WO1997048852A1

WO1997048852A1 - Set of ribs in a dewatering device in a paper machine

Info

Publication number: WO1997048852A1
Application number: PCT/FI1997/000380
Authority: WO
Inventors: Samppa Salminen; Aimo NÄRVÄINEN
Original assignee: Valmet Oy
Current assignee: Valmet Technologies Oy
Priority date: 1996-06-18
Filing date: 1997-06-16
Publication date: 1997-12-24
Anticipated expiration: 1998-12-18
Also published as: ATE217041T1; EP0906468A1; DE69712337D1; EP0906468B1; FIU960367U0; FI3066U1; US5851359A; DE69712337T2

Abstract

The invention concerns a set of ribs (33) in a dewatering device in a paper machine, which set of ribs is used to support and/or to load the wire (10) or wires in the paper machine and/or to doctor water from the inner face(s) of the loop(s) of the wire (10) or wires. The set of ribs (33) comprises at least two cross direction ribs (41), which are placed at a distance from one another in the machine direction (F), whose positions of height can be adjusted, and which have been interconnected in pairs by means of intermediate parts (47). The ribs (41) have been interconnected in pairs by means of crank mechanisms (60) placed at a distance from one another in the cross direction of the wire (10) or wires, in which connection the ribs (41) can be loaded independently from one another.

Description

Set of ribs in a dewatering device in a paper machine

The invention concerns a set of ribs in a dewatering device in a paper machine, which set of ribs is used to support and/or to load the wire or wires in the paper machine and/or to doctor water from the inner face(s) of the loop(s) of the wire or wires, which set of ribs comprises at least two cross-direction ribs, which are placed at a distance from one another in the machine direction, whose positions of height can be adjusted, and which have been interconnected in pairs by means of intermedi¬ ate parts.

In web formers in paper machines, a number of different forming members are used. The primary objective of these members is to produce compression pressure and pressure pulsation in the layer of fibers that is being formed, by means of which pressure and pulsation the draining of water from the web that is being formed is improved and, at the same time, for example, its formation is improved. Said forming members include various forming shoes, which are, as a rule, provided with a curved ribbed deck and over which the forming wires placed one above the other and the web placed between said wires are curved. In the area of these forming shoes, water is drained through the wire placed at the side of the outside curve owing to its tensioning pressure, and this draining of water is promoted further by a field of centrifugal force. Draining of water also takes place through the wire placed at the side of the inside curve, which draining is, as a rule, intensified by means of a vacuum present in the chamber in the forming shoe. The ribbed deck on the forming shoe produces pressure pulsation, which both promotes the draining of water and improves the formation of the web.

Further, from the prior art, what is called MB units (loading element units) are known, through which two wires placed one against the other run, usually as a straight run. In the prior-art MB units, inside the loop of one of the wires, there is a pressure loading equipment, and inside the loop of the other, opposite wire, a dewatering equipment provided with a set of guide and draining ribs is fitted. As is known from the prior art, said MB unit is, as a rule, placed in a fourdrinier wire portion so that the MB unit is preceded by a single-wire portion of considerable length, in which a substantial amount of draining of water takes place before the web passes through the MB unit.

In the prior-art MB formers, the lower unit consists of a support board, which is composed of loaded ribs. Each of these ribs is loaded separately by means of a loading hose of its own.

With respect to the prior art, reference is made to the applicant's FI Patent No. 90,673, in which a twin-wire web former of a paper machine is described, which comprises a carrying wire and a covering wire, which form a twin-wire forming zone between the wires, in which zone a forming unit has been arranged, which comprises a forming board and a water drain box placed one against the other, which drain box is provided with a number of ribs, between which, through the gaps between the ribs, water is drained from the web to a significant extent by the effect of a vacuum into the water drain box, and which forming board includes, placed facing the water drain box, a number of cross-direction loading ribs placed at a considerable distance in the machine direction from one another, and in the area of which forming unit the draining of water can be arranged so that it takes place both through the covering wire and through the carrying wire also towards the forming board through the open gaps placed between its loading ribs. In the solution described in said publication it has been considered novel that successive loading ribs have been interconnected in pairs by means of intermediate parts and that said intermediate parts, together with the loading ribs attached to them, form ribbed shoes, which can be loaded by means of loading hoses to produce a dewatering pressure applied to the web placed between the wires, while the ribs of said water draining box operate, in a way in itself known, as backup members for the loading forces. In the way known from the prior art, the ribs have been interconnected fixedly, in which connection, when the first rib and the upper rib placed between the ribs remove water, the stock web becomes thinner, in which case the latter rib must rise to a level higher than the first rib. It follows from this that the latter rib must be loaded to a greater extent than the first rib, in which case the element is turned into an inclined position, and the tips of the ribs are separated from the wire as a result of the change in angle. In such a case, the rib does not remove water, so that the loading pressure must be increased in order to bring the tip of the rib into contact with the wire. Owing to this employment of an unduly high loading pressure, the base of the paper can also be spoiled. Also, it is quite difficult to operate the latter rib with a slight load. It has also been problematic that such ribs cannot be brought into an asynchronous movement.

One solution related to these problems is described in the applicant's FI Patent No. 95,058, in which a set of ribs in a dewatering device in a paper machine is described, which is used to support/load the wire or wires in the paper machine and/or to doctor water from the inner face(s) of the wire or wires, which set of ribs comprises at least two cross-direction ribs, which are placed at a distance from one another in the machine direction, whose positions of height can be adjusted, and which have been interconnected in pairs by means of intermediate parts. It has been considered a novelty in this set of ribs that the ribs have been interconnected in pairs by means of four-joint articulation mechanisms placed at a distance from one another in the cross direction of the wire/wires, in which connection the positions of the ribs in the horizontal direction remain invariable irrespective of the relative positions of height of the ribs. This solution is, however, not suitable for use in connection with a rib or equivalent in a dewatering device in a paper machine of the type described in the FI Patent No. 95, 935.

In the FI Patent No. 95,935, a rib for a dewatering device in a paper machine is described, which is used to support and/or to load the wire or wires in a paper machine and/or to doctor water from the face(s) of the wire or wires, which rib is loaded by means of the pressure of a medium. Between the rib and its frame part, a pressure space has been formed, which is defined by a flexible belt and into which the loading pressure is passed, and the flexible belt defines the pressure space so that the area of effect of the loading force is independent from the movement of the rib.

The object of the present invention is to suggest a solution by whose means the problems involved in the prior-art ribs in dewatering devices can be solved.

It is a particular object of the invention to provide a solution which is suitable for use in connection with a rib as described in the FI Patent No. 95, 935 or in connec- tion with a rib of similar type.

In view of achieving the objectives stated above and those that will come out later, the invention is mainly characterized in that the ribs have been interconnected in pairs by means of crank mechanisms placed at a distance from one another in the cross direction of the wire/wires, in which connection the ribs can be loaded independently from one another.

In a loading element in accordance with the invention, the water drain ribs have been interconnected by means of an intermediate pin of the type of a crankshaft, in which connection the ribs can be loaded and displaced independently from one another.

According to a preferred exemplifying embodiment of the invention, when a crankshaft mechanism is used for attaching the ribs in pairs, the angles between the ribs do not change, in which case the faces of the ribs remain in the desired posi- tions and the foil angle remains as desired in the case of each rib, in which connec¬ tion the rib can be made to remove water uniformly. Also, in this way, an efficient and controlled ratio of dewatering/loading is achieved.

As further advantages of the invention, it is achieved that when ribs provided with a clearance angle are used, the clearance angle at each rib remains correct, because the crankshaft mechanism prevents turning of one of the ribs into an oblique position. The arrangement in accordance with the invention is in particular suitable for such dewatering taking place in the wire part in which it is desirable to regulate the loading of the ribs.

The arrangement in accordance with the invention is also well suitable for use in projects of modernization of sets of dewatering ribs.

When the web becomes thinner as water is drained, by means of an arrangement in accordance with the invention an increased possibility of regulation of the loading rib is obtained, because each rib can be loaded separately. By means of the number of ribs employed during operation, the quality of the paper is affected, and a suitable number of ribs is chosen depending on the paper stock, running speed, and on the thickness of the slice opening in the headbox.

In the following, the invention will be described in more detail with reference to the figures in the accompanying drawing.

Figure 1 is a schematic illustration of an exemplifying embodiment of an environ¬ ment of application of the invention.

Figures 2A and 2B are schematic illustrations of a loading element in accordance with the invention in a loading position.

Figures 3A and 3B are schematic illustrations of a loading element in accordance with the invention in a non-loaded position.

Fig. 1 is a schematic illustration of an environment of application of the present invention consisting of a former, which comprises a lower-wire loop 10 and an upper- wire loop 20. In connection with the lower-wire loop 10, after the headbox (not shown), there is a single-wire initial portion 10a of the web forming zone, in which initial portion, owing to the water draining elements 11a placed in it, the stock web W₀ reaches a certain dry solids content and, at least at its bottom face, a certain couching degree before it enters into the twin-wire zone, which is formed between the wires 10 and 20. The twin-wire zone starts at the breast roll 21 of the upper-wire loop 20. After the breast roll 21, in the twin-wire zone, inside the lower- wire loop 10, there is a forming shoe 12, after which there follows the loading unit 32 in the MB unit 30 in the twin-wire zone, in which loading unit 32 there are loading ribs interconnected in pairs and placed one after the other, which ribs extend across the entire width of the wires 10,20.

The upper wire 10 has been arranged to run over the turning rolls 16,17, 18 and over the breast roll 21, and the lower wire 20 runs substantially parallel to the upper wire 10 below the upper wire 10. The wires 10 and 20 form a wedge-shaped inlet gap K, in which the web W₀ placed on the lower wire 10 is pressed continuously between the wires 10 and 20 as the wires make progress. After the wedge-shaped inlet gap K, in the direction of progress F, there is the MB unit 30, which comprises a water drain box 51. The bottom of the water drain box 51 consists of ribs 52, water being sucked out of the web W₀ through the gaps placed between the ribs 52 into the water drain box 51 by means of a vacuum. When the upper wire 10 runs, it rests against said ribs 52. The MB unit 30 also includes loading units 32, which permit draining of water downwards and on whose top faces sets of loading ribs 33 are placed. Above the sets of loading ribs 33, inside the upper-wire loop 20, as backup parts for the pressure loading, there are said ribs 52, which are placed facing the gaps between the ribs in the sets of loading ribs 33. Further, in Fig. l a number of other parts and support constructions included in the former are seen, which are known in themselves and which will not be described in more detail in this connection.

In the exemplifying embodiments shown in Figs. 2A...2B and 3A...3B, the set of loading ribs 33 consists of two loading ribs 41. The loading rib 41 comprises a frame part 43, on which the loading rib 41 is supported by means of the glide part 44 in the frame. The loading rib 41 is fitted to move in the vertical direction while supported by the glide part 44. The plane top sides of the loading ribs 41 glide against the wire 10;20 face and load the wires while water operates as a lubricant. By means of the loading ribs 41, water drained from the web W₀ is doctored off the lower face of the wire. The loading rib 41 is supported in its place of operation typically by means of a continuous glide rail 44, which is made of one part with the frame part 43. Preferably to the lower edge of the loading rib 41 , a flexible belt 46 is attached, which is attached to the frame part 43 so that U-shaped loops 48 are formed downwards. To the sides of the rib 41, outside the belt 46, shield plates 55 have been attached, which restrict the movement of the belt 46 towards the sides.

In the construction shown in Figs. 2A...2B and 3A...3B, the loading force is produced by passing the loading pressure p_a,p_D by means of a medium, for example air, into the space defined by the flexible belt 46, by the rib 41, and by the frame part 43. The loading pressure p_a,p_D is relieved by lowering the pressure p_a,p_D, and the force of gravity returns the rib 41 down. The belt 46, whose thickness is, for example, 0.1 ... 3 mm, preferably 1...2 mm, and which is made of rubber or any other, equivalent resilient material, is attached from its upper edge to the rib 41 and from its lower edge to the frame part 43 so that U-shaped loops 48 are formed downwards, which loops permit movement of the rib 41 in the direction up and down. The lateral supports 55 restrict the expansion of the belt 46 towards the sides, in which case the area of effect of the pressure is not changed when the rib 41 moves in the loading direction.

As is shown in the figures, the ribs 41 are interconnected in pairs by means of an intermediate part 60, and the frames 43 by means of an intermediate part 47. The bottom portions of the rib 41 frames are interconnected by means of support rods 47. The top portions of the loading ribs 41 are interconnected by means of a crank mechanism 60, which permits separate loading of each rib 41 and which further secures that the positions of the ribs 41 in relation to the web W₀ remain as desired. The crank mechanisms 60 are placed at a distance from one another in the cross direction of the machine, which distance L_j is about 50...500 mm. The distance L_j between the ribs 41 is about 30...300 mm. The crank mechanism 60 comprises an arm part 61 attached to the rib 41 and, similarly, an arm part 62 attached to the other rib, and an intermediate crank arm 63, which is linked with the arm parts 61 ,62 by means of articulated joints 64.65.

In the loading position shown in Figs. 2A...2B, the crank mechanism 60 is in the upper position, and in the stage shown in Figs. 3A...3B the crank mechanism 60 is in the lower position.

Above, the invention has been described with reference to a preferred exemplifying embodiment of same only. In the following, the claims of protection will be given, and many modifications and variations are possible within the scope of the inventive idea defined in said claims.

Claims

1. A set of ribs (33) in a dewatering device in a paper machine, which set of ribs is used to support and/or to load the wire (10) or wires in the paper machine and/or to doctor water from the inner face(s) of the loop(s) of the wire (10) or wires, which set of ribs (33) comprises at least two cross-direction ribs (41), which are placed at a distance from one another in the machine direction (F), whose positions of height can be adjusted, and which have been interconnected in pairs by means of intermedi¬ ate parts (47), characterized in that the ribs (41) have been interconnected in pairs by means of crank mechanisms (60) placed at a distance from one another in the cross direction of the wire (10) / wires, in which connection the ribs (41) can be loaded independently from one another.

2. A set of ribs as claimed in claim 1 , characterized in that the crank mechanism (60) comprises arm parts (61 ,62), which are attached to the ribs (41), and a crank arm (63) between the arm parts (61,62).

3. A set of ribs as claimed in claim 1 or 2, characterized in that the set of ribs (33) is fitted to be used in a twin-wire web former in a paper machine, in which former, placed above the sets of loading ribs (33) placed inside the lower-wire loop (10), inside the upper-wire loop (20), as backup parts for pressure loading, there are ribs (52) of a water drain box (51), which ribs (52) are placed facing the gaps between the ribs (41) in the sets of loading ribs (33).

4. A set of ribs as claimed in any of the preceding claims, characterized in that the crank mechanisms are placed at a distance of about 50...500 mm from one another in the cross direction.

5. A set of ribs as claimed in any of the preceding claims, characterized in that a pressure space defined by a flexible belt (46) has been formed between the rib (41) and its frame part (43), into which space the loading pressure (p_a,p₀) is passed, and that the flexible belt (46) defines the pressure space so that the area of effect of the loading force is independent from the movements of the rib (41).