During the last decades, the market share of products made of reinforced plastics increased rapidly. The low density, corrosion resistance and high fatigue performance of such materials provide a wide range of benefits for different applications. Parker Hannifin has developed fully composite hydraulic cylinders for 380 bar applications which are up to 60 percent lighter than their standard steel cylinder equivalents. The fully composite cylinders were tested extensively under various mechanical and environmental influences to verify the robustness of the products. The results confirmed that the new composite barrel technology for hydraulic actuators is competitive to standard metal solutions while providing further benefits in terms of weight and corrosion resistance.
Industrial demand on products with low density in combination with outstanding mechanical properties requires continuous R&D effort. While for metals the development of new lightweight alloys and their joining technologies is the common approach, developments and production of composite materials moved into the focus as a reasonable alternative. Compared to metal matrix composites, fibre reinforced plastics offer additional weight savings by the low density of the matrix material.
For high pressure hydraulic cylinders, accumulators and pressure vessels typically high strength steel alloys are chosen. Such materials are not suitable for lightweight applications. Depending on the level of weight efficiency of the original design, utilization of high performance metal alloys, typically based on aluminium or titanium, is the current state-of-the-art lightweight solution. Because an increase in strength typically results in low ductility and, correspondingly, reduced fatigue performance, their benefits for actuators are rather limited. Incorporation of fibre reinforced plastics can overcome the conflict of reduced fatigue at higher strength. Ideally, the load-bearing structure of the products would be made entirely out of composite, thus without a metallic liner, and without a metallic barrel that supports the axial loads applied on the end caps. Parker has developed an ultra-lightweight high pressure fully composite hydraulic cylinder series called Lightraulics®. An example of a Lightraulics® C-Series composite hydraulic actuator is shown in Figure 1.
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Article by Dr.-Ing. Olaf Stelling, the Value Stream Manager for the Composites Technologies Europe Business Unit of Parker Hannifin in Stuhr, Germany. He holds a diploma in Production Technologies and a PhD on New Developed Lightweight Aluminum Alloys, both from the University of Bremen in Germany. He began his career with Parker in 2010 but previously held research engineering positions at the Material Testing Institute University of Stuttgart and the Foundation Institute of Materials Technology, Department Lightweight Materials in Bremen.