The internal stress of PC plastic pepper ball and plastic hollow pepper ball products is mainly caused by orientation stress and temperature stress, and sometimes it is related to the unreasonable mold design. Orientation stress plastic pepper ball and plastic hollow pepper ball injection products are prone to internal stress after orientation, resulting in a large number of excessive stress concentration. When injecting PC plastic hollow ball blank pepper ball, the melt cools rapidly, and the viscosity of plastic melt is high at low temperature, and the oriented plastic molecules can not be fully relaxed. The internal stress of plastic blank ball thus produced has an impact on the mechanical properties, size and precision stability of plastic pepper ball products. Therefore, the melt temperature has the greatest influence on the orientation stress in plastic injection molding. When the melt temperature is increased, the melt viscosity decreases, so the shear stress and orientation of plastic decrease. In addition, the relaxation degree of orientation stress is greater at high plastic melt temperature, but when the viscosity of plastic material decreases, the pressure transmitted by the screw of injection molding machine to the cavity of plastic hollow ball mold increases, which may increase the shear rate of the screw of injection molding machine and lead to the increase of orientation stress. When injection molding is south, the holding time is too long, and the orientation stress increases; Increasing the injection pressure of injection molding machine will also lead to the increase of orientation stress due to the increase of shear stress and shear rate. The size of plastic pepper ball, that is to say, the thickness of plastic blank pepper ball products also affects the internal stress, and the orientation stress decreases with the increase of the diameter and thickness of plastic pepper ball products. Because the large-size plastic pepper ball thick-walled products cool slowly, the melt cools and relaxes in the plastic pepper ball mold cavity for a long time, and the orientation molecules have enough time to return to the random state. If the mold temperature of plastic pepper ball is high and the melt cools slowly, the plastic blank ball can reduce the orientation stress.

Temperature Stress If the temperature difference between the melt temperature of plastic material and the mold temperature of plastic pepper ball is too large during injection molding, the plastic melt near the mold cavity wall will be cooled quickly, so the stress that is unevenly distributed in the volume of plastic pepper ball and plastic hollow pepper ball products will be generated. Due to the large specific heat capacity and low thermal conductivity of PC plastic pepper ball, the surface layer of plastic blank ball product cools much faster than the inner layer, and the solidified shell layer formed on the surface of plastic pepper ball product will hinder the free shrinkage of the inner part when it continues to cool, resulting in tensile stress in the plastic pepper ball product and compressive stress in the outer layer of plastic pepper ball product. The greater the stress caused by shrinkage of thermoplastic plastics, the lower the stress caused by compaction in the mold, that is, the shorter the holding time and the lower the holding pressure, which can greatly reduce the internal stress. The shape and size of plastic pepper ball products also have great influence on internal stress. The greater the ratio of surface area to volume of plastic pepper ball products, the faster the surface cooling, and the greater the orientation stress and temperature stress. The orientation stress mainly occurs in the thin surface layer of the product, so it can be considered that the orientation stress should increase with the increase of the ratio of surface to volume of the product. If the thickness of plastic ball products is uneven or plastic pepper ball products have metal inserts, it is easy to produce orientation stress, so the inserts and gates should be located at the thick wall of the products. From the above analysis, it can be seen that it is impossible to completely avoid internal stress due to the structural characteristics of plastic balls and the limitations of injection molding process conditions, and the internal stress can only be reduced as much as possible or distributed evenly in the product as much as possible.