Device for rotating bands for projectiles

Abstract

 The device is used in connection with rotating bands (2) for projectiles in order to improve their sealing and gliding properties within a gun barrel. To prevent direct contact between the rotating band (2) and the gun barrel, and in order to reduce frictional contact between same, the outer surface (3) of the rotating band (2) is arranged with a layer (4) of a metal or a metal alloy, having a lower melting point than the material used for the rotating band (2). The layer (4), which melts during launch and adheres to the outer surface of the rotating band (2), acting as a lubricating and sealing agent between the rotating band (2) and the internal surface of the gun barrel.

Description

[0001] The present invention relates to rotating bands for projectiles, and in particular to devices intended to improve their sealing and gliding properties within a gun barrel.

STATE OF THE ART

[0002] The rotating band of a projectile fulfills a number of important and essential functions during launch of a projectile. One object is to guide the projectile in such a way, that when leaving the muzzle of the gun, it has correct speed and direction of travel, with a minimum of movement of the projectile length axis in relation to the direction of travel for the center of gravity of the projectile. A second object is to co-act with the rifling of the gun barrel, and to cause rotation of the projectile. As a third object, the rotating band should act as a seal between the gun barrel and the projectile for the combustion gases.

[0003] Previously known rotating bands are usually manufactured from copper, or a copper alloy. This type of material has sufficient properties to withstand the pressure of the combustion gases, and also the pressure imposed by the side surfaces of the rifling when transferring a rotary acceleration to the projectile. It is soft enough to be deformed by the outwardly extending portions of the rifling, whereby the rotating band can sealingly engage the gun barrel during launch. The material also has favourable frictional properties when gliding against the steel surface within the gun barrel.

[0004] During the first stage of launch, the projectile is moved to enter the rotating band into a first portion of the rifling. Due to wedge-action between the outer surface of the projectile and the inside wall of the gun barrel, the rotating band is plastically deformed into sealing contact with the rifled surface of the wall. As a result, tongues are formed, both at the foremost and the rearmost side surfaces of the rotating band.

[0005] After plastic deformation, existing elastic compression within the material causes a pressure directed towards the gun barrel, which must be at least as high as the pressure imposed by the combustion gases to result in a sealing engagement. During this stage, the temperature of the rotating band is increased by the plastic deformation, and with regard to the surface of the rotating band, a temperature increase is caused by friction against the wedge-shaped first portion of the rifling, which is substantial when the material of the rotating band is being compressed. Due to the high velocity of the rotating band when entering the rifJing, in combination with the high pressure imposed on the material of the rotating band by the internal surface of the gun barrel, the temperature of the outer frictional surface of the rotating band is increased extremely rapidly, thereby causing the surface of the rotating band to melt to a depth of a few µm.

[0006] During a second stage, the projectile is moved through the gun barrel, the rifling causing the projectile to rotate or spin. Also during this stage, the surface layer of the rotating band is melted by frictional contact. Frictional forces are maintained against the lands of the rifling by the elastically compressed material of the rotating band. However, the largest frictional forces exist at the side surfaces of the lands, which transfer rotational acceleration to the projectile.

[0007] The melting of the surface layer of the rotating band causes a number of major problems. Not only the melted surface material, but also material below the surface, weakened by heat transfer, is succesively removed from the rotating band, adhering to the passing surface of the jun barrel. This results in a copper deposition inside the gun barrel, ihich must be removed after a certain number of rounds. Apart from naterial being removed from the rotating band, material also flows rearwardly along the frictional surface of the rotating band. The removal and flowing of material affects adversely the sealing properties between the gun barrel and the rotating band and causes a gas by-flow, particularly with regard to the region by the side surfaces of the lands transferring the rotary movement to the projectile. As a result, there is a flow of combustion gases past the projectile, resulting in reduced muzzle velocity of the projectile. Due to variations in the amount of material deposited during each launch, both frictional forces and leakage vary considerably. As a result, the muzzle velocity of successively launched projectiles vary considerably.

[0008] But also each individual rotating band is worn peripherally different. Apart from resulting unfavourable guidance and disreptancy between exit direction and length axis of the projectile at the muzzle of the gun barrel, it also results in unbalance with an increased mutation in ballistic trajectory.

[0009] The tongues formed when entering the first portion of the rifling are normally compressed to such a thickness, that they are not bent outwardly from the projectile by dynamic forces during trajectory. However, flowing and removal of material causes the foremost tongues to be reduced with regard to thickness and length, whereas the material moved to the rearward tongues causes same to be prolonged and thin when the projectile reaches the muzzle. The flowing also influences the structure of the frictional surface. During the final stage of movement for the rotating band within the gun barrel, the surface of the band is rougher and includes hollow portions, the size of which is extended rearwardly on the frictional surface of the rotating band. When leaving the muzzle, the foremost tongues are normally rigid and do not deflect outwardly due to aerodynamic and centrifugal forces. But with regard to the rearwardly directed tongues, having a base weakened by the hollow portions, same deflect outwardly from the projectile. The tongues thereby increase the air drag, with variations between successively launched projectiles. The range and dispersion is further adversely affected by increased dynamic unbalance, caused by differences in size for the tongues of the same rotating band.

[0010] The melting of the surface layer in conventional rotating bands of copper or copper alloy thus causes a deposit within the gun barrel, a decrease in the projectile range, and a reduced probable accuracy. A certain improvement of launch conditions can be obtained by including granulated tin in the combustion charge, or by arranging a projectile with a tin band located behind the rotating band of copper, thereby also slightly reducing the wear imposed on the gun barrel.

SUMMARY OF THE INVENTION

[0011] The object of the present invention is to disclose a device for a rotating band, eliminating or reducing the disadvantages discussed above.

[0012] Previous disadvantages are eliminated or reduced by arranging the outer surface of the rotating band with a material including an additional material, which has the ability, during launch, to form a layer over the frictional surfaces of the rotating band, which substantially prevents direct contact between the rotating band and the adjacent surface of the gun barrel, and which reduces friction between same.

[0013] The material forming an intermediately located layer is preferably the actual additional material, advantageously comprising of a metal or a metal alloy having a lower melting point than the material of the rotating band, and also having good properties of adherance to same. When using conventional rotating band materials, such as copper or copper alloys, tests performed have indicated that use of tin or tin alloys as additional material considerably improves launch conditions, resulting in increased muzzle velocity, increased trajectory range, reduced dispersion and considerably less deposition within the gun barrel.

[0014] Subsequent analysis of the driving bands indicate that the object of the present invention, i.e. to prevent direct contact between the internal surface of the gun barrel and the rotating band, has been achieved. The tin layer has considerably reduced melting of the surface layer of the rotating band material.

[0015] The layer of tin, or tin alloy, applied to the rotating bands of copper 0 or copper alloy, has a melting point of 250 C, to be related to the o melting point of the rotating band material, approximately 1.100 C. As a result of the low melting point of the additional material, a melted layer is formed considerably earlier than for conventional rotating bands, when the rotating band is deformed. By reducing the friction during launch, and by maintaining the reduction during the entire launch procedure, the use of a tin layer results in less formation of heat. Since also heat is consumed by vaporization from the surfaces of the tin layer, only a minor quantity of heat is transferred to the band material without affecting the mechanical properties of same, thus also preventing flow of the surface material of the rotating band.

[0016] When the tin layer is formed, the tin closest to the band material forms an alloy with same. The tin layer thus adheres to the base material, whereby the rotating band can travel through the entire gun barrel, without the layer being removed from the frictional surface. The melted layer thus serves as an effective lubricating agent. The present invention thereby results not only in less formation of deposits, but also reduces the wear imposed on the gun barrel. An interesting feature is also the fact that the internal surface of the gun barrel becomes covered by a thin layer of tin, acting as a protective coating against corrosion.

[0017] With regard to previously known methods for improving launching conditions, no tin layer has been obtained between the rotating band and the gun barrel, since the added tin material has been unable to reach the frictional surfaces. The advantages of the present invention have therefore not been obtained.

[0018] Apart from an additional material, it is also possible to use a mixture of granulated additional material and a binder, a metal alloy, a sintered material or similar, which before, or during launch, serve to bind the additional material.

[0019] Even though tin and tin alloys have been mentioned as preferred and suitable materials for rotating bands of copper or copper alloys, also other materials can be used, e.g. lead or lead alloys. If the material of the rotating band comprises of iron, completely different alloys are preferred.

[0020] The material can be applied to the rotating band either during the manufacture of the projectile, or at any time before launch. If the material is applied during manufacture, application can be carried out in alternative ways, e.g. by dipping, spraying, electrolytic methods of application, rolling, melting or similar operations. After manufacture, the material can be applied e.g. by sliding a tubular member over the rotating band, or application by a mixture of a binder and the material to be added. It would also be possible to apply the material as a thin self-adhesive tape, using an adhesive material which disintegrates when made subject to high temperature. However, the invention is in no way restricted by the type of material applied, or the methods used for application of same.

BRIEF DESCRIPTION OF THE DRAWING

[0021] 

FIG. 1 is a cross-sectional view of a rotating band, onto which a tubular member of tin alloy has been applied before launch.

FIG. 2 is a cross-sectional view showing the shape of a rotating band at a portion compressed by the rifling after launch without a tubular member.

FIG. 3 is a cross-sectional view of a rotating band after launch with a tubular member as disclosed in FIG. 1.

PREFERRED EMBODIMENT

[0022] In this embodiment, the invention has been used to improve the function of a rotating band, manufactured in accordance with previously known techniques. However, the invention is equally well suited for use in connection with the manufacture of the rotating band.

[0023] FIG. 1 shows a cross-sectional view of a part of a projectile 1 having a rotating band 2, manufactured according to state of art. Onto the rotating band 2 has a tubular member 4 been slided to an embracing relationship. The tubular member, which has an abutting edge portion 5 located directed in the launch direction for the projectile, comprises of a tin alloy foil. The foil thus forms a layer on the outer surface 3 of the rotating band.

[0024] When the rotating band 2 is moved into the first portion of the rifling within a gun barrel, the edge portion 5 acts as a driver with respect to the tubular member, forcing same to move together with the rotating band 2. After a very short movement, when contact is established with the protruding portions of the rifling, the temperature at the frictional surfaces between the tubular member 4 and the gun barrel is raised above the melting point of the tin alloy. The melted material of the tubular member 4 in contact with the material of the rotating band 2 then forms an alloy with the surface material of same. The material of the tubular member 4 thereby adheres strongly to the material of the rotating band 2. The layer, now being substantially melted, insulates the rotating band 2 from the gun barrel during the entire movement of the rotating band 2 through same, acting as a sealing agent preventing by-flow of the combustion gases. Furthermore, the melted metal also considerably reduces the friction between the rotating band 2 and the gun barrel.

[0025] FIGS. 2 and 3 show cross-sectional views of the configuration of the rotating bands, when associated projectiles have been launched. The considerable flowing and wear imposed on a conventional rotating band (FIG. 2) results in a considerable loss of material 10, and also in the formation of elongated tongues 6 at the rear edge portion of the rotating band. The tongues 6, which outside the gun barrel are bent or deflected outwardly from the projectile, due to the centrifugal forces imposed by the rotation of the projectile, increase the air drag of the projectile.

[0026] When the tubular member 4 is used during launch, the configuration of a projectile's driving band after launch (FIG. 3) is improved due to the changes achieved in gliding and frictional properties. The loss of material 11 is reduced considerably. The rear tongues 7 remain short and are not bent or deflected outwardly from the projectile. The frictional surface 8 has not become coarse, as with the rotating band without a layer of tin alloy (9 in FIG. 2).

[0027] Tests carried out with a device according to the present invention have established, that the shooting range is increased, that dispersion is reduced and that also deposition of material within the gun barrel is reduced.

Claims

1. Device for rotating bands for projectiles, characterised in
that at least the outer surface (3) of the rotating band (2) is arranged with a layer (4) of metallic material, such as metal, metal alloy or compositions of same, having a melting point below the melting point of the material used for the rotating band (2), the melted layer (4) having good properties of adherance to the material of the rotating band (2), said layer (4) alternatively being applied to the rotating band as a coating of a substance including metal with properties facilitating formation of such a layer (4).

2. Device according to claim 1, in which the metallic material substantially comprises of tin.

3. Device according to claim 1, in which the layer (4) comprises of a foil, wrapped or wound around the rotating band, or entered onto same as a tubular member.

4. Device according to claim 3, in which the foil is arranged with a portion (5) abutting the side portion of the rotating band (2) being foremost during launch.

5. Device according to claim 1, in which the layer (4) is applied to the rotating band (2) by means of dipping, spraying, rolling, electrolytic application, melting or similar method.

6. Device according to claim 1, in which the layer (4) substantially comprises of a mixture of a binder and a granulate of the metallic material, applied by means of a brush, spatula or similar to the rotating band (2).

7. Device according to claim 1, in which the layer (4) comprises of a sintered material.

8. Device according to claim 3, in which the foil is applied to the rotating band (2) by means of an intermediately located adhesive layer, the adhesive layer being arranged to substantially completely disintegrate when made subject to excessive heat.

Drawing