POM (Delrin/Acetal): Complete Processing & Properties Guide
Published: 2026-06-02
Polyoxymethylene (POM, acetal) is the preferred material for precision mechanical components requiring low friction, high stiffness, and excellent dimensional stability. Two grades exist: homopolymer (Delrin, -CH2O-) with slightly higher...
Polyoxymethylene (POM, acetal) is the preferred material for precision mechanical components requiring low friction, high stiffness, and excellent dimensional stability. Two grades exist: homopolymer (Delrin, -CH2O-) with slightly higher crystallinity and mechanical strength, and copolymer (Celcon, Hostaform) with better thermal stability and chemical resistance. POM's 1.8-2.5% mold shrinkage is among the highest for engineering thermoplastics — this must be compensated in tool design.
Critical processing warning: POM degrades exothermically above 230°C, releasing formaldehyde gas. Overheated POM can cause a rapid pressure spike in the barrel due to formaldehyde gas generation. Never shut down a barrel containing POM — purge with HDPE or a commercial purge compound first. The characteristic pungent odor of formaldehyde at the mold is the primary warning sign of overheating. Processing window: melt temperature 190-210°C, mold temperature 80-100°C for optimal crystallinity.
Technical Properties
| Density | 1.41 g/cm³ |
|---|---|
| Tensile Strength | 70 MPa |
| Melting Point | 175 °C |
| Shrinkage Rate | 1.8-2.5% |
| Flexural Modulus | 2.8 GPa |
| Hdt | 110 °C at 1.82 MPa |
Engineering Tool: Shrinkage & Cost Estimator
Calculate part weight, mold cavity dimensions accounting for shrinkage, and material cost — all locally in your browser.
Equivalents & Cross-References
| Equivalent / Alternate | Action |
|---|---|
| Delrin 500P | |
| Hostaform C9021 | |
| Tenac C |
Frequently Asked Questions
What is the difference between POM homopolymer and copolymer?
Homopolymer (Delrin) has ~5% higher tensile strength and stiffness. Copolymer (Celcon/Hostaform) has better thermal stability and chemical resistance, especially to hot water and bases. For most applications, copolymer is preferred unless the extra 5% mechanical performance is critical.
Can POM be overmolded with TPE?
No. POM's low surface energy and high crystallinity prevent adhesion to TPEs and most adhesives. Surface treatment (plasma, corona, or chemical etching) is required. If overmolding is needed, consider PA66 or PBT as the rigid substrate — these bond well with TPEs.
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References & Industry Standards
- ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
- UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
- MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
- ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org