US2503779A - Device for radio frequency treatment of filamentary material - Google Patents

Description

Patented Apr. 11, 1950 UNITED STATES PATENT OFFICE DEVICE FOR RADIO FREQUENCY TREAT- MENT 0F FIL All/IENTARY MATERIAL Theodore H. Story, Merchantvillc, N. J asslgnor to Radio Corporation of America, a corporation oi Delaware I f- Application August 1.3, 1947, Serial No. 768,460

vention being particularly useful in connection through the thread between the electrodes; The

curing or drying process as practiced in accord. ance with the Brown patent is relatively slow.

It is necessary, of course. for the thread to rc-' main in the electric field long enough to complate the desired processing, This has required the thread to move rather slowly past the electrodes. Within limits the time of treatment can be reduced by increasing the volta e applied to the electrodes, but this increases the danger of arcing and burning.

As is well known, radio frequency heating is utilized to cure and dry the wet thread in the process of manufacture, and also to set the twist, either simultaneously with the drying process or as a separate operation. It has been discovered that as the treatment progressesand the material dries, its power factor decreases. Thus, if. the voltage applied to the electrodes remains constant, the power absorbed by the material, and thus the heat generated therein, falls off rapidly as the material becomes dry, In order to main tain the power input, and thus the rateof heating, at the maximum permissible value, it is proposed, in accordance with the presentinvention, to increase progressively the voltage gradient between the applicator electrodes as the operation proceeds. In brief, this is accomplishedby causingthe material such as a filamentary thread or fabric, to pass along a path over a grid-like applicator consisting of a plurality of spaced electrodes. lying side-by-side in a plane. One end of each alternate conductor is grounded,- and the other end of each intermediate conductor. is connected to a bus extending lengthwise or the ap- Thus the strength of the electric ileld;betwccn.

adjacent electrodes increases irom one end of the applicator to the other. The material to be 4 Claims. (01. ZEN-47) treated enters the electric held at the low potcm tial end and leaves at the high potential end.

It is, therefore, the primary object of this invention to heat continuously at a constant power input a material whose electrical characteristics tend to change during the heating process.

A further object of this invention is to provide an improved applicator characterized by an increasing electric field intensity at different positions along its length. A further, and related object, is to establish the progressively increasing field intensity by establishing a standing wave on a portion of the applicator.

In order to insure uniform heating efiect the spacing between the material and the different electrodes must be maintained at a constant value. In accordance with a still further object of this invention, this is assured by constructing the electrodes in the form of cylindrical rollers, and passing the material alternately over and under adjacent rollers. The rollers are preferably covered by a thin insulating material of low heat-absorbing properties.

The novel features that are considered char-ac teristic of this invention are set forth with paring description when read in connection with the accompanying drawings, in which Fig. l is a plan view of the applicator in ac- Referring to Fig. 1, a plurality of rod-likc conductors 5 and 5a are positioned by means of any end of each alternate conductor, identified by reference numerals 5, is grounded. The opposite end of each intermediate conductor, identified by reference numerals 5a, is connected to a distributlon bus 1 extending from one end of the apj plicator to the other adjacent the ends of the conductors to which it is connected;v One end of bus 1 is grounded through a variable inductor 9 which may itself be coupled to a source of high frequency -potential, such as oscillator 11, or x which may be coupled .thereto by a separate secondary It.

frequency of operation may be adjusted so as to produce the same result, as is well known. Thus. the potential of the applicator electrodes connected to the bus will be determined by the standing Wave pattern established on the bus. The physical length will, of course, be less than the efiective electrical length due to inductance 9 and r the capacity between adjacent electrodes 5 and 50,, illustrated as dotted capacitors in Fig. 2, Preferably the electrical length is of the order of a quarter wavelength at the operating frequency, since in that case the potential along the bus will" increase gradually from one end to the other.

The material to be treated, which may be, for example, a plurality of filamentary threads is of a dielectric material, is introduced at the low potential end of the applicator. For example, the threads may be contained initially on a storage drum ll. roller 23 [and then over or under the electrodes in a plane parallel to the plane of the electrodes and in a direction perpendicular thereto, to a second idler roller 25 and then to a take-up drum i9, which may be rotated by a motor 2 i.

As-shown more clearly in Fig. 2, idler rollers 23 and 25 are mounted so that their upper surfaces are just above the upper surface of the electrodes 5, 5a. This holds the material close to but just above the electrodes.

As the wet material comes into the field of the electrodes at the low potential end of the applicatoi', an alternating current is caused to flow from the hot electrodes 5a through the material to the grounded electrodes 5 on either side. This current causes the material to become sufiiciently heated to drive off the moisture. When wet, the thread resistance is relatively low, and thus a heating current is produced with a relatively low voltage. and its resistance becomes higher. But it has then advanced to a position opposite electrodes between which there is a higher potential difference. Consequently, heating current is still caused to flow. This process continues successively'until the substantially dry thread passes onto the take-up drum l9.

Thepverall length of the applicator, from'input The threads pass over an idler As the material moves, it dries out,

end to output end, is made sufficiently long that the material is dried to the desired state in the time required "for it' to cover the distance. The

linear speed of the thread may be adjusted readily'to'control the total efiective heating period.

Where the electric field heating method as described above is employed with materials which are saturated. with water, a modification of the arrangement described above may be employed to advantage.

In such a case it is desirable to have a relatively high initial heating rate to bring the material, and the absorbed moisture,-

then increased again as in the preceding illustrationi This may be accomplished, as shown?" in Fig. 3, which is a partial view of the apparatus shown in Figs. 1 and 2. Inductor 9 is positioned a distance on from the incoming end of the applicator, so that the point of voltage minimum oc curs at the point where the boiling temperature is reached. A standing wave representing somewhat less than electrical degrees, or a quarter wavelength, *i s'established at the short incoming end of bus The longer outgoing end will, as in the preceding case, have a standing wave of greater maximum amplitude, as shown by the curve associated with Fig. 3.

When operated at high speeds, the threads l5 may have a tendency to vibrate and come into contact with the electrodes, or to move too far from the electrodes to effect a uniform energy transfer thereto.' In' order to overcome this the modification illustrated in Fig. 4 may be employed. In this case the electrodes of the applicator all take the form of rollers journalled in electrically conducting supporting members 21, 29. Supporting'member 27 is grounded, while member 29 is the equivalent of bus I, and is tuned by inductor 9 so that a standing wave is produced thereon, as shown by the associated curve.

The rollers are all identical, but are placed in" the support in alternately reversed fashion, so

that one roller is eiIectiv'ely grounded and the next one efi'ectively connected to supporting supported in an insulating sheath 3 4.

member 29.

applicator 'to the other.

trodes and the material. I

Instead of treating a plurality of separate fila mentary threads, a woven fabric may similarly be treated. The treatment may be for simple drying, or for polymerization of a resin as is well known. Various modificationsof the roller construction will occur to those skilled in the art. The actual construction will depend upon the thickness of the insulation desired and the rigidity of the material employed. Other means of',

insulating one end of each electrode may be employed, such as an insulating bushing mounted on It is therefore intended the'supporting member. that the invention shall 'not be limited to the specific embodiments illustrated except insofar as is made necessary by the'prior art and the spirit of the appended claims.

What I claim is:

1. An applicator for high frequency treatment offilamentary dielectric material and the like, 1 comprising a pluralityoi. substantially parallel spaced'conductor'si'n a'single rowlying in a com-.-, monplane, means connectingalternate'conduc tor s to ground,an' electrical distribution bus ex- 1 tending along theen'ds of said conductors on one' side of said row, means connecting intermediate conductors to spaced points along said distribution bus Twhereby. adjacent conductors are oppo sitely polarized in operation to establish electro static fields therebetween along said row, the electrical length of said bus having such a relation to the frequency of operation that azstanding wave is produced along its length whereby the potential of said intermediate conductors is determined by the standing wave pattern'established on said bus, and means establishing apath for work to be treated along the row of conductors and through said fields.

2. An applicator for applying a radio frequency electric field to filamentary dielectric :material comprising a single row of spaced para iconductors lying in a plane in side-by-side relation, means connecting adjacent ends of alternates-ponductors to ground, an electrical distribution bus extending along the opposite ends of said'conductors, means connecting the opposite ends of intermediate conductors to spaced points along said distribution bus, and means providing electrical coupling for said bus with a. source of high frequency energy, and said bus having a length such that a standing quarter wave is produced on said bus at said frequency, the potential along said bus varying from a minimum at one end to a maximum at the other end of said bus; whereby the potential of said intermediate conductors increases successively from one end of said applicator to the other with respect to ground and said alternate conductors.

3. An applicator for applying a radio'frequency electric field to moisture-laden dielectric material comprising a plurality of spaced substantially parallel conductors in a single row lying in a plane in side-by-side relation; means connecting adjacent ends of alternate conductors to ground, an electrical distribution bus extending along the opposite ends of said conductors, means connecting the opposite ends of-in'termediate conductors to spaced points along said distribution bus, and means providing electrical coupling for one end of said bus with a source of high frequency energy having a predetermined operating frequency, the electrical length of said bus being of the order of a quarter wavelength at said frequency, and said coupling means including a reactance element connected between said .one end of said bus and ground for tuning said bus, whereby the potential of said intermediate conductors successively more remote from said one rend of said bus increases from a minimum to a maximum value.

4. A device of the character described in claim 1 which includes an inductor connected between said bus and ground at-a oint intermediate the ends thereof, for establishing thereon a standing wave pattern having a higher potential at the ends of said bus than at a point intermediate the ends. a

THEODORE H. STORY.

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

UNITED STATES PATENTS Number Name Date 2,288,269 Crandell June 30, 1942 2,303,983 Brown Dec. 1, 1942 2,308,043 Bierwirth Jan. 12, 1943 2,308,204 Parry Jan. 12, 1943 2,321,131 Crandell June 8, 1943 2,433,067 Russell Dec. 23, 1947