Black Oxide Finish Provides More Than Just A Finish

When Eliphalet Remington built his first rifle in 1816, James Madison was president of the country. Now, nearly 200 years and 37 presidents later, the Remington Arms Co. is one of the most successful and largest firearms manufacturers in the world. Although Remington is known for its high quality of its firearms, it

Case Study From: 5/1/1997 Modern Machine Shop

When Eliphalet Remington built his first rifle in 1816, James Madison was president of the country. Now, nearly 200 years and 37 presidents later, the Remington Arms Co. is one of the most successful and largest firearms manufacturers in the world.

Although Remington is known for its high quality of its firearms, it is also known for the high quality finish on the rifles and shotguns. Warren Hoffman, company chemist, says, "We compare the finish on our parts to that of jewelry. It must be perfect, with no blemishes or defects."

For this reason, the company recently installed two black oxide finishing lines (manufactured by Napco, Inc., in Terryville, Connecticut). The previous line looked as though it had been around since the early days of the company, but that was the least of its problems. Not only was it massive, but utility costs were high and maintenance costs were upwards of a million dollars a year.

The larger of the two lines installed by Napco is used to black oxide large parts such as receivers and gun barrels. Small parts are finished on the smaller line, which has the capability to color heat-treated parts. The larger system is capable of running 7,000 parts in a 24-hour period and presently it is treating 5500 to 6,000 parts per day.

Prior to receiving the black oxide finish, steel parts are polished in one of three ways. Most parts are polished in a vibratory finishing system using ceramic media and then shot blasted with steel shot to produce a matte finish. Higher degree work is hand polished and then polished with ceramic media in the vibratory finisher. Others are only hand polished. The type of polishing depends on the final finish desired.

After polishing, parts go through a two-stage alkaline cleaner, followed by a counterflow rinse. The first stage is a hot alkaline detergent cleaner (170oF). Parts soak in each cleaner for approximately five minutes to remove buffing compounds, oils and so on.

The next step is a special conditioning bath (235oF) that is critical to achieving a perfectly uniform finish. The conditioning step was added to handle a particular gun model that was polished using lard oil and kerosene, which is smeared into the metal. The conditioning step is necessary to remove this. But Remington found that this conditioning step helped with all parts and now, all of their parts are subject to be conditioned in this manner. An ambient rinse follows the conditioning.

Parts proceed directly into the 750 gallon, 290oF Pentrate Ultra black oxide bath, supplied by Heatbath Corp., Springfield, Massachusetts, which also supplies the cleaners and conditioner. Time in tank averages 45 minutes. A wetting agent incorporated into the Pentrate Ultra minimizes dragout.

Remington uses the liquid form of black oxide. It found that using liquid rather than the powder enhanced safety, since workers did not not have to shovel powder into a 290oF bath. Also, the liquid bath generates considerably less sludge.

The previous 2,000 gallon black oxide tank was de-sludged every two weeks. Now it occurs monthly. This has saved on maintenance and chemical and hazardous waste disposal costs. Mr. Hoffman estimates that the new line has helped Remington decrease sludge by 80 percent, drop operating costs by 70 percent, lower chemical costs by 66 percent, and decrease water use by 100 gpd.

Parts run through two ambient rinses after the black oxide tank. The next step is Pentrate EE 2, a blackening step for silver soldered assemblies. The process blackens the silver solder and blends it with the original black oxide finish. Parts proceed through an ambient rinse.

The final step is a soluble oil. Each morning this oil is heated to 150oF for an hour to pasteurize it. This kills the bacteria feeding on the emulsifier system, splitting oil from the emulsion and rendering the product useless. The oil provides corrosion protection and enhances the appearance of the blackened parts.

After black oxide finishing, the parts move on for assembly and/or the Remington custom shop for further work.

In addition to a high quality finish, the new black oxide system has provided the added benefits of cost savings and a clean environment now and for the future.

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