The Bimetallic screw is a kind of screw spray welding a 1-3mm thick alloy on the flight which has excellent corroion resistance, abrasion resistance and high working temperature. And its useful service life is gratly improved contrast to the common nitrided screw. Single Bimetallic Screw and Barrel has more obvious advantages when processing high calcium carbonate powder PVC mixture to enhance the avbrasion life. The company uses special alloy powders being sprayed and welded on the screw's rige, and uses different alloy and welding methods for the screw of different function.