Several factors affecting the yield of polyurethane spraying construction
发布时间： 2019-10-29 14:03 Author: Polyurethane foam machine Source: http: //motokone.com
Published: 2019-10-29 14:03
Rigid polyurethane insulation material is a polymer with repeating structural unit of urethane segment, which is made by reacting isocyanate and polyol. Because of its good thermal insulation performance and excellent waterproof performance, it is widely used in external wall insulation, roof insulation, and cold storage, grain storage, archives, pipes, doors and windows and other special parts. Polyurethane rigid foam is widely used in roofing and wall insulation in foreign countries. The main application forms are composite panels and field spraying.
Hard foam polyurethane spraying belongs to the on-site processing of chemical products. The spraying technology is difficult to master. Due to different design requirements and external factors, the spraying rate of polyurethane spraying is also different, mainly due to the following factors.
(1) Design requirements determine the basic range of the output rate
Due to the different efficiency of the building, the design requirements for thermal insulation and energy saving are also different, and the density design requirements for polyurethane are different. So when talking about the output rate, first look at the design requirements. For example, the design requires a bulk density (core material density) of 30 kg / m3, and a theoretical (without any loss) rate of one ton is 33 square meters. For a design density of 40KG / m3, the theoretical yield should be 25. According to many years of engineering experience, the actual loss due to many factors during the construction process is between 15% and 25%, resulting in rising costs.
(2) the effect of material ratio deviation on the yield
There is a large difference in the density of machine and manual bubbles. Generally, the fixed material ratio of the machine is 1: 1, but the actual material ratio and the fixed material ratio of the machine sometimes do not match due to factors such as volume calculation and equipment failure. When the amount of white material is excessive, the foam density is low, the color is whitish, the foam strength is reduced, the hand feels soft, and it is easy to shrink when the temperature is low. . In these cases, the material ratio should be checked immediately to see if the filter is blocked and the pressure and temperature indicators are normal to ensure the accuracy of the black and white material ratio. The deviation of the material ratio has a certain effect on the output rate and the construction quality.
(3) the effect of ambient temperature on the output rate
Polyurethane foam is greatly affected by temperature. Foaming relies on heat. Without heat, the foaming agent in the system cannot evaporate, so that foam plastic cannot be formed. Heat comes from both chemical reaction generation and environmental provision. The heat of chemical reaction is not affected by external factors, and the heat provided by the environment changes with the change of 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. It shows that the foam is fully foamed, and the density of the foam surface layer and the core is close. When the ambient temperature is low (such as below 15 ° C), part of the reaction heat will be released to the environment. The loss of heat, on the one hand, causes the foam to mature for an extended period of time, which increases the foam molding shrinkage (the lower the temperature, the higher the molding shrinkage); on the other hand, the amount of foam material is increased. Experiments show that the same foaming material has a foaming volume at an ambient temperature of 15 ° C that is 25% smaller than a foaming volume at 25 ° C, thereby increasing the production cost of the foam. When the ambient temperature is lower than 15 degrees, the construction should pay attention to adjust the temperature control device of the spraying equipment to make up for the reaction limitation brought by the temperature drop to the raw material, so as to simulate the good temperature required for the polyurethane reaction as much as possible.
When spraying, the wind speed should be below 5m / s. When the wind speed exceeds 5m / s, the heat generated by the reaction will be lost, which will affect the rapid foaming reaction of the polyurethane foam and make the product surface brittle. At the same time, because the spray foaming machine mixes the raw materials and sprays them in an atomized state, if the wind speed is too large, the atomized particles will be blown away, increasing the loss of raw materials and polluting the environment.
(5) Basic temperature and humidity
It can be seen from engineering practice that the temperature of the base wall has a great influence on the foaming efficiency of polyurethane. During the spraying process, if the ambient temperature and the temperature of the base wall of the building are very low, after spraying the rigid foam polyurethane once, the reaction heat will be quickly absorbed by the base layer, thereby reducing the amount of foaming of the material. Therefore, the noon break should be shortened as much as possible during construction, and procedures should be reasonably arranged in the construction arrangement process to ensure the foaming rate of rigid foam polyurethane. Rigid polyurethane foam is a polymer product produced by the two-component mixing reaction of isocyanate and combined polyether. The isocyanate component easily reacts with water to form urea. If the urea bond content in the polyurethane increases, the foam will become brittle and the adhesion between the foam and the substrate will be reduced. Therefore, it is required that the surface of the substrate to be sprayed is clean and dry, the relative humidity is less than 80%, and there is no rust, no dust, no pollution, no moisture, and no construction is allowed on rainy days. Dew or frost should be removed and dried.
(6) Effect of sprayed layer thickness on yield
According to the thickness, spraying requires different environments. Generally, the multi-layer spraying method is used. According to the requirements of the national standard, the thickness of the first layer and the thickness of each layer have certain regulations. On the one hand, the thermal insulation performance of the polyurethane is guaranteed; Work reasonably along the response curve of polyurethane. However, as each layer will have crusts, the thicker the thickness of each layer, the more the output ratio will be, but in order to increase the output ratio, it is not advisable to blindly request the output in violation of the polyurethane spraying process requirements. Construction personnel are required to handle the site on the basis of experience and quality assurance.
(7) The impact of construction rate
In the construction of polyurethane spraying, material waste is extremely serious in the construction of corners, decorative lines, ceilings, beam structures, and daughter walls. For example, in the construction of large corners, nearly 1/2 of the material cannot be sprayed onto the wall. In the ceiling construction, because of the small surface of the sprayed construction, material waste is inevitable. Therefore, during the construction of special parts, more attention should be paid to the unification of construction technology and construction conditions.
(8) Effect of flatness on output ratio
During the construction process, the flatness of the grassroots should also be effectively controlled. The flatness of the base wall is too poor, which also causes a certain amount of material waste. In addition, if the flatness error of the base wall is too large during the polyurethane spraying process, it is necessary to saw away the part with a large local positive deviation, which wastes polyurethane material and labor costs, and also brings difficulties to subsequent construction.
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