AU633627B2 - Papermaking machine in which the paper web is supported in the draw between the press and dryer sections - Google Patents

Description

633627 SPECIFICATION COMPLETE FOR OFFICE USE Application Number: Lodged: Class: Int. Class: Complete Specification Lodged: Accepted: Published: Priority: Related Art: TO BE COMPLETED BY APPLICANT Name of Applicant: Address of Applicant: Actual Inventor/s: Address for Service: APPLETON MILLS 2100 North Ballard Road, Appleton Wisconsin 54911, United States of America THOMAS GEORGE GULYA DAVID RAY TURNER SMITH SHELSTON BEADLE 207 Riversdale Road (P 0 Box 410) Hawthorn Victoria 3122 Australia (Attorney Code SA) Complete Specification for the invention entitled: PAPERMAKING MACHINE IN WHICH THE PAPER WEB IS SUPPORTED IN THE DRAW BETWEEN THE PRESS AND DRYER SECTIONS The following statement is a full description of this invention, including the best method of performing it known to me/us: Page 1 Our Ref: #6224 JC:BC:GD 58app f

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-1- The conventional papermaking machine includes a press section having one or more pairs of cooperating press rolls and the wet paper web is supported on a papermaker's felt as it passes through the nip between the cooperating rolls, thereby extracting water from .2 the web. After leaving the press section, the paper web is transferred to the dryer section which can a 0 consist of a plurality of heated dryer rolls. The paper web passes sequentially around the dryer rolls to \0 remove further moisture from the paper.

In some installations, there is a substantial draw or span between the press section and the dryer section. The paper web is fairly wet and heavy, so that the web can sag in this draw and possibly break.

I5 A papermaking machine can be operating at a speed in the neighborhood of 2,000 ft. per minute, and if the web breaks, the paper web must be re-fed th:rough the entire press and dryer sections and this not only a a results in a loss of product, but also results in sub- 0 stantial downtime for the papermaking machine.

Sag in the draw between the press section and the dryer section can be minimized by increasing the tension on the paper web, but an increase in tension will correspondingly tend to stretch the paper web and S increase the tendency for breakage.

A dryer section of a conventional papermaking machine may include about ten to twelve steam heated dryer rolls or cylinders, commonly referred to as cans,

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e i o ft 0 0 ft a o i o t +J4 1 0 eO O 0 0 0t a o+ a 0 0 m a c -2and the first or upstream roll in the section, to which the wet paper web is transferred from the press section of the machine, is at a lower temperature than other downstream rolls. In practice, the upstream dryer roll S will have a surface temperature of approximately 140°F to 150 0 F, and the surface temperature of the next several downstream rolls will be progressively increased to a value of approximately 280 0 F to 325 0 F, and this higher surface temperature will then be maintained lo throughout the remaining rolls of the series. By maintaining the temperature of the first dryer roll at a lower value, possible blistering and delamination of the paper web is prevented, and the lower temperature will also eliminate the tendency of the paper web to s adhere to the roll.

Summary of the Invention The invention is directed to a papermaking machine in which the wet paper web is supported by the press section felt as it is transferred from the press 2-o section to the dryer section of the machine, thereby preventing sagging and possible breakage of the web.

The press section includes a pair of cooperating press rolls and an endless papermaker's felt supports the paper web as it passes between the press rolls to extract water from the wet web.

The papermaking machine also includes a dryer section consisting of a group of heated dryer rolls, and the press section felt travels from the press rolls of the press section and passes around at least one of S0 the dryer rolls, so that the felt acts to support the wet paper web in the span or draw between the press section and the dryer section and insulates the paper web from the dryer roll.

As the wet paper web is supported in the S6 draw, sagging and possible breaking of the web is pre- -3 vented in this area. As the tcndency for breakage is minimized, product loss is minimized and downtime of the machine is correspondingly decreased.

Because the press felt is interposed between the heated dryer roll and the paper web, the paper web is insulated from the heated roll, and as a result the dryer roll can be operated at a substantially higher temperature than normal. By increasing the surface temperature of the upstream dryer roll, the number of dryer rolls in the dryer section can be reduced, thereby providing a substantial saving in capital expenditure.

As a further advantage, the press felt, after passing in contact with the heated dryer roll, will retain a portion of the heat through its endless travel so that the felt will be at an elevated temperature as it passes through the nip between the press rolls. Due to the increase in temperature of the felt at the nip, the viscosity of the water in the paper is reduced, thereby increasing the effectiveness of the water extraction at the nip and thus decreasing steam consumption in the dryer section.

Accordingly, in one aspect, the present invention provides a papermaking machine comprising, a press section including a pair of cooperating press rolls, a papermaker's felt for supporting a paper web in the nip between said press rolls, a dryer section including plurality of heated dryer rolls, said felt being mounted for endless travel and passing around a first of said dryer rolls, said felt being unsupported over a substantial distance extending between said press rolls and said first dryer roll and said web being supported 20 on the upper surface of the felt as said felt passes through said distance, said felt begin in direct contact with said first dryer roll and the portion of the paper web supported on said felt and passing around said first dryer roll being exposed and free of confinement.

Other objects and advantages will appear in the course of the following description.

The drawings illustrate the best mode presently contemplated of carrying out the invention.

The drawing is a schematic representation of a portion of a papermaking machine incorporating the invention.

DjESCRIPION OF THE ILL.U.-STRATED EMBODIMEN' The drawing is a schematic representation of a portion of a papermaking machine including a press section 1 and a dryer section 2. Press section 1 includes a pair of cooperating press rolls 3 and 4 and NB-#6224.spc NB-#624.spc16 Odnbcr IM9 i I. .i iiL rm;iMlia=lii~ -4ps o a 0I *0*f a, a a wet paper web 5 is supported by a papermaker's Eelt 6 as it passes through the nip between the press rolls 3 and 4. The paper web can be any type of paper, preferably heavier paper, such as liner board, newsprint, writing paper, or the like.

The papermaker's felt 6 is endless in configuration and can consist of natural fibers, synthetic fibers, or a combination thereof. The particular construction or composition of the felt is 1o not critical to the invention.

Felt 6 is supported in its endless travel by a plurality of idler rolls, indicated by 7a 7i. In addition, the felt 6 passes around a tensioning or stretch roll 8, which is located between the rolls 7f 15 and 7g. Roll 8 operates in a conventional manner to provide the desired tension on the felt 6.

Dryer section 2 includes a plurality of conventional heated dryer rolls, three of which are shown in the drawing, and indicated by 9, 10 and 11. In 20 practice the dryer section may include up to ten or more rolls which are steam heated to a temperature in the range of 150°F to 280 0 F. The temperature of the rolls in the group may be varied, with the highest temperature being located at the downstream end of the 2-S dryer section.

0 a .a o* o o 0 o oo I o a In certain installations, there may be a considerable gap or draw between press section 1 and dryer section 2 and this draw can be in the neighborhood of to 15 feet. When dealing with a heavier weight 3o paper, such as liner board, the paper web will be fairly wet and heavy as it leaves the press section, with the result that the paper web has a tendency to sag in the draw between press section 1 and dryer section 2.

If the web should break, the paper web from the forming 3S section must be dropped into a disposal site and then 1 ,i i_ re-fed through the press section an dryer section.

Refeeding the web may take from one-half to threequarters of an hour and this down time results in a substantial decrease in the production rate of the papermaking machine.

To eliminate the sagging of the paper web in the draw between the press section and the dryer section and thereby prevent possible breaking of the web, the felt 6 from the press section is passed around at \o least one of the dryer rolls or cylinders in the dryer o section. As illustrated, the felt is passed around dryer roll 9 and thus supports the paper web in the o° draw between the press rolls 3,4 and the dryer roll 9.

As illustrated, the web 5 is located on the 5 outside of felt 6 as it passes around dryer roll 9 and the web then travels around roll 10 and 11. A conventional dryer fabric 12 is mounted for endless travel in the dryer section and as shown, travels around a pair of idler rolls 13. The dryer fabric 12 operates in a 2- conventional manner to support the paper web against the heated dryer rolls to aid in removal of moisture from the web.

In certain installations, the first or upstream heated dryer roll in the dryer section may have a smaller diameter than the remaining dryer rolls SC of the section and, as such, may be referred to as a "baby" roll or can.

As shown in the drawing, the press felt 6 is interposed between the heated upstream dryer roll 9 and the paper web 5, thus insulating the paper web from the heated roll. Because of the insulating effect, the dryer roll 9 can be operated at a higher temperature than normal, generally in the range of about 240 0 F to 280 0 F, as opposed to a conventional system where the upstream dryer roll, such as roll 9, is operated at a

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-6temperature of about 140°F to 150°F. This also results in the succeeding downstream dryer rolls, such as and 11, being operated at a higher temperature than conventional. For example, dryer roll 10, which is in j direct contact with paper web 5, can have a surface temperature of approximately 180°F to 200°F, well above the surface temperature of 140°F to 160°F employed in a conventional dryer section, and dryer roll 11 can be operated at a temperature of 190°F to 210°F, again well 'o above the temperature utilized in conventional practice. Thus, the final elevated temperature of about 280°F is reached at an earlier stage in the dryer section, thus greatly improving the efficiency of the dryer operation, and enabling a lesser number of dryer iS rolls to be used in the dryer section.

As a further advantage, the press felt 6 passing over the heated dryer roll 9 will be heated and will retain a good portion of the heat throughout its endless travel, so that the felt returning to the nip between press rolls 3 and 4 will be at a temperature above 120°F and generally at a range of about 140°F to 180°F. This increased temperature will result in a reduction in the viscosity of the water, thus providing |I a more effective water extraction at the nip. It has been found that for every 18°F increase in temperature at the nip, a 1% increase in water removal is I achieved. In a conventional papermaking machine, a paper web is normally at a temperature of about 100OF as it passes through the nip between press rolls 3 and 4. As this temperature is increased to a range of 140°F to 180°F in the invention, an increase in water removal of 2% or more is achieved, thus resulting in a substantial energy saving in the overall operation.

4 -7- The position and number of the idler rolls 7 in the press section is not critical and various paths of travel for the felt are contemplated depending upon the requirements of the papermaking machine.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

The claims form part of the disclosure of this specification.

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Claims (5)

1. 2. The machine of claim i, wherein said felt is wrapped around said first dryer roll through an arc of at least 900.
2. 3. The machine of claim i, wherein said dryer section includes a second dryer roll spaced from said first dryer roll, said paper web mounted to travel from said first dryer roll to said second drawer roll and being unsupported in the space between said dryer rolls.
3. 4. A method of papermaking, comprising the steps of mounting a press felt for travel in an endless path, positioning a first upstream dryer roll of a series of dryer rolls within said endless path so that said felt passes in direct contact with said first dryer roll, heating said first dryer roll to an elevated temperature, supporting a wet paper web on said felt, passing the felt and the supported web through a pressure nip to thereby extract water from said web, thereafter passing said felt and the supported web around said first heated dryer roll with said felt separating said web from said heated dryer roll, exposing the outer surface of the portion of the web passing around the first dryer roll so that said outer surface is free of confinement to thereby heat said felt gn\01\6224 res 92 11 27 -9 and said web, separating the web from the felt, passing the web around the remaining downstream dryer rolls in said series, and returning the heated felt to the pressure nip in position to support said paper web.
4. 5. A papermaking machine substantially as hereinbefore described with reference to the accompanying drawing.
5. 6. A method of papermaking substantially as hereinbefore described with reference to the accompanying drawing. DATED November 27, 1992 CARTER SMITH BEADLE Fellows Institute of Patent Attorneys of Australia Patent Attorneys for the Applicant: APPLETON MILLS Va 9 i 0 C gn\01\6224.res 92 11 27