Acetal (POM) is the low-friction, dimensionally stable resin for gears, bushings, clips, fuel system parts and conveyor parts. Homopolymer is a little stiffer and stronger. Copolymer holds up better in hot water and chemicals and is easier to process.
Typical Acetal (POM) properties
| Property | Copolymer | Homopolymer | Test method |
|---|---|---|---|
| Density | ~1.41 g/cm³ ~0.051 lb/in³ | ~1.42 g/cm³ ~0.051 lb/in³ | ASTM D792 / ISO 1183 |
| Tensile strength | 60–65 MPa 8,700–9,400 psi | 68–75 MPa 9,900–10,900 psi | ASTM D638 / ISO 527 |
| Flexural modulus | 2.5–2.8 GPa 363,000–406,000 psi | 2.8–3.1 GPa 406,000–450,000 psi | ASTM D790 / ISO 178 |
| Notched Izod impact | 50–80 J/m 0.9–1.5 ft·lb/in | 65–120 J/m 1.2–2.2 ft·lb/in | ASTM D256 |
| Heat deflection, 1.8 MPa (264 psi) | 95–110°C 203–230°F | 110–125°C 230–257°F | ASTM D648 / ISO 75 |
| Water absorption, 24 h | 0.20–0.22% | ~0.25% | ASTM D570 / ISO 62 |
| Mold shrinkage | 1.8–2.2% 0.018–0.022 in/in | 1.7–2.2% 0.017–0.022 in/in | ASTM D955 / ISO 294-4 |
Typical ranges for standard grades, dry as molded, from published data sheets. Your grade’s own data sheet and the lot COA are what count. Notched Izod uses 3.2 mm (1/8 in) bars.
Processing and drying
| Processing | Copolymer | Homopolymer |
|---|---|---|
| Melt temperature | 370–446°F / 188–230°C / never above 460°F / 238°C | Optimum 419±10°F / 215±5°C / keep below 446°F / 230°C |
| Mold temperature | 140–250°F / 60–121°C | 176–248°F / 80–120°C |
| Drying | 180–248°F / 82–120°C, 3–4 h | 176°F / 80°C, 2–4 h; toughened 4–8 h |
| Target moisture | No published maximum / Dry only if exposed to moisture | Dry only above 0.2% / Toughened <0.05% |
| Max barrel residence | 15–20 min above 380°F | >30 min at 419°F / ~8 min at 464°F |
| General | Copolymer | Homopolymer |
|---|---|---|
| Clarity | Opaque | Opaque |
| Chemical resistance | Very good: fuels and solvents; strong acids attack it | Very good: fuels and solvents; strong acids attack it |
Starting points only. See the full processing temperature chart and drying guide for every resin.
What changes these numbers
- Overheating releases formaldehyde. Keep the melt in its window, purge before long stops, and never let acetal and PVC meet in the same barrel.
- High shrinkage. About 1.7–2.2%, and molds are cut for it. A switch between homopolymer and copolymer can change part size.
- Moisture. Acetal barely absorbs water, so parts hold their size. Most standard grades mold without drying.
- Friction grades. Lubricated grades with PTFE or silicone cut friction and wear further.
Common Acetal (POM) grades
- Copolymer
- Homopolymer
- Low-friction lubricated grades
- Glass-filled grades
- Toughened grades
- UV-stabilized grades
- Food-contact grades
Common questions
What is the density of acetal?
About 1.41–1.42 g/cm³ (0.051 lb/in³).
Acetal homopolymer or copolymer?
Homopolymer is stiffer and stronger with higher heat deflection. Copolymer has better resistance to hot water and chemicals and a wider processing window. See homopolymer vs. copolymer.
Does acetal need drying?
Standard grades usually do not. Toughened grades do: about 80°C for 4–8 hours.
Need Acetal (POM), or something close?
A polymer chemist reviews every request, then matches your grade or finds a qualified equivalent and prices it.
What to send for an accurate quote
- The grade name, from any supplier, or a data sheet
- Color (natural, black or a custom match)
- Fill type and percentage, if any
- Melt flow, if you know it
- Quantity for this order and what you use in a year
- Ship-to city and state or province