US3002458A - Electric explosive initiator - Google Patents

Description

Oct. 3, 1961 J. w. HAAS 3,002,458

ELECTRIC EXPLOSIVE INITIATOR Filed Dec. 29, 1955 Fi g1 JohnwHaas INVENTOR.

ATTORNEXS This invention relates to an improved electrical explosive initiator of the type commonly used, for example, in ordnance devices. In initiators of known construction, it is common to provide electrical means for igniting an initiating explosive which, in turn, then ignites and causes explosion of the main charge, either directly or through a delay charge. However, due to the many variable factors involved in manufacturing and assembling such devices there is usually a rather Wide variation among individual initiators with the result that in certain cases an occasional initiator of a particular design will be fired when say only 10 volts is applied to its firing terminals whereas other of the same design will not fire until some considerably higher voltage, say, 50 volts, is applied. While most such devices will not fire until the higher voltage is approached, the fact that an occasional one might fire at a relatively low voltage, greatly increases the danger involved in the manufacture of such devices and severely limits the testing of the devices or their associated fin'ng circuits.

It is an object of this invention to provide an improved electrical explosive initiator of the type under consideration wherein firing of the initiator at a voltage below a pre determined minimum voltage will be prevented.

A further object is to provide such an initiator construction wherein, without requiring unduly painstaking manufacturing procedures, the range of voltage between that voltage which can safely be applied without causing firing of any of the initiators, and that voltage which must be applied to insure that all initiators will be fired, is relatively small.

A further object of this invention is to incorporate in an initiator of the type under consideration, a high resistance material in series with the electrical igniter normally incorporated therein, which material will limit current flow to a value too low to permit firing of any initiator until application of a voltage sufliciently high to insure firing of all initiators, whereupon it will change from its high resistance condition to a condition wherein it afiords a relatively low resistance path, thereby enabling sufiicient current to pass through the igniter to fire the charge.

Further and other objects will become apparent from the following description and claim especially when considered in the light of the accompanying drawing wherein:

FIG. 1 is a sectional view showing the invention applie to an initiator of known type;

FIGS. 2 and 3 are sectional views showing the invention applied to initiators of somewhat difierent type from that shown in FIG. 1.

The initiator shown in FIG. 1 is primarily of known construction and comprises a main cup or casing 1 containing, near its lower end, an explosive charge 2. Directly above the explosive charge 2 is an ignition charge 3 which is confined within a sleeve 4. Immediately above the sleeve 4 is a body or plug of insulating material 5 which is provided with a pair of generally cylindrical bores or recesses 6, extending downwardly from the upper end thereof. These recesses are filled with a fusible, homogeneous mixture 7 of a wax or wax-like dielectric material heavily impregnated with very fine particles 15 of metal, such as aluminum dust or flour. Covering the open end of the casing, is a cap member 9 of insulating material, the casing wall being crimped over the cap member, as clearly EfifiZASS Patented Oct. 3, I961 ice '11 of conductors 10 are the upper ends 12 of a second pair of conductors 13, the lower ends of which are bridged by an igniter 14.

The mixture 7 in the recesses 6 may be formed of substantially equal parts by weight of aluminum dust or flour and some such wax as a ceresine wax. Instead of a wax, other relatively low-temperature fusible dielectric materials, such as some of the commercially available silicones may be substituted. Thus, for example, thesilicones, commercially available from the Dow-Corning Corporation, and designated as DC996 or 997, are suitable for such use. While the ratio of metal to dielectric material may by varied somewhat from the 1:1 ratio mentioned above, the tllescribed ratio has been found to give very consistent I'BSII IS.

FIG. 2 sl ws a somewhat difierent type of initiator 7' which, instead of using a bridge type igniter as in FIG. 1, makes use of an ignition charge 16 which is itself electrically conductive. In this embodiment the recess 17, containing the dielectric-metal mixture, is formed in the cap member 18 rather than in the plug 19. Moreover, but a single terminal conductor 20 is utilized, the casing 21 itself serving as the other side of the electrical firing circuit. Ignition is produced by the flow of current from the lower conductor 22 through the ignition explosive 16 to the casing 21.

FIG. 3 shows an initiator very similar to that illustrated in FIG. 1 but which utilizes a conductive mixture 23 as the ignition explosive. In this case, as in FIG. 1, two separate electrical input conductors 24 are utilized, ignition being obtained as a. result of the flow of current through the ignition charge 23 between the lower conductors 25.

The dielectric-metal mixture utilized in the initiators has very high resistance characteristics under low voltage conditions and will limit current flow through the ignitor to a safe, extremely low valueuntil the applied voltage is raised to a predetermined higher value, at which time the mixture suddenly breaks down to a very low resistance value. The exact voltage value at which such breakdown occurs will depend, of course, upon the spacing between the ends of the conductors 10 and 12 (FIG. 1) and upon the particular composition of the mixture utilized. Representative resistance values from conductor 10 to conductor 12 for an initiator constructed as in FIG. 1 will be well over 100,000 megohms prior to breakdown, and only 2 to 10 ohms after the breakdown voltage of about 50 volts has been reached. Breakdown occurs so rapidly when the predetermined voltage is reached that no undesired time delay is introduced thereby. While, of course, there will be some variation in the value of the voltage required to break down the material, in any particular initiator design the range of voltages between that at which none of the initiators will be fired and that which will insure that all such initiators will be fired, will be relatively small. With an initiator of the type described there is therefore no danger of accidental firing of the initiator so long as any test voltages which might be applied thereto are held a few volts below the lower limit of this range.

The operation of the initiator is believed obvious. When it is desired to cause firing thereof, a voltage slightly above the breakdown voltage is applied to the outer ends of conductors 10, causing breakdown of the impregnated dielectric mixture 7 in the recesses 6, which thereupon permit suflicient current to flow through the ignitor bridge 14, to cause it to ignite the ignition charge 3 which in turn ignites the explosive charge 2.

While the invention has been illustrated in conjunction with but three specific initiator constructions, it is believed obvious that it is equally applicable toothcr types of initia. tors and that many changes may be made without departing from the spirit and scope of the invention as defined by the appended claim.

I claim:

In an electric explosive initiator having a generally cylindrical casing open at its one end, explosive material and electrically controlled ignition means therefor canied Within said casing, a plug of insulating material closely fitted within said casing between said explosive material and said open end, said plug being provided with a pair of laterally spaced, generally cylindrical recesses opening toward said open end and extending inwardly part way through said plug, a first pair of conductors ex-tending outwardly through said plug from said ignition'means into the inner closed ends of said recesses respectively, a cap member of insulating material fitted within and closing the open end of said casing and covering the open ends 4 p of said recesses; said cap member being provided with a second pair of conductors, extending therethrough, the inner ends of said second conductors extending into said open ends of said recesses in substantial axial alignment with the ends of said first conductors but spaced axially therefrom, and a mass of readilyiuslble dielectric material heavily impregnated with finely divided metallic particles which are dispersed throughout said dielectric material filling each of said recesses the ends of the conductors in each recess being embedded in said mass whereby the latter electrically bridges the gap between said conductors.

References Cited in the file of this patent UNITED STATES PATENTS 2,658,451 Home Nov. 10,- 1953 FOREIGN PATENTS 611,915 Germany Apr. 9, 1935

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