What is Black Oxide Coating?

Posted by Brad Roberson in CNC Machining Services and Value Added Services on Jul 17, 2023.

Black oxide is a chemical conversion process used to blacken the surface of a part without adding a thick coating. With the ability to boost a component’s corrosion resistance, as well as its aesthetics, it is one of our most popular metal finishes at Roberson Machine Company, and is included in our value added services.

Call us right away to schedule a black oxide finish as part of your project at 573-646-3996 or contact us online.

How Does Black Oxide Work at Roberson Machine Company?

Black oxide is a finishing procedure that involves immersing a part in an alkaline solution of sodium hydroxide and potassium nitrate. The coating helps improve a metal component’s resistance to corrosion and rust, as well as extending their lifespans and reducing the need for expensive or time-consuming repairs or replacements.

Black oxide enhances the hardness and durability of metal surfaces, reducing wear and tear, and improving the performance of metal components in hard-working or industrial environments. The surface finish also improves your part’s aesthetics – providing a smooth, matte finish. Black oxide also makes the parts easier to incorporate into a variety of applications.

At Roberson Machine Company, we utilize our custom procedure where a part:

  • Runs through the machining and deburring processes
  • Is cleaned using alkaline solutions
  • Is rinsed in water
  • Is black oxidized by soaking in a hot alkaline bath, ranging in temperatures between 275 and 285°, for a period of 5-40 minutes depending on the size of the part
  • Is rinsed in water once again
  • Is given after-finish treatment with oil, lacquer, or wax to seal the oxide surface

The Black Oxide Applications at Roberson Machine Company

Black oxide is well-suited for applications that call for a durable, low-maintenance, and corrosion-resistant coating. GIve Roberson Machine Company a call now at 573-646-3996 or reach out to us online. The following are some common applications of black oxide finishes:

  • Industrial equipment. We use black oxide finishings on a wide range of equipment, including pumps, valves, tubing, metal stampings, and various other parts for machinery.
  • Automotive and aerospace parts. In the automotive and aerospace industries, we use black oxide for a variety of customer parts, including engine components, suspension systems, panels, and landing gear.
  • Fasteners, hardware, and tools. Black oxide is a popular finish for fasteners like screws, bolts, nuts, in addition to hand tools and other hardware, because it provides a matte, visually appealing finish that is resistant to corrosion, durable, and easy to grip.

What Are Some Unique Features of Black Oxide?

A black oxide coating works best on surfaces with a smooth, uniform finish, as rougher surfaces tend to result in a less uniform coating. Also, not all metals are compatible with the surface finish, like aluminum. However, it is still one of our most popular value added services. Some of its unique features include:

  • Decorative finish: The resulting lustrous black finish adds visual appeal and a head-turning part at a very low cost. While softer parts tend to have matte finishes, the harder ones are glossier.
  • Cost competitive: We speak from experience – it is difficult to achieve the same protection, appearance, and performance from other surface finishes at a comparable cost.
  • Dimensional stability: A black oxide finish adds no more than 5-10 millionths of an inch to the dimension of a part. For all intents and purposes, the dimensions do not change – which is not the case with painting or plating.
  • Corrosion protection: Depending on the post-treatment applied, black oxide coating can give corrosion resistance equivalent to 144 hours of salt spray exposure.
  • Reduced light glare: Moving machine parts, hand tools, and surgical instruments coated with black oxide reflect less light and reduce eye fatigue when used under bright lights. These are huge benefits to the user.
  • Pre-treatment for paint: Black oxide greatly improves the adhesive qualities of the metal, allowing paint and primer, as well as other finishes, to hold better and last longer.
  • Anti-galling: Where the break-in of mating parts is necessary, the anti-galling surface lets the outer lubricating layer be sacrificed during initial contact and abrasion while work-hardened surfaces are formed. The black oxide itself has a hardness of 5.5 on the Mohs’ Scale.
  • Conductivity: Parts finished in black oxide experience no more than a 1% reduction in conductivity, making it a suitable treatment for electrical parts.
  • No embrittlement: Unlike painted or plated parts which are frequently acid etched, no hydrogen embrittlement accompanies black oxiding.
  • No welding fumes: If you need to weld your black oxidized parts no noxious fumes will be released, unlike welding painted or plated components.

What is Black Oxide Coating? | Roberson Machine Company

Whenever you are ready to discuss your next custom manufacturing project, we are here. Regardless of the complexity of your project, you can be sure you’re getting the best results. We utilize the expertise of our machinists to provide the best black oxide finishes for your parts.

Call Roberson Machine Company today at 573-646-3996 or contact us online.


Brad Roberson / 

Brad Roberson is one of the owners of Roberson Machine Company. Please feel free to contact us to receive a quote or ask any questions you may have.

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