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  1. Make a written translation of Text 2.

  2. Describe hard-material bits of ithe cutting-abrasive action ty pe using Figure 7.4.

CONTROL TASKS

1 Answer the questions:

    1. What is the drill bit intended for?

    2. How are boring bits classified as regards the principle underlying the breaking up of the rock?

    3. How are boring bits subdivided as regards their purpose?

    4. What are the most widely used bits?

    5. What are the shapes of roller cutters?

    6. What are the patterns of roller cutters arrangement in the bit?

    7. What do diamond-set bits secure?

    8. What do diamond-set bits consist of?

    9. What do hard alloy bits consist of?

    10. What is the difference between diamond-set bits and hard alloy bits?

2 Give English equivalents of the follo wing:

бурове долото

роторне буріння

ріжуче-абразивний

алмазне долото

колона обсадних труб

радіальний

шарошкове долото

спіральний

промивати струменем рідини

швидкість потоку

3 Give Ukrainian equivalents of th e following:

bit of the cutting-abrasive type of action

bit for core drilling

three-roller bit

rotate clockwise

crushing-chipping action

occur at a considerable depth

variously shaped surface of

the, contact sectors

shaped diamond-carrying

head

bort crystal

ensure a continual gap

4 Tell whether each of the following statements is true or false according to the text. Correct the false statements to make them true:

      1. There exist two types of bits each one of which is designed for disintegration of rocks possessing definite mechanical and abrasive properties.

      2. When the bit rotates counter-clockwise the cutters roll over the bottom hole clockwise and accomplish a complicated rotary motion.

      3. Diamond-set bits secure an effective disintegration of nonabrasive and little abrasive rock of medium and great hardness, especially when these occur at a considerable depth.

      4. When excessively exposed, the diamonds crack and break, while with an insignificant exposure the needed penetration of the diamonds into the rock will, be lacking and the drilling will prove ineffective.

5 The contact surfaces of radially running wings are chamfered at 35° in the direction of bit rotation and reinforced with hard alloy teeth.

5 Make a written translation of the following:

By employing diverse materials for the fabrication of the matrix that comes from sintering the mix, the required exposure of diamonds during operation of the bit in the bottom hole is achieved.

When excessively exposed, the diamonds crack and break, while with an insignificant exposure the needed penetration of the diamonds into the rock will be lacking and the drilling will prove ineffective.

In drilling hard and tough rocks, the wear of the matrix is more intensive and therefore it should be made more wear-resistant, for this will preclude the excessive exposure of the diamonds. In rocks of medium hardness the material of the matrix is less susceptible to wear and, therefore, it should be made less wear-resistant.

By adjusting the extent of diamond exposure one can also ensure a continual gap between the matrix and the rock during operation of the bit in the bottom hole.

As a result of this, on leaving the flushing holes of the bit, the drilling fluid can pass all over and along the gap, entrain the minutest particles of the drilled out rock, discharge them into the radial or radial-helical channels running between the contact sectors and then farther on into the annular space.

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