Paper Web Transfer System Carrying The Web From Forming Wire To Press Section

Abstract

Apparatus for transferring a paper web from a papermaking machine forming wire to a press section. A suction pick-up roll located adjacaent the forward run of the forming wire is wrapped in part by a first endless pick-up felt which picks the web up from the forming wire and carries it through the first press nip of the press section. Prior to contacting the paper web the first felt passes through a press nip (for liquid removal) formed between the suction pick-up roll and a press roll. A second felt (i.e., lower support felt) contacts the web carried by the first pick-up felt between the forming wire and press section.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the field of pressing a fiber web in a press section.

2. Description of the Prior Art

Various arrangements have been introduced previously for the pressing of a paper web. U.S. Pat. No. 2,911,040 introduces a pressing part which is situated at a distance from the pick-up roll in the moving direction of the paper. The arrangement introduced in this patent has, however, the disadvantage that the part of the felt between the pick-up point and the first pressing point is under tension and the wet paper web stretches in this area. This takes place, in spite of the fact that the pick-up roll and the pressing roll rotate at the same peripheral speed, since slipping of the felt occurs at the pick-up roll. Due to stretching of the paper web, an orientation of the fibers takes place in the longitudinal direction which diminishes the longitudinal elasticity of the finished paper. Owing to the different longitudinal and transversal orientations of the fibers the finished paper sheet will not remain even.

SUMMARY OF THE INVENTION

According to the invention the pick-up felt is pressed against the pick-up roll by means of a press roll to eliminate slipping of the felt and stretching of the web.

The paper produced in accordance with the invention has better elasticity than paper manufactured by prior known methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematically a press section of a paper machine for carrying out the method according to the invention, and

FIGS. 2-6 illustrate schematically alternative embodiments of the press section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, 13 is the wire of the web-forming part, from where the suction roll 2 working as a pick-up roll moves the paper web 12 with the suction effect of the roll to the endless felt 8. The suction roll, together with roll 1, forms a press nip through which the felt 8 runs. The felt and the paper web run to roll 3 at a distance from roll 2; roll 3 and roll 4 together form another press nip, where liquid is pressed out of the paper web 12. Thereafter the paper web is separated from the felt and it runs to the next pressing point which is formed by roll 4 together with roll 5. A suitable roll combination is a suction roll 3, a stone roll 4, and a grooved roll 5. The direction of the movement of the paper web is illustrated by arrows.

Because the felt runs through two press nips at a distance from each other, with no slipping occuring at the pressing points, it is possible, by choosing a somewhat lower peripheral speed for roll 3 than for roll 2, to obtain a longitudinal shrinking of the felt and thus also of the paper web between the pressing points, in which case the elasticity of the finished paper increases. FIG. 1 also illustrates the drying and cleaning devices 15 of the endless felt 8 and the respective devices 16 of the pressing felt 14.

To keep the felt and the paper track essentially horizontal between the pressing points, an endless, synchronically moving, wire 9 can be placed below them. An arrangement like this is illustrated in FIG. 2. FIG. 5 illustrates a corresponding arrangement in a case in which the rolls 6 and 7 of the supporting wire 9 participate in forming the pressing points.

The felt and the web can be supported in other ways as well. In the application according to FIG. 3, a suction box 10 has been fitted above the felt to keep the felt part horizontal. In the case according to FIG. 4, a blowing device 11 has been respectively fitted below the felt; this device creates a cushion of air to support the felt part.

The pair of rolls 1 and 2 forms the so-called washing press of the felt and removes from the felt liquid that has been absorbed by it. Because the paper web is supported between rolls 2 and 3, the felt can be relatively dry there, in which case the proportionate dryness of the paper web, also, will be high after the first pressing point.

According to another embodiment, shown in FIG. 6, the paper web travels from the upper pick-up felt 8 running around the pick-up roll 2, to the lower support felt 9 at the pressing point formed by pressing roll 6, which is inside the lower felt, together with the pick-up felt. The paper track, supported by the lower felt, runs to the next pressing point formed by pressing roll 7, which is inside the lower-felt loop, together with pressing roll 3, onto which the paper web moves following the pressing point. Thus the embodiment of FIGS. 5 and 6 have in common the passage of the upper pick-up felt alone through a press nip, a second press nip through which the web is passed between two felts, and a third nip through which the paper web passes along with the support felt. In both of these cases the web is separated from the felt by appropriate guide means as shown by the arrows and the small rolls for the departing felts 8 and 9 in the two embodiments.

On the straight part of the felt between the pressing points of shrinking, or in certain cases also a so-called microcreping, of the paper web can be obtained which improved the elasticity of the paper. The pick-up roll is a positive one and the pressing roll in contact with it may also be positive. Both or one of the rolls of the pressing point after the straight felt part may be positive. The numbers of revolutions of the first and the second pressing points can be changed without gradation so that the speed of the felt at these points may be the same or greater at the first pressing point than at the second.

Suction rolls, rolls with different coatings, smooth rolls, or grooved rolls, in suitable combinations, can be used as pressing rolls, as in paper machines in general.

Claims

What is claimed is:

1. An improved press section in a web forming machine of the type having at least two traveling endless felts for contacting and carrying the web, which includes a pick-up roll urging a pick-up felt against the web for transferring the web to the felt, said pick-up felt passing around said pick-up roll and through a press nip for the pick-up felt defined between a press roll and said pick-up roll, a second press roll opposedly positioned to said pick-up roll and defining a second press nip between said pick-up roll and said second press roll through which the web, said pick-up felt and a support felt pass, the web being carried through said second press nip between said felts; a pair of further press rolls located at a distance from said pick-up roll, said pair of press rolls defining therebetween a third press nip through which said support felt and said web pass, the distance between said second press nip and said third press nip serving to eliminate slipping of the felt and stretching of the web; said support felt supporting the web between said second and third press nips; one roll of each of said second and third press nips constituting a guiding roll for said support felt, and roll means for separating the web from the felt after said third press nip.