We are running across a large scale problem with brown clumps accumulating on our fused silica rollers in our horizontal tempering furnace. We have cleaned out our SO2 manifold and even swapped tanks - any ideas on what else to try?
The brown clumps are accululating sparatically across the entire roller hearth in odd corkscrew patterns, with the largest accululation in the last zone. I have pictures for those interested in helping me solve this problem.
Side problem- Concurrently there I have another issue with excessive white line on the glass appearing in squiggling lines across the glass. Most of the white line is in the form of a powder that can be removed with a clean glove, but the short scratches leave behind a hazing effect on the surface.
Can this also be directly related to the SO2 problem?
Any help would be greatly aprreciated!
Ceramic Roller Problems - Horizontal Tempering
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The brown lumps are Sodium Sulphate. Sodium Sulphate forms when the SO2 gas comes into contact with Sodium in the surface of the glass. The Sodium Sulphate is liquid at furnace temperatures and provides lubrication between the roll and the glass, and condenses onto the rolls (especially on the high spots which is the spiral of the roll grinding or mold cast during manufacture, which is why you are seeing a corkscrew pattern). The spots have a coefficient of expansion whereas the rolls effectively do not, so during a cool down the spots solidify and contract and there is a danger they will crumble the surface of the roll. Once the roll is cold they can be washed off using plain hot (70 degrees C) water (DO NOT use abrasives or solvents). Basically you are using too much SO2 because you should only see a brown stain on the rolls, not spots.
The white marking is because the glass is not riding flat in the early stages of heating (try using aspirators to keep it flat) and the weight of the glass is concentrated into smaller areas where it contacts the rolls and is either crushed or abraided. If the factory is dusty (concrete dust is especially bad) dust from the load table will be taken into the furnace on the bottom surface of the glass exacerbating the problem.
You mentioned short scratches – these may be due to the main conveyor snatching during reversals causing the glass to skid slightly.
Hope this info helps.
Jonathan