FI92847B - Paper machine and process for making paper - Google Patents

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

92847

Paper machine and papermaking method. - Pappersmaskin och förfarande för framställning av papper.

The invention relates to a paper machine having a press section comprising a pair of cooperating press rolls, a press felt mounted to move in an endless path and to support a wet paper web through a nip of press rolls, and a drying section comprising a plurality of heated drying rolls. The invention further relates to a papermaking method.

A conventional paper machine includes a press section with one or more pairs of press rolls, and the wet paper web is supported by a papermaking felt as it passes through a nip of cooperating rolls to remove water from the web. After it leaves the press section, the paper web is transferred to a drying section, which may consist of several heated drying rolls. The paper web passes successively around the drying rollers to remove more moisture from the paper.

In some installations, there is a significant tension between the press section and the drying section. The paper web is relatively wet and heavy, so the web may sink and possibly break in this stroke. The paper machine can operate at a speed of the order of 600 m / minute, and if the web breaks, the paper web must be re-fed through the entire press and drying section; this; not only results in product loss, but also significant paper machine downtime.

The depression between the press section and the drying section can be minimized by increasing the tension of the paper web, but at the same time increasing the tension tends to stretch the paper web and increase the tendency to break.

The invention relates to a paper machine in which the wet paper web is supported by a felt of the press section as it passes from the press section of the machine to the drying section, thereby preventing the web from being pressed and possibly broken.

2,92847

The paper machine according to the invention is characterized in that the first of the drying rolls is placed inside said endless path of the press felt, the felt being unprofitable for a considerable distance between the press rolls and the first drying roll, that the paper web is supported on and that the outer surface of the portion of the paper web passing around the first drying roll is exposed and free.

When the wet paper web is supported in the draft, the web is prevented from sagging and possibly breaking in this area. Because the tendency to break is minimized, production losses are minimized and machine failure time is reduced accordingly.

The papermaking method according to the invention is characterized by the features set forth in the characterizing part of claim 3.

Other objects and advantages will become apparent from the following explanation.

The drawing illustrates a presently preferred embodiment of the invention.

The drawing is a schematic representation of a part of a paper machine in which the invention is incorporated.

The drawing is a schematic representation of a part of a paper machine including a press section 1 and a drying section 2. The press section 1 includes a pair of cooperating press rolls 3 and 4, and the wet paper web 5 is supported by a papermaking felt 6 as it passes through the nip between press rolls 3 and 4. The paper web can be any type of paper, preferably heavier paper such as surface paper, newsprint, writing paper or the like.

The papermaking felt is endless in structure and may comprise natural fibers, synthetic fibers, or a combination thereof. The structure or composition of the web is not critical to the invention.

Il 3 92847

The felt 6 is supported in its endless path by a plurality of support rollers, denoted by reference numerals 7A to 71. In addition, the web 6 passes through a tensioning or tensioning roller 8 located between the rollers 7F and 7G. The roll 8 operates in a conventional manner, providing the desired tension to the felt 6.

The drying section 2 contains a number of conventional heated drying rollers, three of which are indicated in the drawing, denoted by reference numerals 9, 10 and 11. In practice, the drying section may contain up to more than 10 rolls which are steam heated to a temperature in the range of 65 ° C to 140 ° C. The temperature of the rolls in the group can be varied, with the highest temperature being placed at the downstream end of the drying section.

In certain installations, there may be a considerable gap between the press section 1 and the drying section 2, i.e. a tension of the order of 3 to 4.5 m. When handling heavier paper such as pinboard, the paper web is relatively wet and heavy when it leaves the press section. in the traction between the press part 1 and the drying part 2. If the web breaks, the paper web must be removed from the forming section to the waste area and then re-fed through the press section and the drying section. Re-feeding the web can take from half an hour to forty-five minutes, and this disruption time causes a significant reduction in production speed on the paper machine.

In order to prevent the paper web from squeezing in the tension between the press section and the drying section, and thus to prevent the web from being broken, the felt 6 coming from the press section is passed around at least one drying roller of the drying section. As shown, so note. pa is guided around the drying roll 9, whereby it supports *. a paper web between the press rolls 3, 4 and the drying roll 9.

According to the figure, the web 5 is located outside the felt 6 as it passes around the drying roll 9, after which the web passes around the rollers 10 and 11. A conventional drying fabric 12 is mounted in the drying section for endless passage, and in the manner shown, it passes around two support rollers 13. The drying fabric 12 conventionally acts to support the paper web against heated drying rollers and to promote the removal of moisture from the web.

Although the figure shows the felt 6 located between the drying roll 9 and the web 5, it has been considered that in other installations the paper web can be guided between the felt and the drying roll. Likewise, the felt 6 of the press section can pass around the roll of several drying sections.

The position and number of the support rollers 7 of the press section are not critical, and different paths of felt may be considered, depending on the requirements set by the paper machine.

The various embodiments of the invention are considered to be within the scope of the patent and the following claims specifically and clearly set forth the subject matter of the invention.

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Claims (3)

92847 A paper machine having a press section (1) comprising a pair of cooperating press rolls (3, 4), a press felt (6) mounted to move in an endless path and to support a wet paper web (5) through a nip of the press rolls (3, 4), and a drying section (2) comprising a plurality of heated drying rollers (9, 10, 11), characterized in that the first (9) of drying rollers (9, 10, 11) is arranged inside said endless path of the compression felt (6), the felt (6) is unprofitable for a considerable distance between the press rolls (3, 4) and the first drying roll (9), that the paper web (5) is supported on the upper surface of the felt (6) as the felt moves said distance, that the felt (6) is in direct contact with the first drying roll (9), and that the outer surface of the part of the paper web (5) running around the first drying roll (9) is exposed and free. Paper machine according to Claim 1, characterized in that the press felt (6) is wrapped around the first drying roll (9) in an arc of at least 90 °. A papermaking method, characterized in that a press felt (6) is arranged to move along an endless path, a first upstream drying roll (9) of a series of drying rolls (9, 10, 11) is placed inside said endless web so that the felt (6) passing in direct contact with said first drying roll (9), heating the first drying roll (9) to an elevated temperature, supporting the wet paper web (5) on the felt (6), passing the felt (6) and the supported web (5) through the press nip to remove water conveying the web (5), the felt (6) and the supported web (5) thereafter around said first heated drying roll (9) with the felt (6) separating the web (5) from the heated drying roll (9), 92847 the web passing around the first drying roll (9) (5) keeping the outer surface of the part exposed and keeping said outer surface free of the felt (6) and the web (5) to heat thus, separating the web (5) from the felt (6), conveying the web (5) around the remaining downstream drying rollers (10, 11) and returning the heated felt (6) to the press nip to support the paper web (5). Il 7 92847 Patentkray