Chapter 13: Problem 17

In your own words, briefly describe what happens as a glass piece is thermally tempered.

Short Answer

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Answer: During the thermal tempering process, a glass piece is heated to a specific temperature (around 620°C to 650°C) and then rapidly cooled, creating compressive stresses on the outer surfaces and tensile stresses in the interior. This results in a stronger and more durable glass piece that is more resistant to breakage caused by impacts, temperature changes, and other physical stresses. Additionally, when it does break, the thermally tempered glass breaks into small, relatively harmless pieces, reducing the risk of injury.

Step by step solution

Understanding Thermal Tempering

Thermal tempering is a process used to increase the strength and durability of glass by heating it to a specific temperature and then rapidly cooling it. This process causes the outer surfaces of the glass to contract, creating compressive stresses, while the interior remains in tension. The result is a stronger, more durable glass piece that is less likely to break and can better withstand temperature changes.

Heating the Glass

During the tempering process, the glass piece is placed inside a tempering oven and heated to a temperature of around 620°C to 650°C (1148°F to 1202°F). The goal is to heat the glass evenly and bring it to a uniform temperature so that it becomes soft and malleable. This needs to be done carefully to avoid any deformation or irregularities on the glass surface.

Rapid Cooling

After reaching the desired temperature, the glass piece is rapidly cooled, typically using high-pressure air jets, over a period of a few seconds to a few minutes. This fast cooling causes the outer surfaces of the glass to contract and solidify quickly, while the interior remains in a molten state for a longer period.

Formation of Compressive Stresses

As the outer surfaces of the glass contract and solidify while the interior remains molten, compressive stresses are created within the glass piece. These stresses make the surface tougher and more resistant to breakage, as they can help to maintain the glass' structural integrity even if the surface is subjected to external forces.

Strengthening and Benefits

The combination of compressive stresses on the outer surfaces and tensile stresses in the interior of the glass result in a thermally tempered glass piece with increased strength and durability. This means that it is more resistant to breakage caused by impacts, temperature changes, and other physical stresses. Additionally, thermally tempered glass breaks into small, relatively harmless pieces when it does break, reducing the risk of injury.

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In your own words, briefly describe what happens as a glass piece is thermally tempered.

Short Answer

Step by step solution

Understanding Thermal Tempering

Heating the Glass

Rapid Cooling

Formation of Compressive Stresses

Strengthening and Benefits

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