Ammunition and explosives – Igniting devices and systems – Fuse cord
Reexamination Certificate
2000-08-24
2004-02-24
Johnson, Stephen M. (Department: 3641)
Ammunition and explosives
Igniting devices and systems
Fuse cord
C102S275800
Reexamination Certificate
active
06694886
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to reactive cords and connectors therefor and, more particularly, to cords which are sufficiently rigid for insertion through a material to be fractured by the cords.
2. Related Art
Detonating cords are well known and typically include a core explosive material covered by a non-metal sheath. The sheath may comprise an extruded flexible plastic inner jacket and a flexible, textile outer jacket composed of, for example, polyester yarn. The detonating cord sheath may also include a waterproofing and sealing material such as asphalt disposed about the core. The core explosive may be composed of, for example, pentaerythritol trinitrate (PETN), cyclonite (RDX), homocyclonite (HMX), tetranitrocarbazol (TNC), hexanitrostilbene (HNS), 2-6-bis picryo-amino 3,5-dinitro pyridine (PYX) or black powder, typically with a plasticizer such as a polysulfide and/or one or more other known additives. A typical core loading of PETN may be on the order of 7.5 to 50 grains per foot (gr/ft) (about 1.6 to 10.6 grams per meter (g/m)) with a detonation velocity of about 21,000 feet per second (about 6400 meters per second) or about 4 miles a second (about 6.4 kilometers per second). Detonating cords are typically used in the initiation of charges of high explosives but have also found other applications, including the removal of combustion residues formed on boiler tubes in steam generation plants as described below. A cross-sectional view of a typical prior art detonating cord
30
′ produced by the Assignee of this application is shown in FIG.
1
A and comprises a core
38
of explosive material, about which a multi-layer, non-metal sheath is disposed. The sheath comprises a thin plastic containment jacket
35
which contains the core material and two layers
31
and
33
of textile casings. The Assignee also produces a detonating cord under the trademark PD CORD. The product is an all-purpose detonating cord comprising an explosive core encased in a textile, which in turn is covered with a plastic jacket. These products remain flexible enough to allow knot tying and spooling of lengths measuring hundreds of feet onto a three-inch diameter spool. A more rigid detonating cord produced by the Assignee is identified by the commercial designation PRIMACORD 400, whose stiffness is a result of its high core load (400 gr/ft) and diameter (about 0.5 inch). Even this product is sufficiently flexible to be wound onto six-inch spools.
Detonating cord as is known in the art is so flexible that it can be tied in knots with other flexible cords for purposes of detonation signal transfer from one to another. The high degree of flexibility of known detonating cord makes it necessary to either lay the cord where desired or pull it into position since it lacks sufficient rigidity to be pushed into place. Like-wise, detonating cord cannot easily be pushed through a small passageway, especially if the passageway is irregular or has bends or kinks, and it cannot be pushed so as to penetrate fly ash or another soft substance for any significant distance.
Steam generation plants generate steam for various uses, e.g., to drive turbines for the generation of electricity or to provide steam to heat large buildings. Such plants typically combust a fuel, e.g., coal, to heat a bank of water-containing boiler tubes to generate the steam. One side product of the combustion is air-borne fly ash, which is typically a mixture of alumina, silica, carbon, hydrocarbons and various metallic oxides. Over time, fly ash, along with other particulates such as dust, builds up and solidifies on the surface of the boiler tubes and may even fill the spaces between the boiler tubes. The fly ash and other residues vary considerably in density from a powdery consistency to a cement-like scale. When such residues cover the boiler tubes, they thermally insulate the tubes from the flames used to heat them and thereby reduce the efficiency of heat transfer and thus the efficiency of the boiler. Accordingly, from time to time, the caked fly ash and other residues must be removed from the banks of boiler tubes in order to return the efficiency of the steam plant to acceptable levels.
Removal of the caked fly ash from a bank of steam or boiler tubes is conventionally carried out by teams of workers, at least one team member standing or crouching on top of the bank of boiler tubes and another team member standing or crouching out of sight under the bank of boiler tubes, which is typically about several feet deep. The work process involves passing a detonating cord through the caked fly ash and around the tubes, and then initiating the detonating cord so that the fly ash and scale are broken up and are dislodged from the tubes. If the fly ash and/or scale leaves sufficient space between the tubes, it may be feasible simply to drop the detonating cord downward between the tubes. However, if the fly ash fills the spaces between the tubes or if the path between the tubes is narrow or irregular because of the fly ash, passages must be created in the caked fly ash to accommodate the detonating cord, which lacks sufficient rigidity to be pushed through the fly ash or to be guided and forced through a narrow or irregular path from above. The process of creating the passages is termed “rodding” and involves the use of, for example, a bar and/or a saw forced between the boiler tubes by hand to create passages through the caked fly ash to receive the detonating cord. The bar and/or saw used is typically about 4 to 6 feet (about 1.2 m to 1.8 m) long in order to cut a passage completely through the caked fly ash on a bank of boiler tubes. This work is physically demanding and is often done in very confined spaces as the distance between banks of boiler tubes within a typical boiler may be as little as about 4 feet (about 1.2 meters). Moreover, many passages must be created as the detonating cord is usually wrapped with adjacent turns spaced apart by a distance of only about 12 to 18 inches (about 30 to 45 cm).
Once the passages have been bored or cut in the caked fly ash, detonating cord may be wrapped about the boiler tubes. First, the detonating cord end is dropped between the tubes from an upper level to workers on a lower level. The detonating cord may either pass through space left by the fly ash between the tubes or through a hole rodded through the fly ash. Thereafter, the detonating cord end is pulled back up to the upper level using a tool, for example, a rod with a hoop on the end. The detonating cord is connected to the hoop and the rod is used to thread the detonating cord through a passage formed in the caked fly ash. After the slack is taken in, the process must be repeated many times. Should the downward path be too irregular, too narrow or too obstructed by fly ash, it may be necessary to thread the flexible detonating cord downwards through the bank of boiler tubes as well as upwards. Finally, the detonating cord is detonated to fracture the scale and fly ash and permit their removal from the tubes. It will be appreciated that the foregoing is a laborious and time-consuming operation resulting in significant downtime for the boiler and significant labor costs.
U.S. Pat. No. 5,056,587, issued to Jones et al, on Oct. 15, 1991 and entitled “Method For Deslagging a Boiler”, discloses the rodding technique described above.
FIG. 3B
shows a cross-sectional view of a horizontal tubing array having a plurality of tubing panels with explosive detonating cord wrapped around the tubes. Detonation of the cords separates the ash from the tubing panels. As taught at column 8, lines 12-14 and 33-38, the detonating cords used are known flexible detonating cords requiring rodding and/or threading, using tools as discussed above, and are wrapped tightly about the banks of tubes.
U.S. Pat. No. 5,211,135, issued to Correia et al, on May 18, 1993 and entitled “Apparatus And Method Of Deslagging A Boiler With An Explosive Blastwave and Kinetic Energy”, shows the use of highly flexible
Gerst Eric C.
Johnson Dennis P.
Woodall Mark E.
Johnson Stephen M.
Libert Victor E.
Libert & Associates
Spaeth Frederick A.
The Ensign-Bickford Company
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