US1976009A - Method of casting refractory metals - Google Patents

Description

1Q6 84 CROSS REFERENCE EXAMINEI U f 5f Oct. 9, 1934. E. A. DE BATS 1,976,009

METHOD OF CASTING REFRACTORY IBTALS Filed Oct. 15. 1932 I IN NTO [Hf/1W5 A 54 ATTORNEYS Patented Oct. 9, 1934 UNITED STATES PATENT OFFICE Etienne A. Do Bats, Millbnrn, N. J.

Application October 15, 1932, Serial No. 637,951

8 Claims. (01. 25-193) This invention relates to improvements in The patterns of fusible metal are accurately methods and apparatus for casting refractory metal compositions in a variety of simple and/or intricate forms, some of which may have convoluted and/or undercut surfaces.

Hitherto, in the preparation of hard wearing machine elements, such as impeller blades for screw pumps, mesh gears and the like, it has been necessary to carry out the forming operations by means of machine cutting tools and/or grinders. With the advent of wear resistant materials, such as tungsten carbide and like mineralogically hard materials, attempts have been made to form involved or intricately shaped articles without success, due to the lack or workability of the materials and to the further fact that machine cutting tools and grinding wheels are not available with sumcient hardness to successfully attack such materials on a production basis. The use of diamond dust, as an abrasive, while possible, is commercially impractical with such materials, due to the rapid wear and loss of abrasive.

It has now been found possible to prepare wear resistant convoluted and other intricately shaped tools, wearing parts, screw pump members and the like from compositions which include exceptionally high wear resisting materials such as tungsten carbide and alloys of the same, with any of iron, cobalt, nickel, as alloying metals, and with or without the inclusion of tantalum metal, chromium, molybdenum and the like, all in metallic form.

The novel process of the present invention comprehends the preparation or forming of an exact copy or duplicate of the article to be formed, either by machining, grinding, casting in plaster of Paris or like casting material, or in any other manner, well known to pattern makers and others skilled in the art. These patterns are preferably made of a fusible metal or metals, such as lead, zinc, tin, bismuth and any of their alloys, such as Woods metal, type metal and solders of varying degrees of hardness. The pattern of the article to be duplicated in the wear resistant composition or compositions is formed from such low melting or fusible compositions, as they will hereinafter be referred to for sake of clarity, and to differentiate them from tungsten carbide compositions, and the like, which are substantially infusible at temperatures commercially available. The fusion temperature of tungsten carbide and like compounds of high wear resistance is well above 2000 C., and furnace installations capable of retaining any such heat are extremely costly.

prepared, as intimated above, either by machining or in any other suitable manner, and these members are thereafter placed in a suitable mold such as a multi-partite mold comprising a series or plurality of interlocking tubes of any desired shape and diameter. The patterns are mounted on a suitable supporting block and disposed inwardly of the mold members so as to be equally spaced from all sides. Thereafter, a mlging compound, such as Fulverizeg silica or any other mes-eta materia pre erably as finely powed or da around the atan extremely'fi'z'i'fiiflice finish is es red on the finished article, the refractory aterial used in the mold should be ground as finely as possible, preferably in the form known commercially as-fioun- The refractory mix material is filled into the sheath or mold casing and tamped or compressed into position by the plunger. This operation is preferably carried out in stages, a small amount of mold material being introduced into the mold and compressed and this step being repeated until the pattern is completely incased in a compacted mold mass. This is continued further to insure proper densifying of the material and to make sure that the top portions of the pattern are uniformly supported. Any excess of mold material will find its way into the center of the hollow piston or plunger on the final compression, due to the lack of lateral support, as afforded in the prior stages by the body of the pattern.

The high compression of the material compacts it to an extraordinary degree and, due to this high pressure, plus the fineness of the material, the surfaces of the mold material contacting with the surfaces of the pattern take on a smooth finish, substantially free from voids and any and all irregularities. The finish so imparted is so fine that cast articles later prepared therefrom require only a lap or finish grinding in 100 order to be rendered suitable for use.

When the mold composition has been compressed into place and to a desired degree, the plunger, and the superposed mold sections, from which the excess mold material has been pressed, 105

are removed. The mold sheath, with its contained compressed mold material, and associated fusible metal pattern, is then introduced into a core ov her suitable ting device, and baked to decompose inder and cause the 110 mold material to set to a hard mass. During this baking, the metal of the fusible pattern is melted and flows out of the mold assembly, leaving a cavity whose surfaces are the exact replica of the article which is to be cast.

While pressures of 50 to tons per sq. in. have been indicated as desirable, the particular pressure used will depend upon the materials to be cast. and also upon the texture or finish of the surface of the mold. In this connection, it is to be noted that the higher the compression to be applied in the mold forming step, the less binder will be used with the pulverized refractory material. Thus, where pressures of the order of 100 tons per sq. in. are to be used, it will be sufficient to merely dampen the particles while, if much lower pressures are to be used, more binding agent will be needed in admixture with the refractory particles.

The mold assembly, after baking, and while still hot, is then inserted in a suitable holder and the latter, with a desired number of like devices,

may be inserted in a centrifugal casting machine, care being taken to balance the mold containers. Suitable inserts such as shafts of steel or other suitable metals may be set in the mold, after melting out the pattern and the refractory metal compositions subsequently cast therearound. The casting machine may then be set in operation and a mass of a refractory material, which has .previously been brought to a desired heat, that is, of the order of incipient fusion, is placed therein. The mass of refractory material still retains its solid structure and may be lifted from the furnace or crucible with tongs, and after dropping into the casting machine will be instantly forced into the mold cavities.

Under ordinary methods of centrifugal casting, pressures exerted by the metal upon the refractory mold material may approach 5 to 6 tons per sq. in., although, it will, of course, be understood that any desired pressure may be attained by suitably designing the centrifugal machine and its driving motor or source of power.

The casting of a refractory metal composition, under pressures of the order of 2 to 10 tons per sq. in., and preferably of 5 to 6 tons per sq. in. into and against mold surfaces which have been formed under pressures of the order of 50 to 100 tons per sq. in. will obviously not introduce any difficulties in the way of the scouring, washing, working or gouging out of mold surfaces, nor of the disintegration of the same by centripetal forces, so that the cast articles will be accurately and completely conformed to unmarred mold surfaces.

After the casting operation has been completed, the mold assembly plus the contained casting is removed from the machine and the compacted mold mass removed, in any suitable manner, as by breaking with chisels, hammering, or in any other way. The casting will be found to be perfectly sound and to have a smooth surface finish, which is free from voids, and which, as indicated above, will require, at the most, but a lap finish or grinding to perfect it for use.

While mm has been mentioned as a preferred refractory material, suitable for use as a mold mass, the invention comprehends the use of other refractory mold materials, including magnesia, alumina, tungsten dioxide, bauxite, zirconia, chromite, and a wide variety of refractory materials. The binding agent will be chosen with a view to its possessing the capacity of decomposing underheat, and, at the same time, of combining with the materials forming the mass of the mold. The mold sheaths are preferably made of seamless tubing of suitable shapes and sizes, and are so conformed as to be capable of being inserted in each other to provide any desired length of finished mold; the excess lengths being removed after the mold material has been compressed into place in and about the fusible metal pattern.

The patterns may, as indicated above. be made in any desirable manner, as by machining, grinding, and the like, and, in the case of relatively simple shapes, which are free from or characterized by very little undercutting, as noted above, plaster of Paris molds may be used, which can be destroyed when removing the cast fusible metal pattern.

Referring now to the drawing, there is shown the details of an apparatus suitable for carrying out the teachings of the present invention, it being understood that the disclosures are presented by way of example only, as it is obvious that other specific devices may be made use of in the practice of the present invention without altering the scope thereof, and it is not intended to be limited to the structures here shown and described, except as such limitations are clearly imposed by the appended claims.

In the drawing, like numerals refer to similar parts throughout the several views, of which Fig. 1 is a vertical section of a mold assembly with the pattern in place, and immediately prior to the compression step;

Fig. 2 is a view similar to Fig. 1 showing the completion of the compression step;

Fig. 3 is an elevation of one-half of a two part mold holder; N

Fig. 4 is a top plan view of a centrifugal casting machine with mold holders disposed therei Fig. 5 is an end view of the interior of a pump casing showing a plurality of screw pump elements in operative position, and

Fig. 6 is an elevation of a screw threaded cast pump member.

Referring more specifically to the drawing, the invention will be described with particular reference to the casting of drill tips and screw pump elements from high melting metal compositions such as one containing 65% tungsten carbide and 35% cobalt, nickel or iron, or a mixture thereof.

In the drawing, numeral 10 designates a fusible metal pattern of a drill tip, which is mounted on a mold base 11 having a centering pin 12. A mold casing or sheath 13 is disposed in the base 11, lugs or ridges 14 serving to center the same. An extra mold member 15 is fitted onto the member 13, a slip joint 16 permitting the locking or aligning of the two mold members. Into this mold chamber, thus formed, a mass of refractory material 1'1, comprising silica flour, or the like, of 200 mesh or liner, and moistened with from 2% to 5% of sodium silicate, is inserted. Sumcient amounts of the material 17 are placed into the mold so that when successively compressed by the plunger of piston 18, the upper level of the finally compressed material will attain the level of the top of the pattern 10. In this connection, it is to be noted that the bottom mold members 13 are preferably so formed as to approximate ,the height of the patterns disposed therein.

Referring to Fig. 2, the same general construction is shown with the piston being shown at the end of the compression stroke and reaching to The castings thus formed, whether of mmthe top of the pattern-- 20, which is shown as a gear screw element of the pump shown in Fig. 5. The'compressed mold material is designated as 17a, to differentiate it from the uncompressed material 17 of Fig. 1, the excess of the latter being designated as 17b.

The pistons or plungers 18 are preferably hollow, the central cavity being of such a size and shape to approximately conform to the diameter of the pattern of the article to be cast. This construction permits the forcing of the excess refractory material down the sides of the pattern and into intimate contact with all the undercut portions thereof, whereas a flat faced piston or plunger would cause the excess material, 17b, immediately above the pattern, to be compressed on top thereof, and not into intimate contact with the sides.

The mold assembly, comprising the sheath 13, the compressed refractory material 17a, and the enclosed pattern 20, or 10, as the case may be, is then placed in an oven or furnace, such as a core baking oven, and heated until the mold material is set. During this heating, the binder material will be driven oil! and/or decomposed, and serve as a bond for the particles of the refractory material, while, at the same time the metal of the fusible pattern member will liquefy and fiow out from the mold. This will leave the mold surfaces clean and an exact counterpart, in reverse, of

the pattern. The mold sheath 13, with the contained compressed refractory material l'la, and the pattern member 20, is inserted in a two part holder 30.

having symmetrical tops and bottoms 31, provided with pins 32 and sockets 33 to assure proper alignment of the several parts. The holders 30 are provided with cutout portions or cavities 34:, which are adapted to receive the sheath members 13 in a snug fit when the two parts of the mold holder are placed in position. The mold holders 30 with the contained molds 13, are placed in position in the centrifuge 40, having a rim 41, recessed, if desired, as indicated at 42 to receive the blocked off ends 35 of the mold holders. Centrally of the centrifuge, there is provided a ring 43 of any suitable refractory material, which ring is provided with a plurality of apertures 44 opening into the casting chambers formed in the centers of the mold assemblies.

when the centrifuge is set in operation and a mass of refractory metal, such as a composition comprising substantially tungsten carbide, and 35% cobalt, which has been heated to a temperature of incipient fusion, such as of the order of 1400 C. and above, depending on the composition andpercentages of the constituents, is placed in the center 45 of the centrifuge and under the conditions of operation is immediately forced into the mold cavities under pressures of the order of 5 to 6 tons per sq. in., more or less, depending upon the distance of throw and the speed of the machine. The material cast is preferably, as noted above, heated to an incipiently plastic condition, in which condition, it may be removed readily from the crucible or other container, as has not been found to be the case where higher temperatures are used to produce a semiplastic or viscous mass which adheres to the crucible walls.

As already noted, castings so prepared are all of uniform density. and, owing to the fineness of the construction of the mold material, and the manner in which it was prepared, the surfaces would require but a lap finish for use.

cate shape or simple shape, where made from tungsten carbide or other high melting carbides, such as those of molybdenum, vanadium, chromium, tantalum and the like, admixed or alloyed with any metal or alloy compositions, will, as already stated, be found to have a smooth surface finish and uniform texture and finished structure,

while exhibiting structural and physical characteristics in the way of tensile strength, which are not found in so called sintered masses of tungsten carbide and/or its alloy compositions. The final pressure step involved in the formation ofsuch high refractory metal or metalloid compositions permits the securing of articles of uniform crystalline structure characterized by sharper cleavage and breaking as opposed to the conchoidal fractures indicative of planes of cleavage, due to preferred orientation of crystals, as found in sintered products'generally.

Referring to Figs. 5 and 6, there is shown a pump casing 50 in which are disposed at driving screw 20, having in engagement therewith a pair of idler pump screws 21, which are formed in the same manner as the member 20. Due to the formation of these members from high refractory, abrasive and corrosion resistant materials such as the 65% tungsten carbide and 35% cobalt.

'composition disclosed, or other suitable compositions, pressure pumps may now be made which can handle corrosive materials such as sea water, brine and a variety of chemicals as well as slur- 4 rice and fluids containing abrasive materials in suspension, as may be found in bilge water of vessels. The helical impeller blades for use in this type of pump have been extremely short lived in screw pumps, some of the hardest steels, when formed up into screw pump elements and used in pumps for handling biige'water, having been found to have a life of the order of only a few weeks in actual service.

It will now be appreciated that there has been provided an improved process for readily and accurately forming intricate shapes of all kinds from high melting materials of the type of tungsten carbide and its various alloy combinations and other like materials, which process permits a desired smooth finish and texture to be imparted to the cast articles without requiring the use of extraneous apparatus. In addition, there has been disclosed a novel abrasion and corrosion resistant pump and helical impelling elements therefor, which pump, due to the longevity of the improved refractory metal parts exceeds in performance anything hitherto available, and thus makes available for heavy duty work, an otherwise highly efiicient pumping device.

What is claimed is:

1. The improved method of preparing smooth surfaced molds for use in pressure casting incipiently fused, high melting refractory metallic compositions, such as carbides of the metals of the VI Periodic Group comprising forming a fusible metal pattern of the article to be cast, dampening a powdered refractory having a melting point of the order of 1500 C. and above, compressing the so prepared refractory material about the pattem and in a metallic mold casing at a pressure above the calculated casting pressure of the refractory metallic compositions, baking the mold assembly and melting out the pattern metal.

2. In the preparation of molds for use in casting high melting refractory metallic compositions such as carbides of metals of the VI Periodic Group to form intricate shapes, the steps comprising moulding a powdered refractory about a fusible pattern and under high pressure above the calculated casting pressure of the refractory metallic compositions, and thereafter melting out the metal of the pattern while baking the mold.

3. An improved process for pressure castin intricate shapes from metals and alloy compositions melting at temperatures of 1500' C. and above, comprising forming a fusible metal pattern of the article to be cast, ramming up a powdexed refractory mold material about the pattern in a continuous metal sheath and under pressures of the order of 50 to 100 tons per square inch and above, baking the mold and contained pattern at temperatures sufilcient to fuse the metal of the pattern, and compresing the high melting metal composition into the finished mold and at pressures of at least one or more tons per square inch.

4. An improved process for pressure casting intricate shapes from metals and alloy compositions melting at temperatures of 1500" C. and above, comprising forming a fusible metal pattern of the article to be cast, ramming up a powdered refractory mold material about the pattern in a continuous metal sheath and under pressures of the order of 50 to 100 tons per square inch and above, baking the mold and contained pattern at temperatures sufllcient to fuse the metal of the pattern, heating a mass of a high melting metallic composition to about the temperature of incipient fusion of the mass, placing the so heated mass in the mold aperture, and compressing the high melting metal composition into the finished mold and at pressures of at least one or more tons per square inch.

5. An improved method for making molds for casting high melting refractory metal compositions such as carbides of metals of the VI Periodic Group, comprising forming a fusible metal pattern of the article to be cast, setting up the pattern in a mold casing and spaced therefrom, compacting a pulverized refractory having a decomposable binder in a mold and about the said pattern at pressures above the calculated casting pressures of the refractory metallic compositions, said refractory being introduced into said mold and compacted in batches, and thereafter heating the mold and contained refractory and pattern at temperatures sufilcient to bake the mold material and to melt the pattern.

thereafter heating the mold and contained re-- fractory and pattern at temperatures sufficient to bake the mold material and to melt the pattern, inserting said baked mold member in a centrifugal machine and casting a refractory metal composition in said mold and at pressures of the order of from 1 to 10 tons per square inch.

7. In the preparation of molds for use in casting high-melting refractory metal compositions such as carbides of metals of the VI Periodic Group, to form intricate shapes, the steps comprising molding powdered magnesia dampened with a decomposable binder such as water-glass about a fusible pattern and under high pressures above the calculated casting pressure of the refractory metallic composition, and thereafter melting out the metal of the pattern while baking the mold.

8. An improved method of casting refractory metal compositions, such as carbides of metals of the VI Periodic Group, comprising forming a fusible metal pattern of the article to be cast,

setting up the pattern in a mold casing and spaced therefrom, contacting pulverized magnesia dampened with water-glass in the mold and about the said pattern and at pressures above the calculated casting pressures of the refractory metallic compositions, said magnesia and water-glass being introduced into said mold and compacted in batches, thereafter heating the mold and contained pattern at temperatures sumcient to bake the mold material and decompose the water-glass and to melt out the pattern, inserting said baked mold member in a centrifugal machine and casting a refractory metal composition in said mold and at pressures of the order of from 1 to 10 tons per square inch and above.

ETIENNE A. DE BATS.

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