Q. I am a loyal reader of PRODUCTS FINISHING and just finished reading the June issue. You are always very thorough and descriptive. I observed your response to E.P. regarding the phosphate cleaning systems. Another suggestion I have regarding cleaning from the bottom up is that it helps keep the part wet while cleaning other areas. I often liken it to my customers who are familiar with conveyorized lines that you want to keep the part wet from the time it enters the 1st stage until it exits the last. By cleaning a large part from the top to the bottom, the top portion may have an opportunity to flash dry depending upon the process temperature and environment. This can allow for soil re-deposition and or drying of un-reacted phosphate salts. Rinsing from the top to the bottom ensures complete rinsing and removal of all cleaner/phos residue. Another option on large work pieces is to have an additional person in the wash bay for rinsing purposes only. T.B.
A. As always, I appreciate the reader feedback. I guess I had just assumed that somebody would know to keep their part wet when doing hand phophatizing (kind of like keeping your car wet when washing it to keep the soap from drying on), but didn’t think that would have been the reason for suggesting that cleaning be done from the bottom to the top. I would still recommend that the cleaning be done from the top down. However, if it is impossible to keep the part wet or if the person doing it can’t be persuaded to do so, it would be preferable to wash from the bottom up rather than allowing chemical and residue to dry onto the surface. Dried on chemical and contaminant residues will be harder to get off once they have dried and could cause more problems than if it were not pretreated at all, if not adequately rinsed. So while it is not optimal to wash from the bottom up, at least it insures that you keep your part wet.