2. Match the words on the left with their definitions on the right

1. the reduction in volume experi­enced by metals or alloys on cooling

2. the heating of molten metal to a temperature exceeding the melt­ing point

3. the increase in volume experi­enced by metals or alloys on heating

4. an element of the gating system designed to hold a fairly large amount of molten metal, the latter serving to compensate for shrink­age

5. an empty space in the casting which is defect when not planned by a designer

6. a defect in a casting due to irregu­larities in the production process or Jo the use of improper materi­als, pattern or tools

7. the reduction experienced by met­als or alloys on cooling

3. Render the following

After a mould has been filled with molten metal, the main prob­lems of the founder begin in the form of shrinkage holes, shrinkage ^Inarks, cracking, and the resultant effects of solidifications shrinkage.

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Solidification shrinkage may be defined in the following way: when solid metal is melted, it increases in volume. Aluminium alloys, for in­stance, increase in volume by 7.6 per cent, and when the metal solidi­fies in the melt or die it reverts to its original volume.

4. Translate at sight

Так как металл усаживается во время кристаллизации в ли­тейной форме, инженер-литейщик должен тщательно рассчитать весь процесс затвердевания материала, чтобы избежать усадочных раковин в самой отливке. Известно, что при нагревании и плавле­нии объём металла увеличивается. При охлаждении происходит обратный процесс, т.е. объём металла сокращается. Поэтому что­бы в готовой отливке не получилось дефектов, пользуются так на­зываемой прибылью.

Прибыль - это специальный элемент литниковой системы, содержащий большое количество жидкого металла, который рас­ходуется на заполнение усадочных пустот до тех пор, пока не произойдёт полная кристаллизация отливки.

ADDITIONAL TEXTS FOR READING AND SPEAKING ABOUT «FOUNDRY» AS A PROFESSION

1. Learning Foundry

2. Metal Casting - a Basic Manufacturing Process

3. Development of Metal-Casting Methods

LEARNING FOUNDRY

A casting may be defined as «a metal object obtained by allow­ing molten metal to solidify in a mould», the shape of the object being determined by the shape of the mould cavity.

Founding, or casting, is the process of forming metal objects by melting metal and pouring it into moulds. A foundry is a commercial

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establishment for founding or production castings. Significant in these definitions is the use of liquid metal to cast the shape of the object di­rectly, producing cast metal. Wrought metal products differ from cast metal products in that the metal has received mechanical working treatments such as forging, rolling, or extruding. Practically all metal is initially cast. Castings obtain their shape principally when molten metal solidifies in the desired form. Wrought objects, however, are cast as ingots and then plastically worked to approximately the desired shape. Since man's present civilization has arisen in a large part from the development of methods of putting metals into shape that will do his work, all these processes are significant.

The strength of the foundry industry rests in the fundamental na­ture of casting as a process for causing metal to take shapes that will serve the needs of man. Other methods of shaping exist, each with its own specific merits. Machining, forging, welding, stamping, hot work­ing, etc., provide other means of shaping metals into objects which have use. Each of the foregoing has applications in which it is unex­celled and others for which it is unsuited. Rarely is an engineering product completed which does not use several or at) of the fundamental metal-processing methods. The foundry industry is thus built on one of the truly basic methods available for shaping metals to useful ends.

Certain advantages are inherent in the metal-casting process. These may form the basis for choosing casting as a process to be pre­ferred over shaping process in a particular case.

Some of the reasons for the success of the casting process are as follows.

1. The most intricate of shapes, both external and internal, may be cast. As a result, many other operations such as machining, forging, and welding may be minimized or eliminated.

2. Because of their metallurgical nature, some metals can only be cast to shape since they cannot be hot-worked into bars, rods, plates, or other shapes from ingot form as a preliminary to other processing. ГЬе highly useful and low-cost cast irons, which exceed all other met-•b in tonnage cast, illustrate this fact.

3. Construction may be simplified. Objects may be cast in a sin-8^,B piece which would otherwise require construction in several pieces ^a"d subsequent assembly if made by other methods.

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4. Metal casting is a process highly adaptable to the require­ments of mass production. Large numbers of a given casting may be produced very rapidly. The use of casting in the automotive industry provides ample illustration of this point.

5. Extremely large, heavy metal objects may be cast if they are difficult or economically impossible to produce otherwise. Large pump housings, valves, and hydroelectric plant parts weighing up to 200 tons illustrate this application,

6. Some engineering properties are obtained more favourably in cast metals. A number of examples arc given below:

1. machinability and vibration damping capacity in cast irons;

2. more uniform properties from a directional standpoint, i. е., property cast metals exhibit the same properties regardless of which di­rection the test piece is selected relative to the original casting. This is not true for wrought metals;

3. good bearing qualities are obtained in cast bearing metals. In general, a wide range of alloy composition and properties is produced in cast form.

7. A decided economic advantage may exist as a result of one or a combination of the points listed above.

The list of advantages occurring in the metal-casting process may be expanded beyond that given above. It is also true that condi­tions may be stated wherein the casting process must give way to other methods of shaping. Such conditions are those in the area of the prin­cipal advantages to be gained by the other metal-processing methods. For example, machining produces smooth surfaces and dimensional accuracy not obtainable in any other way; forging aids in developing the ultimate of fibred strength and toughness in steel; welding provides a convenient method of joining or fabricating wrought or cast products into more complex structures; and stamping produces lightweight sheet-metal parts. Thus, the engineer may choose from a number of metal-processing methods.

METAL CASTING - A BASIC MANUFACTURING PROCESS

One of the basic processes of the metal-working industry is the

production of metal castings. Numerous methods have been developed through the ages for producing metal castings, but the oldest method is

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that of making sand castings in the foundry. Primarily, work consists of melting the metal in a furnace and pouring it into suitable sand moulds, where it solidifies and assumes the shape of the mould. How­ever, the operation of making sand castings is not as simple as it seems.

A study of the foundry industry develops the fact that there are few other industries where successful operation depends so much upon certain shop techniques and procedural refinements. These essentials of «know-how» and «know-why» have been accumulated through the years and constitute at present a broad field of information for use in the modern foundry. Notwithstanding the fact that foundry practice is one of the oldest industries of the word, it still occupies a most impor­tant place in the manufacturing scene - with respect to design, engi­neering, and materials.

There are few metal-working industries that do not make use of castings of one or more kinds. Most castings serve merely as details or component parts of complex machines and products. In most cases, they are found usable only when they are machined and finished to specified manufacturing tolerances, providing easy and proper assem­bly of the product. Some castings, whether finished or rough, form structural units complete in themselves - lamp posts, fire hydrants, pipes, and car wheels for railroad trains, for example.

DEVELOPMENT OF METAL-CASTING METHODS

Metal-casting methods may be classified into three groups, de­pending upon the type of mould used and the manner, in which the molten metal is introduced into the mould.

The mould may be made from a refractory or heat-resistant ma­terial, such as sand, some suitable cerarfiic material, or plaster, which is expendable, i. e. the moulds are used only once. The kind of material chosen to make the mould is, of course, determined primarily by the melting temperature of the cast metal. Other factors involved are the porosity of the moulding material, i. e. the ability to transmit air and Seses, and the type of surface finish desired for the product, a finer moulding sand, or other material for smoother finish, and a coarser moulding sand, or other material for rougher finish. Molten metals may •* poured into the mould by gravity, or, on the other hand, pressure

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4. At what points is the greatest metal movement when other shapes are to be obtained?

5. In what operations does the use of this knowledge have prac­tical applications?

2. Find the English equivalents for the following Russian word combinations

под сильным давлением

можно сравнить

поверхность цилиндра

из вышесказанного очевидно

иметь тенденцию

вытекать

иметь практическое применение

3. Translate at sight

1. Поведение пластичного металла при динамическом дав­лении можно сравнить с течением воды, когда её льют на пло­скую поверхность.

2. Однако движение металла не спокойное, а импульсивное, производимое ударами ковочной установки.

3. Простейшей формой пластической деформации является та деформация, которую получают при осадке цилиндра между двумя плоскими бойками.

4. При динамическом давлении металл течет одинаково во всех направлениях.

5. Очевидно, что пластичные металлы имеют тенденцию течь от центральной точки формы.

Unit 19