The key technical control of hard foam polyurethane spray construction

China Coatings Online News Information: Hard bubble polyurethane (PU) insulation material is a polymer with a repeating structure unit of the chain segment of amino methylate made from isocyanate and polyol reaction. Because of its good insulation performance, excellent waterproof performance, widely used in external wall insulation, roof insulation and cold storage, grain storage, archives, pipes, doors and windows and other special parts of the insulation. Polyurethane hard foam in foreign countries are widely used in roofing and wall insulation, the main application forms are composite plate, on-site spraying two types. Polyurethane hard bubbles have been used in walls and roofs since the 1960s. In the United States in 1996, hard bubbles accounted for 49% of the total consumption of hard bubbles, household, commercial refrigerators and other equipment accounted for only 23.5%. According to the U.S. Polyurethane Industry Association information, in order to achieve the goal of energy saving 50% to 70%, the U.S. housing insulation system used insulation materials from fiberglass generally to polyurethane insulation materials, in order to make full use of polyurethane insulation materials good insulation performance and water resistance.
, the application technology research of polyurethane hard foam in the field of insulation outside the exterior wall of the building began 10 years ago. At present, its application in addition to roof insulation and waterproof, there are cold storage, large and medium-sized chemical facilities, grain storage and so on. Due to the rapid development of China's building energy-saving industry, it is expected that the hard bubble polyurethane materials market for building insulation will show leapfrog development.
1 hard bubble polyurethane spray construction key technology
hard bubble polyurethane spraying technology is difficult to master, easy to produce spray polyurethane bubble hole uneven and other problems. The training of spray construction personnel should be strengthened so that they can master spraying technology and solve the technical problems encountered in spray construction independently. The key technical problems that need to be solved in spray construction mainly have the following aspects.
1.1 milk whitening time and atomization effect
the formation of polyurethane foam needs to go through two stages of foaming and maturation. The process begins with a mixture of black and white material and stops the expansion of the foam volume, a process known as foaming. During the foaming process, the system releases a large amount of reaction hot hard foam polyurethane (PU) insulation material is a polymer with a repeating structure unit of the urethane chain segment made from isocyanate and polyol reactions. Because of its good insulation performance, excellent waterproof performance, widely used in external wall insulation, roof insulation and cold storage, grain storage, archives, pipes, doors and windows and other special parts of the insulation. Polyurethane hard foam in foreign countries are widely used in roofing and wall insulation, the main application forms are composite plate, on-site spraying two types. Polyurethane hard bubbles have been used in walls and roofs since the 1960s. In the United States in 1996, hard bubbles accounted for 49% of the total consumption of hard bubbles, household, commercial refrigerators and other equipment accounted for only 23.5%. According to the U.S. Polyurethane Industry Association information, in order to achieve the goal of energy saving 50% to 70%, the U.S. housing insulation system used insulation materials from fiberglass generally to polyurethane insulation materials, in order to make full use of polyurethane insulation materials good insulation performance and water resistance.
, the application technology research of polyurethane hard foam in the field of insulation outside the exterior wall of the building began 10 years ago. At present, its application in addition to roof insulation and waterproof, there are cold storage, large and medium-sized chemical facilities, grain storage and so on. Due to the rapid development of China's building energy-saving industry, it is expected that the hard bubble polyurethane materials market for building insulation will show leapfrog development.
1 hard bubble polyurethane spray construction key technology
hard bubble polyurethane spraying technology is difficult to master, easy to produce spray polyurethane bubble hole uneven and other problems. The training of spray construction personnel should be strengthened so that they can master spraying technology and solve the technical problems encountered in spray construction independently. The key technical problems that need to be solved in spraying construction mainly have the following aspects.
1.1 milk whitening time and atomization effect
the formation of polyurethane foam needs to go through two stages of foaming and maturation.
from the beginning of the black and white mixture to the foam volume expansion stop, this process is called foaming. During the foaming process, the uniformity of the bubble holes should be considered when the system releases a large amount of reaction heat ester spraying process. Bubble homogeneity is mainly affected by the following factors:
(1) material ratio deviation
machine bubble and manual bubble density is very different. Usually, the fixed material ratio of the machine is 1:1, but due to the large difference in viscosity of the white material of each manufacturer, resulting in the actual ratio of material and machine fixation ratio does not match. When the excess of white material is shown as low foam density, white color, foam strength decreased, soft feel, low temperature easy to shrink, when the black material is too much performance of high foam density, dark color, high foam strength, hard and brittle feel. In these cases, the ratio should be checked immediately to see if the filter is blocked, pressure, temperature indication is correct, to ensure the accuracy of the black and white ratio.
(2) ambient temperature
polyurethane foaming is greatly affected by temperature. Foaming depends on heat, and without heat, the foaming agent in the system cannot evaporate, making it impossible to produce foam. Heat comes from both chemical reaction generation and environmental provision. Chemical reaction heat is not affected by external factors, and the heat provided by the environment varies with the ambient temperature. When the ambient temperature is high, the environment can provide heat to the reaction system, which can increase the reaction speed and shorten the reaction time. The foam foam foaming is sufficient and the foam surface and core density are close. When the ambient temperature is low (e.g. below 18 degrees C), some of the reaction heat is emitted into the environment. The loss of heat, on the one hand, causes the foam ripe period to be prolonged, increasing the shrinkage of foam molding (the lower the temperature, the higher the shrinkage of molding), on the other hand, increases the amount of foam material. Experiments show that the foaming volume of the same foaming material at ambient temperature of 15 degrees C is 25% smaller than that at 25 degrees C, thus increasing the production cost of foam.
(3) wind
require wind speeds below 5m/s for spraying operations. Wind speed of more than 5m/s will blow out the heat generated by the reaction, affecting the rapid foaming reaction of polyurethane foam, making the surface of the product brittle. At the same time, because the spray foaming machine will mix raw materials, sprayed out in a atomized state, such as wind speed is too large, will blow away the atomized particles, increase the loss of raw materials, pollution of the environment. (4) The temperature and humidity of the
can be seen from the engineering practice, the temperature of the grass wall also has a great influence on the foaming efficiency of polyurethane. During the spraying process, if the ambient temperature and the base wall temperature of the building are very low, after the first spray of hard foam polyurethane, the reaction heat will be quickly absorbed by the grass, thereby reducing the foaming amount of the material. Therefore, in the construction should be as short as possible noon rest time, in the construction arrangement process should be reasonable arrangements for the process to ensure the foaming rate of hard foam polyurethane. Hard polyurethane foam is a polymeric product produced by a mixture of isocyanate and combined polyether components. Where isocyanate parts are easy to react with water to produce arbonds, if the content of arbond bonds in polyurethane increases, then the foam will become brittle, foam and substrate bonding force is reduced. Therefore, it is required to spray the surface of the substrate clean and dry, relative humidity is less than 80%, and no rust, no dust, no pollution, no moisture, rainy days must not be constructed. If exposed or frosted, it should be removed and dried.
1.3 on-site foam spray
should try to avoid hard foam polyurethane spray pollution during the construction process. Polyurethane material in the form of foggy droplets sprayed from the gun, coupled with the material density is small, light quality, easy to be taken away by the wind, resulting in material waste and environmental pollution. Polyurethane spraying construction in the construction of building corner lines, decorative lines and other construction material waste is extremely serious. In the construction of the building corner, nearly 1/2 of the material can not be sprayed on the wall, the material waste is serious. In the construction process, we should also effectively control the grass-roots flatness. The flatness of the grass-roots wall is too poor, which also causes a certain amount of material waste. In addition, if the flatness error of the base wall in the polyurethane spraying process is too large, it is necessary to saw off the part where the local positive deviation is too large, thus wasting the polyurethane material and labor costs, but also to the subsequent construction of difficulties.
1.4 Construction site material management
polyurethane foaming principle is to rely on foaming agent heat vaporization into the foam bubble hole to produce bubble hole internal and external pressure difference to complete the foaming process, so the foaming agent content and effective use is also the key to foaming efficiency.
before construction, the foaming agent is mixed in white material in a certain proportion. Because foaming agent is a very volatile substance, during the construction process, if the container is affected by the environment its internal temperature is too high, it will make the foaming agent part of the container began to vaporize, into a gas in the upper part of the container hollow space or through the hole in the container evaporated into the ambient atmosphere, resulting in a reduction in the content of foaming agent in the material, or less than the predetermined ratio. At this time the foam foam bubble is not sufficient, the foam density becomes larger, so that the same amount of material can not produce the expected volume of foam. Therefore, polyurethane black and white materials in technical training and safety education. Spraying operation should be surrounded by a shelter to avoid pollution to the environment. The use of scaffolding construction with a small eye safety net cover tight, the use of hanging basket construction, hanging basket should be done around the height of not less than 1.8m, width is not less than the spray range of anti-splash, so as to avoid polyurethane particles with the wind to pollute the environment. It is strictly forbidden to operate and construct open fires such as welding, and to prepare sufficient fire extinguishers for construction to prevent fires on site. Spray electrical equipment installation operators to be certified on duty, electricity storage process should pay attention to sealing, strictly prohibited sun exposure.
safety measures during the spraying process of 2 hard foam polyurethane
to fully block the work before spraying. General doors and windows are made of plastic strip cloth to cover the area of the door window. For shelf tubes, iron and other irregular need to protect the part, should use polyethylene cling film for winding protection. Spraying is prone to polyurethane foam splashes, construction workers to do a good job of labor protection. Strictly follow the safety rules of high-altitude operation, must wear a hard hat, seat belt, especially the construction of the basket to take effective protective measures to prevent the basket from falling. New workers must receive rigorous technical training and safety education before taking up their jobs. Spraying operation should be surrounded by a shield to avoid contamination of the environment. The use of scaffolding construction should be covered tightly with a small eye safety net, with hanging basket construction, hanging basket should be done around the height of not less than 1.8m, width is not less than spray range of anti-splash, so as to avoid polyurethane particles with the wind pollution of the environment strictly prohibited welding and other open fire operation construction, construction should be prepared fire extinguishers, to prevent the appearance of fire on the scene. Spray electrical equipment installation operators to be certified on duty, electricity should be strictly in accordance with the site management regulations. After spraying, the polyurethane interface mortar is applied in time to play an effective fire prevention role.
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