Views: 0 Author: Site Editor Publish Time: 09-30-2026 Origin: Site
A typical excavator has around 18 grease points, and a 31-ton truck around 22. At 3–5 minutes per point, a machine in daily use can consume 7–10.5 hours of greasing every week. Miss one interval and a pin or bronze bushing runs dry, scores, and takes the machine out of service.
At the same time, commercial vehicle, construction equipment and EV makers are pushing hard on lightweighting. Self-lubricating bearings address both problems: they need no external oil or grease, and their density is roughly one-fifth that of bronze. This guide covers how they work, the three main product families, key specifications, where they fit, and how to size one correctly.
A self-lubricating bearing is a plain bearing whose sliding layer is a polymer compound designed to run dry or with minimal lubrication. It is also known as a plastic bearing, oil-free bushing, maintenance-free bearing or polymer plain bearing. With no rolling elements or cage, it carries load through sliding contact, stays compact in the radial direction, and tolerates shock and dirt well.
1. Built-in solid lubricants — PTFE, graphite or MoS₂ are dispersed through the sliding layer.
2. Run-in transfer — during initial operation, a small amount of lubricant transfers to the mating shaft and fills its surface valleys, forming a thin, continuous film.
3. Stable running — friction then occurs film-on-film; the friction coefficient drops and stabilizes, and wear slows down.
4. Continuous renewal — as the sliding layer wears evenly, fresh lubricant is exposed and the film keeps renewing for the life of the bearing.
This is why a mirror-polished shaft is not the best choice. A shaft roughness of Ra 0.15–0.4 µm gives the best transfer-film adhesion. Rougher shafts abrade the polymer; very smooth shafts cannot hold the film, which shortens dry-running life.
Thermoplastics such as POM, PA, PPS or PEEK are compounded with PTFE, graphite and glass or carbon fiber, then injection-molded in one piece. This is the lightest and most cost-effective family for high volumes, suited to low-to-medium loads with frequent oscillation or rotation.
A sliding layer of wound PTFE and high-strength fibers sits on a backing of glass fiber wound in high-temperature epoxy. Load capacity matches or exceeds metal bearings, thermal expansion is close to steel, and water absorption is negligible. It is the first choice for heavy, shock-loaded pivots such as excavator joints and hydraulic cylinder pins.
A three-layer structure of steel backing, porous bronze sinter and a PTFE- or PEEK-based sliding layer, with walls typically only 0.75–2.5 mm thick. The lightweight benefit here is space saving: thin walls suit compact, higher-speed automotive and hydraulic components.
Typical Specification Comparison
Parameter | Injection-Molded Plastic | Filament-Wound Composite | Metal-Polymer Composite |
Max. static load / recommended pressure (N/mm²) | 80 (general grade) / 150 (PEEK grade) | 207–414 | 250 |
Max. dynamic load (N/mm²) | Falls with temperature; PEEK grade approx. 30 at 250°C | 138 | 140 |
Max. sliding speed, dry (m/s) | 1 continuous, 2 short-term | 0.13 (heavy-duty) / 2.5 (PTFE-tape liner) | 2.5 |
Max. PV, dry (N/mm²·m/s) | 0.42–1.32 | 1.05–1.23 | 1.8 |
Operating temperature (°C) | -40 to +130 (general) / -100 to +250 (PEEK) | -196 to +163 / +204 | -200 to +280 |
Dry friction coefficient | 0.08–0.27 | 0.02–0.07 (under high load) | 0.02–0.25 |
Density (g/cm³) | approx. 1.4–1.5 | 1.85–1.96 | Mostly steel backing, thin wall |
Typical positions | Seat adjusters, hinges, pedals, doors, automation | Excavator pivots, cylinder pins, kingpins, hydro gates | Suspensions, oil pumps, hydraulic motors, shock absorbers |
Values are typical figures from published industry datasheets. Maximum values cannot be reached at the same time; final selection should follow the tested data for the specific material.
Material | Key Properties | Approx. Continuous Temp. (°C) | Typical Use |
POM (acetal) | Low friction, dimensionally stable, cost-effective | 100 | Automotive interiors, office and automation equipment |
PA / PA66 (nylon) | Strong, tough, impact-resistant; watch moisture uptake | 100–120 | Commercial vehicles, agricultural machinery, conveyors |
UHMWPE | Excellent abrasion resistance, low cost, lower load | 80 | Conveyor guides, wear strips |
PBT / PET | Low moisture absorption, stable dimensions | 100–120 | Humid environments, precise fits |
PPS | Chemical and heat resistant, flame retardant | 200 | Pumps, valves, engine-bay surroundings |
PEEK | High temperature, high load, chemical resistant | 250 | Engine bay, transmissions, high-temperature equipment |
PAI / PI | Retains strength at extreme temperatures | 260+ | Specialty high-temperature, high-load duty |
PTFE | Lowest friction; used as filler or sliding layer | 260 | Sliding layers of composite bearings |
Pure resins are rarely used alone. Adding PTFE, graphite or MoS₂ lowers friction, while glass or carbon fiber raises strength and heat conduction. Research on optimized PEEK composites at 33 MPa contact pressure showed 51.6% lower friction and 93.5% less wear depth than the baseline, with temperature rise cut from over 84°C to 37.4°C. The formulation is where performance is really decided.
Design | Load Direction | Features & Use |
Sleeve bearing | Radial | Pressed into the housing; the most common form |
Flanged bushing | Radial + axial | Flange takes axial load and locates the bearing |
Thrust washer | Axial | Pivot end faces, gear faces |
Split bearing | Radial | Replace without removing the shaft; ideal for retrofits |
Clip / double-flange bearing | Radial + axial | Tool-free fitting into sheet metal; body hinges |
Two-hole flange bearing | Radial + axial | Bolted; no toleranced housing bore needed |
Spherical / rod-end bearing | Radial + misalignment | Compensates installation error; linkages and controls |
Slide plate / wear strip | Linear | Truck bodies, guides, telescopic booms |
Custom shapes | As designed | Hex or square bores, grease grooves, integrated mounting features |
Standard bores generally cover 3–150 mm; filament-wound bearings can be made to 500 mm and above. Non-standard sizes and shapes are produced to drawing.
At the same size, a filament-wound bearing is about 75% lighter than a bronze or steel bearing, yet its dry dynamic load is more than 3 times that of lubricated cast bronze.
Self-Lubricating vs. Traditional Metal Bearings
Bearing Material | Lubrication | Max. Dynamic Load, low speed (N/mm²) | Max. Temp. (°C) | Specific Gravity |
Cast bronze | Required | 41 | 71 | 8.80 |
Porous (oil-impregnated) bronze | Oil-impregnated | 28 | 71 | 7.50 |
Steel-backed bronze | Required | 24 | 93 | 8.00 |
Hardened steel | Required | 276 | 93 | 7.90 |
Filament-wound composite | None | 138 | 163–204 | 1.85–1.96 |
The temperature limit of a metal bearing is usually set by its grease, not the metal. Remove the grease and a polymer composite bearing can actually run hotter.
How Much Weight Does One Bushing Save?
Example: a sleeve bearing 40 mm ID × 45 mm OD × 45 mm long (volume approx. 15.0 cm³), compared at identical dimensions:
Material | Specific Gravity | Weight per Piece | Weight Saving |
Cast bronze | 8.80 | approx. 132 g | — |
Filament-wound composite | 1.87 | approx. 28 g | approx. 79% |
Injection-molded plastic | 1.46 | approx. 22 g | approx. 83% |
A construction machine or trailer often has dozens of pivots, and the saving grows quickly with larger bushings.
• No oil, no maintenance: removes grease nipples and centralized lubrication, cutting labor and unplanned downtime.
• Dirt tolerant: no grease to trap dust and grit; small particles embed in the sliding layer instead of scoring the shaft.
• Corrosion and chemical resistant: no rust; resists salt spray, fuels, diesel and dilute acids and alkalis.
• Quieter running: polymers absorb vibration and improve vehicle NVH.
• Electrically insulating: can serve as insulating joints, e.g. railway pantograph pivots.
• Zero oil contamination: suited to food, medical, clean environments and outdoor solar plants.
• Lower total cost: industry data shows polymer plain bearings can cost up to 40% less than metal solutions, with about one-tenth of the manufacturing energy.
Any pivot that moves slowly, is hard to lubricate, sees dust, mud or water, or needs to lose weight is a strong candidate.
Industry | Typical Positions | Recommended Family |
Commercial vehicles & trailers | Tipper mechanisms, swing axles, landing legs, door hinges, side boards, tarpaulin rollers, kingpins, suspensions | Molded plastic / filament-wound / metal-polymer |
Passenger cars & EVs | Seat adjusters, pedals, doors, mirror drives, throttle valves, transmission actuators | Molded plastic |
Construction machinery | Excavator and loader pivots, cylinder pins, steering links, crane booms, forklift masts | Filament-wound |
Rail transit | Pantograph pivots, door mechanisms | Filament-wound / molded plastic |
Solar & wind | Solar tracker bearing blocks, auxiliary wind turbine mechanisms | Molded plastic / filament-wound |
Hydropower, pumps & valves | Wicket gates, sluice gates, spillways, trash racks, valves, fire safety valves | Filament-wound |
Hydraulics & power transmission | Hydraulic motors, oil pumps, shock absorbers | Metal-polymer |
Agriculture, automation, food & medical | Linkages, guides, conveyors, clean-room moving parts | Molded plastic |
Selection comes down to three numbers: bearing pressure P, sliding speed V and operating temperature. All three must stay below the material limits for reliable long-term service.
1. Define the duty: load size and direction, motion type (rotating, oscillating, linear), frequency, ambient temperature, media and contaminants.
2. Calculate bearing pressure: P = F ÷ (Di × B) in N/mm², where F is the load (N), Di the bore (mm) and B the length (mm).
3. Calculate sliding speed: for oscillation, first convert to an equivalent speed N = 4 × φ × Nosc ÷ 360 (φ = swing angle, Nosc = cycles per minute), then V = Di × π × N ÷ 60,000 in m/s.
4. Check the PV value: PV = P × V, compared with the material PV limit; also confirm P, V and temperature individually.
5. Allow for shock and misalignment: heavy equipment should be designed well below the material maximum — see the table below.
Recommended Design Pressure for Construction Equipment Pivots
Application | Design Pressure (N/mm²) | Shock Factor |
Dozer arms, excavators, backhoes, loader linkages | 34 | 3G |
Compactors, bogie pivots, track frame pivots | 48 | 2G |
Steering cylinders, control linkages, dump / swing cylinders | 69 | 1G |
Although the material is rated to 138 N/mm² dynamic, shock, shaft deflection and oscillation keep adding to the real load, so the values above are the safer basis.
Worked Example: Excavator Pivot Bushing
Duty: radial load F = 60 kN, shaft 40 mm, swing angle 30°, 10 cycles per minute, ambient temperature.
Step | First Try: Length 40 mm | Revised: Length 45 mm |
Pressure P | 60000 ÷ (40 × 40) = 37.5 N/mm² | 60000 ÷ (40 × 45) ≈ 33.3 N/mm² |
Equivalent speed N | 4 × 30 × 10 ÷ 360 ≈ 3.33 rpm | Same |
Sliding speed V | 40 × π × 3.33 ÷ 60000 ≈ 0.007 m/s | Same |
PV | ≈ 0.26 N/mm²·m/s | ≈ 0.23 N/mm²·m/s |
Result | Exceeds 34 N/mm² recommended for 3G shock | Pass — select a filament-wound bearing |
The length-to-diameter ratio is 45 ÷ 40 ≈ 1.1, within the recommended range. Note that a low PV does not mean any material will do: in heavy, slow applications the limit is usually pressure, not PV.
• Length / diameter ratio: keep B/Di between 0.25 and 2.0. Too long causes edge loading from shaft deflection; too short weakens retention in the housing.
• Wall thickness: filament-wound bearings need at least 1.5 mm; below 2.5 mm, capacity drops by about half, and above 6.35 mm it no longer increases.
• Mating shaft: above 14 N/mm², use a shaft of at least HRC 50; roughness Ra 0.15–0.4 µm; chamfer the shaft end. Use stainless or hard-chrome shafts where corrosion is a risk.
• Clearance: slow oscillating pivots can run tight; higher speeds or temperatures need thermal clearance. Molded plastic bearings must also allow for moisture swell.
• Housing material: aluminum and other high-expansion housings lose retention when hot; increase the interference fit.
• Sealing: in dusty environments, add seals or wipers to extend life further.
• Breakaway friction: after hours or days at rest, first-start static friction can be up to 200% higher; leave margin in torque-sensitive mechanisms.
Hebei Huami New Material Technology Co., Ltd. (Beijing Stock Exchange: 920247) supplies all three families of self-lubricating bearings — injection-molded polymer, filament-wound composite and metal-polymer — in both standard and custom designs. Its wholly-owned subsidiary, Hebei Tongsource International Trade Co., Ltd., serves overseas customers directly.
Founded / Listed | Founded 1998; listed on the Beijing Stock Exchange in December 2022 |
Recognition | National Specialized and Innovative Little Giant; High-Tech Enterprise |
Capacity | 58,000 t/year modified plastics; 25,000 t/year specialty rubber compounds |
R&D | Provincial key laboratory and industrial technology institute; 72 granted patents (33 invention); contributed to 13 national, 2 industry and 8 association standards |
Certifications | ISO 9001, IATF 16949, ISO 14001, ISO 45001 |
Customs Status | China Customs AEO Advanced (AEOCN1305960055), priority clearance in 50+ mutual-recognition countries and regions |
Key Customers | FAW Group, CRRC, SANY Heavy Industry, Sinopec, BYD, Great Wall Motor and more |
• Own formulations: compounds are designed from resin modification, solid lubricant and fiber ratios up, and tuned to each duty cycle.
• One-stop supply: light-duty hinges, heavy pivots and thin-wall bushings on one machine can come from one supplier.
• Automotive-grade control: IATF 16949 process with co-development, sample validation, pilot runs and volume delivery.
• Listed-company reliability: finance, internal control and supply chain run to listed-company standards for long-term volume supply.
A: Yes. They are designed for dry running. Some materials can also run immersed in oil or water for lower friction, but extra grease is not recommended in dusty conditions because it traps abrasive particles.
A: Most slow oscillating pivots can be converted directly after checking pressure, speed and temperature with the method above. Filament-wound bearings have stiffness and thermal expansion close to steel, so bronze press-fit data usually applies; molded plastic bearings need their clearance recalculated.
A: About 130°C for general molded grades, up to 250°C for PEEK grades, 163–204°C for filament-wound composites and up to 280°C for metal-polymer bearings. Allowable load falls as temperature approaches the limit.
A: It depends on the material. Nylon absorbs more moisture, so for humid or wet service choose POM, PBT, PPS, PEEK or filament-wound bearings (near-zero water absorption) and design in adequate clearance.
A: The standard method divides the material life factor by the PV value, then applies correction factors for load, temperature, mating material, surface finish and size. For example, a 40 × 20 mm filament-wound bearing at 50 kN, 30° swing, 10 cycles per minute and 75°C is estimated at about 3.1 million cycles.
A: Hardened steel is preferred. Above 14 N/mm², hardness should be at least HRC 50, with roughness Ra 0.15–0.4 µm. Stainless or hard-chrome shafts suit corrosive environments; soft plated zinc shafts shorten bearing life.
A: Yes. Beyond standard sleeves, flanged bushings and thrust washers, we produce large diameters, thick walls, hex or square bores, grease grooves and integrated mounting features to drawing.
A: Yes. We support OEM and private-label programs with custom marking and packaging, and provide inspection documents and export paperwork. AEO Advanced status helps shorten customs clearance.
Cut grease points, weight and downtime with self-lubricating bearings. Send us the details below — or your existing bronze bushing drawing or sample — and our engineers will recommend a material and design with a quotation.
• Bearing type: sleeve / flanged / thrust washer / slide plate / custom
• Dimensions: ID, OD, length, shaft diameter, housing bore
• Load: radial / axial load, shock conditions
• Motion: speed, or swing angle and frequency, or stroke and frequency
• Environment: temperature range, media, lubrication, contaminants
• Mating parts: shaft material, hardness, roughness; housing material
• Usage: daily operating hours, target life, annual volume
Contact us today for free samples, a full specification sheet and a competitive quotation.
