Seven Factors To Be Considered In Injection Moulding Process

1. Form and calculation of shrinkage rate of thermoplastics as mentioned above. The factors affecting shrinkage of thermoplastics are as follows: 1.1 During the forming process of thermoplastics, there are still some factors such as volume change caused by crystallization, strong internal stress, large residual stress frozen in plastic parts, strong molecular orientation and so on. Therefore, compared with thermosetting plastics, the factors affecting shrinkage of thermoplastics are as follows:1. The shrinkage rate is larger, the shrinkage range is wide and the orientation is obvious. In addition, the shrinkage rate after moulding, annealing or humidification treatment is generally larger than that of thermosetting plastics. 1.2 The outer layer of the molten material contacting the surface of the cavity is immediately cooled to form a low density solid shell during the characteristic forming of the plastic parts. Due to the poor thermal conductivity of plastics, the inner layer of plastic parts slowly cooled to form a high-density solid layer with large shrinkage. So wall thickness, slow cooling and high density layer thickness shrink greatly. In addition, the layout and quantity of inserts and inserts have a direct impact on the direction of material flow, density distribution and shrinkage resistance, so the characteristics of plastic parts have a greater impact on the shrinkage size and direction. 1.3 The form, size and distribution of inlet and outlet directly affect the direction of material flow, density distribution, pressure holding and feeding effect and forming time. The large cross-section (especially the thicker cross-section) of the direct inlet and the inlet has smaller shrinkage but larger directivity, while the wide and short length of the inlet and the outlet have smaller directivity. Close to the inlet or parallel to the direction of the material flow, the shrinkage is large.