Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

Issue link:

Contents of this Issue


Page 620 of 707

Process Degreasing Cleaning Cleaning Electropolishing Activation Rinsinga Drying a Type Solvent spray Alkaline soak Electrolytic Electrolytic Acids, strikes High-velocity sprays Blown hot air Time (seconds) 10-15 15-30 12-20 5-15 4-12 3-5 15-45 (incl. cool down) Adequate rinsing can be accomplished in approximately 3-5 seconds with well-directed, high- velocity sprays. The importance of good rinsing and the short time usually allowed for this operation in continuous plating equipment dictates the rinsing stations be inspected at regular intervals to assure that all the nozzles are functioning. 2. 0.95 A-hr/200 A = 0.00475 hr at 200 A/ft2 . 3. Rate (ft/min.) immersion time (min.) tank length 25 0ft/min.) [60 0.00475] (min.) = 7.125 ft. Note: When estimating the maximum current density that will be used, an important factor that must be considered is how much current can be carried by the strip, and in particular, the carrying strip, or bandolier, both between the con- tact to strip location and between the carrying strip and the contacts being plated. The small cross-sectional area limits the amount of current that can be conducted without causing excessive heating, thereby drying the strip out between stations, oxidizing the surface, or actually melting it. Because of this, the maximum high current densities allowed by high-speed solutions sometimes can- not be employed. When possible, it is advisable to perform conductivity tests on the actual materials to be plated. A very simple technique is to use a given length of the strip to conduct DC current. Increase the current gradually until water, applied by a spray bottle, dries too rapidly, indicating that in production the strip should not be expected to successfully carry more than that current. PROCESS CONTROL The importance of good process control in continuous reel-to-reel plating cannot be overemphasized. First, there is the fact that but a few seconds are allowed in each solution, rather than several minutes as in barrel or rack lines. Second, electrodeposits on electrical components are there to provide function, reliability, and long life; hence, the quality must be consistently good on every inch and on every part in every reel. Third, there is the aspect of cost. High costs can be incurred as a result of subsequent manufacturing and assembly prob- lems due to intermittent and undetectable plating defects within the plated reels, and can also result from excessive use of gold or other precious metals because of processing irregularities. The frequency of solution analysis, which should include the preplating as well as plating baths, should be established on the basis of operating time, factoring in such items as the types of materials being plated (i.e., plating specifications, drag-out capacity, A-hr consumed, and machine speeds). Process control charts maintained at each station signal trends and help avoid out-of- spec operation. Note: In designing the processing tanks, the reservoir cell should be constructed to hold as much solution as practical to help control fluctuations in concentrations 619

Articles in this issue

view archives of Metal Finishing Guide Book - 2011-2012 Surface Finishing Guidebook