Boring or penetrating the earth – With tool shaft detail – Helix or helically arranged structure
Patent
1995-01-25
1996-02-13
Novosad, Stephen J.
Boring or penetrating the earth
With tool shaft detail
Helix or helically arranged structure
175 69, 175 71, E21B 1718, E21B 1722, E21B 2114, E21C 708
Patent
active
054905710
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to dust suppression in rock drilling operations and in particular to a subassembly to separate the liquid from the gas of the flushing medium used in rock drills.
Drilling into bedrock for example to enable explosive charges to be placed for excavating ore in open-cut mining operations is carried out by rotary air blast drills. Air at high pressure (typically 40 psi) and volume (750 to 2000 cubic feet a minute (cfm)) is delivered through a bore in the drill string to the drill bit. The air supplied to the drill bit, which may for example be a blade or roller type bit, exits from orifices in the bit, cools the bearings of the bit and conveys the debris created by the drilling away from the drilling workface up the borehole. This debris travels up the borehole at a typical (bailing) velocity of 5,000 to 7,000 feet per minute depending on the size of the borehole and the drill string.
BACKGROUND OF THE INVENTION
The debris produced includes particulate matter and dust. To reduce the dispersion of dust into the environment, which has deleterious effects on both equipment and personnel, the debris is sprayed with water. The water is supplied with the air through the drill string to the drill bit and in addition to suppressing dust also causes corrosion, in particular of the bearings. It also produces a slurry which causes wear of the cutting surfaces of the drill bit, reducing the life of the bit and reducing drill penetration rates. The drill bit is a costly item to replace.
A stabiliser may be located behind the drill bit to centre the drill bit within the borehole. The sections of the drill string are joined together by threaded connectors at either end. Two standard threads are generally used in the drilling industry, namely BECO and API, and a crossover connection is often required to accommodate assemblies having these different threads.
DISCLOSURE OF THE INVENTION
According to a first aspect of the invention, there is provided a dust suppression sub-assembly for a rock drill. The sub-assembly is provided with means to secure it into a drill string adjacent the drill bit. The subassembly includes an outer housing and an inner housing, and a helical path extends through the inner housing. Inlet means for a gas and liquid flushing medium are provided at one end of the sub-assembly communicating with the helical path. A plurality of slots are spaced at intervals along the inner housing communicating between the interior of the inner housing and a chamber defined between the inner and outer housings. The liquid part of the flushing medium is centrifuged by its helical motion along the path and exits the slots. A plurality of outlets are provided for the liquid in the outer housing adjacent the other end of the sub-assembly, and exit means are provided for the gas at the other end of the inner housing in communication with the helical path.
The sub-assembly can be fitted behind the drill bit or behind the stabiliser of the drill string of a rock drill. The sub-assembly is attached at either end by hollow threaded connections; the connections may be either male or female.
Preferably, the helical path is formed by a spiral flange. Alternatively the helical path is formed by a plurality of entwined tubes.
Preferably the slots are 180.degree. apart along the helical path.
Preferably the inner and outer housings are co-axial cylinders of different radii.
Preferably scrapers are provided on the interior of the inner housing at the trailing edges of the slots, in the direction of motion of the medium along the spiral path, to direct the liquid radially outwards through the slots. Optionally the scrapers comprise curved extensions of the trailing edges of the slots.
Preferably the sub-assembly further comprises a return path extending between a balance hole adjacent the other end of the sub-assembly, and provided with a one-way check valve; and a return port adjacent the inlet means.
BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the invention will n
REFERENCES:
patent: 3094175 (1963-06-01), Jackson
patent: 3716108 (1973-02-01), Loftis et al.
patent: 4515229 (1985-05-01), Drummond et al.
patent: 5139095 (1992-08-01), Lyon et al.
SU,A,1265311 (MAGN MINE METAL INS) 23 Oct. 1986 Derwent Abstract N87 121381 (PAN 87-161911/23).
SU,A, 866167 (MOSCOW MINING INST) 23 Sep. 1981 Derwent Abstract, J4572E/28 (Bulletin 35/23 Sep. 1981).
Carrall Christopher R.
Hanns David T.
Carrall Christopher Richard
Hanns David Thomas
Nicol Jo-Ann
Novosad Stephen J.
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