In fact, it is not easy to fabricate plastic injection moulds for making transparent plastic material. The hardness of steel on plastic injection mould shall be good enough in order to avoid scratching marks during ejection. Hence, the grade of mold steel is very important for making transparent plastic products. The selling price of Polystyrene (PS) plastic injection products is not so high, however, the cost of moulds is higher for making high-end crystal plastic products.
The issue should be noted in the injection molding process (including injection machine requirement)
To decrease internal stress and surface quality defect, we should pay attention to the following aspects in the injection molding process:
1. use special screw: injection mould with a separate temperature control nozzle
2. use high injection humidity
3. injection pressure: generally, we use high injection pressure, to overcome the shortcomings of high melt viscosity. but high pressure may cause internal stress, it makes stripping and deformation difficult.
4. injection speed: the injection speed should be low, fast, and slow multi-stage injection is the best.
5. holding time and the molding time: under the condition that mould filled fully, holding time and the molding time should short as possible, to minimize the melt residence time in the barrel.
6. Screw speed and back pressure: if quality meets the premise of plastics, screw speed, and backpressure should be as low as possible and prevent the possible solutions down.
7. mold temperature: cooling system have a great impact on the quality of the product, so the mold temperature must precisely control the process, if possible, a higher mold temperature should be good.