A model of the interfacial heat-transfer coefficient for the aluminum gravity die-casting process

Abstract

Interfacial heat-transfer coefficients were measured during the solidification of Al-Si alloys against coated die steel chills with varying chill temperature, coating thickness and coating type. Two principal resistances to heat transfer across the casting-chill interface were identified, namely, (1) the resistance to heat transfer of the coating itself and (2) the resistance to heat transfer of a layer of gas, (assumed to be air), trapped between the coating and casting surfaces by virtue of their roughness. These thermal resistances were evaluated by measurement of the coating thermal conductivity and determination of the thickness of the applied coatings and the thickness of the layer of air between the coating and casting surfaces. This produced a simple equation to predict the interfacial heattransfer coefficient during the solidification of Al alloy die castings, which produced values that were found to agree well with the experimentally determined results. This equation was used to interpret the experimentally measured heat-transfer coefficients and to explain their variation with the different experimental conditions employed. A simple modification of the equation can also take into account the formation of an air gap, where the casting locally retreats away from the die surface, leading to a local reduction in the heat-transfer coefficient.

Experimental and Numerical Determination of Casting-Mold Interfacial Heat Transfer Coefficient in the High Pressure Die Casting of A-360 Aluminum Alloy

“…Srinivarsan [19], Dour [6] and Guo Zhi-Pengvd [20] have stated that increasing the mold temperature reduces IHTC. On the other hand, in studies of Hallam and Griffiths [16], IHTC has increased with the increase of mold temperature. When the casting is made at room temperature, IHTC values are 1700-2250 W/m 2 K, at mold temperature of 573 K these values are 1900-2080 W/m 2 K. Akar et al [10] have determined that maximum IHTC at mold temperature of 373 K is 9749 W/m 2 K, at 423 K it is 14790 W/m 2 K and at 473 K it is 17300 W/m 2 K. Figures 5 and 6 show that when the casting temperature increases, IHTC and heat flux are increasing by 3% in experimental results and by 2% in simulation results.…”

“…The chemical composition of A360 alloy used in the experiments is given in Table I. Thermophysical properties of the mold and the casting material used in the experimental study are given in Table II [16]. The melting of casting material was made in the electric smelting furnace.…”

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

“…In addition, an iterative approach was necessary for heat conduction equations due to temperature-dependent thermophysical properties, the nonlinear heat flux q at the cast-mold interface (Eq. [17]), and especially the stiff, latent heat source term. Treatment of the latent heat source term was realized by using a semi-implicit method proposed by Voller and Swaminathan.…”

“…[15] and [16], coupled by the heat flux at the interface (Eq. [17]), with the air gap thickness d a from the previous time t n and obtain new temperature T and solid fraction g s fields. In our numerical tests, usually between two and five iterations were necessary to drop scaled residuals below 10 9 10 À8 for the latent heat source term and the nonlinear heat flux q, respectively.…”

A Model to Predict the Heat Transfer Coefficient at the Casting-Die Interface for the High Pressure Die Casting Process

“…A few investigations [9,10] reported for liquid-solid contact provide a limited understanding to the actual TCR. Furthermore, these two mentioned investigations don't concern the contact conditions between castings and dies in HPDC.…”