IL37315A - Method and apparatus for producing generally spherical metallic powders from a bar - Google Patents

Description

A FOR SPHERICAL METALLIC POWDERS PROM BAR 01 Generally spherical metallic powder of small is produced in large by extending a long her of the material to he processed into chamber through a sealed rapidly rotating the bar while striking an arc between it and a stationary electrode to melt portions of the bar and oast off these portions by centrifugal force to form the and feedin the bar toward the electrode during to maintain a spark When the is nearly fully it is replaced out the chamber simply by aligning a second bar with the unconsumed portion of the first bar and axially advancing this second bar into the chamber through the sealed A unique seal capable of withstanding high rotational speeds seals the chamber while a dynamic rest restrains the bar from OF THE INVENTION Field of the Invention invention relates powder making and more to a method and apparatus for making generally spherical metallic shot in production Prior Art Metallic powders find frequent application throughout the For intricate parts which cannot readily or economically be formed by metal working processes can frequently be quickly and economically by compacting powders the desired in a Shaped die end sintering the resultant Other include the of composite materials having preselected ing characteristics fully powders of the materials from which the composite la to he these applications require the of powders of very small dimensions 50 to 500 in to achieve the desired many different niques have been utilised to produce metallic e simplest of involves the mechanical comminution of solid stock by a mechanical cutter or This technique is capable of producing powder large the powder is the forts of or is generally epherioal because Of the contact between the and the bareteck being it is dif cult to ensure high purity in the resulting Another technique involves the of powders by chemical of of the metal to be the particles produced by such a generally So not have the desired An especially useful technique for making powder is described in my earlier Patent issue July to assignee of the present The process desoribed therein forms generally powders of various sizes and high purity by rapidly rotating a rod of the materiel be prooessed inside a chamber and opposite an electrode through which current is supplied to the rod to thereby melt portions of it and east off the melted droplets by centrifugal The chamber flooded with inert gas prevent contamination of the particles during their formation end has an aooess port through which the operator of the machine can reach the rod and replace it when it has been nearly fully The rate at which powder be produced in this process is limited by the frequent need replace the consumable The length of these rods limited by the fact that the unsupported tip of rod adjacent the electrode undergoes a high centrifugal acceleration when This acceleration tends deflect rod outwardly of its longitudinal thereby imposing severe stresses on the rotating mechanisms and associated parts interfering with the required arcing relaionship between it and the stationary this process has been limited to use with rods of rather short length in relation to their thickness of the order of in length and in diameter in the ease of a red of This imposes a limitation on the productio A further limitation on the production rate is imposed the fact that the consumable changed from within the cham er This restricts the operator to working within a Confined area and necessitates his protection from the hot metallic parts within the chamber by means of bulky thermally insulated gloves and the like which further restricts the of ments replacing the consumable rod and lengthens the time required An additional limitation is imposed by the fact that the chuck the rod exposed to the molten and to stationary electrode during the melting process and deteriorates in thus requiring frequent OF THE INVENTION Objects is an object of the Invention to provide an improved cess and apparatus enabling higher production rates than heretofore Yet a further object of the invention is provide an improved process and apparatus in which the consumable materials are loaded external to the chamber in which they are a further of the invention ie provide an improved process and apparatus in which the from which powder is to made i3 rapidly loaded external to the chambe in which it is Another object of the invention is to provide an process and apparatus in which only the material to be cessed is exposed to the arcing Yet another object of the invention to provide a more economical and more ef icient process and Brief Description of the Invention In accordance with my ion quantities of generally spherical powder are obtained by feeding an electrode in the form of a long bar of material from which powder to obtained called a into a closed chamber through a sealed port and rapidly rotating the electrode while striking an arc betwee it and a The second electrode may be a stationary electrode of a material such as tungsten which is oonsumed only slowly in comparison with the consumable electrode or may comprise a rotating trode which a of the consumable When the two electrodes are brought opposite each other and supplied with current to form an arc between the consumable melts and casts off liquid droplets by centrifugal force to form the desired In the processed in accordance with the present Invention have a length to diameter ratio such that the frequency at which the bar is rotated in producing powder of a desired size distribution exceeds the frequency at which the tip of bar would deviate from the itudinal during rotation by an amount greater than the radius of the This would severe strains on the rotating machinery and would it if not to maintain an arc between the bar and the electrode were the free end not restrained from eccentric This restraint is provided by extending the forward end of the consumable electrode only slightly into the chamber during its melting so that its tip is supported against eccentric immediately adjacent the sealed port itself consumable electrode is it is continually translated toward the second electrode until only a small portion of extending through the sealed port between the exterior and interior of the remains At this the melting a second consumable electrode is axially aligned with the portion of the consumable electrode external to the and the second electrode is then axially fed through the port into the unconsumed portion of the electrod then into the chamber and the forward end of the second electrode takes it place in the sealed port and opposite the stationary The second electrode is then prepared for Instead o dropping the unconsumed portion of electrode into the thereby necessitating its reprocessing for subsequent may be joined to the second consumable electrode exterior to the chamber and the melting and spinning then resumed to consume it This will be especially advantageous when materials which costly or expensive to process being converted to method and apparatus the present invention allows rapid replacement of the consumable sinc the electrode is replaced external to the chamber in which it subsequently the operator not come into contaot with any machine parts which are at elevated This results in added safety for the it him to work unencumbered by awkward thermal such as asbestos gloves and therefore allows him to the changeover of electrodes rapidly and changing the electrodes in this manner ensures that the seal in the port communicating betwee the exterior and interior of the chamber is maintained relatively intact during and after the changeover operation so that none of the inert gas from the interior of the chamber can leak nor can contaminants from the outside of the chamber be carried into the As a inert gas is conserved and frequent purging of of the chamber to ensure complete cleanliness is All these factors lead to a more economical process for producing generally spherical metallic powder in large Detailed description of the The foregoing and other and further objects and features of the invention will be more readily understood on reference to the following detailed description of the invention in 1 is a front elevational view of a portion of the improved apparatus of the present 2 is a side elevational partly in of the apparatus of the present invention taken along the lines of 1 and showing a consumable bar positioned at the start of the making is a side elevational partly in also taken along the lines of 1 and showing the position of the consummable bar at a time near the end of the 4 is a plan with portions broken of the apparatus of the present invention in position for reloading a second bar to be 5 is a view in perspective of a bar and stub illustrating a method of joining them for 6 is a side sectional view of the chamber seal and dynamic rest utilized in conjunction with the present and 7 is a view in perspective of the dynamic rest of In 1 and the apparatus of the present invention is shown as comprising a vertically gas tight chamber having a front wall concave rear wall ik inclined toward the front and a side wall port not may be provided at the bottom of the chamber for removing powder and spent electrodes The chamber is supported by a truss A gas inlet line 20 and exhaust line 22 continuously recycle inert gsa through chamber 10 to provide cooling to the metal particles formed during the operation and to maintain an inert atmosphere around the particles being formed to thereby maintain their The gas is passed through heat to assist in cooling the molten A flexible seal 2k is formed in the front wall of the chamber An electrode 26 hearing a removable tip portion mounted in a collar 28 extends through a seal 2k into the interior of the chamber The seal 2k allows the electrode 26 and tip to be moved a greater or lesser distance into the A heavy trical lead 30 is connected to the electrode 26 through a conductive clamp The lead 30 is attached to the negative terminal of a high current power supply A second seal 3k in the front wall 1 2 of the chamber has a thermally insulated glove 36 to it and extending into the chamber 1 The tip of the electrode 26 may be changed by the operator when necessary with the aid of this A sealed viewing port is located adjacent the electrode 26 and the seal 5k to enable the ator to monitor the On the rear wall is located a seal Adjacent the seal k a dynamic rest which is attached to the wall by holts The seal and rest are shown i greater detail 5 and One end of an extended extends through the seal and rest the other end of this bar is clamped in a chuck by means of a hex nut The chuck is connected to a motor 52 through a belt a gear box A lead connected to the chuck shaft through a brush connects the bar to the positive terminal of the high current supply to which the terminal 30 is gear 56 rests directly on a table while the motor is supported from the table by support table 62 is driven zontally the chamber 10 along a bed 66 through a lead screw the letter is driven from motor The bed 66 is supported above a platform 72 by of columns A table more clearly in has a pair of extendable arms 78 which are utilized to load the bar to be processed at the appropriate the table slants slightly from rear to front to allow gravity loading of additional bar 80 is positioned on the table and is prevented from moving by pins 82 and which are retracted into the table at the appropriate time the loading this is seen more clearly in The motor 52 rapidly rotates the through the gear As bar an arc struck between the tip of ary electrode 26 and the end of the bar nearest this thus melting portions of the The melted portions are off in the form of small droplets by the centrifugal forces generated by the rapidly rotating these droplets assume a spherical shape in their flight through the chamber toward the chamber The dimensions of the chamber are chosen to sufficiently in relation to the flight path of the droplets that they solidify prior to striking the chamber these droplets retain their The size of the particles is determined by density of the material being the rotational speed of the bar and The production rate determined primarily by the length of the the current and the feed Por a yield of powder mately microns in diameter is readily formed from bar stock in diameter and length which is rotated at speeds of the order of The bar is advanced toward the stationary electrode at a rate of approximately per In the bars to be processed by the present invention will be in excess of 30 inches in 1 inch in and will be rotated to at of from about to yield powders ranging from a microns to several thousand As the bar it is continuously fed to the tip of the electrode 26 by the motor 70 and lead 68 in to maintain the bar in arcing relation with the tip Additional control of the spacing between the tip and the bar 46 is provided by the machine ator who moves the electrode 26 inwardly or as to control the shows the apparatus of the present invention toward the end of a that with the bar nearly fully In this the 62 has advanced toward the chamber to nearly its maximum As long as there is sufficient clearance between hex nut 50 and the dynamic rest the operation can the table 62 advances sufficiently toward the chamber that the hex nut 52 is brought immediately adjacent the rest operation is that the rotation of the bar 46 and its translation toward the trode 26 At this only a short stub more clearly in of the bar 46 remains This stub remains in the seal 40 while the hex nut 50 loosened to remove the stub from the chuck The platform is then hacked its rightmost position as shorn in to allow for the loading of a new In order to load the new the pins 82 on table 76 are dropped into the table to allow the bar 80 to onto the arms These arms are then extended by an hydraulic not so as to carry the bar 80 into a position aligned with the stub and the chuck At this the pins may also be momentarily dropped to allow an additional bar 86 on the table to roll into the position viously occupied by the bar bar 86 is then held in this positio while the bar 80 When the ba 80 aligned with the chuck the table 62 is advanced toward the bar and the latter is pushed into the At this the operator securely locks the bar 80 into the chuck by means of the hex nut The table 62 is then advanced toward the this advance the front end the bar 80 contacts the stub and pushes it toward the interior of the chamber as the bar 80 advances through the rest and seal into the chamber Tip then falls to the bottom of the chamber for subsequent removal after a suf number of bars have been will be noted that the seal is continuously occupied either by the stub or the bar 80 during the changeover Accordingly integrity of the seal is maintained during the changeover and little or no gas escapes from the chamber at this contamination from the environment is also sealed out and there is therefore no need to purge the chamber after the As was noted in many cases it will be found worthwhile to eliminate even the small amount of scrap represented by the stub This can readily be accomplished by the sub to the consumable electrode exterior to the chamber and then resuming the The joining can take any of a variety of For as shown in the bar may have cylindrical bore in the stub end which mates with cylindrical protrusion 80a at the forward end of bar The bore may be slightly in parts so as to a press fit with the protrusion A slot key or other fittings known to those skilled in the may also be used to secure the stub and bar together so that they remain integral during the The stub and bar may natively be welded together by known techniques such as by friction welding or flash among joining techniques may distort the stub and bar and thereby introduce Imbalanoe which may lead to difficulties when rotating the b at high It will be clear from the preceding that efficient operation of the apparatus described herein requires seal that can withstand the high rotational speeds encountered during the operation of the apparatus requires an effective support adjacent the free end of the that end not held in the to prevent unrestrained or eccentric rotation which would quickly damage the seal as well as the rotating A seal and a dynamic which have found especially advantageous in accomplishing these are shown in 6 and 7 in which is a side sectional vie of preferred embodiment of seal and a dynamic and 7 is a view in perspective with portions broken away for of the dynamic rest of In 6 the seal has a threaded collar which may be welded or otherwise ed the frame The collar has a back plate through which a cylindrical bore the extends through this The bore a groove 106 for receiving a resilient ring which forms a seal around the A flexible cylindrical bellows 108 is interposed between the back plate 102 and a graphite ring The bellows 108 and ring 110 have central apertures coincident with the bore A flange 112 threaded into the collar 100 carries a bearing having an inner race an outer race and set of rollers 20 An inner collar having a central aperture coincident with the forme a press fit with the race of the hearings The collar 22 has extending grooves for receiving resilient rings which seal the clearance between the bar and the inner wall of collar The eollar rotates with the inner of the As these elements they press against the graphite ring 0 which is held in tension against them means of the flexible bellows As the face of the collar the bellows continues to press it against the rotating component and thereby maintain tight seal with these Since the ring 22 rotates with the bar extending through the rings placed in the grooves 1 are ary with respect to the bar extending through and thus maintain a tight seal which does not degrade with time except for the slight wear caused by translation of the bar through any leakage of inert gas past the ed in the groove is effectively sealed off from communication with the exterior of chamber by means of the seals formed in the graphite ring 1 0 and the rings in the grooves Since the high rotational speeds encountered herein the order of from to generate large transverse forces on the bar being it is necessary to restrain the end of not clamped in the chuck from while allowing it to rotate freely about its own This is most readily accomplished by the dynamic rest shown in 6 and As shown the rest is formed from an inner plate separated from an oute plate 132 by spacers Rollers 138 and positioned around the periphery of a central circular aperture these rollers are symmetrically and only one of the roller will be described in Roller rotates with a shaft in a set of bearings The periphery of this bearing tangential to the aperture so that it forms essentially a line with the bar extending through apertur to prevent the bar from off its longitudinal axis in the direction of this The is true of the bearings 138 and which also contact the bar being fed through the aperture and rotate with they prevent the bar from whipping outwardly from its longitudinal axis but allow rotation of the about this The lengths of the bars processed in accordance with the present invention are limited only by ability to form a relatively straight bar over the desired length and to properly support it during Because the bar is rotating at high it is necessary to minimize any ricity of the since the eccentricity will become exsgerated If additional supports are provided the chuck holding one end of the ba and the dynamic rest ing the other the effects of these eccentricities will be These al supports will also enable one to utilize bars of longer length than may be used when no such additional supports It is known that for a bar of given and the maximum speed at which it may be rotated in inversely proportional to the of the distance between By providing additional supports between the chuck and the dynamic the length of bar that may be rotated at a given speed is of increases the overall efficiency of the powder production process since the required for replacing the bar is thereby The preferred embodiment of my invention as described in foregoing utilizes an electric arc melting process for rapidly melting the consumable Electric arc melting is preferred since it is readily controllable and does not introduce contaminants into the powder as may for in producing the powder with a hydrocarbon it will be understood that my invention is not so limited and that other melting techniques may also be used in conjunction with be replaced by an open flame a plasma arc or other means of inducing an energy flow into the consumable electrode or bar of sufficient intensity melt portions of it during high speed Prom the foregoing it will be seen that I have an improved powder making method and apparatus enables the production of generally relatively pure metallic The size of the powders produced in accordance with the invention may vary from several microns to thousands of microns dependent on the diameter of the stock being the al speed of the the material stiffness and among other By selectively controlling these the yield of particles of a given size range may be It will also be seen from the foregoing that the method and apparatus of the present tion provide an efficient and economical manner in which to form high purity The ability to rapidly load the materials to be processed external to the chamber enables the operator to maintain accelerated production it increases the safety of the operation since contact of the operator with the consumable electrode within the chamber is eliminated and also minimizes the necessity fo internal access to the thereby reducing requirements frequent purging of the It will also be seen that I have provided a unique seal for sealing the port through which the consumable bar enters the chamber and also provided efficient means for minimizing the rotational stresses on this thereby ing Various changes and modi of the invention may be made by those skilled in the art without departing from the spirit or of the invention and it is therefore intended that the foregoing material will be interpreted as illustrative only and not in a limiting insufficientOCRQuality

Claims (9)

1. 37315/3 Claims : 1. A method of producing generally spherical metallic particles comprising the steps of; A. introducing a source of heat energy into a chamber; B. introducing a consumable bar into said chamber through a port communicating between the interior and 'exterior of sai chamber, said bar (1) extending from the interior of said chamber to the exterior thereof through said port, (2) being consumable along the entire length thereof, and (3) having a longitudinal axis extending therethrough; C. positioning one end of the consumable bar in heat exchanging relation with the source of heat energy; D. restraining the opposite endji of the consumable bar from eccentric rotation; E. melting at least a portion of the consumable bar within the chamber by means of heat applied to it from said energy source; F. rotating the consumable bar about its longitudinal axis at a rate sufficient to cast off therefrom, by centrifugal force, melted portions of said bar; and G. advancing the consumable bar into said chamber at a controlled rate to thereby maintain the bar and the energy source in energy-absorbing relation with each other during rotation of the bar.

2. A method of producing generally spherical metallic particles, comprising the steps of: A. introducing a first electrode into a chamber; B. introducing a second electrode in the form of a consumable bar from which said powder is to be formed into said chamber through a port communicating between the interior and exterior of said chamber, said second electrode 37315/3 (1) extending from the interior of said chamber to the exterior thereof through said port; (2) being consumable along the entire length thereof, and (3) having a longitudinal axis extending therethrough; C. positioning one end of the second electrode adjacent the first electrode; D. restraining the opposite e d/ of the second electrode from eccentric rotation; E. applying an electrical potential between the electrodes to establish a current, therethrough of sufficient magnitude to melt portions of the second electrode; P. rotating the second electrode about its longitudinal axis at a rate sufficient to cast off therefrom, by centrifugal force, melted portions of said electrode, and G. advancing the second electrode into said chamber at a controlled rate to thereby maintain the electrodes in arc-supporting relation with each other.

3. A method according to claim 1 in which the bar is initially characterized by a length-to-diameter ratio such that the frequency at which the bar is rotated in producing powder is in excess of the frquency at which the bar, when supported only at one end thereof, would deviate from the longitudinal axis by an amount greater than the radius of the bar.

4. A method according to claim 2 in which a first end of the second electrode is restrained from eccentric rotation by a dynamic rest adjacent the port communicating between the interior and exterior of the chamber and in which a second end of the second electrode is restrained from eccentric rotation by contact with a driving element which rotates said electrode.

5. -6w A method according to claim 2 in which the second electrode is clamped for rotation with an axially translatable driving element external to the chamber, whereby rotational and translationaj force are simultaneously applied to said electrode by the driving element.

6. -¾ A method according to claim 2 in which a third electrode is aligned exterior to the chamber in abutting relation with an unconsumed portion of the second electrode after the second electrode has been substantially completely consumed and is axially advanced into the chamber with said unconsumed portion for further powder-producing operations. 6

7. -8» & method according to claim i in which said port comprises a sealed port which is maintained substantiallyintact during the replacement of the consumable electrodes by the successive presence of said second and third electrodes therein.

8. -9» method as claimed in claim 2 comprising the further step of axially aligning an additional electrode, exterior to said chamber, in abutting relation with the seeond electrode when the second electrode has an unconsumed portion extending through said sealed port*

9. -†0; A method as claimed in claim 2 comprising the further step of providing translational motion to said additional electrode along said longitudinal axis to thereby move the additional electrode and the unconsumed portion of the second electrode through the sealed port and into said chamber while maintaining a seal between the chamber second and additional electrodes. 10.14» Apparatus for producing relatively pure, generally spherical metallic powder comprising: A. a chamber for maintaining a controlled atmosphere therein; heat B. means introducing a f¾s¾4; energy source into said chamber? C. a port communicating between the interior and exterior of said chamber and adapted to receive a rotating, consumable bar extending therethrough) 37315/4 D. means external to said chamber for receiving one end of said bar therein ^ and for rotating said bar at a speed sufficient to cast off melted droplets therefrom, and means for positioning the other end in heat exchanging relation with said heat energy source. ': E. means for advancing said bar into said chamber at a controlled rate for maintaining said heat energy source and said bar in energy absorbing relation during rotation of said bar to thereby melt portions of said bar and cast them off in the form of spherical droplets by centrifugal forces. 11. Apparatus for producing relatively pure, generally spherical metallic powder comprising: A. a chamber for maintaining a controlled atmosphere therein, B. means introducing a first electrode into said chamber, C. a port communicating between the interior and exterior of said chamber and adapted to receive a second, rotating, consumable electrode extending therethrough, and means for positioning one end of said second electrode adjacent one end of said first electrode, D. means for striking an electrical arc between the adjacent ends of said first and second electrodes to thereby melt portions of said second electrode* B. means external to said chamber for receiving the other end of said second electrode therein and for rotating said electrode at a speed sufficient to cast off melted droplets therefrom, while simultaneously advancing said second electrode into said chamber at a controlled rate, to thereby maintain the said electrodes in arc-supporting relation with each other* 12. Apparatus according to claim 10 in which at least one of the energy source and the bar are translated with respect to the other during rotation of the bar to thereby maintain them in energy-absorbing relation. 13. Apparatus according to claim 10 in which the bar is initially characterized by a length-to-diameter ratio such that the frequency at which the bar is rotated in producing powder is in excess of the frequency at which the bar, when supported , only at one end thereof, would deviate from the longitudinal axis by an amount 15· Apparatus according to claim 12 which includes means for restraining the eccentric rotation of said second electrode at a position adjacent said port whereby the load on said seal due to said rotation is minimized. 16» Apparatus according to claim 1 in which said second electrode is generally cylindrical in shape and is rotated along the major axis of said cylinder, and in which the means for restraining said eccentric rotation comprises a plurality of rotatable cylindrical plates circumferentially spaced apart from each other and in peripheral contact with said electrode adjacent said port, 17· Apparatus according to claim 12 in which said port includes a seal conformable to said second electrode for isolating the interior of said ash chamber from the exterior thereof, 18, Apparatus as claimed in claim 12 for producing powder from a bar of consumable material comprising means for mounting a second end of the consumable electrode for rotation about said longitudinal axis at aspeed sufficient to caet off melted droplets from the exterior of said electrode under the action of centrifugal force, the mounting means being positionable sufficiently far from the restraining means to accommodate therein an electrode having a length of the order of magnitude of the shortest critical length of the consumable electrode when rotated at the selected speed, 9, Apparatus according to claim 17 in which said seal includes a first stationary collar, a rotatable collar mounted in said stationary collar and having an aperture for receiving said second electrode therethrough along a longitudinal axis thereof, the rotatable collar and the second electrode being rotatable with each other, a wearable low friction surface positioned in a plane normal to tsaid longitudinal axis and abutting said rotary collar, and means for holding said low friction surface against said rotary collar to provide a seal therewith, 20, Apparatus according to claim 19 in which the aperture in rotatable collar is adapted to receive at least one resilient sealing element for sealing the clearance between the second electrode and the rotatable collar to thereby a f 21. Apparatus according to claim 12 which includes means t second electrode troards said first electrode to thereby maintain said electrodes in arc supporting relation. 22. Apparatus according to claim 12 in which the means for receiving a second electrode therein comprises a chuck into which said electrode is releasably inserted and connected in drivi relation with a motor for rotation thereby. 23. Apparatus according to claim 22 in which said chuck is mounted for translatxonal motion toward said chamber at a controlled rate whereby said bar is simultaneously translated and rotated during the powder-making operation. 24· Apparatus according to claim 18 in which the mounting means and the restraining means are positionable sufficiently far apart to accommodate a consumable electrode of at least 30 inches in length. 25* Apparatus according to claim 18 adapted to form powder of less than 500 microns in diameter from generally cylindrical bar stock at least 1.0 inches in diarefcer and 30 inches in length. 26. A method for producing generally spherical metallic particles substantially as hereinbefore defined and with reference to the accompanying drawings. 27. Apparatus for producing relatively " pure generally spherical metallic powder substantially as hereinbefore defined and with reference to the accompanying drawings. ttonv- Applicants