US2635352A - Method of drying wound packages - Google Patents

Description

J. E. PHILLIPS, JR

METHOD OF DRYING WOUND PACKAGES Filed June 24, 1948 April 21, 1953 RA 0/0 6 FREQUENCY i OSCILLATOR 52-- 2 FREQUENCY OSCILLATOR RADIO FREQUENCY OSCILLATOR FREQUENC Y OSCILLA Tel? /7 L RAD/0 FREQUENCY OSC/LL A T'OR JNVEN TOR. JOHN E. PH/LL 1P6 JR.

Patented Apr. 21, 1953 METHOD OF DRYING WOUND PACKAGES John E. Phillips, Jr., Chester, Pa., assignor to American Viscose Corporation, Wilmington, Del., a corporation of Delaware Application June 24, 1948, Serial No. 34,943

7 Claims.

This invention relates to a method of drying 'moisture-laden wound packages of filamentary material containing such a large proportion of moisture as to cause shrinkage during the drying thereof. It is particularly concerned with the drying of annular wound packages formed without a central support, such as by collection in a rotating centrifugal pot commonly employed in the rayon industry. In the specification and claims hereof, the term moisture is intended to refer to any liquid and is not restricted to water.

When such a wound package of regenerated cellulose contains 30% moisture by weight (on the basis of the total Weight of the package) or up (and it is quite common for such packages to contain 60 to 80% by weight of moisture even after extraction of water from a soaking wet package in a centrifuge) the drying of such unopposed. This gives rise to what is called a strained yarn by which is meant that the residual shrinkage in the dried yarn taken from the inside of the package is less than that of the yarn taken from the outside of the package and, of course, this difference varies irregularly between the inside and the outside windings. In addition, the dried yarn generally has a different dye absorption depending upon its location in the package during drying. This difference in dyeing may be recognized as between cakes as well as within the cakes, and frequently is accompanied by a barre effect caused by the tendency of the portion of yarn found at the end walls of the annular package or cake to be distributed in the form of a pattern in the fabric ultimately obtained from the yarn. In order to reduce these effects to a practical minimum, it is necessary to control the humidity and the temperature throughout the drying and generally the high humidity and low temperatures require an extremely long drying period amounting to several days or weeks.

In recent years, there have been suggestions to obtain a more uniform product in a lesser drying time by utilizing high frequency electric fields, and particularly those in the radio frequency range. In some of such embodiments,

the cakes are passed between parallel horizontal electrodes, one above the other, but in this arrangement it has been found difficult to control the condensation of the moisture upon the upper electrode and to prevent its dripping upon the lower electrodes. There have also been suggestions to provide a central vertical electrode within the core of the cake and to rotate the cake about the axis of such central electrode and in proximity to a stationary outer electrode. However, in this arrangement, the shrinkage of the cake causes the windings to approach the central electrode in an irregular fashion and in some cases to tightly seize the central electrode; this interferes not only with the evaporation of the moisture of the inside windings but with the uniformity of field to which the different segments of the rotating cake are subjected. The concentration of vapors adjacent the inside electrode also increases the liability to corona and other electric discharges tending to burn and scorch the windings. In such a system, it has even been suggested to cover the central electrode with a Bakelite coating, but this has been found to heat up under the high frequency current so that it heats the cake by radiation and tends to scorch the inside windings.

It has also been suggested to dry the cakes by passing them between two vertical electrodes, but in this system there is a concentration of heating effect in a medial vertical plane through the cake extending parallel to the electrodes. It has been found that cakes dried from a wet condition in this system, although to outward appearances unharmed, frequently contain internal areas in which the yarns have deteriorated because of excessive heat and, in some cases, have been scorched.

It is an object of the present invention to provide a method of drying moisture-laden annular wound packages unsupported at their centers without encountering the above mentioned disadvantages. It is a more specific object of the invention to provide a method of drying such packages within a high frequency electric field while allowing free shrinkage so as to produce a yarn having improved uniformity of residual shrinkage and dyeing characteristics.

Other objects and advantages of the invention will be apparent from the description thereof hereinafter.

In the drawing, which is illustrative of apparatus adapted to perform the present invention- Figure 1 is a plan view of one modification,

is a section taken on line VV of ture by weight (on the basis of the total weight or wet basis) and formed without a central core whereby its windings are free to shrink during the drying by rotating the annular wound package about its axis in a high frequency electric field between two electrodes spaced on opposite sides of the cake, preferably parallel to the axis of rotation thereof. It has been found that such rotation not only improves the uniformity of the dried yarn package and avoids damaging the internal windings, but also reduces the time required for drying to a predetermined moisture content under given conditions and allows the use of higher voltage and more rapid heat input.

As shown in Figure 1, the cake 3 which may be an annular wound package of regenerated cellulose such as may be collected in a centrifugal pot, is rotated in the direction of the arrow between spaced electrodes 4 and 5 which as shown specifically are arcuate and concentrically disposed with respect to the package. One of the electrodes is grounded and the other is connected by a suitable high frequency feed line t to the source of high frequency current 7 such as the high frequency oscillator shown diagrammatically, the other terminal of which is grounded.

In Figure 2, a similar system is shown but the electrodes 4a and 5a are parallel to each other and are flat. The package is shown eccentrically disposed with respect to the electrodes. In both of these embodiments, the cake 3 may or may not be centered with respect to the space between the electrodes, since the rotation of the cake relative to both electrodes assures that all parts of the cake are subjected to the same integral sum of electric energy. In order to minimize the likelihood of excessive concentration of vapor between one of the electrodes and the adjacent windings of the cake, which might give rise to corona or other electrical discharges when the voltage is extremely high, it is preferred to have the cake spaced substantially from the electrodes whether they are centered or not with respect to the electrodes. When the diameter of the inside convolution of the package is less than 1 inches, it is generally necessary in order to prevent internal scorching to dispose the package. eccentrically of the electrodes to the extent of A; to 2 inches depending on the inside diameter, the smaller the diameter the greater the eccentricity. With inside diameters of 1 or more, the packages can be centered without danger of internal scorching.

The systems of Figures 1 and 2are adapted to a batch procedure but in Figures 3 to 5, the system is adapted to continuous production. As shown, an apron-conveyor 9 comprising a plurality of pivotally connected sections or links I0 is driven by means of one or the other of two sprockets or wheels H disposed at the ends of a horizontal zone. Every other section is provided with a shaft [2 rotatably mounted thereon. The shaft carries a plate or disc l3 for receiving the package thereon and a gear M which is adapted to engage a stationary rack l5 disposed below the upper course of the conveyor apron. As the conveyor carries the plates into their upper position at the left end of Figures 3 and 4, an operator may deposit a package on each one, the package being deposited With its axis upright. As the package is moved into the region between electrodes l6 and H, the gear M'meshes with the rack I 5 thereby causing the cake to be rotated as it proceeds through the field. The electrode 11 isconnected by a high frequency feed line IE to a source of electric current at [9, the other terminal 20 of which source is grounded to complete the circuit with the grounded electrode I6. Any speed of rotation may be employed, but it has been found that with a speed of the cake through the high frequency field such that a time of four minutes is required to pass from one end to the other end of the field, a rotation of 1 to 3 R. P. M. is adequate to provide uniformity without danger of scorching. Of course, faster speeds may be employed but are unnecessary. As in the previous embodiments, it is preferred to center the cakes with respect to the electrodes but this is not absolutely necessary.

Any conventional source of high frequency current can be employed. The voltage of the high frequency field may vary from 3,000 to 11,000 and even up to 25,000 volts, whereas the frequency may be from 1 to 50 or more megacycles. The higher the voltage and rate of heat input, the faster the rotation desirable.

The method of the present invention can be employed for the evaporation of any liquid from an annular package which lacks a central core and it assures that a uniform product can be obtained in spite of the fact that the drying is accompanied by considerable shrinkage. The equipment may be operated at atmospheric pressure, or it may be enclosed in a chamber and operated under higher pressure or under vacuum conditions. The drying may be accomplished in accordance with this system at a sufiicient rate to cause the shrinkage to occur visibly. In one variation, the drying may be performed while rotating the package in the high frequency field until substantially all of the visible shrinkage is completed and thereafter the remainder of the drying may be accomplished by other means such as the circulation of hot air through and around the package. If desired, however, the drying within the high frequency field may be complete in itself. In the former case, it has been found that there is a definite region of moisture content during which the largest proportion of shrinkage occurs, such as from to thereof,fdepending upon the particular material undergoing the drying. A cake of regenerated cellulose rayon has practically completed its visible shrinkage when its moisture content has been reduced to about 25% by weight of the rayon on the wet basis. Thus, rayon cakes containing at least 30% moisture content initially (as measured on the wet basis) may be reduced to 25% moisture content while being passed through the high frequency field and rotated therein and thereafter the moisture content may be reduced by any conventional drying system to anywhere from 2 to 11% by weight on the dry basis, depending on the final content desired. It has been found that when the drying by means of a high frequency electric field under the conditions disclosed herein has continued sufilciently to accomplish the major portion of the shrink- .the cake during the drying procedure.

age of the cake, and this may be determined, if desired, by a visual observation of the shrinkage of the cake as a whole, the remainder of the drying procedure can be performed in other ways without sacrificing freedom from strain and good dyeing quality in the product. For example, if circulating heated air is used for the last stage of drying, the temperature used may be far higher (e. g., 180 to 210 F.) than that heretofore recommended in the ordinary drying procedures and similarly the humidity need not be controlled. If desired, however, such final drying may be accomplished with controlled humidity and lower temperatures such as the conventional temperature at 140- F.

A particularly advantageous system of operation involves a rapid heating by means of the high frequency electric field. It has been found that the normal convection currents about a wound package can remove the vapor and yet that the vapor layer around the external wall of the cake can be continually replenished during the critical early part of the drying by establishing a sufficient power input at least in that portion of the system adjacent the point of entrance of the cakes or of the packages. It has been found that a high frequency system having of the order of 9,000 to 11,000 volts or higher, and of the order of 20 to 25 or more megacycles is adequate, because of the development of heat at a sufficient rate to maintain the vapor layer around the external windings of the cakes until the visibly noticeable shrinkage has been completed. This is true even when the cake is provided with no covering of any sort. Generally, the cake is provided with a knit rayon sleeve or stocking. This particular type of cover, however, does not change the character of drying since it is completely permeable to the vapor and does not impose any hindrance to its escape.

If desired, the cakes may be covered with a relatively impermeable or only partially permeable sleeve which hinders the escape of vapor from the external windings thereof. This cover or sleeve may be extended partially or completely around the windings at the end walls of the cake. Such sleeves may be of any semi-permeable or even impermeable material, such as of cellophane, felt, paper, especially impregnated felts and papers, heavily napped wool flannel,

gum rubber, or the like. It is preferably a material which tends to shrink and remain in contact with, or adjacent to, the external surface of When using such covers, a somewhat lower rate of heat development within the cake may be employed during the early part of the drying when shrinkage occurs, though the fast drying afforded by the high rate mentioned for uncovered cakes has the additional advantage of reducing the time during which the cake is subjected to high temperature steam, which in turn reduces the liability to degradation and stewing of the filamentary material.

In operating in accordance with the present invention, it is not only unnecessary that an extreatments normally applied to produce regenerated cellulose rayon from viscose, may be introduced into a spinning pot and rotated between 5,000 and 10,000 R. P. M. for a period of one to three minutes. Such a cake weighing about 1750 grams will contain about 900 to 1,000 grams of water, In the procedure involving the high rate of vapor evolution with the cake disposed in such a way as to be subject to normal convection currents, especially as in Figures 1 and 2, the shrinkage of the cake occurs as a unit and it is plainly visible. In general, in the case of heating a cake six inches in height having the dry and wet weights mentioned hereinabove, the cake as a whole undergoes complete visible shrinkage by the end of three minutes or less. During this three minute period, heat is generated within the cake at an average rate of about ten or more kilowatts, the value being 9.87 kilowatts when the l750-gram cake contains 900 grams water and being correspondingly higher when it contains more water, such as the 1000 grams mentioned above. When such shrinkage has been completed, the balance of the drying may be effected at a lower rate of heat introduction. This may be accomplished by allowing the voltage to taper off to a lower figure such as down to 2,000 to 3,000 volts as compared to the 9,000 to 12,000 or more at the beginning of the drying. Alternatively, after completing such visible shrinkage, the balance of the moisture may be taken out by methods not utilizing the high frequency induction, such as by subjecting to heated air currents. The drying under the high frequency system of the present invention may be adjusted to discharge the cakes with a moisture content between 2 and 11%, or it may even go down to practically 0% moisture content. Generally, it is preferred to terminate within the range between 2 to 11% on the dry basis.

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. It may be employed for the removal of the solvent in the case of 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 knitting sizes, as well as sizes used for setting the twist of lively twisted yarns; for removing the solvent from materials which have been subjected to crease-proofing or other finishing materials. It may also be used for the removal of organic solvents, such as acetone, which have been applied to render poten tially adhesive fibers 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 the solvent, the tacky fibers bind together with themselves 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.

The following examples are illustrative of the invention:

Example I Regenerated cellulose rayon cakes, approximately 5 inches high and 6 inches in diameter, provided with a knit rayon wrapper were centrifuged in individual centrifugal pots. In

ture by weight (wet basis).

'the wet condition as removed from the pots they weighed a total of approximately 1790 grams, and contained approximately 63% mois- They were introduced one at a time into the system shown in Figure .2 in which the electrodes were 9 /2 inches apart and were operated at9 ,000 volts. The cakes were subjected to the field for 14 minutes and were rotated at a speed of 18 R. P. M., and their moisture contents were reduced to approximately 2 to by weight. Heat is generated withinthe cake at an average rate of approximately 49,750 calories per minute or the equivalent of at least about 3 kilowatts, the value being 3.47 kilowatts when the dried package contains 5% moisture, and being somewhat higher when the dried package-contains less moisture such as 2%. The difierence in residual shrinkages, after drying, betweenthe yarn taken at the outside of the cake and the yarn taken from the inside of the cake was found to be 0.33 to 0.35%. The yarn from several cakes was put into a fabric which was foundto dye uniformly with substantially complete absence of barre.

Example II Cakes like those of Example I but weighing 1550grams wet and containing about 60% water (wet basis) were dried for minutes while rotated at 22 R. P. M. between electrodes 8 inches apartandhaving a potential difference of 9,000 volts. The dried .cakes contained 2 to 5% Water and were found to'have a difference in residual shrinkages between the yarn taken at the outside and from the inside of the cake of 0.17%. As in the first example, dyeing was uniform and 'free of barr.

Epample III Cakes 6 inches high and 6 inches in diameter and weighing 1815 grams (62% water on wet Example IV Cakes of regenerated cellulose rayon similar to those, of Example III were subjected to drying under-the conditions of Example III except that they were rotated at a speed of 3 R. P. M. The productswere similar'in characteristics to those of Example I.

The drawing and description thereof are intended to be illustrative in character and it is to be understood that changes and variations may be made from the present examples without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. The method of drying a moisture-laden annular wound package of filamentary material of regenerated cellulose containing at least 30% moisture by weight and formed without a central core whereby its inner windings are free to shrink'comprising disposing the package with its axis substantially vertical in a condition favorable to the development of normal convection currents around the package, and drying the package to a moisture contentrof 2 to while so disposed, at least a part of said drying being affected by: subjecting. the. packageat atmospheric' pressure; with the windings in its. inside periphery free of any force restraining them against shrinkage and with its axis substantially vertical, to a high frequency electric field between substantially vertical electrodes spaced laterally from the package, all of said electrodes being outside the periphery of the package, and generating heat dielectrically therewithin solely by the high frequency current at a rate equivalent to an average of at least about 3 kilowatts to reduce its moisture content from a value of at least 30% down to a value between 2 and 25% during a period of 3 to 14 minutes while continuously rotating the package at constant speed about a vertical axis within its periphery and generally parallel to the electrodes.

2. A method as defined in claim 1 in which the heat generated in the packageby the high frequency current is equivalent to an average of at least about ten kilowatts during a period of about three minutes, the removal of moisture being thereby accomplished at a sufiicient rate to cause the visible shrinkage of the cake during said period.

3. The method of drying a moisture-laden annular wound package of filamentary material of regenerated cellulose containing at least 30% moisture by weight and formed without acentral core whereby its inner windings are free to shrink comprising subjecting the package while it is disposed with its axis substantially vertical in a condition favorable to the development of normal convection currents around the package, at atmospheric pressure, with the windings in its inside periphery free of any force restraining them against shrinkage, to a high frequency electric field between substantially vertical electrodes spaced laterally from, and entirely outside the periphery of, the package, and generating heat dielectrically therewithin by the high frequency current at a rate equivalent to an average of at least about 3 /2 kilowatts to reduce its moisture content to about 2 to 11% during a period of 10 to 14 minutes while continuously rotating the package at constant speed about a vertical axis within its periphery and generally parallel to the electrodes.

4. The method of drying a moisture-laden annular wound package of regenerated cellulose rayon yarn comprising centrifuging a liquidtreated pot-spun package until it contains about 60 to 63% moisture by weight, said package being without a central supporting core whereby its inner windings are free to shrink, then drying the package to a moisture content of 2 to 11%, at least the first part of said drying beingefiected while the package is disposed with its axis substantially vertical in a condition favorable to the development of normal convection currents around the package by subjecting the package at atmospheric pressure, with the windings in its inside periphery free of any force restraining them against shrinkage, to a high frequency electric field between substantially vertical electrodes all of which are spaced from, and outside the periphcry of, the package and generating heat dielectrically therewithin by the high frequency electric current at a rate equivalent to an average of heat generated in the package by the high frequency current is equivalent to an average of at least about 10 kilowatts to reduce its moisture content from a value of at least 30% down to a value of about 25% during a period of about three minutes, the removal of moisture being thereby accomplished at a sufficient rate to cause the visible shrinkage of the cake during said period.

6. The method of claim 1 in which the inside convolutions of the package have a diameter of at least 1 inches and the package is rotated about an axis which is substantially centered with respect to the electrodes.

7. The method of claim 1 in which the inside convolutions of the package have a diameter of less than 1 inches and the package is rotated about an axis that is eccentric of the electrodes.

JOHN E. PHILLIPS, JR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Kooystra Oct. 10, 1933 Engel May 1, 1934 Moog Dec. 29, 1936 Hart, Jr Nov. 25, 1941 Bierwirth Apr. 10, 1945 Hoyler July 9, 1946 Kline et al. May 27, 1947 Brown Oct, 7, 1947 Story Mar. 22, 1949 Hagopian Aug. 16, 1949 Koster et a1 Oct. 25, 1949 Bierwirth June 27, 1950 Burkholder Nov. 21, 1950

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