PC injection molding troubleshooting
1. PC injection molding temperature should be according to the shape, dimension and mould structure of the PC components. Normally the molding temperature should be 270 to 320℃. if the temperature higher than 340℃, PC will become decomposition, the molded PC components surface appear silver line, gray line, black points, air bubbles and so on, in the same time, the physical function will go down.
2. PC injection moldingpressure effect molded PC components physical functions, stress, molded components shrinkage rate, also effect the PC components out looking and de-mold. Both of the low pressure injection or high pressure injection will cause the components occurred some shortcoming. The normal injection pressure is 80 to 120MPa. To the thin wall, longer runner and complex shape and small gate production, in order to make up for the pressure reduction, then we use high pressure for injection, the pressure ranges are from 120MPa to 145MPa.
3. PC injection molding process holding pressure and pressure holding time, the bigger or smaller pressure holding and longer or short pressure holding time effect the molded components stress too much, if the pressure is too small the components will occur the shrinkage marks, sink marks or vacuum bubbles. If the holding pressure is too much big, the gate area’s stress will be very big, during the PC injection molding processing, normally we use high barrel temperature and lower holding pressure to solve so many problems. The pressure holding time should be according with the molded components thickness, normally if the molded components is small volume or it is thin, then we do not need the long pressure holding time. Otherwise, we need longer time. The pressure holding time can be adjusted by the gate pressure sealing time.
4. PC injection speed obviously effect the molded PC components function, beside the small gate, long runner and deep molding area components should use high speed injection, normally we should use medium speed or low speed injection molding speed. And use multi-grade injection, normally should use slow – fast – slow this format.
5. PC injection moldingmold temperature, normally should be 80 to 100℃, to the complex, thin wall or high requirements molded pc components, we can increase the temperature from 100 to 120℃. But we the temperature can be exceeded to the range to make the mould deformed.
6. PC injection molding screw speed and backup pressure, due to the high viscosity of melted PC, in order to make good air venting and convenient for PC injection molding machine’s maintenance, to avoid the screw overloading, we should not make the screw RPM too big, normally should be 30 to 60RPM. The backup pressure should be 10-15%.
7. PC injection molding process should avoid to use de-,mold liquid, meaning while the recycled PC should be reused for more than 3 times. The recycled material percentage should be 30.
8. PC injection molding process has the special requirements to the plastic injection molding machines. Normally the real injection molding short weight should not be bigger then 75% of the machines theory short capacity, the machine’s screw should use single head equal screw thread, with Loop resistance gradient compression screw type. The screw L/D should be 15 to 20, geometric compression ratio ( C/R) should within 2-3.