Sliding-Bearing Pulley Efficiency Calculator

Content

Estimate the steady efficiency, required pull, journal load, bearing-friction torque, and power loss of a load-driven pulley supported by a sliding bearing.

Operating inputs

mm

Stle

mm; smaller than D

dimensionless, 0–0.3

FunctionalProduct

N

rpm; zero for torque only

Ready.

Mechanical efficiency
—
%
Required pull— N
Bearing radial load— N
Friction torque— N·m
Diameter ratio—
Useful / input torque— / — N·m
Power loss— W
Useful power— W
Input power— W

How to use

  1. Confirm the arrangement is a steady load-driven pulley with opposing rope legs and sliding journal support; this calculator has no alternate mode.
  2. Enter effective pulley diameter D and journal diameter d in millimetres, with d smaller than D.
  3. Enter a justified effective bearing friction coefficient μ for the materials, finish, lubrication, temperature, and sliding regime.
  4. Enter useful lifted load W in newtons and pulley speed n in rpm; use zero speed for force and torque results without power.
  5. Select Calculate to update the single result panel, or Reset to restore the worked example.
  6. Read efficiency with required pull, bearing load, friction torque, useful/input torques, and power loss; correct any red warning before using the result.
  7. Do not use the model for non-opposing rope geometry, startup breakaway, hydrodynamic loss, thermal or bearing-life prediction, traction/braking, or safety-critical lifting.

Equations used

The pulley lifts useful load W at steady speed. Input pull P and useful load W act on opposite rope legs with an assumed 180° wrap. Effective pulley radius is R = D/2 and journal radius is r = d/2.

g = D/d
N = P + W
Mf = μNr = μN(d/2000)
PR = WR + Mf
P = W(D + μd)/(D − μd) = W/η
η = (g − μ)/(g + μ)
Tout = W(D/2000)
Tin = P(D/2000) = Tout + Mf
Tloss = Tin − Tout = Mf
ω = 2πn/60
Pin = Tinω; Pout = Toutω
Ploss = Mfω = Pin − Pout

D and d are mm; division by 2000 converts diameter in mm to radius in m. g, μ, and η are dimensionless. P, W, and N are N. Mf, Tin, Tout, and Tloss are N·m. n is rpm, ω is rad/s, and powers are W. Positive P and W denote opposing tangential rope forces; positive torque follows the input-driving direction, and positive loss is dissipated heat.

Assumptions and limits. Steady motion, rigid pulley, 180° opposing rope legs, effective constant Coulomb friction supplied by the user, and friction acting at d/2. This boundary/dry-friction screen excludes groove friction, rope bending, seals, lubricant churning, aerodynamics, startup, transients, temperature, wear, misalignment, and shaft deflection. Do not use it for safety-critical lifting, bearing heat balance, lubricant selection, bearing life, or a different rope-force geometry.

References:Engineers Edge pulley-efficiency relation; Budynas and Nisbett, Shigley’s Mechanical Engineering Design, 10th ed., Chapter 12, publisher record, for journal-bearing friction-model background.

Related calculators:Coulomb friction force and coefficient · Worm gear geometry, sliding, and efficiency