Factors Affecting Physical Tempering

        As we all know, many properties of glass have been improved after tempering. Its bending strength is 4 ~ 5 times higher than that of ordinary glass, its quench and heat resistance is 3 ~ 5 times higher than that of ordinary glass, and its impact strength is several times higher than that of ordinary glass. At present, the main tempering method is physical tempering. What are the factors affecting physical tempering? 

        When a certain thickness of glass is quenched, the stress in the glass increases with the increase of quenching temperature and cooling intensity. When the quenching temperature reaches a certain value, the degree of stress relaxation hardly increases, and the stress tends to a limit value, which is called the quenching degree of glass. It depends on the cooling strength, glass thickness and chemical composition of the glass.



 

        (1) Cooling intensity

        In the glass industry, generally toughened glass adopts air-cooled toughening. The greater the cooling intensity, the more intense the toughening. However, the cooling intensity depends on the wind pressure of the air and the distance between the small hole on the grille and the glass. In addition, the diameter of the nozzle also affects the toughening degree of the glass. The larger the diameter, the larger the area of air contacting the glass, and the cooling intensity also increases.
 

        (2) chemical composition of glass

        The chemical composition of glass has a great influence on the degree of tempering. Because the magnitude of stress is related to the expansion coefficient of glass α、 Young's modulus E and temperature gradient △ T are in direct proportion to Poisson's ratio μ Inversely proportional. and α、 E、 μ It is determined by the chemical composition of glass, and the toughening degree of glass with different chemical composition is different. When 20%ro is used to replace SiO2 in glass in r2o-sio2, the tempering degree is doubled.
 

        (3) glass thickness

        Under the same conditions, the thicker the glass, the higher the degree of tempering. Plate glass is generally tempered with glass of more than 2.5mm to ensure the generation of large permanent stress. If the thickness is small, the corresponding cooling rate is very high, so as to obtain a better degree of tempering. For non flat glass products, the thickness shall be uniform during tempering, and the difference shall not be too large, otherwise it will break due to uneven stress distribution.

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