Electric initiators for high energy firing currents

Claim 2

In an electric delay type initiator assembly for firing under high energy firing current conditions including as an electrical firing circuit a pair of electrical lead wires extending into the ignition area and connecting therein with a resistance wire disposed in operative contact with an ignition composition to ignite said composition in response to heat generated by flow of the high energy firing current through said resistance wire, the improvement comprising means for shunting an arcing firing current from said ignition area after initial flow of same through the firing circuit and before expiration of the circuit reform time, to thereby protect said assembly against arcing across the lead wire terminal ends within said ignition area and accompanying failure of the assembly, said means comprising an electrically conductive material disposed outside, and electrically insulated from, said ignition area along a path in electrically conductive contact with said lead wires as a shunt for diverting flow of an arcing firing current from said ignition area, said shunt having an electrical resistance sufficiently high to be sufficiently non-conductive of a no-arcing firing current to permit flow of same through said circuit, but, in response to flow of an arcing firing current through said circuit, said shunt providing a decrease in electrical resistance across said path to less than that across the lead wires in said ignition area, and the resistance decrease time of said shunt and the circuit reforming time being correlated so that said shunt undergoes said decrease in electrical resistance during the period of said circuit reforming, to thereby conduct the arcing firing current for diversion from said assembly.

Claim 3

An initiator assembly of claim 1 wherein said shunt material is a metal ink type coating.

Claim 4

An initiator assembly of claim 2 wherein said coating is a uniform distribution of particulate silver together with lead and selenium.

Claim 5

An initiator assembly of claim 1 wherein said shunt material is a metal layer supported on a dielectric material.

Claim 6

An initiator assembly of claim 4 wherein said metal layer is a vapor-deposited aluminum on said dielectric material.

Claim 7

An initiator assembly of claim 1 wherein said ignition cOmposition contains an inert diluent in sufficient amount to increase the circuit reform time.

Claim 8

An initiator assembly of claim 6 containing Snow Floss as said diluent.

Claim 9

An initiator assembly of claim 7 containing from 2 to 30 weight percent of said Snow Floss.

Claim 10

An initiator assembly of claim 1 wherein the entire length of the terminal ends of said lead wires within said ignition area are coated with a layer of dielectric material as electrical insulation therefor to increase the circuit reform time.

Claim 11

An initiator assembly of claim 9 wherein the thickness of said layer of insulation material is from about 0.5 to 15 mils.

Claim 12

In an initiator assembly of claim 10, a silicone type rubber as said dielectric material.

Claim 13

An initiator assembly of claim 1 wherein said ignition composition is a member of the group consisting of a Pb/Se, Pb/Se/SF, Pb3O4/B, and Pb3O4/B/SF.

Claim 14

An initiator assembly of claim 1 wherein said ignition composition is a Pb3O4/B/SF, and said shunt material is a member of the group of a metal ink type coating formed from a silver ink and Pb/Se, and a vapor-deposited layer of aluminum on a dielectric support member therefor.

Claim 15

An initiator assembly of claim 13 wherein the terminal ends of said lead wires in the ignition are coated with a dielectric material to increase the circuit reform time.

Claim 16

An initiator assembly of claim 14 wherein said insulation material is a silicone type rubber.

Claim 17

An initiator assembly of claim 1 wherein said shunt material has a resistance of from about 0.2 to 1,000 ohms under no-arcing firing current conditions, and in response to flow of an arc-forming firing current provides a decreased resistance across said path of from 0.1 to 5 ohms and has a resistance decrease time of from about 1 to 15 milliseconds as measured at 440 volts, and said ignition composition having a circuit reform time of from 2 to 20 milliseconds.

Claim 18

In an initiator of claim 1, an elongated shell and said ignition composition contained therein, a dielectric plug member within said shell in closing relationship therewith intermediate said ignition composition and one end of said shell as an ignition plug; said lead wires extending into said shell through said shell end and said ignition plug into the ignition area; a dielectric material superposed on the surface of said ignition plug farthest from said ignition area in direct contact with said lead wires; an electrically conductive material of low resistance on the surface of said dielectric material facing said ignition plug and disposed in two spaced apart sections with each said section in direct electrical conductive contact with a separate one of said lead wires, whereby an electrically non-conductive space, or gap, is disposed adjacent said spaced apart sections intermediate said lead wires; and said shunt material is disposed adjacent said ignition plug across said space in electrically conductive contact with each of said conductor sections.

Claim 19

An initiator assembly of claim 17 wherein said shell is formed from a metal; an additional pair of said low electrically resistant material sections on said surface, and each of said additional sections adjacent a separate one of the first said sections and spaced apart therefrom and extending into direct electrical contact with the inner wall of said shell, whereby an electrically non-conductive space, or gap, is disposed between each of the last said sections and the section adjacently spaced therefrom; and each gap of said assembly being of sufficient width to have a break-down of potential lower than that of said ignition composition to protect said assembly from premature firing by static electric charges.

Claim 20

An initiator assembly of claim 18 wherein said shunt material is a metal ink type coating and said ignition mixture is a Pb3O4/B containinG Snow Floss as a diluent in amount sufficient to extend the reform time of said ignition composition.

Claim 21

An initiator assembly of claim 19 wherein said shunt coating is a silver ink/Pb-Se (65/25.2-9.8) and said ignition composition is Pb3O4/B/SF (87.3/2.3/10).

Claim 22

In an initiator of claim 1, an elongated metal shell and said ignition composition contained therein; a dielectric plug member in closing relationship with said shell intermediate said ignition composition and one end of said shell as an ignition plug; said lead wires extending into said shell through said shell end and through said dielectric plug into the ignition area; a dielectric material superposed on the surface of said ignition plug farthest from the ignition area in direct contact with said lead wires; a plurality of electrically conductive bodies uniformly disposed on the surface of said dielectric material facing said ignition plug; all of said conductive bodies being equilateral hexagons of substantially the same size, except for such equilateral hexagons intercepted as described hereinafter, and disposed in a pattern of separate sets of parallel rows; all adjacent hexagons in each row being equally spaced apart from each other and from adjacent hexagons in each adjacent row, such that the directly opposing sides of all adjacent hexagons in said pattern are parallel, and equally spaced from each other, whereby all hexagons of said pattern are separated by gaps of substantially the same width; any said conductive body at the end of a row of said bodies and intercepted by said inner shell wall having its shape concomitantly altered, and being in electrical conductive contact with the said wall along the entire resulting line of interception; the shortest distance from each of said lead wires to said shell wall being on the line of centers of said lead wires along said dielectric material and equal to the sum of the shortest distance between parallel sides of one of said equilateral hexagon conductive bodies and the width of one of said gaps, and the distance between said conductor wires being at least equal to said sum; said pattern of conductive bodies being disposed on said dielectric material such that the rows of one of said separate sets of parallel rows are parallel to the above said line of centers of said electrical conductor wires; and the voltage breakdown in said ignition area being greater than that between each said lead wire and said shell along said dielectric material; and said shunt material disposed intermediate said ignition plug surface and said electrically conductive bodies in closing relationship with the total gap space separating said conductive bodies intermediate said lead wires, and in contact with said conductive bodies so as to be in electrical contact with said lead wires.

Claim 23

An initiator assembly of claim 21 wherein said shunt material is one of the group of a metal ink type coating formed from a silver ink and Pb-Se incorporated therein, and a vapor-deposited aluminum supported on a dielectric material; and said ignition composition is a Pb3O4/B/SF.

Claim 24

An initiator assembly of claim 22 wherein said ignition composition is Pb3O4/B/SF (73.6/6.4/20), said shunt material is a vapor-deposited aluminum layer of about 0.1 mil thickness supported on Mylar, and the lead wire terminal ends in such ignition area are coated with a layer of a silicone type rubber material of about 4 mil thickness.

Claim 25

An initiator assembly of claim 22 wherein said shunt material is a silver ink/Pb-Se (25/54-21), and said ignition composition is Pb3O4/B/SF (73.6/6.4/20).

Claim 26

In an electric delay type blasting cap assembly of claim 1 a closed elongated metal shell; a high explosive base charge in one end of said shell, a primer charge superposed on said base charge, a slow burning delay type charge superposed on said primer charge, and said ignition comPosition superposed on said delay charge; a dielectric closure member within said shell, as an ignition plug, superposed on said ignition composition; said pair of lead wires extending into said shell, through the opposite end thereof and through said ignition plug into said ignition area, and said resistance wire disposed within said ignition charge.

Claim 27

An initiator assembly of claim 1 wherein said shunt material is a conductive ink type coating.

Claim 28

In an assembly of claim 25, a dielectric material superposed on the surface of said ignition plug farthest from said ignition area in direct contact with said lead wires, and said electrically conductive material disposed on the surface of said dielectric material facing said ignition plug.