Heat Soaked Glass

The heat soaking of glass is an additional process performed on toughened, tempered glass units to reduce its risk of spontaneous breakages, due to Nickel Sulphide Inclusion under testing method EN 14179.

Nickel sulphide inclusion is a natural imperfection in standard float glass that occurs due to the high presence of nickel based substances in glass manufacture. The presence of these imperfections can cause toughened glass to spontaneously break up to 10 years after installation.

Although nickel sulphide inclusions can be present in any form of glass, they are a particular problem in toughened glass units due to the rapid heating and cooling in the tempering process. When heated, the nickel sulphide inclusions shrink under the increased heat. In a normal annealing process, the glass is cooled gradually and the inclusions have time to cool and expand to their low temperature form.

In the toughening process, the cooling happens rapidly to create tensions in the glass for added strength and the nickel sulphide inclusions do not have the time to expand to their ‘cool’ state within the manufacture. This cooling then happens over several months or years, increasing the size of the inclusion by up to 4%. This increase in size can break the tensions within a toughened glass panel and cause spontaneous breakage.

Reducing The Risk of Breakage

Heat soaking is a destructive test that involves placing the tempered glass units onto special racks within an oven, reheating them up to 290 C and cooled slowly. This process is made to induce breakage in any units where nickel sulphide inclusions are present and reduces the risk of spontaneous breakage on site by up to 95%.

Heat soaked glass is still recognised as a safety glass and the strength, appearance and thermal resistance of a toughened glass unit are not reduced under the heat soaking process.

Speak to a member of the London Architectural Glass team to find out how we can help you on your upcoming project.