Hot Dip Galvanising Process
What is Hot Dip Galvanising?
Hot Dip Galvanising is a process developed to prevent steel from corroding. Before the process can take place, the steel goes through a thorough chemical clean; this removes all rust, oil and mill scale from the surface. When the cleaning process has been completed and the cleaning solution has been rinsed off, the coating process can begin. The steel is dipped into a bath of molten zinc that has been heated to around 460 °C (860 °F). The steel is then removed from the bath and left to cool in a quench tank. When the cooling process is complete, the zinc coating is then metallurgically bonded to the steel.
Ten Good Reasons For Hot Dip Galvanising
1 - Long life
Galvanizing provides an easy to clean surface which can give a maintenance-free life of over 50 years. (This is dependent on the environment it is being used in). When maintenance eventually becomes necessary, it is straightforward: no complex preparation treatments are necessary.
2 - Competitive first cost
For many applications the cost of hot dip galvanizing is lower than that of applying alternative coatings. The reason is simple: alternatives - particularly painting - are very labour intensive compared with galvanising which is a highly mechanized, closely controlled factory process.
3 - Lowest lifetime cost
Low initial cost and long life make galvanizing the most versatile and economic way of protecting steel for long periods. There are bonuses from no maintenance or extended maintenance intervals: fewer problems of access in remote areas, difficult terrain or when buildings are closely packed together; also when there are safety restrictions e.g. electricity pylons.
4 - Reliability
The process is relatively simple, straightforward and closely controlled. The thicknesses (weights) of coatings formed are regular, predictable and simply specified. Hot dip galvanizing is one of the few coatings which is completely defined by a British Standard (BS EN ISO 1461).
5 - Speed of application
A full protection coating can be applied in hours; a complicated paint system can require a week.
6 - Coating toughness
Galvanizing is unique: the hot dip 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 construction - an important factor where steelwork is to be shipped around the world.
7 - Complete 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.
8 - Three-way protection
Galvanized coatings protect steel in three ways:
- Firstly, the coating weathers at a very slow rate giving a long and predictable life.
- Secondly, the coating corrodes preferentially to provide cathodic (sacrificial) protection to any small areas of steel exposed through drilling, cutting or accidental damage; scratches are sealed by weathering products from the zinc.
- Thirdly, if the damaged area is larger, the sacrificial protection prevents the sideways creep of rust which can undermine paint coatings.
9 - Ease of inspection
Galvanized steel simplifies inspection of the protective finish. The nature of the process is such that if the coating looks continuous and sound, it is! Thicknesses - simply specified through BS EN ISO 1461 - can be easily checked with an electronic probe.
10 - Faster construction
Galvanized steel is ready for use. No further site surface preparation, painting, touch up or inspection is necessary. Once constructed the galvanized steel is ready for use: and cladding can begin immediately, thus accelerating the construction time.
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