Increased Efficiency With Infrared Radiation in a Vacuum

Rapid and energy-efficient production of lightweight components, March 2, 2016. Image credit: Brett Jordan [CC BY 2.0 ()]

When consolidating carbon fiber reinforced plastics (CFRP), individual layers of fibers and plastic connect to each other under pressure and high temperatures to form a homogeneous plate. Fraunhofer researchers have developed a method which is fast and energy efficient, and which is also suitable for smaller quantities as well as high-temperature plastics: CFRP is directly irradiated in a vacuum by infrared radiation.

Current CFRP production often involves large, expensive equipment. The molten polymer is pressed between the reinforcing carbon or glass fibers. Using this method, the plastic is only heated indirectly by the massive mold. The molds have to be moved, cyclically heated with variotherm process control, and cooled again. Depending on the process, this can require a significant amount of energy and time. The often high investment costs for presses and other large systems mean that smaller and medium-range batches are not profitable. However, there is an alternative for this: Researchers at the Fraunhofer Institute for Chemical Technology ICT in Pfinztal can heat the CFRP directly in a vacuum with infrared radiation. The energy acts where it is needed. Immediately. For the mold wall, the researchers have found a material that transmits infrared radiation in the desired wavelength range, but which undergoes almost no internal heat expansion. Usually, vacuum based variotherm manufacturing processes take between 30 minutes and several hours, depending on the thickness of the component. Using the ICT’s approach, this is done in less than 60 seconds.

The system produces distortion-free plates. “This is a major challenge when manufacturing with CFRP. We heat and cool symmetrically, use a mold wall with minimal thermal expansion and operate at relatively low process pressures, in order to avoid squeeze flow,” says Baumgärtner. The smooth surface of the mold wall also creates an almost reflective CFRP plate surface. This is very advantageous in the final component, particularly for applications in visible areas.

The plastic heats up immediately once the infrared radiator is switched on. Scientists cannot yet say exactly how much energy is saved. “We don’t have the precise comparative figures. The effect is evident, though, since there are no large thermal masses that have to be heated up and cooled down again, as is the case with the pressing process,” the researcher adds.

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