US 3785633 A
An arrangement for atomizing molten metallic material includes a furnace for tapping into a container and a cooling section. The furnace and container (crucible or ladle) are enclosed in a tank wherein they can be subjected to vacuum. The container is raisable and lowerable with respect to the cooling section, so that a closure valve can be inserted between them when suction is being applied. In the lowered position the container rests on a connecting member which contains nozzles for gas directed against the stream flowing from the container to disintegrate the stream into particles.
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Description (OCR text may contain errors)
United States Patent 1191 Karlsson 1 Jan. 15, 1974 MEANS FOR ATOMIZING MOLTEN METAL  Inventor: Gosta Karlsson, Vasteras, Sweden Pr'mary Exam".'er Ge1rald Dost Attorney-Jennings Bailey, Jr.  Assignee: Allmanna Svenska Elektriska v Aktiebolaget, Vastras, Sweden 22 Filed: May a, 1972  ABSTRACT  Appl. No.: 250,922 An arrangement for atomizing molten metallic material includes a furnace for tapping into a container and a cooling section. The furnace and container (crucible Foreign Appllcimon Priority Dam or ladle) are enclosed in a tank wherein they can be May 12, 1971 Sweden 6133/71 subjected to vacuum. The container-is raisable and lowerable with respect to the cooling section, so that a  US. Cl. 266/34 V, 266/34 R closure valve can be inserted between them when suc-  Int. Cl. C2lc 7/10 tion is being applied. in the lowered position the con-  Field of Search 266/34 R, 34 V, 38; tainer rests on a connecting member which contains 75/49; 425/7 nozzles for gas directed against the stream flowing from the container to disintegrate the stream into par-  References Cited ticles.
UNITED STATES PATENTS 6 Cl 2 D 3,692,443 9/1972 Lightner 266/34 v Pmmamms m4- 3785633 sum 1 0F 2 Fig.7,
MEANS FOR ATOMIZING MOLTEN METAL The present invention relates to a means for atomizing a molten metal or metal alloy. The device is of a type known per se, comprising a furnace for tapping into a casting ladle, and a cooling section, the furnace and casting ladle both being enclosed in a vacuum and- /or protective gas tank.
THE PRIOR ART United States patent application Ser. No. 94148 filed Dec. 1, 1970, and now abandoned describes method and means for atomizing melts, such as molten metal, by disintegrating a stream of molten metal by gas or gas-liquid jets directed under high pressure towards the molten flow. A first and a second of these disintegrating jets, spread each in its own plane, are directed towards each other from opposite sides of the molten stream at an angle of 25 60 to each other. The first disintegrating jet and the stream of molten metal form an angle of 30 60, preferably 40 45, to each other. The two disintegrating jets operate at such a distance from each other that after contact with the first jet, the stream of molten metal is substantially entirely deflected owing to the kinetic energy of this disintegrating jet, before the still molten stream of metal meets the second disintegrating jet. The melt is here disintegrated into free drops which form the desired powder particles after solidification. This is one method of obtaining such disintegration, and there are also other methods.
In the last-mentioned application, solidification is facilitated by blowing gas, suitably inert gas, of lower temperature through the disintegrating parts of the melt. The gas is allowed to circulate in the cooling dome and is intended to cool down the molten particles to solidification.
Although melts having low oxygen content are normally used, it may be difficult to prevent oxidation of the surface of the particles, and when high-alloyed steel is atomized the problem is that the alloy constituents in steel usually form extremely stable oxides which are difficult to reduce.
In order to reduce this drawback, both furnace and casting ladle have been located in a vacuum and/or protective gas tank having evacuating members of conventional type, for example multi-stage vapour jet ejection pumps and diffusion pumps which can effect a pressure in the tank of, for example, Torr, possibly before protective gas is allowed in.
One problem here is to be able to connect the atomizing part to the casting ladle after a vacuum valve has been opened without the vacuum or the protective gas atmosphere in the tank being lost and at the sme time to maintain all the advantages achieved by an efficient atomizing equipment, for example of the type described above.
SUMMARY OF THE INVENTION The device according to the invention provides a satisfactory solution of these problems and is characterised in that the casting ladle, which is provided with heat-retaining members and a bottom tapping hole, can be raised and lowered near the connection means to the cooling section, the casting ladle in its raised position exposing a lower space in which the vacuum valve can be moved to close the tank and in its lower position being connectable to the connecting means in or near which are arranged conventional nozzles for blowing gas or gas/liquid to disintegrate the tapping stream.
BRIEF DESCRIPTION OF THE DRAWINGS The invention is further exemplified in the accompanying drawings in which FIG. 1 is a detailed view of the casting ladle, furnace and atomizing part, while FIG. 2 is a total view of an equipment.
DESCRIPTION OF THE PREFERRED EMBODIMENT A furnace 12 for heat-retaining and possibly for heating a melt, for example steel such as high-alloyed steel, is arranged tiltably in a vacuum tank 11 (partly shown in FIG. 1). The furnace may be of crucible type with low or high frequency coils. In certain cases a stirrer may also be arranged with this furnace (or the singlephase feeding current can be switched to multi-phase stirring current) so that the melt can be degassed in the vaccum chamber (pressure for example 10' Torr).
Melt from the furnace 12 is tapped into a casting ladle 13, possibly water-cooled and exchangeable and provided with heat-retaining members 14 such as one or more inductor coils to prevent the melt from freezing in the main space of the ladle and its bottom tapping opening 15. The heat-retaining members permit long storage times in the ladle and the ladle can be tapped at the desired rate, continuously or intermittently. This is important since the tapping often takes a long time. 1
In the drawings the ladle 13 is shown in lowered position, but melt from thefurnace 12 can also be tapped into the casting ladle when it is raised to the position 16 shown in broken lines (see double arrow position A). In raised position a space 17 is exposed below the casting ladle, in which a vacuum sealing valve 18 can be inserted to sealing position for the tank 11.
When the valve (18) has been opened the casting ladle 13 can be lowered to a centered position near the tank wall 19. The ladle can be centered there against a number of conical pins 20, pins or holes being arranged in the lower side of the ladle and corresponding holes or pins in the wall of the tank and parts connected to it.
The ladle 13 has a lower connection part or sealing ring 21 which, in lowered position, is connected to an atomizing part 22 where there is a central opening 23 for the stream of melt and blowing nozzles 24, 25 for inert gas (argon, nitrogen, etc.) for disintegrating the stream into drops (see above). The sealing ring 22 is detachably applied at a gas supply part 26 with gas supply conduits, partly annularly arranged (27, 28). The sealing ring 22 and the part 26 are applied on an annular plate 29 which provides a connection part to the cooling means 30 (cooling dome, granulating tank), and connected to this plate by means of an elastic bellows 31 so that vertical movements of the dome 30 or connecting members 22, 26 may be permitted. The ring 22 and the part 26'may be permanently or detachably attached together.
The bellows 31 is also shown in FIG. 2, together with the vacuum tank 11, furnace l2 and casting ladle 13.
The motor for tilting the furnace is shown at 32, and
the entire vacuum part can be displaced with relation to the cooling dome 30, as can be seen.
The devices operates in the following manner: When the furnace 12 has been charged, the vacuum valve 18 between the tank 11 and cooling dome (granulating tank) 30 is closed. In the meanwhile a cooling ladle 33 is placed below the dome 30 with the help of a transport trolley 34. When this is done, the dome is pressed with the help of hydraulic devices 35 on its upper side against the bellows 31. The cooling dome is evacuated to a pressure of about 1 mm Hg, after which the dome and cooling ladle 33 are filled with inert gas (argon) to atmospheric pressure. The evacuated vacuum tank is then filled with inert gas to the same pressure and the vacuum valve 18 between the furnace tank 11 and the cooling dome 30 is opened. The casting ladle 13 (possibly one of several alternative ladles) is filled and applied in its lower position. Argon gas is supplied to the nozzles 24, 25 and the granulation is initiated.
After casting and granulation, the valve 18 between the furnace vacuum tank 11 and the cooling dome 30 is closed.
The furnace vacuum tank and granulating tower are evacuated and filled with air. The water-cooled casting ladle is exchanged when necessary and the cooling dome lifted (at 35), and the lower part with the cooling.
ladle 33 is moved to the side by means of removable devices 36 for cleaning. This is essential in view of clogging near the cooling ladle and when the alloy is changed before the next granulation batch.
The cooling dome may possibly be provided with a suction fan and cyclone for removal of dust.
After cooling the powder is sieved in a transport container.
The dome (granulation tower) is filled with argon through the cooling ladle 33.
After melting and granulation, therefore, the argon gas is drawn out of the cooling dome (granulation tower) 30 by a cyclone fan which thus removes a not inconsiderable amount of the dust particles in the argon gas. The outlet from the cooling dome also has a vacuum valve.
The device according to the above can be varied in many ways within the scope of the following claims. For example the entire atomization may take place completely or partially under vacuum instead of in a protective gas atmosphere.
1. Means for atomizing a molten metal or metal alloy comprising a furnace for tapping into a container and a cooling section with a connection part, a tank enclosing the furnace and container and provided with at least one vacuum sealing valve, said container being provided with heat-retaining means and a bottom tapping hole, said container being raisable and lowerable with respect to the connection part to the cooling section, the container in its raised position exposing a lower space in which the vacuum sealing valve can be moved in order to close the tank, and in its lowered position engaging the connection part, and nozzles for fluid, at least partly gas, to disintegrate the tapping stream associated with the connection part.
2. Means according to claim 1, having coacting centering members on the wall of the vacuum tank and on the container including conical pins engageable in holes in order to center the casting ladle in the desired position during tapping.
3. Means according to claim 1, having a cooling dome, the connection part engaging the upper part of the cooling dome and elastically displaceable in relation to the dome by means of elastic members.
4. Means according to claim 3, having an annular flange at the upper part of the cooling dome carried by the elastic members and carrying said nozzles.
5. Means according to claim 1, the vacuum tank with furnace and container being movably arranged in relation to the cooling dome after the casting ladle has been raised and the valve sealed.
6. Means according to claim 1, in which the connection part comprises a sealing ring with a melt opening and gas nozzle and a gas supply part.