WO2009125062A1

WO2009125062A1 - A method for manufacturing a belt for a fiber web forming machine, a belt for a fiber web forming machine, and a method for recovering the operating condition of a belt of a fiber web forming machine

Info

Publication number: WO2009125062A1
Application number: PCT/FI2009/050261
Authority: WO
Inventors: Riku Pihko
Original assignee: Metso Paper, Inc.
Priority date: 2008-04-09
Filing date: 2009-04-08
Publication date: 2009-10-15
Also published as: FI20085291A0; FI20085291L

Abstract

The invention relates to a method for manufacturing a belt for a fiber web forming machine where an air impermeable belt (10) of a metal base material (17) forms a closed loop (12) which has an outer surface (16) that comes in contact with a web (66). When forming the outer surface (16) - attachment profiles (26) deviating from the main directions (MD, CD) of the belt are arranged in the belt for fastening a coating layer (20), - the coating layer is fastened to the belt for forming the outer surface. The invention also relates to a corresponding belt for a fiber web forming machine and a method for recovering the operating condition of a belt of a web forming machine.

Description

A METHOD FOR MANUFACTURING A BELT FOR A FIBER WEB FORMING MACHINE , A BELT FOR A FIBER WEB FORMING MACHINE , AND A METHOD FOR RECOVERING THE OPERATING CONDITION OF A BELT OF A FIBER WEB FORMING MACHINE

The invention relates to a method for manufacturing a belt for a fiber web forming machine, where an air impermeable belt of a metal base material forms a closed loop which has an outer surface that comes in contact with the web. The invention also relates to a corresponding belt for a fiber web forming machine and a method for recovering the operating condition of a belt of a fiber web forming machine.

The use of metal belts in several positions of a fiber web forming machine is known from prior art. Metal belts are used in the press section, in the dryer section, and in the calender. In the press section, an air impermeable metallic belt, or a metal belt, can be used, for example, for smoothing out the web surface prior to the dryer section. The use of a metal belt in the press section is proposed, for example, in Finnish patent application 20065447. In the dryer section a metal belt is used in a so called Condebelt® dryer section, for example. In the calender section, in turn, a metal belt can be used in belt calenders .

Belt properties play a significant role in all the above mentioned partial processes. One central problem is web sticking to the belt. When the web is sticking to the belt, the web surface becomes rough. In addition, web sticking to the belt is very problematic at the press where it causes runnability problems. The dry content at the end of the press section is practically below 50%, which means that the web strength is low. When the web is detached from the belt for leading the web to the dryer section, the web may break. Attempts are made to minimize the web from sticking to the belt. The object of the invention is to provide a novel method for manufacturing a belt of a fiber web forming machine. The characteristic features of this invention are that, when forming the outer surface, attachment profiles deviating from the main directions of "the belt are arranged in the belt for fastening a coating layer, and the coating layer is fastened to the belt for forming the outer surface. Another object of the invention is to provide a novel belt of a fiber web forming machine. The characteristic features of this invention are that the belt includes a coating layer for forming the outer surface and the belt includes attachment profiles deviating from the main directions of the belt for fastening the coating layer.

The web refers to board and paper webs, for example. In turn, the term ' fiber web forming machine' is used to refer to machines designed for manufacturing paper, board, pulp or tissue products, for example. Belts are used in a fiber web forming machine. An air impermeable belt with a metal base material forms a closed loop having a surface that comes in contact with the web. In addition, when forming the outer surface, attachment profiles deviating for example from the main directions of the belt are arranged in the belt for fastening a coating layer, and the coating layer is fastened to the belt for forming the outer surface. Attachment profiles deviating from the main directions of the belt that are formed in the base material enable fastening the coating layer to the base material very tightly. Such a method enables covering an air impermeable belt with a metallic base material, or a metal belt, with a coating layer, the fastening of which to metal is challenging.

Covering a belt influences remarkably the properties of the belt outer surface said properties having further an influence in the calender section, dryer section and press section, for example . One central property of the belt surface is adhesion . A second central property of the belt surface is friction . A third central property is the smoothnes s of the belt surface since a smooth surface does not wear a doctor. In addition, a smooth surface improves the surface quality of the web produced as well as the heat transfer from the belt to the web. In calendering, belt adhesion has an effect, for example, on keeping clean of the belt located in the calender. When the belt adhesion is low, attachment of coating, for example, from the web surface to the belt is less significant. In the dryer section, it is possible to make the web surface smoother than before since the web detaches from a dryer section belt more easily than before. In the press section, when adhesion between the web and the belt is lower than before, the web can be detached from the belt applying less force than before.

According to an embodiment, attachment profiles deviating from the main directions can be linear-type surface profiles, for example. Linear-type surface profiles hold up a doctor uniformly whereby the doctor and the belt wear less. This also minimizes vibration.

According to another embodiment, the surface roughness of the outer surface of the base material is modified, for example, to a level of Ra = 0.8 - 3.5, and more specifically to a level of Ra = 1 - 2.5. Such a surface roughness of the base material has been found optimal in pilot stage tests for fastening a coating to the base material.

In a third embodiment, attachment profiles are formed for example by grinding the base material. Grinding can be performed with a band, for example. By grinding, a desired surface roughness can be achieved. According to an embodiment, grinding can be honing, for example. Honing can be performed using a stone or a disc, for example. By honing, the surface profiles formed in the base material can be made multidirectional.

In a fourth embodiment, grinding is performed with a grinding machine that moves in the cross direction during grinding. The belt, in turn, moves in the machine direction during grinding. According to an embodiment, grinding can be performed, for example, using a rolling stone or a disc that moves in the machine direction during grinding. Thus a desired pattern is achieved by grinding using very simple arrangements.

In a fifth embodiment, attachment profiles are formed by processing the base material with an impact method. Hammering or shot blasting, for example, can be used as the impact method. With impact methods, a desired surface roughness is achieved whereby the surface profiles formed in the surface are very irregular .

In a sixth embodiment, the surface roughness of the coating layer and further of the closed loop is modified, for example, to a level of Ra = 0.1 - 0.7, and more specifically to a level of Ra = 0.2 - 0.5. Then the surface roughness of the coating layer is at a level that enables smoothing out the web surface.

On the other hand, the surface roughness of the coating layer is at a level at which the heat transfer from the belt to the web is very efficient.

In a seventh embodiment, a primer layer can be formed in the base material in connection with the attachment profiles. In other words, a primer layer is formed on the surface of the base material said layer entering partially between the attachment profiles . A surface coating layer can be formed in connection with the primer layer, i.e. on top of the primer layer. A primer layer facilitates the fastening of the surface coating to the base material. Typically the thickness of the primer layer can be 10 - 30 μm, for example, and more specifically 15 - 25 μm. In turn, the thickness of the surface coating layer can be 25 - 75 μm, for example, and more specifically 40 - 60 μm. In an eighth embodiment, the primer layer is formed before the surface coating layer . In this case it is possible to use coatings of very many types for creating the primer layer and the surface coating layer .

In a ninth embodiment, the primer layer and the surface coating layer are formed at the same stage. Thus, manufacturing of the coating layer is on the whole even simpler than before.

The invention is described below in detail by making reference to the enclosed drawings, which illustrate some of the embodiments of the invention, in which

Figure 1 shows an example of a belt according to the inven- tion including a bottom layer made of a base material and a coating layer,

Figure 2 shows an example of a belt according to the invention the coating layer of which includes a primer layer and a surface coating layer, Figure 3a shows an example of a belt according to the invention which has a surface profile that is parallel with the machine-directional main direction,

Figure 3b shows an example of a belt according to the invention which has a surface profile that is parallel with the cross-directional main direction,

Figure 3c shows an example of a belt according to the invention which has surface profiles that are parallel with both main directions,

Figures 4a - 4f show examples of linear-type surface pro files, deviating from the main directions of the belts according to the invention.

Figure 5 shows an example of a belt according to the invention which has surface profiles that are parallel with a main direction, Figure 6 shows an example of a belt according to the invention which has surface profiles deviating from the main directions, and

Figure 7 shows an example of a belt according to the invention in the press section.

5 Figure 1 is a cross-sectional view of an exemplary belt 10. In a fiber web forming machine, a belt 10 made of a metal base material 17 and impermeable to air forms a closed loop 12

(Figure 7) . The closed loop 12 has an outer surface 16 that comes in contact with a web 66 (Figure 7) . In addition, the

10 belt 10 includes a coating layer 20 for forming the outer surface 16 and attachment profiles 26 for fastening the coating layer 20. According to an embodiment, the coating layer 20 can be a low-adhesion coating. Coatings reducing adhesion and friction that are made on the surface 24 of the base material

15 17 of the belt 10 without attachment profiles 26, i.e. on the unroughened surface 24 of the base material 17, are not sufficiently wear-resistant as such. Thus the coating and the doctor used for keeping the surface clean wear rapidly. At the same time, the surface properties deteriorate rapidly. When the

20 surface of the base material 17 is provided with attachment profiles 26 for fastening the coating layer 20 to the base material 17, a low-adhesion coating is also present in the recesses and/or grooves of the surface formed by the attachment profiles. Thus the service life of the coating can be in-

25 creased.

The belt 10 shown in Figure 1 forms a closed loop 12 (Figure 7) having an inner surface 14 and an outer surface 16. In the belt 10, the coating layer 20 is present only on the surface of the

30 belt 10 which is on the side of the web 66 (Figure 7) whereby the belt 10 is composed of a bottom layer 18 on the side of the inner surface 14 and the coating layer 20 on the side of the outer surface 16. Thus the base material 17 forms the bottom layer 18. The base material could also be between two coating

35 layers in which case the base material would form the center layer. However, in this case the base material forms the bottom layer which is placed against rolls. Hence, embodiments are broadly described in this application using the term ^Λbottom layer' although the concept 'base material' could be used therein. The bottom layer 18 has a first surface 22 located on the side of the inner surface 14 of the loop (Figure 7) and a second surface 24 located on the side of the outer surface 16 of the loop. Attachment profiles 26 are present on the second surface 24 of the bottom layer for fastening the coating layer 20 to the bottom layer 18. When the second surface 24 of the bottom layer is provided with attachment profiles 26 for fastening the coating layer 20 to the bottom layer 18, a low- adhesion coating is also present in the recesses and/or grooves of the surface formed by the attachment profiles. Thus the service life of the coating can be increased.

When the belt 10 includes a bottom layer and a surface layer, the recycling and repair of belts are facilitated. A belt can damage, for example, when a lump of paper passes beside the belt in the process. Recovering the operating condition of a belt for a fiber web forming machine can be accomplished with the belt installed in the fiber web forming machine in its operating-time position. In this method, attachment profiles are arranged in the belt in a desired area for fastening a coating layer as well as for improving the adhesion between the coating layer and the base. A coating layer is also fastened to the belt for forming an outer layer. Thus the repair of the belt can be performed with the belt in place in the process. In this way, the heat required for fastening teflon, for example, can be taken from existing heating equipment. On the other hand, it is also possible to use separate heating equipment that is brought to the machine.

The bottom layer of the belt is air impermeable metal and the top layer can be other material than metal, for example. The material thickness of the metallic bottom layer is relatively high compared to the thickness of the top layer. Thus it is justifiable to talk about a belt although precisely speaking only the bottom layer of the belt is metal.

In the belt 10 shown in Figure 1 the coating layer 20 is a low- adhesion coating. The use of a coating layer enables thus lower adhesion than before between the web and the belt. According to an embodiment, the adhesion of a low-adhesion coating to a web at a dry content of 40% can be lower than 5 N/m, more specifically lower than 3 N/m, after five detaching times. The expres- sion ^Λfive detaching times' means that the web has been detached five times from the same point of the belt. In other words, regardless of slight belt soiling, the adhesion between the web and the belt is lower than 5 N/m, more specifically lower than 3 N/m.

As the web contains a notable amount of water, hydrophobicity of the belt enables for its part lower adhesion between the web and the belt. According to an embodiment, the contact angle between a low-adhesion coating and water can be more than 95°, more specifically more than 105°.

A low-adhesion coating can be composed of at least one of the following: composite, fluoroplastic or sol-gel. For example, a low-adhesion coating can be a composite coating, which allows wide adjustment of surface properties. According to an embodiment, a composite coating can include diamond since a composite coating can be made resistant with diamond.

A low-adhesion coating can include fluoroplastic or sol-gel. These materials enable reducing remarkably the adhesion between the web and the belt.

In the belts shown in Figures 1 and 2, the surface roughness of the outer surface 16 of the base material 17 can be Ra = 0.8 - 3.5, and more specifically 1 - 2.5. More precisely, in the belts 10, the surface roughness of the other surface 24 of the bottom layer 18 can be Ra = 0.8 - 3.5, and more specifically 1 - 2.5. With such a surface roughness the coating layer can be kept tightly attached to the bottom layer. 5

In the belts shown in Figures 1 and 2, the coating layer has a first surface 28 toward the second surface 24 of the bottom layer 18 and a second surface 30, 34 toward the outer surface 16 of the belt 10. The surface roughness of the coating layer

10 20 and further of the outer surface 16 of the closed loop 12 can be Ra = 0.1 - 0.7, and more specifically 0.2 - 0.5. In other words, the roughness of the outer surface 16 of the belt 10, i.e. of the second surface 30, 34 of the coating layer 20, can be Ra = 0.1 - 0.7, and more specifically 0.2 - 0.5. With

15 this belt roughness, a desired roughness can be achieved on the surface of a web to be produced.

In Figure 1 the surface coating layer 20 is composed of one layer the strength of which is, for example, 30 - 110 μm, more 20 specifically 55 - 85 μm. With this strength, a low-adhesion coating covers well the bottom layer. Thus the belt can be made suitably smooth all over. In addition, the adhesion between the belt and the web can be notably reduced.

25 The coating layer 20 of the belt 10 shown in Figure 2 includes additionally a primer layer 32, which is located on the second surface 24, which includes attachment profiles 26, of the bottom layer 18, and a surface coating layer 34, which is located on top of the primer layer 32. The strength of the

30 primer layer 32 can be 10 - 30 μm, for example, and more specifically 15 - 25 μm. Correspondingly, the strength of the surface coating layer 34 can be 25 - 75 μm, for example, and more specifically 40 - 60 μm. Thus a low-adhesion coating can be kept well attached to the belt.

35 The primer layer 32 and the surface coating layer 34 of the coating layer 20 of the belt shown in Figure 2 can be adapted to be formed at different times . On the other hand, the primer layer 32 and the surface coating layer 34 of the belt shown in Figure 2 can al so be adapted to be formed s imultaneous ly . According to an embodiment, a low-adhesion coating can be, for example , a fluorine coating or a composition of fluorine-containing plastic and primer .

Figures 3a - 3c illustrate enlargements of pieces 42 of belts 10 having attachment profiles formed by surface profiles 44 . In this case the surface profiles 44 are surface profiles 36 that are parallel with the main directions . Figure 3a illustrates machine-directional MD surface profiles 38 . In turn, Figure 3b illustrates cross-directional CD surface profiles 40 . Figure 3c illustrates machine-directional MD surface prof iles 38 and cross-directional CD surface profiles 40 . Surface profiles 36 parallel with the main directions are formed of machine-directional MD surface profil es 38 and/or cro s s -direct ional CD surface profiles 40 .

When the belt 10 i s in a fiber web f orming machine in it s operating-time position, it is cleaned by doctoring off impurities that have attached to the belt from the web, for example . Surface profiles parallel with a main direction included in the belt cause problems under certain conditions . Machine-directional MD surface profiles 38 form machine-directional necks ( Figure 3a ) , which hold up the doctor . Then the doctor and particularly the area between the necks formed by the machine- directional surface profiles are subj ected to more intensive wear . Because the wear is directed particularly to certain areas in the cross-direction of the belt and the doctor, wearing is non-uniform. Non-uniform wear reduces the service life of the doctor and/or the belt . Cross-directional CD surface profiles 40 , in turn, form cross-directional necks (Figure 3b) . Cross-directional necks formed by cros s-directional surface profiles cause a vibrating movement in the doctor. Then the doctor vibration affects the cleaning result of the belt, and the vibration also wears the belt faster than before. Doctor vibration is harmful even for the mere doctoring result. How- ever, even more central is that doctor vibration can function as an excitation source for vibration of the entire press/dryer group/calender. The problem is not resolved with the construction shown in Figure 3c having profiles that are parallel with both main directions.

According to an embodiment, attachment profiles 26 are adapted to be formed of surface profiles 44 which are surface profiles 46 deviating mainly from the main directions MD, CD (Figures 4a - 4g) . The main directions of a fiber web forming machine are the machine direction, or MD, and the cross direction, or CD. In the figures, the main directions MD, CD are illustrated with coordinate systems . The web advances in the machine direction MD whereas the cross direction CD is the longitudinal direction of rolls, for example. With profiles 46 deviating mainly from the main directions MD, CD, specific areas in the cross direction of the belt and the doctor are not subjected to wear but wearing is uniformly distributed in the cross direction of the belt and the doctor, whereby the doctor blade and the belt wear more uniformly than before. Correspondingly, resonance can also be avoided by using profiles 46 deviating mainly from the main directions MD, CD. Surface profiles can be produced by grinding or inclined sand blasting, for example.

Figures 4a - 4g illustrate enlargements of pieces 42 of belts 10 having attachment profiles formed by surface profiles 44.

Attachment profiles are adapted to be formed with surface profiles 44 which deviate mainly from the main directions MD,

CD. The surface profiles 44 of Figures 4a - 4g include surface profiles 46 deviating from the main directions MD, CD. The surface profiles 44 of Figures 4a - 4g can also include surface profiles 36 that are parallel with the main directions MD, CD. According to an embodiment, the surface profile 46 in the belt 10 deviating from the main direction MD, CD can be at least one of the following: a straight line 50, an open arc 54, a closed arc 56, a point 58.

The surface profiles 46 deviating from the main directions MD, CD in the piece of belt 42 shown in Figure 4a are straight lines 50. These straight lines can be provided, for example, by grinding the belt alternately to different directions .

The surface profiles 46 deviating from the main directions MD, CD in the piece of belt 42 shown in Figure 4b are straight lines 50. All straight lines are parallel. In Figure 4b the angle between the lines 50 formed by the surface profiles 46 deviating from the main directions MD, CD and the main direction is approximately 45°. For example, the angle between the lines 50 formed by the surface profiles 46 deviating from the main directions MD, CD and the main direction is more than 5°. Even a small deviation between the line 50 and the main direc- tion MD, CD is sufficient for removing the problems that appear in connection with the lines that are parallel with the main directions. In other words, even a small deviation between the line and the main direction MD, CD is sufficient for removing the problems that appear due to the use of lines which are parallel with the main directions.

The surface profiles 46 deviating from the main directions MD, CD in the piece of belt 42 shown in Figure 4c are straight lines 50. Straight lines are now directed to two directions. The lines could have even more directions. This type of application is shown in Figure 4a.

The surface profiles 46 deviating from the main directions MD, CD in the piece of belt 42 shown in Figure 4d are open arcs 54. These open arcs can be provided by honing the belt surface, for example.

The surface profiles 46 deviating from the main directions MD, CD in the piece of belt 42 shown in Figure 4e are open arcs 54. In addition, the piece has surface profiles 36 parallel with a main direction, which are surface profiles 38 parallel with the machine direction MD. The number of surface profiles 36 parallel with the main direction MD is smaller compared to surface profiles 46 deviating from the main directions. According to an embodiment, surface profiles parallel with the main direction MD, CD have been created in preliminary grinding and the subsequent honing has provided surface profiles deviating from the main direction MD, CD which have a circular arch form. Thus the surface profiles parallel with a main direction are no more dominating.

The surface profiles 46 deviating from the main directions MD, CD in the piece of belt 42 shown in Figure 4f are closed arcs 56. Closed arcs, circles in a special case, can be provided by honing the belt surface, for example.

The surface profiles 46 deviating from the main directions in the piece of belt 42 shown in Figure 4g are points 58. Point patterns can be provided, for example, by shot blasting or sand blasting.

Manufacturing surface profiles 46, shown in Figure 4g, which are points 58, is challenging at a required accuracy. If there are too large deviations between the points 58, vibration is subjected to the doctor. Surface profiles, which are points, can be used among other surface profiles, for example.

Figures 4a - 4f show pieces of belt in which the surface pro- files 46 deviating mainly from the main directions MD, CD and functioning as attachment profiles are linear-type surface profiles 48 . The linear characteristic of the surface profiles allows minimizing vibration when each surface profile or a neck carries the load produced by the doctor for a longer time . Then the doct or cannot penet rat e t o th e s o f t co at ing i n the groove/valley points but the doctor load is uniformly distributed . Thus the necks formed by the surface profiles wear the doctor uniformly and to the same extent in each point . Grooves are not formed in the doctor due to wearing whereby the surface pressure between the doctor and the belt remains stable , and consequently, not even the belt will wear non-unif ormly . A linear-type surf ace profile 48 can be at least one of the following : a straight line 50 ( Figures 4a - 4 c ) , a curve 52 (Figures 4d - 4f ) . A curve 52 can be an open arc 54 (Figures 4d and 4e) or a closed arc 56, a circle as a special case (Figure 4f ) .

Figures 5 and 6 illustrate belts 10 that have been cut open. These belts 10 have formed closed loops 12 (Figure 7) . Thus the first end 60 of the cut belt 10 has been connected to the second end 62 of the cut belt 10. The cut belt 10 is shown for its entire machine-directional MD travel, whereas in the cross direction CD, only a part of the belt 10 is shown. The machine direction MD and the cross direction CD of the cut belt 10 are not correctly scaled relative to each other since the scale has been reduced in the machine direction and increased in the cross direction. Figures 5 and 6 show, as mentioned above, the entire belt 10 in the machine direction MD the length a of which belt can be 2 - 10 m, for example. In the cross direction CD, in turn, only an area of three surface profiles 44 is shown of the belt 10, the length b of which area can be 0.1 mm - 1 mm, for example.

In Figure 5, the cut belt 10 includes surface profiles 36 parallel with a main direction, more precisely they are surface profiles 38 that are parallel with the machine direction MD.

The surface profiles 44 are machine directional MD surface profiles 38 when a certain cross area c of the belt has only one type of a surface profile 44 in the machine direction MD.

In Figure 6 the cut belt 10 includes surface profiles 46 devi- ating from the main directions MD, CD. Surface profiles 44 are surface profiles 46 deviating from the main directions MD, CD when the same main-directional cross area c has several surface profiles 44. As the surface profiles are very close to each other in a roughened surface, even a small deviation from the machine direction MD makes the surface profile deviating from the machine direction MD. According to an embodiment, the angle α between a surface profile deviating from the main direction and the main direction is more than 5°.

Figure 7 shows an example of a press section 64 including a belt 10. The belt 10 forms a closed loop 12 having an inner surface 14 and an outer surface 16. In addition, the belt 10 is composed of a bottom layer 18 on the side of the inner surface 14 and a coating layer 20 on the side of the outer surface 16. The bottom layer 18 has a first surface 22 on the side of the inner surface 14 and a second surface 24 on the side of the outer surface 16.

Attachment profiles 26 are present on the second surface 24 of the bottom layer 18 (Figure 1) for fastening the coating layer 20 to the bottom layer 18. With this construction, the properties of the outer surface 16 of the belt 10 contacting the web 66 can be modified as desired. Among the properties of the belt surface contacting the web, adhesion and surface smoothness, or surface roughness, are particularly significant. The belt surface must be very smooth in order that the web can be smoothed out with the belt as desired already during pressing. In other words, the belt surface must be very smooth in order that the web surface can be smoothed out with the belt as desired already during pressing. The importance of adhesion is also very central since the web must detach from the web with ease. If the adhesion affecting between the web and the belt is remarkable, for example more than 5 N/m, the web surface quality can decrease when the web gets stuck to the belt. In addi- tion, the outer surface of the belt soils whereby the web surface quality deteriorates even more.

In the press section, the web to be detached from the belt is still at a low dry content so that its strength is low. If the press section has a free draw after the belt press, belt adhesion has a particularly great effect on the runnability of a fiber web forming machine. The web must be detached from the connection of a supported transfer and therefore high adhesion between the web and the belt impairs the runnability of a fiber web forming machine. This runnability problem appearing in connection with a free draw grows when the web gets stuck to the belt. In other words, when using a free draw, the runnability problem grows when the web is sticking to the belt. The greater the adhesion, the more draw must be subjected to the web for detaching the web from the belt.

The belt 10 according to the invention shown in Figure 7 is heated with heating equipment 68. The heating equipment 68 includes a heat supply means 72 and typically also a hood 74. The heat supply means 72 can be a roll 76, for example, which is adapted to be heated. The heat supply means can also be a typical heat supply means, such as an infrared heater, or heat can be supplied through a medium. The medium through which the heat is supplied to the vicinity of the belt, i.e. the belt is heated, is typically steam. Heating enables increasing the dry content of the web in the press section. A dry content higher than before after the press improves the runnability of a fiber web forming machine.

In the dryer section heating is necessary in order that water can be evaporated from the web. When calendering the web, heating is advantageous in order to create a temperature gradient for taking the web surface layers to a well modifiable state. Belt calenders are used particularly in calendering after coating. In the press section the temperature of the belt is typically 120⁰C. According to an embodiment, adhesion of a low-adhesion coating to a web at a dry content of 40% is lower than 5 N/m, more specifically lower than 3 N/m, at a belt temperature of 120⁰C. Measuring is performed after five detaching times.

In Figure 7, the press section 64 includes a doctor 70 for cleaning the belt 10. The doctor can be a relatively soft cotton/phenolic resin doctor, for example. On the other hand, the doctor can be fiber-reinforced, i.e. a composite doctor. When cleaning a belt with a doctor, surface profiles parallel with the main directions (Figures 3a - 3c) can be disadvantageous. Cross-directional surface profiles can function as an excitement for resonance. Machine-directional profiles, in turn, cause non-uniform wear in the doctor and the belt itself. According to an embodiment, attachment profiles are therefore adapted to form surface profiles that are surface profiles 46 deviating mainly from the main directions (Figures 4a - 4g) , for example, linear-type surface profiles 48 deviating mainly from the main directions (Figure 4a - 4f) .

Claims

1. A method for manufacturing a belt for a fiber web forming machine, where an air impermeable belt (10) of a metal base material (17) forms a closed loop (12) which has an outer surface (16) that comes in contact with a web (66), characterized in that, when forming the outer surface (16),

- attachment profiles (26, 44) deviating from the main directions (MD, CD) of the belt (10) are ar- ranged in the belt (10) for fastening a coating layer (20), and

- the coating layer (20) is fastened to the belt (10) for forming the outer surface (16) .

2. A method according to claim 1, characterized in that the surface roughness of the outer surface (16) of the base material (17) of the belt (10) is modified to a level of Ra = 0.8 - 3.5, and more specifically to a level of Ra = 1 - 2.5.

3. A method according to claim 1 or 2 , characterized in that the attachment profiles (26, 44) are formed by grinding the base material (17) .

4. A method according to claim 3, characterized in that grinding is performed with a grinding machine and the grinding machine moves in the cross-direction (CD) and the belt (10) moves in the machine direction (MD) during grinding.

5. A method according to claim 3 or 4, characterized in that grinding is honing.

6. A method according to any of claims 1 - 5, characterized in that the attachment profiles (26, 44) are formed by treating the base material (17) with an impact method.

7. A method according to any of claims 1 - 6, characterized in that the surface roughness of the coating layer (20) and further of the outer surface (16) of the closed loop (12) is modified to a level of Ra = 0.1 - 0.7, and more specifically to

5 a level of Ra = 0.2 - 0.5.

8. A method according to claim 1, characterized in that the attachment profiles (26) are of a linear type.

10 9. A method according to any of claims 1 - 8, characterized in that a primer layer (32) is formed in the base material (17) in connection with the attachment profiles (26) and a surface coating layer (34) is formed in connection with the primer layer (32) .

15

10. A method according to claim 9, characterized in that the primer layer (32) is formed before the surface coating layer (34) .

20 11. A method according to claim 9, characterized in that the primer layer (32) and the surface coating layer (34) are formed at the same stage.

12. A belt for a fiber web forming machine, which air imperme- 25 able belt (10) made of a metal base material (17) is adapted to form a closed loop (12) which has an outer surface (16) that comes in contact with a web (66) , characterized in that

- the belt (10) includes a coating layer (20) for forming the outer surface (16) , and 30 - the belt (10) includes attachment profiles (26) deviating from the main directions (MD, CD) of the belt (10) for fastening the coating layer (20) .

13. A belt according to claim 12, characterized in that the 35 coating layer (20) is a low-adhesion coating.

14. A belt according to claim 13, characterized in that adhesion of the low-adhesion coating to a web (66) at a dry content of 40% is lower than 5 N/m, and more specifically lower than 3 N/m, after five detachment times.

5

15. A belt according to claim 13 or 14, characterized in that adhesion of the low-adhesion coating to a web (66) at a dry content of 40% is lower than 5 N/m, and more specifically lower than 3 N/m, at a belt (10) temperature of 12O⁰C.

10

16. A belt according to any of claims 13 - 15, characterized in that the contact angle of the low-adhesion coating and water is more than 95° and more specifically more than 105°.

15 17. A belt according to any of claims 13 - 16, characterized in that the low-adhesion coating includes at least one of the following: composite, fluoroplastic or sol-gel.

18. A belt according to any of claims 12 - 17, characterized in 20 that the surface roughness (Ra) of the outer surface (16) of the base material (17) is 0.8 - 3.5, and more specifically 1 - 2.5.

19. A belt according to any of claims 12 - 18, characterized in 25 that the surface roughness (Ra) of the coating layer (20) and further of the outer surface (16) of the closed loop (12) is Ra = 0.1 - 0.7, and more specifically 0.2 - 0.5.

20. A belt according to claim 12, characterized in that the 30 attachment profile (26) is at least one of the following: a straight line (50), an open arc (54), a closed arc (56), a point (58) .

21. A belt according to claim 12 or 20, characterized in that 35 the attachment profiles (26) are of a linear type.

22. A belt according to claim 21, characterized in that the linear-type attachment profile (48) is at least one of the following: a straight line (50), a curve (52) .

5

23. A belt according to any of claims 12 - 22, characterized in that the coating layer (20) includes a primer layer (32) located on the outer surface (16) of the base material (17) and a surface coating layer (34) located on top of the primer layer

10 (32) .

24. A belt according to claim 23, characterized in that the strength of the primer layer (32) is 10 - 30 μm, .and more specifically 15 - 25 μm.

15

25. A belt according to claim 23 or 24, characterized in that the strength of the surface coating layer (34) is 25 - 75 μm, and more specifically 40 - 60 μm.

20 26. A method for recovering the operating condition of a belt of a fiber web forming machine, said belt (10) being as stated in any of claims 12 - 25, characterized in that the belt (10) is in a fiber web forming machine in its operating-time position and method

25 - attachment profiles (26) deviating from the main directions (MD, CD) of the belt (10) are arranged in the belt (10) in a desired area for fastening a coating layer (20) , and

- the coating layer (20) is fastened to the belt (10) for 30 forming an outer surface (16) .