US2403800A - Method of and apparatus for drying moisture laden articles - Google Patents

Description

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METHQD OFAND APPARATUS FOR DRYING MOISTURE I J ADEN ARTICLES I w Filed Deaf 31, 1941 s She ets-Shet 1 arm/6 CMT/A/UEO I o ,5 2'0 504M060 wav N I 3mm.

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July 9, 1946. c HOYLER 2,403,800

METHOD OF AND APPARATUS FOR DRYING MOISTURE LADEN ARTICLES Filed Dec. 31, 1941 3 Sheets-Sheet 3 I 1 3mientoi:

Cyril N'HOyZer Patented July 9, 1946 METHOD OF AND APPARATUS FOR DRYING MOISTURE LADEN ARTICLES Cyril N. Hoyler, Audubon, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application December 31, 1941, Serial No. 425,170

18 Claims.

This invention relates to a method of and apparatus for expelling moisture irom moisture-laden articles and has special reference to the drying of water-laden rayon cakes, the present invention being an improvement upon that disclosed and claimed in thecopending application of Rudolph A, Bierwirth, Serial No. 407,619, filed August 20, 1941, now Patent No. 2,325,652, and assigned to Radio Corporation of America.

In the manufacture of rayon, after the thread has been formed, it is wound up into what is known as cakes and placed in cloth containers, after which the cakes are thoroughly washed in water to remove the sulphuric acid or other chemical employed in coagulating the viscose material. One of the problems encountered in the manufacture of rayon is the drying of the yarn or thread after it has been through a washing or dyeing process, the rayon absorbing about twice its own weight of water after it is washed. This water must be removed before further operations can be carried out.

In accordance with the prior art practice, it has been customary to pass the cakes through large drying ovens in which they are subjectedto a stream of heated, dry air. This method presents several difflculties. For example, the time required to dry a cake ranges from about 60 to 100 hours, and with ovens having a capacity of even as great as 1000 cakes per hour, it is obvious that a great many ovens are required -to handle the rayon output, which is in the neighborhood of over 20,000 lbs. (each dry cake weighing a pound) per hour. Another difficulty which is encountered is that considerable care must be exercised to prevent the rayon from reaching a temperature in excess of 140 F. since, above that temperature, the qualities of the thread are impaired and further manufacturing e not be carried out successfully. Still another difliculty which is encountered resides in the fact that not only do the outside layers of the cakes dry first with some attendant shrinking and consequent tensioning of the threads at the outer layers, but the inner layers of the thread frequently buckle up and wrinkle as a result of the pressure exerted by the tense, outer thread layers, and an increased possibility of tangling of the thread results. Furthermore, in each strand of thread, a skin shrinkage occurs by reason of the outer surface thereof drying before the inner portion thereof dries with resultant nonuniform appearance in the strand.

The foregoing and other similar difllculties are overcome by the method disclosed in the abovesses canidentified copending application of Bierwirth. According to Bierwirths method, the rayon is placed in a radio frequency fieldand advantage is taken of the impedance of the moist cakes to radio frequency energy to effect heating and drying thereof. The heating takes place in a vacuum so that the moisture-can be expelled at a temperature far below 140 F. Moreover, the cakes are heated uniformly throughout and therefore a thread of higher quality is obtained. Added to these is the very important advantage that the cakes can be dried by the Blerwirth method in about an hour, as compared with to hours required by the previously practiced method.

Now it has been found that, in vacuum drying of the rayon cakes by radio frequency energy as suggested by Bierwirth, the power demands on the oscillation generator change considerably. For example, in one arrangement wherein one cake was placed between a pair of electrodes in an evacuated chamber, an input of considerably over 1200 watts was required during the first thirty minutes or so, while during the last thirty minutes of drying the input dropped to rather low values. Thus, a generator is required which is capable of delivering much more power than is actually used during the major portion of the drying cycle.

The primary object of my present invention is to provide an improved method of and apparatus for drying moisture-laden articles, such as rayon cakes, employing the teachings of Bierwirth but utilizing the output of the radio frequency generator much more efficiently,

More particularly, it is an object of my present invention to provide an improved method and apparatus as aforesaid in which the drying will take place in a plurality of stages and wherein new or fresh, moisture-laden cakes may be loaded into the apparatus while at the same time unloading the dried cakes, thereby making the process a continuous one.

Another object of my present invention is to provide an improved method of and apparatus for drying moisture-laden articles as above set forth in which the drying may be effected rapidly and in great quantities.

In accordance with my present invention, and in order to provide more uniform loading to the oscillator, I provide an arrangement which includes a plurality of operating stations at least one of which is a loading and unloading station, a second of which is an evacuating station, and ne or more other ones of which are drying stations. These stations are arranged in endless fashion and the cakes loaded at the loading station are carried around through the various stations and eventually returned to the first station for unloading the dried cake and loading a new. moisture-laden cake. Suitable means are provided for evacuating. at the evacuating stations, the chambers in which the cakes have been de posited and for thereafter maintaining the vacuum at the successive drying stations.

As each cake becomes drier, its impedance increases and it becomes more difficult to get power into the cake. This is equivalent to saying that the voltage across each cake must be increased as the moisture is expelled therefrom. For this purpose, I arrange the drying stations so that each of the cakes therein constitutes an impedance element in one of a plurality of parallel related lad circuits which are connected in series with the oscillator, each of the load circuits also including a capacitor and each of the capacitors having a different value such that the appropriate voltage is applied to each of the cakes at the respective drying stations. By introducing, at intervals, a fresh cake of maximum moisture content to the load while a dried cake is being removed. it is obvious that, as the input requirements to one cake drop, another cake demanding high input is added to the oscillator load. Thus, the variation in load on the oscillator can be maintained within relatively narrow, predetermined limits, and the output thereof used most ei'liciently.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with additional objects and advantages thereof, will best be understood from the following description of several embodiments thereof, when read in connection with the accompanying drawings, in which Figure 1 is a diagrammatic view of an improved arrangement in accordance with one form of my present invention,

Figure 2 is a central sectional view of one of the drying chambers formed according to my present invention,

Figure 3 is a curve showin the oscillator input for drying a single rayon cake,

Figure 4 is a set of curves showing the oscillator input requirements per cake for a number of such cakes, and the total input to the oscillator when a fresh cake is added at suitably spaced intervals,

Figure 5 is a central sectional view of a modifled form of drying chamber.

Figure 6 is a fragmentary, sectional view of one form of apparatus which may be employed for maintaining a vacuum in the drying chambers and for supplying coolin fluid to the condenser coils therein, and

Figure 7 is a somewhat enlarged, sectional view taken on the plane of the line VII-VII of Figure 6.

Referring more particularly to the drawings, wherein similar reference characters designate corresponding parts throughout, and more particularly, first, to Figure 2, I have shown a suitable enclosure I of dielectric material supported on a base or platform 3 and providin a chamber within which are a pair of spaced, primary electrodes 5 and 1 connected to the tuned circuit 9 of a suitable oscillator through a variable capacitor i i in series with the tuned circuit 9. The interior of the enclosure i may be evacuated by a. su table 4 vacuum pump (not shown) coupled to the charm her through a conduit i3. A cooling coil i5 "within the enclosure I may be connected to a suitable source of cooling fluid for condensing the moisture which is expelled from the cakes, the condensed moisture being "withdrawn in any suitable manner, as through the vacuum line ii.

The primary electrodes 5 and I are preferably constituted by circular plates, the lower electrode 1 being supported on an insulator il. One or more rayon cakes i8 may be placed between the electrodes 5 and l and a high frequency electric field applied thereto by the oscillator. A pair of secondary electrodes, such as the guard rings II and 23, are preferably arranged around the primary electrodes 5 and 1 external to the container i and are connected in shunt relation with the primary electrodes, the secondary electrodes serving to help make the field through the cake or cakes i9, as the case may be, more uniform by confining the end effects between the primary electrodes ii and I to a region well outside of the cake IS, with a consequent improvement in the uniformity of drying.

After the vacuum in the enclosure i has reached a value of about 28 or 29 inches of mercury, the

output of the oscillator is connected across the primary electrodes ii and I through the series capacitor ii. At a vacuum of about 29 inches of mercury, the boiling point of water is in the neighborhood of F. During the early stages of drying, the cake i9 will accept considerable power. As the cake I! becomes drier, its impedance increases and it becomes more difficult to get power into it. Thus, it is necessary to increase the voltage across the cake. This may be done by tuning the capacitor II as frequently as may be found necessary, current through the load being maintained at a suitable level.

Referring, now, to Figure 3, the curve of which represents the average of the power input to the oscillator taken at various times during the drying process of several individual cakes, it will be noted that the total energy used we approximately 1.2 kilowatt hours. This includes platerid and other oscillator losses. The curve also shows that during the first thirty minutes or so of drying, the input was considerably above 1200 watts, but during the last thirty minutes of drying the input dropped to rather low values. If, now. fresh cakes could be introduced in the load at the same time that dried cakes were removed at various intervals, so that, as the input requirements to one cake dropped, another cake demanding high input would be added to the oscillator load, the latter would be kept much more constant. The arrangement shown in Figure l is one way of accomplishing this result.

In the system shown in Figure 1, there is provided a rotatable platform or turntable 25 adapted to be rotated by any suitable means, such as a motor 21, in a manner such that any point on the turntable will successively pass a plurality of stations I to VI, inclusive, arranged in an endless path. At each of the stations may be located an enclosure i and associated parts, as described above in connection with Figure 2. Let it be assumed that station I represents the loading and unloading station from which a fresh, moistureladen cake is started on its path in the drying cycle, and to which it is subsequently returned when dry, stations II and III constitute evacuating stations at which the respective enclosures or chambers l are evacuated, and stations IV, V and VI constitute successive drying stations at which the drying operations take place, in turn. The wet cakes at stations IV, V and VI constitute impedance elements connected in series with their respectively associated capacitors Ila, Nb and I I0, these three series circuits constituting load circuits for the oscillator and being arranged in parallel relation to each other, although each is serially connected to the tuned circuit 9 of the oscillator. In the form of the invention under consideration, each 01' the enclosures I may have united therewith one plate or electrode A1 to Avr, inclusive, of the capacitor H, the plates Ar-Avr moving in unison with their respectively associated enclosures I. The capacitor II may, in each case, be completed by a cooperating elec- -trode Brv, Bv, Bvr in each or the load circuits- 28a, 29b and 290, respectively,'the electrodes BIV,

By, Bv: being stationary. As the turntable 25 isrotated step-by-step at suitable intervals, it is .obvious that each chamber I, after being suitably evacuated at stations II and III, will first reach station IV at which its electrode A will cooperate with the electrode Brv o1 capacitor I Ia to apply a predetermined voltage to the cake or cakes contained therein. Subsequently, when the particular chamber under consideration is moved to station V, its electrode A will cooperate with the capacitor plate Bv and a higher voltage will be applied to the cake or cakes therein. Finally, when the same chamber is moved to station VI,

- its capacitorelectrode A will cooperate with the electrode BVI to cause a still greater voltage to be applied to the cake. Since, however, a fresh cake is introduced to station IV from station III each time the turntable 25 is advanced one step and the cake or cakes previously at station IV are advanced to station V, and so on, it is apparent that the load on the oscillator will be maintained well within certain predetermined limits which have been found expedient.

For producing and maintaining a suitable vacuum in each of the chambers I and for supplying cooling fluid to the several coils I5 as the platform 25 is rotated to carry the several chambers around the endless path. a system such as shown in Figures 6 and 7 may be employed. This may consist of three concentric, stationary pipes l0. I2 and ll of which the pipes Ill and I2 are closed at their upper ends by fluid-tight closures I6 and I8, respectively, and the pipe I4 is open at its upper end. The pipe III is connected to any suitable vacuum pump and is formed, near its upper end, with a plurality of ports IOa, I01), I Do and Ifld. The port Illa is preferably elongated and may extend from a point X between the stations I and II to a point Y shortly in advance of the station IV. The port Iflb may be relatively short and is located between the stations IV and V. Similarly, the ports IDc and Illd are short and are located, respectively, between the stations V and VI and between the stations VI and I. Between the port "id and the station I, the pipe I0 is formed with an opening We in which a tube or pipe 20 is secured with a fluid-tight connection. the pipe 20 being brought out to the atmosphere in any suitable manner.

Surrounding the ports IUa to I02 and rotatable on th pipe I0 is a sleeve valve 22 having a plurality of internally threaded bosses 24 thereon corresponding in number to the number of stations I to VI and spaced circumferentially from each other on the same angles as are the several stations I to VI. Each conduit I3 is connected to a separate one of the bosses 24 whereby each chamber I may be evacuated in a manner shortly to be set forth.

The pipes I2 and I4 extend above the closure I 8, as can be seen from Figure 6, and the pipe I2 is formed near its upper end with a plurality oI. closely spaced ports I 2a extending' circumi'erentially around it. A sleeve valve 26 which is formed with the same number of internally threaded bosses 28 as there are bosses 24 surrounds the ports I2a and is rotatably mounted on the pipe I2. Each of the bosses 28 is connected to the inlet of a separate one of the condenser coils I5 by a coupling tube 20, the outlet of each coil I5 being brought outto the top 01' the pipe I4 by a tube 22.

Assuming that one ormore wet cakes I! have been loaded into one of the chambers I at the loading station I, then, as the platform or tumtable 25 rotates in the direction of the arrow in Figure 1, the sleeve valves" and 26 will rotate with it in the same direction and the newly loaded chamber will soon reach a position where its conduit I3 will be in communication with the vacuum line III through the port I Ila. Evacuation'oi' the air in th chamber will therefore begin and will continue past the stations II and III until the end Y 01' the port Ina will have been reached. At about this time, the condenser plate associated with the particular chamber under consideration (for example, the electrode A!) will have come into cooperative relation with the condenser electrode Biv whereby the wet cakes will become coupled to the oscillator and drying will begin. Meanwhile, since the condenser coil I5 is coupled to the water inlet pipe I2 through the ports I2a. cooling water will flow continuously therethrough and the water vapor driven out of the cakes being dried will be condensed to liquid form and will collect at the bottom of the chamber. As the turntable continues to rotate, the port IUb is eventually reached. This connects the chamber to the vacuum line again for a short period to withdraw the water which has been condensed in the chamber, and this step is repeated at the ports I00 and Illd. Shortly after the chamber being considered has passed the port IUd, its conduit I3 is brought into communication with the opening or port We and the air inlet pipe 20.

Air from the atmosphere then rushes into the chamber to break the vacuum therein just before the station I is reached. When the latter station is reached, the dried cakes are removed and are replaced by wet cakes, and the above described I effect and maintain the desired vacuum in each of the chambers, and (2) to effect circulation of the water or other cooling medium through the condenser coils I5. In a system wherein the condenser plates BIV, Bv and Bvi are rotated, it is obvious that each of the stations will become, successively, first a loading and unloading station, then the first evacuating station, then the second evacuatin station, and then each of the successive drying stations in turn, before again becoming a loading and unloading station. However, the overa l effect is the same in either case.

The curves C of Figure 4 show the loading requirements of each individual cake for a plurality of cakes (assuming only one cake is placed in each of the chambers i at one time). It will be noted that each of the individual curves is similar to the curve shown in Figure 3. It will also be noted that, for drying a single cake, the ratio of maximum to minimum oscillator input is about 3 to 1. The curve D of Figure 4 shows the loading requirements in a system such as that illustrated in Figure l on the basis of a new cake of maximum moisture content added every twenty minutes. From the curve D, it will be noted that the ratio of maximum to minimum oscillator input is approximately 6 to 5. It follows, therefore, that with a system such as that shown in Figure 1, the oscillator may be employed much more emciently than when a single cake is dried at one time, and at the same time the output of dried cakes can be very greatly increased. f course, any number of evacuating and drying stations may be employed, the number shown in Figure 1 being used merely for the purpose of illustration.

In Figure 5. I have shown a somewhat different form of drying chamber which may be used on the turntable 25 instead of the One shown in Figure 2. In the form shown in Figure 5, the enclosure may be constituted by a metal base 3i and a metal cover 33 fitted together with a cylindrical glass drum or spacer 35. Two or more gaskets I1 may be employed for providing airtight connections between the plates 3| and 33 on the one hand, and the drum or cylinder 35 on the other. The advantages oifered by this form of chamber are (1) that a relatively small volume of air would have to be evacuated, (2) that each cake would be dried under uniform ideal conditions, and (3) that high electrica1 efficiency would be obtained because of the insulation afforded by the glass cylinder 36.

Although I have shown and described several forms of my invention, it will be apparent to I those skilled in the art that many other modiiications thereof, as well as changes in those described, are possible, For example, instead of providing turntable 25, the chambers I may be mounted on an endless conveyor of other suitable form, it being advisable, however, in the interest of proper continuity and efiiciency, although not absolutely necessary, of course, that the various chambers return to their original loading stations at the end of the drying operation. Many other similar changes will, no doubt, readily suggest themselves to those skilled in the art. I therefore desire that my invention shall not be limited except insofar as is made necessary by the spirit of the appended claims.

I claim as my invention:

1. In apparatus for drying moisture-laden articles, the combination of means providing a plurality of drying stations, means for supplying heating energy to each of said stations for drying the articles, variably effective means for controlling the energy supplied to said stations by said second named means, and means for bringing said variably effective means successively into cooperative relation with each of said stations whereby to control the energy delivered at said stations.

2. In apparatus for drying moisture-laden articles, the combination of means providing a plurality of drying stations, means for simultaneously supplyin heating energy to each of said stations for drying the articles, a plurality of variably effective control elements for controlling the energy supplied to said stations by said second named means, said elements being each adapted to cooperate with a separate one of said stations during a predetermined drying interval, and means for bringing each of said elements successively into cooperative relation with each of said stations for successive drying intervals.

3. In apparatus for drying moisture-laden articles, the combination of a plurality of enclosures constituting a plurality of drying chambers each adapted to receive at least one article to be dried, means for maintaining a vacuum in each of said chambers, means for simultaneously supplying heating energy in at least certain of said chambers for drying the articles therein, a plurality of control elements for controlling the energy supplied to said stations by said second named means, said elements being each adapted to cooperate with a separate one of said chambers during a predetermined drying interval, and means for successively bringing each of said elements into cooperative relation with each of said chambers for successive drying intervals.

4. In apparatus for drying moisture-laden articles and including a loading station, an evacuating station and a drying station, the combination of means providing a closed chamber adapted to receive at least one of said articles at said loading station, means for successively advancing the loaded chamber to said evacuating and drying stations, means for creating a vacuum in said chamber at said evacuating station and for maintaining the vacuum in said chamber while said chamber is subsequently at said drying station, and means for supplying heating energy to said chamber at said drying station for drying said article.

5. In apparatus for drying moisture laden articles and including a loading station, at least one evacuating station, and a plurality of drying stations, the combination of means providing a closed chamber adapted to receive at least one of said articles at said loading station, means for successively advancing the loaded chamber first to said evacuating station and then to each of said drying stations in turn, means for creating a vacuum in said chamber at said evacuating station and for maintaining the vacuum in said chamber while said chamber is subsequently at each of said drying stations, means for supplying heating energy to said chamber at each of said drying stations for drying said article, and means located at each of said drying stations for controlling the amount of energy delivered by said last named means at the respective drying stations.

6. The invention set forth in claim 5 characterized in that said loading, evacuating and drying stations are arranged in endless formation whereby said chamber is returned to said loading station from the last of said drying stations for unloading of the dried article and loading of another moisture-laden article.

7. In apparatus for drying moisture-laden articles and including a loading station, at least one evacuating station and a plurality of drying stations all arranged in endless formation, the combination of means providing a closed chamber at each of said stations, means for advancing said chambers in an endless path past said stations whereby each of said chambers is brougt, in succession, first from said loading station to said evacuating station, then from said evacuating station to each of said drying stations in turn. and finally from the last oi. said drying stations back to said loading station, said chambers each being adapted to have a dried article therein exchanged for a moisture-laden article when at said loading station, means for creating a vacuum in each of said chambers while at said evacuating station and for thereafter maintaining the vacuum therein while said chambers are subsequently at each of said drying stations, means for simultaneously supplying heating energy to all the chambers at said drying stations for heating the respective articles therein, and means located at each of said drying stations for controlling the amount of energy delivered by said last named means at the respective drying stations.

8. The invention set forth in claim 7 characterized in that the effectiveness of said control means is different at each of said drying stations.

9. In electrical drying apparatus for drying moisture-laden articles, said apparatus including a loading station, at least one evacuating station and a plurality of drying stations, the combination of means providing a chamber adapted to receive at least one of said articles at said loading station, a pair of cooperative electrodes in said chamber between which said article is adapted to be disposed, means for successively advancing the loaded chamber first to said evacuating station and then to each of said drying stations in turn, means for creating a vacuum in said chamber at said evacuating station and for maintaining the vacuum in said chamber while said chamber is subsequently at each of said drying stations, a source of high frequency electrical energy, and means for coupling said source to said electrodes at each of said drying stations, said means including a plurality of reactance elements in circuit with said source, each of said reactance elements being of different value and each being effective to couple said source to said electrodes at a separate one of said drying stations.

10. The invention set forth in claim 9 characterized in that said reactance elements are constituted by capacitors, and characterized further in that each of said capacitors has a different value corresponding to the moisture content of the article being dried when it reaches the respectively associated drying station of each of said capacitors.

11. In electrical drying apparatus for drying moisture-laden articles, said apparatus including a, plurality of drying stations, the combination or means providing a plurality of chambers, one at each of said drying stations, and each adapted to contain at least one article to be dried, a pair of cooperative electrodes in each of said chambers between which the respective articles are adapted to be disposed, means for maintaining a vacuum in each of said chambers at each of said drying stations, 9. source of high frequency electrical energy, a plurality of coupling circuits each including a reactance device and each coupling said source to a separate pair of said electrodes, said reactance devices each including a pair of relatively movable elements one of which is united with its associated chamber and the other of which is connected to said source, and said reactance devices being of different value whereby the energy supplied to said respective articles is dependent upon the particular reactance device coupled thereto, and means for effecting relative movement between said chambers and said source whereby to effect relative movement between said respective elements and thereby alter the value of the reactance device connected to any one of said chambers at any particular time.

12. In electrical apparatus for drying moisture-laden articles, the combination with a high frequency oscillation generator including a tuned circuit of a plurality of parallel-related, movable load circuits selectively coupled in series with said tuned circuit, each of said load circuits including a reactance element and being adapted to receive in series with its reactance element a variable impedance element having a different impedance than the impedance of any other of said load circuits, said impedance elements each consisting of at least one of the articles being dried, and said reactance elements being of different values to couple predetermined high frequency power to each of said impedance elements in accordance with the relative positions of said articles.

13. The invention'set forth in claim 12 characterized in that the articles adapted to be received in and constituting the impedance elements of each of said load circuits have different moisture contents than the articles of any other of said load circuits, the values of said reactance elements corresponding to the moisture content of their respectively associated articles.

14. In electrical apparatus for drying moisture-laden articles, the combination with a high frequency oscillation generator including a tuned circuit of a plurality of parallel-related, movable load circuits selectively coupled in series with said tuned circuit, each of said load circuits being adapted to receive therein atleast one of said articles in a different state of dryness than an article of another of said load circuits and including a serially connected variable reactance element, and means for transferring each of said articles successively from one of said load circuits to another, each of said reactance elements having a different value whereby to couple different predetermined high frequency power to each of said articles in accordance with the relative positions thereof.

15. In electrical apparatus for drying moisture-laden articles, the combination with a high frequency oscillation generator including a tuned circuit of a plurality of parallel-related load circuits connected in series with said tuned circuit, said load circuits each being adapted to receive therein at least one of said articles in a different state of dryness than an article of any other of said load circuits, and means including variable reactance elements for altering the voltages applied by said generator across each of said articles in correspondence with the moisture content therein.

16. In electrical apparatus for drying moisture-laden articles, the combination of a high frequency oscillation generator, a plurality of parallel load circuits coupled in series with said generator and each adapted to receive therein at least one of said articles in a different state of dryness than an article of any other of said load circuits, and means for periodically varying the coupling between said generotor and said load circuits in accordance with the moisture contents of said articles at predetermined times whereby to maintain the power load on said generator within certain predetermined limits.

17.111 electrical apparatus for drying moisture-laden articles, the combination of a pair of primary electrodes disposed in spaced relation to each other and adapted to receive at least one 2,4os,soo

of said articles therebetween, a pair of secondary electrodes surrounding said primary electrodes and connected in shunt relation to said primary electrodes, and means for coupling both said pairs of electrodes to a source of alternating electrical energy, the dielectric losses in said article resulting from the electric field set up by said source between said primary electrodes serving to heat said article sufliciently to.expel the moisture therefrom, and said secondary electrodes serving to provide a substantially uniiorm electric iield between said primary electrodes.

18. In the method 0! drying moisture-laden articles by subjecting said articles to an electric field of high frequency, the steps which comprise simultaneously subjecting a plurality of said articles, each with a diflerent moisture content, to

said electric field, each at a different station and at a diflerent voltage, the article with the great-- est moisture content being subjected to the lowest voltage at the first of said stations, the article with the lowest moisture content being sub- Jected to the highest voltage at the last of said stations, and the articles oi progressively decreasing moisture between said first named article and said last named article being subjected, respectively. to progressively increasing voltages at successive stations intermediate said first named station and said second named station, periodically removing said second named article from said second named station when said latter article is dry, simultaneously advancing each of the remaining articles to stations or successively higher voltages, and simultaneously introducing to said first named station a fresh article of maximum moisture content.

CYRIL N. HOYLER.

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