Glass tempering

There are many different types of manufactured glass and depending on the application, it may need to be tempered to handle the stresses of daily life.

Tempering is the process of strengthening a pre-processed piece of glass. Not only does tempering make the material stronger to physical stresses, it can also increase its functioning temperature range. Tempered glass is used when strength, thermal resistance, and safety are important considerations. Passenger vehicles, for example, have all three requirements. Stored outdoors, they are subject to constant temperature changes. They receive a range of abuse from small rocks to automobile accidents. Because large, sharp fragments would present additional and unacceptable danger to passengers, tempered glass is used so that if broken, the pieces are granular and mostly harmless.

How it’s made:

Glass tempering starts with flat glass which is the first form of glass created from raw materials such as silica, limestone or other sand material. Once the glass has been formed, it is ready to start the tempering process. The glass is then sent through a tempering furnace heated to 620 °C (1150 °F) before being quenched (rapidly cooled).

During this stage, the cooling of the outside material happens quicker than the center which causes an opposition of stresses: the outside is in a state of compression while the inside is in tension. It is this material behavior which results in the strengthening of the glass. The electric heating elements within the furnace deliver the thermal precision required to ensure consistent, high quality glass.

Electric heating is the most important step in the process, making the heating element the most important part in tempering furnaces. Uneven heating can lead to quality issues such as fluctuating stress concentration, unbalanced bowing (center line haze), or even fractured edges from outer heat concentration. To avoid these issues, we source our alloys from the melt to the finished product to assure highest quality control.

Applications

  • Architectural (windows, doors, tables, stairs, railings)
  • Office partitions
  • Automotive
  • Phones/electronics
  • Appliances
  • Bulletproof glass
  • Cookware
  • Diving masks
  • Sports (hockey rinks, backboards)

Take a look at the "Resistance Heating Alloys' handbook which helps you select the right metallic heating element for your furnace.

Our products for Glass tempering