UHMW (Ultra-High Molecular Weight) Polyethylene
Comprehensive technical specification for UHMW (Ultra-High Molecular Weight) Polyethylene, covering Canadian stock sizing, machining parameters, common defects, and handling guidelines for industrial fabrication and woodworking operations.
Material Overview & Common Uses
UHMW (Ultra-High Molecular Weight) Polyethylene is a linear polyethylene with a molecular weight typically between 3.1 and 5.67 million g/mol, offering exceptional abrasion resistance, low coefficient of friction (0.05–0.10), high impact strength, and excellent chemical resistance. It is self-lubricating, non-stick, and absorbs virtually no moisture (0.01% max). Common Canadian industrial applications include: conveyor wear strips, chute liners, guide rails, cutting boards, star wheels, medical prosthetics, food processing equipment, marine dock fenders, and snowmobile ski runners. It is widely used in fabrication shops, woodworking facilities, and machining operations across Canada due to its durability and ease of machining.
Core Technical Properties & Sizing
| Property | Value | Test Method |
|---|---|---|
| Density | 0.930–0.945 g/cm³ | ASTM D792 |
| Tensile Strength | 20–30 MPa | ASTM D638 |
| Elongation at Break | 300–500% | ASTM D638 |
| Impact Strength (Izod) | No break | ASTM D256 |
| Hardness | Shore D 60–70 | ASTM D2240 |
| Coefficient of Friction (static, vs. steel) | 0.05–0.10 | — |
| Melting Point | 130–136°C (266–277°F) | — |
| Continuous Service Temperature | -200°C to +80°C (-328°F to +176°F) | — |
| Water Absorption | <0.01% | ASTM D570 |
| Flammability | HB | UL94 |
| Dimension | Standard Canadian Sizes | Tolerances |
|---|---|---|
| Sheet Sizes | 48" x 96" (1220 x 2440 mm), 48" x 120" (1220 x 3050 mm), 60" x 120" (1524 x 3050 mm) | Length/Width: +1/4" / -0" for sheets up to 120" |
| Common Thicknesses | 1/8" (3.2 mm), 1/4" (6.4 mm), 3/8" (9.5 mm), 1/2" (12.7 mm), 3/4" (19.1 mm), 1" (25.4 mm), 1-1/4" (31.8 mm), 1-1/2" (38.1 mm), 2" (50.8 mm) | ±0.010" for ≤1/2", ±0.015" for >1/2" to 1", ±0.030" for >1" |
| Rod Diameters | 1/4" to 12" (6.4 mm to 305 mm) in 12' (3.66 m) lengths | — |
| Surface Finish | As-extruded (matte) or skived (glossy); typical Ra 20–60 µin (0.5–1.5 µm) for skived | — |
Machinability, Tooling & Feeds
| Operation | Tooling | Speed / RPM | Feed / IPM | Notes |
|---|---|---|---|---|
| Sawing (Sheet) | Carbide-tipped, 10–14 TPI | 3000–5000 SFM | — | 4–6 TPI for thick sections |
| Routing / CNC | Single-flute or O-flute carbide | 18,000–24,000 RPM | 100–200 IPM | Depth of cut 0.020–0.060" per pass |
| Drilling | HSS twist drill, 118° point angle | 2000–3000 RPM | 0.005–0.015 IPR | Use peck cycle |
| Tapping | Roll-form taps (no flutes) | — | — | Pre-drill 0.005–0.010" oversize |
Coolant: Air blast or mist (water-soluble) to prevent melting; avoid flood coolant. Clamping: Use low-pressure clamping or vacuum fixtures to avoid distortion. Deburring: Sharp edge break with a file or deburring tool; avoid excessive heat. Chip formation: Continuous stringy chips; use chip breakers or vacuum extraction.
Common Defects & Quality Control
| Defect | Description | Acceptance Criteria |
|---|---|---|
| Surface scratches / gouges | From handling or storage | Acceptable depth <0.010" for non-cosmetic parts |
| Warpage / bowing | Sheet flatness deviation | Maximum allowable bow 1/8" over 48" length |
| Black specks / contamination | Carbonized material from extrusion | Reject if >5 specks per square foot >0.020" |
| Voids / bubbles | Internal porosity from trapped gas | Reject if any void >1/16" diameter |
| Thickness variation | Measured at 4 corners and center | Reject if outside ±0.010" for ≤1/2" thickness |
| Edge cracks / delamination | Fissures along edges | Reject if crack extends >1/8" into sheet |
| Color inconsistency | Yellowing indicates UV degradation | Natural UHMW is milky white; reject if yellowed |
QC Inspection: Visual under 500 lux lighting, dimensional check with calipers and straightedge, hardness test with Shore D durometer (60–70 acceptable). For critical applications, perform impact test (ASTM D256) or tensile test (ASTM D638) on sample coupons.
Storage, Handling & Racking Guidelines
- Store UHMW sheets flat on a level, clean surface to prevent warpage.
- Maximum stack height: 24" for sheets up to 1/2" thick, 36" for thicker sheets.
- Use plywood or MDF separators between sheets to prevent scratching.
- Keep away from direct sunlight and UV sources to avoid surface degradation (yellowing, embrittlement).
- Ideal storage temperature: 10–30°C (50–86°F).
- Avoid storage near heat sources (radiators, furnaces) as UHMW expands significantly (coefficient of linear expansion ~1.5 x 10⁻⁴ /°C).
- For rod stock: store horizontally on racks with full-length support to prevent sagging; maximum unsupported span 48" for rods up to 2" diameter.
- Handling: use clean gloves to avoid oil transfer; lift sheets with two people for sizes >48" to prevent bending.
- Racking: use cantilever or A-frame racks for sheet storage; label with material grade, thickness, and date received.
- FIFO rotation recommended.
- For long-term storage (>6 months), wrap in opaque polyethylene film to protect from dust and UV.