Metal Finishing Guide Book

2013

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2. Organic contaminant caused by brightener breakdown or soils/oil from poor cleaning. Look at peroxide/carbon treatment for improvement. 3. Stress can be monitored through stress tabs or spiral contractometer. This will allow a more direct evaluation of treatments. 4. Certain metals can co-deposit and cause stress. Look for low current density darkness in the hull cell. These metals can be dummy plated to remove. 5. Check iron levels and peroxide treat if necessary. Iron can cause HCD defects. Keep below 20 ppm for your application. 6. Always make sure basic chemistry is correct. Low nickel, low boric, high pH can all cause high current density issues. Start here. If you find there is no blistering on a test panel, then it is likely that your issue is related to preparation. Investigate to ensure parts are free of water breaks. Check for sufficient oxide removal as well as excess pickling. As Yogi Berra used to say about plating, "90 percent of the plating game is half preparation."  Q: I have alkaline-free cyanide zinc plating baths; the temperature is now 35°C. How can we cool down the solutions in order to have better conditions? Is there a product that works at high temperatures, or what kind of equipment should we use? A: Cooling coils in the plating tank or a heat exchanger connected to an industrial chiller are recommended for alkaline zinc plating. There are zinc brighteners on the market that work well (enough) at elevated temperatures, but none are as bright across all current densities as a lower temperature bath operated at 25 degrees Celcius. Different additive levels and bath parameters are required at the higher temperatures. You can expect to use more brightener, and you will find that some low current density areas tend not to be as bright as the lower temperature process. This may not be objectionable once the parts are bright-dipped and chromated, as both steps will tend to polish out dullness in the deposit. A stronger (or longer) bright dip step will help compensate for poor low current density brightness in the zinc plating. High polishing blue chromates are also available to further your cause. Your ability to produce acceptably uniform brightness may depend upon, to some degree, the geometry of the parts. Large flat surfaces tend not to polish nearly as well as round surfaces. Air agitation during polishing and chromating will tend to help compensate, but areas of the part that remain unagitated (interiors) may remain dull. In general, much of your success will depend on the nature of the work you are doing, (small parts vs. large flat parts) as well as the degree of brightness or uniformity desired. Q: What is best for cleaning parts with small cracks?, I am using 20 pounds, but it seems to not be enough. What should I use? I am using 2 stage ( cleaner and rinse) and times around 35 sec by stage, normal concentration betwen 3 to 4 % of alkaline cleaner and 80°C of temperature in both tanks. A: Cracks and other areas where solution exchange are not good are challenging to clean and may require equipment improvements to address these issues. High-pressure spray cleaning or ultrasonic cleaning are good options for these types of applications. Q: Do you know of any solution to prevent oxide after nickel plating? The coating is nickel on steel, and the thickness is 5 microns average. It is a bright nickel solution, and we need to protect uncoated parts of low current density. 575

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