Apparatus for the section-wise autofrettage of gun barrels

An apparatus for the section-wise autofrettage of gun barrels (22) by a hydraulic pressure generated inside the barrel. The apparatus (1, 1′, 1″) comprises a mandrel-shaped insert (2, 2′, 2″) inserted into the barrel (22) from the breech opening. A first sealing device (3) is disposed at one end of the insert (2, 2′, 2″), and has a seal packet (5) disposed on a seal seat (4) of the insert (2, 2′, 2″). The seal seat (4) is limited at the front by a threaded sleeve (7) screwed onto the insert (2, 2′, 2″), and an annular intermediate part (8) adjoining the threaded sleeve (7) at the rear. The seal packet (5) includes at least one O-ring (10) held by a shoulder (9) of the mandrel-shaped insert (2, 2′, 2″), and a high-pressure seal (15) formed by two partial rings (13, 14) that are connected to one another by a conical contact surface (16).

CROSS REFERENCE TO RELATED APPLICATION

This application claims the priority of German Patent Application DE 102 34 029.3 filed Jul. 26, 2002, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates to an apparatus for the section-wise autofrettage of or cold working barrels, particularly gun barrels, by a hydraulic internal pressure that is generated inside the barrel.

During firing, gun barrels are stressed by extremely high gas pressures, which cause the barrel, and thus the inside barrel surface, to expand. To increase the resistance to barrel expansion during firing, it is known to subject the corresponding barrel to an autofrettage. In the process, pressure exerted on the inside surface of the barrel exceeds the elasticity limit of the inside layers, thereby causing a permanent deformation through the expansion of these layers, which press against the outside layers. The permanent deformation is not subjected to further changes during firing, because the high pressure attained in the autofrettage is not reached again.

German patent DE-PS 1 124 987 discloses a method for the autofrettage of gun barrels, in which a hydraulic internal pressure is generated inside the barrel. The pressure decreases continuously with increasing distance from the charge-side barrel end, taking into account the pressure course of the propellant-charge gases in the barrel during firing. To this end, a highly viscous fluid that is under high pressure flows continuously through the annular gap formed between the inside wall of the barrel and a mandrel-shaped metal insert. The width of the annular gap determines the local pressure stress.

It is further known from German Patent No. DE-PS 1 124 987 that it was not possible up to now to perform a satisfactory section-wise autofrettage, because the sealing devices required between the different longitudinal sections were not available.

SUMMARY OF THE INVENTION

This object is achieved according to the present invention to provide an apparatus of the type mentioned at the outset for performing a section-wise autofrettage.

This object is achieved according to the present invention, which is essentially based on the concept of disposing a first sealing device at one end of a mandrel-shaped metal insert, with the first sealing device having a seal packet that is disposed on a seal seat on the insert. The seat is limited at the front by a holding device comprising a threaded sleeve that can be screwed onto the insert, and an annular intermediate part that adjoins the threaded sleeve at the rear. The seal packet includes at least one O-ring, which is held by a shoulder of the mandrel-shaped metal insert, a leather ring, a bearing ring and a high-pressure seal formed from two partial rings. The two partial rings have conical contact surfaces, so that when pressure is exerted, the high-pressure seal of one of the two partial rings is pressed outward against the inside wall of the barrel, along the conical contact surface, and the other of the two partial rings is pressed inward against the metal insert, along the conical contact surface, thereby effecting a seal under extremely high pressures.

It has proven especially advantageous when the seal packet includes an elastic O-ring that is held by the shoulder of the insert, and a leather ring that is supported between the O-ring and the bearing ring. In this case, the O-ring, which preferably comprises rubber, effects the seal in the lower pressure range. In contrast, the leather ring, made of commercially available cowhide leather, for example, prevents the O-ring from being extruded into the gap of the consecutive bearing ring under higher pressures. The high-pressure seal formed by the two partial rings then only produces the seal under high pressures.

It has proven advantageous for a stud to be inserted into the threaded sleeve of the holding device on the side or end opposite the seal packet. In the region engaged by the stud, the thread of the threaded sleeve runs in the direction opposite that of the remainder of the thread, so the threaded sleeve can be rotated away from the seal packet through the rotation of the threaded pin. As a result, if the seal packet jams, it can be detached in a simple manner from the barrel opening, e.g., the muzzle of the gun barrel.

For also allowing longer mandrel-shaped metal inserts to be inserted easily into the respective barrel, it has proven advantageous for the circumferential surface of the mandrel-shaped metal insert to be provided with annular depressions that are spaced from one another and extend from the surface into the interior of the insert. In this instance, the insert can readily follow the course of the gun barrel when inserted.

Further details about and advantages of the invention ensue from the following description of exemplary embodiments explained in conjunction with figures.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1illustrates an apparatus1in accordance with the invention, which includes a mandrel-shaped metal insert2that has one end connected to a first sealing device3for the caliber region of a gun barrel.

The first sealing device3has a seal packet5, which is disposed on an annular seal seat4on the surface of the metal insert2, with the seal seat4being limited at the front by a holding device6comprising a threaded sleeve7that can be screwed onto the metal insert2, and an annular intermediate part8that adjoins the threaded sleeve7at the rear. The part8thus is disposed between the seal packet and the sleeve7and tends to compress the seals of the seal packet5when the sleeve7is screwed onto the mandrel.

The seal packet5includes a rubber O-ring10, which is held by a shoulder9of the metal insert2, a leather ring11that adjoins the O-ring, a bearing ring12and a high-pressure seal15, which is formed by two partial rings13,14and has conical contact surfaces16. The bearing ring12and the two partial rings13,14are made of steel.

When pressure builds up in the corresponding segment of the gun barrel, the O-ring10is acted upon first from the pressure side100, and effects the seal in the lower pressure range. As the pressure increases, the leather ring11then prevents the O-ring10from being extruded into the gap between the bearing ring12and the inside surface of the barrel. Moreover, the bearing ring12presses against the first partial ring13, which is pushed onto the second partial ring14via the conical contact surface16as the pressure increases. This causes a radial expansion and the pressing of this partial ring13against the inside wall of the barrel, and a radial compression and pressing of the partial ring14against the metal insert2, and thus a seal against extremely high pressures.

Bores18, through which a toggle-like pin (not shown) can be inserted and then manually rotated for adjusting the first seal packet5, are provided for screwing the threaded sleeve7of the holding device6onto the corresponding thread17of the mandrel2of the apparatus1.

A stud19is inserted into the threaded sleeve7, on the side opposite the seal packet5. In this region, the threaded sleeve7has a thread20, which runs in the direction opposite that of the thread21engaging the thread17of the apparatus1. Accordingly, when the stud19is rotated, the threaded sleeve7can be rotated away from the seal packet5. Consequently, if the seal packet5jams, it can be detached simply from the muzzle of the barrel.

FIGS. 2 through 4illustrate a gun barrel22of a tank, whose outside diameter decreases in stages along the barrel, corresponding to the gas-pressure stress during firing.

For optimum material utilization, the gun barrel22is subjected to a hydraulic autofrettage over a variable length. In the example, the barrel is divided into three regions23through25for the autofrettage or cold working process (FIGS.2through4). The autofrettage pressures p1, p2and p3for the individual barrel regions23through25are to be selected according to the dimensions of the barrel22such that p1>p2>p3. For executing the autofrettage, the barrel22is held in a barrel-retaining device32, only indicated schematically. It is conceivable to divide the barrel into more or fewer autofrettage segments.

The barrel regions23through25are subjected to autofrettage consecutively. For this purpose, a separate apparatus1,1′ and1″ in accordance with the invention is provided for each individual autofrettage segment. The apparatuses respectively comprise a metal insert2,2′ and2″ located in a retaining device26, a first sealing device3, which is to be disposed in the caliber region27of the barrel22, and a correspondingly designed second sealing device29, which is to be disposed in the chamber or breech region28of the barrel22.

To keep the required oil volume to a minimum, the outside diameter of the metal inserts2,2′ and2″ nearly matches the inside diameter of the barrel22. In addition, in the chamber region28, an additional filler piece30is used for this purpose.

Oil is supplied via bores31in the metal insert2,2′ and2″ from the respective retaining device26that retains the apparatus1,1′ and1″.

As can be inferred fromFIG. 2, the apparatus1is first inserted into the barrel22and connected to the oil supply, and this region23of the barrel22is then charged with the pressure p1.

After the autofrettage has ended in the barrel region23, the apparatus1is removed from the barrel22, and the apparatus1′ is subsequently inserted into the barrel region24(FIG.3). Oil is then introduced into this barrel region, the barrel22is charged with a pressure p2and the apparatus1′ is removed again from the barrel22.

The autofrettage is then performed in the barrel region25(FIG. 4) through the insertion of the apparatus1″ into the barrel22and the corresponding charging of the barrel22with an oil pressure p3.

As can also be inferred fromFIGS. 2 through 4, the mandrel-shaped metal inserts2,2′ and2″ have annular depressions33, which are spaced from one another and extend from the surface into the interior of the metal inserts2,2′ and2″ for allowing the metal inserts2,2′ and2″ to be easily inserted into the barrel22.