| Rolling electrical contact mainly occurs in key parts of rail transit return system,missile control system,radar collector ring,electromechanical bearing,etc.High-reliability rolling current-carrying friction pair is an important guarantee for the safe service of high-end equipment and technological progress.The system performance of the contact pairs are affected by factors such as service conditions,external environment,and operating time.Among them,the influence of external factors is mainly realized through the material exchange and energy exchange between the surface of the contact pairs an d the environment.One of the typical manifestations is surface oxidation.China is a country with a vast territory and a unique climate.The water and oxygen atmospheres are complex and changeable during the cross-regional and cross-season service of the contact pairs.The failure characteristics and oxidation mechanism of the current-carrying pair materials in different atmospheres are still unclear.In this thesis,the FTM-100 rolling currentcarrying friction tester was used to study the tribology and c onductivity characteristics of the rolling current-carrying contact pair under different water and oxygen environmental conditions.The specific research content and main conclusions are as follows:1.In the atmospheric environment,the influence of humidity(gaseous water)on the performance and damage of the rolling current-carrying contact pair.The impact of different humidity on the rolling current-carrying friction of copper materials was tested at five humidity levels of 10%RH,30%RH,50%RH,70%RH,and 90%RH and three current levels of 0A,1A,and 1.5A.The influence of humidity and current on friction coefficient and contact resistance is summarized.Under medium and low humidity,the coefficient of friction is low,and under high humidity,the coefficient of friction increases sharply.As the humidity increases,the degree of oxidation on the surface of the material increases,resulting in an increase in contact resistance.The surface damage of the friction pair changes from slight adhesion to lamellar fatigue.2.In the atmospheric environment,the influence of liquid water on the performance and damage of the rolling current-carrying contact pair.The friction and conductivity of the rolling current-carrying friction pair show a high sensitivity to added water.Compared with the gaseous water environment,liquid water will cause a higher friction coefficient(over 1)and reduce the conductivity.In a water environment,spalling pits appear on the surface of the material,and plastic deformation along the rolling direction is observed on the subsurface.High-speed can reduce the friction coefficient to a certain extent,but exhibits higher contact resistance.Fatigue damage manifestations are different at low and high speeds.The transition of the fatigue damage form at different speeds is the result of the competition between the reduction of the friction coefficient and the enhanced water pressure.The critical speed for the transition of the surface damage form under the experimental conditions in this thesis is between 200～240 r/min.3.The influence of water and oxygen single factor environment on the friction performance and damage of rolling current-carrying.Dry oxygen alone can cause the surface of the material to oxidize and increase the contact resistance,but when there is no adsorbed water,the increase in the degree of oxidation of the friction surface does not directly cause the friction coefficient to increase rapidly.The surface damage of the material is still dominated by slight adhesive wear,and there is no obvious fatigue damage.Nitrogen environment with different humidity can also cause surface oxidation of the material,but the degree of oxidation is limited,and the friction coefficient is slightly increased under the action of adsorbed water,but it is not enough to cause surface fatigue.Under the action of adsorption,tribochemistry and electrochemistry,the single-factor environment of water and oxygen can cause oxidation of the friction surface.The high friction coefficient is the result of the combined action of water and oxygen.4.The composition of friction under current-carrying friction conditions,that is,the cause of high friction coefficient,and its effect on rolling friction damage are analyzed.The adhesion effect caused by electric current,the meniscus force effect caused by water adsorption,and the meniscus force increase effect induced by electric current are three factors that lead to high friction coefficient.In the environment of high humidity and liquid water,the meniscus force caused by the enhancement of water adsorption caused by oxidation has a more obvious influence on the friction coefficient.The friction-induced stress distribution transforms the form of damage from adhesive wear under low humidi ty to surface fatigue under high humidity and water environment.At the same time,the high friction coefficient leads to deformation of the friction subsurface grains and stress concentration.In summary,based on the changes in the performance and damage of the rolling current-carrying friction pair in water and oxygen environments,this thesis reveals the oxidation evolution mechanism of the friction surface under the conditions of rolling current-carrying contact,analyzes the composition of frictional force under currentcarrying friction conditions and its influence on rolling friction damage.The relevant results of this thesis are expected to enrich the theory of rolling current-carrying tribology,and provide theoretical guidance for material selection,protection and safe service of current-carrying friction pairs. |
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