I — Dictionary of Quarrying Terms

IDO: abbr: see ‘Interim Development Order’.

IQ: abbr. Institute of Quarrying.

idle component: see ‘reactive component’.

idler: A broad roller carrying the weight of the conveyor and its load. Idler rollers are placed symmetrically about the belt centre line, usually in sets of three with the centre one horizontal and the two outer ones at an angle so as to bend the belt into a trough shape.

igneous rock: A rock that has solidified from molten matter (magma) from the Earth’s interior.

igniter cord: A cord which passes an intense flame along its length at a uniform rate to light safety fuses in succession. Usually used where there are more than six safety fuses to be lit; a shotfirer should not attempt to ignite more that six points at anyone time.

illuminance: The luminous flux density at a surface, ie the luminous flux on a surface divided by the area of the element. Symbol: E. Unit: lux (Ix).

impact crushers: Crushers in which the rock is fragmented by kinetic energy imparted into the feed material by a rotating mass (the rotor), which projects the material against a fixed surface, causing it to shatter.

impact hammer: Hydraulic or compressed -air-operated hammer used in quarries, usually mounted on the boom of an excavator, for secondary breakage.

impact idlers: Idlers having rollers of moulded rubber disc construction, mounted on a steel supporting tube, which support and protect the conveyor belt at loading points by cushioning the shock where impact is severe.

impact load: The dynamic forces imposed on a structure by the motion of the live load.

impact plates: The wear plates attached to the inside of the chamber of an impact crusher and against which rocks are projected by the blow bars on the rotor.

impedance triangle: A right-angled phasor triangle the hypotenuse of which represents impedance and the two other sides resistance and reactance.

impeller: The rotating member of a centrifugal pump or of a compressor.

inductance: The ratio of the magnetic flux-linkage of an electric circuit and a current. Self-inductance refers to inductance in which the current is that of the circuit itself and mutual-inductance where the linkage results from the current in another circuit. Symbol: H. Unit: Henry.

induction motor: An ac motor in which the current in the stator windings produces a rotating flux which induces a current in the conductors of the rotor and a magnetic field around them. The two fields react with one another to produce torque and movement of the rotor in the same direction as that of the stator field.

inductive circuit: A circuit having self-inductance that has an appreciable effect compared with its resistance.

inductor: A coil the primary characteristic of which is the property of inductance.

inertia: The property by which a body resists a change in its state of motion.

initiation: In blasting, the method used to fire the charge, or the instant at which the explosion begins.

inspector: see ‘HM Inspector’.

intercooler: A device for cooling air between one stage of compression and the next.

Interim Development Order permission: mineral working permissions granted between 1943-48. Sites operating under an IDO permission must now register with the MPA.

internal-combustion engine: An engine in which the combustion of the fuel takes place within the cylinder, and the products of combustion result in increased gas pressure which causes the piston to be driven down the cylinder.

interpolation: The estimation of the value of a particular point on a graph from values on either side of the point by assuming the line of the graph is smooth.

intrusion: A mass of igneous rock which, while molten, was forced into or between other rocks.

inverse initiation: A method of blasting in which the primer cartridge is placed at the end of the explosive charge farthest from the entrance to the blasthole and the detonator is placed at the inner end of the primer cartridge.

inverse square law: The intensity of a field of radiation is inversely proportional to the square of the distance from the source. This applies, for example, to the intensity of sound at a distance from a source.

iron loss: In an alternating current system, the eddy current and hysteresis losses developed as heat in the ferromagnetic core of a machine or transformer.

isolator: A switch used for disconnecting a circuit from the supply under no-load conditions.

isopachyte, or isopach: A line drawn on a map through points of equal thickness of a specified rock.

isothermal: A process which occurs at constant temperature.

issued capital: The proportion of the authorized capital which has been issued to shareholders.