Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 67 of 707

become further complicated by environmental restrictions imposed by federal and local regulations and by corporations themselves. For example, a specific require- ment given for a spray cleaner was that the product must be safe on most met- als within the specific allowed cleaning time, but must also be free of phos- phates, silicates, chelators, and nitrites; have a low COD/BOD; and have an operating pH between 8 and 9. If, for example, some of the restrictions encountered when formulating a cleaner were applied, it would have to have the following characteristics: Chromate free Phosphate free Silicate free Fluoride free Chelator free Nitrite free Amine free Low COD Borate free Noncyanide Noncaustic Solvent free No foam products High flash point solvents Powders or liquids Low BOD Emulsifier free pH of 7.0-9.0 Some of the reasons for these restrictions are self-evident such as cyanide free, solvent free, chelator free, and phosphate free. From the collection of restrictions given one may readily note that the prod- ucts of the future must be not only safe to the environment, but also relatively safe to use in the work area, and provide a cleaner that will allow the separation of the soil from the cleaning solution. PROCESS ALTERNATIVES The method or combination of methods selected to clean parts is critical and will depend upon the type of final finish (plated, painted, anodized, etc.) and whether it is an in-process cleaning operation, or just a final cleaning. And, of course, the oth- er paramount factor to be considered is the volume of work processed per hour. The cleaning methods given may be used independently or in conjunction with one another, as in a preplate cleaning cycle, where three to four modes of clean- ing are used. Immersion (Rack or Barrel) Rack immersion may utilize air agitation or work agitation to improve or short- en the cleaning time. In barrel lines the movement of the barrel will provide the necessary agitation to flush cleaner solution through the parts. Power, Spray Cleaning Spray washers (spiral spray, belt washer, spray strip line, cabinet, and monorail- type washer) provide reduced cleaning time by utilizing impingement to clean parts that may not respond to conventional soak cleaning. Spray pressures may range from 14 to 200 psi, depending upon the type of machine used. Some continuous strip spray washers may also utilize rotating brushes along with the spray cleaning solution. Ultrasonic Cleaning Ultrasonic energy is utilized in conjunction with aqueous cleaners or hydrocar- bon chlorinated solvents to clean parts. Areas of application are small precision parts, parts with complex configurations, removal of tightly adhering or embed- 66

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