DOCTOR DEVICE FOR A FIBER WEB MACHINE AND DOCTOR ARRANGEMENT IN A FIBER WEB MACHINE

Abstract

 The invention relates to a doctor device for a fiber web machine. The doctor device includes blade devices (19) and holder devices (23). The holder devices (23) are for arranging the blade devices (19) in a fiber web machine to be placed in connection with an adapted doctor blade (18) equipped with a blade holder (38) to the edge areas (20) of said doctor blade (18). The holder devices (23) are arranged to be fastened in connection with the blade holder (38) so that the blade devices (19) are further out than the doctor blade (18). The invention also relates to a doctor arrangement in a fiber web machine.

Description

[0001] The invention relates to a doctor device for a fiber web machine, which doctor device includes blade devices and holder devices for arranging the blade devices in a fiber web machine to be placed in connection with an adapted doctor blade equipped with a blade holder to the edge areas of said doctor blade. The invention also relates to a doctor arrangement in a fiber web machine.

[0002] Finnish patent number 110705 presents an arrangement in a fiber web machine. The arrangement is intended for the so-called wet end of a fiber web machine, where material such as fibers and fillers adhere to the rolls from the moist web and especially from its edges. Accumulations of this kind result in, among other things, the web sticking to the roll surface, which increases web breaks and thus disturbs production. The patent suggests that short blade devices be placed after the doctor blade that is supported to a blade holder, which blade devices enhance the doctoring efficiency of the arrangement at the edges of the doctor blade, i.e. at the edge areas.

[0003] In practice, it is challenging to place a prior art arrangement in the fiber web machine. In fact, the above-mentioned patent describes the arrangement only in principle, without any holder devices for the blade devices. Moreover, the arrangement is unsuited to other locations such as the finishing section, where local fouling of a roll also occurs. As an example, after coating some coating slip accumulates on the surface of a roll, especially at the edge areas of the doctor blade. In such a position, the doctor blade of the application presented in said patent would wear rapidly and unevenly in the same way as a doctor blade currently wears in said position. In this case, streaks remain on the surface of the roll especially at the edge areas, and the streaks remain visible in the end product, too. Moreover, a worn doctor blade needs to be replaced frequently, which causes extra costs. In practice, the fiber web machine must be stopped for the duration of the replacement of the doctor blade, which shortens the efficient production time.

[0004] The object of this invention is to accomplish a new type of a doctor device for a fiber web machine, which doctor device can be used for intensifying the efficiency of the doctor arrangement and at the same for reducing the uneven wear of the doctor blade. Another object of the invention is to accomplish a new type of a doctor arrangement for a fiber web machine, where the doctoring efficiency of the doctor arrangement is better than previously and where the replacement interval of the doctor blade is longer than previously. A characteristic feature of the doctor device according to the invention is that the holder devices are arranged to be fastened in connection with a blade holder so that the blade devices are further out than the doctor blade. Correspondingly, a characteristic feature of the blade arrangement according to the invention is that the blade devices are arranged before the doctor blade in the direction of rotation of the roll. In practice, the blade devices remove a significant portion of the material at the edge areas of the doctor blade even before the doctor blade. In this case, the short blade devices wear, but the costs caused by their replacement are considerably smaller than the cost of replacement of a full-length doctor blade. Moreover, the blade devices can be serviced even during production. In this way, it is possible to avoid quality deviations in the end product and to achieve as uninterrupted production as possible.

[0005] The invention is described below in detail by making reference to the enclosed drawings that illustrate an embodiment of the invention, in which:

Figure 1

shows the finishing section of a fiber web machine,

Figure 2a

shows a doctor arrangement according to the invention,

Figure 2b

shows a partial magnification of Figure 2a,

Figure 3a

shows a doctor arrangement according to the invention seen from the tending side diagonally from the back,

Figure 3b

shows the doctor arrangement of Figure 3a seen diagonally from the front,

Figure 3c

shows a doctor arrangement according to the invention seen from the drive side diagonally from the front,

Figure 4a

shows a doctor arrangement according to the invention seen against the machine direction,

Figure 4b

shows the doctor arrangement of Figure 4a seen in the machine direction.

[0006] Figure 1 shows a finishing section of a fiber web machine which is known as such. Only the last drying cylinder 11 is presented of the dryer section 10 that precedes the finishing section. The web forming machines are usually paper or board machines. The consecutive production sections shown in Figure 1 are - in addition to the dryer section 10 - pre-calendering 12, coating 13 and calendering 14, after which the finished web is reeled with the reel 15. This application represents so-called online finishing, where the web is fed from the dryer section directly to finishing without re-reeling. In order to minimize production losses, it is important to have disturbance-free production from the wet end to the reel.

[0007] Marked with X in the figure are example positions where the doctor arrangement according to the invention is preferably used. Generally speaking, roll 16 included in the fiber web machine is equipped with the doctor arrangement. The doctor arrangement includes a doctor blade 18, which is here supported to the doctor beam 17 arranged in connection with the roll 16 (Figure 2a). The doctor blade is primarily used for keeping the surface of the roll clean, but in certain positions it is also used for guiding the web into a pulper in a web break situation. The doctor beam extends essentially across the width of the entire roll, and it is usually supported by bearings at both ends. By turning the beam 17, the doctor blade 18 can be placed against the surface of the roll 16 and also away from it. The beam 17 can potentially also be moved in the axial direction.

[0008] The doctor arrangement also includes blade devices 19 which are separate from the doctor blade 18 and which are arranged at both edge areas 20 of the doctor blade 18 (Figures 4a and 4b). In practice, the edge areas of the doctor blade correspond to the edge areas of the roll. In the most challenging position, the roll 16 is a drying cylinder 21, which is placed after a coating station 22 included in a fiber web machine. The surface of the drying cylinder is hot, which contributes to the sticking of the coating slip. The doctor arrangement according to the invention works in this position, too, and remains operational for a longer period than previously.

[0009] The coating slip contains substances such as kaolin, calcium carbonate or talc. These are very abrasive substances. Moreover, they accumulate easily on the surface of the roll, which makes the above-described doctor positions demanding. Doctor blades made even completely of carbon fiber are used in prior art arrangements. Such doctor blades are hard and endure wear, but they are expensive. Despite their wear-resistance, the doctor blades wear unevenly, so their replacement intervals are short.

[0010] This is why in the invention the blade devices 19 are arranged before the doctor blade 18 in the direction of rotation of the roll 16. In this way, the blade devices first touch the material that has accumulated on the surface of the roll. In this case, most of the wear impact is directed at the blade devices, while the actual doctor blade is worn less. The doctor blade consequently wears more evenly than previously, which extends the service life of the doctor blade and reduces its need for replacement. At the same time, the material can be removed more efficiently from the surface of the roll.

[0011] Figure 2a shows the roll 16 in part only. Correspondingly, Figure 2b illustrates a prior art doctor blade 18 and doctor beam 17 with a broken line, and the doctor device according to the invention is illustrated with a solid line. The doctor device is intended for a fiber web machine, and it includes blade devices 19 and holder devices 23. The holder devices 23 are intended for the placement of the blade devices 19 in connection with the doctor blade 18 included in the fiber web machine, to the edge areas 20 of said doctor blade 18. In the invention, the holder devices 23 are arranged to be fastened in connection with the blade holder 38 so that the blade devices 19 are further out than the doctor blade 18. With respect to the fastening point of the doctor blade, the blade devices extend further out than the doctor blade, both in the blade direction and radially. With respect to the roll, the holder devices 23 are thus arranged for the placement of the blade devices 19 before the doctor blade 18 in the direction of rotation of the roll 16. In this case, by means of the holder devices the doctor device can be placed in connection with the doctor blade so that the blade devices are located before the doctor blade. In the invention, the blade devices 19 are also preferably supported to said doctor beam 17. In other words, the holder devices 23 include a support structure 24, which has connecting devices 25 for fastening to the doctor beam 17 arranged to support the doctor blade 18. In this case, the blade devices can be simply added to an existing doctor arrangement, and to put it more precisely, by fastening the connecting devices to the doctor beam.

[0012] Figures 3a to 3c show one end of the doctor arrangement at a time. The holder devices 23 according to the invention include a blade holder 26, which is fastened to a support strip 27. The support strip 27 is at least as long as the blade holder 26. The blade holder as such can be different from that presented, but here the applicant's own model provided with one loading hose has been used.

[0013] The supporting of the blade devices is also of a new type: the support structure 24 is fastened to one end of the holder devices 23. In other words, the holder devices are supported in a projection-type manner, whereby the operation of the doctor blade remains unchanged. In the application presented, each blade device 19 includes a support arm 28. Here, the support arm 28 is connected to the support strip 27 by means of two connectors 29. There can also be more numerous connectors, or some other applicable support structure is used in the supporting. The fastening is carried out by means of two pairs of bolts 30, for which bolts there are elongated holes 37 in the support strip 27. In this case, the support strip 27 can be adjusted with respect to the support arm 28. More generally speaking, there are adjusting devices 31 between the holder devices 23 and the support structure 24. Adjustment is needed primarily in the installation of the doctor device. During operation, the blade devices are loaded by means of a loading hose 32.

[0014] The installation of the doctor device according to the invention in connection with the doctor blade has been designed to be especially easy. In the invention, the blade devices 19, more precisely the support arm 28, is fastened to the doctor beam 17 using the same fastening devices 34 that support the doctor blade 18. In other words, there is a similar hole pitch 33 in the support arm 28 for the fastening devices 34 as in the doctor holder 38 of the doctor blade 18. In this way, the doctor device can be fastened as long as bolts 34' that are longer than normally are used at the support arm 28. In Figure 3c, there are six such bolts, only two of which are illustrated.

[0015] It has also been possible to keep the manufacturing costs of the doctor device at a reasonable level. The holder devices 23 according to the invention are symmetrical. In other words, there are almost identical blade holders at both ends of the roll, while the support arms of the doctor devices are mirror images of each other. In this case, spare parts such as a short doctor blade 35 can be used at either end. The symmetrical design is illustrated especially in Figure 4a, where the doctor arrangement is viewed against the machine direction. At both ends of the short blade holder 26, there is a finger plate 36 by which the blade holder 26 can be moved. Moreover, the support strip 27 has two sets of elongated holes 37 for fastening to the support arm 28. There are also compressed air connections at both ends of the loading hose 32, and compressed air supply is connected to the outermost of these connections. In this case, the doctor arrangement can be composed of standard components by arranging two doctor devices according to the invention in connection with an existing doctor blade, on the same doctor beam.

[0016] Figures 4a and 4b might suggest that the blade devices 19 are unnecessarily long. In practice, the length of the holder devices 23 is 800 to 1,200 mm. Moreover, the blade devices 19 extend clearly beyond the edge areas 20. In practice, 40 to 60 per cent of the length of the blade devices 19 extends beyond the edge areas 20. In this case, the finger plate extends to a safe distance from the roll. In other words, the blade holder can be moved by the finger plate also during production. This is why, if the short doctor blade wears locally, it can be moved somewhat manually, whereby the best doctoring result can be achieved at the most critical location. Moreover, the moving is possible without a safety risk. By depressurizing the loading hose and, if necessary, by using vacuum, the short doctor blade can be detached from the surface of the roll and hence the blade holder can be moved. If necessary, the entire blade holder with the doctor blade can be pulled off for service and replacement. The part beyond the roll can also be utilized by exchanging the short doctor blades on the tending and drive sides with each other. In this way, even a short doctor blade can be utilized over its entire length. In the same manner, parts of the doctor blade that have worn unevenly can be removed, and it can be used for reconditioning several short doctor blades. As an example, the width of a roll is currently from 4 to 10 meters, while the length of the blade devices according to the invention is from approximately 0.5 meters to approximately 1 meter.

[0017] Above is a description of one example of a doctor device according to the invention and of its utilization in a doctor arrangement. Generally speaking, the doctor device according to the invention comprises a first blade holder 26, which is short. A short doctor blade 35 is supported to this short blade holder 26. The short doctor blade 35 constitutes part of the blade devices 19. Both the short blade holder and the short doctor blade extend over only a part of the width of the roll surface to be doctored, preferably over its edge areas. The doctor blade 18 included in the doctor arrangement and the blade holder 38 that supports the doctor blade 18 extend essentially over the entire width of the roll to be doctored.

[0018] The doctor device according to the invention is simple and compact. Components proven in practice can be applied to it. If necessary, for example the blade holder is reinforced to increase the load resistance. The doctor device can be placed in connection with various types of doctor blades. Two doctor devices can be used for updating a doctor arrangement quickly to a new level. In this way, the doctoring result is improved even though the replacement interval of the doctor blade extends at the same time. The effective production time is thus maximized while at the same time minimizing the maintenance costs. In conjunction with the installation of doctor devices, a modern blade holder with a new type of doctor blade is preferably replaced in the doctor beam. In this way, the overall doctoring result of the doctor arrangement is improved and serviceability is facilitated.

Claims

1. A doctor device for a fiber web machine, which doctor device includes blade devices (19) and holder devices (23) for arranging the blade devices (19) in a fiber web machine to be placed in connection with an adapted doctor blade (18) equipped with a blade holder (38) to the edge areas (20) of said doctor blade (18), characterized in that the holder devices (23) are arranged to be fastened in connection with the blade holder (38) so that the blade devices (19) are further out than the doctor blade (18).

2. A doctor device according to claim 1, characterized in that the holder devices (23) include a support structure (24), which has connecting devices (25) for fastening to the doctor beam (17) arranged to support the blade holder (38).

3. A doctor device according to claim 2, characterized in that the support structure (24) is fastened to one end of the holder devices (23).

4. A doctor device according to any one of claims 1 to 3, characterized in that the holder devices (23) are symmetrical.

5. A doctor device according to any one of claims 1 to 4, characterized in that the length of the holder devices (23) is 800 to 1,200 mm.

6. A doctor device according to any one of claims 2 to 5, characterized in that there are adjusting devices (31) between the holder devices (23) and the support structure (24).

7. A doctor arrangement in a fiber web machine, where a roll (16) included in the fiber web machine is equipped with a doctor arrangement that includes:

- a doctor blade (18) which extends essentially across the entire width of the roll (16), and

- blade devices (19) which are separate from the doctor blade (18) and which are arranged at both edge areas (20) of the doctor blade (18),

characterized in that the blade devices (19) are arranged before the doctor blade (18) in the direction of rotation of the roll (16).

8. A doctor arrangement according to claim 7, characterized in that the blade devices (19) are supported to a doctor beam (17) included in the doctor arrangement.

9. A doctor arrangement according to claim 7 or 8, characterized in that the roll (16) is a drying cylinder (21), which is placed after a coating station (22) included in a fiber web machine.

10. A doctor arrangement according to any one of claims 7 to 9, characterized in that the blade devices (19) extend beyond the edge areas (20).

11. A doctor arrangement according to claim 10, characterized in that 40 to 60 per cent of the length of the blade devices (19) extends beyond the edge areas (20).

12. A doctor arrangement according to any one of claims 7 to 11, characterized in that each blade device (19) includes a support arm (28) which is fastened to the doctor beam (17) using the same fastening devices (34) that support the doctor blade (18).

13. A doctor arrangement according to any one of claims 7 to 12, characterized in that the doctor arrangement includes two doctor devices according to any one of claims 1 to 6.

Drawing