When a metal part wears out, corrodes or needs constant grease, an engineering plastic is often the fix. Bushings, gears, wear strips, rollers, valve seats and guides all run quieter, lighter and longer in the right plastic.
The trick is choosing the right one. Acetal, nylon, UHMW and PTFE all look like white plastic on the shelf, but they behave very differently in a machine. Here's how we help customers choose.
Acetal (POM), including Delrin®
Acetal is the machinist's favorite. It cuts like brass, holds tight tolerances and stays dimensionally stable because it absorbs very little moisture.
Strengths: stiff and strong, low friction, good wear resistance, excellent dimensional stability, great machinability, good resistance to fuels and solvents.
Limits: attacked by strong acids and oxidizers, including chlorine at higher concentrations. Not a good choice for continuous service above roughly 180°F. Can't be solvent bonded.
Homopolymer vs. copolymer: Delrin® is an acetal homopolymer; it's slightly stiffer and stronger. Copolymer acetal (such as Ensinger's TECAFORM®) has better chemical resistance and is less prone to centerline porosity, the small voids that can appear in the center of thick homopolymer rod. For thick parts or parts that contact hot water or cleaning chemicals, copolymer is often the better pick.
Typical parts: precision gears, bushings, valve components, pump parts, fixtures, jigs, food-processing parts and prototypes.
Nylon
Nylon is tough, wear-resistant and handles shock loads well, which is why it's used for heavy-duty gears, sheaves and wear pads.
Strengths: high toughness and fatigue resistance, good wear and abrasion resistance, good for impact and shock loading, available as extruded rod and sheet or as cast nylon in large shapes.
Limits: absorbs moisture. As it does, it swells and gets softer, which can throw tight tolerances off. Parts that must hold close dimensions in humid or wet service may be better in acetal.
Filled grades: oil-filled and moly (MoS2) filled nylons improve self-lubrication and wear. Glass-filled nylon adds stiffness and strength.
Typical parts: sheaves, large gears, wear pads, rollers, bushings in heavy equipment, and structural parts.
UHMW polyethylene
Ultra-high-molecular-weight polyethylene is the abrasion champion. It slides easily, shrugs off impact and is the least expensive of the four.
Strengths: outstanding abrasion resistance, very low friction, high impact strength (even at low temperatures), excellent chemical resistance, doesn't absorb water, and FDA-compliant grades for food contact.
Limits: soft and flexible, so it can't hold tight tolerances. It has high thermal expansion and creeps under sustained load. It can't be glued or painted easily. Keep service temperatures below roughly 180°F.
Typical parts: chute and hopper liners, wear strips, chain guides, conveyor components, dock bumpers, cutting boards and star wheels.
PTFE (Teflon®)
PTFE has the lowest coefficient of friction of any solid plastic and is nearly chemically inert.
Strengths: lowest friction, resists almost every chemical, wide service range (from cryogenic temperatures up to roughly 500°F), excellent electrical insulation, non-stick.
Limits: soft, with poor creep resistance (cold flow) under load, low wear resistance unless filled, and expensive. Its high thermal expansion and softness make tight tolerances challenging. Filled grades (glass, carbon, bronze) improve wear and creep.
Typical parts: seals, gaskets, valve seats, chemical-handling components, bearings in corrosive environments, slide plates and electrical insulators.
Side-by-side comparison
| Property | Acetal | Nylon | UMHW | PTFE |
| Machinability / tolerance | Excellent | Good | Fair | Fair |
| Wear / abrasion | Very good | Very good | Excellent | Fair (unfilled) |
| Friction | Low | Low–moderate | Very low | Lowest |
| Moisture absorption | Very low | High | None | None |
| Max continuous use temp | ~180°F | ~200°F | ~180°F | ~500°F |
| Chemical resistance | Good | Good | Excellent | Outstanding |
| Impact strength | Good | Moderate | Lowest | Highest |
Values are typical and vary by grade. Always check the manufacturer's data sheet.
A quick decision guide
- Need tight tolerances in a wet or humid environment? Acetal.
- Need toughness and shock resistance in a large part? Nylon, especially cast nylon.
- Need to survive sliding abrasion at low cost? UHMW.
- Need chemical resistance, high heat or the lowest friction? PTFE.
- Food contact? All four come in food-compliant grades. Ask for the specific grade.
Machining tips we've learned
- Keep tools sharp and use positive rake geometry. Dull tools generate heat, which causes melting and poor finishes.
- Plan for thermal expansion. Plastics expand far more than steel. A part measured hot off the machine may shrink out of tolerance once it cools.
- Let stock acclimate before final machining, especially nylon, which changes size as it absorbs moisture.
- Stress-relieve thick or heavily machined acetal and nylon parts to keep them flat and stable.
- Allow for moisture in nylon designs, or switch to acetal when the tolerance matters.
From stock shapes to finished parts
Colorado Plastic Products stocks acetal, nylon, UHMW and PTFE in sheet and rod, including Ensinger engineering plastics, and sells rod by the foot so you buy only what you need. Our shop machines prototypes and production parts from all four. Browse engineering plastics in our online store and add them to a quote, or send us your drawing or the worn-out part, and we'll recommend a material and quote the finished part.
