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PFonline.com/experts DAVID S. PETERSON Consultant David has been involved with the parts cleaning industry for almost 30 years, and is author of "A Practical Guide to Industrial Metal Cleaning." A. Probably not. Cleaners that are formulated to clean metal like stainless steel usually cannot be used for aluminum. Since industrial processing of stainless steel (forming, bending, cutting, etc.) is typically more demanding than a similar operation for aluminum, the lubricants used can be difficult to remove. Therefore, most aqueous alkaline cleaners formulated for use on stainless steel have a high pH and will contain quite a bit of free caustic in the form of sodium or potassium hydroxide (in addition to ingredi- ents like surfactants and buffers). If a cleaner like this is used on aluminum, it tends to etch the surface. This condition will be made worse with elevated temper- ature and longer periods of time. Additionally, the higher the concentration of the cleaner, the worse the etching and discoloration. Free caustic will quickly reduce the naturally-occur- ring oxide on aluminum and immediately start to etch and dissolve it. Most industrial aluminum is alloyed to attain specific properties (typically with copper, manga- nese, silicon, magnesium and zinc). The discoloration of the aluminum is the presence of the undissolved alloying elements and the secondary phases that they form that are not attacked in the high pH bath. They wipe off fairly easily, although chemical removal is generally only attained by use of an acid (like nitric) to dissolve these alloying elements. How to Improve Zinc Phosphate Quality Q. I am a quality inspector and want to know some of the reasons for poor phosphating. Our customer complains that they saw a white spot in the zinc phosphate coating. How do I troubleshoot my zinc phosphate quality issues? A. The zinc phosphate chemistry and process is complex and there are several potential failures. If the problem appears to be one that is localized to a few parts, I suggest further examination of your racking and rinsing process. It is important to identify problem parts as soon as they come off the line. Are the spotted areas occurring Can Aqueous Alkaline Cleaner Be Used on Aluminum? Q. We use an aqueous alkaline cleaner to process parts with ultrasonics and filtered circulation. The process does well on stainless steel parts, but I have an issue with aluminum parts, using the same parameters, minus the ultrasonics. The aluminum parts come out of the bath with dark, black streaks and spots. Should I not use the same bath to process aluminum and stainless steel? Can aqueous alkaline cleaner be used on aluminum? where the parts contact the rack? Are they occurring in an area with the most draining of fluid from the parts? If so, you may need to consider a new method to rack the parts, an alternative material for the rack itself or make improvements to the rinse water quality. This may involve more frequent dumping of the tank or an increased overflow. A good way to monitor and maintain consis- tent water quality is to use a conductivity sensor hooked directly to a solenoid valve that will open when the conductivity of the water becomes too high. How to Control Citric Acid Concentration in Wastewater Treatment Q. We are treating ammonia wastewater, however, it is connected with the sanitary wastewater, which is often blocked. We have used citric acid to effectively clean it in the past. How can we tell the concentration of the acid and whether or not it will adversely affect the system? A. It is easy and relatively quick to make up a control proce- dure for a simple acid or alkaline solution. In your case, you should make up a solution of citric acid at approxi- mately the same concentration that you used by adding a known weight of citric acid to clean water (ideally deion- ized or distilled). You then accurately sample it (25 mL, for example) and titrate that solution with a base of known concen- tration (0.1 N sodium hydroxide, NaOH) using phenol- phthalein as an indicator. As you add more drops of the sodium hydroxide standard to the citric acid solution with stirring or agitation, the phenolphthalein indicator will turn from colorless to pink. At that point, the titra- tion is complete. The next step would be to determine a strength factor for any future titrations by dividing the concentration of the citric acid solution you originally made by the number of milliliters of the sodium hydroxide standard solution used to get to the equivalence point of the titra- tion (when the color change occurred). 34 MARCH 2017 — PFonline.com PARTS CLEANING C L I N I C Industrial processing of stainless steel is typically more demanding than a similar operation for aluminum.