PV limit calculator

Content

Use at your own risk. Verify inputs, assumptions and results independently before applying them.

Compute contact temperature

Use this mode when load and speed are known and you want the operating PV and estimated temperature rise.

Input definitions

Bearing length (L)
Axial length of the loaded journal bearing contact. Unit: selected length unit.
Shaft diameter (D)
Nominal journal or shaft diameter used with bearing length for projected area. Unit: selected length unit.
Radial load (F)
Normal bearing load carried by the projected bearing area. Unit: selected force unit.
Sliding velocity (V)
Relative surface speed at the journal-bearing interface. Unit: selected speed unit.
Coefficient of friction (mu)
Representative friction coefficient for the material pair and lubrication state. Unit: dimensionless.
Thermal resistance (R)
Equivalent thermal resistance from the contact to the environment. Unit: K/W.
Allowable temperature rise (dTmax)
Maximum permitted contact temperature rise before the material or application limit is reached. Unit: K or deg C temperature difference.
Operating PV
Contact pressure multiplied by relative sliding speed for the operating condition. Unit: MPa·m/s.
Material limiting PV
Supplier or test-derived permissible PV for comparable temperature, lubrication and duty. Unit: MPa·m/s. The displayed margin is limiting PV divided by operating PV.

Worked example

For a journal bearing of length L = 20 mm and diameter D = 20 mm, with load F = 80 N and sliding speed V = 0.5 m/s, projected area is 400 mm², pressure is 0.2 MPa and PV = 0.100 MPa·m/s. Enter friction coefficient μ = 0.3 and thermal resistance R = 6.25 K/W: frictional power is 12 W and estimated temperature rise is 75 K.

In Load and LPV mode, allowable rise 75 K with those same geometry, speed, friction and thermal inputs returns a limiting load of 80 N. In PV margin mode, operating PV = 0.100 and a supplier limit of 0.350 MPa·m/s give a ratio of 3.5. This ratio is a screening margin, not proof of acceptable temperature, startup behavior or service life.

Method and assumptions

The calculator follows the “Limiting PV-value of plastic journal bearings” equations: dT = R mu F V, PV = F V / (L D), Fmax = dTmax / (R mu V), and LPV = Fmax V / (L D). PV is displayed as MPa m/s, equivalent to 10^6 Pa m/s.

Rheologylab

Use the projected area L D for journal bearings. The temperature relation uses a user-supplied thermal resistance, so its quality depends strongly on how well that value represents the bearing, housing, ambient cooling, and duty cycle.

Projected journal bearing area A rectangle of axial length L and shaft diameter D represents the projected area used to calculate average bearing pressure F divided by L D. Projected areaA = L × D L — axial lengthD
Projection viewed along the radial load direction; schematic, not to scale. Use L × D for average bearing pressure, not the curved surface area πDL or a local Hertzian contact area. V is relative sliding surface speed, not shaft rotational speed in rpm.

References

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Test Data