US3431848A - Explosive cartridge assemblies - Google Patents

Description

March 11, 1969 s. F. FOSTER 3,431,848

EXPLOSIVE CARTRIDGE ASSEMBLI ES Filed April 28, 1967 Sheet of 2 23 FIG! FIG. 2

FIG.4

STEPHEN E STER IN NTOR.

AGENT March 11, 1969 s. F. FOSTER 3,431,348

EXPLOSIVE CARTRIDGE ASSEMBLIES Filed April 28, 1967 Sheet of 2 Z- 57 54 STEPHEN E FOSTER INVENTOR. 62 I 5 e1 58 BY FIG. 8 PM AGENT United States Patent 3,431,848 EXPLOSIVE CARTRIDGE ASSEMBLIES Stephen F. Foster, Irving, Tex., assignor to Hercules Incorporated, Wilmington, Del., a corporation of Delaware Filed Apr. 28, 1967, Ser. No. 636,572

US. Cl. 10224 Claims Int. Cl. F42b 3/10 ABSTRACT OF THE DISCLOSURE An explosive cartridge assembly particularly adaptable for offshore seismic exploration is provided, of which the shell and at least one end closure is formed of plastic; a plurality of protruding ridge members are disposed transversely on the shell outer wall to facilitate stacking; and each end closure, when plastic, is recessed centrally to provide a remaining peripheral rim portion to facilitate hand handling. In preferred practice the cartridge assembly contains a substantially noncompressible charge to facilitate stacking, and booster well and /or wall structure for self-disarming after a preset period of time in a water environment.

This invention relates to explosive cartridge assemblies particularly adaptable for use in offshore seismic exploration. In one aspect this invention relates to explosive cartridge assemblies affording a maximum energy loading per unit of cartridge gross weight. In another aspect this invention relates to explosive cartridge assemblies that can be more safely handled by hand than heretofore. In another aspect this invention relates to substantially cylindrical shaped explosive cartridges that can be stacked horizontally without incurring slippage along the contacting surfaces with consequent failure of the stack. In another aspect, this invention relates to explosive cartridge assemblies for offshore seismic exploration wherein the explosive is a rigid mass and the individual cartridge assemblies can be stacked without encountering accidental breakage of the cartridge and/ or compression effects leading to distortion of shape of the stacked cartridges and accompanying weakening of the stack. In still another aspect this invention relates to explosive cartridge assemblies, above described, which are self-disarming when misfired in a water environment and there after remaining uncontrolled in that environment. Other aspects of the invention will be apparent to one skilled in the art in light of the accompanying disclosure and the appended claims.

Explosive cartridge assemblies, particularly those utilized in offshore seismic exploration, generally weigh from 25 to pounds, and although in some instances they have been formed from heavy fibrous materials, they have for the most part been formed from metal, not only to ensue protection of the explosive against direct contact with water, but also to minimize breakage of the cartridge. However, the sharp edges extending along the periphery at each end of the conventionally designed cartridge contribute to cuts and bruises of the hands and to the fingers of the operator during handling, and particularly to pinching of the fingers during stacking of the individual cartridge for storage. Such injuries to the hands and fingers have been incurred most frequently during storage, transport and handling for offshore seismic exploration due to the limited working space available for handling.

In offshore seismic exploration practice, the necessary mode of transport of the cartridge assemblies to the shooting site is generally by barge or boat. Working space is limited not only under those transport conditions but also during handling at the shooting site and it is therefore of special importance that the energy loading of each cartridge, i.e. total amount of energy based on the gross weight of the cartridge, be as high as possible so as to afford a most efficient utilization of the available space. However, energy loading for metal cartridges utilized under these conditions has been unduly limited by the weight of the metal components.

In the transport of cartridges, in offshore seismic prospecting, the practice has been to stack the cartridge horizontally in piles of maximum allowable height in order to most efficiently utilize all available, though limited, space. Inasmuch as metal cartridges are necessarily of limited wall thickness, their utilization in this practice has often been disadvantageous due to damage imparted to the shell, including breakage, as a result of the excess weight of the stack, or pile. Also, in the stacking of metal cartridges under the above-described storage and transport conditions, the weight of the pile has often caused deformation of the cartridge with accompanying compression of the charge, which results in an increase in charge density and accompanying loss in sensitivity and/or a change of shape of the cartridge to impair its function as support for the pile, with accompanying weakening of the pile contributing to its failure.

Further, it will be appreciated that the usual vessel for transport of these cartridge assemblies to the offshore seismic shooting site, whether a barge or other relatively small transport means, is of course light in weight and undergoes extensive heaving action on the water surface en route to the site. This has resulted in undue slippage of the stacked cartridges along their horizontal surfaces of contact with adjacent cartridges, which of course contributes to instability, and sometimes failure, of the pile and accompanying breakage and associated handling problems.

Explosive cartridges, when utilized in offshore areas, present a potential hazard when they fail to detonate, i.e. when they misfire, inasmuch as they are thereafter out of control, though still live. The hazard is particularly serious when the misfired, but live, cartridge is ultimately Washed ashore and then becomes a potential danger to the safety of persons in that shore area.

This invention is concerned with watertight explosive cartridges, particularly adapted for offshore seismic exploration, which are fabricated from plastic, have improved energy loadings, can be readily stacked without slippage along the contacting cartridge surfaces, and can be handled by hand without injury to the hands and the fingers of the operator. In preferred embodiments, the invention is concerned with such cartridges containing an explosive charge that is substantially noncompressible when the cartridge is stacked in piles of significant height; and containing self-disarming structure to permit the cartridge to become deactivated after misfiring in a water environment.

In accordance with the invention, an explosive cartridge assembly, particularly adaptable for offshore seismic exploration, is provided which comprises a substantially cylindrical plastic shell, a closure member at each end of said shell in watertight closing relationship therewith and one said closure member containing an opening extending therethrough to the interior of said shell, and at least one of said closure members being formed from plastic; an explosive composition within, and substantially filling, said shell; a well member within said shell in operative contact with said explosive composition to support initiator means therefor, and supported in said shell at its open end in watertight closing relationship with said opening; a plurality of protruding, and transversely extending ridge members on the outer wall of said shell;

and each said closure member, when plastic, containing a central portion thereof recessed into said shell so as to dispose the remaining peripheral portion as an outermost rim to facilitate hand gripping of said shell.

In one embodiment of the invention, all except the booster well and one end closure member of the uncharged cartridge assembly is plastic and is of an integral construction advantageously formed by blow molding. The remaining end member is a metal closure and is crimped into closing position after the charge is in place. The booster well is secured in either of the end closure members as desired. The plastic closure member is recessed along a central portion of its outside surface and has a rounded, or convex, shaped external surface along its remaining peripheral rim portion.

In another embodiment, all but the booster well and a cover member for an opening in one end of the uncharged cartridge is of an integral plastic construction, also advantageously having been formed by blow molding. Each plastic end closure member is recessed along the central portion of its external surface and has a rounded or convex external surface along its remaining peripheral rim portion. The booster well is supported in either of the end members. The end member opposite that supporting the booster well contains the opening for charging the assembly and the cover member therefor placed in position after loading is completed.

The transversely extending ridge members are preferably disposed in a plurality of spaced apart sets of at least two in each set. However, the transversely extending ridges can be positioned in any suitable manner so that when the cartridges are stacked horizontally they (the ridges) engage with corresponding ridge members of adjacent cartridges in the resulting pile to prevent lengthwise slippage of the cartridges along contacting surfaces.

The rounded, or convex, peripheral external surface of each plastic end closure of the cartridge assemblies of the invention, eliminates hazards in handling due to cutting and pinching of the hands and fingers of the operator often incurred during handling in the crowded space that is available, particularly in offshore seismic work during loading and unloading of the barge, and handling at the shooting site for final emplacement.

In a now preferred embodiment of the invention the explosive charge of the cartridge assembly is a formulation which when initially formed is readily handled for charging the assembly but which subsequently sets to a rigid state, as described more fully hereinafter. This charge is utilized in preferred practice of the invention because, as a component of a stacked cartridge, it undergoes substantially no compression in response to weight of the pile, and hence it can undergo no loss in sensitivity when stacked, and it lends mechanical support to the plastic shell of the cartridge assembly, which is also of primary importance when the cartridge is stacked.

In other embodiments the invention utilizes, in combination, certain self-disarming members which, per se, are the inventions of others as disclosed and claimed in the copending U.S. applications Ser. No. 561,550 of Dittman et al., filed June 29, 1966, now Patent No. 3,358,601, and Ser. No. 593,012 of Driscoll et al., filed Nov. 9, 1966, and also in the U.S. application of Hiram E. Driscoll, filed concurrently herewith. The self-disarming features comprise water-deteriorable members supported in the assembly, such as a disc formed from a water-soluble, or water-disintegratable material supported as a section in an end member of the cartridge assembly and in closing relationship with the cartridge; and/or the booster Well formed from such a water-soluble or water-disintegratable material. In any event, when there is a misfire of the cartridge in a water environment, i.e. failure to detonate, the disarming member, due to its resulting prolonged contact with the water, disintegrates or dissolves and thus permits entry of water into the cartridge and ultimate washing or dissolving of the explosive charge from the shell to thereby render the cartridge harmless. This feature is particularly applicable in offshore exploration areas wherein governmental authorities require that precaution be taken to avoid washing ashore of misfired, but live and uncontrolled, cartridge assemblies.

The invention is further illustrated with reference to the drawings of which FIG. 1 is a view in cross-section of a substantially cylindrical cartridge assembly of which the shell and one end closure are plastic and the other end closure is metal, the booster well is supported in the metal end enclosure, the plastic end closure is shaped to facilitate handling by hand, and a plurality of sets of transversely extending ridges are disposed on the exterior shell wall to prevent slippage of the cartridge when horizontally stacked with other cartridges having similar ridge structure; FIG. 2 is the same as FIG. 1 except that both end closures are plastic, and the end closure opposite the booster well contains an opening for charging the shell and a plastic cap, or cover, closure member closing the shell after charging; FIG. 3 is a view in cross section, of a cap closure member, as an alternate form for that shown in FIG. 2 and which contains, as a portion of the wall section, a water-soluble disc-shaped self-disarming member; FIG. 4 is an enlargement, for purpose of clarification, of a portion of the view of FIG. 3; FIG. 5 is the same as FIG. 1 except that both end closure members are plastic, and the end closure, in place of the metal end closure of FIG. 1, contains an opening for charging explosive into the cartridge and is closed by a bung-booster well assembly adapted to close the opening after the cartridge is charged and to secure the booster well in operative position; FIG. 6 is the same as FIG. 2 except that the end closure, opposite that containing the booster well, is metal and the cartridge is charged through the open end prior to crimping the metal closure member in place; and the metal end contains, optionally, a water-soluble or water-disintegratable self-disarming member; FIG. 7 is an enlarged and somewhat more detailed view of a now preferred means for support of a metal booster well in a plastic closure member of a cartridge assembly of the invention; FIG. 8 is an enlarged and somewhat more detailed view of a now preferred structure for support of a plastic booster well in a plastic end closure member; and FIG. 9 is a detailed view of a now preferred structure for supporting a booster well in the bung structure of FIG. 5.

Referring to FIG. 1, elongated substantially cylindrical shell 10, end closure member 11, and ridge member sets 12 and 13 of cartridge assembly 9 are plastic and preferably of integral construction. End member 11 contains a central recessed portion a along its outside surface, i.e. external to shell 10. The remaining external surface portion b of end member 11, is a rim of convex or rounded contour about the periphery of closure 11.

Protruding ridge members of each of spaced apart sets 12 and 13 are transversely disposed on the external surface of shell 10 and preferably are each disposed in a plane substantially normal to the axis of shell 10. Preferably, one of sets 12 and 13 is disposed near one of the shell end closures and the other is disposed near the opposite shell end. These ridge members, e.g., six ridge members of set 12 and three of set 13 are disposed so as to engage with correspondingly positioned ridge members of other cartridges of the invention when they are stacked in horizontal position.

Shell 10 is substantially filled with explosive charge 14 extending from, and in contact with, end member 11, to the opposite end 16 of shell 10. Charge 14 is preferably a rigid set type formulation described more fully herein, which is substantially noncompressible under the weight of the pile when cartridge 9 is stacked with other cartridges. Metal end closure member 17 of shell 10 is secured along its periphery to shell end 16 by a crimp 17a. Metal booster well 18, e.g., bronze, copper, or aluminum, extends, closed end first, into shell 10 through a central section of metal end member 17 and terminates in contact with explosive charge 14, and it is supported at its open end in closure member 17 by any suitable means. Well 18 is preferably supported with its open end flush, or nearly so, with the exterior surface of closure 17. In one embodiment, a flange or rim extends peripherally along, and laterally from, the outer wall of well 18 at its open end, and is seated on metal end closure 17 outside shell 10, and soldered in its seated position to closure 17, to thereby support well 18 in closure member 17 in watertight relationship therewith. Metal bale member 19 is secured to end closure 17 by engagement with metal lug members 21 which are secured in any suitable manner to the exterior surface of metal end closure 17.

A now preferred method for fabrication of assembly 9 of FIG. 1 comprises the steps of forming shell 10 including ridge members of sets 12 and 13 and end closure 11 as an integral product of blow molding. The plastic is advantageously polyethylene preferably containing a filler to increase its density to a value greater than that of sea water so as to enable the after-shot debris to sink after a successful firing and to enable the cartridge assembly to sink in the event of a misfiring. The integral plastic unit is then charged with explosive through the open end thereof (to be closed by metal end closure 17). Closure end 17, with booster well 18 secured therein, is placed in position to close shell 10 while at the same time supporting booster well 18 in operative contact with explosive 14, and is then crimped to the end 16 of shell 10 to complete the closure of the assembly.

Referring to FIG. 2, shell 10, a booster well 18 and separate sets 12' and 13 of protruding ridge members transversely disposed around the shell 10', of cartridge assembly 9, and explosive charge 14' are the same as those corresponding elements of cartridge assembly 9 of FIG. 1 except that the transversely extending sets of ridges 12' and 13' are disposed respectively at the ends of the cartridge opposite those of FIG. 1. As illustrated the positioning of the ridges and the number of ridges in each set are optional, it being important that, in all events, the ridge members associated with one cartridge are positioned so as to engage correspondingly positioned ridge members of another of the cartridges of the invention when the cartridges are stacked horizontally.

End closure members 23 and 24, sets 12 and 13 of the transversely extending ridges, lugs 26, collar 27 and shell 10' of cartridge assembly 9' are plastic and are preferably of integral construction, advantageously formed by blow molding. A central portion of end closure 23 together with cap closure 28 therefor, as described below, forms recess a along its external surface and extending into shell 10, and the remaining rounded peripheral portion b serves as a grip to facilitate hand handling of the cartridge.

End closure 24 of cartridge '9' contains an opening 25 extending therethrough. Collar 27, external to, and connecting in watertight relationship with shell 10, encompasses opening 25 of end member 24. Booster well 18' extends, closed end first, through collar 27 and opening 25 of end member 24 and terminates in direct contact with explosive charge 14' in shell 10'. Booster well 18' is supported in collar 27 at its open end in any suitable manner, preferably substantially flush with the top end 27 of collar 27. In one embodiment booster well 18' when formed from a metal is flanged at its open end as described with reference to well 18- of FIG. 1 and the flange, or rim, is seated in the end 27 of collar 27 and sealed thereto by suitable adhesive means. A now preferred support for a metal well 18 in collar 27 is shown in FIG. 7. However, booster well 18' can be formed from plastic the same as that forming collar 27 and then heat sealed in position in collar 27; or it can be formed from a plastic different from that of collar 27 and supported in collar 27 by a push nut in the manner illustrated with reference to FIG. 8.

End closure 23 of cartridge assembly 9' contains an opening 29 through a central portion thereof to permit charging of explosive into shell 10'. Thus with booster well 18' extending into shell 10', closed end first, in sealed relationship with end closure 24, explosive is charged through opening 29 into shell 10' to substantially fill shell 10'. Plastic cover 28, as a closure for opening 29, has a central portion 31 of its external surface recessed and it is flanged along its periphery so as to engage opening 29 in closing relationship with shell 10'. Upon completion of charging the explosive into shell 10' through opening 29, cap closure 28 is suitably secured along the surface of its peripheral flange portion 31a to the external surface of the correspondingly flanged periphery portion 31b of end member 23 forming opening 29, to thereby complete the assembly. Lugs 26, preferably forming an integral structure with end member 24, are disposed within the recessed central portion thereof, preferably spaced equally away from collar 27 to support bale 30 for carrying the cartridge assembly.

With reference to FIG. 3 is shown an alternate insert cover member 28' for cover member 28 of FIG. 2. Cover 28' is the same as cover 28 of FIG. 2 except that it contains a water-deteriorable disc-shaped wall portion 32 to provide for self-disarming of the cartridge in the event of misfire in a water environment. Thus, wall portion 32, after a preset period for normal firing of the cartridge when in a water environment, disintegrates in response to its contact with the water and permits ingress of water into the cartridge with consequent washing or dissolving of the explosive from the shell to disarm the shell of the main explosive charge. The embodiment of FIG. 3 is most advantageous applied to the assembly 9' of FIG. 2 when booster well 18' is also formed from a water deteriorable member and the primary and secondary initiator means are self-disarming and/or self-desensitizing, as disclosed and claimed in the above referred to US. application for patent of Driscoll, filed concurrently herewith, to provide a resulting cartridge assembly which is self-disarming and/ or self-desensitizing in respect of all its components after a misfire in a water environment.

FIG. 4 is a view of an enlarged portion of closure 28' of FIG. 3 and more clearly illustrates water-deteriorable disc member 32 as a part of the closure cap 28'.

With reference to FIG. 5, cartridge assembly 9" is the same as assembly 9 of FIG. 1 except that in lieu of the end closure member 17 of FIG. 1, and its directly associated elements, assembly 9" of FIG. 5 is closed by end closure member 33 which in turn contains opening 34 extending therethrough into shell 10" for charging explosive into shell 10", and bung-booster well assembly closure 36 for opening 34. Collar 37, attached to the external surface of shell end closure 33 in watertight relationship therewith, encompasses opening 34. End closure member 11', shell 10", sets 12" and 13" of peripheral extending ridge members, end closure 33, collar 37, and lug members 26' for support of bale 30, of assembly 9", are plastic and preferably of integral construction.

End closure 33 of assembly 9" is recessed along a central portiond d thereof with the remaining peripheral portion e as a rim to facilitate ease in hand handling. Peripheral rim e of end closure 33 has a convex, or rounded, contour along its surface external to shell 10" to minimize injuries to the hands and fingers of the operator during handling.

Bung-booster well assembly closure 36 for opening 34 in end closure member 33, i.e. after charging shell 10", is a cover assembly containing, and supporting, booster well 18" at the open end of well 18". Assembly 36 consists of bung 38 containing centrally disposed opening 39 extending therethrough and booster well 18" extending through opening 39 closed end first and secured at its open end in bung 38 in watertight relationship therewith. Bung booster well assembly closure 36 in its watertight relationship with opening 34 supports booster well 18" in operative contact with explosive 14" in shell Lugs 26' support bale member 30 to facilitate hand carrying the cartridge.

Bung-booster well assembly closure 36 can be emplaced in closing relationship with opening 34 in closure member 33 in any suitable manner, a now preferred means being a lug-groove type structure illustrated with reference to FIG. 9.

Cartridge 9" can be assembled by charging the integral plastic unit, including shell 10", through opening 34 in end closure 33 and then inserting bung-booster well assembly closure 36 in place and twist locking it in closing relationship with end member 33 as illustrated with reference to FIG. 9.

With reference to FIG. 6, cartridge assembly 9" is the same as assembly 9' of FIG. 2 except that in lieu of the end closure member 23 and associated structure of FIG. 2, shell 10" is closed by metal closure member 41 which is peripherally crimped to the bottom end 42 of shell 10". Assembly 9" is charged through the open end of shell 10" to be thereafter closed by closure member 41.

Optionally, metal closure member 41 contains a waterdeteriorable element 43 such as a water-soluble or waterdisintegratable plastic or a water-disintegratable fiber material, as a portion of the wall section thereof. Such a water-deteriorable material 43 is supported as a part of the wall of closure 41 in any suitable manner such as by a crimp of two formed flanges along the periphery of an opening extending through member 41.

With reference to FIG. 7 is shown now preferred struc ture for supporting a metal booster well in a plastic end closure of a cartridge assembly of the invention. Thus, as shOWn in FIG. 7 plastic end closure 44 contains opening 46 extending therethrough. Collar 47 is secured to end closure member 44 outside the cartridge shell and encompasses opening 46 in watertight closing relationship therewith. Booster well 48 with peripheral flange 49 about its open end, and rolled bead 51 disposed transversely about its outside wall in close proximity to flange 49, is supported at its open end in end closure 44, with flange 49 seated on the end of collar 47 outside the cartridge shell, and with rolled bead 51 in tight contact with the inner wall of collar 47, to thereby provide a moisture seal and an internal lock to firmly secure well 44 in collar 47. Bulge 52 disposed transversely along the outside of booster well 48, and extending laterally therefrom, is firmly positioned against the inner wall 53 of end closure 44 to secure well 48 in collar 44 in watertight relationship therewith.

In preferred practice, end closure 44 is blow molded as part of an integral construction with the cartridge shell. Metal booster well 48, generally formed from copper, bronze or aluminum, is molded in position as part of the blow molding process. Rolled bead 51, below flange 49, provides the interlocking action above described and in a final step booster well 48 is bulged to form bulge 52 at a point to provide a compressional load on the collar 47 and against the inner wall 53 of the end closure 44 to support the booster well 48 in position.

With reference to FIG. 8 is shown now preferred structure for supporting a plastic booster well in a plastic end closure of a cartridge assembly of the invention. Thus, as shown in FIG. 8, plastic end closure 54 contains opening 56 extending therethrough, and collar 57 is secured to end closure 54 outside the cartridge shell and encompasses opening 56 in watertight closing relationship therewith. Booster well 58, with peripheral flange 59 about its open end, is supported at its open end in end closure 54 with flange 59 seated on the end of collar 57 outside the cartridge shell. Washer-like push nut 61 in engaging relationship with booster well 58 immediately below the inner wall 62 of end closure 54 is adjusted by its forced contact with inner wall 62 to draw booster wall 58 inwardly to thereby firmly secure flange 59 in its seated position against the end of collar 57 to maintain the watertight relationship of booster 58 with collar 57.

FIG. 9 shows a now preferred means for securing a bung-booster well assembly closure, such as assembly 33 of FIG. 5, in closing relationship with a plastic cartridge end closure therefor, such as end closure 33 of FIG. 5. Thus, with reference to FIG. 9, a series of grooves 63 extend longitudinally along the internal wall surface 64 of a collar 60 attached to the plastic end closure of the cartridge, such as of collar 37 attached to end closure member 33 of FIG. 5. Bung 66 contains protruding lugs 67 laterally extending from its external side surfaces, and each lug 67 is spaced apart so as to engage one of the groove members 63, above described, so that when bung 66 is inserted into collar member 60, it is guided in closing position therewith and with the plastic end closure member of the cartridge. Booster well 68 can be either plastic or metal and is supported in watertight relationship at its open end in bung 66 in any suitable manner such as illustrated with reference to FIG. 7 if booster well 68 is formed from a metal or as illustrated with reference to FIG. 8 if booster well 68 is formed from a plastic.

The length of the inner wall of the collar member 60 is correlated with the length of the bung 66 so that when bung 66 is in closing relationship with collar 60 lugs 67 extend just beyond the internal wall of the cartridge shell end closure but only so that when bung 66 in full closing position in the collar, is rotated, say, at about 45, each lug 67 is moved along slightly inclined (toward the interior of the cartridge shell) path 65 on the inner wall of the cartridge end closure into notch 69, in firm locked contact with the inner surface of the closure member, in the respective notches 69, to thereby lock the bung-booster well assembly closure in its closing position.

Plastic cartridge assemblies of this invention can be fabricated from any suitable plastic. A now preferred plastic material is a high densitp polyethylene, e.g. polyethylene filled to the amount of about 16 weight percent with bleached barium sulfate of particle size less than 45 microns, and which provides a polyethylene having a specific gravity in the order of 1.07 grams per cc. as compared with 0.954 grams per cc. when unfilled. This increased density permits the cartridge to sink when it would otherwise float uncontrolled in a water environment. It also permits fragments of the exploded cartridge to sink to thereby minimize littering of the shoreline with washedashore cartridge fragments.

Any suitable explosive material can be utilized in the cartridge assemblies of the invention, such as conventional dynamites, nitrocarbonitrates, and the like. Inorganic oxidizer salt explosives of the aqueous slurry type are often advantageously utilized. However, it is now preferred practice, and particularly in offshore seismic exploration, that a rigid set type formulation be utilized as discussed hereinabove. The preferred rigid type formulations are nitrocarbonitrates (NCNs) and can be prepared in accordance with any of various suitable procedures known in the art. In one such preparative procedure about 1.5 weight percent water is admixed with the formulation at a temperature above about 110 F. and packaged at about that temperature, or at a somewhat lower temperature level, if desired, say, as low as about 95 F. The packaged material becomes rigidly set when it reaches a temperature at or below the transition temperature of ammonium nitrate which is about 86 F. Thus when the formulation is mixed at a temperature above, say, 95 F., it can be charged to the cartridge before becoming set and then permitted to set in the cartridge shell in form ready for use as the explosive charge in an explosive cartridge assembly of the invention.

Generally, the preferred rigid explosive charges of the cartridge assemblies of the invention, prepared as above described with reference to the transition temperature for ammonium nitrate, contain on a weight basis from about 50 to percent ammonium nitrate; from 0 to 10 percent sodium nitrate, often from to percent; from 1 to 2 percent water, preferably about 1.5 percent; and the remainder, as sensitizer and fuel ingredients, such as from 10 to percent aluminum, from 3 to 8 percent DNT oil or solid, and from 1 to 5 percent fuel oil. An exemplary rigid set NCN formulation, prepared as above described, is as follows:

Ingredient: Percent G-rained ammonium nitrate 76.0 Fuel oil 1.5 Dinitrotoluene oil 5.0 Aluminum granules 16.0 H O 1.5

When a metal end closure is utilized in practice of the invention, the other closure member is formed from plastic and is recessed to facilitate hand handling, as above described. In each instance of its utilization, the metal end closure member is of conventional design for being crimped into closing relationship with the cartridge shell. By its conventional design the metal end closure contains a recess on its external surface, in close proximity to its periphery, to form a peripheral rim portion for crimping onto the cartridge shell. Although such a metal closure member utilized at both ends of the cartridge shell would be unsuitable for accomplishing ease in handling in accordance with the invention, one metal end closure in combination with a plastic end closure above described, is nevertheless advantageously utilized inasmuch as once the operator has gripped the plastic end closure, he acquires improved hand control which, to a significant extent, compensates for the lesser degree of control normally effected by utilization of the metal end closure.

A metal end closure is most advantageously utilized, in practice of the invention, when it is desired to load the cartridge through a completely open end of the cartridge shell. However, in preferred practice the cartridge assemblies of the invention contain the plastic closure member at each end of the shell as illustrated with reference to the drawings, and hence to provide maximum protection against physical failure during handling, as well as to provide maximum ease in handling.

In preferred practice involving utilization of a metal end closure, the open end of the plastc shell that is to accept the metal end closure terminates in a V which opens in a direction away from the shell; and the lip of the metal end closure is roll crimped into the V end closure. This is of particular importance when the cartridge shell is maintained at a minimum wall thickness to afford maximum energy loading, and is formed from blow moldmg.

Thus, when utilizing a densified polyethylene plastic, as above described, the shell wall thickness is often within the range of from about 50 to 80 mils. Accordingly, in such practice, the roll crimp of the metal end closure onto the cartridge shell, in combination with the V structure, above described, is necessary in order to provide the required strength at the juncture of the cartridge shell and metal end closure to compensate for loss in juncture strength that would have characterized a conventional crimp of the metal closure to the end of the thin plastic shell wall; for example, to impart strength to preclude popping off of the metal end of a stacked cartridge that often takes place in response to weight of the pile when the metal end closure is conventionally crimped to the thin cartridge shell wall. The V portion is of integral construction with the cartridge shell, being readily formed, for example, during blow molding of the particular plastic unit.

The individual protruding and transversel extending ridge members on the outer Wall of the cartridge shell can extend from the shell to any suitable height, generally, most advantageously from about 0.03 to 0.10 inch, more often in the order of about 0.05 inch.

The individual transverse ridge members around the cartridge shell, e.g., the sets 12 and 13, and of corresponding sets, of the drawings, can be disposed in any suitable pattern to facilitate stacking of the cartridge as above described. Also, the ridge members can advantageously be disposed in a coded pattern so as to indicate to the operator, by a finger touch of the patterned ridges, the end of the cartridge containing the booster well to thereby eliminate loss of time otherwise required for visual inspection of each cartridge to locate the booster well and determine the necessary handling for loading the booster unit into the well. For example, a group of six ridges of set 12" of FIG. 6 or a group of three ridges of set 13" of FIG. 5 can be standardized to form such a coded pattern, e.g., always being adjacent to the cartridge end closure containing the booster well.

The invention also contemplates, as one embodiment, the above described explosive cartridge assembly, in combination with primary and secondary initiator means for the explosive charge to provide a complete assembly ready for firing. Such a complete assembly comprises the explosive cartridge assembly of the invention together with a booster assembly, as a secondary initiator, supported in the booster well and containing a cap-sensitive booster charge such as PETN, tetryl, RDX, or the like, and an electric blasting cap or detonator fuse, as a primary initiator, supported in detonating relationship with the booster charge. The booster charge is detonated in response to initiation of the primary initiator, and the explosive charge is detonated in response to detonation of the booster charge to provide the full explosive force.

The plastic explosive cartridge assemblies of the invention are advantageously applied to service in offshore areas, in lieu of metal cartridge assemblies, inasmuch as, under those conditions, they are not subject to corrosive action of salt air and salt water during handling and storage, whereas metal cartridges rapidly undergo external corrosion leading to physical failure of the cartridge shell there has been an opportunity for firing. Although metal assembly parts can be treated to resist corrosive action of salt water during handling and storage in offshore areas, such treatment of an entire metal assembly is not economically feasible. Accordingly, shelf life of the plastic explosive cartridge assemblies of the invention, as regards corrosion resistance during storage and handling in offshore areas, is markedly superior to that of explosive assemblies of conventional metal or fiber design.

The plastic cartridge assemblies of the invention are particularly advantageously utilized from the standpoint of fire hazard. Thus, a metal cartridge assembly, when exposed to heat in a fire area, undergoes internal heat and pressure buildup and finally explodes to spew all contents over the immediate area to thus create additional fire spread; and particularly so when the explosive charge contains aluminum. On the other hand, the plastic cartridge assembly of the invention, when exposed to subheat conditions, simply melts to slump into a pile with no pressure-driven spewing of its contents.

Disarming members supported in the cartridge assembly, i.e. as a section in an end member of the cartridge and/or as booster well are formed from any suitable water-deteriorable material exemplary of which are carboxymethylcellulose (CMC), paper, poly(vinyl alcohol) and Klucel (a hydroxypropyl cellulose).

Such a water-deteriorable member, now preferred, is a hydroxypropyl cellulose containing at least two and generally from 3 to 5 hydroxypropyl groups per anhydroglucose unit. These hydroxypropyl cellulose compounds are thermoplastic solids and are soluble in cold water, insoluble in hot water, and are soluble in polar organic solvents; and are disclosed and claimed in US. 3,278,521. They can be prepared in accordance with any suitable procedure such as disclosed and claimed in US. 3,278,521 and US. 3,278,520. These compounds are readily moldable as dis closed in US. 3,314,809.

When referring herein to self-disarming structure, it is generally contemplated that during the preset time period there has been an unsuccessful attempt to fire the assembly, i.e. there has been a misfiring. However, in some instances of offshore operations, the cartridge assembly when placed in the water may become disassociated from the firing energy source without any attempt having been made to actually fire it. In all events, in those embodiments of the invention involving self-disarming structure, self-disarming takes place after the preset time period for normal firing regardless of whether there has been an unsuccessful attempt to actually fire the assembly.

A section of water deteriorable material in the cartridge shell end, or wall, employed in the embodiments providing self-disarming, having an area equal to about that of a disc of from A to 1 inch in diameter is generally sufficient for admitting a self-disarming amount of water into the cartridge shell after the preset period of time for normal firing; and if it is utilized in combination with a booster well also formed from a water-deteriorable material for self-disarming, as described, its size can be correlated with the water deteriorability of the well structure as desired.

What I claim and desire to protect by Letters Patent 1. An explosive cartridge assembly for offshore seismic exploration comprising a substantially cylindrical plastic shell; a closure member at each end of said shell in watertight closing relationship therewith and one said closure member containing an opening extending therethrough to the interior of said shell, and at least one of said closure members being formed from plastic; an explosive composition within, and substantially filling said shell; a booster well member within said shell in operative contact with said explosive composition to support initiator means therefor and supported in said shell at its open end in watertight closing relationship with said opening; means on said shell to prevent lengthwise slippage of said assembly when it is stacked horizontally with a like assembly, said means consisting of a plurality of ridge members disposed on the outer wall of said shell transverse to the longitudinal axis of said shell and protruding from said wall so as to interlock with corresponding ridge members of another said assembly when stacked horizontally therewith; and each said end closure member when plastic, containing a central portion thereof recessed into said shell so as to dispose the remaining peripheral portion of said closure member as an outermost rim member having a rounded external surface.

2. An assembly of claim 1 wherein said plurality of ridges comprises spaced apart Sets of ridges, and each said ridge is in a plan substantially normal to the shell axis; and said shell, said ridge members, and each said closure member, when plastic, are of integral construction.

3. An assembly of claim 2 wherein said shell is closed at one end by a metal end closure member.

4. An assembly of claim 3 wherein said booster well is supported in said metal end closure.

5. An assembly of claim 3 wherein said booster well is supported in said plastic end closure member.

6. In an assembly of claim 2, a plastic closure member in closing relationship with said shell at each end thereof; the plastic end closure member, opposite said booster well, containing an opening extending therethrough for loading said explosive into said shell; a plastic cap closure for the last said opening and said cap disposed in closing relationship therewith.

7. An explosive assembly of claim 1 wherein said explosive composition is a nitrocarbonitrate rigid set formulation and contains, on a weight basis, from 50 to 80 percent ammonium nitrate, from to percent sodium nitrate, from 1 to 2 percent water, and the remainder as fuel and sensitizer components, and prepared by mixing all ingredients at a temperature above the transition temperature of ammonium nitrate and subsequently lowering the temperature of the admixture to below said transition temperature, whereby said explosive is a rigid solid.

8. In an explosive cartridge assembly of claim 6, the plastic closure member for said shell opposite said cap closure member containing an opening extending substantially axially therethrough, and a plastic collar attached to the outside surface of the last said end closure member, in watertight relationship therewith and encompassing said opening; and said booster well supported, at its open end, within said collar.

9. In an explosive assembly of claim 1, a plastic closure member in closing relationship with said shell at each end thereof, and one said closure member containing an opening extending therethrough; a bung member as a closure for the last said opening, and supported in closing relationship therewith; and said booster well extending, closed end first, substantially axially through said bung, in watertight relationship therewith, into said shell and terminating in direct contact with said explosive composition therein.

10. In an assembly of claim 1, said closure member, at the end of said shell opposite said booster well, containing an opening extending therethrough into said shell; and a closure member for the last said opening, in closing relationship therewith and water deteriorable after a preset period of contact with water to then permit ingress of a disarming amount of water into said cartridge shell when said cartridge is in contact with water for a period longer than said preset time.

11. An assembly of claim 10 wherein said waterdeteriorable member is a water-soluble plastic.

12. An assembly of claim 10 wherein said waterdeteriorable member is a fibrous material.

13. An assembly of claim 1 wherein said booster well is formed from a hydroxypropyl cellulose containing at least two hydroxypropyl groups per anhydroglucose unit 14. An explosive cartridge assembly for offshore seismic exploration, comprising a substantially cylindrical plastic shell; a plastic closure member at each end of said shell in watertight closing relationship therewith; an explosive composition substantially filling said shell; a booster well member extending through one of said closure members, closed end first, and in watertight relationship therewith, and terminating in direct contact with said explosive; means on said shell to prevent lengthwise slippage of said assembly when it is stacked horizontally with a like assembly, said means consisting of a plurality of ridge members extending around the outer Wall of said shell in planes substantially normal to the longitudinal axis of said shell, and protruding from said wall so as to interlock with corresponding ridge members of another said assembly when stacked horizontally therewith as described; each said plastic end closure containing a central portion thereof recessed into the said shell so as to dispose the remaining peripheral portion of said closure member as an outermost rim having a rounded external surface; the plastic end closure member opposite said booster well containing an opening extending therethrough into said shell for charging said explosive into said shell; and a plastic cover member for closing said opening, and in watertight closing relationship therewith.

15. In an explosive assembly of claim 14, said plastic cover member containing an opening extending therethrough into said cartridge shell, and a water-deteriorable material as a closure for the last said opening in closing relationship therewith, and deteriorable after a preset period of contact time for water to permit ingress of water into said cartridge shell when said shell remains in contact with water for a period longer than said preset time.

16. An assembly of claim 15 wherein said water-deteriorable material is a hydroxypropyl cellulose containing from 2 to 10 hydroxypropyl groups per anhydroglucose unit.

17. An assembly of claim 16 wherein said booster well member is also formed from a hydroxypropyl cellulose containing from 2 to hyd-roxypropyl groups per anhydroglucose unit.

18. An assembly of claim wherein each said plastic end closure, said cartridge shell and said ridge members constitute an integral construction of densified polyethylene.

19. An assembly of claim 18 wherein each of said ridge members extends from said shell at a height in the range of from 0.03 to 0.10 inch.

20. An explosive cartridge assembly for offshore seismic exploration, comprising a substantially cylindrical plastic shell; a plastic closure member at one end of said shell, and a metal end closure member at the opposite end of said shell, each said end closure member being disposed in watertight closing relationship with said shell; an explosive composition substantially filling said shell; a booster Well member extending through said plastic end closure member, closed end first, and in Watertight relationship with said plastic closure member and terminating in direct contact with said explosive; means on said shell to prevent lengthwise slippage of said assembly when it is stacked horizontally with a like assembly, said means consisting of a plurality of ridge members extending around the outer Wall of said shell in planes substantially normal to the longitudinal axis of said shell; and protruding from said wall so as to interlock with corresponding ridge members of another said assembly when stacked horizontally therewith as described; said plastic end closure containing a central portion thereof recessed into said shell so as to dispose the remaining peripheral portion as an outermost rim member having a rounded external surface; said metal end closure being supported in its closing relationship with said shell by a rolled crimp, and containing an opening extending therethrough into said shell; and a fiber closure member as a closure for the last said opening and supported in closing relationship therewith, and water deteriorable after a preset period of contact with water to then permit ingress of a disarming amount of water into said cartridge shell when said cartridge is in contact with water for a period longer than said preset time.

21. An explosive assembly of claim 1 wherein said plastic is a densified polyethylene.

22. An explosive assembly of the claim 21 wherein said polyethylene contains bleached barium sulfate of particle size less than about microns as a densifying agent therefor.

23. An explosive assembly of claim 22 wherein the Wall thickness of said cartridge shell is in the range of from to mils.

24. An explosive assembly of claim 23 wherein each of said ridge members extends from said shell at a height in the range of from 0.03 to 0.10 inch.

25. In an assembly of claim 1, initiator means for said explosive composition, supported within said booster well.

References Cited UNITED STATES PATENTS 2,953,093 9/1960 Chase et a1. 102-24 3,186,340 6/1965 Foster 102-24 3,254,601 6/1966 Grifiith et al 10224 3,306,200 2/1967 Branscum et al. l0224 3,322,066 5/1967 Griflith et al 10224 3,358,601 12/1967 Dittmann et al l0228 VERLIN R. PENDEGRASS, Primary Examiner.

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