Metal Finishing Guide Book

2012-2013

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design and consulting firm, and we currently have a client who is interested in using products that have such alternative finishing treatments. A: I don���t have any dealings with plumbing fixture companies, but there are several non-chromate pretreatments that can be used in finishing processes. Chemical companies, including Henkel Surface Technologies and Chemetall, sell non-chromate products. You can find both companies and many others on the Internet. (Be sure to listen to Chemetall���s recent webinar on www.metalfinishing.com.) CORROSION-RESISTANT PRIMER FOR AUTOMOTIVE REFINISHING Q: I live in England and I am about to rust proof my 36- year-old Mark 2 Ford (Mercury) Capri. What would be the best primer to use after I have taken it back to bear metal? I can get my hands on red oxide fairly cheaply, but I was wondering what would be the most effective primer? After experiencing a few days under my car with a grinder, I never again wish to repeat this tiresome task. A: An inexpensive red oxide primer is not what you want. In my opinion, I would apply an epoxy primer that contains an effective rust-inhibitive pigment, such as zinc chromate. Bear in mind, however, that the use of zinc chromate is being limited in some areas due to its potential toxicity (it is a known carcinogen). Alternatives are strontium chromate, zinc phosphate, and other inhibitors. I suggest you check with your local automotive paint store. VISCOSITY OF AUTO REFINISHING PAINT Q: What is the typical Zahn cup viscosity of paints used in the auto refinishing industry? Would it be possible to coat a sphere evenly on the circumference with paint? Also, what kind of air guns would you use for this process? A: The approximate viscosity of solvent-borne automotive paints is in the range of 22���30 seconds on a Zahn No. 2 cup. It should be possible to coat a sphere evenly at this viscosity. If you are located in the U.S., you would probably want to use an HVLP spray gun. Alternatively, if you live outside the U.S. and are not required to meet environmental regulations, you can use a conventional air spray gun; either pressure fed or siphon will work. SELECTING BETWEEN AIRLESS AND HVLP SPRAY GUNS Q: As part of a low-cost basement-refinishing project, I would like to leave the ceiling unfinished but paint it black. I own a 30-gal compressor and will be using a 2 �� -gallon pressure tank. Which type of spray gun would you suggest for a quick application where coverage is more important than finish: traditional airless or HVLP? Since it is an enclosed area, I am concerned about overspray; ventilation is limited. A: You would be better off using a commercially available airless spray gun rather than a high-volume low-pressure (HVLP) spray gun. HOWEVER, I must warn you to please read the instructions and thoroughly familiarize yourself with its operation. Since such guns operate at pressures usually in excess of 1,000 psig, they can be dangerous, and it is critical you understand how to operate it safely. For your situation, the advantage of airless over HVLP is you can get the job done quickly without generating much overspray. HVLP will generate signifi610

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