There are many factors that may affect the quality of the plastic products in the process of injection mold
, and they can be summed up as follows:
1. Plastic Materials
The complexity of plastic materials' performance determines the complexity of the injection mold
process. The performance of plastic materials varies greatly due to their different varieties, grades, manufacturers or even different batches. Different performance parameters may lead to completely different moldings.
2. Injection Temperature
The melt flows into the cooled cavity and losses its heat due to heat conduction. At the same time, the melt generates heat due to shearing action, and this part of the heat may be more or less than the lost heat caused by heat conduction, which depends on the injection conditions. The viscosity of the melt becomes worse with the increasing of temperature. In this way, the higher the injection temperature is, the worse the melt viscosity becomes and the smaller the required filling pressure needs. Meanwhile, the injection temperature is also limited by the thermal degradation temperature and decomposition temperature.
3. Mold Temperature
The lower the mold temperature is, the faster the heat loses, due to the heat conduction; the lower the melt temperature is, the worse the mobility becomes. This phenomenon is particularly obvious when we adopt a lower injection rate.
4. Injection Time
The influences of injection time on the injection process are in three aspects:
(1)When we shorten the injection time, the shear strain rate of the melt will increase, and the injection pressure which are used for filling the cavity should also be increased.
(2) When we shorten the injection time, the shear strain rate of the melt will increase and the melt viscosity decreases due to the shear thinning characteristic. The injection pressure should also be decreased in order to fill the cavity.
(3)When we shorten the injection time, the shear strain rate in the melt as well as the heat productivity will get higher, and meanwhile, the heat lost due to heat conduction is only a little. Thus, the higher the melt temperature is, the worse the viscosity becomes. And the injection pressure should be decreased so as to fill the cavity. As a result of the above three factors, the curve of the injection pressure which is required to fill the cavity presents in a "U" shape. That is, there exist an injection time when the required injection pressure is minimal.