1.Thermal gravity casting
This is one of the most widely used casting form,namely pouring at high temperature after getting out shell from the roaster.At this time metal is cooling slowly in shell, filling mold under the condition of high liquidity,so the castings can replicate the shape of the cavity, improving the accuracy of the castings.But castings slow cooling in hot type can make coarse grains, which reduce the mechanical properties of castings.In the pouring of carbon steel castings,casting surface with a slower cooling also is easily oxidated and decarburized, thus reducing surface hardness, finish and dimensional accuracy of castings.
2.Vacuum suction pouring
Put shell in vacuum pouring box,suck gas in the cavity by tiny pore in the shell,can make the liquid metal mold filling better,copy the shape of the cavity,improve casting accuracy,prevent defects like gas cavity,misrun,ect.The method has been applied to abroad.
3.Crystallization under pressure
Put the shell into pressure tank for casting,when finished,immediately closed pressure tank,then ventilate high pressure air or inert gas into tank, making castings solidification under pressure to increase the density of castings.The maximum pressure in abroad has reached 150ATM.
Some investment castings such as turbine blades,magnetic steel,ect.If their crystal structure is columnar crystal arranged in a certain direction,which will improve their performance a lot,so directional crystallization technology of investment castings is rapidly developed.