After the screw barrel is used for a period of time, the screw edge and the nitrided layer of the barrel (when making a new screw, both the screw and barrel will be subjected to nitriding heat treatment, so there will be a nitride layer of about 30-60 filaments on the surface. ) It is worn in both directions, and the gap between the two sides increases, which leads to the problem of poor and unstable plastic products. Screw refurbishment is to increase the thickness of the screw edge on the old screw to fill in the gap to achieve the purpose of increasing the output.

　　 There are currently three main refurbishment methods in China:
　　 (1) Electric welding: electric welding with alloy electrode (20-30 yuan/kg)
　　 Disadvantages: not abrasion-resistant, easy to appear false welding, the surface is not smooth, there will be blisters, the pellets will stay in the screw, resulting in yellow small burnt blocks and black spots.
　　 (2) Spray welding: spray alloy powder with a special "acetylene-oxygen" spray gun (30-50 yuan/kg)
　　 Disadvantages: not wear-resistant, blisters, part of the alloy is not completely melted during the spray welding process, alloy powder will come out of the material in the process of use, resulting in material leakage and damage to the die
　　 (3) Surfacing welding: use "acetylene-oxygen" to completely melt the 300 yuan/KG imported alloy electrode on the screw
　　Advantages: Because it is melting, there is no false welding and blistering.

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