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To galvanise or metal spray? The same by definition!

Supplier: MSSA Interweld By: Kevin Healey, MSSA Interweld
22 July, 2015

The dictionary definition of galvanise is 'to coat (iron or steel) with zinc.' Hot dipped galvanising is a well-established process used to protect steel from corrosion by applying a layer of zinc.

Steelwork is immersed briefly in molten zinc with layers, usually of an even thickness, dense and metallurgically bonded to the steel. Thickness is typically .002-.006 in (50 – 150). There is however, another process that can be used to coat steel with zinc.

Metal spraying using arc spray or flame spray is an alternative method of coating with zinc (or many other materials) to hot dipped galvanising. All methods of metal spraying involve the projection of small molten particles onto a prepared surface, where they adhere and form a continuous coating

To create the molten particles, a heat source, a spray material and an atomisation/projection method are required. The small molten particles are projected onto the surface to be coated. Upon contact, the particles flatten onto the surface, freeze and mechanically bond, firstly onto the roughened substrate and then onto each other as the coating thickness is increased.

As the heat energy in the molten particles is small, relative to the size of the sprayed component, the process imparts very little heat to the substrate. Unlike the galvanising process, as the temperature increase of the coated parts is minimal (rarely above 100°C), heat distortion is not normally experienced. This is a major advantage over hot-dipped galvanising.

Metal spraying has proved itself to be extremely effective in its 100 years plus existence, in all manner of applications, ranging from engineering coatings in gas turbines to corrosion protection on park benches.

It is particularly used to apply corrosion protection to large structures such as offshore oil platforms, bridges and construction steelwork. As a protective system for structural steelwork it is unsurpassed, being the only system recommended by International and European Standards EN ISO 14713, as giving greater than 20 years to first maintenance in very aggressive environments. Such environments include the marine splash zone, as well as all other categories.

Galvanising steel is limited to corrosion protection using zinc, whereas metal spraying can also use, amongst other materials, aluminium, which is much more resistant to corrosion in areas typically exposed to salt such as oil platforms and road bridges.

In summary the metalspray process offers:

  • Low heat input during spraying eliminates the risk of component distortion
  • There is no limit to the size of component to be treated
  • Components can be treated on site and therefore no transport or waiting issues and giving you the opportunity to Up Sell to your customer.
  • Metalspraying is used to restore corrosion protection on damaged areas of welded galvanised steel and International Standards exist covering this
  • Coating thickness can be varied from area to area to provide extra protection in critical areas
  • The Metalspray process is not limited to Zinc as Aluminium, Steels, Bronzes etc. can also be applied for a variety of applications
  • No re-work required from Galvanising dross
  • The Metalspray coating is porous and therefore the perfect surface to accept paint (that's if required as it is not necessary). No need to pre-etch etc.
  • "AS/NZS 2312 Guide to the protection of iron and steel against exterior atmospheric corrosion" is the Australian Standard based on the International ISO standard that provides guidance for architects , engineers, builders the surface coating industry and users of protective services in general, on coating system for the protection of iron and steel against exterior atmospheric corrosion.