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Carbon Fibre Reinforced Compounds

Carbon fibre reinforced compounds

Top performance for high-performance materials

We are familiar with carbon-fibre reinforced materials, often called CFK, from more exotic applications such as the construction of racing cars, aircraft or sports appliances. Price plays a minor role in these cases as its light-weight properties are the most important factor in the selection of material. AKRO-PLASTIC would now like to also make these properties accessible to other industrial segments at an economic price point.

Carbon fibre can demonstrate its strengths particularly where low component weight and high stiffness are required. Although these fibres have been manufactured industrially for several decades, the high price of fibre has prevented the widespread use of this reinforcement material.

In the last few years, there has been much more intensive use of carbon-fibre fabric not only for aircraft construction, but also in wind power plants and more recently in vehicle construction as well. This has resulted in new capacities for the production of carbon-fibre. However, this has so far not had any significant impact on the price of fibre.
Carbon fibres are often used as a fabric or composite, whereby there are large quantities of edge cut-offs which can no longer be used in the same process.

In 2013, AKRO-PLASTIC GmbH, a compounder for engineering plastics from Niederzissen, in the German state of Rhineland-Palatinate, took notice of those cut-offs and developed a process to condition them. The objective of this procedure was to transform the cut-offs into a form suitable for the compounding process, which fully maintains the properties of the carbon fibres and at the same time achieves good dosing of the fibres. Sections of fabric which were left over from car body manufacturing at BMW for example, were used as a starting material. After the successful development of the conditioning process, the AKROMID® ICF product portfolio was established at AKRO-PLASTIC within just a few months. The compounder offers carbon-fibre reinforcement of between 10% and 40% for all standard thermoplastic polyamides, whereby even special settings such as mixing with other reinforcement materials are also possible (see table 1).

Lightweight without compromises
If you compare the mechanical properties of the carbon-fibre reinforced polyamides with those of conventional glass-fibre compounds, you can easily see that similar properties can be achieved with a significantly reduced level of reinforcement using carbon-fibre reinforcement. As a result, components with a much lighter inherent weight can be manufactured without any compromises in terms of the technical properties (see graph 1).

After the successful market launch of its carbon-fibre reinforced polyamide compounds, the compounder has now also developed other materials based on polyketone (AKROTEK® ICF) and PBT (PRECITE® ICF). These polymers also demonstrate the sophisticated properties of carbon fibre, like the polyamides (see graph 2).

The ICF compounds offer a comparable property profile as conventional carbon-fibre compounds at a much lower price. This now enables applications which were previously not feasible due to the high cost of materials. Specifically, it is now possible to replace highly reinforced glass-fibre materials with ICF compounds with lower reinforcement level (reducing the component weight) or to use the cheaper ICF materials in established applications with carbon-fibre reinforced thermoplastics to reduce costs. Series applications already implemented now primarily require the functions of electrical conductivity and stiffness.

In fuel-carrying components, a minimum level of electrical conductivity is required for safety reasons. Quick connectors (figure 1), which aft Automotive GmbH in Greven builds into static dissipative fuel systems, are manufactured by MKS Kunststoff-Spritzguß GmbH from the high-temperature material AKROMID® T1 CGM 15/10 S1 (6431). The materials is an impact-modified glass and carbon fibre-reinforced PPA, which in addition to the electrostatic discharge also has mechanical properties allowing the complex latching functions and the assembly of the quick connector.

The ICF compounds offer a comparable property profile as conventional carbon-fibre compounds at a much lower price.

A similar requirements profile is fulfilled by the fuel filter bracket very cheaply manufactured by Hasenthaler Kunststoffverarbeitung from AKROMID® B3 CGM 15/20 1 black (5489). This has also allowed Mann + Hummel to verify the price-performance ratio of the material following comprehensive testing. The balanced ratio of glass fibre and carbon fibre reinforcement also allows precise manufacturing with the strictest tolerances. (Figure 2).  Most components made from ICF compounds use the extreme stiffness of the material at low filler levels. As such, Grammer GmbH successfully replaced a PA66 GF 30 with AKROMID ® A3 ICF 10 (5117) in the centre console for BMW and in doing so reduced the weight by over 15% with the same mechanics. Other examples of successful weight saving are the control panel steering wheel from Joma-Polytec GmbH and a roof rack manufactured by JAC Product in Michigan.

The control panel steering wheel bracket from AKROMID® A3 ICF 20 (5102) carries all the control elements of the steering wheel and must position the components with minimal vibration and with precision. Here, a polyamide 66 GF 50 was replaced saving significantly more than 20% in weight. With the roof rack manufactured from the crabon-fibre-reinforced PA/PP blend AKROMID B3 ICF 15 1L, the maximum weight reduction was achieved with the addition of the AF-Complex TM propellant. The component weight was reduced compared to the glass-fibre-reinforced polyamide 6 by around 600 g to under 1 kg and meets all the requirements in dimensional accuracy and mechanical load. The black color, which is inherent to all carbon-fibre compounds, could be considered a limitation, but is a welcome side-effect for many applications.

Engine covers in cars are almost always black because most plastics discolor significantly within hours under the conditions in the engine compartment. The high temperatures, the unavoidable contact with aggressive media and the necessity to be able to disassemble and reassemble parts in the engine compartment make it necessary to use robust materials. The polymer of choice is polyamide. Today, mineral or glass-fibre mineral reinforced polyamides are often used. These materials are easy to process and meet the mechanical requirements, but the surface quality of these components are not easy to control. The high demands of designers are not always met. Carbon-fibre reinforced materials are an excellent alternative here, because the mechanical properties demanded can easily be met with a 10% filler content. A positive side-effect is a significant weight reduction of around 20% with a significantly more homogeneous surface quality.

Even the most sophisticated visible components can be manufactured. Radiator grilles, which are almost the same in all cars, typically have horizontal blades, which must be highly rigid due to their function. The components are also in the direct field of vision of the car passengers and should therefore fit into the dashboard design, particularly in terms of quality. Accordingly, the requirements for surface quality of the plastic parts are high, especially where an additional lacquering step is to be avoided. With AKROLOY® PARA ICF 40 black (6128), a very stiff material (e-module approx. 40 GPa), the Dr Schneider Group from Kronach-Neuses was not only able to meet the purely technical requirements, but also manufacture blades with excellent surface quality (figure 3). These radiator grilles are used in the current BMW 7 series.

When using ICF compounds, the focus must be not only on the excellent technical properties, especially the high stiffness combined with low component weight, but also the possibility of high-quality surfaces: "Lightweight construction with aesthetics."

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