The importance of quality finishes in galvanising and powder coating

publication date: Sep 8, 2008

 | 

author/source: Medway Galvanising Company Ltd

The protective powers of two separate processes – hot dip galvanising and powder coating - have enabled the architectural metalwork industry to evolve products that offer maximum longevity, durability and aesthetic value. Advances in modern technology have allowed the 150 year old process of hot dip galvanising to become totally compliant with contemporary demands for a corrosion-free metal finish.

Rust is the major problem for mild steel and iron – for every two tonnes of steel manufactured, it is estimated that one tonne is to replace steel lost to rust. For the architectural metalwork industry, this posed a huge problem, but with hot dip galvanising, this issue is eradicated. The procedure involves zinc, one of the most naturally occurring elements on the planet and also one of the most recyclable. A thick zinc envelope covers the metal surface, sealing it via an alloying reaction. This electrochemical, or sacrificial protection as it is also known, occurs because the zinc sacrifices itself to protect the metal to which it is alloyed whenever there is damage to the sealing coat of zinc. This has been a standard and proven method of protecting mild steel and iron for decades, with many companies, including Medway Galvanising performing the process inhouse in order to assure maximum quality control.

However, companies that combine hot dip galvanising and powder coating under one roof are few and far between because of the incredibly complex process involved successfully combining both disciplines, as Phil Roberts from Medway explains. “Problems arose initially with the two industries working in isolation from each other,” he says.

“Powder coating technology was developed over forty years ago but when it was applied to galvanised metal, all sorts of problems emerged, including adhesion, pinholing and rough finishing, due entirely to the fact that neither industry understood the other. At Medway Galvanising we have combined the two procedures under one roof and by adopting a more scientific approach, have removed the risk factor.”

Powder coating is an advanced method of applying decorative and protective finish. This has opened up a new field of creativity for architectural designers, allowing a far broader range of options, for example, dressing a site in corporate colours or turning functional street furniture into a design feature in its own right. The process comprises a mixture of finely ground particles of resins and pigments, sprayed onto the surface of the metal. The charged powder particles adhere to electrically ground surfaces until heated and consequently, fused into a smooth coating.

“After hot dip galvanising, the powder coating process has to be stringently regulated to ensure a completely smooth, uniform finish,” continues Phil. “We utilise a ten stage pre-treatment method. Contracts scheduled for both processes are identified in the production programme and after galvanising, are subject to the pre-treatment, including de-gassing which applies a zinc phosphate conversion coating. Without the pretreatment programme, optimum conversion coating will not be possible.”

Producing the control and balance in the chemical procedures involved in the two disciplines, together with the controlled curing of the powder coating will ensure that the metal is protected to the highest quality standards (BS EN ISO 1461 + BS EN 13438), with up to 25 years guarantee. The finished product, available in a variety of finishes, from metallic to colours in varying gloss, is testament to the research, development and synergy between two essentially different finishing disciplines, into which companies like Medway Galvanising have invested.

Architectural metalwork is by nature prone to the vagaries of the weather and the environment, and therefore metal that is doubly protected will save costs over the long term on maintenance, repair and replacement. The value of hot dip galvanising combined with the design potential and decorative qualities of powder coating ensures longevity for any metalwork product.