US3189988A - Method of making copper tubing - Google Patents

Description

June 22, 1965 E. v. CRANE 3,139,938

METHOD OF MAKING COPPER TUBING Filed April 18, 1961 4 Sheets-Sheet 1 l E XTRUSION LUBSIFQATION OOMPACTS SINTERING COMPACTION FIG. I

BLENDING LUBRICANT INVEVTOR. EDWARD V. CRANE ATTORNEYS FIG. 3

June 22, 1965 E. v. CRANE METHOD OF MAKING COPPER TUBING 4 Sheets-Sheet 2 Filed April 18, 1961 mvmron EDWARD V. CRANE mm 1, u on w. mm HH H HI I l I |.|.l V m llll I =l f A ow m/ T m. I n.\\ ov we 2 r N? w fi ats June 22, 1965 E. v. CRANE 3,189,988

METHOD OF MAKING COPPER TUBING Filed April 18, 1961 4Sheecs-Sheet 3 8 FIG. 8 Y 34 so 70 i 2 I 72 1| 4o 38 I2 22 73 A 5 3| 2o INVENTOR.v EDWARD V. CRANE ATTORNEYS June 22, 1965 E. v. CRANE 3,189,988

METHOD OF MAKING COPPER TUBING Filed April 18. 1961 4 Sheets-Sheet 4 FIG. IO

. I2 I l l I k if INVENTOR. EDWARD v. CRANE BY UmmMT bfiniqk ATTORNEYS United States Patent 3,189,988 METHOD 0F MAKING COPPER TUEING Edward V. Crane, (Canton, Ohio, assignor to E. W. Bliss Company, Canton, Ohio Filed Apr. 18, 1961, Ser. No. 103,868 17 Claims. (Cl. 29-4205) This invention relates to forming tubular products from metallic powder. More particularly, this invention relates to a method of blending and compacting finely divided metallic powder into a green compact, removing impurities from the green compact, coalescing the metallic particles, and, thereafter, forming a tubular article from the compact.

It is well known that copper, nickel, and other nonferrous metals may be recovered from scrap, low grade ores, and from liquors obtained during beneficiation procedures involving high grade ores containing these metals. The metal recovered from these various sources may be precipitated in powder form having greatly varying particle sizes. Attempts to prepare flat shapes such as strips and bars from a green compact to powdered metals have been generally successful. Fabrication of metallic particles into shapes such as tubing by conventional techniques of powdered metallurgy has not, however, proved satisfactory. One of the difiiculties in forming metallic powder into dense shapes, other than strips and bars, has been the inability to avoid the inclusion in the final product of excessive amounts of metallic oxides formed by the readily oxidizable metallic powders. Another difficulty in forming dense shapes is caused by the fact that compacts, heretofore utilized, have been very dense and have resisted conventional metal forming techniques to convert them into shapes.

It is the general object of the present invention to provide an improved method for forming metallic articles in a continuous manner from metallic powder with the final article being substantially pure metal, extremely dense, and substantially oxide free.

It is another object of this invention to provied a method of blending and compacting finely divided metallic powder to obtain a green compact which is sufiiciently dense, having a self-supporting shape, while at the same time being sufiiciently porous to permit further operations for effecting the removal of undesirable oxides.

It is a further object to provide a method for removing from the green compact undesirable oxides, as well as impurities resulting from additives which may have been added to enhance the blending and compaction of the metallic powder.

A still further object of this invention is to prepare a metallic tubular article from a metallic compact by extrusion of the compact.

It is a still further object of this invention to provide a novel extrusion apparatus for forming the metallic tubular article.

Copper has been selected as an example of a metal which may be treated according to this invention. Ferrous and other non-ferrous metals and mixtures of such metals may be converted from metallic powder to extruded shapes according to this invention, as will be obvious to those skilled in the art.. Other objects and advantages will become obvious to those skilled in the 3,139,98 Patented June 22, 1965 art from a study of the specification taken in conjunction with the accompanying drawings.

In the drawings:

FIGURE 1 is a flow sheet illustrating the basic steps of forming metallic tubing from powder according to this invention;

FIGURE 2 is a perspective view of the general structure of the type of metallic tubing which may be formed according to the method of this invention;

FIGURE 3 is a front elevational view, partly in section, of the extrusion apparatus of one type which may be used to form metallic tubing from the compact;

FIGURE 4 is a front elevational view, partly in section, of the extrusion apparatus illustrating the general relationship of the apparatus and the compact before extrusion, and various shapes assumed by the compact before, during and at the end of the stroke of the extrusion punch, according to one embodiment of this invention;

FEGURE 5 is an enlarged view of the encircled portion of FEGURE 4 illustrating the coaction of various parts of the extrusion apparatus;

FIGURE 5A is a view similar to FIGURE 5, but with the punch and mandrel omitted from the View;

FEGURE 6 is a perspective view of a portion of the metallic tube made according to the extrusion apparatus illustrated in FIGURES 3 and 4;

FIGURE 7 is a front elevational view, partly in section, of the extrusion apparatus, illustrating the general relationship of the apparatus and the compact before extrusion, and various shapes assumed by the compact before, during and at the end of the stroke of the extrusion punch, according to another embodiment of the invention for extruding compacts in tandem;

FIGURE 8 is a front elevational view, partly in section, illustrating the coaction of the extrusion punch with compacts arranged in tandem;

FIGURE 9 is a front elevational view, partly in section, similar to FIGURES 7 and 8 outwith the extrusion punch further along in the extrusion stroke;

FIGURE 10 is a front elevational view, partly in section, similar to FiGURE 8 but with the punch at the end of the extrusion stroke in the tandem arrangement of the compact; and

FIGURE 11 is a perspective view of the metallic tube formed according to the embodiment of this invention illustrated in FIGURES 7-l0.

Referring to FIGURE 1, it will be seen that the first step of the method according to this invention is to blend the metallic powder particles prior to compaction. The purpose of this step is to uniformly mix the metallic powder, which is generally composed of minute particles of varying sizes, to obtain a particle mass having a uniform particle distribution. Preferably, the copper powder mass should have an average particle size of approximately 12.3 microns, although average particle sizes ranging from 10 to 12 microns have been found satisfactory for use in this invention. The use of an excessive percentage of copper particles of less than 10 microns has been found undesirable because tubes extruded from compacts formed of such powder have been found to contain blisters and cracks. The increased blistering resulting from the use of smaller than 10 micron size particles appears attributable to the greater amount of oxides due to the greater surface area of the particles. Cracking appears attributable to the presence of other impurities such as carbonaceous residues, which may be entrapped in the compact when it is formed, and which are not readily removed by subsequent procedures.

After the copper powder has been thoroughly mixed, a lubricant may be added to the copper powder mass. The lubricant serves to reduce the friction between individual particles during the compacting process, and to reduce the friction between the particles and the compaction die walls. The lubricant should possess a relatively low melting point, and preferably, be capable of melting under the influence of the heat generated during compaction. Metal soaps have been found to be excellent lubricants for this purpose. Such soaps include the stearate salts of barium calcium, zinc, lithium, and similar metals. A mixture of lubricants such as lithium stearate and Emersol 150 has been found advantageous according to a preferred embodiment of this invention. This lubricant mixture is formed of 0.25% lithium stearate and 0.2% Emersol 150 by weight of copper powder. Other lubricants such as zinc stearate and stearic acid may also be utilized, although each of these lubricants when used alone has been found less effective than the combination of lubricant materials mentioned above. In the event the lubricant, when added, causes lumping of the particles, the lubricantparticle mass may be screened, as with a 30 mesh screen to break up or remove the lumps.

The thoroughly blended mass of copper powder and lubricant is then fed to a compaction press for the formation of the green compact. Any suitable manual or automatic compaction press may be utilized for the formation of the compact. The compact utilized in forming the extruded tube according to this invention is cylindrical in shape and has central bore extending axially throughout the length of the compact. The particular dimensions of the compact, will, of course, vary with the extent to which the powder is compacted, and with the length of tubing desired from each extruded compact. The term green compact, as here used, refers to the compact formed from the metallic particles within the compaction apapratus.

The degree of compaction of the blended particle mass should be sufiicient to form a self-supporting compact, but should not compress the particles so closely together as to obtain substantially full density. Preferably, the compact should be self-supporting, porous, uniformly dense, and approximately 80-90% of full density.

The next step in the method of this invention involves the removal of impurities from the green compact. These impurities comprise oxides of the metallic powder which are entrained Within the compact, lubricant materials added to aid in the compaction process, and small amounts of other impurities residing in the powder mass and not removed during the recovery process. The removal of these undesirable components from the compact may be accomplished either in one step or in two steps depending on the size of the compact and the extent and nature of the impurities contained therein.

The two step procedure involves, first, a pre-burning operation for the removal of the lubricant, which has been added to the copper mass to enhance the compaction process, and other volatile components. The pro-burning of the green compact takes place in a furnace, or in an antechamber section of a furnace, heated to about 1200 F. through which the green compact is passed. The exposure of the compact to heat during pre-burning should be approximately 15-30 minutes, and the heating should take place in an inert atmosphere. In the preferred form of this invention, disassociated ammonia is used as the atmosphere within the slow burning furnace. The slow heating to which the compact is exposed during the preburning stage will cause substantially all of the lubricant materials to volatize and pass off as gases, leaving only minute quantities, if any, of residue lubricant materials,

or their chemical components, remaining within the compact.

The compact may then be subjected to sintering, the second step of the two step procedure, which functions to further remove the lubricant residues, reduce the oxides which have been formed, and to coalesce the metallic particles. Sintering is preferably performed at elevated temperatures in the range of 1920-1950" F, in an atmosphere containing reducing gases and inert gas components to minimize the possibility of oxidation of the metallic particles in the heated compact. The upper sintering temperature is just below the melting point of the metallic copper and is sufliciently high to coalesce the particles within the compact. The porosity of the compact permits effective removal of the undesirable oxides, because the reducing gases are able to permeate the compact. The atmosphere may suitably be disassociated ammonia which provides hydrogen for reducing the oxides, as well as the nitrogen to act as the inert atmosphere for preventing oxidation during the .sintering stage. In pracice, it has been found desirable to introduce the gases near the end, or cooling section, of the furnace, and to pass these gases through the furnace counter-current to the feeding of the compacts into the furnace. In this way, the heated compacts are protected by the inert atmosphere while they cool, and at the same time, heat is imparted to the gases.

It can be seen that the pre-burning stage is, in effect, a mild form of sintering. The pre-burning stage suflices to remove some of the undesirable components (as the lubricant materials), but is not sutlicient to perform all of the sintering functions of the sintering furnace. If the compact is small, preburning is generally not required because the sintering furnace is capable of removing the lubricant materials and the oxides in one step. Both steps are desirable when the compact is of a relatively large size.

The sintered compact is next coated with a lubricant. This lubricant is placed on all external surfaces of the compact, including the surfaces of the axial bore. This lubricant may suitably comprise an admixture of one of the well known stearate lubricant materials, such as lithium and zinc stearate and stearic acid in a volatile solvent as benzene. The solvent should be sufficiently volatile to provide a substantially dry, lubricant coated compact between the time the lubricant solution is applied and the lubricant coated compact is extruded. The use of a solution has the advantage of ease of application, and insures coating all surfaces.

A general arrangement of the extrusion apparatus (according to one form of this invention) found suitable for forming a tube, such as 2 shown in FIGURE 2, is shown in FIGURE 3. The apparatus comprises a punch 10 having an axial bore 12 which houses mandrel 14. The punch is preferably made of a sintcred carbide having a substantial cobalt content, in order that it may withstand the force to which the punch is subjected during the extrusion operation. The punch has a slightly convex face 16 to aid in centering the punch against the compact to be extruded. The punch also has an undercut portion 1% to form a lip 20 for the purpose of pinching off any flash which may extrude backward around the face of the punch, as will be more fully described hereinafter. The mandrel 14 may be made of substantially the same material as punch 10, or of an electrolized high speed steel, lapped lengthwise. The mandrel 14- has a tip 15 which is of a smaller diameter than the body of the mandrel.

Punch 10 has a conical portion 22 which is adapted to be grasped by the punch supporting elements of the ram of the press. A socket 24 is formed in conical portion 22 to accommodate the thickened end 26 of mandrel 14 for firmly seating the mandrel. A pressure plate 28 abuts against the back face of the punch and mandrel as shown to spread or distribute load intensity. The punch may be securely fixed to the ram 31 (see FIG. 8) of the press and aligned with the die opening by means of a suitable retaining rings 30 and 32. It should be understood that the details for securing the punch to the ram 31 form no part of this invention, and any suitable arrangement may be utilized so long as the punch and mandrel are firmly secured to the ram and aligned with the die opening. It should also be understood that the mandrel 14 may be integral with the punch 16, or, preferably, may be a separate element removably secured to the punch as described.

The die holder 34 is provided with a carbide or hardened steel insert 36, both being provided with a bore 38 extending through the insert 36 and the die 34. The hardened insert is preferably made of sintered carbide in order to withstand the extrusion forces. The hard insert or nib 36 has a contour 40 formed therein. The angle ,8 is the included angle of the contour and preferably should be between about 110 to about 150. The included angle of this contour is an important aspect of this invention, because too great an angle imposes excessive tensile strains on the mandrel 14 during extrusion, while too shallow an angle results in lapping of the ends of successive extruded tubes so that the tubes hang together. Bore 38 is slightly divergent in that it has a compensating slight taper outwardly from the entry end adjacent the nib 36 toward theexit end of the bore.

Secured to the face of the die is a container 42 provided with a hardened insert or liner 44, with the bore 46 of the container axially aligned with the mandrel 14 and with the bore 38 provided in die 34 and the insert 36. Bore 46 is slightly convergent in that it has a slight compensating taper inwardly from the end adjacent the punch toward the nib 49. The tapering of bores 38 and 46 is best seen in FIG. 3. The position of the punch with respect to the container and die at the beginning of the stroke is shown in FIGURE 3.

An annular stripping groove 41 (see FIGS. 3 and 5A) is formed at the junction of the liner 44 and the die insert 36. The stripping groove cooperates with the punch lip 29 to shear off that portion of the compact which may be forced behind the punch face 16 during extrusion, as shown in FIG. 5. The stripping groove also serves to keep the compressed butt end 62 of the compact from being pulled out of the die on the mandrel 14, as will be more fully understood from the description of the extrusion process given below.

In the operation of the extrusion apparatus, a compact 43 (see FIG. 4) is fed into position opposite the bore 46 of liner 44 with the bore 54 of the compact axially aligned with the mandrel 14. Preferably, the die should be heated prior to commencing extrusion in order to facilitate the extrusion process. Any heating means associated with the die may be used, as is well known to those skilled in the art. As the punch moves toward the die (from left to right in FIG. 4) the tapered tip of mandrel 14 will enter the bore 5% of the compact 48. As the punch and mandrel continue to move forward, the compact 48 is caused to enter the container and to occupy a position shown at 52. Continued forward movement of the punch and mandrel will compress the compact to the form shown at 54. In compressing the compact from 52 to the position at 54, the punch has in effect increased the density of the compact from approximately 80% to substantially 100%. With further movement of the punch and mandrel, the mandrel will enter the die bore 38, and the punch will force the compact into the contour 40 of the die to extrude the compact into the tube 60. At the end of the forward stroke of the punch and mandrel, the compact has a substantially conical butt end portion 62 residing within the nib 36 of the die, with the balance of the compact extending through and beyond the die in the form of the extruded tube 66. The stroke of the punch and mandrel is of such length as to prevent the punch from being bottomed in the die, i.e., with the punch face in contact with the die insert 36, to avoid damage to the punch or die members (see FIG. 5). The punch and mandrel are then withdrawn, during the return stroke of the press, and when the punch reaches the end of its stroke, another compact 48 is fed into the position shown in FIG. 4. The forward stroke of the punch and mandrel will then feed this compact into the container, will force it against the conical portion 62 remaining in the nib of the die, and will compress this second compact. Upon compression of this second compact, continued forward movement fo the punch and mandrel will force the conical residue 62 through the die to complete the extrusion of the first compact. The second compact will then be extruded by the continued forward movement of the punch and mandrel until it is substantially entirely extruded with the exception of a conical residue remaining in the nib of the'die.

At the end of the forward stroke of the punch and mandrel, the punch face 16 abuts against butt end 62, as shown in FIG. 5. As extrusion of the compact proceeds during this forward stroke, a portion of the compact adjacent the punch face will flow into the stripping groove 41, and a small amount of the compact may be forced between the punch lip 20 and the bore 46, as shown at 47 in FIG. 5. When the punch is withdrawn during the return stroke, the stripping groove 41 will serve to prevent the butt end 62 from coming out of the die on the mandrel, and the shoulder 49 of the stripping groove will coact with the punch lip 20 to shear off the portion 47 which may have been forced around the punch to produce a substantially burr free butt end, as shown in FIG. 5A.

It will be readily understood that one tube is extruded for each stroke of the press. This follows, because one stroke substantially extrudes all of one compact, and the next succeeding stroke extrudes the conical residue of the first compact, if any, and substantially all of the second compact, as described above.

The tube 60 which has been extruded according to the embodiment is shown in FIG. 6. It will be noted that the tube has a slight mark 64 some ditsance from the left end of the tube. This mark is in the form of a ring, indicated at 64, of a slight offset or difference in diameter due to thermal shrinkage, without, however, any appreciable difference in the Wall thickness of the tubing.

The basis for the formation of this ring will now be explained. As shown in FIG. 4, the compact is approximately 75% extruded during the forward stroke of the punch and mandrel. At the neck 66 (see FIG. 5) of the conical portion 62 remaining in the nib 36 of the die, there is a temperature differential. The extruded tube 60 to the right of this neck is at a very high temperature, being in the nature of approximately 800 F. to 1000 F. The substantially conical butt end 62 remaining in the nib of the die cools quickly to a lower temperature resembling the temperature of the die insert 36. This difference in the temperature results in a lesser shrinkage of the cooler butt end as it is extruded, and accordingly leaves the ring offset 64 at a point corresponding to the orifice 66. Although the offset ring is not reflected in a varying wall thickness or strength of the extruded tube, it does present a physical feature visible to the naked eye on the external surface of the tube.

, According to another embodiment of this invention, extrusion is performed under such conditions as to shift the ring 64 to an end position where it will be removed in trimming, without in any way varying the quality of the tube extruded from the compact.

eferring to FIG. 7, there is illustrated an embodiment which utilizes two compacts in tandem within the container. The punch and mandrel utilized in this embodiment are sustantially the same as those illustrated in FIG.

3, with the exception that the body of the mandrel 72 is significantly longer than mandrel 14, in order to be capable of passing through two compact elements in tandem. Mandrel 72 also has a tip 15 which performs the same functions as described above. Similarly, the container 7 7i), and liner 73 according to the embodiment of KG. 7, are substantially wider than container 42 and liner 44 shown in FIG. 4, in order to house the two compacts in tandem. The die and die inserts are the same as those illustrated in FIG. 4.

In the start up of the process according to the embodiment of FIG. 7, the punch 10 and the mandrel '72 are in their retracted position, that is, away from the container and die. The die container 7% contains one compact. For purposes of illustration, the compact adjacent the face of the die insert 36 is designated B, and the compact furthest from the die face, and between the compact B and the punch and mandrel, will be designated as A. At the start of the extrusion operation, compacts A and B are of the same size and shape, both having the same shape as compact A. As the punch and mandrel move toward the container and die during the first stroke of the press, the face of the punch will, contact the face of compact A, feed the compact into the die container, force compact A against compact B, and will compress both compacts A and B. Further movement of the punch will force compact B into the nib of the die and fully extrude compact B. In the tandem arrangement of compacts, the first stroke of the punch and mandrel serves to compress the two compacts within the container, such that a portion of compact B extends to or slightly into bore 38, with the face of the compact within the nib of the die assuming the configuration of the nib. During the next succeeding stroke of the punch, the force applied against compact A is transmitted through compact A to compact B, completely extruding compact B into a tube through bore 38 of the die. At the end of the second stroke, the die container 70 houses a compressed compact A which has a face adjacent the nib of the die conforming to the contour at of the nib. With the container housing one compact which is ready to be extruded, the sequence of operation of the embodiment utilizing compacts in tandem may be more readily explained.

Referring to FIG. 7, there is illustrated a compact B housed within the container 70 with a portion of the compact extending to or slightly into the die insert 36 such that a small portion of the compact may be extruded into the form of a tube :as at 74. While the punch and mandrel are in the return stroke position, as shown in FIGURE 7, a compact A, similar to compact 48, is fed into position opposite the bore 71 of container 70, with the bore of compact A axially aligned with the mandrel 72 and bore 38 of the die. Forward movement of the punch and mandrel will feed compact A into the container 70 such that compact A assumes the position A within the container. The arrangement of the punch, mandrel and compacts A and B at this point of the extrusion operation is shown in FIG. 8. Continued movement of the punch will cause compact A to abut against compact B, with the face of the compact (A) adjacent the face of the punch assuming the configuration of the face of the punch, and the face of compact A adjacent compact B assuming the contour of contact B as shown in FIG. 9. As the punch and mandrel continue to the end of the stroke, compact B is completely extruded through the die to form a tube 76 and compact A assumes the position formerly occupied by compact B, as shown in FIG. 10. The punch and mandrel are then retracted and the apparatus is in position to receive another compact to repeat the extrusion of the compacts in tandem.

As it will be readily understood, two compacts may be placed within the container 70 at the very beginning of the extrusion operation. However, once extrusion according to this embodiment continues, there will be one new compact and one compressed compact within the container at the beginning of the punch stroke, and only one compressed compact in the container at the end of that stroke. The stroke of the punch is of a length required for completely extruding one compact and to 55 forcing the second compact into the position formerly occupied by the extruded compact.

It will be noted that the extruded tube '76 (PEG. 11), has a slight mark 65 substantially at the end of the tube, as distinguished from the mark 64 shown on the tube in FIG. 6. Mark 635 is caused by substantially the same differential shrinkage phenomena which forms the mark in the tube according to the embodiment illustrated in PEG. 4 However, the mark as in the tube of FIG. ll is shifted to the end of the tube, because as noted in PEG. 7, the compact (compact B) is only slightly extruded during the first stroke of the punch. For that reason, only a very small portion of the extruded length of the tube is at a higher temperature, whereas the greater portion of the compact is Within the die, and consequently, at the lower temperature. The tube extruded according to the tandem arrangement of this invention permits the mark to be located near the end of the tube, such that when the tube is trimmed, the mark is removed without substantially affecting the length of the extruded tube. In this way, an extruded metallic tube may be obtained which has no visible marking, either internally or externally, making it suitable for those uses in which a slightly offset diameter is undesirable.

During the extrusion of compacts in tandem the mandrel tip performs an important function in reducing the impact load on the extrusion apparatus. As the tip passes through the compact and the face of the punch forces the compact into the contour 40 of the die during the start of the extrusion, the extrusion ratio will be relatively low because of the narrow mandrel tip. As extrusion continues, the extrusion orifice will be controlled by the difference between the bore diameter 38 and the diameter of the body of mandrel 14. The forward end of the tube will, as a result of the mondrel tip, have a slight thickening evidence by a reduced internal diameter as at 30 (see FIG. 9) due to the momentarily larger orifice at the start of extrusion. This thickened portion may be trimmed oif, if so desired. The mandrel tip, by controlling the change of extrusion orifice, eliminates the high peak load, encountered in extruding metal at the start of extrusion, if an attempt were made to achieve the maximum reduction at the very start of the extrusion.

Tubular articles formed according to the process of this invention have been found to possess properties superior in many instances to tubing extruded from billets of the metal. For example, a copper tube extruded according to this invention has been found to have finer grain size and higher tensile strength characteristics after annealing, than a tube made from commercially available copper metal. Copper tubes extruded from a compact, and annealed, possess a tensile strength of between 35,000 psi and a yield strength of between about 13,000 to 14,000 p.s.i., whereas commercially available tubes prepared, for example, from DHP copper (following ASTM Specification 13-75) and annealed in the same manner as the tubes formed according to this invention, possessed a tensile strength of about 28,000 p.s.i., and a yield strength of about 9,000 p.s.i. Tests for obtaining the above values were carried out using conventional test equipment, following accepted ASTM procedures. In addition, the copper tubes made according to this invention retain the fine grain structure even after annealing. On the other hand, the grains of tubes made from commercially available copper grow as a result of a coarser grain annealing.

Although this invention has been particularly described with respect to extrusion of copper compacts, it should be readily understood that the invention is not limited thereto, but encompasses other non-ferrous metallic compacts. Accordingly, the temperature ranges given, particle size distribution, lubricant materials, time intervals, for example, are to be considered as illustrative and not in a limiting sense. Similarly, the invention is not limited to the specific apparatus disclosed, as any suitable extrusion apparatus, feeding mechanism, compaction apparatus may be used to achieve the objects of the invention, Whether by a continuous operation or otherwise.

What is claimed is: 1. A method of preparing and extruding a sintered shape adapted for use in an extrusion press to form a wrought metallic object substantially 100% dense comprising the steps of:

providing a powder of a ductile metal having a limited number of particles less than microns and having an average particle size distribution in the order of 12 microns;

mixing a quantity of lubricant in said powder to lubricate the particles and to form a lubricant-powder mixture having a substantially uniform powder size distribution;

compacting the lubricated particles to form a porous green compact having a uniform density in the order of 18% of full density but substantially less than 100% dense;

sintering said green compact in a reducing atmosphere at a sintering temperature for said metal powder and for a period of time suificient to cause inter-particle bonding, the rate of heating being such as to first volatilize the lubricant whereby When the sintering temperature is reached substantially all of said lubricant is removed; and

extruding the sintered shape at an extrusion pressure capable of further compressing it to full density whereby the wrought object formed is free of pin holes or internal voids.

2. The method as set forth in claim 1 wherein said lubricant-powder mixture has an average particle size to substantially pass through a standard 30 mesh sieve.

3. The method as set forth in claim 1 wherein the metal powder is copper and the sintering temperature is about 1900 F.

4 The method as set forth in claim 1 wherein said lubricant is an organic composition at least one constituent of which includes lithium stearate and has a melting point sufficiently low to fuse under the influence of heat generated in compacting the lubricated particles.

5. The method as set forth in claim 1 wherein said reen compact has a density of approximately 80% to 90% of full density.

6. The method as set forth in claim 1 wherein the metal powder used is predominantly of copper and said green compact is heated slowly to a final sintering temperature of about 1900 F.

7. The method as set forth in claim 6 and comprising in addition the step of preheating said green compact for about 30 minutes to about 1200 F. in an inert or reducing atmosphere so as to remove substantially all of said lubricant prior to sintering.

3. A method of preparing and extruding a sintered annular compact adapted for use in an extrusion press to form wrought tubing substantially 100% dense comprising the steps of:

providing a powder of a ductile metal having a limited number of particles less than 10 microns and having an average particle size distribution ranging around 12 microns;

mixing a quantity of lubricant into said powder to lubricate the particles and to form a lubricantpowder mixture having a substantially uniform powder size distribution, said lubricant having a melting point sufficiently low to fuse under the influence of heat generated during compaction;

compacting the lubricated particles to form a porous annular green compact having a uniform density in the order of 80% of full density but less than 100% dense;

sintering said green compact in a reducing atmosphere at a sintering temperature for said metal powder and for a period of time sufiicient to cause inter particle bonding, the rate of heating being such as to first volatilize said lubricant so that when the sintering temperature is reached substantially all of the lubricant has evolved leaving a pure sintered compact for use in said extrustion press; and

extruding said compact at an extrusion pressure capable of further compressing it to full density whereby the tubing formed is free of pin holes or internal voids. 9. The method as set forth in claim 8 in which tubing is formed by extruding a plurality of said compacts fed sequentially to the press by the steps of:

partially extruding a first compact by a direct application of the extruding force thereto, the stroke of said press being restrained so as to leave an annular butt portion of the compact in the press compressed to full density; recycling the press and feeding a second compact thereto between the extrusion force and butt portion;

extruding the butt portion by first compressing the second compact to full density and thereafter transmitting the extrusion force through it to said butt portion; and

partially extruding the second compact so as to leave an unextruded and fully compressed annular butt portion in the press at the conclusion of each cycle.

10. The method as set forth in claim 9 comprising deforming said annular butt portion between a punch and mandrel and the threshold of the extrusion orifice of the press so that it is conical in shape and has a conical surface facing the direction of application of said extrusion force against which the second compact abuts.

11. The method as set forth in claim 1'0 wherein the metal powder is predominantly copper and the surface of the butt portion facing the threshold of the extrusion orifice is at an included angle of at least but less than 12. The method as set forth in claim 10 comprising in addition relieving the impact extrusion pressure at the initial application of the extrusion force by temporarily increasing the size of the extrusion orifice so as to extrude a slightly thicker walled tube at the start.

13. The method as set forth in claim 10 comprising in addition deforming a peripheral part of said butt portion into a recess circumjaoent the punch and continuing application of the extrusion force causing a reverse extrusion thereof into an undercut portion of the punch and shearing said peripheral part from the butt portion leaving a substantially burr free butt portion for reception of successive sintered compacts upon retraction of the punch.

14. The method as set forth in claim 13 wherein the radial edge of said butt portion has a smooth curvature in an axial direction and is retained in said recess to prevent said butt portion from being dislodged with the Withdrawal of said punch and mandrel.

15. The method as set forth in claim 8 in which tubing is formed by extruding a plurality of said compacts fed sequentially to the press and comprising;

feeding first and second annular compacts in tandem relationship into the press such that the second compact is behind the first;

compressing both compacts to full density and thereafter applying the extrusion pressure to said second compact to completely extrude the first compact, the press stroke being restrained such that the juncture between said compacts will be adjacent the threshold of the extrusion orifices at the end of the stroke;

recycling the press and feeding a new compact thereto behind the fully compressed second compact; completely extruding the second compact by first compressing said new compact to full density and theremasses 1 1 after transmitting the extrusion force through it to said second compact whereby each new compact will take up the position vacated by its predecessor with each successive application of the extrusion force so as to always leave a fully compressed compact in the press at the conclusion of each cycle.

16. The method as set forth in claim 15 in addition comprising relieving the extrusion pressure at the initial application of the extrusion force by temporarily increasing the size of the extrusion orifice so as to extrode a slightly thicker walled tube at the start.

1'7. The method as set forth in claim 15 comprising deforming the fully compressed compacts so as to form a orifice having an included angle of at least 110 but less than 180.

References Cited by the Examiner UNETED STATES PATENTS 2,001,134 5/35 Hardy.

2,290,734 7/42 Brassert 270-10 2,679,932 6/54 Burns 270-10 2,879,887 3/59 Hawtin 207--10 2,954,869 10/60 Swanson 2072 2,967,613 l/61 Ellis et al. 2072 3,075,244 1/63 Glenn 29-420 X WHITMORE A. WILTZ, Primary Examiner.

conical surface adjacent the threshold of the extrusion 15 PTPUIWD H EANES IR Examiner ,,.s1 Le. 1

Claims (1)

1. A METHOD OF PREPARING AND EXTRUDING A SINTERED SHAPE ADAPTED FOR USE IN AN EXTRUSION PRESS TO FORM A WROUGHT METALLIC OBJECT SUBSTANTIALLY 100% DENSE COMPRISING THE STEPS OF: PROVIDING A POWDER OF A DUCTIBLE METAL HAVING A LIMITED NUMBER OF PARTICLES LESS THAN 10 MICRONS AND HAVING AN AVERAGE PARTICLE SIZE DISTRIBUTION IN THE ORDER OF 12 MICRONS; MIXING A QUANTITY OF LUBRICANT IN SAID POWDER TO LUBRICATE THE PARTICLES AND TO FORM A LUBRICANT-POWDER MIXTURE HAVING A SUBSTANTIALLY UNIFORM POWDER SIZE DISTRIBUTION; COMPACTING THE LUBRICATED PARTICLES TO FORM A POROUS GREEN COMPACT HAVING A UNIFORM DENSITY IN THE ORDER OF 18% OF FULL DENSITY BUT SUBSTANTIALLY LESS THAN 100% DENSE; SINTERING SAID GREEN COMPACT IN A REDUCING ATMOSPHERE AT A SINTERING TEMPERATURE FOR SAID METAL POWDER AND FOR A PERIOD OF TIME SUFFICIENT TO CAUSE INTER-PARTICLE BONDING, THE RATE OF HEATING BEING SUCH AS TO FIRST VOLATILIZE THE LUBRICANT WHEREBY WHEN THE SINTERING TEMPERATURE IS REACHED SUBSTANTIALLY ALL OF SAID LUBRICANT IS REMOVED; AND EXTRUDING THE SINTERED SHAPE AT AN EXTRUSION PRESSURE CAPABLE OF FURTHER COMPRESSING IT TO FULL DENSITY WHEREBY THE WROUGHT OBJECT FORMED IS FREE OF PIN HOLES OR INTERNAL VOIDS.

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