JEC COMPOSITES MAGAZINE - Issue #74 - July 2012 - 16

building
sector. The first step was to find out whether the sandwich construction would perform as well in real life as it had in the feasibility study. So Holland Composites constructed a prototype – a set of 6 panels bound together, sanded and coated just as if they formed an actual part of the façade. This test panel made it possible to confirm that the Twaron-reinforced composite could enable a flat, smooth appearance. Combined with its minimal degree of thermal expansion, which gave the composite material the green light, this meant that Holland Composites could begin construction. Although the largest panel would be 15 metres high and 3.5 metres wide, it wasn’t their size that caused the biggest challenge during production. It was the fact that they had to be perfectly flat. Composites can be moulded in virtually any shape. And curves are easy, because humans can’t spot small differences in angle or direction in a curved surface. However, we are very good at detecting the slightest deviation in a flat surface – especially when the surface is glossy. So Holland Composites had to design a huge table – larger than the largest 15m by 3.5m panel – that they could use as the base for injection moulding the laminates for the composite panels. Once this remarkable table was constructed and in place at their factory in Lelystad, they could start the actual panel production. The panels were produced by a well-known composites production technique called “vacuum injection moulding”. The first step is to lay down the unidirectional fabrics of Twaron para-aramid and Tenax carbon fibre on top of a film on the surface of the giant table. Next, a layer of PIR foam is put in place, and the sandwich is completed with a second set of layers of Twaron and Tenax fabrics. Plastic film is then wrapped around the sandwich to make the mould completely air-tight. A vacuum is created and tubes leading from vats of vinylester resin are attached. Once the valves in the tubes are opened, the vacuum pulls the resin out of the vat and into each and every nook and cranny inside the mould. Once the resin has hardened, the impregnated fabrics and foam are transformed into a tough, durable sandwich construction with a perfectly flat surface. The panels were unloaded into a pretty unique building site. For one thing, it was clean, uncluttered, and sealed off from both traffic fumes and whatever the Dutch winter weather could throw at it. The site was even heated, and had air extractors to ensure that it was virtually dust-free. Why? Once the panels were in place, they needed to be bound, sanded together and finally coated with a slick layer of glossy white paint. And that super-smooth surface would be impossible to achieve with dust and rain settling between the panels or on the wet paint. But first, the architects’ vision of a super-flat façade depended on how the panels were actually mounted. Each one had to be fixed to the steel skeleton with extreme precision. If just one was only a single millimetre too far forward – or too far back – it would distort the shape of the entire 100m-long, 25m-wide façade. And with 185 panels to mount, there were nearly 1,800 mounting points that needed to be positioned with sub-millimetre accuracy. The main contractor and the construction company that built the underlying steel structure had done an excellent job and met the guaranteed accuracy of placing the mounting hooks within 3mm of the designated position. However, to achieve the desired level of smoothness for the façade, an even higher level of accuracy was required. In order to solve this dilemma, Holland Compo

Building the façade
Early one wintry morning, while the rest of Holland was still sleeping, the start of a long convoy of trucks left the workshops of Holland Composites to make the one-hour journey to the Dutch capital. Their load: 185 composite panels made with expertise and precision. The Stedelijk Museum is right in the heart of Amsterdam, so to avoid bringing the city to a halt, Amsterdam traffic regulations only allowed a small window of opportunity for such a big delivery – everything had to be unloaded by 6.30 am. Needless to say, this couldn’t be completed in a single day. The transport operation lasted for six weeks!

Fig. 4: The actual new façade of the Stedelijk Museum

(Photo by Danny Wilms Floet)

16 jec composites magazine / No74 July 2012

JEC COMPOSITES MAGAZINE - Issue #74 - July 2012

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #74 - July 2012