A Ribbon of Glass on a River of Tin
- PDF / 39,647 Bytes
- 1 Pages / 612 x 792 pts (letter) Page_size
- 51 Downloads / 178 Views
HISTORICAL NOTE
A Ribbon of Glass on a River of Tin When Alistair Pilkington (1920–1995) addressed the Royal Society of London on February 13, 1969, on “The Float Glass Process,” he began with a brief history of glass in human affairs. After describing the shaping of glass into useful forms by ancient civilizations, Pilkington asked his audience’s permission to jump forward in time. “Since it is with flat glass that my lecture is concerned,” he said, “I hope you will therefore forgive me for skipping 3,000 years of history.” For it was only ten years before, in 1959, after seven years of experimentation and an investment of £7 million, that Pilkington Brothers Ltd. of St. Helens, Lancashire, introduced an economical means of producing distortion-free flat glass that required no grinding or polishing steps. That it took thousands of years to solve the problem of making truly flat glass is a testament to the difficulty of the challenge. There were several processes that produced useful approximations along the way: the “crown glass” method, which involved spinning a lump of molten glass rapidly until it cooled in a flat disk; the cylinder method, in which a blown cylinder of glass was cut lengthwise and opened into a flat sheet; and the Fourcault method, which involved drawing a continuous ribbon from a pool of molten glass. Though useful, each of these methods yielded glass with optical distortions. An alternative was plate glass, in which molten glass was cast on a table, rolled into a plate, annealed, and then ground and polished to a flat, distortion-free finish. Though the result was excellent and an automated continuous process was developed in the early 1900s, polishing and grinding were expensive and wasted as much as 20% of the product. Pilkington, a mechanical engineer and cousin of the Pilkington Brothers, whose company had been manufacturing glass since 1826, sought to combine the low cost of the sheet process with the optical quality of the plate process. In 1952, while working as the production manager in the plate glass department, he came up with the idea of using a flat surface of molten metal to support a continuous ribbon of glass. Because a molten metal surface is “dead flat,” in Pilkington’s words, the glass would also be flat. “When we started [experimenting],” he said, “we knew that what we were attempting was going to be one of the most exciting things in the history of the flat glass industry if we could pull it off.” The metal to be used had to be liquid
MRS BULLETIN • VOLUME 31 • SEPTEMBER 2006
over the temperature range of 600–1050°C, the processing range of the glass. This narrowed the candidates to seven: bismuth, gallium, indium, lithium, lead, thallium, and tin. Lithium is not dense enough to support a glass ribbon, while bismuth, thallium, and lead would evaporate at 1050°C. Of the remaining three choices, tin was cheap and readily available. In 1953, Pilkington filed a patent application titled “Float glass: Using a bath of molten tin to make plate glass cheaply.”
That it took th
Data Loading...
