US2079777A - Safety igniter for blasting explosive devices - Google Patents

Description

May 1; 1937- J. TAYLOR ET AL ,0

SAFETY IGNITER FOR BLASTING EXPLOSIVE DEVICES Filed April 5, 1935 James Ta [or INVENTOR.

William 02m ATTORNEY.

Patented May 11, 1937 PATENT OFFICE SAFETY IGNITER FOB BLASTING EXPLOSIVE DEVICES James Taylor and William Young,

Saltcoats,

Scotland, assignors to Imperial Chemical Industries Limited, a corporation of Great Britain Application April 5, 1935, Serial No. 14,932 In Great Britain April 7, 1934 9Glaims.

This invention relates to igniters for blasting cartridges or borehole charges, and in particular to igniters suitable for non-detonating blasting charges or cartridges loaded' with non-detonating compositions, the said charges or cartridges being of the kind designed for use in fiery mines. The invention has for an object the provision of ign'iters which, if actuated when exposed in an atmosphere charged with methane, do not them- 10 selves cause ignition.

Non-detonating blasting cartridges or borehole charges are known which, when ignited in fiery atmospheres, do not cause ignitions of gas. However, the ordinary igniting devices such as electric fuseheads or safety fuse are themselves liable to cause such ignitions and consequently the assembly, at the working face, of a blasting charge with such igniting devices is not free from danger. According to the present invention a safety lgniter for non-detonating safety blasting cartridges or borehole charges comprises a container,

9. charge of a low-temperature-reaction material, means for initiating the said charge, and a screen adapted to intercept the productsof combustion of the fusehead but adapted to permit of the ejection of the products of combustion of the charge.

The function of the screen is to prevent the products of combustion of the initiating device, 80 which is preferably a substantially gasless electric fusehead, from escaping from the container until they have been cooled to such an extent as to be incapable of igniting a fiery atmosphere. The partially or wholly reacted products of combustion of the low-temperature-reactive material escape freely during the combustion thereof and after the cooling of the fusehead combustion products.

The container may conveniently take the form 40 of a metal tube having a fusehead sealed into one end in ignition contact with a charge of lowtemperature-reactive material, which charge is provided with a longitudinal passage connecting with an aperture at the other end of the tube in order to permit of the products of the combustion of the charge being vented. The charge is preferably arranged in annular form to leave a central channel or passage.

The screen may, if desired, take the form of a temporary seal of incombustible material, e. g. fireproofed waxed paper, which covers the aper-. ture in the container and is strong enough to prevent the escape of the products of combustion of the fusehead, but which is ruptured by com-' bustion of the charge. In order to prevent the risk of damage to the screen it is preferred, however, to locate it in the interior of the container and when a channelled charge is provided between the fusehead and the aperture of the container the screen may suitably be located be- 6 tween the fusehead and the charge. A screen so positioned may be adapted not only to intercept the products of combustion of the fusehead but also to transmit the ignition of the fusehead to the charge. Thus, for example, the screen may 10 assume the form of a thin heat conducting film, e. g. of metal, but it is preferred to employ a coherent layer of a low-temperature-reactive material of a nature similar to that employed for the charge. If desired, an additional screen, 15 e. g. of waxed paper, may be provided over the aperture of the container and in this case it is not essential that the screen between the fusehead and the charge should contain only incombustible or low-temperature-reactive ingredi- 20 cuts. The container is preferably constructed of a safe metal, e. g. copper, and should, be strong enough to resist deformation by actuation of the device. The fusehead employed is preferably of the gasless type, for example of the kind de-. scribed and claimed 'in pending application No. 753,778, and is located and sealed within the container in known manner, for example as in the manufacture of electric detonators. 30

By the term low-tempcrature-reactive material we mean a material which is capable of undergoing combustion or exothermic reaction at a relatively low temperature such that the products of the combustion or reaction escaping 35 from the tube are sufliciently hot to ensure ignition of the blasting charge with which the igniter is associated, but are incapable of igniting fiery atmospheres if the igniter is actuated when exposed to them.

The charge may comprise or consist of a single reactive substance or a mixture of such substances. The charge may also comprise a mix ture of one or more highly oxidizing salts with combustible substances with or without the addi- 5 tion of cooling and phlegmatizing agents. Thus, for example, the following materials are suitable for use in the present invention:

(1) Ammonium dichromate.

(2) Mixtures of sodium nitrite with ammonium 5o chloride or ammonium sulphate. Small proportions of stabilizing substances are'suitably included in these mixtures, such for example as sodium carbonate. The charges of this nature described in pending application No. 712,050 are 55 particularly suitable for the purposes of the present invention.

(3) Mixtures of charcoal with oxidizing salts such as ammonium nitrate and/or other nitrates and cooling salts such as alkali chlorides or carbonates or other ammonium salts. These mixsuch proportions that the product is a balanced combustible composition. The proportion of cooling salts should not exceed 50% of the total weight of the ingredients. If desired, small proportions of inert materials may be added such for example as china clay or French chalk.

(4) Mixtures of an oxidizing salt such as potassium chlorate or nitrate with resinous materials, filling materials such as powdered glass, metallic oxides and a binding agent, for example glue. These mixtures may suitably be produced in the form of a uniform compact mass by incorporating in the presence of water and subsequently drying.

(5) Mixtures of blackpowder with a binding agent having a cooling eifect such as shellac and, if desired, cooling salts, e. g. borax. Uniform and compact charges may be formed by dissolving shellac in alcohol and incorporating the blackpowder and the cooling salts into the solution until a uniform product is obtained on drying.

(6) Any of the mixtures set forth in the above classes 3, 4 and 5 including also a proportion of finely divided metal such as iron filings.' The highly exothermically reacting metals such as magnesium, zirconium or aluminium are not suitable for the purpose of the invention.

Where charcoal is employed as an ingredient, it may be rendered less liable to burn with flame by impregnation with solutions of fireproofing salts such as ammonium sulphate or ammonium phosphate or mixtures thereof, and subsequent drying.

Preferably we employ a mixture of blackpowder, charcoal, iron filings and a cooling phlegmatizing binding wax, preferably of a not readily inflammable type, such as tetrachloronaphthalene, When the igniter is designed for use under such conditions that it may not be in direct contact with the blasting charge, or when the charge is relatively difficult to ignite, a considerable proportion of iron filings is advantageously incorporated in the low-temperature-reactive composition since a powerful jet of hot iron oxide particles is thereby obtained ensuring initiation of the blasting charge over a considerable area. Conditions such as described may occur when the igniter is used in conjunction with a' blasting cartridge of the venting type in which the charge space is not completely filled, as described for example in pending application No. 712,050. When, however, the blasting charge is relatively easily ignited and has arelatively high velocity of propagation, as for example in a sheathed blackpowder pellet, the iron filings may be reduced in amount or even omitted.

A preferred form of the invention will now be described with reference to the accompanying drawing which represents a longitudinal section through an igniter constructed in accordance with the invention. A copper tube l is provided at the base with an aperture 2 and contains a charge 3 consisting of a low-temperature-reactive composition pressed into position and provided with an axial channel I. Abovethe charge is placed a screen 5, which consists of apressed disc, of material similar to that of the main mixture.

charge. A gasless fusehead 6 and lead-in wires Ill are located in known manner in a fireproofed paper tube 8 with a polychloronaphthalene wax filling 9. The fusehead assembly fits into the tube l above the disc 5 and is retained in position by crimping the wall 01' the tube 1. The aperture at the discharge end of the igniter is sealed, e. g. with a wax such as tetrachloronaphthalene, or with a disc of thin metal foil or fireproofed The action of the igniter is as follows:

When the fusehead 6 is fired, the initial spit is arrested by the disc 5, which is, however, ignited by the products of combustion of the fusehead and ruptured, whereby the ignition is transferred to the main charge. The disc 5 thus prevents the emergence of any fusehead combustion products while they are still sufficiently hot to ignite fiery atmospheres even in the absence of a closure at the base aperture 2. The pressure generated by the combustion of the charge 3 ruptures any seal covering the aperture 2, and the combustion products of the main charge are then free to escape from the tube. While the charge combustion continues, a powerful jet is obtained which is capable of igniting the blasting charge but incapable of igniting fiery atmospheres.

The invention is further illustrated by the following examples.

Example 1 This example describes an igniter suitable for use in cartridges of the venting type as described and claimed for example in applications Nos. 112,050, 712,051 and 712,052. I

Eight parts by weight of acid free chlorinated naphthalene wax, melting point 93 C... are dissolved in carbon tetrachloride. Twenty parts of mealed blackpowder, one part of ground charcoal, and two parts of powdered potassium bicarbonate are successively stirred into the solution until a uniform composition is obtained. Finally, fifteen parts of iron filings are incorporated. The mixture. is carefully dried at a suitable temperature to remove the carbon tetrachloride, and is then powdered.

The igniter is then formed in the manner above described with reference to the accompanying drawing. A copper tube 55 mm. long and 8 mm. internal diameter, suitably of the material and thickness of the tube used in a No. 8 detonator, is provided with a. hole at the base 3 mm. in diameter, and is loaded under pressure with about 4 gm. of the above composition to a depth of 35 mm. from the base, a central channel of 2 mm. diameter being formed axially in the charge during this operation.

A screen composition is made up by incorporating parts by weight of mealed gunpowder, 6 parts of chlorinated naphthalene wax, and 5 parts of charcoal by a solution process as already described. A pressed disc, 1 mm. thick, of this material is placed above the charge in the tube." The construction of the igniter is completed by crimping a gasless fusehead into the head of the tube in known manner.

Igniters constructed as described were tested in a gallery containing a 9% methane in air In six trials, no ignitions were obtained.

Example 2 explosive, e. g. a sheathed blackpowder pellet as described and claimed in application of White and Jones, Serial 136,752 filed July 24, 1934.

A No. 6 detonator size copper tube, mm. by 6 mm. internal diameter, is provided with a 2 mm. aperture at the base. The charge is 0.45 gm. of a mixture prepared as described from 20 parts by weight of mealed gunpowder, 8 parts chlorinated naphthalene wax, 3 parts charcoal, and 10 parts iron filings. The screening disc was 0.05 gm. in weight, 6 mm. diameter and 1.2 mm. thick, and of the same composition as the disc used in Example 1.

We claim:

1. A safety igniter suitable for us in the presence of fire-damp, with non-detonating safety blasting cartridges or borehole charges, said igniter comprising a base charge of low-temperature-reactive material capable of initiating said non-detonating safety charge but incapable of igniting fire-damp, means for initiating said base charge, and means for preventing the combustion products of said initiating means from igniting fire-damp.

2. A safety igniter suitable for use, in the presence of fire-damp, withnon-detonating safety blasting cartridges or borehole charges, said igniter comprising a base charge of low-temperature-reactive material capable of initiating said non-detonating safety charge but incapable of igniting fire-damp, means for initiating said base charge, and means for cooling the combustion products of said initiating means to a temperature sufllcient to ignite said base charge but insuflicient to ignite fire-damp.

3. The safety igniter of claim 2, in which said base charge, initiating means, and cooling means are enclosed in a container provided with an aperture through which the combustion products may be ejected.

4. A safety igniter suitable for use, in the presence of fire-damp, with non-detonating safety blasting cartridges or borehole charges, said igniter comprising a container provided with an aperture through which the combustion products may be ejected, a channeled base charge of low-temperature-reactive material capable of initiating said non-detonating safety charge but incapable of igniting fire-damp, means for initiating said base charge, and a screen adapted to intercept the combustion products of said initiating means whereby said combustion products are cooled to a temperature sufilcient to ignite said base charge but insuflicient to ignite fire-damp.

5. The safety igniterof claim 4, in which said.

screen comprises a coherent layer of low-temperature-reactive material, said screen being located between said initiating means and said base charge.

6. A safety igniter suitable for use, in the presence of fire-damp, with non-detonating safety blasting cartridges or borehole charges, said igniter comprising a container provided with an aperture through which the combustion products may be ejected, a channeled base charge of lowtemperature-reactive material comprising a combustible ingredient and an oxidizing salt and ca- .pable of initiating said non-detonating safety charge but incapable of igniting fire-damp, means for initiating said base charge, and a coherent layer of low-tempcrature-reactive material 10- catedbetween said initiating means and said base charge and adapted to cool the combustion products of said initiating means to a temperature suificient to ignite said base charge but insuflicient to ignite fire-damp.

7. The safety igniter of claim 6, in which said low-temperature-reactive material comprises sodium nitrite and a compound selected from the group consisting of ammonium chloride and arm monium sulfate.

8. The safety igniter of claim 6, in which said low-temperature-reactive material comprises black powder and a cooling, phlegmatizing, and incombustible wax.

9. The safety igniter of claim 6, in-which said low-temperature-reactive material comprises black powder, charcoal, iron filings, and a cooling phlegmatizing, and incombustible wax.

JAMES TAYLOR. WILLIAM YOUNG.

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