WO2007096478A1

WO2007096478A1 - Device for doctoring the belt of a belt roll

Info

Publication number: WO2007096478A1
Application number: PCT/FI2007/050099
Authority: WO
Inventors: Sampo Vörgren
Original assignee: Metso Paper, Inc.
Priority date: 2006-02-27
Filing date: 2007-02-23
Publication date: 2007-08-30
Also published as: FI20065139A0; FI20065139A; AT11253U1; FI122390B; AT505578A2; DE112007000406T5

Abstract

The invention relates to a device f or doctoring the belt ( 12 ) of a belt roll ( 10 ) , the outer surface ( 44 ) of which belt ( 12 ) is partly open . The devi ce includes a blade holder ( 20 ) , which is f i tted with a blade ( 18 ) , in such a way that , in the operating position of the device , the blade ( 18 ) lies against the outer surf ace ( 44 ) of the bel t ( 12 ) . In the devi ce the hardnes s o f the blade ( 18 ) is less than the hardness of the outer surf ace ( 44 ) . The device f urther includes an air doctor ( 14 ) f or removing water from the belt ( 12 ) .

Description

DEVICE FOR DOCTORING THE BELT OF A BELT ROLL

The present invention relates to a device for doctoring the belt of a belt roll, the outer surface of which belt is partly open, and the device including a blade holder, which is fitted with a blade, in such a way that, in the operating position of the device, the blade lies against the outer surface of the belt, and in which device the hardness of the blade is less than the hardness of the outer surface.

The belt of a belt roll, which is also referred to as a long- nip or shoe roll, is conventionally doctored using a mechanical doctor, to which a blade, for example, according to Finnish utility model 5084, can be fitted. A flexible and soft blade is used to doctor the belt of a belt roll, as a hard and inflexible blade would lead to belt damage. Doctoring using a flexible and soft blade is, however, a solution that only works partially. The outer surface of a belt is usually grooved, so that a known mechanical doctor of this type will remove only part of the water on the outer surface of the belt. After mechanical doctoring, water will still remain in the grooves of the belt, and will circulate back to the nip. Water remaining on the outer surface of the belt of the shoe roll and travelling to the nip will cause errors in the moisture profile and limit the amount of water being removed from the web in the nip .

The invention is intended to create a device for doctoring the belt of a belt roll, the use of which will achieve a better doctoring result. Besides an improved doctoring result, the use of the device will attenuate flutter in the belt of the belt roll, i.e. will stabilize the belt. The characteristic features of the present invention are that the device further includes an air doctor for removing water from the belt .

The device according to the invention is intended for doctoring the belt of a belt roll. The outer surface of the belt to be doctored is partly open. The shapes in the open outer surface, which are typically grooves, blind holes, or similar, improve the transfer in the nip of water from the web to the belt. The shapes in the outer surface extend inside the belt for only part of the belt's thickness. The device includes a blade holder, to which a blade is fitted. The blade in question refers to a mechanical doctor. In other words, the mechanical doctor includes a blade holder, to which a blade for doctoring the belt is fitted. The blade is arranged to lie against the outer surface of the belt, when the device is in the operating position. The doctor also includes loading elements, which are used to load the blade holder as desired, thus in turn loading the blade. The hardness of the blade is less than that of the outer surface. In addition, the device further includes an air doctor for removing water from the belt. More specifically, there is an air doctor before or after the mechanical doctor. The essential feature is that the air doctor is used in conjunction with the mechanical doctor. The water removal of the air doctor and the mechanical doctor are different, as the mechanical doctor removes water from the shaped ridges of the belt. The air doctor, for its part, also removes water from the shapes of the open outer surface. When the air doctor precedes the mechanical doctor, the air doctor is used to remove water from the belt. The mechanical doctor, and more specifically its blade, scrapes the water detached from the air doctor off the surface of the belt. This doctors the belt drier than previously.

The aforesaid air doctor includes a body, in which there are lips for forming a blast gap. The lips are positioned in such a way that the airflow coming from the blast gap is sharp . The airflow is also at least partly directed towards the outer surface of the belt. The doctoring with the air doctor therefore preferably takes place on the counter-rotation doctoring principle. The airflow is preferably formed using a unified blast gap covering the entire width of the belt. This achieves even water removal over the entire width of the belt. In addition, the airflow forms an air cushion between the air doctor and the belt, which keeps the air doctor off the belt during doctoring.

In one embodiment, the air doctor is arranged after the blade in the direction of rotation of the belt. In other words, the outer surface of the belt of the belt roll is doctored first by the mechanical doctor, followed by the air doctor, in the direction of rotation of the belt. Thus the water remaining after the blade can be removed from the belt. The mechanical doctor often leaves water, especially in the grooves of the belt. By means of the arrangement in question, the doctoring of the belt is particularly good.

In a second embodiment, the air doctor includes loading means and support means . The support means are used to secure the air doctor to the frame of the paper machine, or to the blade holder of the mechanical doctor. The loading means can be used to control the air doctor separately from the blade. In other words, the desired loading is created in the air doctor using the loading means, irrespective of the loading of the blade. In some embodiments, the loading means of the air doctor can be directly or indirectly attached to the blade holder, so that the loading of the blade can effect the loading of the air doctor. In such situations, the effect of the loading is taken into account in the control of the loading means of the air doctor. Despite the above, the loading of the air doctor is set as desired using the loading means of the air doctor, irrespec- tive of whether the air doctor is attached by the support means to the frame of the paper machine, or to the blade holder.

In a third embodiment, ^• vacuum means are fitted in connection with the air doctor, for more effective water removal. The loading and support means of the air doctor are preferably essentially open in the longitudinal direction of the blade holder. This openness permits the suction effect and water removal of the vacuum means to act through the loading and support means. The vacuum means are used to suck and lead away the air, into which the air doctor has detached water from the belt. In addition, there can be vacuum means in connection with the blade, making water removal by the blade more effective.

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

Figure 1 shows the device according to the invention in operation in a paper machine,

Figure 2 shows a device according to the invention, in which the air doctor is arranged after the blade in the direction of rotation of the belt, in operation in a paper machine,

Figure 3 shows the device according to the invention in greater detail, Figure 4 shows an enlargement of part of Figure 3, as shown in connection with Figures 3 and 4, and

Figure 5 shows a view of the device according to the invention, seen at an angle form the side of the belt roll, so that the grooves in the belt roll and the openness of the attachment of the air doctor are visible.

Figure 1 shows the device according to the invention for doctoring the belt 12 of a belt roll 10. The blade 18 is used to scrape water from the outer surface 44 of the belt 12, from which the water has been detached by an air doctor 14 preceding the blade 18 in the direction of rotation of the belt 12. In the figure, the arrow 46 marks the direction of rotation of the belt 12. The doctoring by the blade 18 is preferably counter- rotation doctoring. Vacuum means 36 can be fitted in connection with the blade and the air doctor 14, to remove water more effectively. In that case, they will be used to lead away the water removed by the blade 18 and the air doctor 14. The vacuum means 36 are used to lead away air and water mist with it. The unnumbered arrows in Figure 1 show the flow of water away from the belt towards the vacuum water-collection trough arranged as the vacuum means 36. Doctoring the belt first with an air doctor and then with a blade removes water more effectively than previously, as the air doctor can be used to detach the water from the belt and then the blade used to scrape the water away. Thus the water is doctored away from the open surface of the belt more effectively than previously.

Figure 2 shows a device according to the invention for doctoring the belt 12 of a belt roll 10. The blade 18 is used to scrape water off the outer surface 44 of the belt 12, after which there is an air doctor 14 in the direction of rotation of the belt 12. In the figure, the arrow 46 marks the direction of rotation of the belt 12. The doctoring by the blade 18 is preferably counter-rotation doctoring. Vacuum means 36 can be fitted in connection with the air doctor 14 to remove the water more effectively. In addition, there can be vacuum means 36 in connection with the blade 18 too, where they are used to lead away the water removed from the belt 12 by the blade 18. The vacuum means 36 lead away both air and water mist with it. In Figure 2, the unnumbered arrows show the flow of water away from the belt towards the vacuum water-collection trough arranged as the vacuum means 36. Doctoring the belt first with the blade and then with the air doctor removes water effectively from the belt, as the air doctor can be used to detach water remaining on the belt after the blade. This effectively scrapes the water off the open surface of the belt.

Figure 3 shows a device according to the invention, in which there is an air doctor 14 after the blade 18. The blade is secured to the blade holder 20, which is equipped with loading elements 22. In the device's operating position, the blade 18 lies against the outer surface 44 of the belt 12. The doctoring result of the blade is based in the blade being in direct contact with the outer surface of the belt being doctored. However, the direct contact is only with the ridges between the grooves in the outer surface, the blade being unsuitable for scraping water out of the bottoms of the grooves in the belt. The blade is softer than the outer surface can also be flexible, thus avoiding the blade catching and thus damaging the belt. Here the term catching refers to, for example, the blade penetrating the outer surface of the belt, or other similar damage caused by the blade. A soft and flexible blade will also reduce belt wear. There is preferably a doctoring support 26 on the inside of the belt 12 against the blade 18, allowing the blade 18 to be loaded indirectly against the doctoring support 26, the belt 12 remaining between the blade 18 and the doctoring support 26. A backing blade 48, made from an inflexible substance, is preferably located next to the blade 18. The backing blade 48 is used to press the actual blade 18 more effectively against the belt 12 and the doctoring support 26. The backing blade 48 reduces the free machine-direction length of the blade 18, over which the blade bends while loaded. Inside the blade and not in contact with the belt there can be a support structure (not shown) made from a more rigid and less flexible substance than the blade itself. The support structure can be used to avoid detrimental deflection of the blade and to adjust simply the properties of the doctor. The blade holder 20 is secured in a support element 52, which is in turn attached to the frame of the paper machine, or to some other sufficiently sturdy structure. The loading elements 22 between the blade holder 20 and the support element 52 are used to adjust the blade holder relative to the support element 52. As the support element is attached to the frame of the paper machine in the same way as the belt roll, adjustment takes place simultaneously relative to both the support element and the belt roll. Figure 3 also shows that, in the device after the blade 18, there is an air doctor 14, which is not in direct contact with the belt 12. Direct contact does not take place, because the airflow cushions the contact of the blade. Most of the doctor- ing effect of the air doctor 14 is based only on the contact of the air with the belt 12. The sharp airflow 34 effectively removes water remaining on the belt 12, particularly in its grooves, after the blade 18. The important point is that the sharp airflow 34 also removes the water that remains in the grooves. The blade holder 20 can be hollow in the longitudinal direction of the blade holder 20, i.e. in the cross direction of the paper machine. The hollow blade holder 20 can be used as a flow channel 50 in the cross direction of the paper machine. Compressed air can thus be conducted in the cross direction of the paper machine in the flow channel in the structure of the blade holder. In the blade holder 20, there are compressed-air connections 38 to the air doctor 14. The flow channel 50 and the compressed-air connections 38 permit compressed air to be fed to the air doctor 14. Compressed air can be fed in the flow channel formed by the blade holder's hollow structure to the centre of the air doctor in the longitudinal direction, without major pressure losses. Compressed-air connections run from the blade holder to several points in the air doctor, giving an even airflow to the air doctor, as the flow channel acts as an, equalization chamber. In other words, by using a hollow blade holder and compressed-air connections running from it, an even flow of compressed air is made to the air doctor. Compressed air can also be fed to the air doctor from compressed-air connections at its ends. In one embodiment, the air is fed to the air doctor only through a compressed-air connection connected to one end of it. In turn, the air doctor is used to direct the compressed-air flow entering it to form a sharp airflow to remove water on the outer surface of the belt.

Figure 4 shows the air doctor 14, which includes a body 28, in greater detail. The body 28 includes lips 32, which form a blast gap 30 . In addition , the lips 32 are shaped and positioned in such a way that the airflow 34 they form is sharp when it impacts the belt 12 . The lips 32 are shaped to create a sharp point in the air doctor 14 . The sharp point of the air doctor allows the lips to be located very close to the belt . The importance of the sharp point is emphasized, because the air doctor too operates preferably on the counter-rotation doctoring principle and is therefore not at right angles to the outer surface of the belt . In other words , the lips should come to a sharp point , to allow the air doctor to be tilted when directing the airf low as desired . The airflow 34 covers the entire width of the belt 12 without a break, so that the airflow 34 is preferably formed using a blast gap 30 covering the full width of the machine . A single continuous blast gap will create a unif ied airflow over the cross direction of the machine . If the blast is formed using several blast gaps , zones without a blast will remain between them . The airflow 34 is directed in such a way that at least part of its movement will be towards the bel t 12 . The angle α is formed between the radius r of the belt roll and the airflow 34 . The angle α is in the range 1 - 89 ° , preferably in the range 10 - 40 ° . In that case, some of the direction components of the airflow 34 will be towards the belt 12 . Thus the air doctor 14 too will operate on the counter-rotation doctoring principle . The width d of the blast gap 3 0 is 0 , 1 - 3 mm , preferably 0 , 3 - 1 mm . Us ing a narrow blas t gap will increase the velocity of the airflow without increasing the consumption of compressed air , which signifies a narrow powerful airflow with a relatively low air consumption .

Figure 3 also shows the loading means 24 of the air doctor 14, by means of which the air doctor 14 can be controlled separately from the loading means 22 used to control the blade 18. The air doctor 14 includes not only loading means 24, but also support means 16, by which it is attached to the frame holder 20. The support means 16 and the loading means 24 can also be used to attach the air doctor 14 directly to the frame of the paper machine (not shown) . The loading means 24 are used to load the air doctor 14 towards the outer surface 44 of the belt 12. The air doctor 14 can be loaded by the loading means 24 in two directions, though only loading in a single direction is essential. An air cushion 42 is formed between the air doctor 14 and the belt 12 by the effect of the airflow 34. The force of the air cushion keeping the air doctor separate from the belt is created mainly by the direction components of the airflow that are at right angles to the web. The air cushion 42, i.e. air layer, in question keeps the air doctor 14 off the belt 12. The air doctor 14 need only be loaded towards the belt 12, so that one-directional loading means 24 will be sufficient. The air cushion forms a force opposing the prefera- bly one-directional loading means of the air doctor. In other words, the loading of the air doctor 14 takes place essentially against the aforesaid air cushion 42, which air cushion 42 acts to keep the air doctor 14 clear of the belt 12. Inside the belt, there is a doctoring support 26 for the blade 18. A corresponding doctoring support for the air doctor is unnecessary, because the loading in the air doctor takes place through the air cushion that adapts to the surface shape of the belt.

The loading means can be preferably springs or similar loading components that permit a sensitive loading. The use of springs will achieve a sufficient sensitivity for the air doctor, so that the air cushion formed by the airflow will act to keep the air doctor off the belt. In other words, the air cushion formed between the belt and the air doctor ensures that the lips of the air doctor remain off the belt. The loading means can also be implemented in other ways, but their essential feature is that they are sufficiently sensitive to permit loading against the air cushion. This also avoids possible catching by the air doctor, which would almost certainly lead to damage in the belt. Without the air cushion, the blade made of hard material could catch, because the air doctor too operates on the counter-rotation doctoring principle. The relatively small loading force of the sensitive loading means permits the air doctor to give way as the belt lives. The living of the belt, i.e. its unstable rotation, for its part causes problems. The aforesaid problems can be avoided by using sensitive loading, when the air cushion will keep the lips off the belt.

Figure 5 shows the device according to the invention seen at an angle from the side of the belt roll. The device is shown from only part of the width of the paper machine, the part of the device shown being located laterally in the centre of the paper machine, so that the attachment of the device to the paper machine does not appear in the figure. The attachment of the device to the frame of the paper machine takes place through a support element 52. The support means 16 and loading means 24 of the air doctor 14 are essentially open in the cross direction of the paper machine, i.e. in the longitudinal direction of the blade holder 20. The essentially open support and loading means fill 5 - 40 %, preferably 10 - 25 % of the area between the blade holder and the air doctor. The openness permits water to escape from between the support means 16 and the loading means 24. The outer surface 44 of the belt 12 is partly open. In the case of the outer surface 44 of the belt 12 in Figure 4, the openness is formed by grooves 40 in the outer surface 44. If the outer surface of the belt is grooved, a higher solids content at the press will be achieved that when using a smooth-surfaced belt. The use of grooves in the outer surface of the belt will improve water removal even at present, even though the belt is doctored only by a blade. The addition of an air doctor according to the invention in connection with the blade will allow the belt to be doctored drier than when using a blade according to the prior art, thus obtaining a higher solids content in the paper web than previously after the press, as well as reducing the errors in the moisture profile after the press. The vacuum means shown in Figure 2, by means of which the water removal of the air doctor and the blade can be increased, have been omitted from Figure 5, in order to illustrate the construction of the device. However, it is preferable to use vacuum means to improve water removal when doctoring the belt.

Though the foregoing description refers to compressed air and an air doctor, steam or some other gas than air can be used in connection with the air doctor. The use of steam can be highly advantageous in some specific applications, as the steam can also be used to raise the temperature of the belt. When the temperature of the belt is high, a significant amount of moisture will evaporate from the belt even after the air doctoring, which in this case takes place using steam.

Above, reference is only made to doctoring water from a belt, though when water is doctored, loose material such as filler and fibres, are also removed from the belt at the same time. Thus the device according to the invention is used to remove water from the belt and simultaneously to clean it.

Claims

1. Device for doctoring the belt (12) of a belt roll (10), the outer surface (44) of which belt (12) is partly open, and the device including a blade holder (20) , which is fitted with a blade (18) , in such a way that, in the operating position of the device, the blade (18) lies against the outer surface (44) of the belt (12), and in which device the hardness of the blade (18) is less than the hardness of the outer surface (44), characterized in that the device further includes an air doctor (14) for removing water from the belt (12) .

2. Device according to Claim 1, characterized in that the air doctor (14) is arranged after the blade (18) in the direction of rotation of the belt (12) .

3. Device according to Claim 1 or 2, characterized in that the air doctor (14) includes a body (28) , in which a blast gap (30) is arranged, in order to create a sharp airflow (34) .

4 . Device according to Claim 3 , characterized in that the blast gap ( 30 ) is formed by lips ( 32 ) in the body ( 28 ) , which are arranged to create an airflow ( 34 ) towards the outer surface ( 44 ) of the belt ( 12 ) .

5. Device according to Claim 3 or 4, characterized in that the width (d) of the blast gap (30) is 0,1 - 3 mm, preferably 0,3 - 1 mm.

6. Device according to any of Claims 1 - 5, characterized in that the air doctor (14) includes loading means (24), which are arranged to be controlled separately from the loading elements (22) arranged in the blade holder (20) .

7. Device according to Claim 6 , characterized in that a single loading direction is arranged in the loading means (24) for loading the air doctor (14) against the outer surface (44) .

8. Device according to Claim 6 or 7 , characterized in that the loading means (24) are at least in part springs.

9. Device according to any of Claims 1 - 8 , characterized in that the air doctor (14) includes support means (16) , which are attached to the blade holder (20) .

10. Device according to Claim 9, characterized in that ^' the support means (16) and loading means (24) belonging to the air doctor (14) are essentially open in the longitudinal direction of the blade holder (20) .

11. Device according to any of Claims 1 - 10, characterized in that vacuum means (36) are fitted in connection with the air doctor (14) , in order to make the water removal more effective.

12 . Device according to any of Claims 1 - 11 , characterized in that the blade holder (20 ) is arranged to be hollow over essentially the entire longitudinal direction of the blade holder (20 ) and there are compressed-air connections ( 38 ) from it to the air doctor ( 14 ) .