US2761386A - Electric initiator and ignition mixture therefor - Google Patents

Description

Sept. 4, 1956 D. T. ZEBREE 2,761,335

ELECTRIC INITIATOR AND IGNITION MIXTURE THEREFOR Filed Dec. 3, 1952 DAVID T. ZEBREE INVENTOR.

BY W (21mm ELECTRIC INITIATOR AND IGNITION MIXTURE THEREFOR David T. Zebree, Kingston, N. Y., assignor to Hercules Powder Company, Wilmington, DeL, a corporation of Delaware Application December 3, 1952, Serial No. 323,866

13 Claims. (Cl. 102-48) This invention relates to blasting initiators and more particularly to ignition compositions and initiators employing such compositions.

For many years mixtures of finely divided lead and selenium have been employed in the electric initiator art with very satisfactory results. As the initiator art developed, it became apparent, however, that this generally satisfactory composition was characterized by certain deficiencies which it has been desirable to correct. For example, it has been discovered that failures in regular delay blasting initiators resulting from the oxidation of lead in the lead-selenium mixture could be overcome by the addition to the mixture of certain amounts of aluminum, antimony, antimony phosphide, boron, cadmium, carbon, iron, magnesium, nickel, phosphorus, and silicon. These improved mixtures are disclosed in copending application Serial No. 78,383, filed February 25, 1949.

Although the addition of such modifiers was found to eliminate overlapping of delay periods in regular delays, that is, delay initiators in which the period between application of current and the firing of the cap is measured in terms of a second or more, the lead-selenium mixtures and the modified lead-selenium mixtures of application Serial No. 78,383 are still characterized by an undesirable lack of uniformity in firing time when employed in short period delay caps wherein the period of delay is measured in terms of milliseconds.

While lead-selenium ignition compositions are generally characterized by satisfactory resistance to premature firing by static discharge, it would, of course, be desirable to increase this resistance to static discharge if such increase can be effected without adversely alfecting the otherwise acceptable performance of the mixture. In like manner, it would be desirable to improve the charging characteristics of a lead-selenium mixture since such mixtures are normally quite dusty. As in the case of any ignition composition which is employed with high explosive materials, it is desirable to increase the impact sensitivity of the mixture in so far as it is possible Patented Sept. 4, 1956 without adversely affecting the ignition characteristics of the composition.

Now in accordance with the present invention, compositions predominantly comprising mixtures of lead and selenium can be prepared which have increased resistance to ignition by static discharge, which have better flowing and charging characteristics, which have lower impact sensitivity, and which, when employed in short period delay initiators, bring about considerably greater uniformity in firing time.

Generally described, the present invention is an ignition composition for electric initiators which comprises lead-selenium and a minor amount of a metal salt of a long chain fatty acid. It has been found that the presence of a suitable amount of such metallic soaps in mixture predominantly comprising lead and selenium efiects highly desirable changes in terms of uniformity of firing time, particularly in short period delay initiators, static resistance, charging ease, and friction and impact sensitivity without detracting from the other widely accepted characteristics of lead-selenium mixtures. While the metal salts of the long chain fatty acids are generally operable, the stearates, oleates, laurates, and palmitates of such metals as lead, cadmium, iron, magnesium, aluminum, and zinc are most readily available and are preferred. Of all of these compounds lead stearate is especially preferred. While the mixtures of this invention are especially adapted for usein short period delay initiators, they may be used as well in instantaneous and regular delay initiators.

The eifect of the presence of metallic soaps in leadselenium on uniformity of firing times of short period delay caps is shown in Table I. The caps employed are illustrated in the drawing and comprise a bronze shell 1 containing a pressed base charge 2 of 0.24 g. of pentaerythritol tetranitrate. A priming charge 3 of 0.38 g. of diazodinitrophenol/potassium chlorate (75/25) was pressed on top of the base charge. A delay fuse consisting of a load tube 4 containing a core 5 of barium peroxide/selenium (/30) is pressed on the priming charge. A loose charge 6 of ignition composition in accordance with the invention is loaded on top of the fuse. An ignition plug 7 is inserted over the ignition composition. Lead Wires 8 pass through the ignition plug into the ignition composition and are connected at their terminals by a bridge wire 9 which is surrounded by the ignition composition. A layer of waterproofing 10 and a sulfur seal 11 complete the initiator.

In the test recorded in Table I, the indicated number of caps was separately fired and the elapsed time (measured in milliseconds) between application of the firing current and the firing of the cap was measured for each. A firing current of 2 amperes was employed. Unless otherwise indicated, a chemically equivalent mixture of lead and selenium was employed (Pb-Se72.4/ 27.6).

Table II Example N o. Ignition Mixture Condens- M.N'.F.

er (mmf.) V.

Pb-Se/Si, 98/2 100 4, 000 Pb-Se/Si, 98/2 750 1, 000 Pb-Se/Si, 98/2 3,000 1,000 Pb-Se (alone) 750 1, 000 Ph-Se/lead stearate, 99. 100 6,000 Pb-Se/lead stearate, 99.5/0.5 750 2, 000 Pb-Se/lead stearate, 99.15/05. 3, 000 1, 000 Pb-Se/Si/lead stearate, 97.5/2.0/0.5 100 6, 000 Pb-Se/Si/lead stearate, 97.5/2.0/0.5 760 2, 000 Pb-Se/S1/lead stearate, 97.5 2 /0 3, 000 1,000 Pb-Se/slllead stea. ate, 97 5/1 0/1 5 750 2, 000 Pb-Se/Sr/lead stearate, 97. [1.0/2 0- 750 3, 000 Pb-Se/Si/lead stearate, 96.5/1.0/2.5 750 4, 000 Pb-Se/Si/calcium stearate, 97.5/l.0/1.5 750 3, 000 Pb-Se/S1/iron stearate, 97. 5/1.0/1 .5 750 2, 000 Pb-Se/Si/rnagnesium stearate, 97.5/1 .0/1.5 750 3, 000 Pb-Se/Si/zinc stearate, 97.5/1.0/l.5 750 3, 000 Pb-Se/Si/aluminum laurate, 97.0/l.0/2.0 750 2, 000 Pb-Se/Si/calcium oleate, 96.0/1.0/3.0 750 2, 000

1 Maximum nonfiring voltage.

The diminution 1n lmpact and friction sensitivity ef- 78,3 83. The amount of metal salt wh1ch can be added fected by addition of the metal soaps is illustrated in Table III. In the experiments recorded, the compositions were tested on a Bureau of Mines impact machine to determine the height and angle necessary to give 50% shots.

to a lead-selenium mixture without desensitizing the composition to ignition will depend on the amount of such other additive employed and on the firing current used. With a firing current of 2 amperes and a basic stoichiometric mixture of lead and selenium containing 1% of Table III Example Weight, Impact Height for 50% N o. Ignition Mixture Kg. A(rg)gle Shots (cm.)

Pb-Se(72.4-27.6)/Sl, 98/2 2 4 16. Pb-Se(72.4-27.6)/Si, 98/2 4 8 11. Pb-Se(72.427.6)/Sillead stearate, 97. 2 4 41. Pb-Se(72.4-27.6)/Si/lead stearate, 96.5/2.0 1. 4 4 48. Pb-Se(72.427.6)/Si/lead stearate, 96.512.0/1. 4 8 5O shots. Pb-Se(72.427.6)/Si/lead stearate, 96.0/2.0/2.0 4 4 7% shots.

1 Maximum height of test machine; hence, height of fall for 50% shots was over 50 cm.

From the foregoing examples it is apparent that the compositions and initiators of this invention are characterized by highly desirable properties. From the examples in Table I, it will be noted that with a firing current of 2 amperes, failures are obtained when enough metal soap is employed to reduce the ignition sensitivity of the mixture. As will be apparent to those skilled in the art, the concentration at which undesirable ignition sensitivity will be obtained depends on the strength of the firing current employed and on the amount of silicon or other ignition desensitizing additive employed. When employing a firing current of 2 amperes, for example, it has been found that up to 6% of lead stearate may be added to a chemically equivalent lead-selenium mixture without undesirably desensitizing the composition to ignition although between .5 and 2% is preferred. A definite benefit was noted when .2% lead stearate was added.

In order to guard against failures due to formation of lead oxide in the mixture, it is desirable to add silicon or other additive in accordance with application Serial No.

silicon, it has been found that the following amounts of metal soaps will desirably be added:

Preferred ignition mixtures in accordance with the invention will contain from about 64 to about lead, from about 20 to about 36% selenium, from about .2 to about 2% silicon, and from about 0.5 to about 2% lead stearate.

With respect to static resistance and impact and friction sensitivity, Tables II and III illustrate that the benefits received increased in proportion to the amount of additive employed. Since the metal soap has a lubricating efl'ect on the powdered lead-selenium mixture, the fiowing and charging characteristics of the mixture are markedly improved.

Since various modifications of the invention not specifically set forth herein will occur to those skilled in the. initiator art, it is intended that the scope of the invention be limited only by the scope of the appended claims.

What I claim and desire to protect by Letters Patent is:

1. An ignition composition for electric initiators which comprises an ignition mixture of lead and selenium and contains a minor amount of metal salt of a long chain fatty acid.

2. An ignition composition for electric initiators which comprises from about 64 to about 80% lead, from about 20 to about 36% selenium, and a minor amount of metal salt of a long chain fatty acid.

3. An ignition composition for electric initiators which comprises a stoichiometric mixture of lead and selenium and a minor amount of metal salt of a long chain fatty acid.

4. An ignition composition for electric initiators which comprises from about 64 to about 80% lead, from about 20 to about 36% selenium, and a minor amount of metal salt of stearic acid.

5. An ignition composition for electric initiators which comprises from about 64 to about 80% lead, from about 20 to about 36% selenium, and a minor amount of metal salt of lauric acid.

6. An ignition composition for electric initiators which comprises from about 64 to about 80% lead, from about 20 to about 36% selenium, and a minor amount of metal salt of oleic acid.

7. An ignition composition for electric initiators which comprises from about 64 to about 80% lead, from about 20 to about 36% selenium, and a minor amount of lead stearate.

8. An ignition composition for electric initiators which comprises from about 64 to about 80% lead, from about 20 to about 36% selenium, and additive amounts of from about .2 to about 2% silicon, and from about .5 to about 2.0% of lead stearate.

9. An electric blasting initiator having in combination an ignition assembly containing a bridge wire and a loose ignition mixture disposed about the bridge wire which comprises an ignition mixture of lead and selenium and contains a minor amount of metal salt of a long chain fatty acid.

10. An electric blasting initiator having in combination an ignition assembly containing a bridge wire and a loose ignition mixture disposed about the bridge wire which comprises from about 64 to about lead, from about 20 to about 36% selenium, and a minor amount of metal salt of a long chain fatty acid.

11. An electric blasting initiator having in combination an ignition assembly containing a bridge wire and a loose ignition mixture disposed about the bridge wire which comprises from about 64 to about 80% lead, from about 20 to about 36% selenium, and additive amounts of from about .2 to. about 2% silicon, and from about .5 to about 2.0% of lead stearate.

1.2. A delay electricblasting initiator having in combination a delay fuse element and a loose ignition mixture in contact with the delay fuse element; said mixture comprising from about 64 to about 80% lead, from about 20 to about 36% selenium, and a minor amount of metal salt of a long chain fatty acid.

13. A delay electric blasting initiator having in combination a delay fuseelement and a loose ignition mixture in contact with the delay fuse element; said mixture comprising from about 64 to about 80% lead, from about 20 to about 36% selenium, and additive amounts of from about .2 to about 2% silicon, and from about .5 to about 2.0% lead stearate.

References Cited in the file of this patent UNITED STATES PATENTS 1,989,729 Alexander Feb. 5, 1935 2,473,405 Zebree June 14, 1949 2,476,370 I-lanley July 19, 1949 2,607,672 Spaeth et al. Aug. 19, 1952 FOREIGN PATENTS 114,993 Australia Mar. 7, 1946

Claims (1)

1. 9. AN ELECTRIC BLASTING INITATOR HAVING AN COMBINATION AN IGNITION ASSEMBLY CONTAINING A BRIDGE WIRE AND A LOOSE IGNITION MIXTURE DISPOSED ABOUT THE BRIDGE WIRE WHICH COMPRISES AN IGNITION MIXTURE OF LEAD AND SELENIUM AND CONTAINS A MINOR AMOUNT OF METAL SALT OF A LONG CHAIN FATTY ACID.

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