Machine and Method for the Production of a Web of Fiber Material with an Increased Volume

Abstract

A machine for the production of a web of paper or other fiber material (1, 6, 17, 37), comprising a belt (14, 26, 43), wherein the length of the belt (14, 26, 43) is elastically extendable, the web of fiber material (1, 6, 17, 37) can be fed to the belt (14, 26, 43) when the belt (14, 26, 43) is in extended state and the belt (14, 26, 43) can be slackened when the web of fiber material (1, 6, 17, 37) is placed thereon, such that the web of fiber material (1, 6, 17, 37) is compressed and the adhesion forces between the web of fiber material (1, 6, 17, 37) and the belt (14, 26, 43) are sufficiently high in order to avoid the formation of folds in the compressed web (1, 6, 17, 37).

Description

The invention relates to a machine for producing a fibrous web of paper or some other material.

A pressing section for a paper machine is known from DE 100 22 087 A1. The pressing section comprises two pressing units, each of which is formed from a press roller working in association with a shoe press roll. A first upper felt runs through the first pressing station together with a paper web passing forward from a forming fabric, an under-felt and a press jacket of a first shoe press roll. Together with the under-felt, the paper web passes on to the second pressing station. Then the paper web together with a second upper-felt and a press jacket of a second pressing station runs through the second pressing station. The paper web continues to follow the under-felt to a pick-up roll by means of which it is transferred to a first drying fabric which conveys the paper web to the drying section. Deflection rolls and suction rolls are provided to deflect the upper-felt and the lower-felt. In the case of pressing sections known from the state of the art the very low strength of the paper web makes it necessary to provide continuous support by felts or a transfer belt.

Particularly in the case of wood-free papers for office use such as copying or printing paper, the volume of the paper for a given degree of smoothness—which when determined by the Bendtsen method amounts to less than 200 ml/min—constitutes a quality feature, the maintenance of which gives rise to problems on fast-running paper machines and high dry-weight contents. The requirement for high dry-weight contents after passing through the pressing section which is made necessary by the increase in the running speeds leads to an undesired reduction in the specific volume of the paper.

It is the object of the invention to create a machine in which the volume of the fibrous web is increased without the need to accept a lower dry-weight content than can be attained within the state of the art.

According to the invention this object can be achieved with a machine of the type initially mentioned by providing a belt which is elastically extensible longitudinally, it being possible for the fibrous web to be led to the belt in its elongated condition after which the belt with the superimposed fibrous web can be relaxed so that the fibrous web is compressed and the adhesive forces between the fibrous web and the belt being sufficiently great that fold formation in the compressed fibrous web is prevented.

According to the invention an infinitesimal compression of the paper web is achieved on the support material on which it is carried. The paper web is first transported on a felt and then transferred to an elastic belt, i.e. a fabric. a felt or a transfer belt which is under tension. The tensioned belt is relaxed with the result that compression of the paper web takes place. The belt is advantageously of such a nature that the high adhesion forces which exist between the fibrous web and the belt prevent fold formation in the paper web and ensure an infinitesimal degree of compression.

An increase in volume can be obtained from the infinitesimal compression of the paper web without a linear increase of substance in relation to the gain in volume. A particular advantage of the invention consists, therefore, of an increase in volume without a superproportional increase in substance.

Advantageous further developments of the invention are described in the subsidiary claims, the description and the drawings.

In an advantageous manner, the elongation and relaxation of the belt are combined with an intermediate de-watering stage. The de-watering can take place at different points of the machine, for example, in the pressing section or the drying section. This manner of processing achieves a particularly high gain in volume.

If the machine possesses at least one pressing section with several press-nips it is advantageous if the belt can be elongated in front of or during its passage through the first press-nip and relaxed after passing through the last press-nip, with the fibrous web and the belt being led together in front of or within the first press-nip. In this way the belt is, therefore, elongated before or in the first press-nip and the fibrous web is de-watered once or several times as it passes through press-nips, after which the belt is again relaxed.

If the machine possesses at least one pressing section with one or more press-nips it is conceivable to elongate the belt in front of its passage through a press-nip, to release the tension after passing through the same press-nip and to bring the fibrous web and the belt together in front of or within the press-nip.

It should be noted here that the elongation and relaxation of the belt can be achieved by two possible mechanisms:

1. Tensioning the belt in advance of the nip by a higher speed relative to the nip together with reducing the speed after the nip.

2. The belt is so flexible in its thickness that when it is exposed to pressure in the nip the reduction in its thickness is associated with a lengthening of the belt. Relaxation of the belt leads not only to expansion in the thickness direction but to a reduction in length and a resulting compression of the belt and of the fibrous web adhering to it.

Advantageously, with the aid of a suitable tilt it is possible for the processes within the nip to proceed in a controlled manner.

In an advantageous configuration of the invention a deflection roll is provided before the at least one press-nip and this can be driven at a lower speed than the first and second press-rollers which together form the press-nip through which both the fibrous web and the belt are fed. The difference in speed between the press rollers on the one hand and the deflection roll mounted immediately ahead of them arises from the fact that relative to the deflection roll the press rollers are driven at a higher speed.

In order then to compress the fibrous web, a deflection roll after the at least one press-nip is provided which is driven at a lower speed than the first and second press rollers.

In an advantageous configuration of the invention, the second belt is a transport belt to transfer the fibrous web to a third belt by means of which the fibrous web can be led through a third press-nip to improve the level of smoothness.

Alternatively, the second belt is a transport belt to transfer the fibrous web to a third belt by means of which the fibrous web can be led through a drying section following the pressing section.

The invention also relates to a process for operating a machine for the production of a fibrous web of paper or some other material by the following steps:

the elongation of a belt length-wise

the forward movement of a fibrous web on the belt in its elongated condition

the relaxation of the belt so that the fibrous web is compressed and

ensuring that the adhesive forces between the fibrous web and the belt are sufficiently high that fold formation in the compressed fibrous web is avoided.

In an advantageous further development the process for operating the machine is characterized in that when the fibrous web is transferred from the belt, for example, to improve its level of smoothness, it is pressed against a succeeding transport belt.

It is of advantage if the fibrous web is compressed by less than 5% and, in particular, by less than 3%.

There follows a more detailed explanation of the invention with the aid of exemplary embodiments.

FIG. 1a, b show schematic sectional elevations of the fibrous web before and after being compressed,

FIG. 2 shows a fibrous web, which is fed through a press nip,

FIG. 3 shows a pressing section with a central roller forming two press-nips,

FIG. 4 shows a pressing section with a central roller forming two press-nips combined with a part of the drying section and

FIG. 5 shows a pressing section with two press-nips, each of which comprises individual pairs of press rollers where the second press-nip is formed of a press roller with a shoe press roll.

A fibrous web 1 (FIG. 1a) passing forward from a forming section is led through a pressing section. There, it is led through at least one press-nip. The fibrous web 1 is deposited upon an elastic belt 2 which finds itself in an elongated condition before it passes through the press-nip. After the press-nip, the elongation of the belt 2 is relaxed by, for example, running a deflection roll following the press rollers at a lower peripheral speed relative to the running direction of the web. In this way the fibrous web 1 is compressed. Instead of the original thickness d it has the thickness D (FIG. 1b).

FIG. 2 shows schematically a press-nip comprising a press roller 3 and a press-shoe (not illustrated) through which the fibrous web 1 is led together with two belts or felts 4, 5.

In a configuration of the invention a fibrous web 6 (FIG. 3) is received on a felt 54 from a forming section 7 and led to the pressing section 8. Here it is first led through a press-nip 51 comprising rolls 10 and 50 and then through two press-nips 12, 13 comprising a central roll 9 with two press rollers 10, 11.

The fibrous web 6 is led through the press-nip 51 together with the felt 54 and an elastic belt. In this way the elastic belt 14 is first led through the press-nip 51. The belt 14 is not elongated ahead of the press-nip 51 but, on the contrary, within the press-nip 51 itself as a consequence of the pressure loading. In this respect, the belt 14 is so flexible in its thickness that when subjected to pressure loading within the press-nip 51 the reduction in thickness is associated with a lengthening of the belt 14. The relaxation of the belt 14 after its passage through the press-nip 51 leads not only to an increase in thickness but also to a reduction in length and an associated compression of the belt 14 and the fibrous web 6 adhering to it. Then the fibrous web 6 passes through the press-nips 12, 13 formed by the central roll 9 and the rolls 10 and 11.

In another embodiment (FIG. 4) a fibrous web 17 travelling from a forming section on an under-felt 18 is led to a pressing section 19 with a central roll 20. This forms two press-nips 21, 22 with the press rollers 23, 24 of which the press roller 23 is simultaneously designed as a suction roll in order to release the fibrous web 17 from the under-felt 18. Before the first press-nip 21 an application of, for example, starch carried on an air-permeable belt 26 is made by a device 25. This belt together with the fibrous web 17 transported upon it is heated and dried by drying devices 27, 28 with heating applied to both sides or at least to one side and, in particular, to the upper side. The upper drying device 28 produces hot air while the lower drying device 27 is, for example, a radiant dryer. In addition, a further drying device 29 for the fibrous web 17 can be arranged in the following area of a drying fabric. To provide for the situation that the belt 26 is permeable to air, both drying devices 27, 28 are radiant dryers. However, the use of an air-permeable belt 26 has the advantage that drying can take place through it.

A conditioning device 30 is fitted to the belt 26. For example, a cleaning agent can be applied by spraying which is subsequently removed by wiping.

In the press-nip 21, the belt 26 transfers the application of the medium made by the device 25 to the fibrous web 17 while it, together with the fibrous web 17, is wrapped around the central roll 20.

Furthermore, the belt 26 is of an elastic nature so that firstly it is elongated by a deflection roll 31 turning at a lower speed than the central roll 20 and the press rollers 23, 24 and it accepts the fibrous web 17 while in this elongated condition. After passing through the press-nips 21, 22 the belt 26 is again compressed by a slower-running deflection roll 32 with similar compression of the fibrous web 17 carried upon it, which as a result simultaneously is endowed with a greater thickness and, thereby, a greater volume.

After passing through the pressing section 19 the fibrous web 17 is led into a single row drying section 33 with drying cylinders 34 and deflection rolls 35 in the form of suction rolls together with low-pressure areas 36. In these a pressure reduction of preferably more than 5 kPa is maintained to facilitate a reliable release of the fibrous web 17 from the drying cylinders 34 because the side of the fibrous web 17 carrying the medium lies upon the peripheral face of the drying cylinders 35.

In a further exemplary embodiment (FIG. 5) a fibrous web 37 is de-watered by press-nips 39, 40 in a pressing section 38. The first press-nip 39 is formed by the pair of rolls 52 and 53. In the second press-nip 40 the fibrous web 37 is led between a press roller 41 and a shoe press roll 42. At the same time moisture is given up to an elastic felt 43. The latter is led over deflection rolls 44, 45, 46, 47. Each of the deflection rolls 44, 47 are designed as driven rolls. The deflection roll 44 runs at a slightly slower peripheral speed than the press roller 41 and the shoe press roll 42 with the result that the felt 43 is elongated when it receives the fibrous web 37 from an upper felt 48 before reaching the press-nip 40.

After passing through the press-nip 40 the felt 43 and the fibrous web 37 carried by it is compressed because the deflection roll 47 turns with a slightly lower peripheral speed than the press roller 41 and the shoe press roll 42. The fibrous web 37 is led by the felt 43 to a drying section 49.

Claims

1. A machine for producing a fibrous web of paper or some other material (1, 6, 7, 37) with a belt (14, 26, 43), characterized in that the belt (14, 26, 43) is elastically extensible longitudinally, it being possible for the fibrous web (1, 6, 17, 37) to be led to the belt (14, 26, 43) in its elongated condition after which the belt (14, 26, 43) with the superimposed fibrous web (1, 6, 17, 37) can be relaxed so that the fibrous web (1, 6, 17, 37) is compressed and the adhesive forces between the fibrous web (1, 6, 17, 37) and the belt (14, 26, 43) being sufficiently great that fold formation in the compressed fibrous web (1, 6, 17, 37) is prevented.

2. The machine as claimed in claim 1, characterized in that the machine comprises at least one pressing section (8, 19, 38) with at least one press-nip (12, 13, 21, 22, 39, 40, 51) and that the belt (14, 26, 43) can be elongated in front of or during its passage through the first press-nip (21) and relaxed after passing through the last press-nip (22) and that the fibrous web (1, 6, 17, 37) and the belt (14, 26, 43) can be led together in front of or within the first press-nip (21).

3. The machine as claimed in claim 1, characterized in that the machine comprises at least one pressing section (8, 19, 38) with at least one press-nip (12, 13, 21, 22, 39, 40) and that the belt (14, 26, 43) can be elongated in front of or during its passage through a press-nip (40, 51) and relaxed after passing through the same press-nip (40, 51) and that the fibrous web (1, 6, 17, 37) and the belt (14, 26, 43) can be led together in front of or within the press-nip (40, 51).

4. The machine as claimed in claim 1, characterized in that a deflection roll (31, 44) is provided before the at least one press-nip (21, 22, 40) and this can be driven at a lower speed than the first press roller (23, 41) and the second press roller (20, 42).

5. The machine as claimed in claim 1, characterized in that a deflection roll (32, 47) is provided after the at least one press-nip (21, 22, 40) and this can be driven at a lower speed than the first press roller (23, 41) and the second press roller (20, 42).

6. The machine as claimed in claim 1, characterized in that after passing through the press-nip (12, 13, 21, 22, 39, 40, 51) the fibrous web (1, 6, 17, 37) led forward together with a belt can be transferred to a second belt running at a lower speed relative to the belt.

7. The machine as claimed in claim 6, characterized in that the second belt is a transport belt to transfer the fibrous web (1, 6, 17, 37) to a third belt by means of which the fibrous web (1, 6, 17, 37) is led through a third press-nip.

8. The machine as claimed in claim 6, characterized in that the second belt is a transport belt to transfer the fibrous web (1, 6, 17, 37) to a third belt by means of which the fibrous web (1, 6, 17, 37) can be led through a drying section following the pressing section.

9. The machine as claimed in claim 1, characterized in that the belt (14, 26, 43) is a fabric, a felt or a transfer belt or a smoothing belt.

10. A process for the production of a fibrous web of paper or some other material (1, 6, 17, 37) having the following steps:

the elongation of a belt (14, 26, 43) length-wise

the forward movement of a fibrous web (1, 6, 17, 37) on the belt (14, 26, 43) in its elongated condition

the relaxation of the belt (14, 26, 43) so that the fibrous web (1, 6, 17, 37) is compressed and

ensuring that the adhesive forces between the fibrous web (1, 6, 17, 37) and the belt (14, 26, 43) are sufficiently high that fold formation in the compressed fibrous web (1, 6, 17, 37) is avoided.

11. A process for operating a machine as claimed in claim 10, characterized in that in order to smooth the fibrous web (1, 6, 17, 37) when it is transferred from the belt (14, 26, 43) the web is pressed against a succeeding transport belt.

12. The process as claimed in claim 10, characterized in that the fibrous web (1, 6, 17, 37) is compressed by less than 5%.

13. The process as claimed in claim 10, characterized in that the fibrous web (1, 6, 17, 37) is led forward with a dry-weight content of less than 60%.

14. The process as claimed in claim 10, characterized in that the fibrous web (1, 6, 17, 37) is compressed by less than 3%.

15. The process as claimed in claim 10, characterized in that the fibrous web (1, 6, 17, 37) is led forward with a dry-weight content of less than 40%.