US2475281A - Delay electric initiator - Google Patents

Description

Filed Jan. 19, 1945 a M 0 a a Edward J Han/e INYEN'IUR.

W Pa. QM.

ATTORNEY Patented July 5, 1949 UNITED STATES AT E N GFFECE DELAY ELECTRIC INITIATOR Edward J. Hanley, Port Ewen, N. Y., assignor to Hercules Powder Company, Wilmington, DBL,

a corporation of Delaware 4 Claims.

cavity-type plugs are employed, the flash mixture must be buttered into the cavity by hand. Where matchhead-type ignition assemblies are employed, dipping of the plugs into the fiash mixture to obtain a definite amount of material and allowing time for drying the matchheads are required.

Now in accordance with this invention, delay electric initiators have been prepared employing electric blasting cap-type ignition assemblies. This has been accomplished by the development of an ignition composition comprising powdered selenium, a powdered metal selected from the group consisting of lead and tin, a flame-spreading material such as an oxidizing material or a gas-producing mixture containing an oxidizing material, and a flash-producing metal such as powdered magnesium or zinc. This ignition mixture is placed in a capsule formed of an inflammable material such as Celluloid, and in this manner is held in position surrounding the bridge wire without danger of falling into the air cavity provided between it and the delay fuse.

In general, delay initiators in accordance with this invention comprise a shell fitted with an ignition assembly and sealing materials of the standard type. The initiator may contain igniting and detonating explosives and a delay fuse train, such as black powder or a mixture of barium peroxide and selenium. In the former case, the initiator will be of the vented type, and in the latter it will be of the ventless type. Above the delay fuse is provided an air cavity. The ignition composition in accordance with this invention is held in a capsule of infidfmmable material, into which the plug and bridge assembly are inserted such that the bridge wire is embedded in the ignition composition. The capsule may be held in place in the shell by the pressure of the plug inserted within it against the sides of the shell or by crimps in the shell at the upper end of the air space, reducing the inside diameter of the shell to the extent necessary to provide a ridge on which the lower end of the capsule may rest. The contents of the capsule may be made waterproof by imbedding its upper open end portion in the layer of waterproofing compound customarily provided above the ignition plug. If desired, the delay electric initiator may be of the igniter type, which lacks both explosive material and a delay fuse, having provided at the lower end of its air cavity an opening for the insertion of a delay train, such as a black powder fuse.

The general aspects of this invention have now been set forth. There follows a more detailed description of a preferred embodiment thereof with reference to the accompanying drawing, in which is shown a cross-sectional view of a delay electric igniter in accordance with this invention.

The igniter comprises a metal shell I, in the lower end of which is inserted a taped black powder fuse 2. This fuse is held in the shell by crimps (not shown). Directly above the fuse train is an air cavity 3 provided with a vent 4 for the escape of gases formed during the burning of the black powder train 2 and the ignition composition 6. The vent usually is sealed by tape to prevent entrance of moisture. The ignition composition 5 contains a mixture of lead, selenium, potassium chlorate, and zinc. The ignition composition is held in an inflammable Celluloid capsule 5. This capsule is held in position by a crimp I in the shell at the upper end of the air cavity 3. The plug 9, 0.230 inch in diameter, inserted in the upper open end of the capsule 5, holds two lead wires 8 in dielectric relation to each other. The terminal ends of the lead wires, 0.090 inch apart and projecting /s4 inch from the plug face, are bridged by platinum wire ID imbedded in the ignition composition. The shell is made waterproof by a layer of waterproofing compound II and a layer of sulfur I2, which is held firmly in the shell by the crimps l3.

By using a closed end metal shell, a delay electric blasting cap containing a suitable base explosive in the closed end beneath the delay fuse train may be provided.

The following example illustrates the practice of this invention:

Example Delay electric igniters were prepared, using 2-- diameter igniter shells. Each of the igniters contained a loose mixture of 0.040 gram of an ignition composition comprising 77% of a mixture of lead and selenium (72.4% lead-27.6% selenium), 20% zinc powder, and 3% potassium chlorate. The ignition composition was placed in Celluloid capsules slightly smaller in diameter than the inside diameter of the igniter shell. The capsules were of an inch long and had an outside diameter of 0.255 inch and an inside diameter of 0.245 inch. These capsules were placed in the shells, their lower end resting upon a crimp in the shell at the top of the air cavity, making the inside diameter of the shell smaller than the outside diameter of the capsule. Electric blasting cap-type plugs 0.230 inch in diameter, prepared with regular igniter-type platinum bridge wire on 0.090-inch terminal centers, were inserted in the capsules such that the bridge wire was imbedded in the ignition mixture. The charge height of the ignition mixture was found to be /64 of an inch. A layer of waterproofing compound and a sulfur seal were inserted. A length of regular black powder igniter fuse was crimped in the bottom portion of the shell and two layers of cellulose acetate tape employed to seal the vent hole in the air chamber.

No failures to ignite the fuse were found in firing 200 igniters. To determine critical firing current, three groups, each containing 30 igniters in series, were fired. They ave critical firing currents of 0.6, 0.6, and 0.7 ampere, respectively. The critical firing current for 30 standard commercial igniters in series is 0.9 ampere. Thus, igniters in accordance with this invention show a reduction of A; in critical firing current.

When these igniters are fired, the fiash mixture burns through the bottom of the capsule, and a hot fiame is thereby directed. down against the top of the fuse, igniting the black powder train and, at the same time, causing the seal over the vent hole to rupture.

The ignition flash mixture in accordance with a this invention contains as essential ingredients a mixture of selenium and either lead or tin, a flash-producing metal such as zinc or magnesium, and a flame-spreading material such as an oxidizing material, as potassium chlorate, or a gas-producing mixture containing an oxidizing agent, as black powder. This ignition mixture may be employed in any delay-type electric initiator.

A stoichiometrically equivalent mixture of powdered selenium and either powdered lead or powdered tin is preferably employed. Such a mixture contains 27.6% selenium and 72.4% lead, or selenium and 60% tin. However, it has been found that mixtures containing between 64% and 80% lead and between 20% and 36% selenium are satisfactory. Similarly, mixtures containing between 46% and 69% tin and between 31% and 54% selenium have given good results. This mixture is added to the ignition composition in an amount between about 57% and about 80% by weight of the total composition. However, amounts between about 50% and about 90% by weight of the ignition composition have proved satisfactory.

As the flash-producing metal, powdered magnesium, zinc, or aluminum are preferred. Of these, magnesium gives somewhat better results. Aluminum on certain occasions shows an undesirable diiflculty in ignition. Between about 3% and about 40% flash-producing ingredient by weight of the ignition mixture may be employed. Between about 17% and about 37% fiash-producing-ingredient is preferred, where zinc is employed. Between about 5% and about 25% is preferred where magnesium is employed.

Other metals may be substituted for zinc or magnesium in stoichiometrically equivalent quantities, such as tin and aluminum. It is sometimes desirable to coat the flash-producing ingredient with linseed oil in order to protect it from reaction with the explosives with which it may be mixed or from reaction, with the atmosphere.

An essential ingredient of the ignition composition is a flame-spreading material, preferably in suchan amount that the ignition composition has a zero or slightly positive oxygen balance. 'Howeven under certain circumstances, a small negative oxygen balance, preferably not lower than approximately 5, may be tolerated. Positive oxygen balances assist in reducing the ignition time to a minimum. Where potassium nitrate is the flame-spreading material, it is employed in an amount between 5% and 30% by weight of the ignition mixture, preferably between 10% and 25% by weight. Where potassium chlorate is the flame-spreading material, it is preferred to employ amounts between about 1% and about 6% by weight of the ignition mixture. Other oxidizing materials, such as barium nitrate, sodium nitrate, sodium chlorate, barium peroxide, and lead dioxide, may be employed in amounts stoichiometrically equivalent to the ranges of potassium nitrate given, within the limitations of the oxygen balance of the composition. However, materials other than oxidizing materials will give this efiect. Black powder, which is a good reducing agent but which contains an oxidizing material and, during burning,

gives off large quantities of gas, has proved it-v self the equal of potassium nitrate in causing the flame to spit out. It appears that any materials containing an oxidizing material which liberates large quantities of gas will serve the same function.

The importance of each of the ingredients in the ignition mixture may readily be demonstrated. If a mixture of lead, zinc, and potassium chlorate were used or if a mixture of zinc, selenium, and potassium chlorate were used, ignition of the mixture by use of a bridge wire would be impossible. If a stoichiometrically equivalent mixture of lead and selenium containing 72% lead and 28% selenium were employed, good lowcurrent ignition could be obtained, but it would fail to create a flash and ignite the fuse. A mixture containing lead, selenium, and potassium chlorate, or containing lead, selenium, and zinc, will ignite the fuse. However, mixtures of lead, selenium, and potassium chlorate give a poor flash. Mixtures containing lead, selenium, and zinc produce only a mild flash. The addition of a small amount of a flame-spreading material, as potassium chlorate, to the latter mixture causes the flame to spit out in a more desirable manner. When an initiator, into which is sealed 9, Celluloid capsule containing 0.4 gram of a mixture of 70-80% lead-selenium, 19-29% zinc, and 1-4% potassium chlorate, is fired, the bottom of the capsule is burned away and a flame spits out sufficient to ignite the attached fuse, at the same time breaking the seal over the vent hole.

The particle size of the ingredients employed must be carefully regulated in order to prevent segregation. While segregation does not necessarily produce failure, it should be avoided, if possible. It has been found. that the fiamespreading material and the flame-producing metal should be of approximately the same mesh size. Satisfactory particle sizes for potassium chlorate have been found to be between 60 and 200 mesh and, for zinc. between 100 and 200 mesh.

Delay electric ignitors in accordance with this invention may be prepared employing any of the usual z-diameter igniter shells, for example, one stepped down from 0.30 inch at the top to 0.22 inch at the lower end, open at both ends, and containing a vent so that it may be used with any type of delay fuse train. The plugs may be formed of sulfur, rubber, plastics or synthetic resins, as polystyrene, phenol-formaldehyde resins, or ethyl cellulose, and are fitted with two lead wires, the terminal ends of which project from the face of the plug and are bridged by an electrically-resistant wire composed of noble or base metals or alloys thereof, such as platinum, Nichrome, copper-nickel, and platinum-iridium. The ignition composition is kept in position about the bridge wire by an inflammable capsule whose outside diameter is slightly smaller than the inside diameter of the shell and whose inside diameter is slightly larger than the diameter of the ignition plug. The capsule is held in position in the shell by crimps which reduce the inside diameter of the shell to a diameter smaller than the diameter of the capsule. The upper open end of the capsule may be imbedded in the layer of waterproofing compound, although capsules too short to permit this may, of course, be used. The capsule may be of any inflammable material, such as paper, cardboard, or Celluloid, stiff enough to retain its shape and thin enough to burn through quickly. The igniters may then be completed by a layer of sulfur held in position by crimps, as desired. When rubber or plastic plugs are employed, waterproofing is usually not required.

, ture.

the mixture. Thus, igniters of this type receive current until one of them actually fires and burns through the Celluloid capsule.

Since the ignition composition contains no sensitive explosives, such as copper acetylide, mercury fulminate, or diazodinitrophenol, delay initiators in accordance with this invention will not fire upon being accidentally crushed. Further,

'delay initiators employing electric blasting captype plugs are simpler and cheaper to manufac- The operations of packing cavity-type plugs by hand, for example, are avoided. The mixing of special ignition mixtures suitable for matchheador cavity-type plugs is avoided. The loose fiash mixture employed in this invention can be charged into capsules by the commercial charging equipment well known to the art.

The term electric blasting cap-type ignition described comprising a shell, a firing assembly,

Delay electric blasting caps may also be prepared in accordance with this invention. Shells of the standard type having one closed and one open end may be employed. Where it is desired to provide an air space, the only modification of the standard shells required is the provision of crimps at the upper end of the air chamber in order to hold the capsule containing the ignition composition in position. A capsule is, of course, unnecessary when there is no air space present. The completed cap comprises a delay fuse, a primary explosive, a base explosive, ignition mixture, and firing assembly. Base=explosives which may be employed include pentaerythritol tetranitrate, tetryl, cyclonite, mannitol hexanitrate, trinitrotoluene, nitrolactose, and nitrosucrose. Primary explosives include diazodinitrophenol, mercury fulminate, and lead styphnate.

The type of delay fuse employed will depend upon whether a vented or ventless-type initiator is desired. For ventless-type initiators, a barium peroxide-selenium fuse train or other similar mixtures, such as described in U. S. 1,999,820 or U. S. 2,139,581 to Nash, may be employed. For vented types, the well-known black powder fuse may be employed.

Delay electric initiators in accordance with this invention have a lower critical firing current than those of the prior art, as illustrated in the example. The reason for this difference is that when current is applied to ignitors using the customary ignition mixtures, it continues to flow only until the first bridge wire in theseries has fused. Thus, any igniters which have not fired by that time fail. When the current is applied to the igniters of this invention, current continues to be carried even after the bridge wire has fused, due to the electrical conductivity of and an open-ended capsule enclosing an ignition composition in its bottom, said composition comprising a mixture of selenium, a metal selected from the group consisting of lead and tin, a fiame- .producing metal, and a flame-spreading material in which the firing assembly has its ignition means embedded in the ignition composition.

2. A delay electric initiator of the character described comprising a shell, a firing assembly, and an open-ended Celluloid capsule enclosing an ignition composition in its bottom, said composition comprising a mixture of selenium, a metal selected from the group consisting of lead and tin, a flame-producing metal, and a flame-spreading material in which the firing assembly has its ignition means embedded in the ignition composition.

3. A delay electrc igniter comprising a shell, an open-ended capsule containing an ignition mixture in the bottom thereof, a firing assembly having its ignition means embedded in the ignition mixture, a delay fuse mounted in the shell in spaced and facing relation to the closed end of said capsule and ignition mixture, said ignition mixture comprising selenium, a metal selected from the group consisting of lead and tin, a flameproducing metal, and a flame-spreading material.

4. A delay electric blasting cap-type ignition assembly comprising a shell, an open-ended capsule containing an ignition mixture in the bottom thereof, a firing assembly having its ignition means embedded in the ignition mixture, a delay fuse mounted in the shell in spaced and facing relation to the closed end of said capsule and ignition mixture, and vent means for the shell, said ignition mixture comprising selenium, a metal selected from the group consisting of lead and tin, a flame-producing metal, and a flamespreading material.

EDWARD J. I-IANLEY.

(References on following page) REFERENCES ci'mn Number The following references are of record in the flle of this patent:

2,228,339 UNITED STATES PATENTS 5 2,370,159 Number Name Date 838,216 Schneider Dec. 11, 1906 938,553 Cahuc Nov. 2, 1909 Pfig g 1,436,248 Hammond Nov. 21, 1922 305'140 1,964,826 Lewis et a1. July 3, 1934 1,989,729 Alexander Feb. 5, 1935 8 Name Date Babbitt et a1 July 16, 1935 Burrowa'et a1. July 12, 1938 Burrows et a1 Jan. 14, 1941 Henley Feb. 2'1, 1945 FOREIGN PATENTS Country Date Germany Apr. 20, 1904- Germany Jan. 10, 1921

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