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By: Wiremark  06-Dec-2011
Keywords: Wire, Corrosion, Fence Wire

HiSPAN zinc-aluminium fencing wire

Corrosion is the relentless degradation of metals due to reaction with their environment and is ultimately enormously costly. Although unavoidable, corrosion can be managed by selecting appropriate materials, and using them correctly. There are a vast number of factors affecting the severity of corrosion, from the actual environment and material properties to construction methods and maintenance.  

Generally, corrosion is accelerated by :

  • temperature
  • moisture
  • contamination (e.g. salt laden air, acids)
  • fretting or abrasion
  • galvanic effects (different metals in contact with each other)
  • coating quality

Considering these factors and New Zealand’s unique environmental conditions (below) controlling the severity of corrosion in this country is certainly a challenge:

  • a temperate climate, relatively warm and wet
  • a very long coastline and therefore a large proportion of land near the sea (salt-laden air and in some cases abrasion from wind-borne sand)
  • geothermal areas producing acidic/sulphurous conditions
  • a wide range of climatic conditions

TUFF TO RUST, TUFF TO BUST !!  

To meet the varied and challenging requirements of fencing in New Zealand, a high level of local manufacturing capability was developed, as well as New Zealand’s own fencing wire standard. Pacific Wire now has over 45 years experience as New Zealand’s only fence wire manufacturer and the national fencing wire standard (NZS3471:1974) surpasses equivalent international standards. NZS 3471 sets down a rigorous specification for zinc coatings; the level, adhesion and concentricity, as well as wire strength and ductility. Zinc-aluminium fencing wires are coated utilising 95% zinc / 5% aluminium alloy coating. The new zinc-aluminium alloy retains the renowned protection of hot-dip galvanised coatings (excellent barrier coating, metallurgically bonded to the steel and providing very effective cathodic protection to any exposed steel). The small aluminium addition however, enhances the anticorrosion performance of the coating by making it more weather resilient. The dull, grey oxide layer formed on zinc-aluminium is more durable than the soft, white layer formed on pure zinc. This oxide layer itself acts as a barrier, retarding corrosion of the zinc-aluminium alloy. Pacific Wire has had accelerated corrosion tests (salt-spray) conducted by an independent research company, Materials Innovations. The tests compared the performance of galvanised wire with identical wire coated in zinc-aluminium alloy. As shown in the graph, long term, the galvanised coating corroded at four times the rate of the zinc-aluminium wire.

Pacific Wire manufactures zinc-aluminium fence wire in two coating weight levels. A heavily coated wire and a medium coated wire (often referred to as “4 life” & “2 life”). The heavily coated zinc-aluminium wire has a guaranteed minimum coating weight equal to the zinc coating weight required by the fencing wire standard NZS 3471.  This wire will last up to four times as long as galvanised wire with the same coating thickness (four times the life).  The minimum coating thickness on medium-coated wire is half that specified for heavily coated zinc or zinc-aluminium wire.  In most situations, this wire will last up to twice as long as a heavily galvanised wire (twice the life).  A wide range of conditions are catered for by the range of fence wires manufactured by Pacific Wire – galvanised wire and zinc-aluminium wire in two coating weight levels. The performance difference between the three coatings available has been illustrated in the table opposite.

Wiremark label, proudly NZ made.

Keywords: Corrosion, Fence Wire, Galvanised Wire, Wire

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