Controlling Your Electrocoating Line

Article From: Products Finishing, , from Gardner Business Media

Posted on: 10/1/2000

Electro-Coat Technologies electrocoats RV chassis and other large parts. While this has helped Electro-Coat Technologies become one of the few suppliers to this niche market, the large tanks have required some extra controls to keep them operating properly...

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Tractor trailer bumpers

Tractor trailer bumpers are processed through the electrocoating line at ECT. Because the tanks are so large, it is necessary to have tight control of both the pretreatment and electrocoat tanks to help keep costs down.

Electro-Coat Technologies (ECT, Elkhart, IN) has one of the largest electrocoating lines in North America. For example, ECT is capable of coating parts up to 50 ft long, 8.5 ft tall and 4 ft wide. Also, ECT has the capability to coat a wide variety of parts including RV chassis, utility trailers, tractor trailer bumpers and Hummer roof tops. But, the massive size and shape of the parts put through the line have created some challenges for ECT.

Electrocoating Challenges

ECT's line operates as a typical batch electrocoating line. This means parts are hung on racks and allowed to dwell in each tank for a set period of time. Due to the high volume requirements of electrocoating and the size and shape of ECT's parts, the company typically racks multiple part configurations on one rack or has a single rack with one large part. Because different parts are placed in the tank at the same time, there may be different voltage requirements to effectively and efficiently coat these parts, and the distance from the part to the anode can vary considerably.

Therefore, the first challenge for ECT is what Bill Banks, Jr., director of operations at ECT, terms product variability. Take a fifth-wheel RV trailer (the kind that is towed behind a pickup truck) for example. "We've got an upper deck on the fifth-wheel trailer," stated Mr. Banks. "There's a lot of square footage on the upper deck and not a lot of square footage at the other end. Right now, the way we've got it set up, we guesstimate our square footage in the tank and we set our voltage accordingly. So, we might put a lot of paint on the one end, some in the middle and a little on the other end."

To overcome this challenge, ECT is installing the Z-Net networked control system for electrocoat anode switching from JP Tech. Basically, this system controls each anode in the electrocoat tank individually to achieve a more consistent film thickness. By turning select anodes on and off, the system can direct current density to areas of the part that need more or less current to achieve the desired thickness. The system knows which anodes to turn on and which anodes to turn off using one of two methods. The first is pre-programmed algorithms. If ECT uses a common racking pattern, it can preprogram which anodes the system should use. If there are several racking patterns being used during a shift, the system can be programmed to know in what sequence the racks are being processed. The second is an automatic part identification based on the parts' physical or electrical profile. The current draw is constantly monitored in either case to ensure that the appropriate anodes are on or off.

By controlling the anodes in this way, ECT will reduce overcoating, decreasing its paint use. Also, the system will reduce undercoating, improving part quality and increasing corrosion protection. "Let's say we're putting too much paint on," said Mr. Banks. "This will enable us to control it. So, instead of putting on an average of 1 mil, we can put on an average of 0.8 mil. That's a 20% savings, which adds up pretty quick."

Pretreatment Challenges

According to Mr. Banks, the second challenge has been controlling the dragout and carryover from the pretreatment system. The parts are processed through an immersion pretreatment system. Unless the parts are designed with the proper holes for drainage, the large parts can cause a significant amount of cross contamination of the cleaning baths. And, since the parts are so large and ECT's cycle times so tight, even parts with the proper drainage can cause some dragout of pretreatment chemicals. If the dragout is not controlled, poor crystal growth of the zinc phosphate can result. And, according to Mr. Banks, instead of electrocoating the zinc phosphate, you begin to coat the base metal, which results in poor corrosion protection.

While the only ways to control carryover and dragout are part design and racking techniques, there are systems that will allow ECT to control the effects of cross contamination that result from carryover and dragout. One such system is the AccuSystem from PPG. The system monitors pH, conductivity and chemical levels and makes the necessary adjustments automatically. By monitoring and adjusting pH, conductivity and chemical concentrations automatically and more frequently, the system keeps those levels from spiking or dropping too low. This provides for more effective pretreatment and better adhesion of the electrocoating. It also decreases chemical costs by allowing ECT to make smaller additions. "All we've got to do is control carryover and dragout. We should reach our goals to reduce costs and tight control of our pretreatment system," explained Mr. Banks.

While electrocoating has higher up front costs, its operating costs can be significantly less than other finishing systems. By installing these two control systems, ECT should be able to reduce its operating costs even further and reduce human error.

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