What Are the Methods of Disassembly and Repair of Screws?

1. Reasons for the damage of screw elements


(1) The temperature of raw materials is low during plasticization.

(2) The raw materials are mixed with metal foreign matters or the raw materials contain many impurities.

(3) The running time of the screw components is too long.

(4) The choice of screw material is unreasonable.

(5) The manufacturing precision of the screw is low, and the heat treatment hardness of the working surface of the screw element is low.


2. The order of disassembly of screw elements


When removing the screw components, special tools should be used. It is forbidden to strike them with a heavy hammer. The specific disassembly steps are as follows:

(1) Remove the nozzle and the connection between the nozzle and the barrel.

(2) Separate the screw joint at the rear of the screw components from the drive shaft.

(3) Remove the connecting flange, and then push the screw forward.

(4) When the screw head is exposed in the barrel, please immediately remove the screw threads which connect screw head (note: most of the threads here are left-handed).

(5) Remove the stop ring and sealing ring from the screw.

(6) Remove the nozzle, check ring, sealing ring and screws. Immediately use a hot copper brush and spatula to clean up the remaining material. Adhesives that are particularly difficult to clean should be heated in the oven to soften the material, and then remove the residue.

(7) Assemble the parts on the screws, and then apply molybdenum disulfide heat-resistant grease on each threaded joint to facilitate the next disassembly.

(8) After cleaning the surface, the screws that are not used temporarily should be coated with protective oil, and then they should be wrapped and hung in a safe place.


3. Repair and replace screw elements


(1) If the working surface of the screw is slightly worn or scratched, please use oilstone or fine emery cloth to grind and repair the damaged parts.

(2) When the working surface of the screw is severely worn and the groove is deep, check the cause of the screw wear and eliminate the fault to avoid similar phenomena, and then repair the deep groove. If the threads of the entire screw are severely worn, the matching gap between the screw and the barrel will increase, the leakage of melt during operation will increase, and the injection volume will be unstable. The outer circumference of the screw thread should be thermally sprayed with wear-resistant alloy, and then the extruder barrel should be sprayed. According to the gap requirements of the parts, they should be screwed for grinding to change the actual size of the inner bore.


If the extruder barrel is severely worn, the diameter of the inner bore will increase after repair, and the grinding after spraying the screw components cannot meet the requirements of the matching gap between the barrel and the screw, so the screw should be remanufactured. The outer diameter of the screw thread should be processed according to the gap requirements of the two parts and the actual gap of the barrel.

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