EP0334201B1 - Process and apparatus for enhancing the functioning of the wet press in a paper machine - Google Patents

Abstract

A process and arrangement of a wet press of a paper-making machine where a felt guide roll (16, 18, 20, 38), around which the felt is looped as fully as possible, is periodically moved backwards and forwards at one end with a stroke of 5 to 15 mm at right-angles to the transverse direction of the machine and as far as possible in the direction of the bisector (40) of the felt wrap angle. In this way, the development of a cross-stripe structure resulting from machine vibrations and other influences as the wet felt ages and which would increase the vibrations is substantially prevented. <IMAGE>

Description

The invention relates to a method for improving the working behavior of a wet press provided with a revolving, at right angles to each other weft and warp threads having a felt cloth of a paper making machine. The invention further relates to a felt running arrangement of a paper machine wet press and the use of a specific roller bearing for such a method or such an arrangement.

When speaking in the context of this invention of papermaking machines, machines of this type are to be understood in the broadest sense of the term. It should also be understood to mean other machines which have a press section of the type which is customary in paper machines and in which corresponding problems can occur.

The wet felt in a paper machine, nowadays mostly one Base fabric made of synthetic fibers, which is needled with a pile of also mostly synthetic fiber material, serves to guide the paper web carried by it through the press nip of a pair of press rolls in order to absorb the water squeezed out of the still wet paper web between the press rolls, whereby the Press roll facing away from the paper web is usually designed as a roll with a perforated jacket, in which a fixed vacuum box is arranged below the press nip, sealed against the circumferential roll jacket on the inside, with which largely the water squeezed out of the paper web and taken over by the felt is to be suctioned off.

The endlessly circulating felt is returned via felt guide rollers, being subjected to water jet cleaning on its way in order to clean it of fine substances taken up from the paper web, which would increasingly reduce the water absorption capacity of the felt, and additional suction devices are usually also arranged with which the cleaning water is to be removed from the felt again so that the felt runs again into the press nip with the lowest possible water content.

As a rule, one of the felt guide or felt guide rollers, which has the largest possible felt wrap angle, preferably an angle in the region of 180 °, is designed as a felt tensioning roller. This means that the roller is provided at its ends with bearings that can be moved perpendicular to the roller axis and can be adjusted via a common drive so that the roller can be adjusted parallel to the transverse direction of the felt if desired, so that the felt can be re-tensioned when it is in the Expands during operation. Furthermore, a felt regulating roller is generally provided, usually only one has very low wrap angle, and one of its bearings is continuously adjustable in a direction perpendicular to the bisector of the felt wrap angle by means of a control device, in order to return the felt to its intended central position when it runs laterally. The felt position is generally sensed by a probe on one of the outer edges of the felt.

With paper machines becoming wider and faster - large machines for the production of printing papers nowadays have paper web widths of the order of 10 m and run at speeds in the range of 1000 m / min - the problems of the smooth running of such machines also increase essential vibration problems. On the other hand, the dewatering dwell times of the paper web in the press nips, which become correspondingly shorter at higher speeds, have made much higher press pressures necessary, which from one press to another are increasingly in the range of 60-120 kg / cm line pressure. These high line pressures in turn cause the slightest irregularities in the felt passed through the press nip to increase the machine's sensitivity to vibration. Vibrations in these machine parts not only affect the machine, they also reduce the quality of the paper web.

As long as a press wet felt is still new and flexible, these problems are generally less. However, the felt hardens with increasing wear of the needle pile. In addition to irregularities that the felt may have had right from the start, other irregularities develop during operation. Since the felt is endlessly circulating, any thickened areas come repeatedly into the press nip. Special problems can arise if the natural frequency of the press arrangement or associated machine parts is a multiple of the rotational frequency of the felt. As a result, the press vibrations can be amplified, which in turn leads to the felt being exposed to periodic pressure fluctuations which ultimately lead to periodic changes in the properties of the felt in the manner of a transverse washboard pattern. If such a condition is reached, the felt usually has to be changed prematurely in order not to transfer these periodic fluctuations to the paper web as periodic changes in properties, on the one hand, and to protect the machine on the other.

As can be seen from the above, the causes that lead to this state or behavior can be of different types.

First, these causes can lie in the felt itself. To control the felt run, it is generally provided with a colored cross stripe, which may have a different drainage behavior and can therefore lead to hydraulic impacts in the press. The width of the felt overlap is sometimes somewhat thicker. The felt at the fleece jetty can also be a little thinner or thicker than average. Other causes can be production-related. If the press is switched off frequently during operation and the upper press roll is not lifted off immediately, the felt is compressed more strongly along the press line in the rest position. If, on the other hand, a felt tube suction device continues to run, the felt becomes more voluminous at this point. Periodically changing hydraulic forces in the press nip can also influence the felt. Periodic influences can arise from the fact that the length of the felt Is a multiple of the diameter of the press roll. Machine-related causes can be inaccuracies of the rolls, the deflection of the rolls and an uneven pressing of the rolls across the width of the machine.

An article from TAPPI, 1970, No. 4, pages 609 to 613 with the title "Controllable-Openness Adjustable Falts Overcome Wet Filling" reports on felts in which the weft threads run diagonally to the warp threads. By changing the path of a felt side, the weft threads can be brought closer to the transverse direction, which increases the mesh or pore size. Not only should there be a constant change with increasing laying of the felt, but also by temporarily transversely aligning the weft threads and thus increasing the size of the pores of the felt, so that fine fibers can be removed, in order to subsequently convert it back into the oblique direction of the weft threads. The method described presupposes a felt in which the pores can be enlarged by tensioning in order to improve the running time of the felt. In the article cited it is pointed out that strict parallel running is to be ensured for felts woven at right angles. It can be seen from this that it was not to be expected that an period of time improvement could be achieved by periodically running a right-angled felt, since with such a felt the pores can only be reduced in size by leaving one side of the felt leading or trailing. Accordingly, there was a prejudice that the runtimes of the felt can be extended even with periodic pore reduction.

The invention has for its object to improve the operation of a wet press of a paper machine in that vibrations in the felt run area are reduced and that the formation of periodic transverse areas of different properties in the felt, i.e. the formation of a so-called washboard pattern is avoided, but is at least delayed, so that the felts can be run for a longer period of time and, moreover, periodic property fluctuations in the paper produced, which are caused by the aforementioned phenomenon, are avoided.

This object is achieved procedurally in that the felt path is reduced by the pair of press rollers and around the felt guide rollers, measured on a lateral outer edge of the felt, compared to the felt path on the other outer edge of the felt periodically lengthened and shortened to reduce vibration. Of course, the change in path length from one outer edge of the felt to the other is continuous at all times, and generally also linear. This behavior is achieved with an arrangement in which one of the felt guide rollers, which should be wrapped as much as possible by the felt, is provided at one end with a bearing which is movable perpendicular to the transverse direction of the felt and which is periodically moved back and forth between two positions, the path length change of the felt on this one side need only be about 10 to 30 mm.

This small change in path length is sufficient for the felt to change at intervals of the roller bearing between about 30 and 120 minutes (the period of the changeover is then twice as long), depending on the width of the paper machine, on one side up to a lead or lag over the other Side of about 100 to 200 mm. A corresponding periodically changing inclination of the transverse weft wires of the felt fabric (if available) compared to the Surprisingly, the true vertical cross machine direction is already sufficient to largely avoid the formation of cross waves in the felt. The originally square stitches of the felt fabric are periodically slightly rhombically distorted in one direction or the other.

Such an advance or lag of one outer side of the felt over the other, which, if it takes on larger dimensions, is undesirable per se in the course of the felt, is intentionally and selectively used periodically in accordance with the invention to reduce the difficulties explained at the outset. Surprisingly, it has also been shown that when the path length changes within the specified limits, the felt does not tend to run much more sideways, since the conventional felt run regulating device can easily compensate for these changes.

Basically, it is possible to provide the movable bearing according to the invention on the felt tensioning roller, which generally has a felt wrap angle in the range of 180 °, which is favorable for the method according to the invention. Only the combination of the adjustable bearing according to the invention with the felt tensioning roller can cause structural problems, especially when retrofitting the bearing according to the invention, because the felt tensioning roller is already provided with adjustable bearings, which however have a coupled parallel drive, which is actuated only when required and with the one exact parallel tensioning of the felt is desired. It is therefore more favorable if the felt guidance conditions make it possible to provide a second largely wrapped felt guide roller which can be selected for the method according to the invention. Is it not possible to use a roller with a 180 ° wrap angle To arrange, in which case the change in felt path length corresponds to twice the roller bearing stroke, a larger roller stroke must be provided in order to achieve the same change in path length of the felt.

If it is mentioned in the wording of the claim that the adjustment direction of the reciprocating bearing "generally" should take place in the direction of the bisector of the felt wrap angle of the associated roller, then it should be expressed that the adjustment direction should be placed in this direction if possible . In any case, the adjustment direction should be such that when the adjustment path is divided into two mutually perpendicular components, the larger component runs in the direction of the bisector. Deviations in the adjustment direction of more than 90 ° from the bisector must therefore be avoided. The greater the angular deviation, the greater the stroke of the roller bearing must be in order to obtain a sufficient adjustment path in the direction of the bisector. Larger angular deviations of the roller adjustment should be avoided if an adjusting component running perpendicular to the bisector of the angle can have an influence on the felt path regulation, especially if the wrap angle of the roller deviates greatly from 180 °. In contrast to the bearing adjustment according to the invention, the felt control rollers are generally generally adjusted in a direction perpendicular to the bisector of the wrap angle.

The invention, inter alia, achieved the following advantages:

With regard to production, improvements in the dry content of the paper web behind the press operated according to the invention can be improved. The moisture profile of the paper web across the web width improves. The felt otherwise washboard structure transferred to the paper web with respect to moisture differences can be avoided in the web. This has a positive effect on the printing result when producing printing paper. Production can possibly be increased because the paper machine can be run faster by reducing the press vibrations. Costs can be saved in that the felt running times can be extended by about 20% by the invention. This reduces the felt use costs and also avoids additional machine downtimes. Finally, the press rolls are also spared more. If vibrations occur, the press rolls also tend to show uneven wear and thus become out of round. The regrinding intervals for the presses can be extended when using the method according to the invention. Vibrations within the press section can also be transferred from a vibrating press to the other presses via the machine frames, which can therefore also be affected. This problem can also be reduced by using the method according to the invention.

Fig. 1

die Filzlaufanordnung der Pressenpartie einer Selbstabnahmepapiermaschine mit mehreren Pressen,

Fig. 2

eine geschnittene Draufsicht auf eine verstellbare Lagerbockanordnung für eine Filzführungswalze,

Fig. 3

die Lageranordnung nach Fig. 2 in Seitenansicht,

Fig. 4

die Lageranordnung nach Fig. 2 in stirnseitiger Ansicht, und

Fig. 5

eine verstellbare Lageranordnung für eine Filzspannwalze.

In the following the invention is further explained with reference to the accompanying drawings. In particular, a possible exemplary embodiment of an adjustable roller bearing suitable for carrying out the method according to the invention is described. In the drawings:

Fig. 1

the felt run arrangement of the press section of a self-acceptance paper machine with several presses,

Fig. 2

2 shows a sectional top view of an adjustable bearing block arrangement for a felt guide roller,

Fig. 3

2 in side view,

Fig. 4

2 in front view, and

Fig. 5

an adjustable bearing arrangement for a felt tensioning roller.

In the schematic diagram of FIG. 1, which shows the felt run arrangements for a group of three presses, the course of the felt guide is shown in solid lines, while the path of the paper web is indicated by dashed lines.

The wet paper web 4 is taken from a sheet forming screen 2 by means of a vacuum-loaded pick-up roller 6 to the underside of a first press felt 8, which feeds the paper web into the first press nip of a twin press 10, which is formed by a suction press roller 12 and a center roller 14 . This press nip forms the press I of the machine. From the press I, the first press felt 8 runs over a series of felt guide rollers 16 back to the pick-up roller 6. The felt guide roller 18 is designed as a felt tensioning roller, while the felt guide roller 20 is a felt regulating roller. On the way to the tension roller 18, the felt 8 is guided past high-pressure spray pipes 22 for cleaning the felt, and then past pipe suction devices 24, which are intended to extract as much water as possible from the cleaned felt in order to make it water-absorbent for the new pressing process.

From the press I, the paper web 4 is guided directly around the middle roll 14 of the twin press into the second press nip of the twin press, which is the press II and is formed from the center roll 14 and a further press roll 26 of the twin press 10. The press roll 26 of the press II can be, for example Grooved roller. In the press II, too, the paper web is guided by a second press felt 28, which is also returned to the press II via felt guide rolls 16, a felt regulating roll 20 and a felt tensioning roll 18. High-pressure spray pipes 22 and pipe suction devices 24 are also arranged in its course.

From the press II, the paper web 4 is introduced directly into the press nip of the third press III via a paper guide roller 30. This press can consist of a lower grooved roller 32 and an upper solid roller 34. In the third press, too, the paper web 4 is carried by a press felt, namely the third press felt 36. This felt also runs over paper guide rollers 16, a felt regulating roller 20 and a felt tensioning roller 18. Only one spray tube 22 and only one tube suction device 24 are provided on this felt, because the paper web passing through the third press III already has a higher dry content, which is why less water and Fines are absorbed by the third press felt.

One of the lower felt guide rollers, namely roller 38, is, as will be described with reference to FIGS. 2-4, provided on one side with a bearing that can be pushed back and forth between two positions, which is why the roller is to be referred to here as a pendulum roller. As can be seen from FIG. 1, the pendulum roller 38 is not wrapped around 180 ° by the felt, but in relation to the other felt guide rollers, apart from the felt tensioning roller 18, it has the largest wrap angle through the felt. The adjustability of one bearing should ideally take place in the direction of the bisector of the felt wrap angle, as indicated by arrow 40, but in practice you will make the bearing displaceable in the vertical direction because it is so easy to construct on a vertical one Part of the machine frame can be attached. In order to achieve a certain felt path length change, the bearing, when mounted vertically movable, must be able to perform a somewhat larger stroke in the vertical direction than if it were movable in the direction of arrow 40.

It is expressly pointed out that the pendulum roller 38 is arranged separately from the tension roller 18. This is useful when guiding the felt 36, since both rollers have a relatively large wrap angle. In the case of the second felt 28 (which cannot be seen in the figure), the felt tensioning roller 18, in addition to its parallel adjustment device in the direction of the arrow shown, is provided at one end with a superimposed reciprocation of the bearing, in order to do this for this felt as well to apply the described method. However, this double function of the felt tensioning roller should only be selected if no other roller offers itself directly as a pendulum roller. In any case, it is structurally easier, especially for retrofitting, if another roller is chosen as the pendulum roller. Under certain circumstances, the felt guide can be changed in a simple manner in order to obtain a roller with a larger wrap angle.

In the example shown, the first felt or pick-up felt 8 is not provided with a pendulum roller, but it can also be easily provided here.

An embodiment of a movable bearing with associated adjustment device is described below with reference to FIGS. 2-4.

In Figure 3 is a pendulum roller 38 from its front Visible at the end, which could be the pendulum roller 38 in FIG. 1, for example, with a slightly changed felt wrap. The roller 38 is rotatably mounted in a bearing 42 which is fastened to a vertical part 46 of the machine frame by means of a bearing block 44. The arrangement can accordingly also be seen in another view in FIG. 4. In Figure 2, the bearing block 44 is shown in a sectional view. It contains a displaceably guided block 48, on which the actual bearing 42 is fastened in order to take part in the displacement movements of the block 48. A spindle 50 is guided through the block, the rotation of which allows the basic position of the bearing 42 to be set. One end of the spindle 50 extends out of the pillow block 44 and has an actuating head 52 there. A bracket 54 is attached to the machine frame 46 on the side of the bearing block 44, on which a two-armed lever 56 is rotatably fastened. One end of the lever 56 is connected to the freely movable end of a pneumatic actuator 58, the fixed end of which is also fastened to the bracket 54. The actuator is an air bellows in the embodiment. In other embodiments, the actuator 58 can also be designed as an electrical, hydraulic or mechanical drive. The other end of the lever 56 rests on the actuating head 52 of the spindle 50 with a roller 60 provided on it. The actuating head 52 of the spindle 50 can be provided with two stop collars 62 which limit its movement play in the passage opening of the bearing box 44 to two end positions.

If the air bellows 58 is pressurized with air, the lever 56, based on the drawing in FIG. 2, turns counterclockwise and presses the actuating head 52 downward with the roller 60 until the upper stop collar 62 rests on the bearing block housing 44. The pendulum roller 38 thus reaches its reference to FIGS lowest position. If the air bellows 58 is vented, the roller 38 automatically moves back into its upper starting position under the tension of the felt 36 (see FIG. 3), as is shown by the stop position of the actuating head 52 in FIG. 2.

The stroke a of the actuating head and thus of the roller bearing 42 is approximately between 5 and 15 mm. This results in a change in the felt path length, which is approximately twice the amount. If the lower stop collar 62 is configured on the spindle 50, for example by means of a thread, the bearing stroke can be changed.

In this arrangement, the pendulum roller 38 is moved back and forth with one end, that is to say not continuously, but rather in each case from its one end position to the other and back again after the selected time interval has elapsed.

5 shows the possibility of arranging the adjustable bearing on a felt tensioning roller 18, the side view being shown only on one side of the bearing, namely that on which the displaceable bearing for the felt tensioning roller 18 is located.

A hollow guide rod 64 is arranged on both sides of the machine frame 46 in a rotationally fixed manner. The sliding block 48 slides on the guide rod 64 and has the bearing block 44 in its interior, which is provided with an internal thread. This internal thread of the bearing block 44 is in engagement with the spindle 50, which is guided along the inside of the hollow guide rod 64 and is also rotatably mounted in the machine frame 46. With the displaceable block 48, the bracket 54 is fixed to the frame, whereby it has an angular shape. The leg of the angular attached to the displaceable block 48 Console 54 has, for example, a dovetail guide 66 in which the bearing 42 for the felt tensioning roller 18 is guided so that it can be moved back and forth. In this embodiment, the bearing 42 consists of two separable bearing shells which receive the journal of the felt tensioning roller 18. Between the bearing 42 and the other leg of the bracket 54, the pneumatic actuator 58 (an air bellows) is arranged, which is attached with its freely movable end to the bearing 42 and with its fixed end to the bracket 54.

The felt 36 is tensioned in that the spindle 50 is rotated by means of a mechanical or electrical drive. As a result, the bearing block 44 and thus the block 48 move in the corresponding direction depending on the direction of rotation of the spindle 50. For tensioning the felt 36, the block is shifted to the left with respect to the drawing, the tensioning of the felt 36 in the opposite direction he follows.

If air is now applied to the actuator 58, this expands and displaces the bearing 42 in the dovetail guide 66 accordingly to the left in relation to the drawing. The felt tensioning roller 18 is shifted on one side and the felt 36 is stretched accordingly. If the actuator 58 is vented, the felt tensioning roller 18 automatically moves back into its starting position under the tension of the felt 36.

The pneumatic actuator 58 is provided with a time control (not shown) which pressurizes it with air at periodic intervals and vents it again. These time intervals can expediently be varied between approximately 30 minutes and approximately 120 minutes.

Claims (14)

1. A process for enhancing the functioning of a wet press in a paper generating machine, said wet press being povided with a returning felted fabric comprising weft and warp threads that are woven at right angles one to another, characterized in that, in order to diminish the vibration, the guideway of the felt across the pair of press rolls (26) and round the guiding rolls of the felt (16, 18, 20, 38) being measured at a lateral outer edge of the felt (8, 28, 36) is periodically extended and shortened by a predetermined stretch as against the course of a felt at the other outer edge of the felt (8, 28, 36), the change of the distance at each particular time running continuously from the one outer edge of the felt to the other.

2. A process according to claim 1, characterized in that, in general, a guiding roll (16, 18, 20, 38) being entwined as largely as possible from the felt (8, 28, 36) is periodically moved to and fro of its ends in the direction of the bisecting line of the angle of the entwining felt.

3. A process according to claims 1 or 2, characterized in that, as regards its chronological course, the periodic and unilateral change of the length of the course of the felt and the periodic to-and-fro movement of the one end of the roll respectively runs in accordance with the periodic rectangular curve or with a slight trapezoid curve.

4. A process according to at least one of claims 1-3, characterized in that the duration of the period amounts to between 30 to 360 minutes, preferably to between 60 and 240 minutes.

5. A process according to at least one of claims 1-4, characterized in that, between the shortest and largest way, the change of the distance of the course of the felt at said one outer edge of the felt (8, 28, 36) amounts up to 60 mm.

6. A process according to at least one of claims 2-5, characterized in that a felt guiding roll (16, 18, 20, 38) is chosen for the shifting, the felt entwining of which amounts to at least 60°, preferably to more than 90° and up to the range of 180°.

7. A felt guide way equipment in a wet press of a paper generating machine wherein a continuously returning felted fabric comprising weft and warp threads that are woven at right angles one to another is led across a pair of press rolls (26) round guiding rolls of the felt (16, 18, 20, 38) and, should the occasion arise, across or past devices for purification and drainage (22, 24) and wherein each one of the felt guiding rolls is developed as a felt stretching roll (18) and a felt guide way adjusting roll (20), characterized in that one out of the felt guiding rolls (16, 18, 20, 38) having an angle of the entwining felt as great as possible comprises a bearing (42) at one of its ends that is vertically adjustable to the cross direction of the felt and which is movable to and fro between two positions at a given traverse (a) by means of an actuator (58), said traverse being preferably adjustable.

8. A felt guide way equipment according to claim 7, characterized in that the bearing (42) is installed in such a manner that, in general, the direction of its adjusting traverse runs in the direction of the bisecting line (40) of the angle of the entwining felt of the roll (16, 18, 20, 38).

9. A felt guide way equipment according to claims 7 or 8, characterized in that the traverse of the bearing (42) is adjustable between 5 and 50 mm.

10. A felt guide way equipment according to at least one of the claims 7-9, characterized in that, for the manipulation of the actuator (58), a timing device is provided by which the actuator (58) is periodically adjustable for the reversion of the bearing of the roll (42) into its mutual positions.

11. A felt guide way equipment according to at least one of claims 7-10, characterized in that the actuator (58) is a pneumatic actuator being conceived thus that, for the adjustment of the bearing in the direction of an elongation of the felt guide way, air is admitted and, for the return travel in the direction of a shortening of the felt guide way, air is removed.

12. A felt guide way equipment according to at least one of claims 1-11, characterized in that the adjustable bearing is provided at one end of the felt stretching roll (18) and that its traversing movement is superimposed to the felt stretching device.

13. A felt guide way equipment according to at least one of claims 1-11, characterized in that the adjustable bearing (42) is provided at a roll (38) being separated from the felt stretching roll (18).

14. The use of a roll bearing being vertically adjustable to its bearing axis between two positions at one end of a felt guiding roll (16, 18, 20, 28) in a wet press of a paper generating machine in order to perform the process according to anyone of claims 1-6.

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