ALUPROF
’ WHY SPECIFY POWDER COATING ’
BY WOJCIECH BROZYNA - MD OF ALUPROF UK
Powder Coating continues to be specified as just a colour . Whilst this approach works well in many instances , especially where there is a substantial supply chain , there are instances where coatings may be applied incorrectly . If a robust specification is not in place , this could cause issues with the finish in a few years after installation .
Architectural powder coating is a twostep process , the cleaning and pretreatment of the aluminium and then the powder coating itself . Only when both processes are correctly specified and completed , with suitably sourced materials for the location of the project , can the project be deemed to offer a sustainable powder coating solution .
Projects often carry not just extrusions but preformed sheet pressings cills , preformed column casings and often aluminium sheet used in composite spandrel panels . These are often powder coated in different locations which can introduce shading issues between batches , or indeed manufacturers of different powders . To further complicate matters , should aluminium castings need to be coated , these may be coated in a further coating facility . The key to success is to discuss the finishes of various suppliers of materials and agree a common specification .
Quality control can be achieved by recognising what variations in finish might be acceptable by agreeing up front both the colour variance and gloss variance on the proposed finish . The main issue is that being prepared for potential colour variation means that this could be potentially controlled to a degree to minimise its effect .
So , starting with the pretreatment specification , sometimes referred to as a conversion coating of the aluminium , either a chrome free or chrome-based system can be used for most locations . The main aim of this pretreatment is to completely seal the aluminium substrate to stop oxidisation and also to provide a key for the powder to adhere too . Alternatively , a thin anodised finish can be used prior to powder coating which offers a more robust pretreatment . There are also variations of pretreatment options when it comes to specifying projects near the coast when a ‘ Seaside ’ class of pretreatment can be used which incorporates a longer or deeper aluminium etch process in its application to remove aluminium substrate contaminants .
Whilst a colour specification may seem fixed , there are variances that need to be considered . Different powder manufacturers of the same RAL colour could vary in shade , indeed , even using the same powder manufacturer with different batches of powder there can be a very slight shading difference . The key here is to agree an upper and lower shading specification , if appropriate , or better still try to specify the powder manufacturer to minimise any colour variance if products are to be produced in different powder coating applicators .
In addition to colour there are a range of gloss levels available , these are generally referred to as , ‘ matt ’, with a 20 % and 30 % gloss level , ‘ semi-gloss ’, having approximately 60-65 % gloss level and ‘ full gloss ’ with 80 % gloss level . As with colours , gloss levels across powder manufacturers vary so care should be taken to agree upper and lower limits so that when the products are placed together there is very little variation .
The main parts of any powder coating specification should contain , details of the pretreatment system to be used , the colour specification , the gloss level and the class of powder to be used . If there are to be parts of the facade that are going to be coated in different plants , such as the addition of aluminium pressings or spandrel panels , the manufacturer of the powder would help further minimise colour variation .
Aluprof are licence holders of QUALICOAT , a globally recognised standard for powder coating procedure and quality . This association recognises the need for quality of the pretreatment systems , the architectural powder colours and the application quality . The association therefore licences both producers of the powders , the pretreatment systems and applicators to ensure that quality levels are attained and maintained . Regular inspections of QUALICOAT licence holders are undertaken by third party test houses . This is a crucial cornerstone of membership of QUALICOAT and something that Aluprof are proud to offer on all specifications .
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