Current trends concerning hydraulic cylinder sealing systems are aimed at decreasing energy consumption which can be materialized by minimizing leaks and reducing friction. The latest developments in the field of materials and sealing system geometries as well as modern simulation possibilities allow maximum performance levels of hydraulic cylinders. Reducing friction is possible by hydro-dynamic separation of the sliding and sealing points already at very low velocities and by using materials, such as plastomers, from polytetrafluoroethylene (PTFE) (virgin PTFE and filled PTFE). It is within this context that this paper discusses a theoretical and experimental study focused on the tribological behavior of coaxial sealing systems mounted on the pistons of hydraulic cylinders. It presents a methodology for the theoretical determination of the lubricant film thickness between the cylinder piston and the seal. The experimental installation used for measuring fluid film thickness is presented, and the results obtained under various working conditions are compared to the theoretical ones. For the analyzed working conditions related to pressure, speed, and temperature, the paper concludes with a set of criteria for the selection of the optimum seal material so as to maximize energy efficiency.
The aim of this paper is to present and discuss an innovative, constructive solution for a gripper system that can be attached to an industrial robot for assembly operations. The construction of this gripper system is based on a linear pneumatic muscle used as the actuator and the transmission of motion by gear-and-rack mechanisms. Air compressibility renders pneumatic muscle behaviour inherently compliant; this favours automated assembly applications as it allows the correction of inevitable lateral and angular misalignments in mating operations. Therefore, the jamming of a peg-like object can be avoided when this is introduced into a hole with tight clearance. In addition to the construction of the gripper system, this paper discusses its actuation, as well other characteristics.
Abrasive waterjet machining (AWJM) has a particularly high potential for the machining of stainless steels. One of the main optimization objectives of the machining of X2 CrNiMo 17-12-2 stainless steel is obtaining a minimal surface roughness. This entails selecting an optimum configuration of the main influencing factors of the machining process. Optimization of the machining system was achieved by intervening on four selected input quantities (traverse speed, waterjet pressure, stand-off distance, and grit size), with three set points considered for each. The effects of modifying the set-points of each input parameter on the surface roughness were studied. By means of response surface methodology (RSM) the combination of factor set points was determined that ensures a minimum roughness of the machined surface. The main benefit of RSM is the reduced time needed for experimenting.
Modelling of the lapping process proves a complex undertaking because of the different forms of the abrasive particles in the working area, the wide dispersion of their dimensions, the modifications of their shape and dimensions during processing. The paper proposes the spherical model of the abrasive grain, based on the known fact that a good quality of the processed surfaces requires compact grains, with a dimensional ratio as close as possible to 1:1:1. Based on the adopted model the distribution of tensions at the grain-workpiece contact is determined, as well as the penetration depths of the abrasive grains into the workpiece and the transfer object, respectively. For this certain initial conditions are necessary, like Hertzian contact between the abrasive grain and the processed surface and the neglecting of strain hardening. Taking into consideration the known fact that only the large abrasive grains participate in the actual cutting process while the rest remain suspended in the gap between workpiece and tool, as well as their dimensional distribution and concentration in the lapping slurry, the volume of abrasive material required for processing was determined by statistical methods.
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