A thrust washer is a flat annular ring that locates axial movement. Where a radial bushing supports load perpendicular to the shaft, a thrust washer supports load acting along the shaft axis. It sits between a rotating face — a gear boss, a pulley hub, a crane sheave — and a stationary housing face, and stops the rotating part walking along the shaft.

Three dimensions define it: inside diameter (ID, clearing the shaft), outside diameter (OD, locating in or against the housing), and thickness. The load-carrying area is the annulus between ID and OD, so increasing the OD is usually the most effective way to reduce bearing pressure — area grows with the square of the diameter while cost grows more slowly.

Thickness sets more than the wear allowance. Too thin and the washer distorts and cannot carry heat from the face; much thicker adds cost without adding life. In service, washers run from 1.5 mm on gearbox parts to 25 mm or more on rolling mill and hydropower equipment, with thickness set as a fraction of the OD.

Wear is concentrated at start-up and shutdown. At speed an oil film or a transferred graphite film separates the faces; at low speed and under reversal the surfaces run in boundary conditions, where the bronze’s conformability and the counterface finish set the wear rate. That is why the counterface specification below matters as much as the alloy.

A thrust washer is not the same thing as the flange on a flanged bushing. A flange takes light axial load in the same part that carries the radial load; a dedicated washer gives a much larger annular area and suits axial load that is significant, continuous or combined with shock. Where both appear, they are sized together — see center flanged bushings.

The geometry solves three problems at once: carrying the axial load, stopping the washer rotating with the shaft, and getting lubricant to the face. The table sets out the common types.

Plain and grooved washers cover the majority of enquiries. They are inexpensive to produce and easy to replace during overhaul, and the groove pattern can be matched to the duty without changing the blank.

Graphite-plugged washers are used where regreasing is impractical — a rudder bearing, a gate trunnion, a pivot at height. Plugs sit in concentric rings covering 20–30% of the face and transfer a film to the counterface in the first hours of running, after which the washer runs dry. See graphite bronze bushings.

Segmented washers solve an assembly problem rather than a load problem. On a rudder stock or a mill chock, stripping the shaft to fit a one-piece washer can take days; a split washer goes in around it. Segments are match-marked so they return as machined.

Spherical-seated washers suit hydro and marine work where the shaft deflects or the seat cannot be held square. The spherical back lets the washer align to the counterface, avoiding edge loading. Our spherical bearings for dam gates use the same principle at larger scale.

Material Options and Indicative Load Ratings

Alloy choice follows the same logic as for a bushing, with one difference: a thrust face sheds heat less well than a cylindrical bore, since no oil is pumped along the bearing. That lowers the PV limit and favours the harder, more conductive alloys.

Reading the table. Where load is moderate and alignment uncertain, the leaded tin bronzes are safer: they deform slightly to share load and tolerate grit without scoring the shaft. Where load is high, the aluminum and manganese bronzes carry more pressure but demand better alignment and a harder counterface.

On graphite-plugged washers. The base alloy — usually high-tensile brass or aluminum bronze — is chosen for strength, since the graphite does the lubricating. Capacity is then set by the dry-running PV limit below rather than by static strength. Our C93500 centrifugal cast and CuSn11P parts are the usual oil-lubricated alternatives.

• Allows maintenance-free and long-life operation;
• Suitable for high static and dynamic loads;
• With low and smoothly coefficient of friction and without stick-slip effects;
• Suitable for dirty, corrosion, impact load, and edge loading;
  The base material provided a good shock-absorbing capacity;
• Can be used over a large temperature range;
• Suitable for reciprocating, rotating and oscillating movement with start frequency and difficulty to form oil film occasions;
• With low wear rate and long life service.

Load Capacity, PV Limit and Surface Speed

Two numbers govern whether a thrust washer survives: the bearing pressure on the face, and the PV product — pressure times sliding velocity — which stands in for the heat generated at the interface.

Why thrust faces run hotter. A cylindrical bushing pumps oil along its length and that flow carries heat away; a thrust face has no equivalent, so the limits above sit below the figures quoted for the same alloy in radial service. Where a design is marginal, increase the OD, add radial grooves, or improve the counterface finish — before changing alloy.

Grooves, Oil Holes and Lubrication Patterns

A groove does two jobs: distributing lubricant across the face and giving wear debris somewhere to go. It also removes load-carrying area, which is why the pattern is chosen rather than maximised.

Practical rules. Grooves stop 1.5–3 mm short of both edges so an unbroken land dams the oil. Depth is usually 0.3–0.5 times the thickness; deeper and the washer loses stiffness. Small washers take four grooves, rising to eight above about 120 mm OD. Grooves are cut in one face only, against the surface to be lubricated.

Graphite plug layout. Plugs sit in concentric rings covering roughly 20–30% of the face. Less leaves dry zones; more thins the bronze web until it cannot carry load. Plugs are finished flush so the counterface runs on both materials. Against a soft counterface the plugs do most of the work, so coverage goes to the upper end.

Pattern selection is covered further on our groove patterns page, which also shows bore patterns for radial bushings.

Housing Design, Fits and Installation

Most thrust washer failures are not material failures. The three causes we see repeatedly are a counterface too soft or too rough, a washer allowed to rotate with the shaft, and end play set so tight the assembly cannot expand.

Counterface requirements

The counterface should be harder than the washer and finished smooth: hardened steel around HRC 45 or above, ground or fine-turned to Ra 0.8 µm or better, and square to the shaft axis. It should cover the full washer face — a narrow collar on a wide washer cuts a wear step that restricts oil flow.

Anti-rotation

A plain washer will rotate if nothing stops it, and a spinning washer wears the housing rather than being worn itself. Use a tab in a slot, a dowel, a press fit or a flange on a shoulder. On reversing or high-cycle duty, use a positive feature rather than friction.

End play

Allow axial clearance for thermal growth and stack-up: 0.05–0.15 mm for small gearbox assemblies, 0.2–0.5 mm or more for large equipment, scaled with diameter and with the expansion difference between shaft and housing. Too tight gives heat and seizure; too loose gives impact at every reversal.

1. Inspect and deburrCheck the faces for burrs and the edges for transit damage. Stone off raised metal at the ID and OD.
2. Verify the counterfaceConfirm hardness, finish and squareness to the shaft axis. Re-grind or replace a scored collar before fitting.
3. Confirm groove directionCheck that the hand of the spiral pumps oil toward the load zone for the actual rotation direction.
4. Fit with anti-rotation engagedSeat the washer fully and make sure the tab, dowel or flange is engaged, not resting against the feature.
5. Check end playMeasure against the drawing. Correct with shims at the housing, not by thinning the washer.
6. Prime and run inCoat the face with the service lubricant before start-up. For graphite-plugged washers, run at reduced load for the first hours.

Applications

Thrust washers appear wherever something rotates and is pushed along its axis. Alloy and pattern change with the industry; the sizing logic does not.

Marine and offshore

Steering gear, rudder stocks, winch drums and hatch pivots combine corrosion with idle periods and intermittent motion. Nickel aluminum bronze or graphite-plugged washers are usual — the former where parts meet seawater, the latter where regreasing is impractical. See bearing pads for marine hydraulic systems and sliding bearings for marine and offshore.

Construction and mining

Excavator pivots, crane sheaves and boom foot pins see shock loading, dust and long gaps between maintenance. Axial load is often underestimated because the pin carries radial load too. Manganese bronze and graphite-plugged washers suit this — see construction equipment bearings and wrapped bushings in crane applications.

Rolling mills and steel plant

Work roll and back-up roll chocks take thrust from roll shifting and drive spindles, in water, scale and heat. Washers are large, thick and usually graphite-plugged or aluminum bronze — C95500 for heavy-duty rollers is a common choice — and nearly always to drawing.

Hydropower and water control

Gate trunnions, hoist sheaves and dam gate bearings work slowly under high load, often submerged, and may sit unmoved for months. That suits graphite-plugged bronze against stainless or hard-chromed faces. See spherical bearings for dam gates and gate operating mechanisms.

Packaging and automation

Indexing tables, cam drives and timing sets run at moderate load but high cycle counts, in lines where oil leakage is unacceptable. Graphite-plugged washers keep the area clean; see thrust washers for packaging machinery and the billet timing set example.

Agricultural machinery

Harvester drives, tractor linkages and seeder openers combine shock with abrasive dust and seasonal idling. Maintenance-free operation matters most in a short harvest window, so solid-lubricated washers are specified despite higher unit cost — see bronze bushings for agricultural machinery.