The glass industry has instituted a number of regulations, or standards, that govern the process of making glass and the final requirements for each type of glass. Quality control testing is performed to ensure public safety for products that include glass as one of the materials used in their manufacturing. An example is found in the automobile industry; tempered glass must be used for side and rear windows. If an accident were to occur, the tempered glass can be broken with a metal object and allow the passengers to escape or allow emergency teams to reach the passengers trapped in the car. One of the requirements tempered glass must meet is that it must remain intact at 10,000 psi (pounds per square inch); most tempered glass can remain intact at 20,000 psi or more. Glass is made from any of a number of materials, including aluminum or magnesium oxides, silica and lime. The raw materials are heated to their melting point, shaped and then cooled. Often the molten glass is plunged into cold water to cool it quickly and retain its shape. you can get additional information at tempered glass
Tempered, or annealed, glass is up to six times stronger than regular glass. Because of the inherent breaking pattern, however, it must be cut to shape before the tempering process. Regular glass is easily cut, but there’s a high probability that if tempered glass is cut, the stress from the cut could reduce it to a pile of rubble. After the regular glass is cut to size and shape, which includes edging or decorative etching, it is inspected for any imperfections. Any flaw in the glass makes it unsuitable for creating tempered glass. The glass is heated to over 1200° F (650° C) and then cooled rapidly. The process of rapid cooling is called quenching. It not only solidifies the molten glass to help it retain its shape, but makes the glass stronger as well. Using the combination of compressive and tensile stress is how tempered, or annealed, glass is made. A compressive stress is when the outside of the glass object is cooled quickly. The inside is still relatively hot and cools more slowly, creating tensile stress. Each time the heating and cooling process is repeated more stresses are eliminated, resulting in stronger glass.
The ovens used to create tempered glass can be small units to accommodate single panes of glass up to huge, conveyer-belt ovens that continuously run products through the oven. The most cost-effective method to quench tempered glass is cold air jets. The jets are placed in close proximity to the glass and blow very cold air on the glass. The use of cold air jets instead of previously used methods, like oil or salt brine, keep the cost of tempered glass production down and make it much more affordable than laminated glass. After the manufacturing process is complete, the glass is tested to verify it conforms to all applicable standards. Any products that do not meet standards are rejected. Tempered glass is the norm for many end products like automobiles, building windows and virtually any product that weaker glass may be unsuitable for.