US2185371A - Delay composition - Google Patents

Description

1940. L. A. BuRRows El AL ,1 5,371

DELAY COMPOSITION Filed June 18, 1937 F 2 Lam Z022 A.Burr0ws INVENTORS Wa/zez" flan son A TTORNEY Patented Jan. 2, 1940 PATENT OFFICE DELAY COMPOSITION Lawton A. Burrows. Wenonah, and Walter E. Lawson, Woodbury, N. .L, assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application June 18, 1937, Serial No. 148,948

8 Claims. (or. 52-15) The present invention relates to a new and improved burning composition, and more particularly to a composition particularly suitable for use as a delay element or time fuse in delay detonators.

Delay detonators may be conveniently classifled into two main types, depending on the purpose for which they are employed. The first type, represented by the delay electric blasting cap, is employed in ordinary commercial blasting operations. The second type, represented by the fuse head. of military shells is employed especially in high explosive shells which burst in air, or in a calculated length of time after impact.

Although the purpose for which these delay detonators are employed is entirely different, in construction they are essentially alike. Both types consist essentially of a detonating base charge separated from an appropriate firing means by a suitable length or column of a slowburning ignition composition. In the fuse head the firing means generally comprises a percussion composition which is initiated by impact. In delay blasting caps, the firing means commonly consists of a high resistance electric wire surrounded by a highly inflammable ignition composition which bursts into flame when an electric current heats the wire to incandescence. .The percussion or ignition composition as the case may be, ignites the fuse or delay element which burns slowly. Eventually, after a definite interval of time, this initiates either a more violent ignition agent, a priming composition or a detonating base charge.

The slow-burning fuse or delay compositions above referred to have heretofore generally been of the gas-generating type. Thus, for example, modified black powder compositions which evolve a great amount of gaseous combustion products, have been extensively employed in both types of delay detonators. Such compositions, however, are highly undesirable both in the military and the commercial type of delay detonator because a vent must be provided for the escape of these gases. In fuse heads, 'this is objectionable because tlie rate of combustion varies with the pressure, and therefore the time interval of the has certain disadvantages.

ingress of moisture or other harmful substances as well as a means of 'eiliux of the gaseous ignition.products. For these and other reasons, substantially gasless delay compositions are highly desirable for use in delay detonators.

Relatively few delay compositions have been proposed heretofore, and all of these appear to possess certain disadvantages which detract from their otherwise desirable properties. Thus, the composition disclosed by Eschbach in GB, 371,596, consisting of antimony and potassium permanganate is not altogether satisfactory for several reasons. In the first place the composition, as disclosed, is difiicult to ignite, for which reason it is not altogether reliable in a delay detonator. In addition, the composition burns rather rapidly, for which reason a very long fuse or delay train must be employed to produce a ten-second delay, for example. Lastly, the composition is diiiicult to standardize so that a given length of delay element will burn within a given length of time.

The selenium-barium peroxide composition disclosed by Nash in U. S. Patent No. 1,960,591 also This composition likewise burns rapidly. In addition the ingredients are not readily available, and the selenium required is unpleasant to work with because of its physiological effects.

The object of the present invention is a new and improved delay composition. A further object is a substantially gasless delay composition I which is readily ignited and reliable in use. A

composition comprising a metal and an oxidizing agent may be varied within wide limits.

We have found that the burning speed of ignition compositions comprising an oxidizing agent and a given metallic element A may be altered within wide limits by alloying said element A with another metallic element 3 which has a heat of combustion per unit volume appreciably different from the corresponding thermochemical 50 property of the given metal A. In order to accelerate the burning speed of the composition, the metallic element A is alloyed with a metal B whose heat of combustion per unit volume is greater than the corresponding property of the where KA is the thermochemical constant of the metallic element A. HAO is the heat of formation of the oxide of the metal A in gram-calories; MA is the molecular weight of the metal A and (1A is the density of said metal A. a: is the number of atoms of element A in the oxide for which the heat of formation is taken.

In order to describe our invention more clearly, reference is made to the accompanying table showing several compositions which demonstrate the control which may be exercised over the burning speed of a given ignition composition by the proper selection of the element B to be alloyed with the reference metal A. It is to be understood, however, that this is done solely by way of illustration, and is not to be construed as a limitation upon the scope of our invention, which has many important applications other than those particularly described hereinafter.

Referring generally to the table, Examples 1 and 2 represent suitable reference compositions in which the metal A is not alloyed with any other element. Example 3 illustrates the accelerating effect of alloying A and B, where KB is greater than KA- Examples 4-9 illustrate the retarding effect of alloying A with B where KB is less than KA. For the purpose of illustrating the relative effects of alloying a given element A with various other elements, Examples 3 and 5-9 relate to delay compositions comprising antimony, while Example 4 illustrates the application of our invention to other elements than antimony. Examples '7 and 9 illustrate the effect of the amount of retarding element B on the burning speed of the composition.

aisaavi respectively) the burning speeds of the compositions comprising these respective alloys will be less than that of a similar composition in which antimony is the only metal present. In the case of the antimony-copper alloy, this effect is accomplished by the use of only two parts of the latter element with 98 parts of antimony, a greater per cent of copper serving to retard the speed still further, as seen in-Example 9.

The converse effect is illustrated by Example 3, where antimony is alloyed with iron. Since KFe is greater than KSb, the burning speed of the composition comprising the alloy is. faster than that of the corresponding composition in which antimony is the only metal.

This peculiar eifect of retarding or accelerating the burning speed of a given composition is not brought about to a controlled extent by mechanical mixtures of the two metallic elements with an oxidizing agent, but the advantageous effect is dependent upon'the fact that the two metals are alloyed together. Thus, for example, a mechanical mixture of copper, antimony and permanganate is very difficult to ignite and. once ignited invariably burns out. On the other hand, a composition comprising these same ingredients, in the same proportion, will ignite readily and burn regularly and smoothly without producing any substantial amount of gas, if the copper is alloyed with the antimony.

In order to describe the application of our invention, we shall refer to the accompanying diagrams which illustrate two embodiments thereof. This is done solely by way of illustrating the utility of our invention, and is therefore not to be regarded as a limitation upon the scope thereof.

Referring to the diagrams, Figure 1 represents a sectional elevation of a delay electric blasting cap in accordance with our invention, while Figure 2 represents a similar view of a military fuse head for an explosive shell, provided with a time ring fuse.

Referring particularly to Figure 1, the detonator comprises a base charge I in a ventless shell 2, said base charge being separated from the ignition composition 3 by the metal delay element Table 50 Metal used i iii mstl B mi a K on m to n ngspee ggggg g sec.lin.when Effect of B Example p composition on burning. is ltigdtedb in speed 55 Per- Per- 7 me u a A B ceiit celi nt :35 4 KA KB 2 3 8. 6 102. 5 Standard 1 2 2. 2 2680 D0. 1 1 3. 68 102. 5 224 Accelerate 1 2 6. 1 2680 307. 5 .Retard. 1 1. 13 10. 9 102. 5 35. 6 D0.' 1 1. 22 9. 1 102. 5 68. 2 D0. 2 3 10. 5 102. 5 65. 8 D0. 1 1. 14 11. 9 102. 5 21. 6 D0. 2 3 13. 2 102. 5 65. 8 Do.

From the foregoing table, .it will be seen that where a given metallicelement A is alloyed with another metallic element B, the burning speed of the composition comprising the resulting alloy will be greater than the burning speed of the composition comprising the unalloyed element A if KB is greater than KA. Conversely the burning speed will be slower, if KB is less than KA. Thus, by alloying antimony with bismuth, cadmium, copper or lead (Examples 5, 6', '7, 8 and 9 '4, theignition composition 5, and the priming composition 6. The metal delay element 4 is tightly packed with a slow burning substantially 'g'asless' composition 1 comprising 1.1 parts of plug I 0. The upper end of the shell 2 is closed by means of a waterproofing composition II and a sulfur seal [2.

The interval of time between the instant of firing the cap and the instant of detonation will, of course, depend on the length of the delay element 4. For example, a delay element may be used in the mannner above described, having a delay of 15.4 seconds, which is obtained with a maximum variation of 0.35 second. Since this maximum variation is considerably less than the interval between successive delays, no overlapping of the delays will be observed.

Referring now to Figure 2, the body of the fuse 20 is of conventional design and construction. Within the chamber 2| of the body 20, the usual magazine charge 22 is placed. The closing cap 23 is of any desired construction except that the usual venting aperture is omitted. Th time train rings 24 and 25 are of usual construction and are clamped in position a ainst the body 20 by the closing cap 23, which engages the threads on the extension 26 of the body 20.

- Washers 33 are provided so that the engagement is water-tight. The extension 26 is drilled out at the upper end to form a plunger-chamber for the plunger 21 and the firing pin 28, which is adapted to strike the percussion composition 29 in the end of the plunger 21.

When the firing pin 28 strikes the percussion composition 29, the flame is communicated through the passage 30 of the powder train 3|, carried by the time train ring 25. The powder train 3! in turn ignites the powder train 32 in the time train ring 24, the point of ignition being determined by the relative adjustment of the time train rings with respect to each other. The magazine charge 22 is fired by the powder train '32, and the former in turn fires the explosive charge contained in the shell proper.

The powder trains above referred to (l and 32) may comprise any of the delay compositions in accordance with our invention. Preferably, however, the composition consists of- 1.1 parts of potassium permanganate and 1 part of an alloy consistingof 50% antimony and 50% bismuth. Such a powder train burns with a slow, even speed, is readily ignited, and is not apt to burn out. Substantially no gas is evolved hence the rate of burning of the composition will not be appreciably affected by changes in pressure during the course of the shells flight.

In the foregoing description of our invention we have cited, by way of example, several compositions comprising an alloy and potassium permanganate. It is apparent that other oxidizing agents may be used in the same manner. Thus,

.for example, we may employ potassium chlorate or perchlorate, sodium dichromate, calcium peroxide, barium peroxide and the like as oxidizing agent. Permanganate is to be' preferred, however, since the composition burns more regularly,

and the products of combustion are substantially gasless under the conditions obtaining.

It is also apparent in the above description that other metals than those specifically cited may be alloyed with antimony in accordance with our invention. The effect upon the 'burn- Metal Oxide K Pb PM). 22. 2 r B1 BHO 33.6 Cu CuO 60. 9 C CdO 67. 1 Sbsbzoa- 103. 5 F8- Fe,0l 226. 0 MIL M1150: 285. 7 Al. A1103. 2600 Mg. MgO 3490 apparent from the foregoing description that the retarding or accelerating effects produced by alloying any element B with any other element A may be predicted on the basis of the disclosed principle. This may be conveniently accomplished by arranging a series comprising any desired number of metallic elements in the order of increasing value of the thermochemical constant K. In this series the effect of alloying anyelement A with any other element B may then be, readfly determined from the relative positions of the respective elements in the series. If B is above A in the series, the burning speed of the ignition composition comprising the alloy AB will be greater than that of the composition comprising the unalloyed element A. The converse will be true if B is below A in the series.

,As illustrative of this application of ourinvention, we may list the given metals, aluminum, antimony, bismuth, cadmium, copper, iron, lead, magnesium and manganese in the order of increasing value of K as in the following table. It will be understood that the heats of combustion of the different metals will be dependent on the degree of oxidation of the metal, where the formation of more than one oxide is possible. This in turn will be influenced by the oxygen balance of the composition. The oxide used as the means of calculation is designated in the table below.

In this series for example, a composition comprising Fe alloyed with Sb, Cd, Cu, Bi or Pb will have a slower burning speed than a similar composition comprising Fe alloyed with Mn, Al or Mg. Many other applications of our invention will be apparent to those skilled in the art. The method presupposes a proper control of oxygen balance in the preparationof delay compositions, by suitable proportioning of oxidizing agent and alloy. I

In the foregoing detailed description of our invention, we have illustrated its application to delay electric blasting caps and to time ring fuses. It is apparent, however, that our invention has many important applications besides those herein particularly described with reference to the diagrams. It is also apparent that many variations in detail may be made without departing from the spirit and scope of our invention. We therefore intend to be limited only in accordance with the following patent claims: We claim: '1. A delaydetonator wherein the delay element is charged with a delay composition of predetermined burning speed consisting of an oxidizing agent and a metal component comprising an alloy of antimony with at least one metal whose heat of combustion per unit volume is substantially different from that of antimony. 2. A delay-detonator wherein the delay'element is charged with a delay composition of predetermined burning speed consisting of an oxidizing agent and a metal component comprising an alloy of antimony with at least one metal whose heat of combustion per unit volume is greater than that of antimony.

3. The delay detonator of claim 2 wherein the metal alloy of antimony comprises iron.

4. A delay detonator wherein the delay element is charged with a delay co position of predetermined burning speed consisting of an oxidizing agent and a metal component comprising an alloy of antimony with at least one metal whose heat of combusion per unit volume is substantially less than that of antimony.

5. The delay detonator of claim 4 wherein the metal alloy with antimony is selected from the group consisting of bismuth, copper, cadmium and lead. 1

6. A delay detonator wherein the delay element is charged with a delay composition of predetermined burning speed consisting of nonexplosive ingredients including an oxidizing agent and an alloy of antimony with at least one metal whose heat of combustion per unit volume is substantially different from that of antimony.

'7. A delay detonator wherein the delay element is charged with a delay composition of predetermined burning speed consisting of nonexplosive ingredients including an oxidizing agent and an alloy of antimony with at least one metal whose heat of combustion per unit volume is greater than that of antimony.

8 A delay detonator wherein the delay element is charged with a delay composition of pre-- determined burning speed consisting of nonexplosive ingredients including an oxidizing agent and an alloy of antimony with at least one metal whose heat of combustion per unit volume is substantially less than that of antimony.

LAWTON A. BURROWS. WALTER. E. LAWSON.

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