Page 324 - Mechanical Engineer's Data Handbook

312 MECHANICAL ENGINEER’S DATA HANDBOOK

atomic weight Relative atomic mass where one unit is blade A curved plate often of aerofoil section used to
1.660 x kg. deflect a fluid flow, e.g. airscrew or propeller blade,
axial flow machines Pumps, fans, compressors, tur- turbine blade, impeller vane.
bines, etc., in which the fluid flows generally parallel to blank A piece of sheet metal cut to a suitable shape to
the axis of rotation. be subject to further pressing processes. A pressed
sintered component requiring further machining, etc.
blower A rotating, usually air, compressor for sup-
plying relatively large flows at a low pressure.
balancing Measuring the static or dynamic out- boiling point The temperature at which a liquid boils
of-balance forces in a rotating part and adding or at standard atmospheric pressure of 101.325 kN m-2.
subtracting mass to cancel them out. bolt A cylindrical partly screwed bar with a (usually)
barometer Instrument for measuring atmospheric hexagonal head used in conjunction with a ‘nut’ to
pressure, the main types being the aneroid and Fortin fasten two or more parts together.
barometers. bore Hole or cavity produced by a single- or multi-
beams Bars, rods, etc., of metal or other material point tool, usually cylindrical.
carrying transverse loads with various types of sup- boundary layer A thin layer of fluid adjacent to a
port, e.g. simple supports, built-in ends, continuous surface over which the fluid flows, which exerts a
supports. viscous drag on the surface due to the large velocity
bearing A fixed support for a rotating shaft or sliding gradient.
part with minimum friction. boundary lubrication A state of partial lubrication in
belt drive The transmission of power from one shaft a plain bearing where there is no oil film, only an
to another by means of an endless belt which may be adsorbed monomolecular layer of lubricant in the
flat or of vee section, etc. surfaces.
bending moment The algebraic sum of the moments Bourdon tube pressure gauge A gauge in which fluid
of all the forces to either side of a transverse section of a pressure tends to straighten a curved, flattened tube
beam, etc. connected to a pointer mechanism; pressure is read
bending modulus A property of a section equal to the from a circular scale. A differential form is available
bending moment divided by the maximum bending having two tubes connected to a single pointer.
stress. Boyle’s law States that, for a ‘perfect gas’ the volume
bend loss The loss of pressure in a fluid flowing of a given mass varies inversely as the pressure at
around a bend in a pipe or duct. constant temperature.
Bernoulli equation States that in a pipe or duct in brake A device for applying resistance to the motion
which a fluid flows, the sum of the pressure, potential of a body, either to retard it or to absorb power
and kinetic energies is equal at any point. (dynamometer).
bevel gear A toothed wheel with teeth formed on a brazing The joining of metals by a thin capillary layer
conical surface used for transmitting rotation from a of non-ferrous metal filler in the space between them.
shaft to one at an angle to it in the same plane, usually Carried out above about 800 “C.
at right angles. brittle fracture Fracture of a material with little or no
binary numbers A scale of numbers with ‘radix’ equal plastic deformation.
to 2 as opposed to the usual scale radix of 10 (decimal broaching The cutting of holes of various shapes or
numbers). Only two symbols are used: 0 and 1. cutting of an outside surface, with a ‘broach’consisting
binomial coefficients Coefficients of terms of the of a tapered bar with cutting edges. The broach moves
expansion of (1 + x)” using the binomial theorem. in a reciprocating axial manner.
bmomial distribution A distribution used in statistics buckling Sudden large-scale deformation of a strut,
based on the binomial theorem which gives the thin cylinder, etc., due to instability when loaded, e.g.
probability of an event taking place. an axial load on a strut.
black body In the study of radiation of heat, a body bulk modulus The ratio of pressure (three-dimen-
which completely absorbs heat or light falling on it. sional stress) to volumetric strain of a material.
black-body radiation The quantity or quality of buoyancy The apparent loss of weight experienced
radiation from a black body, e.g. from the inside of a by a submerged or floating body due to the upthrust
cavity. caused by fluid pressure.