„Glass-Pellets“ provide the basis for the glass fibre products from the Johns Manville company here in Wertheim that used to be Schuller Textile Glass from Thuringia, but moved here in 1952. The pellets are re-melted and the molten glass is passed through bushings, or thread inserts with narrow nozzles that it drips out of and is then drawn into a thread. With this action the drips become glass fibres, fibreglass threads and glass fibre mats. They are then processed into reinforcement for many items including tarred roofing felt, floor coverings, synthetic materials for snowboards, through to items for ship and railway construction.
The Johns Manville Company in Wertheim melts the glass pellets in two modern electric tank furnaces: each with a daily capacity of 63 tons of molten glass. These tank furnaces, with a floor area of 25.5 square metres, have to be replaced every 6 to 8 years because the fireproof cladding becomes thinner and thinner until eventually molten glass could leak through. The rebuild takes 6 weeks. During the tank furnace’s functional lifespan, data is collected to optimise not only the fireproof material, but also the best mode of operation.