Quality control for electrostatically painted objects
24.04.2017
For insuring a proper anticorrosive protection while keeping the costs under control it is recommended to organize sets of checks, both before and after painting operation.
Previous painting operations
check if the surface to be painted is clean
When painting a contaminated surface there is a risk that the paint will detach in time due to reduced adhesive capacity. In order to check the status before starting the painting operation one can use the specialized kits from Elcometer: Elcometer 138 and Elcometer 142
check the roughness level of the surface to be treated
The paint layer sprayed on a too soft profile might have a low adhesion capacity. On the other hand, coating a too rough profile involves the risk that some of its peaks will remain uncovered therefore being exposed to corrosion. In conclusion, insuring an optimum profile of the surface before starting painting it, is highly recommended for obtaining better results and for keeping the costs with the paint under control. The verification of the roughness level of the surface can be done with a digital device – Elcometer 224
monitor the climate conditions
No matter what paint you choose to use, the application will be done respecting the producers’ specifications related to air temperature, surface temperature and relative humidity.
Usually the surface temperature has to be at least 30C above the Dew Point level. The paint applied on a humid surface will have a low adhesive capacity.
A low temperature level will increase the drying time. In order to check these parameters one can choose to use Elcometer 319.
At the end of the painting operation it is recommended:
to monitor the thickness level of the paint layer
When the paint layer is too thick there is a risk of cracking associated to it and an increase of costs with the paint that is used. On the other hand, if the layer is too thin the surface will not be sufficiently covered therefore being exposed to corrosion.
In order to obtain the proper thickness of the paint layer and for avoiding material lost it is recommended to use Elcometer 112 to measure the thickness of the humid film.
If the content of solid substance in paint is known and the thickness of the humid film was measured, then the thickness of the dry layer of coating can be determined based on the following formula.
Dry layer thickness = wet layer thickness x solid paint content(%)
The effective control of the dry paint layer can be done with the help of Elcometer 456.
to check the consistency of the anticorrosive protection
Corrosion usually appears due to imperfections of the paint layer. Pores represent a major cause for it.
Depending on the thickness of the dry paint layer and the testing pressure, the pores can be identified while using:
the humid sponge method – recommended for layers up to 500 microns
the high voltage method – for layers up to 25 mm
The test can also be done with Elcometer 270, Elcometer 266 and Elcometer 280.
detecting the glossiness level of the coating layer
The measurement is to be done from 3 different angles.
200 – for very glossy layers (>70 glossiness units)
600 – for semi glossy layers (10-70 glossiness units)
850 – for matte layers
The measurement angle is specified on the technical sheet of each paint type in part.
The process itself can be organized while using Elcometer 480.
