Metal Finishing Guide Book


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Q: Several years ago we installed variable speed frequency drives to control the rpm rates of the motors on our two plating lines. Since that time there has existed an apparent energy field which radiates throughout the building (11,000 square feet). For example, when I pull up in front of the building to park, my am radio station is overtaken with static, and second the eddymag measuring units on the shop floor continually lose their set points and accuracy during the day and need to be recalibrated every 2 hrs. We were advised and did install filters that were supposed to work but have not. Can you provide some advice? A: From my experience with VFDs I can only think of the 'Carrier Frequency' setting of your drives as a possible source. I've seen situations in the past where the Carrier Frequency setting was set relatively low, resulting in a high level of noise on the motor lines. Q: Reverse pulse plating in a sulfamate Ni electroforming bath. What are the advantages in time savings, etc? A: Reverse pulse plating in a sulfamate Ni bath does bring some advantages. 1. Slight improved throwing power: a standard DC process gives about 10% throwing power, reverse pulse can improve this to 25%. I even heard some customers claiming 50%, but that seems high. Some users benefit from this in their electroforming process: they can skip some steps of mechanical machining during their 900-hour process, due to less whisker forming and improved material distribution. 2. The crystal structure can be influenced, and therefore the hardness. Hardness between 150 and 500 V can be obtained. Plating time savings is minor, but with thick-layer electroforming there are savings possible due to less machining steps. Q: What are the advantages and disadvantages of using a tap switch rectifier for type II anodizing? A: There are no advantages, only disadvantages. The main disadvantages are: 1. No control You can only set the output voltage. The current will first shoot up and will then drop, which results in longer process times in comparison to a controlled system. So your manufacturing cost are higher because you pay more for energy due to the longer process time. If your coat is 0.6 mil instead of 0.5 mil, your energy cost are 20% higher than you have calculated. For a small 3000-A rectifier these are 0.7 U.S. per load. Which totals up to $1.4 U.S. an hour for just one tank. So for just one tank per day it is about $17 U.S.. It sums to about $4,500 U.S. a year for just one tank. Of course it gets worse if your deviation between the requested and achieved oxide thickness is even higher. 2. More manpower To set the rectifier correctly somebody needs to stay next to the rectifier to ramp it up and to re-adjust the taps. Of course this also results in additional costs. 3. Quality Manual operation results in poor repeatability. 4. Maintenance-tap switches need to be maintained and spare parts are very expensive 571

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