Delrin vs UHMW
Delrin is a stiff, hard, precisely machinable acetal. UHMW-PE is a soft, waxy, extremely tough polyethylene that resists abrasion better than almost any other plastic and costs a fraction of the price. They both serve as wear parts, but at opposite ends: Delrin where the part must carry load and hold size, UHMW where it must slide, take a beating and be cheap.
The tell is the tolerance and the load. A part with a ±0.05 mm fit or a bolted joint that must stay tight wants Delrin. A chute liner, chain guide, wear strip or cutting board that only needs to be slippery and survive abuse wants UHMW.
| Property | Delrin (acetal) | UHMW-PE |
|---|---|---|
| Polymer | Acetal homopolymer (POM-H) | Ultra-high-molecular-weight polyethylene |
| Density | 1.41 g/cm³ | 0.93 g/cm³ |
| Tensile strength | ~69 MPa (10 ksi) | ~20-25 MPa (2.9-3.6 ksi) at yield; ~40 MPa (5.8 ksi) at break |
| Flexural modulus | ~2.8 GPa (410 ksi) | ~0.7-0.9 GPa (100-130 ksi) |
| Hardness | ~Rockwell M90 | ~Shore D 62-66 |
| Izod impact (notched) | ~75 J/m | No break |
| Abrasion resistance | Good | Excellent |
| Max continuous service | ~85 °C (185 °F) | ~80 °C (176 °F) |
| Machinability | Excellent, precise | Fair; soft, gummy, tolerance limited |
| Relative cost | Baseline | About 0.3-0.5x |
| Typical uses | Gears, bushings, precision fixtures | Chute liners, chain guides, wear strips, star wheels |
Typical values for the stated conditions. Confirm against the mill certificate and your spec.
Need a Delrin (acetal) or UHMW-PE part made?
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Decision matrix
A check marks the side with the edge on that dimension.
| Dimension | Delrin (acetal) | UHMW-PE |
|---|---|---|
| Machining | ✓ Excellent; holds ±0.05 mm | Fair; sharp tools, deflects, ±0.25 mm is realistic |
| Welding | Poor | ✓ Fair; hot-gas and hot-plate welding possible |
| Forming | Poor; machined or molded | ✓ Fair; heat-formed and pressed shapes |
| Strength | ✓ Stiff, creep resistant | Low stiffness, creeps under sustained load |
| Corrosion resistance | Good with fuels and solvents; not strong acids | ✓ Excellent; inert to most acids, bases and solvents |
| Finishing | ✓ Machined finish; paints poorly | Nothing sticks to it; machined finish only |
| Material cost | Baseline | ✓ Much cheaper per pound and per volume |
| Availability | Rod, plate, sheet | ✓ Sheet, plate, rod, tape, profiles in huge sizes |
Choose Delrin (acetal) when
- Gears, bushings, slides and fixtures with real tolerances
- Bolted or press-fit parts that must not creep
- Loads high enough that UHMW would cold-flow
- A hard, fine machined surface
Choose UHMW-PE when
- Wear liners, chain and belt guides, chute and hopper linings
- Impact and abrasion in sand, grain, gravel or ice
- Food and chemical contact with strong acids or caustics
- Large sheets or blocks where cost per part matters
Frequently asked questions
- Is UHMW harder than Delrin?
- No. Delrin is roughly three to four times stiffer and far harder (Rockwell M90 versus Shore D 65 territory). UHMW is soft and waxy, which is exactly why it resists abrasion and impact so well.
- Can UHMW be machined to tight tolerances?
- Not easily. It deflects, has a high thermal expansion and does not shear cleanly, so ±0.25 mm is a realistic shop tolerance on modest features. Delrin holds ±0.05 mm or better. Design UHMW parts with clearance.
- Which is better for a wear strip or slide?
- For a low-load sliding surface against abrasive product, UHMW: it is slipperier, cheaper and outlasts acetal in abrasion. For a loaded slide that must stay dimensionally true under a bolted preload, Delrin.
- Is UHMW cheaper than Delrin?
- Yes, by a wide margin, typically a third to a half of the price per pound and even less per volume because it is a third lighter. Machining time may erase some of that saving on small precision parts.
