Window Glass - Component Material
A substance without developed structural organization, usually transparent consisting ordinarily of a mixture of silicates, but in some cases of borates, phosphates etc. Most glass is made by fusing silica, as sand, an alkali as potash or soda and some other lead base such as lead oxide.
The choice of window and door glass depends largely on the following factors:
- Environmental considerations: force of wind on glass area - sun
and glare control - admittance of required sunlight
- Aesthetic considerations: the view to be considered - whether
privacy is needed - noise reduction - safety factors
Most glazing in homes today falls into 2 basic types; drawn sheet and float glass. The two types have slightly varying characteristics due to their different manufacturing processes.
Float glass allows completely distortion free vision and because of this factor is now the most commonly used type, where as drawn sheet glass may show a slight waviness.
The Float Process
In the float process, a continuous ribbon of molten glass up to 3.3m wide moves out of a melting furnace and floats along the surface of a bath of molten tin. The ribbon is held in a chemically controlled atmosphere at a high enough temperature for a long enough time for the irregularities to melt out and for the surfaces to become flat and parallel. Because the surface of the molten tin is flat, the glass also becomes flat. Its thickness - in the range 2.5 to 25mm is controlled at this stage.
The ribbon is then cooled down while still advancing across the molten tin until the surfaces are hard enough for it to progress through the annealing without the rollers marking its bottom surface. The glass produced has uniform thickness and bright fire polished surfaces without the need for grinding and polishing. A float glass line, which can have a melting tank capacity of more than 2,000 tons, can operate continuously for several years without major repairs.
Sheet Glass - The Drawn Process
Sheet glass, the first form of which was produced about 1914 has hard fire polished surfaces. It is a transparent glass, but exhibits some distortion.
Up to five drawing towers can be served by a single glass furnace.
A "draw" is started by lowering a "bait"- a webbed metal frame - into the molten glass. As it is withdrawn, the glass adhering to it is teased out manually until it can be gripped by knurled water cooled rollers at either side of the tower. The rollers prevent the semi-molten glass from "waisting" in and losing its ribbon shape.
The ribbon is fed up the 9.5m annealing tower between powered asbestos covered rollers. The "bait" is removed at the top, and the continuing ribbon is automatically cut into predetermined lengths and removed by hydraulic suckers.
Another type of glass is safety glass. This term is usually applied to glass which upon impact does NOT shatter and collapse into long knife like slivers with sharp cutting edges. There are a number of types of safety glass in commercial use, these include: