Q. Dave, how do I keep the odor at bay on a three-stage iron phosphate spray line?
The majority of the stench is in the first rinse after the cleaner phosphate. The rinse is changed at 500 ppm, second rinse at 200 ppm. Due to the economy, the washer is only being used two to three times a week. We presently use calcium chloride tablets on our e-coat washer rinses, per our paint supplier at 1–3 ppm to maintain cleanliness. We also use hydrogen peroxide as a disinfectant for our R.O. storage system, and sodium hypochlorite as a disinfectant in wastewater treatment. What do you recommend for three-stage washer rinses, and what effects will it have on paint/powder adhesion? Thank you.
Looking for some fresh air, K.P.
A. It appears that you have some options available to you to try in-house. I would stay away from the bleach since that is such a strong oxidizer and could alter the chemistry of your pretreatment system and affect the quality of your phosphating. The phosphate stage will typically be formulated with an oxidizing agent to accelerate that reaction, but introducing an uncontrolled level of another oxidizing agent to that stage is inadvisable. Additionally, I do not recommend the use of hydrogen peroxide for similar reasons.
However, if you have found the calcium chloride tablets from your e-coat washer rinses to be effective, I would extend their use to your phosphate system. Calcium chloride at the level you mention (1-3 ppm) would not affect the subsequent phosphating stages or paint quality. I expect you could go higher than this without detriment to the quality of the powder coating.