In mechanical engineering, there is a trend to use new materials which are an alternative to metals. This also applies to construction components and hydraulic systems, where more and more attempts are made to use plastics as construction material. This solution brings design, technological and economic benefits. The researchers from the Fluid Power Research Group of the Department of the Fundamentals of Machine Design and Tribology from Wroclaw University of Technology (www.fprg.pwr.wroc.pl), are working in this area, with an objective to create a complete hydraulic system whose basic elements such as the pump, valve and actuator are, entirely or in their substantial part, made of plastics. The paper presents the course and outcome of the design process and the research, the aim of which was to prepare a demonstration model of the hydraulic cylinder made of plastics.
The work on the model of the actuator started from an analysis of traditional methods of designing hydraulic cylinders made of metal. The authors analyzed the course of the design process, paying particular attention to aspects of the strength of the actuators’ structure. It highlights the main elements and the important nodes occurring in the hydraulic cylinders, namely the sleeve, the bottom, the head, the piston, the piston rod, the fasteners, the hydraulic fluid ducts, the sealing, and the bolts. An algorithm for the procedure in a form of a block diagram was presented, and the necessary calculations were made. Taking the characteristics of the actuator and its respective nodes into consideration, it was found that a number of metal parts may be replaced by plastics. The result of the operations performed is the proposal of a model of the actuator elements made of plastics. For this solution, a 3D computer model was prepared and studied by means of the FEM. The obtained results allowed the identification of the place, the nature and the value of deformation. Based on the results of the theoretical research, it was found that the structure of the actuator will not be effected in the course of its work in the assumed conditions. A demonstration model of the actuator was created according to initial assumptions. The next step was to prepare and conduct preliminary studies on the actual model. The first tests were carried out with no load being applied. The tests were made with different speeds of the piston rod’s movement and the operation of the actuator was observed. Next, tests of the loaded actuator model were conducted. For that purpose, it was put on a special stand with a metal actuator in such a way that a linear displacement of the two rods along a common axis was provided. In that system, the conventional actuator enabled the loading of the model’s piston rod. Tests were carried out at different values of pressure and speed within the full motion range. Based on the prototype’s volumetric efficiency measurement results, the operation of the tested actuator featuring the elements made of plastic was proved correct.
The theoretical and experimental research on the hydraulic actuator confirm the possibility of applying plastics as a construction material in devices of that type. The use of the actuators’ design algorithm showed that it can provide a theoretical basis for the design method of the actuators made of plastics. The algorithm, however, requires modifications taking into account the special properties of plastics due to their anisotropic nature. The development of a definitive method is planned in the context of further research. Additionally, the future development of a design solution for a cylinder of smaller dimensions, which could provide an alternative to traditional low-pressure actuators or pneumatic actuators. The future research direction is the analysis of the processes taking place in the individual parts of the plastic cylinders. A challenge of some kind may be to select sealing’s that will ensure long and trouble-free operation of the actuators.