Sponsored by: MDMD Solidification and SCAMP Committees
Program Organizers: E.F. Matthys, Mechanical Engineering Department, University of California, Santa Barbara, CA 93106; W.G. Truckner, Technical Director--Product Development, Alcoa Technical Center, Alcoa Center, PA 15069
Tuesday, AM Room: B3
February 6, 1996 Location: Anaheim Convention Center
Session Chairperson: C. Levi, University of California, Dept of Mech Engrg, Santa Barbara, CA 93106; and W. Truckner, Alcoa Technical Center, Alcoa, PA 15069
MECHANICAL DESIGN OF TWIN-ROLL IN THIN STRIP CASTING OF METALS: Ampere A. Tseng, Department of Mechanical Engineering and Mechanics, Drexel University, Philadelphia, PA 19104
In recent years, the technology of twin-roll caster has been widely investigated for the application of thin strip casting of both ferrous and non-ferrous metals and alloys. Most of the investigations focused on either microstructural evaluations or transport phenomena behavior. Only limited information on the mechanical aspect of twin-roll casting is available. However, in order to design and put twin-roll mill to practical use, the mechanical information including separating forces, torques, and thermal and mechanical stresses induced in the rolls have to be understood. In this paper, the development of a semi-analytical model to study the interactions between operating and design parameters is presented. While the operating parameters includes casting speed, strip thickness, height of molten pool, and pouring temperature, the design parameter consists of roll geometry, roll material, separating force, and torque. The model predictions agree very well with the on-line measurements.
A SOLIDIFICATION AND COOLING ROLL DEFORMATION ANALYSIS CONSIDERING THERMAL FLOW IN TWIN ROLL STRIP CONTINUOUS CASTING PROCESS: C.G. Kang, Research Institute of Mechanical Technology, Pusan National University, Korea; Y.D. Kim, Engineering Research Center for Near Net Shape and Die Manufacturing, Pusan National University, Korea
The twin-roll type strip continuous casting process of steel materials is characterized by two rotating water-cooled rolls receiving a steady supply of molten metal which solidifies onto the rolls. Mathematical models of the process to determine the role of various process parameter have been proposed to estimation of casting rolls life. The roll deformation leads to short roller life because thermal fatigue cracking of the casting roll. Solidification analysis of molten metal considering phase transformation and thermofluid is performed using finite difference method with curvilinear coordinate to reduce computing time and molten region analysis with arbitrary shape. An enthalpy-specific heat method is used to handle the latent heat effect during the phase change. The computed velocity field is used to determine the temperatures in the roll and the steel. The temperature distribution of cooling roll is calculated using two dimensional finite element method, because of complex roll shape due to cooling hole in the rolls and improvement accuracy of calculation result. The energy equation of cooling roll is solved simultaneously with the conservation equation of molten metal in order to consider heat transfer through the cooling roll. The calculated roll temperature is compared to experimental results and the heat transfer coefficient between cooling roll surface and rolling material (steel) is also determined from comparison of measured roll temperature and calculated temperature. Rolling force in strip continuous casting process has been computed using rigid viscoplastic finite element method. The relation between stress and strain rate is used as a function of temperature. The three dimension deformation analysis of cooling roll has also been performed by using of commercial package ANSYS. We focused our attention on elastic-plastic stress analysis to the estimation of roll life caused by cracking on the hot roll surface. To more accurately model the complete thermal cycle of the roll, creep strain is included in an elastic-plastic analysis. In this study, roll life is predicted in terms of ultimate roll revolution without failure on the roll surface. The thermo-mechanical properties of roll material with copper alloy are obtained by uniaxial tensile test at controlled environmental temperature. The proposed analysis techniques are also used to developed an improved roller design. In particular, we will seek to determine the effect of the various process and cooling roll design parameters on roll deformation behavior and roll life prediction.
3-D BULGING ANALYSIS OF CONTINUOUSLY CAST STEEL SLABS: Tae-jung Yeo, Kyung-hyun Kim, Kyu Hwan Oh, Dong Nyung Lee, Department of Metallurgical Engineering and Center for Advanced Materials Research, Seoul National University, Seoul 151-742, Korea
The deformation behavior of continuously cast steel slabs in the mold exit region has been investigated. To analyze bulging of the solidifying steel shell, it is necessary to obtain the profile of the shell in the mold region. The profile of the shell can be given from the heat transfer analysis which has taken air gap into account and 3-D FEM mesh has been made. Static bulging due to ferrostatic pressure in the mold exit region has been calculated by FEM using thermo-elastic-plastic material model. The effect of support roll pitch and casting speed has been analyzed. Large strain was developed at the right beneath of support roll due to bulging, and its magnitude increased with increasing support roll pitch. Dynamic bulging which takes ferrostatic pressure and the movement of shell into account has been analyzed. This analysis predicted reported deformation geometry of solidifying shell more precisely than static analysis.
10:00 am BREAK
DENSIFICATION KINETICS OF CAST Al-Mn-Mg SLABS AT SOLID STATE: P.T. Wang, Alcoa Technical Center, Alcoa Center, PA 15069
Densification kinetics of cast Al-Mn-Mg slabs containing porosity is investigated at solid state through subscale experimental evaluation and constitutive modeling. Slab samples with two initial porosity levels, 0.4 % and 2% were deformed under axisymmetric compression tests. Experimental data generated from various deformation histories at elevated temperatures revealed that the densification rate, insensitive to strain rate, is higher at the beginning of deformation. The material point at this stage may correspond to the casting location after the solidification front. The densification rate slows down at the later stage of deformation. Optical microscopy revealed that silicon and ironconstituents are usually clustered around the voids that may present weak links if they are brittle. A constitutive model based on the interaction of matrix and voids resulted from local plasticity flow, is tuned using a material function to fit experimental data and a reasonable agreement obtained.
HEAT FLOW, DEFORMATION BEHAVIOR AND CRACK FORMATION DURING CONTINUOUS CASTING OF BEAM BLANK: Kyung-hyun Kim, Heung Nam Han, Tae-jung Yeo, Yong-gi Lee, Kyu Hwan Oh, Dong Nyung Lee, Department of Metallurgical Engineering and Center for Advanced Materials Research, Seoul National University, 56-1 Shinrim-dong, Kwanak-ku, Seoul 151-742, Korea
A two-dimensional transient finite element model has been developed to compute the heat transfer and deformation behavior of the solidifying shell in continuously cast beam blank. The mathematical model developed for this study is capable of treating the heat flow and deformation as coupled phenomena, and of taking into account steel composition through the calculation of the non-equilibrium pseudo binary Fe-C phase diagram. Also, the model incorporates the effects of microsegregation of solute elements on hot tears using the proposed mechanical property model of mushy zone which take d-[[gamma]] transformation into account. The maximum tensile stress develops on the web surface because mold inhibits the thermal contraction of beam blank near the fillet. The surface cracks originate on the web surface at the initial stage and ropagates into the solidified shell during casting. The internal cracks form in the flange tip region at the intermediate stage. These predictions are in agreement with the experimental observation.
MICROSEGREGATION DURING MELT-SPINNING OF DILUTE Pd ALLOYS: D.J. Thoma, E.M. Schwartz, S.R. Bingert, D.R. Korzekwa, R.D.Field, LA. Jacobson, Los Alamos National Laboratory, Los Alamos, NM 87545
Free jet melt-spinning has been used to produce dilute Pd-X alloys (X=Ni, Co, Cr) with reduced segregation. The microsegregation in the alloys was experimentally examined and compared with solidification theory. Increased microsegregation occurred in alloy systems with smaller partition coefficients, steeper liquidus slopes, and higher solute concentrations. In order to further reduce segregation in alloys with higher solute concentrations (~10at.%), statistically designed computer simulations of the melt-spinning process were performed. The modeling incorporated fluid flow, heat transfer, and solidification theory, and three process variables were examined: wheel speed, ejection pressure, and crucible orifice diameter. Based upon the optimized simulations, experiments were performed to yield thinner ribbon with greater compositional homogeneity.
ANALYSIS OF THE RIBBON FORMATION BY PLANAR FLOW CASTING: L. Kubicar, S. Adamisova, Institute of Physics SAS, 84228 Bratislava, Slovak Republik
A model of a basin with a cold bottom is used for ribbon formation by Planar
Flow Casting. The solidification starts by contacting of the melt with the cold
bottom. The solidification front spreads from the cold bottom into the melt and
the solidified ribbon is extruded by the moving bottom. The conditions of the
ribbon formation due to the spreading of the solidification front are studied
in great detail in the framework of the model presented. The thickness of the
ribbon depends on the period during which the solidification front spreads into
the melt. This period is given by the shape of the puddle and by the surface
velocity of the cooling wheel. The temperature gradient inside the melt
influences the structure of the ribbon. While large temperature gradient leads
to the freezing of the melt and thus to the glass formation small temperature
gradient causes redistribution of the melt component, nucleation even
crystallization. As a result a ribbon can be obtained which is not homogenous
across its thickness. Any latent heat corresponding to crystallization retards
the spreading of the solidification front. The theoretical predictions are
compared with experimental facts.
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