Temperature control of injection molding process and each process
1. Mold temperature
Some plastic materials require high mold temperature due to high crystallization temperature and slow crystallization speed. Some plastic materials require higher or lower temperature due to the size and deformation control or the need for demolding. For example, PC generally requires more than 60 degrees. In order to achieve a better appearance and improve fluidity, PPS sometimes requires a mold temperature of more than 160 degrees. Therefore, mold temperature has an inestimable effect on improving the appearance, deformation, size and rubber mold of the product.
The melt overcomes the resistance needed to advance, which directly affects the size, weight and deformation of the product. Different plastic products require different injection pressures. For materials such as PA and PP, increasing the pressure will significantly improve its fluidity and injection pressure The size determines the density of the product, that is, the appearance of gloss. It does not have a fixed value, and the more difficult the mold filling is, the higher the pressure of the injection molded part.
The melt temperature is very important, and the temperature of the shot tank used is only a guide. Melt temperature can be measured at the nozzle or using air jet method. The temperature setting of the shot cylinder depends on the melt temperature, screw speed, back pressure, shot volume and injection cycle. If you have no experience processing a particular grade of plastic, start with the lowest settings.
In order to facilitate the control, the injection cylinder is divided into zones, but not all are set to the same temperature. If operating for a long time or operating at high temperatures, set the temperature in the first zone to a lower value, which will prevent premature melting and divergence of the plastic. Before injection molding begins, make sure that the hydraulic oil, hopper seal, mold, and shot cylinder are at the correct temperature.
Melt temperature plays a major role in the flow properties of the melt. Because plastic does not have a specific melting point, the so-called melting point is a temperature range in the molten state. The structure and composition of plastic molecular chains have different effects on their fluidity. Rigid molecular chains are more obviously affected by temperature, such as PC, PPS, etc., while flexible molecular chains such as PA, PP, PE and other fluidity are not obvious by changing the temperature, so the reasonable temperature of injection molded parts should be adjusted according to different materials. .