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8/1/1998 | 5 MINUTE READ

Blackening System Solves Expansion Plans

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One of the leading manufacturers of tool systems for CNC punching machines has doubled the size of its operation in the last six years.


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One of the leading manufacturers of tool systems for CNC punching machines has doubled the size of its operation in the last six years. Because Mate Precision Tooling's need for finishing tool components has grown dramatically, the company looked for ways to improve its ability to finish parts in-house rather than send parts out for hot oxide blackening.

Because the manufacturer provides 24-hour service on customer tool orders, part turnaround time was a primary concern. The manufacturer had to finish components for these tool orders quickly, often within a day or two of when the order was received. Sending tool components outside for finishing, using hot oxide or any other finishing process, could delay orders for several days, even weeks.

Mate Precision Tooling had used the Presto® Black process on an intermittent basis since 1980 to provide corrosion protection on tool system components such as die holders, tool loading cartridges and die plates. While the tools themselves did not require finishing, the manufacturer's dramatic growth in volume required a faster way to finish and provide corrosion protection to those components needing it.

"The finishing system we had been using didn't have the capacity or efficiency," said Bill Dahlquist, materials manager. "The system was not designed to give us the fast turnaround we required or control we wanted over the end result. So, we began to investigate various finishing alternatives."

Birchwood Casey recommended its pre-engineered, 40-gallon capacity BC-40 part finishing system using the Presto Black process. The recommendation was ideal for the tool manufacturer's needs. The manufacturer was certain from the start that it did not want to deal with the caustic chemicals associated with hot oxide finishing. Nor did it want to deal with the potential pollution problems of the hot oxide process chemicals.

By installing the BC-40 system, the manufacturer was using a process it had prior experience with and confidence that would not pose worker safety or pollution problems. The cold process does not produce dangerous fumes and splattering usually experienced with hot oxide. The cold process is also cleaner and safer. The room-temperature finish has excellent overall uniformity, even on parts with complex shapes and configurations, like many of the manufacturer's tool system components.

With the support of the finishing system's manufacturer, the tool company configured the BC-40 system into a customized finishing cell that included portable immersion and drying racks and a drain table adjacent to a sandblasting machine.

Most of the parts are heat treated and have residue or scale that needs to be removed prior to blackening. The tool manufacturer sandblasts the components to remove the scale so that the parts will accept the blackening process, producing a smooth, deep black finish.

In setting up its new finishing line, the company's engineers wanted to build tanks and a drying table into a partially enclosed 10-by-12 ft room where parts could be moved into the tank area from the adjacent sandblasting machine area.

The BC-40 finishing system consisted of seven 40-gallon tanks constructed of one-half-inch welded polypropylene, complete with stainless-steel heaters, controllers and all plumbing connections. The tank line was positioned along one wall with the end tank fitting into the corner of the room. A stainless-steel drying table was installed so that it connected to the final rinse tank. The tank line and drying table formed a "U" shape and were positioned against the three walls. A series of portable drying racks was installed directly above the drying table and opposite the finishing tanks.

With this setup, unfinished parts are placed on the racks in rows that go into the first immersion tank. They are then moved through the series of tanks for finishing, removed from the last sealant tank and placed back in their original position for drying above the drying table. Excess oil is allowed to drip down onto the table and flow back into the sealant tank.

There are several advantages to this system configuration. One, it is easy for one person to operate because of its simplicity. All components are positioned close together without crowding. Second, one operator can move and finish a batch of parts on the sandblasting machine, move the components to the first finishing tank and begin that process in seconds. Also, while parts were cycling through the processing steps, the operator still has plenty of time to rack incoming unfinished parts for processing and then remove finished parts at the end of the tank line and/or remove dried parts ready for shipping.

The total process time is 10 to 12 min:

  1. Clean at 150F, four to six min;
  2. Rinse in clear water, 20 sec;
  3. Activate at 120F, two to three min;
  4. Rinse 20 sec;
  5. Blacken at room temperature, one min;
  6. Rinse 20 sec; and
  7. Seal out corrosion, one to two min.

The tool manufacturer found the blackening process easy to prepare and work with because the solutions are odorless, non-caustic, non-splattering and only mildly acidic. The process is designed for long bath life without the need for routine dumping. Using a color change test that indicates proper concentration level, solution monitoring and control is simple.

No special venting was needed with the process, further reducing the initial investment costs. Without the noxious fumes associated with hot processes, the room-temperature blackening process promotes greater worker comfort along with fewer health problems.

What kinds of metal does the tool manufacturer finish? What kind of corrosion protection does it get from the process? The components the company finishes include various alloys and tool steels such as 8620, 4150, M2, S7 and A2. Good finishing results are experienced on all of these with a few requiring some additional time in the activation tank or a stronger mix of blackening chemicals to effectively bond with the material. This is the case with high-speed steel such as A2. The corrosion protection experienced, according to verified testing, withstands up to 200 hours of neutral salt spray (ASTM B 117) or several hundred hours of humidity (ASTM D 1748). The manufacturer's blackened parts have an overall uniform appearance, even those that have complex shapes and configurations. The process finish does not affect part dimension or material hardness.