US 3571962 A
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United States Patent  Inventor Merrill Eig pp y. J.
] Appl. No. 831,876
 Filed June 10, 1969  Patented Mar. 23, 1971 I  Assignee The United States of America as represented by the Secretary of the Army  MONOLITHIC METALLIC LINER FOR FIBERGLASS GUN TUBES 10 Claims, 5 Drawing Figs.
 US. Cl 42/76, 89/16  Int. Cl F4lc 21/02, F41d 17/06, F41d 17/08  Field of Search ..42/76, 76.1;
 References Cited UNITED STATES PATENTS 2,845,741 8/1958 D 42/76(.1) 2,847,786 8/1958 Hartley et a1. 42/76(.1) 3,118,243 1/1964 Manshel 42/76(.1) 3,228,298 1/1966 Grandy et al. 42/76(. 1) 351,758 6/1970 Slade 42/76 Primary ExaminerBenjamin A. Borchelt Assistant Examiner-C. T. Jordan Att0rneys-Harry M. Saragovitz, Edward J. Kelly, Herbert Berl and S. Dubroff 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.
MONOLITHIC METALLIC LINER FOR FIBERGLASS GUN TUBES 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, stnictural 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 rpercent, 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 l0, 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. thennal 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 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 xzpercent. 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.
TABLE I.TEST RESULTS FOR CORRUGATED STAINLESS STEEL LINER Percent Specimen strain Number Cycle Number Pressure (p.s.l.): l
l Hydrodynamic testing device used. 2 Strain guage Wire broke.
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 l0, 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 S2 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 209? 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 l fliours at about F. and 250 F. and then about two hours at about 400 F. and 450 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 vious modifications will occur to a person skilled in the art.
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 CO1 lfigurated 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 l.
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.