Study On The Performances Regulatory Mechanisms Of High-speed Rail Grinding Stone Via Corundum Abrasivves

Rail grinding wheel（grinding stone,abbreviated as GS）is one of the most important approaches to remove the rail defects and repair the rail profile.The physical and chemical properties have a significant effect on rail grinding efficiency and ground rail surface integrity,which can influence the rail performance under whole life-cycle.At present,the technologies of home-made active rail grinding stone（A-GS）are seriously behind the foreign owing to the poor anti-wear,low grinding efficiency and burned rail of AR-GS.Additionally,the vital techniques of the high-speed rail grinding stone（HS-GS）are monopolized by the foreign.Hence,the investigations on the regulatory mechanisms and evaluation system are of great scientific interest and major engineering application value.Given that the on-site rail grinding tests are not reversible and high risk,high investment,long-period,etc.,the comprehensive performances were evaluated at multi-dimensions（on-site rail grinding,high-speed bench tests and scaled grinding stone）,which can provide a theoretical basis for the development of full-scaled HS-GS.The interpretational criteria for the GS in multi-dimensions were built,and a more scientific and higher effective development route for GS was put forward.Meanwhile,the properties of abrasives,material removal mechanisms,GS wear mechanisms and the performances regulatory principles of GS via mixed abrasives were investigated systematically.Based on the research results,a high performance HS-GS was manufactured.The main conclusions are summarized as follow:1.Formulated the multi-dimensional performance evaluation criterion.The comprehensive performances of an on-site HS-GS were evaluated at the as-mentioned multi-dimensions,and the performance indicators at the corresponding dimensions were determined,which could guide the performance regulation and evaluation for self-made HS-GS.According to the performance indicators,the bond of self-made HG-GS was regulated and determined.2.Systematical investigation on the fracture behaviors of corundum abrasives.The forth fracture style was dominant during the compression processes of zirconium corundum（ZA）,fused brown corundum（FA）,calcined brown corundum（A）and white corundum（WA）,which indicated that more sharping cutting edges could be generated by these four kinds of abrasives during rail grinding process.The Weibull characteristic crushing strength grew with the decrease of abrasive size.Meanwhile,the ZA presents the largest Weibull characteristic crushing strength,followed by A,and the worst was WA.The calcination improved the crushing strength of FA by approximately 15.56%.3.Clarified the material removal mechanism in the rail grinding processThe cutting processes of the abrasives with different shapes were simulated via the finite-element analysis.The results showed that the small-sized debris,high grinding stress,high grinding temperature,high energy consumption,and the worse ground rail surface integrity were caused by the abrasives with spherical,ellipsoidal and large negative rake angle.The continuous banded debris,lower grinding force and temperature,better surface integrity were formed by the abrasives with a rake angle of 15°.Under the thermo-mechanical coupling effects,the phase transformations were occurred in the ground rail surface materials and a white etching layer with nanocrystalline was generated,which could cause the pre-fatigue and surface quality degradation of ground rail.Therefore,choosing the sharp abrasives with a small tip angle can improve the probability of the abrasives cutting with a positive rake angle,which can effectively reduce the grinding temperature,grinding energy consumption,and optimize the ground rail surface quality.4.Probing the effect of GS wear mechanisms on the grinding behavior（1）The grinding efficiency grew in the order:the GS of ZA（GS-ZA）,the GS of A（GS-A）,the GS of WA（GS-WA）,whereas the decreased grinding ratio order was GS-ZA,GS-WA,GS-A.（2）The wear mechanisms of the GS were attrition wear,abrasive pull-out and fracture,wear of the bond,and material adhesion and clogging.The main wear mechanism of GS-ZA was attrition wear that of GS-WA was abrasives pull-out and fracture.The main wear form of GS-A was abrasives pulled-out which was ascribed to the crack initiation and propagation in the interface between abrasive and bond.The difference in grinding performance of GS is attributed to the different wear forms of abrasive.（3）The comprehensive performance evaluation results of the scaled GS showd that the GS-WA was the best,followed by GS-A,and the worst was GS-WA.5.The performance regulatory mechanisms of GS via mixed abrasives.For the GS with ZA,when the F16 and the F30 abrasives are mixed at a low ratio（G-L group）,the grinding amount（4.0 g）and grinding ratio（46.2）of the GS is the largest comparing with the other groups,and it is close to the corresponding evaluation indicators of the scaled GS.The main wear mechanisms of the F16 ZA abrasives were attrition wear and micro-fracture.The F30 ZA abrasives present a higher crushing strength owing its smaller size and harder to fracture,which made the main wear forms of F30 attrition wear and pulled out.The addition of smaller F30 ZA to the F16 GS not only improved the abrasive concentration,but also caused the main grinding mechanisms gradually changing from rubbing and ploughing to cutting.The coupling effects of wear mechanisms,abrasive concentration and the grinding mechanisms enabled the performance promotion of G-L GS.（2）As for F16 abrasives,the GS with a low percent of ZA and high percent of A（K-L group）exhibited the largest grinding amount（8.1 g,about 2 times of the evaluation indicator）and a higher grinding ratio（37.8）comparing with the other group of different mixed ratios.The coordinate regulations of the attriton wear（ZA）and the pulled out（A）made a good balance between the wear and the self-sharping of GS,which was responsible for the promotion of grinding amount and grinding ratio.6.Successfully prepared the high-performance HS-GS.Based on the research results,a full-scale GS（G₃）with mixed abrasives（different types and granularity）was prepared.The results of the high-speed bench tests showed that the performance of the G₃ was close to or even better than the corresponding evaluation indicators,which verifies that the self-designed G₃ is equivalent to the on-site HS-GS at this dimension.The results of the full-scale GS further prove that the research route promoted in this paper is feasible,effective and scientific.