Sherardizing

Definition - What does Sherardizing mean?

Sherardizing is the formation of a corrosion-resistant, zinc-iron alloy coating, on the surface of steel or iron. The method involves the heating of the object in an airtight container that has zinc powder. A thermal diffusion process occurs and the zinc diffuses into the object’s metal surface, forming the zinc-iron alloy.

The external layer of the zinc-iron alloy formed is a pure zinc adherent coating with a smooth surface and uniform thickness. It provides a very strong and long-term protection against corrosion and abrasion.

This process, which is ideal for small objects, is named after the inventor Sherard O. Cowper-Coles and has been practiced since the year 1900.

Corrosionpedia explains Sherardizing

The Sherardizing process involves diffusing of the zinc into the base metal of the object, which is mainly iron. The temperature of the container is controlled such that the melting point of zinc is not reached and this ranges between 608-932ºF (320-500ºC).

A coating of a uniform thickness of between 15 and 80µm is achievable using this method, which is ideal for both small and geometrically complex objects. The size of the objects that can undergo this process is limited to the container's dimensions, which are 2m × 5m × 4m.

In addition to the high corrosion and abrasion resistance properties, the adherent surface is very good for:

  • Metal to rubber bonding
  • Painting
  • Lubricants
  • Application of organic coatings
  • Sealants
  • Oils

Other advantages include:

  • Use of low temperatures for the process
  • Suitable for irregularly shaped objects
  • Suitable for recessed objects
  • No hydrogen embrittlement
  • Suitable for sintered material since it is a dry process

Objects that have undergone this process have many applications and are commonly used in:

  • Roof support hinge pins in the mining industry
  • For rubber bonding
  • Universal joints and bend limiters in submarine telecommunication systems
  • Rail track Fittings
  • Cable hooks for communication systems
  • Metal fasteners and fittings in construction

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