Float Glass Process / Tin Bath [ Return towards Glass, Cement & Lime ]
Most of the world’s flat glass is now made by the float process developed by Pilkington in the early 1960’s, with typical line sizes ranging from 350 to 750 tons/day. The heart of the process is the tin bath where molten glass flows from the melting.
A typical float tank consumes about 1200 to 1500 Nm³/h of high purity nitrogen and 60 to 100 Nm³/h of high purity hydrogen to provide a reducing and cooling atmosphere for the forming process (tin bath). The hydrogen flow rate is governed by the rate of carry-over of oxygen and sulfur dissolved in the glass. The more oxygen and sulfur dissolved in the glass, the more hydrogen is required to react with it, forming H2O and H2S. Nitrogen is used to dilute the hydrogen to a concentration of 4 to 10 %. High hydrogen concentrations in the atmosphere would lead to bubbles beneath the glass where the hydrogen would come out of the tin. An additional function of the atmosphere is to blanket the exit of the float tank to prevent air infiltration.
Nitrogen is produced by a cryogenic on-site plant (FLOXAL™ APSA L series). Hydrogen can be supplied from liquid or gaseous storage and on-site plant . If available, pipeline is often the preferred mode of supply.
In addition to supplying high purity nitrogen and hydrogen, supply also generally includes the mixing system to generate the atmosphere according to your specifications.
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