Ammunition and explosives – Blasting – Patterned blasting
Reexamination Certificate
1999-11-18
2002-06-04
Nelson, Peter A. (Department: 3641)
Ammunition and explosives
Blasting
Patterned blasting
C102S313000, C086S020150
Reexamination Certificate
active
06397754
ABSTRACT:
The present invention relates to a method for charging boreholes with explosives, comprising the steps of introducing one end of a charging hose into the borehole to a substantially predetermined distance from the bottom of the borehole, pumping a pumpable explosive through the charging hose at a controlled rate and, essentially simultaneously with the pumping of the explosive, withdrawing the charging hose from the borehole at a controlled rate.
The invention also relates to an apparatus for charging boreholes with explosives, comprising a vessel containing a pumpable explosive, a charging hose adapted for insertion into a borehole, pumping means connecting the vessel with the charging hose for transporting the explosive to the borehole and hose operating means for achieving the movement of the charging hose in the borehole at a controlled rate.
Specifically, the invention relates to a method and an apparatus for charging pumpable explosives in a reduced amount in relation to the amount corresponding to the complete fill-up of a borehole.
In connection with blasting, it is often suitable to reduce the charge compared to that which corresponds to completely filling up the borehole. One may wish to achieve a smooth and strong final contour, to reduce vibration in connection with blasting or to follow ore faces and reduce undesired waste rock removal. In driving tunnels or galleries, cautious blasting of the contour holes may give a substantially undamaged rock face with significantly reduced needs for subsequent repair and support work, such as bolting, guniting, concrete reinforcement, etc., and the final profile will be more true to the design size. Similar considerations arise in underground mining and stoping or in attempts to limit the production of fines to meet certain after-processing requirements. Although numerous closely spaced boreholes can be used to produce smooth fracture planes, the method is limited by practical and economical constraints.
One approach could be to use smaller borehole diameters in contour or other holes where reduced explosive power is desirable. This is impractical and would increase the cost of blasting as well as render it more difficult. Instead, the trend is towards wider boreholes, which further increases the need for reduced charges.
A second method is to dilute the explosives with lightweight materials which reduce the density of the charge. U.S. Pat. No. 4,995,925 describes this method in more detail. However, the product has low water resistance and must be used in combination with other explosives.
Common problems associated with the above-mentioned charging methods are inconsistency in charging and uncontrolled coupling between explosive and rock. Detonation failures have also occurred in certain explosives, probably because of precompression from forerunning shock waves in the free gas channel.
A third method, disclosed in U.S. Pat. No. 5,584,222, is to use a string of pumpable or blowable explosive. In the case of a pumpable explosive, the string is obtained by adjusting the withdrawal rate of the charging hose in relation to the product flow rate, i.e. to the speed of the pump. However, the method of using pulverulent or liquid strings is adapted to horizontal or somewhat inclined boreholes.
U.S. Pat. No. 5,105,743 describes a method in which a standard blowable explosive is utilised in partially filling a borehole. The method is limited to particulate and blowable explosives and is of limited use in, for example, wet environments or other situations where pumpable explosives are needed. The method requires different tools for different borehole diameters and tends to result in uneven amounts along the length of the hole.
The object of the present invention is to provide a method and an apparatus for charging boreholes with explosives suitable for all borehole directions, but especially for up-holes.
A further object of the invention is to provide a method and an apparatus allowing filling of only a desired part of the cross-sectional area of the borehole with a pumpable explosive and allowing the explosive to be distributed as uniformly as possible around the entire borehole wall.
Yet another object of the invention is to provide, if applicable, draining of the charged borehole of penetrating ground water.
It is also an object of the invention to obviate the risk of water pockets forming between the explosive and the borehole wall, when water is used as a lubricant in the charging hose.
These objects are achieved according to the invention by a method according to the introductory paragraph, characterised by causing the explosive to flow out in the form of a hollow cone and at high pressure from a nozzle arranged on said end of the charging hose, so that the outflowing explosive is given increased viscosity and consequently adheres in a cohesive manner to the entire cylinder-shaped wall portion of the borehole, upon which the explosive impinges in connection with said outflowing.
An apparatus for carrying out the above-described method is characterised in that the apparatus, in addition to the components mentioned by way of introduction, also comprises a nozzle, from which the explosive is caused to flow out in the form of a hollow cone and at high pressure, that the nozzle is fastened to the end of the charging hose by means of a fastening member, and that at least one centring device is arranged on the charging hose, which centring device comprises a pair of separate, annular members intended to engage with the outside of the charging hose, as well as a plurality of arcuate, resilient members of considerable length in relation to their width and thickness, which latter members are oriented essentially in the longitudinal direction of the charging hose and connected to the annular members as well as adapted under compressive stress resiliently to abut against the cylinder-shaped wall of the borehole.
Further developments of the invention will appear from the features recited in the subclaims.
The method according to the invention has no limitations with respect to the direction of the borehole, and can thus be applied in vertically upwardly directed holes, in vertically downwardly directed holes, in horizontal holes, or in holes of any borehole direction. Nevertheless, the method is particularly advantageous for upwardly directed charging, and particularly if the upwardly directed charging is combined with chemical gassing. By adjusting the degree of charging/amount of explosive to the specific need in each borehole, the range of explosives can be limited to a pumpable emulsion explosive and a primer, and a detonator for initiation. Moreover, the invention is of great practical importance in all types of charging, where the product is sensitised by means of chemical gassing during and after charging.
The method for achieving partial charging of the borehole consists of pressing emulsion explosive under high pressure through a special nozzle in the hose end. For the best results, the nozzle is centred in the borehole. This is effected by providing the outermost part of the hose with a special centring device, preferably comprising fastened, resilient lamellae.
The nozzle sprays the explosive in the form of a hollow cone onto the borehole walls, providing very good anchoring to the borehole surface. The desired charging degree according to the invention is subsequently achieved in the known manner by adjusting the withdrawal of the hose to the flow rate of the explosive, i.e. the pumping and withdrawal rates. The explosive is applied as a cylinder or in the form of a tube to the borehole wall, while the bottom and the innermost portion of the borehole, where the igniting means, i.e. the primer and the detonator, are arranged, are also completely filled with explosive.
By forming a tube of pumpable explosive, only partially filling up a borehole diameter, several objectives are achieved. The explosive itself need not be highly diluted, with corresponding problems; rather energy reduction is accomplished by quantity and by the wal
Burns Doane , Swecker, Mathis LLP
Nelson Peter A.
Nitro Nobel AB
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