In the design process of plastic injection molding die, the importance of forming shrinkage is very important. According to the molding shrinkage rate. The molding shrinkage, the surface temperature of the mold cavity and the pressure of injection molding are embodied.

　　Sprue is a plastic melt into the injection mold cavity is first through the site, it will outpour of the nozzle of the injection molding machine of plastic melt into shunt or injection mold cavity, the shape of the conical, easy to melt the smooth flow forward. Mold sprue and successfully pulled out and sprue size directly affects the plastic melt flow rate and filling time, because the sprue to with the nozzle of the high-temperature plastic injection molding machine and repeated contact and collision, usually do not open directly in the module, but will it separate design into the sprue bushing meditation within the template.

　　Mainstream Tao sets are usually made of high carbon tool steel. The main points of the design of the main channel of the injection mold are as follows:

　　1 in order to facilitate the pulling out of the pouring system from the main stream and the expansion of the plastic melt, the main channel is designed into a conical shape.

　　The 2 main channel end rounded, its radius is r=1 ~ 3mm, in order to reduce the resistance to flow transition.

　　3 in the case of plastic parts forming good, the length of the main stream of the injection mold should be as short as possible, otherwise it will increase the flow of the main road, and increase the pressure loss, so that the plastic melt cooling too much impact on injection molding.

　　4 in order to make the molten plastic completely into the main stream and not overflow, should make the mainstream Road and injection nozzle close to the nozzle, the main channel docking design into a hemispherical pit. The main channel part is often designed to be removable in the main road liner, so that the use of high-quality steel processing and heat treatment alone, so in the mainstream road used to increase the temperature of the electric heating.