US3448529A

US3448529A - Apparatus for stabilizing paper webs

Info

Publication number: US3448529A
Application number: US471573A
Authority: US
Inventors: August S Erspamer; William R Sherman
Original assignee: Scott Paper Co
Current assignee: Kimberly Clark Tissue Co
Priority date: 1965-07-13
Filing date: 1965-07-13
Publication date: 1969-06-10
Anticipated expiration: 1986-06-10

Description

June 10, 1969 R PAM ET AL 3,448,529

APPARATUS FOR STABILIZING PAPER WEBS Filed July 13, 1965 INVENTORS. AUGUST 8. ERSPAMER WILLIAM R. SHERMAN United States Patent 3,448,529 APPARATUS FOR STABILIZING PAPER WEBS August S. Erspamer, Drexel Hill, and William R. Sherman, Chester, Pa., assignors to Scott Paper Company, Delaware County, Pa., a corporation of Pennsylvania Filed July 13, 1965, Ser. No. 471,573 Int. Cl. F26b 13/04; D06c 3/06 US. Cl. 34-416 5 Claims ABSTRACT OF THE DISCLOSURE This invention relates to the art of papermaking and more particularly to apparatus for producing paper having improved dimensional stability.

It has long been recognized that paper made from cellulosic fibers has a tendency to change dimensions when subjected to varying moisture conditions. For example, a conventional paper web will generally increase in length (the direction parallel to the machine direction, or direction in which the web has been run through a papermaking machine) and in width (the direction parallel to its cross-machine) when the moisture content of the atmosphere ambient the web is increased. Most paper webs demonstrate less dimensional stability in the cross-machine direction than in the machine direction, i.e. the width of the sheet undergoes greater dimensional changes than does the length of the web for given changes in the ambient atmosphere surrounding the web. Moreover, it has been found practicable to change and/ or control the machine direction dimensional stability of a paper web by varying the longitudinal tension to which the web is subjected during drying in the papermaking machine. Control of cross-direction dimensional stability has, however, continued to present a problem for the papermaker.

Certain present day applications require papers exhibiting unusual dimensional stability both in the machine and in the cross-machine directions. Card stock used, for example, in making punch cards for use in tabulating and computing equipment is required to have a very high degree of dimensional stability to insure reliable operation of the equipment with which it is used. Up to the present time known methods and apparatus for controlling cross-machine stability have not successfully produced paper sock with the desired stability for this application.

The principal object of this invention, therefore, is the production of paper webs having improved dimensional stability in the cross-machine direction. This objective is achieved through utilization of an improved principle of straining the web in a cross-machine direction durng passage of the web through the drying apparatus of a papermaking machine. Although attempts have been made in the past to stretch paper webs in a cross-machine direction during manufacture of the paper, such attempts have not been successful in materially improving the dimensional stability of the webs.

The underlying principles of this invention reside in the disposition of web straining devices, such as bowed expander rolls, within the drying section, or sections, of a papermaking machine in locations in which these devices impart a cross-machine strain to a parallelly dried web ice which is immediately thereafter subjected to further drying while restrained against cross-machine shrinkage. The invention further contemplates disposition of these straining devices in locations wherein maximum straining effect may be achieved from their use.

More specifically, the invention contemplates a novel arrangement of bowed expander rolls interspersed among the dryers, or drying drums, of a papermaking machine.

Further objects, advantages and features of the invention will be apparent from the following detailed description thereof in which reference is made to the accompanying drawing wherein:

FIG. 1, comprising two parts (1a and 1b), is a schematic elevation view of a portion of a papermaking machine embodying this invention;

FIG. 2 is an enlarged elevation view of one of the straining devices employed in the apparatus of FIG. 1 and,

FIG. 3 is a plan View of the straining device of FIG. 2.

FIG. 1 illustrates the principal components of the drying portion of a papermaking machine in which a wet web, 11, of papermaking fibers passes from a Fourdriner Wire 10 running around a roll 12, on which wire the web has been formed, through a series of press rolls 13 and consecutively through three dryer sections indicated generally by

reference numerals

14, 15 and 16, respectively. A machine of this type may have a pair of size press rolls 17 interposed between

dryer sections

15 and 16 and also is equipped with a reel (not shown) for winding the dried web 11 into a roll after it leaves the last dryer section 16.

Each of the

dryer sections

14, 15 and 16 includes a plurality of heated cylindrical dryers, or drying drums, which are mounted for rotation on horizontal axes. It is conventional practice to arrange such dryers in tiers with the dryers of one tier staggered with respect to the dryers in the tier immediately thereabove or therebelow.

The nine dryers in section 14 have been consecutively numbered 21 through 29 in the sequence in which the paper web 11 is fed thereover in a conventional papermaking machine. It is to be noted, however, that in accordance with this invention and as illustrated in FIG. 1, web 11 is not fed over the dryers in the conventional sequence indicated by the numbers. The preferred sequence of web feed through the dryers of section 14 is 21-22- 24-23-25-27-26-28 and 29. This feed arrangement accommodates the travel of web 11 to a series of four web straining devices, each indicated by reference numera130, which contact the web during its passage, respectively, between

dryers

22 and 24,

dryers

23 and 25,

dryers

25 and 27, and dryers 26 and 28.

Each web starining device 30 preferably consists of a bowed expander roll of the type illustarted schematically in FIGS. 2 and 3. Expander rolls of this type are commonly used for spreading and smoothing webs and comprise a resilient cylindrical surface rotating about a bowed axis and which may, if desired, be equipped with means (not shown) for changing the degree of bow of the axis. A roll of this type is described in greater detail in US. Patent No. 2,960,749 to Robertson et al., granted Nov. 22, 1960.

Web 11 is caused to pass over each straining device 30 in such a manner as to first contact the surface of the bowed roll at a location to the inside of the bow where the surface of the roll is in a relaxed, unstretched condition and to remain in contact with the surface of the roll to a location near the outside of the bow so as to be subjected to a transverse, or cross-machine, strain by virtue of extension of the surface of the roll in passing from the inside of the bow to the outside of the bow (see FIG. 3). In accordance with this invention, the expander devices 30 are positioned between and displaced from the center lines of adjacent dryers over which the web 11 is passing and spaced from the dryer center-lines in a direction opposite the portions of the dryers over which the web passes in order to obtain maximum wrap of the surafce of the devices 30 by the web 11. This preferred relationship between the straining devices 30 and the dryers is illustrated in FIG. 1 from which it will be noted that one straining device 30 is disposed between and above the center lines of

dryers

22 and 24 with web 11 passing consecutively over lower surface regions of these dryers. Similarly, another straining device 30 is positioned be tween, but below, the center lines of

dryers

23 and 25 because web 11 passes consecutively over upper surface regions of the latter two dryers. In each instance the direction of curvature of the web passing over the two dryers is the same and opposite to the direction of curvature of the web in passing over the intervening straining device. This positioning of the straining device allows for maximum wrap, preferably in excess of 150 arcuate degrees, and up to 180 degrees of the surface of the devices 30 by the web 11. The degree of wrap is shown in FIGURE 2 an an angle of contact designated by reference numeral 30a.

It is further to be noted that, in accordance with this invention, the straining devices 30 are positioned within dryer section 14 so as to follow passage of web 11 over the

initial dryers

21 and 22 of the section and precede passage of the web over the last dryers, 28 and 29 in this section. In these locations the straining devices act on web 11 after it has been at least partially dried, so as to impart a cerain degree of physical integrity to the web, with the result that crossmachine direction stretching of the web by devices 30 has the effect of actually straining the web rather than merely separating loosely adhered fiber components of the web.

It is also deemed to be important that the web leaving each of the straining devices 30 be subjected to the restraining action of confinement against a dryer surface immediately after leaving each straining device. This restraining action is preferably accomplished by confining the strained web between the next dryer and a traveling dryer felt, indicated by dotted line 31. Dryer section 14, in accordance with usual dryer practice, employs two felts 31 which pass over the surfaces of the upper and lower tiers of dryers, respectively, and which are held against the dryers by means of rolls 32 positioned between adjacent dryers and at the ends of the dryer section.

It has been ascertained to be of particular importance to allow the strained web 11 to pass over at least two dryers, such as 28 and 29, to be further dryed and set before the web passes through any unrestrained draw such as exists between

dryer sections

14 and 15 and in the region of press rolls 17 between

dryer sections

15 and 16.

Dryer sections

15 and 16 preferably contain crossmachine straining devices 30 disposed among the several dryers in the same order of placement as devices 30 in dryer section 14. Thus, in section 15, in which the conventional dryer sequence is indicated by the sequence of reference numerals 35 through 39, the order of web feed is dryers 35-37-36-38 and 39, with straining devices 30 located in contact with web 11 between

dryers

35 and 37 and 36 and 38, respectively. The web path through dryer section 16 covers in

sequence dryers

41, 43, 42, 44 and 45 with the straining devices being positioned respectively between

dryers

41 and 43 and 42 and 44.

Dryer sections

15 and 16 are both equipped with felt runs 31 similar to dryer section 14.

From the foregoing it will be apparent that this invention provides a novel arrangement for imparting a transverse strain to a partially dried paper web and for subsequently setting the strain in the web for the purpose of improving the transverse dimensional stability of the web. Although the invention has been described in connection with a preferred embodiment thereof it will be apparent to persons skilled in the art that various changes may be made in the apparatus employed without departing from the spirit and scope of the invention.

What is claimed is:

1. Apparatus for stabilizing a paper web comprising at least two heated, rotatable drums, and means comprising a bowed roll disposed intermediate said drums for transversely straining a web passing from one drum to the other drum, the path of travel of said web being such as to undergo the same direction of curvature around said drums and the opposite direction of curvature around said bowed roll, said roll being bowed in a direction to produce maximum transverse stretching of the Web during passage of the web thereover.

2. Appartus for stabilizing a paper web comprising at least two heated, rotatable drums, and means comprising a bowed roll disposed intermediate said drums for transversely straining a web passing from one drum to the other drum, the path of travel of said web being such as to undergo the same direction of curvature around said drums and the opposite direction of curvature around said bowed roll, said roll being disposed in a position approximately equidistant from the axes of said drums to produce maximum wrap of the surface of said roll by said web, and said roll being bowed in a direction generally parallel to a plane containing the axes of said drums to produce maximum transverse stretching of the web during passage of the web thereover.

3. Apparatus for stabilizing a paper web comprising a dryer section including two tiers of drying drums having at least two drums in each tier and the drums of one tier staggered with respect to the drums in the other tier, a web travel path passing around a first drum in one tier, a first drum in the other tier, a second drum in the other tier and then a second drum in the first tier, and a web straining device for transverse stretching the web during its travel between the first and second drums of said other tier.

4. Apparatus as set forth in claim 3, wherein said web straining device is a bowed roll disposed between planes containing, respectively, the axes of the drums in said one tier and the axes of the drums in the other tier, said roll being bowed in a direction to produce maximum transverse stretching of the web during passage of the web thereover.

5. Apparatus as set forth in claim 4, wherein said web is in contact with said roll through an angle in excess of References Cited UNITED STATES PATENTS 6/1881 Piper 34-116 XR 7/1951 Harlow 2663 U.S. Cl. X.R. 26-63