(1) Defect characteristics
(2) Causes of defects and their elimination methods
The main reasons for the appearance of turbidity defects in plastic parts are due to the mold, process and raw materials, and their specific analysis is as follows.
1) Injection mold
(1) If the mold produced by the plastic manufacturer does not vent well, the gas in the cavity will cause the molten material to vibrate irregularly, resulting in turbidity on the surface of the plastic part. Therefore, the design of the exhaust system must be reviewed and the exhaust must be good.
(2) If the mold produced by the injection molding manufacturer uses a sharp bend at the bends and turns in the runner, the molten material will cause flow disturbance when flowing over, resulting in irregular flow and turbidity. Therefore, smooth transition should be used.
(3) If the cross-sectional area of the gate is very small and the flow rate is fast, it will aggravate the irregular flow of the molten material, resulting in turbidity on the surface of the plastic part. Therefore, the cross-sectional area of the gate should be appropriately increased.
(4) If the location of the gate is not correct, if the gate and the plastic part are at a sharp angle, this state makes the molten material flowing into the cavity flow irregularly, resulting in surface turbidity. Therefore, the gate position should be changed.
2) Plastic molding process
(1) If the molten temperature is too high, its fluidity is good, and it is easy to produce turbulence when the molten material flows at high speed, resulting in turbidity on the surface of the plastic part. Therefore, the molten temperature should be appropriately reduced.
(2) If the injection pressure is too high, it will also increase the fluidity and cause surface turbidity. Therefore, the injection pressure should be reduced.
(3) If a small amount of cold material enters the cavity, it will move along the cavity surface and cause surface turbidity. Therefore, the cold material well volume can be increased to accommodate all the cold material, or the mold temperature can be increased to produce less cold material.
(4) If the barrel temperature is too low, the molten material will not be plasticized well, and the plastic parts obtained will be prone to turbidity. Therefore, it should be adjusted to the required temperature.
(5) If the injection speed is too fast, a thin layer of milky turbidity will be produced on the surface of the plastic parts. Therefore, the injection speed should be reduced.
3) Raw materials
(1) If the lubricant is used too much, the fluidity of the molten material will increase, and the possibility of turbulence will increase, which will increase the chance of turbidity. Therefore, the amount of lubricant should be appropriately reduced.
(2) If a crystalline resin is used, its melting temperature is very high and the curing speed is very fast, which is prone to surface turbidity. Therefore, crystalline resins can be used less and non-crystalline resins can be used more.