At present, as a thermal insulation material, polyurethane rigid foam has an irreplaceable position in many aspects due to its extremely low thermal conductivity and convenient molding process. However, as a reaction-molded polymer, its mold shrinkage (the foam volume after completion of the molding reaction is smaller than the maximum volume in the molding process) is inevitably one of its main defects.
The existence of molding shrinkage often causes the final volume of the foam to be smaller than the volume of the filled cavity, and the phenomenon of foam and shell peeling occurs, which seriously affects the appearance, thermal insulation effect and even service life of the product. Therefore, in most applications, polyurethane insulation is often used to improve the density of the filled foam and to take the form of molding to solve this problem.
Changsha solar water heaters and Hunan solar water heaters are incapable of molding due to their special structure (thin shell and liner, complex nozzle shape), and high-density filling will inevitably increase costs. Currently, density is relatively high. High free foam filling, which brings defects to Changsha solar water heaters and Hunan solar water heaters: the foam layer is separated from the outer casing, the outer casing is extruded during foam molding, and the inner tank causes deformation, especially when the above defects occur in the heat collecting nozzle. , resulting in a large number of process defects.
Based on extensive research and analysis, it is recognized that reducing the shrinkage rate during foam molding without increasing the foam packing density is the key to Changsha solar water heaters and Hunan solar water heaters. To this end, from the formulation, material selection and other aspects, developed a suitable combination of water heaters, in some solar water heater production line trials have achieved satisfactory results: the foam and shell peeling degree is light, the casing shell deformation probability is greatly reduced ,safer.
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