Aluminium Extra
THE DEPARTURE OF CHROME USED IN ARCHITECTURAL POWDER COATING
Chrome-based surface treatments for metals have been around for some time providing excellent corrosion resistance by offering an impervious coating to a metal substrate that eliminates surface oxidisation . These systems have been used in the pretreatment of aluminium profiles , sheet and castings for some time and have demonstrated their excellent resistance to extreme weather across the British Isles . So , why are chrome-based pretreatment systems being withdrawn in the UK later this year ?
After forming by either extrusion , rolling or casting , on contact with air , an aluminium surface begins to oxidise . Not seen by the naked eye initially , the aluminium oxide quickly builds up over time and is seen as a light grey surface discolouration . Without any pretreatment a subsequent surface coating will have reduced adhesion on the aluminium . If the applied finish is porous , as is the case for most wet applied and powder coated finishes . then exposed to weathering , the aluminium substrate will slowly continue to oxidise under the applied coating , eventually forcing the applied finish off the aluminium over a period of time , this is seen as surface finish peeling .
The importance of a quality pretreatment process cannot be overstated , it forms the foundation for a robust powder coating finish by cleaning the aluminium surface of all contaminants and oxidisation . The water based immersion or spray pretreatment applied to aluminium by the powder coating applicator includes an initial degrease process followed by an acid or alkaline etch . These processes clean off any surface contaminants and oxidisation . The aluminium pretreatment , sometimes referred to as a ‘ conversion coating ’ or ‘ surface passivation ’, essentially seals the aluminium surface prior to applying a wide choice of powder coated finishes .
Chromates or phosphor-chromates , often referred to as just ‘ Chromates ’, have been the traditional choice of pre-treatment for architectural aluminium since the introduction of powder coating in the 1970 ’ s . Over the last few decades alternative , chrome-free systems have become popular and have gained a reputation for being as robust as their chrome counterpart . Many powder coaters now use chrome-free pre-treatment systems with some UK and Ireland members of QUALICOAT successfully using chromefree pretreatment systems now for over 20 years .
Prior to Brexit the European Court placed a sunset date on the use of Chromates until 21st September 2024 . Following Brexit , the UK set up UK REACH for which the HSE has responsibility for regulatory functions . As the UK grandfathered over the original
termination date for the use of Chromates the termination date was subsequently incorporated into UK legislation .
Last year , following submissions by a consortium of seven Authorisation Holders , the European Court annulled their termination of the use of Chromates . Annulment means that effectively the law never existed , so Chromates can continue to be used as a pretreatment in the Republic of Ireland and Europe , pending any further European legislation being put forward .
Since Brexit , the UK no longer recognises European Law , therefore the termination date for the cessation of use of Chromate remains in the UK as 21st September 2024 irrespective of any developments within the EU after 31st January 2020 . This position has subsequently been confirmed by the UK ’ s HSE .
QUALICOAT continues to undertake extensive research in the pretreatment of aluminium developing further changes in the process that can offer extensive levels of protection for various exposed locations , more information is available on the Association website .
www . qualicoatuki . org
40 AUGUST 2024 CLEARVIEW-UK . COM