POM (Polyoxymethylene)
POM (polyoxymethylene, also polyacetal) is a semi-crystalline thermoplastic widely used as a gear material in precision and instrument engineering because of its good sliding properties, low moisture absorption, and high dimensional accuracy. Compared with metal gears it offers low noise, inherent corrosion protection, and weight savings, but has limited temperature and load capacity.
Properties and Advantages
POM is characterized by a low coefficient of friction (self-lubricating, especially POM-C with MoS2 additive), high rigidity compared with other thermoplastics, good chemical resistance, and excellent dimensional stability. In POM/steel or POM/POM mesh, the gearbox runs significantly quieter than an all-steel gearbox, as the plastic absorbs impact energy. Corrosion resistance allows use in moist environments without protective measures.
POM vs. Steel — Comparison as Gear Material
| Property | POM | Steel (hardened) |
|---|---|---|
| Noise | Very low | Higher |
| Load capacity | Limited (~70°C max) | High |
| Self-lubrication | Yes (especially POM-C) | No |
| Corrosion resistance | Yes | Only with coating/oil |
| Weight | Light (approx. 1.4 g/cm³) | Heavy (approx. 7.8 g/cm³) |
| Part cost | Low (injection-molded) | Higher (machined) |
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