| As the main current-carrying components of subway trains,pantograph-catenary systems are widely used in various subway lines.The catenary-wire systems in the subway lines can be divided into a flexible catenary-wire system,a rigid catenary-wire system,and third-rail catenary-wire system.Among them,the rigid catenary-wire system is widely used in subway lines due to its advantages of less parts,safety and reliability,and low maintenance cost.But the rigid catenary-wire is not elastic,and the vibration and impact during the train operation are more likely to damage the contact wire and cause problems such as hard spots.The presence of a hard spot can further aggravate the vibration,causing arc discharge resulting from the pantograph offline.Under the combination action of arc ablation and mechanical wear,the performance of friction and wear between the contact strip and contact wire is becoming more and more serious.In this thesis,the wear performance of metal-impregnated carbon strips against a rigid catenary wire experimentally studied based on the block-on-ring high-speed friction and wear tester.In order to study the trend of wear rate of the metal-impregnated carbon strips under different test conditions and long service conditions,the sliding distance of 1000 km was adopted for each test.Based on a large number of experimental data,a wear model of metalimpregnated carbon strips is established for subway working conditions,which helps to solve the problem of abnormal wear of the metal-impregnated carbon strips in subway lines.The results show that the current magnitude and the shock vibration between the friction pairs are the main factors affecting the wear rate of the strips.The main conclusions in this thesis are obtained as follows:(1)Among the three test parameters of current,normal force,and sliding speed,the normal force and sliding speed can significantly affect the rate of contact loss between the metal-impregnated carbon strips and Cu-Ag alloy contact wire.With the increase of the normal force,the rate of contact loss decreases significantly,but the arc lasting duration does not change significantly.With the increase of the sliding speed,the rate of contact loss and arc lasting duration between the friction pairs both increase first and then decrease.When the sliding speed is 80 km/h,the arc discharge between friction pairs is more serious.(2)The contact resistance decreases with the increase of the normal force,first increases and then decreases with the sliding speed.The current-carrying efficiency is just the opposite.(3)The influence of the current on the rate of contact loss is not significant,but with the increase of the current,the arc discharge intensity also increases.The friction coefficient between the friction pairs decreases obviously,and the wear rate of carbon strips increases rapidly.Under the arc ablation,obvious cracks and ablation pits appear on the surface of the strips,and the greater the current,the larger the area of the ablation pits.(4)A larger normal force can reduce the rate of contact loss between friction pairs,thereby reducing the heat caused by arc discharge.The wear rate of the strips is continuously reduced,the arc ablation pits on the surface of strips are gradually reduced,and the cracks are relatively fine.When the normal force increases to 45 N,the contact wire is prone to scratches under the ploughing action of hard particles between the friction pairs.(5)With the continuous increase of the sliding distance,the current-carrying efficiency increases,and the wear rate of the strips gradually decreases and tends to be stable.Because the surface of the sliding strip is relatively rough at the beginning of the test,the actual contact area between the friction pairs is small,and the non-contact areas are prone to produce microarcing.In addition,due to a large shrinkage resistance,the resistance heat between the friction pairs is larger,and the wear rate of the carbon strips is also higher.With the increase of the sliding distance,the contact area between the friction pairs increases,and the wear rate of the strips trends to be stable.(6)The research on the wear model of metal-impregnated carbon strips shows that the arc heat and Joule heat are the main reasons for the mass loss of strip material.When the rate of contact loss increases,the mass loss of strips caused by the arc ablation will increase rapidly,resulting in the overall wear increases rapidly.The increase of normal force can reduce the rate of contact loss,and thus reduce the wear of strips caused by arc ablation.(7)Using the established wear model,the optimized contact force between 42 N and 46 N is recommended for Taiyuan subway lines. |
