US2532460A - High-frequency apparatus for drying materials electrostatically - Google Patents

Description

HIGH-FREQUENCY APPARATLiS FOR DRYING MATERIALS ELECTROSTATICALLY Filed Dec. 24, 1947 Dec- 5, 1950 J. E. PHILLIPS JR 2,532,460

IN VEN TOR. JOHN E. PH/LL IPS, JR.

Patented Dec. 5, 1950 uimrao STATES PATENT orncs 2,532,460 IG REQUENCY ARATU EQRD ING MATERIALS 'ELECTROSTATICALLY John E. Phillips, J12, Chester, Pa, assigno'r to American Viscose Corporation, Wilmington, Del, a corporation of Delaware Application December 24, 1947, Serial No. "793,"682

4 Claims.

This invention relates to an improved method and apparatus for drying materials electrostatically, that is, by the impression of high frequency or radio frequency currents thereupon. It is concerned with the evaporation of water or any other vaporizable solvent to effect a drying or a change in moisture content of the material being heated. In this specification and claims, the term moisture is intended torefer'to any liquid and is not restricted to water.

In the past, when subjecting moist materials to be heated to high -frequency electric fields for the purpose of reducing the moisture content or drying the articles, the vapor of water or other solvent frequently would condense on one of the electrodes, generally positioned above-or in such roximit to the material being dried that drops of the condensate would drip back up'on'the material. This effect has the disadvantageous potentialities of producing a non-uniform material because of the local spotting and the arcing caused by the drippings. The arcing frequently produces burning, 'ch'arring, or 'fusion locally or generally through the article. To avoid the difficulties associated with condensation, it has heretofore been suggested to provide special heating means an "the electrode or electrodes giving 'd'ifiiculty. For example, the electrode has been made in the form of a hollow shell through which hot water, steam, or other heated liquid could be passed. Alternatively, it has been suggested to slope the surfaces of the electrodes that would otherwise give difficulty to assure that the condensate would run off to the side away from the material.

While these expedients of the .prior art are e1 fective, they. do have certain disadvantages in that the former requires special source of heat in addition to that provided by the high frequency field and the latter is not always conducive to the-production of a uniform electric field between the electrodes.

:It is an object of the present invention to provide an improved and much simpler method and arrangement for preventing condensation upon one or more electrodes in a high frequency heatingsystem. It is a particular object of the present invention to provide for heating of an electrode =or electrodes to prevent condensation and to derive the power for effecting the heating from the high frequency field itself. 'Other objects and advantages of the invention will be a parent from the drawing and the description thereof hereinafter.

In the drawing,

Figure 1 is a diagrammatic elevation of one embodiment of the invention,

Figure 2 is a plan view of the upper electrode in Figure '1,

Figure 3 is a side elevation, somewhat diagrammatic, of a modification,

Figure 4 is an end view partially in section as indicatedby line IVIV in Figure 3, and

Figure '5 is a similar end view of a modification.

its shown in Figures 1 and 2, the material 3 to be dried is disposed between a lower electrode land an upper electrode 5 within a chamber 6. The electrodes "4 and 5 may be of solid plate material or they may be of foraminou's character and are supported by "insulating rods 2. For example, they may either be made of plates or discs of copper, aluminum, or other conductive steel, or they may be formed of screens made of such conductive metals. The chamber 6 need not be entirely enclosed as it may serve chiefly the purpose of a guard to prevent passersby "from coming into contact with the high voltage equipment. Thus, the chamber 6 may be of a closed box-"like container having solid walls, or it maybe composed of a screen which would permit visual obse'rv'ation or what takes lace wherewithal, screen or box forming the container may be of conductive or non-conductive mat'erial, speaking electrically, but is preferably conductive for shielding effect to prevent radiation that would give rise to radio interference.

The lower electrode 4 is grounded as by a line 1, advantageously to the chamber 6 when it is of a conductlve material, though, if desired, this may be done by replacing the insulating post '2 by a conductive post. The high potential field is imposed upon the upper electrode '5 through the means of the high frequency current feed line 8 connected to one end of the coupling coil '9, the other end of which is grounded as byline l0, advantagecusly to the chamber 6 when it is or a conductive shielding material, as shown. High frequency current 'is introduced into the system from a source thereof, such as 'a radio frequency oscillator H through the means of a coupling coil [2.

So far the apparatus may take any of the convention'al forms and it is customary to turn back the edges of the electrodes as indicated at It.

In order to heat the electrode 5 which would otherwise be'subject to condensation troubles, one or more resistance elements H! are provided in the field adjacent the electrode 5. "Since the effective portion or the i'leld, insofar as the heating eral resistance elements I4 are stretched across between the in-turned edges of the'electrode 5 where they may be conveniently securedin any way desired. Thus, they may be welded thereto or they may merely be hooked about one of the a edges of the screen forming the electrode In Figures 3 and 4, a modification is shown in which the material to be dried is conveyedcon.- tinuously by means of abelt [5 serving also as one electrode of the high frequency heating systerm. This belt may be in the form of a conducvc screen grounded by lead line-1a connected to a brush it which bears againstthe belt as it passes thereover. The belt may be driven by sprockets orrollers Hand passes through the lower portion of a chamber 6a which may be formed without end walls and merely of screened walls, top, sides, and bottom, to facilitate visual observation of the drying operation. Insulating rods 2a suspend the upper electrode 5a from the top'of the chamber. The lead line 8a is connected to the upper electrode 5a and a plurality of resistance elements vhid are stretched from one side to the other of the-upper electrode So. If desired, an additional electric heating element, may be provided for the lower electrode in the form of an electric heater I8 connected by means of the lead lines as to a source of direct or alternating, current of low voltage, such as 110 volts, indicated at l9.. f

In-Figure 5 there is shown a modification in which the resistance element I i-b is not connected conductively to the electrode as in Figures l to 4 except at one end which is. secured to a metallic bar 2| held in place by a stop 22 projecting from the electrode and the downwardly bent edge 23 of the electrode itself. The other end is secured to an insulating bar 2e held back of the stop 25 and the in-turned end 26 along the other side of the electrode. The ends of the resistance coils away from the conductive; bar 2! are secured to a common metallic bus bar 2! which is connected by a flexible lead line v2i? and a sliding conductive contactor 29 to the high. frequency feed line 8b. The slide contactor 29 is.

movable along the feed line 8b to adjust the drop in potential to which the resistance coils or elements are subjected. This adjustment can be made by loosening the set screw30 within the contactor 29. Y

Any conventional source of high frequency current can be employed. The voltage of the high irequency'field may vary from 3,000 to- 1-1,000 and even up. to 25,000 volts, whereas the frequency may be from 1 to' 5001' more megacycles. The value of the resistance and the number of resistances disposed along anelectrode depends entirely upon the particular electrical system and the conditions under which evaporation is effected. Thus, the equipment may be employed for theevaporation of water or any other solvent at atmospheric pressure, in which case a temperature of at least 212 F. in the case I of-Water, or. the. boiling. point in the, caseofthe..-

example, in the embodiment of Figure 3, where water is being evaporated at atmospheric pressure from water-wet cakes of rayon, six transverse elements may be uniformly spaced longitudinally of the electrode, or a greater number of resistance elements may be disposed at the end of the upper electrode below which the cakes first are heated than at the discharge end of the system. Each of such elements may have a resistance between 5 to 30 ohms illustratively, and the heat developed and radiated to the electrode is sufficient to raise the temperature of the electrode throughout its length so as to prevent condensation diirlculties.

The method and apparatus of the present invention can be employed for the vaporization of, any liquidirom any article, such as an annular Or, by makpackage, at atmospheric pressure. ing the chamber 6 tight, such removal can be effected under high vacuums even up to a vacuum of 25 inches of mercury or under superatmospheric pressure, such as up to 2 or 3 atmospheres. be employed for reducing the moisture content to any predetermined extent. For example, in

drying regenerated cellulose rayon in the form,

being subjected to radio frequency and there? after the balance of the moisture may be removed by conventional oven drying systems in which heated air is circulated past the cakes. In such an event, the partially dried materials may be subjected to higher temperatures in the oven drying than would ordinarily be permissible and critical.

tofore practiced.

The method and apparatus may be employed with particular advantage in the drying of wet spun artificial filaments made of regenerated" cellulose, cellulose acetate, vinyl resins, casein,

or the like. It may also be used with advantage" for the drying of annular wound packages (without a central core) of felts and fabrics, which may be employed for the removal of the solvent in the case of the sizing, coating, dressing, or

otherwise conditioning of yarns, fibers, fabrics or the like. For'example, it may be employed for removing the solvent from tire cords which have been impregnated with rubber coating materials, from yarns impregnated with solutions,

dispersions, or emulsions of weaving and knit--= ting sizes, as well as sizes used for setting thetwist of lively twisted yarns; for removing 'the solvent from materials which have been sub terials.

The radio frequency heating may tacky in yarns, fabrics, felts, papers, and the like, and particularly when such articles are extremely thick. In such operation, the material, after treatment with the solvent to activate the fibers to the tacky condition, is wound and the wound package is passed through the drier of the present invention and, after removal of th'e solvent, the tacky fibers bind together with them",- selves and/ or with other non-adhesive fibers that may be present in the article subjected to'the solvent whereby the resulting article has increased coherence and strength.

It is to be understood that the description herein is entirely illustrative and changes and modifications may be made without departing from the spirit and scope of the present invention as defined in the appended claims.

I claim:

1. Apparatus comprising spaced electrodes, means for impressing a high frequency current across the electrodes, and a resistance element disposed in the field adjacent one of the electrodes receiving current exclusively from the field to heat the electrode thereby, at least one end of the element being connected conductively to the electrode.

2. Apparatus in accordance with claim 1 in which one electrode is grounded and a high potential is impressed on the other by a hignfrequency feed line, and the resistance element is disposed adjacent the high potential electrode for heating it.

3. Apparatus in accordance with claim 1 in which one electrode is grounded and a high potential is impressed on the other by a high frequency feed line, and the resistance element is disposed adjacent the high potential electrode for heating it and is conductively connected at both ends to the high potential electrode.

4. Apparatus in accordance with claim 1 in which one electrode is grounded and a high e tential is impressed on the other by a high frequency feed line, and the resistance element is disposed adjacent the high potential electrode for heating it and is conductively connected to the high potential electrode at one end and at the other end is connected to the feed line at a position spaced from the juncture of the feed line with the electrode.

JOHN E. PHILLIPS, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Jordan, Applications of Vacuum Tube Oscillators to Inductive and Dielectric Heating in Industry, Transactions, Electrical Engineering, November, 1942, vol. 61, pages 831-834.

Lion, An Instrument for Measuring Electrical Field Strength in Strong High Frequency Fields, The Review of Scientific Instruments, August 1942, vol. 13, pages 838-341.

The ABC of Electronic Heating, Scientific Electric, published December 1944, pages 1-5.

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