Page 336 - Mechanical Engineer's Data Handbook

324 MECHANICAL ENGINEER’S DATA HANDBOOK

Rankine-Gordon formula An empirical formula for Reynold’s number A dimensionless quantity used in
the buckling load of a strut. the study of fluid flow, particularly in a pipe. If
reaction The equal opposing force to a force applied v = velocity, d = pipe diameter, p = density of fluid,
to a system. The load on a bearing or beam support. p = viscosity of fluid, the Reynold’s number
reaction turbine A water, steam or gas turbine in Re = (pvd)/p.
which the pressure drop is distributed between fixed riveting Joining two or more members by means of
and moving blades. Strictly an impulse-reaction tur- rivets, the unheaded end being ‘upset’ after the rivet is
bine. in place.
reamer Rotary cutter with teeth on its cylindrical rivets A permanent fastener for connecting plates in
surface used for enlarging a drilled hole to an accurate which the unheaded end is upset, or closed, to make
dimension. the joint. There are many types, e.g. snap head, pan
recess A groove or depression in a surface. head, pop, explosive.
rectifier A device for converting a.c. to d.c. by roller bearing A journal or thrust bearing with
inversion or suppression of alternate half-waves, e.g. straight or tapered rollers running between two ‘races’.
diodes, mercury arc rectifier, rotary converter. rolling Reducing the cross-section of metal stock or
refining The removal of impurities from a metal after the shaping of metal products using ‘rolls’ in a ‘rolling
crude extraction from ore. mill’.
refractory Material with very high melting point rolling bearings The general name given to low-
used for furnace and kiln linings. friction bearings using balls and rollers running in
refrigerant The working fluid in a refrigerator. It ‘races’.
may be a gas or a vapour. root mean square (r.m.s.) A measure of the effective
refrigerator A machine in which mechanical or heat mean current of an alternating current. That is, with
energy is used to maintain a low temperature. the same heating effect as a direct current. The square
regenerative heat exchanger A heat exchanger in root of the mean of the squares of continuous ordinates
which hot and cold fluids, usually gases, occupy the for one cycle.
same space alternately. Roots blower An air compressor for delivering large
reheat The process of reheating steam or gas between quantities of air at relatively low pressure. It has two
turbines to obtain higher efficiency. Also the injection hour-glass shaped intermeshing rotors running with
of fuel into the jet pipe of a turbojet to obtain greater small clearances in a casing.
thrust. rotodynamic pump See: ‘pump’.
residual stress Stress existing in a body free from roughness In machining, surface irregularities, the
external forces or thermal gradient. dimensions and direction of which establish the sur-
resistance In electricity, the real part of impedance of face pattern. In fluid flow, the height of irregularities in
a current-carrying circuit characterized by the dissi- pipes, etc.
pation of heat. Unit: ohm (a). In physics, the opposi- runner The rotating part of a water turbine carrying
tion to motion tending to a loss of energy. vanes.
resistance thermometer A thermometer using the running fit Any clearance fit in the range used for
change of resistance with temperature of a conductor. relative motion.
Platinum is used, as are semiconductors (thermistor).
resistance welding and brazing A process in which the screw A general name for fasteners with a screwed
resistance of a pressurized joint causes melting of the shank and a head. Also any section of bar with an
parts in contact. external thread .
resistivity A property of electric conductors which screw jack A portable lifting machine for raising
gives resistance in terms of dimensions. Resistance heavy objects a small height. It uses a nut which carries
R =pL/A, wherep=resistivity, L=length, A=area of the load rotated, usually by hand, through a lever
conductor. system.
resistor An electrical component designed to give a screw thread A helical ridge of vee, square, or
specified resistance in a circuit. rounded section formed on or inside a cylinder the
resistor colour code A method for marking the resis- form and pitch being standardized under various
tance value on resistors using coloured spots or bands. systems.