What is Chemical Blacking?
Chemical Blacking is sometimes referred to as ‘Blackening’ or 'Black Oxide Coating' produces a durable, aesthetically pleasing black finish. Chemical Blacking will improve corrosion resistance and is suitable for decorative applications when an oil is added. Silchrome offer both Hot Blacking Carbon Steels, Hot PX3 Blacking for Stainless Steels and an Ebonol process for Copper Alloys.
What is the Process?
Chemical Blacking is a conversion coating meaning that where in other metal finishing processes a layer is added above the substrate, here a coating is achieved through a chemical reaction between the ferrous metal and the oxidising salts used in the Black Oxide coating. Hot metal blacking is carried out on stainless and carbon steels and operates through the use of sodium hydroxide which is combined with an oxidising agent such as sodium nitrate. This produces a chemical reaction between the Iron of the Ferrous Alloy converting the surface of the steel component into magnetite. In order to obtain the best possible results, parts will first be subject to a number of pre-treatments depending on their material which are all carried out in house. Quite often parts that are Chemically Blacked will also be sealed with either Wax or Oil which further improves their corrosion resistance.
What Are the Advantages?
One of the key differences with the Chemical Blacking when compared with other processes is that it has a very negligible effect on the tolerances of the part. This makes it suitable for small sized components with intricate and complex geometries. Chemical Blacking is often used on components such as Screw Threads, Bearing Fits, Threaded Holes and Internal Machine Parts. The thin nature of the film created does however mean that Chemical Blacking does not offer anything in the way of wear resistance.
Alone, Chemical Blacking offers mild corrosion resistance but when combined with Wax or Oil the Corrosion resistance is greatly enhanced in particular in environments with high amounts of moisture.
Chemical Blacking produces a very smooth and visually appealing black matte finish and as such is often used in decorative applications or to help identify parts. This process is low cost when compared to other processes such as painting and plating. This makes it a popular process for a number of components including: Tool Parts, Jigs and Fixtures, Gears, Transmission Drives, Springs and much more.
ASTM D769, AMS2485, MIL-DTL-13924
What We Offer
Silchrome Plating have two dedicated lines offering Hot Chemical Blacking for Carbon Steels and Hot PX3 Blacking for Stainless Steels and an Ebonol process for Copper Alloys.The maximum length of components we offer is 500mm.