GB2123863A

GB2123863A - Dandy-roll assembly for top- draining a wet web on a fourdrinier machine

Info

Publication number: GB2123863A
Application number: GB08318503A
Authority: GB
Inventors: Emil Holz
Original assignee: Hermann Finckh Maschinenfabrik GmbH and Co
Current assignee: Voith Finckh Fiber Systems GmbH and Co KG
Priority date: 1982-07-21
Filing date: 1983-07-08
Publication date: 1984-02-08
Also published as: FR2530690B1; DE3227189A1; FR2530690A1; SE457540B; SE8304072L; SE8304072D0; GB8318503D0; GB2123863B; DE3227189C2

Abstract

A dandy-roll assembly 26 for top- draining a wet web 22 carried on a Fourdrinier wire 18, comprises a screen drum or dandy roll 28 which is rotatably mounted and adapted to be placed on top of the wet web and a suction box 70 arranged in the ascending circumferential region of the rotating drum or roll on the outer periphery of the latter. The screen drum or roll comprises a filter mesh 46 supported on an inner cylinder 34 and has at least one circumferentially extending channel formed therebetween. <IMAGE>

Description

SPECIFICATION Dandy-roll assemblyfordraining a fibre pulp web in a fourdrinier machine The invention relates to a dandy-roll assembly for draining a web offibre pulp material which is supported on the endlessweb of an endless wet machine of the Fourdriniertype, the assembly comprising a rotatably mounted screen drum or dandy-roll adapted to be applied to the upper sidle of the fibre web and a suction box arranged on said drum for the upper sidle draining ofthefibre pulp.

Particularly in the manufacture of paper upon which it is intended to write or print on both sides thereof it is not enough to draw the water out of the fibre pulp web in a wet machine onlyto one side ofthe web because in that case the fine particles in the fibre pulp which is fed into the endless wet machineto form the web, will be dragged mainlyto one side so that it becomes difficult, or even impossible, to write or print on the other side ofthe finished product.It is for this reason that so-called screen-drum formers have become known in recent years, which are in essence endless wet-Fourdrinier machines in which an endless upper web, running over several backing rolls, is pressed from above againstthe screen drum, with a suction box being arranged inside the drum to suck out the water which has entered into this upper web. However, this kind of upper ortop-web assembly makes the bilateral water extraction from the fibre pulp strip comparatively expensive, even though it offers certain advantages, such as,for example, the facility of running the screen drum at relatively high speeds but at the sametime draining the fibre pulp with the desired degree of efficiency.

It is also already known to arrange a suction box in a dandy-roll which is constructed as a screen drum, in orderto suck out the waterwhich enters the dandy roll from the wetfibre pulp. However, if in an endless wet-machine of the Fourdrinier type thefibre pulp web which is supported on the Fourdrinierweb, is topdrained by means of this known kind of device, the wet part ofthe machine may be operated at relatively slow speeds only because the vacuum which is applied inside the dandy-roll cannot be arbitrarily increased since there is a riskthatthefibre pulp web may be lifted offthe Fourdrinier web.An increase inthespeed of rotation of the dandy-roll, which is inevitably entailed byan increase in Fourdrinierwebspeed, gives rise to higher centrifugal forces being applied to thewaterwhich enters into the dandy-roll so that water-spin-off can be prevented only by increasing the vacuum, whilst, on the other hand, it is of vital importance that no water drops should be flung centrifugally offthe dandy-roll because such water drops could easily mark and thus spoil the finished product.

The object ofthe present invention is to provide a dandy-roll assemblyforthe purpose specified in a simple and convenient form.

According to the invention a dandy-roll assembly for draining a web offibre pulp material carried on the endlesswebofan endlesswet machine ofthe Fourdriniertype, comprising a rotatably mounted screen drum or dandy-roll adapted to be placed on top ofthe fibre strip with a filter mesh forming its peripheral outer wall and a suction box arranged at the outer periphery ofthe screen drum, characterised in that the screen drum comprises a circumferentially closed inner cylinder carrying the filter mesh and between the same and the filter mesh at least one channel extending in the circumferential direction thereofwhich is sealed intheaxial direction relativeto the endsides ofthe screen drum, and in that, for extracting water by suction from the filter mesh the suction box is arranged in the ascending circumferential region of the screen drum.

The basic idea of the invention thus resides in exploiting thefactthat adhesion force, assisted by vacuum, will cause the waterwhich has been transferred from the wet pulp web to the filter mesh ofthe screen drum, to be retained in the mesh openings of the extremely fine-meshed outer filter fabric jacket againstthe action of centrifugal forces until the point is reached where the suction box is connected to the periphery of the screen drum and there actually sucks this water out of the mesh openings.If the screen drum is provided with a peripherally closed inner cylinder and with at least one channel extending in the circumferential direction of said cylinder, or with a plurality of channels which also extend at least partially in the circumferential direction between the outerfilter mesh and inner cylinder, the vacuum applied by the suction box to these channels can propagate over part of the peripheral region of the drum into the region where the drum sits on top ofthe wetfibreweb.Also,whenusingadandy-roll assem- bly according to the invention because of the axial seal which is provided for the peripheral channels at least relative to the end-sides ofthe drum, only a relatively modest vacuum is needed in view of the fact that the suction box may start directly above the fibre web so thatthe waterwhich is being drained from the fibre web into the screen drum requires to be lifted only by a comparatively small height difference and to be retained in the drum only over a relatively short circumferential sectorofdrum rotation before it is extracted from the drum bythe suction box.

In a known dandy-roll assembly (FR-PS 553 198) with a screen drum which is completely open at both sides thereof and in which the peripheral wall ofthe screen drum consists of a fine filter mesh fabric, a suction box is arranged above the highest point of the drum and sucks off any dirt adhering to the filter mesh in orderto prevent marking, or even hole-piercing in the fibre web. However, due to the completely open-ended configuration ofthe screen drum this suction box cannot produce a vacuum inside the drum.

Compared to the earlier mentioned double screenformers, a dandy-roll assembly according to this invention, besides demanding considerably less capital outlay, has the added advantage of lower running costs because, whereas with a double screenformer a relatively powerful vacuum is needed for the suction box in the upperfilter mesh to draw the water up and out ofthefibre web, in the arrangement according to this invention just the pressure applied by the screen drum to the web fibre web assures that waterflowsoutofthewetfibre into the drum and, as already mentioned, only a relatively modest vacuum is needed to transferthe water, once this is in the cylinder, to the suction box.Lastly, using a dandy-roll assembly according to this invention it is no longer necessaryto evacuate all, or a large part ofthe screen drum but only the radially comparatively narrow annularzone between the outerfiltermesh and the inner cylinder.

In orderto provide a plurality of circumferentially directed channels between the filter mesh and the inner cylinder it is recommended to use fins or strips extending in the circumferential direction ofthe cylinderwhich supportthefiltermesh fabric either directly or indirectlywith the aid offurthersupporting elements and between them define such channels.

Such fins may be formed intregrallywith the inner cylinder, for example by milling or cutting circum ferential grooves inthe cylinderwall. However, it is much cheaper and easier ifthe said fins are obtained by means of stretched rings of sheet metal set upright on their narrow edges and fixed e.g. by welding, to the peripheral wall ofthe inner cylinder.

In order to assure a good and even supportforthe filter mesh jacket it is further advisable to interconnect adjacent fins by means of cross bridges which are radially spaced away from the innercylinderwall in order notto interrupt the continuous circumferential channels and which carry the filter mesh fabric. These bridges may consist, in a manner known peruse, of sheet metal rings set upright on their narrow edges and bent to a meander shape, which affords particularly low production costs. It is also an advantage if these bridges, orthese meander-shaped rings of sheet metal project slightly in the radial direction over the circumferentially extending fins so thatthe filter mesh fabric rests only on the said bridges.In this way it is possible to avoid the risk of marking on the topside of thefibre web which could otherwise be caused by water drops driven out radially by centrifugal force along the side walls of the circumferentially directed fins and coming directlyintocontactwiththefilter mesh.

In orderto ensure that the vacuum is applied bythe suction box with maximum uniformity along the wall ofthe screen drum it is recommended to interconnect the channels in the axial direction through openings in the fins, and where these fins consist of up-ended sheet metal rings of meander shape such openings are best arranged next to the innercylinderwall so as not to obstructthe subsequentfitting ofthe meandershaped rings to said fins bearing in mind thatthese meander-rings are to be spaced radially away from the inner cylinder.

A simple draining facilityforthe water which has been sucked out ofthe screen drum and also a simple way of sealing the suction box is obtained ifthe latter is provided on its underside with an outlet into which extends a syphon having an overflow of which the actual overflow-edge or lip is situated at a higher level than the bottom edge ofthe suction box outlet. The vacuum may then be applied laterally to the suction boxandthewaterflowing down and outofthe box provides an effective seal for the box.

In the manufacture of the screen drum for the dandy-roll assembly according to this invention it is recommended to adaptthe height, as measured in the radial direction, ofthe channels between filter mesh jacket and innercylinderto the amount ofwaterwhich isto be extracted inthewetmachineforeach revolution ofthescreen drum.

Finally, it is an advantage if a water-spraying device, particularly a spray-pipe is arranged behind the suction box, as viewed in the direction of screen drum rotation, forthe purpose of cleaning the screen drum.

Further characteristics, advantages and particulars ofthe invention will arise from the following description and the accompanying drawings showing a particularly attractive embodiment of a dandy-roll assembly according to this invention; In the drawings: Figure 1 is part of a vertical longitudinal section through a Fourdrinier machine having a dandy-roll assembly, Figure 2 is a section through one end region ofthe screen drum ofthe said dandy-roll assembly, taken on line 2-2 of Figure 1, Figure 3 shows detail "A" from Figure 1 ,to an enlarged scale, Figure 4 is a section taken on line 4-4 in Figure 3, and Figure is a top view ofthe parts shown in Figure4, as viewed in the direction of arrow B but without the outer filter mesh jacket of the screen drum.

Figure 1 shows a machine bed orbase 10 of an end less wet machine of the Fourdriniertype, which, by means of appropriate supports, not shown, carries atable 12with longitudinal beams 14.

Between two such relatively transversely spaced apart longitudinal beams 14there is arranged a plurality of rotatably mounted backing rolls 16 over which runs the endless Fourdrinierweb 18 of the machine. In the usual way this is an endless belt of filter mesh driven in the direction ofthe arrow shown in the drawing by appropriate driving means, not shown. Beneath this web several suction boxes 20 are arranged along the length oftable 12 and secured to the longitudinal beams 14 by means of which suction boxes 20 a strip of wet fibre pulp 22 which has been applied to the web 18 can be drained in the downward direction. The endless wet Fourdrinier machine so far described is conventional and no further description is needed.

In orderto enablethewetfibreweb 22to be drained upwardly, a dandy-roll assembly generally designated 26 is provided which comprises a screen drum 28 ofwhich the shaft 30 extends parallel with table 12 and at right angles to the direction of movement of the Fourdrinierweb 18. As will be seen from Figure 2, the shaft 30 is a divided or split shaft and by means of supporting and end plates 36,38 carries an inner screen drum cylinder 34. This inner cylinder consists of metal and has a plain, that is to say closed or non-perforated wall which is provided with relatively spaced circumferentially directed fins 40, which consist of stretched rings of sheet metal placed upright on their narrow edges and welded to the outerwall ofthe inner cylinder 34. Between the fins 40 there are bridges 42 which areformed by meandershaped rings 44 welded to the fins 40 and again consisting of sheet metal rings bentto meander configuration and placed upright on their narrow edges, On top of these bridges 42 and the fins 40 rests a filter mesh fabric 46 which is shown in the drawings in the form of a single-layer mesh fabric jacket but which in practice comprises at least two such layers, namely an outer, extremely fine-meshed metal or plastic-wire mesh and an inner, coarser supporting mesh fabric The screen drum 28 is mounted on bearing blocks 48secured to the longitu dinal beams its which are hingedly secured two bearing arms orlevers SD receiving the drum between them The drum shaft 30 is mounted in these bearing leversandthe distance between the drum shaft 30 and the Fourdrinier web 18 is adjusted by means of carrying bolts 52 extending between the beams l4andthe levers 50 and enabling precision adjustmentin respect of the pressure under which the screen drum 28 is pressed against the wet fibre web 22 To this end the bolts 52 are provided with oppositely directed threads (see Figure 2) which engage in corresponding threaded holes provided in the beams and in the bearing levers 50. One end ofthe drum shaft 30 passesthroughthe associated bearing arm 50 and is operatively connected with the shaft of a driving motor 54.

The construction of the screen drum 28 will now be more particularly described with reference to Figures 3to 5. Between the wall ofthe innercylinder34,the fins 40 and the meander-rings 44 define a plurality of channels 60 which extend in the circumferential direction ofthescreen drum 28 and which intercommunicate through openings 62 provided in the fins 40 adjacent the inner cylinder 34 butwhich are sealed off in the axial direction by the end-plates 38 extending radially right up to the mesh fabric 46.

The meander-shaped rings44which are secured to fins 40 in spaced relation with the inner cylinder 34 are formed with cut-outs or recesses 64 in those parts thereof which run parallel to said fins 40, which has the advantage that the over all thickness of the grid structure which supports the filter mesh fabric 46 is not greater in those regions where the said meanderrings are secured to the fins 40 than in any other region of the structure.

Asuction box, generally designated 70 is mounted on the longitudinal beams 14 and embraces, or covers the ascending peripheral sector of the screen drum 28which is driven by the motor 54 in the direction of the arrow shown in Figure 1. The suction box communicates by means of a suction pipe 72 connected to a lateral wall thereof, with a suction fan 74 which maintains a certain vacuum within the box.

To this end the suction box is sealed relative to the screen drum 28 by means of sealing strips 78 which co-act with the screen drum 28 to form a gap-seal.

Such gap-seals are known and consist essentially of nothing more than a narrow gap which is sealed by water constantly entering into this gap.

Behind the suction box 70, as viewed in the direction of rotation of the screen drum, there is arranged a further box 80 in which is arranged a spray pipe 82, extending alongside the drum 28 whereby water is sprayed against the outside ofthe screen drum 28 in orderto dean the liiter raesh 46 and the supporting structure therebeneath The box 80 is also provided with. a seal consisting of a sealing lip 84 made of felt which brush es the screen drum 28.

At the lower end of suction box 70 a discharge or outiet pipe 86 opens into the box 70 and extends into a syphon 88 of which the overflow edge 90 is situated at a higher level than the lower end of the discharge pipe 86, The outlet pipe of syph on 88 is shown at 92 This arrangement ensures that there will beno oss of vacuum through the discharge pipe 86.

When the screen drum m 28 is pressed against the wetfibre web 22water passesfrom thefibrethrough the filter mesh 46 inte the space between the inner cylinder 34 and the filter mesh 46 and the vacuum which is applied to this space prevents, even with a fast rotating screen drum, such waterfrom being flung back onto the wet fibre web 22 by centrifugal force On reaching the suction box7ûthe water contained in the mesh is sucked out ofthefilter mesh 46 and subsequently runsoff.

The extent or measure of top-draining action applied to the fibre web 22 can be regulated by means ofthe vacuum in suction box 70 end by means ofthe bolts 52 which adjust the pressure applied bythe screan drum 28 to the fibre web.

Obviously the dandy-roll assembly must not be arranged precisely in the active region of one ofthe drainage elements, such as one ofthesuction boxes 20. which are arranged belowthe Fcurdrinierweb 1.

The foregoing reveals an essential characteristic of the invention to reside in that the screen drum comprises, between the cuter filter mesh and the inner periphery of the inner cylinder at least one vacuum space or chambsr which extends along the ecreen-clrum circumference.This is sealed to the exterior by the filter mesh, water being retained in the mesh apertures by adhesion against the force which corresponds to the difference between the centrifug a and vacuum forces, with the exception of that particular region in which the vacuum is actually applied to the screen drum and draws the water out of the filter mesh.

@LA@VIS 1. Adandy-roll assembly for draining a web of fibre pulp material caried on the en dless web of an en dless wet machine of the Four drinier type, com prising a rotatably mounted screen drum or dandy roll adapted to be placed on top of the fibre strip with a filter mesh forming its peripheral outer wall and a suction box arranged at the outer periphery ofthe screen drum, characterised in that the screen drum comprises a circumferentially closed inner cylinder carrying the filter mesh and between the same and the filter mesh at least one channel extending in the circumferential direction there of which issealed in the axial direction relative to the endsides ofthe screen drum, and in that, for extracting water by suction form the filter mesh the suction box is arranged in the ascending circumferential region of the screen drum.

2. Adandy-roll assembly according to Claim 1.

characterised by the provision on the inner cylinder of fins extending in the circumferential direction of the cylinder which support the filter rnesh and between them define the said channels.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. configuration and placed upright on their narrow edges, On top of these bridges 42 and the fins 40 rests a filter mesh fabric 46 which is shown in the drawings in the form of a single-layer mesh fabric jacket but which in practice comprises at least two such layers, namely an outer, extremely fine-meshed metal or plastic-wire mesh and an inner, coarser supporting mesh fabric The screen drum 28 is mounted on bearing blocks 48secured to the longitu dinal beams its which are hingedly secured two bearing arms orlevers SD receiving the drum between them The drum shaft 30 is mounted in these bearing leversandthe distance between the drum shaft 30 and the Fourdrinier web 18 is adjusted by means of carrying bolts 52 extending between the beams l4andthe levers 50 and enabling precision adjustmentin respect of the pressure under which the screen drum 28 is pressed against the wet fibre web 22 To this end the bolts 52 are provided with oppositely directed threads (see Figure 2) which engage in corresponding threaded holes provided in the beams and in the bearing levers 50. One end ofthe drum shaft 30 passesthroughthe associated bearing arm 50 and is operatively connected with the shaft of a driving motor 54. The construction of the screen drum 28 will now be more particularly described with reference to Figures 3to 5. Between the wall ofthe innercylinder34,the fins 40 and the meander-rings 44 define a plurality of channels 60 which extend in the circumferential direction ofthescreen drum 28 and which intercommunicate through openings 62 provided in the fins 40 adjacent the inner cylinder 34 butwhich are sealed off in the axial direction by the end-plates 38 extending radially right up to the mesh fabric 46. The meander-shaped rings44which are secured to fins 40 in spaced relation with the inner cylinder 34 are formed with cut-outs or recesses 64 in those parts thereof which run parallel to said fins 40, which has the advantage that the over all thickness of the grid structure which supports the filter mesh fabric 46 is not greater in those regions where the said meanderrings are secured to the fins 40 than in any other region of the structure. Asuction box, generally designated 70 is mounted on the longitudinal beams 14 and embraces, or covers the ascending peripheral sector of the screen drum 28which is driven by the motor 54 in the direction of the arrow shown in Figure 1. The suction box communicates by means of a suction pipe 72 connected to a lateral wall thereof, with a suction fan 74 which maintains a certain vacuum within the box. To this end the suction box is sealed relative to the screen drum 28 by means of sealing strips 78 which co-act with the screen drum 28 to form a gap-seal. Such gap-seals are known and consist essentially of nothing more than a narrow gap which is sealed by water constantly entering into this gap. Behind the suction box 70, as viewed in the direction of rotation of the screen drum, there is arranged a further box 80 in which is arranged a spray pipe 82, extending alongside the drum 28 whereby water is sprayed against the outside ofthe screen drum 28 in orderto dean the liiter raesh 46 and the supporting structure therebeneath The box 80 is also provided with. a seal consisting of a sealing lip 84 made of felt which brush es the screen drum 28. At the lower end of suction box 70 a discharge or outiet pipe 86 opens into the box 70 and extends into a syphon 88 of which the overflow edge 90 is situated at a higher level than the lower end of the discharge pipe 86, The outlet pipe of syph on 88 is shown at 92 This arrangement ensures that there will beno oss of vacuum through the discharge pipe 86. When the screen drum m 28 is pressed against the wetfibre web 22water passesfrom thefibrethrough the filter mesh 46 inte the space between the inner cylinder 34 and the filter mesh 46 and the vacuum which is applied to this space prevents, even with a fast rotating screen drum, such waterfrom being flung back onto the wet fibre web 22 by centrifugal force On reaching the suction box7ûthe water contained in the mesh is sucked out ofthefilter mesh 46 and subsequently runsoff. The extent or measure of top-draining action applied to the fibre web 22 can be regulated by means ofthe vacuum in suction box 70 end by means ofthe bolts 52 which adjust the pressure applied bythe screan drum 28 to the fibre web. Obviously the dandy-roll assembly must not be arranged precisely in the active region of one ofthe drainage elements, such as one ofthesuction boxes 20. which are arranged belowthe Fcurdrinierweb 1. The foregoing reveals an essential characteristic of the invention to reside in that the screen drum comprises, between the cuter filter mesh and the inner periphery of the inner cylinder at least one vacuum space or chambsr which extends along the ecreen-clrum circumference.This is sealed to the exterior by the filter mesh, water being retained in the mesh apertures by adhesion against the force which corresponds to the difference between the centrifug a and vacuum forces, with the exception of that particular region in which the vacuum is actually applied to the screen drum and draws the water out of the filter mesh. @LA@VIS

1. Adandy-roll assembly for draining a web of fibre pulp material caried on the en dless web of an en dless wet machine of the Four drinier type, com prising a rotatably mounted screen drum or dandy roll adapted to be placed on top of the fibre strip with a filter mesh forming its peripheral outer wall and a suction box arranged at the outer periphery ofthe screen drum, characterised in that the screen drum comprises a circumferentially closed inner cylinder carrying the filter mesh and between the same and the filter mesh at least one channel extending in the circumferential direction there of which issealed in the axial direction relative to the endsides ofthe screen drum, and in that, for extracting water by suction form the filter mesh the suction box is arranged in the ascending circumferential region of the screen drum.

2. Adandy-roll assembly according to Claim 1.

3. Adandy-roll assemblyaccording to Claim 2,

characterised in that adjacent fins are mutually connected by bridges which are radially spaced away from the innercylinderand supportthefilter mesh.

4. Adandy-roll assembly according to Claim 1, characterised in that the fins are formed bystretched sheet-metal rings placed upright on their narrow edges.

5. Adandy-roll assembly according to Claim 3, characterised in thatthe bridges are formed by sheet metal rings bent to meander-configuration and placed upright on their narrow edges.

6. Adandy-roll assembly according to any one of Claims 24, characterised in thatthe channels inter communicate in the axial direction through openings provided in the fins.

7. Adandy-roll assembly according to Claim 6, characterised in that said openings in the fins adjoin the inner cylinder.

8. A dandy-roll assembly according to any one of Claims 1-7, charactenised in that the height of the channels, measured in the radial direction, is selected in accordance with the amount of water which is to be extracted bysuctionforeach revolution of the screen drum.

9. Adandy-roll assembly according to anyone of the preceding claims, characterised inthatthe suction box is provided with 3 bottom outlet pipe which extends into a syphon, the syphon having an overflow of which the overflow-edge is situated at a higher level than the bottom edge ofthe suction-box outlet pipe.

O. Adandy-roll asscmc";y according to any one of the preceding ciaims, characterised in that a pipe leading to a suction fan is ccrnected to a sidewall of the suction box.

11. Adandy-roll assembly according to any one of the preceding claims, characterised in thata water spraying device is arranged behind the suction box considered inthedirection screen drum rotation forthe purpose ofcleaning the screen drum.

12. Adandy-roll assemblyaccording to any one of the preceding claims, characterised in thatthefrontal boundaryofthesuction box considered in the direction of rotation ofthe screen drum is situated onlyveryslightiyabovethe lower portion ofthe screen drum circumference.

13. Adandy-rollassemblyfordrainingawebof fibre pulp material carried on the endless web of an endless wet machine of the Fourdriniertype compris- ing the combination and arrangement of parts substantially as hereinbefore described with refer enceto the accompanying drawings.