US 3467576 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
Sept. 16, 1969 uss D'A. CLARK 3,467,576
CONTINUOUS TREATMENT OF FIBROUS MATERIAL AND APPARATUS Filed Dec. 18, 1967 5 Sheets-Sheet 1" FIG. 1
W000 ELEMENTS INVENTOR James dZZ. Clark 5% M,M (H2595 p 16, 1969 JAMES D'A. CLARK 3,467,576
CONTINUOUS TREATMENT OF FIBROUS MATERIAL AND APPARATUS Filed Dec. 18, 1967 5 Sheets-Sheet 2 W000 ELEMENTS Sept. 18, 1969 JAMES D'A. CLARK 3,467,576
CONTINUOUS TREATMENT OF FIBROUS MATERIAL AND APPARATUS Filed Dec. 18, 1967 5 Sheets-Sheet 3 firs. 7
Chips I 52 Y -j m i 32.5 fi I Speni 1 17110,"
(Eda! Coliq a clslrcd) k United States Patent US. Cl. 162-237 16 Claims ABSTRACT OF THE DISCLOSURE An apparatus and process for the treatment of fibrous material with treating liquids in which use is made of an elongate passage with means for introducing a fibrous material into one end portion of the passage and introduction of treating liquid into an intermediate portion of the passage with means for draining treating liquid from the one end portion of the passage and removing treated fibrous material from the other end portion of the passage and including a reciprocating pusher mounted in the passage for reciprocal axial movement with pusher arms inclined in the direction away from the one end of the passage to effect endwise displacement of the fibrous material in the same direction therewith during movement in the direction away from the one end portion of the passage and for disturbing the fibrous material for redistribution in the passage during return movement without substantial axial displacement of the fibrous material therewith thereby to permit efiecting a substantially uniform countercurrent flow through the passage between the fibrous material and treating liquid and which includes means for introducing wash water into the passage beyond the region for introduction of treating liquid whereby the wash water engages the fibrous material subsequent to contact with the treating liquid to leach treating liquid from the fibrous material before removal from the passage and which may include the introduction of steam into the passage beyond the region for introduction of the treating liquid but before introduction of the wash water to raise the wash water to elevated temperature while in contact with the treated fibrous material.
This is a continuation-in-part of my copending application Ser. No. 368,917, filed May 20, 1964, and now abandoned, and entitled Continuous Digester.
This invention relates to the treatment of fibrous material, preferably of the cellulosic type and the like. The apparatus of this invention is particularly suitable for operations which involve the production or treatment of pulp, such for example as digesting wood elements or bleaching or washing or similar treatment thereof.
It has long been recognized that mechanical action on fibrous materials, during digestion at elevated temperatures, adversely affects the quality of the resulting product. For example, treating apparatus which incorporates screw conveyors imparts a rubbing action and compacting action which usually materially reduces the strength of the resulting pulp. Such apparatus requires appreciable energy for operation and still is not sufficiently effective to maintain the contents in uniform distribution. It is difficult to effect uniform countercurrent flow between treating liquid and pulp materials impelled through apparatus with a screw or drag conveyor. For certain steps in the processing of pulp, as during the preliminary stage of cooking or during the final stage of cooling the pulp in digesting ap paratus, countercurrent flow of liquid and pulp is highly desirable.
Patented Sept. 16, 1969 The present invention provides a vessel for the continuous direct or countercurrent flow between treating liquids and fibrous material which vessel comprises a main body portion defining a passage having openings for the introduction and removal of fibrous material and treating liquids, and in which reciprocal pusher means are provided along a substantial portion of the passage for displacement of the solid fibrous material in one direction while enabling countercurrent flow of treating liquors in the opposite direction and in which the passage may be of U-shape or straight tubular configuration.
In a particular form of the apparatus, there is provided an inlet adjacent one end of the passage for introduction of fibrous material and an outlet adjacent the other end of the passage for the removal of fibrous material, and one or more openings located between said ends for the introduction of treating liquids, and one or more openings before said latter openings for the removal of treating liquids. When used as a digester, there are also provided additional openings adjacent the outlet end of the passage for the introduction of cooling liquid.
The present invention also provides, in the treatment of fibrous material, particularly in a continuous countercurrent flow process, a method for intermittently disturbing the mass of individual fibrous elements comprising the material during their advancement along the flow passage. The disturbance is sufficient to prevent the flow of liquid in a fixed pattern of flow channels through the mass, commonly called channeling, which often results in nonuniform treatment of material.
It is an object of this invention to provide a method and means for the continuous treatment of fibrous material whereby the bed of materials being treated with a liquid is intermittently disturbed during passage through the treating apparatus sufficiently to break up any channeling that may have occurred during the preceding intervals.
Another object is to provide an improved form of treating apparatus adapted to advance discrete elements therethrough for treatment with a minimum of applied force or compression on the elements.
Another object is to provide apparatus of the type described embodying a construction which eliminates the formation of channels in the bed of elements continuously being processed therethrough whereby uniform concentration and distribution of the contents is achieved and whereby counter-flow cooking and washing operations can be efficiently conducted.
A further object of this invention is to provide apparatus of the type described which permits an endless variety of combinations of treating steps during passage of the elements of materials therethrough.
These and other objects of this invention will hereinafter appear and for purposes of illustration, but not of limitation, embodiments of the invention are shown in the accompanying drawings in Which FIG. 1 is a schematic elevational view of apparatus embodying the features of this invention;
FIG. 2 is a view taken along the line IIII of FIG. 1;
FIG. 3 is a view taken along the line IIIIII of FIG. 1;
FIG. 4 is a view taken along the line IV-IV of FIG. 1;
FIG. 5 is a schematic elevational view of a modified form of apparatus which may be used in the practice of this invention;
FIG. 6 is a view taken along the line VIVI of FIG. 5;
FIG. 7 is a modified form of pusher arm;
FIG. 8 is a detailed view of a drive employed in a modified form of apparatus embodying the features of this invention; and
FIG. 9 is a schematic elevational view showing the combination which makes use of two units of the type shown in FIG. 5, operated in tandem.
FIGS. 14 schematically illustrate a first embodiment of the invention in the form of a vertical digester for converting wood chips to pulp by the use of chemical solutions in countercurrent flow.
A main body portion 1, in the form of a closed tubular section, defines a passage 2. An inlet opening 3 is provided at the top of the body 10 for the introduction of wooden chips and a chip feeder 4 is connected to the inlet opening 3 to feed the chips into the passage. The chip feeder 4 may be of the type described in my U.S. Patent No. 3,285,669, entitled Feeding and Extracting Apparatus and Method.
The upper part of the body 1 has a larger diameter than the remainder of the body portion and the annular space 5, thus defined, is separated by a screen 6 from the passage 2. An outlet opening 7 for the removal of treating liquid is provided in the part and is connected to a steam trap 8 and a discharge tube 9.
Between the ends of the passage, one or more openings 10, 10 are provided at one or more locations in connection with pipes 11 and 11 respectively for the introduction of treating liquids into the passage. Towards the lower end of the passage, openings 12 are provided for the introduction of steam through pipes 13. Near the discharge end of the main passage, openings 14 are provided for the introduction of cold water and an outlet opening 15 is provided for the removal of pulp through a discharge valve 16. The valve is of the type known as a rotating valve of well-known construction or it may be similar in construction to the chip feeder 4.
A pusher means 17 is located in the main passage 2. The pusher means comprises an elongate shaft 18 axially mounted in the passage for reciprocal axial movement and it is dimensioned of a small cross-sectional area compared with the cross-sectional area of the passage, as shown in FIGS. 1 and 3. A plurality of arms 19 extend radially from the shaft in spaced apart groups, such as four or more, and are inclined away from the inlet opening 3. For certain materials, it may be desirable to hinge the arms 19 on the shaft 18, as shown in FIG. 7, so as to permit their collapse against the shaft during return movement and subsequent extension during pushing movement.
The shaft 18 has a portion which extends beyond the passage 2 through the top of the body portion 10 and the through-extending portion has connected thereto a piston 21 of a double acting hydraulic piston and cylinder assembly 22. If vessel 1 is of large diameter, the shaft and extension may be fabricated with an internal passage for the introduction of liquids from one or more points along the central zone of the passage 2 to supplement fluid added along the peripheral zone of the passage.
Rotor means 23, see FIGS. 1 and 2, is located in the upper part of the body 1 beneath the chip feeder 4. The rotor means is mounted coaxially with the shaft 18 for rotational movement relative thereto. Drive means (not shown) are provided to rotate the rotor means as by means operatively connected to the sheave 23. The rotor means operates to distribute the chips about the passage and, for this purpose, use can be made of a bladed member, such as the four angled blades 24 shown in FIG. 2. In use, the rotor means 23 provides even distribution throughout the cross-section of the passage of chips introduced into the passage through opening 3.
A discharge rotor 25, see FIGS. 1 and 4, is located at the discharge end of the passage 2. The rotor is preferably formed with arms 26 of S-shape which, in response to rotation by the motor 27, assists the displacement of the treated wood pulp into opening 15 connected to the discharge valve 16.
In another embodiment of digester embodying the features of this invention, shown in FIG. 5, the elements 4 have similar construction and function to the elements described in the first embodiment and which bear the same reference numerals.
The main body portion 30 is of generally U-shaped configuration having two vertically disposed legs 31 and 32. As seen in FIG. 5, the right-hand leg extends to a greater height than the left-hand leg 31. The body portion 30 defines a continuous passage 29 of increasing cross-sectional area from the top of leg 31 to the top of leg 32.
An inlet opening 3 for the introduction of wood chips from a chip feeder 4 and an outlet opening 7 connected to steam trap 8 and pipe 9 for the removal of treating liquid, are provided at the upper end portion of the left leg 31. Openings 10, 10' and 10 are provided for the introduction of treating liquid through pipes 11, 11' and 11" respectively and beyond the openings 10 are located openings 12 for the introduction of steam. Additional openings 12' for the introduction of steam may be pro vided near the top of leg 32. Openings 14 and 15 are provided near the top of leg 32 for the introduction of cooling water and for the removal of treated pulp respectively.
Rotor means 23, for distributing wood chips, is located at the top of leg 31 and a discharge rotor 25 for removal of pulp is located in an enlarged portion 33 at the top of the right leg 32.
Separate pusher means 17 are located in each leg 31 and 32 of the digester. Each pusher means is similar in construction to the pusher means described in the first embodiment including a shaft 18 and a plurality of groups of laterally extending arms 19 longitudinally spaced along the shaft. The arms of the pusher means located in the left leg are inclined away from the opening 3 and the arms of the pusher means located in the right leg 32 are inclined towards the discharge opening 15.
Extensions 20 of each of the shafts 18 have a piston 21 of a double acting hydraulic piston and cylinder mechanism 32 attached thereto. The lower ends of the cylinders of the two mechanisms 22 are interconnected by a conduit 34 while the upper ends of the cylinders are connected by a conduit 35, the latter of which is in communication with a reversible hydraulic pump 36. Operation of the pump 36 in one direction directs pressure fluid to the cylinders to cause the pusher means in one leg to descend and the pusher means in the other leg to ascend simultaneously while operation of the pump in the opposite direction brings about the opposite effects.
The cross-section of the arms 19 may be triangular as shown in FIG. 6. The walls of the passage 29 may also be lined with spaced barbs 37 inclined in the direction away from the opening 3. Similarly located barbs may also be provided in the tubular passage of the first embodiment.
As the wood elements progress along the passage, they encounter increasingly stronger or different treating liquids formulated to remove or soften the increasingly resistant ligncous materials binding the fibrous elements of the wood. This permits early removal of the more soluble components making up the greater proportion of the binder so that the increasingly stronger liquids can concentrate on the more resistant binder components thereby to free the pulp with maximum efliciency and minimum utilization of chemicals. In actual operation, a succession of different treating chemicals, e.g. reducing sodium salts of sulfur acids or other protective agents, may be added prior to a main treating chemical, such as caustic soda, or the treatment may comprise two or more successive treating zones embodying separate injections and discharges of different chemicals in order to minimize the attack on the hemi-celluloses which the liquor progressively removes. This includes the possibility that one of the zones may be operated with both the liquid and material flowing in the same direction. This could be effected by extracting the treating liquids at selected zones during passage of the material and injecting the liquids into previous zones, possibly fortified with additional chemicals, by means of positive variable speed liquid displacement pumps. Accordingly, this provides great flexibility in the choice of subsequent steps for the treating process and makes possible greater yields of pulp from the wood elements, as well as better pulp.
After the passage of the wood elements through the regions in which the various treating liquids have been injected, the concentration of the treating liquid in the treated pulp is thereafter continually decreased as chemical is leached from the wood elements by the countercurrent flow of water introduced at the discharge end of the passage.
During the flow of the wood elements through the passage, the pusher means 17 are intermittently reciprocated responsive to the action of the hydraulic piston and cylinder mechanisms 22. In response to reversal of movement of the pusher, the wood elements and treating liquid are slowly shaken up and mixed in the vicinity of each of the arms 19. This shaking and mixing action is effective to prevent channeling of the liquid through the mass of elements or to prevent non-uniform distribution of liquid in countercurrent flow through the advancing mass of wood elements. The amplitude and rate of reciprocation of the pusher means is maintained at a minimum so as to expose the elements being treated to a minimum of mechanical action.
In a further modification, shown in FIG. 8, means are provided to rotate or oscillate the shafts 18 during reciprocal axial movement of the pusher means. For this purpose, the extensions 20 are formed with splines which are slidably received in a splined collar 38 connected to a reciprocating arm 39 eccentrically connected to a drive, such as an electric motor 40. Each shaft 20 can, therefore, be oscillated while moving axially in one direction or the other in the passage 29.
In operation, cold water is introduced under pressure through opening 14 into the digester passage. The water introduced first operates to cool the treated pulp at the point of delivery and it is thereafter heated by steam introduced through openings 12 or 12' more effectively to leach the chemicals from the treated pulp. Cooking liquor or a succession of different cooking liquors is introduced through openings 10, 10" located approximately midway along the passage before the inlet 14 for water but beyond the inlet for introducing the wooden chips. The mixed liquids continue to flow towards the outlet openings 7 for discharge through trap 8 and pipe 9. Wood chips are introduced intermittently from chip feeder 4 through opening 3, preferably during the period of time when the pusher arms are moved in the direction away from the opening 3. The reciprocating pusher operates to displace the wooden elements in one direction through the passage opposite to the direction of movement of the mixed liquids and towards the discharge opening 15.
Wood elements fed into the passage are first immersed and well Wetted in the outgoing or spent treating liquids. A substantial quantity of the non-cellulosic portion of the wood, particularly the sugars and other soluble materials, much of which would ordinarily darken readily under the influence of strong digesting liquid, are thus initially dissolved and discharged with the treating liquor before the wooden elements have progressed far into the passage. Thus such darkening substances are substantially removed from the wooden elements before said elements are engaged with the fresher and stronger chemical treating liquids thereby to provide pulp and the like with a minimum amount of color or hinder. In digesting operations without countercurrent flow of treatin liquid, whereby the treating liquid is at high strength when first brought into contact with fibrous material, the non-cellulose substances darken and become absorbed in the fibrous material which, when subsequently pulped, requires additional bleaching for color removal. This extra bleaching results in greater chemical attack on the wood and the removal of hemi-celluloses. It is normally preferred to retain the hemi-celluloses in the wood because of their weight and their favorable influence on the beating qualities of the pulp.
In a preferred construction, in which the arms of the pusher means are of triangular cross-section, and during the movement of the pusher means in the direction of flow of the wood elements through the passage, the fiat bases of the triangular members tend momentarily to pack the wood elements together effectively to advance the wood elements through the passage with a minimum of applied force. On the reverse stroke, the arms have less tendency to apply force to the materials since the triangular configuration operates as a wedge or cam to separate the mass of elements without substantial endwise displacement. Furthermore, if the pusher means .are oscillated or rotated during the reverse stroke, as by means of the spline collar 38 and motor 40, there is even lesser tendency for displacement of the wood elements in the backward direction. The barbs 37 operate further to inhibit backward flow of the wood elements during the reverse stroke.
In the modification shown in FIG. 7, the pusher arms 19 are hinged for rocking movement radially on the shaft 18 so that they collapse against the shaft during the reverse stroke and project outwardly responsive to the pushing stroke with the amount of extension limited by stops 19*.
Since the specific gravity of the soaked Wood elements is nearly the same as that of the treating liquid, there is little tendency for the elements to compact and rub on the sides of the vessel. As a result, very little force is required to operate the pusher means for displacement of the elements.
It will be apparent that, in the counterflow system described, the volume of the spent liquor removed at the inlet end of the apparatus will be governed somewhat by the volume of water and treating fluid introduced less the volume of water removed with the treating materials and any liquid extracted intermittently. Consequently, the volume of the spent liquor will bear little relation to the ratio of liquid-material in the vessel as would be the case with unifiow treatment of liquor and material. Thus the ratio is somewhat immaterial insofar as it concerns the concentration of the dissolved solids in the spent liquor. This enables the concentration of the spent liquor to be increased substantially over that of the normal unifiow system thereby to avoid the greater expense for evaporation of excess water in the recovery of chemicals or for the disposal or other treatment of the waste liquor-a problem of significance with pulp mills concerned with water pollution.
Flexibility in the choice of treatment is further enhanced by the arrangement of two or more vessels of the type described in tandem, as shown in FIG. 9. Two vessels 50 and 51, of the type shown in FIG. 5, are connected in series. In the first vessel, the chips are treated with liquid in countercurrent flow .and in the second with liquid in parallel flow except at the discharge end embodying the cooling step. Chips introduced at 52 are transferred to the second vessel through passage 53, as by means 25, 15 and 16, shown in FIG. 5. In the event that the second vessel is operated at higher pressure, valve 16 may be replaced by an impeller of well-known construction forceably to convey the chips to the second vessel. By arranging the chip outlet of the first vessel above the liquor outlet, excess liquor will be drained from the chips before transfer to the second vessel.
In the arrangement shown in FIG. 9, cold water is introduced at 54 for flow with the chemicals washed from the pulp to an annular screen 55 through which it is discharged together with spent strong liquor previously added at 56 by pump 57 and which, if desired, may be 7 diluted at 58 with a portion of the used liquor from pump 57. Otherwise, this used liquor can be injected into the first vessel at 59 to flow counter to the movement of the chips and for discharge as spent liquor at 60, as by means such as the elements 6, 7, 8 and 9 shown in FIG. 5.
Additional or different treating liquors may be injected at one or more places along the passage of the chips, such for example at 61, and the injected liquor may be diluted, if desired, by used liquor from pump 57. Steam can be added as required, such for example as at 62, 63 and 64, to make the washing of the pulp more effective.
Although the present invention has been described with respect to a digesting operation in which use can be made of liquids under pressure within closed vessels, the invention may also be employed in processes not requiring pressurized liquids, e.g. certain semi-chemical cooking or bleaching or washing processes. In the event that the apparatus is to be used for bleaching fibrous materials, it is especially desirable to effect modification of the apparatus by placing additional inlets, opening screens and discharge openings at intermediate points in the passage for purposes of removal of a portion of the spent chemicals before adding other or fresh chemicals for the further treatment. For bleaching or other operations that require many stages, it is particularly desirable to place a number of vessels in series for the dilferent successive treatments required.
It will be understood that various changes may be made in the details of construction, arrangement and operation without departing from the spirit of the invention, especially as defined in the following claims.
1. A continuous digester for fibrous materials comprising a main body portion defining a passage, said main body portion having an inlet opening in communication with said passage for the introduction of fibrous material, said body portion having at least one additional inlet opening in communication with said passage remote from said first opening for the introduction of cooking liquor, means for withdrawing digested fibrous material at one end of said digester remote from said first opening, and means for withdrawing said liquor from the opposite end of said digester whereby said fibrous material and said liquor have counterflow movement through said digester, and pusher means in said passage, said pusher means comprising an elongated shaft extending for a substantial distance into said passage, and including spaced apart, laterally extending arms mounted on said shaft at spaced intervals along the length of the shaft, said arms being outwardly inclined toward said one end of said digester whereby the surfaces of the arms facing said one end intersect the axis of said shaft at an acute angle, and means for reciprocating said pusher means longitudinally of said passage.
2. Apparatus as claimed in claim 1 in which there is provided an additional opening near the end of the passage where the fibrous materials are removed, for the introduction of cooling liquid.
3. Apparatus as claimed in claim 2 in which there is provided at least one further opening for the introduction of treating fluid, said further opening being located between said opening for the introduction of treating liquid and said additional opening.
4. Apparatus as claimed in claim 1 wherein the passage increases in cross-sectional area from the opening for introduction of fibrous materials to the opening for removal of fibrous materials.
5. Fibrous material treating apparatus comprising a number of vessels according to claim 1 arranged in series, through which the fibrous material progresses successively and in which series of vessels the treating fluid moves in a direction opposite to that of the flow of the fibrous material in at least one of the vessels.
6. A digester in accordance with claim 1 wherein said main body portion comprises a vertical cylindrical member, and wherein said fibrous material is introduced at the top of said digester and removed at the bottom of the digester.
7. A digester in accordance with claim 1 including rotor means located adjacent the material inlet and discharge ends of said construction respectively to maintain a uniform distribution of material over the cross section of said construction and to discharge the digested fibrous material.
8. A digester in accordance with claim 1 wherein the additional opening provided for the introduction of cooking liquor is stiuated at a point above the discharge end of said construction and wherein further openings are defined in said construction at said discharge end for the introduction of steam and water.
9. A digester in accordance with claim 1 wherein said arms each define a triangular cross-section, the base of each triangle facing said one end of the digester to thereby force said fibrous material toward the point of withdrawal of said fibrous material on the forward stroke of the pusher means, and the apex of each triangle facing the opposite end of the digester to thereby result in minimum disturbance of materials on the return stroke of the pusher means,
10. A continuous digester for fibrous materials comprising a U-shaped tubular construction defining a passage extending therethrough, said tubular construction having a first opening adjacent the upper end of one leg of said construction for the introduction of fibrous materials, said tubular construction having at least one additional opening defined by said construction remote from the first opening, said additional opening being provided for the introduction of cooking liquor, means for withdrawing digested fibrous material at a point adjacent the upper end of its other leg, and means for withdrawing said liquor at a point near the upper end of said one leg whereby said fibrous material and said liquor have counterfiow movement through said digester, and pusher means in each leg of said construction, said pusher means including spaced apart, laterally extending arms outwardly inclined toward said one end of said digester, and means for reciprocating said pusher means longitudinally of said legs simultaneously in opposite directions.
11. A digester in accordance with claim 10 wherein said arms define a triangular cross-section.
12. A digester in accordance with claim 10 including at least one additional opening defined in said construction for the introduction of concentrated liquor, a separate opening for the introduction of steam into said construction, and including a still further opening adjacent the upper end of said other leg for the introduction of water into said construction.
13. A continuous digester in accordance with claim 10 which includes barbs on the side walls of said passage, said barbs being inclined in the direction of flow of said fibrous materials to inhibit back flow of said materials.
14. In a vessel for the continuous treatment of fibrous materials by liquids, which vessel comprises a main body portion defining a passage and having openings for the introduction and removal of the fibrous materials and treating liquids, the improvement in which pusher means are provided to extend a substantial distance along, and reciprocable longitudinally of, the passage, said pusher means including an axially located shaft having spacedapart, laterally-extending arms inclined away from the opening for the introduction of fibrous materials and means for reciprocating the pusher means, in which said arms are hinged to said shaft so that they extend to fixed positions when the shaft is moved away from the opening for the introduction of fibrous material and collapse against the shaft when it is moved in the reverse direction.
15. In a vessel for the continuous treatment of fibrous materials by liquids, which vessel comprises a main body portion defining a passage and having openings for the introduction and removal of the fibrous materials and treating liquids, the improvement in which pusher means are provided to extend a substantial distance along, and reciprocable longitudinally of, the passage, said pusher means including an axially located shaft having spacedapart, laterally-extending arms inclined away from the opening for the introduction of fibrous materials and means for reciprocating the pusher means in which the passage is U-shaped and pusher means are located in each leg of the passage and wherein the means for reciprocating the pusher means comprises reversible hydraulic supply means, a pair of cylinders operatively connected to said supply means, piston means comprising extentions of said pusher means and associated with each of said cylinders, and means for operating said supply means whereby both of said pusher means are moved simultaneously but in opposite directions.
16. In a vessel for the continuous treatment of fibrous materials by liquids, which vessel comprises a main body portion defining a passage and having openings for the introduction and removal of the fibrous materials and treating liquids, the improvement in which pusher means, are provided to extend a substantial distance along-and reciprocable longitudinally of, the passage, said pusher means including an axially located shaft having spacedapart, laterally-extending arms inclined away from the opening for the introduction of fibrous materials and means for reciprocating the pusher means, and barbs on the walls of the passage, said barbs being inclined in the direction of flow of said fibrous materials to inhibit backward flow of said materials.
References Cited UNITED STATES PATENTS 3,130,119 4/1964 Carlsmith 162-237 3,134,384- 5/1964 Rich 162237 X HOWARD R. CAINE, Primary Examiner US. Cl. X.R. 23270