Research on series of hydraulic cylinders made of plastics

Among the materials which are used to design modern machines, growth in participation of plastic materials can be observed. Also in hydraulics, more and more often elements of hydraulic systems or their components, which previously were made of metal, now are replaced with plastic ones. Taking into consideration the structural, technological and economic benefits resulting from the use of plastics in hydraulics, scientists from Fluid Power Research Group from the Department of Fundamentals of Machine Design and Tribology at Wroclaw University of Science and Technology, are working on the development of a complete hydraulic system in which the main elements, such as the cylinder, the valves and the pump, will be entirely or in significant part made of plastic. The article presents the design assumptions of a cylinders series made of plastics, research of prototype models performed in order to verify these assumptions, as well as conclusions and future research aims. The work on development of the series started with an analysis of the so far existing methods of designing hydraulic cylinders. On the basis of the metal cylinder design methods, own algorithm for designing cylinders made of plastics were developed in the form of a block diagram. Calculation carried out according to the algorithm allowed to determine the components in which it is possible to use plastic as a design material. The calculations were made for several variants of conceptual designs having similar features but different dimensions and operating parameters resulting from them. Similarities allowed for considering design variants as a series. Two variants of diameters, ø30 and ø50 were chosen as series representation, for which actual models of plastic cylinders were created. Models of cylinders were placed in sequence on a specially designed test stand which allowed for measurements operating parameters. A second, traditional cylinder made of metal was placed coaxially on the stand, in the way, that its piston rod was a load for the model. The examination was carried out according to the international standards- ISO 10100:2001(E). Recognizing the tests included in the standard as insufficient for a prototype made of material with untypical characteristics, additional tests were performed. Within additional tests, with use of optical displacement sensors, structural deformation measurements were made during piston rod movement, as well as tests of long-time operating of models were performed. Performed tests confirms the right direction in the approach to designing of hydraulic cylinders made of plastics.