Guides / Grades

Bearing Grade PEEK: When a Part Has to Slide Dry

September 20, 2026

Sources: manufacturer datasheets and published standards. See editorial standards.

If a PEEK part slides against something, the grade matters more than the geometry. Unfilled PEEK is tough but not slippery. Glass filled PEEK is stiff and actively destructive to whatever it runs against. Bearing grade PEEK exists because neither of those works in a bushing.

What it is

The common formulation blends PEEK with carbon fibre, PTFE and graphite, around 10% of each. Each additive does one job:

• Carbon fibre carries load and adds stiffness, so the bushing does not deform under pressure
• PTFE lowers friction and helps release
• Graphite helps form the transfer film that makes dry running possible

Typical density lands around 1.44 g/cm³. Dry coefficient of friction against steel is roughly 0.1 to 0.2, against 0.3 to 0.4 for unfilled PEEK. The blend carries far more PV, the pressure times velocity product that decides whether a dry bearing survives.

What you give up is strength. The additives that make it slide take away tensile strength and impact resistance, so this is a surface material, not a structural one. Do not use it for the bracket that holds the bushing.

Where it wins

Bearing grade PEEK is specified when a metal bearing or a cheaper plastic cannot cope:

• Hot service. It keeps working where nylon and acetal soften, up to continuous temperatures no other common bearing plastic reaches.
• No lubrication allowed. Food and pharma equipment, cleanroom mechanisms, vacuum systems where oil would outgas.
• Aggressive media. Pumps and valves where a lubricated metal bearing would be washed out or corroded.
• Electrical isolation, sometimes. Note that carbon filled blends are not insulators. If isolation is the point, this is the wrong material.
• Soft shaft protection. PEEK will not score a shaft the way a hard bronze or a glass filled plastic can.

Typical parts: bushings and sleeve bearings, thrust washers, wear pads and strips, seal rings and backup rings, bearing cages, guide rollers, valve stem bushings.

Designing a bushing that lasts

Clearance. PEEK expands about four times more than steel per degree, and a bearing grade blend sits lower but still well above steel. Calculate clearance at the maximum service temperature, not at 20 °C. A press fit that is correct cold can seize hot.

Wall thickness. Thin walls take heat away better and deform less than a thick section. A thick PEEK bushing holds heat in the sliding surface, which raises wear.

The mating surface. Dry running wants a hard, smooth counterface. Ra 0.2 to 0.4 µm on a hardened shaft is a reasonable target. A rough shaft abrades the transfer film as fast as it forms. A very polished shaft can fail to let the film key in.

PV limits. Ask the stock supplier for the PV chart at your temperature and duty cycle. Continuous rotation, oscillation and intermittent motion are three different loads on the same bushing.

Press fit or retained. A press fit into a metal housing helps the bushing shed heat. It also compresses the bore, so machine the bore after fitting when the tolerance is tight.

Say it on the drawing. The bore tolerance after fitting, the surface finish and the temperature that the clearance applies at. Realistic numbers are in PEEK machining tolerances.

When another grade or material is the answer

• A structural part that also slides a little. CF30 with a hard mating surface, or a separate bearing insert. See CF30 vs GF30.
• Light load, cool, chemically mild. Acetal costs a fraction of PEEK and slides well.
• Pure low friction, no load, no heat. Filled PTFE.
• High static load at room temperature. Bronze, or a metal backed bearing.
• Electrical isolation required. Unfilled or glass filled PEEK, accepting worse friction, or a different bearing concept.

What to send a shop

A bushing drawing that gets a useful quote says: grade, bore and outside diameter with tolerances, whether the bore is finished before or after fitting, shaft material and finish, load, speed, duty cycle and service temperature. Half of that is about the application rather than the part, and it is what tells a shop whether the bushing will survive.

How dry bearings actually fail

A bearing grade PEEK bushing rarely wears out evenly. It fails in one of four ways, and each points at a different fix.

Heat. PV exceeded, or the wall too thick to shed heat. The surface glazes, friction rises and the bushing fails quickly once it starts. Fix: thinner wall, metal housing contact, lower duty cycle or a larger bearing area.

Edge loading. A misaligned shaft puts the whole load on one edge. You see a bright band at one end and no wear elsewhere. Fix: alignment, a crown on the bushing or a self aligning mount.

Transfer film never forming. Usually a counterface that is too rough or too hard to hold the film, or a lubricant contaminating the surface. Fix: shaft finish around Ra 0.2 to 0.4 µm, and keep oil out if the bearing is meant to run dry.

Clearance closing hot. Calculated at 20 °C rather than at service temperature, so the bushing grips the shaft. Fix: recalculate at temperature, both directions.

If you can tell a shop which of the four happened to the last one, the replacement will be a better part than the original.

Bearing grades are one branch of our guide to PEEK grade selection.

Send the drawing with those details and we match you with shops that machine bearing grades regularly, not shops seeing one for the first time.

Frequently asked questions

Keep reading

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• When PEEK Runs Out of Heat and Polyimide Takes Over