Pilkington Glass, now internationally famous as the first float glass, was originated by Pilkington Brothers, (est. 1826 St Helens U.K.). This technological breakthrough made it possible to combine the brilliant surface of drawn sheet glass and the precise parallel surfaces of rolled polished glass. Furthermore, the process could be made continuous with long trouble free production runs with little variation in sheet width. The instigator of the process was Lionel A.B. Pilkington who joined the company in 1947 at the age of 27 after completing his degree in mechanical engineering at Cambridge.
The idea to use the dead flat surface of molten tin over which the molten glass (with a much higher melting point than tin) solidifies was first conceived in 1952 and then tried by L.A.B. Pilkington and K. Bickerstaff on a 12” wide pilot plant in early 1953. Trials were not at all successful and even as late as January 1958 the idea, though now sufficiently mature to patent (1957), could not be perfected. In July 1958, the first ‘good’ glass was made and the invention announced to the world in 1959. However, after three months of production the tin float bath was restructured and this caused a total failure of the process.
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It took three more months of investigation to establish that the original un-flawed glass had been produced through a ‘fluke’ occurrence, and that the real secret of a perfect surface was the relative temperatures between tin and glass and the rate of cooling before rolling and annealing. The glass ‘floated’ because it was of lower density than the liquid metal, but time was needed to allow glass surface irregularities to ‘flow out’ across the dead flat surface of the molten tin.
Problems remained, regardless of the incoming thickness of glass, physical characteristics dictated that 4mm was the ‘natural’ thickness of the final sheet. Fortunately, this was in no way a disadvantage since this was a preferred width for glazing glass. Later development (toothed rollers to increase flow speed) overcame this and made possible sheet glass in a wide range of thicknesses. It is interesting that Pilkington later confirmed that had he been aware of previous unsuccessful efforts to perfect the same technology he might never have tried his method. Two Americans, W.R.Heal in 1902, and H.K. Hitchcock in 1905, had patented very similar methods but, as the U.S Patent office ruled, had not successfully produced an ‘operative process’. Pilkington Brothers spent some £7,000,000 perfecting their process but ultimately reaped enormous profits from licensing the process in 12 countries to some 22 manufacturers. Coloured float glass was subsequently developed, as too the now famous ‘K-Glass; made by depositing a copper metallic coating laid on thinly enough to be transparent to visible light, but tending to reflect heat.
Lionel Pilkington was knighted in 1970 and became chairman of Pilkington in 1973. Intriguingly, Lionel Pilkington was only remotely connected with the Pilkington family which owned Pilkington Brothers.
Lionel (Sir Alistair)
Original Patent Drawing (Click to expand)