The Gas Gravel Wiping System

The PWT designed and installed Gas Gravel Wiping System for galvanising operations that require a thicker layer of zinc at wire speeds normally in the range of DV 120 to DV 160.

Essentially the wire passes through a loose gravel bed in a controlled atmosphere consisting of hydrogen sulphide and a reducing gas for Class 3 Coating. Out of this a zinc sulphide layer (shiny, non-oxidised coating) is formed.

The zinc sulphide layer has greater tensile strength and elasticity than zinc oxide and allows a fast withdrawal of the wire without a break-down of the skin.