1. Design requirements determine the basic range of the rate of delivery
Due to the different functions of the building, the design requirements for thermal insulation and energy saving are also different, and the design requirements for the density of polyurethane are different, so the design requirements should first be considered when discussing the rate of delivery. For example, the design requires a bulk density (core material density) of 30KG/cubic meter, and a theoretical (without any loss) rate of 33 cubic meters per ton. With a design density of 40KG/m3, the theoretical output rate should be 25. According to years of engineering experience, the actual loss due to many factors during the construction process is about 15%-25%, resulting in an increase in cost.
2. The influence of material ratio deviation on the rate of delivery
There is a big difference in density between machine foam and hand foam. Usually, the fixed material ratio of the machine is 1:1, but sometimes the actual material ratio and the fixed material ratio of the machine do not match due to the fact that the equipment calculation is based on volume calculation and equipment failures. When the white material is excessive, the foam density is low, the color is white, the foam strength is reduced, the hand feels soft, and it is easy to shrink when the temperature is low; when the black material is excessive, the foam density is high, the color is dark, the foam strength is high, and the hand feels hard and brittle. . In these cases, the material ratio should be checked immediately to see if the filter is blocked and whether the pressure and temperature indications are normal to ensure the accuracy of the ratio of black and white materials. The deviation of the material ratio has a certain impact on the delivery rate and construction quality.
3. The influence of ambient temperature on the output rate
Polyurethane foam is greatly affected by temperature. Foaming is carried out by heat. Without heat, the blowing agent in the system cannot evaporate, so that foam cannot be formed. Heat comes from both chemical reactions 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 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. It shows that the foam is fully foamed, and the density of the foam surface and core is close. When the ambient temperature is low (eg below 15°C), part of the reaction heat will be dissipated into the environment. The loss of heat, on the one hand, prolongs the foam curing period and increases the foam molding shrinkage rate (the lower the temperature, the higher the molding shrinkage rate); on the other hand, it increases the amount of foam material. Experiments show that: for the same foam material, the foam volume at an ambient temperature of 15°C is 25% smaller than that at 25°C, thereby increasing the production cost of foam. When the ambient temperature is lower than 15 degrees, attention should be paid to adjusting the temperature control device of the spraying equipment to make up for the reaction limitation brought by the temperature drop to the raw materials, so as to simulate the best temperature required for the polyurethane reaction as much as possible.
4. Wind
When spraying, the wind speed is required to be below 5m/s. When the wind speed exceeds 5m/s, the heat generated by the reaction will be blown away, which will affect the rapid foaming reaction of the polyurethane foam and make the surface of the product 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. Base temperature and humidity
It can be seen from the engineering practice that the temperature of the base wall also has a great influence on the foaming efficiency of polyurethane. During the spraying process, if the ambient temperature and the temperature of the building base wall are very low, after the first spraying of the rigid foam polyurethane, the reaction heat will be quickly absorbed by the base layer, thereby reducing the amount of foaming of the material. Therefore, the noon rest time should be shortened as much as possible during construction, and the procedures should be reasonably arranged during the construction arrangement to ensure the foaming rate of rigid polyurethane foam. Rigid polyurethane foam is a polymer product formed by the two-component mixing reaction of isocyanate and combined polyether. Among them, the isocyanate component can easily react with water to form urea. If the content of urea bonds in the polyurethane increases, the foamed plastic will become brittle, and the adhesion between the foam and the substrate will decrease. 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 construction is not allowed in rainy days. Any dew or frost should be removed and dried.
6. The influence of the thickness of the spray coating on the rate of delivery
According to the different thickness of spraying, the use environment is different. Usually, the method of multi-layer spraying 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, it is to ensure the thermal insulation performance of polyurethane. Works reasonably along the reaction curve of polyurethane. However, due to the existence of skinning on each layer, the larger the thickness of each layer, the higher the rate of output will be relatively, but in order to improve the rate of delivery, it is not advisable to blindly require the output to violate the requirements of the polyurethane spraying process. The construction personnel need to deal with it on the spot under the condition of ensuring the quality according to the experience.
7. The impact of the construction face on the rate of delivery
In the construction of polyurethane spraying, material waste is extremely serious in the construction of building corner lines, decorative lines, ceilings, beam structures, and parapets. For example, in the construction of large corners of the building, nearly 1/2 of the material cannot be sprayed on the wall. During the construction of the ceiling, due to the small working surface of the upward spray construction, the phenomenon of material waste is inevitable. Therefore, in the construction of special parts during the construction process, more attention should be paid to the unification of construction technology and construction conditions.
8. The effect of flatness on the rate of output
During the construction process, the flatness of the base layer 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 during the polyurethane spraying process is too large, it is necessary to saw off the part with too large local positive deviation, which wastes the polyurethane material and labor costs, and also brings difficulties to the subsequent construction.