Sherardising or Zinc thermal diffusion is a process of galvanization of ferrous metal surfaces, also called vapour galvanising and dry galvanizing. The process is named after British metallurgist Sherard Osborn Cowper-Coles (son of naval inventor Cowper Phipps Coles) who invented and patented the method c. 1900.[1][2][3][4] This process involves heating the steel parts up to 350-500 °C in a closed rotating drum that contains metallic zinc dust and possibly an inert filler, such as sand.[5] At temperatures above 300 °C, zinc evaporates and diffuses into the steel substrate forming diffusion bonded Zn-Fe-phases.
Sherardising is ideal for mechanical parts and parts that require coating of inner surfaces, threaded connections, and wear. Part size is limited by drum size. It is reported that pipes up to 12 m in length for the oil industry are sherardised.[6] If the metal surface is free of scale or oxides, no pretreatment is needed. The process is hydrogen-free, acid cleaning in pretreatment is not necessary, furthermore processing temperature remove hydrogen potentials and hydrogen embrittlement is prevented.
Application
During and shortly after World War I, German 5 pfennig and 10 pfennig coins were sherardised.
Sherardizing applications categorised by industry. [7]
Burial of pilings for pole line tension wire utilize sherardising, due to its remarkable ability to stave off contact corrosion in burial.[8]
Residential Natural gas meters use sherardising to remove the threat of sour gas stress cracking in cast materials.[9]
Train rail use railroad hardware that has been sherardised, again due to contact in burial, tension springs and threaded screws.[10]
Standards
- ISO 17668:2016 (replaced BS EN 13811:2003): Sherardizing. Zinc diffusion coatings on ferrous products. Specification
- ISO 14713-3:2017: Zinc coatings. Guidelines and recommendations for the protection against corrosion of iron and steel in structures. Part 3. Sherardizing
- ASTM A1059/1059M:2024 (Standard Specification for Zinc Alloy Thermo-Diffusion Coatings (TDC) on Steel Fasteners, Hardware, and Other Products)
See also
References
- ↑ US patent 701298, Sherard & Cowper-Coles, "Process of depositing metals on metallic surfaces and the product thereof", published 3 June 1902
- ↑ "Original Patent (Google patents)".
- ↑ Porter, Frank C. (1991). Zinc Handbook. CRC Press. ISBN 978-0-8247-8340-2.
- ↑ Eric J. Mittemeijer; Marcel A. J. Somers; F. Natrup; W. Graf (18 April 2026). "20 - Sherardizing: corrosion protection of steels by zinc diffusion coatings". Thermochemical Surface Engineering of Steels: Improving Materials Performance (2. ed.). Elsevier Science. pp. 835–. ISBN 978-0-85709-652-4.
- ↑ H. G. Arlt, "Finishes on the Metal Parts of Telephone Apparatus", Bell Laboratories Record, Volume 9(4), 175 (December 1932)
- ↑ "Main - Alteriver". 20 February 2025. Retrieved 4 August 2026.
- ↑ "SHERART - Markets". SHERART. Retrieved 5 August 2026.
- ↑ MacMoy, Richard (8-3-2026). "Helical Piles & Anchors | MacLean Civil Products". MacLean Civil. Retrieved 04-08-2026.
{{cite web}}: Check date values in:|access-date=and|date=(help) - ↑ "AY McDonald - ArmorGalve Service Bulletin". Liberty Sales & Distribution. Retrieved 4 August 2026.
- ↑ "Sherardizing Production Line for Railway Rail Fasteners - Anyang Railway Equipment". www.at-railfasteners.com. Retrieved 4 August 2026.