Mining or in situ disintegration of hard material – Processes – Explosive
Reexamination Certificate
1999-04-09
2002-02-19
Bagnell, David (Department: 3672)
Mining or in situ disintegration of hard material
Processes
Explosive
C102S333000
Reexamination Certificate
active
06347837
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed generally to devices for small charge blasting and specifically to devices for small charge blasting having a retractable gas generator.
BACKGROUND OF THE INVENTION
In mining and civil excavation work, small charge blasting or controlled fracture techniques are being introduced as alternatives to conventional drill-and-blast, mechanical breakers, chemical expansion agents and, in some cases, hand methods. “Small charge blasting” as used herein includes any excavation method where relatively small amounts of an energetic substance (typically a few kilograms or less) are consumed for each hole in a rock breaking sequence or where a pressurized fluid is sealed in the bottom of a drill hole by a stemming member to initiate and propagate a fracture in the material to be broken. “Sealing” refers to the partial or total blockage of the hole to impede escape of the fluid from the hole. Examples of small charge blasting devices and methods are described in U.S. Pat. Nos. 5,765,923; 5,308,149; and 5,098,163.
In many small charge blasting methods, a machine drills a hole into the rock to be broken and then inserts an elongated stemming member, which can be a stemming bar, a gas injector barrel, or other pressurizing device, into the hole. A pressurized working fluid, such as a liquid, gas, or another type of pressurizable fluid, is released rapidly into a portion of the hole, usually the bottom portion. The pressurized fluid is typically generated by combustion of a propellant or explosive source, by an electrical discharge into a conductive fluid, or by mechanical compression of the working fluid. The stemming member seals and stems the pressurized working fluid in the hole bottom and thereby causes fracturing of the rock. Small charge blasting can be highly mechanized and automated so that it can be carried out more or less continuously to increase productivity, can permit excavation machinery to remain near the face due to reduced fly rock discharge, and can have a seismic signature that is commonly relatively small because of the small amount of blasting agent used in the blasting sequence.
In designing a small charge blasting apparatus, there are a number of considerations. It would be desirable to use an inexpensive cartridge for providing the working fluid. By way of example, an all plastic cartridge housing could offer significant cost savings. It would also be desirable to have the drill and stemming member on a common boom to simplify the sequential alignment of the drill that forms the hole and the stemming member that is subsequently inserted into the hole. The boom is typically attached to undercarrier or other mounting mechanism. It would also be desirable to maintain an accurate and stable boom alignment relative to a point of reference on the excavation face for both the drilling process and the subsequent process of stemming member insertion. This is often difficult with an indexer mechanism (such as that shown in FIG. 8 of U.S. Pat. No. 5,098,163) which is front heavy and makes it difficult to maintain accurate alignment. Thus, the weight and moment arm of the boom should be substantially minimized not only to maintain an accurate and stable boom alignment but also to permit the use of lighter weight hydraulic systems and under carriers. Finally, the drill and stemming member should be positioned on the boom to permit the spent cartridge in the stemming member to be replaced with a new cartridge during drilling of the hole. If the drill and stemming member are located in close proximity to one another, mud and rock particles from drilling can enter the breech of the stemming member when the spent cartridge is in the process of being replaced with a new cartridge. This can lead to misfires or plugging or jamming of the breech and/or loading mechanism. Additionally, the mud and rock particles can plug the barrel of the stemming member and thereby cause damage to the stemming member when the pressurized working fluid expands down the barrel.
SUMMARY OF THE INVENTION
These and other objectives are realized by the various embodiments of the present invention.
In a first embodiment of the present invention, a small charge blasting device is provided that includes:
(a) a stemming member (e.g., a stemming bar, a gas-generator barrel, or other device for sealing the hole to pressurizing the working fluid in the hole) for insertion into the hole and
(b) a slide assembly comprised of:
(i) a guide track and proximal and distal ends;
(ii) a drive mechanism (e.g., a belt drive, a chain drive, a worm gear drive, a pusher rod drive, a cable drive, a hydraulic or gas powered extending cylinder, or another suitable drive device) located adjacent to the guide track for moving the stemming member linearly back and forth along the track between the proximal and distal ends of the slide assembly (i.e., between its stowed and deployed (or working) positions); and
(iii) a switching mechanism (e.g., a rotating or translating cradle mechanism, a lifting clamp mechanism, or a tracked switching mechanism) located adjacent to the drive mechanism at the proximal end of the slide assembly for transferring the stemming member from a stowed position at the proximal end of the slide assembly onto the guide track for transport to a deployed position at a distal end of the slide assembly. The ability of the stemming member to be retracted to the proximal end of the slide assembly for stowing lowers the weight and moment arm of the distal end of the boom supporting the slide assembly during positioning of the slide assembly by the boom and therefore permits the use of lighter weight (and less expensive) positioning hydraulics and simplifies alignment of the slide assembly with the hole. The lighter slide assembly weight also enables the slide assembly alignment to be maintained more accurately and with more stability since the large dynamic forces associated with a front-heavy indexer mechanism are substantially eliminated.
The small charge blasting device can include another tool for performing another type of unit operation such as a drill for forming a hole in a material to be broken. When stowed, the second tool is typically located on the proximal end of the slide assembly adjacent to the stowed stemming member and on an opposite side of the guide track from the stowed stemming member. The second tool and stemming member are alternatively and sequentially advanced by the drive mechanism along the guide track after being switched onto the guide track from their respective stowed positions to the excavation face to perform their separate functions. When the second tool is a drill that is located at the distal end of the slide assembly when it performs its drilling function, the stemming member will be in its stowed position at the proximal end of the slide assembly. Accordingly, the spent cartridge (from a previous shot) may be removed and a new cartridge inserted into or onto the stemming member during the drilling process without drilling water, mud and other debris entering the barrel, breech, or cartridge loading mechanism of the stemming member. The second tool and stemming member are thus located on a common boom and can be readily, simply and sequentially aligned with a desired location on the excavation face.
During operation, the drill (or other type of tool) and stemming member may be alternately and sequentially engaged with or disengaged from the drive mechanism and/or guide track by the switching mechanism. Because the dynamic forces are relatively low, the drill typically remains engaged with the drive mechanism during the drilling process. In contrast, because of the relatively large dynamic forces, the stemming member is typically disengaged from the drive mechanism during formation of the controlled fracture in the material. The significant recoil forces exerted on the stemming member resulting from fracture initiation and propagation can damage the drive mechanism.
The slide assembly can include one or more features to dampen re
Carnegie-Smith David B.
Fourie Ockert R.
Gavrilovic Mihailo
Krogh Paul
Watson John D.
Bagnell David
BeckTek Limited
Gay Jennifer H
Sheridan & Ross P.C.
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