Issue link: http://www.e-digitaleditions.com/i/715656
All this may be a moot point. What are the expectations of the coatings perfor- mance? Should it be only decorative with good bonding? Or are you look- ing for superior corrosion perfor- mance? My guess is that it's primarily decorative. In this case, my recom- mendation is to satisfy the customer, give him what he wants, and don't argue! Good luck. Switching from a four-stage washer to a bacteria oil-eating process Problem We are a display manu- facturer, and we have a four-stage washer: typical alkaline, rinse, iron phosphate, and rinse. It was suggested to us to use bacteria cleaning instead of what we do now. It's supposed to be cost-effective compared with heating and chemical use, and it's MWRD (Metropolitan Water Reclamation District) safe. Do you know of any benefits and downfalls with this? Or is it just beneficial to some companies compared with others? J.O., Des Plaines, Ill. Solution First, I haven't seen this process in operation. Generally, I only recommend systems that I have had a chance to really investigate firsthand. So my comments should be taken as more data rather than as an absolute. Some people I have talked with say this process does and can work in certain cases, especially when you have limited parts and very light oil. Others I've talked with say that it's problematic with high production (square footage) and with anything that has more than the light mill oil found on high quality cold rolled steel. If you're processing parts that are formed and drawn with extra processing lubricants, be very cau- tious. Another person I talked with who was going to use it and get back to me if it worked well, never got back to me. You mention that you currently have a four-stage process with an alkaline cleaner in the first stage. If you had said that you had a three-stage process with a cleaner phosphate and had achieved ex- cellent cleaning with it, you could have had a chance to succeed with the bacte- ria oil-eating process. If you could tell me that you really understand what ex- cellent degreasing is and that you have never had any cleaning issues through your four stages, you may still have a chance. My guess is that if you currently need an alkaline cleaner to be successful, then you may not be a candidate for this relatively new process being offered. I would highly recommend that you visit three to five plants currently using it. Compare their incoming metal qual- ity with your metal and soil conditions. Compare the tank volumes and square footage of metal with your situation. Ask the user and the person who main- tains and documents the process tough and direct questions. Most finishers are direct and honest when you personally visit and talk directly with them. I al- ways ask the following questions: • What would you do differently or better given the opportunity to live with this process for a year or two? • What is the best part of this process? • What are the limitations or problems you've had to deal with now that you've worked with the process? Finally, if you are really sold on this technology, do you have the opportu- nity to put in a small pilot process for a limited volume of small parts? You can really determine the positives and neg- atives of any system, once you have it online. I hope this information helps in your decision-making process. Removing ash from racks after cleaning in a burn-off oven Problem Do you have any info on removing ash from racks that have been burned off in a burn-off oven? We use a pressure washer, but it's messy and doesn't do that great of a job. Do you know of any chemical processes that would work in a dip line? T.F., Alexandria, Minn. Solution The problem you refer to is one that plagues many powder coaters. Remaining ash from hangers or hooks presents a problem for virgin parts. If the hanger operators get ash on their hands and then touch raw CRS parts, the ash remains. This new soil isn't alkaline-sensitive; it's acid-sen- sitive. I've seen cases with voids in the phosphate deposition after treatment and drying because the acidity in the phosphate stage was used to remove the ash. There isn't adequate remain- ing time to complete the phosphate deposition, and this leaves the void, or un-phosphatized area, on the part. What to do? First, make sure the strip oven is oper- ating at peak parameters. A well-de- signed and functioning oven should remove the great majority of ash, just like it did when you sent hooks in for a test before buying the strip oven. Second, remove the hooks while they are still warm. The high-pressure spray you mention usually does the job. If not, and your high-pressure hot water sprayer is capable of phosphatizing, spray with a ±5 percent concentration of pH acid additive (phosphoric). If the pressure washer isn't capable of inject- ing acid, then use a small acid-resistant tank for final ash removal. In this case, fill the tank with ambient water, add 5 to 10 percent phosphoric acid and soak ash-laden racks and hooks for 3 to 10 minutes. Follow with a pressure rinse. Make sure to follow all safety require- ments outlined by the chemical com- panies' material safety data sheets (MSDS). If the hooks are carrying heavy parts, cast iron engine blocks, for example, you should ensure that no hy- drogen embrittlement occurred. In those cases, a degassing process in a cure oven may be necessary, so use caution. PC Editor's note For further reading, see articles under the Surface preparation heading in the "Index to Articles and Authors 1990- 2015" Reference and Buyer's Resource Issue, Powder Coating, vol. 26, no. 6 (December 2015), or click on the Article Index at www.pcoating.com. Articles can be bought online. Have a question? Click on Problem Solving to submit one. 28 POWDER COATING, August 2016