POM Bearings — Acetal, Quiet Running, Dimensionally Stable

POM is a semi-crystalline acetal with a high degree of crystallinity, which gives it stiffness, low creep and excellent machinability — it turns and mills like brass. Its moisture absorption is roughly a tenth of nylon's, so a POM bearing made to a clearance stays at that clearance in a humid plant. Homopolymer (POM-H) is stiffer and stronger; copolymer (POM-C) resists hydrolysis better in warm water.

It is not a high-temperature material. Above about 90 °C continuous, stiffness falls and creep accelerates; above 140 °C it degrades. In hot water it hydrolyses, which is why pool and hot-wash applications belong to PEEK or PTFE rather than acetal.

• Light-duty conveyors, rollers and guide wheels at room temperature.
• Office and domestic equipment: printers, copiers, sliding mechanisms, hinges.
• Food handling at ambient temperature — POM grades are available with food-contact declarations.
• Textile and packaging machinery where dry running and low noise matter.
• Replacement for bronze bushings in low-load, low-temperature positions.

Nylon (PA66) is tougher and absorbs impact better, but it takes up 1.5–2.5% moisture and swells — which closes clearance and can seize a tight bearing. POM is stiffer, holds tolerance and has lower friction, but is more brittle under impact. In a humid or wet plant choose POM; in a dry plant with shock loads nylon may last longer.

• 90 °C ceiling; stiffness and creep degrade quickly above it.
• Hydrolyses in hot water and steam — not a washdown material.
• Brittle under impact compared with nylon.
• Low load capacity and significant creep under sustained load.
• Poor UV resistance; degrades outdoors unless stabilised.

1. Say POM-C or POM-H — copolymer resists warm water better, homopolymer is stiffer.
2. Give the running temperature; above 80 °C the allowable load drops sharply.
3. Specify clearance at operating temperature, not at 20 °C.
4. State whether food-contact documentation is needed, and for which grade.