Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 99 of 707

Chemistry, pH 12.5 Turbulation with rotation, no oil separation Cycle time, 10 min. At this point one might need to introduce ultrasonics as the mechanical cat- alyst in the equation. The cycle is getting long and the temperature is getting high. By introducing a high degree of mechanical action it may be possible to reduce both: Temperature, 140° F Chemistry, pH 12.5 Ultrasonic with rotation Cycle time, 5 min. REAL LIFE A manufacturer of aviation hardware was using a vapor degreaser to remove oil and 50% nitric acid at 170° F to deoxidize aluminum parts prior to brazing. By using ultrasonics it was possible to combine both processes in one clean line. 1. Ultrasonic degrease in an aqueous-based solution pH neutral at 140° F. 2. Hot water rinse. 3. 5% citric acid at 140° 4. Deionized rinse at 160° 5. Deionized rinse at 160° F with ultrasonics. F. F. 6. Hot air dry. The capital equipment cost to the manufacturer was $160,000; however, because of savings in operating costs by eliminating the degreaser and eliminating waste dis- posal of the nitric acid, the R.O.I. was less than eighteen months. Moreover, this process is much safer and gave the user a dramatic increase in quality. The main factor in this application is that the ultrasonics allowed this man- ufacturer to use a much less hazardous acid by adding a high degree of mechan- ical energy to the process, thereby enhancing a neutral pH bath for thorough degreasing instead of 1,1,1-trichloroethane. Another example of the successful application of ultrasonics is in plating; espe- cially in reel-to-reel plating of strip. Most plating lines use strong alkalines at approximately 170° F and electrocleaning for soil removal at the beginning of the plating line. In many cases the strip or parts have gone through a vapor degreas- er. The problems with this type of cleaning are that it limits line speed, and high pH chemistries are usually not free-rinsing. This causes contamination of the plat- ing baths with carryover and high rinsewater usage. The parts also must be degreased prior to plating because high pH tends to emulsify oil and deplete the chemistry. By using high-intensity ultrasonics most of these problems are elim- inated. Ultrasonics is being used in reel-to-reel plating with a pH neutral deter- gent at 140° F in place of the electrocleaner. Because of the neutral detergent any oil will float and can be separated with a coalescer. This often leads to the elim- ination of the vapor degreaser prior to plating as well. It is free-rinsing and, in most cases, the line speed can be doubled. The advantages are many: the plating baths do not get contaminated, water usage is cut in half, product quality is more consistent, chemical and waste treatment costs are lower, and output of the 98

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