Page 323 - Mechanical Engineer's Data Handbook

Glossary of terms

abrasion The process of rubbing, grinding or wearing phosphorus, added to change the mechanical and
away by friction using an abrasive such as emery, physical properties.
corundum, diamond, etc. altersrtingcenzllt Abbreviation a.c. Electric current
abdste pmmre Pressure measured from absolute whose flow changes direction cyclicly. The normal
zero pressure as opposed to ‘gauge pressure’. waveform is sinusoidal.
aesdate tempentare Temperature measured with alternator A type of a.c. generator driven at constant
respect to ‘absolute EM temperature’, units are ‘kel- speed to generate the desired frequency.
vin’ (symbol K). K=”C+273.15. anemometer A mechanical or electrical instrument
accelerrtba The rate of change of velocity with for measuring the velocity of a fluid stream, particular-
respect to time, (d2x/dt2) or R metres per second per ly wind velocity. The main types are, cup, vane and hot
second (ms-*). wire.
a.c. III(IcLi.es machines producing or using alternat- aneroid buometer A barometer with a partially
ing current, e.g. alternator and a.c. generator. a.c. evacuated bellows chamber connected to a pointer
motors with a pen recording atmospheric pressure on a drum
A&kdun The radial distance between the pitch chart. The bellows responds to atmospheric pressure.
circle and the major diameter of a gear. angle gauges Sets of metal blocks with two opposite
dhcsivc Substances used for joining materials, faces at various angles to one another, used separately
usually without the necessity for heat, based on natural or jointly to measure angles to a high degree of
substances (animal bone, casein, rubber, etc.) or accuracy.
synthetic resins. angular accekratioa The rate of change of angular
adiabatic proeess A thermodynamic process in which velocity expressed in radians per second squared:
there is no transfer of heat between the working d20/dt2 or # (rads-2).
substance and the surroundings. angular momentom The product Iw of the moment
add A body shaped so as to produce an appreci- of inertia, I and the angular velocity o of a body
able ‘lift’, Le. a force normal to the direction of fluid moving in a curve, e.g. a flywheel.
flow relative to the body, and a small ‘drag’ force in the angular velocity The rate of change of angular dis-
same direction as the flow. Aerofoil sections are used placement with respect to time, expressed in radians
for turbine blades, wing sections, etc. per second, dO/dt or 0 (rad s- ’).
air-fuel ratio The ratio of the mass of air to mass of atmedog Heating a metal to, and holding at, a
fuel entering an internal combustion engine, gas suitable temperature and cooling at a suitable rate so
turbine or boiler furnace. as to reduce hardness, improve machineability, ease
air motor A motor which converts the energy of cold working, etc.
compressed air into mechanical energy, usually as a AreLimccles pri.Ciple States that a body wholly or
rotation. The main types are axial or radial piston, and partially submerged suffers an apparent loss of weight
vane. equal to the weight of fluid displaced.
alloy A substance with metallic properties composed are wddiag A process for joining metals by fusion in
of two or more chemical elements, at least one of which which heat is produced by an electric arc.
is a metal. uitbmetic mean The sum of n numbers divided by n.
aUoy std Steel containing significant quantities of aritbwrie prognssioa A series of numbers where
alloying elements other than carbon and commonly each number is obtained by adding a fixed quantity to
accepted amounts of manganese, sulphur, silicon and the previous number.