Analysis of the Causes of the Scattering of the Insulating Glass Image of the Curtain Wall

April 27, 2021

[China Glass Net] Coated insulating glass is generally used for the glass curtain wall of buildings. As an architectural ornament, it brings a beautiful, generous and bright image to the building, enhancing the beauty of the building. However, in actual use, we often find that some buildings using coated insulating glass show image scattering. Make the beauty of the building disappear and even have a negative impact. The author conducted a detailed study on this issue, surveyed the experiment and consulted relevant data at home and abroad, collected data for analysis, and made the following observations for reference only.

The basic principle of scattering of the coated hollow glass image is that the glass cannot form an integral plane on the curtain wall or the local part is not a plane, but is curved, which causes the image to scatter, even into a mirror shape. The reasons for this phenomenon are complex and multifaceted:

First, the reasons for design and installation:

With the rise and increase of high-rise buildings, people's requirements for the aesthetic appearance of buildings have increased, and the actual use of glass panels has become larger and larger. The wind pressure load on the glass itself also increases. There are two types of wind pressure loads on the glass: internal wind pressure and external wind pressure load. When the external wind pressure of the insulating glass is greater than the internal wind pressure, the glass surface is curved inward, and the surface of the glass is concavely curved; and when the internal wind pressure is greater than the external wind pressure, the surface of the glass is outwardly curved to be convex; only when inside and outside When the compressive loads are equal or close, the glass can form a plane. Therefore, in the design and installation, the wind pressure load of the glass should be fully considered. This wind load is not only the external wind pressure load on the glass itself, but also the combination of the wind pressure load inside and outside the hollow glass.

The change of load inside and outside the insulating glass varies with the change of the ambient temperature and the installation area. The difference in pressure between the regions is very large, especially in the plains and plateaus. When the products produced in the plain area are used in the plateau area, the inside of the insulating glass is positively pressed and the glass is drummed outward. On the contrary, it becomes a negative pressure and the glass is concave inward. Therefore, when designing the insulating glass to be installed in different areas, the structure and specifications of the insulating glass product should be designed according to the different regions and the maximum wind pressure. The influence of the change of the ambient temperature on the load change of the insulating glass is mainly manifested by the change of the volume of the dry air sealed inside the hollow glass with the change of the temperature, thereby causing the internal load to change, and the glass surface is bent inward and outward. After repeated experiments, the 550mmx1100mm (5+9+5) mm rectangular coated hollow glass has a displacement change of about 0.03mm at the center of the single-sided glass surface for every 1°C change in ambient temperature. It can be seen that the change in temperature has a considerable influence on the flatness of the insulating glass.

Insulating glass has unique installation and construction conditions. 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 peripheral sealant is uniform, and the metal frame plus itself has deflection or joint connection, so that the glass cannot be in the same plane or although the whole In the same plane, there is a local variation, which can also cause image scattering.

Second, the reason for the processing of glass, production methods

As we all know, most of the insulating glass produced in China is vertical laminated and horizontally sealed. During the splicing process, the glass itself is not affected by the force and does not deform. However, when the glue is sealed, the upper glass is bent by its own gravity, and the lower glass is bent upward, and the air that presses the inner space overflows outward. Although it is only a trace amount, after the sealant, a slight negative pressure is generated inside the insulating glass. The two pieces of glass will bend inward. Especially when the two pieces of glass are thin, the product specifications are more obvious. When the ambient temperature is lowered and the external air pressure is increased, the curvature of the glass is also increased until the two pieces of glass are bonded together, and the energy saving effect of the insulating glass is lost.

Third, the inevitable cause

In order to ensure the airtightness of the window during installation, it is generally necessary to seal the glass and the metal frame with a sealant. However, as the temperature changes, the coefficient of expansion between the glass and the frame is different. Tensile or compressive stress is generated around the glass. Although there is a sealant as a buffer, this stress cannot be completely eliminated. If the ambient temperature changes, the stress is also increased. As a result of the stress, the deformation of the edge of the glass is increased, and even the glass is broken. This situation is often found on monolithic glass.

In the actual production process, the selection of the original glass piece has a great influence on the bending resistance of the glass. Generally, in tempered glass, heat-strengthened glass and ordinary glass, from the aspect of wind pressure resistance, tempered glass is the largest, and heat enhancement is second. These two glasses are better to withstand external stress than ordinary glass. Therefore, we recommend to use tempered coating or heat-enhanced coated glass as the original film when producing coated insulating glass; the product variety should use inflatable glass as much as possible, and it is suitable to reduce the specification of glass and reduce the glass deformation caused by various reasons.

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