Beckers has many successful examples of chrome-free coating systems in the field. Chrome-free primers over chrome-containing pretreatments generally produce few difficulties. Polyurethane primers, both conventional and high build, are generally most successful when it comes to incorporating the new chrome-free pigments. Some systems perform at the same level as chro-mates. Chrome-free epoxy primers can be produced, but their inherently lower flexibility introduces points of weakness for corrosion initiation at micro cracks in severely formed areas. If a chrome-free pretreatment is to be used, Beckers' ongoing exposure series must be checked for compatibility and interactions. Chrome-free pretreatments and primers can be produced successfully and with a high level of anticorrosive activity. The difficulty lies in getting the two to work together, as these systems seem, in general, to be more critical for substrate, paint and pretreatment combinations. Chromates are more forgiving, but chrome-free primers can be produced that are as effective as their chromate-containing analogs, providing sufficient attention is paid to these interactions and material selection. Accelerated tests still appear to favor chromates, but, despite all efforts to date, the answer to anti-corrosive performance in service can only be gained from real, natural exposures.
展开▼
