In the HVAC industry, the most popular production material is galvanised sheet and stainless steel sheet. At Alnor, we use a variety of galvanised sheet coatings, ranging from Z100 to Z600, where the number indicates the minimum amount of zinc (Zn) in g per m2. Acid-resistant stainless steel sheets, on the other hand, are sold in grades 304 and 316L, according to AISI. In both cases, the aim is to increase corrosion resistance. While sheets with typical Z140 or Z275 zinc coatings are affordable while offering sufficient protection, stainless steel sheets have significantly higher resistance at a materially higher cost, even several times higher.
So is there anything in between, a product that would provide increased corrosion resistance at a moderate investment cost?
Aluminium and magnesium to the rescue
The answer to this demand is the elements AL and Mg, which, when added alongside Zinc to the typical continuous flame coating technology, enhance the properties of the protective layer. Little is needed, 2.5 to 3.5 per cent Aluminium and 1.5 to 3 per cent Magnesium (depending on the smelter), to form a stable barrier against corrosive agents.
Coating ZM310
t Alnor, we have started production from ZM310 sheet metal according to EN 10346, which means 310g / m2 and a typical thickness of 24 µm. These sheets can be formed, cut and welded analogous to those ‘Zinc plated'. They can also be painted. With thicker sheets, there is a self-regenerating effect of the coating on the cut edges, leading to even more effective corrosion protection. Long-term sample tests showed at least twice the resistance of 'galvanised' in all categories of environmental corrosivity. Magnelis® ZM310 from ArcelorMittal has even received RISE approval for use in C5 environments to EN ISO 12944-2 with an expected life of 15 years.
The coating is also highly resistant to scratches and damage, and the sheet metal is 100% recycled.
The photo shows the level of corrosion in the salt spray, showing the clear superiority of the ZM coating (author: Voestalpine).
In the Eurovent Association's official guide REC 6-16, ZM310 zinc-magnesium coated sheets are indicated for use in category C5 environments. (link: https://www.eurovent.eu/publications/eurovent-6-16-2021-corrosion-protection-of-air-handling-units-first-edition/)
What's on offer from Alnor?
The Spiral System® in diameters DN 80-500 mm is now available, which includes, among other things, ducts, elbows and T-pieces, caps, dampers, ejectors and roof bases, as well as silencers. You can recognise the products by the ZM symbol in the code, e.g. BSL-ZM-200-90
Summary
ZM310-coated sheet steel ventilation products have increased durability extending service life, generate lower operating costs and are more cost-effective compared to post-galvanised zinc plating, aluminium or stainless steel.