Consistency-dependent optical properties of lubricating grease studied by terahertz spectroscopy

The optical properties of four kinds of lubricating greases （urea, lithium, extreme pressure lithium, molybdenum disulfide lithium greases） with different NLGL （National Lubricant Grease Institute of America） numbers were investigated using terahertz time-domain spectroscopy. Greases with different NLGL grades have unique spectral features in the terahertz range. Comparison of the experimental data with predictions based on Lorentz Lorenz theory exhibited that the refractive indices of each kind of lubricating grease were dependent on the their consistency. In addition, molybdenum disullfide （MoS2） aa a libricant additive shows strong absorption from 0.2 to 1.4 THz, leading to higher absorption of MoS2-1ithium grease than that of lithium grease.

Numerical Visualization of Grease Flow in a Gearbox

Lubricating greases are widely used in e.g.open gear drives and gearboxes with difficult sealing conditions.The efficiency and heat balance of grease-lubricated gearboxes depend strongly on the lubrication mechanisms channeling and circulating,for which the grease flow is causal.The computational fluid dynamics opens up the possibility to visualize and understand the grease flow in gearboxes in more detail.In this study,a single-stage gearbox lubricated with an NLGI 1-2 grease was modeled by the finite-volume method to numerically investigate the fluid flow.Results show that the rotating gears influence the grease sump only locally around the gears.For a low grease fill volume,the rotation of the gears is widely separated from the grease sump.For a high grease fill volume,a pronounced geargrease interaction results in a circulating grease flow around the gears.The simulated grease distributions show good accordance with high-speed camera recordings.

Discussion on the Mechanism of Boric Acid and Phosphoric Acid to Improve the Hardening of Complex Calcium Lubricating Grease

In order to solve the hardening problem of complex calcium lubricating grease, the water absorption test of several calcium salts was carried out, and it was found that calcium 12-hydroxystearate did not absorb water, and calcium acetate, calcium phosphate and calcium borate had different degrees of water absorption. Calcium acetate has the highest water absorption rate, while calcium phosphate and calcium borate show comparable water absorption rates. Upon using the molecular simulation technology, it is found that in the complex calcium grease system, calcium phosphate and calcium borate tend to combine with water, which inhibits the water absorption of calcium acetate and alleviate the hardening problem.

Preparation and Rheological Properties of Vacuum Lubricating Grease

A kind of vacuum lubricating grease was prepared by using perfluoropolyether as base oil,perfluorinated polymer as thickener,and self-made additives.The colloidal stability of the grease was greatly improved by introducing a colloidal structure modifier.The rheological properties of the self-made grease(SMG),such as viscosity versus time,thixotropy,etc.,were studied by a rheometer at different temperatures and were compared with those of foreign brand grease(FBG).The results show that the performance of SMG reached the level of similar FBG,and some properties such as mechanical stability,colloidal stability,extreme pressure and antiwear properties were better.It can be used for long life lubrication of moving parts in a vacuum environment.

Surface Modified TiO2 Nanoparticles-an Effective Anti-wear and Anti-friction Additive for Lubricating Grease

The surface modified TiO_2 nanoparticles were prepared by using 12-hydroxystearic acid chemically modified on the TiO_2 surface. The average size of the TiO_2 particles is about 30 nm. The optimum ratio of tetrabutyl titanate to 12-hydroxystearic acid was 1/0.5. The bonding form between 12-hydroxystearic acid and TiO_2 nucleus was investigated by FTIR, DSC, TGA and XRD techniques. The lubricating grease containing the surface modified TiO_2 nanoparticles possesses excellent anti-wear and anti-friction properties. Compared with the grease without TiO_2, the PB value can be increased by 52% as the best performance of the grease containing surface modified TiO_2 nanoparticles, while the friction coefficient can be reduced by 33% with the addition of a small amount of TiO_2 nanoparticles, and meanwhile the wear scar diameter decreases by 25%.

Synthesis and Evaluation of 4-Hydroxy Quinolinone Derivatives as Antioxidants of Lubricating Grease

3-(5-(2.4-dichlorophyenyl)-4.5-dihydro-1H-pyrazol-3-yl)-4hydroxy-1-methylquinolin(1H)-one, 5-((4-hydroxy-8-methyl-2-oxo-1.2-dihydroquinolin-3-yl)methylene)-1-phenyl-2-hioxodihydropyrimidine-4.6(1H.5H)-dione, and 1-butyl-4-hydroxy-3-(5-styryl-4.5-dihydro-1H-pyrazol-3yl)quinolin-2(1H)-one were synthesized and characterized by spectroscopy analysis. These compounds are designated I, II and III, respectively. The antioxidants efficiency of the synthesized compounds in lubricating greases had been investigated using ASTM d-942 and ASTM d-664. The obtained data showed that the total acid number and oxygen pressure drop of these compounds in lubricating greases decrease in the order: Comp.III. < Comp.I. < Comp.II. The antioxidant efficiency of the prepared quinolinones derivatives was discussed. Acceptable correlations were obtained between the obtained oxidation inhibition and the calculated quantum chemical parameters.

An approach of the internal friction-dependent temperature changes for conventional and pure biogenic lubricating greases

This work investigated the temperature changes inside the bulk of lubricating greases under controlled high-shear stress conditions(250-500 s-1).For this purpose,a newly developed temperature-measuring cell called Calidus was successfully tested.The temperature changes(ΔT)have been related to the greases'components(thickener,base oil-type,and composition)and the structural degradation of the lubricating greases.Furthermore,a theoretical approach was proposed for calculating the internal temperature change of lubricating greases during shear stress.All greases showed an internal temperature profile characterised by a sudden rise inΔT within the first 4 h from starting the test and subsequentΔT decay until it reaches the steady state value.Furthermore,it was found that greases C1 and C5,formulated with lithium and calcium soap,respectively,with different soap content(16.1 wt%and 9.7 wt%,respectively),but the same base castor oil,showed the highest value of the maximumΔT,c.a.3.2 K,and the most drastic drop ofΔT.These greases showed both the highest specific densities and heat capacities.In addition,they showed the lowest ratio of expended energies(Rtee),which means more structural degradation in the stressed grease.On the contrary,the grease C3,with 13 wt%of Li-soap but the lowest base oil's viscosity,showed the lowest maximumΔT and the temperature profile was characterised by a moderate variation ofΔT along the test.The biogenic grease B3 developed a low-temperature change in the group of pure bio-genic greases close to grease C3.

Comparative Studies on Low Noise Greases Operating under High Temperature Oxidation Conditions

Oxidation induction time(OIT) testing by differential scanning calorimetry(DSC) was used to evaluate the oxidation resistance of lubricating greases. Under the high temperature condition, bearing noise was detected when grease passed the initial stable stage of oxidation. The chemical and physical structure of grease samples before and after high temperature oxidation were also analyzed by FT-IR spectrometry and scanning electron microscopy(SEM), then the effects of oxidation at high temperature on bearing noise were investigated. It is found out that for lithium greases, oxidation of base oil and thickener is the main reason responsible for the increasing bearing noise. As regards the polyurea greases, the change of fiber microstructure at high temperature is the main reason for the increasing bearing noise.

Influence of Two Preparation Methods on Rheological Properties of Lithium Grease

The dropping point,cone penetration,corrosion,oil separation rate and oxidation stability of lithium grease prepared by two different processes at room temperature and high temperature were measured.The rheological properties of the samples were studied and analyzed with the microstructure of soap fiber.The results show that the content of thickener used in grease prepared by the room temperature method is higher in order to obtain the same consistency.The dropping point and evaporation loss of grease samples prepared by two processes are similar,and the oil separation rate of the lubricating grease prepared by the room temperature method is smaller.The preparation process has a great influence on the rheological properties of grease,and the higher content of thickener is beneficial to improving the rheological properties of grease.

Running Temperature and Mechanical Stability of Grease as Maintenance Parameters of Railway Bearings

Spherical roller bearings in railway car wheels are critical components whose failure may have catastrophic consequences. The present study aims to analyse the mechanical stability of greases and temperature of bearings as indicators for condition-based bearing maintenance. The performed case study includes nine fully-formulated commercial greases examined in the wheel bearings of five ore cars operated in northern Scandinavia. The studied ore cars travelled a distance of about 300 000 km during a period of three years. Small samples of the greases were taken on eight occasions to test their mechanical stability. In addition, the temperatures of the bearings were continuously recorded. After the test period, the wear, electrical damage, and corrosion of the bearings were examined. One of the findings is that the shear stress of the grease at a certain shear velocity （the certain yieldstress （CEY） value） is a good maintenance indicator and is highly dependent on the grease type. The bearing＇s wear, electrical damage and corrosion also depend on the grease type. However, no oxidation of the greases was identified. The paper also outlines a systematic methodology to determine an overall maintenance indicator for railway roller bearings which is based on the field measurements.

Research on Lubrication Model of Rock Bit Bearings with Non-Newtonian Medium

Lubrication media of rock bit journal bearing is non-Newtonian fluid, and because of structure limitations, lubricant supply is only from the inside track and its rheological properties are relatively complex. In general studies, the non- Newtonianism of lubrication media of rock bit journal bearing is neglected to simplify the research process. Based on the universal Reynolds equation of non-Newton media, the mathematical model of lubrication analysis was suitable for the rock bit bearing working conditions was established. Then according to the experimental results of rheological properties of RB-type lubricating grease, the equivalent viscosity of the model was established and this model can be solved by the method used in solving the Reynolds equation of Newton fluid.

The Development and Application of Automotive CVJ Grease

The development trend of the CVJ (constant velocity joint) greases is briefly introduced in this paper. Based on the evaluation of various base stocks, thickeners and additives, the formulation and manufacture of the long-life CVJ grease is finalized. Bench tests and vehicle performance evaluation tests have showed that the ‘Great Wall brand’ new polyurea-based CVJ grease can meet the demand of automo- tive CVJ. This grease features an outstanding low and high temperature performance, extreme pressure, anti-corrosion and anti-rust properties equivalent to those of similar overseas greases. Compared with the traditional MoS2 containing lithium based CVJ grease, the performance of the new grease is much better.

分形粗糙面的主轴承弹流脂润滑分析

为探究弹性流体动压润滑(弹流润滑)状态下RV减速器主轴承接触表面之间的润滑特性,基于润滑脂的非牛顿特性以及粗糙表面分形理论,提出一种主轴承的点接触弹流脂润滑数值模型。首先,对该模型进行数值求解,得到脂膜压力、脂膜厚度的分布规律;然后,将其分别与其他点接触弹流润滑模型的数值结果和实验结果进行对比,验证了所建模型的正确性;最后,分析了主轴承表面光滑和粗糙状态下流变指数、分形维数、卷吸速度、载荷和润滑脂黏度对润滑性能的影响。结果表明:润滑脂的非牛顿性越明显,脂膜厚度越小且颈缩现象愈加不明显,接触区附近脂膜压力越符合赫兹压力分布,二次压力峰逐渐消失;考虑主轴承分形粗糙表面的弹流润滑特征更切合实际,增大分形维数,接触区真实接触面积增大,有利于降低脂膜压力,增加脂膜厚度;卷吸速度、载荷和润滑脂黏度对脂膜厚度分布的影响显著,对脂膜压力分布的影响较小;脂膜厚度以及最小膜厚越大,主轴承接触区脂膜不易破坏且越容易形成动压润滑。

纤维素/SiO_(2)润滑脂的制备及性能分析

【目的】旨在以可再生的天然纤维素为稠化剂制备可持续发展的环保型润滑脂产品。【方法】分别以纯纤维素、气相二氧化硅(SiO_(2))以及纤维素/SiO_(2)为稠化剂制备了3组稠度等级为2#的润滑脂产品,并对其进行了锥入度测试、滴点测试、分油率测试、流变性能测试以及摩擦学性能测试。【结果】SiO_(2)表面的硅羟基与纤维素羟基可以发生氢键作用,改善了润滑脂的理化性质、流变性能以及摩擦学性能。理化性质方面:相较于纤维素润滑脂和SiO_(2)润滑脂,纤维素/SiO_(2)润滑脂具有较低的分油率,胶体安定性得到提高,并且在327℃时出现了滴点,改善了SiO_(2)润滑脂在高温下易失去流动性的缺点。流变特性方面:纤维素/SiO_(2)润滑脂的黏温性能和抗剪切能力较SiO_(2)润滑脂得到了提高,且剪切破坏后的结构恢复速度更快,结构体系更加稳定。摩擦学性能方面:纤维素/SiO_(2)润滑脂相较于纤维素润滑脂和SiO_(2)润滑脂,其减摩性能得到了提高,具有最低的摩擦系数和摩擦力。【结论】获得了具有实用前景的纤维素基润滑脂,符合国家低碳及可持续发展战略。

石墨烯对聚脲脂高温流变和摩擦学性能的影响

目的保证轴承体系的安全性和可靠性,研究轴承润滑脂在不同工作温度下的摩擦学性能和流变学性能。方法用机械剥离法制备的石墨烯作为聚脲脂的润滑添加剂,通过四球摩擦试验机、旋转流变仪,研究石墨烯在不同工作温度下对聚脲润滑脂流变行为和摩擦学性能的影响,并通过三维轮廓仪、扫描电子显微镜和拉曼光谱仪对磨斑形貌和结构进行分析。结果添加石墨烯润滑添加剂使聚脲润滑脂的高温硬化现象明显改善,同时提高了聚脲润滑脂的结构稳定性和抗剪切能力。工作温度为75、150℃时,与空白聚脲润滑脂相比,含1.0%(质量分数)石墨烯的聚脲润滑脂润滑下的轴承钢摩擦副的摩擦系数和磨斑直径分别降低49%、20%和10%、20%。随着工作温度的升高,含石墨烯的聚脲润滑脂样品在钢滑动表面形成的沉积膜的结构有序化碳的含量稍有下降,但与空白聚脲润滑脂相比,石墨烯-聚脲润滑脂沉积膜的结构有序化碳含量高得多。结论结构有序化碳的形成对提高基础脂的减摩抗磨性能起至关重要的作用,石墨烯润滑添加剂还可以有效改善聚脲润滑脂的高温硬化性能、胶体稳定性以及稠化剂的结构稳定性。

长寿命低挥发性润滑脂的性能研究

针对航空航天装备苛刻工况环境对润滑脂性能的更高要求,分别制备了酰胺钠基润滑脂和全氟聚醚润滑脂,并将二者混合后加入抗氧剂、防锈剂、极压抗磨剂等添加剂,制备得到长寿命低挥发润滑脂(简称长寿低挥脂);研究了商品酰胺皂基润滑脂(简称商品酰胺脂)和长寿低挥脂的理化性能、润滑性能、轴承寿命及流变学等性能。结果表明:与商品酰胺脂比,长寿低挥脂的高温损失更小、钢网分油率更低,说明其具有更优的挥发性能和胶体安定性;长寿低挥脂四球试验钢球的磨斑直径为0.46mm,远低于前者的1.03 mm,轮毂轴承寿命为1228 h,远高于前者的760 h,说明其具有更优的极压抗磨性能、润滑性能和氧化安定性;长寿低挥脂的线性黏弹区更宽、高温结构保持能力更强,说明其具有更好的流变学性能和高温稳定性能。因此,长寿低挥脂的综合性能优良,可用于苛刻的特殊工况环境。

高频交变电场作用下静态绝缘轴承中润滑脂的老化行为

高频电压诱导的电机轴承电蚀和润滑失效是影响变频驱动系统可靠性的关键问题。为探究高频交变电场环境下润滑脂的老化机制,基于绝缘轴承耐高频交变电压性能试验,详细研究了球与沟道接触区润滑脂的老化特性,结果表明:尽管有绝缘涂层的保护,润滑脂在无机械剪切作用下仍然会发生明显的性能衰退,具体表现为颜色加深,分油率降低,稠度增大以及导电性能和介电性能的改变。测试发现,在高频交变电场作用下绝缘轴承润滑脂稠化剂结构被破坏并发生团聚,其中夹杂有以金属纳米颗粒为核心的黑色团块,老化润滑脂的直流体积电阻率明显下降并具有更高的等效串联电阻和损耗因子。

滚动轴承润滑研究中的几个问题

滚动轴承是高端装备中不可缺少的重要部件,轴承润滑问题的研究为滚动轴承设计、润滑剂选择、轴承可靠服役等提供理论基础。针对滚动轴承润滑相关的几个科学问题,重点概括了滚动轴承润滑数值计算方法及应用,总结了润滑油膜厚度和轴承内部润滑介质流动分布可视化测量技术,阐述了与润滑脂组分相关的机械剪切与温度等参数对润滑特性的影响机制,介绍了滚动轴承固体润滑机制,并从工程设计角度分析了轴承的润滑设计。基于当前研究现状,认为轴承润滑研究应重点面向真实条件下轴承润滑理论计算、与应用工况匹配的先进润滑材料的开发以及轴承润滑评测方法研发3个方面进行发展。

国内特种油产业发展现状及趋势展望

在“双碳”目标的驱动下,国内低碳产业正在快速成长,石油石化行业转型发展势在必行。特种油产品作为“油转特”的一部分,包括润滑油脂、橡胶增塑剂、白油、轻质白油等四大类,涉及应用领域极广,不仅是国民经济与工业体系自主化发展的重要保障,也是石油石化企业长期盈利的突破点和后备军。文章从市场发展的角度剖析国内特种油品需求走势,阐明“双碳”新形势下特种油品的产业定位,并为石油石化企业进一步发展特种油业务提供建议。

直接法制备聚脲润滑脂工艺研究及分析

考察了直接法制备工艺条件(加料顺序、炼制温度、炼制时间)对聚脲润滑脂性能的影响,重点分析了加料方式对聚脲稠化剂化学组成与平均分子结构的影响,及其与聚脲润滑脂性能的关联性;采用红外光谱、热重分析仪、扫描电镜对直接法聚脲润滑脂进行表征,深入探讨了其构效关系,并与预制法制备的润滑脂产品进行了比较。优化的直接法制备方案为:将有机二胺溶于基础油中,升温至80~90℃后同时加入异氰酸酯和有机单胺,反应60 min,然后在170~180℃下炼制1.5 h。结构和性能表征结果表明:在基础油和稠化剂种类与配比相同、制备条件相同情况下,由直接法与预制法得到的聚脲稠化剂中脲基基团数量及比例存在差异,从而导致聚脲润滑脂产品的性能出现差异;当稠化剂质量分数均为20%时,预制法所制备的四聚脲润滑脂的滴点比直接法高20℃,钢网分油量仅为直接法的21.8%,水淋流失量仅为直接法的41.3%,铜片腐蚀比直接法高一个等级,最大无卡咬负荷比直接法高24.5%。总之,直接法得到的聚脲润滑脂的胶体安定性、氧化安定性及极压抗磨性能略逊于预制法,但其机械安定性优于预制法。