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pfonline.com/experts 44 NOVEMBER 2015 — pfonline.com p f o n l i n e . c o m / e x p e r t s PAINTING C L I N I C MARTIN POWELL Global Finishing Solutions paintingclinic@pfonline.com Importance of Drain Stage Length Q. What is the importance of drain stage length in pretreat- ment systems? A. Many people in the industry do not believe that drain length is important because it's not a process. But it is a process. Simply put, it is the process of drainage. In manual systems, drain time is not as important because many times overflow is sent to waste. In inline systems, everything is governed by time/line speed, and for drainage, how far the water flows in either direction. Chemical processes are designed by chemical strength, temperature and takt time. Rinses need to be clean water (city water, RO water, DI water and so on). Try not to rinse with dirty water, and remember that some city water and tap water is not clean enough for industrial use. Lack of chemical strength due to dilution does not provide the correct process function. Contaminated rinse water does not rinse and does not allow the next process to be properly performed. Drain time and stage length keeps the next tank clean and does not dilute chemical concentration. Everything in a system is designed to provide the end result that you the customer has deemed important. Make sure to hang your parts to watch how far water drains in both directions and how far it "shoots" off the part. Design the drain stage to capture this draining water so the process parameters will remain where they are supposed to be. Grit Blasting versus Washing Parts Q. Can you please explain the difference between grit blasting versus washing parts? Which is best? A. This is an easy question if the finishing specification is defined. In most cases, we want the best finishing and adhesion we can get, but getting the ultimate can be very expensive and may not be required. If not required, is it a waste of money and effort? Only the customer can answer this. Once you know what is needed you can move forward. In grit blasting, an abrasive material is used to remove scale, rust, hard rough contamination on the surface of your product, which must be able to withstand such an aggressive process. It is not used to remove oils and it does not apply a conversion coating. It is the most basic method of cleaning and can be very effective depending on the finish requirement and product end use. Be aware of a product that must be blasted. Wash off oil or grease before you blast. If you don't, then all your grit will be contaminated and your part will still be dirty after you blast. Washing is more accurately described as pretreatment because that is exactly what is happening: treatment of the product. The highest performance of coatings and product pretreatment is aqueous cleaning. A manual high pressure wand system may be the most effective for larger products. Dig Deeper Searching for in-depth analysis of a painting process or technology? Look no further than PF's new Research and White Paper Zone, an entire section of our site dedicated to free papers and presentations from leading researchers in the finishing industry. pfonline.com/zones/technology Inline washers and pretreatment systems are the ultimate. When the cleaning method has been defined by a chemical company to match your specified requirements, the equipment supplier can build the proper pretreat- ment system. These systems offer consis- tency and repeat- ability for an excellent finish. Plastics and composites are typi- cally cleaned with aqueous solu- tions to remove mold release agents and surface contamination. Various suppliers can help you determine the best process for you once you have the following information: • Define the finish requirement (do some reading!): Salt spray? Adhesion standard? Indoor use or outdoor use? • Define the coating type: Water-based coating (requires excellent cleaning), powder coating (requires excellent cleaning) or solvent-based paints or coatings (slightly more forgiving of surface oils). • Look at your budget, but make your decision based on the quality of your personnel and equipment. • Quantity of parts: Is production required? Low produc- tion enables more flexibility, while high production can be much more challenging and more expensive. • The area you have available for these processes. • Talk to many suppliers, ask for proof and go look at other installations. Global Finishing Solutions' Martin Powell has 33 years of expe- rience in the finishing industry. He has bachelor's degrees in marketing and business administration with a minor in inter- national management. He has been published in several trade journals. For information, please call GFS at 800-848-8738