The screw barrel is damaged due to various causes like
- The temperature of the raw material is low at the time of plasticization
- If there is any metal matter or many impurities in the raw material
- If the screw is run for a longer time
- The material used to make screw
- There is low precision in screw manufacturing and not proper heat treatment for hardened the thread working face
- If the screw is not suitable for forming the material like PVC molding need corrosion resistance
How to disassemble the molding machine?
There are special tools used for disassembling the screw and heavy hammer cannot be used. The disassembly steps are stated below:
First, remove the nozzle and connection between the nozzle and barrel
Then separate the screw back joint from the driveshaft
After that remove the connecting flange and push the screw forward
Now screw head is exposed to the barrel and remove screw head connection thread immediately
Then remove the check ring and seal ring from the screw
The disassembled nozzles, check rings, seal rings and screw should be cleaned with a copper brush and residual material is clean by a shovel
Then the molybdenum disulfide heat-resistant grease for each threaded joint before the next step
The screw which is not in service should be coated with protective oil and wrapped well
How to repair and replace the screw?
If the screw has slight wear or scratch on the working face it is repaired by oil stone or fine sand cloth for grinding
Now if the working surface of the screw is worn and the groove is deep, examine the cause and repair the fault to avoid similar problems occur again. Then repair the deep groove
If the thread of the screw is worn, matching clearance between screw and barrel is increased, the leakage of the melt is higher in operation, and injection volume is unstable. First, the outer circumference of the thread of the screw should spray with wear-resistant alloy. Then as per the size of the barrel grind, the screw for fitting required parts.
Now if the barrel is worn, the inner hole is increased after a repair, grinding after the screw to unable to match the gap requirement of the barrel and screw. The screw should be remanufactured. The outer diameter of the screw is processed as per the actual clearance of the barrel to match the clearance requires for two parts.
