| Bainitic hardening |
Quench-hardening treatment resulting principally in the formation of bainite. |
| Balance piston |
(balance drum, dummy piston) A disc attached to the shaft of a turbine or compressor, to one side of which high or low pressure is applied to counteract the axial thrust produced by the pressure change across the machine. A form of thrust bearing. |
| Balance weight |
A corrective mass used in the static or dynamic balancing of a rotating object. |
| Balancing machine |
A device that assesses the state of static and dynamic balance of a rotating part, and indicates the magnitude and location of weights to be added to give balance. |
| Ball mill |
A mill for grinding and pulverizing materials, consisting of a horizontal rotating drum containing loose steel or ceramic balls. |
| Ball screw and nut |
A nut and bolt assembly having semi-circular helical grooves, as opposed to threads, in which run ball bearings. On rotation of the nut, the balls move along the helix and carry the axial load. Balls reaching the end of the groove are recirculated back to the beginning. Such devices have low friction and very little backlash, and are used in some steering mechanisms. |
| Ballonet |
An airbag used in a hybrid airship. Helium gas expels air from the ballonet during ascent. Fans draw air in during descent. |
| Band clutch |
A friction clutch in which drive is achieved by a band contracting on to the rim of the clutch. |
| Bánki turbine |
A cross-flow, impulse-type water turbine for very low heads in which a jet of water in the form of a flat sheet passes transversely through the turbine, so going through the runner twice. The thin runner blades which run horizontally across the turbine parallel to the axis of rotation are profiled in cross section. |
| Bar |
A widely used (non-SI) unit of pressure approximately equal to normal atmospheric pressure at sea level. The conversion to SI is 1 bar = 105 Pa. |
| Bar |
Unit of pressure – the pressure created by a column of€mercury 75.006 cm high at 0ºC, or about 33.45 feet of water at 4ºC. It is equal to 105 pascal. Standard atmospheric pressure (at sea level) is 1.01325 bar, or 1013.25 mb. |
| Barcol hardness test |
An indentation test, similar to the Shore hardness test but using a pointed indentor with a flat tip, used to determine the hardness of such materials as rigid plastics and composites. |
| Barometer |
An instrument used to measure atmospheric pressure. |
| Barometer |
An instrument for measuring atmospheric pressure. There are two main types – the mercury barometer, and the aneroid barometer. |
| Barrier protection |
The coating on a fastener is said to provide barrier protection if it merely isolates the fastener from the environment. Paint, for example, provides barrier protection. |
| Base metal hardness |
Hardness closest to the surface (when traversing from core to outside diameter) just before an increase or decrease occurs, denoting, respectively, carburization or decarburization. |
| Batch |
A definite quantity of some product or material produced under conditions that are considered uniform. A batch is usually smaller than a lot. |
| Batch furnace |
A furnace used to heat treat a single load at a time. Batch-type furnaces are necessary for large parts such as heavy forgings and are preferred for complex alloy grades requiring long cycles. |
| B-basis |
Mechanical property value above which at least 90% of the population of values is expected to fall, with a confidence of 95%. |
| Bearing area |
The product of the pin (or hole) diameter and specimen thickness in a bearing test. |
| Bearing area |
(bearing surface) (Unit m2) The projected area of a hole, such as a rivet hole, that carries a transverse load. |
| Bearing failure |
A failure that occurs in a riveted or bolted joint when the transverse load divided by the bearing area results in a stress that leads to permanent plastic deformation. |
| Bearing strain |
The ratio of the deformation of the bearing hole, in the direction of the applied force, to the pin diameter in a bearing test. |
| Bearing strength |
The maximum bearing stress that a material is capable of sustaining. |
| Bearing stress |
The force per unit of bearing area. |
| Bearing test |
A method of determining the response to stress (load) of metal products that are subjected to riveting, bolting, or a similar fastening procedure. The purpose of the test is to determine the bearing strength of the material and to measure the bearing stress versus the deformation of the hole created by a pin or rod of circular cross section that pierces the sheet perpendicular to the surface. |
| Bearing yield strength |
The bearing stress at which a material exhibits a specified limiting deviation from the proportionality of bearing stress to bearing strain in a bearing test. |
| Belt drive |
Transmission of motion from one shaft to another by means of a continuous plain, or toothed, flexible band (belt) passing over pulleys. In contrast to chain drives, belt drives tend to be employed in low-torque applications. Reduction in transmissible power may occur due to stretch of a plain transmission belt which results in slack in the drive (belt creep) or slip of a belt on a driving or driven pulley (belt slip). |
| Belt furnace |
A continuous-type furnace which uses a mesh-type or cast-link belt to carry parts through the furnace. |
| Bend test |
A test for determining the relative ductility of metal that is to be formed (usually sheet, strip, plate, or wire) or for determining soundness and toughness of metal (after welding, for example). The specimen is usually repeatedly bent over a specified diameter through a specified angle and then unbent for a specified number of cycles. There are four general types of bend tests, named according to the manner in which the forces are applied to the specimen to make the bend: free bend, guided bend, semiguided bend, and wrap-around bend. |
| Bernoulli’s law |
For a steadily flowing fluid (liquid or gas), the sum of the pressure, kinetic energy per unit volume and potential energy per unit volume is constant at any point in the fluid. Using this relationship, it is possible to measure the velocity of a fluid by measuring its pressure at two points, as with a manometer or Pitot tube. |
| Beta annealing |
Producing a beta phase by heating certain titanium alloys in the temperature range of which this phase forms followed by cooling at an appropriate rate to prevent its decomposition. |
| Bias pressure (Unit Pa) |
In a fluidic device controlled by pressure difference, the magnitude of that difference. |
| Biaxial stress |
Generalized loading of a body in a single plane with no loading normal to it. |
| Bimetallic strip |
A strip formed by welding, riveting or brazing together two metals having different coefficients of expansion, which causes the strip to curl when its temperature changes. Typical combinations are steel and copper or steel and brass. |
| Binary vapour cycle |
A power cycle which combines a steam cycle at relatively low temperature (the bottoming cycle) with a higher temperature cycle (the topping cycle) in which a working fluid such as mercury, sodium or potassium is used. |
| Biodiesel |
A substitute for diesel fuel derived from the oily seeds of sunflowers, oilseed rape, soya beans, etc. |
| Bioenergy |
1. Energy derived from materials such as purpose-grown energy crops, including sugar cane, maize, wheat, and rice, as well as wood, straw, and animal waste, including sewage, manure, and animal litter. 2. A term sometimes used to cover biomass and biofuels together. |
| Bioengineering |
(biological engineering) The application of engineering principles to biology, medicine, agriculture, etc. |
| Biomechanics |
The application of mechanical-engineering principles, including thermodynamics, fluid mechanics, and solid mechanics together with materials engineering, to biological systems. |
| Biomedical engineering |
The application of engineering principles and methodology to the medical field. Examples involving mechanical engineering include the design and construction of artificial limbs and hearts, heart-lung machines, prosthetic eyes, and orthopaedic implants such as hip joints and pins to stabilize fractured bones. |
| Black annealing |
Box annealing or pot annealing ferrous alloy sheet, strip, wire to impart a black color to the oxidized surface. |
| Black oxide |
A black finish on a metal produced by immersing it in hot oxidizing salts or salt solutions. |
| Blade compressor |
An oil-free, double-acting rotary compressor in which an angled blade attached to the inner surface of a rotating housing passes through a slot in a disk rotating about an axis perpendicular to that of the housing but offset from it. Air enters through apertures in the housing and leaves through a port in the housing. |
| Blank carburizing |
Simulating the carburizing operation without introducing carbon. This is usually accomplished by using an inert material in place of the carburizing agent, or by applying a suitable protective coating to the ferrous alloy. |
| Blank nitriding |
Simulating the nitriding operation without introducing nitrogen. This is usually accomplished by using an inert material in place of the nitriding agent or by applying a suitable protective coating to the ferrous alloy. |
| Blanking shear test |
A method used to determine the through-thickness shear strength of sheet material that involves blanking a disk out of flat strip using a simple punch-and-die method. Alson known as punching shear test. |
| Blind rivet |
A rivet that enables a connexion to be made from one side only of an assembly. |
| Blow moulding |
The manufacture of hollow polymer objects (e.g. bottles) by expanding, with internal air pressure, a tube sealed at one end (parison) against the walls of a cavity mould. |
| Blowing |
The process by which a gas is transferred through a porous surface over which there is a gas flow. The effect is used to decrease skin friction and increase heat transfer, for example in turbine-blade cooling. |
| Blue annealing |
Heating hot-rolled ferrous sheet in an open furnace to a temperature within the transformation range and then cooling in air, in order to soften the metal. The formation of a bluish oxide on the surface is incidental. |
| Blue brittleness |
Anomalous loss of ductility when quenched steels are tempered in the range 250–350°C (temperatures that produce blue tints on the surface of components). |
| Blue brittleness |
Brittleness exhibited by some steels after being heated to some temperature within the range of about 205 to 370 °C (400 to 700 °F), particularly if the steel is worked at the elevated temperature. Killed steels are virtually free of this kind of brittleness. |
| Blueing |
Application of blue dye (‘engineers’ blue’) to identify high spots on surfaces in contact, or for marking out. |
| Boiler and Pressure Vessel Code |
A large and complex document, maintained and published by the American Society of Mechanical Engineers. The code |
| Bolt |
(machine bolt) A fastener in the form of an externally-threaded cylinder with a head on one end that is inserted through holes in assembled parts that are then held together by a nut tightened on to the thread. A bolt has an unthreaded region below the head so that when located in a hole, transverse loads are borne by two plain cylindrical surfaces in contact. In contrast, use of a machine screw, that has threads all along its length, results in threads bearing against the plain surface of a hole. |
| Bolt |
Officially, a threaded fastener designed to be used with a nut. |
| Bolt blank |
A rod on which a head has been formed, but on which no thread has been cut, from which bolts or screws may be made as required. |
| Bolt gage |
An ultrasonic instrument used to measure the stress or strain in bolts. |
| Bolt length |
The bolt length shall be the distance measured parallel to the axis of the product from the bearing surface of the head to the extreme end of the bolt including point. |
| Bolt stress (Unit Pa) |
The axial tensile stress induced in a bolt by tightening. |
| Bond strength (Unit Pa) |
The tensile, compressive or shear stress at which joints fail, e.g. by fracture or excessive deformation. |
| Box annealing |
Annealing a metal or alloy in a sealed container under conditions that minimize oxidation. In box annealing a ferrous alloy, the charge is usually heated slowly to a temperature below the transformation range, but sometimes above or within it, and is then cooled slowly; this process is also called close annealing or pot annealing. |
| Boyle’s law |
The product of the pressure of a gas p and its volume is constant at a given absolute temperature T. Together with Charles law, it yields the ideal gas equation p = Mrt where m is the mass of gas and R is the specific gas constant. |
| Boyle’s law |
The volume of a gas at constant temperature is inversely proportional to the pressure. This means that as pressure increases, the volume of a gas decreases. |
| Brake fluid |
The hydraulic fluid used to transmit force to the pistons in disc brakes or the wheel cylinders in drum brakes. Requirements include a high boiling point and low hygroscopy. |
| Brake lining |
The replaceable friction material that covers a brake shoe in an internally expanding brake. |
| Brayton cycle |
(Joule cycle) An air standard cycle that is the ideal cycle for a gasturbine engine. As shown on the diagram of pressure (p) ʋs specific volume (ʋ), it consists of four internally reversible processes: isentropic compression in a compressor (1–2), isobaric heat addition in a combustor (2–3), isentropic expansion in a turbine (3–4) and isobaric heat rejection. The cycle can be extended to include regeneration, reheating, and intercooling. |
| Breaking load |
The maximum load (or force) applied to a test specimen or structural member loaded to rupture. |
| Breaking load (Unit N) |
The load applied at some point to a component or structure which leads to fracture. The breaking stress (breaking strength) is the average stress at which a member breaks, given by the breaking load divided by the area over which it acts. |
| Breaking stress |
The stress at failure. Also known as rupture stress. |
| Breaks |
Creases or ridges usually in “untempered” or in aged material where the yield point has been exceeded. Depending on the origin of the break, it may be termed a cross break, a coil break, an edge break, or a sticker break. |
| Bright annealing |
Annealing in a protective medium to prevent discoloration of the bright surface. |
| Bright nitriding |
Nitriding in a protective medium to prevent discoloration of the bright surface. |
| Brine quenching |
A quench in which brine (salt water-chlorides, carbonates, and cyanides) is the quenching medium. The salt addition improves the efficiency of water at the vapor phase or hot stage of the quenching process. |
| British Standards Institution (BSI) |
The Institution in the UK responsible for the preparation and publication of standard specifications (British standards) for manufactured goods, their design, manufacture and testing. |
| British thermal unit (BTU, Btu) |
An obsolete (non-SI) imperial unit of energy defined as the energy required to raise the temperature of one pound of pure water at 68°F by 1°F. The conversion to SI is 1 Btu = 1.055 056 × 103 J. |
| Brittle |
A brittle material is one that breaks, often suddenly, with no permanent deformation. Examples of brittle materials are some cast irons, glass, concrete, and some plastics. |
| Brittle |
A bolt is said to be brittle if it will break when stretched only a small amount past its yield point, |
| Brittle fracture |
The fracture of a component or structure in the globally-elastic range of loading, so that the broken pieces may be refitted to regain the original article. |
| Brittle fracture |
Separation of a solid accompanied by little or no macroscopic plastic deformation. Typically, brittle fracture occurs by rapid crack propagation with less expenditure of energy than for ductile fracture. |
| Brittle lacquer coating |
A lacquer that, when painted on to an unloaded body, reveals the direction of maximum tension stresses from the pattern of cracking produced in the lacquer when the body is loaded. |
| Bucket |
1. A cup-shaped vane with a central dividing ridge attached to the periphery of the runner of an impulse water turbine such as a Pelton turbine. 2. A rotor blade in a compressor or turbine. |
| Bulk density (Unit kg/m3) |
The average density of a mass of granular or powdered material at ambient conditions. |
| Bulk velocity |
(average velocity, V) (Unit m/s) For fluid flow in a pipe or duct, the average flow velocity, given by V = ṁ/ρA where ṁ is the mass flow rate, ρ is the fluid density, and A is the duct cross-sectional area. |
| Burning |
(1) Permanently damaging a metal or alloy by heating to cause either incipient melting or intergranular oxidation. See overheating, grain-boundary liquation. (2) In grinding, getting the work hot enough to cause discoloration or to change the microstructure by tempering or hardening. |
| Butt joint |
The end-to-end joining of two plates either by welding or by overlapping plates that are bolted or riveted. |
| Butterfly valve |
A valve in which a disc rotates on a shaft at right angles to the axis of a pipe to regulate flow. When open, the disc is edge-on to the flow and offers limited resistance. When closed, the disc is pressed against a seat in the valve body. |
| Bypass flow meter |
(shunt flow meter) A flow meter installed in a pipework bypass which may itself be part of the flow meter. An orifice plate is used to ensure a fraction of the main flow passes through the bypass. |
| Bypass ratio |
In a turbofan engine, the ratio of the mass flow rate of the bypass stream to the mass flow rate through the core of the engine. |
| Bypass valve |
A valve that directs flow through a bypass. |
