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The thermal stress of glass bottles has permanent stress
A glass bottle is heated to a temperature higher than the glass strain point. After soaking, both sides of the plate are cooled evenly and naturally. After a certain period of time，glasscookware, the temperature field in the glass exhibits a parabolic distribution. The outer layer of the glass is tensile stress and the inner layer is compressive stress. Since the glass above the strain point has viscoelasticity, that is, the glass at this time is in a plastic state. Stress relief. This process is called the stress relaxation process, at this time there is a temperature gradient between the inner and outer layers of the glass but there is no stress. When the glass is cooled below the strain point, the glass has become an elastomer, and the subsequent cooling and stress changes are the same as the aforementioned temporary stress. The stress generated above, at this time, the stress direction is exactly the opposite, that is, the surface is compressive stress, the interior is tensile stress, and this stress is permanent stress.
The stress caused by the uneven structure of the glass bottle due to uneven chemical composition is called structural stress. It is a permanent stress, which cannot be eliminated even by annealing the glass bottle. The compositional inhomogeneity in the glass has a different thermal expansion coefficient than that of the main glass, so the shrinkage and expansion of the main glass and the inhomogeneous body are also different, and stress is generated on the interface, so annealing cannot eliminate such stress. . For example, when stones, striations and nodules are present in the glass, stress is induced at the interface of these defects.
The stress caused by the uneven structure of the glass bottle due to uneven chemical composition is called structural stress. It is a permanent stress, which cannot be eliminated even by annealing the glass bottle. The compositional inhomogeneity in the glass has a different thermal expansion coefficient than that of the main glass, so the shrinkage and expansion of the main glass and the inhomogeneous body are also different, and stress is generated on the interface, so annealing cannot eliminate such stress. . For example, when stones, striations and nodules are present in the glass, stress is induced at the interface of these defects.
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