Design rules

Some of the design rules for the process are as follows:

1. When specifying dimensional tolerances, be more liberal with the length dimensions. Since the length of a part will depend upon the amount of the powder placed into the die cavity it may vary somewhat. Length tolerance on short parts should be from ±0.002 to 0.005 in.

2. Avoid narrow, deep sections because the powder at the time of filling may bridge across the narrow sections and not completely fill the die cavity.

3. Avoid abrupt changes in section thickness, since the expan­sion or contraction during the sintering operation may cause a change in the shape or the dimensions.

4. When flat thin parts requiring a high density are pressed, be sure the section is not too thin because the punches may break when pressure is applied due to the lack of cushioning effect of the powder. It is recommended that flat sections be pressed not less than 0.032 in. in thickness.

6. Prepare a report on the topic «The Powder Metallurgy Process» taking in Units 29-33. Use the word combinations from Chapter 3, Appendix 4 «English for Scientific Discussions».

154

TERMINOLOGY GLOSSARY

A abrasive

adhere

advantage

benefit

profit

affect

allowance

alloy alumina annealing box ~

Syn. close ~ pot~ bright ~ Syn. white ~ dead

Syn. full ~ true ~ lead ~ liquid -local -

Syn. selective ~ magnetic ~ pact~ process ~

Syn. recrystallization step-

абразивный (шлифовальный) материал, абразив; абразивный прилипать, сцепляться преимущество польза, выгода прибыль

воздействовать, оказывать влия­ние

зазор, допус, припуск (на номи­нальные размеры проката) сплав; сплавлять, легировать глинозем, окись алюминия отжиг

отжиг в ящиках или горшках, отжиг в кол па ко вой печи

светлый отжиг

полный отжиг

отжиг в свинцовой ванне отжиг в расплавленных солях местный отжиг

термомагнитная обработка отжиг пачками

промежуточный, рекристалли-зационный отжиг

отжиг со ступенчатым охлажде­нием

155

stress-relief -

water -

atomize

atomizer

atomization

В

backing

basket

batch

bearing

bond

bone brake

brittle

brittieness

base

отжиг для снятия внутренних

напряжений

отжиг с конечным охлаждением

в воде

распылять,дробить

форсунка, распылитель

распыление

поддержка, подпорка корзина, ковш

партия, группа, пачка, загрузка подшипник

связь, сцепление, соединение, связующее вещество; связывать, соединять, сцеплять глинистый уголь, углистый сла­нец

тормозное устройство, тормоз; тормозить хрупкий хрупкость

материал основы, основа (сплава) железная основа

С

capacity

carbide cemented ~

carboloy

case case-hardening

производительность, выработка, мощность карбид спеченный металлокерамический твердый сплав (карбид вольфрама или титана)

карболой (твердый режущий сплав)

внешняя оболочка, корпус, кожух цементация, поверхностная за­калка

156

casting cavity die-cementite

chamber

cbar charred charcoal charge

chemical poisonous chilling chipping

chips clutch

coarse

coarseness

coarsening

coarse-grained

coining

coke

petroleum -

coke-oven gas

collector

dost-

commercial

отливка

пустота, полость полость матрицы цементит, или карбид железа камера, полость, отсек

обжигать, обугливать обугленный древесный уголь шихта, загрузка, колоша; загру­жать

химический продукт, химикат отравляющий химикат охлаждение, закалка обрубка, обдирка, вырубка де­фектов на слитке щепа, стружка

сцепление, муфта (сцепление); сцеплять соединять сырой (о материале); большой, крупный (о подаче); грубый, не­обработанный (о поверхности) укрупнение

увеличение, укрупнение (зерна) крупно-зернистый чеканка кокс

нефтяной кокс коксовый газ коллектор; сборник пылевая камера

коммерческий, торговый; заво­дской, промышленный (процесс или оборудование); имеющий промышленное значение; рента­бельный

157

compact

compress

compressed

condensation

conductivity

electric ~ constituent

conventional cooler

core

inside ~

costs

initial ~

cracking

crankshaft

cross-section

crushing

coarse ~

cutter

cyaniding

прессовка, прессованная порош­ковая заготовка; прессовать, уп­лотнять; плотный, уплотненный, компактный сжимать

сжатый, сдавленный конденсация, сгущение; сжиже­ние

удельная проводимость; прово­димость

электропроводимость компонент, составляющая часть, элемент обычный

холодильник, охладитель, ра­диатор

стержень, сердцевина внутренний стержень затраты

первоначальные растраты растрескивание коленчатый вал поперечное сечение дробление, измельчение первичное (крупное) дробление режущий инструмент жидкое цианирование, жидкое азото науглероживание

D

degree

dendritic

deposit

deposition

dendritic

степень

дендрировать, отлагаться,

осаждаться

отложение, осаждение

древовидный, дендрированный,

древовидно-разветвлённый

158

density deteriorate

die

forging ~ Syn. press — diffusion discolour dissociate

dissociation

distort

distortion

deviation

drawing

dynamo

плотность, густота

ухудшать(ся), изнашивать(ся),

портить(ся)

матрица, пуансон, штамп

ковочный штамп

диффузия, рассеяние обесцвечивать

разъединять, разобщать, диссо­циировать, разделять, разлагать разложение, распад, диссоциация деформировать, искажать искривление, искажение, де­формация отклонение волочение

генератор с самовозбуждением; генератор постоянного тока

E

effect

elevate

at an elevated temperature

eliminate

emerge

enable

energizer

enrich

enrichment

ensure

extend to

extraction

solvent ~

действие, влияние, результат; выполнять, осуществлять поднимать, повышать при повышенной температуре удалять, устранять возникать, появляться позволять, давать возможность аютивизатор обогащать обогащение

гарантировать, обеспечивать распространять на экстракция, извлечение, экстра­гирование

экстрагирование растворителем, жидкостная экстракция

159

oil-fired ~	пламенная печь, работающая на
	жидком топливе
fusible	плавкий

G

gauge

gear

Syn. gearwell gradual

мера, масштаб, размер, калибр; калибровать, тарировать, изме­рять

шестерня, зубчатая передача, зубчатое колесо

последовательный (о процессе)

160

grade grain grind

grinding

H

harden

hardening heavy duty

homogeneous honing

hopper

hydride

качество, степень, фракция зерно

измельчать, дробить, размалы­вать, шлифовать дробление, шлифовка

закаливать, твердеть, задубли-вать закалка

мощный, тяжелого типа, пред­назначенный для тяжелой рабо­ты, с тяжелым режимом работы однородный

хонингование, хонинг, истира­ние металлических поверхностей бункер, воронка (загрузочная), загрузочный желоб, загрузоч­ный люк

гидрид (водородистое соедине­ние элемента)

I incorporate

install

instantaneous

intricate

монтировать, помещать, соеди­нять, смешивать

устанавливать, монтировать, со­бирать

мгновенный, мгновенного дей­ствия запутанный, сложный

jet

струя

161

L

lapping	нахлестка, перекрытое, притирка
lateral	боковой, горизонтальный, попе-
	речный
load	груз, нагрузка
shock~	ударная нагрузка
lubricant	смазочный материал, смазочное
	вещество, смазка
lubricate	смазывать
lubrication	смазывание, смазка

м

mac hi liability	способность к механической об-
	работке
machine	обрабатывать на станке, подвер-
	гать механической обработке
machining	механическая обработка
maintain	обслуживать, эксплуатировать,
	ремонтировать, содержать
maintenance	техническое обслуживание, экс-
	плуатация, текущий ремонт
manufacture	изготовление, обработка; изго-
	тавливать, обрабатывать
matrix	основа, матрица, форма
medium (a)	среда (среды)
melting	плавка, расплавление, плавление
mercury	ртуть
mill	завод, фабрика
ball ~	шаровая, мельница
milling	измельчение, помол
minute	мелкий, крохотный, подробный,
	детальный
moulding	формовка, отливка, отлитая

деталь

162

N nitriding

normalize normalizing

novel

азотирование, азотация, нитри­рование, нитрация закаливать на воздухе нормализация, закалка на возду­хе новый, необычный

О offset

orifice originate

Р patenting

peariite

pickling pin

pinion

plunge

point

boiling ~

melting ~

yield-

porosity

porous

potassium

precipitate

precipitation precision

смешать, возмещать, уравнове­шивать

отверстие, устье, сопло, насадок возникать, появляться

патентирование, закалка в свин­цовой ванне

перлит, жемчужный блеск (це­ментит с ферритом) травление

шрифт, штырь, стержень; про­капывать

шестерня, зубчатое колесо погружение; окунать, погружать точка

точка кипения трчка плавления (физический) предел текучести пористость пористый калий

осадок; осаждать; осажденный, осевший осаждение точность, прецизионность

163

process

процесс, технологический при­ем; обрабатывать

processing	обработка, технология
projection	выступ, рельеф, проекция
punch	штамп (прессовка), пуансон
previous	предшествующий, предвари-
	тельный
Q
quench	закалка; закаливать
	закалка, резкое охлаждение
dry ~	сухое тушение
fixture ~	закалка в зажатом состоянии
fog~	закалка в распыленной сфере
incomplete ~	неполная закалка
interrupted ~	ступенчатая закалка
Syn. step ~
lead~	закалка в свинцовой ванне
negative quenching	низкий отжиг
oil-	отжиг в масле
pot~	закалка непосредственно после
	цементации
regenerative ~	двойная закалка (цементованной
	стали)
spark ~	искрогашение
spray ~	закалка распыленной водой
time-	закалка с выдержкой
water ~	закалка в воде
wet-	мокрое тушение

R

range temperature-

проточный канал, подводящий канал, отводящий канал, обойма подшипника, бегунок выемка, ряд, предел, амплитуда диапазон температур

164

rate	степень, скорость
production ~	производительность
red beat	красное каление, красный накал
reduce	уменьшать, понижать, восста-
	навливать
reducing atmosphere	восстановительная атмосфера
redaction	уменьшение, сокращение, вос-
	становление
refractory	огнеупорный, тугоплавкий, жа-
	ростойкий
relieve (stresses)	снимать (напряжение)
result (from)	проистекать (из чего-либо)
result (in)	иметь результатом (что-либо)
rod	прут, пруток, стержень, брус
core~	сердечник
rolling	прокатка

score

screw set screw

section secure

segregate

shot

shotting

shrinkage

silica

silicon

sinter

зазубрина, царапина; задирать, надрубать винт, шуруп

винт без головки, установочный винт, стопорный винт, нажим­ной винт сечение

надежность, безопасность; за­креплять, соединять сегрегат, выделившийся компо­нент {сплава); сегрегировать, ликвировать

сферические частицы металла, сферический порошок гранулирование металла усадка

кремнезем, кварц кремний спекать (ся), агломерировать

165

sintering sizing

soaking

sodium softening

soak

спекание, агломерация калибровка, обработка точно по заданному размеру томление, прогревание, выдержка при определенной температуре натрий

размельчение, смягчение вымачивать, выдерживать (при определенной температуре), под­вергать томлению (слитки в то­мильных колодцах)

solute	растворенное вещество
solution	раствор
solid ~	твердый раствор
solvent	растворитель
spongy	губчатый, пористый, ноздрева-
	тый
spray	разбрызгивать, распылять
stack	куча, груда (угля), стояк, вывод-
	ная труба, шахта (печи)
state	состояние
steel	сталь
alloy (ed) ~	легированная сталь
hardened ~	закаленная сталь
high carbon -	высокоуглеродная сталь
low carbon ~	низкоуглеродная сталь
strength	прочность
tensile -»	прочность на разрыв, временное
	сопротивление разрыву
ultimate tensile ~	предел прочности на разрыв или
	растяжение
subject (sth) to (sth)	подвергать (что-либо) (чему-либо)
subsequent	последующий
surface	поверхность
bearing ~	несущая (опорная) поверхность,
	направляющая поверхность
	166

т

tank technique

temper

tempering

sand ~ surface -water ~ tend tensile stress-relief

tolerance

toughness

tray

treat

treatment beat-

high-temperature (high-heat)

reheat ~

solution ~

stabilizing *-thermal oxidative

бак, резервуар

метод, способ, методика, техно» логия

отпуск стали; закалка с отпус­ком; отпускать

отпуск, закалка, искусственное старение, смешивание увлажнение формовочной смеси поверхностный отпуск отпуск в воде склоняться {к чему-либо) прочный на разрыв отпуск для уменьшения оста­точных напряжений допуск, наибольшее допустимое отклонение

жесткость, прочность, вязкость поток, желоб

обрабатывать, подвергать обра­ботке обработка

термообработка, тепловая обра­ботка

высокотемпературная термооб­работка

повторная обработка термообработка на твердый рас­твор

термообработка для стабилиза­ции структуры сплава термоокислительный

167

CHAPTER

3

SUPPLEMENTARY MATERIAL

Appendix 1 INTERPRETATION DICTIONARY ON METALS AND MANUFACTURING PROCESSES

Age hardening. A process of ageing that in­creases hardness and strength and ordinarily decreases ductility.

Ageing. In a meta! or alloy, a change in properties that gener­ally occurs slowly at room temperature and more rapidly at higher temperatures.

Alloy. A materia! consisting of two or more elements, with the elements ordinarily metals, whereby they are at least partly soluble in each other in the liquid state.

Annealing. Heating to above the critical range, holding it at that temperature for the required time, and slowly cooling it through the critical range.

Auxiliary operations. Additional processing to the forging to obtain shapes, surface conditions, or other properties not obtainable in the regular forging operation.

Basic process. The basic process relates to the melting furnace practice, where the lining is used, which is basic in nature, usually con­sisting of dolomite, magnesite, etc.

Billet. Steel with a round cornered square or rectangular cross-section to which further processing, such as forging, or rolling, is given.

168

Binders. Binders are used chiefly in dry sand moulding in order to hold or bind the sand together after the mould or core has been dried. Various types of powder, pastes and oils are employed for this purpose.

Blackheart process. The method employed in the production of malleable casting wherein most of carbon is retained, being converted during annealing treatment from its combined form to a graphitic state.

Blackings are used as a facing in moulding and are available in a variety of forms and proprietary brands; some being made from ground charcoal of carbon; others including plumbago. Blacking may be used either dry or wet; in the latter they may be mixed with a clay wash and applied by dusting, brushing or spaying.

Blast cleaning. A process for removing the oxide surface, or scale, from forgings by propelling grit or shot at high velocity at the work in order to clean it.

Blind riser. A form of riser which may project upwards from a runner gate or other location but does not emerge through the top sur­face on the mould.

Blocking. A forging operation which imparts to the forging its general but not exact or final shape.

Box annealing. An annealing process whereby the steel to be annealed is parked in a closed container to protect the surface from oxidation. This term is sometimes applied to forging being placed in closed container directly from the forging operation, which permits the forging to cool somewhat slower and tends to reduce forging strains.

Brazing. A method of joining metals together by introducing a film of «spelter» or copper-zink alloy between the adjoining faces of the two metals while they are at a red "heat. This method is employed for cast iron, steel, brass, copper, etc. or any combination of these. Bo­rax or some other similar agent is used as a flux.

Bright annealing. Annealing in a protective medium to prevent discolouration of the bright surface. A process of annealing bright steel strip, wire and articles, in such a manner as to prevent oxidation taking place, which is usual at the temperatures employed in annealing. The metal is heated in a furnace in a controlled atmosphere usually of am-

169

monia gas, and the cooling may take place with the articles in a partial vacuum or in similar inert atmosphere.

Carl»arising. Adding carbon to low carbon steel by heating to above the critical range when in contact with some carbonaceous mate­ria!. Commercially, carbon is added to the outer section of the steel so that when a subsequent heat treatment is added, the outer surface has greater hardness than the core.

Case-hardening. A process of hardening a ferrous alloy so that the surface layer or case is made substantially harder than the interior or core.

Cementite. Cementite or iron carbide (FeC) occurs free in the higher carbon steels and may be in the form of white sports, bounda­ries or streaks running through or surrounding the areas of pearlite. It is the hardest constituent found in steel and an estimated hardness ex­ceeding 600 Brinell.

Centrifugal casting. This is a method which is now successfully employed in producing casting, such as pipes, rolls, gear rims, etc. by pouring molten metal into the rotating mould. Castings produced by this method have a greater consistency and freedom from porosity.

Check. A crack in a die impression comer, generally due to forging strains localized at some relatively sharp corner.

Chills. Pieces of iron or copper set up in a sand mould in posi­tions where it is required to chili the casting locally and produce a hard and dense condition at the surface.

Closed dies. Forging dies in which the compressive force is ap­plied to the whole of the surface of the forging. In open dies there is no constraint to lateral flow in some directions.

Cleaning. The operation of removing the oxide coating, or scale, from of the surface of the forging.

Cogging The reducing operation in working the ingot into a bil­let by the use of a forging hammer or a forging press.

Cold shut.

1. A defect in a casting resulting from pouring at too low a tem­perature so that a partial solidification of one stream of metal occurs before the mould is completely filled, and there is no union between meeting streams.

170

2. The section or sections of a forging where two surfaces of metal have folded against each other, producing a lack of continuity of metal in the cross-sectional area.

Cold trim. Removing the flash, or excess metal, from a forging after it has been cooled.

Cold work. Cold deformation of meta! below its recry stall iza-tion point. Generally performed in forging practice to increase hard­ness or to gain closer limits than practical with hot working.

Complex alloy. An alloy, generally an alloy steel, having three or more alloying elements in addition to carbon, to impart to the metal certain desirable properties.

Compact. An object produced by the compression of meta! powders with or without the inclusion of non-metallic constituents.

Cope. In foundry practice the top part or section of a moulding box or flask is referred to as a cope.

Core. In general, a cope of a mould represents the inside or hol­low cavity of a casting. Cores are usually made in sand, although, in certain cases, metal cores are employed. Metal cores are, of course, confined to comparatively simple shapes which can easily be with­drawn; whereas sand cores, which can be crushed to retrieve, can be made in any complicated shape.

Cupola. The vertical cylindrical type of furnace used for cast iron melting for general foundry uses.

Cyaniding. Surface or skin hardening of low carbon steel by adding a cyanide salt to the steel heated above the critical range and quenching.

Decarburization.

1. The removal of carbon from the surface of solid steel which often occurs during heating, prior to rolling forging or hardening op­erations.

2. Deep-drawing-forming cup-shaped articles or shells by using punch to force a sheet metal into a die.

Die shift. The portion of the impression in one die not being in perfect alignment with the impression in the other die after they have been set in the forging unit.

Die sinking. Forming or machining a depressed partem in a die.

171

Die-casting. Generally, a die-casting refers to a casting which has been made in a metal mould or die. The molten metal being forced under pressure into the mould is distinct from hot «pressing», forgings, etc., which are made from metal hi its plastic state.

Dies. Steel blocks into which desired impressions are machined and from which forgings are produced. Forging dies usually come in pairs, with part of the impression in one of the blocks and the balance of the impression in the other block.

Draw bench. The stand that holds the die and drawhead used in drawing wire, rod and tubing.

Drop forging. The shape obtained by working metal in a pair of dies to produce the form in the finishing under a drop hammer.

Dry sand. The most generally employed method of moulding consists of using dry sand mould and cores. There are moulds or cores dried before being used.

Electric furnace. A furnace whose heat source is derived from electricity, which may range from the small resistance type used for laboratory work to the large kinds used for melting and other heat-treatment.

Electric. A term now used in ferrous and non-ferrous metallurgy to define an alloy which has the lowest melting point possible with the given composition of elements. The word is of Greek origin, and may be translated as «easy melting».

Eutectoid steels. Steels which are composed wholly of pearlite are called eutectoid. Such steels would contain about 0.85-0.9 per cent carbon. Steels with a carbon content below this figure are known as hyper-eutectoid and consist of pearlite and free ferrite. Where the car­bon content is in excess of 0.9 per cent, the steel is called hyper-eutectoid and consists of pearlite and free cementite.

Extrusion. Shaping metal into a chosen continuous form by forcing it through a die appropriate shape.

Facings. The facings of a mould or core may be treated in vari­ous ways in order to ensure a smooth skin on the casting by filling in the spaces which would, otherwise, exist between the particles of the ordinary sand. The facings employed, such as coal dust, plumbago, talc, etc., may be dusted, brushed, or sprayed on.

Flash. Flashing or fins may be found on casting, drop forging and rolled sections. In castings, they are in the molten metal creeping

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through small cavities formed by an imperfect seal between two adja­cent boxes. In drop forging it is the metal that is fa excess of that re­quired to fill out the final impression in a pair of dies and moves out as a thin plate around the parting line of the dies.

Flop forging. A forging in which the bottom and top die im­pression parts are identical, permitting the forging to be turned upside down during the forging operation.

Forging. Metal which has been worked to some definite prede­termined shape by a process of hammering, upsetting, or pressing ei­ther hot or cold, or a combination of several of these processes.

Gate. The portion of drop forging dies cup out to permit a short connection between the impression and outer edge of the dies.

Gating. Relation to the number, size and shape of runner and riser gates as necessary in order to produce a sound casting.

Grain size. Generally to the size of the crystals or grains in the structure of a metal, though, in some instances, referring to the grain size of sands of sands used in moulding.

Green sand. The term is used in connection with moulding sands, and refers to sand which is in its moist or «green» state.

Grey cast iron. Where the graphite carbon present is in excess of that of the combined carbon, the iron is classed as «grey». The greater the percentage of graphitic carbon present, the darker becomes the appearance of the iron at a fracture.

Hardening. The operation of heating steel to above the critical range, holding at that temperature for the required time, and following this by a rapid cooling in quench.

Heading. An upsetting process used to form riser, screw and bolt heads in making these products from wire or rod.

Heat treating. Any operation or operations of heating metal and cooling it in order to bring out desired physical properties.

High frequency induction furnace, A furnace in which the metal charge acts as the secondary of a transformer, the primary con­sisting of a water-cooled copper winding supplied with a high fre­quency current. These fiimaces are used in the production of certain high grade alloy steels and non-ferrous metals.

Hot stamping. Shaping or forming metal in a press or hammer with the metal in a heated state.

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Hot work. The mechanical working of a metal at the tempera­ture above its recrystallization point.

Hub. A boss which is in the centre of the forging and forms a part of the body of the forging.

Impact extrusion. A cold forming process in which the metal is forced by impact to flow around the punch forming a tube with a solid bottom.

Impression. The portion of the dies which has been machined so as to produce a shape of the forging.

Inclusion. Dirt and other impurities which may be in metal as a mechanical mixture.

Ingot. The steel casting from which the rolled or forged steel is to be produced.

Investment moulding process. A method of forming a mould in a refractory material around a pattern of wax plastics or low melting point alloy. The pattern is first formed in a mould or die and runs out during drying operations leaving a cavity as required and without need for parting lines. Strict control of the whole process enables precision casting to be made in steel or non-ferrous alloys to within 0.001 in. re­quired dimension.

Killed steel. Steels from which all the dissolved gases have been removed in the furnace prior to pouring are said to be «killed» steels.

Lap. A surface defect in the forging caused by the folding of metal surface against each other.

Layout. Transferring drawing or sketch dimensions to templates or dies for use in sinking dies. Also checking a forging to determine whether its dimensions are in accord with those given on the drawing or model.

Lost wax process. The same as the investment process, al­though, the latter may employ plastics or low melting point alloys in lieu of the wax.

Machine forging. The product of the forging machine or upset-ter. In this machine the metal is moved to the impression by the pres­sure of the moving punch while the dies remain in position during the time the pressure is applied.

Monel. A non-ferrous alloy first produced in 1905 and contain­ing approximately two-thirds of nickel and one-third copper, with

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small percentages of iron and manganese and traces of carbon, silicon and sulphur. It has excellent stain resisting qualities and is used largely in chemical plants. Its specific gravity is 8.8 and the melting point is 1350 °C.

Nitriding. A system of hardening suited to special alloy steels, whereby, the articles to be hardened are heated in a furnace under the action of the nitrogen in ammonia gas. This method gives moderate toughness, together with an extremely high resistance to wear. No quenching of the treated parts is necessary in this process.

Normalizing, Heating a ferrous alloy to above its critical range, holding it at that temperature for the required time, and then, cooling it in still air to room temperature.

Oxidation is the chemical term which relates to the combining of oxygen with various elements and compounds. It may be due to cor­rosion in the form of rust more rapidly due the heating at temperatures in an oxygen-bearing atmosphere of flux.

Patenting. A form of heat treatment used during steel wire drawing. This consists of passing the wire through small tubes in a fur­nace at a temperature of about 950-970 °C and then, cooling in air or alternately in molten lead. This process favours the formation of a sor-bitic-pearlite structure rather than ferrite.

Pearlite exists in the form of a mechanical mixture of ferrite and cementite, varying in proportion with both the carbon content the steel has and the heat treatment given. The latter governs its formation, which takes place during the cooling period after the steel has been heated beyond the critical temperature.

Piekling. Stock or casting may be «pickled» or immersed in a bath of acid in order to soften and remove the surface scale and sand. Various baths are used containing chiefly dilute solutions of nitric, sul­phuric or hydrochloric acids.

Powder metallurgy. The art of producing metal powders and of utilizing metat powders for the production of massive materials and shaped objects.

Precipitation-hardening. (Age-hardening). This type of hard­ening is caused by the travel at lowered temperatures of particles of in­soluble, supersaturated material from the inside of a crystal to the

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boundary, thereby, straining the space lattice. It occurs in materials which are more soluble at high temperatures than at low temperatures. Precision moulding. The production of moulds in plaster or re­fractory investment by which it is possible to achieve very precise lim­its and frequently eliminate the need for machining. Press forging.

1. A forging produced by a mechanical or a hydraulic press.

2. The forging process in which metal stock is formed between dies, usually, by hydraulic pressure.

Pressure tight. A term that describes a casting free from poros­ity of the type that would permit leaking.

Quenching. Rapid cooling of metal from above the critical range in some quenching medium.

Ram. The moving part of a drop hammer or a press to which one of the dies fastened.

Ramming. The operation, which may be either manual or me­chanical, of packing or ramming sand round a pattern in order to form the mould.

Reverberatory furnace. The reverberatory or air furnace is a type in which the heat to the charge is obtained by hot gases from ei­ther coal or pulverized fuel fire burnt in an adjoining grate and thrown back or «reverberated» from the furnace roof. In this way, the charge does not come into direct contact with the fuel the sulphur absorption is, therefore, reduced to minimum. The furnace is used for producing wrought iron and cast iron melting.

Scale. The oxide film that is formed on hot metal by chemical action of the surface metal with the oxygen in the air.

Scale pit. A surface depression formed on the forging due to scale in the forging operation.

Segregation. Concentration of carbon and other impurities (in solution) into a portion or region of a casting or ingot which is last to solidify.

Shrinkage. The contraction of metal when cooled from an ele­vated temperature.

Shrinkage allowance is made in patterns to compensate for the shrinkage taking place in the casting, between the time metal is poured until it has finally reached a cold state.

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Sink. The specialized operation of machining impressions into forging dies. Skin dried moulds are made in the first place with green sand and then, dried only on the surface or skin.

Slag. In furnace operations various residues or inclusions, such as ash from the fuel, impurities, etc., can only be separated from the molten metal by converting them into a fusible state. This is achieved by the addition of suitable fluxes and thus enables the slag, which is of higher density than the molten metal, to be tapped off at a higher point than the metal tapping position.

Smith forging. Forging made by hand or under some power hammer without dies containing an exact finishing impression and without having the commercial exactness of producing die forgings. It is also called hand forging, or flat die forging.

Smith hammer. Any power hammer applied when impression dies are not used for the reproduction of commercially exact forgings.

Snap flask. A moulding box which is hinged at one side and held by a snap fastening at the opposite corner. This enables the box or flack to be removed after one mould is made and used again for moulding up another job. Its use is usually confined to light work.

Soaking heat. Holding the metal at a desired temperature suffi­ciently long so as to permit complete penetration of the heat through­out the piece.

Space lattice. The term «space lattice» indicates the arrange­ment and spacing of the atoms in a crystal.

Specific gravity. The specific gravity number relating to a mate­rial indicates the comparative weight of a certain volume of the sub­stance compared with an equal volume of water. The specific gravity (s. g.) of water is 1.

Spheroidizing. A special annealing process consisting of pro­longed heating of iron base alloys at just below the lower critical tem­perature range followed by slow cooling.

Spiegeleisen. An alloy of iron and manganese used to recarburize molten steel. It contains about 2 per cent carbon and 20 per cent manganese. Spiegeleisen means «mirror iron» and is called so be­cause of the brilliance of its fracture.

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Straightening. Decreasing misalignment between various sec­tions of a forging.

Tempering. Reheating steel after the quenching operation to some temperature below the critical range to produce desired physical properties.

Tolerance. The permissible deviation from the exact dimensions given on the drawing or model.

Tote box. Metal container used to convey forging to the various processing operations.

Trimmer. The dies used to remove the flash or excess stock from the forging.

Tuyeres. These are air nozzles through which the blast or draught is actually admitted into either a furnace or a forge. In case of ordinary blacksmith's forger and other furnaces working at compara­tively low temperatures, they may be made of metal, but for high tem­perature furnaces some refractory material is necessary.

Up-end forging. A forging in which the metal has been placed in the die so that the direction of the fibre structure is at right angles to the faces of the die.

Upset forging. A forging formed by pressure upon hot or cold metal between dies operated in a horizontal plane.

Vacuum casting. A method of casting applied particularly to steel foundry work, in which partial vacuum is created in the mould af­ter the pouring of the metal. The system aids the removal of dissolved or occluded gases and helps to prevent the formation of blow holes.

Vacuum melting. A modern melting practice applied especially to high-grade alloys, in which oxidation during melting is minimized by the use of vacuum or controlled atmosphere within the furnace.

Venting. In moulding and core making venting is a means of providing vents or outlets through which the gases may escape during pouring operations. The moulding sand or loam may be vented in some cases, and additional vents may be formed by piercing the sand with suitable tools.

Work-hardening. Also called strain-hardening. The increase in hardness due to inelastic deformation below the recrystallization tem­perature.

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Appendix 2 AUTHENTIC ARTICLES