According to the molding theory, the main reason for the brittleness of injection molded parts is the directional arrangement of internal molecules, excessive residual internal stress, etc. If the injection molded parts have water inclusion lines, the situation will be worse.
Therefore, it is necessary to maintain high mold temperature and melt temperature to reduce the brittleness of injection molded parts when producing large injection molded parts. In addition, it is also helpful to reduce the pressure by properly increasing the injection speed. Because the speed is low, the heat dissipation of the glue melt will increase greatly, and the temperature will drop too much. It is bound to require greater glue injection pressure to fill the cavity.
In order to ensure stable and qualified product quality, at the beginning of production, since the temperature of the injection mold has not yet risen, it is better not to use the first 20 injection molded parts, because they are relatively brittle, especially the injection molded parts with slightly greater brittleness, such as fire retardant, should be more than 30 pieces.
The weather also has a great impact on the brittleness of large injection molded parts. When the cold weather comes, we will find that many injection molded parts that have been normally produced, such as PP, ABS, PC, K materials and other parts with good impact resistance, suddenly become brittle. Sometimes even small pieces may be blown out, so they are often returned by customers.
In order to eliminate the influence of excessive residual internal stress and serious molecular orientation on the brittleness of injection molded parts, heat treatment of injection molded parts is an effective measure to prevent brittleness.
In order to ensure the reliability of the product in winter, if the product design allows, and all tests are qualified, appropriate flexible materials compatible with the raw materials are added to the production raw materials, such as a small amount of EVA material in PP material, a small amount of K material in HIPS material, etc., which is a good solution to prevent the brittleness of injection molded parts.
Reasons for brittleness of large injection molded parts:
1. High glue injection pressure;
2. During mold filling, the temperature drops too fast;
3. The internal molecules are arranged directionally, and the residual internal stress is too large;
Anti brittleness measures:
1. Maintain high mold temperature and melt temperature;
2. Properly increase the glue injection speed;
3. The first 20 injection molded parts should not be used;
4. Add the test of the influence of weather temperature change;
5. Heat treatment;
6. Avoid contacting and approaching corrosive solvent or environment;
7. Properly add flexible materials compatible with raw materials into the production raw materials.
Post time: Nov-08-2022