Q. We have a turntable washer with two stages: cleaner coater and rinse with tap water. The parts to be cleaned and powder coated are CRS sheetmetal boxes, enclosures, etc. The cleaner we used for four years worked great until recently. After the initial few days of the new bath, the parts start to develop a haze when cleaned. When it’s been long enough it’s so thick you can’t see the metal in areas where the sprays don’t directly hit. Every time I titrate and add the chemical, it disappears for a short time. The rep says the product has changed and to try something else but this was their best “iron phosphate cleaner coater.”
Right now a different product from another company is in the washer and the haze is coming back. Is this a water issue? Should I put a water softener on the water supply? Is it some kind of build up inside the washer? Should I descale? Any Ideas? J.F.
A. Since you have changed chemical suppliers and still experience the same problem, you could be on the right track with the water. First, you should check with your local POTW (Publicly Owned Treatment Works) to see if anything was changed with the way they treat the water. Have they experienced anything different? Are they treating it differently and can they show you their most recent data compared to a year or so ago (prior to the onset of the problem), regarding their water controls (which should be a matter of public record)? If you are on a well, it could be that the aquifer has changed due to varying conditions (drought or wet periods) that could change chemistry of the incoming water. Generally speaking, well water is too hard for use in most paint pretreatment systems and a deionizer would be useful. Deionizer systems can be rented and these companies have water analysis kits where they can check the level of dissolved solids and hardness.
An additional place to investigate is related to the incoming material you are cleaning. With steel coming from all over the world today, it is likely that mill and surface treatment conditions change regularly and you have to hope the pretreatment works in all the different scenarios possible. If you have a new source for your steel or if your steel service center has gotten into new sources, it is possible that there could be a different mill lubricant and/or rust preventative on the surface of your product. Also check to see if they have changed from cold rolled to hot rolled without notifying you. Some dry-film lubricants are very effective and will withstand long in-service times without corrosion, but they could also be very tenacious and difficult to remove. The combination cleaners/coaters are not formulated to be able to tackle heavy-duty soils. Some of these could leave residues that just cannot be cleaned with your current system and would require a large system with separated cleaning and phosphating. That may be why you see an improvement when you make additions, but the effect is short lived. If this is the case, you should ask your chemical supplier if it is possible for them to compound the cleaner-coater with additional surfactant in an attempt to better clean your part.
Finally you could go to an outside lab to assist in determining surface residue. A good, reasonably quick technique would be to find a lab with a scanning electron microscope (SEM) that also can perform elemental analysis by electron dispersive spectroscopy (EDS). That one test will be able to tell you what you have on the surface and roughly how much. If it is organic (carbon residue) it is likely residual lubricant. If it is inorganic (magnesium, calcium), it would probably be from the water source. This one test will cost in the neighborhood of $500-$1,000, but may save you a lot of time and rework/scrap.