The stress of glass refers to the inner force of interaction between the various parts of the glass when the glass is deformed due to external causes (force, humidity, temperature field changes, etc.) in order to resist the effect of this external cause, and attempts to restore the glass from the deformed position to the pre-deformation position. Can be divided into:
1. Plane stress: It is caused by the horizontal temperature of the de-ignition kiln. This is the kind of stress measured by various in-line stressors. Its size is independent of the length of the average kiln, i.e. the absolute cooling speed of the glass belt, depending only on the horizontal temperature distribution of the glass plate. Plane stress has a great effect on the broken glass band and the edge of the edge. After breaking off the edge, most of the plane stress disappears, which has little effect on glass-step processing. For thick glass, plane stress caused by the problem is mainly many missing angles, as well as split edges, white slag and so on.
2. Thickness stress: also known as end face stress, is caused by the temperature difference between the glass surface and the core during cooling. It is determined by the length of the de-ignition kiln, and when the length of the de-ignition kiln is certain, the import and export temperature of each region, i.e. the cooling speed, directly determines the size of the stress. Thickness stress not only has an impact on the production of glass but also has a great impact on subsequent deep processing, it should be an important indicator of the factory quality of glass products. The effect of thickness stress on thick glass production is mainly sugary, and the effect on deep processing is mainly not easy to cut and tempered blast furnace.
Flat glass is generally divided into tempered glass, semi-tempered glass and defying glass according to the difference in surface pressure stress size. According to the U.S. ASTMC1048-1997b standard, the surface pressure stress range of various glass is tempered glass >69MPa (10,000psi),
(1) Tempered glass
The traditional method of testing tempered glass is impact test, GB9963 and GB9656 stipulate that the number of fragments in the 50mm'50mm range must be greater than 40. The experiment shows that there is a good correspondence between surface stress value and the number of fragments in the range of tempered glass stress, and the surface stress value corresponding to the number of 40 fragments is about 82MPa. Homogenized tempered glass should be used as far as possible in high-rise buildings.
(2) Heat-reinforced glass
Thermal reinforced glass is often referred to as "semi-tempered glass" in China. It is very common in architecture and has good wind pressure resistance. Such glass tends to remain in the window frame after being damaged by a natural disaster and does not fall, while ensuring that it does not explode. ASTM specifies that the stress range for thermally reinforced glass is 24-52Mpa, and the stress of tempered glass must be greater than 69MPa. Glass with a stress range of 51-69MPa is waste and cannot be used as tempered glass or as thermally reinforced glass.
(3) Tempered safety glass
A great deal of experience has shown that when tempered glass is used for safety glass purposes, its surface stress value is usually greater than 105MPa. A common example is an automotive glass, where the stress is less than 105MPa, and although the number of fragments can still meet the relevant standard requirements, the glass strength is slightly inadequate.
(4) Hot curved glass
Hot-bending glass is an gathering glass that requires as little stress as possible in the glass to ensure that the glass does not break due to too large uneven stresses. Stress is concentrated in the bending part, and the surface stress is around 15MPa, which can easily lead to broken glass. Surface stress should be reduced below 7MPa, which can basically solve the problem of corner breakage.
