US2086531A - Electric blasting initiator - Google Patents

Description

y 1937- A. BURROWS ET AL 2,085,531

ELECTRIC BLASTING INITIATOR Filed OGt. 30, 1935 Law/017 A Burrows INVENTORS Wa/zer E. Lawson A TTORNEY Patented July 13, 1937 ELECTRIC BLASTING INITIATOR- Application October 30, 1935, Serial No. 47,383

19 Claims.

The present invention relates to electric blasting initiators generally, and more particularly to an electric blasting cap without appreciable time lag and substantially free from susceptibility to static electricity.

Electric blasting caps of all types may be classified as relatively fast and relatively slow caps on the basis of the time required for the cap to detonate after the firing current has been applied.

Such a classification is made to distinguish between blasting caps'which are suitable for ordinary blasting operations and those which are adaptable to rather special uses, as, for example, in seismographic exploration for mineral or other deposits, where a fast cap is highly desirable.

Heretofore, however, this distinction between fast and slow caps has been rather qualitative in nature, since all the available electric blasting caps possessed an inherent, measurable,

o and significant time lag or interval between the instant the firing current was applied and the instant the blasting caps detonated.

The time lag above referred to is the overall lag resulting from two separate factors, the first of which is the interval of time between the application of the firing current and the breaking or fusion of the high resistance bridge wire. This interval, which we may term the bridge wire lag is generally dependent upon the firing cur- 3() rent used. For many practical purposes, however, the bridge wire lag is not significant, since in seismographic explorations and other types of work requiring a fast cap, the instant the bridge wire breaks or fuses may be conveniently assumed as to be the instant of detonation.

A far more serious factor affecting the overall time lag, and one which is of great significance in the special uses above referred to, is the interval of time between the breaking of the bridge 40 wire and the actual detonation of the cap. This lag, which we shall hereinafter refer to as the induction period, depends to a certain extent on the amperage of the firing current. At a given amperage, however, the induction period is a 45 definite characteristic property of the ignition composition employed. Thus certain materials have an inherently long induction period, whereas in others. this period is not significant.

Although a number of materials of the latter 50 type are available, the use of these fast ignition 55 auction period are very susceptible to static electricity; that is to say, electrostatic charges of low voltage, which are well within the range of that which may be accumulated by a man of ordinary electrical capacity, are capable of igniting these fast ignition compounds and thereby initiating the blasting cap. While, in general, it appears that all ignition compositions can be fired by an electrostatic discharge, this susceptibility to static electricity increases very markedly as the induction period approaches zero. These rapid ignition compounds cannot, therefore, be employed safely in electric blasting caps unless the electrostatic susceptibility of the finished blasting cap is substantially reduced or eliminated by means which are certain in effect and sumciently rugged in construction to withstand mechanical handling in the field. Such means are disclosed and claimed generally in co-pending application, Serial No. 47,385 filed October 30, 1935.

The object of the present invention is a new and improved electric blasting cap which is substantially free from susceptibility to electrostatic charges. A further object is an electric blasting cap without an appreciable induction period, and substantially free from susceptibility to static electricity. A still further object is an electric blasting cap containing an improved ignition composition possessing very rapid ignition characteristics, the electrostatic susceptibility of said cap being substantially eliminated by means which are certain in effect and sufiiciently rugged in construction to withstand mechanical handling in the field. Additional objects will be apparent as the invention is hereinafter more fully described.

We have found that these objects may be accomplished by providing an electric blasting initiator containing copper acetylide with a means for substantially reducing the electrostatic susceptibility of said initiator. This means may comprise any of the embodiments of the invention disclosed and claimed generally in co-pending application, Serial No. 47,385 filed October The copper acetylide may be employed, if desired, as the ignition composition in all types of electric blasting initiators. including electric squibs, electric blasting caps and delay electric blasting caps, whether of the bridge plug, the concave plug, or the match-head type. In order to produce an electric blasting initiator, however, which is substantially free from susceptibility to static electricity, it is necessary to provide the firing circuit of the initiator with one of the v Referring nownparticularly to Figure 1, the blasting cap-illustrated comprises av capsule or ,shell ,1 of a, suitable electrically-conducting maembodiments of the invention disclosed in the co-pending application above referred to.

Although our invention is applicable to all types of electric blasting initiators, it is particularly applicable to electric blasting caps, since copper acetylide is more especially useful in this type of initiator. The resulting detonators according to our invention have the advantage not only of being substantialy free from susceptibility to static, but also of being very rapid, without appreciable time lag. The invention therefore makes it possible to produce a safe, reliable electric blasting cap suitable for certain special uses where the speed of the detonator is an important consideration.

Our invention comprises an electric blasting initiator containing an ignition composition comprising copper acetylide. The firing circuit of the initiator is provided with a means whereby the susceptibility of the initiator to static electricity is substantially eliminated or greatly reduced. The means provided causes the static charge'to pass harmlessly to the shell wall at a point outside the locus of the ignition composition, and may be formed by two general types of procedure, as more fully described in the co-pending application, Serial No. 47,385, filed October 30, 1935. In the first place, the static electricity may be caused to pass to the shell wall by forming an actual, physical electrically conducting connection between the shell wall and one of the leg wires at a. point outside the locus of the ignition composition. In the second place, the static electricity may be caused to pass to the shell wall by forming a spark gap or are between the shell wall and one of the leg wires at a point outside the locus of the electrostatic-susceptible ignition composition, such that the resistance across the are provided is substantially less than that of the arc formed by the firing circuit and the shell wall at the locus of the ignition composition. In either case the static electricity will pass harmlessly to the shell wall, where it will be effectively grounded.

' In order to disclose our invention more fully, reference is made to the accompanying drawing which illustrates several embodiments. It is to be understood, however, that this is to be taken solely by way of illustration, and is not to be regarded as a limitation upon the scope of our invention, which has many important applications other than those herein particularly illustrated.

Referring generally to the drawing, Figures 1, 2, and 3 represent respectively vertical sections of a bridge plug type, a concave plug type, and a match-head type of electric blasting cap made in accordance with our invention. Similar characters are used throughout the several views and in the accompanying description to indicate corresponding parts.

terial, such as a metal, as for example copper, vand th e like. ;In the base of the shell I I? as" ba e 'zxc n m r uwiu u aes .12 btase on composition 14' comprising copper e latter surrounds the'bridge wire 8',

tri 2 pmchlorate,

are 1 heldin fixed-space relationsmp: l 'b" rneans*of the-'br idge plugi. 'rhe capiscIosed- ,byi-m'eans of thex'waterpro'ofing composition 9 and", thex'sulfur; seal l0...rIhe -'leg. wirel. is providedwithlan elbow 'lfikwhich formswith, the shellcwall I an arc, the resistance of which is substantially less than that of the are formed by the shell wall I and the firing circuit at the locus of the ignition composition l. If desired, the elbow may contact the shell wall and form an electrical connection therewith.

In the electric blasting cap as illustrated in Figure 1, charges of static electricity which may be inadvertently applied to the shell wall I or the leg wires 6 and I will be harmlessly discharged across the arc formed between the elbow II and the shell wall I without firing the ignition composition 4 and detonating the blasting cap. The electric blasting cap, in accordance with our invention, is therefore substantially free from susceptibility to static electricity. It is also apparent that, since the means provided is effectively sealed within the blasting cap, it cannot be subsequently impaired by handling in the field.

Referring now to Figure 2, the base charge 2 consists of tetryl, and the priming charge 3 of lead azide. The bridge wire 8 connected between the ends of the leg wires 6 and l is surrounded by an ignition composition comprising copper acetylide, potassium chlorate and carbon, gelatinized with collodion. The leg wires are held in fixed space-relationship by the concave plug 13, and the cap is sealed by the waterproof composition 9 and the sulfur seal I0. Affixed to one of the wires 1 by suitable means, as for example by solder, isa short length of wire l4 which forms an electrically conducting connection between the shell wall I and the leg wire 1. By this means the blasting cap will be effectively protected from inadvertent firing by static electricity, since the charge will pass to the shell wall through the connection l4 and thence to the ground without affecting the ignition composition 4.

In Figure 3, the match-head type of electric blasting cap illustrated comprises a detonating base charge 2 of tetryl, a priming charge 3 of hexanitromannite and a match-head flash or ignition composition 4 comprising copper acetylide, potassium chlorate and carbon. Disposed within the paper cylinder I8 is the match-head, which comprises two metal plates or foils separated by a strip of insulating material I5. One leg wire is soldered to each place, and the bridge wire 8 forms the connection between the foils. In the diagram, only the forward plate I4 is represented. The blasting cap is closed with the waterproof composition 9 and the sulfur seal Hi.

In Figure 3, the plates or foils of the matchhead, as for example the forward foil I4, are provided with long handles or tabs 16 and rather broad shoulders I! which extend substantially to the paper tube l8, which is" in contact with the shell wall I. The shell wall I and the shoulders I! will therefore form a low-resistance are or spark gap which is well outside the locus of the ignition composition 4. The static charge will therefore jump across this are without affecting the ignition composition 4. It is, of course, essential that the ignition composition 4 should cover only the lower part. of tab l6 of the match-head, andshould notbe disposed between thev "shoulders I! and the shell wall 1. In shape,

the match-head shown .is somewhat different J from the conventional design'in that the shoulders I! are appreciablywider and the -tab'or ,handle- 16 is somewhatsvlongerg: This change, though apparently slight xmechanical ly, is

evertheless of great significance from the point of vi 'ewpf'static susceptibility, for it substantially preveiitsithe shoulders ill from being inaccumulate, will advertently covered with the ignition composition 4, which condition we have found will render the finished cap so sensitive to static that charges of low voltage, well within the range of that which a man of average capacity can invariably fire the ignition composition and detonate the cap.

As an additional precaution against static, the electric blasting cap as illustrated in Figure 3 is provided with a plug of electrically conducting material H! which engages the leg wire 6 and the shell wall I in electrically conducting relationship. The plug I9 is separated from the leg Wire 1 by the insulation 20. If desired, the plug I9 may consist of a low-melting metal or alloy, as for example Babbitt metal, which is poured into th cap abou't'the' dielectric material 20 surrounding the leg wire I. The plug 19 may also consist of compressed graphite or'other electrically conducting material, if so desired.

We have illustrated our invention with particular reference to electric blasting caps, as the preferred embodiment thereof. It is apparent, however, that the invention may also be employed in other electric blasting initiators such as electric squibs, delay electric detonators, and the like, since the electrostatic susceptibility of all initiators employing copper acetylide in the ignition composition may be substantially reduced by employing any of the means disclosed herein or in copending application, Serial No. 47,385, filed October 30, 1935. Again, the invention is equally applicable to the concave plug type, the bridge plug type or the match-head type of electric blasting initiator. Furthermore, it may be employed regardless of the base or priming charge used. Thus, for example, we

may employ any of the well known base charges such as tetryl, trinitrotoluene', picric acid, nitromannite, pentaerythritol tetranitrate and the like. We may likewise use any of the Well known priming compositions, as, for example, lead azide, diazodinitrophenol, mercury fulminate, nitromannite and the like.

All of the electric blasting initiators illustrated in the drawing and described in the foregoing paragraphs possess a number of very desirable properties. In the first place, all of the detonators herein described have an overall time lag of less than 9x10" seconds when fired at 12 amperes. In the second place, the induction period of the caps according to our invention is negligible when a firing current of 12 amperes. is used. Finally, the finished electric blasting initiators in accordance with our invention are substantially free from susceptibility to static electricity. The voltage required to detonate the blasting caps of our invention is far beyond that which a man of ordinary capacity can accumulate. It is apparent, therefore, that the detonators may be used under normal conditions without danger from electrostatic discharge.

The advantages in the use of our invention are numerous and important. It provides a permanent, simple, easily manufactured and effective means for substantially completely eliminating the hazards involved in the use of copper acetylide. The invention therefore makes it possible to produce an electric blasting cap without appreciable time lag and substantially free from susceptibility to static. Heretofore, such a blasting cap could not be manufactured by any known means.

In the foregoing detailed description of our invention, it is apparent that many variations may be made without departing from the spirit and scope thereof. We. therefore, intend to be limited only in accordance with the following patent claims:

We claim:

1. An electric blasting initiator containing an ignition composition comprising copper acetylide, the firing circuit of said initiator being provided with a means whereby the susceptibility of the initiator to static electricity is substantially reduced.

2. An electric blasting initiator containing an ignition composition comprising copper acetylide, the firing circuit of said initiator being provided with a means whereby static electricity is caused to passhafinlessly to the shell "wall of "said in itiator.

3. An electric blasting cap containing an ignition composition comprising copper acetylide, the firing circuit of said blasting cap being provided with a means whereby static electricity is caused to pass harmlessly to the shell wall of said blasting cap at a point outside the locus of said copper acetylide.

4. An electric blasting cap containing an ignition composition comprising copper acetylide, the firing circuit of said blasting cap being provided with a means whereby static electricity is caused to pass harmlessly to the shell wall of said blasting cap across an are between the shell wall and said firing circuit at a point outside the locus of said ignition composition, the resistance of said are being substantially less than the resistance of the are formed by said shell Wall and the firing circuit at the locus of said ignition composition.

5. An electric blasting cap containing an ignition composition comprising copper acetylide, the firing circuit of said blasting cap being provided with a means whereby static electricity is caused to pass harmlessly to the shell wall of said blasting cap through an electrically-conducting connection between said firing circuit and said shell wall, at a point outside the locus of said ignition composition.

6. An electric blasting cap of the concave plug type containing an ignition composition comprising copper acetylide, the firing circuit of said blasting cap being provided with a means whereby static electricity is caused to pass harmlessly to the shell wall of said blasting cap at a point outside the locus of said copper acetylide.

'7. The electric blasting cap of claim 6, in which said means whereby static electricity is caused to pass harmlessly to the shell wall comprises an electrically-conducting connection between said firing circuit and said shell wall. a

8. The electric blasting cap of claim 6, in which said means whereby static electricity is caused to pass harmlessly to the shell wall comprises an are between the shell wall and the firing circuit, the resistance of said are being substantially less than that of the arc between said shell wall and the firing circuit at the locus of said ignition com-.

position.

9. The blasting cap of claim 6, in which the ignition composition comprises copper acetylide gelatinized with nitrostarch.

10. An electric blasting cap of the concave type, containing an ignition composition comprising copper acetylide gelatinized with nitrostarch, one of the leg wires of said blasting cap being grounded to the shell wall thereof at a point outside the locus of said ignition composition.

'11. An electric blasting cap of the concave type, containing a base charge comprising tetryl, a priming charge comprising lead azide, and an ignition composition comprising copper acetylide gelatinized with nitrostarch, one of the leg wires of said blasting cap being grounded to the shell wall thereof at a point outside the locus of said ignition composition.

12. An electric blasting cap of the concave type, containing a base charge comprising tetryl, a priming charge comprising lead azide, and an ignition composition comprising copper acetylide gelatinized with nitrostarch, one of the leg wires of said blasting cap being provided with a. means whereby static electricity is caused to pass harmlessly to the shell wall thereof through an electrically-conducting connection between the leg wire and shell wall, at a point outside the locus of said ignition composition.

13. The electric blasting cap of claim 12, in which the means causing the static electricity to pass to the shell wall comprises a length of wire, one end of which is aflixed to the leg wire and the other end of which is in contact with the shell wall.

14. An electric blasting cap of the bridge plug type containing an ignition composition comprising copper acetylide, the firing circuit of said blasting cap being provided with a means whereby static electricity is caused to pass harmlessly to the shell wall of said blasting cap at apoint outside the locus of said ignition composition.

15. The electric blasting cap of claim 14, in. which said means whereby static electricity is caused to pass to the shell wall comprises an electrically-conducting connection between said shell wall and said firing circuit.

16. An electric blasting cap of the match-head type provided with an ignition composition comprising copper acetylide, the firing circuit of said blasting cap being provided with a means whereby static electricity is caused to pass harmlessly to the shell wall at a point outside the locus of said ignition composition.

17. The electric blasting cap of claim 16, in which said means whereby static electricity is caused to pass harmlessly to the shell wall comprises an electrically-conducting connection between said shell wall and said firing circuit.

18. An electric blasting cap of the match-head type provided with a match-head ignition composition comprising copper acetylide, the foils or plates of said match-head forming with the shell wall an arc at a point well outside the locus of LAWTON A. BURROWS. WALTER E. LAWSON.

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