Coated insulating glass is an insulating glass composed of a piece of coated glass and a piece of other glass. To protect the film from atmospheric erosion and increase its service life, the coating surface should face inwards.
Coated insulating glass is generally used for glass curtain walls of buildings. As architectural decorations, it brings a beautiful, generous and lively image to the building and enhance the beauty of the building. But in actual use, we often find that some buildings that use coated insulating glass have the phenomenon of image scattering. Make the beauty of the building disappear, and even have a negative impact. The author has conducted meticulous research on this issue, conducted various investigations and experiments, consulted relevant domestic and foreign data, collected data for analysis, and put forward the following opinions for reference only.
Figure 1 The coated insulating glass for curtain walls 1
The basic principle of causing the coated hollow glass reflects that the glass cannot form a whole plane or a part of it is not a plane on the curtain wall, but is curved, which causes the reflection to scatter and even becomes a haha mirror. The reasons for this phenomenon are complex and multifaceted:
1. Reasons for design and installation:
With the rise and increase of high-rise buildings, people's requirements for the beauty of the appearance of buildings have increased, and the actual use of glass panels has become larger and larger. The wind pressure load that the glass itself bears also increases. There are two wind pressure loads on the glass: internal wind pressure and external wind pressure load. When the external wind pressure of the hollow glass is greater than the internal wind pressure, the glass surface will bend inward and the glass surface will be concave; when the internal wind pressure is greater than the external wind pressure, the glass surface will bend outwards and become a convex surface; When the compressive load is equal or similar, the glass can form a plane. Therefore, in the design and installation, the wind pressure load of the glass should be fully considered. This kind of wind load is not only the external wind pressure load on the glass itself but also the combination of the internal and external wind pressure loads of the insulating glass.
Insulating glass internal and external load changes vary with environmental temperature changes and different installation areas. Because of the great difference in air pressure in various regions, the difference between plain areas and plateau areas is even greater. When the products produced in the plain area are used in the plateau area, the inside of the hollow glass becomes positive pressure, and the glass bulges outward. On the contrary, it becomes a negative pressure, and the glass is concave inward. Therefore, when designing insulating glass to be installed and used in different regions, the structure and specifications of the insulating glass product should be designed according to the difference of the region and the size of the maximum wind pressure. The influence of environmental temperature change on the load change of the insulating glass is mainly manifested in that with the temperature change, the volume of the dry air sealed inside the insulating glass changes accordingly, which causes the change of the internal load and causes the glass surface to bend inward and outward. After repeated experiments, the author shows that for the rectangular coated insulating glass of 550mm*1100mm (5+9+5)mm, the displacement of the center of the glass surface on one side changes about 0.03mm for every 1°C change in the ambient temperature. It can be seen that temperature changes have a considerable impact on the flatness of insulating glass.
Insulating glass has unique technical conditions for installation and construction. During the construction of the glass curtain wall, in the case of construction within the installation and construction specifications, when the glass is sealed, the thickness of the surrounding sealant is uniform and the strength is Being in the same plane and local variation can also cause image scattering.
2. Glass processing and production methods:
As we all know, most of the insulating glass produced in various countries in the world is vertical laminated and horizontal sealing. In the process of combining the sheets, the glass itself is not affected by force and does not deform. However, when sealing the glue, the upper glass will bend downwards under its gravity, and the lower glass will bend upwards, and the air that presses the internal space will overflow outwards. Although it is only a small amount, after sealing, a slight negative pressure will be generated inside the hollow glass. The two pieces of glass will bend inwards. Especially when the two pieces of glass are thinner and the product specifications are too large, it is more obvious. When the ambient temperature decreases and the external air pressure increases, the curvature of the glass will increase until the two pieces of glass are bonded together, losing the energy-saving effect of insulating glass.
Figure 2 The insulating glass vertical laminated processing 1
Figure 3 The insulating glass horizontal sealed processing 1
3. The inevitable reason
When installing the glass, to ensure the airtightness of the window, a sealant is generally used to seal the glass and the metal frame. But as the temperature changes, the expansion coefficient between the glass and the frame is different. Tensile stress or compressive stress will be generated on the periphery of the glass. Although there is a sealant as a buffer, this kind of stress cannot be eliminated. If the environmental temperature changes more, the stress will also increase, and the result of the stress will increase the deformation of the glass edge, and even cause the glass to burst. This situation is often found on a single piece of glass.
Figure 4 The tempered glass production 1
In the actual production process, the selection of the original glass sheet has a great influence on the bending resistance of the glass. Generally, among tempered glass, heat-strengthened glass, and ordinary glass, in terms of wind pressure resistance, tempered glass is the largest, followed by heat-strengthened glass. These two kinds of glass are better than ordinary glass in bearing the deformation of external stress. Therefore, we suggest that in the production of coated insulating glass, try to use tempered coated or heat-strengthened coated glass as the original sheet; try to use gas-filled insulating glass for product varieties, and it is suitable for reducing glass specifications to reduce glass deformation caused by various reasons.