US3553845A - Method and apparatus for impregnating and drying material in a fibrous web - Google Patents

Abstract

A CONTINUOUSLY TRAVELING WEB IS IMMERSED IN AN IMPREGNATING MATERIAL, AND A CONTROLLED PRESSURE IS APPLIED TO THE WEB TO SQUEEZE IMPREGNATING MATERIAL THEREFROM TO LEAVE A DESIRED, PREDETERMINED ACCRETION OF IMPREGNATING MATERIAL PER UNIT AREA OF THE WEB. THE WET, IMPREGNATING WEB IS SUBJECTED TO CONTROLLED DISTORTION AS IT

TRAVELS IN A SUBSTANTIALLY VERTICAL PLANE THROUGH A DRYING STATION TO PROVIDE A DRY, FLAT, DIMENSIONALLY STABLE AND SUBSTANTIALLY UNIFORM END PRODUCT.

Description

Jan. 12, 1971 I c, LEE ETAL 3553;845

METHOD AND APPARATUS FOR IMPREGNATING AND DRYING MATERIAL IN A FIBROUS WEB 2 Sheets-Sheet 1 Filed June 9, 1969 &

ATTYS.

am e N N g INVENTORS CHARLES A. LEE WARREN R. FURBEOK Jan. 12, 1971 c, LEE ETAL 3,553,845

METHOD AND APPARATUS FOR IMPREGNATING AND DRYING v MATERIAL IN A FIBROUS WEB v Filed June 9, 1969 2 Sheets-Sheet 2 21 INVENTORS Mal-E5 fi- LEE WARREN R. FURBECK ATTVS.

United States A Patent METHOD AND APPARATUS FOR IMPREGNATING AND DRYING MATERIAL IN A FIBROUS WEB Charles A. Lee and Warren R. Furbeck, Knoxville, Tenn.,

assignors, by mesne assignments to Southeastern Products, Inc., Knoxville, Tenn., a corporation of Tennessee Filed June 9, 1969, Ser. No. 831,524

Int. Cl. F26b 3/00 U.S. Cl. 34-9 8 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method of and an apparatus for impregnating and drying a material in the form of a continuously traveling web.

The method and apparatus described herein are suitable for making various web products having a dried impregnant therein and are particularly useful for impregnating a thin, lightweight, permeable material with a uniformly distributed impregnant, the sheet being dried to produce a ilat, dimensionally stable sheet. The method and apparatus of the invention have particular application in impregnating lightweight materials with resins to produce fiat, dimensionally stable sheets which are used for crossbanding veneers, for filter sheets, for dimensionally stable backing sheets and the like.

When such webs are treated by ordinary impregnating methods with liquid resin dispersions, the resin pickup is not uniform and because of dimensional changes during impregnation and drying (e.g., it stretches and shrinks as it undergoes treatment), the resulting web in addition to containing varying amounts of resin has localized strains which cause it to wrinkle and bow thereby making it undesirable for incorporation in subsequent structures which require flat, dimensionally stable sheets.

Accordingly, an object of the invention is to provide an improved apparatus and method for impregnating a continuously traveling web with a controlled amount of impregnating material and for drying the web to a flat, dimensionally stable sheet.

A further object of the invention is to provide a simple method of producing such materials on an economical, large scale, continuous commercial basis.

Other objects and advantages of the invention will become known from the detailed description taken in connection with the accompanying drawings in which:

FIG. 1 is a diagrammatic, perspective illustration of an apparatus embodying various of the features of the invention; 1

FIG. 2 is a diagrammatic view of the drive means for the apparatus of FIG. 1;

FIG. 3 is a diagrammatic illustration of the means employed for subjecting the web to controlled distortion prior to drying;

FIG. 4 is a diagrammatic cross section of the distorting roll which appears in FIG. 3; and

FIG. 5 is a diagrammatic view of a mixing and re circulating system for the resin mixture.

In general, as has been pointed out, the invention is directed to a method and an apparatus for impregnating Patented Jan. 12, 1971 a wide, continuously traveling web of thin, lightweight material with a metered, uniform accretion of impregnating material and drying or curing the impregnating material without wrinkling or distorting the web. We have discovered that if webs of the class described are maintainedin a condition of neutral tension (i.e., a condition in which the tension is adjusted to minimize sagging but is not great enough to cause the material to appreciably neck-in) and treated in a particular manner while in that condition, that the web will contain a uniform distribution of the impregnant and will dry into a flat, dimensionally stable product. In particular, we have found that uniform impregnation may be obtained by impregnating the web in two stages. In the first stage, the web in the neutral tension condition is submerged in the impregnant so as to thoroughly saturate the web and thereafter the web is removed from the impregnant, pressed, reintroduced into the impregnant and thereafter passed through a metering nip to cause the impregnant to be forced into all of the interstices of the web. The amount of impregnant in the sheet may be readily controlled by varying the pressure at the metering nip.

In order to dry the sheet to a fiat, dimensionally stable product, the wet, impregnated web is caused to travel vertically through a dryer wherein it is subjected to heat while still in a condition of substantially neutral tension; however, prior to entering the dryer, the web is deformed by training it around a curved surface running transversely of the web so that the central portions of the web are bowed outwardly relative to the margins of the web. This subjects the central portions of the web to slightly increasing tension as compared to areas of the web to ward its marginal edges. It has been found that when the web is handled in this manner that the dried web does not exhibit wrinkling and, unexpectedly, is dimensionally stable and remains flat after drying.

Referring now in detail to the apparatus illustrated in FIG. 1, a web 11 is drawn from a supply roll 13, which is mounted on a support shaft 15. A brake 17 is provided on the shaft 15 to provide a sufiicient resistance to maintain the web in a flat condition.

broken line 27 in FIGS. 1 and 5.) The roll 25 is supported on a pair of pivotally mounted arms'29 so that the weight of roll 25 is applied to the nip so as to compress the web 11 thereby driving any entrained air from it and forcing the impregnant into the interior of the web. Means such as adjustment screws (not shown) may be provided for the arms 29 and so as to adjust the pressure in the nip.

After leaving the surface of roll 25, the web 11 is again submerged in the impregnant in a similar manner by means of a pair of metering rolls 31 and 33. More specifically, the web 11 wraps the lower metering roll 31 under the surface 27 of the impregnant and moves upwardly to the nip formed by the rolls 31 and 33. At this nip, the web 11 is subjected to controlled pressure to control the amount of impregnant left in the web 11. To this end, the upper roll 33 is journaled for rotation about its longitudinal axis on pivotally mounted support arms cise manner. Preferably, the rolls 33 and 35 are jacketed, one with Teflon and the other with rubber to provide resilient pressure surfaces which aid in metering. Thus, the pickup of impregnant may be periodically adjusted to compensate for other changes such as, for example, a change in the permeability of the raw material or a change in thespeed of travel of the web.

The reverse wrap of the web about the sets of rolls 23-25 and 3133 effects suflicient friction so that changes in the speed of the rolls permits accurate adjustment of the draw on the web in the impregnating tank 2-1.

One factor which is desirably controlled in the impregnation step is the solids content of the impregnant, e.g., resin. Solids may tend to settle out causing a change in the viscosity of theimpregnant and hence a change in the pickup of. the web. The preferred manner of preventing settling or accumulation of solids is to continuously recirculate and agitate the resinous mixture. Such a system is shown diagrammatically in FIG. 5. As illustrated, the immersion tank 27 is divided into three sections, 21a, 21b, and 21c by a pair of spaced weirs 39 and 41. The outer two sections of the tank 21a and 21c receive the lower portions of rolls 23 and 31, respectively, while the central section 2112 receives excess resinous material overflowing the weirs 29 and 41 from the outer sections 21a and 21c. The weirs 39 and 41 in this instance are vertically disposed plates having the upper edges thereof formed with suitable notches (not shown) through which the impregnating material can flow from the outer sections 21a and 210 into the central section 21b in the event excessive quantities of resinous material accumulates in the outer sections. The bottoms of sections 21a, 21b and 21c are connected by valved pipes 43a, 43b and 43c, respectively, to a collection manifold 43, thence to a pump 45, a pipe 47 and a tank 49. A rotating mixer 51 is provided in the tank 49 to agitate the impregnant thereby minimizing any tendency of the heavier solids to settle out or agglomerate thereby assuring a relatively uniform solids content and viscosity. From the tank 49, the mixture flows through a pair of valved pipes 53 and 55 to the respective outer sections 21a and 21c of the immersion tank. The tank 49 may be used to mix the ingredients for the impregnant; however, it is preferable that the preliminary mixing and preparation of the impregnant be carried out in a separate agitator equipped tank 57 connected to the tank 49 by suitable conduits 59 and 61 and a pump 63.

The flow into each of sections 21a and 210 of the immersion tank ismaintained constant and continuous by adjustment of valves 53a and 55a. Likewise, there is maintained'a controlled constant and continuous outflow of resinous material from each of sections 21a, 21b and 210 through valved pipes 43a, 43b and 430, By adjustment of these valves, more or less outflow is selected so as to maintain a predetermined level of resinous material in each of sections 21a and 210 of the immersion tanks. This continuous inflow and outflow of resinous material affords continuous replenishment of thoroughly agitated impregnant to the immersion tank outer sections.

Having been impregnated with the controlled amount of the impregnant, the web 11 moves upward from the nip of the rolls 31 and 33 to engage the face of a rotatable, bowed roll 65 which serves to deform the wet web in the controlled manner which is important in obtaining a flat, dimensionally stable dried sheet. The bowed roll 65 exerts outwardly directed forces which tend to spread the web, and as illustrated in FIG. 3. to gradually increase the length of travel of the web from its marginal edges to the center line of the web prior to the time the web enters the drier station 67. As illustrated in the drawings and particularly FIG, 3, the bowed roll 65 is disposed at the lower end'of the vertical run of travel of the web through the drier station 67.

As illustrated in FIG. 4, the bowed roll 65 is supported on a bowed shaft 69 which is attached in pillow blocks 71 (only one shown) at each of its ends. It has been found satisfactory for a 48inch wide web to provide a bow in the shaft giving a maximum throw of approximately 1 inch. By rotating the shaft 69 to various positions in the pillow blocks .71 it is possible to adjust the bow imparted to the web frorn practically none to as much as 1 inch. As shown in FIG. 4, the surface of the bowed roll 65 is fabricated from a tube 73 of resilient material and is preferably surfaced with an outer layer 75 of Teflon. In order to support the resilient roll surface tube 73, spaced-apart, low friction bearings 77 are attached to the bowed shaft 69 along its length, the bearings 77 having an outer diameter which corresponds to the inner diameter of the resilient tube'73 so that the tube 73 is effectively supported. along its length; An .end c ap; 79 is attached to each end of the tube 73 for rotation therewith, the end cap 79 preferably being attached to the end one of the bearings 77. v j

The drier station 67 preferably includes a pair of vertically disposed spaced-apart heater banks 81 and 83 positioned on opposite sides of the web 11 to heat both sides thereof. Each of heater banks 81 and 83 includes a blower 85 positioned in its lower end for circulating air between the heater banks so as to remove moisture from the atmosphere between the banks thereby facilitating drying.

Desirably, the banks 81 and 83 are divided into three or more zones vertically and several transverse sections with means for controlling the heat applied in each zone. This makes possible ready operations on webs of various widths and the use of impregnants having differing heat sensitivity. Satisfactory heater banks for Webs having a width of up to 52 inches have been constructed using quartz heater lamps sold by Fostoria Infra-red Systems, Fostoria, Ohio, the bank measuring 66 inches in height by 55 inches in width.

At the top of the drier 67, above the banks 81 and 83 there is provided an idler roll 87 around which the dried web is trained. From the idler roll 87 the'web 11 travels downwardly over a second idler roll 89 and then is reversely wrapped around a set of draw rolls 91 as illustrated in FIG. 1. 7

Between the draw rolls 91 and a winding stand 93 there is provided a slitting means 95 which may be used to slit the web 11 into a plurality of strips. The preferred form of slitter comprises a rotatable shaft 96 which carries slitting discs 97 which have sharpened cutting edges for slitting the web. The slitting discs 97 are desirably driven by a separate drive motor 99 through an arrangement of shafts and belts 100.

The preferred form of winding stand 93 is a so-called surface winder which provides a uniform winding speed despite an increasing diameter of web roll being formed. The leading end of the Web 11 is fastened to a core (not shown) supported on a shaft 101 which is guided to move vertically between opposed spaced guides or brackets 103. The roll core and material rolled thereon, is centered on and bears against a pair of lower support and winder drive rolls 105 and 107. The drive rolls are driven to have a surface speed corresponding to the reference speed established by the draw rolls 91.

To provide a tight roll it is necessary to provide a high initial pressure between the winder drive rolls 105 and 107 and the roll of dried web material. To this end, the drive rolls 105 and 107 are separated so that the weight of the roll of material bearing thereon has a relatively large force component in the horizontal direction or pressure direction and a smaller vertically directed, weight-force component. It will be appreciated, however, that as the diameter of the web rollincreases, the angle between the support rolls and the roll axis is reduced thereby affording a greater weight and lesser pressure component of the surface winding. This eliminates the need for additional rolls or loaded bearings of the prior art and provides an economical wind stand.

The,shaft s 105a and 107a of winder drive rolls 105-107 w are interconnected by .a belt and pulley drive. 1 21. The pulleys; of thedrive 121 are of equalsize sothat the rolls 105 and 107 rotate at .the, same peripheral speedsfAs illustrated, the, shaft 105a is also connected to the line shaft 109 by a power train 123 which. includes a belt and pulley drive 123a, a variable speed reducer 123k and a belt and pulley drive123c. I

Thus, it will be seen that-the speed of the draw rolls 89 and 91 may be adjusted by adjusting the speed reducerl ll on the main drive motor 110, Thereafter; the

speed of various other driven rolls may be correlated as required to the speed of the draw rolls 91 by the variable speed reducers 115b, 117b, 11% and 1231;. During" operation, a simple adjustment of the speed-reducer 111 ,on the main motor 110 will cause all of the rolls to change speed in unison. TI f I 1 I As pointed out previously, it is important that "the web 11 during its treatment is maintained in a condition of neutral tension. To this end, a drive means is provided which makes possible incremental changes in draw while the equipment is running at each point where the web undergoes treatment so that the neutral tension condition can be maintained. A preferred drive means is diagrammatically illustrated in FIG. 2. As illustrated, each of the driven rolls is operatively connected to a common drive or line shaft 109 which extends substantially the length of the apparatus. The line shaft 109 is driven at one of its ends by a main drive motor 110 which is connected to the shaft 109 by means of a speed reducer and variable speed drive 111 and a belt and pulley power transmission 112. In the illustrated apparatus the preferred speed for the web 11 is determined by the peripheral speed of the draw rolls 91. These rolls are powered by connecting the supporting shaft 91a of one of the set of rolls to the line shaft 109 by means of a power train 113 which includes a belt and pulley drive 113a, a speed reducer 113b and a belt and pulley drive 1130.

The first set of nip rolls 23-25 is powered by connecting the shaft 23a of roll 23 of that set to the line shaft 109 by means of a power train 115 which includes a belt and pulley drive 115a, a variable speed reducer 115b and a belt and pulley drive 1150.

In the illustrated apparatus, the bowed roll 65 is not driven. However, under some adverse conditions especially where the impregnant is extremely viscous, it may be desirable to drive the bowed roll 65. This may be accomplished, if desired, by providing a sprocket or pulley on one of the end caps 79 of the bowed roll which may be connected by a suitable drive to the shaft 33a of its adjacent roll 33.

In operation, the web 11 is threaded through the machine in the manner which has been described and the desired speed is established by the draw rolls 91. The metering rolls 31-33 are adjusted to provide the desired metering action of impregnant through the action of the adjusting screws 37. After this has been accomplished, the speed of the rolls 31-33 is adjusted so as to provide in the dryer a vertical run of the web 11 which is in a condition of neutral tension. With most materials, the web shrinks as it is dried and therefore the rolls 31-33 ordinarily operate at a slightly greater peripheral speed than the draw rolls 91. Simultaneously, with this adjustment, the adjustment of the nip rolls 23-25 is made and since the material normally stretches somewhat after being wetted, it is normally found'that these rolls should be driven at a speed slightly less than the speed of the rolls 31-33. In order to obtain a tight wrap on the roll .of the final product the drive rolls -107 are driven at a slightly fasterperipheral speed than the draw rolls 91 so as to provide tension which facilitates splitting and insures a tight wrap on the take-up roll.

.The position of the bowed roll must be determined by experiment and depends upon the amount of shrinkage in the dryer and the characteristics of the material being treated. Generally, however, for a 48 inch wide sheet, the throw of the bowed roll is maintained within about A to A of an inch. In other'words, the central portion of the 48 inch. sheet as it enters its vertical run is offset forwardly of. the marginal edges of the sheets 4 to of an inch, causing the central portion of the sheet to be under slightly greater tension than the edges so that as the sheet shrinks in the dryer it becomes dimensionally stable in a fiat plane.

The method and apparatus described herein are particularly successful in overcoming the problems encountered in impregnating and drying continuously traveling webs of thin, lightweight permeable materials. Moreover, the invention makes possible closely controlled impregnation with minimal variation at commercially ac.- cepted speeds.

Various features of the invention believed to be new are set forth in the appended claims.

What is claimed is:

1. A method of impregnating and drying in a continuous web of material with a liquid impregnating material comprising the steps of continuously feeding said web forwardly to an impregnating station at a predetermined speed, immersing said Web in said impregnating material, exerting a metering pressure on said web to remove impregnating material from said web in excess of a predetermined accretion per unit area of said web while maintaining the web in a condition of substantially neutral tension, directing said web into a vertical run, subjecting said web while in said vertical run to heat so as to dry said impregnating material, and deforming said web at the entrance of said vertical run by bowing its central portion outwardly relative to its marginal edges, and maintaining said web in a condition of substantial neutral tension while it is in said vertical run whereby a dimensionally stable, flat sheet is produced after drying.

2. A method in accordance with claim 1 in which said web is immersed in said impregnating material and then is squeezed in a nip to force said impregnating material into the interior of said web and in which said web is immersed again into said impregnating material prior to moving into a second nip which exerts said controlled pressure.

3. A method in accordance with claim 2 in which said web is tensioned and held fiat :as it is passed through said first and second nips.

4. A method of drying a traveling web which is impregnated with a liquid impregnant comprising directing said impregnated web into a vertical run, subjecting said web to heat while in said vertical run to dry the same, said impregnated web being maintained in a flat condition transverse to its line of movement both before and after said vertical run, maintaining said web in a condition of substantially neutral tension while in said vertical run and distorting said sheet from its flat transverse condition immediately prior to entering said vertical run by bowing it transverse to its line of movement so that .the central portion of said web has a greater length of travel than the marginal edges of said web whereby a dimensionally stable, fiat sheet is produced after drying.

5. An apparatus for impregnating a continuously traveling web with a liquid impregnant and for drying the same comprising means for feeding said web along a path of travel into and through an impregnating means,

said impregnating means including a tank for holding the impregnating liquid at a predetermined level, means for su'bmerging said web in said impregnating liquid, and roll means for compressing said web after immersion for limiting the accretion of said impregnating liquid in said web, a vertically disposed drying station, means for feeding said impregnated web in a vertical direction through said drying station, means located along the line of travel of said web forwardly of said drying station including a bowed roll for distorting said web in such manner that the central portions of said web progressively traverse a greater length of travel than the marginal portions thereof, and roll means for drawing said web through said drying means.

6. An apparatus in accordance With claim 5 wherein said impregnating means includes a first set of horizontally disposed rolls in generally vertical alignment and positioned to provide a nip, a portion of the surface of the lower roll of said first set extending below the level of said impregnating liquid said web being trained under said lower roll and through the nip of said first set of rolls, and a second set of horizontally disposed rolls in generally vertical alignment and positioned to provide a second nip, a portion of the surface of the lower roll of said second set extending below the level of said impregnating liquid, said web from said first set of rolls being trained under said lower roll of said second set of rolls and through the nip of said second set of rolls, and means 8 for adjusting the pressure in the nip of said second set of rolls.

7. An apparatus in accordance with claim 5 in which the roll means for compressing said web after immersion and said roll means for drawing said web through said drying means are provided with drive means for effecting differential surface speeds between said roll means for compressing said roll means for drawing to maintain said web in a condition of neutral tension.

8. An apparatus in accordance with claim 6 wherein said first set of rolls, said second set of rolls and said roll means for drawing said web through said drying means are provided with drive means for varying the surface speeds of each of said sets of rolls to maintain said web in a condition of neutral tension during impregnation and drying.

References Cited UNITED STATES PATENTS 2,445,443 7/1948 Long 34-154); 2,669,031 2/1954 Chase a a1. 34 154x- 2,679,086 5/1954 Andrews, Jr. 34l54X 2,785,478 3/1957 |Avdas et a1. 3-4 9 JOHN J. CAMBY, Primary Examiner U.S. c1. X.R. 34 157 w .7 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,553,845 Dated January 12, 1971 Inventor) C. A. Lee and Warren H. Furbeck It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

JP age 7, line 2, change "27" to 21 line 7, change "29" to 39 Page 9, line 16, change "end one of" to end of one Page 11, line 18, change "31" to 33 line 21, change "117a" to ll7c line 22, change "33" to 31 Page 12, delete paragraph commencing on line 6 and ending on line 13. Page 12, following line 5, insert the following paragraph:

The first set of nip rolls 23-25 is powered by connecting the shaft 23a of roll 23 of that set to the line shaft 109 by means of a power train 115 which includes a belt and pulley drive 115a, a variable speed reducer ll5b and a belt and pulle drive ll5c.

Page 113, delete paragraph commencing on line 7 and ending on line 11. Page 13, following line 6, insert the following paragraph:

Thus, it will be seen that the speed of the draw rolls may be adjusted by adjusting the speed reducer 111 on the main drive, motor 110. Thereafter, the speed of various other drive rolls may be correlated as required to the speed of the draw rolls 91 by the variable speed reducers 115b, 117b, 1191: and 123b. During operation, a simple adjustment of the speed reducer 111 on the main motor 110 will cause all of the rolls to change speed in unison.

Page 13, line 18, change "33a" to 31a Page 14, line 20, change "sheets" to sheet Claim 1, line 1, delete "in".

Claim 2, line 6, change "said" to a Claim 3, line 2, delete "tensioned and".

Claim 6, line 7, after "liquid" and before "said", insert a comma.

Claim '7, line 6, after "compressing" and before "said", insert said web and line 6, after "drawing" at end of line Ensert said web Signed and sealed this 16th day of May 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. RORER'P GOTTSCHALK Attesting Offi er Commissioner of Patents

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