Study On The Ceramic Bearings Used For RP-3 Fuel Feeding Pump

The supporting bearings of the fuel feeding pump of the aviation and spaceflight engine work in the fuel directly. The performance of these bearings is affected by the fuel. With the demand to the performance of the aviation and spaceflight engine becomes higher, the working rotational speed and load of the pump becomes higher and higher. The higher demand is advanced to the bearings'performance. In this paper, the high-speed and high-load ceramic ball bearing working in RP-3 fuel was studied, which provided theory foundation for the application.The tribological properties of the contact pairs of bearing are related to the wetting ability of the work medium to the material surface. In order to obtain the wetting ability of the fuel to elements of ceramic bearings, three kinds of reagent known surface performance parameter: de-ion water, glycerin and formamide were chosen. The contact angle of the three kinds of reagent on the surface of Si3N4 and Cr4Mo4V were measured. By the Young equation and the surface free energy estimation theory, the surface free energy was calculated. Then the effect of three kinds of surface modified with ion-implanted N+, DLC, TiC, on surface free energy of Cr4Mo4V were investigated. The wetting ability of RP-3 fuel to Si3N4 and Cr4Mo4V was also measured. The results show that the descending sequence of the surface free energy is Si3N4, Cr4Mo4V implanted with TiC, Cr4Mo4V implanted with DLC, unmodified Cr4Mo4V and Cr4Mo4V implanted with N+. The wetting ability of RP-3 is in sequence of unmodified Cr4Mo4V, Cr4Mo4V implanted with N+, Cr4Mo4V implanted with DLC, Cr4Mo4V implanted with TiC.The tribological properties of contact pairs composed of Si3N4 ball and Cr4Mo4V disc were investigated under dry friction and in RP-3 fuel by a ball-on-disc tribometer. And the effect of surface modified of Cr4Mo4V on tribological properties was studied. After surface modified, the fiction coefficient and antiwear increase evidently under dry friction condition. And the increasing degree is in sequence of Cr4Mo4V implanted with TiC, DLC, N+. In RP-3 fuel, the friction coefficient changes with the change of the surface wettability, and decreases evidently compared to under dry friction condition. The wear of Cr4Mo4V implanted with DLC is less. While the large flake appears on Cr4Mo4V implanted with TiC. However, the wear mechanism of Cr4Mo4V implanted with N+ is almost the same as the unmodified steel.The numerical simulation of the contact stress of pairs composed of Si3N4 ball and Cr4Mo4V disc was performed by ANSYS. The effect of Cr4Mo4V surface modified on the contact stress was researched. Taken the load which produces the maximum contact stress of 2.2GPa, 2.5GPa, 2.8GPa and 3.2GPa of unmodified steel as a reference respectively, the stress distribution and the maximum equivalent stress of the modified steel were compared with the unmodified steel. The results show that the maximum contact stress decreases about 12% after Cr4Mo4V implanted with DLC. While Cr4Mo4V implanted with TiC, the maximum contact stress decreases a little.