Q: We notice that the cured powder does not stick readily to edges that have been cut by a laser. What are the causes of this and what can be done to overcome the adhesion issues?
A: Cutting steel with a laser offers many advantages, including precision, speed, fewer rejects, and low labor costs. However, one of the problems inherent to laser cutting is the blue oxide edge it leaves on carbon steel.
Powder coatings don’t like to adhere to this oxidized surface. Conventional iron or zinc phosphate doesn’t adequately penetrate the oxide to provide adhesion of the cured powder. This results in a loss of adhesion and the potential for serious corrosion problems.
There are a few paths to compensate for this shortcoming. One is to employ a more aggressive pretreatment process. Using a strong acid etch prior to the phosphate stage can attack the oxide layer enough to allow the phosphate to do its thing. Another option is to avoid creating the oxidation by using nitrogen in the laser cutting process. It’s more expensive than using oxygen, but it minimizes oxidation from the laser and therefore allows a conventional iron or zinc phosphate process to provide a surface more amenable to adhesion of a cured powder.
A third option is physically abrading the edges. This can be accomplished either automatically (blasting or wheel abrading) or manually. If you opt for a blasting process, it is imperative to keep your media clean; otherwise, you can contaminate the surface you are attempting to clean. ScotchBrite® pads or wheels work well but require additional labor. Keep in mind that these extra steps can be cost-prohibitive.