| With the development of space technology, working conditions of some bearings which are applied in the extreme conditions of deep cooling, high speed and heavy load are very adverse. Such as rolling bearings which are used in hydrogen-oxygen rocket engines turbopump, it is lubricated only depend on the transfer film which is supplied by retainer. Large thrust rocket engine which is being developed in our country and reusable delivery systems both propose rigid requirement to developing long life and high reliability lubricate material. So it has important significance to develop new self-lubricating cage materials and reveal their lubricating mechanism for solving the problem of prolonging bearing life and bearing reliability in ultra-low temperature.The main failed modes of rolling bearings in ultra-low temperature were analyzed. Aiming at these failed modes which are related to the cage, design basis of component of self-lubricating cage materials was put forward, and based on the basis, four schemes of material component were devised.The forming techniques conditions of PTFE based self-lubricated composite were studied, the reasonable mixing speed, the press load and the sinter temperature curves are studied. The effect of strengthening agent content in each scheme on friction and wear properties and mechanical properties of the composite material was researched. Test results indicated that friction coefficient of PTFE based composite filled with carbon fiber was the biggest one in the four schemes, it ranged from 0.2 to 0.25, wear rat of this material was also higher, shock resistance of the composite material was better when the content of carbon fiber increased from 10% to 20%; friction coefficients of composite material in the other three schemes were at range of 0.15~0.18, and wear rat of them were lower, wear resistance of Ekonol and PAB fiber reinforced PTFE based composite was the best among them, graphite and nanometer ZnO were both able to reduce the impact ductility of composite material, and the impact ductility was higher when the content of Ekonol was lower than 15%.Comprehensively considered friction and wear properties and impact ductility, composite material that had lower friction coefficient, mezzo wear resistance and better impact ductility in each scheme were selected out. Dynamic mechanical properties of the selected composite material were tested, the results showed that the storage modulus of composite material except composite filled with carbon fiber were higher than pure PTFE in the same temperature when temperature varied at 25℃~200℃, the storage modulus of composite filled with carbon fiber was closed to pure PTFE; in the range of experimental testing temperature, loss factors of composite material were reduced evidently after filling strengthening agent, which can decrease the deformation retardation friction coefficient of the composite.Thermal expansion property and thermal conductivity of PTFE and its composites were researched. The results showed that PTFE and its composites occurred crystal transformation and crystal relaxation in the temperature range of 15℃～32℃. The macro behavior of the phenomenon was the volume expanded suddenly. Due to the processing temperature of the cage just between the temperature range, dimension error of the composite material caused by crystal transformation and crystal relaxation needed to be considered during the cage was machined and tested. Because the linear expansion coefficient of composite material is bigger than metal, the guide fit clearance vary obviously under the influence of temperature in the condition of large temperature difference. Thermal conductivity of PTFE was improved if graphite filled in it. Except graphite, using fiber as filler was distincter than using powder as filler in improving the thermal conductivity of composite material. The research result provide authority to design structure parameter of cage accurately and optimize manufacture techniques of cage.Mechanism of friction property which influenced by structural characteristics of polymer based self-lubricated composite, environmental temperature and working conditions were discussed; using XPS, chemical composition of the transfer film formed under dry friction and in liquid nitrogen and chemical reaction generated between transfer film and coupled parts surfaces were studied. The results showed that the significant factors which affect friction coefficient of the polymer based composite were molecular force between composite material and coupled parts, nominal contact stress, loss factor of composite material, hardness and storage modulus. If nanometer ZnO/PAB/PTFE composites rubbed with 9Cr18, transfer film formed under dry friction was deep and compact, however in low temperature it was thin and discontinuous. In these two conditions, transfer films both existed that parts of the CF2 bounds in PTFE were ruptured. F atomic and Fe atomic which existed on the surface of steel pin occurred chemical reaction and FeF3 was generated.Low temperature and high speed friction experimental system was developed, friction property and limiting PV value of five species of PTFE based composite used in liquid nitrogen were tested, meanwhile, the temperature of composites contact surfaces were calculated. Experimental results indicated that friction coefficients of composite filled with carbon fiber rubbing with 9Cr18 and Si3N4 were closed. Friction coefficients of other four species composites rubbing with 9Cr18 were smaller than rubbing with Si3N4. If Ekonol and PAB fiber reinforced PTFE based composite rubbed with 9Cr18 and Si3N4 in liquid nitrogen, the friction coefficient all increased with the increase of velocity when the load was a constant, the friction coefficient all decreased with the increase of load when the velocity was a constant. Whether composites rubbed with 9Cr18 or rubbed with Si3N4, the limiting PV value of PTFE based composite filled with carbon fiber was the least, but the limiting PV value of Ekonol and PAB fiber reinforced PTFE based composite was the most. The significant factors which affect the limiting PV value of the polymer based composite were friction coefficient of composites rubbing with coupled parts,γtransition temperature in the temperature chart of composites dynamic mechanical properties, as well as thermal parameters and densities of the coupled parts.
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