US2885287A - Method of forming elongated compacts - Google Patents

Description

May 5, 1959 H. F. LARSON METHOD OF FORMING ELONGATED COMPACTS a Sheets-Sheet 2 Filed July 14, 1954 a my; mm A May 5, 1959 v H. r-'w LARSON Q 2,885,287 METHOD OF FORMING ELONGATED COMPACTS 7 Filed' July 14. 1954 Y s Sheets-Sheet 3 Pic-3.7.

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3/ INVENTOR v 671E010 1F L/IEJO/V ATTORNEY Patented May 5, 1959 ice METHOD OF FORMING ELONGATED COMPACTS Harold F. Larson, Gates Mills, Ohio, assignor, by mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission Application July 14, 1954,. Serial No. 443,451

Claims. (Cl. 75-226) This invention relates to the art of preparing compacts from powdered materials and especially to a new and improved method and apparatus for forming elongated compacts of substantially uniform density. In general, however, the invention is suitable for forming homogeneous compacts as described, for cladding articles with compacted powder surfaces and for preparing compacted articles which later can be subjected to conventional die forging, coining and shaping operations. useful in the field of powder metallurgy wherein metal powders may be formed either with or without sintering into useful compacted articles. While for purposes of illustration, the invention is described in connection with the preparation of beryllium compacts, as an example of a metal powder, it will be apparent to those skilled in the art that the same teachings are equally applicable to other materials.

Conventional processes for forming compacts of metal powders have encountered great difiiculty' in forming articles: of substantially uniform density when the length of the compact is greater than two diameters. As a result, recourse has been had to time consuming andexpensive procedures for making elongated compacts progressively section by section. In general, this has been necessitated by the failure to provide adequate lubrication between the powder material being compressed and the confining die walls. Lack of adequate lubrication prevents powder flow at the compact surface and engenders extremely high frictional forces. In the absence of such lubrication the powder seizes the surface of the die, or die insert if such is employed, reducing the effective force acting to a fraction of the applied force and resulting in non-uniform densification of the compact. In some cases the result is a non-densification of the center portions of elongated compacts. In addition, the powder seizure leads to difiiculty inremoving the compact without damaging the same. Furthermore, in the preparation of many typesof compacts the use of conventional high-pressure organic or inorganic lubricants cannot be considered in view of their contaminating influence on the powder being treated.

This invention, therefore, has as an object the provision of a simple and reliable method and apparatus for overcoming the above and other common disadvantages of the present practices for forming elongated compacts. In its broader sense the invention teaches the interposition of a suitably chosen metallic member between the material being compacted and the rigid die wall, such member being available for seizure by the powdered material and serving as the primary lubricant between the powdered material and die wall by itself undergoing plastic deformation during the compat-tion procedure. In contrast with the art wherein the compacted material is to remain within the confining member as a package, this invention is directed preferably In a more limited aspect the invention is especially to the manufacture of compacts wherein the formed article is to be removed from such confining. member.

The invention, accordingly, has as an object the provision of an improved method and apparatus for forming elongated compacts of substantially uniform density and having a length of diameter ratio greater than two to one. Another object is the provision of an improved compacted powder article and articles having uncontaminated outer surfaces of compacted metal powder.

Another object is the provision of an improved method and apparatus for forming elongated compacts uncontaminated with lubricating material.

A further object is to provide an improved method for forming elongated compacts with reduced compacting forces resulting in lowered wear of dies and use of less expensive apparatus.

Still a further object is to provide an improved method suitable for forming an article clad with compacted powder surfaces.

An additional object is to provide an improved method suitable for forming elongated compacts in tubular form.

Other objects and advantages will become apparent to those skilled in the art when the following description is considered in conjunction with the accompanying drawing in which:

Figure 1 is a view showing the arrangement of dies and powder charge prior to compaction when using an open-ended metallic member for a lubrication function;

Figure 2 is a diagrammatic view of apparatus suitable for preheating of the powder charge illustrated in Figure .1;

Figure 3 is a view of the apparatus employed in Figurel at the conclusion of the compaction stroke;

Figure 4 is a View of an alternate form of metallic member for the lubrication function and shown prior to compaction;

Figure 5 is a view of the alternate form of member at the conclusion of the compaction stroke;

Figure 6 is a view of the elongated compact following removal of the metallic member;

Figure 7 is a plan view of an alternate form of apparatus suitable for making elongated compacts in tubular forms; and

Figure 8 is a vertical form of apparatus.

The improved technique of compacting a powder, as taught by this invention, may be appreciated by reference to Figures 1 and 3, wherein a thin metal sheath section view of the alternate or tube 10 contains the powder and is shown mounted withina conventionaldie member 11. A coating of high pressure lubricant may be applied to the outer face of the tube or to the inner face of the die to enhance relative motion of these two faces during compaction of the powder. The tube may be sealed at each end by hardened steel punches 12 and 13 actuatable by any conventional press and preferably one which may have a capacity to apply a pressure as high as tons per square inch. When it is desired to preheat the powder charge, the tube and punch assembly may first be disposed within any suitable heating means, for example a dielectric water-cooled heating coil 14, such as illustrated in Figure 2, a resistance heating means, or any other conventional metal powder heating device. After heating, the assembly may then be mounted within die 11. in this preheated condition. The invention, however, comprehends the pressing of the powder in cold, warm or hot condition, ranging from ambient temperature to as high as 1100 C. It also will be understood that the powder charge may be loaded into the tube or may be pressed within. die 11 in an environment of inert gas, or other specially chosen gas, if so desired. Conventional apparatus for providing such special atmospheres during pressing operations are known and accordingly are not illustrated. Likewise, if desired, the powder may be consolidated within the tube by means of vibration or tamping prior to conducting the heating or to inserting of the loaded tube within the pressing die.

Tube 10, which for convenience may be termed the lubricating envelope, preferably is constructed of a metallic material such as mild steel, stainless steel, brass, molybdenum or the like having the ability to undergo a relatively high degree of plastic deformation coupled with intermediate hardness at the operating temperatures. Moreover, for production of the best compacts, the material of which the tube is made must be chemically resistant to the atmosphere used during pressing, to the die and to the powder under treatment.

Furthermore, for best results in order to obtain the most efficient action of the lubricating envelope and to avoid buckling, the wall thickness should be carefully chosen. In pressing compacts of beryllium powder having a length of five diameters, I have found for example that a steel tube with 0.016 inch wall thickness with an outer diameter of about 1.25 inches is satisfactory. In general, a wall thickness of at least 5 to 8 mils should be employed for the tube used in making beryllium compacts in the order of 1 inch diameter and for such compacts in the order of 2 inch diameter the wall thickness may be from 28 to 65 mils.

As a convenient feature, the tube 10, as shown, may be longer than the powder column it contains by at least 1% times its diameter at each end. This allows the punches 12 and 13 to fit snugly into the tube a distance of at least of their diameter in order to give good alignment to the punches. The inner squared ends of the punches are inserted into die 11, a distance just sufiicient to guarantee a start to the pressing operation. A tap fit may be used in sealing the ends of the tube with the punches, especially if loss of material to the air is to be avoided. Otherwise, a very loose fit is workable.

With the apparatus arranged as thus described, at the start of the compacting stroke immediate densification of the powder near the punches occurs and the powder and punches move, but the tube does not. Sufficient density is quickly built up with concomitant pressure on the inner surface of the tube adjacent the punches so that the powder seizes the metal surface of the tube. Application of further pressure and movement of the punches then carries the seized portion of the tube along with the powder whereupon the tube wall is upset and thickened. As shown in Figure 3 representing the apparatus at the conclusion of the compacting stroke, most of the tubing wall in contact with the punch has been thickened and the overall length of tube 10 is materially shorter. The thus deformed tube, however, does not wrinkle since the powder receiving the pressure in turn exerts an outward pressure radially upon the central portion of the tube. Despite this radial pressure which is opposed by the confining wall of die 11, the central portion of the tube does not adhere to the die wall when a proper type of tube material is employed. For compacting beryllium powder, aluminum is unsatisfactory as a tube material since it tends to adhere to the die, does not maintain the external lubricant coating and may in fact extrude past the punch permitting the powder to penetrate the tube and score the die wall. Lead likewise would be unsatisfactory due to its ease of extrusion, as exemplified by the Gero Patent 1,685,915.

Upon conclusion of the pressing stroke the punches and upset tube 10 containing the compact are removed from die 11, the punches are removed and the tube 10 may be slit and peeled from the compact. A typical form of compact thus manufactured is illustrated in Figure 6 and may have a length of 2 to 6 and more times its diameter while possessing substantially uniform density throughout.

It will be apparent that pressing may be conducted from one end only by applying pressure to one punch, the other punch or plug being held rigidly upon any suitable support. It also will be apparent that intermediate plugs may be employed to press upon the powder by being interposed between the powder and the main punch exerting the pressure.

In one example of the thus described invention when using pressing from one direction only, a tube was filled with 200 mesh beryllium powder separated by thin, mild steel discs and was pressed at 425 C. using a mild steel tube 10 having a wall thickness of 5 mils. As shown by Table I, the total density variation over five diameters is seen to be only about 2%, a very marked deviation from conventional practices in which the density variation of 20% may be found in compacts of not more than two diameters.

TABLE I Compacting of --200 mesh beryllium powder variation in density along length of compact Length of Density 0! N o. of Diameters From Punch Segment, Segment,

inches g./ce.

Compacting pressure= TSI. Compact diameter-=1. Pressing in one direction only.

In general, when forming articles of beryllium powder at room temperature having a length of 2 to 6 diameters, an average density of 88% of theoretical may be secured without difiiculty in the practice of the invention.

As a further example of the invention, the variation in wall thickness of the lubricating member during the manufacture of compacts from beryllium powder within a type 304 stainless steel tube having a wall thickness of 35 mils may be noted in Table II. It will be observed that the finished compact has a length to diameter ratio greater than four to one.

TABLE II Variation in diameter along length of compacts illustrating extent of tube thickening during compaction Compact Pressed at Compact Pressed at Compact Pressed at 54 T81 and 420 C. 76.5 T81 and 430" C. 90 T81 and 435 0.

Compact Compact Compact Distance Dlam- Distance Diam- Distance Diamfrom end etcr, from end eter, from end eter,

inches inches inches at one end 1.101 at one end. 1.190 at one end. 1. 195 1 1.174 A- 1.164 V 1.184

1. 170 1. 162 1. 169 1. 1. 165 1.159 1. 164 1. 160 1. 167 1.164 1.174 1. 1.191 1. 187 at other end. at. other end Compacting Die ID. was 1.250". Tuba was Type 304 S.S. 0.035 wall.

The invention may be practiced without the use of the open-ended tubes by enclosing the powder within a sealed metal can or container 22 such as shown in Figure 4. Upon mounting this container within die 11 between the punches 12 and 13 and applying pressure thereto, a similar lubricating action is secured and the upsetting of the can'walls occurs in .the isame mann'er as above described with the tube. At the endof the compacting stroke the can is shortened as shown in Figure 5 and after being stripped from the compact, a final product as shown in Figure 6 is produced.

Experience-has shown'that in carrying outthe process a clearance of 0.3 to 1.0% of the radius of the die opening may be provided between the outer surface of the tube or can .and the inner surface'of the die wall for ease of insertion of the assembly into the die. Conventional practice wherein no lubricating member is employed is limited to clearances of between 0.05 and 0.1% of the radius of the die. Preferably, I employ a die cavityof uniform cross section With a hardened die material and with the surface ground or honed. In the following this technique wear of the expensive die is lessened and friction values between the lubricating envelope and the die Wall are reduced to only about 10-20% of the friction values obtained when the powder is compacted indirect contact with such wall.

While the foregoing has described the invention in connection with the manufacture of compacts in rod-like form with a high volume to surface ratio it is apparent that compacts of other shapes may be formed following the same teaching. For example in Figures 7 and 8, apparatus for forming elongated compacts of tubular form is disclosed. In this arrangement the surrounding compactin-g die 30 has an inner mandrel 31 located concentrically therein and two lubricating tubes 32 and 33 are arranged concentrically adjacent the mandrel and die respectively. Tubular punches 34 and 35 project a suitable distance within said tubes and enclose the powder therein. After the compaction stroke of the punches the assembly is removed from the die and mandrel and the punches withdrawn from the upset tubes. Thereafter, the tubes are stripped from the compact leaving an elongated compact of substantially uniform density but in tubular form.

As will be apparent to those skilled in the art, the essential features of the invention can be applied in the fabrication of various other designs and shapes of articles. For example, a metallic rod to be clad with another metal can be disposed concentrically within an envelope with the powder disposed between such rod and envelope. Upon application of pressure to the rod and to the powder, the powder is compacted axially and radially, the rod of material meanwhile exerting complementary pressure upon the powder by its own deformation. Articles of uranium clad with beryllium have been formed in this manner, although the invention is in no Way limited solely to these particular metals.

As a distinct practical advantage resulting from use of the described invention, it now is possible to provide fabricated articles from reactive metals such as beryllium, uranium, titanium, zirconium, molybdenum, vanadium and the like which will be uncontaminated with lubricants. The interposition of the lubricating metal envelope or shield provides a positive barrier to contact between the article under fabrication and the lubricant material adjacent the die surface.

Compacts such as above described may be formed at ambient or at elevated temperatures. The limits to the temperature used in carrying out the invention are determined by the elevated temperature properties of the material being pressed, of the lubricating envelope, and of the die materials. Such limits are reached when the powdered material becomes molten or the envelope or die materials become too weak to Withstand the pressures required at the temperatures involved. The abovedescribed relatively large clearances, made possible by this invention, are found to aid in preventing interference in the fitting of the parts, which otherwise would occur due to thermal expansion at elevated temperatures. When employing a die material, such as hardened high speed tool steel, to press beryllium powder in mild steel 16 lubricating envelopes, 'pre'ssuresof'np to l00tsimay be used .at-die temperatures of up to 600 C. In the hot pressing technique taught by the invention, the metal envelope has also been found to provide adequate lubrication withitemperatures .as high as 1100 C.

While the above embodiments of my invention have been described as preferred forms, his to be understood that the invention may take other forms all'of which are intended to come within .thespirit and scope of claims appended 1 hereto.

I claim:

1. The method of forming an elongated compacted article .having a length to diameter ratio greater than two from amass 'of metal powder comprising, confining said powder within a thin deformable elongated container, mounting said container within a die with clearance betweensaid container -and theadjacent wall of'said die to,permit upsetting :ofsaid container, applying pressure to said powder in adirectionalong'the longitudinal axis of :said container :thereby .to establish an :initial compaction of the powder therein and to cause said initially compacted powder to seize the inner surface of said container, continuing the application of pressure to establish a further degree of compaction while simultaneously upsetting and shortening the length of said seized container, relieving the pressure upon the shortened container and removing the compacted article from said shortened container.

2. The method of forming an elongated compacted article having a length to diameter ratio greater than two from a mass of metal powder comprising, confining said powder within a thin deformable elongated container having the outer wall thereof lubricated, mounting said container within a die with clearance between said die wall and said container to permit upsetting of said container material, applying pressure to said powder in a direction along the longitudinal axis of said container thereby to establish an initial compaction of the powder therein and to cause said initially compacted powder to seize the inner surface of said container, continuing the application of pressure to establish a further degree of compaction while simultaneously upsetting and shortening the length of said seized container, relieving the pressure upon the shortened container and removing the compacted article from said shortened container.

3. The method of forming an elongated compacted article having a length to diameter ratio greater than two from a mass of metal powder comprising, confining said powder within a thin deformable elongated container, heating the powder and container, mounting said heated container within a die with clearance between said die wall and said container to permit upsetting of said container material, applying pressure to said heated powder in a direction along the longitudinal axis of said container thereby to establish an initial compaction of the heated powder therein and to cause said initially compacted powder to seize the inner surface of said container, continuing the application of pressure to establish a further degree of compaction while simultaneously upsetting and shortening the length of said seized container, relieving the pressure upon the shortened container and removing the compacted article from said shortened container.

4. A method of forming an elongated uniformly dense beryllium compacted article having a length-to-diarneter ratio greater than two from a mass of beryllium powder comprising confining said powder within a thin deformable container, heating the powder and container, mounting said heated container within a die with clearance between said die wall and said container to permit upsetting of said container material, applying pressure to said heated powder in a direction along the longitudinal axis of said container thereby to establish an initial compaction of the heated powder therein and to cause said initially compacted powder to seize the inner surface of taneously upsetting and shortening the lengthofsaid seized container, relieving the pressure upon the 'shortened I container and removing the compacted article from said shortened container. i I

said container, continuing the application of pressure to I "establish a. further degree of compaction while sitnul- -5.- A method of forming an elongated uniformly dense beryllium compacted article having a length-to-diameter ratio greater than two from a mass, of beryllium powder comprising confining said powder within a thin deformsaid container to permit upsetting of said container material, applying a pressureof50 to 100 tons per square 'inch'to' said powder in a direction along the. longitudinal axis of said container thereby to establish an initial compaction of the powder thereinand to cause said initially compacted powder toseize the inner surface of said con-' tainer, continuing the application of pressure to establisha further degree of compaction while simultaneously able metal container, mounting .said container within a die with sufiicienti clearance between said die wall and upsetting and shortening thelen gth of said container,

relieving the pressure upon the shortened container. and. l removing the compacted article from said shortened container.- I j l 1 References Cited inthe file of this patent UNITED STATES PATENTS Shaw et a1. Apr. 24, 1951 I

Claims (1)

1. THE METHOD OF FORMING A ELONGATED COMPACTED ARTICLE HAVING A LENGTH TO DIAMETER RATIO GREATER THAN TWO FROM A MASS OF METAL POWDER COMPRISING, CONFINING SAID POWDER WITHIN A THIN DEFORMABLE ELONGATED CONTAINER, MOUNTING SAID CONTAINER WITHIN A DIE WITH CLEARANCE BETWEEN SAID CONTAINER AND THE ADJACENT WALL OF SAID DIE TO PERMIT UPSETTING OF SIAD CONTAINER, APPLYING PRESSURE TO SAID POWDER IN A DIRECTION ALONG THE LONGITUDINAL AXIS OF SAID CONTAINER THEREBY TO ESTABLISH AN INITIAL COMPACTION OF THE POWDER THEREIN AND TO CAUSE SAID INITIALLY COMPACTED POWDER TO SEIZE THE INNER SURFACE OF SAID CONTAINER, CONTINUING THE APPLICATION OF PRESSURE TO ESTABLISH A FURTHER DEGREE OF COMPACTION WHILE SIMULTANEOULY UPSETTING AND SHORTENING THE LENGTH OF SIAD SEIZED

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