The Influencing Factors And Control Methods of The Flatness of Tempered Glass

Whether it is curved glass or flat glass, we have certain requirements for the surface smoothness of their finished products. Poor flatness not only affects aesthetics, but also affects the transmittance of glass and, in severe cases, the service life and safety level of glass. Therefore, we should fully understand the factors affecting the flatness of tempered glass and find specific control methods to improve the overall production level and product quality of the glass tempering furnace.

1、 Factors affecting the flatness of tempered glass

1. Roller conveyor problem in glass tempering furnace

(1) Roller bending deformation

The deformation of ceramic rollers in the heating or air-cooled section of a tempering furnace is related to the quality of the ceramic rollers. Low quality ceramic rollers have poor heat resistance, impact resistance, and thermal stability, making them prone to thermal bending and causing glass deformation. The roller path in the air-cooled section must also be straight and non curved, and the glass is still in a softened state. If the roller path is not smooth, it will also affect the flatness of the glass.

(2) Wear of impurities on the surface of Roller

During the heating process of tempered glass, various situations may occur, such as furnace explosion, edge collapse, etc. When tempered glass breaks and is not cleaned in a timely manner during the heating process, if there are residual impurities on the surface of the ceramic roller after heating and softening, they will remain on the glass during the glass tempering process, thereby affecting the flatness of the glass.

2. Improper temperature control of glass tempering furnace

(1) Temperature difference between upper and lower heating sections

The heating temperature of the upper and lower surfaces during the glass tempering furnace is not set properly. As the lower surface of the glass directly contacts the ceramic roller for heat conduction, while the upper surface is heated through thermal radiation, the heating temperature of the upper and lower surfaces cannot be consistent during the tempering heating process. The heating temperature should be adjusted according to factors such as the thickness, area, and heating time of the glass. Otherwise, when the lower surface of the glass reaches the softening temperature first, roller marks are easily formed. At the same time, the coolant is the same. If the temperature of the lower surface of the glass is higher than the upper surface during cooling, it will also cause the glass to bend downwards, affecting the flatness of the glass.

(2) Temperature difference between different parts of the glass surface

The irregular temperature distribution on the surface of glass may be caused by equipment failure in the tempering furnace, damage to local furnace wires, distortion of temperature sensors, and unreasonable placement of glass sheets. Uneven heating can lead to poor glass flatness.

3. Unbalanced air pressure in the cooling section

The cooling section of the flat steel tempering furnace mainly relies on blowing air up and down to cool down, and the uneven pressure of the upper and lower air during blowing can cause the glass to bend. When the stress inside the glass is uneven, it can cause the glass to bend towards the side with lower compressive stress, thereby affecting the flatness of the glass.

2、 Control method for flatness of tempered glass

1. Replace the high-quality ceramic roller conveyor and clean it in a timely manner to avoid dust or impurities remaining on the roller conveyor. Before heating, the roller conveyor should be preheated to evenly heat all parts, eliminate stress, and reduce thermal deformation of the roller conveyor.

2. Accurately controlling the appropriate temperature and time for glass tempering of each model and specification can enable furnace production and record the tempering furnace adjustment data with better finished product effects. Ensure even temperature distribution inside the furnace. For situations where the temperature distribution is irregular and uneven, it is necessary to rule out whether there is a malfunction in the tempering furnace, whether the furnace wire status and temperature sensor are normal, and avoid continuous placement of glass in the same position. Changes should be maintained to avoid uneven temperature.

3. Ensure a balanced blowing pressure between the upper and lower air grilles, and maintain pressure balance by adjusting the blowing distance and pressure.