DE29617881U1 - Device for producing a material web - Google Patents

Description

Tracks & Large

Patent Attorney's Office
Stuttgart Berlin Hamburg

Description

The invention relates to a device for producing a material web, in particular a paper or cardboard web, with a drying section according to the preamble of claim 1.

Devices of the type discussed here are known (US-PS 5,291,666). They have a drying section with at least one drying group, which comprises a number of cylinders which - viewed in the direction of travel of the material web - are alternately heated and cooled. The material web is guided around the cylinders together with a porous conveyor belt, which is also referred to as a screen, and with a metal belt in a meandering manner, with the material web being arranged between the conveyor belt and the metal belt. It has been found that the drying rates within the drying section are insufficient in many cases, so that relatively large drying sections must be provided in order to ensure sufficient drying. Another disadvantage is that the material web rests freely on the conveyor belt in some areas of the drying section, which causes the material web to shrink unhindered. This leads to different material web properties across the width of the web and thus to a reduction in the quality of the material web.

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14 October 1996

It is therefore an object of the invention to provide a device which does not have these disadvantages.

To solve this problem, a device is proposed that has the features mentioned in claim 1. The device is characterized by the fact that high pressure forces are built up perpendicular to the thickness of the material web, which lead to good heat transfer to the material web. In addition, the heat transport within the material web is significantly improved. Finally, the steam from the material web is also optimally passed on to the conveyor belt or drying screen due to the high pressure forces. In addition, the largest possible temperature differences are built up in order to ensure a large heat flow. For this purpose, additional heating and cooling devices are assigned to the cylinders, which act on areas of the circumference in which the material web with the conveyor and metal belt rests on the cylinders. Because the additional heating and cooling devices are provided in the area where the material web rests on the cylinders, a large heat flow is ensured, especially in the areas in which there is a high surface pressure. The high surface pressure is achieved by pre-tensioning the metal belt and/or the conveyor belt so strongly that a pressure of preferably 10 kPa to 100 kPa is exerted on the web.

Particularly preferred is an embodiment of the device in which the metal strip rests directly on the heated cylinder, while the

The external conveyor belt is cooled by a cooling device. Because the metal belt transfers the heat from the heated cylinder well to the material web, there is a strong temperature gradient within the material web to the external conveyor belt, which, as mentioned, is cooled. The moisture is therefore intensively conveyed to the conveyor belt and removed from there by the cooling device.

Furthermore, an embodiment of the device is preferred in which the cooled cylinder is provided with circumferential grooves. The conveyor belt resting on the cylinder can thus transfer moisture to the cylinder particularly well.

A particularly preferred embodiment of the device is one in which a cylinder provided with grooves is additionally suctioned, for example by means of an external suction box. With such a design, the moist air is drawn off, resulting in particularly effective drying of the material web.

Further details emerge from the remaining subclaims.

The invention is explained in more detail below with reference to the drawing.

Figure 1 shows a section of a device for producing a material web in side view, namely a part of a drying group;

Figure 2 shows a larger part of a device according to Figure 1, namely a transition between two drying groups;

Figure 3 shows a modified embodiment of a transition according to Figure 2;

Figure 4 shows a modified embodiment of a drying group with a transition to a subsequent drying group and

Figure 5 shows a transition from a press section to the first drying group of a drying section.

The device described below can generally be used for producing a material web. For the sake of example only, it is assumed that this is a paper production machine.

Figure 1 shows a section of a device or papermaking machine 1, namely a part of a drying section 3, which comprises at least one drying group 5. Within a drying group, a number of cylinders are provided around which the material web 7 or paper web is guided in a meandering manner together with a conveyor belt 9, also referred to as a drying screen, and a metal belt 11.

Figure 1 shows two heated cylinders 13 and 15, the centers of which lie on an imaginary plane El, between which a preferably cooled cylinder 17 is arranged below the plane El. The material web 7 is guided between the conveyor belt 9 and the metal belt 11, whereby the belts are arranged in such a way that the metal belt 11 lies directly on the heated cylinders 13 and 15, while the conveyor belt 9 located on the outside in the area of these cylinders lies directly on the surface

of the cylinder 17, while the metal band 11 is on the outside.

Cooling devices 19 and 21 are provided in the peripheral area of the heated cylinders 13 and 15, which are designed here as suction blow boxes. Hot air is supplied to the cooling devices, which acts on the surface of the conveyor belt 9 in order to absorb the moisture present there. The moist exhaust air is sucked out of the suction blow boxes, as indicated by an arrow A. The moist air does not reach the environment, so that the hood for the drying section can be constructed relatively simply.

The temperature in the suction blow boxes is in a range of 100° C to 200° C, while the temperature of the heated cylinders 13 and 15 on the surface is 150° C to 300° C. The heating of the cylinders 13 and 15 can be carried out with steam or hot gas. It is important that the temperature in the heated cylinders 13 and 15 is higher than that in the suction blow boxes, also referred to as cooling devices 19 and 21. In this way, a temperature gradient is set from the surface of the heated cylinders 13 and 15 across the metal belt 11 and the material web 7 and across the conveyor belt 9, due to which the moisture from the material web passes through the conveyor belt 9 into the suction blow boxes. The conveyor belt is porous and can be made of plastic or metal.

The diameter of the heated drying cylinders 13 and 15 can be in the range of 1.5 m to 5.0 m.

However, drying cylinders with an outer diameter of 2.2 m are preferred.

The cylinder 17 has a smaller diameter. It is in the range of 1.0 m to 1.5 m. Steam or water can be used to cool the cylinder 17 in order to set a temperature on the outer surface of the cylinder 17 of 90° C to 120° C.

The metal band 11 running around the outside of the cylinder 17 is heated in the support area of the cylinder 17 on the side opposite the cylinder 17. A heating device 23 is indicated here. This external heating can be operated either with hot gas or with infrared or electrically.

The heat transport from the metal belt 11 to the material web 7 creates water vapor within the paper web, which condenses on the cooler conveyor belt 9, which acts as a drying screen. The water is removed from the paper web through these combined heat and material transport processes.

To support this material transport, the surface of the cylinder 17, also referred to as the cooling cylinder, can be provided with grooves 25 running in the circumferential direction into which the moisture can enter. The removal of the moisture is particularly effective if the grooves 25 are subjected to a negative pressure using a suitable negative pressure source 27 and an external suction box 29.

The conveyor belt 9 and the metal belt 11 are pre-tensioned so that in the area of the heated cylinders

Linder 13 and 15 with an outer diameter of 2.2 m results in a surface pressure of 10 kPa to 100 kPa. It has been found that the drying section can also have a surface pressure of > 2 kPa or > 4 kPa.

Under the high pressure and under the influence of the high temperature, the paper web achieves very high strength properties, which are based on the softening of the lignin and hemicellulose present in the paper as well as the increased fiber connection points.

In order to be able to achieve even higher pressing pressures if necessary, a press device 31 is provided here, which comprises a press roller 33 that interacts with the surface of the cooled cylinder 17. The press roller 33 acts on the metal strip 11, whereby the underlying material web 7 and the conveyor belt 9 are strongly compressed.

The conveyor belt 9 running from the surface of the cylinder 17 - which is preferably cooled here - is relatively moist because it has absorbed the moisture escaping from the material web 7 or paper web in the area of the cylinder 17. The conveyor belt 9 is exposed to hot air H in the area of the suction blow boxes or cooling devices 19 and 21, which removes the moisture from the conveyor belt and dries it. At the same time, the moisture escaping from the material web 7 heated from below is absorbed in the area of the cooling devices and removed with the exhaust air A. The use of the cooling devices 19 and 21 designed as suction blow boxes leads to a significantly higher drying

effect than other devices. Another advantage is that the exhaust air on the surface of the conveyor belt 9 or the paper web carries moisture escaping directly away from the area where it is created.

The high contact pressure results in optimal heat transport from the heated and cooled surfaces to the material web or paper web, which leads to very good heat transfer. In addition, the paper web is subjected to additional heating or cooling as it passes through the cylinders, which are alternately heated and cooled (seen in the direction of travel of the paper web), in order to set a large temperature gradient within the paper web. This results in high evaporation performance, so that the drying section can be constructed very compactly. In many cases, the number of cylinders used can be reduced compared to conventional systems.

The material web 7 is permanently clamped between the conveyor belt 9 and the metal belt 11 as it passes through the drying group 5. This is clearly shown in Figures 2 to 5. By clamping or clamping the material web, free shrinkage is prevented, whereby it has the same properties across the width of the web. The quality of the material web is thus significantly increased.

The drying section 3 can, as indicated in Figure 1, have several drying groups 5. In Figure 2 it is indicated that a drying group 5 is followed by a further drying group 5a.

In addition to the heated cylinders 13 and 15, the drying group 5 has, for example, a third heated cylinder 15', to which the heated cylinder 13a of the second drying group 5a is connected. In addition to the cylinder 17, another cylinder 17' of the first drying group 5 - also preferably cooled - can be seen here. The conveyor belt 9 is guided back from the end of the first drying group 5 via a deflection roller 35 to the beginning of the drying group 5 on a deflection roller 37. The metal strip 11 is guided back to the beginning of the drying group 5, for example on a deflection roller 37.

The conveyor belt 9a of the second drying group 5a is brought to the peripheral surface of the heated cylinder 15', so that the material web 7 between the metal belt 11 and the conveyor belt 9a is transferred from the heated cylinder 15' to the first - also preferably cooled - cylinder 17a of the second drying section 5a. The metal belt 11a is guided onto the first cylinder 17a via a deflection roller 39a, so that the material web 7 or paper web is also safely guided between the conveyor belt and the metal belt in the area of the second drying group 5a.

In the embodiment shown here, the heated cylinders of the two drying groups 5 and 5a lie in a common plane El. Accordingly, the centers of the cooled cylinders of both drying groups 5 and 5a lie in an imaginary plane E2.

For the structure of the drying groups 5 and 5a, please refer to the illustration in Figure 1 and the associated explanations.

In one embodiment of the papermaking machine 1 or the drying section 3, even when moving from one drying group to the other, the underside of the material web 7 or paper web is always heated by the surface of the heated cylinders 13, 15, 15', 13a and so on, while the top side of the paper web is assigned to the surface of the cooled cylinders 17, 17', 17a and so on.

In order to reduce the two-sidedness of the material web, alternating drying is also possible. This is evident from the illustration in Figure 3, which again shows two adjacent drying groups 5 and 5a of a drying section 3. The transfer of the paper web takes place here in such a way that the material web 7 is transferred from the last - also preferably cooled - cylinder 17" of the first drying group 5 to the first cooled cylinder 17a of the second drying group 5a. From there, the paper web runs together with the metal belt 11a located at the top and the conveyor belt 9a located at the bottom to the first drying cylinder 13a of the second drying group 5a. The centers of the drying cylinders of the first drying group 5 lie in a plane El, while the centers of the cylinders 17, 17' and 17" lie in a second plane E2. The centers of the heated cylinders 13a and so on of the second drying group 5a lie in the plane EIa, while the centers of the preferably cooled cylinders 17a and so on lie in the imaginary plane E2a.

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Here the level E2a lies below the level EIa, while the situation is reversed in dry group 5.

Figure 4 shows a modified form of a drying group 50, in which the heated cylinders 13, 13', 13", 15, 15', 15" are arranged on an imaginary V-shaped line. This also applies to the heated and cooled cylinders of the subsequent drying group 50a. In the embodiment of the drying section 30 of the papermaking machine 1 shown in Figure 4, the material web 7 is transferred in such a way that its underside is always assigned to the heated cylinders and its top side to the cooled cylinders of the drying groups 50 and 50a.

According to the illustration in Figure 3, the drying section 30, as shown in Figure 4, can also be redesigned in such a way that alternating drying of the paper web is ensured, so that in the first drying group 50 the underside of the paper web comes into contact with the heated cylinders and in the second drying group 50a the top side of the paper web comes into contact with the heated cylinders. In this respect, reference is made to what has been said about Figure 3, where such a change has already been explained.

Finally, Figure 5 shows a section of the papermaking machine 1, namely the transition from a press section 43 to the first drying group 5 of the drying section 3. The drying group 5 has parts that correspond to those in Figure 1. These have been given the same reference numerals, so that reference can be made to the description of Figure 1.

The press section 43 has a web guide roller 45, which together with a press cylinder 47 and a dewatering belt 48 forms a gap 53 in which the material web 7 is compressed and dewatered. The web guide roller 45 is followed - viewed in the machine direction - by a so-called central roller 51, which is designed as a web guide roller. A press cylinder 49 and a dewatering belt 50 are assigned to the central roller 51 in such a way that a gap 55 is formed. A transfer belt 52 that transfers the material web 7 from the press section 43 to the drying section 3 is brought to the central roller 51, i.e. to the last web guide roller of the press section 43. The end of the press section 43 or the beginning of the drying section 3 is marked with a dot-dash line V.

The material web 7 runs around the web guide roller 45 and is pressed together in the gap 53, whereby the material web 7 is compacted. The liquid squeezed out is absorbed by the dewatering belt 48. The compaction leads to an increase in the subsequent drying. The material web runs off the web guide roller 45 and, together with the transfer belt 52, onto the central roller 51. The material web 7 is guided around the central roller 51, resting on the outside of the transfer belt 52, and is compacted and dewatered in the gap 55. After the material web 7 runs off the central roller

51, the web is guided by the transfer belt 52 to the deflection roller 37 of the drying group 5, which guides the metal belt 11. As can be seen from Figure 5, the material web 7 is guided in the area of the deflection roller 37 between the metal belt 11 and the transfer belt

52 and a web guide roller 57 is pulled

The metal strip 11, the material web 7 and the transfer belt 52 run around the web guide roller 57, where the transfer belt 52 is fed again to the central roller 51 arranged within the press section 43 after running off the web guide roller 57 by means of a deflection roller 61. The metal strip 11 and the material web 7 run together onto the first drying cylinder 13 of the drying group 5, where a web stabilizer 59 arranged in the transfer area between the web guide roller 57 and the drying cylinder 13 exerts an attractive effect on the porous metal strip and the material web. The web stabilizer 59, which is preferably designed as a suction box and connected to a vacuum source, prevents the material web from fluttering in the transfer area, whereby a web break can be practically ruled out. The conveyor belt 9, also referred to as a drying felt or screen, is fed to the metal belt 11 and the material web 7 in the run-up area of the drying cylinder 13 by means of deflection rollers, of which only the deflection rollers 63 and 65 are shown here. The material web 7 is clamped between the conveyor belt 9 and the metal belt 11 resting on the drying cylinder 13 and, together with these - as already described above - is guided around the cylinders 13 to 17, to which heating or cooling devices are assigned.

The transfer of the material web 7 from the press section 43 to the drying section by means of the transfer belt 52 offers the possibility of guiding a transfer belt quickly and safely through the paper production machine 1 in the event of a material web break. The paper production machine 1 therefore has

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due to relatively short downtimes, which increases their profitability.

After all, it is clear that the high surface pressure and the high temperature differences achieved by special heating and cooling ensure a high drying performance, while at the same time producing a paper web with particularly high strength values. The drying section can be made relatively short due to the good drying values.

At the same time, it is clear that the risk of tearing is reduced to a minimum due to the guidance of the paper web as described here. The firm clamping of the paper web prevents shrinkage across the width of the web, so that the paper properties are very uniform across the width.

In particular, when guiding the paper web between the conveyor belt and the metal belt, there is the advantage that the introduction of a so-called paper strip, namely a narrow strip of material, can be carried out fully automatically before the paper production machine is operated. This makes the device ideal for a so-called tower or V-arrangement of the drying cylinders, as explained in Figure 4.

The material web rests on the metal belt as it passes through the drying group, preventing it from coming into contact with the surface of the drying cylinder. This prevents the material web from sticking or adhering to the drying cylinder and ensures safe passage through the drying group.

of the material web through the drying section.

From the above it is clear that the cylinders 17, 17', 17' and 17a, which are in contact with the conveyor belt, can also be designed without cooling and can be of conventional design. It is conceivable to design these cylinders as externally and/or internally suctioned suction rollers. It has also been shown that the very high surface pressure mentioned above can also be below 10 kPa, i.e. it can also assume values of >2 kPa or >4 kPa.

Claims (19)

Gleiss & Große Patent Attorneys Stuttgart Berlin Hamburg Protection Claims 1. Device for producing a material web, in particular a paper or cardboard web, in a drying section which comprises at least one drying group which has a number of cylinders which - viewed in the direction of travel of the material web - are alternately heated and cooled, around which the material web is guided in a meandering manner together with a porous conveyor belt and with a metal belt, the material web being arranged between the conveyor belt and the metal belt, characterized in that the metal belt (11) and/or the conveyor belt (9) are strongly pre-tensioned and that additional heating devices (23) and/or cooling devices (19,21) are assigned to the cylinders (13, 15, 17), which act on regions of the circumference in which the material web (7) rests with the conveyor belt (9) and the metal belt (11). 2. Device according to claim 1, characterized in that the metal strip (11) rests directly on the heated cylinders (13, 15), that the conveyor belt (9) rests directly on the preferably cooled cylinder (17) and the metal strip (11) is heated in the region of the cylinder (17) by means of an external heating device (23) and the 13 416GL-ho
!4 October 1996 -2- Conveyor belt (9) is cooled in the area of the heated cylinder (13,15). 3. Device according to claim 1 or 2, characterized in that the surface of the cylinder (17) is provided with circumferential grooves (25). 4. Device according to one of the preceding claims, characterized in that the cylinders (17) are suctioned - preferably by means of an external suction box (29). 5. Device according to one of the preceding claims, characterized in that a pressing device (31) is provided in the region of a cylinder (17). 6. Device according to one of the preceding claims, characterized in that a cooling device (19, 21) designed as a blowing, suction or suction-blowing box is provided in the peripheral region of the heated cylinder (13, 15) for drying the conveyor belt (9). 7. Device according to one of the preceding claims, characterized in that the centers of the heated cylinders (13, 15) are arranged in an imaginary plane (El) and those of the cylinders (17) are arranged in an imaginary second plane (E2) which is arranged at a distance from the first plane (El). -3- 8. Device according to one of the preceding claims, characterized in that the drying section (3) has at least two drying groups (5,5a). 9. Device according to one of the preceding claims, characterized in that the centers of the heated cylinders (13a) of the second drying group (5a) are also arranged in the plane (El) and those of the preferably cooled cylinders (17a) are also arranged in the plane (E2). 10. Device according to one of the preceding claims, characterized in that the centers of the heated cylinders (13a) of the second drying group (5a) are arranged in a third plane (EIa) and those of the cylinders (17a) in a fourth plane (E2a). 11. Device according to one of the preceding claims, characterized in that the heated cylinders (13, 15) of the first drying group (5) are arranged above or below the cylinders (17) and that the heated and cooled cylinders (13a, 17a) of the second drying group (5a) are arranged opposite to those in the first drying group (5). 12. Device according to one of claims 1 to 6, characterized in that the centers of the cylinders (13,13·,13",15,15',15") are arranged on a V-shaped line. -4- 13. Device according to one of the preceding claims, characterized in that the material web (7) is guided in such a way that only the upper side or lower side is cooled or heated within the drying section (3). 14. Device according to one of the preceding claims 1 to 12, characterized in that the material web (7) is guided in such a way that the upper and lower sides are alternately cooled and heated from drying group to drying group. 15. Device according to one of the preceding claims, characterized in that each drying group (5, 5a) has a separate conveyor belt (9, 9a) and/or separate metal belt (11, 11a). 16. Device according to one of the preceding claims, characterized in that the metal strip (11) is guided so that it always comes into contact with the surface of a heated cylinder. 17. Device according to one of the preceding claims, characterized in that the conveyor belt (9) is guided so that it always comes into contact with the surface of a cooled cylinder. 18. Device according to claim 1, characterized in that the pre-stressed metal band (11) and/or conveyor belt (9) results in a surface pressure of > 2 kPa or > 4 kPa, preferably from 10 kPa to 100 kPa. -5- 19. Device according to one of the preceding claims, characterized in that the cylinders (17, 17', 17", 17a) are designed as externally and/or internally suctioned suction rollers.