Patent Application
20080028970
Detonating cords described herein comprise an outer sacrificial jacket which has the protective ability to prevent cut-off due to the initiation of another length of detonating cord of the same or similar core loading in contact therewith. Such a detonating cord can be used under conditions in which a section of the cord comes in contact with a similar section of detonating cord (i.e., another section of the same cord or a section of detonating cord having a like core load of explosive material) without experiencing cut-off at the point of contact. This is achieved without the need to provide a jacket that completely contains the explosive output of the core of the detonating cord. Thus, the detonating cord exhibits some degree of brisance and may, in fact, cause cut-off of a length of detonating cord not configured in accordance with this invention. Various embodiments of detonating cord described herein can be made without a metal jacket layer in the interior jacket or in the sacrificial jacket, i.e., the cord may comprise a composite jacket that is substantially free of any metal layer.
In addition, some embodiments of a detonating cord as described herein meet a cross-sectional outside diameter constraint that enables the cord to be capped, i.e., inserted into the shell of a standard-sized detonator having an inside diameter of about 1.3 mm (about 0.5 inch), without the need to strip any part of the jacket of the detonating cord before inserting it into the shell.
The subject detonating cords comprise a core of explosive material surrounded by a composite jacket having two components: an interior jacket and an outer sacrificial jacket, both of which comprise one or more jacket layers. The outermost layer (relative to the core) of the interior jacket is in contact with the sacrificial jacket, which is disposed thereon. Upon exposure to the brisance of an adjacent similar section of detonating cord, the sacrificial jacket is broken and peeled away from the interior jacket beneath it, but at least part of the interior jacket and explosive core of the detonating cord remain intact, without having suffered cut-off, leaving the cord functional. In some embodiments, the sacrificial jacket comprises a sacrificial extruded layer comprising extruded polymeric material, which may be in direct contact with the interior jacket, or the sacrificial jacket may optionally further comprise additional sacrificial layers, such as a sacrificial textile layer, within the sacrificial extruded layer and in contact with the interior jacket. Without wishing to be bound by any particular theory, it is believed that the fracture and peeling of the sacrificial jacket absorbs and diverts sufficient energy from the adjacent functioning detonating cord to preserve the integrity of the explosive core and interior jacket therein, so that cut-off is avoided and the utility of the remaining detonating cord is preserved.
To allow the sacrificial jacket to peel away from the interior jacket, the sacrificial jacket is not tightly bound to the interior jacket, i.e., the sacrificial jacket must be relatively easily separable from the adjacent outermost interior jacket layer. The sacrificial jacket can be rendered separable from the interior jacket by several methods. When the sacrificial jacket comprises a sacrificial extruded layer extruded directly onto the interior jacket, adhesion between the two jackets can be minimized to make the sacrificial jacket separable from the interior jacket by cooling the outermost layer of the interior jacket before extruding the sacrificial jacket over it. Cooling can be achieved, in one embodiment, by passing the interior jacket through a cooling bath before extruding the sacrificial extruded layer onto it. This procedure facilitates the use of a sacrificial extruded layer that comprises a material that is compatible with the material of the outermost interior jacket layer. In another embodiment, a sample detonating cord was prepared by slipping a sheath of polyolefin heat-shrink tubing having a thickness of about 0.02 inch (about 0.5 mm) over a length of premanufactured, room-temperature detonating cord comprising an outermost jacket comprising a blend of about 80 percent LDPE low density polyethylene) and about 20 percent HDPE (high density polyethylene) having an outer diameter of about 0.130 inch (about 3.3 mm). The sheath was then heated sufficiently to shrink it onto the detonating cord. Alternatively (or, in addition) to cooling, the sacrificial extruded layer and the outermost interior jacket layer may comprise chemically incompatible or immiscible materials. Allowing for separation of an extruded jacket layer from one beneath it is contrary to standard practice in the art because it is normally desired that each successive extruded layer form a tight bond with the layer beneath it.
In other embodiments, the sacrificial jacket is made separable from the interior jacket by providing a sacrificial jacket comprising a sacrificial textile layer woven around the interior jacket and a sacrificial extruded layer thereon. Even if the sacrificial extruded layer bonds tightly to the sacrificial textile layer, the sacrificial textile layer will easily separate from the interior jacket layer around which it was woven. Therefore, when the sacrificial jacket functions, both the sacrificial extruded layer and the sacrificial textile layer separate from the interior jacket.
One embodiment of such a detonating cord is illustrated in schematic cross section in
Core 12 may comprise any suitable explosive material; a typical core material comprises PETN. A detonating cord in accordance with this invention may have a core load of explosive material of less than about 3.2 grams/meter (g/m), optionally in the range of about 0.2 to 2 g/m (1 to 10 grains per linear foot (grains/ft)), optionally less than 1.25 g/m (6 grains/ft), e.g., from about 0.2 to 1.25 g/m (about 1 to 6 grains/ft). In one optional embodiment, the detonating cord may have a core loading of about 1 to 1.5 g/m (about 5 to 7 grains/ft).
Textile sleeve 16 may comprise any suitable textile suitable for maintaining the lengthwise continuity of core 12. Providing a textile sleeve around a core of explosive material for use in detonating cord is well-known in the art, as is the deposition of additional extruded and woven layers thereon, such as extruded interior jacket layer 18. Alternatively, the innermost jacket layer may be extruded over the core.
Interior jacket layer 18 surrounding textile sleeve 16 is the outermost layer of interior jacket 14. Interior jacket layer 18 may be a polymeric material extruded over textile sleeve 16. For example, jacket layer 18 may comprise a blend of about 80 percent LDPE (low density polyethylene) and about 20 percent HDPE (high density polyethylene), as is well-known in the art. In a particular embodiment, jacket layer 18 may have a thickness of about 0.5 millimeter (mm) (about 0.02 inch), which is slightly less than the thickness of an outer jacket layer in a corresponding prior art device, which has a thickness of about 0.75 mm (about 0.03 inch) but which lacks an outer sacrificial jacket.
The sacrificial jacket 20 comprises a sacrificial extruded layer extruded over jacket layer 18. Optionally, sacrificial jacket 20 may comprise a material that is chemically compatible or miscible with the material comprising jacket layer 18, e.g., sacrificial jacket 20 may comprise the same kind of polymeric material comprising the interior jacket layer on which it is disposed. For example, layer 18 and layer 20 may both comprise polyolefins, e.g., a mixture of 80% LDPE and 20% HDPE. To reduce the bonding that would otherwise occur between two extruded polymeric layers of like materials, interior jacket layer 18 is allowed to cool before sacrificial outer jacket 20 is extruded thereon so that the sacrificial jacket 20 does not meld into or strongly adhere to interior jacket layer 18. Cooling may be achieved by, e.g., passing the interior jacket through a cooling water bath before sacrificial jacket 20 is extruded thereon. The thickness of sacrificial jacket 20 is about 0.25 mm (0.01 inch), e.g., from about 0.125 mm to 0.36 mm (about 0.005 to 0.014 inch), optionally from about 0.2 to about 0.3 mm (about 0.008 to 0.012 inch). In particular embodiments, the total outside diameter of detonating cord 10 may be not greater than about 3.8 mm (0.15 inch), e.g., in the range of from about 3.3 to about 3.8 mm (about 0.13 to 0.15 inch), thus facilitating its use with a detonator having a standard size detonator shell, e.g., a No. 8 detonator shell having an inner diameter of about 6 millimeters (mm), e.g., 5.7 mm (about 0.22 inch).
In use, when a section of detonating cord 10 as shown in
In an alternative embodiment, jacket layer 18 may comprise a polymeric material that is incompatible with that of the sacrificial jacket layer in contact therewith, so that even if interior jacket layer 18 is not cooled before sacrificial jacket 20 is extruded onto it, jacket 20 will not strongly adhere to layer 18, although cooling may optionally be performed to enhance the separation of the sacrificial jacket from the interior jacket. In another embodiment, the sacrificial jacket could be made separable from the interior jacket by extruding the sacrificial jacket at a lower temperature than the interior jacket. The cooler temperature of the sacrificial jacket material inhibits intermingling of the polymeric materials of the sacrificial jacket and the interior jacket. For example, a detonating cord may comprise a core of explosive material surrounded by an outmost interior jacket comprising SURLYN™ polymer that may be extruded at 325° F. (about 163° C.) and a sacrificial jacket comprising polyethylene (e.g., a blend of about 80% LDPE and about 20% HDPE) that may be extruded over the SURLYN™ polymer at about 300° F. (about 150° C.).
In yet another embodiment, the sacrificial jacket is rendered separable form the interior jacket therein by using a sacrificial jacket material whose melting temperature and/or extrusion temperature are significantly lower than the corresponding temperature(s) of the interior jacket layer material. The sacrificial jacket layer may then be extruded at a cooler temperature than the extrusion temperature of the interior jacket layer, so that the cooler temperature of the sacrificial jacket layer material diminishes its tendency to blend with the jacket layer 18 on which it is disposed.
One specific embodiment of a method for producing detonating cord comprising a sacrificial jacket as shown in
An alternative embodiment of a detonating cord in accordance with this invention is shown in
One embodiment of a method for making detonating cord 10′ is depicted in
A section of a detonating cord comprising a sacrificial jacket as described herein may be disposed in adjacent relationship to a similar section of detonating cord and will survive the functioning of the adjacent section of detonating cord without experiencing cut-off. Such adjacent relationships include side-by-side, generally parallel relation, one embodiment of which being depicted, e.g., in
In other alternative embodiments, the interior jacket of a detonating cord may have a lesser or a greater number of layers than the interior jacket of the illustrated embodiments.
Although the invention has been illustrated and described with respect to a single embodiment thereof, it would be recognized by one of ordinary skill in the art, upon a reading and understanding of the foregoing, that numerous alterations and variations to the disclosed embodiment fall within the spirit of the invention and the scope of the following claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US04/17354 | 6/1/2004 | WO | 00 | 8/1/2007 |
