TL;DR
Oxygen or moisture contamination in the tin bath atmosphere oxidizes the tin surface and creates glass defects. Identify the ingress point and restore the protective gas flow before the tin surface is significantly oxidized.
What you might see
- glass surface tin bloom defect
- O2 or H2O reading above the maximum in the bath atmosphere
- nitrogen and hydrogen supply flow rate drop
- top roller marks on glass surface
Likely causes
Bath seal at the glass entry or exit lip worn or poorly fitted, allowing air ingress
Protective gas (N2/H2) supply pressure drop allowing atmosphere reversal
Top roller seal degraded, creating a gap for air to enter along the roller shaft
Tin bath roof panel joint or expansion joint opened from thermal cycling
Required tools
- O2 and dew point monitoring from DCS
- Gas leak detection equipment
- LOTO kit for roller seal replacement
Safety first
- The tin bath atmosphere contains hydrogen. No ignition sources near the bath access points or seals.
- Extreme thermal radiation inside the tin bath. All access requires full radiant-heat PPE.
- Molten tin is above 600 degC. Avoid contact with molten tin or hot metal at the bath entry and exit.
Procedure
- 1
Read the O2 and dew point sensors in the bath atmosphere from the control system. Identify which zones are showing contamination.[1]
- 2
Verify the N2/H2 supply pressure and total flow. If flow has dropped, restore it immediately.[1]
- 3
Inspect the glass entry seal and exit seal for visible air ingress by watching the flame or smoke at seal gaps.
Warning: The tin bath atmosphere contains hydrogen. No ignition sources near the bath seals or access points. - 4
Check each top roller seal for visible air ingress along the roller shaft. Mark leaking seals for replacement at the next planned stop.
- 5
Increase the protective gas flow to purge the contaminated atmosphere from the bath.
- 6
Monitor the O2 and dew point sensors until they return to the target range.
- 7
After restoration, inspect a length of glass from the affected period for tin bloom before releasing to the next process.
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 atmosphere control and seal maintenance procedures (general)
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