1. Answer the following questions

1. What are the principal advantages of shell moulding com­pared with green-sand moulding?

2. Why are the gains in precision made?

3. Is water used when a phenolic resin is mixed with silica sand?

4. What type of pattern is required for shell moulding?

5. How is the shell formed?

6. Where is the mould cured?

7. When and how can the shell be stripped from the pattern?

8. How are the two halves of the mould assembled?

9. What position may shell moulds be placed for pouring in?

10. What kind of castings is shell moulding ordinarily used for?

11. Why is shell moulding more economic versus sand moulding?

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

1) binder, bond a) sand moulding is which the fin-

ished mould does not require dry­ing out

2) clip b) adhesive substance insoluble in

water

3. resin c) a casting made in a shell mould

4. shakeout d) the ingredient (usually used to in-

dicate other than clay, which is artificially added to moulding sand mixure in order to give it the reguired strength

5) green-sand moulding e) appliance for holding things to-

ge'thef

6) shell moulding f) the removal of solidified castings

from their moulds

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

1. A phenolic resin is mixed with fine silica sand in the presence of alcohol or water.

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2. The completed shell mould may be stored for several days or even weeks before pouring.

3. In most cases green sand castings will cost more than shell-moulded castings.

2. After the casting cools, it is removed from the shell.

4. Read the following text and find the answers to the ques­tions below

1. What pattern is used in sand moulding?

2. What are the sand grains bonded by?

3. When is the process of sand moulding named green sand mould?

4. Why are the gains in precision made in shell moulding com­pared with sand moulding?

5. What castings are produced by shell moulding?

Shell moulding has some principal advantages compared with green-sand moulding. The process of shell moulding is more precise in comparison with green sand moulding. In sand moulding a relatively inexpensive pattern of wood or light metal is used. The sand grains are bonded together by the addition of a few per cent of clay, or other ma­terial with a small amount of water. In shell moulding stable phenolic resins are used, that is why the gains in precision are made. The mould is rigid before removing the pattern.

Shell moulding is usually used only for castings which are run in reasonably high volume. Most shell-moulded castings are small in size. It is likely that the economy of shell moulding versus sand moulding will improve rapidly for small parts which are made in relatively high volume.

5. Give the title to the text above.

5. Use your translation of 4 in describing the process of «Shell Moulding» as compared with «Sand Moulding».

5. Translate at sight

Процесс производства оболочковых форм коркового литья заключается в следующем: фенольная смола смешивается с мел-

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ким кремнеземным песком. Причем, смесь должна быть сухой или с добавлением спирта и не смачивается водой.

Чтобы проводить процесс коркового литья для изготовле­ния форм, необходима механически обработанная металлическая модель обычно из серого чугуна, алюминия или латуни. Модель нагревается до 450-550 °F. Затем готовая смесь опрокидывается или вдувается на поверхность модели.

При соприкосновении с горячей моделью смола плавится на глубину от 1/8 дюйма и больше, закаляется и прочно связывает песчаные зёрна. Так образуется оболочка, корка, имеющая форму модели, которая после вулканизации в печи в течение 15-20 се­кунд может быть снята с модели посредством выталкивающих штифтов.

Unit 9