GB1598718A

GB1598718A - Method of and a device for adjusting a fibre web profile in a paper machine

Info

Publication number: GB1598718A
Application number: GB23840/78A
Authority: GB
Original assignee: Tampella Oy AB
Current assignee: Tampella Oy AB
Priority date: 1977-09-21
Filing date: 1978-05-30
Publication date: 1981-09-23
Also published as: FI63077C; DE2830046C2; BR7805561A; SE434412B; DE2830046A1; FI772783A; SE7808011L; FI63077B

Description

(54) A METHOD OF AND A DEVICE FOR ADJUSTING FIBER WEB PROFILE IN A PAPER MACHINE (71) We, OY TAMPELLA AB, aFinnish Company, of PL 256 33101 Tampere 10, Finland, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a method of and a device for producing a fiber web in a paper machine.

According to a known method of producing a fiber web, a fiber suspension is fed from a headbox into a forming zone formed between two wires and converging in the flow direction of the fiber suspension, and is subjected to dwatering by means of a pressure difference across both wires in order to form a fiber web between the wires leaving said forming zone.

Web formers with a converging forming zone defined by wires are known from USpatents 3645842, 3 743 571, 3 823 062, 3823064 and 3944464. This kind of web forming method is used for example in the production of multi-ply webs by means of one headbox by supplying fiber streams of different suspensions one upon the other between two converging wires and removing water from said suspensions in the converging forming zone. This zone is a hydraulically sealed space wherein water is removed by means of a pressure difference across the wires while these are travelling through the forming zone supported by dewatering boxes.

It is earlier known from a traditional fourdrinier machine to control the basis weight distribution of the web in the cross machine direction i.e. the transverse profile of the fiber web by adjusting the profile of the slice opening of the headbox and thus also the thickness of the stock jet in the cross machine direction. However, this control method cannot be applied in web formers according to the above-mentioned US patents due to their sealed construction.

The aim of this invention is to provide a method which facilitates the adjustment of the transverse profile of the fiber web in web formers comprising a sealed forming zone as described, and according to the invention there is provided a method of producing a fiber web in a paper machine, comprising feeding a fiber suspension under pressure from a headbox into a pressure-sealed forming zone defined between two wires which converge in the feed direction of the fiber suspension, whereby a difference is established between the pressure acting upon the fiber suspension in the forming zone and the pressure acting upon the opposite sides of the wires respectively and water is thereby removed from the fiber suspension in the forming zone by being forced through the wires to said opposite sides thereof, thus forming a fiber web between the wires leaving the forming zone, and controlling the transverse weight profile of the fiber web by establishing a variation, in a direction transverse to the direction of movement of the wires, in the resistance to flow of water of said opposite side of at least one wire, thereby to vary the pressure difference across said one wire in said transverse direction and consequently establish a variation, in said transverse direction, in the rate of removal of water from the fiber suspension through said one wire in order to cause transverse suspension flows and thereby move fibers in said transverse direction.

By adjusting the pressure difference in different parts of the forming zone in the transverse direction of the wires different amounts of water can be removed in the transverse direction from the fiber suspension into the dewatering boxes. Due to this the fiber suspension is caused to move in the forming zone in the transverse direction of the wires and this makes it possible to affect the transverse profile of the formed fibre web.

The adjustment of the pressure difference across the wire is preferably accomplished by changing the flow resistance in the dewatering box by control means, for example valves.

It is preferable to perform adjustment of the pressure difference in the transverse direction of the wires in several successive points along the wires.

This invention also provides a device for producing a fiber web, comprising two wires, means supporting said wires in converging relationship within a pressure-sealed forming zone of the device, means for driving said wires to move in the direction in which they converge, a headbox for feeding fiber suspension under pressure between the wires in the forming zone in the direction in which the wires converge thereby to establish a difference between the pressure in the forming zone and the pressure on the opposite sides of the wires respectively, the support means comprising dewatering boxes for removing water forced through the wires from the fiber suspension by means of the pressure differece between the forming zone and said opposite sides of the wires, and comprising means for establishing a variation, in a direction transverse to the direction of movement of the wires, in the resistance to flow of water at said opposite side of at least one wire, thereby to vary the pressure difference across said one wire in said transverse direction and consequently establish a variation, in said transverse direction, in the rate of removal of water from the fiber suspension through said one wire in order to cause transverse suspension flows and thereby move fibers in said transverse direction.

In the following the invention will be described in more detail with reference to the accompanying Figures in which: Figure 1 is a diagrammatic illustration of a web former; Figures 2, 4 and 6 are enlarged sectional views of three embodiments of the invention, equivalent to sections taken along line I-I in Figure 1; Figures 3, 5 and 7 are sectional views along lines Ill-Ill, V-V and VIZ VIZ respectively in Figures 2, 4 and 6.

In Figure 1 two wires 1, 2 are passed over rolls 3, 4, 5 to form an evenly converging forming zone 6. In the forming zone, on the outer sides of the wires there are dewatering boxes 7. At the inlet end of the forming zone 6 there is a headbox 8 provided with several manifolds for supplying separate fiber suspensions into the headbox. The separate fiber suspensions flow from the headbox between tbe wires 1, 2 and further through the forming zone 6, in which water is removed from the stock 9. Water removal is effectu aèd by means of a pressuredifference across the wires Each dewatering box 7 is divided by division walls 10, which extend in the transverse direction of the wires, into several sections 7A extending crosswise over the wires and arranged side by side in the longitudinal direction of the wires.Each section 7A is connected with an individually adjustable throttle valve 11 or discharge pump 12, a valve and pump having been shown in Figure 1 for convenience only. The amount of water flowing through the wires from the fiber suspension into each section 7A is controlled by the pressure of the pump or by the throttle valve, whichever is present.

The continuous web 13 formed by the fiber suspension between the wires passes between the wires over the guide rolls 5 and further, supported by the wire 1. to the press section of the paper machine. The wires 1, 2 are returned back to the rolls 3, 4 over stretcher rolls, carrying rolls and guide rolls. This kind of web forming arrangement as such is earlier known and therefore its construction and operation are not described in greater detail.

According to the present invention the construction shown in Figures 2, 3 or 4, 5 or 6, 7 respectively is substituted for one, several or all of the sections 7A.

In Figures 2 and 3 the dewatering box section 7A is divided by division walls 14 extending in the longitudinal direction of the wires into separate compartments 7B, which are located side by side in the transverse direction of the wire 2. Each compartment is provided with a discharge pipe 15 and a valve 16 mounted in the pipe to control the flow of water through said pipe.

If the water flow resistance from a compartment through the outlet pipe is increased by throttling the valve 16, the flow of water from the fiber suspension into this compartment decreases correspondingly. Therefore water tends to flow in the forming zone in the transverse direction towards those compartments where the flow resistance is smaller. At the same time fibers flow with the water away from such a compartment in which the flow resistance is bigger. The object is in this way to control the flow of the fiber suspension in the forming zone by adjusting the water flow resistance and thus the pressure difference across the wire in different parts of the forming zone in the transverse direction, in order to move fibers in said transverse direction to desired places of the forming zone.

In the embodiment according to Figures 4 and 5 section 27A of the dewatering box is divided by means of division walls 24 extending in the longitudinal direction of the wires into compartments 27B located side by side in the transverse direction of the wires. The compartments are further divided by means of transverse walls 21 into two chambers 27B' and 27B" connected with each other by a passage 22 provided in the wall. For each passage there is a valve 26 arranged in the compartment. which valve is operated by an adjusting spindle 28. For all compartments 27B of a section there is a common discharge pipe 25. Also in this case the flow resistance in different compartments of the section is individually adjustable by means of the valves 26.Thus it is possible to control the amount of water flowing into each compartment and hence also the movement of fibers in the transverse direction of the wires as explained above.

In the embodiment according to Figures 6 and 7 the section 37A of the dewatering box is divided by means of only one transverse division wall 31 into two compartments 37B' and 37B" which are connected with each other by means of a slot 32 provided in the division wall, which slot extends substantially over the section in the transverse direction of the wires. The slot is covered on one side by a flexible strip 36 which is fastened to the spindles 38 supported by the section. The section is provided with a discharge pipe 35.

By displacing the strip 36 by means of the spindles 38 closer to or apart from the slot the flow resistance through the slot can be either increased or decreased locally in the longitudinal direction of the slot to accomplish the desired flow of water and fibers in the transverse direction of the wire.

The object of the drawings and the specification is only to illustrate the idea of the invention. In details the method and the device according to the invention can vary considerably within the scope of the claims.

WHAT WE CLAIM IS: 1. A method of producing a fiber web in a paper machine, comprising feeding a fiber suspension under pressure from a headbox into a pressure-sealed forming zone defined between two wires which converge in the feed direction of the fiber suspension, whereby a difference is established between the pressure acting upon the fiber suspension in the forming zone and the pressure acting upon the opposite sides of the wires respectively and water is thereby removed from the fiber suspension in the forming zone by being forced through the wires to said opposite sides thereof, thus forming a fiber web between the wires leaving the forming zone, and controlling the transverse weight profile of the fiber web by establishing a variation, in a direction transverse to the direction of movement of the wires, in the resistance to flow of water at said opposite side of at least one wire. thereby to vary the pressure difference across said one wire in said transverse direction and consequently establish a variation, in said transverse direction, in the rate of removal of water from the fiber suspension through said one wire in order to cause transverse suspension flows and thereby move fibers in said transverse direction.

2. A method as claimed in claim 1, wherein the said variation in pressure difference is established in a plurality of separate regions along the direction of movement of the wires.

3. A method as claimed in claim 2, wherein the separate regions are successively disposed in said direction of movement.

4. A method as claimed in claim 1, 2 or 3, wherein the variation in the flow resistance is established by establishing different flow resistances in a plurality of separate areas along said direction transverse to the direction of movement of the wires.

5. A device for producing a fiber web, comprising two wires, means supporting said wires in converging relationship within a pressure-sealed forming zone of the device, means for driving said wires to move in the direction in which they converge, a headbox for feeding fiber suspension under pressure between the wires in the forming zone in the direction in which the wires converge thereby to establish a difference between the pressure in the forming zone and the pressure on the opposite sides of the wires respectively, the support means comprising dewatering boxes for removing water forced through the wires from the fiber suspension by means of the pressure difference between the forming zone and said opposite sides of the wires, and comprising means for establishing a variation, in a direction transverse to the direction of movement of the wires, in the resistance to flow of water at said opposite sides of at least one wire,. thereby to vary the pressure difference across said one wire in said transverse direction and consequently establish a variation, in said transverse direction, in the rate of removal of water from the fiber suspension through said one wire in order to cause transverse suspension flows and thereby move fibers in said transverse direction.

6. A device as claimed in claim 5, wherein the dewatering boxes are divided into separate transverse sections located side by side in the direction of movement of the wires, and at least one of said sections is divided into separate compartments located side by side in said transverse direction, which compartments are each provided with a water passage and said passages are provided with means for adjusting the resistance to flow of water from the compartments respectively.

7. A device as claimed in claim 5, wherein each compartment is provided with a discharge pipe and a valve for adjusting the resistance to flow of water through said pipe.

8. A device as claimed in claim 6, wherein said section of the dewatering box is provided with a discharge pipe, and each compartment of said section is provided with

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. passage 22 provided in the wall. For each passage there is a valve 26 arranged in the compartment. which valve is operated by an adjusting spindle 28. For all compartments 27B of a section there is a common discharge pipe 25. Also in this case the flow resistance in different compartments of the section is individually adjustable by means of the valves 26. Thus it is possible to control the amount of water flowing into each compartment and hence also the movement of fibers in the transverse direction of the wires as explained above. In the embodiment according to Figures 6 and 7 the section 37A of the dewatering box is divided by means of only one transverse division wall 31 into two compartments 37B' and 37B" which are connected with each other by means of a slot 32 provided in the division wall, which slot extends substantially over the section in the transverse direction of the wires. The slot is covered on one side by a flexible strip 36 which is fastened to the spindles 38 supported by the section. The section is provided with a discharge pipe 35. By displacing the strip 36 by means of the spindles 38 closer to or apart from the slot the flow resistance through the slot can be either increased or decreased locally in the longitudinal direction of the slot to accomplish the desired flow of water and fibers in the transverse direction of the wire. The object of the drawings and the specification is only to illustrate the idea of the invention. In details the method and the device according to the invention can vary considerably within the scope of the claims. WHAT WE CLAIM IS:

1. A method of producing a fiber web in a paper machine, comprising feeding a fiber suspension under pressure from a headbox into a pressure-sealed forming zone defined between two wires which converge in the feed direction of the fiber suspension, whereby a difference is established between the pressure acting upon the fiber suspension in the forming zone and the pressure acting upon the opposite sides of the wires respectively and water is thereby removed from the fiber suspension in the forming zone by being forced through the wires to said opposite sides thereof, thus forming a fiber web between the wires leaving the forming zone, and controlling the transverse weight profile of the fiber web by establishing a variation, in a direction transverse to the direction of movement of the wires, in the resistance to flow of water at said opposite side of at least one wire. thereby to vary the pressure difference across said one wire in said transverse direction and consequently establish a variation, in said transverse direction, in the rate of removal of water from the fiber suspension through said one wire in order to cause transverse suspension flows and thereby move fibers in said transverse direction.

a division wall which separates a part of the compartment facing the wire from the discharge pipe and which is formed with said passage.

9. A device as claimed in claim 5, in which the dewatering boxes are divided into separate transverse sections located side by side in the direction of movement of the wires. and wherein at least one of said sections is provided with a slot extending across said section, said slot being provided with means for local adjustment of the resistance to flow of water through said slot.

10. A device as claimed in claim 9, wherein said section is provided with a discharge pipe and is also provided with a division wall which separates a part of the section facing the wire from said discharge pipe and which is formed with said slot, and wherein the adjustment means comprise a flexible strip extending along said slot and adjusting spindles connected to the flexible strip and spaced apart from one another in the longitudinal direction of the strip for displacing the strip locally towards or away from said slot.

11. A device as claimed in any of claims 6 to 10, wherein several of said transverse sections are each provided with means for establishing a variation, in said transverse direction, in the resistance to flow of water at said opposite side of said one wire.

12. A method of producing a fiber web in a paper machine, according to claim 1 and substantially as herein described.

13. A device for producing a fiber web, substantially as herein described with reference to Figures 2 to 7 of the accompanying drawings.