St Augustin, Germany - Machinery expert Hennecke GmbH says use of fibre composites often starts when the characteristics of other materials no longer meet the customer's requirements. In the manufacture of car load floors, the specific properties of light composites combined with a polyurethane matrix completely meet the mark: complex geometries that are extremely stable and very light.
The process can make a high-quality trunk load floor with minimised warpage and low weight.
Hennecke explains that a three-layer sandwich structure is often used in composites, especially in for automotive lightweight construction in which flat and shellshaped panels have to resist high bending loads.
The top and lower facings are made of a fibre-reinforced composite that ensures the compound's flexural strength and resists the pressure and tension stress that arise. The fibres function as reinforcement components and are connected to each other by a fabric construction or a solid mat.
In the automotive area, materials such as carbon or glass are mainly used because of their extremely high strength values. According to Hennecke, cost reasons mean that carbon fibre is usually applied only in the high-end of the market whereas glass features in serial applications.
Polyurethane (PU) is preferably used for fixing glass fibre mats because its controllable foaming properties facilitate lightweight construction. Thanks to its fast reaction, it also meets the short cycle times required. In a sandwich construction, the PU matrix not only fixes the glass mat but also links the core, which is made out of a paper honeycomb structure, to the facings.
The core itself can be composed of different geometries and materials. In serial automobile manufacture, paper honeycombs are often used as the core of sandwich structures. This combination of materials allows for the manufacture of composites that exploit and boost the positive characteristics of the individual components while cancelling out unwanted features. End products thus benefit from high component strength and stability combined with low weight.
"For an efficient coating process, PUR-CSM technology is indispensable," said Hennecke. The advantages consist above all in the very even and reproducible distribution of the polyurethane and the fibres, which, among other things, has a significant effect on the warpage and contributes to reducing the required amount of material and thus the weight of the component.