US3075464A - Blast hole charge and charging method - Google Patents

Description

M. G. WOODLE ETAL BLAST HOLE CHARGE AND CHARGING METHOD Filed March 20, 1959 INVENTOR. MERLYN G. WOODLE RAYMOND J'. BERTIE BY %'4,W779 4 Z M ATTORNEYS MY x Jan. 29, 1963 rates atent dfilfiflh i Patented Jan. 29, 1963 free 3,975,464 BLAST HQLE HARGE AND (IHARGTNG METHQD Marlyn G. Woodie and Raymond 3'. Bertie, Babbitt, Minn, assignors to Reserve Mining Company, Silver Bay, Miriam, a corporation of Minnesota Filed Mar. 2d, 1%9. er. No. 8%,694 1 Claim. (Ci. lii223) The invention relates to the intimate mixing of a plurality of explosive ingredients in a blast hole, and particularly to a novel and improved explosive charge, and methods of charging a Wet blast hole in open pit mining practice.

While the invention can be used to advantage in any type of rock strata blasting involving the use of drill holes of substantial depth wherein a certain amount of water may be encountered (known in the art as Wet holes) it will be described with occasional reference to the mining of taconite, a so-called low grade ferrous metal ore existing in large quantities in the ore ranges in Minnesota. The taconite occurs in strata at or near the surface, the layers being substantially horizontal or at an acute angle to the surface. In such cases it is customary to make an initial or development cut of indefinite length, from which box cuts are blasted at spaced intervals along the sides of the development cut. Mining then proceeds from one box cut to the next, parallel to the development cut, the object of course being to shatter predetermined volumes from the vertical face of the development cut into fragments which can be loaded into trucks by power shovels. For greatest efiiciency a preponderating amount of the fragments should be small enough to be receivable in the throat of a rock crusher for further reduction in size.

For some time, in the art of blasting taconite in open pit mining, there has been extended use of ammonium nitrate with a carbon-containing additive such as a hydrocarbon oil or a carbonaceous material such as coal dust, or charcoal granules. Since these mixtures were not believed to be adaptable to wet holes it was necessary to substitute, below the water level, different and usually considerably more expensive charges such as desensitized gelatine or a non-cap-sensitive explosive surrounded by pellets of trinitrotoluol (TNT).

It was desirable however to provide an intimately mixed charge, and a method of securing it beneath the water level in a wet hole, and the attainment of this objective constitutes a major object of the present invention.

A further object of the invention is to provide a method of charging a wet blast hole with a homogeneously mixed, low cost, high density explosive load.

Another object of the invention is to provide a simple and eifective method of charging a wet blast hole, which is not necessarily limited to the use of Water soluble ingredients, but which permits the use of insoluble carbonbearing materials such as hydrocarbon oils, or anthracite coal dust, in preferred conjunction with ammonium nitrate, in the form of prills, for example, and conventionally termed prilied ammonium nitrate.

A further object or" the invention is to provide a method of charging a wet blast hole with ammonium nitrate in an amount sufiicient to provide a saturated aqueous solution of the ammonium nitrate in intimate association with a carbon-supplying substance, Whether soluble or insoluble.

A further object of the invention is to provide a method as defined in the last preceding paragraph and wherein the carbon-supplying substance is anthracite coal in comminuted form.

A further object of the invention is to provide a method of charging a wet blast hole with ammonium nitrate in aqueous solution in intimate association with a carbonsupplying substance of approximately the same specific gravity as that of the ammonium nitrate solution.

A further object of the invention is to facilitate achievement of the foregoing objects, including securement of an intimate mixture of the components of the explosive material, and solution of the soluble constituents, by discharge of a current of air beneath the liquid surface in the blast hole.

Other objects and advantages will be apparent from the study of the following description of several exemplifications of the invention, in conjunction with the accompanying drawings, in which FIG. 1 shows a previously-known charge distribution in a wet blast hole,

FIG. 2 shows a somewhat enlarged and fragmentary vertical section of a wet blast hole, and pictorially indicating a charging method in accordance with the present invention,

FIG. 3 shows a fragmentary vertical sectional view of the lower part of a wet blast hole showing another method and means of loading a charge, and

FIG. 4 shows an improved bottom end portion for a compressed air discharge line.

Referring first to FIG. 1 there is shown a hole loading arrangement previously used in a specific location in a taconite bed, involving a balst hol approximately eight or nine inches in diameter and about forty feet deep, and having a Water level, for example, at the broken line WW. The hole is preferably formed by a jet piercing tool known in the art and not necessary to describe here. This type of tool pierces the rock by directing a jet of high velocity flame around the base of the tool, heating and cracking the rock, and driving a stream of fine spalled rock fragments upwardly out of the hole. The tool advances at a steady rate, providing a hole of fairly uniform diameter, but the diameter may be increased, as in the chambered section 10, by holding the jet for a somewhat longer time than in the upper portion of the hole.

In the previous hole charging practice two cartridges 1]. and 12 of heavy density blasting agent, for example desensitized gelatin, each about two feet long and of a diameter such that it could pass through the hole, were loaded, end to end, into the chambered area, and free running bulk blasting agent such as pelletized trinitrotoluol was poured in to completely load the chamber. Three additional cartridges 13, 14 and 15 of heavy density blasting agent were placed in the column above the two in the chambered area. A primer load, or a heavy density cartridge with an inserted booster was placed at 16 and tied in with a Primacord detonating fuse. Primacord is a commercially available fuse which has a tremendously fast burning speed, around twenty thousand feet per second.

Above the cartridge 16, and above the water line WW as shown, the water was sealed off with three-inch to six-inch chunks of ammonium nitrate. Above this plug a certain latitude was permitted because the balance of the hole was dry, but in one advantageous arrangement a distance of approximately eleven feet was filled with ammonium nitrate prills 18 to which some hydrocarbon fiuid such as fuel oil had been added, followed by a primer cartridge 19. The remainder of the hole to within about two feet of its top was filled with oil treated ammonium nitrate prills 2.0. The top 21, two or three feet in height, was stemmed with any granular sandy or earthy material, or with tail-ings from the taconite beneficiation process. The primer cartridge 19 was tied in with the detonating circuit through the Primacord fuse above mentioned.

As heretofore indicated the presence of water in a wet hole imposed a restriction on the choice of explosive materials in the portion of the blast hole below the water level, including the bottom chambered portion. While ammonium nitrate is a relatively cheap and efiicient explosive when combined with a carbon-bearing compound, one of the cheapest of such compounds is carbon in the form of coal dust and this has been deemed not practical to use in a wet hole since it has not been possible to intimately mix it with an ammonium nitrate aqueous solution. Other ingredients, for example hydrocarbon liquids, are neither soluble in nor miscible in water, and will settle in layers dependent on gravity and charging methods.

In accordance with the present invention a method will now be disclosed forsimultaneously charging and homogeneously mixing or associating a mixture of ingredients to provide a relatively cheap and powerfully effective blasting compound, for example a suitable compound including ammonium nitrate, and sugar, starch, anthracite coal dust, or other carbon-containing solid.

Referring now to FIG. 2, an air pipe 24 (which may be flexible but i here shown as solid) is inserted do-wn-' wardly into the chambered portion 25 of the hole. The pipe 24' should reach to below the water level in the hole bottom, as shown. A stream of compressed air of moderate intensity, from a source (not shown) is passed through a flexible connector pipe 26, and down through pipe 24 withthe result that it bubbles through the water in chamber 25, and upwardly through the annular space 26 between the pipe and the blast hole wall. This annular space is filled'with water up to the'line W--W. The air current will be at a pressure suitably predetermined so that it agi-tates the'water but does not expel any water from the blast hole. The pressure of course will drop as the air issues from the relatively small pipe into the larger space outside the pipe.

While the air is thus being introduced to the water, the desired explosive compound, in mixed granular form, is poured, for example from containers 27', into the annular space 26, and it drops to the bottom into the water and into chamber 25. It has been determined that this procedure assures a homogeneous mixture of the'ingredients.

into an aqueous slurry which increases in solid consistency until the hole fills to the rising water level and becomes, so to speak solid-saturated, so that further charging pro-. cedure does not affect the mix. Soluble ingredients will of course dissolve gradually in the liquid up to the limit of' the liquids capacity to dissolve them. Ingredients such as insoluble or immiscible hydrocarbon fluids, or insoluble solids will not stratify since the air agitation effect will continue as long as the slurry has any mobility and 'beyond that point no stratification takes place.

The escaping air is at such low pressure that it will not interfere with the pouring procedure, and the pipe may be gradually raised as the liquid level rises so that its lower end remains beneath the surface of the slurry. The air current can be shut off and the pipe Withdrawn after the solid constituents build up to the water level. Detonating fuses, and primer cartridges may be inserted in the chambered portion prior to execution of the disclosed method, if such items are to be used in said chambered portion.

Above the water level any suitable charging arrangement can be used, for example that disclosed for use above the line W-..W' in FIG. 1.

FIG. 3 shows an embodiment in which we provide a flexible pipe 30 here shown as made of rubberlike material, having at its lower end a metal tip or nipple 31 several feet long. In this embodiment the carbon-bearing additive is anthracite coal dust. To minimize the possibility that the coal dust might be blown out of the hole, at least in part, if charged in particle form from open boxes or otherwise as shown in FIG. 2, the dust may be furnished in frangible sacks 33 which are dumped into the water. The sacks may be of material which deteriorates rapidly in water, or they may be fractured by rais- 4 ing and lowering the pipe 30 repeatedly to cut or tear the sacks. Another expedientis to dampen the coal dust before charging, although this might be a handicap if the coal dust is exposed to freezing conditions while sitting at ground level.

FIG. 4 shows a metal nipple provides with side perforations 34 which permit free air flow and uniform distribution even if the bottom of the nipple becomes clogged with high consistency slurry.

One of the advantages of the present method is that it can be used with any of the explosive mixture-s heretofore known in the blasting art, including both water-soluble and insoluble solids, and miscible or immiscible liquids. Some of these ingredients suitable for use (either single or in various combinations) with ammonium nitrate, are sugar, glucose, starch, coal, lampblack, charcoal, alcohol, TNT, fuel oil or other hydrocarbon oil.

Another of the definite advantages of the present invention resides in the fact that the presence of water in a blast hole does not restrict the choice of the-operator to materials miscible or soluble in water, but'the operator may use any ingredient indicated by the nature of the terrain to be blasted, in the light of economic considerations.

A preferred explosive mixture to be achieved is the combination of ammonium nitrate, which is a relatively cheap explosive ingredient, with a similarly cheap carbonbearing material which is either soluble in water, orif insoluble, which is of approximately the same specific gravity as a saturated solution of ammonium nitrate. Under either of these alternative conditions we have provided an explosive charge for a wet hole which will not stratify even if the charge is permitted to stand in the hole for twenty-four hours or more before it is detonated, particularly when the carbon-bearing material happens to be an insoluble solid such as anthracite coal dust, and when the air-agitation method as hereinabove described has been used.

While we are not limited to a specific depth ofwater in the hole we prefer to operate with a'water content such that no'excess water flows from the hole at the end of the charging step, and preferably the upper surface of the water should be beneath ground level. We have found that under'preferred conditions the water content should be such as to leave what we have previously termed a We have found that with the above described charging method the charge in the hole contains more ammonium nitrate and carbon bearing'additive than with previously known methods because the voids between solid particles are filled with saturated solution. 7

It would be entirely feasible to uniformly mix an explosive compound such as hereinabove described in comminuted form so that it could be introduced through the air pipe and carried below the liquid surface by the air current, or a slurry of the compound could be mixed at the surface and poured into the hole in the annular space beside the air pipe.

What is claimed is:

A method of charging a blast hole having water in a bottom end portion thereof, said method comprising introducing an air-carrying pipe into the hole so that its lower end portion is below the water surface, continuously discharging an air current downwardly through said pipe so that it escapes upwardly while agitating the water, and, while said air current is being thus discharged, pouring a previously compounded explosive mixture of granular ingredients in said hole in the annular space between said pipe and the inner wall of said hole, whereby said mix-. ture drops into the agitated water and forms with the water an intimately mixed aqueous slurry, so as to cause the slurry top surface to rise, and, while said surface is rising and said pouring continues, withdrawing said pipe upwardly in such manner that its lower and remains beneath but near the said top surface.

References Cited in the file of this patent UNITED STATES PATENTS McFarland -s Mar. 8, 1949 6 Lee et a1 Mar. 8, 1955 Nowak May 24, 1955 Aitchison et al May 15, 1956 Edgerton May 22, 1956 Rinkenbach et a1 Dec. 24, 1957 Streng et a1. May 28, 1958 Hradel Jan. 6, 1959 Kolbe Sept. 15, 1959 Lambert et a] Oct. 11, 1960

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