US2216167A - Method of producing metal powders - Google Patents

Description

Oct. 1, 1940.

. FISHER 5 3 METHOD OF PRODUCING METAL POWDERS Aug. 24. 1936 Filed 2 Sheets-Sheet l i'llllllllllllnl IIIIIIIIIIIIIIII IIIIIIIIIIIIII IIIIIIIIIIIIIII IIIIIII'IIIIII it Sm illllllllllllll WIIIIIIIIIIIIIIIIKII- IIIIIIIIIIIIIIII 'IIIIIIIIIIIIIIIIIIIIA IIIIIIIIIIIIII INVENTOR.

JOHN S. F/Sf/Eir? ATTORNEYS C 4 J. s. FISHER METHOD OF PRODUCING METAL POWDERS Filed Aug. 24, 1936 d Sheets-Sheet 2 f 11111 ll IL I fwnnHH |nU 1111111111 II III II IIIIIII L l l l Illllll-IIIIFII; IL

INVENTOR. JOHN '5. F/SHER ATTORNEYS Patented Oct. 1, 1940 UNITED STATES METHOD OF PRODUCING METAL POWDERS John S. Fisher, Akron, Ohio,

assignmto The General Metals Powder Company, Akron, Ohio,

a corporation of Ohio Application August 24, 1936, Serial No. 97,643

4 Claims.

This invention relates to an improved method of and apparatus for producing metallic powders and more particularly to certain improvements in the electrolytic production of copper powder and the like of the general type described in the United States patent to Koehler No. 1,777,371.

In my co-pending United States patent application, Serial No. 743,870, filed September 13, 1934, now abandoned, I have described and claimed a method of producing metallic powders of this type which includes the disposition of a plurality of metallic electrodes in spaced relation in an electrolyte and the passage of an electric current through the electrodes in series. The present development may be considered to include certain improvements upon the procedure outlined in my said co-pending application and, in its illustrated embodiment, is similar to the procedure of my prior application in that the series arrangement of electrodes is preferably used and the current passes through the electrolyte from electrode to electrode, making one face of each electrode an anode and the opposite face a cathode. It is among the objects of the present inl vention to provide an improved series system for the production of metallic powders and to pro- "ride an exremely simple apparatus for carrying out the process.

Other objects of the invention are: the provi- I slon of a process for producing metallic powders in which the consumption of current is reduced, less acid is consumed and better over-all efliciency is obtained than has been previously possible with commercial methods and apparatus; the

I provision of a system in which the electrode plates may be practically completely consumed and converted into powder thus eliminating scrap loss; the provision of an apparatus for the production of metallic powders having a minimum I of moving parts and which may be arranged to be largely automatic in its operation; the provision of a system for depositing metallic powders in which it is possible to maintain substantially uniform spacing of the electrode plates throughl out the entire life of the electrodes and in which new electrodes may be inserted in the space made available by conversion of portions of the original electrodes into powder, and the provision of a method of producing metal powder which simplifies and improves the operation of both series and multiple electrode arrangements.

The above and other objects of and advantages achieved by my invention will appear from the following description of my process and one i type of apparatus adapted to carry out the process, reference being had to the accompanying drawings, in which- Figure 1 is a transverse vertical cross-section through the electrolyte tank of an apparatus for carrying out my improved method.

Figure 2 is a longitudinal vertical cross-section taken substantially on line 2-2 of Figure 1, illustrating my apparatus and showing, diagrammatically, a current reversal means.

Figure 3 is a fragmentary enlarged view illus- I trating a preferred method of attaching the rubber band sweepers to their supporting members.

Figure 1 is an enlarged diagrammatic representation of an arrangement for causing the rubber band sweepers to traverse the space between the electrodes.

Figure 5 is a side elevation illustrating a modifled form of apparatus in which vibratory means are provided for assisting in freeing the deposited powder from the electrodes.

Figure 6 is a fragmentary vertical section taken substantially on line 6-6 of Figure 5.

Referring now to the drawing'athe apparatus described is suitable for carrying out the steps of my process but it will be understood that different types of apparatus may be utilized for the practicing of my invention. The tank T, as illustrated, is of rectangular form and is provided with a sloping bottom portion 1 which has its high point 2 at approximately the middle of the tank and slopes downwardly toward each end. The angle of the slope of the bottom portion is preferably made such that the copper powder, which drops ofi the electrodes as will be later explained, will slide down to the ends of the tank under the influence of gravity where it may be removed through the powder discharge pipes 3 and 4. The walls of the tank T may be made of steel or wood but the entire tank is preferably lined with rubber 5 or other similar acid resisting and non-conducting material. Moreover, the inlet and outlet pipes are all rubber lined and all parts of the apparatus which may come in contact with the acid electrolyte except the electrodes themselves, areeither rubber covered or made of suitable acid resisting and non-conducting material.

The electrolyte enters the tank T through the central inlet pipe 6 and longitudinally extending outlet pipes I and 8 are provided adjacent the top level of the electrolyte. As is seen in Figure 2 these outlet pipes are provided with a plurality of perforations 9 and extend the entire length of the tank. By this means the desired uniform circulation of electrolyte through the tank is fa- 5o cilitated.

The upper side edges of the tank T are turned into form flanges l0 for supporting the electrode plates P. As illustrated these electrode plates, which are, of course, of the same material as the powder which is to be produced, are provided with oppositely disposed supporting lugs or flanges II and i2. As is seen in Figure 2 these flanges may be considerably thinner than the electrode plates P as their only function is to support the plates 0 P in the electrolyte bath. In order to prevent the electrolytic action from destroying the connection between the lugs II and I2 and the plates P they are preferably painted at the electrolyte level with a suitable acid resisting paint, as is clearly seen at I3 in Figure 1. As the plates P are supported on the rubber covering of the tank T they are insulated from each other and suitable means are provided for connecting the end plates of the series to the opposite terminals of a source of direct current of suitable voltage.

Extending down into the tank at each end thereof are the sweeper bar supporting members l4 and I5. These are made of any suitable acid resisting and non-conducting material and are connected at their lower ends by the bars l6 and I! which extend lengthwise of the tank and are disposed between the edges of the electrodes and the side walls of the tank. Extending across between the bars l6 and I1, and disposed between each pair of electrode plates P, is a sweeping member. As illustrated in Figure 3 these sweeping members consist of rubber bands I8 which are carried by hooks I9 and stretched across between the bars Hi and H. These rubber bands are preferably disposed approximately midway between adjacent electrodes so that they may be moved up and down between the electrodes without direct contact therewith.

In order to effect this up and down movement of the sweepers I8 I provide a suitable mechanism for moving the entire frame structure comprising the members l4, I5, l6 and I! up and down. As-illustrated diagrammatically in Figure 4 this apparatus consists of a rack 20 mounted on the supporting members [5 and a pinion 2| engaging the rack 20, together with suitable means, such as the motor 22, for driving the pinion 2|. A timed contacting mechanism or switch diagrammatically illustrated at 23 is preferably provided for causing the motor 22 to operate to move the sweeping members l8 from top position tobottom position, and back to top position, remain idle at the top position for a predetermined period and repeat this cycle during the operation of the apparatus.

By connecting one of the end electrodes to the terminal of the circuit and the other end electrode to the other terminal the current is passed-. in series from electrode to electrode througlisthe electrolyte. As is well understood, the passage of such a direct current of the proper voltage and amperage will result in the copper, assuming for purposes of illustration that copper powder is being produced, being removed from the electrode plates on the anode or positive side thereof and deposited in powder form on the cathode or negative sides of the adjacent plates. In my said co-pending application the procedure is described-in which the electrodes are periodically removed from the electrolyte bath and the deposited copper powder scraped therefrom. This necessitates the frequent lifting of the copper plates from the bath and the provision of some mechanical means for removing the deposited powder therefrom. When the plates, become too thin, due to the removal of copper, to permit their being handled they must be discarded as scrap and this involves considerable expense. The present invention eliminates these undesirable features and provides a method by which the plates P may be allowed to remain in the bath from the time they are initially placed therein until they are entirely consumed and only the supporting lugs II and I2 remain.

I have found that if the energizing current is allowed to flow through the bath and the plates therein in one direction for a period of time and then reversed and caused to flow in the opposite direction for a period of time, and this reversal of the current continued at intervals during the process, the copper powder which is deposited upon the cathode surface of the electrode plates P will not tenaciously adhere thereto but will drop, to a large extent, 011 into the bottom of the tank from whence it may be removed through the pipes 3 and 4 or by any other suitable removal means.

I have illustrated in Figure 2 a means for periodically reversing the current supplied to the electrodes. This means includes the pole changing switch S having two contact arms 24 and 25 which are pivotally connected to the positive and negative leads 26 and 21 from a suitable source of current for energizing the field coil F of the direct current generator G. Three contact points 28, 29 and 30 are provided for the opposite ends of the contact arms 24 and 25. A connector 3| extends from the contact point 29 to one end of the field coil F and a connector 32 extends from the contact point to the other end of the field coil F. The switch arms 24 are joined together and connected to the core members 33 and 34 of the solenoids 35 and 36 respectively. The terminals of thesolenoid 35 are connected to a suitable source of energizing current at A and a switch 31 included in the circuit. The solenoid coil 36 is similarly connected to a source of energizing current A and a similar switch 33 is provided. The switches 31 and 38 are so disposed relative to a cam 39 that when the cam 39 is in the position illustrated it will close the switch 31 thus energizing the solenoid 35. At this time a suitable spring (not shown) will maintain the switch 38 in open position and the solenoid 36 will not be energized. The cam 39 is mounted on a shaft 40 which is adapted to be driven by a clock mechanism 4|.

When the solenoid 35 is energized the pole changing switch will be moved into the position illustrated in Figure 2 and the positive side of the source of generator field current will be connected through the switch arm 24, the conductor 42 and the conductor 32 to the upper end of the field coil F. In like manner the negative side of the circuit will be connected to the lower end of field coil F through the switch arm 25 and conductor 3|. When the clock mechanism 4| turns the cam 39 so that it opens the switch 31 and closes the switch 38 the solenoid 36 will be energized and the pole changing switch will be moved over to its opposite position in which the positive side of the direct current source will be connected to the lower end of field coil F through the switch arm 24 and the conductor 3|, while the negative side of the circuit will be connected to the upper end-of field coil F through the switch arm 25 and the conductor 32.

Thus, it will be seen that by regulating the clock mechanism 4| and its driving connection to the cam 39 the polarity of the current applied to the D. C. generator G, which supplies the current used in the process, may be reversed at predetermined regular intervals. When such reversal takes place the polarity of the generator output, which is connected to the end electrodes by suitable conductors iii and G" is also reversed and the sides of the electrode plates P which have been anodes immediately become cathodes and vice verse.

I have found that when this reversal operation is carried out at proper intervals the copper powder which is deposited will not adhere to the electrode surfaces but will drop off into the bottom of the tank. The rubber band sweepers I8 which I provide are effective in preventing the powder from bridging the gap between two adjacent electrodes and thus short circuiting the two and stopping the powder production therebetween and also facilitate the removal of the loosened copper powder from the electrodes.

I believe, although it may be that my explanation of the phenomena which occur is not entirely accurate, that when the surface of an electrode plate P is used as an anode for a certain period of time it acquires characteristics, unknown to me at the present time, which make it a poor cathode for a certain length of time, at least insofarv as the property for retaining the deposited powder in adherence thereto is concerned. In other words, it appears that if a surface of one of the electrode plates has been used as the positive or anode for a certain length of time the copper powder upon reversal of the current and the anode surface becoming the cathode surface, will not adhere thereto with anything like the tenacity which it will if the surface has been used as a cathode for a considerable period of time.

Moreover, I believe that the act of reversing the current is effective in loosening the powder which may be adhered to the surface of an electrode which becomes an anode after having been used as a cathode for a timed cycle.

In the practice of my improved process in the production of copper powder I have employed an electrolyte tank in which I have disposed 21 copper plates each approximately 24" wide, 20" deep and /2" thick when new. These plates are spaced in the electrolyte at the start of operations approximately 1 5" apart and, as will be explained later, this spacing can be maintained substantially the same throughout the life of the plates by moving adjacent plates closer together when they become thin and inserting additional new plates in the tank. These plates were suspended in an electrolyte bath maintained at approximately 54 C. The composition of the bath was substantially 4.5% sulphuric acid, approximately 1% metallic copper or 4% copper sulfate, approximately .8% sodium sulfate and the remainder water. The direct current applied to the end electrodes was about 460 amp. at approximately 15 volts. It will be seen that this current caused a current density of approximately 138 amp. per square foot of cathode surface and the voltage between plates was approximately .775 volt.

In the carrying out of the process with the above setup the current was reversed approximately every 12 minutes and the rubber band sweeps operated to traverse the space between the electrodes approximately every 4 minutes. The sweeping operations were so timed relative to the current reversals that a movement of the bands between the electrodes took place approximately 2 or 3 minutes after each current reversal. The removal of the powder from the plates is not dependent upon engagement of the rubber bands with the plates and, although the rubber band sweeps referably do not engage the I plates inserted electrodes, the operation of the process is not interfered with if they occasionally do.

At intervals the deposited copper which drops oif of the cathode surfaces may be withdrawn from the tank through the pipes 3 and 4. A certain amount of electrolyte will, of course, be withdrawn with the powder but this may be re-- moved in any suitable manner, as by centrifuging, and the electrolyte returned to the tank. The electrolyte is maintained in circulation between the plates by causing it continuously to enter the tank through the inlet 6 and be removed through the elongated perforated outlet pipes I and 8.

After the electrodes P have been consumed to a certain extent they can be moved closer together, as is illustrated on the right hand side of Figure 2, so that the space from the surface of one plate to the surface of the next adjacent plate will be maintained at substantially the original and desired value. In the space thus gained additional new plates may be inserted and new rubber band sweeps may be hooked into place on the bars I6 and 11 while the sweeping mechanism is in its upper position. When the plates are entirely consumed the supporting lugs II and I! will, of course, be removed and new and it will be seen that in this manner the process may he kept in continuous operation for as long as desired. The composition of the electrolyte may be controlled in the usual manner by periodic testing and adding the necessary materials. In some instances it may be found desirable continuously to remove the powder from the bottom of the tank by means of a conveyor belt or the like and with such an arrangement the only attention which the ap-- paratus requires is the re-spacing and replace ment of the electrodes.

I have set forth above data relating to an actual successful use of my process and apparatus. However, I have found that the time interval between current reversals may be varied within quite wide limits while still retaining the important advantages of 'my process. Likewise, the time between movements of the sweeping device may be increased or diminished from that noted above without seriously interfering with the operation of the process. Although I have noted that I prefer to operate the sweeps a short time, i. e. 2 or 3 minutes, after the current reversal, excellent results may be obtained if the sweeps are operated simultaneously with the current reversal. I believe, however, that by operating the sweeps slightly after the current re versal the time interval between the reversal and the movement of the sweeps will permit the loosening action of the reversal of the current on the deposited powder to become effective and the passage of the sweeps between the adjacent electrodes will further facilitate the loosening of the powder from the electrode surfaces.

Figures 5 and 6 of the drawings illustrate a modified type of apparatus for carrying out my reversal process of producing metallic powders. In this apparatus the tank 50 is generally similar to that previously described and a plurality of electrode plates 5| are supported in the e1ectrolyte 52 in the tank 50. It will be understood that the various parts of the apparatus will be properly protected against the acid in the electrolyte and will be made of insulating materials where necessary to prevent electrical connection between the electrode plates. The electrodes 5| are provided with supporting arms 53, generally (ill similar to the supporting portions H and I2 of the electrodes P illustrated in Figures 1 and 2. The portion of these supporting members 53 which contacts with the electrolyte is preferably painted with acid resisting protective paint at 54. The upper ends of the supports 53 rest upon longitudinally extending supporting bars 55 and 56, which in turn are held above'the top edges of the tank 50 by the springs 51. Locating pins 58 preferably extend downwardly from the supporting bars 55 and 56 in order to hold the bars in position on the springs, and it will be understood that the springs are secured in position on the top edge of the tank. The upwardly extending end portions 59 of the bars 55 and 56 are secured to the operating arms 60 of the vibrating devices 6|. These vibrating devices 6| may be of any suitable type and as illustrated are of the electrical variety in which the operating members 60 are caused to vibrate rapidly-by electro-magnets which are intermittently energized or in which the current is rapidly reversed. Of course, other vibrating mechanisms such as oscillating pistons or plungers operated by compressed air might be utilized and I do not desire to be limited to any particular mechanism for vibrating the bars 55 and 56 which support the electrodes 5|.

In the operation of the apparatus of'Figures 5 and 6 the electrodes are connected to a suitable current supply in the same manner as described above in connection with the other figures of the drawings. For purposes of simplicity the electrical connections to the electrodes 5| are not shown in Figures 5 and 6. The operating current is reversed in the manner previously described and the vibrating devices 6| may be operated either intermittently or continuously to cause any metallic powder which collects upon the electrode surfaces to be moved downwardly over the electrode surface until it drops off into the electrolyte and is deposited on the bottom of the tank from which it may be removed through the outlets 62, or in any other suitable manner. It is well understood that rapid vibratory movement of relatively small amplitude will cause particles of material which are resting upon a plate or the like to move along the plate. By taking advantage of this action I am able to provide an apparatus for producing metallic powders in which there are, in effect, no moving parts and no complicated plate lifting or scraping mechanisms. The spring support for the electrode supporting bars 55 and 56 permits them to be vibrated without transferring serious vibrations to the tank 50, and, with the arrangement of Figures 5 and 6, the electrode plates may be moved closer together as they become thinner and new plates continuously added as required,

thus maintaining the maximum powder produc- In my improved method the electrodes may be spaced very close together as they do not need to be moved into and out of the electrolyte for scraping. This close spacing assists in the more eflicient production of powder because less current is required to cause the copper to be deposited across a relatively narrow gap. This saving in current is of great importance in this art as the chief cost in the manufacture of electrolytic copper powder is that of electrical energy.

It will be understood that the benefits of my current reversal system for controlling the surface conditions of the electrodes will also be obtained when the electrodes are arranged in multiple and that the sweepers or electrode vibrators may be utilized with such a multiple arrangemnt of electrodes.

Although I have described a particular procedure for the production of metallic powders in considerable detail and although I have illustrated and described an apparatus for carrying out this procedure it will be understood by those skilled in the art that the steps of my process may be varied and the apparatus described herein may be modified without departing from the spirit of my invention, and I do not, therefore. wish to be limited to the specific embodiments thereof herein described and illustrated, but claim as my invention all forms thereof coming within the scope of the appended claims.

I claim:

1. The method of producing metallic powder which consists in immersing a plurality of electrodes in spaced relation in an electrolyte, passing direct current through said electrodes and electrolyte in series, imparting a vibratory movement to said electrodes, periodically reversing the .direction of flow of said current at intervals of from 5 to 25 minutes and removing deposited metallic powder from below said electrodes.

2. The method of making metal powder which comprises the steps of immersing a plurality of metal plate electrodes in closely spaced, parallel so relation in an electrolyte, passing thru said plates and electrolyte in series direct current of sumciently high amperage to deposit metal in finely divided form on the cathode plates, periodically reversing the direction of flow of said current at intervals of from about five minutes to about twenty-five minutes to deposit finely divided metal on the then cathode plates, and, within a few minutes after each such reversal, mechanically removing from said plates the finely divided metal deposited thereon prior to each such re versal. I

3. The method of making copper powder which comprises the steps of immersing a plurality of copper plate electrodes in closely spaced, parallel relation in an acid electrolyte, passing thru the plates and electrolyte in series direct current of sufficiently high amperage to deposit copper in finely divided form on said cathode plates, periodically reversing the direction of flow of said current at intervals of from five minutes to about twenty-five minutes to deposit finely divided copper on the then cathode plates, and, a few minutes after each such reversal, mechanically removing the finely divided copper from the plates on which it was deposited before each such current reversal.

4. The method of making copper powder which comprises the steps of immersing a plurality of copper plate electrodes in closely spaced, parallel relation in a sulphuric acid electrolyte, passing thru said plates and electrolyte in series a current having an amperage on the order of about one ampere per sq. in. of cathode area, thereby depositing finely divided copper on the cathode plates, periodically reversing the direction of flow of said current at intervals of from about five minutes to about twenty-five minutes to deposit similar copper on the then cathode plates, and;

versal.

JOHN S. FISHER.

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