H24 Engine - The basic design is that of two flat horizontally opposed 12 cylinder engines geared onto a common shaft.

Half Male Centre - A dead center that has a portion of the 60 degree cone cut away.

Handbrake - Vehicle brake that is applied by hand to hold the vehicle when stationary.

Handwheel - Any adjusting or feeding mechanism shaped like a wheel and operated by hand.

Hard Facing - A particular form of surfacing in which a coating or cladding is applied to a surface for the main purpose of
reducing wear.

Hard Surfacing - The application of a hard, wear-resistant alloy to the surface of a softer metal.

Hardenability - In a ferrous alloy, the property that determines the depth and distribution of hardness induced by quenching.

Hardening - Increasing the hardness by suitable treatment, usually involving heating and cooling.

Hardness - Resistance of metal to plastic deformation usually by indentation.

HAZMAT - Hazardous materials

HDPE - High density polyethylene

Head Loss - The loss of pressure in a flow system measured using a length parameter

Head Pressure - Expression of a pressure in terms of the height of fluid

Headstock - The fixed or stationary end of a lathe or similar machine tool.

Heat Check - A pattern of parallel surface cracks that are formed by alternate rapid heating and cooling of the extreme
surface metal.

Heat Exchanger - A device in which energy is transferred from one fluid to another across a solid surface.

Heat Pump - A reversible heat engine that acts as a furnace in winter and an air conditioner in summer.

Heat Recovery Steam Generators (HRSG) - A boiler that recovers heat from a gas turbine exhaust and converts it to usable
steam to improve efficiency.

Heat Sink - A body which can absorb thermal energy

Heat Transfer - The process of thermal energy flowing from a body of high energy to a body of low energy

Heat Treatment - Heating and cooling a solid metal or alloy in such a way as to obtain desired conditions or properties.

Helical Spring - A coiled spring.

Helix - A path formed as a point advances uniformly around a cylinder, as the thread on a screw or the flutes on a drill.

Hermetic - Sealing of an object so it is airtight.

HgS - Mercuric Sulphide, the ore of mercury. Occuring as red crystals.

High Carbon Steel - Steel with a carbon content greater than 0.85%.

High Impact Characteristics - Product and/or process characteristics that, when outside of the specification tolerance,
severely affect subsequent manufacturing operations or customer satisfaction.

High Impedance State - The state on a signal that is not being driven by any value.

Hob - A cylindrical cutting tool shaped like a worm thread and used in industry to cut gears.

Hobbing - The operation of cutting gears with a hob.

Honing - The process of finishing ground surfaces to a high degree of accuracy and smoothness.

Hookes Law - A Law stating that, in a linear system, the restoring force is proportional to the displacement of the body,
acting in a direction as to restore equilibrium.

Horsepower - Mechanical engineering unit of power.

Hot Air Engine - The Stirling Engine is an external combustion engine.

Hot Pressing - A method used to increase the density of a material.

Hot Working - Any metal forming operation that is performed above a metal recrystallization temperature.

hp - Horsepower. Mechanical engineering unit of power.

Hydrocarbon - Any organic compound composed entirely of carbon and hydrogen.

Hydrocracking - This exposes heavy fuel oil to hydrogen at high pressure and temperature in the presence of a catalyst to
reduce sulfur and produce lighter oils by cracking the heavy oil molecules.

Hydrodynamic Bearing - A bearing which supports the shaft on a thin film of oil, the fluid-film layer is generated by journal

Hydroelectric Energy - Electricity generated by harnessing the energy of flowing water.

Hydrogen Brazing - A method of furnace brazing in a hydrogen atmosphere.

Hydrolysis - A chemical reaction between a mineral and water that results in dissolution of the mineral.

Hydrometer - Floating instrument used to measure specific gravity of a liquid.

Hydrostatic Bearing - A bearing which supports the shaft on a thin film of oil, the fluid-film layer is generated by externally
applied pressure.

Hydrostatic Pressure - The pressure at any point in a liquid at rest; equal to the depth of the liquid multiplied by its density.

Hypereutectic Alloy - Any binary alloy whose composition lies to the right of the eutectic on an equilibrium diagram, and which
contains some eutectic structure.

Hypersonic - A range of speed that is five times or more the speed of sound in air.

Hypervelocity - A range of speed that is about 12 times or more the speed of sound in air.

Hypoeutectic Alloy - Any binary alloy whose composition lies to the left of the eutectic on an equilibrium diagram, and which
contains some eutectic structure.

Hysteresis - If the input varies from an initial point to a final point and then retraces its value back to the initial point, then
the two paths of the output should be identical. If there is hysteresis in the system then the output paths will not coincide.

Hysteresis Damping - Hysteresis damping produces a force which is in phase with the velocity and proportional to the
displacement, resulting in a linear equation of motion.

Hz - Hertz. The SI unit of frequency.
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