2. Make up word combinations from two columns

small-diameter deposits

Percussive working

Rotary drilling

Opencast ground

mining overburden

surrounding drilling

total holes

3. Read the text and answer the questions Methods used in boring from the surface

Boring may be divided into two operations: (1) piercing the crust of the earth with small-diameter holes and (2) the removal of debris from the bottom of these holes. The second operation is by far the more difficult to perform.

Two distinct methods are adopted in cutting the holes:

1. Percussive drilling, which chips the rocks into fragments;

2. Rotary drilling, whereby a tubular drill is made to revolve rapidly, cutting an annular groove in the rocks and leaving a central core which can be extracted from the borehole.

Various tools are used to shear the cuttings from the boreholes and these cuttings are examined and tabulated.

In percussive drilling the accuracy of the information obtained regarding the various beds of rock passed through depends entirely on the skill of the operator, as details can be obtained only by the sense of touch when passing through rocks of varying hardness. On the other hand, with rotary boring the complete core of the strata is brought to the surface in sections, where the information is visible and accurate measurement and sampling can be done.

Answer the questions:

1. How may boring be divided?

2. What is percussive drilling?

3. What is rotary drilling?

4. What are tools used for?

5. Name differences between percussive and rotary drilling.

4.Complete the sentences

1…., which chips the rocks into fragments.

2. With ... boring the complete core of the ... is brought to the surface in sections.

3. ... may be divided into ... operations: (1) ... the crust of the earth with small-diameter holes and (2) the ... of debris from the ... of these holes.

LESSON 13

1. Read more information about the ways of drilling.

Percussive drilling

This is the oldest known method of boring and is said to have been used by Chinese as early a 500B.C. when drilling for salt. The principle remains the same as it did in those early days, but adaptations and improvements have been made until the present-day percussive methods are the cheapest and speediest means of drilling holes where speed is more important than accuracy of details. The principle is to strike a series of continuous blows on the rock by means of a chisel, thus shattering the rock, and at the same time the chisel is slightly turned between each blow so that a circular hole is formed.

Hand boring is suitable for 2 ½ in. diameter holes up to a depth of 200 ft., but beyond this it is advisable to utilize motive power, which can be steam, electricity, compressed air or internal combustion engine.

Rotary drilling

In the rotary system the cutting tool receives a rapid rotary motion transmitted from an engine situated on the surface, through the boring rods. The drilling is done by abrasion.

The cutting tool may be a hollow bit with the cutting edge set with diamonds or with an annular groove on the cutting edge in which chilled shot revolves, a saw-tooth crown made of finest steel and tipped with a special hard alloy, or a roller bit.

The tool used depends on the strata to be cut.

All rotary bores are equipped with water-flushing systems and their big advantage is that in most cases a complete core is cut from the strata and brought to the surface for examination.

2. Point to the Participle I, and Participle II.

3. Say what is the difference between rotary and percussive drilling.

4. Translate into native language following words and words combinations:

Cutting tool, engine, transmit, cutting edge, drill, shot, bore, strata, saw-tooth crown, roller bit, blow, chisel

LESSON 14

1 Read more information about types of excavators and say what the differences and resemblances are in these two texts.