Method of drying moisture laden articles

April 2, 1946. w. d. wenger 2,397,897

METHOD OF DRYING MOISTURE LADEN ARTICLES

Filed May 29, 1943

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Snoenfor

IVZZezy Ό. 'We.TLcje.r attorney

Patented Apr. 2, 1946

2,397,897

UNITED STATES PATENT OFFICE

2,397,897

METHOD OF DRYING MOISTURE LADEN ARTICLES

Wiley D. Wenger, Camden, N. J., assignor to Radio Corporation of America, a corporation of Delaware

Application May 29,1943, Serial No. 489,089

Claims.

This invention relates to a method of drying moisture laden articles, and more particularly to a method of drying thin, sheet-like, dielectric articles by the use of high frequency electric energy.

In the manufacture of thin, sheet-like articles, such as wooden separator plates used in storage batteries, the articles or plates are saturated with certain solutions during their manufacture, and it is necessary to dry them before they can be put to use. Drying methods heretofore generally used have the disadvantage of not drying the articles uniformly throughout, with the result that the finished articles curl more or less. In he case of battery separator plates, when curled separators are placed between the electrodes of e battery, they often crack and are thereby endered useless. To overcome this difficulty, the ;parators may be subjected to a high frequency sctric field which would tend to dry them uni□i mly by reason of the dielectric losses which the ' eld produces therein.

Battery separator plates are usually made with ; series of parallel ribs, the ribs at the longitudinal edges being much wider than the intermediate bs. If the separators are stacked on top of each her and the stack is placed between a pair of ctrodes which terminate a high frequency gentor in such relation to the electrodes that the -ctrodes are parallel to the planes of the separators, it is found that the ribs at the edges of he separators reach a higher temperature than ae remainder of the plates, and the separator elates therefore do not dry uniformly.

Another difficulty encountered in drying ma'2rials by means of a high frequency electrical held rather than by applying heat to the work through such means as hot plates or an oven is ^; hat the moisture which is rapidly removed from '.he inside of the material being dried condenses .ipon contact with the adjacent electrodes and equipment. This condensed moisture retards heating of the outer portion of the material and in many instances results in failure to properly dry materials near the applicator plates or electrodes, thereby causing waste. It has been proposed to maintain the moisture in the vaporized state until it is absorbed by the surrounding air by heating the applicator plates or the adjacent parts of the heating units, as by steam or electrical resistance elements. However, to heat the applicator plates and other adjacent parts of the heating apparatus is not desirable since it tends to defeat the purpose of using high frequency heating because it would require that the heating of the electrodes or applicator plates be adjusted (CI. 34—1) separately in accordance with the heat being generated in the material being dried, if best results are to be obtained.

The primary object of my invention is to provide an improved method of drying moisture laden articles by means of a high frequency electric field which will be free from the above mentioned disadvantages.

More particularly, it is an object of my present invention to provide an improved method of drying thin, sheet-like, moisture laden, dielectric articles uniformly throughout by means of high frequency electric energy.

Another object of my present invention is to provide an improved method of heating thin, dielectric articles as aforesaid wherein moisture condensation on the surface of the electrodes supplying the high frequency electric field is avoided.

Still another object of my invention is to provide an improved method of drying thin, dielectric articles as aforesaid wherein the rapid absorption of the vapor expelled from the material being dried by the surrounding air will be facilitated so that condensation of the vapor on the applicator electrodes will not take place.

A further object of my invention is to provide an improved method of drying moisture laden, dielectric articles whereby the heating of the material being dried is equalized throughout all parts thereof so that its surface temperature more nearly equals its inner temperature.

It is also an object of my present invention to provide an improved method of drying moisture laden articles as above set forth which is highly efficient and simple to carry out in practice.

In accordance with one feature of my invention, the thin separator plates or other similar dielectric articles are stacked in parallel, coaxially aligned relation, and the applicator electrodes are applied thereto in such relation that the electric field set up between the electrodes extends substantially parallel to the planes of the stacked articles. For this purpose, the sheet-like articles may be stacked in the direction of their respective, thin dimensions and the electrodes applied thereto along their longitudinal edges. An electrical field set up between the electrodes will then extend in directions parallel to the planes of the stacked articles. Thus, uniform heating throughout each of the articles is assured and therefore the entire stack will be uniformly heated and uniformly dried.

In accordance with another feature of my invention, and in order to maintain the temperature of the outermost articles of the stack equal to that

2,387,897 of the inner ones, as well as to assist in the removal of the vaporized or expelled moisture, there may be placed around the articles being dried, or adjacent thereto, one or more layers of moisture absorbing material. For example, in the case of the battery separator plates, the separators may be stacked alternately with layers or sheets of blotting paper and as the moisture is driven from the articles being dried, it is forced into the blotting paper or other similar material which has a relatively greater moisture absorbing property than the articles being dried. The absorbing material is preferably also placed within the electric field and becomes hot in proportion to the moisture driven .from'the articles being, dried. While still in a vaporized state, the moisture is then dissipated into the surrounding air before condensation thereof occurs on the cold parte of the heating equipment. As less moisture is driven from the articles being dried into the absorbing substance, the latter tends to attain the same temperature as that of the articles under treatment, and a point is reached where the inner and surface heat of the articles is substantially the same. This condition is not possible without the use of the moisture absorbing material because of heat conduction by the cold electrodes and the surrounding air, as well as liquid accumulation on the surface of the articles being dried and on the electrode plates.

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, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawing, in which

Figure 1 is a perspective view of one arrangement for carrying out my present invention,

Figure 2 is a sectional view of a somewhat different arrangement for carrying out the present invention, and

Figure 3 is a perspective view of a separator plate of the type to which my present invention is particularly applicable.

Referring more particularly to the drawing, wherein similar reference characters designate corresponding parts throughout, there is shown, in Fig. 3, a conventional type of battery separator plate I made of wood or other dielectric material which is more or less moisture absorbent. The separator I is formed with a plurality of parallel ridges or ribs 3 and β, the ribs 3 along the longitudinal edges of the separator I being relatively wide and the intermediate ribs 5 being relatively narrow. Separators of this type are subjected to various treatments with liquids in the course of manufacture, and it is necessary to dry them before they can be put to use. For this purpose, such separators have generally been dried on hot plates or in ovens. Drying by such means causes the separators to curl more or less, and in some instances to such a degree as to render them unfit for use.

To insure uniform heating and drying of the separators in accordance with the present invention, they are preferably stacked in axially aligned, parallel relation alternately with one or more layers or sheets 7 of moisture absorbent material, such as blotting paper. That is to say, when the separators I are thus stacked, their principal planes, or the planes of the back surfaces thereof opposite the ribs 3 and 5 in each case, are parallel to each other. The longitudinal edges of the separators I are aligned in common, parallel planes normal to the aforesaid principal planes, since the separators all have the same peripheral contours. To further insure against curling, the stack may be confined in a suitable press represented by the press plates 3 whereby they are maintained in parallel relation, each in its own plane. Sheets of blotting paper or the like la are placed between the separators at each end of the stack and the adjacent presss plates 9. The exposed, longitudinal edges of the separators I may also be covered with layers of blotting paper or the like 7b, and the assembled stack is placed between a pair of electrodes If which are connected through a transformer 13 to a source of radio frequency energy 15, such as a vacuum tube oscillation generator. The electric field set up between the electrodes 11 will be substantially parallel to the planes of the several separator plates I and of a magnitude sufficient to heat the separators I by reason of the dielectric losses it produces therein to a temperature sufficient to expel the moisture therefrom.

Since the electric field is uniform throughout, it is apparent that the separators I will be uniformly heated throughout. As the moisture expelled from the articles progresses through the blotters, further evaporation takes place into the air surrounding the blotters. Thus, the moisture at no time reaches the applicator plates to condense into liquid form. At the same time, the heated blotters tend to heat the electrodes II, thereby further reducing the likelihood of moisture condensation. If desired, a suitable blower 17 may be provided to increase the air movement and to force the moisture expelled from the articles I and the blotters 7, la, lb away from the vicinity of the stack. This, however, is not always necessary, particularly where the drying is carried out at a relatively slow rate.

In the arrangement shown in Fig. 1, the separators I are disposed in vertical planes and are stacked in side by side, face to back relation, that is, with the ribs of one separator facing toward the back of the next succeeding one. The separators I or other similar article may, however, be disposed in parallel horizontal planes together with the interposed layers of absorbing material, as shown in Fig. 2. In any case, it is to be noted that the thin articles to be dried are stacked in the direction of their respective thin dimensions and are dried uniformly throughout and therefore they do not curl to any marked degree, if at all.

Although I have described my invention in considerable detail, it will, no doubt, be apparent to those skilled in the art that many variations thereof are possible. I therefore desire that my invention shall not be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims.