锂基润滑脂流变性及摩擦学性能相关性研究

以锂基润滑脂为例,通过 R／S 锥板式流变仪和四球摩擦磨损试验机,对其流变性能及摩擦磨损性能进行研究,探讨润滑脂流变性能与摩擦磨损性能的相关性。结果表明：润滑脂表观黏度随剪切速率的增大逐渐减小,随锥板间隙的增大逐渐增大,随温度的升高逐渐下降,最后均趋于稳定值。润滑脂的平均摩擦因数和磨斑直径随速度的增大先增大后减小,随载荷的增大逐渐增大,随温度的升高先增大后减小。润滑脂的流变性能和摩擦磨损性能随速度、载荷、温度变化的趋势大体一致,表明锂基润滑脂流变性能与其摩擦磨损性能有一定的相关性,为进一步研究润滑脂流变性能与使用性能之间的关系打下了基础。     

基础油对锂基脂安定性的影响

为研究基础油对锂基脂安定性能的影响。在相同酸碱比例、皂份和相同工艺等条件下,采用12-羟基硬脂酸体系稠化相同黏度不同组分的基础油,制备系列通用锂基润滑脂,分析基础油黏度指数、苯胺点和饱和烃含量对锂基润滑脂安定性能的影响。结果表明:随基础油黏度指数、苯胺点和饱和烃含量的升高,锂基脂工作锥入度、抗水喷雾和压力分油增大,而十万次剪切差值和蒸发量减小;基础油黏度指数、苯胺点和饱和烃含量三者与锂基脂安定性能呈现正相关性,与锂皂的溶解性呈现负相关性。     

基于AR 2000ex型流变仪的润滑脂性能研究

不同基质的润滑脂由于其成分的差异,受到剪切后黏度的变化程度不同。利用AR2000ex型流变仪研究3种不同基质的润滑脂在不同工作阶段的流变性能。结果表明,通过控制剪切速率得到特定条件下的流变曲线,可以分析出润滑脂在性能上的差异;锂基润滑脂无论是停止工作时的稳定性,还是工作时受剪切情况下的润滑性能,都优于钙基润滑脂和尿素基润滑脂;润滑脂的流变曲线基本符合Herschel-Bulkley模型,而且润滑脂的触变性表现为影响润滑脂的屈服应力。     

机械衰减对锂基润滑脂流变特性的影响

采用万次剪切机对一种锂基润滑脂进行不同剪切次数下的剪切,得到衰减程度不同的锂基润滑脂。采用微牵引力试验机对经过机械衰减的锂基润滑脂进行弹流润滑状态下的摩擦力测试,并计算得到润滑脂的流变特性参数。分析不同温度、不同滚动速度和不同载荷下,衰减程度不同的锂基润滑脂的流变特性。结果表明:锂基润滑脂的剪应力随机械衰减程度的增大而增大,其抗剪切性能随机械衰减程度的增大而下降;锂基润滑脂衰减程度越大,速度增加造成的润滑脂剪应力下降程度越大,载荷增加造成的润滑脂剪应力增大的程度越小,温度升高造成的润滑脂剪应力下降的程度越小,即机械衰减程度越大的锂基脂对温度和载荷变化越不敏感,对速度变化较敏感。     

润滑介质对织构化表面摩擦学性能影响的实验研究

采用纳秒激光烧蚀技术在铍青铜盘试样表面加工3种不同参数圆形微凹坑织构,选用石油装备中常用的低黏度L-CKD150润滑油和高黏度复合锂基润滑脂为润滑介质,开展不同润滑环境下销-盘摩擦学实验,对比分析L-CKD150润滑油和复合锂基润滑脂对织构表面摩擦磨损性能的影响差异。实验结果表明:2种不同润滑环境下,合理参数织构均可有效提高表面润滑性能、减少摩擦磨损;润滑介质对织构表面摩擦磨损性能的影响差异与接触压力有关,接触压力较低时,L-CKD150润滑油润滑性能优于复合锂基润滑脂,接触压力较高时则复合锂基润滑脂润滑性能更优;相同工况下,相比于L-CKD150润滑油润滑,复合锂基润滑脂润滑时最优织构直径更大。     

含超细SiO_2/MoS_2粉锂基润滑脂摩擦学性能研究

采用四球摩擦磨损试验机研究了纳米SiO_2及超细MoS_2的粒径、添加量和载荷对2~#锂基脂摩擦学性能的影响,并研究了2种超细粉复配比例和载荷对2~#锂基脂摩擦学性能的影响。结果表明:单一纳米SiO_2和超细MoS_2的加入均能明显减小润滑脂的摩擦因数和钢球磨斑直径,纳米SiO_2和超细MoS_2的复配有助于进一步改善含超细粉锂基脂的摩擦学性能。当纳米SiO_2与MoS_2质量比为2∶8,总加入质量分数为2.0%时,润滑脂的摩擦因数和钢球磨斑直径较基础脂分别减小了77.1%和46.42%。利用SEM和EDS分析磨斑表面形貌及元素组成,初步探讨了含超细复合粉润滑脂的抗磨减摩机理。SEM和EDS分析表明:纳米SiO_2在摩擦过程中主要作用是填补磨痕沟壑,而超细MoS_2除填补沟壑外还对摩擦副表面有抛光研磨和形成减摩膜的作用,2种超细粉的协同使润滑脂具有自修复和抗磨、减摩作用。     

含纳米CuO锂基润滑脂摩擦学性能研究

为改善锂基润滑脂摩擦学性能,制备不同添加量纳米CuO改性的锂基润滑脂。采用3H-2000PS2比表面及微孔分析仪对纳米CuO粒子进行表征,采用四球摩擦磨损试验机分析纳米CuO添加量对锂基润滑脂摩擦学性能的影响,采用扫描电镜(SEM)和三维形貌分析仪分析试验后钢球磨痕形貌。结果表明:纳米CuO质量分数为0.60%时锂基润滑脂具有最佳的抗磨减摩效果,摩擦因数和磨斑直径较基础脂分别降低24%和12%;一定添加量下,纳米CuO对磨损表面具有修复作用,含质量分数0.60%纳米氧化铜的润滑脂润滑时,磨损表面具有较低的表面粗糙度和较少的犁沟,表现出最佳的抗磨性能。     

不同润滑条件下HIP-Si3N4/GCr15摩擦副摩擦特性的研究

在干摩擦、水润滑、锂基脂润滑和锂基脂＋MoS2润滑不同条件下,利用MPX-2000型盘销式摩擦磨损试验机,对HIP－Si3N4/GCr15摩擦副进行了摩擦磨损性能的对比试验研究,通过扫描电子显微镜对试件的表面形貌进行观察分析。结果表明:磨损速率的表现,Si3N4为水润滑＞干摩擦＞锂基脂润滑＞锂基脂＋MoS2润滑;GCr15为干摩擦＞水润滑＞锂基脂润滑＞锂基脂＋MoS2润滑。在锂基脂＋MoS2润滑条件下,HIP－Si3N4/GCr15摩擦副摩擦特性最佳。     

基础油黏度对锂基脂和聚脲脂流变特性的影响

利用旋转流变仪测试锂基润滑脂和聚脲润滑脂在不同温度和基础油黏度下的流变特性,观察润滑脂的微观结构并计算润滑脂的平台模量,探讨基础油黏度和温度对润滑脂流变特性的影响机理,结果表明：平台模量在一定程度上可以表征同种润滑脂稠化剂纤维的纠缠程度;锂基脂稠化剂纤维纠缠程度、表观黏度、剪切应力和黏弹性随基础油黏度的增大先增大后减小;聚脲润滑脂稠化剂纤维的纠缠程度、表观黏度、剪切应力和黏弹性随基础油黏度的增大而增大;润滑脂的平台模量、表观黏度、剪切应力和黏弹性随着温度的升高而降低。     

导电复合锂基润滑脂润滑的制备及性能研究

以聚α烯烃(PAO)为基础油,以复合锂皂为稠化剂,并添加抗氧、极压和导电添加剂,制备一种导电复合锂基润滑脂,用高速往复摩擦磨损试验机和表面电阻测定仪测定其润滑性能和导电性能,并与国外商用润滑脂和国产导电润滑脂进行比较。通过光学显微镜观察磨斑表面发现,自制的复合锂基脂润滑的表面光滑平整,其润滑性能优于其他2种润滑脂;体积电阻测量结果表明,复合锂基脂的体积电阻率要远远小于国外商用润滑脂和国产导电脂,说明其导电性也要优于其他2种润滑脂。研究表明,选用的有机导电介质不但降低了体积电阻,而且形成的摩擦保护膜也提高了其润滑性能。     

Conductive and Tribological Properties of Lithium-Based Ionic Liquids as Grease Base Oil

This article reports several conductive greases prepared by ionic liquids (ILs) that are synthesized by mixing lithium tetrafluoroborate (LiBF₄) or lithium bis(trifluoromethane-sulfonyl) imide (LiNTf₂) in diglyme (G2) and tetraglyme (G4) with appropriate weight ratios at room temperature (RT). The ILs have good solution in poly(ethylene glycol-ran-propylene glycol) monobutyl ether (PAG) and thus can be used as a base oil for preparing grease for steel–steel contacts. The electrical conductive properties of the grease prepared with the mixed oil of PAG plus ILs were evaluated using the DDSJ-308A conductivity tester, GEST-121 volume surface resistance tester, and HLY-200A circuit resistance tester. Combining the free volume with viscosity, the conductivity is inversely proportional to viscosity. The tribological properties were investigated using an MFT-R4000 reciprocating friction and wear tester. The results demonstrated that the prepared greases possess better conductive and tribological properties than the commercial grease with Cu powder as an additive.     

Rheological and Tribological Characterization of a New Acylated Chitosan–Based Biodegradable Lubricating Grease: A Comparative Study with Traditional Lithium and Calcium Greases

This work compares the thermal, rheological, and tribological properties of a new gel-like biodegradable formulation, prepared using an acylated chitosan thickener and castor oil, with properties exhibited by two conventional greases thickened with lithium and calcium soaps, respectively, taken as benchmarks. Thermogravimetric (TGA), rheological (small-amplitude oscillatory shear [SAOS], rheodestruction, and viscous flow) and tribological (friction and wear analysis) tests, as well as roll-stability measurements were carried out to characterize the three grease samples. In addition, infrared spectroscopy and differential scanning calorimetry (DSC) were used to chemically characterize the acylated chitosan thickener agent. From a thermogravimetric point of view, the new formulation displayed better thermal resistance than the calcium and lithium lubricating greases. The evolution of the linear viscoelasticity functions with frequency and viscosity values in the shear rate and temperature ranges studied were similar to those obtained with the commercial lubricating greases. However, the linear viscoelasticity functions of the biodegradable formulation were slightly more affected by temperature. The mechanical stability behavior and recovery of the rheological functions found in the biodegradable formulation were also better than that exhibited by the calcium-based grease. However, the friction coefficient measured at low rotational speed is slightly higher than that obtained with the benchmarks, with similar or lower values obtained at a high rotational speed. Resulting wear marks obtained after the frictional tests using the acylated chitosan–based grease were larger than those obtained with the commercial greases.     

Frictional performance of lithium 12‐hydroxystearate greases with different soap fibre structures in sliding contacts

The effect of the fibre structure of the grease on the frictional performance of lithium 12‐hydroxystearate greases with different fibre lengths was investigated in face, line, and point contact sliding tests. At high sliding speeds where the lubrication regime was practically hydrodynamic, the coefficient of friction of the base oil alone was lower than that of the greases. The coefficient of friction was roughly estimated as follows: base oil < long‐fibre grease < medium‐fibre grease < short‐fibre grease. The supply or replenishing capability of the grease played a critical role in maintaining hydrodynamic lubrication. At high contact pressures, the short‐fibre grease was superior in frictional performance to the long‐fibre grease due to the firm fibre network structure of the latter. In mixed and boundary lubrication regimes, the greases were superior in frictional performance to the base oil, since the soap fibres of the greases had a superior load‐carrying capacity. The long‐fibre grease, with a firm fibre structure, offered better frictional performance than the short‐fibre one.     

Friction torque in grease lubricated thrust ball bearings

Thrust ball bearings lubricated with several different greases were tested on a modified Four-Ball Machine, where the Four-Ball arrangement was replaced by a bearing assembly. The friction torque and operating temperatures in a thrust ball bearing were measured during the tests. At the end of each test a grease sample was analyzed through ferrographic techniques in order to quantify and evaluate bearing wear.A rolling bearing friction torque model was used and the coefficient of friction in full film lubrication was determined for each grease, depending on the operating conditions.The experimental results obtained showed that grease formulation had a very significant influence on friction torque and operating temperature. The friction torque depends on the viscosity of the grease base oil, on its nature (mineral, ester, PAO, etc.), on the coefficient of friction in full film conditions, but also on the interaction between grease thickener and base oil, which affected contact replenishment and contact starvation, and thus influenced the friction torque.     

润滑剂对轮轨摩擦与磨损的影响

利用MMS-2A磨损试验机模拟轮轨系统在润滑油、二硫化钼锂基脂、植物油和石墨钙基脂4种润滑剂润滑下的摩擦与磨损行为,研究润滑剂对轮轨副摩擦、磨损特性的影响.结果表明:与干态相比,4种润滑剂均使摩擦副的摩擦因数减小,表面磨痕深度减小,磨损量降低,其中石墨钙基脂的减摩和抗磨效果最好;试验结束后,轮轨试样接触表面的硬度均有不同程度的增加,其中涂有石墨钙基脂的轮轨试样的表面硬度增加最小.     

An Investigation into Grease Behavior in Thermal EHL Circular Contacts

The behaviors of two lithium lubricating greases were investigated under EHL circular contact through measurements of traction coefficients on a self-made rig in which the contact was continuously fed with fresh grease. The average values of Erying shear stress and shear modulus of the two lithium greases were obtained from traction experimental data using this rig. Based on the Evans-Johnson model and thermal analysis, we calculated the values of shear stress and traction coefficients of the two greases. The results show that the calculated traction coefficients agree fairly well with the measured data.     

Synthesis,Characterization, and Tribological Behavior of Neopentyl Polyol Ester-Based and Mixed Oil-Based Titanium Complex Grease

Four types of titanium complex grease were synthesized using a 3-l reaction vessel, and their friction and wear behavior were evaluated using a four-ball tester in the presence of two base oils: neopentyl polyol ester and a mixture oil of neopentyl polyol ester, 650SN, and epoxidized soy bean oil (4.5:2.5:1), with two compositions: benzoic acid/stearic acid and sebacic acid/stearic acid. The results indicate that mixed oil-based titanium complex grease has excellent tribological properties. Moreover, compositions affect the physical characteristics of titanium complex grease but have little effect on the friction-reduction, antiwear, and load-carrying capability of the same types of oil-based titanium complex grease. In addition, base oils also affect the tribological property of titanium complex grease. Based on scanning electron microscopy and x-ray photoelectron spectrometer of the worn surfaces of steel balls lubricated with the different types of grease, synergistic boundary lubrication was proposed to illustrate the friction-reduction and antiwear properties of titanium complex grease.     

Total vegetable‐oil based greases prepared from castor oil

Total vegetable oil greases are those in which both the lubricant and gellant are formed from vegetable oil. Vegetable oil may be used as a lubricant as such or, with appropriate structural modification, as an ester or alkylated ester. Total vegetable oil greases have the advantage of good biodegradability and conform to the requirements for high performance. Total vegetable‐oil based greases can be formed by mixing preformed soap and lubricant in the required proportions to form a grease with the desired properties. Alternatively, a grease can be formed from the same vegetable oil by simultaneous alcoholysis and saponification of the oil to form the lubricant and soap. The alkali used as a catalyst for the alcoholysis reaction serves as a reactant for the saponification reaction. The use of the appropriate proportion of oil, alcohol, and alkali will thus form a grease of the desired composition. A simultaneous reaction scheme to form sodium and lithium grease using castor oil has been studied. The alcoholysis reaction is separately studied for its kinetics, and the kinetics of the alcoholysis and saponification reaction are reported. Greases with 20% soap have been formed and their properties evaluated.     

Impact of Water on the Rheology of Lubricating Greases

The operational life of bearings is often determined by the performance of the lubricating grease. The consistency of the grease prevents it from leaking out of the bearing and provides good sealing properties. The possible ingress of water into the bearing will have a considerable impact not only on this consistency but also on the lubricating ability of the grease. There are numerous applications where water ingress may occur, such as in the steel, food, pulp, and paper industries. Some greases are less sensitive to water than others. No specific guidelines are available to select the proper grease for bearings subjected to water ingress. The goal of the article is to contribute to the development of such guidelines for greases subjected to water ingress by studying the impact of water on grease rheology. Fully formulated, commercially available greases with the most common thickeners and base oils are used as model greases. It will be shown that water strongly influences rheological properties such as zero-shear viscosity, yield stress, and storage modulus. Calcium sulfonate greases were found to become stiffer after absorbing a considerable amount of water, leading to an increase in zero-shear viscosity and yield stress. However, lithium, lithium complex, and polyurea greases were found to soften, with appreciable changes in measured rheological properties.