US2371125A - Method of making gun barbel - Google Patents

Description

March 1.3, 1945. i B. BANNlsTl-:R 2,371,125

METHOD OF MKING GUN BARREL FORGINGS 2 Sheets-Sheet 2 B. BANNISTER METHOD OF MAKING GUN BARREL FORGINGS Filed Jan. 16, 1942 March 13, 1945.

, rections.

Patented Mn. 13,1945

METHOD F MAKING GUN BARREL FQRGINGS Bryant Bannister, Mount Lebanon, Pa., assignmto National Tube Company, a corporation of New Jersey Application January 16,1942, Serial No. 427,075

(ci. so-sm 3 Claims.

This invention relates to the manufacture of Vgun barrels, and more particularly to those which in the past have to a large extent been formed by forging steel ingots in one or more operations into stock which can be turned and. bored to the final dimenions. For guns of smaller size, centrifugal casting has been resorted to in order to eliminate a considerabley portion of machine work involved in boring which is required where solid stock is employed. However, since a centrifugal casting cannot bev tapered on the outside', this taper must be obtained by a machining operation. Machine work is expensive and slow and in times of national emergency, reduction in the extent thereof is very essential.

The stresses to which a gun barrel is subjected in service are so severe that the strength of ma` terial of which it is made must be high in all di- To determine this strength, tests are made on specimens taken in both a longitudinal and transverse direction with respect to the axis ofthe barrel.v Generally, the greatest strength is shown in the direction of metal flow during the forming `or forging operation, as this ow orientates theshear planes in the direction of ow; thus the strength transversely to the direction of flow is at a minimum. Since a. gun bar-l rel forging originates from a chunky ingot, the greatest flow of metal occurs lengthwise of the barrel; consequently the greatest strength is in this same direction. It has been proposed to reduce this disparity in strength by twisting the forging or casting while at an elevated temperature, to orientate the lines of weakness in a helical direction, thereby reducing the longitudinal and increasing the transverse strength. This twisting is in the nature of a separate operation, whereas in the practice of my invention it can be accomplished automatically as a part of the forming operation.

Conventional forging and centrifugal casting are inherently slow operations, necessitating the employment of great numbers of units and man power to produce the huge quantity of gun barrels required by a `natiorial emergency, whereas my method is capable of producing forgings at a tremendously greater rate per producing unit, the labor involved being correspondingly reduced.

It has long been known that the soundness and homogeneity of an ingot is greatly influenced by its contour and that the round corrugated design produces the best castings. Fortunately this type of ingot lends itself extremely well to my method of forging, which is in effect a rotary blooming operation wherein the ingot is rotated and advanced helically between rolls which may rbe proled to work the metal at the most desirable rate as the' cross section is reduced, thereby maintaining the metal being worked in compression, and also, since the ingot is vsimultaneously pierced, the flow of metal proceeds* both from the outside and the inside. By proper selection of ingot size with respect to the desired product, an exceptionally uniform, concentric and sound forging results. It has been found that in seamless tubular products which require exceptional quality of inside surface the above relationship is important to avoid surface imperfections which arise from segregations which are naturally located near the center of the ingot from which the seamless product is fabricated. In the case of gun barrel forgings, this undesirable material must be concentrated entirely within the surplus metal which is to be machined out in finishing. the forging. This is easily provided for by first producing clean steel followed by proper teeming into ingot molds of the correct' To so work the metal of the forging during 4the forming operation that at all times it is subjected only to compressive stresses, thereby producing a pressure forging wherein the metal is workedthroughout its mass;

To provide a method of the class described which has' great productivity and requires a minimum of man hours of labor per forging produced.

The foregoing and other objects will become more apparent after referring'to the following specification and drawings wherein' suitable apparatus for performing the method of my invention is disclosed, in which:

Figure 1 is a plan view of apparatus suitable -'for performing the method of the present invention.

Figure 2 is a side elevation partly in section. Figure 3 shows a typical round corrugated ingot.

piercing operation being performed on an ingot.

Figure shows the hollow forging after the above operation.

Figure 6 is a view showing a 'workpiece being reduced to final form between the rolls and the mandrel.

Figure 'l is a longitudinal section of the article produced by the method of the invention.

Referring more particularly to the drawings, the numeral 3 designates a pair of metal-working rolls disposedrso as to helically advance a workpiece A over an interiorly disposed mandrel B. The rolls 3 are -driven by motors 4 through shafts 5 and slip couplings 6. The shafts 5 are mounted in housings I which are slidably carried by bases 8. Also mounted on the bases 8, and at the rearward end thereof, are screw-nuts IG engaging screws II whicnare secured to the housings l. Screws II are connected by worm gears I2, shafts I3 and I4, gears I5 and speed reducer I6 to suitable motive power, such as a reversible electric motor Il, and it is seen that actuation thereof will move the rolls to enlarge or decrease the pass formed thereby.

Disposed adjacent the pass formed by the rolls 3, and intermediate thereof, are guides 20 which are pivotally mounted as at 2l and have grooved guiding surfaces 22, the grooves ming of. varying diameter and longitudinally curved on an arc having its focus oiset with respect to the pivotal axis of the said guides. A frame, or

housing Ia is disposed between and adjacent the housings l which carry the shafts 5 for the rolls t. Mounted on this housing 1 are interior screw-nuts 23 having worm gear exteriors 24. Shafts 25 are connected to the guides 20 and have screw-threaded ends 26 disposed in the screw-nuts 23. A shaft 2l carries worms 28 which are in mesh with the gears 24, and this shaft is connected through aspeed reducer 30 During the initial piercing and subsequent operations, the forming rolls may be proportioned to produce a twist of the desired direction and extent to the workpiece or they may be so designed that no twist is produced. If a twist in the direction of rotation is desired, the roll speed to a reversible motor or other source of power.

Accordingly it is seen that operation thereof will move the guides 20 to enlarge or diminish the pass defined thereby.

In producing gun barrels by my method, itis possible to produce those of small caliber in one operation wherein the piercing and tapering is accomplished in one pass through the mill. In such cases it is also permissible `to use a rolled round billet instead of an ingot, but for larger bore guns the method should employ at least two operations.

Where two operations are employed, the first may be either a simple piercing (wherein the solid ingot is reduced in diameter and sirnultaneously pierced, thereby producing a' cylindrical hollow forging as shown in Figure 5), or the forging may be'slightly tapered externally with a uniform bore. In the first instance. the forming rolls and guides remain a. constant distance from the axis of the pass. In the second instance, the forming rolls and guides change distance from the axis of the pass during the rolling operation. The second operation (that of tapering the outside but maintaining the bore uniform) is carried out with a cylindrical mandrel inside the workpiece and with the rolls and guides varying in distance from the mill axis. This movement is controlled as hereinbefore described.

For very large bore guns, where large reductions are involved, a third operation similar to the second may be required.

at theV gorge (or end of the reducing section of the pass) must be relatively faster than the speed at the beginning of rolling. Stated in another way, the roll must tend to rotate the billet a greater number of revolutions per unit of time at the gorge than it does at the inlet end of 4the pass. If a twist is desired opposite the direction of rotation, the reverse relationship must exist except that it has been found that the gorge roll speed can tend to rotate the billet faster than the roll does at the inlet without producing any twist. The twist in a gun barrel forging' .should be in a direction opposite the helical direction of the bore riiiing to be machined into the barrel. Roll proportions may be such that substantially all twist can be imparted 'during the piercing operation, or in subsequent operations, or both. f

While I have shown and described several specific embodiments of the present invention, it will'be seen that I do not wish to be limited exactly thereto, since various modifications may be made -without departing from the scope of the invention as defined in the appended claims.

I claim:

1. In the manufacture of gunbarrel forgings, the method which includes the steps of helically rolling a heated metallic workpiece over a mandrel to reduce the outside diameter thereof and to simultaneously pierce the same to provide a tion of the workpiece being worked under comy pression thereby producing a forging wherein the metal is worked throughout its entire mass.

2. In the manufacture of gun barrel forgings,

1 the method which includes the steps of helically rolling a heated metallic workpiece over a mandrel to reduce the outside diameter thereof and to simultaneously pierce the same to provide a cylindrical forging having a bore of substantially the diameter desired in the nished article throughout the length thereof, then passing the workpiece over a mandrel between opposed spaced-apart rolls whereby the workpiece is helically rolled and tapered by varying the distance between the rolls while maintaining the bore substantially uniform, twisting said workpiece while it is helically rolled and maintaining the portion of the workpiece being worked under compression thereby producing a forging wherein the metal is worked throughout its entire mass.

3. In the manufacture of gun barrel forgings, the method including the steps as defined in 2, wherein the twisting of workpiece during the'i'olling thereof is in a direction opposite the direction of the subsequent helical riing of the bore of the workpiece.

BRYANT BANNISTER..

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