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Galvanising (also known as Hot Dip Galvanising) is the process of applying a zinc coating to steelwork which prevents corrosion of the protected metal by forming a protective physical barrier. The process of galvanising steel has been in use for over 150 years. Galvanized steel is widely used in applications where rust resistance is required, and can be identified by the crystallization patterning on the surface often called a ‘spangle’.
Process
Pre-Treatment Inspection
Pre-treatment inspection ensures that all products are safe and suitable to galvanise. The inspection process checks for contamination on the products which could dislodge the zinc coating later in the products lifetime; for example: welding slag, excessive grease, oils and paint.
Galvanising Treatment
Steel products are dipped into molten zinc at a temperature of approximately 450°C until the temperature of the steel products reaches the same as the zinc. During this process the molten zinc reacts with the surface of the steel to form a series of zinc/iron alloys. These alloy layers protect steel from corrosion typically for up to 40 years and more in the UK external environment.
As the products are removed from the zinc, the zinc on the products surface will begin to solidify, as this happens excess zinc is removed to ensure a smooth finish. The products are then usually transferred to a quench tank or drying area where they are cooled to allow handling.
Visual Inspection
Galvanised products are visually inspected to ensure that all internal and external surfaces are fully coated.
Benefits
Protection
The zinc coating deteriorates at a very slow rate giving the products a long and sustained life.
The zinc coating corrodes to provide sacrificial cathodic protection to any small areas of steel exposed through drilling, cutting or accidental damage; scratches are sealed by weathering products from the zinc.
Where the damaged area is larger, the sacrificial cathodic protection prevents the sideways creep of rust which can undermine later applied paint coatings.
Coverage
Because it is formed by dipping steel in molten zinc, all parts of the surface of the steel are coated - inside, outside, awkward corners, and narrow gaps which would be impossible to protect in any other way.
The coating actually tends to build up at vital corners and edges - rather than thinning out as do brushed, sprayed and other dipped coatings.
Coating toughness
Galvanising is unique: the process produces a coating which is bonded metallurgically to the steel. No other coating process has this feature, and as a result galvanised steel has by far the greatest resistance to mechanical damage during handling, storage, transport and erection - an important factor where steelwork is to be shipped around the world.
Applications / Uses
Virtually any steel product can be galvanised, however typical products include:
• Bolts, Nuts and Washers
• Steelwork prior to powder coating application
• Pipe
• Corrugated Roofing
• Wire Mesh
• Conduits
• I-Beams and Sections
• Gates
• Bins and Buckets
