Small glass tempering furnace is another form of glass tempering furnace, its volume is only smaller than that of tempering furnace. It uses physical or chemical methods to form compressive stress layer on glass surface and tensile stress layer inside. When the glass is subjected to external force, the compressive stress layer can offset part of the tensile stress and avoid glass breakage. Thus, the purpose of improving glass strength is achieved. Moreover, the microcracks on the glass surface become more subtle under this compressive stress. The strength of glass is also increased to some extent. The glass tempering unit of the small tempering furnace is mainly composed of four parts, i.e. release section, convection heating section, flat tempering section and pick-up section, as well as high-pressure centrifugal fan, air supply pipeline, air collecting box, air passage, electric control cabinet and operating table.

　　At present, the commonly used physical toughening method is to heat the glass to the softening point (about 650 C). At this time, the glass can still maintain its original shape, but the particles in the glass have a certain migration ability, and the structure is adjusted. In this way, the internal stress can be quickly eliminated, and then the tempered glass of the small tempering furnace is blown and quenched. When the temperature is balanced, compressive stress occurs on the glass surface and tensile stress occurs on the inner layer. That is to say, glass produces a uniform and regular distribution of internal stress, which improves the tensile strength of glass as a brittle material, thereby improving the bending and impact strength of glass. At the same time, due to the existence of uniform stress in the glass, once the glass is partially ruptured by impact beyond its strength, it will self-explode into small particles under the action of internal stress, which improves its safety. Therefore, toughened glass can also be called pre-stressed glass or safety glass.

　In the tempering process of glass tempering furnace, wind spot and stress spot usually occur. Wind spot is formed in the process of cooling, which is caused by uneven stress of glass due to uneven cooling. It can be seen from a special angle that the surface of glass is striped with light and dark. Stress spot is also caused by uneven stress, for example, in the heating process, there is a temperature difference between the edge and the middle of the furnace, which results in uneven stress. At present, there is no way to avoid the stress spot completely, but a well-designed steel equipment can reduce the visibility of the stress spot.