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The purpose of this paper is to investigate the thermal elastohydrodynamic lubrication (TEHL) flash temperature of the helical gear pairs considering profile modification.

A flash temperature model of the helical gear pair considering the profile modification is proposed based on the TEHL and meshing theories. In doing so, the slicing, fast Fourier transform and chase-after methods are applied to accurately and rapidly obtain the flash temperature of the gear pair. Then, the effects of the modification, input torque and rotation speed on the flash temperature are studied.

With the increment of the tip relief amount, the flash temperature of the helical gear pair with the axial modification decreases first and then increases, and the meshing position of the maximum flash temperature moves toward the pitch point. Moreover, reducing the input torque or increasing the rotation speed can efficiently reduce the TEHL flash temperature.

This work is a valuable reference for the profile design and optimization of the helical gears to avoid the excessive flash temperature.

Due to high speeds, heavy loads, large slide-to-roll ratios (SRR) and other variable operating conditions, some rolling bearings that have been working in harsh conditions may experience flash temperatures in the contact area, which may result in early damage like smearing and then affect service life. This study aims to investigate the flash temperature phenomenon of rolling bearings through theoretical and experimental analysis.

A technology for measuring temperature distribution in rolling ball on disk contact under lubrication was developed. The test-rig can simulate the ball bearing contact. The effects of working conditions such as entrainment speed, load, SRR and lubricating oil viscosity on the flash temperature were investigated.

The results of the theoretical calculation and experiments indicate that the parameters promoting the reduction of film thickness in elastohydrodynamic lubrication are always related with the number of flash points, even film thickness reduced to mixed lubrication. The flash temperature is easier to happen in conditions of high SRR, heavy load, slow entrainment speed and low viscosity oil.

This work conducts an experimental study on the flash temperature phenomenon, providing a test technology for bearing lubrication and failure investigation.

This author has opted into Transparent Peer Review available at: https://publons.com/publon/10.1108/ILT-04-2023-0104

This paper aims to study the effects of MnO₂ on the ZnO–Bi₂O₃-based varistor prepared via flash sintering (FS)

MnO₂-doped ZnO–Bi₂O₃-based varistors were successfully prepared by the FS with a step-wise increase of the .current in 60 s at the furnace temperature <750°C under the direct current electric field of 300 V cm⁻¹. The FS process, microstructure and the electrical performance of ZnO–Bi₂O₃-based varistors were systematically investigated.

The doping of MnO₂ significantly decreased the onset temperature of FS and improved the electrical performance of FS ZnO varistor ceramic. The sample with 0.5 mol% MnO₂ doping shows the highest improvement, with the nonlinear coefficient of 18, the leakage current of 16.82 µA, the threshold voltage of 459 V/mm and the dielectric constant of 1,221 at 1 kHz.

FS is a wonderful technology to enhance ZnO varistors for its low energy consumption, and a short sintering time can reduce grain growth and inhabit Bi₂O₃ volatilize, yet few research studies work on that. In this research, the authors analyzed the FS process and improved the electrical characteristics through MnO₂ doping.

The purpose of this paper is to investigate thermal protection provided by the fire fighting fabric systems with different layer under high-level thermal hazards with a typical temperature range of 800-1,000°C. The purpose of these fabric systems was to provide actual protection against burn injuries using garments worn by industrial workers, fire fighters and military personnel, etc.

The fabric system was consist of glass with aluminum foil as an outer layer, non-woven basalt, non-woven glass fabric containing NaCl-MgCl₂ and Galactitol phase change materials (PCM) which simulate multilayer fire fighter protective clothing system. Thermal protective performance tests were applied for thermal analysis and used as an attempt to quantify the insulating characteristics of fabrics under conditions of flash over temperature. The surface of fire fighting multilayer protective fabric has been characterized using the UV-Vis-NIR (ultraviolet-visible-near infrared) spectrophotometer

The clothing shows good thermal insulation and high-temperature drop during flash over environment and avoid second degree burn. The current PCM obvious advantages such as the ability to work in high temperature, high efficiency a long period of practical performance.

Using this design of composite multilayer technology incorporating two stages of PCM may provide people with better protection against the fire exposure and increasing the duration time which was estimated to be more than five minutes to prevent burn injuries.

Although dependence of contact surface temperatures between rough sliding bodies on surface topography is more explicitly described in terms of three‐dimensional (3D) topographic parameters, no work has yet been reported on this aspect. The paper seeks to carry out experiments to systematically correlate the 3D surface parameters to the contact temperature rise.

The surface temperatures at the contact between a relatively smooth zinc sulphide pin held against a rotating mild steel disc of varying surface topography were measured using an infrared thermal imaging system under different load and sliding velocity conditions. The main objective was to study the effect of 3D surface roughness parameters on the contact temperature rise.

The results indicate a rise in maximum contact temperature with the increase in a number of 3D parameters, such as, average surface roughness Sa, ten‐point height parameter Sz, skewness of the surface height distribution Ssk, mean summit curvature Ssc, and developed interfacial area ratio parameter Sdr while temperature was found to decrease with increasing values of another set of parameters, such as, kurtosis of the 3D surface texture Sku, summit density of the surface Sds, surface bearing index Sbi, core fluid retention index Sci, valley fluid retention index Svi, and root mean square slope of the surface Sdq.

In any sliding system, with mixed or boundary lubricated conditions, it can be attempted to find the optimum value of the roughness parameters so that on suitable processing of the surfaces a lower contact temperature rise can be achieved.

No work has yet been reported on the effect of 3D roughness parameters on contact temperature.

FIRES and oil explosions are known to have occurred in compressed air systems since the earliest days of the air compressor. Attempts to make systematic surveys of the extent of the hazard have never given very comprehensive results, but there is no doubt that it deserves serious attention.

This paper aims to establish a prediction model of stable transmission time of spiral bevel gear during a loss-of-lubrication event in helicopter transmission system.

To observe the temperature change of spiral bevel gear during working condition, a test rig of spiral bevel gear was developed according to the requirements of experiments and carried out verification experiments.

The prediction is verified by the test of detecting the temperature of oil pool. The main damage form of helicopter spiral bevel gears under starved lubrication is tooth surface burn. The stable running time under oil-free lubrication is mainly determined by the degree of tooth surface burn control.

The experimental data of the spiral bevel gear oil-free lubrication process are basically consistent with the simulation prediction results. The results lay a foundation for the working life design of spiral bevel gear in helicopter transmission system under starved lubrication.

3.2.5 Proportion of functional groups in the binder From fig. 14 we can see how the proportion of carboxyl groups in an acrylate resin at otherwise constant conditions can influence the rub‐out effect in two different polar coloured pigments.

The paper is devoted to presenting a systematic investigation on the mechanical model and nonlinear dynamic characteristics of spur gear system with and without input shaft crack.

Considering the backlash, load-distribution, time-varying meshing stiffness and sliding friction, the modelling of a 5DOF gear system is proposed. Likewise, stiffness and damping models under elastohydrodynamic lubrication are developed, and sliding friction between gear pair is also outlined. In particular, a cracked input shaft which affects the support stiffness is presented, and breathing crack in keyway is adopted. On this basis, the dynamic responses of a gear system with and without input shaft crack are examined using numerical method, and some classical response diagrams are given, illustrating the effect of the important parameters on the gear system.

Dynamic simulation demonstrates that there exist periodic, quasi-periodic and chaotic motions in the gear system, and rational speed of the gear pair has noteworthy effects on vibration characteristic. Besides, comparison between healthy and cracked condition of input shaft indicates that occurring of crack convert periodic motion to quasi-periodic or chaotic motion.

The results give an understanding of the operating conditions under which undesirable dynamic behavior occurs, and provide some useful information to design and diagnose such gear system with crack fault.

This paper aims to provide an analytic technique for determining the convection heat transfer and temperature of oil jet lubricated spur gears.

A multiphase flow model is developed to calculate the convection heat transfer coefficients on different gear faces during different contact conditions. The frictional heat is calculated and a method to distribute between the two gears is developed. A finite element model is established to calculate the temperatures in both meshing and cooling processes.

The convection heat transfer coefficients on different surfaces are obtained successfully. Area-related formulae are developed to calculate the heat distribution coefficients. The gear temperature reaches a maximum at the beginning of meshing, then reduces and gets minimum at pitch point, after that it increases again. The gear temperature descends rapidly to steady temperature during the short time of jet cooling process. The tendency of computational results coincides well with the experimental results.

The research presented here could be used in the design phase of the jet lubricated spur gears. The precise temperature is obtained to assess the thermal capacity of gears, from which the gear parameters and oil supply conditions could be adjusted and designed.