U.S. patent application number 15/825783 was filed with the patent office on 2019-01-24 for cast explosive composition.
This patent application is currently assigned to BAE SYSTEMS plc. The applicant listed for this patent is BAE SYSTEMS plc. Invention is credited to Ronald Edward HOLLANDS, Ian Ewart Paterson MURRAY.
Application Number | 20190023628 15/825783 |
Document ID | / |
Family ID | 40289469 |
Filed Date | 2019-01-24 |
United States Patent
Application |
20190023628 |
Kind Code |
A1 |
HOLLANDS; Ronald Edward ; et
al. |
January 24, 2019 |
CAST EXPLOSIVE COMPOSITION
Abstract
The invention relates to a cast explosive composition comprising
a polymer-bonded explosive and a defoaming agent, and to a process
for reducing the number and/or total volume of voids in a cast
explosive composition comprising the steps of: combining a
polymer-bonded explosive and a defoaming agent; and casting the
explosive composition. The defoaming agent may be used for reducing
the number and/or total volume of voids in a cast explosive
composition and the cast explosive composition may be used in an
explosive product.
Inventors: |
HOLLANDS; Ronald Edward;
(Usk, GB) ; MURRAY; Ian Ewart Paterson; (Ponthir,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BAE SYSTEMS plc |
London |
|
GB |
|
|
Assignee: |
BAE SYSTEMS plc
London
GB
|
Family ID: |
40289469 |
Appl. No.: |
15/825783 |
Filed: |
November 29, 2017 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13061308 |
Feb 28, 2011 |
|
|
|
PCT/GB2009/002081 |
Aug 27, 2009 |
|
|
|
15825783 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C06B 45/10 20130101;
C06B 23/009 20130101; C06B 21/0058 20130101 |
International
Class: |
C06B 21/00 20060101
C06B021/00; C06B 45/10 20060101 C06B045/10; C06B 23/00 20060101
C06B023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 29, 2008 |
GB |
0815936.0 |
Claims
1-16. (canceled)
17. A method for producing a cast and cured explosive composition,
the method comprising vacuum casting a castable explosive
composition comprising a polymer-bonded explosive in admixture with
0.01-2 wt % of a silicone-free defoaming agent and wherein said
castable explosive composition contains entrained bubbles therein
which become substantially removed by coalescence and egress, as
facilitated by the silicone-free defoaming agent, during casting;
and curing the cast; wherein said polymer-bonded explosive
comprises an explosive and a polymer binder; and wherein said cast
and cured explosive composition possesses a substantial absence of
voids, wherein said silicone-free defoaming agent possesses the
characteristic of being surface active at interfaces between
bubbles and the polymer-bonded explosive and facilitating the
coalescence and egress of bubbles.
18. The method according to claim 17, wherein the defoaming agent
is present in an amount of 0.03-2 wt %.
19. The method according to claim 17, wherein said defoaming agent
is present in an amount of 0.5 to 2 wt %.
20. The method according to claim 17, wherein said defoaming agent
is present in an amount of 0.25 to 1 wt %.
21. The method according to claim 17, wherein said defoaming agent
is present in an amount of 0.5 to 1 wt %.
22. The method according to claim 17, wherein said defoaming agent
is present in an amount of 0.25 to 2 wt %.
23. The method according to claim 17, wherein the polymer-bonded
explosive and the defoaming agent are combined in the presence of a
solvent.
24. The method according to claim 17, wherein the polymer-bonded
explosive and the defoaming agent are combined in the absence of a
solvent.
25.-27. (canceled)
28. The method according to claim 17, wherein the defoaming agent
comprises a combination of silicone-free defoaming agent with a
polysiloxane.
29. The method according to claim 17, wherein said polymer binder
is selected from polyurethane, cellulosic materials such as
cellulose acetate, polyesters, polybutadienes, polyethylenes,
polyisobutylenes, PVA, chlorinated rubber, epoxy resins, two-pack
polyurethane systems, alkyd/melanine, vinyl resins, alkyds,
self-crosslinking acrylates, butadiene-styrene block copolymers,
polyNIMMO, polyGLYN, GAP, and blends, copolymers, and combinations
thereof.
30. The method according to claim 17, wherein said polymer binder
comprises polyurethane.
31. The method according to claim 30, wherein said polyurethane
includes a hydroxyterminated polybutadiene.
32. The method according to claim 17, wherein said explosive is
selected from RDX, HMX, FOX-7, TATND, HNS, TATB, NTO, HNIW, GUDN,
picrite, tetryl, ethylene dinitramine, nitroglycerine, butane triol
trinitrate, pentaerythritol tetranitrate, DNAN trinitrotoluene,
ammonium nitrate, ADN, ammonium perchlorate, energetic alkali metal
salts, energetic alkaline earth metal salts, and combinations
thereof.
33. The method according to claim 17, wherein said explosive
composition further comprises a metal powder.
34. The method according to claim 33, wherein said metal powder is
selected from aluminum, magnesium, tungsten, alloys of these
metals, and combinations thereof, in admixture with the
polymer-bonded explosive.
35. The method according to claim 17, wherein said explosive
comprises RDX.
36. The method according to claim 17, wherein said explosive
comprises RDX and said polymer binder comprises polyurethane.
37. The method according to claim 36, wherein said RDX is in an
amount in the range of about 75-95 wt % and said polyurethane
binder is in an amount in the range of about 5-25 wt %.
38. The method according to claim 17, wherein said silicone-free
defoaming agent is present in an amount of about 1 wt %.
39. The method according to claim 17, wherein said silicone-free
defoaming agent is an alkoxylated alcohol.
40. The method according to claim 17, wherein said vacuum casting
is conducted under a vacuum at a pressure of less than 10 mm Hg.
Description
[0001] This invention relates to cast explosive compositions, their
preparation and use. In particular, the invention relates to
polymer-bonded explosive compositions.
[0002] Explosives compositions are generally shaped, the shape
required depending upon the purpose intended. Shaping can be by
casting, pressing, extruding or moulding; casting and pressing
being the most common shaping techniques. However, it is generally
desirable to cast explosives compositions as casting offers a
greater design flexibility than pressing.
[0003] Polymer-bonded explosives (also known as plastic-bonded
explosives and PBX) are typically explosive powders bound into a
polymer matrix. The presence of the matrix modifies the physical
and chemical properties of the explosive and often facilitates the
casting and curing of high melting point explosives. Such
explosives could otherwise only be cast using melt-casting
techniques. Melt casting techniques can require high processing
temperatures as they generally include a meltable binder. The
higher the melting point of this binder, the greater the potential
hazard. In addition, the matrix can be used to prepare
polymer-bonded explosives which are less sensitive to friction,
impact and heat; for instance, an elastomeric matrix could provide
these properties. The matrix also facilitates the fabrication of
explosive charges which are less vulnerable in terms of their
response to impact, shock, thermal and other hazardous stimuli.
Alternatively, a rigid polymer matrix could allow the resulting
polymer-bonded explosive to be shaped by machining, for instance
using a lathe, allowing the production of explosive materials with
complex configurations where necessary.
[0004] U.S. Pat. No. 6,893,516 describes an explosive mixture in
which the crystalline explosive is coated with polysiloxanes to
produce a granular product. The application of this coating to each
crystal smoothes the surface of the crystals eliminating fine pores
which could otherwise trigger unwanted reaction of the explosive.
As such, the polysiloxane coating reduces the sensitivity of the
granular explosive, improving safety in handling and during any
subsequent shaping steps.
[0005] Conventional casting techniques often result in a solidified
composition which retains air bubbles introduced during mixing of
the material and by the placing of the composition into the mould.
Typically such placing of the composition into the mould will be by
pouring of the composition. These voids can reduce the performance
of the composition as less explosive is present per unit volume. In
addition, porosity or voids, where present in sufficient quantity,
can affect the shock sensitivity of the composition, making the
composition less stable to impact or ignition from a shock
wave.
[0006] The invention seeks to provide a cast explosive composition
in which the stability of the composition is improved, this may be
through the reduction of the number and/or total volume of voids,
or through other means, such as a reduction in the number of
volatile components present. Such a composition would not only
offer improved stability, but also a reduced sensitivity to factors
such as friction, impact and heat. Thus, the risk of inadvertent
initiation of the explosive is diminished.
[0007] In one aspect of the invention there is provided a cast
explosive composition comprising a polymer-bonded explosive and a
defoaming agent.
[0008] The presence of the defoaming agent may reduce or
substantially eliminate the voids which would often remain in the
composition. Accordingly, where used herein the term "defoaming
agent" is intended to mean an additive with surface active
properties which acts to eliminate voids from within the polymeric
binder of the cast explosive composition. Any additive which does
not perform this function is not regarded as constituting a
defoaming agent within the meaning of the invention. In the art,
such additives are also known as "anti-foaming agents", "deaerating
agents" and "air release agents".
[0009] The voids are typically found within the body of the binder
component of the polymer-bonded explosive, rather than at the
interface between the binder and the explosive component. Removal
of these voids is particularly desirable where the intended use of
the explosive will result in exposure to high g-forces, such as
would be the case in an artillery shell, mortar bomb or missile. It
is believed that under such conditions, adiabatic compression of
the voids occurs making the region around the void more prone to
premature ignition. Another application where the removal of voids
is of particular importance is where the intended use of the
explosive will result in rapid deceleration on impact with a target
but where penetration of the target is required before the munition
is detonated. This would be the case with bombs and missiles. Where
voids are present, adiabatic compression of these may result in
ignition on impact, before penetration of the target has
occurred.
[0010] In addition, the defoaming agent reduces the viscosity of
the composition, allowing the casting process to be carried out
more rapidly than in the absence of this additive. Further,
compositions containing the defoaming agent have been seen in some
instances to have a higher density in terms of % TMD achieved than
when this additive is absent. This increase in density has also
been linked to an improved stability and reduction in sensitivity
of the explosive. In many cases, the reduction of voids will
correlate with an increase in density; however as the compositions
of the invention are complex, an increase in density can only be
taken as an indication that the number of voids has been reduced.
In many instances other methods, such as X-radiography are used to
directly visualise the voids and to determine the effect of the
defoaming agent.
[0011] In an additional aspect of the invention there is provided a
process for reducing the number and/or total volume of voids in a
cast explosive composition comprising the steps of:
[0012] combining a polymer-bonded explosive and a defoaming
agent;
[0013] and
[0014] casting the explosive composition.
[0015] Another aspect of the invention relates to the use of a cast
explosive composition as described herein in an explosive product,
and a further aspect of the invention relates to an explosive
product comprising a cast explosive composition as described
herein.
[0016] Polymer-bonded explosives include a polymeric binder which
forms a matrix bonding explosive particles within. The binder thus
may be selected from a wide range of polymers, depending upon the
application in which the explosive will be used. However, in
general at least a portion of the binder will be selected from
polyurethane, cellulosic materials such as cellulose acetate,
polyesters, polybutadienes, polyethylenes, polyisobutylenes, PVA,
chlorinated rubber, epoxy resins, two-pack polyurethane systems,
alkyd/melanine, vinyl resins, alkyds, self-crosslinking acrylates,
thermoplastic elastomers such as butadiene-styrene block
copolymers, and blends, copolymers and/or combinations thereof.
Energetic polymers may also be used either alone or in combination,
these include polyNIMMO (poly(3-nitratomethyl-3-methyloxetane),
polyGLYN (poly glycidyl nitrate) and GAP (glycidyl azide polymer).
It is preferred that the binder component be entirely selected from
the list of binders above either alone or in combination. In some
embodiments the binder will comprise at least partly polyurethane,
often the binder will comprise 50-100 wt % polyurethane, in some
instances, 80-100 wt %. In some embodiments the binder will consist
of polyurethane. Polyurethanes derived from MDI (methylene diphenyl
diisocyanate) and TDI (toluene diisocyanate) and IPDI (isophorone
diisocyanate) may be used. IPDI is generally preferred as it is a
liquid and hence easy to dispense; it is relatively slow to react,
providing a long pot-life and slower temperature changes during
reaction; and it has a relatively low toxicity compared to most
other isocyanates. It is also preferred that, where the binder
comprises polyurethane, the polyurethane binder includes a
hydroxyterminated polybutadiene.
[0017] The explosive component of the polymer-bonded explosive may,
in certain embodiments, comprise one or more heteroalicyclic
nitramine compounds. Nitramine compounds are those containing at
least one N--NO.sub.2 group. Heteroalicyclic nitramines bear a ring
containing N--NO.sub.2 groups. Such ring or rings may contain for
example from two to ten carbon atoms and from two to ten ring
nitrogen atoms. Examples of preferred heteroalicyclic nitramines
are RDX (cyclo-1,2,3-trimethylene-2,4,6-trinitramine, Hexogen), HMX
(cyclo-1,3,5,7-tetramethylene-2,4,6,8-tetranitramine, Octogen), and
mixtures thereof. The explosive component may additionally or
alternatively be selected from TATND (tetranitro-tetraminodecalin),
HNS (hexanitrostilbene), TATB (triaminotrinitrobenzene), NTO
(3-nitro-1,2,4-triazol-5-one), HNIW
(2,4,6,8,10,12-hexanitrohexaazaisowurtzitane), GUDN (guanyldylurea
dinitride), FOX-7 (1,1-diamino-2, 2-dinitroethene), and
combinations thereof.
[0018] Other highly energetic materials may be used in place of or
in addition to the compounds specified above. Examples of other
suitable known highly energetic materials include picrite
(nitroguanidine), aromatic nitramines such as tetryl, ethylene
dinitramine, and nitrate esters such as nitroglycerine (glycerol
trinitrate), butane triol trinitrate or pentaerythritol
tetranitrate, DNAN (dinitroanisole), trinitrotoluene (TNT),
inorganic oxidisers such as ammonium salts, for instance, ammonium
nitrate, ammonium dinitramide (ADN) or ammonium perchlorate, and
energetic alkali metal and alkaline earth metal salts.
[0019] The explosive component of the polymer-bonded explosive may
be in admixture with a metal powder which may function as a fuel or
which may be included to achieve a specific terminal effect. The
metal powder may be selected from a wide range of metals including
aluminium, magnesium, tungsten, alloys of these metals and
combinations thereof. Often the fuel will be aluminium or an alloy
thereof; often the fuel will be aluminium powder.
[0020] In some embodiments, the polymer-bonded explosive comprises
RDX. The polymer-bonded explosive may comprise RDX as the only
explosive component, or in combination with a secondary explosive
component, such as HMX. Preferably, RDX comprises 50-100 wt % of
the explosive component.
[0021] In many cases the binder will be present in the range about
5-20 wt % of the polymer-bonded explosive, often about 5-15 wt %,
or about 8-12 wt %. The polymer-bonded explosive may comprise about
88 wt % RDX and about 12 wt % polyurethane binder. However, the
relative levels of RDX to polyurethane binder may be in the range
about 75-95 wt % RDX and 5-25 wt % polyurethane binder.
Polymer-bonded explosives of this composition are commercially
available, for example, Rowanex 1100.TM..
[0022] Many defoaming agents are known and in general any defoaming
agent or combination thereof which does not chemically react with
the explosive may be used. However, often the defoaming agent will
be a polysiloxane. In many embodiments, the polysiloxane is
selected from polyalkyl siloxanes, polyalkylaryl siloxanes,
polyether siloxane co-polymers, and combinations thereof. It is
often preferred that the polysiloxane be a polyalkylsiloxane;
polydimethylsiloxane may typically be used. Alternatively, the
defoaming agent may be a combination of silicone-free surface
active polymers, or a combination of these with a polysiloxane.
Such silicone-free polymers include alkoxylated alcohols,
triisobutyl phosphate, and fumed silica. Commercially available
products which may be used include, BYK 088, BYK A500, BYK 066N and
BYK A535 each available from BYK Additives and Instruments, a
subdivision of Altana; TEGO MR2132 available from Evonik; and BASF
SD23 and SD40, both available from BASF. Of these, BYK A535 and
TEGO MR2132 are often used as they are solventless products with
good void reduction properties.
[0023] The defoaming agent may be added to the composition in a
solvent carrier. However, it is generally preferred that solvents
be absent. It has been found that the use of defoaming agents which
are not carried in a solvent, or even the use of entirely
solventless systems, is advantageous as there are fewer (or
substantially no) volatile components present during processing of
the composition, reducing the safety precautions and/or plant
modifications needed. Further, the exclusion of solvents eliminates
the risk of residual volatiles separating (for instance by
evaporation or leaking) from the composition during storage
resulting in unpredictable modifications of the properties of the
compositions such as the creation of voids as a result of volatile
evaporation.
[0024] Often the defoaming agent is present in the range about
0.01-2 wt %, in some instances about 0.03-1.5 wt %, often about
0.05-1 wt %, in many cases about 0.25 or 0.5-1 wt %. At levels
below this (i.e. below 0.01 wt %) there is often insufficient
defoaming agent in the composition to significantly alter the
properties of the polymer-bonded explosive, whereas above this
level (i.e. above 2 wt %) the viscosity of the cast solution may be
so low that the composition becomes inhomogeneous as a result of
sedimentation and segregation processes occurring within the
mixture.
[0025] Without being bound by theory, it is believed that the
defoaming agent not only acts to reduce viscosity, facilitating the
casting process and the egress of voids from the composition during
casting, but that the defoaming agents are surface active at the
void-composition interfaces, causing the void bubbles to coalesce
and hence be expelled from the composition as a result of the
greater buoyancy of the larger bubbles produced. This results in
compositions with fewer visible voids, which are more stable than
known explosive compositions.
[0026] The explosive composition may include a solvent, any solvent
in which at least one of the components is soluble and which does
not adversely affect the safety of the final product may be used,
as would be understood by the person skilled in the art. However,
it is preferred, for the reasons described above, that in some
embodiments that solvent be absent.
[0027] Where present, the solvent may be added as a carrier for the
defoaming agent or another component of the composition. The
solvent will typically be removed from the explosive composition
during the casting process, however some solvent residue may remain
due to imperfections in the processing techniques or where it
becomes uneconomical to remove the remaining solvent from the
composition. Accordingly, in some embodiments the polymer-bonded
explosive and the defoaming agent are combined in the presence of a
solvent. Often the solvent will be selected from diisobutylketone,
polypropylene glycol, isoparaffins, propylene glycol,
cyclohexanone, butyl glycol, ethylhexanol, white spirit,
isoparaffins, xylene, methoxypropylacetate, butylacetate,
naphthenes, glycolic acid butyl ester, alkyl benzenes and
combinations thereof. In some instances, the solvent is selected
from diisobutylketone, polypropylene glycol, isoparaffins,
propylene glycol, isoparaffins, and combinations thereof.
[0028] Although melt casting processes are compatible with the
invention, typically the inventive composition will be cast using
"cast and curing" techniques. Accordingly, where the components of
the cast explosive composition are not inherently curable (for
instance, where all polymer components are thermoplastic polymers)
a curative may optionally be present. In many embodiments the
casting technique used is vacuum casting as the resulting product
is generally of greater density and no visible voids compared with
the equivalent air-cast product. In general, the curing step will
take place after the casting step has occurred.
[0029] The composition may also contain minor amounts of other
additives commonly used in explosives compositions. Examples of
these include microcrystalline wax, energetic plasticisers,
non-energetic plasticisers, anti-oxidants, catalysts, curing
agents, metallic fuels, coupling agents, surfactants, dyes and
combinations thereof. Energetic plasticisers may be selected from
eutectic mixtures of alkylnitrobenzenes (such as dinitro- and
trinitro-ethyl benzene), alkyl derivatives of linear nitramines
(such as an N-alkyl nitratoethyl-nitramine, for instance
butyl-NENA), and glycidyl azide digomers.
[0030] Casting the explosive composition offers a greater
flexibility of process design than can be obtained with pressing
techniques. This is because the casting of different shapes can be
facilitated through the simple substitution of one casting mould
for another. In other words, the casting process is
backwards-compatible with earlier processing apparatus. Conversely,
where a change of product shape is required using pressing
techniques, it is typically necessary to redesign a substantial
portion of the production apparatus for compatibility with the
mould, or the munition to be filled, leading to time and costs
penalties. Further, casting techniques are less limited by size
than pressing techniques which depend upon the transmission of
pressure through the moulding powder to cause compaction. This
pressure falls off rapidly with distance, making homogeneous
charges with large length to diameter ratios (such as many shell
fillings) more difficult to manufacture.
[0031] In addition, the casting process of the invention offers a
moulded product (the cast explosive compositions described) with a
reliably uniform fill regardless of the shape required by the
casting. This may be partly attributed to the use of a casting
technique, and partly to the presence of the defoaming agent. The
defoaming agent substantially reduces the number of voids within
the binder and hence the cast explosive composition. In some
instances, the voids are substantially eliminated. Casting can
occur in situ with the housing (such as a munition) to be filled
acting as the mould; or the composition can be moulded and
transferred into a housing in a separate step. Often casting will
occur in situ.
[0032] Further, compositions including polymer-bonded explosives
and hydroxyterminated polybutadiene binders in particular, are more
elastomeric when cast than when pressed. This makes them less prone
to undergoing a deflagration-to-detonation transition when exposed
to accidental stimuli. Instead, such systems burn without
detonating, making them safer to use than pressed systems.
[0033] Additionally, the shapes that pressing processes can be
reliably applied to are more limited. For instance, it is often a
problem achieving a complete fill of a conical shape using pressing
techniques as air is often trapped at or towards the tip of the
cone. Casting processes, being intrinsically "fluid" processes, are
not limited in this way.
[0034] The process of the invention may be a continuous or batch
process as appropriate. Many known casting processes will be
compatible for use with the invention as modification of these
processes to allow for the addition of the defoaming agent to the
polymer-bonded explosive and to allow the defoaming agent to
perform its defoaming function during casting, is within the
capabilities of the person skilled in the art. Where a continuous
process is used this may make use of static mixing technology such
as the technology described in EP 1485669.
[0035] The process may utilise a premix or precure as a starting
material, although these are not essential. A premix will typically
be a mixture of an explosive component and a binder component,
usually a plasticiser. In some instances the explosive component is
desensitized with water prior to formation of the premix, a process
known as wetting or phlegmatization. However, as retention of water
within the premix is generally undesirable it will typically be
removed from the premix prior to further processing, for instance
by heating during the mixing of the explosive component and the
plasticiser.
[0036] In some cases the plasticiser will be absent; however the
plasticiser will typically be present in the range 0-10 wt % of the
plasticiser and explosive premix, often in the range 0.01-8 wt %,
on occasion 0.5-7 wt % or 4-6 wt %. The plasticiser will often be a
non-energetic plasticiser, many are known in the art; however
energetic plasticisers may also be used in some instances. A
precure will typically be a combination of the premix and the other
components of the composition with the exception of the catalyst
and the curing agent. In some instances the defoaming agent will
also be absent from the precure.
[0037] The cast explosive composition of the invention has utility
both as a main charge or a booster charge in an explosive product.
Often the composition will be the main charge. The composition of
the invention may be used in any "energetic" application where the
presence of voids causes safety or functional problems. Such uses
include mortar bombs and artillery shells as discussed above.
Additionally, the inventive composition may be used to prepare
explosives for gun-launch applications, explosive filings for bombs
and warheads, propellants, including composite propellants, base
bleed compositions, gun propellants and gas generators.
[0038] Except in the examples, or where otherwise explicitly
indicated, all numbers in this description indicating amounts of
material or conditions of reaction, physical properties of
materials and/or use are to be understood as modified by the word
"about." All amounts are by weight of the final composition, unless
otherwise specified. Further, the cast explosive composition may
comprise, consist essentially of, or consist of any of the possible
combinations of components described above and in the claims except
for where otherwise specifically indicated. The process for
reducing the voids in the composition may comprise, consist
essentially of, or consist of the steps specified above and in the
claims.
[0039] The following non-limiting examples illustrate the
invention.
EXAMPLES
Example 1
[0040] A series of commercially available defoaming agents were
cast and cured with Rowanex 1100 (88 wt % RDX and 12 wt %
polyurethane agent). Curing occurred over 5 days at 65.degree. C.
105 mm and 155 mm shells prepared using the resulting composition
were found to have no detectable voids, and no adverse effect on
the chemical or mechanical properties of the polymer-bonded
explosive were observed. Table 1 below illustrates the effect of
binder type and level on the viscosity and density of the
composition.
TABLE-US-00001 TABLE 1 Den- Den- Dos- sity - sity - % age Vis-
Vacuum Air TMD.sup..sctn. (wt cosity Cast Cast (air 1. Defoaming
Agent* %) (cps).sup.# (g/cm.sup.3) (g/cm.sup.3) cast) No Additive
-- 0.12 1.608 1.608 99.3 Solution of foam-destroying 1.0 0.035
1.608 1.602 99.6 polymers and polysiloxanes in isoparaffin solvent
(BYK 088) Solution of silicone-free 1.0 0.033 1.612 1.606 99.9
foam-destroying polymers in Alkylbenzene/ methoxypropylacetate 12/1
(BYK A500) Solution of foam-destroying 0.1 0.12 1.614 1.619 99.6
polysiloxanes in diisobutylketone (BYK 066N) Solution of
foam-destroying 0.5 0.063 1.618 1.608 99.6 polysiloxanes in
diisobutylketone (BYK 066N) Solution of foam-destroying 1.0 0.04
1.620 1.605 99.8 polysiloxanes in diisobutylketone (BYK 066N)
Solvent free mixture of 0.1 0.076 1.6 1.6 98.9 foam-destroying
polymers silicone free (BYK A535) Solvent free mixture of 0.5 0.07
1.612 1.608 99.6 foam-destroying polymers silicone free (BYK A535)
Solvent free mixture of 1.0 0.034 1.59 1.597 99.3 foam-destroying
polymers silicone free (BYK A535) Concentrate based on 0.1 0.12
1.605 1.622 100 organosiloxanes plus fumed silica (TEGO MR2132)
Concentrate based on 0.5 0.073 1.613 1.609 99.7 organosiloxanes
plus fumed silica (TEGO MR2132) Concentrate based on 1.0 0.047
1.594 1.561 97.1 organosiloxanes plus fumed silica (TEGO MR2132)
Solvent free, silicone free 0.1 0.133 1.611 1.612 99.6 alkoxylated
alcohol (BASF SD23) Solvent free, silicone free 0.5 0.09 1.597
1.597 98.9 alkoxylated alcohol (BASF SD23) Solvent free, silicone
free 1.0 0.28 1.623 1.623 100 alkoxylated alcohol (BASF SD23)
Solvent free, silicone free 0.1 0.08 1.609 1.610 99.5 triisobutyl
phosphate (BASF SD40) Solvent free, silicone free 0.5 0.06 1.598
1.603 99.3 triisobutyl phosphate (BASF SD40) Solvent free, silicone
free 1.0 0.07 1.596 1.598 99.4 triisobutyl phosphate (BASF SD40)
Dibutylketone only 1.0 -- 1.599 1.598 99.4 Dibutylketone only 0.5
-- 1.597 1.602 99.2 *defoaming agents were procured from BYK
Additives and Instruments, a subdivision of Altana; Evonik or BASF
.sup.#Viscosity determined at 60.degree. C. .sup..sctn.TMD is the
Theoretical Maximum Density of the composition calculated to allow
for the intrinsic density lowering effect arising when additives
are added. The TMD is the sum of the relative volume of each
component as determined from their relative mass within the
composition and known density. As a result, the TMD gives a true
indication of the density modification arising as a result of a
change in the number of voids.
[0041] As can be seen, the presence of each of the defoaming agents
at levels above 0.1 wt % reduces the viscosity of the composition
making it easier to cast. Further, as the level of defoaming agent
is increased to 1.0 wt %, the viscosity of the composition is
further reduced.
[0042] The presence of defoaming agent also increases the density,
providing an indicator that the number of voids has been reduced.
Calculation of the TMD provides a further indicator, as an increase
in the TMD relative to that obtained where no additive is present
shows that the number of voids in the sample has been reduced
relative to the additive free composition.
[0043] It is clear that it is the defoaming agent having a density
increasing effect as the addition of dibutylketone only (i.e.
solvent only), reduces the density of the composition whether
prepared by a vacuum or an air casting technique.
[0044] The data above shows that vacuum casting generally produces
compositions of a higher relative density than air casting
techniques where defoaming agents are present. Further, vacuum
casting techniques generally have a more marked effect upon the
density of compositions containing defoaming agents when compared
to additive free or solvent only compositions.
[0045] However, even where air casting techniques are used, it is
clear that the defoaming agents are acting to reduce the number of
voids in the compositions tested as each defoaming agent provides a
composition which is either of higher density, or has a higher TMD,
than the control compositions including either no additive, or
solvent only.
Example 2
[0046] The compatibility of the defoaming agents with the Rowanex
1100 was also tested, and the results set out in Table 2 below.
TABLE-US-00002 TABLE 2 1. Defoaming Agent Compatibility BYK 066N *
Pass Solution of foam-destroying polysiloxanes in Pass propylene
glycol (BYK 088A) * BYK 088 * Pass BYK A500 * Pass BYK A535 * Pass
TEGO MR2132.sup.# Pass BASF SD23 .sup..sctn. Pass BASF SD40
.sup..sctn. Pass * Procured from BYK Additives and Instruments, a
subdivision of Altana .sup.#Procured from Evonik .sup..sctn.
Procured from BASF
[0047] Compatibility was measured following STANAG 4147 Test 1:
Procedure B, at a temperature of 100.degree. C. for 40 hours. All
of the defoaming agents tested were found to meet the requirements
of this test, and hence to be compatible with the Rowanex 1100 PBX
product, as illustrated by the results in the table above which
indicate that each of the materials tested evolved less than 1 ml/g
of gas for a 5 g sample. No adverse reaction was observed with any
of the defoaming agents, although a particularly good compatibility
was observed between Rowanex 1100 and BYK A535. Indeed, the use of
BYK A535, a solventless defoaming agent, has been found to provide
a particularly stable product with acceptable activity in terms of
void removal.
Example 3
[0048] The sensitivity of the Rowanex 1100 and defoaming agent
mixtures was tested for sensitivity to mechanical impact (Rotter
Impact) to determine the relative hazard associated with using the
mixture as opposed to the pure PBX product. The results are set out
in Table 3.
TABLE-US-00003 TABLE 3 1. Additive Concentration (wt %) F of I None
-- 100 BYK 088 1 130 BYK A500 1 130 BYK 066N 1 130 BYK A535 0.5 102
TEGO MR2132 1 109 BASF SD23 1 112 BASF SD40 1 121
[0049] The test determines the 50% drop height for the test sample.
This examines the whole probability of ignition versus
stimulus-level relationship. Seven test heights equally spaced on a
logarithmic scale are chosen and caps are tested to see if
ignitions take place. Results are expressed in terms of Figures of
Insensitiveness (F of I) relative to standard RDX. All tests are
carried out on samples of ground up material. The Rotter Impact
Test method was used to determine the F of I using an LSM Rotter
machine.
[0050] The F of I value for all of the Rowanex 1100/defoaming agent
samples was found to be greater than or equal to the F of I value
for Rowanex 1100 alone. This indicated that the presence of the
defoaming agent has no adverse effect on the sensitivity of the PBX
to mechanical impact and that as a result the combination products
are no more hazardous, and in some cases less hazardous, to use
than Rowanex 1100 alone. Without being bound by theory, this may be
due to the marginal increase in binder, and resultant reduction in
nitramine content because of the presence of the defoaming agent.
It is further indicated that the Rowanex 1100/defoaming agent
samples are likely to be no more sensitive to ignition than
untreated Rowanex 1100.
Example 4
[0051] A series of compositions including RDX were prepared, three
of these compositions included defoaming agents.
TABLE-US-00004 TABLE 4 Examples of Polymer-bonded Explosive (PBX)
Compositions containing Defoaming Agents PBX with PBX with PBX with
0.1% BYK- 0.5% BYK- 1% BYK- A500 A535 066N PBX Defoamer Defoamer
Defoamer Abbreviation Full name Function (wt %) (wt %) (wt %) (wt %
DOA Dioctyl Adipate Plasticiser 7.00 6.99 6.96 6.93 HTPB
Hydroxyterminated Pre- 4.28 4.28 4.26 4.24 Polybutadiene polymer
Lecithin Surfactant 0.30 0.30 0.30 0.30 AO2246 2,2'-methylenebis-
Anti- 0.10 0.10 0.10 0.10 (4-methyl-6- oxidant tertiary-
butylphenol) IPDI Isophorone Curing 0.42 0.42 0.42 0.42
Diisocyanate Agent DBTDL dibutyltin dilaurate Catalyst 0.05 0.05
0.05 0.05 Additive 0.00 0.10 0.50 1.00 RDX* Hexogen Explosive QS QS
QS QS Filler *May be present as pure RDX or combined with a
plasticiser, for instance in the ratio 94:6 RDX:plasticiser.
[0052] The compositions were prepared using cast and curing
processes as described in Example 1 and no voids were detected. No
adverse effect on chemical and mechanical properties was observed
relative to the defoaming agent free RDX composition.
Example 5
[0053] The following example illustrates a method of preparing PBX
compositions of the invention, such as the compositions of Example
4, using a premix. The techniques used would be well known to the
person skilled in the art.
[0054] A water-jacketed, vertical mixer fitted with a rotating
stirrer blade was used for the preparation of the composition. All
mixing was carried out under vacuum at a pressure of less than 10
mm Hg. The compositions of this example were prepared on a 5 Kg
scale using the relative proportions of components set out in
Example 4 above.
[0055] The premix was prepared from RDX desensitised with water.
The water was then driven off using techniques common in the art.
The desensitised RDX (94 wt %) was then mixed with DOA plasticiser
(6 wt %) to form the premix.
[0056] The mixer was preheated to 60.+-.2.degree. C. and the
following ingredients weighed into the mixer in sequential order in
relative amounts as described in Example 2 above: [0057] 1. HTPB
[0058] 2. DOA [0059] 3. Lecithin [0060] 4. AO 2246 [0061] 5. Premix
(first quarter portion, i.e. 25 wt % of total premix to be
added)
[0062] The composition was mixed for 15 minutes. The second, third
and final quarter portions of premix were then added with 10
minutes of mixing between each addition and after the final
addition. The mixer blades and bowl were scraped down to ensure
that any unmixed material was transferred to the mixing zone of the
bowl and the composition mixed for a further 60 minutes.
[0063] Defoaming agent was then added and the composition mixed
until the maximum reduction in viscosity upon addition of the
defoaming agent to the composition was observed. In this case
mixing was for 25 minutes and viscosity reduction was measured
using a torque meter fixed to the mixer, when the torque required
to complete the mixing stabilised at a lower level than before the
addition of the defoaming agent, the maximum reduction in viscosity
is regarded as having been observed.
[0064] The DBTL was added and the composition mixed for 15 minutes,
then the IPDI added and the composition mixed for a further 15
minutes. After mixing the viscosity of the composition was recorded
using a Brookfield viscometer (60.degree. C.).
[0065] The composition was cast and any excess mixture removed from
the shell housings. The shells were placed onto a vibrating table
and allowed to vibrate for 5 minutes. The charges were cured for 5
days at 65.+-.2.degree. C.
Example 6
[0066] The following example illustrates a method of preparing PBX
compositions of the invention, such as the compositions of Example
4, from a precure. The techniques used would be well known to the
person skilled in the art.
[0067] Mixing conditions were as for Example 5. The precure was
prepared from the premix described in Example 5 above. To this
premix was added all of the components of the composition of
Example 5 except for the defoaming agent, catalyst and curing
agent.
[0068] The mixer was preheated to 60.+-.2.degree. C. and the
components of the precure added and heated for 15 minutes. The
precure was then mixed for 30 minutes and the mixer blades and bowl
scraped to ensure that any unmixed material was transferred to the
mixing zone of the bowl. Defoaming agent was added and the
composition mixed until the viscosity reducing effect of the
defoaming agent is observed, this was measured as described in
Example 5 and in this example required stirring for 25 minutes. The
DBTL was added and the composition mixed for 15 minutes, then the
IPDI added and the composition mixed for a further 15 minutes. The
mixer blades and bowl were scraped to ensure that any unmixed
material was transferred to the mixing zone of the bowl. After
mixing the viscosity of the composition was recorded using a
Brookfield viscometer (60.degree. C.).
[0069] The composition was cast and any excess mixture removed from
the shell housings. The charges were cured for 5 days at
65.+-.2.degree. C.
[0070] It should be appreciated that the compositions of the
invention are capable of being incorporated in the form of a
variety of embodiments, only a few of which have been illustrated
and described above.
* * * * *