Theoretical And Experimental Research On The Generation Mechanism Of Wheel Tread Spalling Of High-power Electric Locomotive

Wheel tread spalling is exposed in the service process of high-power electric locomotive,which greatly increases wheel reprofiling.As a result,the service life of wheelset is greatly shortened,and the operation and organization of railway department are disturbed.It is one of the urgent needs to explore the generation mechanism of tread spalling and propose technical countermeasures.Therefore,funded by the National Natural Science Foundation of China(No.51825504)and major science and technology projects of related enterprises,the generation mechanism of wheel tread spalling of the high-power electric locomotive is studied based on simulations and field experiments,with the support of the research team and railway departments.Firstly,the thesis systematically investigated and tested the wheel tread conditions of mainstream locomotives in China,and the common types of tread spalling and its main features of a certain types of high-power electric locomotive are summarized.It can be seen that,the surface pitting or fatigue cracks are initially observed on the damaged wheels,which gradually expanded into metal pieces and deep cracks,even severe defects.With the gradual deterioration of surface pitting,adjacent pits are connected and penetrated,then visible metal layers initiate from the area with deep and dense pitting;under the wheel and rail tangential forces,the pits are gradually closed,therefore,the lateral cracks are left on tread;further extends to the wheel circle after running 20,000 to40,000 km;the deep transverse cracks are always observed on the surface of a reprofiling wheel,which depth is about 4 mm.For fatigue cracks,there are three types of cracks commonly observed on tread surface,circumferential cracks on field side(concentrated on 95 mm from flange back),transverse cracks between 65-90 mm(concentrated on 80mm),and transverse cracks near flange root.Surface cracks are mainly caused by the plastic flow of metal materials,and are accompanied by a significant incr ease in surface hardness;a circumferential cracks first appeare on wheels,which are located in the band of 80 to 100 mm from flange back;the transverse cracks in the center of tread are concentrated in the band of 80 mm from flange back;with the increase of running mileage,the transverse cracks near tread center deteriorate significantly and propagate deep into material,reaching a depth of 5-15 mm.In addition,severe metal pieces,metal defects,continuous scratches and abrasion are observed mainly on wheels of locomotive with C₀-C₀ bogies,which mainly distributed in the tread centre.Secondly,to reveal the generation mechanism of wheel tread spalling of high-power electric locomotive,this thesis analyzes its potential causes from the perspective of wheel-rail dynamic based on testing data.Pitting is mainly related to the sand.Larger particle and higher content of ferric oxide and aluminum oxide indeed injure the surface of wheel tread,forming a large and deep indentation.In the condition of wheel idling,the sand also causes a continuous scratch in the circumferential direction.For the wheelset with large initial wheel diameter difference(WDD),the wheel with a smaller diameter is more likely to suffer crack damage as well as partial wear,whereas the wheel on the other side is always in good condition.In curves,locomotives with C₀-C₀ bogies are suffered serious wheel tread spalling,whereas the wheel tread of the locomotive with B₀-B₀ bogies is well on the same operational conditions.It is mainly due to the deficiencies of locomotive with C₀-C₀ bogie in curving performance and its traction capacity,resulting in the increase of wheel-rail tangential forces and even the accidents of wheel idling or sliding.Therefore,the wheel tread spalling of high-power electric locomotives is mainly related to the quality of sand,locomotive operating conditions,bogie types,initial WDD,and flange lubrication failure.Then,the wheel tread spalling of the high-power electric locomotive is theoretically predicted and analysed.The multi-body dynamic model of locomotive is established to calculate the index of wheel-rail dynamic interaction under different operating conditions,and then post-processed in the predicted models of wheel tread spalling.The bogie structure,key parameters,and operating conditions of wheel and rail are mainly analysed,which provides theoretical support for the generating mechanism and countermeasures of wheel tread spalling.The results of theoretical calculation and analysis show that,in curves with a 400 m radius,the transverse cracks occur on the outer wheels of rear wheelset for the locomotives with C₀-C₀ bogies,and located on the band of 65-95 mm from flange back(mainly concentrated on 80 mm).While for the locomotives with B₀-B₀ bogies,the surface cracks are predicted on the position of 60 to 80 mm from flange back(concentrated on 65 mm),which have a greater chance to wear off.In traction or braking operations,the crack damage of wheels on the locomotive with C₀-C₀ bogies is more severe than locomotive with B₀-B₀ bogies,especially under large braking forces.The suspension stiffness and free lateral displacement of middle wheelset have less effect on wheel tread damage.From the perspective of operational conditions,with the increase of curve radius,fatigue cracks decreased significantly,and the position of the cracks moves to the wheels centre correspondingly.The measured tread profile after running 30,000km could theoretically reduce tread spalling of the locomotive with C₀-C₀ bogies on small curves.The initial WDD and unworn wheel profile have less chance to increase the surface cracks,especially those located in the field side of wheel tread.However,the initial WDD and the failure of flange lubricating device(such as non-injection,deviation in injection position,etc.)firstly cause the partial wear,and the worn profile and WDD further induce the wheel tread spalling,which is in accordance with the field observation.A circumferential crack occurs when the front wheelset has a WDD,while a transverse crack occurs when the rear wheelset has a WDD.The failure of wheel lubrication increases both the wheel wear and the fatigue cracks.When wheel lubrication is added on the middle wheelset of C₀-C₀ bogie,the tread spalling and flange wear can be effectively reduced,in which,the spalling on a small curve is reduced by about 40%,and the wear number is reduced by about 58%.Finally,aiming at the practical case of wheel tread spalling occured in Houma to Jiexiu section of Nantongpu line,the technical measures to alleviate the tread stripping are put forward,including reducing the maximum electric braking force of locomotive,running on mixed lines,improving the quality of sand,and updating the traction control software.In order to verify the effectiveness of the technical measures,an operational technical scheme was developed and a one-year follow-up observation study was carried out.The results show that the condition of wheel surface is improved significantly,the annual reprofiling times is reduced by 53.49%,the mileage of wheel reprofiling is increased by 28.53%,the consumption rate of wheel diameter is reduced by 124.8%.It is shown that the technical measures can effectively alleviate the tread spalling and prolong the service life of wheel.