Aluminum plate, a metal that is expensive and not strong enough, was not used in construction until the beginning of the 20th century = mainly used to decorate architectural details. Aluminum began to be used in roofs, waterproof boards, wall panels and spandrels. The first widespread use of aluminum in construction was in the Empire State Building (1930-1932). The tower structure and spire are made of aluminum, as well as components such as entrances, elevator doors, decorative panels and more than 6000 window arches.
As a material, aluminum also has an excellent strength-to-weight ratio, which means that the exterior wall system made of aluminum can be smaller than steel. Modern aluminum alloys can also support the weight of heavy glass spans, thereby maximizing the building's ability to use natural sunlight. The metal and its alloy components are light, durable, corrosion-resistant, and can be used endlessly. According to statistics, there are still nearly 75% of all aluminum products still in use
At present, the design and construction of curtain wall has formed a misunderstanding in the industry. Whether it is aluminum or stone curtain wall, all the gaps between the unit panels on the exposed surface of the curtain wall are coated with weather-resistant silicone sealant, and the stricter the better. If you don't apply glue, he says you are cutting corners. This concept has been developed in the curtain wall in China to this day, and it has been formed in the minds of some owners and even many curtain wall technicians. As a result, the quality of the standard specifications is not high, the product level is low, the manufacturer is shoddy, and the installed aluminum curtain wall is deformed. Although some architects and consultants require the curtain wall to adopt a slitting system, it is often difficult to implement or the effect after implementation is not satisfactory due to the construction technology of the construction manufacturer, construction cost and other reasons. Of course, some owners have found that the weather after the slitting is more polluted as in the north , There is a large amount of dust accumulation between the joints, and the design and construction of waterproof measures between the joints are not reasonable, resulting in serious leakage, which must be rectified later. Therefore, the slitting system has never been used in a large scale.
In developed countries such as Germany, the structural design of curtain wall products is very rigorous. After years of technical discussion and practice summary, they divided curtain wall products into two categories, one is the warm wall system, and the other is the decorative cold wall system. . The special introduction is as follows:
Warm wall system
As the name implies, the main function of this wall is heat preservation, that is, a wall that has a certain blocking effect on the heat exchange between indoor and outdoor. For example, both sides of the inner and outer sides are composed of aluminum plates or other metal plates, and polyurethane and polystyrene are used in the middle. Or rock wool and other thermal insulation materials composite insulation wall; another example is the hidden frame glass curtain wall, all-glass curtain wall, and point-connected glass curtain wall used in the outer protective structure of the building. These walls are just like poured concrete and brick walls. There is only one shielding tape that separates the indoor and outdoor shields. The indoor and outdoor air is not allowed to generate convection on this shielding tape. Therefore, the curtain wall must be sealed from the process. All gaps that may cause air infiltration, and guarantee a permanent seal within the service life.
Decorative cold wall system
This kind of cold wall has two effects on the building. One is to enhance the building effect, and the other is to prevent the erosion and corrosion of the building surface by rainwater and improve the durability of the building. In terms of materials, aluminum, stone, glass and other materials are mostly used, and most of the used parts are the outer surface of the building with no sunlight; from the structure, it is required to maintain a certain interval with the building structure, and the rainwater leakage is designed with the principle of equal pressure. There is an air exchange channel to keep the curtain wall and the building structure dry, and the dew condensation water is easy to drain. The more modern open hot aisle curtain wall, in principle, is to add a decorative cold wall system outside the original warm wall curtain wall.
If the decorative cold wall system is constructed as a warm wall, that is, all passages on the decorative cold wall in Figure 2 are sealed with sealant, it will bring the following hidden dangers to the room:
Regardless of whether the outer layer is made of aluminum or stone, there is a barrier layer that will inevitably cause condensation due to temperature differences, and the connectors of the curtain wall will rust, especially between the two different metal connectors due to the difference in potential, which will increase under the medium of condensation Electrochemical corrosion causes the curtain wall structure to relax and reduce the service life.
Especially after the outer layer is coated with anti-corrosion paint on the back of aluminum or slate, the board itself is not air-permeable, and all the gaps on the board are blocked. If the distance between the board and the wall is greater than 40mm, a chimney effect will occur, causing moisture to evaporate from the foundation of the interval. Speeding up will promote the increase of moisture concentration in the interval. At this time, if the moisture-proof layer of the insulation layer is not tightly closed, the moisture content of the insulation material will be saturated and the insulation effect will be lost.
Due to economic factors, some projects require a good external surface without spending too much money. There is no insulation and waterproof layer on the outside of the civil structure. The moisture in the partition between the curtain wall and the structural wall is caused by aluminum panels or stone surfaces coated with antiseptics. The layer is very dense (gluing treatment between the seams), can not volatilize to the outside, can only penetrate into the room through the concrete or brick wall. A layer of plywood is generally added to the walls of high-end decorated houses on the indoor side, so that the moisture that penetrates the room cannot be volatilized, especially the kitchens with high humidity and the warehouses that do not open frequently. When the solar terms are over, the sun will be difficult to The moldy gas entering the nose severely damaged the sanitary environment of the room.
A large amount of dew water is deposited on the surface of the ground on the first floor and penetrates into the wall, which will reduce the thermal resistance of the wall, prematurely pulverize the wall, and reduce the service life.
Most of the aluminum curtain walls used in architecture in our country are mainly to enhance the architectural effect, and the reasonable combination with glass shows the elegant and upright or solemn and majestic modern architectural modeling artistic effect. This type of aluminum curtain wall products are both designed and constructed. It is classified as a decorative cold wall system. But in fact, what about the aluminum curtain walls of each building? From the product structure design and installation process, more than 90% are thermal insulation wall systems. The weather-resistant sealant applied from the gap between the kanban blocks is not flat, vertical, or smooth, and the silicone oil of the sealant adsorbs more dust, making the surface of the curtain wall dirty and unsightly. In the north, at least 30% of the aluminum curtain wall panels are deformed, especially the panels sprayed with metal fluorocarbon paint. If the surface of the panel is slightly uneven, there will be a large contrast. From a distance, the surface of the overall aluminum curtain wall is like a breeze lake. , Very ugly, seriously affecting the style of the building.