US1896854A - Apparatus for making hard metal compositions - Google Patents

Description

Feb. 7, 1933. G F TAYLOR 1,896,854

` APPARATUS FOR MAKING HARD METAL CoMPosITIoNs Original Filed June 19, 1930 Invehtor: Geov' e T1 Taglor;

His At torneg.

v Patented Feb. 7,`I 1933 UNITEDV STATES PATENT ori-lcs GEORGE F. TAYLOR, OF NISXAYUNA, NEW YORK, AASSIGIEN'OB. T0 GENERAL ELEU'IBIO COIPANY, A CORPORATION OF NEW YORK APPARATUS FOB MAKING HARD METAL COHPOSITIONS Orlginal application med .Tune 19, 1930, Serial No. 462,888. Divided and this application illed July 7,

This application is a division of my copending application Serial No. 462,368, filed June 19, 1930.

The present-invention relates to a process and apparatus for simultaneously pressing and sintering powdered materials. The invention is particularly adapted for use in pressing hard metal compositions of the character described in Schrter Patents No. 1,549,615 and No. 1,721,416. Ordinarily, compositions of this character contain from about 97% to about 80% of tungsten carbide and from about 3 to about 20% of an auxiliary cementing or binding metal, for example cobalt, the tungsten carbide particles being distributed through a substantially continuous cementing matrix consisting mainly of the auxiliary metal.

Heretofore such compositions have been made by processes disclosed either in the above .Schrter patents or in the copending application of Samuel L. Hoyt, Serial No. 181,536, filed April 6, 1927, now Patent No. 1,843,764, or in' the Gilsonv Patent No. 1,7 56,857. The present process is closely related to the processes disclosed in the Hoyt -application and Gilson patent since the present process as well as the Hoyt and Gllson processes are carried out by simultaneously heating and pressingpowdered materials. wThe present disclosure however differs materially from the prior Hoyt and Gilson disclosures. First, it is carried out in a vacuum or attenuated hydrogen atmosphere` duce-a sintered product which is unusually Serial No. 549,150.

gowth does not take place and a ve strong e grained material is obtained. l.,.Yl'here is also insuicient time during the process for an exchange of elements between the mold and the pressed material. An exchange, for

example, such as graphite in the mold aber surface of the `pressed material nor squeezed into crevices such as the crevices around a loose fitting plunger since the walls of such a crevice are cold and a fused Huid or plastic material would freeze u on its first attempt to enter such a crevice. ourth, the present method has a particular advantage over prior processes for sintering powdered materials in thatpthe sintering temperature of various powdered mixtures is auto-` matically determined or controlled and never exceeds the sintering temperature of the mixture irrespective of the portions of materials employed in the pressed composition.

The novel features which I believe to be characteristic of the invention are set forth with particularity in the appended claims. `The invention itself however will best be understood from reference to the following specification when considered in connection with the accompanying drawing in which Fig. 1 shows diagrmmatically an apparatus whereby .my invention may be carried into effect; Fig. 2 is a perspective view partly broken away of an alternative form of an electrical insulating or non-conducting tube within which the powdered materials may be formed into a solid mass, while Fig. 3 is a dia# grammatical view of an electrical system which may be employed to automatically interrupt the electric current supplied to the pressed materials. c

Referring more particularly to the drawing, I have designated at 1 a receptacle comprising a `hollow glass cylindrical member 2 More- 1 tra 5 manner. The upper end of'cylinder 2 is provided with a flanged metal ring 6 similar to ring 4. Rng'6 provides a seat for a closure member 7.

The closure member 7 comprises a pair of 1 parallel metal plates 8 and 9 connected by a cylindrical, flexible, corrugated metal member 10 commonly known as a sylplion bellows. The up rplate 9 has an area preferably apprecie ly smaller than the arca of plate 8 so that atmospheric ressure will hold plate 8 firmly on ring 6. late 9 is movable and provided with a depending stem 11 adapted to have a reciprocating movement in an upwardly extending centrally disposed 9 guide or lbearing 12 integral with plate. 8. A

series of relatively small circumferentially disposed openings 13 extend through plate 8 adjacent the base of guide 12 so that pressure within the bellows member 10 and receptacle 2 may be equalized.

Plate 3 is provided with a central openingA 14 in alignment with the stem 11. A plug 15 having external screw threads a countersunk screw threaded ortion 16 is positioned in the opening 14. P ug 15 carries at its upper end a detachable extension 17 which has a short screw-threaded stem engaging the countersunk portion 16 of plug 15. A central bore 18 extends throu h plug 15 and. extension 17 and is connecte by means of a crossbore 19 with the( interior of container 1. A pipe 20 connects plug 15 to an evacuating pump not shown. Pipe 2O 1s also connected through a branch pipe 21 to a source of hydrogen supply.

In operation, the tube or mold 22, which may be made of ordinary glass or any well known heat-resistant glass, is partly filled with powdered material for exam le tungsten carbide and cobalt. terial is slightly compressed by means of molybdenum or steel plungers 23 and 24 inserted in opposite ends of the tube. Stem 11 and the extension 17 are in alignment and provided with slight depressions 25 and 26 within which the outer ends of plungers 23 and 24 may be seated.

To heat the powdered materials to the desired sintering temperature, an electric current is sup lied thereto by means of conductors 27 an 28 connected respectively to plug 15 and to an extension 29 which is integral with plate 9. v The pressure supplied to the powdered materials may be obtained entirely by atmospheric pressure. This source however may be supplemented to any desired extent by means of a lever 30 pivoted to a standard 31 and provided with a member 32 adapted to engage extension 29 on the plate 9. A'suit- The pow ered ma- 1,see,as4

able weight may be -applied to the lever 30 at any point therein to rovide any desired pressure on the owde material in tube 22.

The powdere material 33, which may consist of tungsten carbide and cobalt, is thoroughl mixed in a ball niill before bei place in the tube or mold 22. The mixe( powders are compacted slightly by lungers 23 and 24 and tube 22 positioned on t ie extension 17. The plate 8 is then positioned on ring 6 with stem 11 in engagement with plun r 23, as indicated in Fig. 1.

A r insertion of the tube 22, receptacle 1 is dashed out with hydrogen and then evacuated b means of a pump connected to pipe 20. en u suitable degree of vacuum is attained, as indicated by a mercury or other gage 34, valve in pi electric current appli to the powdered material 33 through the conductors 27 and 28.

The/powdered material is almost instantly heated to its sinterin temperature and the stem 11 simultaneously actuated by atmospheric pressure in a downward direction to thereby com act the powdered material into a dense har mass. The downward movement of stem 11 is only momentary. When the powdered material has been sintered and pressed into a compact mass the sintered material resists further. movement of the stem or plunger 11. This conditionof the compacted material which resists fuither movement of the plunger causes actuation of switching means to terminate the electric heating current.

In manufacturing cemented tungsten carbide, it is necessary to control the temperature accurately so that the material is heated to its sintering temperature and not to a lower or higher temperature.` The sintering temperatures of diiferent powdered mixtures however vary` depending on their composition. For example, a cemented tu n carbide containing about 16% cobalt with the remainder tungsten carbide has a materially differentsintering temperature from cemented tungsten carbide containing about 5% cobalt with the remainder tungsten carbide. Ordinarily, the sintering temperature of each different mixture is predetermined and controlled accurately as otherwise inferior tool material would be produced. An important feature of the present invention resides in the fact that, irrespectiveof the different proportions of materials employed in the mixtures, the sintering temperature of each mixture is automatically determined and the mixture never heated beyond that temperature.

The sintering temperature is that temperthe heat is substantially cut off although 20 is closed and an' Landau current ma still flow through the pressed material. his will be clear when it is observed that the original loosely compacted powdered mixture has a very high resistance whereas in its final highly compressed form it is a solid, dense mass having a relatively low resistance.

The operation of flushing out receptacle 1, evacuating it and heating the powdered materials to the desired temperature requires only one or two minutes or less, depending on the volume of the receptacle l. After the electric current is cut oli, hydrogen gas may be introduced into the container 1 and the plate 8 removed therefrom. The glass tube or mold 22 together with plungers 23 and 24 may then be taken out of the receptacle and the pressed mixture removed from the tube.

Although I prefer to employ a glass mold 22, the invention is not limited to molds of that type. Other molds may be employed if desired. For example, I have indicated in Fig. 2 an opaque tube or mold 36 which may be made of porcelain, magnesia, thoria or other suitable electrically insulating material. The opening through tube 36 may be of any desired shape. A transparent material, such as class or quartz, has the advantage that the process can be observed. Plastic materials such as porcelain have the greater advantage in that they can be extruded to any desired shape such as squares or triangles and also since they are opaque heat is not lost by radiation when they are employed as the mold material.

It has heretofore been impossible to successfully apply pressure ina lengthwise direction and to simultaneously sinter a powdered composition, such as tungsten carbide and cobalt, when the pressed material has a length materially greater than its diameter due to the fact that the pressure through Such material is not transmitted in the same manner as hydraulic pressure. Carbon molds and pistons which have heretofore been employed when such materials have been simultaneously -pressed and sintered break under the pressure required to form such a product in the above manner. With a substantially cold mold such as disclosed in the present application, it is `possible to apply pressure in a lengthwise direction and to simultaneously sinter a mass vhaving a length many times greater than its diameter.

ditions. The heating and pressing operation in the present case however is of such short duration that the body portion of the steel plungers cannot melt in that time. At the temperatures employed however, the inf ner end surfaces of the steel lungers that are in contact with the pressed) material be come fused thereto and a rigid joint is formed between the steel and the pressed composition.

Diliculty may sometimes be experienced in initiating a flow of current through certain powdered material when conductors 27 and 28 are connected directly to a relatively low voltage source of alternating current due to the high initial resistance of the powdered material. readily overcome however by connecting the terminals 27 and 28 to a suitable condenser 37. Condenser 37 is connected to a 2500 This dilliculty may be volt source of direct current 38 through a 2000 ohm resistor 39. When it is desired to initiate a How of current through the powdered material 33, a switch 40 is closed and the condenser permitted to discharge through the powdered material. The'switch 40 is then opened to' permit the condenser to be recharged. The condenser discharge reduces the resistance of the powdered material in tube 22 to such an extentthat when switch 41 is closed to connect terminals 27 and 28 directly to the low voltage side of a transformer the primary of which is connected to a commercial source of alternating current supply, current will flow through the powdered material and heat ,it to the desired sintering temperature.

The termination of the current flow from the main source of supply 42 may be controlled either manually or automaticall by a clock mechanism or electrical timing evice. If an electrical timing device is Vemployed an inertia switch designated as a whole by numeral 43 is mounted on the end of the lever 30. As shown inFig. 3 the switch 43 comprises an arm 44 which is pivoted at its inner end and carries at its outer end an iron armature 45 which cooperates with magnets .46 and l47 (Fig. l) `Inounted on the `lever arm 30. Armature 45 carries double contacts 48 adapted to engage a pair of upper contacts 49. and 50 and a pair of lower contacts 51 and 52.

Normally the switch arm 44 is heldf. by a slight magnetic force in the position indicated in Fig. 1, with contacts 48 :engaging contacts 49 and 50, as indicated in Fig. 3 of vthe drawing. In this position a condenser 534 is negatively charged and a connection is closed from the negative side of a battery .53 through contacts 50 and 49 to the grid member 54 of an electrostatically controlled arc discharge device 55. The discharge device 55 is employed in the system mainly for the purpose of maintaining a flow of electric current through the powdered materials 4 l meegaatA 33 for a predetermined period of time after initiation of the current How.

In operation, after the condenser 37 has been discharged, switch 40 is opened and switch 41 closed thereby connecting the secondary winding of a transformer 56 to the terminals 27 and 28.' To close the rimary circuit of the transformer 56, a p button switch 57 is operated closing a circuit for a coil 58 from line 59 through coil 58, ush button switches 57 and 60 to line 61. nergization of coil 58 closes a circuit for the primary win of transformer 56 from line 59 throng contactor 62, the primary winding of the transformer, contactor 63 to line At the same time a maintaining circuit 1s completed for coil 58 through the contactors 65 and 66, push button 60 and line 61.

When current ows through the secondary windin of transformer 56 and the powdered material 33, the latter becomes heated to a sintering temperature, softens, and lever arm descends with the plate 9 under atmospheric pressure. As the stem 11 reaches the end of its travel, the member 45 of the inertia switch continues its movement in a downward direction until the armature 45 engages magnet 47. The movement of amature 45 from magnet 46 to magnet 47 causes disengagement of the double contacts 48 and contacts 49 and 50 and engagement of contacts 48 with contacts 51 and 52 which are connected to the positive side of the battery 53. This action maintains the current through the pressed material for a redetermined short period of time after e plunger 11 reaches the end of its travel. The current is then interru ted by deenergizing coil 58, as hereinafter `sclosed. Armature 45 remains in engagement with magnet 47 and contacts 51 and 52 until raised manually to the position indicated in Fig. 1.

The length of time during which the cur rent is supplied to the ressed material after stem 11 reaches the en of its travel is determined by adjustment of a resistor 67, the capacit of condenser 53' and the character istics o the discharge device 55. Ordinarily condenser 53 is negatively charged and grid 54 is connected to the negative terminal of the battery 53 so that it has a negative potential impressed thereon of such value that no current flows in the output circuit of the discharge device 55, which controls the maintaining circuit for the coil 58. However, when switch member 48 is moved out of engagement with the contacts 49 and 50 and into engagement with the contacts 51 and 52, the grid 54 is connected to the positive terminal of the battery 53 through the adjustable resistor 67 and a positive charge is supplied to condenser 53'. The discharge device 55 may be made conducting Vwhen the negative charge on the grid element 54 is re* duced to a certain value or when a desired positive char is built up on the grid. The gridpotenti at which current ispermitted to flow will depend upon the construction of the particular device used and the anode potential employed. In the present instance there is illustrated a device having such characteristics that current will start to flow only when the plositive charge has neutralized the negative c arge on condenser 53 and a positivel potential is built up on the grid. This is accomplished after a predetermined period of time (for example from a fraction of a second up to about two and one-half seconds) and current then flows in the output circuit of the discharge device 55. Coil 68 is thereby energized and opens the inaintainingcircuit for the coil 58 at the contacter 66. When the maintaining circuit for the coil 58 is opened, the circuit for the primary winding of the transformer 56 is interrupted at the contactors 62 and 63 and current ceases to.

flow through the pressed material 33.

The temperature employed during the pressing operation is above 1000 C. but below the melting point of tungsten carbide, so that the resulting prod uct is sintered and not cast.

Material has been produced in accordancewith my process having a hardness number varying from about 88 to 91on the Rockwell C scale with kilogram load and a transverse modulus of rupture of about 350,000 pounds per square inch.

The time required for sintering the powdered materials may be only a second or a fraction thereof. Due to the shortness of the heating period and to the fact that substantially all the energy supply is employed in heating the powdered materials practically none is lost by radiation or otherwise. The energy required by the proce is therefore only a fraction of that heretofore required in sintering powdered materials such as cemented tungsten carbide.

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

1. In combination, an evacuated receptacle having a member provided with a depending stem, iexible means connecting said member and receptacle, an insulating tube adapted to contain powdered material positioned in said receptacle, means whereby said powdered material may be compressed by said stem, and means for simultaneously heating the powdered material to an elevated temperature whereby the powdered material may be formed into a compact mass.

2. In combination, a receptacle, a closure member connected thereto, said closure member includinglr a dependent stem, a flexible connection between said closure member and receptacle, means for positioning a container between one end of said receptacle and said stem whereby pressure may lie applied to material in said container.

3. In combination, a receptacle, means whereby said receptacle may be evacuated, a closure member for said receptacle, said closure member including a dependent stem rigidly secured thereto, a flexible connection between said closure member and receptacle, means for positioning a container between one end of said receptacle and said stem whereby pressure may be applied to material in said container, and electrical means for simultaneously heating said material.

4. In combination, a receptacle, a closure member for said receptacle, said closure member including a dependent stem rigidly secured thereto, a iiexible connection between said closure member and receptacle, means for positioning a container between one end of said receptacle and said stem whereby pressure may be applied t0 material in said container, means for simultaneously supplying an electric current to heat said material, and switching means actuated by a condition of said pressed material when it reaches the sintered state for automatically terminating said current. i

5. In combination, an electrical non-conducting tube partl filled with powdered material, a pair o electrically conducting plungers mounted in opposite ends of said tube, means for applying pressure to one of said plungers, means for supplying an electric current to said plungers and switching means actuated by a condition of said pressed material when it reaches the sintered state for automatically terminating said current.

6.. In combination, a mold, a plunger mounted in the mold and adapted to apply pressure to material in the mol-d, means for simultaneously heating said material, said means comprising a circuit including a source of power, and switching meansy actuated by a condition of said pressed material when it reaches the sintered state for automatically interrupting said circuit.

7 In combination, a' mold, a pair of plungers mounted in opposite ends of the mold, means for applying pressure to said plungers to thereby compact material in said mold, means for completing an electric circuit 'through said plungers to thereby heat the material in said mold and switching means actuated by a condition of said pressed material when it reaches thesintered state for automatically terminatin said current.

8. In combination a mo d, a plunger mounted in said mold and adapted to ap ly pressure to material in the mold, means or simultaneously heating said material, said means comprising an electric circuit including a source of power, switching means connected to said plunger for movement therewith, said switching means being automatically operable substantiall at the lower limit of travel of the plunger t ereby to interrupt said circuit.

9. In combination, a mold, a plunger application of heat to said material, said i switch being connected to said plunger for movement therewith.

In witness whereof, I have hereunto set my hand.

GEGRGE F. TAYLOR.

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