US 3873786 A
A severing device is provided for severing a mechanical element such as a strip, bar or the like using pure shear forces generated by ignition of an explosive charge having an energy per unit of mass of more than 1,000 joules/gram and a detonation speed of over 3,000 ms. In a first ultra-high speed, high amperage circuit breaker embodiment of the invention, the mechanical element comprises a cylindrical portion and an annular portion which extends outwardly therefrom, the internal diameter of the annular portion being approximately equal to that of the cylindrical portion and a fracture initiator in the form of opposed grooves having the same diameter is located in the area joining the two portions. The explosive charge, along with a firing unit therefor, is located in a recess in the cylindrical portion of the element to be severed.
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Description (OCR text may contain errors)
i 1 EXPLOSIVE TYPE SWITCH WITH CIRCUIT SERVING MEANS Inventor:
Guy Lagoiun, Tarbes, France Assignee: Etat Francais represente par Le Delegue ministeriel pour Larmement, Paris, France Filed: May 8, 1973 Appl. No.: 358,407
U.S. Cl. ZOO/61.08 Int. Cl. H0lh 35/00 Field of Search ZOO/61.08; 89/1 B; 102/28 R, 28 EB, 31, 32, 70.02 R, 70.2 A; 337/142, 401, 413, 416: 83/639  References Cited U NITED STATES PATENTS 12/1944 Temple 83/639 3/1960 Blomgren 200/6108 X 10/1966 Mattsson et a1. H 200/6108 7/1968 Parnell 89/1 13 1 1 Mar. 25, 1975 3,640,169 2/1972 Rosenthal 83/63) 3,732,129 5/1973 Martin 102/28 EB X 3,742,859 7/1973 Finnegan et a1. 102/24 R X 3,745,276 7/1973 McPherson 200/6108 Primary Examiner-James R. Scott Attorney, Agent, or Firm-Larson, Taylor & Hinds  ABSTRACT A severing device is provided for severing a mechanical element such as a strip, bar or the like using pure shear forces generated by ignition of an explosive charge having an energy per unit of mass of more than 1,000 joules/gram and a detonation speed of over 3,000 ms. In a first ultra-high speed, high amperage circuit breaker embodiment of the invention, the mechanical element comprises a cylindrical portion and an annular portion which extends outwardly therefrom, the internal diameter of the annular portion being approximately equal to that of the cylindrical portion and a fracture initiator in the form of opposed grooves having the same diameter is located in the area joining the .two portions. The explosive charge, along with a firing unit'therefor, is located in a recess in the cylindrical portion of the element to be severed.
8 Claims, 4 Drawing Figures PATENTEDMARZSI ms SHEET 1 [1F 2 EXPLOSIVE TYPE SWITCH WITH CIRCUIT SERVING MEANS FIELD OF THE INVENTION The invention relates to a method and apparatus for severing a mechanical element, such as a wire, bar, strip or the like, using the energy of an explosive.
BACKGROUND AND SUMMARY OF THE INVENTION The invention concerns severing or shearing an element or part which is introduced into a chamber together with an explosive charge the latter of which causes a shear pressure to be exerted on the element to be severed either directly, or indirectly through an intervening member, by means of the expanding gases released by the explosion of the charge.
The invention provides a number of important advantages as compared with the prior art. For example, in accordance with one aspect of the invention, severing of the mechanical element, and, in a preferred embodiment, displacement of the severed portion of the element over a predetermined distance, takes place within a period of approximately seconds from the instant a firing signal is initiated. A further important feature of the invention is that devices built in accordance therewith vary from one another in response time only by a matter of microseconds. These high performance features of the invention, which, to the knowledge of the applicant, have not been heretofore obtainable, provide new utilization possibilities and enable the use of high power explosives which are nor mally difficult to use industrially. Further, these explosives can be put to use without damage to the device or the need for special protection. In accordance with a further aspect thereof, the invention is adapted for use in devices of limited size such as circuit-breakers for electrical installations. Other purposes or uses of the invention are set forth in, or will be apparent from, the description of two embodiments of the invention set forth hereinbelow.
In accordance with the invention, a element or part to be severed is subjected to pure shear stresses caused by the explosion of explosive materials having a useful energy per unit mass of over 1,000 joules/gram (j/g), and preferably between 2,000 and 5,000 j/g, and a rate of detonation of over 3,000 ms., preferably between 7,000 and 8,000 ms. The explosive materials are arranged or housed in a recess which opens onto a delim' ited surface of the element to be severed, or a movable part which bears directly or indirectly on the element to be severed, so that the initial volume of the gas from the explosion is at least equal to the volume covered by the delimited surface adjacent to the charge housing during the useful displacement of the severed portion of the element, or of the movable part.
The severing method and apparatus of the invention utilizes the extraordinary effectiveness of pure shear so as to limit as much as possible the energy and time required. To explore this point further, if it be assumed, for example, that Aa is the elastic slip caused by a shear force T corresponding to, for a given cross section, the shear rupture stress P, the relevant relationships can be expressed by the formula Aa/a P/G, where a is the thickness of the part and G is the cross-sectional modulus of elasticity or, more accurately, the shear modulus (G 0.38 E where E. Youngs Modulus). For soft brass, P 350 Newtons/mm (N/mm and G 40,000 N/mm and, thus, assuming that the quantity PAu/a remains constant during shearing Aa/a 1.10". It will be appreciated that shear will be achieved as soon as the crystals have been displaced in the plane of the shear to a distance x (a)( 10), the shear energy being given by the expression (T) (a) (10) where T is the breaking load.
The shear process of the invention is extremely rapid because of the short distance the shear forces act. Shearing is initiated as soon as the shear stress exceeds a particular threshold and hence it is desirable to reach this threshold as rapidly as possible. To this end, an explosive material is utilized which has a high rate of propagation and a high energy per unit mass as set forth above. Examples of such explosives are those known commercially as Hexogen, Octogen," Pentrite, Tetryl, Trinitrotoluene and the like. Such explosives ensures that prior to any geometrical change in the severing device due to displacement of the part to be severed, the gas pressure acting directly orindirectly on this part is raised within a time of less than one mi crosecond to a level higher than that corresponding to the shear threshold and is maintained at this level for the time necessary for the shearing process to take place.
In order to prevent any damage to, or deterioration of, the severing device as a result of the use of an explosive having a high rate of detonation and high internal energy, it is important that the major portion of this energy be used rapidly in the shear process and in the attendant displacement of the sheared part. This consideration dictates that, firstly, the sheared part be given the lowest possible mass consonant with effective operation and secondly, that the severing device be configured such that the efficiency of conversion ofthe internal energy of the explosive into mechanical and kinetic energy is as high as possible.
According to research conducted by applicant, the desired results discussed above can be achieved when the initial volume offered to or available to the explosive gases prior to any movement taking place is, at most, equal to the volume swept by the gases during the useful displacement of the sheared part. This initial volume can, at least, equal the covolume of the explosive material and this is a reason why, as discussed above, it is advantageous to use an explosive which has a high energy per unit of mass and a high rate of propagation.
According to a first embodiment of the invention, an ultra-high speed, high amperage circuit breaker is provided wherein the element to be severed comprises a cylindrical portion and a coaxial annular portion, the internal diameter of the annular portion being approximately equal to the external diameter of the cylindrical portion, means for initiating fracture, in the form of opposed grooves of the same diameter, being located in the area or zone where the cylindrical and annular portions of the element to be severed are joined together. The cylindrical and annular portions are connected to respective terminals and the cylindrical portion is adapted to house the explosive charge and a firing unit therefor.
In a second embodiment, the element to be severed is a conductive strip or bar which extends through an insulating cover of a metal housing. A conductive member located within the housing itself houses the explosive charge, a firing unit for the charge and a metal anvil which is displaced by explosion ofthe charge. An insulating member located between the anvil and the conductive bar is displaced with the anvil to a position between the ends of the bar, after the bar is severed, to prevent flashover.
Other features and advantages will be set forth in, or apparent from, the detailed description of the preferred embodiments found hereinbelow.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view, partially in section and partially broken away, of an ultra-high speed, high amperage circuit breaker in accordance with a first embodiment of the invention; and
FIG. 2 is a view similar to FIG. 1 of an ultra-high speed, high amperage circuit breaker in accordance with a second embodiment of the invention;
FIG. 3 is a view similar to that of FIG. 1 showing the circuit breaker of FIG. 1 in the actuated position thereof; and
FIG. 4 is a view similar to that of FIG. 2 showing the circuit breaker of FIG. 2 in the actuated position thereof.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, the invention is illustrated as incorporated in an ultra-high speed, high amperage circuit breaker, which is generally denoted 10. Circuit breaker includes upper and lower electrical terminals l2 and 14 which are adapted to be connected to the appropriate leads or conductors of the electrical system in which the relay is to be included. Terminal 12 is mounted on a metallic body member or casing 16 by mounting nuts 12A and 12B and is insulated from body member 16 by a set of first and second insulating washers 18A and 20A. Terminal I4 is mounted on a metallic cap member 22 by a pair of mounting nuts 14A and 14B and is insulated from cap member 22 by a further set of first and second insulating washers 18B and 208. An electrical contact 24, which is electrically connected to terminal 12, is formed by sectors cut out of a cylinder and held together by an annular spring 26.
A metal fracture member or part 28 which is coaxial with, and is screwed, onto terminal 14, frictionally engages contact 7 when cap member 22 is screwed onto body member 16. Fracture member 28 is provided with grooves 28A and 28B which serve as so-called fracture initiators, grooves 28A and 28B providing beginnings for the fracture and defining and limiting the area in which the shear stresses are to act. Fracture member 28 also includes a recess 28C which serves as a housing for an explosive charge 30 and a charge initiator block or firing assembly 32. The latter is fitted with connections 34 which pass through member 28, contact 24 and body or casing 16 to a control unit 36. It is noted that explosive charge 32 and firing assembly 34 are manufactured separately so that the two elements are brought into contact only just prior to closing and sealing of the relay. This approach both provides improved safety by reducing the possibility of an explosion occurring during handling and enables standardization of the firing assembly 34 so as to permit firing assembly 34 to be used with explosive packages of widely varying charges. An annular insulating washer 38 is positioned between member 28 and the innermost end of terminal 14. Finally, a lead ring 40 is positioned within contact 24 between contact 24 and terminal 12 which, as set forth hereinbelow, limits the travel of the upper portion of member 28 that is sheared off.
In operation, a firing signal is transmitted from control unit 36, through leads 34, to firing assembly or initiator 15 to cause charge 30'to explode. The gas pressure from the explosion subjects member 28 to shear stresses in the area defined by grooves 28A and 28B, shearing or rupturing of the member 28 taking place as soon as these stresses exceed a particular level. At this time, the upper portion of member 28 is separated from the lower portion thereof and is driven upwardly at high speed. After traveling a preselected distance determined by the position of lead ring 40, the separated portion of member 28 impacts against ring 40 to cause permanent deformation of the latter, this effect being enhanced by the fact the upper edge of member 28 is of triangular profile in cross section, The actuated position of the circuit breaker of FIG. 1 is shown in FIG. 3.
A specific embodiment of the circuit-breaker described hereinabove, of cylindrical form having a diameter of 45 to 50mm. and a length of mm, designed for a continuous current of 600 to 800 amperes, and charged with mg. of pentrite, effects severance within microseconds of the firing signal. The term severance as used here means shearing of the portion of the member 28 between grooves 28A and 28B and the separation and displacement of the upper movable portion of member 28 for a distance of about 5mm.
Referring to FIG. 2, a further embodiment of the invention is illustrated which effects the severance or fracture of a calibrated strip and blade and provides subsequent translation or displacement of the sheared part. The calibrated strip can comprise a calibrated prismatic fuse. In the specific embodiment shown in FIG. 2, a metal casing or housing, denoted 50, houses a metallic member 52 which includes a recess 52A which, in turn, houses a firing unit or assembly 54 of the exploded wire type, an explosive charge 56 and a metal anvil member 58. Firing unit 54 is connected through a pair of leads or wires 60 to a suitable actuator (not shown), wires 60 extending through a correspond ing pair of openings or holes 52B in member 52. As discussed hereinabove, firing unit 54 and explosive charge 56 are manufactured separately and are operatively connected together only at the final moment of assembly of the circuit-breaker. An insulating member 62 positioned above anvil member 58 includes a recess in the lower surface thereof inwhich the head of anvil 58 is received. Member 62 is constructed of a suitable insulating material such as Nylon or Celoron and hence serves in insulating anvil 58 from the conductor to be severed which is denoted 64 in FIG. 2.
The conductor 64, as mentioned above, preferably comprises a calibrated fuse which, in an exemplary embodiment, is 25mm. in width and 2.5 mm. thick. Conductor 64 includes first and second spaced perforations or points of weakness 64A and 648 which are spaced apart a distance equal to the width of insulating member 62 and located opposite the parallel edges or side walls of member 62. A cover 66, which is preferably constructed of an insulating material such as Nylon or Celoron, screws onto casing 50 and includes a pair of openings 66A and 66B through which conductor 64 extends. Cover 66 defines a space 68 above conductor 64 as indicated in FIG. 2.
in operation, when a firing signal is transmitted through leads 60 to firing unit 54, the wire therein immediately melts and causes ignition of explosive charge 56. The pressure generated by the expanding gases cause upward displacement of anvil 58 and insulating member 62 thus causing shearing of calibrated conductor 64 along perforations 64A and 648, the sheared part of conductor 64, together with anvil 58 and insulating member 62, being driven upwardly into the space 68 defined by cover 66 as shown in FIG. 4. Insulating member 62 is thus positioned between the ends of conductor 64 thereby limiting the danger of flashover.
it is pointed out that a specific embodiment of a circuit-breaker constructed as described above in connection with H6. 2 and having a cylindrical form with a diameter of 55mm. and a length or height of 45mm, charged with 20mg. of lead nitride and 20mg. of pentrite, causes the severance of a calibrated fuse or. conductor, having a useful width of 20mm. and a thickness of 25mm., within 155 microseconds. The term severance" as used here means the shearing of the conductor as well as the displacement of the sheared part of the conductor over a distance of 5mm.
it is noted that, depending on the nature of insulating member 62, the latter may be lined on its surface in contact with the conductor 64 by a metal blade (not shown) to enhance the shear effect. The severance energy required may also be reduced by subjecting the conductor or fuse to the overcurrent to which the circuit-breaker responds since the thermal energy developed in the fuse will lessen the necessary shear energy. It is also noted that the circuit breaker of FlG. 2 can be modified where desired so that the severed or sheared portion of conductor 64 comes into contact with a set of normally open terminals at the end of its travel to thereby complete a control of measuring circuit.
Devices incorporating the invention possess a number of other advantages in addition to the capability of operating with a very short time period (about seconds) and the interchangeability of the devices owing to the very small differences (less than a few microseconds) in operating times from device to device. For example, such devices are suitable for utilization in any application where the switching components are inaccessible during use, e.g., undersea work at great depths,-underground work and space applications. Further, the devices are capable of use in any electrical circuit requiring an ultrarapid response in the event of an overload, the practically simultaneous operation characteristics thereof enabling power to be interrupted, or connected, at a considerably higher level than would conventionally be the case.
Although the invention has been described with reference to exemplary embodiments thereof it will be appreciated by those skilled in the art that variations and modifications can be effected in these embodiments without departing'from the scope and spirit of the invention.
1. A device for severing a mechanical element comprising an electrical current conductor including a cylindrical portion and a coaxial annular portion extending outwardly from said cylindrical portion, the internal diameter of the annular portion being approximately equal to the external diameter of said cylindrical portion, said device comprising an explosive charge having an energy per unit of mass in excess of 1,000 joules/- gram and a speed of propagation in excess of 3,000 ms, firing means for detonating said charge, housing means for housing and supporting the mechanical element and said explosive charge including a first electrical terminal connected to said annular portion of said mechanical element and a second electrical terminal connected to said cylindrical portion of said mechanical clement, said mechanical element including means for initiating fracture comprising means defining first and second coaxial grooves located in the area joining said cylindrical portion and said annular portion, and said cylindrical portion including recess means for housing said explosive charge and said firing means such that the initial volume presented to the explosive gases, defined by the volume of said explosive charge and the housing therefor, is no greater than the volume swept by the gas during the useful displacement of the sheared portion of the mechanical element to be severed, said swept volume being equivalent to the volume of a cylinder having a diameter equal to the internal diameter of the annular portion and a height equal to the distance between the said first and second coaxial grooves.
2. A device as claimed in claim 1 wherein said explosive charge has an energy per unit mass of between approximately 2,000 and 5,000 joules/gram and a speed of propagation of 7,000 to 8,000 ms.
3. A device as claimed in claim 1 wherein said cylindrical portion and said second terminal are connected by contact means comprising an annulus formed by a plurality of sectors and spring means for holding said sectors in place.
4. A device as claimed in claim 1 further comprising a deformable annulus positioned in the path of said cylindrical portion of the element to be severed for absorbing the kinetic energy of said cylindrical portion when the latter is sheared from said annular portion.
5. A device as claimed in claim 1 wherein said housing means comprises a metal case and a cap secured to said case, one of said first and second terminals being insulatingly mounted on said case and the other of said terminals being insulatingly mounted on said cap.
6. A device for severing a mechanical element comprising a current carrying conductive strip, said device comprising an explosive charge having an energy per unit of mass in excess of 1,000 joules/gram and a speed of propagation in excess of 3,000 ms, firing means for detonating said charge, means for housing the mechanical element to be severed including a conductive case and an insulating cover secured to said case, the said current carrying conductive strip extending through said cover, said housing means further comprising a conductive member located within said case and including means for housing said explosive charge and a conductive anvil member which is displaced responsive to ignition of said charge and an insulating member located between said anvil member and said conductive strip; the initial volume presented to the explosive gases defined by the volume of said explosive charge and the housing therefor being no greater than the volume swept by the gas during the useful displacement of the sheared portion of the element to be severed, said swept volume being equivalent to the volume of the cylinder having a diameter equal to the internal diameter of the anvil housing means and a height equal to the thickness of the element to be severed.
7. A device as claimed in claim 6 wherein said explosive charge has an energy per unit mass of between approximately 2,000 and 5,000 joules/gram and a speed of propagation of 7,000 to 8,000 ms.
8. A device as claimed in claim 7 wherein said conductive strip is weakened at spaced points which are located opposite the side walls of said insulating mem-