Industrial MRO Reference Library · Technical Reference

Plain Bearings & Bushings

Plain bearings and bushings support a shaft on a sliding surface with no rolling elements. This sheet compares bronze, oil-impregnated sintered, polymer and composite bushings and explains fit and lubrication basics.

Ref MRO-0013

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

A plain bearing (bushing or sleeve bearing) is a tube, flanged tube or thrust washer that a shaft turns or slides in. It is simple, quiet, takes shock loads well and fits small spaces. Main types are cast or wrought bronze, oil-impregnated sintered bronze (powdered metal soaked with oil), polymer (such as nylon, acetal or filled PTFE) and composite (a steel back with a porous bronze layer and PTFE or polymer lining).

How to identify

Bronze is yellow to reddish and heavy. Sintered bronze looks dull and slightly porous and may feel oily. Polymer bushings are plastic, often white, black or colored. Composite bushings are thin-walled with a steel outside and a gray or dark lining, and usually have a split seam. Measure ID, OD, length and flange size for flanged types.

Bushing material comparison

Type	Lubrication	Strengths	Limits
Cast bronze (such as C93200 bearing bronze)	Grease or oil; often grooved	High load, shock, wear resistance	Needs regular lubrication
Oil-impregnated sintered bronze	Self-lubricating from stored oil	Clean, low maintenance, low cost	Lower load; loses oil if overheated or washed out
Polymer	Dry or light lubrication	Corrosion-proof, quiet, light	Lower load and temperature; can swell with moisture
Steel-backed composite	Dry or marginal lubrication	Thin wall, good load, low friction	Lining wears through; do not machine bore
Graphite-plugged bronze	Solid lubricant plugs	High temperature, little maintenance	Higher cost

Key points

Press-fitting a bushing closes up the bore. The maker's data gives the housing bore and final ID allowance.
Do not ream or machine oil-impregnated or composite bushings unless the maker allows it. Machining smears or removes the working surface.
Shaft finish and hardness matter. A rough or soft shaft wears the bushing fast.
Sintered bushings should be re-oiled with a compatible oil after long storage or heat.
Load and speed limits (often given as a PV value) are in the maker's data.

Common mistakes

Greasing a dry-running polymer or composite bushing with a grease that attacks it.
Reaming a sintered bushing after pressing it in.
Using a nylon bushing in wet service where it swells and binds.
Ignoring shaft wear when replacing a bushing.

Governing standards: No single consensus standard covers all plain bearings. Bronze alloys follow ASTM B505 and related specs; sintered bearings follow ASTM B438. Follow the bushing maker's fit and load data.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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