Task 4. Fill in the gaps with the verbs given below in proper tense form.

to form, to achieve, to taper, to reduce,

to tap, to line with, to pour, to heat, to fill

1. The finished steel ____ from the furnace into a well heated steel ladle of the required capacity.

2. From the ladle the steel ____ into metal moulds to produce ingots or into sand moulds to obtain steel castings.

3. The mould walls ____ to facilitate stripping from the solidified ingots.

4. As the liquid metal poured into the mould cools, its volume ____ thereby leading to shrinkage of the ingot.

5. A shrinkage cavity, or pipe, ____ in the upper central portion of the ingot where the metal continues to be in the molten state for a long time.

6. Hot tops are extensions of the moulds, they ____ a refractory material.

7. In the top pouring of steel each mould ____ with liquid steel separately.

8. A large economy ____ in the continuous casting of steel.

Task 5. Make up sentences and translate them into Ukrainian:

1. The mould has a tapered shape	Ø to prevent the first portion of the molten metal from dropping straight through the solidifier.
2. Vacuum treatment is used	Ø to obtain steel castings.
3. The seeder is designated	Ø to facilitate stripping from the solidified ingots.
4. The purpose of the hot tops is	Ø to minimise the content of gases and non-metallic inclusions in steel
5. Sand moulds are used	Ø to retard the process of solidification and to retain the metal in the liquid state for a comparatively long time

Task 6. Answer the following questions:

1. How does the tapping of steel start?

2. What size should the ladle be?

3. What cross section may the moulds have?

4. Why the mould walls are tapered?

5. Ingots are produced in a wide size range, aren’t they? Which ingots are the most common size?

6. What is the difference between top and bottom pouring? Which of them provides better surface quality of the ingot? And what is the advantage of the other pouring?

7. When does the shrinkage occur?

8. Where is solidification first in the outside or interior part of the ingot?

9. Where a shrinkage cavity is formed? Why?

10. How can the extent of the pipe (shrinkage cavity) be reduced?

11. How can the metal in hot top be heated?

12. What method of casting is widely applied at the plants?

13. Is vacuum casting as widely applied as continuous casting? Why?

Task 7. Put the following sentences into the proper sequence 1-9. Speak about the continuous casting. Start with: The continuous casting of steel is a new method that is being applied at a number of plants.

a) The completely solidified ingot next passes to the gas-cutting trucks.

b) The ingots continue to travel downwards together with the trucks and are cut into billets of definite length.

c) And at last the billets are rolled into sections of the required shape and size.

d) Then the billets are delivered to the store house.

e) Liquid metal runs in a continuous stream from the ladle into the intermediate device.

f) Upon contact with the seeders and water-cooled walls the liquid metal begins to solidify rapidly on the ingot surface.

g) The billets are carried by conveyers over the inspection table.

h) After that liquid metal runs into the water-cooled solidifiers.

i) It welds to the seeders with which it is pulled downwards, out of the solidifier, by rollers.

UNIT 10

GATING METHODS AND TYPES OF GATING SYSTEMS

In choosing the method of gating and the design of a gating system, it is necessary to keep in mind that the molten metal must steadily flow into the mold, without swirling or impinging on the projecting parts of the mold and cores. The pouring methods must also permit gradual escape of the air and gases from the mold and enable directional solidification of the casting, taking into account its shape and the properties of the alloy cast.

In gating of gray iron casting, it is common to supply the metal to a narrow portion of the casting in order to level off the rate of cooling in its individual portions. As it passes through a narrow portion of the casting, the metal heats up the mold at the inlet section and goes on moving now cooled to a certain extent into a massive part of the casting. The thin portion in the heated part of the mold and the massive part filled with a somewhat cooled metal solidify at the same rate, which makes for a higher quality of the casting, decreases internal stresses

However, in running of casting with massive members, along with the method of supplying metal to a casting through its narrow portion, in use is the gating method by which the gate delivers the metal to a massive part, into the base of the riser, in order that the metal in the riser may long stay in the liquid state and thus feed the casting.

The melt that fills the mold should not flood cope seats or impede the escape of gases from the cope and mold. The pouring rate (rise of metal in the mold per second) must be sufficient for the gases being evolved and the air found in the mold cavity to leave freely the mold. On the other hand, a slow pouring may lead to a decrease in the fluidity of metal, to poor filling of the mold, and, in large molds with a developed metal surface, to excessive heating of mold walls due to thermal radiation of the melt, and slag spots on the surface of the casting.

The types of running used with each of the chief gating methods are bottom gating, mold-joint gating, top gating, step gating, stack gating, side gating, composite gating. Each of the gating methods has its own advantages and disadvantages. The choice of a gating method depends on the shape of the casting, the purpose it must serve, and the metal employed.

The gating method and the design of a gating system and its elements depend not only on the shape and size of the casting, but also on the properties of the alloy cast.

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