ASTM F2488-05(2013)
(Terminology)Standard Terminology for Rolling Element Bearings
Standard Terminology for Rolling Element Bearings
SCOPE
1.1 This terminology covers terms and their definitions relevant to the materials and processes associated with rolling element bearings.
General Information
Standards Content (Sample)
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Designation: F2488 − 05 (Reapproved 2013)
Standard Terminology for
Rolling Element Bearings
This standard is issued under the fixed designation F2488; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope ball gage deviation (∆S), n—difference between the lot mean
diameter and the sum of the nominal diameter and the ball
1.1 This terminology covers terms and their definitions
gage.
relevant to the materials and processes associated with rolling
element bearings.
ball grade (G), n—specific combination of dimensional form
and surface roughness tolerances.Aball grade is designated
2. Terminology
by a grade number followed by the letter “C” indicating
silicon nitride ceramic.
2.1 Definitions:
absolute viscosity (η), n—(sometimes called dynamic viscos-
boundary lubrication, n—condition of lubrication in which
ityorjust viscosity)—ameasureofthetendencyofthefluid
the friction between two surfaces in relative motion is
to resist shear.
determined by the roughness of the surfaces and by the
properties of the lubricant other than viscosity.
acid number, n—measure of the quality of a lubricant. High
DISCUSSION—Antiwear and extreme pressure additives reduce the
acid numbers (much higher than the fresh oil) are an
wear of components operating under this regime.
indication of lubricant oxidation/degradation.
DISCUSSION—Oils with high acid numbers should not be used. Acid
case depth, n—thickness, measured radially from the surface
number is measured as milligrams of KOH needed to neutralize1gof
of the hardened case to a point at which carbon content or
oil.
hardness becomes the same as the ball core.
additive, n—any chemical compound added to a lubricant to
centipoise, n—unit of dynamic viscosity.
improve or meet special needs necessary for service (formu-
DISCUSSION—The unit in the cgs system is 1 centipoise (cP). The SI
lated lubricants). The most important additives are
unit of dynamic viscosity is 1 Pa-s and equivalent to 10 cP.
antioxidants, rust, and corrosion inhibitors, and extreme
centistoke, n—unit of kinematic viscosity.
pressure (EP) and antiwear (AW) additives.
DISCUSSION—The unit in the cgs system is 1 centistoke (cSt). The SI
2 6
antioxidants (oxidation inhibitors), n— chemical compounds
unit of kinematic viscosity is 1 m /s and is equivalent to 10 cSt.
used to improve the oxidation stability and subsequent
compatibility, n—measure of the ability of a lubricant to be
deterioration of lubricants.
mixed with other lubricants or bearing preservatives (fluids
average life (L ), n—for a radial roller bearing, the number of
that form films on metal surfaces to prevent corrosion during
revolutionsthat50 %ofagroupofbearingswillcompleteor
storage) to form a uniform mixture without causing any
exceed before the first evidence of fatigue develops.
resultant reaction or precipitation of material. Compatibility
DISCUSSION—The average life maybe as much as five times the rating
isalsoameasureoftheabilityofalubricantnottocauseany
life.
detrimental effect to metal, plastic, or elastomer materials.
DISCUSSION—It is recommended that any preservative material be
ball gage (S), n— prescribed small amount by which the lot
removed from bearings before lubrication.
mean diameter should differ from nominal diameter, this
amount being one of an established series of amounts.
contamination, n—(1) presence of mostly solid foreign mate-
DISCUSSION—A ball gage, in combination with the ball grade and
rials like sand, grinding powder, dust, and so forth, in a
nominal ball diameter, should be considered as the most exact ball size
lubricant that might cause an increase in wear, torque, and
specification to be used by a customer for ordering purposes.
noise and result in reduced bearing life; and (2) presence of
fluids like water, solvents, and other oils that might cause
accelerated oxidation, washout, rusting, or crystallization of
This terminology is under the jurisdiction ofASTM Committee F34 on Rolling
the additives and other phenomena that reduce a bearing’s
Element Bearings and is the direct responsibility of Subcommittee F34.91 on
life.
Editorial and Terminology.
Current edition approved May 1, 2013. Published May 2013. Originally
corrosion, n—gradual destruction of a metal surface as a result
approved in 2005. Last previous edition approved in 2005 as F2488 – 05. DOI:
10.1520/F2488-05R13. of chemical attack caused by polar or acidic agents like
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2488 − 05 (2013)
humidity (water), compounds formed by lubricant interfacial tension, n—when two immiscible liquids are in
deterioration, or contaminants from the environment. contact, their interface has many characteristics in common
with a gas-liquid surface.This interface possesses interfacial
corrosion inhibitors, n—corrosion inhibitors protect metal
free energy because of the unbalanced attractive forces
surfaces against corrosion or rust by forming a protective
exerted on the molecules at the interface by the molecules
coating or by deactivation of corrosive compounds formed
within the separate phases. This free energy is called the
during the operation of a bearing.
interfacial tension.
density, n—mass per unit volume of a substance.
kinematic viscosity, n—ratio of absolute viscosity to fluid
DISCUSSION—The cgs unit of density (ρ) is 1 g/cm , and the SI unit
density.
of density is 1 kg/m . Density depends on the chemical composition
DISCUSSION—This ratio arises frequently in lubrication analyses, and
and in itself is no criterion of quality. It is a weak function of
thus, kinematic viscosity has become a separate term describing the
temperature and pressure for liquids and solids.
viscosity of a fluid. Many experimental measurements of viscosity of
fluids result in a measure of kinematic viscosity from which absolute
deviation from spherical form (∆Rw), n—greatest radial
viscosity is calculated. See absolute viscosity. The cgs unit of
distance in any radial plane between a sphere circumscribed 2
kinematic viscosity is cSt and the SI unit is m /s. The viscosity of a
around the ball surface and any point on the ball surface.
PREB oil is a major factor in lubricant selection. The viscosity is
directly involved in frictional, thermal, and fluid film conditions that
DN value, n— product of the bearing bore diameter in
reflect the influence of load, speed, temperature, and design character-
millimetres multiplied by the speed in revolutions per
istics of the bearing being lubricated.
minute (compare to nD value).
m
marking increments, n—standard unit steps to express the
dynamic viscosity, n—another name for absolute viscosity. specific diameter.
mineral oil, n—oils based on petroleum stocks. These oils
EP lubricants (extreme pressure lubricants), n—lubricants
come in two types, naphthenic and paraffinic. The naph-
(oil or greases) that contain extreme pressure additives to
thenic oils contain unsaturated hydrocarbons, usually in the
protect the bearings against wear and welding (scoring).
form of aromatic species. The paraffinic oils are primarily
esters, n—esters are formed from the reaction of acids and
saturated hydrocarbons with only low levels of unsaturation.
alcohols. Esters form a class of synthetic lubricants.
nD value (index), n—also called speed index—relative
DISCUSSION—Esters of higher alcohols with divalent fatty acids form m
indicator of the lubricant stress imposed by a bearing
diester lubricants while esters of polyhydric alcohols are called the
polyol ester lubricants.These latter esters have higher viscosity and are
rotating at a given speed, where n is the rotational speed of
more heat resistant than diesters.
the rolling element bearing in revolutions per minute and D
m
is the mean diameter in millimetres (arithmetic mean of bore
evaporation loss, n—lubrication fluid losses occurring at
diameter d and outside diameter D).
higher temperatures or under vacuum, or both, as a result of
DISCUSSION—The speed index is multiplied by a factor k depending
a
evaporation.
on the roller element bearing type:
DISCUSSION—This can lead to an increase in lubricant consumption
k = 1 for deep groove ball bearings, angular contact ball bearings,
a
and also to an alteration of the fluid properties of a lubricant (especially
self-aligning ball bearings, radially loaded cylindrical roller bearings,
an increase in the viscosity of blended lubricants).The evaporation loss
and thrust ball bearings;
-6
is expressed as a weight loss in milligrams (10 kg) or wt %.
k = 2 for spherical roller bearings, taper roller bearings, and needle
a
roller bearings; and
fire point, n—lowest temperature at which the vapor or a
k = 3 for axially loaded cylindrical roller bearings and full
a
lubrication fluid ignites under specified test conditions and
complement roller bearings.
continues to burn for at least 5 s without the benefit of an
The factor k takes into account the various rates of sliding friction
a
that usually occurs during the operation of a rolling element bearing.
outside flame. The fire point is a temperature above the flash
The nD value is an aid in choosing a suitable lubricant viscosity for
point. m
agivenbearingspeedandisparticularlyapplicabletogrease-lubricated
DISCUSSION—Perfluoropolyethers have no fire point.
bearings.
flash point, n—lowest temperature of a lubrication fluid at
neutralization number, n—measureoftheacidityoralkalinity
which the fluid gives off vapors that will ignite when a small
of a lubricating fluid. The test determines the quantity of
flame is periodically passed over the liquid surface under
base (milligrams of potassium hydroxide) or acid (also
specified test conditions.
expressed as milligrams of potassium hydroxide) needed to
DISCUSSION—The flash and fire points provide a rough characteriza-
neutralize the acidic or alkaline compounds present in a
tion of
...
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