#### 1. The introduction

With the development of energy saving and low-carbon economy, more and more high-end buildings adopt glass curtain wall design. People's understanding of insulating glass is gradually deepening. The reflection image distortion phenomenon of the glass curtain wall puts forward higher requirements.

Generally speaking, tempered or tempered laminated insulating glass is mostly used in curtain wall glass buildings. It is composed of 2 or more pieces of tempered, coated, glazed, laminated glass, etc., to effectively support and evenly separate and connect and seal the periphery to make the color of the glass an article is formed having a dry gas space. Due to the processing method, ambient temperature and air pressure, installation method, and other factors of the insulating glass substrate, there is more or less certain reflection image distortion, and even the shape of the reflection object cannot be recognized in severe cases. To understand the relationship between the concave-convex deformation of insulating glass and the change in temperature and air pressure, this article tests the degree of deformation of insulating glass with different structures and sizes under different temperature and air pressure conditions by simulating the experiment of environmental temperature changes.

#### 2. Analysis of the deformation of insulating glass with changes in air pressure or temperature

In theory, the two or more pieces of glass that make up the insulating glass should be parallel surfaces, but because the insulating glass is in a completely sealed state, the gas in the cavity is sealed under the ambient temperature and pressure during processing. According to the principle of the ideal gas state equation pV=nRT, when there is a certain difference in atmospheric pressure or temperature between the processing place and the place of use, or when the temperature difference is caused by changes in different seasons, the gas sealed in the insulating glass will expand with heat and contract with cold, so that in A pressure difference is formed on the inner and outer surfaces of the insulating glass. Under the action of this pressure difference, the two pieces of glass that make up the insulating glass will be deformed to adapt to the change of the gas volume, and the insulating glass will form a concave or convex state, as shown in Figure 1. At this time, the reflected image of the insulating glass is similar to that of a concave mirror or a convex mirror, and the image of the reflecting object is distorted. Figure 2 shows the concave-convex deformation that occurs in the actual use of insulating glass.

a The theoretical shape

b When the external pressure is high

c. When the external pressure is low

Figure 1 Schematic diagram of concave-convex deformation of insulating glass

a The image effect at 23 ℃

b The image effect at 7 ℃

Figure 2 Concave-convex deformation occurring in actual engineering

#### 3. The simulation experiment of deformation of insulating glass with temperature change

3.1 Description of the experimental device

Generally speaking, when the ambient temperature is higher than the temperature at which the insulating glass is manufactured, the insulating glass will be convex; when the ambient temperature is lower than the temperature at which the insulating glass is manufactured, the insulating glass will be concave. However, to calculate the degree of deformation of insulating glass with temperature changes, we can simulate the change of ambient temperature through a test device to test the degree of concave-convex deformation of insulating glass. The experimental device is shown in Figure 3.

ACE THICKNESS (mm)

a sealed test chamber

b measuring thickness tool

Figure 3 The real device and measuring tool for the concave-convex deformation of the insulating glass with the temperature change

Use angle steel to make a cube frame, and seal it with glass around it, one of the facades is used as the sample area to be tested, use sealant to bond the glass and angle steel to form a closed cavity, and put a heating device inside the cavity, to heat the gas to simulate the change of ambient temperature. During the experiment, the thickness of the gas layer in the middle of the sample was measured at different temperatures to determine the degree of concave-convex deformation of insulating glass with a certain size and structure with temperature changes.

3.2 Insulating glass test one

Make 1 piece of insulating glass, adopt the structure of 8mm white glass semi-tempered + 12+6mm/1.52PVB/6mm double semi-tempered, the size is 1485mm*2416mm, and seal it vertically at an ambient temperature of 35 ℃. The piece of insulating glass is used as a surface of the aforementioned device, and the 8mm glass faces into the cavity, simulating the outside of the outdoor in actual use. The air temperature in the heated cavity is controlled, and the thickness of the gas layer of the insulating glass is measured at different temperatures. Table 1 is the experimental test data.

Table 1 8mm white glass+12+6mm/1.52PVB/6mm hollow glass middle gas layer thickness change value with temperature

 Glass structure 8mm white glass half tempered+12+6 mm/L52 PVB/6 mm double half tempered Glass size 1485mm*2416mm Ambient temperature 2℃ Composite room temperature 35℃ Temperature in the experimental chamber/℃ 2 10 35 40 50 Air layer thickness/mm 10 10.8 12.8 14 14.6 The difference from the theoretical air layer thickness/mm -2 -1.2 0.8 2.0 2.6

Note:

1) Ambient temperature refers to the atmospheric temperature of the day.

2) The temperature of the laminating chamber refers to the air temperature in the laminating chamber when the insulating glass is laminating, that is, the temperature at the time of making the insulating glass.

3) The temperature of the experimental chamber refers to the controlled temperature in the chamber of the experimental device in Figure 3 after heating.

4) The measurement point of the air layer thickness is the geometric center of the glass, and the theoretical air layer thickness of the insulating glass of this structure is 12mm.

3.3 Insulating glass test two

Changing the structure and size of the insulating glass and repeating the above experiments can verify the degree of concave-convex deformation of the insulating glass with different sizes and structures with temperature changes under the same conditions. This time, the insulating glass with a structure of 8 mm white glass semi-tempered + 12+6mm white glass semi-tempered, with a size of 820mm*2000mm, is vertically combined and sealed at an ambient temperature of 35 ℃ so that the 8mm glass faces the cavity. Heating the air temperature in the cavity, measuring the thickness of the gas layer of the insulating glass at different temperatures, Table 2 is the measured data.

Table 2 8nlm+12mm air+6mm insulating glass middle gas layer thickness change value with temperature

 Glass structure 8mm white glass half tempered+12+6 mm/L52 PVB/6 mm double half tempered Glass size 820mm*2000mm Ambient temperature 2℃ Composite room temperature 35℃ Temperature in the experimental chamber/℃ 2 10 20 30 50 Air layer thickness/mm 10.4 10.8 11.3 12.0 13.0 The difference from the theoretical air layer thickness/mm -1.62 -1.2 0.7 0.0 1.0

Note:

1) Ambient temperature refers to the atmospheric temperature of the day.

2) The temperature of the lamination chamber refers to the air temperature in the lamination chamber when the insulating glass is laminating, that is, the temperature at the time of making the insulating glass.

3) The temperature of the experimental chamber refers to the controlled temperature in the chamber of the experimental device in Figure 3 after heating.

4) The measurement point of the air layer thickness is the geometric center of the glass, and the theoretical air layer thickness of the insulating glass of this structure is 12mm.

3.4 Analysis of experimental results

The above experimental results show that the size is 1485mm*2416mm> the structure is 8mm white glass (semi-tempered)+12+6mm/1.52PVB/6mm (semi-tempered glass) insulating glass, when the temperature changes by 10°C, the unevenness of the middle part becomes about 1 mm; the size is 820mm*2000mm, and the structure is 8mm white glass+12+6 mm white glass (semi-tempered glass) Tempered glass) hollow glass, when the temperature changes by 10°C, the unevenness of the middle part changes by about 0.5mm. It can be seen from this that the degree of concave and convex changes of insulating glass due to temperature changes is related to factors such as glass thickness and size.

Generally speaking, the smaller the size, the thicker the glass substrate, the smaller the degree of concave-convex deformation of the insulating glass with temperature changes, and the greater the temperature deviation between the operating environment and the insulating glass, the smaller the range of concave-convex changes. Although the degree of concave-convex deformation of small-sized glass with temperature changes is small, it does not mean that the degree of image distortion of small-sized glass is small. On the contrary, because the smaller the glass, the curvature of the reflecting surface will be affected when it is deformed due to temperature differences. The greater the effect of the radius. According to the optical imaging principle of a convex mirror or a concave mirror, the smaller the size of the glass, the greater the distortion of the reflected image.

In addition, the experiment shows that when the ambient temperature is 35°C, the concave-convex deformation of the insulating glass in "Test 1" is the smallest; when the ambient temperature is 30°C, the concave-convex deformation of the insulating glass in "Test 2" is the smallest. The temperature of the insulating glass sheets in the two tests is both 35°C, which shows that the closer the ambient temperature is to the temperature of the insulating glass sheets, the smaller the deformation of the insulating glass is.

The concave-convex deformation caused by the difference in altitude between the processing place and the place where the insulating glass is used is similar to the concave-convex deformation caused by the temperature change, which is due to the change of the gas pressure in the insulating glass cavity. The air pressure difference in different regions can be easily obtained. The range of change can be calculated according to the ideal gas state equation pV=nRT.

#### 4. The epilogue

From the perspective of temperature change, this article discusses the dimension design of the curtain wall insulating glass, the temperature of the insulating glass, and the relationship between the temperature change and the convex deformation of the insulating glass. Choosing a reasonable design size and structure during design, and controlling the appropriate insulating glass plate pressing temperature during production can effectively improve the concave-convex deformation of insulating glass. Of course, many factors affect the image distortion of insulating glass, which needs to be controlled from design, production, installation, and other aspects to meet the increasing aesthetic requirements of curtain wall glass.