What is the most popular surface stress of glass

2022-07-25
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What is the surface stress of glass

the stress of glass refers to the internal force that interacts between various parts of the glass when the glass is deformed due to external factors (stress, humidity, temperature field changes, etc.), so as to resist the effect of such external factors and attempt to restore the orientation of the glass from the deformed orientation to the orientation before deformation. It can be divided into:

1. Plane stress: it is caused by uneven transverse temperature of annealing kiln. This kind of stress is measured by various stress meters. Its size has nothing to do with the length of the annealing furnace, that is, it has nothing to do with the definite cooling rate of the glass strip, and only depends on the transverse temperature distribution of the glass plate. The plane stress has a great influence on the breaking and edge breaking of glass ribbon. After breaking off the edges, most of the plane stress disappears and has little effect on the further processing of the glass. For thick glass, the problems caused by plane stress are mainly multi angle defects, edge splitting, white slag, etc

2. Thickness stress: also known as end face stress, which is caused by the temperature difference between the glass surface and the plate core during cooling. It is determined by the length of the annealing kiln supported by professional software. When the length of the annealing kiln is punctual, the inlet and outlet temperature of each zone, that is, the cooling rate, directly determines the size of the stress. Thickness stress not only has an impact on the primary production of glass, but also has a great impact on the subsequent deep processing. It should be an important target for the ex factory quality of glass products. The effect of thickness stress on thick glass production is mainly sugar; The main impact on deep processing is not easy to cut, tempering and furnace blasting

plate glass is generally divided into tempered glass, semi tempered glass and annealed glass according to the magnitude of external gauge stress. According to the American astmcb code, the external compressive stress scale of various glasses is: 69mpa (10000psi) for tempered glass,

24MPa (3500psi) ~52mpa (7500psi) for semi tempered glass The national specifications for tempered glass and semi tempered glass for curtain wall issued by China also have clear requirements for the stress. The semi tempered glass is MPa, and the tempered glass is more than 90Mpa

(1) tempered glass

the traditional way to inspect tempered glass is impact test. According to GB9963 and gb9656 rules, the number of fragments within the scale of 50mm ′ 50mm must be greater than 40. The experiment shows that within the stress scale of tempered glass, there is a good corresponding relationship between the external stress value and the number of fragments, and the external stress value corresponding to the number of 40 fragments is about 82mpa Tempered glass with homogeneous treatment shall be selected for high-rise buildings

(2) thermally reinforced glass

thermally reinforced glass is often called "semi tempered glass" in China. It is widely used in buildings and has good wind pressure resistance. This kind of glass tends to stay in the window frame after being damaged by natural disasters, and at the same time, it can ensure that it will not explode. According to ASTM rules, the stress scale of heat strengthened glass is MPa, and the stress of tempered glass must be greater than 69mpa. Glass with a stress of MPa is a waste product, which can neither be used as tempered glass nor as heat strengthened glass

(3) a large number of experiences of tempered safety glass indicate that when tempered glass is used for safety glass, its surface stress value is usually greater than 105Mpa. A common example is automobile glass. If the stress is less than 105Mpa, although the number of fragments can still meet the requirements of relevant specifications, the strength of the glass is slightly insufficient

(4) hot bending glass

its relative humidity will reach 100%rh

hot bending glass is a kind of annealed glass, which requires that the internal stress of the glass should be as small as possible to ensure that the glass will not crack due to excessive uneven stress. The stress is concentrated in the bending part, and the external stress is about 15MPa, which is easy to cause glass fragmentation. The external stress should be reduced below 7MPa, which can fundamentally solve the problem of corner cracking

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