[China Glass Net] Principle: The existing glass tempering process is mostly heated by electric heating wire, and the heat transfer mode is mainly convection. If infrared heating technology is applied to the production of tempered glass, the heat transfer mode becomes radiation-based. According to the theoretical calculation, the tempering temperature is 650-700 degrees in the medium temperature zone, and the radiation heat transfer is 7.9 times of the convective heat transfer. Obviously, the infrared heater can be used to save energy during the heating process.
Infrared radiant heater is based on the fact that many materials are easy to absorb infrared rays. The general thermal energy is converted into infrared radiant energy, which is directly radiated onto the heated object, causing the resonance of the object molecules, thereby achieving lower energy and faster speed. Heat the object to the desired temperature. The infrared rays that can pass through the atmosphere are generally divided into three bands: the near-infrared band of 1-2.5 microns; the mid-infrared band of 3-5 microns; and the far-infrared band of 8-13 microns.
Ordinary infrared heaters are still not significant due to the wide range of wavelengths of radiation. In order to increase the thermal efficiency, it is necessary to make the radiation wavelength of the infrared radiant heater coincide with the absorption wavelength range of the material to be heated. To do this, it is first necessary to find the effective absorption wavelength of the material being heated. Each material has its own specific absorption characteristics, that is, it absorbs heat at a certain wavelength higher than other wavelengths. From some data reports, in the general processing technology, the effective absorption wavelength of glass is 2.4-6 microns; in the heating process of tempered glass, the effective absorption wavelength of glass is 2.7-3 microns. This is basically in the mid-infrared band and slightly close to the near-infrared region, which is equivalent to 704-843 degrees. If this temperature is not reached, the glass will not be tempered very well; beyond this temperature, heat will be wasted.
The second is to find a suitable infrared radiant heater. The tungsten wire vacuum tube can radiate near infrared rays, and the wavelength does not correspond, so it is not suitable for the tempered glass process. Silicon carbide is a long-wavelength far-infrared radiant heater that not only has a wavelength that does not correspond, but also has a low thermal efficiency and is not suitable. Quartz glass and ceramic infrared heaters can radiate mid-infrared, so it is more suitable. Different types of quartz glass, the structure of the heater is different, and the infrared wavelength of the radiation is also different. According to the characteristics of infrared absorption of tempered glass, it is a very important problem to select and research and develop quartz glass suitable for varieties and infrared heaters with suitable structure. In this way, the infrared radiation wavelength of quartz glass heater can be adjusted to adapt to the infrared of tempered glass. Absorption characteristics to achieve the purpose of improving thermal efficiency.
Another feature of infrared radiation heating is that radiation heat transfer does not require a medium and can be transported in a vacuum. The main components of air in the atmosphere, oxygen and nitrogen, rarely absorb infrared light, so the energy lost during the flow of the medium and medium Rarely, according to thermal calculations, the utilization of radiative heat transfer at 700-1000 degrees is 5.7-7.4 times that of convective heat transfer. In addition, the infrared radiation heating also has the characteristics of very uniform heating. In order to make better use of this feature, the shape of the heater is very important. For tempered flat glass, the heating uniformity of the tubular heater is not as good as that of the plate heater. It has been proved that the flat type heater is suitable, which is beneficial to improve the quality of the tempered glass, improve the product yield and the glazed glass which is more difficult for tempering. Therefore, it must be emphasized that the plate heater for tempered flat glass is better, and any heater that requires a reflector is not as effective as flat glass. Because in most cases, due to the high temperature generated by the heater, the reflective surface inevitably turns black, and over time, heat is radiated from its back side, causing the reflector to become a heat sink.
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