Plain bearing PV calculator
Enter the radial load, the bore, the length and the motion. The calculator returns the specific load p, the sliding speed v and their product PV, and compares each with the published limit of the bushing material you select, so you can see at once whether the material fits the duty.
The three numbers that decide a plain bearing are the specific load (force divided by projected area), the sliding speed at the bore surface, and their product PV, which is a measure of the frictional heat the bearing must dissipate. Every bushing material publishes a limit for each; a design is workable when all three are within the limits of the chosen material, with a margin for shock, misalignment and dirt.
The formulas
Specific load: p = F / (d × L) in N/mm² (= MPa), where F is the radial force in newtons, d the bore and L the loaded length in millimetres. Sliding speed for rotation: v = π × d × n / 60 000 in m/s, with n in rpm. For oscillation through a total angle θ at f cycles per minute (one cycle = out and back): v = 2 × (θ / 360) × π × d × f / 60 000. For linear motion with stroke s (mm) at f strokes per minute: v = 2 × s × f / 60 000. PV is simply p × v in N/mm²·m/s.
For imperial input the calculator converts to N and mm first and shows psi and ft/min alongside. 1 N/mm² = 145 psi; 1 m/s = 196.85 ft/min; 1 N/mm²·m/s ≈ 28 550 psi·ft/min.
Reading the result
Each of p, v and PV is compared with the limit published for the selected material and lubrication; the utilisation shown is the highest of the three ratios. Under 80 % is a comfortable design; 80–100 % works when the load is steady, the shaft is to specification and the temperature is moderate; over 100 % means a different material, a longer bushing, a larger bore or better lubrication. When the speed is entered as zero the load is checked against the static rating where the material publishes one.
The limits are separate published values, not one guaranteed operating point, and they assume the shaft, fits, alignment and environment described on each product page. Cast bronze and hardened steel publish no PV figure, so for those the calculator checks p and v only.
Oscillating and intermittent motion
Pivot bushings move slowly and the mean sliding speed is low, so PV is rarely the limit; the specific load is. But oscillation is harder on a bearing than the mean speed suggests: the film breaks down at each reversal and the same arc of the bore carries the load every cycle. Use the oscillating or dynamic load rating (60 N/mm² for PTFE and POM composite, 40 N/mm² for wrapped bronze) rather than the static one, and for very small angles at high frequency (fretting) ask for a review.
What the calculator does not do
It does not estimate wear life, temperature rise or the effect of dirt, misalignment and shock; those need the full application. It does not size the housing fit (use the press-fit calculator) or split a load between two bearings (use the load calculator). Use the result to shortlist a material, then send the duty with the numbers and our engineers confirm the material and the size.
Frequently asked questions
What is PV in a plain bearing?
The product of specific load p (N/mm²) and sliding speed v (m/s). It is proportional to the frictional heat generated per unit of bearing area and is the usual limit for dry-running and boundary-lubricated bushings.
What is a good PV value?
It depends on the material: about 1.8 N/mm²·m/s long-term for PTFE composite dry, 2.8 for greased bimetal and wrapped bronze, 10 for bimetal in oil, 22 for POM composite in oil, 1.65 for graphite bronze dry. Stay under 80 % of the limit for a comfortable design.
How do I calculate the sliding speed of an oscillating bushing?
Multiply the fraction of a full turn swept per cycle (angle / 360, twice for out and back) by the bore circumference π × d and the cycles per minute, then divide by 60 000 to get m/s.
Why does the static limit differ from the dynamic one?
A stationary load only has to be carried without deforming the bearing layer; a moving load also generates heat and wear. Materials therefore publish a higher static rating (250 N/mm² for composite bushings, 45 for cast bronze) and a lower moving one.
Can I use the calculator for a thrust washer?
Yes, by entering the annular face area as d × L (any d and L whose product equals the face area) and the sliding speed at the mean diameter; the material limits are the same.
Over the limit, or close to it?
Send the load, speed, motion and environment. Our engineers propose the material, the size and the lubrication and quote within 12 hours. Samples are free.