“What would prevent or what would be a possible cause for a powder paint not to adhere to the surface of a steel tube?
Water soluble rust proofing has been applied to this tube. The pretreatment process has 5-stages including a phosphate wash. The steel tube isn’t the only problem,
the painter is having problems with a pure aluminum also.
The painter says they haven’t changed any processes and the tubes look just as they have for several years. The painter goes on to say that just over the past 6 months have they had any problems.The painter is also having problems paint thickness and has slowed down the conveyer so that the parts have a longer cure time. What can you tell me?”
“Loss of adhesion can happen as a result of several process issues. First, is the part clean? A five stage washer should clean most organic soils from the part if it is properly maintained. However, if you have inorganic soils on the part or the process is out of control, then the washer (no matter how many stages) is not doing the job.
Second, is the powder out of date or too old? As powder coatings reach their maximum shelf life (approximately 6 months) then the powder’s properties can start to fail and result in loss of adhesion.
Thirdly, is the part fully cured? Performing a solvent cure test in accordance with PCI Test Procedure #8 should tell you if the part is fully cured. Uncured powder coatings can easily fail adhesion tests. The vendor’s cure oven may not be operating properly, so just slowing the line speed down will not correct the problem. An oven profile should be performed on your part in a fully loaded oven to ensure that the part’s metal temperature reaches the temperature specified by the powder supplier for the prescribed amount of time (dwell time or cure time).”