Float Glass Imperfections

Float glass isn’t flawless; nickel sulfide (NiS) inclusions are a concern. Most inclusions are stable, but some can cause tempered glass to spontaneously break without load or thermal stress.

Heat Soaking Process

Heat soaking targets NiS inclusions in tempered glass. Glass is placed in a chamber and heated to ~290ºC, making inclusions expand and break the glass, reducing future breakage risk. But it has downsides: not 100% effective, raises cost, and may reduce compressive stress.

We offer coated glass products that can safely undergo heat soaking when needed.

Heat-Strengthened Glass vs. Tempered Glass

Heat-strengthened glass has less spontaneous breakage than tempered glass. For applications needing strength due to thermal stress and without strict safety glass mandates, CN Glass suggests heat-strengthened or laminated glass to avoid fractures.

Nickel Sulfide (NiS) inclusions

NiS inclusions are rare but can break glass. They form during production if nickel-rich contaminants (like stainless steel) mix with sulfur. Heat-treating glass changes NiS size; rapid cooling stops full reversion. Over time, NiS expands (2 – 4%) and may break the glass. Manufacturers control quality to limit inclusions.

Role of Design Professionals

Design pros can lower breakage risk. They can specify heat-strengthened glass for strength, recommend heat-soaking for tempered glass, or choose laminated glass.

Our Heat Soak Ovens

Our advanced Heat Soak Ovens handle up to 4000mm x 2100mm glass, meeting diverse customer needs.