The mold temperature has a great influence on the mechanical properties of the product. With the increase of mold temperature. The temperature difference between the material temperature and the mold temperature becomes smaller, the shear stress is reduced, the melt can be slowly cooled in the mold cavity, the molecular chain is relaxed, and the degree of orientation is reduced, thereby reducing the internal stress of the product, but the impact strength of the product is The elongation is significantly reduced, and it will be difficult to demold the product at the same time. It is easy to deform during demolding, which prolongs the molding cycle and reduces production efficiency; while the lower mold temperature will increase the internal stress of the product. Therefore, the mold temperature must be controlled well. Generally, the mold temperature of PC is 80 to 120°C. Ordinary products are controlled at 80-100°C, while for products with complex shapes, thin walls and higher requirements, it is controlled at 100-120°C, and the heat distortion temperature is not allowed to exceed.
When forming PC thick-walled products, the control of mold temperature is particularly important. For example, when forming a simple beam impact test sample (thickness of 10mm), if the mold does not control the temperature, there will be many shrinkage holes in the formed sample, and it is also very large. At this time, if the mold is not equipped with a heating device, a simple method can be used to heat the main runner of the mold. The simple method is to tie a cotton ball to a piece of iron wire, dipped in industrial alcohol, and heat the main flow channel. In this way, although the shrinkage holes cannot be eliminated, the number of shrinkage holes is greatly reduced. The degree is greatly reduced. certainly. This is a no-brainer method, a native method, and is not recommended. Because of this, it is easy to deform and oxidize the main runner of the mold.
Although the injection pressure has little effect on the melt strength and fluidity during injection molding, because the PC melt has high viscosity and poor fluidity, the injection pressure should not be too low, generally controlled at 80-120MPa, using a plunger injection molding machine The injection pressure should be 100-150MPa; and for products with thin wall, long flow distance, complicated shape, and small gate size, in order to make the melt smooth and fill the mold in time, the injection pressure should be appropriately increased to 120-150MPa. The general principle of PC injection molding process control is: high material temperature, low pressure.
The holding pressure and the holding time directly affect the quality of the product. If the holding pressure is too small, the feeding effect will be small, bubbles will be formed inside the product due to shrinkage, and dents will appear on the surface of the product; the holding pressure is too large. Large internal stress is likely to occur around the gate. The holding time is long, the product has high dimensional accuracy, low shrinkage, and good surface quality, but it increases the internal stress in the product and prolongs the molding cycle. The holding pressure is 80-100 MPa. As mentioned above, heat the main runner with fire to extend the solidification time of the melt in the gate to increase the feeding effect. When PC injection molding, the back pressure can be increased.