EP1363034B1 - Elastic smoothing roll and it's production method - Google Patents

Description

The present invention relates to an elastic smoothing roll, in particular for the smoothing of paper webs, with a hard roll core and provided on the outside of the roll core, multi-layered, elastic matrix material comprising elastic cover layer. Furthermore, the invention is directed to a method for producing such an elastic smoothing roll.

Elastic rolls of this type are used, for example, in the calendering of paper webs. In each case, an elastic roller together with a hard roller forms a press nip through which the paper web to be processed is passed. While the hard roller has a very smooth surface consisting, for example, of steel or chilled cast iron and is responsible for the smoothing of the side of the paper web facing it, the elastic roller acting on the opposite side of the paper web causes equalization and densification of the paper web in press nip. The order of magnitude of the rolls lies with lengths of 3 to 12 meters or diameters of 450 to 1500 millimeters. They withstand line forces of up to 600 N / mm and compressive stresses up to 130 N / mm ² .

Since the tendency in papermaking is that the calendering takes place in on-line operation, ie that the paper web leaving the paper machine or coater is passed directly through the paper calendering device, higher demands are placed on the rollers of the smoothing device, in particular with regard to temperature resistance previously submitted. Due to the high required in online operation Transport speeds of the paper web and the associated high rotational speeds of the calender rolls is the nip frequency, which is the frequency at which the reference is compressed and relieved, increased, which in turn leads to increased rolling temperatures. These high temperatures produced in online operation lead to problems that can lead to the destruction of the plastic coating in known elastic rollers. On the one hand, maximum temperature differences of about 20 ° C. across the width of the roller are permissible in known plastic coverings and, on the other hand, the plastics conventionally used for the coating have a significantly higher coefficient of thermal expansion than the steel rollers or chilled cast iron commonly used, so that a high temperature increase causes high temperatures Tensions between the steel roller or chill roller and the associated plastic coating occur.

As a result of these high voltages, in particular with the occasional occurrence of heating points within or on the surface of the plastic coating, so-called hot spots may occur, at which detachment or even bursting of the plastic layer takes place.

These hotspots occur in particular when, in addition to the mechanical stresses and the relatively high temperature, crystallization points in the form of, for example, defective adhesions, deposits or above-average indentations of the elastic covering, for example due to folds or foreign bodies on the paper web, are present. In these cases, the temperature at these crystallization points of usual 80 ° C to 90 ° C rise to above 150 ° C, whereby the mentioned destruction of the plastic layer takes place.

To control the properties of the elastic cover layer, it is known to introduce powdered fillers and / or fibers into the matrix material. Depending on the amount and physical property of these fillers or fibers, the physical properties of the elastic cover layer are dominated or influenced by the fillers or the fibers. However, the powdery or fibrous fillers often worsen the smoothness of the surface of the elastic roll. This is undesirable because the paper quality depends directly on the smoothness of the surface of the smoothing roll.

Furthermore, reference layers of plastic material have a relatively low abrasion resistance, so that the life of the corresponding smoothing rollers is often insufficient. Due to the plastics used for the cover layer, there is also the risk that in operation by the existing friction between the plastic roller and the paper web to be smoothed the elastic smoothing roller is statically charged, creating the risk that attracted by this charge particles, such as dust particles or the like, settle on the surface of the smoothing roller and thus cause a reduction in the smoothing quality or at worst even damage to the roll coating.

From DE 199 25 419 A1 a smoothing roll is known, in which in addition to the outer plastic layer, a plastic layer covering this metallic cover layer is provided. In this case, the metallic outer layer is produced by winding liquid-metal-coated fibers onto the elastic plastic layer. Due to the fibers used as a carrier for the metal coating, the smoothness of this roller depends on the fiber diameters used.

From DE 199 25 418 A1 it is known, in a smoothing roll, the elastic cover layer is not made of plastic, but exclusively of a soft metal. Such trained rollers have a very smooth surface and a very high thermal conductivity. However, these rolls are not suitable for all types of paper due to the pure metal surface, since the elasticity of these rolls is less than the elasticity of smoothing rolls with a plastic coating.

It is an object of the present invention to provide an elastic smoothing roll of the type mentioned above and a method for producing a corresponding smoothing roll, wherein the risk of the occurrence of hot spots is reduced, the surface at the same time a very good abrasion resistance and an extremely high smoothness having.

According to the invention, the part of the object relating to the smoothing roller is achieved on the basis of a smoothing roller of the type mentioned at the outset, wherein the thermal reference layer comprises a radially inner, fiber-reinforced base layer, wherein the coefficient of thermal expansion and modulus of elasticity of the base layer through the fibers is equal to the coefficient of thermal expansion and Are approximated elastic modulus of the roll core, that a middle elastic layer is provided whose elastic modulus is smaller than the elastic modulus of the base layer, that a radially outer outer layer is provided, which consists of a mixture of molten metal and molten plastic, and that the coefficient of thermal expansion and the Young's modulus of the middle layer are at least in the radially outer region of the temperature expansion coefficient and the elastic modulus of the outer layer approximated.

The inventive method is characterized in that the existing of a mixture of molten metal and molten plastic outer layer is applied by a spraying, casting, coating or painting on the middle layer.

In the case of the smoothing roller formed according to the invention, the advantages of the different known methods are thus combined with one another by producing the outer layer from a mixture of metal and plastic and by longitudinal stresses occurring between the individual layers of the reference layer during operation as a result of a corresponding configuration of the remaining layers reduced or avoided in the optimal case completely. Furthermore, in addition to the pure combination of metal and plastic to form the outer layer, both the metal and the plastic are mixed with each other in the molten state and applied to the surface of the roll core, thereby achieving significant advantages. In contrast to a mixture of, for example, powdered metal particles with a liquid plastic matrix material, a mixture according to the invention of molten metal and molten plastic has a substantially more homogeneous structure and thus an increased strength. Furthermore, it is avoided that crystallization points for hotspots caused by particles arranged in the matrix material, which could lead to destruction of the roll reference layer.

At the same time, the physical properties of the cover layer, such as abrasion resistance and smoothness, are optimally homogeneous over the entire cover layer. In particular, the smoothness of the cover layer can be extremely high, for example, by grinding and subsequent polishing, set as no particles, be it in Powder form, in fibrous form or in any other form, are present in the matrix material, which could ultimately lead to the surface of the cover layer to an undesirable roughness.

By mixing the molten plastic with molten metal, an antistatic effect is further achieved, so that during operation, electrostatic charges of the roller are prevented. As a result, no deposits on the surface of the smoothing roll are caused by electrostatic attraction, which could lead to a reduction of the smoothness quality of the paper web to be treated and in the worst case to hot spots and thus to the destruction of the roll reference layer.

Finally, the roll produced according to the invention has a heat conduction coefficient which is significantly improved in comparison to a roll with a plastic layer, so that the heat occurring during operation can be dissipated very quickly and thus the danger of the occurrence of hotspots can be further reduced.

According to an advantageous embodiment of the invention, the outer layer is formed substantially free of fibers. As a result, on the one hand optimum homogeneity of the outer layer and on the other hand an extremely smooth surface of the outer layer is achieved. The smoothness can be optimized by grinding and / or polishing the surface. The surface of the outer layer preferably has an Ra value which is less than 0.05 μm, in particular less than 0.03 μm.

According to a further advantageous embodiment of the invention, an abrasion-resistant metal is used for the outer layer. The more abrasion resistant the metal used, the greater the life of a corresponding trained roller, so that the economy of such a roller can be significantly improved.

Advantageously, for the mixture of the outer layer as plastic, a high performance plastic, i. a high melting point plastic, especially a polyimide (PI), polyamideimide (PAI), polyetherimide (PEI), polysulfone (PSU, PES), polyethersulfone (PESU) or a poly (phenylene sulfone) (PPSU), a mixture of one or more high performance plastics with other plastics or a mixture of high performance plastics.

In order to achieve the desired physical properties of the smoothing roll, it is advantageous if for the outer layer, a plastic or a plastic mixture having a melting point of more than about 300 ° C, in particular more than about 400 ° C, preferably from about 500 ° C or more and / or with a modulus of elasticity of less than about 4 GPa, preferably of about 3.5 GPa or less is used.

According to a further preferred embodiment of the invention, the middle layer is substantially thicker than the outer layer and / or formed as the base layer. By a corresponding thickness of the middle layer, a "soft" course of the essential physical properties such as thermal expansion coefficient and elastic modulus over the radial thickness of the reference layer is adjustable. This prevents a separation of individual layers from one another due to stresses or temperature differences occurring during operation.

According to a further advantageous embodiment of the invention, the outer layer has a high thermal conductivity. This ensures that that occurring during operation heat can be derived quickly and reliably from the respective overheating point.

According to a further preferred embodiment of the invention, the middle layer at least partially contains fibers. These are preferably fibers with a relatively high thermal conductivity, the number within the middle layer can be radially variable so that the thermal conductivity of the middle layer increases radially outward until it is approximately equal to the heat conductivity of the outer layer at the transition to the outer layer. Furthermore, with the fibers, the modulus of elasticity can be increased radially outwards and / or the coefficient of thermal expansion can be set to decrease radially outwards in order to achieve an alignment with the outer layer. This can be achieved, for example, by using carbon fibers in the middle layer.

According to a further advantageous embodiment of the invention, the fibers of the base layer at least partially comprise aramid and / or glass fibers. Preferably, the fibers are wound as rovings on the roll core and embedded in the elastic matrix material of the base layer. Furthermore, the material and the amount of fibers are chosen so that the temperature coefficient and the elasticity model in the radially inner region of the base layer are approximated to the corresponding parameters of the roll core. Radially outward, the amount of fibers is chosen to give a smooth transition of these parameters to the middle layer.

The matrix material may preferably be formed as a resin-hardener combination and comprise, for example, epoxy resin.

Depending on the application, the roll core can be made of metal or fiber-reinforced plastic in particular. The use of a plastic roller as a roll core has the advantage that the weight and thus the inertia of the smoothing roll can be significantly reduced compared to a use of a metal core. Particularly in the case of the high rotational speeds occurring during operation, the reduction of the roll weight is advantageous. Furthermore, the use of especially fiber-reinforced plastic rollers, especially in so-called Breitnipkalandern advantageous since a roll core made of plastic over a metallic roll core has a certain flexibility, which causes a homogenization of the paper web in the nip.

According to a further advantageous embodiment of the method according to the invention, the outer layer is applied to the roll core by a flame or plasma spraying process. By means of a corresponding flame or plasma spraying process, it is possible to produce very high-quality outer layers and to produce a very strong bond between these outer layers and the middle layer. The metal and / or the plastic are preferably melted during the flame or plasma spraying. In this case, the metal and / or the plastic may be present as starting material in each case, for example, in powder form and be converted into liquid state only during the flame or plasma spraying. In principle, however, it is also possible that the metal and the plastic are melted before being applied to the roll core and mixed together.

With the method according to the invention, a very precise production of extremely smooth, abrasion-resistant, antistatic reference layers with high thermal conductivity is possible, with the inventive In particular, a plurality of such layers can be applied to one another.

Furthermore, with the method according to the invention also a very good repairability of the smoothing rolls is given. Thus, after a corresponding damage to the surface, the outer layer can be easily repaired, for example, simply by spraying a mixture of molten metal and molten plastic according to the invention - optionally over the entire surface of the roll or only in the region of damage. A removal of the roller from the calender, which would be associated with correspondingly long downtimes, is not required, so that the cost-effectiveness of a corresponding calender can be significantly improved by the possibility of repair.

Further advantageous embodiments of the invention are specified in the subclaims.

The invention will be described below with reference to an embodiment with reference to the single figure.

The figure shows a schematic cross section through an inventively designed smoothing roll. The illustrated smoothing roll comprises a roll core 1, which is made, for example, of metal or fiber-reinforced plastic, for example polymer, and which is rotatably mounted about an axis of rotation 2. For example, carbon fibers, aramid fibers, glass fibers or other suitable fibers can be used as fibers.

On the outside of the roller core 1, a relatively thin base layer 3 is provided, which consists of a fiber-reinforced elastic matrix material consists. The material, the number and the orientation of the fibers are selected so that the coefficient of thermal expansion of the base layer 3 is at least approximately as large as the temperature expansion coefficient of the roll core 1, at least in its radially inner region.

The base layer 3 is followed by a middle layer 4, which is formed substantially thicker than the base layer 3. This middle layer 4, as a continuation of the base layer 3, may also consist of fiber-reinforced matrix material. Since the thickness of the middle layer 4 substantially determines the elasticity of the entire reference layer, the number of fibers within the middle layer 4 is usually significantly reduced from the base layer 3, so that the elastic modulus of the middle layer 4 is less than the elastic modulus of the base layer 3.

The middle layer 4 is in turn divided into a radially inner region 5 and a radially outer region 6, which are separated from each other in the figure by a dashed line 7. While the ultimately existing elasticity of the overall roller is essentially determined by the matrix material used and the fibers embedded therein in the radially inner region 5, the radially outer region 6 forms a transition region to an outer layer 9 forming the surface 8 of the roller.

In this case, the region 6 of the middle layer 4 is significantly thinner than the region 5 and contains fibers embedded in the matrix material, by means of which the elastic modulus and the coefficient of thermal expansion approach the corresponding parameters of the outer layer 9. The fibers can be variable radially outward, in particular be increasingly distributed in order to achieve the closest possible approximation of said parameters. Furthermore, it is ensured by appropriately selected fibers, such as carbon fibers, that the region 6 has a high thermal conductivity and a high temperature resistance to allow the application of the outer layer 9, for example by plasma or flame spraying.

The outer layer 9 is formed as a thin elastic layer, which according to the invention consists of a mixture of molten metal and molten plastic. The outer layer 9 is therefore consistently homogeneous and has an extremely smooth surface 8, for example, due to an accomplished grinding and / or polishing process.

The mixture of molten metal and molten plastic can be applied, for example, as indicated schematically, by a flame spraying device 10 on the surface of the middle layer 4. For example, the coating can be applied by the roller core 1 is set in rotation and the flame spraying device 10 is moved slowly in the axial direction parallel to the axis of rotation 2. While it is possible in the flame spraying process that the starting materials (metal / plastic), for example, still in powder form and transferred by the heat used in the flame spraying process in liquid state and mixed together, it is in principle also possible that the two starting materials already by a Pretreatment in the liquid state and be applied by a simple spray, casting or painting on the surface of the roll core.

LIST OF REFERENCE NUMBERS

1

roll core

2

axis of rotation

3

base layer

4

middle class

5

inner area of the middle class

6

outlying area of the middle class

7

parting line

8th

surface

9

outer layer

10

Flame sprayer

Claims (22)

1. An elastic smoothing roll, in particular for the smoothing of paper webs, having a hard roll core (1) and an elastic covering layer provided at the outer side of the roll core (1), made with a plurality of layers and including elastic matrix material, characterized
   in that the elastic covering layer includes a radially inwardly disposed base layer (3) reinforced with fibers, with the coefficient of thermal expansion and the modulus of elasticity of the base layer (3) being approximated by the fibers to the coefficient of thermal expansion and the modulus of elasticity of the roll core (1);
   in that an elastic central layer (4) is provided whose modulus of elasticity is smaller than the modulus of elasticity of the base layer (3);
   in that a radially outwardly disposed outer layer (9) is provided which consists of a mixture of melted metal and melted plastic; and
   in that the coefficient of thermal expansion and the modulus of elasticity of the central layer (4), at least in its radially outwardly disposed region (6), are approximated to the coefficient of thermal expansion and the modulus of elasticity of the outer layer (9).
2. A roll in accordance with claim 1, characterized in that the outer layer (9) is made substantially free of fibers.
3. A roll in accordance with claim 1 or claim 2, characterized in that the surface (8) of the outer layer (9) is extremely smooth, in particular polished.
4. A roll in accordance with claim 3, characterized in that the surface (8) of the outer layer (9) has an Ra value which is less than 0.05 µm, in particular less than 0.03 µm.
5. A roll in accordance with any one of the preceding claims, characterized in that the metal used for the mixture of the outer layer (9) is an abrasion resistant metal.
6. A roll in accordance with any one of the preceding claims, characterized in that the plastic used for the mixture of the outer layer (9) is a high performance plastic, i.e. a plastic having a high melting point, in particular a polyimide (PI), a polyamidimide (PAI), a polyetherimide (PEI), a polysulfone (PSU, PES), a polyethersulfone (PESU) or a polyphenylsulfone (PPSU).
7. A roll in accordance with any one of the preceding claims, characterized in that the plastic used for the mixture of the outer layer (9) is a mixture of one or more high performance plastics with other plastics or a mixture of high performance plastics.
8. A roll in accordance with any one of the preceding claims, characterized in that the plastic used for the mixture of the outer layer (9) or the plastic mixture used has a melting point of more than approximately 300°C, in particular of more than approximately 400°C, preferably of approximately 500°C or more.
9. A roll in accordance with any one of the preceding claims, characterized in that the plastic used for the mixture of the outer layer (9) has a modulus of elasticity of less than approximately 4 GPa, pref erably of approximately 3.5 GPa or less.
10. A roll in accordance with any one of the preceding claims, characterized in that the central layer (4) is substantially thicker than the outer layer (9).
11. A roll in accordance with any one of the preceding claims, characterized in that the central layer (4) is substantially thicker than the base layer (3).
12. A roll in accordance with any one of the preceding claims, characterized in that the outer layer (9) is made anti-static.
13. A roll in accordance with any one of the preceding claims, characterized in that the outer layer (9) has a high thermal conductivity.
14. A roll in accordance with any one of the preceding claims, characterized in that the central layer (4) includes fibers, at least regionally.
15. A roll in accordance with claim 14, characterized in that the fibers of the central layer (4) include at least carbon fibers.
16. A roll in accordance with any one of the preceding claims, characterized in that the fibers of the base layer (3) include aramide fibers and/or glass fibers, at least in part.
17. A roll in accordance with any one of the preceding claims, characterized in that the matrix material includes epoxy resin.
18. A roll in accordance with any one of the preceding claims, characterized in that the roll core (1) consists of metal or in particular of fiber reinforced plastic.
19. A method of manufacturing an elastic smoothing roll in accordance with any one of the preceding claims, characterized in that the outer layer (9) consisting of a mixture of melted metal and melted plastic is applied to the central layer (4) by a spray method, a casting method, a brushing method or a painting method.
20. A method in accordance with claim 19, characterized in that the mixture is applied to the central layer (4) by a flame spraying process or by a plasma spraying process.
21. A method in accordance with claim 20, characterized in that the metal and/or the plastic is melted during the flame spraying or during the plasma spraying.
22. A method in accordance with any one of claims 19 to 21, characterized in that the metal and the plastic are melted and mixed with one another before the application onto the central layer (4).

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