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Mechanical Glossary-B

BABBITT METAL – White metal bearing alloy, suitable for bearings subjected to moderate pressures, contains tin 59.5% min, copper 2.25- 3.75%, antimony 9.5-11.5%, lead 26% min, iron 0.08% max, bismuth 0.08% max.

BABCOCK AND WILCOX MILL – Dry grinding mill using rotary steel balls.

BABCOCK and WILCOX BOILER – A water tube boiler consisting in its simplest form of a horizontal drum from which is suspended a pair of headers carrying between them an inclined bank of straight tubes.

BACK BONE FRAME – Frame which uses the engine as a structural member for load carrying.

BACK DRAFT – Taper or draft which prevents removal of pattern from the mould.

BACK GEARS – Gears applied to machine tools to increase the number of speed changes obtainable with a cone or step pulley belt drive.

BACK KICK – Violent reversal of an internal combustion engine crankshaft rotation, during starting due to backfire.

BACK KICK – Violent reversal of an internal combustion engine crankshaft rotation, during starting due to backfire.

BACK LOCKING – The steering gear is so constructed that it is easy to turn the vehicle by steering wheel, but it is difficult to turn the steering wheel by turning the front wheels. This back locking prevents the bumps and shocks experienced by the wheel on the road surface from being transmitted to the steering wheel.

BACK PRESSURE TURBINE – A steam turbine from which the whole of the exhaust steam, at a suitable pressure, is taken for heating purposes.

BACK PRESSURE – A pressure exerted by a fluid contrary to the pressure producing the main flow. For example, pressure in the exhaust manifold, the higher the back pressure, greater is the resistance to flow of exhaust gases through the exhaust system. This lowers volumetric efficiency.

BACK STICK – Piece of wood used when spinning sheet metal by hand in a lathe.

BACK WELD – A weld deposited at the back of a single groove weld.

BACKFIRE (exhaust system) – Passage of unburned air fuel mixture into the exhaust system where it is ignited by some hot spot and causes a loud explosion.

BACKFIRE (intake system) – Preexplosion of air fuel mixture so that the explosion passes the open intake valve and flashes back through the intake manifold. May be caused by faulty timing, crossed plug wires, leaky intake valve etc.

BACKFIRE (intake system) – Preexplosion of air fuel mixture so that the explosion passes the open intake valve and flashes back through the intake manifold. May be caused by faulty timing, crossed plug wires, leaky intake valve etc.

BACKHAND WELDING – A welding technique in which the welding torch or gun is directed opposite to the progress of welding.

BACKING PLATE – A mounting plate that holds the brake shoes, cam lever, pivot pins and springs inside the brake drum.

BACKING SAND – Foundry sand placed next to the facing sand after the latter is in place. It forms the bulk of sand used to complete the mould.

BACKING SAND – Sand between the facing sand and the flask.

BACKLASH – The clearance or amount of movement between the tooth profiles of a pair or train of gears in mesh. Also refers to the looseness or lost motion between screw threads which have been badly worn.

BAFFLE – A device which slows down or diverts the flow of gases, liquid, sound etc.

BAG – A bulged out section of a portion of the shell, extending through the full thickness of the shell, caused by over heating and pressure.

BAGASSE – A fuel produced as a by product of the abstraction of juice from sugar cane. The dried cane (fibrous residue) is usually fed into a specially designed furnance by means of overfeed stokers.

BAINITE – A structure in steel named after E.G. Bain that forms between 481° C and the M’s temperature. At the higher temperatures, it is known as upper or feathery bainite. At the lower temperatures it is known as lower or a acicular bainite and resembles martensite.

BAKED CORE – The core which has been subjected to heating or baking until it is thoroughly dry, as opposed to green sand core which is used in the moist state.

BAKELITE – Trade name for one of the first used thermo-setting synthetic resins. It is derived from the name of the inventor Dr. L.H. Backeland, and its formation is the result of a chemical action between formaldehyde and phenol.

BALANCE BOX – A box, filled with heavy material used to counter balance the weight of the job and load of a crane of the cantilever type.

BALANCE CRANE – A crane with two arms, one having counterpoise arrangements to balance the load taken by the other.

BALANCED CARBURETTOR – Carburettor in which the float bowl is vented into the air horn, below the air cleaner, to compensate for the effects of a clogged air filter.

BALANCED CARBURETTOR – Carburettor in which the float bowl is vented into the air horn, below the air cleaner, to compensate for the effects of a clogged air filter. battery induces a high secondary emf in another winding on the same magnetic circuit, the high potential being distributed in synchronism with the contact breaker in the primary circuit and the engine firing order.

BALANCED DRAFT – A boiler using both forced draft fan and induced draft fan, can be regulated and balanced in the amount of air and flue gases handled so that the furnace pressure is almost atmospheric.

BALANCED DRAUGHT – A system of air supply to a boiler furnace, in which one fan forces air through the grate, while a second, situated in the uptake, exhausts the flue gases. The pressure in the furnace is thus at atmospheric i.e., is balanced.

BALANCED LUFFING – Luffing mechanism, in which the moment due to the weight of the jib is at balance with the moment produced by the counterweight.

BALANCING MACHINE – A machine for testing the extent to which a revolving part is out of balance, and to determine the weight and position of the masses to be added or removed, to obtain balance.

BALL AND TRUNNION JOINT – A type of universal joint which combines the universal joint and slip joint in one assembly.

BALL BEARING – An antifriction bearing where the rolling elements are spherically shaped. Bearing consists of an inner and outer hardened steel races separated by a series of hardened steel balls.

BALL JOINT ROCKER ARMS – Rocker arms that instead of being mounted on shaft, are mounted upon ball shaped devices on end of stud.

BALL JOINT STEERING KNUCKLE – Steering knuckle that pivots on ball joints instead on king pin.

BALL JOINT SUSPENSION – A type of front suspension, which does not use a steering knuckle. Instead, the wheel spindle is attached directly to the upper and lower suspension arms through ball joints. Allows movement up and down as well as rotation.

BALL JOINT – Flexible joint utilizing ball and socket type of construction, used in steering linkage set ups, steering knuckle pivotsupports etc.

BALL STUD – Stud with a ball on end, commonly used in steering linkage to connect pitman arm to linkage, or to connect tie rods.

BAND SAW – A narrow endless strip of saw blading running over and driven by pulleys, as a belt used for cutting wood or metal to intricate shapes.

BAND or BELT CONVEYOR – An endless band passing over, and driven by horizontal pulleys, thus forming a moving track which is used to convey loose material or small articles.

BANDED STRUCTURE – A segregated structure of nearly parallel bands aligned in the direction of working.

BANKING LOSS – The fuel used in maintaining a floating bank or to maintain a dead bank and then raise the steam pressure to normal.

BANKING UP – Reducing the rate of combustion in a boiler furnace by covering the fire with slack or fine coal.

BAR LATHE – A small lathe of which the bed consists of a single bar of circular, triangular or rectangular section.

BAR – A piece of material thicker than sheet, long in proportions to its width or thickness, and whose width to thickness ratio is much smaller than sheet or plate, as low as unity for squares and rounds.

BARE ELECTRODE – A filler metal electrode of a single metal or alloy, produced into a wire, strip or bar form and without any coating or covering on it.

BARE METAL ARC WELDING – Process which produces coalescence of metals by heating them with an electric arc between a bare or lightly coated metal electrode and the work piece.

BARGES AND LIGHTERS – Shallow draft, box like vessels used for cargo transport in protected waters such as bays, rivers and canals.

BARK – The decarborized layer just beneath the scale that results from heating steel in an oxidizing atmosphere.

BAROMETRIC CONDENSER – A high level jet condenser.

BARREL ELEVATOR – This comprises parallel travelling chains, with curved arms projecting. The chains pass over sproket wheels at the top and bottom of the elevator, and lift barrels from a loading platform to a runway.

BARREL HOPPER – A machine for unscrambling, orientating and feeding small components during a manufacturing process, in which a revolving barrel tumbles the components onto a sloping, vibrating feeding blade.

BARREL TYPE CRANKCASE – A petrol engine crankcase so constructed that the crankshaft can be removed from one end, in more normal construction, the crankcase is split.

BARREL – Refers to the cylinders in an engine or to the number of throttle bores in a carburettor.

BASE CIRCLE – As applied to camshaft, lowest spot on the cam. Area of cam that is directly opposite lobe.

BASE METAL – Metal present in the alloy in largest proportion.

BASE METAL – The metal to be welded, brazed, soldered or cut.

BASIC REFRIGERATION CONTROL – Device that starts, stops, regulates and/ or protects the refrigeration system and its components.

BASIC SIZE – The theoretical or nominal standard size from which all variations are made.

BASIC UNITS – are length, mass, time, temperature and angle.

BASIN – A cavity on top of the cope into which molten metal is poured before it enters the sprue.

BASTARD – Not standard, irregular. A bastard cut file is a rough cut file having coarse teeth than a second cut file.

BASTERED CONDENSER – It is an atmospheric keel condenser, which are sometimes fitted to canal boats or other sea vessels.

BASTERED FILE – File of approximately middle grade in regard to cut or tooth pitch.

BASTERED THREAD – A screw thread which does not confirm to any recognized standard dimensions.

BATH LUBRICATION – Lubrication system in which the bearing contains a space filled with oil, which is in contact with a portion of the journal.

BATTERY – An electrochemical device for storing energy in chemical form so that it can be released as electricity. It is a group of electric cells connected together.

BAUDELOT EVAPORATOR – An open type of cooler in which the liquid to be cooled flows from distributing troughs or headers over a cooling surface consisting of sets of grids or a pair of stamped corrugated metal sheets forming channels.

BAY – An area used for the open storage of heavy items.

BEAD (tyre) – Steel wire reinforced portion around a tyre opening that engages the wheel rim.

BEAD – The portion of the tyre which holds it onto the rim.

BEADING – Process of forming a bead or lapped edge on a sheet metal article.

BEARING CAPS – On an engine, caps held in place by bolts or nuts which, in turn, hold bearing halves in place.

BEARING CRUSH – The additional height over a full half which is purposely manufactured in each bearing half. This ensures complete contact of the bearing back with the housing bore when the unit is assembled.

BEARING FAILURE – Failure of a bearing due to continued flexing of the bearing surface from the applied load.

BEARING METALS – Metals (alloys) used for that part of a bearing which is in contact with the journal e.g., bronze or white metal, used on account of their low coefficient of friction when used with a steel shaft.

BEARING OIL CLEARANCE – The space purposely provided between the revolving shaft and the bearing in which it rotates. Through this space lubricating oil can flow.

BEARING PRELOAD – Amount of static pressure exerted on a bearing or a set of bearings. Preload is usually adjusted by a threaded collar or shims.

BEARING PRELUBRICATOR – A special tank attached to an airline which supplies oil at a predetermined and maintained pressure to the engine lubricating system when the engine is not operating.

BEARING SPACER – A piece of tubing used between the two wheel bearing inner races to prevent unwanted bearing preload as the axle is tightened.

BEARING SPIN – A type of bearing failure caused by lack of lubrication which overheats the bearing while the crankshaft is still in place.

BEARING SPREAD – A purposely manufactured small extra distance across the parting faces of the bearing half in excess of the actual diameter of the housing bore.

BEARING – The part which transmits the load to the support and in so doing, takes the friction caused by the moving parts in contact. Area of the unit in which the contacting surface of a revolving part rests.

BED PLATE – A cast iron or fabricated steel base, to which the frame of an engine or other machine is attached.

BED – One of the principal parts of a machine tool having accurately machined ways or bearing surfaces for supporting and aligning other movable parts of the machine.

BEDDED IN MOULD – is the mould, the bottom half of which is made in the sand in the floor of the foundry. It may be covered with a cope, or cast open, according to the type of work.

BEL – A unit denoting the ratio of power levels of signals or sound. The number of bels may be given as the common logarithm of the ratio of powers.

BELFAST SAND – Red moulding sand of fine grain, and good bonding qualities with moderate refractoriness, suitable for use as a facing sand.

BELL CENTER PUNCH – Device used for rapidly locating and marking the centre of the flat end of a cylindrical workpiece, preparatory to heavier centre punching, centre drilling, turning in a lathe etc.

BELL HOUSING (clutch housing) – Metal (cast iron or aluminium) cover that surrounds flywheel and clutch, or torque converter assembly.

BELL METAL – High tin bronze, used in the casting of bells, which is composed of up to 30% tin, together with some zinc and lead.

BELL MOUTH – The taper of a brake drum.

BELL MOUTHED HOLE – A hole which is rounded or tapered slightly larger at one end or both ends and is not exactly cylindrical throughout its entire length.

BELLCHUCK – Hollow cylindrical chuck bolted to the main chuck for the purpose of giving additional support to work of awkward shape.

BELLOWS – A device, usually metal that can lengthen or shorten much like an accordian. Some cooling system thermostats are of bellows type.

BELT CONVEYOR IDLERS – Number of idler rolls provided between the terminal pulleys to prevent the belt from sagging due to gravity and under the load.

BELT CONVEYOR PULLEYS – Wheels used to support and drive the belt. They include drive, terminal or bend, take up and snub pulleys.

BELT CONVEYOR – A conveyor which consists of a belt of suitable material such as rubber, canvas, balata etc., running over a pair of end drums or pulleys and supported at intervals by a series of rollers called idlers, these in turn being supported on a conveyor frame.

BELT SHIFTER – A flat hardwood strip of suitable length having shifter fingers attached at one end and used to shift a belt from one pulley to another or to replace a belt which has run off a pulley on an overhead drive shaft.

BELTED TYRE – A tyre that is reinforced with a build up of cord under the tread area.

BENCH BLEEDING – Process of removing air from the master cylinder pressure area before installing it in the vehicle.

BENCH LATHE – A lathe of small dimensions that can be mounted on a bench or stand.

BENCH – The name applied to a complete plant for the manufacture of coal gas. Also called RETORT BENCH.

BENDING (by forging) – In bending there is a thinning of the material, accompanied by a spreading of the metal on the inside of the bend and a narrowing at the outside.

BENDING MACHINE – Machine designed to bend and fold sheet metal.

BENDIX TYPE STARTER – A self engaging starter drive gear. Gear moves into engagement when starter armature shaft starts spinning and automatically disengages when starter stops and engine speed increases.

BENSON BOILER – A high pressure boiler of the once through type in which water is pumped through the successive elements of the heating surface, firing being by gas, oil, or pulverized coal.

BENZOL – Crude benzene, used as a motor spirit, generally mixed with petrol, and valued for its antiknock properties.

BERNOULLIS PRINCIPLE – Given a fluid flowing through a tube, any constriction or narrowing of the tube will create an increase in the fluid velocity and a decrease in pressure. This principle is used in the venturi tube of the carburettor.

BESSEMER STEEL – Steel manufactured in a Bessemer converter, and sometimes referred to as mild steel.

BETA RAY – A ray of electrons emitted during the spontaneous disintegration of certain atomic nuclei.

BEVEL – Any surface not at right angle to the rest of the workpiece. If a bevel is at a 45° angle, it is frequently called a MITER.

BEVEL GEARING – Gearing arrangement in which the axes of the shafts connected by gears intersect.

BEZEL – Piece of metal surrounding head lights, gauges or similar components, sometimes used to hold the glass face of a gauge in the dashboard.

BIAS BELTED TYRE – A tyre in which plies are laid on the bias, criss crossing each other, with a circumferential belt on top of them. The rubber tread is vulcanized on top of the belt and plies.

BIFUEL ENGINE – has two injectors to inject two fuels. In this a small amount of a suitable auxiliary fuel is injected into the cylinder either during the intake stroke or early in the compression stroke. Slightly latter in the stroke, the primary fuel is injected.

BILLET – A solid semifinished round or square product that has been hot worked by forging, rolling or extrusion.

BIMETAL – A thermostatic bimetal element made up of two different metals with different heat expansion rates. Temperature changes produce a bending or distortion movement of the element.

BIMETALLIC STRIP – A strip of metal consisting of one metal (or alloy) in the top portion bonded to a different metal in the bottom portion. A straight strip becomes curved when heated.

BIN TICKET – Tickets attached to storage places to provide information on the quantity of goods received, issued and on hand.

BIN – An enclosed space for storing certain types of goods.

BINARY VAPOUR ENGINE – A heat engine using two separate working fluids, generally mercury vapour and steam, for the high and low temperature portions of the cycle respectively, thus enabling a large temperature range to be used, with improved thermal efficiency.

BINDER – Material used to hold the grains of sand together in moulds or cores. May be cereal, oil, clay, resin, pitch etc.

BINDER, PLASTIC (resin) – Synthetic resin material used to hold grains of sand together in moulds or cores, may be phenol formaldehyde or urea formaldehyde thermosetting types.

BINDERS – Compounds that hold the friction materials together in brake linings.

BIOGAS – Obtained by fermentation in the sewage disposal system, or by fermentation of cattle waste, farm waste etc.

BIOSPHERE – The portion of earth and its atmosphere that can support life.

BISECTING AN ANGLE – Dividing an angle into two equal parts.

BLACK BODY – A body which absorbs all the radiation falling on it i.e., has a non-reflecting surface. A black body emits the maximum amount of radiation possible at a given temperature, and the amount is proportional to the fourth power of the absolute temperature.

BLACK LEAD – Graphite for facing moulds and cores.

BLACK OXIDE COATING – Coating produced by converting the surface of iron or steel to black iron oxide having a thickness of about 0.0025 mm.

BLACKING – Carbonaceous material for coating mould or core surfaces.

BLADE SPEED RATIO – Ratio of mean blade speed to the absolute velocity of the fluid stream at the blade inlet.

BLADE VELOCITY COEFFICIENT – The ratio of the relative velocity of steam at outlet to the relative velocity at inlet of the blade.

BLADE – Part attached to the rotating element of the machine or rotor, in which the stream of steam particles has its direction and hence its momentum changed. Also called DEFLECTOR.

BLADES or BUCKETS – The parts that form the rotor flow passages and serve to change the direction, and hence the momentum, of the fluid received from the stationary nozzles.

BLANK FLANGE – A disc, or solid flange, used to blank off the end of a pipe.

BLANKING AND CUPPING TOOL – Tool used to cut a blank and form a cup from sheet or strip metal at one stroke of the press.

BLANKING – Cutting or shearing a shape (called blank) with a die from sheet metal stock. The hole material is saved and used for further operation.

BLAST CLEANING – Blast cleaning involves the forcing of a stream or spray of sand or other abrasive material against the surface of metal, stone, and other materials by means of compressed air.

BLAST CLEANING – Removal of sand or oxide scale from castings by the impinging action of sand, metal shot or grit projected under air, water or centrifugal pressure.

BLAST FURNANCE GAS – A gas of low calorific value, a by product of iron smelting due to burning of coke in the furnance with limited air, used for preheating the blast, for steam raising etc. It may contain up to 30% carbon monoxide.

BLAST MAIN – The main blast air pipe supplying air to a furnace.

BLAST PIPE – The exhaust steam pipe in the smoke box of a locomotive, which terminates in a nozzle to provide draft by entraining the flue gases in the steam jet and exhausting them through the chimney.

BLEED – Molten metal oozing out of a casting stripped or removed from the mould before solidification.

BLEEDER TURBINE – A steam turbine in which the steam is extracted at one or more intermediate stages for industrial use, often at comparatively high pressure.

BLEEDER – A pipe sometimes attached to a condenser to lead off liquid refrigerant, parallel to the mainflow.

BLEEDING (brakes) – Removal of air from hydraulic system. Bleeder screws are loosened at each wheel cylinder (one at a time) and brake fluid is forced from master cylinder through lines until all air is expelled.

BLEEDING (steering) – A process by which air is removed from a hydraulic system (power steering) by bleeding off part of the fluid or operating the system to work without the air.

BLEEDING – A method of improving the thermal efficiency of steam plant by withdrawing a small part of the steam from the higher pressure stages of a turbine to heat the boiler feed water.

BLEEDING – Removing air, pressure, fluid etc. from a closed system as in the brake system or air conditioning system.

BLENDED SAND – Mixture of sands of different grain sizes, clay content etc. to produce one, possessing characteristics more suitable for foundry use.

BLIND HOLE – A hole which is made to a certain depth of a workpiece but does not pass through it.

BLIND JOINT – A joint, no portion of which is visible.

BLIND RISER – An internal riser which does not reach to the exterior of the mould.

BLISTER – A separation of the metal from the shell plate, caused by impurities rolled into the shell plate when formed.

BLISTER – Defect on the surface of a casting appearing as a shallow blow with a thin film of metal over it.

BLOCK (engine) – Basic part of the engine casting containing cylinders.

BLOW BY – Leakage of unburned air fuel mixture and some burned gases past the piston rings into the crankcase during the compression and combustion strokes.

BLOW OFF VALVE – The valve which empties the boiler for cleaning, inspection, or repair. It blows out mud, scale, or sediment when the boiler is in operation and prevents excessive concentration of soluble impurities in the boiler. Also used for rapid lowering of boiler water level if it is too high.

BLOW PIPE – Gas welding torch in which oxygen and acetylene are mixed and ejected from a nozzle.

BLOW TORCH EFFECT – In gas or oil burning furnaces, when the flame impinges on any surface, such as a tube or refractory wall, that surface is burned as by a blow torch. This is a combustion condition to be avoided as destructive to the surface.

BLOWBY – Piston rings do not effectively seal compression pressure, and as such allows hot gases to blow between rings and cylinder wall into the crankcase. This causes overheating of piston and poor performance.

BLOWDOWN OF SAFETY VALVE – The difference between the pressure at which the safety valve pops and that at which it closes.

BLOWER – A low pressure air pump, usually of one rotary or centrifugal type.

BLOWER – Supercharger or engine intake air compressor, a low pressure air pump, usually rotary or centrifugal type.

BLOWING OFF – Act of letting out water and steam from a boiler to carry off accumulated mud and scale.

BLOWN CASTINGS – Castings in which bubbles, or blowholes, have been caused through gases, steam etc., generated when the mould is cast, finding their way into the metal.

BLUE PRINTING (engine) – Dismantling the engine and reassembling it to exact specifications.

BLUE SMOKE – The smoke that results from the burning of lubricating oil that reaches the combustion chamber.

BLUE VITRIOL – A chemical mixture of copper sulphate, water and sulphuric acid. Applied to polished metal for layout purposes, it turns to copper colour.

BLUE WATER GAS – A mixture of approximately equal proportions of carbon monoxide and hydrogen made by passing steam over incandescent coke in special generators.

BOARD DROP STAMP – A stamping machine in which the frictional grip of opposed rollers on either side of a vertical board lifts a tup, which falls when the roller pressure is released.

BODY PANELS – Sheets or panels of steel which are fastened together by welding to form the vehicle body.

BODY ROLL – The vehicle body leaning sideways as the vehicle turns.

BODY – The assembly of sheet metal sections together with windows, doors, seats and other parts, that provides an enclosure for the passengers, engine and so on.

BOGIE – A small truck, of short wheel base running on rails, commonly used for the conveyance of coal, gold or other ores, concrete etc.

BOILER CAPACITY –The weight of steam, usually expressed in kg/hour, which a boiler can evaporate, when steaming at full load output.

BOILER COMPOSITION – Chemicals introduced into the boiler feed water to inhibit scale formation and corrosion, or to prevent priming or foaming.

BOILER CROWN –The upper rounded plates of the boiler of shell type.

BOILER EFFICIENCY – The ratio of heat supplied by a boiler in heating and evaporating the feed water to the heat supplied to the boiler in the fuel. It may vary from 60 to 90 per cent.

BOILER PATCH – A small piece of metal used to cover and strengthen a weak spot. A soft patch is a covering over a leak or defect which is fastened with bolts, as distinguished from a hard patch which is riveted.

BOILER PLATE – Mild steel plate, generally produced by the open hearth process, used mainly for the shells and drums of steam boilers.

BOILER PRESSURE – The pressure at which steam is generated in a boiler.

BOILER SETTING – The supporting structure on which a boiler rests, usually of brick for land boilers and steel for marine boilers.

BOILER TAP – Hand tap specially designed for tapping holes for use with boiler stays.

BOILER TRIAL – An efficiency test of a steam boiler, in which the weight of feed water and of fuel burnt are measured and various sources of losses are assessed.

BOILER TUBES – Steel tubes forming part of the heating surface in a boiler. In water tube boilers, the hot gases surround the tubes. In locomotive and some marine boilers (fire tube boilers) the gases pass through the tubes.

BOILER – A closed pressure vessel in which a fluid is heated and converted to vapour for use external to itself, by the direct application of heat resulting from the combustion of fuel (solid, liquid or gaseous) or by the use of electricity or nuclear energy.

BOILING POINT – The temperature at which a liquid begins to boil.

BOILING POINT – The temperature at which a liquid begins to boil.

BOILING POINT – The temperature at which a liquid boils for any given surrounding atmospheric pressure. Now the saturation pressure of the vapour equals that of the atmosphere.

BOLSTER – It is a block of mild steel with a hollow in it to accommodate the rivet head.

BOLSTER – Support for dies and tools in forging presses and drop stamps.

BOLT MAKING MACHINE – A machine which forges bolt by forming a head on a round bar.

BOMB CALORIEMETER – An apparatus used for determining the calorific values of fuels. The bomb consists of a thick walled steel vessel in which a weighed quantity of fuel is ignited in an atmosphere of compressed oxygen. The bomb is immersed in a known volume of water, from the rise of temperature of water the calorific value is calculated.

BOND – The holding together of different parts.

BOND CLAY – Any clay suitable for use as a bonding material in the moulding sand.

BOND – In grinding wheels and other relatively rigid abrasive products, the material that holds the abrasive grains together. In welding, the junction of joined parts.

BONDED BRAKE LINING – Brake lining that is attached to the brake shoe by adhesive.

BONNET – British term for car hood.

BOOST FAN – A fan for restoring the pressure drop of air or gas, used for restoring the pressure drop in transmission pipes, and for supplying air to furnaces.

BOOST VENTURI – also called secondary venturi is a smaller venturi or restriction, incorporated in some carburettors in the middle of the primary venturi. It increases air speed, vacuum created and hence fuel flow.

BOOST – The amount by which the induction pressure of a super charged internal combustion engine exceeds atmospheric pressure, expressed in kg/sqcm.

BOOSTER PORT – In a two stroke engine, the port that allows an extra amount of air fuel mixture from the intake port into the combustion chamber.

BOOSTER – Device incorporated in a car system (such as brake and steering), to increase pressure output or decrease amount of effort required to operate or both.

BORAX – is the old standard flux for brazing, exists in two forms—ordinary borax and amorphous or fused borax.

BORE – The inside diameter of a cylinder, or a hole for a shaft. Also the operation of machining a circular hole in a metal workpiece.

BORE DIAMETER – Diameter of a hole or a cylinder.

BORE – A cylinder, hole, or the inside diameter of the cylinder or hole. May refer to cylinder itself or to diameter of the cylinder.

BORG WARNER OVER DRIVE – A method of reducing engine rpm in relation to road speed. The unit is attached at the rear of the gear box and operates through epicyclic gears.

BORIC ACID – Inhibitor used in facing sand for magnesium base and aluminium base alloys high in magnesium to prevent reaction with moisture in the sand.

BORING AND TURNING MILL (vertical) – Machine designed for boring and turning castings and forgings.

BORING BAR MICROMETER – On boring operations, it is often necessary to adjust the cutter setting by a few thousandths of an inch. With this, it is possible to determine exactly the depth of cut taken.

BORING BAR – Bar carrying a cutter or cutters to enable holes to be bored which are larger in diameter than can be conveniently drilled by means of twist drills.

BORING BAR – Tool used to cut engine cylinders to specific size. As used in garages, to cut worn cylinders to a new diameter.

BORING MACHINE (horizontal) – Machine used for boring, the spindle being horizontal. In one type, the spindle only rotates and in another type the spindle rotates and also has a horizontal movement.

BORING MACHINE (vertical) – Machine used for boring, the spindle being vertical, very similar to a radial driller. Also called BORING MILL.

BORING TOOL – Single or double ended tool for machining a drilled or cored hole.

BORING – Opening out or increasing the diameter of an existing drilled or cored hole by means of a boring tool.

BORING – Renewing or enlarging cylinders by cutting and honing them to a specified size. Boring bar is used to make the cut.

BORON CARBIDE – An abrasive used in cutting tools, a compound whose chemical formula is B4 C and obtained from borontrioxide (B2O3) and coke at a temperature of 2500°C. Fine powder as hard as diamond.

BORON TRICHLORIDE – A product used for degasification of aluminium alloys.

BOSCH METERING SYSTEM – A fuel metering system in a diesel engine, with a helical groove in the plunger which covers and uncovers ports in the pump barrel and thereby varies the effective stroke of the fuel pump.

BOSSES – Bosses are often located on a wall of a casting and should be so designed that a heavy section of metal leads to the riser.

BOT – Clay wedge used in a cupola to stop the hole through which the metal is run.

BOTTLED GAS – LPG (liquefied petroleum gas) compressed into strong metal containers. Gas when confined in tank, under pressure, is in the liquid form.

BOTTOM DEAD CENTER (BDC) – Lowest position of the piston in the cylinder.

BOUND ELECTRONS – The inner orbit of electrons around the nucleus of the atom.

BOUNDARY FRICTION – The resistance to relative motion when one solid surface is caused to move tangentially over another, the surfaces being covered only by an adsorbed contamination film.

BOUNDARY LAYER – A thin layer of fluid adhering to a surface, when the fluid flows along the surface, in which there is a steep velocity gradient due to viscous friction, the velocity dropping to zero at the boundary surface.

BOUNDARY LUBRICATION – Type of lubrication in which the two surfaces have between them a more or less complete layer of oil which is only, at the most, a few molecules thick.

BOUNDARY – is a real physical surface or an imaginary surface enclosing some matter. The boundary may be a fixed one or a varying one.

BOWL VENT – is an opening in the carburettor float chamber. This hole prevents pressure or vacuum from building up in the bowl.

BOX ANGLE PLATE – An angle plate made of cast iron, usually with slots cast in it and accurately machined on the outside.

BOX JIG – A jig made in the form of a box into which the job to be drilled is inserted.

BOX SPANNER – Spanner in the form of a hollow tube, shaped at the end (or ends) to fit a nut.

BOX WRENCH – A type of closed end wrench made in many styles for specific sizes and shapes of bolt heads or nuts.

BOXED I ROD – Connecting rod in which I beam section has been stiffened by welding plates on each side of the rod.

BOYLE’S LAW – At constant temperature, the absolute pressure of a gas varies inversely as its volume.

BOYLE’S LAW – The absolute pressure of a gas will vary inversely as the volume, if the temperature remains constant. Or conversely, the volume will vary inversely as the absolute pressure, if the temperature remains constant.

BRACING – Securing the contents of a shipment to prevent shifting and damage.

BRAKE (disc type) – Braking system which uses steel disc with caliper type lining application. When brakes are applied, section of lining on the caliper piston on each side of the spinning disc is forced against the disc thus imparting braking force. This type of brake is very resistance to brake fade. Also called disc brake system.

BRAKE ACTUATOR CAM – Small cam that pivots in brake backing plate and forces brake shoes into brake drum.

BRAKE ANCHOR – Steel stud upon which one end of brake shoes is either attached to or rests against. Anchor is firmly affixed to backing plate.

BRAKE ANTIROLL DEVICE – Unit installed in brake system to hold brake line pressure when car is stopped on upgrade, and brake pedal is released. Antiroll device will keep brakes applied until either clutch is released or, as in some models, accelerator is depressed.

BRAKE BACKING PLATE – Rigid steel plate upon which brake shoes are attached. Braking force applied to shoes is absorbed by backing plate.

BRAKE BAND – Band faced with brake lining, that encircles a brake drum. Used on several parking brake installations.

BRAKE BIAS – The stopping effort of the front wheels compared to that of the rear wheels.

BRAKE CALIPER – Part of a disc brake which holds friction pads and encloses disc. As the brake is applied, hydraulic fluid forces a piston in caliper towards disc, causing disc to be pinched between brake pads.

BRAKE CALIPER – The hydraulic cylinder at the wheel used to apply the disc brake linings against the rotor.

BRAKE CLEARANCE – is the clearance provided between the lining and the drum or disc. Wear and tear of the lining increases this clearance and hence to be adjusted periodically.

BRAKE DISC – A round, flat disc made of steel or cast iron. It is mounted on outside of wheel hub.

BRAKE DRUM – A circular ring of cast iron that is part of wheel hub. It provides a place for brake lining to be applied.

BRAKE DRUM – Metal drum mounted to the vehicle wheel which forms the outer shell of the brake. Brake shoes when moved out or moved apart press against the rotating drum to slow or stop drum and wheel rotation.

BRAKE EFFECTIVENESS – is how effectively the brakes perform their function. This depends on the area of the brake lining, amount of pressure applied to the brake shoes, radius of the brake drum, vehicle wheel radius, coefficient of friction of braking surfaces and coefficient of friction between the tyre and the road surface.

BRAKE FADE – A reduction or fading out of braking effectiveness due to loss of friction between brake shoes and drum. This is caused by overheating (heat build up) from excessively long and hard brake application for instance, when coming down a long hill or mountain.

BRAKE FADE – Loss of braking power, usually caused by excessive heat after repeated brake applications.

BRAKE FEEL – The reaction of the brake pedal against the drivers foot, that tells him how heavily he is applying the brakes.

BRAKE FLUID – A special non -mineral oil fluid used in hydraulic braking system. Never use anything else in place of regular fluid.

BRAKE FLUSHING – Cleaning brake system by flushing with alcohol or brake fluid. Done to remove water, dirt or any other contaminant. Flushing fluid is placed in master cylinder and forced through lines and wheel cylinders where it exits at cylinder bleed screws.

BRAKE HORSE POWER (BHP) – Actual usable power delivered by an engine at the crankshaft for driving a vehicle or any other unit. Computed using the engine coupled to a dynamometer.

BRAKE HORSE POWER – Useful power available from an engine. Also called SHAFT HORSE POWER.

BRAKE LINE – Special hydraulic tube made of steel, plastic or reinforced rubber suitably designed to withstand extreme pressure without deforming.

BRAKE LINE – Special hydraulic tubing made of steel, plastic or reinforced rubber. Hydraulic lines must be capable of withstanding extreme pressure without deforming.

BRAKE LINING – A special high friction material made of asbestos and other materials bonded to brake shoes and brake pad plates. Brake lining produces friction and heat when it is forced against brake drum.

BRAKE LINING – A special high friction material made of asbestos and other materials bonded to brake shoes and brake pad plates. Brake lining produces friction and heat when it is forced against the brake drum or disc.

BRAKE MEAN EFFECTIVE PRESSURE (BMEP) – Mean effective pressure (imaginary) which when assumed to be acting on the piston during the power stroke would result in the given brake horse power output. Equal to mean indicated pressure times mechanical efficiency.

BRAKE PAD – The friction pad on a disc brake system.

BRAKE SHOE – The friction lining on a drum brake system.

BRAKE THERMAL EFFICIENCY – Ratio of heat equivalent of power output in the form of brake horse power to the corresponding heat input from fuel.

BRAKE WEAR INDICATOR – Index grooves, tabs, or reference lines to indicate amount of brake lining or pad wear.

BRAKE – An energy conversion device that converts the energy of motion into heat energy and thereby slows down or stops a moving vehicle.

BRAKE – Arrangement in the hoisting machinery to stop the load and hold it when applied to the hoisting motion or bring the relevant mechanisms at rest within specified braking distances. May be a band brake, disc brake or a cone brake.

BRASS FINISHERS LATHE – Lathe specially designed with attachments to machine brass work in quantities. The chief feature is the provision of special hand operated rests.

BRASS – A range of copper zinc alloys, usually those containing 55-80% copper. Alloys containing not less than 63% of copper are called ALPHA

BRASSES. When less than 63% of copper is present, the alloy is called ALPHA-BETA alloy.

BRAYTON CYCLE – Basic cycle for gas turbines. The cycle in which air is compressed isentropically, heated at constant pressure and expanded isentropically thus delivers work until the low pressure is reached and then heat is rejected. Also called JOULE CYCLE.

BRAZING ALLOY – Copper zinc alloy, which sometimes includes small percentages of tin, and lead, used for brazing, the melting point of which is governed by the percentage of zinc.

BRAZING – A group of welding processes that produces coalescence of materials by heating them to the brazing temperature, using a filler metal having a liquidus above 450°C and below the solidus of the base metal.

BRAZING – Joining two pieces of metal without melting either one by using a brazing alloy (copper zinc alloy i.e., brass) that melts at a lower temperature than the materials being joined.

BREAK LATHE – Heavy lathe with sliding bed to accommodate large work. The machine comprises a fast and a loose head stock, and a base plate upon which the bed is mounted.

BREAKER ARM – The movable arm upon which one of the breaker points of the ignition system is affixed.

BREAKER POINTS (ignition) – Pair of points, one fixed and another movable, that are opened and closed to break and make the primary circuit. When the circuit is broken by opening the points, the spark plug fires.

BREAKIN – Period of operation between installation of new or rebuilt parts and when the parts are worn to the correct fit. Driving at reduced and varying speed for a specified distance or duration permits parts to wear out to the correct fit.

BREAKING POINT – The final rupture of a material which is being pulled in tension, after it has reached its ultimate strength.

BREAST DRILL – Has an adjustable breast plate, by means of which a much greater pressure may be applied to the drill. This hand-drill has double ratio drive.

BREATHER PIPE – A pipe opening into the interior of an engine i.e., crankcase. Used to assist ventilation.

BREECHING – The metal duct that carries the smoke and gases of combustion from a furnace to the stack or chimney for ultimate discharge to the atmosphere.

BRIDGED PORTS – A vertical port division in a two stroke cycle engine cylinder which allows use of a large port without the danger of ring or piston catching.

BRINE SYSTEM COOLING – Any system whereby brine, cooled by a refrigerating system, is circulated through pipes to the point where the refrigeration is needed.

BRINE – Any liquid cooled by the refrigerating system and used for the transmission of heat.

BRINE – Water that has been saturated or nearly saturated with salt.

BRINELL HARDNESS – The hardness of metal or alloy measured by pressing a hard ball (usually 10 mm diameter) with a standard load into the specimen. A number is derived by measuring the indentation with a special microscope.

BRIQUETS – Coherent masses of uniform size made by the application of pressure to any powdery material placed in a suitable mould with or without a binder.

BRIQUETS – Compact cylindrical or other shaped blocks formed of finely divided materials by incorporation of a binder, by pressure, or both. Materials may be ferroalloys, metal borings or chips, silicon carbide etc.

BRITTLE METAL – A metal which exhibits only a very small change in dimensions before it fractures.

BRITTLENESS – The property of materials to not deform under load, but to break suddenly, for example, cast iron and glass are brittle. Brittleness is opposite to plasticity.

BROACH – A long tool with number of cutting teeth which is pushed or pulled through a hole or across a surface to form the desired shape and size.

BROACHING MACHINE – Machine designed to drive a tappered tool of special form, known as a broach, through a hole or over a piece of work, which bring the hole or the surface to the desired finished size.

BROACHING – Consecutive shearing of a hole or contour by a series of stepped cutting edges similar to a saw used in low acting presses for accurate sizing of holes or contours, such as gear teeth, and keyways.

BRONZE – A copper rich, copper tin, copper lead or copper beryllium alloy to which often alloying elements (phosphorous, aluminium, zinc, silicon) may be added. Usually bronze is a copper tin alloy containing 90% copper and 10% tin.

BRUSH – Pieces of carbon or copper that make a sliding contact against the commutator or slip rings.

BTDC – Before top dead center, also called BUDC-before upper dead center.

BUCKET ELEVATOR – Conveyor equipped with buckets which carry bulk material in the vertical or near vertical direction, loading is at the bottom and discharging is at the top.

BUCKET OR SKIP HOISTS – Hoisting equipment for handling of bulk materials in self dumping buckets or skips.

BUCKLE – Defect in a casting surface appearing as an indentation resulting from an expansion scab.

BUILDING BRICK – These are made from clay. Generally, the clay is mixed with water to a plastic state and extruded in a column that is wire-cut crosswise to the desired size. Occasionally the dry pressing process is used.

BULK COMMODITY TRUCK – Trucks used to transport loose bulk materials, such as sand and gravel.

BULK MODULUS OF ELASTICITY – Ratio of a uniform, triaxial (equal in all directions) tensile or compressive stress to the change in volume it produces.

BULL WHEEL – The large gear wheel of a planer which meshes with therack under the table and drives it. The large crank gear of a shaper is often called a bull wheel.

BULLDOZER – A pendant attachment mounted on crawler and wheel tractors, that strips off soil surface and transports it to the required spot.

BURN ON – Adhesion of sand to the casting, usually due to the metal penetrating into the sand.

BURN OUT – Usually refers to the removal of the disposable wax or plastic pattern in the investment moulding process by heating the mould gradually to a sufficiently high temperature to consume any carbonaceous residues.

BURNISHING – Bright, polished finish produced on the surface of a metal by rubbing it with another metallic harder surface, which smooths out small scratch marks.

BUSHING – A member that takes up space and usually allows movement at the attachment point. A one piece replaceable sleeve placed in a bore to serve as a bearing surface. Bearing for shaft, spring shackle, piston pin etc. A metallic or synthetic lining for a hole.

BUTANE – A hydrocarbon gas formed synthetically, by the action of zinc or ethyl iodide. Petroleum gas, that is liquid, when under pressure. Often used as engine fuel in trucks.

BUTANE – A hydrocarbon, flammable refrigerant used to a limited extent in small units.

BUTT JOINT – A joint between two members aligned approximately in the same plane.

BUTT RAMMAR – The flat end of the molders rammer.

BUTT-WELDING – Form of electrical resistance welding, the passage of current between the ends of the sections to be joined causing a rise in temperature sufficient to fuse the metal.

BUTTERFLY VALVE – A type of valve used for choke and throttle valve in a carburettor that is so named due to its resemblance to the insect of same name. This valve controls charge flow.

BYPASS FILTER – An oil filter that constantly only filters a portion of the oil flowing through the engine or machine.

BYPASS GOVERNING – Governing arrangement in which part of the steam that enters the turbine is bypassed depending upon the extent of load reduction.

Mechanical Glossary-A

ABOUTSLEDGE – The large hammer used by a blacksmith’s mate, turnabout with the smaller hammer of the blacksmith.

ABRASIVE – A natural or artificial material such as sand stone, emery, aluminium oxide or silicon carbide.

ABSOLUTE HUMIDITY – Actual quantity of water vapour in the air, usually expressed as so many grains of moisture in a cubic foot of air.

ABSOLUTE HUMIDITY – The weight of the water vapour which is associated with unit quantity of air.

ABSOLUTE MOTION – Motion of a body in relation to some other body which is at rest.

ABSOLUTE PRESSURE – Pressure measured from the true zero or point of no pressure.

ABSOLUTE TEMPERATURE SCALES – Used for calculating changes in refrigerant vapour pressures.

ABSOLUTE TEMPERATURE – The temperature of a substance measured above absolute zero.

ABSOLUTE VISCOSITY – Force per unit area required to move a surface at unit velocity, when it is separated by a fluid of unit thickness from a stationary surface.

ABSOLUTE ZERO TEMPERATURE – Temperature at which all molecular motion ceases, according to the kinetic theory of gases. A point which has been determined on the thermodynamic scale (by theoretical considerations) beyond which a further decrease in temperature is inconceivable. This is equal to – 459.6° on the fahrenheit scale and – 273.1° on the centigrade scale.

ABSORBER – A device for absorbing a refrigerant, a low side element in an absorption system.

ABSORPTION REFRIGERATION SYSTEM – One in which the refrigerant, as it is absorbed in another liquid, maintains the pressure difference needed for successful operation of the system.

ABSORPTION REFRIGERATOR – A plant in which ammonia is continuously evaporated from an aqueous solution under pressure, condensed, allowed to evaporate (so absorbing heat), and then reabsorbed.

ABSORPTIVITY – Ability of a material to absorb heat.

ACCELERATED FLOW – Type of flow that takes place in nozzles. The flow accelerates and pressure reduces.

ACCELERATING PUMP – A small cylinder and piston fitted to some types of SI engine carburettor, and connected to the throttle so as to provide a momentarily enriched mixture when the engine is accelerated.

ACCELERATION – Rate of change of velocity with respect to time, of a particle which is in motion. It is a vector quantity.

ACCELERATOR PUMP – In the carburettor, a small pump linked to the accelerator which momentarily injects a charge of fuel into the intake tract in addition to that supplied by the normal metering components, and thus enriches the mixture when the accelerator pedal is depressed.

ACCELERATOR – A pedal connected to the carburettor throttle valve of a motor vehicle, or to the fuel injection control where oil engines are used.

ACCELERATOR – Device for rapid control of speed, for quick opening and closing of the throttle. It is a foot or hand operated, spring returned, linked to the throttle valve in the carburettor. The minimum throttle opening is controlled by the setting of the throttle screw.

ACCELERATOR – Device for rapid control of the speed of an engine, for quick opening and closing of the throttle which regulates the quantity of air fuel mixture into the engine cylinder.

ACCUMULATOR – A device used for storing liquid under pressure (sometime used to smooth fluid flow).

ACCUMULATOR – A device used for storing liquid under pressure (sometimes used to smooth out pressure surges in a hydraulic system).

ACCUMULATOR – A steel shell partly filled with liquid refrigerant, the space above which is maintained by the compressor at a pressure corresponding to the required refrigerant temperature. The shell is placed in a suction line for separating liquid entrained in the suction gas.

ACCURATE – Without error within tolerances allowed, precise, correct, confirming exactly to standard.

ACHESON GRAPHITE – That made from coke in an electric furnance.

ACHME THREAD – A screw thread having an included angle of 29° and largely used for feed screws on machine tools.

ACICULAR STRUCTURE – A microstructure characterized by needle shaped constituents.

ACID – A chemical term to define a material which gives an acid reaction.

ACKERMAN PRINCIPLE – Steering geometry in which the outer ends of the steering arms are bend slightly inward so that when the vehicle is making a turn, inside wheel will turn more sharply than the outer wheel. This principle produces toe out on turns.

ACKERMAN STEERING – Arrangement whereby a line extended from the track arms, when the wheels are set straight ahead, should meet on the chassis centre line at 2/3 of the wheel base from the front, allowing inner stub axle to move through a greater angle than the outer.

ACME THREAD GAUGE – A gauge used for checking and testing the 29° angle and the width at the end of a thread cutting tool while grinding it. It is also used for setting the tool square with the axis of the workpiece.

ACROLEIN – A warning agent having the formula CH2 CH CHO is often used with methyl chloride to call attention to the escape of refrigerant. The material has a compelling, pungent odour and causes irritation of the throat and eyes.

ACTIVATED AMMONIA – Desiccant which operates by adsorption of water molecules. A form of aluminium oxide AlO2·

ACTIVATED CARBON – A highly absorbent form of carbon used to remove odors and toxic substances from gaseous emissions or to remove dissolved organic matter from waste water.

ACTUATOR – A device which uses fluid power to produce mechanical force and motion.

ACTUATORS – Secondary control mechanisms which function in response to the requirements of the primary group in actually controlling some part of the refrigeration system.

ACUTE ANGLE – An angle which is less than a right angle, 90°.

ADDENDUM – The portion of the tooth of a gear that extends from the pitch line to the outside.

ADDENDUM – The radial distance from the pitch circle to the top of the tooth.

ADDITIVE – A substance added to fuel, or oil or grease which improves the properties of the same.

ADDITIVES – Chemical compounds used to alter the characteristics of lubricating oils.

ADDITIVES – Chemicals added to oil or fuel to increase its effectiveness and obtain desirable qualities.

ADHESIVES – Materials or compositions that enable two surfaces to join together. An adhesive is not necessarily a glue, which is considered to be a sticky substance, since many adhesives are not sticky.

ADIABATIC COMPRESSION – Compression of a vapour or gas in such circumstances that there is insufficient time for any substantial exchange of heat between it and its surroundings.

ADIABATIC COMPRESSION – Compression of air without receiving or giving up heat.

ADIABATIC COOLING – Method in which paramagnetic salts are precooled, and then demagnetized, thereby producing further cooling.

ADIABATIC EXPANSION or COMPRESSION – Expansion or compression where the temperature rises during compression and falls during expansion without any loss of heat to the cylinder walls or absorption of heat from the walls.

ADIABATIC FLAME TEMPERATURE – The maximum possible temperature attained by the products of reaction, when the reaction goes to completion and all the heat released is used to heat up the products.

ADIABATIC HEAT DROP – The heat energy released and theoretically capable of transformation into mechanical work during the adiabatic expansion of unit weight of steam or other vapour or gas.

ADIABATIC PROCESS – Thermodynamic process in which no heat is transferred to or from the system during the process. A reversible adiabatic process is called ISENTROPIC PROCESS.

ADIABATIC SYSTEM – is the system which is insulated from its surroundings. In this system no heat transfer takes place i.e., either into the system or out of the system. It can however exchange work with the surroundings.

ADJUSTABLE RAMP – A loading platform that is power operated or mechanically operated.

ADMISSION – The point in the working cycles of a steam or IC engine at which the inlet valve allows entry of the working fluid into the cylinder.

ADVANCE (injection timing) – To set the timing of the injection pump or injectors for an earlier injection.

ADVANCE – Setting the ignition timing so that spark occurs before the piston reaches top dead center.

AERATION TEST BURNER – Apparatus by which the combustion characteristics of commercial gases can be correlated and calibrated.

AERATION – A term generally employed with reference to air circulation or ventilation. In milk cooling, it refers to a method where the milk flow over refrigerated surfaces is exposed to the atmosphere.

AERATOR – A device for fluffing (or decreasing the density of ) and cooling the sand by the admixture of air.

AERODYNAMIC DRAG – is the air resistance to the motion of the vehicle. This consists of profile drag, induced drag, skin friction drag, interference drag, and cooling and ventilation drag.

AERODYNAMIC LIFT – is the vertical component of the resultant force caused by the pressure distribution on the vehicle body.

AEROSOL – A particle of solid or liquid matter that can remain suspended in the air because of its small size. Particulates under 1 micron in diameter are called aerosols.

AFTER BOIL – Boiling of the fuel in the carburettor or coolant in the engine immediately after the engine is stopped.

AFTER BURNER – In an automobile engine, a type of exhaust manifold that burns the hydrocarbon and carbon monoxide remaining in the exhaust gas.

AFTER BURNING – In an internal combustion engine, the persistence of the combustion process beyond the period proper to the working cycle, i.e., into the expansion period.

AFTER BURNING – The burning of fuel that is left in the combustion space when the fuel injection stops.

AFTER COOLER – A device used on the turbocharged engines to cool the air which has undergone compression.

AFTER COOLER – A device used on turbocharged engines to cool air which has undergone compression.

AFTER COOLER – A device used on turbocharged engines to cool the air which has undergone compression, before its entry into the engine cylinder.

AFTER COOLER – A type of surface heat exchanger in which compressed air is cooled after compression.

AGE HARDENING – Change in the physical properties, e.g., hardness and strength, that occurs in certain light metals after heat treatment.

AGGREGATE – Small particles such as powders that are used for powder metallurgy, that are loosely combined to form a whole, also sand and rock as used in concrete.

AGING OF A PERMANENT MAGNET – It is the process of normal or accelerated change, under continued normal or specified artificial conditions, in the strength of the magnetic field maintained.

AGING – The process of holding metals at room temperature or at a predetermined temperature for the purpose of increasing their hardness or strength by precipitation. Aging is also used to increase dimensional stability in metals such as castings.

AIR ASPIRATOR SYSTEM – An air injection system using a valve opened and closed by pulses in the exhaust system.

AIR BLEED – An opening into a gasoline passage through which air can pass or bleed into the gasoline as it moves through the passage, to weaken the air fuel mixture.

AIR BLEEDER – A device used to remove air from a hydraulic system. Types include a needle valve, capillary tubing to the reservoir, and a bleed plug.

AIR BRAKE – A braking system which uses compressed air to supply the effort required to apply brakes.

AIR CELL – A small auxiliary combustion chamber used in certain types of compression ignition engines, for promoting turbulence and improving combustion.

AIR CIRCULATION – A method for natural or forced motion of air.

AIR CLEANER – A device mounted on the intake manifold for filtering out unwanted solid impurities such as dirt and dust from air that is being drawn into the engine cylinder through the inlet manifold.

AIR COMPRESSOR – A device used to increase air pressure.

AIR COMPRESSOR – A machine (driven by any prime mover), which compresses air into a receiver to be used at a greater or shorter distance.

AIR CONDITIONER – A device used to control the temperature, humidity, cleanliness and movement of air inside a room or a car.

AIR CONDITIONING UNIT – Equipment designed as a specific air treating combination, consisting of means for ventilation, air circulation, air cleaning and heat transfer with control means for maintaining temperature and humidity within prescribed limits.

AIR CONDITIONING – The simultaneous control of all, or at least the first three of the following factors affecting the physical and chemical conditions of the atmosphere within a structure: Temperature, humidity, motion, distribution, dust, bacteria, or lesser degree human health or comfort.

AIR COOLED COMPRESSOR – A compressor whose cylinder has cast integral numerous thin fins to form excess cooling surface exposed to a draught of cool air which forms the medium to carry off some of the heat of compression.

AIR COOLED CONDENSERS – Condenser used to cool the refrigerant, the cooling effect depends on air drawn through tubes and fins for a good distribution of air.

AIR COOLED ENGINE – An engine that is cooled by passage of air around the cylinder, not by passage of a liquid through water jackets.

AIR COOLED ENGINE – An engine that is cooled by the passage of air around the cylinders, not by passage of a liquid through water jackets.

AIR COOLER – The cold accumulator used in the Linde process of air liquefaction for the preliminary cooling of the air.

AIR DUCTS – Pipes or channels through which air is distributed throughout building or machinery for heating and ventilation.

AIR ENGINE – A very small reciprocating engine driven by compressed air.

AIR EXHAUSTER – A suction fan, a vacuum pump.

AIR FUEL MIXTURE – Air and fuel travelling to the combustion chamber after being mixed by the carburettor.

AIR FUEL MIXTURE – Finely atomized mist of fuel and air necessary for combustion. This mixture consists of approximately 15 parts air to one part fuel (15 : 1) at cruising speed.

AIR FUEL RATIO – At full load operation, the air fuel ratio is at least 35 to 50 per cent greater than the stoichiometric value. Air fuel ratio in a normal diesel engine varies from around 100 : 1 at idle speed to about 30 : 1 at full load.

AIR FUEL RATIO – Ratio (by weight) between air and fuel that makes up engine fuel mixture.

AIR FUEL RATIO – The proportion of air to fuel in the working charge of an internal combustion engine, or in other combustible mixtures, expressed by weight for liquid fuels and by volume for gaseous fuels.

AIR GATE – A vertical channel for the removal of gases from the mould; checking of the filling of the mould cavity with metal and feeding up the casting with metal during solidification.

AIR HAMMER – Power hammer, used for roughening out heavy forgings in foundry work.

AIR HOLE – Hole in a casting caused by air or gas trapped in the metal during solidification.

AIR HORN – In the carburettor, the tubular passage through which the incoming air must pass.

AIR INFILTRATION – The inleakage of air through cracks and crevices and through doors, windows or other openings, caused by wind pressure or temperature difference.

AIR INJECTION SYSTEM – A system which injects air into the exhaust manifold or thermal reactor so that the combustion of the carbon monoxide and unburned hydrocarbons in the exhaust can be completed.

AIR INJECTION SYSTEM – The system which injects the required quantity of fuel into the combustion space with the aid of compressed air.

AIR JET – A small jet in the air passage of a carburettor. This jet meters the amount of air fed to the diffuser in an air bleed type carburettor.

AIR LIQUEFIER – A type of gas refrigerating machine based on the STIRLING CYCLE, the cycle of the hot air engine.

AIR MASS METERING – In some fuel injection systems, fuel metering is controlled primarily by engine speed and the amount of air actually entering the engine.

AIR METER – An apparatus used to measure the rate of flow of air or gas.

AIR POLLUTION – Contamination of earths atmosphere by various natural and man made pollutants such as smoke, gases, dust etc.

AIR PREHEATER – A device that makes the final heat recovery from boiler flue gases and uses the same to preheat the incoming furnace air for its reaction with fuel.

AIR PUMP – A reciprocating or centrifugal pump used to remove air, and sometimes the condensate, from the condenser of a steam plant.

AIR RATE – Kilograms per second of airflow required per net horse power developed. Also called FLOWRATE.

AIR RECEIVER – A vessel into which compressed air is discharged, to be stored until required.

AIR RESISTANCE – The motion of an automobile is associated with the displacement of air particles, which requires some power of the engine. Air resistance depends on the size and shape of the vehicle body, speed of the vehicle and wind velocity.

AIR SPRING – Container and plunger are separated by air under pressure. When container and plunger attempt to squeeze together, air compresses and produces a spring effect. Air spring has been used in some suspension systems.

AIR STANDARD CYCLE – A standard cycle of reference by which the performance of the different internal combustion engines may be compared, and their relative efficiencies calculated.

AIR STANDARD EFFICIENCY – The thermal efficiency of an internal combustion engine working on the appropriate air standard cycle.

AIR STARTING VALVE – A valve which admits compressed air to the air starter for starting purposes.

AIR VENT – Arrangement that helps to remove air from the fuel injection system.

AIR WASHER – An enclosure in which air is forced through a spray of water in order to cleanse, humidify or dehumidify the air.

AIR – A gas consisting of mechanical mixture of 23.2% (by weight) of oxygen 75.5% nitrogen and 1.3% argon, 21 % (by volume) of oxygen, 78.06% nitrogen and 0.94% argon.

AIR – A gas consisting principally of a mechanical mixture of 23.2 per cent (by weight) of oxygen, 65.5 per cent of nitrogen and 1.3 per cent of argon.

AIRFOIL DRAG FORCE – Force acting on the airfoil in the direction of motion, represents frictional forces.

AIRFOIL LIFT FORCE – Force acting on the airfoil in the direction perpendicular to the direction of motion. Basic force causing the aeroplane to maintain its lift.

AIRFOIL – A streamlined form bounded principally by two flattened curves and whose length and width are very large in comparison with thickness. The airfoil may be a symmetrical airfoil or a non-symmetrical airfoil.

AIRFOIL – Device, similar to a stubby wing.

AIRGAP (spark plug) – Distance between centre and side electrodes, in a spark plug. Spark jumps across this gap.

AIRLESS BLAST CLEANING – A process whereby the abrasive material is applied to the object being cleaned by centrifugal force generated by a rotating vane type wheel.

AIRLESS INJECTION – Injection of liquid fuel into the cylinder of an oil engine by a high pressure fuel pump, so dispensing with the compressed air necessary in the early diesel engines. Also called SOLID INJECTION or MECHANICAL INJECTION.

AKROYD ENGINE – The first compression ignition engine, patented by Akroyd Staurt in 1890.

ALCOHOL – Volatile liquid fuel consisting wholly or partly, of alcohol, able to withstand high compression ratios without detonation.

ALFOL – Technical name for thin corrugated aluminium foil in narrow strips, used for heat insulation, for which it is effective by reason of the numerous small air cells formed when packed.

ALIGN – To bring two or more components of a unit into correct positions with respect to one another.

ALL WEATHER TYRE – A tyre designed to provide good traction on dry, wet and dirt and snow covered roadways.

ALLAN VALVE – A steam engine slide valve, in which a supplementary passage increases the steam supply to the port during admission to reduce wire drawing.

ALLOTROPIC METALS – Metals which exist in one lattice form over a range of temperature, but at a certain temperature the lattice form changes to another type which is stable over another temperature range.

ALLOTROPY – Ability of a material to exist in several crystalline forms.

ALLOWANCE – The intentional or desired difference between the maximum limits of mating parts to provide a certain class of fit.

ALLOY STEEL – Steel containing significant quantities of alloying elements (other than carbon and the commonly accepted amounts of manganese, silicon, sulphur and phosphorus) added to effect changes in mechanical and physical properties.

ALLOY – A substance having metallic properties and is composed of two or more chemical elements, of which at least one is a metal.

ALLOYING ELEMENTS – Elements either metallic or non-metallic added intentionally to the base metal, to make a marked change in the properties of the base metal and to secure certain desirable properties.

ALLOYING OF METAL – The addition of varying proportions of other elements to a basic metal in order to produce an alloy having specific properties.

ALNICOS – Alnicos materials are composed mainly of aluminium, nickel, cobalt and iron. Some include additions of copper and titanium. They are high-coercive force, high magnetic energy alloys.

ALOXITE – Artificial abrasive material used in the manufacture of grinding wheels. Essentially it consists of alumina, or aluminium oxide, the chemical symbol for which is Al2O3·

ALPHA IRON – The body centered cubic form of pure iron, stable below 1025°C.

ALTERNATOR – A electrical generator that produces alternating current (flow of current is considered to change in direction with each half cycle).

ALUMEL – A nickel base alloy containing about 2.5% Mn, 2% AI, and 1 % Si, used chiefly as a component of pyrometric thermocouples.

ALUMINIUM ALLOY – Aluminium which is alloyed with other metals to give it strength and desirable properties.

ALUMINIUM BRONZE – Alloy containing 90% copper and 10% aluminium, extensively used for diecasting.

ALUMINIUM CYLINDER BLOCK – An engine cylinder block cast from aluminium or aluminium alloy, and which usually has cast iron sleeves installed for use as cylinder bores.

ALUMINIUM – Grayish white metal, very light in weight, and having in its pure form low mechanical strength, frequently alloyed with other elements to improve its physical characteristics.

AMBIENT SENSOR – A temperature sensor that provides an outside air temperature signal for an automatic temperature control type air conditioning system.

AMBIENT TEMPERATURE – In a domestic or commercial system having an air cooled condenser, it is the temperature of the air entering this condenser.

AMBIENT TEMPERATURE – Temperature (usually of the air) surrounding the operating equipment.

AMMONIA MACHINE – An abbreviation for a compression refrigerating machine using ammonia as a refrigerant. Similarly, freon, sulphur dioxide machine etc.

AMMONIA-NH3 – One of the earliest compounds used as a refrigerant.

AMORPHOUS – Non-crystalline, a random orientation of the atomic structure.

ANALYSER – Device used in the high side of an absorption system for increasing the concentration of vapour entering rectifier or condenser.

ANEMOMETER – An instrument for measuring the velocity of flow of a gas, either by mechanical or electrical methods.

ANGLE CUTTER – Type of milling cutter used for single or double angles. The term angle cutter covers three types of milling cutters, the single or half-angle, the double angle and the equal or combined angle.

ANGLE OF ADVANCE – The angle in excess of 90 degree by which the eccentric throw of a steam engine valve gear is in advance of the crank.

ANGLE OF ATTACK – The angle of inclination of the non-symmetrical airfoil with the direction of the undisturbed flow.

ANGLE OF DEVIATION – The difference between the fluid angle at outlet and the blade angle at outlet. This may be positive or negative. Sometimes called DEVIATION.

ANGLE OF INCDIENCE – The difference between the fluid angle at inlet and the blade angle at inlet. This may be positive or negative. Sometimes called INCIDENCE.

ANGLE OF REPOSE – The minimum inclination which a plane can have consistent with the body on it sliding down the plane by the force of gravity. It is the same as the friction angle.

ANGLE OF THREAD – The included angle between the sides forming the groove of the screw thread.

ANGLE PLATE – Right angled metal plate used to secure parts during machining or when taking measurements.

ANGLE PLATES – Some work has to be set at a particular angle to the surface of the table, and this is often effected by bolting it to an adjustable angle plate.

ANGLE – The amount of opening or divergence between two straight lines that meet at a vertex or that intersect each other.

ANGULAR ACCELERATION – The time rate of change of angular velocity.

ANGULAR VELOCITY OF PRECISION – The rate of change in the direction of the plane of rotation of a rotating disc.

ANGULAR VELOCITY – The time rate of change of angular displacement of a point rotating about a fixed axis (expressed in radians per unit time) Angular velocity of a machine part is often expressed in revolutions per minute (RPM) and is denoted by n.

ANILINE POINT – The lowest temperature at which an oil is completely miscible with an equal volume of aniline.

ANISTROPY – A material that has specific physical properties in different directions. Rolled steel is strongest in the direction of rolling.

ANNEALING – A heat treatment in which metals are heated and then cooled very slowly for the purpose of decreasing hardness. Annealing is used to improve machinability and to remove stresses from weldments, forgings and castings. Also used to remove stresses resulting from cold working and to refine and make uniform the microscopic internal structures of metals.

ANNULAR TYPE COMBUSTION CHAMBER – The combustion chamber which is made up of four concentric surfaces surrounding the axis of the rotor, forming three chambers on either side of the rotor, the middle casing acts as a flame tube and the inner and outer casings act as air casings, with a series of burners at the front end.

ANNULUS – A figure bounded by concentric circles or cylinders (e.g., a washer, ring, sleeve etc.).

ANODIC TREATMENT – Formation of a protective layer of oxide on the surface of aluminium and its alloys by electrolytic action, in order to resist corrosion.

ANODIZING – To subject a metal to electrolytic action, as takes place at the anode of a cell, in order to coat it with a protective or decorative film, used for nonferrous metals.

ANTECHAMBER – A small auxiliary combustion chamber, used in some compression ignition engines, in which partial combustion of fuel takes place and this is used to force the burning mixture into the cylinder, so promoting more perfect combustion.

ANTHRACITE COALS – Slow burning coals which yield very little ash, moisture and less than 10 per cent volatiles, generally used in closed stoves.

ANTI CORROSION ADDITIVES – Chemical compounds added to lubricating oil to reduce or prevent the chemical reaction of acids (formed by the oxidation of oil) which destroy some bearing materials, such as lead in lead copper bearings, used for crankshafts and connecting rods of engines.

ANTI DAZZLE MIRROR – One having a photoeltric control circuit which changes it from a fully reflecting condition to partial reflection from a glass air interface when actuated by the head lamp beam of a following vehicle.

ANTI DIVE SYSTEM – A system installed with some brakes that uses front fork damping and the front brake assembly to prevent excessive fork compression and to improve handling when brakes are applied.

ANTI ICING SYSTEM – A carburettor unit designed to prevent formation of ice on a surface or in a passage.

ANTI OXIDATION ADDITIVES – Chemical compounds added to decrease oxidation of the oil. These have a greater affinity for oxygen than does the oil.

ANTI SIPHON SYSTEM – Use of a small passage designed into a carburettor to prevent fuel from siphoning from the float bowl into the engine.

ANTI-INCRUSTATOR – A substance used to prevent the formation of scale on the internal surfaces of steam boilers.

ANTIBACKFIRE VALVE – Valve used in air injection reaction cexhaust emission control system to prevent backfiring during the period immediately following sudden decleration.

ANTIFREEZE LIQUID – A substance added to the refrigerant to prevent formation of ice crystals at the expansion valve.

ANTIFREEZE – A chemical added to the coolant in order to lower its freezing point.

ANTIFREEZE – A chemical, added to the coolant (usually ethylene glycol) to lower its freezing point and thereby prevent the coolant from freezing in cold weather.

ANTIFRICTION BEARINGS – Ball, roller and needle bearings exhibit very low friction and are suitable for very high speeds, and high loading.

ANTIKNOCK COMPOUND – An additive put into gasoline to suppress knocking or detonation e.g., Tetra ethyl lead.

ANTIKNOCK SUBSTANCES – Substances added to petrol to lessen its tendency to detonate, or knock in an engine, i.e., Tetra ethyl lead.

ANTIKNOCK VALUE – The relative immunity of a volatile liquid fuel from detonation, or knocking, in a petrol engine, as compared with some standard fuel.

ANTIKNOCK – In engine fuels, that property which opposes knocking i.e., autoignition.

ANTILOCK BRAKE SYSTEM (ABS) – If the brakes are applied so hard that the wheels tend to stop turning and thus a skid starts to develop, the antilock brake system comes into operation and partly releases the brakes. This makes the wheels continue to rotate. However, intermittent braking continues. But it is held below the point where the skid would start.

ANTIMIST PANEL – A panel fitted to the rear window enclosing a volume of still air between itself and the outer glass.

ANTIMONY – Brittle, bluish white metallic element designated Sb. Melting point 630°C. Used as a constituent in some alloys, for instance, bearings and storage battery plates.

ANTIPERCOLATOR – Device for venting vapours from main discharge tube or well of a carburettor.

ANTIPERCOLATOR – Device for venting vapours from main discharge tube, or well, of a carburettor.

ANTIPIPING (material) – Usually refers to an insulating material placed on the top of a sprue or riser that keeps the metal in liquid or semiliquid form for a long period of time and minimizes the formation of the usual conical pipe or shrink in the top of a sprue or riser.

ANTIPRIMING PIPE – A pipe placed in the steam space of a boiler, so as to collect the steam while excluding entrained water.

ANTIROLL BAR – Torsion bar mounted transversely in the chassis in such a way so as to counteract the effect of opposite spring deflections.

ANVIL – Heavy block on which to hammer and shape metals.

API GRAVITY – Gravity expressed in units of standard American Petroleum Institute (hydrometer).

API GRAVITY – The American Petroleum Institute (API) has established the formula for calculating the specific gravity of a fuel or oil as Degree

API HEAVY DUTY TYPE OIL – Motor oil having oxidation stability, bearing corrosion preventive properties, and detergent-dispersant characteristics necessary to make it generally suitable for use in both high speed diesel and gasoline engines under heavy duty service conditions.

API PREMIUM TYPE OIL – Motor oil having the oxidation stability and bearing corrosion preventive properties necessary to make it generally suitable for use in internal combustion engines where operating conditions are more severe than regular duty.

API REGULAR TYPE OIL – Motor oil generally suitable for use in internal combustion engines under moderate operating conditions.

API= ((141.5/specific gravity at 60/60 degree F)–131.5). The symbol 60/60 degree F is interpreted as the ratio of the weight of a given volume of oil at 60 degree F to the weight of the same volume of water at 60 degree F.

APIEZON OILS – The residue of almost zero vapour pressure left by vacuum distillation of petroleum products.

APPLIED THERMODYNAMICS – Also called engineering thermodynamics deals with special applications such as energy transfer as power generation, refrigeration and, compression and expansion of gases and fluids.

APRON CONVEYOR – A conveyor for transporting packages or bulk materials, consisting of a series of metal or wood slats (also rubber, cotton, felt wire etc.) attached to an endless chain. Also called SLAT CONVEYOR.

APRON – The function of a lathe apron is to carry the mechanism for sliding and surfacing motions and screw cutting.

ARBOR PRESS – A hand operated machine capable of applying high pressure for the purpose of pressing parts together or removing parts.

ARBOR – A metal barrel, frame, or plate to support or carry part of a mould or core.

ARC CUTTING – Process which melts the metals to cut with the heat of an arc between an electrode and the base metal.

ARC EYE – A burn on the exterior surface of the operators eye, due to its exposure to an open arc. Also called FLASH EYE.

ARC GAP – Distance between the tips of two electrodes, normally between an electrode and the workpiece. Also known as ARC LENGTH.

ARC OF CONTACT – The arc traced out along the pitch circle while one pair of teeth of gear wheels is in contact (divided into arc of approach and arc of recess).

ARC PLASMA – A gas that has been heated to an at least partially ionized condition, enabling it to conduct an electric current.

ARC SPOT WELD – Spot welding made by an arc welding process.

ARC WELDING – A group of welding processes which produces coalescence of metals by heating them with an arc, with or without the application of pressure, and with or without the use of filler metal.

ARC WELDING – Method of welding or uniting two metallic pieces in which the metal is melted by the heat of an electric arc.

ARC – A circular section of the circumference of a circle bounded by two equal radii.

ARC – A sustained electric discharge, where current flows through the gap between two electrodes.

ARCH – The curve of a leaf spring. If the centre is lower than the ends, it is called positive arch, if the centre is higher than the ends, it is called negative arch.

ARCING (brakes) – Grinding new brake linings to the same diameter (arc) as that of the brake drum surface.

ARDOMETER – A type of total radiation pyrometer.

ARGON – An inert gas used in certain welding and heat treatment processes.

ARRESTING GEAR – Means of sustaining the load which do not interfere with the hoisting gear but prevent it from coming down due to gravity e.g., ratchet and pawl arrangements and friction type.

ARSENIC – A brittle, grayish metallic element designated As. Melting point 814°C. Used as a constituent in some alloys, and in the manufacture of lead shot.

ARTICULATED CONNECTING ROD – The auxiliary connecting rods of a radial engine, which work on pins carried by the master rod instead of on the main crankpin. Also called LINK RODS.

ASBESTOS – A fibrous organic mineral that is non-combustible, non-conducting and acid resistant.

ASH AND SLAG – Impurities that do not burn and usually troublesome elements in coal fired boilers.

ASH FREE BASIS – When fuels are delivered on an ash free basis, it means that the percentage of the ash has been deducted and the other constituents have their percentages recalculated on 100 per cent total without the ash.

ASH – An inorganic non-combustible residue obtained by combustion of an oil or fuel in the presence of air.

ASPECT RATIO OF BLADE – Ratio of blade height to blade chord.

ASPECT RATIO – The ratio of the width to the length. On tyres, it is the fully inflated height divided by the cross section.

ASSEMBLY – A unit that contains the parts that make up a mechanism or a machine.

ATDC – After TDC, After top dead centre.

ATKINSON CYCLE – A working cycle for internal combustion engines, in which the expansion ratio exceeds the compression ratio, more efficient than the Otto Cycle, but mechanically impracticable.

ATMOSPHERIC CONDENSER – A condenser operated with water which is exposed to the atmosphere.

ATMOSPHERIC ENGINE – An early form of steam engine in which a partial vacuum created by steam condensation allowed atmospheric pressure to drive down the piston.

ATMOSPHERIC GAS BURNER SYSTEM – A natural draught burner injector, in which the momentum of a gas stream projected from an orifice into the injector throat inspirates from the atmosphere a part of the air required for combustion.

ATMOSPHERIC LINE – A datum line drawn on an indicator diagram by allowing atmospheric pressure to act on the indicator piston or diaphragm.

ATMOSPHERIC PRESSURE – Force exerted by the weight of the atmosphere on every point with which it is in contact. It is generally taken as 1.03 kscm at sea level.

ATMOSPHERIC PRESSURE – The force exerted by the weight of the atmosphere on every point with which it is in contact.

ATMOSPHERIC RISER – Blind riser which employs atmospheric pressure to aid feeding.

ATOM – The smallest particle of an element.

ATOMIC HYDROGEN WELDING – An arc welding process which produces coalescence of metals by heating them with an electric arc maintained between electrodes in an atmosphere of hydrogen. Shielding is provided by hydrogen.

ATOMIC HYDROGEN WELDING – Welding of metallic pieces in which heat is liberated by hydrogen atoms when combining into molecules, is used to fuse the metal.

ATOMIZATION – The breaking up of fuel jet into fine particles as it is sprayed into the combustion chamber.

ATOMIZATION – The spraying of a liquid through a nozzle so that the liquid is broken into a very fine mist.

ATOMIZED – Tiny particles of fuel mixed with air, making a fine mist.

ATOMIZER – A device which disperses liquid fuel into fine particles (pulverized spray).

ATOMIZER – A nozzle through which oil fuel is sprayed into the combustion chamber of an oil engine or boiler furnace. It breaks up the fuel into a fine mist so as to ensure good dispersion and combustion.

AUSTEMPERING – A heat treating process consisting of quenching a ferrous alloy at a temperature above the transformation range in a medium such as molten lead, the temperature of the quenching medium is maintained below that of pearlite and above that of martensite formation to produce a tough, hard microstructure.

AUSTENITE – A solid solution of cementite or iron carbide, Fe3C in iron.

AUSTENITE – A solid solution of iron and carbon and sometimes other elements in which gamma iron, characterized by a face centered crystal structure, is the solvent. This is stable only within a particular range of composition and temperature, and is non-magnetic.

AUSTENITIC CAST IRON – Cast iron containing such a proportion of alloying constituents (nickel, chromium, copper or manganese) that the structure in the cast state is completely austenitic at ordinary temperatures.

AUSTENITIZING – The process of forming austenite ( a solid solution of iron and carbon and sometimes other elements ).

AUTOGENOUS WELD – A fusion weld made without the addition of filler metal.

AUTOIGNITION – The self-ignition or spontaneous combustion of a fuel when introduced into the heated charge in the cylinder of a compression ignition engine.

AUTOMATIC ARC WELDING – Method of arc welding in which the arc moves along the joint to be welded, feeds the electrodes to the arc, and governs the arc length, by automatic means.

AUTOMATIC CHOKE – A carburettor choke device (valve) that automatically positions itself in accordance with carburettor needs or engine temperature.

AUTOMATIC CHOKE – A carburettor choke device (valve) that automatically positions itself in accordance with the carburettor needs or engine temperature.

AUTOMATIC EXPANSION VALVE – A pressure actuated device which regulates the flow of refrigerant from the liquid line into the evaporator to maintain a constant evporator pressure.

AUTOMATIC FEED WATER REGULATOR – Device that regulates feedwater supply to the boiler according to load, and so does away with hand operation of valves on feed lines. It is controlled by temperature, its action depends upon expansion and contraction of some metal part.

AUTOMATIC GRAB – A crane grab in which the grasping and releasing of the load are effected without manual assistance.

AUTOMATIC INJECTOR – One that is self starting after its operation has been stopped by the interruption of its water supply.

AUTOMATIC LATHE – Specialized development from capstan and turret lathes, with a full automatic cycle of turning, boring and drilling of the workpiece, the function of the operator consists of loading or taking finished work from the machine.

AUTOMATIC LEVEL CONTROL – A suspension system which compensates for variations in load in the rear of the car, positioning the rear at a predesigned level regardless of load.

AUTOMATIC OXYGEN CUTTING – Cutting with an equipment without constant observation and adjustment of the controls by an operator.

AUTOMATIC REFRIGERATION SYSTEM – One which regulates itself to maintain a definite set of conditions by means of automatic controls and valves usually responsive to temperature or pressure.

AUTOMATIC SCREW MACHINE – Fully automatic single spindle or multiple spindle bar stock turret lathe.

AUTOMATIC TRANSMISSION – A power transmission system for road vehicles, in which the approximately optimum engine speed is maintained through mechanical or hydraulic speed changing devices which are automatically selected and operated by reference to the road speed of the vehicle.

AUTOMATIC TRANSMISSION – A transmission not using a manually operated clutch.

AUTOMATIC WELDING MACHINE – Machine designed to carryout high speed electric arc or resistance welding in mass production processes, combining rapid production with accurate control of temperature.

AUTOMATIC WELDING – Welding which permits the operation without adjustment of controls by an operator.

AUTOMOBILE – is a self propelled vehicle. The power required to propel the vehicle is supplied by the engine (also called prime mover). Scooters, motor cycles, cars, buses, trucks etc., are different types of automotive vehicles.

AUTOVAC – A vacuum operated mechanism for raising fuel from a tank situated below the level of the carbutettor to a position from which it may be fed to the latter by gravity.

AVAGADRO’S LAW – Equal volumes of different gases at the same temperature and pressure contain the same number of molecules.

AVAILABLE ENERGY – That portion of a quantity of heat which could be transformed into work by means of a reversible engine.

AXIAL COMPRESSOR – A multistage, high efficiency compressor comprising alternate rows of moving and fixed blades attached to a rotor and its casing respectively. The flow of fluid is essentially parallel to the axis of the compressor.

AXIAL DISCHARGE TURBINE – A steam turbine in which the absolute velocity of steam flow at exit is a minimum i.e., the steam discharges in the axial direction.

AXIAL FLOW COMPRESSOR – A type of compressor in which the fluid flow is almost parallel to the axis of the compressor and the flow is decelerating or diffusing and pressure rises are obtained by causing the fluid to pass through a number of expanding spaces with consequent reduction in velocity.

AXIAL FLOW TURBINE – Steam turbine in which the general direction of steam flow has been roughly parallel to the turbine axis.

AXIS – The line real or imaginary, which passes through the center of a body and about which the body would rotate if set revolving.

AXLE (full floating) – Axle used to drive rear wheels. It does not hold the wheels on nor support them.

AXLE (semiquarter or one quarter floating) – Axle used to drive wheels, hold them on and support them.

AXLE FLANGE – A flat surface on the outboard end of the axle shaft to allow wheel attachment.

AXLE GEAR – A gear in the differential carrier that drives the driving wheels.

AXLE RATIO – Relationship or ratio between the number of times the propeller shaft or drive shaft must revolve to turn the axle shafts one turn.

AXLE SHAFT – The shaft used to transmit power from the differential to the wheels.

AXLE THREE QUARTER FLOATING – Axle used to drive rear wheels as well as hold them on and support them.

AXLE – A cross bar supporting a vehicle on which one or more wheels turn.

AXLE – A shaft used to support a part or parts across the frame or forks. e.g., front and rear axles.

Mechanical Placement Questions

1.          What is the difference between Critical Speed and Whirling Speed?

Ans.     In Solid mechanics, in the field of rotor dynamics, the critical speed is the theoretical angular velocity which excites the natural frequency of a rotating object, such as a shaft, propeller or gear. As the speed of rotation approaches the objects natural frequency, the object begins to resonate which dramatically increases system vibration. The resulting resonance occurs regardless of orientation.Whirling Speed is due to the unbalanced forces acting on a rotating shaft.


2.          How a Diesel Engine Works as Generator?

Ans.     Diesel engine is a prime mover, for a generator, pump,and for vehicles etc. generator is connected to engine by shaft. mostly in thermal power plat ,there is an engine is used to drive generator to generate power.


3.          Explain Second Law of Thermodynamics?

Ans.     The entropy of the universe increases over time and moves towards a maximum value.


4.          Compare Brayton Cycle and Otto Cycle?

Ans.     The heat addition and rejection processes in Otto cycle are of constant volume, whereas in Brayton cycle, they are of constant pressure.

-Otto cycle is the ideal cycle for spark ignition engines.
-Brayton cycle is the ideal cycle for gas power turbines.


5.          What is the purpose of Scrapper Ring?

Ans.     scrap the excess lube oil from the cylinder walls. there by preventing oil from entering combustion zone.


6.          What is DTSI Technology?

Ans.     DTSI stands for Digital Twin Spark Plug Ignition. The vehicles with DTSI Technology use 2 spark plugs which are controlled by digital circuit. It results in efficient combustion of air fuel mixture.

  • Digital – Since the spark generation will be initiated by a microchip.
  • Twin Since two spark plugs will be used.
  • Spark ignition – Since the ignition will be done via a spark.


7.          How to Find, Ductile-Brittle Transition Temperature in Metals?

Ans.     The point at which the fracture energy passes below a pre-determined point for a standard Impact tests. DBTT is important since, once a material is cooled below the DBTT, it has a much greater tendency to shatter on impact instead of bending or deforming.


8.          What is the importance of Thermodynamics?

Ans.     All the mechanical engineering systems are studied with the help of thermodynamics. Hence it is very important for the mechanical engineers.


9.          What is the difference between P11 and P12 Pipes?

Ans.     P11 the chromium molybdenum composition that is 1% ofchromium and 1/4% of molybdenum

P12 the chromium molybdenum composition that is 1% ofchromium and 2% of molybdenum


10.         State difference between AnitiFriction Bearing and Journal Bearing?

Ans.     Generally, journal bearings have higher friction force, consume higher energy and release more heat, but they have larger contact surface, so normally used in low speed high load applications. In anti friction bearings friction is less.  One object just rolls over each other.

Steam Engine By Watt

Steam Engine by Watt

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Herons Steam Ball

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Mechanical Job Interview Question

1.          What is the difference between Technology and Engineering?

Ans.    Engineering is application of science. Technology shows various methods of Engineering. A bridge can be made by using beams to bear the load,by an arc or by hanging in a cable; all shows different technology but comes under civil engineering and science applied is laws of force/load distribution.


2.          How to Measure Temperature in Wet Bulb Thermometer?

Ans.      Wet bulb temperature is measured in a wet bulb thermometer by covering the bulb with a wick and wetting it with water. It corresponds to the dew point temperature and relative humidity.


3.          What are the Advantages and Disadvantages of using LPG in Car?

Ans.    Advantages

1. Complete combustion

2. Fuel saving

3. Homogenous combustion


1. As complete combustion is occurring ,more heat liberated,not advised for long journey, engine will be over heated

2. Installation is difficult

3.  Reduce engine life efficiency


4.         What is the difference between Speed and Economic Speed?

Ans.     The rated speed tells us about the maximum speed which can be achieved by a vehicle or some other machine but the economical speed means the speed limit at which the machine works efficiently with least consumption of normal bikes(not racing),the max.speed limit shown on speedometer is upto 120 kmph but companies always advice their customers to drive such bikes at around 60 kmph to have maximum mileage.


5.         What is Powder Technology?

Ans.    Powder technology is one of the ways of making bearing material. In this method metals like bronze, Al, Fe are mixed and compressed to make an alloy.


6.         State all the laws of Thermodynamics?

Ans.    There are three laws of the thermodynamics.

First Law: Energy can be neither created nor destroyed. It can only change forms. In any process in an isolated system, the total energy remains the same.

Second Law: When two isolated systems in separate but nearby regions of space, each in thermodynamic equilibrium in itself, but not in equilibrium with each other at first, are at some time allowed to interact, breaking the isolation that separates the two systems, and they exchange matter or energy, they will eventually reach a mutual thermodynamic equilibrium. The sum of the entropies of the initial, isolated systems is less than or equal to the entropy of the final exchanging systems. In the process of reaching a new thermodynamic equilibrium, entropy has increased, or at least has not decreased.

Third Law: As temperature approaches absolute zero, the entropy of a system approaches a minimum.


7.         State the difference between Unilateral and Bilateral Tolerance?

Ans.    A unilateral tolerance is tolerance in which variation is permitted only in one direction from the specified direction.e.g. 1800 +0.000/-0.060

Bilateral tolerance is tolerance in which variation is permitted in both direction from the specified direction.e.g. 1800 +0.060/-0.060


8.         What is the abbreviation of welding rod 7018?

Ans.    7018 =

70=tensile strength 70000psi

1= welding position

8=current flux


9.         What is difference between Welding and Brazing?

Ans.    In Welding concentrated heat (high temperature) is applied at the joint of metal and fuse together.

In Brazing involves significantly lower temperatures and does not entail the melting of base metals. Instead, a filler metal is melted and forced to flow into the joint through capillary action.


10.         Which has more Efficiency Diesel Engine or Petrol Engine?

Ans.     Diesel engine has the better efficiency out of two.

Mechanical Placement Interview Question

1.          What is Sentinel Relief Valve?

Ans.     It’s a special type valve system. The valve will open when exhaust casing pressure is excessive (high). The valve warns the operator only; it is not intended to relieve the casing pressure.


2.          What is the difference between Specification,Codes, Standards?

Ans.     Specification is describing properties of any type of materials.

Code is procedure of acceptance and rejection criteria.

Standard is accepted values and compare other with it.


3.          Which is heavier 1kg Cotton or 1kg Iron?

Ans.     Both of them have same weight.


4.          What is Auto Dosing?

Ans.     Auto dosing is an automated system of feeding the equipment with liquid products. It is the ideal way to ensure the correct calibrated dose at the right time every time in auto.


5.          What is the difference between Sudden Force and Impact Force?

Ans.     · An impact is a high force or shock applied over a short time period when two or more bodies collide.

· A force which applies on the body (material) suddenly is known as sudden force.


6.          What is Geyser Pressure Valve?

Ans.     To release the pressure created inside due to evaporation of water.


7.          What is difference between Corrective actions and Preventive actions?

Ans.     Corrective actions are taken on discrepancies noticed during inspection of products/documents/process whereas preventive actions are taken to eliminate the possibility ofdiscrepancy in future.


8.          How do you know air is fully saturated?

Ans.     In its Dew point. (100% relative humidity condition)


9.          What is the function of scoop in BFP (Boiler Feed water pump) in Thermal Power Station?

Ans.      The Function of Scoop tube is regulating the varying amount of oil level in the coupling during operation of infinite variable speed.


10.          What is Operating Pressure?

Ans.      The amount of pressure nearest the point of performing work at the output end of a pneumatic system. The system operating pressure is used to specify the capability of valves and actuators.

Mechanical Engineering Interview Qusetions For Freshers

1.          What is Difference between stamina and strength?

Ans.    Strength is capability over a short length of time and Stamina is the ability to keep going continuously.


2.          What is Hydrostatic System?

Ans.    Hydrostatics is the study of fluid bodies that are

  • At rest
  • Moving sufficiently slowly so there is no relative motion between adjacent parts of the body

For hydrostatic situations

  • There are no shear stresses
  • There are only pressure forces that act perpendicular to any surface.

It’s a closed loop hydraulic systems. It comprises of motor and pump. Here pump supplies energy to motor and motor gives return energy to pump supply.


3.          What is Cotter joint?

Ans.     A cotter joint is used to connect rigidly two co-axial rods or bars which are subjected to axial tensile or compressive forces. Here shaft is locked in place by a smaller pin that passes through the side of the lug and partly or completely through the shaft itself. This locking pin is named as cotter.


4.          How is the excess discharge pressure prevented?

Ans.     Discharge pressure prevented by a pressurized spike cushion. Here the system employs a pressurized cushion of air and a two o-ring piston, which permanently separates this air cushion from the water system. When the valve closes and the water flow is suddenly stopped, the pressure spike pushes the piston up the arrester chamber against the pressurized cushion of air. The air cushion in the arrester reacts instantly, absorbing the pressure spike that causes water hammer.


5.          What is the difference between Strainer and Fitler?

Ans.     Strainer for coarse size, Filter is more accurate than Strainer.


6.          What is the position of Piston Ring?

Ans.     In 180 degree angle the Top ring, Second ring and Oil ring are fixed. Position the ring approximately 1 inch gap below the neck.


7.          Why Deareator are placed at Hieght, In Thermal Power Plant?

Ans.    To build a Very high pressure and the temperature for a boiler feed water pump and it discharge high pressure water to the boiler.

And to provide the required Net Positive Suction Head (NPSH) for the BFW pump and to serve as a storage tank to ensure a continuous supply of feed water during rapid changes in BFP.


8.          What is meanst by One Tonn Air-Conditioner?

Ans.     1 ton refrigeration means 210 kJ/min extracts heat from thesystem.


9.          State 1st Law of Thermodynamics?



10.          If you heat a steel pipe with the hole at center, does heat affects the hole diameter?

Ans.     It gets bigger.