A plain bearing supports a rotating or sliding shaft through direct surface contact, not rolling elements. No balls, no rollers — just a shaft riding against a bearing surface, usually separated by a thin film of lubricant. Engineers also call them sliding bearings, sleeve bearings, journal bearings, or bushings, and in casual shop talk those terms get used interchangeably. The point of contact on the shaft itself has its own name too: the journal.
It's one of the oldest bearing designs in use, and it hasn't been retired for a reason. Plain bearings still outperform rolling-element bearings on cost, load capacity per unit size, and tolerance for shock loads or contamination — which is why they show up everywhere from car engines to wind turbine pitch systems to kitchen hinges.
How a Plain Bearing Works
Without rolling elements to carry the load, a plain bearing relies on one of three lubrication regimes:
Hydrodynamic lubrication. Shaft rotation drags oil into a wedge shape that physically lifts the shaft off the bearing surface. This is how most engine main and rod bearings survive — once the shaft is spinning, metal never touches metal. At startup and shutdown, though, the film hasn't formed yet, which is when most wear happens.
Hydrostatic lubrication. An external pump forces pressurized oil (or occasionally air) between the surfaces regardless of shaft speed. This shows up in large, slow equipment — machine tool ways, telescope mounts, big turbine bearings — where you need full separation even before the shaft starts turning.
Boundary (dry or near-dry) lubrication. A self-lubricating liner, such as PTFE or oil-impregnated bronze, carries the load with a minimal or absent fluid film. PTFE sliding surfaces are commonly cited at a coefficient of friction around 0.05–0.10.
A U.S. Department of Transportation PTFE bearing study found the real figure shifts with contact pressure, sliding speed, and — most sharply — surface contamination, which can multiply friction tenfold. That sensitivity is exactly why boundary-lubricated liners can skip external lubrication in clean environments but still need protection from dust and debris.
Which regime applies depends on the bearing's structural type and its material — covered next.
Types of Plain Bearings by Structure
Sleeve bearings and bushings. The simplest form: a cylindrical liner pressed into a housing bore. A bushing is machined from a single material all the way through; a sleeve bearing bonds a thin bearing-grade lining (bronze, PTFE composite) onto a stronger backing, usually steel. The lining takes the wear so the backing doesn't have to. Our sleeve bearings line covers both oil-embedded and dry-running versions of this structure.
Flanged bushings. A sleeve with an integral flange at one end, combining radial support with light axial (thrust) capacity in a single part — common in linkages and light machinery where adding a separate thrust washer isn't worth the space.
Thrust washers. Flat, ring-shaped bearings that carry axial load only. Pair one with a radial sleeve bearing and you've covered both load directions without a combined bearing.
Split (half) bearings. Two semicircular shells that clamp around a shaft — the design behind virtually every automotive engine's main and connecting-rod bearings. Splitting the bearing means you never have to slide it over the full length of the shaft during assembly or replacement.
Spherical plain bearings. An inner ring with a crowned (spherical) outer surface slides inside a matching spherical bore in the outer ring, which lets the bearing accommodate angular misalignment that a straight sleeve can't. They're sold in radial, angular-contact, and thrust configurations, and frequently as rod ends for linkages that need to articulate. Corrosion-resistant grades in 303 and 440C stainless steel are standard for outdoor or washdown environments. Browse our full spherical plain bearings and rod ends line.
Tilting-pad bearings. Several independently pivoting pads surround the shaft and self-align to the running clearance under load. These are the standard choice for large turbine, compressor, and generator thrust loads, where a fixed bearing surface would be vulnerable to shaft whirl.
Plain Bearing Materials Compared
Material choice affects load capacity, temperature range, and maintenance far more than the structural type does. Three families cover most applications.
The figures below come from LILY's own sleeve bearing catalog rather than generic industry ceilings, so they reflect what's actually stocked. Three parts anchor the numbers in this table: our oil-embedded GDJBKBB bronze bushing, our PTFE-lined FEEFKB high-load dry-running bearing, and our acetal CGBATBG light-duty bushing.
Material | Typical Static Radial Load in LILY's Catalog | Lubrication Need | Best Suited For |
|---|---|---|---|
Sintered bronze (oil-impregnated) | Roughly 2,000 psi (14 MPa) at common bore sizes | Self-lubricating via absorbed oil; needs periodic replenishment | General machinery, moderate loads, cost-sensitive designs |
PTFE-lined composite | Roughly 20,000 psi (140 MPa) at common bore sizes | Dry-running, no external lubrication | High-load, high-precision, or high-temperature applications |
Solid polymer (acetal, injection-molded) | Under 500 psi (3 MPa) | Fully lubrication-free | Wet, dirty, or corrosive environments where oil attracts contamination |
The gap between the first two rows is worth pausing on: a PTFE-composite bearing in LILY's high-load dry-running line carries roughly 10 times the static load of an oil-embedded bronze bushing at a comparable bore size. That's why PTFE composites dominate in hydraulic cylinders and structural pivots, despite costing more per part. Sintered bronze bushings are commonly built to ISO 3547-1 (plain bearings — wrapped bushes), which governs dimensions and tolerances for wrapped and sintered bronze liners; sizing to that standard is what keeps a replacement bushing interchangeable across suppliers.
Pure PTFE by itself is too soft to hold up under real loads — every commercial PTFE bearing liner is filled with bronze powder, graphite, or glass fiber to control wear rate, not run as unfilled PTFE.
Temperature range tracks size and duty class, not just material
It's tempting to assume temperature rating maps cleanly onto liner material, but LILY's own catalog doesn't split that neatly. Looking at actual listed ranges rather than a generic chart:
Small-bore radial spherical plain bearings — whether steel/steel (like our GEZ 012 ES) or steel/PTFE-fabric lined — commonly sit in the -20°C to 80°C band.
Large-diameter, heavy-duty spherical plain bearings — such as our GEP 1000 FS, used in construction and mining equipment — extend to -45°C to 110°C or -50°C to 150°C depending on bore size.
Inch-sized sleeve bushings built to imperial standards show the widest spread of any group sampled: oil-embedded bronze bushings are commonly rated -35°F to 300°F, PTFE dry-running composites reach -60°F to 320°F, and light-duty acetal designs are limited to -20°F to 180°F.
The practical takeaway: don't rely on a single temperature figure by material family. Check the individual product page for the specific part number — the same liner type can carry a different rating depending on size and duty class. When a bearing is quoted outside its rated range, the sliding layer either loses its lubricating film (too hot) or turns brittle (too cold) well before the steel structure itself would fail, so the liner's rating — not the bearing's steel — is usually the limiting factor.
Suffix codes tell you the liner, but check the individual listing for maintenance
In practice, suppliers label liner types with short suffix codes rather than spelling out the material each time:
Suffix | Liner Material | Typical Maintenance |
|---|---|---|
E / ES | Steel/steel | Requires periodic lubrication |
ESL | Steel/steel, heavy-duty multi-groove | Requires periodic lubrication |
TXE | Steel/PTFE fabric | Generally self-lubricating |
FBAS / F | Steel/PTFE fiber-reinforced plastic | Varies by size — see note below |
C | Steel/PTFE sintered bronze | Generally self-lubricating |
One Catch Worth Flagging
The "maintenance-free" label commonly attached to PTFE-fiber liners doesn't hold uniformly across every size in this family. Our large-diameter GEC 950 FBAS spherical plain bearing — 950 mm bore, built for heavy construction and mining equipment — is listed with lubrication ports and a lubrication-required designation despite its PTFE-lined construction, likely because the duty cycle and contact pressure at that size call for periodic relubrication regardless of liner chemistry.
Suffix code narrows down the liner material reliably; it's not a substitute for checking the lubrication field on the specific part number when cross-referencing a competitor's catalog.
Plain Bearing vs. Ball Bearing, in Brief
Plain bearings win on load-per-size, cost, and shock tolerance; ball bearings win on speed, precision, and running friction once the loads are within a rolling element's rating. Neither is a universal replacement for the other — the deciding factors are usually speed, precision requirement, and duty cycle. For the full comparison, including specific speed thresholds and noise data, see our sleeve bearing vs. ball bearing guide.
Choosing the Right Plain Bearing
Four questions narrow the type quickly:
What direction is the load? Purely radial → sleeve bearing or bushing. Purely axial → thrust washer. Both → flanged bushing or a combined sleeve-plus-thrust-washer setup.
Does the shaft need to articulate or misalign? If yes, a spherical plain bearing or rod end is the only structural type built for it.
Is the motion continuous rotation or oscillation? Continuous high-speed rotation favors hydrodynamic designs with a reliable oil supply. Oscillating linkages, where a stable oil film never fully forms, favor self-lubricating bronze or PTFE composites.
What's the environment and size? Dirty, wet, or corrosive conditions push the choice toward solid polymer bearings or stainless spherical plain bearings — sintered bronze's open pore structure and standard steel backings are both vulnerable to contamination and corrosion. And regardless of liner family, confirm the temperature and lubrication rating on the specific part number once size is known, since both can shift meaningfully between a small bushing and a large heavy-duty bearing in the same product line.
FAQ
What's the difference between a bushing and a sleeve bearing on a drawing?
A bushing is machined from one material end to end — solid bronze or solid polymer, for instance. A sleeve bearing bonds a thin bearing-grade lining onto a separate, stronger backing, usually steel with a bronze or PTFE-composite liner pressed or bonded in.
The distinction matters for repair: a worn bushing gets replaced whole, while a sleeve bearing's liner is what actually wears — the steel backing usually outlasts several liner cycles in a design meant for relining. For a deeper side-by-side, see our bushing vs. bearing guide.
Does a "dry-running" rating mean the bearing never needs attention?
Not automatically. Dry-running means the liner doesn't rely on an oil film to separate the surfaces — PTFE composites and solid polymers are built that way from the start. But as the suffix-code table above shows, some large, high-load PTFE-lined bearings still carry a "lubrication required" note in the catalog, because periodic relubrication extends service life at high contact pressure even when the liner itself doesn't strictly need it to function. Sintered bronze and babbitt-lined journal bearings are a different case entirely: they depend on at least a residual oil film, and running them dry for extended periods leads to rapid wear or seizure.
What typically causes a plain bearing to fail?
Lubrication film breakdown is the most common one — it tends to happen at startup, before hydrodynamic lift has formed, when metal briefly touches metal. Misalignment is next: it concentrates load on one edge of the liner instead of spreading it across the full surface. Contamination embedding into a soft liner and simply exceeding the material's rated load or temperature account for most of what's left.
Are plain bearings cheaper than ball bearings?
Usually, on unit cost — fewer precision components to machine. Total cost of ownership depends on the application, though. At higher speeds, a ball bearing's lower running friction and longer service interval can make it the cheaper option over the equipment's lifetime, even with a higher purchase price.
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