MECHANICAL EQUIVALENT OF HEAT – Relationship between the unit of heat and unit of work.

MEAN EFFECTIVE PRESSURE – The average resultant pressure acting on the piston during the stroke that is the effective pressure which compresses and discharges the air. This is the difference between the mean forward pressure and the mean back pressure.

MECHANICAL EFFICIENCY – The ratio of the air indicated horse power to the brake horse power supplied to the compressor shaft.

MULTISTAGE COMPRESSION – Dividing the compression of air into two or more stages so as to obtain the work saving due to a nearer approach to isothermal compression by using intercooling.

MCPHERSON STRUT SUSPENSION – A suspension system in which both wheels are attached to a rigid rear axle housing.

MANUALLY OPERATED TRANSMISSION – A transmission that is shifted from one speed to another by the operator (driver).

MASTER CYLINDER – The liquid filled cylinder in the hydraulic braking system where hydraulic pressure is developed by depression of the brake pedal or movement of the brake lever.

MECHANICAL BRAKES – Brakes operated by mechanical linkage (cables and levers) between the brake pedal and the brakes at the car wheels.

METALLIC BRAKE LINING – A lining having metallic properties used to provide high temperature braking efficiency.

METERING VALVE – A valve that delays pressure build up to the front brakes of a four wheeled vehicle.

MINOR BRAKE ADJUSTMENT – Adjustment of brakes to compensate for brake lining wear.

MODULATOR – A vacuum canister mounted to the outside of the automatic transmission that senses engine load.

MULTIPLE DISC CLUTCH – A clutch that has more than one friction disc, usually there are several driving discs and several driven discs, alternately placed.

MASKED VALVE – An inlet valve which has a mask i.e., a projection, at the rear of the valve head over a part of the periphery so as to admit air in the desired direction.

MAXIMUM SPEED GOVERNOR – limits the maximum speed of operation of a diesel engine.

MECHANICAL INJECTION – Mechanical force pressurizing the metered fuel and causing injection.

METERING FUEL PUMP – A fuel pump delivering a controlled amount of fuel per cycle.

MINIMUM AND MAXIMUM SPEED GOVERNORS – are used predominantly in motor vehicles. The idle and maximum speeds are governed, but not the range in between where the quantity of fuel injected is controlled by the accelerator pedal.

MIXED CYCLE – An engine in which fuel burns partly at constant volume and partly at constant pressure. Sometimes applied to the actual combustion cycle in most high speed diesel engines.

MAGNETIC CRACK DETECTION – Method of locating cracks in materials which can be magnetized, done by applying magnetizing force and applying finely divided iron powder which then collects in the region of the crack.

MASTER PATTERN – The pattern from which the working pattern is cast.

MATCH – A form of wood, plaster of Paris, sand, or other material on which an irregular pattern is laid or supported while the drag is being rammed.

MATCH PLATE – A metal or other plate on which patterns, split along the parting line, are mounted back to back with the gating system to form an integral piece.

METAL PENETRATION – Defect in the casting surface which appears as if the metal has filled the voids between the sand grains without displacing them.

MOULD CAVITY – Impression left in the sand mould by the pattern. Also called MOULD.

MOULD CLAMPS – Devices used to lock or hold cope and drag together.

MOULD HARDENER – In sand moulds in which sodium silicate is the binder, injection of CO2 causes a chemical reaction which results in a rigid structure.

MOULD WASH – Usually an aqueous emulsion containing various organic or inorganic compounds or both, which is used to coat the face of a mould cavity. Materials include graphite, silica flour etc.

MOULDING SAND – Mixture of sand and clay suitable for mould making.

MOULD WEIGHTS – Weights placed on top of moulds to offset internal and ferrostatic pressure.

MOULDABILITY – The ability of the sand mixture to fill in perfectly the cavity of a flask with a pattern or a corebox.

MULTIPLE MOULD – Composite mould made up of stacked sections. Each section incorporates a complete gate for casting. All castings are poured from a central downgate.

MAGNESIUM – A very light metal (about 106 Ibs/cuft) that alloys readily with aluminium and other metals.

MAGNESIUM ALLOY – Alloy containing at least 85% of magnesium and having a specific gravity of 1.8, alloying elements include aluminium, manganese, zinc, and silicon. Widely used for aircraft components, their weight is only two thirds that of aluminium, and a quarter of that of steel.

MAGNETICALLY HARD ALLOY – A ferromagnetic alloy capable of being magnetized permanently because of its ability to retain induced magnetization and magnetic poles after the removal of externally applied fields, an alloy with high coercive force.

MAGNETICALLY SOFT ALLOY – A ferromagnetic alloy that becomes magnetized readily upon the application of a field and that return to practically a non-magnetic condition when the field is removed, an alloy with the properties of high magnetic permeability, low coercive force, and low magnetic hysteresis loss.

MAGNOLIA METAL – White metal bearing alloy containing 4.75-6% tin, 78-80% lead and 15-16% antimony.

MALLEABLE CAST IRON – A cast iron made by a prolonged anneal of WHITE CAST IRON in which decarbonisation or graphitization, or both, takes place to eliminate some or all of the CEMENTITE. The graphite is in the form of temper carbon. This is less brittle than gray cast iron.

MANGANESE – A brittle, hard metallic element used as an alloy in steel to give it toughness to withstand wear and strain.

MANGANESE BRONZE – A group of special alloys, not really bronzes at all, containing about 1% manganese, 60% copper, 40% zinc and small traces of iron, tin, lead or aluminium, the total percentage of these not exceeding 5%.

MARTENSITE – An unstable constituent that is formed by heating and quenching steel. It is formed without diffusion and only below certain temperature known as M’s temperature. Martensite is the hardest of the transformation products of austenite, having an acicular or needle like microstructure.

MATTER – Any substance which occupies space and has weight. The three forms of matter are solids, liquids and gases.

MEDIUM CARBON STEEL – Steel with a carbon content of 0.3-0.6%.

METAL – An opaque lustrous elemental chemical substance that is a good conductor of heat and electricity and when polished, a good reflector of light.

METALLOID – A non-metal that exhibits some, but not all, of the properties of a metal. Examples are sulphur, silicon, carbon, phosphorous and arsenic.

METALLURGY – The science and study of the behaviours and properties of metals and their extraction from their ores.

MILD STEEL – Carbon steel with a maximum of about 0.25% carbon.

MOLECULE – The smallest portion to which a substance may be reduced by subdivision and still retain its chemical identity.

MOLYBDENUM – Element used in alloying steel, including high speed steel. It gives red hardness and increases the strength of steel at high temperatures. It increases the corrosion resistance of stainless steels at high temperatures, increases the machinability of carbon steels and reduces the temper brittleness of aluminium steels.

MONEL METAL – Trade name for a nickel copper alloy (67% nickel, 28% copper, 5% iron, manganese, and silicon combined) which exhibits high strength and toughness and corrosion resistance.

MU METAL – Special alloy of nickel and iron, also containing copper and manganese, requiring only a very small magnetizing force to produce a normal flux density i.e., the alloy is said to have high permeability (Greek letter MU for permeability).

MUNTZ METAL – Alloy of brass family containing 60% copper and 40% zinc used for manufacturing condenser tubes.

MUSIC WIRE – A high carbon steel wire of the highest quality used for making mechanical springs.

MYCALEX – It is the trade name for a ceramic product made up of glass bonded mica flakes that possess a combination of properties found in other insulating materials.

MAIN BEARINGS – In the engine block, the bearings that support the crankshaft.

MICHELL THRUST BEARING – Type of tilting pad thrust bearing, the thrust supporting surface is divided into a number of segmental pads, which pivot on a radial edge at the back, and so automatically adjust themselves to the required slope.

MULTIGRADE OIL – An oil that retains its viscosity under varying temperature conditions better than a single weight oil.

ML OIL – Oil for light automotive service.

MM OIL – Oil for medium or average automotive service.

MS OIL – Oil for severe automotive service.

MULTI WEIGHT OIL – Type of oil that provides adequate lubrication at both high and low temperatures.

MULTIPLE VISCOSITY OIL – An engine oil which has a low viscosity when cold (for easier cranking and a higher) viscosity when hot (to provide adequate lubrication).

MECHANICAL DRAFT – Draft produced artificially by means of forced or induced draft fans.

METHANOL – Methyl alcohol produced from coal by its liquifaction, by pyrolysis, or by its reaction with high pressure hydrogen.

MACH NUMBER-M – Ratio of the stream velocity to the local acoustic velocity.

MULTI SHAFT GAS TURBINE – Turbine unit in which two or more compressor combinations or turbines are carried on independent shafts. In each turbine compressor combination, the machines are coupled to each other in a series arrangement.

MARTEMPERING – The process of quenching an austenitized ferrous alloy to a temperature just above or near the M’s point and maintaining until the temperature throughout the part is uniform. The alloy is then allowed to cool slowly in air through the range of martenistic formation.

METALLIZING – Metal spraying process in which the coating metal is melted (either in a gas flame or in a separate melting pot), then atomized by an air blast and deposited in atomized form on the surface to be coated.

MAIN BEARINGS – The cylinder block and crankcase unit is provided at the bottom with split main bearings for supporting the crankshaft journals.

MANIFOLD – Intake manifold or exhaust manifold. A casting connecting a series of outlets to a common opening.

MECHANICAL EFFICIENCY – In an engine, the ratio between brake horse power and indicated horse power.

MUFFLER – In the exhaust, a device through which the exhaust gases must pass and which muffles the sound.

MICROMETER – A precision, screw adjusted measuring instrument with which dimensions can be read in thousandths and ten thousandths of an inch.

MICROMETER COLLAR – A dial on the screw of a machine to indicate the extent of the movement of the screw or parts attached to the screw and usually graduated to read thousandths of an inch.

MICROMETER DEPTH GAUGE – The ordinary depth gauge has been

elaborated by the addition of a micrometer head.

MINNIMETER – Delicate form of indicator showing the movement of a projecting plunger usually placed at one end.

MACHINE VICE – A work holding device used on machine tools to seat and hold work securely in position while machining is done.

MAGNETIC BLOCK – Laminated block for use in conjunction with a magnetic chuck.

MAGNETIC CHUCK – Magnetic device for holding work during machining and grinding.

MANDREL – A turned, hardened and accurately ground cylindrical bar or shaft or spindle, incorporating a slight taper, used for holding bored parts in a lathe while the outside surface is being turned.

MANDREL PRESS – Press for the purpose of fitting mandrels to the bore of the work.

MANIPULATOR – Fixture in which work is held for welding.

MILLING HEAD – An attachment or device for the milling machine to add to the range of operations for increasing production, versatility, and accuracy of the machine. A vertical attachment makes it possible to do vertical milling on a horizontal machine.

MITER GEARS – Bevel gears which have a center or pitch angle of 45°.

MORSE TAPER – Standard system of tapers widely used on lathes and drilling machines.

MULTIPLE THREAD SCREW – A screw with two or more threads cut around the periphery of the workpiece to provide an increased lead with a specified pitch.

MACHINE – A mechanical device, mechanism, or apparatus which transmits power and motion to perform work.

MACHINE TOOL – Type of power driven machine for cutting metal as employed in machine shops, the term being usually restricted to those which use the tool that produces waste material in the form of chips or cuttings. Typical machine tools are lathes, planers, shapers, slotters, borers, drills, broaches, millers and saws.

MAJOR DIAMETER – On a straight thread, the diameter of the imaginary cylinder that just touches the crest of an external thread or the root of an internal thread.

MALE PART – The external part of any workpiece which fits into a hole, slot or groove of the mating part.

MANUAL VALVE – A valve which is opened or closed or adjusted by hand.

MESH – Engaging one part with another, as the teeth of one gear mesh with the teeth of a mating gear.

MICRON – One millionth of a meter or 0.039370 inch.

MINOR DIAMETER – On a straight thread, the diameter of the imaginary cylinder which just touches the root of an external thread or the crest of an internal thread.

MORSE TAPER – A self holding, standard taper largely used on drilling tools, drilling machine spindles, and some lathes.

MULTIPLE THREADED SCREW – A screw with two or more threads cut around the periphery of the workpiece to provide an increased lead with a specified pitch.

MANDREL PRESS – Press for the purpose of fitting mandrels to the bore of the work.

MICHIGAN GEAR SHAPER – Machine incorporating a number of shaped cutters, used to produce all the teeth on spur or helical gears simultaneously.

MILLING MACHINE – Machine tool designed to remove metal from the surface so as to size and shape it by means of a revolving multiple toothed cutter called milling cutter.

MOTOR – A rotating electromagnetic device used to convert electrical energy into mechanical energy.

MOTOR VEHICLE – Any type of self propelled vehicle mounted on wheels or tracks.

MOULDING MACHINE – Mechanical device for making moulds at a much faster rate.

MULTIPLE SPINDLE DRILLING MACHINE – Machine used for drilling a large number of holes in one operation, built purely for repetition work.

MULTIPLE SPINDLE LATHE – Machine, generally of the automatic type, with up to six spindles mounted in a drum, this indexes in sequence, so that a different operation is performed at each station, and one revolution of the drum completes a piece of work.

MANIPULATOR – A device that grasps an item and moves it to a new position or orientation for the next operation. It may be a simple pincer or complicated robot.

MATERIALS HANDLING – Procedures involving receiving, storing, sorting, packing, shipping, freight handling and controlling of goods and materials.

MONORAILS – An overhead track (usually an I beam) upon which the carriers or hoists move.

MULTIPLE RACK CAR – Special equipment designed to carry motor cars.

MACHINABILITY – The relative ease of machining that is related to the hardness of the material to be cut.

MACROSTRUCTURE – The structure of metals as revealed by examination of the etched surface of a polished specimen at a magnification not exceeding ten diameters.

MALLEABILITY – In metals, the property of being able to undergo mechanical deformation (flattened by rolling or hammering) without rupturing or developing a marked increase in resistance to change of shape.

MELTING POINT – The temperature at which a pure metal, compound or eutectic changes from solid to liquid, the temperature at which the liquid and the solid are in equilibrium.

MICROPOROSITY – Porosity visible only with the aid of microscope.

MICROSTRUCTURE – The structure of polished or etched metal specimens as seen enlarged through a microscope.

MODULUS OF ELASTICITY – A measure of the rigidity of metal. Ratio of stress, within proportional limit, to corresponding strain. Also called ELASTIC MODULUS and COEFFICIENT OF ELASTICITY and YOUNGS MODULUS.

MODULUS OF RIGIDITY – Ratio of shearing stress to shearing strain, within the proportional limit.

MODULUS OF RUPTURE – A fictitious stress calculated for either bending or torsion tests on the basis of the load causing failure, and the assumption that the elastic equation for stress applies up to the point of failure.

Ms TEMPERATURE – The temperature at which martensite begins to form in an alloy system on cooling.

MOTTLED – White iron structure interspersed with spots or flecks of gray.

MAAG PROCESS – The process combines precision grinding of the flanks of the gear teeth with a generating action which ensures that a correct involute form will be maintained, or restored if distortion has taken place as a result of hardening and heat treatment.

MACHINING – Machining is the art of using machine tools and cutting tools in combination to reduce a piece of material to some specified shape and dimensions.

METALLIZING – Process of spraying metal on to a metallic or non-metallic surface, for building up of worn parts and for the protection of components against corrosion.

MILLING – Operation in which a workpiece is given a specific shape or form by means of a rotating cutter having many cutting teeth.

MILL WRIGHTING – General maintenance, repair and the making of parts for machinery in a factory. A millwright is a craftsman in the true sense of the word.

MOULDING – Practise of making moulds in which to pour molten metal to form castings.

MACHINE – A combination of resisting bodies, with successfully constrained relative motions, which is used for transmitting or transporting available energy so as to do some particular kind of work e.g., electrical motor, internal combustion engine.

MASS OF A BODY – The property of a body which determines its resistance to change its velocity.

MECHANISM – A constrained kinematic chain which means the motion of anyone link will give a definite, predictable motion to each of the others.

MODULE – Reciprocal of diametral pitch.

MOMENTUM – The product of the mass and velocity of a body.

MANIFOLDING – In direct expansion or dry evaporators, the method of circulating the refrigerant through separate rows of tubes.

MANUAL CONTROL SYSTEM – An A/C system in which the driver of an automotive vehicle selects heating and cooling by use of a lever which mixes warm and cold air to desired temperature.

METERING DEVICES – Restrict the flow of the refrigerant from the high to the low side, regulate the flow of the refrigerant according to the needs of the system.

METHYLENE CHLORIDE (CH2Cl2) – A halogenated hydrocarbon which is considered a safe refrigerant.

MODULATING CONTROLS – Provide for variations by steps as contrasted to the off and on operation of the refrigeration systems with ordinary controls.

MODULATING THERMOSTAT – Used to operate dampers on DX coils and valves for varying the flow of chilled water.

MODULATING THERMOSTATIC EXPANSION VALVE – Varies the capacity of the valve in response to variations in load on the system.

MOISTURE VAPOUR SEAL – A tight barrier placed outside the insulation to prevent pushing of moisture through the insulation by vapour pressure.

MULTIPLE UNIT INSTALLATION – One in which two or more evaporators in different refrigerators are operated from one compressor, or vice versa.

MAIN FUEL NOZZLE – The fuel nozzle in the carburettor venturi that supplies fuel when the throttle is opened partially to fully opened position.

MANIFOLD VACUUM – The vacuum in the intake manifold that develops as a result of the vacuum in the cylinders on their intake strokes.

METERING ROD AND JET – A device, consisting of a small movable rod, which has a varied diameter, and a jet (which accommodates the movable rod) that increases or decreases fuel passage and hence the flow of fuel according to engine throttle opening, engine load or a combination of both.

MISSING – In the engine, the failure of the air fuel mixture in a cylinder to ignite when it should and thus causing the engine to run roughly.

MULTIPOINT FUEL INJECTION (MPFI) – has one injector for each cylinder. Fuel is injected in more than one location. This is often called port injection.

MAKE UP WATER – Additional water to be put into the boiler periodically to make up for the loss due to leakage or exhausting of steam without condensation.

MARINE BOILER – A low head type special design boiler meant for ocean cargo and passenger ships with an inherent fast steaming capacity.

MECHANICAL DRAFT – The draft artificially produced by mechanical devices such as fans and in some units by steam jets.

MECHANICAL STOKER – A device constructed to automatically feed fuel to a furnace. Its use results in more efficient combustion owing to constant instead of intermittent firing.

MINIATURE HIGH PRESSURE BOILER – A boiler which does not exceed the following limits: (1) 16″ inside diameter of shell. (2) 5 cuft. gross volume exclusive of casing and insulation (3) 100 psi gauge. If it exceeds any of these limits, it is called a power boiler.

MISSISSIPPI COCK – A cock in which steam pressure keeps the cock closed and a push button is provided to open the cock.

MISSING QUANTITY – In a steam engine, this is the lack of volume due to the steam not remaining dry and saturated during expansion.

MIXED PRESSURE TURBINE – A turbine designed to work on two or more pressures.

MATTER – General name for all material substances, gaseous, liquid or solid forming the earth and its surrounding atmosphere.

MEAN EFFECTIVE PRESSURE – The difference between the mean forward pressure and the mean back pressure acting on a moving piston during a cycle of operation.

MECHANICAL CYCLE – is one wherein during the various processes, the properties of the working fluid change.

MECHANICAL EFFICIENCY – Ratio of mechanical energy available at the brake or flywheel to the mechanical energy put into the moving mechanism at the piston of the engine.

MECHANICAL EQUIVALENT OF HEAT – 1 kcal is equal to 1427 Mt.kg of mechanical energy.

MOLE OF GAS – Quantity of gas, the weight of which is equal to the molecular weight in pounds.

MOLAR HEAT – is the quantity of heat required to raise the temperature of one mole of a substance through one degree.

MOLLIER DIAGRAM – A graphical representation of the properties of a fluid in which enthalpy is plotted as abscissa and pressure as ordinate.

MASTER LINK – A pin link which has one removable side plate located by a clip. This allows a convenient way of separating the chain.

MECHANICAL BRAKE – A brake system which uses a mechanical advantage by way of levers and cables or rods to apply brakes. A brake system not using hydraulic fluids or hydraulics.

MILD PORT TIMING – Two stroke cycle engine ports open for a relatively short time, providing for a broad power band.

MOTOR CYCLE – A two wheeled vehicle powered by an internal combustion engine.

MULTI PLATE CLUTCH – A clutch assembly using more than one driving plate and more than one driven plate.

MULTIPLE PORTS – Use of many small transfer ports rather than two large ports in the two stroke cycle engine cylinder.

MACHINE OXYGEN CUTTING – Cutting with an equipment that performs the operation under the constant observation and control of an oxygen cutting operator.

MACHINE WELDING – Welding with an equipment which performs the operation under the constant observation and control of a welding operator.

MANUAL WELDING – Welding performed and controlled completely by hand.

MELTING POINT – The temperature at which a metal melts.

MELTING RANGE – Temperature range between solidus and liquidus.

MELTING RATE – The weight or length of electrode melted in unit time.

METAL ARC CUTTING – Processes that sever metals by melting them with the heat of an arc between a metal electrode and the base metal.

METAL BATH BRAZING – is a dip process wherein the filler metal is obtained from the molten metal bath. This is confined to joining comparatively small work such as joints in wire.

METAL CORED ELECTRODE – A composite filler metal electrode consisting of a metal tube or other hollow configuration containing alloying ingredients.

METAL ELECTRODE – A filler or non-filler metal wire or rod, either bare or covered, used in an arc welding or cutting.

METAL POWDER CUTTING – An oxygen cutting process that severs metals through the use of powder such as iron, to facilitate cutting.