Heat Treated Glass

Heat Treated Glass

Many of the world’s most dramatic and visually breathtaking buildings incorporate large expanses of glass.heat treated glass But before such architectural masterpieces can be created, the glass must undergo a heat-treating process for durability and safety. The type of processing required depends on the specific application of the glass. The most common is tempering, the process that makes glass twice as strong as annealed glass. It also increases the glass’s resistance to thermal and wind loads and meets safety glazing requirements set forth by codes or federal standards.

Tempering is accomplished by heating glass to about 1,200 degrees F and then force-cooling it in a rapid procedure called “quenching.heat treated glass ” The cooling creates surface and edge compression. Because the glass cools so quickly, its outer surfaces cool more rapidly than the center. This causes the center of the glass to become compressed and develop a characteristic pattern known as a “strain” or “quench” pattern.

The appearance of the strain pattern varies depending on viewing angle, lighting conditions and the viewer’s perception.heat treated glass While the strain pattern may be a visual concern for some, it is not considered a flaw or defect and cannot be eliminated in the manufacturing process.

Glass is subject to internal stresses from the molten state, cooling and the mechanical work of fabrication.heat treated glass This is why all fabrication such as cutting, hole-drilling and notching must be completed and the glass placed in an annealing oven before the tempering process can take place. If this step is not followed, the resulting high internal stresses can cause glass to spontaneously break.

All annealed glass must be tempered to achieve the desired strength and optical quality for its intended use. The rate at which the glass is cooled during tempering determines its strength. During this process, a glass lite is heated to the sintering point and then quenched in cold air, either continuously or by batch. Glass cooled at a slower rate is temperable while glass cooled at a faster rate produces tempered glass.

Because of the different rates of cooling, tempered glass has a different texture than annealed glass. It can be a bit rough to the touch and is more easily scratched than annealed glass. In addition, the textured surface may be susceptible to condensation and water spots.

It is a good practice to periodically clean the glass surface with a mild cleaner and soft cloth. It is also important to handle the glass with care, especially when moving it and if there is any possibility of it coming into contact with abrasive or sharp objects. If possible, glass should be kept away from abrasive surfaces such as aluminum or iron.

A glass processor can guarantee a flatness of.005 inches (five-thousandths of an inch) or less over a 12-inch area. However, there are many other factors that contribute to the overall quality of the glass such as roller wave. Roller pick is caused by the self-weight of the glass as it is being processed on ceramic rollers and can appear as slight dimples in the surface. This is not a problem for most commercial applications but can be a significant issue in lamination as out of sync roller wave can lead to lensing of PVB causing poor thermal performance and/or optical distortions.

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