What is the principle of curtain wall glass coating technology to make the light reflected on it reflect more?
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definition
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eigenfunction
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definition
low emissivity
LOW-E is the abbreviation of English ~Low emissivity, which is low-emissivity coated glass. Compared with heat reflective glass, it is an energy-saving glass.
Glass is an important building material. With the continuous improvement of architectural decoration requirements, the use of glass in the construction industry is also increasing. However, when people choose the glass doors and windows of buildings, they pay more attention to issues such as heat control, cooling cost, comfortable balance of internal sunlight projection and so on, in addition to aesthetic and appearance characteristics. This makes Low-E glass, a upstart in the coated glass family, stand out and become the focus of people's attention.
Excellent thermal performance
The heat loss of exterior door window glass is the main part of building energy consumption, accounting for more than 50% of building energy consumption. Relevant research data show that the heat transfer on the inner surface of glass is mainly radiation, accounting for 58%, which means that the most effective way to reduce heat loss by changing the performance of glass is to suppress the radiation on its inner surface. The emissivity of ordinary float glass is as high as 0.84, which can be reduced to below 0. 15 after plating with low emissivity film mainly composed of silver. Therefore, building doors and windows made of Low-E glass can greatly reduce the transmission of indoor heat energy to the outside caused by radiation, and achieve ideal energy-saving effect.
Another significant benefit of reducing indoor heat loss is environmental protection. In cold season, harmful gases such as CO2 and SO2 emitted by building heating are important pollution sources. If Low-E glass is used, the fuel consumed by heating can be greatly reduced due to the reduction of heat loss, thus reducing the emission of harmful gases. [ 1]
The heat passing through the glass is two-way, that is, the heat can be transferred from indoor to outdoor, and vice versa, and it is carried out at the same time, only the problem of poor heat transfer. In winter, the indoor temperature is higher than the outdoor temperature, so it needs heat preservation. In summer, the indoor temperature is lower than the outdoor temperature, so it is required that the glass can be insulated, that is, the outdoor heat is transferred to the room as little as possible. LOW-E glass can meet the requirements of winter and summer, which is both warm and heat-insulating, and achieves the effect of environmental protection and low carbon.
Good optical properties
In theory, the visible light transmittance of Low-E glass ranges from 0% to 95% (it is difficult to do with 6mm white glass), and the visible light transmittance represents indoor lighting. The outdoor reflectivity is about 10%-30%, and the outdoor reflectivity is visible light reflectivity, which represents the reflection intensity or dazzling degree. Up to now, China requires that the visible light reflectivity of curtain walls should not be greater than 30%.
The above characteristics of Low-E glass make it widely used in developed countries. China is a country with a relative shortage of energy, and the per capita energy consumption is very low, while the building energy consumption has accounted for about 27.5% of the total energy consumption in China. Therefore, vigorously developing the production technology of Low-E glass and popularizing its application fields will certainly bring remarkable social and economic benefits.
Special cleaning brush for Low-E glass In the production of low-e glass,
Because of the particularity of the material, there are higher requirements for the cleaning brush when passing through the cleaning machine. Brush wire must be PA 10 10, PA6 12 and other high-grade nylon brush wires. The wire diameter is preferably 0.1-0.15mm ... Because the brush wire has good flexibility, strong elasticity, acid and alkali resistance and temperature resistance, the dust on the glass surface can be easily removed without scratching the surface.
Application and development of low emissivity glass
In the United States and Europe, Low-E coated glass has attracted much attention because of its superior properties. Especially the Wschvo regulations in Germany make the development of Low-E glass rapid.
European manufacturers began to study "low radiation" in the laboratory in the late 1960s. 1978, American interqane successfully applied "Low-E" glass to buildings.
The superiority of "Low-E" is beyond doubt. Since 1990, the amount of "low e" in the United States has increased by 5% every year. Whether "Low-E" will become the dominant position of window glass in the future is unknown, but both owners and door and window companies attach great importance to energy-saving doors and windows. Moreover, the vast majority of buildings this year are judged by energy-saving effects.
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manufacture
Two Current Production Methods of Low-emissivity Glass
On-line pyrolysis deposition method;
On-line high-temperature pyrolysis deposition of "Low-E" glass has products from many American companies. Such as Surgate200 of PPG Company and Sunglas H.R. "P" P "of Ford Company. These products are completed in the cooling process of float glass. Liquid metal or metal powder is directly sprayed on the surface of hot glass. As the glass cools, the metal film becomes a part of the glass. So the film is hard and durable. The "Low-E" glass produced by this method has many advantages: it can be hot bent and tempered, and can be stored for a long time without being used in a hollow state. Its disadvantage is poor thermal performance. Unless the film is very thick, its "U" value is only half that of sputtered "Low-E" coated glass. If we want to improve its thermal performance by increasing the film thickness, then its transparency is very poor.
Off-line vacuum sputtering method
Off-line production of Low-E glass is a vacuum magnetron sputtering coating technology widely used in the world at present. Unlike high temperature pyrolysis deposition, sputtering is off-line. And according to the different transmission positions of glass, there are horizontal and vertical points.
The production of "Low-E" glass by sputtering requires a layer of pure silver film as a functional film. The pure silver film is between two metal oxide films. The metal oxide film provides protection for the pure silver film, as an intermediate layer between the film layers, increasing color purity and light transmittance.
In the vertical production process, the glass is vertically placed on the shelf, sent into the vacuum environment of 10- 1 Pa, and an appropriate amount of process gas (inert gas Ar or reaction gases O2 and N2) is introduced to keep the vacuum degree stable. Targets such as silver and silicon are embedded in the cathode, and a magnetic field is placed in the horizontal direction perpendicular to the cathode to form a magnetically controlled target. Using magnetron target as cathode and DC or AC power supply, the process gas is ionized to form plasma under the action of high voltage. Among them, under the action of electric and magnetic fields, electrons make high-speed spiral motion and collide with gas molecules to produce more positive ions and electrons; Under the action of electric field, positive ions hit the cathode target after reaching a certain energy, and the sputtered target is deposited on the glass substrate to form a thin film. In order to form a uniform film, the cathode target moves back and forth near the glass surface. In order to obtain multilayer films, multiple cathodes must be used, and each cathode moves back and forth on the glass surface to form a certain film thickness.
The horizontal method is similar to the vertical method to a great extent. The main difference lies in the placement of glass, which is transported by horizontally arranged wheels, passes through the cathode and a series of needle valves, and the vacuum degree changes accordingly. When the glass reaches the main sputtering chamber, the coating pressure reaches, the metal cathode target is fixed and the glass moves. When the glass passes through the cathode, a film layer is formed.
At present, the target products of domestic and most imported magnetron sputtering coating production lines are solar control film glass mainly coated with elemental films and metal films. This kind of products have relatively simple technology and low requirements for equipment. Therefore, these production lines can not meet the requirements of LOW-E glass plating.
The "low-emissivity" glass produced by sputtering has the following characteristics:
There are many choices and combinations of metal targets, so there are many configurations for producing "Low-E" glass by sputtering. Sputtering coating is also superior to thermal spraying in color and purity, and it is more flexible in new product development because it is offline. The main advantage is that the "U" value of "Low-E" insulating glass produced by sputtering is better than that of pyrolysis products, but the disadvantage is that the silver oxide film is very fragile and cannot be used like ordinary glass. It must be made of insulating glass, and it is not suitable for long-distance transportation before it is made into a hollow product.
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eigenfunction
97% of the solar radiation energy is concentrated in the wavelength range of 0.3-2.5um, which comes from outdoor; The radiation energy of objects below 100℃ is concentrated in the long wave band above 2.5um, mainly from indoors.
If the room window is taken as the boundary, we hope that the outdoor radiation energy will come in in winter or at high latitudes, but the indoor radiation energy will not leak out. If the wavelength of radiation is taken as the boundary, the dividing point of indoor and outdoor radiation energy is at the wavelength of 2.5um, so it is the key to choose a room window with certain functions.
The transmittance of ordinary transparent glass with a thickness of 3mm to solar radiation energy is 87%, and most of the radiation energy from the outside can be transmitted during the day; However, at night or in rainy weather, 89% of the thermal radiation energy of indoor objects is absorbed by it, which makes the glass temperature rise, and then the heat is dissipated through radiation and convection exchange indoors and outdoors, so it cannot effectively prevent indoor heat from leaking to the outside.
Low-E insulating glass has a transmittance of more than 60% for solar radiation of 0.3-2.5um, and can transmit most of the energy radiated outside during the day. However, at night and in rainy weather, more than 50% of the thermal radiation of indoor objects is reflected back indoors, and less than 65,438+05% of the thermal radiation is absorbed by it, and then it is dissipated through re-radiation and convection exchange, so it can effectively prevent indoor heat from leaking outside. This characteristic of Low-E glass enables it to control the unidirectional flow of heat energy to the outside.
Short-wave sunlight shines on indoor objects after passing through the window glass. When heated, these articles will radiate again in the form of long waves. These long waves are blocked by the "Low-E" window glass and return to the room. In fact, the re-radiation through the window glass is reduced to 85%, which greatly improves the thermal insulation performance of the window glass.
The thermal insulation performance of window glass is generally expressed by the value of "U", and the value of "U" [2] is directly related to the emissivity of glass [3].
The value of "U" is defined as the heat transfer from air to air due to the heat conduction of glass and the temperature difference between indoor and outdoor under ASHRAE standard conditions. English units are: English thermal units per hour per square foot per degree Fahrenheit temperature, and metric units are: watts per square meter per degree Celsius temperature. The lower the "U" value, the lower the heat transfer through the glass, and the better the heat insulation performance of the window glass. Emissivity is the ratio of the heat radiated per unit area of an object to the heat radiated per unit area of a black body at the same temperature and under the same conditions. Emissivity is defined as the ability of an object to absorb or reflect heat. Theoretically, the absorption rate of a complete blackbody at all wavelengths is 100%. That is, the reflectivity is zero. Therefore, the blackbody emissivity is 1.0.
The emissivity of ordinary float white glass is 0.84. However, the emissivity of most on-line thermal polymerization "low emissivity" coated glasses is between 0.35 and 0.5. The emissivity of "Low-E" coated glass sputtered by magnetron vacuum is between 0.08-0. 15. It is worth noting that low emissivity directly corresponds to a low "u" value. The closer the emissivity of glass is to zero, the better its thermal insulation performance.
The advantage of "energy-saving lighting system" must be reflected in the highest possible total solar energy penetration and the lowest "U" value. By considering both energy gain and heat loss, the energy balance equation is established, Ueg=UF-RFg. The best lighting system with energy balance characteristics is vacuum magnetron sputtering "Low-E" coated hollow glass. Although the solar energy transmittance of single-layer glass is the largest, its "U" value and "Ueg" value are the worst. Therefore, the demand for good energy balance cannot be met.
Simple high solar energy transmission can effectively maintain these energies, so it cannot be considered as an energy-saving material. Low-E coated insulating glass is a good energy-saving lighting material. It has high solar energy transmittance and very low "U" value. Moreover, due to the coating, the heat reflected by the "Low-E" glass returns to the room, which makes the temperature near the window glass higher, and people will not feel too uncomfortable near the window glass. However, the indoor temperature of buildings with "Low-E" window glass is relatively high, which can be kept relatively high in winter without frost, so that indoor people will feel more comfortable. "Low-E" glass can also block a lot of ultraviolet light transmission and prevent indoor objects from fading.
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colour
Low-E can be divided into online deposition coating method and offline vacuum magnetron sputtering method. Color, the most basic color, three basic tones of blue, green and gray can be treated differently according to the reflection of different elements. Such as gold and silver.
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problem solving
At present, there are two kinds of LOW-E glass: online LOW-E glass and offline LOW-E glass. Online LOW-E glass is single, and LOW-E glass is limited by mass production of float glass. At present, it is only 6mm thick and colorless and transparent. Off-line Low-E glass has many products with high, medium and low transmittance according to different climatic characteristics, and the colors are silver gray, light gray, light blue, colorless and transparent. Colored glass can also be used to make many other colors, such as green. The thickness can be 3 to 12 mm, and it should be noted that: 1. On-line Low-E glass will be subjected to high temperature close to the softening point of glass during tempering, and the color of the film may change at this time, resulting in color difference. In addition, the online tempering of Low-E glass is tempered by film. The existence of thin film makes the heating on both sides of glass asymmetric, and the tempering process is difficult to control, which may lead to a series of problems such as large tempering deformation. Off-line Low-E glass is tempered first and then coated, no problem. In order to avoid the toughening problem of online Low-E glass, some people use non-toughened online low-e glass as the inner sheet of insulating glass, and put toughened transparent glass on the outer side. This usage will not only have a certain influence on the effect of South Low-E glass, but also enlarge the stress spots of the outer tempered white glass by the inner Low-E glass. In contrast, there is no such problem when the tempered offline Low-E glass is placed outdoors. 2. Off-line Low-E glass film is soft, and it will slowly oxidize when it is attacked by moisture and some oxidants. 3. The online Low-E glass is "hard coated" and the shelf life of the film is 30 years. Off-line Low-E glass is a "soft coating", and the film is weak, so it can hardly be bare. 4. Off-line Low-E glass must be processed into insulating glass in a short time, and the edge coating must be removed when forming insulating glass. Due to the weak respiration of insulating glass, the thermal insulation performance of off-line Low-E glass will gradually lose after water vapor, sulfide and oxide enter the cavity, and the appearance will become dark and discolored, and a large number of mildew spots will gradually appear.
LOW-E glass is also called low-emissivity coated glass. Globally, the production and application of low-e glass is in a period of rapid growth. According to the requirements of the Ministry of Construction, green energy-saving buildings will become the mainstream of domestic buildings in the future, and the Ministry of Construction will promote the certification of energy-saving signs and corresponding preferential tax policies to promote the development of energy-saving buildings. Therefore, whether new buildings and existing buildings can save energy is not only related to whether the tight situation of energy supply and demand in China can be alleviated, but also related to the realization of the goal of energy saving and consumption reduction in the Eleventh Five-Year Plan. As the three major energy-using fields, the energy-saving situation in the construction industry is very severe, so it is urgent to save energy and reduce consumption.
According to market analysis and forecast, by 20 15 years, the international market demand for LOW-E glass will exceed 10 billion square meters, and the global market demand for LOW-E glass will increase at an average annual rate of 18% or more in the next decade.