Custom plain bearings
The demand for custom non-standard plain bearings is increasing. We can manufacture copper alloy materials to meet China’s national standards as well as the ASTM (UNS, SAE), EU, and JIS standards.
Bespoke plain bearings
viiplus collaborates with customers to find tailored solutions, offering plain bearings in various materials, sizes, tolerances, and designs.
Timely Delivery
Committed to meeting tight deadlines without compromising on quality, we ensure reliable and efficient production timelines.
Versatility
Capable of handling both small-scale and high-volume orders, we provide seamless support for projects of any size. Additionally, we can develop custom copper alloy materials based on specific customer requirements and drawings.
Specialized in Composite PTFE Bushings — Steel-Backed, Dry-Running, Low Friction
A composite bushing from VIIPLUS is a three-layer PTFE bearing: a steel backing for strength, a sintered bronze interlayer, and a PTFE-based running surface that slides dry with extremely low friction. As a bushing it needs no oil; as a POM variant it takes a light grease charge for higher load. Ideal for automotive, hydraulic, and precision mechanisms.
Where space is tight and maintenance access is nil, a steel backed ptfe bearing outperforms thick bronze: it is thin, dimensionally stable, and runs clean. Below is the complete guide to how ptfe composite bearings are built, rated, and applied — and how to choose PTFE vs POM for your mechanism.
A steel-backed PTFE composite bearing is a thin wrapped bushing or thrust washer whose running face is a self-lubricating PTFE layer. It runs dry with very low friction, accepts oscillation and linear slide, and is the standard answer where a bronze bushing cannot be re-lubricated or where water is the only medium available. This page sets out how the construction works, where its load and speed limits sit, and how to decide between composite and solid bronze.
Custom Machined Bronze Parts & Bearings
What Are Composite PTFE Bearings?
Composite (also called metal-polymer) bushings solve the problem of “no room for oil and no time for relubrication.” The steel shell carries radial load and holds tolerances in the housing; the sintered bronze layer bonds the liner and spreads heat; the PTFE-based surface does the sliding. Because the lubricant is built into the liner, the PTFE bushing material delivers a low, stable coefficient of friction from the first cycle.
The appeal of a composite bushing is threefold. First, the thin steel shell lets you put a bearing where a solid bronze wall would not fit. Second, the low, stable friction reduces starting torque and stick-slip, which matters in positioning mechanisms. Third, with no grease there is nothing to attract grit or contaminate a clean process — a decisive advantage in food, textile, and office-equipment duty. For many designs, a steel backed ptfe bearing is the difference between a reliable pivot and a maintenance headache.
Composite bushings became the default in automotive and hydraulic design precisely because they remove the grease nipple from mass-produced mechanisms. The same logic scales to any product where service access is limited or where contaminating grease is unacceptable — which is most modern equipment.
Because the liner does the work, the bushing’s performance is built in at the factory rather than maintained in the field, which is the essence of a truly low-maintenance component.
Oilless Bushing Material, Machining Parts
Structure & Material Layers
PTFE (dry)
- Steel backing + porous sintered bronze + PTFE/lead or lead-free filler layer. Runs dry; for clean, moderate-PV duty where oil would contaminate or attract debris.
POM (greased)
- Same steel + bronze base, but the running surface has indentation pockets pre-filled with grease at assembly. Intended for initial lubrication; supports higher PV and shock loads, common in hydraulics and suspension.
- The bronze interlayer is sintered onto the steel, then impregnated and roll-bonded with the polymer liner. This metallurgical bond is what lets a thin part carry real radial load without the liner delaminating — a key reason composite bushings can replace thicker bronze in weight- and space-sensitive designs. The liner itself is only a fraction of a millimeter thick, yet it defines the entire wear life of the part.
Custom Bearing Capabilities
PTFE Composite vs Bronze vs JDB
| Bearing | Wall | Friction | Lubrication | Best Use |
|---|---|---|---|---|
| PTFE composite | Thin | Very low | Dry / none | Fast, light, precise |
| Oil bronze | Thick | Low–med | Oil/grease | Lubricated, long life |
| JDB graphite | Medium | Low | Oilless (graphite) | Heavy, hot, dirty |
See the broader comparison in our self-lubricating bearings guide.
The practical decision is rarely “which is best” but “which failure do I want to avoid.” If contamination and relubrication access are the problem, the oilless PTFE or JDB route wins. If raw load dominates, bronze or JDB. If package size and friction dominate, composite. Many machines use all three in different joints — a hydraulic cylinder with a POM bushing at the rod, a JDB pivot at a hot hinge, and a bronze sleeve in a heavily loaded shaft — which is why we keep the full range in one catalog.
1. Construction: steel, sintered bronze, PTFE
The material is a bonded three-layer composite, usually supplied as strip that is then wrapped and sized into a bushing, or blanked into a thrust washer:
| Layer | Typical thickness | Function |
|---|---|---|
| PTFE running layer PTFE with fillers |
0.01–0.03 mm | Low friction; releases a transfer film onto the shaft |
| Sintered porous bronze bonding / reservoir |
0.2–0.35 mm | Bonds the PTFE, carries it, and conducts heat away from the surface |
| Steel backing low-carbon steel |
0.7–2.3 mm | Carries the load and gives the part its structural strength |
An outer tin or copper plating protects the steel from corrosion. This construction is widely known by the descriptive label of a steel-backed or wrapped PTFE bushing; the specific layer arrangement and materials are detailed on the PTFE composite material page.
2. The transfer-film principle
Composite bearings do not rely on a reservoir of grease. Under load and motion, a microscopically thin layer of PTFE transfers from the running face onto the shaft, and sliding then occurs between PTFE and PTFE rather than between PTFE and steel. This is what keeps the friction low and the wear gradual over the whole service life.
Two consequences follow. First, the shaft does not need to be especially hard — composite bearings accept a softer, easier-to-machine shaft than many solid-bearing systems. Second, the running-in period matters: the part develops its working film during early cycles, and sudden heavy loading before the film forms should be avoided.
Why the sintered bronze layer matters
It is the thermal backbone. Under dry sliding the friction heat has to leave the surface; the porous bronze conducts it out to the steel backing and away. A PTFE layer without this structure would soften and wear far sooner at the same duty.
3. Load, speed and PV limits
The operating envelope is defined by a PV (pressure × velocity) limit rather than a fatigue life. Typical published limits for a steel-backed PTFE composite are:
| Parameter | Typical value | Notes |
|---|---|---|
| Static load | 250 N/mm² | Non-moving, bearing load |
| Dynamic load | 140 N/mm² | At low speed |
| Oscillating / rotating load | 60 N/mm² | Continuous motion |
| Dry-running PV, continuous | 1.8 N/mm²·m/s | Long-term running |
| Dry-running PV, short-term | 3.6 N/mm²·m/s | Brief peaks only |
| Dry speed limit | 2 m/s | Above this, lubricate |
| PV with oil lubrication | up to ~50 N/mm²·m/s | Only when the film is maintained |
| Temperature range | −200 to +280 °C | Depends on the exact filler / liner |
| Friction coefficient (dry) | 0.03–0.25 | Falls after running-in |
Values are typical published limits from established composite-bearing data and are for guidance; the governing duty and the supplier’s datasheet for the exact construction take precedence. PV is a product of load and sliding speed — the same PV can mean high load and low speed, or the reverse, and each has its own safe region.
4. Dry, greased or water-lubricated running
The composite gives real dry-running capability, and it also performs with lubrication when the application provides it:
- Dry running is the primary use — low friction, no maintenance, no contamination. This is where the thin-wall composite earns its place over a bronze bushing that needs grease.
- Marginally lubricated — a trace of grease or oil lowers friction further and extends life; the part runs well even if the supply is intermittent.
- Water-lubricated — PTFE composite is inert and works when the only medium is water, making it a standard choice for water pumps, rudder and shaft-type applications and food/process washdown positions where oil is prohibited.
“Water lubricated” means the medium carries the interface; it is not a substitute for a load and PV check, and chemical compatibility with the actual water chemistry and temperature must be confirmed for each duty.
Lubrication decision — verify, do not assume
Whether to run dry, greased or water-lubricated has to be decided against the actual medium, temperature and load cycle. A data sheet phrase like “also runs with lubrication” is not a licence to assume an oil-lubricated PV; the running conditions must be verified against the supplier’s recommendation for the specific construction.
5. Forms: bushings, thrust washers, strip
The composite is supplied in a set of standard forms, all sharing the same running face and limits:
- Cylindrical bushings — wrapped from strip, sized to the bore, for radial loads on a shaft.
- Flanged bushings — combine the radial bearing with an integral axial thrust face, locating the part in one piece.
- Thrust washers — flat washers that carry axial load between two rotating or oscillating faces.
- Strip and wear plates — for linear slide or where a surface must be faced with the composite.
Dimensional standards for wrapped bushings and washers follow the wrapped-bearing and washer systems; confirm the applicable standard and tolerance for the specific form.
6. When composite beats solid bronze — and when it does not
This is the decision a buyer most often gets wrong, so it is worth being explicit:
| Condition | Steel-backed PTFE composite | Solid bronze (graphite / grooved) |
|---|---|---|
| Dry or water-lubricated duty | Strong fit — self-lubricating | Only with graphite plugs |
| Very high dynamic load | Limited by ~140 N/mm² | Bronze carries higher sustained loads |
| High sliding speed | Dry limit ~2 m/s; oil extends it | Greased bronze handles faster rotation |
| Impact / shock load | Thin wall less tolerant | Solid bronze better under impact |
| Thin-wall, compact geometry | Strong fit | Needs wall for strength |
| Aggressive chemical / washdown | Inert, corrosion resistant | Depends on the bronze alloy |
| High-temperature dry (>~280 °C) | Out of range | Graphite bronze extends further |
This is an orientation matrix. The actual choice turns on the load, speed, temperature, medium and whether re-lubrication is possible in the specific machine.
7. Machining and installation rules
The composite running face is thin, and the biggest installation error is to machine it:
Do not machine the running face
Never re-machine or bore the PTFE sliding layer after installation. The running face is 0.01–0.03 mm thick; cutting it removes the self-lubricating surface entirely. The part is supplied pre-sized — install it and let the bore land where the press fit takes it, or specify a finish-bore compensation at design time.
- Press fit into a housing bore, per the wrapped-bearing system, with a suitable chamfer on the housing and the bushing edge.
- Housing bore to a controlled tolerance (commonly an H7-class bore with a press-fit outer diameter).
- Shaft finish — the counterface should be smooth (commonly a fine turned or ground finish); a rough shaft abrades the PTFE.
8. Data a supplier needs
To quote a composite bearing correctly, a supplier needs the geometry, the duty and the confirmation that a composite is the right call:
- Geometry and formBushing bore and length, flange, or washer OD/ID/thickness; drawing or target envelope
- Wall and constructionStandard composite, or a specific lead-free / filler variant
- MotionRotation, oscillation or linear; stroke and frequency
- Load and speedStatic/dynamic load, sliding speed, calculated PV
- LubricationDry, greased, oil or water-lubricated; the actual medium
- TemperatureAmbient and surface, plus any peaks
- EnvironmentCorrosive, washdown, cleanroom, or food-contact requirement
- CounterfaceShaft material, hardness and finish
