【作者】 贾晓梅；

【导师】 王黎钦；

【作者基本信息】 哈尔滨工业大学 ， 机械设计及理论， 2008， 博士

【摘要】 随着空间技术的发展,一些深冷高速重载极苛刻工况条件下工作的轴承如氢氧火箭发动机涡轮泵用滚动轴承只能依靠保持架提供的转移膜来润滑,工作条件十分恶劣,我国正在研制的大推力火箭发动机与将来可重复使用运载系统都对发展长寿命高可靠转移膜润滑材料提出了迫切而苛刻的要求,因此,研制新型自润滑保持架材料并揭示其润滑机理对解决超低温条件下轴承的延寿及可靠性问题具有重要意义。本文分析了在超低温条件下与保持架有关的滚动轴承的主要失效形式,提出了相应的自润滑保持架材料的成分设计依据,设计了四种材料组分方案。研究了PTFE基自润滑复合材料成型工艺条件,确定了合理的搅拌速度、压制压力和烧结温度曲线。考察了每种方案中增强剂含量对复合材料摩擦磨损性能和力学性能的影响。测试结果表明:四种方案中,碳纤维增强PTFE复合材料的摩擦系数最大,其范围在0.2～0.25之间,磨损率也较高,当碳纤维含量由10%增加到20%时,复合材料抗冲击能力较好;其它三种方案中复合材料的摩擦系数在0.15～0.18之间,磨损率也较低,其中聚苯酯和PAB纤维增强PTFE复合材料的耐磨性最好,石墨和纳米ZnO均能降低复合材料的冲击韧性,当聚苯酯含量低于15%时,复合材料的冲击韧性较高。综合考虑摩擦磨损特性和冲击韧性,在每种方案中优选出摩擦系数较低、耐磨性适中和冲击韧性较好的复合材料。测试了优选出的复合材料的动态力学特性,研究结果表明:在25℃~200℃之间,在同一温度下,除填充碳纤维复合材料的储能模量与纯PTFE接近外,其它复合材料的储能模量均比纯PTFE高;在实验测试温度范围内,填充增强剂后,可明显降低复合材料的损耗因子,从而可降低复合材料的形变迟滞摩擦系数。研究了PTFE及其复合材料的热膨胀特性及导热性能。研究结果表明:PTFE及其复合材料在15℃～32℃之间发生结晶转变与结晶松弛,宏观表现为体积突然膨胀,而保持架的加工温度恰好在此范围内,因此,保持架在加工和检测时,要考虑复合材料由于结晶转变和结晶松弛造成的尺寸误差。由于复合材料线膨胀系数比金属线膨胀系数大,在大温差环境下导向配合间隙受温度的影响变化显著。PTFE中填充石墨可明显改善其导热性能,除石墨外,填充纤维对复合材料导热率的提高比填充粉末材料显著。研究结果为精确设计保持架结构参数和优化加工工艺提供了依据。探讨了PTFE基自润滑复合材料结构特性和环境温度及工况条件对其摩擦性能影响机理;并且用XPS分析了在干摩擦和在液氮介质中形成的转移膜的化学成分及转移膜与对偶件表面发生的化学反应。研究结果表明:影响聚合物基复合材料摩擦系数的主要因素是复合材料与对偶件之间的分子作用力、名义接触应力、复合材料的损耗因子、硬度、储能模量。纳米ZnO/PAB/PTFE复合材料与9Cr18对摩,在干摩擦条件下形成的转移膜厚而致密,在低温条件下形成的转移膜薄且不连续。两种条件下形成的转移膜都存在PTFE中的部分CF2键断裂,F原子与钢销表面的Fe发生化学反应,生成FeF3。研制了低温高速摩擦实验系统,测试了5种PTFE基复合材料在液氮介质中的摩擦性能及极限PV值,并计算了复合材料接触表面的温度。实验结果表明:在液氮介质中,碳纤维增强PTFE复合材料与9Cr18对摩的摩擦系数和与Si3N4对摩的摩擦系数比较接近,其它四种复合材料与9Cr18对摩的摩擦系数比与Si3N4对摩的小。聚苯酯和PAB纤维增强PTFE复合材料在液氮介质中与9Cr18和Si3N4对摩,当载荷一定的情况下,摩擦系数都随着速度的增大而增大,当速度一定时,摩擦系数都随着载荷的增大而减小。无论复合材料与9Cr18对摩还是与Si3N4对摩,碳纤维增强PTFE复合材料的极限PV值最小,而聚苯酯和PAB纤维增强PTFE复合材料的极限PV值最大。影响聚合物基复合材料极限PV值的主要因素是:复合材料与对偶件的摩擦系数、复合材料动态力学性能温度谱中的γ转变温度,以及对偶件的热特性参数和密度。更多还原

【Abstract】 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.更多还原