Processed Glass is that which is subjected to different types of treatment to make it suitable for diverse applications.
Annealed Glass is unprocessed glass or glass which has not been subjected to any treatment – for instance, toughening, lamination or heat strengthening. Commonly known as 'normal' glass, it is typically used for residential windows. Annealed Glass has minimal residual stress, with the stress being uniformly distributed. With a sudden change in temperature, the glass can break into very sharp fragments. Because of its low levels of toughness, tensile strength and thermal shock resistance, the use of Annealed Glass is not very prevalent.
Tempered Glass is glass that is processed by treatment – either thermal or chemical. It is also known as Safety Glass because it is known to be four times stronger than regular annealed glass. Unlike normal glass, it shatters into small fragments when it breaks, thereby lowering the risk of injury. Tempered Glass has much higher tensile or bending strength as well as better thermal shock resistance, with the ability to withstand temperature changes of up to 200 Degree Celsius without breaking.
In the Tempering Process, stress is developed in the glass in order to increase its mechanical strength up to 4 times that of annealed glass. The stress is so created to bring the outer surface under compression and the core under tension. When the outer surface is under compression, the glass gets its strength; when the core is under tension, in the event of a breakage, the glass breaks into small pieces.
There are two types of Tempering: Thermal Toughening and Chemical Toughening.
The process of Heat Strengthening is similar to toughening, but in this, cooling is done in a slower manner. Heat Strengthened Glass is that which has been subjected to heat in order to increase Mechanical Strength and Resistance to Thermal Breakage (The process increases resistance to mechanical and thermal stress up to 130 Degree Celsius). The glass is twice as strong as annealed glass; however, its fragmentation pattern is also much the same.
Tempering vs Heat Strengthening
Heat Strengthened Glass is cooled down with lesser pressure. The key lies in creating sufficient stress level.
Applications of Heat Strengthened Glass
Though not suitable for safety glazing applications, Heat Strengthened Glass is ideal where optical requirement is high. It is used in high wind load areas, and general glazing where additional strength and/or resistance to mechanical and/or thermal strength are desired. It is popularly used in laminated glass for additional strength (overhead or sloped glazing).
Laminated glass comprises two pieces of glass with a PVB interlayer. In the event of a breakage, this interlayer holds the glass in place so that shards of glass are not strewn around and cause injury.
Benefits of Lamination
Safety, Resistant to bullets, blasts and cyclones, Acoustic control and Privacy
01 Outer Lite
The Outer Lite can be tempered, heat strengthened or annealed. The thickness could range from 2mm to 19mm.
02 Inter Layer
The Inter Layer is a PVB film between the two sheets of glass. It is designed to improve the impact resistance of the glass by distributing any force that acts on glass and holds the two layers of glass together in the glass frame in case of a breakage.
03 Inner Lite
The Inner Lite can be tempered, heat strengthened or annealed. The thickness could range from 2mm to 19mm.
Heat Soak Test
Glass is heated to 290 +/- 10 Degree Celsius with a testing time for 2 hours. This test is used to to reduce the possibility of spontaneous glass breakage which can occur in tempered glass due to the presence of activated Nickel Sulphide. Although Nickel Sulphide is present in glass as part of the glass composition, it can get activated only during the process of tempering. The Heat Soak Test conforms to EN14179.