Page 333 - Mechanical Engineer's Data Handbook

GLOSSARY OF TERMS 32 1

limit The maximum or minimum size of a compo- mass The quantity of matter in a body. Equal to the
nent as determined by a specified tolerance. inertia or resistance to acceleration under an applied
linear bearing A bearing in which the relative motion force. Unit: kilogram (kg). Symbol: m.
is linear, as opposed to rotary. mass flow rate The rate at which mass passes a fixed
lock nut An auxiliary nut used in conjunction with a point in a fluid stream. Unit: kilograms per second
normal nut to lock the latter. (kgs- I).
lock washer A name for many types of washer used matrix The material in a composite in which fibres,
with nuts, etc., to prevent loosening. whiskers, etc., are embedded.
logarithmic mean temperature difference In heat ex- mean etTective pressure (m.e.p.) The average absolute
changers the ‘effective’ difference in temperature of the pressure during an engine cycle. It gives a measure of
fluids used in calculating heat transfer. the work done per swept volume.
logarithms The logarithm of a number N to a base b mechanical advantage In a ‘machine’, the ratio of
is the power to which the base must be raised to load to effort.
produce that number. This is written log, N or log N if mechanical efficiency In an engine, the ratio of useful
the base is implied. Common logarithms are to the power delivered to the ‘indicated power’, i.e. the
base 10. Natural logarithms (Naperian logarithms) are efficiency regarded as a machine.
to the base e (e=2.7183 . . .). Merchant’s circle A diagram showing the forces on a
lubricant Any substance, solid, liquid or gaseous, single-point machine tool.
which may be used to reduce friction between parts. metal forming The shaping of metals by processes
lumiwus flux The flux emitted in a unit solid angle of such as bending, drawing, extrusion, pressing, etc.
1 steradian by a point source of uniform intensity of 1 micrometer gauge A hand held, U-shaped length
candela. Unit: lumen (Im). gauge in which the gap between measuring faces is
luminous inteaeity Unit: candela (cd). The luminance adjusted by means of an accurate screw.
of ‘black body’ radiation at the temperature of solidifi- mild steel Carbon steel with a maximum carbon
cation of platinum (2042K) is 60cdcm-2. content of about 0.25%.
milling The removal of metal by a ‘milling cutter’
with rotating teeth on a ‘milling machine’.
machinability The relative ease of machining a par- mixed-flow heat exchanger A heat exchanger in
ticular material. which the flow of one fluid is a mixture of types, e.g.
machine In mechanics, a device which overcomes a alternatively counterflow and cross-flow.
resistance at one point known as the ‘load’, by the mixed-flow pump A rotodynamic pump in which the
application of a force called the ‘effort’ at another general flow is a combination of axial and radial.
point; e.g. inclined plane, lever, pulleys, screw. mixture strength The ratio of ‘stoichiometric’ air/fuel
machining Removal of metal in the form of chips, ratio, to the ‘actual’ air/fuel ratio, used for engines. 0.8
etc., from work, usually by means of a ‘machine tool’. is ‘weak’ and 1.2 is ‘rich’.
Mach uumber The ratio of velocity of a fluid relative modulus of elasticity A measure of the rigidity of a
to a body and the velocity of sound in the fluid. Symbol material. The ratio of stress to strain in the elastic
M. region.
magnetism The science of magnetic fields and their modulus of seetion A property of plane sections used
effect on materials due to unbalanced spin of electrons in bending-stress calculations. It is equal to the ratio of
in atoms. bending moment to maximum bending stress.
malleability The property of metals and alloys by molecular weight The mass of a molecule referred to
which they can easily be deformed by hammering, that of a carbon atom (12.000). The sum of the relative
rolling, extruding, etc. atomic masses in a molecule.
mandrel An accurately turned spindle on which Mollier diagram See: enthalpy-entropy diagram.
work, already bored, is mounted for further machin- moment The moment of a force (or other vector
ing. quantity) about a point is the product of the force and
manometer An instrument used to measure the the perpendicular distance from the line of action of
pressure of a fluid. The simplest form is the ‘U tube’ the force to the point.
containing a liquid. See: pressure, Bourdon gauge. moment of inertia The moment of inertia of a body of