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[China Glass Network] Temperature control is the core part of the tempered glass production process. It has an extremely important impact on the quality of the product. How to control the production process of tempered glass must first have a detailed understanding and mastery of the temperature control process.
At present, most of our manufacturers use horizontal tempering furnaces for the production of tempered glass. Therefore, the author focuses on the horizontal tempering furnace to talk about the temperature control process. In order to achieve qualified high quality tempered products, in terms of temperature control, In simple terms, there are two basic requirements. In the front, the glass must be heated quickly to the required temperature; in front, the temperature of the various parts of the glass surface cannot be too different, that is, uniform heating is required; during the tempering process, Temperature control is carried out around these two core aspects.
A. The heating temperature of the glass. The effect of tempering temperature on product quality. Inappropriate temperature during tempering will have a series of effects on the quality of tempered glass, such as excessive glass fragments, glass bending, glass roller track marks, white glass under the glass surface, pitting of the glass surface, and glass cooling. Broken and so on. How to quickly reach the required temperature of the glass, we should pay attention to the following aspects in the process of heating:
To avoid the overload phenomenon of the electric furnace, the electric furnace overload mentioned here does not refer to the area occupied by the glass in the electric furnace, but refers to the relationship between the thickness of the glass, the heating temperature and the heating time, and in the normal operation, the heating element in the central part of the electric furnace In the heating area, there is always glass in the heat absorption. In this area of ​​the electric furnace, there is always glass. If the heat consumption in a certain area of ​​the electric furnace exceeds the heating effect, the temperature in this area begins to decrease and drops to the temperature balance. So far, if the electric furnace is overloaded, it will cause the glass to break in the cooling section.
The heating temperature required for different thickness of glass is different. 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 mutual temperature of the furnace and the heating time. The relationship and the temperature of the electric furnace vary depending on the thickness of the glass. Therefore, in the tempered glass process, it is not clear which temperature setting is better. The choice of temperature is determined to a certain extent by the quality of the original glass and the adjustment of the operator. Process parameters. The glass tempering temperature of 5mm-15mm thickness is between 680-720. In actual production, the adjustment of heating temperature is mainly achieved by adjusting the heating time to control the heating temperature. The basic calculation method of heating time is The operator should master that the basic calculation method is about 40 seconds to 50 seconds per mm thickness of glass. If there are holes, holes, and slots in the glass, the heating time should be increased by 1.5-based on this. 2.5%. In addition, the larger the surface of the glass, the longer the heating time should be, and vice versa.
The bottom temperature measured by the heating system is not the roller temperature, but the average temperature after the heating element at the bottom of the tempering furnace compensates for the heat absorbed by the roller glass. due to this reason. The measured temperature is generally higher, higher than the measured upper temperature, so in general the upper heating is higher than the lower heating temperature setting.
Second, add even heating. The success of glass tempering depends mainly on the lower temperature of the glass plate. To achieve tempering, the glass must first reach the tempering temperature. Therefore, it is necessary to achieve uniform heating of all parts of the glass surface. We must heat the glass in the electric furnace. To understanding. The heating of glass in electric furnace mainly includes three ways: conduction, radiation and convection. Conductive heating is mainly the process of transferring the heat of the ceramic roller in the horizontal tempering furnace to the glass. The conduction heating only occurs on the lower surface of the glass. The lower surface of the glass has a more heat acquisition path than the upper surface, which inevitably causes the upper and lower temperature difference of the glass surface in the horizontal tempering furnace; the convection heating is mainly the heat balance in the electric furnace. The hot air is compressed by the compressed air or the circulating fan. The heat transfer process to the surface of the glass; 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 panel, and then radiating it onto the glass to be heated. The heating process. After understanding the heating method in the furnace, in actual production, we can adopt different temperature control strategies at different stages of heating. How to make the glass as uniform as possible, we should pay attention to the following aspects:
When the glass enters the furnace body, the original heat balance state in the furnace body is suddenly broken, which will cause the furnace temperature to drop sharply, and the drop range is between 20 and 100 °C. Therefore, during the first half of the glass heating, the glass is heating up. In the middle, it is more prone to uneven temperature rise at each point. At this time, if the convection heating method is added, the upper and lower heat balances are turned on, and the high temperature air circulation system in the furnace is used to perform hot air circulation in the furnace. The problem of solving the large temperature difference between the various points of the glass is solved. In the second half of heating, as the temperature of the glass rises, the furnace temperature gradually approaches the set value. The temperature difference between the various points of the glass is not obvious. The heating rate should be increased, and the heat balance can be turned off until the glass temperature is set. The furnace temperature is the same and the heating process is over.
When the temperature of the external environment is the same, the surface area of ​​the glass and the heat medium have a large surface area, and the reflection of the radiant heat is small, so that the heat absorption efficiency is faster than the middle part. That is, the temperature rise of the edge of the glass is fast, especially the extra large piece of glass. The temperature difference between the edge of the glass and the middle part is more obvious. The temperature difference between the middle part and the edge of the glass excessively causes the convexity and concave of the edge of the glass. If this phenomenon occurs, we can get from two On the one hand, it can improve the heat balance pressure in the furnace body, increase the heat convection, and adjust the heat balance in the furnace to reduce the temperature difference between the middle and the edge of the large-area glass. On the other hand, the heating time of the glass can be appropriately extended. Thereby, the temperature difference between the middle portion and the edge of the glass can also be reduced.
It is necessary to avoid the influence of the temperature difference between the upper and lower surfaces of the glass on the glass tempering effect. When the glass enters the quenching section from the heating furnace, if the upper temperature of the glass is higher than the lower temperature, the front and rear ends of the glass will be bent upwards; if the temperature above the glass is lower than the lower temperature, the glass will be raised upward in the middle. The upper sheet arrangement of the glass has an effect on the uniform heating. When placing the film, the arrangement of the glass of each furnace and the gap time of each furnace should be uniform. If the glass plate moves forward in the same position in the tempering furnace, the temperature difference of each roller is relatively obvious, and the position of the film is one. If it changes, it will cause deformation of the glass or breakage in the cooling section. In order to ensure the uniformity and consistency of the temperature of the roller, the temperature of the roller between the glass plates is not too high, and if there is a gap in the longitudinal direction when the film is released, when the furnace glass is placed To make up this gap.
How to better master the temperature control process of tempered glass, every operator, in the actual production, should pay attention to the summary of heating control experience, because temperature control is a relatively complex and variable process process, affecting its factors There are many, so that we can achieve accurate control of heat, quickly and evenly achieve the desired temperature of the entire part of the glass.
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