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Optimized heat insulation

Bayer MaterialScience AG : 15 June, 2004  (Company News)
With the lowest thermal conductivity of all insulation materials used in practical applications, high compressive and shear strength and low water absorption, polyurethane rigid foams are tried-and-tested insulation materials that have also proved their worth in the pipe and pipeline insulation sector over the last 30 years.
Bayer MaterialScience AG has played its part in the growth of this technology by developing tailored raw material systems and distributing appropriate processing technology right from the outset. Now Bayer has made another significant advance with one of these pipe insulation processes. The enhanced mixing head draw-through method with specially formulated polyurethane raw material systems enables the thermal conductivity of the polyurethane insulation layer to be reduced much further, because now developers of polyurethane systems can focus even more closely on creating optimum foam structures.

'Manufacturers of polyurethane rigid foam for pipe insulation now have a whole range of production techniques at their disposal,' says Dr. Ingo Brassat, thermal insulation specialist at Bayer MaterialScience. 'Our program includes raw material systems to fit any requirements, from casting and spray application to polyurethane insulation in situ. As a leading provider on this market, we work in close partnership with our customers to continuously develop insulation methods and the associated raw material systems.'

As part of this work, the developers of Bayer MaterialScience were also working on the foam density distribution of insulation layers produced by the widely used casting process. During this process, the polyurethane raw material mixture is dispensed into the pipe via a stationary mixing head. Through a process of slow expansion, it gradually fills the entire area between the outer casing and the pipe itself. With this method, the polyurethane system has to travel considerable distances and curing times must therefore remain slow. A certain amount of compression is also required to remove air bubbles. Usually, therefore, depending on the process, pore sizes are not optimum, density distribution is not homogeneous and comparatively large amounts of material are used.

The means to overcome these challenges has been known in principle since the 1960s. 'Instead of moving the foam, the technique is simply to move the mixing head through the pipe using the draw-through method,' says Dr. Brassat. The advantage of this is that the polyurethane can react in situ, and the foam only needs to expand in the circumferential direction. This ensures the density distribution of the foam is particularly homogeneous.

Today's mixing head draw-through method offers a further advantage thanks to the moveable mixing head. Because the drawing process means there is no need for increased flowability, this allows developers to concentrate on creating optimum foam structures for minimum thermal conductivity when developing the polyurethane mix.

'Our task was to take this good idea and use state-of-the-art methods to bring it into line with current technology,' says Dr. Brassat. As their starting point, the Bayer MaterialScience experts used a c-pentane-blown polyurethane rigid foam system that had been a tried-and-tested pipeline insulation material for years. This was adapted for the mixing head draw-through method using mainly specially adapted catalysts.

The results were a great success. The polyurethane systems modified in this way and dispensed by a special mixing head made by the polyurethane machinery manufacturer Hennecke, a wholly-owned subsidiary of Bayer MaterialScience, produce foam with a particularly micro-cellular structure. The Lambda values (thermal conductivity coefficients, measured at 50 C) achieved were around 24 W/cmK, i.e. around ten percent below the values achieved using the casting method. Because the foam density distribution is better overall, the draw-through method also enables pipes to be produced with EN 253 conformity using considerably fewer raw materials. 'Now there's even more reason for companies to use the intelligent mixing head draw-through technology,' says Dr. Brassat.
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