US3916486A

US3916486A - Apparatus for impregnating textile fibers

Info

Publication number: US3916486A
Application number: US328870A
Authority: US
Inventors: Werner Naegeli
Original assignee: Pavena AG
Current assignee: Pavena AG
Priority date: 1972-02-09
Filing date: 1973-02-01
Publication date: 1975-11-04
Anticipated expiration: 1992-11-04
Also published as: AT332348B; GB1396212A; IT976782B; JPS4887195A; AR201828A1; DE2301521A1; DD102083A5; ATA10273A; CS161977B2; FR2171126B1; FR2171126A1; CH563487A5; NL7300474A; BR7300977D0; USB328870I5; ES411285A1

Abstract

Apparatus for continuously impregnating a textile fiber assembly or arrangement with a liquid, comprising a pair of discs and two cover plates arranged at the face sides or end faces of the pair of discs. The cover plates together with the discs form a pressure zone. A collecting or compacting zone is arranged in front of the pressure zone as seen in the direction of the flow of the fiber arrangement. The cover plates in the region of pressure zone, and as seen in the direction of flow of the fiber arrangement, are inclined towards the face sides of the pair of discs.

Description

United States Patent 1191 Naegeli 1 1 Nov. 4, 1975 APPARATUS FOR IMPREGNATING 3,426,389 2/1969 Naegeli 19/66 R TEXTILE FIBERS 3,562,863 2/1971 Fornes 19/288 3,662,439 5/1972 Baken 28/l.6

Inventor: Werner Naegeli, Winterthur,

Switzerland Assignee: Pavena AG, Basel, Switzerland Filed: Feb. 1, 1973 Appl. No.: 328,870

Published under the Trial Voluntary Protest Program on January 28, 1975 as document no. B 328,870.

Foreign Application Priority Data Feb. 9, 1972 Switzerland 1886/72 US. Cl 19/66 R Int. Cl. D01B 3/04 Field of Search 19/66 R, 288; 26/l.6

Primary Examiner-Dorsey Newton Attorney, Agent, or FirmWerner W. Kleeman [57] ABSTRACT Apparatus for continuously impregnating a textile fiber assembly or'arrangement with a liquid, comprising a pair of discs and two cover plates arranged at the face'sides or end faces of the pair of discs. The cover plates together with the discs form a pressure zone. A collecting or compacting zone is arranged in front of the pressure zone as seen in the direction of the flow of the fiber arrangement. The cover plates in the region of pressure zone, and as seen in the direction of flow of the fiber arrangement, are inclined towards the face sides of the pair of discs.

18 Claims, 6 Drawing Figures US. Patent N0 v.4, 1975 Sheet 1of3 3,916,486

COATING MATERIAL 2 US. Patent Nov. 4, 1975 Sheet2of3 3,916,486

U.S. Patent Nov. 4, 1975 Sheet 3 of3 3,916,486

APPARATUS FOR IMPREGNATING TEXTILE FIBERS BACKGROUND OF THE INVENTION The present invention relates to a new and improved apparatus for continuously impregnating a textile fiber assembly or arrangement with a liquid.

The term fiber assembly or arrangement, as employed herein, is intended to designate natural as well as man made stable fibers, such as delivered in the form of a continuous fiber arrangement or structure, e.g. as card or drawframe sliver or as web at the delivery zone of a drafting arrangement. Also, these terms are intended to designate bundles of endless filaments.

The term liquids, as employed herein, is intended to designate water or other solvents or any solutions, dispersions and emulsions of any substances (e.g. adhesives, colorants, etc.) in water and/or other solvents.

The term impregnate, as employed herein, is intended to designate the covering or coating of the individual fibers of the fiber assembly with a liquid coat as well as homogenous, fine droplet-shaped distribution of the liquid throughout the fiber assembly, or combination of both.

Devices for treating a fiber assembly with a liquid are already known to the art, wherein there is employed a pair of discs and in which the fiber assembly is penetrated by a liquid before it passes into a pressure zone formed by a pair of discs and lateral cover plates. At the pressure zone the fiber assembly is condensed under high specific pressure into a compact sliver.

Even if the clearance between the face sides of the pair of discs and its lateral cover plates is maintained as small as possible in such devices, penetration and jamming of fibers passing through the device between the discs and their lateral cover plates cannot be avoided due to the extreme fineness of the fibers. In the delivery zone of the impregnated sliver so-called moustaches or beards build-up from the cover plates and which are formed from previously jammed fibers. Such results in disturbances in the operation.

Further reduction of the clearance between the face sides of the pair of discs and the lateral cover plates only brings temporary relief. Since the clearance is too small, the wear of the discs and/or the lateral cover plates is greatly increased so that jamming of fibers, as described above, again occurs. Also, it has been found that the total clearance between the discs and lateral cover plates in many cases shifts to one side, so that there results a greater clearance on the opposite side of the discs. Jamming of fibers between the discs and their lateral cover plates thus is further facilitated and uniform condensation of the fiber mass in the pressure zone is impaired.

in another prior art device for continuously impregnating a fiber assembly using a pair of discs, the lateral cover plates enclosing the pair of discs with a small clearance are provided with openings at the region of the face sides or end faces of the pair of discs for the introduction of impregnating liquids. In this arrangement the openings for infeeding the liquid can merge into liquid distribution grooves, these grooves being shaped as converging recesses extending outside the pressure zone to the middle of the pressure zone.

The last-mentioned device in comparison with devices previously known to the art already brought the advantages of increased life span of the discs and the lateral cover plates and an improved reduction in the jamming of fibers between the discs and their lateral cover plates at least at the region in front of the pressure zone. The considerably higher requirements in the pressure zone itself, however, were not satisfied by this improved device, as the circular recesses in the cover plates forming wedge surfaces did not extend to the disc outer circumference which is subject to the most severe loads, so that this zone is merely protected against wear by a lubricating film of insufficient load capacity, necessitating exchange of the discs within a relatively short time.

Another disadvantage of this device resides in the fact that recesses creating the hydrodynamic pressure only extend to the middle of the pressure zone. Thus, the hydrodynamic pressure forces are effective only to the middle of the pressure zone. The pressure distribution, however, between two discs pressed against each other is symmetrical with respect to the pressure zone, i.e. increasing from zero to a maximum in the input quadrant of the fiber assembly and decreasing from the maximum to zero in the adjacent delivery quadrant. Due to the decrease of pressure in the delivery quadrant, a suction action is created as the discs and the fiber assembly expand. This suction action is directed from the outer disc circumference towards the disc center. Due to this suction action outer fibers of the impregnated fiber assembly emerging from the pressure zone are sucked from the disc circumference towards the disc center, i.e. between the disc and the lateral cover plate. In this region there is thus caused undesirable jamming of fibers between the disc face sides and the cover plate, resulting in the formation of so-called beards and corresponding disturbances in operation.

SUMMARY OF THE INVENTION Hence, it will be noted from what has been discussed above that this particular field of technology is in need of apparatus constructions for impregnating textile fibers which are not associated with the aforementioned drawbacks and limitations of the prior art proposals. It is therefore a primary object of the present invention to provide a new and improved construction of apparatus for impregnating textile fibers which effectively and reliably overcomes the aforementioned drawbacks and limitations of the state-of-the-art proposals.

Another and more specific object of the present invention relates to an apparatus for impregnating textile fibers in an extremely reliable and efficient manner, wherein the apparatus itself is of relatively simple construction and design, not readily subject to malfunction or breakdown, and requires a minimum of maintenance and servicing.

The inventive apparatus for continuously impregnating a textile fiber assembly or arrangement with liquid embodying a pair of discs and two cover plates arranged at the face sides or end faces of the pair of discs, and forming a pressure zone together with the discs, and having a collecting or compacting zone arranged in front of the pressure zone, as seen in the direction of the flow of the fiber arrangement, eliminates the abovementioned disadvantages in that the cover plates in the region of the pressure zone and as seen in the direction of the flow of the fiber arrangement are inclined towards the face sides or end faces of the pair of discs. The inclination of the cover plates can also extend over the collecting or compacting zone. According to a further embodiment of the invention the inclination can also extend further than or past the pressure zone. At the inclined cover plates, or at a suitable region of the inclined cover plates there can be provided liquid infeed or inlet openings and the inclined portion of each cover plate can be formed by an insert member.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood and objects other than those set forth above, will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:

FIG. 1 illustrates an apparatus for continuously impregnating a fiber assembly with liquids and shown in cross-section, taken substantially along the line II of FIG. 2;

FIG. 2 is a cross-sectional view of the apparatus depicted in FIG. 1, taken substantially along the line lI-II thereof;

FIG. 3 is an alternative embodiment of the apparatus shown in FIG. 1, in cross-sectional view taken substantially along the line III-III of FIG. 4;

FIG. 4 is a cross-sectional view of the apparatus depicted in FIG. 3, taken substantially along the line IVIV thereof;

FIG. 5 is a further variant construction of apparatus depicted in cross-sectional view, taken substantially along the line V-V of FIG. 6; and

FIG. 6 is a cross-sectional view of the apparatus depicted in FIG. 5, taken substantially along the line VIVI thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus for continuously impregnating a fiber assembly or arrangement as depicted in FIGS. 1 and 2 consists of a pair of discs 1 and 2 of the same diameter and lateral cover plates 3 and 4. The cover plate 3 is mounted at the machine frame (not shown). The discs 1 and 2 are rotatably and axially movably supported in the cover plates 3 and 4. The disc 2 is subjected to a suitable load or biasing force and thus is pressed against the disc 1 and adapting itself to the cross-section of the fiber material passing through a pressure zone, generally indicated by reference character 50 in FIG. 1. For each cover plate 3 and 4 there is defined the pressure zone 50 of a length D, a collecting or compacting zone 51 located in front of the pressure zone 50 in the input quadrant and of length E, and a delivery zone 52 following the pressure zone 50 in the delivery quadrant of a length F and extending to the delivery point 5 of the material. The term input quadrant and delivery quadrant respectively, as employed herein, designate the quadrant of the cylindrical surface of the discs 1 and 2, each of which face a fiber assembly entering or delivered respectively from the apparatus. The collecting zone 51 consists of a respective half of a

funnel

6 and 7 arranged at the cover plates 3 and 4 respectively. The two cover plates 3 and 4'are mutually maintained at a distance from one another by means of spacer pins 8 or the like and are rigidly held together by screws 8a or equivalent fastening devices, as best seen by referring to FIG. 2.

The clearance or spacing between the surfaces of the discs 1 and 2 in the pressure zone, i.e. the thickness of a fiber assembly compressed between the discs 50, designated by reference character a in FIG. 1, is a function 1 of a number of variables, for example the mass of fiber material per cross-section of the fiber assembly, the pressure applied between these discs, the specific weight of the fiber material, of the elastic properties of the discs, the liquid content of the impregnated fiber assembly, etc. At the region of the pressure zone 50, and as seen in the direction of flow or movement of the fiber assembly, the cover plates 3 and 4 are inclined towards the face sides or and faces 53 of the pair of discs 1 and 2 (FIG. 2). For this purpose each cover plate 3 and 4 is locally constructed or designed such that, again as seen in the direction of passage or flow of the fiber assembly, over the length G=E+D+F, such cover plates are inclined towards the end faces or face sides 53 of the pair of discs 1 and 2, it being recalled reference character D indicating the length of the pressure zone, E the length of the collecting zone and F the length of the delivery zone to the point of delivery 5, and such inclination extending substantially across the entire width between the disc axes 8 and 8". Within this inclination zone there are furthermore provided for each cover plate 3 and 4 liquid inlet or

infeed openings

9 and 10 respectively through which impregnating liquid can be brought or injected at low pressure into the tapered spaces or clearances 54 formed by the inclined surfaces of the cover plates 3, 4 and the discs 1 and 2.

As further shown in FIG. 2 the discs 1 and 2 are of a width or thickness b. The cover plates 3 and 4 are provided with a

surface

11 and 12 respectively, inclined with respect to the corresponding end faces 53 of the discs 1 and 2 and extending up to the smallest mutual spacing or distance 0 between the cover plates at the point of delivery 5, said distance r: advantageously being chosen to be somewhat larger than the width b of the discs, so as to provide a clearance being adequate for rotation of the discs I and 2. The distance 0 can be chosen for instance, according to the viscosity and the type of liquid employed, the elasticity of the disc material, the pressure applied between the discs 1 and 2, approximately within the range of (b 0.01 mm) to (b 0.3 mm). The

surfaces

11 and 12 respectively of the cover plates 3 and 4, respectively, are inclined with respect to the face sides or end faces 53 of the pair of discs 1 and 2 atan angle a, which for achieving the desired taper effect is, for example, larger than 3 and smaller than 30. The

inclined surface

11 or 12 respectively of the cover plate 3 or 4 respectively can be covered by a coating material, such as hard metal, ceramics, sapphire, ruby and synthetic hard stones, which is harder than the rest of the corresponding cover plate so that there can be prolonged the life of the gliding zones of the cover plates 3 and 4 loaded most by the fiber assembly and the zones at which the flange pressure of the elastic discs 1 and 2 against the cover plates 3 and 4 is greatest.

In the embodiment shown in FIGS. 1 and 2 the

inclined surface

11 and 12 respectively of the cover plate 3 or 4 respectively can be realized by localized shaping or configuring of the cover plates having otherwise parallel surfaces.

In operation the apparatus shown in FIGS. 1 and 2 functions as follows: A continuously infed fiber assembly or arrangment 13, supplied from above in the direction of the arrow depicted in FIG. 1 (the path of the material is shown interrupted for better clarity), is col lected in the collecting zone 51 by means of the

funnel

6, 7 formed by the two

funnel halves

6 and 7, and in the adjacent pressure zone 50 is strongly compressed. Through the

openings

9 and 10 respectively of the cover plates 3 and 4 respectively there is introduced an impregnating liquid and owing to the rotational motion of the discs 1 and 2 this liquid is entrained in the direction of the arrows by the friction at the disc faces and is transported into the increasingly converging space or room 54. Owing to the very small angle a, causing a very intensive taper or wedge action of the clearance space 54, there is realized a very intensive increase in the hydrodynamic pressure in the liquid, under the action of which the impregnating liquid tends to escape laterally. The following effects are caused during this process:

1. The impregnating liquid laterally emerges at the input quandrant of the discs 1 and 2 at their end faces and surrounds the continuously supplied fiber assembly in the

funnel

6, 7 of the collecting zone 51. The fiber assembly is subsequently compressed in the pressure zone 50 during which process excessive liquid contained in the pressure zone 50 laterally escapes over the funnel halves 6 and 7.

2. Over the entire length G of the inclination of the cover plates 3 and 4, or in their inclined zone respectively, the impregnating liquid tends to escape laterally towards the center and the periphery of the discs. This occurs in the input quadrant of the discs as well as in their delivery quadrant below the line connecting the centers of the disc axes 8' and 8", i.e. in the lower part of the pressure zone 50 and in the adjacent delivery zone 52. The liquid which is continuously expelled at the disc periphery over the full length thus prevents any jamming of fibers between the disc end faces 53 and the cover plates 3 and 4 so that formation of beards is also prevented in the delivery quadrant.

3. The film formed by the impregnating liquid over the entire region of inclination of the cover plates 3 and 4, or over their inclined zones or surfaces 1 l and 12 respectively, in which seen in the direction of rotation of the discs, there is generated an increasingly high hydrodynamic pressure, achieves proper lubrication of the disc end faces, which thus can no longer directly contact the inclined surfaces of the cover plates. Wear of the discs due to friction is thus practically eliminated and disc life is thus decisively increased.

The fiber assembly upon passing the delivery point 5 can leave the impregnating apparatus freely or under tension in the form of an impregnated compact fiber assembly or arrangement 14.

The impregnating apparatus shown in FIGS. 3 and 4 constitutes an alternative embodiment of the apparatus from that considered above with respect to FIGS. 1 and 2, identical elements having been generally indicated by the same reference characters. This variant form of apparatus contains a pair of

discs

15 and 16 and lateral

rigid cover plates

17 and 18, the cover plate 17 here also, like the cover plate 3 shown in FIG. 1, is mounted at the machine frame (not shown). The

discs

15 and 16 and the

cover plates

17 and 18 correspond in their functions exactly to the discs 1 and 2 and the cover plates 3 and 4 shown in FIGS. 1 and 2 and thus are not again here described in detail. The impregnating apparatus according to FIGS. 3 and 4 also contains a pressure zone 50 of the length D, a collecting or compact ing zone 51 of the length E containing the funnel halves 19 and 20 respectively, and a delivery zone 52 of the length F.

The apparatus according to FIGS. 3 4 differ from the one shown in FIGS. 1 and 2 in as much as the

cover plates

17 and 18 are maintained at a mutual spacing or distance not by spacer pins but in this case by two tapered

intermediate plates

21 and 22. The

cover plates

17 and 18 and the

intermediate plates

21 and 22 are fastened together by screws 23 or the like and thus form a unit. The

discs

15 and 16 are inserted into the tapered or wedge-like clearance space or room 54 formed between the

cover plates

17 and 18 left open between the

intermediate plates

21 and 22. Seen in the direction of movement of the material, the

intermediate plates

21 and 22 extend to a material delivery edge 24. At this location the fiber assembly leaves the impregnating apparatus and here the distance c between the

intermediate plates

21 and 22 is smallest and only somewhat larger than the width b of the discs 15 or 16 (analogous to the arrangement shown in FIGS. 1 and 2). The

cover plates

17 and 18 also in this case are provided with two

liquid input openings

25 and 26 each of which is located in the input quadrant. The impregnating liquid, as described with reference to the embodiment of FIGS. 1 and 2, is introduced via these

openings

25 and 26 into the clearance space formed between the disc end faces and the cover plates.

Due to this inclined arrangement of the

cover plates

17 and 18 realized by means of the tapered

intermediate plates

21 and 22 tapered or wedge-like clearance spaces 54 are formed between the

cover plates

17 and 18 and the end faces 53 of the

discs

15 and 16, these wedge-like spaces extending to the material delivery point 24, as shown. At the inclined region of the

cover plates

17 and 18 the same geometrical conditions are thus created as were heretobefore described with respect to the embodiment of FIGS. 1 and 2 so that the function and effect of the apparatus according to the showing of FIGS. 3 and 4 is identical, and therefore, need not require further description.

A further variant of the inventive apparatus is depicted in FIGS. 5 and 6. This embodiment of apparatus also corresponds to the one shown in FIGS. 1 and 2, as it contains a pair of

discs

28 and 27 and then laterally arranged

rigid cover plates

30 and 31 maintained at a mutual spacing by spacer pins 29. This apparatus, however, basically differs from the one shown in FIGS. 1 and 2, in as much as each

cover plate

30 and 31 respectively, contains an insert or

inset member

32 and 33 respectively, at the region of the pressure zone 50. These

insert members

32 and 33 are, as viewed in the direction of passage the fiber material inclined towards the end faces 53 of the

discs

27 and 28. In FIGS. 5 and 6

insert members

32 and 33 are of, for instance rectangular shape, and their dimensions are chosen such that, seen in the direction of passage or flow of the fiber material, they extend over the pressure zone 50 and the entire collecting zone 51 and that, seen transversely or at right angles thereto, practically the entire space between the disc axes of the pair of

discs

27 and 28 is covered by the

insert members

32 and 33. The

insert members

32 and 33, however, also can be of any other suitable shape. As compared to the embodiments shown in FIGS. 1 to 4 the embodiment according to FIG. 5 also differs in that the

insert members

32 and 33 are provided with

grooves

34 and 35 which are radially arranged around the disc axes. These

grooves

34 and 35 are flow connected with liquid input or

infeed openings

36 and 37 respectively, arranged externally of the in sert

members

32 and 33 respectively.

According to a further aspect of the embodiment shown in FIGS. and 6 the

insert members

32, 33 can be fabricated from a material which is harder than the material of the

corresponding cover plates

30 and 31, for instance from hard metal, ceramics, sapphire, ruby or other synthetic hard stones. The life span of the inventive impregnating apparatus thus can be substantially prolonged, as the harder materials are more slowly worn by the passing fiber assembly and such inserts can be exchanged whenever they are worn. The life span also can be prolonged by covering the region of the cover plates in the region of the pressure zone with a coat of a material which is harder than the material of the other zones of the cover plates. Once this coat or coating is worn, only such coat must be renewed and the apparatus is again ready for use.

The function of the apparatus according to FIGS. 5 and 6 at the region of the pressure zone is identical to that described in conjunction with the apparatus considered with reference to FIGS. 1 and 2, so that further description of such function can be dispensed with.

The axial dimension b of the discs is by no means limited to the proportions indicated in the drawings, and they can be chosen to.be much larger, i.e. a multiple of the diameter. This choice, of course depends on the fiber assembly or arrangement to be processed.

While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention isnot limited thereto, but may be otherwise variously embodied and practiced within the scope of the following claims.

Accordingly, what is claimed is:

1. An apparatus for continuously impregnating with a liquid a textile fiber arrangement moving in a predetermined direction of travel, comprising a pair of rotatable discs having peripheral faces and end faces, two cover plates arranged at the region of the end faces of said pair of discs, said discs being arranged with said peripheral faces opposite to each other, including a liquid infeed opening in each of said cover plates, said liquid infeed openings, viewed in the direction of travel of the fiber arrangement, being located in front of a line connecting the axes of said pair of discs, said two cover plates together with said pair of discs forming a collecting zone into which impregnating liquid is delivered from said infeed openings of said cover plates, said cover plates, viewed in the direction of travel of the fiber arrangement, having portions inclined towards the end faces of said pair of discs and extending beyond said collecting zone for forming wedge faces covering the end faces of said pair of discs after the collecting zone.

2. The apparatus as defined in claim 1, wherein the inclined portions of said cover plates also extend over the region of the collecting zone.

3. The apparatus as defined in claim 1, wherein the inclined portions of said cover plates, viewed in the direction of travel of the fiber arrangement, extend over the position where the peripheral faces of said pair of discs have the least distance between each other.

4. The apparatus as defined in claim 1, wherein the inclined portions of the cover plates, in a direction transversely with respect to the direction of travel of the fiber arrangement, extend at least over twice the least distance between the peripheral faces of said pair of discs.

5. The apparatus as defined in claim 1, wherein the inclined portions of the cover plates, in a direction transverse to the direction of travel of the fiber arrangement, extend to the axes of the pair of discs.

6. The apparatus as defined in claim 1, wherein the inclined portions of the cover plates, viewed in the direction of travel of the fiber arrangement, extend to a delivery point of the fiber arrangement from the cover plates.

7. The apparatus as defined in claim 1, wherein predetermined localized regions of said cover plates are configured to provide said inclined portions to effect the inclination of said cover plates towards the end faces of said pair of discs.

8. The apparatus as defined in claim 7, wherein the cover plates are otherwise parallel with the exception of the localized inclined portions.

9. The apparatus as defined in claim 1, further including tapered intermediate plates provided for said cover plates defining said inclined portions of said cover plates inclined towards the end faces of the pair of discs.

10. The apparatus as defined in claim 1, further including insert members provided for said cover plates and defining said inclined portions to effect the inclination of said cover plates toward the end faces of said pair of discs.

11. The apparatus as defined in claim 1, wherein the inclination of the portions of said cover plates with respect to the end faces of the discs is greater than 3 and less than 30.

12. The apparatus as defined in claim 1, wherein at least the inclined portions of the cover plates are provided with a coating formed of a material which is harder than the remainder of the corresponding cover plate.

13. The apparatus as defined in claim 10, wherein each of said insert members consists of a wear-resistant material.

14. The apparatus as defined in claim 10, wherein said insert member comprises a hard metal.

15. The apparatus as defined in claim 10, wherein said insert member comprises a ceramic material.

16. The apparatus as defined in claim 10, wherein said insert member comprises sapphire.

17. The apparatus as defined in claim 10, wherein said insert member comprises ruby.

18. The apparatus as defined in claim 10, wherein said insert member comprises synthetic hard stones.

Claims

1. An apparatus for continuously impregnating with a liquid a textilE fiber arrangement moving in a predetermined direction of travel, comprising a pair of rotatable discs having peripheral faces and end faces, two cover plates arranged at the region of the end faces of said pair of discs, said discs being arranged with said peripheral faces opposite to each other, including a liquid infeed opening in each of said cover plates, said liquid infeed openings, viewed in the direction of travel of the fiber arrangement, being located in front of a line connecting the axes of said pair of discs, said two cover plates together with said pair of discs forming a collecting zone into which impregnating liquid is delivered from said infeed openings of said cover plates, said cover plates, viewed in the direction of travel of the fiber arrangement, having portions inclined towards the end faces of said pair of discs and extending beyond said collecting zones for forming wedge faces covering the end faces of said pair of discs after the collecting zone.

11. The apparatus as defined in claim 1, wherein the inclination of the portions of said cover plates with respect to the end faces of the discs is greater than 3* and less than 30*.