What is sherardizing coating and how it differs from hot dip galvanizing?

Sherardizing is a solid diffusion process in which goods are heated in the presence of zinc dust and inert material as sand. The process is normally carried out in a slow rotating closed container at temperatures ranging from 320 ºC to 500 ºC. The zinc / iron alloyed coating is subsequently zinc phosphated resulting in clean passivated surface. The coating closely follows the contours of the basis material, and uniform coatings are produced on articles, including those of irregular shape. Process follows international standard EN 13811 "Sherardizing. Zinc diffusion coating on ferrous products. Specification"

Sherardize coatings have a mat grey surface and may show scratches resulting from normal contact with other fasteners. Due to the hardness of the coating, such scratches are superficial and not detrimental to its corrosion resistance.

Due to the diffusion on zinc in the base material surface, coating adhesion is better than hot dip galvanized and mechanical galvanized coatings.

Sherardizing coatings show a harder, smoother surface finishing compared to hot dip galvanizing, as well as a better control of coating thickness. These facts allow a better control of friction between cone shape of wedge bolt and their expansion clips, making they convenient for expansion anchors. On the opposite, hot dip galvanizing items may not provide sufficient control of friction sensitive parts, and its operation can be adversely affected. While achievable coating thickness of sherardize are similar to HDG ones, control thickness is superior.

HDG wedge bolt

Sherardized wedge bolt

The service life of sherardize coatings in a given environment is approximately proportional to their coating thickness.

Typical minimum sherardize coating thickness for our products is 40 μm.

For estimated life of sherardized coatings, you can read corrosion resistance HDG.