Ammunition and explosives – Blasting – Plug
Patent
1998-06-26
1999-11-09
Nelson, Peter A.
Ammunition and explosives
Blasting
Plug
F42B 300
Patent
active
059793279
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and apparatus for use in charging blastholes.
In mining operations the main objective of blasting is to break rock and shift material 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. In mining applications this generally consists of locating explosive charges in blastholes drilled in ore, rock, coal or the like. 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 and/or packaged explosives. 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 packaged explosives in a blasthole has a large influence on the results of a blast.
Often the blasthole is not completely filled with explosive charges. Often there is a gap between the top of the column of explosive charge and the collar of the blasthole which is either left open or filled with non-explosive material called stemming. The column itself may not necessarily be continuous; 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 explosive. 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 plugging device which can perform the function of air decking and/or stemming. For example 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.
Australian Patent Application No. 41907/93 describes an inflatable plugging device for stemming blastholes. This particular device 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 device in place and maintain suspension of the stemming. This device however does not necessarily eliminate the use of stemming material and it is not always possible for a preformed, 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 plugging devices of the prior art is that when such devices are used for decking, it is necessary to interrupt the charging of the blasthole with explosive in order to put the plugging device in place. When charging a deep blasthole full of emulsion explosive it is very inconvenient and inefficient to have to cease pumping or pneumatically conveying the emulsion and remove the loading hose in order to insert a plugging device. This method of operation is particularly inconvenient when charging upholes where the bulk emulsion already in the blasthole starts to slowly flow ou
REFERENCES:
patent: 1642118 (1927-09-01), Lindner
patent: 1751015 (1930-03-01), Mora
patent: 1772994 (1930-08-01), Halverson
patent: 5092245 (1992-03-01), Douglas et al.
Nelson Peter A.
Orica Australia PTY LTD
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