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Paint/Protective Coatings Engineering: We have a crazing problem in our powder coating . Give us some direction

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    • CommentAuthormatco
    • CommentTimeFeb 14th 2007
     permalink
    All cracking in paint coatings are caused by stresses on the film and
    substrate. Following are definations and my comments relevant to crazing:

    Cracking - An advanced stage of checking or crazing whereby the breaks in
    the film are so deep as to expose the underlying substrate. Usually occurs
    as straight lines, often running with the grain.

    Checking - In between cracking and crazing. Larger cracks than crazing,
    less total cracks than crazing, but not always seen in straight lines with
    the grain unlike cracking.

    Crazing - The appearance of minute, interlacing cracks or checks on the
    surface of a dried film. Usually seen as an extreme amount of tiny cracks.

    Causes of Cracking/Checking/Crazing:

    Improper cure of a coating.
    Excessive build of a coating.
    Over catalyzed product.
    Cold coating, material, and/or environmental conditions during
    application, drying, and curing.
    Extreme variations in environmental conditions the finished product is
    subjected to.



    Prevention of Cracking/Checking/Crazing:

    Allow coating to cure under normal room temperature conditions.
    Avoid excessive build (more than 3 coats).
    Apply coating in thin (3-5 wet mil) coats.
    Catalyze at the correct ratio.
    Have and use all coating, material, and environment at normal room
    temperature conditions. Avoid excess heat, cold, humidity.
    Avoid having the finished product in an environment with extreme
    variations in environmental conditions.

    Possible Fixes for Cracking/Checking/Crazing:

    What are the environmental conditions, both during application and cure?
    Have things changed, including equipment and personnel?
    When in the finish process did you notice the problem?
    Has this problem happened before?
    If so, what were the conditions at that time, especially compared to the
    current conditions?
    Has the product been catalyzed properly?
    Where are the cracks located on the finished product?
    Has the finished product been through any extreme environmental changes?
    Protection Protection
  2.  permalink
    I Know that this sounds stupid but how do you store you powder? What product is it? Is it in date?

    If all is good, then how about taking a DSC and getting it lab tested.

    If the DSC is good, check your substrait preporation. If its grit like G24 for e.g. drop some in water to see if there is any trace of the oil look. so you know to replace it. What are you preping to and with?

    Are you using a temp stick to check the substrait stemp before application? There is no better way for powder application. Dont use pyrometers or I.R, guns. Myself and many others are not big belivers in them.

    I hope that some of this will help.

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