Commercial Greases Research Articles

Dynamic performance of newly developed environmentally friendly greases containing polysaccharide gums in rolling bearing

The present study explores the performance of novel vegetable oil-based greases containing polysaccharide gums as additives. Two series of greases with varying concentrations of gum acacia (GA) and guar gum (GG) are evaluated in a rolling bearing at various speeds and loads. The vibrations and shock pulse measurements (SPM) quantified the tribo-dynamics of the developed greases against two commercial greases used as the benchmark. The vibration and SPM assessment suggest that the newly developed eco-friendly greases are at par with the commercial ones; the performance varies with the concentration and type of gum. Where a cumulative effect of rheology and gum size seems to influence the vibrations, the entrainment of gums in the contact zone governs the SPM carpet values. The developed greases show great prospects as a sustainable, potential, and commercial alternative to existing environmentally unfriendly greases.

Use of Functionalized Graphene-Based Materials on Grease

The growing awareness of reduced friction losses and new demands for electrical powertrains demand improved lubricants. Due to their unique properties, such as high thermal and electrical conductivity, graphene and its derivatives have been investigated for tribological applications, especially as lubricant additives. In this work, we investigated three commercially available graphene variants, one comprising a few layers and the other two comprising nanoplates, after functionalization as additives to lithium soap grease. The grease temperature dropping point increased by approximately 6 °C. Additionally, during the reciprocating friction test, friction increased with the test duration for the baseline grease, whereas it decreased for the ones containing graphene-based additives. On the test end, friction was reduced by 8% compared to the baseline grease. On a four-ball tribometer, the wear scar was reduced from 10 to 18% compared to the baseline grease. In general, no significant difference was seen between the three graphene-based variants. The promising results found with graphene nanoplates, a less expensive material than a few graphene layers, creates opportunities for a cost-competitive additive to commercial greases.

Wind turbine lubrication: Low temperature fretting wear behaviour of four commercial greases

Fretting tests on four commercial greases were run on a ball-on-disc machine at 25, 7, − 20, − 40 °C. Post-test wear was measured on the ball and the chemical composition of lubricant films in the wear scar analysed by FTIR (RA-IRS), Raman and SEM-EDS. At 25 and 7 °C the greases had similar friction and wear properties. At − 20 and − 40 °C the highest base-oil viscosity grease gave an inferior friction and wear performance. RA-IRS analysis showed thickener remaining in the wear scar for most test conditions. The highest wear was linked to the absence of thickener in the scar. Better wear and friction performance at low temperatures was associated with thickener present in the lubricated contact and lowest base-oil viscosity.

Oil Separation of Lubricating Greases under Static Conditions: Analytical Photo-Centrifuge and DIN 51817

Lubricating greases enclose oil in porous structures of aggregated thickener particles. Their tendency to separate oil under static conditions is evaluated according to DIN 51817 or DIN ISO 22285 in tests of up to 168 h with the mass fraction of separated oil as result. With an analytical photo-centrifuge, separated oil mass fractions can be tracked in real time in the instrument operating temperature range from 4–60 °C. Due to the higher mechanical load compared to standard tests, the grease samples separate more and faster oil, significantly speeding up the analysis process. Fitting the measured data from both methods with the function wO = wO,∞ exp(−t/tc), the parameters maximum oil separation wO,∞ and characteristic time tc are obtained as measures of oil separation extent and rate. Both parameters help to compare the two methods and to interpret the oil separation characteristics of greases. Using four commercial greases of NLGI classes 0–2, the analytical photo-centrifuge measuring method is presented in detail and its results are discussed in reference to those of standard DIN 51817.

Some rheological properties of plastic greases by Carreau-Yasuda model

Various greases are often used for lubrication of various roller bearing and more seldom for slide bearings operating under rather lower speed values, when the mixed or boundary friction occur, for example, during operation in the start-stop regime. Three various commercial greases were tested, differing in the value of the kinematic viscosity of the base oils used in them, measured at temperature 40 °C and 100 °C, and the resulting different dropping point temperature. The rheological properties of such greases have been determined using the rotary rheometer. Based on the resulted dependencies of the apparent viscosity on the shear rate the parameters of the Carreau-Yasuda rheological model chosen, have been estimated. The prediction of rheological parameters for three plastic greases studied obtained with particularly good accuracy. Among the tested greases, the grease with the highest drop point temperature turned out to be a mechanically stable grease. The differences in parameters values could be affected by differences in the compounds of the greases studied.

Unexplored potential of acacia and guar gum to develop bio-based greases with impressive tribological performance: A possible alternative to mineral oil-based greases

A potential, sustainable, and economical eco-friendly alternative to harmful petroleum-based lubricants is a big challenge for the 21st-century lubricant industry. The present study explores, for the very first time, polysaccharide gums like gum acacia (GA) and guar gum (GG) as additives (0.5–10 %w/w) to enhance the extreme-pressure (EP) performance of greases (based on vegetable oil and organoclay). The greases are evaluated on a four-ball tester for the standard EP test (ASTM D2596). Adding GA or GG to greases enhances EP performance significantly. The performance ameliorates with the gum's concentration showing impressive results at higher concentrations (up to ≈ 60% better than a commercial grease). The superior performance is attributed to an in-situ formed polymer-layered silicate nanocomposite tribofilm at the interface via chemisorption (for GA) or physisorption (for GG). The formulated greases are a possible replacement for existing mineral oil-based commercial greases.

CPU Performance Improvement Using Novel Thermally Conductive Carbon Nano Grease

Electronics depend on their ability to shed operational heat to maintain operating temperature. Inferior grease can create preventable problems in electronics. This is typically achieved through a thermal grease or paste. If this grease fails to dissipate heat or maintain thermal contact, then the equipment will have faults. Greases with less-than-optimal performance create excessive wear, heat, and reduced life expectancy. This can cause equipment failures and malfunctions at the most inopportune moments. Thermal greases are applied to Central Processors (CPU) and Graphics Processors (GPU) in avionics LRUs, computers, Solar panels, HVAC systems, and other electronics. A high-performance novel nano grease will shed excess heat and increase device life expectancy. The fabricated nano greases show improvements of up to 80% in thermal conductivity measurements. CPU testing resulted in a 100% decrease in the standard deviation of temperature variation from commercial greases.

Mitigation of False Brinelling in a Roller Bearing: A Case Study of Four Types of Greases

Four commercial greases with various thickeners and base oils were experimentally examined to compare their false brinelling wear resistance in a test rig simulating roller bearings during rail/sea transportation for the first time. Greases containing zinc dialkyl dithiophosphates (ZDDP) showed superior false brinelling reduction, evidenced by no visible wear mark in the raceways. The mechanism for false brinelling mitigation was shown to be from a ZDDP-induced tribofilm which decreases the friction and wear coefficient in the contact area. Surface chemical analysis showed that for grease lubricated fretting contacts, ZDDP-derived tribofilms can be generated in the presence of micro-sliding motions and energy dissipation at the contact interface at low frequency (i.e., 4–8 Hz), due to the mechanochemical reactions. For greases without ZDDP, false brinelling wear was reduced by 97% when using grease with a more abundant and less viscous oil, which bleeds readily from an open structured thickener. The results highlight the ability of ZDDP as an additive in grease to better protect roller bearings against false brinelling during rail/sea transportation.

Selection of radiation tolerant commercial greases for high-radiation areas at CERN: Methodology and applications

At the European Laboratory for Particle Physics (CERN), commercial greases and oils are extensively used to lubricate moving devices operating in high-radiation areas, absorbing doses up to the MGy range. Due to their sensitivity to radiation, lubricants can become fluid or solid in operation, potentially causing component failures and compromising the operation of the accelerator complex. CERN is therefore developing methodologies to select radiation tolerant commercial lubricants for critical Beam Intercepting Devices (BIDs) such as high-power targets, dumps and collimators. A careful selection of greases is fundamental to reduce the risk of failure, to optimize equipment lifetime and to minimize maintenance and unwanted radiation exposure of personnel in high radiation areas. Three different parameters are considered to select commercial lubricants: the expected total dose absorbed in operation, the maintenance feasibility and the failure impact in terms of accelerator downtime and of personnel involvement in replacement procedures. Based on these criteria, an example of relevant application is presented: the lubrication of the new internal beam dump of the Super Proton Synchrotron (SPS). Experimental radiation damage data allowed the identification of two radiation tolerant commercial greases to lubricate the dump support jack assembly.

Tribological Behavior of Novel CNTs-Based Lubricant Grease in Steady-State and Fretting Sliding Conditions

The tribological behavior of novel 7.5 wt% carbon nanotube-based lubricant greases in PAO (polyalphaolefin) oil with and without 1.0 wt% MoS2, together with several other commercial greases such as calcium, lithium, were studied. The test results showed a marked reduction of frictional coefficient achieved by the CNTs based grease samples with an average benefit of around 30% compared to conventional greases. The steady state test under 1.00 GPa average contact pressure in a mixed lubrication regime and the fretting test showed the best results in terms of friction reduction obtained by CNTs greases. Steady state tests at higher average contact pressure of 1.67 GPa proved to have a lower friction coefficient for CNTs grease containing MoS2; otherwise CNTs grease without MoS2 showed an average value of CoF comparable to calcium and lithium greases, both in a boundary and a mixed regime. The protection against wear, a considerable decrease (−60%) of reference parameter was measured with CNTs grease with MoS2 (NLGI 2) in comparison with the worst conventional grease and −22% in comparison with the best conventional grease. The data indicated that our novel carbon nanotube greases show superior tribological properties and will have promising applications in the corresponding industry.

Investigation of Tribological Behavior of Lubricating Greases Composed of Different Bio-Based Polymer Thickeners

One commonly used lubricant in rolling bearings is grease, which consists of base oil, thickener and small amounts of additives. Commercial greases are mostly produced from petrochemical base oil and thickener. Recently, the development of base oils from renewable resources have been significantly focused on in the lubricant industry. However, to produce an entirely bio-based grease, the thickener must also be produced from renewable materials. Therefore, this work presents the design and evaluation of three different bio-based polymer thickener systems. Tribological tests are performed to characterize lubrication properties of developed bio-based greases. The effect of thickener type on film thickness and friction behavior of the produced bio-based greases is evaluated on a ball-on-disc tribometer. Moreover, the results are compared to a commercial petrochemical grease chosen as benchmark.

Analysis On Crystal Formation And Physio-Tribological Properties Of Lithium Based Grease Developed From Coconut Oil (Cocos Nucifera)

The increase in demand for alternative base oil for lubricant has led to the study of non-depleting source like vegetable oils. Some studies have reported the development of grease from sunflower oil and castor oil, which establish the probability of use of vegetable oil as potential base oil. In the present study, an eco-friendly NLGI grade 3 grease was developed using coconut oil as base oil and lithium stearate as thickener. The inherent tribological properties of the coconut oil and grease were evaluated. Tests results of newly formulated grease procured from cone penetration, rolling stability, water wash out, grease leakage, friction and wear are compared to a commercial sample of same grade. Even though the newly formulated grease is found to be competent to the commercial sample, the crystal formation at low temperature has restricted its applications at lower temperatures. Crystal formation at low temperature is due to the agglomeration of saturated fatty acids commonly known as wax occurred due to the low cold flow characteristics of the oil (pour point of coconut oil 26.55°C). The tribological results show that the performance of the newly formulated grease is comparable to commercial greases and its application is restricted to moderate climatic conditions.

Neutron Radiation Effects on Lubricants and O-Rings for Target and Accelerator Applications

Lubricants and O-rings are necessarily used for the construction of many accelerator-driven facilities as spallation sources or facilities for the production of radioactive isotopes. During operation, such component will absorb high doses of mixed neutron and gamma radiation, that can degrade their mechanical and structural properties. Experimental radiation damage tests of these components are mandatory for the construction of the facility. Methodologies for irradiation in nuclear reactor mixed fields and post-irradiation examination of lubricating oils, greases and O-rings were developed and are here presented. Samples were characterized with standard mechanical and physical-chemical tests. Parametric studies on the dose rate effects have been performed on O-rings. A case studies for a specific O-ring application in a gate valve has been developed. Some of the tested samples showed a dramatic change of their properties with dose, while others remain stable. Results were collected on nine commercial greases, on one oil and on four commercial elastomeric O-rings. The most radiation resistant among the selected products are now considered for application in facilities under construction. The main mechanisms of neutron and gamma radiation damage on these polymers were investigated at the mechanical and structural level.

Tribological and rheological properties of the ultrafine CaCO3 blended nano grease

Calcium carbonate uniform nanoparticles of the tailored morphologies were produced under a narrow set of experimental parameters. The as-synthesized CaCO3 particles of novel morphologies were used as lubricant additives in commercial grease and the effect of these additives on the tribological properties of the commercial Lithium greases (CLG) was studied by the four-ball tribometer. The grease blended with commercially available CaCO3 powder was also analyzed under the same conditions for comparison study. Results showed that the as-prepared monodispersed CaCO3 particles considerably improved the tribological properties of the CLG as compared to the irregular particles of the commercial calcium carbonate. The grease blends showed the best results at the optimum amount of 3 weight % of the added CaCO3 oval and rod shape particles. Among the as-synthesized ultrafine calcium carbonate particle systems, oval shape particles exhibited more improvement in the anti-wear performance than rod shape particles. Preliminary experiments regarding the rheological study of the grease blends showed a decrease in the shear stress as compared to their blank partners. The oval calcium carbonate particles showed the lowest values of the shear stress at any shear rate as compared to the rod and commercial CaCO3 particles. Furthermore, the anti-wear/friction and rheological properties of the greases were enhanced in the order of Momin > Awami > Sinopec by blending with the as-synthesized CaCO3 particles.

Antiwear Properties of Commercial Grease as a Function of Particle Morphology and Uniformity of the As-Synthesized Calcium Carbonate Additive

AbstractCalcium carbonate powder comprising uniform nanoparticles of novel morphology was synthesized under extensively optimized trial parameters. The as-prepared ultrafine rod shape CaCO3 particles after characterizations were used as an antiwear/antifriction additive in commercial lithium grease (CLG) of different specifications. The effect of the added particles on the antifriction and antiwear properties of the blended commercial greases was explored by using a ball-on-disk tribometer. The observed data were compared with the additized grease having commercially available CaCO3 powder. Results exposed that uniformity in particle size and shape is a key factor for the improvement of tribological properties and reproducibility of the experimental results. Therefore, the as-prepared monodispersed rod shapes CaCO3 particles as additives considerably improved the tribological properties of the CLG as compared with the irregular particles of the commercial calcium carbonate. These blends showed the best results at the optimum amount of 3 wt% of the added CaCO3 particles. Among the three selected greases, the additized Momin grease exhibited best antiwear/antifriction performance as compared with the additized Awami and Sinopec greases.

Carbon nanotubes grease with high electrical conductivity

While most commercial greases are used to prevent wear and tear in machinery, many specialized applications require electrically conductive grease. Applications include, but are not limited to, use in next generation electric vehicles (NGEVs), superb electric motor bearing protection, and electrical contact improvement. Using recently new invented methods, electrically conductive greases have been prepared. Petro-Canada N650HT oil with 7.5 wt% hydroxyl functionalized multiwall carbon nanotubes (MWNT-OH), yielded a surprising resistivity of 22.4 Ω cm, compared to the resistivity of 7880 Ω cm of an almost identical sample made with multiwall nanotube (MWNT). Another sample, 75 % Glycerol, 25 % Water, 4.5 wt% MWNT-OH, yielded the lowest resistivity of all samples measured, at 10.0 Ω cm. Hydrogen bonding is believed to be attributed to the best performing samples. The introduction of hydrogen bonding in any form into the grease increases electrical conductivity. This finding can be extended with further research to other nanomaterials with functional groups like OH, COOH, F, and NH.

Experimental study of consistency degradation of different greases in mixed neutron and gamma radiation

Many of the moving components in accelerator and target environments require lubrication. Lubricants in such environments are exposed to high fluxes of secondary radiation, which originates from beam interactions with the target and from beam losses. The secondary radiation is a mix of components, which can include significant fractions of neutrons. Lubricants are radiation-sensitive polymeric materials. The radiation-induced modifications of their structure reduce their service lifetime and impose additional facility maintenance, which is complicated by the environmental radioactivity. The study of the lubricants radiation resistance is therefore necessary for the construction of new generation accelerators and target systems. Nevertheless, data collected in mixed radiation fields are scarce. Nine commercial greases were irradiated at a TRIGA Mark II Research Reactor to serve for the construction of new accelerator projects like the European Spallation Source (ESS) at Lund (Sweden) and Selective Production of Exotic Species (SPES) at Legnaro, (Italy). Mixed neutron and gamma doses ranging from 0.1 MGy to 9.0 MGy were delivered to the greases. For an experimental quantification of their degradation, consistency was measured. Two of the greases remained stable, while the others became fluid. Post-irradiation examinations evidence the cleavage of the polymeric structure as the dominant radiation effect. Dose and fluence limits for the use of each product are presented. Apart from the scientific significance, the results represent an original and useful reference in selecting radiation resistant greases for accelerator and target applications.

Yield Stress Analysis of a Fumed Silica Lubricating Grease

Yield stress is an important property for identifying the suitability of a grease for a lubrication system. There is no consensus on the definition of the yield stress or its measurement method. Although fumed silica can be a suitable thickening agent, studying fumed silica–based lubricating greases has not received much attention. In this work, the authors performed different rheological tests on fumed silica–based lubricating grease to study its yielding behavior. The results revealed that the yield points obtained by most of these methods are roughly similar. The slight differences between these results have been explained as well. The microstructure of this grease is visualized using scanning electron microscopy (SEM) in cryo and non-cryo modes, demonstrating the fractal structure of the thickener and its corresponding structural hierarchy. Steady-state flow curves and microstructural analysis revealed some of the differences between this grease and other commercial greases.

Hybrid Nanocomposite Thermal Interface Materials: The Thermal Conductivity and the Packing Density

We have investigated a novel hybrid nanocomposite thermal interface material (TIM) that consists of silver nanoparticles (AgNPs), silver nanoflakes (AgNFs), and copper microparticles (CuMPs). Continuous metallic network form while AgNPs and AgNFs fuse to join bigger CuMPs upon hot compression, resulting in superior thermal and mechanical performances. The assembly temperature is as low as 125 °C due to the size effect of silver nanoparticulates. The thermal conductivity, k, of the hybrid nanocomposite TIMs is found to be in the range of 15–140 W/mK, exceeding best-performing commercial thermal greases, while comparable to high-end solder TIMs. The dependence of k on the solid packing density and the volume fraction of voids is discussed through comparing to model predictions.

AFM and SEM Assessment of Lubricating Grease Microstructures: Influence of Sample Preparation Protocol, Frictional Working Conditions and Composition

The microstructure of lubricating greases greatly conditions their in-service performance. In that sense, optimal testing protocols are required in order to accomplish their correct morphological characterization. This study explores and compares the suitability of atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques for imaging six different commercial metallic soap-based greases and two novel biopolymer-based formulations. Pros and cons of both techniques and the effect of sample preparation protocol were analysed. The results revealed a wide variety of morphological characteristics depending on composition. Thus, the four anhydrous calcium-based greases demonstrated two clearly distinct microstructures (fibrous and granular) determined by the type of base oil employed. With regard to the lithium complex greases, the typically reported microstructure characterized by well-defined entangled and fibrous network was observed in both AFM and SEM techniques. As for the two biopolymer-based greases, fibre networks were also encountered. Besides this, selected greases were subjected to different tribological tests, and the effect of high-shear frictional working treatments on their microstructure was also analysed. As a result of the friction and internal wear, the AFM results evidenced microstructural changes which depended on grease composition. Overall, the combined use of AFM and SEM techniques was demonstrated to be a powerful approach to microstructurally characterize lubricating greases.