EP2480715A1

EP2480715A1 - Dewatering element for a fiber web machine

Info

Publication number: EP2480715A1
Application number: EP10818461A
Authority: EP
Inventors: Antti Ahmaniemi; Timo Koskela
Original assignee: Metso Paper Oy
Current assignee: Valmet Technologies Oy
Priority date: 2009-09-24
Filing date: 2010-09-16
Publication date: 2012-08-01
Also published as: CN102575427B; FI20095978A; CN102575427A; FI20095978A0; FI121797B; EP2480715A4; WO2011036339A1

Abstract

The invention relates to a dewatering element for a fiber web machine. The dewatering element includes a frame (10) and a dewatering organ (12) supported thereto with a supporting structure (11). The dewatering element further includes loading elements (13) for loading the dewatering organ (12). The supporting structure (11) includes several brackets (14) which are arranged at a distance (d) from each other in the longitudinal direction of the frame (10) for creating an essentially open interval between the frame (10) and the dewatering organ (12) and thereby providing a flow-through channel (15). The width w of the bracket (14) is 0.5 - 20 mm, more advantageously 1 - 15 mm.

Description

DEWATERING ELEMENT FOR A FIBER WEB MACHINE

The invention relates to a dewatering element for a fiber web machine, which dewatering element includes a frame and a dewatering organ supported thereto with a supporting structure, and the dewatering element further includes loading elements for loading the dewatering organ, and the supporting structure includes several brackets, arranged at a distance from each other in the longitudinal direction of the frame for creating an essentially open interval between the frame and the dewatering organ and thereby providing a flow-through channel.

A dewatering element is a part of dewatering equipment used in a fiber web machine. Usually one dewatering device includes several . dewatering elements which are adapted at a distance from each other in the travel direction of the web. As a fabric supporting the web produced in a fiber web machine travels past the dewatering elements, pressure pulses are generated which remove water from the web. In practice, the web chafes against the dewatering element, and therefore the dewatering element also includes a dewatering organ which is wear resistant.

US patent No. 5078835 discloses a dewatering element which also includes loading devices for loading a dewatering organ. Attempts have been made to make the dewatering element as narrow and mobile as possible using a certain type of supporting structure. Here the frame of the dewatering element is provided with support arms connected thereto with a flatlike and two-part dewatering organ fastened in front of the support arms. In the application disclosed, loading elements are arranged between the frame and the dewatering organ.

Using the support arms, it has been possible to achieve a small friction surface; at the same time, however, the stress during use is applied in a point-like manner. Another remarkable disadvantage is the supporting structure and the dewatering organ that are high relative to the width. In this case, water hitting against the dewatering organ causes remarkable tilting forces to act upon the dewatering element. The collision of water also generates splashing. In addition, the dewatering element has multiple protrusions that are evidently accessible, which increases soiling of the dewatering element.

Various brackets are disclosed in the US patent application publication No. 2001/0002692.

The object of the invention is to provide a novel dewatering element for a fiber web machine, the dewatering element being more economical to manufacture and use than before, yet more mobile and more precisely loadable than earlier. The characteristic feature of this invention is that the width of the bracket is 0.5 - 20 mm, more advantageously 1 - 15 mm. Due to the flow-through channel, water removed by the dewatering organ can pass by the dewatering element without hitting upon it. Thus the tilting forces generated by the water pressure remain low, and consequently, the dewatering element is highly moveable. The dewatering element and the supporting structure have other surprising features as well, which make the dewatering element compact and non-soiling. The invention is described below in detail by making reference to the enclosed drawings that illustrate one of the embodiments of the invention, in which is a rear oblique view of the dewatering element according to the invention,

is a rear and partly cross-sectional view of the dewatering element according to the invention, without one frame component,

is a partly cross-sectional rear view of the dewatering element according to the invention in an installation-ready state, Figure 3a is a cross-sectional view of level B-B of Figure 2b,

Figure 3b is a cross-sectional view of level A-A of Figure

2b.

Figure 1 shows an installation-ready dewatering element according to the invention which is used particularly in a dewatering device of a fiber web machine. One dewatering device has usually several dewatering elements , although an individual dewatering element can also be used as such. Generally, a dewatering device is located in the forming section of a fiber web machine, below the fabric that supports the web to be formed. During use, a dewatering organ included in the dewatering element touches the fabric and removes water. Often a vacuum is also arranged inside the dewatering device for improving dewatering. In the positions below the fabric, gravity has a significant effect and therefore a vacuum can prevent splashing and misting of water. A dewatering element is thus meant particularly for a fiber web machine. Known fiber web machines include, for example, paper and board machines as well as pulp drying machines the forming sections of which are provided with multiple dewatering elements. As basic structures, a dewatering element includes a frame 10 and a dewatering organ 12 supported thereto with a supporting structure 11. In addition to passive dewatering elements, active dewatering elements also exist to which loading elements 13 are further included for loading the dewatering organ 12. Loading elements can be used to change the position of the dewatering organ relative to the fabric and loading elements can also function as a certain type of shock absorber. The dewatering element according to the invention is advantageously used in the double—fabric zone of the forming section of a fiber web machine. The supporting structure 11 includes several brackets 14 which are arranged at a distance d from each other in the longitudinal direction of the frame 10 for creating an essentially open interval between the frame 10 and the dewatering organ 12 and thereby providing a flow-through channel 15. The longitudinal direction of the frame is illustrated with a double-headed arrow in Figure 1. Using a construction described above, a completely novel open dewatering element is formed through which a water shower can pass without obstacles. Thus collision of water and the relative tilting forces are avoided, which remarkably reduces stresses directed to the dewatering element. At the same time, water splashing is avoided. Due to the free interval, it is additionally possible to use a completely novel dewatering organ which is additionally positioned in a new way. Thus the dewatering organ 12 is arranged in an oblique position relative to the frame 10 such that the dewatering organ 12 or its extension passes by the frame 10 on the trailing side. The extension is illustrated with a broken line in Figure 3a. The dewatering organ touches the fabric, shown basically in Figure 3b with a broken line, by its front surface. Immediately after releasing from the fabric, water advances following the bottom surface of the dewatering organ 12 without hitting onto the frame 10. Thus the flow of water removed is unobstructed, which essentially reduces splashing and tilting forces.

According to the invention, the bracket is notably narrow in the travel direction of the web. Generally, the width w of the bracket 14 is 0.5 - 20 mm, more advantageously 1 - 15 mm. In spite of a narrow bracket, the supporting structure resists well loading, because the free length of the bracket is short, whereas it is abundantly dimensioned in the longitudinal direction of the fiber web machine. Thus the brackets resist loads caused by the fabric chafing and water removal. The load caused by water can be further reduced by chamfering the bracket. Thus the leading edge 16 of the bracket 14 is advantageously chamfered. The chamfer 17 is shown in Figure 3a. Despite the brackets, the flow-through channel is essentially open. Narrow brackets affect the water flow only slightly. Openness is increased by the generous distance between the brackets. Generally, the distance d between two adjacent brackets 14 is 50 - 500 mm, more advantageously 100 - 200 mm. The narrower the bracket is, the shorter is the distance between the brackets. For example, a 10 mm wide bracket can be adapted at a distance of 150 mm from another bracket with the dewatering element resisting the loads generated by the use. More generally, the distance is so dimensioned that a uniform load is achieved in the dewatering organ without the dewatering organ bending.

A supporting structure of a new type also enables positioning the dewatering organ in a new way. According to the invention, the doctoring angle a between the center axis x of the dewatering organ 12 and the fabric-contacting wear surface y of the dewatering organ 12 is an acute angle, advantageously 30° - 70° and more advantageously 40° - 60° (Figure 3b) . In other words, the doctoring angle is notably large, which improves water removal. In addition, the doctoring angle can be easily modified to suit each specific need by changing the dewatering organ. In principle, the supporting structure can be used to support quite variable dewatering organs. Advantageously, however, the dewatering organ 12 is one continuous slat 18 extending essentially over the entire length of the dewatering element and provided with a wear resistant coating. In other words, it is possible to use a slat material with a thickness of a few millimeters, coated with a spray coating, for example. Thus a light and durable dewatering organ is advantageously achieved which is additionally easy to replace when required. On the other hand, the slat can be used as a support onto which one or more ceramic blocks, for example, can be fastened as a wearing part. Then the slat can also be manufactured from fiber-reinforced plastic, for example. As shown in Figure 1, the dewatering element according to the invention is compact without harmful protrusions. In the application example, the dewatering element is approximately 150 mm high and approximately 50 mm wide. Here the frame 10 includes a bottom rail 19 and a U-profile 20 arranged around it. The brackets 14 extend through the U-profile and the loading elements 13 are fastened to the bottom rail 19. The bottom rail 19 is also provided with a T-groove 21 for a T-slat 22. The T-slat is fastened to the dewatering device and the whole dewatering element can be installed and removed by pulling towards the lateral direction of the fiber web machine.

Figures 2a and 2b show a rear view of a dewatering element in the machine direction. In Figure 2a, the dewatering element is without a U-profile, which allows to see the slide blocks 23 of which each one is fastened to one bracket 14 and upon which the loading elements 13 are adapted to act. Particularly from the cross-sections of Figures 2a, 2b and 3b, it becomes evident that the bracket 14 extends through the slide block 23 and is fastened to the slide block 23 with a screw. The slide block has many important functions. Firstly, it conveys the load applied to the bracket uniformly to the U-profile and further to the entire frame. Secondly, the slide block provides a low- friction movement. Thirdly, the slide block equalizes and transmits the force of the loading elements to the dewatering organ through the brackets. In the application disclosed, the slide blocks 23 are additionally provided with springs 24 which return the dewatering organ 12 to a bottom position when the loading effect of the loading elements 13 is removed. Here the loading elements 13 are composed of a loading hose which is adapted between the bottom rail 19 and the slide blocks 23 and fastened to the bottom rail 19. In the application disclosed, the U-profile 20 is fastened to the bottom rail 19 whereby a rigid frame is formed. The slide blocks 23 and the brackets 14 fastened thereto thus move together. The design of the slide blocks can vary in different applications. Here both edges of the slide block 23 are at least partially composed of flexible skirts 25 which contact the inner surface of the U-profile only at the top and bottom edges (Figure 3a) . Thus friction remains advantageously small while the skirts are still always kept in contact with the U- profile. At the same time, the slide block becomes light. Advantageously, the slide blocks as well as the bottom rail are made of plastic.

Deviating from the application examples, one or more slide blocks can be fastened to the bottom rail. Then the U-profile is adapted to be mobile relative to the bottom rail while the brackets are fastened to the U-profile (not shown) . In other words, the loading elements act upon the U-profile while the slide blocks remain in place. At the same time, it is possible to avoid openings in the U-profile which are required for the brackets in the application described first.

With a loading hose, sufficient force and stroke are achieved in most positions. In Figures 3a and 3b, the slat 18 is shown in the center position from which there is a movement tolerance of about 10 mm both up and down. A loading hose with a diameter of about 20 mm provides a load of two kN/m to the slat at a pressure of about one bar. In addition, the load changes linearly with the pressure, which facilitates the adjustment of the dewatering element. Instead of a loading hose, pneumatic cylinders or compressed air boxes, for example, can be used. In some applications, even mere springs are sufficient for the required load. Due to the flow-through of water, loads applied to the dewatering element are essentially reduced. Particularly the tilting forces that have produced problems earlier are small. At the same time, the movement of the dewatering organ is agile, which improves the dewatering capacity and reduces the risk of fabric damage. In other respects, too, the design of the dewatering element is simple and well protected. Additional savings are achieved by a simple and easily replaceable slat whose doctoring angle can be adjusted.

Claims

1. Dewatering element for a fiber web machine, which dewatering element includes a frame (10) and a dewatering organ

5 (12) supported thereto with a supporting structure (11), and the dewatering element further includes loading elements (13) for loading the dewatering organ (12), and the supporting structure (11) includes several brackets (14), arranged at a distance d from each other in the longitudinal direction of the 0 frame (10) for forming an essentially open interval between the frame (10) and the dewatering organ (12) and thereby providing a flow-through channel (15) , characterized in that the width w of the bracket (14) is 0.5 - 20 mm, more advantageously 1 - 15 mm.

15

2. Dewatering element according to claim 1, characterized in that the distance d between two adjacent brackets (14) is 50 - 500 mm, more advantageously 100 - 200 mm.

20 3. Dewatering element according to claim 1 or 2, characterized in that the dewatering organ (12) is arranged in an oblique position relative to the frame (10) such that the dewatering organ (12) or its extension passes by the frame (10) on the trailing side.

25

4. Dewatering element according to claim 3, characterized in that the doctoring angle between the center axis x of the dewatering organ (12) and the fabric-contacting wear surface y of the dewatering organ (12) is an acute angle, advantageously

30 30° - 70° and more advantageously 40° - 60°.

5. Dewatering element according to any of claims 1 - 4, characterized in that the dewatering organ (12) is one continuous slat (18) extending essentially over the entire

35 width of the dewatering element and provided with a wear resistant coating or a ceramic wear surface.

6. Dewatering element according to any of claims 1 - 5, characterized in that the leading edge (16) of the bracket (14) is chamfered.

7. Dewatering element according to any of claims 1 - 6, characterized in that the frame (10) includes a bottom rail (19) and a U-profile (20) arranged around it while the loading elements (13) are fastened to the bottom rail (19) .

8. Dewatering element according to claim 7, characterized in that inside the U-profile (20) fastened to the bottom rail (19), slide blocks (23) are provided each of which is fastened to one bracket (14) and upon which the loading elements (13) are adapted to act,

9. Dewatering element according to claim 7, characterized in that one or more slide blocks (23) are fastened to the bottom rail (19) and the U-profile (20) is adapted to be movable relative to the bottom rail (19) while the brackets (14) are fastened to the U-profile (20) .