Black oxide coating, also known as chemical blackening, is a kind of conversion coating, which is usually used for small and complex moving parts in applications such as gears, hydraulic blocks and tools and machine parts. This coating is unique because it can provide you with the same effect as other finishes, but at a lower cost and has unique advantages. The following is a detailed introduction to the definition, process and advantages of black oxide coating.
What Is Black Oxide Coating?
The process of forming black iron oxide into ferrous metals and other types of materials is commonly referred to as black oxide. The black oxide process is a chemical conversion coating for ferrous metal materials, stainless steel, copper and copper based alloys, zinc, powder metal and silver solder. This process is done to increase corrosion resistance, enhance appearance and minimize light reflection.
Unlike electroplating nickel or zinc, black oxides do not deposit on the substrate surface. On the contrary, there is a chemical reaction between the iron on the surface of the ferrous metal and the oxide salt present in the black oxide solution. The resulting chemical reaction results in the formation of black iron oxide magnetite on the surface of the coating material.
Black oxide coating is applicable to the following metal materials:
- Stainless Steel
- Copper
- Copper Based Alloys
- Zinc
- Powdered Metals
- Silver Solder
The Black Oxide Processes
There are three different coating methods: hot, medium and cold. Different materials use different coating methods due to their unique composition and density. The general process of black coating involves the chemical reaction that occurs when the ferrous material is mixed with an alkaline saline solution at a certain temperature.
Hot Process
The process of treating fasteners with different chemicals to convert surface materials into magnetite. This process is accomplished by immersing the fasteners in different water tanks and occasionally in water. After the impregnation process is completed, the top layer of the fastener is porous and coated with a layer of oil. Oil penetration into the material increases additional corrosion resistance to rusting.
Cleaning and flushing of materials must be carried out in a warm water bath of up to 160 ° F. On the other hand, the blackening temperature must be between 265 ° F and 285 ° F. The last step in hot working is to apply oil to the heated parts. To avoid corrosion, the oil seals the black finish by sinking into a porous layer of black oxide.
Mid-Temperature Process
Similar to the hot bath treatment method, but does not produce the same toxic fumes as the hot bath, and the surface is converted to magnetite at a much lower temperature.
Cold Process
Only the cold black oxide is introduced because it can reduce harm and save energy. In the cold process, a compound called copper selenium is applied to the material at room temperature. This process is the opposite of the thermal process in which the parts are subjected to a variety of chemicals at high temperatures. The last step of the cold oxidation process also involves coating the parts with oil to increase corrosion resistance.
Although cold oxidation black can provide better productivity and convenience for blackening in the hose, its coating performance is often easier to wipe off and its wear resistance is lower. On the other hand, it is well known that thermal blackening is cost-effective, provides excellent coverage, and provides enhanced corrosion resistance.
Advantages Of of Black Oxide Coating
Stealth Appearance
One of the advantages of the black oxide coating is that it gives the material a hidden appearance. The coating process can make parts and products appear dark black without any copper green or rainbow effect. However, if these things already have a glossy or material surface before the black oxide coating process, they are expected to retain their default surface unless additional surface treatments are applied.
Keep Dimensions
Another advantage of the black oxide coating is that it can retain the size of the part being processed. Since the black oxide coating only changes the surface characteristics of the parts, manufacturers can ensure that their parts and products do not have additional dimensional changes. They will not find any deposited or removed surfaces or areas on newly coated parts and products.
Additional Resistance
Black oxide coating can not only improve the appearance of parts and products, but also improve their service life. The elements produced by black oxide coatings and their accompanying post-treatment can provide much-needed corrosion and wear resistance for parts and products. Manufacturers can expect their parts and products to be more durable and last longer.
Improve lubricity
Some parts and products must be lubricated to be effective and functional. Fortunately, the black oxide coating ensures better lubricity of these materials. Due to the use of finishing elements such as oil or wax, the process can also introduce better anti-wear properties for parts and products.
Corrosion Resistance
The black oxide coating provides mild corrosion resistance, but is usually used in combination with oil and wax, which is usually enhanced. One of the advantages of this process is that it does not appear “white corrosion” over time like some electroplated parts. This makes it very suitable for internal electronic applications because small white corrosive spots are actually conductive and may cause electrical short circuits.
Find the right supplier. Through the black oxidation process, you can easily obtain products and tools with excellent surface appearance and enhanced corrosion resistance.