Yes, acetal plastic is widely used in injection molding and is one of the most popular engineering thermoplastics for producing precision mechanical parts. Sold in granule form specifically for injection molding and extrusion, acetal (also called polyoxymethylene or POM) combines high stiffness, dimensional stability, and a naturally low-friction surface that makes it ideal for parts that move, slide, or bear loads.
Why Acetal Works Well for Injection Molding
Acetal is a semicrystalline thermoplastic, which means it melts cleanly and flows predictably into mold cavities. That crystalline structure gives finished parts tight tolerances and minimal warping, two things that matter when you’re producing gears, bearings, or any component where a fraction of a millimeter counts. Parts come out of the mold with a smooth, hard surface that resists wear without needing secondary finishing.
The combination of properties is hard to match with other plastics. Acetal delivers high tensile strength under load, excellent stiffness so parts don’t flex when they shouldn’t, and a naturally slippery surface that lets components slide against each other with minimal friction and energy loss. That low friction also reduces wear over time, extending part life in assemblies with continuous motion.
Homopolymer vs. Copolymer Acetal
Acetal comes in two main grades, and which one you choose affects what you can do with the molded part.
Homopolymer acetal (POM-H) has a single repeating molecular unit, giving it higher tensile strength, greater impact resistance, and better creep resistance than the copolymer version. It’s also stiffer, with a higher flexural modulus at both room temperature and elevated temperatures. If your part needs to hold its shape under sustained mechanical load, homopolymer is the stronger option.
Copolymer acetal (POM-C) introduces a second monomer into the polymer chain, which creates longer hydrocarbon linkages and more space between the oxygen atoms that are most vulnerable to heat and oxidation. That molecular spacing makes copolymer more resistant to thermal and oxidative degradation. It also handles a broader range of chemicals, which is why it’s often preferred for parts exposed to harsh environments or elevated temperatures over long periods. For most general-purpose injection molding, copolymer is the more common choice because of its wider processing window and better chemical tolerance.
Design Guidelines for Acetal Parts
Acetal has specific design parameters that differ from commodity plastics like polypropylene or ABS. Recommended wall thickness for injection-molded acetal parts ranges from 0.76 mm to 3.05 mm (0.030 to 0.120 inches). Staying within that range helps ensure the melt fills the cavity evenly and the part cools without sink marks or voids.
Uniform wall thickness matters more with acetal than with many other resins. Abrupt thickness changes create uneven cooling, which can lead to internal stresses and warping in a material this crystalline. Where walls do transition, a gradual taper works best. Draft angles of at least 0.5 degrees on vertical surfaces help the part release cleanly from the mold, though slightly more draft is common for deeper features.
Chemical Resistance and Limitations
One of acetal’s biggest selling points for molded parts is its resistance to fuels and organic solvents. It earns top compatibility ratings with diesel fuel, unleaded and leaded gasoline, jet fuel, kerosene, and transformer oil. It handles common solvents like acetone, ethanol, isopropyl alcohol, benzene, chloroform, and mineral spirits without degrading. That fuel resistance is a major reason acetal shows up so often in automotive fuel system components.
Acids are a different story. Acetal is highly sensitive to most acids, including acetic acid, nitric acid (even at low concentrations), sulfuric acid, hydrofluoric acid, and chromic acid. Contact with these substances causes rapid degradation. Strong bases present a mixed picture: acetal resists potassium hydroxide and sodium hydroxide at moderate concentrations, but fails against calcium hydroxide, liquid ammonia, and concentrated sodium hydroxide. If your application involves acidic fluids, acetal is not the right material.
Common Injection-Molded Acetal Parts
The combination of strength, low friction, and dimensional precision makes acetal a go-to for mechanical components across industries:
- Gears and bearings: The low-friction surface and high stiffness let acetal gears run quietly against metal or other plastic gears with minimal lubrication. Bearings and bushings benefit from the same wear resistance.
- Rollers and guides: Belt feeds, conveyor guides, and rollers rely on acetal’s smooth surface to move materials without sticking or excessive friction.
- Fasteners: Clips, snaps, and threaded inserts molded in acetal hold up under repeated assembly and disassembly cycles.
- Automotive parts: Fuel sender units, valve components, door lock mechanisms, and window regulator parts all take advantage of acetal’s fuel resistance and mechanical stability.
You’ll also find acetal in consumer products like zipper sliders, pen mechanisms, and coffee machine internals, anywhere a small part needs to be precise, durable, and low-friction without costing as much as metal.
How Acetal Compares to Other Molding Resins
Nylon is acetal’s most frequent competitor in injection molding. Both are engineering thermoplastics used for mechanical parts, but they behave differently. Nylon absorbs moisture, which causes parts to swell and shift dimensionally after molding. Acetal absorbs very little water, so parts stay true to their molded dimensions in humid or wet environments. On the other hand, nylon offers better impact resistance and can handle higher temperatures before softening.
Compared to ABS or polycarbonate, acetal trades some toughness and aesthetic versatility for superior stiffness, chemical resistance, and self-lubricating properties. You wouldn’t choose acetal for a housing that needs to look good on a shelf, but for the mechanical guts inside that housing, it’s often the better pick.