JPH0149768B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the preparation of rapidly solidifying microparticles. In particular, the present invention heats a portion of a mass of solid material, not confined by a crucible or similar vessel, to form molten droplets or spheres, and when the droplets are brought into contact with a rapidly rotating liquid cooling fluid in a centrifugal arrangement. The present invention relates to a method for producing solid microparticles in which the falling molten droplets are broken up and divided into smaller droplets or granules, which are then scavenged and rapidly cooled to form solid microparticles, which are then recovered from a cooling fluid.

P. P. Duwez et al. “J.
Appl.Phys, 31 p1136-37 (1960),
A small droplet of liquid alloy is ejected at an appropriate angle to a target on the inner surface of a high-speed rotating cylinder by the centrifugal force acting on the contact droplet, allowing good heat exchange with the target at a high heat exchange rate. teachings to ensure that the metal droplets diffuse into a thin layer of solidified material. R. Pondojiunia et al. (R.
Pond.Jr.et al) is ``Trans.Met.Soc.AIME
Vol. 245, p. 2457-2476, No. v. 1969, a flow of molten alloy is pumped through an orifice to the inner surface of a rotating drum, and the radial acceleration of the drum leads to good thermal contact. A method for casting metal fibers is disclosed in which a flow of molten alloy is diffused into a flat filament prior to complete solidification.

J.A. Tei. Gow (JTGow) US Patent No.
No. 2439772 uses a rotating container containing coolant,
The rotation forms an annular vertical wall of the rotating liquid, into which a spherule of molten metal is injected with a trajectory generally perpendicular to the wall, and the spherule rather than being hit by the wall of the liquid. invade. In this method, Gow discharges a stream of molten material (e.g. steel) into a rotating saucer when a small sphere is introduced into a rotating annular vertical wall of liquid. Metal is introduced from around it. In his discussion of the prior art, Gow also discusses methods for dividing molten metal into small spheres by bombarding the stream with high-pressure steam or water, and methods for dividing molten metal into small spheres by bombarding the stream with high-pressure steam or water, and methods for dividing molten metal into small spheres by using a high-speed rotating drum or paddle wheel. describes another method of impacting the flow of water and throwing or launching a small sphere from it.

B. B. Haak, whose U.S. patent no.
No. 1,782,038 converts salt into droplets by injecting molten metal onto a rotating disk which then dumps the droplets against the wall of a container containing a rotating liquid. The water level of the rotating liquid is higher than the rotating disk due to the intense rotation of the agitator.

R. E. REMaringer et.
al) in its U.S. Pat. No. 3,896,203 teaches rotating a disc-like member in contact with an unrestricted dripping droplet of molten material to form a filament-like material; E. REMaringer also has its U.S. patent no.
No. 4,124,664 teaches employing a rotating disk to form filamentary material from dripping droplets of molten material. The droplet and disk are in constant contact.

Generally, the method according to the present invention involves heating the lowermost end of a generally solid mass of material that is suspended to some degree freely without a containing container such as a crucible to form a molten mass, forming molten spherules or droplets that are separated from the mass; The spherules are brought into contact with a rotating cooling fluid in a centrifugal arrangement, upon which the spherules are fragmented or disintegrated into many smaller spherules or particles, which are swept away by the cooling fluid and rapidly cooled in the cooling fluid. Solid granules.

Further disclosure of the invention will become apparent from the description of the accompanying drawings.

Apparatus useful in carrying out the invention is generally shown in FIG.
Indicate by 10. The device 10 includes a slightly laterally inclined cup-shaped member, generally indicated at 11, having a shaft 12 fixed to a bottom 13 in the center. Although not shown, the shaft 12 can be rotated by a conventional motor arrangement at any selected speed. bottom part 13
is connected at its outer periphery to an angularly projecting cylindrical side wall 14 at an angle generally of 90 degrees or slightly less, which side wall is connected at its upper part to an inwardly projecting ring-shaped arm 15. . An opening 16 is positioned in the portion of the bottom 13 close to the side wall 14, which is closed by means such as, for example, a threaded machine screw 17.

A rod, round bar or ingot 18 of the material to be granulated is inserted into the circular opening surrounded by the ring-shaped arm 15. The drawing shows that this bar is suspended in the intermediate space, but
In the practice of the present invention, the lowermost portion 19 is used or consumed by being tightened or held by conventional tightening and/or movement devices at one or more locations remote from the lowermost portion. As the process progresses, the bar 18 is gradually lowered or fed. In the illustrated apparatus, a flame 20 from a conventional torch 21, e.g.
The lowermost end portion 19 of the tube is heated to form a bulb-shaped molten mass. From the molten mass in the lowermost portion 19, large spheres 22 of molten material are to be formed into granules.
It shows that the water is dripping downward.

During operation of the method according to the invention, the tip-shaped member 11
has a cooling fluid 23 therein which is deposited on the inside of the side wall 14 of the socket 11 by the centrifugal force exerted by the rapid rotation of the shaft 12 and its associated socket 11. Arranged as a high-speed motion rotating wall. The positional relationship between the lowest end portion 19 of the rod 18 and the cooling fluid 23 is such that as the large molten spheres 22 drip from said end 19 they can descend and come into contact with the centrifugally disposed wall of the rapid motion rotation of the cooling fluid 23. It is.

Although not shown, the device 10 can be completely enclosed in a not-shown enclosure or the like to create or release pressure within the tip or around the end of the rod as required. Alternatively, if desired, an atmosphere of an inert gas such as argon, helium, or other specified gas may be provided.

Once the adjustment of the small solid particles has been completed, the tip 11 can be positioned so that its hole or opening 16 and the closing means consisting of the screw 17 are in their lowest rotational position. Then, the screw 17 is removed and the liquid cooling fluid 23 and the prepared particles can be easily discharged from the pot 11 in preparation for the next step. An alternative, not shown, to the holes 16 and screws 17 is to mount the entire socket 11 on a tiltable plate.

In the practice of the invention, the free portion of a suitable solid mass is heated to a molten state, creating a molten sphere that descends therefrom. At the same time, a ring-shaped rapidly moving mass of suitable rotating liquid cooling fluid in a centrifugal arrangement is prepared. Positioning of a rapidly moving ring mass of rotating liquid cooling fluid in a centrifugal arrangement relative to a descending molten sphere such that the sphere contacts the lower portion of the exposed inner surface of the moving ring mass of rotating liquid cooling fluid in a centrifugal arrangement. be made to do. When they come into contact, a loud sound, almost like an explosion, is generated, and the molten sphere breaks up and breaks into many pieces. These fragments are quickly captured and swept away by the rapidly moving liquid cooling fluid. Inside the liquid cooling fluid, the fragments are rapidly cooled and become fine solid particles. These microparticles are then separated from the liquid cooling fluid by conventional equipment and used for a variety of purposes, including powder metallurgy applications.

In order to facilitate the implementation of the method according to the invention, the free portion or equivalent portion of the solid mass serving as a source of molten spheres has a circumference defined by a rapidly moving ring-shaped mass of rotating liquid cooling fluid in a centrifugal arrangement. located generally within a space surrounded by a space. Generally, the distance from the source of molten droplets to contact with the kinetic coolant is relatively short. 0.635cm in experimental equipment
(0.25 inch) to 2.54 cm (1 inch) are useful. Although the preferred distance can vary widely depending on the various process parameters and specific materials employed, the preferred distance is approximately
0.635cm (0.25 inch) to 1.27cm (0.5 inch)
It is. The size and shape of the prepared granules appears to be greatly influenced by the particular combination of materials employed (i.e., the particular coolant and the particular solid material from which the granules are made) as well as the particular combination of preparation process parameters. be. The greatest influence on the size and shape of the prepared microsolid particles appears to be the velocity of the coolant movement as it contacts the molten spheres. The minimum coolant speed is approximately 2500rpm or 1140m/sec (3750ft/
It seems to be about 10 min). At such speed the molten sphere is divided into at least 100 pieces. clearly,
The higher the speed, the more the molten spheres are divided into a larger number of particles, and the finer the size of the solid particles. The maximum speed appears to be limited only by factors such as workmanship, safety factors, etc.

Compared to other known methods of preparing rapidly solidifying granules, the method according to the invention offers a number of advantages. Virtually any liquid material, or material that can be made into liquid form, may be a candidate for the cooling fluid, but particularly suitable cooling fluids can be selected for the various molten materials to be granulated. The surface velocity adopted for the walls of the centrifugal arrangement of the liquid coolant is easily obtainable and this velocity can easily be changed to another with good control if required, and the granules prepared in this way The dimensions can be controlled very precisely. The centrifugal force technique according to the present invention appears to be less costly than prior art techniques involving high speed pumping and other motion devices for the coolant. moreover,
The coolant centrifugation technique according to the present invention provides more adequate cooling capacity and temperature control. When the molten sphere is broken into minute droplets by contact with the moving coolant, these broken pieces or minute droplets immediately or very quickly form into a moving mass of liquid coolant. very high cooling rates are obtained. Heat exchange from the molten metal particles to the cooled solid particles occurs substantially continuously while within the liquid coolant. Additionally, a major problem associated with conventional water spray techniques, where the vapor layer is insulating and prevents further cooling, is eliminated by the technique according to the present invention, which creates a thick layer of coolant and particles trapped therein. are excluded because they move at the same time. Furthermore, it is of great importance in the method according to the invention that the material formed into granules is melted only in free space;
In this free molten state, the raw materials are prone to pick up impurities from the container in which they are being melted, so that great care must often be taken to prevent possible contamination and reduction of purity. There should be no contact with the container. If deposited, such impurities are likely to be carried over and found in the prepared granules. Because of this important advantage, the present invention can be considered truly a crucible-free method for the preparation of rapidly solidifying granules. Also, the present invention does not require a suitable crucible for it, or is reactive and would damage the crucible, e.g.
Highly reactive materials such as metals or alloys such as Ti, Zr, etc., and certain high melting point materials such as steel and crucible-produced alloys that either do not have suitable crucibles or are very expensive if available. Applicable to materials.

The top-shaped member that rotates at high speed is made of metal such as stainless steel, aluminum, molybdenum, copper, or the like. Due to the high rotational forces to which this rotating member is subjected, the following precautions are required in its manufacture. Selection of materials of construction and methods of construction with a view to providing sufficient strength to withstand the forces encountered in use; construction involving very careful motion balancing to ensure vibration-free and uniform rotation; preferably the overall structure employed. The equipment must be surrounded by a protective safety enclosure.

Devices not shown for holding and transporting shapes of rods, wires, ingots or other solid materials whose free portions are melted to provide molten spheres are, for example, devices for holding and transporting welding rods, metal Any of the numerous conventional devices known in the art, such as tuned feed devices, can be used with little or no modification.

The liquid cooling fluid employed may be a pure liquid, a solution, at higher speeds a liquefied gas, or a suspension of solid and liquid. The cooling fluid need only be, and generally is, inert and chemically non-reactive with respect to the melting material with which it is used. However, in the present invention, whether the reaction mainly reacts with the surface layer or
or for specific uses, as long as the molten spheres are surface coated and the reaction does not significantly impair the disintegration or fragmentation of the molten spheres when they come into contact with a rotating liquid cooling fluid in a rapidly moving centrifugal arrangement. This does not exclude liquid cooling fluids that may react with the molten material.

The selection of a particular cooling fluid and its temperature depends on the particular material used to form the particles, as well as the dimensions of the molten spheres and the contact forces with the cooling fluid, as well as the depth of the liquid cooling fluid in a rapidly moving centrifugal arrangement. , in relation to other process parameters such as thickness and motion speed. Preferred qualities and properties of the cooling fluid include having a high heat capacity, non-toxicity, relatively non-flammability, and low cost. For example, water is extremely useful for molten spheres of various types of materials whose temperatures are above 1204°C (2200°C); as well as for various low temperature aqueous salts (e.g. NaCl, MgCl ₂ , ZnCl _{2 )} . )
Brines can be used with certain materials; petroleum and synthetic oils are also useful; liquefied gases are also considered useful, and so on. Almost any liquid coolant or cooling fluid may be used if it can be formed into a rapidly moving, centrifugally arranged, rotating wall liquid mass having the concentration, motility and thermal capacity to break up and fragment the particular molten material spheres. Particularly useful and preferred for various molten materials are the following liquid coolants: Cold water or a combination of brine and cold water for molten Fe, Ni and other non-reactive transition alloys; inert fluids such as liquefied helium for reactive materials; granules produced with varying cooling rates. For oils whose cooling rate changes. Of course, the foregoing are merely representative of typical useful cooling fluids, and a wide variety of alternative cooling fluids may be used.

Here, the molten material formed into granules has been explained through its melting, particularly from a metal or alloy feedstock, and has been illustrated by specific examples, but the physical property that it becomes molten at a temperature fairly close to the melting point of the molten metal is It is thought that the work can be done using any material that has the following properties. The molten material should have the following physical properties at a temperature of 25% of the equilibrium melting point, indicated by 〓;
Surface tension ranging from 10 to 2500 dynes/cm, viscosity ranging from 10 ^-3 to 1 poise and moderately discontinuous melting point (i.e. discontinuous temperature with respect to the viscosity curve). The present invention is believed to be operable with most metals and chemical compounds and elements meeting the above criteria. Furthermore, the present invention provides that the alloy has a temperature at which any component in the alloy first solidifies (liquidus temperature) and a temperature at which the component with the lowest melting point solidifies (solidus temperature) to form a completely solid material. even exhibiting a wide range of temperatures between. As a definition, even if some molten material is present at a temperature between the liquidus and solidus temperatures, such an alloy is considered to be "molten" if the temperature is above the solidus temperature.

The molten spheres formed into granules by the method of the invention can _be melted in conventional heating equipment by melting metals such as aluminum, zinc, lead, tin, copper, etc., or by _melting metals such _{as e.g.} Si ₈ or
Melt nickel-based alloys such as Fe ₄₀ Ni ₄₀ P ₁₄ B ₆ or the compositions described in, for example, _{U.S. Pat} . ,
_{Glassy or _ _ _ _ _ _ _} It can be obtained by melting metastable alloy components which are known to be obtainable in an amorphous state.

As is clear from the drawings and description of the illustrated apparatus for carrying out the method according to the invention, the molten spheres traverse a limited distance before coming into contact with the rotating cooling fluid, and thus the molten material before being broken up into granules. Limited exposure to the atmosphere surrounding the stream. Therefore, the oxidizing properties of many metals and alloys do not limit the practice of the present invention. Metals known to be worked with without the need for full protection against oxidation include iron, silver, nickel tin and zinc. If it is desired to expose the molten spheres to a particular atmosphere, this atmosphere can be provided, for example, inside the previously described, but not shown, container for apparatus 10. The process according to the invention can then be carried out in an inert atmosphere or even under reduced pressure. If the molten sphere has significant vapor pressure, the composition and pressure of the gas in the vessel can be manipulated to reduce evaporation and maintain the integrity of the sphere until it contacts the coolant. In place of said vessel, another conduit, not shown, is used to provide a path for the sphere to descend into contact with the rapidly moving coolant and to provide the desired gas environment near the point of formation of the sphere. You can also do it. Metals preferably used in the oxidation-reducing atmosphere include titanium, niobium, tantalum, zirconium, magnesium, aluminum and molybdenum. Although not shown, other torches, such as electron beam heating, arc melting, laser beam heating, induction coil heating, etc. Other devices for heating to create molten spheres may be used, including conventional heating devices.

Once the operation is complete and the mixture of granules and cooling fluid formed is discharged from the spout or drum, the cooling fluid may be decanted, filtered, etc.
It is separated from the granules by conventional means such as centrifugation and washing, and the granules are cleaned by washing, etc., and then separated into the shape, size, and grade of the granules by conventional equipment. Conventional sieves, precision sieves, roll tables, fine powder classifiers, etc. are useful for such separation operations.

The best presently known method of carrying out the invention has been set forth in the foregoing description of the apparatus shown in the drawings and its operation, and is also illustrated in the examples below.
However, these examples are laboratory-scale implementations, and the overall benefits gained upon scaling up to commercial implementation and commercial granule product preparation are assumed to be much more valuable.

In the following example, an experimental apparatus of the same general nature and nature as that shown in FIG. 1 is used. The device used has an aluminum pot with an average inner diameter of about 6.5 inches and a height of about 2 inches, and can hold up to 200 ml or more of liquid coolant. The motor device that drives the shaft of the tip-shaped member is
It is a 0.5 HP electric motor whose speed is variable and can be set to a desired constant and stable speed by electrical input regulated by a controller.

The procedure involves placing a desired amount of liquid cooling fluid into the tip, positioning the tip at the desired velocity, and as a centrifugally arranged ring adhering to the inner wall of the tip. rotate at a sufficient speed. A solid wire or rod of the material to be formed into granules is then positioned so that one end thereof is directly above the passageway traversed by the rotary motion of the liquid cooling fluid and the lower portion of the centrifugally disposed ring.
In general, a heating means such as a propane torch flame is applied to the lower end of the rod, and the molten spheres of the raw material are dripped or dropped, and the liquid cooling fluid is rotated in a centrifugal manner. Adjust and use the flame of the torch so that it makes contact with the ring of placement. When the molten sphere comes into contact with the cooling fluid, a high-pitched explosion-like sound is heard and the sphere appears to break up into extremely small fragments, which are captured by the rotational movement of the liquid cooling fluid in a centrifugally arranged ring.
and be swept along it. Inside the coolant,
The fragments or granules are cooled very rapidly, and depending on the size of the granules, even the degree of cooling necessary to provide metallic glassy or other metastable or crystalline granules. However, this phenomenon clearly depends on the temperature and velocity of the cooling fluid and the temperature and dimensions of the falling molten sphere.

Example A A generally pure tin rod with a square cross section measuring 0.25 inches on a side and approximately 4 to 5 inches in length was used as the material for making the microgranules. Using water as cooling fluid (about 150ml),
The speed of the tip-shaped member is approximately 10,000rpm, i.e. ~1,400m/min.
(4000ft/min). Using a propane gas torch, the flame was placed on a tin rod approximately 1 cm (0.4 in.) inside and directly above the inner surface of the lowest end of the centrifugal ring in which the liquid water was rotating. towards the bottom. Water is approx. at startup
The room temperature was 20℃ (68℃). The water rotated and the centrifugal ring moved in a generally vertical plane. When the flame of a torch was brought to the end of the tin rod and it melted, a molten sphere of tin about 3.18 millimeters (0.125 inches) in diameter fell. The molten sphere made an explosive sound when it hit the high-velocity water. After a short period of time, the torch flame was extinguished, the tip stopped rotating, and the mixture of water and fine solid particles was discharged from the tip. After evaporation of the water from the small solid particles, observation of the particles revealed significant fragments of tin particles, primarily flake-like in shape and measuring -325 mesh (according to US sieve standards).

Example B Cross-sectional area is 0.103 cm ² (0.016 square inches) to 6.45
cm ² (1 square inch) of zinc, lead, titanium,
Fe ₄₀ Ni ₄₀ P ₁₄ B ₆ solid material and substantially in weight ratio
Aluminum alloy rod and/or wire consisting of 4.4% Cu, 1.5% Mg, 0.6% Mn, and the rest Al.
Military Specification based on water, automotive motor oil, and mineral oil containing antioxidants
Using a liquid cooling fluid selected from metal heat treatment oils, such as Houghton's K-Oil, that meets MIL-H-6875D, the distance of the molten sphere relative to the liquid coolant in a centrifugal arrangement is controlled by rotating motion. Various additional preparations were made from 0.25 inches to 1 inch. In each run, fine solid particles were prepared with dimensions less than one-hundredth of the volume of the molten spheres.

As is clear from the foregoing examples, solid particles of flake, spherical, irregular shapes and various sizes can be prepared from a wide variety of materials in the molten state. for example,
Water as a coolant tends to form fibrous and spherical particles, and oil as a coolant tends to form mainly spherical or nearly spherical particles. These shapes and sizes can then be separated and classified into various specific shapes and/or size ranges as desired. These granular fragments can be consolidated by conventional techniques and used in the field of powder metallurgy to make useful articles, as feed powder for plasma injection, as feed powder for making alloys that are difficult to make with conventional equipment, or as raw powder for making alloys that are difficult to make with conventional equipment, or It is used for many purposes as granules used in tapes, etc.

[Brief explanation of drawings]

FIG. 1 is a perspective view, partially in vertical section, showing somewhat schematically a simplified form of an apparatus useful for carrying out the method according to the invention. In the figure, 10: Overall device, 11: Cup-shaped member, 12: Shaft, 13: Bottom, 14: Side wall, 18: Bar, 19: Lowermost end of bar, 21:
Torch, 22: Sphere, 23: Cooling fluid.

Claims (1)

Claims: 1. (a) heating the free portion of the mass of solid material to a molten state from which droplets of molten material may drip; (b) a rotating liquid cooling fluid in a centrifugal arrangement; (c) a droplet of molten material falls onto said heated portion of solid material and said rapidly moving ring-shaped mass to form a rotating liquid mass in said centrifugal arrangement; (d) positioning relative to each other in contact with rapidly moving ring-shaped masses of cooling fluid; (d) rapidly-moving ring-shaped masses of rotating liquid cooling fluid having a smaller size than said droplet of molten material and in said centrifugal arrangement; 10 at a temperature in the range of 25% of the equilibrium melting point indicated by from
A method for producing solid microparticles from a normally solid material having a surface tension of 2500 dynes/cm and a viscosity of 0.001 to 1 poise. 2. The method according to claim 1, wherein the rapidly moving ring-shaped mass has a diameter of at least 1140
A method for producing solid microparticles that move at a speed of m/min (3750 ft/min.). 3. A method according to claim 2, comprising the step of creating an inert gas atmosphere in the immediate vicinity of the molten portion of the mass of solid material and the droplets of molten material. . 4. The method according to claim 2, wherein the free portion of the mass of normally solid material is tin. 5. A method for producing solid microparticles, which uses water as the liquid cooling fluid in the method according to claim 4. 6. A method for producing solid microparticles according to claim 2, wherein the divided solid microparticles have a volume of 1/100 or less of the volume of the molten droplet. 7. In the method according to claim 1, the droplet of the molten material is a molten sphere, and the divided solid microparticles are solid particles having a volume of 1/100 or less of the molten sphere. A method for producing microparticles. 8. A method according to claim 7, wherein a normally solid material, which is a metal or an alloy, is used, and the rapidly moving ring-shaped mass comprises at least
A method for producing solid microparticles moving at a speed of 1140 m/min (3750 ft/min). 9. A method for producing solid microparticles according to claim 8, in which an inert gas atmosphere is created near the location where the decomposition is performed and the molten spheres. 10. A method according to claim 9, which provides solid microparticles of titanium or a titanium-based alloy.