FI20215369A1

FI20215369A1 - Doctor blade for a fiber web machine and doctor arrangement in a fiber web machine

Info

Publication number: FI20215369A1
Application number: FI20215369A
Authority: FI
Inventors: Qingyuan Sun
Original assignee: Valmet Technologies Oy
Priority date: 2021-03-30
Filing date: 2021-03-30
Publication date: 2022-10-01

Abstract

Keksintö koskee kaavinterää kuiturainakonetta varten. Kaavinterässä (11) on foiliosa (14) terävä kärjellä (21). Foiliosassa (14) on useita läpimeneviä reikiä (22) jaettuna oleellisesti koko kaavinterän (11) pituudelle (L). Keksintö koskee myös kaavinjärjestelyä kuiturainakoneessa.

Description

DOCTOR BLADE FOR A FIBER WEB MACHINE AND DOCTOR ARRANGEMENT

IN A FIBER WEB MACHINE

The invention relates to a doctor blade for a fiber web ma- chine, the doctor blade including a foil section having a sharp tip. The invention also relates to a doctor arrangement in a fiber web machine.

US-patent number 6491791B1 discloses a doctor blade for cleaning the surface, especially grooved, or drilled roll surface of a roll in a fiber web machine. The doctor blade has a chamber opening near the tip of the doctor blade. Com- pressed air fed to the chamber bursts out via the opening and forms vacuum into the grooved or drilled holes thereby im- proving water drainage. However, the mentioned doctor blade is complex and thereby hard to manufacture. It also with- stands wearing poorly and compressed air causes great operat- ing costs.

Another known doctor arrangement includes two subsequent doc- tor blades. Specifically, the first blade is a foil blade which removes water from roll shell grooves or perforations with the help of a vacuum created between the foil blade and — roll. The second blade is a standard doctor blade which re-

O 25 moves water sucked out by the foil blade and also cleans the se roll surface. Two doctor blades reguire a lot of space and

S the doctor blades must be orientated is a specific way. = Thereby the known doctor arrangement suits only in few posi- 2 . tions.

O

N It is an object of the invention to provide a novel doctor

N blade for a fiber web machine with more versatile functions and positioning than before. Another object of the invention is to provide a novel doctor arrangement in a fiber web ma-

chine which arrangement can be adapted in totally new posi- tions. The characteristic features of the doctor blade and the doctor arrangement according to this invention are stated in the accompanying Claims. The doctor blade generates vacuum as before, but the sucked water can be drained easier than before without extra structures. At time same time, the doc- tor blade can be positioned more freely compared to the known doctor blades. With a new kind of doctor blade, the doctor arrangement remains simple and it is easy to place even in tight or in other ways demanding positions.

The invention is described below in detail by referring to the enclosed drawings which illustrate some of the embodi- ments of the invention, in which

Figure 1 shows one known doctor arrangement adapted to the vicinity of a surface to be doctored,

Figure 2 shows one doctor arrangement according to the in- vention adapted to the vicinity of a surface to be doctored,

Figure 3a shows a cross section of the first doctor blade ac- cording to the invention,

Figure 3b shows a cross section of the second doctor blade — according to the invention,

O 25 Figure 3c shows a cross section of the third doctor blade ac- se cording to the invention,

S Figure 4a shows a partial enlargement of the doctor arrange-

I ment according to the invention, > Figure 4b shows an axonometric cross-sectional view of the e 30 blank of the doctor blade according to the inven- 3 tion.

Figure 1 shows one known doctor arrangement adapted to the vicinity of an open surface 10 to be doctored. The doctor ar-

rangement is especially for a fiber web machines such as pa- per, board, and tissue machines. Here there are two subse- quent doctor blades 11. The first doctor blade 11 is a foil blade 12 and it is meant particularly for removing water and fine matter from the open surface 10 to be doctored. Here the open surface 10 rotates clockwise. Specifically, this doctor arrangement is suitable for doctoring polymer coated rolls, belts, and transfer belts as well as open-surfaced rolls. In a fiber web machine, such as a paper or board or tissue ma- chine, open-surfaced rolls are used for several different reasons. In a suction roll, for example, the shell is perfo- rated for leading a vacuum effect from the inside of the roll to the outside of it. The holes make the shell open-surfaced.

On the other hand, grooved rolls are also used, in which the shell surface is grooved mainly for improving dewatering. A suction roll with a grooved surface also exists, the shell of which is provided with both holes and grooves. In addition to or instead of grooves, blind bores, for example, can be used.

Soft coatings are also used in the rolls while belts and transfer belts are soft surfaced by their nature. In addi- tion, the surface of a belt, for example, can be grooved.

Between the foil blade 12 and the open surface 10 to be doc- — tored there is a narrow cap. While the roll 16 rotates, vacu-

O 25 um is created in gap the due to the mutual movement of the se open surface 10 and the foil blade 12. This vacuum absorbs

S water and fine matter from the open surface, which is advan- z tageous for the operation of the fiber web machine. The re- > moved water drops down by gravity to a trough 13 beneath. The e 30 optional second doctor blade 11 removes the rest of water and

N impurities from the open surface. Due to gravity assisted wa-

N ter removal, positioning of the doctor blade has its limita- tions.

The doctor blade 11 has a length of several meters, from 1 to 11 meter extending in cross-machine direction and a width from 5 to 20 centimeters extending in machine direction. Fur- ther the doctor blade 11 includes a foil section 14 and a fastening section 15. In the embodiment shown in Figure 2, the foil section 14 is adapted to a light contact with the open surface 10 of a roll 16. The doctor blade 11 is support- ed by a blade holder 17, which includes a fastening plate 18 and a jaw part 19. The jaw part 19 comprises two jaws between which the doctor blade 11 is assembled, the first jaw on the side of the open surface to be doctored and the second jaw opposite to it. In the design of Figures 1 and 2 the second jaw is shorter than the first jaw but a separate pressing blade 29 is provided. The fastening plate 18 is supported to the constructions of the fiber web machine and a loading hose is provided between the fastening plate 18 and the jaw part 19. Here the doctor blade 11 is loaded by pressurizing the loading hose 20. Correspondingly, the doctor blade can be 20 detached from the open surface to be doctored by leading a vacuum to the loading hose for a doctor blade replacement, for example. With a blade holder design of Figures 1 and 2? utilizing the pressing plate 29, the supporting and loading — effect of the blade holder 17 can be extended sufficiently

O 25 far. In addition, the characteristics of the blade holder can se be varied by changing the pressing plate. However, it is to

S be understood that holders of traditional designs with jaws z of equal length or with the second jaw being longer than the > first jaw are very much applicable to hold the doctor blades e 30 of the invention.

S

Figure 2 shows the doctor arrangement according to the inven- tion. Here, like in Figure 1, in the vicinity of the open surface 10 to be doctored, there is arranged a doctor blade

11 including foil section 14 having a sharp tip 21. However, according to the invention, in the foil section 14 there is a plurality of through holes 22 distributed essentially over the whole length L of the doctor blade 11 and the tip 21 is 5 arranged to point downward. The through holes extend from one planar surface to the opposite planar surface of the doctor blade. First, the doctor blade itself is and can be posi- tioned totally in a new way. Now the doctor blade can be po- sitioned with the tip down on the rising side of the roll.

The tip may be situated between 6:30 and 8:30 in the clock- face. In this position the doctor blade generates vacuum and water drops by gravity on the top of the doctor blade. Then water runs via the through holes into a trough 13 beneath.

The flow of the water is shown with arrows with dashed line.

With this new doctor blade water is effectively removed even with a single blade. More generally, the doctor blade 11 may be the only doctor blade in the doctor arrangement. This re- duces the operation costs while the water removal keeps con- tinuous.

Figures 3a - 3c show three doctor blades 11 for a fiber web machine. As mentioned earlier, these are foil blades. Each doctor blade 11 includes a fastening section 15 for being re- — tained in the jaw part 19 of the blade holder 17 and a foil

O 25 section 14 for water and dirt removal from the open surface se 10. The fastening section 15 is thinner than the foil section

S 14 and may have a fully planar profile or, preferably, a gen- = erally planar profile with a bulkier part as a detent member > 30 and a thinner fastening neck 31 for adapting against the e 30 second jaw of the jaw part 19 of the blade holder 17. The

N foil section 14 includes a foil 25 starting from the sharp

N tip 21, and a foil neck 32 at the opposite end of the foil section 14. In other words, the foil section 14 has a thinner foil neck 32 between fastening section 15 and the foil 25.

The foil neck 32 has a thickness which is greater than the thickness of the fastening neck 31 and may be less than or equal to the thickness of the detent member 30. In Figures 3a and 3b the foil section 14 includes a wedge 33 having a bulky head 26 tapering towards the sharp tip 21. More generally, the wedge 25 has a bulky head 26 and two opposing surfaces which are planar but non-parallel and meet at the sharp tip 21. Thus, the wedge 33 is tapering from the bulky head 26 to- wards the sharp tip 21. According to the invention, in the foil section 14 there is a plurality of through holes 22 dis- tributed essentially over the whole length 1 of the doctor blade 11. In the shown embodiments, the through holes 22 ex- tend through the thickness of the wedge 25 from its one pla- nar surface to the opposite planar surface. In this way the water can flow through the doctor blade even when the blade is installed the tip down.

Advantageously, each through hole 22 is a round hole 23 hav- ing a diameter D which is greater than the thickness T of the foil neck 32. First, the cylindrical or round hole is easy to machine. Second, the large hole remains open despite impuri- ties along with the water. Also, conical holes opening in flow direction of the water can be utilized. This facilitates — further the drainage. Despite of the structure, the through

O 25 holes 22 are perpendicularly oriented or slightly obligue in se relation to the doctor blade 11. This kind of holes are easy

S to machine. Also, the hole length is minimized. x a o Here the foil section 14 has a wedge 33 which may be asymmet- e 30 ric with a bevel on one side of the blade near the tip 21 as

N in Figure 3a or more symmetric as in Figure 3b. The through

N holes 22 are situated in the area of the head 26 of the wedge 25. The head is the thick end of the wedge 33 and is located next to the thin foil neck 32. Like in Figure 2, the wedge 25 is arranged towards the open surface 10. Here, when the roll 16 rotates, the doctor blade 11 generates vacuum which sucks water out of the open surface 10. After the wedge 33 water runs via the through holes 22. At this point the through holes do not change the strength of the doctor blade.

Advantageously, the head 26 of the wedge is sloping down to- wards the foil neck 32 so that there is an angle o between the head 26 and the foil neck 32, the angle o being 100 - 160, preferably 120 - 140 degrees. In this way, the wedge prevents water running back between the doctor blade and the open surface. Also, the wedge collects and guide water into the holes. Also, for collecting water, on the head 26 there is a groove 27 extending essentially over the whole length L of the doctor blade 11. The size and shape of the groove may vary and there can be more than one groove. In the shown em- bodiments, the groove 1s continuous and has an even depth.

Alternatively, the depth as well as the width may vary. For example, at the point of the through hole there can be a sem- icircular slot for collecting water. Regardless of the embod- iment, the through holes 22 are arranged to open on the groove 27. This facilitates drainage. Figure 4b shows a blank of the doctor blade according to the invention. Here the — groove 27 is already machined and the position of the through

O 25 hole is shown with two dash-dotted lines. g

S Figure 3c shows the third embodiment of the doctor blade 11 z according to the invention. Here the wedge 33 is formed with > a wing 28, having thus a shape of a letter V being open be- e 30 tween the forks of the V. The partly open construction reduc-

N es the amount of raw material and the design is also suitable

N for manufacturing by pultrusion. On the other hand, the doc- tor blade can be manufactured by combining several pieces.

For example, a key-like component can be fastened to a wedge-

shaped blade blank. Simultaneously the volume for removed wa- ter is big. Thus, any overflow will be avoided. Also, the wa- ter may run in the deep groove sideways towards the ends of the doctor blade. This assists the drainage of the water.

The doctor blade according to the invention is so universal in design that it can be adapted to almost all known blade holders. Moreover, the surprising drainage function enables most doctoring positions and requirements. Moreover, a novel doctor blade can be taken into use without major equipment changes or investments. When the water is drained properly, the foil effect of the doctor blade remains and thereby water is sucked effectively. Also, the doctor arrangement with a single doctor blade can be installed even in tight positions.

Despite of the through holes and the groove, the doctor blade according to the invention can be utilized also in the doctor arrangement shown in Figure 1. =

O

N

O

<Q oO

O

I a a o

O

0

N

O

N

Claims

1. Doctor blade for a fiber web machine, the doctor blade (11) including a foil section (14) having a sharp tip (21), characterized in that in the foil section (14) there is a plurality of through holes (22) distributed essentially over the whole length (L) of the doctor blade (11).

2. Doctor blade according to claim 1, characterized in that the foil section (14) includes a foil (25) starting from the sharp tip (21), and a foil neck (32) at the opposite end of the foil section (14).

3. Doctor blade according to claim 2, characterized in that each through hole (22) is a round hole (23) having a di- ameter (D) which is greater than the thickness (T) of the foil neck (32).

4. Doctor blade according to any of claims 1 - 3, char- acterized in that the through holes (22) are perpendicularly oriented or slightly obligue in relation to the doctor blade (11).

—

5. Doctor blade according to any of claims 1 - 4, char- O 25 acterized in that the foil section (14) includes a wedge (33) se having a bulky head (26) tapering towards the sharp tip (21) S and the through holes (22) are situated in the area of the z head (26). a O 2 30

6. Doctor blade according to claim 5, characterized in N that there is an angle (a) between the head (26) and the foil N neck (32) the angle (a) being 100 - 160, preferably 120 - 140 degrees.

7. Doctor blade according to claim 6, characterized in that on the head (26) there is a groove (27) extending essen- tially over the whole length (L) of the doctor blade (11), and the through holes (22) are arranged to open on the groove (27).

8. Doctor arrangement in a fiber web machine, wherein, in the vicinity of the open surface (10) to be doctored, there is arranged a doctor blade (11) including a foil sec- tion (14) having a sharp tip (21), characterized in that in the foil section (14) there is a plurality of through holes (22) distributed essentially over the whole length (L) of the doctor blade (11), and the tip (21) is arranged to point downward.

9. Doctor arrangement according to claim 8, character- ized in that the doctor blade (11) included in the doctor ar- rangement is a doctor blade according to any of claims 2 - 7.

10. Doctor arrangement according to claim 8 or 9, charac- terized in that the open surface (10) belongs to a roll (16), advantageously a couch roll. N O N O <Q oO O I jami a o O O 0 N O N