In past blog posts, we’ve talked about tempered glass commercial application usage as well as its use in glass shower doors. In the field, an image glass installer will get questions about different types of glass and its strength. Based on those questions, we decided to provide a primer on how tempered glass and heated glass are made and what properties they bring to safety.
Both heat-strengthened and tempered glass are manufactured using a hat treating process with the same processing equipment. The glass is heated to 1200 degrees in each process followed by forced cooling for surface and edge compression. The process used is determined by the specific application of the glass.
To make heat-strengthened glass, the glass is reheated after forming to just below melting point and then air-cooled more slowly than tempered glass. This slower cooling forms a compressed surface, which increases its strength to approximately twice as strong as annealed or untreated glass.
As discussed in past blogs, tempered glass (or safety glass) is typically specified for security. It is often used in patio and entrance doors, sidelites and other locations where the safety of occupants is paramount in the event of broken glass. When shattered, tempered glass breaks into thousands of small particles.
The manufacturing process for tempered glass involves reheating it to nearly the melting point. It is then quickly air-cooled to create the necessary surface and edge compression. This process makes the glass nearly five times stronger and safer than annealed or untreated glass, which reduces the chances of thermal breakage.
Heat-strengthened glass also provides additional strength for things like wind pressure resistance, thermal stress or both, but is more along the lines of two to three times a strong as annealed or untreated glass. That means it is used in situations where wind and thermal pressure resistance are needed but fully tempered glass is not a requirement.
A common use of heat-strengthened glass is in spandrel glass where the opaque nature is meant to conceal features between the floors of a building, including vents, wires, slab ends and mechanical equipment. An advantage of heat-strengthened glass is that, when broken, the glass fragments are more similar in size and shape to annealed glass fragments and thus tend to stay in the opening longer than fully tempered glass particles. Although heat-strengthened glass is not a safety glazing by building code, this breakage pattern prevents the glass from falling and injuring someone.
Effects of heat-treating glass
The process of heat strengthening glass and tempering glass can leave some optical image distortion depending on a number of variable factors including:
- Glazing pressure
- Wind load
- Temperature and barometric pressure changes
- Altitude changes between manufacturing and installation environment
Glass distortion may also occur due to strain patterns in heat-treated glass or interference fringe patterns in the fabrication of insulating glass units. Because of its fluidity at higher temperatures, glass also is inherently susceptible to roller wave, bow and warp while it is being heat-treated.
To minimize the potential impact of the glass distortion that is inherent with heat-treating processes, many commercial projects will call for the installation of thicker glass that is less prone to distortion. Next time we’ll discuss different types of glass where clarity, heat transfer and other comfort and aesthetic aspects come into play for commercial and residential glass for architectural glass installation.
At Image Glass, our glass installer and glass repair experts have a great deal of knowledge about how different types of glass are manufactured and the best practices for use and installation. This enables them to ensure your satisfaction and safety today and tomorrow.
To learn more about how the Image Glass team can help you to achieve beauty, efficiency, safety, and comfort with each installation, call us at 732-438-8551 to speak to one of our glass specialists.