Ammunition and explosive-charge making – Miscellaneous
Reexamination Certificate
2000-07-31
2002-02-19
Carone, Michael J. (Department: 3641)
Ammunition and explosive-charge making
Miscellaneous
C102S275800, C102S275900, C086S020100
Reexamination Certificate
active
06347566
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improved signal transmission fuse, such as shock tube, of the type used for transmitting a detonation signal and, more particularly, to an improved tape-containing structure of such fuse, and to a method of making the same.
RELATED ART
Signal transmission fuses of the type commonly referred to as shock tube are well-known in the art. U.S. Pat. No. 3,590,739, issued Jul. 6, 1971 to Per-Anders Persson, discloses a hollow elongated plastic tube having a pulverulent reactive substance, which may be constituted by a highly brisant explosive such as PETN, RDX, TNT or HMX, adhered by various means to the interior wall of the shock tube.
U.S. Pat. No. 4,328,753, issued May 11, 1982 to L. Kristensen et al, discloses a low energy fuse in the form of a plastic tube comprised of concentric tubular plies of material on the inner surface of which is disposed a pulverulent reactive material. One of the problems which Kristensen et al seeks to redress is the art-recognized problem of migration of the reactive material powder from the inner surface of the tube to form a loose powder in the tube. Kristensen et al does this by making the inner or sub-tube of a polymeric material, such as an ionomeric plastic of the type sold under the trademark SURLYN by E. I. Du Pont de Nemours and Company (“Du Pont”), to which the pulverulent reactive material will cling. The patentee states that the reactive material will be dislodged substantially only by the shock wave generated by reaction of the explosive powder. While ionomers such as SURLYN plastics provide good adhesion of such reactive material, such ionomers are susceptible to degradation by ultraviolet radiation, have unacceptably high water vapor and oil permeabilities, and are insufficiently tough for field use. Kristensen et al offers as a solution surmounting the sub-tube with an outer tube made of a less permeable and mechanically tougher material such as a polyamide, polypropylene, polybutylene or other such polymer better able than the sub-tube to withstand the environment and the stresses of deploying the flise at a work site. The reactive material is a powdered mixture of an explosive and aluminum powder and Kristensen et al discloses that the adhesive nature of the sub-tube enables adherence of about 7 grams of explosive powder per square meter of surface of the inner surface of the tube. Test data are presented that show dislodgment by mechanical forces of about 3 to 61 percent by weight of the amount of reactive material initially present on the inner surface of the tube, depending on the particular type of SURLYN material used for the sub-tube.
Ionomers of the SURLYN type are also advantageous for deposition of the pulverulent reactive material thereon because they can be reliably extruded at a relatively low temperature of about 185° C. (As described below, the reactive material is deposited on the inner surface of the tube at the tube extrusion head.) A reactive material powder containing a thermally stable explosive such as HMX, which has a degradation temperature of about 275° C., can safely be deposited directly on a plastic which is at or near its extrusion temperature of about 185° C. However, the extrusion temperature of SURLYN plastics is too high to permit use of less expensive explosives such as PETN, which has a melting point of only about 141° C., or even RDX, the 204° C. melting point of which is less than about 20° C. higher than the lowest SURLYN plastic extrusion temperature. The thermally less sensitive explosives, such as HMX, are not only more expensive, but are less sensitive than explosives such as PETN and RDX, therefore reducing the reliability of initiation of the signal transmission fuse.
As is well known in the art, the pulverulent reactive material is introduced into the SURLYN or other ionomer tube at the point at which the tube is being extruded, the reactive material powder normally being fed by gravity concentrically within the parison being pulled from the extrusion head. It has been found that extremely fine particles of such reactive material are difficult to uniformly and reliably apply by gravity flow. This problem is overcome by using a somewhat larger particle size of the reactive material, but the larger particle size results in aggravating the problem of migration of the powder from the tube surface because the larger particles, being heavier, adhere less well to the tube inner surface.
The use of a larger particle size of the reactive material also tends to reduce the sensitivity of the reactive material to initiation, thereby requiring depositing somewhat heavier loadings of the reactive material powder which, in turn, further aggravates the powder migration problem.
Powder migration is a problem because, in products where lengths of the signal transmission fuse are connected to devices such as detonators, migrating powder can collect atop the explosive or pyrotechnic contained within the detonator and shield the explosive or pyrotechnic from the signal generated in the shock tube, thereby resulting in a misfire. Further, deployment of a shock tube in the field results in bends and kinks in the shock tube, and a collection of migrated powder can block the shock tube at such bends or kinks, thereby interrupting transmission of the signal and also resulting in misfire. Of course, if powder migration is so severe as to leave sections of the fuse with insufficient powder adhered thereto to sustain the reaction, a misfire will occur.
Despite the problem of powder migration, the art has persisted in using a loose pulverulent reactive material in signal transmission fuses such as shock tube, deflagrating tube and the like, because it is believed that the reactive material, which is believed to be retained on the ionomer only by Van der Waals forces or the like, must be dislodged at the point of reaction so that it can react, in a manner analogous to a dust explosion, to sustain the reaction and transmit it through the entire length of the tube.
Russian Patent 2,005,984 of Pechenev et al, entitled “Initiating Waveguide”, discloses a signal transmission fuse (which is referred to as “an initiating waveguide” in the translation of the Russian Patent). The Patent discloses applying the reactive mixture (“explosive”) on a film at a core loading of 5 to 40 g/m
2
, the film being enclosed within a surrounding sheath or tube “with a gap of 0.5 to 7 mm”. The Russian Patent thus provides a film or tape to which an explosive powder is applied and which is then encased within a surrounding tube to provide the finished “initiating wave-guide” or signal transmission fuse.
U.S. Pat. No. 4,290,366, issued Sep. 22, 1981 to F. B. Janoski, discloses a signal transmission tube within the bore of which is disposed a self-oxidizing material which extends substantially throughout the length of the tube. The self-oxidizing material may comprise a monofilament or a multifilament of fine, hair-like strands of material that loosely fills the flexible tubing and which may carry explosive modifying materials to alter the density and/or detonation rate of the self-oxidizing material.
The prior art also uses, as a fuse, cotton strings or cords coated with black powder and contained within a hollow plastic tube. The black powder is mixed with a binder to adhere it to the strings or cords.
The present invention provides a fuse structure and method of making a fuse which overcomes the foregoing problems.
SUMMARY OF THE INVENTION
Generally, in accordance with the present invention, there is provided a signal transmission fuse in which a support tape has a reactive material containing a binder coated onto the tape. The reactive material, which may comprise known explosive/fuel mixtures or deflagrating compositions, or a mixture thereof, may be applied to the tape in the form of a reactive paint comprising the pulverulent reactive material, a binder and, optionally, a solvent. The coated tape is then encased within a tube, which may be a plastic (synthetic organic polymeric) tub
Beljankina Irina Genadievna
Furne Vladimir Vasilievitch
Gladden Ernest L.
Nikitin Igor Vasilievitch
Pechenev Uriy Gennadievitch
Carone Michael J.
Libert Victor E.
Libert & Associates
Semunegus Lulit
The Ensign-Bickford Company
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