Showing papers in "Tribology Transactions in 2003"
TL;DR: In this article, the potential use of a new technology of laser surface texturing (LST) in parallel thrust bearings is theoretically investigated, where the surface texture has the form of micro-dimples with pre-selected diameter, depth, and area density.
Abstract: The potential use of a new technology of laser surface texturing (LST) in parallel thrust bearings is theoretically investigated. The surface texture has the form of micro-dimples with pre-selected diameter, depth, and area density. It can be applied to only a portion of the bearing area (partial LST) or the full bearing area (full LST). Optimum parameters of the dimples, and best LST mode, are found in order to obtain maximum load carrying capacity for a thrust bearing having parallel mating surfaces. A comparison is made with optimum linear and stepped sliders showing that parallel LST sliders can provide similar load carrying capacity. Scheduled for Presentation at the 58th Annual Meeting in New York City April 28–May 1, 2003
475 citations
TL;DR: An elastic-plastic model for contacting rough surfaces that is based on accurate Finite Element Analysis (FEA) of an elasticplastic single asperity contact is presented in this paper.
Abstract: An elastic-plastic model for contacting rough surfaces that is based on accurate Finite Element Analysis (FEA) of an elastic-plastic single asperity contact is presented. The plasticity index π is ...
373 citations
TL;DR: In this paper, it was shown that zinc dialkyl dithiphosphates (ZDDP) reaction films, whether rough or smooth, enhance friction by adding other additives to ZDDP solutions.
Abstract: Many phosphorus-based antiwear films, including those formed by zinc dialkyl dithiphosphates (ZDDP), cause a significant increase in friction in thin film, high-pressure, lubricated contacts. This can have a deleterious effect on engine oil fuel efficiency. Previous work has shown that friction is increased not under boundary, but under mixed lubrication conditions and it has been suggested that this phenomenon results from an effective roughening of the rubbing surfaces by the formation of unevenly-distributed reaction films. In the current paper it is shown that, when other additives commonly used in engine oils are added to ZDDP solutions, quite smooth ZDDP reaction films can result. Despite this, the ZDDP still produces a marked increase in friction in mixed lubrication conditions, which suggests that surface roughening is not the main origin of friction enhancement by ZDDP reaction films. In a companion paper, Part II, it is shown that ZDDP reaction films, whether rough or smooth, enhance friction by...
161 citations
TL;DR: In this paper, the authors used simple empiricisms that can be used to describe the pressure-viscosity response piecewise over the entire range from ambient to glass transition.
Abstract: The numerical simulation of elastohydrodynamic lubrication has evolved in terms of solution detail, speed and robustness. However, if EHL is to begin to solve practical quantitative problems involving differences among lubricants, practitioners must begin to utilize pressure-viscosity relationships in their numerical schemes that can describe real liquid response. The authors begin with the simple empiricisms that can be used to describe the pressure-viscosity response piecewise over the entire range from ambient to glass transition. Then various free volume formulations are introduced and compared. Finally, empirical expressions that can describe some essential features over the entire pressure range are presented. An example of the utility of one empirical equation is offered. Scheduled for Presentation at the 58th Annual Meeting in New York City April 28–May 1, 2003
104 citations
TL;DR: In this article, a general fully coupled finite element approach is presented for the prediction of steady operating characteristics such as minimum film thickness, load capacity, and drag require the coupled solution of the shell structure and the gas flow.
Abstract: Foil gas journal bearings consist of a compliant metal shell structure that supports a rigid journal by means of a gas film. The prediction of steady operating characteristics such as minimum film thickness, load capacity, and drag require the coupled solution of the shell structure and the gas flow. A general fully coupled finite element approach is presented. A single four noded finite element that incorporates the elastically supported shell structure of the foil and the gas film modeled by a compressible Reynolds equation is developed. The resulting system of nonlinear finite elements is solved by the Newton Raphson method. Presented at the 58th Annual Meeting in New York City April 28–May 1, 2003
82 citations
TL;DR: In this article, the authors show the correlation between the tribological behavior of grease and its composition and structure, and show that Greases with low elastic modulus have a greater capacity to form a thick EHD film compared to greases with large G'.
Abstract: The aim of this work is to show the correlation between the tribological behavior of grease and its composition and structure. A tribological investigation was conducted on various lubricants. The following parameters were varied: base oil, soap and presence of additives. To ensure efficient control of grease composition, greases containing the same type of soap were manufactured from the same concentrated soap sample. Film thickness measurements showed that the thickener microstructure (revealed by TEM observations) is not the determining factor for the formation of a thick lubricant film, i.e. a film following EHL equations. Nevertheless, the soap - base oil interaction is an essential parameter. The composition of a grease influences oil bleeding, mechanical stability, and rheological behavior. The elastic modulus G' seems to be the only parameter directly linked to tribological behavior. Greases with low G' have a greater capacity to form a thick EHD film compared to greases with large G'.
79 citations
TL;DR: In this article, it was shown that the presence of a ZDDP reaction layer inhibits the entrainment of liquid lubricant into rolling/sliding contacts, and that these contacts operate in boundary lubrication, with consequently high friction, up to higher speeds than would otherwise be the case and the attainment of full film elastohydrodynamic lubrication is also postponed.
Abstract: In a companion paper, Part I, it was shown that the friction enhancement produced in mixed lubrication conditions by ZDDP reaction films is not due to surface roughening as has previously been supposed. Instead, optical measurement of elastohydrodynamic film thickness shows that the presence of a ZDDP reaction layer inhibits the entrainment of liquid lubricant into rolling/sliding contacts. As a result, these contacts operate in boundary lubrication, with consequently high friction, up to higher speeds than would otherwise be the case and the attainment of full film elastohydrodynamic lubrication is also postponed. Possible mechanisms by which ZDDP reaction films might inhibit fluid entrainment are discussed.
67 citations
TL;DR: In this article, the authors used X-ray absorption near-edge spectroscopy (XANES) to study the antiwear films formed from the commonly used combination of ZDDP and calcium sulfonate in both neutral and basic forms.
Abstract: Zinc dialkyldithiophosphates (ZDDPs) from very effective antiwear films in boundary lubrication applications In most cases, however, the ZDDPs do not work alone They are formulated with many other additives to provide the performance required by today's modern oils X-ray absorption near-edge spectroscopy (XANES) has been used to study the antiwear films formed from the commonly used combination of ZDDP and calcium sulfonate in both neutral and basic forms The results are presented in two papers: Part 1 for the phosphorus species and Part 2 for the sulfur species XANES showed conclusively that in the presence of LOB (low overbased) or HOB (high overbased) calcium sulfonate under sliding conditions, ZDDPs do not form long-chain polyphosphates that have been associated with antiwear action Instead, short-chain polyphosphates calcium phosphate are formed The relative amounts of calcium phosphate formed depend on the ester group of the ZDDP: aryl > n-alkyl > sec-alkyl Interestingly, this order of ester
65 citations
TL;DR: In this article, a rolling/sliding contact fatigue model for machine components in mixed lubrication undergoing cyclic loading is proposed, where surface roughness and texture have a significant impact on fatigue life.
Abstract: The paper proposes a rolling/sliding contact fatigue model for machine components in mixed lubrication undergoing cyclic loading. The model consists of two distinct components. The first is a full-scale mixed lubrication analysis of interacting rough surfaces, during which surface pressure distribution is calculated. The second is the computation of subsurface stresses and determination of fatigue life using the Zaretsky fatigue model. Numerical examples are presented for a variety of surfaces with different finishes. The model predictions confirm that surface roughness and texture have a significant impact on fatigue life.
52 citations
TL;DR: A plasma spray deposited solid lubricant coating developed for high temperature sliding contacts was deposited on nine different substrate metals, heat treated at 650C in either air or argon and subsequently tested for strength using a commercially available pull-off adhesion test as discussed by the authors.
Abstract: PS304, a plasma spray deposited solid lubricant coating developed for high temperature sliding contacts was deposited on nine different substrate metals, heat treated at 650C in either air or argon and subsequently tested for strength using a commercially available pull-off adhesion test. Some samples were examined metallographically to help elucidate and explain the results. As deposited coatings exhibit pull-off strengths typically between 16 and 20 MPa with failure occuring (cohesively) within the coating. Heat treatment in argon at 650 C results in a slight increase in coating (cohesive) strength of about 30 percent to 21 to 27 MPa. Heat treatment in air at 650 C results in a dramatic increase in strength to over 30 MPa, exceeding the strength of the epoxy used in the pull test. Cross section metallographic analyses show that no microstructural coating changes occur following the argon heat treatments, however, exposure to air at 650C gives rise to the formation of a second chromium-rich phase precipitate within the PS304 NiCr constituent which provides a strengthening effect and a slight (approximately 5 percent) coating thickness increase. Subsequent heat treatments do not result in any further coating changes. Based upon these studies, PS304 is a suitable coating for use on a wide variety of high temperature substrates and must be heat treated following deposition to enhance strength and ensure dimensional stability.
43 citations
TL;DR: In this article, the authors describe an implementation of a genetic algorithm scheme suitable to the optimal shape design of finite-width, isoviscous, fluid film journal bearings under steady load and steady journal rotation.
Abstract: This paper describes an implementation of a genetic algorithm scheme suitable to the optimal shape design of finite-width, isoviscous, fluid film journal bearings under steady load and steady journal rotation. Assuming perfect journal cylindricity, the optimization objective is to determine the circumferential variation of sleeve geometry that maximizes bearing load capacity, subject to specified minimum film thickness. Particular emphasis is placed on the selection of the number of design variables, chromosomes per generation, crossover and mutation probabilities, and the number of generations that promote convergence to one or more optimal designs. Optimal film thickness specifications obtained using this genetic algorithm are found to be generally superior to random search methods and comparable with previously published results based on traditional optimization strategies. For finite-width bearings, optimal bearing geometry is found to offer a small improvement in load capacity and a substantial improvement in oil flow over purely cylindrical designs.
TL;DR: In this article, a fast approach for the calculation of 3D pressures and subsurface stresses in pure rolling EHL contacts with real (measured) roughness is presented, which is then applied to several types of surface finish.
Abstract: A fast approach for the calculation of 3-D pressures and subsurface stresses in pure rolling EHL contacts with real (measured) roughness is presented. For the calculation of pressures the model uses the analytical work of Greenwood and Morales-Espejel for transverse (to the rolling direction) moving sinusoidal waviness. The model is extended to handle longitudinal waviness as well. By using these two basic components the pressure distribution for real rough surfaces can now be calculated form the 3-D roughness map. From the surface pressures, the sub-surface stress field can then be calculated with a similar technique. The result is the total Stress State in a rolling rough EHL contact. In this paper the method for calculating the pressures and stress fields is first described. It is then applied to several types of surface finish. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Cancun, Mexico October 27–30, 2002
TL;DR: In this paper, physical and chemical characterizations of diesel engine oils are conducted to investigate the impact of soot properties on friction coefficient between reciprocating rubbing metal surfaces, and the results showed that soot in an engine oil categorized in API CC-4 appeared to act as friction modifiers, since a higher content of SOOT in the oil caused lower friction, especially in the low temperature range between 40° and 90°C.
Abstract: Physical and chemical characterizations of soot in diesel engine oils are conducted to investigate the impact of soot properties on friction coefficient between reciprocating rubbing metal surfaces. In SRV friction tests, soot in an engine oil categorized in API CC-4 appeared to act as friction modifiers, since a higher content of soot in the oil caused lower friction, especially in the low temperature range between 40° and 90°C. In contrast, there is no significant difference obtained in friction coefficient between the presence and absence of soot in other CD and CG-4 oils. Distribution of soot particle sizes was measured with the DLS (Dynamic Light Scattering) technique to examine the correlation between lower frictional characteristics and fraction of soot particle sizes less than the estimated oil film thickness. Soot aggregates dispersed in the oils were also observed with the TEM-FFR (Freeze Fracture Replica) technique to investigate the impact of the actual state of soot in oils on frictional beha...
TL;DR: In this paper, a quasi-static and quasi-dynamic analysis of double-row tapered roller bearings (DRTRB) is presented to determine the internal load distribution, bearing stiffness and fatigue life.
Abstract: The first part of this two-part paper presents an analytical model to predict the performances of double-row tapered roller bearings (DRTRB). The model has been structured in two major parts: (1)- A conventional quasi-static analysis to determine the internal load distribution, the bearing stiffness and the fatigue life and (2)- A quasi-dynamic analysis which integrates the differential equations for each bearing element in order to determine the amount of skidding, the friction forces and moments and consequently the heat dissipation. The proposed model allows one to take into account a general external loading (shaft tilting moments, radial and axial loads), the initial axial compression introduced while mounting, the operating speed and the lubricant properties. Some numerical results are presented in the second part of this two-part paper. Presented at the 56th Annual Meeting in Orlando, Florida May 20–24, 2001
TL;DR: In this paper, the effects of friction on the contact and deformation behavior of sliding asperity contacts were investigated. And the authors showed that the deformation deformation increases significantly as the friction in the contact increases, particularly the approach that causes plastic flow of the as perity contact.
Abstract: Finite-element analyses are carried out to study the effects of friction on the contact and deformation behavior of sliding asperity contacts In the analysis, on elastic-perfectly-plastic asperity is brought in contact with a rigid flat at a given normal approach Two critical values of the normal approach are used to describe the asperity deformation One is the approach corresponding to the point of initial plastic yielding, and the other at the point of full plastic flow Additional variables used to characterize the deformation behavior include the shape and size of the plastic zone and the asperity contact size, pressure, and load capacity Results from the finite-element analysis show that the two values of critical normal approach decrease significantly as the friction in the contact increases, particularly the approach that causes plastic flow of the asperity The size of the plastically deformed zone is reduced by the friction when the contact becomes fully plastic The reduction is very conside
TL;DR: In this paper, a rolling contact tribometer based on a planar thrust bearing geometry is described, where the bearing races are flat plates that drive a ball into a near-circular, spiral path.
Abstract: A new rolling contact tribometer based on a planar thrust bearing geometry is described. The bearing 'races' are flat plates that drive a ball into a near-circular, spiral path. The spiraling ball is returned to its initial radius each revolution around the race by a 'guide plate' backed by a force transducer. The motions of the ball are analyzed and the force exerted by the ball on the guide plate is related to the friction coefficient of the system. The experimental characteristics of the system are presented and the system is shown to exhibit the behavior expected for a tribometer.
TL;DR: In this article, an efficient and comprehensive macro-micro-fatigue approach for analyzing the effect of roughness on fatigue life in mixed elastohydrodynamic lubrication contact is presented.
Abstract: An efficient and comprehensive Macro-Micro-Fatigue approach for analyzing the effect of roughness on fatigue life in mixed elastohydrodynamic lubrication contact is presented. It involves two macro-micro approaches, one for mixed lubrication analysis and the other for contact stress evaluation. The macro-micro approaches make it possible to efficiently model pressure and film thickness distribution over the entire area of contact, at the same time allowing a detailed account of asperity interaction effects. The three-stage process comprises a dry rough contact solver, a simplified mixed elastohydrodynamic lubrication solver, and a hydrostatic rough contact solver, all of which are presented. Subsurface stresses are calculated and fatigue life is estimated using the Zaretsky fatigue model. Numerical simulations are performed for several cases of point contacts of rough surfaces and results are presented on a comparative basis.
TL;DR: In this paper, a simple algebraic relation was established for the upper and lower L(sub 10) life limits as a function of number of bearing failures for any bearing geometry, and the maximum and minimum variation between the bearing resultant life and the calculated life correlate with the 90 percent confidence limits for a Weibull slope of 1.5.
Abstract: Two types of rolling-element bearings representing radial loaded and thrust loaded bearings were used for this study. Three hundred forty (340) virtual bearing sets totaling 31400 bearings were randomly assembled and tested by Monte Carlo (random) number generation. The Monte Carlo results were compared with endurance data from 51 bearing sets comprising 5321 bearings. A simple algebraic relation was established for the upper and lower L(sub 10) life limits as function of number of bearings failed for any bearing geometry. There is a fifty percent (50 percent) probability that the resultant bearing life will be less than that calculated. The maximum and minimum variation between the bearing resultant life and the calculated life correlate with the 90-percent confidence limits for a Weibull slope of 1.5. The calculated lives for bearings using a load-life exponent p of 4 for ball bearings and 5 for roller bearings correlated with the Monte Carlo generated bearing lives and the bearing data. STLE life factors for bearing steel and processing provide a reasonable accounting for differences between bearing life data and calculated life. Variations in Weibull slope from the Monte Carlo testing and bearing data correlated. There was excellent agreement between percent of individual components failed from Monte Carlo simulation and that predicted.
TL;DR: In this article, the coefficients of friction and degradation rates of three lubricants run in the boundary regime in vacuum were evaluated in a Spiral Orbit Tribometer, which subjected the lubricants to rolling contact conditions similar to those found in angular contact ball bearings and showed that multiply alkylated cyclopentane (MAC) hydrocarbon lubricants suffered degradation at a rate almost two orders of magnitude less than the degradation rate of two perfluoropolyalkylether (PFPE) lubricants.
Abstract: The coefficients of friction and relative degradation rates of three lubricants run in the boundary regime in vacuum are evaluated in a Spiral Orbit Tribometer. This tribometer subjected the lubricants to rolling contact conditions similar to those found in angular contact ball bearings. A multiply alkylated cyclopentane (MAC) hydrocarbon lubricant suffered degradation at a rate almost two orders of magnitude less than the degradation rate of two perfluoropolyalkylether (PFPE) lubricants.
TL;DR: In this paper, the effect of surface roughness on the mixed EHD lubrication characteristics has been studied by using a numerical approach developed recently by Zhu and Hu (1), (2).
Abstract: The effect of surface roughness on the mixed EHD lubrication characteristics has been studied in this paper by using a numerical approach developed recently by Zhu and Hu (1), (2). This approach is capable of handling measured rough surfaces under very severe operating conditions, and simulating the entire transition from the fill film EHD, mixed, down to boundary lubrication. In the present study a set of sample cases in a circular contact is analyzed. Three typical machined surfaces are used, representing different types of topography and orientation. The original RMS roughness (before deformation) is adjusted to 8 different levels, from 0.1 μm up to 1.5 μm, in order to cover a practical range for industrial applications. Results show that in the typical mixed EHL the maximum pressure, contact load ratio, friction, flash temperature as well as maximum subsurface shear stress, are all increased significantly as the roughness increases. The effect on the average film thickness (or gap), however, is relati...
TL;DR: In this paper, a more realistic shaft surface with asperities is included in a full film lubrication model, and an elastohydrodynamic analysis, incorporating both the fluid mechanics of the lubricating film and the elastic behavior of the lip, is performed to predict the hydrodynamic effect of the shaft surface on lip seal operation.
Abstract: In most pervious numerical studies of lip seal behavior, the shaft surface is modeled as perfectly smooth. In the present study, a more realistic shaft surface with asperities is included in a full film lubrication model. An elastohydrodynamic analysis, incorporating both the fluid mechanics of the lubricating film and the elastic behavior of the lip, is performed to predict the hydrodynamic effect of the shaft surface on lip seal operation. Operating characteristics such as load support, reverse pumping rate, cavitation area, average film thickness and liftoff speed are investigated. Scheduled for Presentation at the 58th Annual Meeting in New York City April 28–May 1, 2003
TL;DR: In this paper, the performance of double-row tapered roller bearing (DRTRB) was investigated and the initial compression between bearing rows was found to play a major role upon bearing behavior and therefore should be considered carefully for each application.
Abstract: The model developed to predict the performance of double-row tapered roller bearings (DRTRB) and described in the first part of the paper is now exemplified. For a given example results on the internal load distribution, bearing fatigue life and hear generation are presented and discussed for various operating conditions including the mounting preload. It is revealed that some sliding occurs at the contact between the rollers and the cone that contributes significantly to the total power dissipated within the bearing. It is also shown that an optimum axial compression (or mounting preload) may be found in terms of fatigue life and heat dissipated. As the main conclusion the initial compression between bearing rows was found to play a major role upon the bearing behavior and therefore should be considered carefully for each application. Presented at the 56th Annual Meeting in Orlando, Florida May 20–24, 2001
TL;DR: In this paper, the integrated adhesive wear model was used to analyze experimental wear data obtained previously for an A6061-T6 alloy and MMC-D, an aluminium alloy matrix composite containing 20% spherical alumina particles.
Abstract: The integrated adhesive wear model tokes into account both the transient wear and the steady-state wear in wear testing. The transient wear volume is described by an exponential equation while the steady-state wear by a revised Archard's equation. In this study, the integrated wear model was used to analyze experimental wear data obtained previously for an A6061-T6 alloy and MMC-D, an aluminium alloy matrix composite containing 20% spherical alumina particles. Two loads of 7.5 kgf and 10.0 kgf, and a speed of 4.58ms−1 were used in conducting the experiments. Both the standard wear coefficient and the net steady-state wear coefficient values for both types of materials were determined. On the average, the average standard steady-state wear coefficient, as compared with the net steady-state wear coefficient, was about 52% higher for MMC-D and 246% higher for A6061-T6. A higher load was found to have the effect of increasing the wear coefficient values. Scheduled for Presentation at the 58th Annual Meeting i...
TL;DR: In this article, two types of subsurface-originated failure modes are investigated: macroscopic contact fatigue and microscopic pitting, and the cracks responsible for both modes of failure initiate in polyethylene material that has been embrittled by oxidation; this oxidation is an undesirable outcome of the gamma irradiation (in air) used to sterilize the tibial bearings.
Abstract: Tibial hearings of total knee replacements are generally made from ultra-high molecular weight polyethylene (UHMWPE). Failure of those hearings has been found to result in many cases from subsurface crack initiation and propagation. Two types of subsurface-originated failure modes are investigated in this study: macroscopic contact fatigue and microscopic pitting. The cracks responsible for both modes of failure initiate in polyethylene material that has been embrittled by oxidation; this oxidation is an undesirable outcome of the gamma irradiation (in air) used to sterilize the tibial bearings. Accelerated aging was used in this work to achieve oxidation levels similar to those found in retrieved bearings. Tribotesting of the aged bearing materials was carried out under simulated service conditions using a rolling/sliding tester. Macroscopic fatigue cracks and microscopic surface pitting developed in UHMWPE specimens tested on the rolling/sliding tester, and the damage was similar to that found in retrie...
TL;DR: In this article, a simple and easy-to-rise TEHD model is presented, which allows for the determination of mean face temperature, power loss, leakage rate, axial stiffness and fluid film thickness.
Abstract: Numerous studies have shown that the properties of non-contacting liquid face seals depend greatly on thermal effects. A complex numerical TEHD (ThermoElastoHydroDynamic) model is needed to accurately determine seal temperature. Moreover, this temperature is influenced by a significant number of parameters (such as operating conditions or seal ring shape). This makes the task of design and optimization of mechanical face seals difficult. This paper presents a simple and easy-to-rise TEHD model, which allows for the determination of mean face temperature, power loss, leakage rate, axial stiffness and fluid film thickness. It is demonstrated that the results depend on a single dimensionless parameter. The simplified model is validated by comparison with an accurate numerical TEHD model.
TL;DR: In this article, the authors present a simulation of the motion of two high pressure (HP) and one low pressure (LP) fingers arranged axially in a staggered configuration and subject to an axial pressure drop.
Abstract: The technology of shaft compliant seals was revolutionized when brush seals first replaced the labyrinth seals at many locations along compressor and turbine shafts. Finger seals present a compliant seal alternative to brush seals and through their geometric configuration bring about the added potential of hydrodynamic lifting and thus non-contacting operational features. Their manufacturing costs are well below those of brush seals and their potential lifting capability, by eliminating the wear factor, increases considerably their life span while making them a preferred embodiment to brush seals. The fingers' compliance allows both axial and radial adjustment to rotor excursions without damage to the integrity or performance of the seal. The work to be presented here concerns design development through numerical simulation of the motion of an assembly of two high pressure (HP) and one low pressure (LP) fingers arranged axially in a staggered configuration and subject to an axial pressure drop. This combi...
TL;DR: In this paper, the authors analyzed the effectiveness of the effective lubricating phase in grease-lubricated contact and determined the shear rate experienced by lubricants in the contact.
Abstract: The first aim of this work is to analyze the nature of the effective lubricating phase in grease lubricated contact. The second aim is to determine the shear rate experienced by lubricants in the i...
TL;DR: In this paper, the authors present a system that provides to the ball-race contact fresh lubricant in-situ and on demand, using a porous cartridge attached to the inner or outer ring of a ball bearing.
Abstract: Many of today's spacecraft have long mission lifetimes. Whatever the lubrication method selected, the initial lubricant charge is required to last the entire mission. Fluid lubricant losses are mainly due to evaporation, tribo-degradation, and oil creep out of the tribological regions. In the past, several techniques were developed to maintain the appropriate amount of oil in the system. They were based on oil reservoirs (cartridges, impregnated porous parts), barrier films, and labyrinth seals. Nevertheless, all these systems have had limited success or have not established a proven record for space missions. The system reported here provides to the ball-race contact fresh lubricant in-situ and on demand. The lubricant is stored in a porous cartridge attached to the inner or the outer ring of a ball bearing. The oil is released by heating the cartridge to eject oil, taking advantage of the greater thermal expansion of the oil compared to the porous network. The heating may be activated by torque increases that signal the depletion of oil in the contact. The low surface tension of the oil compared to the ball bearing material is utilized and the close proximity of the cartridge to the moving balls allows the lubricant to reach the ball-race contacts. This oil resupply system can be used to avoid a mechanism failure or reduce torque to an acceptable level and extend the life of the component.
TL;DR: In this paper, the authors show that the notch wear rate increases with higher coolant supply pressure due to significant erosion of the tool material by the high pressure coolant jet, leading to inconsistency in tool performance, accelerated by fluctuations in thermal and mechanical properties.
Abstract: Chip breakability is significantly improved with the use of high pressure coolant supply. This is a result of the reduction in the tool-chip contact length during machining as the coolant under high pressure lifts the chip up after passing the deformation zone. Increasing the coolant pressure results in shorter ceramic tool life when machining Inconel 718 suggesting that the high pressure coolant supply reduces temperature at the cutting zone below a critical level where ceramic tools can perform satisfactorily. The inadequate fracture toughness of ceramic tools makes them more susceptible to failure by mechanical action such as notching at the depth of cut line and premature fracture. The notch wear rate increases with higher coolant supply pressure due to significant erosion of the tool material by the high pressure coolant jet. This mechanically related failure mode occurs on a random basis leading to inconsistency in tool performance, accelerated by fluctuations in thermal and mechanical properties wh...
TL;DR: In this article, the performance of various blends consisting of base oil and additives containing sulfur and phosphorus and a metal deactivator, in conjunction with those of a blend of the same base oil, and all the studied additives in the same amounts as in the single blends were investigated at 32°C and 100°C.
Abstract: The tribological behaviors of various blends consisting of base oil and additives containing sulfur and phosphorus and a metal deactivator, in conjunction with those of a blend of the same base oil and all the studied additives in the same amounts as in the single blends were investigated at 32°C and 100°C. Balls and flat disks of AISI 52100 steel were tested in baths of the different blends using a ball-on-disk tribometer under a load of 147 N and sliding speed of 0.34 m/s that resulted in sliding in the boundary lubrication regime. Measurements of the coefficient of friction and electrical contact voltage were used to characterize the tribological performance of each blend and to confirm the formation and removal of antiwear tribofilms. Surface profilometry was performed to evaluate the wear resistance of the tribofilms, and scanning electron microscopy to characterize the dominant wear mechanisms. Endurance tests were conducted with the phosphorus-containing blend that presented in-situ evidence of tri...