PTFE bushes — also called PTFE plain bearings, journal bearings, or sliding bushes — are cylindrical sleeves that support a rotating or sliding shaft with exceptionally low friction, no external lubrication requirement, and complete compatibility with aggressive chemical environments. They are the maintenance engineer's favourite bearing solution in situations where conventional metal or polymer bearings with grease lubrication are impractical, undesirable, or simply too short-lived.
This guide covers the design, grade selection, installation, and application of PTFE molded bushes across the full range of industrial contexts where they are used.
Why PTFE for Bushes and Bearings?
Conventional bearing materials — bronze, brass, sintered metal, nylon — all require periodic lubrication and have limited compatibility with corrosive environments. PTFE bushes offer three advantages that make them uniquely suited to difficult applications:
- Self-lubricating: PTFE's coefficient of friction (0.04–0.10) is low enough that external lubrication is not required in most applications. This is essential in food processing, pharmaceutical, clean-room, and submerged applications where grease contamination is unacceptable.
- Chemical compatibility: PTFE bushes handle virtually all process chemicals — acids, solvents, caustics — that would corrode or degrade metal or standard polymer bearings within months.
- Wide temperature range: From cryogenic service (−200°C, LNG pumps) to high-temperature process equipment (260°C), PTFE bushes maintain function across ranges impossible for nylon or acetal bearings.
PTFE Bush Grades and Selection
| Grade | Load Capacity | Wear Life | Best Application |
|---|---|---|---|
| Virgin PTFE | Low–Moderate | Moderate | Chemical environments; food/pharma; light loads; static or slow oscillating |
| 25% Glass Filled | High | Good | Moderate speed rotating shafts; valve spindles; static loads with occasional movement |
| 25% Carbon Filled | Moderate–High | Excellent | Continuous rotation; pump bearings; where wear rate is the primary concern |
| Graphite Filled | High | Excellent | High-load, low-speed bearings; wet/submerged service; self-lubricating in corrosive media |
| 60% Bronze Filled | Very High | Excellent | Heavy duty rotating shafts; high pressure; hydraulic equipment bearings |
Standard Sizes and Tolerances
Hindustan Nylons manufactures PTFE molded bushes to standard ISO bearing tolerances and custom dimensions:
- Bore diameters: 6 mm to 300 mm (custom above 300 mm)
- Wall thickness: Typically 3 mm to 25 mm depending on bore size
- Length: 10 mm to 300 mm (custom lengths available)
- Tolerance classes: H7 bore (standard); H6 for precision fit; custom tolerances to drawing
Fit Guidance for PTFE Bushes
PTFE has a high coefficient of thermal expansion (approximately 10× that of steel). This means a PTFE bush pressed into a steel housing at room temperature will expand radially at elevated temperature, tightening the fit in the housing and reducing the bore clearance. Design recommendations:
- Press-fit PTFE bushes into housing: interference of 0.01–0.02 mm per 25mm of bush OD
- Shaft clearance: minimum 0.003–0.005 mm per mm of bore diameter at the operating temperature
- At elevated service temperatures, increase bore clearance in the design to prevent bush seizing on the shaft as PTFE expands inward
- Consider pinning or bonding large bushes in critical applications to prevent rotation in housing
Applications by Industry
| Industry | Application | Recommended Grade |
|---|---|---|
| Chemical Processing | Agitator shaft bearings, pump shaft seals, valve spindles | Virgin or Carbon Filled |
| Pharmaceutical | Tablet press guides, filling machine slides, vessel agitators | Virgin PTFE only (FDA) |
| Food Processing | Conveyor rollers, packaging machine guides, mixer shafts | Virgin PTFE only (FDA) |
| Water & Sewage Treatment | Gate valve spindles, sluice gate slides, pump bearings | Glass or Graphite Filled |
| Hydraulics & Pneumatics | Cylinder guide rings, piston bearings, rod seal backup | Bronze or Carbon Filled |
| Paper & Pulp | Roll bearings in wet chemical environments | Carbon or Graphite Filled |
| LNG / Cryogenic | Pump shaft bushes at −160°C service | Virgin PTFE |
Mating Surface Requirements
The shaft or mating surface running inside a PTFE bush should be:
- Material: Stainless steel 316 or 304 preferred; hardened steel; chrome-plated steel. Avoid soft aluminium or brass mating against glass-filled PTFE (abrasive wear on soft metal).
- Surface finish: Ra 0.4–0.8 µm (N6–N7) for optimum wear performance. Too rough — high wear on PTFE; too smooth — less PTFE transfer film development.
- Hardness: Shaft hardness of HRC 55+ recommended for rotating applications to prevent shaft scoring by hard filler particles in filled grades.
Frequently Asked Questions
Do PTFE bushes need lubrication?
No — this is one of their primary advantages. PTFE operates at its lowest friction dry, without any grease or oil. In fact, oil lubrication can increase PTFE's friction in some conditions by preventing the formation of the PTFE transfer film on the mating surface, which is what provides long-term low friction. Specify PTFE bushes specifically to eliminate the maintenance requirement for periodic re-greasing.
How long do PTFE bushes last in service?
Service life depends on load, speed, and shaft surface finish. In low-speed oscillating applications (valve spindles, gate valves, structural pivots), virgin PTFE bushes commonly last 10–20 years. In continuous rotation at moderate speed and load with a properly finished stainless shaft, carbon or bronze-filled PTFE bushes give 3–8 years of trouble-free service before bore wear exceeds the clearance limit.
Can PTFE bushes be used submerged in water or chemicals?
Yes — this is another key advantage. PTFE absorbs virtually no water (less than 0.01%) and is chemically compatible with almost all process liquids. PTFE bushes in submerged pumps, chemical agitators, and water treatment equipment perform as well or better submerged than in dry service, since the liquid provides some cooling and removes wear debris from the contact zone.
PTFE Molded Bushes — Custom Bore, All Grades
Standard bore sizes in stock. Custom bore diameter, wall thickness, and length manufactured to your drawings. All PTFE grades available.
Request Bush Quote →