Consistently good galvanised steel products will be produced when the essential requirements listed are incorporated at the design and fabrication stages of production. Design features should be discussed with the galvaniser. Close liaison between design engineer, materials engineer, specifier, fabricator and galvaniser will ensure high quality galvanised products, minimum cost and faster delivery.
Size and shape
Facilities exist to galvanise components of virtually any size and shape. When an article is too big for single immersion in the largest bath available it may be possible to galvanise it by double-end dipping, depending on the handling facilities and layout of the galvanising plant. Large cylindrical objects can often be galvanised by progressive dipping.
Design and fabrication of components for galvanising
Vessels or hollow structures which incorporate enclosed sections must have provision for adequate venting during galvanising. At galvanising temperatures any moisture present in closed sections is rapidly converted to superheated steam, generating explosive forces unless adequately vented to the atmosphere. For the safety of galvanising personnel, equipment and the work being galvanised, it is essential that venting is provided.
Barrier protection, cathodic protection and the zinc patina are what provide the galvanised coating its long-lasting protection.
1 The galvanised coating provides complete coverage of all steel surfaces and acts as a barrier protecting the steel from the surrounding environment.
2 The galvanised coating cathodically protects the steel from coating imperfections caused by accidental abrasion, cutting, drilling, or bending.
3 The zinc patina is insoluble and passive, which slows the corrosion rate of the zinc. The zinc patina is a critical part of the galvanised coating’s longevity and requires natural wet and dry cycles to form.
Painting of hot dip galvanised steel is sometimes required for decorative purposes, to provide an identifying colour or to enhance the service life of the article.
The GAA can provide guidelines which direct specifiers and applicators to recommended paint systems and advice on surface preparation and application practices that will provide a durable paint finish over galvanising for a particular application. Where a paint or similar type coating is to be applied to the galvanised coating, the galvaniser should be advised at the time of order.
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Galvanizing Association of Australia (GAA)
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