With the advent of winter, the breakage rate of tempered glass, especially outdoors, is higher than in previous seasons. Tempered glass is a pre-stressed glass. It has compressive stress on the surface and tensile stress inside. Generally, the glass is in a state of force balance. However, there are impurities in the glass ingredients.
As time goes by, and the temperature difference between day and night in winter increases, phase changes occur, resulting in expansion. In particular, when the indoor temperature is high and the outdoor temperature is low, there are differences in the temperatures of the glass on both sides, which disrupts the balance of compressive and tensile stresses in the tempered glass, causing it to self-destruct. This phenomenon is known as "spontaneous combustion" in the industry.
To increase the production yield of tempered glass, the following points must be achieved:
First, the edges of the glass must be ground before steelization. The quality of the edge grinding directly affects the high or low production yield of tempered glass. When cutting the glass, very small and fine cracks are left on the edges, which are almost invisible to the naked eye. Grinding the edges has two purposes: one is for aesthetics, and the other is to make it less likely to fracture during the tempering process, thereby increasing the production yield of tempered glass.
Second, adjust the parameters of the tempering process. The main parameters of the tempering process include the heating temperature, heating time, wind pressure, and duration of the tempering cycle. Heating temperature and duration are inversely related; as the temperature increases, the duration typically decreases. However, when tempering glasses thicker than 12 mm, setting the furnace temperature too high can lead to premature failure of the glass. Therefore, it is suggested to set the furnace temperature at around 665 degrees Celsius for glasses thicker than 12 mm and to appropriately increase the heating time. After determining the temperature, it is important to choose the right heating duration, which is usually about 40 seconds per millimeter of thickness. For large-format glasses, a 10% increase in heating duration is recommended, as well as for glasses with holes or angles. Dialectically understanding the relationship between heating duration and temperature is key to enhancing the quality and uniformity of tempered glass.
Third,the importance of uniform heating of glass. Glass is actually a cube with 4 sides and 6 faces. The heating of the upper and lower surfaces of glass is relatively slow. When tempering large glass panels, the middle of the glass is often heated the slowest. Sometimes, the tempered glass will form a pot shape (especially for large glass panels that are close to a square). This is because the heating of the edges is too fast and the heating of the middle is too slow, which means that after heating is completed, the temperature of the edges of the glass is much higher than that of the middle of the glass. To achieve uniform heating of large glass panels, it is best to set the furnace temperature to a heating curve (horizontal) where the temperature in the middle is 10 degrees higher than the set temperature and the temperature at the edges is 10 degrees lower than the set temperature. The tempered glass produced in this way has both uniform particle size and uniformity.
