US 3281951 A
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Nov. 1, 1966 D. H. GREENE 3,281,951
FILM DRYING PROCESS AND APPARATUS Filed July 31, 1963 2 Sheets-Sheet 1 INVENTOR.
0A V/D H. GEL'ZA/Z BY WW ATTOQ/L/EVJ Nov. 1, 1966 D. H. GREENE FILM DRYING PROCESS AND APPARATUS 2 Sheets-Sheet 2 Filed July 31, 1963 INVENTOR.
0,4 V/D H GI ZM United States Patent Office 3,281,951 FILM DRYING PROCESS AND APPARATUS David H. Greene, 2626 Oakland Drive, Kalamazoo, Mich. Filed July 31, 1963, Ser. No. 298,896 9 Claims. (Cl. 3412) This invention relates to a process and apparatus for drying web-form materials, and it relates particularly to a process and apparatus for drying a continuous web of a transversely shrinkable, nonfibrous, cellulosic film while maintaining control over said web so as to minimize such shrinkage in order to produce a nonoriented film having substantially the same wrapping, stretch and dimensional characteristics both laterally and longitudinally of the web.
This invention arose in connection with the manufacture of hydroxy alkyl cellulose films and therefore as a matter of convenience the discussion hereinafter (follow ing) will be set forth for illustrative purposes in terms of such a film. However, it will be understood that the same problem exists wit-h a variety of other nonfibrous cellulosic films, including but not limited to films of regenerated cellulose, and accordingly in its broader aspects the invention will be recognized as applicable thereto.
In the manufacture of such films, means have long been known for forming and satisfactorily controlling such a film in the initial state of its handling. However, certain dimensional control problems appear in the drying operation which have not as yet been satisfactorily solved. As the film is dried a tendency appears for both longitudinal and transverse shrinkage. Since the drying rolls hold the film firmly against actual longitudinal dimensional change, the film undergoes a substantial transverse shrinkage. This is undesirable in itself and. is further undesirable in that it creates nonuniform tension conditions in the film. This not only represents a loss as a result of the transverse shrinkage itself, but also causes a further loss because edges of the web become thickened. The thickened edge portions are undesirable and usually are trimmed off. As a result of both the shrinkage itself and the loss from the trimming, as high as 30 percent of the intial Width of the web may be lost.
This problem has been recognized for many years and many procedures have been devised for dealing with it. In certain prior attempts, this problem has been dealt with by carrying a hydroxy alkyl cellulose film on a very long continuous belt during drying. The film is said to adhere to the belt sufiiciently to inhibit transverse shrinkage during the drying procedure. However, in a practical case the use of a belt for this purpose is unacceptable because the belt must be of an impracticably great length in order to be effective. Therefore, while this procedure is effective on a laboratory scale, it has not been acceptable commercially.
Accordingly, the objects of the invention include:
(1) To provide a process and. apparatus in which a continuous web of nonfibrous cellulosic material will be maintained in continuous contact with a supporting surface during the period that same is drying and which apparatus can be placed in an area of commercially acceptable length.
(2) To provide a process and apparatus, as aforesaid, in which both sides of the film will be exposed to ambient, radiant or contact heat, whereby such heat may be used for drying same and the longitudinal curl due to drying only one side will be avoided.
(3) To provide an apparatus, as aforesaid, which is sufficiently similar in its construction and operation to conventional drying machines used in the paper industry that it can be readily manufactured and operated by personnel acquainted with paper industry operations.
Patented Nov. 1, I966 (4) To provide a process and apparatus, as aforesaid, in which the web is maintained in continuous contact with the surfaces of a plurality of successively located dryer rolls and particularly wherein such web is for a time contacted by the surfaces of two adjacent dryer rolls as it is being transferred from one of said dryer rolls to the other.
(5) To provide an apparatus, as aforesaid, wherein both sides of said film are exposed to the surrounding atmosphere sufiiciently often as to prevent formation of vapor pockets between the film and its supporting surface whereby higher drying temperatures may be employed for faster drying.
Other objects and purposes of the invention will become apparent to persons acquainted with devices of this general sort upon reading the following description and inspecting the accompanying drawings.
In the drawings:
FIGURE 1 is a diagrammatic side elevational view of an apparatus embodying the invention.
FIGURE 2 is a fragmentary oblique view of the dryer roll supporting mechanism for one of the adjustable dryer r0 ls.
FIGURE 3 is a fragmentary view of the nip area of a pair of adjacent dryer rolls showing the relationship therebetween.
FIGURE 4 is a fragmentary, the line lVIV of FIGURE 1.
' FIGURE 5 is a diagrammatic side elevational view of the apparatus of FIGURE 1 showing the side thereof opposite that shown in FIGURE 1 and illustrating a modified drive system.
FIGURE 6 is a fragmentary sectional view taken on the line VI-VI of FIGURE 5.
GENERAL DESCRIPTION The invention in general contemplates the placement of a plurality of dryer rolls closely adjacent each other whereby the web may pass from one dryer roll directly to the next without being at any point unsupported, the spacing between the rolls when in operation being only suificient to permit the passage therebetween of the web being dried. Irregularities in the diameter or lack of concentricity of said rolls is absorbed by the presence of a resilient surface on at least one of each pair of adjacent rolls. Variations in the diameter of said rolls or in the adjustment of one roll with respect to an adjacent roll resulting from changes in web thickness and/ or changes in the diameter of said rolls due to heating beyond those variations which said resilient surface can absorb are met by adjustably and yieldably supporting at least one of each pair of adjacent rolls. The rolls are driven by a slip-type drive, such as a belt drive, so that the peripheral speeds of the rolls remain equal. Thus, it becomes possible to place said rolls sufiiciently close to each other that the web will contact both thereof simultaneously as it passes between them and can therefore travel from one roll to the next without being unsupported at any time, whereby transverse shrinkage of the web is minimized.
DETAILED DESCRIPTION Referring to FIGURE 1, there is shown a drying system it) comprised of a lower deck of drying rolls 1]. and an upper deck of drying rolls 12. The rolls 11 in the lower deck are horizontally staggered with respect to the rolls 12 in the upper deck in such fashion that the axis of each of the rolls 11 is located equidistantly from and is disposed below the axes of the two adjacent rolls 12 in the upper deck. The upper rolls 12 have shafts 14 which are rotatably supported on journals mounted in pillow blocks 16 which are fixedly mounted on the horizontal member 17 of the support framework 18.
sectional view taken along The horizontal member 17 is supported by a plurality of horizontally spaced, vertical posts 19 which extend upwardly from a suitable base 21. Thus, the upper rolls 12 are mounted for rotation, but are held against radial movement, with respect to the framework 18.
The lower rolls 11 have shafts 13 which are rotatably supported on journals mounted in pillow blocks 22. Each of the pillow blocks 22 is mounted on a plate 23 which is supported at one of its ends for pivotal movement about a horizontal axis by means of a bracket 24 and a pivot pin 24a. The brackets 24 are afiixed to another horizontal member 25 of the support framework 18. The free end of each of the plates 23 is engageable by a suitable adjustable stop device 26, comprising a screw 26a and a lock nut 26]), whereby upward movement of the lower rolls is limited.
A force-applying device 27 is provided to continuously urge each of the lower rolls 11 upwardly with a constant, but preferably adjustable, force. Here the force-applying device includes a plunger 28 which is slidable within a cylinder 29. The cylinder 29 is mounted by a bracket 31 onto the horizontal member 25. The plunger 28 extends upwardly from the cylinder 29 and engages the lower surface of the plate 23. A pair of conduits 32 and 33 are connected for supplying suitable pressure fluid, usually compressed air, to the opposite end of the cylinder 29. The pressure fluid is supplied from any suitable conventional source and said pressure fluid is supplied at a constant, but preferably adjustable, pressure so that the plate 23 is continuously urged upwardly against the stop device 26. When the free end of the plate engages the stop device 26, the lower roll 11 is held in a selectable position with respect to the two adjacent upper rolls 12, and usually contacts said upper rolls with a light force, the lower roll being sufficiently yieldable to permit entry of the web between the rolls. By adjusting the screw 26a, the uppermost position of the lower roll 11 can be precisely controlled. Means such as interference between abutment means 23a on the underside of the plate 23 and the adjacent surface of the member 25, limits the downward movement of the shaft 13 for purposes appearing hereinafter.
While the plate 23 is shown as being mounted for pivotal movement about a horizontal axis, it is apparent that it can be mounted for vertical sliding movement, if desired. Further, a suitable spring or counterweight structure could be used in place of the plunger 28 and cylinder 29 as the means for urging the lower roll upwardly with a substantially constant force. Still further, where the yieldability of the lower roll can be otherwise provided or can be dispensed with, the plunger 28 or equivalent structure may be supported on cam or screw, or other positive but adjustable, means as desired.
The upper rolls 12 have a corrosion resistant, highly polished surface and are made of any suitable material, such as polished stainless steel. The upper rolls 12 and the lower rolls 11 are made to have as uniform a diameter as possible and usually the diameter of said rolls is from 48 inches to 72 inches. Further, the upper rolls 12 and the lower rolls 11 preferably are of the same diameter.
Because rolls of the size here involved are of quite large diameter, there will inevitably be some minor variations in diameter from point to point along the circumference. In order to make it possible to continuously maintain a surface-to-surface contact between the web, on the one hand, and the peripheries of each lower roll 11 and the two upper rolls 12 adjacent thereto, on the other hand, each lower roll has a compressible, resilient covering 34 thereon. The covering 34 has a smooth surface and preferably is made of a suitable rubber or plastic composition, such as a silicone rubber or polyvinyl chloride, capable of withstanding high heat and humidity conditions.
The force-applying device 27 urges its associated roll 11 upwardly with sufficient force that the covering 34 thereon contacts under a light pressure and is slightly compressed by the web being fed therebetween. In the usual case, the roll 11 is adjusted so as to contact the two adjacent upper rolls 12 when the web is not present so that there is provided an area contact between each lower roll 11 and each of the two upper rolls 12 adjacent thereto and this area contact is maintained even if the diameter of one or more of the rolls is somewhat irregular. Thus, simultaneous contact of the web by both adjacent rolls is assured.
The stop device 26 is carefully adjusted so as to make this contact of the lower roll 11 with the two adjacent upper rolls possible. It is to be noted that when the apparatus is cold, there may be some spacing between the lower roll and the adjacent upper rolls, as shown in solid lines in FIGURE 3. However, when the apparatus is heated during a drying operation, the parts will expand so that the area contact above referred to will occur as shown in broken lines in FIGURE 3. Moreover, in appropriate cases the peripheries of the lower roll and adjacent upper rolls may be spaced apart at the drying temperature so long as such spacing is somewhat less than the thickness of the web being dried.
The contact pressure between the lower roll 11 and the web, which is determined by the pressure applied to the cylinder, must be carefully adjusted so that it will be just sufficient to hold the film being dried against transverse shrinkage at the point of transfer. Although this may vary from time to time, it will be possible to adjust the apparatus as needed in order to maintain the proper contact pressure.
The rolls 11 and 12 ordinarily will be made hollow and they may be provided with means whereby a suitable heating medium, such as hot water, hot air or steam, can be continuously circulated therethrough.
The rolls 11 and 12 are continuously driven at substantially the same peripheral speeds. For this purpose the shafts 13 and 14 of said rolls each have a pulley 35 and 36, respectively, mounted thereon and said pulleys are engaged by belts 37 and 38 which are driven by a suitable motor (not shown), the belts being driven at the same speed when the rolls 11 and 12 are of the same diameter. The belt drive of the rolls 11 and 12 makes it possible for the drive of said rolls to slip as needed so that the rolls will run at the same peripheral speeds, even though there may be some minor variations in the diameter of the rolls either because of their original construction or because of changes in diameter as a result of heating conditions, wear or other causes.
Drying may be accomplished by hot air, hot water, steam or any other suitable conventional means. Here the drying system 10 is placed within a suitable housing 41. Hot air is supplied to the housing 41 by a suitable mechanism, such as a blower 42, so that it continually circulates therethrough and is removed therefrom through a suitable conduit 43. Suitable heating means, such as lamps 44, may be provided, if desired, in the housing to maintain the proper temperature conditions.
OPERATION The film F to be dried is fed onto the first (rightwardmost in FIGURE 1) upper roll 12 and moves therewith until it reaches the area where said upper roll is in contact with the first lower roll 11, the lower roll yielding sufficiently to permit passage of the film between said rolls but in snug contact with both. The film is then transferred to said first lower roll and travels therewith until it reaches the area where said first lower roll contacts the second upper roll 12, the film similarly passing between said-rolls but contacting both thereof. The film is then transferred to the second upper roll. Thus, the film is transferred from roll to roll and finally is withdrawn in an acceptably dry condition from the final (leftwardmost in FIGURE 1) upper roll 12 of the drying system.
The film at all times during normal operation engages the peripheral surface of and is supported by, at least one of the rolls so that at no time is it free to undergo transverse shrinkage.
The film F is maintained in snug engagement with the periphery of each of the rolls as it moves therewith by the longitudinal tension caused by shrinkage due to drying. At the zone where the film is transferred from one roll to the next, the light contact pressure between these two rolls before the film enters therebet-ween insures a firm engagement of the film by both of said rolls when the film enters therebetween and thereby insures a firm engagement of the film by at least one of the rolls at all times, thus positively holding the film at all times against transverse shrinkage. Further, the longitudinal tension resulting from drying Will apply sufiicient, but not excessive, longitudinal tension to the film to maintain same in smooth and wrinkle-free condition on the surfaces of the rolls. Thus, orientation of the film is substantially minimized. It will also be noted that the opposite surfaces of the film F will be alternately exposed to the circulating hot air or other drying means. This is advantageous because it minimizes warping or curling of the sheet.
While the plate 23 is shown as being mounted for pivotal no part of the invention, it will be understood that the film supplied to the drying system is in a wet condition and will be supplied from the conventional apparatus used to form the film. Further, the film exiting from the drying system will be wound up on suitable take-up rolls in a conventional fashion.
Thus, according to this invention, it is possible to produce substantially nonoriented film which is fiat and smooth and of substantially the same transverse width as the wet film originally fed into the drying system.
FIGURES 5 and 6 indicate a modified drive system for the apparatus of FIGURE 1. Those parts of FIGURES 5 and 6 which are identical to comparable parts of FIG- URES 1 and 4 will carry the same reference numerals with the sufiix added thereto. In the modified drive system, the shafts 13c and 140 carry fixed to at least one end thereof crowned fiat belt pulleys 61 and 62, respectively. The pulleys 61 and 62 have the same diameter ratio as the effective diameter ratio of the rolls 11c and 120 whereby the pulleys 61 and 62 will drive said rolls with equal peripheral speed. The outside diameters of the pulleys 61 and 62 preferably approach but are slightly less than the outside diameters of the corresponding rolls 11c and 12c for purposes appearing hereinafter. A fiat drive belt 64 is wound about the driving surfaces of the various pulleys 61 and 62 along a route corresponding to that of the film F on the peripheral surfaces of the rolls 11c and 120. The belt 64 is slightly narrower than the pulleys 61 and 62 whereby the crowning of said pulleys will maintain said belt axially spaced from the rolls 11c and 120. The belt 64 is routed past suitable drive means such as a drive pulley 66 driven by a motor 67, such routing being accomplished, together with tensioning of said belt, by suitable idler pulleys 71 and 72. The belt 64 will have sufiicient slippage with respect to the pulleys 61 and 62 that the peripheral speeds of adjacent roll surfaces may be maintained equal without undue stresses being imposed upon the film F passing over said rolls.
An advantage of the modified drive system of FIG- URES 5 and 6 is its ability to assist in the threading of the end of a new film into the apparatus of the invention. Briefly, a new film to be dried may be placed upon the leftward surface of the leftwardmost roll 120 (FIGURE 5). The corner of the film adjacent the belt 64 may be 7 along therewith. The web will travel with the leftwardmost roller 120 until said roller contacts the leftwardmost roller 11!: whereat the web is transferred to said roller 110 by the gripping of said tag between the belt 64 and the surface of the pulley 61 fixed to said roller. Hence, the web is constrained by said tag to move with the roller 11c until same contacts the second roller 120. In this manner, the web is threaded by the belt 64 through the series of rollers 11c and 12c to completely thread said rollers and operation continues as in the above-described embodiment. As a result of using the modified drive system of FIGURES 5 and 6 the immediate difiiculty of threading the series of rollers due to the influence of gravitational forces on the web as its leading edge moves along the underside of the rollers lie is eliminated and the threading made rapid, easy and virtually automatic. It will be recognized that other means may be employed to attach the leading edge of the web to the belt, as for example, extending said tag through a suitable slit in the drive belt to fix it thereto. In any event, succeeding portions of the web do not contact the belt 64.
While particular preferred embodiments of the invention have been described, the invention contemplates such changes and modifications therein as lie within the scope of the appended claims.
What is claimed is:
1. Apparatus for drying a film while positively holding same against appreciable transverse shrinkage, comprising:
a plurality of dryer nolls arranged in a series and mounted for rotation about parallel axes, alternate ones of said rolls having a resiliently compressible peripheral surface;
means supporting selected ones of said rolls for movemen-t toward and away from the other rolls so that the rolls with the compressible peripheral surface can maintain resilient and constant close proximity to the other rolls, whereby the fihn may move around and enter between said rolls and at all times will be in contact with the surface of at least one roll; and
slip drive means drivingly connected to each of said rolls for rotating each of said nolls so that the peripheral speeds of all of said rolls will be the same.
2. In apparatus for drying a film, the combination comprising:
an upper deck of spaced apant dryer rolls mounted for rotation about parallel axes;
a lower deck of spaced apart dryer rolls mounted for rotation about parallel axes, the rolls of the lower deck being disposed alternately with respect to the rolls of the upper deck so that the peripheries of each of said rolls, except the endmost rolls, are opposed to the peripheries of the adjacent two rolls in the other deck;
means for moving the dryer rolls of one deck toward the dryer rolls of the other deck to maintain a selectable spacing between the axes thereof less than the thickness of the film to be dried;
the dryer rolls of one deck having a resiliently compressible peniphenal surface so that when a film to be dried is positioned therebetween the dryer rolls with the compressible peripheral surface will yield :sufiiciently to maintain with the other dryer rolls a constant contact against opposite sides of said film so that the film can pass over and under said dryer rolls in series and as it passes from one dryer roll to the next it will be in contact with the peripheral surfaces of both dryer nolls whereby to eliminate transverse shrinkage of said film; and
slip drive means for rotating said dryer rolls so that the peripheral speeds of all of said dryer rolls will be the same.
3. Apparatus according to claim 2, in which said means for moving the dryer rolls of one deck toward and away from the other rolls of the other deck includes independent force-applying means associated with each of the dryer rolls of said one deck for moving same independently of each other.
4. Apparatus according to claim 3, in which said independent means includes means resiliently urging its associated dryer roll toward the adjacent two dryer rolls in the other deck.
5. Apparatus according to claim 4, in which the forceapp-lying means are associated with the dryer rolls having the resiliently compressible peripheral surface.
6. Apparatus according to claim 5, in which the rolls having the resiliently compressible surface are the Lower deck of rolls.
7. In a series of rotatable, parallel, rolls wherein each intermediate roll lies in sufficiently close proximity to its succeeding and preceding roll that a Web threaded through said rolls will have points thereon contacting both said intermediate roll and the preceding roll and will have points thereon in simultaneous contact with said intermediate roll .and the succeeding roll, the combination comprising:
a crowned pulley coaxial with and drivingly fixed to each of said rolls, said pulleys defining a plane perpendicular to the rotational axes thereof;
a flat belt entrained on said pulleys on a path identical to that of the film through said rollers, said pulleys being each of a radius substantially equal to, but not greater than, the radius of the roll associated with each respective pulley;
a source of motor power and idler means causing said belt to rotate said rolls;
whereby said rolls will be urged to rotate at equal peripheral speeds and whereby said belt may be used to assist the threading of said rolls with said web.
8. An apparatus according to claim 9, including means applying a part of the web adjacent the leading edge thereof to said belt and maintaining engagement therebetween when said part of said web is not retained between said belt and a pulley, whereby said belt will move the leading edge of the web along a desired path through the series of rolls to thread said web through said series of rolls.
9. In a process for drying a nonfibrous cellulose film, which is capable of substantial lengthwise and transverse shrinkage during drying, by using a series of dryer rolls, the steps comprising:
arranging a plurality of the rolls for rotation around parallel axes, the periphery of each roll being opposed to and closely adjacent the periphery of at least one other roll so that nips are formed between ad jacent rolls, at least alternate ones of said rolls having a resiliently compressible surface layer thereon;
continuously and successively moving a web of said film around said series of dryer rolls so that the entire width of said web is in continuous contact with a substantial part of the periphery of each dryer roll in said series, said web passing through the nip between adjacent rolls as said web moves from one of said rolls to the next, said web at all times during a normal drying operation being in continuous contact wtih each of said rolls;
positioning said rolls so that the spacings therebetween at the nips are less than the thickness of the web passing through the respective nips so that each pair of adjacent rolls simultaneously applies a light contact pressure on opposite sides of said web as it passes through the nip therebetween during its movement from one roll to the next, each resilient surface layer being compressed and deformed so that the portion thereof forming one side of the nip assumes substantially the shape of the portion of the other roll fo ming the other side of the nip so that the contact pressure is simultaneously applied over an area of said web on opposite sides thereof by both rolls as said web passes through each nip and the contact pressure is sufiicient to hold the web against transverse shrinkage;
causing said dryer rolls to rotate and permitting slippage of the force applied to each of said rolls so that the rolls rotate at the same peripheral speeds and the web is thereby advanced from one roll to the next at a uniform speed, so that said film is held snugly against said portion of the peripheral surface of each of said dryer rolls; and
subjecting said web to a drying action as it passes around the dryer rolls.
References Cited by the Examiner OTHER REFERENCES 11/1917 Schenck 34--117 7/1960 Faeber 34120 8/1962 Nakaguchi 34242 FOREIGN PATENTS 51,448 3/1920 Sweden.