Sherardizing process

Zinc dust is used in the sherardizing process where work pieces are tumbled with zinc dust in rotating steel dmms which are heated electrically or by gas to 370—420°C (149). The steel parts are uniformly coated with zinc. In the chemical and metallurgical industries, zinc dust is used as a reducing agent, in the manufacture of hydrosulfite compounds for the textile and paper industries, and to enhance the physical properties of plastics and lubricants (2). 

The sherardizing process involves diffusion of a zinc coating into steel by tumbling steel parts with zinc dust at high temperatures. 

Sherardizing-the process of coating iron or steel with zinc by heating the product to be coated in zinc powder at a temperature below the melting point of zinc. 

Sherardizing [After the inventor, Sherard Cowper-Cowles, 1900] A process for coating iron articles with zinc. The articles are placed in a sealed drum with zinc dust and sand. The drum is rotated and maintained at a temperature below the melting point of zinc. The mechanism is not understood. In 1990 the world consumption of zinc for this process was several thousand tons. See metal surface treatment. 

SHERARDIZING. The process for applying an adherent protective coating of zinc to steel parts by heating at 700°F (371°C) in contact with zinc dust in a rotating-drum container. 

Zinc is frequently applied to the surface of iron or steel by other methods. In the Schoop process, molten zinc is sprayed onto the surface by a blast of air in a manner similar to that used in spraying paint. In addition to metals, objects made of wood, leather, paper, and the like may be coated with zinc by this process. In the process of sherardizing, iron is covered with a thin layer of zinc dust at temperatures of 700 to 800°C. Under these conditions, zinc penetrates the surface of the iron to a considerable extent. 

MTiat is the difference in nature and process of manufacture of galvanized iron and Sherardized iron ... 

Cementation 350-800 10-50 75-125 Solid solution of zinc in 6 phase Cementation pack process known as sherardizing... 

Fig. 1.1 Effect of zinc coating weight on corrosion rate (for different zinc coatings) at Sheffield, England. Coating process = sherardizing, O = zinc plating, B = hot dipping, = zinc spraying, (Hudson, 1959).

Sherardizing is a diffusion process in which the steel parts are heated in the presence of zinc dust or powder in inert medium. Aluminium oxide or sand in amount of 20 % is added to the zinc powder as inert filler and 1 to 2 % halide salts are used as activator. The thermochemical treatment can be carried out in retort, rotated drum or as a pack-cementation process at 350 to 500 °C for three to twelve hours. The structure of the obtained layer is the same as the structure on steel surface after hot-dip galvanizing with a thickness about 50 - 400 pm... 

---