WO2007031233A1

WO2007031233A1 - Heatable calender roller

Info

Publication number: WO2007031233A1
Application number: PCT/EP2006/008755
Authority: WO
Inventors: Bernhard Brendel; Peter Svenka
Original assignee: Andritz Küsters Gmbh
Priority date: 2005-09-15
Filing date: 2006-09-08
Publication date: 2007-03-22
Also published as: ATE435940T1; DE102005044099A1; EP1929086B1; DE502006004201D1; EP1929086A1

Abstract

The invention relates to a heatable calender roller which comprises a hollow roller body (15) having a calender bowl and configured to conduct a heat transfer medium. The roller body (15) carries a wear-resisting peripheral surface, said wear-resisting peripheral surface being formed by at least one functional layer (16) applied by fusion-welding. Said functional layer has a welding additive-specific thermal expansion that is different from the thermal expansion of the roller body (15) to such an extent that the functional layer (16), in the heated condition of the calender roller (4, 9), has an internal prestress in the form of compressive stresses (17) as the stress buffer that counteract the tensile stresses (19) produced during operation by heat dissipation.

Description

Heatable calender roll

The invention relates to a heatable calender roll according to the preamble of claim 1.

In calendering, the paper web to be treated is treated between rolls using mechanical and thermal energy to treat and deform the paper to conform the paper, particularly the paper surface, to final use. The thermal energy required for the treatment is introduced by the heat supply from the heated roll in the nip.

From EP 0 710 741 B1 a heated calender roll is known which is designed as a hollow roll and has a roll shell which is made of a first material of forged steel, cast steel, cast iron or spheroidal graphite cast iron and with a thin circumferential surface layer of a second hard, abrasive resistant material is provided. The thin peripheral surface layer has the disadvantage that the abrading of operational markings on the circumferential surface is generally possible only once. Then make a new coating. A larger supply of reserve rollers is therefore required. The use of such thermo rolls is therefore complicated and expensive.

Heated calender rolls are also known with a roll shell made of hard shell. The usable hardening layer is considerably thicker in single-layered roller shells, whereby the service life of the thermo roll is increased. Finally, thermo rolls of tempered or surface hardened materials are also known. But the few eligible special materials are expensive, cause difficulties in procurement and put because of their sensitivity extremely high demands on the manufacturing process. Such thermo rolls are therefore very expensive.

The requirements for the heated calender roll in operation have also increased significantly in recent years. With the increase of the production speed of the paper machines, the required heat input to be supplied has increasingly increased because of the area-related heat requirement for the calendering. For paper, as it is in calendering for paper technology reasons, which is a good heat insulator, the surface temperature of the heated roll must be raised in order to transfer the required amount of heat in the shorter by the increase in production residence time on the paper web. This means an increase in the roll surface temperature for the heated rolls in calenders in addition to increasing the heat output. Also because of this double increase, the thermo rolls used so far have reached their limits.

The object of the invention is therefore to provide a heatable calender roll, which combines high heat output with high service life at high production speeds and is inexpensive to produce. This object is solved by the features of claim 1.

In this way, a heatable calender roll is provided, in which a functional layer for the calendering process is applied to the roll body via build-up welding. Thus, there is a separation of functions between the roller body as a support body and the roller body as a surface body, which determines the paper technology properties and the roller life. The presence of compressive stresses in the functional layer in the warm operating state protects the functional layer or the roller by the creation of safety reserves against damage during operation.

In the heated calender roll, the functional layer is materially equipped with an inner bias against the roller body, so that without heat transfer to a paper or board web, the functional layer is in a state of tension. Accordingly, a voltage buffer is incorporated into the functional layer. In operation, the bias voltage is reduced by increased heat dissipation. Tearing of the peripheral surface of the roller body in operation is thereby avoided. These heated calender rolls are highly resilient and have a long service life. Be when used in multinip calenders with double over-rolling of the heated calender roll and thus double heat roll surface temperatures can also above 200 ⁰ C at production speeds of over 1500 m / min is set.

The materials of the functional layer and the roll body can be optimized separately from each other in terms of their intrinsic properties. Thus, the material of the functional layer can be optimized in terms of high heat capacity and hardness, whereby the temperature control of the heat treatment processes and the service life can be improved. By contrast, the material of the roller body can be optimized with regard to thermal conductivity, machinability and strength, which improves the introduction of the heating devices, for example peripheral bores, and the support body properties. As a material for the roll body and a commercially available material is used. Beispiels- example, the roll body from a commercially available steel, eg St 52, be made.

The functional layer can be reground several times, wherein the thickness can be controlled by multi-layer welding, that is to say the number of weld layers which can be applied one above the other. Preferred layer thicknesses are 3 to 10 mm. The heating of such a thermo roll can be done in a known manner from the inside and optionally in addition from the outside.

The functional layer may have a smaller thermal expansion than the roller body and be post-treated by low-stress annealing, so that the welding layer has compressive stresses as residual stresses. This inner bias has the functional layer, as long as no heat is transferred to the paper or board web, so there is a substantially uniform heating. The inconsistent heat distribution in the roll body which occurs during operation generates tensile stresses in the functional layer, which are compensated in whole or in part by the built-in compressive stresses.

Alternatively, the functional layer may have a greater thermal expansion than the roller body, so that tensile stresses are present in the functional layer by simply cooling during build-up welding. These tensile stresses are in the heated calender roll, due to the ratio of the thermal expansion of the functional layer and the roll body to each other, converted into compressive stresses. Compressive stresses are also incorporated here as a voltage buffer in the functional layer. The non-uniform temperature distribution in the roller body which occurs during operation generates tensile stresses in the functional layer, which are compensated there by the built-in compressive stresses.

Further advantages and embodiments of the invention can be taken from the subclaims and the following description. The invention will be explained in more detail with reference to the embodiments illustrated in the accompanying drawings.

1 shows schematically a side view of a first embodiment of a calender with a heated calender roll according to the invention,

2 shows schematically a side view of a second embodiment of a calender with heated calender rolls according to the invention,

3 shows schematically a side view of a heated calender roll according to the invention with a central heating,

4 shows schematically a cross section of the heated calender roll according to FIG. 3, FIG.

5 shows schematically a side view of a heated calender roll according to the invention with a peripheral bore for internal heating,

6 shows schematically a cross section of the heated calender roll according to FIG. 5, FIG.

7 shows schematically a segment section of FIG. 4 in an enlarged view and indicating the states of stress,

Fig. 8 shows the change in temperature across the wall thickness of the heated calender roll of FIG. 3 and 4 in operation at heat output to a paper or board web.

Fig. 1 shows a calender 1 for the treatment of a web, in particular a paper or board web. The calender 1 comprises for this purpose at least one roll stack 2, which here comprises two rolls 3, 4, which are arranged in a known manner on a calender stand 5. The rollers 3, 4 define a nip 6, the nip, which passes through a web W and in which the web is subjected to pressure and temperature. The treatment time of the web W in the nip depends on the length of the nip and the throughput time, which depends on the production speed in online operation. The length of the nip is selectable and is usually between 3 and 300 mm. For this purpose, a roller, here the roller 3, as a hard roller, soft roller or shoe roll can be formed. The roller 3 can furthermore be designed as a bending compensating roller. The other roll 4 is a heatable calender roll according to the invention, the formation of which will be described in detail below.

The roll stack may be loadable from one or both ends to set selectable line loads in nip 6. If the roller 3 is designed as a shoe roller, the line loads can be adjusted via a stroke of the shoe. For guiding the web W between nips or after the nip 6 guide rollers 7 are provided in a known manner.

This 1-nip calender can be used both online and offline.

FIG. 2 shows a multi-nip calender for smoothing a paper or board web with at least one roll stack 2 with a plurality of rolls 3, 4, 8, 9, 10 which bound nips 6, 11, 12, 13. The number of rolls is preferably between three and twelve rolls. The end rollers 3, 10 of the roller stack 2 are preferably formed as a bending compensating rollers. Each nip 6, 11, 12, 13 is preferably limited by a heated calender roll according to the invention. These are here the rollers 4, 9, which are formed according to the invention, as described below. All rolls can be designed as hard rolls. Preferably, the nips 6, 11, 12, 13 are formed as soft nips, d. H. they are bounded by a hard and a soft roller.

The heatable calender rolls 4, 9 according to the invention are basically hard rolls with a wear-resistant surface, so that in each case the other roll, which delimit a nip with the heatable calender roll 4, 9 according to the invention, can be soft rolls. 2, these are the rollers 3, 8, 10. The heatable calender roll according to the invention is preferably a center roll, which is double-rolled over in operation, that is, two nips 8, 11 and 12, 13 limited. The roll stack 2 can be loaded from one end via a pressure cylinder 14. Between the nips, the web W is guided over guide rollers 7. For a two-sided treatment of the web W, a second, not shown, roll stack may be provided, which may be before or downstream of the roll stack 2. Alternatively, the roll stack 2 may have a changeover tip. The calender 1 according to FIG. 2 can be operated offline as well as online.

The two calender embodiments of FIGS. 1 and 2 can be operated online at production speeds of over 1500 m / min, wherein the heatable calender rolls 4, 8 can be driven according to the invention with roll surface temperatures of up to 350 ° C and thereby heating powers of up to 200 kW / m own.

The design of the heatable calender rolls 4, 9 according to the invention will be explained below with reference to FIGS. 3 to 8. By way of example, the heatable calender roll 4 will be described. The statements apply correspondingly to the calender roll 9. The statements apply equally to the heatable calender roll 4 as the end roll (FIG. 1) and the heatable calender roll 4, 9 as the center roll (FIG. 2).

The heatable calender roll 4 comprises a hollow, a roll shell having roll body 15, which is designed for the passage of a heat transfer medium. The roller body 15 carries a wear-resistant peripheral surface, which is formed by at least one fusion-deposited functional layer 16 which has a welding additive-dependent thermal expansion which is so different from the thermal expansion of the roller body 15 that the functional layer 16 in the heated, operating condition of the calender roll 4 a inner bias in the form of compressive stresses 17 (Figure 7) as a voltage buffer, which counteract the tensile stresses generated during operation by heat dissipation.

The heatable calender roll 4 has in the heated, warm operating condition a substantially uniform heating. Will the heated by the Calender roll 4 limited Nip 6 closed, the heat transfer to the web W leads to a low temperature of the functional layer 16 as in the heated state before startup. This leads to an uneven temperature distribution in the roller body 15. FIG. 8 shows the temperature profile relative to the wall thickness.

As FIG. 7 illustrates, the temperature gradient in the roller body 15 causes a spreading 18 of the roller body 15 on the outside and thus a buildup of tensile stresses 19 in the functional layer 16. This then leads to a rupture of the functional layer, in particular if the material web controls certain paper properties enters the nip 6 with a higher moisture content.

If, according to the invention, a voltage buffer in the form of compressive stresses 17 is incorporated in the functional layer 16, ie if voltages with the reverse direction of action are integrated as tensile stresses 19, the functional layer 16 is given a deformation capability that allows the functional layer to give way when subjected to tensile stress, thereby preventing cracking.

For this purpose, the functional layer 16 may have a smaller thermal expansion than the roller body 15, this being aftertreated by stress-relieved annealing, so that the functional layer has the compressive stresses 17 as a voltage buffer.

Alternatively, the functional layer 16 may have a greater thermal expansion than the roller body 15, so that when heated to the operating temperature, the functional layer 16 of tensile stresses in the compressive stresses 17 transferred residual stresses as a voltage buffer.

The functional layer 16 may consist of at least two superposed layers, which are applied by build-up welding. An outer layer and a release layer can be formed in this way to form an outer layer which has no material components of the roller body 15. These Therefore, superimposed weld layers are preferably discrete layers.

As heating for the heatable calender roller internal heating is provided. The heatable calender roll 4 according to FIGS. 3 and 4 is a centrally heatable roll with a displacement body 20, which has an annular gap 21 for the passage of a heat medium. The connections for the inlet and outlet of the heat transfer medium, in particular oil, is indicated by arrows.

The embodiment of Figs. 5 and 6 differs from that of Figs. 3 and 4 only in that no inner body for displacement, but peripheral bores 22 are provided for a flow of the heat transfer medium. For the rest, the above statements apply accordingly.

In both embodiments of the internal heating, an external heating of any type can be additionally provided.

The material for the roller body is preferably provided with a thermal conductivity of> 30 W / m ° K.

As a material for the functional layer, it is further preferable to provide one having a thermal conductivity of> 20 W / m ° K and a specific heat capacity of> 400 J / kg ° K.

The filler metal, from which the functional layer 16 is applied to the roll body 15 by fusion welding, preferably has a hardness between 450 HV and 650 HV. Furthermore, the reversible hardness drop of the filler metal from room temperature to operating temperature is preferably less than 5%. The build-up welding is preferably carried out by the so-called strip welding method with welding bands of a width of for example 15 to 60 mm in order to achieve a non-porous surface and homogeneous application layer in terms of Young's modulus and wear resistance. The layer thickness of the functional layer 16 is at least 3 mm and is preferably in the range between 3 and 10 mm.

The roller body 15 is arranged in a known manner as a support body via roll neck 23, 24 in the calender stand.

The above statements regarding FIGS. 7 and 8 apply correspondingly to a heatable calender roll 4 with a heating via peripheral holes 22, as shown in FIGS. 5 and 6. The designs apply to every type of internal heating.

Claims

claims

A heatable calender roll having a hollow roll body (15) having a roll shell, which is designed to pass a heat transfer medium, and the roll body (15) carries a wear-resistant peripheral surface, characterized in that the wear-resistant peripheral surface is formed by at least one by fusion welding applied functional layer (16) which has a welding additive-dependent thermal expansion, which is so different from the thermal expansion of the roller body (15) that the functional layer (16) in the heated state of the calender roll (4, 9) an internal bias in shape of compressive stresses (17) as a voltage buffer, which counteract the tensile stresses generated during operation by heat dissipation (19).

2. Heated calender roll according to claim 1, characterized in that the functional layer (16) has a smaller thermal expansion than the roller body (15) and is treated by low-voltage annealing, so that the functional layer (16) compressive stresses (17) has as a voltage buffer.

3. Heatable calender roll according to claim 1, characterized in that the functional layer (16) has a greater thermal expansion than the roller body (15), so that when heated to the operating temperature, the functional layer (16) of tensile stresses in compressive stresses (17) transferred residual stresses has as a voltage buffer.

4. Heatable calender roll according to one of claims 1 to 3, characterized in that the functional layer (16) consists of at least two superimposed layers.

5. heatable calender roll according to claim 4, characterized in that the superimposed layers are discrete layers.

6. Heatable calender roll according to one of claims 1 to 5, characterized in that the heating is designed as an internal heating.

7. Heatable calender roll according to claim 6, characterized in that the roller body (15) has peripheral bores (22) for a flow of the heat transfer medium.

8. Heatable calender roll according to claim 6, characterized in that the internal heating (20, 21) takes place centrally.

9. Heatable calender roll according to one of claims 1 to 8, characterized in that the roller body (15) has a thermal conductivity of> 30 W / m ° K.

10. Heatable calender roll according to one of claims 1 to 9, characterized in that the functional layer (16) has a thermal conductivity of> 20 W / m ° K and a specific heat capacity of> 400 J / kg ° K.

11. A calender for treating a material web, in particular a paper or board web, with at least one roll stack (2) with two or more rolls (3, 4; 3, 4, 8, 9, 10) to form one or more nips ( 6, 6, 11, 12, 13), characterized in that at least one heatable, hard roller (4, 9) according to one or more of claims 1 to 10 is formed.

12. A calender according to claim 11, characterized in that the heatable hard center rollers (4, 9) are formed according to one or more of claims 1 to 10.