FI85998C - Rolling machine in paper machine and method for making roll coating g - Google Patents

Description

85998

Roll of a paper machine and method of making a roll coating Rolls of papermakers and rolls for the production of rolls 5

The invention relates to a roll for direct contact with a fibrous web to be produced for use in a paper machine or the like, in particular a wet press roll having a roll body and a substantially metallic coating forming the outer surface of the roll 10 consisting of strip-like coating elements. a profile strip from a helically rotating profile strip, and the coating elements are connected to each other by groove / shoulder adapters formed on their long sides or the like so that the coating elements 15 are in adjacent tightly adjacent contact with the coating, forming a uniform substantially smooth connection there are at least two and they are each substantially rectangular in cross-section so that the radial dimension of the roll of each coating element o is substantially greater than its transverse axial dimension of the roll, i.e. the thickness of the element strip.

The invention further relates to a method for coating a smooth-surfaced roll from a strip material by wrapping so that the roll body is rotated. 25 about its axis, whereby the strips attached to the end of the roll and coming through the braking device are tightened and the rotational movement begins; when wrapped around the roll body in a screw manner.

The fibrous web, e.g. paper or paperboard, comes into direct contact with several different rolls or cylinders at different stages of its manufacture or processing in a paper machine or the like. Some of these rolls have a decisive effect on both the operation of the paper machine and the V! the properties of the fibrous product to be manufactured, in particular the surface properties of the paper, such as smoothness and / or gloss. These rollers are e.g.

35 calender rolls used in the finishing treatment of the web and the so-called smooth press rolls used in a paper machine either in the wet press section at the beginning or in the adhesive or intermediate presses in the drying section.

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The present invention is intended to be applied in particular to paper machine rolls on the surface of which the fibrous web is in direct contact in a relatively wet state. Such rollers are, for example, smooth upper rollers in such so-called in straight-through presses, in which the web is supported by a nip between two press rolls supported by a single press fabric to remove water from the wet web. It is known that these nips can be two or three in a row. The roll inside the felt loop in the nip, usually the lower roll, is usually hollow and is able to receive in its surface structure the water which leaves the web and felt due to compression. The upper roll, against which the web is in direct contact, is smooth and is usually mounted on load arms, by means of which the pressure acting on the nip is adjusted.

15 Smooth press rolls are also used as an integral part of the so-called in compact press parts, in which two or even three single-felt press nips can be arranged against the same smooth conversation, in which the second roll is usually a hollow surface roll.

It is well known that in a single-felt press nip, the wet fibrous web tends to adhere more strongly to the smooth roll surface than to the opposing, coarse press felt or similar fabric. Adherence of the web to the surface of the smooth roll is a prerequisite for the operation of most press structures. The adhesion of the web to the roll surface after the press nip substantially reduces the so-called rewetting effect and prevents the web from leaving the affected area of the nip to follow the compression fabric uncontrollably.

Thus, it is desired that the web adhere to the surface of the smooth roll in the single-felt press nips 30 of the press sections of the above-mentioned press sections and remain therein in a certain post-nip roll sector, the extent of which may be about 10 ° to 250 ° depending on the type and structure of the press section. Small · / ·: sector values come into question in straight presses, while large ones in discussions of compact press parts.

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The web must be detached from the surface of the roll after that sector, at its boundary line, and the adhesion must not be too strong. In addition, the adhesion must be as even as possible over the entire width of the machine without large local variations.

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The detachment of the web from the surface of the roll takes place under the effect of the tensile stress due to the speed difference. Therefore, the line of detachment must be parallel to the axis of the roll and as straight as possible so that the stretching of the web at this stage is uniform over the entire width of the machine and no local anisotropy to the web strength properties occurs.

The adhesion of the web to the smooth roll surface has a large effect on both the surface and strength properties of the paper to be produced and the reliability of the paper machine, especially in the case of a web with low wet strength. The adhesive force of the smooth roll surface to the web may be at least to some extent greater than the cohesive force that holds the fibers of the web together.

It is common that as the web passes through the single felt press nip, individual fibers and possibly filler particles of web material are continuously detached from the web and adhering to the surface of the smooth roll. These tend to soil the roll surface even so that the adhesion of the dirt cumulatively increases. In general, this does not have a major effect on the operation of the paper machine and the quality of the paper, as the surface of the roll can be kept clean with a scraper. Sometimes, however, the adhesion of the fibers to the surface of the smooth roll can be so severe that it results in visible "fluffing" on the surface of the finished paper or poor surface strength of the paper, which can impair the printability of the paper. At worst, this continuous adhesion of the web material can result in the sudden adhesion of the wet web to the surface of the smooth roll, either over the entire length of the roll or over it. In such a case, there is always an immediate production interruption in the operation of the paper machine.

The reason for the sudden adhesion of the web to the roll surface may be the uneven dry content of the web in the transverse direction, a malfunction of the scraper device or some process failure of the wire section of the paper machine. In all these cases, the type and nature of the roll coating can have its own effect on the susceptibility of the press to malfunction. The coating of the roll as a whole may have an excessive tendency to adhere to the fibrous web to be produced in each case. The adhesion tendency 5 of different types of pulps can vary within very wide limits.

The principal and actual cause of adhesion is the water film between the web and the roll surface. This is formed when the wet web is pressed in a nip against the roll. Much of the water that then separates from the web 10 penetrates the press fabric and a smaller but sufficient amount of adhesion spreads on the surface of the roll. This water is the same as the circulating water of the wire section of the paper machine, in which the fibers of the web to be formed are slurried in a headbox mixing pump. The composition of this water depends on the type of raw material of the paper to be produced. The dilution water of newsprint pulp containing mainly groundwood 15 is known to be different from the dilution water of unbleached sulphate pulp or fine pulp containing bleached pulp fiber. The chemical properties of the suspension or dilution water are one of the contributors to the adhesion of the web to the roll surface.

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Most essential in said water film, which thus acts as a kind of adhesive for attaching the web to the roll surface, is its physical properties. Of these, however, viscosity and surface tension are largely dependent on the chemical composition of the water. Instead of water film; 25 thickness and uniformity, ie continuity, must be considered as purely physical • properties. The most important should probably be the thickness of the water film, to which the adhesion energy is inversely proportional. The integrity of the water film is also an essential factor influencing the strength of the adhesion.

____; 30 However, the water film and its properties alone do not solve the adhesion of the web to the smooth roll surface. An important role in the adhesion of the web is played by the chemical and physical properties Vi of the surface material of the roll, such as the hydrophilicity or hydrophobicity of the surface and the roughness of the surface. These factors affecting the surface energy of the roll material are; in Finnish patent application FI-85 0107.

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Yet another main group of factors influencing the adhesion of the web to the surface of the smooth roll is the process parameters of wet compression such as nip pressure, nip extent, nip compression time and roll temperature.

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Studies have shown that the strength of the adhesion increases to 22-26% of the dry matter content of the web, after which the adhesion deteriorates. One explanation for this finding is that the water film between the web and the roll surface thins up to that limit, resulting in an increase in adhesion because the adhesion energy is inversely proportional to the thickness of the water film. After said limit value, the water film apparently loses its uniformity and the adhesion force starts to decrease again as the dry matter content of the web increases.

15 In addition, studies have confirmed the following empirical findings on web adhesion to the surface of a smooth press roll. The stronger the adhesion - the wetter the web is pressed against the roll - the higher the possible nip pressure used 20 - the more consecutive nips formed against the same roll, without removing the web between the nips from the surface of the roll

The requirements for the press rolls of paper machines have increased at the same time as other developments in paper machine structures. In the early days of mechanical papermaking, when technology was underdeveloped and science was simple, the top rollers of wet presses could even be made of wood, for example by turning maple. Subsequently, castings were made on cast iron rolls which, either as such or coated with copper plate, were usable on low speed and / or coarse paper-30 machines. As paper machines were further developed and their speed increased, the requirements increased, especially for roll materials. As early as about 90 years ago, it was discovered that granite is • a material that is almost ideal in terms of adhesion properties *: · for the smooth upper rolls of wet presses. These were granted German patents DE-99215 and DE-103677, in which, in addition to granite, porphyry and syenite were disclosed as suitable rock types.

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A particular advantage of granite or a similar press roll material is its surface structure and other physicochemical properties, which on the one hand suitably adhere the web to the roll surface and on the other hand generally easily detach from it after the press nip. In addition, granite-5la has good resistance to the abrasive effect of the scraper.

The development of the paper industry over the last couple of decades has presented paper machine manufacturers with new problems, e.g. for granite rolls. Production efficiency requirements require ever larger working widths for paper machines. For this reason alone, the diameters of the press rolls must be chosen to be considerably large so that the deflections of the rolls do not cause inconvenience. Another factor that increases the diameter of these rolls is the constant effort to use ever-increasing nip pressures in the compression process. Obtaining raw stone for such large rolls 15 has become increasingly difficult and expensive. The larger the roll, the greater the possibility that there is a latent defect in the natural granite roll blank that can cause the roll to break during operation of the paper machine due to nip load vibrations and / or large temperature fluctuations. Granite 20 may also have such inhomogeneity that the surface properties of the roll that affect adhesion are not the same at different points on the long roll.

These disadvantages of granite rolls have given rise to research and development aimed at finding solutions for the material of smooth press rolls that have all the good properties of granite without its mentioned disadvantages. It is known that various substitutes for granite rolls have long been proposed, but only economic factors ____ · 30 such as easy availability and cheap price have been used as a starting point. The purpose of the latest developments ... is to find a material with good surface properties.

Such rollers are shown e.g. in the applicant's Finnish patent applications FI-854748, FI-853544, FI-850806, FI-850107.

.1. 35 German patent publication DE-559 025, dated 1932, discloses a coating for a press roll with a cast iron body, which consists of a mixture of ground 7 85998 granite and vulcanized rubber. Such a coating has become known e.g. as stonitis. This coating is not chemically resistant in all conditions, for example, which is why granite grains or particles are constantly released from it. This phenomenon gradually changes the coating to rough, causing excessive web adhesion to the roll surface.

British Patent Publication GB-880 125 also discloses a roll coating based on the use of granite powder with an acrylic resin binder as a binder. By selecting the grain size of the granite powder as "suitable", it is possible, according to the description of the 10 patents, to make the surface of the coating slightly porous, which reduces the excessive adhesion of the web. This coating is also intended for use in the repair and repair of old granite rolls.

The roll coating according to EPO patent publication 53 804 consists of rock powder and hard polyurethane resin. The rock material can be e.g. granite powder, quartz sand and the like and its main components are SiO 2 and / or Al 2 O 3.

U.S. Pat. No. 4,316,769 discloses a granite roll to be replaced by a cast iron frame coated with a steel alloy having a chromium content of 15-35%, preferably 25%. Such a steel surface has good hydrogenation properties that allow easy removal of the web from the roll surface. Chrome steel in this respect is comparable to granite. The hard surface of chrome steel is also very resistant to scratching.

U.S. Pat. No. 2,114,072, issued in 1938, discloses a method for treating the surface of a metal roll so that its adhesiveness. The 30 paper webs would be similar to the surface of a granite roll. The starting point of the method is the observation of the effect of the porosity of the granite surface on the adhesion of the web. With the pores of the granite, the air passing between the paper web and the roll reduces the effect of the capillary forces between these surfaces. In the method, the surface of the roll is roughened by a strong sand-35 blast to a suitable roughness and the resulting sharp edges are removed by grinding. Finally, the roll is electroplated with a layer of chromium 0.02 to 0.2 mm thick and polished.

What all the granite-5 roll substitutes presented in the above-referenced references have in common is that their surface is completely homogeneous throughout, i.e. it has the same adhesion energy at each point of the roll. This is precisely the aim of their development, as one of the aims has been to eliminate the possible inhomogeneity of natural granite. In addition, although some coatings have tended to have a grain size of some 10, the grain size is generally microscopic. For example, the coating according to FI-85 0107 consists of metallic and ceramic components, in which case in one embodiment the size of the Cu granules is 5-40 μπι and the size of the ceramic granules is 40-100 μm. In natural granites and the like, which have several different species, the granules of quartz, feldspar, etc. contained in them are known and visibly several millimeters in diameter. Such large granules are a factor in the adhesion and other properties of granite required in the smooth rolls of a paper machine wet press.

The object of the present invention is to provide such a smooth roll of a paper machine, the coating of which is resistant to abrasion and which has good other e.g. adhesion properties and which can only be easily renewed if necessary if its surfactant properties do not meet the requirements of the paper to be produced.

:; In order to achieve the above objects, the roll according to the present invention is mainly characterized in that the adhesion properties of the materials of the different coating elements as seen in the fibrous web. 30 den differ substantially. 1

The method according to the invention, on the other hand, is mainly characterized in that at least two coating strips of different strip materials are pressed by a roller device connected to the power unit, which presses the formed strip turns tightly against each other to form a uniform coating to be continuously machined.

Coatings for paper machine rolls made of a wrapper-5 web of strip-like cover material as the outermost cover of the roll body are already known, e.g., from U.S. Pat. Nos. 3,718,959, 4,084,302 and 4,065,842. the roll referred to in said patent is primarily smooth-faced. Regardless of the purpose of the roll coatings disclosed in the above-mentioned reference patents, the technique used in their manufacture can be applied in certain respects in the manufacture of the roll coating according to the present invention.

In the invention, the strip elements may be separate rings, but most preferably they are a continuous strip wrapped around the roll body shell. The material of one strip element is preferably hard, e.g. chromium-containing steel and the material of one strip is preferably a continuous strip, e.g. sintered material. These strips may each be substantially rectangular in cross-section, the long side of which will be parallel to the radius of the roll and the short side of the rectangle will be parallel to the axis of the roll. The tape elements are wrapped. . on the roll body so that the long side of the rectangle will be parallel to the radius of the roll * and the short side parallel to the axis of the roll.

25 Although recoating is a more demanding operation, in some cases it can even be carried out in the paper mill's own roll handling department, where, for example, equipment for grinding and bombarding the rolls is usually available.

In the following, the invention will be described in detail with reference to some embodiments of the invention shown in the figures of the accompanying drawing, to which the invention is not limited.

Fig. 1 is a schematic plan view of a device by means of which the coating strips 35 are wound on a roll body, viewed in the direction of the roll axis.

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Figure 2 schematically shows an apparatus and arrangement for wrapping cover strips on a roll body, viewed perpendicular to the plane of the roll axis.

Figure 3 shows a cross-section of a partially wound strip coating and a press roll used to wrap the strip.

Figure 4 shows one cross-section of a cover strip according to the invention.

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Figures 5A, 5B and 5C show an alternative of the invention in wrapping a coating strip using one actual profile strip and a narrower strip formed between its layers.

Figures 1 and 2 show schematically the principle of performing a tape coating. The frame cylinder 1 of the roll to be coated is fastened from its shaft pins, e.g. to a lathe, with which the roll body is rotated. The lathe or the like carriage, which is moved in a manner known per se in the axial direction of the roll to be coated and synchronously with the rotational movement, is provided with straightening, braking, shaping and support devices for the coating strips a and b. Figure 1 shows a preliminary view of these devices. . straightening rollers 4 and braking devices 5 are provided, through which the coating strips a and b are passed to the body 1 of the roll to be coated.

Reference numerals 6a and 6b denote first guide rollers at which the coating strips a and b begin to rotate on the surface of the roll body 1.

'. *: After the first guide rollers, the cover strips are further pressed ·. ": By means of one or more shaping rollers 7, first against a fixed end: 3: and then against the coating already formed. The shaping roller 7 is acted upon by suitable power devices (not shown). 30 The required force is about 400 kN to 450 kN Figure 1 also shows a guide roller 8, which • ensures that the finished coating does not loosen.With devices 5 the coating strips a and b are individually braked so as to provide a suitable amount of tension to ensure the evenness of the coating formed 35. It is preferable to equip the devices 5 to measure and adjust the braking force known per se.The suitable braking force is 11 85998 about 300 kN to 400 kN when wrapping a steel strip. e.g. plastic, the braking force correspondingly can be considerably lower.

The present invention thus requires the use of at least two different coating tapes a and b. These strips, which have a profile e.g. as shown in Figures 3 and 4, are wound on the roll body 1 simultaneously. In addition, the apparatus of Figures 1 and 2 may be provided with heating devices (not shown) by means of which the coating strips a 10 and b can be heated, if necessary and separately, in order to facilitate the coating process and ensure its result. Heating helps to provide tension and heating makes some tape materials more elastic. In addition, if there are, for example, three coating strips, each of them can be provided with its own control and braking device or 15 operations so that two strips with similar properties are guided together to the coating process.

According to Fig. 3, a ring 3 is attached to the end of the roll body 1, to which the end of the coating strip a is attached, e.g. by welding, before starting the coating process. Figures 3 and 4 show a preferred profile, i.e. cross-section, of the coating strips a and b according to the invention. . -section. The implementation of the method generally requires that the height h of the strips be considerably greater than their thickness 1. This applies in particular to metallic strips. Since one of the covering strips a or b · '25 according to the invention can be e.g. an organic material, it can then ·. ·; ’It may be necessary for the thickness of such a strip to be proportional to the dimension; h is clearly greater than the thickness of the metal strip.

The substantially rectangular profile 30 of the cover strips a, b has a corresponding groove 11 on one vertical side 14 and a corresponding groove 11 on the other vertical side 15. This groove / shoulder arrangement 10,11 ensures the non-release of the coating even if the cover strip a, b breaks for some reason. There are several options for selecting the profile of the cover strips for groove / shoulder fit, which have been presented e.g.

U.S. Patent Nos. 4,104,772 and 4,104,773 to 35 applicants.

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The outer surfaces 16 of the adjacent strips a and b, when pre-wound, form a uniform roll surface, which, however, may be very uneven immediately after the coating process has ended. This unevenness is due to the material differences between the different strips used and the method used to wrap them. Even if the strips a and b initially have the same profile (e.g. as shown in Figure 4), their dimensions in the finished coating can differ considerably, e.g. due to different tensile stresses on the strips. The resulting roll surface must be machined smooth and continuous at the end of the coating process. The idea of the present invention is specifically to select the material of the coating strips a and b so as to obtain the desired surfactant and adhesion properties on the final smooth roll surface using the coating method described above.

15 The machining of the obtained roll surface to the final and desired smoothness takes place as a separate work step. It is essential that the bases of the used coating strips, which will thus face the roll body to be coated, have a uniform profile with respect to the groove / shoulder arrangement 10/11, which ensures the mechanical attachment of the strips a and b to each other.

,. According to the description of the invention above, the main reason for the web adhering to the surface of the smooth roll is the water film formed between the web and the roll surface and its physical and chemical properties. The most essential of the physical properties is the integrity of the water film, which or lack thereof may be large-scale or ... classified as microscopic. Only on a perfectly smooth and homogeneous::: surface can a continuous and uniform water film be formed, an important additional condition for the formation of which is that the surface in question has ____: 30 the same surface energy throughout. One idea of the present invention is that the integrity of the water film formed on the smooth roll surface is broken by the coating being formed of at least two rings a and b or · ”· * corresponding in sufficient material.

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The simplest solution is to use two steel strips a and b, one of which is made of low-alloy steel and the other of, for example, stainless or acid-resistant steel. It has proven to be particularly advantageous for the alloy steel to have a high chromium content, up to 30%. In many cases, conventional stainless steel with a chromium content of 18% and a nickel content of 8% can be used with ordinary steel. Other metals can also be considered for use as such strip materials, e.g. copper alloys, which in certain cases may be straight and smooth on vertical sides 14,15 as starting blanks, but which are adapted to the profile of the hard steel strip during the coating-10 process. The latter strips can have a thickness (- dimension 1, in Fig. 4) only e.g. 1-2 mm, while the thickness of the steel strips is generally of the order of 3-4 mm. As for the width of the profile strip, i.e. the height h, which determines the thickness of the resulting coating layer, it is usually 15 to 10 mm. In this regard, reference is made to the applicant's Finnish patent No. 54,953.

When wrapping two cover strips a, b on the roll body 1 at the same time, it is possible - if the strips a and b have essentially the same profile · 20 usually with one weight roll. If, on the other hand, one of the strips is a thin strip of relatively soft material which is suitable for one of the invention. . wrapped as a straight intermediate layer of a kind in accordance with between the turns of the strip, two pressure rollers 6a and 6b may be used, the use of which is shown schematically in Figures 5A, 5B and 25C, in which the straight intermediate strip b 'is sufficiently wide in width, i.e. it in the non-machined coating will be at least flush with the final roll surface, but preferably outside the surface for safety.

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As shown in Figs. 5A, 5B and 5C, which show the fabrication of the roll coating step by step, the narrow spacer strip b 'is formed in the shape of the groove / cantilever arrangement 10,11 when pressed against the previous turn of the profile strip a. The spacer b 'is, for example, copper, 35 polymer and / or a mixture of polymer and ceramic, or other sufficient ____; soft and formable material.

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Since in practice the roll will sometimes operate at a considerably high temperature, the material of the intermediate strip must be chosen to have a coefficient of thermal expansion of the same order as in the actual profile strip. For example, the thermal expansion of nickel is of the same order as 5 of several possible stainless steel alloys.

Another possibility for providing the roll coating according to the present invention is to use a strip made of an organic material, e.g. a polyurethane synthetic resin, with a steel strip. The composition, manufacture and properties of such 10 materials are described e.g. in U.S. Pat. No. 4,438,063. It should also be noted that according to this publication, the coating material in question may be a mixture of, for example, an organic polyurethane component and an inorganic, e.g. rock powder.

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From the foregoing, it will be apparent that the invention may be practiced using a variety of material combinations. At least one strip material should be very durable, such as any suitable steel grade. The requirements for the parallel material to be used with it are e.g. Sufficient surface energy deviating from the hydrophobicity / physiology of the steel, e.g. the roughness of the material is. . as one component.

The properties of the roll coating according to the invention can also be influenced by the choice of the widths of at least two strip materials to be used so that both are equally wide or, more preferably, the proportion of more wear-resistant steel is e.g. about three times that of the other strip material, preferably by wrapping two steel strip one eg ceramic strip per --- - · 30 den.

As can be seen from the above and from some reference publications, the most suitable thickness of steel strip, i.e. width 1 in the direction of the roll axis, is n.

’* * 0.5-4 mm and these strips may be in the coating two in parallel.

35 The thickness of any soft metal strip that may be used can only be ____; 0.5-2 mm. The thickness of the ceramic or polyurethane strip may have to be chosen to be relatively large for technical reasons and may be e.g. 4-6 mm.

It should be emphasized once again that the invention seeks to influence the adhesion between the web and the roll surface in two ways: on the one hand by destroying the integrity of the resulting water film and on the other hand by influencing the physicochemical properties of this water film.

The invention is not limited to the above, but its details 10 may vary within the scope of the inventive idea defined by the following claims.

Claims (8)

A roll for direct contact with a fibrous web to be produced for use in a paper machine or the like, in particular a wet press roll having a roll body (1) and a substantially metallic coating forming the outer surface of the roll consisting of surrounding strip-like coating elements (a, b), the coating elements (a, b) are each separate rings or each consist of a profile strip (a, b) helically rotating the roll body shell, and which coating elements (a, b) are connected to each other by their long sides (14,15) via groove / shoulder adapters (10,11) or the like so that the coating elements (a, b) are in close contact with each other in close contact with the coating, forming a uniform substantially smooth roll surface, the coating elements (a, b) having at least two and they are each substantially rectangular in cross-section so that each coating element the radial dimension (h) of the roll (a, b) of the element (a, b) is substantially larger than its transverse, axial dimension (1), i.e. the thickness of the element strip, characterized in that the adhesion of the materials of the different coating elements (a, b) 20 the properties with respect to the fibrous web differ substantially from each other. Roll according to Claim 1, characterized in that. . at least one strip of metal is an alloy or metal alloy. : ’25 Roll according to Claim 2, characterized in that one of the coating strips is an alloy and the other is non-metallic. Roll according to one of Claims 1 to 3, characterized in that the non-metallic strip is an organic compound. . *. Roll according to one of Claims 1 to 4, characterized in that the proportion of the metallic surface formed by the strips is 50 to 90% of the total surface of the roll shell. 35 17 85998 Roll according to one of Claims 1 to 5, characterized in that one of the strips is a hard alloy and the other a soft alloy. Roll according to one of Claims 1 to 6, characterized in that the organic compound is polyurethane, epoxy or the like, optionally doped with an inorganic substance such as Al 2 O 3, quartz, feldspar or the like. A method for coating a smooth-surfaced roll according to claim 1 by wrapping tape material on a roll body (2) so that the roll body (2) is rotated about its axis, whereby the strips (a, b) attached to the roll end and coming through the brake device tighten and begin to wrap screw-like for the mango, characterized in that at least two coating strips (a, b) of different strip materials 15 are pressed by a roller device (6a and / or 6b) connected to the power unit, which presses the formed belt turns tightly against each other as a uniform tight working step, into a continuous smooth cylinder surface. 20 ie 85998