How does temperature affect nylon bushing performance?

How does temperature affect nylon bushing performance? — 7 practical questions for buyers

Below are seven long‑tail, buyer‑focused questions often asked by engineers procuring nylon (PA6/PA66) bushings. Each answer is technical, actionable, and oriented to procurement and specification—covering when a part will fail, what to specify to suppliers, and which tests or design changes reduce thermal risk.

1. At what temperature range will a nylon bushing start to lose significant load‑bearing capacity, and how should I specify allowable temperature in procurement?

Key points:

• Nylon’s glass transition temperature (Tg) for typical PA6/PA66 is roughly 40–70°C; above Tg stiffness and modulus begin to drop noticeably. Melting occurs much higher (~215–265°C depending on grade), but mechanical performance is already degraded long before melting.
• For unfilled nylon (standard injection grades) continuous service is commonly limited to ~80°C. For glass‑reinforced PA66 (e.g., 30% glass), continuous service can be extended toward ~100–120°C depending on the specific compound and load condition.
• Procurement recommendation: specify a continuous operating temperature and a short‑term peak temperature. Example: service temp 0–80°C continuous, allowed short peaks to 120°C for <1 hour per day. Require supplier material datasheet with mechanical properties at 23°C and at the elevated service temperature (e.g., tensile/compressive strength at 80°C).

Why this matters: modulus and yield strength decline with temperature, so a bushing sized for room temperature may deflect and creep under the same load at elevated temperature. Require design verification testing at the expected maximum working temperature.

2. How does temperature change wear rate and friction of nylon bushings in dry vs lubricated systems?

Key points:

• Higher temperature generally reduces hardness and resin shear strength, which can increase wear rate and tendency for adhesive wear when sliding against metal. The coefficient of friction often increases slightly with temperature for unfilled nylon under comparable loads.
• Lubrication behavior changes: oil/grease viscosity falls with temperature, which can reduce hydrodynamic film thickness and increase boundary contact. Some self‑lubricating fillers (e.g., PTFE, graphite) preserve low friction across a wider temperature range.
• Procurement recommendation: for elevated temperatures, specify a compound with high‑temperature stabilizers and/or solid lubricants (PTFE/graphite). Request supplier wear test data (ASTM G133 or DIN wear tests) at the temperature(s) of interest and against the shaft material/finish actually used.

Design tip: If the application is dry running and near the upper service temperature of nylon, prioritize PTFE‑filled or specialty high‑temp polymer bushings, or consider alternative polymers (e.g., PEEK) if continuous temperatures exceed ~120–150°C.

3. How should I account for thermal expansion when fitting nylon bushings in metal housings (what clearance/interference should I order)?

Key points:

• Typical coefficient of linear thermal expansion (CLTE) for nylon is roughly 70–120 x10^–6/°C, while steel is ~10–20 x10^–6/°C. That means nylon expands substantially more than the metal housing as temperature rises.
• If bushings are press‑fit at room temperature and then exposed to higher service temperatures, radial interference can relax or the bushing can create high contact stress. Conversely, if fitted hot then cooled, they can tighten.
• Procurement/specification guidance:
  
  • Provide the supplier with the assembly and max service temperatures and specify whether the fit is press, slip, or floating.
  • For standard nylon bushings, consider specifying a light interference or transition fit at installation temperature with allowances for CLTE difference. For many small bushings, designers use clearances in the range of 50–200 µm (0.05–0.2 mm) depending on diameter and expected delta‑T—exact value must be calculated from part geometry and expected ΔT.
  • Require supplier to provide thermal growth calculations or recommend using an engineered interference (supplier should validate by test or FEA).

Actionable check: ask the vendor to quote the recommended installation temperature and the maximum recommended operating ΔT for the proposed fit tolerance.

4. How does temperature interact with moisture absorption to change bushing dimensions and strength—and how should I specify conditioning?

Key points:

• Ambient moisture changes nylon properties significantly. Typical moisture uptake for amorphous PA6 can be ~1–3% by weight in equilibrium with humid air; PA66 usually absorbs a bit less but still measurable (exact numbers depend on grade and fillers).
• Moisture generally reduces modulus and tensile strength but increases ductility and impact resistance. Temperature affects both the rate of moisture absorption and the equilibrium moisture content.
• Procurement/specification guidance:
  
  • Specify the expected environmental humidity range and whether parts should be supplied conditioned (e.g., dried) or equilibrated to typical service humidity.
  • Ask suppliers to provide dimensional tolerances in both dry and conditioned states, and provide mechanical data for both dry and humid conditions (e.g., tensile and compressive strength at 23°C dry and 23°C saturated).
  • For precision fits, request pre‑conditioning (controlled humidity soak) before final machining or order compensations for hygroscopic expansion.

Practical note: If you require tight bearing clearances, either machine after final conditioning or specify a non‑hygroscopic or low‑absorption polymer compound.

5. What are safe short‑term/high‑temperature limits (assembly, sterilization, paint baking) for nylon bushings without permanent damage?

Key points:

• Short‑term exposure at temperatures above the continuous service limit can be tolerated to some extent, but thermal oxidation and loss of crystallinity begin to accelerate at higher temps. Many nylon compounds can tolerate brief exposures to 120–150°C without visible melting, but performance (creep resistance, color, surface finish) can be affected.
• If a process (e.g., powder coat curing, sterilization) requires elevated temperatures, specify maximum allowed cycle temperature and duration. Require that the supplier certify that the specified compound and geometry are compatible with those cycles.
• Procurement test: ask for short‑term thermal aging data (e.g., tensile/compression after X hours at specified temp) or require you to be supplied with sample parts for the exact thermal cycle used in production.

Conservative practice: avoid exposing standard nylon bushings to repeated cycles above ~120°C. For repeated or continuous exposure above ~100–120°C, select high‑temperature polymers or specially stabilized nylons.

6. How does temperature affect creep and fatigue life of nylon bushings under sustained or cyclic loads?

Key points:

• Creep (time‑dependent deformation under load) is strongly temperature dependent. At higher service temperatures (especially above Tg) creep rates accelerate and permanent deformation under compressive loads can reduce bearing clearance tolerance and increase friction.
• Fatigue under cyclic loads also worsens with temperature due to reduced modulus and local softening; micro‑creep can accumulate over cycles causing dimensional drift.
• Procurement/specification guidance:
  
  • Specify expected static and dynamic loads, duty cycle, and operating temperature profile. Request long‑term creep test data (creep modulus or strain vs time) at the specified temperature and load.
  • For heavy or sustained loads at elevated temperature, require reinforced grades (glass fiber) or alternative high‑performance polymers (e.g., PEEK) with published creep data.
  • Ask for recommended safety factors and expected life estimates under specified temperature and load based on supplier test data.

Design tip: Use finite element analysis including viscoelastic creep properties when bushings are critical to alignment or clearance under load.

7. When should I specify heat‑stabilized or reinforced nylon vs choosing a different polymer (e.g., PEEK) for high‑temperature applications?

Key points:

• Reinforced nylons (glass‑filled PA66) are cost‑effective up to around 100–120°C continuous service when elevated stiffness and reduced creep are required. They also have lower moisture absorption and better dimensional stability than unfilled grades.
• If continuous service exceeds ~120°C or repeated exposure to >150°C is expected, consider higher‑temperature polymers such as PEEK, polyimide (PI), or high‑temperature PTFE blends. These materials retain mechanical properties at much higher temperatures but cost more.
• Procurement checklist:
  
  • List continuous and peak temperatures, loads, lubrication, environment (chemicals, humidity), and desired lifetime cycles in RFQs.
  • Request alternative material proposals from vendors and require comparative performance data (mechanical at temp, wear tests, creep tests, thermal aging).
  • Ask suppliers for cost vs performance tradeoffs, lead times for specialty grades, and sample testing programs.

Bottom line: specify the performance envelope, not just the material name. This allows suppliers to propose the best grade—standard PA6, glass‑filled PA66, PTFE‑filled PA, or PEEK—based on measured performance at the stated temperatures and loads.

Practical procurement checklist for temperature‑sensitive nylon bushings

• State continuous and peak service temperatures explicitly in RFQs.
• Provide environmental details: humidity, chemical exposure, UV, cyclic thermal profile.
• Specify load cases: static loads, dynamic/cyclic loads, expected rpm/linear speed, shaft material/finish.
• Request mechanical and wear data at room temp and at the specified elevated temperature(s); include creep tests and wear tests.
• Ask for dimensional data in both dry and conditioned states; require recommended fit tolerances for specified ΔT and installation temperature.
• Consider requiring sample qualification runs mimicking the exact thermal cycle of your process (paint bake, sterilization, etc.).

Why testing and supplier data are essential (don’t rely on generic tables)

Material properties vary significantly by compound and filler. Generic tables may show wide ranges; real performance depends on the exact grade, additives (heat stabilizers, UV stabilizers), fillers (glass, PTFE, graphite), and processing history. Always require the vendor to supply tested data for the specific part geometry and intended service temperature profile.

Bost brand advantages for temperature‑sensitive nylon bushings

• Technical support that evaluates your thermal and mechanical requirements and recommends compound/grade and tolerances.
• Ability to source or compound heat‑stabilized or filled PA grades and to provide comparative test data (wear, creep, tensile) at specified temperatures.
• Manufacturing and quality controls that include dimensional checks after conditioning and traceability of material lots.
• Options for prototyping and qualification runs to validate performance in your exact thermal cycles before full production.

References

• MatWeb, “Nylon 6 (Polyamide PA6) Material Properties,” MatWeb material property database — accessed 2024‑05‑01.
• MatWeb, “Nylon 6/6 (Polyamide PA66) Material Properties,” MatWeb material property database — accessed 2024‑05‑01.
• DuPont, Zytel (PA66) technical information and product literature — accessed 2024‑05‑10.
• igus GmbH, Plain Bearings / iglide materials temperature and wear guidance — accessed 2024‑04‑20.
• Engineering Toolbox, “Thermal Expansion Coefficients,” reference table (steel, polymers) — accessed 2024‑04‑25.
• McMaster‑Carr, Nylon (Polyamide) material and application notes — accessed 2024‑05‑05.