Coating porosity is a unit of measurement to describe the compactness of the coating, and it is one of the quantitative indicators reflecting the quality of the coating. The coating is formed by the accumulation of coating material particles on the surface of the substrate. Affected by the spraying method, process and quality, there are tiny pores in it, and its density is smaller than that of the original coating material. Different substrates and different materials have different requirements for compactness. (Related instrument: density cup) Generally, the denser and the smaller the porosity, the better. For example, for functional coatings (anti-carburization, nitrogen, etc.) that require dense coatings, porosity is an important index to measure the quality of coatings, and for anti-corrosion coatings, corrosive gases and fluids flow to the surface of the substrate through pores, Corrosion matrix, harmful porosity. Of course, there are also opposite situations. For example, for the coating of the grinding parts, the pores can store the slippery agent, the pores are favorable, and there can be larger pore strings.
The porosity of the coating is essentially the volume expansion rate of the coating material before and after spraying, that is, the relative volume change rate of the coating material before and after spraying is defined as the coating porosity, which can be expressed as
