Subsequent to the preparation process described in Section 5, the surface must receive additional cleaning to achieve maximum performance. The cleaning stage is accomplished by
Subsequent to application of the cleaning agent, the surface is rinsed with a water rinse to neutralize the surface.
After the first rinse, an agent to promote a proper conversion coating, usually a phosphoric acid is applied. These agents may include iron,
After phosphatizing, the surface is again rinsed to flush any remaining phosphate solution, stop the phosphatizing process, and
The final pretreatment stage is seal rinsing. The purpose of the sealing rinse is to enhance the coating’s resistance to surface corrosion and paint adhesion. The sealing rinse consists of a sealing agent and water. As a rule of thumb, water with hardness above the moderately high range (i. e. greater than 250 ppm as CaCO3) should not be used as make up water for the final rinse. Likewise water with a level of combined chlorides and sulfates greater than 100 ppm should not be used. In these cases, demineralized water should be substituted. The most common methods for demineralized water are ion exchange or reverse osmosis. The chemical pre-treatment process employed must be monitored through daily chemical analysis.
The use of deionised water is essential and the conductivity levels must be controlled.
All ovens will have their temperature profiles measured using a data logger every shift.
A sampling regime must be in place to measure the salt spray and mechanical resistance of coated panels and the chromate weight of the pre-treatment.
Measurement equipment such as gloss meters and thickness testers must be externally calibrated.
The above items are indicative of some of the lengths to which, and the importance attached to, the technical competence and management control required of the coating company. These processes must be recorded in detail and made available to the powder manufacturers. Once satisfied, approved status will be awarded. Regular auditing of at least one visit per year means applicators must retain these quality procedures to keep their status.