PC has excellent performance, high transparency, good impact toughness, creep resistance, wide range of temperature. The process characteristics of PC are: the sensitivity of melt viscosity to shear rate is small, but it has great sensitivity to temperature, no obvious melting point, high viscosity of melt, easy hydrolysis of resin at high temperature and easy cracking of products. In view of these characteristics, we should pay special attention to the different treatment: to increase the fluidity of the melt, we should not increase the injection pressure but also adopt the method of increasing the injection temperature. The runner and gate of the mould are required to be short and thick to reduce the pressure loss of the fluid and to have a higher injection pressure. Before forming and processing, the resin should be dried sufficiently to keep its moisture content below 0.02%. In addition, heat preservation measures should be taken to prevent moisture absorption during the process. Not only the reasonable product design is needed, but also the molding process should be correctly mastered, such as increasing the mold temperature and post-treatment of the products, etc. can reduce or eliminate the internal stress. Adjust the process parameters according to the different conditions of the product.
Here is the forming process
1. Injection temperature must be integrated with the shape, size and mold structure of the product. The performance and requirements of the products can only be made after considering the conditions. Generally, the temperature of the molding is between 270-320 ℃, if the material temperature is higher than 340 ℃, PC will decompose, the product color will become darker, and the surface will show defects such as silver wire, dark strip, black spot and bubble, and the physical and mechanical properties also decrease significantly.
2. Injection pressure has a certain influence on the physical and mechanical properties, internal stress and molding shrinkage of PC products, which has a great influence on the appearance and demoulding performance of the products. Low or too high injection pressure will cause some defects of the products. Generally, the injection pressure is controlled between 80-120MPa, and for products with thin wall, long process, complex shape and small gate, In order to overcome the resistance of melt flow and fill the cavity in time, the higher injection pressure (120-145mpa) is selected. Thus, the products with complete and smooth surface are obtained.
3. The pressure maintaining pressure, the pressure holding time and the length of the holding time have a great influence on the internal stress of PC products. The pressure maintaining pressure is too small, and the small shrinkage effect is easy to appear vacuum bubble or concave surface, too much pressure retaining pressure, and the large internal stress is easily produced around the gate. In the actual processing, the method of high material temperature and low pressure keeping is often used to solve. The selection of pressure holding time should be determined by the thickness of the product, the size of the gate and the mold temperature. Generally, the small and thin products do not need a long holding time. On the contrary, the pressure holding time of the large and thick products should be longer. The length of pressure holding time can be determined by the test of gate sealing time.
4. The injection speed has no obvious influence on the performance of PC products. Except for thin-walled, small gate, deep hole and long process products, medium speed or slow processing is generally adopted, preferably multi-stage injection, and the slow fast slow multi-stage injection method is generally adopted.
5. The mold temperature can be controlled at 80-100 ℃, and the shape of the products with complex shape, thin and high requirements can also be increased to 100-120 ℃, but it can not exceed the hot deformation temperature of the mold.
6. Screw speed and back pressure are characterized by high viscosity of PC melt, which can be beneficial to plasticizing, exhaust and maintenance of plastic machine, to prevent screw overload. The speed requirement of screw should not be too high. Generally, it is appropriate to control the screw speed at 30-60r/min, while the back pressure should be controlled between 10-15% of injection pressure.
7. PC should strictly control the use of mold release agent in the process of injection molding, and the use of recycled materials should not exceed three times, and the usage should be about 20%. Requirements for the molding machine for PC products: the maximum injection volume (including runner, gate, etc.) of the products shall not be greater than 70-80% of the nominal injection quantity. The screw shall be of single head thread equal pitch and gradient compression screw with check ring. The length diameter ratio of screw l/d is 15-20, and the geometric compression ratio c/r is 2-3.
About JasonMould Industrial Company Limited
Jasonmould is a China mold maker of plastic molds- injection mold, die casting moulds, plastic blow molding, rotational molding, medical plastic injection molding, two shot plastic injection molding, insert molding, overmolding, metal injection molding, micro injection molding, powder injection molding, ceramic injection molding, liquid injection molding, husky injection molding, household mold, casting mold, die mold tool, custom molds, china moulds, rapid prototyping tooling, plastic prototyping tooling, punch press tooling, die and tooling for mobile/ cell phone parts, automotive parts, vacuum cleaners, rechargeable tools, telephones, copiers, computers, multimedia speakers, and many other electronic products and household appliances. And also a plastic product manufacturer, mold manufacturer China– plastic parts, plastic water tank, plastic balls, plastic containers, plastic buckle, plastic anchor, plastic hanger, plastic spoon, plastic pipe fitting, plastic tumble, plastic tableware, plastic cups, plastic bottles, plastic tray, plastic cosmetic container, plastic case, plastic food container, plastic chairs, plastic caps, plastic cap closure, plastic tubes, plastic water pipes, plastic knobs, plastic tubing, plastic utility boxes, plastic racks and so on.
Person: James Yuan
Company: JasonMould Industrial Company Limited
Add: LongGang Village,LongXi Town,BoLuo County,HuiZhou City,GuangDong Province, China
Email: [email protected]