This paper reports a comprehensive laboratory study into the thermophysical, physical-mechanical characteristics, and tribological properties of the designed composite materials based on polytetrafluoroethylene. In the structures of machines and mechanisms, a significant role belongs to the tribological conjugations made from polymeric and polymer-composite materials. The reliability of machines, in general, depends to a large extent on the reliability of movable connections. Composite materials of nonmetallic origin have a low cost, they are resistant to most aggressive chemicals and are capable of operating under conditions without lubrication. It was established that the characteristics and properties of materials must be adapted to the working conditions of separately considered tribological conjugations. The mechanisms of thermal destruction have been established, both in the basic material and the carbon fiber based on it. It was found that carbon fiber, regardless of its content (quantity) in the polymer-composite material based on polytetrafluoroethylene, is mainly oriented perpendicular to the force application plane. It was found that with an increase in the carbon fiber content from 10 to 40 % by weight, the heat capacity decreases by 16‒39 % compared to the main material. The optimal operating modes for the designed composite materials have been substantiated on the basis of a pv factor: under a dry friction mode – up to 4 MPa∙m/s; at friction with lubrication – up to 36.4 MPa∙m/s. The dependence has been established of the friction coefficient on the operating modes of a composite material based on polytetrafluoroethylene containing 20 % by weight of carbon fiber when lubricated with oil and water. The results reported here make it possible to synthesize the physical-mechanical characteristics and tribological properties of composite materials in accordance with the required modes of tribological conjugation.
The introduction of polymer-composite materials makes it possible not only to solve the problem of increasing durability, reducing the mass and cost of machines, but also, by introducing fillers, to adapt them to the required operating conditions. At the same time, there is a problem regarding the high cost of technologies for obtaining composites, which limits their widespread implementation. That is why the object of this research is the processes of influence of the filler on the characteristics and properties of polymer-composite materials. Complex laboratory studies of physical and mechanical characteristics, tribological and thermophysical properties of the developed polymer-composite materials based on Phenylone C2 were carried out. The dependence of the coefficient of friction and wear of the material based on Phenylone C2, containing thermally expanded graphite, on the pressure and nature of counter-bodies during friction with lubrication and without it was established. It was revealed that the minimum amount of wear of the material, with friction with lubrication, is achieved under the pressure on tribojunction of 5 MPa. It was established that with an increase in the concentration of filler from 5 to 25 wt% the coefficient of thermal conductivity increases by 4–40.8 %, compared with that non-filled with Phenylone C2. It was found that the introduction of thermally expanded graphite into Phenylone C2 in the amount of 5 wt % leads to a decrease in heat capacity by 34 %. The proposed technology of obtaining polymer-composite materials in the electromagnetic field provides sufficient physical and mechanical characteristics, tribological properties and low cost of finished products (parts). The results reported here make it possible to adapt the physical and mechanical characteristics, thermophysical and tribological properties of polymer-composite materials to certain modes of operation of movable junctions
Machine milking is one of the main technological processes in the dairy industry whose efficiency level largely affects cattle breeding in general. The key role, in this case, belongs to milking equipment. The design and use of technical means of milking are associated with certain difficulties related to the imperfection of milk discharge. Therefore, the current study is due to the need to investigate the process of moving the milk mixture in a milking machine. A physical-mathematical model of the process of moving the two-phase milk-air mixture along the milk-conducting line of a milking machine has been built. The mathematical model relates the value of the fluctuating of vacuummetric pressure ΔP, the rate of milk discharge QM, the pulse rate ζ, and the value of working vacuummetric pressure P. It was found that in the milk-conducting system with the upper milk pipeline there is a large fluctuation of vacuummetric pressure ΔP=1.02–4.69 kPa, which exceeds the regulated value (2.5 kPa). In a milk-conducting system with a lower milk pipeline, the vacuummetric pressure fluctuation is ΔP=0.59–1.84 kPa. The patterns of change in the value of working pressure P and the frequency of pulsations ζ in the milking machines of simultaneous and pair action depending on the rate of milk discharge from the udder have been determined. It is established that the maximum deviation of the value of fluctuation of vacuummetric pressure ΔP between the experimental and theoretical data within a predefined range of factors is 0.81 kPa. The correlation coefficient is 0.92, which indicates the adequacy of the constructed models. Owing to this, the task of the rational choice of milking equipment is resolved
The productivity of the feed preparation line and its technical and economic efficiency are affected by the design and technological parameters of the equipment. The geometry of the expander screw and its operating modes are no exception. To reduce the specific energy consumption of the expander, it is necessary to establish its rational design and operating parameters. This can be done using analytical calculation methods that consider the mechanisms of movement and destruction of solid substances. Modelling using the discrete element method is becoming increasingly common to describe the movement of solid components in granulators, extruders, or expanders. The purpose of the study is to improve the physical and mathematical apparatus of movement of solid feed components in the screw channel of the feed expander and develop a method for its numerical modelling. Numerical modelling was performed using a model of the movement of a multiphase Euler mixture with a split flow in three-dimensional space. In this case, the motion was subject to an admissible two-layer k-ε model of turbulence and the multiphase equation of state. The physical and mathematical apparatus for the movement of solid feed components in the screw channel of the feed expander was improved, which is the basis for the numerical modelling technique in the Star-CCM+ software suite, based on the fact that the conglomerate of feed components is represented as a package of spherical particles. In this case, the pressure force must be compensated by the total force of contact interaction of particles with each other and the wall. Preliminary numerical modelling of the process of expanded feed preparation was performed in the Star-CCM+ software suite. The practical significance lies in the fact that the improved physical and mathematical apparatus and the developed method of numerical modelling of the feed expander operation process allow substantiating its design and regime parameters to ensure low specific energy consumption without losing the quality of the technological process
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