Core Temperature Critical for Economical Operation
Gentle and Energy-Efficient Forming of Composites
In order to produce, by hot forming, high-performance components out of planar and pre-formed composite semi-finished products, circulating hot air ovens are required to heat thermoplastic composite materials homogenously: that means temperatures have to be the same in the surface and the core. Temperature tolerance is merely ± 2 °C here. This also enables precise results with hybrid semi-finished products, i. e., tailored parts.
According to information provided by producer HK Präzisionstechnik GmbH in Oberndorf, Germany, their circulating hot air ovens consume up to 90 % less energy than units operating on a conventional process. The largest type they supply to the automotive industry in the U.S. of America. "Major users have rated our circulating hot air ovens as efficient and process-secure, and an energy supplier has made the same statement", points out Heinrich Ernst, head of marketing at HK Präzisionstechnik.
He states that their oven can also pre-heat pre-formed composite semi-finished products in a gentle, homogenous and precise way. Such types of semi-finished products are, e. g., glass mat reinforced thermoplastics (GMT) or low weight reinforced thermoplastics (LWRT), pre-formed prepregs as well as hybrid materials.
A new variant of the oven is designed to heat "advanced" GMT, which is a semi-finished product based on polyamide and reinforced with carbon fibers. The challenge of the process is to thoroughly heat the semi-finished products to approx. 280 °C, while applying nitrogen for inertization. The share of oxygen inside the oven needs to be under 2 %, to prevent the material from oxidizing. The required amount of nitrogen the unit withdraws directly from the atmosphere, feeding it into the oven.
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