Temperature Control Parameter Setting of Glass Tempering Process.

Temperature control is the core part of the tempered glass production process, which has an extremely important impact on the quality of glass products. 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 glass deep-processing manufacturers use horizontal tempering glass furnaces for the production of tempered glass, so we will focus on the horizontal tempering furnace to talk about the process of temperature control. To achieve qualified and high-quality tempered products, in terms of temperature control, Simply put, there are two most basic requirements. First, the glass must be heated to the required temperature quickly; second, the temperature of each part of the glass surface should not differ too much, that is, to achieve uniform heating; The control of the system is carried out around these two core aspects

Process parameter setting of glass heating control

Parameter setting of upper temperature and lower temperature of heating furnace

The setting of the furnace temperature is mainly based on the thickness of the glass, and the tempering temperature of the glass decreases gradually with the increase of the glass thickness. The thicker the glass to be tempered, the lower the temperature; the thinner the glass, the higher the temperature setting. When tempering glass, the glass itself must be required to reach a semi-plastic state, to eliminate the residual stress inside the glass. The tempering temperature of flat glass is about 630°C. That is to say, when the glass is air-cooled and tempered, its temperature must reach 630°C. For the temperature setting of the upper and lower parts of the heating section of the tempering furnace, the ultimate goal is to make the glass reach the upper surface. Consistent with the temperature of the lower surface, its specific setting can refer to the table below.

When tempering glass with a thickness of more than 10mm, if the heating temperature is not properly controlled, it is easy to drop the corner of the glass when the glass is air-cooled, especially the glass with holes in the edge. When such problems occur, it is necessary to consider the rationality of the heating temperature setting of the glass. If the temperature is set too high or the glass is heated too fast, it will lead to the phenomenon of a corner drop of thick glass.

The setting of heating time parameters

The setting of the heating time should be based on the thickness of the glass, but also refer to the size, color, opening state of glass, and the molding state of the glass. For a reasonable setting of the heating time, the thickness of the glass must first be considered. The heating power of the tempering furnace is certain. Theoretically, the heating time of the glass is about 40s~45s per mm thickness of the glass, but if there are holes or openings in the glass, the heating time can be increased by 2.5%~5%; for 15mm, and 19mm glass; the heating time can be increased by 5% to 15%; in addition, the larger the glass layout, the heating time should be extended accordingly on this basis.

^{Figure 1 The heating time of tempered glass furnace 1}

Heating balance on and off

Generally, the heating section of the tempering furnace has this function. The heating of glass in the heating furnace is accomplished in three ways, namely radiation, convection, and heat conduction. The opening of the heating balance can increase the flow rate of the air in the heating furnace, change the flow state of the air in the furnace, improve the efficiency of convective heating, and make the temperature of each area in the heating furnace relatively more uniform. For large-area enclosed glass, turn on convection heating in actual production. On the one hand, it can increase the speed of glass heating, and on the other hand, it can help the heating of various areas on the glass surface to be more uniform. For the hole in the middle of the glass, sometimes it is necessary to fine-tune the temperature of the area in the heating furnace. At this time, it is recommended to turn off the heating balance.

Zone temperature fine-tuning setting

Generally, the temperature adjustment of the heating section of the tempering furnace has this function, which can realize the fine adjustment of the local temperature in the furnace. In actual production, when producing curved tempered glass, the temperature at the exit end near the furnace door should be appropriately increased.

The setting of glass thermal swing speed

The speed of the thermal swing will affect the uniform heating of the glass. Unreasonable thermal swing speed will affect the flatness and tempering effect of tempered glass, resulting in roller marks and uneven fragments after tempering, which is not conducive to glass-even heating. The process of thermal pendulum movement of glass in the heating furnace is also the process of heat exchange between the glass and the conveying roller table. The faster the swing speed of the glass in the furnace, the heat transfer area between the glass and the conveying roller table can be increased to a certain extent. Increase the heating rate of the glass. In addition, since the thinner the glass, the faster the temperature rise of the glass itself, the stricter the temperature requirements for the glass itself during air-cooling tempering. To make each area of the glass surface evenly heated and achieve a good tempering effect, it is necessary to increase the thermal swing speed of the glass in the heating furnace accordingly. The thicker the glass, the slower the temperature rise rate of the glass itself, and the thermal swing speed of the glass can be reduced accordingly. For example, when producing tempered glass with a thickness of when using glass, the thermal swing speed of the glass can be appropriately reduced to 200mm/s.

^{Figure 2 The thermal swing speed of tempering glass furnace 2}

Glass length setting

All horizontal tempering furnaces need to set the glass length parameter during production. The position of the glass in the furnace depends entirely on the setting of the glass length parameter. The setting of this parameter should be set according to the actual length of the glass. If the glass length parameter is set too long, the reciprocating distance of the glass in the heating furnace will be shortened.

The setting of empty furnace time

The reasonable setting of the empty furnace time cannot be ignored. Generally, tempering furnaces have the function of displaying the temperature of each area in the heating furnace. If the heat consumption of a certain area in the heating furnace exceeds the heating effect, the temperature in this area will drop. Once the heating furnace is overloaded, it may cause the glass to break in the cooling section. By checking the temperature display of each area in the heating furnace, you can grasp the temperature of each area in the furnace. The setting of the empty furnace time is based on the temperature in the heating furnace returning to the temperature setting value after the above piece of glass is released from the furnace.

Summarize

Different tempering furnaces have different parameter operating systems and parameter control methods, but the tempering glass furnace control parameters and control processes are the same. How to better grasp the temperature control process of tempered glass, every operator should also pay attention to the summary of heating control experience in actual production because temperature control is a relatively complex and changeable process technolog. So there are many factors, only in this way can we achieve precise control of heat, quickly and evenly make all parts of the glass reach the required temperature, and ensure the high-quality and efficient process quality of tempered glass.

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