Selection Control Methods For Explosive Systems

Abstract

Selective control methods are provided for explosive systems which involve the placement of agents which act by dilution, physical or chemical means to alter the sensitivity of explosive (including pyrotechnic) materials or devices wherein: (1) the release may occur by the melting of the agent, rupture of a container or by pumping; (2) the agent is confined as a solid, is within a container capsule, is physically placed or mixed within the explosive as small or large pieces, is coated or molded on the walls or other parts of the device, or is held in an inactive position outside the action zone but is so arranged that it will be effectively placed on receipt of signal; (3) the signal to deactivate or activate may be heat supplied by the environment, or from an activating unit incorporated in the system, or pressure, or mechanical activation, wherein the signal may be the result of a command or set, or the output of a transducer control system.

Description

SUMMARY OF THE DISCLOSURE

The present invention provides methods whereby deactivating materials may be put into or removed from explosive systems through techniques which prevent their interference with normal system operation yet will allow them to alter that operation if a predetermined event has occurred which makes it desirable or important to alter the system output. In the simplest type example an annular wax washer in a pyrotechnic material train allows ignition to transfer readily through its central hole, but if the arrangement has been subjected to an elevated temperature the wax will melt and contaminate the pyrotechnic material and thereby deactivate the device with respect to its usual initiation signal. The effects have been shown with pyrotechnic, primary explosive, and secondary explosive materials in deactivate processes, and with pyrotechnic materials in activate processes.

In addition some specific agents for preventing detonation of lead azide on heating are presented.

BACKGROUND OF THE INVENTION

The control of sensitivity of explosives has long been studied and a brief summary is given here from ENCYCLOPEDIA OF EXPLOSIVES AND RELATED ITEMS, by Basil T. Federoff, et al., Picatinny Arsenal, Dover, New Jersey, AD 653,029, Volume 3, 1966, pages D88, 89, 90. "Desensitization or phlegmatization of an explosive means rendering it insensitive, or less sensitive to the following actions: heat, shock, impact, percussion, rifle bullet or friction. Desensitizer (or phlegmatizer) is a substance which makes insensitive or reduces the sensitivity of an explosive. -- Desensitized explosives are those which are made insensitive to the above listed actions. Such explosives are safe to handle and transport. Typical examples are: RDX Composition A; PETN/ wax compositions -- "

"Most of the primary explosives (mercury fulminate, lead azide, Tetracene, etc.) and many high explosives (nitroglycerine, Tetryl, PETN, RDX, etc.) are too sensitive to be used per se and must be desensitized. For example lead azide may be desensitized by coating its crystals either with dextrin or with polyvinyl alcohol. It can be desensitized by controlling the size and shape of its crystals, or by precipitating it in colloidal form."

"Liquid high explosives (such as nitroglycerine, nitroglycol or some other nitric esters) can be desensitized by mixing them with substances absorbing, or absorbing them. -- The resulting substances are known as Dynamites. -- As some industries -- require the use of powerful explosives -- it was necessary to devise safe methods for their delivery. -- One of the European methods is to mix nitroglycerine with kieselguhr, ship it, and then leach with warm water; the nitroglycerine settles to the bottom of the tank and could easily be removed."

"For desensitization of solid high explosives, the usual procedures are to coat them with one or more of the following: paraffin, paraffin oil, waxes, stearic acid, stearates, polyvinyl acetate, dinitrotoluene, etc. Wohler determined the maximum percentage of paraffin oil which could be incorporated in a high explosive without making it detonate incompletely. He name this value `Phlegmatization Limit` -- "

While the number of means for deactivating explosives is voluminous and many compositions have been used for both military and commercial purposes it does not appear that the concept of the present invention has been applied in the earlier work wherein the explosive in containment is subjected to an action within the container to either incorporate or remove a desensitizing agent. It does not appear in the literature that explosive which has been prelocated and affixed by either its particulate nature or its confinement is then subject to controlled or programmed introduction of a deactivating agent although R. W. Lawrence U.S. Pat. No. 2,363,254 made use of a wax liner to provide blasting caps which would not detonate when heated in a fire.

It has also been found that in addition to the mechanical placement of deactivating agents in devices designed to show a change in reaction to the usual activation signal on exposure to heat, that it is possible with certain selected mixtures to rely on simple mixing. This has been made to perform in a desired fashion such as burning if the mixture has not been subjected to elevated temperature. Application of heat, however, will make the material inactive.

There has been an increasing use of pyrotechnics and explosives in systems where the ultimate operation of a device or unit would desirably be related to an experience which that unit has seen prior to the time for use. For instance, in an arming or firing system it would be desirable to produce the ignition of the round if that round had not been exposed to an excessive temperature, as the excessive temperature might well cause the round to malfunction in terms of a premature or delayed explosion. In addition, the use of pyrotechnic and explosive materials to convey information which is in the nature of logic in isolated systems which contain their own stored chemical energy for activation is of increasing interest.

Such links may be provided in an explosive system where the network may be preset so that if Item A or Event A has occurred a thermal switch may be thrown to divert the course of a subsequently fired explosive to Network 1 or Network 2. These may be on either relatively long time scales or on quite short time.

A conceived utilization of these devices might comprise fuze systems for stored munitions which in the event of exposure to the heat of a fire would deactivate or "dud" the usual firing systems. At the same time or at a slightly higher temperature a destruct or abort system could be activated by heat to be set off by a temperature controlled igniter.

The present invention in addition permits the working with explosive and pyrotechnic assemblies in deactivated form through such hazardous operations as welding or pressing, bonding, and the like and would permit the ultimate removal of the deactivating material from the explosive to activate the device. This would then consequently provide materials in the nature of explosives which could be handled as deactivated devices for assembly, storage, and shipment and which could be subsequently activated at the site of final use, should this be of importance.

The methods utilized here in addition to being applicable to small confined units are also suitable to the general procedures involved in the handling and processing of explosives. Thus the use of a duddant agent which is subsequently removed in processing would permit the formation of pyrotechnic and explosive circuits which would be printed in a dudded form, carried through several operations and then activated for final use.

OBJECTS OF THE PRESENT INVENTION

It is an object of the present invention to provide systems for deactivating explosives wherein a solid duddant material is placed in close proximity, but in an ineffective location, to an explosive charge and provide that exposure to externally supplied heat or a selected heat input signal will produce deactivation of the explosive charge.

It is the object of the present invention to provide dudding material which may be contained in capsular form or which may be contained in small plastic or metal containers for release on command or through the influence of heat or pressure to produce deactivation of an explosive material.

It is an object of the present invention to provide a system wherein a dudding agent is physically arranged to be continuous to the explosive but is in an inactive form.

It is an object of the present invention to provide a system wherein deactivating material is mixed with a particulate form of the explosive in such a way that the explosive will propagate unless the system has been subjected to a certain minimum amount of heat to allow the dudding agent to deactivate the explosive.

It is an object of the present invention to provide explosive systems which can be handled while in a deactivated form for processing and subsequently be activated by simple techniques prior to use.

It is an object of the present invention to provide a system where combinations may be used to provide pyrotechnic logic systems by selective control of different parts of the arrangement with the introduction or removal of dudding agents on command.

It is a further object of the invention to provide new dimensions in the concepts of explosive and pyrotechnic logic systems.

BRIEF DESCRIPTION OF THE DRAWING

To illustrate the findings of the present invention a number of specific examples are described below and several are shown in the drawing.

FIG. 1 shows a pyrotechnic delay with a wax washer to cause dudding on heating.

FIG. 2 shows a pyrotechnic delay with a duddant present in its housing.

FIGS. 3 and 4 show a duddant in a position contiguous to a pyrotechnic train.

FIG. 5 illustrates a wax washer in position to dud a primary explosive.

FIG. 6 illustrates a system in which wax may dud a secondary explosive.

FIGS. 7 and 8 show pyrotechnic material containing wax before and after heating.

FIG. 9 shows one way heat melting wax activates a system.

The following examples set forth specific embodiments of the invention and are given in order that the effectiveness of the invention may be more fully understood. They are included for illustration only and are not intended in any way to limit the practice of the invention.

EXAMPLE I

Two assemblies for conducting a burning pyrotechnic signal in a confined system were constructed as shown in FIG. 1 by placing three sections of lead 1 jacketed 0.123 inch outside diameter by 0.04 inch inside diameter boron-red lead pyrotechnic material 2 inside a glass tube 3 one-eighth inch in diameter. The two three-eighths inch long sections of the pyrotechnic material were separated by a wax washer 4 in which a 0.04 inch hole was present and which was 0.035 inch thick. This wax washer was made of pentaerythritol hexastearate which had a melting point of 147.degree. C. It had been melted on an aluminum sheet and allowed to cool so that the one-eighth inch diameter washer could be cut from it. The components were held in position by an igniter piece 5 at left and by a smaller piece of glass tubing 3 at right. ght.

One of the assemblies was then ignited and by visual observation it was determined that the burning signal propagated through the entire length.

The second assembly was subjected gently to external heat from a gas burner to allow the wax washer to just melt. Since glass tubing was being used it was possible to observe that the wax melted without disturbance of the components in the assembly. The assembly was fired and burning propagated up to a point where the pyrotechnic material had been "dudded" by the melted but by then frozen wax.

EXAMPLE II

A similar experiment was carried out with ceresene wax with a melting point of 48.degree.-53.degree. C in place of the hexastearate and gave similar results.

EXAMPLE III

In assemblies similar to those in Example I, washers were prepared of Halowax 1014 (mp 130.degree.-2.degree. C). Halowax is a trade name of Koppers, Inc. and is used for chlorinated naphthalenes. One completed assembly unit was placed in a oven at 80.degree. C for 30 minutes and then removed and fired. This demonstrated that temperature below the melting point of the wax did not cause deactivation. A companion test unit was heated by an infrared heat lamp until visible signs of melting of the wax appeared. This unit was then tested and failed to propagate. This demonstrated that "dudding" was effected when the wax was heated to the melting point. Heating for a modest time below the melting point had been shown to have no effect on the performance of the unit.

EXAMPLE IV

Glass tubes of the type used for the preparation of the pyrotechnic assemblies as described in Example I were treated by allowing wax, in this case Esso Household Wax with a melting point of 50.degree.-3.degree. C and a softening point of 48.degree. C, to coat the interiors of the tubes with wax films 6, as shown in FIG. 2. Two of the pieces of pyrotechnic material were then inserted as shown. One test unit was fired at room conditions with a fresh igniter 5 and propagated in normal fashion. A companion test unit was then placed in an oven at 80.degree. C for 15 minutes, removed and a fresh piece of pyrotechnic was attached as an igniter. When the fresh material was fired it burned normally but the ignition of the other parts of the assembly did not occur. The wax coating on the interior surface of the tubing had produced a thermally controlled dudding effect.

EXAMPLE V

Two assemblies containing three pieces of pyrotechnic material in a one-eighth inch bore brass tube 7 were made as shown in FIGS. 3 and 4. The center piece on line 4--4 was about one-eighth inch long and was carefully sliced parallel to and just into the pyrotechnic core with a razor blade. A formed piece of Esso Household Wax 8 was inserted above it. The arrangement was made to provide a piece of wax in contact with the active core of the device. One unit fired in the usual fashion propagated. A companion unit heated to 180.degree. C in an oven for 10 minutes could not be fired as the wax in this case had produced a dudding effect in the pyrotechnic material.

EXAMPLE VI

Two explosive assemblies as shown in FIG. 5 were made to provide control of initiation of an explosion in a primary explosive from associated pyrotechnic igniters. Each assembly contained two one-sixteenth inch thick slices of lead azide 10 in lead separated by a wax washer 0.07 inch thick 4 and separated in turn from a three-fourths inch length of boron-red lead pyrotechnic material 5 in lead by a plastic washer 0.04 inch thick 9. The wax used was Kindt Collins 278B, mp 89.degree.-90.degree. C. One assembly was placed in an oven at 120.degree. C for 2 hours. When removed and fired by ignition of pyrotechnic material 5, the pyrotechnic material burned but did not cause the lead azide 10 to detonate. The unit was examined and it was established that the pyrotechnic material had been burned and that the wax had not reached the pyrotechnic material. In this experiment the primary explosive, lead azide, was dudded. In the test of the unheated unit the pyrotechnic material caused the detonation of both pieces of lead azide.

EXAMPLE VII

Two explosive assemblies were prepared as shown in FIG. 6 to carry pyrotechnic ignition to detonation of a primary explosive and in turn to propagate the explosion to a secondary explosive. A very small core PETN (pentaerythritol tetranitrate) of 2 grains per foot 12 in a lead jacket 0.05 inch in diameter was wrapped with tape 11 to provide a snug fit in a one/eighth inch diameter brass tube. This was separated by a wax washer 0.04 inch thick having a 0.04 inch hole, and made of Kindt Collins 278V wax, mp 135.degree. C, from a one-eighth length of lead azide 10 in lead. The lead azide was separated in turn by a plastic washer 9 from a boron-red lead igniter. One unit was heated in the oven for 1 hour. When it was fired the pyrotechnic material burned, the lead azide detonated, but the PETN did not. The second unit when fired gave detonation of both the lead azide and the PETN. From examination of the first unit and other experiments with the PETN in lead and wax it was determined that the PETN had been dudded by the melted wax.

EXAMPLE VIII

A pyrotechnic mixture was prepared by mixing 15 parts of powdered boron, 85 parts of red lead (Pb.sub.3 O.sub.4) and 25 parts ground Fisher No. 700263 HIGH-PYSEAL CEMENT which softens at 130.degree. C and which resembles sealing wax. The mixture was put into a lead tube 0.188 inch I. D. .times. 0.290 inch O. D. and reduced in size by roll drawing in seven stages to an outside diameter of about 0.140 inch. Four 2 inch lengths were cut from the material and showed the appearance of finely packed powder indicated by 13 in FIG. 7. Two lengths were ignited with hot wires and burned completely through. The companion pieces were placed in an oven for two hours and on examination had the appearance of sintered powder and some voids as indicated by 14 in FIG. 8. When tested with a pyrotechnic igniter both of the heated samples failed to ignite and propagate.

This experiment indicates that pyrotechnic mixtures which will propagate can have a duddant material incorporated in them which will cause them to be deactivated by exposure to heat.

EXAMPLE IX

An inactive pyrotechnic material which could be made active later by removal of a duddant was made in the following experiment. Twenty parts of boron, 80 parts of barium chromate (BaCrO.sub.4), both finely divided and 42 parts of paraffin wax (Esso Household Wax) and about 150 parts of toluene were mixed to form a paste. Some of the paste was painted on aluminum foil and allowed to dry. When ignition of the dry mixture with a flame was attempted it did not ignite. Another portion of the painted foil was activated by placing a piece of blotting paper over the mixture and pressing with a hot household iron. This caused the wax to melt and be drawn into the paper. Following this treatment the residual pyrotechnic material ignited readily.

EXAMPLE X

In an experiment using similar materials and procedures to those in Example IX the same dudded pyrotechnic mixture was made. A portion was placed on aluminum foil in an area about one-eighth inch wide and 0.015-0.030 thick in a manner to resemble printing. When dry it was cut into two pieces. One piece was tested with a vigorous flame and failed to ignite although a small amount of wax vapor did burn momentarily after the assembly had been heated for several seconds.

The second piece of foil and dudded pyrotechnic material was firmly held against a 100 mesh screen with two pieces of blotting paper along side the mixture. This assembly was then gently washed several times with carbon tetrachloride (CCl.sub.4) to remove the wax. After washing the foil with the pyrotechnic was removed and allowed to dry. When tested with a match it burned vigorously and intensely.

This experiment demonstrated the removal of a duddant material from a pyrotechnic mixture by solvent extraction.

EXAMPLE XI

Two units of an ignition transfer system involving a pyrotechnic delay mixture (boron-red lead) in lead in a brass tube were assembled as shown in FIG. 9. The pyrotechnic pieces were separated by solid wax discs 15 located between rolls of filter paper 16 which were about three-eighths inch long and had inside diameters of about 0.06 inch. One unit was placed in an oven to allow the wax disc to melt and be absorbed by the paper. This unit when fired gave ignition transfer and all the pyrotechnic material was consumed. The other unit was not heated before firing and did not transfer ignition to the second piece of pyrotechnic material. In this case the wax prevented transfer until the unit had been heated. This may be regarded as a "heat to open explosive or pyrotechnic valve."

EXAMPLE XII

A large number of tests were carried out to show that lead azide would be deactivated when exposed to heat in the presence of certain chemical materials. Thus a pellet of lead azide in lead when heated with tricresyl phosphate, tri p-tolyl phosphate, D.D.T. (Dichloro diphenyl trichloroethane, mp 107 C), or antimony sulfate in a small aluminum cap may be carried to 900.degree.-1,100.degree. F without out explosion. This is far beyond the usual explosion temperature of about 640.degree. F and was shown with both dextrinated and polyvinyl alcohol treated lead azide. In addition as the temperature increased to and passed 640.degree. F fire, flame or smoke might result but detonation did not occur. In these experiments the deactivating agents were introduced as solids, liquids, or as the contents of small plastic pouches. These released the agents when heat was applied. The amounts of the materials used were a substantial percentage of the weight of the explosive. When conventional waxes were used in similar experiments the lead azide detonated or decomposed sharply at about 640.degree. F. The rate of heating in these experiments produced 600.degree. F in about 5 minutes.

Claims

I claim:

1. A component section for a pyrotechnic and explosive train designed to be unable to transfer ignition and explosion until activated comprising: a tubular body serving as a housing means and having a first end capable of receiving and propagating an ignition signal and a second end capable of performing a useful explosive work function, said housing means containing segments of compacted particulate pyrotechnic and explosive material, at least two segments of which are separated by a barrier of meltable solid material and annular sections of absorbent material capable of absorbing said meltable solid when said meltable solid is heated to be changed to a flowable liquid phase, said absorbent material located in proximity to said barrier, wherein said pyrotechnic and explosive train will be unable to propagate an ignition from said first end to said second end until an explosure of said component section to sufficient heat to allow said barrier material to melt and flow into said absorbent material, said flow will occur and the component section will transfer an ignition signal from said first end to said second end and perform a useful explosive work function.

2. Method of producing pyrotechnic structures in inactive form for later activation comprising: preparing of a mixture of active particulate solid pyrotechnic material with a solid deactivating agent, said deactivating agent being a poor solvent for said pyrotechnic material, depositing said mixture on a supporting sheet means in the structure desired for a pyrotechnic function, said deactivated mixture being solid after deposition has completed, and wherein said pyrotechnic structure is inactive to initiation signals due to the presence of said deactivating agent, transporting said deactivated structure to the point of desired use, combining said deactivated structure with a layer of material absorbent to said deactivating agent, causing said pyrotechnic structure to become active to initiation signals by heating said structure when in contact with said absorbent material to melt said deactivating agent and cause said agent to flow into said absorbent material.

3. The method of producing pyrotechnic structures of claim 2 wherein the mixture of solid pyrotechnic material and solid deactivating agent is dispersed in and is applied from a liquid medium.

4. The method of producing pyrotechnic structures of claim 2 wherein the solid deactivating agent is removed by extraction with a solvent. 5A component section for a pyrotechnic train designed to carry ignition signals comprising: a tubular body serving as a housing means and having a first end capable of receiving an ignition signal and a second end capable of performing a useful ignition work function, said housing means containing segments of compacted particulate pyrotechnic compositions; means for deactivating said pyrotechnic train upon receipt of a predetermined heat signal, said deactivation means comprising an insert of solid deactivating agent between said pyrotechnic segments, wherein said component section will allow propagation of an ignition signal from said first end to said second end, and wherein upon receipt of said predetermined heat signal, said deactivating agent will flow into said pyrotechnic material and render said component section unable to propagate

said ignition signal from said first end to said second end. 6. The component section of claim 5 wherein wax is used as the solid deactivating

agent. 7. The component section of claim 5 wherein the solid deactivating agent is contained in an annular opening external to said pyrotechnic

segments. 8. The component section of claim 5 wherein a longitudinal segment of compacted particulate pyrotechnic material is replaced with

said solid deactivating agent. 9. The component section of claim 5 wherein one segment contains particulate pyrotechnic composition to which a solid

deactivating agent has been added in particulate form. 10. A component section for a pyrotechnic and explosive train designed to transfer ignition and explosive signals comprising: a tubular body serving as a housing means and having a first end capable of receiving and propagating an ignition signal and a second end capable of performing a useful explosive work function, said housing means containing a segment of compacted particulate pyrotechnic composition and a segment of compacted particulate explosive material capable of detonating from the ignition signal of said segment of pyrotechnic composition, means for deactivating said pyrotechnic and explosive train upon receipt of a predetermined heat signal, said deactivating means comprising an insert of solid deactivating agent between said pyrotechnic and explosive segments, wherein said component section will allow propagation of ignition and explosive signals from said first end to said second end, and wherein upon receipt of said predetermined heat signal, said deactivating agent will flow into said explosive material and render it incapable of detonating from the ignition

signal of said segment of pyrotechnic composition. 11. A component section for an explosive train designed to carry explosive signals comprising: a tubular body serving as a housing means and having a first end capable of receiving an explosive signal and a second end capable of performing a useful explosive work function, said housing means containing a segment of compacted particulate explosive composition, means for deactivating said explosive train upon receipt of a predetermined heat signal, said deactivation means comprising a solid deactivating agent in non-interferring location in proximity to said explosive segment, wherein said component section will allow propagation of an explosive signal from said first end to said second end, and wherein upon receipt of said predetermined heat signal, said deactiviating agent will flow into said explosive material and render said component section unable to propagate

said explosive signal from said first end to said second end. 12. A component section for an explosive train designed to carry explosive signals comprising: a tubular body serving as a housing means and having a first end capable of receiving an explosive signal and a second end capable of performing a useful explosive work function, said housing means containing a segment of compacted particulate explosive composition; means for deactivating said explosive train upon receipt of a predetermined heat signal, said deactivating means comprising a liquid deactivating agent contained in a sealed plastic container in non-interferring location in proximity to said explosive segment, wherein said component section will allow propagation of an explosive signal from said first end to said second end, and wherein upon receipt of said predetermined heat signal, said deactivating agent will flow into said explosive material and render said component section unable to propagate said explosive signal from said first end to said second end.