Low-pressure casting For some castings with spe […]
Low-pressure casting For some castings with special structures or special performance requirements, it is difficult to meet the requirements, and on the basis of low-pressure casting, some special low-pressure casting processes have been developed.
Differential pressure method for low pressure casting
Some castings have high internal quality requirements and are expected to crystallize at higher pressures, but generally the crystallization pressure during low pressure casting cannot be too large. Thus, a differential pressure method for low pressure casting has been developed. The process of the process is to seal all the electric resistance holding furnace and the mold, and the compressed air in the sealed cover is as large as 500 kPa.
At this time, since the pressure inside the mold and the pot is equal, the molten metal does not rise, and then the molten metal is supplemented with a pressure of 50 kPa, and the molten metal rises to fill the cavity. At the same time, the molten metal in the mold is also crystallized and solidified under high pressure.
This method results in a denser crystalline structure of the casting and improves the mechanical properties of the casting. According to the data, this process improves the casting strength by about 25% and the elongation by about 50% compared to the general casting method. However, the equipment is relatively large, and the operation is troublesome. It is only applied when there are special requirements.
Second, vacuum low pressure casting
For thin-walled or complex large-scale castings, when the above-mentioned low-pressure casting process is also difficult to meet, it is easy to solve by vacuum low-pressure casting. Its device is basically similar to differential pressure low pressure casting. Before the pouring, the gas in the cavity is extracted and then poured, and the casting speed can be increased without causing defects such as oxidation inclusions and pores.