GOING TO EXTREMES!
Published by: Composites in Manufacturing
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The ability of composites to operate effectively under very high and very low temperature conditions is well documented and the capabilities to deliver these products can be found throughout the UK supply chain.
But one Devon-based company is taking this to extremes – manufacturing components which can handle temperatures as low as -269°C – that’s just four degrees higher than absolute zero – through to 600°C.
Rockwood Composites in Newton Abbot has capability in producing components which need to function effectively at extremely low temperatures of cryogenic suspension systems of MRI scanners, and also extremely high temperatures at the rear end of missiles or rockets.
Composites have been used in cryogenic suspension systems for a long time. It started with filament wound bands (hoops of fibre that suspend a magnet in a cryostat vessel containing liquid helium, say) and these are still made in large volumes. Rockwood Composites uses prepreg for its bands, not wet filament winding.
Mark Crouchen, Rockwood Composites managing director (right), explains: “The advantages of this are the material properties are very tightly controlled. You’re not having to mix resin or catalyst, which can mean varying viscosity and physical properties. The material we use comes in with certification. We can then deposit/lay down material at a much faster rate than filament winding. This ensures our bands have high performance, and cost is relatively low.
“We are involved in a lot of cryogenic insulation systems, for components under high stress, and under extreme temperatures, operating at liquid helium temperature – that’s 4.2 kelvin.”
For one particular Rockwood Composites band, an axial strut for an MRI scanner, the temperature gradient from one end to the other is over 300K. It is also very highly stressed and there is a need to strike a balance between strength, stiffness and thermal conductivity. Composite bands can be made of carbon fibre or glass, depending on the required thermal load and stress.
At the other end of the spectrum, at 600°C plus, Rockwood Composites provides components for missile fins, and cowlings and covers on the back of large missile systems. With missiles, as with rockets, there are two sources of high temperature; firstly, at the front, because of the high speed of the missile travelling through air; secondly from engine plumes and propellants around the back of the missile.
A lot of the latter is generated in the early stage of launch, with very high transient temperatures. Missile components can reach up to 600°C albeit for limited periods, then have sustained temperatures of over 200°C for long periods, up to 15 minutes.
These effects result from hot gases impinging around rocket motors and stabilising fins, and that’s where high temperature capabilities are most needed.
Composite materials can soften and degrade in high temperature, so a great deal of effort goes into choosing the right resin system for each component.
Full article can be found here