EP0726354A1 - Dryer group of a dryer section for web material - Google Patents

Abstract

The drying group of the drying section of a machine for a web material, and especially a papermaking machine, has a number of permeable drying blankets (9,11,13,15) at the drying cylinder (1), passing round it over each other, with at least two blankets at different positions on the peripheral surface of the drying cylinder (1). Pref. the drying blankets (9,11,13,15) have different permeabilities, decreasing from the lowest level at the drying cylinder (1), outwards. The angle (a-d) round the drying cylinder (1), covered by the drying blankets (9,11,13,15), decreases outwards from the lowest level. The strength of the innermost blanket (9) is less than the others (11,13,15), and it is finer and/or thinner than them. The drying blankets (9,11,13,15) are applied simultaneously or in succession to the web material. The system uses 2-4 blankets, in a drying group in a single row, with alternating drying cylinders and deflection rollers in separate rows, using drying suction rollers for the path deflection. The drying cylinders and the deflection rollers have about the same dia..

Description

The invention relates to a dryer section of a dryer section for web-like material, in particular a paper machine according to the preamble of claim 1.

Such a generic drying group is known for example from DE 44 16 585 A1. In this document, several drying groups forming a drying section are shown, each of which has a multiplicity of heatable drying cylinders and an endless pressure belt (also referred to below as a drying sieve) which presses the material web to be dried onto the drying cylinders.

Basically, single-tier and double-tier dryer groups are known from the prior art. In the case of a single-row dryer group, the material web alternately runs around the drying cylinder and deflection rollers in a meandering shape. When passing through the drying group, only one side of the material web comes into contact with the drying cylinder surface while the other side of the material web is supported by the pressure belt.

In the case of a two-row dryer group, the material web likewise runs through a meandering web, but in each case it is guided from one drying cylinder in one row to the subsequent drying cylinder in the other drying cylinder row. Thus one side of the material web comes into contact with the drying cylinders of the one row and the other side comes into contact with the drying cylinders of the second row of drying cylinders. Usually, each of the two rows of drying cylinders is assigned a pressure belt, which presses the material web onto the drying cylinder surface.

In a dryer section of a paper machine, single-row and double-row dryer groups are often used in combination to influence the material properties, such as the shrinkage behavior and the strength of the web.

A further increase in the material web strength can be achieved in that the temperature inside the material web reaches a value of more than 100 ° C. if possible. For this, gas-fired drying cylinders are often used, which enable temperatures of around 300 ° C. Through the additional use of strongly tensioned, fixed pressure bands, the vapor pressure inside the material web rises to a value that is high compared to the ambient pressure.

However, this gives rise to the problem that when the pressure band is lifted off the surface of the material web, the vapor pressure prevailing inside the material web suddenly relaxes. A sudden bursting of the material web or in the worst case a material web tear are the result of this sudden steam escape from the interior of the material web.

The object of the invention is therefore to propose a drying group, in which the web of material bursts and / or web breaks are prevented in a simple manner.

This object is achieved by means of a drying group with the features mentioned in claim 1.

In this dryer group, several dryer fabrics are used, which loop around a drying cylinder with different angles. The fact that at least two of the several dryer fabrics are removed from the dryer cylinder at different positions makes it possible to prevent the abrupt steam discharge mentioned above and thus the risk of the paper web bursting or tearing.

In particular, by using, for example, three or more drying screens which are successively guided away from the drying cylinder, the contact pressure acting on the material web can be gradually reduced, the vapor pressure decreasing can also gradually dismantle. This effect of the gradual vapor pressure reduction can be improved in a further embodiment of the invention in that the individual dryer fabrics have different permeabilities, that is to say vapor permeabilities, the - from the drying cylinder, the outermost dryer fabric preferably having a permeability of zero and the more internal dryer fabrics from Have zero different permeabilities, which preferably increase inwards.

In a further embodiment of the invention, the outer dryer fabrics enclose a smaller area of the drying cylinder than dryer fabrics located further inside. Preferably, the wrap angle of the individual dryer fabrics - as seen from the dryer cylinder - increases from the outside to the inside.

In a further advantageous embodiment of the invention, the innermost dryer fabric is made finer and / or thinner than dryer fabrics located further outside. A very good smooth surface structure of the material web can be achieved with the fine dryer fabric lying directly on the material web. Since large sieve tensions cannot be reached with such fine dryer fabrics, firmer or thicker dryer fabrics that allow higher fabric tensions are used for the dryer fabrics located further out.

The invention can be provided in both single-tier and double-tier dryer groups.

Further advantageous embodiments of the invention result from the subclaims.

Figur 1

schematisch einen Ausschnitt aus einer einreihigen Trockengruppe;

Figur 2

schematisch einen Ausschnitt aus einer weiteren einreihigen Trockengruppe;

Figur 3

schematisch einen Ausschnitt aus einer zweireihigen Trockengruppe;

Figur 4

schematisch einen Ausschnitt aus einer mehrere Trockengruppen umfassenden Trockenpartie und

Figur 5

schematisch einen Ausschnitt aus einer weiteren Trockenpartie.

The invention will now be described with reference to exemplary embodiments and the drawing. Show:

Figure 1

schematically shows a section of a single-tier dryer group;

Figure 2

schematically a section of another single-tier dryer group;

Figure 3

schematically a section of a two-tier dryer group;

Figure 4

schematically a section of a dryer section comprising several dryer groups and

Figure 5

schematically a section of another dryer section.

A drying cylinder 1 shown in FIG. 1 and two deflection rollers 3 and 5 adjacent to it are part of a single-row drying group. Such a single-row dryer group usually consists of a plurality of drying cylinders, for example arranged in a row, and a plurality of deflecting rollers. Drying cylinders and deflection rollers are arranged in such a way that the paper web meanders Drying group passes through, the paper web alternately passing the deflecting rollers and drying cylinders.

In the exemplary embodiment shown, a paper web 7 first runs around the deflection roller 3, then around the drying cylinder 1 and then around the further deflection roller 5. The angle α wrapped around by the paper web 7 on the drying cylinder 1 or wrapping area depends on the distance or the arrangement of the two deflection rollers 3 and 5. In this wrap area defined by the wrap angle a, the paper web 7 is heated via the outer surface of the drying cylinder 1. Usually the inside of the drying cylinder is fed with steam. If, however, higher temperatures are to be reached, for example of approximately 300 ° C., then the cylinders are gas-fired, that is to say combustion of gases in the interior of the cylinder.

In addition to the first endless dryer fabric 9, three additional endless dryer fabrics 11, 13 and 15 are provided in the area of the drying cylinder 1. All three dryer fabrics 11, 13 and 15 are brought together via a common deflecting roller 17 with the first dryer fabric 9 at a common point 19. Thus, in this area on the paper web 7 there are first the dryer fabric 9, then the dryer fabric 11, the dryer fabric 13 and on the very outside the dryer fabric 15.

The contact pressure exerted on the paper web 7 is consequently composed of the individual force components generated by the four dryer fabrics 9, 11, 13 and 15.

After a wrap angle b, the outermost dryer fabric 15 is removed from the drying cylinder 1 via a deflecting roller 21 and returned to the deflecting roller 17 via a further deflecting roller 21a.

The same procedure is followed with the dryer fabric 13 via deflection rollers 23 and 23a according to a wrap angle c and with the dryer screen 11 via deflection rollers 25, 25a and 25b according to a wrap angle d. The drying fabric 9 alone remains in contact with the paper web 7 even when the deflecting roller 5 rotates.

It is clear from FIG. 1 that the wrap angle a of the innermost dryer fabric 9 is greatest, while the wrap angles d, c, b of the successive dryer fabrics 11, 13, 15 gradually decrease.

With this embodiment according to the invention, the contact pressure acting on the paper web 7 can be gradually reduced, all four dryer fabrics 9, 11, 13 and 15 being in the angular range b and thereby the greatest contact pressure being applied while it becomes zero at the end of the angular range a. So there are four different pressure zones Z1, Z2, Z3 and Z4.

If the paper web 7 runs into the printing zone Z1, it is subjected to a very high contact pressure, so that there is a particularly good heat transfer from the drying cylinder 1 to the paper web 7. This also has the consequence that the water vapor which forms as a result of the heating cannot escape inside the paper web. The result is a high vapor pressure compared to the ambient pressure. In the pressure zone Z2, the contact pressure is somewhat reduced, which also lowers the vapor pressure. A further reduction in the contact pressure and the vapor pressure in the interior of the paper web takes place in the pressure zone Z3 and then in the pressure zone Z4, the difference between the vapor pressure in the interior of the paper web and the ambient pressure being relatively small.

When the paper web 7 is subsequently removed from the drying cylinder 1, the paper web 7 does not burst due to the aforementioned low vapor pressure, since a large part of the vapor pressure has previously been able to relax in the pressure zones Z2 and Z3 or Z4 or a part of the steam could escape.

An increase in the effect caused by the pressure zones can be achieved by selecting dryer fabrics 9, 11, 13 and 15 with different permeabilities.

In the pressure zone Z1 you want to have a high pressure or a high water vapor pressure. For this reason, the outermost dryer fabric web 15 is included a permeability of 0, i.e. impermeable to water vapor. The permeability of the underlying dryer fabrics 13, 11, 9 then increases from web to web, so that the water vapor permeability gradually increases from pressure zone Z2 to pressure zone Z4. With this, the vapor pressure can additionally be gradually reduced to a value which is harmless with regard to the bursting of the paper web.

The choice of a very fine first dryer fabric 9 can effectively prevent screen markings 7 from forming on the paper web surface on the paper web coming into contact with the dryer fabric. The sieve tensions that can be achieved with such finer dryer fabrics are indeed very low, but can be compensated for by the further dryer fabrics 11, 13 and 15 which are of correspondingly stronger design.

FIG. 2 shows a further exemplary embodiment of the drying group, which in turn is a single-row drying group. In comparison to FIG. 1, however, several drying cylinders 1 lying in a row and a plurality of dryer fabric suction rolls 27 are shown.

In this embodiment, instead of the four dryer fabrics described above, only three dryer fabrics 9, 11 and 13 are used. In contrast to the example shown in Figure 1, the individual dryer fabrics 9, 11 and 13 are not after each Drying cylinder returned, but only at the end of the drying group.

Otherwise, the basic structure of this exemplary embodiment corresponds to that shown in FIG. 1. Here too, in addition to the dryer fabric 9 running with the paper web 7, two additional dryer fabrics 11 and 13 are used, which converge with the dryer fabric 9 at the beginning of a drying cylinder and are removed from the drying cylinder again after different wrap angles c and d. Between the individual drying cylinders 1, the dryer fabric 13 is assigned to the deflection rollers 23 and the dryer fabric 11 to the deflection rollers 25. The respective wrap angle c or d per drying cylinder 1 can be set by the corresponding arrangement of these deflecting rollers. Furthermore, the two dryer fabrics 11 and 13 can also be successively applied to the drying cylinders via the deflection rollers 23 and 25, as can be clearly seen in FIG. 2 for the rear drying cylinders. At the end of the drying group, the two additional drying fabrics 11 and 13 are removed from the last drying cylinder 1 via the common deflecting roller 23 and guided to the beginning of the drying group.

The functioning of this exemplary embodiment corresponds to that of FIG. 1, which is why a further description is not given here.

In contrast to the arrangement shown in FIG. 1, so-called dryer fabric suction rolls 27 are used instead of the simple deflection rolls 3 and 5. These have suction zones 29 which lie in that circumferential region of the rollers, past which the dryer fabric 9 and the paper web 7 are guided.

With the help of these dryer fabric suction rolls, the paper web 7 can be sucked onto the dryer fabric 9 in the area of the suction zones 29. Due to the increased frictional forces of the paper web on the dryer fabric, shrinkage is prevented or reduced. In addition, fluttering of the paper web 7 is avoided when the dryer fabric suction roller rotates.

From Figure 2 it can also be seen that the diameters of the dryer fabric suction rollers 27 correspond approximately to the diameters of the drying cylinders 1. In comparison to the exemplary embodiment shown in FIG. 1, the drying cylinder diameters are somewhat smaller and the deflecting roller diameters, that is to say suction roller diameters, have become larger. Such an adjustment of the diameter leads on the one hand to a particularly wide wrapping of the drying cylinders through the paper web 7, with the result of improved heat transfer from the drying cylinder to the paper web. On the other hand, the dryer fabric suction rolls can be made stiffer, so that an increase in the longitudinal tension of the dryer fabric is possible.

Due to the higher longitudinal tension of the dryer fabric and the resulting pressure force on the paper web, its strength can be increased by additional compression of the material.

FIG. 3 shows an exemplary embodiment in which the principle of the invention is applied to a two-row dryer group. As already mentioned, a two-row drying group is usually composed of drying cylinders 31 and 41 arranged in two rows. The paper web 7 passes through the drying group alternately from a drying cylinder 31 in the upper row to a drying cylinder 41 in the lower row, etc.

Corresponding to dryer fabrics 9, 11, 13 and 15 of FIG. 1, dryer fabrics 32, 33, 34 and 42, 43, 44 are assigned to each dryer cylinder row.

At the beginning of the two-row dryer group, the dryer fabric 32 is brought together with the paper web 7 via a deflection roller 35 and, after a wrap angle a, is removed from the drying cylinder 31 via a further deflection roller 35a. This deflecting roller 35a in turn serves to bring the dryer fabric 32 together with the paper web 7 on the next drying cylinder 31 of the upper drying cylinder row. This process is then repeated until the last drying cylinder 31 of the upper row, with a deflecting roller 35c returning the drying wire 32 to the beginning of the drying group.

Deflection rollers 36a, 36b and 37a, 37b corresponding to the deflection rollers 35a, 35b are assigned to the dryer fabrics 33 and 34, respectively. Only the feed at the beginning of the drying group and the return at the end of the drying group are each carried out via a common deflecting roller 38 or 38a.

A correspondingly offset arrangement of the deflection rollers 35a, 36a, 37a or 35b, 36b and 37b results in a different looping of the drying cylinders 31 by the drying fabrics 32, 33 and 34, as has already been described in detail in connection with FIGS. 1 and 2. The wrap angle c of the outermost dryer fabric 34 is the smallest, the wrap angle a of the innermost dryer fabric 32 is the largest. The effect of these different wrap angles was also explained in detail using the exemplary embodiment according to FIG. 1. A repeated description is therefore omitted.

Since the two-row drying group shown in FIG. 3 is constructed symmetrically, the drying screens 42 to 44 assigned to the lower drying cylinder row 41 are guided in the same way by means of deflecting rollers 45 to 48 corresponding to the drying screens of the upper drying cylinder row.

In Figure 4, a section of a dryer section is shown schematically, the several in a row switched single and double row dryer groups 51, 53, 55 and 57.

The paper web, for example coming from an upstream press section, first runs into the two-row dryer group 51 and is heated there. In the subsequent single-row dryer group 53, in which the drying cylinders are at the top, the paper web is heated more and is pressed against the cylinders more strongly than in dryer group 51 by means of increased dryer fabric tension (arrow S), in order to achieve good heating and compression of the material. In this example, only the last two drying cylinders of dryer group 53 are assigned the plurality of dryer fabrics according to the invention, while in FIG. 2 several dryer fabrics run over all cylinders 1 of the dryer group.

In the subsequent single-row dryer group 55 of FIG. 4, in which the drying cylinders are arranged in the lower row, the paper web is again subjected to an increased contact pressure, the several dryer fabrics according to the invention being assigned to two drying cylinders which are arranged in the front region of the dryer group.

The end of the dryer section can then form a two-row dryer group 57.

In the exemplary embodiment shown in FIG. 4, the drying cylinders interacting with the plurality of dryer fabrics are dryer group 53 and the dryer group 55, each gas-fired, in order to reach higher temperatures in the range of approximately 300.degree. C., the risk of bursting on these dryer cylinders then being particularly great without the dryer fabrics according to the invention.

FIG. 5 shows an embodiment similar to FIG. 4, but differences can be seen in the single-row dryer groups 53 and 55. In the dryer group 53, all dryer cylinders are assigned two dryer fabrics, while the dryer cylinders of dryer group 55 are assigned three dryer fabrics, corresponding to the example shown in FIG.

Of course, the present invention, that is to say the assignment of a plurality of dryer fabrics to a dryer cylinder within a dryer group or a complete dryer section, can be carried out as desired. The use is not only limited to the single-tier dryer groups shown in FIGS. 4 and 5. It is therefore also possible to provide a two-row dryer group in which a plurality of dryer fabrics lying one above the other are assigned to both the upper and the lower row of dryer cylinders.

Claims (10)

Drying group of a dryer section for web-like material, in particular a paper machine, with at least one drying cylinder (1), a drying wire (9) which partially wraps around the drying cylinder (1), the web-shaped material (7) between drying cylinder (1) and drying wire (9 ), characterized in that the drying cylinder (1) is assigned a plurality of drying screens (9, 11, 13, 15) which are guided one above the other around the drying cylinder (1), with at least two drying screens at different circumferential positions from the drying cylinder (1) be removed. Drying group according to claim 1, characterized in that the drying fabrics (9, 11, 13, 15) have different permeabilities, the respective permeability - seen from the drying cylinder (1) - preferably decreasing from the inside to the outside. Drying group according to one of the preceding claims, characterized in that the wrap angle (a to d) of the individual drying fabrics (9, 11, 13, 15) - seen from the drying cylinder (1) - decreases from the inside to the outside. Drying group according to one of the preceding claims, characterized in that the strength of the innermost dryer fabric (9) is lower than the strength of the dryer fabrics (11, 13, 15) located further out. Drying group according to one of the preceding claims, characterized in that the innermost dryer fabric (9) is made finer and / or thinner than dryer fabrics (11, 13, 15) located further out. Drying group according to one of the preceding claims, characterized in that the drying fabrics (9, 11, 13, 15) are applied to the web-shaped material simultaneously or in succession. Dryer group according to one of the preceding claims, characterized in that two to four dryer fabrics are used. Drying group according to one of the preceding claims, characterized in that it is a single-row drying group in which drying cylinders and deflecting rollers are alternately arranged in different rows. Drying group according to claim 8, characterized in that the deflecting rollers (27) are constructed as dryer fabric suction rollers. Drying group according to claim 8 or 9, characterized in that the diameters of the drying cylinders and the deflecting rollers are approximately the same.

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