What are the requirements of the plastic machine for the production of PC products?


1. The injection temperature must be integrated with th […]

1. The injection temperature must be integrated with the shape, size and mold structure of the product. The product performance, requirements and other aspects can only be made after consideration. Generally, the temperature used in molding is between 270~320℃. If the temperature of the material is too high, if it exceeds 340℃, the PC will decompose, the color of the product will become darker, and defects such as silver wire, dark stripes, black spots, and bubbles will appear on the surface. , At the same time, the physical and mechanical properties are also significantly reduced.

2. The injection pressure has a certain influence on the physical and mechanical properties of PC products, internal stress, molding shrinkage, etc. It has a greater impact on the appearance and mold release of the product. Too low or too high injection pressure will cause the product to appear certain For some defects, the general injection pressure is controlled between 80-120MPa. For products with thin walls, long processes, complex shapes, and small gates, in order to overcome the resistance of melt flow and fill the mold cavity in time, the higher one is selected. Injection pressure (120 -145MPa). In order to obtain a complete and smooth surface product.

3. Holding pressure and holding time The size of holding pressure and the length of holding time have a great influence on the internal stress of PC products. If the holding pressure is too small, the feeding effect is small, and it is easy to cause vacuum bubbles or surface shrinkage. Concave, the holding pressure is too large, and large internal stress is likely to occur around the gate. In actual processing, it is often solved by high material temperature and low holding pressure. The selection of the holding time should depend on the thickness of the product, gate size, mold temperature, etc. Generally, small and thin products do not need a long holding time. On the contrary, the holding time of large and thick products should be longer. The length of the holding time can be determined by the test of the gate sealing time.

4. The injection speed has no obvious effect on the performance of PC products. Except for thin-walled, small gate, deep hole, and long-flow products, medium-speed or slow-speed processing is generally used, and multi-stage injection molding is best. Slow processing is generally used. -Fast-slow multi-stage injection molding method.

5. The temperature of the mold is generally controlled at 80-100°C. For products with complex shapes, thinner and higher requirements, it can also be increased to 100-120°C, but the heat deformation temperature of the mold cannot be exceeded.

6. Screw speed and back pressure. Because of the high viscosity of PC melt, it is beneficial to plasticization, exhaust, and maintenance of the plastic machine, to prevent the screw from being overloaded, and the screw speed should not be too high, generally controlled at 30 -60r/min is appropriate, and the back pressure should be controlled between 10-15% of the injection pressure.

7. During the injection molding process of PC, the use of release agent should be strictly controlled. At the same time, the use of recycled materials should not exceed three times, and the use amount should be about 20%.

Requirements for the plastic machine for the production of PC products: The maximum injection volume of the product (including runners, gates, etc.) should not be greater than 70-80% of the nominal injection volume. The screw uses a single thread with equal pitch and a gradual change with a non-return ring. Compression type screw, the screw length to diameter ratio L/D is 15-20, and the geometric compression ratio C/R is 2-3.