The tempering furnace temperature is not set properly, and the lower temperature is too high. In the first third of heating, the warping time of the glass is too long, and the glass rubs the track repeatedly, which will produce white fog.

Tempered glass is made by cutting ordinary annealed glass into required sizes, then heating it to about 700 degrees near the softening point, and then rapidly and uniformly cooling it (usually, 5-6MM glass is heated at 700 degrees for about 240 seconds, and the temperature is reduced by about 150 seconds). 8- 10MM glass is heated at 700℃ for about 500 seconds and cooled for about 300 seconds.

In short, according to the thickness of the glass, the heating and cooling time is different. After tempering, uniform compressive stress is formed on the glass surface and tensile stress is formed inside, which improves the bending and impact strength of the glass, and its strength is about four times that of ordinary annealed glass.

Extended data:

Classification:

1. Physical tempered glass is also called quenched tempered glass. When the ordinary flat glass is heated to the softening temperature (600℃) of the glass in the heating furnace, the internal stress is eliminated by its own deformation, and then the glass is moved out of the heating furnace, and then high-pressure cold air is blown to both sides of the glass with multi-head nozzles, so that it can be quickly and uniformly cooled to room temperature, and tempered glass can be made.

This kind of glass is in a stress state of internal tension and external pressure. Once damaged locally, the stress will be released and the glass will be broken into countless small pieces. These small pieces have no sharp edges and corners, so they are not easy to hurt people.

2. Chemically toughened glass is used to improve the strength of glass by changing the chemical composition of the glass surface. Generally, ion exchange method is used for tempering.

In this method, silicate glass containing alkali metal ions is immersed in molten lithium (Li+) salt, so that Na+ or K+ ions on the glass surface are exchanged with Li+ ions, and a Li+ ion exchange layer is formed on the surface. Because the expansion coefficient of Li+ is smaller than that of Na+ and K+ ions, the outer layer shrinks less and the inner layer shrinks more during cooling.

When cooled to room temperature, the glass is also in a state of tension in the inner layer and compression in the outer layer, and its effect is similar to that of physically tempered glass.

References:

Baidu encyclopedia-toughened glass