1. Answer the following questions

1. Which mouldings process is the most widely used one?

2. What moulds are referred to sand casting?

3. Name the main qualities of silica sand.

4. How does a foundry-man combirte the sand binders?

1. Does binder and sand selection depend on a construction of a mould? Give an example.

5. What property is permeability, in what terms is it measured?

6. What characteristics is binder selection based on?

7. How do typical compression strength vary?

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

1. permeabi 1 ity a) the material used for making moulds

2. refractoriness b) the ingredient, which is added to a

moulding sand mixture in order to give it the required strength

3. to bake c) a specialist in casting

4. sand d) to remove moisture by heating in

order to increase permeability or strength

5) binder e) the resistance of ceramic materials

to a high temperature (when not subjected to a load)

6) a foundry-man f) the rate of flow of gas through a layer

of foundry sand under a pressure

3. Find out which sentences correspond to the contents of the text

1. Sand moulding is widely used to produce castings in all cast-able metals.

2. Good foundry sand is found in a varienty of locations of this country.

1. There is a great variety of binders, which are added to sand.

3. Sand mixure that is used for making a mould has the propetry which is called permeability.

4. Sand is combined with the binders very accurately in definite proportions.

4. Render the following

After the casting procedure has been chosen it is necessary to make a mould. Most castings are made in sand moulds, in which only one casting may be made. An inexpensive pattern of wood or light metal is used in this process. The moulds are made of silica sand. This sand is mixed with a few per cent of clay or other material. These sub­stances are called binders, Binder selection is based on the strength the binder will develop when mixed with sand. The sand mixture must have an ability to allow the air and gas to move out of the mould through the sand itself. This property is called permeability.

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5. Translate at sight

Многие отливки производятся в земляных формах. Для из­готовления земляных форм необходима деревянная модель, сде­ланная по форме изделия. Формовочная земля смешивается с гли­ной или другими связующими. Иногда земля смачивается водой. Литейщик соединяет землю с глиной очень точно, в определен­ных пропорциях. Смесь должна пропускать газы и воздух. Это свойство называется проницаемостью.

Unit 4 MELTING UNITS

Cupola Furnace. The most widely used furnace for melting iron for ordinary castings of all kinds is the cupola. It is the oldest type of furnace and the most economical. The cupola consists of a cylindrical shell lined with refractory brick with the bottom door closed; the charge consists of alternate layers of coke, metal scrap, and limestone. These charges are placed in the furnace through a side charge door and dropped down on the coke bed located in the well area. Heat from the coke bed is generated supplying air uniformly in­side through the tuyeres. The heat rises and melts the metal in the first charge on the bed and progressively preheats the upper charge. The scrap metal melts and drops into the well area. Metal is tapped out at the breast. The rate of melting in tons per hour is a function of the di­ameter of the furnace.

Crucible Furnace. Melting in a crucible consists of charging ei­ther scrap metal and alloys or specification ingot. Heat applied by a blower and burner combusting either oil or gas in the area around cru­cible. The heat provided melts the nietah Crucible furnaces produce metal in batches.

Open-hearth Furnace. Open-hearth furnace is continuously op­erated, because once up to temperature the refractory life is increased by continuous operation. The charge is usually added by a charging machine or by a manipulator, which places the charge into the molten

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bath. The metal melts as a result of hot gas and preheated air burned over the bath. The hot gas heats up a network of refractories known as checkers to preheat incoming air and gas. After the proper composition of metal is achieved the furnace is tapped by opening the tap hole and allowing metal to run gravitationally into a ladle for transport to the moulds.

Electric-arc Furnaces

Indirect-arc Furnace. Heat is provided by the arching of two electrodes protruding through the sides of the furnace.

Direct-arc furnace. Heat is provided by three electrodes striking an arch against the cold metal charge. The heat of each arch causes the scrap to melt.

Electric Induction Furnace. Heat is produced by inducing a cur­rent in the scrap charge. The outer coil provides a primary alternating current. Because of the alternations, a secondary current is produced in the scrap. The resistance of the scrap to the passage of the current causes heating the scrap, and ultimately it melts. In the molten state the bath is continuously in molten according to the lines of the force of the primary coil. Thus, intimate mixing of alloys occurs.

Exercises

1. Answer the following questions

1. What does the cupola consist of?

2. What are the constituents of the charge?

3. Where is the coke bed located?

4. In what way is air supplied?

5. What is the function of the diameter of the furnace?

6. What does melting in a crucible consist of?

7. How is heat applied in a crucible?

8. In what form is metal produced in a crucible?

9. When and how is an open-hearth furnace tapped?

10. Name the types of electric furnaces?

11. How is heat provided in different types of electric furnaces?

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