The use of Tin in the ‘Float Glass’ Production Process

Posted in The World Of Metal on 7th June 2011

One particular area of business for William Rowland is in the supply of tin to the ‘Float Glass' Industry.

So, what is Float glass?

Float glass is essentially the process of producing ‘sheet glass' or window glass. This type of glass is made by floating molten glass onto a bed / bath of molten tin. This technique gives it a flat surface and a uniform thickness that we expect of modern glass in domestic and commercial properties where full transparency is required. It also used as the ‘base material' for safety glass, self-cleaning glass and reflective glass. It is also where extreme flatness is required, such as visual displays.

The Float Glass Process

The tin bath is usually between 4-8 metes wide and 60 meters long and is always protected by a gas atmosphere that prevents the tin from oxidizing. This gas atmosphere is carefully controlled, as the contact surface between the tin and glass will directly influence the glass thickness.

When the glass first comes into contact with the tin, the high temperature of the liquid metal is 600˚C. Tin is the metal of choice as it the only metal that remains in a liquid state at 600˚C. As the molten glass spreads on to the surface of the tin, it creates the glass ribbon effect. It is manipulated by using rollers to control thickness. Once it eventually cools it leaves behind a flat sheet of glass that is later heat polished. Despite this process being around since 1850s it is still to this day the standard process in ‘mass' glass production. Figures estimate that 90% of the world's production of sheet glass is done by using the float glass method.

Although each glass manufacturing differs the float glass production process can be divided into five steps;

1. Batching of raw materials

2. Melting of raw materials

3. Drawing the molten glass onto the tin bath

4. Cooling of the molten glass in the annealing lehr

5. Quality checks, automatic cutting, and storage

History of float glass
In 1848 Henry Bessemer, an English engineer from Sheffield (who has been mentioned on this website before for his contribution to the Metals Industry and in particular his invention of the Bessemer Convertor) was the first to patent the technique. Although many historians credit Alastair Pilkington as the ‘father' of the float glass process.

Before the float glass technique was mastered, larger sheets of glass were produced by casting a ‘large puddle' of glass on to an iron surface. This was then grinded and polished on both sides for clarity - this was, as you can imagine an expensive way of producing flat glass.

William Rowland Ltd are tin suppliers, and if you would like to find out how we can meet your requirements, please contact us using the Quick Enquiry Form on the right-hand side of this website.

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