Hot dipping galvanisation

As well as causing brittleness, the absorbed gas combines to form molecular hydrogen on the surface of inclusions and voids within the steel. Thus a gas pressure is set up in the voids and this may be sufficient to cause blisters to appear either during pickling or during subsequent processing such as hot-dip galvanising. 

BS729 1971 (1986), Specification for hot-dip galvanised coatings on iron and steel articles ... 

Although hot-dip aluminising of sheet might appear to resemble hot-dip galvanising very closely, there are several important differences which combine to make the process more difficult to operate. The main difficulties are ... 

It is estimated that approximately 40% of the world production of zinc is consumed in hot-dip galvanising of iron and steel, and this adequately demonstrates the world-wide use of zinc as a protective coating. The success of zinc can be largely attributed to ease of application, low cost and high corrosion resistance. 

In practice the thickest zinc coatings can be obtained by hot-dip galvanising or spraying. Table 13.7 compares the essential aspects of each coating. Plated coatings can also be produced mechanically in a wide range of thicknesses as well as electrochemically. 

Characteristics of coating Hot-dip galvanising A/etai spraying Plating Sherardising Zinc dust painting... 

Paint applied to a suitably prepared zinc coating will last longer than would be the case if it were applied direct to iron or steel, and the need for repainting thus becomes less frequent. With hot-dip galvanised or zinc-plated coatings, however, it is necessary either to use special primers or to prepare the surface before painting. This is primarily because most oil-based paints react with the unprepared zinc surface to form zinc soaps resulting in poor adhesion. 

In the Forth, Severn and many other suspension bridges, zinc coatings have an important function. The whole main structure is of steel and has been zinc-sprayed on the external surfaces, while the main cable and hanger ropes have been coated by continuous hot-dip galvanising. Case histories of galvanised multi-truss bridges cover more than 30 years. 

Hot Dip Galvanised Coatings on Iron and Steel Articles, BS 729 1971 (1986), British Standards Institution, London (1986)... 

Field of activity Egyptian market leader in Hot Dip Galvanisation industry (zinc galvanisation), specialised in galvanising towers for power transmission, lighting, communication, etc. 

Chemical Leasing in hot dip galvanisation - fluxing process Zinc Misr El Sewedy Egypt... 

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