Recently, a barrel customer was experiencing a lot of rejects in their plating process for battery caps and asked Hardwood for help. The reject rate using traditional barrels was 40%. “Visually sorting the rejects is next to impossible when there are as many bad as good parts,” says Tony Lazaro, Hardwood president. “And we’re talking about millions of small, very thin caps.”
The philosophy of barrel plating is fairly simple—tumble parts until all of them have been completely plated. That process is difficult with thin washers and battery caps because those parts tend to stick together. “Clients have problems breaking apart flat, thin parts. Just because of their shape and the constant revolution at the same RPM, those parts seem to align and form chains,” Lazaro says. “When that happens, you just don’t get good plating because you need to expose all the surfaces of the part in order to plate it.”
High rejection rates result in a time-consuming sorting process; all at a high cost and low margin. What can platers do? According to Lazaro, many companies that plate thin washers or caps usually minimize load size or increase cylinder speed to try get the load to break apart, but the outcome often doesn’t change.
“It was only through trial and error that we stumbled upon an answer to part separation,” Lazaro says. Each of the changes Hardwood made resulted in only incremental improvements. It was only when they put all the changes together that they were able to fully eliminate rejects.
The first step was the addition of breaker bars to the existing cylinder. Breaker bars, by design, lift and drop parts, but that only reduced rejects slightly.
The next change was to replace the cylinder with an oscillating plating barrel that, by design, forces parts to move in a figure eight path. That dropped the reject rate to 10%, but it still wasn’t good enough.
For the third—and perhaps most important—step, Hardwood’s head engineer Frank Pusateri came up with idea of either mechanically or electrically forcing the cylinder to jump during each rotation. Hardwood did this by adding compound (or nautilus) gearing to replace the tradition idler so that each revolution includes a snap that creates enough turbulence to kick the parts away from each other. “It’s the kick that differentiates it from a traditional, constant-speed cylinder,” Lazaro says. “That’s what breaks them apart.”
The compound gear cut the number of rejects in half, but the customer asked for one last tweak. Could Hardwood speed up the barrel rotation? Hardwood responded by doubling the motor speed and the result was zero rejects. “The trial-and-error approach works, if you stick with it,” Lazaro says.