The main cause of discoloration and coking of injection molded products is that plastic or added ultraviolet absorbers, antistatic agents, etc. are decomposed in the cylinder, or decomposed and coked in the barrel for too long, and then injected with the melt. The cavity is formed. analyse as below:
1. Mold aspect:
There are improper oil release agents and lubricants in the mold. The mold is not exhausted, it is easy to burn, or the size of the pouring system is too small, and the shearing is too strong to cause coking. 3. Plastics: There are too many volatiles in plastics, too much humidity, too much impurities, too much recycled material, and pollution.
2. Machine side:
Due to the defects of the screw or the barrel, the melt card is further accumulated, and is subjected to long-term fixed heating to cause decomposition. The rubber head kit should be inspected for wear or metal objects inside or if the heating control system is out of control, causing the barrel to overheat and causing decomposition and blackening.
3. Processing: The barrel should be cleaned regularly to remove additives that are less resistant than plastic. If the pressure is too high, the speed is too high, the back pressure is too large, and the speed is too fast, the material temperature will be decomposed.
Layered peeling occurs: the injection speed is too low and should be slowed down appropriately. The material temperature is too low and the mold temperature is too low, causing internal stress and weld seams.
Swelling and bubbling: This is caused by the expansion of the gas released by the internal pressure of the plastic that is not completely cooled and hardened.
Solution: Reduce the filling speed, reduce the forming cycle and reduce the activity resistance. Progressive pressure and time. Improve the condition that the wall of the part is too thick or the thickness changes greatly. Effective cooling. Reduce the mold temperature, extend the mold opening time, and reduce the drying and processing temperature of the material.
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