Lubrication Science最新文献

This research proposes a complete analysis of the use of physical vapour deposition coated dies in the sheet metal forming process for high-strength-steel sheets. The goal of the proposed approach is to investigate how PVD coatings affect die performance and how that affects the formability and quality of the high-strength-steel-sheets that are made. The finite element analyses are used to simulate and evaluate the mechanical behaviour and deformation characteristics during the forming process. Studies to enhance the forming characteristics of these materials, typically denoted by limiting draw ratio and maximum punch force are required. A reduction in punch force required and improved limiting draw ratio is observed that is attributed to the enhanced contact with friction-conditions in the die-sheet interfaces. The experimental results are compared with simulation results from DD3IMP, a code used for deep drawing simulations, and it is evident that the experimental outcomes are analysed well with the simulation results.

In view of the large temperature rise and impact load of thrust bearings in the main shaft system of large wind turbines, this article takes the circular tilting pad thrust bearings in large wind turbines as the research object, and analyses the basic theory of bearing lubrication. The lubrication performance calculation model established for this bearing includes the Reynolds equation, energy equation, film thickness equation, and elastic deformation equation. Theoretically analysing and calculating the lubrication performance of the circular tilting pad thrust bearing, the key performance parameters have identified such as minimum film thickness (h_min), temperature rise (ΔT), power consumption (W), and flow rate (Q). The calculation results show that the eccentricity ratio has a significant impact on the lubrication performance of the circular tilting pad thrust bearing. When both radial and circumferential eccentricity ratios are around 0.5, the bearing exhibits a high temperature rise, leading to a potential risk of bearing burnout. The results also show that at a radial eccentricity ratio of approximately 0.54, the minimum film thickness reaches its maximum value of 10.34 μm. Similarly, at a circumferential eccentricity ratio of about 0.60, the minimum film thickness reaches its peak value of 21.89 μm. This indicates that the eccentricity ratio plays a crucial role in the lubrication performance. In addition, the lubrication performance of the bearing under varying loads has been calculated at a speed of 9.5 r/min. The results demonstrated that the applied load significantly impacts the thrust bearing's performance. The findings elucidate the critical role of considering the eccentricity ratio and operational external load during the bearing design process. This study validates the potential of replacing rolling bearings with sliding bearings in wind turbine main shafts. It also provides a theoretical reference for the future design of sliding bearings.

This work is focused on performance computation of high speed rotor bearing system with partial composite texture. Since its viscosity at varying speeds affects working performance in different partial composite texture, therefore at design and development stage, it is necessary to know the composite texture and thermal effect acting on rotor-bearing system that causes variation of performance. The effects of partial composite texture size and position on the performance of the bearing are studied. After the optimal structural parameters are determined, the effects of the partial composite texture and fluid thermos structure coupling on the bearing capacity, stiffness, and friction coefficient of the oil film are analysed. The results show that after considering the influence of thermal effect, the performance enhancement of composite texture bearing is better than that of smooth bearing. Considering the temperature effect, the bearing capacity of the composite textured bearing is increased by 51.4% compared with that of the smooth bearing, and the friction coefficient is reduced to 22.4%, which is better than the value without considering the temperature effect, the accuracy of the results is verified by experiments. This study provides a theoretical basis for the design of hydrostatic bearing and improving its performance.

The purpose of this paper is to carry out parameter design and dynamic stability verification experiment of controllable damping ferrofluid bearing. A new type of ferrofluid bearings is designed, and its internal magnetic fields are simulated by the finite element analysis software ANSYS. In this paper, the coefficient of magnetic leakage is taken as the optimization object, and the optimal parameters of ferrofluid bearings are updated. At the same time, the working principle of the ferrofluid bearings test platform is introduced, which includes a servomotor with a controller, an eddy displace sensor, an amplifier and a power supply. Finally, the dynamic stability of ferrofluid bearing is verified by experiments. The experimental results show that when the applied current is less than or equal to 0.08 A, the amplitude of the rotor supported by the ferrofluid bearing decreases with the applied current increment. Besides, the dynamic stability of the rotor is also related to the rotational speed. When the applied current is 0.08 A, the amplitude of the rotor supported by the ferrofluid bearing firstly increases and then decreases with the rotational speed increment. It is proved that the ferrofluid bearings have a strong function of the dynamic stability, which can suppress the vibration of the rotor, and have high accuracy of both position and rotation.

With the gradual increase of the demand for wooden products, people's requirements for processing quality of wooden products become higher. In this work, the dimension of groove micro-texture is determined by finite element simulation analysis of tool structure strength. In this article, by designing milling experiments, the wood surface quality and wood surface morphology after milling with ordinary tools, micro-textured tools, coated tools and micro-textured coated tools are compared. The experimental results show that the quality of wood surface after milling with micro-texture coating tool is better than that of the other three kinds of tools. And the wood surface after milling with micro-texture coating tool is smooth, and the processing defects, such as burr and crack are less. In other words, micro-texture technology combined with surface coating technology can effectively improve the surface quality of wood after milling.

Based on the theory of fluid mechanics, the lubrication performance of micro-textured hydrostatic bearings is derived. Under extreme operating conditions, the lubrication performance of clearance oil film without micro-texture and with rectangular and triangular micro-textures added to the oil sealing edge is simulated, and the experimental verification of the lubrication performance of the double rectangular cavity without micro-texture is conducted. The results show that regardless of whether micro-texture is added or not, the oil film pressure is distributed in a stepped shape, and the highest temperature of the oil film occurs at the intersection of the oil sealing edges on the outside of the double rectangular cavity. When the maximum depth of triangular micro-texture is 1.5 mm and the dimension of a segment is 1 mm, triangular micro-texture with an obtuse angle of 103° has the best comprehensive lubrication performance, but its oil film bearing capacity still does not exceed that of rectangular micro-texture.

This manuscript proposes a hybrid method to predict the optimal nano-metal matrix composites. The proposed hybrid technique is the wrapper of the Fire-Hawk Optimizer (FHO) and Spiking Neural Network (SNN). Commonly it is known as FHO-SNN method. The main objective of the proposed method is to improve the method parameters for better enhancement in mechanical properties. FHO approach is used to improve the process parameters of stirring squeeze casting method. The SNN predicts optimal parameters. Moreover, the problem based on the casting is reduced. By then the proposed hybrid technique performance is performed in the MATLAB platform and associated with various existing approaches. The proposed system shows the high tensile strength, impact energy and hardness compared with other existing methods.

In this work, the tribological properties of a novel iron-based self-lubricating composite as the tribopairs of a plunger pump were systematically studied on an end-face tribometer, and the tribological mechanism was also revealed. The results show that the wear mechanism of the composite can be ascribed to adhesive wear when the sliding speed is lower than 1.5 m/s. As the sliding speed increases from 1.5 to 2.0 m/s, the wear type transforms to oxidative wear due to the increase of tribo-oxidation. In addition, the failure criteria of the tribopair composite materials are summarised. When the average coefficient of friction is greater than 0.04, or the wear rate is greater than 9.66 μm³/(N m), the tribopair fails. This offers a valuable reference for industrial application of the tribopairs made from the iron-based self-lubricating composite.

Nowadays, researches on the use of alkali metal salts as friction-reducing and anti-wear oil additives are continuing. In this study, the tribological effects of heavy metal containing MoS₂ and alkali metal salt CaF₂ additives on pure engine oil (20W50) were investigated using block-on-ring tester configured as surface contact geometry. The tests were performed at various contact loads, revolutions, and additive ratios. The crystal structure of the additives and their effects on surface quality and surface roughness analysed by x-ray crystallography, scanning electron microscope and profilometry. Moreover, Energy dispersive spectrometry was used for element detection on worn surfaces. Results indicated that additives of MoS₂ and CaF₂ can reduce the friction, increase the capacity of load-carrying and the wear resistance of surfaces. The additives improved the operation of the base oil in boundary lubrication zone by increasing the tribofilm forming effect. It was observed that the CaF₂ additive exhibited more stable friction behaviour, while the MoS₂ additive has better protective effects against scratches on the block surface.

The oil film lubrication performance of a large hydrostatic turntable operating at the model of constant surface cutting speed is studied. Firstly, the rotary speed equation which is bound by the constant surface cutting speed is established. According to the fluid lubrication theory, the gap flow equation, the oil film temperature rise equation and the double-rectangular-cavity oil pad bearing capacity equation are derived. Further, a prediction model of oil film lubrication performance in the operating mode is established. The change rules of temperature, pressure and other performance indexes of the film with time are obtained by numerical simulation. And, the above laws are verified by design experiments. It is found that the cutting speed, feed rate leaves a significant impact on the law of variations of oil film performance with time. According to the conclusions, it will be beneficial to improve the bearing capacity of the hydrostatic turntable and further improve the machining accuracy by using cutting parameters reasonably to control the speed within a certain range.