Composite PTFE-Lined Bushings: Complete Technical Specifications for Engineering Applications
Composite PTFE-Lined Bushings: Complete Technical Specifications for Engineering Applications
High-Performance Self-Lubricating Bronze Bushing Solutions & Technologies. Minimize downtime, extend service life, and reduce costs for dynamic applications.
Composite PTFE-Lined Bushings: Complete Technical Specifications for Engineering Applications
A Critically Reviewed, Brand‑Neutral Technical Reference
This document provides verified specifications for multilayer PTFE‑lined composite bushings used in dry or boundary lubrication conditions. All data have been cross‑checked against industry standards (ISO 3547, DIN 1494) and corrected for inconsistencies or unsupported claims. Use this as a reliable basis for long‑term project selection and design.
1. Structure Overview
The bushing features a four‑layer metal‑polymer composite:
| Layer | Material | Function | Critical Note |
|---|---|---|---|
| 1 – PTFE + fillers | Modified PTFE + graphite, MoS₂ (lead‑free option available) | Low‑friction sliding surface, forms transfer film | Thickness <10 µm risks rapid wear; >50 µm reduces load capacity |
| 2 – Sintered bronze | CuSn8 or CuSn10 (spherical bronze powder) | Mechanical anchoring + heat dissipation | Porosity 15–30% – uniform distribution essential |
| 3 – Steel backing | Low‑carbon steel (DC04/SPCC/SAE 1008‑1010, C 0.08–0.15%) | Load‑bearing structure | Lower carbon reduces strength; higher reduces formability |
| 4 – Outer plating | Tin / Zinc / Copper / Nickel or duplex | Corrosion protection | Not all platings suit all environments – see Section 6 |
2. Thickness Distribution by Total Wall Thickness
Four standard grades – always verify against actual PV (pressure‑velocity) conditions.
(A) Ultra‑Thin (< 1.0 mm)
| Total thickness | 0.75 – 0.95 mm |
|---|---|
| PTFE layer | 0.010 – 0.025 mm (10–25 µm) |
| Bronze layer | 0.15 – 0.20 mm |
| Steel backing | 0.60 – 0.75 mm |
| Plating | 0.002 – 0.008 mm (2–8 µm) |
Limitation: Not recommended for continuous dynamic loads >20 MPa due to reduced bronze thickness.
(B) Standard (1.0 mm)
| Total thickness | ~1.00 mm |
|---|---|
| PTFE layer | 0.020 – 0.030 mm |
| Bronze layer | 0.20 – 0.25 mm |
| Steel backing | 0.73 – 0.78 mm |
| Plating | 0.003 – 0.008 mm |
(C) Medium Duty (1.5 mm)
| Total thickness | ~1.50 mm |
|---|---|
| PTFE layer | 0.020 – 0.040 mm |
| Bronze layer | 0.25 – 0.30 mm |
| Steel backing | 1.15 – 1.22 mm |
| Plating | 0.003 – 0.010 mm |
(D) Heavy Duty (2.0 mm)
| Total thickness | ~2.00 mm |
|---|---|
| PTFE layer | 0.030 – 0.050 mm |
| Bronze layer | 0.30 – 0.35 mm |
| Steel backing | 1.60 – 1.68 mm |
| Plating | 0.005 – 0.012 mm |
Engineering insight: Edge loading requires bronze layer ≥0.30 mm and tighter PTFE thickness control.
3. Functional Layer Specifications
3.1 PTFE + Fillers (Sliding Layer)
-
Thickness range: 10 – 50 µm (recommended 20–30 µm)
Caveat: Below 15 µm – poor debris embedability. Above 40 µm – increased creep under sustained load. -
Composition (typical): PTFE 70–80% + fillers (graphite, bronze powder, optional MoS₂)
-
Friction coefficient (dry): 0.08 – 0.20 (steady state)
Reality check: 0.03 only achievable with perfect lubrication or very low speed. -
Maximum temperature: ~260 °C (continuous use above 200 °C degrades fillers; load capacity drops significantly)
3.2 Sintered Bronze Layer
-
Material: CuSn8 or CuSn10
-
Thickness: 0.15 – 0.35 mm (typical 0.20–0.30 mm)
-
Porosity: 15% – 30% (measured by oil absorption or image analysis)
-
Critical factor: Uniform pore distribution – clustering causes stress risers, fatigue, and PTFE delamination.
-
Thermal conductivity (layer): ≈35 W/(m·K)
3.3 Steel Backing
-
Material: Low‑carbon steel (DC04, SPCC, SAE 1008‑1010)
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Carbon content: 0.08% – 0.15%
-
Thickness: 0.6 – 1.7 mm (design‑dependent)
-
Optional: Stainless steel backing for corrosive environments (reduced formability); phosphated surface for better adhesion.
3.4 Outer Plating – Corrosion Protection
| Coating | Thickness | Characteristics | Limitation |
|---|---|---|---|
| Tin (Sn) | 3 – 8 µm | Standard protection, ductile, anti‑seizure | Soft – scratches easily |
| Zinc (Zn) | 5 – 15 µm | Higher corrosion resistance (outdoor) | Galvanic corrosion risk with aluminum |
| Copper (Cu) | 2 – 5 µm | Good adhesion, conductive, low cost | Poor corrosion resistance – not for exposed final layer |
| Duplex (Cu+Sn) | Cu 2–3 + Sn 3–6 µm | High reliability for humid/export conditions | Higher cost, two plating steps |
Selection guidance (corrected):
-
General indoor → Tin (Sn) 3–8 µm
-
Humid / outdoor → Zinc (Zn) 5–15 µm (check compatibility with mating materials)
-
Cost‑sensitive, non‑exposed → Copper (Cu) alone – only if sealed from moisture
-
High reliability → Duplex (Cu+Sn) or Tin
4. Manufacturing Tolerances & Quality Control
| Parameter | Typical tolerance | Risk if out of spec |
|---|---|---|
| Total wall thickness | ±0.02 – ±0.05 mm | Press‑fit failure or excessive clearance |
| PTFE layer uniformity | Should be ±5 µm (not always specified) | Uneven friction, localized overheating |
| Bronze porosity | 15–30% with <10% variation | Bond failure or poor heat transfer |
| Sintering bond strength | Minimum 20 MPa (recommended) | Delamination under cyclic load |
| PTFE surface roughness | ≤0.8 µm Ra | Inconsistent friction |
5. Key Technical Parameters (Verified)
| Parameter | Range / Value | Confidence |
|---|---|---|
| PTFE layer thickness | 10 – 50 µm | High |
| Bronze layer thickness | 0.15 – 0.35 mm | High |
| Bronze porosity | 15% – 30% | Medium (method‑dependent) |
| Steel carbon content | 0.08% – 0.15% | High |
| Steel thickness | 0.6 – 1.7 mm | High |
| Plating thickness | 3 – 15 µm | High |
6. Performance Parameters with Engineering Limits
Values below are maximum references under standard test conditions (ISO 3547‑4). Derating is mandatory based on actual temperature, shaft hardness, and vibration.
| Parameter | Value | Required conditions |
|---|---|---|
| Max static load | 250 N/mm² | Shaft hardness ≥55 HRC, PTFE ≤25 µm, no shock |
| Max dynamic load | 140 N/mm² | Sliding speed ≤0.1 m/s, cycles ≤10⁶ |
| Max dry sliding speed | 2.5 m/s (briefly 5 m/s) | At 5 m/s, PV ≤1.0 N/mm²·m/s |
| Max PV value (dry) | 2.8 N/mm²·m/s | Temperature ≤100°C, shaft Ra ≤0.2 µm, no edge loading |
| Friction coefficient (dry) | 0.08 – 0.20 | Post‑run‑in steady state |
| Operating temperature | -195°C to +260°C | Above 200°C, load capacity drops linearly; at 260°C <30% of room‑temperature value |
| Thermal expansion coefficient | 11×10⁻⁶/K | Matches steel shafts |
| Overall thermal conductivity | ≈40 W/(m·K) | Steel‑back dominated |
Important: PV claims above 2.8 N/mm²·m/s require forced cooling or lubrication – not reliable for dry operation.
7. Outer Plating: Tin vs Copper – Detailed Comparison
| Parameter | Tin (Sn) | Copper (Cu) |
|---|---|---|
| Thickness (typical) | 3–8 µm | 2–5 µm |
| Corrosion resistance | High | Low (oxidizes rapidly) |
| Surface hardness | Soft (~6 HV) | Moderate (~50 HV) |
| Anti‑seizure property | Excellent | Poor (galls with steel) |
| Primary function | Final protection | Bonding layer / temporary |
Tin plating advantages:
-
Strong corrosion resistance, industry standard
-
Protects shaft during installation
-
❌ Soft – susceptible to abrasive wear if debris present
Copper plating advantages:
-
Excellent adhesion to steel backing
-
Low cost, good thermal conductivity
-
❌ Poor corrosion resistance – rusts in humid air within days
-
❌ Not suitable as final exposed layer
Practical engineering rule:
For corrosion protection → Tin (Sn) 3–8 µm is the default.
Copper (Cu) alone should only be used when:
-
The bushing is sealed inside an assembly (no moisture exposure), or
-
It is a temporary process layer before final tin plating.
8. Installation & Design Requirements
Recommended Fits
| Component | Tolerance | Notes |
|---|---|---|
| Housing bore | H7 | Must be calculated with bearing OD interference |
| Shaft | h8 or h6 | Shaft hardness ≥45 HRC recommended |
| Shaft surface roughness | Ra ≤0.4 µm (ideal ≤0.2 µm) | Reduces run‑in wear |
| Installation method | Press‑fit with mounting mandrel | No hammering |
Post‑Press Inner Diameter Reduction
ΔID ≈ 0.8 × effective interference
Effective interference = bearing OD upper deviation – housing bore lower deviation. Final operating clearance should be 0.02–0.10 mm (depending on shaft diameter).
Critical Missing Information – Request from Supplier for Long‑Term Projects
-
Wear rate (mm/1000 h or μm/km) – typical 0.005–0.02 mm/1000 h depending on PV
-
PV limit curve (20–200°C) – a single number is insufficient
-
Fatigue limit (cycles before bronze cracking)
-
Grease compatibility (if initial lubrication is added)
-
Storage life (dry, no UV; tin plating ≤2 years)
9. Selection Matrix (Engineering‑Constrained)
| Operating Condition | Recommended Variant | Engineering Notes |
|---|---|---|
| Dry, dusty | Standard PTFE‑lined | PTFE does not actively attract dust, but static may – periodic inspection |
| High temperature >200°C | High‑temp PTFE formulation | Max 260°C, but load must be reduced to <30% of room‑temperature value |
| Food / medical | Lead‑free PTFE | Requires FDA or EU 10/2011 certificate – RoHS alone insufficient |
| Humid or mild corrosive | Zinc or nickel plating | Zinc not suitable for pH<5 or pH>12 |
| High‑load reciprocating | Custom design (non‑standard) | Standard version has higher wear rate under reciprocation – add initial lubrication |
| Strong acid/alkali/seawater | Stainless steel backing + nickel plating | Specify 316L stainless steel with passivation |
10. Verifiable Quality Requirements for International Projects
Each batch must include traceable test reports:
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Material chemistry (steel backing, bronze powder)
-
Bronze porosity (Archimedes or image analysis, target 15–30%)
-
Bond strength (ASTM D3164, minimum 20 MPa)
-
Salt spray test (ISO 9227: tin ≥72 h no red rust; nickel ≥500 h)
-
Dimensional report (wall thickness, OD, ID, roundness, PTFE thickness)
Recommended additional: Independent type test report (wear test, PV limit verification).
11. Summary & Engineering Caveats
PTFE‑lined composite bushings offer a well‑balanced trade‑off between friction, load capacity, and durability for applications such as automotive suspensions, hydraulic cylinders, and heavy machinery linkages. However, performance is highly sensitive to:
-
Actual PV value – Do not exceed ~2.8 N/mm²·m/s without lubrication. Above that, specify forced cooling or lubrication.
-
PTFE layer uniformity – Require statistical process control from supplier; thickness deviation ≤±5 µm.
-
Environmental corrosion risk – Select plating correctly per Section 6. Avoid exposed copper.
-
Press‑fit interference calculation – Always verify post‑press ID reduction to ensure final operating clearance.
Final recommendation for long‑term projects: Do not rely solely on this document or any supplier datasheet. Request a PV‑life calculation based on your actual load, speed, and temperature, and perform prototype validation before series production.
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