Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F42—AMMUNITION; BLASTING
  • F42D—BLASTING
  • F42D1/00—Blasting methods or apparatus, e.g. loading or tamping
  • F42D1/04—Arrangements for ignition
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F42—AMMUNITION; BLASTING
  • F42B—EXPLOSIVE CHARGES, e.g. FOR BLASTING, FIREWORKS, AMMUNITION
  • F42B3/00—Blasting cartridges, i.e. case and explosive
  • F42B3/10—Initiators therefor

Definitions

• This invention relates to explosives and, more particularly, to a method of and apparatus for effecting detonation of an explosive mass.
• the detonation means include a primary charge of rapidly deflagratable and/or detonatable material or materials, such as lead azide, lead styphnate, salts of f ⁇ ___minic acid, gun powder or other such easy to deflagrate/detonate materials, capable of being fired by heat and/or a shock wave of. lower value than that required to detonate a secondary explosives material.
• a primary charge of the type defined is, hereinafter, referred to as "a primary charge of the type defined".
• Aproblem has always existed in translating the energy generated by the primary charge to a self-_n__3ta__ning detonation front in the secondary explosives material.
• the detonator for such method comprised a primary charge of readily deflagratable material, or a primary charge of the type defined, and the said primary charge was fired by a flame front, such as is generated by a slow fuse, or electrically, using a spark or heating element, or by a shock wave generated by, for example, a detonation cord.
• the primer comprised an explosives material, having a mass many times greater than the primary charge, capable of being detonated by the fire front and/or the press ⁇ re or shock wave generated by the firing of the primary charge.
• a thin-walled detonator in another proposed arrangement for effecting detonation of a secondary explosives, disclosed in for example the U.S.A Patent No 4727808, includes a primary charge of fine particles separated from the secondary explosives by a thin wall, generally having a hole therethrough, and the primary charge is fired at that end remote from the secondary explosives.
• the term "thin" when applied to a wall shall mean that the thickness of the wall is equal to or less than one fifth of its major dimension
• An object of the present invention is to provide a method for effecting detonation of a secondary explosives material and which method is reliable in operation and relatively inexpensive to practice.
• a method for detonating a secondary explosives material comprising the steps of confining a primary charge of the type defined in a chamber, locating the said chamber adjacent to but spaced from the secondary explosives material to be detonated, and initiating deflagration of the primary charge, characterised by the steps using a microfine primary charge, forming the said chamber to define one thin wall, locating said thin wall to be directed towards said secondary explosives material and spaced therefrom by an air gap between 5mm and 20 mm, and arranging the said thin wall, in whole or in part or parts, to separate from the chamber when the pressure against said wall, generated by the deflagrating primary charge, has reached a predete__mined value to cause said separated part or parts of said thin wall to be accelerated across said air gap whereupon to strike said secondary explosive material and thereby induce a detonation front in the secondary explosive material.
• said method is characterised by the steps of weakening the chamber and /or said thin wall to define a predetermined line or lines of weakness along which the said wall or a wall part or parts will separate from the said chamber when subjected to said predetermined pressure.
• the said predetermined pressure is conveniently defined as the pressure at which the said wall or wall parts separate from the chamber and the said pressure can be varied by the manner in which the said lines of weakness are determined and applied to the container.
• the invention also envisages a detonator for carrying out the method according to the invention, characterised by a tubular element, means supporting an ignition means closing one end region of said tubular element, an internal thin wall formed separately from said tubular element located in the bore of said tubular element intermediate the ends of said bore, and a primary charge, of the type defined, located between said means supporting the ignition means and said internal thin wall.
• the detonator is characterised in that said means supporting an ignition means comprise a second tubular element, of thin-walled construction, located in one end region of the first tubular element, one end of said second tubular element has said ignition means supported therein, the other end of said second tubular element locates said internal wall within the first tubular element and said second tubular element contains the said primary charge.
• the detonator is characterised in that said second tubular element is a sliding fit in the bore of said first tubular element.
• the detonator is characterised by abutment means for limiting the penetration of the second tubular element into said first tubular element.
• said internal wall located by said second tubular element is separately formed from said second tubular element and comprises a metal element, a rigid plastics element or an explosives material.
• said internal thin wall is formed integral with said second tubular element.
• said ignition means comprise flame-front producing means, conveniently defined by a tubular plastics element having its bore coated with a deflagratable or detonatable material.
• said ignition means comprise electrical ignition means.
• the detonator according to the invention is characterised in that the said first tubular element is open at that end remote from said means supporting an ignition means and a target secondary explosives material is located in said open end and is spaced from said internal wall by an air gap having an axial length between 5mm and 20 mm.
• the open end of said tubular element is insertable directly into a mass of secondary explosive to be detonated and the surface of the secondary mass exposed within the bore of the first tubular element comprises the surface of said secondary explosives material in which detonation is to be initiated.
• a target secondary explosives material is disposed in that end of said first tubular element closed by said end wall and the said first and second tubular elements are so axially related that an air gap, having an axial length between 5mm and 20 mm, separates the said thin internal wall from the free surface of said target secondary explosives material.
• the said air gap has an axial length between 7 mm and 12 mm.
• the detonator according to the invention is characterised by a delay element located between said ignition means and said primary charge.
• the said second tubular element and/or said internal thin wall is weakened to define a predetermined line or lines of weakness along which the said internal thin wall or a part or parts thereof will separate from the second tubular member when the internal thin wall is subjected to said predetermined pressure.
• the present invention recognises that whilst the sensitivity to deflagration of a primary charge of the type defined increases with increase in temperature and pressure the charge is rendered less sensitive to detonation by a gradual increase in pressure .
• a pressure build-up in the deflagrating charge is rapidly released the charge, and/or its detonatable component or components, is rendered very sensitive to detonation and is readily driven into detonation by the sharp pressure drop-Che detonation of the primary charge elements contributes greatly to the acceleration of the internal wall or the internal wall parts towards the secondary explosives material.
• the internal thin wall can separate from the container, in whole or in parts, at relatively low pressures, sometimes as low as 1000 p.s.i. and in some cases as low as 500 p.s.i. depending upon the composition of the primary charge, and still effectively strike the secondary charge with sufficient energy as to ensure detonation thereof.
• the present invention also recognises that, contrary to the teachings of prior art slapper- type detonators, it is not essential for the slapper-plate to impact the second-try explosives material in one piece and, equally, that it is not essential that the leading face of the slapper-plate be parallel to the target surface of the secondary explosive on impact.
• the said internal wall may conveniently comprise a metal or rigid plastics material.
• the first and second tubular elements include cooperating means for varying the axial length of the air spacing between the said internal wall and the end of the first tubular element and, conveniently, such cooperating means may comprise screw threads or bayonet fittings between the first and second tubular elements which allow the relative positions of said elements to be adjusted.
• the primary charge comprises a solids material in divided form and may conveniently comprise or include RDX, PETN, HMX, gunpowder, flash powder or any other material capable of sustaining deflagration when confined.
• the axial length of the primary charge is less than twice the diameter of the bore of the tubular element containing the said charge and, more preferably, the axial length of the primary charge is less than the diameter of the bore of the tubular element containing the said charge.
• Fig. 1 shows, diagrai ⁇ matically and in longitudinal cross section, one simple detonator in accordance with the invention
• Fig. 2 shows, diagrammatically and in longitudinal cross section, a second embodiment of a detonator in accordance with the invention
• Fig. 3 shows, diagrammatically and in longitudinal cross section, a third detonator in accordance with the invention
• the internal wall 12 is thin, as hereinbefore defined, and may be a friction fit in the bore lie or held by an adhesive in said bore, thus to maintain said wall 12 in a desired position during normal handling and render said wall 12 resistant to displacement up to a predetermined pressure value.
• the resistance of said thin wall 12 to displacement from its "held" position determines said predetermined pressure.
• the detonation tube 14 may comprise a slow fuse or a detonation tube, as defined hereinafter.
• That bore lie between the plate 15 and the internal wall 12 is filled with a microfine primary charge 16 of the type defined.
• the end lib of the tubular element 11 is inserted into a mass of secondary explosive M to be detonated and the depth of insertion of the tubular element 11 into the mass M is sufficient to leave an air volume 17 between the internal wall 12 and the free surface ML of the mass M within the bore lie.
• a flange 18, shown in broken line in Fig.l, is located on the tubular element 11 and serves to abut the mass M to limit the penetration of tubular element 11 into the mass M.
• the rate of deflagration through the charge 16 is very rapid and as the pressure and temperature generated by the microfine deflagrating charge 16 increase the rate of deflagration increases until the pressure on that face of the wall 12 facing the charge 16 reaches said predetermined pressure to cause the internal wall 12 to breaks away from its securement with the tubular element 11.
• the restrictor plate 15 may have been blown out of the element 11 and the element 11 may be failing under the internal pressure but the very rapid rate of deflagration ensures that the wall 12 will break away from the element 11 under pressure and be directed towards the surface Ml.
• the pressurized deflagrating charge 16 is released towards the target secondary explosives material M and, with the rapid fall in pressure, the unconsumed elements of the primary charge are rendered sensitive to detonation and detonate to drive the wall 12 into high velocity impact with the surface Ml to induce a self-sustaiiiing detonation front in the secondary explosives material M.
• the detonator comprises a tubular element 21 with ends 21a, 21b and a bore 21c. That end region of the element 21 adjacent end 21b_ is closed by a plug 22 of a target secondary explosive material.
• the element 23 is inserted into the open end 21a_ of tubular element 21, with the internal wall 24 leading.
• the end 23b of the second tubular element 23 is deflected outwardly, in the form of a bell-end, to define an abutment engageable with the end 21a of the first tubular element 21 and serves to limit the penetration of the element 23 into the element 21.
• the axial length of the tubular element 21 between end 21a and the free face of the plug 22 within the element 21 can be calculated to obtain the desired air gap between the said plug 22 and the internal wall 25.
• the tubular elements 21 and 23 may be secured against relative axial displacement, as for example by crimping.
• a tubular element 31 is closed at one end by an integral end wall 32 and that end of the bore 31a of the element 31 adjacent the end wall 32 is charged with a target secondary explosive material 33.
• the open end 31b of element 31 is closed by a second tubular element 34 having an end wall 35 formed integral therewith.
• the end wall 35 has a circular recess C in its exposed face defining a weakened aimulus in the wall 35.
• the element 34 is slideably inserted into the bore 31a of element 31, end wall 35 leading, and the open end 34a of tubular element 34 is closed by an annular element 36, the cylindrical surface of which is tight fitting in the bore 34b_ of the second tubular element 34, and the bore of the annular element 36 firmly retains a delay element 37.
• the volume within tubular element 34 is charged with a primary charge 38.
• the delay element 37 conveniently comprises a tubular element 39, the bore 39ja of which opens to the primary charge 38.
• Electrical ignition means illustrated as a coil 40, are entered into the bore 39a of tube 39 remote from the second tubular element 34 and the bore 39a ⁇ of the tubular element 39 is charged with an exothe ⁇ r ⁇ c-l__rning composition 41, preferably a gas-less mixture of solid oxidising and reducing agents.
• exothe ⁇ r ⁇ c-burning materials are well known in the art and may for example comprise such mixtures as boron-red lead, boron-red lead silicon, boron-red lead-dibasic, lead phosphite, aluminium-cupric oxide, magnesium-barium peroxide- selenium and silicon-red-lead.
• the ignition front of the delay material travels slowly along the tube 39 and, after the predetermined delay, produces a flame-front at that end of the tube 39 exposed to the primary charge 38, thus causing the primary charge 38 to fire.
• the deflagration continues, in exactly the same way as that described with respect to Figs. 1 and 2,until the end wall 35 fails along the weakened annulus C, releasing the central part of the end wall defined by the recess C.
• the central part of the end wall 35 is accelerated towards the free surface of the explosive plug 33 and, again as in the examples illustrated in Figs 1, and 2, with the failure of the wall 35 the unconsumed primary charge 38 is driven into detonation to accelerate the separated end wall part against the free surface of the target secondary plug 38 to induce a self-sustaining detonation front in said plug.
• the detonator comprises a tubular element 51 having a screw thread 51a_, rolled into its cylindrical wall.
• One end of the element 51 is closed by an integral wall 52, having a central opening 52a therethrough and the other end of the element 51 is closed by a wall 53 which is tight fitting in the element 51.
• a microfine primary charge 54 is packed in the tubular element 51 between the walls 52 and 53 and a detonation tube 55 is tightly inserted through the central opening 52a whereupon the bore of the detonation tube 55 is open to the primary charge 54.
• the external diameter of the detonation tube 55 is smaller than the internal diameter of the sleeve 51 and thus, when the charge 54 is fired, the escape of gases down the tube 55, and the loss of gases through the central opening 52a should the tube 55 be blown out of the central opening 52a is restricted.
• An outer tubular element 56 has an screw thread 56a formed thereon,cooperating with the screw thread 51a_ on the element 51, and element 56 includes a radial wall 57 at one end thereof which is pierced by an aperture 56b to allow the detonation tube 54 to pass therethrough and, at its end remote from the radial wall 57, the element 56 is closed by a plug 58 of a secondary explosives material.
• the internal axial length of the tubular element 56 between the end wall 57 and the plug 58 is greater than the axial length of the element 51.
• the element 56 can be rotated relative to the element 51 and, via the cooperating screw threads 51a and 56a, the element 51 can be displaced axially displaced relative to the element 56 between a "safe" condition, as illustrated in Fig. 4 and wherein the plug 58 is immediately adjacent the plate 53, and a condition for firing, as illustrated in Fig. 5, wherein the end wall 52 abutts the wall 57 and the plug 58 is spaced a predetermined distance from the plate 53.
• the element 56 is simply rotated, to effect axially displaced of the element 51 to the position shown in Fig. 5, whereupon the plate 53 is axially spaced from the plug 58. Thereafter the detonator is inserted into a mass of secondary explosive, which may be a solids, plastics or liquid explosives, and on firing of the primary charge 54 by the combustion/detonation front released from the adjacent end of the detonation tube 55, the primary charge 54 is driven to deflagration, the rate of deflagration increases as the pressure generated by the deflagrating charge 54 increases and, on the internal pressure reaching the pressure necessary to blow the wall 53 out of the sleeve 51 said wall is driven towards the plug 58 and accelerated by detonation of the primary charge 54.
• secondary explosive which may be a solids, plastics or liquid explosives
• the detonation tubes 15 and 55 referred to above may comprise commercially available detonation tubing comprising a hollow tube of a plastics material with a dusting of microfine co bustible/detonatable material on the surface of its bore.
• detonation tubing is normally fired by detonating a percussion cap, at that end of the tube most remote from the detonator and, on firing of the percussion cap, the flame front therefrom ignites or detonates the dusting of material on the bore of the tube and the combustion/detonation of said material continues along the tube to ignite the primary charge.
• the primary charge comprised PETN but in other experiments said charge comprised or included RDX, HMX, gunpowder, and/or flash powder and all such materials showed themselves capable of sustaijiing deflagration when confined and detonation when subject to a rapid pressure drop.
• the tubular elements 11, in the above experiments conveniently comprised thin walled aluminum tubing having a wall thickness less than one tenth of the bore diameter.
• the rema__ning detonators were placed on bulk explosives, the air space was adjusted to an axial length of 10mm and the detonators were fired.
• the primary charge had an axial length equal to the diameter of the bore of the cliarge-containing tubular element.
• the density of the primary charge will, to a degree, be dependant upon its composition but, using PE ⁇ N or HMX as the charge or the principal component of the charge, the density can vary between 0.1 and 1.96 gms/cm , preferably between 0.2 and " 1.0 gms/cm? and most pre ferably between 0.2 and 0.6 gms/cm .

Landscapes

• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Drilling And Exploitation, And Mining Machines And Methods (AREA)
• Air Bags (AREA)
• Portable Nailing Machines And Staplers (AREA)

Applications Claiming Priority (4)

Publications (1)

Family

ID=26294806

Family Applications (1)

Country Status (3)

Families Citing this family (4)

Family Cites Families (7)

• 1990
  • 1990-01-05 WO PCT/GB1990/000017 patent/WO1990007689A1/en not_active Application Discontinuation
  • 1990-01-05 EP EP19900901860 patent/EP0403640A1/de not_active Ceased
  • 1990-01-05 AU AU49472/90A patent/AU4947290A/en not_active Abandoned

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events