Due to the violent temperature changes, the annealed basic sensible glass is in the molding process. The inner and outer layers are subjected to a temperature gradient, and due to the divergence of the glass machinery such as the shape, thickness, and degree of cooling of the finished product, irregular thermal stress is generated in the product. This thermal stress can reduce the mechanical strength and thermal stability of the product, as well as the optical uniformity of the glass. If the stress exceeds the ultimate strength of the finished product, it will rupture on its own. Therefore, the presence of uneven thermal stress in the glass article is a serious error. Annealing is a heat treatment process that minimizes or reduces the thermal stress in the glass to an allowable value. In addition to glass fiber and thin-walled small hollow products, it is true that all glass products must be annealed. The thermal stress in glass products is divided into temporary stress and long-term stress according to its existing characteristics. Due to its poor thermal conductivity, 1 temporary stress. The glass is heated or cooled below the strain point temperature.
Each part will form a temperature gradient, resulting in inevitable thermal stress. This thermal stress, as the temperature difference exists, has a larger temperature difference, and the stress is also larger, and disappears as the temperature difference disappears. This thermal stress is called a temporary stress. But before the temperature is out of balance, it should be noted that the stress can be dispelled by itself. When the stress value exceeds the ultimate strength of the glass, the glass abnormality will rupture on its own, so the heating or cooling rate of the glass in the brittle temperature range should not be too fast. Thermal stress caused by temperature difference, 2 longer stress. The glass is cooled from the beginning of the strain point temperature. After the glass is cooled to room temperature and the temperature of the inner and outer layers is out of adjustment, it cannot be completely dissipated. The glass still bears a certain stress in the same way. This stress is called water long-term stress. The magnitude of the longer-term stress depends on the glass machinery such as the cooling rate of the finished product above the strain point temperature, the viscosity of the glass, the thermal shortening factor, and the thickness of the product. It is to reheat the glassware with longer stress to the temperature at which the particles inside the glass can move and anneal the glass.
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