US805694A - Method of electrostatic separation. - Google Patents

Description

2 SHEETS-SHEET 1.

PATENTED Nov. 2s, 1905.

P. H. WYNNB. METHOD F ELEGTROSTATIC SEPARATION.

APPLITION FILED UG.2, 1904. I v

No. 805,694. l

P. H. WYNNE.

METHOD 0F ELEGTROSTATIC SEPARATION. APPLIoATIoN FILED AUG. 2, 1904.

2 SHEETS-SHEET 2.

PATENTED NOV. 28, 1905.

TED4 As'riuns PATENT OFFICE.

PHILIP HENRY WYNNE, OF BOSTON, MASSACHUSETTS, ASSIGNOR TO CHARLES HENRY HUFF, OF BROCKTON, MASSACHUSETTS.

METHOD F ELECTROSTATIC SEPARATION.

Specification of Letters Patent.

Patented Nov. 28, 1905.

Application led August 2, 1904. Serial No. 219,240.

To alZZ 'whom .it may concern.-

Be it known that I, PHILIP HENRYWYNNE,

va citizen ofthe United States, and a resident of Boston, in the county of Suiolk and State of Massachusetts, have invented new and .l My invention relates to the art of electrostatic separation or concentration; and it consists of anew and improved method Whereby substances of different degrees of electroconductivity are separated, concentrated, or classiiied by the employment of static charge.

My new method is characterized by the regulation and time limitation of static charge with respect to the elapsed times required for different substances to become charged by static electricity. Y

My process is correctly deiined as one of electrostatic separation, concentration, or classification, although the primary source of electricity which l prefer to employ is a high-frequency alternating-current dynamo, because in its immediate application to the materials treated there is no electric current manifested, except possiblyin the`form of inappreciable leakage, the working terminals or electrodes of the circuit employed immediately upon the material receiving a charge which is to all substantial intents and lpurposes va static charge which is not transferred between the said terminals in such manner as to produce an electric current by conduction. Because of the rapid variation of relative potential of the electrodes there is, however, a displacement-current in the intervening dielectric.

The practical applications of my new process are diverse. A typical example is aHorded Aby the separation, concentration, or classification o metallic ores and their. removal from the gangue, Wherewith they are more or less intimately mixed.

` Mine is a method in which the potential at the electrodes oia static separator is 'suddenly or abruptly raised or applied and suddenly withdrawn or lowered, the application of potential enduring throu h a very brief interval of time, also in whic these applications or variations of potential recur'rapidly# that is to say, frequently-alsoinwhich the electrodes possess no potential or potential to an ineffective degree in the intervals between successive applications of eiective potential.

I have discovered that in processes of electrostatic separation or concentration the best results are produced by rapidly varying or oscillating the potential of the electrode or electrodes employed by reducing the time during which the maximum emphatic or ronounced potential is applied to periods o eX- treme brevity, that itis usually preferable, but not always necessary, that these intervals of pronounced potential be brief both absolutely in time and relatively also to the entire period or cycle of otential'variation.

All existing processes o electrostatic separation or concentration, including that hereinafter described, are carried out by subjecting the mixture of' two or more materials which it is desired to separate to the influence of a charge of static electricity. 'lhe principle of operation of the class-of proc- -esses to which my invention belongs is and has been to charge conductive particles in contact with an electrode While not` charging the non-conductive particles. A charged pai-.ticle being electrically one with While mechanically separable from the electrode which defines the iield responds to the convective force of the iield and is conveyed away, or, as prior atents have said, is repelled from the e ectnode. An uncharged particle does not become electrically one with the electrode and is not conveyed away or repelled, but falls from the electrode or, it may be, clings thereto. The fundamental principle ofiorce on which all the electrostatic separators of this class heretofore known tome have operated is the mechanical convection by a static field of conductive particles which by conduction become one electrically with while they are mechanically separable from an electrode in c ontrast to the indifferent behavior of non-conductive articles, which receive no such charge and eel no such convective influence. My invention rests on the same fundamental principle, but is distinguished by a regulation of the static charge and its controlled application to the electrodes and to the material treated, as will hereinafter appear. Prior to this my invention and my discovery of the practical economies and benefits to be derived from the use of rapidly-varied or mo- ICO mentarily-applied lpotential in electrostatic separation 1t has een, so far as I am informed, the aim of inventors and experimenters in the eld of electrostatic-separation to employ a continuously-applied potential, and it Was due to this fact that the resulting concentrates were necessarily impure. The unsatisfactory results were not due to insuficient potential or poor insulation of the machines; but the reason was probably to be found in the tendency of the continuouslymaintained static charge to influence the less susceptible particles of the mass under treatment-as, for instance, the particles of crushed rock Wherewith metallic ore is mingled-either directly by contact With the electrode or by indirect communication from neighboring conducting particles,` thereby causing them to mix themselves to a reater or less extent with the more susceptib e particles from which it was desired to separate them. It is possible also that the machine portionsadjacent to the charged electrode under a continuously-ap lied potential retain a certain portion of the char e and that .the non-conducting particles ten to become charged therefrom. These rior rocesses had for their Working hypot esis t at conductors would be' charged andv carried over, (repelled,) While lnon-conductors would not be charged, not be conveyed away, and Would merely fall from the electrode, and in so far as examples could be found that presented materials which were actually conductors and non-conductors under the electrical conditions existin the prior processes succeeded; but ortunately very many materials acted as conductors under those conditions, and While repulsion took place abundantly too many materials Were repelled.

Whatever may be the electrical conditions to which the term conductivity is made to refer it can only possess a relative significance. All solid substance transmit electricity to some extent and all to a greater or less degree resist the transmission of electricity. Substances which are practical insulators under some conditions become conductors under other conditions. IV shall herein use the word conductivity in asense which is exact, as defined hereinbelow, but Which involves some extension of the mean-I ing ordinarily understood or conveyed by the word. By the conductivity of a body I mean the measure of thc ability of that body to assume a charge of electricity when put into effective contact with another body which is charged. This uality-conductivity--is also measured (ot erl things being equal) by the rapidity with which the body can assume a charge when put into effective contact with another charged body. This definition is necessary, because the theory of the conditions under which a body can receive a charge is now undergoing consider- Vsparks Without mec soeces able revision on account of sundry electrolytic lthe electric charges carried or assumed by bodies which Would ordinarily be considered to be non-conductors or insu tors.

My invention, therefore, relates to bodies or particles defined or characterized simply by their ability or non-ability to recelve static charge by `effective contact, and shouldv not be understood in a limited sense by reason of uncertain hypotheses concerning the elementary mechanism of charge transmission. 'I use the term effective contact, because in the actual operation of my process the repulsion from an electrode of a particle may e due to charge communicated to it .by a

short electric spark before or-Without absolute mechanical contact being established, just as a Leyden 'ar may be charged by anical contact.

So far as I have observed inthe treatment of very many substances all solid particles will if subjected long enough -to contact with a continuously statically char ed body receive or assume the charge. oreover, substances differ between each other in the elapsed times required to become char ed under stated sustained charge. I have iseovered that the communication of charge may be confined to selected bodies in a mixtureby limiting the duration of charge on the contact-body to a period too short to enable bodies other than those selected to receive the char e, While long enough to enable the selected Iiodies to receive it. Under roper.I mechanical conditions the selected best conductors Will thus be charged and repelled, Whereas the poorer conductors are now char .ed and are not repelled.

WIiile under the conditions of continuous charge peculiar to prior stances of different de ees of conductivity were repelled together, y my process such a selection is made according to degrees of conductivity that under the conditions imposed all but a selected portion of the mixture treated are to all practical intents and purposes as if they were absolute non-conductors. 1 v

The practical application of this method is susceptible of variation Within wide limits, and these are ascertained, so far as I am aware, by determining the combination or relation of the capacity and potential, so as not to make the time during which the conductive particles are influenced long enough to enable the static charge to reach and influence the less `conductive particles. I have found that provided certain exceptional conditions'subsist separation can be obtained under Widely diverse conditions of electric supply. For instance, 'a current having the general characteristics of what is known as IOO the simple sine-Wave, such as is given b the ordinary alternating-current dynamo, wi l v produce se aration provided the maximum potential o the sine-Wave is sufficiently high and provided that the frequency be not too 10W. A simple sine-wave of a frequency of sixty cycles will under exceptionalconditions produce fair separation.

So many variables enter into the problem that it is, I believe, impracticable to attempt to prescribe 'except generally the upper and lower limits" of frequency. The substances of which a mass to be treated is composed, the degree of their comminution, the rate of speed at which they pass through the effective electrode field, the-distance and rate of travel of the mass of material between the point of delivery to the repelling-electrode, and the region where the separation of the particles becomes final all are factors which must enter into consideration, and with each given actual problem the best conditionsmechanical and electrical-must be worked out before the best results can be obtained. From my own experience with many variations of all these factors, I am of opinion that the fre uency of the potential cycle should not beclless than ten or twelve potential imulses during thetime of transit of material om the point of delivery to the repelling-l electrode to the region Where separation is conclusively effected and that practically an absolute frequency of not less than twenty impulses per second is desirable. As to the upper limit of frequency that will under any given conditions eect economical separar` tion it is not possible at present to assign a maximum. I haveobtamed good separation under conditions wherein computation indicated a frequency of many thousands per second, the exact eriod of cycle recurrence not being measurable without more elaborate l apparatus than I have had at command.

The rapidity of recurrence of potential imulses has a mechanical significance. A con# uctive particle may be interfered with by accidental conditions which tend to hinder4 its effective contact with the electrode. Therefore, it is advisable to give eachconductive particle many chances to receive a charge, and if there are many potential accessions on the electrode during the time reuired for the transit of a particle throu h t e field territory, the better will be t e chance of its receiving the charge at one point or another.

' Various, devices can be employed to produce the rapidly varied or changed potential effective in obtaining ore concentration free from'crushed rock, sand, or other impurities. l can use a common commutator, the potential being generated by astatic-iniiuence machine -or an electrolytic interrupter operating an induction-coil. A more practical commercial arrangement consists of a transformer operated by an alternating-current dynamo of proper frequency, together With certain subsidiary devices in the form of resistances, capacities, and spark-gaps, as described hereinbelow The result to be attained by the devices employed is the production of a change of potential that is re resented b a pointed or eaked wave. T e rise and fall of potential s ould be very steep or raid, especially'in the neighborhood of the e ective range, and the duration of--the high potential very brief.

As hasbeen already stated, the form of electric wave producing the desired. separation may vary within wide limits, provided only the potential be suiiiciently high and the variation of potential sufficiently rapid. I have shown in Figs. 1 to 7 the formof po' tential wave and the arrangements for producing the results aimed at.

Figure 1 illustrates diagrammatically an arrangement of circuits for producing the ordinary sine-wave; Fig. 2, a graphic representation of the sine-wave; Fig. 3, the arrangement preferred by me for producing a preferred form of wave Fig. 4, a diagram of the wave produced by the afpparatus of Fig. 3; Fig. 5, an arrangementA or producing apotential-wave form suited to particular mixtures, and Figs. 6 and 7 such s ecial waveforms. Fig. 8 shows substantia y the same electrical arrangement as Fi 3, associated with electrodes of a preferre form.

Similar reference-numbers designate cor-4 responding parts in all the figures.

The arrangement shown in Fig. 1, provided, as has been stated above, the potential (and frequency be sufficiently high, pro- -duces a so-called sine-wave. that will accom lish separation for someplasses of ma teria 1 is a source of alternating current; 2, a transformer connected therewith 3,' one electrode; 4, a second electrode adjacent thereto and. separated from electrode 3 by the non-conducting partition 5. When the alternating-current source'is operated, a current is produced that is represen-ted vby the 'ico sine-Wave, Fig. 2, in which the current, starty.

ing at zero, rises comparatively rapidly until .it reaches its maximum positive potential,

(represented by 6,) then falls to zero, and passes to its maximum-negative potential,

l(represented by 7,) the cycle being repeated.

This arrangement gives good results with certain` ores or other mixtures of material; but there is danger that the non-conducting portions of the ore or the less conductive materials of the mixture, Whatever ma betheir diff ferentiated characteristics, Will e submitted so llong t0 the electric charge as to become charged and "to respond -to the repelling influence ofthe field. Better separation is 'produced .by the arrangement shown in Fig. 3, and this for most ores ormasses of mixed materials is my preferreiia'-fform. e In this lance 11 arev associated, as in Fig. 3. A hopper His arran ed to deliver comminuted material to the electrode 3, wherefrom separation takes place, the more hivhly conductive particles being thrown over tile divider 5 toward electrode 4, While the less conductive `.material falls behind the divider on the side toward electrode 3. The result of this arrangement is to produce an electric Wave which may be graphically represented by Fig. 4, in which the potential rises almost instantly toits maximum positive otential 12, sinks very rapidly to zero, an after a certain time interval, relatively long as compared with the interval occupied by the rapid rise and fall of potential, instantaneously attains its maximum negative potential 12a, after which the cycle is recurrently continued. rThis preferred form of electric Wave gives an especially appropriate example of rapidly-varied and briefly-applied potential-and is attained asfollowsz'lhe source 1 of alternating electricity by means of the transformer 2 charges the condenser 9. When the condenser 9 attains a sufiicient charge, the spark-gap 10 breaks down, the

electrodes 3 and 4 receive-instantaneously a` high potential, but are shunted through the non-inductive resistance 11. which shortcircuiting swiftly lowers the potential back to zero. With such an apparatus I have found good working conditions are afforded v by a maximum dpotential of forty thousand volts or u war a condenser capacity 4of .006 micro arad, no resistances and inductances being introduced except those low ones ,incidental to the necessary Wiring. The short circuiting non -inductive resistance may be about one thousand ohms. The result is a wave of potential represented by Fig. 1, in which thepeaks are 12 and 12a.4

This is an ideal form of wave, because the rise and fall of potential is very rapid, the electrode has not sufficient time to assume a continuing charge, and the non-conductors or poor conductors of the mass receive no effective repellent impulse whatever in the short time interval. Of course the conducting particles take their charge /or receive their repelling impulse immediately and. are thrown out, and the separation is almost perfeet.. The results attained bysch a form of potential Waveare so perfect/as to make this a method of se aration rather than of concentration, at W ch others have aimed.

In certain ores or analogous mixtures it is found that better results. are arrived at by submitting them to a potential which, While rapidly varied, remains either always positive or always negative, such a potentialwave being represented in Figs. 6 and 7, in

high frequency employed in this method the terms conductors and non-conductors or poor conductors are merely relative, meaning simply that one constituent of a compound' is more susceptibleto electrica.- tion than another; My rocess of electrical separation characterized y the employment of rapidly-varied and briefly-applied'potential is ca able, moreover., of effecting a separation of particles Whichdiffer in respects other than electrical conductivity, as the term is ordinaril understood. ,For instance, particles of equa specific conductivity, but of ierent specific gravity, or particles which differ in mechanical flneness of subdivision can be separated or classified according to these differentiating hysical characteristics by my process, these iiferences between particles rendering them unequally responsive to the repelling influence due to reception of the static charge of the electrode, and in some cases separation is eiiected by the heterogeneous particles being thrown to diierent distances, though all the particles may be reelled in greater or less degree. `It is even likely that differences in such :conditions as the state of the particles in relation to their moisture or hygroscopic qualities may be made the basis of eectual separation by my method. I have demonstrated in actual tpractice that the use ofrapidly-varied and rieily-applied potential permits the emloyment of potentials in the electrostatic Field so extremely intense as to be effective in differentiating particles which cannot satisfactorily be separated by any other known means. f

The manifold possibilities of my process are illustrated by the treatment of comminuted -masses in which several characteristics coexist which may serve as differentiating properties. Some particles, though speciiically more highly conductive, possess greater specific gravity than oorer conductors, and the particles of spec' cally conductive or non-conductive material are graded according to size or differ among themselves in chemical composition or hygroscopic character. It is possible with my method to ad- IUC IIO

usual procedure.

` all non-conductors of all classes and just the mechanical and electrical conditions, 4especially the latter, in respect to fre uency,l

brevity, and abruptness of otentia variation, so as to separate the liglht specific nonconductors by repellent impulses which have no appreciab e eiiect upon the heavier speciiic conductors, almost reversing the more After such separation is effected the heavier particles, s ecic conductors, and non-conductors a ke can be treated by another electrode, whereof the electrical conditions are adjusted differently from those at the first electrode, so that the speciiically-conductive particles are separated by repulsion Without regard to their actual size or specic gravity, the speciica es being left as tailings.' The heads an tail- I may each be re-treated on electrodes having still other adjustment of electrical conditions, so that the specific conductors will be graded according to existing differentiations and the specific non-conductors also.

With respectto the drawings which represent wave forms it is to be understood that .a mathematically-exact illustrationof the wave forms is not thereby attem ted. These drawings show qualitatively-o y the character o the potential variations and sug est different forms whereby the same genera res ults ma be obtained.

1. The method of electrostatic separation, which consists in subjecting a mixture to static electricit ap lied in potential accessions where'oi t e e ective durationsare adjusted to operate separatively on the 'better conductive particles of the mixture.

2. The method of separating commin led particles of different conductivities, w 'ch consists in subjectin themto effective contact with a body w ereon a charge' is produced by briefl -enduring `potentlal accessions, whereor` t e durations are adjusted to communicate charge to the particles of better conductivity.

3. The method of separating commingled piarticles according to differences in their conuctivities, which consists in applying thereto under conditions favorable to effective charge transmission, a static charge characterized by recurrent potential accessions, whereof the duration is adjusted to operate separatively on the better conductive particles.

4. The method of separating commin led particles according to their diverse con uctivities which consistsin subjecting them to static electricity a plied in a recurrent cycle of potential perio s, which periods are brief in relation to the complete cycle, and are of effective duration to charge the better conductors, and of ineffective duration to charge inferior conductors.

5. The method of separating commin led particles 'according to their diverse con uctivities, which consists in passing them through a static field under mechanical conditions favorable to conductive charge of the particles, the said static field produced b recurrent accessions 'of potential, each of rief Vduration adjusted to o erate separatively on particles of better con uctivity than others, and whereof the freuency is such that several accessions occur uring the time required for a particle to complete its transit from the point of entrance into the effective field to that of departure therefrom.

6. The method of separating commin led particles according totheir diverse con uctivities, which consists in subjecting them to static electricity on an electrode, under conditions of effective contact with the electrode, the said static electricity applied in recurrent potential' accessions whereof the durations are adjusted to operate se aratively upon the particles of better con uctivities, and maintaining relatively long time intervals of substantially no potential between the said recurrent accessions. l

7. The method of separating commin led particles according to their diverse con u 'ctivities which consists in subjecting them to static electricity on an electrode under conditions favorable to effective contacttherewith, the said static electricit a plied in recurrent accessions of potentiaallbf one sign, whose durations are adjusted to operate separatively upon the partlcles of better conductivities.

8. .The methodf separating particles of matter which consists in subjecting them to the convective -force of a static eld produced by recurrent accessions of potential adjusted to less vtime duration than re uired to convey the less conductive partie es, but to sufficient time duration to convey the more conductive particles.

9. The method of electrostatic separation, which consists in subjecting a mass of material to a recurrent series of static electric charges, each of infinitesimal duration, the

successive charges separated by vrelatively long time intervals, and the duration of the charges being adjusted to operate separatively on the particles of better conductivity. Signed by me at Boston, Suolk county, Massachusetts, this 9th day of June, 1904. PHlLlP HENRY VVYNNE. Witnesses:

HOWARD P. WITHINGTON, ELEAZAR GATE. i

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