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The float process
Today, almost all flat glass is made by means of theprocess in plants which operate continuously 24 hours a day, 365 days a year for uninterrupted periods of over 15 years.
Flat glass is primarily made of raw materials like sand and soda ash, but also from recycled glass i.e. 'cullet'. Mixing recycled glass with raw materials allows a reduction of CO2 emissions from production and recourse to less virgin raw materials. It contributes to greater product sustainability.
Main stages of flat glass production
1) Sand, limestone, soda ash, dolomite, iron oxide and salt cake are mixed together with cullet in the batch plant.
2) The raw materials are then charged into a large furnace to be melted at 1600°C. They combine in a process of physical transformation to form molten glass.
3) A continuous ribbon of molten glass is fed out of the melting furnace onto the surface of an enclosed bath of molten tin at 1100°C. The molten glass literally floats on top of the tin, and as it flows along the surface of the tin bath away from the delivery canal, it forms a ribbon of uniform thickness. Thickness is controlled by the speed at which solidifying glass ribbon is drawn off from the bath.
4) The glass is then lifted from the tin bath onto rollers to the annealing lehr to be cooled down. At this stage the internal stresses are released ensuring perfect flatness and solidity.
5) Once cooled down and solidified the glass goes to the cutting area where it is cut in to a large sheet of 'jumbo size' (6×3.21 meters) or 'cut-size' which are specific to customer orders, before being stacked for transportation.
The float process produces glass sheets with a uniform thickness and perfectly smooth surfaces that need no further grinding or polishing.
Sources: NSG Group (Float installation graph), AGC Glass Europe (Pictures)
Flat glass processing and transformation
Most often, the resulting glass will be further processed and transformed to increase some of its properties before being installed onto a final product. These glass processing and transformation activities take place on other industrial sites operated by either Glass for Europe member companies as well as thousands of SMEs all across Europe. Depending on the end-product and application for which it is destined, processing activities will aim to enhance the countless properties of glass.