Please advise if you know of a best practice for cleaning or other surface preparation for e-coating that needs to be “secondary crimped.” L.N.
I guess I am not sure of the exact manufacturing process you intend to do when you describe “secondary crimping”. I will have to assume there is an initial crimping in your manufacturing process, followed by a secondary crimping after the part is painted. In general, there is nothing in particular you can do to the pretreatment to make the paint more flexible. Proper selection of the paint will probably be the most important factor to consider. To achieve the maximum performance from that paint, a high-quality surface preparation would allow the paint to achieve its highest performance.
In general, I do not think there is a significant difference in the flexibility and adhesion resistance of the two general resin systems for e-coat (epoxy and acrylic). Within those categories, however, there may be formulations from specific suppliers that are made to be more flexible than others. Considering the growing size of the pre-finish metals market, there must be many paints out there that can handle relatively severe forming without adhesion loss.
A paint’s performance can only be as good as it’s pretreatment, though. As mentioned above, there are no pretreatments available that will actually enhance the flexibility of a paint, but choosing the proper pretreatment in order that a paint can perform optimally is important. In your case I would recommend an iron phosphate system. If the part requires removal of a significant amount of forming oil, then a five-stage system would be preferred. The first stage would be to degrease the part followed by a rinse (second stage). The third stage would be the iron phosphate followed by a rinse (fourth stage) and seal (fifth stage). If there is minimal or no oil on the part, then a three-stage system could be used. You can eliminate the first two steps mentioned above. The iron phosphate would then incorporate some surfactants into it to remove any light oils that may be on the part. You would have to let your chemical supplier know of your intentions before they would be able to make a recommendation. To find a list of suppliers, visit www.pfonline.com/suppliers.htmland search under “Cleaning and Pretreatment,” “Cleaning and Pretreatment Chemicals” and finally “Phosphate Coating Chemicals.” There are a number of good suppliers that will be able to further specify your process.