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Helical rolling (HR) with high temperature is an efficient forming process to produce bearing steel balls with diameter more than 25 mm. This article discusses the advantages and disadvantages of two HR roller designing methods: single side variable lead method and double side variable lead method. Finite element (FE) simulations of HR processes based on the two methods indicate that the double side variable lead method has higher forming accuracy and is more suitable for forming bearing steel balls. Experiments based on the double side variable lead method are carried out to verify the validity of FE model. The distributions of strain and stress, temperature evolution and rolling force parameters are analyzed based on the FE method. Axial motion analysis shows that the axial velocity of the rolled piece is closely related to axial push velocity of roller convex rib. Microstructure evolution indicates that grains near ball connector area and ball surface get refined due to drastic plastic deformation. The forming accuracy of HR process including radius deviations and ovalities of three cross sections are measured. The statistical results indicate that radius deviation of rolled balls can be controlled within 0.1 mm and ovality can be as small as within 1%. Effects of roller parameters on forming accuracy are analyzed including volume coefficient at groove closed position, forming zone length and starting height of convex rib. Forming accuracy gets better with the increase of volume coefficient, the increase of forming zone length, and the decrease of staring height of convex rib. [ABSTRACT FROM AUTHOR]

The aim of this study was to assess intra-arch mandibular dimensional changes that may occur during mouth opening using cone beam-computed tomography (CBCT). Fifteen patients in need of any type of treatment whose execution considered a pre- and post-CBCT assessment consented and were enrolled. CBCTs were taken with the following settings: 90 kV, 8 mA, field of view (FOV) 140 by 100 mm (height and diameter), Voxel size 0.25 mm (high resolution). The pre-CBCT was executed in the maximum mandibular opening (MO), while the post-CBCT was in the maximum intercuspation (MI). A thermoplastic stent with radiopaque fiducial markers (steel ball bearings) was fabricated for each patient. Measurements were made using radiographic markers between contralateral canines and contralateral first molars and between ipsilateral canines and first molars on both sides. Paired t-tests were performed to evaluate the difference between open and closed positions on these four measurements. In the MO position were registered a significative tightening of the mandible at the canine (−0.49 mm, SD 0.54 mm; p < 0.001) and molar points (−0.81 mm, SD 0.63 mm; p < 0.001) and a significative shortening of the mandible on the right (−0.84 mm, SD 0.80 mm; p < 0.001) and left sides (−0.87 mm, SD 0.49 mm; p < 0.001). Within the study limitations, mandibular flexure determined a significant shortening and tightening between maximum intercuspation to maximum opening positions. Mandibular dimensional changes should be considered in light of other patient factors in the treatment planning of implant positioning and long-span complete arch implant-supported fixed prostheses in order to avoid technical complications. [ABSTRACT FROM AUTHOR]

Polyimide-bearing retainer has been successfully used in space environment. However, the structural damage of polyimide induced by space irradiation limits its wide use. In order to further improve the atomic oxygen resistance of polyimide and comprehensively investigate the tribological mechanism of polyimide composites exposed in simulate space environment, 3-amino-polyhedral oligomeric silsesquioxane (NH2-POSS) was incorporated into a polyimide molecular chain and silica (SiO2) nanoparticles were in situ added into polyimide matrix and the combined effect of vacuum environment, and atomic oxygen (AO) on the tribological performance of polyimide was studied using bearing steel as the counterpart by a ball on disk tribometer. XPS analysis demonstrated the formation of protective layer induced by AO. The wear resistance of polyimide after modification was enhanced under AO attack. FIB-TEM confirmed that the inert protective layer of Si was formed on the counterpart during the sliding process. Mechanisms behind this are discussed based on the systematic characterization of worn surfaces of the samples and the tribofilms formed on the counterbody. [ABSTRACT FROM AUTHOR]

This article presents the results of a study on resistance to motion in a multi-stage planetary transmission, built with lightweight structural materials such as aluminum alloy 2017, with bearing nodes featuring steel ball bearings made from X65Cr14 alloy and lubricated with molybdenum disulfide powder. Details of the planetary gear construction were presented, followed by operational performance tests. During the performance tests, the temperature of the running transmission was gradually lowered with liquid nitrogen to as low as − 190 °C. The analysis covered, among others, the power consumption of the mechanism as a function of temperature. The results were compared with the parameters of the mechanisms already working in space. The measurements were carried out to confirm the applicability of the gearing in drive systems of manipulators intended to operate in open space or under extraterrestrial conditions such as on Mars. [ABSTRACT FROM AUTHOR]

Bearing elements under rolling contact fatigue (RCF) exhibit microstructural features, known as white etching bands (WEBs) and dark etching regions (DERs). The formation mechanism of these microstructural features has been questionable and therefore warranted this study to gain further understanding. Current research describes mechanistic investigations of standard AISI 52100 bearing steel balls subjected to RCF testing under tempering conditions. Subsurface analyses of RCF-tested samples at tempering conditions have indicated that the microstructural alterations are progressed with subsurface yielding and primarily dominated by thermal tempering. Furthermore, bearing balls are subjected to static load tests in order to evaluate the effect of lattice deformation. It is suggested from the comparative analyses that a complete rolling sequence with non-proportional stress history is essential for the initiation and progression of WEBs, supported by the combination of carbon flux, assisted by dislocation and thermally activated carbon diffusion. These novel findings will lead to developing a contemporary and new-fangled prognostic model applied to microstructural alterations. [ABSTRACT FROM AUTHOR]

In this paper, the effect of minimum quantity lubrication (MQL) on tool wear in the hard turning of 100Cr6 ball bearing steel has been investigated and the results are compared to those obtained through dry and wet lubrication methods. The tools used in the study include CBN and nano-CBN tools. The nano-CBN tool is a new generation of CBN tools manufactured based on nanotechnology. No research has been conducted on the impact of this tool on machining processes. The ratio of NCBN tool flank wear land to the CBN tool flank wear land in dry, wet and MQL methods were 0.18, 0.23 and 0.28, respectively. The wear of CBN tool in turning with MQL was 2.8 times greater than the wear of nano-CBN tool in dry machining. In turning with nano-CBN tool, the height of the tool flank wear with MQL was reduced by 22% and 7% concerning wet and dry methods, respectively, while these values were 51% and 24%, respectively, for the CBN tool. The CBN tool wear depends on the lubrication method but the wear of the nano-CBN tool is almost independent of the lubrication method. [ABSTRACT FROM AUTHOR]

Precision steel balls enable the bearings of machine parts to maintain their relative position, and they reduce operating time during relative movement, reduce friction force, improve efficiency and extend service life. Inspections are mainly conducted manually by eye, with classification of detected defects. Such visual inspections may cause accuracy imbalances and cost problems. For this reason, deep learning technology has been introduced into production lines. The innovation of the research presented here was to use an object-detection model to detect defects on the surface of steel balls to reduce manpower consumption and improve accuracy in detection of steel ball defects. The "You Only Look Once" algorithm (YOLOv5) was used, along with a fast-region convolutional neural network (R-CNN), finally obtaining an average recall rate of 99% and a detection accuracy rate of 93%. The results showed the YOLO algorithm to be more capable of judging good products. The contribution of this research, the efficiency of production lines can be enhanced through better detection of flaws on steel balls. The comparison showed that YOLO and Faster R-CNN are better than traditional IP detection, and the above results constitute an 80% improvement in the current detection system of the partner company. [ABSTRACT FROM AUTHOR]

The wear resistance of 440C bearing steel balls significantly impacts the reliability of bearings. Our method for increasing the wear resistance of steel balls combines mechanical alloying to create nanogradient structures with ZrO 2 doping on the surface of the steel balls. The results revealed that ZrO 2 formed mechanical alloying on the surface of the steel balls. Under all loads, the processed samples exhibited excellent wear resistance. Compared to untreated samples, the wear of processed samples subjected to 20, 40, and 60 N loads decreased by 28.82 %, 50.25 %, and 50.79 %, respectively. The existing literature indicates that adding ZrO 2 powder during mechanical alloying is a promising method for improving the friction performance of bearing steel balls. • The processed sample had a maximum microhardness of 803.4 HV, while the untreated sample had increased by 22.13 %. • The micro pits, nano-gradient structure, and ZrO 2 all improved the wear resistance of steel balls. • The friction experiment revealed that the processed sample had a 50.79 % lower wear rate than the unprocessed 60 N load. [ABSTRACT FROM AUTHOR]

Polymer composites are common materials for tribological components, even at relatively high operating temperatures. One advantage is the possibility to add low friction additives, such as PTFE, to the base material. In this paper the influence of such additives was studied, with focus on surface and sub-surface damages. The polymer composites were PPS with glass fibers (PPS-F), PPS with glass fibers and PTFE (PPS-L) and PEEK with carbon fibers, graphite and PTFE (PEEK-L). A reciprocating ball-on-disc test set-up, with ball bearing steel balls as counter material, was used with 5 N and 15 N normal load. The tests were run for 2,000 and 10,000 cycles in room temperature, 80 °C and 120 °C. PPS-F showed high friction (µ ≈ 0.4–0.5) and severe surface damage of both the polymer and the counter surface. Sub-surface cracks, detachment of fibers from the polymer and a deformed surface layer was revealed, when studied in cross section. The load and temperature had negligible effect on the friction, however a higher temperature resulted in more surface damage of the PPS-F. PPS-L and PEEK-L showed relatively low friction (µ ≈ 0.1) and superficial surface damage. XPS analysis revealed a thin tribofilm of PTFE in the wear track for PPS-L. [ABSTRACT FROM AUTHOR]

A dicationic liquid (DIL) was synthesized and used as a base lubricant. IL-grafted graphene oxides (MGO) were manufactured as an additive to the DIL lubricant. Then, the MGO/DIL was applied as a lubricant for the surface contact between a stainless steel ball and bearing steel. The tribological performance of MGO/DIL was measured and compared to those from a monocationic liquid (MIL) based lubricant. The MGO/DIL lubricant produced better friction and wear performance at room temperature but poor wear at 100 °C. Through novel instrumentation techniques, it could be found that when DIL is exposed to air at higher temperatures, more oxygen is adsorbed into DIL, which accordingly reacts with underlying bearing steel, resulting in critical surface oxidation and wear. • The DIL [(C 1 im) 2 C 6 ][NTf 2 ] 2 lubricants and IL-grafted GO additive were synthesized • Wear and COF of steel alloy were investigated at room temperature and 100 °C • Compared to MIL, the DIL showed better thermal stability but poor friction and wear • Due to its doubly charged cation, the DIL produced severe wear at high temperature [ABSTRACT FROM AUTHOR]

This study explored 440 C steel ball wear resistance via mechanical ball milling with Al 2 O 3 powder. We used a customized grinding jar to compare heat-treated, untreated, Al 2 O 3 -treated, and Al 2 O 3 + distilled water-treated samples. We assessed wear resistance, residual stress, microhardness, and surface roughness. Results revealed that the combination of distilled water and Al 2 O 3 powder induced nanostructured stacking faults, increased dislocation density, and grain refinement. Treated samples had a > 200 µm thick strengthened layer, − 355 MPa residual stress, and max microhardness of 776.6 HV. These samples showed superior wear resistance, reduced wear volume, and lower friction. This suggests that Al 2 O 3 powder and distilled water in mechanical ball milling enhance ball mechanical part wear resistance, offering industrial potential. [ABSTRACT FROM AUTHOR]

Working conditions such as lubrication, preload, and rotational speed have important influence on vibration and temperature rise of the spindle motor. In this study, controlled variable experiments are carried out on the silicon nitride (Si3N4) full-ceramic ball bearing and steel bearing of the same type, and the vibration signal characteristics and temperature rise of the spindle motor are tested and analysed, by changing the lubrication conditions, preloads, and rotational speeds of the spindle motor. Through the research, it is found that as the rotational speed increases, the vibration velocity of the Si3N4 full-ceramic bearing spindle motor under different preloads and lubrication conditions shows an overall increasing trend; kurtosis generally presents a downward trend and gradually flattens, indicating that although the vibration velocity increases at high speeds, the vibration signal shows a relatively stable state. As the rotational speed increases, the difference of vibration velocity under the condition of applying preload and no preload decreases, indicating that the influence of preload on the vibration of full-ceramic bearing spindle motor decreases with the increase in rotational speeds. At the same time, it is found that fr and 5fr have greater impact on the vibration of full-ceramic bearing spindle motor, where fr is the frequency of the bearing in normal operation, and 5fr is 5 times of the normal operating frequency. Lubrication conditions have little effect on the temperature rise of full-ceramic bearing spindle motor, and the temperature rise under nonlubricated conditions is even slightly lower than that under grease lubrication conditions. The research results show that the vibration velocity and temperature rise of Si3N4 full-ceramic bearing spindle motor are less than those of steel bearing with the same type, indicating that full-ceramic bearing has better performance than steel bearing under the same working conditions. [ABSTRACT FROM AUTHOR]

This study investigates the role of sliding counterbodies, which significantly affect the wear properties and friction of nanocrystalline diamond (NCD) film. The bearing steel balls exhibit a high friction coefficient of 0.12, whereas a ceramic ball of Si3N4 achieves an ultralow friction coefficient of 0.06. The evolution of different friction coefficients with different counterbodies is associated with the formation of a tribolayer at the sliding interface. The decreased friction coefficient in NCD films sliding against Si3N4 ball is likely linked to the occurrence of lubricating nanostructures, especially the silica‐like oxide compounds and graphite‐like carbon phases. The findings of this study may provide new avenues for the design and development of wear‐resistant and environment‐friendly hard carbon films. [ABSTRACT FROM AUTHOR]

In this study, the wear resistance of AISI M2 high-speed tool steel produced using direct energy deposition (DED) was investigated in detail. Wear behavior was studied under different wear loads and sliding speeds using ball-on-disk tribology tests with two different counterpart balls (bearing steel and ZrO2). The wear test results revealed that there was almost no wear damage in the M2 alloy when a bearing steel counterpart ball was used. When a ZrO2 ball was used as the counterpart, a measurable, but small, amount of wear weight loss of M2 was observed. It was found that M2 alloy fabricated by DED has excellent wear resistance, greater than fully carburized conventional steel and high wear resistance steel produced by DED. The formation of a lubricious tribo-oxide film on the worn DED M2 surface is likely the reason for its excellent wear performance. The total wear weight losses of only ~1.5 mg was observed for the M2 produced by the DED, both in the as-DEDed and heat treated states against ZrO2 balls, under the wear loading conditions of 50 N wear load, 100 mm/s sliding speed and total sliding distance of 500 m. In comparison to the other wear-resistance materials, the wear weight loss of the M2 produced by the DED was more than 6 times smaller than the fully carburized structural steel and 1.5–4 times smaller than high wear resistance steel produced by the DED. Thus, DED of the M2 alloy offers a great potential for the production of wear-resistance hard-facing of tribological components. [ABSTRACT FROM AUTHOR]

This paper presents the compressive behavior of tortoise carapace at high strain rates and its protection mechanisms under impact loading. Both experimental and numerical results are reported. Tortoise is a land-based desert-dwelling animal taxonomically classified in the order of Testudines. The carapace is the dome-shaped upper part of the tortoise shell that protects its body from predator attacks. The carapace structure is composed of four layers formed as a composite structure with a porous core. The outer surface is keratin scutes made of fibrous structural proteins. The remaining layers are bone-like materials which are dorsal cortex, cancellous interior and ventral cortex. The compressive behavior at high rate of deformation is examined using split Hopkinson pressure bar (SHPB) technique. The results shown in the stress-strain plot illustrate a strain-rate hardening effect. The impact test is conducted using a gas gun with 6.35-mm diameter steel bearing balls as projectiles. The responses of carapace sample under a range of impact velocities are investigated to analyze its protection mechanisms. The numerical model of impact test is created to obtain an insight into mechanical behaviors of the carapace structure that cannot be observed in the experiments. The strain rate dependent material model is defined based on the SHPB test results. The distributions of stress and rebound velocity are presented and discussed. [ABSTRACT FROM AUTHOR]

If a smooth ball is dropped vertically without spin on a smooth horizontal surface then one might expect the ball to bounce vertically without spin. If it does not then the centre of mass of the ball does not coincide with its geometric centre. An experiment is described where a billiard ball and a superball are deliberately biassed by adding a small steel ball on one side. The results agree well with theoretical calculations. [ABSTRACT FROM AUTHOR]

Direct simple shear (DSS) testing allows observation of load-deformation response under rotation of the major principal stress plane, which is descriptive of many actual field problems. While the simplicity of the test configuration makes its use popular in research and industry, key uncertainties still remain regarding the interpretation of the laboratory data. This study uses laboratory validated discrete element method (DEM) models to examine the stress transmission in laminar-type direct simple shear devices under drained constant effective stress conditions. The DEM models (comprised of spheres) closely replicate physical specimens of precision chrome steel ball bearings for which the properties (e.g., shape, surface friction, and stiffness) were measured directly. The DEM models were also validated using experimental tests, so that conclusions regarding the system response can be derived with confidence from the available DEM data. The testing program included both loose and dense specimens, allowing for a comparison of the influence of density on stress state which has not been examined in previous simple shear DEM studies. Differences were observed between vertical effective stresses and shear stresses derived from boundary measurements (as commonly carried out in experimental programs) and those derived from force measurements within the DEM specimens. The failure state of the material in simple shear was also examined through Mohr's circles of stress. The evolution of stresses on both the horizontally and vertically oriented planes were considered so that established methods of direct simple shear interpretation could be critically assessed. For the loose specimens, the angle of shearing resistance can be confidently estimated considering the maximum shear stress acting on the horizontal plane, which is easily inferred from measurements of the shear force during the physical test. This was true considering both internal and boundary calculated stresses. This approach, however, is inaccurate for the dense specimens. Analysis of the particle-scale kinematics of the response illustrates that the deformation field within the central portion of the specimen is in simple shear, although the magnitude of this shearing was significantly larger than what was measured on the boundary. This study and the conclusions derived focus on smooth spherical particle specimens; the objective was to examine the stress distribution within DSS devices and the implications for test interpretation using DEM models that more closely matched the physical laboratory specimens tested than in previous studies. When considered alongside the existing studies, the findings show that there is no broad conclusion that can be applied for all materials and all conditions in simple shear and that interpretation should be carefully tied to the physical conditions simulated. [ABSTRACT FROM AUTHOR]

In this work, we designed three series of tribo-couples based on amorphous carbon films including GLC, DLC and PLC that were modified by graphene quantum dots (GQDs). The tribo-testing environment was controlled at harsh conditions (like heavy load and high speed) in dry nitrogen atmosphere using bare and film-coated bearing steel balls as counterbodies, respectively. Through the tribochemical interactions, the self-mated DLC system obtained a surperlubricity state (μ = 0.01). During the whole sliding, the contact surface of the upper counterfacing ball was covered by 2D-layered carbon and graphitic lubricants induced via structural transformation of GQDs. Meanwhile, the tribofilm of the disc wear track was composed of a silica-like SiO x boundary layer and a multicomponent mixed-layer induced by tribochemistry. Compared to the self-mated DLC system, the structural boundary enriched with SiO x compounds was not formed at the bottom region of the tribofilm for the bare steel system; meanwhile, the disc wear track was covered by a thicker tribofilm containing plenty of degraded GQDs. This inferred the fact that the formation of a nanostructured sliding interface was the key to realize superlubricity. These discoveries successfully afforded a lubrication mechanism of GQDs for solid lubricant in applications of engineering and industry. Image 1 • Graphene-quantum-dots lubricants with effective friction-reducing effects are achieved. • The lubricity depends strongly on the tribo-couple materials and surface strucutre. • The nanostructured tribofilms formed on the contacts govern the superlubricity mechanisms. [ABSTRACT FROM AUTHOR]

The aim of this study is to evaluate the bonding and wear properties of self-adhesive flowable resin composites. The four self-adhesive flowable resin composites used in this study were: 1) Constic (CO, DMG), 2) FitSA F03 (FS, Shofu), 3) Fusio (FU, Pentron Clinical), 4) Vertise Flow (VF, Kerr). Two hundred and eighty bovine mandibular incisors were used for shear bond strength testing to both enamel and dentin, and the teeth were mounted in self-cure acrylic resin. The labial surfaces of the coronal central portion were ground using P120- and P400-grit silicon carbide papers. A mold insert was clamped against the specimens and filled with self-adhesive flowable resin composite. After storage at 37°C for 24 h, shear bond strength testing was carried out using a universal testing machine. Twelve specimens of each of the four self-adhesive flowable resin composites were prepared for simulated localized wear testing. An Alabama wear testing machine with a four-station plastic water bath in which stainless steel ball bearings served as the wear antagonists was used. Load of up to 78.5 N was applied over 400,000 cycles at 2 Hz. Scanning electron microscopy observation of bonding interfaces and wear facets was conducted. Bond strength to dentin ranged from 1.3 MPa to 4.2 MPa, while bond strength to ground enamel ranged from 6.5 MPa to 12.2 MPa, and bond strengths to etched enamel ranged from 23.7 to 32.5 MPa. The rank order for bond strength to dentin and ground enamel was FS = CO > FU = VF, and for etched enamel was FU = CO ≥ VF > FS. There was significant variation in wear between the materials, from 0.099 mm3 to 0.367 mm3 in volume loss, and 148.6 µm to 327.4 µm in facet depth. The rank order for both measures of wear was FS > CO > FU = VF. The bonding performance and occlusal wear resistance of self-adhesive flowable resin composites is still weaker than resin composites with adhesive systems, but selective enamel etching can improve bonding performance. In addition, the relationship of the rank orders for the results may indicate that bonding to ground enamel and dentin relies more on chemical bonding, while bonding to etched enamel relies more on the mechanical properties of the materials. [ABSTRACT FROM AUTHOR]

The tribological failures of poly-α-olefin (PAO) oil-impregnated porous polyimide (PPI) undermine the long-term reliability of aerospace bearing cages, often resulting in black product formation. Thus, addressing blackening is crucial. This study uncovers distinct tribological behaviors of PAO oil-impregnated PPI surfaces when sliding against 440 C and GCr15 steel bearing balls. Compared to GCr15/PPI, the 440 C/PPI interface exhibits fewer black products, lower friction, and reduced wear. Analysis attributes this to the higher Cr content in 440 C steel balls, facilitating a robust and dense Cr oxide film on their surfaces, which mitigates PAO oil degradation from tribo-chemical reactions with iron. Lastly, a universal approach involving Cr ion injection onto steel ball surfaces significantly enhances the tribological performance and blackening resistance of PAO oil-impregnated PPI. [ABSTRACT FROM AUTHOR]

Purpose: Bearings in electric machines often work in high speed, light load and vibration load conditions. The purpose of this paper is to find a new fatigue damage accumulation rating life model of ball bearings, which is expected for calculating fatigue life of ball bearings more accurately under vibration load, especially in high speed and light load conditions. Design/methodology/approach: A new fatigue damage accumulation rating life model of ball bearings considering time-varying vibration load is proposed. Vibration equations of rotor-bearing system are constructed and solved by Runge–Kutta method. The modified rating life and modified reference rating life model under vibration load is also proposed. Contrast of the three fatigue life models and the influence of dynamic balance level, rotating speed, preload of ball bearings on bearing's fatigue life are analyzed. Findings: To calculate fatigue rating life of ball bearings more accurately under vibration load, especially in high speed and light load conditions, the fatigue damage accumulation rating life model should be considered. The optimum preload has an obvious influence on fatigue rating life. Originality/value: This paper used analytical method and model that is helpful for design of steel ball bearing in high speed, light load and vibration load conditions. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2019-0180/ [ABSTRACT FROM AUTHOR]

The traditional high-speed ball bearing analysis is based on the quasi-static model proposed by Jones-Harris (J-H). This study gives another bearing analysis model based on the relative position of the ball center and the centers of curvature of the raceway grooves, described by the virtual rods. Specifically, the load and deformation of the virtual rods are determined according to the principle of force transmissibility, the translation theorem of a force, and elastic-contact deformation between steel ball bearings and raceway grooves. And the iterative variables such as the axial, radial and angular deformations are gradually introduced into the calculation model to solve the force and kinematic parameters under pure axial load, bidirectional and tri-directional combined loads. The correctness of the virtual rods model is verified by the contact angle for axial and bidirectional load. The influence of gyroscopic moment and raceway grooves control parameter on the actual contact angle under tridirectional loading conditions are calculated and analyzed respectively. The proposed model uses fewer equations and lower-dimension parameters than those used by the traditional highspeed ball bearing analysis method, improves the solution rate of the equations. [ABSTRACT FROM AUTHOR]

The Mn3B7O13Cl nanoparticle (~30 nm) has been prepared by sol‐gel method and characterised by powder X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The tribological properties of prepared Mn3B7O13Cl nanoparticle and the common nano‐Cu and nano‐Fe nanoparticles as antiwear additives with various concentrations in polyalphaolefin (PAO) base oil have been investigated. PB values of nano‐Mn3B7O13Cl added oil are superior to base oil, nano‐Cu and nano‐Fe added oil with the same content, and it reaches the value of 637 N. The wear scar diameter is 0.52 mm when the concentration is only 0.2 wt.%. And meanwhile, Mn3B7O13Cl nanoparticle as efficient antiwear lubricant and commercial oil was measured in the sliding wear between tantalum strip and 52100 bearing steel ball by MFT‐3000 friction and wear tester at an optimised additive concentration (0.2 wt.%). Coefficient of friction of tantalum strips is reduced by 41.5% compared with that of the commercial oil. Surface morphology studies and X‐ray photoelectron spectroscopy (XPS) analysis have revealed that the prominent tribological behaviour of Mn3B7O13Cl was caused by the formation of ~ 30‐nm tribofilm made of adsorbed boron and tribosintered nano‐Mn3B7O13Cl. Therefore, Mn3B7O13Cl nanoparticle has a potential to develop as friction‐reducing and antiwear lubricant in the sliding wear between tantalum strips and steel ball to avoid the severe wear. [ABSTRACT FROM AUTHOR]

Results of the study on the internal friction of steel ball bearings made of X65Cr14 alloy and ceramic bearings made of zirconium oxide operating at temperatures lowered by liquid nitrogen down to -195 °C are presented in this paper. Standard grease added by the manufacturer, while graphite and molybdenum disulphide powder were used for lubrication of the bearings during the measurements. Tests were also carried out to examine the performance of the bearings operating without lubrication. The power of bearing internal friction versus temperature was measured. The lowest bearing internal friction was observed for molybdenum disulphide, whose effective lubricating performance was verified for both types of ball bearings. Graphite powder was almost equally effective with the advantage of being suitable for use in machines that come into contact with food. [ABSTRACT FROM AUTHOR]

This study has been conducted with the purpose of studying the tribological properties the mixture of soybean oil and used frying oil the Fatty Acid Methyl Esters(FAMEs) under boundary lubrication conditions. Tests have been conducted between steel ball and the journal bearing material sample connecting to the disc of Pin-on-Disc Test apparatus. It was selected experimental parameters such as 5, 10 and 20 N loads, 100, 300, 500 rpm sliding velocities and 500 m sliding distance. The surface roughness of the samples has been measured prior to and after each test. Wear rate has been measured through mass loss method prior to and after each test. Also, specific wear rates (w s) of the test specimens were calculated. SEM and EDS analyses were also conducted to wear contact surfaces. When all the friction coefficient (μ) values acquired from boundary lubrication conditions are compared to μ values acquired from dry (lubricant-free) test conditions, very lower friction coefficients have been achieved. Usage of the mixture of soybean oil and used frying oil FAMEs as lubricant candidates are quite good a performance under boundary and/or mixed lubrication. It has also been observed that with the increase of load, specific w s values are generally decreasing. • An overview of the lubricity of biodiesel fuel based on soybean oil and used frying oil methyl ester. • The boundary or mixed lubrication and tribological performance of this mixture of is quite good. • In general, an increase in load and speed yielded lower average μ values in the study. • Also, this mixture is environmentally friendly lubricating oil candidate. [ABSTRACT FROM AUTHOR]

This study attempts to use ionic liquids (ILs) as oil additives to lubricate oxygen-diffusion (OD) case-hardened titanium for improved friction and wear behavior. Four oil-soluble ILs were used as additives in a base oil for boundary lubrication of an OD-treated Ti-6Al-4V surface sliding against a bearing steel ball. The ILs improved the friction behavior to various extents and the two phosphate ILs clearly outperformed the conventional ZDDP. Unlike ZDDP that adversely caused a higher material loss, ILs exhibited excellent wear protection suggesting good material-chemical compatibility. Particularly, the carboxylate IL protected the OD-Ti surface from any measurable wear. The morphology and chemical composition of the worn surfaces and tribofilms were examined to gain insights of the anti-wear mechanism. • Ionic liquids (ILs) as oil additives showed superior performance in lubricating oxygen-diffused titanium alloy (OD-Ti). • Phosphate ILs outperformed phosphinate and carboxylate ILs as well as the traditional ZDDP in friction behavior. • While phosphate and phosphinate ILs protected both OD-Ti and steel to some extent, carboxylate IL minimized the titanium wear. • The protective tribofilm on the OD-Ti surface was found to be deposit of reacted wear debris from the steel counterface. [ABSTRACT FROM AUTHOR]

Electrostatic charging, discharging, and consequent surface modification induced by sliding dissimilar surfaces have been studied. The surface-charge related phenomena were monitored by using a home-built capacitive, non-contact electrical probe, and the surface chemistry was studied by X-ray photoelectron spectroscopy (XPS). The experiments were performed on the disk surface of a ball-on-rotating-disk apparatus; using a glass disk and a Teflon (polytetrafluoroethylene) ball arrangement, and a polyester disks and a diamondlike carbon (DLC) coated steel ball arrangement. The capacitive probe is designed to perform highly resolved measurements, which is sensitive to relative change in charge density on the probed surface. For glass and Teflon arrangement, electrical measurements show that the ball track acquires non-uniform charging. Here not only the increase in charge density, but interestingly, increase in number of highly charged regions on the ball track was resolved. Threefold increase in the number of such highly charged regions per cycle was detected immediately before the gas breakdown-like incidences compared to that of other charge/discharge incidences at a fixed disk rotation speed. We are also able to comment on the behavior and the charge decay time in the ambient air-like condition, once the sliding contact is discontinued. XPS analysis showed a marginal deoxidation effect on the polyester disks due to the charging and discharging of the surfaces. Moreover, these XPS results clearly indicate that the wear and friction (sliding without charging) on the surface can be discarded from inducing such a deoxidation effect. [ABSTRACT FROM AUTHOR]

Concentrated polymer brushes (CPBs) synthesized by advanced surface-initiated controlled radical polymerization have received increasing attention in the tribological field because CPBs in good solvents exhibit superlow friction phenomena under macroscopic severe sliding conditions. To realize tribological applications of CPBs, an understanding of the wear mechanisms of CPBs is required to develop a method to enhance their durability. In this study, an operando tribo-Raman spectroscopic experiment, which is an effective approach for revealing the wear mechanisms of tribo-materials, was conducted on the frictional interface between a polymethyl methacrylate (PMMA)-CPB and a bearing steel ball immersed in an ionic liquid (IL), which is a good solvent for PMMA-CPBs. From the operando tribo-Raman results, the concentrations and molecular structures of the PMMA-CPBs and IL at the frictional interface were found to be constantly changing with the sliding cycles during operation. Moreover, their time-dependent changes strongly affected the wear process and superlow friction phenomena of the PMMA-CPB lubricated with the IL. Consequently, our results suggest that controlling the degree of swelling of CPBs at frictional interface is an effective approach for realizing a durable-superlow frictional tribo-system of CPBs. • Tribological phenomena of CPB–steel tribo-systems in ionic liquids were investigated. • The Tribo-Raman method was conducted to reveal the tribological phenomena. • The conformation of CPB chains and ILs were changed during friction test. • The concentration of CPB chains and ILs decreased during friction test. • Their conformation is a key factor for achieving superlubricity of the system. [ABSTRACT FROM AUTHOR]

This article clarifies that the influence of volcanic particles (VPs) and calcium carbonate particles (CaCO3) on the scratch behavior of high‐density polyethylene (HDPE). Melt compounding was carried out using a twin‐screw microcompounder and then injection molding with various VPs and CaCO3 contents such as 0, 6, 12, 18, and 24 wt% was performed for preparing test samples. Scratch testing was performed using the testing apparatus and methodology outlined in ASTM D7027–05 with 60 mm/min scratch velocities of 200 μm stainless steel ball bearing scratch tip. Coefficient of friction (COF) and scratch hardness values of various VPs‐ and CaCO3‐filled HDPE composites were determined. Results showed that COF and scratch hardness values were improved with higher inorganic particle concentrations. It was found that VPs was more effective filler for the scratch properties of HDPE than CaCO3. After scratch tests, scratch damage mechanisms were analyzed by scanning electron microscopy. POLYM. COMPOS., 40:2564–2572, 2019. © 2018 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The nano-scale studies in the literature have revealed the excellent anti-friction properties of graphene and its great potential as a nano solid lubricant. However, for macro-scale applications the integrity and durability are main problems for most graphene-based surface coatings. One way to mediate the durability issue while exploiting the tribology of graphene is graphene-based composites. In this work, nickel-graphene oxide (GO) composite coatings were fabricated on steel by electro-brush plating. The effects of GO on the tribological properties were investigated. The results show that the composite coatings possess much lower friction than GO-free nickel coating (up to 47% less against a bearing steel ball, and 30% less against an alumina ball). As the GO load increases from 0 to 4 mg/ml, the wear rate of the resulting composite can be reduced significantly by approximately 90%. Detailed post-test studies of the wear tracks and the counterpart were conducted using SEM, EDS, Raman and FIB/SEM. The improved tribological properties can be attributed to the strengthening effect, the retention of oxide tribo-films and the formation of GO rolls during sliding. The tribological behaviour of the Ni-GO nano-composite coating and a Ni-graphite composite coating was compared, and their different wear mechanisms have been discussed. • Novel Ni/GO nano-composite coatings by brush-plating. • Significantly reduced reciprocating sliding wear rate by 88%. • Effectively reduced coefficient of friction by 30–47%. • First time observation of GO rolls on wear track. [ABSTRACT FROM AUTHOR]

Abstract: There is a need to reduce the friction and to prevent the galling between the galvanised steel and the shaping tools during the metal working process. Zinc phosphate (ZP) coatings are limitedly used as solid lubricant due to intrinsic high‐friction properties. This investigation explores the use of stearic acid overcoat on ZP coatings to produce surface coatings with low friction and high durability. A simple hydrothermal process was developed to fabricate ZP coatings on zinc. A stearic acid overcoat was then deposited on ZP coatings. Infrared microscopy and water contact angle measurements were used to analyse the chemical composition and the hydrophobicity of modified ZP coatings. The tribological behaviour of modified ZP coatings was evaluated by sliding against a steel ball by using a reciprocating ball‐on‐plate tribotester. Tribological results show that stearic acid overcoat on ZP coatings led to a decreased friction with greatly extended life. [ABSTRACT FROM AUTHOR]

The conventional impact-echo analysis applies the Fourier transform to the surface response of the target structure due to an impact of a steel ball. Then, the amplitude spectrum is used to determine the frequency of the echo signals. Although the amplitude spectrum may disclose the existence of an interface in the structure, it contains no information about the type of interface. This research group has proposed using the phase spectrum to differentiate reflections from cracks and reinforcing bars. Through numerical and physical tests, it was found that the phase of reflections at an air interface and reflections at steel interface fall within two distinct ranges, - π , π / 4 and π / 4 , π , respectively. This study aims at examining the influence of the impact duration, the inclusion size/depth ratio, the sampling rate, and the sampling duration on the effectiveness of the impact-echo phase method. Numerical simulations and physical tests were conducted considering various combinations of impact sizes, inclusion sizes and depths, sampling rates, and sampling durations. The results suggest that the phase offset is an effective indicator of the inclusion type under the following conditions: (1) the product of the impact duration and depth frequency falls in the range 0.25 , 0.8 ; (2) the length-depth ratio of the crack exceeds 0.33; (3) the radius-depth ratio of the reinforcing bar exceeds 0.4; (4) the sampling rate exceeds 6 times of the depth frequency; (5) the product of sampling duration and depth frequency exceeds 33.3. [ABSTRACT FROM AUTHOR]

Magnetically hard Sm2(Co0.8Fe0.2)17 and SmCo5 nanoparticles have been produced by using surfactant-assisted low- and high-energy ball milling techniques. Surfactants prevent the rewelding of the crashed particles during the milling process. Heptane was used as the milling medium and oleic acid as the surfactant. High-energy ball milling experiments took place in a milling vial with carbon steel balls by using an SPEX 8000M high-energy ball milling machine. The coercivity was found to increase with milling time with values of 2.3 kOe for Sm2(Co0.8Fe0.2)17 and 18.6 kOe for SmCo5 after 4 h of milling. Transmission electron microscopy data showed that the milled powders consisted of nanoparticles with an average size of 5–6 nm and a narrow size distribution. Samples deposited on copper coated carbon grid showed self-assembled nanoparticles which could be further aligned when subjected to a magnetic field. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to present a method to measure the rolling friction coefficient in an easy and fast way. The aim is also to measure the rolling friction coefficient between a small steel ball and a cylindrical aluminum surface.Design/methodology/approach An analytical model of the tribosystem of a freely rolling ball and a cylindrical surface is established. The rolling friction coefficient is evaluated from images recorded by a high-speed camera. The coefficient between a 1.58-mm diameter steel ball and a cylindrical aluminum surface is measured. A background subtraction algorithm is used to determine the position of the small steel ball.Findings The angular positions of the ball are predicted using the analytical model, and a good agreement is found between the experimental and theoretical results.Originality/value An optical method for evaluating the rolling friction coefficient is presented, and the value of this coefficient between a small steel ball and a cylindrical aluminum surface is evaluated. [ABSTRACT FROM AUTHOR]

To eliminate internal void and improve the mechanical properties of steel balls formed by skew rolling, the floatingpressure method (FPM) using high-pressure gas to compact void is applied in this paper. By establishing void closure mechanical model, effects of various factors on void closure are obtained. The change rule of microstructures and outline of steel ball is investigated using DEFORM-3D Finite element software, and results show that when void is entirely closed, steel ball diameter decreases by less than 2 %, and its dimensional accuracy is guaranteed; the dynamic recrystallization of the metal around void promotes the healing of micro-cracks. The FPM experiments are performed, which verify the accuracy of the finite element model. [ABSTRACT FROM AUTHOR]

Results of experiments on indentation of steel balls of various diameters into glass specimens shaped as rectangular parallelepipeds are reported. The limiting load of formation of an annular crack near the contact area and the radius of this crack are experimentally determined. The field of the contact stress in the fracture region is found by using the Huber solution of the Hertz problem of ball indentation into an elastic half-space. Modeling fracture caused by contact interaction is based on using the local criterion of the maximum stress and several nonlocal criteria: average stress criterion, Nuismer criterion, and gradient criterion. For calculating the parameter that has the length dimension and is included into the nonlocal fracture criteria, the ultimate tensile stress and the critical stress intensity factor of glass are experimentally determined for beams without and with a notch. It is demonstrated that the experimental data on the annular crack radius are most adequately predicted by the gradient criterion among all criteria considered in the study. However, this criterion overpredicts the ultimate tensile stress in the course of beam bending, which is caused by the scale factor. [ABSTRACT FROM AUTHOR]

In this paper, we propose a robust nonlinear control design concept based on a coefficient diagram method and backstepping control, combined with a nonlinear observer for the magnetic levitation system to achieve precise position control in the existence of external disturbance, parameters mismatch with considerable variations and sensor noise in the case, where the full system states are supposed to be unavailable. The observer converges exponentially and leads to good estimate as well as a good track of the steel ball position with the reference trajectory. A simulation results are provided to show the excellent performance of the designed controller. [ABSTRACT FROM AUTHOR]

The paper describes the design of a flat-wedge reversing mill used for forming balls directly from heads of scrap railway rails. At the beginning an innovative rolling method for producing balls is presented. This two-stage method consists in forming balls from heads of scrap railway rails using plate-shaped flat tools. The first stage involves preparation of a workpiece by changing the irregular shape of the rail head into a round bar. Next, the workpiece is automatically moved to the working space of the other tool set, where forgings of balls are formed on return motion of the slide. To enable the production of balls under industrial conditions in accordance with the above concept, a flat-wedge rolling mill was designed and constructed. The results demonstrate that the machine can be used to produce balls from heads of scrap railway rails. [ABSTRACT FROM AUTHOR]

Steel ball surface-defect inspection was performed by using a new saddle-type eddy current sensor (SECS), which included a saddle coil and a signal conditioning circuit. The saddle coil was directly wound on the steel ball's outer bracket in a semi-circumferential direction. Driven by a friction wheel, the test steel ball rotated in a one-dimensional direction, such that the steel ball surface was fully scanned by the SECS. There were two purposes for using the SECS in the steel ball inspection system: one was to reduce the complexity of the unfolding wheel of the surface deployment mechanism, and the other was to reduce the difficulty of sensor processing and installation. Experiments were carried out on bearing steel balls in diameter of 8 mm with three types of representative and typical defects by using the SECS, and the results showed that the inspection system can detect surface defects as small as 0.05 mm in width and 0.1 mm in depth with high-repetition detection accuracy, and the detection efficiency of 5 pcs/s, which meet the requirement for inspecting ISO grade 10 bearing steel balls. The feasibility of detecting steel ball surface defects by SECS was verified. [ABSTRACT FROM AUTHOR]

Molecular orientation of the lubricating film will affect the lubrication state, especially in boundary lubrication. In this work, electrical field was used to affect the orientation of liquid crystal molecules during friction. We demonstrated that the use of an electric field applied between the steel ball and the chromium film on the surface of the glass plate provided an effective method for controlling the orientation of the liquid crystal molecules in a sliding point contact. The coupling effects of shear and electric field on friction were investigated with an in situ Raman spectrometer. This work shed new light on the influence of the adsorbed film on sliding friction coefficient, especially in thin-film lubrication regime. [ABSTRACT FROM AUTHOR]

Annotation High-temperature sliding experiments have been carried out to study both direct and back adhesion transfer between Al-Mg alloy metal and the ball bearing steel sample. It was shown that a transfer layer consisting of aluminum alloy formed on the trailing hemisphere of the steel ball. The amount of transferred metal increased with the test temperature from 25 to 200 °C. The periodical back transfer from the steel ball to the aluminum alloy disk was observed at the test temperature 100 °C. The wear groove bottom was characterized by the presence of large aluminum alloys transfer layer bulges, transfer layer film and plastically deformed subsurface layer. It was found that aluminum alloy transfer layer might accumulate on the trailing hemisphere of the ball and then could stick back to the wear groove surface of the disk. Such an adhesion transfer mechanism may be effective for metal transfer during friction sir welding by not threaded pins or pins fully covered by the transfer metal film. [ABSTRACT FROM AUTHOR]

Chip-sprinkling cement concrete (CSCC) pavement can provide satisfactory friction and has potential for noise attenuation due to its exposed surface texture, making abrasion resistance significant. The abrasion resistance of CSCC pavement was evaluated using the Cantabro test method, with smooth surface concrete as the control group. This method uses a Los Angeles Abrasion Machine without steel balls. Using the same method, the abrasion durability of CSCC was also assessed using different concentrations of sodium chloride solutions. The effects of different water/cement ratios and chip-sprinkling parameters were analyzed. The latter variables included aggregate particle size, aggregate spreading area ratio, and aggregate pressing depth ratio. Data indicate that the abrasion losses of CSCC specimens change quickly at first, but later they change more gradually. Aggregate particle sizes of 9.5–13.2 mm may be better when just considering the effect of aggregate particle size on the abrasion resistance. Abrasion losses of CSCC specimens multiply with increasing aggregate spreading area ratios and decrease with the rising aggregate pressing depth ratios. On the whole, abrasion resistance of CSCC is superior to the smooth surface concrete in the control group. [ABSTRACT FROM AUTHOR]

A measuring method was studied to further improve the manufacturing accuracy of the lead screw. Firstly, factors that can axially displace the screw shaft were analyzed and a relationship between factors and axial displacement was given. The axial displacement of the screw shaft was measured using a laser interferometer, and results show that the variation amplitude of the screw-shaft axial displacement was about 80 nm while the variation period was consistent with the rotation period of the screw shaft. Next, two methods of measuring the manufacturing accuracy of the lead screw were considered: a traditional method that measures the absolute position of the nut and an improved method that measures the displacement between the nut and screw shaft. A No. 4 screw shaft was manufactured under the guidance of results obtained using the improved measuring method. Experimental measurements were then made; results show that the pitch displacement errors obtained using the traditional and improved measuring methods were 0.6 and 0.4 μm, respectively, indicating that the improved measuring method is more exact. Finally, an echelle grating ruled by a grating ruling engine that used the No. 4 screw shaft as a macro-positioning element was introduced. Its excellent parameters indirectly show that the improved measuring method has better accuracy. [ABSTRACT FROM AUTHOR]

The tribological properties of lithium-based grease with nanometer Cu additive are studied in this paper. The feasibility of Cu nanoparticle as grease additive is evaluated by four ball friction tester. Both the bearing temperature rise and the vibration acceleration at different lubrication states are investigated using the bearing test machine. Results show that when the adding amount of nanometer Cu is 0.25% in grease, the friction coefficient and the wear scar diameter of the steel ball are the smallest. Moreover, the vibration acceleration and temperature rise of bearing in 1171-0.25 lithium-based grease are decreased and the bearing speed limit is improved because of the self-repair role of Cu nanoparticles on bearing rolling surfaces. [ABSTRACT FROM PUBLISHER]

Two running-in processes, i.e., polishing a diamond-like carbon (DLC) coated disk and pre-sliding in ambient air, were suggested as a delamination suppression method for self-mating DLC coatings in water, and the effects of these methods were verified using a ball-on-disk tribometer. An a-C:H-type DLC coating was deposited on SUJ2 bearing steel balls and disks using plasma chemical vapor deposition. It was confirmed that delamination of DLC coatings was suppressed because microcracks were not generated by removing droplets on the DLC coated disk using the polishing process. The friction coefficient in that condition was reduced to about one-fifth of that of the untreated disk. The running-in process of pre-sliding in ambient air also suppressed delamination of DLC coatings. Moreover, the friction coefficient after this process was reduced to half of that with the other polishing process in the boundary lubrication condition. It was found that these effects have a relationship with surface smoothness and hydrophilicity. [ABSTRACT FROM AUTHOR]

In this article, the breakage behavior of a bed of silica particles is tested to identify optimum operating parameters to get products in three different previously defined particle size classes. This is done by drop weight tests with steel balls of different sizes (10, 20 and 30 mm) from different heights (up to 2.0 m). Many different techniques have been adopted in comminution in order to find ways of optimizing energy consumption in the size reduction process. In this paper, we apply one such method called the Attainable Region (AR) analysis technique to optimize the impact energy on a bed of silica particles. The attainable region is a fundamental approach that is equipment-independent and can be used to analyze breakage processes. The AR is defined as a set of all possible outcomes, for the system under consideration that can be achieved using fundamental processes operating within the system. The main finding of the article is that the 20 mm steel ball leads to a maximum yield in the intermediate size class. [ABSTRACT FROM AUTHOR]