US2553714A - Process for making, and an article of, porous cemented carbide - Google Patents

Description

May 22, 1951 G. w. LUCAS 2,553,714

PROCESS FOR MAKING, AND AN ARTICLE 0F, POROUS CEMENTED CARBIDE Filed March 5, 194'? 2 Sheets-Sheet 1 ATTCRNEYS May 22, 1951 2,553,714

G. W. LUCAS PROCESS FOR MAKING, AND AN ARTICLE OF, POROUS CEMENTED CARBIDE Filed March 5, 1947 2 Sheets-Sheet 2 GROU ND SURFACE LSFHEROIDAL GRANULES DOINTED EDGE GROUND SURFACE? %volos IRREGULAR SHAPED PARTICLES ATTORNEYS Patented May 22, 1951 PROCESS 'FORYMAKING, AND AN ARTICLE or, POROUS CEMENTED CARBIDE George W. Lucas, St. Clair Shores, Mich, assignoll' to Carboloy Company, Inc., a corporation of New York Application March 5, 1947, Serial No. 732,581

I 4 Claims.

1 This invention relates to a process for making porous cemented carbide and articles of cement.-

. ed carbide having capillary porosity.

This invention contemplates a porous cement.- ed .carbide and a method of producing the same, which has a high degree of hardness, wearresistance, and capillarity which makes this ma- ;terial especially useful, for example, for bearings, drawing dies, and wear parts. The porosity or capillarity of thematerial gives it the highly desirable ability to retain, spread and transmit lubricant or coolant through the body and over the wear orbearing surfaces thereof.

In the drawings:

Fig. 1 is a side elevation partly in vertical section of an apparatus useful in preparing my pcrous cemented carbide.

Fig. 2 is a section along the line .22 of Fig. 11.

Fig. 3 is aplan viewof my apparatus.

Figs. 4 and 5 are sketches illustrating the wear surface comparison of my porous cemented carbide made from spheroidal granules (Fig. 4) and conventional cemented carbide made from irregular shapedparticles (Fig. 5).

In making my .porous :cemented carbides, I start with a powder consisting of any of the well known hard metal carbides, such as tungsten carbide, tantalum carbide, titanium carbide, and mixtures thereof, together with abinder metal of the iron group, such as cobalt, nickel or iron. When a mixture of tungsten carbide,

tantalum carbide and titanium carbide is used,

then preferably the tungsten carbide forms the larger component of said mixture. Thepro'por tion of iron group .metal binder used can vary over a wide range but usually the iron group metal will not fall below 3% by weight of the cemented carbide composition. The

.can vary as taught by the Schroter Reissue Patent 17,624 and Schroter 1,721,416, or over the wide range commonly used in the commercial production oftheabove cemented hardmetal carbides. The powder mixture of hard metal carbides and iron group metal will be reduced by any conventional method such, for example, as ballmilling, to an exceedingly fine powder having .a grain size usually not exceeding 20 :microns, and preferably well under-the 40 micron opening of-a. 325 mesh screen. To thi fine powder mixture I add a small amount of temporary binder such as .parai'fin, carnauba wax, candelilla wax, or oneof the many petroleum waxes, in an amount up to about 3% by weight. In addition small amounts of themoistening agent, suchas Water, acetone,

benzol, may be added if desired to facilitate converting the powdered mixture to a multiplicity of spherical or spheroidal particles. Preferably only sufficient temporary binder and moistening agent is used to cause the grains of powder to agglomerate or adhere to each other to form spheres or spheroids while being processed. The term spheroid will .be used herein to include any spherical or substantially spherical or essentially round or spherical body. The converting of the powdered mix into an aggregate of spheroidal bodies can be accomplished by any suitable method such, for example, as by tumbling in acylindrical container or by vibratory motion.

By way of example, I have illustrated one satisfactory apparatus for producing spheroids from this powdered mixture. This apparatus comprises a trough preferably inclined to the horizontal somewhere between 15 and .45. The trough l is preferably made from metal and positioned upon a flexible supporting frame generally designated 2. An electric vibrator 3, producing a strong, substantially vertical upward impulse, indicated by the arrow 4, is secured on the underside of trough I. Vibrator 3 can be of any conventional make, but 1 preferably use an electric vibrator which is sold under the trade-name Syntron. This .electric vibrator comprises in general a simple pulsating electromagnet and the air gap between the magnet and the armature of the vibrator is closed and opened every cycle of the current setting up several thousand vibrations per minute. The heavy mass of the armature moving at such a high speed causes a positive flow of powderful vibrations which are upwardly applied to the chute l in a vertical direction.

The powder and binder is spilled or flowed on to the trough l to give a thin layer. The vibration causes the powder to move upwardly along the inclined chute, as indicated by the arrows, and the powder spills back upon itself as it travels up the curved return bent portion 5 of the chute, thus forming spheroids. The spheroid size is determined by the angle of the trough, intensity of vibration and amount of powder spilled into the trough. The higher the degree of inclination the smaller the speroids. Thus, when the trough'is inclined from the horizontal, the spheroids produced will be smaller than when the trough is inclined, at say, 15 from the horizontal. It will be noted that the trough l in longitudinal section resembles a toboggan.

The bottom of the trough I will preferably have a parabolic curve, as shown in section Fig. 2. The spheroids, generally designated 6, automatically roll down the trough where they are screened by screen and are collected in container 8. The spheroids are all coarser than a 325 mesh screen opening and are comprised of thousands of individual powder particles. Sizing of the spheroidal aggregates is easily eifected by screen size separation. The selection of th size of aggregate depends upon the degree of porosity desired in the finished product. For example, for a fine type of porosity aggregates which will pass through a 100 mesh screen opening and be deposited upon a 325 mesh screen and for a coarser porosity aggregates which will pass through a mesh screen and collect upon a 100 mesh screen may be selected.

The spheroids thus formed are now subjected to complete sintering after first being mixed with a material such as alumina powder or lamp black which keeps the spheroids separated. The complete sintering consists of subjecting the spheroids first to pro-sintering at approximately 700 0., followed by sintering at about 1400" C. for approximately fifteen minutes. Th sintering changes the soft powder spheroids or aggregates into hard, fully sintered spheroidal granules such as illustrated at 9, Fig. 4. The spheroids are of the same shap as the original powder aggregates but they are smaller in size due to mass shrinkage resulting fromsintering. Volumetrically the shrinkage is about 40%. The sintered grains are now separated from the enveloping medium (such as alumina powder or lamp black) by screening, washing, or by air separation. The sintered granules may, if desired, be further sorted by screen size operation and are then ready for fabrication into the article desired.

To the spheroids which have been separated according to the siz desired, is now added a temporary binder such as paraffin, or one of the other petroleum or other waxes above mentioned. The sintered spheroids with their temporary binder are now pressed into their desired shape in a conventional steel mold and the pressure used will depend upon the percentage of voids desired. The pressure may vary from about 2 to about 30 tons per square inch. The spheroidal particles are thus brought into intimate contact with each other and are thereafter sintered which causes the particles to cement or fuse together at the points of contact. The resulting article, designated l6, Fig. 4, is comprised of firmly associated spheroids with the interstices between the granules providing voids of the capillary nature required. When the iron group binder is low, for example, from 3% to 6% by weight, it has been found advantageous to coat the spheroids with a thin layer of the iron group metal binder used in order to insure efficient fusing together at the points of contact. The coating of the spheroids with the iron group metal binder can be accomplished in any suitabl manner such, for example, as by electrodeposition.

As an alternate method, the granules may be lightly compacted in a graphite mold of the desired shape and sintered therein under the same sintering conditions as before. This method is especially advantageous when spheroids of relatively coarse size are used, for example, those which will pass a 20 mesh screen and collect upon a 100 mesh screen. Since the spheroids used in the final fabrication have been previously fully sintered, there is practically no additional shrinkage in the final sintering operation.

In articles made by the above-mentioned methods, thin oil is carried vertically by capillarity, inch in 30 seconds. This material can be advantageously used wherever a high degree of hardness, wear resistance, and self-lubrication by capillarity is desirable, for example, in bearings, drawing dies, and wear parts. Most applications of this material use small spheroids, for example, somewhere between 20 and 325 mesh, but for some applications it may be desirable to use larger spheroids, for example, spheroids having a diameter of anywhere from about .040 inch to about (.125) inch. Such spheroids can be made by mechanically pressing the powder to the size desired, or on the above described apparatus.

The chief advantages of a porous material made from sized spheroids is the fact that the rounded contours of the particles 9 when ground to a flat surface ll offer no tendency to cause scuffing on the opposing surface. This is not true of porous materials made from irregularshaped particles (Fig. 5) for upon grinding such a material to a flat surface, jagged edges and pointed surfaces may easily present themselves at the wear surface. This may be easily seen from the accompanying drawing comparing spheroidal and irregular-shaped particles. Other advantages that my material offers over solid cemented carbides are its oil retaining and spreading features plus its ability to transmit coolant or lubricant through the body of the material.

I claim:

1. A process for making porous cemented hard metal carbide articles having substantially continuous porosity comprising the steps of (l) forming spheroidal bodies by tumbling in the presence of a plasticizing agent a mixture of powdered hard metal carbide selected from the group consisting of tungsten carbide, titanium carbide, tantalum carbide and combinations thereof in which tungsten carbide is the major component and a powdered iron group metal, said hard metal carbide and said iron group metal having a grain size not exceeding ZOmicrons in diameter, (2) fully sintering these spheroids, (3) selecting sintered spheroids having a size falling within a range of from about 20 screen mesh to about 325 screen mesh, (4) pressing a multiplicity of the said sintered spheroids into contact with each other and heating the same to a sintering temperature at which thesaid sintered spheroids fuse together at their points of contact and maintain their identities as spheroids.

2. A process for making porous cemented carbide articles comprising the steps of (l) mixing powdered hard metal carbideselected from the group consisting of tungsten carbide, titanium carbide, tantalum carbide and combinations thereof in which tungsten carbide is the major component and a powdered iron group metal, said powdered hard metal carbide and said iron group metal having a grain size of less than 20 microns, (2) mixing a plasticizing agent with the aforesaid mixture, (3) forming spheroidal bodies from the plasticized mixture by tumbling the said powdered mixture, (4) fully sintering the said spheroidal bodies into sound imporous hard metal carbide bodies having a size falling within a range of from about 20 screen mesh to about 325 screen mesh, (5) pressing a multiplicity of the said sintered bodies into contact with eachother and heating the same to a sintering temperature at which the said sintered bodies fuse together at their points of contact and maintain their identities as spheroidal bodies.

3. A porous cemented hard metal carbide article produced by the process set forth in claim 1.

4. A porous cemented hard metal carbide article produced by the process set forth in claim 2.

GEORGE W. LUCAS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Welch Nov. 24, 1931 Number OTHER REFERENCES Powder Metallurgy by Schwarzkorf, 1947, page 13.

Claims (1)

1. 2. A PROCESS FOR MAKING POROUS CEMENTED CARBIDE ARTICLES COMPRISING THE STEPS OF (1) MIXING POWDERED HARD METAL CARBIDE SELECTED FROM THE GROUP CONSISTING OF TUNGSTEN CARBIDE, TITANIUM CARBIDE, TANTALUM CARBIDE AND COMBINATIONS THEREOF IN WHICH TUNGSTEN CARBIDE IS THE MAJOR COMPONENT AND A POWDERED IRON GROUP METAL, SAID POWDERED HARD METAL CARBIDE AND SAID IRON GROUP METAL HAVING A GRAIN SIZE OF LESS THAN 20 MICRONS, (2) MIXING A PLASTICIZING AGENT WITH THE AFORESAID MIXTURE, (3) FORMING SPHEROIDAL BODIES FROM THE PLASTICIZED MIXTURE BY TUMBLING THE SAID POWDERED MIXTURE, (4) FULLY SINTERING THE SAID SPHEROIDAL BODIES INTO SOUND IMPOROUS HARD METAL CARBIDE BODIES HAVING A SIZE FALLING WITHIN A RANGE OF FROM ABOUT 20 SCREEN MESH TO ABOUT 325 SCREEN MESH, (5) PRESSING A MULTIPLICITY OF THE SAID SINTERED BODIES INTO CONTACT WITH EACH OTHER AND HEATING THE SAME TO A SINTERING TEMPERATURE AT WHICH THE SAID SINTERED BODIES FUSE TOGETHER AT THEIR POINTS OF CONTACT AND MAINTAIN THEIR IDENTITIES AS SPHEROIDAL BODIES.

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