Heat soaked glass

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Heat Soaked Glass

Heat Soaked Toughened Glass

If you have worked in the glass industry long enough you will have experienced a mysterious breakage of an in situ glass panel, whether in a shop front, shower screen or glass balustrade. It’s a scary and potentially dangerous experience for a customer and an inconvenient costly event for a business, not forgetting the confidence zapping affect it can have in the eyes of your customer and implications for your business reputation.

Toughened safety glass as its names states is tough but not unbreakable, so what would cause a glass panel to just explode with no physical impact?

The culprit is Nickel Sulphide (NiS) Inclusions.

What are they?

NiS inclusions are small contaminants, “tiny stones”, that are rarely found in batches of float glass during the manufacturing process, they are undetectable to the naked eye and currently there is no test to determine the presence of such an imperfection in the glass.

image of nickel

So how does a NiS inclusion cause the glass panel to explode?

Whilst the glass in its annealed state is relatively safe from the risk of spontaneous explosion, the risk occurs during the toughening process, which transforms the state of the NiS inclusion once the glass has been toughened in a furnace. The trouble begins with a phase transformation in the nickel sulphide inclusion from high to low temperature forms. During the toughening process the rapid cooling of the outer surface of the glass and slow internal cooling results in the NiS inclusion being trapped in its high temperature phase and this can cause spontaneously breakage even years later.

What’s the Solution? – Heat Soaking

How Heat Soaking Works

Heat soaking is a secondary process, completed after the glass has already been toughened and is undertaken to prevent any later problems.

The process is known as “Heat Soaking to EN14179” as this represents the accepted standard. The heat soaking process involves a specialized oven that heats the processed glass to 290˚C and holds it at that temperature for two hours. The test is detructive as 95% of inclusions present in the glass will explode and destroy the glass. As this is a destructive test it also has the potential to damage adjacent glass in the oven.

Heat Soaking adds time and cost to processed toughened glass due to failure rates during testing and rework costs.

The process eliminates up to 95% of spontaneous breakage problems without interfering with the positive properties that toughened glass brings to many projects.

What products are required to be heat soaked?

International Building Codes require different glass products to have different processing attributes. We suggest that glass used a physical barrier should be heat soaked to the European Standard: EN14189.

Testing for Exakt Glass Balustrade Systems are all using heat soaked glass to EN14189

Our Glass Plant holds third party accreditation to EN14189 from CSI International.

Have you any questions or comments about the use of heat soaked glass? If so, please contact our experienced team to discuss.