Patterned glass tempering process leaving marks

The tempering process (horizontal) is leaving white marks (haze) on the flatter side of patterned glass (aquatex, rain). We are not having a problem with pattern 62 since its underside is completely flat but the others do not have a completely flat side. The flatter side is placed down for the process and the rollers are scorching the "convex teets" (for lack of proper/better terminology). We have attempted raising the convection air supply, wave speed in furnace and drastically lower bottom temperatures, all to no avail. Any suggestions or would our only choice be to order from a different supplier with hopes for a much flatter side?

Guest User
Mon, 04/08/2008 - 15:07

The white marking is not scorching but abrasion due to the point loading (all the weight of the glass is carried by the small points of contact between the high points of the pattern and the rollers). Firstly, thoroughly clean the ceramic rolls with de-mineralised water and see if this cures the problem. If the marking still occurs, then try injecting Sulphur Dioxide (SO2) gas when running the glass. SO2 reacts with the Sodium in the surface of the glass to produce Sodium Sulphate (which is liquid at furnace temperatures) and this helps reduce marking by acting as a lubricant between the glass and the rolls. There will be a slight bloom on the glass but this simply washes off with water and is harmless.

If you cannot source SO2 gas readily then you can put a tablespoon of Sulphur (a yellow laxative powder) into an envelope and throw it into the furnace with the first load of glass. (When Sulphur powder burns it produces SO2 gas).

Do not use the SO2 without glass present, and do not use it unless the furnace is at full temperature as SO2 + H2O (moisture) makes H2SO4 (sulphuric acid) which won´t do the furnace shell a lot of good over time.

Hope this helps cure the problem.

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