Insight into the hidden dangers of aluminum alloy

Insight into the hidden dangers of aluminum alloy hidden frame glass curtain wall

aluminum alloy hidden frame glass curtain wall is a new comprehensive technology product. This curtain wall does not have an aluminum alloy outer frame used to hold glass and bear load. It completely relies on structural glue to bond hundreds of pieces of heat reflection coated glass to the aluminum profile frame, and the gap between the glasses is bonded with sealing structural glue, forming a large-area glass mirror, A curtain wall decorated on the facade of a building. It makes the building look unique, bright, bright and straight. Compared with other decorative materials, it gives a new concept in terms of color and gloss. In particular, the heat reflective coated glass is used to reflect the street view, blue sky, white clouds and other natural scenes around the building on the outer surface of the building, which changes with the season, time and light intensity, so that the appearance of the building is staggered layer by layer. The scene melts to form a gorgeous and colorful effect, which is rich in scenery at a close view and glittering at a distance. In addition, the light transmittance of the heat reflective coated glass selected for the hidden frame glass curtain wall is below 20, so it has a strong anti peeping function, that is, the indoor scenery of the building can not be seen outdoors, which plays the role of a tent, while the indoor can still look out to the outside without obstruction. Because of this charm, China has formed the hidden frame curtain wall heat. However, we must know that the technical requirements for the design, manufacture, installation and construction of this kind of curtain wall and materials are particularly strict, and the difficulty, technical complexity and risk are also particularly large

because some manufacturers do not fully follow the standards and procedures, curtain wall projects have collapsed many times in China, causing heavy losses and shocking, which cannot but attract our great attention. In order to prevent personal injury and property loss, users and relevant departments should pay attention to tracking the insight into the potential quality hazards of hidden frame glass curtain wall, which is introduced as follows

I. hidden dangers in materials of hidden frame glass curtain wall

1. adding waste aluminum wires, waste aluminum pots, etc. to replace aluminum metal and aluminum elements during melting and refining

the leading element to ensure the quality of curtain wall is profile. Because the coated glass of hidden frame glass curtain wall has no outer frame, it is completely bonded to aluminum by structural adhesive, so the requirements for aluminum, glass and structural adhesive are extremely strict

the commonly used aluminum materials for curtain walls should meet the requirements of gb/t5237. Its original state is composed of elements such as aluminum, magnesium and silicon, and its composition is shown in Table 1

qualified strength can be achieved only when the composition is guaranteed. However, in order to reduce the cost, some aluminum factories add waste aluminum wires, waste aluminum pots and so on to replace aluminum metal and aluminum elements. It is very dangerous to make any curtain wall with this kind of aluminum material. Because it can not meet the strength requirements and ensure the function and service life of the curtain wall, this is one of the hidden dangers

2. Aluminum alloy profile not prepared according to element content

aluminum alloy elements can be seen from the above table that each element in its prepared alloy has a certain range of content, and the price of magnesium is high. In order to reduce costs, some manufacturers reduce the amount of magnesium to the minimum allowable content. Some even worse, the content of magnesium is lower than the minimum allowed. This aluminum alloy profile, which is not prepared according to the element content, is basically not 6063 alloy. Finally, the mechanical strength of the profile is very low and it is easy to bend, which is also the reason why some aluminum materials are cheap. The price of aluminum is cheap, and the whole cost will be reduced, but how to process it in the future will not improve the quality. This is what Peng Zhengguo, the former chairman and Secretary General of the aluminum products committee of China Association for decoration, said, "the glass curtain wall with hidden dangers is a time bomb in the air". Of course, the dosage of other elements not according to the content formula in the above table will also cause the same consequences

3. aluminum alloy smelting furnace also affects its alloy quality.

how to melt the prepared 6063 alloy and what furnace to use are crucial. At present, the furnaces used by domestic and foreign manufacturers are also very different, which are at the level of the 1970s; There are also those at the level of the 1990s, including coal-fired, oil-fired, gas fired and electric furnaces. Some furnaces have chimneys, and some have no chimneys. Generally, square furnaces (rectangular furnaces) are used. The advanced ones are round furnaces, and some round furnaces can be tilted to molten aluminum

in terms of tonnage, there are several tons to dozens of tons of aluminum melting furnace. The more advanced one is to add a static furnace under the aluminum melting furnace to prepare 6063 alloy. It can remove slag, gas and static in this furnace, and then cast aluminum rods for extrusion. The quality of the alloy prepared by this kind of furnace is absolutely different from that of the original coal-fired furnace. Generally, no matter what fuel is burned in the furnace, there is a chimney, and most of the waste gas and slag generated during the combustion of fuel can be discharged from the chimney; If there is no chimney, all the waste gas and slag will be melted in the aluminum water, so there are serious slag bubbles in the cast aluminum rod, and the extruded profile must have serious quality problems, which will seriously degrade its physical properties. First, the strength is not enough. Second, the surface dimension tolerance and surface finish are poor. It must not be used on the hidden frame curtain wall

4. The quality of profile extrusion

there are many types of profile extruders in China, and the grades differ greatly. There are simple extruders, plastic extrusion machines, a small number of domestic ones, followed by most of Taiwan, Japan, the United States and West Germany. There are all kinds of hydraulic and oil pressure extruders. Good and bad extruders are in the same cast bar, and the quality of extruded profiles is never the same. There are also water-cooled quenching and air-cooled quenching on aluminum quenching. 6063 profile for construction is quenched by air cooling. The quenched aluminum is aged in the aging furnace for a certain time. The internal crystallization of the aluminum is rearranged, and the mechanical strength is significantly improved. Among all metal alloys, only aluminum alloy has aging state, but although all manufacturers have aging, the effect is very different, which is related to the extrusion temperature and speed of aluminum profile, and the air cooling speed when the profile is out of the extruder is related to the air volume. If the extruded profile of more than 500 degrees can not be quickly cooled to below 200 degrees, this is called incomplete quenching, After aging, the strength of aluminum is not ideal

5. The thickness of oxide film on the surface of aluminum profile used for hidden frame curtain wall

shall not be less than 15 according to the requirements of national standards μ m. Otherwise, the bonding firmness will be significantly reduced. Now many manufacturers supply aluminum profiles for hidden frame curtain walls, and the thickness of their surface oxide film cannot meet this requirement, and some even less than 12 μ m. This is very dangerous. Because the thickness of the oxide film increases, the cost will increase, and the manufacturer will make less profit, but the users don't understand it, the price is high, and they are unwilling to accept it. They have to listen to it and recognize it, and finally something happens, lacking heart

6. Surface treatment of aluminum profile

in addition to the above anodic oxide film, there are electrophoretic coating, powder coating and fluorocarbon coating. Electrophoretic coating has good surface gloss and strong anti-corrosion ability, but the firmness of the paint film is poor, so it cannot be used on the bonding surface of hidden frame glass curtain wall, and users are expected to pay special attention. For the surface treatment of aluminum profiles used on hidden frame glass curtain walls, only anodic oxide film profiles are preferred

II. Hidden dangers in the use of coated glass

glass is one of the main materials of aluminum alloy curtain wall, which directly restricts the performance of the curtain wall and is also the main embodiment of the artistic style of the curtain wall. Therefore, the selection of coated glass is an important part of curtain wall design. If it is improperly selected, serious consequences will occur, which is reflected in two aspects

1. The production method and thickness of coated glass raw sheet

at present, there are mainly two kinds of glass raw sheet production methods: upward method and float method. The leading up method is to lead up directly from the liquid glass and cool it slowly to form an ordinary glass plate with low surface flatness. Float glass is a relatively advanced production process at present. It floats on the tin bed with dissolved glass, and forms a smooth surface by the action of self weight and surface tension. Its surface is flat, smooth and smooth, with good quality, no ripple and no image. Therefore, when selecting the raw sheet of coated glass, it must be the first-class glass produced by float, and the appearance quality must comply with the provisions of the current national standard gb11614. Moreover, the freshness of the original piece of coated glass should not exceed one week, otherwise the poor firmness of the film will affect the functional effect. At the same time, the thickness of the original piece cannot be chosen at will. It must be calculated and checked according to the effect combination of wind load and action, otherwise it is easy to break and destroy. For example, the 60th floor of John cork building in Boston, USA, was severely damaged by a strong wind in the summer of the 1970s, from local crushing to 100 pieces of cracking, and finally 10348 pieces of glass had to be replaced

on January 17th, 1995, Kobe earthquake, Japan, a large number of curtain walls were damaged, and the glass was broken and flew out, causing great casualties. China also has similar accidents, such as the hidden frame glass curtain wall of the hardware and electrical store in Kunqu District, Baotou City, Inner Mongolia was completed less than two months, and hundreds of pieces of glass were all broken. Therefore, the production method and thickness of the coated glass must be carefully selected

2. methods of producing coated glass

at present, there are many methods of producing coated glass, including chemical method, physical deposition method, vacuum ion method, vacuum magnetron cathode sputtering method, thermal spraying coating method, etc. In China, some manufacturers do not have complete formal equipment and stable process parameters, and there are many local methods to transform, so the firmness of the membrane is different. At present, the coated glass used in hidden frame curtain walls at home and abroad must be produced by vacuum magnetron cathode sputtering method and thermal spraying method. The coated glass by vacuum magnetron cathode sputtering has the following characteristics:

first, the sputtering rate is high, the rake size is large, the production capacity is large, and the format is large

second, the film is uniform, the color difference is small, and the process control is stable

third, the film combination is convenient, and there are many color varieties and film types, such as sunlight reflection film, low radiation film, conductive film, hydraulic film, etc

fourth, the sputtered film has large particle energy, complete process measures for various film materials, strong film adhesion, compact film structure and good mechanical strength

fifth, the magnetron film is luxurious and bright, with many varieties of reflective colors

sixth, it has strong light control, which can ideally control the luminous flux and thermal radiation entering the room, and realize people's requirements for shading, cold protection and energy saving

therefore, buildings and other buildings that can reflect the level of modern buildings use vacuum magnetron cathode sputtering coated glass as hidden frame curtain wall glass

thermal spraying coated glass is a thin film formed by chemical vapor deposition (CVD) combined with float production process. When the glass is still at 600 ~ 700 ℃, it has a thermal stability of more than 700 ℃, and has a unique position in the application of curtain wall glass requiring hot bending processing

III. hidden dangers in the use of structural adhesives

silicone structural sealant is a polymer of organosiloxane, which is composed of more than 100000 siloxane bond monomer molecules, with the linear bond of macromolecules as the primary key, combined with different organic groups and cross-linked reaction to form a polymer with different characteristics. Because it requires a lot of energy to destroy the silica bond, it has excellent aging resistance. For example, it is resistant to ultraviolet radiation and ozone in the sun, and has the characteristics of heat resistance and low temperature resistance. It is composed of silicone polymer, coupling agent, catalyst and filler, coloring ingredients, etc. The introduction of phenyl groups into silicone molecules can keep the flexibility of silicone adhesive at -40 ~ 60 ℃. The substrate friendly gene in the coupling agent forms a similar bond with the surface of the substrate, which reflects the adhesion to the substrate