1. Molding characteristics of pp plastic
1. Low hygroscopicity, easy to melt fracture, and easy to decompose in long-term contact with hot metal.
2. Good fluidity, but with large shrinkage range and value, shrinkage holes, dents and deformation are easy to occur.
3. The cooling rate is fast, the pouring system and the cooling system should slowly dissipate heat, and pay attention to controlling the molding temperature. The material temperature is easy to be oriented at low temperature and high pressure. When the mold temperature is lower than 50 degrees, the plastic part is not smooth, which is easy to produce poor welding, flow marks, Warping and deformation are prone to occur above 90 degrees.
4. The plastic wall thickness must be uniform to avoid lack of glue and sharp corners to prevent stress concentration.
2. Process conditions of pp plastic
1. Drying treatment: if stored properly, no drying treatment is required.
2. Melting temperature: 220~275C, be careful not to exceed 275C.
3. Mold temperature: 40~80C, 50C is recommended.
4. The degree of crystallization is mainly determined by the mold temperature.
5. Injection pressure: up to 1800bar.
6. Injection speed: Generally, high-speed injection can reduce the internal pressure to a minimum. If there are defects on the surface of the product, low-speed injection at a higher temperature should be used. Runners and gates: For cold runners, the typical runner diameter range is 4~7mm. It is recommended to use a circular injection port and runner.