US2882820A - Electric blasting initiator - Google Patents

Description

April 21, 1959 G. B. YOUNG ELECTRIC 'BLASTING INITIATOR Filed Aug. 11. 1954 INVENTOR. 6U Y BAX IRD YOU/V6;

ATTORNEX ELECTRIC BLASTING INITIATOR Guy Bayard Young, New Castle, Pa., assignor to American Cyanamid Company, New York, N.Y., a corporation of Maine Application August 11, 1954, Serial No. 449,175

1 Claim. (Cl. 102-28) This invention relates to the production of an electric blasting initiator and more particularly to an ignition plug and related sealing means for an electric blasting initiator with unusual resistance to ingress of water, and extremes of pressure,'temperature and physical abuse.

In the past, electric blasting initiators have been assembled with insulated lead wires positioned and secured by a plug or bushing of sulfur, rubber, or plastic composition. The wires that pass through the plug are attached to the plug by physical or chemical adhesion, since the plug had been formed or molded about a section near one end of the wires. Frequently, the wire section encompassed by the plug is formed into a symmetrically tortuous pattern to improve the tensile strength of the bond between the wires and the plug. The plug is positioned in and retained within the open end of the metal capsule or shell by a seal which is formed in place by alternate layers of molten asphalt and sulfur, by thermoplastic compositions, or, in the case of rubber plugs, by crimping the walls of the capsule into the body of the plug. These prior methods of assembly and construction result in a product with limited resistance to deformation, temperature variations and ingress of water.

It is an object of the present invention to overcome the difficulties of the prior practices. It is a further object to provide an electric blasting initiator with unusual resistance to extremes of pressure, temperature and physical abuse or mechanical deformation. It is a further object to provide an electric blasting initiator with unusual resistance to water penetration. It is a still further object to provide an electric blasting initiator comprised of a shorter dielectric plug, seal and metal shell than heretofore known. Other objects and advantages will become apparent to those skilled in the art from the description which follows.

In general, the above objects have been accomplished in a surprisingly simple manner. To this end, a dielectric plug is provided with two properly spaced apart holes for attaching lead wires. The ends of the holes or apertures are chamfered or counterbored and the recessed area metallized for direct soldering to the bared wire ends with the Wires placed through the holes in the plug. A metallized band is provided around the periphery of the plug for attaching and/or sealing the plug within the open end of a capsule or metal shell, contain ing initiation mixtures or explosives, by soldering. The dielectric plug may be finally covered within the cap assembly by asphaltic, thermoplastic, thermosetting or similar mixtures. This top fill provides an insulative seal over any bare wire between the terminus of the wire insulation and the top of the plug. The dielectric plug may be composed of any suitable rigid material, such as porcelain, glass or a thermosetting resin such as the phenol formaldehyde type. However, because of their rigidity, high dielectric properties and low cost, ceramic plugs are preferred.

According to the present invention, an electric blasting States Patent initiator is provided that includes a metal shell, initiating charge, a bridge wire, insulated lead wires and a closure consisting of an upper sealing member and a lower dielectric member. If desired, an igniter charge can be placed around the bridge wire. The lower dielectric member or dielectric plug which may be disc-shaped is provided with two properly spaced apertures connecting opposing facings of the plug and having metallized facings positioned inside the apertures. A metallized band is unitarily attached to the annular surface of the plug. Apertures are provided for the passage of the bared ends of lead wires so as to obviate migration of these lead wires. The holes of the dielectric plug may be counterbored or countersunk on either or both ends. holes, which provide for the passage of the lead wires are metallized for direct soldering by well-known methods in the art. One such method is the application of a metallic paste or paint comprising a powdered metal, such as silver, a vehicle, such as turpentine, and a vitreous binder such as powdered low-melting glass, with subsequent drying and firing. A second method is by chemical deposition or vacuum deposition of metal. A third method is by dusting with metal powder and temporary binders, as for example leafed silver powder and shellac, with subsequent firing. The entire bore of the aperture may be metallized or the metallization of the bores may be confined to a part thereof, to the counterbores or countersinks on either or both ends, or to the area around the ends of the holes or any combination of these procedures. The bared ends of the lead wires are inserted through the metallized holes in the dielectric plug and are attached thereto by dipping in molten solder, the solder adhering also to the metallized band unitarily attached to the annular surface of the plug. The peripheral or circumferential band of metallizing may extend over the entire annular surface of the plug or over a portion thereof. As in the case of the metallization of the holes, the band is prepared for direct soldering by the application of the metallic paste whose composition has been noted above; or by dusting with a metal powder and binders with subsequent firing. The circumferential band is next freshly coated with solder during the attachment of the plug to the wires. By inserting the plug into the top of the metal cap, the plug can be attached to the inner walls of the cap by the application of heat and additional solder. However, this attachment can be greatly facilitated by the previous tinning of the inner walls of the cap. However, subsequent to the insertion of the dielectric plug into the cap and its attachment thereto, the plug may be finally covered in the cap assembly with an asphaltic, thermoplastic or thermosetting composition. The purpose of the final seal is to provide insulation for any bare wire between the plug and the terminus of the Wire insulation.

In order to describe my invention more clearly, I shall refer to the drawings in which:

Figure 1 is a vertical view and cross section of a com plete assembly of an electric blasting initiator and Figure 2 is a vertical cross-sectional view of the dielectric, disc-shaped plug.

It is to be understood, however, that these figures are presented solely by way of illustration, and are not to be regarded as a limitation upon the scope of the invention.

Referring to the drawings, the electric blasting initiator of Figure 1 comprises a metal shell 1, which may, for example, be made of copper, aluminum or the like and may be of the conventional open and closed end type or it may be a multiple-piece construction for bottom filling. In the base of the shell is placed the usual initiation charges 2. If desired, an ignition charge or match com- These lead wires '4 at 10. The bared lead wires are soldered to the metallized facing of the aperture 8 in the dielectric plug 7. The dielectric plug is secured to the metal cap by a soldered hermetic joint 9. The dielectric plug is covered with a suitable insulating and sealing material designated as 6 which imbeds both the bare lead wire and the terminal insulation around said lead wire. The insulation material may be of the conventional type such as for example, fibrous cotton or nonfibrous plastics such as polyvinyl chloride, ethylcellulose or nylon. As depicted in the drawing (Figures 1 and 2), the dielectric plug is slightly recessed on a portion of its outer wall to provide for the inclusion of additional solder. The total combined height of the dielectric plug and the sealing material is not more than one half 0/2) an inch and preferably not more than one quarter A) of an inch, the dielectric plug being A to A; of an inch and the seal for the bare wire above the plug being not more than Ma of an inch.

In practice, as is shown in Figure 2, the dielectric plug, which may be made from a ceramic such as porcelain, steatite; a glass or a thermosetting type resin, is provided with two spaced apertures 14 and 15 connecting opposing facings, 16 and 17. The apertures are counter-sunk at their ends and the aperture facings 11 is metallized as noted above. The annular surface 18 of the plug is advantageously slightly recessed and is metallized at its midsection as depicted in Figure 2. Lead wires (not shown) are. inserted into and through the holes. The plug and the wires are dipped into molten solder at their ends. By properly positioning the plug, the mid-section of the outer walls can likewise be dipped into the molten solder. The ends of the lead wires are connected by a bridge wire (not shown). The plug is then set into the open end of the metal cap where heat and additional solder are provided to form a continuous solder joint between the inner wall of the cap and the outer wall or annular surface of the plug. This attachment is greatly facilitated by previous tinning of the inner walls of the metal cap. The solder joint which is formed provides an hermetic seal for the contents of the capsule. A thermoplastic seal may be added to obviate water penetration to the bare section of the lead wires. In Figure 2, 12 represents a metallized band unitarily attached to the annular surface of the plug, and 13 represents the dielectric material.

As a consequence of the aforementioned assembly of the electric blasting initiator of my invention, resistance to deformation with resultant fracture of the sealing means is obtained. Further, it should be noted that resistance to temperature is limited only by the explosives employed and the wire insulation and solder used. Additionally,

and of particular importance, an hermetic seal between 5 the wires and the plug and between the plug and the metal cap is provided. Because of the greater strength of the plug and sealing means, the length of both may be reduced with marked reduction of the length of the electric blasting initiator assembly.

It will be understood, however, that many variations may be made without departing from the spirit and scope of the invention. For instance, any suitable modification of the dielectric plug design is contemplated. Although electric blasting initiators have been described quite broadly as a class, it will be appreciated that the present invention is applicable to all of the various conventional species of said electric blasting initiators; for example, electric blasting caps, short-period delay electric blasting caps, long-period delay electric blasting caps, electric squibs, electric delay squibs and initiators of the conventional-open-bridge plug, pasted-cavity bridge plug, beadedbridge plug and match-head types. While ceramic, glass and thermosetting plastic composition plugs have been here described, it will be apparent to those skilled in the art that any thermally-stable dielectric material that can be metallized and subsequently soldered may be utilized to form the body of the plug within the purview of the invention.

I claim:

An electric blasting initiator comprising a metal shell, containing a detonating charge, the said shell being hermetically sealed. by a closure through which two lead wires pass, the said lead wiresbeing connected by a bridge wire extending into said shell beyond said closure, said closure comprising a disc shaped ceramic plug pierced by two apertures for; said lead wires, a metallized facing around the. periphery of said plug and around the inside of: said apertures, said lead wires being hermetically sealed to said, ceramic. plug by solder connecting said metallized facing of said apertures with said lead wires, said ceramic plug being hermetically bonded to said metal shell by a soldered connection between said metallized facing on the periphery of said plug, the said metal to ceramic solder bonds between said plug and said lead wires and metal shell being characterized by the absence of a sharp phase boundary between the respective ceramic and metal phases, such that the said shell, said dielectric plug and said lead wires form one unitary structure.

References Cited in the file of this patent UNITED STATES PATENTS 2,137,069 Vatter Nov. 15, 1938 2,240,438 Durant Apr. 29, 1941 2,282,106 Underwood May 5, 1942 2,456,653 'Snow et al Dec. 21, 1948 2,462,070 Chatterjea et al Feb. 22, 1949 2,498,644 Billings Feb. 28, 1950 2,695,563 Mulqueeny Nov. 30, 1954 FOREIGN PATENTS 543,500 Great Britain Feb. 27, 1942 552,223 Great Britain Mar. 29, 1943 171,646 Austria June 25, 1952 899,965 Germany Dec. 17, 1953

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