UHMW-PE is likely the best known plastic in the sawmill industry and with good reason. The material is relatively inexpensive, as engineering plastic goes, yet has a number of useful properties: impact strength, low coefficient of friction, and ease of machining among others. But no material is without its concerns or drawbacks. These are the top three concerns to be aware of:
1.) Thermal Expansion/Contraction
UHMW is not very dimensionally stable and expands and contracts with changing temperature. This is especially important when fabrication work is involved. For example, if the fabricator drills holes to your specifications for a wear guide at room temperature and the UHMW profile is installed in summer heat, the holes likely would not line up with your guide’s backing. The calculations can be done as follows:
Thermal expansion: (length) x (change in degrees F) x .0001
Thermal contraction: (length) x (change in degrees F) x .000078
It is always best to discuss the application environment with your distributor, however. Also, remember to let your distributor know you have an outdoor application so material with a UV-stabilizer can be quoted!
UHMW does not do well with abrasive materials impacting on an angle. For example, if you have a conveyor where wood chips are propelled into a wear strip on an angle you do not want to use UHMW. Polyurethane is a much better alternative.
This concern might be surprising to some. UHMW is available in a variety of grades with differing quality. The mostpopular is the black reprocessed material. It is a good plastic; however, as a recycled material with additives it does not have the same properties as the more expensive white virgin and premium Tivar 88 or Titanium grades. In particular, there have been a number of applications where reprocessed and virgin UHMW have had limited success. However, a switch to the higher quality Redco Titanium has performed very well in the same application, with a value that far exceeds the cost difference between grades.
The take away point is not all UHMW is created equal!