Abstract:
A device including a ring for linking a case and a projectile carrying a sealing band having a rear skirt providing low pressure sealing and a front rib lodged in a first groove in the projectile. The ring has a flared rear part connected with the case and a front part connected with the projectile by attachment means. The front part of the ring is lodged between the rear skirt of the band and the projectile and has a lip co-operating with the first groove or with a second groove in the projectile. A process for mounting the sealing band and ring to link the case and projectile includes sliding the sealing band and ring along the projectile in a single operation.

Description:
BACKGROUND OF THE INVENTION 
     The technical scope of the invention is that of devices linking a case and a projectile and more particularly devices allowing a combustible case and a large caliber projectile (caliber of over 45 mm) to be linked together. 
     DESCRIPTION OF THE RELATED ART 
     Such a device is known by patent EP-0307307 that comprises a sealing band incorporating a rear skirt linked to the case and providing low pressure sealing (pressure of around a few MPa) and a front rib housed in a groove in the projectile and providing high pressure sealing (pressure of around several hundred MPa), such as is the case in a classical band. 
     Low-pressure sealing is essential in the first few tenths of milliseconds following the ignition of the propellant charge contained in the combustible case. Indeed, the containment provided by such a case is less than that obtained using a metallic case and the displacement of the projectile occurs at a lower pressure. Sealing that is not sensitive enough to be operational from the point of ignition is likely to allow gases to escape towards the front of the projectile, thereby reducing the efficiency of the propellant charge. 
     Such a device, however, has certain drawbacks. 
     The case is generally fastened by riveting its skirt, which is integral with the band. 
     The fracture of the skirt when passing through the forcing cone of the weapon leads to a reduction in the effective width of the bard. This results in a reduction in the firing capacity of the projectile in worn barrels. 
     Moreover, the mechanical loads and stresses received by the munition are transmitted to the band whose gas-tightness properties are likely to be deteriorated, thereby leading to dispersion from a ballistic point of view. 
     SUMMARY OF THE INVENTION 
     The aim of the invention is to propose a device to link a case and a projectile that does not suffer from such drawbacks. 
     Thus, the device according to the invention provides for simple reliable attachment whilst increasing the effective length of the band, thereby improving sealing, even for firing from worn barrels. 
     Thus, the subject of the invention is a device to link a case and a projectile carrying a sealing band having a rear skirt providing low pressure sealing and a front rib housed in a first groove i n the projectile, such device comprising a ring having a flared rear part intended to be made integral with the case and a front part made integral with the projectile by attachment means, wherein the front part of said ring is housed between said rear skirt of said band and said projectile and has a lip co-operating with said first groove or with a second groove in the projectile. 
     According to a first embodiment, the lip is housed in the first conical-bottomed groove, the tip of the cone being placed on the side of a rear part of the projectile. 
     The front part of the ring can abut against an inner profile of the band. 
     The front part of the ring can incorporate an external profile that will co-operate with a matching profile on the band. 
     According to a second embodiment, the device also prevents the band from being subjected to mechanical stresses transmitted by the projectile or the case. 
     Such a result is obtained by providing separate first and second grooves. 
     Advantageously, the front part of the ring will be housed in a second groove and can incorporate at least one inner fluting arranged along a generating line and allowing the gases to pass through the ring up to the band. 
     According to one variant, at least one fluting can co-operate with an obstacle, such as a pin or a peg, integral with the projectile, such a co-operation enabling the ring and the projectile to be joined together in rotation. 
     The front part of the ring can incorporate an abutment surface able to co-operate with a matching rear surface of the band, a first play existing between these two surfaces when the band and the ring are in their respective grooves. 
     The ring can incorporate an inner counter-sink forming an abutment and intended to co-operate with an abutment surface on the projectile, a second play existing between said counter-sink and the projectile, the second play being greater than the first play. 
     A further aim of the invention is to propose a process to mount, a band onto a projectile, said process being simpler and less expensive that the known process described notably in patent EP-0307307. 
     According to said patent the band/linking part is fastened to the projectile by injection around the projectile. 
     Such a process requires the bands to be produced directly on the sabots thereby complicating the production process. 
     The process according to the invention allows the linking part and band to be produced independently of the sabot. Assembly is only carried out at a later stage. Production is thereby simplified and its cost reduced. 
     Thus the process according to the invention to mount a band onto a projectile is characterized in that the band and linking ring are made to slide along the projectile in a single operation, the ring pushing the band until both ring and band are clipped into their respective grooves. 
     Both ring and band can be made of a plastic material and the ring and band will be heated before being put into place. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood after reading the following description of the different embodiments, said description being made with reference to the appended drawings, in which: 
     FIG. 1 shows a partial section of a projectile fitted with a linking device according to a first embodiment of the invention, 
     FIG. 2 shows a partial section of a projectile fitted with a linking device according to a second embodiment of the invention, and 
     FIG. 3 is a detailed view of a variant of this second embodiment. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to FIG. 1, a projectile  1 , that here is a fin-stabilized projectile comprising a sabot  3  surrounding a penetrator  4 , is made integral with a combustible case  2  by a linking device according to a first embodiment of the invention. 
     This device comprises a ring  5  having a flared rear part  6  that is made integral with the combustible case  2 , for example by rivets  7  evenly spaced angularly. The ring has a front part  8  that is made integral with the projectile  1  by fastening means. 
     The projectile  1  carries a sealing band  9  that has a rear skirt  10  intended to provide low pressure sealing in the gun barrel. The band  9  incorporates a front rib  11  housed in a first ring-shaped groove  12  arranged in the projectile. The groove  12  has a conical bottom. The tapering of the groove is oriented such that the tip of the cone is arranged on the side of a rear part AR of the projectile. Thus, the diameter at the bottom of the groove  12  increases between the rear AR and the front AV of the projectile. 
     In accordance with the invention the front part  8  of the ring  5  is housed between the rear skirt  10  of the band  9  and the projectile  1 . This front part  8  of the ring has a lip  13  that is housed in the groove  12  of the projectile. 
     The front part  8  of the ring  5  incorporates an external profile that co-operates with a matching profile of the band. Thus, the external surface of the ring comes into contact with the inner surface of the skirt  10  of the band and the lip  13  has a rounded external profile  14  that is housed in a matching pocket arranged in the band  9 . 
     Both ring and band are made of plastic materials, for example of the polyethylene type for the ring and polyamide for the band. 
     The band and ring are assembled as follows. 
     First of all, the ring and the band are heated in a steam oven to a temperature of around 90° C. for around 20 minutes. 
     Such an operation results in the slight softening of the material constituting the ring and the band thereby facilitating its deformation. The band  9  is thereafter slipped over the projectile  1  from its rear AR. The ring is also slipped over the projectile, and is used to push the band. Both ring and band are radially deformed and are both housed in the groove  12 . 
     The length of the lip  13  is defined such that the ring ensures the axial immobilization of the band in the groove  12 . The lip  13  is thus pinched between the front rib  11  of the band and the rear rim  12   a  of the groove  12 . 
     Such an assembly operation can be easily carried out on a projectile during the integration of the munition. It is thus no longer necessary to carry out a duplicate-molding operation around the projectile. Both linking ring and band are made elsewhere by conventional means, for example by injection. 
     The linking device according to the invention allows a projectile to be defined that is fitted with a band  9  having a relatively long rear skirt  10  (25 to 30 mm for a caliber of 120 mm). This skirt ensures an excellent level of gas-tightness at low pressures. 
     When the munition is fired, the gas pressure ensures the separation of the ring  5  and the combustible case  2 . As proposed in patent EP 307307, the ring will advantageously be equipped with incipient fractures arranged along its generating lines so as to facilitate its fragmentation under the effect of the gas pressure. 
     A further effect of the gas pressure is to push the band firmly into its groove  12 . Said band&#39;s conical bottom takes up the play caused by the wear of the band on the inner walls of the gun barrel. Thus, gas-tightness is ensured during the whole of the interior ballistic phase of the projectile and this even when firing from worn barrels. 
     Such a band also reduces barrel wear since the skirt provides better protection for the inner walls with respect to the hot gases. 
     Firing reliability is also improved, gas-tightness being ensured during the whole ballistic phase. 
     FIG. 2 shows a second embodiment of the invention. 
     This embodiment differs from the previous one mainly in that the ring  5  and the band  11  are each housed in a different groove of the projectile  1 . The front rib  11  of the band  9  is housed in a first groove  15  and the lip  13  of the ring  5  is housed in a second ring-shaped groove  16 . The two grooves  15  and  16  both have conical bottoms oriented in the same direction and such that the tips of the cones are on the side of a rear part AR of the projectile  1 . 
     When ring and band are in their respective grooves, a first play J 1  remains between an abutment surface  19  arranged to the front of the lip  13  and a rear surface  20  of the band  9 . 
     The front part  8  of the ring  5  firstly incorporates the lip  13  that hooks the ring into the second groove  16  and secondly an inner countersink  17  that forms an abutment intended to co-operate with an abutment surface  18  on the projectile  1 . 
     After has ring  5  has been mounted there is a second play J 2  between said countersink  17  and the abutment surface  18  on the projectile  1 . 
     Production dimensions and tolerances will be selected such that the second play J 2  is greater than the first play J 1 , this for reasons explained hereafter. 
     The countersink  17  and lip  13  are connected by a conical profile  21 . 
     Lastly, the front part  8  of the ring incorporates at least one inner fluting arranged along a generating line and allowing the gases to pass through the ring up to the band. 
     Thus, the flutings  22 , evenly spaced angularly (for example four flutings) are made in the lip  13 . 
     Other flutings  23  also evenly spaced angularly (for example four flutings) are made in the countersink  17 . 
     Thus, the propellant gases that develop after the powder load contained in the case  2  has been ignited can move through the flutings  23  of the volume delimited by the conical profile  21  and the flutings  22  until reaching the rear surface  20  of the band. 
     Such an arrangement allows the gases to push directly on the band  9  and this from ignition of the propellant charge. Gas-tightness is thus improved as it is independent of the fracturing the linking ring  5 . 
     As in the previous embodiment, as the band advances, the conical profile of the first groove  15  makes up for the wear of the band on the inner walls of the gun barrel. 
     This embodiment also allows a band to be used that has a skirt  10  of great length that is not deteriorated by the action of the linking means. 
     This band and this ring are assembled as for the previous embodiment. 
     The ring  5  allows the band  9  to be pushed into its groove  15 , the abutment surface  19  of the ring acting directly during assembly on the matching surface  20 . As play J 1  is less than play J 2 , it is possible for the band to be pushed to its position in its groove  15  without countersink  17  interfering with the abutment surface  18  of the projectile  1 . 
     The role of the countersink  17  is to take up the load during shocks and handling of the munition. The loads received on the projectile  1  are transmitted to the linking ring  5  via the countersink  17 . Thus, the band is neither greatly stressed nor strained and thus retains its full effectiveness during firing. 
     This embodiment thus enables the sealing function provided by the band  9  to be separated from the projectile/case linking function provided by the linking ring  5 . 
     This separation of functions is provided whilst ensuring the easy assembly of the ring and the band without duplicate-molding being required. 
     The projectile  1  shown schematically in this Figure is, for example, a calibred projectile, such as a shaped charge. 
     It may naturally also be a fin-stabilized projectile such as that shown in FIG.  1 . 
     According to a variant embodiment, means will advantageously be provided ensuring the joining in rotation of the ring  5  with the projectile  1 . Indeed, assembly by clipping the lips  13  into the first groove  16  does not ensure joining in rotation by friction of a sufficient level to prevent the projectile from pivoting with respect to the ring further, for example, to the vibrations withstood by the munition. 
     At least one obstacle, such as a pin  24 , will be provided that is housed in a hole made radially in the projectile  1 . 
     When the ring  5  is mounted, it will be oriented angularly such that the pin is positioned in the fluting  22 . 
     The pin  24  will be of a diameter substantially equal to the width of the fluting  22 . Its height will be less than the depth of the fluting so as not to prevent the gases from passing. 
     It is naturally possible for as many pins to be provided as there are flutings. Another type of obstacle may also be used, for example one or more pegs.