Plain Bearing PV

Notes & Use

Calculates design values (velocity, force, and combined) of plain bearings when the following are true:

  • For radial (journal) applications
    • the bearing rotates around a shaft,
    • the rotational motion is continuous (as opposed to an ocillating),
    • the load is applied perpidicular to the axis of rotation (radial).
  • For thrust applications:
    • the load rotates upon the bearing, around a fixed center point,
    • the thrust bearing’s bearing surface is circular or annular,
    • the rotational motion is continuous,
    • the load is applied parallel to the axis of rotation,
    • the load is uniform across the surface area of the bearing.

This calculator does not address any issues beyond P, V, and PV calculations, such as:

  • Effects of friction,
  • Additional heat and energy-dispersal concerns,
  • Dimensional changes due to heat deformation,
  • Tribology/lubrication concerns,
    • including cleanliness and suitability of lubricants
  • Wear factors
  • Operating Temperatures
  • Lifetime calculations
  • Shock-load and impact factors

Calcuations

Radial Figure

Radial Figure

Radial Terms

$L$ = load on bearing, pounds force

$n$ = Shaft speed, rotations per minute

$d$ = Diameter of shaft (ID of bearing), inches

$w$ = Bearing width, inches

$P$ = Pressure on bearing, psi

$V$ = velocity of bearing surface, feet per minute

$PV$ = Pressure × Velocity

Radial Equations

$$ P_{actual} = \frac {L} {w d} $$

$$ V_{actual} = \frac {n d \pi} {12} $$

Thrust Figure

Thrust Figure

Thrust Terms

$L$ = load on bearing, pounds force

$n$ = Rotation speed, rotations per minute

$d$ = Inner diameter of bearing’s surface area, inches

$D$ = Outer diameter of bearing’s surface area, inches

$P$ = Pressure on bearing, psi

$V$ = velocity of bearing surface, feet per minute

$PV$ = Pressure × Velocity

Thrust Equation

$$ P_{actual} = \frac {4L} {\pi (D^2 - d^2)} $$

$$ V_{actual} = \frac {n \left( \frac{D - d}{4} \right) \pi} {12} $$

Pass/Fail Test

$P_{actual}$, $V_{actual}$, and $PV_{actual}$ are compared to the respective allowable values:

  • Pass = actual < allowable
  • Fail = actual ≥ allowable

Material P, V, and PV values

The design values provided by the drop-down material box are culled from various sources, notably Mcmaster-Carr and Wikipedia. A full table of those values is as follows:

Material P V PV
psi fpm psi×fpm
SAE 841 2,000 1,200 50,000
Graphite SAE 841 1,600 1,000 40,000
SAE 660 4,000 750 75,000
SAE 841 2,000 1,200 50,000
SAE 863 4,000 225 35,000
Nylon 400 360 3,000
Nylon MDS #1 2,000 393 3,400
UHMWPE 1,000 100 2,000
Acetal 1,000 1,000 2,700
Ptfe 500 100 1,000
Ptfe (glass filled) 1,000 400 11,000
Rulon 641 1,000 400 10,000
Rulon J 750 400 7,500
Rulon LR 1,000 400 10,000
Peek (blend 1) 8,500 400 3,500
Peek (blend 2) 21,750 295 37,700
Vespel 4,900 3,000 30,0000

Sources