Rifled fiber reinforced gun barrel

Abstract: The disclosure relates to a method of producing rifled, non-metallic barrels of composite material in the form of a fibre-reinforced thermosetting matrix for rocket and grenade launcher ordnance, and barrels produced in accordance therewith. The characterizing feature of the present invention is that this results in barrels with the same fibre content in both the lands (2) of the barrel rifling and in its rifling grooves (3), which has been realized in that a porous fluffy mat with a high capacity to absorb the matrix material is employed in the rifled portion of the barrel.

Description: TECHNICAL FIELD The present invention relates to a method of producing for use as a rocket launcher or grenade launcher ordnance a rifled, non-metallic barrel, having, in cross section, lands alternating with grooves with smooth transitions therebetween, said barrel being made from a composite material comprising a thermosetting matrix material and reinforcing fibres, and barrels produced according to the method and formed from a thermosetting matrix and a reinforcing fibre material, said barrel having rifling grooves and lands located therebetween. The barrels according to the present invention are produced from a composite material of per se known type, comprising reinforcement fibres of glass, carbon or suitable polymer material, for example polyamide, nylon or the like, baked into a matrix of a curable synthetic plastic material of, for instance epoxy or ester plastic type. BACKGROUND ART Non-metallic barrels of fibre-reinforced thermosetting resin are primarily employed today for such recoil-less weapons of the rocket launcher or blow-back type which are equipped with once-only use disposable barrels. As far as we are aware, these barrels are always smooth-bored. However, primarily in the patent literature, a number of different proposals have already been presented for methods of producing light, rifled barrels by encasing a thin-walled, interiorly rifled steel tube with a sufficiently thick outer layer of a fibre-reinforced thermosetting resin. However, the method is expensive, since the inner metal tube must be worked and rifled in the usual way and, moreover, it would probably be difficult to avoid experiencing problems in the different expansion coefficients of the metal tube and the surrounding outer reinforcing layer. Moreover, there are prior art proposals for methods of producing rifled, non-metallic barrels of a composite material of corresponding type. Thus, SE-A- 8106590-6 describes a method of producing non-metallic, rifled, fibre-reinforced barrels on a rotary mandrel provided with a number of helically arranged grooves, the grooves being first completely filled with a "yarn" impregnated with a thermosetting plastic material, or ropes of carbon fibre which extends in the longitudinal direction of the grooves, whereafter an additional fibre material impregnated with a thermosetting plastic material is wound about the mandrel, either in the form of thread or textile material, until a tube of desired thickness has been attained, whereafter the plastic material (which, according to the text, may for instance consist of an epoxy resin) is cured, the thus obtained tube being then removed from the mandrel. Concerning the grooves in the mandrel - which would thus provide the lands of the finished barrel - the text discloses that these may preferably be substantially rectangular in cross-section. EP-A-0 170 353, on which the preambles of independent claims 1 and 5 are based, discloses a method of producing rifled, non-metallic barrels, which is an improvement of the method disclosed by said Swedish patent application. Specifically, the method of EP-A-0 170 353 is concerned with the manner in which the fibre material is wound or placed on the mandrel and the effects thereof on the capability of the barrel to withstand high transient gas pressures and hot propellant gas erosion of its inner surface. If the methods disclosed in the above-mentioned patents function satisfactorily, the thus obtained barrel would then have riflings of virtually rectangular cross-section, and display, on the one hand, a first axial reinforcement extending in the longitudinal direction of the lands, and, on the other hand, a substantially peripheral reinforcement. SUMMARY OF THE INVENTION The present invention now implies a simplified method for producing rifled, non-metallic barrels made of a composite material in the form of a thermosetting matrix such as a polyester or epoxy resin or other thermosetting synthetic resin or plastic, and one or more reinforcing fibre materials of per se known type, such as glass, carbon, polyacrylic or corresponding fibres. According to the present invention this is obtained - in a manner corresponding to that of the above-considered laid-open Swedish patent application - by a method according to the opening paragraph, which is characterized by the following steps: providing a rifled mandrel having a length at least as great as the length of the desired barrel, and an outer diameter which corresponds to the inner diameter of the desired barrel, said rifled mandrel having a substantially circular cross section, with longitudinal rifling grooves alternating with longitudinal rifling lands with smooth transitions therebetween, said lands and grooves corresponding to the grooves and lands respectively for the rifling of the desired barrel; surrounding said rifled mandrel with a continuous, porous, fluffy mat formed of a fibrous material, said mat being capable of absorbing said matrix material in its uncured or prepolymer state, and being drenched with said matrix material; thereafter surrounding the mat with a plurality of fibre layers drenched with matrix material, so as to dispose said layers peripherally about the mandrel; applying said fibre layers against said fluffy mat with the matrix material absorbed therein to compress said mat and to fill the rifling grooves of the mandrel, the mat and its content of matrix material being thereby compressed to a smaller thickness above the lands than above the grooves of the mandrel, with the thicker parts thereof penetrating into said rifling grooves, at the same time forcing out surplus matrix material and entrapped air; continuing the application of additional drenched fibre layers until the barrel wall has reached a desired thickness; curing the matrix material; and removing the resulting barrel from the mandrel. We have now surprisingly found that, in trial shoots, we have obtained a desired rotation of the projectile with helical riflings with sinusoidal configuration. Thus, this is the most advantageous profile cross-section according to the present invention of the lands and grooves of both the mandrel and the finished barrel. The desired durability of the rifling grooves is obtained by first, before the mat is applied, surrounding the mandrel with a glass fibre fabric impregnated with the resin matrix which thus may follow the contours of the rifling grooves, and only then surrounding the mandrel with the contemplated mat in accordance with the foregoing. Trial firings have been carried out using barrels produced in accordance with the above-intimated method, these trials demonstrating that such barrels may be employed for discharing shells provided with driving bands of both metal and plastic. Since the lands and rifling grooves of the mandrel are gently helical in configuration, the projectiles will execute a rotary movement even outside the barrel, whereby it will be possible to discharge the projectile without the use of guide fins. In the barrel which we have trial fired, the inner wear layer consisted of a plain woven glass fibre fabric of a thickness of 0,10 mm and grammage of 70 g/m², while the mat forming the rifling grooves and lands was of non-woven type and consisted of polyacrylic fibres having a weight of 60 g/m². The plastic matrix was of epoxy type. The present invention has been defined in the appended Claims, and accompanying Fig. 1 shows a cross-section through a finished barrel of the type obtained in accordance with the present invention, while Fig. 2 shows the inner, sinusoidal cross section of the barrel in the folded-out state. In Fig. 1, reference No. 1 relates to the inner glass fibre layer, reference No. 2 to the mat forming the land (b) filled with the cured plastic material, while it is possible to see, at the rifling grooves (r) how, at reference No. 3, the mat has been compressed to a minimum of its largest thickness. In addition, the barrel according to the present invention includes a number of layers of plastic-impregnated glass fibre thread winding 4 which provide the thickness of the barrel. The length of the sinus wave may be varied within the fundamentals of the present invention, in accordance with tests and depending on the calibre of the barrel. The present invention should not be considered as restricted to that described above and shown on the Drawings, many modifications being conceivable without departing from the scope of the appended claims.

Claims: A method of producing for use as a rocket launcher or grenade launcher ordnance a rifled, non-metallic barrel, having, in cross section, lands (b) alternating with grooves (r) with smooth transitions therebetween, said barrel being made from a composite material comprising a thermosetting matrix material and reinforcing fibres, characterized by the following steps: providing a rifled mandrel having a length at least as great as the length of the desired barrel, and an outer diameter which corresponds to the inner diameter of the desired barrel, said rifled mandrel having a substantially circular cross section, with longitudinal rifling grooves alternating with longitudinal rifling lands with smooth transitions therebetween, said lands and grooves corresponding to the grooves and lands respectively for the rifling of the desired barrel; surrounding said rifled mandrel with a continuous, porous, fluffy mat (2) formed of a fibrous material, said mat being capable of absorbing said matrix material in its uncured or prepolymer state, and being drenched with said matrix material; thereafter surrounding the mat with a plurality of fibre layers (4) drenched with matrix material, so as to dispose said layers peripherally about the mandrel; applying said fibre layers against said fluffy mat with the matrix material absorbed therein to compress said mat and to fill the rifling grooves of the mandrel, the mat and its content of matrix material being thereby compressed to a smaller thickness (3) above the lands than above the grooves of the mandrel, with the thicker parts thereof penetrating into said rifling grooves, at the same time forcing out surplus matrix material and entrapped air; continuing the application of additional drenched fibre layers (4) until the barrel wall has reached a desired thickness; curing the matrix material; and removing the resulting barrel from the mandrel. The method as claimed in claim 1, characterized in that a porous, matrix material-drenched, polyacrylic fibre mat of a non-woven type is provided for surrounding said mandrel and forming the lands (b) of the barrel. The method as claimed in claim 1, characterized in that the mandrel has at least weakly helical, continuous rifling grooves and intermediate rifling lands, the sequence of grooves and lands defining a sinusoidal cross-sectional profile. The method as claimed in claim 1, characterized by the further step of covering the mandrel, prior to the application of the porous, fluffy mat (2), with a matrix material-impregnated reinforcing fabric (1), which follows the contour of the mandrel for imparting an inner durability to the finished barrel. A non-metallic rifled barrel formed from a thermosetting matrix and a reinforcing fibre material, said barrel having rifling grooves (r) and lands (b) located therebetween, characterized by a wear-resistant inner layer (1) comprising a thermosetting matrix reinforced with glass fibres, an intermediate layer covering said inner layer and comprising a fibre mat (2) substantially completely filled with matrix material, said fibre mat being compressed at said grooves to a thickness (3) less than the thickness of said lands, the sequence of lands and grooves showing a sinusoidal cross-sectional profile; and an outer layer covering said intermediate layer, said outer layer comprising a plurality of layers (4) of fibres helically wound about said intermediate layer and impregnated with matrix material. The non-metallic barrel as claimed in claim 5, characterized in that said thermosetting matrix is an epoxy resin, and said reinforcing fibre material comprising carbon fibres.

Inventors: ANDERSSON SIGGE, OSKARSSON LEIF, PETTERSSON BENGT, ANDERSSON, SIGGE, OSKARSSON, LEIF, PETTERSSON, BENGT
Applicants: STATOIL EUROPARTS AB
Application year: 1991
Main classification: F41A21
IPC codes: F41A21, B29C70, B29C53