Four-ball Friction Tester Research Articles

Tribological Properties and Lubrication Mechanism of Nickel Nanoparticles as an Additive in Lithium Grease.

Nanomaterials exhibit intriguing tribological performance and have received particular attention in the lubrication field. However, little research has been found that surveyed the application of nanometer Ni in lithium grease. In this study, nanometer Ni with an average size of 100 nm was synthesized by the direct reduction method and dispersed in lithium grease. The feasibility of nanometer Ni as a grease additive in different lubrication scenarios was evaluated by a four-ball friction tester and a TE77 reciprocating friction tester. The lubrication mechanism was analyzed based on the evaluated physical properties of lithium grease and the characterization of the wear surface. The tribology test results showed the tribological properties of lithium grease were enhanced after introducing nanometer Ni. When the dosage was 0.2 wt%, the friction-reducing and anti-wear properties of point-to-point contact increased by 34.8% and 35.2%, respectively, while those of the point-to-flat contact increased by 28.8% and 38.7%, respectively. Our work not only provides theoretical guidance and practical reference for the utilization of nanometer Ni in grease, but also explains several possible lubrication mechanisms of nanomaterials in grease.

Tribological performances of α-Zrp as the additive of the grease used for mine hoisting wire rope

Considering that the lubrication failure of the wire rope in mine hoisting is easy to occur under harsh conditions, which will accelerate the wear of the wire rope and seriously threaten the safety of hoisting. Therefore, the anti-wear characteristics of α-type zirconium hydrogen phosphate (α-ZrP) on the wire rope grease used for mine hoisting were studied. First, the modified greases with different mass fractions of α-ZrP were prepared, and then the dispersion of α-ZrP in the original grease was discussed. Finally, the friction and wear properties of the α-ZrP modified greases were investigated by the four-ball machine, fretting wear test rig of steel wire and sliding wear test rig of wire rope. The results show that the coefficient of friction (CoF) increases first and then decreases with the increase of α-ZrP added in the grease in the four-ball friction test and the sliding wear test of wire rope. In addition, it will agglomerate in the original grease when the addition of α-ZrP is too large, which will worsen the lubrication effect, and the wear mechanism also changes from abrasive wear to abrasive wear and adhesive wear. Moreover, dry friction may occur between steel wires when the additive content is low, thus accelerating their wear. The improvement effect of the original grease is the most significant for the mine hoisting wire rope when the mass fraction of α-ZrP is 2.5% according to the principal component analysis theory.

Extraction and expression of deformation features for wear images from four-ball friction test: For classification purpose

The shape characteristics of wear spot in the four-ball wear test are often qualitatively identified by human testers based on experience, which are subjective, unquantifiable and biased. This paper proposes an automated method for extracting and expressing the shape features, which is effective for the deformed classification of the wear images. First, the wear spot is segmented from the background, and the geometric parameters of the wear spot are extracted. Based on this, the optimal standard wear spot which match the segmented (or actual) wear spot best is constructed. The established feature variables (i.e. abnormality rate and eccentricity rate) are used to quantitatively assess the deformation degree of segmented wear spot, by comparing the segmented wear spot with the constructed standard wear spot. Finally, Kmeans clustering algorithm is used to verify the validity of deformation features in the classification application. Simulation test results show that feature variables are valuable for identifying the deformation of wear images, and three effect evaluation indicators (CH/SI/DB) shows that the classification effect of the wear images is better.

Highly dispersed dialkyl dithiophosphate-functionalized ZIF-8 particles as additives of the lubricating oil

PurposeThis paper aims to propose a new strategy to functionalize zeolitic imidazolate frameworks (ZIF-8) to improve its dispersion stability and tribological properties in lubricating oil.Design/methodology/approachDialkyl dithiophosphate polydopamine ZIF-8 (DDP@PDA@ZIF-8) was prepared via mussel-inspired chemistry and the Michael addition reaction. The tribological properties of DDP@PDA@ZIF-8 as an additive in the white oil were evaluated with four-ball friction and wear tester at different temperatures. The worn surface was analyzed using X-ray photoelectron spectrum (XPS).FindingsThe as-prepared DDP@PDA@ZIF-8 shows high dispersion stability in the white oil. Tribological results confirmed that the DDP@PDA@ZIF-8 exhibited a small wear scar diameter at 25°C. However, excellent friction reduction and anti-wear properties were observed at 75°C. The XPS result indicates that a series of tribochemical reactions occurred on the worn surface, forming the complex protective film.Originality/valueThis paper provides a study of highly dispersed ZIF-8 as lubrication additives.

Study on the preparation and tribological properties of BN@C-OA nano-additive lubricants

The advanced nano-additives can improve the lubrication performance of nanolubricants efficiently, which could greatly reduce energy consumption. Here, we prepared the BN coated with carbon layer (BN@C) by a novel hydrothermal coating method with pristine BN nanosheets as matrix material and glucose as carbon source. And the BN@C exhibited excellent lubrication performance as a lubricant additive. In order to investigate the tribological properties, BN@C was modified with oleic acid as a surfactant, and the friction tests were carried out on an MRS-10A four-ball friction and wear tester. Benefitting from the stable dispersity, ultrasmall particle size and the surface carbon layer of BN@C-OA, the lubrication performance was significantly improved. More impressively, BN@C-OA could enter the interface of friction pairs. The interlayer sliding occurred to improve the anti-wear and anti-friction properties. This study could provide a new avenue to synthesize the coating-containing nanocomposite additive to promote the lubrication properties of nanoparticles in oil.

Preparation, characterization and tribological properties of coal indirect liquefied diesel soot modified by oleylamine

Coal indirect liquefied diesel soot (Fischer-Tropsch synthesis diesel soot, F-T DS) was collected by burning coal indirect liquefied diesel (F-T Diesel) with a self-made soot trap device in the laboratory. F-T DS was modified with oleylamine modification method to obtain oleylamine modified F-T DS (F-T DS-OLA). The effect of 10# white oil with F-T DS or F-T DS-OLA on the lubrication performance was investigated using a long-time four-ball friction and wear tester. The composition, structure, morphology and tribological mechanism for F-T DS and F-T DS-OLA had been studied by using FTIR, XPS, Raman, XRD and other instruments. The results show that F-T DS modified by oleylamine can increase lipophilic groups. The average particle size of F-T DS and F-T DS-OLA are 64 nm and 38 nm respectively. The main structure component is amorphous carbon with a small amount of graphite crystallites. The average friction coefficient (AFC) first decreases and then increases as the mass fraction of F-T DS and F-T DS-OLA increases in 10# white oil. When the mass fraction of F-T DS is 0.6 wt%, the AFC reaches the minimum, and the AFC reaches the minimum when the mass fraction of F-T DS-OLA is 0.8 wt%. The average wears scar diameter (AWSD) of the steel ball also decreases first and then increases. F-T DS reaches the minimum at 0.6 wt%, and F-T DS-OLA reaches the minimum at 0.8 wt%. Comprehensive AFC and AWSD analysis, the antifriction and anti-wear effect of F-T DS is greatly improved after oleylamine modified. Through the analysis of the surface morphology of the upper ball wear scar and valence state of the surface elements, it can be obtained that the wear scar of the upper test ball becomes shallow after adding F-T DS-OLA. A lubricating film containing C, O and iron oxides is formed on the surface, which can improve the antifriction and anti-wear effects of 10# white oil.

Tribological Property of Biocarbon-Based Magnesium Silicate Hydroxide Nanocomposite as Lubricant Additive at Different Concentrations of Additive and Dispersant

Abstract The tribological performance of biocarbon-based magnesium silicate hydroxide nanocomposite was examined as a lubricant additive by using a four-ball friction and wear tester. The effect of different concentrations of additives and dispersants was evaluated. The results show the nanocomposite exhibits excellent anti-wear performance and the optimal value is proposed when the content of additive and dispersant is 0.7 wt% and 3 wt% respectively. Through analyzing the friction surfaces by scanning electron microscope and Raman, we proposed the additives acted by a combination of “bearing,” “third body,” and sliding effect to achieve outstanding tribological properties.

Impact of Boron Nitride Nanoparticles on the Wear Property of Lithium Base Grease

In order to satisfy the requirement of lubrication under extreme working conditions (e.g., heavy load, high speed, and high temperature), a lubricating grease containing boron nitride (BN) nanoparticles was prepared by ultrasonic dispersion. And the effect of different content of nanoboron nitride on the tribological properties of lubricating grease was studied by means of a four-ball friction tester. The results showed that the grease containing 0.60 wt.% BN nanoparticles had the best anti-friction performance, as well as the smallest friction coefficient and wear scar radius. Additionally, a Raman spectrometer, scanning electron microscope, and three-dimensional profilometer were used to analyze the chemical composition, characterize the morphology of the wear scar in the steel balls after the friction tests, and the analysis results show that BN nanoparticles can not only produce lubricating film to protect friction pairs, but also its layered structure is easy to cause sliding of the friction pairs under the action of friction. Therefore, under the synergism of lubricating film and layered structure, the friction coefficient is obviously reduced and the friction reduction performance of grease is improved.

Absorption of fuel containing esters on iron surface based on molecular simulation and its effects on lubricity

ABSTRACT Appropriate amount of methyl myristate (C14), methyl palmitate (C16), methyl stearate (C18), methyl oleate (C18:1), methyl linoleate (C18:2), and methyl ricinoleate (C18:1OH) were blended into low-sulfur diesel to conduct the lubrication experiment on four-ball friction tester. Then, based on Materials Studio software, adsorption models of n-tetradecane with various esters on the iron surface were built up. The lubrication performance of diesel blends with 1.0%, 2.0%, 3.0%, and 5.0% (volume fraction) of different esters was improved with the increase of the esters’ fraction. Meanwhile, it is revealed by molecular simulation that the adsorption energy in the film was augmented greatly with the increase in the volume fraction of C14 ester; however, the cohesive energy varied slightly. Therefore, the ester fraction puts more influence on the adsorption energy. Moreover, lubrication experiment of low-sulfur diesel with a given fraction of different esters indicated that the diameter of worn scars decreased with the increase in the length of carbon chain and the number of unsaturated C = C double bond, and at the presence of polar group as well. While via the molecular simulation, the adsorption energy in the films of n-tetradecane with 5% various esters was roughly comparable, but the cohesive energy changed with the carbon chain length, the degree of unsaturation, and the polar group. Namely, the variation of ester composition causes a significant difference in the cohesive energy. Consequently, both the increase of ester fraction and the change of ester composition are effective measures to improve the lubricity of low-sulfur diesel fuel.

In Situ Study of Structure-Activity Relationship between Structure and Tribological Properties of Bulk Layered Materials by Four-Ball Friction Tester.

Encouragingly, a lot of research studies have demonstrated that two-dimensional (2D) nanosheets applied as an additive in oils show preferable friction-reducing and wear resistance performance. However, the current issue was that an elusive way could be adopted to probe the structure–activity relationship between the structure and tribological properties of bulk layered materials due to the structural evolution during friction testing. In this study, we studied the structure–activity relationship between the structure and tribological properties of bulk layered materials (graphite, h-BN, WS2, and MoS2) by an in situ four-ball friction tester. The morphological and structural changes of the layered materials after in situ four-ball-milling were detected by a series of characterizations. This study revealed the friction-induced nanostructural evolution behaviors of bulk layered materials by a four-ball mode.

Ultrasound-assisted Li+/Na+ co-intercalated exfoliation of graphite into few-layer graphene.

In this work, we developed a novel approach for few-layer graphene by employing Li+/Na+ co-intercalated exfoliation assisted by ultrasound method. The experiments were conducted under the ultrasonic power of 300W and the frequency of 40kHz without the participation of any organic solvent. The effect of Li+/Na+ proportion on the exfoliation of graphite was intensively investigated. The structure and morphology of the as-exfoliated graphene nanosheets (UGN) was determined by a series of characterizations. The results showed that the thicknesses of the as-exfoliated graphene nanosheets were about 2.38-2.56nm (about 7-8 layers) at the optimal Li+/Na+ ratio. The potential application of the as-exfoliated graphene nanosheets as additive in grease was evaluated by four-ball friction tester. The results demonstrated that the antifriction and antiwear performances of the grease with 0.06wt% graphene were significantly improved by 21.35% and 30.32% relative to pure grease, respectively. The friction mechanism was proposed by detecting the worn surfaces.

Effect of paraffin oil with XGnP and Fe2O3 nanoparticles on tribological properties

Recent studies have utilized different nanoparticle elements in oil added substances with base fluid, which improves their lubricating properties. In this study, the four-ball friction tester and viscosity nanofluid, which is prepared with the suspension iron oxide nanoparticles (Fe2O3) and xGnP (exfoliated nanographene) nanoparticles, in paraffin oil as base fluid. The viscosity and friction coefficient of lubricating properties of nanoparticles that was added at varying concentrations of 0.4% (1.6 g), 0.8% (3.2 g), and 1.2% (6.4 g) by weight of (Fe2O3) and xGnP with the size of less than 10 nm was added for 400 g of paraffin oil. The viscosity of nanolubricant at the temperature range (40 °C−100 °C) was increased at a percentage of 0.29%, 0.08% in both nanoparticles XGnP and Fe2O3. To measure the corrosion resistance and friction rate, a four-ball test is used nanolubricant was observed to influence these properties of paraffin oil for all concentration levels.

Effect of different preparation processes on tribological properties of graphene

Two processes of physical liquid phase stripping and chemical redox reduction were used to obtain graphene sheets. Fourier transform infrared spectroscopy and Raman spectroscopy test methods were used to compare and analyze the structure and disorder of graphene. The obtained graphene was modified with oleic acid and stearic acid. The dispersion stability of graphene as a lubricating oil additive was investigated by natural sedimentation method and spectrophotometry. The tribological properties of the graphene dispersion were investigated by a four-ball friction and wear tester. Scanning electron microscope and energy spectrometer were used to characterize and analyze the microscopic morphology and composition of the worn surface. The results showed that the modified liquid phase stripping graphene demonstrated the best anti-wear and anti-friction properties of the dispersion, the lowest friction coefficient is 0.0677, and the average friction coefficient is reduced by about 26%.

Friction and wear property of lithium grease contained with copper oxide nanoparticles

In general, the friction and wear property of lubricating grease has great influence on the usability of bearings. Copper oxide (CuO) was added in the base grease to prepare composite grease, followed by the investigation of anti-fraction properties to analyze the role of CuO and identify the optimum content. CuO nanoparticles were characterized first by series of techniques, including surface area and micropore analysis, particle size analysis, X-ray diffraction (XRD) analysis, atomic force microscope (AFM) scanning, infrared and Raman spectroscopic analysis. Composite greases were prepared by added CuO nanoparticles into the base grease, then examined via AFM and infrared spectrum. The friction and wear property of composite greases was investigated by friction test on a four-ball friction test machine. Scanning electron microscope (SEM) and three-dimensional (3D) profilometer were utilized to observe the wear surface and helped to unravel the anti-friction mechanism. The formation of oil films on wear surface was identified and investigated by Raman spectrum and 3D morphology height, demonstrating the anti-friction effect. When CuO content was 0.60 wt%, only a small number of furrows were observed on the wear surface. The composite grease showed the lowest average friction coefficient and wear scar diameter, which were 30% and 13% lower than the base grease, respectively. According to 3D morphology scanning and Raman spectrum, CuO-contained oil films were detected on the wear surface. This lowered furrow number and the roughness of wear surface, demonstrating the great role of CuO in the enhanced anti-friction property of composite grease.

Engine Oil Degradation Induced by Biodiesel: Effect of Methyl Oleate on the Performance of Zinc Dialkyldithiophosphate.

In the present work, the oxidation stability of blends of methyl oleate, zinc dialkyldithiophosphate (ZDDP), and a high viscosity index mineral base oil was determined by the method of a rotating pressure vessel, while the antiwear abilities were evaluated on a four-ball friction tester. Thereafter, the thermal decomposition characteristics and oxidation products of the oxidized blends were analyzed by a thermogravimetric analyzer and a gas chromatograph coupled to a mass spectrometer, respectively. The results showed that the antioxidation ability of ZDDP was substantially improved by methyl oleate, while the antiwear capacity is markedly impaired by methyl oleate. Furthermore, the thermal decomposition characteristics and oxidation products of ZDDP-containing oils were altered by methyl oleate. The present study evidently convinced that chemical interactions between ZDDP and methyl oleate had occurred, which were attributed to the increased antioxidation ability and decreased antiwear capacity of ZDDP in oils contaminated with methyl oleate.

Preparation and Tribological Properties of Carbon-Coated WS2 Nanosheets.

WS2-C is produced from a hydrothermal reaction, in which WS2 nano-sheets are coated with carbon, using glucose as the carbon source. In order to investigate the tribological properties of WS2-C as a lubricant additive, WS2-C was modified by surfactant Span80, and friction tests were carried out on an MRS-10A four-ball friction and wear tester. The results show that Span80 can promote the dispersibility of WS2-C effectively in base oil. Adding an appropriate concentration of WS2-C can improve the anti-wear and anti-friction performance of the base oil. The friction coefficient reached its lowest point upon adding 0.1 wt % WS2-C, reduced by 16.7% compared to the base oil. Meanwhile, the wear scar diameter reached its minimum with 0.15 wt % WS2, decreasing by 26.45%. Moreover, at this concentration, the depth and width of the groove and the surface roughness on the wear scar achieved their minimum. It is concluded that WS2-C dispersed in oil could enter friction pairs to avoid their direct contact, thereby effectively reducing friction and wear. At the same time, WS2-C reacts with the friction matrix material to form a protective film, composed of C, Fe2O3, FeSO4, WO3, and WS2, repairing the worn surface.

Synthesis and Characterization of Polycaprolactone Modified Trimellitate Nano-Lubricant.

The application of trimellitate (TMT) in the lubricating oil industry was seriously restricted because of its low viscosity index. In the work reported here, polycaprolactone (PCL) soft chain was embedded into the structure of TMT in order to improve the viscosity index. Characterization of the polymers was done by proton nuclear magnetic resonance (1H-NMR), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TG). Results supported our design and were consistent with the target product structure. Performance of the prepared materials was evaluated by standard ASTM methods. Noticeably, the viscosity index of the modified TMT increased from 8 to above 100, which greatly improved its viscosity-temperature performance. As the initiator, tetrabutyl titanate (TBT) can not only complete the ring-opening polymerization of caprolactam (ε-CL) at room temperature, but also generate nano-TiO2 by-products with excellent anti-wear properties during the synthesis. Characterization of the nano-TiO2 was done by scanning electron microscopy (SEM), FT-IR, TG and X-ray diffractometry (XRD). The friction and wear tests were conducted on a four-ball friction tester and the surface morphologies of worn surfaces were investigated by SEM. The experimental results clearly showed that the modified TMT showed better viscosity index and thermal stability as compared to the unmodified one. The modified nano-TMT base oil features excellent lubricant performance with good viscosity–temperature properties, thermal stability and anti-wear properties.

Investigate on the tribological properties of additives in tetra polyurea grease

In this paper, the effects of five different additives on the tribological properties of tetra polyurea greases prepared under the same conditions were studied. The friction coefficient, friction force, wear scar diameter, PB and PD of the tetra urea greases prepared under the conditions of the five additives were examined by a four-ball friction tester. The steel mesh oil separation of the tetra polyurea grease prepared with different additives under the same conditions was tested and compared with the tetra polyurea grease prepared without additives. The results showed that the type and amount of additives basically had no effect on the steel mesh oil separation of the tetra plolyurea grease. The steel mesh oil separation content was maintained at 0.6% around. The tetra polyurea grease prepared with the additive of fluorinated graphite has excellent lubricating properties and abrasion resistance compared to several other additives. In addition, the tribological properties of tetra polyurea grease prepared with the constant change of fluorinated graphite content are also constantly changing. The wear scar diameter at the content of 2% is 0.3146mm. At this time, the friction coefficient and friction force value are the minimum.

Tribological Performance of Phosphonium Ionic Liquids as Additives in Lithium Lubricating Grease

Three oil–miscible phosphonium ionic liquids with different structures were synthesized and used as additives for a Poly Alpha Olefin 10 (PAO 10) lithium lubricating grease. Different from other additives, the ionic liquids participated in saponification and were trapped in the entanglement network formed by the thickener. The effects of the ionic liquids on the rheological properties of lithium lubricating grease were characterized through a small-amplitude oscillatory shear (SAOS) measurement. The tribological performances of the lubricating greases were determined on a four-ball friction tester. The addition of phosphonium ionic liquids caused a decrease in the storage (G′) and loss (Gʺ) modulus of lubricating grease. However, the ionic liquids were found to be effective lubricant additives for improving the friction-reducing and antiwear properties of PAO 10 lithium lubricating grease.

The synthesis of magnesium silicate hydroxide with different morphologies and the comparison of their tribological properties

Abstract The tribological properties of magnesium silicate hydroxide (MSH) synthesized at different hydrothermal conditions as lubricant additives were investigated. The morphologies and structures of synthetic MSH were characterized by SEM, TEM, XRD and XRF. The tribological properties of MSH were evaluated using a four-ball friction and wear tester. It is found that different morphologies and structures of MSH are formed through different mechanisms depending on the temperature and reaction-time. Using synthetic MSH as an additive forms a tribofilm on the sliding surface and significantly improve the tribological properties of the oil. MSH with a tubular crystal structure has the best anti-wear property because it is more likely to deposit, adsorb and spread on the friction surface, and thus forms a denser tribofilm.