Friction, Lubrication, and Wear Technology (1997) Part 15 pptx

Note: The term erosion erosive wear is preferred in the case of multiple impacts and when the impacting body or bodies are very small relative to the surface being impacted.. 2 The proc

• Note: This number is normally written as:

• in which Z denotes the dynamic viscosity, N the frequency of rotation, and p the pressure (Ref 1)

See also Ocvirk number , Sommerfeld number , and Stribeck curve

• Hertzian contact area

• (1) The contact area (also, diameter or radius of contact) between two bodies calculated according

to Hertz's equations of elastic deformation (Ref 1m) (2) The apparent area of contact between two nonconforming solid bodies pressed against each other, as calculated from Hertz's equations

of elastic deformation (Ref 2)

• Hertzian contact pressure

• (1) The pressure at a contact between two solid bodies calculated according to Hertz's equations

of elastic deformation (Ref 1) (2) The magnitude of the pressure at any specified location in a Hertzian contact area, as calculated from Hertz's equations of elastic deformation (Ref 2)

• high-stress abrasion

• A form of abrasion in which relatively large cutting forces are imposed on the particles or protuberances causing the abrasion, and that produces significant cutting and deformation of the

wearing surface Note: In metals, high-stress abrasion can result in significant surface strain

hardening This form of abrasion is common in mining and agricultural equipment, and in highly loaded bearings where hard particles are trapped between mating surfaces (Ref 3m) See also low-stress abrasion

• highly deformed layer

• In tribology, a layer of severely plastically deformed material that results from the shear stresses imposed on that region during sliding contact See also Beilby layer and white layer

• Hohman A-6 wear machine

• A widely used type of wear and friction testing machine in which a rotating ring specimen is

squeezed between two diametrically opposed rub blocks Note: This design is said to eliminate

shaft flexure such as that found in other machines whose load application from the rub block to the ring is from one side only Block geometry can be changed from flat to conforming or V-block This type of machine is designed for use with either lubricated or unlubricated specimens

Hohman A-6 wear machine testing arrangement Courtesy of Hohman Plating and Manufacturing Company

• horseshoe thrust bearing

• A tilting-pad thrust bearing in which the top pads are omitted, making an incomplete annulus (Ref 1)

• hydraulic fluid

• A fluid used for transmission of hydraulic pressure or action, not necessarily involving lubricant

properties Note: Hydraulic fluids can be based on oil, water, or synthetic (fire-resistant) liquids

(Ref 1)

• hydrodynamic lubrication

• A system of lubrication in which the shape and relative motion of the sliding surfaces causes the formation of a fluid film that has sufficient pressure to separate the surfaces (Ref 1) See also elastohydrodynamic lubrication and gas lubrication

• hydrodynamic seal

• A seal that has special geometric features on one of the mating faces These features are designed

to produce interfacial lift, which arises solely from the relative motion between the stationary and rotating portions of the seal (Ref 4)

• hydrostatic bearing

• A bearing in which the solid bodies are separated and supported by a hydrostatic pressure, applied

by an external source, to a compressible or incompressible fluid interposed between those bodies

• hypoid gear lubricant (hypoid oil)

• A gear lubricant with extreme-pressure characteristics used in hypoid gears (Ref 1)

• I

• impact velocity

• The relative velocity between the surface of a solid body and an impacting liquid or solid particle

Note: To describe this velocity completely, it is necessary to specify the direction of motion of

the particle relative to the solid surface in addition to the magnitude of the velocity The following related terms are also in use: (1) absolute impact velocity the magnitude of the impact velocity, and (2) normal impact velocity the component of the impact velocity that is perpendicular to the surface of the test solid at the point of impact (Ref 2)

• impact wear

• Wear of a solid surface resulting from repeated collisions between that surface and another solid

body Note: The term erosion (erosive) wear is preferred in the case of multiple impacts and

when the impacting body or bodies are very small relative to the surface being impacted

• impaction ratio

• See collection efficiency

• impingement

• A process resulting in a continuing succession of impacts between liquid or solid particles and a

solid surface Note: In preferred usage, impingement also connotes that the impacting particles

are smaller than the solid surface, and that the impacts are distributed over the surface or a portion of the surface If all impacts are superimposed on the same point or zone, then the term repeated impact is preferred (Ref 2m)

• incubation period

• (1) In cavitation and impingement erosion, the initial stage of the erosion rate-time pattern during which the erosion rate is zero or negligible compared to later stages (2) In cavitation and impingement erosion, the exposure duration associated with the initial stage of the erosion rate-

time pattern during which the erosion rate is zero or negligible compared to later stages Note:

Quantitatively, incubation period is sometimes defined as the intercept on the time or exposure axis, of a straight-line extension of the maximum slope portion of the cumulative erosion-time curve (Ref 2m) See also cavitation erosion and impingement erosion

• indentation hardness

• Resistance of a solid surface to the penetration of a second, usually harder, body under prescribed

conditions Note: Numerical values used to express indentation hardness are not absolute

physical quantities, but depend on the hardness scale used to express hardness See also Brinell hardness test , Knoop (microindentation) hardness number , microindentation hardness number , nanohardness test , Rockwell hardness number , and Vickers (microindentation) hardness number

• indenter

• In hardness testing, a solid body of prescribed geometry, usually chosen for its high hardness, that

is used to determine the resistance of a solid surface to penetration

• initial pitting

• Surface fatigue occurring during the early stages of gear operation, associated with the removal of highly stressed local areas and running-in (Ref 1)

• instantaneous erosion rate

• The slope of a tangent to the cumulative erosion-time curve at a specified point on that curve (Ref 2)

• interval erosion rate

• The slope of a line connecting two specified points on the cumulative erosion-time curve (Ref 2)

• IRG transition diagram

• Developed by the International Research Group (IRG) on Wear of Engineering Materials of the Organization of Economic Cooperation and Development (OECD), it is a plot of normal force in newtons (ordinate) versus sliding velocity in meters per second (abscissa) wherein boundaries identify three distinct regions of varying lubricant effectiveness

• J

• jewel bearing

• A bearing made of diamond, sapphire, or a hard substitute metal (Ref 1)

• journal

• The part of a shaft or axle that rotates or oscillates relative to a radial bearing Note: A journal is

part of a larger unit, for example, a crankshaft or lineshaft, and it is preferred that the term shaft

be kept for the whole unit (Ref 1)

• journal bearing

• A sliding-type bearing in which a journal rotates or oscillates relative to its housing Note: A full

journal bearing extends 360°, but partial bearings may extend, for example, over 180° or 120° (Ref 1)

• kinetic coefficient of friction

• The coefficient of friction under conditions of macroscopic relative motion between two bodies (Ref 2)

• kinetic friction

• Friction under conditions of macroscopic relative motion between two bodies Note: This term is

sometimes used as a synonym for kinetic coefficient of friction ; however, it can also be used merely to indicate that the type of friction being indicated is associated with macroscopic motion rather than static conditions

• kinematic wear marks

• In ball bearings, a series of short curved marks on the surface of a bearing race due to the kinematic action of imbedded particles or asperities rolling and spinning at the ball or roller

contact points Note: The length and curvature of these marks depend on the degree of spinning

and on the distance from the spinning axis of the rolling element (Ref 3m)

• Kingsbury bearing

• See tilting-pad bearing

• knock

• In a spark ignition engine, uneven burning of the air/fuel charge that causes violent, explosive

combustion and an audible metallic hammering noise Note: Knock results from premature

ignition of the last part of the charge to burn (Ref 8)

• Knoop (microindentation) hardness number

• Developed by F.C Knoop in the late 1930s, it is the numerical value of microindentation hardness obtained using the Knoop indenter (diamond) and calculated as follows:

• where HKP (units of GPa) is the ASTM symbol used to represent Knoop microindentation

hardness number (with the subscript indicating applied indenter load), P is the applied load (in grams), and d is the length of the long diagonal of the impression (in micrometers) Note: To

obtain HK in kg/mm2, replace 139.6 by 14229.0 See ASTM Standard Test Method E 384 for further details

• L

• L 10-life

• See rating life

• lacquer

• In lubrication, a deposit resulting from the oxidation and/or polymerization of fuels and lubricants

when exposed to high temperatures Note: Softer deposits are described as varnishes or gums

(Ref 1)

• lapping

• (1) A surface finishing process involving motion against an abrasive embedded in a soft metal (Ref 1) (2) Rubbing two surfaces together, with or without abrasives, for the purpose of obtaining extreme dimensional accuracy or superior surface finish (Ref 11)

• See bearing bronzes

• lemon bearing (elliptical bearing)

• A two-lobed bearing (Ref 1m)

• light fraction

• The first liquid produced during the distillation of a crude oil (Ref 1)

• limiting static friction

• The resistance to the force tangential to the interface that is just sufficient to initiate relative

motion between two bodies under load Note: The term static friction, which properly describes a

tangential resistance called into operation by a force less than this, should not be substituted for limiting static friction (Ref 1)

• linishing

• A method of finishing by grinding on a continuous abrasive belt (Ref 1)

• liquid impact erosion

• See erosion (erosive wear)

• liquid impingement erosion

• See erosion (erosive wear)

• little-end bearing

• A bearing at the smaller (piston) end of a connecting rod in an engine (Ref 1) See also big-end bearing

• load

• In tribology, the force applied normal to the surface of one body by another contacting body or

bodies Note: The term normal force is more precise and therefore preferred; however, the term

normal load is also in use If applied vertically, the load can be expressed in mass units, but it is preferable to use force units such as newtons (N)

• load-carrying capacity (of a lubricant)

• (1) The maximum load that a sliding or rolling system can support without failure (Ref 1m) (2) The maximum load or pressure that can be sustained by a lubricant (when used in a given system under specific conditions) without failure of moving bearings or sliding contact surfaces as evidenced by seizure or welding (Ref 11)

• loading

• (1) The filling of an abrasive paper or other bound abrasive material by abraded material from a second body (2) The concentration of abrasive bound in a matrix material or added to a lap wheel as a loose abrasive

• lubricant

• Any substance interposed between two surfaces in relative motion for the purpose of reducing the

friction or wear between them (Ref 1) Note: The above definition implies intentional addition of

a substance to an interface; however, species such as oxides and tarnishes on certain metals can also act as lubricants even though they were not added to the system intentionally

• macroslip

• A type of sliding in which all points on one side of the interface are moving relatively to those on

the other side in a direction parallel to the interface Note: The term macroslip is sometimes used

to denote macroslip velocity This usage is not recommended (Ref 1) See also microslip

• magnetic bearing

• A type of bearing in which the force that separates the relatively moving surfaces is produced by

a magnetic field

• magnetic seal

• A seal that uses magnetic material, instead of springs or bellows, to provide the closing force (Ref 4)

• magnetohydrodynamic lubrication

• Hydrodynamic lubrication in which a significant force contribution arises from electromagnetic

interaction Note: Magnetohydrodynamic bearings have been proposed for very high-temperature

operation, for example, in liquid sodium (Ref 1)

• magnetostrictive cavitation test device

• A vibratory cavitation test device driven by a magnetostrictive transducer (Ref 2)

• main bearing

• A bearing supporting the main power-transmitting shaft (Ref 1)

• mass concentration (in a slurry)

• The mass of solid particles per unit mass of mixture, expressed in percent (Ref 13)

• maximum erosion rate

• The maximum instantaneous erosion rate in a test that exhibits such a maximum followed by

decreasing erosion rates Note: Occurrence of such a maximum is typical of many cavitation and

liquid impingement tests In some instances it occurs as an instantaneous maximum; in others it occurs as a steady-state maximum that persists for some time (Ref 2)

• maximum rate period

• In cavitation and liquid impingement erosion, a stage following the acceleration period, during which the erosion rate remains constant (or nearly so) at its maximum value (Ref 2)

• mechanical activation

• The acceleration or initiation of a chemical reaction by mechanical exposure of a nascent solid

surface Note: Metal cutting is an effective method of exposing large areas of fresh surface

• mechanical seal

• See face seal

• mechanical stability (of a grease)

• Grease shear stability tested in a standard rolling tester (Ref 1)

• mechanical wear

• Removal of material due to mechanical processes under conditions of sliding, rolling, or repeated

impact Note: The term mechanical wear includes adhesive wear , abrasive wear , and fatigue

wear (Ref 1) Compare with corrosive wear and thermal wear

• (1) In hardness testing, the small residual impression left in a solid surface when an indenter,

typically a pyramidal diamond stylus, is withdrawn after penetrating the surface Notes:

Typically, the dimensions of the microindentations are measured to determine microindentation hardness number, but newer methods measure the displacement of the indenter during the indentation process to use in the hardness calculation The precise size required to qualify as a

"microindentation" has not been clearly defined; however, typical measurements of the diagonals

of such impressions range from approximately 10 to 200 m, depending on normal force and material (2) The process of indenting a solid surface, using a hard stylus of prescribed geometry and under a slowly applied normal force, usually for the purpose of determining its microindentation hardness number See also Knoop (microindentation) hardness number , microindentation hardness number , and Vickers (microindentation) hardness number

• microindentation hardness number

• A numerical quantity, usually stated in units of pressure, that expresses the resistance to penetration of a solid surface by a hard indenter of prescribed geometry and under a specified,

slowly applied normal force Notes: The prefix "micro" indicates that the indentations produced

are typically between 10.0 and 200 m across See also Knoop (microindentation) hardness number , nanohardness test , and Vickers (microindentation) hardness number

• microslip

• Small relative tangential displacement in a contacting area at an interface, when the remainder of

the interface in the contacting area is not relatively displaced tangentially Notes: Microslip can

occur in both rolling and stationary contacts (2) The term microslip is sometimes used to denote the microslip velocity This usage is not recommended (Ref 1) See also macroslip and slip

• mild wear

• A form of wear characterized by the removal of material in very small fragments Notes: Mild

wear is an imprecise term, frequently used in research, and contrasted with severe wear In fact, the phenomena studied usually involve the transition from mild to severe wear and the factors that influence this transition Mild wear may be appreciably greater than can be tolerated in practice With metallic sliders, mild wear debris usually consists of oxide particles (Ref 1m) See also normal wear and severe wear

• Miller number

• A measure of slurry abrasivity as related to the instantaneous mass-loss rate of a standard metal wear block at a specific time on the cumulative abrasion-corrosion time curve (Ref 13) See also slurry abrasion response number

• A seal that is basically of the windback type, but that is used for sealing vapors or gases Note:

Because of this use, the grooves and lands are dimensioned differently from those of a windback seal (Ref 4)

• multigrade oil

• An oil having relatively little change in viscosity over a specified temperature range (Ref 1)

• N

• nanohardness test

• An indentation hardness testing procedure, usually relying on indentation force versus tip displacement data, to make assessments of the resistance of surfaces to penetrations of the order

of 10 to 1000 nm deep Notes: The prefix "nano-" normally would imply hardnesses one

thousand times smaller than "microhardness"; however, use of this prefix was primarily designed

as a means to distinguish this technique from the more traditional microindentation hardness procedures Most nanohardness testing procedures use three-sided pyramidal diamond indenters first described by Berkovich

• Hydrocarbon oil with or without additives, used undiluted Note: This term is used particularly in

metal cutting to distinguish these fluids from soluble oils (emulsions) (Ref 1m)

• needle bearing

• A bearing in which the relatively moving parts are separated by long, thin rollers that have a length-to-diameter ratio exceeding 5.0 (Ref 1m)

• net positive suction head

• The difference between total pressure and vapor pressure in a fluid flow, expressed in terms of equivalent height of fluid, or "head," by the following equation:

• where Po is the static pressure, Pv is the vapor pressure, V is the flow velocity, w is the specific weight of fluid, and g is the gravitational acceleration Note: This quantity is used in pump design

as a measure of the tendency for cavitation to occur at the pump inlet It can be related to the cavitation number (Ref 2)

• nominal area (of contact)

• The area bounded by the periphery of the region in which macroscopic contact between two solid

bodies is occurring Note: This is often taken to mean the area enclosed by the boundaries of a

wear scar, even though the real area of contact, in which the solids are touching instantaneously,

is usually much smaller See also area of contact and apparent area of contact

• nonconformal surfaces

• (1) Surfaces whose centers of curvature are on the opposite sides of the interface, as in element bearings or gear teeth (Ref 1) (2) In wear testing, a geometric configuration in which a

rolling-"point" or "line" of contact is initially established between specimens before the test is started

Note: Examples of nonconformal contacts are ball-on-ring and flat block-on-ring geometries

(tangent to the circumferential surface) When wear occurs, the nominal area of contact tends to increase

Nonconformal (left) and conformal (right) test geometries

• noncontact bearing

• A bearing in which no solid contact occurs between relatively moving surfaces Note: Strictly

speaking, a bearing in which full-film lubrication is occurring would be considered a noncontact bearing; however, this term is more typically applied to gas bearings and magnetic bearings See also gas lubrication and magnetic bearing

• Loss of material within the design limits expected for the specific intended application Note: The

concept of normal wear depends on economic factors, such as the expendability of a worn part

• normalized erosion resistance

• The volume loss rate of a specified reference material divided by the volume loss rate of a test

material obtained under similar testing and analysis conditions Notes: "Similar testing and

analysis conditions" means that the volume loss rates of the two materials are determined at the corresponding portions of the erosion rate-time pattern, for example, the maximum erosion rate

or the terminal erosion rate A recommended complete wording has the form: "the normalized erosion resistance of (test material) relative to the (reference material) based on (criterion of data analysis) is (numerical value)" (Ref 2m)

• O

• Ocvirk number

• A dimensionless number used to evaluate the performance of journal bearings, and defined by the following equation:

• where P is the load per unit width, is the dynamic viscosity, U is the surface velocity, c is the radial clearance, r is the bearing radius, b is the bearing length, and d is the bearing diameter

Note: This number may be used in its inverted form and is related to the Sommerfeld number

• oil fog lubrication

• See mist lubrication

• oil groove

• A channel or channels cut in a bearing to improve oil flow through the bearing Note: A similar

groove may be used for grease-filled bearings (Ref 1)

• oil pocket

• A depression designed to retain oil in a sliding surface (Ref 1)

• oil ring lubrication

• A system of lubrication for horizontal shafts A ring of larger diameter rotates with the shaft and collects oils from a container beneath (Ref 1)

• oil starvation

• A condition in which a bearing, or other tribocomponent, receives an inadequate supply of lubricant (Ref 1m)

• oil whirl

• Instability of a rotating shaft associated with instability in the lubricant film Note: Oil whirl

should be distinguished from shaft whirl, which depends only on the stiffness of the shaft (Ref 1)

• oiliness

• See lubricity

• overbasing

• A technique for increasing the basicity of lubricants Note: Overbased lubricants are used to assist

in neutralizing acidic oxidation products (Ref 1)

• oxidative wear

• A corrosive wear process in which chemical reaction with oxygen or oxidizing environment

predominates Note: Usually, oxidative wear is a form of mild wear , but it can sometimes be

serious, for example, in liquid oxygen or liquid fluorine (Ref 1)

• P

• pad lubrication

• A system of lubrication in which the lubricant is delivered to a bearing surface by a pad of felt or similar material (Ref 1)

• partial (journal) bearing

• A bearing in which the bore extends not more than half the circumference of the journal (Ref 1)

• partial hydrodynamic lubrication

• See quasi-hydrodynamic lubrication

• penetration (of a grease)

• The depth in mm that a standard cone penetrates the sample in a standard cup under

prescribed conditions of weight, time (5 s), and temperature (25 °C, or 77 °F) Notes: The result

depends on whether or not the grease has been subjected to shear In unworked penetration, the

grease is transferred with as little deformation as possible or is tested in its container In worked penetration, the grease is subjected to 60 double strokes in a standard device In prolonged worked penetration, the grease is worked for a specified period before the 60 strokes The results may be quoted as penetration number or penetration value (Ref 1m)

• penetration hardness number

• Any numerical value expressing the resistance of a body to the penetration of a second, usually harder, body

• penetrometer

• In grease technology, an instrument for measuring the consistency of a grease by allowing a cone

to penetrate into the grease under controlled conditions (Ref 1) See also penetration (of a grease)

• petroleum oil

• See mineral oil

• Petroff equation

• An equation describing the viscous power loss in a concentric bearing full of lubricant The

resisting torque on the shaft (To = shear stress × shaft radius × bearing area) is given by:

• where = 3.1416, is the dynamic viscosity, N is the shaft speed, L is the bearing length, D is the shaft diameter, and 2c is the diametral clearance (Ref 1m)

motion Notes: The typical pin-on-disk arrangement resembles that of a traditional phonograph

Either the disk rotates or the pin specimen holder rotates so as to produce a circular path on the disk surface An arrangement wherein the pin specimen is loaded against the curved circumferential surface of a flat disk is not generally considered to be a pin-on-disk machine

Pin-on-disk machine test configuration

• plain bearing

• Any simple sliding-type bearing, as distinct from pad- or rolling-type bearings (Ref 1)

• plain journal bearing

• A plain bearing in which the relatively sliding surfaces are cylindrical and in which there is

relative angular motion Note: One surface is usually stationary and the force acts

perpendicularly to the axis of rotation (Ref 1)

• plain thrust bearing

• A plain bearing of the axial-load type, with or without grooves (Ref 1)

• plastohydrodynamic lubrication

• A condition of lubrication in which the friction and film thickness between two bodies in relative motion are determined by plastic deformation of the bodies in combination with the viscous properties of the lubricant at the prevailing pressure, temperature, and rate of shear (Ref 1) Compare with elastohydrodynamic lubrication

• plowing (ploughing)

• The formation of grooves by plastic deformation of the softer of two surfaces in relative motion

Notes: The contribution of plowing to frictional resistance is to be distinguished from the

contribution of shearing, especially in the classical hemisphere-on-flat model system In plowing, local solid-phase welding is ignored (Ref 1m)

• (P1) The meter-kilogram-second (mks) or Système International d'Unités (SI) unit of dynamic

viscosity Note: 1 Pl = 10 P (Ref 1)

• porous bearing

• A bearing made from porous material such as compressed and sintered metal powder Note: The

pores may act as reservoirs or passages for supplying fluid lubricant, or the bearing may be impregnated with solid lubricant (Ref 1)

• positive-contact bushing

• A bushing, the inside diameter of which has direct contact with the outside diameter of a shaft or

sleeve Note: Radial or axial clearances are provided in the housing (Ref 4m)

• positive-contact seal

• A seal, the primary function of which is achieved by one surface mating with another Note:

Examples include lip, circumferential, and face-type seals (Ref 4m) See also face seal

• The slope of a graph showing variation in the logarithm of viscosity with pressure Note: The use

of the term pressure-viscosity coefficient assumes a linear relationship (Barus equation) (Ref 1)

• pressure lubrication

• A system of lubrication in which the lubricant is supplied to the bearing under pressure (Ref 1)

• pressurized gas lubrication

• A system of lubrication in which a gaseous lubricant is supplied under sufficient external pressure

to separate the opposing surfaces by a gas film (Ref 1)

• race (or raceway)

• The groove or path in which the rolling elements in a rolling-contact bearing operate (Ref 1m)

• radial lip seal

• A radial type of seal that features a flexible sealing member, referred to as a lip Note: The lip is

usually of an elastomeric material It exerts radial sealing pressure on a mating shaft in order to retain fluids and/or exclude foreign matter (Ref 4m)

• radial-load bearing

• A bearing in which the load acts in a radial direction with respect to the axis of rotation (Ref 1)

• rain erosion

• A form of liquid impingement erosion in which the impinging liquid particles are raindrops Note:

This form of erosion is of particular concern to designers and material selectors for external surfaces of rotary-wing and fixed-wing aircraft See also erosion (erosive wear)

• rating life

• Currently the fatigue life in millions of revolutions or hours at a given operating speed that 90%

of a group of substantially identical rolling-element bearings will survive under a given load

Note: The 90% rating life is frequently referred to as L10-life or B10-life (Ref 1) From Ref 6, the rating life in revolutions can be obtained from:

• where C is the basic load rating (in pounds), P is the equivalent radial load (in pounds), and K is a

constant (3 for ball bearings and 10/3 for roller bearings) For a rating life in hours, use:

• where N is the rotational speed in rev/min

• Rayleigh step bearing

• A stepped-pad bearing having one step only in each pad (Ref 1)

• real area of contact

• In tribology, the sum of the local areas of contact between two solid surfaces, formed by contacting asperities, that transmit the interfacial force between the two surfaces (Ref 2) Contrast with apparent area of contact

• red mud

• See cocoa

• Redwood viscosity

• A commercial measure of viscosity expressed as the time in seconds required for 50 cm3 of a

fluid to flow through a tube of 10 mm length and 1.5 mm diameter at a given temperature Note:

It is recommended that fundamental viscosity units should be used (Ref 1)

• A regime of lubrication in which the rheological (non-Newtonian) properties of the lubricant

predominate Note: This term is especially applied to lubrication with grease (Ref 1)

• ripple formation (rippling)

• Formation of periodic ridges and valleys transverse to the direction of motion (Ref 1)

• Rockwell hardness number

• A number derived from the net increase in the depth of impression as the load on a penetrator is increased from a fixed minor load to a major load and then returned to the minor load (Ref 11)

Note: Various scales of Rockwell hardness numbers have been developed based on the hardness

of the materials to be evaluated The scales are designated by alphabetic suffixes to the hardness designation, for example, HRB, HRC A detailed description of the Rockwell hardness testing procedure can be found in ASTM Standard E 40

• Rockwell superficial hardness test

• The same test as used to determine the Rockwell hardness number except that smaller minor and major loads are used (Ref 11m)

• rolling-contact fatigue

• Repeated stressing of a solid surface due to rolling contact between it and another solid surface or

surfaces Note: Continued rolling-contact fatigue of bearing surfaces may result in rolling-contact

damage in the form of subsurface fatigue cracks and/or material pitting and spallation

• run in

• (verb) In tribology, to apply a specified set of initial operating conditions to a tribological system

in order to improve its long-term frictional or wear behavior, or both (Ref 2) Note: The run-in

may involve conditions either more severe or less severe than the normal operating conditions of the tribosystem, and may also involve the use of special lubricants and/or surface chemical treatments See also break-in

• running-in

• The process by which machine parts improve in conformity, surface topography, and frictional

compatibility during the initial stage of use Note: Chemical processes, including formation of an

oxide skin, and metallurgical processes, such as strain hardening, may contribute (Ref 1)

g of oil under test conditions Note: Saponification number is a measure of fatty materials

compounded in an oil (Ref 5m)

• sauter mean diameter

• The diameter of a drop that has the same ratio of volume-to-surface area as the ratio of total volume-to-total surface area in a distribution of drops, as computed from the equation:

SMD = ini / ini

• where i is a sampling size interval, d i is the drop diameter, and n i is the number of drops in that interval (Ref 2)

• Saybolt Universal Viscosity

• A commercial measure of viscosity expressed as the time in seconds required for 60 cm3 of a fluid to flow through the orifice of the Standard Saybolt Universal Viscometer at a given temperature under specified conditions (Ref 1)

• scabbing

• (1) In wear, a loosely used term referring to the formation of bulges in the surface (Ref 1) (2) In fracture mechanics, it is identical with spalling (Ref 1)

• scaling

• The formation of a thick oxide on the surface of a heated metal Note: Scaling is to be

distinguished from rusting, which involves the formation of hydrated oxides (Ref 1)

• scoring

• (1) The formation of severe scratches in the direction of sliding Notes: Scoring may be due to

local solid-phase welding or to abrasion In the United States, the term scuffing is sometimes used as a synonym for scoring Minor damage should be called scratching rather than scoring (Ref 1) (2) In tribology, a severe form of wear characterized by the formation of extensive grooves and scratches in the direction of sliding (Ref 2) (3) The act of producing a scratch or narrow groove in a surface by causing a sharp instrument to move along that surface See also galling

• scratch hardness test

• A form of hardness test in which a sharp-pointed stylus or corner of a mineral specimen is traversed along a surface so as to determine the resistance of that surface to cutting or abrasion

Notes: The Mohs hardness test is among the most widely used forms of scratch hardness tests,

but is mainly applied to mineralogical specimens or abrasives Other scratch hardness tests involve using diamond cones, pyramids, and spherical tips, but such scratch hardness tests have not been established and standardized to the extent that macro- and microindentation hardness tests have been

• scratching

• The formation of fine scratches in the direction of sliding Notes: Scratching may be due to

asperities on the harder slider or to hard particles between the surface or embedded in one of them Scratching is to be considered less damaging than scoring (Ref 1) See also abrasion , plowing (ploughing) , and ridging wear

• scratching abrasion

• See low-stress abrasion

• scuffing

• (1) Localized damage caused by the occurrence of solid-phase welding between sliding surfaces,

without local surface melting Notes: In the United Kingdom, scuffing implies local solid-phase

welding only In the United States, scuffing may include abrasive effects and the term scoring is sometimes used as a synonym (Ref 1) (2) A mild degree of galling that results from the welding

of asperities due to frictional heat The welded asperities break, causing surface degradation (Ref

4) Note: In general, the term scuffing has been used in so many different ways that its use should

be avoided whenever possible, and instead replaced with a more precise description of the specific type of surface damage being considered

• seal

• (1) In tribology, a device designed to prevent leakage between relatively moving parts (Ref 1) (2)

A device designed to prevent the movement of fluid from one chamber to another, or to exclude contaminants (Ref 4)

• sealing face

• The lapped surface of a seal that comes in close proximity to the face of the mating ring of a face seal, thus forming the primary seal With reference to lip seals, the preferred term is seal contact surface (Ref 4)

• seal nose

• The part of the primary seal ring of a face seal that comes in closest proximity to the mating surface and that, together with the mating surface, forms the primary seal (Ref 4)

• secondary seal

• A device, such as bellows, piston ring, or O-ring, that allows axial movement of the primary seal

of a mechanical face seal without undue leakage (Ref 4)

• seizure

• The stopping of relative motion as the result of interfacial friction Notes: Seizure may be

accompanied by gross surface welding The term is sometimes used to denote scuffing (Ref 1m)

• selective transfer

• A process involving the transfer and attachment of a specific species from one surface to the

mating surface during sliding Notes: This term is to be distinguished from the general

tribological term transfer , which involves the same general process, but which, when used by itself, does not discriminate as to which of the species present in a multiconstituent surface is transferred during sliding This term is more commonly used in the Russian literature of tribology

• A bearing independent of external lubrication Note: These bearings may be sealed for life after

packing with grease or may contain self-lubricating material (Ref 1)

• self-lubricating material

• Any solid material that shows low friction without application of a lubricant Notes: Examples are

graphite, molybdenum disulfide, and polytetrafluoroethylene Taken in a broader context, the term can also refer to a composite material into which a lubricious species has been incorporated (Ref 1m) See also solid lubricant

• separator

• In rolling-element bearings, the part of a cage that lies between the rolling elements Note: This

term is sometimes used as a synonym for cage (Ref 1m)

• severe wear

• A form of wear characterized by removal of material in relatively large fragments Notes: Severe

wear is an imprecise term, frequently used in research, and contrasted with mild wear In fact, the phenomena studied usually involve the transition from mild to severe wear and the factors that influence that transition With metals, the fragments are usually predominantly metallic rather than oxidic Severe wear is frequently associated with heavy loads and/or adhesive contact (Ref 1)

• shaft run-out

• Twice the distance that the center of a shaft is displaced from the axis of rotation; that is, twice the eccentricity (Ref 4)

• shake-down (of surface layers)

• The establishment of a state of stress in which no further plastic flow occurs (Ref 1m)

• A decrease in viscosity with an increase in shear stress or time Note: The decrease in viscosity

may be temporary or permanent The latter happens when the shear stress is sufficiently large to rupture a chemical bond, so that the sheared liquid has a lower viscosity than it had prior to shearing (Ref 1) See also shear thickening

• shelling

• A term used in railway engineering to describe an advanced phase of spalling (Ref 1)

• skidding

• A form of nonuniform relative motion between solid surfaces due to rapid periodic changes in the traction between those surfaces

• sleeve bearing

• A cylindrical plain bearing used to provide radial location for a shaft, which moves axially Note:

Sleeve bearing is sometimes used to denote journal bearing (Ref 1) See also sliding bearing

• slide-roll ratio

• See slide-sweep ratio

• slide-sweep ratio

• The ratio of sliding velocity to sweep velocity, for example, in a pair of gears Note: In rolling,

the slide-sweep ratio is called the slide-roll ratio (Ref 1)

• sliding

• (pure sliding with no rolling or spin) A motion of two relatively moving bodies, in which their surface velocities in the common contact area are different with regard to magnitude and/or direction (Ref 1) See also rolling , spin , and specific sliding

• sliding bearing

• A bearing in which predominantly sliding contact occurs between relatively moving surfaces

Note: Sliding bearings may be either unlubricated, liquid lubricated, grease lubricated, or solid

• The flow of gravity of a grease in a container, allowing it to feed out into a pump or can Note:

Slumpability also influences the leakage of grease from a bearing (Ref 1)

• slurry

• A mixture of solid particles in a liquid, of such consistency so as to be capable of being pumped like a liquid (Ref 13)

• slurry abrasion response (SAR) number

• A measure of the relative abrasion response of any material in any slurry, as related to the instantaneous rate of mass loss of a specimen at a specific time on the cumulative abrasion-

corrosion time curve, converted to volume or thickness loss rate (Ref 13) Notes: The SAR

number is determined by a procedure described in ASTM Standard Test Method G 75 The Miller number , also described in ASTM G 75, is a measure of the abrasivity of a slurry

• In lubrication, a compound formed by the reaction of a fatty acid with a metal or metal

compound Note: Metallic soaps formed by reaction in situ are an important group of boundary

lubricants (Ref 1)

• solid-film lubrication

• Lubrication by application of solid lubricants (Ref 1)

• solid lubricant

• Any solid used as a powder or thin film on a surface to provide protection from damage during

relative movement, and to reduce friction and wear Notes: Many solid lubricants have a layer

(lamellar) structure, for example, graphite and molybdenum disulfide Certain solid materials lubricate only in the molten state at the interface Examples are glass and ice, which are not solid lubricants (Ref 1)

• soluble oil

• A mineral oil containing additives that enable it to form a stable emulsion with water Note:

Soluble oils are not soluble in water (Ref 1)

• in which N is the frequency of rotation and p is the pressure, is sometimes referred to as the

Sommerfeld number, particularly in the United States (Ref 1m) See also Hershey number and Ocvirk number

• spalling

• (1) Separation of particles from a surface in the form of flakes Notes: The term spalling is

commonly associated with rolling-element bearings and with gear teeth Spalling is usually a result of subsurface fatigue and is more extensive than pitting (Ref 1) (2) In tribology, the separation of macroscopic particles from a surface in the form of flakes or chips, usually associated with rolling-element bearings and gear teeth, but also resulting from impact events (Ref 2) See also fatigue wear , scabbing , and shelling

• specific wear rate

• In journal bearings, the proportionality constant K in the equation:

• A bearing that is self-aligning by virtue of its partially spherical form (Ref 1)

• spherical roller bearing

• (1) A spherical bearing containing rollers (Ref 1) (2) A roller bearing containing barrel-shaped or hour glass-shaped rollers riding on spherical (concave or convex) races to provide self-aligning capability (Ref 8)

• starting torque

• The torque that is required for initiating rotary motion (Ref 4)

• static coefficient of friction

• The coefficient of friction corresponding to the maximum friction force that must be overcome to initiate macroscopic motion between two bodies (Ref 2)

• static equivalent load

• (Po) In rolling-element bearings, the static load which, if applied, would give the same life as that which the bearing will attain under actual conditions of load and rotation (Ref 6m)

• static friction

• See limiting static friction

• static load rating

• (Co) In rolling-element bearings, the static load that corresponds to a permanent deformation of rolling element and race at the most heavily stressed contact of 0.00001 of the rolling-element diameter (Ref 6m)

• stepped bearing

• A thrust bearing in which the working face consists of one or more shallow steps Notes: Bearings

of this type were originally described by Rayleigh A distinction should be drawn between a stepped bearing and a step bearing (Ref 1)

• stern-tube bearing

• The final bearing through which a propeller shaft passes in a boat or ship (Ref 1m)

• stick-slip

• A relaxation oscillation usually associated with a decrease in the coefficient of friction as the

relative velocity increases Notes: Stick-slip was originally associated with formation and

destruction of interfacial junctions on a microscopic scale This is often the basic cause The period depends on the velocity and on the elastic characteristics of the system Stick-slip will not occur if the static friction is equal to or less than the dynamic friction The motion resulting from stick-slip is sometimes referred to as jerky motion (Ref 1) See also spragging

• Stribeck curve

• A graph showing the relationship between coefficient of friction and the dimensionless number

( N/P), where is the dynamic viscosity, N is the speed (revolutions per minute for a journal), and P is the load per unit of projected area Note: The symbols Z and v (linear velocity) may be substituted for and N, respectively (Ref 1)

Stribeck curve: coefficient of friction (and type of lubrication) versus dimensionless

variable N /P

• sulfochlorinated lubricant

• A lubricant containing chlorine and sulfur compounds, which react with a rubbing surface at

elevated temperatures to form a protective film Note: There may be a synergistic effect,

producing faster reaction than with sulfur or chlorine additives alone (Ref 1)

• sulfurized lubricant

• A lubricant containing sulfur or a sulfur compound that reacts with a rubbing surface at elevated

temperatures to form a protective film Note: The shear strength of the sulfide film formed on

ferrous materials is lower than that of the metal but greater than that of the film formed by reaction with a chlorinated lubricant (Ref 1)

• superficial hardness test

• See Rockwell superficial hardness test

• surface damage

• In tribology, damage to a solid surface resulting from mechanical contact with another substance, surface, or surfaces moving relatively to it and involving the displacement or removal of

material Note: In certain contexts, wear is a form of surface damage in which material is

progressively removed In another context, surface damage involves a deterioration of function of

a solid surface even though there is no material loss from that surface Surface damage may therefore precede wear

• surface distress

• In bearings and gears, damage to the contacting surfaces that occurs through intermittent solid

contact involving some degree of sliding and/or surface fatigue Note: Surface distress can occur

in numerous forms depending on the conditions under which the bearing or gear was operated and on the nature of the interaction between the contacting surfaces

• surfactant

• A chemical substance characterized by a strong tendency to form adsorbed interfacial films when

in solution, emulsion, or suspension, thus producing effects such as low surface tension, penetration, boundary lubrication, wetting, and dispersing (Ref 1) See also Rehbinder effect

• sweating

• Exudation of bearing material or lubricant due to high temperature (Ref 1)

• sweep velocity

• The mean of the surface velocities of two bodies at the area of contact Notes: Occasionally the

sum of the velocities is quoted instead of the mean In rolling, the sweep velocity is also called the rolling velocity (Ref 1)

• syneresis (of a grease)

• See bleeding

• synthetic oil

• Oil produced from chemical synthesis rather than from petroleum Note: Examples are esters,

ethers, silicons, silanes, and halogenated hydrocarbons

• A section cut obliquely through a surface and prepared metallographically Note: The angle is

often chosen to increase the vertical magnification of surface features by a factor of 5 or 10 (Ref 1)

• tapered land bearing

• A thrust bearing containing pads of fixed taper (Ref 1)

• tapered roller bearing

• A rolling-element bearing containing tapered rollers (Ref 1)

Tapered roller bearing (cutaway view) Courtesy of D Huffman, The Timken Company

• The final steady-state erosion rate that is reached (or appears to be approached asymptotically) after the erosion rate has declined from its maximum value This occurs in some, but not all, cavitation and liquid impingement tests (Ref 2)

• terminal period

• In cavitation and liquid impingement erosion, a stage following the deceleration period, during which the erosion rate has leveled off and remains approximately constant (sometimes with superimposed fluctuations) at a value substantially lower than the maximum rate attained earlier (Ref 2)

• textile oil

• (1) An oil used to lubricate thread or yarn to prevent breakage during spinning and weaving (2)

An oil acceptable for direct contact with fibers during textile production (Ref 1)

• thermal taper

• See thermal wedge

• thermal wear

• Removal of material due to softening, melting, or evaporation during sliding or rolling Notes:

Thermal shock and high-temperature erosion may be included in the general description thermal wear Wear by diffusion of separate atoms from one body to the other, at high temperatures, is sometimes denoted as thermal wear (Ref 1)

• thermal wedge

• The increase in pressure due to the expansion of the lubricant, for example, in a parallel thrust

bearing Note: Thermal distortion of the bearing surfaces may also form a wedge shape This is

referred to as thermal taper (Ref 1)

• thermoelastic instability

• (TEI) In sliding contact, sharp variations in local surface temperatures with the passing of asperities leading to stationary or slowly moving hot spots of significant magnitude (Ref 8)

• thickener

• A solid material dispersed in a liquid lubricant to produce a grease Note: Silica, clays, and

metallic soaps are widely used as thickeners (Ref 1)

• thick-film lubrication

• A condition of lubrication in which the film thickness of the lubricant is appreciably greater than that required to cover the surface asperities when subjected to the operating load, so that the effect of the surface asperities is not noticeable (Ref 1) See also thin-film lubrication

• thin-film lubrication

• A condition of lubrication in which the film thickness of the lubricant is such that the friction and wear between the surfaces is determined by the properties of the surfaces as well as the viscosity

of the lubricant Notes: Under thin-film conditions, the coefficient of friction is often 10 to 100

times greater than under thick-film conditions and wear is no longer negligible Boundary lubrication and elastohydrodynamic lubrication are better-defined terms that should be used where possible (Ref 1)

• thixotropy

• The property of recovering consistency after a decrease as a result of shearing Note: Thixotropic

age hardening is a more prolonged process than the instantaneous increase in apparent viscosity

as shear rate decreases, which is found in non-Newtonian fluids (Ref 1) See also rheopectic material

• As applied to sealing, a resistance to shaft rotation caused by the frictional drag of the seal It is

normally expressed in foot-pound or inch-pound units (Ref 4) Note: The metric equivalent is N ·

m (force times distance)

• In rolling contacts, the tangential stress transmitted across the interface Notes: The traction will

in general vary from point to point over the contact area More generally, traction may denote the force per unit area of contact (Ref 1)

• tractive force

• The integral of the tangential surface stress over the area of contact (Ref 1)

• transfer

• In tribology, the process by which material from one sliding surface becomes attached to another

surface, possibly as the result of interfacial adhesion Notes: Transfer is usually associated with

adhesion, but the possibility of mechanical interlocking adherence, without adhesive bonding, exists in certain occurrences Material may also back transfer to the surface from which it came See also selective transfer

• In tribology, a plot of two or more experimental or operating variables that indicates the

boundaries between various regimes of wear or surface damage Notes: The IRG transition

diagram is a plot of normal force (ordinate) versus sliding velocity (abscissa), and is used to identify three regions with differing lubrication effectiveness Various plots have been called transition diagrams, and the context of usage must be established

• tribo-

• A prefix indicating a relationship to interacting surfaces in relative motion

• tribochemistry

• The part of chemistry dealing with interacting surfaces in relative motion (Ref 1) Note:

Tribochemistry broadly encompasses such areas as lubricant chemistry, changes in reactivity of surfaces due to mechanical contact, oxidative wear, and other phenomena

• triboelement

• A solid body that is bounded by one or more tribosurfaces and that resides within a tribosystem

Note: This term is often associated with H Czichos, whose systems approach to tribology

identified triboelements For example, in a pin-on-disk tribosystem, the pin is one triboelement and the disk is another

• tribology

• The science and technology of interacting surfaces in relative motion and of the practices related

thereto Notes: This term was introduced in a report by a group set up by the British Department

of Education and Science It was defined in their report "Lubrication (Tribology)" in 1966 The study of wear by erosion or cavitation erosion is included in tribology (Ref 1) (2) Friction, lubrication, and wear science and technology

• tribometer

• (1) An instrument or testing rig to measure normal and frictional forces of relatively moving surfaces (Ref 1) (2) Any device constructed for or capable of measuring the friction, lubrication, and wear behavior of materials or components

• tribophysics

• That part of physics dealing with interacting surfaces in relative motion (Ref 1)

• triboscience

• The scientific discipline devoted to the systematic study of interacting surfaces in relative motion

Note: Triboscience includes the scientific aspects of tribochemistry , tribophysics , contact

mechanics, and materials and surface sciences as related to tribology

• tribosurface

• Any solid surface whose intermittent, repeated, or continuous contact with another surface or

surfaces, in relative motion, results in friction, wear, and/or surface damage Note: The surface of

a body subjected to a catastrophic collision would not generally be considered a tribosurface because significant damage to the entire body is involved

• A bearing consisting of three layers Note: Trimetal bearings are usually made of bronze with a

white metal facing and a steel backing (Ref 1)

• A general term expressing the slippery feel of a lubricant when rubbed with the fingers Note: It is

recommended that this term not be used in English (Ref 1)

• uniformly distributed impact test

• See distributed impact test

• unlubricated sliding

• Sliding without lubricant but not necessarily under completely dry conditions (Ref 1) Note:

Unlubricated sliding is often used to mean "not intentionally lubricated," but surface species such

as naturally formed surface oxides and other interfacial contaminants may act in a lubricious manner in nominally unlubricated sliding

• V

• V-ring seal

• A seal consisting of a ring or nested rings that have a V-shaped cross section and that are

commonly made from elastomeric material Note: Spring loading is sometimes used to maintain

contact between the seal and its mating surface It is normally used to seal against axial motion (Ref 4m)

Note: The surface to be lubricated may exhibit a catalytic effect to permit formation of the

lubricating film

• varnish

• In lubrication, a deposit resulting from the oxidation and/or polymerization of fuels, lubricating

oils, or organic constituents of bearing materials Note: Harder deposits are described as lacquers,

softer deposits are described as gums (Ref 1)

• Vickers (microindentation) hardness number

• The numerical value of microindentation hardness obtained using the Vickers (diamond) indenter and calculated as follows:

• where HVP (in units of GPa) is the ASTM symbol indicating Vickers microindentation hardness,

P is the applied load (in grams), and d1 and d2 are the two diagonal lengths of the impression (in

m) Notes: To obtain the HV P in kg/mm2, as was customary in the past, the factor 18.192 is replaced with 1854.4 The Vickers microindentation hardness test is described in ASTM E 384

A higher-load, macro-Vickers test has also been developed

• viscoelasticity

• A combination of viscous and elastic properties that makes the deformation dependent upon both temperature and strain rate (Ref 1)

• viscosity

• The bulk property of a fluid, semifluid, or semisolid substance that causes it to resist flow Notes:

Viscosity is defined by the equation:

• where is the shear stress, v is the velocity, and s is the thickness of an element measured perpendicular to the direction of flow; (dv/ds) is known as the rate of shear Newtonian viscosity

is often called dynamic viscosity, or absolute viscosity Kinematic viscosity, or static viscosity

(v) is the ratio of dynamic viscosity ( ) to density ( ) at a specified temperature and pressure (v

= / ) It is recommended that the term static viscosity should not be used (Ref 1m)

• viscosity, units of

• For absolute viscosity, the centimeter-gram-second (cgs) unit is the poise (dyne · s/cm2), the meter-kilogram-second (mks) unit is the Poiseuille (newton · s/m2), which is equal to the Système International d'Unités (SI) unit (1.0 N · sm-1 = 10 poise), and the English unit is the Reyn (lb · s/in.2), which is not commonly used For kinematic viscosity, the cgs unit is the Stoke (cm2/s), the

SI unit is m2 · s-1 (1.0 m2 · s-1 = 106 centistokes), and the English unit is the Newt (in.2/s), which is not commonly used (Ref 1m)

• viscosity index (VI)

• A commonly used measure of the change in viscosity of a fluid with temperature Notes: The

higher the viscosity index, the smaller the relative change in viscosity with temperature Two different indices are used: The earlier usage, according to Dean and Davis, applies to oils having

a VI from 0 to 100 Extended VI applies to oils having a VI of at least 100 It compares the oil with a reference oil of VI 100 (Ref 1m)

• viscous

• Possessing viscosity Note: This term is frequently used to imply high viscosity (Ref 1)

relative motion at the surface (Ref 1) Note: The first definition would not necessarily exclude

scuffing or galling , in which surface material may be displaced but not removed; however, the second definition requires substance to be removed in order to be considered wear Sometimes surface damage , which may not involve material removal, is differentiated from wear as defined under the first definition This Handbook treats wear and surface damage individually

• wear rate (of seals)

• The amount of seal-surface wear, stated in terms of mils worn in some designated time period

Note: One commonly used unit is mils per hundred hours (Ref 4m)

• wear resistance

• The resistance of a body to removal of material by wear processes, expressed as the reciprocal of

wear rate Notes: Wear resistance is a function of the conditions under which the wear process

takes place These conditions should always be carefully specified Relative wear resistance is sometimes quoted, using arbitrary standards (Ref 1m)

• wear scar

• The portion of a solid surface that exhibits evidence that material has been removed from it due to the influence of one or more wear processes

• wear transition

• Any change in the wear rate or in the dominant wear process occurring at a solid surface Note:

Wear transitions can be produced by an external change in the applied conditions (for example, load, velocity, temperature, or gaseous environment) or by time-dependent changes (aging) of the materials and restraining fixtures in the tribosystem

• wedge effect

• The establishment of a pressure wedge in a lubricant (Ref 1) See also wedge formation (2)

• wedge formation

• (1) In sliding metals, the formation of a wedge or wedges of plastically sheared metal in local

regions of interaction between sliding surfaces Note: This type of wedge is also known as a

prow It is similar to a built-up edge (Ref 1) (2) In hydrodynamic lubrication, the establishment

of a pressure gradient in a fluid flowing into a converging channel Note: This is also known as

wedge effect (Ref 1)

• weepage

• A minute amount of liquid leakage by a seal Note: It has rather arbitrary limits, but is commonly

considered to be a leakage rate of less than one drop of liquid per minute (Ref 4m)

• In tribology, a white-etching layer, typically associated with ferrous alloys, that is visible in

metallographic cross sections of bearing surfaces Note: Some interpretations of white layers

involve the presence of amorphous material; however, in other cases, the layer is thought to be finely microcrystalline such that no structure is visible by optical microscopy See also Beilby layer and highly deformed layer

• white metal (whitemetal)

• A light-colored bearing alloy based on tin or lead Note: Babbitt metal is one of the white metals

• A measure of the stability of a lubricant when subjected to an endurance test Note: The work

factor is expressed as the average value of the ratio of three characteristics (viscosity, carbon residue, and neutralization number) as measured before the test to those same characteristics as measured after the test (Ref 5)

• wrapped bush (bearing)

• A thin-walled steel bush lined with a bearing alloy, or any other bearing bush made from strip (Ref 1)

• wrist pin bearing

• The bearing at the crankshaft end of an articulated connecting rod in a "V" engine (Ref 1)

References

1 Glossary of Terms and Definitions in the Field of Friction, Wear and Lubrication (Tribology), Research

Group on Wear of Engineering Materials, Organisation for Economic Cooperation and Development (OECD), Paris, 1969

2 "Standard Terminology Relating to Erosion and Wear," G 40, Annual Book of ASTM Standards, ASTM

3 M.B Peterson and W.O Winer, Ed., Wear Control Handbook, American Society for Mechanical

Engineers, 1980

4 A Glossary of Seal Terms, Special Publication SP-1, Society of Tribologists and Lubrication Engineers,

1983

5 E.L McMurtrey, Ed., High Performance Solid and Liquid Lubricants, Noyes Data Corp., 1987, p 399-402

6 E.A Avallone and T Baumeister III, Ed., Marks Standard Handbook for Mechanical Engineers, 9th ed.,

1987, p 8-133 to 8-135

7 E.E Bisson and W.J Anderson, "Advanced Bearing Technology," Special Publication SP-38, National Aeronautics and Space Administration, 1964