the change in perimeter of the wide face, because of the funnel shape. 2 2 a + b 2ab EL = 2 sin 2 2 2b a + b a University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 34

35 Extra length in funnel University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 35

36 Thin slab casting ideal taper Higher casting speeds than conventional slab casting. Funnel shape effect. IT= Shell shrinkage(z) (Mold distortion(z) Mold distortion meniscus) (flux thickness(z) flux thickness meniscus) (funnel extra length meniscus funnel extra length(z)) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 36

37 Thin slab casting conditions Operating Conditions. Mold geometry Slab thickness mm Mold Heigth mm Cu plate thickness 2 mm Funnel Funnel width: a 2 mm Funnel depth at top: b 6 mm Funnel heigth 75 mm Description Carbon Content Casting Speed Mold Width Meniscus level Difficult to cast low carbon.4% 4.5 m/min 28 mm 83 mm Low Carbon.6% 4.7 m/min mm 83 mm Approximately Peritectic.74% 3.9 m/min 2 mm 83 mm High Carbon.83% 4 m/min 2 mm 58 mm University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 37

38 Thin slab casting ideal taper Heat flux and surface temperatures 5 55 HEAT FLU (MW/m 2 ) % C, 4.5 m/min Casting speed, 28 mm Mold Width.55% C, 4.7 m/min Casting speed, 5 mm Mold Width.74% C, 3.9 m/min Casting speed, 2 mm Mold Width.83% C, 3.7 m/min Casting Speed, 2 mm Mold Width SHELL SURFACE TEMPERATURE(C) % C, 4.5 m/min Casting Speed, 2 mm Mold Width.55% C, 4.7 m/min Casting Speed, 5 mm Mold Width.74% C, 3.9 m/min Casting Speed, 2 mm Mold Width.83% C, 3.7 m/min Casting Speed, 2 mm Mold Width DISTANCE BELOW MENISCUS (mm) DISTANCE-BELOW-MENISCUS(mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 38

39 Thin slab casting ideal taper Solidified steel shell thickness SHELL THICKNESS (mm) % C, 4.5 m/min, 28 mm Mold Length.55% C, 4.7 m/min, 5 mm Mold Length.74% C, 3.9 m/min, 2 mm Mold Length.83% C, 4. m/min, 2 mm Mold Length DISTANCE BELOW MENISCUS (mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 39

40 Thin slab casting ideal taper Difficult to cast low carbon DISTANCE (mm) % Carbon Content, 4.5 m/min Casting Speed 28 mm Mold Width Steel shell shrinkage Mold narrow face distortion Mold flux layer thickness Funnel extra length Ideal Taper DISTANCE BELOW MENISCUS (mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 4

41 Thin slab casting ideal taper Common low carbon steel DISTANCE (mm) % Carbon Content, 4.7 m/min Casting Speed mm Mold Width Steel shell shrinkage mold narrow face distortion Mold flux layer thickness Funnel extra length Ideal Taper DISTANCE BELOW MENISCUS (mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 4

42 Thin slab casting ideal taper Approximately peritectic steel DISTANCE (mm) % Carbon Content, 3.9 m/min Casting Speed 2 mm Mold Width Steel shell shrinkage Mold narrow face distortion Mold flux layer thickness Funnel extra length Ideal Taper DISTANCE BELOW MENISCUS (mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 42

43 Thin slab casting ideal taper High carbon steel DISTANCE (mm) % Carbon Content, 3.7 m/min Casting Speed 2 mm Mold Width Steel shell shrinkage Mold distortion Mold flux layer thickness Enter-Y Data Ideal Taper DISTANCE BELOW MENISCUS (mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 43

44 Thin slab casting ideal taper.3 IDEAL TAPER (%) %C, 4.5 m/min.55%c, 4.7 m/min.74%c, 3.9 m/min.83%c, 3.7 m/min DISTANCE BELOW MENISCUS (mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 44

45 Thin slab casting ideal taper Results Case (carbon content %) Recorded T ( C) Recorded Heat Flux (kw/m 2 ) Computed T ( C) Computed Heat Flux (kw/m 2 ) Suggested Taper from Calculations (%/mold) Taper used currently (%/mould) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 45

46 Thin slab casting ideal taper Results The shell shrinks more on the top of the mold than in the bottom of the mold, so it is difficult to match the shrinkage of the shell shell with a linear Taper. Mold distortion, flux layer thickness and extra length of funnel significantly affect the Ideal taper. The Ideal Taper predicted is for all cases smaller than the taper used currently. University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 46

47 Effect of ferrostatic pressure TOTAL SHELL SHRINKAGE STRAIN (%) Without ferrostatic pressure Width: 2 mm with Ferrostatic pressure Width: 2 mm with ferrostatic pressure DISTANCE-BELOW-MENISCUS(mm) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 47

48 Conclusions More taper is needed near the top of the mold, such as achieved using parabolic taper. As casting speed increases, shrinkage decreases (for same conditions and heat flux profile). Mold length affects the taper only by extending the nonlinear curve (for the same conditions and heat flux profile). Mold taper depends mainly on the heat flux profile, which in turn depends on the casting speed and interface conditions (powder, steel grade, etc.). Peritectic steels generally require slightly less taper than either low or high carbon steels, owing to their lower heat flux. Mold powders with higher solidification temperature have lower heat flux (compared with both oil lubrication or low solidification temperature powders) and consequently have less shrinkage and less ideal taper (other conditions staying the same). Flux layer thickness, mold distortion and extra length of funnel (thin slabs) make important contributions to Ideal Taper. University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Claudio Ojeda 48