TL;DR
Nip vibration produces CD caliper bands and audible chatter. Check roll surface condition and nip load first, then measure roll roundness with a profilometer at the next outage.
What you might see
- periodic CD caliper variation in finished paper
- audible chatter or beating at the nip
- vibration at a frequency matching roll rotational speed
- roll bearing temperature rising intermittently
Likely causes
Roll out-of-roundness from thermal crowning or surface wear
Worn roll bearing with excessive radial play creating a periodic impulse
Nip loading pressure set above the roll crown compensation range
Contamination on the roll surface causing periodic traction variation
Required tools
- QC caliper profile system access
- Vibration meter
- Roll profilometer (for outage measurement)
- IR thermometer for roll surface temperature
Safety first
- Calender nips are pinch points. Never reach into or near an open nip, even at low speed.
- Hot rolls retain heat after shutdown. Verify surface temperature before any contact during measurement or inspection.
Procedure
- 1
Pull the CD caliper profile from the quality control system and identify the wavelength of the variation. Calculate the corresponding roll diameter to identify which roll is the source.[1]
- 2
Inspect the roll surface visually for scoring, contamination, or uneven wear while the machine is at low speed.
- 3
Check the nip load setting against the roll supplier's recommended range for the current paper grade.
- 4
Measure vibration at the roll bearing housings with a vibration meter. Note the dominant frequency and compare to the roll rotational frequency.[1]
- 5
If bearing vibration is elevated above 0.3 in/s, inspect the bearing for wear at the next scheduled outage.
- 6
Schedule a roll profilometer measurement at the next planned outage to quantify out-of-roundness.
- 7
If out-of-roundness exceeds the roll supplier's tolerance, grind or resurface the roll.
Warning: Hot calender rolls retain heat for an extended period after shutdown. Verify roll surface temperature is below 40 deg C before allowing contact during measurement.
Sources
Valmet Valmet OptiCalender / OptiWin Calender / Winder general technical documentation, Valmet
Calender roll vibration diagnosis and CD caliper analysis, general paper machine maintenance practice (general)
More guides for Valmet Valmet OptiCalender / OptiWin
How to inspect and respond to hot roll surface damage on a Valmet OptiCalender
Surface damage on a hot calender roll shows as streaks or embossing in the paper. Stop the nip, reduce roll temperature, and inspect visually. Grinding is required for anything beyond minor marking.
How to reduce web breaks on a Valmet OptiWin Winder
Web breaks on the winder are usually caused by edge cracks, incorrect tension, or reel defects carried from the paper machine. Check the tension profile and inspect incoming reel edges before each set.
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