Guangzhou tempered glass manufacturers why glass will appear stress spots

The reason for the stress spots in the glass is mainly related to the uneven heating and cooling during the glass tempering process. The following is a detailed explanation of this phenomenon:

Generation Principle of 1. Stress Spots

Stress spots, also known as wind spots, are caused by uneven heating and cooling processes during the glass tempering process, resulting in different stress distributions on the glass plate surface. When a beam of polarized light passes through the tempered glass, due to the stress difference inside the glass, the beam of light will become larger at the relative light density, and the angle of refraction at the light density will become relatively smaller, thus breaking down into two beams with different propagation speeds. Polarized light.

When the two beams of light intersect at a certain point, there is a phase difference at the intersection of the beams due to the difference in the speed of light propagation, resulting in the interference of the two beams of light. When the amplitude direction of the two beams is the same, the light intensity is enhanced to produce a bright field of view, that is, a bright spot; when the light amplitude direction is opposite, the light intensity is weakened to produce a dark field of view, that is, a dark spot.

Stress spots due to non-uniform 2. heating

In the process of glass tempering, uneven heating is one of the main causes of stress spots. Uneven heating can be caused:

Heating furnace wire power difference: If the power value of the heating furnace wire is not uniform, it will cause uneven heating of the glass during the heating process. This can be determined by measuring the current intensity through the furnace wire to determine whether the furnace wire is aging or there is a power deviation.

Heater failure: Heater failure may cause some areas to be unable to heat normally, resulting in uneven heating.

Temperature sensor failure: If the temperature sensor fails or the calibration is inaccurate, the temperature setting will be unreasonable, which will affect the heating effect of the glass.

Uneven heat dissipation of the furnace body: the side of the furnace body dissipates more heat. If the temperature setting is not reflected, it will lead to uneven heating.

Stress spots due to non-uniform 3. cooling

In addition to uneven heating, uneven cooling is also an important cause of stress spots. Uneven cooling can be caused:

Unreasonable distribution of fan nozzle: unreasonable distribution of nozzle or uneven gap will lead to uneven distribution of wind pressure on the glass surface, resulting in uneven cooling.

Air nozzle blockage: part of the air nozzle blockage will cause abnormal air supply, which will affect the cooling effect of the glass.

The thermal conductivity of the roller table is too large: the part in contact with the roller table will be rapidly cooled, and the part that is cooled first will form a large compressive stress, which will lead to the generation of stress spots.

4. other influencing factors

In addition to uneven heating and cooling, there are other factors that may also affect the generation of stress spots:

Glass thickness: Thick plate glass due to long heating time, large cooling difference, stress spots are usually heavier.

Glass type: The effect of stress spots in laminated glass is more difficult to control because stress spots may overlap after lamination. Coated glass is more prominent by color, especially double silver Low-E, three silver Low-E and other coated glass, the interference color of the stress spot has a color effect, the color of the stress spot is more obvious.

Use environment: In extreme environments, such as high temperature, low temperature or humidity, the stress state of tempered glass will change, which may also lead to the appearance of stress spots.

5. methods for reducing stress spots

In order to reduce the visibility of stress spots, the following measures can be taken:

Optimized tempering equipment: A well-designed tempering equipment can minimize the visibility of stress spots. For example, in continuous production using a radiant furnace, the stress spot effect is generally better than in a convection furnace for batch production.

Improving the heating process: ensuring uniform heating is the primary factor in reducing stress spots. The heating process can be improved by adjusting the power of the heating filament, optimizing the layout of the heater, calibrating the temperature sensor, etc.

Optimize the cooling process: reasonable distribution of fan nozzle, keep the nozzle clean, adjust the heat conduction capacity of the roller table, etc. help to optimize the cooling process, thereby reducing the generation of stress spots.

Choosing high-quality glass: Choosing good-quality tempered glass and ensuring that the production process meets the standards also helps to reduce the appearance of stress spots.

To sum up, the stress spots in the glass are mainly caused by the non-uniformity in the heating and cooling process. The visibility of stress spots can be effectively reduced by optimizing tempering equipment, improving heating and cooling processes, and selecting high-quality glass.