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Патент USA US3046839

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July 31, 1962
Filed June 22, 1959
FIG. 1
FIG. 2
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Patented July 31,1962
‘ plete the setting" of the binder if necessary.
Theodore L'Roemer, Herrin, llL, assignor to Olin Mathis
son Chemical Corporation, East Alton, 11]., a corpoy
ration of Virginia
More spe
ci?cally, this invention contemplates tamping ‘a com
posite propellent charge consisting 'of a predominant pro
portion of an inorganic oxidizer suspended in a‘ plastic
matrix into a mold separator which is substantially con
centric but not in contact with the side walls of the mold.
The annular'space between the separator and the mold
wall is then ?lled with a material which may-be the same
as that used as the matrix in the grain. After ?lling the
Filed Jame 22, 1959, Ser. No. 821,921
1 Claim. (Cl. 86—1)
This invention, relates to composite solid ~propellent
grains and particularly tosuch grains having a lateral in
mold, the separator is removed and the two charges in the
hibitor sheath.
mold are pressed into intimate contact While the ex
ternal inhibitor sheet can be formed entirely of the pro
Large diameter propellent powder grains formed of in-'
organic particulate oxidizing agents together with modify
pellent grain matrix material, or another plastic material,
.it is preferable to incorporate therein an inert material
generally referred to as composite solid propellant grains. 15 which serves as a cooling agent upon combustion‘of the
They ‘are used extensively as gas generating charges, rock
composite propellant.
The composite propellants of this invention are formed
et fuels, engine starters, and other applications relying
of a preponderant amount of solid particles of an inor
for power generation upon the combustion products of
' ing agents uniformly suspended in a binding matrix are
a charge. Composite solid grains normally burn on all
ganic oxidizing agent uniformly distributed throughout
exposed surfaces. .Thus, when all surfaces are free to
a matrix or binder. Various inorganic oxidizing agents
can be used. Those meeting commercial acceptance in
burn, the rate of gas evolution decreases progressively as
In a
clude the nitrates, chlorates, and perchlorates of the alkali
number of commercial and military applications, when
metals, alkaline earth metals, and ammonia. Of this
uniform thrust is desired throughout the entire combus
group, ammonium nitrate and ammonium perchlorate are
tion period, the‘ composite grains must ‘be provided with‘ 25 considered most important. Suitable binders include as
the surface area of the burning grain ‘diminishes.
phaltic materials, natural and‘ synthetic rubbers, synthetic
plastic materials, and the like. Synthetic rubbers based
lateral inhibitors to insure that the grains will burn only
from end to end.
on the copolymers of polybutadiene with acrylic acid,
methacrylic acid, vinylidine chloride, or the like, are par
Such inhibitors normally take the form of a plastic
seal or sheet which is cemented to the lateral surface.
ticularly advantageous. Similarly, chemical rubbers of
the polyurethane type may be employed. The propor
Assemblies of this type have inherent weaknesses because
of the lack of cohesion between the inhibitor and the
grain surface and also because of the differences in co
efficients of expansionof the di?erent materials. Many
of the prior art inhibited composite grains fall after be
ing subjected to varying temperatures before being used
because the seal between the inhibitor and the grain is
Composite propellent charges also normally contain
‘combustion modi?ers which may constituteup to 10%
or 15% of the weight of the grain. Suitable modi?ers
ruptured by different rates of expansion and contraction,
or for other physico-chemical reasons.
tions of the propellent binder and solid components can
vary widely, but in most instances it is preferred to pro
vide compositions in which the oxidizer is predominant.
include guanidine nitrate, nitroguanidine, cyclotrimethyl
enetrinitramine, melamine, 2,4-dinitrophenoxyethanol,
Another problem inherent tothe use of solid propel
lants as sources of gaseous. working fluid ‘for auxiliary
power systems, rather’ than for rocket propulsion, is the‘
and the like. Relatively small amounts of'carbon black
and-other-opaci?ers, as well as minor; proportions of com
bustion catalysts, such as chromates and the like, can
relatively high temperature of the gas generated. This
difficulty is normally combatted by the use of cooling
also be advantageously incorporated into the propellant
to enhance its burning characteristics.
agents which can be in the form of a sheath about the
grain or incorporated therein. When the inhibitor is 45
The inhibitor sheath of this invention may be formed
of the same material as is used for the binder matrix in
sheathed about the grains, it presents the same problems
that are encountered with laterally inhibited grains. On
the other hand, the amount of cooling agent that can be
incorporated into the grain is necessarily limited because 50
compositions containing excessive proportions of coolant
will not perform satisfactorily.
It is, therefore, an object of this invention to provide
a laterally inhibited composite solid propellent grain
overcomingthe disadvantages of the prior art. It is also 55
the composite grain, or of a dissimilar material. While
the binder alone can be used as the inhibitor, particularly
advantageous results are obtained when the inhibitor
sheath consists of between about 70% to about 80% of
an object of this invention to provide a novel process
absorbing diluent gases.
for the manufacture of improved composite propellants.
include ammonium oxalate, oxamide, melamine, urea,
and the like. The heat absorbing inert materials func
A more speci?c object’r'of this invention is to provide a
new and novel composite propellent grain having a lat
a cooling salt or 'a heat-absorbing material and from
about 20% to about 30% binder. These materials are
preferably in a state of ?ne subdivision. The cooling salts
undergo endothermic decomposition and liberate heat
Suitable materials of this kind
tion primarily by reason of their speci?c or heat ca
eral inhibitor containing a coolant and a method of 60 pacity so as to hinder decomposition, collapse and com
bustion of the inhibitor matrix. Suitable materials of this
making the same.
In accordance with this invention, generally speaking,
kind include clay, various types of silicates, asbestos, and
these and other objects are accomplished by molding a
the like. The thickness of the inhibitor sheath can vary
charge of composite solid propellant, molding inhibitor
about the composite charge but separate therefrom, and
subsequently pressing the propellent charge and. inhibitor
65 the propellant but in all instances must be su?icienth
into intimate contact to form a unitary laterally inhibited
grain. The same binder is preferably used for the pro
pellant and the inhibitor. However, two compatible
binders can be used provided they are readily cohesive
and do not have greatly divergent coef?cients of expan
sion. After the grain is formed, it can be cured to com
widely depending upon the operational speci?cations oi
thick to keep the lateral surfaces of the grain from burn‘
ing. It has been found that the sheath must be at leas‘
0.1 inch to insure such protection.
After the composite charge and inhibitor sheath havi
been blocked or pre-pressed in position, the separator be
tween them is removed and while the grain and inhibito:
are still in the mold, they are subjected to heat and pres
sure which consolidates the charge and brings the in~
lized in carrying out the process of this invention. It is
hibitor into intimate contact with the lateral surface of
only necessary that the apparatus be provided with means
the grain. Generally, the grain and inhibitor are con
for separating the inhibitor and the propellant and that
solidated under an axial pressure of about 5,000 psi.
these means can be readily removed prior to consolidation
and are subjected to a curing temperature in the neighbor
of the materials in the mold, preferably by axial com
hood of 180° F. These values are not critical and pres
sures, curing times, and temperatures vary with the par
In accordance with this invention, it is possible to
ticular binder being used.
' fabricate inhibitors of any desired thickness and com
The manner in which these objects are accomplished
position and propellant charges of any size or chape con
will become clear when the following preferred embodi 10 sistent with engineering practices used in compression
ment is read in connection with the accompanying draw
molding. Although the above speci?c embodiment illus
ing in which:
trates a solid cylindrical charge and its preparation, per
FIGURE 1 is a longitudinal cross-sectional view of
forated charges can be readily made by the insertion of
molding apparatus that can be utilized 'in accordance with
one or more appropriately shaped rods into the mold
this invention; and
15 cavity prior to the introduction of the composite charge.
‘FIGURE 2 is a longitudinal cross-sectional view of a
Thus, various modi?cations which are encompassed by
laterally inhibited grain made in accordance with the prcs- , the present invention will be evident to those skilled in
ent invention.
the art.
About 1,000 parts by weightof a composite propellant
What is claimed is:
charge consisting of an intimate mixture of about 75% 20 A process for the manufacture of inhibited composite
ammonium nitrate, about 10% guanidine nitrate, and
solid propellant grains comprising tamping a composite
about 2% carbon black in a matrix of about 13% of
propellant charge including an inorganic oxidizing agent
acrylic acid-modi?ed polybutadiene rubber were tamped
and a binder into a cylindrical shape, tamping an in
into mold separator 1. Approximately 200 parts by
hibitor containing a cooling agent and a second binder
weight of an inhibitor mix composed of about 20% 25 as in the composite charge into an annular shape about
acrylic acid-modi?ed polybntadiene rubber and 80%
the composite charge, separating means being positioned
ammonium oxalate were tamped into the annular space 2
between the composite charge and inhibitor during tamp
between mold separator 1 and wall mold 3. After the
ing, removing the separating means, subjecting the com
mold was substantially ?lled, the separator was removed
posite charge and inhibitor to axial consolidating com
from its position between the composite charge and the 30 pression, and simultaneously curing the. binders in the
inhibitor. These materials were then subjected to an‘
composite charge and in the inhibitor.
axial pressure of about 5,000 psi. for about 15 minutes
in the mold. This pressure forced the inhibitor and the
:omposite charge into intimate contact and consolidated
the charge. The binder in the consolidated propellant 35
:harge was then cured by subjecting the grain to a tem
perature'of about 180° F. for about 16 to 24 hours.
[he grain thus obtained is shown in FIGURE 2 and con
;ists of a composite propellant charge 4 having an in
:eparable inhibitor coolant sheath 5.
.Although, as shown in the drawing, the mold sepa-'
'ator 1 is cylindrical, it is preferably provided with a
?ight draft to facilitate its removal from the mold. Also,
my other type of molding apparatus can be readily uti
References Cited in the ?le of this patent
White et ‘al. -. _________ __ Apr. 6, 1937
Gcckler _____________ __ Aug. 23, 1949
Meister ______________ __ Aug. 1, 1950
O’Neill _______ _____ -_ June 17, 1952
Sage et al. ___________ _._ Feb. '17, 1953
Miller et al __________ .. Nov. 19, 1957
Bohn et a1 ____________ __ Oct. 28, 1958
Precoul _____________ __ Aug. 4, 1959
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