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Патент USA US3075474

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Jan. 29, 1963
Filed March 20, 1959
%'4,W77��) ZM
? atent
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. r. No. 8%,694
Patented Jan. 29, 1963
supplying substance of approximately the same speci?c
gravity as that of the ammonium nitrate solution.
A further object of the invention is to facilitate achieve
ment of the foregoing objects, including securement of an
intimate mixture of the components of the explosive ma
terial, and solution of the soluble constituents, by dis
charge of a current of air beneath the liquid surface in
the blast hole.
The invention relates to the intimate mixing of a plu
Other objects and advantages will be apparent from the
rality of explosive ingredients in a blast hole, and particu 10 study of the following description of several exempli?ca
larly to a novel and improved explosive charge, and
tions of the invention, in conjunction with the accom
methods of charging a Wet blast hole in open pit mining
panying drawings, in which
FIG. 1 shows a previously-known charge distribution
1 Claim. (Ci. lii2?23)
While the invention can be used to advantage in any
type of rock strata blasting involving the use of drill 15
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
in a wet blast hole,
FIG. 2 shows a somewhat enlarged and fragmentary
vertical section of a wet blast hole, and pictorially indi
cating a charging method in accordance with the present
FIG. 3 shows a fragmentary vertical sectional view of
metal ore existing in large quantities in the ore ranges in 20 the lower part of a wet blast hole showing another method
Minnesota. The taconite occurs in strata at or near the
and means of loading a charge, and
surface, the layers being substantially horizontal or at an
FIG. 4 shows an improved bottom end portion for a
acute angle to the surface. In such cases it is customary
compressed air discharge line.
to make an initial or ?development? cut of inde?nite
Referring ?rst to FIG. 1 there is shown a hole loading
length, from which ?box cuts? are blasted at spaced inter
arrangement previously used in a speci?c location in a
vals along the sides of the development cut. Mining then
taconite bed, involving a balst hole approximately eight
proceeds from one box cut to the next, parallel to the
or nine inches in diameter and about forty feet deep, and
development cut, the object of course being to shatter pre
having a Water level, for example, at the broken line
determined volumes from the vertical face of the devel
W??W. The hole is preferably formed by a jet piercing
opment cut into fragments which can be loaded into 30 tool known in the art and not necessary to describe here.
trucks by power shovels. For greatest e?iciency a pre
This type of tool pierces the rock by directing a jet of
ponderating 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 hy
drocarbon 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).
high velocity ?ame around the base of the tool, heating
and cracking the rock, and driving a stream of ?ne
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
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
It was desirable however to provide an intimately mixed 45 running bulk blasting agent such as pelletized trinitrotol
charge, and a method of securing it beneath the water
uol was poured in to completely load the chamber. Three
level in a wet hole, and the attainment of this objective
additional cartridges 13, 14 and 15 of heavy density blast
constitutes a major object of the present invention.
ing agent were placed in the column above the two in the
A further object of the invention is to provide a method
chambered area. A primer load, or a heavy density car
of charging a wet blast hole with a homogeneously mixed, 50 tridge with an inserted booster was placed at 16 and tied
low cost, high density explosive load.
in with a Primacord detonating fuse. Primacord is a
Another object of the invention is to provide a simple
commercially available fuse which has a tremendously
and eifective method of charging a wet blast hole, which
fast burning speed, around twenty thousand feet per sec
is not necessarily limited to the use of Water soluble in
gredients, but which permits the use of insoluble carbon 55
Above the cartridge 16, and above the water line
bearing materials such as hydrocarbon oils, or anthracite
W?W as shown, the water was sealed off with three-inch
coal dust, in preferred conjunction with ammonium ni
to six-inch ?chunks of ammonium nitrate. Above this
trate, in the form of prills, for example, and conven
plug a certain latitude was permitted because the balance
tionally termed ?prilied ammonium nitrate.?
of the hole was dry, but in one advantageous arrange
A further object or" the invention is to provide a method 60 ment a distance of approximately eleven feet was ?lled
of charging a wet blast hole with ammonium nitrate in
with ammonium nitrate prills 18 to which some hydro
an amount su?icient to provide a saturated aqueous solu
carbon ?uid such as fuel oil had been added, followed
tion of the ammonium nitrate in intimate association
by a primer cartridge 19. The remainder of the hole to
with a carbon-supplying substance, Whether soluble or
within about two feet of its top was ?lled with oil treated
ammonium nitrate prills 2.0. The top 21, two or three
A further object of the invention is to provide a method
feet in height, was stemmed with any granular sandy or
as de?ned in the last preceding paragraph and wherein
earthy material, or with tail-ings from the taconite bene
the carbon-supplying substance is anthracite coal in com
?ciation process. The primer cartridge 19 was tied in
minuted form.
with the detonating circuit through the Primacord fuse
A further object of the invention is to provide a method 70 above mentioned.
of charging a wet blast hole with ammonium nitrate in
As heretofore indicated the presence of water in a wet
aqueous solution in intimate association with a carbon
hole imposed a restriction on the choice of explosive
materials in the portion of the blast hole below the water
ing and lowering the pipe 30 repeatedly to cut or tear
the sacks. Another expedientis to dampen the coal dust
level, including the bottom chambered portion. While
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 perfora
tions 34 which permit free air flow and uniform distribu
ammonium nitrate is a relatively cheap and e?icient ex
plosive 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 in
timately mix it with an ammonium nitrate aqueous solu
tion even if the bottom of the nipple becomes clogged
dust, or other carbon-containing solid.
tion resides in the fact that the presence of water in a
with high consistency slurry.
tion. Other ingredients, for example hydrocarbon
One of the advantages of the present method is that it
liquids, are neither soluble in nor miscible in water, and 10
can be used with any of the explosive mixture-s heretofore
will settle in layers dependent on gravity and charging
known in the blasting art, including both water-soluble
and insoluble solids, and miscible or immiscible liquids.
In accordance with. the present invention? a method will?
Some of these ingredients suitable for use (either single
now be disclosedv for- simultaneously charging and homo
geneously mixing or associating a mixture of ingredients 15 or in various combinations) with ammonium nitrate, are
sugar, glucose, starch, coal, lampblack, charcoal, alcohol,
to provide a relatively cheap and powerfully effective blast
TNT, fuel oil or other hydrocarbon ?oil.
ing compound, for example a suitable compound includ
Another of the de?nite advantages of the present inven
ing ?ammonium nitrate, and sugar, starch, anthracite coal
Referring now to FIG. 2, an air pipe 24 (which may be 20 blast hole does not restrict the choice of the-operator to
materials miscible or soluble in water, but'the operator
?exible but is here shown as solid) is inserted do-wn-'
may use any ingredient indicated by the nature of the
wardly into the chambered portion 25 of the hole. The
terrain to. be blasted, in the light of economic considera
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 25 A preferred explosive mixture to be achieved is the
combination of ammonium nitrate, which is a relatively
through a ?exible connector pipe 26, and down through
cheap explosive ingredient, with a similarly cheap carbon
pipe 24 with- the 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 an-v
bearing material which is either soluble in water, or- if
insoluble, which is of approximately the same speci?c
nular space is ?lled'with water up to the'line W--W. The 30 gravity as a saturated solution of ammonium nitrate.
Under either of these alternative conditions we have pro
air current will be at a pressure suitably predetermined
vided an explosive charge for a wet hole which will not
so that it agi-tates the'water but does not expel any water?
stratify even if the charge is permitted to stand in the
from the blast hole. The pressure of course will drop
hole for twenty-four hours or more before it is detonated,
as the air issues from the relatively small pipe into the
larger space outside the pipe.
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
desired: explosive compound, in mixed granular form, is
has been used.
poured, for example from containers 27', into the annular
space 26, and it drops to the bottom into the water and 40 ?While we are not limited to a speci?c depth of- water in
the hole we prefer to operate with a'water content such
into chamber 25. It has been determined that this pro
cedure assures a homogeneous mixture of the'ingredients.
that no'excess water ?ows from the hole at the end of
While the air is thus being introduced to the water, the
the charging step, and preferably the upper surface of the
into an aqueous slurry which increases in solid consistency
until the hole ?lls to the rising water level and becomes,
water should be beneath ground level. We have found
so to speak solid-saturated, so that further charging pro-..
that under'preferred conditions the water content should
cedure does not affect the mix. Soluble ingredients will 45 be such as to leave what we have previously termed a.
of course dissolve gradually in the liquid up to the limit
solid-saturated solution. _This will normally occur in
?of' the liquid?s capacity to dissolve them. Ingredients
the neighborhood of ten percent Water.
such as insoluble or immiscible hydrocarbon ?uids, or
We? have found that with the above described charging
insoluble solids will not stratify since the air agitation
method the charge in the hole contains more ammonium
effect will continue as long as the slurry has any mobility 50 nitrate and carbon bearing'additive than with previously
and 'beyond that point no stratification takes place.
known methods because the voids between solid particles
The escaping air is at such low pressure that it will not
are filled with saturated solution.
interfere with. the pouring procedure, and the pipe may
It would be entirely feasible to uniformly mix an ex
?be gradually raised as the liquid level rises so that its
plosive compound such as hereinabove described in com
lower end remains beneath the surface of the slurry. The 55 minuted form so that it could be introduced through the
air current can ?be shut off and the pipe Withdrawn after
air pipe and carried below the liquid surface by the air
the solid constituents build up to the water level. Det
current, or a slurry of the compound could be mixed at
onating fuses, and primer cartridges may be inserted in
the surface and poured into the hole in the annular space
the chambered portion prior to execution of the disclosed
beside the air pipe.
method, if such items are to be used in said chambered 60 What is? claimed is:
Above the water level any? suitable charging arrange
A method of charging a blast hole having water in a
bottom end portion thereof, said method comprising in
ment can be used, for example that disclosed for use
troducing an air-carrying pipe into the hole so that its
above the line W-..?W' in FIG. 1.
lower end portion is below the water surface, continuously
FIG. 3 shows an embodiment in which we provide a 65 discharging an air current downwardly through said pipe
?exible pipe 30 here shown as made of rubberlike mate
so that it escapes upwardly while agitating the water, and,
rial, having at its lower end a metal tip or nipple 31
while said air current is being thus discharged, pouring a
several feet long. In this embodiment the carbon-bear
compounded explosive mixture of granular in
ing additive is anthracite coal dust. To minimize the
said hole in the annular space between said
possibility that the coal dust might be blown out of the 70
pipe and the inner wall of said hole, whereby said mix-.
hole, at least in part, if charged in particle form from
ture drops into the agitated water and forms with the
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 deterio
water an intimately mixed aqueous slurry, so as to cause
the slurry top surface to rise, and, while said surface is
rates rapidly in? water, or they may be ?fractured by rais 75 rising and said pouring continues, withdrawing said pipe
upwardly in such manner that its lower and remains be
neath but near the said top surface.
References Cited in the ?le of this patent
Borchgrevink __________ -_ Ian. 19, 1932
Kirst et a1 _____________ __ Feb. 26, 1935
Cairns ________________ __ Aug. 8, 1944
McFarland ____________ -s Mar. 8, 1949
Lee et a1 _______________ _- Mar. 8,
Nowak ______________ __ May 24,
Aitchison et al _________ .... May 15,
Edgerton _____________ __ May 22,
Rinkenbach et a1 _______ .. Dec. 24,
Streng et a1. __________ __ May 28, 1958
Hradel ________________ __ Jan. 6, 1959
Kolbe _______________ __ Sept. 15, 1959
Lambert et a] __________ __ Oct. 11, 1960
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