Wedge Mill Tool, Inc. (Brighton, Michigan) made the change from cold to hot black oxiding in 1997. The company manufactures anvils, shim seats, clamps, wedges, dovetails, form tools, fixtures and other special tooling. Parts are fabricated from alloy steels and carbides in quantities ranging from 2 to 10,000.
John Yaros, Wedge Mill's vice president, originally purchased hot black oxiding services on an outsource basis. Eventually, logistics became an issue. "Most of our 300,000 part were outsourced for black oxiding," he explains, "and although the quality was good, handling and delivery costs, turnaround and convenience became an issue. Cold processing was getting a lot of attention at that time, and we decided to try it."
Quality Assurance Manager Harold Allison was the first to notice the difference. "The cold blackening simply couldn't produce the appearance or corrosion performance we'd experienced with the `hot' processing we'd bought on the outside," he says. "Re-work definitely went up. Batch-to-batch, the cold processing could not oxidize as consistently as hot processing."
Several things came into play that changed Wedge Mill's direction. Says Mr. Yaro, " First, the popularity of JIT programs meant we had to stock greater quantities of more kinds of parts." This created a need for longer shelf life. "Also, there were many orders with short turnaround times." Also about the same time, quality specs on all six categories of products Wedge Mill makes were becoming more stringent—not just in terms of dimensional accuracy and hardness, but in the performance and appearance of the finish as well. And black oxiding was listed as a blueprint requirement in an increasing number of instances.
"Today, there's a higher standard for finish quality, even on components that are barely visible in the tool assembly," says Mr. Yaros. "If you're going to call yourself a manufacturer of `world-class tooling'—or world class anything else for that matter, your product had better look—and last—like world class."
That mindset, and the company's pursuit of ISO9002 certification (granted in 1996) tipped the scales solidly in favor of a return to hot black oxide processing, this time, on an in-house basis.
"We were probably a tough prospect," says Mr. Yaros, "because by then, we'd seen it all. The stakes for us were high. More than 90 percent of the component parts we produced are black-oxided."
Wedge Mill selected a product, and equipment, manufactured by Heatbath, Corp., in Springfield, Massachusetts. The product, Pentrate Ultra-L is said to be the most recent and most advanced black oxiding system developed to date by Heatbath.
Wedge Mill purchased a five-stage, manual system with a small footprint—just six linear feet. It is gas-fired for maximum utility efficiency and was installed on a single shift.
Parts preparation begins with a five-minute immersion in a dilute (7-14 ounces per gallon) solution of Heatbath's Pentrate cleaner. This heavy-service alkaline was created specifically to provide a physically and chemically clean surface prior to black oxiding. It was engineered for use alone on steel, cast iron and malleable iron. Wedge Mill's application is primarily 4140 material.
The Pentrate cleaner runs at 180o for five minutes. An agitated rinse is followed by immersion in the 290o Pentrate Ultra-L bath. The Heatbath system uses a Model 900 controller to automatically control black oxide concentrations. Operating virtually maintenance-free, the system is all solid state, provides accuracy and hysteresis of less than 1oC and has an always-visible digital set and readout. The controller prevents the red, brown and green films—as well as reprocessing—that have plagued users of many black oxiding systems.
After a five-minute bath in the Pentrate Ultra bath, parts are rinsed and then immersed for one minute in Heatbath's Pen Dip 300, a barium-free, thin film rust preventative.
The Heatbath system is ventilated using Wedge Mill's existing plant-wide system. Waste disposal is simplified too, in part because the bath contains no selenous acid (an additive common to cold blackening systems that is toxic by both inhalation and skin absorption). Unless there is nonferrous metal contamination, Pentrate Ultra never requires dumping, only replenishment.
Mr. Yaros is satisfied with both the results and the cost. "Heatbath made the cost to implement this change very affordable," he says. "The investment has proven to be very cost-effective."
The company's next step is to selectively market its black oxiding services. Yaros believes this will benefit the company in three ways. "This move will put Wedge Mill in a better competitive position, due to a lowering of our production costs," says Mr. Yaros. "Of course, it will also become a profit center of its own—which gives us not only a revenue stream from a new source, but real business diversification. Finally, you can't overstate the value of the quality blackening service as a way to open doors to new business—in the real business we're in—which is providing tooling that is, in every way, truly world class."