RPM from Surface Speed

Paper machine speeds are specified as web surface speed in m/min. The roll RPM depends on the roll diameter.

Typical Balance Grades for Paper Machine Rolls

Roll Type	Recommended Grade	Notes
Calender rolls	G1.0 – G2.5	Highest precision required
Press rolls (solid/vented)	G2.5	Standard for most press sections
Suction rolls	G2.5 – G6.3	Shell perforations complicate balancing
Dryer cylinders	G2.5 – G6.3	Condensate shifting changes balance
Wire/fabric guide rolls	G2.5	Small diameter, moderate speed
Felt rolls	G6.3 – G16	Low speed, less critical
Reel spool	G2.5	High speed, affects winding quality

Centrifugal Force from Unbalance

The centrifugal force generated by unbalance at the tolerance limit is:

Where U_per is in g·mm and ω in rad/s. This force rotates at shaft speed and is transmitted to the bearings and support structure.

Correction Mass Calculation

The correction mass to be added or removed at a given radius:

Where r is the correction radius in mm (typically at the roll OD or at a specific correction plane location).

Special Considerations for Paper Rolls

• Suction rolls: Shell perforations create periodic mass variations. Balance should be checked after re-drilling or shell replacement.
• Covered rolls (rubber/polyurethane): Cover thickness variations affect balance. Re-balance after re-covering.
• Dryer cylinders: Condensate redistribution during startup causes transient unbalance. Allow stabilization before measuring.
• Variable crown rolls: Hydraulic crown pressure changes can affect balance state.
• Thermal crown: Uneven heating can cause temporary bowing — check that thermal steady state is reached before balancing.

Vibration Limits for Paper Machine Rolls

Paper machines require very low vibration levels for paper quality. Typical bearing housing velocity limits:

• Calender rolls: < 1.0 mm/s RMS (affects paper surface quality)
• Press rolls: < 2.0 mm/s RMS
• Dryer cylinders: < 2.5 mm/s RMS
• Wire/felt guide rolls: < 2.0 mm/s RMS
• Reel spool: < 1.5 mm/s RMS (affects winding quality)