The float glass manufacturing process was developed by Pilkington in 1959, taking flat glass technology to a revolutionary new level. The glass gains its lustrous finish and perfect flatness by floating on a bath of molten tin in a chemically controlled atmosphere. The ribbon of glass is then cooled, while still moving, until the surfaces are hard enough for it to be taken out of the bath without the roller marking the surface. The glass is then automatically cut and stacked, ready to be packed for distribution to local and international customers.
1 Raw material feed: Silica sand, soda ash, dolomite, limestone, sodium sulphate and cullet are mixed together to form the raw material batch.
2 Float bath: A continuous ribbon of molten glass floats along the surface of molten tin. All irregularities are melted out of the ribbon, to give the glass a flat, parallel surface.
3 On-line cutting: The ribbon moves to the ‘cold end’ of the line where it is washed and automatically cut, as it travels along the rollers.
4 Distribution: The glass is distributed throughout South Africa and exported into regional and overseas markets. PFG’s distribution hubs are in Springs, Durban and Cape Town.
5 Furnace: The batch is fed into the furnace and melted at a temperature of around 1 500°C.
6 Annealing lehr: The glass is annealed and gradually cooled to around 200°C, to relieve stresses in the glass and prevent splitting and breaking in the cutting phase.
7 Stacking and offloading: Automatic stackers offload the glass sheets. The glass is then warehoused for distribution.