U.S. patent number 3,571,962 [Application Number 04/831,876] was granted by the patent office on 1971-03-23 for monolithic metallic liner for fiberglass gun tubes.
This patent grant is currently assigned to N/A. Invention is credited to Merrill Eig.
United States Patent |
3,571,962 |
Eig |
March 23, 1971 |
MONOLITHIC METALLIC LINER FOR FIBERGLASS GUN TUBES
Abstract
A tubular device suitable for use as gun barrels and the like
and being capable of withstanding sudden high pressures normally
encountered in ordnance use, the device having a nonstructural
metallic inner liner of noncircular configuration overwrapped by
fiberglass windings acting in a structural capacity, and a
resilient elastomeric material disposed between the liners at
substantially uniform spaced intervals.
Inventors: |
Eig; Merrill (Parsippany,
NJ) |
Assignee: |
N/A (N/A)
|
Family
ID: |
25260073 |
Appl.
No.: |
04/831,876 |
Filed: |
June 10, 1969 |
Current U.S.
Class: |
42/76.02;
89/16 |
Current CPC
Class: |
F41A
21/02 (20130101) |
Current International
Class: |
F41A
21/02 (20060101); F41A 21/00 (20060101); F41c
021/02 (); F41d 017/06 (); F41d 017/08 () |
Field of
Search: |
;42/76,76.1 ;89/16 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Borchelt; Benjamin A.
Assistant Examiner: Jordan; C. T.
Claims
I claim:
1. A tubular device comprising:
a nonstructural inner liner and a structural outer liner, said
liners being strain-compatible when said tube is subjected to
sudden high internal pressures;
said inner liner being so configurated that inner surfaces of said
outer liner are contacted by said inner liner at uniformly spaced
intervals while providing enclosed air spaces at those portions not
contacting said inner surfaces of said outer liner; and
an elastomeric material disposed in said air spaces.
2. The device of claim 1 wherein said inner liner is stainless
steel.
3. The device of claim 1 wherein said outer liner is made of
fiberglass wrappings.
4. The device of claim 1 wherein said elastomeric material is
selected from the group consisting of high temperature silicone,
high temperature epoxy-novolac, high temperature hard resin of high
elongation, and high temperature polyurethane.
5. The device of claim 1 wherein the ratio of outer liner to inner
liner thickness is about 20--30 to 1.
6. The device of claim 1 wherein said inner liner has a sine wave
configuration in cross section.
7. The device of claim 1 wherein said inner liner has a square wave
configuration in cross section.
8. The device of claim 1 wherein said inner liner has a modified
square wave configuration in cross section, as shown in FIG. 3 of
the drawings.
9. The device of claim 1 wherein said inner liner has a Z-shaped
configuration in cross section, as shown in FIG. 4 of the
drawing.
10. The device of claim 1 wherein said inner liner has a square
wave configuration in cross section where uniformly spaced
nonadjacent waves have amplitudes greater than its neighbor, said
inner liner being twisted relative to its longitudinal axis to
provide rifling.
Description
STATEMENT OF GOVERNMENT INTEREST
The invention described herein may be manufactured, used and
licensed by or for the Government for governmental purposes without
the payment to me of any royalties thereon.
BACKGROUND OF THE INVENTION
This invention relates to tubes or cylinders useful as gun barrels
and the like and more particularly concerns composite tubes having
a monolithic, nonporous, nonstructural, metallic inner liner
surrounded by a nonmetallic, structural overwrap liner wherein good
strain compatibility is effected between the liners when the tube
or cylinder is subjected to sudden high pressures.
The desirability of improving gun barrels has long been recognized
among the military, not only from the standpoint of enhanced
logistics but also troop combat efficiency. The military have long
sought to achieve gun barrels which are inexpensive to manufacture,
light in weight, and yet erosion resistant and long lasting. The
long felt need for a gun barrel characterized by these properties
is evidenced by the efforts of prior patentees whose inventions for
various and sundry reasons fell short of filling the existing
hiatus in the art. Illustrative prior art gun barrels are disclosed
in the following patents, among others: U.S. Pats. Nos. 2,249,899
issued Jul. 22, 1941; 2,845,741 issued Aug. 5, 1958; 2,847,786
issued Aug. 19, 1958; 2,935,913 issued May 10, 1950; and 3,118,243
issued Jan. 21, 1964. For the most part these patents suggest a
composite gun barrel construction wherein a metal core or liner is
jacketed by plastic or resinous glass fibers. The function of the
outer jacket material is dictated by considerations of lightness
and strength while the selection of the core or liner material is
dictated by considerations of resistance to wear and erosion. While
the underlying rationale in the construction of the prior art
launcher barrels appears sound, other considerations of a
controlling nature either have gone unnoticed or have presented
difficult problems for which solutions were found wanting.
A primary consideration in the construction of composite gun
barrels is strain compatibility of the materials of construction.
High rate of loading conditions of short duration normally
encountered in gun barrel usage make for an even more difficult
problem because of the necessary multiple considerations of the
coefficients of expansion and thermal conductivity.
Another consideration closely related to strain compatibility is
the obtention of more elastic means in the liner material. Where,
as in the prior art gun barrels, a jacket of relatively elastic
material having an elastic limit approaching 3 percent surrounds an
inner liner of relatively inelastic material having an elastic
limit approaching 1/2 percent, it is obvious that the latter value
is controlling. Accordingly, the use of a low elastic limit
material in the inner liner limits the full utilization of the
fiberglass potential and results in a less efficient composite
structure.
Accordingly, it is a principal object of the present invention to
provide a gun barrel of composite construction which is unattended
by the aforementioned disadvantages of the prior art.
Another object of the invention is to provide a lightweight gun
barrel of composite construction characterized by freedom from
defects attributable to strain incompatibility arising from firing
conditions normally encountered in usage.
The exact nature of the invention as well as other objects and
advantages thereof will be readily apparent from consideration of
the following specification relating to the attached drawings
wherein:
FIG. 1 illustrates a sectional view of an embodiment of my
inventive tubular device as represented by a gun barrel showing the
outer nonmetallic liner, inner metallic liner, and elastomeric
material between the liners.
FIG. 2--5 illustrate modifications of the inner liner
configuration.
Referring to the drawings and more particularly to FIG. 1 thereof,
there is shown a gun barrel having a nonmetallic outerwrap liner
10, suitably of fiberglass windings, and a metallic, expandable
inner liner 12 of corrugated or sine wave configuration. Any
formable metallic material which is capable of providing the
required degree of erosion resistance may be used for the
expansible inner liner. Stainless steel works admirably, and when
so used, I have found that a thickness of about 0.010 to 0.020 inch
is structurally satisfactory in obtaining large elastic strains,
i.e., greater than about one-half percent. The ratio of outer liner
to inner liner thickness is no particular importance since as a
result of the high pressures prevailing in gun tubes upon firing
therethrough, the outer fiberglass is designed to be the structural
member. The role of the liner is to resist erosion of the barrel
and this liner does not significantly contribute to the strength of
the overall system. Ordinarily, the ratio of fiberglass to metallic
liner thickness is of the order of about 20 or 30 to 1.
Disposed between the inner liner 12 and outer liner 10 is a high
temperature elastomeric backup material 14, which aids in
preventing crushing of the inner liner and yet permits relative
movement between the inner liner and itself. The elastomeric
material may be of high temperature silicone, flexible epoxy or
epoxy-novolac, a hard resin of high elongation, or a high
temperature polyurethane.
In order to more fully appreciate the invention, it must be
remembered that a basic problem in the successful cooperation
between fiberglass and metallic components is that of strain
incompatibility due to different expansion characteristics of these
materials. This incompatibility is induced by one or a combination
of the following:
a. internal pressurization
b. thermal expansion
c. thermal contraction
If one considers as a representative case the condition which
exists when a thin monolithic metallic liner contacts the inner
wall of a fiberglass tube, the resultant composite tube being
heated rapidly to a high temperature, it will be realized that
because of the difference in thermal conductivities, among other
properties of the materials, the metallic liner will expand at a
faster rate than the fiberglass to cause buckling of the restrained
inner liner. Thus, to effect compatibility between the liners, the
geometry of the monolithic liner must be altered such that the
desired strain is a combination of material and geometric
expansion. The capability of the inner liner to be successfully
subjected to large strains, i.e., greater than about 1/2 percent,
beyond which point stainless steel and most other metals become
substantially inelastic, is accomplished by means of flexing and
extending the corrugations as shown in FIG. 1 in the
circumferential direction similar to movement of an accordion. In
Table I below, results are presented for the corrugated or sine
wave inner liner. It can be seen that both specimens resisted
strains greater than 1/2 percent. Specimen No. 1 was subjected to a
second cycle of 2,000 p.s.i., which yielded a strain of only 0.42
percent. The specimen was discarded as having served its purpose
but was still very elastic in nature. The elastomeric material used
was a high temperature polyurethane. ##SPC1##
Referring again to FIG. 1, if a high pressure is generated within
the barrel, as upon the firing of a projectile therethrough, the
erosion resistant corrugated inner liner 12 will be caused to
expand against the elastomeric material 14 and fiberglass 10,
portions of both the inner and elastomeric material being
structurally restrained by the outer fiberglass liner.
The modification of FIG. 2 employs a square wave inner liner 22
which contains elastomeric material 24. If the square wave liner 52
is periodically altered at a specified uniform spacing as at 52',
all as shown in FIG. 5, such that its amplitude is higher than its
adjacent wave, and the liner is then twisted at a desired angle
relative to the longitudinal axis of the barrel, (depending on the
desired angle of rifling) rifling may be obtained. The elastomeric
material is shown at 54.
The modification of FIG. 3 shows a modified square wave
configuration, the inner liner 32 containing the elastomeric
material 34.
In the modification of FIG. 4, the inner liner 42 is Z-shaped, the
elastomeric material being shown at 44.
Tests conducted on the square wave configuration, modified square
wave or "gear tooth" configuration, and the rifling and Z-shaped
inner liners indicated that these modifications could be
successfully substituted for the corrugated inner liner
configuration.
When over-winding the inner metallic liner with fiberglass,
buckling of the former does not occur since;
(1) it is backed-up and supported by a mandrel, and
(2) the expansion characteristics of the inner liner will movably
adjust in response to motion of the fiberglass. The mandrel need
have no special configuration but should be of such as material to
resist the high temperature experienced during the cure cycle, and
will preferably be cylindrical, upon which mandrel the inner liner
may be rolled. The elastomeric material will be coated or painted
on the inner liner while flat, the task being relatively simple,
the configuration of the inner liner being considerably exaggerated
in each of the drawings.
At this point, the outer surfaces of the inner liner may be coated
with a thin layer of epoxy-novolac resin and the entire resultant
assembly overwrapped in accordance with the following
procedure:
Means are provided for rotating the mandrel about its longitudinal
axis while drawing fiberglass strands from a spool riding on a
reciprocating carriage which moves from one end of the mandrel to
the other. Where the strands are not preimpregnated, means may be
provided for coating such strands with resin as they are drawn from
the spool to the mandrel. Subsequent windings should comprise
alternate groups or layers of helical and circumferential windings.
Preferably, three-layers of helical windings at an angle of
201/2.degree. relative to the mandrel axis follow the initial layer
of circumferential windings. While both types of windings provide
circumferential strength, the helical windings contribute to
strength in the longitudinal direction. For example, in the
construction of an 81mm. mortar, it is contemplated that the base
plug, preferably metallic, adapted to seat in a base plate and
housing the firing pin will comprise a ball or knob-shaped
projection coaxial with and attached to a closure or end cap, the
latter having an outer diameter substantially the same as that of
the gun barrel to which the base plug is attached. It is further
contemplated that the base plug will have a flange projecting from
the end gap and forming a coaxial, hollow cylinder of reduced outer
diameter, the inner diameter of the cylinder being equal to the
inner diameter of the gun barrel. By providing the attachment end
of the gun barrel with an undercut which will mate with the
cylindrical flange of the base plug, proper alignment and seating
may be effected and attachment of the gun barrel to the base plug
will be facilitated. Accordingly, circumferential windings may be
applied over the aforementioned helical windings until the
thickness of the gun barrel is built up to that of the base plug
flange. Thereafter, another 3 layers of helical windings may be
applied followed by sufficient layers of circumferential windings
to build up to the predetermined gun barrel outer diameter. The
wound mandrel can then be rotated in an oven to effect curing and
upon completion of the curing operation, finish sizing may be
effected by cutting off barrel ends to arrive at the final barrel
length and by machining the barrel to arrive at the final outer
diameter. The mandrel can then be removed and the undercut to
effect mating with the base plug flange may then be made.
Preliminary attachment may thereafter be made advantageously by
coating with resin the mating surfaces of the base plug and gun
barrel and rigidly holding the mating surfaces in contact while
subjecting them to a curing operation. To promote adherence it is
desirable to knurl or roughen the mating surfaces prior to coating
with resin.
Final attachment of the base plug to the gun barrel preferably
makes use of undercuts on the base plug which promote rigidity and
strength of adherence. These undercuts comprise annular grooves on
the periphery of the base plug and preferably comprise an annular
groove on the lateral periphery of the end cap and an annular
groove on the neck of the knob-shaped projection adjacent the end
cap. A continuous layer of fiberglass cloth impregnated with resin
is wound advantageously warp direction parallel to longitudinal
axis of barrel abut a 6 to 12 inch longitudinal section of the
barrel adjacent the end cap and about the end cap almost to the
neck of the knob-shaped projection. The fiberglass cloth is then
cut and folded in such a manner as to permit it to lie snugly
against the domelike surface of the end cap. The circumferential
fiberglass windings impregnated with resin are thereafter applied
over the fiberglass cloth to compress it around the barrel and end
cap and depress the cloth into the angular groove of the lateral
surface of the end cap. Additional circumferential windings are
made in the region of this angular groove until flush. Repetition
of this procedure, with the exception that the windings are carried
out helically rather than circumferentially, and that the windings
are carried down to tether the end cap and fill the angular groove
at the neck of the projection adjacent thereto, is continued until
about 4 alternate layers of cloth and windings are applied. The
resultant base plug fitted barrel is subjected to a curing
operation wherein it is rotated in an oven at an elevated
temperature. Additional circumferential strength may be given the
adjoining areas by overlaying the last layer of helical windings
with two layers of circumferential windings prior to curing.
The curing cycle comprises about 11/2 hours at about 175.degree. F.
and 250.degree. F. and then about two hours at about 400.degree. F.
and 450.degree. F. After this final cure, the mortar gun tube is
machined to the desired dimensions and the mandrel if, salt,
leached out by ordinary tap water, or if made of aluminum or other
material, merely tapped out.
Actual field testing of my monolithic configurated inner liner
barrel indicates that over 1,000 81mm. mortar rounds could be fired
therethrough successfully. Slight erosion did occur however at that
portion of the barrel where the hot gases emanate from the mortar
flash hole. If my inventive device is employed as the erosion
resistant liner, longer barrel life may be expected.
Other uses for my expansible liner devices may be found where it is
desirable to pipe fluids under high pressures creating large strain
therewithin, and the like. Further my device may be used
advantageously in such applications as buried pipe where porosity
and corrosion are a problem.
I wish it to be understood that I do not desire to be limited to
the exact details of construction shown and described, for obvious
modifications will occur to a person skilled in the art.
* * * * *