The unsteady energy and mass transport of magnetohydrodynamics (MHD) second grade nanofluid via an exponentially extending surface with Dufour and Soret effects are investigated in this study. Variable thermal conductivity and mixed convection effects are used to investigate the heat transfer mechanism. There are also new characteristics such as slip flow, viscous dissipation, Brownian motion, nonlinear thermal radiation, and thermophoresis. In the problem formulation, the boundary-layer approximation is used. Using the suitable transformations, the energy, momentum, and concentration equations are generated into non-linear ordinary differential equations (ODEs). The solution to the resultant problems was calculated via the Homotopy analysis method (HAM). The effects of environmental parameters on velocity, temperature, and concentration profiles are graphically depicted. When comparing the current results to the previous literature, there was also a satisfactory level of agreement. In comparison to a flow based on constant characteristics, the flow with variable thermal conductivity is shown to be significantly different and realistic. The temperature of the fluid grew in direct proportion to the thermophoresis motion, buoyancy ratio, and Brownian motion parameters. According to the findings, the slippery porous surface may be employed efficiently in chemical and mechanical sectors that deal with a variety of very viscous flows.

In this paper, the mathematical model of the oscillation-assisted cylindrical plunge grinding process has been presented. In this model, the dynamical properties of the grinder, self-excited vibration (regenerative chatter), and nonlinear behavior of the grinding force have been taken into consideration. This mathematical model has been applied to analyze both formation and development of chatter on the workpiece and the grinding wheel surface during oscillation-assisted cylindrical plunge grinding. The frequency response function (ERE), describing dynamical properties of the grinder, has been determined by means of modal experiment. The model has been implemented in MATLAB-SIMULINK environment in order to perform simulations. The results of the simulations confirmed the antiregenerative properties of the oscillations of the workpiece rotational movement during cylindrical plunge grinding.The research has been carried out on the test stand, including cylindrical grinder SWF-25, equipped with hydrostatic bearings of the grinding wheel spindle and hydrostatic slideways of the grinding wheel headstock and the workpiece table. The grinding wheel spindle is powered with asynchronous electric motor through v-belts transmission system. In the bearing system of the Journal of Manufacturing Science and Engineering

Cast iron and mineral cast are the materials most often used in the machine structural elements design (bodies, housings, machine tools beds etc.). The materials significantly differ in physical and mechanical properties. The ability to suppress vibration is one of the most important factors determining the dynamic properties of the machine and has a significant impact on the machining capabilities of a machine tool. Recent research and development trends show that there is a clear tendency to move away from the traditional iron casting to the mineral casting, due to better dynamic properties of the latter. However mineral cast as a structural material for the whole machine tools bed turns out to be insufficient due to its poor mechanical strength properties. The best solution should benefit from the advantages of the cast iron and mineral cast materials while minimizing their drawbacks. The paper presents numerical modal analysis of two lathe beds: the first one made of gray cast iron and the second one made of hybrid connection of cast iron and mineral cast. The analysis was conducted in order to determine the dynamic properties of two bodies of similar shapes made in the traditional (cast iron) and innovative hybrid (cast iron and mineral cast) technology. In addition, an analysis of the static structure rigidity of the two beds was performed. During the simulation studies it was found a significant increase in dynamic stiffness and static rigidity of the machine tool body made of hybrid connection of cast iron and mineral cast. The results of numerical simulations have confirmed the desirability of using hybrid construction because the dynamic properties of such a body are more advantageous in comparison with the conventional body made of cast iron.Keywords: cast iron, mineral cast, dynamic properties, modal analysis, machine tool bed Żeliwo oraz odlewy mineralne są materiałami konstrukcyjnymi najczęściej wykorzystywanymi w dziedzinie projektowania elementów strukturalnych maszyn (korpusy, obudowy, łoża obrabiarek). Te materiały znacząco różnią się pod względem zarówno właściwości fizycznych, jak i mechanicznych. Zdolność do tłumienia drgań jest jednym z najważniejszych czynników determinujących właściwości dynamiczne urządzenia i ma znaczący wpływ na możliwości obróbkowe maszyny technologicznej. Najnowsze badania oraz trendy rozwojowe pokazują, że istnieje wyraźna tendencja do odchodzenia od tradycyjnych odlewów żeliwnych w kierunku odlewów mineralnych, ze względu na lepsze właściwości dynamicznych tych ostatnich. Jednakże odlewy mineralne jako materiał konstrukcyjny na całe łoże obrabiarki okazuje się być niewystarczający ze względu na słabe właściwości mechaniczne. Najlepsze rozwiązanie powinno korzystać z zalet żeliwa i odlewów mineralnych, jednocześnie minimalizując wady obu materiałów. W artykule przedstawiono teoretyczną analizę modalną dwóch korpusów obrabiarki: jednego wykonanego z żeliwa szarego oraz drugiego wykonanego z hybrydowego połączenia żeliwa i odlewu mineralnego. Analiza została przeprowa...

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Results of the study on the internal friction of steel ball bearings made of X65Cr14 alloy and ceramic bearings made of zirconium oxide operating at temperatures lowered by liquid nitrogen down to -195 °C are presented in this paper. Standard grease added by the manufacturer, while graphite and molybdenum disulphide powder were used for lubrication of the bearings during the measurements. Tests were also carried out to examine the performance of the bearings operating without lubrication. The power of bearing internal friction versus temperature was measured. The lowest bearing internal friction was observed for molybdenum disulphide, whose effective lubricating performance was verified for both types of ball bearings. Graphite powder was almost equally effective with the advantage of being suitable for use in machines that come into contact with food. (-195 °C) the type of lubrication used in the bearing is of much greater importance than the material of which the bearing is made. • Steel bearings can be used in machines operating at very low temperatures provided that viscous lubricants are replaced with dry lubricants. • The lowest bearing internal friction was observed for molybdenum disulphide, whose effective lubricating performance was verified for both steel and ceramic types of ball bearings. • The performance of the bearings at low temperatures was supported by measuring the power of the internal friction as well as with the microscopic analyses of the surface structures of cooperating elements of the bearings. Highlights • At very low temperatures