DE20106685U1 - Press arrangement - Google Patents

Description

Voith Paper Patent GmbH File: PC11221 DE G Sankt Pöltener Strasse 43 "Sandwich vacuum cleaner" D-89522 Heidenheim

Press arrangement

The invention relates to a press arrangement for dewatering a paper, cardboard, tissue or other fibrous web in a machine for producing the same with at least one press nip formed by two press rolls, through which a press felt runs on both sides next to the fibrous web.

However, particularly at high web speeds, the removal of the upper press felt from the fibrous web after the press nip causes problems. The edge area of the fibrous web is particularly critical. The edge often does not separate from the upper press felt immediately, resulting in what is known as edge picking. As a result, tears or even breaks in the fibrous web are not unusual.

The object of the invention is therefore to ensure a safe guidance of the fibrous web during and after the removal of the upper press felt.

According to the invention, the problem was solved in that after the press nip, both press felts, together with the fibrous web, partially wrap around a guide roller of the lower press felt and run to a suction box that is in contact with the lower press felt, whereby the upper press felt is guided away from the fibrous web in the area of the suction box. The deflection at the guide roller causes the upper press felt to be easily detached from the fibrous web - especially when the guide roller is being vacuumed. The negative pressure emanating from the suction box then enables the upper press felt to be guided away from the fibrous web without any problems.

The negative pressure of the guide roller and the suction box acts through the lower press felt and thus strengthens the adhesion of the fibrous web to the lower press felt. The upper press felt is advantageously guided away from the fibrous web in the initial area of the suction box.

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In order to stabilize the movement of the lower press felt, the contact surface of the suction box should be convexly curved towards the lower press felt at least in one section, preferably at the beginning. However, it can also be advantageous if the entire or at least the majority of the contact surface of the suction box is convexly curved towards the lower press felt. A special design is achieved if the contact surface of the suction box has a stronger convex curvature in a section, preferably at the beginning, than in the rest of the section. Advantages in terms of guiding the fibrous web can be seen if the upper press felt is guided away from the fibrous web in the area of the section of the contact surface that is convexly curved at all or most.

To ensure the limitation of the interior space of the suction box, which is connected to a vacuum source, the box has several suction slots running approximately transversely to the web travel direction.

The device according to the invention allows the upper press felt to be guided away from the fibrous web in the region of the first suction slot, so that the adhesion of the fibrous web to the lower press felt can be further increased in the further course of the suction box.

In order to counteract edge fluttering and edge picking of the fibrous web, the suction box should have a separate vacuum zone with increased negative pressure in the area of the edges of the fibrous web.
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The invention will be explained in more detail below using an exemplary embodiment. In the attached drawing, the figure shows a schematic cross section of a press arrangement of a paper machine for dewatering the fibrous web 1.

The fibrous web 1 runs with a press felt 4,5 on both sides through a press nip formed by two press rollers 2,3. While the lower press roller 3 is cylindrical

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is designed, the upper press roller 2 has a flexible roller shell which runs over a pressure shoe with a concave contact surface to form an extended press gap. Of course, a reversal of this press roller arrangement, i.e. an upper cylindrical press roller 3, is also possible.
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The press felts 4, 5 absorb the water pressed out of the fibrous web 1 in the press nip. The water that reaches the press rollers 2, 3 via the press felts 4, 5 is spun off by these after the press nip and collected by suitable, known water collecting devices 12.

After the press nip, the fibrous web 1 runs together with both press felts 4, 5 over a suction-operated guide roller 6 of the lower press felt 5. This guide roller 6 has a perforated roller shell, the interior of which is connected to a vacuum source. This vacuum acts on the fibrous web 1 through the lower press felt 5 and thus strengthens the adhesion of the fibrous web 1 to the lower press felt 5.

The press felts 4, 5 with the fibrous web 1 then reach a suction box 7 that is in contact with the lower press felt 5. This suction box 7 has a contact surface that is convexly curved towards the lower press felt 5. The demarcation of the interior of the suction box 7, which is connected to a vacuum source, from the lower press felt 5 is ensured by the formation of several suction slots 9 in the contact surface that run transversely to the web travel direction 8.

Here too, the negative pressure of the suction box 7 causes an increased adhesion of the entire fibrous web 1 to the lower press felt 5, so that the upper press felt 4 can be guided away from the fibrous web 1 already in the area of the first suction slot 9 of the suction box 7.

The immersion of the suction box 7 into the path of the lower press felt 5 causes stabilization so that no vibrations of the lower press felt 5 and detachment of the fibrous web 1 can occur.

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The fibrous web 1 is then transferred to a belt 10, for example a drying screen of a subsequent drying section of the paper machine, which is supported by a suction-fed guide roller 11.

In the interest of good guidance of the fibrous web 1, a guide roller of the lower press felt 5 following the suction box 7 should be driven.

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Claims (10)

1. Press arrangement for dewatering a paper, cardboard, tissue or other fibrous web ( 1 ) in a machine for producing the same with at least one press nip formed by two press rollers ( 2 , 3 ), through which a press felt ( 4 , 5 ) runs on both sides next to the fibrous web ( 1 ), characterized in that after the press nip both press felts ( 4 , 5 ) together with the fibrous web ( 1 ) partially wrap around a guide roller ( 6 ) of the lower press felt ( 5 ) and run to a suction box ( 7 ) in contact with the lower press felt ( 5 ), the upper press felt ( 4 ) being guided away from the fibrous web ( 1 ) in the region of the suction box ( 7 ). 2. Press arrangement according to claim 1, characterized in that the guide roller ( 6 ) of the lower press felt ( 5 ) is designed as a suction-fed guide roller. 3. Press arrangement according to claim 1 or 2, characterized in that the upper press felt ( 4 ) is guided away from the fibrous web ( 1 ) in the initial region of the suction box ( 7 ). 4. Press arrangement according to one of the preceding claims, characterized in that the suction box ( 7 ) has a contact surface which is convexly curved towards the lower press felt ( 5 ). 5. Press arrangement according to claim 4, characterized in that the contact surface of the suction box ( 7 ) has a stronger curvature in a section, preferably at the beginning. 6. Press arrangement according to one of claims 1 to 3, characterized in that the contact surface of the suction box ( 7 ) is convexly curved in a section, preferably at the beginning, towards the lower press felt ( 5 ). 7. Press arrangement according to one of the preceding claims, characterized in that the suction box ( 7 ) has a plurality of suction slots ( 9 ) running approximately transversely to the web running direction ( 8 ). 8. Press arrangement according to claim 7, characterized in that the upper press felt ( 4 ) is guided away from the fibrous web ( 1 ) in the region of the first suction slot ( 9 ). 9. Press section according to one of claims 5 to 8, characterized in that the upper press felt ( 4 ) is guided away from the fibrous web ( 1 ) in the region of the generally or most strongly convexly curved section of the contact surface. 10. Press section according to one of the preceding claims, characterized in that the suction box ( 7 ) has a separate vacuum zone with increased negative pressure in the region of the edges of the fibrous web ( 1 ).