US2737456A

US2737456A - Process of making powdered metal articles without briquetting

Info

Publication number: US2737456A
Application number: US210259A
Authority: US
Inventors: Haller John
Original assignee: Allied Products Corp
Current assignee: Allied Products Corp
Priority date: 1951-02-09
Filing date: 1951-02-09
Publication date: 1956-03-06
Anticipated expiration: 1973-03-06

Description

March 6, 1956 J. HALLER 2,737,456

PROCESS OF MAKING POWDERED METAL ARTICLES WITHOUT BRIQUETTING Filed Feb. 9, 1951 Snneutor Gltornegs PRGCESS OF MAKING POWDERED METAL ARTICLES WITHOUT BRIQUETTENG John Haller, Northville, Mich., assignor, by mesne assignments, to Allied Products Corporation, Detroit, Mich, a corporation of Michigan Application February 9, 1951, Serial No. 210,259 1 Claim. (Cl. 75-400) This invention relates to powder metallurgy and, in particular, to processes of making powdered metal articles such as bearings.

One object of this invention is to provide a process of making powdered metal articles without the need for compacting or briquetting operations, thereby eliminating the necessity for compacting or briquetting presses and the equipment required for them.

Another object is to provide a process of making powdered metal articles wherein the powdered metal is placed in a mold to which it is non-adherent and which is capable of withstanding a sintering temperature, the mold and its contents being then heated to this sintering temperature in order to complete the process.

Another object is to provide a process of making powdered metal articles of the foregoing character wherein a core or insert of infiltratable metal is inserted in the powdered metal at a predetermined location, a chamber of the same shape and size as the core or insert being left in the powdered metal mass after sintering has been carried out.

Another object is to provide a process of making powdered metal articles of the foregoing character wherein the mold is chosen so as to have a lower coefiicient of expansion than the powdered metal so that during the cooling after the sintering operation, the powdered metal article shrinks more rapidly and more completely than the mold so as to be easily removable from the mold when the mold and its contents have cooled down to room temperature.

In the drawing:

Figure 1 is a top plan view, partly in horizontal section, of a mold containing a core or insert of infiltratable material, surrounded by powdered metal prior to sinter- 111g;

Figure 2 is a central vertical section through the mold and contents shown in Figure 1, also prior to sintering;

Figure 3 is a central vertical section similar to Figure 2, but showing the mold and its contents after sinter- 2;

Figure 4 is a central vertical section through the powdered metal article after its removal from the mold following the sintering operation; and

Figure 5 is a perspective view of the mold used for producing the sintered powdered metal article shown in Figure 4.

Heretofore, the manufacture of powdered metal articles, such as bearings, has required the use of briquetting presses wherein the powdered metal was compacted prior to its being placed in the sintering oven for sintering. Such compacting or briquetting presses are expensive to purchase and maintain and occupy considerable floor space in a factory. The compacting or briquetting operation also adds to the cost of the product and requires a skilled operator.

The present process enables the production of powdered metal articles without requiring a compacting or bri- 2,737,455 Patented Mar. 6, 1956 ice quetting press, particularly where high precision as to dimensions is not required in the article, or where subsequent machining of the article to the desired dimensions is necessary in any case. The present process employs a mold of high temperature resistant material, such as carbon, having a cavity corresponding to the shape and size desired for the powdered metal article. The powdered metal is placed in this mold, together with the core or insert of infiltratable material if a recess or chamber is desired in the article itself. The entire assembly is then subjected to the sintering operation in a sintering oven, whereupon the powdered metal particles become firmly and tenaciously united with one another and the insert or core, if any, infiltrates into the powdered metal, leaving a void or chamber of substantially the same size and shape as the core or insert. Moreover, the core or insert,-if made of suitable metals or metal alloys, densifies and thereby strengthens and reduces the porosity of the powdered metal article as well as making it more suitable for the use to which it is to be put, for example, sleeve bearings.

Referring to the drawing in detail, Figures 1 and 2 show a mold, generally designated 10, of a conventional high temperature resistant material, such as carbon, for example, graphite, in which a mold cavity 11 of suitable shape has been formed. The mold 10 must also be of material which will not allow with or be penetrated by its contents and thus make its contents not removable. For purposes of illustration, the drawings show a mold 10 with a cavity 11 suitable for the production of a sleeve bearing, generally designated 12 (Figure 4) and the proceeds if described herein as adapted to the production of a sleeve bearing 12 with a lubricant reservoir or oil well 13 encircling its central bore 14. The bearing 12 also has an outer surface 15, the

surfaces

14 and 15 being coaxial cylindrical surfaces with annular top and bottom surfaces 16 and 17 respectively.

The mold cavity 11, to produce the oil well bearing 12, is of annular or hollow cylindrical shape having outer and inner coaxial

cylindrical surfaces

18 and 19 respectively (Figure 2) interconnected by an annular bottom surface 20. The central portion 21 of the mold is thus of solid cylindrical shape and the outer portion 22 of hollow cylindrical shape. It will be understood, however, that these shapes may be varied in order to produce articles of different configuration, the annular sleeve bearing 12 being chosen merely for purposes of illustration.

If a chamber, recess or void 13 is to be formed in the article, an insert or core 23 is prepared of the desired size and shape and of metal or metal alloy which is infiltratable into the powdered metal of which the article is to be made. If, for example, the article is to be composed of powdered iron, then an insert of copper and 15% zinc has been found suitable for this purpose. Depending upon the characteristics desired in the final article, how-' ever, the composition of the insert 23 may be varied accordingly. Inserts of bronze, copper and even lead have been successfully used, the latter sometimes containing antimony.

In charging the mold 10, a suflicient quantity of the loose powdered metal, such as powdered iron, is poured into the mold cavity 11 up to the level at which it is desired to locate the lower end of the core or insert 23, if one is to be used. The insert 23 is then laid on the top of this layer of powdered metal and located in the desired position relatively to the

mold walls

18 or 19, with a view to locating the oil well or article chamber 13 at the desired location within the powdered metal article 12. When the core or insert 23 has thus been properly located, the filling of the mold with powdered metal is continued by pouring the loose powder into the mold on both sides of the insert 23 until the insert is completely covered and the mold cavity 11 is filled to the level of the top surface 24 of the mold 10.

The mold 10 with its contents (Figures 1 and 2) is then transferred to a sintering oven and sintering is carried out at an appropriate temperature above the melting point of the insert 23 but below the melting point of the powdered metal charge 25 and for a time period suitable for the particular powdered metal composition being used. For a powdered iron sleeve bearing 12 of the type shown in Figure 4, a sintering temperature of approximately 2020" F. for 30 minutes has been found suitable. During the sintering operation, the insert 23 melts and becomes a molten liquid which infiltrates into the pores of the powdered metal mass 25, densifying and strengthening this mass as well as leaving a chamber or void 13 where the insert or core 23 has been previously located, and of the same size and shape (Figure 3).

If a chamber or void is not to be formed in the article, and densification is still desired, this may be accomplished by placing a suitable quantity of infiltratable metal or metal alloy on top of the powdered metal charge 25, for an example, a cooper-zinc alloy. For the annular article 12, this may be in the form of a ring laid on top of the charge 25. When sintering takes place, the copperzinc alloy melts and infiltrates into the powdered metal 2S, densifying and strengthening it.

The mold and its contents are then allowed to cool down to a suitable handling temperature, during which cooling period the contents shrink slightly due to the lower coefiicient of expansion of the mold 22 relatively to the powdered iron charge 25 therein. Consequently, the sintered article 12 is easily removed from the mold 1t) and either used as it is or subjected to further machining operations. If the article 12 is a bearing, it is of course charged with lubricant in one of several ways known to those skilled in the powdered metal bearing art. One method is to immerse the bearing in heated oil, preferably in a vacuum tank which draws the air or other gases out of the chamber or void 13 and permits the oil to enter. Another method is to inject the lubricant, either in the form of a liquid or a thin grease, through the pores of the bearing body into the oil well 13 by means of a suitable pressing operation, or by means of a plunger in a cylinder containing the bearing and the grease or oil.

If it is desired to further improve the bearing qualities of the article, this can be done in the manner disclosed in my co-pending application, Serial No. 210,368 filed February 10, 1951 for Powdered Metal Bearing and Process of Improving the Bearing Qualities Thereof.

What I claim is:

A process of simultaneously shaping, strengthening and reducing the porosity of a powdered metal article while forming a completely enclosed chamber without compacting the powdered metal thereof, said process comprising providing a mold of sintering-heat-resisting material with a mold cavity of size and shape corresponding to the external size and shape desired for said article, forming a core of a densifying metal infiltratable into the powdered metal of which said article is to be composed into a predetermined size and shape corresponding substantially to the size and shape desired for said chamber, positioning said core in said mold cavity at the location desired for said chamber, placing a sufiicient charge of said powdered metal in a loose condition entirely around and above said core to completely bury said core in the loose powdered metal and fill said mold cavity to the desired level, maintaining said loose powdered metal charge in its loose condition while heating said mold containing said loose powdered metal charge and its buried core to a suitable sintering temperature above the melting point of said core but below the melting point of said powdered metal charge whereby to melt said core and infiltrate the metal thereof into said powdered metal charge so as to simultaneously create said chamber while strengthening and reducing the porosity of the powdered metal article thereby formed, cooling the mold and its contents, and removing the chambered sintered article from the mold cavity.

References Cited in the file of this patent UNITED STATES PATENTS 2,198,702 Koehring Apr. 30, 1940 2,227,308 Hildabolt Dec. 31, 1940 2,363,337 Kelly Nov. 21, 1944 2,571,868 Haller Oct. 16, 1951 FOREIGN PATENTS 452,503 Great Britain Aug. 17, 1936 564,905 Great Britain Oct. 18, 1944 591,142 Great Britain Aug. 8, 1947 595,793 Great Britain Dec. 17, 1947 608,124 Great Britain Sept. 10, l948 611,466 Great Britain Oct. 29, 1948