Belt-driven shaft bearing load calculation (crusher pulley)
Work out the belt pull from power and pulley diameter, add weights and the coupling force, then find the load and life of each bearing with a shock factor. The Rotec AI worked template does every step.
What loads the bearings
- Belt pull is the largest load. The radial belt load is a factor k times the tangential force, with k about 1.1 for synchronous belts, 1.5 to 2.0 for V-belts and 2.5 to 3.0 for flat belts.
- Weights of the shaft, pulley and coupling add a vertical load.
- The coupling adds a small radial force in an unknown direction.
- Shock on a crusher multiplies the equivalent load by 1.5 to 3.
The method in five steps
- Torque. T in N·m = 9,550 × power in kW ÷ speed in rpm.
- Belt force. Ft = 60,000,000 × P ÷ (π × D × n) newtons, with D the pulley pitch diameter in mm. Radial belt load = k × Ft.
- Coupling force. F = 5,600 × √(P/n) as a rule of thumb, or the coupling maker's figure.
- Reactions. Take moments about each bearing. Try the belt both ways and the coupling in every direction.
- Life. Multiply the load by the shock factor, then L10h = (C/P)^p × 1,000,000 ÷ (60 n).
Worked example
A 300 kW crusher motor at 735 rpm, pulley 620 mm, k = 2.5, shaft plus pulley 12,000 N, coupling half 2,000 N. The pulley is 660 mm from bearing A, the bearings are 1,320 mm apart and the coupling is 400 mm beyond B.
| Quantity | Value |
|---|---|
| Torque | 3,898 N·m |
| Belt tangential force | 12,573 N |
| Radial belt load | 31,433 N |
| Coupling force | 3,578 N |
| Bearing loads, all added in one line (A / B) | 20,026 N / 28,984 N |
| Life of a 23032 bearing (C 585 kN) at fw 1.1 / 2 / 3 | about 368,000 h / 50,000 h / 13,000 h |
The lesson: the bearing is generous for a smooth drive, but a crusher needs a shock factor, and the life drops by a factor of about 28 between smooth and very heavy shock.
Check the inputs
- State the load on each bearing, not only the total at the pulley.
- Check the shaft: d = 118 × (HP/n)^0.25 mm, using twice the power for the start-up torque.
- Check the minimum load: about 1% of C for a roller bearing.
Do it in Rotec AI
The licensed Load Calculator has a worked template for a belt-driven shaft with the pulley between the bearings. A free preview shows the layout and an example.
Related tools and guides
Questions
How do I calculate the load on a crusher pulley shaft bearing?
Find the belt tangential force from power, pulley diameter and speed, multiply by the belt factor, add the weights and the coupling force, and take moments about each bearing. Then apply a shock factor of 1.5 to 3 for the life.
What shock factor should I use for a crusher bearing?
Use 1.5 to 3 for heavy shock. A smooth-running factor of 1.0 to 1.2 is optimistic for a crusher.
Why does the sheet total not give the bearing load?
The total at the pulley is shared between the two bearings by the distances. Take moments about each bearing to find each load.
Results are starting points from standard engineering practice. Confirm critical selections with the bearing or lubricant maker.