US3797384A

US3797384A - Multiple belt press

Info

Publication number: US3797384A
Application number: US00209941A
Authority: US
Inventors: D Hoff
Original assignee: Beloit Corp
Current assignee: Beloit Corp
Priority date: 1971-12-20
Filing date: 1971-12-20
Publication date: 1974-03-19
Anticipated expiration: 1991-03-19
Also published as: ZA728929B; FI61930C; FI61930B

Abstract

A press structure for pressing a traveling fibrous web including a support roll with first, second and third belts wrapped over a portion of the roll and forming an extended pressing zone with the belts engaging each other successively along the zone so that the pressure will increase with each additional belt applied to the pressing zone.

Description

United States Patent 1191 Mar. 19, 1974 MULTIPLE BELT PRESS [75] Inventor: Donald I. Hoff, Beloit, Wis. [73] Assignee: Bloit Corporation, Beloit, Wis.

[22] Filed: Dec. 20, 1971 21 Appl. N6; 209,941

52 U.S. c1. 100/154, 162/360 51 161. c1 13211 3/00, D21f 5/02 [58] Field of Search 100/153, 154,151, 208, 100/152; 210/401, 400; 162/305, 318, 396, 358, 359, 360

[56] References Cited UNITED STATES PATENTS 3,110,612 11/19 3 GOttWalCl e161,", 162/359 645394 3/1900 1-16mme1 100/153 2,365,658 12/1944 Schumacher 100/154 x FOREIGN PATENTS OR APPLICATIONS 26,981 11/1964 Japan 100/153 Primary Examiner-Leon G. Machlin Attorney, Agent, or Firm-I-Iill, Sherman, Meroni, Gross & Simpson 57 ABSTRACT A press structure for pressing a traveling fibrous web including a support roll with first, second and third belts wrapped over a portion of the roll and forming an extended pressing zone with the belts engaging each other successively along the zone so that the pressure will increase with each additional belt applied to the pressing zone.

10 Claims, 3 Drawing Figures PAIENIEBMAR 1 9 m4 3. 797384 Y ig z MULTIPLE BELT PRESS BACKGROUND OF THE INVENTION The invention relates to improvements in presses for extracting water from a continuous traveling web such as a newly formed paper web in a paper machine, and particularly, the invention relates to a structure for providing an extended press nip which applies a pressing force to a web for a longer continuous time than structures heretofore available which merely pass the web through the nip of an opposed roll couple and which obtains a unique controllable pressure profile to which the web is subjected.

In the copending application of Busker and F rancik, Ser. No. 193,272, the principles and advantages of pressing a paper web for an extended period of time, and the advantages thereof, are discussed. In the present structure the principles of an extended time nip are utilized in a structure affording advantages over prior art arrangements in that substantial flexibility is afforded in obtaining increased pressure stepwise along the nip.

As will be seen from the teachings of the disclosure, the featuresof the inventionmay be employed in the dewatering of other forms of webs than a paper web in a paper making machine. However, for convenience, a preferred embodiment of the invention will be described in the. environment of a paper making'machine which conventionally forms a web by depositing a slurry of pulp fibers on a travelingfourdrinier wire, transfers the web to a press section where the web passes through a number of press nips formed between roll c uples, and the web then passes over a series of heated dryer drums and usually through a calender and I then is wound on the roll. The present structure may form the entire press section and take the place of other forms of press sections heretofore available. Many modifications can be made in. this type of overall machine, as to the forming section, the press section, the dryer section, andthe structure of the instant disclosure may be employed in pressing webs of various synthetic fibers.

The present invention relates to improvements for the press sections of a paper making machine. In such a machine the web usually arrives at the press section with about 80 per cent wet basis moisture (ratio of water tofiber plus water) and leaves the presssection with approximately 60 per cent moisture, with the remaining moisture having to be removed by thermal evaporation in the dryer section as the web passes over a series of heated dryer drums. Because of various inherent limitations in the operation of roll couples form ing press nips for the press section in a conventional paper making machine, only a given amount of water can be removed in each nip and, therefore, in a conventional paper making machine, a series of three press nips are usually employed. It has been found impractical to attempt to remove a significant amount of additional water by increasing the number of pressnips, although'the further removalof water by pressing can greatly reduce the expense and size of the dryer section. It is estimated that if the water removed in the press section can be reduced from 60 per cent to, 50 per.

cent, the length of the dryer section can be reduced by one-third. This is significant in a typical 3,000 feet per minute newsprint machine which employs approxi- 2 mately 100 dryer drums. This significance can be appreciated in considering that the dryer drums are each expensive to construct and to operate and require the provision of steam fittings and a supply of steam for each drum. The relative importance of the removal of water in the press section is further highlighted by the fact that one of the most important economic considerations in justifying a satisfactory return on investment in the operation of a paper making machine is to obtain the highest speed possible consistent with good paper formation and better pressing will shorten the necessary time in the dryer section and permit higher speeds.

It is accordingly an object of the present invention to provide an improvement in the press section of a paper machine which makes it possible to remove an increased amount of water in this press section and makes it possible to provide a press section having only a single pressing nip of a unique elongated or extended nature which does not have the performance limitations of conventional roll couple presses and which requires far less space in terms of requirements as to the overall length of the press section. By increasing the amount of water removed from the web inthe press section, increased speeds are possible with existing equipment, i.e., a given length of dryer section can operateat higher speeds since it is required to remove less water. Also, new equipmentcan be constructed requiring less machine length and expense.

The present invention employs a principle which may be referred to as the extended nipconcept wherein the time the web is subjected to a pressing action is greatly extended, i.e., a single pressing is provided having a residence time which exceeds that of the time of the web in a number of conventional roll couple press nips. With the reduction to a single pressing operation, the compound effects of rewetting the web as it leaves a plurality of hips are avoided.

A factor which presently limits water removal from paper by mechanical web pressing is the flow property of water within the paper sheet. It has been found that other factors are not of dominant significance, for example, the effects of the moisture in the felt which travels with the web are small. It has been found further that the length of time that the web is in the nip, in other words the residence in the nip, can have a significant effect in overcoming the difficulties created by the flow properties of the water within the sheet. It has also been found that merely by increasing the residence time of the web in the nip, the water content of the sheet coming out of the press can be decreased so that the web will have 46 per cent dryness rather than 40 per cent dryness with other variables remaining constant. As is evident, the residence time'of a web in a conventional roll couple press nip is limited and can only be increased by decreasing. the speed of travel of the web, or can be increased slightly by increasing the diameter of the press rolls, but these factors are indeed limiting. Ithas been found, for example, that by applying a 1,300 pound per square inch pressure on a web for five minutes, a moisture level of less than 30 per cent can be attained. Yet, under the dynamic short term mechanical pressing of a paper machine press section using roll couples, even with a plurality of nips, a great deal of effort is required to maintain moisture levels below per cent.

It has been found that significant losses in dryness occur at higher speeds and that a loss in dryness of over 5 per cent is experienced in going from 300 feet per 1 minute to 1,000 feet per minute with typical press loadings in a suction press. It has been found that a hydraulic pressure or wedge effect develops during the passage of the wet that through the wet press nip. The hydraulic pressure that develops subtracts from the applied load and reduces the mechanical compacting pressure. The result is a loss in dryness. As the machine speed increases, the compacting rates are higher resulting in higher hydraulic pressures within the paper mat. These hydraulic pressures react against the pressure of the rolls and prevent the moisture from being squeezed from the web. The exact value of hydraulic pressure is difficult to determine either by direct measure or analysis because of the space and speeds involved. It is be lieved, however, that hydraulic pressure predominately determines press performance on machines operating at high speeds. Accordingly, the instant invention relates to avoiding disadvantages encountered with high speed press nips of the conventional type used in most commercial applications today, and provides a substantial increase in residence time within a press nip to allow time for flow to occur-within the mat and for the hydraulic pressure to dissipate.

A further object of the invention is to provide a press wherein pressure can be utilized for an extended nip press to achieve improved and higher pressures with a mechanism capable of operating at high speeds.

Other objects, advantages and features will become more apparent with the disclosure of the principles of the invention, and it will be apparent that equivalent structures and methods may be employed within the principles and scope of the invention in connection with the description of the preferred embodiment and the teaching of the principles in the specification, claims and drawings, in which:

DESCRIPTION OF THE DRAWINGS FIG. 1 is an end elevational view shown in schematic form of a press constructed and operating in accordance with the principles of the present invention;

the press, it will be dewatered an amount at least equal to the dewatering attained in the usual three press sections of a paper making machine.

The paper web carried on the felt is fed over the surface of a support roll 10 and the web is subjected to a pressing action throughout the pressing zone which begins at 14 and extends to 15 on the support roll 10.

The web is pressed against the roll by tensioned pressing belts ll, 12 and 13 which wrap a portion of the support roll to define the pressing zone 14 15. In a preferred form the belts 11, 12 and 13 are sequentially laid on top of each other at spaced locations so that the pressing pressure is increased with each successive belt being laid over the support roll 10. The belts are under relatively high linear tension to generate a pressing pressure normal to the press roll 10. The press roll is a rigid roll which, of course, has some bending due to the forces of the belts, but inasmuch as the belts are flexible, the pressure across the web will remain uniform. In handling relatively wide widths of paper web, it may be desirable to provide deflection control means for the roll 10 to prevent excess bending. Such means may be in the form of a structure which provides a hollow roll shell for the press 10 with a stationary shaft extending therethrough and fluid force transfer means within the shell. The fluid force transfer means for transferring the forces on the roll shell to the FIG. 2 is a schematic view somewhat similar to FIG.

l, but showing additional structure of the press; and FIG. 3 is a graph illustrating the pressure profile of the press.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As illustrated in FIGS. 1 and 2, the press includes a rotationally mounted support roll 10. The support roll is cylindrical in shape and has a smooth outer surface and is supported by end bearings 10a for rotation. It may be driven in rotation or may be rotated by its contact with the paper web and felt and with the belts which may be driven.

The paper web will pass to the press after being formed in the 'fourdrinier section of a paper making machine. In the press the water will be squeezed from the web W into the felt F and suitable drying means will be provided for removing the moisture from the felt. The paper web will then travel on to the dryer drums and to a calender for completion of the paper making operation. It is contemplated that the present press will complete the entire mechanical pressing operation and no additional presses need be provided. Because of the relatively high pressures and the relatively long residence time which can be obtained for the paper Web in shaft may be in the form of a body of liquid contained between the press zone and the shaft by seals, or may be in the form of a shoe supported on a piston mounted in a cylinder on the shaft with the shoe being in the form of a slipper bearing and being lubricated by lubricating fluid passing between the shoe and the inner surface of the roll shell. Several shoes spaced circumferentially may be employed, and be circumferentially adjustable to be changable in position with change in the angle of wrap by the belts.

As the web W passes beneath the first belt 11 at point 14 which is the beginning of the pressing zone, it is subjected'to a pressure which is a function of the tension of the belt 11. The web is then subjected to a first pressing pressure P-I where it.travels from point 14 to point 16. At point 16, a secondbelt is laid over the first belt, and the web then becomes subjected to the combined force of both of thebelts. Frompoint 16 to point 17, the web is subjected to a second pressing pressure P-2. At point 17, the combined forces of all three belts are felt by the web, and it is subjected then to a third pressing pressure P-3 extending from point 17 to the end of the pressing zone 15. These successive pressures are shown in the graph of FIG. 3. The length of time that the web is subjected to each of the pressures is dependent upon the angle of wrap. I

If the second pressure is to be applied sooner or later, the second belt 12 is over-laid onto the first belt sooner orlater so that the pressure line will follow the dotted lines 27b or 27c as shown in FIG. 3.

Also, if the pressure to be applied in the'first portion of the zone P-l is to be less, then the tension in the first belt 11 is relaxed, and the curve will follow the line 27a shown in FIG; 3. The total pressure can remain the same if desired by merely increasing the pressures in the over lying belts 12 and 13.

Thus, extreme flexibility can be achieved with the amount and duration of time of the pressure applied in each of the three portions of the pressure zone indicated as P-l, 1L2 and P-3 in FIG. 1. Asis dictated by different webs of different physical characteristics it may be desirable to increase the diameter of the press roll to be able to increase the total length of the pressing zone. As the length of the zone is increased, the tension in the belt will have to be increased to attain the pressure desired.

As an example of a pressing arrangement, the belt 11 may be tensioned to provide 200 pounds per square inch of pressure on the web, and belt 12 may be tensioned to provide an additional 200 pounds with belt 13 tensioned to provide a still additional 200 pounds. Thus, the belt for the portion P-1 of the pressing zone will be subject to 200 pounds of pressure, for the portion P-2 will be subjected to 400 pounds, and for the remainder of the pressing zone, that is the portion P-3, the web will be subjected to 600 pounds of pressure.

Inasmuch as it is believed that one of the paramount factors affecting the removal of water from the web is the hydraulic pressure within the web, by building up the pressure in steps or stages, dewatering can occur while this hydraulic pressure is being overcome, for more effective dewatering. Further, the web is not re leased for each step, but is continuously subjected to pressure throughout the entire pressing zone, and the pressure within each zone is uniform throughout the time of travel of the web through that portion of the zone.

For controlling the pressures within the zones, the tension on the belts is controlled, and for controlling vthe length of each portion of the zone, the position of the belts as they are laid on the previous belt is controlled. An arrangement for attaining this is shown in FIG. 2. Ina preferred arrangement all three belts are lifted off of the web at the same time, and for this purpose, the belts pass over a common turning roll 19. The

outer belt is supported on a tensioning roll and passes down over a positioning roll 21. The tensioning roll is movable by force means shown schematically at 200 to control the tension in the belt. The position at which the belt 13 is laid onto the belt 12 is controlled by moving the positioning roll 21 by means 21a. The tensioning means 20a may be in the form of hydraulic cylinders or other equivalent structure. Similarly, movable support bearings operated by hydraulic cylinders may be provided for the positioning roll 21a, and suitable mechanical means are provided for tensioning and positioning each of the three belts.

The intermediate belt 12 passes over a tensioning roll 22 which is moved for tensioning the belt by power means 22a. The position where it is applied over the lower belt is controlled by the position of'a positioning roll 23 which is moved by force means 23a.

The innermost belt which is applied over the web is tensioned by a tensioning roll 24 which is moved by force means 24a. Theposition at which the belt 11' is applied onto the supporting roll 16 is determined by the location of the positioning roll 25 which is moved by force means 25a.

It may be desirable to provide annular grooves such as shown at 18 in FIG. 2 in the outer surface of the support roll to aid in the transfer of water from the web W to the felt F. In some cases the web may be sandwiched between two felts.

Thus, by arrangement as shown and described, a relatively high pressing pressure can be attained through the pressing zone with the forces of the belts supplementing each other. This makes it p'ossible to get a higher pressing pressure and eliminates the necessity of providing excessively strong belts. The belts may be of a reinforced rubber or a nylon, and are preferably nonporous. Variations in pressures and times may be attained rapidly, and even during operation, eliminating the necessity of the change of parts for varying operating conditions and by measuring the moisture of the web passing through the press, changes may be made during operation until optimum dryness of the web is attained.

I claim as my invention:

1. A press structure for pressing and dewatering a traveling fibrous web in a paper making machine comprising in combination:

a support roll mounted for rotation for receiving and carrying a moisture containing web from a web forming section;

a first tensioned pressing belt wrapping a portion of the support roll and defining with the roll an extended pressing zone through the area of wrap throughout which the web is pressed;

a second tensioned pressing belt laid over the first belt for at least a portion of said pressing zone with the web subjected to the forces of both belts against the roll for the area wrapped by said second belt and subjected. to forces of the first belt in the area wrapped solely by the first belt;

and means between the belts and roll positioned against the web for receiving water expressed from the web.

2. A press structure for pressing and dewatering a traveling fibrous web in a paper making machine constructed in accordance with claim 1 and including a third tensioned pressing belt laid over the second belt for at least a portion of the pressing zone with the web subjected to the forces of each of the belts against the support roll in said zone.

3. A press structure for pressing and dewatering a traveling fibrous web in a paper making machine constructed in accordance with claim 1 wherein said second belt engages the first belt at a secondary location after the starting point of said pressing zone.

4. A press structure for pressing and dewatering a traveling fibrous web in a paper making machine constructed in accordance with claim 2 and including a third tensioned pressing belt laid over the second belt for at least a portion of the press zone with the web subjected to the forces of each of the belts in said zone and with said third belt engaging the second belt at a location after said secondary location.

5. A press structure for pressing and dewatering a traveling fibrous web in a paper making machine constructed in accordance with claim 1 and including first tension control means for the first belt,

and second tension control means for the second belt so that different tensions can be placed in each belt for controlling the pressure on the web along said pressing zone.

6. A press structure for pressing and dewatering a traveling fibrous web in a paper making machine constructed in accordance with claim 5 and including a third tensioned pressing belt laid over the second belt for at least a portion of the pressing zone,

and a third tension control means for the third belt.

7. A press structure for pressing and dewatering a traveling fibrous web in a paper making machine constructed in accordance with claim 1 and including means for changing the angle of wrap of said first belt to change the length of said pressing zone.

8. A press structure for pressing and dewatering a traveling fibrous web in a paper making machine constructed in accordance with claim 1 with means for changing the angle of wrap of the second belt to change the length of time that the web is subjected to the pressures of both belts in said pressing zone.

9. A press structure for pressing and dewatering a traveling fibrous web in a paper making machine constructed in accordance with claim 1 and including means for controlling the tension of at least one of said belts for controlling the pressure applied to the web in said pressing zone.

10. A press structure for pressing and dewatering a traveling fibrous web in a paper making machine constructed in accordance with claim 1 wherein a felt is passed through said pressing zone between the roll and the web and the roll is provided with grooves for aiding in the transfer of moisture from the web to the felt.

Claims

1. A press structure for pressing and dewatering a traveling fibrous web in a paper making machine comprising in combination: a support roll mounted for rotation for receiving and carrying a moisture containing web from a web forming section; a first tensioned pressing belt wrapping a portion of the support roll and defining with the roll an extended pressing zone through the area of wrap throughout which the web is pressed; a second tensioned pressing belt laid over the first belt for at least a portion of said pressing zone with the web subjected to the forces of both belts against the roll for the area wrapped by said second belt and subjected to forces of the first belt in the area wrapped solely by the first belt; and means between the belts and roll positioned against the web for receiving water expressed from the web.

5. A press structure for pressing and dewatering a traveling fibrous web in a paper making machine constructed in accordance with claim 1 and including first tension control means for the first belt, and second tension control means for the second belt so that different tensions can be placed in each belt for controlling the pressure on the web along said pressing zone.

6. A press structure for pressing and dewatering a traveling fibrous web in a paper making machine constructed in accordance with claim 5 and including a third tensioned pressing belt laid over the second belt for at least a portion of the pressing zone, and a third tension control means for the third belt.