1. Answer the following questions

1. Why is the use of die casting growing faster than that of any other type of casting?

2. What metals are commonly die cast?

3. For what parts does die casting represent the ultimate in economy?

4. What are the most important limits of applicability of the process?

5. What kind of machines are used when the die casting opera­tion is usually done?

6. How is the moulding operation performed?

7. In what way is the pouring operation performed?

8. What is the only operation required after casting, and how is it done?

9. What is the die produced from?

10. How does the die life vary?

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

1) sound casting a) the operation of removing fins

from castings

2) trimming b) a narrow channel connecting the

mould cavity or the core with at­mosphere serving to carry off the gases generated in the mould dur­ing casting

58

3) vent c) a portion of a material taken a lar-

ger mass of the same material for examination purposes

4) die casting d) a long raised piece often of thicker

material across trimmer surface serving to support or strengthen it

5. piece e) a casting showing no defects

6. rib f) the production of a casting in die-

casting machines where the liquid metal is pressed into the casting die by plunger or compressed air

3. Find out which sentences do not correspond to the con-teats of the test

1. In the die-casting process molten metal is forced into an iron die under low pressure.

2. The casting operation is usually done in high-speed automatic machines.

3. The casting operation is rather simple.

4. After the excess metal is trimmed off, the casting is not ready for use. Some more operations are required.

4. Render the following

The die-casting process is noted for high production close di­mensional tolerances, high degree of surface finish, accuracy in repro­ducing fine details, and higher strength properties made possible by the fine-grain structure produced. The casting size is limited to the capac­ity of available machines and overall dimensions of die blocks. Sec­tions as thin as 0.15 in. may be produced in small castings, and cores • small as 1/32 in. in diameter can be used. Metal inserts may be cast *s M integral part of some castings.

S.Trsnslate at sight

Литьё под давлением чаще всего используется для получе-•Ч«" отливок из цветных металлов и их сплавов. Процесс этот не Дорогостоящий, т.к. очень прост. Операция заливки выполняется

59

автоматически. При этом виде литья форма может использоваться много раз для получения отливок.

Используя литьё под давлением, можно получать отливки большой точности. Материалы, используемые для литья под дан лением, должны иметь низкую точку плавления. Хотя процесс ли­тья имеет некоторые ограничения, он является самым быстро раз­вивающимся видом литья.

6. Speak about the process of die-casting.

Unit 11

PERMANENT MOULDING

Making a mould is generally the most costly single operation in making a casting by sand, shell, or investment method. This operation must be repeated for each casting because the sand or ceramic mould is not reusable. In some cases, the mould mate­rial cannot be reused either. In permanent moulding, the metal mould can be reused for several thousand castings. The process is very adapt­able to a high degree of mechanization. Requirements for skill are minimized by the fact that control of quality can be ensured by good design of the mould, engineering heat transfer characteristics, auto­matic timing of cooling in the mould, and scientifically designed gat­ing system built into the mould, In its most mechanized form, the proc ess is extremely simple. The only manual operations are setting cores, if required, pouring metal into the mould, and removing the solidified casting from the mould.

Permanent moulding is not a precision casting process because there is some less accuracy across the parting line of the mould. This is characteristic of all two-part moulds. However, when moulds and ma­chines are kept in good condition, the process yields very consistent dimensions. Metal structure and soundness are influenced greatly by the rates of cooling and solidification in various sections of any cast part. In the permanent mould process it is possible to engineer the heat-transfer characteristics of the mould very accurately and to control

60

them reliably. This is done by applying controlled and direct quantities of cooling or heating to the mould during the cycle.

Low cost, consistency of dimentions, and consistency of metal structure, and soundness are the principal advantages of the permanent-mould process.

Grey iron, aluminium alloys, and magnesium alloys are pro­duced in a large volume by this process. Development and pilot opera­tions involving silver-alloy and copper-alloy moulds give promise of the eventual production of steel castings in permanent moulds, as well.

In general, although, there are many exceptions, the process is best adapted to small, relatively simple shapes produced in a large volume.

Exercises

1, Answer the following questions

1. What is the most costly operation in making a casting by sand, shell or investment method?

2. Why is making a mould known to be the most costly operation?

3. For how many castings can the metal mould be reused in permanent moulding?

4. Is this process adaptable to a high degree of mechanization?

5. What are the only manual operations?

6. Why is permanent moulding not considered to be a precision casting process?

7. When doesn't the permanent moulding process yield very consistent dimensions?

8. What are the principal advantages of the permanent mould process?

9. What alloys are produced in a large volume by this process?

10. What shapes is the process best adaptable to?

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

О permanent mould a) alloys with good casting properties

2) parting line of a pattern b) the drop in temperature of a body

in a time unit

61

3) two-part mould c) an iron-carbon alloy containing

less than 2 per cent carbon in addi­tion to other elements, obtained by melting and designed for plastic working

4) rate of cooling d) the line of intersection between the

point face of a pattern and its ex­ternal surface

5) steel c) a mould consisting of two mould-

ing boxes

6) casting alloys 0 a mould, usually made of metal.

which can be repeatedly used for making castings of the same shape