Types of Sheet Glass

Float Glass

• Float glass makes up about 90 percent of the glass made in the world today. It is made from a combination of sand, sodium carbonate, limestone, dolomite and sodium sulfate. This mixture is heated to 2,700 degrees Fahrenheit, at which it becomes molten, and is poured onto a large surface of molten tin.

  Tin has a much lower melting point than glass and does not mix with the molten glass. Because tin is heaver than glass, the molten glass floats on the surface of the molten tin. The glass spreads smoothly and evenly along the tin. When it has cooled enough to be lifted, the glass is pulled from the tin surface by rollers and gradually cooled further until it completely hardens.

Chemically Strengthened Glass

• Chemically strengthened glass is manufactured in the same way as float glass, but it is dipped in a solution of potassium salt at 840 degrees. The surface of glass treated this way is much denser than regular float glass, resulting in glass six to eight times stronger.

Tempered Glass

• Tempered or toughened glass is float glass that has gone through two extra stages of processing. The first is called "annealing," in which glass is heated until it slightly softens, allowing any internal stresses or tensions to relax, then cooled slowly. It is then heated in a furnace to just above its melting point, then rapidly cooled with forced air. Tempered glass should not be cut after this process is completed.

Laminated Glass

• Laminated glass is made from one sheet of poly vinyl butyral, or PVB, sandwiched between two pieces of sheet glass of identical size. Laminated glass does not shatter and remains in the form of a sheet when broken. Car windows and windshields are made from laminated glass.

  The process of binding the glass to the PVB is called lamination. It is done in a room completely free of dust to ensure nothing is caught between the sheets. The glass sheets are thoroughly cleaned before laminating. The PVB sheet is placed over one sheet of glass, and then the second sheet of glass is laid over top. The edges of the glass sheets are then aligned, and a heavy roller presses them to eliminate any air bubbles. The sheets then are heated under pressured, causing the PVB to bond to the glass.