United States Patent: 3552259

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( 205704 of 205704 )

United States Patent	3,552,259
Griffith	January 5, 1971

PROCESS AND APPARATUS FOR PREPARING DETONATING AND DEFLAGRATING FUSE AND PRODUCT

Abstract

Process and apparatus are provided for preparing detonating and deflagrating fuse or cord, simultaneously forming the wrapper for the fuse or cord and filling the wrapper with detonating or deflagrating low explosive. The apparatus also desirably includes means for cracking or pulverizing and desirably increasing the degree of confinement of the continuous column of detonating or deflagrating fuse or cord, so as to form a product of high sensitivity and high rate.

Inventors:	Griffith; George L. (Coopersburg, PA)
Assignee:	Commerican Solvents *Corporation* (New York, NY)
Appl. No.:	04/752,114
Filed:	July 19, 1968

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
503796	Oct., 1965	3327582	Jun., 1967
596028	Sep., 1966	3367266
574881	Aug., 1966

Current U.S. Class: 86/20.1 ; 264/3.1; 425/113; 425/133.1; 425/377; 425/71

Current International Class: C06C 5/00 (20060101); C06C 5/08 (20060101); F42c 009/10 ()

Field of Search: 86/1,20,20.1,20.5 264/3,3B 18/13N,13K

References Cited [Referenced By]

U.S. Patent Documents


1923761	August 1933	Snelling et al.
2363569	November 1944	Caldwell et al.
2687553	August 1954	Colombo
2940352	June 1960	Grow
3224317	December 1965	Gould
2371709	March 1945	Rineer
3265778	August 1966	Griffith

Primary Examiner: Borchelt; Benjamin A.
Assistant Examiner: Bentley; Stephen C.

Parent Case Text

This application is a continuation-in-part of applications Ser. No. 503,796, filed Oct. 23, 1965, now U.S. Pat. No. 3,327,582, patented Jun. 27, 1967; Ser. No. 596,028, filed Sept. 1, 1966, now U.S. Pat. No. 3,367,266; and Ser. No. 574,881, filed Aug. 3, 1966, and now abandoned.

Claims

I claim:

1. A process for forming explosive fuse, which comprises forming from a softened and pliable wrapping material a seamless continuous tube of flexible wrapping material, filling the tube with an explosive composition in a continuous solid column while at least one of the explosive and the tube is soft and pliable, and supporting and constraining the tube throughout substantially its entire exterior while both the explosive and the tube are soft and pliable to maintain the shape and diameter of the fuse until both the explosive and the tube are sufficiently hard so as to form a self-supporting composite which retains its shape and diameter and cracking the solid column of explosives within the tube to reduce it to a plurality of particles closely confined within the tube, and having an enhanced sensitivity due to their discontinuity.

2. A process in accordance with claim 1 in which the explosive composition is filled into the tube in a semisolid condition, and is brought to a hardened solid condition prior to cracking.

3. A process in accordance with claim 1 in which the explosive is filled into the tube in a molten condition and is brought to a hardened solid condition prior to cracking.

4. A process in accordance with claim 1 in which the explosive is reduced during the cracking to particles of which at least 50 percent are less than one thirty-second inch in diameter.

5. A process in accordance with claim 1 in which the tube is also reduced in diameter when the explosive is cracked.

6. A process in accordance with claim 1 in which the explosive is a detonating explosive.

7. A process in accordance with claim 1 in which the explosive is a deflagrating low explosive.

8. A process for forming explosive fuse in accordance with claim 1 which comprises extruding a softened plastic flexible wrapper material in the form of a seamless continuous tube; extruding an explosive composition in the shape of a continuous column, and filling the column into the tube; pushing the continuous explosive column forward under the pressure of explosive material, and pushing the tube forward under the pressure of plastic wrapper material, thereby pushing the tube and explosive columns forward together, an and substantially filling all of the voids in the tube with explosive during the forward movement of the continuous explosive column: and supporting and constraining the tube throughout substantially its entire exterior while both the explosive and the tube are soft and pliable in the desired configuration until both the explosive and the tube are sufficiently hard so as to form a self-supporting composite which retains its shape and diameter.

9. A process in accordance with claim 8 which includes swaging the filled tube.

10. A process in accordance with claim 8 in which the explosive composition is fed in a semisolid condition, and is brought to a hardened solid condition prior to crushing.

11. A process in accordance with claim 8 in which the explosive is fed in a molten condition, and is brought to a hardened solid condition prior to crushing.

12. A process for forming an explosive fuse in accordance with claim 1 which includes simultaneously cooling the composite of the tube and explosive while supporting and constraining them so as to harden the composite into a self-supporting position.

13. A process in accordance with claim 12 in which the composite of the tube and explosive is cooled by applying a pressurized cooling fluid to the exterior of the tube.

14. Apparatus for the continuous formation of explosive fuse, which comprises, in combination, means for forming a softened and pliable plastic wrapping material into a seamless continuous tube; means for forming an explosive composition into a continuous elongated column; means for feeding the column into the tube and filling the tube therewith; means for imparting to the extruded explosive column and to the tube a sufficient driving force to push both forward together, and means for supporting and constraining the tube throughout its entire exterior while both the tube and the explosive are soft and pliable in the desired configuration until both the explosive and the tube are sufficiently hard so as to form a self-supporting composite which retains its shape and diameter, and means for cracking the solid column of explosive in situ within the tube to introduce discontinuity into the column and increase sensitivity.

15. Apparatus in accordance with claim 14 in which the cracking means comprises means for swaging the explosive filled tube.

16. Apparatus in accordance with claim 14 in which the means for applying constraint is a sizing die.

17. Apparatus in accordance with claim 14 in which the means for applying constraint is a plurality of sizing rollers.

18. Apparatus for the continuous formation of explosive fuse in accordance with claim 14 which comprises, in combination, means for extruding a softened plastic wrapping material into a seamless continuous tube; means for extruding an explosive composition into a continuous elongated flowable column; means for substantially completely filling the tube with the column while it is flowable; means for bringing the explosive column to a hardened solid condition; and means for cracking the explosive column in situ within the tube after it is hardened to introduce discontinuity into the column and increase sensitivity.

19. Apparatus in accordance with claim 14 including means for cooling the composite of the tube and the explosive while the composite is constrained and support it so as to harden it until it is self-supporting.

20. Apparatus in accordance with claim 19 in which said means for cooling the composite comprises a porous tube through the pores of which a cooling liquid is passed.

21. Apparatus in accordance with claim 19 in which the cooling means comprises a cooling jacket positioned about the composite and through which a cooling fluid is circulated.

Description

This invention relates to process and apparatus for preparing detonating and deflagrating fuse or cord by simultaneously forming the wrapper and filling it with detonating or deflagrating explosive, and to the detonating or deflagrating fuse or cord obtainable by this process and apparatus.

There are two main types of chemical explosives, detonating or high explosives, characterized by very high rates of reaction and high pressure, and deflagrating or low explosives, which burn more slowly, and develop much lower pressure. Detonating explosive explosives are usually subdivided into primary and secondary explosives. The primary explosives nearly always detonate by simple ignition, such as by means of a spark, flame, or impact, whereas secondary explosives require the use of a detonator, and frequently a booster. A detonator contains a primary explosive as an essential element, but it may be even more complex, and include a number of modifying ingredients as well.

The oldest type is the mercury fulminate cap, first used as a detonator by Nobel. Many variations of this came into use during the latter part of the 19th century, but they are used very little at the present time. Electric blasting caps were introduced early in the present century, and these have now reached a high state of development, and contain elements each of which plays its part in the complicated process of developing the necessary high-pressure detonation wave needed to detonate the secondary explosive. However, it is not very well suited for the simultaneous detonation of multiple charges.

For this purpose, the detonating fuse was developed. This is composed of a long narrow tube filled with high explosive. When a detonation is initiated at one end, by means of a detonator, the explosive shock or detonating wave travels along the fuse with a high velocity, and causes the detonation of other high explosives which lie in its path. In this way, it can initiate the almost simultaneous explosion of a number of charges.

The first form of detonating fuse was a lead-bound trinitrotoluene core fuse, called Cordeau fuse, or Cordeau detonant. A long thick-walled lead tube is filled with molten trinitrotoluene, which is solidified, and the tube and its contents are then drawn out in a series of successive drawing operations, until reduced in diameter to the size of a straw, in which condition it is highly flexible, and at the same time of a very considerable length, as compared to the original tube. Later, aluminum or block tin tubes were prepared, filled with picric acid. However, this type of fuse has now almost entirely been replaced by a detonating fuse composed of a tube of woven fabric filled with RDX (cyclotrimethylenetrinitramine) or with Pentaerythritol tetranitrate. Such a tube can be made in continuous lengths much more simply and less expensively than Cordeau fuse. The cloth binding is normally waterproofed with wax or other water-resistant fillers, and is usually reinforced with a wire or cord binding. This cord has a detonation velocity of about 6500 meters per second, as compared with about 5000 meters per second for Cordeau fuse. However, neither of these are the maximum velocities of detonation of these explosives. The velocities could be greater, and would be, if the explosives were more densely packed.

Both Cordeau fuse and the cloth or plastic bound detonating fuse contain finely divided crystalline explosives, but the explosive is in a somewhat different condition in each. Cordeau fuse is filled with cast trinitrotoluene, and as the lead tube is drawn out, the cast trinitrotoluene becomes pulverized, so that the finished tube is tightly packed with finely divided crystalline trinitrotoluene. The cloth or plastic bound fuse is made by filling the tube with finely divided pentaerythritol tetranitrate, which is packed in the tube as tightly as possible. The problem of packing the explosive in the cloth tube is quite difficult to resolve, and because of the difficulty of packing, it is not possible to realize the full velocity of detonation that might otherwise be obtainable with pentaerythritol tetranitrate or RDX. Furthermore, the packing operation itself can be dangerous.

In accordance with U.S. Pat. Nos. 3,327,582 and 3,367,266, process and apparatus are provided for manufacturing detonating fuse and deflagrating fuse filled with a column of solid detonating or deflagration explosive cracked in situ so as to cause discontinuity throughout the column of explosive. The cracking increases the surface area of the explosive in the column increasing its sensitivity to a detonating wave or deflagration. The process is adapted for continuous production of fuse, so as to make detonating fuse and deflagrating fuse in any desired length, and without restriction as to diameter, ranging upwards from one thirty-second inch to approximately 1 inch or higher, as required. In this process detonating fuse and deflagrating fuse are formed in one of two principal ways. A preformed tube or shell of the desired length and diameter can be filled with molten or semisolid detonating fuse high explosive or deflagrating fuse low explosive, and allowing this to harden or solidify to a solid column within the tube, filling it substantially completely. In this way, endless tubes previously formed in a continuous tube extruder can be employed. In another and preferred process of that invention, the filling of the tube is made to form the tube or enclosing wrapper as well, by extruding the detonating or deflagrating explosive with which it is to be filled in a column of the desired diameter and length, and forming the fuse wrapper about and enclosing the extruded column of explosive. The extruded column of explosive as soon as it has become sufficiently hard after leaving the extruder, is brought into contact with the enclosing feed of wrapper material and, through frictional engagement therewith, draws with it the sheet of wrapping material. Upon continued outward movement of the wrapper with the extruded column, the wrapping material is caused to form an envelope about the column, thereby enclosing it in a wrapper of the wrapping material. After completion of the fuse wrapper, the explosive column is desirably subjected to compressive stress in situ, so as to crack or pulverize the column, and render it discontinuous within the wrapper.

The process and apparatus described in U.S. Pat. Nos. 3,327,582 and 3,367,266 offers the alternatives of either filling a preformed continuous length of tubing or else forming a wrapper which has either a spiral or longitudinal seam which must be held tightly closed and then sealed at some stage of the operation. It is clearly preferable, in a commercial operation, to form a seamless package for detonating or deflagrating fuse or cord. However, given the choice of filling a preformed continuous length of tubing, or forming a wrapper with a seam, the latter is clearly to be preferred, as these patents indicate.

In accordance with the instant invention, process and apparatus now are provided that make it possible to simultaneously extrude a continuous seamless wrapper, and fill the wrapper with detonating or deflagrating explosive composition. The process and apparatus also preferably include means for cracking or pulverizing and optionally for swaging the continuous wrapped column of explosive composition that is formed in the course of this process, thus producing a detonating or deflagrating fuse or cord having greater flexibility, because of the cracking or pulverizing, and the development of maximum sensitivity. As a result of the cracking or pulverizing operation, the fuse will transmit a detonating wave from one end to the other.

In accordance with the invention, it is possible to ensure close packing of the explosive in the continuous length of tubing, substantially without voids between the particles of explosive, thus ensuring a high density, and a uniform density, even in the cracked condition of the fuse. In fact, because the continuous length of tubing can be filled with explosive while the explosive and/or the wrapper is still soft and pliable, it is possible to form an explosive package in which the explosive is more firmly packed, and under a higher degree of confinement, or at a higher density, than in the fuse obtainable in accordance with these patents. Moreover, an explosive that is in plastic condition and that completely fills such a wrapper can be constrained even more, if the wrapper is drawn or swaged after it has hardened sufficiently, to obtain an even higher density and a higher velocity of travel of the detonating wave or deflagration through the fuse.

In accordance with the process of this invention, detonating fuse and deflagrating fuse are formed by continuously forming an endless tube or shell of the desired length and diameter, continuously filling this tube or shell with detonating fuse high explosive or deflagrating fuse low explosive, preferably while either the explosive or the wrapper, or both, are still soft and pliable, and while supporting the tube or shell so as to preserve its shape under the weight and pressure of explosive therewithin, until the explosive and the tube have hardened and solidified so as to form a solid column of explosive within a hardened tube, filling the tube substantially completely and uniformly.

In one embodiment, the moving column of explosive is brought into contact with the continuous tube or shell of wrapper material as soon as the wrapper material has become sufficiently hard to retain its tubular shape, and through frictional engagement therewith, the moving column of explosive draws with it, in its forward progress, the continuous tube of wrapping material. In another embodiment, the tube or shell is too soft to retain its shape, and is supported within a shape-retaining die of the same internal diameter as the tube or shell. The tube can be moved forward also by feed pressure or extrusion pressure forcing the plastic wrapping material through a tube-forming die or extrusion nozzle. If desired, propelling means can be provided externally of the tube to assist in this forward movement.

If necessary, due to the pressure of the explosive and the softness of the tube or shell, the explosive-filled tube or shell can be confined or restrained within an enclosure of like dimensions, which tends not only to support the filled soft and pliable shell or tube, but also to retain the explosive therewithin, and prevent distortion of the column of explosive under pressure. Preferably, the explosive is brought to a cast or virtually solidified condition as rapidly as possible after it contacts the soft and pliable wrapper material.

After completion of the filled tube or shell, the explosive column therewithin is desirably subjected to compressive stress in situ, so as to crack or pulverize the column, and render it discontinuous within the tube. At the same time, because the column is held within the tube, the cracked or pulverized particles of explosive are prevented from significant displacement, relative to each other, and thus retain the form of a cast column, as originally formed. The cracking is sufficiently thorough to reduce the particles to a small size, of which at least 50 percent are less than one thirty-second inch in diameter, and preferably approximates a crushing operation, as a result of which at least 50percent pass through a 35 mesh screen and at least 25percent through a 120 mesh screen. All of the particles, of course, have a diameter appreciably less than the diameter of the fuse. The cracking or pulverizing, as previously indicated, renders the fuse more flexible, and ensures the development of maximum sensitivity. As a result of this cracking operation, the fuse will transmit a detonating wave from one end to the other.

After cracking or crushing, the fuse is complete. Any desired length of fuse can be obtained by measuring and cutting off an appropriate length of the tube.

If desired, and preferably, if fuse or cord of rather small diameter is to be prepared, the tube is formed and filled at a larger diameter, and is then reduced in diameter by a swaging operation after the explosive is partially or completely hardened. This not only reduces it in diameter, but at the same time cracks the column, and reduces it to a pulverulent, confined condition. This also can considerably increase the degree of confinement, and the density.

In accordance with the invention, apparatus also is provided for the continuous formation of explosive fuse or cord, which comprises, in combination, means for forming a tube or shell in a continuous elongated column, means for forming an explosive composition into a continuous elongated column, means for feeding the column of explosive composition into the interior of the tube or shell, preferably while either the explosive or the tube, or both, are soft and pliable, means for applying to the explosive column a sufficient driving force to completely fill the tube with explosive to a substantially uniform density, substantially free from gas-filled voids, means for supporting and retaining the explosive-filled continuous column of tube or shell, to control the diameter and configuration of the wrapped explosive fuse until the tube and the explosive column have become self-supporting, and, optionally, means for cracking the columnar explosive in situ within the tube to introduce discontinuity into the column, and increase sensitivity.

In a preferred embodiment of the apparatus of the invention, means is provided for swaging the partially or fully hardened packaged columnar explosive to a small diameter, at the same time cracking or pulverizing the explosive to introduce discontinuity into the column, and increase sensitivity. Because the swaging operation also reduces the diameter of the fuse or cord, the confinement of the explosive can be increased considerably, increasing sensitivity. It is also possible to control the diameter and the configuration of the cord better, since any possible variation in diameter of the explosive during the extrusion can be compensated for during the swaging, because the diameter of the continuous length of explosive is reduced at this stage. The swaging operation has the further advantage that it makes it possible to form and fill a larger diameter tube in the first instance, reducing this tube to a diameter more suitable for detonating or deflagrating fuse or cord during the swaging. This makes it possible to increase the output, since it is more difficult to fill a small tube than a large one.

The process of the invention is applicable to detonating fuse high explosive and deflagrating fuse low explosive compositions of all types. It is of particular application to extrudable explosives or cast explosives, which can be extruded or filled in semisolid or liquid form, and which can harden to form a solid in situ in the wrapper. If it be brought to a solid state in the form of a column prior to or shortly after contact with the wrapping material, it can in the hardened condition act as a motive force to aid in drawing forward with it the tube of wrapping material from the tube-forming operation.

The usual detonating and deflagrating explosives can be modified to improve flowability or fluidity by the addition of plasticizing or softening additives, and additives also can be added to harden an otherwise too soft explosive composition that is not readily cracked or broken up, in reduction of the cast or hardened material to smaller particle size.

When a molten filling is used, or when the column of explosive is under sufficient feed pressure, and the tubular wrapper is under constraint, consolidation of the explosive composition within the tube to a uniform density of explosive is ensured. Thus, it is possible to avoid the accidental formation within the fuse tube of partially filled areas, or of voids or open areas, in which the explosive composition is at a lower density, or is completely missing, with disastrous effects upon propagation of the detonating wave or deflagration beyond that point. This also ensures that the explosive composition will more or less completely fill the tube, and, being tightly held therein, will be kept in a columnar form by the tube after cracking. This ensures close juxtaposition of the explosive particles in the cracked product, which makes it possible for the detonating wave or deflagration to travel along the fuse at a high velocity. As a result, the detonating velocity of Pentolite in the detonating fuse prepared in accordance with the invention has exceeded a velocity of 6200 to 6500 meters per second.

In order to ensure uniformity of an extruded column of semisolid or thixotropic explosive in the tube, it is necessary that the tube be under constraint from the time it is filled with explosive until both tube and explosive are sufficiently hard to form a self-supporting composite. The pressure necessary to achieve this can be applied to the tube package by any of several means. The tube can be constrained within a confining tubular guide. The tube also can be retained between vanes or guides, or a series of circular rolling surfaces, which can be driven to aid in the forward movement of the tube.

In order to render the explosive filled tube self-supporting as rapidly as possible, while it is under constraint, it is cooled and/or freed from any solvent as rapidly as possible. This can be done by enclosing the supported tube in a cooling and/or drying chamber or jacket.

In one embodiment, the explosive filled tube is constrained within and passed through a porous tube having an interior diameter substantially the same as the outside diameter of the tube. A jacket is provided around the porous tube, and pressurized cooling fluid is circulated through the jacket. This fluid permeates through the pores of the confining housing, and thereby directly contacts the exterior of the tube. This in turn achieves rapid cooling of the tube and its explosive contents, at the same time provides a lubrication effect, whereby the tube passes through the tube with little or no friction. In this particular embodiment of the invention, the tube and the explosive composition are confined under both mechanical and fluid pressure, the mechanical pressure being exerted by the porous housing, and the fluid pressure by the cooling fluid, as both contact the tube.

For the cooling fluid various gases such as air, carbon dioxide, helium, nitrogen, etc. can be used. Also, flowable liquid cooling mediums can be used, such as wt water, brines and other conventional cooling liquids. The cooling fluid, either gaseous or liquid, is continuously passed through a heat exchanger outside the jacket, in order to remove the heat that is taken up by the fluid from the tube.

The entire tube can be coated with a surfacing material, if desired, to add greater strength and rigidity to the fuse, and this coating material will at the same time cover over and seal any breaks or holes in the tube. Thus, for example, the tube can be coated by application of a plastic coating or wax through spraying or brushing of the wrapper, or by application of kissing rolls, or by passing the fuse over a continuous surface or film of the bonding material. Such coatings can improve rigidity, and add protection from weather and abrasion.

Any type of thermoplastic or solvent-soluble wrapping material can be employed, including, for example, polyethylene, polypropylene, polyvinyl chloride, copolymers of vinyl chloride and vinyl acetate, cellulose acetatepropionate, cellulose acetate, and copolymers of vinyl chloride and vinylidene chloride. Extrudable plastic materials are particularly useful in the formation of extruded tubes in continuous lengths.

The thermoplastic wrapping material can be formed into a continuous tube or shell in any desired manner. A pulverulent material can be extruded under heat and pressure while soft or molten into the tubular shape. Solutions of a solvent soluble material can be spun in the tubular shape, and the solvent rapidly evaporated to form the tube or shell. Other methods will be apparent to those skilled in the plastic tube-forming art.

Cracking of the cast or hardened explosive is effected after filling and solidifying are completed. For this purpose, the fuse can be passed between crushing rollers, which subject the tube and its contents to compressive stress, sufficient to crack the column into small particles, of the order of one thirty-second inch in diameter, and preferably, to a finely divided condition. The pressure is not critical, but will be no greater than required to crack, because of the possibility of detonation at excessive pressures. Thus, the cracking pressure limit is established by detonation pressure, and is usually below about 60 p.s.i. Cracking results in a small increase in volume, due to the spaces introduced between the particles by the cracks, even when the particles are not appreciably displaced with each other. However, most cast explosives shrink slightly on solidifying, due to the decrease in volume upon cooling, and these two factors usually result in a cracked fuse which is substantially unchanged in volume from the original fuse, due to the compensating effect of the two opposing tendencies.

If the fuse is distorted in shape, due to the cracking operation, it can be passed between forming rolls or through a forming die, so as to restore it to the desired shape, such as a round configuration.

A combined cracking and size-reduction operation, or swaging, is particularly advantageous. Swaging can be effected when the explosive has completely or partially solidified. Any type of swaging equipment can be used, such as a low friction Teflon, Teflon-coated or metal sizing die or rollers. The swaging system can be combined with cooling means for hardening the explosive filled tube immediately after filling, so as to support the filled tube until it is self-supporting, and reduce its diameter to a uniform smaller diameter, cracking the explosive column at the same time. The surfaces in contact with the tube should be low friction, since the tube may be soft, and somewhat sticky.

The swaging equipment used in Cordeau fuse manufacture is useful. Such equipment draws the filled tube, thus reducing its diameter, while cracking the columnar explosive. An array of rapidly moving hammers which beat the tube uniformly about its entire circumference can be used, and the tube can be merely reduced in diameter, or also changed in cross section from a round tube to an elliptical or flattened tube or ribbon.

In the preparation of detonating fuse, the process is applicable to detonating fuse explosives of any type. Preferred explosives are those which can be molten and then cast, such as, Pentolite (a mixture of equal parts by weight of pentaerythritol tetranitrate and trinitrotoluene), trinitrotoluene, the amatols (combinations of ammonium nitrate and trinitrotoluene), the sodatols (combinations of sodium nitrate and trinitrotoluene), Composition B (a mixture of up to 60percent RDX, up to 40percent TNT, and 1 to 4percent wax), Cyclonite (RDX or cyclotrimethylenetrinitramine), tetryl, Cyclotol (Composition B without the wax) mixtures of Aluminum and TNT and combinations of these.

The process is also applicable to deflagrating low explosives of any type, such as black powder, smokeless powder, gun powder, and mixtures of these.

Cast explosives are best filled in the following manner. They are first brought in the molten condition, and then delivered into the center of the tube shortly after it is formed, and preferably while it is still soft and pliable. The explosive can be delivered to the tube by a gravity feed or can be passed into the tube from an extruder under pressure, or fed by a peristaltic pump. Excellent results can be achieved with use of a peristaltic pump whereby the explosive composition is flowed through a flexible tube which is sequentially compressed by rollers so that there is no direct contact between the explosive composition and the pump parts. Also useful are a hydraulic ram, or gas pressure over the reservoir of explosive. In each case, this is done under conditions such that it can harden into a solid or semisolid not necessarily finally hardened cast condition, shortly after being brought into the interior of the tube of wrapping material. In the solid or semisolid condition, it can be used as a motive force to aid in drawing the tube forward, and filling the tube, and pressure can be applied thereto by the fluid explosive being fed to the tube, so as to push the solidified explosive column forward for this purpose. Solidification to this extent requires careful control of temperature at the point of contact between the explosive and the wrapper, but this is readily achieved by conventional equipment, such as by an extrusion nozzle provided with a temperature control jacket.

The invention also is applicable to explosive materials that can be brought into a semisolid condition for the purpose of extrusion, and then become hard upon curing or aging, or heating, or cooling, according to the explosive composition. Such explosives are readily extruded in the semisolid condition, and in this condition pressure can be applied thereto so as to fill the tube completely, and also provide a motive force for drawing the tube forward and completely filling the package, and they can be allowed to harden either before or after the fuse package has been formed, but before cracking or crushing.

Explosives of this type to which the invention is applicable include combinations of nitrostarch and nitrocellulose with gelatinizing or plasticizing agents, such as nitroglycol, dinitrotoluene, and trimethylolethanetrinitrate, combinations of tetranitrodiglycerine with nitrocellulose, and combinations of nitromannite and trimethylolethanetrinitrate

Various additives can be incorporated in the detonating or deflagrating explosive composition, either to improve to or to reduce hardness. Trimethylolethanetrinitrate and dinitrotoluene are good hardness-reducing additives, which will improve lubricity during extrusion, and indeed, any liquid explosive will serve this purpose. Only small amounts are usually required, of the order of from 0.5 to about 20percent by weight of the explosive composition.

It is generally preferable that the detonating or deflagrating low explosive have a softening point above the temperatures to which the fuse may be subjected during storage and use. Usual use conditions will require that the explosive have a softening point of at least 120.degree. F., and preferably above 150.degree. F. There is no upper limit on softening point, except as may be dictated by the filling or extrusion conditions and equipment that may be available for preparing the fuse, in bringing the explosive composition into the necessary molten or semisolid condition required for forming and filling the tube.

It is also possible to apply the process to the formation of detonating or deflagrating fuse using detonating or deflagrating explosive powders as the filler material. These are, however, more difficult to process, and accordingly the use of explosives which can be made molten or semisolid for filling or filling and wrapping are preferred.

When the explosive composition itself serves as a motive force for pushing the filled tube forward, the column of explosive will move forward, drawing the tube of wrapping material with it, only when explosive material is being pushed forward. Where there is an air pocket in the interior of the mass of explosive, there is no explosive mass to apply the necessary motive force, and hence there is no further movement of the extruded explosive until the air pocket has been eliminated.

The finished detonating fuse or deflagrating fuse can be disposed of in any manner known to the art. Very long and continuous lengths of fuse can be stored by winding the fuse on a spool or roll. The fuse may be packaged to any desired length by cutting it off either automatically or manually at the desired length. The exposed ends can be protected or closed off by spraying, dipping, applying caps, or other well known packaging methods. It is also possible to improve the strength of the outer covering by means of gluing, spraying, coating or continuous dipping. All such procedures are well known to those skilled in the explosives and packaging arts.

FIG. 1 is a top plan view of a continuous tube and explosive extrusion apparatus for carrying out the invention, designed for use with castable detonating or deflagrating explosive compositions;

FIG 2 is a cross-sectional view on an enlarged scale of the apparatus to the FIG. 1, taken along the line 2-2;

FIG. 3 is a view on an enlarged scale, and partly in section, of the explosive filled tube cooling and hardening and cracking portions of the apparatus of FIG. 1, viewed from the back;

FIG. 4 is a view of another embodiment of apparatus, adapted to swage the cast detonating or deflagrating fuse into a smaller diameter crushed fuse;

FIG. 5 is a side view, partially in section, of a continuous tube-forming explosive extruding apparatus for carrying out the invention, designed for use with castable detonating or deflagrating explosive compositions and forming the continuous tube of wrapping material from an extrudable thermoplastic resin such as for example, polyvinyl chloride or polyethylene.

The apparatus shown in FIGS. 1 to 3 comprises an extruder 1 equipped with an extrusion nozzle 4 from which the detonating or deflagrating explosive composition emerges in a semisolid condition in the form of an extruded column 2. Explosive compositions which can be extruded in this way are, for example, a combination of dinitrotoluene and nitrostarch, or a mixture of nitrocellulose, nitroglycerine and nitroglycol. Positioned at a point a short distance from the extruder is a heated hopper 3, from which molten thermoplastic resin material such as polyethylene is fed to a jacket tube 5 surrounding the nozzle 4. The jacket is heated by a heating means, such as an electric coil or a heating fluid (not shown). The plastic flows along the nozzle 4, via the annular space surrounding the nozzle, which is about one thirty-second inch wide, and thereby is formed into the tube, which by the time it reaches the tip 11 of the extrusion nozzle, is sufficiently hard to retain its shape but is still soft and pliable, and is filled with explosive 2, in columnar form.

Surrounding the filled tube 7 beyond the nozzle tip 11 is a cooling jacket 8, through which water or cooling fluid is circulated via pipe 9, to cool the extruded column of explosive 2 and the tube 7 to a solidifying temperature, bringing both into a hard, solid condition. The jacket is sufficiently long to assure completion of solidification before the filled tube, now a detonating or deflagrating fuse 13, emerges from the jacket, while supported therein by rolls 14, at the travel speed of the fuse through the system.

A pair of carrying belts 45 are provided, to support the fuse. Just after it contacts the belts 45, the fuse passes into the adjustable bite of a pair of cracking or crushing rollers 60 and 61, and then into the adjustable bite of a second pair of crushing rollers 62, 63, which grip the fuse at the top and bottom, in sequence, to ensure thorough cracking, and even crushing, if desired, depending on the width of the gap between the rollers, of the solid cast explosive column within the tube. The second set of rollers 62, 63 can alternatively be arranged to grip the fuse at the sides, if desired.

Finally, a storage roll 50 receives and winds up the fuse 13 emerging from the system.

In operation, detonating or deflagrating explosive composition 2 in a semisolid condition is passed through the extruder 1. The plastic material in hopper 3 is fed by gravity to and through the annular space 6 in jacket 5, where it is formed into a tube 7 surrounding the exterior of the extruder nozzle 4, and feeds forward under gravity pressure along the outside of the extruder nozzle 4 over the end 11 thereof, at which point it comes into contact with the semisolid extruded column 2 of detonating or deflagrating explosive composition emerging from the extruder nozzle 4. The explosive composition contacts and draws the soft but now shape retaining tube 7 of wrapping material with it, as it emerges from the extruder, and this is continuously replaced by gravity feed of explosive from hopper 3. Simultaneously the filled tube 7 is carried forward within the cooling jacket 8 while supported on rolls 14 and thus can retain the detonating or deflagrating explosive composition therein without distortion. As the tube and the explosive are solidified and hardened with in the cooling jacket 8, it becomes unnecessary to provide external support for supporting the tube against the weight of explosive, and the cast column and tube are carried on rolls 14 to the point of application of cracking pressure. The finished cast column of explosive within the tube is then cracked or crushed in situ between the rolls 60, 61, 62 and 63, and the finished fuse 13 emerges from the system in a flexible continuous length, which can be wound up on the storage roll 50 as shown, and packaged as such.

The apparatus shown in FIG. 4 is adapted for use of powdered detonating or deflagrating explosive, and swages the explosive filled tube to a smaller diameter cord, while at the same time pulverizing the cast explosive therewithin. The explosive in powdered form 15 is fed into the hopper 17, which is heated to a temperature at which the explosive powder melts into a viscous fluid, which is then fed by the screw loader 19 through the feed nozzle 21, which is also heated to maintain the explosive in fluid condition, and emerges into the extrusion nozzle 4, which shapes it into columnar form. A hopper 3 feeds powdered plastic material, such as polyethylene or polyvinyl chloride, into the annular space 6 between heating jacket 5 and the nozzle 4. The jacket 5 is kept at a temperature sufficient to fuse the plastic to form a soft shape retaining tube 7. Beyond jacket 5, the tube 7 enters the atmosphere, where it is rapidly cooled and becomes self-supporting.

The nozzle 4 extends well into the tube 7, and at its end 11 feeds molten explosive into the now self-supporting tube 7 at a rate sufficient to completely fill the tube with explosive. Since the tube is still soft, it is supported on rollers 14 from the end of the nozzle into and through the cooling jacket 8, into which it then passes. A cooling fluid such as water is circulated through the jacket via pipes 9 at a temperature sufficient to solidify the molten explosive in the course of its passage through the jacket. Usually a temperature of from 10 to 20.degree. C. below the softening temperature of the explosive is adequate to ensure complete solidification of the explosive into a cast solid form by the time the tube emerges from the cooling jacket.

The tube then passes into the bite of a swaging die 70, in which its diameter is reduced by one-fourth, thus cracking or crushing the cast explosive into pulverulent form. The swaging die has porous walls through which a lubricant is circulated via pipes 72, 73 to facilitate passage of the tube therethrough, without generation of excessive heat. The fuse 13 then is rolled up on a storage roll 50, as in FIGS. 1 to 3.

In operation, the molten explosive 15 is fed at the required rate to completely fill the tube 7, fed to it over the outside of the nozzle 4. The feeding pressure is sufficient to ensure that the force fed molten explosive will provide the sole motive force for carrying the tube forward through the system, thus making possible consolidation of the explosive within the tube, and the elimination of any air pockets.

In the case of a mixture of pentaerythritol tetranitrate and trinitrotoluene, such as Pentolite, the operating temperature in the explosives hopper 17 is approximately 90.degree. C. and this temperature is maintained through the first portion of the extrusion nozzle 4. Thereafter, the apparatus is open to atmospheric temperature, and some cooling is effected. By the time the explosive has reached the heat-cooling jacket 8, it is in a semisolid condition, virtually ready to solidify, and the temperature is within the range from 85 to 77.degree. C. The cooling jacket is maintained at 60.degree. C., and this quickly brings the temperature of the explosive to below 76.degree. C., whereupon it solidifies in cast form, and can then be swaged, and the explosive cracked or crushed in the bite of the swaging die 70. The finished fuse 13 is then wound upon roll 50.

The apparatus shown in FIG. 5 comprises an extruder 10 having an extrusion barrel 12, an extrusion nozzle 24, a screw impeller 14, driven by motor 16, and a heating jacket 18 through which a supply of heating fluid can be circulated, or which can be heated electrically for applying heat to the interior of the extrusion barrel 12. A hopper 20 holds a supply of particles of thermoplastic synthetic resin 22, for example, granular polyvinyl chloride homopolymer. These particles are discharged by gravity continuously into the back end of the extruder barrel 12. Directly forward of the hopper 20, the barrel 12 is enclosed within the heating jacket 18, so as to melt the plastic particles. The screw impeller 14 disposed in the center of the extruder barrel 12 carries the particles forward through the barrel to the extrusion nozzle 24.

Disposed concentrically within the nozzle 24 is an explosives feed tube 36, the outer wall of which defines a narrow annulus 25 between the inside wall of the nozzle 24. The molten plastic is constrained within the annulus, and thereby shaped into a tube 26, which is continuously pushed forward under the pressure of the extruder impeller 14 through this annular space 25.

A jacketed supply tank or reservoir 28 holds a supply of molten castable deflagrating or detonating explosive composition 30. A flexible tube 32 extends from an opening in the lower portion of the reservoir to a connection with the hollow tube 36 within the nozzle of the extruder on the other side of the peristaltic pump 38. The tube 32 is enclosed within windings of electrical heating tape 34, which serve to maintain the temperature of the explosive passing within the tube 32. The explosives feed tube 36 enters the extrusion nozzle 24 at one side of the tapered nozzle portion, and terminates at the other end of nozzle 24, opening into the interior 27 of the plastic tube 26 formed in the annular space 25.

The peristaltic pump 38 provided near the end of the flexible tube 32 has a plurality of rollers 40, three in number as shown, which successively squeeze the tube 32, to cause a pumping movement of the explosive composition 30, thrusting it along the tube 32 into and through the tube 36 into the interior of plastic tube 26.

The walls of the tube 25 can be made of any suitable material. If desired, the walls can be made of a low thermoconductivity material, which prevents substantial transmission of heat between the molten plastic material in the annular space 25 and the explosive composition 30 which is passing through the tube 36. In this case, the wall of the tube 25 can be made of a laminate having an interior first layer of nickel-chromium, a next layer of sulfur, a next layer of graphite, and a final layer of nickel-chromium. Such an insulated passageway decreases the rate of transmission of heat between the plastic material 26 and the explosive material 30, and thus makes it easier to maintain these compositions at different temperature levels.

Alternatively, the tube 25 can be made of a heat-conducting material, such as any suitable metal, for instance, stainless steel or a stainless alloy. Such a wall tends to reduce any difference in temperature between the plastic material and the explosive material before they actually come into contact at the end of the tube 25, and this makes it easier to control the sizing of the extruding detonating or deflagrating fuse.

The tube 25 terminates at the end of the nozzle 24. The nozzle end is attached to and opens into a porous supporting tube 44, enclosed within a cooling jacket 46, thus constituting a cooling zone, indicated generally by the numeral 42. The supporting tube 44 can be porous, as shown in the drawing, but it need not be, and can in fact be any good heat-conducting material to which the plastic material of the wrapper does not adhere i.e., a material presenting a low friction or frictionless surface to the plastic tube. The tube 44 as shown is made of a porous material composed of discrete metal particles which are sintered together with a large number of voids and pores therebetween, permitting fluid to circulate through the material 44. A tube made of porous metal bearing material for instance is quite satisfactory. The tube 44 constrains the tube to the inner diameter of the tube 44, and resists expansion due to internal pressure exerted by the explosive upon the tubing wall, thus making it possible to retain the desired diameter in the tube 26, at the same time supporting the tube, and preventing distortion of the wrapped cord or fuse.

A cooling fluid can be circulated through the jacket 46 by means of lines 48 and 50 and pump 52. A heat exchanger 54 between lines 48 and 50 permits the adjustment of the temperature of the cooling fluid. Since the cooling fluid passes through the pores and voids of the tube 44, it can come into direct contact with the exterior surface of the plastic tube 26, thus facilitating the cooling, and at the same time lubricating the surface of the tube, so as to reduce friction as the tube passes along the porous tube 44. The length of the tube and the cooling capacity of the jacket are adjusted so that by the time the explosive-filled tube emerges from the jacket, both explosive and tube are hard and self-supporting, requiring no further support by the tube 44. The final product can be cracked or crushed, as in FIGS. 1 to 3, or swaged, as in FIG. 4, and then wound on a spool or otherwise packaged and stored. It can also be cut into lengths, if desired.

In operation, plastic particles 22 are continuously gravity fed through the hopper 20 into the extrusion barrel 12, melted in the portion within jacket 8, and then out through the nozzle 24, via the annular space 25, where it is formed in the shape of a hollow tube 26. Explosive of a detonating or deflagrating type is continuously drawn through the tube 32 from reservoir 28 by the peristaltic pump 40, and then fed through the tube 36 into the hollow interior 27 of the plastic tube 26, while it is still soft and pliable. The forward movement of the explosive and the impelling movement of the impeller 14 force the tubing 26 forward, and at the same time completely fill the hollow interior of the tubing with explosive 30, eliminating voids, and filling the tubing to a substantially uniform density of explosive. The filled tube then passes through the supporting tube 44, where it gradually becomes hard, due to the cooling action of the cooling fluid. At the same time the explosive 30 also solidifies, so that by the time the tubing and explosive emerge from the support tube 44, these are both hard.

If it is then necessary to crack the explosive, the tube can be passed into the bite of the two pairs of crushing rollers 60, 61, 62, 63, over a carrying belt 45, as shown in FIGS. 1 to 3, or swaged, as in FIG. 4. Finally, a storage roll 50 receives and winds up the fuse 13 emerging from the system.

The following Examples in the opinion of the inventor represent preferred embodiments of the invention.

EXAMPLE 1

Using the apparatus shown in FIG. 4, a one-eighth inch detonating fuse in a polyvinyl chloride sheath or tube was prepared, using Pentolite (a 50-50 mixture of pentaerythritol tetranitrate and trinitrotoluene). The detonating explosive was fed at 95.degree. C., and the tube polyvinyl chloride was fed at 150.degree. C. to form a tube one-fourth inch in diameter, and cooled to 95.degree. C. before contacting the explosive. The explosive solidified in the jacket 8, which was held at 60.degree. C. The filled tube was then swaged to a diameter of one-eighth inch, in the course of which the explosive was crushed.

A 36 inch length of the fuse that was obtained was detonated with a No. 6 duPont blasting cap, butted against one end. Seventeen inches out of 36 inches were detonated.

Another length of the same fuse was opened, and the crushed Pentolite subjected to screen analysis, with the following results: ##SPC1##

A length of the fuse was removed before reaching the crushing rolls, and detonation was attempted on the cast fuse. The fuse detonated only 6 inches out of 36 inches. The effectiveness of the crushing in improving sensitivity is evident from this test.

EXAMPLE 2

A one-eighth inch detonating fuse was prepared using the apparatus of FIG. 4, and following the procedure of Example 1, with Composition B as the detonating explosive. The detonating explosive composition contained 60percent RDX, cyclotrimethylenetrinitramine, 39percent trinitrotoluene, and 1 percent wax. The hopper of explosive was held at 85.degree. C., and the tube material was cooled to 85.degree. C. before contacting the explosive. The explosive was cooled to solid cast condition in the jacket 8, held at 60.degree. C.

A 36 inch length of the detonating fuse that was obtained was detonated with a No. 6 duPont blasting cap butted against one end. Eighteen inches out of 36 inches detonated.

Another length of the detonating fuse was removed before passing through the crushing rollers, and then tested for detonating ability. The fuse detonated only 7 inches out of a 16 inch length, thus evidencing the importance of crushing, in imparting the necessary sensitivity to the fuse.

A length of the crushed fuse was opened, and subjected to screen analysis, with the following results: ##SPC2##

The detonating fuses of Examples 1 and 2 were compared to Primacord for rate of detonation and cavitation in a lead plate. The lead plate cavitation was determined by placing a length of detonating fuse or 50 grain Primacord core load with the reinforcement removed; only the black asphalt countering remaining on a lead plate. The length of cord was held in contact with the plate by a strip of masking tape running its entire length. Initiation was by No. 6 duPont blasting cap. ##SPC3##

It is apparent that the Examples 1 and 2 fuses had a higher bristance than Primacord, and that Example 1 had a faster rate of detonation than did Primacord.

EXAMPLE 3

Using the apparatus of FIGS. 1 to 3, a one-eighth inch detonating fuse was prepared from Pentolite. The fuse that was obtained detonated 30 inches out of 30 inches, when initiated by a duPont No. 6 blasting cap butted against tube end of the fuse. One the other hand, an uncrushed cast fuse detonated only partially under the same conditions.

EXAMPLE 4

Using the apparatus of FIG. 5, a three-sixteenth inch deflagrating fuse is prepared from nitrocellulose, gelatinized by trimethylolethanetrinitrate. The fuse deflagrates well, and at a consistent rate, throughout its entire length.

EXAMPLE 5

Using the apparatus of FIG. 5, a one-eighth inch deflagrating fuse is prepared from a mixture of nitrostarch gelatinized by dinitrotoluene. The fuse detonates well and a constant rate throughout its entire length.

* * * * *

Current U.S. Class:	86/20.1 ; 264/3.1; 425/113; 425/133.1; 425/377; 425/71
Current International Class:	C06C 5/00 (20060101); C06C 5/08 (20060101); F42c 009/10 ()
Field of Search:	86/1,20,20.1,20.5 264/3,3B 18/13N,13K