US2492187A - Method and apparatus for electrical heating - Google Patents

Description

,Dea. 27, 1949 usg METHOD AND APPARATUS FOR ELECTRICAL HEATING 2 Sheets-Sheet 1 Filed Jan. 5, 1945 Y 4 m Y RALPH A. RUSCA SWIM-Md Dec. 27, 1949 R. A. RUSCA 2,492,187

METHOD AND APPARATUS FOR ELECTRICAL HEATING I Filed Jan; 5, 1945 -2 Sheets-Sheet 2 gwvumd/f/Ob RALPH A. RUSCA Patented Dec. 27, 1949 MErhozehis Ahrsmrrs hon ehnerhiohnhmrm Ralph A. Rusca,

United States of New Orleans, La., assignor to America 235 representcdzby the Secretary .of Agriculture Application Januar 5 1945, Seria No- 571 49 :1 Claim.

Granted =under the act of March 1 This application is made under the ,act of March 3, 1883, as at mended by the act of April 30, 1928, and the invention herein described and maimed i a ented {ma he eh ured a he d J or o the o e nm nt of th llhite t tes o Amer ee o ern nta ee -rose w th ut the pa men to m o any royauy the on- This n nt on rela e t h ds o a d ape l hv t e-eot oh o e h t ble fie ds r a ed b hig hev.eh-ehsare reel ur ents- {The art of fu ing high oy i leetros eti fields tor ;producing heat in materials is well known, but heretofore no successful application of the art has been made to heating, drying or treating of textile materials, in the form ,of rovi g, yam co d r p or sh e e oohti pus pr oce ss In general, heating such materials in a continuous process is very difficult because the relative low density and thinness of the'material is conducive to electricalineificiency and e eotri e a h v be he spp oe electrodes- T is i pec t u wh n wa e or other solvents are being evaporated from the m ter e b ca e e or itt d o e lo res an e electrica th h v e n the elect odes, resulting in flashover with attendant damage .or

ties, hon of e materiel e he e tedobv a t ble t s me t nt. u Wi l??- a r h he Pot ntia on t e ele tr e o obm the em r e o he ti es se ure with his tro narrow electrode spacing, and this higher potee h! in itse a our e fla her ere enera obiee o t s i v n on is to p de a oo hmeroiauy practical and veffieieht eppen t s or uni orm h atin dr n or otherwise treall h o textile materials in a continroo ss;

ihvehhoh is espeoia ap licable to th .rehio d yin o e ioh or e t e no stru tio o hehmet c ve ie e tires after he sore has ee sub t d t e t atme wher at other olvent has bee emp oy d I th ne tioelar application, it is usual to wet the cord and then dry the cord while it is stretched and held under tehsionh eo ioa y r s eam-h Pl es so e, et with thi m hod? or tee-t ,hetweeh the ord and th heated plate is d oi ai ein resultin i llfill -"l k f im dl?" "l ased th ho shrfeee .oeose a n oi th i iPh jry of the so e, ther by .deljrimentally ex e rely idesPe e hetwee th eleotrooosrha l of ihe hei he a to her mplo ed ior ij ventioh we o be rnerization of plastic or resin impregnants in such "lth ue th s inven ion s h r aiter d sc bed in oohh etion w th he a pl ation thereo to the he tin o h tt cord, i is ot l n ;itcd to this type of material and is generally applicable to all operations that involve heatfme d in or t ating of textiles, paper and like materials in a continuous process. This inused for the (curing or polymaterials. Other objects, advantages, and uses vofthe invention will become apparent from the following description of various embodiments there con ction w e o pa yin drawing illustratingthe embodiments.

.1 2 he drawing:

F ure l i a p a View of o e or of t e ahpereths in a co da ce wi th in entio re 2 is a 'de elevational view along the e 219: Figu 1- g nre 3 is aisection along the line 3?-3 of Figero Figures 4, 5, an d 6 are views similar to Figure ,3 .01 three additional embodiments, respectively,

of the apparatus of the invention.

Re erring wit mor par ulari y t ur 1, :2, and 3 in which like numerals refer to like parts, the embodiment illustrated comprises a suitable base H, upon which bus bars or cables 12 and 13 are secured by means of electrical insulating ,cleats L4, 15, Hi and 11 that are ,atteehed to the hose 11- ee the bus ba s I2 13, there is disposed-a rowof metallic plates sho n in the d ewihs- The ooro emay be so? 3 ported at the ends of the row of plates by any suitable means, such as the rollers 22 and 23, illustrated in the drawing. By providing sufiicient tension in the cord 2| between the supports 22 and 23, undue sagging may be avoided.

The bus bars l2 and i3 are connected to a source of high frequency current, such as an oscillatory generator 24 energized by a source of electrical energy controlled by a switch 25. The generator may be any suitable device, such as a vacuum tube oscillator that converts input electrical energy into output high frequency at high potential oscillations on the order of 1 million cycles per second and above. The output circuit of the generator may be resonated in any known manner and may be provided with the usual controls for adjusting the magnitude of the output energy.

In operation, the high frequency oscillations pass through the bus bars [2 and I3 and create an electrostatic field across consecutive pairs of plates I8. The cord 2|, or other material to be treated, is drawn through the apertures IQ of the plates l8 by any suitable means at a predetermined rate of speed. Heat will be generated by the high frequency current within and through out the cord. In practical use, the material will have first been treated in some manner that requires the evaporation of water, solvent or other liquid, and the heat generated will eifect such evaporation. Also, if the cord has been previously exposed or treated with thermoplastic or thermosetting resins, they will become polymerized to a greater or lesser extent upon exposure to the electrostatic field, depending upon the length of time of the exposures and the power applied. In actual practice, many free ends of individual fibers on the periphery of the cord tend to erect them selves due to the influence of the field thereon. This increases the adhesive properties of the cord as compared with similar cords dried by other methods of the prior art, whereby a smooth or glazed surface is obtained. If the cord has been previously impregnated with a thermoplastic or thermosetting material in solution, the free fiber ends become encased in the polymerized material and stand out stiflly from the cord, which further increases the adhesive properties. Although in most commercial applications, the material will be treated while being drawn through the apparatus at a definite or variable speed, it is, of course, also possible to treat the material while stationary for any special purpose.

Devices for producing high frequency currents are well known in the art, and it is unnecessary to describe them fully herein. Such devices may be obtained with means for varying the output energy by means of tuning devices, which may be adjusted to change the amount of heat produced in the material being treated. Such control provides the operator with complete and instantaneous adjustments of the heating without time lag, which is not possible with other prior methods of heating.

One advantage of the apparatus illustrated resides in the fact that, within limits, variations in the amount of water, solvent, or other liquid in the cord are automatically compensated for to produce a cord that can be treated more nearly uniformly than it could be by other prior methods or devices. It is well known that a material of higher electrical power loss absorbs moreelectrical energy, and hence generates more heat within itself than a material of lower power loss.

Since the power loss of water is higher than cotton fibers, the heat generated in the cord will vary directly with the moisture content thereof. Changes in the moisture content of the cord as it moves through the apparatus utilize the electrical energy of a correspondingly varying number of plates. In the manner in which the electrodes are designed, the overall impedance of the load circuit, which includes both the electrode and the material being treated, remains substantially constant although the moisture content of the material may vary considerably from the average. As will be apparent from the above description, the electrodes essentially comprise a plurality of condensers connected in parallel with each other, in view of which a relatively high impedance is provided which is affected more by the total fixed reactance than by the series resistance of the load. The formula for impedance Z of a condenser having a reactance X and a dielectric, the power loss through which is R, as an equivalent series resistance, is

Since X is a constant composed of the total reactances of all the condensers which comprise the electrode, it is very large in comparison with the changes in resistance R due to the changes in the power loss of the dielectric as the cord dries. The overall impedance of the circuit, therefore, varies little with relatively large changes of moisture, and the generator may operate with constant output and maximum efiiciency without requiring continuing adjustments to correspond to a change of impedance due to moisture variation in the cord.

I have found that with a generator having an energy output of 1 kW., 35 percent moisture in 17/4/3 cotton cord can be reduced to a minimum of 6 percent by approximately 5 seconds exposure to the electrostatic field, the cord being moved through the electrodes at a rate of about 144 yards per minute.

In Figures 1, 2, and 3, the plates iii are illustrated as being equidistantly spaced. However, in some instances, it is advantageous to use differential spacing. For example, by spacing the first plates farther apart from each other than the last plates of the series, the cord moving through the electrostatic field is subjected to gradual increasing intensities of energy. If it is desired to subject the cord to decreasing intensities of energy, the spacing may be reversed. Also, any intermediate eifects of increasing and decreasing of energy may be provided.

A plurality of the units may be electrically con nected together in any of the well-known types of electrical circuits, such as in series, parallel or series-parallel to provide a flexible method of obtaining desired heating effects and to permit the control of the number of plates which a single generator may resonate. In any of the circuit arrangements, any electrode, or any plurality of electrodes of the same instantaneous polarity, may be grounded without significantly affecting the operation of the apparatus. The size and shape of the individual plates of the electrodes may be modified to adapt them to the material to be treated.

Where it is desired to treat a number of cords 26 simultaneously, the embodiment illustrated inFigure 4 maybe used where the plate 21 is elongated and the aperture 28 therethrough is similarly elongated. Although it is not indispensable, it is preferred that the width of the aperture 28 be substantially one-third the width of the plate. A certain amount of electrostatic field concentrates at the points 29, 29 of the plates. It is, therefore, important that the aperture 28 be suiiiciently long so that the outermost cor- ds 30, 30 are not too close to these points of concentration. To facilitate placing the cords through the plates, each plate is provided with a slot 3!, which passes from the aperture 28 to the exterior. However, this feature is not indispensable and may be eliminated, if desired. Although the slot may be disposed at any point on the plate, it has been found that its location at the end of the major axis of the orifice is most satisfactory.

In Figure 5, there is illustrated an embodiment wherein the entire end of each plate 32 is open, and the plate is mounted with the major axis in a vertical position. This may be referred to as a horseshoe or U-type, and it has the advantage that when material is being treated which emits vapors, the tendency to fiashover is reduced due to the fact that the vapor is provided with an unrestricted path to the atmosphere above the plates.

The embodiment illustrated in Figure 6 is preferred for the heating of sheeting or fabric in wide widths. This embodiment is similar to the one illustrated in Figure 4, except that instead of providing a slot for the introduction of the material, the plate is fabricated into two parts 33 and 34, which are hinged together substantially as shown. The lower half is secured to the bracket 35 and may be considered the stationary half, while the upper half may be moved to an open position for the purpose of admitting the material to be treated and then pushed down again into closed position. In order to insure a satisfactory electrical connection between the two halves of the plate and to obviate any power loss or sparking which may occur at the hinge point, a flexible metallic strip 36 may be provided to connect the two halves of the plate electrically and insure a satisfactory electrical connection.

In operating any of the embodiments illustrated above, it is not necessary to maintain them in any particular position relative to the horizontal or vertical. To suit the convenience of any particular operation, the plates may be disposed in any special position desired so long as the same axial relationship exists among the plates.

Having thus described my invention, I claim:

A heating device for continuous heating of sheets and filaments, comprising a row of at least four relatively thin fiat electrode plates, said electrode plates being disposed in spaced, parallel relation facing each other and having aligned openings through which a material to be heated may be made to pass from one electrode to the other, the distance between consecutive electrodes being substantially greater than the thickness of the electrodes and in an amount sufficient to prevent electrical flashover under the influence of vapor rising from the material, the flat faces of the plates having no lateral projections, means for supporting said electrodes and for securing them in position, and means for establishing a high frequency electrostatic field across each consecutive pair of electrodes, whereby a series of contiguous electrostatic fields may be established in a path surrounding the longitudinal axis of the aligned openings, said electrodes being fabricated of two half sections hinged together at one side, one section being secured in position, the other section being movable about the hinge to open the electrode and facilitate threading through of the sheet or filament, and guide rolls for continuously feeding and removing the sheet or filament.

RALPH A. RUSC'A.

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

UNITED STATES PATENTS Number Name Date 1,813,591 Ulrey July '7, 1931 2,291,807 Hart Aug. 4, 1942 2,303,341 Dufour et al. Dec. 1, 1942 2,303,983 Brown Dec. 1, 1942 2,319,174 Wilson May 11, 1943 2,368,809 Denneen et al. Feb. 6, 1945 2,379,059 Ashley et al June 26, 1945 2,384,982 Walton et al Sept. 13, 1945 2,390,572 Brabander Dec. 11, 1945 2,401,991 Walton et al June 11, 1946 2,404,283 Gieringer July 16, 1946 2,405,037 Hsu July 30, 1946 2,433,842 Grifiin Jan. 6, 1948 FOREIGN PATENTS Number Country Date 682,375 Germany Oct. 13, 1939

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