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emulsified oils in the solution. This soil load can be performed by collecting a specific volume in a stoppered graduated cylinder, and carefully adding phosphoric or sulfuric acid (for alkaline cleaners) and/or excess table salts. The soils will float to the surface of the cylinder, and the volume can be measured. The surfactants in the cleaner may also come out of the solution, so you want to perform this test when the bath is fresh, and compare to future values as they increase. While many programs use single-stage washers, adding a rinse stage will improve cleaning and reduce residues. The rinse stage will flush away the soil-detergent complexes and complete the cleaning process. Rinses, monitored by conduc- tivity, should be neutral and overflowed to remain clean. With any aqueous program, corrosion of cleaned parts is a concern. Corrosion can occur within the washer program or after the cleaning stage is complete, or while parts are in storage. To mitigate corrosion, cleaners can be formulated to include rust preventive agents, which can be used in single- stage washers, or applied with an aqueous rust preventive after the rinse stage. Rinsing will eliminate the rust preventive's performance, so allow the rust preventive to dry on the surface of the parts. Drying of parts will lessen the potential of surface corro- sion. Air blow off, drying media or ovens can aid the drying process, as does heating the final stage of the washer. Potential for corrosion in aqueous washers increases when "afflictive ions" cycle up in the final stage. These are most typically chlorides and sulfates, which are present in most tap water at various levels. As water evaporates from the cleaning stage, these afflictive ions increase in concentra- tions. Monitoring the level of chloride and sulfate over time and establishing upper limits for your process will help assure corrosion-free production. Use of RO or DI water may be required if levels are significantly high in your tap water. The potential for corrosion is directly related to humidity levels, so the summer months are the most challenging periods. Adjusting the level of rust preventive to compensate for humidity levels is a very good idea. Cleaning and rinsing are the most important steps in any aqueous cleaning or pretreatment program. Having a full understanding of the machining program and the specific challenges that it poses to the cleaning of parts, a shop can design and operate a parts washing process that ideally fits its requirements. Controlling the chemistry and the filtration process, both in the machining and washing steps, are essential for success. This includes proactive maintenance (filtration, soil removal and cleanliness testing) and effective troubleshooting. With proper design and operation, you can be assured of consistent premium quality production at a controlled cost— the foundation for a sustainable and competitive manufac- turing program. David Gotoff is a product manager at Chemetall US. Call 800-526-4473, or visit chemetallna.com ® Clean Parts. Tel. 716.763.4343 ■ www.miraclean.com ■ Clean Lines ■ Passivation Lines ■ Aqueous C hemistries ■ Data Management 36 NOVEMBER 2015 — pfonline.com PARTS CLEANING