Overview
UHMW (ultra-high molecular weight polyethylene) is the toughest commercial plastic by impact strength — standard Izod tests don’t break it. It’s slippery (coefficient of friction 0.10–0.20), absorbs essentially no moisture, resists nearly every chemistry an industrial environment can throw at it, and machines decently. The cost is competitive with commodity polymers like PP and HDPE.
The downside list is real: low stiffness (modulus ~0.7 GPa versus POM’s 3 GPa), high thermal expansion (CTE 2× POM, 7× aluminum), low maximum service temperature (~82°C continuous), and essentially unbondable surfaces (UHMW’s chemical inertness is exactly what makes it slippery — and what makes adhesives slide off). UHMW is a wear-and- impact specialist, not a structural plastic.
The classic UHMW selection criteria: impact, abrasion, or chemical resistance in a wet/cold environment where the part doesn’t need to hold tight tolerances and doesn’t see sustained load. Truck bed liners, chute liners, dock fenders, conveyor wear strips, ice rink boards.
Manufacturing — UHMW is not injection-moldable
This is the single most important production fact about UHMW that non-plastics-engineers often miss: true UHMW cannot be injection molded. Its molecular weight (>3 million g/mol) makes the melt viscosity too high to flow through gates and runners. Stock shapes (sheet, rod, plate) are produced by:
- Compression molding — UHMW powder loaded into heated platen press at 200–230°C under pressure, then cooled slowly. Standard process for sheet stock up to 60″×120″.
- Ram extrusion — UHMW powder forced through a die at temperature and pressure. Standard process for rod and tube up to ~10″ diameter.
When someone says “injection-moldable UHMW,” they almost always mean HMWPE — high-molecular-weight polyethylene at ~250k–500k g/mol, which has properties between HDPE and true UHMW. HMWPE injection molds but loses much of UHMW’s signature impact and abrasion resistance. Verify the molecular weight on any “moldable UHMW” datasheet before specifying.
Machining notes
UHMW machines well, with two consistent gotchas:
- Heat is the enemy. UHMW melts at 130°C. Aggressive cuts without coolant generate enough localized friction heat to smear, gum, and melt the surface. Flood coolant or generous chip clearance solves it.
- Workholding is hard. UHMW is so compliant that clamping pressure deflects parts. Use distributed clamping (vacuum tables, fixture jigs), minimal vise force, and wax-based holding for thin parts.
Practical recipe:
- Sharp HSS or carbide, positive rake, generous relief angles
- Speed: 500–1500 SFM
- Feed: 0.005–0.020 in/rev — slower feeds produce stringy chips
- Coolant: flood emulsion strongly recommended
- Tool wear is minimal; UHMW doesn’t abrade tooling
Surface finish maxes out around 16 Ra — UHMW’s softness makes finer finishes hard to achieve and not very meaningful in service (the surface deforms under any contact pressure).
Variant selection guidance
- Virgin UHMW (Tivar 1000 / Polystone M / GUR) — the default. Food contact, general wear strips, marine fenders. FDA compliant.
- Reprocessed UHMW — non-critical industrial applications where cost is the driver. Properties slightly lower, not FDA.
- LubX C / Tivar HPV — high-speed sliding where slip-stick matters. Conveyor lines, packaging machinery.
- MD/XDT — food-industry parts that could fragment into product stream. Blue color + detectable.
- GF-MPG — when stiffness matters more than impact (rare for UHMW — if you need stiffness, you probably want POM or PA66 instead).
- Outdoor black / Tivar Marine — anything in continuous sunlight. Carbon pigment is the UV stabilizer.
Failure modes worth designing around
Creep is the #1 design issue. UHMW deforms permanently under sustained load even at room temperature, well below its yield stress. Parts under continuous compression (gasket seals, bearing pads under static load) will cold-flow over months to years. Either accept the deformation, use springs/preload to compensate, or pick a stiffer material.
Thermal expansion is 2× POM’s. A 1-meter UHMW part that sees a 40°C temperature swing changes length by 8mm. For fitted parts or assemblies spanning thermal cycles, design with expansion gaps and floating mounts rather than rigid constraints. The classic failure mode: UHMW chute liner bolted rigidly to a steel frame, gets hot in the sun, buckles.
Softening above 80°C is harder than it sounds because UHMW’s strength falls off rapidly between 60°C and the 80°C continuous-service limit. Published high-temperature data varies across sources, but the consensus is a major property reduction (50%+ tensile loss is documented in multiple distributor datasheets) by the time the material reaches its nominal max-service temperature. Don’t push the temperature — UHMW does not have the gradual high-temperature shoulder that POM or PA66 do.
Bonding doesn’t work without surface treatment. Plasma activation, flame treatment, or chromic acid etch can prepare UHMW for adhesives, but the design-stage assumption “I’ll just glue it” leads to field failures. Plan for mechanical fasteners.
Applications by industry
- Material handling — chute liners, hopper liners, truck bed liners, conveyor wear strips, idler sprockets. The #1 application space. Mining, bulk material, agriculture all run on UHMW liners.
- Food and beverage processing — conveyor parts, cutting boards, wear strips. UHMW’s combination of FDA compliance, low friction, and chemical resistance is unbeatable in this space.
- Marine — dock fender pads, pile guards, boat slide pads, ice rink boards. UHMW doesn’t rot, swell, or corrode — replaces wood and steel in wet environments.
- Packaging machinery — high-speed conveyor components, star wheels, guide rails, dead-plates. Low friction + low cost + machinability.
- Pulp and paper — wear strips, scraper blades, doctor blades.
- Medical — orthopedic joint replacements (hip and knee bearing surfaces are typically UHMW), surgical instrument handles. Medical UHMW is a specific grade with extreme purity requirements.
- Recreation — ski bases (sintered UHMW is standard), ice rink surfaces, skateboard bushings.