Showing papers in "Tribology Transactions in 1981"

The Thermal Degradation and EP Performance of Zinc Dialkyldithiophosphate Additives in White Oil

Abstract: The oil-soluble degradation products formed in heated samples of oil containing zinc di(n-, iso- or s-butyl)dithiophosphate (ZDTP) additives have been identified using 1H and 31P nuclear magnetic resonance spectroscopy. The final degradation product in each case is S,S,S-trialkyltetrathiophosphate, SP(SR)3. The intermediate degradation products are O,S,S-trialkyltrithiophosphate, SP(SR)2(OR) and O,O,S-trialkyldithiophosphate, SP(SR)(OR)2. The rate of thermal degradation of the ZDTPs follows the order s-butyl > > n-butyl > isobutyl. A white, noncrystalline precipitate is formed in the heated oils which is rich in zinc and oxygen and low in phosphorus and sulfur compared with the original ZDTP. In four-ball tests, synthesized degradation products were shown to have EP activity comparable with that of the ZDTP additives. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Dayton, Ohio, October 16–18, 1979

The Chemistry of the Thermal Degradation of Zinc Dialkyldithiophosphate Additives

Abstract: A mechanism for the thermal decomposition of zinc dialkyldithiophosphate additives has been proposed that accounts for the major degradation products and their dependence on the nature of the alkyl group. The proposed mechanism generally follows well-known rules of phosphorus chemistry. The major points are as follows. (1) The decomposition is initiated by a general migration of alkyl groups from oxygen atoms to sulfur atoms. The rate of this reaction is governed by the ease with which nucleophilic substitution can take place at the α-carbon atom of the alkyl group. The well-established correlation between decreasing number of β-hydrogen atoms and increasing thermal stability is, therefore, explicable in terms of increasing steric hindrance, by the β-subtituents, of nucleophilic attack on the α-carbon atom. (2) Olefin elimination successfully competes with substitution where the alkyl group structure is favorable (i.e. secondary alkyl groups), leading to the formation of phosphorus acids. (3) Nucleophilic...

Elastohydrodynamic film thickness measurements of artificially produced nonsmooth surfaces

Abstract: Optical interferometry is used to measure the elastohydrodynamic (EHD) film thickness associated with artificially produced nonsmooth surfaces. The nonsmooth surfaces are produced by modifying the surfaces of highly-polished balls with irregularities in the form of multiple grooves and dents. By closely spacing these irregularities it is possible not only to produce depressions on the surface of the balls but also to generate pseudo asperities. The average roughness wavelength of this artificially-produced, nonsmooth, surface approximates the average fundamental roughness wavelength found on surfaces of some mechanical elements operating under concentrated contact. By comparing the measured film thickness profiles to the stylus traces of the irregularities, it was possible to observe the local deformations associated with micro-EHD pressure generation. In both pure rolling and pure sliding conditions the artificially-produced asperities are deformed and complete separation exists between them and the mating surface. Such findings demonstrate the importance of local surface topography and resulting micro-EHD effects on the film thickness between rough surfaces in concentrated contact. Sliding data are presented which demonstrate a severe constriction, caused by the irregularities, at the exit of the Hertzian region.

The Adhesive Transfer of the Slip-tongue and the Wedge

Abstract: The adhesive wear process was analyzed microscopically by successive observations in the SEM. Fractographic analysis of the transferred fragment was also conducted. Two modes of adhesive transfer were identified. In the first mode, successive slip occurs on the slip planes within the prow and forms an extrusion called “slip-tongue.” A shear crack subsequently propagates from the root of the slip-tongue. In the second mode, successive plowing takes place at the head of the wedge by accompanying the shear crack growth at its trailing end. In both cases, cracks produce a dimpled fracture surface. It was also found that the fragment transferred from the sharp asperity to the blunt asperity. The slip line field solution was introduced to explain the shape effect on wear.

Design Data for Three-Lobe Bearings

Abstract: Three-lobe bearing design data, which include both static and dynamic characteristics, are presented for laminar as well as turbulent regimes of operation. The results have been computed for ellipticity ration δ = 0.5, aspect ration λ = 1/3, 1/2, 2/3, and 1, and Reynolds numbers Re = 0, 3000, 6000, 9000, and 12000.

Surface Hardness and Abrasive Wear Resistance of Ion-Implanted Steels

Abstract: The hardnesses of nitrogen-implanted steel surfaces have been measured with an abrasive wear technique capable of characterizing surface layers as thin as 25 nm. Treated steel disks and reference disks were abraded with 1–5 μm diamond, and relative wear resistances were calculated from the mass losses. Surface hardness was obtained from a relationship between wear resistance and hardness. The surface of a hardened and tempered carbon steel implanted with nitrogen ions (1017/cm2) was significantly harder than with other treatments including quench hardening and nitriding. The hardness decreased to the bulk value over a depth corresponding to the initial implantation depth. Nitorgen-implanted stainless-steel surfaces wore faster than un-implanted ones, possibly due to interference with transformation hardening which normally occurs during wearing. This “softening” effect persisted to depths several times the depth of implantation, and may help to explain the reduction of sliding wear produced by the implant...

Some Effects of Amines on Zinc Dialkyldithiophosphate Antiwear Performance as Measured in 4-Ball Wear Tests

Abstract: Adverse interactions of zinc dialkyldithiophosphate (ZDPs) with other required additives in an engine oil is one factor contributing to the high phosphorus content of some engine oils. Sine phosphorus poisons exhaust gas emission catalysts, ways to reduce the adverse interactions are being sought. The ZDP-amine interaction was investigated as a model of such an interaction. Above a critical concentration, amines can cancel the antiwear performance of ZDPs as measured in a 4-ball machine. At amine concentrations below the critical value, a synergistic antiwear effect was observed at higher loads. The tolerance of different ZDPs to the presence of amines was the same as the ranking of the ZDPs in terms of antiwear performance. A mechanism for the antiwear action of ZDPs involving the formation of an acid phosphate decomposition product has been proposed. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Lubrication Conference in San Francisco, California, August 18–21, 1980.

Ester Oxidation Under Simulated Boundary-Lubrication Conditions

Abstract: Measurement of lubricant oxidation rates at high temperatures is complicated by the influence of oxygen diffusion. Consequently, determination of kinetic rates of oxidation above 450 K has previously been limited to reactions conducted to only 2-percent conversion of the reactant. Using the Penn State microoxidation test, we quantified the effect of oxygen diffusion on the oxidation of two esters at temperatures of 448 to 518 K. Reaction rates and product compositions were followed for reactant conversions of up to 50 percent. The rate coefficients and activation energies for the initial reactions (approximately first order) were determined using a diffusion-reaction model to separate kinetics from oxygen diffusion. Oxidation intermediates react with the iron surface, which catalyzes formation of a polymeric precursor of sludge and varnish. Proximity of the primary oxidation reaction to the iron surface influences the amount of iron-corrosion product and the molecular weight of the polymer. Differences ar...

Film Thickness of Grease in Rolling Contacts

Abstract: Optical Interferometry is used to study the film thickness of greases, and of soap suspensions and of their base oils in point or line contact. In one case, samples were taken from a grease-lubricated plain-bearing test after 5 1/2- and 25-million revolutions. The effective viscosity of a grease under the very high shear rates of the order of 1/2 × 10-6 s-1 encountered in rolling contacts can be calculated. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Lubrication Conference in San Francisco, California, August 18–21, 1980.

Oxidative Degradation of Phosphate Esters

Abstract: A thin film oxidation (microoxidation) test has been developed to simulate severe liquid phase oxidation in typical lubrication systems. Tributyl phosphate (TBP), tricresyl phosphate (TCP), trixylyl phosphate (TXP) and t-butylphenyl diphenyl phosphate (TBB) have been evaluated and compared. At low rates, oxidation is not limited by oxygen diffusion at the air-liquid interface. Gel permeation chromatography (GPC) has been adapted to the microoxidation test with the phosphate esters to provide a quantitative analysis of the reaction products as a function of molecular weight. The hydrocarbon portion of the phosphate appears to oxidize as the first step. The oxidized material then reacts further to form a product of about twice the molecular weight of the original phosphate. The formation of polymers appears to be a result of condensation through the oxidized hydrocarbon portion of the molecule. There is little evidence of condensation through the phosphate groups to form P-O-P linkages. The P-O-P condensati...

Dynamic Behavior of Surface-Adsorbed Molecules Under Boundary Lubrication

Abstract: Friction under boundary lubrication was measured using a pendulum-type friction machine. Long straight-chain fatty acids with even carbon numbers, amine, and alcohol were used as additives, and n-hexadecane was used as the base oil. Effect of the temperature, chain length of additives and additive concentration were investigated. The phenomena obtained under 373 K were as follows: 1) “Transition concentration” wherein a drastic change of friction coefficient appeared were observed. 2) “Transition concentration” of amine or alcohol solutions appeared at higher concentration than that of acid solution. 3) In “high concentration region,” the friction coefficient gradually increased with the decrease of the concentration. 4) Temperature raise caused a high friction coefficient. 5) Friction coefficient gradually decreased with an increase in chain length. 6) “Transition concentration” shifted toward low concentration with an increase in chain length. 7) No chain-matching effect was observed. These results are ...

Formation of Subsurface Zones in Impact Wear

Abstract: Recent studies have established that subsurface material structures are altered in processes giving rise to wear. This is the case both for sliding contact and repetitive compound impact loading. It is not surprising that the thermal and mechanical processing due to solid contact and relative motion lead to localized material property change. Yet subsurface material characteristics (such as degree of plastic deformation, void and crack content, layer formation, grain refinement, etc.) may be of considerable significance in terms of fundamental wear processes. Accordingly, a series of tests has been undertaken to determine the onset of characteristic subsurface zone formation arising in repetitive compound impact wear. The repetitive load cycling is convenient for such investigations (incubation studies) since a contact event is discretized a priori. The test series and subsequent analyses seek primarily to determine the dynamics of formation of subsurface material zones, and also to characterize these zon...

Performance Characteristics of Noncircular Bearings in Laminar and Turbulent Flow Regimes

Abstract: Using linearized turbulent lubrication theory of Ng and Pan, the modified Reynolds equation has been solved by finite element method using Galerkin's technique. Static and dynamic performance characteristics of the noncircular (two-lobe) bearings have been studied, both for laminar and turbulent flow, in terms of load support, oil flow, fluid film stiffness coefficients, damping coefficients, and critical mass for various Reynolds numbers.

Dynamic Tracking of Angular Misalignment in Liquid-Lubricated End-Face Seals

Abstract: End-face seals sometimes fail because the flexibly mounted face is unable to track the inevitable angular misalignment (relative to the shaft axis) of the fixed face, resulting in rubbing contact. It is important, then, that the critical amount of misalignment just to cause contact in a fully liquid-lubricated seal should be known so allowances can be made in the manufacturing and assembly tolerances. An analysis of dynamic tracking is presented for both common end-face seal arrangements. Expressions for critical misalignment are derived in terms of inertia, elastomer stiffness and damping, and fluid-film hydrostatic and hydrodynamic moment effects in the diametral tilt mode. Fluid-film effects are found to promote tracking, elastomer effects to resist. Tilt inertia resists tracking only for the flexibly mounted stator arrangement. However, as the inertia term is generally insignificant, this arrangement is preferred because, in practice, it is much easier to achieve good alignment of a rotating face fixe...

Lubrication in Cutting—Critical Review and Experiments with Restricted Contact Tools

Abstract: The paper is concerned with the lubricating action of cutting fluids. In a critical reivew of the different theories for lubrication in cutting, three main approaches are discussed: 1. the assumption that lubrication in cutting is due to the presence of a soft film between the tool and the chip; 2. the theory that the lubricating effect of a cutting fluid consists in a physio-chemical reduction of the work material shear strength; 3. the theory describing cutting fluid action in term of a reduction of the length of contact between the tool and the chip. An investigation on lubrication in cutting carried out with tools with restricted contact is described. Presented at the 35th Annual Meeting in Anaheim, California, May 5–8, 1980.

A Method to Calculate the Pressure-Viscosity Coefficient from Bulk Properties of Lubricants

Abstract: A relationship between the pressure-viscosity coefficient of a liquid lubricant and the ambient pressure densities and viscosities at two or more temperatures has been derived. The emphasis was to derive a relationship based on fundamental properties of a liquid lubricant rather than to propose an empirical correlation. This relationship is then tested in representative lubricants by comparing the calculated values with experimental values. Presented at the 35th Annual Meeting in Anaheim, California, May 5–8, 1980

Mechanisms of lubrication and wear of a bonded solid-lubricant film

Abstract: To obtain a better understanding of how bonded solid-lubricant film lubricate and wear (in general), the tribological properties of polyimide-bonded graphite fluoride films were studied (in specific). A pin-on-disk type of testing apparatus was used; but in addition to sliding a hemispherically tipped rider, a rider with a 0.95-mm-diameter flat area was slid against the film. This was done so that a lower, less variable contact stress could be achieved. Two stages (regimes) of lubrication were found to occur. In the first, the film supported the load and the lubricating mechanism consisted of the shear of a thin surface layer (of the film) between the rider and the bulk of the film. The second occurred after the bonded film had worn to the substrate, and consisted of the shear of very thin lubricant film between the rider and flat plateaus generated on the metallic substrate asperities. The film wear mechanism was found to be strongly dependent on contact stress. Presented at the 35th Annual Meeting in An...

Lubricant Chemistry in Rolling Contact Fatigue—The Performance and Mechanism of One Antifatigue Additive

Abstract: The paper describes studies towards developing lubricant additive technology to improve the fatigue performance of an oil. The extraordinary performance of a particular organic phosphonate antifatigue additive observed in the authors' laboratory and elsewhere is reviewed together with conflicting EHD film thickness studies of this additive reported in the literature. New optical EHD measurements and electron microscope and microprobe studies which define the mechanism by which the additive acts, are presented. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Dayton, Ohio, October 16–18, 1979

Behavior of Polar Compounds in Lubricating-Oil Films

Abstract: The effect of oil films was investigated under comparatively mild conditions of boundary lubrication (up to 10 MPa) using electrical methods. For a dynamic investigation, a pin-on-disk-type friction apparatus was uses. The capability of oil films for preventing metal-metal contact was estimated by measuring the contact resistance of the mating surfaces. For a static investigation, the characteristics of oil films while being squeezed from a very narrow slit between mercury and steel surfaces was observed by measuring the capacitance and conductance of oil films. Squalane was used as a base oil. Saturated straight chain carboxylic acids (C6-C18), and methylesters and alcohols which had the corresponding chains to the acids were used as additives. The following were found for the capability of oil films for preventing metal contact: 1) Prevention depended on the concentration of the additives (5—20 mol·m-3), and increased with the increase of the concentration. 2) Prevention did not necessarily correspond t...

Force and Energy Measurements During Controlled Grooving—A Basic Study of Abrasive Wear

Abstract: Basic studies of abrasive wear have been performed by controlled grooving in a modified impact tester equipped with a cemented carbide tip. Specimen holders were constructed to permit normal and tangential force measurements during grooving and to enable quick-stop tests. The grooving energy is read directly from the standard pendulum meter or integrated from tangential force curves. A series of metals were studied by single-tip grooving and the grooving energy was plotted versus weight loss W within a large W interval. Mettallographic studies reveal characteristic friction layers in the groove bottom and walls and also show that the development of these layers is governed by the mechanisms of chip formation. A particular purpose of this work is to find relations between internal structure and microhardness profiles on one hand and grooving forces/energy and wear resistance on the other. There are indications that the specific grooving energy e = E/W can be used to predict abrasive wear resistance under w...

The Wear of PTFE-Containing Dry Bearing Liners Contaminated by Fluids

Abstract: The influence of fluid contamination on the wear of a number of aircraft dry bearing liners has been examined using a recently developed, accelerated test procedure. It is shown that fluids generally increase wear to an extent depending on the level of stress, the type of fluid and the structure and composition of the liner material. Water is invariably deleterious but, at low stresses, mineral and diester oils can sometimes reduce the wear rate below that obtained in dry conditions. Explanations for the trends observed are deduced from a detailed examination of worn surfaces by X-ray photo-electron spectroscopy (XPS) and scanning electron microscopy (SEM). The relevance of the results to current specification requirements for aircraft dry bearings is discussed, and a number of inadequacies exposed. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Lubrication Conference in San Francisco, California, August 18–21, 1980.

On Performance Characteristics of Three-Lobe Porous Hydrodynamic Journal Bearings

Abstract: This paper presents an analysis of a three-lobe porous hydrodynamic journal bearing for its static and dynamic performance characteristics. The performance characteristics of the bearing have been computed and presented in graphical form for a wide range of permeability parameter to investigate the effect of porosity on bearing performance. The stability margin of the three-lobe journal bearing system, in terms of crtical mass of journal, has been established using Routh's criteria. The nature of transient motion of the journal has been analyzed using the complex eigen values of characteristic equation and motion trajectories obtained by numerical integration of equations of motion.

The Elastohydrodynamic Film Thicknesses of Binary Ester-Ether Mixtures

Abstract: Mixtures of various proportions of a polyolester and a polyphenylether (5P4E) have been prepared and their elastohydrodynamic film thicknesses measured in a rolling point contact. It has been found that small amounts of polyolester reduce the film thickness of 5P4E far more than viscosity values would predict. One explanation for this is that the pressure-viscosity coefficient of 5P4E is very sensitive to small amounts of polyolester, and is reduced by a factor of five with only 20 percent of polyolester. This might result from the ester acting as a plasticizer in reducing the glass transition temperature of 5P4E. Alternatively, 5P4E may be behaving in a non-Newtonian fashion over the range of shear rates studied. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Lubrication Conference in San Francisco, California, August 18–21, 1980.

Analysis of wear debris from full-scale bearing fatigue tests using the ferrograph

Abstract: The Ferrograph was used to determine the types and quantities of wear particles generated during full-scale bearing fatigue test. Deep-groove ball bearings made from AISI 52100 steel were used. A MIL-L-23699 tetraester lubricant was used in a Recirculating lubrication system containing a 49-μm absolute filter. Test conditions included a maximum Hertz stress of 2.4 GPa, a shaft speed of 15 000 rpm and a lubricant supply temperature of 74°C (165°F). four fatigue failures were detected by accelerometers in this test set. In general, the Ferrograph was more sensitive (up to 23 h) in detecting spall initiation than either accelerometers or the normal spectrographic oil analysis (SOAP). Four particle types were observed: normal rubbing wear particles, spheres, nonferrous particles, and severe wear (spall) fragments. Presented at the 35th Annual Meeting in Anaheim, California, May 5–8, 1980

Lubricant Degradation and Wear IV. The Effect of Oxidation on the Wear Behavior of Pentaerythrityl Tetraheptanoate

Abstract: Wear studies carried out in conjunction with a study of the kinetics and mechanism of the autoxidation of pentaerythrityl tetraheptanoate (PETH) showed that small degrees of oxidation produced large increases in wear rate. The results indicate that monoesters of dicarboxylic acids in conjunction with hydroperoxides are the oxidation products which result in the increased wear. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Lubrication Conference in San Francisco, California, August 18–21, 1980.

Analysis of Magnetic-Fluid Seals

Abstract: The paper offers a basic investigation of magnetic-fluid sealing. The objectives aimed at quantitative relationships between the parameters of the magnetic circuit, the properties of the fluid, and the resulting Δp capacity of a single or multistage seal. The pole pieces were investigated with the aim of arriving at an optimum configuration which would yield maximum sealing capacity for a given total space. It is shown that lines of constant intensity represent to a good approximation also lines of constant pressure and thus potential interfaces for the magnetic fluid; and that maximum sealing capacity is obtained when tooth width is twice and intertooth spacing three times the clearance. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Lubrication Conference in San Francisco, California, August 18–21, 1980.

Wear Rate Prognosis Through Particle Size Distribution

Abstract: Diagnosis of wear regime can be made by examination of the wear particles in terms of the number or weight fraction in each size range. Consideration of the alternatives lends to the conclusion that a Weibull plot by weight (Rosin-Rammler) is the most useful. Application of this diagnosis to simplified wear rate equations can result in more meaningful prognosis of life expectancy. The relations to the more familiar SOAP, Ferrograph and chip detector methods are explored. Presented at the 35th Annual Meeting in Anaheim, California, May 5–8, 1980

A System for Viscosity Measurements at Pressures up to 3 GPa and Elevated Temperatures

Abstract: A falling body viscometer was developed to measure viscosity of lubricants between 10-1 to 105 Pa.s at high pressures (up to 3 GPa) and temperatures of 20–200°C. The viscometer was incorporated into a variable-support pressure vessel mounted in an O-frame press. A solenoid is used to raise the falling soft iron plunger to its upper position, where it closes a pair of contacts. On deactivating the upper solenoid, the plunger, falls to the lower position to close a second pair of contacts. Fall times are measured by a timer in 0.1s increments. Viscosity of a few fluids, namely a synthetic turbine engine oil, a mineral oil, white gasoline and a 1:1 mixture of the mineral oil and white gasoline were measured to demonstrate capability of the system. For the synthetic turbine engine oil, isoviscous curves for 102, 103 and 104 Pa.s are presented on a P–T diagram and estimates are made of the viscosity at which dynamic effects can be expected. Presented as an American Society of Lubrication Engineers paper at the...

Specific Film Thickness—A Closer Examination of the Effects of EHL Film Thickness and Surface Roughness on Bearing Fatigue

Abstract: Analysis of literature bearing-fatigue life results shows that fatigue life is not a simple function of the widely accepted specific film thickness, λ, which is the ratio of the EHL film thickness h to composite surface roughness [sgrave]. Instead, the influence of film thickness on bearing life increases with increasing surface roughness; at about 0.20 micrometer (8 microinch) composite roughness life increases with the square root of h while at about 0.46 micrometer (18 microinches) life increases with h squared. The negative effect of surface roughness on bearing life appears to be relatively independent of film thickness. This suggests that surface roughness affects fatigue life by some mechanism in addition to the degree of interaction of asperities through an intervening EHL film. Additional test results are needed to confirm this point. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Lubrication Conference in San Francisco, California, August 18–21, 1980.

The Influence of Thermal Oxide Characteristics on the Friction Behavior of Aluminum Auto Body Sheet Alloys

Abstract: The influence of the thickness and structure of thermally produced aluminum oxides on the microscopic frictional response of aluminum auto body sheet alloys 6010-T4, 6009-T4, and 2036-T4 has been investigated. A variety of oxide thicknesses and structures were produced through variation of exposure temperature and quench medium. Coefficients of friction for the surfaces were subsequently determined using a tool steel slider under three conditions of lubrication: unlubricated sliding, lubrication with oil-based DG4247, and lubrication with water-based DA4251. For unlubricated sliding, friction was high for all alloys at low oxide thicknesses, corresponding to metal-to-metal contact and adhesive wear. With increasing thickness, friction coefficient changed in a manner controlled by the underlying strength of the material and the level of surface MgO. Lubricated sliding tests with DG4247 and DA4251 showed a uniformly low friction coefficient, independent of oxide thickness. However, after selective removal o...