Casting process refers to the process of pouring high-temperature liquid metal into the mold to obtain a certain shape of castings after cooling and solidification. The spiral bevel gear studied belongs to small thin-walled precision steel castings. The casting material 20CrMoH belongs to low alloy steel, which has high liquidus temperature, poor fluidity of liquid metal, obvious oxidation tendency, large shrinkage of casting body, and casting defects such as shrinkage porosity, insufficient pouring and sand sticking are easy to appear in the solidification process.
At present, the casting process in the market can be divided into sand casting, pressure casting, lost foam casting, coated sand casting and other types.
Sand casting is the most widely used because of its cheap and easily available mold materials and strong casting adaptability. The number of castings produced by this process accounts for more than 80% of the total every year. However, the surface accuracy of castings produced by traditional sand casting process is not high, and casting defects such as sand inclusion, porosity, shrinkage and shrinkage are easy to appear.
Pressure casting refers to the method of rapidly forming castings by pressing molten metal liquid into the mold cavity at high speed. Compared with other casting processes, this method has the highest production efficiency and is suitable for mass production of parts. However, this method is easy to involve gas in the process of high-pressure filling metal, and is only suitable for the casting of low melting point metal.
Lost foam casting is a method of moulding the plastic parts with plastic foam and then applying the refractory material on the surface. The molten metal melts and melts away from the foam mold during the pouring process and eventually fills the cavity and solidified. However, if the lost foam process is applied to low alloy steel materials, it is very easy to produce carburizing effect, resulting in the increase of carbon content of castings and affecting the forming effect of castings.
The above casting processes are not suitable for the production of precision steel castings of driven spiral bevel gears. Coated sand casting is a new type of precision casting technology. Firstly, resin coated sand is used to cover the metal mold preheated to a certain temperature and heated to make a thin shell with certain strength and stiffness; Then the thin shell is put into the sand box as a mold and compacted; Finally, the metal is poured and the thin shell is broken after solidification to obtain the precision casting with smooth surface. This method has a series of advantages, such as high production efficiency, less molding sand, less production dust, low casting surface roughness and ideal dimensional accuracy. It is very suitable for large-scale production of spiral bevel gear precision castings.
Therefore, it is decided to use coated sand casting as the casting process of driven spiral bevel gear.