Discussion on the causes of reducing the self expl

  • Detail

Discussion on the reasons why homogenizing furnace reduces the self explosion rate of tempered glass

the self explosion of tempered glass is the main reason affecting its safety performance. The particles of non vitreous substances (such as nickel sulfide) in the tempered glass will lead to the self explosion of tempered glass, which is brought into the glass by the impurities in the raw materials of glass production. There are some nickel sulfide particles whose crystal structure changes from α State transition to β In this transition process, the volume of nickel sulfide particles expands to a large extent. This volume expansion process forms a strong internal stress of tempered glass, resulting in self explosion of tempered glass

tempered glass is widely used in modern buildings because of its superior performance, and its self explosion characteristics have been plagued the whole industry. At present, most enterprises control the self explosion rate of tempered glass within 1.5 ‰, and the self explosion rate of tempered glass treated by the homogenizer equipment is reduced to less than 1 in 10000. Therefore, the equipment can greatly improve the safety performance of tempered glass, and has a broad application prospect

process principle

the tempered glass homogenizer is a device for the indirect safety of tempered glass. After the glass is tempered, it enters the homogenizer. Through the high-temperature heating principle of the homogenizer, the detonating test is carried out and the residual nickel sulfide is eliminated. There will be a hidden danger of "self explosion", that is, the tempered glass with uneven stress in the glass will detonate in advance during the test process, so as to avoid the "self explosion" again after the installation of the tempered glass, The qualified rate of tempered glass after homogenization will be greatly improved, thus improving the safety and reliability of tempered glass in buildings

nickel sulfide in tempered glass, as a non vitreous substance particle, has always existed in the glass, which is the main factor leading to the self explosion of tempered glass. Nickel sulfide is brought into the glass by impurities in the raw materials (quartz sand, silica powder, etc.) for the production of glass. The crystal structure of some nickel sulfide particles changes from α State transition to β In this transition process, the volume of nickel sulfide particles expands greatly. This volume expansion process forms a strong internal stress of tempered glass, resulting in self explosion of tempered glass. Nickel sulfide, which causes glass self explosion, is directly between 0.04mm and 0.65mm, with an average particle size of 0.2mm

due to the crystal transformation of nickel sulfide, the volume increases, and the self explosion caused by it will produce radioactive cracks locally. As shown in Figure 1, if the glass is still left in the frame after being broken, it is easier to find a "Butterfly" shaped pattern feature at the starting point of the breakage. From the "butterfly spot" produced in the glass fragments after self explosion, it is inclined at an angle of 45 degrees, It is easy to see a small black spot in the center of the glass. As for the "Butterfly", it is between the cracks, and the recycle bin only carries out rough sorting, and the direction of the self exploding broken glass crack is scattered from the center to the surrounding

homogenization treatment of tempered glass by secondary heating and annealing (also known as hot dip treatment) is recognized as an effective method to solve the problem of self explosion. Heat the tempered glass again to about 290~300 degrees Celsius, and cool down slowly after holding for a certain time, so that the nickel sulfide particles in the tempered glass can complete the crystal phase transformation in the homogenization treatment, so that the glass that may self explode can be broken in advance in the factory. This method can effectively reduce the self explosion rate of tempered glass after leaving the factory, improve the yield, and reduce the impact of transportation, installation and subsequent process rework caused by self explosion. At present, the forced convection electric heating hot dip furnace is mainly used to treat tempered glass in China. The heating box of the existing tempered glass homogenizing furnace is mostly located at the top or rear of the furnace body. The fan is used to convey the hot air to the tempered glass to be homogenized in the furnace through the air duct, and the hot air is sucked back to the fan through the gap between the tempered glasses. It is repeated continuously to heat the tempered glass to the rated temperature and maintain the constant temperature for a long time, which has achieved the purpose of detonating the tempered glass with the hidden danger of "self explosion". However, the disadvantages are poor temperature uniformity, high energy consumption, inconvenient maintenance and cleaning, which brings a lot of inconvenience to production

structure of tempered glass homogenizing furnace

first, when the temperature in the furnace rises to 280 ℃, it is required to keep the heat preservation for more than two hours, which puts forward strict requirements for the heat preservation performance of the furnace body. If the heat preservation effect is not good, it will be difficult to control the temperature in the furnace at a level, which will make the temperature in the furnace rise and fall, seriously affecting the glass quality. According to the research, the phase transformation rate at 280 ℃ is 100 times that at 250 ℃, Therefore, it must be ensured that each glass in the furnace experiences the same temperature curve. Otherwise, on the one hand, the temperature of some glasses is too high, which will cause the reverse phase transition of nickel sulfide; On the other hand, the glass with low temperature has incomplete phase transition due to insufficient holding time. Both cases will lead to invalid homogenization treatment, so the processing space is 4400mm on the insulation of the homogenizer itself × 3700mm × Take 3300mm as an example, at least 200mm insulation layer should be used around the furnace body. Since most homogeneous furnaces use the heating device on the top of the furnace body, the insulation requirements on the top are more strict. This is because most of the upper part of the furnace body should be covered with cable lines, in order to have better insulation effect, at least 500mm insulation layer should be used. This can not only improve the reliability of homogenization, but also save a lot of electric energy and contribute to the construction of an energy-saving society

secondly, in order to ensure that the temperature inside the homogenizer can be at the same level, it is also required that there is a smooth air flow inside the homogenizer to prevent the dead corner of the air flow, resulting in the failure of glass homogenization due to local high or low temperature. The air flow inside the furnace body is provided by the fan placed on the top of the furnace body. Leading, requiring that the fan is a high-temperature fan, which can work in a high-temperature environment for a long time, and the high temperature resistance is at least 400 ℃; Second, the air duct system is made of stainless steel, which can improve its service life. The circulation of air in the furnace can be achieved by transferring air into the furnace through the air duct, as shown in Figure 2

the arrow direction in the figure indicates the direction of wind flow. The fan blows cold air to the heating area, and forms hot air through heating to circulate in the furnace at 4400mm × 3700mm × Taking the size of 3300mm furnace as an example, the internal air volume is required to be more than 40000m3/h, and the circulation speed is required to be 1. About 5m/s, which is also in order to make the internal air circulation uniform, it is recommended to adopt the method of multiple fans and multiple air inlets to improve the uniformity of air in the furnace. It should also be emphasized here that the insulation of air ducts and fans is also crucial

as for the main framework of the furnace body, try to use high-quality steel. Because of the long-term heating and cooling, such a cold and hot cycle has a very serious impact on the steel, so we must pay more attention to the selection of steel, and the inner wall of the furnace body should be made of stainless steel

as shown in Figure 2, open the furnace door, put the A-frame with existing glass into the chamber ① of the homogenizer, and close the self-locking device in the furnace; Set the temperature and heat the modular heater to form heater ②; Start the fan ③ to send the air flow to the heating chamber ⑤ through the air inlet ④, and the air flow flows along the heating chamber to send the heat to the furnace body. Before entering, the air duct ⑥ must be closed first; There are regular side holes ⑦ on the chamber surface of the air inlet channel of the furnace body, and the side holes are equipped with air regulating wrenches ⑧ that can adjust the air flow. The air flow enters the chamber through these side holes, and the temperature is uniform; The air flow flows to the outlet duct ⑨, and then returns to the fan along the outlet duct to form a circulating constant temperature air flow. In order to make the air flow temperature uniform more effectively, in addition to adjusting the side air plate, a built-in air duct ⑩ is added in the chamber, which effectively ensures the uniformity of the temperature in the chamber, so as to achieve the homogenization effect of glass. Insulation layer around the furnace body? Roll? Edit? It prevents the heat exchange between the heating chamber and the outside world, and greatly saves electric energy

advantages of this homogenizer

first, the homogenizer door uses pneumatic linkage mechanism to flexibly open and close, which facilitates the loading and unloading of glass and reduces labor intensity. It is worth noting that when designing the door of homogenizing furnace, it is necessary to avoid the use of electric door as much as possible, because in the process of glass heating up, the motor is prone to failure after heating, and once the door is not closed tightly, the homogenization effect will be greatly reduced. Secondly, there are many factors that affect the price of the intelligent electronic tensile testing machine in the top cabinet and the inner cabinet of the furnace. An independent frame is welded in front to seal with the furnace door to achieve a good sealing effect. Homogenization heats the glass through thermal convection. If the sealing is not added, it will lead to a slow temperature rise, thereby reducing efficiency. Thirdly, this equipment intends to place the fan at a distance higher than the top of the furnace body to reduce the vibration generated by the fan during operation, and provide a larger safety space for the connection between the furnace wire terminal and the power line. Finally, the equipment adopts modular heating, making each group of furnace wires into a compact cuboid, which is evenly distributed in the heating area, so as to facilitate the maintenance and replacement of the heating body. Moreover, the air inlet duct is equipped with an air volume adjusting device, which can make the upper, middle and lower air speeds in the cavity uniform, which is conducive to the uniformity of the temperature in the cavity and the constant temperature level in the cavity

after the test, statistics show that after the homogenization treatment of this equipment, the probability of self explosion of tempered glass will be greatly reduced, and the probability of self explosion of one piece of glass per 10000 square meters in two years is less than one in ten thousand. At this time, the tempered glass can be called the real safety glass. After the homogenization treatment technology is adopted for tempered glass, the cost has increased to a certain extent, and the price of glass has also increased. However, considering that the coated and oiled aluminum foil product developed by Huyuan Aluminum Co., Ltd. for social and public safety is the first in China, glass manufacturers should still recommend customers to buy tempered glass after homogenization treatment

China glass () Department

Copyright © 2011 JIN SHI