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POWDER COATING, March 2016 35 By popular demand, we're bringing you a series of past pretreatment problem columns, representing the best of Brad B. Gruss, our columnist for more than 20 years, who has retired as president of the consulting firm, Pretreatment & Process Con- sulting LLC. Brad specialized in training, troubleshooting, and inde- pendent line audits for pretreatment processes. In his more than 30 years in the industry, he made numerous presentations on pretreatment for powder coating. Extending bath service life when prepping aluminum Problem In my powder coating shop, we're working with a substrate from a client that is 91 percent alu- minum and 9 percent silicon. The product is for architectural use next to the Caribbean sea. We use a degreasing and phosphatizing tank (both in one tank). We would like to increase the service life of this product, so I'm won- dering what would be the best pretreat- ment option. Also, is there any other test or machine available that could predict the service life of the parts faster than that of the salt-fog test, or is the salt-fog test ideal for predicting the ser- vice life of this type of part? Thanks in advance. J.S., Medellin, Antioquia, Colombia Solution Thanks for the question. For starters, I think you should read the two-part article titled "Aluminum pretreatment: Old issues and new developments, part I and II" that ran in t his m aga z i ne 's Octobe r a nd November 2003 issues. You state that you have a cleaner-phos- phate in one tank for the aluminum preparation. I hope you also have at least two rinse tanks after the combina- tion cleaner-coater. An ideal final rinse for any aluminum preparation is deionized water. You also mention that you would like to extend the service life of the bath. You didn't mention what you are currently getting for bath service life or how many lineal feet or square feet of production you're doing. When you have a very limited process, you should be careful when trying to extend the service life of a bath that is probably already highly burdened. However, one method to ex- tend bath service life in your particular case is to bleed and feed the chemical tank. Consider draining approximately 10 percent to 25 percent of the bath and then replenishing with fresh water and chemical. This will drain off spent chemicals, dissolved and precipitated solids, and reacted aluminum from the substrates you're pretreating. You may also want to check with your chemical supplier to find out if the chemical you're using has some fluoride source. This is a common ingredient for iron phosphates that are used in a mixed-metal line. Some companies offer a fluoride additive to boost or in- crease the etch rate of the chemical. I hope this gives you a starting point. Good luck with your efforts. Lowering energy bills Problem Is there a nonsolvent-based, ambient-temperature pretreatment avail- able that can perform like my current pretreatment process, which is a four- stage wash system (phosphate, rinse, rinse, and reverse-osmosis and sealer)? I would like to cut my energy costs with- out compromising quality. I use three heated wash systems on all kinds of sur- face conditions (oil and grease). Are there some chemicals available that could do the job? Maybe some citrus-based prod- ucts? M.S., Phoenix, Ariz. Solution Saving money is a good idea, especially energy savings in monorail spray power washers. A lot of studies have been done in energy cal- culations for washers. The great major- ity of energy is consumed or wasted in the heat loss caused by the solution being sprayed. Most energy surveys I've been involved in show that the greatest savings can occur at 140°F or greater. You don't mention what tem- perature you're operating at, but if it's greater than 140°F, you can probably save energy. Chemicals are designed to provide effective cleaning at 85°F to 95°F. Ask your chemical suppliers if they have a cleaner-phosphate that will operate in that range. In addition, ask your suppliers what the cloud point of the surfactant pack- age is. Cloud point is the temperature at which a detergent or surfactant be- comes partially insoluble. This is the temperature at which the solution be- comes nonfoaming or at which point controlled foaming can take place in spray applications. Should you desire to save energy, you should also conduct a soil audit in your plant. Identify all incoming soils on the metal you're pretreating, and look at all the additional soils you apply in fabrica- tion. Make changes in any soils that con- tain heat-sensitive waxes, such as paraf- fin wax. When you control the incom- ing soils and select those soils for less dif- ficult removal, you can then place less demand on the washer and process. Remember, it's great to save money in any finishing process, but if you save so much that you no longer provide a 100- percent water-break-free surface with an effective clean water rinse and a com- pletely dry surface, then you are dollar foolish. The other caution on cleaner- coaters designed for low temperatures is that they generally must be highly accel- erated. They work best when you set them up properly and control the chem- ical parameters consistently. Good luck in your investigation. Brad B. Gruss Pretreatment & Process Consulting LLC BEST OF PRETREATMENT PROBLEM SOLVER