US 2977666 A
Description (OCR text may contain errors)
April 4, 1961 P. H. BRACE ETAL 2,977,666
METHOD OF MAKING GUN LINER ELEMENTS Filed Dec. 29. 1954 FIG. 5
VENTOR PORTER H. ACE JOHN C. LAFFAN, JR.
6 1/3 dual ATTCRNEYS METHOD or MAKING GUN LINER ELEMENTS Porter H. Brace and John C. Lalfan, Jr., Pittsburgh, Pa., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Dec. 29, 1954, Ser. No. 478,552
. Claims. (Cl. 29-1.1)
The present invention relates to a method of making gun liner elements and more particularly to a method of making gun liner elements from molybdenum and molybdenum alloy cylindrical slugs.
It is known that when molybdenum or molybdenum alloys are subjected to plastic deformation and suitable heat treatment the strength and ductility of the metal are markedly improved in the direction of extension. However, these same properties are found to have been impaired asmeasured normal to the plane of extension due to coarse elongated grain structure apparent in molybdenum or molybdenum alloy metals. Thus, when a gun is lined with a series of rings machined from fiat rolled bar stock or from discs formed by upstanding cylindrical slugs, the circumferential strength and ductility are favorable while the properties in the axial direction are relatively poor. When the gun is fired, the bore surface is subjected to severe thermal and mechanical stresses, and a phenomenon known as watering occurs; i.e., the formation of a somewhat regular pattern of circumferential cracks whose planes are substantially normal to the axis of the gun. The conformation of the watering planes reflect the flow patterns of the metal during working of the metal in a plastic state. If these watering planes, or rupture planes, are not approximately normal to the axis of the gun, cresent-shaped segments may become detached from the liner, flake off, and obstruct the bore of the gun with detrimental results.
The instant invention overcomes the prior are deficiencies above-mentioned by the provision of a gun liner element in which the watering planes, or planes of weakness, approximate planes normal to the axis of the liner thereby increasing the strength and ductility of the element along a plane perpendicular to the axis of the gun bore.
An object of the present invention is the provision of a method of making gun liner elements having improved rupture strength characteristics.
Another object is to provide a method of making gun liner elements from specially shaped compacts of molybdenum or molybdenum alloys.
A further object of the invention is the provision of a method of preparing a gun liner element to eliminate wedge-shaped rupture planes in a finished gun liner element.
Still another object is to provide a method of making gun liner elements which allows cold working of molybdenum to a final form for machining.
Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to tl e following detailed description when considered in connection with the accompanying drawings wherein:
Fig. 1 is illustrative of the prior art and shows a plan view of a cylindrical compact about to undergo compression;
l atented Apr. 4, 1961 Fig. 2. is also illustrative of the prior art and is a view of the compact of Fig. 1 under compression;
Fig. 3 illustrates the compact of Fig. 2 machined as a gun liner element;
Fig. 4 is a sectional view of a compact formed in accordance with the invention; and n Fig. 5 is a sectional view of a finished gun liner element made in accordance with the invention.
Referring to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in Fig. 1 an upsetting cylindrical compact 11 formed by conventional mechanical means, such as flat dies, prior to compression, by dies 12. Fig. 2 shows the compact ll of Fig. 1 under slow compression by dies 12 which compact is approaching a barrel shape due to the bulging of sides 13 of the compact. Sides 13. proportionally enlarge as compression is increased. The compact 11 of Fig. 2 contains a flow pattern having divergent concave surfaces of weakness 1:; which are spaced normal to the axis of the compact, and Fig. 3 illustrates the compact 11 of Fig. 2 upon completion of machining operations to form gun liner elements. Individual wedge-shaped washer formations 15 are indicated in the liner structure of Fig. 3, and, when subjected to axial or longitudinal stresses, the formations 15 create cracks in the gun bore. This failure is known as watering action and is caused by differential movements of the formation 15 when counteracting stresses introduced by firing of the gun.
The present invention overcomes the objectionable feature of watering as is evidenced in liners formed by the prior art method illustrated by Figs. 1, 2 and 3. A compact 16 of Fig. 4 is provided by compacting molybdenum powder or alloys thereof by mechanical means such as dies or molds, and sintering the compact in a controlled atmosphere such as hydrogen at an elevated temperature of approximately 1700 C. for a substantial period of time, for example twenty hours. The sintered compact is then machined to a uniform diameter and length with re-entrant conical end surfaces 17. The planes of weakness 14 of Fig. 4 are held substantially normal to the longitudinal axis of the compact by the conical compressing method which obviates side bulging as illustrated by sides 13 of Fig. 2. When working the sintered compact at room temperature, the angle 0 of the conical surfaces 17 should be approximately 10 for best results, but angle 0 is generally determined by the coefiicient of friction of the metal of the compact with reference to conical compression dies 18 by the following formula:
=Tan 0; where 1. equals the coefficient of friction, and 0 equals the cone angle.
The finished gun liner element produced by the method outlined above is shown in Fig. 5. The compact of Fig. 4 is machined to a hollow cylindrical shape by conventional means, and the planes of weakness 14 of Fig. 5 remain in parallel spaced relationship and normal to the axis of extension of the compact as in Fig. 4. A series of the finished elements depicted in Fig. 5 are placed on a mandrel, and a gun barrel is then shrunk-fit onto the aligned elements to completely line the barrel.
We have found, for example, that sintered Mo+0.l5% Co alloy compacts can be reduced in height by approximately 50% from a cold start and that the external form of the upset compact can be made to approach that of a right circular cylinder. By further experimentation we have found that the watering surfaces approach planes nearly normal to the axis of the upset compact. By approximate heat treatment at, for example, 1000 C. for one hour followed by a slow cool for two hours to room temperature, circumferential mechanical properties 3 corresponding to 148,000 p.s.i. yield strength, 152,000 p.s.i. tensile strength, and ductility as high as 25% in terms of elongation of a standard tensile specimen may be obtained.
Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.
What is claimed is:
1. The method of manufacturing gun liner elements from powdered molybdenum comprising providing a compact of powdered molybdenum compressed to a desired shape, heat treating the pressed shape to about 1700 C. for approximately 20 hours in a hydrogen atmosphere to form a sintered homogeneous compact, machining the sintered compact to uniform diameter and length and with re-entrant conical end surfaces with a cone angle of approximately compressing the machined compact at room temperature with end-surfacematching conical dies to retain substantially the uniform diameter of said compact, heat treating said compressed compact at approximately 1000 C. for at least one hour followed by a slow cool for approximately two hours to room temperature to relieve residual stresses of said com pact, and finally machining said compressed compact to form a ring-like gun liner element.
2. In a method for making gun liner elements comprising machining a cylindrical compact of powders of molybdenum to have re-entrant conical end surfaces therein, the tangent of the angle of the conical surfaces being defined by the coefficient of friction of the metal at the compressing temperature, compressing the compact with conical dies to establish planes of weakness only substantially normal to the longitudinal axis of said compact, and stress relieving said compressed compact by appropriate heat treatment to form an element having circumferential mechanical properties in the order of 148,000 p.s.i. yield strength and 152,000 p.s.i. tensile strength, and finally machining the compact into a hollow cylinder.
3. A method of making gun barrel liner elements comprising providing a charge of powdered molybdenum, compressing the charge to provide a mass of a desired shape, heat treating the mass to sintering temperature to form a homogeneous compact, machining the compact to provide a cylinder of uniform diameter and length and with re-entrant conical end surfaces, compressing the cylinder at room temperature with conical dies to maintain the diameter of said cylinder uniform so as to allow planes of weakness only to be present in planes normal to the longitudinal axis of the cylinder, heat treating the compressed cylinder to stress relieving temperature, machining the cylinder into a ring shape liner element, mounting the element on a mandrel to form one of a number of like elements disposed on said mandrel in abutting registration with respect to each other upon which may be shrink fitted a gun barrel.
4. A method for compacting ductile metals to establish parallel planes of Weakness substantially normal to th direction of compaction comprising machining a meta slug to form a cylinder with re-entrant conical end su faces, and compressing the machined slug with conica dies mating the conical end surfaces thereby to obta uniform axial side bulging of the slug, the shape of th dies being determined by the formula t=Tan 0 where equals the coefficient of friction of the slug metal and equals the cone angle in order to restrict planes of wea ness of the slug to planes normal to the longitudinal ax of the slug when the slug is compressed by the dies.
5. The method of manufacturing gun barrel liner ele' ments from a pressed and sintered compact of powdered molybdenum comprising machining the compact to form a cylinder having re-entrant conical surfaces, compressing the machined compact at room temperature with conical dies which mate with the conical end surfaces, stress relieving the compressed compact at 1000 C. for one hour, cooling the article to room temperature from 1000 C. for two hours, and machining the article to form an element having a hollow cylindrical form.
References Cited in the file of this patent UNITED STATES PATENTS 475,071 Willson May 17; 1892 2,238,670 Traversi et a]. Apr. 15, 1941 2,494,935 Dunn Jan. 17, 1950 2,499,944 Brace et a1 Mar. 7, 1950 2,592,128 Engstrom Apr. 8, 1952 2,628,516 Brace Feb. 17, 1953