US2128576A - Blasting explosive cartridge or borehole charge - Google Patents

Description

Patented Au 30,1938

BLASTING EXPLOSIVE CARTRIDGE OR BOREHOLE CHARGE Albert Greville- White, Saltcoats, Scotland, as-

signor to Imperial Chemical Industries Limited, a corporation or Great Britain No Drawing. Application December 11', 1935,

Serial No. 54,855. 22, 1934 f 10 Claim.

This invention relates to blasting explosive cartridges or borehole charges suitable for use in quarries and non-fiery mines,

According to the present invention a composi blasting cartridge or borehole charge comprises in juxtaposition a continuous charge of a buming explosive having a relatively high rate of combustion, e; g. black powder, and an exother mic power-producing combustiblemixture'having a rate of combustion lower than that of the said burning explosive and comprising a carbonaceous combustible material and an inorganic oxidizing agent.

It will be understood that the terms burning explosive and combustible mixture" are used hereinafter ,for convenience in order to distinguish the two components of the composite charges of the invention. These terms are not mutually exclusive; thus, for example, the exothermic combustible mixture may itself be a burning explosive adapted for blasing purposes, but insofar as such a composition isv employed in the invention it is essential that it should be associated in the manner described with another burning explosive having a higher rate of combustion. C

The charge of burning explosive is conveniently employed in the form. of a core extending throughout substantially the whole length of the cartridge, the combustible mixture being arranged around the core in the form of a sheath or annulus. Alternatively, the burning explosive may form the annulus surrounding, a core of the combustible mixture. In either modification, since the continuous charge of burning explosive extends throughout substantially the whole ,length of ,the cartridge or charge, the ignition is readily transmitted from the faster to the slower burning composition.

The burning explosive employed in the present invention may be any such explosive as is commonly used or suitable for blasting purposes. The preferred explosive, however, is black powder and this may conveniently be employed in the form of a compressed pellet and the com bustible mixture may, if desired, be compressed i also be prepared by retaining the-charges of a rate.

In Great Britain, December ,burnlng explosive and of combustible mixture in juxtaposition by means of appropriate wrappings.

The relatively slow burning combustible mixture employed in the present invention preferably consists of a mixture of charcoal or wood- 5 meal with ammonium nitrate and/or an alkali metal perchlorate and/or ammonium perchlo- The salts mentioned are particularly valuable on account of the high power value of compositions containing the same. The mixtures de- 10 scribed may, if desired, be made by impregnating a carbonaceous ingredient such as woodmeal with concentrated aqueous solutions of the oxidizing salt or salts, and drying. The product may subsequently, if necessary, be mixed with a further quantity of one or more oxidizing salts and may then be pressed around a core consisting of a black powder pellet. The ingredients,- however, may usually be mixed together in the dry way. As the slow burning combustible mixture there may also be used a mixture of the ingredients used in the manufacture of black powder, such mixture having been lightly incorporated and not having undergone the full milling and granulating processes which are an essential feature of the manufacture of black powder itself. It is also possible to employ sodium nitrate black powder which is characterized by a lower-rate of combustion than black powder manufactured with potassium nitrate. Similarly a lightly incorporated mixture of the ingredients of sodium nitrate black powder may be used.

If desired, other ingredients may be employed to assist in forming the slow burning combustible mixture into a coherent. product, for instance, wax, hydrocarbons, ultra-hydrocarbons, resins and the like.

It will be understood that the composition of the combustible mixture may also include minor proportions of other ingredientssuch assensitiz- 40 log ingredients, and it is sometimes desirable to "include a proportion of waterproofing agents amongst the carbonaceous materials. For this purpose resins and waxes are particularly useful besides enabling the mixture to be moulded whether bypartial fusion or with the aid of pressure. 3

It will be understood that the composition of the combustible mixture will usually be arranged so as to avoid noxious gases; thus where am monium perchlorate is used it is often convenient to employ in addition a proportion of an alkali nitrate.

The proportion of the burning explosive to the relatively slow burning combustiblemixture may depend upon the extent of the free space in the borehole, since the rate of propagation of the ignition through the slow burning constituent will in general be very much accelerated once a moderate pressure has been built up, and in order to facilitate the rapid building up of such a moderate pressure, the proportion of the buming explosive should be substantial. Excellent results have been obtained with a ratio of burning explosive to combustible mixture ranging from about 1:2 upwards.

The invention is further illustrated by the following examples, in which the parts are parts by weight:-

Example 1 Example 2 A pellet made from the product obtained by lightly milling the ingredients of a normal blackpowder, for about one third of the usual period was introduced as a core into an annular cylindrical pellet of blackpowder provided with a suitable recess for the fuse; the core and the annulus being of approximately equal weight.

The present invention renders it possible to employ for blasting purposes composite cartridges or charges containing a considerable proportion ample in respect of cost, convenience and ease of manufacture. Thus the combustible mixtures may in certain cases contribute morepower than an equivalent quantity of the burning explosive similarly located in the cartridge or borehole charge. For example, mixtures of carbonaceous material with ammoniumnitrate or perchlorate or alkali metal perchlorates in amount at least sufiicient to afford a satisfactory oxygen balance may be utilized in a composite cartridge in the manner of the invention, and the resultant cartridge is characterized by'a greater power value than a cartridge of equal weight consisting of the burning explosive alone. Furthermore, the invention renders it possible to use as constituents of the composite charge or cartridge, compositions not normally suitable form for blasting purposes, e. g. a mixture of blackpowder ingredients, which has been prepared in a simple manner and without the exhaustive processing necessary in the manufacture of blackpowder.

As the burning explosive for use in the present invention I may use any suitably prepared mixture of one or more highly oxygenated salts with one or more carbonaceous materials and with or without other combustiblefingredients such for example as sulphur. Suitable salts are the nitrates, chlorates or perchlorates of the alkali metals, or ammonium perchlorate. Suitable carbonaceous materials are charcoal, carbon black, woodmeal, carbohydrates such as starch or sugar or lwdrocarbons such as naphthalene. It is to be noted'that the use of carbohydrates or wax-like hydrocarbons cause a reduction in the burning speed of the composition.

In order to illustrate the invention the properties of a number of compositions are set out in the following table:

Comparrative values Oomposi- V fi tion by zfi Maximum Time of weight pressure burning uced of given y given charge in V charge given space Percent 4 1 Pomsiiium perchlorate 80. 6 Well milled and 1. 7 0. B

granulated. Charmal 19.5 2 Ammonium perchlorate 78 Well milled and 3. 0 0. 9

/ granulated. Charmin] 22 3 N. P. blasting blackpowder (standard)- W611 muil igd 1- 0 l. 0

- n a N. s. blasting blackpowder.- ell milled and i. 1 3.0

granulated. 5 Ammonium perchlorate 78 Ground, mixe 3. 0 3. 0 U and grannlated. Chm-01ml c N. B. blackpowder composition Ground, mixed 1.1 16.0

. 113d granulate 7 Ammonium nitrate 91 Ground, mixed 2.7 30.0

egd granulate Charcoal 9 of exothermic combustible mixtures which are themselves characterized by a rate of combustion which is either too low to afford satisfactory results when such mixtures are used as blasting explosives or even too low to permit of their use for such purposes at all. The composite cartridges or charges have a rate of combustion comparable to the relatively high rate of combustion of the burning explosive which forms an integral part thereof. The possibility of using relatively slow burning combustible mixtures for blasting purposes presents advantages, for ex- In forming the composite cartridges of the present invention I may associate a relatively fast with a relatively slow burning composition as set out in the above table. Thus for example I may associate two charges of equal weight of compositions numbers 3 and 7. The maximum pressure developed by this composite cartridge amounts to about 1.8 measured .on the same scale as in the foregoing table, while the burning time similarly is only slightly greater than 1.0 which is the period for the fast burning composition number 3. Thus the composite charge is more .a composite cartridge may be made from a mixture of numbers 4 and 6, in which the expense of intensively milling the blackpowder ingredient may be avoided without a consequent loss of efliciency.

It is to be noted that materials numbers 6 and 7 are useless for blasting purposes when employed separately under most ordinary blasting conditions.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiment thereof except as defined in the appended claims.

I claim:

1. A composite blasting cartridge or borehole charge comprising in juxtaposition a continuous charge of a relatively faster burning explosive having a relatively high rate of combustion, and

a charge of a relatively slower burning exothermic power-producing combustible mixture having a rate ofcombustion lower than that of the said faster burning explosive and comprising a carbonaceous combustible material and an inorganic oxidizing agent.

2. The composite blasting cartridge or bore-- hole charge of claim 1 wherein the burning explosive is blackpowder.

3. The composite blasting cartridge or borehole charge of claim 1, wherein the inorganic oxidizing agent comprisesammonium nitrate.

4. The composite blasting cartridge or borehole charge of claim 1, wherein the inorganic oxidizing agent comprises amonium perchlorate.

5. The composite blasting cartridge or borehole charge of claim 1, wherein the inorganic oxidizing agent comprises an alkali metal perchlorate.

6. The composite blasting cartridge or bore-.

hole charge of claim 1 wherein the exothermic combustible mixture comprises a lightly incorporated mixture of ammonium nitrate and a carbonaceous material.

7. The composite blasting cartridge or borehole charge of claim 1 wherein the exothermic combustible mixture consists of incompletely incorporated blackpowder ingredients.

8. The composite blasting cartridge or borehole charge of claim 1, wherein the exothermic combustible mixture consists of a carbonaceous ingredient impregnated with the inorganic oxidizing agent.

9. The composite blasting cartridge or bore hole charge of claim 1 wherein the burning explosive is arranged as an annulus around a core of the exothermic combustible mixture.

10. The composite blasting cartridge or borehole charge of claim 1 wherein the exothermic combustible mixture is arranged as-an annulus round a core of the burning explosive.

ALBERT GREVILLE WHITE.