Ammunition and explosives – Blasting – Plug
Reexamination Certificate
1999-07-06
2001-04-03
Nelson, Peter A. (Department: 3641)
Ammunition and explosives
Blasting
Plug
C102S313000
Reexamination Certificate
active
06209458
ABSTRACT:
The present invention relates to a method and apparatus for use in charging blastholes. More particularly the present invention relates to a device for location and inflation of plugs in blastholes and a method of locating and inflating the plug in blastholes using the device of the present invention.
In mining operations the main objective of blasting is to break rock and shift material such as ore, rock, coal or the like in a useful way. When an explosive charge explodes there is a powerful force exerted in all directions and any earth surrounding the explosive charge will break along the line of least resistance. In order to achieve an optimal result in blasting the location and degree of confinement of an explosive charge must be carefully designed and blastholes drilled in appropriate locations. Factors such as the diameter, length, angle and spacing of the blastholes are critical to the success of a blast.
Charging a newly drilled blasthole with explosives generally involves careful placement of an initiation device such as a detonator, a primer and bulk explosive and/or packaged explosives in the blasthole. Detonators are small, compact, high energy explosives which can initiate a larger body of explosive such as a primer, which in turn may detonate with enough force to initiate bulk or packaged explosives. The nature, quantity and arrangement of the initiation device, primer and bulk or package explosive in a blasthole has a large influence on the results of a blast.
Often the blasthole is not completely filled with explosives. Often there is a gap between the top of the column of explosives and the open end of the blasthole (known as the “collar”). This gap may be either left open or filled with non-explosive material called stemming which helps to confine the charge and improve blast results.
Furthermore, the column itself may not necessarily be continuous from the closed end of the blasthole (known as the “toe”) to the collar; sometimes the column comprises several charges or short columns separated by inert material or devices referred to as “decks” are inserted into blastholes to provide discontinuities in the column of explosives. Decking tends to lower the explosion pressure in a blasthole and provide a more even distribution of energy than can be achieved in the absence of decking.
In the past many attempts have been made to provide a blasthole plug which can perform the function of air decking and/or stemming. Desirably these plugs should also be suitable for plugging unwanted ruptures in a blasthole, such as when the blasthole has broken through into a tunnel, fissure or other discontinuity in the earth. In the past attempts have been made to stem blastholes using polymeric containers filled with water and sealed closed at each end. One end is well rounded for easy insertion of the containers into the blasthole where they are secured in place by driving a wedge made of wood or plastic material between the container and the blasthole wall. This type of stemming is inconvenient to use because of the difficulty of manually forcing a water filled container into a blasthole and then driving in wedges while avoiding rupturing the container. These containers are particularly difficult to place into upholes, that is blastholes which are drilled vertically upward or at an upward angle into the walls or roof of a mine because gravity tends to cause them to fall out of upholes. They are quite unsuitable for use in decking because of the difficulty of locating and maintaining them at the required position in a blasthole.
Another simple type of blasthole plug comprises an inflatable bag having a valve. The uninflated bag is lowered into a downhole on a string or pushed into an uphole or downhole using a stick or bulk explosives loading hose. The bag is then inflated using compressed air, the inflated bag engaging the walls of the blasthole and remaining in place by interference fit.
Australian Patent Application no. 41907/93 describes an inflatable blasthole plug for stemming or decking blastholes. This particular plug comprises a flexible, inflatable body member which is contained within an inflexible container. Inflation of the flexible member acts to engage the walls of a blasthole to keep the plug in place. It is particularly important that the plug remains in position when in use in an uphole to support a column of explosive in the uphole. This plug however does not necessarily eliminate the use of stemming material. Furthermore, such plugs are difficult to locate in position in a blasthole and it is not always possible for a performed, inflexible container to conform to the irregular cross section of a blasthole and thus form a seal.
Blastholes are commonly charged with bulk explosives by pumping or pneumatically conveying the bulk explosive through a loading hose into the blasthole. One of the drawbacks of most of the blasthole plugs of the prior art is that when such plugs are used for decking, it is necessary to interrupt the charging of the blasthole with explosive in order to put the plug in place.
In order to overcome these difficulties, other types of blasthole plugs have been developed which can be placed in position in a blasthole prior to charging. Generally these plugs comprise an outer member adapted to engage the walls of a blasthole and an inner member comprising a conduit through which bulk explosive material can be pumped or blown. A typical plug of this type is described in Australian Provisional Patent Application No. PN6377 corresponding to U.S. Pat. No.
5
,
979
,
327
. The outer member of such a plug is generally inflatable and constructed of a deformable material such as rubber or synthetic polymers which provides a good contact between the plug and the walls of the blasthole. Any suitable liquid or gas or finely divided particulate matter can be used to inflate the outer member. Water and air are particularly inexpensive and convenient fluids for use in inflation.
While the inflatable plugs of the prior art have been relatively successful in use, they are often quite difficult to locate and hold the deflated plug in position in a blasthole prior to inflation, particularly in the very longest blastholes. Downholes in large mines may be at least 100 metres in length while upholes may be up to 60 metres in length. While the deflated plug can be lowered by a string into position in a downhole, this can be a relatively difficult task because the deflated plug and string tend to become hung up on the rough walls of the blasthole. Upholes are particularly problematic because the plug must be manoeuvred into place using a stick or a loading hose and held in position until inflated. This is clearly difficult as gravity tends to make the uninflated plug fall out of the uphole.
It has now been found that a device can be provided for relatively quick and simple location and inflation of plugs in blastholes.
The present invention provides a device for locating and inflating a blasthole plug comprising;
(i) a shroud adapted to enclose at least part of a deflated plug as the deflated plug is passed along a blasthole,
(ii) an ejection means for removing the deflated plug from the shroud into a desired location in a blasthole, and
(iii) an inflation means adapted to be removably connected to the plug, such that when the deflated plug is removed from the shroud, fluid material may be passed through the inflation means to inflate the plug.
The shroud may be generally cylindrical in shape and open at one end to receive the uninflated plug. As the uninflated plug is passed along a blasthole the shroud serves to protect the uninflated plug from the sides of the blasthole and avoid any damage due to the plug catching or tearing on pieces of rock or ore in the blasthole walls. The shroud may be sufficiently large to enclose the whole of the uninflated plug or just enough of the plug as to prevent damage of the plug as the locating device is moved along a blasthole.
The device of the current invention is preferably generally elongate and cylindrical to facilitate mov
Gresham Andrew M
Thomson Stephen
Nelson Peter A.
Orica Australia Pty Ltd.
Pillsbury & Winthrop LLP
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