Interactive Effect between Organic Friction Modifiers and Additives on Friction at Metal Pushing V-Belt CVT Components

The interactions between organic friction modifiers (FMs) and other additives in a continuously variable transmission (CVT) fluid (CVTF) are investigated with the goal of optimizing friction management of metal pushing V-belt CVTs. Three types of FMs (oleic acid, oleyl alcohol, and glycerol mono-oleate [GMO]) were formulated in poly-α-olefin (PAO) and a fully formulated CVTF, and the friction performance was evaluated in a reciprocating test apparatus (TE77). To estimate their effect on the major frictional components in the CVTs, a steel belt–pulley and a torque converter clutch, the tribotests were carried out with both steel–steel and paper–steel sliding configurations. Then, the posttest materials were assessed by surface analysis techniques to observe the chemical nature of any reacted layers at the surface.

The results indicate that the friction on the steel surface was significantly influenced by a combination of the FMs and the CVTF additives as well as the functional group of the FMs. Although oleic acid and GMO typically present greater friction reduction than oleyl alcohol under most conditions, oleic acid did not decrease friction at the steel–steel contact with the presence of the other additives in the CVTF formulation; the friction reduction effect was impaired by the presence of other additives. Surface analysis of the posttest specimens implied that it was interactions with the calcium detergent that inactivated the FM effect of oleic acid.     

High-Speed Elastohydrodynamic Lubrication by a Dilute Oil-in-Water Emulsion

When a concentrated contact is lubricated at low speed by an oil-in-water emulsion, a film of pure oil typically separates the surfaces (stage 1). At higher speeds, starvation occurs (stage 2) and the film is thinner than would be expected if lubricated by neat oil. However, at the very highest speeds, film thickness increases again (stage 3), though little is known for certain about either the film composition or the mechanism of lubrication, despite some theoretical speculation.

In this article, we report the film thickness in a ball-on-flat contact, lubricated by an oil-in-water emulsion, at speeds of up to 20 m/s, measured using a new high-speed test rig. We also investigated the sliding traction and the phase composition of the film, using fluorescent and infrared microscopy techniques.

Results show that, as the speed is increased, starvation is followed by a progressive change in film composition, from pure oil to mostly water. At the highest speeds, a film builds up that has a phase composition similar to the bulk emulsion. This tends to support the “microemulsion” view rather than the “dynamic concentration” theory.     

Palm oil and mineral oil based lubricants—their tribological and emission performance

A comparative study of wear, friction, viscosity, lubricant degradation and exhaust emissions was carried out on a palm oil and a mineral oil-based commercial lubricating oil. The wear and friction test was at first conducted using a reciprocating universal wear machine followed by a two-stroke gasoline Yamaha portable generator set, ET 950. The test conditions for the bench test were: pressure, 3.0 MPa; sliding speed, 0.20 m s⁻¹; sliding stroke, 80 mm; room temperature, 25°C. The test conditions for the actual engine were: constant load, 0.4 kW for wear of the piston ring but various loads for exhaust emissions and constant speed, 2800 rpm. Analysis of post bench test lubricating oils was performed using ISL viscometer, TAN/TBN analyzer and FT-IR spectroscopy to investigate viscosity, TAN value and the oxidation level, respectively. Exhaust emission analysis was also performed using a BOSCH exhaust gas analyzer. Experimental results demonstrated that the palm oil based lubricating oil exhibited better performance in terms of wears, and that the mineral oil based lubricating oil exhibited better performance in terms of friction. However, the palm oil based lubricant was the more effective in reducing the emmission levels of CO and hydrocarbon.     

Effect of the Grooved Rod on the Friction Force of U-Cup Hydraulic Rod Seal with Rough Lip

There are few works that have studied the sealing mechanism between two rough surfaces. In the present article, an elastohydrodynamic one-dimensional model of the U-cup hydraulic seal is performed by taking into account both the shaft and the lip roughness. The numerical results are compared with the inverse hydrodynamic lubrication (IHL) theory and are validated with previously published experiments. Differences confirm the accuracy of the elastohydrodynamic lubrication (EHL) modeling with a gap of about 5% between numerical and experimental results.

The study of the textured shaft effect is performed in three steps: by first changing the shape of the grooves, then changing their amplitudes, and finally by varying their densities. The results demonstrate that a dry contact could occur for some pattern profiles, whereas full-film lubrication is verified for other profiles. The numerical simulations confirm that the asymmetric groove shape affects the friction and show a significant impact of the pattern amplitude on the power loss. Additionally, a slight effect of the groove density is observed on the friction force.     

Influence of Temperature and Relative Humidity on the Friction and Wear of Unlubricated Reciprocating Sliding Steel/ Steel Couples

Many tribosystems are subjected to different conditions with respect to temperature and humidity. Reciprocating sliding tests with steel/steel couples were performed using a laboratory test rig in air with varying relative humidity and temperature. During each test the friction force, the total linear wear, the electrical contact resistance, and the acoustic emission were recorded. Tests with self‐mated couples of bearing steel (100r6) and of stainless steel (X10CrNiMoNb18‐10/X5CrNi18‐9) in a ball‐on‐disc arrangement revealed small effects of temperature and humidity on friction, but a strong effect of the water vapour content on the wear rate of the system. Attempts were made to correlate changes of wear behaviour with different wear mechanisms.     

Investigation of the Transition State in the Wear of Polyphenylene Sulfide Sliding Against Steel

The effect of sliding variables, including counterface roughness, sliding speed, and contact pressure, on the run-in state of wear and friction was studied. Sliding was performed in the pin-on-disk configuration with a polyphenylene sulfide (PPS) pin resting on the flat steel counterface. Some experiments were also run to study the effect of air cooling and heating. Optical microscopy and scanning electron microscopy were used to study the shape and size of the wear debris, worn pin surface, and the transfer film formed on steel counterfaces. It was found that friction and wear in the run-in state were significantly affected by the sliding variables studied and their influence was closely related to the development of a transfer film during the run-in state. If the transfer film developed during initial sliding, the coefficient of friction increased and wear rate decreased. The wear rate in the run-in state increased with the increase in initial counterface roughness and there was an optimal counterface roughness of 0.06 m Ra for minimum steady state wear rate. A higher applied load led to a higher wear rate in the run-in state but that was not the case with steady state wear rate.     

Investigation of wear mechanism of SiC particulate-reinforced Al-20Si-3Cu-1Mg aluminium matrix composites under dry sliding and water lubrication

Unreinforced Al-20Si-3Cu-1Mg (ASCM) aluminium alloy and SiC particle reinforced Al-20Si-3Cu-1Mg (ASCM-SiC) aluminium matrix composites were fabricated by powder metallurgy (). The samples were slid against 4Cr13 stainless steel in a reciprocal friction tester under a load of 25 N to 175 N and sliding velocity of 0.3 to 1.2 m s⁻¹ at ambient conditions. The results show that SiC particulate-reinforced aluminium matrix composites possess good wear resistance at dry sliding and less wear resistance under water lubrication. Ploughing wear is the dominant wear mechanism at dry sliding and tribochemical wear is dominant under water lubrication. SEM, AES and XPS were used to examine the wear morphology and surface chemistry.     

The Influence of Water Addition on High-Temperature Tribological Properties of Interstitial Free Steel Sliding against Different Counterparts

The influence of only water addition on the hot metal forming process has not yet been reported in regard to tribological performance. In the present study, simulation tests were carried out on a pin-on-disc tribometer to evaluate the effects of water lubrication on the wear and friction behaviors of interstitial free (IF) steel sliding against different countersurface materials at 800°C in comparison with those in dry sliding. The opposing materials were selected as GCr15 steel and ceramic-based compounds including ZrO₂, SiC, and Si₃N₄. It has been found that Si-based component–IF steel pairs exhibit the lowest wear losses despite achieving relatively high friction. Water addition adversely impairs the friction and wear characteristics on steel-steel tribopairs, whereas it shows insignificant effects on the pair involving ceramic-based components except ZrO₂. Varying tribological responses can be found among different mated surfaces under water lubrication. X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy were utilized to examine the worn surface. The acting mechanism of water addition for different rubbing pairs was further discussed from the aspects of oxide tribochemistry.     

Measurements of Flow Rate and Force Coefficients in a Short-Length Annular Seal Supplied with a Liquid/Gas Mixture (Stationary Journal)

Deep sea compression systems must work under strenuous conditions with either gas in liquid or liquid in gas mixtures, mostly inhomogeneous. Off-design operation affects the mechanical system's overall efficiency and reliability, with penalties in leakage and rotordynamic performance of secondary flow components, namely, seals. This article introduces a test rig to characterize the leakage and dynamic force coefficients of a short-length annular seal (L/D = 0.36, clearance = 0.127 mm) operating under various flow regimes ranging from pure gas, to bubbly (liquid in gas), to foamy (gas in liquid), to pure liquid. The test rig includes of rotating journal and a softy supported cartridge that make a clearance annular seal that is supplied with a liquid/gas mixture. Flowmeters record the fluid's passage, and with manual control of the streams, the mixture has a known liquid (or gas) volume fraction at the seal inlet plane. Two orthogonally mounted electromagnetic shakers excite the cartridge with periodic (single-frequency) forces spanning a wide frequency range. Eddy current sensors and accelerometers record the seal cartridge motions and a frequency domain parameter identification method delivers the seal dynamic force coefficients.

For tests with a pressure supply/pressure discharge ratio = 3.0 and 3.5 and a nonrotating journal, the article reports the flow rate for an ISO VG10 oil in air mixture with liquid volume fraction (LVF) at the inlet plane increasing from pure gas to pure liquid. Wet seal stiffness and mass and damping force coefficients follow for a seal operating with a pressure supply/pressure discharge ratio = 2.0 and operating with air (only) and also with an oil-in-air mixture with inlet LVF = 2% and 4%. The experimental results, the first reported, reveal that a small amount of liquid increases the damping coefficients of the wet seal 10-fold (or more). Predictions from a computational bulk flow model also demonstrate that the seal damping coefficient varies greatly with small contents of liquid in the oil/gas mixture, although agreement with the experimental force coefficients is not compelling due to the likely inhomogeneity of the mixture flowing though the seal.     

Transfer Solid Lubrication of Aluminum Sliding Contacts

The effects of transfer from solid lubricant sticks of unfilled, glass-filled, and bronze-filled PTFE on the room-temperature wear and friction of trailing primary contacts of aluminum (6061 T6) rods in repetitive intermittent contacts were investigated in a ring-on-rod configuration. The materials of the ring countersurfaces upon which the solid lubricants transferred and against which the trailing aluminum rods wore included steel, aluminum, copper, and an oxide dispersion-strengthened copper alloy. This sliding of the unlubricated copper ring countersurfaces against the aluminum led to the roughening of the copper as large (> 1 mm) aluminum particles embedded themselves upon the countersurface, with consequent transitions in the aluminum wear rate and the coefficient of friction to values exceeding 6 × 10^{? 3} mm³/Nm and 0.6, respectively, after an incubation period of several initial contacts of lower wear rate and friction. The other ring countersurface materials resulted in similarly high aluminum rod wear rate and coefficient of friction, more nearly from the onset of sliding. The application of unfilled PTFE solid lubricant transfer reduced the aluminum's gouging of the copper countersurfaces and correspondingly reduced the aluminum rod wear rate and the coefficient of friction against the copper, as well as against all other countersurface materials, towards 2 × 10^?3 mm³/Nm and 0.3 or less, respectively. Glass- and bronze-filled PTFE transfer lubricants provided reductions in the wear rate of the aluminum rod comparable to or in some cases better than the unfilled PTFE, though the unfilled PTFE transfer lubricant in several cases provided better friction reduction.     

弹性金属塑料复合材料的摩擦磨损特性研究

在MPX-2000摩擦磨损试验机上，用环盘摩擦副，结合扫描电镜分别评价了弹性金属塑料（EMP）复合材料与钢在油润滑和干摩擦条件下的摩擦磨损特性。结果表明：两种试验条件下，相同滑动速度的摩擦系数随载荷的升高而减小，当载荷为2000N，滑动速度小于3.52m/s时，摩擦系数基于趋于稳定，EMP磨损率随滑动速度和载荷的升高耐增加，但不同试验条件的增幅不高，油润滑下滑动速度小于3.52m/s和干摩擦条件下滑动速度小于1.96m/s时，EMP以微切削，塑性变形和梨沟磨损为主，并在摩擦副两表面形成转移物。     

Comparison of Power Losses and Temperatures between an All-Steel and a Direct Outer Ring–Cooled,Hybrid 133-mm-Bore Ball Bearing at Very High Speeds

Next-generation aircraft engines will have to face more stringent requirements for reliability, thrust to weight, efficiency, environment protection, and profitability. These requirements affect all engine modules and components, including rolling element bearings. To cope with the above-mentioned requirements, next-generation aircraft engine main shaft bearings will operate under higher loads, speeds, and temperatures and increased reliability. In addition, lighter weight components are desirable. Hence, new material and cooling technologies including weight- and stress-optimized designs need to be developed.

In this article, the experimental investigation results of a novel main shaft ball bearing featuring ceramic balls, direct outer ring cooling, squeeze film damping, as well as surface-nitrided raceways are presented. Bearing rig testing under typical aircraft engine flight conditions has been performed. Savings for oil flow quantity of more than 45% and for power loss of more than 15% were identified. Outer ring temperature reductions of more than 20 K were achieved due to the use of ceramic ball material and the direct outer ring cooling concept. The ultra-high-speed capability of the bearing was demonstrated. Rotational speeds of 24,000 rpm were achieved at bearing temperatures below 200°C. The fundamental experimental results including oil and bearing temperature distribution, power dissipation, and bearing efficiency are presented. In addition, experimental power loss and temperature results are compared with data for a conventional all-steel bearing.     

A Parametric Study on Friction Instabilities in Mechanical Face Seals

The present article aims to analyze and evaluate how dynamic parameter design influences the behavior of mechanical face seals and improves their performance by detecting undesirable phenomena like stick–slip and ringing. Those phenomena occur in situations of boundary lubrication.

A new lumped parameter model is proposed to study mechanical face seals used in automotive cooling water pumps in order to examine how dynamic parameters such as mass, moment of inertia, and stiffness are involved in stick–slip phenomena. The aim of this work is to provide a practical design tool to predict stick–slip conditions and to choose the optimal mechanical specifications. Numerical simulations demonstrate how the critical service conditions vary with design parameters and permit tabulation of the results.     

Influence of Currents from Electrostatic Charges on WEC Formation in Rolling Bearings

White etching crack (WEC) early bearing failures occur when the rolling contact is subjected to a so-called additional load such as an electrical current flowing through the bearing, in addition to the pure rolling load (p_Hz). Tests on rolling bearings showed that a low electrical direct current flow, such as that resulting from electrostatic charges, can lead to WEC failures in oil-lubricated roller bearings and greased ball bearings.

The WEC formation in the performed tests was dependent on the current, electrical polarity, load type (rotating or stationary ring load), and bearing load. A black oxidation of the WEC critical bearing ring led to a significant increase in lifetime. Based on the findings, the failure hypothesis “cathodic WEC fatigue” for electrical direct current-initiated WEC failures was established.     

Effect of Blowing Air and Floating Sand-dust Particles on the Friction and Wear Behavior of PTFE, UHMWPE and PI

The friction and wear behaviors of polytetrafluoroethylene (PTFE), ultra-high molecular weight polyethylene (UHMWPE), and polyimide (PI) have been comparatively evaluated under dry sliding, blowing air, and simulated sand-dust conditions. The tribological tests were conducted on an improved block-on-ring test rig equipped with an attachment for simulating the sand-dust environment. The reason for the difference in the tribological behavior of these polymers under the three test conditions was also comparatively discussed, based on scanning electron microscopic examination of the worn polymer specimens and counterfaces. Under blowing air conditions, the decrease of the contact temperature produced by blowing air led to the increase in the shearing strength of the sliding surface when compared with dry sliding conditions and hence to cause an increase in the friction coefficient and a remarkable decrease in the wear rate of PTFE and UHMWPE. On the contrary, blowing air produced a decrease in the friction coefficient of PI because of the formation of transfer film on the counterfaces, and an increase in the wear rate, because the blowing air considerably promoted the transfer of PI onto the counterfaces when compared with dry sliding conditions. Both PTFE and UHMWPE registered the lowest wear rate under sand-dust conditions, owing to the tribolayer formation on the worn surfaces, while PI exhibited the highest wear rate because no tribolayer was formed during the abrasive wear process.     

Tribological Studies of Some Quinoline Derivatives and Their Synergistic Interaction with Phosphate Ester

Antiwear properties of metal and sulfur-free synergistic formulations containing quinoline derivatives (QDs)—4-N-(7-chloroquinolin-4-yl)-1-N,1-N-diethylpentane-1,4-diamine (QD-1), 4-N-(6-methoxyquinolin-8-yl)pentane-1,4-diamine (QD-2) and 1-N,1-N-diethyl-4-N-(6-methoxy quinolin-8-yl)pentane-1,4-diamine (QD-3)—with triphenyl phosphate (PE) in polyethylene glycol (PEG) at a very low concentration, 0.25% w/v of each, have been studied on a four-ball tester using ASTM D4172 and D5183 standards. Phosphorus content in the formulations was significantly reduced compared to the frequently used antiwear additive zinc dialkyldithiophosphate (ZDDP) and it was much lower than the allowed concentration suggested by various norms. The synergistic admixtures, SQD-2 and SQD-3, significantly improved the antiwear properties of base lube compared to the ZDDP/PE/QDs alone but the behavior of SQD-1 is comparable to that of ZDDP. Minimum values of mean wear scar diameter and average coefficient of friction were found to be 0.458?mm and 0.034, respectively, for SQD-3, the admixture with the maximum antiwear efficiency. However, these values were 0.538?mm and 0.083, respectively, for ZDDP, and for base oil the values were 1.185?mm and 0.126, respectively. The load-carrying capacity was found to be much higher for the synergistic formulations than for ZDDP.

Atomic force microscopy (AFM) and scanning electron microscopy (SEM) micrographs of the wear track support the tribological behavior of the above additives. The presence of nitrogen, oxygen, and phosphorus in energy-dispersive X-ray (EDX) spectra of the worn surface lubricated with SQDs indicates the adsorption of additive on the surface. The magnificent tribological behavior of SQDs may be attributed to the tribochemical film formed on the steel surface invoking phosphorus–nitrogen synergy. Quantum chemical calculations (density functional theory) for interactions of QDs with a steel surface agree well with the experimental observations.     

Analysis of Turbulence and Convective Inertia in a Water-Lubricated Tilting-Pad Journal Bearing Using Conventional and CFD Approaches

The influence of turbulence and convective fluid inertia in a water-lubricated journal bearing was investigated using two types of models: a “conventional” solution based on traditional lubrication theory (Reynolds equation) and a more rigorous computational fluid dynamics (CFD) program containing a full Navier-Stokes solution. The calculations reveal that turbulence accounts for around 50% of the load capacity in the water-lubricated bearing studied, highlighting the importance of accurate characterization of turbulence in such applications. Convective inertia, also referred to as transport inertia because it depends only on the spatial parameters within the film rather than time-dependent journal motions, was found to lower the static film pressures (load capacity) by about 6% compared to an inertialess solution.

Hydrodynamic pressures calculated by the conventional Reynolds solution were initially about 30% lower than those of the more rigorous CFD model for the water-lubricated bearing operating in the turbulent regime. The mesh spacing of the conventional model was refined and a method was developed to adjust the turbulence model within the Reynolds solution as a function of the pivot Reynolds number. These refinements brought the calculated bearing load capacities and power losses of the conventional Reynolds model into better agreement with those of the CFD model for a broad range operating conditions.     

ACCELERATED WEAR TESTS FOR THE ASSESSMENT OF MACHINING MODELS CALIBRATION DATA *

This paper documents the release of the accelerated wear tests for the Assessment of Machining Models (AMM) calibration data set, including some brief background material and a summary of previously published results. Measurements and results for the accelerated wear tests are summarized and a representative plot is given. Sources of uncertainty associated with the accelerated wear test measurements are discussed. The paper closes with a brief discussion of the wear test data and the complete data files, which are available through the project web site athttp://www.nist.gov/amm/.