Why should the glass be tempered?
- After the glass is tempered, its strength is several times higher. Its bending power is 3 to 5 times that of normal glass. Its impact strength is 5 to 10 times that of normal glass, which improves stability and safety simultaneously. The tempered glass can generally withstand drastic temperature changes of more than 150LC, significantly preventing thermal cracking.
- It is safe to use, and the load-bearing capacity is increased to improve the fragile nature. Even if the toughened glass is damaged, there are small fragments without acute angles, which significantly reduces the damage to the human body after the accidental broken glass.
How is the glass tempered?
The ordinary glass is cut to the required size and then heated to about 700 degrees close to the softening point of the glass, and after that quickly and uniformly cooled (usually 5-6MM glass is heated at 700 degrees for about 240 seconds, and then cooled down for approximately 150 seconds.), the glass is heated to an appropriate temperature and then quickly cooled, causing the glass surface to shrink sharply, resulting in compressive stress. However, the middle layer of the glass cools slowly, and it is a bit late to shrink, so tensile stress is formed, which makes the glass obtain higher strength.
What are the disadvantages of tempered glass?
- The toughened glass can no longer be cut and processed. The glass can only be processed to the required shape before tempering.
- Although the strength of tempered glass is stronger than that of ordinary glass, there’s still have the possibility of spontaneous explosion (breaking by itself) when the temperature difference changes significantly. In contrast, normal glass does not have the chance of spontaneous explosion.
Why does tempered glass explode?
Because the glass raw material contains nickel sulfide crystals, it is impossible to avoid the existing manufacturing technology in the world entirely. This kind of nickel sulfide crystal has two forms, A form and B form. Under particular time and temperature conditions, the A form will change to the B form, and the volume of the B form is 3-5 times the volume of the A form.
Although the volume of this kind of crystal is tiny, if this kind of crystal becomes B-shape inside, the increase in volume will affect the internal compressive stress balance of the whole piece of glass and cause the glass to break. There is no compressive stress inside an ordinary one. The deformation of its nickel sulfide crystals will not cause these problems. There is enough space for it to deform.
How to reduce the spontaneous explosion rate of tempered glass?
The self-explosion rate of tempered glass recognized in the industry is 3‰-5‰.
- Reduce glass impurities and improve purity from the production source.
- In the glass tempering process, use better equipment to function to make sure the internal stress of the glass is uniform, which leads to a lower spontaneous explosion rate.
- In the case of reaching the required strength, control the stress value of the tempered glass. The lower the stress, the lower the self-explosion rate.
- Do hot-dip treatment. After tempering, put the glass in a furnace at 300°C for about 8 hours to simulate extreme environmental factors so that the potential self-exploration glass may explode in advance, which can be understood as detonation treatment. Note, however, that there is still a risk of self-explosion of glass after hot dipping, and the self-explosion rate of glass is one in a thousand.
- Use ultra-white glass. When the glass is produced, the nickel sulfide impurity inside the glass is eliminated through a chemical displacement reaction. The self-explosion rate of this glass after tempering is one in 100,000.
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