Gong Guofang

Tribological properties of kaolin filled UHMWPE composites in unlubricated sliding

The two kinds of kaolin filled ultra-high molecular weight polyethylene (UHMWPE) based composites (UHMWPE/kaolin) were prepared by means of polymerization filling and melt mixing, respectively. The unlubricated sliding wear behavior of the composites was tested on an MM200 rig. The effects of sliding speed and load on the sliding wear of UHMWPE were determined. Scanning electron microscopy (SEM) was employed to examine the worn surfaces and the wear mechanisms of the composites discussed. It has been found that appropriate kaolin filling can greatly improve the tribological behavior of UHMWPE. It has also been found that the UHMWPE/kaolin composites prepared by polymerization have much better tribological properties than the ones prepared by mixing with the same components and are promising self-lubricated material candidates for engineering application.

Positioning Precision and Impact Force Control of Segment Erector for Shield Tunneling Machine

This paper deals with the control system of the segment erector of a shield tunneling machine and reducing the steady-state error and impact force during the positioning process. A segment erector with six degrees of freedom driven by electro-hydraulic system is designed, and the segment erecting process is introduced. The kinematics and dynamics models, as well as the mathematical model of the electro-hydraulic system are proposed to facilitate the positioning process and joint force analysis. Three different segment positioning control strategies are employed separately, and comparisons are made in terms of precision and impact force. Special reference speed and displacement/angle run curves are selected to control the segment positioning process. Simulations are carried out to calculate the impact force and positioning error. The simulation results verify the validity of each proposed control system.

Research into the intelligent control of the cutter head drive system in Shield tunnelling machine based on the pattern recognition

This article discusses an intelligent expert control system for the cutter head speed of the shield tunneling machine, in which the earth layer recognition method and the drive power efficiency appraise method are proposed. The earth layer recognition system was based on the statistical pattern classification method and the method of calculation to the approach degree to the feature area by the data gained in simulation tunneling test. The power of the cutter head drive system was appraised by the power efficiency index proposed in this paper which is the key parameter to the speed control system of the cutter head. Finally, this paper discusses a closed loop controlled hydraulic system which dominated by the expert control system.

Research on Dynamic Characteristics of the Rotary Valve

In order to get an electro-hydraulic vibrator with high frequency, great exciting force and large flow, a new type of rotary valve with four-way commutation was designed. The rotary valve is worked under special environment, so the characteristic of the valve must be studied. Based on the structure and working principle of this valve, the mathematical expressions of steady-state axial flow force and flow torque were derived. The effect of the rotary vales structure parameters is analyzed, and the response characteristic of rotary valve is studied. The results show that the flow force can be reduced by minimizing the axial valve port opening and spool radius, increasing the opening depth in the premise of meeting the design requirements, and a set of optimal parameters was got. The result indicated that the factors can be optimized to improve the performance of the rotary valve, providing guides for new generation rotary valve.