With the arrival of winter, the damage rate of tempered glass (especially outdoor) is 0.2% higher than in previous seasons. Tempered glass is a type of prestressed glass. It has compressive stress on its surface and tensile stress inside. Normally, glass is in a state of force equilibrium. But there are a small amount of impurities in the glass raw materials.
With the extension of time and the large temperature difference between day and night in winter, phase transition will occur and the volume will increase. Especially when the indoor temperature is high and the outdoor temperature is low, the temperature inside and outside the glass on the window is different, which can disrupt the balance of compressive and tensile stresses in tempered glass and cause it to break on its own. It is called self explosion in the industry.
To improve the yield of tempered glass, the following points must be achieved:
1, Glass must be edged before tempering. The quality of glass edge grinding plays a decisive role in the yield of tempered products. When cutting glass, small and fine cracks will be left at the edges, which are almost invisible to the naked eye. The purpose of edge grinding is twofold: first, it is aesthetically pleasing, and second, it is to prevent breakage during tempering and improve the yield of tempered glass products.
2, Adjust the process parameters for tempering. The main process parameters for tempering are heating temperature, heating time, wind pressure time for tempering cooling, and tempering cooling time. The temperature of tempering is inversely proportional to the heating time, and the higher the temperature, the shorter the heating time. However, when tempering glass with a thickness of over 12mm, if the furnace temperature is too high, it is easy to explode inside the furnace. Of course, there are many reasons for furnace explosion, and setting the furnace temperature too high is the main reason. It is recommended to set the furnace temperature at around 665 degrees Celsius and extend the heating time appropriately when tempering glass with a thickness of 12mm or more. After determining the temperature, it is necessary to choose a reasonable heating time, usually around 40 seconds per millimeter. However, when tempering large glass panels, an additional 10% heating time is required, and when tempering glass with holes or corners, an additional 10% heating time is also required. Dialectically mastering the heating time and temperature is very important, and it is also the key to improving the yield of tempered glass products.
3, 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.