Case Study: Finding solutions to why my parts are burning
Mickabooh Systems has installed controller systems at many different facilities located all around the United States. At one facility in Oklahoma, we installed a controller system for an anodizing company that has large tanks for bigger parts to be anodized. After completing and certifying the installation, we released the software system for production runs. Everything was running smoothly according to plan. The real time charts created by the controller system showed no signs of burning or arcing or any other problems during the production runs which led the operator to continue to run the programs.
The Mickabooh Controller was running a difficult alloy at 24 ASF with a coating thickness within specification. The system continued to run smoothly for a couple of weeks, until a problem arose. All parts that were anodized were burning with no explanation to why. The first step in the diagnosis was to check the process reports to see if there were any anomalies in the process. However, the process reports showed the system was calibrated correctly and the operators were running the correct program, along with the tank temperature within spec. Yet, the charts on the process reports were showing signs of severe burning. Unfortunately, this was an early version of our control system, and there were no burning alarms to alert the operator of a problem.
The next step we took to diagnose the issue was to rule out any problems with the control system. We looked at all the process data files which showed the controller set points and rectifier outputs at every second during the process. In each report, we found the rectifier output voltage and current was consistent with the program the operator ran. This definitively ruled out a problem with the controller system. Since having dissolved Aluminum in the bath helps to prevent burning, we titrated to get to the Aluminum content. The titration results showed the sulfuric and aluminum content were within acceptable limits, so we ruled out the bath chemistry, as the issue. Immediately after, we considered the physical geometry of the tank itself; anode-cathode ratio, tank materials, flight bars, and anything else in the anodizing circuit. This was quickly ruled out because all parts ran fine for weeks prior to the burning and if there was something physically wrong with the setup, there would have been a problem from the start.
At this point we were puzzled with what the issue could possibly be. The rectifier program was correct, the chemistry was in spec and there were no obvious signs of what is causing the parts to burn. We then made another site visit to diagnose the problem further and that is when we saw the problem; copper. When the tank was built, copper rails were used to hang the aluminum cathodes from. Looking at the bath tanks, the copper rails were 6-7 inches above the solution level which did not seem to be an issue. Once the parts were in the tank, and the agitation was turned on, the solution level rose and was now only 2-3 inches below the copper. This meant the rails were receiving a constant splash of acid, dissolving copper that cascading back into the bath.
An indicator the copper was the issue causing the burning, was the color of the cathode rails. Normally, copper would look old and have a greenish patina, whereas the copper rails were bright and shiny like a new penny. This could only happen if copper patina is continuously removed exposing new copper. Our suspicion was finally confirmed when we further analyzed the bath and we found a high amount of copper. Knowing there is copper in the bath, they replaced the bath chemistry and lowered the solution level. Soon after, they began to run without any issue for months before finally replacing the copper rails with 6061 aluminum.
Since copper is a great conductor, it is a great idea to use copper for the tank’s electrical bussing. However, too much copper in a sulfuric anodizing solution will cause the bath conductivity to increase substantially, which in turn will increase the likelihood of burning your part
Kevin Bodily, is a software and electrical engineer with over 15 years of experience in the metal finishing industry. He is Founder and President of an industrial automation software company, Mickabooh Systems LLC, located in Gardnerville, Nevada. Connect with Kevin Bodily on LinkedIn, Facebook, and Twitter.
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