US1918064A - Method of making strong, thin, cemented carbide disks - Google Patents

Description

July 11, 1933. G.'F. TAYLOR METHOD OF MAKING STRONG, THIN, CMENTED, CARBIDE DISKS Filed sept.v 8'," v195o wmmm |.i4 will@ l Il.

Inventor: George FITQSIOY;

His Attorheg.

Patented July ll, 1.933

GEORG-E F. TAYLOR,

on N'ISKAYUNA', NEW YORK, AssIGNoR 'ro GENERAL ooMPANY, A coRPoRATIoN or NEW Yonx ELECTRIC METHOD oF MAKING STRONG, THIN, CEMENTED oARBipEDIsxs Application md september s, 193e. serial No. 430,330.

The present invention relates to the manufacture of strong, thin, fine-grained, cemented carbide disks, and particularly to disks of this character which have a central opening therethrough and are suitable for use as glass cutters and the like. Cemented carbide compositions are well known and are disclosed in Schrter Patents .#1,549,615 and #1,721,416. Such compositions generally consistof a sintered mixture of a carbide for example tungsten carbide, with a cementing or binder medium which has alower melting point than the carbide, for example cobalt, the cobalt usually comprising from about 3 to about of the'composition with the remainder tungsten carbide. While tungsten carbide and cobalt provide the preferred composition other carbides `such as molybdenum carbide and other binder elements such as nickel, iron, manganese and uranium I may be employed if desired.

Heretofore cemented carbides have been employed extensively as bits for cutting tools.' Such bits are relatively thick and mounted on suitable supporting Shanks.

Whileattempts have been made to manufacture thin cutting disks of the order of -llg inch in thickness or less from this material, it has been impossible prior to the present invention, to produce a satisfactory, tough,

fine-grained disk which Awould be fiat andA capable of ltaking a smooth, sharp, cutting edge when unsupported in a lateral direction. i

Cemented carbide is ordinarily somewhat brittle but when formed into very thm secy tions, it is so brittle that it is practically impossible to grind such a disk to astine, smooth cutting edge.l In addition to brlttleness, it is dithcult to produce 'very thin plates of cemented carbide thaty will lie perfectly ilat. Very thin plates of this material whether produced by squirting or by the process outlined in the above Schrter patents are somewhat porous and coarsegrained and have a tendency to becomev warped when red at the sintering temperature. If thin plates are made by the hotpress methods disclosed in the copending application of Samuel L. Hoyt, Serial N 0.181,-

composition.

536, led A ril 6, 1927 and in Gilson Patent No. 1,7 56,85 such plates are brittle and also coarse grained.

In the prior processes for making cemented carbide, the powdered materials from -which the cemented carbide is made is usually in direct contact for an appreciable periodbf timeeither with a carbon boat or mold during the sintering operation. It is my present opinion that this'contact with o0 carbon for an appreciableltime at a high temperature'is themain cause of the brittleness and coarse-grained structure'found in very thin plates formed by prior; processes.' Graphite ,has a tendency tov absorb cobalt at o5 the sintering temperature of cemented tungsten carbide and this action tends to increase the brittleness of the cemented material. Coarseness of the fgrain structure also has the same effect and this latter condition is a function of the time during which the cementing material is heated at the sintering temperature.

In my copending application Serial No. 363,079, filed May 13, 1927, I have disclosed J5 a method for producing thin plates of ce- 'mented carbide which are supported laterally by substantially coextensive molybdenum plates. When the sintered plates are supported, as disclosed in the above application, it is possible to produce a sharp cutting edge on the disk. The method disclosed in my prior application however is not suitable Afor the production oflaterally unsupported thin plates of cemented carbide of. the type described in the present application.

In my prior application, Serial No. 462,368, filed June 19, 1930,1` have disclosed an apparatus whereby a hard, tough and unusually fine-grained cemented carbide 90 may be produced by simultaneously applying heat and pressure in a vacuum to powdered materials comprising a hard `metal l employ the apparatus disclosed in the latter application in carrying out the present invention.

It is an object of the present invention to provide an improved methodyfor producingl thin, cementedcarbide disks which are capable of operation without lateral support.

understood from reference to the following specification when considered in connection with the accompanying drawlng 1n which Fig-1 represents a view partly in sectionv and partly 1n elevation of an apparatus whereby my invention may be carried into effect. Fig. 2 is a view partly in section and partly in elevation on an enlarged scale of a portion of the apparatus disclosed in Fig. 1, while Figs. 3 and 4 are detail views of portions of the apparatus disclosed in Fig. 1.

` ,per end' of the plug 4. TheA closure member 2 is provided with a central upwardly extending guide portion 9 adapted to accommodate a movable rod 10. The rod 10 is provided at its lower end with an extension 10 and carries at its upper end a iatm'etal plate 11 lprovided with an extension 12. Plate 11 is of smaller diameterthan closure member 2 and isconnected to the latter by means of a corrugated flexible member 13;. commonly known as a sylphon bellows. The portion of the member 2 which separates the interior of the sylphon from the interior of receptacle 1 is perforated with holes 14 whereby the pressure within the sylphon bellows 13 and the receptacle 1 may be equalized.

Pressure may be applied to the plate '11 through a lever 15 pivoted to a standard 16 and provided'with a depending portion 17 which is pivotcd `to lever 15 and. adapted to engage the extension 12 on plate 11. A weight (not shown) may be positioned at any desired point along` the lever 15 in order to apply a suitable pressure to the plate 11.

If desired, however, the standard 16 and lever 15 may be omitted and pressure apas hereinafter disclosed.

In fabricating .small cemented carbide metal cutting disks, for example disks about 0.15 inch in diameter, a hard glass tube 18 is employed as the mold, the latter having substantiallyeo|ual` to the diameter of the disks to be fabricated,

a wall thickness of about 1/8 inch or greater, and a length of about 4 inches or less. Plungers 19 and 20. made of iron or steel or other suitable metal, are mounted in opposite ends of the mold 18. The plungers are each about 2 inches long and provided with central holes 21 and 22' respectively. These holes extend in a lengthwise or axial direction about one-half way through the plungers andA accommodate a removable or temporary plug 23, about 30 mils in diameter, which is preferably made of quartz but may be made of graphite.

' In carrying out my invention, the tubular glass mold 18 is loaded by placing it in a vertical position, inserting the lower plunger 20l therein to the extent of about lg inch, then fixing the graphite rod 23 in the hole 22 of the plunger. 24 having a central opening therein of the same diameter as the graphite rod 23 is slid vover the rod 23 so as to rest on the upper end of the plunger 20. Pulverized cemented tungsten carbide 25, for example a powdered mixture consisting of about 13% cobalt and about 87% tungsten carbide in suiiicient quantity Atoproduce a sintered disk of about 1/64 inchY thick and about 0.15 inch diameter, is weighed out and placed on the graphite disk 24. The powdered material in the. mold 18 until the latter is filled to the desired extent. Plunger 19 is then inserted in the upper end of the mold and the latter positioned in receptacle 1 between cxtensions 8 and 10 as indicated in Fig'. 1. The extensions 10 and 8 are provided with adjustable bearing sleeves 26 and 27 respectively which accommodate the out/er ends of the plungers 19 and 20 and center mold 18 in receptacle and h'old the plungers rigidly in such .positions that their axes always fall along the same line. Bearing sleeves 26 and 27 may be constructed with openings of various diameters extendingl therethrough and may be employed to accommodate any desired diameter of plunger.

When the mold. 18 has been placed in position, the receptacle 1 is flushed out with plied to plate 11 `by the atmosphere only,

hydrogen which may be supplied through the 'opening 5 in the plug 4. After the hydrogen supply is cut off the receptacle is A thin, graphite disk of current supply (not shown) connected to the plug 4 and to the extension 12. This current is of suliicient intensity to heat the several layers of powdered materials 25 to to theirsintering temperature. The powdered materials are heated almost instantly tothe desired temperature and as they become heated plunger 19 descends and thepowdered materials are compressed i11- to a hard, tough, metallic composition which is uniformly fine-grained and capable of taking a very tine smooth cutting edge.

If a glass tube employed as the mold, the process may be observed clearly. YVhen the electric circuit 1s closed, the graphite disks within the mold are hea-ted' to a visible redness increasing to.incandescenee` In the meantime the sections 4of mixed tungsten carbide and cobalt powders are heated to their sintering temperature partly by radiation from the carbon disks and part-ly by the electric current which flows through the 1 powdered material. At the instant when the various separate portions of powdered material arrive at their sintering temperature, each portion is simultaneously compressed to about one-halt its original thickness. lThis compression of all the disks is completed in merely a fraction of a second. The electric heating circuit is then opened and hydrogen gas readmitted to the receptacle 1. 'lhemold i8 and plungers 19 and 2() are removed from receptacle 1 and while still hot plunged into water thereby breaking the mold and permitting removal of the pressed disks.

Ordinarily, atmospheric pressure alone is sutlicient to compress the powdered material to the desired thickness. This pressure however may be supplemented by pressure applied to the lever 15. As in my .copending application Serial-No. 462,368, the heating current may, if desired, be supplied to the pressed materialfor a predetermined length of time after the powdered materials have4 been pressed to the desired thickness, the circuit being controlled, as in the prior application, by a switch. 28 -mounted on the outer end of lever 15.

Since mold 18 is' electrically non-conducting, it is practically a cold mold'and there- `fore a very high pressure may be applied'to the sintered material. Moreover, since the powdered materials are heated for an unusushort period of time, for example for about 1/300th or 1 500th ofthe time required .to hot press similar powdered materials aceording tothe process disclosed in the above Hoyt application or Gilson patent, there is practically no opportunity either for grain growth in the pressed material or for absorption of cobalt by the carbon disks. As a result, a very. hard, tough and uniformly {ine-grained product is Obtained which mayv be supplied with a smooth keen cutting edge.

Cutting disks produced according to my process have a hardness of about to 92 on the Rockwell A scale. lVhile these disks may be supplied with a keen smooth cutting edge, this cannot ordinarily be done with the usual grinding apparatus but may be accomplished by a grinding wheel made ot' a mixture of cemented tungsten carbide and diamond powder as disclosed in my copen-ding application Serial No. 357,536, l'iled April 23, 1929.`

The small graphite disks may be prepared by cutting off sections otsuitable thickness i rom a graphite rod ot the same diameter. The graphite disks keep the siutered disks separate from one another and also prevent plungers 19 andl 20 from sticking to the pressed material.

` Instead of weighing the separate portions 25 of mixed powdered materials so as to obtain an exact quantity of material in each disk, I may squirt a tube-made from a suitable mixture Y of tungsten carbide, cobalt and starchpaste, remove the .paste by firing in hydrogen and then cut equal lengths of the tube and separate them, if desired, with paper. The latter may be reduced to carbon by charring, the heat for the latter purpose being furnished by the central graphite rod when heated by the electric current supplied through plug 4 and extension 12.

Although I have illustrated my invention in connection with cemented tungsten carbide,'it is not limited to that material alone. For example, I may hot press in a similar manner `a mixture 'of diamond dust and cemented tungsten carbide such as disclosed Vin thc copending application 'Serial No.

357,536 and form for example disk saws as thin aslg inch and l@ inch diameter. While such 'material is not as strong as cemented tungsten carbide alone, its strength may be materially increased by the addition of small molybdenum wires thereto. These wires should be about 0.010 inch in diameter and preferably in the shape of a Cor O should give it an eiiiciency far exceeding that of any small abrasive saw now in use. Small molybdenum wires may also if desired be added to the cemented tungsten carbideJ powdered materials' in the proportions inicated above. The molybdenum wires Vin either case act to reinforce the pressed owdered material in much the same way that steel reinforces concrete.

What I claim as new and desire to secure by Letters Patentof the United States, is:

' 1. The method of producingthin metallic verized mixture of tungsten carbide and.

cobalt between two layers of carbonaceous material in an electrically non-conducting mold, placing said mold in a receptacle, evacuating the receptacle, completing an electric circuit through the pulverized material to thereby heat it to itssintering temperature and simultaneously applying pressure thereto, said circuit being maintained not more than a .few seconds.

3. The method of simultaneously making a plurality of thin, cemented carbide disks which ,comprises placing alternate layers of carbon disks and powdered material comprising said carbide in an electrically nonconducting mold, placing said mold in a receptacle, evacuating said receptacle,- completing an electric circuit through said layers to thereby heat the powdered material to its sintering temperature, maintaining said circuit for a few moments, and simultaneline-grained ously applying pressure to the material in said mold.

4. The method for making a plurality of thin, cemented carbide disks which comprises placing a layer of powdered material comprising said carbidevin an electrically non-conducting mold, levelling said powdered material, superimposing a layer ofcarbonaceous material on said powdered material, lling said mold to a desired extent with alternate layers of said powdered material and carbonaceous material, positioning said mold ima receptacle, evacuating said receptacle, passing an electric current through said powdered and carbona-I.r ceus materials to thereby heat the powtemperature, pressure to dered material to its sintering and simultaneously applying the material in said mold.

5. In combination, a mold, a pair of oppositely disposed plungers mounted in the mold, means for positioning said mold and plungers in a receptacle, said means comprising a member with an opening therein to accommodate one of saidV plungers and an oppositely disposed movable member adapted to'accommodate the other of said plungers, said members each comprising an adjustable bearing sleeve engaging one of said'plungers. f

In witness whereof, I have hereunto set my hand this 6th day of September, 1930. GEORGE F. TAYLOR.

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