Tempered glass is a type of safety glass stronger than regular glass. Its unique manufacturing process gives it enhanced strength and causes it to shatter into small, relatively harmless pieces instead of large, jagged shards. Despite its robust nature, tempered glass is not unbreakable. This article will explain how and why this specialized glass can break.
Understanding Tempered Glass Breakage
Tempered glass undergoes a thermal tempering process. Regular glass is heated to high temperatures (above 600°C/1,112°F) until it is softened. Immediately after, surfaces are rapidly cooled with forced air (quenching). This rapid cooling causes outer layers to solidify and contract quickly.
As outer surfaces cool and compress, the inner core remains hotter and contracts at a slower rate. This differential cooling creates a stress pattern: outer surfaces are in high compression, while the inner core is in tension. This balanced system of internal stresses gives tempered glass its strength, making it four to five times stronger than annealed (regular) glass.
When the compressed outer layer is breached by a concentrated force, the stored energy is suddenly released. This rapid release causes the pane to disintegrate instantly into many small, blunt, granular pieces. This controlled breakage minimizes severe injury risk compared to large, sharp shards from regular glass.
Common Causes of Tempered Glass Failure
Tempered glass can break due to external factors that compromise its internal stresses. These factors often involve localized damage that overcomes the surface compression.
Sharp, concentrated impacts frequently cause breakage. While tempered glass resists blunt force effectively, a small, pointed object impacting a single, small area can breach the compressed outer layer. This impact, even if not forceful, can initiate a crack that rapidly propagates, leading to shattering. The impact area, rather than overall force, is often the critical factor.
The edges of tempered glass are particularly vulnerable. Unlike main surfaces, edges are not subjected to the same uniform compression during the tempering process, making them inherently weaker. Minor chips, nicks, or impacts to the edges can create stress concentrators, allowing the stored energy to release and cause the glass to shatter. Improper handling or installation that damages the edges can significantly increase the risk of breakage.
Surface scratches and imperfections can compromise the integrity of tempered glass. Deep scratches or flaws on the glass surface can act as points where stress concentrates, weakening the protective compressed layer. Over time, or under additional stress, these imperfections can serve as starting points for cracks, leading to unexpected breakage.
Thermal stress or shock results from rapid and significant temperature changes across the glass pane. If one part of the glass heats or cools much faster than another, such as direct sunlight hitting a partially shaded pane or hot liquid contacting cold glass, uneven expansion and contraction occur. This creates internal stresses that can exceed the glass’s tolerance, causing it to shatter. Tempered glass is more resistant to thermal changes than regular glass, but extreme differences can still cause failure.