NZ224687A - Papermaking press nip using elastic belt longer than press roll circumference - Google Patents

Description

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NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION ■V A BELT AS A REPLACEMENT FOR A CONVENTIONAL PRESS ROLL COVER We, ALBANY INTERNATIONAL CORP., a corporation organized and existing under the laws of the State of New York, United States ^ of America of 1 Sage Road, Menands, New York 12204, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following s tatement A BELT AS A REPLACEMENT FOR A CONVENTIONAL PRESS ROLL COVER BACKGROUND OF THE INVENTION Field of the Invention This invention relates to the removal of water from the papersheet, wet felt combination in the nip of the press rolls in a papermaking machine. More specifically, it presents an elastic, compressible belt, whose total length is greater than the circumference of a press roll, for use as a replacement for a conventional press roll cover.

Description of the Related Art An important step in the production of paper occurs in the press section of the papermaking machine. There, a sheet of fibrous material, either carried on top of a belt of water-absorbing felt or held between two such belts, passes through a series of openings between rolls. In each passage through such an opening, referred to as the nip of the rolls, water is squeezed from the fibrous material and absorbed by the felt. The aim of this procedure is to remove as much water as possible from the sheet before it emerges from the press section of the machine and enters the dryer section. In this way, less water will remain to be removed by heat in the dryer section, and costs related to heat production will be reduced.

In the dewatering presses, however, it is desirable to apply pressure to the paper sheet, wet felt combination over various time elements, depending on the type of paper being manufactured. This so-called dwell time is related not only to the speed of the sheet-felt combination, but also to the compressibility of the roll surfaces. For short time elements requiring high specific pressure, the press rolls are equipped with very inelastic surfaces. Where it is desirable to extend this time element and to reduce the specific pressure, the press rolls are equipped with covers that are compressible and elastic. The exact compressibility characteristics of the press roll cover used depend on the particular conditions desired in the nip of the press.

Eventually, due to cyclical compressive fatigue, press roll covers will fail in operation. It will then become necessary to remove the press roll from the paper machine for either regrinding or recovering. Such a procedure can remove the paper machine from operation for a considerable length of time.

This invention provides a alternate method of supplying an elastic, compressible media in the nip of the press instead of using the conventional press-roll cover. It is now possible to produce a belt which has an elastic, compressible surface similar to that of a conventional, press-roll cover. Using the method envisioned here, such a belt, wrapped around the shell of the press roll, would replace the press-roll cover. In this way, the papermaker can be provided with the elastic media needed in the press ' nip without actually covering the press roll.

SUMMARY OF THE INVENTION This invention consists of an elastic, compressible belt, whose total length is greater than the circumference of a press roll, to be used as a replacement for the conventional press roll cover now used in the papermaking industry. Supported by the shell of the press roll, the belt would run independently through the nip in conjunction with the sheet of fibrous material and wet felt combination.

Guide and stretch rolls would be required to direct and 2 control the motion of the belt around the press roll and to maintain its tension at a suitable level. The outer surface of such a belt can be smooth, grooved, or have holes so that it can replace roll covers having those surface characteristics.

The user will benefit from the numerous, novel advantages to be obtained through the application of this invention. When compressive fatigue failure eventually occurs in the elastic media of the belt, it would not be necessary to remove the press roll completely from the paper machine for recovering. Instead, one would simply shut down the papermaking machine for the comparatively short span of time required to remove the used belt from the machine and install a new one in its place.

Assuming that compressive fatigue failure occurs after some large number of compressive cycles, through the use of a belt of the kind shown by this invention, a longer machine running time will elapse before a given portion of the length of the belt will have experienced the same number of compressive cycles of passage through the nip as a given portion of the press roll cover. This is because the belt will be longer than the circumference of the press roll. The belt will then by comparison have a much longer running life than the press roll cover.

Since it will be easier to change a cover belt than change a press roll cover, and since a cover belt represents a smaller capital investment, in applying this invention the papermaker will have an increased flexibility to change his nip conditions as called for by the given application, and will be required to carry fewer press rolls in his maintenance inventory. Machine "down" time during changes will be shorter than would be the case if an entire roll or roll cover were being replaced.

Because of the ease of changing belts, the papermaker will also be able to change from a smooth belt to a grooved or perforated belt at his discretion.

BRIEF DESCRIPTION OF THE DRAWING In Figure 1 is shown a set of press rolls in a papermaking machine to which this invention has been applied.

Figures 2a-2d show portions of the surfaces of belts of this invention having different surface characteristics.

Figures 3a-3d show side sectional views of the belts depicted in Figures 2a-2d respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT The main purpose of this invention is to provide the papermaker with an elastic, compressible belt for use in the press section of the papermaking machine. It is intended that such a belt form the basis of an alternate method of supplying an elastic media to the press nip and make it unnecessary in the future to actually cover the press rolls with an elastic, compressible material. A mode in which this invention can be put into use is illustrated in Figure 1. The wet sheet of fibrous material 1, from which water is being removed, is held between the top 2 and bottom 3 water-absorbing felts as it passes between the upper 4 and lower 5 press rolls. The actual removal of water from the sheet 1 occurs in the press nip 6, the region between the upper 4 and lower 5 press rolls, where the combination of wet sheet 1 and water-absorbing felts 2,3 is squeezed together. An elastic, compressible belt 7 having a total length greater than the circumference of the lower press roll 5 and approximately the supported by the lower press roll 5 and moves through the nip 6 with and below the combination of sheet 1 and water absorbing felts 2, 3. Guide rolls 8 maintain a requisite level of tension on the belt 7 and control and direct its motion through the nip 6. A movable stretch roll 9 is used to adjust the level of tension desired in the belt 7. The mobility of the stretch roll 9 is indicated by the vertical arrows above and below the circle representing it. All other arrows indicate the motions of components of this system during its regular operation.

Figures 2a-2d show four variants for that surface of the belt 7 which makes contact with the press felt 3. Figure 2a represents a smooth belt 7; Figure 2b shows a belt 7 whose surface has grooves 10. Figure 2c shows a perforated belt 7 with holes 11 passing completely through its structure.

Figure 2d shows a belt 7 whose surface has depressions 12 not passing completely through its structure.

Figures 3a-3d show side sectional views of the belts 7 in Figures 2a-2d respectively to present the grooves 10, holes 11, and depressions 12 in greater detail.

Modifications would be obvious to one skilled in the art without departing from the scope of the invention as defined in the appended claims. of same width in the cross-machine direction, is * 13

Claims (6)

WHAT WE CLAIM IS:

1. A method for removing water from a wet sheet of fibrous material in the press section of a papermaking machine, said wet sheet of fibrous material being carried in said press section by a water-absorbing felt, said wet sheet and said water-absorbing felt moving as a combination through a press nip in said press section which comprises: using a first press roll of a pair as a support for an elastic, compressible belt, said belt having a smooth outer shell surface and a length greater than the circumference of said first roll; directing the motion of said belt around said first roll by means of a plurality of guide rolls; regulating the degree or level of tension in said belt by means of a movable stretch roll; and passing the combination of wet sheet of fibrous material and water-absorbing felt through the press nip using the gap between the second press roll of said pair of press rolls and the belt, such that the smooth outer surface of the belt makes contact with the combination of wet sheet and water-absorbing felt in the press nip.

2. A method for removing water from a wet sheet of fibrous material in the press section of a papermaking machine, said wet sheet of fibrous material being carried in said press section by a water-absorbing felt, said wet sheet and said water-absorbing felt moving as a combination through a press nip in said press section which comprises: using a first press roll of a pair as a support for an elastic, compressible belt, said belt having an outer surface that has regularly spaced parallel grooves and a length greater than the circumference of said first roll; directing the motion of said belt around said first roll by means of a plurality of guide rolls; regulating the degree or level of tension in said belt by means of a movable stretch roll; and passing the combination of wet sheet of fibrous material and water-absorbing felt through the press nip using the gap between the second press roll of said pair of press « ^ ' ' c C L. C .. / rolls and the belt, such that the outer surface of the belt makes contact with the combination of wet sheet and water-absorbing felt in the press nip.

3. A method for removing water from a wet sheet of fibrous material in the press section of a papermaking machine, said wet sheet of fibrous material being carried in said press section by a water-absorbing felt, said wet sheet and said water-absorbing felt moving as a combination through a press nip in said press section which comprises: using a first press roll of a pair as a support for an elastic, compressible belt, said belt having perforations passing completely through its structure and a length greater than the circumference of said first roll; directing the motion of said belt around said first roll by means of a plurality of guide rolls; regulating the degree or level of tension in said belt by means of a movable stretch roll; and passing the combination of wet sheet of fibrous material and water-absorbing felt through the press nip using the gap between the second press roll of said pair of press rolls and the belt.

4. The method of any one of claims 1, 2 or 3 where the belt used has the same width as said first press roll in the cross-machine direction. t

5. A method according to^H^one of claims 1, 2 or 3 substantially as herein ft K L. described or exemplified. ysfa'1 t '

6. A method according to any one of claims 1, 2 or 3 substantially as herein described with reference to the accompanying drawings. ^ ALBANY INTERNATIONAL CORP. By Their Attorneys HENRY HUGHES LTD \ ■ J /' > " o A"' ' ■, •i i f- 2 OD lnn-N i