U.S. patent number 3,749,023 [Application Number 05/163,287] was granted by the patent office on 1973-07-31 for instantaneously completely combustible cartridge case member of polyvinyl acetal.
This patent grant is currently assigned to Technical Research and Development Institute. Invention is credited to Kanegafuchi Boseki Kabushiki Kaisha, Kunihiko Kawaguchi, Hidemichi Kazama, Nippon Koki Co., Ltd., Mitsuzo Ono, Kenji Takahashi, Yoshimitsu Takeda, Hisao Yamazaki.
United States Patent |
3,749,023 |
Kawaguchi , et al. |
July 31, 1973 |
INSTANTANEOUSLY COMPLETELY COMBUSTIBLE CARTRIDGE CASE MEMBER OF
POLYVINYL ACETAL
Abstract
By first radially compression-molding a hollow cylindrical foam
of a synthetic resin such as polyvinyl acetal, polyurethane and
polystyrene in a mold utilizing a pressurized fluid and then by
expanding the compressed foam with heat -- after moistening it --
in a heat-expansion mold, an instantaneously completely combustible
cartridge case member is obtained. By the inclusion in the foam of
at least one kind of reinforcement filler selected from two groups,
i.e., fibers of the said resins and a cloth of said resins, prior
to being compressed, the said foam can have an increased strength.
By also including a binder of a synthetic resin after compression,
further increased strength and hardness of the foam is obtained.
The outer surface of the case member may be given an easily
combustible thin film and also a damp-proof thin coating on top of
the said film. This cartridge case member does not combust
spontaneously during handling or during transportation since it
combusts at a high temperature. This case member leaves no solid
combustion residues at the time of combustion within a firearm.
Also, the aforesaid cartridge case members are suitable for
manufacture on a mass production basis and the cost of manufacture
can be lowered greatly.
Inventors: |
Kawaguchi; Kunihiko (Tokyo,
JA), Takahashi; Kenji (Sashima, JA),
Kazama; Hidemichi (Yokohama, JA), Ono; Mitsuzo
(Sahima, JA), Yamazaki; Hisao (Tokyo, JA),
Takeda; Yoshimitsu (Yokohama, JA), Kanegafuchi Boseki
Kabushiki Kaisha (Tokyo, JA), Nippon Koki Co.,
Ltd. (Tokyo, JA) |
Assignee: |
Technical Research and Development
Institute (N/A)
|
Family
ID: |
13243034 |
Appl.
No.: |
05/163,287 |
Filed: |
July 16, 1971 |
Foreign Application Priority Data
|
|
|
|
|
Jul 23, 1970 [JA] |
|
|
45/63913 |
|
Current U.S.
Class: |
102/466;
102/700 |
Current CPC
Class: |
F42B
5/181 (20130101); B29C 44/10 (20130101); B29C
44/5636 (20130101); F42B 5/188 (20130101); F42B
5/30 (20130101); Y10S 102/70 (20130101) |
Current International
Class: |
B29C
44/34 (20060101); B29C 44/56 (20060101); F42B
5/188 (20060101); F42B 5/00 (20060101); F42B
5/30 (20060101); F42b 005/18 (); F42b 005/30 () |
Field of
Search: |
;102/38,43R,43P,39,DIG.1,97 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Stahl; Robert F.
Claims
We claim:
1. An instantaneously and completely combustible cartridge casing,
comprising: a hollow cylindrical casing made of thermoplastic
polyvinyl acetal foam having uniformly distributed,
intercommunicating fine pores and having a substantially uniform
density in the range of from about 0.25 to about 0.30 g/cm.sup.3,
the casing being made from polyvinyl acetal foam having an average
polymerization degree of from 1,000 to 2,500, an acetalization
degree of from 65 to 86 percent, a porosity of from 90 to 95.5
percent and an apparent specific gravity of from 0.06 to 0.12, by
compressing a hollow cylinder of said polyvinyl acetal foam on a
male mold member by applying a uniform radially inwardly directed
pressure on the entire external surface of the cylinder, then
wetting the cylinder with water, heating the cylinder to expand
same into contact with a female mold member and then drying the
cylinder before removing it from the female mold member.
2. An instantaneously and completely combustible cartridge casing
according to claim 1, in which said foam contains therein at least
one kind of reinforcement filler selected from the group consisting
of polyvinyl acetal fibers and polyvinyl acetal cloth.
3. An instantaneously and completely combustible cartridge casing
according to claim 1, in which said foam contains polyvinyl acetal
fibers mixed therein and also contains a layer of polyvinyl acetal
coth embedded therein.
4. An instantaneously and completely combustible cartridge casing
according to claim 1, in which said foam contains distributed
therein synthetic resin reacted with the residual hydroxyl groups
contained in the said polyvinyl acetal foam to form a cross-linked
structure.
5. An instantaneously and completely combustible cartridge casing
accoridng to claim 4, in which said casing has on its external
surface an easily combustible thin film comprising nitrocellulose
and a thixotropic agent.
6. An instantaneously and completely combustible cartridge casing
according to claim 5, in which said easily combustible thin film is
covered with a water-proof thin vinylidene chloride coating.
7. An instantaneously and completely combustible cartridge casing
according to claim 1, in which the said casing has a metal bottom
member securely bonded to the bottom thereof.
Description
BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention is concerned with a cartridge case for rounds
of firearms, and more particularly, it relates to a hollow
cartridge case member which will combust completely instantaneously
when ignited by the propellant contained therein before the shot is
discharged from the muzzle of the firearm, without leaving any
solid residues of combustion. The present invention further relates
to a method of manufacturing the cartridge case member of the type
described.
B) Description of the Prior Art
The cartridges which are currently used are made of a metal such as
brass or steel. These metallic cartridge cases can resist the high
pressure produced in the cartridge chamber at the time of firing.
Such a cartridge case is structured so that the highly pressurized
gases produced within the cartridge chamber are prevented from
leaking through the bottom of the chamber. Thus, these cartridge
cases of the prior art function as they should. However, the metals
with which the cartridge cases of the prior art are made are rather
expensive and could be difficult to procure at any emergency time,
and this is especially so with brass. Also, weapons such as tank
and wheeled guns are designed so that firing is performed within a
narrow space of the chamber or turret. In such an instance, a large
number of hot empty metallic cartridge cases will be delivered one
after another from the firearm and will scatter close to the
marksman and they will hamper his otherwise normal fighting
actions. In addition, a large volume of toxic gases is produced as
the cartridge cases are emptied by firing, and these gases will
endanger the physiological conditions of the marksmen. The
foregoing facts will effect a marked lowering of the efficiency of
fighting actions.
The aforesaid disadvantages and inconveniences of the metallic
cartridge cases of the prior art may be solved by the provision of
instantly combustible cartridge cases. However, a cartridge case
which is merely combustible -- whether in whole on in a greater
portion thereof -- is far from being practical for the reasons
stated below. A practically useful cartridge case ought to satisfy
at least the following requirements:
1) At the time of firing, it leaves no solid residues from
combustion.
2) It is impact-proof in rough handling or during
transportation.
3) It is moisture-proof.
4) When charged in the heated cartridge chamber of a firearm during
successive firing, the cartridge case must never combust
spontaneously.
5) It does not produce toxic gases at the time of firing.
6) Materials of the case must be availalbe easily and at low
cost.
7) It can be manufactured easily and at lost cost.
The cartridge cases of the prior art invariably have failed to
satisfy many of these requirements.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a
new cartridge case member which is free of the aforesaid
disadvantages and inconveniences and can satisfy substantially all
of the above-listed requirements.
Another object of the present invention is to provide a new
cartridge case member which satisfies substantially all of the
aforesaid requirements by being constructed with an instantaneously
completely combustible foam of a synthetic resin selected from the
group consisting of polyvinyl acetal, polyurethane and polystyrene
-- which become hard enough when molded into a cartridge case.
Still another object of the present invention is to provide a new
cartridge case member of the type described, which has a highly
enhanced mechanical strength and hardness by the inclusion therein
of a reinforcement material which may be a reactive lower polymeric
binder and/or polyvinyl acetal fibers and/or a coarse polyvinyl
acetal cloth.
Yet another object of the present invention is to provide a new
cartridge case member of the type described, which -- in addition
to the features mentioned above -- is damp-proof due to the fact
that the surface of the said case member is coated with a
damp-proof material.
A further object of the present invention is to provide a simple
and easy and low-cost method for producing the new cartridge case
member which satisfies substantially all of the aforesaid
requirements by being constructed with an instantaneously
completely combustible foam of a synthetic resin of the type
described -- which is hard enough when molded into a cartridge case
member.
A still further object of the present invention is to provide a
simple, easy and low-cost method for producing the new cartridge
case member of the type described above which possesses an enhanced
mechanical strength and hardness by the inclusion therein of a
reinforcement material, i.e., a reactive lower polymeric binder
and/or polyvinyl acetal fibers and/or a coarse polyvinyl acetal
cloth.
A yet further object of the present invention is to provide a
simple, easy and low-cost method for producing a new cartridge case
member of the type described which -- in addition to the features
mentioned above -- is moisture-proof by the fact that its surface
is coated with a moisture-proof material.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevational view, partly in section, showing an
example of a cartridge case having an instantaneously completely
combustible cartridge case member of the present invention.
FIG. 2 is a longitudinal sectional view of a compression-molding
apparatus suitable for use in performing an excessive compression
of a foamed material, representing a first step of the
manufacturing method of the present invention.
FIG. 3 is a longitudinal sectional view of a heating apparatus
suitable for use in performing heat-expansion of the compressed
foamed material, representing a second step of the method of the
present invention.
FIG. 4 is a chart showing the results of ignition point tests
conducted on the cartridge case members produced acording to the
method of the present invention as compared with that of the
ignition point of the propellant.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention contemplates the provision of a new cartridge
case member which is instantaneously completely combusted at the
time of firing and which satisfies substantially all of the
aforesaid requirements of a cartridge case. The present invention
is also concerned with a method for producing this new cartridge
case member. The present invention has been worked out based on the
discovery that cartridge case members made of foams of various
kinds of synthetic resins can satisfty the above-mentioned
requirements to a certain degree.
Foams of synthetic resin may be divided roughly into two types, one
of which has pores or cells which are sealed from each other and
the other is such that the pores of cells intercommunicate with
each other. Of these two types, foams having the intercommunicating
pores are more desirable for use as the material of instantaneously
completely combustible cartridge case member from the viewpoint of
enhanced combustibility of same. However, foams having independent
cells can be as equally effectively used as those of the
intercommunicating type if they have a sufficiently large porosity
and if the cell walls have an effectively small thickness. Foams
having thin sealed cells will break easily into fine fragments upon
being exposed to a high temperature and a high pressure within the
cartridge chamber so that the surface area of the cells per unit
weight will suddenly increase to a tremendous extent, enabling the
whole of the foam to combust instantaneously.
For the reasons described above, it is possible to use foams of
almost all kinds of synthetic resins and cellulose derivatives as
the material of the instantly completely combustible cartridge case
member of the present invention provided that they have a desirable
condition of pores of cells. From the viewpoints of high mechanical
strength, hardness, quick combustibility, easy moldability and easy
processability which are important requirements of the material,
however, the use of polyvinyl acetal, polyurethane and polystyrene
has been found suitable. Of these three types of synthetic resins,
polyvinyl acetal is found to be especially suitable for the
aforesaid purpose. A major reason therefor may be explained as
follows. Foam of polyvinyl acetal is of a structure which is
characterized by the fact that fine fibrous polyvinyl acetal
product which is produced from a reaction between polyvinyl alcohol
and aldehyde in an aqueous solution forms a three dimensional
reticular structure of molecules. Since polyvinyl acetal is
thermoplastic by nature, it can be molded easily by subjecting same
to compression-molding while being heated. On the other hand,
polyvinyl acetal having an acetalization degree of the order of
65-86 percent tends to become pliant and swollen when heated with
steam. This nature of polyvinyl acetal is utilized to give a
desired configuration. This property of polyvinyl acetal to become
swollen is considered to be due to the fact that the residual
hydroxyl group in the molecules of polyvinyl acetal has affinity to
water. Foam of polyvinyl acetal which is suitable for use as the
material of cartridge case member of the present invention is of
the following conditions, i.e., an average polymerization degree of
1,000-2,500, a polyvinyl alcohol to polyvinyl acetal intermolecular
rearrangement ratio or acetalization degree of 65.0-86.0 percent,
an apparent specific gravity of 0.06-0.12 and a porosity of
90.0-95.5 percent. Un-processed foam of polyvinyl acetal which is
available as the material of the instantaneously completely
combustible cartridge case member of the present invention, like
foams of polyurethane and polystyrene, can have an enhanced
mechanical strength and hardness by first subjecting it to a
compression process and then blending therein a binder which may be
either a polymer or a reactive intermediate product of a lower
polymerization degree in an amount 30 percent or less, by weight,
relative to the gross weight of polyvinyl acetal. The strength of
this polyvinyl acetal foam can be improved further to suit for
practical use by including, in the polyvinyl acetal, a
reinforcement filler which is one or both of polyvinyl acetal
fibers and a coarse polyvinyl acetal cloth prior to the compressing
process.
Description will hereunder be made, by referring to FIG. 1, on the
structure of an example of the instantaneously completely
combustible cartridge case member manufactured according to the
method of the present invention and having the optimum
conditions.
In FIG. 1, reference numeral 1 represents generally a hollow
cartridge case. Numeral 2 represents an instantaneously completely
combustible cartridge case-constituting hollow member. This
cartridge case member 2 is made of polyvinyl acetal foam. In order
to enhance the mechanical strength of this member 2, the latter
contains uniformly throughout therein polyvinyl acetal fibers 3,
and in addition, the case member 2 has a coarse polyvinyl acetal
cloth 4 which is embedded in the member 2 at a position close to
the inner surface thereof in such a way that the surface of the
cloth is substantially exposed to the external atmosphere and
visible externally. Numeral 5 represents a bottom member made of a
metal. Numeral 6 represents a hole formed through the bottom
portion of said bottom member 5 for the attachment of a fuse.
Numeral 7 represents a shoulder portion. Numeral 8 represents a
shot or shell. Numeral 10 represents a layer of bonding agent with
which the lower portion 9 of the said case member 2 is securely
bonded to the upper portion 9a of the said base 5.
The instantaneously completely combustible hollow cartridge case
member 2 having the aforesaid structure is made with a polyvinyl
acetal foam having numerous very fine intercommunicating pores
throughout the entirety thereof, and accordingly, the case member 2
is of a very large surface area. It should be understood that the
length of time consumed from the time the propellant contained in
the cartridge case starts to combust till the time the shot is
discharged from the muzzle of a firearm is of the order of several
milli-seconds. Therefore, at the time of firsing, the case member 2
made with the aforesaid materials and having the above-mentioned
structure will be exposed -- during such a momentary short period
of time -- to a very high temperature and a very high pressure
produced from the combustion of the propellant, and will be
combusted completely instantaneously, neither leaving any solid
residues nor producing an objectionably large amount of toxid gases
at the time of firing. Moreover, this case member 2 will not
combust spontaneously when a round having a cartridge case made
with this case member 2 is charged in the heated cartridge chamber
of a firearm during successive firing. Furthermore, as will be
discussed later, this case member 2 is of a mechanical strength
necessary and sufficient for a satisfactory cartridge case
member.
It should be understood that it is mainly from rough handling that
cartridge cases sustain damages. Such damages caused during
handling are not only due to the intensity of tension, compression
or impact applied to the cartridge cases, but also -- and quite
often actually -- due to dropping of rounds, in which instance the
cartrdige cases are subjected to combined forces of tension,
compression and impact. In the example of round shown in FIG. 1,
the cartridge case member 2 is made of a basic material which is
polyvinyl acetal foam. Accordingly, the case member 2 is of
elasticity of an appropriate degree. Moreover, this case member 2
contains polyvinyl acetal fibers 3 distributed uniformly throughout
its porous structure and also it has a coarse polyvinyl acetal
cloth 4 embedded in the entire surface region of the polyvinyl
acetal foam, and in addition, the shoulder portion of this case
member 2 is of a greater thickness than the remaining portions.
Therefore, the cartridge case member 2 is especially of an
increased strength against impact. Cartridge case members made
according to the present invention and having the aforesaid
structure were subjected to a strength test, the result thereof is
as shown in Table 1.
TABLE 1
Cartridge Tensile Anit-impact member strength strength structure
(kg/cm.sup.2) (kg.cm/cm.sup.2) A approx. 10 approx. 3.0 A + B
approx. 15 approx. 5.0 A + B + C approx. 22 approx. 6.0 wherein: A
represents polyvinyl acetal foam; B represents polyvinyl acetal
fibers; and C represents coarse polyvinyl acetal cloth.
Let us now assume that a round having a cartridge case made of
brass is represented by I, and that a round having a cartridge case
member made of a polyvinyl acetal foam containing polyvinyl acetal
fibers distributed uniformly throughout thereof and also a coarse
polyvinyl acetal cloth embedded in the entire surface region
thereof is represented by II. The results of drop tests of these
two kinds of rounds are compared as shown in Table 2.
TABLE 2
Type Number of rejectable Number of still of round rounds usable
rounds Group I 7 3 Group II 1 9 wherein: Drop tests were conducted
by dropping, from a height of 50 cm above a horizontal concrete
floor, two rounds each of Group I and Group II held in the
following five different positions: horizontal; vertical (shot
facing downwardly); vertical (shot facing upwardly; at 45.degree.
(shot inclined downwardly; and at 45.degree. (shot inclined
upwardly).
From the results of this drop test, it may be said that those
rounds in Group II are of a greater anti-impact strength so far as
the dropping test alone is concerned.
As stated above, an aspect of the present invention concerns a
method for manufacturing, in a reasonable manner, an
instantaneously completely combustible hollow member of a cartridge
case having the aforesaid features. More specifically, it concerns
a method for maufacturing cartridge case members of the type
described by the use of a hollow cylindrical polyvinyl acetal foam
containing therein at least one of the following two kinds of
reinforcement fillers, i.e., polyvinyl acetal fibers and a coarse
polyvinyl cloth, and by first excessively compressing this
cylindrical foam on a male mold member of a compression molding
apparatus with a pressurized fluid applied onto the external
circumference of the cylindrical foam radially against the surface
of the mold member and then expanding, with heat, the resulting
compressed cylinder -- which is then positioned in the space
between an inner male mold member and an outer female mold member
of a separate expansion molding apparatus -- after applying an
appropriate amount of humidity to the foam, to thereby urge this
foam tightly against the inner surface of the outer female mold
member.
A modified method of the present invention comprises the use of a
hollow cylindrical polyvinyl acetal foam containing therein at
least one of the reinforcement fillers, i.e., polyvinyl acetal
fibers and a coarse polyvinyl cloth, and by first excessively
compressing this cylindrical foam on a male mold member of a
compression mold with a fluid pressure applied onto the external
circumference of the cylindrical foam radially against the surface
of the mold member, then expanding, with heat, the resulting
compressed cylindrical foam -- which is then positioned in the
space between an inner male mold member and an outer female mold
member of a separate mold -- after applying an appropriate amount
of humidity to the foam, to thereby urge this foam tightly against
the inner surface of the outer female mold member, thereafter
treating the resulting molded cylindrical foam with a synthetic
resin, and the forming an easily combustible thin film on the
entire outer surface of the treated cylindrical foam by applying a
thixotropic solution of a low concentration containing
nitrocellulose and a thixotropic agent.
Description will hereunder be directed to an embodiment of the
present invention by referring to the accompanying drawings.
FIG. 2 shows a longitudinal central sectional view of a compression
molding apparatus utilizing a pressurized fluid. In this drawing,
reference numeral 13 represents a male mold member having generally
a cylindrical configuration. This male mold member has a central
longitudinal gas-passage channel 11 communicating with the outside
of this mold member 13 and a plurality of radial gas-passage
channels 11a opening at one end to the circumferential surface of
the mold member and communicating at the other end with the said
central longitudinal gas-passage channel 11, and also has a closed
region 12. Numeral 15 represents a pressure-resistant cylindrical
frame having an inlet 18 for introducing a pressurized fluid -- a
pressure medium -- into the space inside this pressure-resistant
cylindrical frame 15. The fluid which may be used in the present
invention includes water, oil and gas such as air. A hollow
cylindrical foam piece 17 covered externally with an elastic cover
16 such as a rubber bag is mounted on the male mold member 13 and
is set in the mold as shown in FIG. 2. Then, a pressurized fluid 14
is introduced into the space within the pressure-resistant
cylindrical frame 15 of the mold through the pressurized fluid
inlet 18 from an appropriate compression pump to compress the
hollow cylindrical foam piece 17 radially against the
circumferential surface of the male mold member 13. This hollow
cylindrical foam piece 17 is the material for producing an
instantaneously completely combustible hollow cartridge case member
2 shown in FIG. 1. This cylindrical foam piece 17 is made with a
principal material which is polyvinyl acetal foam of an
acetalization degree of 65-86 percent and having numerous
intercommunicating fine pores throughout its structure and having
polyvinyl acetal fibers 3 distributed uniformly throughout therein
and also having a coarse polyvinyl acetal cloth 4 embedded close to
one surface of the foam piece 17.
Let us now assume that, in FIG. 2, the pressure of the fluid 14 is
introduced into the space inside the cylindrical frame 15 by an
appropriate means. Whereupon, the elastic cover 16 will be caused
to tightly contact the external circumferential surface of the
hollow cylindrical foam piece 17 to compress this foam piece 17
evenly radially against the external circumferential surface of the
male mold member 13. During this process of compression, the
pressure of the fluid 14 is controlled so that the molded hollow
cylindrical foam piece 17 will have an outer diameter appropriately
smaller than the inner diameter of the outer mold member 20 shown
in FIG. 3. The foam piece 17 which has been compression-molded in
the aforesaid manner is indicated by a reference numeral 21 in FIG.
3. By molding the foam piece 17 only by utilizing a pressurized
fluid without the application of heat in the first step, the
pressure can be applied evenly to the entire outer surface of the
hollow cylindrical foam piece 17. Thus, it is possible to mold the
foam piece 17 so as to have a uniform desired thickness and a
uniform desired density throughout the entirety thereof with no
difficulty and without undesirable partial compression and density
which would tend to take place in heat-compression molding as will
be discussed below.
More specifically, the heat-compression molding comprises the steps
of first inserting a hollow cylindrical polyvinyl acetal foam piece
in a hollow cylindrical female mold member so that this foam piece
is in tight contact with the inner face of the female mold member,
thereafter supplying excessively heated steam having a temperature
of 120-130.degree. C onto the tightly contacting surface of the
foam piece externally of the female mold member through numerous
small perforations formed through the wall of the female mold
member to cause the steam to be absorbed in the porous structure to
sufficiently soften same, thereafter inserting a male mold member
heated to a temperature substantially the same as that of the steam
into the hollow space of the foam piece up to a predetermined
position by means of, for example, a hydraulic pressing device,
then passing steam for 1-2 minutes to the foam piece to remove and
correct any deformation of the foam piece, thereafter stopping the
supply of the steam, and supplying dry gas such as air heated at
120-130.degree. C to dry the damp foam piece until the residual
moisture in the foam structure drops to two percent or less. The
said steam and the said dry air invariably pass through the porous
structure and are discharged from a gas outlet provided in the end
of each of these two mold members. When the residual moisture of
the foam piece at the time the latter is taken out of the mold is
two percent or less, there hardly occurs any restoration of the
initial configuration of the foam piece. Since this
heat-compression molding method uses a temperature of
120-130.degree. C for heating, it should be understood that if the
foam piece is dried excessively by heating, polyvinyl acetal may be
decomposed. Also, there is the fear tha only those portions of the
surface of the foam piece which are exposed to heat may be
compressed and that only the resulting compressed portions of the
foam piece will have an increased desnity. If these phenomena
occur, the foam piece will have a difference in density between its
inner surface region and its outer surface region. Also, the
surfaces of the foam piece and their adjacent regions will show an
injury in the pore structure, which leads to a much lowered
combustibility.
FIG. 3 is a longitudinal central sectional view of a heat-expansion
molding apparatus. In this drawing, reference numeral 20 represents
an outer female mold member having a generally cylindrical
configuration and having a heater 19. A hollow cylindrical foam
piece 21 which has been compression-molded by a pressurized fluid
and which is mounted on a cylindrical inner male mold member 22 is
inserted in an appropriate manner in the outer female mold member
20. Numeral 23 represents a central longitudinal channel provided
in the inner male mold member 22 for the passage of gas such as
air. Numeral 23a represents a radial channel communicating at one
end to the outer circumferential surface of the inner male mold
member and at the outer end with the central longitudinal gas
channel 23. In the heat-expansion molding apparatus shown in FIG.
3, the foam piece 21 which has been compressed with a pressurized
fluid is impregnated with moisture to an appropriate degree, for
example about 10 percent, prior to being heat-molded in this
apparatus. Along therewith, the outer female mold member 20 is
heated at an appropriate temperature of 100.degree. C or higher,
whereas the inner male mold member 22 is held at an appropriate
temperature of 100.degree. C or lower. By keeping the said foam
piece 21 in the mold under these conditions for an appropriate
length of time, the hollow cylindrical foam piece 21 expands to
tightly contact the inner circumferential surface of the outer
female mold member 20. It should be noted that, at this stage of
heat-expansion, the hollow cylindrical foam piece 21 is still
impregnated with moisture, and that, if this foam piece 21 is taken
out from the heat-expansion apparatus at the said stage, there is
the fear that the foam piece 21 would tend to resume its initial
size which it has prior to being compression-molded with a
pressurized fluid. Accordingly, there arises the necessity for
expelling the moisture from the porous structure. For this reason,
a dry gas such as dry air is supplied onto the foam piece 21
through the gas channel 23 and accordingly through the radial gas
channels 23a. After the moisture present in the porous structure
has been removed substantially therefrom in this way, the
heat-molded foam piece 21 is taken out from the heat-expansion
molding apparatus. It should be noted also that the weight of the
foam piece 21 before being subjected to the method of the present
invention is regulated so that the foam piece after heat-molding
will have a density of 0.25-0.30 g/cm.sup.3 which is a desirable
condition of the foam piece suitable for use in the present
invention. As stated previously, a polyvinyl acetal foam is of
inter-communicating pores, and has a tremendously large surface
area of pores and has an acetalization degree of 65 -86 percent and
contains therein polyvinyl acetal fibers and a coarse polyvinyl
acetal cloth. Therefore, the foam piece 21 not only satisfies the
requirements of an instantaneously completely combustible cartridge
case member, but also permits compression-molding utilizing a
pressurized fluid as well as permits heat-expansion molding. More
specifically, the fact that the foam piece of polyvinyl acetal has
an acetalization degree of 65-86 percent means that is has 35-14
percent of residual hydroxyl groups. Accordingly, the moisture
contained in the polyvinyl acetal porous structure will evaporate
as it is brought into contact with the heated surface of the outer
female mold member 20, and the resulting vapor of water will fill
in the intercommunicating pores of the porous structure of
stimulate the said residual hydroxyl group, thus rendering the foam
piece soft and pliant. Until this evaporation takes place, the
polyvinyl acetal foam piece has been in the compressed state which
was produced previously in the first compression-molding step
utilizing a pressurized fluid. Therefore, the foam piece 21 now
gains the force to resume its initial configuration and size which
it has prior to being compressed. As a result, the foam piece 21
will tightly contact the inner circumferential surface of the outer
female mold member 20. The inner surface of this outer mold member
20 is of a temperature which is elevated to the decomposition point
of the polyvinyl acetal foam. However, as moisture evaporates, the
polyvinyl acetal foam is deprived of evaporation heat, and
accordingly the polyvinyl acetal foam per se will never reach its
decomposition point.
The aforesaid molding method of the present invention not only is
advantageous from the economical point of view, but also
contributes greatly to the easy combustibility of the cartridge
case member. More specifically, if the case member is produced by
relying on a heat-compression method, only those facial portions of
the foam piece exposed to heat during the heat-compression process
will be compressed, and only such portions will have an increased
density as compared with the remaining portions not having been
heated nor compressed sufficiently. In other words, according to
the heat-compression method, the molded porous structure will have
a difference in density between its inner facial region and its
outer facial region, and also lose its porous structure in the
vicinity of its surfaces, developing blocked pores and accordingly
having a substantially decreased surface ara of pores. When a round
having such a cartridge case member is fired, there will remain
uncombusted surface portions of the foam like a crust of bread.
Accordingly to the aforesaid method of the present invention,
however, the foam piece obtained is of a uniform density and is
free of the aforesaid disadvantage and inconvenience which are
encountered in the products of heat-compression method, and
moreover, the cartridge case member made with such a foam piece of
the present invention will never give rise to the development of
solid combustion residues which are encountered, at the time of
firing, in cartridge case members produced by heat-compression
method.
The aforesaid polyvinyl acetal foam which is molded according to
the method of the present invention may have an increased strength
and also may be kept from resuming its initial configuration and
size after being molded, by treating same with a synthetic resin as
will be discussed below.
An increase in the strength of polyvinyl acetal foam is attained,
as stated previously, by including in a polyvinyl acetal foam at
least one, preferably both, of two kinds of reinforcement fillers,
i.e., polyvinyl acetal fibers and a coarse polyvinyl acetal cloth.
By doing so, the tensile strength and the anti-impact strength of
the foam as a cartridge case member are both markedly increased as
shown in Table 1. More specifically, a polyvinyl acetal foam not
containing any reinforcement filler exhibits a tensile strength of
about 10 kg/cm.sup.2 and an anti-impact strength of about 3.0
kg/cm/cm.sup.2, as compared with the foam pieces containing one or
both of the reinforcement materials, which exhibit a tensile
strength of about 15-22 kg/cm.sup.2 and an anit-impact strength of
about 5.0-6.0 kg cm/cm.sup.2, indicating an increase as great as
about two times. These reinforced foam pieces permit the rounds
having a cartridge case made of such a case member to have a
strength sufficient for use even when the rounds are dropped from a
height of 50 cm onto a concrete floor. Also, by impregnating the
compressed polyvinyl acetal foam with a reactive resinous
intermediate product which is capable of combining with the
residual hydroxyl group contained in the polyvinyl acetal foam to
form a three dimensional molecular structure, the resulting foam
not only will have an improved mechanical strength but also will
hardly develop any deformation of its configuration after being
compressed, and furthermore will have an enhanced water-proofness
since hydrophilic hydroxyl groups contained in the foam are
destroyed. This treatment of polyvinyl foam with the aforesaid
synthetic resin provides such a number of advantages as stated
above An example of the blended resin composition which satisfies
these requirements is:
polyurethane ?isocyanate group (mol)/hydroxyl group (mol) >1! --
5 parts (including hardening agent)
penetrant -- 1 part
moisture repellant -- 1 part
solvent (a mixture of xylene, methylisobutylketone and butyl
acetate) -- 40 parts.
The polyvinyl acetal foam after being heat-expanded is impregnated
with a solution having the aforesaid composition. By arranging the
isocyanate component of polyurethane to be present therein in an
excessive amount as mentioned above, it is possible to cause the
residual hydroxyl group contained in the polyvinyl acetal foam to
be united with the said isocyanate group in an appropriate manner
and to thereby obtain an instantly completely combustible cartridge
case member having a three dimensional molecular structure.
The polyvinyl acetal foam which has been treated in the manner
stated above has surfaces having numerous pores with a diameter of
the order of 100 microns, and are of good gas-permeability.
However, unless these surface pores are blocked, there will arise
the possibility for the instrusion of moisture into the interior of
the cartridge case. It is considered that, by forming a thick film
on the external surface of the case member, the case member will
have an improved water-proofness. On the other hand, however,
residues from combustion at the time of firing will undesirably
tend to develop easily. A film which is considered to be suitable
for the aforesaid purpose in contributing to easy combustibility is
such that it contains an explosive component such as
nitrocellulose, or such that a thin film is formed only at the
surface of the foam without the resin penetrating into the porous
structure through the pores present in the surface thereof. It
should be noted, however, that in case a film is formed on the
surface of the foam by the use of only an explosive component such
as nitrocellulose, there will arise the problem of a difficulty to
maintain its chemical stability and also of the danger of being
easily ignited when a round having such a cartridge case member is
charged in the cartridge chamber of a firearm in case the cartridge
chamber has been heated to a high temperature from successive
firing. It should be understood also that the formation of a thin
film will require that the solution is of a low concentration.
However, a solution of a low concentration is, in general, of a low
viscosity which, in turn, will be insufficient for blocking the
surface pores of the porous structure. Not only that, the thin
solution will easily penetrate into the interior of the porous
structure. Accordingly, it will become impossible to have the
porous structure keep satisfactory water-proofness or
damp-proofness. On the other hand, a solution having a low
concentration and a high viscosity will not penetrate into the
interior of the porous structure, but such a solution will
deteriorate workability in such a way that, when the solution is
applied onto the surface of the surface of the porous structure, it
will be deposited as a thick and plump layer.
It is therefore proper to use an under-coating consisting of a
thixotropic solution of a low concentration, and to apply a
water-proof coating on top of this under-coating. An example of the
under-coating composition is:
nitrocellulose -- 2 parts
nitrocellulose stabilizer -- 0.02 parts
pigment -- 1 part
thixotropic agent -- 2 parts
solvent (a mixture of xylene, methylisobutylketone and butyl
acetate) -- 50 parts.
An under-coating solution having the aforesaid composition will
exhibit thixotropy when this solution having a concentration of
about five percent is heated and then quenched while being stirred.
This solution under this condition is creamy and is not tacky but
is of a good ductility, so that it can be applied lightly on the
surface of the porous structure without penetrating into the
interior thereof. This solution is applied with a brush to the
surface of the porous structure. After being dried, a film of 10
micron or less is obtained. This film, however, is of a poor
water-proofness. Accordingly, after the surface pores of the porous
structure have been blocked substantially by the application of the
said under-coating solution thereto, a water-proof coating is given
on top of the said under-coating. As a water-proof coating, the use
of a vinylidene solution is suitable. Furthermore, a pigment
consisting of flaky aluminum powder will be effective in improving
water-proofness. As a result of these treatments, the resulting
porous structure can stand its exposure to a rainfall of not only
the order of 4 .+-. 1 inches/hour, but also of the order of several
times as great as that.
Cartridge cases having instantaneously completely combustible case
members which were prepared in the manner described above were
subjected to a number of different tests. The result of these tests
is as follows.
1. Firing fitness:
No residues of combustion were left. No gas leakage occurred.
Pressure in the cartridge chamber and initial velocity of shot were
both found satisfactory.
2. Tensile strength:
Test samples were tested by Amsler tester according to JIS-Z-2112.
The tensile strength of the case members was noted to be about 45
kg/cm.sup.2.
3. Compression strength:
Pieces cut out from the case members were tested on Amsler tension
tester. Their compression strength was found to be about 20
kg/cm.sup.2.
4. Anti-impact strength:
Test samples were tested by Sharpi impact tester according to
JIS-Z-2202, with the result that their anti-impact strength was
about 6 kg.cm/cm.sup.2.
5. Water-proofness:
Samples were left in water for 48 hours at the depth of 300 mm
below the water surface without any loss of water-proofness.
6. Shot holding strength:
Complete rounds having the said cartridge cases were tested by
Amsler tension tester. The strength required for pulling out shots
from case members was noted to be about 650 kg.
7. Vibration test:
Samples were subjected to vibration at: amplitude 3.0 mm, frequency
1,500 cpm and acceleration 3.9 G., without being affected
adversely.
8. Drop test:
The result is as per Table 2. The result showed only an appreciable
degree od deformation in case members, with very few being found
rejectable.
9. Stability test:
Samples were subjected to Abbel heat-resistance test according to
NDS-XK4811 for 50 minutes with no appreciable change; Samples
subjected to heat-resistance test at 134.5.degree. C for 60 minutes
neither showed any appreciable change (NDS XK 4811).
10. Ignition point test:
The result is as shown in FIG. 4. In this drawing, vertical axis
represents the temperature (.degree.C) at which samples were
heated; horizontal axis represents the lapse of time (sec.)
consumed till samples began to develop smoke. Curve A shows the
result of test conducted on the instantaneously completely
combustible cartridge case members of the present invention,
whereas Curve B shows the result of test conducted on propellant.
As is clear from FIG. 4, these case members develop smoke at the
end of 50 seconds at 250.degree. C. Whereas, the propellant is
ignited at the end of 10 seconds at the same temperature. When the
quick heat-transmitting property of brass cartridge cases is taken
into account, the cartridge cases made of the case members of the
present invention are noted to be much safer.
11. Analysis of gases produced from combustion:
The result is as per Table 3. No substantial difference from the
gases produced from propellant contained in brass cartridge cases
is noted. ##SPC1##
As has been stated above, the cartridge case member of the present
invention is made with a polyvinyl acetal foam which is the
principal material and in which is contained at least one of the
two kinds of reinforcement fillers, i.e., polyvinyl acetal fibers
and a coarse polyvinyl acetal cloth. Therefore, this case member
can satisfy most of the requirements of an instantaneously
completely combustible cartridge case. Also, the said reinforced
foam is prepared in a hollow cylindrical shape which is mounted on
a male mold member of a compression-molding apparatus to be
diametrically compressed excessively by utilizing a pressurized
fluid in the first step, and then the resulting compressed hollow
cylindrical foam is positioned between an inner male mold member
and an outer female mold member of separate heat-expansion molding
apparatus to be subjected -- after being moistened to an apropriate
degree -- to expansion, by heating, to become in tight contact with
the said outer female mold member, thus being molded into the
configuration of a case member. Therefore, unlike the molding by a
heat-compression molding, the case member of the present invention
can be molded quite reasonably so as to have a uniform density and
uniform desired thickness. As a final product, the cartridge case
member of the present invention leaves no appreciable residue at
the time of firing.
The molded case member can have an enhanced strength and hardness
by being treated with a synthetic resin. Moreover, it can have a
very desirable water-proofness and combustiblity by being given --
at its surface -- a thin under-coating with a solution containing
nitrocellulose and a thixotropic agent and being capable of
exhibiting thixotropicity at a low concentration, and thereafter by
forming a water-proof thin film on top of the said under-coating.
Besides, the applications of these solutions is easy and needs no
well-trained skill.
It is to be understood that the currently used firearms are not
designed so as to have a gas-enclosing function in the bottom
portion of their cartridge chambers. In order to suit for these
current firearams, the cartridge case member 2 of the present
invention desirably is provided -- at its bottom -- with a metal
bottom member 5 having a small longitudinal length which is bonded
by a layer of adhesive 10 at its portion of juncture 9a to the
corresponding portion of juncture 9 of the case member 2, in a
manner as shown in FIG. 1, for establishing the enclosure of the
gases produced at the time of firing. The adhesive which is most
suitable for use in these portions of juncture is an epoxy
resin.
* * * * *