Note: Descriptions are shown in the official language in which they were submitted.
'I
Desc_i~t_ n
SYSTEM FOR MAKING AN A~UROUS
SLURRY-TYP _ LASTING COMPOSITION
Technical Field
This invention relates to a homogeneous slurry-type
blasting composition, and to a method and system for making
such.
Backc~round Art
Aqueous and oil-based inorganic nitrate slurry
explosives are extensively used in strip mining oE coal and
other construction usesO These slurry-type explosives gen-
erally contain a major amount oE an inorganic nitrate and a
fuel together with water or oil and a thickening or gelatin-
izing agent. ~he most common way of making slurry-type
explosive compositions has generally involved employing an
aqueous solution of ammonium nitrate or alkali or alkaline
earth metal nitrates to which the other components are
added. Finely divided aluminum flakes are commonly used in
such compositions; however, "dusting" of this particulate
material during manufacture of blasting compositions pre-
sents an extreme hazard. It is also difficult to obtain a
homoqeneous mix of the metal nitrate and metal particles
without segregation. If the components are not uniEortnly
mixed, the explosive composition either does not detonate or
performs unsatisEactorily.
~t has remalned a problem to develop a slurry-type
exPlosive composition which can be manufactured quickly,
without the need for special equipment, at reasonable cost,
and with safety.
The following UOS. patents disclose slurry-t~lpe
blasting compositions and methods of making them; however,
none of them employ a method or composition as describec~ and
claimed herein.
~,
.JI.~ .D
U.S. Patent No. 3,Z94,601 discloses a slurry-type
blasting composition oE ammonium nltrate as an oxidizerl
hexamethylenetetramine as a fuel, water~ and a thickening or
gelling agent. No particulate metal as a fllel is employed.
The blasting composition i5 formed by mixing the ammonium
nitrate, gelling agent together in a steam-jacketed vessel
to melt them and s]owly adding to the dry, hot melted mix-
ture hexamethylenetetramine dissolved in boiling water, the
mixture being blended until a cohesive mass is formed.
U.S. Patent No. 3,765,967 discloses a slurry
explosive prepared by dissolving an inorganic metal per-
chlorate in water toqether with a thickener and particulate
pentaerythritol tetranitrate and adding finely divlded
alumlnum to the aqueous slurry.
U.S. Patent No. 5,985,593 discloses a method of
making a slurry explosive by solubilizing nitromethane in an
aqueous gel oE sodium perchlorate which includes a solubil-
i~ing agent for the nitromethane, such as ethylene glycol.
U.S. Patent No. 3,787,254 discloses a water-base
slurry composition made by distributing a liquid hydrocarbon
fuel in an emulsion-like form of a mixture of ammonium
nitrate and calcium nitrate, and then adding a thickening or
gelling agent. Aluminum metal is added as a secondary fuel
for certain of the compositions.
U.S. Patent No. 3,886,n10 discloses a water-base
slurry composition made by incorporating a small amount of a
thickener to an aqueous oxidizing solution of ammonium ni~
trate and thereafter adding a dry mix of a particulate solid
fuel, such as finely divided aluminum, to the solution by
stirring and mixincl, the dry mix including a supplemental
thickening agent and a cross-linking agent.
U.S. Patent No. 3,378,415 discloses an explosive
slurry made by melting together the li~uefiable component of
the composition, i.e., ammonium nitrate and sodium nitrate,
and then mixing in a dough~type mixer the mixture of the
metal nitrates and a carbonaceous fuel, such as starch or
woodmeal; a particulate metal, such as aluminum powder or
flake; water; and a thickening agent, if needed. It is
esserltial to melt the LiqueEiable incJredients ~irst ~nd then
add the fuel an~ other inq~ec3ients to avoid spontaneous
ignition thereof.
UOS. Patent No. 3,235,425 discloses a sequence o
steps for mixing a slurry-type blasting composition by mix-
ing together a dry mixtllre of ammonium nitrate and a gelling
agent, then adding the resulting dry mix to water, and
thereafter mixing in a smokeless powder.
None of the patenks disclose a sequence oE mixing
steps to avoid dusting of particulate metal such as aluminum
used as a fuel in the production of blasting compositions
nor a method which avoids desensitizinc~ the composition
during manufacture.
Disclosure of Inventio
Ik is a primary object of this invention to pro-
vide a method of quickly formulating an aqueous, slurry-type
blasting agent safely and economically.
It is a further object of this invention to pro-
vide a method of formulating a homogeneous, aqueous, slurry~type blasting agent using flaked aluminum, with little or no
dusting of the aluminum.
It is a further object oE this invention to pro-
vide an aqueous, slurry-type blasting composition wherein
the two components of the hlasting composition can be sepa-
rately packaged and mixed together quickly and safely with-
out the need for sophisticated equipment and without desen-
sitizing the composition.
It is a Eurther object oE this invention to pro-
vide an aqueous, slurry-type blasting agent employing no
toxic ingredients and which can be handled in an open plant~
It is a further object oE this invention to pro-
vide an aqueous, slurry-type blasting agent employing a high
proportion oE water and a relatively small amount oE parti-
culate aluminum and still obtain a blasting compositionhaving good blasting characteristics.
It is a further object oE this invention to
provide a two-component aqueous slurr~-type blastinq agent
3q.'~
employing dry, particulate ammonium nit-rate, the endothermic
reaction occurring when the dry amrnonium nltrate is mixed
with the aqueous fuel suspension providing greater thermal
stabiliy and insensitivity.
These and other objects are accomplished by
premixing a fuel with water and a gelling agent to Eorm a
stable suspension of the fuel in the water, mixing together
(in dry Eorm) a particulate nitrate oxidizer together with a
gelling agent, and blending the suspension and dry mixture
by subjecting them to a slow tumbling action -for a brie
period of time. The blasting composition comprises 50-80
percent by weight ammonium nitrate, 0~5-10 percent uel,
preferably flaked aluminumin an amount ranginy from 1-4 per-
cent, 15-35 percent by weight water, 0.5~10 percent gelling
15 a~ent, preferably 1--2 percent, 0.02-0.5 percent of a cross-
linking agent and, optionally, 0~05-1 percent o-E a glycol,
such as ethylene or propylene glycol.
Brief Description of the Drawinqs
The drawing illustrates a schematic diagram of a
batch mixing system for formulation of an aqueous, slurry-
type blasting composition of the type disclosed herein.
Best Mode for Carr~ing Out the Invention
The inorganic nitrate which is preferably employed
as the nitrate component of the explosive composition of
this invention is ammonium nitrate; however, other inorganic
nitrates can be employed alone or in admixture with the
ammonium nitrate, such as the alkali or alkaline earth metal
nitrates; e.g., sodium nitrate, potassium nitrate, calcium
nitrate. IE a mixture is used, it should generally contain
a predominant amount of ammonium nitrate in preEerence to
the other nitratQs. The nitrate used can be in an~ form;
i.e., crushed, prill or a combination of the two, reasonably
oil- and water-free. Fertilizer-grade ammonium nitrate is
suitable. The particulate nitrate is usually processed
through a hammermill or other means to grind it to a uniform
particulate size before being blended with the other compo-
nents in the explosive compoC3ition. ~lthollclh a clr~ ge1:LincJor thickening agent may be added to the oxidizer, it is
preferable to adcl the gelling agent and cross-linking a~ent
to the aqueous suspension to avoid any problems of (1) pre-
mature cross linkinq, should the ammonium nitrate becomedamp, or (2) toxicity, which is a problem with certain of
the cross-linking compounds. rrhe thickening agents may be
any of the conventional thickening agents employed in the
preparation of slurry explosives, such as guar gum, starches
and synthetic polymers, such as the polyacrylamides. Cross-
linking agents may also be added for the thickening agent.
Cross-linXing agents are especially useful where the stabil-
ity or integrity of the composition needs to be maintained.
The cross-linking agents are generally metal salts, such as
ferric nitrate, sodium dichromate, ammonium, antimony salts,
etc. The inorganic nitrate, with or without the gelling
agent and cross-linking agent, in dry form, Eorms one compo-
nent of the two--component explosive composition.
The second component of the explosive composition
~o is comprised of a fuel, preferably a finely divided metal,
such as aluminum, which is premixed with water and a gelling
or thickening agent which suspends and causes the aluminum
to be absorbed by the water. Preferred is de-dusted alumi-
num flake which includes a coating of a polyfluorocarbon
and/or a metal stearate to prevent reaction with water.
Alcoa 1651, manufactured by the Aluminum Company of America,
is suitable, as are other commercially available aluminum
flake products. This particulate aluminum is susceptible to
dus-ting i~ diskurbed, or example~ by vibration, and is
extr~mely hazardous to use if dusting cannot be prevented
durlng mixing of the explosive composition. It was found
that premixing the aluminum particles with water and a ge3l-
ing agent substantially eliminated dusting. The gelling or
thickening agent employed can be the same as that blended
with the dry inorganic oxidizer. Preferred is one oE the
guar gums, preferably used without a cross-linking agent~
It is also desirable to add a small amount of a glycol, such
as propylene glycol, to the suspension to aid in dispersing
the yel]inq agent. ~rhe amollnk 0~ wa~e~ blendetl with the
particulate aluminum an~ ~elLing aclerlt shollld be only enouqh
to form a concerltrate of aluminum suspende(J in an aqueous
system. An impeller, vortex mixer is preEerred for prepara-
tion of the concentrate This concentrate can be packagedin suitable cartridges and shipped to the intended blending
site for blending with the first component. ~t the use
site, the two components of the explosive composition are
blended together with additional water to produce an aque-
ous, slurry-type blasting agent which can be used with
safety.
Reference is made to the drawing illustrating a
schematic diagram of the equipment used for blending the
explosive composition. The particulate ammonium nitrate or
other inorganic nitrate or mixture thereof is delivered into
a bin 10 by an ~uger 12 coming from a bulk facility holding
the nitrate. The inorganic nitrate drops into a hammermill
14 which grinds the inorganic oxidizer to a uni~orm particle
size. The ground inorganic nitrate exits Erom the hammer-
mill and is conveyed by auger 16 -to a mixer 18, similar to a
conventional mortar mixer. A dry gelling agen-t may be added
to the oxidizer in the mixer. The mixer incorporates mixing
blades within it which slowly tumble the dry, particulate
mixture. The mixer i5 pivotally mounted at pivot point 19
to frame members 20 for dumping the mixture, aEter blending
of the second component, into a bin and auger packer 22 as
illustraked. A scale 24 is included beneath hopper 10 for
measuring a predetermined weight oE the dry particulate
oxidizer to be fed into the mixer 18. When formulating the
explosive composition, a predetermined weight of the dry
particulate oxidizer, as weighed by the bag scale 2~, is fed
into the hammermill 14 and into the mortar mixer 18.
The second component oE the explosive composition
(the concentrate o~ particulate aluminum suspended in an
aqueous slurry) is poured into the mortar mixer simultane-
ously with or prior to the addition of a predetermined
amount of additional water. Once the second component is
added to the dry particulate mixture in the mixer, the mixer
5~
i9 act:ivated to ~lowly tumble the Inixlur~ or1ly ~or: a sho~k
perio~ of tirne, gene~ally 2 to 3() seconds. C~ the ~ixture
is mixed too rapidly, the sensitivity oE the explosive corn-
pOSitiOIl is destroyed. IE mixed too slowly, a non-uniform
composition is obtained~ If the mixture is mixed too rapid-
ly, the aluminum will dust. After the short mixing time of
the two components, the mixture, having a molasses-like con-
sistencv, is dumped into the auger pacXer 24, where it is
packed in polyethylene or other plastic packages or car-
tridges. The mixer 18 is provided with an interlock mechan-
ism which prevents mixing until the proper amounts oE the
two components have been added to the mixer. The final
explosive composition should have a composition consisting
essentially of 50-80 percent by weight ammonium nitrate or
other inorganic nitrate or mixtures thereof, 0 n 5-10 percent
particulate aluminum, preferably 1-4 percent, l5-35 percent
water, 0.5-10 percent gelling agent, 0.02-0.5 percent cross-
linking agent and 0.05-1.0 percent oE a glycol, such as
ethylene or propylene glycol.
The equipment needed to formulate the explosive
composition is unsophisticated and the components, particu-
larly the aluminum-containing component, can be packaged as
a gel in concentrated form for transport to the formu]ation
site. The ammonium nicrate or other inorganic nitrate can
be acquired from any suitable source. The composition can
be formulated quickly with no dusting problems and with
safety. The Einal composition uses a relatively small
amount of particulate aluminum. No other fuel is needed. A
relativ~ly high proportion of water is used in contrast to
other commercially used slurry-type explosive compositions.
The aluminum content may be varied to vary the sensitivity
of the explosive composition. Above about 3 percent alumi
num the explosive composition is cap-sensitive. Below about
3 percent, a booster i5 necessary. It is important that the
aqueous suspension of aluminum be added to the dry particu-
late mixture to avoid dusting of the particulate aluminum
and to insure a uniform, homogeneous composition which does
not segregate.
Fxample 1
The exploslve composition described is generally
prepared in batches weighing from 200 to 400 pounds each.
In a given day 20,000 pounds of the composition may be pre-
parecl. To formu1ate 20,000 pounds of the explosive composi-
tion requires 13,750 pounds of particulate prilled ammonium
nitrate and 358 pounds of guar gum.
A batch amount of the ammonium nitrate was fed by
auger into bin 1 n from a bulk facility and then fed through
a hammermill which crushed the prills. The crushed ammonium
nitrate was then fed by auger 16 into mixer 18 and mixed
with a batch amount of guar gum~ The dry mixture was tum-
bled slowly to orm a uniform mixture of the oxidizer and
dry gelling agent.
An aqueous slurry concentrate of particulate
aluminum was prepared by blending together with an impeller,
vortex mixer 358 pounds of a de~dusted flake aluminum (Alcoa
1651), 1,076 pounds water, about 10 pounds of a gelling
agent (MP 11, hydroxypropyl guar), and 20 pounds oE propy-
lene glycol.
The concentrate of the gelatinous mixture of
aluminum suspended in the aqueous gel was prepacka~ed in 300
pound polyethylene cartridges~ each cartridge weighing about
15 pounds, and shipped to the use site. ~t the use site the
packages were slit and added to the batch quantity of the
c]ry particuLate mixture of ammonium nitrate in the mixer
with slow tumbling. ~Simul~aneously with addition of the
aluminum concentrate (or separately), an additional batch
amount o~ water was added to the composition (4,428 pounds
water per 20,000 pounds oxiclizer). The mixture was blended
after introduction of the water and concentrate Eor a time
less than 5 seconds and was then fed into an auyer pac]cer
which packed it into polyethylene cartric19es. The set-up
time of the composition ranged from 24 to 48 hours. The
blended and formulated explosive composition incorporated
the following:
_ercenk
Ammonium nitrate 68.75
Guar gum 1.79
Water --
(1) Present in the aluminum-
containing concentrate 5.33
(2) Added at the time of
formulation 22.14
Gelling agent Jaguar HP~11
(Stein-Hall, a division
of Celanese Corporation) 0.05
Propylene glycol 0.10
Flake alumimum (Alcoa 1651) 1.79
The explosive composition, on plate dent tests,
detonated completely and gave plate dents comparable to
other slurry explosives.
