Tool driving or impacting – Processes
Patent
1997-11-24
2000-02-29
Smith, Scott A.
Tool driving or impacting
Processes
173115, 173206, 173207, 173 11, 173126, B25D 904
Patent
active
060297530
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a drilling apparatus furnished with a percussion piston and more particularly to a percussion piston producing an energy pulse having a shape best absorbable by the rock material that is being drilled, and a method for drilling using the percussion piston.
BACKGROUND OF THE INVENTION
Generally, percussion pistons comprise a piston in which one flange portion formed in the piston, is a means moving the piston to and fro by varying the pressure on either side of the flange. The pressure puts the piston into acceleration towards the drill rod and the piston is also returned to its initial position by pressure. From the bit of the drill rod, the impact energy is absorbed into rock that is being drilled. The required drilling force grows as a function of penetration, when the bit starts to penetrate from its initial position against the rock by impact force. If, with regard to time or penetration, the shape of the energy pulse transmitted to the drill rod does not correspond to an energy pulse shape which the rock being drilled can absorb, a portion of the energy pulse must, inconveniently, reflect back to the drill rod. The pulse shape transmitted to the drill rod on percussion, depends on the piston length and its sonic speed in the piston material. In previous designs no attention has been paid either to the shape of the onward pulse or to shaping it in the drill rod.
SUMMARY OF THE INVENTION
According to the invention an almost optimal energy pulse shape is achieved, which the material to be drilled can absorb almost completely from the drill bit without any inconvenient reflections backward.
The advantage of this invention is that, the impact energy will be better used for rock drilling, reflection as energy pulses back to the piston will lessen and the stress on the drill rod and the drill bit will diminish along with the reduction of their alternating stress. With a piston diameter growing stepwise, the piston movements can be produced, advantageously, by means of hydraulic pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following the invention is disclosed with reference to the enclosed drawing, where
FIG. 1 shows the dependency between force directed on the bit and penetration.
FIG. 2 shows a conventional percussion piston and the drill rod.
FIG. 3 shows a stress pulse from the piston in FIG. 2 getting transmitted to the bit.
FIG. 4 shows a combination of FIGS. 1 and 3.
FIG. 5 shows an ideal piston construction.
FIG. 6 shows a piston and its travel system, according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1 the dependency between force F on the bit and bit penetration s is illustrated. The required force, e.g. on drilling rock, grows according to the exponential curve as a function of penetration s, when in starting position the bit rests against the rock.
FIG. 2 shows drill rod 1 drilling rock 3 and a conventional piston 2 hitting the rock. The piston length is 1 and piston 2 comprises three cylindrical parts with cross-sections A1, A2 and A3. By impact on both flange surfaces of the middle cylindrical part, which has the largest diameter of the three parts the piston is moved to and fro.
FIG. 3 an energy pulse being transmitted while piston 2 as per FIG. 2 is striking. The stress is shown by U1, U2 and U3. Time T is 2.times.I/U, where U is the sonic speed in the piston material. The energy pulse shape reflects the different masses of the three cylindrical parts comprising piston 2, when they are travelling at sonic speed, U.
In FIG. 4 the delineators of FIG. 1 and FIG. 3 have been put in the same coordinate system. This shows that the rock to be drilled cannot absorb, completely, the energy pulse produced by piston 2 of FIG. 2. Area 4 shows energy absorbed into rock 3, area 5 shows energy reflecting back as a tensile pulse along the drill rod and area 6 shows energy reflecting back as a compression pulse. These pulses of tensile stress, reflected on the drill rod, add to the fatigue stress of the d
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patent: 4899836 (1990-02-01), Venot
patent: 5056606 (1991-10-01), Barthomeuf
Kuusento Jaakko
Paasonen Hannu
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