The enemy of screw and barrel efficiency is wear and Tear. Screw wear is a result of the flow of plastic against the screw and barrel as well as metal contact between the flights and barrel evens some lots of engineering plastic lead a important role for wear of screw and barrel.
So, to enhance the life of a screw, wear resistance alloys are applied over the top of the flights. The thickness of such alloys varies from 1.2(0.05”) mm to 2.5(0.1”) mm. This method of application is known as “Hard Facing”. The different methods of applying hard facing are:
- Oxyacetylene Welding
- Tungsten Inert Gas (TIG)
- Plasma Transfer Arc (PTA)
- Metal Inert Gas (MIG)
Hard facing alloys are normally welded or on the top of the flights instead of the root and side of the flight. In extreme wear conditions, such as fiberglass fillers in processing, etc., welding of the roots and sides of feed and first transition can be justified.
The top of the flight of a screw is exposed to metal to metal rubbing contact with the barrel. Therefore, the integrity of hard facing alloy to the base of the flight is very important.