Attributes of Chemical Blacking

 

What is it?

Chemical Blacking is sometimes referred to as ‘Blackening’ or ‘Blackodising’and 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.

 

Dimensional Changes

One of the key differences with chemical blacking is that unlike processes such as anodising where a coating is formed both above and below the surface, Chemical Blacking has a negligible effect on the dimensional tolerances of the part. Blacking produces a smooth, even coating making it ideal for components such as screw threads, bearing fits, threaded holes and internal machine parts. Chemical Blacking also offers increased lubricity and anti-galling properties to components.

 

Corrosion Resistance

Chemical Blackening increases resistance to corrosion and is particularly effective in environments with moisture. Typically this is improved through immersing components in wax, oil and other preventative sealants which are absorbed by the coating.

 

Hot & Cold

Depending on the material that is being coated, either a ‘Hot’ or ‘Cold’ process can be used in order to apply chemical blacking. 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. A ‘Cold’ process can also be applied to ferrous metals (except stainless steel) where the coating can be applied at room temperature and no hot solution is needed. This ‘cold’ process consists of a copper selenium compound rather than black oxide.

 

Low Cost

One of the main benefits of this process is its 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.

 

Get in touch

Silchrome have one of the widest arrays of metal finishing processes in the UK, all carried out in our production facility in Leeds. We are fully ISO certified and pride ourselves on our fast lead times and exceptional service.