Introduction

Tempered glass is made from normal annealed glass via a thermal tempering process in which the glass is subjected to heat till its softening point and then rapidly cooled. This gives the glass its strength. A fully tempered glass is 4 to 5 times stronger then an annealed glass of similar thickness. A fully tempered glass is regarded as a safety glass and when it breaks it disintegrates into small blunt pieces which greatly reduces the chances of injuries and if there are any then they are superficial in nature.

A fully tempered glass is used in most modern glass facade, where glass strength is required. A fully tempered glass is recommended for windows that are on high floors or skylights where people are required to stand on top for cleaning. Also areas where risk of thermal breakage or impact breakage is high, fully tempered glass should be used so as to avoid risk of injury. Glass strength is also required in point fixed glazing, bolted and patch fittings.

Manufacturing Process

Step I

First and foremost the right glass combination is selected according to the clients' requirement. The choices are limitless, for e.g. the glasses can be Clear, Tinted and/or reflective.

Step II

The glass is then cut to size and then its edges are treated. Holes and cutouts are then drilled onto the glass. Then the glass is washed by deionised water and loaded onto the transportation bay of the furnace.

Step III

The glass is then transferred into the heating chamber of the tempering furnace. Here the glass is heated till its softening point.

As soon as the glass temperature reaches its softening point the glass is transported to the next part of the furnace where it is rapidly cool or quenched.

The quenching of the hot glass produces different stress that results in inducing the various stress zones and hence gives the tempered glass its strength. Heat-treated glass has two compression layers or zones, one starting at each surface, plus an interior tension zone centered in the middle of the glass. Each of the two compression zones is approximately 20% of the glass thickness. The middle 60% of the glass thickness is the tension zone. So to break the tempered glass one has to penetrate the compressive zones and hence enable the glass to release its energy and disintegrate into small pieces.

Step IV

The glass that comes out at the other end of the furnace is either a fully tempered glass or heat strengthened glass depending upon the operating cycle set by the operator in accordance with the client's order.

Heat-Treated Glass is separated into two products, heat-strengthened glass and fully tempered glass, by definition of the degree of residual surface compression or edge compression. Most furnaces can produce both. Its operator must adjust a furnace and its quench for one or the other type of a product “run.” The adjustments may include changes in furnace temperature, exit temperature of the glass, residual time in the furnace, and volume and pressure of the quench air.

Properties of Tempered Glass

Flexibility

Tempered glass is less brittle because the tempering process eliminates the imperfections that weaken regular glass.

Density

The intense heat (over 750 degrees Celsius) used to harden the glass creates a dense outer envelope as it cools, which creates improved insulating properties.

Impacts

Three-quarter-inch thick tempered glass can withstand the impact of a half-pound iron ball dropped from a height of 36 feet, but a comparable piece of plate glass will generally break if the weight is dropped from a height of 3 feet.

Load Strength

Tempering makes glass that can withstand thousands more pounds per square inch than plate glass, making it a favorite material for tabletops and other weight-bearing surfaces.

Transparency

ecause of its density, tempered glass is generally less clear or transparent than comparable plate glass and is often colored or coated with reflective materials, which also protects its surface.

Safety

Tempered glass crumbles rather than shattering, which is a preferable trait for uses that may be subject to sudden forces, like car windshields.

Applications

Suitable where safety glazing is required by building codes or design specifications

Fire knock-out panels

All glass entrances and storefronts

Extreme wind loads

Fireplace enclosures

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