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Reasons for screw damage
1. The temperature of the raw material is low when plasticizing.
2. The raw material is mixed with metal foreign matter or there are many impurities in the raw material.
3. The screw idle time is too long.
4. Unreasonable selection of screw materials.
5. The screw manufacturing precision is low, and the heat treatment hardness of the thread working surface is low.

Disassembly sequence of the screw
Special tools should be used when the screw is disassembled, and no heavy hammer is allowed. The specific disassembly steps are as follows.
1. Remove the nozzle and the connection between the nozzle and the barrel.
2. Separate the key connection at the rear of the screw from the drive shaft.
3. Remove the connecting flange and move the screw forward.
4. When the screw head is exposed to the barrel, immediately remove the screw head connecting thread (note: the threads here are generally left-handed).
5. Remove the check ring and sealing ring on the screw.
6. The disassembled nozzle, check ring, sealing ring and screw should be cleaned immediately with copper brushes and shovel tools while it is still hot. The special hard-to-clean sticky material should be heated in an oven at the lowest temperature that can soften the material, and then remove the residual material.
7. Assemble the parts on the screw together, and apply molybdenum disulfide heat-resistant grease to each threaded connection part to facilitate the next disassembly.
8. After the surface is cleaned, the screw that is not in use should be coated with protective oil, wrapped, and hung in a ventilated and safe place.

Repair and replacement of screw:
1. If the working surface of the screw is slightly worn or scratched, it can be ground and polished with oil stone or fine emery cloth.
2. When the working surface of the screw is severely worn and the scar groove is deep, the reasons for the wear of the screw should be checked and analyzed, and the fault should be eliminated to avoid similar phenomena again, and then repair the deep scar groove by repair welding. If the thread of the entire screw is severely worn, the matching gap between the screw and the barrel increases, the melt leakage increases during operation, and the injection volume is unstable, the outer circle of the screw thread should be thermally sprayed with wear-resistant alloy, and then according to the barrel. The actual size of the inner diameter, the screw grinding is carried out according to the requirements of the fitting clearance of the parts.
If the barrel is seriously worn, the diameter of the inner hole increases after the repair, and the grinding of the screw after spraying can no longer meet the requirements of the matching gap between the barrel and the screw, the screw should be remanufactured. The thread outer diameter of the screw should be processed according to the matching clearance requirements of the two parts and the actual inner hole diameter of the barrel.
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