US3093535A

US3093535A - Method of dewatering pulp webs

Info

Publication number: US3093535A
Application number: US748420A
Authority: US
Inventors: Otto L J Brauns; Lars B Jordansson
Original assignee: Stiftelsen Pappersbrukens Forskningsinstitut
Current assignee: Stiftelsen Pappersbrukens Forskningsinstitut
Priority date: 1958-07-14
Filing date: 1958-07-14
Publication date: 1963-06-11
Anticipated expiration: 1980-06-11

Description

June 11, 1963 o. 1.. J. BRAUNS EI'AL METHOD OF DEWATERING PULP WEBS Filed July 14, 1958 O O O O O O O O O O O 0 0 O O o o O O O O O O O 0 FIG. 2.

0 s8 3 Z n: INVENTORS E 0N0 L.J. Brauns 5 3 8 Lors B. Jordonsson 0. Q- E 5;

RNEYS Patented June 11, 1963 3,093,535 Mansion on DEWATERlNG PULP wuss Otto L. J. Brauns, Stockholm, and Lars B. .lordausson,

The present invention relates to an improved method for increasing the removal of water from moist or wet webs, and is particularly directed to the removal of water from continuously formed webs in the manufacture of paper and the like.

During the conventional production of paper, a sup ported wet paper Web leaves the forming wire of a paper making machine and travels through one or more rotary presses which remove water from the wet web. These presses usually consist of a rotating pair of rolls, either both of which are solid or one of which is hollow. In the latter case, the hollow roll is provided with a perforated shell and one or more suction chambers to assist in the removal of water and is referred to as a suction press. In the hollow roll of such a suction press, one or more suction chambers or so-called boxes, are positioned inside the roll and are stationary with respect to the roll so that when rotating, the perforated shell is placed under vacuum from the inside of the roll as by vacuum pumps. This vacuum increases the water removal from the traveling wet web, but due to the construction of the perforated shell, such suction presses have an inherent disadvantage when operating at high speeds since the water remaining in the perforations of the shell is ejected radially outwards when the shell moves out of the created vacuum of suction zone. In many instances, this rejected water is thrown back onto the web, thereby causing undesirable rcwetting of the web.

The hollow perforated rolls required for a suction press are also expensive to manufacture and difficult, When in use, to keep clean and hence there is a tendency for the perforations in the shell to become clogged with particles of paper pulp. Also, despite the fact that suction presses are generally eificient, if said presses are operated at very high speeds very powerful vacuum pumps are required, and in use the noise created by the suction press is objectionable.

A primary object of this invention is to provide an improved method for removing water from wet or moist traveling webs, said method overcoming the aforementioned disadvantages and affording excellent web formation under positive control and at speeds of operation materially in excess of those obtainable by known methods of the prior art.

Another object of this invention is to provide such an improved method which is characterized by utilizing relatively simple and low cost press constructions.

Other and more specific objects, as well as the novel characteristics of the method and functional improvements, will appear hereinafter.

According to the present invention a method of dewatering wet or moist travelling webs of paper, or other absorbent material, is characterized by passing the web through the nip of a pair of co-operating press rolls together with a water receiving mat having openings to receive and hold water squeezed out of the web at the nip of the press rolls and entraining the Water receiving mat, after passage through the nip, so that it diverges from the path of travel of the web, and then, at a point remote from the web, it changes in direction so as to subject the water held in the mat to centrifugal force, the mat and the openings therein being such that at least a substantial part of the water held in said openings will be released by a centrifugal force and discharged clear of the web.

The mat may be made of rubber, plastic or similar flexible solid material and is formed with holes, cavities or pores suiiiciently large to prevent water received therein from being held by capillary action to an extent which would prevent release of the water by the said centrifugal force. Alternatively the mat may be Woven from relatively non-absorbent material or may constitute flexible wire net-ting, the interstices thereof constituting the openings.

The water discharged from the mat preferably is caused to impinge on a baffle from whence it falls and is collected. And the web and mat may pass through the nip of the press rolls at a linear speed exceeding 600 feet per minute.

The Web may be supported in its passage to and I through the nip of the press rolls by a carrier of felt or similar absorbent material, said carrier being between the web and the mat. The mat may be entrained in an endless path and after discharging water may be subjected to drying before return to the nip between the press rolls. The system of entrainment of the mat may be over a series of rollers, some of which are positively driven so that the mat likewise is positively moved. The rolls preferably are so located that the mat diverges away from the travelling web after passage through the nip of the press rolls, in such manner that the water received within the openings in said mat is not thrown therefrom back on to the traveling web. At a point remote from the web, the mat is entrained around a roller of such diameter that the water received in the openings of the mat will be released therefrom by centrifugal force and discharged away from the web.

In FIGURE 1, an apparatus for carrying out the essential steps of the invention is diagrammatically illustrated. In FIG. 2 a perforated roll which may be employed in the process and apparatus of the invention is shown. And the following description of the exemplary type apparatus is merely to assist in an understanding of the preferred procedure of the present invention.

7 Referring to the drawing, there is shown in side elevation, a system of entrainment of a Water receiving mat 1 through the nip of a pair of cooperating press rolls 3 and 4. The mat 1 shown in the drawing is in the form of an endless "belt containing perforations which receive Water pressed from the web 5 andfelt carrier strip 6 at the nip 2 of the press rolls 3 and 4. That mat carries the water from the nip 2 of the press rolls 3 and 4, thus preventing reabsorption of the water by the felt 6 and the web 5 or a rewetting of the web 5 or felt 6 by water thrown from the press roll 4. A wet or moist traveling web 5 of paper is fed through the nip 2 of the cooperating press rolls 3 and 4 together with a supporting felt 6. The path of the web 5 of paper and the supporting felt 6 after passage 3 through the nip 2 is indicated at 7 and the path of the water receiving mat 1 after passage through said nip is indicated at 8. The path 8 diverges downwardly away from the path 7, as shown, at an acute angle with respect to the supporting felt 6 after passage through nip 2, so that water which is held by the mat 1 along path 8 will not be thrown back therefrom onto the supporting felt 6.

Located at the end of the path 8 of the water receiving mat 1 is a roll 9 of such diameter that as the mat travels therearound water held in the openings in said mat is subjected to centrifugal force whereby it is discharged into a receiving trough 10. The mat 1 is then led around a plurality of rolls 11, 11a, 11b and 110 and in its course of travel therearound is subjected to drying before return to the nip 2 between the press rolls 3 and 4. Water collected in the trough 10 is led away through an outlet pipe 12. A second water trough 13 is located below the path 8 so that any water falling from the mat 1 as it travels along said path 8 is collected in the trough 13 from whence it is led away through an outlet pipe 14.

The two press rolls 3 and 4 may be of any known construction and, due to the provision of the water receiving mat 1, the lower press roll 4 need not have a perforated shell and include a suction chamber but instead may be provided with a smooth and continuous surface. The wet paper web 5 is carried by the supporting felt 6 into and through the nip 2 of the press rolls 3 and 4 and as they pass therebetween, water is squeezed out and is received by and held in the openings in the mat 1. The mat 1 carries the squeezed out water through the nip 2 and down the path 8 but as hereinbefore mentioned the direction of the path 8 is such that the water held in the openings of the mat 1 is not thrown back by centrifugal force, after passage through the nip 2, onto the supporting felt 6.

As will be seen from the accompanying drawing, after passage through the nip 2 there is a tendency for the travelling web of paper 5 to billow up momentarily as indicated at 15 off the supporting felt 6. The paper web which now is partially .dry, then falls back onto the supporting felt 6 and is carried thereby along the path 7 over guide roll 16 for passage through subsequent drying stages of the paper making machine.

While it is preferred to employ solid press rolls in the process and apparatus of the invention, perforated rolls such as that illustrated in FIG. 2 may be employed. Although suction applied interiorly of the rolls is unnecessary to achieve the objects of the invention, suction may be employed if desired.

The method of de-waten'ng a wet or moist travelling web of absorbent material is particularly useful in papermaking machines which run at a speed exceeding 450 feet per minute and more desirably at a speed exceeding 600 feet per minute, and in fact can be used in apparatus running up to speeds exceeding 3000 feet per minute.

The water receiving mat preferably is made of rubber, plastic or like flexible solid substance which mat is in the order of /2" thick and is perforated to provide the openings. These perforations are sufficiently large to prevent water being received therein from being held by capillary action to an extent which would prevent release of the water by centrifugal force. Furthermore the perforations are preferably so dimensioned as not to cause impressions to be left in the travelling web as it passes from the nip between the press rolls. Alternatively, the mat can be formed from open mesh fabrics and possibly felts, woven from relatively non-absorbent material, the interstices of the fabric or felt constituting the openings.

A press constructed as hereinbefore described and incorporated in a paper making machine considerably improves the efficiency and simplicity of operation of the press as compared with existing solid or suction presses. In a solid press, the water squeezed out thereby runs off in front of the nip against the travel of the web therethrough and down the front of the lower press roll. With a press constructed as hereinbefore described the water squeezed out of the wet travelling web is carried through the nip of the press by the water receiving mat which water is subsequently removed therefrom by centrifugal force. It will be understood, of course, that not all the water necessarily will be removed by centrifugal force and therefore it is preferable to subject the mat to further drying operations prior to being passed back into the nip between the press rolls. Such drying operations may conveniently be performed by the application of pressure or suction to the mat.

While the method herein described is for the purpose of illustration only, it is to e understood that the present invention includes all modifications and equivalents which fall within the scope of the invention which is defined in the appended claims.

What is claimed is:

1. A method of dewatering a wet or moist web of paper or a web of other absorbent material comprising passing the web through the nip of a pair of cooperating press rolls together with a water-receiving mat having cavities at the nip of the rolls to receive and hold water squeezed out of the web at the nip of the press rolls, entraining water pressed from the web in the cavities of the waterreceiving mat after passage through the nip, moving the web and the mat carrying entrained water along divergent paths away from the surface of said rolls, said mat being removed at an acute angle to the Web.

2. A method according to claim 1 in which the surfaces of the press rolls are free from suction applied interiorly of the rolls.

3. A method of dewatering a wet or moist web of paper or a web of other absorbent material comprising passing the web through the nip of a pair of cooperating press rolls together with a water-receiving mat having sufiicient cavities at the nip of the rolls to receive and hold substantially all the Water squeezed out of the web at the nip of the press rolls, entraining water pressed from the web in the cavities of the water-receiving mat after passage through the nip, moving the web and the mat carrying entrained water along divergent paths away from the surface of said rolls, said mat being moved in the general direction of a tangent to the rolls at the nip thereof.

4. A method according to claim 3 in which the mat is in the form of a continuous belt and entrained water is removed therefrom subsequent to its divergence from the path of the web.

5. A method according to claim 3 in which the web and mat are passed through the nip of the press rolls together with a water absorbent strip of material.

6. A method according to claim 3 in which the surfaces of the press rolls are free from suction applied interiorly of the rolls.

7. Dewatering apparatus for removal of water from a traveling web of paper or other absorbent material comprising a pair of press rolls; a water-receiving mat adapted to pass through the nip of the rolls with the web, said mat containing cavities at the nip of the rolls to receive and hold water squeezed out of the 'web at the nip of the press rolls; means for insertion of said mat into the nip of the press rolls with the web and means for removing the mat from the press rolls at an acute angle to the web.

8. Dewatering apparatus for removal of water from a traveling web of paper or other absorbent material comprising a pair of press rolls substantially free from internally applied suction; a water-receiving mat adapted to pass through the nip of the rolls with the web, said mat containing sufficient cavities at the nip of the rolls to receive and hold substantially all of the water squeezed out of the web at the nip of the press rolls; means for insertion of said mat into the nip of the press rolls with the web and means for removing the mat from the press rolls in a direction generally tangent to the rolls at the nip thereof.

9. Apparatus according to claim 8 in which the mat is in the form of a continuous belt.

10. Apparatus according to claim 8 in which the web and mat are passed through the press rolls with a waterabsoribent strip. 5

11. Apparatus according to claim 8 in which the press rolls have solid surfaces.

12. Apparatus according to claim 8 in which at least one of the press rolls has a perforated surface.

13. Apparatus according -to claim 8 in which the surfaces of the press rolls are free from suction applied interioi'ly of the rolls.

References Cited in the file of this patent UNITED STATES PATENTS Sheehan May 5, 1925 Asten Dec. 14, 1926 Geer et a1 Mar. 20, 1928 Chalon Sept. 5, 1933 Blarstow Oct. 30, 1934 Brodin Apr. 28, 1936

Claims

1. A METHOD OF DEWATERING A WET OF MOISTE WEB OF PAPER OR A WEB OF OTHER ABSORBENT MATERIAL COMPRISING PASSING THE WEB THROUGH THE NIP OF A PAIR OF COOPERATING PRESS ROLLS TOGETHER WITH A WATER-RECEIVING MAT HAVING CAVITIES AT THE NIP OF THE ROLLS TO RECEIVE AND HOLD WATER SQUEEZED OUT OF THE WEB AT THE NIP OF THE PRESS ROLLS, ENTRAINING WATER PRESSED FROM THE WEB IN THE CAVITIES OF THE WATERRECEIVING MAT AFTER PASSAGE THROUGH THE NIP, MOVING THE WEB AND THE MAT CARRYING ENTRAINED WATER ALONG DIVERGENT