A shaft bushing (or bush) is a cylindrical machine element fitted around a rotating or oscillating shaft to support, guide or secure it. In its most common sense, a bushing acts as a plain bearing between shaft and housing: the shaft turns or slides on the bore of the bushing on a film of oil or grease. Taper lock bushes that secure a shaft to a pulley or gear, and repair sleeves that renew worn shaft surfaces, are also called shaft bushes.
In this guide we look in detail at what a bushing is and what it does, bushing types and materials, the difference between a rolling bearing and a bushing, fitting and lubrication practice, signs of wear and the critical bushings used in mining machinery.
What Does a Bushing Do?
- Supports the shaft: As a plain bearing it carries radial and, in some types, axial loads.
- Takes the wear: The bushing wears instead of the shaft and housing; replacing the bushing protects expensive parts.
- Absorbs shock: It is more tolerant of heavy and shock loads than rolling bearings.
- Secures and centres: Taper lock bushes fix a pulley, gear or drum to the shaft, with or without a key.
- Repairs: Repair sleeves make worn shafts or housings usable again.
Bushing Types
| Bushing Type | Feature | Typical Use |
|---|---|---|
| Plain sleeve bushing | Cylindrical; lubricated with oil or grease | Pins, pivots and low-speed shafts |
| Flanged bushing | Also carries axial load | Where axial location is needed |
| Self-lubricating bushing | Porous (oil-impregnated) bronze or solid lubricant inserts | Where lubrication is difficult |
| Polymer and composite bushing | Light, corrosion-resistant, can run without oil | Wet environments, low–medium loads |
| Eccentric bushing | Wall thickness varies around the circumference | Cone crusher eccentric (eccentric bushing guide) |
| Spider bushing | Carries the top end of the main shaft | Gyratory and some cone crushers |
| Taper lock bush (shaft locking bush) | Secures a pulley/gear to the shaft by wedging on a taper | Pulleys, couplings, drums |
| Adapter sleeve | Secures a taper-bore bearing to the shaft | Bearing mounting |
| Shaft repair sleeve | Thin-walled sleeve; renews a worn seal surface | Shafts worn in the seal area |
| Rubber–metal bush (silentbloc) | Damps vibration | Suspension, motor mountings |
Bushing Materials
| Material | Advantage | Caution |
|---|---|---|
| Tin bronze | Good sliding properties, wear resistance | Needs proper lubrication |
| Leaded bronze | Tolerant of lubrication lapses, embeddability | Load capacity must be assessed for the application |
| Aluminium bronze | High strength, impact and corrosion resistance | Shaft hardness must be adequate |
| White metal (babbitt) lined bushings | Excellent sliding, embeddability | Limited temperature and load |
| Steel and hardened steel | High load, wear resistance | Lubrication is critical |
| Polymers and composites (PTFE, polyamide, etc.) | Oil-free running, corrosion resistance | Temperature and load limits |
Rolling Bearing or Bushing?
| Criterion | Rolling Bearing | Bushing (Plain Bearing) |
|---|---|---|
| Friction | Low | Higher; reduced by the oil film |
| Shock load | Limited tolerance | High tolerance |
| Space required (radial) | More | Compact |
| High speed | Suitable | Depends on the lubrication system |
| Cost | Standard, variable | Usually economical; large bushings are custom-made |
| Tolerance of contamination | Sensitive | Tolerant with some materials |
Large bronze bushings are preferred for very heavy, shock loads such as cone crusher eccentrics and countershafts, while rolling bearings are common on screens and conveyors. For bearing selection see our bearing guide.
Fitting and Fits
- Fitting into the housing: Bushings are usually fitted into the housing bore with an interference fit, using a suitable press or by cooling (for example shrinking the bushing with dry ice or liquid nitrogen). Hammering a bushing in can deform it.
- Bore check: An interference fit reduces the bushing bore; the bore should be measured after fitting and machined if necessary.
- Running clearance: The clearance between shaft and bushing should be sufficient for an oil film but not excessive.
- Oil grooves: The bushing’s oil grooves and holes must line up with the oil feed points in the housing.
- Taper lock bushes: Screws must be tightened to the manufacturer’s torque in the correct sequence; surfaces must be free of oil.
Lubrication
The life of a plain bearing bushing depends on lubrication. Oil or grease forms a film between shaft and bushing and prevents metal-to-metal contact. On large crushers, bushings are fed by a pressure lubrication system, and oil temperature, pressure and cleanliness are monitored continuously. An increase in bronze particles in oil analysis is the earliest indicator of bushing wear. For lubrication unit maintenance see our lubrication unit guide.
Signs of Bushing Wear
| Symptom | Possible Cause |
|---|---|
| Rising oil return temperature | Inadequate lubrication, bushing damage |
| Bronze particles in the oil | Bushing wear |
| Shaft play and knocking | Excessive bushing wear |
| Smearing and scoring on the bushing bore | Contamination, lack of oil, overload |
| Bushing spinning in its housing | Loose fit, excessive friction |
Critical Bushings in Mining Machinery
- Cone crusher eccentric bushing and main shaft bushings: The crusher’s most critical plain bearings (eccentric bushing, main shaft and head). Where the eccentric bushing is secured with a poured compound, our Aurox eccentric liquid wedge stops it spinning in place.
- Countershaft bushings: Support the pinion shaft (countershaft and pinion).
- Socket liner and spherical bearing: The surfaces on which the main shaft sits (socket liner).
- Spider bushing: The upper bearing of the main shaft in gyratory crushers (gyratory crusher).
- Pin and pivot bushings: Impact crusher apron pivots, conveyor take-up pivots.
- Taper lock bushes: Pulleys and conveyor drums (conveyor pulley).
Repair with a Shaft Repair Sleeve
A shaft with a wear groove in the seal area can easily be repaired with a thin-walled repair sleeve. The sleeve is pressed over the worn area and provides a new, smooth surface for the seal. For heavier wear, the shaft surface can be machined and a thicker sleeve fitted, or the surface renewed by metal spraying. For shaft repair and drive shafts see our drive shaft guide.
Frequently Asked Questions
What is a shaft bushing?
A shaft bushing is a cylindrical machine element that acts as a plain bearing between shaft and housing, supporting or securing the shaft.
What does a shaft locking bush do?
It secures a pulley, gear, coupling or drum firmly and concentrically to the shaft; it is usually made as a taper lock bush.
When should a bronze bushing be replaced?
When the shaft–bushing clearance exceeds the manufacturer’s limit, when oil analysis shows significant wear, or when the bushing surface is damaged.
What is a bushing as an engineering term?
As a machine element, a bushing is a cylindrical part used as a plain bearing, sleeve, liner or securing element.
Information Needed to Manufacture a Bushing
- Bore, outside diameter and length (with tolerances),
- Flange dimensions (if any),
- Position of oil grooves and oil holes,
- Material (bronze grade, steel, polymer),
- Fitting method and type of fit,
- Operating conditions: load, speed, temperature, lubrication,
- A sample bushing or technical drawing.
For bushings with special geometry such as eccentric bushings, the eccentricity value and its position must also be stated.
Factors Affecting Bushing Prices
| Factor | Effect |
|---|---|
| Material | Bronze alloys are more expensive than steel because of their copper content |
| Size and weight | Large crusher bushings require heavy castings |
| Casting method | Centrifugal casting gives denser, higher-quality material |
| Machining precision | Tight tolerances and oil grooves increase labour |
| Quantity | One-off manufacture raises unit cost compared with batch production |
Glossary
- Plain bearing: A bearing in which the shaft turns by sliding on an oil film.
- Interference fit: A fit in which the bushing is installed in the housing by pressing or by temperature difference.
- Eccentric bushing: A bushing whose wall thickness varies around the circumference.
- Adapter sleeve: A sleeve that secures a taper-bore bearing to the shaft.
- Repair sleeve: A thin-walled sleeve that renews a worn shaft surface.
- Embeddability: The ability of a bearing material to protect the shaft by embedding small foreign particles in its surface.
More Questions
How do you choose between a shaft bushing and a rolling bearing?
A bushing is preferred for heavy and shock loads, low–medium speeds and compact space; a rolling bearing where high speed, low friction and the advantage of standard parts are needed.
How is a bronze bushing removed?
With a suitable puller or press; seized bushings can be removed after thinning the bore by machining. The housing bore must not be damaged.
CSP Mühendislik Support
CSP Mühendislik manufactures and supplies cone crusher eccentric and main shaft bushings, countershaft bushings, pin bushings, taper lock bushes and repair sleeves to drawing or sample. See our cone crusher spare parts page for cone crusher bushings and our spare parts page for other equipment, or ask about our service, maintenance and repair services.
