Paper machine press section rolls bearings: arrangement, lubrication and failures
The press section squeezes water out of the wet paper sheet between heavy rolls. The rolls turn slowly, carry large weight and nip load, and sit in a wet, humid area. The bearings are usually large spherical roller bearings, one at each end of the roll, with one fixed axially and one free.
Typical duty
| Speed | Load | Temperature | Typical life |
|---|---|---|---|
| Typically about 100 to a few hundred rpm | Very heavy: the roll weighs tens of tonnes, plus the nip load | Warm from the process and the felts, often with oil circulation | Planned around the grinding or roll change cycle |
How the bearings are arranged
Press roll journal bearings
Used when: Bearings at each end of a heavy press roll
A large spherical roller bearing sits at each end of the roll. One is located and the other is free to move as the roll grows with heat. The bearings tolerate the bending of a heavy roll under nip load.
Common failures and how to prevent them
| Failure | What you see | Why it happens | Prevention |
|---|---|---|---|
| Outer-race fatigue under heavy load Subsurface-initiated fatigue | Spalling in the loaded zone of the stationary ring, with a clean fault frequency in the spectrum. | Heavy load at low speed, load changes with nip pressure, or reduced film. | Monitor the fault line, repeat the measurement within days of a sign, and plan the roll change. |
| Water in the bearing Moisture corrosion | Rust marks, milky grease or oil, corrosion pits. | Worn seals, spray from the section, or humid air. | Check seals at every stop, use a water-resistant grease or clean circulating oil. |
| Contamination from the process Abrasive wear | Dull, scratched rolling surfaces. | Fibres, filler or dirt entering past the seal. | Keep the labyrinth purged and clean the surrounding area. |
Lubrication
Oil circulation
Common on heavy rolls. It carries heat away, and the oil can be filtered and checked.
Grease
Where used, choose a water-resistant grease and short enough intervals for wet duty.
Sealing
- Labyrinth with water slinger: Throws process water away from the seal.
- Purge: A steady flow of grease or air keeps spray out.
What to watch
- Fault-line trend at the bearing housing, with speed and load recorded.
- Bearing temperature at each end and the difference.
- Oil cleanliness and water content in the circulation.
Questions
Which bearings are used in paper machine press section rolls?
Press roll journal bearings: Bearings at each end of a heavy press roll.
What are the common bearing failures in paper machine press section rolls?
Outer-race fatigue under heavy load: Heavy load at low speed, load changes with nip pressure, or reduced film. Water in the bearing: Worn seals, spray from the section, or humid air. Contamination from the process: Fibres, filler or dirt entering past the seal.
How should paper machine press section rolls bearings be lubricated?
Oil circulation: Common on heavy rolls. It carries heat away, and the oil can be filtered and checked. Grease: Where used, choose a water-resistant grease and short enough intervals for wet duty.