The present invention relates to an arrangement in the press section of a web-forming machine, which press section includes at least one nip and at least one impenetrable belt arranged to travel through the nip, in order to support in the press section the web being manufactured on the web-forming machine, and which arrangement includes reconditioning means for the belt. The invention also relates to a doctor blade.

Press felts, to which water transfers in the press nip from the web, are used in the press section of a web-forming machine. The press felt can be one both sides, or only one side of the web. Nowadays, dense belts that are impenetrable by water are also used, especially as belt sleeves of long-nip rolls, and as a transfer belt used in connection with them. A doctor, also combined with water-jet lubrication, is usually used to condition the transfer belt.

The conditioning effect of known conditioning means is often insufficient. In practice, dirt and water remain on the surface of the belt, despite conditioning. In addition, the belts are soft, so that soft doctor blades at a gentle angle must be used when doctoring them. The edge of a soft doctor blade quickly becomes rounded, or else rapidly forms a wide wear bevel, which is liable to aquaplane. The dirt and water-removal ability of the doctor then diminishes substantially. This reduces the solids content of the web after the press section and leads to a deterioration in the moisture profile of the web, as water remains unevenly on the surface of the belt. At the same time, material accumulates on the surface of the belt, which limits the production of the web-forming machine and acts to reduce the quality of, the end product. Poor and particularly uneven conditioning a)lso limits the running speed of the press section and also causes shutdowns. Correspondingly, a poor web moisture

profile will reduce the quality of the end product and cause broke. In addition, in terms of certain paper grades and production costs, the use of advantageous paper chemicals

(particularly AKD and ASA) is limited, because they have the effect of accelerating the dirtying of the belt, despite conditioning. In particular, doctoring of the belt sleeve is difficult, due to the movement of the belt sleeve while the maintenance of effective doctoring demands short doctor-blade replacement intervals.

The invention is intended to a new type of arrangement in the press section of a web-forming machine, by means of which the belt can be conditioned more effectively than before and water removed from it more evenly than before. The invention is also intended to create a new kind of doctor blade, which is highly suitable for use with soft belts. The characteristic features of the arrangement according to the present invention are stated in the accompanying Claim 1. Correspondingly, the characteristic features of the doctor blade according to the invention are stated in the accompanying Claim 24. In the arrangement according to the invention, the belt can be conditioned in various ways. A good conditioning effect can be achieved by better cleaning than before and by more precise water removal. The belt entering the nip will then be clean and evenly wet. For example, more water than before can be used in cleaning, because the excess water can be easily and reliably removed before the nip. On the other hand, the amount of water can be reduced by arranging the water to be used more efficiently and on only part of the belt at one time. In addition, the effect of the conditioning means remains unaltered, despite use, thus reducing maintenance and shutdown costs. The conditioning means can also be situated more freely than before and can be used even with soft belts, without risk of damaging the belt. The doctor blade according to the invention adapts to the movements of the belt and remains sharp for its entire operating life.

In the following, the invention is examined in greater detail with reference to the accompanying drawings showing some embodiments of the invention, in which

Figure 1 shows the arrangement according to the invention fitted to the press section of a web-forming machine, Figure 2 shows a side view of the conditioning means belonging to the arrangement according to the invention,

Figure 3 shows a side view of a second embodiment of the conditioning means according to the invention,

Figure 4 shows a schematic drawing of one preferred combination of the conditioning means according to the invention, in connection with a transfer belt,

Figure 5 shows a schematic drawing of a second preferred combination of the conditioning means according to the invention, in connection with a transfer belt, Figure βa shows a trailing doctor, seen in the machine direction,

Figure 6b shows a side view of a third embodiment of the conditioning means according to the invention.

Figure 1 shows, as one example, the applicant's OptiPress press section, in which there are two press nips 10 and 13 one after the other. In this case, the first press nip 10 is a so-called roll nip, through which two press felts 11 and 12 are arranged to travel. The second press nip 13 is a so-called long nip, in which an upper press felt 14 and a lower impenetrable transfer belt 15 are used. The press section in question permits a good solids content and a symmetrical web to be obtained. In addition, runnability is good, thanks to the closed draw. In practice, the first nip too can be a long nip. In practice, the belt can also be arranged in such a way that it runs, for example, through a transfer nip. In other words, the nip is not necessary a press nip.

Thus, the invention relates to an arrangement in the press section of a web-forming machine. Generally the press section includes at least one nip and at least one impenetrable belt arranged to travel through the nip. The belt is mainly used to support the web being made on the web-forming machine in the press section, as the belt itself is impenetrable by water. In addition, the arrangement includes conditioning means for the belt. For example, in Figure 1 the conditioning means of the transfer belt is a conventional doctor 18, in connection with which there is also a lubricating spray 19. According to what is stated above, the doctor in question is ineffective in terms of conditioning and the doctor blade in it must be changed frequently. In addition, due to the scraping, a very small blade angle and soft blade materials must be used, due to the soft transfer belt.

According to the invention, the conditioning means 17 include a trailing doctor 20, 20', in which there is a doctor blade 21. The doctor blade, which is arranged in a new and surprising manner, remains in good operating condition, without damaging the belt. The forward-facing arrangement of the doctor also prevents the doctor blade from catching on the surface of the belt. In addition, it is possible to use considerably thinner, though harder doctor blades than before, which further improves the doctoring result and extends operating life. In practice, a thin doctor blade sharpens as it wears. Due to the thinness of the blade, the wear bevel that arises remains small, so that aquaplaning can be avoided. This means that even with a worn doctor blade the doctoring result will remain good. The thickness of the doctor blade according to the invention is 0,1 - 2 mm, preferably 0,2 - 0,8 mm. In addition, the doctor blade 21 is supported in such a way that its point of contact 45 with the belt 16 is, in the direction of travel of the belt 16, after the projection point 42 of the support point 22 of the doctor blade 21 (Figures 2 and 3) . In other words, in the operating position the doctor blade is bent in the direction of

travel of the belt. Thus the doctor blade is continually in tension, while simultaneously conforming to the movement and deformations of the belt. The projection point of an unloaded straight doctor blade is nearly the same as the point of contact of the doctor blade, but in the operating position the doctor blade bends to act as a trailing doctor.

In Figure 1, the arrangement according to the invention is arranged in connection with the transfer belt 15 arranged to travel through the press nip 13. The belt could quite as well the belt sleeve of a long-nip roll belonging to the press nip. The arrangement according to the invention can also be used with other belts, for example, in a calender, in which the dirtying problem is, however, smaller than in the press section.

In the first embodiment of the trailing doctoring according to the invention, the length of the doctor blade is substantially the same as the width of the belt. Thus a full-width doctor blade will continuously doctor all of the belt. The solution in question will create an evenly dry belt. Particularly in the case of a transfer belt, the trailing doctor is preferably located at the end of the belt circulation, i.e. as close as possible to the press nip. In that case, most of the water will be able to leave, for example, by gravity. On the other hand, for a short distance the dirtying of the belt will be prevented by the surrounding water mist. Figure 1 shows two advantageous locations for a full-width trailing doctor 20', which are preferably situated at a crease roll 23. A full-width trailing doctor 20' can also be located in connection with the two following crease rolls, even on an unsupported section of the belt. The same reference numbers are used for components that are functionally similar.

Instead of a full-width doctor blade, it is also possible to use a short doctor blade. In other words, the length of the

doctor blade according to the invention is substantially less than the width of the belt. In that case, the conditioning effect can be arranged locally as desired. For example, short doctor blades can be fitted to both edge areas of the belt. On the other hand, suitable support elements can be used to arrange the doctor blade to be moveable in the cross direction of the web-forming machine. This will create a traversing trailing doctor, which can be used to condition the belt over its entire width, despite the short doctor blade.

Even the doctor blade set in the new manner will by itself improve the effect of the conditioning devices . On the other hand, the doctor blade can be set in a normal blade holder, especially if a full-width doctor blade is used. The condition- ing effect can be further improved by using a washing head 25 fitted to support elements 24, which is intended to wash the belt 16 (Figure 3) . In that case, the washing head too is traversing, so that the belt can be conditioned over its entire width. In addition, the movement of the washing head can be adjusted, which will permit, for example, the conditioning of problem areas to be increased. In practice, the washing head can be moved more slowly at certain points than at others, or the washing head can be moved several times over those points. In that case, the entire belt can be conditioned while, if necessary, the cleaning can be targeted. Unlike in Figure 2, the washing head 25 can be used without a trailing doctor 20. The washing head can then be easily located, for instance, in the unsupported section of the belt 16 (Figure 1) .

Figure 3 shows a traversing trailing doctor 20 with its support element 24. The support element 24 includes, for example, a beam, in which there is a carrier fitted in guides . The carrier is moved in the cross-direction of the machine using some suitable operating device (not shown) . The construction of the support element can also vary in different applications. For example, the washing head 25 can be located in existing

structures, for example in the beam 30 of a diagonal water cutter (Figure 1) . In Figure 2, the support element 24 includes a beam, to which a blade holder and doctor blade 21, which are as such conventional, are fitted. Other kinds of support elements and blade holders can also be used to create a trailing doctor according to the invention.

Figure 3 also shows in combination with the trailing doctor 20 a washing head 25, which according to the invention is arranged before the doctor blade 21 in the direction of travel of the belt 16. In this case, in practice the washing head is first used to wash the belt, after which the trailing doctor is used to remove the detached dirt and water. At the same time, the trailing doctor detaches any material that may have remained on the surface of the belt. This creates a belt surface that is clean and dry, despite the effectiveness of the washing. According to the invention, high-pressure needle and fan nozzles 31 and 32 are used in the washing head 25. Thus by suitably setting the nozzles, a powerful but full wash jet is created. The alignment of the washing head can also be changed. The use of a fan nozzle creates a fan-shaped or conical spray, whereas the use of a needle nozzle creates a point spray. In addition to fan nozzles, hollow-cone nozzles are also dispersing nozzles. According to the invention, in the washing head there are 2 - 12, preferably 3 - 10 needle nozzles 31 and fan nozzles 32, in which case a washing area about 40 - 100-mm wide is created. Correspondingly, the length of the doctor blade is about twice the width of the washing area, so that the surface of the belt is sure to be dried. In practice, needle nozzles with a jet size of 0,15 - 0,4 mm and correspondingly fan nozzles with a jet size of 0,15 - 1 mm are used in the high- pressure nozzles. Water is led to the nozzles at a pressure of 60 - 140 bar, preferably 80 - 120 bar. In practice, the pressure depends mainly on the type of belt and the water- pressure devices available.

The use of a sufficiently high pressure achieves two significant advantages . Firstly, the wash result is good and secondly smoothing of the belt is avoided. In practice the belt becomes smoother in operation, so that the adhesion between the belt and the web increases. In other words, the separation of the web from the web becomes more difficult. This reduces the surface quality of the web and can cause web breaks. Often, the problems force a belt change, even though the belt might be otherwise still usable. According to the invention, a pressure of more than 80 bar is preferably used. This avoids the smoothing of the belt and at the same time washing becomes more effective. On the other hand, a great deal of ASA size must be used in some pulp grades, which rapidly dirties the belt. With these pulps grades it is then preferable to use a higher pressure than above, of even 120 bar, without wearing the belt. In other words, the power of the spray is used to detach dirt, instead of wearing the belt. In practice, it is also possible to use a momentarily increased pressure to make washing more effective. At the same time, it is possible to influence the surface roughness of the belt.

In addition to trailing doctoring, the effect of the arrangement according to the invention can be further improved. The conditioning means according to the invention can include low- pressure lubricating sprays in the washing head, or means for heating the belt before the trailing doctor, or both. In addition, means 33 for feeding a detergent and/or anti-dirtying agent to the surface of the belt 16 can be combined with the lubricating sprays forming part of the conditioning means 33. Correspondingly, it is also possible to feed a chemical preventing dirtying. It is preferable to feed the detergent as soon as possible after the separation of the web, so that the detergent can take effect before the washing head. The means 33 are preferably fitted in connection with the already existing lubricating sprays 19 (Figure 1) . In its simplest form, the pipe creating the lubricating spray is attached to the auxil-

iary device dosing the detergent (not shown) . However, before a leading doctor there is a great deal of water on the belt and its surface is dirty. Thus a great deal of detergent or another chemical should be fed and it has little time to act, most of it leaving with the water removed by the scraper. Thus, according to the invention the detergent is sprayed on only after the scraper. Most of the water has then been removed, so that even a small amount will achieve a good effect. In addition, the surface of the belt has already been partly cleaned, so that the detergent is able to act of the surface of the belt. The remaining water is then removed using the trailing doctor according to the invention. In Figure 4, the means 33 are located immediately after the scraper.

According to the invention, devices 24 for increasing the temperature of the detergent can also be combined with the washing head 25. Warm water will then be used in the high and/or low-pressure nozzles, which will increase the conditioning effect. In the washing head, the water consumption is relatively small, so that the operating costs remain reasonable. According to the invention, the increased temperature of the water is about 20 - 100 ⁰ C. The devices for heating the water are selected case-specifically and their construction can vary in different applications. Figure 1 also shows means 43 for heating the belt 16 before the trailing doctor 20. The belt can be heated, for example, by steam, for example, using a steam-box .

Figure 3 shows the construction of a traversing trailing doctor in greater detail. In this case, the trailing doctor 20 includes not only a doctor blade 21, but also a second doctor blade 35, the properties of which are essentially the same as those of the first doctor blade 21. Thus, it is possible to ensure the cleanness and even wetness of the surface after the doctor blade. At the same time, it is possible to use a lower loading than would be necessary when using a single doctor

blade. According to the invention, in the washing head 25 the doctor blades 21 and 35 are fitted at a distance s from each other, in this case s being less than 60 mm. Thus both doctor blades doctor more or less the same location, which eliminates the problems arising from movement in the belt. The doctor blades thus operate in essentially the same way, so that they also wear at the same rate. Figure 3 also clearly shows the baffle 36 fitted to the washing head 25, which limits the amount of water going to the trailing doctor 20. The location of the baffle relative to the washing head can be adjusted and it is substantially as long as the doctor blade. In connection with the trailing doctor it is also possible to use a trough to collect the wash water. The trough can be full-width and fixed, or else a narrow trough attached to support elements can be used.

Thus, in the trailing doctor according to the invention thinner than normal doctor blades, which are preferably straight, can be used. The embodiment in Figure 3 shows one example of a support for one or more doctor blades. In this case, the doctor blades 21 and 35 are set in compression between two pairs of tubes 38. The pairs of tubes 28 are fitted to threaded bars 39 and are tightened at suitable places using nuts 40. The solution in question is easy to implement while the mutual position of the doctor blades can be altered. The compression support of the kind in Figure 3 is advantageous particularly in applications, in which the trailing doctor is supported on a traversing washing head. Conventional blade holders can also be used (Figure 2) .

When a trailing doctor is started to be used the doctor blades are nearly vertical to the belt. When the belt moves, the doctor blades bend in the direction of movement of the belt (Figures 2 and 3) . Thus each doctor blade touches the belt only on its narrow edge. In addition, the edge in a thin doctor blade will remain sharp, due to the wear of the doctor blade.

Forward-facing doctor blades will also flex, if material accumulates on the surface of the belt, despite the washing spray. As the conditioning effect and sharpness of the doctor blade remain however, the material will gradually detach from the surface of the belt. In the operation situation in Figure 3, the blade angle α of the doctor blade 21 relative to the tangent and the blade angle β of the second doctor blade 35 relative to the tangent are about 33°. In addition the doctor blades 21 and 35 are 35 mm apart from each other. Generally the blade angles are 10 - 70°, preferably 20 - 50° while the distance between the doctor blades is 20 - 100 mm.

In the solutions shown, the doctor blade is essentially straight. According to the invention, the doctor blade can also be arranged at an angle relative to the belt. In other words, the ends of the doctor blade are at different heights. In that case, the doctor blade will effectively plough water, without the water becoming dammed behind the doctor blade. In addition, the water can be directed to the side of the belt in a con- trolled manner. The embodiment in question is particularly advantageous when using a full-width doctor blade. In the trailing doctor according to the invention, it also possible to use different kinds of doctor blade. The material of the doctor blade can be plastic, fibre-reinforced plastic, or metal, preferably stainless steel, or some other flexible material. Due to the trailing doctoring, the doctor blade can thus even be of a hard metal. Wear resistance can be further improved by using a surfacing on the material of the doctor blade. The surfacing can be ceramic, metal-ceramic, or metal, preferably a wolfram-carbide metal.

Figure 1 shows a schematic diagram of the locations of the various components of the arrangement . Figures 4 and 5 shows two preferred assemblies. Generally, the arrangement includes a trailing doctor 20 and 20' fitted at two different places. The assembly of Figure 4 is particularly suitable for existing

press sections, in which the trailing doctors can be easily placed. The first trailing doctor 20 in the direction of rotation of the belt 16 with a doctor blade that is substantially shorter that the width of the belt 16. Correspondingly, the second trailing doctor 20' is equipped with a doctor blade that is substantially the width of the web. Both trailing doctors are shown in greater detail in Figures 3 and 6b. The washing head is preferably arranged in connection with the first trailing doctor 20 in the direction of rotation of the belt 16. The belt treated with detergent is then washed by a traversing washing head and the water is doctored by the short doctor blade. The remainder of the water is then removed by a full-width trailing doctor 20' according to the invention. Thanks to its construction, the second trailing doctor 20' can also be arranged in an unsupported section of the belt 16 (Figures 4 and 5) .

The assembly shown in Figure 5 is preferable particularly when designing new web-forming machines. In this case, the first trailing doctor 20 is fitted to a beam 30, which is part of the diagonal water cutter belonging to the arrangement. This also includes the washing head. It is then possible to move the diagonal water cutter and the trailing doctor on the same beam, which will simply the construction of the arrangement. In a solution of this kind, a splash guard of a flexible material is also fitted above the washing head. The splash guard prevents the water coming from the spray from splashing onto the web travelling above. At the same time, the washing head is brought sufficiently close to the belt, without risk of damage and the jets can be directly optimally at the web. The splash guard can be of, for example, plastic or rubber while its edges are preferably rounded. In practice, the width of the splash guard is about 200 - 400 mm and its height 50 - 150 mm.

Figures 6a and 6b show the construction of the trailing doctor according to the invention in greater detail. Such a trailing

doctor 20' includes a blade holder 44, which is preferably of a composite material. The blade holder in question is light, but durable. This it is easy to install and operate and has little need for maintenance. In addition it avoids the problems caused by thermal expansion while its smooth shape reduces the dirtying of the trailing doctor. In the blade holder 44 according to Figure 6b, a thin doctor blade 21 according to the invention is used, which bends in trailing doctoring. The properties of the trailing doctor can be altered, not only by altering the doctor blade, but also by altering the properties of the press blade 45. When using the trailing doctor in question, the preferred blade angle is 35 - 40°. In practice, the length of the blade is about 100 mm.

In addition, the full-width doctor blade of the trailing doctor is dimensioned in a new manner. According to the invention, the doctor blade is arranged to be only slightly wider than the web. In other words, the length of the doctor blade is substantially the same as the width of the web. This avoids the deflection of the doctor blade previously caused by the deflection of the belt, which previously weakened the doctoring result. In addition, there is a bevel or rounding 46 at both ends of the doctor blade 21 on the belt side 16. This avoids belt damage caused by the doctor blade when then belt moves laterally. There is preferably also a corresponding bevel in the short doctor blade according to the invention. In Figure 6a, the edges of the belt 16 are shown by dot-and-dash lines and the edges of the web by broken lines. In practice, the doctor blade is about 50 - 100 mm wider than the web.

The arrangement according to the invention has been shown in practical tests too to prevent the dirtying of the belt, or even to clean a belt that has already become dirty. In addition, with the aid of the trailing doctor a transfer belt in particular is dried evenly. Thus the web moisture profile after the press is further improved while at the same time the solids

content increase. With the aid of the arrangement according to the invention, greater production and a higher end-product quality than previously are achieved. The arrangement is also economical in investment and operating cost and can be easily retrofitted. In practice, the conditioning effect can be adjusted case-specifically and the doctor blades have a long life, as they remain sharp throughout their entire operating life, without a risk of damaging the belt.

Usually, the transfer belt is formed of a woven core, which is surfaced on at least one side with an impenetrable and wear- resistant multi-component polymer. The use of a transfer belt avoids open draws when the web is being taken from the press section to the dryer section. In addition, the smooth transfer belt evens the surface of the web, which improves the quality of the end product. The impenetrable surfacing also prevents re-wetting in the press nip and thus promotes the achievement of a good moisture profile. Transfer belts are about 5-mm thick, as are belt sleeve. However, the belt sleeve is surfaced on both sides while its outer surface can be grooved. Besides plastic, particularly a transfer belt can also be of some other material .