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Патент USA US2107157

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Patented Feb. 1, 71938
-'
I
UNITED ‘STATES PATENT OFFICE
arouse
/
EXPLOSIVE
Harold A. Lewis, Wilmington, Del, and Fred R.
Wilson, Bloom?eld, N. 3., assignors to E. ll. du
Pont de Nemours & Company, Wilmington,
, lDeL, a corporation of Delaware
No Drawing. Application January 22, 1936,
Serial No. 60,260
8 (Claims. (Cl. 52-14)
This invention relates to a new and improved the time of maximum hot pressure development
detonating explosive and more particularly to one
. adapted for use in coal'mining vwhere the pro-
have not been standardized, and in the case of
detonating explosives in particular, no reliable
duction of coal in the form of large lumps is
procedure is known whereby reproducible results
5 desirable.
may be obtained. Indeed, the data obtained by
The blasting impulse which is imparted by'the ‘ the known methods are of such doubtful value
explosive to its environment is, in part, a function
as to be lacking in signi?cance.
For these rea- .
of the reaction rates of two closely related consecutive chemical reactions, namely: (1) the rate
ill of initiation of the explosive decomposition; and
(2) the rate at which the explosive decomposition
takes place after initiation. Based on the wide
differences in the reaction rates of various explo-
sons, the performance of the explosive in actual
blasting is a‘ more reliable, indication of the
rate of pressure development than the results of 10
comparative tests in a Bichel bomb, for example.
One of the most accurate of these ?eld tests
is a statistical study of the amount and size of
sives, ity is customary to classify them into (a) def15 lagrating explosives, in which the two rates mentioned above are relatively slow; and (b) detonafing explosives, in which the two rates are generally extremely rapid.
'
The ?rst of the two factors mentioned above
may be expressed in slightly di?‘erent terms as the
rate of propagation, or the rate at which the initiating impulse travels down a column of explosive. In the case of de?agrating explosives, the
initiating impulse is a ?ame which travels down
the lumps produced in the shooting of coal with
the powder under evaluation. With typical clef- l
lagrating explosives, such as black powder for
example, large amounts of lump coal will be pro
duced, since the characteristically low velocity of
the propagation and low rate of pressure develop
ment will produce a heaving rather than a shat- 20
tering effect on the material blasted down. With
detonating explosives on the other hand, a great
er proportion of pulverized material or “?nes”
will be produced depending on the magnitude of
If) Ll a column of black powder, for example, at a rate
the two rates mentioned above.
‘
25
of about 300 m./sec. For detonating explosives
on the other hand, the initiating impulse is a
Shock Such as & “detonation Wave”, which procoeds down a column of dynamite, for exampla.
39 at a Velocity generally in excess Of 1700 m-/Se0The rate of propagation of an explosion Wave is
From the foregoing, it will be seen that de?a
grating explosives such as black powder are
,more satisfactory in coal shooting, from the point
of view of execution, than the detonating ex
plosives heretofore available, due to the greater 30
economic value of lump coal. Black powder has
readily measured by fairly accurate methods
whioh generally oonsistlin measuring the time roquired for an explosion wave to pass from one
point to another along a column of the explosive
being tested, for example in the case of detonating explosives, by means of the well known Mettegang Recorder 01‘ the Dautriche methodTho Second factor in the blasting impulse,
4o namely, the rate at which the chemical dooome
a characteristic disadvantage, however, of pro
ducing a ?ame of considerable length and dura
tion, which makes this explosive out of the ques
tion for safety reasons in mines where in?am- 35
mable gases are present.
For the reasons given above, coal mining 0p
erations frequently require a detonating explo
sive which may be safely used in ?ery mines. For
such purposes the most approxed explosives are 40
position takes place at a given point alter the
initiating impulse has‘ reached that point and
Started the deFompositloni is a true reactlon ate
and as such, is extremely. dimcult to determme
‘15 wlth accu,ra°y' some mdlcation of the magmtude of this rate may be obtained by observing the
plie?sure changes in au-closed System and deter‘
mining the so-called rate of pressure development”. Since this is a rapidly changing differen50 tial function, it is the common practice to determine the so-called “time of pressure develop-
the so-called “permissible explosives” which are
designated as Such by the U_ S_ Bureau of mnes
after passing certain prescribed and o?‘icial tests.
The great majority of the Smwned “permissb
ment”, or the time required for the explosive to
develop the maximum hot gas pressure, when
bles” contain ammonium nitrate as the principal 45
ingredient These ammonium nitrate “permissi
bles” generally comprise, for example, 50 to 80%
a
onium nitrate 10 to 157 nitroglycerme as
,mm _t_ _
i
nt u to” 10 and as hi h as
g Sens‘ 12mg ngre e ' g {bl
t 1 1g
d
0% of ca'rbonaPfaous com us 1 8 _ma er?‘ 5’ an
frequently addltwns of_ Safety mgl‘edlents' 01'
cooling salts such as sodium nitrate,
ammonium
'
suitably initiated.
chloride, sodium chloride, ammonium oxalate and
' The methods of measuring either the rate or
the like in varying percentages-
Thus, for ex- 55
2,107,157
Table II
ample, in the case of sodium nitrate, the most
commonly used safety ingredient, the percentage
varies from about 3 to 10%.
A
B
0
Typical examples of “ammonia permissibles”
according to the prior art are shown in Table I.
Table I
Ingredients
Nitroglycerine __________________ ._ 4. 5—6. 5%
Ammonium nitrate__
Safety ingredients _ . _
A
B
C
Carbonaceous combus bl
D
l0. 0
75. 0
5. 5
11. 0
78. 5
3. 0
1i. 0
75. 0
4. 0
14. 0
65. 5
3. 0
carbonaceous combusti
bles _____________ __
_Antucid _______________ __
15
9. 2
0.3
7. 2
0.3
9. 7
0. 3
17. 2
0.3
0—10
6—8%
21-10%
75-85%
05-757
0—10%
0-10 0
4'—10%
7—15%
l0—20%
Antacid ________________________ __ 0 l—1.0%
0. l—l.0%
0 1—l.0%
10
Nitroglycerine _________ __
Ammonium nitrate ____ __
Safety ingredients _____ _.
75—85%
_ __
Properties
10
‘
Density ________________________ _.
Nitroglycerine~grams per 100 cc.
1.0
0. 8
explosive ______________________ _-
4. 5-6. 5
4. 8-6. 4
0.65
-
5. 243. 5
In the foregoing table the ammonium nitrate
100. 0
100. 0
100. 0
100. 0
Velocity, m./sec. ______ _ _
2750
2200
1900
1850
substantially the greater part thereof (e. g., over
Density ________________ _-
1. 0
1. 0
0. s
0.65
10.0
11.0
8. 8
9. 1
80%) passes a IO-mesh screen but is held on a
zi-mesh screen.
20
employed is of a degree of coarseness such that
Nitroglycerine—grams
per 100 cc. explosive . _ _ _
In explosive compositions of the type shown in
20
From the safety standpoint, such permissible
detonating explosives have given great satisfac
tion and they have been excellently adapted for
use with many types of coal from the viewpoint
25
of execution. In cases, however, where the coal
is soft and offers little resistance, and where a
high percentage of lump coal is desired, such
explosives are too violent in their action to give
the desired results. This violence of action, as
above explained, is due in part to the velocity of
propagation, but by far the more important fac
tor is believed to be the rate of pressure develop
ment. Since, however, the rate of pressure devel
opment can only be inferred indirectly from the
performance of the explosive in actual use in the
?eld, the exact explanation of the failure of prior
“permissibles” to give the desired results under
these circumstances is not de?nitely known, but
the explanation given above appears to be correct.
40
The object of the present invention is an im
proved detonating explosive adapted for use in
coal mining and producing a relatively large per
centage of lump coal. A further object is such an
explosive characterized by high strength, but hav
45 ing at the same time a low rate of pressure de
velopment. A still further object is a detonating
explosive having a very low velocity and a very
low rate of pressure development. Additional ob
jects will be disclosed as the invention is herein
50 after more fully described.
We have found that the foregoing objects are
accomplished by introducing into the explosive
composition ammonium ‘nitrate in an amount at
55 least equal to 65% and preferably 75 to 80%,
said ammonium nitrate being so controlled as
to grain size and so sensitized with nitroglycerine
Table II there is a minimum amount of sensitizer
which is necessary for detonation; this is usually
3.0 to 4.0 grams of sensitizer per 100 cc. of ex
plosive. In practice, it is necessary to use an
amount slightly above the minimum in order to
obtain a practical explosive composition. On
the other hand, if an amount of sensitizer is used
that is too far above the necessary minimum,
then the reactions are set up with such violence 30
that the rate of pressure development is increased
vand thus adversely affected for the purposes of
our invention. The compositions shown in Table
II therefore all contain an amount of sensitizer
less than 7.5 grams per 100 cc. and within the
preferred range of 4.5 to 6.5 grams per 100 cc.
The safety ingredients preferably comprise
sodium nitrate, but any other of the well known
cooling salts may be used if desired. The car
bonaceous combustibles may consist of oat hulls,
corn meal, bran, ground coal, wood pulp, expand
ed cereal products, cottonseed hulls, rice hulls,
ivory nut meal, starch, flour and the like, or any
mixtures thereof. Preferably, however, we use
those combustibles which give compositions of a
high degree of sensitiveness, particularly in those
compositions of low density. As an example of
this type of combustible, we may‘ mention ?aked
cereal products such as ?aked corn, wheat, rye,
starch, hominy grits and the like. The antacid 50
may consist of calcium carbonate, magnesium
carbonate, magnesium oxide and the like.
As speci?c examples of a “permissible” type
explosive in accordance with our invention, we
may cite the compositions illustrated in Table III. 55
Table III
or other nitric esters as to make certain a velocity
less than 1700 meters per second and a low rate
of pressure development.
A
65 such for example that substantially the greater
Nitroglycerine____. _
Ammonium nitrate
_
5. 0
84. 0
Sodium nitrate-.Absorbent combustible"
Chalk ______________________________________ ._
100 0
_
which the various‘ingredients of ‘our explosive
75 may be used, reference is made to Table II.
7. 0
80.0
9. 0
71. 0
3.0
7. 5
3.0
9. 5
3.0
10. 5
0. 5
0.5
0.5
100.0
100.0
65
Properties
24-mesh screen. The sensitizer used, nitroglycer
70 explosive, and preferably between 4.5 and 6.5
grams per 100 cc. of explosive.
As illustrative of the preferred ranges within
0
Ingredients
proportion thereof (i. e. over 80%) is held on a
ine or other explosive nitric esters, is used in an
amount not exceeding 7.5 grams per 100 cc. of
B
60
The ammonium ni
trate used is of such a degree of coarseness that
substantially the greater part thereof (i. e. over
90%) is held on a 35-mesh screen, and preferably
we ?nd it desirable to use even coarser grains,
25
Velocity, m./sec ............................ _.
1500
1520
58%
60%
51%
Density ____________________________________ . _
1.0
0. 8
0. 65
Nitroglycerine—grams per 100 cc. explosive...
5. 0
5. 6
5. 9
St
1450
A typical screen analysis of the ammonium ni
trate employed in the examples given in Table III
' is indicated in Table IV.
75
2,107,157
Table IV
of from 36 to 44% represents an actual increase of
22% in the lump coal produced.
As mentioned above, the velocities of composi
Pei-cent
Held on 10 mesh__v _____________________________________ __
tions A, B and C in Table III are somewhat lower
than the corresponding properties of the common 5
Held on 10-14 mesh ____________________________________ _.
Held on 14-20 mesh
Held on 20-24 mesh ___________________________ ._
prior art “permissibles”. By far the more impor
Held on 24-28 mesh ___________________________ __
. tant change, however, resulting from the selection
of grain sizes is an unexpected and very appre
Held on 28-35 mesh
Held on 35—65 mesh
Scoi-wasu
Held on 65—100 mesh _________________________ _: ________ __
Passing 100 mesh ______________________________________ __
10
0
From the foregoing table it is apparent that
99% of the ammonium nitrate employed passed a
IO-mesh screen and 88% thereof was held on a
15 24-mesh screen.
We are aware that “relatively coarse ammo
nium nitrate” has been used heretofore in ex
20
plosive compositions. Thus Woodbury in U. S.
1,113,275 and 1,124,679 disclosed that the substi
tution of “relatively large particles” of ammo
nium nitrate for the random sizes employed be
fore that time caused a signi?cant lowering of
the velocity of detonation. Ward in U. S. 1,743,
172 disclosed that relatively coarse ammonium
nitrate could be successfully detonated at full'
strength ,with as little as 4 to 7% nitroglycerine.
In particle size, the “relatively coarse” ammo
nium nitrate heretofore employed was such that
so
at least 80% was held on a GO-mesh screen, and
not more than 20% passed therethrough.
Our
. invention, however, contemplate-s the use of much
coarser ammonium nitrate, for example such that
at least 80% is held on a 24i-mesh screen.
At ?rst glance, this may appear to be an incon
sequential difference from the ammonium nitrate
heretofore employed, for example by Woodbury
and Ward. This increase in the particle size,
however, produces the surprising result that the
40
powders according to our invention have a much
lower rate of pressure development, and there
fore produce an appreciably higher percentage of
lump coal.
Heretofore no one appears to have
recognized that the rate of pressure development
of ammonia dynamites may be lowered by em
ploying ammonium nitrate of very large particle
sizes as above described. By actual tests, how
ever, we have found this to be the case.
This is
clearly indicated in Table V.
Table V
Explosive used
Percent coal
held on 2-inch
mesh
Composition A of Table I ________________________ _.
Composition B of Table I ________________________ __
Composition A of Table III ______________________ __
3
32
36
44
Table V gives the results of a statistical study
60 of the percentage of “?nes” produced by various
“permissibles” when used to “pull” coal in the
same mine under comparable blasting conditions.
In this table the results obtained by the use of
the composition A of Table III according to our
‘invention are compared to those obtained with
the prior art compositions A and B of Table I.
It will be noted that whereas there was an in
crease of 4% of 2-inch lump coal obtained by the
use of composition B of Table I having a velocity
of 2200 meters as compared with composition A
of Table I having a velocity of 2750 meters, there
was an increase of 2-inch lump of from 36 to
44% when employing composition A of Table III
25. in accordance with our invention. This increase
ciable reduction in the rate of pressure'develop
ment of the explosive, as indicated by actual tests
in the ?eld, for example, as shown in Table V.
An explosive such as those described in Table III
will possess to an unexpected degree the properties necessary for producing lump coal and
10
will have high strength, between 50% and 60% 15
straight dynamite, due to its high content of \ex
plosive material, namely, nitroglycerine and am
monium nitrate. The strength, however, ‘will
develop slowly because of the presence of am
monium nitrate in the form of. very coarse grains. 20
The low nitroglycerine content will be insu?icient
to cause the rapid development of pressure from
the coarse grains of ammonium nitrate, but will
be ample to develop the maximum strength of
the explosive when the latter is shot in cartridges 25
of sufficiently large diameter.
An explosive such as the foregoing is not con
sistently capable of detonation at its full explo
sive strength when shot in the smaller diameters
usual in prior art coal blasting. It has been the 30
custom, for example, to consider cart-ridges of
11/4" diameter as a standard. Our explosive,
however, cannot effectively be used in diameters
appreciably lower than 13/4" since the danger of
mis?res is too great. Consequently, the utiliza 35
tion-of explosives according to our invention in
diameters not less than 11/2" is a prerequisite,
and preferably the cartridge should have a di
ameter of 1%" or more.
It will be apparent to any one skilled in the
art that a notable advance has been made possible
by our new explosive. The superior qualities of
black powder in the breaking down of coal in
the form of large lumps has long been recognized.
To the best of our knowledge, however, the pres
ent invention is the ?rst to recognize that deto
nating explosives of the dynamite type, containing
very large particles of ammonium nitrate, are
capable of producing similar favorable results.
Thus, by the use or" our explosives, it is possible
to produce a signi?cantly higher percentage of
lump coal in the presence of ?re~damp than has
ever been achieved before with a permissible am~
monium nitrate dynamite.
In the foregoing detailed description or" our 55
invention, it is apparent that many changes and
modi?cations may be introduced Without depart
ing from the spirit and scope thereof. For ex
ample, the term “nitroglycerine” as employed in
this speci?cation and the appended claims is used 60
in the sense in which it is employed in the art.
i. e. it includes not only nitroglycerine as. such,
but the various explosive nitric esters commonly
used in place of, or in mixtures with, nitroglyc
crime, for example ethyleneglycol dinitrate, tetra 65
nitrodiglycerine, nitrated sugars, nitrostarch, ni
trochlorhydrins, pentaerythritol tetr'anitrate and
various mixtures of these and similar substances.
In addition, aromatic nitrocompounds such as the
dinitrotoluenes, the nitroxylenes, and the like,
and similar explosive materials may be added if
desired. Furthermore, the liquid nitric esters
may be slightly gelatinized if desired by the ad
dition of small percentages of nitrocotton or other
gelatinizing agents. Other variations will be an“
aroma’?
parent to‘anyone skilled in the art. We, there
fore, intend to be limited only in accordance with
the following patent claims:
We claim:
1. An ammonium nitrate explosive charge
Cl
adapted for use in coal mining, and having a low
velocity and a low rate of pressure development,
said explosive comprising more than 65% am
monium nitrate of a degree of ?neness such that
10 substantially the greater part thereof will be held
on a 24-mesh screen and substantially all thereof
will be held on a 35-mesh screen, said explosive
being cartridged in a diameter not less than 11/2",
whereby a substantially complete utilization of
15 the explosive strength of the ammonium nitrate
is assured.
2. An ammonium nitrate explosive charge
adapted for use in coal mining, and having a low
velocity and a low rate of pressure development,
20 said explosive comprising at least 65% ammonium
nitrate of 'a degree of ?neness such that substan
tially all thereof will be held on a 35-mesh screen,
and a sensitizing agent comprising not more than
7.5 grams explosive nitric ester per 100 cc. of ex
25 plosive, said explosive being cartridged in a di
ameter not less than 11/2”, whereby a substan
tially complete utilization of the explosive
strength of the ammonium nitrate is assured.
3. An ammonium nitrate explosive charge
30 adapted for use in coal mining, and having a low
velocity and a low rate of pressure development,
said explosive comprising not more than 7.5 grams
of nitroglycerine per 100 cc. of explosive, and at
least 75% ammonium nitrate of a degree of ?ne
ness such that substantially all thereof will be
held on a 35-mesh screen, said explosive being
cartridged in a diameter ‘not less than 11/2",
whereby a substantially complete utilization of
the explosive strength of the ammonium nitrate
40
is assured.
'
4. An ammonium nitrate explosive charge
adapted for use in coal mining, and having a low
velocity and a low rate of pressure development,
said explosive comprising 4.5 to 6.5 grams of
nitroglycerine per 100 cc‘. of explosive and at
least 75% ammonium nitrate of a degree of ?ne
ness such that substantially all thereof will be
held on a 35-mesh screen, said explosive being
packaged in a diameter not less than 11/2 inches.
5. An ammonium nitrate explosive charge
adapted for use in coal mining, and having a low
rate of pressure development, said explosive com 1O
prising 4.5 to 6.5 grams of nitroglycerine per 100
cc. of explosive and from '75 to 85% ammonium
nitrate of a degree of ?neness such that substan
tially all thereof will be held on a 35-mesh screen,
said explosive being packaged in a diameter not
less than 11/2" and having a velocity lower than
1700 m./sec.
6. A high strength ammonium nitrate permis
sible-type explosive charge adapted for use in
coal mining, and having a low rate of pressure
development, comprising approximately 4.5 to 6.5
grams nitroglycerine per 100 cc. of explosive, 75 to
85% ammonium nitrate of a degree of ?neness
such that substantially the greater part thereof
will be held on a 24-mesh screen and substan
tially all thereof will be held on a 35-rnesh screen,
1 to 5% of sodium nitrate, 5.0 to 15% of a car
bonaceous combustible which favors sensitiveness
at low percentages of nitroglycerine, and 0.5%
chalk, said explosive having a velocity lower than 3O
1700 m./sec. and being cartridged in a diameter
not less than ll/z'?whereby a substantially com
plete utilization of the explosive strength of the
ammonium nitrate is assured.
\
'7. The composition of claim 6, in which said 35
carbonaceous combustible comprises a ?aked
cereal product.
8. The composition of claim 6, in which said
carbonaceous combustible comprises a ?aked
40
corn product.
HAROLD A. LEWIS.
‘FRED R. WILSON.
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