The Effect of the Technological Heredity of the Stress–Strain State on the Accuracy of Nonrigid Parts

Journal of Machinery Manufacture and Reliability - The effect of the technological heredity of the stress–strain state on the accuracy and dimensional stability of nonrigid parts such as...     

The effect of basecoat pigmentation on the scratch resistance and weathering performance of an acrylic–melamine basecoat/clearcoat automotive finish

Scratch resistance of an acrylic/melamine clearcoat (on the black and silver basecoats) was studied by means of laboratory simulator carwash and nano-scratch tests before and after carrying out a weathering test. The scratch morphology was studied by scanning electron microscope (SEM). Gonio-spectrophotometer and micro-indentation were utilized to investigate appearance changes and mechanical properties of the clearcoats. Results showed that scratch resistance of the silver sample was higher than the black one. The scratch resistance of the black and silver samples was improved at short exposure times. A decrease in scratch resistance of the coatings was obtained at long times.     

The influence of the valena metal-plating additive on tribotechnical characteristics of the Steel–Bronze tribological system

The paper considers a change in the coefficient of friction and the temperature distribution in the contact zone of the steel–bronze tribosystem. Investigations were carried out by the shaft–bushing system for three values of the load in the mixed-to-boundary lubrication regime with SAE 80W transmission oil without and with Valena additive. It is found that the additive presence in oil decreases the coefficient of friction by 11–21%, depending on the applied load. At the same time, the maximum decrease in the coefficient of friction is observed at a maximum applied load of 1500 N.     

Method of calculating the cross-wind speed at the entrance aperture of an adaptive system based on Shack–Hartmann wavefront sensor measurements

This paper presents a method for calculating the cross-wind speed at the entrance aperture of an adaptive system from the coordinates of the energy centers of gravity of the focal spots measured by a Shack–Hartmann wavefront sensor. The range of applicability of the method are determined for data obtained in an experiment on an atmospheric path depending on the intensity of turbulent distortions and the optical parameters of the sensor.     

The effect of various designs of six-curved blade impellers on reaction rate analysis in liquid–liquid mixing vessel

The mixing efficiencies of impellers vary according to their designs. In this work, the effects of 6-curved-blade impellers of different curvature angles and central disk sizes on the reaction in a stirred vessel were investigated and the results were compared to that of a Rushton turbine. The impeller efficiency was defined by the ratio of reaction rate to power consumption, (r_A/P). The experiments were performed at the rotational speeds of 5, 6 and 7 rps. The interaction among the experimental parameters was investigated using Response Surface Methodology. The r_A/P values were found to decrease with increasing curvature angles. The lowest r_A/P value was obtained for the impeller with curvature angle of 140°. The result showed that the results for Rushton turbine was relatively low compared to curved-blade impellers and increase in central disk size did not significantly affect r_A/P. In conclusion, curved-blade impellers were more economically efficient than Rushton turbine.     

The effects of nickel and carbon concentrations on the wear resistance of Fe–Ni–C austenitic alloys

The effects of nickel and carbon concentrations on the wear resistance of Fe–xNi–yC (x = 14–20 wt.%, y = 0.6–1.0 wt.%) were investigated with respect to strain energy initiation of the martensitic transformation and hardness. The strain energy needed to initiate the martensitic transformation increased with increasing carbon and nickel concentrations, except in 1.0 wt.% C alloys. The wear resistance of the material decreased with increasing carbon concentration up to 0.9 wt.% C. This effect is most likely due to decrement of the martensite volume fraction with increasing carbon concentration induced by the incremental strain energy required to begin the martensitic transformation. In the case of 1.0 wt.% C, the improved wear resistance may be due to carbide precipitation.     

The effect of equal channel angular pressing on the mechanical and magnetic properties of 09Γ2C steel

The physical and mechanical properties of 09Γ2C steel that was subjected to strengthening by intense plastic deformation using the method of equal channel angular pressing (ECAP) are studied. An unambiguous interrelationship between the magnetic (coercive force, maximal permeability, Barkhausen magnetic noise parameters) and mechanical (rupture limit, conditional yield strength, relative elongation and narrowing upon damaging) characteristics of 09Γ2C steel, which was strengthened using ECAP following different technological regimes, is demonstrated. Therefore, it is possible to estimate the strength and plasticity characteristics of the analyzed material based on the measurement of its magnetic parameters. It has been revealed that under conditions of uniaxial tension in the range from 0 to (0.2–0.6) of the conditional yield strength (depending on the ECAP regime), it is possible to diagnose changes in the stressed state of items that are made of 09Γ2C steel that is hardened in accordance with the ECAP technique using magnetic structuroscopy methods.     

Additive–additive interaction: an XPS study of the effect of ZDDP on the AW/EP characteristics of molybdenum based additives

The effect of zinc dialkyldithiophosphate (ZDDP) addition on the antiwear (AW) and extreme pressure (EP) properties of molybdenum dialkyldithiocarbamate (MoDTC) and molybdenum dialkyl dithiophosphate (MoDTP) are evaluated by standard Four-Ball friction test and also by the determination of coefficient of friction using an oscillating SRV apparatus. The boundary lubrication film formed on the worn surface using the two molybdenum additives and their combination with ZDDP is investigated by depth profile X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to find out the chemistry of tribochemical reaction occurring at the surface during friction. It is seen that MoDTP possesses better AW properties than MoDTC due to its high reactivity with the metal surface. Nevertheless, the AW characteristics of MoDTC could be improved by the addition of ZDDP. The frictional properties of MoDTP, however, do not change by the addition of ZDDP. The synergistic action of ZDDP on MoDTC is attributed to the enhanced decomposition of MoDTC in presence of ZDDP. This is tentatively explained in terms of some interaction of zinc with the electron donating nitrogen present in MoDTC, which would have helped to increase its tribo-reactivity. XPS studies revealed that in the presence of ZDDP, MoDTC form mainly metal sulphides like MoS₂ and FeS under friction. The MoDTP+ZDDP derived surface, on the other hand, produced mainly metal phosphate along with molybdenum oxysulphides and small amount of MoS₂ and FeS. The mechanism of action of additives is explained.     

The Effect of Spherical Silica Powder on the Tribological Behavior of Phenolic Resin–Based Friction Materials

The friction and wear behavior of friction materials filled with irregular silica, spherical silica and surface-treated spherical silica particles is discussed in this paper. Compared to irregular silica, spherical silica powders improve the wear resistance, but decrease the friction coefficient. Surface-treated spherical silica powder is more effective in the improvement in the wear resistance, but with the similar friction coefficient of irregular silica-filled materials. This makes it possible to be used as friction-improving fillers in brake materials. Mechanisms for the improvement are also discussed in this paper.     

The influence of a change in the electron trajectory in the vacuum-diode anode–cathode gap on the impedance

The analysis of the influence of the electron-trajectory curvature in the anode–cathode gap of a vacuum diode on its impedance during generation of high-current electron beams is performed, and the applicability of the one-dimensional Child–Langmuir formula for the electron-current calculation is evaluated. The results of an experimental study of a flat diode with explosive-emission graphite, copper, and carbon- fabric cathodes and also with a multipointed cathode are presented. These investigations were performed on the TEU-500 accelerator (350–500 kV, 60 ns). A strip diode with a graphite cathode was also studied in the mode of magnetic self-insulation of electrons. The experiments were performed on the TEMP-4М accelerators (150–200 kV, 400–600 ns). The investigation results showed that the satisfactory coincidence of the experimental values of the total current with those calculated from the one-dimensional Child–Langmuir formula (for the working area of the cathode) is observed in diodes not only in the absence of a change in the electron trajectory in the anode–cathode gap but also upon a deflection of the trajectory from the normal to the cathode surface by an angle of <90°. An increase in the electron current owing to a decrease in the anode–cathode gap and an increase in the emission area of the cathode during the cathode-plasma production and also at the expense of the presence of microirregularities on the cathode is properly described by the onedimensional Child-Langmuir formula, if the above factors are taken into account.     

The effect of a prosthetic crown’s design on the accuracy of mapping an abutment teeth’s shape

The objective is to carry out an in vitro assessment of tightness of Co–Cr–Mo alloy premolar and molar crowns manufactured with the use of the following technologies: casting, milling and laser melting. In order to compare the fit of crowns to abutments that served as the reference models, the Geomagic Qualify 12 software for structured-light 3D scanning and modelling was used. According to analyses of reports in the form of maps and summaries, all histograms and maps are characterized by low positive and negative values of shape deviations. All employed technologies were found to have a comparable, satisfactory accuracy of mapping the shape both in the area of the stair step and the area of side walls. The results of the studies enable to conclude that the tightness of prosthetic crowns manufactured with the use of the studied technologies is comparable and meets clinical criteria.     

Compensation for Joule–Thomson effect in flowrate measurements by GMDH polynomial

The international standard for flowrate measurements ISO-5167 recommends the temperature sensor to be located downstream of the differential device what may cause a significant error in the measurement of the flowrate of natural gas, especially at high differential pressure, low temperature and low diameter ratio. The flowrate generally needs to be compensated for the temperature change due to the Joule–Thomson effect caused by the constriction of the metering device. The accurate compensation involves double calculation of both the natural gas properties and the flowrate. To decrease the computational load, an automatic correction of the flowrate by the GMDH polynomial surrogate is proposed. By using the compound measure of the approximation error and the execution time for model selection, the modified GMDH algorithm searches for the satisfactory model fulfilling the constraints of real-time application. The automatic correction of the flowrate measurements of a natural gas is simulated and the corresponding results are discussed. The derived model can be equally used for a natural gas specified by composition or by physical properties.     

Development of a tool–work thermocouple calibration system with physical compensation to study the influence of tool-holder material on cutting temperature in machining

The main objective of this work is the experimental investigation of the influence of tool-holder material on tool–chip interface temperature and on the surface temperatures of the cutting tool and tool-holder. The study was conducted in dry machining of grey iron with uncoated cemented carbide inserts, using identical cutting parameters. Five tool-holders were made with materials having different thermal conductivity: copper, brass, aluminium, stainless steel and titanium alloy. The tool-holders are identical and have the same constructive aspects obtained from the commercial tool-holder for machining grey iron. The temperature at the tool–chip interface was measured using the tool–work thermocouple method and the surface temperatures on the insert and tool-holders, by conventional T type thermocouples. The system was modified in order to develop an experimental procedure for the physical compensation of the secondary junctions and parasite thermoelectric e.m.f. signals. Also, modifications were carried out in a conventional tail-stock to obtain the e.m.f. signal between the rotating workpiece and the stationary insert, without significantly altering the stiffness of the system. The tail-stock with mercury bearing inside was insulated electrically. The internal connections became reference junctions at room temperature; otherwise, they would act as secondary junctions. The calibration of the tool–work thermocouple was developed in the experimental apparatus using the same modifications as implemented in the system. Besides the results obtained with the investigation of the effects of the tool-holder materials on the surface temperatures of the insert and the tool-holder and the tool–chip interface temperature, this research presents also contributions to the calibration and performance of the tool–work thermocouple method with physical compensation.     

Rheological behavior’s effect on the work performance of oil film

A 3D model of hydrostatic turntable’s oil chamber is established to investigate the lubricants performance with different rheological properties by using FLUENT software and the finite volume method. Newtonian oil and non-Newtonian oil’s performance under varied speeds are compared on the large size hydrostatic turntable system considering the temperature-viscosity relationship and pressure-viscosity relationship. The results show that the property of non-Newtonian fluid viscosity influenced by shear rate largely affects the lubricants performance for most oil added polymer additives. Lubricants cannot simply be regarded as Newtonian fluid. The shear thickening non-Newtonian fluid has a better work property. The results are important to design a large size and high-speed hydrostatic support system, choose lubricant oils, and investigate oil film’s work properties.     

A calibration system for microwave radiometers based on a modulator–calibrator

A system for automatic internal calibration of millimeter-range radiometers is described. This system is based on an electrically controlled modulator–calibrator, which is a compact solid-state device that combines the functions of a modulator and a source of stable noise calibration signals. Stability of the calibration levels is provided by thermostatting the modulator–calibrator case and stabilization of the control currents. The calibration and data-collection process is governed by software using a special digital module and a personal computer.     

The influence of friction and wear on the generation of surface microprofile of steel–sintered friction powder based on copper in the course of operation in lubricated medium

The development of new compositions of sintered friction powders based on copper that operate in lubricated states should be based on deep knowledge of peculiar features of break-in and wear mechanisms of both counterbody and friction material. The obtained data have enabled the determination of the existence of the transferred bronze layer of friction material, the peculiarities of the generation of the surface microprofile of the counterbody during operation, these data can be useful upon assessing the thermal loading of the friction zone.     

Influence of the Mechanical Seals on the Dynamic Performance of Rotor–Bearing Systems

In this paper, to consider the effects of mechanical seals, a lumped-mass model and the transfer matrix method are used to establish the equations for the dynamics performance of rotor bearing system. The general inverted iteration method is also used to solve the eigenvalue problem of these equations. To check the response of the rotor bearing system under unbalance motivation, the Gauss method is used to calculate the dynamic response of the constrained vibration. The results, based on the dynamic properties calculation of a typical mechanical spiral seal, such as stiffness coefficients and damping coefficients, exert the influence of the mechanical seal on the rotor bearing system of the high-speed machinery. Meanwhile, some structure parameters that may affect the dynamic performance and forced vibration under unbalance motivation of the rotor bearing system considering mechanical seals are analyzed in the paper. The analysis results show that the mechanical seal more or less has effects on the rotor bearing system. The mechanical seal has much more effects on the flexible rotor bearing system than on the rigid one. For instance, in a certain case, if the effects of the mechanical seal were taken into account, the system s critical speed may increase by 70 80%.     

Experimental method of fabrication of a matched metal–dielectric structure for a sensor based on the effect of frustrated total internal reflection

An experimental method of fabrication of a sensor based on a metal–dielectric structure (Al + ZnS) and optimization of its characteristics is described. The coefficient of light reflection (p-polarization) from the aluminum layer is studied as a function of the layer thickness for different angles of incidence at the wavelength of 532 nm. Based on calculations, which are qualitatively consistent with experimental results, a structure consisting of matched layers of aluminum and zinc sulfide is fabricated; this structure has a higher angular resolution than the aluminum film with no dielectric coating. The detection limit of angular measurements by the sensor based on this structure is estimated as 2.6 · 10^-5 RIU (refraction index units).