Seal for sliding breech

Abstract: The disclosure relates to a breech mechanism for large-calibre guns such as artillery pieces being characterized by a specifically designed sealing function in the form of an intermediate layer between the mechanism breech (4) proper and a seating portion (7) displaceable in relation thereto by the gas pressure in the gun, the seating portion, on being displaced towards the breech (4), compressing the intermediate layer (8) disposed therebetween and consisting of an elastically deformable refractory material which, on its deformation, is urged into tight abutment against the rear portion of the gun barrel about the loading space of the gun along a gap between the seating portion (7) and the mechanism breech (4) proper.

Description: IMPROVEMENTS TO BREECH MECHANISMS TECHNICAL FIELD The present invention relates to a mechanism for large-calibre guns including a mechanism breech laterally displaceable transversely of the rear region of the gun barrel and disposed in a groove adapted therefore in the breech piece of the gun, this in its turn being fixedly connected to the barrel of the gun. In a conventional manner, the breech in question is displaceable from a first loading position where it leaves the rear loading aperture of the barrel completely open, to a second position where it wholely seals the loading aperture. By means of a special design of the breech, it has become possible to render the breech so gastight in the closed position that it may also be employed for caseless ammunition and ammunition with combustible cases. BACKGROUND ART In particularly large-calibre ordnance such as artillery guns, only two different mechanism types are fundamentally conceivable. The first and most widely used but at the same time also most expensive and difficult to manufacture is the so-called screw mechanism in which the loading aperture of the gun barrel is closed by means of a special impact base with associated obturation pad, a so-called Crossly pad, which in its turn is supported by the chamber screw functioning as an abutment. This latter displays outer alternatingly smooth and threaded sectors which are inserted into a correspondingly adapted and correspondingly sectorwise threaded locking portion in the breech piece of the gun, where the chamber screw is then locked by a turning movement which causes the different threads to intermesh. The major advantage inherent in this mechanism type is that it is so gastight that it can be employed for caseless ammunition, for example when the gun is loaded with a shell and one or more separate propellant charges, so-called bag charges or when use is made of combustible cases, and thus provides no sealing aid whatever on firing as is provided by a cartridge case expanded by the gas pressure. The second basic mechanism type is the so-called sliding breech mechanism in which use is made of a mechanism breech displaceable transversely of the loading aperture of the gun barrel in a groove adapted therefore in the breech piece of the gun fixedly connected to the gun barrel, for rearward closing and sealing of the gun barrel. Even if the mechanism breech may be provided with such a path of motion that it is urged against the rear portion of the gun barrel when it is displaced from its open loading position to its fully closed firing position, this mechanism type will not in itself be sufficiently gastight to cater for other than cased ammunition. On the other hand, it functions very well in connection with such cased ammunition, in which the cartridge cases may be utilized as a seal against the inner gas pressure. However, a considerable amount of development work has been devoted to producing "tight" breech mechanisms. In one of these, use is made of an annular resilient sealing plate of metal as a seal between the gun barrel and the mechanism breech. The sealing plate under consideration here has an angular cross-section and is turned with its one flank to face the outer edge of an annular groove disposed about the inside of the rear portion of the gun barrel, while the other free flank of the sealing plate is turned to face the mechanism breech. The sealing function is based on the concept that the gas pressure within the gun barrel will urge the free flank of the sealing plate against the mechanism block and seal thereagainst. The design as such may be rendered sufficiently tight for employment together with caseless ammunition, but at the same time it is prone to damage, not least to the resilient sealing flank of the sealing plate and consequently there has been general reluctance to introduce this type of design, since such damage to the sealing plate may cause a considerable blow-back, which would of course constitute a serious risk to the gun crew. Patent specification EP-A1-0014559 and its US-equivalence US-A-4.308.785, on which disclosure the preamble of independent claim 1 is based, further describes a two-part breech mechanism (previously unknown to us) comprising a first locking device displaceable transversely of the longitudinal direction of the gun barrel and a sealing device interconnected therewith which, in its turn, is displaceable both transversely of the gun barrel and, in the closing position, partly into the rear opening thereof where it is blocked by the locking device. The configuration of that part of the sealing device which is inserted in the rear region of the gun barrel is described in the text as a mushroom provided with a stem seal disposed about the neck of the mushroom. The problem which may be directly foreseen with this design is that the stresses on parts of the stem seal must be extremely high, since parts thereof, even if the greater part is protected by the mushroom hat, are disposed directly in the line of fire from the propellant charge combustion. SUMMARY OF THE INVENTION In accordance with the present invention, use is made of a two-part mechanism breech consisting of a conventionally designed main portion and a seating portion journalled therein and restrictedly movable. Between the seating portion which, with the locking breech in the closed position, wholly covers the rear loading aperture of the gun barrel, and the main portion of the locking breech, there is provided according to the present invention an elastically deformable intermediate layer of a refractory natural or synthetic rubber, for example nitrile rubber. The main portion and seating portion of the mechanism breech display mutually facing concave and convex defining surfaces between which the elastically deformable intermediate layer is thus disposed. These defining surfaces are formed by different concave and convex cams respectively, for example in the form of parabolic parts which have been rotated about a common axis. The shape of these cams must be empirically tested in view of calibre, gas pressure in the gun and the thickness and physical properties of the intermediate layer. It has also proved appropriate to cause the space which the intermediate layer has accessible between the two parts to flare somewhat towards the annular gap which is formed about the outer surface of the seating portion turned to face the loading aperture of the gun barrel. On firing of the gun contemplated here, the outer surface of the seating portion is influenced by the gas pressure, the intermediate layer being compressed and its only direction of creepage being then towards the rear portion of the gun barrel around the loading aperture. There will thus be obtained - because the seating portion lacks a counter-abutment for its central region in the block - an elevation of the gas pressure in the gun barrel to a higher pressure in the intermediate layer. Consequently, the interface contact pressure between the intermediate layer and the gun barrel will always be higher than the gas pressure, which thus ensures the sealing function. In other words, the higher the gas pressure in the gun, the more efficient will be the sealing. Along the gap in question, the intermediate layer should be shod with metal rings or rings of other material which is intractable both in a direction in towards the loading aperture and away therefrom. In the first case mainly as protection against flash jets and in the second case to prevent creepage of the intermediate layer between the breech and the rear portion of the gun barrel. The material in the intermediate layer must be hard but elastically deformable, while on the other hand it should possess only very slight natural compressibility. In addition, it must be of a refractory nature, for which reason nitrile rubber material, for instance, should be ideal. For elevation of the gas pressure and for guiding the seating portion in the main portion of the mechanism breech, the seating portion is provided with a central pin which runs through a specifically adapted aperture in the intermediate layer and is restrictedly displaceable in the main portion of the mechanism breech. The detonation mechanism may also be disposed in this pin. This central pin may further be employed for precompressing the intermediate layer already before the seating portion is actuated by the gas pressure and thereby positively realize the sealing function already prior to firing of the gun, i.e. as soon as the breech has been closed. This is achieved most simply in that the central pin is mechanically or hydraulically retracted in the main portion of the mechanism breech, in which event the intermediate layer is, thus, urged towards the rear portion of the gun barrel along the previously mentioned annular gap around the seating portion. Another variation is based on the concept that the intermediate layer is always given a certain precompression via a continuous pull in the central pin so that it constantly protrudes out beyond the mechanism breech, and that the latter, when the mechanism is closed, is urged via a somewhat oblique path in relation to the gun barrel in towards the rear wall of the barrel and thereby further compresses the intermediate layer along the annular gap towards the rear region of the gun barrel around the loading aperture. The device according to the present invention has been defined in the appended claims and will now be described further with reference to the accompanying Drawings and the embodied, non-restricting example. In the accompanying Drawings: Fig. 1 is a longitudinal section through the apparatus according to the present invention with the mechanism breech in the open position; and Fig. 2 shows the same section, but with the mechanism breech in the closed position and the gun ready for firing. DESCRIPTION OF PREFERRED EMBODIMENT The accompanying Drawing figures show only the rear portion of the gun presently under consideration, with a gun barrel 1, a breech piece 2 fixedly connected to the gun barrel, with a guide groove 3 for the mechanism breech 4. This latter is operated from its open position illustrated in Fig. 1 to its closed position illustrated in Fig. 2 by means of the crank 5. A charge 6 is already placed in the chamber of the barrel 1, the charge being of bag charge type or with a combustible case. The seating portion 7 is journalled in the main portion 4 of the mechanism breech. Between the seating portion and the main portion of the mechanism breech, there is provided an intermediate layer 8 of a hard but deformable refractory natural or synthetic rubber or plastic material. The convex and concave defining surfaces 9, 10, respectively of the seating portion and the main portion of the mechanism breech are formed by cams which constitute parts of different parabola rotated about one and the same axis which coincides with the bore axis 17 of the gun barrel. As will be apparent from the Drawings, the gap accessible for the intermediate layer is flared towards the annular gap 18 which is formed about the front face 11 of the seating portion turned to face the charge. The intermediate layer is shod with metal rings 12-14. The ring 13 primarily protects against flash jets, since it is turned to face towards the loading space of the gun, while both of the other rings 12 and 14 are intended to prevent the material of the intermediate layer from creeping out into the gaps between adjacent mechanism parts. As will further be apparent from the Drawings, the seating portion is journalled in the major portion of the mechanism breech by means of a pin 15 which passes through an aperture 16 in the intermediate portion, flush with the ring 14. The detonation system 19 is also disposed in the pin 15. When the gun loaded in accordance with Fig. 2 is fired, the gas pressure in the gun barrel will act upon the front face 11 of the seating portion 7. The intermediate layer is thus compressed and may only move slightly in a direction towards the rear portion of the gun barrel 1. The higher the gas pressure acting on the seating portion, the greater will be the force with which the seal is urged about the loading aperture where the material of the intermediate layer is protected from flash jets by the ring 13. As soon as the pressure in the gun barrel falls, the seating portion and seal return to their respective unloaded positions and the breech may be opened for reloading. As was mentioned above, the pin 15 may be provided with a device which urges it rearwardly in relation to the main portion of the mechanism block 4 already prior to firing of the gun, in order thereby to urge the intermediate layer 8 into tight abutment already at this point in time. This arrangement may be mechanical or, for instance, hydraulically actuable. However, for purposes of maximum clarity in the Drawings, we have refrained from depicting this pretensioning device which could thus be designed in any number of different ways. 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 breech mechanism for large-calibre guns such as artillery pieces comprising a mechanism breech (4) displaceable transversely of the rear portion of gun barrel (1) thereof, the mechanism breech being disposed in a groove (3) adapted therefore in the breech piece (2) thereof fixedly connected with the gun barrel, said mechanism breech (4), which is comprising a first main portion displaceable in said groove (3) and a second seating portion (7) which furthermore is moveable in a direction away from the gun barrel, is moveable in said groove from a first, open position in which it leaves the rear portion of the gun barrel (1) with its loading aperture, fully open for loading, to a second, closed position in which said seating portion (7) wholly closes and seals said loading aperture characterized in that said seating portion (7) has been made restrictedly moveable in connection to the main portion (4) of the mechanism breech by way of the action of an elastically deformable intermediate layer (8) disposed between mutually facing defining surfaces (9, 10 respectively) of the seating portion (7) and the main portion (4) of the mechanism breech, said surfaces consisting of convex and concave rotational surfaces formed by cams rotated about a common axis (17), which when the breech is in its closed position, coincide with the bore axis if the barrel, while the sole defined creepage possibility of the intermediate layer (8) on its deformation is at the gap (18) filled by the intermediate layer and formed between the seating portion (7) and the main portion of the mechanism breech (4) in a direction towards the gun barrel (1) about the loading aperture thereof. The breech mechanism as claimed in Claim 1, characterized in that the elastically deformable intermediate layer is defined by rings (12, 13) of metal or other intractable material along its defining edges in a direction towards the loading aperture and away therefrom, respectively. The breech mechanism as claimed in Claim 1 or 2, characterized in that the mutually facing convex and concave defining surfaces (9, 10, respectively) of the seating portion and the main portion of the mechanism breech, respectively are each formed by different cams rotated about the same axis (17) which, with the breech in the closed position, coincide with the bore axis of the barrel, and in which the cams are selected such that the gap formed therebetween and filled by the elastically deformable intermediate layer is flared forwardly in a direction towards the gun barrel (1). The breech mechanism as claimed in one or more of Claims 1-3, characterized in that the mutually facing defining surfaces (9, 10 respectively) of the seating portion (7) and the main portion of the mechanism breech (4) respectively have been formed of parts of two different parabolic cams rotated about the same axis (17). The breech mechanism as claimed in any one or more of Claims 1-4, characterized in that the seating portion (7) is guided in the main portion of the mechanism breech (4) by means of a central pin (15) which is displaceably disposed in a recess (16) adapted therefore in the main portion of the mechanism breech (4), and in which the pin heads passes through a central aperture in the elastically deformable intermediate layer (8), said aperture being shod with a ring (14) of metal or other rigid material which prevents the elastically deformable material from creeping in between the pin (15) of the seating portion (7) and its recess (16) in the main portion of the mechanism breech (4). The breech mechanism as claimed in any one of Claims 1-5, characterized in that the main portion of the mechanism breech (4) is provided with a bevelled oblique keyway towards the rear portion of the gun barrel (1), the region about the loading aperture of the gun barrel being flat without manifest grooves. The breech mechanism as claimed in Claim 5, characterized in that the central pin (15) intended for guiding the seating portion (7) in the main portion of the mechanism breech (4) is connected to a mechanically or possibly hydraulically acting pretensioning device for the intermediate layer, with which the pin (15) may be urged rearwardly in relation to the mechanism breech (4).

Inventors: ERIKSSON KJELL, LINDBERG SVEN, ERIKSSON, KJELL, LINDBERG, SVEN
Applicants: BOFORS AB, AKTIEBOLAGET BOFORS
Application year: 1990
Main classification: F41A3
IPC codes: F41A3