4822 Southerland Road
Houston, TX 77092

(713) 353-5800 Tel.
(800) 238-3548 Toll Free
(713) 353-5333 Fax
(800) 825-9607 Toll Free Fax
E-mail: sales@craftsmanfab.com

Tempered Glass

Overview

Taking ordinary glass into a tempered state involves heating the glass in a special furnace to approximately 1260deg Fahrenheit, then setting a permanent tension between the glass “core” and outer surfaces by rapidly cooling the glass in a high pressure quench. When fully tempered glass is broken, the release of tension between the surfaces initiates a cascade of much smaller glass fragments than ordinary annealed glass. While a person can still get cut by this safety glass, the objective is to eliminate as much as the dangerously long shards of glass raining down within the broken debris as possible. Ideal applications for tempered glass are those in which safety is a priority. Such applications include code mandated shower and bath enclosures, sliding and swing glass doors, and glass adjacent to pedestrian traffic. Other tempered applications include windows, skylights, atriums, as well as glass used in motor vehicles and appliances such as refrigerator shelving, microwave ovens, etc.

Convection Technology

All heat treated glass fabricated by Craftsman is produced in equipment utilizing the newest convection technology available in the world. While traditional “old world” tempering ovens rely on radiant heat, our convection equipment heats the glass much more efficiently, thus greatly reducing the amount of time the glass must be in the heating chamber. Simply stated, controlling the surface temperature of the glass is extremely important for keeping glass flat. The superior heating efficiency of convection equipment means minimized roller imperfections that permeate the glass surface and reduced bow, warp and faint heat streak blemishes, resulting in a much higher, consistent optical quality.

Optical Quality

Tempered and heat-strengthened glass posses the fundamental optical qualities of annealed glass. Because glass is heated and cooled through a furnace, the induced stress will sometimes produce a bow or warp in glass lites, or the glass may have slight-to-heavy surface wave from being very near melting temperature while conveyed over the furnace’s ceramic rollers. This “roller wave” can be detected when viewing reflected images from a distance, and is inherent with heat treated glass. Craftsman’s convection system is much more efficient compared to older technology furnaces that rely solely on radiant heat is typically better quality and more consistent. This is especially important when tempering the new generations of high performance and low-emissivity glass.

Fully Tempered Glass

Craftsman Fabricated Glass produces fully tempered safety glass in compliance to the federal safety glazing standard, CPSC 16 CFR 1201. According to ASTM C 1048, fully tempered glass is required in to have either a minimum surface compression of 10,000 psi (69 MPa) or an edge compression of not less than 9,700 psi (67 MPa) or meet ANSI Z 97.1 or CPSC 16 CFR 1201. Simply stated, this compression level yields glass that is generally 4 times stronger than annealed glass. If fully tempered glass is broken by impact, the release of tension between the surfaces initiates a cascade of much smaller glass fragments than ordinary annealed glass thereby greatly reducing the likelihood of serious cutting or piercing injuries in comparison with ordinary annealed glass.

Heat Strengthened Glass

According to ASTM C 1048 the surface compression level of heat-strengthened glass must be between 3,500 psi to 7,500 psi. This lower compression level results in a relatively large breakage pattern as compared to fully tempered glass. These larger glass pieces will typically remain engaged in the glazing pocket, decreasing the probability of fall out. It must be noted that heat-strengthened glass does not meet the safety glazing requirements of the American National Standards Institute (ANSI) Z97.1, or the federal safety standard Consumer Products Safety Commission 16 CFR 1201. Heat-strengthened glass is generally 2 times stronger than annealed glass. Heat-strengthened glass is generally used in situations where improved resistance to thermal stresses and thermal shock is required in an area that codes do not mandate the use of safety glass.

Iridescence

Iridescence or strain pattern is related to the stresses introduced in the cooling process of tempered or heat treated glass. This looks very similar to the “shadow spots” in glass you might see in vehicle back lites through polarized sunglasses. This iridescence is usually not visible at normal viewing angles, but may become visible under certain light conditions, at sharp angles or through polarized lenses. This phenomenon is normal in heat treated glass and is not a defect.

Edgework and Fabrication Options

Craftsman utilizes state-of-the-art CNC drilling and milling equipment in the fabrication of all of our glass products. This CNC technology insures accurate location and precision sizing of notches and holes. The unmatched quality and brilliance of the edgework is achieved because of optically flat, cerium polished edges, including the aris. That little “flash” of brilliance that you subconsciously see when looking at our work is the effect of our premium edgework.