EP0748895A2 - Calender - Google Patents

Abstract

A calender has at least one roll stack (1), the upper roll (2) and lower roll (3) of which are each designed as a deflection compensation roll. The roller jacket (15, 15a) of the top roller (2) and / or the bottom roller (3) is covered with an elastic plastic or consists entirely of elastic plastic and is designed to be flexible. The adjacent center roll is a hard roll (4, 13). This leads to improved setting options for achieving the desired parameters of the paper web. <IMAGE>

Description

The invention relates to a calender with at least one roll stack, each as a top roll and bottom roll, a deflection compensating roll with a roll shell, which is supported by hydrostatic support elements on a rotating carrier that passes through it, and as middle rolls, hard rolls and elastic rolls, which rolls form at least four working gaps, which are delimited by a hard and an elastic roller, and optionally an alternating gap, which is delimited by two elastic rollers.

Calenders of this type are widely known, for example from the brochure "The New Super Calender Concepts" from Sulzer Papertec Krefeld GmbH from 1994 (code number 05/94 d). They are used for the final treatment of a paper web so that it has a desired one Value of smoothness, gloss, thickness, bulk and the like. receives. The "soft" or elastic rollers carry a cover consisting mainly of fiber material. If part of the deformation energy is to be supplied as heat, the heating is carried out by means of the hard center rolls. The top roller and bottom roller are also to be regarded as hard rollers because their roller shells are made of chilled cast iron. The third roller is usually driven from below.

The invention is based on the object of specifying a calender of the type described at the outset which offers better setting options with regard to the uniformity of the desired paper parameters.

ausgelegt ist, wobei
E = E-Modul des Walzenmantels in N/mm²
S = Wandstärke des Walzenmantels in mm,
und daß die jeweils benachbarte Mittelwalze eine harte Walze ist.This object is achieved in that the roller shell of the top roller and / or the bottom roller has a cover made of an elastic plastic or consists essentially entirely of elastic plastic and is flexible with a deformability factor $$\mathit{\text{F}}\text{= (}\frac{{\text{1.4 · 10}}^{\text{5}}\text{)}}{\mathit{\text{E}}}\text{)}\mathit{\text{x}}\text{(}\frac{\text{100}}{\mathit{\text{S}}}{\text{)}}^{\text{2.65}}\text{≧ 4}$$

is designed, whereby
E = modulus of elasticity of the roll shell in N / mm ²
S = wall thickness of the roll shell in mm,
and that the adjacent center roll is a hard roll.

The flexible roll shell is much easier to deform than the known chilled cast iron shells. This can be achieved with a smaller modulus of elasticity than with hard cast iron and / or with smaller wall thicknesses. Since the roller shell is provided with an elastic plastic at least on the surface, the roller shell acts as an elastic roller to which a hard roller can be assigned as the top or bottom middle roller. The improved adjustability arises because the forces exerted by the support elements act on the paper to a much greater extent and are not distorted by the rigidity of the roller shell, and also because the hard roller fully absorbs local changes in the line load of the deflection compensation roller and therefore the reactions of the deflection compensation roller to this Paper are stronger.

With a smaller wall thickness, the effective weight of the deflection compensation roller is considerably reduced. This is noticeable in terms of costs. In the case of a top roller designed according to the invention, the minimum line load with which the calender can be operated is also reduced. The smaller wall thickness also leads to a smaller outer diameter and thus, with the same line load, to a higher compressive stress in the roll gap, which leads to better results. Another advantage is that the calender runs more smoothly. The elastic plastic dampens shocks from the roll stack.

It is preferred that the deformability factor is> 5. Values between 6 and 10 and more are also possible.

It is also favorable that the roller jacket consists of a material with insufficient wear resistance and has a cover made of the elastic plastic, and that the plastic has a higher wear resistance than the jacket material.

This applies in particular if the roller jacket is made of lamellar graphite cast iron, ie a cast iron with lamellar cast iron Graphite. This material has a modulus of elasticity which is about 25% lower than that of chilled cast iron. The wall thickness can be reduced by almost 50% compared to the chilled cast iron roll jacket. With this material, deformability factors F between 6 and 8 can be achieved. However, this cast iron is not very wear-resistant. This disadvantage is compensated for by the fact that the cover made of elastic plastic, which is provided for other reasons, also serves as a wear protection layer. For this purpose a plastic layer between 8 and 15 mm, preferably 10 mm is sufficient.

An alternative provides that the roll shell consists of spheroidal graphite cast iron, ie a cast iron with spherical graphite, and has a cover made of elastic plastic. This allows a reduction in wall thickness compared to chilled cast iron of up to 59% and thus leads to a deformation factor F above 8.

The plastic is particularly advantageous as a fiber-reinforced epoxy resin. Glass or carbon fiber reinforced epoxy resin can be designed so that on the one hand the desired elasticity and on the other hand the required wear resistance is present. An example of this is a cover from "TopTec 4" from Scapa-Kern, Wimpassing / Austria.

It is also favorable that the deflection compensation roller has a multi-zone control in which hydraulic fluid with different pressure can be supplied to the support elements individually or in pairs. While such a single or pair control would hardly have had an impact on the outside of a chilled cast iron roll jacket, it is now possible to influence the paper individually over very narrow areas even in the uppermost working gap, which leads to a high level from the outset Uniformity of the desired parameters leads across the paper web.

Another decisive advantage is obtained if at least the top middle roll can be heated. Deformation energy in the form of heat is therefore already supplied to the paper web in the first working gap. This has the advantage over an otherwise necessary heating of the top roller that the top roller can be made much simpler and cheaper, is exposed to lower temperatures and can be deformed more without the seal suffering as a result.

However, it is even cheaper if all hard center rolls can be heated. The fact that the top and possibly also the bottom center roll is designed as a hard roll, the number of hard and thus heatable center rolls can be increased by one while maintaining the total number of rolls. This allows more thermal energy or the same thermal energy to be supplied at a lower temperature level in a simple manner.

In particular, heating can be carried out here by means of steam, which can be supplied with excess pressure. This type of heating is much simpler and cheaper than heating with oil, as would be required with a heated deflection compensation roller.

It is also advantageous that in a 12-roll stack the 4th roll is driven from below. The fact that the drive is moved from the third to the fourth roller results in a better power division and thus less lateral deflection of the drive roller and the adjacent center rollers. It is therefore possible to dimension them smaller, which results in higher compressive stresses in the nips with the same line load and thus better results in paper treatment.

Fig. 1

eine Ausführungsform eines erfindungsgemäßen Kalanders in schematischer Darstellung,

Fig. 2

einen Teilschnitt durch den obersten Walzenspalt,

Fig. 3

schematisch einen abgewandelten Kalander mit acht Walzen,

Fig. 4

einen abgewandelten Kalander mit sechs Walzen und

Fig. 5

einen abgewandelten Kalander mit zwei Stapeln zu je fünf Walzen.

The invention is explained in more detail below with reference to preferred exemplary embodiments illustrated in the drawing. Show it:

Fig. 1

an embodiment of a calender according to the invention in a schematic representation,

Fig. 2

a partial section through the top nip,

Fig. 3

schematically a modified calender with eight rolls,

Fig. 4

a modified calender with six rolls and

Fig. 5

a modified calender with two stacks of five rolls each.

The calender illustrated in FIG. 1 has a roll stack 1, which consists of twelve rolls, namely an upper roll 2 and a lower roll 3, both of which are designed as deflection compensating rolls, and ten intermediate rolls arranged in between. Here a heatable hard roller 4 is followed from above by an elastic roller 5, a heatable hard roller 6, an elastic roller 7, a heatable hard roller 8, two elastic rollers 9 and 10, a driven, heatable hard roller 11, an elastic one Roller 12 and a heatable hard roller 13. The elastic rollers 5, 7, 9, 10 and 12 each carry a cover 14 made of elastic plastic. The jacket 15 of the top roller 2 and the jacket 15a of the bottom roller 3 consist essentially of elastic plastic or have a cover 27a made of such an elastic plastic (FIG. 2), so that the top roller 2 and bottom roller 3 also act as elastic rollers. Therefore, an alternating gap 16 is formed between the elastic rollers 9 and 10. All other gaps are working gaps 17, each of which is limited by an elastic roller and a hard roller.

A paper web 18 is fed either directly from a paper machine or from an unwinder 19, first passes through six working gaps 17, then the changing gap 16 and finally four further working gaps 17 under the guidance of guide rollers 20, whereupon it is wound up in a winding device 21. In the six upper working columns, the paper web 18 rests on one side and in the four lower working columns on the other side on the elastic rollers, so that the desired surface structure, for example gloss or smoothness, is achieved on both sides.

2 shows a possible embodiment of the rolls in the region of the uppermost working gap 17. The upper roll has a carrier 22 which is held in the stand 23 of the calender in a rotationally fixed manner and can be loaded by a force 24. The jacket 15 of the top roller 2 is supported on this carrier 22 with the aid of closely adjacent hydrostatic support elements 25. Each support member 25 - or pair of support members 25 - is pressurized by an individual control line 26. The roll shell 15 is formed by a carrier 27 in the form of an inner tube 27 made of lamellar graphite cast, which carries an outer cover 27a made of elastic plastic, which has a higher wear resistance than this cast. Preferred is a material that has an average compressive stress of more tolerates as 45 N / mm ² , preferably up to 60 N / mm ² and has a low marking sensitivity. An example is an epoxy resin reinforced by fibers, in particular carbon fibers, such as the reference material "TopTec 4" already mentioned. The carrier 27 forming the roll shell 15 has a substantially smaller wall thickness than a chilled cast iron shell which has the same inside diameter. Compared to chilled cast iron jackets that have a thickness of 80 to 145 mm, only 45 to 70 mm and a wall thickness of the plastic cover 27a in the range of 8 to 15 mm, preferably 10 mm, are required for lamellar or spheroidal graphite cast iron jackets. In the case of the hard roller 4, channels 28 running near the surface are provided, to which superheated steam at elevated pressure is supplied via control lines 29, for example at a temperature of 220 ° C., which corresponds to a pressure of 22 bar and to a surface temperature of approximately 150 ° C. leads.

• a) Über eine Leitung 31 wird die Kraft 24 festgelegt, mit der die Oberwalze 2 bzw. ihr Träger 22 nach unten gedrückt wird, wobei die ähnlich ausgestaltete Unterwalze 3 zweckmäßigerweise ortsfest gehalten ist. Die Belastung kann auch in umgekehrter Richtung erfolgen, wobei die Kraft 24 auf die Unterwalze wirkt und die Oberwalze 2 ortsfest gelagert ist. Durch die Belastung ist auch die Druckspannung bestimmt, die in den einzelnen Arbeitsspalten 17 herrscht. Diese Druckspannung nimmt von oben nach unten zu, weil sich zu der Belastungskraft 24 jeweils noch das Gewicht der einzelnen Walzen addiert. Wegen des geringen Gewichts des Mantels 15 der Oberwalze 2 ist der Kraftzuwachs geringer als bei bekannten Superkalandern mit zwölf Walzen.
• b) Über die Leitungen 26 und 26a werden die Stützelemente 25 zum Durchbiegungsausgleich der Oberwalze 2 und der Unterwalze 3 mit Druckmittel beaufschlagt. Änderungen im zugeführten Druck führen zu einer entsprechenden Verformung des Walzenmantels 15. Wegen der höheren Elastizität des Walzenmantels 15 und des Zusammenwirkens mit der harten Walze 4 ergibt sich eine entsprechend starke Reaktion auf die hindurchlaufende Papierbahn. Bereits im ersten Arbeitsspalt 17 erfährt die hindurchlaufende Papierbahn 18 eine starke Beeinflussung, mit der eine hohe Gleichmäßigkeit der angestrebten Parameter vorbereitet werden kann.
• c) Die harten Walzen 4, 6, 8, 11 und 13 sind über die Steuerleitungen 29, 29a, 29b, 29c und 29d beheizbar. Schon im ersten Arbeitsspalt 17 wird daher die Papierbahn 18 auf ein erhöhtes Temperaturniveau gebracht. Hierdurch werden die Reaktionen der druckbelasteten Stützelemente 25 auf die Papierbahn 18 noch verstärkt.

A control device 30 has several functions:

• a) The force 24 with which the upper roller 2 or its carrier 22 is pressed down is fixed via a line 31, the similarly designed lower roller 3 being expediently held stationary. The loading can also take place in the opposite direction, the force 24 acting on the lower roller and the upper roller 2 being mounted in a stationary manner. The compressive stress prevailing in the individual working gaps 17 is also determined by the load. This compressive stress increases from top to bottom because the weight of the individual rollers is added to the loading force 24. Because of the light weight of the jacket 15 of the top roller 2, the increase in force is less than in known supercalenders with twelve rollers.
• b) Via the lines 26 and 26a, the support elements 25 for the deflection compensation of the upper roller 2 and the lower roller 3 are pressurized. Changes in the pressure supplied lead to a corresponding deformation of the roll shell 15. Because of the higher elasticity of the roll shell 15 and the interaction with the hard roll 4, there is a correspondingly strong reaction to the paper web passing through. Already in the first working gap 17, the paper web 18 passing through is strongly influenced, with which a high uniformity of the desired parameters can be prepared.
• c) The hard rollers 4, 6, 8, 11 and 13 can be heated via the control lines 29, 29a, 29b, 29c and 29d. The paper web 18 is therefore brought to an elevated temperature level in the first working gap 17. As a result, the reactions of the pressure-loaded support elements 25 to the paper web 18 are intensified.

3 shows a calender with a stack 101, which consists of eight rolls. The elastic rollers are identified by hatching. The stack 101 therefore comprises an upper roller 102 and a lower roller 103 and between them a heatable hard roller 104, an elastic roller 105, a heatable hard roller 106, two elastic rollers 109 and 110 and a heatable hard roller 111.

4 illustrates a calender with a stack 201 of six rolls, namely an upper roll 202 and a lower roll 203 and in between a heatable hard roll 204, two elastic rolls 209 and 210 and a heatable hard roll 211.

In many cases, this smaller number of rollers in the stack is sufficient to produce paper with a high surface quality on both sides. This applies in particular if at least in the lowest working gap with compressive stresses above 42 N / mm ² , preferably between 45 and 60 N / mm ² , and on the surfaces of the heated rolls with temperatures above 100 ° C, preferably between 130 and 160 ° C, is worked.

5 shows a calender with two stacks 301 and 301a of five rolls each. The stack 301 has an upper roller 302 and a lower roller 303 and between them a heatable hard roller 304, an elastic roller 305 and a heatable hard roller 306. The stack 301a has the same structure. However, the paper web is guided in such a way that it rests on one side in the first stack and on the other side in the second stack and is therefore satinized on both sides.

The roll stack 1 of the 12-roll calender of FIG. 1 has five heatable hard rolls 4, 6, 8, 11, 13. Known 12-roll calenders, on the other hand, have only four such heated rolls. As a result, it is possible to add 25% more thermal energy and therefore to increase the available deformation energy accordingly. The same applies to the other calenders, in each of which one more heatable roll or even two more heatable rolls can be used in the 2-stack calender of FIG. 5.

The desired deformability of the shell of the upper roller 2 and, if appropriate, of the lower roller 3 should lead to a deformability factor which is at least four times, but preferably more than five times as large as in a hard cast iron shell. This can be achieved, for example, with a lamellar or spheroidal graphite jacket, which is provided with a plastic cover with a low modulus of elasticity. Instead, however, jackets 15 are also considered, which consist entirely of plastic and whose modulus of elasticity is less than half that of chilled cast iron.

While in the drawings the embodiment with a roll stack each shows an even number of rolls, stacks with an odd number of rolls can also be used if the lower roll is provided with a hard roll casing in the usual way. Of course, the illustrated calenders can be provided with other known means for improving the paper treatment, for example the middle rollers can be mounted on levers, by means of which the influence of overhanging weights can be compensated with the aid of compensation devices.

Claims (11)

Calender with at least one roll stack, the upper roll and lower roll each a deflection compensating roll with a roll shell, which is supported by hydrostatic support elements on a rotating support that passes through it, and as middle rolls hard rolls and elastic rolls, which rolls have at least four working gaps, the a hard and an elastic roller, and possibly form an alternating gap, which is delimited by two elastic rollers, characterized in that the roller shell (15, 15a) of the top roller (2; 102; 202; 302) and / or the Bottom roller (3; 103; 203; 303) carries a cover (27a) made of an elastic plastic or consists essentially entirely of elastic plastic and is flexible with a deformability factor $$\mathit{\text{F}}\text{= (}\frac{{\text{1.4 · 10}}^{\text{5}}}{\mathit{\text{E}}}\text{)}\mathit{\text{x}}\text{(}\frac{\text{100}}{\mathit{\text{S}}}{\text{)}}^{\text{2.65}}\text{≧ 4}$$

is designed, whereby
E = modulus of elasticity of the roll shell in N / mm ²
S = wall thickness of the roll shell in mm,
and that the adjacent center roll (4; 104; 204; 304; 13; 111; 211; 306) is a hard roll. Calender according to claim 1, characterized in that the deformability factor is> 5. Calender according to claim 1 or 2, characterized in that the roller jacket (15, 15a) consists of a material with insufficient wear resistance and carries a cover (27a) made of the elastic plastic, and that the plastic has a higher wear resistance than the jacket material. Calender according to claim 3, characterized in that the roller jacket (15; 15a) consists of lamellar graphite cast iron. Calender according to one of claims 1 to 4, characterized in that the roller jacket (15) consists of spheroidal graphite cast iron and carries a cover (27a) made of elastic plastic. Calender according to one of claims 1 to 5, characterized in that the plastic is a fiber-reinforced epoxy resin. Calender according to one of claims 1 to 6, characterized in that the deflection compensation roller has a multi-zone control in which hydraulic fluid with different pressure can be fed to the support elements (25) individually or in pairs. Calender according to one of claims 1 to 7, characterized in that at least the top middle roll (4) can be heated. Calender according to one of claims 1 to 8, characterized in that all hard center rolls (4, 6, 8, 11, 13) can be heated. Calender according to claim 8 or 9, characterized in that the heating takes place by means of steam which can be supplied with excess pressure. Calender according to one of claims 1 to 10, characterized in that in a 12-roll stack (1) the 4th roll (11) is driven from below.

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