For our bimetallic screw,we have adopted advanced technique (HP/HVOF) of surface harding process by the whole screw surface,WPT1 alloy with corrosion resistant suits for nylon,PVC ,PC,PMMA and so on.WPT2 alloy with corrosion resistant and high temperature resitant suits for magnetic powder,magnesium and alumium powder,bakelite injection and so on.WPT3 is compatible with WPT1 and WPT2.For our bimetallic,we have raised the proportion of tung- sten contained in alloy to 30% and 50% from the previ-ous 10%,and we also have increased the processing length to 4000mm from the previous length of 3000mm.