Analysis and solution of stress cracking and melt fracture in plastic mold processing
In the process of injection molding, a variety of plastics often have the problems of stress cracking and melt fracture, which is a common challenge for injection molding manufacturers. In order to provide better products and services, injection molding technicians from injection molding manufacturers conducted in-depth research and testing, summarized the causes and solutions of these problems, so as to pass on these technical knowledge and enable more people to quickly master these skills.
1. Some plastics are very sensitive to stress and are prone to internal stress during the molding process, resulting in increased brittleness and cracking of plastic parts. In order to solve this problem, in addition to adding crack resistance agent to the raw material, it is also necessary to keep the raw material dry and select the appropriate molding conditions to reduce the internal stress and improve the crack resistance. In addition, the appropriate shape of plastic parts should be selected to avoid setting inserts and other measures to reduce stress concentration. During the mold design, it is necessary to increase the demoulding slope, select the appropriate feed inlet and ejection mechanism, and properly adjust the material temperature, mold temperature, injection pressure and cooling time, so as to avoid too fragile demoulding of plastic parts. After molding, the plastic parts can be post treated to improve the crack resistance and avoid contact with solvents.
2. When the flow rate of some polymer melts through the nozzle at constant temperature exceeds a certain value, transverse cracks will appear on the melt surface, which is called melt fracture, which will damage the appearance and physical properties of the plastic parts. In order to solve this problem, when selecting polymer with high melt flow rate, the cross-section of nozzle, sprue and feed port should be increased, the injection speed should be reduced, and the material temperature should be increased.
3. Different types of plastics have different thermal properties, such as specific heat, thermal conductivity and thermal deformation temperature. Therefore, for plastics that need a lot of heat in the plasticizing process, the injection molding machine with strong plasticizing ability should be selected.
4. Various plastics need to maintain appropriate cooling rate according to their performance and shape. Therefore, the mold should be set with heating and cooling system according to the molding requirements to maintain a constant mold temperature.
Through the above analysis and solutions, injection molding manufacturers can better deal with the problems of stress cracking and melt fracture, improve product quality and provide customers with better service. It is hoped that these experiences and skills can help more injection molding manufacturers solve similar challenges and promote the development and progress of the industry.