OBTURATOR FOR A GUN

Abstract: According to the invention there is provided an obturation assembly (100) for a gun of the type comprising a barrel (12) of which a rear end defines a firing chamber (14) having an obturation seat (22) and the gun further having a breechblock (16), the obturation assembly (100) comprising: an obturation set (134) including an annular obturator pad (36) for sealing against the obturation seat (22); an obturation spindle (26) having a shaft (30) and a head (28), the shaft (30) extending coaxially through the obturator pad (36); a first shim (52) for location between the obturation set (134) and the breechblock (16); and a second shim (102) for location between the obturation set (134) and the head (28) of the obturation spindle (26).

Description: OBTURATOR FOR A GUN INTRODUCTION AND BACKGROUND A gun such as a cannon or the like is usually adapted to fire either cased or caseless ammunition. A gun having a firing chamber adapted to fire caseless ammunition is provided with an obturation assembly for sealing the rear end of the firing chamber when a propellant charge is combusted inside the firing chamber to launch a projectile In the instance of guns adapted to fire cased ammunition, such sealing is effected by the case of the ammunition itself held in position by a breechblock. A conventional obturation assembly comprises a spindle having a shaft and a mushroom shaped head; and an obturation set including a resilient obturator pad for mating with and sealing against an obturation seat, an inner ring and two retaining rings. The obturation seat is usually defined by the rim of the mouth at the rear end of the firing chamber. When the spindle is displaced axially relativ e to the barrel of the gun by the combustion of the propellant charge in the firing chamber, the obturator pad deforms radially outwardly into sealing engagement with the obturation seat with the retaining rings limiting deformation of the obturator pad and preventing extrusion of the obturator pad. The obturation assembly is usually held in position by the breechblock of the gun and the shaft of the spindle usually extends through a hole in a carrier abutting the breechblock. A chamber for a cased primer for igniting the propellant charge, is provided in the shaft and a so called primer head space is defined between the rear end of the primer case and the breechblock. When installing the obturation assembly, it is known to provide a shim, from a set having a range of different thicknesses, between the rear end of the obturation set and the breechblock in order to adjust the position of the obturator pad relative to the obturation seat and to optimise the mating of the obturation set with the obturation seat. A disadvantage of the conventional method of adjusting the obturation set is that because the spindle abuts the obturation set directly, adjustment of the position of the obturation set, adjusts the position of the obturation spindle accordingly and the primer head space is thus varied . When the primer head space becomes too large, the primer case tends to slide out of the primer chamber thus allowing propellant gas to escape from the firing chamber past the primer. OBJECT OF THE INVENTION It is an object of the present invention to provide an obturation assembly for a gun utilising caseless ammunition and a method of optimising the mating of an obturator pad with an obturation seat and a shim kit with which the aforesaid disadvantage can be overcome or at least minimised. SUMMARY OF THE INVENTION According to the invention there is provided an obturation assembly for a gun of the type comprising a barrel of which a rear end defines a firing chamber having an obturation seat and the gun further having a breechblock, the obturation assembly comprising: an obturation set including an annular obturator pad for sealing against the obturation seat; an obturation spindle having a shaft and a head, the shaft extending coaxially through the obturator pad; a first shim for location between the obturation set and the breechblock; and a second shim for location between the obturation set and the head of the obturation spindle. Further according to the invention, the second shim is one of a set of shims having different thicknesses enabling a user to select a suitable shim for a particular position of the obturator pad relative to the breechblock. Further according to the invention, the second shim is contoured to match an inner contoured surface of the head of the spindle. Preferably the second shim has an outer circumferential edge which extends transversely to the general plane of the shim and an inner pointed circumferential configuration for merging with the contour of the inner surface of the head of the spindle. According to another aspect of the invention there is provided a method for use with a gun utilising caseless ammunition of the type having a barrel of which a rear end defines a firing chamber having an obturation seat, the gun further having a breechblock and an obturation assembly including an obturation set for sealing against the obturation seat and an obturation spindle having a head and a shaft, the method including the step of optimising the mating of the obturation set with the obturation seat without altering a preselected position of the obturation spindle relative to the breechblock by: providing a first shim between the obturation set and the breechblock, the thickness of the first shim being selected to ensure an optimal mating of the obturation set with the obturation seat; and providing a second shim between the obturation set and the head of the obturation spindle, the thickness of the second shim being selected to ensure that the preselected position of the obturation spindle relative to the breechblock is attained. According to yet another aspect of the invention there is provided a shim kit for an obturation assembly of the type comprising an obturation set including an annular obturator pad for sealing against an obturation seat, and an obturation spindle having a shaft and a head, the shaft extending coaxially through obturator pad, the shim kit comprising: - a first set of shims having different thicknesses for location between the obturation set and a breechblock; a second set of shims having different thicknesses for location between the obturation set and the head of the spindle; each of the shims of the first set being associated with one of the shims of the second set. Further according to the invention the thicknesses of associated shims complement each other so that the combined thicknesses of the different pairs of associated shims are the same. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described further by way of example only with reference to the accompanying drawings wherein: figure 1 is a diagrammatical longitudinal sectional view of a rear end of a barrel assembly of a gun such as a cannon or the like suitable for firing caseless ammunition, having a conventional obturation assembly; figure 1 A is an enlargement of part of figure 1 ; figure 2 is a similar view to that of figure 1 with the exception that it shows an obturation assembly according to a preferred embodiment of the invention; figure 2A is an enlargement of part of figure 2; figures 2B and C are similar views to that of figure 2 with the exception that in each view the obturation assembly is provided with a different pair of shims; and figures 3A and B show partial cross-sectional side views of two sets of shims. DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Referring to figure 1 , a rear end of a barrel assembly of a gun such as a cannon or the like suitable for firing caseless ammunition, is generally designated by reference numeral 10. The barrel assembly 10 comprises a barrel 1 2 of which the rear end defines a firing chamber 14; a swinging breechblock 1 6; a conventional obturation assembly (generally designated by reference numeral 1 8); and a sliding breechblock 20. The configuration of the conventional obturation assembly 1 8 will be described first and an obturation assembly according to a preferred embodiment of the invention will then be described in the light of the conventional obturation assembly 1 8. The mouth of the firing chamber 14 provides an obturation seat 22 and the sliding breechblock 20 is provided with a trigger housing 24. The breechblocks 1 6 and 20 are moveable between an open or inoperative position (not shown) and a closed or operative position shown in figure 1 , wherein the swinging breechblock 1 6 is held in position by the sliding breechblock 20. The obturation assembly 18 includes a metal spindle 26 having a mushroom shaped head 28 and a shaft 30 (shown more clearly in figure 1 A) extending through a stepped hole 32 in the swinging breechblock 1 6. The obturation assembly 1 8 further includes an obturation set (generally designated by reference numeral 34) including an assembly of an annular obturator pad 36 of relatively hard resilient polymeric material or the like for mating with and sealing against the obturation seat 22; a metal inner ring 38; and front and rear metal retaining split rings 40. The shaft 30 is connected to the swinging breechblock 1 6 by a nut 42. The shaft 30 is provided with an axially extending stepped bore 44 of which the rear end is provided with a chamber 46 for a primer case 48 for igniting a propellant charge when firing the gun. A primer head space 50 is defined between the rear end of the primer case 48 and the trigger housing 24. When the spindle 26 is displaced axially relative to the barrel 1 2 by the combustion of the propellant charge in the firing chamber 14, the obturator pad 36 deforms radially outwardly to seal against the obturation seat 22 and the rings 40 limit the radial and axial expansion of the obturator pad 36 to prevent extrusion of the obturator pad 36 under pressure. When the mating of the obturation set 34 with the obturation seat 22 is to be optimised, the position of the obturation set 34 relative to the sliding breechblock 20 and thus relative to the obturation seat 22 is adjusted by providing a shim 52 from a first set of shims (figure 3A), having a range of different thicknesses, between the obturation set 34 and the sliding breechblock 20. The obturation set 34 is thus moved further away or closer to the sliding breechblock 1 6, depending whether a relatively thicker 52.1 or thinner shim 52.7 is selected from the first set of shims 52. In the conventional configuration of the obturation assembly 1 8, the spindle 26 abuts the obturation set 34 directly and a change in the position of the obturation set 34 relative to the breechblock 1 6 will thus change the position of the spindle 26 accordingly. Referring to figures 2 and 2A, an obturation assembly according to a preferred embodiment of the invention is generally designated by reference numeral 100. The obturation assembly 100 is similar to the conventional obturation assembly 1 8, with the exception that the obturation assembly 1 00 is provided with a second shim 1 02 for location between the leading end of the obturation set 1 34 and the rear end of the spindle head 28, so that the thickness of the second shim 102 which is used, is selected according to the thickness of the first shim 52. Referring further to figures 2B and C, for example when a shim 52.1 (figure 2B) is selected which is approximately 1 mm thicker relative to the shim 52.7 (figure 2C) which is replaced, a shim 102.1 (figure 2B) is selected which is approximately 1 mm thinner than the shim 102.7 (figure 2C) which is replaced. A preselected position of the spindle 26 relative to the sliding breechblock 20, and thus the size of the head space 50, is thus maintained notwithstanding the adjustment of the position of the obturation set 1 34. The second shim 102 is selected from a second set of shims (shown in figure 3B) of different thicknesses and each of the shims 52 of the first range (shown in figure 3A) is associated with one of the shims 102 from the second set. The primer head space thus remains constant at a predetermined value. Referring to figures 3A and 3B, according to another aspect of the invention there is provided a shim kit comprising a first set of seven shims 52 and a second set of seven shims 102. The shims of each set vary in thickness and each shim of the first set 52 is associated with one of the shims of the second set. For example, when a shim 52.7 from the first set is replaced by a shim 52.6 from the same set but of increased thickness, to move the obturation set 1 34 further away from the sliding breechblock 1 6, the shim 102.7 from the second set is replaced by a shim 102.6 from the same set but of decreased thickness so that the position of the spindle 26 relative to the sliding breechblock 20 remains unchanged. Each shim 102 of the second set is contoured to match an inner contoured surface 104 (figure 2A) of the spindle head 28 and has an outer circumferential edge 106 (figures 2A and 3B) which extends transversely to the general plane of the shim 102. Each shim 102 further has an inner pointed circumferential configuration 108 for merging with the contour of the inner surface 104 of the spindle head 28. It will be appreciated that an obturation assembly according to the invention could be adapted for use with virtually any gun using caseless ammunition It will be appreciated further that a large number of variations in detail are possible with an obturation assembly, a kit and a method according to the invention for optimising the mating of an obturation assembly with an obturation seat without departing from the scope and/or spirit of the appended claims.

Claims: CLAIMS 1 . An obturation assembly for a gun of the type comprising a barrel of which a rear end defines a firing chamber having an obturation seat and the gun further having a breechblock, the obturation assembly comprising: an obturation set including an annular obturator pad for sealing against the obturation seat; an obturation spindle having a shaft and a head, the shaft extending coaxially through the obturator pad; - a first shim for location between the obturation set and the breechblock; and a second shim for location between the obturation set and the head of the obturation spindle. 2. An obturation assembly according to claim 1 wherein the second shim is one of a set of shims having different thicknesses enabling a user to select a suitable shim for a particular position of the obturator pad relative to the breechblock. 3. An obturation assembly according to claim 1 or claim 2 wherein the second shim is contoured to match an inner contoured surface of the head of the spindle. 4. An obturation assembly according to claim 3 wherein the second shim has an outer circumferential edge which extends transversely to the general plane of the shim and an inner pointed circumferential configuration for merging with the contour of the inner surface of the head of the spindle. 5. A method for use with a gun utilising caseless ammunition of the type having a barrel of which a rear end defines a firing chamber having an obturation seat, the gun further having a breechblock and an obturation assembly including an obturation set for sealing against the obturation seat and an obturation spindle having a head and a shaft, the method including the step of optimising the mating of the obturation set with the obturation seat without altering a preselected position of the obturation spindle relative to the breechblock by: providing a first shim between the obturation set and the breechblock, the thickness of the first shim being selected to ensure an optimal mating of the obturation set with the obturation seat; and providing a second shim between the obturation set and the head of the obturation spindle, the thickness of the second shim being selected to ensure that the preselected position of the obturation spindle relative to the breechblock is attained. 6. A shim kit for an obturation assembly of the type comprising an obturation set including an annular obturator pad for sealing against an obturation seat, and an obturation spindle having a shaft and a head, the shaft extending coaxially through obturator pad, the shim kit comprising: a first set of shims having different thicknesses for location between the obturation set and a breechblock; - a second set of shims having different thicknesses for location between the obturation set and the head of the spindle; each of the shims of the first set being associated with one of the shims of the second set. 7. A shim kit according to claim 6 wherein the thicknesses of associated shims complement each other so that the combined thicknesses of the different pairs of associated shims are the same.

Inventors: MUELLER ERNST JOHANN HEINRICH, MUELLER, ERNST, JOHANN, HEINRICH
Applicants: DENEL PTY LTD, KISCH OCTROOIBUREAU, MUELLER ERNST JOHANN HEINRICH, DENEL (PROPRIETARY) LIMITED, MUELLER, ERNST, JOHANN, HEINRICH, OCTROOIBUREAU KISCH N.V.
Application year: 1997
Main classification: F41A3
IPC codes: F41A3