Precision machined parts made of ferrous materials (stainless steel alloys) can be designated with black oxide as a surface finish to provide additional protection for the parts.
Black oxide finish is one of the various surface finishes used in machining. Surface finish is very important in precision machining, because they can improve the life and beauty of machined parts. However, one of the problems brought by many finishing machining is that they tend to increase the size of finished mechanical parts. This is detrimental to the functionality of these components, because precise dimensions are required for correct installation.
However, in this respect, compared with other metal surface finishes, black oxide finish is more prominent. This is because it can give good surface finish to machined parts with minimum size expansion. In this article, we will explain the black oxide coating process, the types of black oxide finishes, their applications, and other contents.
What is Black Oxide Coating?
Black oxide coating is a kind of coating that belongs to the category of conversion coating. Conversion coating is a kind of coating made by chemical process. The name “black oxide” comes from the fact that the coating makes the color of any metal surface black/matte.
The black oxide polishing process involves immersing machined metal parts in alkaline solution. Then, the solution converts the iron on the metal surface into magnetite. This magnetite forms a black coating on the metal surface.
Black oxide coating can be applied to stainless steel, copper, copper base alloy, zinc and other materials. This provides many benefits. First of all, black oxide surface treatment not only improves the appearance of parts, but also enhances the dimensional stability of parts. It also reduces the light reflection on the surface, which is an important requirement for components involving radiation, because for IR sensors, UV sensors, passive infrared detectors and other products, excessive or reflected light will completely change the results.
In addition, black oxide coating is beneficial because it increases the thickness of steel. Even if it is microscopic, it also helps to maintain the sharpness of things such as drill bits or screwdrivers. In addition, it helps to reduce corrosion and friction caused by the presence of oil or wax. Wax or oil also allows the material to be waterproof.
Applications Of Black Oxide Finish For Precision Machining
Due to the smallest size expansion, this kind of finish machining provides precision machining parts, so it is not surprising that it is popular in various industries. Other characteristics, such as light absorption and wear resistance, make it an excellent finish, although its price is low.
Due to the light absorption characteristics of black oxide surface parts, they can be used in photosensitive medical instruments such as X-ray machines.
Strippers, timer gears, cutters, etc. are examples of electrical components with black oxide finish.
Many automobile parts also use black oxide finish. You can find them in parts such as oil filter, suspension bushing, spark plug, brake valve components, etc.
Medium temperature black oxide finish is commonly used in military applications. It is commonly found in the turret of military Hummer, shotgun magazine, etc.
Precision machine tools used to manufacture components also usually have a black oxide finish. Tools such as bearings, fasteners and gauges are good examples.
Factors To Consider When Using Black Oxide Finish
Before deciding to use black oxide surface treatment for precision machined parts, various parameters must be considered. These factors will help determine whether black oxide finish is a good choice for parts. These factors include:
Application of parts
Which industry do you manufacture parts for? Are they suitable for light absorption environment such as medical industry or wear-resistant environment such as military? The application of precision parts determines whether black oxide is suitable for machining parts.-
Part use position
When selecting black oxide as the finish, it is also important where you plan to use the part. Generally, when the surface treatment is used indoors, the service life will be longer. The same rules apply to black oxides. Due to its thin layer, outdoor conditions such as humidity and continuous high temperature may lead to faster wear of black oxide.
Ideal finished product appearance
The final appearance of the part is also very important, especially when the aesthetics of the part is very important. After applying the black oxide coating, you can have two final appearances: matte or gloss. The type of post-treatment you pursue will determine the final appearance of black oxide parts. Therefore, the limitation of the final appearance of black oxide parts is an important parameter to be considered.
Recommended service life
How long you plan to use precision machined parts is also the key to choose the best surface finish. Black oxide finish can be used for a long time due to its antirust performance. However, this factor depends on other factors, such as the application and location of the part.