Rotary kiln bearings: arrangement, lubrication and failures
A cement kiln is a 60-metre-plus steel tube turning slowly on support rollers. A plant has one or two, and when the kiln stops, the plant stops. The support roller bearings, the tyres, and the open gear drive are the lubrication priorities.
Typical duty
| Speed | Load | Temperature | Typical life |
|---|---|---|---|
| Very low (kiln about 1 to 5 rpm), moderate (drive) | Very heavy radial, slight axial thrust from the kiln slope | High: hot shell radiates onto the bearings | Planned around the annual shutdown |
How the bearings are arranged
Support roller station · trunnion bearings
Used when: Rollers that carry the kiln tyres
The kiln shell sits in tyres and rolls on support rollers. Each roller shaft turns in bearings at its ends. The load is enormous and the speed is low, so the bearings run with very little film.
Girth gear drive · pinion shaft bearings and open gear
Used when: The ring gear around the kiln and its pinion
A large ring gear (the girth gear) around the kiln meshes with a pinion driven by a gearbox and a motor. The pinion shaft turns in heavy-duty bearings. The gear mesh is open, so it is lubricated by a spray system.
Common failures and how to prevent them
| Failure | What you see | Why it happens | Prevention |
|---|---|---|---|
| Smearing from thin film at low speed Adhesive wear (smearing & skidding) | Smeared, scuffed track | Film too thin for the load | Use a high-viscosity grease with solids |
| Dust in the lubricant Abrasive wear | Gritty grease, scored tracks | Worn seals | Improve seals and add purge grease |
| Misalignment of pinion or roller Misalignment & distorted seats (edge loading) | Wear on one side | Shell deformation, base settlement | Check alignment at each shutdown |
Lubrication
Support rollers
High-viscosity grease with solid lubricants, fed in small regular doses.
Tyres and pads
Solid-lubricant grease through nozzles from a drum pump.
Girth gear
Spray system with open-gear grease.
Gearbox
Circulation oil, filtered and temperature controlled.
Sealing
- Roller bearing seals: Labyrinth and contact seals keep dust out and grease in.
What to watch
- Bearing temperatures on each roller.
- Tooth contact pattern on the girth gear.
- Motor current and gearbox vibration.
- Support wheel bearings turn at only a few rpm (a quartz sand calciner example runs at about 3.5 rpm). Ordinary vibration checks struggle there, so use an impact-based online measurement with enveloping, and trend each bearing every few hours.
Questions
Which bearings are used in rotary kilns?
Support roller station · trunnion bearings: Rollers that carry the kiln tyres. Girth gear drive · pinion shaft bearings and open gear: The ring gear around the kiln and its pinion.
What are the common bearing failures in rotary kilns?
Smearing from thin film at low speed: Film too thin for the load. Dust in the lubricant: Worn seals. Misalignment of pinion or roller: Shell deformation, base settlement.
How should rotary kilns bearings be lubricated?
Support rollers: High-viscosity grease with solid lubricants, fed in small regular doses. Tyres and pads: Solid-lubricant grease through nozzles from a drum pump.