Conveyor pulley and idler bearings: arrangement, lubrication and failures
A conveyor looks simple, but there may be hundreds of bearings along its length and they all sit outdoors in dust, rain and spillage. A pulley bearing carries big loads at low speed. An idler bearing carries small loads but there are thousands of them. Sealing decides life in both.
Typical duty
| Speed | Load | Temperature | Typical life |
|---|---|---|---|
| 20 – 500 rpm (pulleys), 100 – 1,000 rpm (idlers) | Heavy radial from belt tension, shock at loading | Ambient to 70 °C | 50,000 – 100,000 h (pulleys), 30,000 h and up (idlers) |
How the bearings are arranged
Drive or tail pulley · plummer blocks
Used when: Head, tail, take-up and bend pulleys on belt conveyors
The pulley shaft rests in two plummer blocks, one on each side. One is fixed to the frame and holds the shaft position. The other is allowed to slide, because the shaft changes length with temperature.
Carrying idler · fixed shaft
Used when: Troughing, return and impact idler rolls
The shaft stays still. The roller shell turns around it, with a small ball bearing at each end hidden inside the shell. The bearing’s outer ring turns with the shell. A maze seal around the shaft is all that keeps dirt out for years.
Common failures and how to prevent them
| Failure | What you see | Why it happens | Prevention |
|---|---|---|---|
| Dust and slurry ingress Abrasive wear | Scored, dull raceways and gritty grease. | Worn labyrinth, damaged seal or a build-up of material around the housing. | Keep seals intact, clear spillage regularly, and use grease purging on pulleys. |
| Water and corrosion Moisture corrosion | Rust-coloured wear, pitting at the ball spacing. | Wet or washdown environments, a seal that has failed, condensation in idle idlers. | Use sealed bearings with seals that match the climate and replace idlers before they seize. |
| Fretting on the shaft or in the sleeve Fretting corrosion | Brown-red powder and polished areas on the shaft. | Loose adapter sleeve, bent shaft, or movement under changing load. | Follow the sleeve mounting procedure and check shaft deflection. |
| Misaligned or twisted blocks Misalignment & distorted seats (edge loading) | Hot bearing on one side and uneven wear. | Bent frame, soft foot or the two pillow blocks not in line. | Align pillow blocks to each other and check the base after belt tensioning. |
| Over-greasing Overheating & lubricant breakdown | Hot housing and grease squeezed out of the seal. | Too much grease or grease that is too stiff for the speed. | Grease by quantity and not until grease comes out, and use the right grease. |
| Shaft fracture Fatigue fracture | Fatigue crack at the pulley hub or sleeve. | Shaft bending stress cycles with each revolution, often from a worn key or stress raiser. | Check shaft size for bending, fillet radii, and avoid fretting on the shaft. |
Lubrication
Idlers
Greased for life at the factory. Choose a grease that suits the temperature range, because a cold-site idler needs a low-temperature grease.
Pulley blocks
Relubricate at set intervals with a lithium-complex grease with EP additives. Grease slowly while turning if you can. Fill the housing no more than 30 to 50%.
Purge grease
A little extra grease at the seal in dirty areas keeps the labyrinth clean.
Sealing
- Labyrinth seals: Multi-stage maze on idlers, filled with grease. Non-contact, so no friction and no wear. They are the main protection against dust.
- Pulley housing seals: Labyrinth rings or double-lip seals, often with a grease purge channel that keeps pushing clean grease out and dirt away.
- Shielding: Rain covers and shields on exposed pulleys reduce water ingress.
What to watch
- Hot spots found with an infrared camera along idler lines.
- Walk-by listening and trending of idler noise.
- Vibration at pulley bearings.
- Pulley shaft deflection and sleeve nut tightness at planned stops.
Questions
Which bearings are used in belt conveyors?
Drive or tail pulley · plummer blocks: Head, tail, take-up and bend pulleys on belt conveyors. Carrying idler · fixed shaft: Troughing, return and impact idler rolls.
What are the common bearing failures in belt conveyors?
Dust and slurry ingress: Worn labyrinth, damaged seal or a build-up of material around the housing. Water and corrosion: Wet or washdown environments, a seal that has failed, condensation in idle idlers. Fretting on the shaft or in the sleeve: Loose adapter sleeve, bent shaft, or movement under changing load.
How should belt conveyors bearings be lubricated?
Idlers: Greased for life at the factory. Choose a grease that suits the temperature range, because a cold-site idler needs a low-temperature grease. Pulley blocks: Relubricate at set intervals with a lithium-complex grease with EP additives. Grease slowly while turning if you can. Fill the housing no more than 30 to 50%.