This article will explain the issues about producing PC products in detail.
And this is the Part Two which includes the following 5 aspects:
Mold temperature control: 85 ~ 120 ℃, generally controlled at 80-100 ℃. For products with complex and thin shapes, and higher requirements, it can also be increased to 100-120 ℃, but can not exceed the mold thermal deformation temperature. With the high mold temperature, the temperature difference between mold and PC material can be reduced and also the internal stress of parts.
Screw speed and back pressure
Due to the high viscosity of the PC melt, to faciliate the plasticizing, exhaust, the maintenance of plastic machine and prevent the screw load from being too large, the speed of the screw mustn’t be too high. It’s generally controlled at 30-60r / min. And the back pressure should be controlled between 10-15% of the injection pressure.
Use of additives
The use of release agent should strictly be controled in the PC injection molding process. At the same time, the use of recycled materials can not exceed three times and the amount should be about 20%.
PC injection molding has high requirements on the mold
1) The design of the flow channel should be as thick and short with few bending positions as possible. Also, the round cross-section flow channel and ground and polished flow channel can reduce the flow resistance of the melt.
2) Any type of gate can be used for the injection gate, but the diameter of the water inlet can not less than 1.5mm.
Requirements for injection molding machines for the production of PC products
1)The maximum injection volume of products (including flow channels, gates, etc.) should not exceed 70-80% of the nominal injection volume;
2)Clamping pressure: 0.47 to 0.78 tons per square centimeter of the projected area of the finished product (or 3 to 5 tons per square inch);
3)Machine size: The best weight of the finished product is about 40 to 60% of the capacity of the injection molding machine. For example, when the machine expresses its capacity (ounce) in polystyrene, it needs to be reduced by 10%. 1 ounce = 28.3 grams
4)Screw: The screw length should be at least 15 diameters long, and its L / D best is 20: 1. The compression ratio is preferably 1.5: 1 to 30: 1. The check valve at the front end of the screw should be of slip ring type, and its resin flowable gap should be at least 3.2MM.