Proper surface preparation is the single most important aspect of a powder finishing system should you wish to maximise powder performance.
The following tests and requirements are directly influenced by the type and quality of the pretreatment on the metal substrate that is to be powder coated:
The procedure required to obtain a suitably prepared surface depend heavily on the type of substrate but in most cases the following steps are required:
The cleaner will depend on both the substrate and the soils to be removed e.g. synthetic draw lubricants are much easier to remove than a buffing or polishing compound. Metal oxides (rust) need to be removed at this point as they will act as a barrier to powder coating film adhesion. This is normally achieved by using an acid deruster.
The effectiveness of the cleaning operation can be checked by:
Conversion coatings are materials and processes that impart corrosion resistance better adhesion properties to a metal substrate. The type of conversion coating depends heavily on the nature of the substrate as well as the desired properties of the coating.
A passivator (seal rinse) is applied over a zinc or iron phosphate to increase the corrosion resistance of the coating and to improve adhesion of paint and organic finishes. Passivation is important if components are going to be stored or transported between chemical treatment and powder coating.
The work pieces are rinsed between stages to prevent cross contamination of process solutions and to reduce chemical consumption. The final rinse prior to drying is to remove any unreacted chemical or salts that could adversely affect adhesion. Remember that a part is no cleaner than the quality of the rinse water used.
Click here for a process example - Mild Steel Components