H — Dictionary of Quarrying Terms

HaSaWA: abbr. Health and Safety at Work etcAct 1974.

HMS: abbr. see ‘heavy-media separation’.

HMSO: abbr. Her Majesty’s Stationery Office.

HM Inspector: A Crown official with statutory powers of inspection, investigation, inquiry and enforcement of safety law.

HSE: Health and Safety Executive

hade: The angle of inclination of the plane of a fault to the vertical.

half-wave: A term used mainly in connection with rectifiers to describe a system in which one half-cycle of an alternating voltage produces current while the other half-cycle produces no current.

hammer mill: An impact crusher consisting of a rotor, rotating at high speed, to which hammers are attached by hinge pins.

hand sprayer: A binder distributor in which the spray is directed on to the surface by means of a spray lance. Pressure is provided by a hand- or power-driven pump.

hanging wall: The rock immediately overlying a mineral deposit.

hard-facing: The application, usually by welding, of a layer of hard material on the surfaces of the parts of machinery which are subject to heavy wear, eg shovel buckets.

hard-standing: A hard surface used for parking vehicles.

hardcore: Recovered stone, broken brick or the like which, when spread and compacted, can be used as a rough filling material.

hardness of rock: see ‘Moh’s scale of hardness’

hardware: General term for all electrical and mechanical components of a computer or data-processing system.

harp wire: Wire used in alternating straight and undulating warps or paired undulated wires, crossed periodically by wire binding to maintain the mesh structure of a screening surface. Used where sticky or damp material causes blinding in conventional screening media and where deflaking is required.

Hartz jig: A mechanically operated jig in which water is pulsated through a fixed screen by a plunger. Used in the separation of heavy minerals from gangue, including the beneficiation of witherite and the extraction of galena from fluorspar ore.

hatching: The parallel lines filling areas in a drawing to indicate for instance, differences in materials.

haul: The distance quarry or opencast products must be moved to the treatment plant or dump.

hazard: the potential to do harm to the health and safety of any person.

head: 1 The potential energy per unit weight of fluid above a datum, ie the height in metres of the water level above that point. In theory this should include its actual potential energy, its kinetic energy and its pressure energy. 2 Geological term, describing scree-like accumulations of rubble formed under sub-arctic conditions.

health and safety document: an essential requirement of the Quarry Regulations 1999 containing all matters related to safety e.g. policy, appointments, management structure, risk assessments, rules, inspections and procedures.

heaped capacity: The SAE heaped capacity for loaders and haulers is the capacity assuming the load above the sides has a slope of 2:1 and that of scrapers when the slope is 1:1.

heat exchange: The process of transfer of heat energy from one stream of matter (solid or fluid) to another by radiation, convection or conduction, to effect a change in temperature of the two streams.

heat exchanger: Equipment for effecting heat exchange between two fluid streams without their admixture, for the purpose of cooling one, or for the conservation of heat from a waste stream.

heat treatment: Any heating or controlled cooling of a metal to change its properties.

heater planer: A road heater fitted with cutters and used for removing irregularities or a course of material from a road surface by planing or milling action prior to resurfacing; the process is preceded by softening of the surface by heat.

heavy-media separation: A mineral-processing operation in which mineral fragments can be separated on the basis of differences in density by being allowed to sink or float in a medium of intermediate density. The medium consists of a suspension of a finely ground high density solid (eg magnetite) in water.

hectare: An area equal to 10,000m².

hecto-: A prefix denoting one hundred times.

helical conveyor: see ‘screw conveyor’.

henry: The inductance of a closed circuit in which an electromotive force of one volt is produced when the electric current in the circuit varies uniformly at the rate of one ampere per second. Symbol: H.

hertz: The unit of frequency: one cycle per second. Symbol: Hz.

high explosive: An explosive which contains at least one compound which, when fired, produces a chemical reaction which takes place at very high speed, producing a shattering type of detonation.

high-tensile steel: Steel with a higher yield point than that of mild steel and which is used, where necessary, for engineering structures or machine parts.

highwall: In opencast mining, the wall of the pit at which work is in progress; the coal or ore and the overburden above it.

historical costing: The form of costing concerned with costs which have been incurred and recorded. Comparisons are made with costs during similar accounting periods in the past.

hoggin: A naturally occurring mixture consisting mainly of gravel and sand and containing sufficient clay to bind the mixture together when rolled.

holdback: A device used on an inclined conveyor to prevent the loaded belt from running downhill in the event of a power failure.

holding-down bolt: see ‘foundation bolt’.

Holocene: an alternative term for the Recent epoch.

Hooke’s law: Within the elastic limit, the extension of a material is proportional to the applied stress.

hopper: A vessel into which materials are fed, usually constructed in the form of an inverted pyramid or cone terminating in an opening through which the materials are discharged.

horsepower: A practical unit of power approximately equal to 746 watts. Symbol: hp.

hot storage: Heated and insulated above-ground storage hoppers for mixed asphalt or coated macadam.

hutch: The part of a jig situated below the screen plate in which the controlled pulsating movement of water takes place.

hydration: The addition of water to anhydrous minerals, resulting in the production of hydrous minerals, eg anhydrite is converted in to gypsum.

hydraulic: Relating to the flow of fluids.

hydraulic accumulators: An accumulator consists of a chamber into which hydraulic fluid enters under pressure and in so doing compresses either a gas or a spring. A fall in the pressure at the inlet results in fluid being forced back into the system by the compressed gas or spring.

hydraulic mining: A method of winning mineral by washing it with high-pressure jets of water, and subsequently transporting it in flumes or pipes.

hydraulic motors: Multi-cylinder reciprocating machines which are essentially similar units to hydraulic pumps. See ‘gear pump’, ‘piston pumps’ and ‘vane pump’.

hydraulic reservoir: A reservoir which caters for varying oil volumes in the system as cylinders extend or compress, also for changes in volume due to temperature.

hydraulic test: A test for boilers, pipes, pressure vessels etc by filling them with water to the required pressure.

hydrocyclone: see ‘cyclone’.

hydrodynamics: The use of the energy of a fluid in motion, as in power-transmission.systems such as hydraulic couplings and torque converters.

hydrographical surveying: Surveying of bodies of water at the coast, estuaries and rivers, but may also be applied to lagoons, flooded workings etc.

hydrology: The study of water on the Earth’s surface.

hydrometer: An instrument which, when floated in a liquid, gives a measurement of its relative density by the level on the stem to which it is submerged.

hydrostatics: The study of forces arising from the presence of fluids, eg the use of pressure energy to transmit force as in a hydraulic press.

hygrometer: An instrument for measuring the relative humidity of the atmosphere.

hypabyssal: Medium-grained, intrusive igneous rocks forming dykes and sills.

hypoid bevel gear: A bevel gear in which the teeth are of hypoid shape. This permits a shaft arrangement in which the two gear axes are offset so that they do no lie in the same plane. Used in the back-axle drive of some motor vehicles. Since, with this gear form, some sliding action between the teeth is involved, an extreme pressure lubricant must be used.