Research On Friction And Wear Characteristics Of Drive Wheels In The Traction Single-track Hilly Transporter

In recent years,researchers have conducted a lot of research to enhance the level of transportation mechanization in the hilly areas of our country.A lot of transport machines of hilly orchard mainly consisting of wheeled transporters,crawler transporters,ropeway transporters,self-propelled track transporters,and traction track transporters were successfully developed.Among these transporters,the traction single-track hilly transporters with easy accessibility and strong climbing ability are most widely used in the orchards for fruit transportation.This type of transporter makes use of the friction between rope and wheel to achieve transmission.Thus,the drive wheels could be severely worn,which further affect transportation safety and restrict the potential applications.To address this issue,theoretical analysis,numerical simulation,and bench test were carried out to characterize the friction and wear properties of the drive wheels in this paper.In addition,the protective coatings,comparative tests,and related theoretical basis to reduce the wear of the drive wheels were also developed.The major conclusions of this thesis are as follows:(1)The motion and wear status of the components of the "rope-wheel" drive system were analyzed during operation.The forces acting on the drive wheel were also explored.The process of the movement was divided into three stages: initiating stage,smooth operation,and holding stage.The slip ratio of the "rope-wheel" drive system was defined and it was found to be equal to the wire rope strain during operation.The abrasion of the wheels mainly occurred in the initiating stage and holding stage.Taking the characteristics of the motion as the reference,a simulation test platform was designed and manufactured for the experimental study of the wear characteristics of the drive wheels.The formula of the maximum friction force was derived to determine the traction capacity of the transporter and the effects of the installation parameters(center distance,preload and circles number)and operating parameters(speed and load)on the maximum friction,which provided insights for the understanding of friction and wear characteristics of the drive wheel.By constructing a maximum contact stress model based on hertz elastic contact theory,the influence of rope diameter,wheel diameter,and preload was investigated.The results of the stress analysis provided guidance for the selection of parameters in bench tests.By analyzing the pressure distribution,the sum of the single-lap pressure and the pressure distribution trend were obtained,resulting in the theoretical basis for setting the static model and selecting the axial loads when the COF was measured.(2)The simulation model was built to analyze the distribution of friction,stress and strain of the drive wheel.The bench tests were conducted based on the equivalent maximum contact stress to explore the influence trend of various parameters on wear.The research results showed that larger center distance,smaller preload,and more circles number were beneficial for reducing wear loss and induced the uniform distribution of friction force.Therefore,the center distance,preload and number of the circles were determined to be 720 mm,1280 N,and 10,respectively.Obvious stress-concentrated areas were uniformly distributed in the grooves of the drive wheels and the stress at the center of the area was relatively large.The maximum stress of the entire groove was generated at the edge of the "rope-wheel" contact position near the edge,which could induced great deformation of the grooves and led to accelerated abrasion.When large abrasion has been occurred in the grooves,the contact area between rope and wheel would shift down and the wear process would continually repeat the running-in period and stable wear period until the wire rope reached the bottom end of the wheel groove.With a certain displacement,the wear loss increased by 0.66% and 5.41% when the maximum speed of the drive wheel increased by 1 and 2 times from 8.6 rad/s.It indicated that the increase in speed had no obvious effect on wear loss.However,it could reduce the uniformity of friction force.After the 2-hour bench test,the corresponding quality losses were 183.6mg,726.2 mg,and 966.83 mg when the loads were 62.5 N,125 N,and250 N,respectively.The degree of wear of the drive wheel was proportional to the load.Meanwhile,a smaller load led to the more even distribution of friction force,but it could also cause the wire rope to twist which might induce serious wear.(3)Quenching and chromizing were proposed as protective methods to against the wear between rope and wheel.The wear behaviors of these samples have been studied under dry friction and lubrication conditions taking the as-received sample as reference.The results showed that the COF of quenched and chromized drive wheel was reduced from 0.36 to 0.31 and 0.35 under dry friction conditions.The corresponding traction capacity was reduced by 10.76% and 2.05%,respectively.At lubrication conditions,the COF of the quenched drive wheel reduced to 0.14 and the traction capacity decreased by50.63%.In comparison,the COF of the chromized drive wheel reduced to 0.34 and the traction capacity only decreased by 2.15%.Both quenching and chromizing could reduce the quality loss of the drive wheel,but the effect of chromizing was more significant.Under a favorable lubrication state,the quality loss of the chromized drive wheel was reduced by 95.83% compared to the as-received sample.The wear condition of the wire rope corresponding to the as-received sample under the dry friction state,the quenching and chromizing samples under the favorable lubrication state were close.They were within an acceptable level.Improving the lubrication conditions of the "rope-wheel" drive system after chromizing could maintain traction capacity and prolong the service life of the drive wheel,which was promising in addressing current wear issue of the drive wheel.