BOTTOM PLATE MEMBER

Bottom plate member

This invention relates to a bottom plate member which is designed and made for initially tightening a chamber in which a high gas pressure is generated. Examples of such chambers can be found in ammunition rounds for recoilless weapons but also in pipes and containers within the pro¬ cess industry. Specifically, the invention relates to a bottom plate member which is located at the rear end of a propellant charge chamber of an ammunition round for a re¬ coilless weapon. Initially the bottom plate member pro¬ vides a tightening and barrier for the propellant gases, for instance gases of powder, generated in the chamber when the round is fired, but is broken when the gas pres- sure within the chamber exceeds a certain level so that the gases are allowed to exit from the rear end of the am¬ munition round.

Bottom plate members of this type have previously been used in ammunition rounds for recoilless weapon systems. It is the gas outlet rearwards, when the rear bottom plate is broken, that makes the weapon recoilless. It is also previously known to use similar bottom plates as so-called blasting foils in the process industry, in which the func- tion of the bottom plate is to break and evacuate the gas¬ es as soon as an inadmissible gas pressure is generated in a pipe or a container.

When the bottom plate is broken it is thrown rearwards with great force and it is a high risk that personnel and equipment behind the weapon or the process equipment in question will be damaged. This is a well-known problem to which one has tried to find a solution by providing the plate with fractural impressions which divides the plate into a number of smaller and then less dangerous parts.

It has turned out, however, that the methods that have been used so far for reducing the risks for personal inju- ries and other damages have been unsatisfactory. Even those fragments which are coming from the broken bottom plate could hurt persons that are staying behind the weap¬ on. On the whole, previously known methods with fractural impressions, light-weight bottom plate materials or the like, have not been satisfactory with respect to a safe and predictable process for the gas outlet.

The object of this invention is to solve the problems that have been discussed above and provide a more controlled and splinterfree process for the opening of the plate so that a substantially 100% safety is achieved for this pro¬ cess. According to the invention this is achieved by pro¬ viding the bottom plate with a through hole in the center which gives an effective starting point for the cracking process, fractural impressions for controlling the crack¬ ing process so that the plate after the cracking start is divided into a number of well defined flaps, but which are connected to each other, and a number of straight edges, which number corresponds to the number of flaps, against which edges the base of the flaps are arranged to be fold¬ ed when the plate is opened up due to the gas pressure.

One embodiment of the invention is schematically illus- trated in the accompanying drawings, in which figures 1 and 2 show a complete ammunition round for a recoilless weapon system before firing as well as after firing, fig¬ ure 3 shows the bottom plate with the fractural impres¬ sions more in detail, figure 4 shows an insert member for the bottom plate and figure 5 shows the two members bottom plate and insert member put together.

Figure 1 shows a complete ammunition round 1 in firing po¬ sition in a launching barrel 2 of a recoilless weapon sys- tern, for example a 20 mm ammunition round. The launching barrel 2 has a rear conventional nozzle 3 for the exhaust¬ ing propellant gases. The ammunition round 1 comprises a chamber 4 with a propellant charge therein and a detonator 5. A bottom plate 6 is located at the rear end of the chamber 4 for tightening the chamber and providing a bar¬ rier for the generated powder gases so that an efficient ignition over the propellant charge is guaranteed. The bottom plate consists basically of a comparatively thin, circular disc 7 and a flange 8 arranged at the rearmost part of the chamber wall 9.

The bottom plate 6 is dimensioned so that it is broken and blown open by the gases as soon as a specific gas pressure has been reached within the chamber. It is this gas pres¬ sure that makes the weapon recoilless.

As already mentioned in the introductory portion of the specification it is very important that the plate itself, when forced backwards by the gas pressure, or small frag¬ ments from the broken plate, does not hurt persons staying behind the weapon. According to the invention, therefore, the plate member has been designed and made in such a way that basically 100% safety against such small and harmful fragments is guaranteed when the plate member is opened up by the gas pressure.

The design of the bottom plate is illustrated more in de- tail in figure 3 by means of a front view as well as a cross-section. As illustrated in the figure the circular disc part 7 of the plate member has a star fracture so that six flaps 11 are formed. The star-shaped fractural impression is made by means of material-reducing notches in the plate, in this case six symmetrically arranged notches 10. The notches are not extending all the way to the periphery of the plate, but end up at a certain dis¬ tance d from the edge of the plate so that an integral, annular part with no material reductions is remained. In addition to the star fracture the center of the plate has a through hole 12. The hole is small compared to the di¬ mension of the plate, specifically the diameter of the hole is approximately 10% of the plate diameter. As this hole 12 is a through hole and located in the center of the plate it provides an efficient starting point for the cracking process. With fractural impressions 10 alone, it has turned out that small fragments are broken away from the central portion of the plate 6 which fragments might be harmful for personnel and/or equipment. By introducing the through hole in the center of the plate the risk for such undesired fragments is substantially reduced, the central portion of the plate which otherwise might give rise to said loose fragments is simply removed from the beginning.

The through hole in the plate has also another purpose. When the propellant charge is ignited a high-amplitude pressure peak is obtained which might give rise to a pen¬ dulum pressure in the chamber. The hole 12 in the plate has a damping ability with respect to such pressure peak and reduces the risk of dangerous pendulum-type pressure.

Figure 2 illustrates the ammunition round 1 after firing with the now empty propellant charge chamber and the opened bottom plate 6. The flaps 11 of the plate have been bent backwards and bear against the inner wall of the noz¬ zle with their tips. In order to obtain an even more con- trolled and predictable opening process for the plate and thereby reducing the risk for fragments to be separated from the flaps when they are bent backwards by the gas pressure, the bottom plate member comprises a ring-shaped insert member 14, see figure 4, which insert member abuts the flange 8 of the bottom plate with its outer, circumfe¬ rential surface 15 and which has a hexagonal inner part, i e six straight edges 16 against which the base portions of the flaps are bent. Thereby the risk for damages due to tear forces in the base portion of the flaps, when the bottom plate is blown up by the gas pressure, is substan¬ tially reduced. In order to minimize the cost for the bot¬ tom plate it is made as two parts, the tightening part 6 with the fractional impressions and the insert member 14 with the straight edges against which the flaps are bent. In figure 5 these two parts are shown put together by means of press fitting.

The bottom plate itself according to figure 3 is prefer¬ ably made of a ductile stainless steel material. The in¬ sert member 14 for the plate, see figure 4, is preferably made of a sintered stainless steel material or made from a rod-shaped material which is finish-turned on its outer surface and then cut off in suitable lengths.

The invention is not limited to the embodiment which has been illustrated so far but can be varied within the scope of the accompanying claims. Specifically, it should be un- derstood that the bottom plate also could be made as a unitary member, in which case the straight edges 16 against which the flaps are bent are made directly in the flange 8 of the bottom plate itself. In the described em¬ bodiment the fractional impression is made as a star- shaped pattern so that six flaps are formed when the bot¬ tom plate is blown up. Of course any other pattern formed by the fractional impressions can be used so that the num¬ ber of flaps can be varied. It is then important, however, that the flaps are so designed so that they are not ex- posed to any fractional forces anywhere in the flap mate¬ rial which forces are too high as it would otherwise be a risk for loosened small fragments. The insert member 14 is made with a number of straight edges, which number corre¬ sponds to the number of flaps, which means that each flap has a straight edge to be bent around upon the release of gas pressure.

The hole 12 has been illustrated as a through hole, but it is understood that the hole can be sealed by means of a foil or the like to make the chamber damp-proof, especial¬ ly during transport and storage. Such a thin sealing mem¬ ber does not change the described function of the hole 12, however. The invention has been described in connection with a pro¬ pellant charge chamber for a recoilless weapon system. It should be understood that the bottom plate can be used al¬ so in other applications in which a controlled opening of a plate is required when a certain pressure has been ex¬ ceeded. Examples of such applications can be found in the process industry.