Encapsulating Hard-Chrome Plating Tanks

A December 1998 EPA Capsule Report, "Hard Chrome Fume Suppressants and Control Technologies,¹ (see below)" lists encapsulating tank covers as one of the acceptable devices for controlling emissions from hexavalent chromium processes.

Techmetals Inc., Dayton, OH, decided it was the only way. During the past several years, Techmetals has worked closely with the EPA and Responsible Alternatives to develop encapsulating tank covers, EED II (emission elimination device) for use on its two automated hexavalent chromium plating lines.

The EED II encloses the process tank during chromium plating using a specialized sealing method. It incorporates strategically located and appropriately sized membranes that allow for free passage of gasses while effectively blocking the escape of water vapor and chemical mists. Because of the system's design, Tech-metals did not need to install fume scrubbers (which eliminated stack testing). The tanks do not require fume suppressants either.

However, Techmetals Inc. also had to prove to the EPA that the encapsulating cover worked. The EPA used stack testing to assure compliance; however, with this technology there were no stacks. Therefore, Techmetals and its supplier devised a test method. A smoke device was used under the cover for qualification testing. If the cover contained the smoke, it was effective, since smoke particles are smaller than chromium particles. It worked, and this qualification test was approved by the EPA, and became the standard compliance test method for EED covers.

The hydrogen and oxygen gases generated during hard chromium electroplating escape through a membrane system. Fumes and mist are contained inside the cover. Water vapor condenses on the inside walls and top of the enclosure, and the condensate returns to the plating tank, creating a self-cleaning action. Because there is no air movement during plating, chromium mist, the heaviest by-product, rises to a limited height and then returns to the plating solution. The water vapor also reduces the upward mobility of the chromium mist particles.

"Techmetals was committed to using the technology because we see it as the environmentally responsible way to run a plating shop," stated Steve Deisher, director of marketing. "We needed to develop the technology to fit our processing needs." Other issues Techmetals Inc. addressed in relation to the encapsulating tank covers included heat buildup. Additional tank cooling was added to keep the tanks at temperature during heavy plating loads. Mechanical rather than air agitation was also required.

Although the technology is simple enough, installing it on the two new hard-chromium plating lines was not a simple operation. "We had to take the concept of how we covered one tank and do that effectively for an entire line," Mr. Deisher explained. "The greatest challenge was keeping it simple."

Techmetals Inc. and its supplier had numerous brainstorming sessions and developed many ideas before they decided on one, affixing the carriage system to the encapsulating cover. This may sound limiting, but it isn't. Multi-function racks hold a variety of parts. Fixtures are simply changed out as needed.

No plating occurs when the tank cover is off, which may also appear limiting. "It has forced us to rearrange our thinking," noted Mr. Deisher. The line operator thinks about less movement and how to group together products with similar characteristics. "Although we were a bit skeptical about throughput, using the encapsulating cover has actually helped us increase productivity," noted Mr. Deisher.

TABLE I—Operation of the Encapsulating Tank Cover During Plating

Parts are placed on the buss bar. Tank cover is closed and secured with clamps. Rectifier is turned on. Interlocks automatically engage to secure the access door so it cannot be opened during plating. Rectifier is turned off and the evacuation unit automatically turns on for one to five min. Interlocks automatically disengage. Parts are removed.

Not only has productivity increased, but also Techmetals Inc. has saved on maintenance costs, since the system has virtually no moving parts, such as high-hp electric motors and blowers. It has also saved on chemical costs, since all chemicals are returned to the bath. Waste treatment was another savings area, since no fumes are emitted from the tanks and solutions are protected from contamination.

The encapsulating cover also reduces the danger of hydrogen explosion, since tanks are off during startup, preventing arcing. It also reduces energy and water use 60 to 70%. And, it is quiet. When asked to compare working on a regular plating line to working on Techmetals' hard-chromium plating line, Operator Steve Gunn said it is like night and day. "It is quieter. There are less fumes and much less heat," he commented.

Both hard-chromium plating lines are also closed-loop systems. All rinses counterflow and then are evaporated. "We close-loop all of our plating systems and rinses," stated Mr. Deisher. "Our corporate vision is to eliminate or reduce emissions of any kind, anywhere in the plant. Our goal is to be completely contained. If we emit neither waste air nor effluent to the atmosphere, we should have no environmental problems. That way we can ensure that those running Techmetals Inc. 30 years from now won't have problems either," summed up Mr. Deisher.

¹To order the document, contact the National Service Center for Environmental Publications, 800-490-9198 and ask for publication EPA625R98002.

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