Making Glass

**Float Glass Manufacture**

Introduction. The Float glass process was invented by Alastair Pilkington in 1952 and has been adopted as the universal method for the manufacture of high quality flat glass to this day. Process. In the float process, a continuous ribbon of glass moves out of the melting furnace and then floats across the surface of an enclosed bath of molten tin. The Semi-molten ribbon is held in a chemically controlled atmosphere at a high temperature for a long enough time for the irregularities to flow out and for for the surfaces to be flat and parallel. Because the surface of the molten tin is dead flat, the glass also becomes flat. The ribbon is then cooled down while still advancing across the molten tin until the surfaces are hard enough to be take out of the bath without the rollers marking the bottom surface; so a ribbon is produces with a uniform thickness and bright polished surfaces without the need for further processing. Raw Materials. Sand, Soda Ash, Limestone, Dolomite, Felspar, Sodium Sulphate, Coal Dust & Cullet (Broken Glass). Different agents may also be added to the batch for finishing and colouring purposes. Colours and tints. The following agents can be added to the batch to create the different coloured glasses you will encounter. Green -Iron & Chromium oxides. Blue -Cobalt & Copper oxides. Violet -Manganese oxide. Amber -Carbon & Sulphur. Red -Selenium & Cadmium sulphate. Temperatures. The Raw materials are mixed and heated to around 1500º C, as the ribbon of glass leaves the furnace and enters the float bath the temperature comes down to around 1050º C. The glass continues to cool as it is drawn along the bath of molten tin and enters the cooling lehr at approx 600º C. As it progresses along its journey it continues to cool and leaves to cooling lehrs at 200º C. It is now cool enough to cut and stack.