Two ways to slide on a shaft
A bushing is the simplest bearing: a sleeve in which a shaft slides or oscillates. It has no rolling elements, so it needs little radial space, tolerates shock and dirt, and runs quietly. What changes between types is the sliding surface. A bronze bushing slides on a metal alloy that is usually lubricated with oil or grease. A composite bushing has a thin low-friction layer, often PTFE-based, bonded to a metal backing, and can run with little or no added lubricant. Plain bearings in general are introduced in what is a plain bearing and compared with rolling designs in rolling vs sliding bearings.
Bronze bushings
Bronze is an alloy of copper with tin, lead, aluminium or other elements, and the choice of alloy sets the properties. Widely used families include tin bronze for general service, leaded bronze for better embedding and lower friction under marginal lubrication, and aluminium bronze for high load and strength. Sintered (powder metal) bronze is another route: a porous sleeve impregnated with oil, giving a self-lubricating bushing for light to moderate load.
Solid cast bronze bushings carry high loads and handle shock, and can be machined to custom sizes or fitted with grooves and pockets for grease. They are usually the first choice in heavy, slow, oscillating joints such as press machinery, hydraulic cylinders, farm implements and pivots. Their weakness is that they need lubrication, and they can seize if lubricant is lost; they also work-harden or score a soft shaft, so shaft hardness and finish matter.
Composite bushings
Composite bushings come in two common constructions. A steel or bronze backing with a sintered bronze interlayer and a PTFE-based overlay is a metal-polymer type; its sliding layer transfers a thin film to the shaft, providing low friction and permitting dry running. The second kind is fibre-wound or filament composite with resin and a solid lubricant, used in heavy-duty or marine pivots where corrosion and washout matter. Both provide low friction with little maintenance.
Composite bushings give consistent friction, handle dry or marginal lubrication, resist corrosion, and tend to be lighter. Their limits are the shaft finish and hardness, the temperature capacity of the polymer, and sensitivity to edge loading and abrasive contamination, which can score the thin layer. Capacities and temperature ranges differ by product family, so use the supplier datasheet.
Side-by-side comparison
| Item | Bronze (solid or sintered) | Composite (metal-polymer or filament) |
|---|---|---|
| Lubrication | Needs oil or grease; sintered types hold oil | Self-lubricating; many run dry |
| Load capacity | High, especially solid cast; handles shock | Good to high; depends on family and backing |
| Speed | Moderate; limited by heat and film | Low to moderate; limited by polymer heat |
| Corrosion | Good in water, poor with ammonia and some chemicals | Good; matched to media by layer |
| Shaft requirements | Hardened and ground shaft recommended | Hard, smooth shaft required, often chrome or stainless |
| Machinability | Easy to machine to custom size | Standard sizes mostly; cutting damages the layer |
| Maintenance | Regreasing schedule | Low maintenance |
| Relative cost | Low to moderate | Moderate to high per part |
All figures here are qualitative. Load and speed ratings come from the manufacturer, and PV values (pressure times velocity) are the common way to compare plain bearings. Always confirm them from the supplier datasheet.
Lubrication in practice
For bronze bushings, grease grooves and a regular regreasing schedule matter more than the alloy label. Grease must reach the loaded zone, and the groove layout should be agreed on the drawing. In oscillating motion, a bushing can run with a surprisingly small film, so the lubricant should be matched to speed, load and temperature; see bearing grease. For composite bushings, the layer provides the lubricant, but grease can still help in contaminated settings by flushing particles. A few composite families do not tolerate certain greases or oils, so ask before adding any.
Fits, shafts and installation
A bushing is only as good as its fit. Most are pressed into the housing with an interference fit, and the bore closes slightly after pressing, so the finished running clearance must be checked on the installed part, not on the loose sleeve. Too tight and the bushing runs hot and seizes; too loose and it hammers in the bore and wears the seat. Bronze bushings are often finish-reamed after pressing, while composite bushings are designed to work at their pressed-in size and should not be reamed, because cutting removes the sliding layer.
Shaft surface is the other half. For bronze, a hardened and ground shaft with a fine finish extends life significantly. For composite types the datasheet normally gives a minimum hardness and a maximum roughness, and a shaft outside these limits produces rapid wear that looks like a bushing fault. Edge chamfers on both parts and a lead-in on the shaft prevent shaving the layer during assembly. Press with a stepped mandrel and never hammer directly on the bushing face.
A short method for choosing
- Define the motion: continuous rotation, oscillation or linear sliding, and its speed.
- Estimate the specific load on the projected area (load divided by diameter times length).
- Decide whether regular lubrication is realistic. If it is not, choose composite or sintered.
- Check the environment: water, chemicals, dust, temperature.
- Review the shaft: material, hardness and finish, because the shaft is half of the bearing.
- Check the housing bore tolerance and the press-fit interference for the chosen type.
Heavy, shock-loaded, grease-lubricated pivots favour solid bronze. Wet, dirty, hard-to-reach joints that cannot be regreased favour composite. Light-duty rotating assemblies in appliances and office equipment often use sintered bronze or polymer sleeves. Bushing size and tolerances should be given on the drawing, together with the fit, and checked by sample. The related spherical types for swivelling motion are covered under spherical plain bearings.
Sourcing notes
Bushings are available as standard stock sizes in both families, and as custom machined parts. Standard stock sizes can usually be quoted at the reference quantities on the MOQ and lead time page, and custom machining is quoted from the drawing. State the sleeve dimensions, material or family, flange or plain type, groove pattern, required fit and application load in the quote form. Plain bearing lines are listed on the plain bearing page, and the desk will propose options from partner plants and confirm the data in writing.