Thermal resistance of"aging-fresh"coating of intumescent coatings
The formation of the"aging-fresh"composite layer in intumescent coatings involves the applica-tion of a new coating onto an existing coating.It is important to note that the thermal resistance of this com-posite layer cannot be simply calculated by superposing the thermal resistance of the two individual coatings.In order to determine the constant effective thermal resistance of these composite layers,fire tests were carried out.The aim of these tests was to investigate the impact of recoating on the thermal resistance of the existing coating and the resulting composite layer.A comparative analysis was conducted on the constant effective thermal resistances of various specimens.The results of the analysis indicate that the thermal resistance of the existing coating decreases as the thickness of the recoated coating increases.Additionally,when the thickness of the recoated coating exceeds 1.0 mm,the contribution rate of the thermal resistance from the existing coat-ing does not surpass 20%.Therefore,it can be disregarded when calculating the thermal resistance of the com-posite layers.However,in cases where the recoated coating is thin(e.g.,0.5 mm)and the existing coating,without a topcoat,has undergone moderate environmental aging(e.g.,fewer than 21 cycles of aging test),or when the existing coating has a topcoat,the contribution of the existing coating becomes significant(with a contribution rate exceeding 20%).Moreover,the utilization of a new coating type different from the existing one results in higher thermal resistance and enhanced insulation properties of the composite layer.
Intumescent coatings for steel elementsRecoatedComposite layersInsulation propertiesConstant effective thermal resistance
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