Study On Performance Modification Of Spindle-sleeve Based On Dimple And Coating

As a key component of a cotton picker, the spindle is responsible for picking cotton,whose performances determine the cost and efficiency of picking cotton. The spindleand its matched sleeve form a set of tribological pair. Owing to the direct contactbetween the spindle and the cotton, the failure phenomena such as fatigue, wear and tearoften occur during its practice operation. The cotton picker used in China, however, ismainly imported from America, whose price is very expensive. In order to save the cost,it is essential to conduct a study about the tribological modification of the sleeve andspindle to achieve localization of the picker cotton.The present research is supported by the State Key Laboratory of MechanicalTransmission Chongqing University (No.0301002109174). According to the currentdevelopment of cotton picker in China, the tribological performances of spindle andsleeve are studied based on their surface texturing and coating material. The maincontents are as follows:First, surface texturing, a hot spot in tribological researches at present, is applied tothe spindle. To simplify the analysis, A plate model were adopted to study the effects ofdimples located on the surfaces on their tribological performances. The main content inthis thesis contains the comparison between tribological performances with and withoutcavitation effects. Further, an analysis was made about the influences of geometry sizesand arrangements for the dimples on the load-carrying capacity, frictional force, frictioncoefficient and stress of the surfaces. The numerical results show that when thecavitation model is used, the negative film pressure and surface stress caused bynegative film pressure are both eliminated, while the amplitudes for the film pressureand surface stress both increase, as compared with those without caviation consideration.The changes in the dimple size will result in changes in the tribological properties of thesurfaces. With the synergic interaction among the dimples, the appropriate size anddistribution of the dimple can improve well the tribological performances on thesurfaces.Then, a finite element model with both a sleeve and lubricant film was established,and further influences of the elastic modulus, Poisson’s ratio and thickness of thecoating on the mechanical performances of the sleeve are investigated withfluid–structure interaction method. The simulation shows that the three influencing factors can significantly change the tribological performances of the sleeve, and theformer two factors have optimum values within the range of a certain dimension.Finally, the tribological performances of two kinds of coating materials (i.e. chemicalnickel and hard chrome), desired to used for the spindle-sleeve, were studied in dryfriction and oil lubrication conditions by ball-disc friction test experiments. Theirtribological performances were compared under the various test times, applied loadsand reciprocal frequencies. Meanwhile, the conclusions about effects of the applied loadand frequency on the friction coefficient obtained with the author’s code were verifiedthrough the experimental data present. The numerical and experimental results showthat the load and velocity have significant influences on the friction coefficient. Thehard chrome has better wear resistance, compared to the chemical nickel.