Ordnance – Breech closures – Gas checks
Reexamination Certificate
1999-01-11
2001-05-01
Johnson, Stephen M. (Department: 3641)
Ordnance
Breech closures
Gas checks
C089S023000
Reexamination Certificate
active
06223643
ABSTRACT:
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, such as the one described in U.S. Pat. No. 2,482,865, 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 relative 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.
The specification of patent number CH 1579 A (Schneider) dated Nov. 16, 1889 reveals an obturation assembly comprising an obturation pad located between two shims, two split rings and four separate resilient retaining rings. Some of the disadvantages of an obturation assembly of this type are that it is not suitable for use with a gun of the type having a breechblock and a cased primer for igniting the propellant charge.
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;
the obturation assembly being characterised in that the first shim is one of a first set of shims having different thicknesses and the second shim is one of a second set of shims having different thicknesses; each of the shims of the first set being associated with one of the shims of the second set, thus enabling a user to select a suitable pair of associated shims for a particular position of the obturator pad relative to the breechblock.
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.
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 set of shims having different thicknesses;
providing a second set of shims having different thicknesses, each of the shims of the first set being associated with one of the shims of the second set;
selecting a shim from the first set and locating the 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 which is associated with the first 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.
Further according to the invention there is provided use of a shim kit as described above with 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; and
an obturation spindle having a shaft and a head, the shaft extending coaxially through the obturator pad.
REFERENCES:
patent: 539733 (1895-05-01), Gerdom
patent: 819186 (1906-05-01), Vollmer et al.
patent: 1376130 (1921-04-01), Asbury
patent: 2457266 (1948-12-01), Oliver
patent: 2482865 (1949-09-01), Oliver
patent: 1579 (1889-11-01), None
patent: 3247744 (1984-06-01), None
patent: 9610 (1890-01-01), None
Denel (Proprietary) Limited
Johnson Stephen M.
Ostrolenk Faber Gerb & Soffen, LLP
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