US2991714A - Delay composition - Google Patents

Description

July 11, 1961 NODDIN 2,991,714

DELAY COMPOSITION Filed 001;. 7, 1959 INVENTOR. GEORGE A. NODDIN BY A United States Patent 2,991,714 DELAY COMPOSITION George A. Noddin, Sewell, 'NJ., assignor to E. I. du Pont de Nemours and Company, WilmingtornDeL, a corporation of Delaware Filed Oct. 7, 1959, Ser. No. 844,908 3 Claims. (Cl. 102-28) -tial initiation of the explosive charges in an array of boreholes. By such sequential initiation, a more efficient blasting action can be achieved both with respect to the amount of material i.e., burden, blasted in one operation and to the degree of fragmentation of the material. Owing to the fact that each detonator in the array is initiated simultaneously with the other detonators, the movement of burden following the detonation of an explosive charge cannot cut 0 the initiation of the nearby and as yet.

unexploded charges; thus misfires are avoided. Sequential initiation of an array of explosive charges permits the achievement of the blasting action equivalent to initiation of each of the sequences in separate operations.

Electric delay detonators employed in ordinary blasting operations comprise a base charge of a detonating high explosive, a primer charge of lead azide or other heat-sensitive detonating compound, a deflagrating composition in the amount and length required to provide the desired time delay, an ignition charge, and a pair of lead wires connected by a high-resistance bridge wire, all sequentially arranged within a thin-walled metal shell. As the defiagrating mixture have been employed countless fuel-oxidizer combinations. Naturally, 'these different mixtures have met with varying degrees of success. An entirely satisfactory mixture from the standpoint of reliability and resistance to slow-up on storage is a charge comprising 0.53.0% of amorphous boron' and 99.5

. 97.0% of red lead. This composition, described in U.S.

Patent 2,717,204, possesses an extremely high burning rate, and has found extensive use in delay detonators where short delay periods, e.g., 25 to 500 milliseconds, are desirable. Unfortunately, the high burning rate of this composition precludes the extension of its use into detonators having longer delay periods. For example, in order to provide a delay interval of 5 seconds, a detonator would require a delay train of the boron-red lead composition of more than seven inches in length. Obviously, then, a detonator of the length necessary to contain such a delay charge would encounter serious objections and is inherently impractical for field use. Moreover, in largescale blasting as many as twelve or fifteen sequences frequently are fired in one operation; hence delay detonators of the millisecond type are employed in the first-fired sequences, and slow delays in the latter sequences in order to provide the desired number of sequential blasts. A blaster requiring, say, fourteen different intervals for a particular operation might employ, for example, millisecond detonators having delay periods of 25, 300, 500, and 700 milliseconds for sequences one, two, three, and four, respectively. He then would select suitable slow delay detonators, for example, of delay periods 1, 1.6, 2.3, 3.0, 3.8, 4.6, 5.5, 6.4, 7.4, and 8.5 seconds to provide, with adequate spacing, the desired number of delay intervals.

Patented July 11, 1961 Unfortunately, the defiagrating compositions employed at the present time in detonators of the longer periods sulfer from serious deficiencies in a number of respects. That composition which displays relatively few of these deficiencies, and which, consequently, has been employed most frequently as the delay composition in long-period delay detonators is a mixture of barium peroxide and selenium. This powder, although adequately slow burning to enable it to be used in shells which are not excessively long, and although undoubtedly superior to other known slow-burning mixtures, is subject to considerable shortcomings and disadvantages.

The most serious shortcoming of detonators containing the heretofore mentioned delay composition, as well as other less popular mixtures, has been that despite every manufacturing precaution, delay periods of supposedly identical detonators are not only unequal, but frequently may vary appreciably from the desired time. Inasmuch as the detonator is inevitably destroyed by a timing test, no means exist for identifying those detonators whose delay times depart most widely from the standard for the lot. Thus, while the average delay time for any large sampling may lie close to the design interval, many indlvidual detonators may have delay times appreciably greater or less than the design interval. Consequently, the danger exists that a detonator having the maximum delay time of one delay series may have the same or even a longer delay time than that of a detonator having the minimum delay time in the next delay series. If such detonators are used in conjunction in the field, obviously the desired blasting action cannot be achieved; in fact harmful action may be incurred.

A further disadvantage of present slow delay compositions is that their burning rate changes upon storage. Such a change also can result in an overlapping of delay intervals between successive delay series.

Accordingly, an object of this invention is to overcome the foregoing disadvantages of present delay compositions and to provide a novel delay composition characterized by great uniformity in burning speed and by resistance to slow-up during storage. Another object is to provide a delay composition which exhibits improved static resistance, and which is suitable for use in both slow and fast delay detonators. Additionally, this invention furnishes a delay composition which is characterized by all the desirable features of boron-red lead fast delay powders, but

which is suitable for use in detonators of longer delay intervals. Other objects will become apparent as the invention is described.

I have found that the foregoing objects are achieved when I include as a diluent in delay mixtures of boron and red lead from 25 to by weight of dibasic lead phosphite. This compound corresponds to the formula 2P-bO-PbHPO- /2H O and is described in detail in U.S. Patent 2,483,469. Although dibasic lead phosphite enhances the static, burning, and storage properties of any oxident/fuel delay mixture into which it is incorporated, I have found that it is particularly suitable for use with boron/red lead delay mixtures. A desirable composition comprises a mixture of from /2 to 3% boron, 25 to 75 dibasic lead phosphite, and 74 /2 to 22% of red lead.

The invention will be understood more clearly by reference to the accompanying drawing and following examples which are intended to be illustrative only, and are not to be taken as limiting in any way.

The drawing shows the position of a composition in accordance with the foregoing in a delay electric initiator. In the drawing, for example, 1 designates an aluminum shell having as its base charge 2 a pressed 99.5/0.5 mixture of pentaerythritol tetranitrate and l 3 graphite. Srepresents a primer charge of a heat-sensitive high explosive, for example, lead azide. The novel delay composition 4 is present within a swaged, lead tube carrier 5. Immediately above the delay composition is an aluminum capsule 6 having a perforation 7 adjacent the delay composition. A polyethylene cup 8 is seated above the metal capsule and contains a loose ignition charge 9 of, for example, a 2/98 boron/red lead composition. The upper end of the shell is sealed by -a rubber plug 10 through which pass insulated lead wires 11 which extend beyond the lower portion of the plug and are joined by .a high resistance bridge wire 12 of, for example, a platinum-tungsten alloy. The rubber plug is retained in the shell by means of circumferential crimps 13. Upon application ofelectric current to the bridge wire 12 the combustible ignition charge 9 becomes ignited, ruptures the polyethylene cup 8, and thrusts a flame through the capsule 6 to ignite the delay composition 4.

Example 1 In order to compare the performance of the boron-red lead-dibasic lead phosphite delay composition with that of a conventional mixture, a series of timing tests Was carried out with detonators of the type described, one group containing as the delay-producing element an 80/20 mixture of barium peroxide and selenium and the other group a l.37/45.50/53.13 boron/red lead/dibasic lead phosphite composition. The results of the tests, conducted in water at 80 F., are given in the following table.

Variation No. Av. between tested (sec high and low tsec.)

50 1.00 0. 16 B/PbaO4/2PbO-PbHPOa Hz 40 1. 04 0.09 50 1. 81 0. 29 B/Pb3O4/2PbO-PbHPO3 %H2O.- 20 1. 83 0.16 BaO 2 Se 5O 2. 62 0.38 B/Pba04/2Pb0 PbHPOs'%HzO. 20 2. 61 0.23 60 3. 76 0. 65 40 3. 82 0. 24 50 4. 32 0. 49 20 4. 0. 36 50 5. 41 0. 81 40 5. 40 0.35 50 6. 55 0. 79 40 6. 51 0. 28 a r/Se 50 8.19 0.96 B/PbaOl/ZPbO-PbHPO 21110 20 7. 93 0. 46 Ba 2 Se 50 9. 67 0. 90 B/Pb O4/2PbO-PbHP 03-%Hz0 20 9. 38 0. 69

Example 2 In low temperature firing-tests tencarrier tubes containing a 83.7/ 16.3 barium peroxide/selenium composition and ten tubes containing a 1.12/48.88/50 boron/ red lead/dibasic lead phosphite composition Weresubmerged in Dry Ice (-7S C.) for one hour, ignited, and checked for their ability to burn the entire length of the tube.

Example 3 The effect of the dibasic lead phosphite diluent on timmg was determined in thefollowing tests on compositions containing various percentages of t-hediluent. Thetest :75

compositions were loaded into detonators of the described type, and the detonators were fired in water at 80 F.

Example 4 A composition containing 1.6% boron, 88.4% red lead, and 10% dibasic lead phosphite was prepared and loaded in a l-inch-long carrier tube into a detonator of the type described. A similar composition containing in place of 10% dibasic lead phosphite 10% lead oxide also was prepared. Thirty detonators containing the dibasic lead phosphite composition were tested; these detonators produced an average delay time of 0.627 second with a variation between the longest and shortest delay period of 0.042 second. Tests with the same composition containing lead oxide instead of dibasic lead phosphite indicated an average delay time of 0.648 second with a variation of 0.304 second.

Example 5 In order to evaluate the performance of detonators containing dibasic lead phosphite on a scale as employed in field use, a composition containing 1.37% boron, 45.50% red lead, and 53.13% dibasic lead phosphite 'was prepared. The composition was loaded in detonators of the type described in carrier tubes 0.295, 0.410, 0.605, 0.855, 1.105, 1.375, 1.660, 1.950, 2.275, 2.620, and 3.000 inches in length in order to provide delay periods of nominally 0.7, 1.0, 1.6, 2.3, 3.0, 3.8, 4.6, 5.5, 6.4, 7.4, and 8.5 seconds, respectively. The results of timing tests on 40 detonators of each period is shown in the following table. The detonators were shot in water The foregoing examples clearly illustrate the reduction in variation and thus random shots that is accomplished according to this invention.

Although the compositions of the present invention would function satisfactorily without the use of a graining agent, it is preferable to use such an agent in order to be able to load the detonators with commercial equipment. Conventional graining agents, such as Thiokol LP-2 and neoprene in amounts from 0.5 to 1.5% of the weight of the composition are considered satisfactory.

Naturally as the percentage of dibasic lead phosphite diluent in the mixture is increased, the burning rate decreases accordingly. A particular advantage of the compositions of this invention is that delay mixtures can be prepared therefrom which are suitable for fast, i.e., millisecond, or for slow delay detonators. Mixtures containing more than dibasic =lead phosphite are not satisfactory however, as their rate of burning is so low as to make them unreliable. On the other hand, the inclusion of less than 25% of the dibasic lead phosphite diluent provides a reduction in burning speed which is so small as to be insignificant from the standpoint of Practical values. Desirably, the composition will not contain more than 3% by weight of boron, owing to the greatly increased static sensitivity which results when higher percentages are present.

Additional advantageous features of delay mixtures containing dibasic lead phosphite include the fact that they are adequately insensitive to impact. Illustrative of this is the fact that a 0.005-inch thick layer of a 1.4/48.6/50 boron/red lead/dibasic lead phosphite mixture on a steel plate could not he ignited by a /z-inchdiameter steel ball dropped from a height of 42 inches. Furthermore, the compositions display excellent resistance to static electricity. In static sensitivity tests conducted across a /32-111011 spark gap, 24,000 volts and 330 micromicrofarads failed to ignite a 1.2/48.8/50 boron/ red lead/dibasic lead phosphite composition.

In the examples and drawing, the use of the novel composition loaded in lead tubes as a carrier has been shown. This, however, is not to be construed as limiting the the invention, for it is within the scope thereof to replace the exemplified carrier by other suitable carriers, or indeed, to eliminate a carrier completely and to load the delay mixture directly into the shell.

The uniformity of burning provided by delay compositions containing dibasic lead phosphite have been illustrated in the examples, and will be recognized by those familiar With the art of blasting as a significant and long-desired contribution to the art. An additional feature of these mixtures is that they display the already recognized resistance to slowp on storage associated with boron-red lead delay powders.

The invention has been described fully in me foregoing, and, accordingly, I intend only to be limited by the following claims.

I claim:

1. A novel deflagrating composition comprising 25 to by weight of dibasic lead phosphite, V2 to 3% by weight of boron, and 74 /2 to 22% by weight of red lead.

2. In an improved electric delay initiator of the type wherein a delay composition is interposed between an ignition composition and a priming composition, a delay composition comprising 25 to 75 by weight of dibasic lead phosphite, /2 to 3% by weight of boron, and 74 /2 to 22% by weight of red lead.

3. A delay electric initiator in accordance with claim 2, wherein the delay composition is contained within a swaged metal tube.

References Cited in the file of this patent V UNITED STATES PATENTS 2,478,415

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