偶件表面粗糙度对PTFE材料摩擦磨损性能的影响

为了研究干摩擦条件下偶件表面粗糙度对聚四氟乙烯(PTFE)密封材料摩擦磨损性能的影响,利用MMW-1立式万能摩擦磨损试验机,在不同载荷和转速下研究由PTFE材料制作的试验环分别与316L不锈钢和45#钢配副时的摩擦磨损性能,并利用粒形分析仪对PTFE试验环试验前后端面的形貌进行观测;利用触针式轮廓仪对摩擦配副钢环的端面粗糙度进行精确测量,分析表面粗糙度对PTFE试验环摩擦磨损性能的影响。试验结果表明:在干摩擦条件下,摩擦配副钢环的表面粗糙度过高或者过低都会引起PTFE试验环磨损量的增加;定载荷时,PTFE试验环磨损量随摩擦配副钢环表面粗糙度的增大先减小后增大,随转速的增大而增大;定转速时,PTFE试验环摩擦因数随摩擦配副钢环表面粗糙度的增大稍减小后而后增大,随载荷的增大先减小后增大;在相同工况下,316L不锈钢对PTFE试验环的切削和犁沟作用比45#钢更加明显。     

SiC/石墨配副密封端面织构低速磨损特性

采用端面上加工有倾斜椭圆微孔的SiC环和石墨环配副,实验研究椭圆微孔机械密封端面的低速摩擦磨损性能。实验测量干摩擦及油润滑条件下SiC环的磨损率和温升,分析表面织构对密封端面磨损特性的影响规律。结果表明:接触干摩擦条件下,与织构面配副的石墨环的磨损率明显高于光滑表面;油润滑条件下,转速相对较低时,织构面的温升高于光滑表面,表现出增磨效果;转速相对较高时,织构面的温升小于光滑表面,表现出减磨效果;并且干摩擦和油润滑条件下,表面织构均可减少磨屑的切削和犁削作用,起到表面研磨作用,使得石墨环表面更为光滑。     

镶嵌MoS2的Al2O3/TiC基陶瓷刀具材料微孔表面摩擦磨损性能研究

采用Nd:YAG激光器在Al2O3/TiC陶瓷刀具材料表面加工出不同密度的微孔,并涂覆填装MoS2固体润滑剂,在UMT-2摩擦磨损试验机上进行往复摩擦试验,研究其在不同载荷和速度下的摩擦磨损性能,通过白光干涉仪、光学显微镜和扫描电镜观察激光织构化后表面特征和磨损后表面形貌。结果表明:激光织构化后,陶瓷材料表面发生了氧化;在相同的实验条件下,与光滑表面相比较,填装MoS2固体润滑剂的微孔表面能够有效地降低摩擦因数,减小磨损率。这主要是由于填装在微孔中的润滑剂在摩擦作用下涂覆到基体表面,形成润滑膜,起到减摩降磨作用,同时激光加工后微孔周围凸起及氧化后形成的摩擦特性优良的TiO2也能起到良好的减摩降磨效果。通过对磨损形貌分析,光滑表面磨损较为严重,有大量的犁沟产生,主要的磨损形式为磨粒磨损及脆性断裂;微孔表面磨损较为轻微,其主要磨损发生在微孔周围。     

表面织构在脂润滑条件下的摩擦性能研究

采用声光调Q二极管泵浦Nd:YAG激光加工系统在H13钢表面加工出不同密度的织构,以润滑脂作为润滑剂,利用MMW-1A型微机控制万能摩擦磨损试验机考察表面织构在不同载荷、不同转速条件下的摩擦磨损特性。实验结果表明:在脂润滑条件下表面织构能有效改善摩擦副表面的摩擦性能;与光滑无织构试样相比,表面织构试样的摩擦因数显著降低;一定范围内,随着织构密度的增加,平均摩擦因数呈现出先减小后增大的趋势,且织构密度为10%时的平均摩擦因数最小,最小平均摩擦因数为0.18,较光滑无织构试样减小32.23%;摩擦因数随着试验载荷的增大而减小,但随着转速的增加呈现出先减小后增大的变化趋势。     

考虑粗糙度效应的微孔化机械密封摩擦副接触特性分析

针对机械密封装置在启停阶段或某些特定工况下出现高温以及摩擦磨损严重等问题，探究考虑粗糙度效应的微孔化机械密封端面接触压力及温升的变化规律，以揭示机械密封端面的真实接触状态。基于分形理论建立机械密封静环粗糙表面和动环微孔接触模型，采用数值计算方法，研究微孔对机械密封端面接触压力和温升的影响，以及表面粗糙度对机械密封端面接触面积、接触压力、温升的影响。结果表明：微凸体经过微孔时，微凸体嵌入微孔边缘使得接触压力峰值增大，导致切削发生；摩擦过程中，压力最高点位置因为微凸体的弹塑性变形而不固定，改善了微凸体的受力情况；微孔降低了密封端面的接触面积，从而使得微凸体的接触减少、压力极值点减少，降低了密封端面摩擦副的温度，改善了密封端面的磨损状况；表面粗糙度越小，接触面积越大，接触压力、端面温度更加均匀，表面粗糙度越大，端面磨损风险更加严重。     

液体椭圆孔端面泵用机械密封特性试验北大核心CSCD

为了探究液体椭圆微孔端面密封特性,通过液体密封试验考察了微孔端面密封的泄漏控制规律,对2种椭圆微孔端面和1种光滑端面开展对比研究,研究了不同压力和转速工况下泄漏率和温升的变化规律。试验结果表明:密封表面双列椭圆微孔设计在高速下可明显降低摩擦温升,转速达到15000 r/min时,最高可降低80℃;合理的反向椭圆微孔可以降低并控制密封泄漏;椭圆多孔密封端面在多转速工况时存在增加磨损的风险,通过合理的反向椭圆微孔设计可一定程度上减缓端面磨损。     

激光加工多孔端面机械密封的摩擦性能分析

分析了工况参数和结构参数对激光加工多孔端面机械密封摩擦性能的影响。建立了激光加工多孔端面机械密封的计算模型和边界条件,采用有限差分法求解液膜控制方程,获得在不同操作工况和表面微孔结构参数下的密封开启力。理论推导得到了激光加工多孔端面机械密封的摩擦扭矩表达式,并对其进行了分析。结果表明,密封端面间的摩擦扭矩随着密封环转速的增加而增大;微孔深度和微孔密度有最佳参数,使密封端面间的摩擦扭矩最小,且与试验结果吻合。     

直流稳恒磁场条件下45钢小位移摩擦磨损试验研究

基于HSR-2M高速式往复摩擦磨损试验机,试验了直流稳恒磁场条件,往复速度、法向载荷、往复行程、磁场强度等对45钢的摩擦系数和磨损量的影响,通过磨痕形貌分析了其磨损机制.试验结果表明:磨损主要为黏着磨损、剥落并伴有氧化磨损;载荷的增大使得摩擦热增多,摩擦副表面的塑性增强,磨损量加大;同时摩擦副表面接触区域的真实接触面积变大,造成摩擦系数减小;试验的研究结果对在施加直流稳恒磁场情况下45钢摩擦磨损性能的正确评估有重要的意义.     

45钢的摩擦磨损特性实验研究

采用自制的销盘式干滑动摩擦磨损试验机,研究了45钢配副的摩擦磨损特性.结果表明:材料的磨损率随着速度、载荷的增加而增大;摩擦系数随着速度、载荷的增加而减小.磨损机理主要为磨粒磨损和粘着磨损.     

永磁场条件下45钢与GCr15钢摩擦磨损性能试验研究

基于HSR-2M高速往复摩擦磨损试验机,研究在永磁体磁场条件下滑动速度、载荷等参数对45#钢/GCr15钢摩擦副摩擦学性能的影响,通过磨痕形貌分析其磨损机制,并与无磁场条件下的试验结果进行对比。试验结果表明:磁场的引入可以在一定程度上减小摩擦因数和降低磨损率,证明磁场能够改善45#钢/GCr15钢摩擦副的摩擦学性能;增大滑动速度将降低摩擦因数和磨损率,增大载荷将降低摩擦因数,增加磨损率。无磁场时,摩擦副的摩擦磨损为典型的磨粒磨损,磨损系统的磨损率和摩擦因数较大;有磁场时,磨损形式主要为黏着磨损,摩擦因数和磨损率较小。     

Binder extrusion in sliding wear of WC-Co alloys

It has previously been proposed that preferential removal of the cobalt binder is an important mechanism in the abrasive wear of cemented carbides in the WC-Co family. It is here demonstrated that binder extrusion occurs also in metal-to-metal sliding wear contacts. The wear scar generated by sliding a hardened steel ball repeatedly over a polished WC-Co surface was studied by scanning electron microscopy. The extruded cobalt fragments accumulate at surface defects, such as cracks caused by the sliding loaded ball, and gradual microfragmentation of the carbide grains follows. The energy required to extrude the cobalt and to cause the gradual change in surface layer microstructure is provided by the frictional forces.     

Ultra-High-Speed Performance of Ball Bearings and Annular Seals in Liquid Hydrogen at Up to 3 Million DN (120,000 rpm)©

The ultra-high-speed performance of a hybrid ceramic 25-mm-bore ball bearing, as well as that of floating-ring seals with a sealing diameter of 30 mm, was determined in liquid hydrogen at speeds to 120,000 rpm, 3 million DN, under thrust loads to 3,140 N and sealed pressures to 1.7 MPaG. The bearings had Si₃N₄ balls and a single outer land-guided retainer. The hybrid ceramic bearing exhibited excellent performance at high load, contrasting with the seized all-steel bearing; however, the ceramic balls developed superficial micro-cracks due to frictional heating. Effective cooling of the bearing was achieved by increasing the jet speed through the nozzles. The bearing power loss drastically increased with increasing speed and cooling flow rate. The critical load capacity without bearing damage was also evaluated. Furthermore, the sealing performance of the one-ring seal was superior to that of the two-ring seal in preventing the sealing ring seizure against the runner.     

Observations of thermoelastic instability in mechanical face seals

Sliding contact between the primary and mating rings of a mechanical seal will result in the generation of frictional heat. In some cases this resulting frictional heat will lead to a condition of thermoelastic instability of the sealing planes. Various field and laboratory cases are reviewed with respect to the development of surface disturbances at the seal interface. The effect of interface cooling on the sealing planes is also shown.     

The effect of flat-on-ring sample alignment on sliding friction break-in curves for aluminum bronze on 52100 steel

The effects of test sample fixturing on the interpretation of frictional break-in behavior are described for dry sliding flat-on-ring tests of CDA 688 bronze on 52100 steel. It is demonstrated that for otherwise similar test conditions (i.e. 10 N load, 20 cm s^?1 velocity, 1 μm polished block surfaces and flowing argon gas environment) tilt of the fixed flat block can affect the break-in duration for friction and for wear because of the rate at which a balance of steady state sliding surface contact conditions is achieved.     

高压高水基棉麻动密封软填料的摩擦学特性分析

分析了高压高水基棉麻动密封软填料的摩擦界面形态，采用环块试验机研究了载荷、表面粗糙度和转速对其摩擦因素的影响。结果表明：随载荷增加，摩擦因数减小；表面粗糙度和速度增加，摩擦因数增人本文还指出了该软填料每次预紧载荷的限量。     

不同激光表面造型机械密封环的性能试验研究

将2种典型表面造型机械密封环,即微凹腔造型和腔与槽结合造型的密封环,与未造型密封环进行了密封和摩擦性能的对比试验。试验结果表明2种造型的机械密封与未造型的相比具有明显优越性能:凹腔机械密封在一定工况范围内无泄漏,且具有相对于未造型良好的摩擦性能;槽腔结合机械密封在整个过程中均无泄漏,其摩擦系数远小于未造型的。凹腔机械密封也存在一些缺点:在介质压力较小工况下试验时泄漏较大;在介质压力大而转速小时摩擦扭矩较大。分析表明:凹腔环的凹腔造型在端面载荷较大,存在轴向振动的情况下会增大摩擦系数;槽腔结合环的泵送槽能够容纳液体,具有润滑和缓冲振动的作用。     

Parametric study on balance ratio of mechanical face seal in steam environment

An experimental study on friction and wear of carbon-graphite mechanical face seal, used in rotary joints of paper industries, has been presented. Experimental setup has been designed and developed to simulate the actual industrial environment faced by mechanical seal. Actual mechanical face seals (same material, surface roughness and dimensions) have been used to explore the effect of operating environments, steam pressures, speeds and balance ratios on the wear rates and friction losses. An experimental parametric study on four balance ratio conditions with constant speed and variable steam pressures has been performed, which has shown that a substantial reduction in frictional torques and wear rates is achievable with low balance ratios. The photomicrographs of seal wear and list of weight loss data have been reported in the present paper. The measured frictional torque data are also plotted against the balance ratios and finally the required balance ratio condition, to achieve an approximately 2 year's service life of mechanical seal, has been proposed.     

Valvetrain Friction Reduction through Thin Film Coatings and Polishing

In a direct-acting mechanical bucket tappet–type valvetrain, the cam and tappet contact is responsible for about 85% of the total valvetrain frictional losses. Because this contact operates primarily in a mixed lubrication regime, it offers an opportunity for friction reduction through surface engineering. The friction reduction potential of thin Mn-phosphate coating, diamond-like carbon coating, and polishing on the bucket surface was explored using a motored valvetrain rig equipped with 3.5L V6 engine head. The durability of tappets and cam lobes was also evaluated using a different motored valvetrain rig consisting of a single lobe and a single tappet. The polished buckets demonstrated substantial friction benefit over current production buckets at all speeds investigated. The diamond-like carbon coated buckets did not show any additional friction reduction benefit. The wear data demonstrated much less wear with polished buckets and also for cam lobes when in contact with polished buckets compared to current production buckets and cam lobes. The composition of antiwear surface films on polished buckets was found to be similar to that on current production buckets.     

Imaging friction tracks at diamond surfaces using reflection electron microscopy

Reflection electron microscopy (REM) is applied to image the structure of polished natural diamond (001) surfaces (of 5 × 4 mm size) after friction experiments under a pressure below the critical value. Friction tracks marked by a diamond needle after a single pass movement under a pressure of 13 GPa can be seen in REM images and show non-uniform contrast. The surface shows relatively dark image contrast at the light contacted area, which is possibly due to the structural modification at the top atomic layer. The high local contacting pressure pushes part of the needle into the surface which causes fracture, resulting in the formation of grooves at the surface. It is possible to have plastic deformation in this process, but no evidence has been found for the presence of cracking. The observations support the adhesion frictional mechanism rather than the micro-cleavage model.     

Effects of Sliding Velocity and Normal Load on Tribological Characteristics in Powder Lubrication

The antifriction ability of powder lubrication and the state of powder layer are strongly related to the service conditions. Therefore, the effects of sliding velocity and normal load under powder lubrication were studied using a face-to-face contact tribometer. In our work, some graphite, a widely used solid lubricant, was introduced into the frictional interface in the state of free powder. Varying friction coefficient and temperature rise were recorded online. The powder layer formed on the frictional surface of the bottom samples was observed by an optical microscope after tests. The comparative research demonstrated the tribological characteristics of powder lubrication are similar to that of polytetrafluoroethylene coating. Besides, the powder lubrication provides longer lubrication life, although the powder was difficult to seal and control during the tests. Within the proper range of sliding velocities and normal loads, the powder layer dynamically formed on the contact surface of the bottom samples, which resulted in the self-replenishing and oil-free lubrication. The powder layer inclined to deteriorate under lower velocity and higher load. The tests with higher velocity exhibited lower friction coefficient and higher temperature rise. The tests with lower load exhibited higher friction coefficient and lower temperature rise. The state of powder layer included typically four stages such as the full layer, the partial detachment, the serious detachment, and the complete destruction. The damage degree of powder layer is not in proportion to the friction coefficient or the temperature rise due to the particularity of powder lubrication.