Quote

Physical tempering process parameter setting

Whether the quality of tempered glass meets the standards depends on the original glass plate and whether the process parameters are set reasonably. All parameters are designed around “uniform heating and rapid cooling”, but they are not isolated but an organic whole. Comprehensive consideration is required to obtain a perfect process.

Heating

Uniform heating is a crucial factor in tempered glass. The main parameters related to heating are upper temperature, lower temperature, heating power, heating time, temperature adjustment, balance device, forced convection (heat circulation wind) device, etc.

(1) Setting of upper and lower temperatures Due to the different thicknesses of glass, the setting of the heating temperature is also different. The principle is that the thinner the glass, the higher the temperature, and the thicker the glass, the lower the temperature. The specific data is shown in the table below.

Heating Temperature for Different Thicknesses of Glass

Heating Temperature for Different Thicknesses of Glass

Thickness (mm) Upper Temperature (°C) Lower Temperature (°C)
3.2 720 - 730 713 - 728
5 - 6 710 - 720 705 - 716
8 - 10 705 - 710 700 - 705
12 690 - 696 685 - 690
15 - 19 660 - 665 605 - 660
After the heating temperature is determined, the heating time is very important. These are two closely related parameters. The heating time varies for a glass of different thicknesses. The relationship between glass thickness and heating time is shown in the following table.
Relationship Between Glass Thickness and Heating Time

Relationship Between Glass Thickness and Heating Time

Glass Thickness (mm) Heating Time per mm Thickness (s)
3.2 - 4 35 - 40
5 - 6 40 - 45
8 - 10 45 - 50
12 50 - 55
15 - 19 55 - 65
Since different manufacturers use different glass raw plates, different softening points, different colors, and different thickness errors, the set temperature and power are also different, and the heating time will vary. It is necessary to summarize in practice. But there is one thing worth referring to: when the glass is broken during the rapid cooling period after it comes out of the furnace, it means that the heating time is not enough; if there are ribs and pitting on the surface of the glass, it means that the heating time is too long. In the actual production process, corresponding adjustments should be made according to the specific situation.
(2) Application of heating power Heating power refers to the heating capacity of the tempering furnace, which is generally set to 100%, which is determined during the design. Due to the different heating methods of the upper and lower parts, the upper part is mainly heated by radiation, while the lower part is heated by conduction and radiation. When the glass enters the furnace in the initial stage, the lower surface of the glass curls due to being heated first. As the temperature of the upper part gradually radiates to the upper surface of the glass, the glass will gradually flatten. If the glass curls severely within these tens of seconds, there will be a white mark or light distortion in the middle of the lower surface of the glass after it comes out of the furnace. In order to solve this problem, in addition to setting the lower temperature lower than the upper temperature, the power of the lower part should be reduced to reduce the surface temperature of the ceramic roller and reduce the degree of curling of the glass at this stage.
(3) Heat balance device It is a device that uses compressed air to form convection in the furnace, and the pressure can be manually adjusted as needed to accelerate radiation and balance the temperature.

Cool Down

Parameters related to cooling: quenching air pressure, quenching time, cooling air pressure, cooling time, delayed blowing time, fan waiting frequency, fan advance time, furnace exit speed, and other cooling-related

Mechanical Guarantee: upper and lower wind grille blowing distance, the height of air duct guide plate, flow adjustment bolt of the air inlet.

(1)Quick cooling air pressure Quick cooling air pressure refers to the air pressure required for glass tempering. The principle is that the thinner the glass, the greater the air pressure, and the thicker the glass, the smaller the air pressure. The air pressure of the NORTH GLASS tempering furnace is set by computer to change the opening degree of the air inlet, and its value is a percentage. The unit with the fan inverter changes the frequency of the fan through the computer to achieve the required air pressure, and its value is also a percentage. The theoretical air pressure required for rapid cooling of glass of various thicknesses is shown in the following table

Theoretical Air Pressure for Rapid Cooling of Glass

Theoretical Air Pressure Required for Rapid Cooling of Glass of Various Thicknesses

Glass Thickness (mm) Theoretical Air Pressure (Pa)
3 16000
4 8000
5 4000
6 2000
8 1000
10 500
12 300
15 200
19 200
Due to the different altitudes and air densities, ambient temperatures and wind directions in different countries and regions, the actual wind pressure required may be different from the value in the table and needs to be adjusted to meet the particle size requirements.

(2) Rapid cooling time Rapid cooling time refers to the time required for glass tempering. The rapid cooling time for glass of various thicknesses is shown in the following table.

Rapid Cooling Time for Glass of Various Thicknesses

Rapid Cooling Time for Glass of Various Thicknesses

Glass Thickness (mm) Cooling Time (s)
3 3 - 8
4 10 - 30
5 40 - 50
6 50 - 60
8 80 - 100
10 100 - 120
12 150 - 180
15 250 - 300
19 300 - 350

(3) Cooling air pressure and cooling time Cooling air pressure and cooling time refer to the air pressure and time required for cooling after the glass is quenched. Its function is only to cool the glass to the required temperature. The principle of setting is that the cooling air pressure of thin glass should be less than the quenching air pressure, and the cooling air pressure of thick glass should be greater than the quenching air pressure. The theoretical air pressure and cooling time of glass of different thicknesses are shown in the following table

Theoretical Air Pressure for Glass of Different Thicknesses

Theoretical Air Pressure for Glass of Different Thicknesses

Glass Thickness (mm) Theoretical Air Pressure (Pa)
3 1000
4 1000
5 1000
6 1000
8 1500
10 1500
12 2000
15 2000
19 2000
Cooling Time for Glass of Different Thicknesses

Cooling Time for Glass of Different Thicknesses

Glass Thickness (mm) Cooling Time (s)
3 20
4 30
5 50
6 60
8 80
10 120
12 180
15 250
19 300
Since it is only for cooling the glass, the requirements for the setting of cooling air pressure and cooling time are not strict, but it should be noted that if the glass explodes frequently, the quenching air pressure should be reduced. If the air pressure is already low but there are still a lot of spontaneous explosions, in addition to the high nickel sulfide content in the raw materials, it is necessary to check whether the quenching time is too short. At present, tempering furnaces generally have a special cold section, and the cooling time and cooling air pressure do not need to be set.

(4) Delayed blowing time Delayed blowing time is a parameter set specifically for curved glass. The glass cannot be blown immediately after it comes out of the furnace. It must be blown after the glass is formed. It has a great relationship with the shape and particles of the glass. The longer the lag time, the longer the reciprocating time of the glass in the wind grid when it is soft, the better the curvature will be, but the more glass will be damaged and the particles will be poor. This requires organically combining these parameters to find the best point.

(5) Fan waiting frequency and fan advance time The fan waiting frequency and fan advance time are set separately for production lines with fan inverters. When the glass is heated in the furnace, the fan does not need to run at high speed. The frequency can be set low and the speed can be increased to the required level before the glass is taken out of the furnace. The setting principle is: that the waiting frequency should be higher for thinner glass; the waiting frequency should be lower for thicker glass. Generally, it is better to set the waiting frequency 10 to 15 Hz lower than the working frequency. The fan advance time is the time required to increase from the waiting frequency to the working frequency. 10 Hz takes about 15 to 20 seconds. If the waiting frequency is set low, the fan advance time will be longer; if the waiting frequency is set high, the fan advance time can be shorter. Proper setting can save power consumption.
(6) The distance between the upper and lower wind grilles is closely related to the granularity and flatness of the glass. Under the condition of constant wind pressure, the closer the wind grille distance is, the better the granularity is. Generally, the bending of flat glass is basically solved by adjusting the distance of the upper wind grille. The wind grille distance of glass of different thicknesses is shown in the following table.
Air Grid Distance for Glass of Different Thicknesses

Air Grid Distance for Glass of Different Thicknesses (Unit: mm)

Glass Thickness (mm) Air Grid Distance (mm)
3 12
4 15
5 20
6 25
8 30
10 40
12 50
15 60
19 70

Contact Us

Your feedback fuels our growth, and your questions drive our solutions.

We value your feedback, inquiries, and suggestions. Please feel free to get in touch with us

General inquiries

Please contact us via sales@bo-glass.com, and we will reply to you as soon as possible.

Interested to work with us

Drop your resume at info@bo-glass.com
and we will get back to you shortly.

    We uses the contact information you provide to us to contact you about our relevent content, products, and services.

    1