TL;DR
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.
What you might see
- longitudinal streaks or marks in finished paper
- embossing or gloss variation in the CD direction
- visible scoring on the roll surface
- paper sticking to the roll surface
Likely causes
Foreign object entering the nip and scoring the roll surface
Paper sheet collapse or sheet fragment welding to the hot roll
Lubricant or coating deposit hardening on the roll surface
Roll surface fatigue cracking from thermal cycling over long service life
Required tools
- IR thermometer for roll surface temperature
- Surface depth gauge
- Wooden scraper (for deposit removal only)
- Portable work light
Safety first
- Hot calender rolls exceed 200 deg C. Do not touch or approach while rotating. Wait for temperature below 60 deg C before inspection.
- Never use metal scrapers or abrasive tools on a calender roll surface. Damage will be worsened.
Procedure
- 1
If paper quality defects are detected, immediately notify the control room and request a speed reduction to allow visual inspection.
Warning: Do not attempt to touch or clean a hot calender roll while it is rotating. Temperature can exceed 200 deg C. - 2
Stop the calender and open the nip. Allow the rolls to cool below 60 deg C before inspection.
- 3
Inspect the roll surface with adequate lighting for scoring, cracks, indentations, or adhered paper deposits.[1]
- 4
Measure the depth of any scoring with a surface depth gauge. Scratches deeper than 0.05 mm require grinding to prevent continued paper marking.
- 5
If adhered paper or coating is present, attempt removal with a wooden scraper only after confirming roll temperature is below 40 deg C. Never use metal tools on the roll surface.
- 6
If damage is limited to minor surface deposits, clean with the approved roll surface cleaner and resume at reduced speed for one reel to confirm paper quality.[1]
- 7
If scoring or cracking is present, remove the roll for grinding. Do not return a damaged roll to service without grinding, as damage propagates under nip load.
Sources
Valmet Valmet OptiCalender / OptiWin Calender / Winder general technical documentation, Valmet
Calender roll surface inspection and damage assessment, general paper machine roll maintenance practice (general)
More guides for Valmet Valmet OptiCalender / OptiWin
How to diagnose roll nip vibration on a Valmet OptiCalender
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.
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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