Experimental analysis and preliminary model of non-conventional lip seals

The paper describes the tests carried out to determine the applicability of a simple means for reducing friction force in linear pneumatic actuators. The idea is based on the use of commercial lip seals mounted in the direction opposite to that used in conventional systems. Two different non-conventional installations were tested using commercial spring-energized seals consisting of two different materials: virgin PTFE and graphite-filled PTFE. Tests assessed the effect of bore manufacturing tolerances with nominal bore diameters of 50.0 mm and 50.2 mm. Performance was evaluated in terms of leakage flow rate and friction force, comparing the proposed installation with conventionally mounted seals. Friction coefficient and stiffness of the two seal materials were measured on a seal segment mounted on a pin-on-disk tribometer featuring a special pin design. Tests were carried out by loading the seal segment against a portion of the cylinder barrel in reciprocating motion. Stiffness and friction coefficient measurements served as the basis for developing a preliminary lumped parameter model of the lip seal which was used to analyze lip deflections, exchanged forces and leakage flow rate between seal and barrel

Non-conventional lip seal mountings for pneumatic cylinders

Sliding lip seals are used in pneumatic cylinders to prevent leakage past the piston and rod. Though they guarantee excellent sealing, the friction forces at contact between lip and counterpart can be relatively high. This results in energy losses and problems with wear on components in relative motion, as well as difficulties in controlling actuator positioning. Standards for compressed air cleanliness restrict the use of greases and lubricants, especially in applications such as the food processing and pharmaceutical industries. A number of studies are thus under way in order to find effective alternatives to the use of common lubricants. These studies address both seal configuration [1-4], and the use of innovative materials [5-7]. Other approaches employ systems permitting small amounts of air leakage that operate as lubricated supports, variable-profile pistons [8], or rings with special micromachined surfaces [9-10]. Such solutions are not always economical, both because they require precision tolerances and geometries, and because they use special seals, often produced ad hoc. This paper discusses the possibility of using commercial lip seals with a non-conventional mounting on the piston in order to obtain a simple controlled-leakage system that reduces friction forces in pneumatic cylinders economically and effectively. The non-conventional mounting consists of positioning the lip seal in the direction opposite to that used in a conventional installation, so that the contact pressure reduces as air pressure in the chamber rises. In this way, an air gap is created at the sliding interface which allows air in the pressurized chamber to escape past the seal lip, thus reducing the contact force on the barrel. The piston is provided with a hole which exhausts the leakage flow to the atmosphere. To evaluate the validity of this approach, a number of preliminary tests were carried out in [11] to measure flow rate on a type of spring-loaded lip seal consisting of graphite-filled PTFE for barrel diameters of 50 mm. In particular, the tests determined air leakage behavior for different mounting tolerances. This paper presents further tests conducted on the same samples examined in [11] and on another PTFE and graphite-filled PTFE configuration, measuring leakage flow rates and friction forces. Leakage flow rate measurements were carried out with single and double seal installations. The results obtained are discussed together with the advantages of the proposed solution compared to the conventional mountings in ordinary use

Design and Analysis of an Aerostatic Pad Controlled by a Diaphragm Valve

Because of their distinctive characteristics, aerostatic bearings are particularly suitable for high-precision applications. However, because of the compressibility of the lubricant, this kind of bearing is characterized by low relative stiffness and poor damping. Compensation methods represent a valuable solution to these limitations. This paper presents a design procedure for passively compensated bearings controlled by diaphragm valves. Given a desired air gap height at which the system should work, the procedure makes it possible to maximize the stiffness of the bearing around this value. The designed bearings exhibit a quasi-static infinite stiffness for load variation ranging from 20% to almost 50% of the maximum load capacity of the bearing. Moreover, the influence of different parameters on the performance of the compensated pad is evaluated through a sensitivity analysi

An Identification Method for Orifice-Type Restrictors Based on the Closed-Form Solution of Reynolds Equation

Even though the behavior of aerostatic bearings has for long been the topic of extensive research, there are still many aspects that require further investigation. Among these, the identification of the discharge coefficients is one the most crucial. This paper presents a hybrid method to identify the discharge coefficients of aerostatic bearing orifices. The method is termed as hybrid since it exploits experimental data and the equations of the analytical model of a circular and centrally fed aerostatic pad. The obtained results demonstrate the accuracy of the method. The proposed method further offers practical advantages compared to the conventional methods

Indirect contact pressure evaluation on pneumatic rod seals

This paper deals with the experimental evaluation of contact pressure at the interface between an elastomeric rod seal for pneumatic cylinders and its metallic counterpart without interposing any intrusive measuring device. A new test bench, which is able to measure the radial force exerted by a rod seal displaced at constant velocity on a sensorized portion of a cylinder rod over time, was designed and manufactured. The seal was pressurised to reproduce actual working conditions. A data postprocessing methodology was developed for an indirect evaluation of contact pressure starting from the experimental data set of the radial force exerted by the seal on the rod. At first, the measured radial force signal was filtered and properly fitted obtaining a differentiable function; then, contact pressure distribution was computed as a function of radial force time derivative, seal velocity and rod diameter. Preliminary experimental results are presented

Risparmio energetico con gli eiettori

L’automazione industriale moderna presuppone sistemi pneumatici performanti, efficienti e a basso consumo energetico. In operazioni pick-and-place con ventose è quindi fondamentale utilizzare eiettori efficienti e soluzioni circuitali che utilizzano serbatoi di accumulo del vuoto

Exploring forest infrastructures equipment through multivariate analysis: complementarities, gaps and overlaps in the Mediterranean basin

The countries of the Mediterranean basin face several challenges regarding the sustainability of forest ecosystems and the delivery of crucial goods and services that they provide in a context of rapid global changes. Advancing scientific knowledge and foresting innovation is essential to ensure the sustainable management of Mediterranean forests and maximize the potential role of their unique goods and services in building a knowledge-based bioeconomy in the region. In this context, the European project FORESTERRA ("Enhancing FOrest RESearch in the MediTERRAnean through improved coordination and integration”) aims at reinforcing the scientific cooperation on Mediterranean forests through an ambitious transnational framework in order to reduce the existing research fragmentation and maximize the effectiveness of forest research activities. Within the FORESTERRA project framework, this work analyzed the infrastructures equipment of the Mediterranean countries belonging to the project Consortium. According to the European Commission, research infrastructures are facilities, resources and services that are used by the scientific communities to conduct research and foster innovation. To the best of our knowledge, the equipment and availability of infrastructures, in terms of experimental sites, research facilities and databases, have only rarely been explored. The aim of this paper was hence to identify complementarities, gaps and overlaps among the different forest research institutes in order to create a scientific network, optimize the resources and trigger collaborations