Precision casting process and classification characteristics

[xuanxuan geng]

Precision casting refers to a general term for a process. It refers to the process of obtaining precise castings by using precise molding methods. Many castings can be obtained by precision casting, such as: hardware parts, auto parts, locomotive parts and various valves. Etc. So it is a very important process in the industry today. So when we are doing precision casting, we need to pay attention to what factors may affect the precision of precision casting size?
First, the structure of the casting is a very important influencing factor. Generally, the thicker the wall of the casting, the larger the shrinkage rate, and the smaller the opposite;
Second, the material of the casting will also affect the intensive reading of precision casting. The higher the carbon content in the general material, the smaller the line shrinkage rate, and the greater the line shrinkage rate;
Third, the mold has a great influence on the shrinkage rate of the casting. Generally, the temperature and pressure of the wax and the time of holding the pressure have a great influence on the size;
Fourth, shell making is also a very important factor, usually using zircon sand, zircon powder, Shangdian sand, Shangdian powder, etc., because their expansion coefficient is very small;
Fifth, the temperature of casting is also a very important factor. The higher the temperature of casting, the greater the shrinkage rate, so it is necessary to control the casting temperature.
Due to the different purposes of precision castings, there are many heat treatments, which can be mainly divided into two categories. One is that the structure will not change or should not be changed through heat treatment, and the second is that the basic structure changes. A heat treatment procedure is mainly used to eliminate internal stresses caused by different cooling conditions and conditions during the Stainless steel casting process. The structure, strength and other mechanical properties are not significantly changed by heat treatment.
For the second type of heat treatment, Al Qaeda has undergone significant changes and can be broadly divided into five categories:
1. Softening annealing: Its purpose is mainly to decompose carbides, reduce their hardness and improve processing performance. For ductile iron, the purpose is to obtain more ferrite structure.
2. Normalizing treatment: The main purpose is to obtain pearlite and sorbite structure to improve the mechanical properties of stainless steel casting.
3, quenching treatment: mainly in order to obtain higher hardness or wear strength, while at the same time to very high surface wear characteristics.
4. Surface hardening treatment: mainly to obtain a surface hardened layer, and at the same time obtain a very high surface wear resistance.
5. Precipitation hardening treatment: Mainly to obtain high strength and elongation does not change drastically.
In precision casting processes, especially in "equal" processes, metal temperature is a dominant factor and, therefore, has a direct impact on many quality characteristics. If the measurement and control are not proper, the difference in metal temperature will affect the finished casting size, grain size, porosity (surface and interior), mechanical properties, product quality (ie, the tendency of hot tear), and the fullness of the thin-walled portion. Have an impact.