So how do you produce a true durable black oxide conversion coating on steel, stainless steel and copper alloys? Before we talk about the steps that go into the black oxide finishing process, let's talk a bit about the benefits.
Tactile Benefits of Black Oxide Finishes
These are the types of benefits that can set your parts and accessories apart from the rest. Smoother to the touch with less friction and improved lubrication, quality finishing with oil, wax, or laquer with options for glossy or smooth finishes, and more.
- Reduced light glare
- Decorative Finish
- Provides anti-galling properties
Technical Benefits of Black Oxide Coatings
In addition to the tactile benefits, you also achieve a class of critical technical benefits, especially with a hot black oxide coating process. Here are a few of those benefits:
- No dimensional change
- Does not affect conductivity
- Increased corrosion resistance
- No hydrogen embrittlement
- Base for organic coatings
When is it up to high-grade specifications?
It's the combination of the tactile and technical benefits that when applied properly to parts give them the properties and characteristics required in mission-critical applications for the automotive, aerospace, and military industries. Especially when black oxide finishing is applied to stainless steel, such as to 300 and 400 series and the precipitation hardened 17-4 PH stainless steel alloys, it sets the stage to achieve heavy duty results. The process can also be applied to cast iron and mild low-carbon steel. Hot black oxide can significantly improve wear and corrosion protection. When applied properly, the process complies with military specifications and provides abrasion resistance.
How do you achieve effective Black Oxide Finishes?
To correctly apply a black oxide finish, the process must be planned according to the configuration and intended use of the parts to be treated. The process generally involves the following steps:
- Rinse
- Black Oxide bath
- Rinse
- After-Finish
Extra steps that may need to be taken include:
- Stripping parts of scale and/or rust by acid pickling or alkaline de-scaling
- Neutralizing parts with blind holes
- Additional rinsing
There's a world of knowledge to be attained about choosing and applying the proper supplementary coating or after-finish. By default, most hot black oxide processes assume a minimum of an Oil after-finish. Other after-finishes available include wax and lacquer. An after-finish like wax can give your parts a more matte appearance and further reduce glare, while a popular oil finish will make your parts look a bit glossier or slicker.
Depending on what grade of wear and corrosion resistance you're looking for and whether your parts will need to function in high friction environments, in extreme temperatures and or humidity, you'll want to choose an after-finish that compliments your intended use.
Resources for Learning More
Pro-Tec Metal Finishing in Chicago, Illinois has a number of
articles about black oxide finish on their website. Pro-Tec Metal's Process Line of hot black oxide is used to produce a true durable black oxide conversion coating on steel, stainless steel and copper alloys. They're able to provide a high quality of finishing to most major certifications.
Here are two other industry resources where you can find more information about various aspects of the black oxide finishing process.
National Association for Surface Finishing
Chicago Metal Finishers Institute