There are many questions and misconceptions over the different types of coatings and finishing available for fencing applications. This does sometimes lead to incorrect specifications and confusions when specifying and ordering fences and can also lead to unexpected results over time, particularly in relation to corrosion resistance in highly corrosive conditions.
There is also a possibility that as a result of this confusion, a manufacture with the best intentions may give incorrect advice to his customer. Therefore, I hope that today we will be able to share some basic information about the common finishes in the market and their common used. I will share them in order from the lowest to the highest in both cost and quality (as with all things in life there is a cost and quality correlation).
1. POWDER COATED BRIGHT WIRE
Bright wire actually means an untreated steel wire. This means that there are no coatings applied and this is the wire that be rusted easily when exposed to atmospheric conditions. So the basic type of coating or protection that is being applied to bright wire is Polyethylene Powder. When it comes to Powder Coating, there are 2 main types of coating available and each type with its own unique characteristics.
1) Polyethylene Powder common named PE, is the most common plastic. Its primary be used in packaging such as plastic bags, plastic films and containers including bottles, etc.
2) Polyvinyl chloride, common named PVC, is the world’s third-most widely produced synthetic plastic polymer, after polyethylene and polypropylene.
While PE is relatively lower in cost as compared to PVC, they are not as durable lasting as PVC and hence, we recommend a PVC coating where higher corrosion resistance is required. PVC coating is normally added to galvanized wires for extra durability and long life. PVC coating is not affected by high salinity, acidity or alkalinity. Therefore, it is suitable to be used places that are subjected to volatile fumes such as; paper, cardboard or ceramic tiles manufacturing; water desalination plants, swimming pools with chlorine or coastal locations.
This product is commonly used to produce fence for fencing purposes in most of the abovementioned places. Fencing mesh and post, is one of the products that we stock. Also Chain Link Fence, it comes in various roll lengths. It normally comes in either black or green and gives a great visual appearance and better corrosion resistance especially when it needs to be partly buried in some situations. The flexible is that colors can be required by customer's needs.
Galvanized wire is basically bright wire that has been protected against corrosion through the chemical process of galvanising. This 300 year old process involves coating the steel wire with a protective, rust-resistant metal, like zinc. Zinc is most commonly used because it offers the best cathodic protection in comparison to other source material. The coating weight or thickness of the zinc is usually determined by considerations such as; the life expectancy of the wire, the intended purpose of the wire or the environment to which the wire is going to be exposed and of course, cost.
The advantage of galvanising is its excellent flexibility and softness. There are 3 types of zinc coatings, Standard, Medium & Heavy Coating, and we produce them in compliance to the Australian Standards AS/NZS 4534-2006 & AS2423. The difference in the coatings are the amount or thickness of coating which is measured by grams/m2 of coverage.
Common applications include tie wire in for use in agriculture such as for vines, orchards and farms, weaving wire in the fencing and netting industry, as well as for packaging of products and many other day to day uses.
The galvanising process used for fence applications is generally a hot dip galvanising process in order to give coating weights that are consistent with the AS 2423 specifications. Although electro-galvanising is offered for some applications, this does not give the corrosion protection required in fencing applications, albeit that it looks bright and shiny. The zinc forms a barrier against corrosion by providing cathodic protection to the ferrites in the steel. It is different from a paint or plastic coating as it protects by chemical reaction and not surface cover.
In the fencing industry, there are different manufacturing methods used in producing finished product. Typically the fences are manufactured from pre-galvanised wire where the wire itself is galvanised and then worked into the various fence types. In some instances the fences are produced from bright wire and then hot dip galvanised after manufacture. This does result in a less uniform looking finished product and does sometimes give a somewhat lumpy looking surface. Generally ASW will use pre-galvanised wire for production of our Galvanised Weld Mesh Panels and Galvanised Chainmesh Rolls.
3. Zn/Al ( GALFAN)
A newer form of coating commonly known as Galfan® was introduced in the 1980s. It’s superior corrosion resistance has led to acceptance in uses such as wire ropes, fencing, springs and many more. The Galfan® coating on the wire is a special alloy of Zinc and Aluminium in a ratio of either 95%/5% (ZnAl) or 90%/10%. Most Galfan® galvanised wire is produced using a double-dip process in which the wire is first hot-dipped in a regular galvanising bath, then immediately re-dipped in a Galfan® bath.
The 3 types of Standard, Medium & Heavy Coating also applies to our Galfan® mesh and is also manufactured in compliance to Australian Standards AS/NZS 4634-2006 & AS2423.
Notable products that we produce that has Galfan® finishing (Al5%, Zinc 95%) is the 358 High Security Fencing Weld Mesh and Fixed Knot Field Fence. This Zn/Al shield protects the parent material giving superior corrosion resistance properties to that of conventional 100% Zinc hot dipped galvanising.
4. Zn/AL + POWDER COATING
This combination simply means the addition of Powder Coating to Galfan® wire to further enhance the durability and lifespan. This is considered top-of-the-range finishing and is used in places where there is exposure to highly corrosive compounds such as chemical fumes or very high salinity. Australian Steel & Wire can produce this fine product on request.
Should you require more enhanced corrosion resistance, then the next most logical choice would be 100% high grade stainless steel.
5. STAINLESS STEEL
Stainless Steel is one of the few products that are used commercially to produce fences that can last much longer than coated mild steel fences due to the presence of Chrome in the alloy.
However, these alloys are harder to work with and the material cost is significantly higher than corresponding coated ferrite wires. That is why Stainless Steel fences are not common other than in extreme weather condition areas.
Generally other products such as sinks, appliances and other high cost end products are more likely to be produced from Stainless Steel.
The above are the 5 most common types of finishing found in the market.
Before you decide which type of finishing would best suit your application, there are also other variables that you should also consider such as the tensile Strength (MPa), Steel Chemistry, Wire Diameter and local conditions.
I trust that you find the above information regarding different finishing options useful.