Temperature control during plastic injection molding

The temperature to be controlled during plastic injection molding includes barrel temperature, nozzle temperature and mold temperature. The first two temperatures primarily affect the plasticization and flow of the plastic, while the latter temperature primarily affects the flow and cooling of the plastic.

Barrel temperature
Each plastic has a different flow temperature. The same plastic has different flow and decomposition temperatures due to different sources or grades. This is due to the difference in average molecular weight and molecular weight distribution. Plastics are used in different types of injection molding machines. The plasticizing process is also different, so the temperature of the selected cylinder is also different.

Nozzle temperature
The nozzle temperature during plastic injection molding is usually slightly lower than the maximum temperature of the barrel. This is to prevent the "over-flowing phenomenon" of the melt in the straight-through nozzle.

The nozzle temperature should not be too low, otherwise it will cause early condensation of the melt to block the nozzle, or affect the performance of the plastic product due to the injection of the early material into the cavity.

Mold temperature
The temperature of injection mold has a great impact on the intrinsic properties and apparent quality of the injection molded plastic parts.

Mold temperature is the most important variable in injection molding. Regardless of the type of plastic being molded, it must be ensured that the mold surface is substantially wetted. A hot mold surface keeps the plastic surface liquid for a long time, enough to create pressure in the cavity.

For each type of plastic and plastic part, there is a limit to the mold surface temperature beyond which one or more adverse effects may occur (for example, the component may overflow the burrs). Higher mold temperatures mean less flow resistance.
Generally, an increase in mold temperature reduces the amount of condensation that the plastic has in the mold cavity, making it easier for the molten material to flow within the cavity, resulting in greater plastic part weight and better surface quality. At the same time, the increase in mold temperature also increases the tensile strength of the part.

The temperature of the injection mold depends on the presence or absence of crystallinity of the plastic, the size and structure of the plastic product, performance requirements, and other process conditions (melt temperature, injection speed and injection pressure, injection molding cycle, etc.).