[China Glass Network] 1: Introduction
For insulating glass, warm edge technology has become an industrial term. After decades of development, the structure of insulating glass is basically similar, but with the development of materials science, the physical and chemical properties of glass have been greatly improved, and the combined application of coated glass and various polymer materials has made The thermal insulation properties of the insulating glass are greatly changed to meet the needs of various occasions. Developed countries can design various types of insulating glass according to specific application requirements, and do not break the new varieties of warm-side spacers. China's Ministry of Construction has also listed hollow glass as one of the building materials energy-saving products for promotion and application, which makes China's insulating glass development and production face a good development opportunity.
2: The generation of warm edge technology
The insulating glass is composed of two or more glass plates which are separated by an edge sealing system and filled with gas. The glass plate may be ordinary flat glass, tempered glass or Low-E glass, which is selected according to the place of use of the insulating glass and the role played. The glue is edged to bond the glass together and prevent gas from escaping inside the layer. When there are two different temperature fluids on both sides of the insulating glass, the heat passing through the middle portion and the edge portion is different in heat. The heat is transmitted through the glass plate, and the thermal resistance is also the same. The separated gas mainly generates heat conduction, and convective heat transfer may also occur. The insulating ability of insulating glass is mainly from the sealed air layer. At a temperature of 20 ° C, the thermal conductivity of air is 0.026 W / m · K, while the thermal conductivity of ordinary transparent glass plate is 0.76 W / m · K [1] ], the ratio is 1:29. In the air layer sealed by the insulating glass, the convective heat exchange has a small share, which is basically a heat conduction mode, so that the thermal resistance of the insulating glass can be greatly improved. At the edge of the insulating glass, since the sealing system is in close contact with the glass plate, it is a conduction heat transfer between the plurality of flat walls. The thermal conductivity of the spacer material has a great influence on the thermal resistance. The aluminum spacer used in the initial stage has a large thermal conductivity and a small thermal resistance. For the hollow portion, the thickness of the air layer is close to the size of the spacer strip, so their thermal resistance ratio also approximates the ratio of their thermal conductivity. The thermal conductivity of pure aluminum is 202W/m·K, and the thermal conductivity of aluminum alloy is also generally 130-150W/m·K [2]. Therefore, the thermal resistance of the edge is much smaller than that of the middle part. Figure 2 shows the change in the temperature of the edge of the insulating glass when different spacers are used.
In winter, the thermal resistance of the surrounding glass of the building is small and the temperature drops significantly. Due to the certain humidity in the room, the glass in the air hits the lower temperature and the glass plate is condensed, causing condensation and frost on the edge of the insulating glass, which affects the appearance and damage to the sealing material.
In order to improve the thermal resistance of the surrounding part of the insulating glass to be too small and easy to dew condensation, the research direction focuses on the thermal properties of the spacer material and the shape of the spacer strip. The results show that replacing the traditional aluminum spacer with a material with lower thermal conductivity can make the ambient temperature of the inner glass higher than in the past and avoid condensation at the edge of the inner glass. Therefore, various materials having a small thermal conductivity and spacer strips of various shapes have been extensively developed, and the term warm edge technology has appeared.
3: Types of warm edge spacing systems
The hollow glass spacer system can be basically divided into two categories: one is a rigid space composed of a metal frame with a low thermal conductivity and a sealant, and the other is a non-rigid spacer made mainly of a polymer material. Before 1995, it was mainly aluminum spacers. After the generation of warm-edge technology, the warm-edge spacer system accounts for about 82% of the entire North American market, with a rigid spacing of 54%, mainly U-shaped stainless steel; non-rigid spacing of 28%, such as Swiggle strips and other dry Silicone foaming product. The remaining 18% is still an aluminum spacer.
3.1 frame type rigid spacing system
Since the thermal conductivity of stainless steel is much lower than that of aluminum, the aluminum spacer is replaced by a stainless steel material, and their thermal conductivity ratio is 1:11, so that the thermal resistance of the edge of the insulating glass is too small. Intercept, the product of PPG Company of the United States, is first made into a trough shape by using a stainless steel belt, and then the clay containing the molecular sieve is placed in the tank, and then the rubber is coated on the side, and then the frame is folded, and the sheet is later combined. The utility model is characterized in that the folding frame device is fully automatic and the production speed is fast, and is suitable for producing hollow glass of a civil building with large batch size and simple specifications.
The spacer system provides sufficient strength to keep the glass sheet flat and prevent insulation gas from escaping and moisture ingress. The key technology is the sealant. The insulating glass is affected by temperature difference, air pressure and wind load from the outside during use. Therefore, the sealant must ensure the structural stability of the system and prevent the external water vapor from penetrating into the air layer of the insulating glass.
The performance requirements of the sealant mainly include the adhesion ability to the substrate (glass, spacer), water resistance under the use environment, ultraviolet light resistance to sunlight, high temperature resistance and low temperature resistance. It is required that the sealing material does not crack and age under the dynamics of expansion and contraction. Sealants can be classified into two broad categories: structural seals and low moisture permeability seals (lowMVTsealants). Mainly used for structural sealing are thermosetting materials, such as polysulfide rubber, polyurethane glue and silicone rubber, which enhance the stability of the insulating glass and have high modulus values. However, the airtightness is poor, the water vapor permeability resistance is poor, generally greater than 15g/m2·d, and the silicone rubber reaches 50g/m2·d. The low water vapor permeability seal is mainly a thermoplastic material, and the commonly used polyisobutylene (PIB) has a water vapor permeability of less than 1 g/m 2 ·d. Since it is hot melt, its operating temperature is about 150 °C. Sealing technology is closely related to warm-edged products, and different warm-edged products have their corresponding sealing processes. They all affect the quality of the insulating glass and are also closely related to its thermal insulation function.
3.2 strip type non-rigid spacing system
Due to the small thermal conductivity of polymer materials, the use of thermosetting materials as spacers has been greatly developed. TruSeal's Swiggle strips are made of a combination of desiccant and plastic with corrugated metal spacers in the middle, which is common in China. Another product, Insuledge, is a non-metallic rectangular tubular spacer with a corrugated tubular core in the middle that resists pressure and stretches properly. A rectangular tubular foil is arranged on the outside to enhance the resistance of the spacer to water vapor permeation. The edge rubber layer is moisture-proof, the inner layer contains a desiccant, and the shape is beautiful, and both single-channel and double-channel seals can be used. It is characterized by the use of a hollow to replace the solid material or the foamed material, which makes full use of the characteristics of small thermal conductivity of the air, and the strength is enhanced by the bellows. The space is 13 mm, the thermal conductivity is 0.08 W/m·K, and the water vapor permeability is 0.098 H2 O/m 2 ·d. The product DuraSeal can be applied to double-layer and three-layer insulating glass, which is sealed by hot pressing method and made in one step. The space is 6-18mm.
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