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The Failure Analysis Forum: Metal to Primer to Polyurethane Failure

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    • CommentAuthorRon
    • CommentTimeMar 3rd 2010 edited
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    I am having some bonding issues with a metal primer to polyurethane. All I have is the failed parts and no idea of the processing of these parts as it occured. I feel like a time detective having to go back in time to the scene of the crime....but I am not having much luck. I am trying to duplicate the same failure now with times/temps/prep/etc, but I am unable to reproduce the same effect. Actually, I am quite impressed with the primer and how much abuse I can give it and still have it bond with the Polyurethane.
    The general process for manufacturing is sandblast the part, blow off with compressed air, clean with MEK until no residue comes off, prime the part, cure in an oven at 200 F for 30 min, remove, and than process in a P.U. mold back at 200 F for 20 min. All parts follow this process with no problems.

    The (second) picture is of Naval Brass. The primer seems quite well bonded to the metal as it is hard to scrape off. I am curious to know what caused those swirl marks in the P.U./primer interface. Generally speaking, the P.U. did not bond at all with the primer.

    The (first) picture is on Stainless Steel. The primer that remains on the Steel seems to be well bonded. The big area of primer missing did pull off and remain on the Polyurethane. As for the P.U./primer interface, the P.U. pulled off very easily with no bonding at all.

    If anyone has seen similiar scenarios or has any input on possible casues, I am all ears. Thanks.

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