US1918920A - Ignition composition - Google Patents

Description

.July 18, 1933'. H, A, I Ewls 1,918,920

A IGNITION COMPOSITION Filed Aug. 8. 1930 11u11 FIClZ Harold/Iw, Ima@ tion is fired in which the priming HAROLD A. LEWIS,

s garant naaien NEMOURS @c COMPANY, WARE 0F WOODBURY, NEW XERSEY, SSGNOR TO E. DU' lONT 'DE OF WELMINGTON, DELAWARE, A GOREOBATION OF DELA- renrrrou conrosrfrron Application led August 8 1930. Serial No. 534,016.4

This invention relates to ignition compositions, and more particularly to improved ignition compositions comprising a sulphocyanate, an oxidizing agent, and a low flashpoint fuel, as ignition materials for blasting zps, squibs, igniters,fmatch heads, and the Ignition compositions of the type covered by this invention have numerous applications. One use is as a loose charge in electric blasting caps in which the ignition composiby the heat 0f an incandescent Wireembedded in the loose charge; an elec.- tric blasting cap embodying this improvement is disclosed and claimed in my co-'pendin application Serial No. 3417 ,915 led March 18, 1929, issued as Patent No. 1,797,- 509, March 24, 1931, of which this application is a continuation in part. A second use is as a loose charge in electric squibs which are completely enclosed by a metallic shell, a paper container, or the like, in which case, also, the ignition is caused by the heat of an incandescent Wire embeddedi in said loose charge. v so-called match heads; in thiscase the ignition material may be cemented to the firing bridge Wire by forming the ignition composition into a paste With various solvents, and if desirable, it may be subsequently covered and Waterproofed by solutions of nitrocellulose and the like. A fourth and important application of my invntion is in blasting caps generally, and more particularly in composition blasting caps. Here these ignition compositions may be employed in detonators4 containing inner capsules in order to hide the expose an increased ignition area to the spit of the igniting fuse, or they maybe employed in non-capsule caps,

charge comprises a material which is diiiicultly ignitable.

As commonly manufactured a composition i blasting cap-comprises a metallic shell `consecondary detonating taining a charge of compound in its base, of a primary detonatin gether with a charge o and above this a charge composition, toignition material i either mixed with, or superimposed upon,

said primary detonating composition.V Sevv for the u purpose.

A third use 1s 1n igniters and/oreral metals and alloys have been in common use for the manufacture of these shells, notably aluminum and gilding metal (copperzinc) As secondary detonating compounds tetranitromethylaniline (tetryl), pentaerythrite tetranitrate, trinitrotoluene, and picric acid have been in most general use, although others, such as erythritol tetranitrate, hexanitrodiphenylamine, and mixtures of any of these materials are altogether satisfactory rlhese materials may be pressed or cast into the metallic shells. Mert cury fulminate, either alone or mixed With an oxidizing agent such as potassium chlorate, and lead azide have been most frequently employed as primary detonators. Inner capsules are often employed with both of these materials in order to add connement and hence eiiiciency of action to these primers;

With mercury fulminate primed caps containing capsules, a common ignition composition is a mixture of fulminate and potassium chlorate in the ratio of parts to 35 parts. With lead azide in both capsules and non-capsule caps the normal or basic lead salts of styphnicand picric acids have been in most general use. In addition, a mixture of a sulphocyanate such as lead sulphocy'anate and anvoxidizing agent such as potassium chlorate or perchlorate, proposed in lead azide primed caps.

All of the ignition materials heretofore used have distinct and Well known disadvantages. Mercury fulminate is an expensive compound and its mixtures are objectionable because of high cost. Furthermore, as prepared commercially, this compound almost invariably contains free mercury Which amalgamates with certain cap shell metals,

notably aluminum; aluminum shell fulminate has heretofore been these materials arelikewise expensive. Mixtures of sulphocyanate and oxidizing agents such .as chlorates and perchlorates have an undesirably high Hash point, low total heat of combustion, and slow, uneven rate of burning.

One object of my invention is to provide an ignition composition which is relatively insensitive to shock, friction, and static electricity. Another object is-to provide such a composition which is more satisfactory for use in shells made of the metals or other .materials'customarily used for the manufacture of blasting caps. A further object of my invention is to provide an ignition composition having the above properties and at the same time possessing relatively low flash point, high heat of combustion, and regular rate of burning. A still further object of my invention is to provide a less expensive ignition composition than heretofore used.-

I have discovered that an improved ignition composition, fulfilling the objects of my invention as above stated, may be obtained by the use of a mixture of a sulphocyanate, an oxidizing agent, and a low flash point fuel. I have found lead sulphocyanate to be a satisfactory sulphocyanate, although others, such for example as copper sulphocyanate, may be used. Potassium chlorate is a very suitable oxidizing material for use in my composition, although'other agents such as potassium perchlorate, barium nitrate, red lead, etc., may be employed. I have found nitrocellulose, or pyro powder, and particularly that ground to pass a 100 mesh sieve, to be an altogether satisfactory fuel of low ignition point. In addition to other nitric esters, such as nitrostarch, the salts of cervtain organic acids, such as the lead salts of styphnic and picric acids, may be used as By way of further illustrating my invention, I give the following composition for my ignition material. It will be understood, however, that this invention is not limited to the materials or proportions given below, and that this example is merely illustrative Percent v Lead sulphocyanate 30-50 Potassium chlorate 10-30 Ground pyro powder 30-40 A composition comprising the above materialis decidedly cheaper than fulminate mixtures, the lead salts of styphnic or picric acids, or eventhe plain mixture of lead sulphocyanate and potassium chlorate, this latter being true since by-product pyro powder dust is entirely satisfactory for replacing a portion of the sulphocyanate, which must be manufactured from relatively high cost ingredents. Furthermore, the addition of pyro to sulphocyanate-chlorate mixtures gives a product of lower density, and hence smaller quantities are necessary in order to provide the desired binding and ignition charge; an important result is increased economy in the use of these compositions. Such a composition is much less sensitive to shock and friction than materials heretofore proposed for this purpose; it has been found that this composition containing as much as 10% of abrasive materials, such as ground glass or ground quartz, is less liable to detonate from impact of a falling body than fulminate mixtures or lead styphnate containing no abrasive. These mixtures have been found to be compatible with the several metals which have been used for the manufacture of blasting caps, namely gilding metal, brass, aluminum,copper nickel, and steel. They have also been found to have a liash point, as determined by the current necessary to lire with a ho't wire, which is essentially equal to that of mercury fulminate mixtures. Furthermore, by incorporating the low iash point fuel into the sulphocyanatechlorate mixture, it has been found that the total heat of combustion is thereby increased and the rate of burning, as determined in a standard burning bar test, is thereby made more rapid and regular.

As further examples ofthe use of my composition there is shown diagrammatically in the attached sketch two blasting caps, Figs. l and 2. The cap shown in section in Fig. 1 comprises a metallic shell a, a base charge of tetryl b, a priming charge of mercury fulminate potassium chlorate mixture c, a confining inner capsule d, and a pressed charge of my ignition mixture e. In this cap the ignition mixture is used primarily to increase the igniting surface to be exposed to the spit of fuse customarily used with these caps and to transmit the iiame from the fuseto the primer charge through the small opening in the confining capsule. The cap shown in section in Fig. 2 comprises a metal shell a, a base charge of tetryl-b, a primer charge of lead azide c, and a charge of my ignition composition d. In this case the ignition material functions as a binding and ignition agent for lead azide; this is a particularly important usesi'nce it has long been known that lead azide is unsatisfactory for use in blasting caps except as it is provided with a binding and ignition agent.'

It will be apparent from the foregoing that various embodiments of my invention exist and may be practiced within the scope of my (invention, and it is to be understood that I do not intendto be limited except as indicated in the following patent claims.

I claim: v

1. lAn ignition composition as the top charge in a composition blasting cap containing a charge of a secondary detonating compound anda priming charge, said top charge comprising sulfocyaaate, an oxidizing agent and a solid low ignition point fuel.

2. An ignition composition as the top charge in a composi'fon blasting cap containing a char-ge of a secondary detonating compound and a priming charge, said top charge comprising sulfocyanate, an oxidizing agent and ground pyro powder.

` 3. An ignition composition as the top charge in a composition blasting cap containing a charge of a secondary detonating compound and a priming charge, said top charge comprising sulfocyanate, potassium chlorate, and ground pyro powder.

4. An ignition composition as the top charge of a composition blasting cap comprising a mixture of 30-50% lead sulphocyanate,

10-30% potassium cblorate, and 30-50% of ground pyro powder.

5. An ignition composition as the top charge in a composition blasting cap containing a charge of a secondary detonating compound, a priming charge of lead azide, said composition comprising lead sulphocyanate, potassium chlorate, and ground pyro powder.

6. An ignition composition as the top charge in a composition blasting cap containing a charge of a secondary detonating compound, a priming charge of lead azide, said composition comprising 50% lead sulphocyanate, V10-30% potassium chlorate and SSO-50% ground pyro powder.

- HAROLD A. LEWIS.

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