US 2878752 A
Description (OCR text may contain errors)
March 24, 1959 c. R. JOHNSON ETAL 2,878,752
BLASTING INITIATOR Original Filed March 15, 1955 INVENTORS CHARLES RUSSELL JOHNSON MERRILL EDWARD SWANSON ATTO United States Patent 2,878,752 BLASTIN G INITIATOR Charles Russell Johnson, Glen Mills, Pa., and Merrill Edward Swanson, Pitman, N.J., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Continuation of abandoned application Serial No. 494,316, March 15, 1955. This application December 5, 1956, Serial No. 627,539
Claims. (Cl. 102-43 The present invention More. particularly, blasting initiator assembly;
This application is a continuation of our prior application Serial No. 494,316 filed March 15, 1955, now abandoned.
Electric blasting initiators are widely used in mining, quarrying, and construction industries and large numbers are produced annually. Essentially, the electric blasting initiators consist of a metal shell enclosing a base charge of a detonating explosive, a priming charge, and an electrical ignition means. Thev electrical ignition means comprises a burning composition readily ignitable by the heat from an incandescent wire, a high-resistance bridge .wire imbedded in theburning composition, and a pair of leg wires leading from outside the metal shell and connected within the shell by means of the bridge wire. The leg wires are maintained in a parallel spaced relationship within the shell by a plug sealing the open end of the shell. This plug, or some element associated with the plug, must hold'theleg wires with sufiicient firmness so that they will not be pulled out of the shell during normal handling, nor will they be moved sufficiently to break the bridge wire connection or to produce a short circuit with each other or the shell wall. The bridge wire is imbedded in the burning composition either by introducing the leg wire-bridge wire assembly into a shell containing a loose ignition charge until the bridge wire is surrounded by this loose charge, or by incorporating a binder with the ignition compositions and applying the composition in the form of a bead to the bridge wire and thereafter introducing the beaded assembly into the shell.
In the past, the electric blasting initiators have been assembled primarily by hand, and the assemblers exercised considerable caution and skill to prevent breaking relates to a blasting initiator. thisinvention relates to an electric particularly adapted for mechanical tioned between the electrical ignition means and the priming charge, and the same problems regarding mechanical assembly exist as in the case of the regular electric blasting initiators.
Electrical blasting initiators are frequently used in areas where only the current produced by conventional blasting machines is available, and in many cases, a large number of the initiators connected in series or in parallel are preferably initiated simultaneously. Therefore, the ignition means should function when only a small current (for example, 0.5 ampere or less) is applied. On the other hand, the initiators are frequently used in areas where high voltages (440 volts) are used to power equipment and to initiate the blast. When a high voltage current is applied to an electrical initiator, an arc may be formed which will pierce the shell walls. In the case of delay initiators, such piercing may interfere with the functioning of the delay train. Therefore, the ignition means should function when a high voltage power source is applied, and, in the case of a delay initiator, the formation of an arc should not render the initiator ineifective. In many field areas, initiators are exposed to very high voltage static discharges. The initiators should not be initiated by the influence of such discharges. Therefore, a preferred electric blasting -initia-' tor should be resistant to static discharges, be resistant to high voltage arcing damage, and yet be ignitable by the application of a relatively small current.
Accordingly, an object of the present invention is to provide an electrical blasting initiator adapted for me chanical assembly. Further, an object of this invention is to provide an electrical blasting initiator which has excellent static resistance. A still further object of this invention is to provide a delay blasting initiator which will not be rendered ineffective by the formation of an arc. Additional objects will become apparent as this invention is more fully described.
The foregoing objects are attained by providing an electric blasting initiator having an elongated ventless tubular metal shell, a base charge of a detonating explosive within said shell, a priming charge adjacent to the base charge, and an ignition assembly comprising a. rigid cup-shaped capsule of a non-metallic composition, said capsule having a larger diameter at the open end than at the closed end and side walls of greater thickness than the bottom Wall thereof, and ignition composition substantially filling said capsule, a bridge-wire emthe bridge wire during the assembly operation. Also,
in the case where the leg wire-bridge wire assembly is introduced into a loose mass of powder, the assemblers exercised judgment in positioning the assembly so as to avoid defective assemblies due to irregularities in either the shell length or the height of the loose powder within the shell. For example, if the bridge wire is pressed beyond the loose powder portion, it may be broken by contact with the unyielding pressed charge. On the other hand, if the bridge wire is not introduced'sufficiently to be imbedded,in the loose ignition composition, no initiation may occur when a current is applied. At present, the assembly of initiation devices by mechanical means instead of hand means is of growing importance. Therefore, it is desirable to provide an electrical blasting initiator design wherein the exercise of caution and judgment during assembly is not a requirement.
The same construction features are found in electric delay blasting initiators, wherein a delay train is posibedded in said ignition composition and connecting a pair of leg wires, and a plug of insulating material completely surrounding said leg wires, said plug having its base flush with the top of said capsule and said capsule being prevented from inward movement within said shell by a peripheral crimp in the sidewalls of the shell. Delay initiators will include a delay train interposed between the ignition assembly and the priming charge. '7
In order to more fully describe the initiator of the present invention, reference is now made to the accompanying drawing in which:
Figure 1 represents a cross-sectional view of a blasting cap of the present invention containing a delay carrier.
Figure 2 is a cross-sectional view of the plastic capsule contained in the blasting cap of Figure 1.
Figure 3 is a cross-sectional view taken along the line 3-3 of Figure 1, and
Figure 4 is a cross-sectional view of a regular, nondelay cap of the present invention.
Throughout the several views, like numerals represent like parts. 7
In the drawing, 1 is an elongated tubular shell, for example, of gilding metal or aluminum, 2 is a base charge of a detonating explosive, for example, tetryl, cyclonite,
or pentaerythritol tetranitrate, 3 is a priming charge, for example, lead azide or mixtures of lead azide and a bisbasic salt of lead nitrate with a nitrophenol, 4 is a delay train carrier, for example, leador. synthetic, plastic tubing, 5 is a. delay charge, for example,,an 85/ 15 barium oxide/ selenium mixture. or 2/98 baron/red lead. mixture, 6v is a peripheral crimp in the shell wall which. prevents the delay train carrier 4 from damaging the ignition assembly in. the event itis. jarred loose, 7 is an ignition. composition-,, for example, a 50/25/25. smokeless. powder/potassium chlorate/dibasiclead salt. ofv a nitro-phenol mixture or a. 2/98. boron/redv lead. mixture, 8 is. a. nonmetallic capsule, for example, of. molded polyethylene or nylon, St rs a peripheral crimp in shell 1- supporting capsule 8 having a continuous side wall 8a of substantial thickness compared to, a very thin bottom. wall 8b, 10 is a bridge wire. imbedded in theignition composition 7 and connectmg; legwires 11, 12 is a mechanically assembled plug of arubber-like. compositionpreformedinto two halves and heldtogether. prior. to insertion into shell 1 by means of metal-,ferrule.-13,,14-is a groove. through the plug,. 15 is a beaded= portion on leg; wires 11, and 16 are crimps in the wall of shell lwhich hold plug 12 firmly in position. 9 In the assembly of the initiator depicted in the drawmg, base charge 2 is first introduced into shell 1, and pressed with a pin which produces the hollow to be filled with priming charge 3. The priming charge 3 is then loadedinto shell 1 and pressed into position, after which delay carrier 4 containing delay composition 5 is pressed intoshell 1. The length of the delay train and the nature of compositionS determine the period of delay. Peripherial crimps 6 and. 9. are nextformed. Capsule 8 is then pressed. into, shell 1 until seated. on the inward projection formed by crimp 9,, after which ignition composition 7 is, introduced in looseform. The mechanically assembled plug 12, including leg wires 11 and bridge wire 10 is introducedinto shell 1 and pressed in until the bottom is flush with the top of capsule. 8. Peripheral crimps 16 complete" the assembly. If aregular initiator is being as.- sembled, the delay carrier 4 anddelaycomposition 5 are omitted, and a considerably. shorter shell 1 is used.
, When an electric current is applied to the initiator of the present invention, bridge wire 10 becomes incandescent, igniting composition 7. The rapid combustion of the. ignition composition 7 pushes out the thin bottom 8b of capsule 8, sending a hot, short duration flash to the top of, delay composition 5. or to the priming charge 3 if; the initiator does not contain a delay train. The delay composition, 5 burns essentially without the evolution of gas. and the heat of combustion is transmitted through the composition 5. to priming charge 3, which is thereby ignited. and in turn detonates base charge 2.
In, the. event the initiator of the present invention is exposed to. stray currents (static), the capsule 8. serves toinsulate the portionof the leg wires 11. surrounded by ignitioncomposition 7 so that no, spark. can jump, from the leg wireto the-.wall ofi shell. 1. at thispoint. and prematurely ignite thecomposition. 7. In. the event excessive current'isapplied so that an arc isformed', the groove 14. in alignment, with thebeaded portions 15 of leg wires .11 provides a path for the arc and the wall of shell 1 is pierced, if at all, only above a portion of plug 12 and the necessary confinement for efiective combustion of the delay composition 5, is retained.
From the foregoing description, it is. apparent that variations in the length of the shell, the length of the delay train, the height of the pressed charges, etc., will not haveadeleteriouseffect on the assembly of theignition means. This is particularly important in the case of delay" initiators of the ventless type because the amount ofignition composition which can be used is limited. If too much ignition composition is included, the shell may be burned through, thus removing the confinement needed for accurate burning of the delay composition, or, in
4 some cases, the shell may even be burst by the presence of too much ignition composition.
The improved resistance to the effect of static is i1lustrated by the following test results. In the test, initiators containing base charges, priming charges and delay charges of the same kind and weight were provided with identical loose ignition mixtures comprising boron and red lead around the bridge wire. spark current from I a charged condenser was passed simultaneously through both. leg; wires to the. grounded. metal shell of the: initiator with the bridge wire in place. I
The initiators tested were as follows:
A. As shown in the. drawing, using; a molded polyethylene capsule.
B. Similar to A, except transverse groove.
C. A standard delay initiator having no capsule, and no. transverse. groove in the plug,
Tiiezmihimum energy Type flre any one otten detonators It is apparent from the foregoing table that the presence i i of the capsule produces a tremendous improvement, in
static resistance, and that the additionaof the transverse.
the application of'a 4'4'03V0ltm1f1'fii1tt Those. having-plugsv 0 without the groove wereerraticiin their in several instances failed? to.fire.-. Those having theplug' with a transverse groove c'onsistently'fired atthe' specified delay interval.
As will be. seen front. chanically assembled plug having a transverse: groove in.
The use of a plug preparedlby assemblingpreformed 1 halves:is;advantageous; from a'mechanicalassembly stand point, particularly when a transversegroove is desired.; Other well-knownmethods of forming plugs-to seal initiators and to. retain. the; leg wires in position can he-used without departing from the spirit of this'inventiom The use. of a. cup-shaped capsule? having. sidewalls of; t greater thickness than, the. bottom wall and having a con-g tour, suchthat theinner: diameter at-the topis-greaterthan the. diameter at .the 1 bottom is arcritical feature. .of. this in.- vention. The reduced thickness oithebottom wallcauses the flash from the, ignition compositionlto be. directed on the priming charge or thedelay composition rather than toward a side wall of the shell. Tests-have shown thata 5 bottom wall thickness of more than about 0.012 inch is undesirable because the ignition composition may notilash through the heavier walls. If'thesides are taperedthey I i willtend to insure proper. seatingot the capsulev on the.
inward projection formed by theperipheral crimp. The
thick. sidewalls also providesuflicient rigidity to the capsule to preventcollapsewhen the plugis. pressed into theshell. The capsule is. of a nonmetallic composition in order to provide the desired insulating characteristics Preferably, the capsule will befabricated'from a thermo, plastic or. thermosetting synthetic. composition such as polyethylene or nylon, althoughmaterials such" as wood or paperboard can be used.
that the plug contained no in joules required to.
delay periods, and
the foregoing, the. use of. 31 1118 I The present invention has been described in detail in the foregoing. We intend, however, to be limited only by the following claims.
1. An electric initiator adapted for mechanical assembly comprising an elongated tubular metal shell, a base charge of a detonating explosive at the bottom of said shell, a priming charge adjacent to said base charge, a peripheral crimp in said shell above said base and priming charges to prevent said charges from undue shifting in the event they are jarred loose, a second crimp in said shell above said first-named crimp, a rigid cupshaped capsule of non-inflammable plastic supported in an upright position by said second crimp, said capsule having a substantially larger inner diameter at its open upper end than at its closed lower end and having side walls of substantially greater thickness than its base, an ignition composition within said capsule, a bridge wire connecting a pair of leg wires embedded within said igniton composition, and a plug of insulating material surrounding and supporting said leg wires, the base of said plug lying flush with the top of said capsule whereby an electric current impressed across said leg wires will heat the bridge wire to incandescence and initiate the ignition composition with a downward flash directed toward the base and priming charges.
2. A device as in claim 1 wherein the leg Wires are each provided with an anchor portion of enlarged diameter at an intermediate point and the plug has a transverse groove in which the enlarged anchor portions of the leg wires are seated.
3. An electric initiator adapted for mechanical assembly comprising an elongated tubular metal shell, a base charge of a detonating explosive at the bottom of said shell, a priming charge adjacent to said base charge, a delay train having a delay charge above said priming charge, a peripheral crimp in said shell above said delay train to prevent said delay train from undue shifting in the event it is jarred loose, a second crimp in said shell above said first-named c a rigid cup-shaped capsule stantially greater thickness than its base, an ignition composition within said capsule, a bridge wire connecting a pair of leg wires embedded within said ignition composition, and a plug of insulating material surrounding and supporting said leg wires, the base of said plug lying flush with the top of said capsule whereby an electric current impressed across said leg wires will heat the bridge wire to incandescence and initiate the ignition composition with a downward flash directed toward the base and priming charges.
4. An electric initiator adapted for mechanical assembly comprising an elongated tubular metal shell, a base charge of a detonating explosive at the bottom of said shell, a priming charge adjacent to said base charge, a crimp in said shell above said priming charge, a rigid cup-shaped capsule of non-inflammable plastic supported in an upright position by said crimp, said capsule having a substantially larger inner diameter at its open upper end than at its closed lower end and having side walls of substantially greater thickness than its base, an ignition composition Within said capsule, a bridge wire connecting a pair of leg wires embedded within said ignition composition, and a plug of insulating material surrounding and supporting said leg wires, the base of said plug lying flush with the top of said capsule whereby an electric current impressed across said leg wires will heat the bridge wire to incandescence and initiate the ignition composition with a downward flash directed toward the base and priming charges.
5. A device as in claim 4 wherein the leg wires are each provided with an anchor portion of enlarged diameter at an intermediate point and the plug has a transverse groove in which the enlarged anchor portions of the leg wires are seated.
No references cited.