FI85885B - FOERFARANDE FOER FORMERING AV EN FIBERBANA I EN PAPPERSMASKIN SAMT EN ANORDNING FOER UTFOERING AV FOERFARANDET. - Google Patents

Abstract

In a method for forming a fibrous web in a papermachine, stock suspension is supplied into a wedge-like space or a gap (13), converging in the direction of supply of the stock and being formed between fabrics (1,2) pervious to water, such as wires. The fabrics (1,2) are supported on deck elements of dewatering spaces (5,6). The deck elements of the dewatering space (6) on the side of one (2) of the fabrics effect a load with a desired force resiliently on said fabric (2).

Description

85885

A method for forming a fibrous web in a paper machine and an apparatus for carrying out the method

The invention relates to a method for forming a fibrous web to be produced by filtration from a pulp suspension in a paper machine, which method is more specifically defined in the preamble of claim 1. The invention furthermore relates to a web-forming zone as defined in the preamble of claim 5, in which the above-mentioned method can be carried out.

The two-wire web-forming zones of the paper machine, i.e. the so-called the former have been the subject of intensive development over the last couple of decades. Known structures can be divided into three basic types, such as rotary formers, blade formers and force-guided guitar formers.

The round formers are characterized in that the headbox jet 15 is guided in a gap formed by two wires. Both wires pass over a large diameter, usually open-surface roll. Due to the tension of the outer wire, a pressure is created in the web which compresses the water out of the suspension, filtering the fiber suspension into a paper web. The dewatering process is fast, even crowded: 20 huge. As a result, the web formation is granular and the filler particles present in the suspension and the fines of the fibers ____ are washed away. However, their retention in the paper would be desirable for the printability of the paper.

25 The so-called blade former also have a gap formed by two wires, but now the curvature is formed by the blades of the foils mounted in the direction of the web on the circumference of a large circle. The radius of curvature may be several meters. If the web were to run in the arc of said circle, the average pressure formed would be less than. However, the wires and the web pass between them: V: directly from one blade to another, forming a polygon and foils. they cause pressure shocks to the web as it passes over the blade.

The result is usually a better formation of the bottom of the web, i.e. the quality of the paper, than in the previous case, but the disadvantage is that the flushing of fines is even more efficient than in round rotors. A further disadvantage is the wear of said foils, as well as the consequent high need for maintenance and operating power.

In addition, a forced guided gut consisting of fixed dewatering members, which is the basis of the present invention, is known. The kit is adjustable and tapers in the direction of web travel. The pressure generated in the web compresses the water through the perforated or slotted lids into drain boxes which are divided in the transverse direction of the machine into separate chambers. Water from each chamber exits through the control valve back into circulation. By adjusting the valves, the pressure and thus also the dewatering conditions in the web can be completely controlled. Such a guitar former is shown e.g. in Finnish Patent Application 63077 and U.S. Patent Publications 3,823,062 and 3,847,731.

The weakness of the structure of the above-mentioned former is the forces generated by pressure, bending the boxes, which are difficult to control with the current large machine widths. Furthermore, the structure 20 requires a complex control system to achieve the desired dewatering.

The object of the invention is to provide a method and an apparatus by means of which the above-mentioned disadvantages can be avoided and the weaknesses of all the above-mentioned former types can be eliminated while at the same time achieving their advantages.

According to the invention, this is achieved by a method, the features of which are set out in the characterizing part of claim 1. The apparatus with which the above advantages are achieved, in turn, has the features set out in the characterizing part of claim 6. By loading the lid elements of the dewatering chambers with the desired and suitable force against the mass layer moving between the wires, a controlled leaching of water from the pulp suspension can be achieved and the bending of the boxes caused by pressure can be avoided.

3 85885

Some advantageous features of the invention are set out in the appended subclaims. Thus, the cover elements can be loaded separately from each other, with each desired force against the wire. In addition, the formation of the resulting flocs can be prevented by suitable mechanical high-cycle vibration or steam implantation. In addition, the invention has several advantageous structural alternatives, e.g. the cover elements can be supported by resilient means providing resilience to the machine body either in the drainage spaces, which in turn are fixed by said resilient members to the machine body or to a fixed part during the drainage operation. or in such a way that the resilient members enabling resilience support the cover elements in the structure of the dewatering spaces, which are fixed to the machine body or during the dewatering operation relative to the part fixed to the body. The dewatering spaces can be set to a suitable position relative to the machine frame by means known per se for adjusting the width of the groove.

The flexible loading force according to the invention, i. applying a load-20 pressure to the pulp suspension creates a infiltration pressure therein and provides a controlled infiltration in which a uniformly growing fiber layer is formed against each wire, which acts as a filter for the remaining suspension. The invention makes it possible to carry out the infiltration as slowly as possible in a long narrow gutter:. so that more fibers flow into the thinner point, which naturally penetrates water more easily than the surrounding areas. In this way, the formation of flocs can be avoided in order to achieve the best possible paper quality.

30

It is still necessary to have dewatering due to the different paper types and available paper raw material components! · .. very manageable right at this early stage. It is further important that the flocculation inherent in the fibers can be prevented and. The flocs already formed are decomposed until a later dewatering step is reached, where the flocs can no longer be formed after the fibers have bonded into a coherent fiber network.

4 85885

Once said infiltration layer has formed against the wire, the remainder of the suspension can be rapidly infiltrated to prevent or at least minimize the spontaneous formation of harmful flocs.

5

The invention will now be described in more detail with reference to the accompanying drawings, in which Figures 1a and Ib show the web-forming zone according to the invention in side views and Figure 2 shows a preferred embodiment of the cover elements according to the invention in side view.

The gap 13 of the web-forming zone according to the invention consists of a wedge-shaped space formed between two wires 1 and 2. As is known per se, the wires 1 and 2 pass through their own chest rolls 4 and, after passing in a certain sector around the rollers, they converge upwards towards each other to form the above-mentioned space 20 and merge with a large diameter (2000 mm) former roll 3.

The wires 1 and 2 run straight at the groove 13, forming the walls of the groove, and the wires are supported on opposite sides by this portion in slotted drainage boxes. Boxes supporting wire 1 are indicated by reference numeral 5 and boxes supporting wire 2 by reference numeral 6.

Figure Ib shows the structure of the gill in more detail. Vii-30 ra 1, which in this example is a primary wire, rests on the cover elements 11a, 11b, ... of the drainage boxes 5a, 5b, .. located in succession in the direction of travel of the wire ... The drainage boxes 5 are in turn supported fixedly on the machine frame beam 8. The wire 2 , is supported on the opposite side 35 in the direction of travel of the wire by the lid elements 12a, 12b, .. of successive dewatering boxes 6a, 6b, .. which are perforated or slotted. The lid elements are fixed in the dewatering boxes 6 immobile relative to them and in order to load the lid elements against the surface of the wire 2 with the desired force, the bottoms of the dewatering boxes 6 are resiliently supported on the machine frame beam 9 at least at both ends of the boxes (Fig. 1a). In the longitudinal direction of the box, i.e. in the transverse direction of the machine, there are preferably several supporting bellows 7. In the case shown in the figure, the secondary wire 2 has a wet suction box 10 located after the resiliently supported boxes 6, which supports both wires before they turn on the roll 3.

Viewed in the direction of travel of the wire 2, it is supported by a plurality of successive boxes 6a, 6b, each of which is fastened at its ends to its frame beam 9 by its own bellows, 7a, 7b, respectively. successively in the direction of travel of the web, each of which is individually loaded with a certain force against the wire, the machine-direction dewatering profile of the former 20 is desired.

The dewatering boxes 6 can furthermore be adjusted by a known, suitable mechanism, to a suitable predetermined position during the dewatering operation in order to adjust the width of the groove.

The following describes the dewatering operations in the direction of travel of the web.

The pulp suspension is fed vertically upwards to the grate 13 by a feeder 14, from which the pulp suspension passes to a grate where dewatering begins immediately to take place through the wires 1 and 2. In the mouth of the kidney 13, a high-cycle mechanical vibration, i.e., is applied to the pulp suspension to break up the flocs. 35 ultrasound frequencies, or steam implantation is utilized at this point. This point of disintegration of the flocs is indicated by an arrow A in Fig. ____ 1a. The mechanical vibration can be produced 6 85885, e.g.

The Kita 13 tapers slowly in the direction of travel of the wires so that a careful watering of the 5-5 can take place. In this case, unnecessarily sharp pressure fluctuations, possible damages and a complicated control system are avoided by the flexible support of the above-mentioned boxes 6a, 6b, .. on the side of the service wire 2 on the machine frame. The elasticity is obtained by feeding the ball into the spools 7a, 7b, .. a suitable compressible medium, such as air pressure, whereby each lid element 12a, 12b, .. can be loaded with the desired force Fa, Fb, .. against the wire without the boxes said to bend in its longitudinal direction. Even a slight deflection of the box would lead to a transverse variation in the thickness of the web, which in turn would make the paper produced unusable.

Each cover element 12a, 12b, ... is loaded separately with the desired force, respectively Fa, Fb, ... against the wire 2. In this way, the dewatering operation is controlled in the longitudinal direction of the gill.

By means of a suitable pressure in the beams 7a, 7b, ... the cover elements are pressed against the wire 2, causing an external pressure in the pulp layer 25. Since it is a rapidly flowing liquid, the external pressure causes the flow rate to slow down so that the static pressure generated is exactly equal to the external pressure according to Bernoulli's law. The current flow in the pulp layer, parallel to its plane, is necessary to break up the generated flocs and bring new pulp to the points where drainage through the wire is easiest.

The water leaving on both sides through the wires 1 and 2 is compressed into boxes 5 and 6, from which it is directed back into circulation in a manner known per se. Since the dewatering is effected by means of a seepage pressure, it is not necessary to use suction. However, a vacuum can be provided in the drainage boxes, e.g.

7 85885 ns. by means of a suction foot. It is still important to be able to adjust the amount of water removed from different parts of the web. This can be achieved in the former according to the invention in two ways, firstly as in a known forced-controlled former, i.e. by adjusting the amount of water leaving the boxes, for example as described in Finnish Patent Publication No. 63077 and U.S. Patent No. 3,823,062, by flow restrictor replaceable cover elements.

10

Once the fibrous layer has formed on the surface of both wires and coalesces at the end of the girder 13, a second part of the former is formed, which in turn consists of a large diameter (2000 mm) open surface roll 3. Here, the dewatering takes place due to the tension of the secondary wire 2, and the dewatering pressure is now constant, which gives the best possible retention.

After the roll 3, the wires are guided apart and the web 15, supported by the primary wire 1, continues to the press part of the paper machine, which is not shown in more detail here.

: Figure 2 shows a side view of an embodiment of the apparatus 25 according to the invention, which has fixed dewatering spaces and cover elements which are resiliently loaded against the wire and which rest on them. The unitary dewatering box 6 is divided into compartments 6a, 6b, .. The corresponding lid element 12a, 12b, .. at each compartment is detached from the dewatering box. Each cover element comprises longitudinal support strips 16 in the direction of travel of the wire 2, to which ceramic drainage strips 17 transverse to the direction of travel of the wire are attached, which are against the lower surface of the wire 2. The cover elements are connected in succession by connecting the support strips 16 to each other at their ends by means of step joints 18 at the ends of the support strips, which allow the strips 16 to move in a direction perpendicular to the plane of the wire 2. At each step connection 8 85885 1a there is a transverse support strip 19 on the side of the drain box 6, which thus supports the joint of two successive cover elements. At each partition separating the successive compartments 6a, 6b, a trough 20 transverse to the direction of travel of the wire is arranged, in which a pneumatic load hose 7 'is placed, which is in contact with the support strip 19 at the joint of the cover elements running parallel to it. The principle of operation of the pneumatic load hose 7 'is similar to that of the bellows 7 in Fig. 1a. When the pressure in the hose 7' is adjusted, the deformation of the hose causes a movement which changes the position of the successive cover elements 12a, 12b relative to the dewatering box 6. Thus, for each flow element 12a, 12b ..., the desired infiltration pressure-15 can be provided for the flow in the gill according to the invention.

As the wires run vertically, the lowest resiliently loadable cover element can be supported at its lower edge in the dewatering box 6 and subsequent elements can always be supported at the top of the lower element 20 by means of step joints 18. The fastening of the cover element is further ensured by securing springs 21 attached to them, which can be fastened at one end to e.g. the bottom of the dewatering spaces 6a, 6b, ...

The invention may, of course, be modified within the scope of the inventive idea set forth in the appended claims. It is essential that the invention provides a long, forward-tapering gap in which paper is formed from the pulp suspension as a result of controlled infiltration, which control is based on generating infiltration pressure by loading dewatering boxes against the pulp layer moving between the wires with the desired and suitable force. Due to the long gap, the pulp layer is always subjected to a constant pressure at each point of the grit for a sufficiently long time, due to which the square mass in the resulting web 35 is smoothed.

Claims (12)

A method of forming a fiber web in a paper machine, in which the pulp suspension is applied in a wedge-shaped tapered space or a gap (13) formed by the water-permeable webs (1, 2) formed in the belt suspension zone (1). these, while the wires (1, 2) are supported against the tire element (s) on the drainage compartments (5, 6), characterized in that the tire element (s) (12) on the dewatering space (6) on the side of at least one ( 2) the wires are loaded in a resilient manner against the wire (2) with the desired force (F). Method according to claim 1, characterized in that the tire element (s) (12) on the drainage space (6) on the side of one (2) of the wires 20 is loaded in a resilient manner against the wire (2) with the desired force (F ) while the tire element (s) (11) in the dewatering space (5) on the side of the second wire (1) are stationary in relation to the body (8) during the dewatering stage. 25 Method according to claim 1 or 2, characterized in that the resilient load is carried out by means of the tire elements (12a, 12b) which are successively and separately from each other in the direction of movement of the wire and which are to be loaded with a desired force (Fa, Fb) against in front (2). 13 85885 A belt forming zone in a paper machine comprising between two wires (1, 2) existing, in the direction of feeding of the pulp suspension, a tapered wedge-shaped space or a gap (13), the wires (1, 2) being supported against the tire elements of the dewatering spaces (5, 6), characterized in that the tire element (s) (12) in the dewatering space (6) on the side of at least one (2) of the wires are resiliently supported by spring means (7; 7 ') during dewatering. the stage towards a stationary part (9) relative to the body of the machine for loading the tire element (s) (12) against the wire (2) with the desired force (F). 5. Band forming zone according to claim 4, characterized in that the tire element (s) (12) in the dewatering space (6) on the side of one wire (2) are supported in a resilient manner and the tire element / tire elements (11) in the dewatering space (11). (5) on the side of the second wire (1) is arranged stationary relative to the body (8) of the paper machine during the dewatering stage. Tape forming zone according to claims 4 and 5, characterized in that in the direction of movement of the wire (2) there are successive, separate tire elements (12a, 12b), which are secured by means of their own suspension means (7a, 7b; 7 ') in the machine's body (8). Band forming zone according to any of claims 4-6, characterized in that the dewatering space consists of separate, successive dewatering spaces (6a, 6b), the bottom of which is resiliently supported by resilient means (7a, 7b) supported relative to the body of the machine. stationary part during the drainage stage. 35 14 85885 Tape forming zone according to claims 4-6, characterized in that the tire elements (12a, 12b) are pk a resilient means by means of resilient means (71) supported during the dewatering stage towards the stationary part of the machine relative to the body, such as a dewatering space (6). ). 9. A belt forming zone according to any of claims 4-6, characterized in that suspension of the suspension means 10 (7) is adjustable for control of the load force (F) against the wire. 10. Band forming zone according to claim 9, characterized in that the spring means are controlled by medium pressure blisters, hoses or the like (7; 7 '). 11. Band forming zone according to claim 10, characterized in that the medium is compressible medium, such as air. 20 Tape forming zone according to any one of claims 4-8, characterized in that one or more resilient means (12) supported by the spring means (7), in the mouth (12) of the gaps (13) constitute means for directing mechanical, flock failure. , high-periodic, preferably ultrasonic frequency oscillation against the gaps.