Abstract: This paper reports a case of lubricating property test of bearing. In order to seize the performance and the reasonable work condition of Ф480mm elliptical bearing with groove on all pads for 1000MW steam turbine, an experimental method that load is on the rotor was adopted in this paper. And the test focused on the bearing characteristics which is most concerned by designers such as power loses, temperature, flow, and flow state, etc. The influence on power loses, temperature rise, flow by the temperature and pressure of inlet oil, load, speed was studied in this test. The results show that the flow state in this bearing is changed from laminar to turbulent in the speed range 2000rpm~2200rpm and in the Reynolds number range 1325.8~1556.5. The specific pressure for the bearing with groove on the down pad is proper between 1.57MPa and 1.96MPa.
Abstract: A finite element cavitation algorithm to Reynolds equation is presented for the calculation of the flow field in the film between the faces of the mechanical seal. As using free mesh, the algorithm is particularly useful for the computational domain which shape is complex. The JFO boundary condition which satisfies mass conservation is implemented by introducing Kumar and Booker’s algorithm. A non-traditional finite element method is derived to avoid the process of the functional analysis and can obtain the flow rate on boundaries conveniently. The results show that the algorithm is reliable, effective and correspond to the literature results. Moreover, the algorithm can be also used for the sliding bearings lubrication problem which shows the well adaptability.
Abstract: Wettability of solid surfaces is one of very important properties, which is governed by both the interface energy and the microstructures. In the paper, four microstructure surfaces were designed such as square concave, column concave, square convex and column convex. The contact angle and wettability of solid surfaces with regular microstructures were discussed for five contact angle models such as Young, Wenzel, Cassie, Cassie-Baxter and Wenzel-Cassie models. Then, the impacts of interfacial energy and microstructures to wettability were analyzed. The study shows that the character of hydrophobic or hydrophilic is decided by the interfacial energy between solid and liquid, and the wettability can be changed by adjusting the parameters of microstructures, such as the ratio of transverse spacing and diameter α, the ratio of longitudinal spacing and diameter β, the ratio of the deep and diameter γ or the ratio of soaking deep and diameter λ. And, the convex microstructure is more propitious to hydrohobic surface than concave microstructure.
Abstract: The Diamond-like carbon coating (DLC) was derived by the PVCD method on the 45 steel surfaces. The frictional properties and fatigue failure of 45 steel with the DLC films were investigated under three different conditions including full contact condition, horizontal reciprocating movements and vertical reciprocating movements. It was found that (a) at full contact conditions: the increase in the load leads to the initial decrease in the frictional coefficient and then increase, and a lowest frictional coefficient of 0.205 appears at 250N; (b) at horizontal reciprocating conditions: the slow decrease in the frictional coefficient was caused by the increase in load, and frictional coefficients of 0.213 and 0.178 appears at 100N and 300N, respectively; (c) at vertical reciprocating conditions: the frictional coefficient was initially enhanced and then followed by a decrease trend; the highest frictional coefficients of 0.640 appears at load of 200N. The wear rate was slightly enhanced as the load is lower than 200N, and was sharply increased with the further increase in the load. The lowest wear rate was 1.55 mg/10000r, and the highest wear rate was 15.6mg/10000r.
Abstract: The cylinder-piston ring pair is one of the most important rubbing pairs of the internal combustion engine. The current studies showed that the micro geometry of friction surface morphology has a great effect on the performance. In this study, the terminological system of cylinder liner - piston ring was regarded as the object. The surface of each cylinder was treated with some pits and grooves. Then, the cylinder-piston ring experiments were implemented using a tester. The comparison analysis of vibration signals from diesel engine condition body surface and tribiological properties between conventional cylinder and a variety of surface treatment of cylinder was conducted. The effects of cylinder surface on diesel engine performance were investigated and some conclusions were obtained and presented in the paper.
Abstract: The Ni-P composite coatings onto 4043 aluminum alloy were prepared by electroless plating with nickel sulfate and sodium hypoposphite as raw material. The Ni-P composite coatings were heat-treated for 1 hour at 200°C, 300°C, 400°C, 500°C and 600°C, respectively. The tribological behaviour of the coatings was investigated on a vertical universal friction/wear tester under dry friction. The morphology and phase structure of the composite coatings were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM), and the microhardness of the composite coatings were measured by Vickers diamond indenter. The results showed that the as-deposited coatings had smooth cellular pattern and amorphous structure, and the microhardness of the coatings reached the maximum at 400°C heat treatment, the reason is the formation of Ni3P alloy phase with increasing of the heat treatment temperature. The friction coefficient of coatings annealed at 400°C is the lowest. The wear loss was found to increase with corresponding increase in load and sliding speed. It was found that the wear mechanism of the as-deposited Ni-P composite coatings was dominated by adhesive wear and scuffing under the experimental conditions, but the wear mechanism of the coatings annealed at 400°C was scuffing.
Abstract: In this paper fully flooded and starved lubrication models considering surface roughness are developed for the piston ring and cylinder bore lubrication. The effect of oil available in the inlet region of a top ring is studied by comparing predicted oil film thickness, asperity contact friction and power loss under different oil supply conditions. The simulation results show that the proper oil supply is important in controlling the piston ring frictional power loss. The influences of lubricant viscosity and composite roughness on frictional power loss of piston ring are also discussed.
Abstract: The contact between balls and screw races or nut races is a kind of typical non-conformal contact. The study of contact characteristics of ball screw will provide theoretical bases for improving transmission efficiency and working properties of ball screw. In this study, hertz contact theory was adopted to construct the solution formula of ball screw’s contact stiffness, ball screw’s contact characteristics in terms of axial load, design parameters and material properties was analyzed, and the contact deformation value of the contact between ball and screw races was got using finite element simulation method. The simulation result is close to the theoretic value, which proves the correctness of the theory analysis. The present study offers theoretical support for the design and application of high speed, heavy load and precision ball screws.
Abstract: Aqueous solutions have found broad usages as lubricants, in conjunction with other possible utilizations, in metal working and other industries. Due to the inferior lubricity, functional additives are needed to improve their tribological performances, including oil-in-water (O/W) emulsions or aqueous surfactants. The rheology of aqueous solution with polyethoxylated ether added (PEOE) is measured, including the influences of the temperature and the concentration on dynamic viscosity variation. The dynamic viscosity of PEOE aqueous solutions increases with PEOE concentration. The dynamic viscosity of PEOE aqueous solutions decreases with the rise of temperature up to cloud points. If the temperature is higher than cloud points, however, the dynamic viscosity will increase, through which a non Newtonian characteristic, i.e., the shear thinning, is expressed.
Abstract: The nonlinearity of material properties at different temperatures and the manner of braking force applying on a brake system are two key factors to affect the coupling of temperature and thermal stress. Considering these two factors, a finite element analysis model of automobile brake disc and pad is established. By using the model, the dynamic frictional heat and thermal stress of braking friction pair could be simulated and the coupling characters of temperature and thermal stress on friction surfaces could be studied, where the braking force is constant or controlled by an anti-skid brake system(ABS). The study results shown that the friction temperature of brake disk rises in periodic and fluctuant tendency. The fluctuant increase of temperature will influence the character of braking. The increase of friction temperature between a brake disc and pad can decrease under the control of ABS, so the effect of thermo-mechanical coupling could be reduced.