US3590739A

US3590739A - Fuse

Info

Publication number: US3590739A
Application number: US745276A
Authority: US
Inventors: Per-Anders Persson
Original assignee: Nitro Nobel AB
Current assignee: Nitro Nobel AB
Priority date: 1967-07-20
Filing date: 1968-07-16
Publication date: 1971-07-06
Anticipated expiration: 1988-07-06
Also published as: DE1771851B1; CU35214A; SE333321B; ES356293A1; FR1578274A; GB1238503A

Abstract

A fuse apparatus including an elongated hollow tube with a reactive substance coating the inner periphery and adapted to support a gaseous percussion wave throughout the length of the tube.

Description

United States Patent 13,590,739

[ 72] inventor Per-Anders Persson [56] References Cited 5949mm, Swede" UNITED STATES PATENTS 745376 2,482,091 9/1949 Audriethetal 149/93x 'f 1;? 2,726,602 12/1955 Dal/18ml. 102/29 2,938,432 5/l960 Grandy et al. 89/1 01 [73] 2 g: 3,027,839 4/1962 Grandy et al. 102/27 32] P 1 3 3,296,968 l/l967. Shulrnan et al. 102/27 Y i 3,332,353 7/l967 Burkard at al. 102/70 [31] 10726 FOREIGN PATENTS 7l6,835 8/1965 Canada l02/49.7 [54] FUSE Primary ExaminerVerlin R. Pendegrass 10 Claims 9 Drawing Figs Attorneys-A. Yates Dowell and A. Yates Dowell, Jr.

[52] U.S. Cl 102/27,

102/70 ABSTRACT: A fuse apparatus including an elongated hollow [5] 1 Int. Cl C06c 5/04 tube with a reactive substance coating the inner periphery and [50] Field of Search 102/27, 70, adapted to support a gaseous percussion wave throughout the 49.7; 89/1 .01; 149/93 length ofthe tube.

llllllllll lllllllfi FUSE This invention relates to a fuse.

More particularly this invention relates to a fuse for transfer 5 of a detonation from an explosive charge to another or for initiating or igniting a detonation in an explosive charge. The fuse consists of an elongated wrapping having the shape of a tubular, rigid or flexible, dust which contains a quantity of explosive or other reactive substance which is distributed along 4?" the duct and which occupies a portion only of the cross-sectional area of the channel otherwise filled by gas of the duct.

In the mining technique substantially three methods have been used for igniting or priming the detonating caps or detonators which is turn initiate the detonation in the explosive charges. These methods are electric ignition by means of electrically actuated detonating caps interconnected in series and/or in parallel, powder fuse ignition by means of a train of black powder or a priming composition encased within a wrapping, and detonating fuse ignition by means of a train of explosive encased within a wrapping.

In the electric ignition method each detonating cap is ignited by electric current or a current pulse which through insulated connector wires is transmitted from a current source located at a safe distance from the explosive charges. Electric ignition involves the risk of nonintended priming due to electromagnetic disturbances and other factors, resulting from lightning, earth currents, electrical high-voltage conductors or broadcasting stations or radar transmitters, for example.

In the fuse ignition method each detonating cap is ignited by combustion of the black powder train which combustion is propagated along the fuse train with a velocity of the order between 0.01 and 200 meters per second. Due to inevitable variations in the velocity of propagation of the combustion in the powder fuse ignition, a scattering of the moments of the ignition of the various charges is caused which renders impossible or at least difficult to apply this type of ignition to the ignition with very short intervals. I

In the method'of igniting by means of a detonating fuse a 40 detonation is initiated at one end of the train of explosive of the fuse duct and propagated with a velocity of .the order of 6,000 meters per second through the train of explosive to each of the charges. In order; toensure the propagation of the detonation the train of explosiveof the fuse duct must contain 4 so great a quantity of explosive per length unit, namely of the order of 10 grams per running linear meter, that itin itself possesses a relatively strong blowing effect for which reason damages to objects positioned nearby often are caused. This igniting method can therefore generally not be used for conducting a detonation through such explosive which not earlier but at a later moment is to be caused to detonate, either for the reason that the fuse directly primes the explosive or because the action of the fuse on the explosive prevents the explosive from detonating at a later moment. The great'quantity of explosive contained in a detonating fuse has further resulted in the fact that such fuse must be carried and shipped as an explosive under observation of the special precautional measures prescribed for such dangerous goods.

In another embodiment of the detonating fuse method the quantity of explosive per unit length has been reduced by encasing the train of explosive within a wrapping of lead. This wrapping can in turn be encased in an exterior wrapping which additionally contributes in moderating the effect. Fuses of this kind have been manufactured with down to 0.1 gram explosive per running meter, but they have the disadvantage that they because of the feeble diameter of the explosive train require good contact between their end face and the detonating cap. In addition they require specific detonator caps which generally must be attached at the place of their manufacture under strict control. This type of fuse is also relatively expensive.

One main object of the invention is to provide a fuse or detonation transmitter duct or hose which does not include the drawbacks inherent to the above-described methods for ignition or detonation transmission.

A more specific object of the invention is to provide a fuse which is insensitive to electric and electromagnetic actions.

A further object of the invention is to provide a fuse for transfer of a detonation from one explosive charge to another, which causes slight effect only or no effect at all on objects positioned nearby both in normal use or in the case of fire.

Still another object of the invention is to provide a fuse for transmission of a detonation, which permits a velocity of propagation of the ignition impulse sufficiently high, such as of the order of 2,000 meters per second, to permit priming of a plurality of charges with small deviations from predetermined moments of ignition.

A still further object of the invention is to provide a fuse, which is robust and insensitive.

Further objects and advantages of the invention will become apparent from the following description considered in connection with the accompanying drawing, which forms part of this specification and of which:

FIG. 1 is a diagrammatic view of a fuse made in accordance with the invention and with detonating caps attached to the ends thereof.

FIG. 2 is a partial sectional view of the fuse of FIG. 1 with its detonating caps represented in a larger scale.

FIG. 3 is a sectional view in a still larger scale of a portion of the wrapping through which the percussion wave of gas sustained by the explosive is being propagated.

FIGS. 4 to 9 are cross-sectional views of various embodiments of the fuse wrapping, partly with elements inserted thereinto.

Referring to the drawing, reference numeral 10 denotes the outer wrapping of a fuse which wrapping has the shape of a tube or hose suitably made of some flexible material and which may possess some elasticity as is the case with plastic substances of the elastomer type, for example. The fuse has one end connected to a detonating cap 12 of known type which in the embodiment shown is adapted to be ignited by means of an electric current supplied through conductors 14. Attached to the other end of the fuse is a fuse-igni'tible detonating cap 16 also of conventional type.

Disposed on the interior wall of the tube 10 is a thin layer 18 of an explosive or reactive substance which occupies a small fraction of the interior of the tube only. The main portion of such' tube is formed as a longitudinally coherent, uninterrupted gas channel or duct 20 between the two detonating

caps

12 and 16.

The explosive may be constituted of pentaerythritoltetranitrate (PETN), or cyclotn'methylenetrinitramine (RDX), or cyclotetramethylenetetranitramine (I-IMX) or trinitrotoluene (TNT), ordinitroethylurea, or tetryl, or a mixture of two or more ofsaid substances. All these substances are highly brisant, i.e. highly shattering or explodable, which means that-they by themselves due to their chemical decomposition produce at leastthe main portion of the quantity of energy set free. If desired, a desensitizing means such as paraffin or wax, may be added. The explosive can be pulverulent and in one or other manner be caused to adhere to the interior tube wall. It is also conceivable to make the layer 18 from solid or liquid explosive. In all of these alternatives the layer 18 must be coherent, but may only partially cover the walls of the channel. It is essential only that the mechanical properties of the fuse are of such character that the channel is open along the entire length of the fuse and that the pressure wave primed by the detonating cap 12 is propagated in the longitudinal direction of the tube or hose to the detonating cap 16 in the form of a gaseous percussion or impact wave having high velocity such as 1,500 meters per second or more and sufficiently high pressure and elevated temperature to prime the detonating cap 16. This gaseous percussion or impact wave is propagated within the gas channel 20, the purpose of the layer 18 of explosive being by an exothermic chemical reaction to sustain the percussion wave while adding enough energy as to compensate for the losses which are connected with the deformation of the tube wall or the friction of the gas against the tube wall.

FIG. 3 illustrates how the gaseous percussion or impact wave traveling in the direction of the arrow 22 has reached a 5 place 24 sustained by the thin layer of reactive substance 18. The percussion wave and the reaction of the layer of explosive produce an increase in pressure which results in that the tube 18 is temporarily expanded. If the tube is resilient it will at least partly regain its initial cross section.

The quantity of explosive in the layer 18 is so small that the tube is not perforated. This implies that the gaseous percussion wave is propagated within the fuse without producing any injury on the surroundings even in the immediate vicinity of the tube. From the outset the channel 20 contains air or some other suitable gas.

The lower limit for the quantity of explosive is determined by the losses encountered within the duct during the propagation of the wave, which losses if they are allowed to preponderate would cause the gaseous percussion wave to die down.

The upper limit is defined by the requirement that the radially directed mechanical effect on the fuse during the passage of the gaseous percussion wave is to be so limited that it does not prime a surrounding explosive, such as gelatined AN- dynamite containing percent of nitroglycerine/nitroglycol. The upper limit of the layer 18 may be defined as a volume which shall not exceed 10 percent of the interior volume of the tube. Calculated in weight the quantity of explosive is to be lower than 0.5 and preferably lower than 0.1 gram per running meter of the tubular fuse, the interior diameter of which may be less than 7 millimeters, such as between I and 4 millimeters. According to a particularly suitable embodiment the layer 18 is so thin that if applied in the same layer thickness on a plane surface it would not be capable of 35 propagating the detonation or reaction.

The detonating cap 16 has an outer shell of metal within which explosive having the form of a primary charge 24 and a secondary charge 26 may be housed. The metal shell encloses the end of the tube 10 by means of a portion 28 of reduced diameter. Provided between the reduced portion and the primary charge 24 is a pyrotechnical delay composition 30 of a kind known per se.

FIG. 4 shows a mode of execution of the tubular fuse 10 formed with a circular inner cross section. FIG. 5 illustrates an element 32 presenting the form of a cross in transverse section secured within the tube. The explosive is in the form of a thin layer deposited on the cross-shaped element and/or the circular interior wall ofthe tube.

According to FIG. 6 the tubular fuse 34 includes an inner section 36 having the contour of a trefoil or similar configuration, and according to FIG. 7, the tube is provided with radially inwardly projecting ridges 38. As shown in FIG. 8, a separate insert element 40 is provided within a tube having a circular cross section, and the element itself may have a crosssectional contour resembling a Y. The layer of explosive may be applied onto the insert element prior to its insertion into the tube 10. -r

In the embodiment shown in FIG. 9 the fuse wrapping 42 is provided with four longitudinal channels 44 separated from one another and on their inner surfaces carrying thin layers of explosive.

The illustrated embodiments have the same feature common to all of them in that the wrapping includes one or several gas channels extending uninterrupted in the longitudinal direction of the fuse.

It is a primary condition for the correct operation of the fuse according to the invention that a chemical reaction is initiated in the explosive disposed along the interior tube wall in or behind the percussion wave front through mechanical or thermal actuation emanating from the gas, such as the air, which in the percussion wave has been compressed, heated and brought to rapid flow within the tube behind the front of the percussion wave. The propagation of the percussion wave is maintained by the addition of energy set free by the reaction compensating for the losses in energy due to deformation of the tube wall and the friction of the air against the wall, which losses without the existence of the layer of explosive would gradually reduce the active force of the percussion wave.

The following examples are intended to illustrate some embodiments of detonationtransferring ducts or hoses falling within the scope of the invention without, however, limiting it to the same.

Example 1 A hose of soft polyvinyl chloride having a length of 3 meters, an outer diameter of 5 millimeters and an inner diameter of 3 millimeters was coated with a thin layer of petroleum jelly, whereupon PETN-powder with a maximum particle size of 0.2 millimeters was poured through the hose so as to cause a thin layer of powder to adhere to the layer of petroleum jelly. The thickness of the powder layer corresponded to a quantity of 0.3 gram of explosive per running or linear meter of the hose. The free end face of the secondary charge of an electrically ignitible detonating cap of the type represented by part 12 in FIG. 2 from which the metal bottom had been removed, was placed against one end of the hose treated in the described manner. The other end of the hose was inserted loosely into the opening of a conventional fuse-ignitible detonating cap of the type represented by part 16 in FIG. 2. The hose was placed on the ground in irregular windings. Upon ignition of the electrically ignitible detonating cap 12 in a conventional manner by means of an electric current pulse, the hose was found to be partly ruptured along its entire length, and the fuse-ignitible detonating cap 16 had detonated and brought about the same impact on a test sheet made of brass and having a thickness of 5 millimeters and placed against the free bottom of said detonating cap as is normally obtained with fuse-ignitible detonating caps of the same kind when ignited in the conventional manner. In a control test the same experiment was repeated with a hose of plastic material of the same kind but nontreated and at its both ends provided with detonating caps in the same manner as in the first experiment. After the electrically ignitible detonating cap had been ignited, the plastic hose was found to be undamaged and nonactuated along its entire length except for a short portion nearest to the electrically ignitible detonating cap where the hose had been blackened on its interior surface. The fuse-ignitible detonating cap did not detonate and the test sheet was undamaged.

Example 2 In three tests hoses of the same kind as in example 1 were used, such hoses having a length of 0.8, 3 and 10 meters, respectively, and'were arranged in the same manner as in example l. The hoses were not pretreated with petroleum jelly. Instead, a powder of finely sized PETN was poured through each hose, a layer of PETN having a weight of 0.05 gram per running meter of hose staying as dust on the hose wall. Each hose was provided with detonating caps as in example 1. To each detonating cap on both ends of each hose electric contact conductors of the type generally used for indicating moments of detonation were fixed. Upon ignition of the electrically ignitible detonating cap by electricity all three test hoses were found to be unperforated but internally slightly brown colored and scratched, the fuse-ignitible detonating cap had detonated and the test sheet showed normal impact. The intervals between the detonations of the electrically ignited detonating caps and the fuse-ignited detonating caps were measured by means of an electronic counter and were of the order of 370, 2,446 and 4,851 microseconds corresponding to propagation velocities of, respectively, 2,160, 2,044 and 2,061 meters per second.

Example 3 A tube made of paper-reinforced Bakelite having a length of I meter, an outer diameter of 4 millimeters and an inner diameter of 3 millimeters was powdered with an explosive in the amount of 0.3 gram over the length of the tube. Detonating caps were provided at opposite ends of the tube. The tube bores of the cartridges and the cartridges were positioned between the detonating caps. Upon ignition of the electrically ignitible detonating cap by electricity, the dynamite cartridges were recovered unbroken and undeformed but slightly blackened within the steel tube, whereas the fuse-ignitible detonating cap had been ignited and produced normal impact on the test sheet. The dynamite cartridges proved to be capable of becoming ignited later on by means of a detonator in conventional manner and they detonated normally. Example 4 An elastic hose of soft polyvinyl .chloride having a length of 10 meters and otherwise the same dimensions and subjected to the same treatment as in example 2 so a'sto receive a quantity of explosive corresponding to 0.05 gram per running meter, was provided at one end with an electrically ignitible detonating cap as in example 1. The other end was loosely insert into the open end of a detonating cap of the type shown in F IG. 2, placed against a test sheet and provided with a delayed action element having a pyrotechnic burning or blowing composition for a delay of 200 milliseconds. The delayed action element which was of the type used for electrically ignitible detonators for short-interval ignition consisted of a pyrotechnic composition with a burning speed of 50 millimeters per second which was pressed into a sleeve of aluminum. The interval in time between the detonation of the detonating caps was measured in the 'same manner as in example 2. Upon ignition of the electrically ignitible detonating cap the detonating cap with the delayed action element was found to have detonated with normal effect on the test sheet. From the measured time the delay time in the delayed action element was calculated to have been 268 milliseconds. Example 5 In a series comprising four tests arranged as in example 4 the delay times of the delayed action elements were measured to have been 268, 273, 265 and 268 milliseconds, respectively. The scattering of the times lies thus within the normal limits for similar detonating caps (:Gmicroseconds), while the ignition of the delayed action element required about 70 microseconds more time than in a normal, electrically ignited detonating cap. Example 6 in a test with a resilient hose made of soft polyvinyl chloride having a length of 5 meters and treated as in example 2, two pointed metallic electrodes were introduced diametrically against one another through the wall of the hose about 10 centimeters from the free end of the hose. The other end of the hose was provided with a fuse-ignitible detonating cap of the type shown in FIG. 2. The electrodes were connected to the two poles of a 3/ F. condenser, and the spacing between the electrodes was adjusted to a spark overvoltage of 4 kilovolts. The condenser was charged to 4 kilovolts whereby a spark discharge was produced between the electrodes. The air percussion wave created thereby was propagated through the channel of the hose and ignited the fuse-ignitible detonating cap which produced normal impact on the test sheet. Example 7 The tests of example 2 were repeated with the sole difference that instead of PETN, 005 gram per running meter of a pulverulent mixture comprising 60 percent by weight of. RDX and 40 percent by weight of TNT was used. The mea sured times were, respectively, 308, 2,607 and 5,176 microseconds, corresponding to velocities of propagation of,

' respectively, 2,600, l,920 and L930 meters per second.

Example 8 The tests of example 2 were repeated with the sole difference that instead of PETN a pulverulent mixture of 97.5

percent by weight of dinitroethylurea and 2.5 percent by weight of wax were used. The measured times were, respectively, 297, 2,798 and 5,864 microseconds corresponding to velocities of propagation of, respectively, 2,700, 1,790 and 1,700 meters per second.

The entering percussion wave can be produced in some other way than by means of detonating explosive, for example by means of an electric spark discharge between electrodes placed in the tube or adjacent its open end.

.While several more or less specific embodiments of the invention have been shown and described, it is to be understood that this is for the purpose of illustration only and that the invention is not to be limited thereby, but its scope is to be determined by the appended claims.

What I claim is:

l. A fuse consisting of wall structure defining a hollow elongated tube forming a coherent gas channel, means for creating a percussion wave within said tube, means for sustaining said percussion wave, said percussion sustaining means comprising a reactive substance distributed as a thin layer on the inner surface of said tube and being directly exposed to said gas channel, so that said percussion wave will be successively sustained at high temperature and high velocity by the reactive substance for the entire length of the tube.

2. The structure of claim 1 in which the quantity of the reactive substance is no more than 0.5 gram per meter length of said tube.

3. The structure of claim 1 in which the quantity of reactive substance is no more than 0.2 tube.

4. The structure of claim 1 in which the quantity of reactive substance is no more than 0.1 gram per meter length of said tube.

5. The structure of claim 1 in which the reactive substance partially covers the inner surfaces of said tube.

6. The structure of claim 1 in which the reactive substance is a highly shattering explosive which at least partly is constituted of the group including the substances pentaerythritol' tetranitrate (PETN), cyclotrimethylenetrinitramine (RDX), cyclotetramethylenetetranitramine (l-lMX tetryl, ditrinitroethylurea and trinitrotoluene (TNT).

7. The structure of claim 1 including means for supporting the wall structure of said tube.

8. The structure of claim 7 in which said supporting means includes projections integrally formed with said wall structure and extending inwardly into said gas channel.

9. The structure of claim 7 in which said supporting means includes a separate insert element extending in the longitudinal direction of said tube.

10. The structure of claim 9 including a reactive substance carried by said insert element.

gram per meter length of said 9

Claims

1. A fuse consisting of wall structure defining a hollow elongated tube forming a coherent gas channel, means for creating a percussion wave within said tube, means for sustaining said percussion wave, said percussion sustaining means comprising a reactive substance distributed as a thin layer on the inner surface of said tube and being directly exposed to said gas channel, so that said percussion wave will be successively sustained at high temperature and high velocity by the reactive substance for the entire length of the tube.

3. The structure of claim 1 in which the quantity of reactive substance is no more than 0.2 gram per meter length of said tube.

6. The structure of claim 1 in which tHe reactive substance is a highly shattering explosive which at least partly is constituted of the group including the substances pentaerythritoltetranitrate (PETN), cyclotrimethylenetrinitramine (RDX), cyclotetramethylenetetranitramine (HMX), tetryl, ditrinitroethylurea and trinitrotoluene (TNT).