Nowadays, glass is increasingly favored by more and more customers. There are not only artistic glass with strong decoration effects such as frosted glass, hot-melt glass, and painted glass, but also various functional glass such as soundproof and noise reducing laminated glass, insulating glass, and heat-insulating and flame-retardant fire-resistant glass. Today, let's introduce how tempered glass is made?

Tempered glass is heated to a temperature close to softening, in a state of viscous activity. This temperature scale is called the tempering temperature scale (620 ℃ -640 ℃), which is formed by holding for a certain period of time and then rapidly cooling.

a. Initial heating stage:

The glass sheet enters the tempering furnace for heating at room temperature. As glass is a poor conductor of heat, the inner layer temperature is low while the outer layer temperature is high. The outer layer begins to expand, while the inner layer does not. Therefore, the expansion of the outer layer is temporarily suppressed by the inner layer, resulting in a tensile stress in the outer layer. Due to the high compressive shrinkage of glass, even with rapid heating, the glass sheet does not break.

Note: From here, it can be understood that once the glass enters the furnace, there is a temperature difference between the inner and outer layers of the glass, which creates stress on the inner and outer layers of the glass. Therefore, thick glass should be heated slower and at a lower temperature, otherwise the glass will break inside the furnace due to the large temperature difference between the inside and outside

b. Continuous heating stage:

When the glass is continuously heated and the temperature difference between the inner and outer layers of the glass is reduced, the stress inside the glass plate is equal when both the inner and outer layers reach the tempering temperature

c. Start of rapid cooling phase (1.5-2 seconds before the start of blowing)

The glass sheet enters the wind grille from the tempering furnace for blowing, and the temperature of the outer layer drops below the center temperature. The outer layer begins to shorten, while the center layer does not. Therefore, the shortening of the outer layer is suppressed by the center layer, causing temporary tensile stress on the outer layer and compressive stress on the center layer

d. Continuous rapid cooling phase:

The inner and outer layers of the glass are further quenched, and the outer layer of the glass has hardened (the temperature has dropped below 500 ℃), stopping shortening. At this point, the inner layer also begins to cool and shorten, and the hardened outer layer suppresses the shortening of the inner layer, resulting in compressive stress on the outer layer and tensile stress on the inner layer

e. Continuous rapid cooling (within 12 seconds)

The temperature of both the inner and outer layers of the glass has further decreased, and the inner layer of glass has dropped to around 500 ℃ at this moment, shortening and accelerating. At this stage, the compressive stress of the outer layer and the tensile stress of the inner layer have been fundamentally formed, but the central layer is still relatively soft and has not completely detached from the viscous activity state, so it is not yet a complete stress state

f. Tempering completed (within 20 seconds)

At this stage, both the inner and outer glass layers are thoroughly tempered, and the temperature difference between the inner and outer layers is reduced. The stress of the tempered glass is formed, that is, the outer surface is compressive stress and the inner layer is tensile stress.

Article source: Tempered glass coverwww.yinghuade.com