Float glass (also called “flat” glass) that has not been heat-strengthened or tempered is annealed glass. Annealing float glass is the process of controlled cooling to prevent residual stress in the glass and is an inherent operation of the float glass manufacturing process. Annealed glass can be cut, machined, drilled, edged and polished. Heat-Strengthened Glass Heat-strengthened (HS) glass has been subjected to a heating and cooling cycle and is generally twice as strong as annealed glass of the same thickness and configuration. HS glass must achieve residual surface compression between 3, 500 and 7, 500 PSI for 6mm glass, according to ASTM C 1048. Please contact Guardian regarding thicker glass standards. HS glass has greater resistance to thermal loads than annealed glass and, when broken, the fragments are typically larger than those of fully tempered glass and initially may remain in the glazing opening. Heat strengthened glass is not a safety glass product as defined by the various code organizations. This type of glass is intended for general glazing, where additional strength is desired to withstand wind load and thermal stress. It does not require the strength of fully tempered glass, and is intended for applications that do not specifically require a safety glass product. HS glass cannot be cut or drilled after heat-strengthening and any alterations, such as edge-grinding, sandblasting or acid-etching, can cause premature failure. Tempered Glass Fully tempered glass is approximately four times stronger than annealed glass of the same thickness and configuration, and residual surface compression must be over 10, 000 PSI for 6mm, according to ASTM C 1048. Please contact Guardian for thicker glass standards. When broken, it will break into many relatively small fragments, which are less likely to cause serious injury. Tempered glass is often referred to as “safety glass” because it meets the requirements of the various code organizations that set standards for safety glass. This type of glass is intended for general glazing, and safety glazing such as sliding doors, storm doors, building entrances, bath and shower enclosures, interior partitions and other uses requiring superior strength and safety properties. Tempered glass cannot be cut or drilled after tempering, and any alterations, such as edge-grinding, sandblasting or acid-etching, can cause premature failure. Laminated Glass Laminated glass is two or more lites (pieces) of glass permanently bonded together with one or more plastic interlayers (PVB) using heat and pressure. The glass and interlayers can be a variety of colors and thicknesses designed to meet building code standards and requirements as necessary. Laminated glass can be broken, but the fragments will tend to adhere to the plastic layer and remain largely intact, reducing the risk of injury. Laminated glass is considered “safety glass” because it can meet the requirements of the various code organizations that set standards for safety. Heat strengthened and tempered glass can be incorporated into laminated glass units to further strengthen the impact resistance. Insulating Glass Insulating glass refers to two or more lites of glass sealed around the edges with an air space between, to form a single unit. Commonly referred to as an “IG unit, ” insulating glass is the most effective way to reduce air-to-air heat transfer through the glazing. When used in conjunction with low-E and/or reflective glass coatings, IG units become effective means to conserve energy and comply with energy codes. The most common architectural insulating glass unit configuration is ¼” glass – ½” air space – ¼” glass (6 mm – 12 mm air space – 6 mm).
