Babbitt: a soft alloy of tin, copper and antimony used for plain bearings.
Backlash (gears): loose motion or play between the nondriving surfaces of
adjacent gear teeth, arising from necessary clearance, wear or incorrect
Backup roll bearings (Morgan or Mesta design): special sleeve bearings of the
Morgoil design, with very large projected areas to reduce unit pressure. These
large-diameter oil-film bearings support backup rolls in rolling mills by means of
a hydrodynamic film.
Bactericide: additive used with water-soluble cutting fluids to inhibit bacterial growth and unpleasant odors.
Ball bearing: a roller bearing whose rolling elements are balls (see roller
Bang-bang valve: conventional hydraulic or pneumatic valves operated by
solenoids with either two or three distinct positions.
Barium/barium complex grease: a grease thickened with either barium soap or
complex barium soap.
Barrel (drum): a standard container size, depending on context, e.g.: a 400-lb
open top container (gear lubes and greases are sold by the pound), a 55-gal liquid
container (most liquid lubricants) or a 42-gal charge (standard for crude oils).
Base circle (gears): the circle from which the involute tooth profile is derived.
Basic bearing number: for purposes of identification, anti-friction bearings are
assigned numbers, referred to as basic bearing numbers. In most cases, they
have four digits: the first indicates the TYPE of bearing, the second the bearing
SERIES and the third and fourth the BORE SIZE of the bearing. Some
manufacturers replace the first digit with letters of the alphabet to identify their
bearings, others use numbers and letters.
Basic dynamic capacity: the radial load that 90% of identical bearings will bear
for 1,000,000 revolutions before the first evidence of fatigue; also known as basic
Basic static capacity: the static load endured by a bearing before the most
heavily loaded ball or roller experiences sufficient stress to cause a permanent
deformation of the element or race equal to 0.0001 in. of the ball or roller
Beam strength (gears): capability of a gear tooth to withstand repeated bending
that occurs whenever it is under load.
Bearing: machine element designed to support or position loads and, properly
lubricated, to reduce friction between them. There are two basic designs, rolling
element bearings and plain (sliding) types.
Bearing crush: the height by which half of the bearing exceeds the half diameter
of the bore into which it is assembled.
Bench test: a modified service test in which the service conditions are
approximate in the laboratory.
Bentonite thickener: clay, composed mainly of silicon dioxide and aluminum
oxide, used to thicken greases. Such greases have no dropping points because
the bentonite does not melt.
Benzene: the simplest aromatic hydrocarbon (C6H6) used in petrochemical
processes and as a solvent. It must be used with caution because of its toxicity.
For safety considerations, laboratories have substituted other solvents like
toluene in its place.
Bernoulli’s Theorem: theory developed by Daniel Bernoulli, 18th century Swiss
scientist, one implication of which is that any rise in hydraulic fluid velocity is
accompanied by a drop in static pressure and vice versa.
Bevel gears: gears, conical in form, that operates on intersecting axes, usually at
Biodegradable: capable of decaying through the action of living organisms.
Biodegradability – can be defined as the ability of a substance to degrade over
time to carbon dioxide and water in the presence of water, nutrients and
Biotoxic: toxic to the environment.
Black oils: dark-colored lubricants containing asphaltic materials, with medium
flash points and medium to high viscosity, used in heavy-duty applications
requiring adhesiveness under exposed conditions.
Bleeding (grease): the tendency of a liquid component to separate from a liquid-
solid or liquid-semisolid mixture, as oil may separate from a grease.
Blending: the process of combining fluid and/or solid components into a
finished mixture, particularly with liquid lubricants. Though compounding is
similar, the purpose of compounding is to obtain properties not usually
attainable with blending.
Block/brick grease: a grease of moderate dropping point, NLGL grade 5 or 6,
firm to the touch at normal temperatures, that can be handled in block or stick
form. The penetrating powers of such greases are measured at 77°F; grade 6
grease has a penetration range of 85-115.
Blown oils: natural fatty oils, of animal or vegetable origin, are artificially
oxidized and thickened by blowing air through them. They are used primarily
for compounding petroleum oils, to give them a strong affinity for metal
Bomb: in lubrication terminology, a closed container used for conducting tests
under elevated pressures.
Bomb oxidation stability: resistance of oils and greases to oxidation when
subjected to accelerated oxidation in a sealed unit filled with pure oxygen under
pressure and at elevated temperatures. As the lubricant absorbs oxygen, the
pressure drops to indicate oxidation resistance. ASTM test D-2272, the Rotary
Bomb Oxidation Test, rotates the container during the test.
Bonnet (lube systems): upper portion of packing gland assembly that serves as
a viewer for movement of indicator.
Bottoms (residuum): the liquid that collects at the bottom of the distillation
column, consisting of high-boiling residual liquids like heavy fuels and asphaltic
Boundary Lubrication: lubrication between two rubbing surfaces in the absence
of a full fluid lubricating film. Boundary lubrication is often accomplished with
the use of extreme pressure additives. Example – high pressure gears.
Brake valve: a device that permits a machine component driven by a hydraulic
rotary motor to revolve unimpeded during operation but restrains the motor
return line fluid to slow the machine when it is desired to stop.
Brass: a non-ferrous alloy consisting of varying proportions of tin, zinc and
copper; lead is added to attain higher machining speed. Brasses may or may not
be lined with babbitt metal (see bronze).
Breather: an air filtering device placed on top of a reservoir to allow it to
“breathe” as the oil level rises and falls. All incoming air is thereby filtered to
keep out airborne contaminants.
Bright stock: describes high-viscosity lubricating oils that are refined to make
them clear products of good color. Bright stocks are made from residuals or
bottoms, solvent dewaxed and deasphalted; they may be used for blending.
Brinell hardness: a system to measure the hardness of metals by indentation. A
hardened steel ball is pressed into a smooth surface of the metal under a fixed
load and the resulting indentation is microscopically measured. With a
conversion chart, this number can also be used to determine the approximate
tensile strength of the same metal.
BHN: Brinell hardness number
Bromine number: see iodine number.
Bronze: a non-ferrous alloy of copper and a metal other than zinc or nickel. The
family of bronzes includes: copper-tin, aluminum (for high tensile strength),
phosphor (for corrosion resistance and low friction), leaded phosphor (for
machinability) and silicon. ASTM distinguishes five grades of bronze casting
BS&W: an acronym for the material that settles to the bottom of a storage tank,
namely bottoms, sediment and water. Laboratories sometimes quantify and
report this information when examining oil in service.
BTU: British thermal unit: the amount of heat required to raise the temperature
of a pound of water one degree Fahrenheit.
Buffer solution: a solution that prevents drastic changes in pH values when
moderate amounts of acid or alkali are added.
Builder: any substance that increases the effectiveness of a cleaner, e.g., water-
softening agents, buffer agents, alkalies.
Bulk appearance (grease): visual appearance when the undisturbed surface is
viewed in an opaque container. Bulk appearance should be characterized in the
following terms: bleeding (free oil shows on surface or in cracks of a cracked
grease), cracked (showing surface cracks of appreciable magnitude), grainy (a
surface with small granules or lumps of constituent thickener particles), rough
(many small irregularities on the surface), smooth (surface relatively free of
Bulk modulus: the resistance to compressibility of a fluid or elastomer; the
reciprocal of its compressibility.
Buna-N/S: Buna-N and Buna-S are types of synthetic rubber. Buna-N is a
copolymer of butadiene and acetonitrile; Buna-S is a copolymer of butadiene and
Butyl: copolymer of isobutylene and various amounts of isoprene and