Temperature control is the central part of the tempered glass production process. It has an extremely important influence on the quality of the product. How to control the production process of tempered glass, it is necessary to have a detailed understanding and mastery of the temperature control process.
Now most of our manufacturers are choosing the level of tempering furnace for tempered glass production, so the author focuses on the level of tempering furnace to talk about the temperature control of the process, in order to end with the grid of high quality steel products, in the temperature control, In brief, there are two most basic requirements. First, it is necessary to quickly heat the glass to the required temperature. First, the temperature of each part of the glass surface cannot be too different, that is, uniform heating; during the tempering process The control of the temperature is the coiling of these two centers.
A. The heating temperature of the glass. The effect of tempering temperature on product quality. Unsuitable temperature during tempering will have a series of effects on the quality of toughened glass, such as excessive glass fragments, glass bending, glass roller marks, white surface under glass, pitting on glass surfaces, and glass cooling. Broken and so on. How to quickly reach the required temperature of the glass, in the heating process, we should pay attention to the following aspects:
To prevent overloading of the electric furnace, the electric furnace overload referred to here does not refer to the area occupied by the glass in the electric furnace, but refers to the thickness of the glass, the heating temperature and the heating time, and the heating element in the center of the electric furnace under normal operating conditions. In the heating area, there is always glass that absorbs heat. In the area of the electric furnace, there is always glass. Assuming that the heat consumption in a certain area of the electric furnace exceeds the heating effect, the temperature in this area will initially drop, and it will always fall to the temperature equilibrium. Suspension, so once the electric furnace overload phenomenon, it will cause the glass in the cooling section of the broken.
Different thicknesses of glass require different heating temperatures. The thinner the glass to be tempered, the higher the heating temperature. The thicker the glass, the lower the heating temperature. The operator should understand the temperature of the furnace and the heating time of each other. The contact and the temperature of the electric furnace change the thickness of the glass. Therefore, in the tempered glass process, it is not clear which temperature setting is best. The selection of the temperature depends on the quality of the original glass and the adjustment of the operator. The process parameters. The glass tempering temperature of the 5mm-15mm thickness is between 680-720. In practice, the adjustment of the heating temperature is first performed through the adjustment of the heating time to complete the control of the heating temperature, and the calculation method of the heating time base is The operators should master that the accounting method of the base is about 40 seconds to 50 seconds per millimeter of thickness of the glass. Assume that the glass is drilled, opened, and grooved, and the heating time should be increased by 1.5- 2.5%, other, the larger the surface of the glass, the heating time should correspond to the longer, and vice versa, the corresponding reduction.
Second, add even heating. The success of glass tempering depends primarily on the locality where the temperature of the glass sheet is the lowest. It is necessary to reach the tempering temperature when the glass is to be finished. Therefore, it is necessary to uniformly heat all parts of the glass surface. It is necessary to heat the glass in the electric furnace. Have some understanding. Glass heating in the electric furnace is mainly: conduction, radiation, convection three methods. The conduction heating is mainly the progress of the heat of the ceramic roller in the horizontal tempering furnace to the glass, and the conduction heating only occurs on the lower surface of the glass. The lower surface of the glass has a more heat-receiving path than the upper surface, which can unavoidably cause a temperature difference between the upper and lower sides of the glass surface in the horizontal tempering furnace; the convection heating is mainly the heat balance in the electric furnace and the use of compressed air or the stirring of the circulation fan will heat the air. The heat transfer process to the glass surface; radiant heating refers to the heat generated by the electric heating wire in the tempering furnace, directly radiating to the surface of the glass, or transferring heat to the radiant plate and radiating it to the glass to be heated The heating process. After understanding the heating methods in the furnace, we can use different temperature control strategies at different stages of heating in practice. How to make the glass as uniform as possible, we should pay attention to the following aspects:
When the glass just enters the furnace, the original heat balance in the furnace is suddenly broken, causing a sharp drop in the temperature of the furnace, falling between 20 and 100°C, so during the first half of the glass heating, the glass is heating up. In the middle, the phenomenon of unequal temperature rise is the simplest. At this moment, it is assumed that the method of convection heating is increased, the upper and lower heat balances are opened, and the high temperature air circulation system in the furnace is used to carry out hot air circulation of the high temperature air in the furnace. Deal with the problem of large temperature differences at various points in the glass. In the second half of heating, following the rise of glass temperature, the furnace temperature gradually tends to set value, the temperature difference between the glass points is not obvious, and the main heating rate should be increased, and the heat balance can be closed until the glass temperature and the set furnace Together, the heating process is over.