PA66 Nylon Bearings — Tough, Cheap, Moisture-Sensitive

Polyamide 66 is a semi-crystalline polymer with a strong hydrogen-bonded structure: stiff when dry, tough in impact, and resistant to repeated loading. It is also hygroscopic. Water molecules push between the chains, acting as a plasticiser — the part grows, the modulus falls, and a bearing that had clearance when dry may have none after a humid month.

That single property decides where nylon belongs. In a dry indoor mechanism it is an excellent, cheap, quiet bearing. In a wet plant, POM or PEEK holds the fit and nylon does not.

• Light-duty dry mechanisms: domestic appliances, power tools, office equipment.
• Impact-loaded positions where POM would crack: casters, rollers, linkages.
• Bearing cages — glass-filled PA66 is the standard TN9/TVP cage material up to about 120 °C.
• Agricultural and outdoor equipment at low load, where moisture swell is tolerable.
• Rapid replacement parts where cost per piece dominates.

Design the clearance for the saturated condition, not the dry one, and check the interference fits: a nylon ring pressed into a steel housing can split when it swells. Glass-filled grades absorb less and expand less, at the cost of impact toughness. If the environment is wet and the clearance is tight, POM is the cheaper answer than a redesigned nylon bearing.

• Moisture absorption of 1.5–2.5% changes dimensions and closes clearance.
• Modulus falls sharply when wet — a wet nylon bearing is a softer bearing.
• 100 °C ceiling; strength drops quickly above 80 °C.
• UV degradation outdoors unless stabilised.
• Creep under sustained load, especially warm and wet.

1. State dry or wet service, and design the clearance for the saturated condition.
2. Say whether the part is a cage or a bearing ring — the requirements are different.
3. Give the temperature; above 100 °C a different polymer or a metal cage is needed.
4. Ask for the grade: unfilled, GF30 or MoS2-filled change friction and strength.