DE102007034645A1 - Press arrangement for dehydrating e.g. paper, has two press nips formed from cylindrical press roller and shoe press roller, where length of one of press nips is reduced to specific range - Google Patents

Abstract

The arrangement has two press nips formed from a cylindrical press roller (4) and a shoe press roller (2), where the length of one of the nips is reduced to more than 80 percentage. A fibrous material web (1) is provided with water-absorbed dehydration volumes (6, 7) through the press nips. A pressing element is provided in a form of a hydraulic piston cylinder unit. The shoe press roller consists of a flexible roller mantel supported by a press shoe with a concave press surface.

Description

The The invention relates to a press arrangement for drainage a paper, board, tissue or other fibrous web in a machine for the production and / or refinement thereof, in which the fibrous web together with at least one in each case water-absorbing drainage tape by at least two Press column is performed and the second or a following Pressing gap extended is executed.

such Press arrangements, in particular with two extended press nips are known and allow for continuous support the fibrous web an intensive drainage at high machine speeds.

Indeed is also an increased initial roughness (aura) to observe what is unacceptable on certain papers.

The The object of the invention is therefore the surface quality to improve as necessary.

According to the invention was solved the problem by the length of the first press nip is changeable.

investigations have shown that the surface quality essentially determined by the length of the first press nip becomes. By changing the press nip length can be relatively easy on the required surface qualities be reacted without major renovations necessary become.

simultaneously the advantages of this press arrangement remain with regard to high machine speeds and get good moisture cross profiles. The length of the second extended press nip remains unchanged.

Around the achievable surface quality as possible To be able to influence comprehensively, the length should be of the first press nip from a maximum value of at least 30%, preferably at least 50% and in particular at least 80% reducible be.

This means that the length of the first press nip is approximately between 30 and 350 mm is changeable. The length of the second Pressing gap is usually between 200 and 400 mm.

there it is in the interest of a simple structure of advantage, if at least the first press nip, preferably at least two press nips each formed by a cylindrical press roll and a shoe press roll become.

A advantageous construction for changing the press nip length Is characterized in that the shoe press roll of the first Pressing gap has a flexible roll shell, of a Press shoe supported with concave pressing surface is, wherein the press shoe of at least two separately controllable and in the web running direction one behind the other pressing elements is pressed to the opposite press roller.

about a change in the compression pressures of the pressing elements can the running in the running direction pressure profile in the first press nip be adjusted according to the requirements. Should the press nip be shortened, the pressing pressure of the preferred reduced in the web running direction first contact element or even set to 0. This leads to a shift of the press nip beginning in web direction.

in principle However, it is also a reduction of the pressing pressure in the web running direction last contact element possible.

there must be taken into account that the press nip length the extent of the area of the press nip in the web running direction is, in which the pressing pressure exceeds a minimum pressure of about 5 bar.

A alternative possibility of changing the press nip length is that the shoe press roll of the first press nip a flexible roll shell has, from a press shoe to the opposite Press roll is pressed, wherein on the axis of the shoe press roll at least two circumferentially successively arranged press shoes different length, especially with different long pressing surface, are present.

In this case, each press shoe should be movable over a rotation of the axis in the press plane of the press nip, as for example in the DE 32 05 664 is described.

While the pressing surface of the long press shoe should be concave, the short press shoe may have a concave or convex pressing surface have.

Should the length of the press nip be changed, so All you have to do is relax the active contact element and activate it Press shoe with the desired length in the press plane to be turned around.

Due to the high water attack in the ers In the press nip, the fibrous web should be guided together with a dewatering belt at least through the first press nip on both sides.

Because of the reduction of the pressure pulse in the first press nip and the associated reduction in dry matter content and wet strength The fibrous web can be advantageous if the maximum machine speed reduced at a shortening of the first press nip, preferably is reduced by 5 to 10%.

Furthermore should be the length of the first press nip at high quality requirements to the fibrous web, in particular to increase the smoothness of shortened fibrous web shortened, preferably to a Pressing gap length shortened between 50 and 150 mm become. This may be required especially for heatset or flexo printing be where the roughness of the fibrous web between 50 and 100 Bendtsen should lie.

on the other hand can in particular at standard newspaper printing the use of an extended, preferably extended to a nip length between 250 and 350 mm, first press nip associated with a slightly reduced surface quality the fibrous web, in particular a lower smoothness satisfy the finished fibrous web. The roughness values in such fibrous webs are between 120 and 200, preferably between 140 and 180 Bendtsen.

following the invention should be closer to several embodiments be explained. In the attached drawing shows:

1 a schematic cross section through a press arrangement;

2 a partial cross section through the first press nip with the pressure course through the first press nip;

3 a partial cross section through another first press nip and

4 a cross-section through another press arrangement.

The pressing arrangement according to 1 has two press gaps, each of which is exemplified by an upper shoe press roller 2 . 3 and a cylindrical press roll 4 . 5 be formed.

Through this press column, the fibrous web runs 1 together with a water-absorbing and permeable drainage band on both sides 6 . 7 . 8th . 9 in the form of an endless revolving press felt.

The upper drainage band takes over 6 the first press nip the fibrous web 1 from a forming sieve 10 an upstream shaper for sheet formation. After the first press nip, the fibrous web becomes 1 until the removal of the upper drainage band 6 from both drainage tapes 6 . 7 guided.

The lower drainage band 7 hands over the fibrous web 1 then to the upper drainage band 8th of the second press nip. After the second press nip leads the lower drainage tape 9 the second press nip the fibrous web 1 until transfer to an air-permeable dryer 11 a subsequent drying arrangement alone.

In the drying arrangement, the fibrous web becomes 1 from the dryer 11 alternately over heated drying cylinders 17 and guide rolls.

To the adhesion of the fibrous web 1 on the respective air-permeable belt 6 . 7 . 8th . 11 during the takeover of the fibrous web 1 or the routing of a band 6 To improve, the accepting ligaments entwine 6 . 7 . 8th . 11 during the takeover or the Wegführung an evacuated guide roller 13 . 14 . 15 . 16 ,

At the in 4 shown pressing assembly wraps around the upper drainage tape 6 after the first press nip together with the fibrous web 1 an evacuated guide roll 14 so that the lower drainage tape 7 from the fibrous web 1 can be carried away.

The vacuumed guide roller 14 in turn forms with one of a smooth transfer ribbon 18 entangled central press roll 5 a press nip with pressing pressures between 10 and 150 kN / m, preferably between 10 and 80 kN / m.

After this transfer press nip the fibrous web runs 1 alone on the transfer belt 18 to one between the press roll 5 and one, from an upper drainage band 8th looped shoe press roll 3 formed, extended press nip.

Because of the increased adhesion of the fibrous web 1 on the smooth transfer ribbon 18 can the upper drainage tape 8th easily after the press nip of the fibrous web 1 be carried away.

The transfer band 18 hands over the fibrous web 1 then to the drying wire 11 a following drying arrangement.

Such press arrangements are with a large dewatering performance and high Maschi connected speeds. In addition, the constant support of the fibrous web decreases 1 through at least one band 6 . 7 . 8th . 9 . 18 the risk of demolition considerably.

In the interest of intensive, yet volume-saving drainage, at least the second press nip is extended. This is achieved by the shoe press roll 2 . 3 , whose flexible roll shell 20 from a press shoe 19 with concave pressing surface to the opposite press roller 5 is pressed. The pressure is thereby from a on the axis 21 the shoe press roll 3 supporting and on the press shoe 19 acting pressing element 18 produced in the form of a hydraulic piston-cylinder unit.

In contrast, the length of the first press nip is variable. This allows adjustments to the required surface quality of the fibrous web 1 , With relatively low requirements, as can be found in standard newspaper printing, the first press nip is as long as possible.

Although this leads to an increased roughness in the fibrous web 1 , but allows high maximum machine speeds.

are the requirements for the surface quality, such as in flexo printing relatively high, so is the length of the first press nip shortens and the maximum machine speed around 5 to 10% less.

A preferred way to change the length of the first press nip is in 2 shown.

This is the press shoe 19 the shoe press roll 2 of two in the direction of web travel 12 arranged one behind the other, axially extending and separately controllable rows of pressing elements 18 to the press roll 4 pressed.

In the associated pressure curve, the continuous line shows a possible pressure curve, as it appears when activating both pressing elements 18 can result. The press nip length is determined by the area of the press nip in which the press pressure is above the minimum press pressure P _min .

If now the press nip should be shortened, this is simply possible because of the in web running direction 12 first row of pressing elements 18 no or only a small contact pressure generated. This can lead to a dashed pressure curve. As a result, the pressing pressure does not exceed the minimum pressing pressure P _min until much later, so that the press nip commences later and the effective length of this press nip decreases by about 40%.

Another preferred way to change the length of the first press nip is in 3 shown. The shoe press roll 2 owns here two diametrically opposed press shoes 19 each with a contact pressure element 18 ,

The opposite the press roller 4 acting press shoe 19 has a concave pressing surface and thus forms an extended press nip. The other press shoe 19 has a convex pressing surface and thus can have a short press nip similar to that between two cylindrical press rollers 4 form.

If the press nip is to be shortened, then the active pressing element 18 relieved. Subsequently, the press shoe 19 with the convex pressing surface by rotation of the axis 21 the shoe press roll 2 in the press plane opposite the press roll 4 to be moved.

hereby the length of the press nip can be increased by more shorten as 80%.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 3205664 [0016]

Claims (10)

Press arrangement for dewatering a paper, board, tissue or other fibrous web ( 1 ) in a machine for producing and / or finishing the same, in which the fibrous web ( 1 ) together with in each case at least one water-absorbing dewatering belt ( 6 . 7 . 8th . 9 ) is guided by at least two press gaps and the second or a subsequent press nip is executed extended, characterized in that the length of the first press nip is variable. Press arrangement according to claim 1, characterized in that that the length of the first press nip of a maximum value by at least 30%, preferably at least 50% and in particular by at least 80% reducible. Press arrangement according to claim 1 or 2, characterized in that at least the first press nip, preferably two press nips each of a cylindrical press roll ( 4 ) and a shoe press roll ( 2 ) are formed. Press arrangement according to claim 3, characterized in that the shoe press roll of the first press nip a flexible roll shell ( 20 ) possessed by a press shoe ( 19 ) is supported with concave pressing surface, wherein the press shoe ( 19 ) of at least two separately controllable and in the web running direction ( 12 ) one behind the other pressing elements ( 18 ) to the opposite press roll ( 4 ) is pressed. Press arrangement according to claim 3, characterized in that the shoe press roll ( 2 ) of the first press nip a flexible roll shell ( 20 ) possessed by a press shoe ( 19 ) to the opposite press roll ( 4 ), whereby on the axis ( 21 ) of the shoe press roll ( 2 ) at least two circumferentially successively arranged press shoes ( 19 ) of different lengths are available. Press arrangement according to claim 5, characterized in that each press shoe ( 19 ) about a rotation of the axis ( 21 ) is movable in the pressing plane of the press nip. Press arrangement according to one of the preceding claims, characterized in that the fibrous web ( 1 ) together with a dewatering band on both sides ( 6 . 7 ) through the first press nip. Method for operating a press arrangement according to one of the preceding claims, characterized that the maximum machine speed at a shortening the first press nip reduced, preferably reduced by 5 to 10% becomes. Method for operating a press arrangement according to one of claims 1 to 7, characterized in that the length of the first press nip with high quality requirements is shortened. Method for operating a press arrangement according to one of the preceding claims 1 to 7, characterized in that the length of the first press nip for increasing the smoothness of the finished fibrous web ( 1 ) is shortened.