Heat Transfer Coefficient at Cast-Mold Interface During Centrifugal Casting: Calculation of Air Gap

• Published in: Metallurgical and materials transactions. B, Process metallurgy and materials processing science Process metallurgy and materials processing science, 2018-06, Vol.49 (3), p.1421-1433
• Main Authors: Bohacek, Jan, Kharicha, Abdellah, Ludwig, Andreas, Wu, Menghuai, Karimi-Sibaki, Ebrahim
• Format: Article
• Language: English
• Subjects: AIR; Air gaps; CASTING; CASTING MOLDS; Centrifugal casting; Centrifugal force; Characterization and Evaluation of Materials; Chemistry and Materials Science; COATINGS; Computer simulation; Continuous casting; Deformation mechanisms; ENGINEERING; HEAT TRANSFER; Heat transfer coefficients; MATERIALS SCIENCE; Mathematical models; Metallic Materials; Metallurgy; Modulus of elasticity; Molds; Nanotechnology; Plane stress; PLASTICITY; REFRACTORIES; Refractory coatings; ROTATION; SHRINKAGE; Solidus; STRESSES; Structural Materials; Surfaces and Interfaces; Temperature; TEMPERATURE DEPENDENCE; THERMAL CONDUCTIVITY; Thermal resistance; THICKNESS; Thin Films; TIME DEPENDENCE; YOUNG MODULUS
• ISSN: 1073-5615; 1543-1916
• DOI: 10.1007/s11663-018-1220-0

During centrifugal casting, the thermal resistance at the cast-mold interface represents a main blockage mechanism for heat transfer. In addition to the refractory coating, an air gap begins to form due to the shrinkage of the casting and the mold expansion, under the continuous influence of strong centrifugal forces. Here, the heat transfer coefficient at the cast-mold interface h has been determined from calculations of the air gap thickness d a based on a plane stress model taking into account thermoelastic stresses, centrifugal forces, plastic deformations, and a temperature-dependent Young’s modulus. The numerical approach proposed here is rather novel and tries to offer an alternative to the empirical formulas usually used in numerical simulations for a description of a time-dependent heat transfer coefficient h . Several numerical tests were performed for different coating thicknesses d C , rotation rates Ω , and temperatures of solidus T sol . Results demonstrated that the scenario at the interface is unique for each set of parameters, hindering the possibility of employing empirical formulas without a preceding experiment being performed. Initial values of h are simply equivalent to the ratio of the coating thermal conductivity and its thickness (~ 1000 Wm −2  K −1 ). Later, when the air gap is formed, h drops exponentially to values at least one order of magnitude smaller (~ 100 Wm −2  K −1 ).