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Powder Coating – New Trend

ENVIRAL® large-scale powder coating
ENVIRAL® large-scale powder coating  
16 steel columns with double powder coating
16 steel columns with double powder coating  
Steel columns with anti-graffiti powder coating, photos: ENVIRAL® GmbH
Steel columns with anti-graffiti powder coating, photos: ENVIRAL® GmbH  

Magazine: Bauingenieur
Edition: January 2006

Powder coating – The new trend in surface finishing of steel


In aluminium construction, powder coating has been well established for centuries when it comes to high-quality, visually appealing finishing of surfaces. The process is now also increasingly used for the surface finishing of steel. The possibilities and options are best illustrated by the building project of the Leibniz Grammar School in Berlin.
Structural steelwork has for several years been enjoying a Renaissance in architecture: “light” and transparent facades and building components characterise modern residential and office buildings. This architectural trend is made possible by the use of steel that facilitates the building of lean, elegant structures. The only weak point in the use of steel is permanent corrosion protection. Structural steel parts for outdoor use must meet the corrosion protection requirements of corrosion protection classes up to C5 long, which means a protection time (forecasted service life of the coating system before first repair) of more than 15 years. To fulfil these demands hot-galvanising and/or wet enamel systems have so far been mainly used for corrosion protection. However, thanks to the development of powder coating systems designed specifically to ensure corrosion protection, powder coating – which is becoming more and more popular in structural steel engineering as an ecological alternative to solvent-containing wet paints – can also be used to ensure optimum corrosion protection.
ENVIRAL® Oberflächenveredelung GmbH is taking this new trend into account. The company has been successful as a leading supplier of powder coating services to customers from the façade, structural and building construction trade since August 1996. The company is located in Niemegk (state of Brandenburg, at the BAB9, approx. 25 km south of the Berlin Ring). In September 2004, they added a system for the powder coating of large parts to their company facilities, thereby opening up new dimensions for powder coating: Components of up to 13 m length, 3.60 m height and 2.50 m width, weighing up to 3,000 kg can be coated automatically or in a skilled manual process in the new, 1,800 sq.m. hall. The daily coated surface capacity is 2,000 sq.m.

Advantages of powder coating

The aluminium, untreated steel and galvanised steel parts are – depending on their size and quality of the material – prepared for powder coating. This is done with a wet-chemical or mechanical process. The methods employed include degreasing/iron phosphatising and chromium-free aluminium preparation, pressure or airless blast cleaning. Afterwards a powder coat of approx. 50 to 120μm is applied – one layer for indoor use, 2 layers for outdoor use (up to 160-180µm) to achieve corrosion protection class C2 to C5 long according to DIN EN ISO 12944-2. Such powder coating can be used instead of wet coating substances that – depending on the coating system chosen – have to be applied in three to six layers on the blasted steel surface to achieve corrosion protection category C5 long according to DIN EN ISO 12944-5. Wet coats have to have an overall nominal layer thickness of 240 to 500µm. And powder coating has other advantages, too:

  • It is environmentally friendly, since no solvents are used.
  • It is economic, since material utilisation is as high as 98%.
  • It is of top quality, since there are no runs or drops.
  • It is independent from weather, since it is processed at the plant.
  • It can be immediately put to use, since the best mechanical properties and weathering resistance is achieved immediately after coating and thermal curing
  • More than 3000 colours and effects are available.
  • It is flexile, since the most diverse requirements can be fulfilled (e.g. anti-graffiti properties ensured by special, high-gloss clear powder top coats)
  • It is durable, since any surface quality can be reproduced


The prerequisite for passive corrosion protection through powder coating is the respective constructional corrosion protection to be planned and implemented by designers, builders, metal and steel engineers, i.e.

  • no false edges of any kind whatsoever (especially for outdoor structures)
  • no inaccessible areas, acute angles, sharp edges
  • no porous or interrupted welding seams (especially for outdoor structures)
  • no components that are not designed with corrosion protection in mind, i.e. components with unfavourably placed reinforcement plates
  • no oozing of grease, oil or lubricants from false edges if they were not removed prior to the assembly of the components


ENVIRAL® - Introducing: Powder coating of large parts

One of the first large-scale powder coating projects of ENVIRAL® was the powder coating of the steel structure of Leibniz Grammar School in Berlin Kreuzberg. 96 tons of steel incorporated in the roof structure, in load-bearing columns and in design elements on the outside had to be protected from corrosion, and at the same time a harmonious colour concept had to be achieved for the new sports hall. The contracting authority, the Department of Education, Administration and Organisation of the District Office Berlin Friedrichshain-Kreuzberg, commissioned architect Dieter Hundertmark of the Hundertmark Berlin architects’ office with the job. Mr. Hundertmark decided for powder coating of the steel structure. His decision was based not only on the high quality of the surface finish, but also on the ecological and economic processing of powder coating and above all on the very high corrosion protection achieved with this process.

The parts for the inside of the roof structure – trusses, purlins, tension bars, etc. – were airless blasted to a surface roughness of Rz = 50-70µm (cover ratio Sa = 2.5), then dedusted and tempered. After the steel surface had been prepared by this means, one layer of powder coat in RAL 9010 mat was applied (layer thickness of average 80µm) and thermally cured in the powder gelling oven. The elements to be used on the outside were prepared the in the same way. To achieve passive corrosion protection, a corrosion protection primer (thickness of 80µm on average) was applied and baked. The second layer was a top powder coat in RAL 7044 mat (layer of 80µm minimum) which was again cured in the powder gelling oven.

An extraordinary challenge from the technical point of view was the powder coating of the 16 load-bearing columns that support the roof of the sports hall on the gable sides of the building. Each of these columns is 9 m long, has a diameter of approx. 40 cm and weighs about 900kg. In addition to the pre treatment required for powder coating of steel structures for outdoor use, and two layers of powder coating (primer plus RAL 7044 mat top coat) a third top coat was added with anti-graffiti powder coating (special, transparent powder coating with anti-graffiti properties).

All elements and components were then individually wrapped in tubular foam bandages, stacked on pallets where possible and loaded on trucks for transportation to the building site, lot after lot. Only the columns were wrapped in stable adhesive film to protect their anti-graffiti finish. Unloading and assembly of the individual parts was very carefully done by the structural steel company Loharens GmbH, using textile hoisting equipment. Thanks to the careful handling of the elements – from loading in the coating plant, transportation to the building site to unloading and assembly – there were only a few scratches or damaged sports on the powder coated surfaces that needed repair. ENVIRAL® was responsible for repairing damaged surfaces of the total 96-ton steel structure. The repairs were carried out within forty hours. A wet enamel in the same colour and shine as the powder coat as well as a suitable wet-enamel primer were used. The entire steel structure including powder coating and repair was accepted and taken over without any complaints in early August 2005.


Conclusion:

The possibilities and advantages of powder coating for architectural steel structures are increasingly, albeit somewhat hesitantly, discovered. ENVIRAL® is taking up this trend in steel finishing. First successful projects confirm the high expectations and demands that planning architects and building owners place both on the quality of powder coated steel surfaces and corrosion protection.


Category: Press
10.01.2006




More information.


ENVIRAL ® Oberflächenveredelung GmbH – D-14823 Niemegk, Altdorfer Weg 6 – Telefon +49 (0)33843 642-0 – Telefax +49 (0)33843 642-24 – 0800 368 47 25