Page 331 - Mechanical Engineer's Data Handbook

GLOSSARY OF TERMS 319

helical gear A gear in which the teeth are not parallel illnmimnce The quantity of light or luminous flux on
to the axis but on a helix. unit surface area. Unit: lux (Ix)= 1 lumen per square
helix A line, thread or wire curved into a shape it metre (Imm-2).
would assume if wrapped around a cylinder with even impact extrusion A high speed cold working process
spacing. for producing tubular components by a single impact
Mix angle In screw threads, etc., the angle of the by a punch. A slug of material placed in a die flows up
helix to a plane at right angles to the axis. and around the punch into the die clearance.
honing The removal of metal, usually from a cylinder impact test A test to determine the behaviour of
bore, by means of abrasive sticks on a rotating holder. materials subjected to high rates of loading in bending,
Hooke’s law States that stress is proportional to torsion and tension. The quantity measured is the
strain up to the limit of proportionality. ‘impact energy’ required to cause breakage of a
hoop stress The circumferential stress in a cylinder specimen.
wall under pressure or in a rotating wheel. impulse When two bodies collide the impulse of the
hot forming Forming operations such as bending, force during impact is JFdt. Defined as the change of
drawing, forging, pressing, etc., performed above the momentum produced in either body.
recrystallization temperature of a metal. impulse reaction turbine A steam turbine with im-
hot wke ammometer An instrument for measuring pulse stage@) followed by reaction stages.
the flow of air (or other fluids) from the cooling effect impalse turbine A steam, gas or water turbine in
on an electrically heated sensor, in the fluid stream, the which the working fluid is accelerated through nozzles
resistance of which changes with temperature. and impinges on blades or buckets in which there is no
hydraulic cylinder A cylinder with piston and piston pressure drop.
rod supplied by a liquid under pressure to provide a incW plane For a smooth plane at an angle 8 to the
force with linear motion. The cylinder may be single or horizontal, the force parallel to the plane to move a
double acting. mass m up it is mg sin 8. It is equivalent to a ‘machine’
hydraulicjnck A device for lifting heavy loads a short having a velocity ratio of cot 8.
distance using a hydraulic cylinder supplied by a inductance The property of an electric circuit carry-
pump, often hand operated. ing a current is characterized by the formation of a
hydraulic motor A motor operated by high-pressure magnetic field and the storage of magnetic energy.
liquids. Types: radial piston, axial piston, vane, etc. Unit: henry (H).
hydraulic press A press using a hydraulic cylinder. idmctioo hardening The use of induction heating for
hydraelk planp A machine which delivers fluids at hardening metals.
high pressure. Types: radial piston, axial piston, induction heating The heating of conducting ma-
reciprocating, vane, gear pump. terials by inducing electric currents in the material,
hydraulics The science relating to the flow of fluids. usually by a high-frequency source.
hydrocarbon fuels Solid, liquid and gaseous fuels induction motor An ax. motor in which the primary
composed primarily of hydrogen and carbon. winding current sets up a magnetic flux which induces
hydrodynnmic lubrication Thick film lubrication in a current in the secondary winding, usually the rotor.
which the surfaces are separated an8 the pressurized indoctor An electriccircuit component which has the
film supports the load. property of inductance. Usually a coil with air or
hydrodynamics The branch of dynamics which re- magnetic core.
lates to fluids in motion. inertia The property of a body proportional to mass,
hyperbola A conic section of the form but independant of gravity. Inertia opposes the state of
(x2/U2) - (yz/b2) = 1. motion of a body.
hyperbolic functions A set of six functions, particular- insulation I. Heat Material of low thermal conduc-
ly useful in electrical engineering, involving the terms tivity used to limit heat gain or loss, e.g. pipelagging. 2.
ex and e -x. Analogous to the trigonometrical functions Electricity A material with very high resistivity
sin, cos, tan, etc., they are sinh, cosh, tanh, cosech, through which there is virtually no flow of current, e.g.
sech, cotanh. plastic covering on wires.