Hard foam polyurethane spray The technology is difficult to master, and it is easy to produce problems such as uneven polyurethane foam holes. The training of spraying construction personnel should be strengthened so that they can master spraying technology and independently solve the technical problems encountered in spraying construction. The key technical problems that need to be solved in spraying construction are mainly in the following aspects. Control of whitening time and atomization effect

Polyurethane foam The formation needs to go through two stages of foaming and curing.

From the mixing of black and white materials to the foam volume expansion stop, this process is called foaming. During the foaming process, when the system releases a large amount of reactive hot ester spraying process, the uniformity of the bubble holes should be considered. The cell uniformity is mainly affected by the following factors:

Material ratio deviation

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There is a great difference in density between machine bubble and manual bubble. Usually, the fixed material ratio of the machine is 1∶1, but due to the large difference in the viscosity of the white material of each manufacturer, the actual material ratio does not match the fixed material ratio of the machine. When the white material is excessive, the foam density is low, the color is white, the foam strength is decreased, the feel is soft, and the temperature is low. When the black material is excessive, the foam density is high, the color is deep, the foam strength is high, and the feel is hard and brittle. In these cases, the material ratio should be checked immediately to see whether the filter is blocked, and whether the pressure and temperature indicators are normal to ensure the accuracy of the black and white material ratio.

(2) Ambient temperature

Polyurethane foam It is greatly affected by temperature. Foaming depends on heat, if there is no heat, the foaming agent in the system can not evaporate, so that the foam can not be generated. 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 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 is fully foamed, and the density of foam surface and core is close to each other. When the ambient temperature is low (such as below 18 ° C), part of the reaction heat will be emitted into the environment. On the one hand, the loss of heat causes the foam to prolong the curing period and increase the foam Molding shrinkage (The lower the temperature, the higher the molding shrinkage); On the other hand, the amount of foam material is increased. The experiment shows: same Foaming material The foam volume at the ambient temperature of 15℃ is 25% smaller than that at 25℃, thus increasing the production cost of foam.

(3) Wind power

When spraying operation, 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, affecting the rapid foaming reaction of the polyurethane foam and making the surface of the product brittle. At the same time, because the spray foam machine will mix the raw materials and spray in the atomized state, such as the wind speed is too large, it will blow away the atomized particles, increase the loss of raw materials, and pollute the environment. ^[1]

Market prospect

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At present, the total annual output of polyurethane reaches 10 million tons, which is still in a period of rapid growth, and the annual average growth rate is twice that of GDP. In China, polyurethane has maintained a growth rate of more than 20%, and the total output of polyurethane in China reached more than 3 million tons in 2007. Polyurethane provides excellent thermal insulation in the field of construction, Energy conservation The performance and contribution to environmental protection determine the unlimited prospects of the polyurethane insulation market. Some delegates said: polyurethane is the only and best at present Building insulation material . Continuous increase in building area and for energy saving ^[2] Environmental protection update requirements, polyurethane market prospects are promising, in China is on the rise.

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