Papermaking machine in which the paper web is supported in the draw between the press and dryer sections

Abstract

 The invention is directed to a papermaking machine in which the wet paper web (5) is supported by the press section felt (6) as it is transferred from the press section (1) to the dryer section (2) of the machine, thereby preventing sagging and possible breakage of the web. According to the invention, the felt (6) is mounted for endless travel and passing around at least a first (9) of said dryer rolls, said felt being unsupported over a substantial distance extending between said press rolls (3, 4) and said first dryer roll (9) and said web being carried on the upper surface of the felt as said felt travels through said distance.
As the wet paper web is supported in the draw, sagging and possible breaking of the web is prevented in this area. As thee tendency for breakage is minimized, product loss is minimized and downtime of the machine is correspondingly decreased.

Description

Background of the Invention

[0001] 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 the web. After leaving the press section, the paper web is transferred to the dryer section which can con­sist of a plurality of heated dryer rolls. The paper web passes sequentially around the dryer rolls to remove further moisture from the paper.

[0002] 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. 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 through the entire press and dryer sections and this not only results in a loss of product, but also results in sub­stantial downtime for the papermaking machine.

[0003] 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 increase the tendency for breakage.

Summary of the Invention

[0004] 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 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.

[0005] 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 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.

[0006] As the wet paper web is supported in the draw, sagging and possible breaking of the web is pre­vented in this area. As the tendency for breakage is minimized, product loss is minimized and downtime of the machine is correspondingly decreased.

[0007] Other objects and advantages will appear in the course of the following description.

Description of the Drawings

[0008] The drawings illustrate the best mode presently contemplated of carrying out the invention.

[0009] The drawing is a schematic representation of a portion of a papermaking machine incorporating the invention.

Description of the Illustrated Embodiment

[0010] The drawing is a schematic representation of a portion of a paper making 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 a wet paper web 5 is supported by a papermaker's felt 6 as it passes between through the nip between the press rolls 3 and 4. The paper web can be any type of paper, preferably heavier weight paper, such as liner board, newsprint, writing paper, or the like.

[0011] 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 not critical to the invention.

[0012] 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 and 7G. Roll 8 operates in a conventional manner to provide the desired tension on the felt 6.

[0013] 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 practice, the dryer section may include up to 10 or more rolls which are steam heated to a temperature in the range of 150°F to 280°F. The temperature of the rolls in the group may be varied, with the highest temperature being located at the downstream end of the dryer section.

[0014] 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 10 to 15 feet. When dealing with a heavier weight 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 tendecy to sag in the draw between press section 1 and dryer section 2. If the web should break, the paper web from the forming section must be dropped into a disposal site and then re-fed through the press section and dryer section. Refeeding the web may take from one-half to three-­quaters of an hour and this down time results in a substantial decrease in the production rate of the papermaking machine.

[0015] 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 least one of the dryer rolls in the dryer section. As illustrated, the felt is passed around dryer roll 9 and thus supports the paper web in the draw between the press rolls 3,4 and the dryer roll 9.

[0016] As illustrated, the web 5 is located on the 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 conventional manner to support the paper web against the heated dryer rolls to aid in removal of moisture from the web.

[0017] While the drawing illustrates the felt 6 being located between the dryer roll 9 and the web 5, it is contemplated that in other installations the paper web may be sandwiched between the felt and the dryer roll. Similarly, the felt 6 from the press sec­tion can travel around a plurality of rolls in the dryer section.

[0018] 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.

Claims

1. In a papermaking machine, a press section including a plurality of cooperating press rolls, a papermaker's felt for supporting a paper web in the nip between said press rolls, a dryer section including a plurality of heated dryer rolls, said felt being mount­ed for endless travel and passing around at least 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 carried on the upper surface of the felt as said felt travels through said distance.

2. The machine of claim 1, wherein said press section includes a plurality of idler rolls to support said felt in said endless travel.

3. The machine of claim 1, wherein said felt is wrapped around said first dryer roll through an arc of at least 90°.

4. The machine of claim 1, wherein said dryer section includes a second dryer roll spaced adjacent said first dryer roll, said paper web mounted to travel from said first dryer roll to said second dryer roll and being unsupported in the space between said dryer rolls.

5. In a method of papermaking, the steps consisting of supporting a wet paper web on an endless papermaker's felt, passing the felt and the supported web through a nip between a pair of cooperating press rolls to extract water from said web, passing the felt through a span of distance from the nip to a heated dryer roll, supporting the paper web on the upper sur­face of said felt as said felt passes through said span, separating the web from the felt, and passing the web in heat transfer relation with a plurality of dryer rolls to remove moisture from said web.

6. The method of claim 5, wherein said felt is unsupported in said span.

7. The method of claim 5, and including the step of mounting the felt for travel in an endless path.

Drawing