The coating process used in our facility is a flow through system using a water soluble enamel. We are having an issue with inadequate coverage of frame assemblies. The parameters being monitored currently are the pH of the wash, rinse and paint; the viscosity of the paint; and the temperatures of the wash system and dry-off and bake ovens. What other factors are significant in controlling this type of coating process? R.W.
You seem to be monitoring many important parameters. Water soluble paints can sometimes be difficult to control. Since they often follow Izzo’s Law, “The Innate Perversity of Inanimate Objects,” difficult can become impossible. It seems that one problem with these coatings is “false viscosity.” The apparent viscosity is higher than it really is. This leads to viscosity reduction by addition of water. The net result is a reduction of the percent solids by volume, which really determines your coating thickness (read coverage).
The one important parameter you are not testing and monitoring is percent solids by volume. This property is covered by ASTM Designation D 2697, Standard Test Method for Volume Non-Volatile Matter in Clear or Pigmented Coatings.