Vertical roller mill bearings: arrangement, lubrication and failures
A vertical roller mill is among the most process-critical machines in a cement plant. The rollers crush material on a rotating table under huge hydraulic load, in a dust-laden, hot-gas environment. Three bearing groups decide its uptime: the grinding rollers, the main drive and the separator.
Typical duty
| Speed | Load | Temperature | Typical life |
|---|---|---|---|
| Low (rollers and table), moderate (separator) | Moderate to very high, with shock and vibration | Hot gas around the mill, 60 to 90 °C at the bearing | Planned around a major shutdown interval |
How the bearings are arranged
Grinding roller · rotating roller on a fixed axle
Used when: Rollers pressed onto the table by hydraulic cylinders
Each grinding roller turns on a fixed shaft through a pair of large roller bearings. The bearings carry the grinding force and the roller's own weight, at low speed. Seals and air purge keep the very fine dust out.
Main drive and separator · bearings above and below the table
Used when: Mill table drive and the dynamic separator on top
The table sits on a thrust-carrying drive bearing assembly, driven through a gearbox and a motor. The separator, a rotating cage above, has its own bearings at moderate speed.
Common failures and how to prevent them
| Failure | What you see | Why it happens | Prevention |
|---|---|---|---|
| Fine dust in the roller bearings Abrasive wear | Dull tracks, gritty lubricant | Failed air barrier or worn seal | Keep the air supply healthy and check seals at each stop |
| Fatigue from sustained high load Subsurface-initiated fatigue | Spalling on the loaded zone | Overload from feed variation, vibration | Stabilise feed and watch vibration trends |
| Lack of lubricant or hot gas heat Overheating & lubricant breakdown | Discoloured tracks, burnt grease | Empty lubrication line, high gas temperature | Alarm on line status and track bearing temperature |
Lubrication
Rollers
High-load grease through a central line while the mill runs, in small, frequent doses.
Main drive
Circulating oil with filtration and cooling.
Separator
Grease in small, regular doses; use a high-temperature type near hot gas.
Sealing
- Air barrier: Pressurised sealing air keeps the very fine dust out of the roller bearing cavity.
- Contact seals: A sealing lip behind the labyrinth gives a second barrier.
What to watch
- Vibration at the gearbox, separator and motor.
- Roller bearing temperature and lubrication line pressure.
- Oil analysis from the gearbox and the circulation system.
Questions
Which bearings are used in vertical roller mills?
Grinding roller · rotating roller on a fixed axle: Rollers pressed onto the table by hydraulic cylinders. Main drive and separator · bearings above and below the table: Mill table drive and the dynamic separator on top.
What are the common bearing failures in vertical roller mills?
Fine dust in the roller bearings: Failed air barrier or worn seal. Fatigue from sustained high load: Overload from feed variation, vibration. Lack of lubricant or hot gas heat: Empty lubrication line, high gas temperature.
How should vertical roller mills bearings be lubricated?
Rollers: High-load grease through a central line while the mill runs, in small, frequent doses. Main drive: Circulating oil with filtration and cooling.