US2127603A - Gasless igniter - Google Patents

Description

E. JONES GASLESS IGNITER Fild Dec. 19, 1934 Elwyn Jones INVENTOR.

AT TORNE Y.

Patented Aug. 23, 1938 UNITED STATES PATENT OFFICE GASLESS IGNITER.

Application December 19,' 1934, Serial No. 758,317 In Great Britain December 20, 1933 v10 Claims.

This invention relates to a device suitable in particular for igniting explosives of the burning or nondetonating type, for example gunpowder, and has for its object the provision of an improvedigniter which may be used with safety in fiery or dusty mines. More particularly an object of the invention is the provision of an improved igniter suitable for use with blasting cartridges which comprise an explosive of the kind described, the said cartridges having been rendered safe for use in fiery or dusty mines, for example by means of a sheath of borax.

Explosives of the burning or non-detonating type are customarily ignited by means of safety fuze, or by an electric powder fuze which contains a charge of combustible material ignited by means of an electric fuzehead. In each case the flame or spit from the'combustible material comes into direct contact with the explosive. The flame or spit from these devices is capable of igniting dangerous mixtures of methane and air or suspensions of coal dust, and hence the functioning of these devices when exposed in a mine is a source of danger which has hitherto hindered the development of safety explosives comprising black powder and the like.

According to the present invention a safety igniter suitable in particular for igniting explosives of the burning or non-detonating type, comprises an electric fuzehead and a quantity of combustible material sealed together'within a metal container, the arrangement being so adapted that the products ofcombustion of the said fuzehead and/or combustible material cannot escape therefrom, the temperature of a portion at least of the external surface of the metal container being raised, however, to a temperature sufflcient to ignite a blasting charge but insuflicient to ignite mixtures of air with methane or coal-dust. The attainment of a surface temperature of 300 C. is suflicient to ignite a blackpowder explosive, whereas a surface temperature of about 650 C. is required to ignite a methane air or coal-dust air mixture.

In the igniters of the present invention the products of combustion can come into contact neither with the explosive to be ignited nor with ignitable mixtures of air with methane or coaldust which may be present.

The fuzehead and combustible material employed are suitably of the kind yielding little or no gas on combustion. The metal container must be so adapted as to be capable of withstanding the pressure developed by any gas which is evolved, and even when substantially gasless materials are used itis desirable to leave a considerable free space above the combustible composition in order to minimize any rise in pressure which may occur as a result of the incidental amounts of gas usually generated.

The fuzehead may suitably comprise mixtures of finely divided zirconium with an oxidizing agent and in particular may comprise a mixture of finely divided zirconium and lead mono-nitroresorcinate.

The combustible material may, for example, comprise a finely divided metal together with an oxidizing agent and the following mixtures are suitable in particular for use in the invention. In each of the following combustible mixtures the ingredients are finely divided, e. g. to pass a 200 mesh sieve and uniformly mixed:-

Percent Red lead 87 Ferrosilican 13 Lead chromate 90 Calcium silicate 10 Zinc Potassium permanganate 40 Iron 30 Potassium permanganate '70 Tin 35 Lead peroxide Tin 40 Potassium permanganate 60 Magnesium 6 Barium peroxide 94 Calcium silicide 30 Red lead It will readily be understood by those skilled in the art that maximum temperature attained by the external surface of the container is influenced by a number of factors and that by suitable variation of these factors any temperature within reasonable limits may be arrived at.

Thus, for example in igniters having a constant ratio between thevolume of the heating charge and the surface in contact therewith, the maximum external surface temperature will tend to be increased by increasing (1) the calorific value of the combustible materlal;

(2) the density of the combustible material when loaded into the con ainer; or

(3) the thermal conductance of the walls of the container,

or vice versa. The maximum external surface temperature will tend to be decreased by and increase in (1) the thermal capacity of the container; or

(2) the thermal capacity of the combustible material or of its solid residue, or vice versa.

Any of the above conditions may be varied within suitable limits. In general, however, it is preferred to use a container of such dimensions and of sufficient length to afford a suitable area of maximum temperature to contact with the explosive. Caution must also be observed in varying the thickness of the metal container since if the thickness is made too small there is a risk that the walls may be melted with consequent failure of the purpose of the invention. The thickness and other variables of the container should also not be such as to provide an undue delay in the attainment of the maximum external temperature.

In order to vary the calorific value of the combustible material the proportions of the constituents may be altered, those materials in which the constituents are present in stoichiometric proportions having the greatest calorific value. Alternatively, the calorific value may be decreased by dilution with a non-volatile inert material.

The combustible material is introduced into the metal container under a moderate pressure sufficient to locate the charge securely in position. A common detonator loading pressure, e. g. 150 lbs. per square inch may be used, but

P preferably the loading pressures are lower than this and excessive pressures should be avoided, since the sensitiveness to ignition of the charge is thereby reduced.

The metal container may suitably be an ordinary copper detonator tube, but the container may be constructed of other metals or alloys which are non-combustible and of sumciently high melting point. The constructional material must also be generally serviceable and in particular must be capable of undergoing the customary crimping operation.

The igniters of the present invention are particularly useful, as already stated, for igniting burning explosives, for example, blackpowder. The said igniters, however, are also useful for initiating blasting devices of the kind comprising a charge adapted, on initiation, to generate gas, the said charge being enclosed together with the igniter in a pressure-resistant metal vessel adapted to release the generated gases at a sufficient pressure to cause a blasting effect in the borehole.

The invention is illustrated in the accompanying drawing, in which Figures 1 and 2 represent central longitudinal sections of two forms of igniter. In each form the igniter comprises a copper tube i closed at one end and partly filled with a charge of combustible material 2. A gasless electric fuzehead 3 with insulated leads 5 is sealed into the tube by means of a plug 6 constructed of lead or other deformable non-combustible material upon which the tube may be crimped to make a gas tight seal. When a metallic plug is used, ,the fuzehead may be insulated therefrom by means of a non-conducting incombustible washer i:

In the form of the invention illustrated in Figure 1 the lead plug is secured in a copper sleeve 0 which projects slightly beyond the end of the fuzehead. This sleeve is a push fit within the copper tube I, and on assembly it is passed down to make contact with the surface of the combustible material, thus ensuring that the fuzehead is close to the combustible material and at the same time projecting the fuzehead from damage by pressure. The outer tube l and the sleeve l are preferably crimped together after assembly.

In the alternative form illustrated in Figure 2 a shoulder is provided on the plug 6 in order to indicate when the fuzehead has been inserted to the correct distance.

The tubes may also be constructed of an alloy or metal other than copper, which does not burn with flame nor spark under blasting conditions.

Example A copper tube is employed 35 mm. long, 6 mm. internal diameter and having walls 0.2 mm. thick. A suitable charge for such a tube would be 0.75 gm. of a mixture containing 60% finely divided zinc and 40% potassium permanganate, pressed into the tube under a pressure of 60 lbs. per square inch. A fuzehead comprising zirconium and lead 2-mononitroresorcinate is positioned close to the composition, the free space between the top of the composition and the washer I being more than twice the internal diameter in length, and advantageously 20 mm.

Other combustible compositions may be substituted as described above. Considerable latitude in the amount of charge is permissible, amounts from 0.25 to 1.25 gm. being usually suitable in the above tube, but 0.5 to 1.0 gm. is preferred.

I claim:

1. A safety igniter for a blasting charge of defiagrating explosive, said igniter being free from bursting and detonating charges and comprising tion temperature of said charge, said charge being adapted to heat the outer surface of said container, without rupture of the walls thereof, to a temperature sumcient to ignite said blasting charge indirectly by heat transfer through the walls thereof, but insufficient to ignite a mixture of air with methane.

2. A safetyigniter for a blasting charge of defiagrating explosive, said igniter being free from bursting and detonating charges and comprising an electric fusehead and a substantially gasless combustion charge having a maximum combustion temperature lower than 650 C. enclosed in a 'ventless metal container having a fusion temperature above the maximum combustion temperature of said charge, said charge being adapted to heat the outer surface of said container, without rupture thereof, to a temperature exceeding about 300 C. but substantially lower than 650 0., whereby said blasting charge may beignited indirectly by heat transfer through the walls thereof without danger of igniting a mixture of air with methane.

3. The igniter of claim 2, in which said combustible charge comprises a metal forming a solid oxide at its temperature of combustion, and an inorganic salt having a high content of available oxygen.

4. The igniter of claim 2, in which said combustion composition comprises a metal and potassium permanganate.

said charge, said combustion charge being adapted to heat the outer surface of said con- F tainer, without rupture of the walls thereof, to

a temperature sufficient to ignite said 'blasting indirectly by heat transfer through the walls of said container, but insuflicient to ignite a mixture of air with methane.

7. The blasting assembly of claim 6, in which said defiagrating explosive comprises black powder enclosed ina sheath of cooling salts comprising borax.

8. "A safety igniter for a blasting charge ofdeflagrating explosive ,said igniter being free from bursting and detonating charges and comprising an electric fusehead and a substantially gasless (combustion charge comprising zinc and potassium permanganate having a maximum combustion temperature lower than 650 C, enclosed in a ventless metal container having a fusion temperature above the maximum combustion Patent No. 2,127,603.

e I Emmi JTONES.

is hereby certified that error appears in the printed specification temperature of said charge, said charge being adapted to heat the outer surface of said container, without rupture thereof, to a temperature exceeding about 300 (3. but substantially lower than,650 C., whereby said blasting charge may be ignited indirectly by heat transfer through the walls thereof without danger of igniting a mixture of air with methane.

9. A safety igniter for a blasting charge of "deflagrating explosive said igniter being free from bursting and detonating charges and comprising an electric fusehead and a substantially gasless combustion charge comprising zinc and potassium permanganate having a predetermined maximum combustion temperature below the ignition temperature of a mixture of 'air with methane, enclosed in a ventless, copper container having a fusion temperature above the maximum combustion temperature of said charge and having walls approximately 0.2 millimeter thick.

10. A safety igniter for a blasting charge of deflagrating explosive, said igniter being free from bursting and detonating charges and comprising an electric fusehead and a substantially gasless combustion charge comprising from 0.25 to 1.25 grams of a mixture comprising approximately 60% finely divided zinc and potassium 'permanganate having a maximum combustion temperature lower than 625 C. and enclosed in a ventless copper container having walls approximately 0.2 millimeter thick.

ELWYN JONES.

CERTIFICATE OF CORRECTION.

August 2}, 958- of: the above numbered patent requiring correction as follows; Page 3 first column, line it? claim 6, after the word "blasting" insert charge; and that the said Letters Patent shouldbe read with this correction therein that the same ma'y conform to.) the recorder the case in the "Patent Office.

Signedand sealed this 25th day of October, A. D. 1958;

(Seal) Henry vVan Arsdal'e Acting Commissioner of Patents.

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