US2112974A - Electric initiator - Google Patents

Description

G. A. NODDIN April 5, 193.,

ELECTRIC INITIATOR Filed Sept. 50, 1936 m m w m 7 .H m N A 6 i 6 G ATTORNEY.

Patented Apr. 5, 1938 UNITED STATES PATENT OFFICE ELECTRIC INITIATOR Application September 30, 1936, Serial No. 103,287

6 Claims.

The present invention relates to a new and improved electric initiator, and more particularly to a new type ventless electric squib wherein the shell is opened at the propitious moment by a new and improved arrangement.

As is well known, electric squibs are employed in igniting deflagrating explosive compositions, for example black powder, where the nature of the explosive is such that it is desirable to effect 10 initiation by means of a flame rather than by a detonator, as is the case with dynamites and other high explosives. It is common to use electric current for firing the squibs.

The electric squibs known to the art generally consist of a shell or tube of metal or other material, a deflagrating explosive charge enclosed therein, and an electrical firing element. The latter element is desirably formed by passing two leg wires through a mass of insulating material which closes the end of the shell, and joining the ends of these wires within the shell. This joinder is effected by means of a highly resistant connecting wire which is heated to incandescence with the passage of electric current therethrough. This fine connecting or bridge wire is surrounded by, embedded in, or cemented to the ignition charge so that the passage of current through the circuit causes the charge to deflagrate. When the squib is fired thus, the flame plays upon the explosive charge to be ignited.

A special form of squib is the delay electric squib which resembles the ordinary electric squib with the difference that, in the delay squib, the firing element is separated from the main explosive charge within the shell by a tube or carrier charged with a column of material having a uniform rate of combustion, which column serves as a time or delay element.

In the squibs known to the art it is common to have the lower end of the shell either open or perforated in some way to permit the escape of flame on ignition. Sometimes a stopper is provided for this venthole, to be removed just prior to use. With or without the stopper, however, such squibs have been found to be very susceptible to the effects of moisture to which they may be exposed, in storage or at any time prior to or during use, and thus they may be rendered entirely worthless, or at least less eflicient for the purpose for which they were intended. The situation is rendered particularly serious in the case of delay squibs, in view of the fact that the admission of moisture through a vent may cause the delay column to be damped out or to burn non-uniformly, thus rendering the entire round of shots unsatisfactory, due to the deviation from the calculated delay periods of one or more of the squibs in the group.

Numerous attempts have been made to remedy this imperfection. With this object in view, the ventless type of squib originated. In this type the shell is completely closed so that no vent is provided for the emission of the flame. In order that the squib may function properly, the flame must be allowed to escape. If no vent in the shell is provided, some other means of outlet must be furnished. In the art this has been attempted in several ways, none of which furnishes a squib without imperfection. In one type of ventless squib, the shell is provided with weakened portions of the wall in the region containing the charge to insure the rupture of the shell at such points on ignition. This has been effected in several ways. For example, weakening scores, furrows, or scratches have been made in the shell walls, or the shell itself has been drawn thin enough to permit such rupture, or crimps have been provided in the upper region to insure bursting in the lower region of the shell.

Other inventors, instead of weakening the shell to aid its rupture, have increased the disruptive power of the charge employed to the extent that it will rupture 'the shell and cause it to fly to pieces from the pressure which said charge produces in burning. As examples of closed shell squibs may be cited the products of Rolland (U. S. Patent 1,856,431) and of Lewis and Woodbury (U. S. Patent 1,964,826).

Although the inventors of the art have developed electric squibs impervious to moisture penetration, they have not produced an altogether satisfactory squib, for, in overcoming the moisture penetration difficulty, they have introduced other disadvantages. Weakening the shell by scoring requires additional operations which rob the art of simplicity and efliciency. Yet, if the shell is weakened by drawing it thin enough to rupture without violence, difiiculties arise in the manufacture of delay squibs, inasmuch as the longer the period of delay required, the greater is the length of the shell required for a given. delay composition. Unfortunately it is practically impossible to draw the shells long enough for the squibs of the higher delay periods, and thin enough to be ruptured without violence by a simple ignition charge, when the metal used is of the nature best adapted to shell manufacture. On the other hand, if the charge is adapted to insure bursting of the unweakened shell by pressure, in the manner known to the art, the

squib bursts into many pieces and is practically demolished, thus presenting a hazard in handling approaching that of the blasting cap. This property renders the squib less desirable for handling in production and in the field. For example, in spite of the exercise of a high degree of caution in coal mining, it is possible that a squib may misfire and remain in the coal. Under such conditions, the closed shell squibs of the prior art present an undesirable hazard.

The object of the present invention is a new and improved electric squib. A further object is an improved delay squib of this nature when controlled delay intervals are desirable. Additional objects will be apparent from the general description of the invention which follows.

The invention described herein is concerned with a completely molstureproof electric squib of the closed shell or ventless type, which is nevertheless as safe to handle as the vented types. This squib is constructed without scratching or otherwise weakening the shell. Any metal may be used for the shell which is suitable for the manufacture of initiators generally. I have accomplished these advances over the art by introducing into the squib vicinal to the base thereof, a minute shell-opening charge of a detonating explosive composition. This charge is desirably so limited in power as to cause a perforation in the shell of the squib sufficient to permit the emission of the flame from the deflagrating base charge, without creating an explosion of sufficient violence to cause complete fragmentation or splattering of the metal comprising the base of the shell.

In order to disclose the nature of my invention more clearly, reference is made to the accompanying drawing which illustrates a. preferred embodiment thereof. It is to be understood, however, that this is done solely by Way of illustratlon'and is not to be regarded as a limitation on the scope of my invention which has many important applications other than those hereinafter more particularly described.

Referring generally to the drawing, Figure I is a sectional elevation of a. delay electric squib in accordance with my invention, while Figure II is a cross section of the squib shown in Figure I, through the line 11-11.

The present invention may be embodied in the ventless delay electric squib of the type shown in Figure I, which squib consists essentially of a ventless metal shell I, a base charge 2, a delay carrier element 3, charged with a delay powder composition 4, a peripheral cavity 5 in the carrier element, said cavity being charged with a detonating explosive composition 6, and an electric ignition and closure means of well known arrangement I, 8, 9, "I, H, l2.

Figure -II represents a horizontal cross-sectional view of the carrier along line A-A' of Figure I and serves to illustrate more clearly the preferred location of the peripheral cavity 5 and the shell-opening charge 6.

With regard to-the foregoing illustrations, 'it may be remarked that the peripheral cavity in the carrier is preferably extended in toward the central axial boring of said carrier, wherein the delay powder is charged, but not far enough to open into said boring. The reason for this construction may be best understood through a summary of the function of the improved squib. The electrical firing means ignites the top of the column of delay powder 4, which burnsdownarmors ward at a predetermined rate until it reaches and inflames the deflagrating explosive base charge i. But an instant before the burning delay powder reaches the base charge, it burns past the point in the carrier wherein the cavity 5 is located, and the heat from the burning delay powder ignites the shell-opening charge 6 in said cavity, causing detonation and a localized explosion which forces an opening in the shell at that point and vicinal to the base, so that when the base charge is ignited, immediately afterward the flame therefrom. escapes from the squib through said opening and fires the material to be initiated.

The shell-opening charge preferably comprises a detonating explosive of the type which rapidly acquires a. high velocity of detonation after ignition by heat. For this purpose I prefer to employ a charge comprising lead azide, which may desirably be gelatinlzed with nitrostarch. However, any suitable detonating composition may be employed, for example those comprising lead styphnate, mercury fulminate, nitrostarch, cyanurlc triazide, diazo-dinitrophenol, hexanltromannite, and the like.

The application of my invention may be clearly understood from the foregoing description without the enumeration of the various materials which may be used to form the base charge, delay powder composition, and other parts of the squib. Any materials employed therefor in the art will be suitable in completing the squib wherein my invention may be embodied, just as suitable charging and other operating methods will be known to the skilled worker and need not be enlarged upon herein. In summary, the new and improved feature of my invention comprises a novel and efi'lclent method of manufacturing closed-shell or ventless electric squibs, in which a minute charge of a detonating explosive composition is placed vicinal to the base charge of the squib in such a manner as to effect a localized opening in the wall of the squib to permit emission of the heat and flame generated by the deflagration of the base charge. Although the foregoing effect is desirably accomplished by the charged peripheral cavity in the carrier, as illustrated, I do not intend to be limited thereto. My invention is to be understood as including within its scope any suitable means of incorporating in the squib said shell-opening charge in a position suitable to permit the performance of the described function. For instance, the minute detonating charge might be pressed into a bead-like irregularity in the shell in any effective position, or afllxed thereto, or vicinal to said shell by any number of methods.

The squibs constructed according to my invention represent a marked advance over those of the art, in that ventless electric squibs may be made to function satisfactorily, and delay electric squibs in particular may be constructed according to the ventless design excluding all moisture, yet the shell thereof is caused to open satisfactorily at the opportune moment without scratching or weakening the shell thereof in advance, and without introducing sufllcient quantities of detonating explosive therein to cause fragmentation or dangerous explosion.

In the foregoing embodiments of my invention, it is apparent that many variations in detail may be made without departing from the spirit or scope thereof. Thus it is possible to vary the composition of the shell, the closure means, the firing means, the delay column, or any such structural detail without circumventing the scope of this invention. Other changes in detail and other mechanical, electrical, or chemical equivalents of the means shown will be apparent to those skilled in the art. I, therefore, intend to be limited only in accordance with the following patent claims. I a I claim: I I v 1. An electric squib comprising a ventless rigi shell, a deflagrating base charge, a localized shellopening'charge of a detonating'explosive composition juxtaposed against the inner surface of said shell at a locus vicinal to the region 'thereof' wherein said base charge is contained.

2. A'delay electric squib comprising a ventless metal shell, a deflagrating base charge, a localized charge of detonating explosive composition sufiicient to perforate said shell and juxtaposed against the inner wall 101 the shell at a locus vicinal to the region thereof wherein said base charge is contained, a delay element, and means for electrically igniting said delay element.

3. A delay electric squib comprising a ventless metal shell, a deflagrating base charge, a delay element which comprises a carrier charged witha composition which burns with substantially no generation, of gas, said carrier having a peripheral cavity vicinal to that end of the carrier adjacent to said base charge, 'said cavity being charged with a quantity of a detonating explosive composition sumcient to perforate said shell and permit emission of the burning products of combustion of said base charge. I

4. The delay electric squib according to claim 3, in which the cavity in the carrier is charged with a detonating explosive composition which rapidly attains a high velocity of combustion upon ignition by heat.

5. The delay electric squib according to claim 3, in which the cavity in the carrier is charged with an explosive composition comprising lead azide.

6. The delay electric squib according to claim 3,

in which the cavity in the carrier is charged with an explosive composition comprising lead azide go gelatinlzed with nitrostarch.

A I I GEORGE A. NODDIN.

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