Complex Grease Research Articles

Probing the Synergy of Calcium Sulfonate Complex Soap and Polyurea Complex Thickener Towards Good Lubrication and Rheological Properties

Abstract Polyurea complex thickener was introduced into calcium sulfonate complex grease (CSCG) to prepare a new type of grease. The microstructure, rheological properties, and tribological properties of new greases were studied in detail. The experimental results show that the combination of calcium sulfonate complex soap and polyurea complex thickener can form a new thickener system, which combines the layered structure of calcium sulfonate complex soap and the rod-shaped structure of polyurea complex thickener. The thermal decomposition temperature of new greases is reduced, but its fluidity is improved and the friction coefficient is lower. Their synergistic effect is related to the special structural skeleton of the new thickener system, and calcium sulfonate and urea molecules share the same calcium ion, which may be an important reason for maintaining the stability of this special structure skeleton.

Synergistic lubricating effect for calcium phosphate modified calcium sulfonate grease with highly load bearing capacity

Calcium sulfonate complex grease exhibits different lubrication mechanisms due to its different combination of calcium carbonate soap and complex agents. In an effort to explore the synergistic lubricating effect of complex agents and find breakthroughs in the performance of calcium sulfonate grease, calcium phosphate modified calcium sulfonate grease was prepared and tested compared with borates. At high loads of 600 N, the introduction of P-containing complex improved load bearing capacity of calcium sulfonate grease. The advantage it exhibited in terms of lubrication was attributed to the synergistic effect of calcium carbonate and calcium phosphate in thickener under harsh condition. The synergistic films about 30 nm depth composed of iron oxide, calcium oxide and iron phosphate played a decisive role in lubrication.

Visualization techniques of grease fluidity

Energy-saving technology has become increasingly significant as one of the carbon-neutral options for suppressing recent global warming. Grease-lubricated bearings have been used in various automotive and industrial machinery, requiring low torque and long service life for energy-saving performance, which is greatly influenced by grease fluidity. A numerical approach for understanding grease fluidity is very complex since grease is a non-Newtonian fluid with thixotropic properties. Visualization technique is one of the helpful methods to understand the complex grease fluidity and apply it to practical use. This paper describes state-of-the-art visualization techniques, such as fluorescence method, particle imaging velocimetry, infrared spectroscopy, X-rays, and neutron beams.

Lubrication mechanism of C@Ag core–shell materials as grease additive

The preparation of a low shearing shell on the surface of carbon spheres (CS) is an attractive strategy to improve the lubrication properties of CS. In this study, core–shell structural C@Ag particles were prepared using CS as the hard core and Ag nanoparticles as the soft shell. Then, the additives were mixed with Polyalphaolefin 20 to prepare the C@Ag core–shell-enhanced lithium complex grease (C@Ag-LCG). The physicochemical properties, corrosion resistance, and tribological behaviors of LCGs were investigated. C@Ag-LCG exhibited the best high-temperature resistance and colloidal stability compared with the CS-enhanced lithium complex grease (LCG) and pure LCG. The dropping point and oil separation rate of 0.05 wt% C@Ag-LCG were 255 °C and 2.36 %, respectively. The tribological behavior of greases was tested using a four-ball friction tester, and the main damage mechanism was abrasive wear. The C@Ag additive reduced the average friction coefficient and wear spot diameter by 27.17 % and 26.12 %, respectively. The improved properties were attributed to the synergistic lubrication of hard CS core and soft Ag shell with the rolling, filling, and self-repairing effects, C@Ag deposit films and the self-lubricating oil film, as well as the thickener film and the tribochemical film at the frictional interfaces.

Investigation of friction and vibration performance of lithium complex grease containing candle soot on aviation electrical machine

The prolonged operation of the motor in the all-electric aircraft can cause the fragmentation and shortening of grease thickener fibers, ultimately resulting in the lubricating grease becoming ineffective. In order to avoid grease failure causing motor winding burnout, this paper uses a four-ball friction testing machine to test the tribological properties of six composite greases containing candle soot with different concentrations, and analyzes the changes in friction coefficient and wear diameter. In addition, by building a test platform for motor vibration and noise, this paper studies the influence of lithium complex grease on vibration and noise characteristics of aviation electrical machine at different propeller speeds. The results show that the addition of 0.04 wt% candle soot lithium grease has the best tribological properties and vibration inhibition properties, because the candle soot in the oil film changes the sliding friction into rolling friction in the contact area of some friction pair. The temperature rise test of aviation electrical machine shows that the lithium complex grease plays an active role in the heat dissipation performance of the high-speed rotating motor.

Effect of hydroxyl functionalized ionic liquid additives on rheological and tribological properties of titanium complex grease

In this work, two kinds of hydroxyl functionalized ionic liquids (ILs) 1-butyl-3-methylimidazole salicylate [BMIM][SA] and 1-butyl-3-methylimidazole caffeate [BMIM][CA] were synthesized as additives for titanium complex grease (TCG). Two ILs can effectively improve the physicochemical properties of TCG. Among them, [BMIM][CA] significantly improves the yield stress of TCG and improved its ability to resist deformation. Tribological tests showed that both ILs improved the friction reduction and antiwear properties. And [BMIM][CA] containing two adjacent phenolic hydroxyl group performed the best. This may be because it can effectively participate in tribochemical reactions, forming a large number of organic tribochemical products, which play a key role in promoting lubrication.

TiO2 and CeO2 nanoparticles as lithium complex grease additives for enhanced lubricity

PurposeThis paper aims to improve the tribological properties of lithium complex greases using nanoparticles to investigate the tribological behavior of single additives (nano-TiO2 or nano-CeO2) and composite additives (nano-TiO2–CeO2) in lithium complex greases and to analyze the mechanism of their influence using a variety of characterization tools.Design/methodology/approachThe morphology and microstructure of the nanoparticles were characterized by scanning electron microscopy and an X-ray diffractometer. The tribological properties of different nanoparticles, as well as compounded nanoparticles as greases, were evaluated. Average friction coefficients and wear diameters were analyzed. Scanning electron microscopy and three-dimensional topography were used to analyze the surface topography of worn steel balls. The elements present on the worn steel balls’ surface were analyzed using energy-dispersive spectroscopy and X-ray photoelectron spectroscopy.FindingsThe results showed that the coefficient of friction (COF) of grease with all three nanoparticles added was low. The grease-containing composite nanoparticles exhibited a lower COF and superior anti-wear properties. The sample displayed its optimal tribological performance when the ratio of TiO2 to CeO2 was 6:4, resulting in a 30.5% reduction in the COF and a 29.2% decrease in wear spot diameter compared to the original grease. Additionally, the roughness of the worn spot surface and the maximum depth of the wear mark were significantly reduced.Originality/valueThe main innovation of this study is the first mixing of nano-TiO2 and nano-CeO2 with different sizes and properties as compound lithium grease additives to significantly enhance the anti-wear and friction reduction properties of this grease. The results of friction experiments with a single additive are used as a basis to explore the synergistic lubrication mechanism of the compounded nanoparticles. This innovative approach provides a new reference and direction for future research and development of grease additives.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-09-2023-0291/

Investigating the effect of overbased sulfonates on calcium sulfonate complex grease: enhancements in physicochemical, rheological, and tribological properties.

Overbased sulfonate plays a crucial role in calcium sulfonate complex grease, significantly impacting the grease's performance characteristics. Herein, the calcium sulfonate complex grease was formulated using overbased calcium sulfonate (T106D) and overbased magnesium sulfonate (T107) in ratios of 1 : 2, 1 : 1, and 2 : 1, labeled as CMSCG (1 : 2), CMSCG (1 : 1), and CMSCG (2 : 1), respectively. This study examined the effects of overbased sulfonates on the physicochemical, anti-corrosion, rheological, and tribological properties of the grease. Results showed that CMSCG (1 : 2) exhibited superior physicochemical properties, with the highest dropping point (354 °C), the lowest penetration (161 (0.1 mm)), and the least oil separation (1.25%). Exposure to a salt spray environment significantly altered the grease's rheological properties. The combination of T106D and T107 enhanced the corrosion resistance of the grease, attributed to the formation of a corrosion inhibition layer. Incorporating T107 increased both the yield stress and hysteresis area of the calcium sulfonate complex grease. The CMSCG (1 : 2), CMSCG (1 : 1), and MSCG showed the high thixotropic ring area, indicating the poor thixotropy. The calcium sulfonate complex grease formulated with T107 showed the highest yield stress (558 Pa). The friction mechanism revealed that MSCG showed the optimal friction reduction properties, and CMSCG (1 : 1) demonstrated the optimal wear resistance, which are attributed to the synergistic effects of tribo-chemical films composed of CaO, CaCO3, FeSO4, MgCO3, and iron oxide.

Effects of Erucamide and N-phenyl-α-naphthylamine on the Friction and Torque Behaviors of Grease on Roller Bearings

To evaluate the impact of various proportions of erucamide and N-phenyl-α-naphthylamine on grease’s tribological performance for roller bearings, lithium complex grease (LCG) and polyurea grease (PG) were prepared with erucamide and N-phenyl-α-naphthylamine proportions of (0,0), (0,3), (1,2), (2,1), and (3,0). An investigation was conducted into the microscopic structures of the ten greases and their effects on the friction coefficients and wear scars of GCr15 steel. These findings were validated through bearing friction torque tests. The results indicate that the addition of 2 wt. % erucamide and 1 wt. % N-phenyl-α-naphthylamine to PG/LCG significantly enhances their tribological properties and reduces friction torque, with PG exhibiting superior performance. This enhancement was attributed to the synergistic interaction of erucamide and N-phenyl-α-naphthylamine with the lamellar thickener within PG. Erucamide contributed to friction reduction, while N acted as an antioxidant.

Investigation of Tribological Performance of Eco-friendly Pentaerythritol Tetraoleate Ester Based Calcium Complex Grease

Investigation of Tribological Performance of Eco-friendly Pentaerythritol Tetraoleate Ester Based Calcium Complex Grease

Ionic liquids enhance electrical conductivity of greases: an impedance spectroscopy study

Ionic liquids (ILs) have emerged as viable solutions for developing new-age lubricants, both as neat lubricants and lubricant additives. Enabled by the presence of discrete ions, ILs have the possibility to render electrically conductive lubricants, which is a feasible strategy for developing lubricant systems compatible with modern e-drive conditions. However, this requires the characterization of the electrical properties of lubricants, which is a bottleneck for developing electrically conductive greases, given their complex architecture. This work introduces an electrochemical impedance spectroscopy measurement methodology to evaluate grease samples’ electrical properties. Compared to the commonly used conductivity meters, this method, through its multi-frequency alternating current (AC) impedance approach, can effectively distinguish the individual contributions of the bulk and the sample-electrode interface to the measured electrical response. Impedance spectra of grease samples are obtained using an electrochemical cell with parallel plate electrodes, mounted on a temperature-controlled cell stand and coupled with a potentiostat. The grease’s bulk conductivity is extracted by fitting the impedance data to relevant equivalent electrical circuits. The bulk conductivity of lithium complex grease doped with ILs is evaluated and compared to greases with conventional conductivity additives (copper powder and conductive carbon black). The analysis of temperature-dependent conductivity reveals the rather different conductivity mechanisms for different additives. For greases doped with ILs, a comparison against the electrical conductivity of neat ILs reveals that, in addition to the ion dissociation, the interaction of the ions with the different grease components (base oil, thickener) is crucial in defining the grease conductivity.

Mercaptobenzothiazole functionalized ionic liquids as additive in lithium complex grease: rheological and tribological performances

PurposeThis study aims to probe the applicability of 2-mercaptobenzothiazole (MBT) functionalized ionic liquids (ILs) as additives in lithium complex grease (LCG) by researching the corrosion inhibiting, rheological and tribological performances.Design/methodology/approachElectrochemical tests such as electrochemical impedance spectroscopy and potentiodynamic polarization curves were used on Gamry electrochemical workstation to research the corrosion inhibition properties of ILs in 1.0 M HCl corrosive solution. The rheological properties of different grease samples were tested on a rheometer. The tribological properties were investigated on SRV-V oscillating reciprocating friction and wear tester. Scanning electron microscope, X-ray spectrometer and X-ray photoelectron spectrometer were used to characterize the lubricating mechanism.FindingsThe 2-MBT functionalized ILs have excellent corrosion inhibition properties. When used as additives in LCG, they both exhibited enhancing effects on thermostability, colloid stability and structural recoverability, and furthermore, outstanding friction-reducing and antiwear properties were also obtained. Surface analysis indicated that the superior lubricating performances of 2-MBT functionalized ILs were mainly ascribed to the formation of tribochemical products on wear tracks, including organic compounds with C–O bond, Fe2O3 and FeS2.Originality/valueThe 2-MBT-based ILs synthesized in this study were multifunctional additives with excellent corrosion inhibiting and tribological properties, which would have a very broad application prospect in lubricating grease industry.

Well-Dispersed Graphene Enhanced Lithium Complex Grease Toward High-Efficient Lubrication

Graphene as a lubricating additive holds great potential for industrial lubrication. However, its poor dispersity and compatibility with base oils and grease hinder maximizing performance. Here, the influence of graphene dispersion on the thickening effect and lubrication function is considered. A well-dispersed lubricant additive was obtained via trihexyl tetradecyl phosphonium bis(2-ethylhexyl) phosphate modified graphene ([P66614][DEHP]-G). Then lithium complex grease was prepared by saponification with 12-OH stearic acid, sebacic acid, and lithium hydroxide, using polyalphaolefin (PAO20) as base oil and the modified-graphene as lubricating additive, with the original graphene as a comparison. The physicochemical properties and lubrication performance of the as-prepared greases were evaluated in detail. The results show that the as-prepared greases have high dropping point and colloidal stability. Furthermore, modified-graphene lithium complex grease offered the best friction reduction and anti-wear abilities, manifesting the reduction of friction coefficient and wear volume up to 18.84% and 67.34%, respectively. With base oil overflow and afflux, well-dispersed [P66614][DEHP]-G was readily adsorbed to the worn surfaces, resulting in the formation of a continuous and dense graphene deposition film. The synergy of deposited graphene-film, spilled oil, and adhesive grease greatly improves the lubrication function of grease. This research paves the way for modulating high-performance lithium complex grease to reduce the friction and wear of movable machinery.

Investigation on friction characteristics of imitation clamshell textured surfaces under MXenes-enhanced grease lubrication

To enhance the performance and longevity of bearings by addressing the issue of insufficient lubrication, this research paper introduces a multi-drive lubrication system. Inspired by the micro-texture of clamshells, bionic textured surfaces (BTSs) were designed and fabricated. Calcium complex grease (CCG), aluminum complex grease (ACG), lithium complex grease (LCG), and these three greases containing 2[Formula: see text]wt.% accordion-like MXenes Ti3C2 were prepared, respectively. This study commits to evaluating the tribological properties of BTSs with different densities under different grease lubrication. The results showed that BTSs ([Formula: see text] = 38%) had the best anti-friction and anti-wear under the MXenes lithium complex grease lubrication, the average friction coefficient (0.113) and wear rate reached the smallest ([Formula: see text][Formula: see text]mm3[Formula: see text]N[Formula: see text][Formula: see text]m[Formula: see text]), and only slight wear occurred. This was mainly attributed to the synergistic and complementary lubricating effects of BTSs and MXenes-enhanced grease.

Enhancing Lubrication Performance of Calcium Sulfonate Complex Grease Dispersed with Two-Dimensional MoS2 Nanosheets

Calcium sulfonate complex greases (CSCG) have proven to be a sustainable alternative to lithium complex greases, which still require appropriate additives to deliver lubrication performance benefits under extreme working conditions such as heavy load, high speed, and high temperature. The anti-wear and friction reducing properties of CSCG enhanced by two-dimensional MoS2 nanosheets (2D MoS2) with a narrow lateral size and thickness distributions were evaluated by a four-ball tribometer. The results showed that the CSCG with 0.6 wt.% 2D MoS2 performs best, with a 56.4% decrease in average friction coefficient (AFC), 16.5% reduction in wear scar diameter (WSD), 14.3% decrease in surface roughness, and a 59.4% reduction in average wear depth. Combining SEM-EDS images, Raman, and X-ray photoelectron spectra, it is illustrated that the physical transferred film and tribo-chemical film consisting of MoS2, Fe2O3, FeSO4, CaCO3, CaO, and MoO3 were generated on the worn surface, which improves the lubrication performance of CSCG considerably.

Effect of the grease thickener on tribological properties of Si3N4/GCr15 contact interface and the performance in hybrid ceramic ball bearing

Si3N4 hybrid bearings are considered the most promising motor bearings due to their characteristics of electrical insulation, high speed, low friction coefficient, and wear resistance, which can better meet the requirements of driving motors of electric vehicles. However, the tribological mechanism between the ceramic-grease-steel complex interface is unclear. Three kinds of greases, namely lithium, polyurea, and calcium sulfonate complex grease, were synthesized from poly alpha olefin 40 as base oil. The effects of grease thickener morphology on the tribological properties of Si3N4/GCr15 contact surfaces at different slip speeds were investigated, and the vibration and friction torque performances in 6204 hybrid ceramic balls were evaluated. The results showed that the thickener could form physical deposition film and friction film to protect the worn surface at low speed. The friction and wear conditions were significantly improved at high speed under lithium grease and polyurea grease lubrication, being a mixed lubrication state. In presence of lithium grease, the tribological performance of the Si3N4/GCr15 interface and the vibration performance, impacted condition, starting torque, and friction torque of the hybrid ceramic ball bearings were all the best. Because lithium grease is subjected to continuous shear of the ceramic ball, which releases the base oil stably, and forms a thick oil film with the broken thickener in the center of the raceway, the bearing is in a mild lubrication state. Therefore, for Si3N4 hybrid ceramic ball bearings, lithium grease is a lubricant with good application prospects.

Reduced Friction and Excellent Anti-Wear Performance of QBe2 Beryllium Bronze against 38CrMoAlA Steel in Pneumatic Downhole Motor under Grease Lubrication

To improve the service life of the newly designed pneumatic downhole motor, a kind of commercially available lithium complex grease was used to help avoid the rapid wear-induced failure of the dynamic seal of pneumatic downhole tools in operation. The investigation on the tribological behaviors of QBe2 beryllium bronze and 38CrMoAlA steel tribo-pairs in pneumatic downhole motor revealed that under lubrication, the instantaneous friction coefficient and wear volume became very low, showing greatly reduced friction and excellent anti-wear performance. Compared with the case without lubrication, the adhesive wear mechanism and ploughing effect of the tribo-pairs were significantly alleviated. Moreover, Cu and Fe were oxidized to form composite oxides between the frictional surface, further improving the lubrication effect between the QBe2 beryllium bronze and 38CrMoAlA steel. Notably, the test could be operated stably for more than 150 h under lubrication, fully reaching the requirement of pneumatic downhole tools under actual drilling conditions. These results provide a solid support for the practical application of the reported pneumatic downhole tools.

Dependency of Lithium Complex Grease on the Size of hBN Particles for Enhanced Performance

Dependency of Lithium Complex Grease on the Size of hBN Particles for Enhanced Performance

Investigation of mixed hBN/Al2O3 nanoparticles as additives on grease performance in rolling bearing under limited lubricant supply

Grease plays an important role in reducing friction and wear of rolling bearings and improving their service life and reliability. However, increasing attention is being paid to the environmental pollution caused by discarded grease. In this paper, calcium sulfonate complex grease (CSCG) was prepared by using green raw materials, namely poly-alpha-olefin oil as the base oil and complex calcium sulfonate soap as thickener. In order to improve the lubrication and damping performance of the grease, hexagonal boron nitride (hBN) and nano-Al2O3, which have the potential to replace toxic additives, are mixed into the grease in different mass proportions. The thickener structure of each grease was characterized and analyzed. According to the bearing vibration and life of the two key performance indicators, four-ball tests and bearing vibration tests under limited lubricant supply (LLS) were performed. The results show that CSCG with 0.75 wt% hBN and 0.25 wt% Al2O3 (BN75AL25) has the best tribological and vibration suppression performance. The mean friction coefficient decreased by 11.3%, the wear scar diameter decreased by 6.1%, and the worn surface morphology improved significantly compared with CSCG. The frequency domain analysis showed that high, medium and low frequency vibrations were suppressed by 19%, 11.7% and 16.4%, respectively. In conclusion, BN75AL25 has the potential to become a green high-performance grease under LLS, which is worth further research and exploration.

Improved tribological and bearing vibration performance of calcium sulfonate complex grease dispersed with MoS2 and oxide nanoparticles

Molybdenum disulfide nanoparticles is an effective additive used to enhance the tribological properties of greases. However, there are four main mechanisms for improving the tribological properties of nanoparticles. Nano-MoS2 mainly plays the role of film formation, but it is difficult to achieve rolling, mending, and polishing effect. In this paper, based on addition of MoS2 nanoparticles, CuO, SiO2, and Al2O3 nanoparticles are further added to calcium sulfonate complex grease to achieve the other three effects, hoping to further improve the tribological performance of the grease. The tribological properties and the suppression effect on bearing vibration of the five greases were studied by four-ball friction experiment and bearing vibration experiment. The results show that a protective film consisting of MoS2 and MoO3 is formed on the worn surface. The addition of three oxide nanoparticles can further improve the properties of the calcium sulfonate complex grease containing MoS2 nanoparticles. Among them, calcium sulfonate complex grease with MoS2 and SiO2 nanoparticles performs the best, with 11.9% decrease in friction coefficient, 5.9% reduce in wear scar diameter, 27% decrease in the high frequency vibration of the bearing. The wettability test shows that the contact Angle of polyα-olefin 40 base oil on the thickening agent surface of calcium sulfonate complex grease containing MoS2 and SiO2 nanoparticles is the smallest, and it can be quickly added to the raceway.