Polyacetal (POM, Delrin®) – copolymer and homopolymer
Precision engineering plastic: stiff, stable and low-friction up to about 100 °C
Polyacetal is the engineering plastic for precision parts: stiff, with low water absorption, excellent dimensional stability, low friction and excellent machinability. The copolymer (POM-C) resists hydrolysis and bases better; the homopolymer (POM-H, Delrin®) is stiffer and harder, with higher creep resistance.
Designations and equivalents
| System | Designation |
|---|---|
| Abbreviation (ISO 1043) | POM-C / POM-H |
| Trade names | TECAFORM AH natural (Ensinger); Ertacetal C (MCAM Europe); TECAFORM AD natural (Ensinger, Delrin resin); Ertacetal H (MCAM) |
Standards by product form
| Form | Standard |
|---|---|
| POM resins | ASTM D6778* |
| Extruded and molded shapes | ASTM D6100* |
| Food contact | FDA 21 CFR 177.2470; EU 10/2011 |
| Machined part to drawing | ISO 2768 tolerance or as per drawing |
Composition and filler
Pure polymer
| Component | Content |
|---|---|
| Polyoxymethylene (copolymer or homopolymer) | 100% |
Mechanical properties
Typical values from the stock-shape manufacturer's catalog, 23 °C (POM-C, POM-H); ISO/ASTM methods as per the source
| Property | Value |
|---|---|
| Tensile strength | POM-C: 67 MPa · POM-H: 79 MPa |
| Modulus of elasticity (tensile) | POM-C: 2,800 MPa · POM-H: 3,400 MPa |
| Elongation at break | POM-C: 32% · POM-H: 45% |
| Compressive strength | POM-C: 68 MPa · POM-H: 69 MPa |
| Hardness | POM-C: Shore D 82 · POM-H: Shore D 85 |
| Notched impact | POM-C: 8 kJ/m² · POM-H: 15 kJ/m² |
Typical physical and thermal properties
| Property | Value |
|---|---|
| Density | POM-C: 1.41 g/cm³ · POM-H: 1.43 g/cm³ |
| Maximum continuous service temperature | POM-C: 100 °C · POM-H: 110 °C |
| Maximum short-term temperature | POM-C: 140 °C · POM-H: 150 °C |
| Minimum service temperature | -50 °C |
| HDT (1.8 MPa) | POM-C: 100 °C · POM-H: 110 °C |
| Melting point or glass transition | POM-C: 166 °C · POM-H: 182 °C |
| Linear thermal expansion | POM-C: 140 µm/m·K · POM-H: 130 µm/m·K |
| Thermal conductivity | POM-C: 0.39 W/m·K · POM-H: 0.43 W/m·K |
| Water absorption (24 h) | POM-C: 0.05-0.1% · POM-H: 0.05 / 0.1% |
| Water absorption (saturation) | 0.8% |
| Dielectric strength | POM-C: 49 kV/mm · POM-H: 20 kV/mm |
| Flammability (UL 94) | HB |
Calculate the weight of Polyacetal (POM, Delrin®) – copolymer and homopolymer bar, plate or pipe →
Friction, wear and PV limit
| Property | Value |
|---|---|
| Dynamic coefficient of friction against steel | POM-C: 0.21 (dynamic, ASTM D3702) · POM-H: 0.2 (dynamic, ASTM D3702) |
| PV limit (pressure × velocity) | POM-C: 0.095 MPa·m/s (MCAM QTM 55007, dry against steel, safety factor 4:1 already applied; original 2,700 psi·ft/min) |
PV and friction depend on the test method, the mating surface (steel, stainless, roughness), lubrication and each manufacturer's safety factor: compare values from the same source and confirm by testing in critical applications.
Chemical resistance
| Medium | Resistance |
|---|---|
| Acids | Poor in strong acids (pH below 4) |
| Bases (alkalis) | Good in weak bases; strong bases unacceptable (MCAM) |
| Solvents | Good (ketones and esters acceptable); chlorinated solvents limited |
| Hydrocarbons and oils | Very good |
| Steam and hot water | Limited (the copolymer resists hot water better than the homopolymer) |
Stock forms and sizes
- Rod (round bar)
- Sheet (plate)
- Tube and bushing
- Raw material: rod (round bar), sheet (plate) and tube, cut to size
- Machined part to drawing or sample, in the same order as the metal parts
- Lot certificate of conformity; FDA/EU 10/2011 declaration when the grade allows
Service temperature, machining and assembly
| Item | Usual practice |
|---|---|
| Service temperature | Continuous service up to 100 °C, short peaks up to 140 °C; minimum -50 °C (unloaded; under load, limited by HDT and creep). |
| Annealing (stress relief) | Stress-relief annealing before precision machining. |
| Bonding and welding | Difficult to bond; ultrasonic welding is possible. |
| Machining | Excellent machinability, continuous chips; ideal for tight tolerances. |
Typical applications
- Precision gears, cams and rollers
- Tight-tolerance bushings and bearings
- Water pump and valve parts
- Food and packaging machinery parts
- Electrical and instrument components
Alternatives: Nylon for impact; PET for stability and wear in humid environments; PEEK above 100 °C.
Frequently asked questions
Which standards cover Polyacetal (POM, Delrin®)?
POM resins: ASTM D6778*. Extruded and molded shapes: ASTM D6100*. Food contact: FDA 21 CFR 177.2470; EU 10/2011. Machined part to drawing: ISO 2768 tolerance or as per drawing.
Up to what temperature can Polyacetal (POM, Delrin®) be used?
Continuous service up to 100 °C, short peaks up to 140 °C; minimum -50 °C (unloaded; under load, limited by HDT and creep).
Which materials can replace Polyacetal (POM, Delrin®)?
Nylon for impact; PET for stability and wear in humid environments; PEEK above 100 °C.
POM-C or POM-H?
POM-C for hot water, bases and general use; POM-H (Delrin) for higher stiffness, hardness and creep resistance.
Are polyacetal, acetal and Delrin the same material?
They are names for the same polymer, polyoxymethylene (POM). Delrin® is the trademark of the homopolymer.
