1) There are several methods for hot type gravity casting.
This is the most widely used form of casting, where the shell is taken out of the roasting furnace and poured at high temperatures. At this time, the metal cools slowly in the mold shell and can fill the mold with high fluidity, so the casting can well replicate the shape of the mold cavity and improve the accuracy of the casting. However, slow cooling of the casting in the hot mold can cause coarse grains, which reduces the mechanical properties of the casting. When pouring carbon steel castings, the surface of the castings that cool slowly is also prone to oxidation and decarburization, thereby reducing the surface hardness, smoothness, and dimensional accuracy of the castings.
2) Vacuum suction casting
Place the mold shell in a vacuum casting box, and suck up the gas in the mold cavity through the tiny pores in the shell, so that the liquid metal can better fill the mold cavity, replicate the shape of the mold cavity, improve casting accuracy, and prevent defects such as porosity and insufficient casting. This law has been applied abroad.
3) Crystallization under pressure
Place the shell in a pressure tank for pouring, and immediately seal the pressure tank. Inject high-pressure air or inert gas into the tank to solidify the casting under pressure and increase its density. The maximum pressure abroad has reached 150atm.
4) Directional crystallization (directional solidification)
Some investment castings such as turbine blades, magnets, etc., if their crystalline structure is columnar crystals arranged in a certain direction, their working performance can be greatly improved. Therefore, directional crystallization technology in investment casting is rapidly developing.