U.S. patent application number 10/345207 was filed with the patent office on 2005-08-25 for semi-continuous two-pack process for casting solid propergol paste.
This patent application is currently assigned to SNPE. Invention is credited to Gaudre, Marie, Giraud, Eric-Serge, Tauzia, Jean-Michel.
Application Number | 20050183804 10/345207 |
Document ID | / |
Family ID | 8871444 |
Filed Date | 2005-08-25 |
United States Patent
Application |
20050183804 |
Kind Code |
A1 |
Gaudre, Marie ; et
al. |
August 25, 2005 |
SEMI-CONTINUOUS TWO-PACK PROCESS FOR CASTING SOLID PROPERGOL
PASTE
Abstract
A process for casting propellant paste into a mould to
manufacture a block of solid propellant includes first mixing two
groups of components briefly at low pressure, mixing the two groups
of components at high pressure, and casting the mixture in a mould.
The first group of components represents about 80% to about 99% of
the finished product and essentially comprises a liquid prepolymer,
at least one pulverulent solid charge and some of the various
additives of the propellant paste. The second group of components
represents about 20% to about 1% of the finished product and
comprises the crosslinking agent and the rest of the additives.
Inventors: |
Gaudre, Marie; (Le Haillan,
FR) ; Giraud, Eric-Serge; (Bordeaux, FR) ;
Tauzia, Jean-Michel; (Blanquefort, FR) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
SNPE
Paris
FR
|
Family ID: |
8871444 |
Appl. No.: |
10/345207 |
Filed: |
January 16, 2003 |
Current U.S.
Class: |
149/19.92 |
Current CPC
Class: |
C06B 21/0058 20130101;
C06B 45/10 20130101 |
Class at
Publication: |
149/019.92 |
International
Class: |
C06B 045/10 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 1, 2002 |
FR |
02 01214 |
Claims
1-18. (canceled)
19. A semi-continuous two-pack process for making a block of solid
propellant, comprising: mixing a first group of components and a
second group of components to form a mixture; casting the mixture
in a mould; wherein the first group of components represents about
80% to about 99% of the finished product and comprises essentially
a liquid polymer, at least one pulverulent solid charge and at
least one additive; wherein the second group of components
represents about 20% to about 1% of the finished product and
comprises a crosslinking agent; and wherein the first group of
components and the second group of components are separately mixed
prior to the mixing step.
20. The process according to claim 19, wherein the first group of
components represents about 90% to about 99% of the finished
product and the second group of components represents about 10% to
about 1% of the finished product.
21. The process according to claim 19, wherein the second group of
components comprises the crosslinking agent and at least one
additive.
22. The process according to claim 19, wherein the mixing step
comprises: setting the ratio of the first group of components to
the second group of components to the right amount, by means of
precise metering of the two groups of components; mixing the first
group of components and the second group of components under low
pressure to form the mixture; passing the mixture into a buffer
tank; homogenization mixing of the mixture.
23. The process according to claim 22, wherein the mixture is
passed into a buffer tank between the mixing and homogenization
mixing steps.
24. The process according to claim 22, wherein the mixing step is
performed in a static mixer and the homogenization mixing step is
performed in a static mixer.
25. The process according to claim 22, wherein the mixing step is
performed at a pressure between 0.006 MPa and 1 MPa.
26. The process according to claim 22, wherein the homogenization
mixing step is performed at a pressure between 2 MPa and 2.5
MPa.
27. The process according to claim 26, wherein the homogenization
mixing step is performed at a curing temperature of between
20.degree. C. and 80.degree. C.
28. The process according to claim 19, wherein the mixing step is
performed in a static mixer at high pressure.
29. The process according to claim 28, wherein the mixing step is
performed at a curing temperature of between 20.degree. C. and
80.degree. C.
Description
[0001] The present invention relates to the field of blocks or
charges of solid propellant.
[0002] More particularly, the invention relates to a process for
preparing and casting a propellant paste, of composite type, in a
mold for preparing a block or a charge of solid propellant. The
invention applies especially to the manufacture of large charges
for space launchers.
[0003] A solid propellant of composite type comprises a solid
polymer matrix or binder, pulverulent solid charges, such as
oxidizing agents, optionally reducing agents and/or energetic
agents and also various feasibility and performance additives.
[0004] The binder is prepared from a liquid polymerizable resin
with chemically reactive end groups, which will be crosslinked by
means of at least one liquid crosslinking agent. The various
ingredients of the propellant, and then the crosslinking agent, are
introduced into the liquid resin, in a suitable order. On hardening
of the resin by curing at a temperature that is compatible with the
presence of pyrotechnic materials, it coats all of the ingredients
and especially the pulverulent charges to form a solid.
[0005] The ingredients are chosen so as to ensure combustion of the
propellant to produce gases. This combustion generally takes place
by parallel layers; that is, the speed of regression of the flame
front is from a few millimeters per second to a few centimeters per
second.
[0006] Further details regarding the various ingredients forming
part of the composition of propellants of composite type will be
found, for example, in DAVENAS "Technologie des propergols solides
[Technology of solid propellants]", chapters 10 and 11, Masson
1989.
[0007] The process currently used to manufacture such blocks is a
"batch" process, which consists of preparing a certain quality of
product and of casting a certain number of charges.
[0008] In a first step, the various ingredients are introduced in a
suitable order. The ingredients are blended carefully over a long
time, under very specific temperature and pressure (generally under
vacuum) conditions. For the next step, this mixture, which is in
the form of a paste, is cast in a mold with shaping tools. The
assembly is cured to harden the paste. In certain cases, the mold
constitutes the actual envelope of the propellant, this envelope
being suitably prepared for the production of the charge.
[0009] The crosslinking agent is introduced into the mixture
towards the end of the blending step. The paste then begins to
harden. The casting can only be performed for a limited time, known
as the pot life, during which the mixture remains fluid enough to
be cast. It is therefore necessary for the casting in the mold to
follow the end of the blending step as quickly as possible; this
furthermore involves making a compromise between the pot life and
the duration of the curing operation.
[0010] For the manufacture of large charges, from a few tens to a
few hundreds of tons, generally used in the aerospace field
(accelerators attached to the launcher), a sequence of several
blends-casts needs to be set up in the same envelope. The sequence
of blends and casts must be set up in a precise and rigorous
manner. An economic choice between the size of blenders available
and that of the charge must also be made. In all cases, the
manufacturing cycle is long and expensive since there is
considerable immobilization of the materials and personnel during
the manufacture.
[0011] One solution to the problem of the pot life, in the case of
the manufacture of small objects, is suggested by a semi-continuous
two-pack process described by J. M. Tauzia in "Some comments on
processing energetics materials--Compatibility and Processing
Symposium--ADPA--23-25 October 1989 (at Virginia Beach).
[0012] The process described in the Tauzia article consists of
separating the composition into two groups of components of
equivalent viscosity that are then mixed together, in a mass ratio
of close to 1/1, just before casting in the mold. One of the groups
of components comprises the polymer that constitutes the binder,
half of the pulverulent charges and certain additives; the other
group of components comprises the crosslinking agent, which is also
in polymer form, the other half of the pulverulent charges and the
rest of the additives. These two groups of components are
chemically stable when they are separate.
[0013] However, this process has several drawbacks. The two groups
of components each comprise half of the pulverulent charges and
thus pyrotechnic ingredients. Also, the two groups of components
must be prepared and stored in suitable installations that satisfy
strict security standards (hereinbelow, secure installations).
[0014] Moreover, it is difficult to produce a homogeneous mixture
of these two groups of components, which are viscous.
[0015] Lastly, the final composition obtained is different from
that of the "batch" process, especially with regard to the binder.
The two-pack process forms the binder from the mixture of two
polymers; thus, the propellant obtained must undergo a further
approval for the intended use. This is a long and expensive
operation.
[0016] The two-pack process with a mixture in a 1/1 ratio of two
groups of components is therefore not entirely satisfactory, and
does not appear to be easily applicable to the manufacture of large
charges.
[0017] The aim of the present invention, adopting a two-pack
technique, is to solve the problems posed above.
[0018] The present invention thus relates to a semi-continuous
two-pack process for casting propellant paste in a mold to
manufacture a block of solid propellant by curing the paste. The
paste comprises a liquid prepolymer, a liquid crosslinking agent,
at least one pulverulent solid charge and various additives. The
casting is performed using the mixture of two groups of components,
and the process is characterized in that the first group of
components represents about 80% to about 99% of the finished
product and comprises essentially the prepolymer, all the
pulverulent solid charges and some of the additives; and that the
second group of components represents about 20% to about 1% of the
finished product and comprises all the crosslinking agent and the
remainder of the additives. The additives will especially comprise
some of the propellant plasticizer. It may also be stated that the
mass ratio of the mixture of the two groups of components is
between 80/20 and about 99/1.
[0019] Preferably, the first group of components represents about
90% to about 99% of the finished product, and the second group of
components represents about 10% to about 1% of the finished
product. The mass ratio of the mixture of the two groups of
components is between about 90/10 and about 99/1.
[0020] The propellant binder may be obtained from a
carboxytelechetic polybutadiene or, preferably, from a
hydroxytelechetic polybutadiene crosslinked in the latter case with
an isocyanate in monomer form. The binder may also be obtained from
a substituted oxetane or oxirane prepolymer; from nitramine or
nitrate polymer; from polyester or from polyether.
[0021] The pulverulent charges comprise at least one oxidizing
charge chosen from the group of non-organic nitrates or
perchlorates, for example ammonium nitrate or ammonium perchlorate.
Some of these oxidizing pulverulent charges may be replaced with
energetic charges such as nitramines, for example octagon or
hexagon.
[0022] Finally, the pulverulent charges may also comprise, in order
to increase the performance qualities of the propellant, reducing
charges in the form of metal powder, for example aluminum.
[0023] The various additives usually used for manufacturing
propellants also include the plasticizer and the crosslinking
catalyst, the natures and contents of which may have advantageous
effects in the present invention, as will be seen hereinbelow.
[0024] The choice of the plasticizer and of its contents in the
first group of components especially avoids the problems of
settling of the solid charges in the course of the storage of this
group of components.
[0025] Advantageously, the second group of components comprises
only the liquid crosslinking agent in monomer form, without any of
the propellant additives, which are all incorporated in the first
group of components.
[0026] According to a first variant of this process, the mixing is
performed in two steps:
[0027] a first step of setting the ratio of the first group of
components to the second group of components to the right amount,
by means of precise metering of the two groups of components in the
desired mass ratio, and briefly mixing the two groups of
components,
[0028] a second step of homogenization mixing, during which the
above brief mixture is mixed thoroughly, before casting into the
mold.
[0029] Advantageously, the two mixing steps are separated by
passing the mixture into a buffer tank, before taking it up for the
homogenization mixing. The residence time in the buffer tank is as
short as possible.
[0030] The two mixing steps are performed by any suitable means,
but are preferably performed by means of static mixers.
[0031] Preferably, the mixing of the first step is performed at low
pressure and the homogenization mixing is performed at high
pressure.
[0032] The separation of the two steps by passing the mixture into
a buffer tank makes it possible to take up the mixture at high
pressure to perform the step of homogenization mixing and of the
casting the paste with a high flow rate. This high flow rate is
necessary for the casting, under satisfactory economic conditions,
of large charges. Increasing the pressure of the mixture is
performed by means of a pump placed at the outlet of the buffer
tank.
[0033] Advantageously, the mixing of the first step is performed at
low pressure of between about 0.006 MPa and about 1 MPa; and the
homogenization mixing is performed at high pressure of between
about 2 MPa and about 2.5 MPa.
[0034] Also advantageously, the homogenization mixing is performed
at a propellant paste curing temperature of between about
20.degree. C. and about 80.degree. C. The expression "curing at
about 20.degree. C." should be understood simply as meaning
maintaining the temperature of the propellant paste at room
temperature. The curing temperature may be lowered by increasing
the content of crosslinking catalyst among the additives. The
mixing and casting at the same temperature as the curing
temperature has the advantage of limiting the problems of thermal
shrinkage.
[0035] According to a second variant of the process, the two groups
of components are mixed together in a single step.
[0036] In this case also, the mixing is performed by any suitable
means, but is preferably performed in a static mixer set with the
desired mass ratio. The static mixer operates at high pressure, of
between 2 MPa and about 2.5 MPa. Adantageously, the mixing is
performed, as previously, at the propellant paste curing
temperature of between about 20.degree. C. and about 80.degree. C.
This curing temperature may be lowered towards the lower limit by
increasing the content of crosslinking catalyst.
[0037] This invention essentially characterized by a particular
choice of the two groups of components that will be mixed together
in a precise mass ratio to resolve the problems left unanswered by
the two-pack process of the prior art.
[0038] This process of course retains the advantage of the two-pack
process, namely that of dispensing with the pot life.
[0039] The blending sequences to prepare the two groups of
components are entirely independent of the sequences for mixing and
casting the said components, which may take place a very long time
after these two groups of components have been prepared.
[0040] Only the first group of components, which contains all the
pulverulent charge, and thus the pyrotechnic products, needs to be
prepared with care and stored in secure installations. The second
group of components, which may amount to the crosslinking agent
alone, is prepared and stored under very simple conditions.
[0041] Moreover, the second group of components is essentially
liquid and mixes without problem with the first group of
components, which itself is in the form of a paste.
[0042] This makes it possible to readily adapt the pressure and
flow rate conditions to the time of casting of a large charge. This
therefore considerably reduces the duration and cost of the
manufacturing cycle.
[0043] Finally, in the process of the invention, since the
crosslinking agent is introduced in the form of a liquid monomer,
the binder obtained will be identical to that of the "batch"
process, and thus since the final composition will be the same, the
propellant will not need to be approved again, which considerably
reduces the costs.
[0044] The invention will be described in greater detail with the
aid of FIGS. 1 and 2, which represent in a very schematic manner
examples of installations for carrying out the two variants of the
process.
[0045] FIG. 1 describes an installation for carrying out the
invention according tot a first mode in two separate steps.
[0046] FIG. 2 describes an installation for carrying out the
invention according to the second mode in a single step.
[0047] These two variants of the process of the invention assume
the prior preparation of the two groups of components.
[0048] Firstly, the second group of components, which essentially
comprises the liquid crosslinking agent in monomer form and
optionally some of the additives, is very simple to prepare. For
example, it involves mixing with mechanical stirring. This group of
components represents only a small mass of the finished product,
and a single tank will be sufficient to store it.
[0049] In contrast, the first group of components, which comprises
the liquid prepolymer, all of the pulverulent solid changes and the
additives, must be prepared with the same precautions and care as a
propellant. The mixture constituting this group of components is
chemically stable since there is no crosslinking agent; a suitable
choice of plasticizer prevents settling of the solid charges and
allows this mixture to be stored for a long time in suitable secure
installations.
[0050] The first group of components represents the majority of the
finished product and, in the case of a large charge (for example
100 tons), a large amount of product that needs to be prepared by
several blends and stored in several tanks, given the sizes of the
blenders and tanks available.
[0051] FIG. 1 shows very schematically an installation for carrying
out the process of the invention according to a first variant.
[0052] Tanks 1 and 2 containing the first and second groups of
components, respectively, feed a static mixer 3.
[0053] On the tanks 1 and 2, the pistons 8 and 9, driven by a
mechanism that is not shown, feed the first and second groups of
components, respectfully, in the desired mass ratio into the static
mixer 3, which performs a brief mixing of the two groups of
components set to the desired ratio, and feeds a buffer tank 4. At
the outlet of the buffer tank, a pump 5 raises the pressure of the
mixture to feed a static mixer 6, working at high pressure, the
outlet 7 of the mixer directly feeding the casting mold.
[0054] For the manufacture of a large charge, the required amount
of mixture of the first group of components exceeds the
capabilities of a single tank. It suffices to have available
several tanks of the type 1 on the feed into the static mixer 3
and, via a special valve system, to deplete the mixture
successively in the tanks.
[0055] FIG. 2 shows very schematically an installation for carrying
out the process according to a second variant.
[0056] The tanks 10 and 12 contain the first and second groups of
components, respectively. Pumps 11 and 13, working at high pressure
and the flow rates of which are in the desired mass ratio, feed a
static mixer 14, the outlet 15 of which directly feeds the casting
mold.
[0057] The metering and pressurization pumps are chosen from
standard equipment, such as either peristaltic pumps or screw pumps
(for example of the Steible brand), or alternating twin-piston
pumps (for example of the Putzmeister brand) or pistons placed
directly on the tanks of the two groups of components.
[0058] The static mixers are pipes containing cross braces that
oblige the paste passing therethrough to become separated and to
remix. These pipes are sized in diameter as a function of the flow
rate and the number of unit elements ensures the quality of mixing
as a function of the available pressure. 4 unit elements are used
for low-pressure mixing and up to 12 unit elements are used for
high-pressure mixing. A mixer consisting of jacketed unit elements
makes it possible, by circulating a suitable heat-exchange fluid,
to heat the propellant paste to the desired casting
temperature.
[0059] The mechanical properties of the propellant manufactured by
the process of the present invention were measured for a propellant
whose polymer matrix based on a hydroxytelechetic polybutadiene
resin represents 14% by mass of the finished product, containing
82% by mass of ammonium perchlorate and 4% by mass of aluminum. The
density is 1.72, the Young's modulus is between 5 and 7 MPa and the
breaking strength is 1.1 MPa. These values are comparable with
values obtained by the "batch" process.
* * * * *