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LandGlass: combined forced convection technology

LandGlass has developed a new combined tempering furnace which, the company says, eliminates quality defects such as optical deformation (waviness), spherical bending of thin glass, hot spots on thick glass, white haze and glass breaking inside the furnace.

Quality defects such as optical deformation (waviness), spherical bending of thin glass, hot spots on thick glass, white haze and glass breaking inside the furnace exist to some degree in the production of high-quality tempered glass for household electrical appliances and buildings using conventional tempering furnaces, especially in the tempering of coated glass and glass for laminating. However, these defects have been eliminated by the combined tempering furnace developed by LandGlass.
The basic construction of combined tempering furnaces is similar to that of conventional tempering furnaces. Combined tempering furnaces, however, have two heating sections with the same basic structure. The first heating section – the preheating section – preheats glass from room temperature to about 500°C, and the second section heats glass from 450~500°C to tempering temperature.
Once the glass has reached tempering temperature, it is transported to a cooling section, resulting in the production of high-quality tempered glass. Then, how can combined tempering furnaces avoid the shortcomings of conventional tempering furnaces and realize high-quality tempering?
When glass at room temperature is sent to conventional tempering furnaces, the temperature difference between the glass and heating section is nearly 700°C. Because of thermal shock, glass edges usually bend upward, and the central part of the lower surface of the glass has to bear the total weight, often causing quality defects such as hot spots, white haze and waviness. Moreover, such glass with pre-treatment defects may even break inside the heating section due to thermal shock.
However, a different result can be gained with combined tempering furnaces, as the glass experiences two different phases during the heating process. First, the glass is preheated at low temperature in the preheating section. Since glass absorbs heat faster in a cold state, it can be heated uniformly and effectively in a uniform and controllable low-temperature environment in the preheating section, which avoids too fast temperature increase at the glass edges and corners, reducing the temperature difference between the glass edges and central parts. This, in turn, will effectively eliminate the optical deformation of sheet glass and spherical shapes as well effectively avoiding hot spots, white haze and breaking of thick glass inside the heating section.
The glass is then sent to the heating section for the second heating process. Similarly, heat absorption efficiency of glass at high temperature is lower than that in the first phase because of the relatively stable furnace temperature and small temperature difference, which stabilizes the glass shape and reduces the possibilities of deformation. In this way, combined heating furnaces finish heating by reducing thermal shock and stabilizing furnace temperature in an atmosphere more suitable to the physical properties of glass. Therefore, the rate of finished products and the quality of glass are both greatly improved, which provides an optimal process condition for the lamination of tempered glass and insulating glass.
The frequently used heating configurations of LandGlass combined tempering furnace include but are not limited to upper/lower jet convection mode, upper jet convection mode, and radiation plus auxiliary convection mode, which are respectively applicable to different glass processing and different customer budgets. Moreover, LandGlass combined tempering furnaces can realize a high growth rate of output, or the processing of glass in extra-large specifications thanks to flexible settings of temperature and motion modes of preheating and heating sections.
In recent years, LandGlass has closely adhered to its R&D strategy of providing users with international technologically leading tempering equipment, successively promoting new products and technologies influencing the pattern of technological development, and led the development and progress of tempering technology. Nowadays, the application of LandGlass jet convection technology in combined tempering furnaces provides a perfect solution for the high-quality tempering of various kinds of off-line coated low-E glass.

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