PROCESSING | WINDOW PROFILES
In the new design, a PBT blend (with 55% glass
fibre reinforcement) is co-extruded with PVC “in mechanically strategic areas”, said McMaster. In one example – that of wind load – a steel
Right: BASF has replaced metal stiffeners in window profiles with co-extruded sections of its Ultradur PBT
stiffener placed at the centre of the profile would not reduce bending by much, as it is not actually touching the PVC (there is a large toler- ance required between metal and plastic). However, the new design has PBT and PVC connected for the whole length of the profile – which more effectively prevents bending. A similar effect is seen under thermal load, when the profile wants to expand on the outside. Another important factor
is that a metal insert transfers significant amounts of thermal energy – from inside to outside. This is avoided in the case of PBT. There are also some production aspects to bear in mind: for instance, the higher abrasiveness of glass-filled PBT means that hardened screws, cylinders and die parts are needed. Finally, BASF carried out a cost comparison of the two systems. “The earlier system has a strong cost depend- ence on the price of steel,” said McMaster. “The new system relies on extrusion speed and fibre orienta- tion – which you can manage. Our evaluation in Germany showed cheaper total production costs.”
Efficiency drive PVC profiles have an important role to play in making buildings more energy efficient – and a key technology here is the incorporation of insulating foam into the window profile design. Keith Scutter, a consultant at Resin Technology in the US, said that ‘inward foamed’ Celuka technology has steadily
Right: Though PVC window profile recycling fell in the UK last year, Veka is planning a new plant there
opened up more opportunities in PVC profiles. “As material formulations, process controls and technology have advanced, this product has grown in use dramatically – especially over the last 15 years,” he said.
As well as the self-skinning technology of the original Celuka process, he said that co-extrusion – with a thin capping layer of UV-resistant material – has further improved profile design. “Co-extrusion allows for cost savings, with the expensive colouring and additives being concen- trated only in the profile faces,” he said. The density of the product
is critical, and is controlled by two factors: the production process; and the design. During production, factors such as barrel and die heating, screw speed and the level of regrind material
will all affect final density. Similarly, specialist tooling maintains a consistent temperature profile across the profile, allowing closer control of density. “Celuka melt does not have the same flow
characteristics as rigid PVC due to the gases that are in solution within it,” he said. n Profiles 2019 takes place in Pittsburgh in the USA on 4-5 June next year. More information on the event, organised by Applied Market Information, is available HERE.
Sealing the deal Teknor Apex has developed a new series of thermoplastic vulcanisate (TPV) compounds that have the high resilience needed for door and window seals – and are an effective alternative to widely used thermoset polyurethane foams. Available from 40 to 70 Shore A, the Sarlink 8100 series can be foamed to a density of 0.20 g/ cm3
range, which is comparable to those of
urethane foam used in door seals but is difficult to achieve with standard TPEs. As TPVs, they have lower compressive set than standard TPEs, providing more of the resilience needed to withstand repeated opening and closing. The new compounds can be foamed using both chemical and physical blowing agents and are processed in standard equipment for thermoplastics. In other key differences from urethanes, TPVs do
not require a curing step, are recyclable, and do not present concerns about isocyanate monomer, said the company. Door and window profiles for sealing are
22 PIPE & PROFILE EXTRUSION | September 2018
www.pipeandprofile.com
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