US2188873A - Making articles from powdered components - Google Patents

Description

latented Jan. 30, 1940 PATENT OFFHQ MAKING ARTICLES FROM POWDERED COMPONENTS Gregory J. C'omstock, Fairfield, Conn., assignor to Handy & Harman, New York, N. Y., a corporation of New York No Drawing.

Application January 10, 1988,

Serial No. 184,235

11 Claims. (01. 29-1605) This invention relates to the utilization of the noble metals, this term being used to include not only the metals'gold, palladium, platinum, and silver, as such, but also alloys containing a high percentage of one or more such metals. These metals possess properties which make them advantageously suitable for various industrial uses, but their employment in such fields has been restricted because of high cost, or

because they lack a property or properties necessary or desirable for particular uses. Accordingly an important object of the present invention is to provide these noble metals in forms in which their advantageous properties can be utilized at low cost, thus extending their range of use for purposes where cost is an important if not a controlling factor. Another object is to provide articles possessing not only the desired advantageous properties of these metals, go but also advantageous properties of other ma terials, as for example carbon (in the form of graphite), nickel, chromium, molybdenum, titanium, tantalum, and tungsten, and the carbides of the four last named. In general, the non-noble metallic components have melting points between about 2645 F. to 6150 F. The objects stated, and other objects, are accomplished by a process by which the metals are combined in such way that their individal properties, as for example ductility, malleability, hardness, resistance to wear and oxidation, are preserved. For this purpose the component metals of the combination are not alloyed together or dissolved one in another to any substantial extent but are in the form of interlocking networks which are, however, molecularly adherent to one another. In the process by which I attain this condition and state of the component metals the several components, at least one of which is a noble metal, are mixed in powder form until the powders are uniformly dispersed in each other, after which the mixture is subjected to high compression (preferably, but not necessarily, without simultaneous heating) 5 to produce a compacted billet. The billet is then subjected to alternate heating and mechanical deformation until the whole is converted into the interlocking network condition, in which the individuality of the component metals is preserved. In this way the original billet can be converted into a product in which the distinctive properties of the individual components are substantially maintained instead of undergoing the modification which occurs when a the component metals are mixed with all or any of them in the molten state. Thus, for example, from silver and nickel powders I am able to produce strip, sheet, rod, and wire, in which the silver and nickel exist as such and have their distinctive properties substantially 5 unimpaired. From products so obtained, articles can be made by ordinary shaping and fabricating operations, such as, for example, bending, stamping, coining, drawing, and forging.

It is to be understood that the components 10 need not all be metals. One may be non-metallic, for example graphite or a carbide, but in such case the network is composed of the metallic component with the non-metallic material in its interstices. In any case one component at 15 least is a noble metal, and this, from its importance in the processand product, may be conveniently termed the major component; the non-noble material, whether wholly or partly metallic or non-metallic, being termed the minor 20 component.

The content of noble metal in the powder mixture should not be less than 40 per cent by weight, and should be higher in mixes containing an appreciable amount of a non-metallic 25 material. Thus where the components are silver and graphite the former should be at least per cent, preferably not less than 93 per cent, better still 94 or 95 per cent. If the minor component is wholly metallic the preferred lower 30 limit of content of the major component is from 60 to '70 per cent, particularly advantageous amounts being 80, 85, 90, and 95 per cent, especially when the major component is silver and the minor is molybdenum or tungsten with or 35 without 4 or 5 per cent of graphite.

In most cases the particles composing the powder mixture are not coarser than -mesh, preferably finer. Powder particles small enough to 'pass through a 150-mesh screen but remain on one of 300-mesh have been found suitable.

The mixing of the selected components should be thorough, and in some cases hours of agitation in a paddle mixer may be required, especially when the components differ much in specific gravity. To avoid gravitative separation, the mixture should be used promptly or carefully protected from vibration.

The selected mixture is compressed in a die, preferably one with plane perpendicular walls, 50 under a pressure great enough to produce a billet which, though somewhat brittle, is sufliciently firm to be handled without breaking or crumbling. A pressure of at least 20 tons per square inch, gradually applied, is desirable and in some 5 cases may with advantage be much higher and may be repeated several times. The compression can be effected at room or climatic temperature, or with heat at a temperature well below the -melting point of the lowest melting component. In the case of silver 1350" F, is in general high enough.

The billet, hot or cold pressed, with or without cooling, is heat-treated, at a temperature which is below the melting point of the lowest melting component but which will weld or sinter the noble metal particles together, and preferably to the particles of the non-noble metal or metals also. The time required to produce an efiective adhesion of the particles composing the billet depends to a considerable extent upon its composition and size, and a full hour or more may be necessary. For accurate temperature control the heat-treatment is conveniently effected in an electric furnace. The atmosphere in which the heat treatment is carried out should be reducing or non-oxidizing. For silver-nickel, molecular hydrogen is preferred. Split ammonia may be used with silver-nickel, and nitrogen or combusted illuminating gas for silver-graphite, but for silver-molybdenum, silver-tungsten and any other carbide-forming metal molecular hydrogen should be employed unless a carbide is present or desired in the billet.

The billet can now be worked cold by rolling, coining, or forging, attempts to work by extrusion or drawing not being recommended at this stage, even at a high temperature. Using several roll passes at room temperature a reduction of 15 to 25 per cent in thickness of the billet is obtainable without great diiiiculty with a noble metal content of 60 per cent.

Before further reduction is attempted a further heat-treatment should be applied. In this step the temperature may be slightly less than that of the first heat treatment, but with the time and other conditions the same. After this treatment the cooled .work is again rolled or other wise cold worked, in which step a less proportional reduction is usually desirable than in the first reduction, as for example a decrease of 10 to 20 per cent in thickness, with corresponding increase of length or width or both.

In succeeding heat treatments, between further reduction by cold working, the time and temperature can in most cases be considerably less than in the previous steps, as for example (in the case of silver as the major component) a temperature of 1500 F. or even lower, for less than half an hour. Also, reductions of as much as 30 per cent can be effected by cold working.

By alternating heat treatments and workings, sheets and rods can be produced, suitable for further reducing or shaping by rolling, pressing, drawing, spinning, bending, forging, extruding, stamping, coining, and other mechanical operations. Such work as extruding is better done hot.

The following is given as a specific example of the process as practiced in the preferred manner to produce sheets with 60 to per cent silver and the rest cobalt, molybdenum, nickel or tungsten.

A homogeneous mixture of silver powder fine enough to pass a -mesh screen but be retained on a 300-mesh screen, and nickel powder of about '250-mesh particles, is prepared, with a silver content of 60 per cent and the rest nickel.

650 grams (20.9 oz. troy, 22.9 oz. av.) of the mixture is put into a square die 3 inches on the side, and subjected to a pressure of 200 tons to reduce the mass to a thickness of from .52 to .57 of an inch. The mixture may be gradually heated, during pressure, to a temperature not nipre than about 1450" R, but heating is not necessary. In either case a billet is produced which is strong enough to be handled. The billet, or a stack of similar billets, is placed in an electric furnace of the tunnel type, through which a stream of moi ecular hydrogen is maintained, and is heated therein for an hour at a temperature of 1710" to 1740* F., preferably the latter. After cooling, the billet is passed one or more times between rolls'and its thickness reduced to, say, .45 or .425 of an inch. A second heat-treatment is then applied, like the first but at a slightly lower temperature, say from 1680 to 1700 F., followed by rolling to a thickness of from about .37 to .35 of an inch. If the material still needs further reduction to fit it for final shaping, additional heat treatment and rolling steps are effected. These additional heat treatments are usually carried out at a temperature of about 1200 F. and for a time of about 3 to 10 minutes, and in most cases can be effected in a bath of a molten salt or mixture of salts.

For a product in which the refractory component is non-metallic in whole or in part, the following preferred practice with a silver-graphite mixture is given as an example.

The silver powder is 300-mesh or finer and the graphite at least as fine, the silver being 95 per cent, graphite 5 per cent. The powders are mixed for from 3 to 4 hours in a paddle mill. Single charges of 250 grams each are cold pressed in 3x3 inch dies using 200 tons total pressure, 1. e., about 22 tons per square inch. These billets, about .200 to .210 of an inch thick, are sintered in combusted illuminating gas 1350 F. t0,1650 F. and holding them at heat for about 30 minutes. They are then hot pressed, using an approximate temperature of 1350 F. and applying 3000 pounds pressure as a final pressing load, with but slight decrease of thickness, say not more than a few thousandths of an inch. They are then sintered at about 1650 F. and rolled at room temperature by passing them through a rolling mill to about ,180 of an inch in two passes. They are again heat-treated as previously. They are then rolled at room temperature at about .160 of an inch (in two passes through the rolls), are reheat-treated as before and rolled as before to about .140 of an inch. Alternate reductions and heat-treatments are continued until a sheet of the final desired gauge is produced, for example .012 of an inch. The last reduction may be followed by annealing at a relatively low temperature to remove work hardness if the soft sheet is wanted. This may also be done with silver-nickel and other all metal compositions.

If the product is to be used as stock for drawing wire or rod. the billet should be made in bar form, preferably square in cross-section. The following is the preferred practice for producing a wire of 95 per cent silver, 5 per cent molybdenum. Wire-billets are pressed %x%x6 inches, 22 tons per square inch. The first heat-treatment is in hydrogen to a temperature of 1675 F. to 1700 F. The billets are then reduced about 10 per cent on square rolls with relieved edges and are again heated, further reduced in rolls, again heat-treated and reduced. After this the billets are usually sufliciently non-porous in character to permit their being heat-treated in a molten salt bath. The alternate mechanical deformation by rolling at room temperature and heat treatment in hydrogen or salt is continued until the billets have been reduced to about .125 of an inch in thickness (approximately square). They are then drawn through suitable wire drawing dies to a finish gauge, being annealed (when necessary because of work hardening) in molten salt at 1200 F. This practice is continued until pable of being readily shaped by ordinary fabrieating operations to provide articles which can be used with substantially the same advantages as like articles made wholly of the noble metal component, and in some cases more advantageously, as for example where one or more properties of the non-noble component are necessary or desirable. The product finds marked utility for making jewelry and for ornamenting articles made of common metals or materials, for making hollow ware, table ware, and the like, and for making articles and parts desired in the electrical and other arts and industries.

It is to be understood that the invention is not limited to the specific details herein described but may be carried out in other ways without departing from its spirit as defined by the following claims.

I claim: a

1. In a method of making sheet, strip, rod and other articles from a mixture of powders consisting of a noble metal component and a minor component, wherein the noble metal component is at least about 40 per cent of the whole,-and

wherein the powders are mixed until the components are evenly distributed and wherein the mixture is compressed to form a billet, the procedure for producing a wrought article which includes successively heat-treating the billet and working by mechanical deformation intermediate successive heat-treatments, to cause adherence of the metallic particles into a network form in the final wrought article, said heat-treating and working procedure at least comprising first heating the unworked compressed billet to cause the metallic particles to adhere one to another, then working the billet with substantial mechanical deformation thereof, and then heating the deformed billet to cause further adherence of the metallic particles one to another, and at least said first and second heating steps consisting, in each instance, of heat treatment below the melting point of the lowest melting component but at a temperature, not lower than about below the melting point of the lowest melting component in degrees Fahrenheit, for promoting the welding of the metallic particles together without substantial solution or alloying of any component in or with another.

2. In a method of making sheet, strip, rod, and other articles from a mixture of powders consisting of a noble metal component and a minor metallic component, the steps comprising mixing at least about 60 per cent of silver powder and a powdered minor component, until the mixture is substantially uniform in distribution; compressing the mixture in a die and producing thereby a compacted billet; and converting the billet into a workable condition by heating the billet to cause the metallic particles to adhere one to another, preliminarily working the billet by substantial mechanical deformation thereof, and again heating the billet to cause further adherence of the metallic particles one to another, said heating steps each consisting of heat treatment below the melting point of the lowest melting component but at a temperature, not lower than about 10% below the melting point of the lowest melting component in degrees Fahrenheit, for promoting the welding of the silver particles together, whereby the adhering metallic particles of the components are converted into an interlocking network form without substantial solution or alloying of any component in or with another.

3. In a method of making sheet, strip, rod and other articles from a substantially homogeneous mixture of powders consisting of a metallic silver component and a minor component, wherein the silver powder constitutes at least 60 per cent of the mixture and the rest is nickel, and wherein the mixture is compressed to form a billet, the procedure for producing a wrought article which includes successively heat-treating the billet and working by mechanical deformation intermediate successive heat-treatments, to cause conversion of the silver and nickel powders into interlock.

ing networks in the final wrought article, said heat-treating and working procedure at least comprising first heating the unworked compressed billet to cause the metallic particles to adhere one to another, then working the billet with substantial mechanical deformation thereof, and then heating the deformed billet to cause further adherence of the metallic particles one to another, and at least said first and second heating steps consisting, in each instance, of heat treatment below the melting point of silver but at a temperature in the range from about 1680 F. to about 1740 F., for promoting the welding of the metallic particles together without substantial solution or alloying of any component in or with another.

4. In a method of making sheet, strip, rod, and other articles from a mixture of powders consisting of a noble metal component and a minor component, the noble metal component being at least about 40 per cent of the whole, the steps comprising mixing the powders until the components are evenly distributed, compressing the mixture to form a billet; and converting the billet into a workable condition by heating the billet to cause the metallic particles to adhere one to another, preliminarily working the billet by substantial mechanical deformation thereof, and again heating the billet to cause further adherence of the metallic particles one to another, said heating steps each consisting of heat treatment below the melting point of the lowest melting component but 'at a temperature not lower than about 10% below the melting point of the lowest melting component in degrees Fahrenheit, for promoting the welding of the metallic particles together, whereby the adhering metallic particles are-converted to a network form without substantial solution or alloying of any component in or with another.

5. As a new product, a wrought article of not less than about per cent of a noble metal component in the form of a substantially continuous network containing a minor component in its interstices, the noble metal and the minor component being substantially unalloyed either with the other and neither being substantially in solution in the other, said article having the properties, including coherence, network form and less than about 70 per centof a noble metal and characteristic of an article wrought by heattreatment and mechanical deformation, from a compressed billet of the components in powder,

, the welding of the metallic particles together.

6. As a new product, a wrought article of not the rest a minor metallic component substantially infusible below a temperature of 264=5 F., the components being in the form of interlocking networks substantially unalloyed' with or undissolved in one another, said article having the properties, including coherence, network form and uniformity of component distribution, which are characteristic of an article wrought by heattreatment and mechanical deformation, from a compressed billet of the components in powder form, by procedure which includes first heating the unworked compressed billet to cause the 7 metallic particles to adhere one to another, then working the billet with substantial mechanical deformation thereof, and then heating the deformed billet to cause further adherence of the metallic particles one to another, said heating steps each consisting of heat treatment below the melting point of.the lowest melting component but at a temperature, not lower than about 10% below the melting point of the lowest melting component in degrees Fahrenheit, for promoting the welding of the metallic particles together.

'7. As a new product, a wrought article of about to 95 per cent of silver and the rest a minor metallic component having a melting point not less than about 2645 F., the silver being in the form of a substantially continuous network containing the minor component in its interstices, the silver and the minor component being substantially unalloyed with or undissolved in one another, said article having the properties, including coherence, network form and uniformity of component distribution, which are characteristlc of an article wrought by heat-treatment uniformity of component distribution, which are and mechanical deformation, from a compressed billet of the components in powder form, by procedure which includes first heating the unworked'compressed billet to cause the metallic particles to adhere one to another, then working the billet with substantial mechanical deformation thereof, and then heating the deformed billet to cause further adherence of the metallic particles one to another, said heating steps each consisting of heat treatment below the melting point of the lowest me ting component but at a temperature, not low than about 10% below the melting point of a he lowest melting component in degrees Fahrenheit, for promoting the welding of the silver particles together.

8. As a new product, the wrought article described in claim '7, wherein the minor metallic component comprises nickel contained in the inierstices'of the network of the silver componen 9. As a new product, the wrought article described in claim 7, wherein the minor metallic component comprises molybdenum contained in the interstices of the network of the silver component.

10. As a new product, a wrought article of at least about silver in the form of a substantially continuous network containing in its interstices a minor component substantially infusible below a temperature of 2645 F., said article having the properties, including coherence, network form and uniformity of component distribution, which are characteristic of an article wrought by heat-treatment and mechanical deformation, from a compressed billet oi the components in powder form, by procedure including first heating the unworked compressed billet to cause the metallic particles to adhere one to another, than working the billet with sub- 'stantial mechanical deformation thereof, and

then heating the deformed billet to cause further adherence of the metallic particles one to another, said heating steps each consisting of the heat treatment below the melting point of the lowest melting component but at a temperature, not lower than about 10% below the melting point of the lowest melting component in degrees Fahrenheit, for promoting the Welding of the silver particles together.

11. As a new product, the wrought article of claim 10, wherein the silver is at least about 93% of the article and wherein the minor component comprises graphite in the interstices of the network of silver.

GREGORY J. COMSTOCK.