Rebuilding Worn Screws and Barrels

In a correctly designed extruder, the majority of the wear should be concentrated on the screw because the screw can be replaced and rebuilt more easily than the barrel. In fact, the rebuilding of extruder screws has become so common that the rebuilding business has become a major segment of the extrusion industry. There are more than 70 companies in the U.S. involved in the rebuilding of extrusion equipment. For a number of these companies, screw rebuilding constitutes the major part of their business. 

One reason for the popularity of screw rebuilding is the fact that rebuilding is usually considerably less expensive than replacement with a new screw. Rebuilding is usually done with hardfacing materials. With the proper choice of hardfacing material, the rebuilt screw can be better than the original screw. It usually makes no 

Properties of several hardfacing materials are listed in Table 8.9 [104]. 

Product Base material Hardness Rc Cracking Tendency % Carbon % Chro- mium % Tungs- ten % Boron Cost/lb [ ] 

The screw is set up in a lathe and a center is found. At this time the screw is checked for straightness and concentricity  

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