Pressure casting is divided into high pressure casting and low pressure casting. What is the difference between high pressure casting and low pressure casting? With the development of die casting industry, vacuum system is used by more and more die-casting manufacturers. At present, many manufacturers have higher and higher requirements for die casting. In addition, there are not many domestic die-casting manufacturers using vacuum, and the vacuum system manufacturers are also mixed, which leads to die-casting manufacturers feel helpless when choosing vacuum equipment. The practical effect of the application of the lower vacuum system in the high pressure casting is analyzed in the hope of being helpful to the die casting manufacturers.
What is the difference between high pressure casting and low pressure casting?
High pressure casting is a kind of casting method in which the molten alloy is poured into the pressure chamber to fill the cavity of the steel mold at high speed, and the alloy liquid solidifies under pressure to form the casting. The main characteristics of high pressure die casting different from other casting methods are high pressure and high speed. ① the liquid metal is filled in the cavity under pressure and crystallized and solidified under higher pressure, the common pressure is 15-100mpa. ② the filling time of liquid metal is very short, about 0.01-0.2s (depending on the size of the casting), which can fill the cavity.
The technological process of low-pressure casting is: in the sealed crucible (or sealed tank), dry compressed air is introduced into the crucible. Under the action of gas pressure, the liquid metal enters the direct runner along the riser and rises up. It enters the mold cavity smoothly through the internal runner and maintains the gas pressure on the liquid surface in the crucible. Until the casting is completely set. Then, the gas pressure on the liquid surface is relieved to make the non solidified metal liquid in the riser flow back to the crucible. Open the mold again and take out the casting.
Principle of vacuum system for die casting:
The vacuum system for die casting mainly consists of three parts: vacuum valve, vacuum unit and control system. Among them, the vacuum unit part includes vacuum tank, vacuum pump and other parts.
When the vacuum system is used in the die casting machine for injection, the air in the cavity is quickly drawn out, so as to realize the vacuum die casting. Because of the short time of injection process, it is impossible to exhaust air by vacuum pump. The realization of this process depends on vacuum tank. The function of the vacuum pump is to exhaust the air in the vacuum tank and keep the vacuum tank at a high vacuum level. Then, at the moment of die casting, the control system turns on the switches of the vacuum tank and the cavity, so that the cavity vacuum can be realized quickly.
With the improvement of product quality requirements of die-casting manufacturers, vacuum system will be adopted by more and more enterprises. The vacuum system should not only draw the air out of the cavity, but also realize the functions of blowing, measuring, testing and data recording.
From the above analysis of the application of vacuum system in high-pressure casting, we can draw a conclusion that there are two main advantages of using vacuum system to produce castings, the first is to reduce product porosity, so as to improve the product qualification rate, the second is to reduce the front pressure of liquid metal, which is conducive to filling and forming.