Blacking is a process that enhances the looks and durability of parts that are made of iron or steel. It is used in antiquing applications as well as in the making of auto parts and components. Other applications for blacking include industrial machinery parts, cutting tools, springs, clutch drives, drill bits, fasteners, jigs and fixtures, hydraulic machinery, and ball screws.
Therefore, black oxide or blacking is a specialised finish for colouring iron and steel parts black. Safe and convenient to use, the chemical immersion process can be completed at room temperature. The unique quality of the chemical does not result in any change to the dimension of a component. Therefore, precision-engineered parts that require a decorative finish are enhanced by blacking without having their functionality altered.
Blacking should not be confused with such processes as phosphating or Parkerising. The black and uniform finish that is obtained from these processes is from 0.2 to 3 microns thick and has a greater decorative value than protective. Because blacking does not materially alter dimensions, it is eminently viable for small machine parts. Processing involves degreasing, and, if required, de-rusting before immersion in a bath set at room temperature. Corrosion protection is supplied by one final immersion in a dewatering type of oil.
Reducing Vendor Costs
A chemical blacking kit usually makes use of room-temperature blackening. Therefore, this in-house blackening method is easy to do. You do not need to wait for heat-up of the blackening solution. As a result, high vendor costs are also reduced. You can use this type of kit for both short runs and high volume processing.
When you make use of this method, parts can be blackened in as little as two minutes. Compare that with the 15 to 30 minutes required for hot oxide immersions. Therefore, you can blacken twice the number of parts with this type of solution.
The long-life bath and versatility of this type of blacking method enables you to blacken cast iron, forged steels, mild steel, powdered metal parts, and hardened tool steels. Also, salt bleed-out does not occur as it does with hot oxide.
The Hot Process of Blacking
Hot black oxide is used for the conventional hot process of blacking. This immersion method leads to a true black oxide iron magnetite finish. The premium-grade salt mixture blackens a broader range of steel alloys.
When mid-temperature oxide is used, it creates a true black oxide iron magnetite finish as well. This type of blacking process creates no caustic boiling fumes, thereby providing safer working conditions.
Hot and mid-temperature black oxide is applied in a seven-step type format whilst room-temperature applications are done in five steps. Both hot and room-temperature black oxide can be used for blacking steel, stainless steel, cast iron, copper, cadmium, brass, zinc, electroless nickel, and nickel.
Needless to say, you won’t find a better finish than oxide to prevent corrosion, add dimensional stability, improve lubricity, or provide a decorative finish to auto parts and other machine components. The oxide also improves the adhesion quality of metal, thereby permitting paint and other finishes to last longer and hold better.