The gating system of lost mold casting
When analyzing the case, it is found that when the pouring system design is unreasonable, even if the temperature of pouring liquid metal is high enough, the same casting will appear in high temperature area and low temperature area, shrinkage hole loosening defects in the high temperature area, the foam gasification in the low temperature area is slow and incomplete, and defects such as wrinkled skin, carbon slag, and pores appear. The thorough study of this phenomenon leads us to summarize the three theories of "flow field, thermal field and negative pressure field".
The pouring system is the general term of the cavity channel of liquid metal injected by the pouring package. The filling track formed by the metal liquid guided by the pouring system has specific forms to follow, so we call it "flow field".
The pouring system of die casting is not only for filling liquid metal, but also for distributing the heat carried. After the end of liquid metal filling, the temperature of liquid metal and the amount of heat stored in each area will be different. The virtual distribution of temperature and heat that we call the "thermal field". Although the hot field is invisible to find, but there are results shown. That is, the forming defect in high temperature area and the incomplete defect of foam gasification in low temperature area.
At the same time of three theory, put forward the disappear die casting must follow the third basic principle: through the regulation of the flow field heat field reasonable distribution, the realization of the casting and solidification or sequential solidification, and minimize the heat loss of the pouring system, make the type cavity metal liquid temperature close to the temperature of the metal liquid in the pouring package. The sequential solidification is the process of liquid metal.
The discussion of "negative pressure field", in foreign and domestic, up to now is still limited to myself and this book.
Take the negative pressure sand box as an example, how to evaluate its "excellent" and "inferior"? There are usually a few air chambers available. This is one-sided, bluntly said is wrong! Because, the gas pulled by the negative pressure, foam gasification will only go straight to the vacuum interface, walk a nearest straight line, will never turn the curve. Therefore, the main factor determining the performance of the sand box is: the position and number of vacuum interface, not the number of vacuum air chamber.
In the process of liquid metal casting, negative pressure pulling is strong and directional. During the pouring process, the metal liquid level keeps rising, the foam mode keeps retreating, and the air gap gap keeps changing. The trajectory of the foam gasification products is also constantly changing, and the negative pressure value of each area of the sand box will also change accordingly, but the direction straight to the vacuum interface will not change. The trajectory of the negative pressure difference formed by the negative pressure sand box is called the negative pressure field.
The direction of the liquid metal filling flow field must be consistent with the pulling direction of the negative pressure field. This is the fourth basic principle that must be followed in disappearing die casting.
