What is UHMWPE?
UHMWPE (Ultrahigh Molecular Weight Polyethylene) is a thermoplastic engineering plastic with superior performance. Ultra-high molecular weight means that the average molecular weight is greater than 2 million.
Its advantages include extremely high abrasion resistance, impact resistance, low friction coefficient, good self-lubricating ability, low temperature resistance, corrosion resistance, non-toxic and odorless, etc. Excellent chemical and mechanical properties make UHMWPE sheet widely used in electric power, marine, coking, coal, paper, textile, chemical and other industries.
Ultra High Molecular Weight Polyethylene (UHMW) is one the most widely used thermoplastic materials today. It is defined as having a minimum molecular mass (molecule length) of 3.2 million; some resins go as high as 7.5 million (for reference, HDPE = ~1MM, LDPE = ~500,000)
UHMWPE advantages in its virgin form:
Easily modified, this base material is used in applications as diverse as cargo dock impact bumpers to dump truck liners to food equipment to orthopedic joint replacements. Essentially a poor mans Teflon®, it shares similar properties, with some significant limitations.
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Like PTFE, UHMW cannot be melt processed, as this breaks down the molecular chain. It is made using compression and heat to fuse the material below its melting point. It is available in compression molded sheets up to 8 x 20, and ram-extruded rod, tubes & profile shapes.
The largest industrial markets for UHMW are food processing and heavy equipment, both primarily for bearing & wear components. For such applications, the limitations versus nylon or acetal are:
Where food contact is not an issue, reprocessed UHMW is a cost effective alternative. Using clean regrind mixed with virgin black resin yields a material with the same low friction, low moisture absorption and impact resistance of virgin at lower material cost. Due to the inclusion of the larger regrind particles, it is actually slightly harder and some OEMs prefer it over virgin.
There many modifications of UHMW available, including colors; UV stabilized; lubricant filled (solid, oil or MoS2), ceramic filled; anti-static/conductive; metal/X-ray detectable; high temperature.
This last version needs come clarification. Some mills offer an anti-oxidant filled UHMW touted to withstand 275F HOWEVER -THE HEAT DEFLECTION TEMPERATURE IS THE SAME AS VIRGIN, 116F! What the 275F means is that, where pure virgin UHMW starts to oxidize (turn brown) over time @ ~175F, this version adds ~100F heat resistance before oxidation.
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Tom Connelly is a self proclaimed street engineer with over 40 years in the plastics industry.
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