ON ALUMINIUM SLAB CASTING

Abstract

(1) The CastingThe effect of Fe, Si, Cu or Mn upon casting cracks of aluminium ingots were investigated by measuring shrinkages or cracks which were found in casting into a particular metal mould (See Fig. (2)). Results obtained are as follows: There is a relationship of casting and mould temperature within a limited range which favors prevention of cracking, varying according to the kind and the content of the impurities. The higher the casting temperature, the larger the shrinkage, and so the casting at higher temperature promotes the opportunity for cracks. Cracks which were found in such cases as hindrance of free contraction, become finer by slow cooling but larger by the rapid cooling, and also the higher the purity of Al, the finer they become generally.In this experiment, the cause of cracking was assumed, in a general way, to lie in the stress due to the disparity of the solidification range of the alloy, but in practical operation, the tendency to cracking is to a marked degree affected by other factors for example, the casting technique.(2) On the Developement of the Faults in the Slab Ingots.The relation between casting techniques and cracks appearing in aluminium ingots has been studied with a practical tilting mould. These experiments were made for the purpose to find and prevent the developement of faults in aluminium ingots. The faults of the ingots were examined by means of specific gravity and hardness tests or microscopic examinations, and also the change of temperature inclination in the course of pouring.The pouring temperature and the temperature of moulds affect seriously the cracks. The rate of casting, the shape of the runner, the degree of tilting the mould, etc. also influence the cracking. Among these, it was found: when the pouring temperature is high the temperature gradient along the vertical direction becomes large, and the gradient in the neighbourhood of the gate becomes much larger than in the opposite portion, and in such a condition, cracking appears mainly on the gate side.From change of the thickness of slabs, the following formula was introduced:Hy=(2Ha+ql2)/2lx-q/2x2On the other hand, the developement of faults were identified by calculating the ratio of q to H, where the former is the force by which the slab tends to contract to the inner direction and the latter is that by which it tends to maintain the original form (See Fig. 50)