TEMPERING PROCESS: HOW A GLASS FIVE TIMES STRONGER IS MANUFACTURED

By: Ing. Marlene Calderón and Mónica Cortez

Did you know that glass, in its natural state, tends to break into large, sharp pieces? However, there is a process that causes it to break into small particles: tempering, thereby providing greater safety to its environment.

The Step-by-Step Process

Once the glass is in its final state (cut and processed), it must go through a washing stage, as dust particles or fingerprints can cause permanent stains when entering the tempering furnace.

1. Heating: Once clean and with all required fabrications completed, the glass enters the tempering furnace at a temperature between 620°C and 750°C, where it remains for 8 to 12 minutes (depending on the thickness and type of glass) until it reaches its softening point.
2. Softening: At this point, the glass molecules do not "separate," but rather increase their mobility: the material becomes flexible enough to allow for a redistribution of internal stresses.
3. Rapid Cooling (Thermal Shock): Subsequently, it passes through a cooling section, where the glass is subjected to strong blasts of air from both sides for approximately 5 to 8 minutes. This rapid cooling hardens the surface before the interior, creating a temperature difference between the external and internal layers.

This thermal shock process allows the glass to be up to five times more resistant to impacts than non-tempered glass. The complete cycle inside the furnace lasts between 15 and 20 minutes in total.

Important Fact: Tempered glass can no longer be cut or subjected to any other type of fabrication after the process, as it would break instantly.

How can I know if a glass is tempered?

It is very easy to identify:

• Look for the Stamp: All tempered glass, per Mexican standards, must bear an irreversible stamp that may contain the word "Templado", "Tempered Glass", or the logo of the processing company along with its certification.
• Polarized Lens Test: If you cannot see the logo on an already installed glass, another way to check is by using polarized sunglasses under sunlight. When viewed from a certain angle, tempered glass will show rainbow-like spots caused by the material's internal stress; this is completely normal.

Safety for your Home

Imagine the glass in a house with children: windows, railings, or shower doors. In the event of an accidental impact or a ball strike, tempered glass provides the peace of mind that if it breaks, it will do so into small granular pieces that do not cause serious cuts.

Tempering represents daily safety and is a key factor in the glass industry. At Inova Glass, we guarantee the quality and safety of every tempered glass that comes out of our furnaces.