Why is the strength of tempered glass so high

Source：www.cnxingfu.net Release date： 2025-02-05

Information summary：The high strength of tempered glass is mainly achieved by forming a compressive stress layer on the surface of the glass through physical or chemical methods, as well as improving the internal structure of the glass. The following is a specific introduction: 1. Heat treatment process generates compressive stress Principle: Physical tempered glass is made by heating ordinary glass to a tempe

The high strength of tempered glass is mainly achieved by forming a compressive stress layer on the surface of the glass through physical or chemical methods, as well as improving the internal structure of the glass. The following is a specific introduction:
1. Heat treatment process generates compressive stress
Principle: Physical tempered glass is made by heating ordinary glass to a temperature close to its softening point (600-650 ℃) and then rapidly cooling it. During this process, the surface of the glass rapidly cools and solidifies, while the interior remains at a high temperature. As the internal glass continues to cool and shrink, it is limited by the already solidified surface layer, resulting in compressive stress on the glass surface and tensile stress inside.
Mechanism of action: When glass is subjected to external forces, it first needs to overcome the surface compressive stress. Only when the external force is large enough to counteract the surface compressive stress and make the internal tensile stress reach the strength limit of the glass, will the glass break. The presence of this compressive stress greatly enhances the glass's ability to resist external forces, resulting in a significant increase in strength compared to ordinary glass, typically reaching 3-5 times that of ordinary glass.
2. Ion exchange generates compressive stress
Principle: Chemical tempered glass is achieved through ion exchange technology. Immersing glass into a molten salt bath, such as potassium nitrate (KNO3) molten salt, the alkali metal ions on the glass surface (such as sodium ions Na ⁺) will exchange with the potassium ions (K ⁺) in the molten salt. Due to the larger radius of potassium ions compared to sodium ions, a compressive force is generated upon entering the glass surface, resulting in the formation of a compressive stress layer on the glass surface.
Mechanism of action: Although the compressive stress layer formed by chemical tempering is relatively thin, the compressive stress value is high, which can effectively improve the surface hardness and scratch resistance of the glass, thereby enhancing the overall strength of the glass. The strength of chemically tempered glass can reach 4-6 times that of ordinary glass, and the glass will not deform during processing, making it suitable for applications with high precision requirements.
3. Improved uniformity of internal structure
Principle: During the tempering process, the microstructure inside the glass is improved and optimized to a certain extent. On the one hand, the high temperature and rapid cooling process make the stress distribution inside the glass more uniform, reducing the possibility of fracture caused by stress concentration. On the other hand, tiny defects in glass, such as bubbles and impurities, have been "healed" or reduced to a certain extent, making the internal structure of the glass more dense.
Mechanism of action: Glass with uniform and dense structure can more evenly disperse stress when subjected to external forces, avoiding stress concentration at defects and causing crack generation and propagation, thereby improving the strength and stability of the glass.
4. Increased surface hardness
Principle: Both physical and chemical tempering can significantly improve the hardness of the glass surface. Physical tempering makes the molecular structure of glass surface more compact through rapid cooling, while chemical tempering introduces large ions through ion exchange to increase surface density, making the glass surface more wear-resistant and scratch resistant.
Mechanism of action: In practical use, scratches and wear on the surface of glass often become the starting point of cracks, reducing the strength of the glass. The increased surface hardness of tempered glass can effectively resist various frictions and collisions in daily use, reduce surface damage, and maintain the integrity and strength of the glass.

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