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The aviation industry has shown the way. In areas where extreme weight reduction really matters, you will find that state-of-the-art sandwich materials have been flourishing for a long time.
(Published on January-February 2006 – JEC Magazine #22)
The current need to adapt sandwich parts to the specific component requirements in automotive mass production will continue into the future. This goes especially for developing PU systems that are suitable for special applications. True, other plastics are also used in combination with natural or glass fibres to produce composite materials – but when it comes to reducing weight while maintaining extra-high flexural strength, PU composites are simply unbeatable.
PU composite spray moulding, or PU-CSM
Glass-fibre- and natural-fibre-reinforced PU composite materials in the form of thin-walled products and PU sandwich structures with lightweight core layers made of paper are already on the market. PU-CSM (from Composite for fibre-reinforced parts and Spray Moulding as the core element of processing and shaping) has become the buzz word for various proven spraying technologies offered by Hennecke for the production of fibre-reinforced components. The names of these technologies are FipurTec Plus, NafpurTec, Com-purTec and MproTec.
The MproTec method just being launched is very similar to FipurTec Plus, a cost-effective process for manufacturing longglass- fibre reinforced automotive mouldings. Polyurethane and glass rovings are injected simultaneously into the open mould. Once the mould has been closed, the moulded part is shaped by the expanding foam of the glass fibre-PU reaction mixture.
When Multitec®, an innovative raw material developed by Bayer MaterialScience AG, is processed using the MproTec method (Multitec® Processing Technology), long chopped fibres are also combined with the PU mix-ture and injected into an open mould. The decisive difference with the FipurTec Plus process is that the PU mixture is applied in several layers – compact or foamed, and optionally reinforced or without reinforcement – and cured in the open mould at ambient temperature within reasonable moulding times. NafpurTec technology is a process where natural fibre mats made of hemp, sisal, flax, etc. are compression-moulded into a composite material using the Baypreg® F PU system. It can be used to manufacture thin-walled and extremely lightweight automotive parts with a strong weight-specific performance potential. Weight reductions of 30 to 45% can be achieved, compared to identical parts made of conventional materials.
Composite-PUR-Technology is the perfect choice producing PU sandwich structures efficiently. Its process steps are very similar to NafpurTec technology. The finished parts have a number of specific properties, such as high flexural strength, and are much more suitable for lightweight construction than other types of sandwich element.
Mouldings produced in the CompurTec way consist of core layers with a honeycomb or corrugated structure and glass-fibre-reinforced facings with the special Baypreg® F polyurethane matrix. Depending on the application, a great variety of core materials can be chosen from, including paper, aluminium and plastic materials – or even foams. Compression moulding of facings and core layers and shaping all take place in the mould in a single operation.
Specific process characteristics
In addition to the general features, CompurTec technology is distinguished by a number of specific process characteristics, including an extremely even spray application that allows “mass per unit area” fluctuations of under 10%.
Hennecke has a sound expertise in the special spray distribution qualities of the spraying nozzles i.e. working-point-specific characteristic spray-nozzle lines. The typical, bell-shaped spray application allows speedy adaptation of the spraying process to a specific component, by simple overlapping of the individual sheets. Shotto- shot cleaning of the spraying nozzle is unnecessary.
Even during spray application, the machine output can be adjusted without having to replace the spraying nozzle (e.g. output range 20-80 g/s). Hence, PU processors can flexibly adjust the material dispense in running production – from large-surface application to precise application in selective areas. If required, the CompurTec process can be complemented by the FipurTec Plus method, for instance to obtain additional, partial reinforcements.
A well-directed in-house technological consolidation resulted in the two processes being combined. The synergetic effect thus achieved is the ideal solution to counteract the rising cost pressure efficiently and, at the same time, obtain an improved functionality of components. Moreover, the operator is able to run CompurTec or FipurTec Plus on the same production line – either in combination or separately. CSM technology gives him ample flexibility.
Koller Formenbau und Kunststofftechnik GmbH in Dietfurt, Germany has already used CompurTec with success. Since the end of 2000, the company has been manufacturing trunk floors for Audi and Opel at its site in Pécs, Hungary. “The excellent mechanical properties of the parts produced using CompurTec and the specific process advantages achieved by the raw material Baypreg® F have enabled us to establish a new line of business,” summarises Max Koller, the company’s founder and managing director.
NafpurTec technology: Hennecke offers special NafpurTec production systems. These consist of modules that are optimisedfor the certain product types and required output quantites. - Finishing equipment. - HK-type high-pressure foaming machine. - Robot-guided dispensing system plus extraction booth. - SSH-type mould carriers. - Handling systems.
Key advantages of NafpurTech: - Substantially lower weight of automotive parts compared with conventionally used materials. - Production of lightweight, natural fibre reinforced moulded parts. - Short moulding cycle times. - Internal Mould Release (IMR) formulations feasible. - Process automation options. - Good break characteristics.