The Process of Black Oxide Coating and Its Applications

26 April 2023

Many coating processes can be utilised by a wide range of industries to ensure their parts and products will remain durable over time. One of these processes is black oxide coating.

Black oxide coating is a conversion coating process used to enhance the corrosion resistance and aesthetics of ferrous metals like steel, iron, and stainless steel. The process involves the immersion of the metal part in a hot alkaline solution, which creates a black oxide layer on the metal surface. This layer is chemically bonded to the metal, generating a durable finish that does not chip, flake, or peel.

Black Oxide Coating General Steps

Different steps are associated with a black oxide coating. These steps are as follows.

• Degreasing: The metal parts and products are first cleaned to remove dirt, grease, or oil from their surface. It can be done using various methods like solvent cleaning, alkaline cleaning, or electrolytic cleaning.
• Pickling: Subsequently, the metal parts are dipped in an acidic solution. This solution is often a mixture of sulfuric and hydrochloric acid. Using this solution on metal parts can conveniently remove any surface rust or scale.
• Activation: The metal parts are then dipped in an alkaline solution, which is often comprised of sodium hydroxide and sodium nitrate. It is intended to activate the surface of the metal and prepare it for the subsequent black oxide process.
• Blackening: Blackening is the next step in the black oxide coating. It involves immersing the metal parts in a hot solution of sodium hydroxide, sodium nitrite, and water. The workpieces are often exposed to a solution temperature of 285-310°C, with an immersion time that can vary depending on the desired depth of the black oxide layer. During this step, a chemical reaction may occur between the metal and the solution, constructing a black oxide layer on the surface of the metal.
• Sealing: After the blackening step, the metal workpieces are normally treated with a sealant to improve the corrosion resistance of the coating. This step can be done by utilising methods such as oiling, waxing, or lacquering.

Applications of Black Oxide Coating

The black oxide coating process is widely used in numerous industries, which include automotive, aerospace, and medical devices. Some applications of black oxide coating include:

• Automotive: Black oxide coating is used to protect various automotive components like nuts, bolts, and brake parts from corrosion. It is also used for aesthetic purposes, such as on exhaust systems or wheels.
• Aerospace: This process can also be utilised to protect aircraft components from corrosion. It can also improve their wear resistance, reduce glare, and improve the visibility of instruments and gauges that are crucial to aircraft functionalities.
• Medical Devices: Another industry that can take advantage of black oxide coating is the medical industry. This process can be maximised to improve the corrosion resistance of medical devices like surgical instruments and implants. It can likewise minimise the risk of infection by providing a surface that can deter bacteria from staying and infiltrating.
• Consumer Products: Ultimately, black oxide coating is used in a variety of consumer products like kitchenware, jewellery, and musical instruments. Once they undergo this process, it can easily make their surface appealing and durable.

Black oxide coating can swiftly provide products with a finish that is corrosion-resistant and appealing. It is also expected for the products from various industries to last for a long time.

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