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运用传热学原理,通过对复杂、非稳态问题的简化,揭示出用金属型在最佳温度场中凝固获得无缩孔铸件的条件:金属型铸件成形时,在顺序凝固方向上及在壁厚两侧向中心方向,凝固的最佳温度梯度和浇注温度与固相线温度之差成正比,与液态金属在凝固方向上的流程成反比,且3个方向上的温度梯度应同步相等。实现方法是:在对应的金属型型腔侧面内壁,喷涂沿凝固方向上逐渐增厚的梯度涂层。金属型壁越薄,顺序凝固的起始段有强制冷却,金属型涂料层的导热系数越小,铸件的导热系数越大。为了在最佳温度梯度下生产出无缩孔铸件,其金属型上所需的涂料层的厚度梯度尽量小。
Based on the principle of heat transfer, through the simplification of the complex and unsteady problems, the conditions of obtaining non-shrinkage castings by metal-type in the optimum temperature field are obtained. When the metal castings are formed, Wall thickness on both sides of the center direction, the best solidification temperature gradient and casting temperature is proportional to the difference between the solidus temperature, and liquid metal in the solidification direction is inversely proportional to the process, and the three directions of the temperature gradient should be synchronized equal . The realization method is as follows: spraying a gradient coating gradually thickening along the solidification direction on the inner side wall of the corresponding metal cavity. The thinner the wall of the metal is, the more the initial stage of solidification in the order is forcibly cooled. The smaller the thermal conductivity of the metallic coating is, the larger the thermal conductivity of the casting is. In order to produce non-shrinkage castings at optimum temperature gradients, the thickness gradient of the desired coating layer on the metal type is as small as possible.