Boring or penetrating the earth – Below-ground impact members – Fluid-operated
Patent
1994-12-27
1996-08-06
Tsay, Frank
Boring or penetrating the earth
Below-ground impact members
Fluid-operated
173 73, E21B 704, E21B 414
Patent
active
055424848
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a drilling arrangement wherein there is included a reciprocating piston hammer effecting a hammering against a drill bit.
BACKGROUND OF THE INVENTION
The invention has particular application to a hydraulic down-the-hole piston hammer assembly directly acting against a drill bit which in turn is mechanically rotated and which is adapted to use the hydraulic fluid to. recover at least in part cuttings resulting from the actions.
The problem to which this invention is directed relates to the situation where the reciprocating piston hammer is driven by a fluid at pressure and the impacting faces between the hammer and the drill bit are within the fluid.
Conventionally the fluid is water.
The problem is that where the hammer is caused to strike a first end of the drill bit, upon removal of the striking face of the hammer, there will be caused, in view of the rapidity of the action, some cavitation which in turn will cause, upon collapsing of voids, significant stress forces in the localised vicinity of the impacting faces.
Such an effect has the capacity to effect significant and relatively rapid removal of parts of the material of the impacting surfaces.
BRIEF DESCRIPTION OF THE DRAWINGS
An object of this invention is to provide an arrangement which has the ability to reduce this problem.
According to this invention there is a drilling arrangement of a type using fluid for driving a reciprocating piston hammer, with respective impacting surfaces between the hammer and the drill characterised in that at least one of the surfaces includes at least one channel.
In preference but not essentially, the surface opposite the surface containing the channel, includes a protrusion located so as to be coincident with the location of the channel.
In preference but not essentially, the channel is located in the surface of the first end of the drill bit so as to define therebetween two annular faces and the piston hammer has a correspondingly located outer surface with a correspondingly located circular protrusion located so as to be located when the two impacting surfaces are together, in the channel shape.
In preference but not essentially, the surfaces impacting one against the other are planar across their impacting faces except for the channel and protuberant shapes and the orientation of the respective planar surfaces is at right angles to the direction of relative movement between the two parts.
It is thought that the effectiveness of this described feature arises from the factor that as the faces are impacted together, there is some trapped fluid within the channel shape which as it is caused to be compressed, will cause some fluid to escape past the surfaces coming together and that such action will significantly retard the force of the piston hammer as it approaches the surface of the bit to the extent that most of the impact will be effected through the medium of the fluid acting as an interface between the respective surfaces.
The part of the piston hammer protruding has the effect of additionally forcing fluid at the last moment at a more rapid rate through the closing gap to assist this effect.
In preference, but not essential, the fluid is water.
Ideally, the actual surfaces do not contact directly so that when the surfaces are then drawn away, there is a film of fluid already existing so that the restoration of fluid behind the retreating surface is effected with much less negative pressure and minimal cavitation.
For a better understanding of this invention it will now be described with reference to an embodiment it being emphasised that this is illustrative and not intended to be a limiting explanation of any aspect of the invention.
Accordingly, the embodiment will be described with the assistance of drawings in which:
FIG. 1 is a cross sectional view of an assembly including a reciprocating piston hammer and a drill bit,
FIG. 2 is an enlargement of a part of the view in FIG. 1,
FIG. 3 is a plan view of the impact surface of the inner side of the drill bit, and
FIG. 4 is a p
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patent: 1940846 (1933-12-01), Curtis
patent: 2786451 (1957-03-01), Dulaney
patent: 2837317 (1958-06-01), Hulshizer
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patent: 3403739 (1968-10-01), Brown
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patent: 4402370 (1983-09-01), Gein et al.
patent: 5305837 (1994-04-01), Johns et al.
Meller Michael N.
SDS PTY, Ltd.
Tsay Frank
LandOfFree
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