Study On Preparation And Performance Of Modified Resin Bond Composite Abrasive Tool For Rail High-speed Grinding

With the development of high-speed and heavy-haul railways and the increase of train running density,the rail grinding operation cycle and window time have been significantly shortened.To this end,a new passive high-speed grinding(HSG)technology was introduced into railway preventive grinding and became the main rail maintenance operation.Grinding wheels are the most consumables in high-speed rail grinding operations,and their performance significantly affects the grinding efficiency,operating time and grinding costs.However,due to the limitation of the technical barriers to import high-speed rail grinding from abroad,there are no mature supporting products and technologies in China.Therefore,it is of great significance to study the preparation technology of HSG grinding wheels and optimize them.The HSG grinding wheel was taken as the research object in this study.The passive grinding mode and grinding principle of rail HSG were analyzed,and a passive grinding test machine simulating the relative motion between HSG grinding wheels and rails was designed in this paper,which provided the test method and equipment support for the passive grinding test of HSG grinding wheels.Effects of modified resin bond,grinding wheel structure,abrasive and grinding parameters on mechanical properties,grinding performance,grinding effect,and service life of HSG grinding wheels were investigated by using Differential Thermal Analysis(DTA),Fourier Transform Infrared(FTIR),Scanning Electron Microscope(SEM),Energy Dispersive Spectroscopy(EDS),X-ray Diffraction(XRD),and other methods.On this basis,HSG grinding wheels were prepared and tested on the railway.First,methyltrimethoxysilane(MTMS)and epoxy resin(EP-20)modified phenolic resin(PF)binders were prepared by a two-step synthesis method.The effects of MTMS and EP-20 on the thermal resistance and mechanical properties of the binders were investigated.The results showed that the thermal stability,flexural strength and impact strength of epoxy-modified silicone phenolic resin(ESPF)binder with 10%EP-20 based on 40%MTMS modified PF were respectively improved about 43%,27.5%,and 13.9%compared to the ordinary PF,which was attributed to the Si-C bond,Si-O bond and epoxy group being introduced into the macromolecular chain structure of phenolic resin.The HSG grinding wheels were prepared with ESPF based on modified phenolic resin binder,and the effects of forming density and ESPF binder amount on the porosity,mechanical properties,grinding efficiency,service life and grinding quality of HSG grinding wheels were studied.The porosity of the grinding wheel decreases with the increase of the forming density and binder amount,which will improve the hardness,bending strength,impact strength and grinding life of the grinding wheel,but will reduce the grinding efficiency of the grinding wheel.Based on the research results of the mechanical properties,grinding performance and grinding effect of the grinding wheel,when the grinding wheel density is 3.0 g/cm~3,the binder amount is 13%,and the porosity is controlled to around 10%,the HSG grinding wheel can obtain good comprehensive performance.The effects of grinding pressure and grinding time on the grinding performance of HSG grinding wheels in the high-speed grinding process of rails were studied by the passive grinding test machine.It was found that the increase of grinding pressure will improve the grinding efficiency of HSG grinding wheels on rails,but will reduce their service life and rail grinding quality.When the grinding pressure is in the range of 2000 N～2400 N,the HSG grinding wheel shows a relatively balanced grinding performance.Under the condition of a certain total grinding time,the passive grinding operation with multiple passes can effectively slow down the accumulation of grinding heat,optimize the rail grinding quality of the HSG grinding wheel,and prolong the service life of the HSG grinding wheel.To further improve the performance of HSG grinding wheels on the basis of the above study,a new idea was proposed to prepare HSG grinding wheels by prefabricating metal matrix composite abrasives by coordinating the differences between super-hard abrasives and zirconia alumina abrasives.A metal-based cubic boron nitride(CBN)composite abrasive with porous surface but dense interior was designed and fabricated,and HSG zirconia alumina/CBN composite abrasive grinding wheels were prepared.Compared with the zirconia alumina grinding wheel,the grinding efficiency and grinding ratio of the composite abrasive grinding wheel were improved by about 100%,and the grinding quality of the rail with grinding wheels was significantly improved.The proposal of composite abrasive grinding wheels provide a new direction for the development of high-performance HSG grinding wheels.Based on the laboratory research,HSG zirconia alumina abrasive grinding wheels and HSG zirconia alumina/CBN composite abrasive grinding wheels were tested on the railway.The results show that the average grinding mileage of the composite abrasive grinding wheels is more than 60%longer than that of the zirconia alumina abrasive grinding wheels,and the surface quality of the rail after grinding is better.CBN composite abrasives and composite abrasive grinding wheels provide a development direction for breaking through the performance limit of ordinary abrasive grinding wheels and improving the high-speed grinding efficiency and grinding quality of rails.