How to select the right nylon bushing for your application?

How to select the right nylon bushing for your application — 7 hard questions beginners miss

For engineers and buyers in machinery, automotive, consumer appliances and industrial equipment, nylon (polyamide) bushings are attractive for low-cost, lightweight, low-maintenance plain bearings. But selection mistakes — wrong grade, ignoring moisture, incorrect fit, or misunderstanding PV limits — lead to unexpected wear, creep, or cracking. Below are 7 specific long‑tail buyer questions that are frequently asked but often poorly answered online, followed by precise, practical answers you can use in procurement and design specifications.

1) How do I quickly assess whether a nylon bushing will survive my mixed (oscillatory + rotary) duty rather than running expensive lifetime tests?

Practical first‑pass assessment (no substitute for validation testing):

• Calculate contact pressure (p) = static load (N) / projected bearing area (m2). For a cylindrical bushing use projected area = bore diameter × length.
• Calculate sliding speed (V). For oscillatory motion use equivalent sliding speed: Veq = (stroke/2 × ω) / bore circumference approximation; for complex motion use average absolute sliding speed over cycle.
• Compute PV = p × V (units MPa·m/s). Compare PV to manufacturer PV limits for the chosen nylon grade (see next Q). If PV < manufacturer limit and contact pressure is well under the material's compressive strength, initial risk is low.
• Estimate wear tendency qualitatively: high load with low speed → adhesive wear/creep risk; moderate load with continuous sliding → abrasive/adhesive wear; many reversals (oscillation) → edge loading risk where small misalignments concentrate stress.
• Specify an accelerated validation test: replicate full motion cycle at multiplied speed or load until a practical wear run‑in (e.g., 1,000–10,000 cycles) and measure diametric/clearance change. Use this to extrapolate service life conservatively.

Why this works: PV screening and contact pressure quickly identify risky regimes. For oscillatory systems, edge stresses and micro‑abrasion dominate — so specify tests that reproduce angular reversal and side loads rather than relying on continuous rotation tests alone.

2) What are realistic PV and continuous temperature limits for common nylon grades (PA6, PA66 and filled variants) in continuous operation?

Typical guidance (use manufacturer data for your specific compound):

• Unfilled Nylon (PA6 / PA66): low PV capability — conservative engineering limits often 0.1–0.8 MPa·m/s for long life in plain bearing use. Continuous service temperature commonly limited to about 80–100°C; short excursions up to ~120°C accelerate hydrolysis and loss of properties.
• Filled (PTFE, graphite, MoS2) and glass‑filled nylon: PV capability increases substantially — many self‑lubricating compounds are rated up to ~1–4 MPa·m/s depending on filler type and content. Continuous temperature capability varies: glass‑filled PA66 can run around 120–140°C for limited durations; PTFE‑filled PA grades often have lower maximum continuous temperatures due to the filler binder system.
• Design rule: Always cross‑check the chosen compound’s PV and temperature curves from the supplier. If operating near limits, choose a higher‑performance compound or a metal‑backed solution.

Notes: PV and temperature capability vary widely between formulations. Supplier material datasheets and tribology guides (PV curves, wear rates vs pressure and speed, and temperature derating) are essential. When in doubt, specify an elevated safety factor (e.g., design for <50% of rated PV for continuous duty).

3) How does nylon’s moisture absorption affect press fits and running clearance — and how should I specify tolerances to avoid seizure or slop?

Key facts and specification steps:

• Polyamide absorbs moisture from air; dimensional changes are primarily a linear expansion/contraction. Typical equilibrium conditioning at 23°C/50% RH produces a few tenths to a few percent linear change depending on grade (amorphous vs semi‑crystalline and fillers reduce absorption).
• Procurement action: state the dimensional reference condition in the drawing/spec: either condition bushings to standard humidity (per ASTM D618 conditioning) before measurement, or specify bore and OD dimensions measured dry and define the moisture state (e.g., conditioned at 23°C / 50% RH until equilibrium).
• For press fits: plastics are less tolerant of high interference than metals. Use low interference values and consider these rules of thumb: radial interference typically in the low micrometer range (e.g., 0.05%–0.3% of bore diameter) rather than the percent levels used for steel. When in doubt, ask supplier for installation interference recommendations for the specific material grade and housing material.
• If moisture swelling could reduce running clearance, design clearance for the wet (conditioned) state or specify a reaming/finishing operation after conditioning.

Always require the supplier to state the conditioned dimensions and provide a dimensional control plan in the purchase order so installed parts behave predictably in the target environment.

4) When should I choose self‑lubricating (PTFE/graphite‑filled) nylon versus oil‑lubricated bronze or oil‑impregnated variants?

Decision factors:

• Maintenance: use self‑lubricating nylon when re‑lubrication must be avoided (sealed systems, food equipment, consumer goods). They perform well at low‑to‑moderate loads and speeds and are low cost and light weight.
• Load and shock: for sustained high loads, heavy shock, or high temperature, metal bearings (bronze, oil‑impregnated) usually outperform nylon. Metal-backed polymer or composite bushings can be a compromise when needing higher load capacity but lower friction/noise.
• Environmental exposure: aggressive chemicals, fuels, or hot steam favor metal or special polymer grades — choose a polymer only if chemical compatibility is confirmed by data/tests.
• PV and contact pressure: specify PV and max contact pressure. If your application requires a PV beyond common self‑lubricating nylon compounds (check supplier curves), switch to a metal or high‑performance composite solution.

Procurement tip: include required PV, max static contact pressure, temperature and environmental chemicals in RFQs so vendors recommend appropriate polymer families (PTFE filled, graphite filled, glass reinforced) or metal alternatives.

5) How should I specify interference fit, housing hardness, and installation procedures to avoid radial cracking or gross deformation of the nylon bushing during press‑in?

Engineering and procurement checklist:

• Get supplier recommended maximum radial interference for the exact nylon grade and wall thickness. Do not use general metal rules — plastics tolerate far less hoop stress.
• Specify housing bore finish and hardness. A rigid, tight‑tolerance metal housing reduces extrusion and uneven support. Avoid press‑fitting a soft housing that may deform and over‑stress the bushing.
• Use controlled, uniform press‑in tooling and low, even force. For certain sizes, consider thermal assembly (cool the bushing or warm the housing) if recommended by supplier to reduce assembly stress.
• For long, thin‑walled bushings, specify support features (flange, metal sleeve) or split bushings to avoid hoop fracture during assembly.
• Document installation acceptance criteria in the PO (e.g., allowable bore out‑of‑round, max insertion force) and require a supplier installation/inspection plan if assembled by vendor.

Detailing these items in purchase documents prevents many field failures caused by improper press‑fits or unsupported geometries.

6) How can I reduce extrusion and edge‑wear in thin‑walled nylon bushings under side loads without switching to metal bearings?

Design and specification remedies:

• Add radial support: require a metal backing sleeve or flanged design so the polymer cannot extrude into gaps under side load.
• Increase wall thickness locally where loads concentrate (use a shoulder or flange) or use a composite design (thin polymer liner bonded to metal carrier).
• Specify a harder, polished mating shaft (surface hardness and finish) — typical advice: smoother and harder shafts reduce abrasive wear and limit polymer transfer. For polymer-on-steel, recommend shaft hardness and surface roughness per the polymer supplier guidelines.
• Consider a low‑friction filler grade (PTFE/graphite) if edge wear is a result of adhesive friction; also consider a re‑designed clearance/transition radius to avoid notch effects at edges.

Testing: validate with side‑load oscillation tests reproducing expected misalignment and edge contact to confirm the chosen mitigation works before committing to large production runs.

7) Which solvents, cleaners or fuels will damage nylon bushings, and what mitigations or alternative materials should I specify in the RFQ?

Chemical compatibility guidance:

• Nylon is generally compatible with many hydrocarbons (oils, greases) but can be attacked or swollen by strong acids, strong bases, and some polar aprotic solvents (e.g., concentrated ketones, chlorinated solvents depending on grade and temperature). Fuels containing oxygenates (ethanol) increase swelling and may affect mechanical properties over time depending on grade.
• If the application exposes bushings to solvents, fuels, cleaners or aggressive chemicals, always require a supplier chemical‑compatibility statement for the exact compound; include test exposure time and temperature limits in RFQs.
• Where chemical resistance is critical, either specify a chemically resistant polymer (e.g., PTFE for extreme solvents) or specify protective seals/barriers and periodic inspection intervals.

Procurement practice: add a mandatory line in RFQs: Provide chemical compatibility data (immersion tests) for candidate material vs. specified chemicals, at specified temperature and exposure time. This moves the burden of proof to the supplier.

Practical procurement checklist for including in RFQs and drawings

• Material family and exact grade (e.g., PA66, PA6/GF30/PTFE‑filled) with manufacturer part number and alternative acceptable suppliers.
• Operating conditions — continuous temperature range, max short‑term temperature, static and dynamic loads, type of motion (rotary/oscillatory/reciprocating), expected duty cycle.
• Required PV or required wear performance (e.g., maximum linear wear rate or acceptable clearance increase per million cycles) or a required test method and acceptance criteria.
• Dimensional reference condition (conditioning standard and humidity) and tolerance class (specify finish, bore concentricity/out‑of‑round and max insertion force if pressed in by vendor).
• Chemical exposures — list all chemicals, concentrations, temperatures and exposure durations; require compatibility report.
• Installation instructions, permissible interference fit range, housing hardness, and requirement for installation validation (sample assembly report or witness testing).
• Quality and traceability: require material certificates, batch traceability, and supplier test records for dimensional and tribological testing (where required). Include ISO/TS or ISO9001 requirement if needed.

References and data sources

• Supplier technical datasheets and material guides (examples: DuPont Zytel technical pages; igus iglidur material selection guides) — consult the chosen supplier for compound-specific PV and temperature data (supplier websites: DuPont, igus). (Accessed 2024‑05)
• ASTM standards for plastics conditioning and water absorption — ASTM D618 (conditioning of plastics) and ASTM D570 (water absorption of plastics). (ASTM standards pages accessed 2024‑05)
• Engineering Toolbox — coefficients of linear thermal expansion and general polymer property references (useful for thermal expansion estimates). (Accessed 2024‑05)
• Tribology literature and established screening method: PV = p × V principle and Archard wear concepts for wear estimation — standard tribology references and manufacturer tribology charts. (Classical references and manufacturer tribology guides; accessed 2024‑05)

Why sample testing and detailed RFQs matter

Many field failures are due to missing specification details more than poor materials. If you provide suppliers with motion profiles, contact pressures, environmental data, and required life or wear limits up front, vendors can recommend the right compound and demonstrate it with test data. Require conditional acceptance on sample testing under reproduced operating conditions before large orders.

Closing — Why choose Bost for nylon bushings

Bost offers an experienced product portfolio and technical support tailored to engineering plastics plain bearings. Advantages you can expect: a range of engineering nylon grades including filled and reinforced options, technical selection assistance (PV/pressure guidance), in‑house or partner testing capability for motion/chemical exposure validation, and assistance with tolerance/installation recommendations. For procurement teams, Bost can provide material traceability, drawing‑level support and supply flexibility to match production ramp needs.

Use the guidance above to structure RFQs, demand the right test evidence, and reduce risk when switching to or designing with nylon bushings.