Desorption-adhesion mechanism of wear under boundary lubrication

Experimental results of studying the wear of a model sliding tribosystem, which consists of a rotating shaft and a plane bearing, are presented. An interrelation between dynamic processes that occur in boundary films and processes of adhesive wear of surfaces under friction has been established. A desorption-adhesion mechanism of wear under boundary lubrication has been proposed; this mechanism is based on the localization of the adhesive wear of surfaces in the diffuser zone of a contact.     

A disc-on-flat wear test under starved lubrication

The ‘disc-on-flat’ system has been used for testing wear under starved lubrication conditions. The rotating discs were made of a carbon steel, the surface finish of the discs being ground. Some of the discs were treated by ‘vibrogrooving’, to form regular microrelief. The flat counterface was made of a ground copper alloy. An industrial oil was used as a lubricant in a one-drop test procedure. Microreliefs of a non-touching design with a relative groove area of 34% caused less wear than microreliefs of a touching type with a relative groove area of 50%, whereas the wear caused by the ground disc was high, with seizure after 200–250 m of sliding distance. A one-drop disc-on-cylinder test also showed that the wear caused by discs with regular microrelief was considerably less than that caused by discs treated by conventional finishing (grinding, polishing).     

The lubrication effect of hyaluronic acid and chondroitin sulfate on the natural temporomandibular cartilage under torsional fretting wear

The aim of this study is to investigate the lubrication of hyaluronic acid (HA) and chondroitin sulfate (CS) on the condylar cartilage of the temporomandibular joint. The wear behaviour of bovine condyle cartilage was explored against a zirconia ball with different lubrications under torsional fretting mode. The worn cartilage morphologies were observed using scanning electron microscopy and hemotoxylin and eosin staining. The results indicated that HA or CS could significantly lower the friction torque and dissipated energy of fretting interface and reduce the damage of the articular cartilage surface compared to the control (phosphate‐buffered saline). The mixture (HA and CS) could provide better protection for the cartilage layer. Absence of good lubrication in overloading torsional fretting process caused excessive cartilage wear. High concentration and high molecular weight HA or CS acted as good boundary lubricants, and the lubrication effect of their mixture was better due to their synergistic function. Copyright © 2014 John Wiley & Sons, Ltd.     

Model of wear in a plain bearing under boundary lubrication

Wear in a plain bearing under boundary lubrication is described by three groups of related dimensionless numbers obtained from dimensional analysis. Experimental results verify the proposed model to a high degree of correlation     

Velocity analysis for layered viscosity model under thin film lubrication

The lubrication of bearings is directly affected by the flow properties of the liquid lubricant. One key feature of lubricant is its viscosity distribution in the bearing. The distribution is dependent on the adsorbent properties of the surface and the velocity distribution of the lubricant. This paper is only connected with the velocity analysis on the cross-gap flow. Because of increasing the speed, apart from increasing the temperature, the other features of lubricant will be changed. When fluid film is thin, the speed effects become important due to the increased shear rate. This paper describes the fluid velocity profiles produced for the case where layers of greater viscosity than the bulk occur on the bearing surfaces.     

A mixed lubrication model of a rotary lip seal using flow factors

A mixed lubrication model of a rotary lip seal using flow factors has been developed. The model consists of coupled fluid mechanics, contact mechanics and deformation mechanics analyses. The fluid mechanics analysis is described by a Reynolds equation that takes into account the surface roughness effect using flow factors. The contact mechanics analysis uses the Greenwood and Williamson model to compute contact pressure. The deformation mechanics analysis utilizes the influence coefficient approach to compute deformation of the seal. Results for a typical seal show how the operation parameters and the surface roughness affect seal behavior.     

Numerical analysis of a surface-textured mechanical seal operating in mixed lubrication regime

This paper presents a numerical study of the behavior of a mechanical seal with textured surfaces. It is used to analyze the mechanisms underlying the enhancement of the hydrodynamic lift associated with surface texture in mechanical seals. The model solves the Reynolds equation coupled with a mass-conservative cavitation algorithm and takes into account asperity contact. It is shown that, unlike rough-textured surfaces, smooth-textured surfaces are unable to generate a load. The performance of two rough surfaces are compared with those of the same surfaces equipped with dimples. The effect of texture density and aspect ratio are studied as well.     

Friction and wear properties of bronze–graphite composite under water lubrication

Bronze–graphite composite was prepared using powder metallurgy. The friction and wear behaviors of the resulting composites in dry- and water-lubricated sliding against a stainless steel were comparatively investigated on an MM-200 friction and wear tester in a ring-on-block contact configuration. The wear mechanisms of the bronze–graphite composite were discussed based on examination of the worn surface morphologies of both the composite block and the stainless steel ring by means of scanning electron microscopy equipped with an energy dispersion spectrometry and on determination of some typical elements on the worn surfaces by means of X-ray photoelectron spectroscopy. It was found that the friction coefficient was higher under water lubrication than that under dry sliding and it showed margined change with increasing load under the both sliding conditions. A considerably decreased wear rate of the bronze–graphite composite was registered under water-lubricated sliding than under dry sliding, though it rose significantly at a relatively higher load. This was attributed to the hindered transfer of the composite onto the counterpart steel surface under water-lubricated sliding and the cooling effect of the water as a lubricant, while its stronger transfer onto the steel surface accounted for its higher wear rate under dry sliding. Thus, the bronze–graphite composite with much better wear-resistance under water-lubricated sliding than under dry sliding against the stainless steel could be a potential candidate as the tribo-material in aqueous environment.     

Mechanisms of wear of metal by nitrile rubber under boundary lubrication conditions

The wear mechanisms for metal being worn by nitrile rubber under boundary lubrication conditions were investigated. We examined the surface profiles of both metal and rubber with SEM, and studied the chemical states of the elements in both surfaces with XPS. The functional groups in the rubber were analysed with FT‐IR. Under the action of shear forces, the metal lattice was disordered and new dislocations were formed; as a result, the chemical activity of the metal was increased. The macromolecular chains of the nitrile rubber and the alkane chains of the mineral oil were broken at stress concentration sites. These broken macromolecular chains produced active macromolecular free radicals, which reacted with the activated iron atoms and iron oxides, and generated a metal‐polymer film on the metal surface. This metal‐polymer film was destroyed and removed by the action of the debris on the sliding surface. Thus the rubber wore away the metal. Under boundary lubrication conditions with mineral oil, the physical processes of wear of T10 steel by nitrile rubber are microcutting and surface peeling.     

Integrated wear prediction model for cylindrical gear with variable hyperbolic circular arc tooth trace under mixed elastohydrodynamic lubrication

Cylindrical gear with variable hyperbolic circular arc tooth trace (VH-CATT) is a new type of gear. Sliding wear is the main mode of the surface failure of multiple mechanical parts. Both the lubrication state and contact temperature considerably influence wear characteristics, which may aggravate the transmission performance of gear pairs. Wear, contact temperature, as well as lubrication states are jointly explored. Therefore, an integrated wear prediction model was proposed through taking into account flash contact temperature and surface roughness of VH-CATT cylindrical gears in mixed elastohydrodynamic lubrication. According to the equivalent ellipse contact model of VH-CATT cylindrical gears and tooth surface equation, normal curvature and velocity relations for VH-CATT cylindrical gears were observed, and the normal meshing force was obtained through the consideration of load sharing coefficients and quality grades. Flash contact temperature was estimated by using the literature. This study proposes analytical solutions for investigating how various surface roughness, operation, and geometric parameters affect asperity contact ratio (ACR), asperity contact pressure (ACP), flash contact temperature (FCT), as well as wear depth (WD) related to driving gears. ACR, ACP, FCT, as well as WD initially decrease and then increase from engaging-in to engaging-out processes. The minimum occurs at the pitch point. The WD declines as module, cutter radius, and rotational velocity increase while augmenting when surface roughness and torques increase. The maximum and minimum wear depths in driving gears occur at the dedendum and pitch point, respectively. Its overall wear is reduced by 23.16 % compared to the wear of spur gears. The results are valuable for the studies of tooth pitting, wear resistance, and fatigue life improvement for VH-CATT cylindrical gear. These studies can provide verification data and references required for engineering designs and VH-CATT cylindrical gear operations.

     

Fretting wear behavior of nanocrystalline surface layer of pure copper under oil lubrication

Lubricated fretting tests in mineral oil were performed with a nanocrystalline surface layer on a pure bulk Cu prepared by surface mechanical attrition treatment (SMAT) against a WC-Co ball. It was found that the nanocrystalline surface layer exhibited a markedly enhanced fretting wear resistance and higher friction coefficient relative to the coarse-grained (CG) form. The wear volume of the SMAT Cu is one order of magnitude lower than that of the CG Cu. The friction coefficient of the SMAT Cu increases with an increasing load and frequency, while for the CG Cu, the friction coefficient increases with an increasing fretting frequency up to 100 Hz and thereafter decreases. The higher hardness of the SMAT Cu is suggested to be the main factor causing its improved wear resistance and higher friction coefficient. A discontinuous metal transfer layer can be found on the WC-Co ball only after fretting against the SMAT Cu, which may partly account for the higher wear resistance of the SMAT Cu in comparison with the CG Cu.     

Some aspects of the friction and wear of electrical sliding contacts under conditions of boundary lubrication

The friction characteristics of lubricated electrical sliding contacts are considered. Data are presented concerning the effects of the current, the lubricant properties, the velocity and the load on the friction and wear behaviour of the contacts. In light-current electrical contacts the effectiveness of the lubricant does not depend on its conductivity but on its ability to prevent the formation of a non-conductive film by lubricating action. Under semifluid lubricating conditions the heavy current acts by discharge through the lubricant film, and the lubricant conductivity generally determines the friction and wear characteristics of the contact. Colloidal metal particles produce additional conductivity in the clearance between the contacting surfaces, prevent electrical erosion and, in some cases, form plastic films which decrease the coefficient of friction and the wear rate of the contact.     

Friction and wear of PTFE seal materials

Shaft seals made from polytetrafluoroethylene (PTFE) materials, called PTFE lip seals, have been successfully used for decades in the chemical industry. Owing to their chemical and thermal stability, PTFE lip seals are used instead of elastomeric lip seals in many automotive and hydraulic applications. This paper deals with the fundamental tribological properties and effects of filled PTFE materials employed in rotary shaft seals, mainly on the basis of experimental work done in the authors' laboratory. The tribological components of a sealing system and the main influences on the sealing function are briefly surveyed. The test methods and conditions used are also described. The experimental results show that the fillers used in the PTFE compounds, as well as the topography of the shaft, play a crucial role in fluid sealing.     

TEM studies of anti-wear films/wear particles generated under boundary conditions lubrication

Friction and wear performance of engine oil were studied in presence of Zinc-dialkyldithiophosphate (ZDDP) and ZDDP–iron fluoride (FeF₃) combination using a ball-on-ring wear testing device under boundary conditions. Friction and wear performance of engine oil improves in presence of ZDDP–FeF₃ combination. In order to understand the wear mechanisms the microstructure and the chemical composition of wear debris generated during wear process were investigated using TEM together with EDX analyzes. Novel observations on the wear debris generated at different testing loads are presented. Independent of normal loads, amorphous debris containing P, O, Fe and Zn elements and crystalline debris of Fe₂O₃ are formed. No trace of S is present in amorphous debris under low load (2.32 GPa) conditions while S is a dominating element under high loaded (3.68 GPa) conditions. On the other hand, at lower loads a few iron oxide is formed while at higher loads larger sizes of iron oxides are formed resulting in larger friction and wear.     

The effect of femoral head diameter upon lubrication and wear of metal-on-metal total hip replacements

It has been found that a remarkable reduction in the wear of metal-on-metal hip joints can be achieved by simply increasing the diameter of the joint. A tribological evaluation of metal-on-metal joints of 16, 22.225, 28 and 36 mm diameter was conducted in 25 per cent bovine serum using a hip joint simulator. The joints were subject to dynamic motion and loading cycles simulating walking for both lubrication and wear studies. For each size of joint in the lubrication study, an electrical resistivity technique was used to detect the extent of surface separation through a complete walking cycle. Wear of each size of joint was measured gravimetrically in wear tests of at least 2 x 10(6) cycles duration. Joints of 16 and 22.225 mm diameter showed no surface separation in the lubrication study. This suggested that wear would be proportional to the sliding distance and hence joint size in this boundary lubrication regime. A 28 mm diameter joint showed only limited evidence of surface separation suggesting that these joints were operating in a mixed lubrication regime. A 36 mm diameter joint showed surface separation for considerable parts of each walking cycle and hence evidence of the formation of a protective lubricating film. Wear testing of 16 and 22.225 mm diameter metal-on-metal joints gave mean wear rates of 4.85 and 6.30 mm3/10(6) cycles respectively. The ratio of these wear rates, 0.77, is approximately the same as the joint diameters ratio, 16/22.225 or 0.72, as expected from simple wear theory for dry or boundary lubrication conditions. No bedding-in was observed with these smaller diameter joints. For the 28 mm diameter joint, from 0 to 2 x 10(6) cycles, the mean wear rate was 1.62 mm3/10(6) cycles as the joints bedded-in. Following bedding-in, from 2.0 x 10(6) to 4.7 x 10(6) cycles, the wear rate was 0.54 mm3/10(6) cycles. As reported previously by Goldsmith et al. in 2000 [1], the mean steady state wear rate of the 36 mm diameter joints was lower than those of all the other diameters at 0.07 mm3/10(6) cycles. For a range of joints of various diameters, subjected to identical test conditions, mean wear rates differed by almost two orders of magnitude. This study has demonstrated that the application of sound tribological principles to prosthetic design can reduce the wear of metal-on-metal joints, using currently available materials, to a negligible level.     

一种新型自补偿组合式机械密封的设计与应力分析

本研究设计了一种由二级油沟(或迷宫)密封、一级锥形端面密封构成的新型自补偿组合式机械密封,并利用ANSYS软件分析了锥形端面密封中锥形静环厚度变化对密封面接触压力、O形圈的Von.mises应力和弹簧推力的影响.应力分析表明:锥形静环厚度在设计范围内变化时,密封面处的最大接触压力大于或远大于密封介质工作压力,说明所设计的新型自补偿组合式机械密封具有良好的密封性和自补偿能力,可实际应用于转轴的密封.     

Friction and wear behavior of diamond-like carbon coating on plasma nitrided mild steel under boundary lubrication

The friction and wear properties of synthetic ionic liquid functionalized borate esters as additives in poly-alpha-olefin (PAO) were measured for diamond-like carbon (DLC) coating on plasma nitrided AISI 1045 steel. Results show that the borate esters gave much better friction–reduction and antiwear properties for DLC coating/steel and DLC coating/DLC coating sliding pairs than zinc dialkyldithiophosphate (ZDDP). In addition the DLC coating had much better wear resistance than the nitrided mild steel substrate, indicating that duplicate surface modification was more effective in significantly increasing the wear resistance of mild steel.     

Behavior of medium carbon steel under combined fatigue and wear

The combined fatigue-wear life of medium carbon steel (AISI 1045) was investigated under various combinations of loads and sliding wear conditions using a rotating beam test. The direction of the maximum tensile stress due to bending was perpendicular to that due to wear [1]. Tests were also performed with specimens plated with a thin layer of cadmium or nickel-gold. All of the tests were conducted in the high cycle regime. The results show that the fatigue life of all the specimens at a stress level higher than the endurance limit of the specimen was within the experimental scatter of a typical fatigue test. The effect of sliding wear on fatigue life is manifested primarily by the stress field imposed by the slider on the specimen. In the case of plated specimens, the fatigue life was not significantly affected, although the wear rate was decreased by an order of magnitude.     

Friction and wear behaviors of aluminum-on-steel under the lubrication of grease containing a complex of lanthanum dialkyldithiocarbamate and phenanthroline

A complex of lanthanum dialkyldithiocarbamate and phenanthroline was synthesized, and its lubricating and antiwear behaviors as an additive in lithium grease were evaluated using a Timken tester with a SAE52100 steel ring sliding under an A1 2024 block. As a comparison, the wear behavior of a steel-on-steel system under the lubrication of the same grease was also investigated under the same test conditions. The protective film formed on the rubbed surface of aluminum was investigated by both XPS and AES. Results of friction and wear tests indicate that this rare earth complex possess good antiwear ability for aluminum, and its antiwear and friction reduction properties for the aluminum-on-steel system is even superior to that for the steel-on-steel system. The results of AES and XPS analyses illustrate that the prepared La complex as an additive in lithium grease forms a protective film containing lanthanum oxide, aluminum sulphide, and an organic compound containing sulfur and nitrogen on the rubbed surface of aluminum.