Injection molding materials that do not meet the application requirements can also lead to poor surface gloss. The causes and handling methods are as follows:

1. During injection molding, if the moisture or other easily evaporated substances are too high, the evaporated components will condense between the mold cavity wall and the molten material, resulting in poor surface gloss of the plastic parts. Pre drying treatment should be carried out on the materials.

2. Differentiation and discoloration of materials or colorants lead to poor gloss. High temperature resistant materials and colorants should be selected.

3. The poor activity function of the material causes the surface of the plastic parts to be not dense, resulting in poor gloss. Resin with better activity function should be replaced, or an appropriate amount of lubricant should be added and the processing temperature should be improved.

4. The original guess was mixed with different or immiscible materials. New materials should be used instead.

5. The particle size of the material is uneven. Materials with significant differences in particle size should be screened out.

6. Crystalline resin has poor gloss due to uneven cooling. The temperature of the injection molding process should be controlled reasonably. For thick walled plastic parts, if there is a lack of cooling, the surface of the plastic part may become rough and the gloss may be dull. The solution is to take the plastic part out of the mold and immediately put it into a cold press mold soaked in cold water for cooling and shaping.

7. The original guess is that the proportion of recycled materials used is too high, which affects the uniform plasticization of the melt. The dosage should be reduced.

During injection molding, the control of injection pressure is usually divided into primary injection pressure, secondary injection pressure (holding pressure), or more than three injection pressure controls. Whether the pressure switching opportunity is appropriate or not, it is very important to avoid excessive pressure in the mold, overflow or shortage of materials, etc. The specific volume of the molded product depends on the pressure and temperature of the molten material when the gate is closed during the pressure holding stage. If the pressure and temperature during each transition from holding pressure to the cooling stage of the product are the same, then the specific volume of the product will not change.

At a stable molding temperature, the important parameter that determines the size of the product is the holding pressure, and the important variables that affect the size of the product are the holding pressure and temperature. For example, after the filling of the mold is completed, the holding pressure immediately decreases. When a certain thickness is formed on the surface, the holding pressure rises again. This can use low clamping force to form thick walled large products, eliminating collapse pits and burrs.

The holding pressure and speed are usually 50% to 65% of the high pressure and speed during plastic filling of the mold cavity, which means that the holding pressure is about 0.6 to 0.8 MPa lower than the injection pressure. Because the holding pressure is lower than the injection pressure, during a considerable holding time, the load of the oil pump is low, and the service life of the solid oil pump is extended, and the power consumption of the oil pump motor is also reduced.