Quality control of industrial painting operations
22.02.2017
In order to obtain a long resistant protective coating, the base material should be clean (free of salts, dust, oil, etc.) and it should have a proper roughness.
Applying a coating on a salt or dust contaminated surface will lead to poor adhesion of the coating to the base material, the result being in the end coating failure. To avoid such an unpleasant situation, is recommended to check the surface before painting. Specialized kits - Elcometer 138 and Elcometer 142 should be used for checking the surfaces.
Surface roughness is another important factor that should be taken into consideration. A coating applied on a too low profile surface will have a poor adhesion to the substrate. In case of a coating applied on a too high profile surface, there is the risk that the peaks of the profile remain uncovered, being therefore exposed to corrosion. In the end, if the roughness value is within the range requested by the paint manufacturer, then paint consumption can be optimized and the operation associated costs will significantly decrease. Surface profile control can be done using a digital device – Elcometer 224.
No matter what type of paint you intend to use, it should be applied in accordance to air temperature, surface temperature and relative humidity requirements. Normally, surface temperature should be with at least 30C higher than the dew point temperature. A coating applied on a wet surface will have a very poor adhesion to the base material. A low air temperature will lead to extension of paint drying time and therefore to work completion delaying. The solution for climatic condition monitoring is to use a digital thermohygrometer – Elcometer 319.
Another important aspect is the coating thickness checking. Applying a too thick layer of paint not only it will waste the substance and increase the costs, but there is also the risk the coating will crack during drying process.
If the applied layer of paint is too thin, the base material will not be enough covered, remaining exposed to corrosion.
In order to obtain an optimal coating thickness and to avoid additional paint consumption it is recommended to measure the wet film thickness during the painting process. It can be done using a hexagonal comb – Elcometer 112.
If both paint solid content and wet film thickness are known, the dry film thickness can be estimated using the following formula:
Dry film thickness = wet film thickness x paint solid content (%)
The dry film thickness can be determined at the end of painting operation, when the coating is dried out using a portable digital device – Elcometer 456.
