EP0543017A1 - Method and device for making metallic powder - Google Patents
Method and device for making metallic powder Download PDFInfo
- Publication number
- EP0543017A1 EP0543017A1 EP92911022A EP92911022A EP0543017A1 EP 0543017 A1 EP0543017 A1 EP 0543017A1 EP 92911022 A EP92911022 A EP 92911022A EP 92911022 A EP92911022 A EP 92911022A EP 0543017 A1 EP0543017 A1 EP 0543017A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- cooling liquid
- cooling
- tubular body
- molten metal
- metal powder
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 239000000843 powder Substances 0.000 title claims abstract description 86
- 238000000034 method Methods 0.000 title claims abstract description 20
- 239000000110 cooling liquid Substances 0.000 claims abstract description 143
- 229910052751 metal Inorganic materials 0.000 claims abstract description 129
- 239000002184 metal Substances 0.000 claims abstract description 129
- 238000001816 cooling Methods 0.000 claims abstract description 47
- 230000002093 peripheral effect Effects 0.000 claims abstract description 31
- 238000007599 discharging Methods 0.000 claims abstract description 6
- 239000007789 gas Substances 0.000 claims description 49
- 239000007788 liquid Substances 0.000 claims description 37
- 238000002347 injection Methods 0.000 claims description 33
- 239000007924 injection Substances 0.000 claims description 33
- 239000011261 inert gas Substances 0.000 claims description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 6
- 230000005484 gravity Effects 0.000 claims description 2
- 238000007711 solidification Methods 0.000 abstract description 2
- 230000008023 solidification Effects 0.000 abstract description 2
- 238000013467 fragmentation Methods 0.000 abstract 1
- 238000006062 fragmentation reaction Methods 0.000 abstract 1
- 239000002245 particle Substances 0.000 description 19
- 238000004519 manufacturing process Methods 0.000 description 15
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 10
- 238000002360 preparation method Methods 0.000 description 10
- 229910000838 Al alloy Inorganic materials 0.000 description 7
- 229910052786 argon Inorganic materials 0.000 description 5
- 230000001105 regulatory effect Effects 0.000 description 5
- 239000000498 cooling water Substances 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 150000002739 metals Chemical class 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 229910000640 Fe alloy Inorganic materials 0.000 description 3
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 239000000112 cooling gas Substances 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 238000001035 drying Methods 0.000 description 3
- 239000010419 fine particle Substances 0.000 description 3
- 230000006698 induction Effects 0.000 description 3
- 238000002844 melting Methods 0.000 description 3
- 230000008018 melting Effects 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 238000010924 continuous production Methods 0.000 description 2
- 230000001276 controlling effect Effects 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910052581 Si3N4 Inorganic materials 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 239000000356 contaminant Substances 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 239000002826 coolant Substances 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000009689 gas atomisation Methods 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 239000002923 metal particle Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 238000007712 rapid solidification Methods 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 239000011819 refractory material Substances 0.000 description 1
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 description 1
- 238000009751 slip forming Methods 0.000 description 1
- 238000004544 sputter deposition Methods 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/02—Making ferrous alloys by powder metallurgy
- C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
- C22C33/0278—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5%
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
- B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
- B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
- B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
- B22F2009/0804—Dispersion in or on liquid, other than with sieves
- B22F2009/0812—Pulverisation with a moving liquid coolant stream, by centrifugally rotating stream
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
- B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
- B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
- B22F2009/084—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid combination of methods
Definitions
- the present invention relates to a method of and an apparatus for producing metal powders by supplying a molten metal to a cooling liquid layer in a swirling movement.
- Rapidly solidified metal powders are in the form of fine crystal grains and can be adapted to contain alloy elements to supersaturation, so that the extrudates and sintered materials prepared from rapidly solidified powders are superior to materials prepared by melting in characteristics and have attracted attention as materials for making machine parts.
- the methods of producing rapidly solidified metal powders include the rotary drum method as disclosed in Examined Japanese Patent publication HEI 1-49769. With this method, a rapidly solidified metal powder is prepared by rotating a cooling drum having a bottom and containing a cooling liquid to centrifugally form a cooling liquid layer over the inner periphery of the drum, and injecting a molten metal into the cooling liquid layer to divide the metal by the cooling liquid layer in a swirling motion.
- U.S. Patents No. 4,787,935 and No. 4,869,469 disclose methods and systems for producing a metal powder by atomizing a molten metal stream into spherical molten droplets and supplying the droplets to a swirling downward flow of cooling gas within a cooling cylinder for cooling and solidification.
- the rotary drum method is adapted for a so-called batchwise operation and therefore has the problem of being low in productivity. Furthermore, the speed of rotation of the cooling drum, which is limited,poses the probelm in that it is difficult to give an increased flow velocity to the cooling liquid layer and to obtain a fine powder.
- the production methods of the U.S. patents are adapted to continuously prepare a fine powder of 0.1 micrometer in size to a coarse powder of about 1000 micrometers.
- the cooling rate is limited to about 102 - 107 o C/sec and fails to achieve a sufficient rapid cooling effect.
- the molten droplets encounter difficulity in undergoing a swirling motion in the central portion of the swirling cooling gas flow and are cooled at a reduced rate, there arises the problem that the quality of the powder produced is liable to involve variations.
- the cooling cylinder needs to have a considerably large size to form therein a swirling cooling gas flow which is suitable for cooling the molten droplets. This poses another problem in that the methods are difficult to practice readily in view of the installation space and equipment cost.
- An object of the present invention which has been accomplished in view of the above problems, is to provide a method of producing metal powders which is less likely permit variations in cooling rate, ensures rapid solidification at a great cooling rate and readily gives fine particles, and a production apparatus which is suitable for practicing this method.
- the present invention provides a method of producing a metal powder by injecting a cooling liquid into a cooling tubular body along an inner peripheral surface thereof to form a cooling liquid layer moving toward a cooling liquid discharge end of the tubular body while swirling along the tubular body inner peripheral surface; supplying a molten metal to a space inside the cooling liquid layer; applying a gas jet as directed toward the cooling liquid layer to the molten metal to divide the molten metal and supply the divided molten metal to the cooling liquid layer; and discharging the cooling liquid containing a metal powder solidified in the liquid layer from the cooling liquid discharge end of the tubular body to outside.
- the cooling liquid containing the metal powder is discharged to outside preferably through a discharge pipe attached to a closure provided at the discharge end of the tubular body while filling the pipe with the cooling liquid.
- the present invention further provides a production apparatus comprising a cooling tubular body having a cooling liquid injection channel for injecting a cooling liquid into the tubular body along an inner peripheral surface thereof; molten metal supply means for supplying a molten metal into a space inside a cooling liquid layer formed by the cooling liquid injected from the injection channel and moving toward a cooling liquid discharge end of the tubular body while swirling along the tubular body inner peripheral surface; gas jet injection means for producing a gas jet to divide the molten metal and supply the divided molten metal to the cooling liquid layer; and cooling liquid supply means for supplying the cooling liquid to the cooling liquid injection channel.
- the tubular body has a closure attached to its cooling liquid discharge end, and a discharge pipe attached to the closure for discharging the cooling liquid therethrough with the pipe filled with the cooling liquid.
- the cooling liquid injected from the injection channel into the tubular body along the inner peripheral surface thereof moves toward an opening at the discharge end of the body while swirling along the inner peripheral surface, whereby a cooling liquid layer of approximately uniform inside diameter is formed on the inner peripheral surface of the tubular body by virtue of the centrifugal force of the swirling motion.
- This layer is formed by the cooling liquid which is newly supplied at all times, and therefore readily maintained at a constant temperature. Since the cooling medium is a liquid, the medium is superior to gases in cooling ability. For these reasons, the cooling liquid layer can be small in the radius of swirling motion and in thickness, with the result that the cooling tubular body for forming the layer therein can be compact.
- the gas jet injected from the injection means and directed toward the cooling liquid layer is forced against the molten metal supplied from the molten metal supply means into the space inside the cooling liquid to divide the molten metal.
- the divided molten metal (molten droplets) is sputtered toward the cooling liquid layer, and all the droplets are reliably supplied to and injected into the liquid layer.
- the molten droplets injected into the cooling liquid layer produce a vapor of the cooling liquid therearound, whereas the vapor is rapidly released from around the droplets.
- the reason is that since the liquid layer has a flow velocity which increases toward the center of the swirling motion, i.e., a gradient distribution of flow velocities, the molten droplets injected into the layer are in rotating motion.
- the molten droplets have their outer peripheral surfaces always held in contact with the cooling liquid, are therefore cooled at a high rate and make particles which are free of surface contamination with the vapor. Further because the size of molten droplets to be formed by dividing is adjustable easily by controlling the flow velocity of the gas jet and the flow rate thereof, the desired rapidly solidified fine powder can be prepared with ease. Moreover, the cooling liquid layer remains unchanged and stabilized in temperature and surface condition, permitting the molten droplets to cool under a definite condition to give a powder of stabilized quality.
- the powder can be produced also continuously by continuously supplying the molten metal and continuously applying the gas jet to the molten metal to divide the metal and supply the divided metal to the liquid layer.
- the metal powder solidified within the cooling liquid layer is continuously discharged from the liquid discharge end opening of the tubular body along with the cooling liquid.
- a suitable nonoxidizing gas such as inert gas or reducing gas, as this gas.
- FIG. 1 shows a metal powder production apparatus embodying the present invention.
- the apparatus comprises a cooling tubular body 1 having an inner peripheral surface for forming a cooling liquid layer 9 thereon, a crucible 15 serving as means for supplying a molten metal 25 in the form of a thin downward stream to a space 23 inside the cooling liquid layer 9, a pump 7 serving as means for supplying a cooling liquid to the tubular body 1, and a jet nozzle 24 serving as gas jet injection means for injecting a gas jet 26 for dividing the downward stream of molten metal 25 into molten droplets and supplying the droplets to the cooling liquid layer 9.
- the tubular body 1 is hollow cylindrical, is installed with its axis positioned vertically and has an upper-end opening provided with an annular closure 2.
- the closure 2 is centrally formed with an opening 3 for supplying the molten metal to the interior of the cooling tubular body 1 therethrough.
- the cooling body 1 is formed at an upper portion thereof with a plurality of cooling liquid injection tubes 4 having a cooling liquid injection channel 5 and arranged at equal spacings circumferentially of the body.
- the channel 5 has an outlet (discharge outlet) which is so opened as to inject the cooling liquid into the tubular body 1 along the inner peripheral surface tangentially thereof.
- the center line of the opening portion of the channel 5 extends obliquely downward at an angle of about 0 to about 20 o with respect to a plane orthogonal to the axis of the tubular body.
- the liquid injection tubes 4 are connected by piping to a tank 8 by way of a pump 7, which forces up the cooling liquid within the tank 8 and supplies the liquid to the inner peripheral surface of the tubular body 1 through the injection channels 5 of the injection tubes 4.
- the cooling liquid layer 9 is formed on the inner peripheral surface of the tubular body 1. This layer flows down while swirling along the inner peripheral surface.
- the tank 8 is provided with an unillustrated a cooling liquid replenishing pipe.
- a cooler may be provided suitably within the tank 8 or at an intermediate portion of a channel for recycling the cooling liquid.
- Water is generally used as the cooling liquid since water is excellent in cooling ability and inexpensive. Alternatively, oil or like liquid for use in quenching hot metals may be used. When water is to be used, it is desired to remove dissolved oxygen from the water before use. Oxygen removing devices are readily available commercially.
- a ring 10 for adjusting the thickness of the cooling liquid layer 9 is attached to an inner peripheral lower portion of the cooling tubular body 1 with bolts removably and replaceably.
- the thickness adjusting ring 10 limits the downward flow velocity of the cooling liquid, whereby the cooling liquid layer 9 can be readily formed with an approximately uniform inside diameter at a low flow rate.
- the tubular body 1 has a cooling liquid discharge end, i.e., a lower-end opening, which is provided with a hollow cylindrical draining net 11.
- a funnel-shaped powder collecting container 12 is attached to the lower end of the net 11.
- a cooling liquid collecting cover 13 is provided around and covers the net 11. The collecting cover 13 is provided in its bottom with a liquid outlet 14, which is connected to the tank 8 by piping.
- the crucible 15 serving as the molten metal supply means and disposed above the cooling tubular body 1 is made of graphite, silicon nitride or like refractory and comprises a hollow cylindrical crucible body 16 having a bottom 19, and a clousre 17 for closing an opening at the upper end of the body 16.
- the crucible body 16 is provided with a heating induction coil 18 therearound and has a nozzle orifice 20 extending vertically through the bottom 19.
- the nozzle orifice 20 is opposed to the opening 3 of the annular closure 2.
- the closure 17 of the crucible 15 has a bore 21 for injecting a pressure medium such as Ar, N2 or like inert gas and molten metal sent forward into the crucible therethrough.
- the molten metal 22 within the crucible 15 is forced through the nozzle orifice 20 and then through the opening 3 into the space 23 inside the cooling liquid layer 9 by the inert gas or the like injected into the crucible through the injection bore 21 under pressure.
- a jet nozzle 24 Disposed in the space 23 inside the cooling liquid layer 9 is a jet nozzle 24 for jetting a compressed gas, such as air or inert gas, which is used in the usual gas atomization process.
- the nozzle 24 is attached to the forward end of a compressed gas supply pipe 27 inserted through the opening 3 of the annular closure 2 and has an orifice which is directed toward the thin stream of molten metal 25 forced out from the nozzle orifice 20 and toward the cooling liquid layer 9.
- the outlets of the cooling liquid injection channels 5 are formed in the side surface of an upper portion of the cooling tubular body 1 as illustrated, the distance of the outlets from the thickness adjusting ring 10, if large, results in the likelihood that the liquid layer 9 will have a reduced thickness at its midportion when the cooling liquid flows down at an increased velocity. It is therefore desirable that the outlets of the injection channels 5 be positioned between the upper face of the adjusting ring 10 and the midportion between the upper end of the tubular body 1 and the upper face of the ring 10. Even when the outlets are so positioned, the cooling liquid is centrifugally forced upward above the outlets, forming the same liquid layer of definite thickness as below the outlets.
- the apparatus described operates in the following manner to produce a metal powder.
- the pump 7 is operated to form a cooling liquid layer 9 on the inner peripheral surface of the tubular body 1.
- the molten metal 22 within the crucible 15 is forced out downward through the nozzle orifice 20, with a gas jetted from the jet nozzle 24 at a high speed as indicated at 26.
- the gas jet 26 from the jet nozzle 24 is applied to the molten metal 25 forced out from the crucible 15 in the form of a thin stream, dividing the molten metal 25 and sputtering the resulting molten droplets against the cooling liquid layer 9.
- the molten droplets thus sputtered are injected into the cooling liquid layer 9 which flows down while swirling and are rapidly cooled and solidified into metal particles.
- the shape of the particles can be altered from spherical to flat indefinite forms by suitably determining the distance from the location where the gas jet 26 collide with the molten metal 25 to the cooling liquid layer 9. For example, if the distance to the liquid layer 9 is small, the molten droplets divided by the gas jet 26 are injected into the liquid layer 9 before a soldified shell is formed over the surface, and are divided by the liquid layer 9 again to form fine particles of indefinite shape. Conversely, if the distance is sufficiently large, the solidified shell is formed over the surfaces of the molten droplets, permitting the droplets to remain substantially spherical when injected into the cooling liquid layer 9.
- the metal powder in the cooling liquid layer 9 then flows down over the thickness adjusting ring 10 while swirling with the cooling liquid and enters the draining net 11 from the lower-end opening of the cooling tubular body 1.
- the cooling liquid in the net is centrifugally forced radially outward from the net 11, whereby the metal powder has its liquid content reduced by primary draining.
- the metal powder thus drained of the liquid enters the powder collecting container 12.
- the powder is discharged from the container, futher drained of the liquid by a centrifuge or like liquid removing device and dried by a dryer.
- the cooling liquid forced out from the net 11 is returned from the collecting cover 13 to the tank 8 and recylced for use.
- FIG. 2 shows another metal powder production apparatus embodying the invention.
- like parts are designated by like reference numerals.
- This embodiment has a cooling tubular body 1 which is installed with its axis inclined, and a cooling liquid injection channel 5 formed directly in the tubular body 1 which has a large wall thickness.
- the channel 5 has an inlet formed in the outer peripheral surface of the tubular body 1 and connected to a pump 7 by piping.
- the body 1 has a lower-end opening which is provided with a funnel-shaped closure 31 for closing the opening.
- the closure has a discharge pipe 33 attached to its bottom. The interior of the pipe serves as a discharge channel 32 for a cooling liquid.
- a thickness adjusting ring 10 having a tapered upper face is attached with bolts to the inner periphery of a lower portion of the tubular body 1.
- the discharge pipe 33 so extends that an outer-end opening (outlet) thereof is positioned above a tank 8, and is provided with a flow regulating valve 34 at an intermediate portion thereof.
- the tank 8 has an upper opening which is removably provided with a net basket 35.
- the cooling liquid can be discharged with the discharge channel 32 filled with the liquid by suitably adjusting the opened position of the flow regulating valve 34.
- This makes it possible to prevent gas from flowing out through the discharge pipe 33 and to fill the space 23 inside the cooling liquid layer 9 with the gas of gas jet 26 from a jet nozzle 24. Accordingly, the oxidation of divided molten droplets can be prevented effectively by using an inert gas or like nonoxidizing gas.
- FIG. 3 shows a third embodiment of metal powder production apparatus, wherein a cooling tubular body 1 is formed in its inner peripheral surface with outlets of cooling liquid injection channels 5 as arranged in a plurality of (two) stages.
- the number of stages of injection channels 5 and the spacing therebetween with respect to the axial direction of the tubular body differ in accordance with the inside diameter of the tubular body, rate of discharge of the cooling liquid, pressure of injection, position of lower thickness adjusting ring 10, etc.
- a suitable number of stages may be provided as approximately equidistantly spaced apart so as to obtain a cooling liquid layer of substantially uniform inside diameter.
- the present embodiment has a plurality of stages of cooling liquid injection channels 5 above the thickness adjusting ring 10.
- This arrangement serves to prevent the liquid layer 9 above the ring 10 from decreasing in thickness owing to an increase in the downward flow velocity of the cooling liquid.
- the liquid layer 9 can therefore be formed easily with a substantially uniform inside diameter and a constant swirling velocity over an elongated region on the inner peripheral surface of the tubular body 1, hence an elongated cooling zone.
- the thickness adjusting ring may be provided between the stages of injection channels 5 adjacent to each other axially of the tubular body as indicated at 10A, whereby the thickness and flow velocity of the layer 9 can be more stabilized.
- the cooling liquid injection channel 5 provided in a single stage in combination with a plurality of thickness adjusting rings is also effective for preventing the decrease in the thickness of the layer 9.
- a buffer flange 28 is removably attached to the inner periphery of the net 11 as by bolts.
- the flange 28 reduces the downward flow velocity of the cooling liquid to ensure drainage for a longer period of time for effective centrifugal removal of the liquid.
- FIG. 4 shows a fourth embodiment of metal powder production apparatus, which has a cooling tubular body 1 installed with its axis inclined, and two jet nozzles 24, 24 attached to compressed gas supply pipes 27, 27 for producing gas jets 26 intersecting each other in a V-form in a space 23 inside a cooling liquid layer 9 on the inner peripheral surface of the body.
- Each of the jet nozzles 24, 24 has an orifice which is in the form of a slit, and the gas jet 26 is in the form of a film having a given width.
- the intersecting gas jets are V-shaped in section as illustrated in the drawing.
- a molten metal 25 flows out from a nozzle orifice 20 of a crucible 15 downward to the region where the V-shaped gas jets intersect, and is thereby divided.
- a jet nozzle may be used which has a nozzle orifice in the form of an inverted conical slit for forming a gas jet defining an inverted conical face, such that the molten metal is supplied to the vertex of the jet.
- a plurality of jet nozzles each adapted to produce a linear gas jet may be arranged in an inverted conical form to provide an inverted conical assembly of linear gas jets for the molten metal to be supplied to the vertex of the assembly.
- the cooling tubular body 1 is provided at its lower-end opening with a draining net 11, through which the gas forming the jet or jets 26 flows out.
- the lower-end opening may be provided with the closure 31 shown in FIG. 2 and having the discharge pipe 33.
- the space 23 inside the cooling liquid layer 9 can then be readily filled with the jet-forming gas by controlling the flow regulating valve 34 mounted on an intermediate portion of the discharge pipe 33.
- the cooling tubular body 1 is in the form of a hollow cylinder, but is not limited to this shape.
- the body may be so shaped as to have a rotationally symmetric inner peripheral surface the diameter of which gradually decreases toward the direction of movement of the cooling liquid.
- the body may be in the form of a funnel.
- a cooling liquid layer of uniform inside diameter can be formed even if no thickness adjusting ring is used.
- the cooling tubular body is installed with its axis positioned vertically or obliquely, whereas this position is not limitative.
- the axis of the tubular body may be in any position insofar as cooling water can be injected into the body at a sufficient rate so as to form a cooling liquid layer 9 on the tubular body inner peripheral surface.
- the thickness adjusting ring 10 has a horizontal or tapered upper face, which nevertheless is not limitative.
- the ring may have a streamlined curved face extending from the outer peripheral edge of its upper end toward the inner peripheral edge of its lower end with a gradually decreasing diameter.
- the powders to be produced according to the invention are not limited to those of metals having a low melting point, such as aluminum and alloys thereof, but include those of metals having a high melting point, such as titanium, nickel, iron and alloys thereof.
- the metals to be treated are not limited specifically.
- FIGS. 5 and 6 show the overall construction of an example of metal powder continuous production equipment which includes the metal powder production apparatus already described with reference to FIG. 1 as the first embodiment and which is adapted to carry out a sequence of operations from the supply of molten metal through the production of metal powder, removal of the liquid and drying.
- the molten metal supplied from a molten metal continuous feeder 41 is treated by the metal powder production apparatus 42 already described, a continuous liquid removing device 43 and a continuous dryer 44 and made into a metal powder product.
- One of the other embodiments is of course usable as the metal powder production apparatus.
- the molten metal continuous feeder 41 comprises a container 46 made of a heat-insulating refractory material.
- the container 46 has a molten metal inlet 48 closable with a closure 47, a pipe 49 for supplying an inert gas or like pressure medium, a discharge pipe 50 for molten metal 53 within the container, and a bottom cavity 52 provided with an induction heating coil 51.
- the molten metal 53 in the container 46 has its temperature controlled by the coil 51 and is fed to the crucible 15 of the apparatus 42 through the discharge pipe 50 under the pressure of the inert gas, such as argon gas, injected through the supply pipe 49.
- the discharge pipe 50 is heat-insulated by suitable means such as a heat-insulating layer or induction heater.
- the metal powder produced by the apparatus 42 is fed to the continuous liquid removing device 43 by way of the powder collecting container 12 along with the cooling liquid remaining after the primary draining by the draining net 11, and is centrifugally acted on and thereby separated from the liquid.
- the continuous liquid removing device 43 comprises a rotary drum 55 flaring upward and having an intermediate peripheral wall which is formed by a screen plate with a multiplicity of small holes.
- the drum 55 has a multiplicity of projecting ribs 56 on its inner periphery for upwardly delivering the powder separated from the liquid.
- the rotary drum 55 is surrounded by a cooling liquid collecting cover 57, from the bottom of which the cooling liquid separated off is collected in the tank 8.
- a metal powder collecting cover 58 having a discharge chute 59.
- the wet metal powder delivered from the discharge chute 59 of the device 43 is subsequently fed to the continuous dryer 44.
- the dryer 44 comprises a drying container 62 having a porous membrane 61 with a multiplicity of pores, feed means 63 having a rotary feeder for supplying the wet material to an upper portion of the container 62, a hot air producing device 64 for supplying hot air from the bottom of the container 62, and a cyclone 65 for collecting fine particles from the air discharged from the top of the container 62.
- a discharge pipe 66 is attached to the side wall of the container 62 at its upper to lower portions.
- a fluidized layer 67 is formed inside the drying container 62.
- the wet metal powder is vigorously mixed with the hot air within the layer 67 for heat exchange, rapidly dried and discharged usually in the form of an overflow from the container through the discharge pipe 66.
- molten metal continuous feeder, continuous liquid removing device and continuous dryer for use in practicing the present invention are not limited to those described above, but suitable devices commercially available are usable.
- the production apparatus shown in FIG. 7 was used for preparing an aluminum alloy powder.
- the cooling tubular body 1 shown was 100 mm in inside diameter D.
- the cooling liquid injection channel 5 had outlets positioned at the midpoint between the upper end of the body 1 and the upper end of the thickness adjusting ring 10. Cooling water was injected into the body at a flow rate of 0.3 m3/min from the channel outlets which were 11.5 mm in diameter. Consequently formed above the ring 10 was a cooling liquid layer 9 which was 55 mm in inside diameter d, 50 mm in length h and 43 m/sec in flow velocity at the surface of the water layer.
- a molten aluminum alloy (composition: Al-12 Si-1 Mg-1 Cu, in wt. %) was prepared in the crucible 15 at 1000 o C.
- the molten metal 22 in the crucible 15 was pressurized by supplying argon gas thereto at 1.0 kgf/cm2, and a thin stream of molten metal 25, 2 mm in diameter, was injected from the nozzle orifice 20 of the crucible 15 into a space 23 inside the liquid layer 9.
- the stream of molten metal 25 made an injection angle ⁇ 1 of 30 deg with a horizontal plane.
- An air jet 26 was forced out at 5 kgf/cm2 from the jet nozzle 24 with a nozzle orifice diameter of 6 mm against the molten metal 25 in the space 23, at an angle ⁇ 2 of 45 deg between the jet 26 and a horizontal plane.
- the angle ⁇ 3 made by the jet 26 with the thin stream of molten metal 25 was 45 deg as measured from the molten metal 25 in the swirling direction A of the cooling liquid layer.
- the aluminum alloy powder consequently obtained had a particle size distribution (relation between the particle size of particular particles in the powder and the content in wt. % of the particles of the size based on the whole amount of the powder) indicated at A in FIG. 9.
- the powder was 291.8 micrometers in mean particle size and 0.90 g/cm3 in bulk density.
- the particles were found to be flat and indefinite in shape. This appears to indicate that the molten droplets divided by the air jet were divided again by the cooling liquid layer.
- an aluminum alloy powder was prepared under the same conditions as above except that no air jet was applied to the molten metal.
- the result achieved is shown also in FIG. 9 as indicated at B.
- the powder was 420 micrometers in mean particle size and 0.70 g/cm3 in bulk density. This reveals that the application of the air jet according to the invention readily produces finer particles.
- An aluminum alloy powder having the same composition as in Preparation Example 1 was prepared using the apparatus shown in FIG. 2.
- the cooling tubular body 1 was 200 mm in inside diameter, and the axis of the body was inclined at an angle of 25 deg with respect to a vertical.
- the cooling liquid injection channel 5 had outlets which were 11.5 mm in diameter and through which cooling water was injected into the body at a flow rate of 0.3 m3/min.
- the flow regulating valve 34 was adjusted to fill the discharge channel 32 with the cooling liquid.
- a molten aluminum alloy was prepared at 1000 o C in the crucible 15, and the molten metal 22 within the crucible was forced out in the form of a thin stream of molten metal 25, 2 mm in diameter, from the nozzle orifice 20 of the crucible 15 vertically downward into a space 23 inside the liquid layer 9 by supplying argon gas to the crucible 15 at 1.0 kgf/cm2.
- An argon gas jet 26 was applied at 10 kgf/cm2 from the jet nozzle 24 with a nozzle orifice diameter of 6 mm to the molten metal 25 in the space 23, whereby the molten metal 25 was made into particles.
- the angle made by the argon gas jet 26 with the molten metal 25 was 30 deg.
- FIG. 10 shows the relation between the particle size and the cooling rate.
- the cooling rate was determined from the metal structure of particles of the powder.
- the drawing shows that in the case of the metal powder prepared according to the invention, the cooling rate is 104 to 105 o C/sec even when relatively large particles, 100 to 1000 micrometers in size, are formed. This indicates that the invention affords a microfine structure.
- the drawing appears to indicate that the cooling rate for giving particles of 0.1 micrometer in size is at least 108 o C/sec.
- the powder was checked for gas contents, which were found to be 12 ppm of H2 and 500 ppm of O2.
- an aluminum alloy powder was prepared under the same conditions as above except that the flow regulating valve 34 was fully opened so as not to close the discharge pipe 33 with the cooling water.
- the resulting powder was found to contain 20 ppm of H2 and 820 ppm of O2. This indicates that the product of the invention is much lower in gas contents than the comparative example.
- An iron alloy powder was prepared under the same conditions as in Preparation Example 2.
- the iron alloy had the composition of Fe-1.3 C-4 Cr-3.5 Mo-10 W-3.5 V-10 Co as expressed in wt. %, and was melted at 1600 o C.
- the powder obtained was 250 micrometers in mean particle size. When checked for gas contents, the powder was found to contain 9 ppm of H2, 580 ppm of O2 and 720 ppm of N2. When an iron alloy powder of the same composition as above was prepared under the same conditions as above except that the average flow velocity of the cooling liquid layer was 5 m/sec, the powder was found to contain 15 ppm of H2, 1200 ppm of O2 and 740 ppm of N2. This reveals that as the flow velocity of the cooling liquid layer is increased, the molten droplets can be more rapidly separated or released from the vapor of the cooling liquid produced therearound so as to be free from contaminants more effectively.
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Abstract
Description
- The present invention relates to a method of and an apparatus for producing metal powders by supplying a molten metal to a cooling liquid layer in a swirling movement.
- Rapidly solidified metal powders are in the form of fine crystal grains and can be adapted to contain alloy elements to supersaturation, so that the extrudates and sintered materials prepared from rapidly solidified powders are superior to materials prepared by melting in characteristics and have attracted attention as materials for making machine parts.
- The methods of producing rapidly solidified metal powders include the rotary drum method as disclosed in Examined Japanese Patent publication HEI 1-49769. With this method, a rapidly solidified metal powder is prepared by rotating a cooling drum having a bottom and containing a cooling liquid to centrifugally form a cooling liquid layer over the inner periphery of the drum, and injecting a molten metal into the cooling liquid layer to divide the metal by the cooling liquid layer in a swirling motion.
- On the other hand, U.S. Patents No. 4,787,935 and No. 4,869,469 disclose methods and systems for producing a metal powder by atomizing a molten metal stream into spherical molten droplets and supplying the droplets to a swirling downward flow of cooling gas within a cooling cylinder for cooling and solidification.
- The rotary drum method is adapted for a so-called batchwise operation and therefore has the problem of being low in productivity. Furthermore, the speed of rotation of the cooling drum, which is limited,poses the probelm in that it is difficult to give an increased flow velocity to the cooling liquid layer and to obtain a fine powder.
- On the other hand, the production methods of the U.S. patents are adapted to continuously prepare a fine powder of 0.1 micrometer in size to a coarse powder of about 1000 micrometers. With these production methods, however, the cooling rate is limited to about 10² - 10⁷ oC/sec and fails to achieve a sufficient rapid cooling effect. Further because the molten droplets encounter difficulity in undergoing a swirling motion in the central portion of the swirling cooling gas flow and are cooled at a reduced rate, there arises the problem that the quality of the powder produced is liable to involve variations. Additionally, the cooling cylinder needs to have a considerably large size to form therein a swirling cooling gas flow which is suitable for cooling the molten droplets. This poses another problem in that the methods are difficult to practice readily in view of the installation space and equipment cost.
- An object of the present invention, which has been accomplished in view of the above problems, is to provide a method of producing metal powders which is less likely permit variations in cooling rate, ensures rapid solidification at a great cooling rate and readily gives fine particles, and a production apparatus which is suitable for practicing this method.
- The present invention provides a method of producing a metal powder by injecting a cooling liquid into a cooling tubular body along an inner peripheral surface thereof to form a cooling liquid layer moving toward a cooling liquid discharge end of the tubular body while swirling along the tubular body inner peripheral surface; supplying a molten metal to a space inside the cooling liquid layer; applying a gas jet as directed toward the cooling liquid layer to the molten metal to divide the molten metal and supply the divided molten metal to the cooling liquid layer; and discharging the cooling liquid containing a metal powder solidified in the liquid layer from the cooling liquid discharge end of the tubular body to outside. The cooling liquid containing the metal powder is discharged to outside preferably through a discharge pipe attached to a closure provided at the discharge end of the tubular body while filling the pipe with the cooling liquid.
- The present invention further provides a production apparatus comprising a cooling tubular body having a cooling liquid injection channel for injecting a cooling liquid into the tubular body along an inner peripheral surface thereof; molten metal supply means for supplying a molten metal into a space inside a cooling liquid layer formed by the cooling liquid injected from the injection channel and moving toward a cooling liquid discharge end of the tubular body while swirling along the tubular body inner peripheral surface; gas jet injection means for producing a gas jet to divide the molten metal and supply the divided molten metal to the cooling liquid layer; and cooling liquid supply means for supplying the cooling liquid to the cooling liquid injection channel. Preferably, the tubular body has a closure attached to its cooling liquid discharge end, and a discharge pipe attached to the closure for discharging the cooling liquid therethrough with the pipe filled with the cooling liquid.
- According to the present invention, the cooling liquid injected from the injection channel into the tubular body along the inner peripheral surface thereof moves toward an opening at the discharge end of the body while swirling along the inner peripheral surface, whereby a cooling liquid layer of approximately uniform inside diameter is formed on the inner peripheral surface of the tubular body by virtue of the centrifugal force of the swirling motion. This layer is formed by the cooling liquid which is newly supplied at all times, and therefore readily maintained at a constant temperature. Since the cooling medium is a liquid, the medium is superior to gases in cooling ability. For these reasons, the cooling liquid layer can be small in the radius of swirling motion and in thickness, with the result that the cooling tubular body for forming the layer therein can be compact.
- The gas jet injected from the injection means and directed toward the cooling liquid layer is forced against the molten metal supplied from the molten metal supply means into the space inside the cooling liquid to divide the molten metal. The divided molten metal (molten droplets) is sputtered toward the cooling liquid layer, and all the droplets are reliably supplied to and injected into the liquid layer. The molten droplets injected into the cooling liquid layer produce a vapor of the cooling liquid therearound, whereas the vapor is rapidly released from around the droplets. The reason is that since the liquid layer has a flow velocity which increases toward the center of the swirling motion, i.e., a gradient distribution of flow velocities, the molten droplets injected into the layer are in rotating motion. Consequently, the molten droplets have their outer peripheral surfaces always held in contact with the cooling liquid, are therefore cooled at a high rate and make particles which are free of surface contamination with the vapor. Further because the size of molten droplets to be formed by dividing is adjustable easily by controlling the flow velocity of the gas jet and the flow rate thereof, the desired rapidly solidified fine powder can be prepared with ease. Moreover, the cooling liquid layer remains unchanged and stabilized in temperature and surface condition, permitting the molten droplets to cool under a definite condition to give a powder of stabilized quality.
- Since the cooling liquid layer is continuously formed, the powder can be produced also continuously by continuously supplying the molten metal and continuously applying the gas jet to the molten metal to divide the metal and supply the divided metal to the liquid layer. The metal powder solidified within the cooling liquid layer is continuously discharged from the liquid discharge end opening of the tubular body along with the cooling liquid.
- It is desired to provide a closure for the liquid discharge end opening of the tubular body and to attach a discharge pipe to the closure so that the cooling liquid containing the metal powder can be discharged to outside through the pipe with the pipe filled with the cooling liquid. When the liquid is discharged in this way, the space inside the cooling liquid layer can be filled with the jet-forming gas easily. The molten droplets can be prevented from oxidation by using a suitable nonoxidizing gas, such as inert gas or reducing gas, as this gas.
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- FIG. 1 is a fragmentary sectional view of a metal powder production apparatus embodying the invention;
- FIG. 2 is a fragmentary sectional view of another embodiment of apparatus;
- FIG. 3 is a fragmentary sectional view of a third embodiment of apparatus;
- FIG. 4 is a fragmentary sectional view of a fourth embodiment of apparatus;
- FIG. 5 is a sectional diagram illustrating a molten metal continuous feeder;
- FIG. 6 is an overall layout of metal powder continuous production equipment;
- FIG. 7 is a fragmentary sectional view of a metal powder production apparatus used in a preparation example of the invention;
- FIG. 8 is a diagram showing the relation in position between a thin stream of molten metal and a gas jet used in the preparation example and as seen from above;
- FIG. 9 is a graph showing the particle size distribution of metal powders prepared in the example and a comparative preparation example; and
- FIG. 10 is a graph showing the relation between the cooling rate and the particle size of metal powder prepared in another preparation example of the invention.
- FIG. 1 shows a metal powder production apparatus embodying the present invention. The apparatus comprises a cooling
tubular body 1 having an inner peripheral surface for forming acooling liquid layer 9 thereon, acrucible 15 serving as means for supplying amolten metal 25 in the form of a thin downward stream to aspace 23 inside thecooling liquid layer 9, apump 7 serving as means for supplying a cooling liquid to thetubular body 1, and ajet nozzle 24 serving as gas jet injection means for injecting agas jet 26 for dividing the downward stream ofmolten metal 25 into molten droplets and supplying the droplets to the coolingliquid layer 9. - The
tubular body 1 is hollow cylindrical, is installed with its axis positioned vertically and has an upper-end opening provided with anannular closure 2. Theclosure 2 is centrally formed with an opening 3 for supplying the molten metal to the interior of the coolingtubular body 1 therethrough. Thecooling body 1 is formed at an upper portion thereof with a plurality of coolingliquid injection tubes 4 having a coolingliquid injection channel 5 and arranged at equal spacings circumferentially of the body. Thechannel 5 has an outlet (discharge outlet) which is so opened as to inject the cooling liquid into thetubular body 1 along the inner peripheral surface tangentially thereof. The center line of the opening portion of thechannel 5 extends obliquely downward at an angle of about 0 to about 20o with respect to a plane orthogonal to the axis of the tubular body. Theliquid injection tubes 4 are connected by piping to atank 8 by way of apump 7, which forces up the cooling liquid within thetank 8 and supplies the liquid to the inner peripheral surface of thetubular body 1 through theinjection channels 5 of theinjection tubes 4. Thus thecooling liquid layer 9 is formed on the inner peripheral surface of thetubular body 1. This layer flows down while swirling along the inner peripheral surface. Thetank 8 is provided with an unillustrated a cooling liquid replenishing pipe. A cooler may be provided suitably within thetank 8 or at an intermediate portion of a channel for recycling the cooling liquid. Water is generally used as the cooling liquid since water is excellent in cooling ability and inexpensive. Alternatively, oil or like liquid for use in quenching hot metals may be used. When water is to be used, it is desired to remove dissolved oxygen from the water before use. Oxygen removing devices are readily available commercially. - A
ring 10 for adjusting the thickness of thecooling liquid layer 9 is attached to an inner peripheral lower portion of the coolingtubular body 1 with bolts removably and replaceably. Thethickness adjusting ring 10 limits the downward flow velocity of the cooling liquid, whereby the coolingliquid layer 9 can be readily formed with an approximately uniform inside diameter at a low flow rate. Thetubular body 1 has a cooling liquid discharge end, i.e., a lower-end opening, which is provided with a hollowcylindrical draining net 11. A funnel-shapedpowder collecting container 12 is attached to the lower end of the net 11. A coolingliquid collecting cover 13 is provided around and covers the net 11. The collectingcover 13 is provided in its bottom with aliquid outlet 14, which is connected to thetank 8 by piping. - The
crucible 15 serving as the molten metal supply means and disposed above the coolingtubular body 1 is made of graphite, silicon nitride or like refractory and comprises a hollowcylindrical crucible body 16 having a bottom 19, and aclousre 17 for closing an opening at the upper end of thebody 16. Thecrucible body 16 is provided with aheating induction coil 18 therearound and has anozzle orifice 20 extending vertically through the bottom 19. Thenozzle orifice 20 is opposed to the opening 3 of theannular closure 2. Theclosure 17 of thecrucible 15 has abore 21 for injecting a pressure medium such as Ar, N₂ or like inert gas and molten metal sent forward into the crucible therethrough. Themolten metal 22 within thecrucible 15 is forced through thenozzle orifice 20 and then through the opening 3 into thespace 23 inside the coolingliquid layer 9 by the inert gas or the like injected into the crucible through the injection bore 21 under pressure. - Disposed in the
space 23 inside the coolingliquid layer 9 is ajet nozzle 24 for jetting a compressed gas, such as air or inert gas, which is used in the usual gas atomization process. Thenozzle 24 is attached to the forward end of a compressedgas supply pipe 27 inserted through the opening 3 of theannular closure 2 and has an orifice which is directed toward the thin stream ofmolten metal 25 forced out from thenozzle orifice 20 and toward the coolingliquid layer 9. - While the outlets of the cooling
liquid injection channels 5 are formed in the side surface of an upper portion of the coolingtubular body 1 as illustrated, the distance of the outlets from thethickness adjusting ring 10, if large, results in the likelihood that theliquid layer 9 will have a reduced thickness at its midportion when the cooling liquid flows down at an increased velocity. It is therefore desirable that the outlets of theinjection channels 5 be positioned between the upper face of the adjustingring 10 and the midportion between the upper end of thetubular body 1 and the upper face of thering 10. Even when the outlets are so positioned, the cooling liquid is centrifugally forced upward above the outlets, forming the same liquid layer of definite thickness as below the outlets. - The apparatus described operates in the following manner to produce a metal powder. First, the
pump 7 is operated to form a coolingliquid layer 9 on the inner peripheral surface of thetubular body 1. Next, themolten metal 22 within thecrucible 15 is forced out downward through thenozzle orifice 20, with a gas jetted from thejet nozzle 24 at a high speed as indicated at 26. Thegas jet 26 from thejet nozzle 24 is applied to themolten metal 25 forced out from thecrucible 15 in the form of a thin stream, dividing themolten metal 25 and sputtering the resulting molten droplets against the coolingliquid layer 9. The molten droplets thus sputtered are injected into the coolingliquid layer 9 which flows down while swirling and are rapidly cooled and solidified into metal particles. In this case, the shape of the particles can be altered from spherical to flat indefinite forms by suitably determining the distance from the location where thegas jet 26 collide with themolten metal 25 to the coolingliquid layer 9. For example, if the distance to theliquid layer 9 is small, the molten droplets divided by thegas jet 26 are injected into theliquid layer 9 before a soldified shell is formed over the surface, and are divided by theliquid layer 9 again to form fine particles of indefinite shape. Conversely, if the distance is sufficiently large, the solidified shell is formed over the surfaces of the molten droplets, permitting the droplets to remain substantially spherical when injected into the coolingliquid layer 9. - The metal powder in the cooling
liquid layer 9 then flows down over thethickness adjusting ring 10 while swirling with the cooling liquid and enters the draining net 11 from the lower-end opening of the coolingtubular body 1. The cooling liquid in the net is centrifugally forced radially outward from the net 11, whereby the metal powder has its liquid content reduced by primary draining. The metal powder thus drained of the liquid enters thepowder collecting container 12. The powder is discharged from the container, futher drained of the liquid by a centrifuge or like liquid removing device and dried by a dryer. The cooling liquid forced out from the net 11 is returned from the collectingcover 13 to thetank 8 and recylced for use. - FIG. 2 shows another metal powder production apparatus embodying the invention. Throughout FIGS. 1 and 2, like parts are designated by like reference numerals.
- This embodiment has a cooling
tubular body 1 which is installed with its axis inclined, and a coolingliquid injection channel 5 formed directly in thetubular body 1 which has a large wall thickness. Thechannel 5 has an inlet formed in the outer peripheral surface of thetubular body 1 and connected to apump 7 by piping. Thebody 1 has a lower-end opening which is provided with a funnel-shapedclosure 31 for closing the opening. The closure has adischarge pipe 33 attached to its bottom. The interior of the pipe serves as adischarge channel 32 for a cooling liquid. Athickness adjusting ring 10 having a tapered upper face is attached with bolts to the inner periphery of a lower portion of thetubular body 1. Thedischarge pipe 33 so extends that an outer-end opening (outlet) thereof is positioned above atank 8, and is provided with aflow regulating valve 34 at an intermediate portion thereof. Thetank 8 has an upper opening which is removably provided with anet basket 35. - With the present embodiment, the cooling liquid can be discharged with the
discharge channel 32 filled with the liquid by suitably adjusting the opened position of theflow regulating valve 34. This makes it possible to prevent gas from flowing out through thedischarge pipe 33 and to fill thespace 23 inside the coolingliquid layer 9 with the gas ofgas jet 26 from ajet nozzle 24. Accordingly, the oxidation of divided molten droplets can be prevented effectively by using an inert gas or like nonoxidizing gas. - FIG. 3 shows a third embodiment of metal powder production apparatus, wherein a cooling
tubular body 1 is formed in its inner peripheral surface with outlets of coolingliquid injection channels 5 as arranged in a plurality of (two) stages. The number of stages ofinjection channels 5 and the spacing therebetween with respect to the axial direction of the tubular body differ in accordance with the inside diameter of the tubular body, rate of discharge of the cooling liquid, pressure of injection, position of lowerthickness adjusting ring 10, etc. A suitable number of stages may be provided as approximately equidistantly spaced apart so as to obtain a cooling liquid layer of substantially uniform inside diameter. The present embodiment has a plurality of stages of coolingliquid injection channels 5 above thethickness adjusting ring 10. This arrangement serves to prevent theliquid layer 9 above thering 10 from decreasing in thickness owing to an increase in the downward flow velocity of the cooling liquid. Theliquid layer 9 can therefore be formed easily with a substantially uniform inside diameter and a constant swirling velocity over an elongated region on the inner peripheral surface of thetubular body 1, hence an elongated cooling zone. As seen in the drawing, the thickness adjusting ring may be provided between the stages ofinjection channels 5 adjacent to each other axially of the tubular body as indicated at 10A, whereby the thickness and flow velocity of thelayer 9 can be more stabilized. However, the coolingliquid injection channel 5 provided in a single stage in combination with a plurality of thickness adjusting rings is also effective for preventing the decrease in the thickness of thelayer 9. - With the third embodiment of FIG. 3, a
buffer flange 28 is removably attached to the inner periphery of the net 11 as by bolts. Theflange 28 reduces the downward flow velocity of the cooling liquid to ensure drainage for a longer period of time for effective centrifugal removal of the liquid. - FIG. 4 shows a fourth embodiment of metal powder production apparatus, which has a cooling
tubular body 1 installed with its axis inclined, and twojet nozzles gas supply pipes gas jets 26 intersecting each other in a V-form in aspace 23 inside a coolingliquid layer 9 on the inner peripheral surface of the body. Each of thejet nozzles gas jet 26 is in the form of a film having a given width. The intersecting gas jets are V-shaped in section as illustrated in the drawing. Amolten metal 25 flows out from anozzle orifice 20 of acrucible 15 downward to the region where the V-shaped gas jets intersect, and is thereby divided. The V-shaped gas jets effectively divide the molten metal, forcing the divided molten droplets from the region of intersection into the inner periphery of the coolingliquid layer 9 over a specified area for the injection of the droplets even if themolten metal 25 flows down as somewhat deflected. Incidentally, a jet nozzle may be used which has a nozzle orifice in the form of an inverted conical slit for forming a gas jet defining an inverted conical face, such that the molten metal is supplied to the vertex of the jet. Alternatively, a plurality of jet nozzles each adapted to produce a linear gas jet may be arranged in an inverted conical form to provide an inverted conical assembly of linear gas jets for the molten metal to be supplied to the vertex of the assembly. - With the third and fourth embodiments, the cooling
tubular body 1 is provided at its lower-end opening with a drainingnet 11, through which the gas forming the jet orjets 26 flows out. However, the lower-end opening may be provided with theclosure 31 shown in FIG. 2 and having thedischarge pipe 33. Thespace 23 inside the coolingliquid layer 9 can then be readily filled with the jet-forming gas by controlling theflow regulating valve 34 mounted on an intermediate portion of thedischarge pipe 33. - With the foregoing embodiments, the cooling
tubular body 1 is in the form of a hollow cylinder, but is not limited to this shape. The body may be so shaped as to have a rotationally symmetric inner peripheral surface the diameter of which gradually decreases toward the direction of movement of the cooling liquid. For example, the body may be in the form of a funnel. In the case where the body is trumpet-shaped with a paraboloid of revolution, a cooling liquid layer of uniform inside diameter can be formed even if no thickness adjusting ring is used. Further with the illustrated embodiments, the cooling tubular body is installed with its axis positioned vertically or obliquely, whereas this position is not limitative. The axis of the tubular body may be in any position insofar as cooling water can be injected into the body at a sufficient rate so as to form a coolingliquid layer 9 on the tubular body inner peripheral surface. - Further in the case of the illustrated embodiments, the
thickness adjusting ring 10 has a horizontal or tapered upper face, which nevertheless is not limitative. For example, the ring may have a streamlined curved face extending from the outer peripheral edge of its upper end toward the inner peripheral edge of its lower end with a gradually decreasing diameter. Although themoltem metal 22 in thecrucible 15 is forced out through thenozzle orifice 20 under the pressure exerted by a pressure medium, themetal 22 may be forced out (caused to flow out) from thenozzle orifice 20 under gravity acting on itself without using the pressure medium. - The powders to be produced according to the invention are not limited to those of metals having a low melting point, such as aluminum and alloys thereof, but include those of metals having a high melting point, such as titanium, nickel, iron and alloys thereof. Thus the metals to be treated are not limited specifically.
- FIGS. 5 and 6 show the overall construction of an example of metal powder continuous production equipment which includes the metal powder production apparatus already described with reference to FIG. 1 as the first embodiment and which is adapted to carry out a sequence of operations from the supply of molten metal through the production of metal powder, removal of the liquid and drying. With this equipment, the molten metal supplied from a molten metal
continuous feeder 41 is treated by the metalpowder production apparatus 42 already described, a continuousliquid removing device 43 and acontinuous dryer 44 and made into a metal powder product. One of the other embodiments is of course usable as the metal powder production apparatus. - The molten metal
continuous feeder 41 comprises acontainer 46 made of a heat-insulating refractory material. Thecontainer 46 has amolten metal inlet 48 closable with aclosure 47, apipe 49 for supplying an inert gas or like pressure medium, adischarge pipe 50 for moltenmetal 53 within the container, and abottom cavity 52 provided with aninduction heating coil 51. Themolten metal 53 in thecontainer 46 has its temperature controlled by thecoil 51 and is fed to thecrucible 15 of theapparatus 42 through thedischarge pipe 50 under the pressure of the inert gas, such as argon gas, injected through thesupply pipe 49. Thedischarge pipe 50 is heat-insulated by suitable means such as a heat-insulating layer or induction heater. - The metal powder produced by the
apparatus 42 is fed to the continuousliquid removing device 43 by way of thepowder collecting container 12 along with the cooling liquid remaining after the primary draining by the drainingnet 11, and is centrifugally acted on and thereby separated from the liquid. The continuousliquid removing device 43 comprises arotary drum 55 flaring upward and having an intermediate peripheral wall which is formed by a screen plate with a multiplicity of small holes. Thedrum 55 has a multiplicity of projectingribs 56 on its inner periphery for upwardly delivering the powder separated from the liquid. Therotary drum 55 is surrounded by a coolingliquid collecting cover 57, from the bottom of which the cooling liquid separated off is collected in thetank 8. Provided over thedrum 55 is a metalpowder collecting cover 58 having adischarge chute 59. - The wet metal powder delivered from the
discharge chute 59 of thedevice 43 is subsequently fed to thecontinuous dryer 44. Thedryer 44 comprises a dryingcontainer 62 having aporous membrane 61 with a multiplicity of pores, feed means 63 having a rotary feeder for supplying the wet material to an upper portion of thecontainer 62, a hotair producing device 64 for supplying hot air from the bottom of thecontainer 62, and acyclone 65 for collecting fine particles from the air discharged from the top of thecontainer 62. Adischarge pipe 66 is attached to the side wall of thecontainer 62 at its upper to lower portions. - A
fluidized layer 67 is formed inside the dryingcontainer 62. The wet metal powder is vigorously mixed with the hot air within thelayer 67 for heat exchange, rapidly dried and discharged usually in the form of an overflow from the container through thedischarge pipe 66. - The molten metal continuous feeder, continuous liquid removing device and continuous dryer for use in practicing the present invention are not limited to those described above, but suitable devices commercially available are usable.
- Metal powder preparation examples will be described below in detail.
- The production apparatus shown in FIG. 7 was used for preparing an aluminum alloy powder. The cooling
tubular body 1 shown was 100 mm in inside diameter D. The coolingliquid injection channel 5 had outlets positioned at the midpoint between the upper end of thebody 1 and the upper end of thethickness adjusting ring 10. Cooling water was injected into the body at a flow rate of 0.3 m³/min from the channel outlets which were 11.5 mm in diameter. Consequently formed above thering 10 was a coolingliquid layer 9 which was 55 mm in inside diameter d, 50 mm in length h and 43 m/sec in flow velocity at the surface of the water layer. - A molten aluminum alloy (composition: Al-12 Si-1 Mg-1 Cu, in wt. %) was prepared in the
crucible 15 at 1000o C. Themolten metal 22 in thecrucible 15 was pressurized by supplying argon gas thereto at 1.0 kgf/cm², and a thin stream ofmolten metal nozzle orifice 20 of thecrucible 15 into aspace 23 inside theliquid layer 9. The stream ofmolten metal 25 made an injection angle ϑ₁ of 30 deg with a horizontal plane. - An
air jet 26 was forced out at 5 kgf/cm² from thejet nozzle 24 with a nozzle orifice diameter of 6 mm against themolten metal 25 in thespace 23, at an angle ϑ₂ of 45 deg between thejet 26 and a horizontal plane. When seen from above as shown in FIG. 8, the angle ϑ₃ made by thejet 26 with the thin stream ofmolten metal 25 was 45 deg as measured from themolten metal 25 in the swirling direction A of the cooling liquid layer. - The aluminum alloy powder consequently obtained had a particle size distribution (relation between the particle size of particular particles in the powder and the content in wt. % of the particles of the size based on the whole amount of the powder) indicated at A in FIG. 9. The powder was 291.8 micrometers in mean particle size and 0.90 g/cm³ in bulk density. The particles were found to be flat and indefinite in shape. This appears to indicate that the molten droplets divided by the air jet were divided again by the cooling liquid layer.
- For comparison, an aluminum alloy powder was prepared under the same conditions as above except that no air jet was applied to the molten metal. The result achieved is shown also in FIG. 9 as indicated at B. The powder was 420 micrometers in mean particle size and 0.70 g/cm³ in bulk density. This reveals that the application of the air jet according to the invention readily produces finer particles.
- An aluminum alloy powder having the same composition as in Preparation Example 1 was prepared using the apparatus shown in FIG. 2. The cooling
tubular body 1 was 200 mm in inside diameter, and the axis of the body was inclined at an angle of 25 deg with respect to a vertical. The coolingliquid injection channel 5 had outlets which were 11.5 mm in diameter and through which cooling water was injected into the body at a flow rate of 0.3 m³/min. As a result, a coolingliquid layer 9, 250 mm in inside diameter, 300 mm in length and 20 m/sec in average flow velocity, was formed between theannular closure 2 and thethickness adjusting ring 10. Theflow regulating valve 34 was adjusted to fill thedischarge channel 32 with the cooling liquid. - A molten aluminum alloy was prepared at 1000o C in the
crucible 15, and themolten metal 22 within the crucible was forced out in the form of a thin stream ofmolten metal nozzle orifice 20 of thecrucible 15 vertically downward into aspace 23 inside theliquid layer 9 by supplying argon gas to thecrucible 15 at 1.0 kgf/cm². - An
argon gas jet 26 was applied at 10 kgf/cm² from thejet nozzle 24 with a nozzle orifice diameter of 6 mm to themolten metal 25 in thespace 23, whereby themolten metal 25 was made into particles. The angle made by theargon gas jet 26 with themolten metal 25 was 30 deg. - The powder obtained was 200 micrometers in mean particle size and 1.3 g/cm³ in bulk density. FIG. 10 shows the relation between the particle size and the cooling rate. The cooling rate was determined from the metal structure of particles of the powder. The drawing shows that in the case of the metal powder prepared according to the invention, the cooling rate is 10⁴ to 10⁵ oC/sec even when relatively large particles, 100 to 1000 micrometers in size, are formed. This indicates that the invention affords a microfine structure. The drawing appears to indicate that the cooling rate for giving particles of 0.1 micrometer in size is at least 10⁸ oC/sec.
- Next, the powder was checked for gas contents, which were found to be 12 ppm of H₂ and 500 ppm of O₂. For comparison, an aluminum alloy powder was prepared under the same conditions as above except that the
flow regulating valve 34 was fully opened so as not to close thedischarge pipe 33 with the cooling water. The resulting powder was found to contain 20 ppm of H₂ and 820 ppm of O₂. This indicates that the product of the invention is much lower in gas contents than the comparative example. - An iron alloy powder was prepared under the same conditions as in Preparation Example 2. The iron alloy had the composition of Fe-1.3 C-4 Cr-3.5 Mo-10 W-3.5 V-10 Co as expressed in wt. %, and was melted at 1600o C.
- The powder obtained was 250 micrometers in mean particle size. When checked for gas contents, the powder was found to contain 9 ppm of H₂, 580 ppm of O₂ and 720 ppm of N₂. When an iron alloy powder of the same composition as above was prepared under the same conditions as above except that the average flow velocity of the cooling liquid layer was 5 m/sec, the powder was found to contain 15 ppm of H₂, 1200 ppm of O₂ and 740 ppm of N₂. This reveals that as the flow velocity of the cooling liquid layer is increased, the molten droplets can be more rapidly separated or released from the vapor of the cooling liquid produced therearound so as to be free from contaminants more effectively.
- 1
- cooling tubular body
- 4
- cooling liquid injection tube
- 5
- cooling liquid injection channel
- 7
- pump (cooling liquid supply means)
- 9
- cooling liquid layer
- 15
- crucible (molten metal supply means)
- 23
- space
- 24
- jet nozzle (gas jet injection means)
- 25
- molten metal
- 26
- gas jet
- 31
- closure
- 33
- discharge pipe
Claims (11)
- A method of producing a metal powder characterized in that the method comprises:
injecting a cooling liquid into a cooling tubular body along an inner peripheral surface thereof to form a cooling liquid layer moving toward a cooling liquid discharge end of the tubular body while swirling along the tubular body inner peripheral surface,
supplying a molten metal to a space inside the cooling liquid layer,
applying a gas jet as directed toward the cooling liquid layer to the molten metal to divide the molten metal and supply the divided molten metal to the cooling liquid layer, and
discharging the cooling liquid containing a metal powder solidified in the liquid layer from the cooling liquid discharge end of the tubular body to outside. - A method of producing a metal powder as defined in claim 1 wherein the cooling liquid containing the metal powder solidified in the liquid layer is discharged to outside through a discharge pipe attached to a closure provided at the discharge end of the tubular body while filling the pipe with the cooling liquid.
- A method of producing a metal powder as defined in claim 1 or 2 wherein water is used as the cooling liquid, and the gas jet is formed by an inert gas.
- A method of producing a metal powder as defined in claim 1 or 2 wherein the cooling tubular body is in the form of a hollow cylinder.
- A method of producing a metal powder as defined in claim 1 or 2 wherein the molten metal is supplied by gravity.
- A method of producing a metal powder as defined in claim 1 or 2 wherein the metal powder discharged along with the cooling liquid is continuously drained of the liquid and subsequently dried continuously.
- An apparatus for producing a metal powder characterized in that the apparatus comprises:
a cooling tubular body having a cooling liquid injection channel for injecting a cooling liquid into the tubular body along an inner peripheral surface thereof,
molten metal supply means for supplying a molten metal into a space inside a cooling liquid layer formed by the cooling liquid injected from the injection channel and moving toward a cooling liquid discharge end of the tubular body while swirling along the tubular body inner peripheral surface,
gas jet injection means for producing a gas jet to divide the molten metal and supply the divided molten metal to the cooling liquid layer, and
cooling liquid supply means for supplying the cooling liquid to the cooling liquid injection channel. - An apparatus for producing a metal powder as defined in claim 7 wherein the tubular body has a closure attached to its cooling liquid discharge end, and a discharge pipe attached to the closure for discharging the cooling liquid therethrough with the pipe filled with the cooling liquid.
- An apparatus for, producing a metal powder as defined in claim 7 or 8 wherein the cooling tubular body is in the form of a hollow cylinder.
- An apparatus for producing a metal powder as defined in claim 9 wherein a ring for adjusting the thickness of the cooling liquid layer is attached to the inner peripheral surface of the cooling tubular body.
- An apparatus for producing a metal powder as defined in claim 10 wherein a plurality of rings for adjusting the thickness of the layer are provided.
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP13434991 | 1991-06-05 | ||
JP134349/91 | 1991-06-05 | ||
JP23641491 | 1991-09-17 | ||
JP236414/91 | 1991-09-17 | ||
PCT/JP1992/000710 WO1992021462A1 (en) | 1991-06-05 | 1992-06-01 | Method and device for making metallic powder |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0543017A1 true EP0543017A1 (en) | 1993-05-26 |
EP0543017A4 EP0543017A4 (en) | 1994-01-26 |
EP0543017B1 EP0543017B1 (en) | 1998-02-25 |
Family
ID=26468477
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP92911022A Expired - Lifetime EP0543017B1 (en) | 1991-06-05 | 1992-06-01 | Method and device for making metallic powder |
Country Status (6)
Country | Link |
---|---|
EP (1) | EP0543017B1 (en) |
KR (1) | KR0174749B1 (en) |
AU (1) | AU645908B2 (en) |
CA (1) | CA2088054C (en) |
DE (1) | DE69224505T2 (en) |
WO (1) | WO1992021462A1 (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1285710A1 (en) * | 2000-04-21 | 2003-02-26 | Central Research Institute of Electric Power Industry | Method and apparatus for producing fine particles |
EP1285709A1 (en) * | 2000-04-21 | 2003-02-26 | Central Research Institute of Electric Power Industry | Method and apparatus for producing amorphous metal |
Families Citing this family (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
KR100768804B1 (en) * | 2000-04-21 | 2007-10-19 | 자이단호징 덴료쿠추오켄큐쇼 | Method for producing amorphous metal, method and apparatus for producing amorphous metal fine particles, and amorphous metal fine particles |
FR2814097B1 (en) * | 2000-09-21 | 2002-12-13 | Commissariat Energie Atomique | PROCESS FOR THE PREPARATION OF METAL PARTICLES OR A NUCLEAR METAL ALLOY |
KR102193651B1 (en) * | 2019-07-26 | 2020-12-21 | 코오롱인더스트리 주식회사 | Manufacturing Apparatus for Metal Powder |
CN111001817A (en) * | 2019-12-26 | 2020-04-14 | 中天上材增材制造有限公司 | Powder collecting tank for vacuum gas atomization powder preparation |
CN113798502B (en) * | 2021-09-16 | 2023-07-07 | 无锡锋速钢丸有限公司 | Cooling forming device and production process of stainless steel shot |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
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US3320338A (en) * | 1965-10-22 | 1967-05-16 | Jerome H Lemelson | Particle manufacture |
US4405535A (en) * | 1980-06-27 | 1983-09-20 | Battelle Memorial Institute | Preparation of rapidly solidified particulates |
EP0226323A1 (en) * | 1985-11-14 | 1987-06-24 | Dresser Industries, Inc. | Apparatus for preparing metal particles from molten metal |
WO1989000470A1 (en) * | 1987-07-20 | 1989-01-26 | Battelle Development Corporation | Double disintegration powder method |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS6144111A (en) * | 1984-08-07 | 1986-03-03 | Kawasaki Steel Corp | Apparatus for producing metallic powder |
JPH01198410A (en) * | 1988-02-02 | 1989-08-10 | Furukawa Electric Co Ltd:The | Apparatus for manufacturing metal powder |
JPH06144111A (en) * | 1992-11-14 | 1994-05-24 | Yasuo Isobe | Total resistance adjusting device for auxiliary winker of automobile |
-
1992
- 1992-06-01 DE DE69224505T patent/DE69224505T2/en not_active Expired - Lifetime
- 1992-06-01 EP EP92911022A patent/EP0543017B1/en not_active Expired - Lifetime
- 1992-06-01 KR KR1019930700241A patent/KR0174749B1/en not_active IP Right Cessation
- 1992-06-01 CA CA002088054A patent/CA2088054C/en not_active Expired - Fee Related
- 1992-06-01 AU AU17768/92A patent/AU645908B2/en not_active Ceased
- 1992-06-01 WO PCT/JP1992/000710 patent/WO1992021462A1/en active IP Right Grant
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3320338A (en) * | 1965-10-22 | 1967-05-16 | Jerome H Lemelson | Particle manufacture |
US4405535A (en) * | 1980-06-27 | 1983-09-20 | Battelle Memorial Institute | Preparation of rapidly solidified particulates |
EP0226323A1 (en) * | 1985-11-14 | 1987-06-24 | Dresser Industries, Inc. | Apparatus for preparing metal particles from molten metal |
WO1989000470A1 (en) * | 1987-07-20 | 1989-01-26 | Battelle Development Corporation | Double disintegration powder method |
Non-Patent Citations (1)
Title |
---|
See also references of WO9221462A1 * |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1285710A1 (en) * | 2000-04-21 | 2003-02-26 | Central Research Institute of Electric Power Industry | Method and apparatus for producing fine particles |
EP1285709A1 (en) * | 2000-04-21 | 2003-02-26 | Central Research Institute of Electric Power Industry | Method and apparatus for producing amorphous metal |
EP1285709A4 (en) * | 2000-04-21 | 2006-11-22 | Central Res Inst Elect | Method and apparatus for producing amorphous metal |
EP1285710A4 (en) * | 2000-04-21 | 2006-11-22 | Central Res Inst Elect | Method and apparatus for producing fine particles |
Also Published As
Publication number | Publication date |
---|---|
DE69224505T2 (en) | 1998-07-02 |
AU645908B2 (en) | 1994-01-27 |
CA2088054A1 (en) | 1992-12-06 |
AU1776892A (en) | 1993-01-08 |
EP0543017B1 (en) | 1998-02-25 |
EP0543017A4 (en) | 1994-01-26 |
WO1992021462A1 (en) | 1992-12-10 |
CA2088054C (en) | 1999-08-10 |
DE69224505D1 (en) | 1998-04-02 |
KR0174749B1 (en) | 1999-02-18 |
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