Zhu Zhencai

Influence of initial braking velocity and braking frequency on tribological performance of non‐asbestos brake shoe

Purpose – The purpose of this paper is to find the influence of the initial braking velocity and braking frequency on the tribological performance of the non‐asbestos brake shoe used in mine hoisters during some continuous emergency brakings.Design/methodology/approach – The tribological performance experiments of the WSM‐3 non‐asbestos brake shoe braking on the 16 Mn steel are investigated on the X‐DM friction tester, by simulating continuous emergency brakings of a mine hoister ten times. Three kinds of tribological indexes: friction coefficient, its stability coefficient, and wearing rate are considered to score the tribological performance of the brake shoe.Findings – When the initial braking velocity increases, the mean friction coefficient of the brake shoe decreases at first, then rises, and falls again finally. But when the braking frequency exceeds seven times, the falling process of the friction coefficient at low‐velocity period does not appear again. Second, when the initial braking velocity i...

Effect of PTFE Addition on the Properties of Electroless Ni-Cu-P-PTFE Deposits

Abstract The effect of PTFE addition on electroless Ni-Cu-P-PTFE deposit was investigated, such as surface morphology, phase composition and microhardness, as well as adhesion strength and friction properties. The electroless Ni-Cu-P-PTFE deposits with different PTFE contents were prepared on mild steel (1015) substrate surface by adjusting different process parameters. The surface morphologies and microhardnesses of the deposits were investigated by SEM and MH-6 Vickers, respectively. Adhesion strength and friction coefficient were measured by using MFT-4000 multifunctional surface material performance instrument. The results show that the deposition rate of the Ni-Cu-P-PTFE deposit increases with the increase of PTFE concentration. Further experiments indicate that the PTFE particles co-deposited in the composite deposit will reduce the microhardness due to their softness properties and loose structure. With the increasing of PTFE concentration, the adhesion strength decreases. Moreover, the addition of PTFE particles reduces the friction coefficient, and the friction coefficient is in inverse proportion to the content of PTFE particles in the deposits, but not to the concentration of PTFE in the bath.

Preparation and tribology performance of nano magnetic grease

Purpose – The purpose of this paper is to prepare a novel nano magnetic grease with favorable lubricating performance; to contrast the tribology performance of the magnetic grease with the original grease, and to find the lubricating mechanism of the magnetic grease.Design/methodology/approach – The nano Fe3O4 magnetic fluids are added into the general urea grease to synthesize the nano magnetic grease. Tribology performance tests of the magnetic grease and the original grease are contrasted on a MMW‐1 four‐ball tester. Based on three kinds of effects caused by the nano magnetic fluids, the lubricating mechanism of the magnetic grease is discussed.Findings – Nano magnetic grease with favorable lubricating performance can be synthesized by adding the nano Fe3O4 magnetic fluids into the general urea grease. The nano magnetic grease has better lubricating performance and more steady bearing capability than the original grease, and is especially available for the lubricating of equipment with high speed and h...

Tribological Behavior of Ni-P Deposits on Dry Condition

Abstract The deposits of electroless Ni-P prepared by different process were studied by means of EPMA, XRD, microhardness tester, friction-wear instrument. The experimental results show that the microhardness of the deposits will change with different microstructures and heat treatment temperatures. The microhardness of as-plated deposit will increase upon increasing the content of the nanocrystalline phase in the matrix, which can be up to the microhardness of the Ni-P deposit heat treated at 400 °C for 1 h. The strengthening mechanism for Ni-P deposit is either solid solution strengthening or precipitation strengthening, which depends on the phosphorus content and the heat treatment temperature. The friction-wear results show that the Ni-P deposits consisting of more nanocrystalline phase exhibit better microhardness, lower friction coefficient before and after heat treatment at 400 °C, and good wear-resistant performances.

Friction heat conduction and entransy of friction lining

Purpose – This paper aims to analyze the friction heat conduction and entransy of two friction linings in the high‐speed slide accident of a mine friction hoist.Design/methodology/approach – Firstly, the dynamic thermophysical properties were analyzed and their fitting equations were also obtained. Additionally, the dynamic heat partition ratio was obtained according to the dynamic thermophysical properties. Then, a simple method was developed to solve the temperature rise of friction lining. Finally, based on the theoretical model of temperature rise, the entransy of friction lining with respect to T and t were gained.Findings – The error of temperature rise between simulation result and experiment result is less than 7 per cent, which proves that the theoretical model is correct. The entransy decreases with the temperature below 40°C and it increases after 40°C. The entransy of lining K is a little higher than that of lining G within 19 s, but the entransy of lining G is much higher than lining K after ...

Dynamics of 3-DOF spatial parallel manipulator with flexible links

The dynamics of 3-DOF spatial parallel manipulators with flexible links were performed. Firstly, a model of spatial flexible beam element was proposed, and the dynamic equations of elements and branches of the parallel manipulator were derived. Secondly, using the kinematic and dynamic constraint equations of the parallel manipulator, the overall system dynamic equations of the parallel manipulator were obtained by assembling the dynamic equations of branches. Thirdly, the dynamic responses of the 3-RRS parallel mechanism with flexible links were analyzed through numerical simulation. This paper can provide necessary information for the dynamic performance analysis, dynamics optimization design and control of the 3-RRS flexible parallel mechanisms.

Virtual prototype simulation of a 3-RRS flexible parallel manipulator

In applications where high structural stiffness, position accuracy, speed motion, and good dynamic performance are predominant requirements, parallel manipulators offer obvious advantages over serial ones. However, dynamic modeling and analysis of parallel manipulator, which are characterized by multiple closed-loop chains, are generally more complex than in the serial mechanism case. Especially, dynamic problems of the parallel manipulators with flexible links have not been studied as extensively. The primary goal of this research is the virtual prototype simulation of spatial flexible parallel manipulator. Firstly, the virtual prototype of a 3-RRS flexible parallel manipulator is established on the basis of the finite element software SAMCEF. Then, the displacement, velocity and acceleration of the 3-RRS flexible parallel manipulator are analyzed. The simulation results show that the flexibility of link has important influence on kinematics and dynamics performance of the flexible parallel manipulator.

Notice of Retraction Simulation of stress field of hoist sheave wheel and experimental validation

This study presents stress analysis of sheave wheel by a finite element analysis model and experimental tests. Simulation of stress field under two kinds of load condition was carried out with ANSYS. The corresponding relationship between stress and load of hoist as well as sheave wheels phase angle were obtained. Then field experiments of sheave wheel stress under three kinds of conditions, which were no-load, heavy-load and rope-slack, was conducted using the wireless stress monitoring system and the experimental data were analyzed and compared with simulation results. It is found that the spoke of sheave wheel is the ideal position for stress measurement. Moreover, the spokes stress increases linearly with the hoist load and changes periodically as sheave wheel rotates. Consequently, it is verified that the hoist parameters such as load, displacement and velocity can be monitored real-timely by calculation of the detected stress changes of sheave wheel, which proves the validity and feasibility of this novel monitoring method of hoist.

Atomistic simulation of topaz: Structure, defect, and vibrational properties*

The clay force field (CLAYFF) was supplemented by fluorine potential parameters deriving from experimental structures and used to model various topazes. The calculated cell parameters agree well with the observed structures. The quasi-linear correlation of the b lattice parameter to different F/OH ratios calculated by changing fluorine contents in OH-topaz supports that the F content can be measured by an optical method. Hydrogen bond calculations reveal that the hydrogen bond interaction to H1 is stronger than that to H2, and the more fluorine in the structure, the stronger the hydrogen bond interaction of hydroxyl hydrogen. Defect calculations provide the formation energies of all common defects and can be used to judge the ease of formation of them. The calculated vibrational frequencies are fairly consistent with available experimental results, and the 1080-cm−1 frequency often occurring in natural OH-topaz samples can be attributed to Si–F stretching because of the F substitution to OH and the Al–Si exchange.

Kinematic constraint conditions and dynamic equations of spatial flexible parallel manipulator

The primary goal of this research is dynamics modeling and analysis of spatial parallel manipulator with flexible links. A new model of spatial finite element beam model is proposed. The kinematic constraint conditions of the moving platform and the branches of the spatial flexible parallel manipulator are derived. The dynamic model of the moving platform is developed based on the Newton-Euler principle. Then, using the kinematic constraint equations and dynamic model of the moving platform, the overall system dynamic equations of the parallel manipulator are obtained through assembling the dynamic equations of elements. Finally, the numerical simulation of a 3-RRS parallel manipulator was presented and compared with the results of SAMCEF software simulation. The results showed that the effectiveness and correctness of the dynamic models proposed in this paper.