Aluminium finishing first

By Nick Cooper, technical director at Aluk.

At the start of 2019, Aluk will become the first aluminium systems company in the UK to have a flash anodising pre-treatment plant fully integrated into an inline vertical polyester powder coating line.

We’ve invested close to £3 million in this technology to give us – and our customers – a massive competitive advantage in the market. It means we will be able to offer all our aluminium products with an exceptional quality finish and a market leading warranty.

We see consistency, quality and durability of finish on aluminium as being potentially just as important as product design and performance in terms of winning future business.

Currently aluminium systems companies have relied on a mix of third-party suppliers for the pre-treatment of their aluminium, while also using a mix of horizontal, vertical and outsourced powder coating technologies.

There has been slow investment in plant and machinery in the market, with only a small number of companies able to cope with the volumes required without compromising on quality.

The lower end of the powder coating market is entirely unregulated, with applicators spraying everything from bicycles and steel sheet to aluminium profiles in the same facility, which can lead to contamination and quality issues. In contrast, at the top end, applicators, including Aluk, are certified and licensed by third-party certification bodies such as Qualicoat.

In between of course, there are powder approved applicators, which might have limited process controls but may not work to certification standards; so, the only way that a customer can be sure that the powder coating on their aluminium is truly up to a high standard is to look for the Qualicoat label. That indicates that the applicator has been subject to independent unannounced inspection visits by Qualicoat and that rigorous certification audits have been completed.

When it comes to pre-treatment, flash anodising is increasingly being recognised as the Rolls Royce solution, delivering significant benefits over both the chromium trioxide and later chrome-free chemical systems.

While it has been possible over recent years for pre-treatment companies supplying powder coat applicators to go chrome free in response to environmental concerns about chromium trioxide, switching to flash pre-anodising is a game changer because it requires investment in a completely new kind of plant.

Flash anodising essentially involves creating an unsealed anodised layer of aluminium oxide somewhere between 3 and 8 microns on the surface of the substrate. This delivers better protection against filiform corrosion as well as a marine grade finish as standard, but the surface needs to be sealed very quickly to maintain the optimum level of oxidisation. It can only generally be used then if the flash oxidisation plant is fully integrated into a powder coating line, as it is now at Aluk.

We have achieved almost zero manual handling within our process which reduces risk of contamination as well as eliminating the cost of flash anodising separately – and no other systems company in the UK can match that.

BS EN12206-1:2004 is the current British and European standard governing architectural powder coating, but this is included within the Qualicoat specification which is generally recognised as being more comprehensive. Both allow chrome, chrome-free and anodised pre-treatment to be used, but Qualicoat sets out minimum etch requirements within the pre-treatment process and a finished powder coated surface test for filiform corrosion resistance.

The Qualicoat etch requirement for standard certified powder coating is 1g/m2 and 2g/m2 for ‘Seaside’ classification which is Aluk’s current standard, but it has just introduced a third level of pre-treatment called Type OX for ‘Enhanced Seaside’ class of powder coating, which is specifically developed for anodic pre-treatment. As you might expect, it is this Enhanced Seaside classification that Aluk now has the capability to apply for with our fully integrated flash oxidisation and vertical powder coat paint line.