US 2189387 A
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Feb. 6, 1940. w. A. .WISSLER METHOD OF MAKING HARD COMPOSITIONS Filed March 5, 1938 INVENTOR WILLIAM A.WISSLER ATTORNEY METHOD OF HARD COMPOSITION? William A. Wissler, Niagara Falls, N. Y., assignor to Haynes Stellite Company, a corporation of Indiana Application March 5,
This invention relates to the production of cast hard compounds of diflicultly fusible metals, and compositions containing such compounds.
To produce hard, strong casings of the carbides 5 or other hard compounds of difl'icultly fusible metals, or of alloys containing such compounds, mixtures of the desired ingredients are ordinarily melted and the fused products rapidly solidified in molds and rapidly cooled directly after their solidification. The methods of melting and cooling heretofore in use involve the melting of small individual batches of compound, or the constituents thereof, in a crucible. The extremely high temperature required to melt the compounds limits the amount of material that can expediently be melted in any one batch by these methods and also causes excessive burning or scoring of the molds and crucibles. Ordinarily, a mold or crucible can be used only once, or at most only a few times. Further, such molds and crucibles usually consist of carbon and at the high temperatures involved the melt tends to pick up a substantial proportion of this element. Inasmuch as the carbon content of the cast hard compound must be within certain well defined limits to obtain a material of optimum physical properties much of the cast compound produced by the methods heretofore in use is often unsatisfactory.
An object of this invention is to provide a continuous or semi-continuous process, free from the disadvantages mentioned above, for the production of cast carbides, borides, silicides, nitrides, and other hard compounds, of the diflicultly fusible metals of the fourth, fifth, and sixth groups of the Mendelejeif periodic arrangement of the elements, with or without auxiliary metals such as iron, cobalt, and nickel. Another object is to provide apparatus suitable for use in practicing the process of the invention- A further object is to provide cast compounds of the class defined above in the form of elongated pellets.
These and other objects are attained in the process of the present invention which comprises preparing bonded mixtures of the desired ingredients and melting and cooling said mixtures in the manner explained below.
The invention will be described in connection with the attached drawing, in which:
Fig. 1 is a sectional schematic view of a form of an apparatus embodying the invention; and
Figs. 2 and 3 are sectional schematic views of alternative forms of the apparatus shown in Fig. 1.
In the production of cast hard compounds by a continuous process of the invention employing 1938, Serial No. 194,109 (01. -137) the form of the apparatus shown in Fig. 1, a mix 21, consisting of the desired ingredients, suitably in comminuted form, in the desired proportions together with a carbonaceous binder such as pitch, glue, or oil, or other binder, is placed in a mixing chamber 24 which suitably comprises a continuous screw 25, a die 23 having a plurality of small holes, and a second die 26 having a single opening preferably centrally located. The chamber 24 may, if desired be heated, in any suitable manner, to lower the viscosity of the bonding materials of the mix, thus ensuring a more intimate mixture between the comminuted dry ingredients and the bonding materials. The bonded mix 2! essentially contains at least one of the diflicultly fusible metals of the fourth, fifth, and sixth groups of the periodic system, for example, chromium, molybdenum, tungsten, titanium, zirconium, vanadium, columbium, or tantalum, or compounds of such metals, and at least one of the hard compound forming elements such as carbon, boron, or silicon, or nitrogen, or compounds of said elements, with or without one or more auxiliary metals such as iron, cobalt, and nickel.
The bonded mix 21 is forced, by means of thescrew 25, through the die 23 and the die 26 into and through a baking furnace 22, from which it emerges as a solid coherent mass or rod II. The baking furnace is heated by an electric resistance 28 or by other appropriate means.
' The rod H is connected as one electrode in an electrical circuit, and an electrode I2, preferably of carbon or graphite, is connected as the other electrode. Inasmuch as the process is continuous, the electrical connection may be made to the rod II by suitable contact with the mix 21 at a point near the baking furnace 22. Preferably, the rod II is made the positive electrode, and the carbon I 2 the negative electrode, but the polarity of the two electrodes may be reversed or an alternating current may be substituted for a direct current. The electrode l2 may be held by an electrode holding and feeding device M of any desired type to establish and maintain an electric are H] of constant length and of sufficient intensity to melt 'the electrode H. A cover l5 may be provided, if desired containing openings for the insertion of the electrodes and for the insertion of a tube 20 through which an inert or reducing gas, such as hydrogen or nitrogen, may be introduced. The cover I5 preferably consists of a non-conducting material; if the cover is a conducting material, it should be insulated from the electrode. The cover l5 and the electrode holding and feeding device M are supported on a platform 16 provided with an' opening I! through which compound melted by the heat of the arc ID, in the form of individual elongated pellets i9, is discharged by gravity into a receptacle l8 located under the opening I! and containing a quenching medium 2| such as oil, water, gas, or molten salt. The pellets l9 do not agglomerate or cohere, and theymay be removed from the quenching medium without interrupting the melting operation. If-desired, the pellets of cast compound may be cooled by other means, for example, by air cooling or by permitting the compound to remain in close proximity to a colder solid body.
In the production of cast hard compounds employing the alternative form of apparatus shown in Fig. 2, the rod II is prepared independently of the melting operation, and is melted in the simplified apparatus shown. The various parts of the apparatus of Fig. 2 are designated by numerals corresponding to those of Fig. 1 so that the description of meltingand quenching given in connection with Fig. 1 applies, in a like manner, to Fig. 2.
In the production of cast hard compounds employing the form of the apparatus shown in Fig. 3, the rod II, which may be prepared either as described in connection with Fig. l or independently of the melting and quenching operations, is melted by the heat of an electric are formed between carbonaceous electrodes I2. The method of quenching the melted compound is the same as that described in connection with Fig. 1. The form of the apparatus shown in Fig. 3 is especially applicable to the melting of bonded rods which are substantially non-conducting, for example, rods bonded with soluble silicate bonding materials such as sodium silicate.
Alternatively a conductive composite rod similar in composition to he rod ll may be substituted for the carbp electrode l2 in any of the forms of the apparatus and process described above.
A typical procedure for the production of cast tungsten carbide, employing the form of apparatus shown in Fig. 2, is as follows:
A pulverized mixture consisting of: Tungsten carbide (2.58% C.) 1 gm 2400 Cobalt gm 24 Carbon gm 12 Pitch gm 184 Oil cc 40 was heated and formed into a plastic mass and extruded, while hot, intoa composite rod fivesixteenths of an inch in diameter. The rod was then baked to convert the pitch into coke and to form a solidly cohering mass. An arc was formed between the composite rod connected as the positive electrode, and a graphite rod connected as the negative electrode, in a direct current circuit. A currentofabout 200 to 250 amperes was used. As the composite metal rod melted, the molten material, in the form of individual elongated drops or pellets, was immeamass? diately discharged by gravity into a receptacle containing water. A chemical analysis 01' the cast tungsten carbide and cobalt composition so produced revealed that it contained 3.6% carbon, which is approximately the carbon content required for optimum physical properties in a cast hard compound of this type. Furthermore,
of illustration, and the present invention is not limited to or by such examples. Although I have described the production of cast tungsten carbide alloy as an example, it is within the invention to produce carbides, borides, silicides, nitrides, or other hard compounds of any of the difiicultly fusible metals such as chromium, molybdenum, tungsten, vanadium, columbium,
tantalum, titanium, or zirconium, or alloys containing such hard compounds.
By the method of the present invention, crucibles, molds, and other expensive refractories heretofore used in the production of cast hard compounds are eliminated. Also, the recovery of cast compound in relation to the amount of composite rod melted is comparatively high. Further, the carbon content of the compound may readily be held within the narrow composition limits necessary to produce a cast hard compound of optimum physical properties. The method of the present invention may be made either continuous or semi-continuous, thus permitting greater flexibility in the production of cast hard compounds than heretofore available.
Cast hard compounds produced in accordance with the invention are ordinarily in the form of elongated pellets which are substantially homogeneous in structure and composition. Such pellets are suitable for use as hard facing material for tools, or in other applications where high resistance to wear and abrasion is one of the requisites of the material. They may readily be applied to metal surfaces by welding, either electric or oxy-acetylene, or by any other well known methods. If desired, the pellets may be enclosed in a metal sheath, or bonded with a suitable binder, and advantageously employed in this manner as hard facing welding rods.
A method of producing cast compositions of the class described which comprises mixing the ingredients thereof with a binder; forming said bonded mixture into a solid rod; melting said rod by the heat of an electric arc formed between said rod and a carbonaceous electrode, and promptly discharging the fused composition by gravity'into a cooling medium.
- WILLIAM A. WISSLER.