EP0221239B1 - Method for applying a rotating band to a projectile wall with a reduced thickness, and projectile manufactured according to this method - Google Patents

Description

The invention relates to a method for applying a metallic guide tape to a projectile casing, in which the finest particles are sprayed onto the corresponding surface section of the projectile casing at high speed until the desired layer thickness is reached.

Such a method for applying a metallic guide tape to a projectile casing is known from FR-A 936 684. The high thermal load when the particles are sprayed on and the resulting change in structure and properties of the projectile shell would, however, lead to the fact that the projectile is no longer fireproof.

• Im Heckbereich eines Artelleriegeschosses sind ein oder mehrere umlaufende Führungsbänder angeordnet. Hierbei handelt es sich um Metallringe, die in einer korrespondierenden Ringnut auf der Oberfläche der Geschoßhülle einliegen. Die Dicke eines Führungsbandes ist größer als die Tiefe einer zugehörigen Ringnut, so daß das Führungsband die Oberfläche der Geschoßhülle nach außen überragt.

For a more detailed explanation of the problems, the following is pointed out:

• One or more circumferential guide bands are arranged in the rear area of an artillery storey. These are metal rings that lie in a corresponding ring groove on the surface of the projectile casing. The thickness of a guide band is greater than the depth of an associated annular groove, so that the guide band projects beyond the surface of the projectile casing.

The projectile is pressed into a gun barrel provided with so-called trains and fields, the guide bands having to deform in accordance with the shape of the fields and trains in order to be able to reliably perform their guiding function when the projectile is fired.

The guide bands must therefore have a certain ductility on the one hand, and on the other hand have sufficient stability to transmit an optimal swirl to the projectile when the projectile is deployed. This also includes a secure connection with respect to the projectile casing, since considerable transverse forces act on it during use. This is taken into account by pressing the guide bands into the corresponding ring grooves, where they are firmly seated.

However, the formation of the annular groove described has the disadvantage of mechanical weakening of the corresponding part of the projectile casing. This disadvantage becomes clearer the smaller the wall thickness of the projectile casing, which results in corresponding limitations. As a rule, bullet casings have to be made more than ten millimeters thick today.

The invention is based on the object of offering a projectile casing with a circumferential guide band in which the described loss of strength is minimized without having to forego an absolutely secure connection between the casing and the guide band.

The invention is based on the knowledge that it is not necessary to provide an annular groove on the surface of the projectile casing into which the guide band is pressed, but that there are also methods with which the guide band can be securely applied directly to the closed surface of the projectile casing can, so that the choice of the thickness (to achieve a minimum strength) of the projectile casing is no longer determined by the guide bands, but only by the material properties of the projectile casing itself. The invention thus offers a possibility of using the same materials for the Projectile shell to provide much smaller wall thicknesses, since there is no need for cross-section-reducing and strength-reducing ring grooves.

The method according to the invention for applying a metallic guide band is thus in particular also adapted to projectile casings which are thinner than the prior art and consists in spraying the finest particles plastically deformable by prior heating onto the corresponding surface sections of the projectile casing to apply the metallic guide band. until the desired layer thickness of the guide belt is reached. There is therefore an immediate support of a guide band on the surface of the projectile casing, the guide band no longer being applied in the form of a preformed metal band, but being gradually applied and formed by spraying the finest deformable metal particles. The particle size must be set individually depending on the temperature, the spraying speed, the thermal conductivity of the material and its melting point, but will usually be in the Jlm range. It is important to throw particles of the most appropriate size at such a speed in the heated state on the shell surface that the particles with their plastically deformable areas can deform when struck while setting a compact overall structure.

In order to avoid excessive heating of the surface of the projectile shell and thus (undesirable) structural changes, an advantageous embodiment of the invention provides for heating the particles only to such an extent that they are melted only in their surface area. This superficial plasticization is sufficient to deform the particles when impacting the projectile casing or the particles previously encountered there and gradually build up a tight packing, which preferably leads gradually to the desired guide band when the projectile casing is rotated with the sprayer stationary.

Such methods are known under the name of flame or arc spraying in other technical fields, for example for repairing damaged silos etc. The application of the principle of these methods for applying a guide tape to a projectile casing, on the other hand, represents a new use. In the field of defense technology and here in particular The production of artillery bullets has so far found no entry, since all known developments, such as the replacement of metallic guide bands with plastic guide bands which always propose the formation of an annular groove on the surface of the projectile casing (US Pat. No. 3,910,194).

In this respect, it is surprising that guide tapes can be formed by such a spray application, which on the one hand have sufficient adhesion to the projectile casing, but on the other hand also show the necessary deformability in order to be pressed into the trains of the gun barrel.

As a rule, the projectile casings are made of high-strength steel, for example an alloy of the type 30CrNiMb8, while copper-zinc alloys are preferably provided as the material for the guide bands. However, since copper and iron are difficult to connect to one another, an advantageous embodiment of the invention provides that an adhesive layer is applied to the surface of the projectile casing before the particles are atomized to form the guide band, preferably also by spray application. It can be advantageous, particularly in the case of projectile casings coated with an oxide skin, to activate them first, that is to say to free them from the oxide skin and to roughen them in order to provide more attack-connecting surfaces for the adhesive layer. In the case of the above-mentioned materials for the projectile casing and the guide band, molybdenum, but also nickel aluminide or cermets based on aluminum nickel oxide are suitable as the material for the adhesive layer. Since a molybdenum-sprayed binding layer has a relatively low tensile strength, nickel aluminide (80 percent by weight nickel, 20 percent by weight aluminum) is generally preferred, the tensile strength of which is approximately twice that of a molybdenum layer.

In order to pretreat the surface of the projectile shell before the adhesive application, the invention proposes, in an advantageous embodiment, the use of fine-grained corundum or chilled cast iron as a radiation agent.

The heating of the metal particles during the spray application of the guide belt can be carried out either by a gas flame, preferably an acetylene / oxygen mixture, or electrically. If necessary, a protective gas can be added to minimize oxidation. It is also provided according to the invention to carry out the entire process in a closed chamber in which a protective gas atmosphere, for example argon, is set.

In contrast to flame spraying, the melting rates that can be achieved with arc spraying are theoretically unlimited. They increase almost linearly with the current output from a power source. Limitations of the spraying capacity result, however, in so far as, on the one hand, a certain amount is to be applied only within a certain time interval, and on the other hand, overheating of the spray layer and thus the surface of the projectile shell is to be avoided, which would lead to loss of strength.

In a further advantageous embodiment, the invention provides that, in order to avoid overheating, the projectile casing is cooled from the inside during the spray application.

As a result of the spray application according to the invention, a more or less dense layer occurs, particularly as a function of the particle size, temperature and kinetic energy with which the particles strike the surface. This can be varied almost as desired by setting the above-mentioned parameters, which, together with the selection of the material of the projectile casing, makes it possible to set different strengths / ductilities and / or porosities of the guide bands. It has been shown that porosities of up to five percent are advantageous since this has a favorable influence on the deformability.

The process parameters mentioned above also have an influence on how strongly the sprayed-on particles deform the surface of the projectile casing. An advantageous embodiment of the invention provides that with a material thickness of the projectile casing of only 2 to 4 mm, the deformed area of the projectile casing is less than 0.1 mm. This layer then forms a kind of diffusion layer between the projectile shell and the adhesive / binding layer. The example shows that the projectile envelope thickness according to the invention is significantly reduced while maintaining the strength compared to conventional envelope thicknesses and thus the usable space of the projectile can be increased considerably with the same caliber, which is a further considerable advantage of an envelope according to the invention.

Further advantageous embodiments of the invention are described by the subclaims. Instead of heating the solid particles by means of a gas flame, electrical heating can also be provided. In addition to the materials mentioned for the projectile casing and the guide band, other materials can of course also be used. The bullet jacket will preferably always consist of tempered steel grades. For the guide belt, alloys have proven to be particularly advantageous compared to physical substance mixtures.

For faster and more targeted processing, an embodiment of the invention proposes to place a stencil provided with a recess corresponding to the width of the guide band on the casing during spraying. This allows the occupied area to be limited. If necessary, the described production can be followed by machining of the applied guide belt in order to give it a defined shape.

To further clarify the invention described above, reference is made to the drawing.

• Fig. 1 einen längsaxialen Schnitt durch einen einseitigen Bereich einer dünnwandigen Geschoßhülle mit einer dünnwandigen Geschoßhülle mit einem Führungsband nach der Erfindung und
• Fig. 2 einem vergrößerten Ausschnitt etwa des Bereichs in Fig. 1.

It shows:

• Fig. 1 shows a longitudinal axial section through a one-sided area of a thin-walled shell with a thin-walled shell with a guide tape according to the invention and
• FIG. 2 shows an enlarged detail of approximately the area in FIG. 1.

Shown in FIG. 1 is the thin wall 11 of the projectile casing, an intermediate layer 12 and an alloy 13 of the guide band.

The structure shown in detail is evident from FIG. 2. The material 11 of the wall of the projectile shell has a boundary layer region 11 a roughened on the outside and treated with deoxidizing. (See claim 6). An intermediate layer 12 then follows the boundary layer region 11 a, which can consist of molybdenum, nickel aluminide or nickel oxide and in turn has a roughened outer boundary layer region 12 a; this creates a particularly intensive physical connection with the particles of alloy 13 of the guide belt. The alloy is preferably represented by a type CuZn85 / 15 with a porosity of about 5 vol%.

Claims (19)

1. Method for applying a metal guide band to a projectile casing, wherein very fine particles are sprayed at a high speed onto the corresponding portion of the surface of the projectile casing until the guide band has acquired the required layer thickness, characterised by the fact that the parti- des are heated up in such a manner that only a plas- ticisation is present in the surface zone of the parti- des and the thin-walled projectile casing, which consists of tempered steel, is cooled from the inside when the particles are sprayed on.

2. Method in accordance with Claim 1, characterised by the fact that the heating is effected by a gas flame, preferably using an oxyacetylene or oxyhy- drogen mixture.

3. Method in accordance with Claim 1 , characterised by the fact that the heating is effected electrically.

4. Method in accordance with any one of Claims 1, 2 or 3, characterised by the fact that the spraying of the particles is carried out in a protective-gas atmosphere.

5. Method in accordance with any one of Claims 1 to 4, characterised by the fact that prior to the spraying process that surface of the projectile casing which is to be sprayed is roughened and/or deox- idised.

6. Method in accordance with Claim 5, characterised by the fact that the surface of the projectile casing is treated by blasting with a fine-grained material of greater hardness than the projectile casing itself.

7. Method in accordance with Claim 6, characterised by the fact that a projectile casing of tempered steel is blasted with corundum grit or case hardened grit.

8. Method in accordance with Claim 7, characterised by the fact that after the blasting but before the spraying of a layer serving to connect the materials, the projectile casing and the guide band is applied by spraying pre-heated very fine solid particles thereon.

9. Method in accordance with Claim 8, characterised by the fact that molybdenum, nickel, aluminium or cermets with an aluminium nickel oxide base is (are) applied in powder form.

10. Method in accordance with any one of Claims 1 to 9, characterised by the fact that an alloying powder is sprayed on for the purpose of forming the guide band.

11. Method in accordance with Claim 10, characterised by the fact that an alloy of the type CuZn85/15 is sprayed onto the surface.

12. Method in accordance with any one of Claims 1 to 11, characterised by the fact that before the particles forming the guide band are sprayed on the projectile casing is heated to a temperature above room temperature but well below that of the particles sprayed on.

13. Method in accordance with any one of Claims 1 to 12, characterised by the fact that in order to delimit the guide band sprayed on a suitable template is placed on the projectile casing.

14. Method in accordance with any one of Claims 1 to 13, characterised by the fact that for continuous and uniform application of the guide band the projectile casing is guided in rotation under a stationary spraying device or the spraying device is guided in rotation around the stationary projectile casing.

15. Method in accordance with any one of Claims 1 to 14, characterised by the fact that the guide band, after being applied to the projectile casing, undergoes a finishing cutting operation.

16. Projectile casing with a circulating guide band, produced by the method described in any one or more of Claims 1 to 15.

17. Projectile casing in accordance with Claim 16, characterised by an unbroken material connection between the projectile casing and the guide band.

18. Projectile casing in accordance with Claim 16 or 17, characterised by a maximum porosity of 5% by volume for the guide band.

19. Projectile casing in accordance with any one of Claims 16 to 18, characterised by the fact that with a material thickness of only 2-4mm for the projectile casing the deformed zone of the projectile casing is below 0.1 mm.

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