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铸件与铸型的相互机械作用过去研究较少,而铸件收缩过程中,由于与铸型间的相对运动而产生的摩擦问题,则基本上还是一个空白点。Kain〔1〕于1933年曾指出,砂型与正在收缩着的铸件之间具有很大的摩擦系数,以致后者的自由收缩受到相当强烈的阻碍。Andrew和Protheroe〔2〕用粗细不同的型砂进行的实验,由于没有发现它们对铸件产生热裂有什么不同的影响,因而作出“浇铸后,与液态金属接触的砂型表面失去强度,摩擦阻力亦即消失”的结论。Parkins等〔3〕第一次用比较精确的方法测量了铸件在不同砂型内的收缩值。实验结果说明,旧砂对铸件的摩擦阻力远大于这种型砂的体积阻力(试样两端法兰盘所受之阻力)。我们认为,Parkins等在实验中忽略了一个重要问题—不同型砂的热物理系数对铸件收缩的影响〔4〕。由于实验者采用了干湿两
The mechanical interaction between the casting and the mold is less studied in the past, and the friction problem caused by the relative movement between the casting and the mold during casting shrinkage is basically a blank point. Kain [1] pointed out in 1933 that there was a large coefficient of friction between the sand mold and the shrinking casting, so that the latter’s free shrinkage was considerably hampered. Andrew and Protheroe 〔2〕 with different thickness of the sand experiment, because they did not find the casting of hot cracking have any different effects, thus making “after casting, contact with the liquid metal loss of strength of the surface of the sand, the friction resistance that Disappear ”conclusion. For the first time, Parkins et al. [3] measured the shrinkage of castings in different sand molds by a more accurate method. The experimental results show that the frictional resistance of the old sand castings is much larger than the volumetric resistance of the sand (the resistance of the flanges at both ends of the specimen). In our opinion, Parkins et al. Have neglected an important issue in the experiment - the effect of different physical properties of sand on shrinkage of castings [4]. As the experimenter used wet and dry two