TL;DR
A top roller alignment fault shifts the ribbon off-center and creates thickness asymmetry. Adjust the offending roller angle in small increments and allow the ribbon to respond over several ribbon lengths.
What you might see
- glass ribbon deviating from the centerline
- glass edge becoming non-parallel
- glass thickness profile asymmetric
- edge draw defect correlating to one roller
Likely causes
Top roller angle setting drifted from the design value, changing the lateral draw force
Top roller drive speed unequal from roller to roller, creating asymmetric pull
Top roller worn, reducing its grip on the glass ribbon
Glass ribbon temperature profile asymmetric from an upstream bath temperature imbalance
Required tools
- Ribbon centerline measurement (camera or laser)
- Roller angle adjustment tool
- Roller speed tachometer
- LOTO kit for roller replacement work
Safety first
- The tin bath interior is above 600 degC. Full radiant-heat PPE is required for any bath area work.
- The tin bath atmosphere contains hydrogen. No ignition sources near open access points.
Procedure
- 1
Observe the ribbon centerline from the exit end of the bath. Confirm the direction of the ribbon deviation.[1]
- 2
Identify the roller or rollers in the region where the deviation originates by tracing back from the exit.[1]
- 3
Adjust the angle of the suspect roller by a small increment (typically 0.1 to 0.2 degrees) in the direction that will steer the ribbon back toward center.
- 4
Allow the ribbon to travel 3 to 5 roller pitches after the adjustment before evaluating the response.
- 5
Check the individual roller drive speeds. A roller running faster than its neighbors pulls the ribbon edge asymmetrically.
- 6
If roller wear is suspected, confirm by measuring the roller contact diameter and comparing to the new roller specification.
Sources
Pilkington (NSG) Custom-engineered tin baths up to 60 m long Float Glass Tin Bath general technical documentation, Pilkington (NSG)
General float glass tin bath top roller alignment and ribbon geometry control procedures (general)
More guides for Pilkington (NSG) Custom-engineered tin baths up to 60 m long
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