Fluorographene(FG)with narrow lateral size and thickness distributions was prepared by a liquid-phase exfoliation method,based on liquid cascade centrifugation.The Rtec MFT-5000 tribo-meter was used to investigate the...Fluorographene(FG)with narrow lateral size and thickness distributions was prepared by a liquid-phase exfoliation method,based on liquid cascade centrifugation.The Rtec MFT-5000 tribo-meter was used to investigate the lubricating performance of bentonite grease enhanced by the as-prepared FG.The results showed that the coefficient of friction and the wear volume of bentonite grease with 0.3 wt%FG were decreased by 20.4%and 44.9%,respectively,as compared to those of the base grease.The main reason is that FG can promote the formation of the tribo-chemical reaction film consisting of complex carbon oxide,Fe_(2)O_(3)and FeF_(3)on the friction surface,which can remarkably improve the performance of friction reduction and prevent the appearance of severe wear.展开更多
This study prepared four types of ionic liquid-modified polypyrrole(IL-modified PPy)as conductive additives and investigated their tribological performance and conductivity in polytetrafluoroethylene lubricating greas...This study prepared four types of ionic liquid-modified polypyrrole(IL-modified PPy)as conductive additives and investigated their tribological performance and conductivity in polytetrafluoroethylene lubricating grease.The results indicated that IL-modified PPy effectively enhanced the anti-wear performance and conductivity of the base grease.Among the additives,1-octyl-3-methylimidazolium tetrafluoroborate([OMIm][BF4])modified PPy showed superior performance compared to the other three additives,with the best effect observed at a mass fraction of 0.5%.X-ray photoelectron spectroscopy analysis revealed that IL-modified PPy forms a stable friction chemical film during the friction process,effectively enhancing the lubrication performance and conductivity of the base grease.This indicates broad potential applications in the field of conductive lubrication.展开更多
A new category of lithium greases was synthesized by using poly-a-olefin(PAO8) and alkyl-tetralin as base oil, where the alkyl-tetralins were synthesized by the alkylation of tetralin and olefins. The influence of thi...A new category of lithium greases was synthesized by using poly-a-olefin(PAO8) and alkyl-tetralin as base oil, where the alkyl-tetralins were synthesized by the alkylation of tetralin and olefins. The influence of thickener concentration, alkyl-tetralin content and type of blend oils on the rheological and tribological performance of lithium grease was investigated. The microstructures of soap fibers were measured to reveal the structure-property correlations. The concentration of thickener and alkyl-tetralin content obviously affect the lubricating performance of lithium grease, while the molecular structure of alkyltetralin has no obvious impact on their properties. It was found that alkyl-tetralin could significantly enhance the thickening ability of PAO8 base oils, and decrease the amount of thickeners by 1.5%(mass).Lithium greases prepared using 20%(mass) alkyl-tetralin as co-base oil exhibited high colloidal stability,excellent rheological behaviors and tribological properties.展开更多
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 infuence of graphe...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 infuence of graphene dispersion on the thickening efect and lubrication function is considered. A well-dispersed lubricant additive was obtained via trihexyl tetradecyl phosphonium bis(2-ethylhexyl) phosphate modifed graphene ([P_(66614)][DEHP]-G). Then lithium complex grease was prepared by saponifcation with 12-OH stearic acid, sebacic acid, and lithium hydroxide, using polyalphaolefn (PAO20) as base oil and the modifed-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, modifed-graphene lithium complex grease ofered the best friction reduction and anti-wear abilities, manifesting the reduction of friction coefcient and wear volume up to 18.84% and 67.34%, respectively. With base oil overfow and afux, well-dispersed [P_(66614)][DEHP]-G was readily adsorbed to the worn surfaces, resulting in the formation of a continuous and dense graphene deposition flm. The synergy of deposited graphene-flm, 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.展开更多
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 ...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.展开更多
Polypropylene(PP)grease holds great potential for special industrial applications.In this study,synthetic conditions,thickener content,and the ratio of two different molecular weight PPs were investigated systematical...Polypropylene(PP)grease holds great potential for special industrial applications.In this study,synthetic conditions,thickener content,and the ratio of two different molecular weight PPs were investigated systematically using a rheometer,scanning electron microscope,X-ray diffraction,Fourier transform infrared spectrometer,oscillating tribometer,and 3D surface profiler measurements.The results showed that suitable synthetic conditions are two quenching cycles,and the synthetic temperature and time is 240℃for 12 h.The rheological analysis showed that thickener content and different proportions of the two PP molecular weights have a significant influence on the rheological properties of PP grease.High molecular weight PP(H-PP)has a stronger thickening ability than low molecular weight PP(L-PP).The higher the amount of H-PP in the fixed thickener content or the higher the thickener content with a specific proportion,the higher the viscoelasticity of PP grease.The tribological performance is related to the rheological properties.The proportion of two different molecular weight PPs in the thickener content should be appropriate;excessive H-PP content leads to lubrication failure.展开更多
Increased environmental and health concerns over the use of plastic packaging or fluorine-containing coatings,in combination with increased market demand for products with a longer shelf life,make bio-based materials ...Increased environmental and health concerns over the use of plastic packaging or fluorine-containing coatings,in combination with increased market demand for products with a longer shelf life,make bio-based materials one of the most important research candidates for alternative paper packaging materials for oil resistance.These bio-based materials have excellent oxygen and oil barriers,which are critical for food packaging.Moreover,they are biodegradable,naturally renewable,and safe.In this artical,two main groups of bio-based oil repellents for paper food packaging,including polysaccharide-based biopolymers and protein-based biopolymers,are enumerated,and the advantages and weaknesses of bio-based oil repellents are discussed,and effective solutions are proposed.Finally,research status and prospects on the development of bio-based oil-resistant coatings for the food packaging industry are presented.展开更多
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 pr...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.展开更多
Grease life refers to the time it takes for the grease to lose its ability to keep the lubrication due to grease degradation. As grease life is generally shorter than fatigue life of bearing, the service life of greas...Grease life refers to the time it takes for the grease to lose its ability to keep the lubrication due to grease degradation. As grease life is generally shorter than fatigue life of bearing, the service life of grease-lubricated rolling bearings is often dominated by grease life. When designing a bearing systemolecular weightith grease lubrication, it is necessary to define the operating conditions limits of the bearing, for which grease life becomes a determining factor. Prolongation of grease life becomes an especially important challenge when the bearing is to be operated trader high-speed, high-temperature, and other severe conditions. Selecting a number of commercially sold greases composed of varying base oils, the author evaluated their properties and analyzed how each property affected the grease life by performing a multiple regression analysis. The optimum grease composition to best exploit each property was also examined. The results revealed among others that one would need to first determine the base oil type and then maximize ultimate bleeding while minimizing the evaporation rate.展开更多
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 wh...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.展开更多
Titanium complex greases were prepared by using naphthenic mineral oil and polydimethylsiloxane as the mixed base oil. The effect of polydimethylsiloxane molecular weight and polydimethylsiloxane content in mixed base...Titanium complex greases were prepared by using naphthenic mineral oil and polydimethylsiloxane as the mixed base oil. The effect of polydimethylsiloxane molecular weight and polydimethylsiloxane content in mixed base oil on the physicochemical and tribological properties of titanium complex greases was investigated.As compared to the sole mineral oil-based titanium complex grease, the use of polydimethylsiloxane(H201-350)as a co-base oil increased the dropping point from 310 to 329℃, decreased the oil separation from 3.7% to 2.3%,reduced the corrosion extent, and obviously improved the tribological properties. When the mixed oil-based titanium complex grease was used as a lubricant, lubricating films of polydimethylsiloxane were probably formed on the surfaces of friction pairs, giving good lubricating property.展开更多
The tribological properties of graphene(GN) and graphite(G) as lubricant additives in lithium greases were investigated with a four-ball tribotester. The micro-morphology as well as the content and chemical state of e...The tribological properties of graphene(GN) and graphite(G) as lubricant additives in lithium greases were investigated with a four-ball tribotester. The micro-morphology as well as the content and chemical state of elements on the worn surfaces was characterized by scanning electron microscopy(SEM) and X-ray photoelectron spectroscopy(XPS). The results showed that the tribological performance of lithium grease could be significantly improved by the addition of graphene. During the friction process, an adhesion film and a deposition film consisted of graphene as well as a tribochemical reaction film composed of FeO, Fe_2O_3, FeOOH and LiOH could be formed on the tribosurface, and these complex films were responsible for the improved tribological performance of lithium grease.展开更多
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） numb...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.展开更多
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 introd...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.展开更多
Till now, most part of the biodiesel is produced from the refined vegetable oils using methanol as feedstock in the presence of an alkali catalyst. However, large amount of waste edible oils and grease are available. ...Till now, most part of the biodiesel is produced from the refined vegetable oils using methanol as feedstock in the presence of an alkali catalyst. However, large amount of waste edible oils and grease are available. The difficulty with alkali-catalyzed esterification of these oils is that they often contain large amount of free fatty acids （FFA）, polymers and decomposition products. These free fatty acids can quickly react with the alkali catalyst to produce soaps that inhibit the separation of the ester and glycerine. An esterification and transesterification process is developed to convert the high FFA oil to its monoesters, The first step, the acidcatalyzed esterification with glycerine and these FFA reduces the FFA content of the oil and grease to less than 3%, and then an azeotropic distillation solvent is used to remove the water. The major factors affecting the conversion efficiency of the process such as glycerol to free fatty acid molar ratio, catalyst amount, reaction temperature and reaction duration are analyzed, The second step, alkali-catalyzed transesterificatiou process converts the products of the first step to its monoesters and glycerol, and then the glycerol is recycled for utilization in the first step. Technical indicators of the biodiesel product can meet the ASTM 6751 standard.展开更多
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,...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.展开更多
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 ...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%.展开更多
Effects of nano SbSbS4particles on contact fatigue life of a steel ball were evaluated on a self-made ball-rod contact fatigue tester. The anti-fatigue mechanisms of SbSbS4 additive were analyzed by means of SEM and E...Effects of nano SbSbS4particles on contact fatigue life of a steel ball were evaluated on a self-made ball-rod contact fatigue tester. The anti-fatigue mechanisms of SbSbS4 additive were analyzed by means of SEM and EDAX. It was shown that, when the grease contained SbSbS4, contact fatigue life was improved compared with that of base grease. Nanoparticle absorption action, nanoparticle infiltration action, and extreme pressure and anti-friction performance, explained why SbSbS4 increased the contact fatigue life of the steel ball tested.展开更多
Ball bearings’ rating life is reduced with the presence of hard particle contaminants in the lubricant. This life reduction is taken into account when calculating the modified rating life by using the contamination f...Ball bearings’ rating life is reduced with the presence of hard particle contaminants in the lubricant. This life reduction is taken into account when calculating the modified rating life by using the contamination factor. The contamination factor is based on a general characterization of the lubrication conditions but the impact of contaminant’s variables such as size, hardness and concentration level is not determined in detail. In this work, greases contaminated with hard corundum (alumina, Al2O3) particles of different sizes are tested aiming at finding a pattern in the relationship between particle sizes’ and wear’s progress. A laboratory rig is utilized for these tests and vibration analysis tools regarding bearings’ condition and estimated residual life are being assessed. After the tests, optical inspections using a stereoscope verify the vibration analyses results. The experimental results show that wear is progressing faster when smaller particles are used. The crystalline structure of the corundum and the different degree of brittleness of the contaminants seem to be the reasons for this behavior, whereas severe abrasion and deformation of the raceways have been detected.展开更多
CeF3. CaF2, (CF)n, SbF3, and CeO2 were selected as the high temperature solid additives in a lithium grease, and their friction, wear, and extreme pressure properties were evaluated on an Optimol-SRV wear tester. The ...CeF3. CaF2, (CF)n, SbF3, and CeO2 were selected as the high temperature solid additives in a lithium grease, and their friction, wear, and extreme pressure properties were evaluated on an Optimol-SRV wear tester. The effect of additive on the fiber structure of soap was studied by means of the transmission electron microscopy(TEM). The corrosive property of grease containing additive was evaluated by copper strip corrosion test. Thermal decomposition behaviors of the additives were studied by thermogravimetry(TG) tester. The adhesive strength of rubbing surface film was measured by automatic scratch tester and the wear surface was detected by means of X-ray photoelectron spectroscopy (XPS). The test results showed that the grease containing CeF3 has good anti-wear, anti-friction, and EP performances, and has high adhesive strength of rubbing surface film.The greases containing CaF2 or (CF)n are good in antiwear and anti-friction properties, but poor in extreme pressure function. The tribological properties of the grease containing SbF3 are decreased.And the addition of CeO2 in grease was useless. Finally the mechanism of fluoride additive was proposed in this paper.展开更多
基金Funded by Science and Technology Research Program of Chongqing Municipal Education Commission(No.KJZD-K202212905)Natural Science Foundation of Chongqing,China(No.cstc2019jcyj-msxmX0453)。
文摘Fluorographene(FG)with narrow lateral size and thickness distributions was prepared by a liquid-phase exfoliation method,based on liquid cascade centrifugation.The Rtec MFT-5000 tribo-meter was used to investigate the lubricating performance of bentonite grease enhanced by the as-prepared FG.The results showed that the coefficient of friction and the wear volume of bentonite grease with 0.3 wt%FG were decreased by 20.4%and 44.9%,respectively,as compared to those of the base grease.The main reason is that FG can promote the formation of the tribo-chemical reaction film consisting of complex carbon oxide,Fe_(2)O_(3)and FeF_(3)on the friction surface,which can remarkably improve the performance of friction reduction and prevent the appearance of severe wear.
基金The authors would like to appreciate the financial support extended for this academic work by the Beijing Natural Science Foundation(Grants 2172053,2232066)the Open Project Foundation of State Key Laboratory of Solid Lubrication(Grant LSL-2212).
文摘This study prepared four types of ionic liquid-modified polypyrrole(IL-modified PPy)as conductive additives and investigated their tribological performance and conductivity in polytetrafluoroethylene lubricating grease.The results indicated that IL-modified PPy effectively enhanced the anti-wear performance and conductivity of the base grease.Among the additives,1-octyl-3-methylimidazolium tetrafluoroborate([OMIm][BF4])modified PPy showed superior performance compared to the other three additives,with the best effect observed at a mass fraction of 0.5%.X-ray photoelectron spectroscopy analysis revealed that IL-modified PPy forms a stable friction chemical film during the friction process,effectively enhancing the lubrication performance and conductivity of the base grease.This indicates broad potential applications in the field of conductive lubrication.
基金financially supported by the National Natural Science Foundation of China (U1910202, 21978194)the Key Research and Development Program of Shanxi Province (202102090301005)+1 种基金the Fund for Shanxi “1331 Project”the Shanxi Natural Science Foundation for Young Scientists (202103021223064)。
文摘A new category of lithium greases was synthesized by using poly-a-olefin(PAO8) and alkyl-tetralin as base oil, where the alkyl-tetralins were synthesized by the alkylation of tetralin and olefins. The influence of thickener concentration, alkyl-tetralin content and type of blend oils on the rheological and tribological performance of lithium grease was investigated. The microstructures of soap fibers were measured to reveal the structure-property correlations. The concentration of thickener and alkyl-tetralin content obviously affect the lubricating performance of lithium grease, while the molecular structure of alkyltetralin has no obvious impact on their properties. It was found that alkyl-tetralin could significantly enhance the thickening ability of PAO8 base oils, and decrease the amount of thickeners by 1.5%(mass).Lithium greases prepared using 20%(mass) alkyl-tetralin as co-base oil exhibited high colloidal stability,excellent rheological behaviors and tribological properties.
基金Supported by National Natural Science Foundation of China(Grant Nos.52075458 and U2141211).
文摘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 infuence of graphene dispersion on the thickening efect and lubrication function is considered. A well-dispersed lubricant additive was obtained via trihexyl tetradecyl phosphonium bis(2-ethylhexyl) phosphate modifed graphene ([P_(66614)][DEHP]-G). Then lithium complex grease was prepared by saponifcation with 12-OH stearic acid, sebacic acid, and lithium hydroxide, using polyalphaolefn (PAO20) as base oil and the modifed-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, modifed-graphene lithium complex grease ofered the best friction reduction and anti-wear abilities, manifesting the reduction of friction coefcient and wear volume up to 18.84% and 67.34%, respectively. With base oil overfow and afux, well-dispersed [P_(66614)][DEHP]-G was readily adsorbed to the worn surfaces, resulting in the formation of a continuous and dense graphene deposition flm. The synergy of deposited graphene-flm, 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.
基金Supported by the German Research Foundation e.V. (DFG).The presented results are based on the research project STA1198/14-1。
文摘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.
基金the financial support provided by the National Natural Science Foundation of China Project (U21A20315,21978186)the Fund for Shanxi“1331 Project” (1331)。
文摘Polypropylene(PP)grease holds great potential for special industrial applications.In this study,synthetic conditions,thickener content,and the ratio of two different molecular weight PPs were investigated systematically using a rheometer,scanning electron microscope,X-ray diffraction,Fourier transform infrared spectrometer,oscillating tribometer,and 3D surface profiler measurements.The results showed that suitable synthetic conditions are two quenching cycles,and the synthetic temperature and time is 240℃for 12 h.The rheological analysis showed that thickener content and different proportions of the two PP molecular weights have a significant influence on the rheological properties of PP grease.High molecular weight PP(H-PP)has a stronger thickening ability than low molecular weight PP(L-PP).The higher the amount of H-PP in the fixed thickener content or the higher the thickener content with a specific proportion,the higher the viscoelasticity of PP grease.The tribological performance is related to the rheological properties.The proportion of two different molecular weight PPs in the thickener content should be appropriate;excessive H-PP content leads to lubrication failure.
文摘Increased environmental and health concerns over the use of plastic packaging or fluorine-containing coatings,in combination with increased market demand for products with a longer shelf life,make bio-based materials one of the most important research candidates for alternative paper packaging materials for oil resistance.These bio-based materials have excellent oxygen and oil barriers,which are critical for food packaging.Moreover,they are biodegradable,naturally renewable,and safe.In this artical,two main groups of bio-based oil repellents for paper food packaging,including polysaccharide-based biopolymers and protein-based biopolymers,are enumerated,and the advantages and weaknesses of bio-based oil repellents are discussed,and effective solutions are proposed.Finally,research status and prospects on the development of bio-based oil-resistant coatings for the food packaging industry are presented.
文摘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.
文摘Grease life refers to the time it takes for the grease to lose its ability to keep the lubrication due to grease degradation. As grease life is generally shorter than fatigue life of bearing, the service life of grease-lubricated rolling bearings is often dominated by grease life. When designing a bearing systemolecular weightith grease lubrication, it is necessary to define the operating conditions limits of the bearing, for which grease life becomes a determining factor. Prolongation of grease life becomes an especially important challenge when the bearing is to be operated trader high-speed, high-temperature, and other severe conditions. Selecting a number of commercially sold greases composed of varying base oils, the author evaluated their properties and analyzed how each property affected the grease life by performing a multiple regression analysis. The optimum grease composition to best exploit each property was also examined. The results revealed among others that one would need to first determine the base oil type and then maximize ultimate bleeding while minimizing the evaporation rate.
文摘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.
基金Supported by the National Natural Science Foundation of China(21506078,21506082)China Postdoctoral Science Foundation(2016M591786,2016M601739)
文摘Titanium complex greases were prepared by using naphthenic mineral oil and polydimethylsiloxane as the mixed base oil. The effect of polydimethylsiloxane molecular weight and polydimethylsiloxane content in mixed base oil on the physicochemical and tribological properties of titanium complex greases was investigated.As compared to the sole mineral oil-based titanium complex grease, the use of polydimethylsiloxane(H201-350)as a co-base oil increased the dropping point from 310 to 329℃, decreased the oil separation from 3.7% to 2.3%,reduced the corrosion extent, and obviously improved the tribological properties. When the mixed oil-based titanium complex grease was used as a lubricant, lubricating films of polydimethylsiloxane were probably formed on the surfaces of friction pairs, giving good lubricating property.
基金financially supported by the program of the General Logistics Department (AX214C002)the Chongqing Postgraduate Research and Innovation Project (CYB16130)the Young Scientist Fund of Logistical Engineering University (YQ16-420801)
文摘The tribological properties of graphene(GN) and graphite(G) as lubricant additives in lithium greases were investigated with a four-ball tribotester. The micro-morphology as well as the content and chemical state of elements on the worn surfaces was characterized by scanning electron microscopy(SEM) and X-ray photoelectron spectroscopy(XPS). The results showed that the tribological performance of lithium grease could be significantly improved by the addition of graphene. During the friction process, an adhesion film and a deposition film consisted of graphene as well as a tribochemical reaction film composed of FeO, Fe_2O_3, FeOOH and LiOH could be formed on the tribosurface, and these complex films were responsible for the improved tribological performance of lithium grease.
基金Project supported by the New Century Excellent Talents in University(Grant No.NCET-08-0841)the National Natural Science Foundation of China(Grant Nos.60778034,60877038,and10804077)+2 种基金the Beijng Natural Science Foundation(Grant No.4082026)the Research Fund for the Doctoral Program of Higher Education(Grant No.200804250006)the State KeyLaboratory of Heavy Oil Processing,China University of Petroleum(Grant No.2008-14)
文摘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.
文摘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.
文摘Till now, most part of the biodiesel is produced from the refined vegetable oils using methanol as feedstock in the presence of an alkali catalyst. However, large amount of waste edible oils and grease are available. The difficulty with alkali-catalyzed esterification of these oils is that they often contain large amount of free fatty acids （FFA）, polymers and decomposition products. These free fatty acids can quickly react with the alkali catalyst to produce soaps that inhibit the separation of the ester and glycerine. An esterification and transesterification process is developed to convert the high FFA oil to its monoesters, The first step, the acidcatalyzed esterification with glycerine and these FFA reduces the FFA content of the oil and grease to less than 3%, and then an azeotropic distillation solvent is used to remove the water. The major factors affecting the conversion efficiency of the process such as glycerol to free fatty acid molar ratio, catalyst amount, reaction temperature and reaction duration are analyzed, The second step, alkali-catalyzed transesterificatiou process converts the products of the first step to its monoesters and glycerol, and then the glycerol is recycled for utilization in the first step. Technical indicators of the biodiesel product can meet the ASTM 6751 standard.
文摘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.
文摘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%.
基金Sponsored by State Key Laboratory of Solid Lubrication Opening Foundation(Grant No.0303).
文摘Effects of nano SbSbS4particles on contact fatigue life of a steel ball were evaluated on a self-made ball-rod contact fatigue tester. The anti-fatigue mechanisms of SbSbS4 additive were analyzed by means of SEM and EDAX. It was shown that, when the grease contained SbSbS4, contact fatigue life was improved compared with that of base grease. Nanoparticle absorption action, nanoparticle infiltration action, and extreme pressure and anti-friction performance, explained why SbSbS4 increased the contact fatigue life of the steel ball tested.
文摘Ball bearings’ rating life is reduced with the presence of hard particle contaminants in the lubricant. This life reduction is taken into account when calculating the modified rating life by using the contamination factor. The contamination factor is based on a general characterization of the lubrication conditions but the impact of contaminant’s variables such as size, hardness and concentration level is not determined in detail. In this work, greases contaminated with hard corundum (alumina, Al2O3) particles of different sizes are tested aiming at finding a pattern in the relationship between particle sizes’ and wear’s progress. A laboratory rig is utilized for these tests and vibration analysis tools regarding bearings’ condition and estimated residual life are being assessed. After the tests, optical inspections using a stereoscope verify the vibration analyses results. The experimental results show that wear is progressing faster when smaller particles are used. The crystalline structure of the corundum and the different degree of brittleness of the contaminants seem to be the reasons for this behavior, whereas severe abrasion and deformation of the raceways have been detected.
文摘CeF3. CaF2, (CF)n, SbF3, and CeO2 were selected as the high temperature solid additives in a lithium grease, and their friction, wear, and extreme pressure properties were evaluated on an Optimol-SRV wear tester. The effect of additive on the fiber structure of soap was studied by means of the transmission electron microscopy(TEM). The corrosive property of grease containing additive was evaluated by copper strip corrosion test. Thermal decomposition behaviors of the additives were studied by thermogravimetry(TG) tester. The adhesive strength of rubbing surface film was measured by automatic scratch tester and the wear surface was detected by means of X-ray photoelectron spectroscopy (XPS). The test results showed that the grease containing CeF3 has good anti-wear, anti-friction, and EP performances, and has high adhesive strength of rubbing surface film.The greases containing CaF2 or (CF)n are good in antiwear and anti-friction properties, but poor in extreme pressure function. The tribological properties of the grease containing SbF3 are decreased.And the addition of CeO2 in grease was useless. Finally the mechanism of fluoride additive was proposed in this paper.
