Proceedings of the JSLE international tribology conference, Tokyo, Japan, July 8–10, 1985

Wear, 111 (1986)

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Book Review

Proceedings of the JSLE International Tribology Conference, Tokyo, Japan, Jury B- IO,1985 edited by Y. Tamai; published by Elsevier, Amsterdam, 1985; 3 volumes, 1230 pp.; price, U.S.$277.75, Dfl. 750.00; ISBN O-444-99537-4

These proceedings constitute a fitting commemoration of the thirtieth anniversary of the foundation of the Japan Society of Lubrication Engineers. Three volumes totalling 1170 pages are required to record the 30 sessions spread over three days during which no fewer than 186 papeis were presented. Although a majority of the contributions were of Japanese origin, the conference was genuinely international as demonstrated by the inclusion of 65 papers originating from practically every country in the developed world. It is characteristic of the breadth of vision of the society that the papers are published in the English language. The 25 gubject divisions which were used as a basis for organizing the sessions are not mutually exclusive but the contents list is well organized. There is no subject index but an alphabetical list of authors is provided. In this review the name of the first or sole author of a paper is given in parentheses to facilitate reference to the proceedings themselves.

Fundamental studies -friction

and wear

Among the basic techniques employed were old friends such as exoelectrons (Oshmira), field ion microscopy (Tsukizoe) and Auger spectros copy (Lauer) (Hua) together with innovative technology as exemplified by the use of quadruple mass spectroscopy to measure adsorption (Mori), by the use of cathodoluminescence to reveal defects in ceramics (Enumoto) and of acoustic microscopy to demonstrate that cracks developed in ceramics during repeated sliding contact may have their ofigin in the grinding process (Yamanaka). Numerical analysis of rigid body asperity contacts conforms to Hertz theory as a special case (Ono) and calculations of microdisplacements of contacting bodies are in agreement with measurements of sand-blasted surfaces (Funabashi). Work hardening of asperities is significant (Nitta). When hard cones interact with soft surfaces, ribbing has little effect for deeper “Severe wear” and “mild wear” are regarded as penetrations (Ishizuka). modes of adhesive wear and the transition is attributed to lubrication by gas or liquid molecules (Sasada, a). Specific grooving energy is proposed as a measure of abrasion resistance and can be measured by a pendulum (Vingsbo). Friction and wear usually increase in vacuum but medium humidity reduces @ Elsevier Sequoia/Printed

in The Netherlands

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friction. The only substances which reduced friction in vacuum are MoS, or those with similar structure (Tsuya, a). Impact wear is not in itself a form of wear but represents one mechanism by which direct and shearing stresses can be applied. Adhesive wear is an important factor (Rabinowicz). So-called amorphous alloys are actually composed of crystallites smaller than 4 nm in size. They provide very stable surface oxide layers (Miyoshi). Thermochemical treatment of steel can confer good wear resistance (Senatorski) and the main reason for the success of ion implantation in enhancing the wear resistance of mild steel and titanium was shown to be work hardening of the surface material at the depth of action of the maximum shear stresses (Belyi). Measurement of contact electrical resistance during sliding on boron- and argon-implanted stainless steel indicated that the near-surface layer which exerts a dominant effect on tribological properties is extremely thin (M. Hirano). The term “third body”, defined as an accumulation of transfer elements produced from two interacting bodies, can represent many phases composed of atoms, molecules or particles. They pile up to form load-bearing areas which may eventually be ejected. Amorphous material is dominant, being created by one of two processes: fine-scale fragmentation and auto-adhesion (Georges). Thin flake-like particles of a type frequently observed in ferrographs and referred to as “filmy” wear debris can be formed by sliding in a pin-and-disc configuration. Plastic flow of asperities at a rate of 3 - 7 pm km-’ has been demonstrated by hardness indentation (Akagaki). Corrosive wear may be quantified by Faraday’s law. It is powerfully influenced by static corrosion occurring during unloaded periods (Yahagi). Sand-blast tests of AISI 4140 steel indicate that the erosion rate increases with the hardness and ultimate strength but reduces with the ductility (Ambrosini). It cannot be over emphasized that wear resistance is a “system-specific” proper-Q as exemplified in a series of tests on a medium carbon steel with differing hardness (Czichos). Scanning electron microscopy studies of abrasion reveal fo-ur modes of wear (cutting, flaking, wedge action and ploughing) according to the degree of penetration (Kayaba, a). Adhesion accompanies ploughing (Ura) and three phases of contact, bulk elastic contact, totally plastic contact and totally elastic contact, can be identified in microscopic studies of copper sliding on glass. The transition is determined by the yield condition for plastic flow (Ike). Interaction of asperities on metal surfaces is conditioned by the accumulation of dislocations which may behave like three-dimensional defects of a metal structure, i.e. acting as an inclusion of a harder phase (Prancs). The wear rate of carbon steel is affected by the normal stiffness of the loading system (Kato). Relaxation oscillation or “stick-slip” behaviour can be quantified by Lienard’s construction but normal (perpendicular) displacements are attributed to different contact conditions during different phases of the oscillation (Sakomoto). The limiting value of static friction is not necessarily higher than the kinetic value (Eguchi, a) and careful measurements indicate that the

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coefficient of stick friction depends on the stationary contact time (Eguchi, b). Instrumentation is available for measuring the friction force and related quantities at intervals of 100 ps (Ohmae)._ The fretting corrosion of austenitic stainless steels depends on the ambient pressure and the slip amplitude. Oxidative wear occurs at higher pressures and adhesive wear at lower pressures (Iwabuchi). A significant reduction in fretting of lubricated flat steel surfaces results from grooving them (Imai). Commercial transmission fluid and samples containing P-S hypoid gear additives produced considerable fretting with an increase in the additive content (Law). Corrosion by seawater produced reaction products which were beneficial from the point of view of fretting (Sato). At room temperature, fretting of titanium alloys occurs by delamination but at 400 “C a glaze of randomly oriented polycrystahine TiOz occurs which reduces friction and wear. At 600 “C there is no glaze and zero wear. Implantation with barium reduces, and with bismuth increases, the oxidation rate (Waterhouse). Boundary lubrication Transition temperatures which characterize the kinetic action of boundary lubricants and determine the type of friction and wear occurring under given conditions can form a basis for the optimal selection of lubricants (Matveevsky). It is assumed that fatty acids are effective as boundary lubricants because they produce soap films but fatty alcohols which do not react are also effective. This is thought to be due to the action of negative ions or exo-electrons (Kadjas). Four-ball tests indicate that a wide molecular weight distribution is advantageous at low speeds but not at high speeds (Marakami) and low viscosity components can cause local breakdown of elastohydrodynamic (EHD) films (Matsui). Twin-disc machine tests indicated that resistance to scuffing was enhanced by smoothing and work hardening during running-in (Yamoto). Solid lubricants may be assessed by the rate of wear of ball-bearings in the ASTM-D137 machine (Fischer). Electron probe microanalysis shows that niobium sulphide forms films similar to those of MO& (Hironake) and graphite fluoride has similar properties (H. Miyake). Carbon with a diamond structure can act as a solid lubricant (S. Miyake). Cr-Mo electrodeposits are superior to those of pure chromium (Yuan). A bonded film comprising combined MO&, graphite and Sb(SbS4) was superior to oneor two-component films (Bartz) and the thickness of MoS, coatings is an important factor in their performance (Shimazaki). A databank model for solid lubricants is proposed (Matsunga). Properties of lubricants The basic properties to be sought in base oils are oxidation resistance, solvent power, viscosity and chemical activity (sulphur). Nitrogen compounds in the base oil can contribute to lacquer formation in engines and clay adsorbants can adversely affect foaming (Webster). Under high pressure, hydrocarbons containing fatty acids produced crystallites and mineral oils showed dense clouds of atomized particles. A typical oil solidified at 0.31 GPa at

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21.7 “C (F. Hirano). Surface wetting was important to the lubrication of precision rolling bearings, i.e. an EHD film formed more readily with a contact angle of 18” than 37”. Soluble metal-organic compounds generated in automobile bearings affect the rate of primary oxidation. Some corrosion products such as copper, zinc or tin compounds inhibit oxidation at high temperatures. Small amounts of soluble iron corrosion products may be catalytic to oil oxidation and to sludge and varnish formation (Klaus). Some fireresistant hydraulic fluids have been classified as regards pump wear using a Falex ring-and-block test machine (Mizuhara). Some fungi grow in aqueous solutions even under anaerobic conditions (Ono).

Lubricant additives A special symposium was confined to four papers from British or U.S. laboratories. Experiments on cam and follower emphasized thermal factors (Watkins) and instrumentation of the big-end of a fired engine promises repeatable results (Bates). A new evaluation procedure based on simplified LFW-1 and SAE number 2 friction tests is proposed (Papay) and the concept of super high performance diesel oils is proposed. These are intended to allow engines to operate on normal fuels (0.5% S) for 300 000 km between drainage. Detergent systems based on calcium phenate and calcium sulphonate give good performance in European engines and the Ford Tornado engine has been used for testing. Satisfactory bore-polishing performance bore no direct relationship with piston deposits (Mays). Four-ball tests on sulphur and oxygen films formed in the contact region indicated that an optimum condition resulted when the proportion of sulphur to oxygen was between 0.5 and 0.8 (Sakai). The load-carrying capacity of S-P lubricant additives has been investigated in several laboratory machines. Results varied from machine to machine but dilaurylhydrogen phosphate was much more effective than dibenzyldisulphide although there was synergism (Kubo). Auger electron depth profile analysis of worn Falex test pins lubricated with gear oils containing sulphurized isobutylene, tricresyl phosphate, dibutyl phosphate and dodecyl amine salt of benzotriazole demonstrate the growth of a sulphur-rich layer and the conversion of elemental sulphur into iron sulphide (Hua). Antagonistic interaction occurs between zinc dialkyldithiophosphate (ZDDP) and ashless dispersant in oil. Complex formation is accompanied by diminished antiwear performance of the ZDDP (Shiomi). Over-based detergent oils produce wear increases of rougher cast iron because of the formation of colloidal particles such as calcium carbonate (Tamura). Over heating of the workpiece is a common grinding. Monoalkyl phosphate, dialkyl phosproblem with “creep-feed” phate and alkyl acid phosphate were the only additives which counteracted grinding bum (Hirobe). Friction-polymer-type additives function as antiwear agents after polymerizing on the friction surface. Polymerization is enhanced by the catalytic action of the iron in the friction surface (Okabe).

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Polymers A systems approach is essential in studying the wear of polymers and two broad classes of wear action are proposed: cohesive wear and interface wear. The former class includes abrasion, subsurface fatigue and possibly subsurface melting while the latter embraces transfer wear, chemical action and superficial fatigue. Lubrication of polymers may be a mixed blessing (Briscoe). Many semicrystalline polymers have spherulitic structure which can sustain quite large deformations by elongation into elliptical form. The friction of polypropylene was at a minimum when the mean diameter of the spherulites was 85 pm. When cast, polypropylene can be treated to give much lower friction and wear than when moulded (Tanaka). Flight control bearings in aircraft comprise a polymer acting against stainless steel. No evidence of chemical action has been found and the hardness and smoothness of the counterface are all-important (Birkett). The wear rate of polyimide was directly correlated with the flexibility of molecular chains (ChitzasZadeh). Tests in vacuum and various gases show an important effect of oxygen on the friction and wear of natural rubber. The friction of synthetic rubber (styrene butadiene) is also affected but not the wear. Oxygen forms softened layers and the effect of antioxidants depends on the ambient conditions (Uchiyama). Shear took place in molecularly oriented surface layers of nylon at low speeds (0.1 mm s-i) but at 10 mm s-l it took place between amorphous nylon and steel surfaces (Watanabe). The wear of phenolic resin increases monotonically with the roughness of the metal counterface. A large decrease in friction occurs at 150 “C owing to the formation of a liquid phase by degradation of resin (Mitzutani). Fluid lubrication The performance of a tilting thrust bearing was improved by using a modified design incorporating better load distribution between pads (Gardner). The effect of misalignment on the performance of a journal bearing with a circumferential groove is calculated and the results are shown to be in good agreement with experiment (Ikeuchi). Addition of 0.3% potassium oleate to water in a journal bearing gave optimum performance with a coefficient of friction of 0.002 (Yamaguchi). Pulsating load in a journal bearing causes pressure variations which may cause fatigue failure in the lining. The calculations and experiment show that the central area of a bearing is the most critically stressed (Peeken) and that failure was affected by the nature of the load cycle (Fukuoka). The wear of journal bearings is generally proportional to the number, size and hardness of contaminant particles (Watanabe). Isoviscous calculations of the effect of asperities, performed by deriving average flow factors, indicate that transverse roughness generates higher average pressures than does longitudinal roughness. A rough runner interacting with a smooth slider generates lower pressures than the converse (Cheng). A three-dimensional sinusoidal roughness model also indicates the possibility of generation of hydrodynamic pressure between nominally flat surfaces

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(Kimura, a) and similar conclusions are reached by the application of a standard computational technique to Reynolds’ equation. The effect of compressible fluids on viscosity is taken into account but those of pressure and temperature are not (Tender, a). A transparent bearing shell was used to study the boundary conditions applicable to dynamic loading. The “separation theory” and Reynolds’ conditions were compared and the results were shown to approach Reynolds’ conditions as the load was increased (Morishita). When an elastic rotor was supported on tilting pads, the radial factors were stabilizing and the tilting factors were destabilizing (Zhang). Turbulence decreases the unstable region for journal bearings with a circumferential groove for a wide range of eccentricity ratios (Hashimoto). On tilting-pad bearings the maximum temperature occurs at the trailing edge. As the speed is increased the inner periphery is lifted. The pad surface becomes convex (M. Tanaka):Thermal reduction factors for smooth plane sliding bearings calculated using an improved method are in agreement with classical solutions (Chien). Turbulence in a hydrostatic water bearing affects the stiffness and tends to reduce the flow and to increase the system damping (Sugati). The addition of certain macromolecules to turbulent systems was shown by Toms in 1949 to reduce frictional drag. The pressure is affected to a lesser extent but can be determined using a model based on turbulent energy and dissipation rate (Kato). Cavitation erosion can be a factor in the wear of bearing alloys (Okada).

Gas lubrication Analysis of a journal bearing which is pressurized through small closely based feed holes shows that exit flows are subsonic. The interaction between the Reynolds number and the Mach number becomes important at higher pressure levels which require a smaller bearing clearance for optimum load capacity (Pan). Circular thrust bearings, externally pressurized and having flexible surfaces, have higher stiffness and load capacity than rigid bearings for lower gas consumption (Hayashi). Finite element calculations are applicable to orifice-compensated bearings (Liu). An intermediate floating bush driven independently by a gas turbine was shown to enhance the stability when rotated in the opposite direction from the shaft (Inoue). An intermediate bush which is prevented from rotating, and is provided with holes connecting the pressure film with the space between the bush and housing of a journal bearing, provided a gas cushion which damped out shaft vibrations (Tsumaki). Striated roughness on gas-lubricated systems governed by Reynold’s equations are not normally significant although pressure ripples may occur under special conditions (Tsnder, b). A method of calculating the effect of fluid inertia on externally pressurized circular thrust bearings in which all the inertia terms are averaged out across the film thickness agrees with experimental results (Haruyama). A proposed design of a gas journal where the pressurization does not depend on the viscosity but on the gas choking has been investigated theoretically (Inaba).

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Swift-Steiber boundary conditions are also applicable to dynamic problems if the ratio of the velocity at the cavity-liquid interface to the entraining velocity is less than unity. Problems arise, however, when the subambient pressure loop becomes significant (Mori). When cavitation occurs between flat non-parallel surfaces, discontinuous changes in pattern occur with varying speed accompanied by abrupt changes in pressure (Nakahara). The fluid inertia effect in squeeze films has been quantified (Kurado). The effect of surface roughness on lubrication is quantified using a numerical perturbation method (Hu). In mixed lubrication, isotropic surface topography (electropolished) gives greater film thickness than anisotropic surface topology (Qi). Two-phase lubrication (liquid-solid) gives a slight increase in load capacity of journal bearings at intermediate values of the Sommerfeld number. Side leakage decreases with increasing solid content (Yousif). Inclusion of MoS, powder in oil increased the friction of hydrodynamically lubricated bearings (Aoki). Elastohydrodynamic lubrication When oil-water emulsions are used for EHD lubrication, the film thickness increases disproportionately with the increase in oil concentration. Larger oil particles are favourable (Kimura, b). Study of the effects of newtonian and non-newtonian lubricant properties in helicopter transmissions reveals that for similar viscosities, the power efficiency and minimum film thickness are related (Jakobson). The rolling resistance was measured in a twin-disc machine and compared with Cheng’s theory. Increased surface roughness led to reduced rolling friction (Aihara). A simplified thermal theory is applicable over a full range of slide-to-roll ratios (Muraki) and maps showing different regimes of EHD lubrication have been codified (P. Zhang). The application of EHD theory to cam and tappet design is discussed (Holland). Rolling bearings Various factors affecting rolling resistance have been measured. Diameter and roughness are significant at the 5% level (Matsubara). The ball motion in a radial bearing has been measured using the Hall effect. At low speeds, random motion occurred in the unloaded region, but at higher speeds slip was substantially reduced if not entirely eliminated (Kawakita). Similar results are reported for angular contact bearings where gyroscopically induced motion is important (Touma). Skidding damage of high speed cylindrical roller bearings occurs at slip velocities of about 50 m s-l. Oil films formed between the ball and cage pocket are at least partially hydrodynamic (Fujii) although adhesive wear occurred in the pockets of a self-lubricating ball-bearing in a liquid-hydrogen turbopump operating at 50 000 rev min-' . Oval pockets were preferable to circular pockets (Oike). Film thicknesses between 1 and 10 pm have been measured by alternative methods based on electrical resistance (Nakashima). Improved performance of roll-neck bearings resulted from better sealing, water drainage, inclusion of rust preventative

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in grease and condition monitoring using grease analysis (Yamamoto). Life tests on over 1100 bearings have been plotted on Weibull paper to yield improved life adjustment factors for reliability prediction (Takata). The torque performance of bearings operated in vacuum and lubricated by solid lubricants was investigated. Excellent performance was obtained from a bearing having a cage containing lead and in which the raceways were lead ion plated (Kondo). Rolling con tat t fatigue Crack growth is influenced by the surface traction, the frictional force between crack faces and the hydraulic pressure. Inclined cracks grow faster than vertical cracks. As propounded by Way in 1935, a microcrack can be developed to form a pit by oil penetration. This does not occur in cracks which are inclined to be shallowing in the direction of contact movement (Kaneta). In disc machine tests pitting occurred readily on the low speed roller when the specific sliding was 20%. A hardness difference reduced the fatigue strength, accompanied by plastic flow of the softer roller (Huang). Steel rollers, chromium plated to a depth of 0.11 mm, were fatigue tested under rolling-sliding conditions. 0.45% C steel was hardened to 893 HV. D values (ratios of film thickness to roughness) exceeded unity. The effect of an increase in hardness outweighs that of an increase in the amplitude of shearing stress caused by plating (Yoshida). Minor modifications of test discs resulted in greatly improved performance which was attributed to enhancement of the EHD lubrication regime because of work hardening (Kita). Seals Conventional soft-packed stuffing boxes were investigated both theoretically and experimentally. Radial pressures are higher for the packing-stem interface than the packing-housing interface (Ochonski). Observation of the contact area of rotary lip seals through a hollow glass shaft revealed an important role of microasperities in the sealing action (Nakamura). Rings for mechanical seals are prone to damage by thermocracking, blistering and cavitation. Damage to carbon seal rings is more severe with tungsten carbide mating rings than with silicon carbide mating rings (Koga). Mechanical seals for air-conditioning compressors for cars were studied. The friction of an O-ring was shown to depend on a hydrodynamic parameter of the ZN/P type (Shimomura). A mechanical seal operating at 50 000 rev min-’ at 25 K and 1.35 MPa gave low friction values after running-in. A sealing balance ratio of 0.77 was required because of the tendency of the fluid to evaporate owing to viscous friction heating. An integral vibration damper was composed of polytetrafluoroethylene (PTFE) sheets (Nosaka). Magnetic fluid seals may become unstable and an optimum fluid volume exists for establishment of the maximum seal pressure (Kamiyama). Ceramics The behaviour of oil-lubricated ceramics is influenced greatly by the environment as demonstrated by tests on magnesium oxide. The micro-

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hardness is increased by additives containing sulphur, decreased by chlorine and little affected by water which, however, increases the fracture toughness (Ishigaki). Sensitive compatibility between ceramics and oils containing S-Ptype additives is observed because of the interaction of chemicomechanical effects and adsorbability (Tsuya, b). In vacuum (lo-’ Pa) the friction of silicon and gallium arsenide against pure metals is an order of magnitude higher than that in air and is influenced by the Schottky barrier height (Mishina). The unlubricated wear of ceramics against hardened steel depends on the composition and processing (Libsch). Silicon nitride (Si3N4) gives low friction and wear in rolling contact but its resistance to wear becomes inadequate when relative sliding occurs ( Akaswa). Self-lubricating materials

MO& films bonded by polyamide-imide resin are superior to those bonded by paste when both dry and under oil (Kawamura). Dry lubricating films obtained by electrodeposition of copper and MoSz are proposed for electrical contacts (Caiazzo). Good lubrication can be obtained in vacuum (low6 Pa) by pressing solid Pb-Sn alloy onto a moving substrate. If this is continuous a satisfactory film can be maintained for 2 X lo5 cycles (Kayaba, b). Greases

A criterion proposed for the performance of lubricating grease in vacuum is the “critical sliding distance”. A specially prepared vacuum grease gave much better results than PTFE, MoS2 and ASC (Kim). Urea greases are thermally and oxidatively stable but friction and wear tests show no advantage over conventional lithium-based grease. However, rig tests monitored by using ferrography revealed excellent antiwear properties (Matuzuwa). Tests with ball-bearings showed that the bulk texture and microstructure of grease influence noise generation (Moriuchi). Corrosion prevention tests on greases mixed with water have been developed which show better correlation with practice than do standardized tests (H. Kimura). Deterioration indices have been formulated which can quantify grease life as a function of bearing temperature and speed (Tomaru). Electrical and magnetic effects

A steel shaft running in a polyamide bearing produced a potential difference of several volts. This effect was correlated with the rate of wear (Rymuza). Wear of ferromagnetic materials, nickel and iron, can be affected by the magnitude and direction of the magnetic field. In air a vertical, i.e. acting perpendicular to the motion, field brings forward the transition from “severe” to “mild” wear with beneficial effects, whereas a horizontal field increases the wear. A vertical magnetic field is thought to activate the chemisorption of oxygen. This effect does not occur in the absence of oxygen (Hiratsuka)

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Mechanisms including gears A magnetic recording material, T-Fe203, is deposited by sputtering onto aluminium alloy discs; the surfaces of which have been anodized. The durability of the outer layer is optimized by making the thickness of the anodized layer about 10 pm (Kita). Delicate machinery is often lubricated for life and synthetic oils are often the most durable. Spreading is prevented by using either a non-spreading oil or a non-wetting barrier film (Mock). Nitriding and extreme pressure (EP) lubricants reduce the wear of crossedhelical gears and increase the limiting load (Naruse). Gear flanks can experience self-hardening. Resistance to pitting is governed by the hardenability of a material rather than its original treatment (Taki). A phenomenon known as “whitening” appears on automobile gear teeth during the initial stage of distress. It is related to tempering arising from frictional heating. Ashless dispersants may impede the protection of hypoid gears (Ohashi). The equivalent cylinder analogy of gear action introduced by Merritt has been developed into a theory of conjugate surfaces (Chen). Practical factors such as the action of tip meshing can vitiate EHD action and refined calculations are necessary to embody the actual contact conditions. Design should be based on the minimum oil film thickness at the first contact point (Pu). It is often assumed that worm gears are boundary lubricated but detailed thermoelastohydrodynamic calculations show that viscosity has an important effect (Simon). Novikov gears can develop about ten times the film thickness and half the friction than involute gears (Hanna). The helix angle of planetary gears is influential from the point of view of generation of EHD films (Jarchow). When gears operate at speeds above 100 m s-l the main source of power loss is the bearings although the energy lost in accelerating the oil is considerable (Matsumoto).

Engine lubrication A major cause of energy loss in road transport is the dissipation of the kinetic energy of vehicles because of braking. The development of hybrid power systems is therefore promising. However, when the internal combustion engine itself is considered, the piston assembly is a critical area. A reduction in ring width and skirt length by 50% is recommended. A total reduction in the U.S. petroleum requirement of 7.4% is envisaged (Pinkus). Simulation of the interaction of piston ring and liner using a specially developed test rig provided evidence of additive metals in the liner when examined by an electron probe (Mitsutaki). Oil consumption is increased by evaporation when the temperature of the cylinder wall exceeds 150 “C. Ring movement may either increase or reduce oil consumption and the use of lighter rings is recommended (Furahama). Engine soots are aggregates of basic particles about 20 nm in diameter and are made up of graphite planes, growth centres and porous substances. Agglomerate sizes depend on the lubricating oil formulation; an oil of high detergency gave distributions below 0.5 pm whereas the base oil spread from 0 to 2.2 pm in diameter (Masuko). The antiwear behaviour of engine oils at various stages of use is investigated using a crossed-

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cylinder machine. A good action is maintained after running for 10 000 km and it may be concluded that the decomposition of zinc dithiophosphate (ZDTP) forms a complex with a dispersant (Kawamura). An offset-type crosshead bearing carries more than twice the load of a conventional bearing with axial oil grooves (Wakuri, a) and simultaneous solution of Reynolds’ and the elastic equations for a crosshead pin bearing in a two-stroke engine shows that the oil film is inevitably thin because of the constant unidirectional load. Oil grooves are necessary and the groove angle is critical (Wakuri, b). Engine tests showed that valve train scuffing occurred below a certain temperature which depended on additive interactions. Bowden-Leben tests indicated that a certain temperature is required for ZDTP to form a surface film (Shirahama). Industrial aspects Comparison of mineral and synthetic gear oil tests using the FZG machine revealed excessive wear due to local rupture of the EHD film with synthetic oil (Ohkawa). A new hypothesis to explain the difference between the effects of the driving force and the braking force for a given angle of slip of an elastic wheel is based on a redistribution of contact pressures occasioned by longitudinal forces (Vyrabov). Energy losses in the bearings of turbogenerators range from 0.22% in nuclear plants to 0.79% for gas turbines. Both gas-path and labyrinth seals are major sources of energy loss, which is quantified as a potential for saving U.S. $910 000 000 annually in the U.S.A. alone. Improved reliability is the next most significant potential saving (Pinkus). The performance of water-based cutting fluid used in broaching is improved by chlorine-based EP additives and high molecular carboxylic acid salts (Nakai). An insight into an industry not usually represented at tribotechnical gatherings was provided by a study of the conversion of maize from a freeflowing powder to a coherent solid by a process known as “extrusion cooking”. Both interface rheology and bulk friction are involved. The friction behaviour of starch compounds can be modelled by Archard’s method in conjunction with the adhesion theory of friction (Briscoe, b). When aluminium is hot rolled, the so-called roll coating consists of aluminium oxide with a small quantity of the metal, depending on the rolling emulsion used. The surface quality of the product depends on the properties of the roll coating (Yoshida). The addition of mineral oil to cooling water during the hot rolling of steel is beneficial and a significant reduction in friction results from the introduction of oleic acid (K. Nakamura). A concentration of EP additive (alkyl phosphate ester) of 0.6% is an optimum in an emulsion used in the cold rolling of steel. The best surface quality of product was obtained with the emulsion showing the least spreading. The Marangoni effect governs spreading in the presence of a temperature gradient (Miyagawa). In orthogonal cutting surface plastic displacement increases with tool nose radius (Moneim). The wear of high speed steel progresses from edge chipping through abrasion and mild adhesive wear to severe adhesive wear.

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Wear can be minimized by selecting the grade of steel most appropriate to the wear mode encountered in the particular operation (Soderberg). Cemented-carbide cutting tools are subject to crack formation which occurs both during preparation by grinding and when actually cutting. The crack density due to grinding reaches a maximum value at a cooling rate of 80 K s-l and can be minimized by the use of an appropriate cutting fluid. Similarly, in machining, the density of cracks which occur at tool disengagement can be reduced by lowering the rate of cooling to below 70 K s-l (Imai). It is generally assumed that the wear that occurs where the tubes of heat exchangers are supported by plates is due to a fretting mechanism, but it now appears that material is removed from the oxide film by hydraulic erosion (Hogmark). Little concern with condition monitoring was evidenced throughout the conference except for the case of biomedical research where ferrography has been used to study human and artificial joints (Norose). It is reassuring to learn that EHD conditions apply to hip-joint replacements and that a film thickness of 3.1 pm is maintained between the ball and the pelvic socket during normal walking (Sasada, b). It is very much to be regretted that the opportunity was not taken of recording and publishing the discussion of the great range of material presented at the conference. For example, a record of the differing views of some leading Japanese scientists on the relative importance of adhesion and fatigue in sliding wear would have been most illuminating. F. T. BARWELL

26 Woodland Way

Brighton BNl 8BA, U.K.