US2858565A - Method and apparatus for pressing powdered metal - Google Patents

Description

Nov. 4, 1958 F. J. LOWEYR 2,858,565

0 AN CORE ABOVE RAM! CE LL OWDE ED MA AL L6. AN RAML ULTANEOUS F0 CORE .16 ENG PRES D F R CE T ADVANC RA BY R @3151 '25 //A\\ Wmxm METHOD AND APPARATUS FOR PRESSENG POWDERED METAL Application June 23, 1955, Serial No. 517,519 5 Claims. (Cl; 1816.5)

This invention relates to a briquetting press for the production of powdered metal articles. 1

The formation of parts from powdered metals involves first the application of substantial pressure to the powdered metal material in a mold having the shape of the desired part. Pressure alone merely results in a self-sustaining compact which is quite weak, and high temperatures are necessary to effect sintering of the individual metal particles so that these in effect are welded one to the other to produce the rigid part desired. In most instances the application of pressure and heat occur as independent conditions, a so-called green compact or briquette being first produced which is extracted from the mold and then placed in a sintering furnace. The present invention is concerned primarily with the first of these two steps.

As was mentioned, substantial pressures are required to produce a powdered-metal briquette or so-called green compact in a mold activity. A problem that is commonly encountered during stripping or removal of the powdered metal briquette from the.mold is that the nited States Patent 0 briquette tends to expand as successive increments thereof are freed from the mold cavity. Thus, when the briquette is relieved of the pressure established in the briquetting press and stripped from the mold, the briquette, because of the tendency to expand in all directions upon release of the molding pressure, exerts a great deal of radial force of its own against the walls of the mold. While the briquette is being stripped, this radial force is gradually dissipated as successive increments of the briquette emerge from the mold cavity, but inasmuch as not all portions of the briquette emerge from the mold cavity simultaneously or in an absolutely "uniform or even plane circumstances thereby arise that tend to cause the briquette to crack or spaal and become distorted. Inasmuch as one advantage of powder metallurgy is to produce a part that requires substantially no finishing, it will be recognized that the foregoing are out of harmony with this.

Further undesirable manifestations of the foregoing tendency for the compact to expand upon emergence from the mold are that the mold, especially at the outer edge, is subjected to extreme wear conditions; the briquette undergoes an undesired cold working flashes are produced on the briquette; the walls of the mold tend to become worn unduly and such contributes to the loss or so-called blow-by of powdered metal from the mold during formation of the compact; and especially in deep molds, there is a tendency for the trailing corner or edge of the briquette to break 01f as this emerges last from the mold.

The object of the present invention is to overcome substantially the foregoing problems and disadvantageous effects by tapering or rounding the periphery of the mold cavity in a powdered metal briquetting press.

I Other and further obejcts of the present invention will be'apparent from the following description and claims and are illustrated in the accompanying drawing which while expanding;

by way of illustration, show a preferred embodiment of the present invention and the principle thereof and what I now consider to be the best mode in which I have contemplated applying that principle may be used and structural changes may be made as desired by those skilled in the art Without departing from the present invention and the purview of the appended claims.

In the drawings:

' Fig. 1 is a diagrammatic side elevation, part in section, of a press for briquetting powdered metal constructed in accordance with the present invention;

Fig. 2 is a sectional view on a reduced scale taken on the line 22 of Fig. 1 with the upper or stationary ram removed; and

Fig. 3 is a detail sectional mold wall.

The present invention is illustrated schematically in the drawing as embodied in a press 10 adapted to produce so-called or self-sustaining compacts of powdered metal that are to be subsequently sintered in a furnace. Such compacts may take various forms, and for the purpose of disclosure the press of the present invention will be described in respect to the production of bronze base annular powdered metal compacts of a well known kind that are adapted when subsequently sintered to be used as clutch facings. This of course is exemplary.

The press 10 includes a stationary ram 11, and at the under side the ram 11 is provided with an annular pressure ring 12 having diameter dimensions that will be mentioned below.

Arranged below the stationary, ram of the press is a movable'ram 15. The ram 15 is annular, serving as the movable bottom wall of a mold cavity, and is adapted to be actuated hydraulically in a Well known manner for a purpose to be mentioned;

Disposed within the inside diameter of the ram 15 is a mold core or plug 16, and surrounding the ram 15 is an outer mold ring 20.

Thus, the core 16 represents the inner wall and the ring 20 the outer wall of an annular mold cavity, open at one end and closed at the other by the ram 15 as will be described.

The core 16 and the outer mold ring 20 represent mold wall structure'adapted in a known manner to move or advance together relative to and independently of the ram 15. On the other hand, the ram 15 'is adapted to move independently of and relative to the aforementioned mold structure afiorded by the outer ring and the core to compress powdered metal in the mold. United States Patent No. 2,259,094 is illustrative of the relative mold movements involved. Thus, when the core 16 and the outer mold ring 15 are raised from the normal position shown in Fig. 1, a mold cavity is produced with the ram 15 serving as a movable bottom wall, and the core 16 and the ring 20 serving as inner and outer side view of the tapered walls, respectively.

by air under pressure (through means not shown) relative to the ram 15 as aforesaid so that the ram 15 in effect assumes a relative position below the dotted line position shown in Fig. 1. This defines a relatively shallow mold cavity having as a bottom wall the ram 15 and in this connection it is appropriate to point out that annular clutch facings as produced by the press 10 in the present instance may vary in thickness between 0.020 inch and 0.161 inch, although of course thicker compacts may be desired in some instances.

Under the present invention, the ring 20 having an inside diameter affording an outer wall of the mold cavity is tapered outwardly at 20T in the direction proceeding from the bottom of the mold cavity as above defined. Thus, when the ring 20 affording the outer wall of the mold cavity is raised the outer wall 20T of the mold cavity will be tapered outwardly in a direction proceeding from the bottom wall of the mold cavity. The vertical depth of the taper wall 20T represents the depth of the completed briquette, and hence when the press is operated to produce a briquette, as will be described, the bottom Wall of the cavity afforded by the pressure ring or ram will terminate at the lower edge of the tapered wall T, that-is, the smallest diameter of the tapered wall 20T.

In other words, the powdered metal article produced in the mold cavity thus defined will have a tapered outer circumferential edge, but inasmuch as this taper is slight the taper about the circumferential edge of the finished article is scarcely observable. In Fig. 3, the parts adjacent the outer wall of the mold cavity are shown on an enlarged scale, and the taper of the outer wall 20T relative to the straight side of the ram 15 is defined by the angle A. The depth of the mold cavity when full pressure is applied to the powdered material is indicated by the distance B, which as was mentioned will represent the thickness of the finished article. The angle A Will vary with the mold depth B, and the following is a tabulation of the typical relations found to be satisfactory for bronze base materials:

Mold depth B: Angle A 0.020 inch 15 0.022 inch 15 0.024 inch 15 0.045 inch 9 0.047 inch 9 0.161 inch 2.5

It will be observed from the above table that the taper of the outer mold wall is inversely proportional to the depth of the mold. For all except the 2.5? taper, the angle A may vary plus or minus one degree, and for the exception the tolerable variance is a half degree.

The amount of expansion of a powdered metal briquette when relieved of the molding pressure will depend primarily in part upon the kind of powdered metal used, and the foregoing table as was mentioned, is for bronze base materials such as a mixture including primarily copper, and some tin and lead. Empirically, the amount of expansion of a given powdered metal briquette when compressed can be first determined, if desired, and then the wall of the mold will be outwardly tapered as at 20T as that the distance D by which the wall as 20T is spaced from the opposed side of the ram as 15 will be equal to the amount of expansion to be expected. Since the thickness B of the compact will be predetermined, and since the expansion D to be expected of the pressed material is known, the angle A can then be calculated. Suitable functions or curves can be derived if found expedient for those situations where different kinds of briquettes are to be produced in a press as 10 at different times.

After the mold cavity has been defined in the manner set forth above, the stationary ram 11 is opened, and a spreader of a well known kind is interposed between the mold cavity and the upper pressure plate 12 to deposit the selected powdered material in the mold cavity. This deposit is then leveled ofl by the spreader so that the powder is substantially at the level of the upper faces of the core 16 and the outer ring 20.

The bottom wall of the mold cavity for the uncompressed powder will be below the plane indicated by dotted lines in Figs. 1 and 3 which is the plane assumed by the bottom wall of the mold cavity when full pressure has been applied to the powdered material. Empirically, the mold cavity for the uncompressed powder will have from the mold 4 a depth approximately two and a half times the thickness of the completed briquette. This factor will of course depend in part upon the pressure to be applied, which may vary between 10 and 15 tons per square inch.

Therefore, after the powdered material to be compressed has been leveled off in the mold cavity, and the spreader withdrawn, bearing in mind that the outer wall 20T and the plug or core 16 are held up by a first force alforded by air under pressure to define a full-depthed mold cavity, a second force afforded by hydraulic means is then operative to advance the lower ram 15, the core 16, the outer ring 20 together upwardly toward the stationary ram 11. As shown in Fig. 3, the outer edge of the pressure plate 12 overhangs the outer wall 20T of the mold cavity by'a distance C, and this distance may be of from one-eighth to one-fourth inch. Likewise, the pressure plate 12 is formed with an inside diameter ID, Fig. 1, that is of less dimension than the diameter of the core 16. Consequently, the core 16 and the outer ring 20 eventually will engage the pressure plate 12 about inner and outer circumferential edge portions respectively, and such halts advancing movement of the outer ring 20 and the core 16, and closes off the open end of the mold cavity. Further application of the second force will then advance only the ram 15, and this will account for compression of powdered material to the density desired in a mold cavity of gradually diminishing depth. In this connection, it should be stressed that the ram 15 will advance, while compressing the powdered material, from a plane below the lower or inner edge of the tapered wall 20T that is indicated by dotted lines in Figs. 1 and 3 to the plane which is at the aforesaid dotted line position. Thus, it was mentioned that the original depth of the mold cavity is approximately two and a half times the depth of the mold cavity when the briquette has been completely compressed, and referring to the table above for a final mold depth of 0.020 inch corresponding to a briquette of 0.20 inch, the original depth of the mold would have been approximately 0.050 inch so that the extent of travel of the ram 15 during compression of the powdered material would have been approximately 0.030 inch.

After the briquette has thus been formed, the outer wall or ring 20 may be first lowered while the ram 15 remains operative to clamp the briquette to the pressure plate 12 with approximately the final molding pressure. However, this is not essential and the ram 15, core 16 and outer ring 20 may be released simultaneously to free the finished article. As .the outer ring 20 is thus stripped away from the briquette the latter in efiect gradually emerges from the mold and because of the tapered wall 20T there is a uniform release of stress within the briquette and the undesirable effects that would be otherwise incident to expansion 7 of the briquette during stripping are nullified by the tapered wall 20T. There is thus produced a completely acceptable briquette in nearly every instance, and after the briquette has been removed from the press 12 the mold parts are redisposed in the normal position indicated in Fig. 1. As was mentioned, the resultant tapered outer edge of the finished briquette is scarcely apparent and moreover has no efiect on-operation of a finished article such as a clutch facing or the like.

It is not believed necessary to specify in detail the kind of powdered material to be compressed. These of course may vary extensively. Where clutch facings are being produced,-such may consist of a bronze, copper, iron or like base of corresponding powdered metal, suitably modified as to friction by additions of lead, silica and the like. Because of the tapered wall 20T, it is not necessary to operate the press in such a manner that during stripping the molding pressure is maintained against the opposed faces of the briquette. Thus, and such facilitates simplification of press operation and construction, shipping details set forth, but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

I I claim:

1. In a press of the kind described for applying compressive forces to powdered metal to produce a powdered metal briquette, means affording a side wall of a mold cavity for receiving the powdered metal to be compressed, said mold cavity having a predetermined width, a pressure plate for compressing powdered metal in said mold cavity, said pressure plate having a predetermined width greater than the width of said mold cavity, means to produce relative movement between said plate and wall means, means to produce relative stripping movement between a completed briquette and said side wall, and said side wall including a substantially true vertical portion merging in to an outwardly tapered portion terminating at the end edge of the mold cavity where a briquette subjected to stripping action as aforesaid first emerges from the mold cavity.

2. In a press of the kind described for applying compressive forces to powdered metal to produce a powdered metal briquette of predetermined thickness, means afiording a pressure plate, means affording an outer wall of a mold cavity, means for producing relative advancing movement between said wall'means and said pressure plate, said mold cavity having a predetermined width and said pressure plate having a width greater than the width of said mold cavity so as to have outer portions overhanging the means alfording said outer wall, said means defining the outer wall being adapted to engage said outer portions of said pressure plate incidental to said relative advancing movement so that the pressure plate merely closes oif and does not enter the mold cavity at the termination of said relative advancing movement, a movable ram means serving as the movable bottom wall of the mold cavity, said movable ram means, when the means defining the outer wall engages said portions of the pressure plate as aforesaid, being adapted to advance from a retracted position toward said compress powdered metal in the mold cavity between said pressure plate and said ram means, the periphery of said outer wall being tapered outwardly in a direction proceeding away from said movable ram means, and said outer wall in the portion between said periphery and the movable ram means in its retracted position being substantially truly vertical to define -a mold cavity for placement therein of powdered metal having a greater depth than said predetermined thickness of the briquette.

3. A method of producing a compressed briquette of powdered metal comprising, afiording a mold cavity having in its opened state :a bottom wall in the form of a movable ram and a side wall including a substantially true vertical portion extending above said bottom wall and an outwardly tapered portion defining the upper section of said mold cavity, filling said mold cavity thus afiorded with the powdered metal to be compressed, con1- pressing said powdered metal by advancing said ram in the direction of an opposing pressure member adapted to close 01f entirely the mold cavity at the wide end of said tapered portion of said side wall without entering said mold cavity, stopping said advancing movement of the movable ram substantially at the plane of the narrow end of said tapered portion of said side wall to produce a compressed briquette having a thickness corresponding substantially to the vertical depth of said tapered portion of said side wall, and stripping said side wall so that the compressed briquette first emerges at the wide end of the tapered portion of said side wall.

4. In a press of the kind described for applying compressive forces to powdered metal to produce a powdered metal briquette of predetermined thickness and outer dimension, pressure applying means, means affording an outer wall of a mold cavity of predetermined width, means for producing relative advancing movement between said wall means and said pressure applying means, said means affording said outer wall being adapted to engage said pressure applying means incidental to said advancing movement and said pressure applying means being of greater outside dimension than the outside dimension of said outer wall so that the pressure applying means merely closes off and does not enter the mold cavity at the time of such engagement, a movable ram means serving as a movable wall for the mold cavity, said movable ram means, when the means affording the outer wall engage the pressure applying means as aforesaid being adapted to advance from a retracted position toward said pressure applying means to compress powdered metal in the mold cavity, the periphery of said outer wall being tapered outwardly in a direction proceeding away from said movable ram means, and said outer wall in the portion between said periphery and the movable ram in its retracted A position being substantially truly vertical.

pressure plate to 5. A method of producing a compressed briquette of powdered metal of predetermined thickness comprising, aifording a mold cavity having in its opened state a bottom wall and a side wall including a substantially true vertical portion above said bottom wall and an outwardly tapered portion defining the upper section of said mold cavity, filling said mold cavity thus afforded with the powdered metal to be compressed to a depth greater than the thickness of said brequette, compressing said powdered metal by producing relative advancing movement between said bottom wall and an opposing pressure member adapted to close off entirely the mold cavity at the wide end of said tapered portion of said side wall without entering said mold cavity, said advancing movement being terminated substantially at the plane of the narrow end of said tapered portion of said side wall to produce a briquette having a thickness corresponding substantially to the vertical depth of said tapered portion of said side wall, and stripping said side wall so that the compressed body first emerges at the wide end of the tapered portion of said side wall.

References Cited in the file of this patent UNITED STATES PATENTS 2,111,701 Straub Mar. 22, 1938 2,509,783 Richardson May 30, 1950 2,543,439 Coomes et a1. Feb. 27, 1951 2,724,145 Hall Nov. 22, 1955 2,777,162 Banzhof Jan. 15, 1957

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