WO1990010527A1

WO1990010527A1 - Method and apparatus for extrusion processing of wood products and fibrous materials

Info

Publication number: WO1990010527A1
Application number: PCT/US1990/000111
Authority: WO
Inventors: Gordon R. Huber; Lawrence E. Schmelzle
Original assignee: Wenger Manufacturing, Inc.
Priority date: 1989-03-10
Filing date: 1990-01-05
Publication date: 1990-09-20
Also published as: AU5280490A; KR920700096A

Abstract

A method and apparatus for the extrusion processing of wood particles and fibrous material is provided which uses an extruder (20) having an axially rotatable flighted screw (96) to subject the material to impregnation by a chemical treating agent by constricting the fibers, concentrating the agent in the material, and then permitting the material to expand in a sponge-like manner to absorb additional treating agent. The impregnation is accomplished within impregnation zones (A, B, C) along the extruder and defined by structure within a groove (106, 108) on the flighted screw (96). A plurality of chemical injection ports (56) may be circumferentially spaced around the barrel (26) of the extruder to ensure thorough and even chemical distribution through the material to be treated. In the process hereof, the material may be exposed to a first agent in a preconditioner (208) and thereafter exposed to a second, complementary agent in the extruder (20).

Description

I METHOD AND APPARATUS FOR EXTRUSION PROCESSING OF

WOOD PRODUCTS AND FIBROUS MATERIALS

5 Background of the Invention

1. Field of the Invention

This invention broadly relates to a method and apparatus for the extrusion processing of wood chips, shavings, sawdust, food fibers, agricultural

"L_Q residues or other fibrous materials to produce a refined product by impregnating the fibers with a desired chemical, such as in the production of pape pulp or bleached food products. More particularly, the invention is concerned with an extruder having

!5 at least one injection port through the barrel thereof for introducing a chemical processing agent into the material during processing with the inter¬ nal screw having sequential compression and absorp¬ tion zones for enhancing the chemical impregnation

20 of the fibrous material.

2. Description of the Prior Art The use of particle board in furniture, cabinets and other types of finished construction products has significantly increased in recent

25 years. Particle board has replaced plywood due to the improved dimensional stability of particle board and the lower cost of the same. In most cases, particle board is comprised of relatively flat, small wood chips that are bonded together with an

30 adhesive such as an epoxy resin, and are relatively untreated in the sense that the chips have not been impregnated with any chemical processing agents. However, it is becoming increasingly desirable to impregnate the fibers with fire retardant or anti-

35 rotting agents during manufacture. Furthermore, many other products use chemically treated fibers in their final formulation and makeup. For example, in the production of paper, the wood pulp is chemically treated and bleached to produce fine, usable sheets. The bene¬ fits of fiber in the human diet have also been recognized, with the associated desirability of bleaching food fibers to be introduced into dietary products. Finally, a variety of substances or products needing to be impregnated such as the hulls of nuts may be used in environments where it is desirable to chemically treat and impregnate such materials with chemical agents to alter their physi¬ cal properties. In the past, processors have faced an alternative of essentially destroying the fibrous qualities of starting materials during processing by cooking and mashing the materials into a liquid, or soaking the starting materials in a solution until uniform absorption of chemical treating agent is achieved. The first alternative of course destroys the fibers while the latter may require extended vat time and is therefore costly.

Hence, there is a decided need in the art for an improved, low cost method and apparatus for the chemical impregnation of starting materials such as wood chips, food fibers or other fibrous materials, without destroying their fibrous charac¬ ter.

^•Summary of the Invention

The present invention represents an espe¬ cially effective means for impregnating wood prod¬ ucts and other fibrous starting materials with chemical agents to produce an extrudate having an essentially uniform distribution of chemical agents throughout the fibrous structure thereof. The various fibrous components may be refined to a greater degree (as in the case of some food pro¬ cessing and the paper industry), or on the other hand a lesser degree of refinement for chip board and the like. In accordance with the invention, an extruder of novel construction is provided for producing the impregnated product with an operating cost far lower than costs normally associated with other refining and chemical impregnating processes.

The extrusion apparatus of the present invention includes a tubular extruder barrel en- closing an elongated, axially rotatable screw. A downstream section of the barrel and the screw have generally conical configurations with flighting means defining respective elongated, helically shaped grooves that cooperate to advance the wood particles toward an annular extruder outlet which takes the form of an open, unrestricted area between the downstream end of the screw and the surrounding regions of the bore. A port for introducing a chemical into the bore is provided through the barrel downstream from the inlet, and preferably multiple injection ports are provided to ensure thorough wetting and distribution of the desired chemical into the bore. The flighting of the screw defines a helical groove therebetween. The groove is designed such that the wood material goes through a series of compressions and decompressions which assist in causing the chemical additive to be first driven into the fibrous materials and then absorbed during the decompression stage. In preferred forms, the root diameter groove increases with each successive compression zone and absorption zone for gradual treatment of the processed material.

In certain forms of the invention, the screw is double flighted, whereby each of the side- by-side grooves formed in the screw section adjacent the chemical introduction ports presents three pro¬ cessing zones which are sequentially arranged along the length of the groove. Each of the processing zones includes a compression region wherein the root diameter between flight portions of the groove is increased to compress the particles, followed by an absorption zone wherein the root diameter is dramat¬ ically decreased to present a sudden decompression of particles. Each of the absorption or decompres- sion regions are located immediately downstream of the corresponding compression or restriction region, and preferably the absorption region is established by significantly reducing the root diameter of the groove between the flighting portions to create an enlarged free volume that enables the particles to expand somewhat and rearrange before reaching the compression region of the next adjacent, downstream processing zone.

Thus, the advancing fibrous particles encounter a series of compression regions wherein the velocity of the particles along with the amount of pressure applied to the particles is steadily in¬ creased, forcing the treating chemical into the particles, as well as a series of decompression regions wherein the velocity of the particles is decreased while pressure applied to the particles is relieved to enable the particles to mix, expand, and thereby draw in additional treating chemical. The grooves of the screw are of relatively wide width so that the fibers are separated by the grinding action of wood particles against other wood particles, in contrast to disk refiners where grinding occurs by shearing wood against metal.

In preferred embodiments of the invention, drain holes are supplied downstream from the injec¬ tion ports in order to remove the treating chemical and thereby limit the amount of time during which the particles may be subject to chemical introduc¬ tion. In yet further forms of the invention, por- tions of the bore adjacent the flighting are pro¬ vided with longitudinally extending ribs adjacent the flighting of the screw to assist in fibrillation of the particles, and at least one bar may extend transversely across the groove to further compress the particles and force the same through a rela¬ tively narrow, restricted gap between the outer surfaces of the bar and adjacent, stationary por¬ tions of the head. In yet further embodiments of the invention, the inclined bottom wall of the screw within the compression regions is roughened to retard the advancement of wood particles and further promote the grinding action between adjacent par¬ ticles.

In preferred forms of the invention, the grooves of the final, downstream head section are also of particular configuration which establishes a compression region and a restricted region located adjacent the third processing zone of the screw. In addition, bars extending transversely across the groove in the restricted region of the head are oriented at a slight acute angle relative to the bars in the third restricted region of the screw. The stationary bars of the head cooperate with the bars of the rotating screw in a scissors-like fash- ion so that the fibers are twisted apart during passage through the relatively narrow area between the bars without excessive severing of the length of the same. As a consequence, the longitudinal integ¬ rity of the fibers is, in large part, retained which renders the refined product extremely desirable for use in the manufacture of fiber board cores for particle board as well as in other applications.

These and other objects of the invention will be made more clear in the course of the fol- lowing description of a preferred embodiment of the invention.

Brief Description of the Drawings

Figure 1 is a cross-sectional view of an extruder apparatus constructed in accordance with the present invention;

Fig. 2 is an enlarged, cross-sectional view of the final or downstream conical head section of the extruder depicted in Fig. 1 and illustrates cross-bars disposed in the grooves of the flighted head section;

Fig. 3 is a vertical cross-sectional view taken along line 3-3 of Fig. 2;

Fig. 4 is a side elevational view of the final, double flighted conical screw section shown in. Fig. 1, depicting the location of three proces¬ sing zones located along the length of the screw;

Figs. 5-10 are respectively cross- sectional views of the final screw section shown in Fig. 4, with each view illustrating a different 180° section of a groove;

Fig. 11 is a vertical cross-sectional view taken along line 11-11 of Fig. 1 to illustrate the injection ports through the second head section of the extruder barrel; Fig. 12 is side elevational view of a portion of the extruder screw positioned adjacent the injection ports, showing the progressive com¬ pression and absorption zones defined between the screw flighting;

Figs. 13-18 are respectively cross- sectional views wrapped around the second screw section and following 180° sections of the grooves of the second screw section depicted in Fig. 12; and Fig. 19 is a schematic representation of an extrusion apparatus useful in accordance with the invention, including a preconditioner and extruder barrel.

Detailed Description of the Drawings

Referring now to the drawing, an extruder constructed in accordance with the present invention is broadly designated by the numeral 20 in Figs. 1-19 and includes a barrel 22 having four inter- connected tubular head sections 24, 26, 28 and 30 as is illustrated in Fig. 1. Each of the sections 24-30 includes an outer casing 32 and an inner tubular sleeve 34, the latter cooperatively defining an elongated, central bore 36. The inlet head 24 includes an inlet 38 at the upstream end thereof, whereas final conical head section 30 presents an outlet opening 40 remote from inlet 38. A similar apparatus for extruding fibrous materials to produce a fiberized product is shown, for example, in co- pending U.S. Application Serial No. 07/280,009 filed October 19, 1988, the disclosure of which is incor¬ porated herein by reference.

As shown in Figure 1, the sleeve 34 of inlet head section 24 presents a series of straight, convergent, rectangular ribs 42 circumferentially spaced in surrounding relationship to the perimeter of adjacent regions of the bore 36 and which extend in planes parallel to the longitudinal axis of the bore 36. Similarly, the sleeve 34 of the third head section 28 also has a spaced series of rectangular, essentially straight ribs 44 that extend in planes generally parallel to the longitudinal axis of bore 36. The inserts of head sections 24 and 28 are both tapered to present a generally conical configura¬ tion.

The sleeve 34 of the second head section 26 has a plurality of ribs defining quadruple flighting 46 which presents four separate, side-by- side sleeve grooves 48, 49, 50 and 51 (see Fig. 11). Each such sleeve groove is elongated and has a generally helical configuration; furthermore, the region of bore 36 within the flighting 46 is of untapered, generally cylindrical shape, in contrast to the conical region of the bore 36 that are formed by the tapered configuration of sleeves 34 within the head sections 24, 28. Furthermore, sleeve 34 of head 26 is provided with a series of radially in¬ wardly extending ports 52 extending through the casing 32 and sleeve 34 as shown in Fig. 11. The ports include connectors 54 for receiving conduits from a chemical source and define passageways 56 in fluid communication with connectors 54 and sleeve grooves 48, 49, 50 and 51 as shown in Figs. 1 and 11. A second series of radially extending ports 58 identical in all respects to ports 52 and are ^•located downstream therefrom in head 26. As is the case with ports 52, there are four ports 58 extend¬ ing inwardly through casing 32 and sleeve 34 for communication with such sleeve grooves, with each of the ports being evenly spaced about the circum¬ ference of the sleeve 34.

Third section 28 is substantially similar to first section 24, as noted hereinabove, with the addition of drains 60 and 62 for permitting chemi¬ cals introduced through ports 52 and 58 to pass through sleeve 34 and surrounding casing 32.

The final or downstream head section 30 has "quad" flighting 64 that defines four juxta- posed, separate helical grooves 66-72. Referring to Fig. 2, and also to Fig. 3 (which depicts only groove 70), each of the grooves 66-72 presents in sequential .order a passage region 74 that is fol¬ lowed by a processing zone 76 having a compression region 78, a restricted region 80 and a decompres¬ sion region 82. Viewing Fig. 3, it can be seen that the root diameter of the groove 70 decreases in such fashion that a bottom wall 84 of the groove 70 is inclined in the form of a ramp 86 between the pas- sage region 74 and the compression region 78. Thereafter, the bottom wall 84 continues along the length of the groove 70 in a steadily decreasing, spiral fashion corresponding to the tapered profile of the bore 36. The compression region 78 extends through an arc of approximately 135 degrees between ramp 86 and the beginning of the restricted region 80.

Two elongated, rectangular elements or cross bars 88 are disposed within the restricted region 80 of each of the grooves 66-72, and extend in transverse relationship to adjacent portions of the flighting 64 as can be appreciated by reference to Fig. 2. The bottom wall 84 of grooves 66-72 between the bars 88, 88 is spaced from the innermost surface of bars 88 in general alignment with the bottom wall 84 within the compression region 78, although the free incremental volume, (i.e., the groove volume per incremental or unit length of the groove along its helical path) of the grooves 66-72 between the bars 88 of the restricted region 80 is somewhat less than the incremental volume of the grooves 66-72 within the compression region 78 due to the conical configuration of the bore 36 within the head section 30. The decompression region 82 begins immediately downstream of the second bar 88, and is formed by removing material from the asso¬ ciated sleeve 34 so that the diameter of the bottom wall 84 within the decompression region 82 is greater than the diameter of the bottom wall 84 within the compression region 78 or between the bars 88 of the restricted region 80.

Preferably, the top surface of the bars 88 are substantially flush with the adjacent portions of the flighting 64. As such, the grooves 66-72 present incremental volumes in locations 90, 92 (Fig. 3) in both the compression region 78 and the decompression region 82 respectively and directly adjacent the restricted region 80 which is greater than any incremental volume of the groove 70 in a location 94 that is between the bar 88 and the longitudinal axis of bore 36, since the free incre¬ mental volume of the grooves 66-72 inwardly from the bars 88 is equal to zero. Moreover, the restricted region 80 is disposed upstream from the outlet 40 of the bore 36 to restrict or choke the passage of wood chips or other fibrous material advancing through the extruder 20 before the same reach outlet 40.

The configuration of grooves 66, 68 and 72 is similar in essential respects to the configura- tion of groove 70 (shown in Fig. 3). However, as can be appreciated by reference to Fig. 2, the processing zones 76, including the bars 88, are disposed approximately 90° around the longitudinal axis of the bore 36 from each other so that the respective compression regions 78 and bars 88 of grooves 66-70 are spaced across from each other within the bore 36 while the compression regions 78 and bars 88 of grooves 68, 72 are located across from each other in transverse relationship to the compression regions 78 and restricted regions 80 of grooves 66, 70.

Referring again to Fig. 1, an elongated rotatable screw, broadly designated 96, extends along the length of bore 36. The screw 96 is com- prised of four screw sections 98, 100, 102 and 104 which are supported on a central splined shaft (not shown) for simultaneous rotation. Each of the sections 98-104 presents at least one helically- shaped groove for receiving material to be processed and advancing the same in downstream direction toward the outlet 40 of bore 36 as the screw 96 is rotated. In the embodiment shown in the drawings, the sections 98, 100, 102, and 104 are each double flighted, and the overall screw 96 is configured for rotation in a clockwise direction as viewed along its axis from inlet 38 to outlet 40.

In more detail, the first or inlet screw section 98 which is depicted in Fig. 1 is preferably a double flight, tapered screw that presents a decreasing volume in direction leading away from the inlet 38 of bore 36. The second screw section 100 is of a modified, double flighted construction presenting grooves 106, 108 between the flights thereof. That is, the grooves 106, 108 of the second screw section are provided with built up surfaces defining the root diameter of the groove. Portions of the grooves 106, 108 have gradually increasing root diameters, followed by a rapid decline in root diameter, with the average root diameter increasing in a downstream direction.

As shown in greater detail in Fig. 12, second section 100 is provided with two flights 110 of a generally uniform configuration each defined by upstream wall 112, downstream wall 114 and margin 116. The radial distance between the longitudinal axis of the screw 96 and the margin 116 is constant along the length of screw section 100. The flights cooperatively define grooves 106, 108 therebetween. The grooves 106, 108 are of increasing average root diameter and define successive constriction regions 118 and concentration regions 120, succeeded by absorption regions 122.

For ease of discussion, respective impreg¬ nation zones A, B and C (see Fig. 12) have been shown on screw section 100 and are defined by the structure within the grooves 106, 108.

It is to be further understood that because section 100 is double flighted, the grooves 106 and 108 are not interconnected. Thus, groove 106, as shown in Fig. 12, defines successively more restrictive impregnation zones A and B and C along the groove 106 as the groove 106 extends in a helical manner around second section 100, while groove 108 also defines corresponding restrictions for the same zones A, B and C, on the opposite side of section 100 of the impregnation zones on groove 106.

Constriction region 118 within each suc¬ cessive zone begins with an incline of increasing root diameter in a clockwise direction when viewed from inlet to outlet. Constriction region 118 is followed downstream by concentration region 120 of generally constant root diameter, the root diameter of the concentration region 120 being the same as the maximum root diameter of the constriction region 118. Concentration region 120 is then succeeded by absorpotion region 122.

Absorption region 122 is initiated by a step at which the root diameter decreases or drops off from the increased diameter of concentration region 120. Absorption region 122 has a relatively large incremental free volume compared to the pre¬ ceding concentration region 120. Absorption region 122 ends where the root diameter increases to begin compressing the fibrous material to be processed, at which point the succeeding constriction region 118 begins. Thus, it can be appreciated that the free incremental volume within a groove 106 or 108 be¬ tween second section 100 and head 26 is greater in absorption region 122 that the preceding concentra¬ tion region 120, and that the free incremental volume between the head 26 and section 100 decreases from absorption region 122 through the successive and adjacent constriction region 118 until reaching the next concentration region 120 of a more restric¬ tive free incremental volume for the next succeeding impregnation zone. While the average incremental free volume generally decreases for each successive zone, the root diameter of section 100 remains generally constant at each base of each absorption zone 122 as described hereinafter.

Referring now to Figs. 13-18, it can be apprecited that the zones A, B and C become succes¬ sively more restrictive in the constriction region 118 and concentration region 120 in a downstream direction. Each of Figs. 13-18 is a partial section wrapped around the screw to show the respective region within each zone. Zone A, with the corre¬ sponding second section 100 shown in partial-section by Figs. 13 and 14, is upstream with respect to the flow of product through the extruder 20 relative to zones B and C. Because grooves 106 and 108 are helically oriented and double-flighted on the screw 96, a portion of the second section 100 is omitted from each of the Figs. 13-18 which represents the other opposing groove. Figs. 13, 15 and 17 show zones A, B and C on groove 108, while Figs. 14, 16 and 18 show zones A, B and C on groove 106.

Referring now to Fig. 13, zone A on groove 108 includes incline 126 which defines constriction region 118 of increasing root diameter. A concen¬ tration region 120 extends from constriction region 118 around second section 100 to step 130, followed circumferentially by a base 128 corresponding to an absorption zone 122. Base 128 has a root diameter which is the same as that of the part of groove 108 just upstream from incline 126. Figs. 13 and 15 show the locations of step 130 and base 128 relative to the portions of groove 108 upstream and down- stream therefrom.

As shown in Fig. 15, zone B commences with incline 127 and progresses circumferentially around screw 96 through a constriction region 118 defined by incline 127 and concentration region 120 to step 132. Step 132 is followed by base 131 corresponding to another absorption region 122.

As is shown in Figs. 15 and 17, zone C commences with incline 133 corresponding to con¬ striction region 118, followed downstream by a region of constant root diameter corresponding to concentration region 120. As shown in Fig. 17, step 134 on the side of section 100 not visible in Fig. 12 precedes final absorption region 122 correspond¬ ing to base 135. It will be appreciated that the zones A, B and C follow in a clockwise direction around the grooves 106, 108 as viewed downstream to upstream, while the screw 96 is adapted for counter¬ clockwise rotation when viewed from the same direc¬ tion. In a similar manner, as groove 106 pro¬ gresses in a helical direction around second section 100, zone A commences with incline 136 in groove 106 on the opposite side of screw section 100 and in the same vertical plane as incline 128 of groove 108. Incline 136 defines constriction region 118, fol¬ lowed circumferentially by a concentration region 120 of generally constant root diameter to step 137, followed by an absorption region 12-2 corresponding to base 138. The cycle of absorption region 122, compression region 118 and concentration region 10 progresses in a clockwise circumferential path around groove 106 of second section 100 from step 138.

Referring now to Fig. 16 showing impreg- nation zone B on groove 106, incline 139 is of increasing root diameter and corresponds to con¬ striction region 118 of zone B following base 138 corresponding to absorption region 122. This con¬ striction region 118 is succeeded by a concentration region 120 to step 140. Following step 143, groove 106, retains the same root diameter as at bases 138, 141 and 144 as the grooves 106, 108 spiral the remaining distance of second section 100 in a down¬ stream direction. Figs. 16 and 18 show step 140, followed by base 141 corresponding to an absorption region 122. Thereafter Fig. 18 shows impregnation zone zone C on groove 106 commencing with incline 142 corresponding to constriction region 18, followed by a region of constant root diameter corresonding to concentration zone 120. Finally, step 143 marks the commencement of the final absorption region 122, at base 144.

The screw section 102 has a conical con¬ figuration complemental to the tapered profile of the bore 36 within head section 28. The screw sec¬ tion 102 is in this instance a double-flighted screw that is aligned with first and second screw sections 98, 100 such that the flighting 145 of screw section 102 are closely adjacent the respective ends of the flighting of sections 98, 100 to present a smooth transition for material passing along each of the two grooves 106, 108.

The screw section 104 is depicted in greater detail in Fig. 4 and has a double flighting 146 defining two juxtaposed, elongated grooves 148, 150 having a generally helical configuration. The flighting 146 is fixed to a shank portion 152 and presents an overall tapered profile or conical con- figuration.

A relatively short passage region 154 is located at the upstream end section of each groove 148, 150 and presents an available or free incre¬ mental volume that is approximately equal to the free incremental volume of the adjacent reaches of the grooves at the downstream end section of third screw section 102. Each groove 148, 150 of the screw section 104 also presents, in sequential order, three processing zones, 156, 158, 160 which correspond to zones A, B and C that are designated in Fig. 4.

The three processing zones 156, 158, 160 of groove 148 can be better understood by comparison of Figs. 4 to Figs. 5, 7 and 9. As shown in Fig. 5, the bottom wall of the groove 184 within the first processing zone 156 steadily increases to present a compression region 162 that extends in this instance in an arc approximately 235° about the longitudinal 0 axis of screw 96. A restricted region 164 is formed immediately downstream of compression region 102 and includes three spaced, parallel elements or rectan¬ gular bars 166 that extend across the groove 90 be¬ tween adjacent, continuous portions of the flighting 5 146 and lie in planes parallel to the longitudinal axis of bore 36. Also, as shown, a decompression region 168 is disposed downstream of the third bar 166 of the restricted region 164.

The second processing zone 158 of groove o 148 is shown in Fig. 7, and includes a compression region 170 that extends approximately 90° about the longitudinal axis of screw section 104 until reach¬ ing a restricted region 172 having a single bar 174 which extends between adjacent portions of flighting 5 146 in a plane parallel to the longitudinal axis of bore 36. Downstream of bar 174, a bottom 176 of groove 148 is inclined in the nature of a ramp and leads to a relatively short decompression region 178. 0 The nature of the third processing zone

160 of groove 148 can be understood by reference to Fig. 9. Zone 160 includes a compression region 180 that extends along an arc of approximately 45° about the central axis of screw section 104. A restricted region 182 is located immediately downstream of com- pression region 180, and includes four spaced, elon¬ gated elements or elongated bars 184 that extend between adjacent, continuous portions of the flight¬ ing 146 and lie in planes parallel to the longitudi- nal axis of bore 36. The restricted region 182 lies along an arc of approximately 90° about the screw section 104, and terminates in a final decompression region 186 that begins with a ramp-like section of the bottom wall 176 of groove 148. In similar manner, groove 150 also pre¬ sents three distinct processing zones 188, 190 and 192 substantially similar to corresponding zones 156-160, but disposed on opposite sides of the screw section 104 at 180° around the perimeter of the same. Each of the zones 188-192 present, in sequen¬ tial order, a compression region 162, 170, 180 re¬ spectively followed by a restricted region 164, 172, 182 having transverse bars 168, 174, 184, and a decompression region 168, 178, 186 wherein the root or bottom wall of the groove 150 is undercut to present a free incremental volume greater than any free incremental volume of the groove 150 within the corresponding restricted regions or compression regions. By observation of Figs. 5-10, it can be appreciated that the grooves 148, 150 within the respective processing zones 156-160, 188-192 have free incremental volumes of values within the com¬ pression regions 162, 170, 180 which are greater than any incremental volume of the corresponding groove 148, 150 in the next adjacent, downstream restricted regions 164, 172, 182 in a direction radially outwardly from the respective bars 166, 174, 184. As an example, in Fig. 6 the incremental volume of groove 150 at location 194 in compression region 162, as well as the incremental volume of groove 150 at location 196 in decompression region 168, is greater than the incremental volume of groove 150 outwardly from bar 166 at location 198. In addition, the disposition and configur¬ ation of the rectangular, parallel, elements or bars 166, 174, 184 is such as to cause the passage areas or gaps radially outwardly of the bars to be smaller as the outlet 40 of bore 36 is approached. In par- ticular, Fig. 5 shows that an outer surface 200 of bar 166 is spaced slightly from the outer surface 202 of the adjacent portions of the flighting 146 while in Figs. 7 and 9 the outer surface 204 of bars 174, 184 is substantially flush with the outermost surface 206 of adjacent portions of flighting 146 (in this regard, see also Fig. 4). The outer sur¬ faces of bars of the restricted regions within the processing zones 188-192, as shown in Figs. 6, 8 and 10, are substantially identical in disposition and configuration to the aforementioned surfaces 200, 204 of bars 166, 174, 184 relating to the respective outer surfaces 200, 204.

The flighting 146 has an outer diameter which gradually decreases along the length of grooves 148, 150 such that the screw section 104 presents an overall conical configuration. Thus, the pressure exerted on materials passing through the extruder 20 increases as the materials sequen¬ tially advance through the compression regions and the restricted regions of each of the processing ^•zones 156-160 and 188-192. Moreover, the bottom walls 176 of grooves 148, 150 may be roughened with¬ in the corresponding compression region of each zone 156-160, 188-192 to further promote rolling and twisting of the materials as the same advance toward bore outlet 40.

Each of the outwardly projecting bars 166, 174 and 184 extend completely across the reaches of corresponding grooves 148, 150 and lie in planes ex¬ tending along the longitudinal axis of bore 36. Moreover, by comparison of Figs. 2 and 4, it can be observed that the outwardly projecting bars 88 within each of the restricted regions 80 of the grooves 66-72 of head section 30 are oriented in acute angular relationship relative to the direction of extension of the bars of screw section 104, in¬ cluding the four bars 184 of each restricted region 182 of the final, third processing zone 160, 192 of screw section 104. As such, the stationary bars 88 of the final head section 30 are disposed in scis¬ sors-like fashion relative to the bars 184 within the restriction region 182 of the third processing zones 160, 192 of final screw section 104, which has been found to promote twisting and separation of the fibers of wood particles when the same are intro¬ duced into the barrel 22 of extruder 20.

Axially rotatable screw 96 is supported by bearings 210, 212 as shown in Fig. 1. Screw 96 is mounted on a splined shaft 50 so as to be axially shiftable within bore 36. The shaft is mounted within a quill housing to the left of bearings 210, 212 in Fig. 1 (not shown) and having a quill shaft therein whereby the quill shaft is mounted on a main thrust bearing and positioned axially by at least one adjustment bolt. When the sleeves 34 or screw sections 98, 100, 102 or 104 suffer wear, or alter¬ natively when it is desired to increase the refine¬ ment of the product by changing the clearance between screw section 104 and sleeve 34 of head section 30, the screw 96 may be axially shifted by movement of the adjustment bolt.

Operation As may be appreciated from the foregoing structural recitation, the extruder 20 hereof is especially adapted for impregnation of fibrous material with a chemical additive. Such impregna¬ tion may be desirable to enhance processing effi¬ ciency and reduce the energy required for proces¬ sing. For example, sodium sulfite (NaS0₂ ) or other sulfite solutions may be introduced through the ports 52, 58 to reduce the energy requirements necessary to extrude wood chips, sawdust, shavings and the like into a fiberized product. Alterna¬ tively, a bleaching agent may be introduced for bleaching wood or food fibers. Such bleaching agents may include hydrogen peroxide (H₂0₂), sodium hydroxide (NaOH) , ammonium hydroxide, potassium hydroxide, hydrogen sulfide, sodium silicate, sodium hypochlorite, ammonium sulfate, ammonium sulfide, sulfuric acid, sulfurous acid, hydrochloric acid, calcium hydroxide, calcium chloride, titanium di¬ oxide and ethylenedinitrile tetracetic acid. For different types of paper production or other bleach¬ ing operations, a plurality of ports may be used sequentially to introduce two or more different chemicals during the treatment process. Finally, food fibers, agricultural residues or any other organic or inorganic substances which are to be impregnated with a solution may be processed by the method hereof.

The material to be processed may be con¬ veyed from a storage bin by a feeder into a precon- ditioner 208 for mixture of the material with a suitable quantity of water or other solvent to provide an appropriate moisture constant prior to processing. A bleaching agent may be added in the preconditioner 208 such as sodium hydroxide, and the material will be retained in the preconditioner for a period of 5 to 240 seconds and preferably 60 to 90 seconds. Total moisture in the mixed material including added water, is about .5% to 80%, although in wood fiber refining, the moisture content should be 10% to 50% and better results have been obtained when the moisture content of the fibers is 25% to 30% by weight of water. On the other hand, when food pulps are to be bleached, the preferred mois¬ ture content is 50% to 60% upon entering the ex- truder 20.

Such materials are retained in the extru¬ der 20 for 10 to 90 seconds and preferably 45 to 60 seconds at a maximum temperature of about 90 to 500°F, and preferably about 200 to 300°F before pro¬ ceeding to a washing process and/or dryer. Alter¬ natively, some impregnation processes may be more advantageously performed where the material within the extruder barrel is chilled to about 50°F.

The wood chips, sawdust, shavings, food fibers, agricultural residue or other fibrous or porous material enters the extruder 20 through inlet 38. The material enters inlet 38 by gravity, force feed or other means while screw 96 is rotating. As shown in Fig. 1, screw 96 will rotate in a clockwise direction when viewed from inlet to outlet 40 at a speed of about 25 r.p.m. to about 600 r.p.m., al¬ though better results can be observed when the screw 96 is rotated at a velocity within the range of about 250 to about 350 r.p.m. for wood chips and 400 to about 500 r.p.m. for food fibers or pulp. The particles of wood are advanced first through head section 24 by the flighting on first screw section 98. During this advancement, the material is reduced in size and fiberized by the frictional force of the material against itself by the com¬ pression of the material as it advances through the progressively more restrictive first head section 24.

As the material enters second head section 26, acid sulfites, dyes or other processing agents are introduced through passageways 56 into grooves 48 and 50. The processing agent is effectively dis¬ tributed through the material by the rotation of the screw and the use of multiple injection passageways 56 as shown in Fig. 11. The rotation of the screw 96 causes the material and processing agent to advance through head section 26 toward outlet 40.

Turning now to Figs. 12, the material is successively advanced through a sequentially more restrictive series of impregnation zones A, B and C as hereinabove described. Zone A is the least restrictive zone in that the free incremental volume, defined by the difference in the average root diameter of the respective groove 106, 108 and the interior diameter of the head section 26, is greater in zone A than zone C. Zone B has a free incremental volume intermediate that of zones A or C.

Turning specifically to Fig. 13, the mate- rial is first compressed in constriction region 118, by the axial rotation of the screw section 100 within bore 36 of head section 26. The processing agent is driven into the material through rapid compression of the material as the root diameter of the screw section 100 in a constriction region 118 increases. In concentration region 120, the proces¬ sing agent further concentrates in that portion of the material into which it has been driven, and the root diameter of the screw section 100 and thus the free incremental volume within the bore 36 remaining constant. In absorption region 120, the root di¬ ameter rapidly decreases at a step, whereby the material rapidly expands from its compressed state and more processing agent is absorbed into the material. The rapid expansion takes place after each step with the resulting action of the material being much like a household sponge which is succes¬ sively compressed and released during immersion in a liquid.

Thereafter, the material again re-enters constriction region 118, concentration region 120, and absorption region 122 in zone B, as shown in Fig. 15, and thereafter in zone C, as shown in Fig. 17. Figs. 13, 15 and 17 show the successive impreg¬ nation zones on groove 108, while the same process¬ ing takes place in groove 106 as shown in Figs. 14, 16 and 18.

With each succession of constriction, con¬ centration and absorption, the material undergoes additional fibrillation and the processing agent is further impregnated. The impregnation zones A, B and C are successively more restrictive to cause successively greater penetration of the processing agent into the fibrous material and to ensure no particles of material which are too bulky to receive the processing agent throughout are able to pass through the second head section 28. The number of zones required to treat a specific material may vary, but the three zones depicted herein should ordinarily be sufficient for most fibrous materials as recited hereinabove. The material has a strong tendency to remain between flights 110, thus re¬ maining within a respective groove 106, 108, to pass through the three successive zones A, B and C of either groove 106, 108 rather than escaping one such zone by moving across flights 110.

The fibrous material is further worked and fibrillated in head section 18 by the narrowing of the insert 34 and screw section 102 to reduce and accelerate the material as it passes therethrough. One or both of longitudinally spaced drains may be employed to remove excess treating agent from the bore or to limit the length of exposure of the materials to conditions of saturation by the treating agent.

Next, the wood material reaches the first processing zones 156, 188 in head section 30 and is further compressed due to the increase in root diameter of the bottom wall 176 between the flight- ing 146 within compression region 162 (see Fig. 5). The bottom wall 176, as described earlier, is preferably roughened to promote rolling of the fibers and cause the fibers to grind against each other and separate from adjacent fibers of the same particle.

Subsequently, as the material reaches the restricted region 164, the particles are forced over the top of the bar 166 which presents. a narrow area or gap through which the same can pass. Consequent-^' ly, additional fiber separation occurs in area of the groove 148 adjacent the bars 166. Next, the particles approach the decompression region 174 wherein the bulk density of the material is de¬ creased and the particles expand somewhat, which further facilitates rolling and mixing of the par- tides before next advancing to the compression region 170 of the second processing zone 158.

Similarly, the material during advancement through zones 158, 160 and 190, 192 are subjected to processing similar to the processing occurring in zones 156, 188. In zones 158, 160, 190, 192 how¬ ever, the material is exposed to higher pressures due to the fact that the same amount of material must flow through an increasingly smaller free in- cremental volume because of the tapered or. conical profile of screw section 104. In addition, the flush dispostion of the outer surfaces 202 of the bars 174, 1,84 forces the material to pass through a smaller restricted opening than is presented out- wardly of the bars 166 in the first processing zone 156.

Importantly, the material when passing through the third processing zones 160, 192 is sub¬ jected to the action of bars 184 in the restricted regions 182 which move relative to the stationary bars 88 of the restricted regions 80 of head section 30. Bars 88, 184 being disposed in acute angular relationship relative to each other, function in a scissors-like fashion to facilitate additional twisting of the fibers of the material without shortening the length of the excessive number of the same.

In preferred embodiments of the invention, the free incremental volume of the bore 36 in the first head section 24 adjacent the inlet 38 is in the range of about 100 times to about 20 times the free incremental volume of the bore 36 surrounding the end of the final screw section 104 in the region adjacent outlet 40. Better results are observed, however, when the same, aforementioned free incre- mental volume adjacent the inlet 38 is in the range of about 70 times to about 50 times the free incre¬ mental volume adjacent outlet 40. In particularly preferred embodiments, the free incremental volume in the bore 36 adjacent inlet 38 is about four times the free incremental volume of bore 36 at the down¬ stream end of the third head section 28, and in turn the latter free incremental volume is about 15 times the free incremental volume in bore 36 in the region adjacent outlet 40.

The particles of fibrous material, during advancement through the bore 36, are compressed in the final restricted region 182 of the third pro¬ cessing zones 160, 192 to a bulk density in the range of approximately seven to approximately 20 times the bulk density exhibited by the material when introduced through the inlet 38 of extruder 20. The temperature of the material during passage through the barrel 22 is advantageously in the range of about 199°F ^"(93°C) to about 347°F (175°C), and preferable at about 230°F (110°C). If desired, moisture may be added to materials such as wood prior to extrusion in order to increase steam generation during the refining process and soften the particles to further facilitate separation of the fibers.

After the material travels along the length of the three processing zones 156-160 and 188-192 of grooves 148, 150 respectively, the mate¬ rial is discharged through outlet 40 which takes the form of an annular opening surrounding the down¬ stream end portion of final screw section 104 and the adjacent, surrounding portions of the final head section 30 downstream of bars 88. The compression regions 162, 170, 180 and particularly the restricted regions 164, 172, 182 of each of the processing zones 156-160 and 188-192, along with the compression region 78 and restricted region 80 of the four grooves 66-72 in head section 30, are operable to restrict or choke the advance¬ ment of materials passing through the extruder 20, with the materials being subject to a greater co - pressive. force in each successive processing zone. The materials may be discharged directly through the annular outlet 40 into the atmosphere, or alterna¬ tively through dies or other types of restricted orifices disposed on the downstream end of the final head section 30. When such dies are used, the ex- truder 20 hereof may be used as a feeding device for a plug flow reactor, with the die apparatus used to control pressures and inhibit plugging within the reactor.

Advantageously, the configuration of the extruder barrel 22 in combination with the configur¬ ation of the screw 96 causes the material particles to rub against each other for proper rollling and twisting and produce a refined product having separ¬ ated fibers of relatively long length. . The "par- tide against particle" action promoted by extruder 20 causes significantly less wear on components of the latter in comparison to, for instance, disc re¬ finers where "material against material" forces are presented. Additionally, the energy requirements of extruder 20 are significantly less than the energy that would be required for processing a similar amount of e.g., wood material by a disc refiner.

Claims

Claims ;

1. An extruder, comprising: an elongated tubular barrel presenting a material inlet and a material outlet; an elongated, axially rotatable, flighted screw within said barrel presenting at least one helical groove along the length thereof, said screw serving to move said material from said inlet towards and through said outlet; means for impregnating said material with a treatment agent during passage of the material through said barrel, said material-impregnating means including — structure located at an impregnation zone between said barrel inlet and outlet for initially constricting said material by subjecting the material to a localized increased pressure and for subsequent decompression of the material, said helical groove being continuous throughout the length of said impregnation zone, both said material constriction and decompres¬ sion structure being within the confines of said barrel; and means for introducing said agent into said barrel at a point upstream of said decom¬ pression structure.

2. An extruder as set forth in Claim 1, said introducing means comprising an injection port intermediate said inlet and outlet.

3. An extruder as set forth in Claim 2, said port being located adjacent said impregnation zone.

4. An extruder as set forth in Claim 3, further comprising a plurality of said ports cir¬ cumferentially spaced around said barrel.

5. An extruder as set forth in Claim 3, including a plurality of said ports longitudinally spaced along said barrel.

6. An extruder as set forth in Claim 1, including means for removing a portion of said agent from said barrel downstream from said introducing means and upstream from said outlet.

7. An extruder as set forth in Claim 6, said agent removing means being located downstream from said impregnation zone.

8. An extruder as set forth in Claim 6, said purging means comprising of at least one drain opening.

9. An extruder as set forth in Claim 8, including a plurality of said drain openings longi¬ tudinally spaced along said barrel.

10. An extruder as set forth in Claim 1, said barrel presenting a helical rib coterminous with said impregnation zone and defining a sleeve groove therealong.

11. An extruder as set forth in Claim 10, said sleeve groove being continuous and uninterupted throughout said impregnation zone.

12. An extruder as set forth in Claim 1, said impregnation zone structure being located in said groove on said screw.

13. An extruder as set forth in Claim 12, said impregnation zone structure comprising a con¬ striction region within said groove of increasing root diameter for constricting said material, and an absorption region downstream of said constriction region of decreased root diameter for decompression of said material.

14. An extruder as set forth in Claim 13, including a concentration region located on said surface of said groove of substantially constant root diameter located intermediate said constriction region and said absorption region.

15. An extruder as set forth in Claim 14, wherein said absorption region is immediately down¬ stream from a step of rapidly decreasing root di¬ ameter on said groove.

16. An extruder as set forth in Claim 15, said constriction region, concentration region and absorption region being successively defined by said

^•surface of said groove and collectively defining said impregnation zone between said screw and said barrel.

17. An extruder as set forth in Claim 16, there being a plurality of said impregnation zones on said screw.

18. A screw section rotatable about a longitudinal axis and adapted for use in advancing material through a barrel of an extruder, said screw section including: at least one outwardly extending flight hel- ically oriented on said screw section from an inlet end to an outlet end thereof for defining a groove on said screw section, s-aid groove presenting a root diameter, said groove also presenting a constriction region of gradually increasing root diameter followed downstream on said groove by an absorption region of abruptly stepped-down root diameter, said constric¬ tion region and absorption region collec- tively defining an impregnation zone on said screw section, said groove being substantially continuous throughout the length of said screw section.

19. A screw section as set forth in Claim

18, said flight presenting an outermost margin, the radial distance between said margin and said longi¬ tudinal axis being substantially constant along the length of said screw section.

20. A screw section as set forth in Claim 18, said screw section successively presenting a plurality of said impregnation zones.

21. A method of bleaching fibrous mate¬ rials comprising the steps of: introducing a mixture of fibrous material and solvent into the inlet of the barrel of an extruder separate from said preconditioner and equipped with a flighted, rotatable screw and an agent introducing means; rotating said screw to advance said material through said extruder to yield an extruded product; elevating the temperature of said material in said barrel to a range from about 50°F to about 500°F; introducing a solution of an oxidizing agent and water into said extruder downstream from said inlet; advancing said material to an impregnation zone comprising a constriction- region and an absorption region; constricting said fibrous material in the presence of said oxidizing solution in said constriction region; decompressing said fibrous material in the presence of said oxidizing solution in said absorption region; said material being advanced through said groove during said constriction and de¬ compression; and passing said material through an outlet of said extruder.

22. A method as set forth in Claim 21, including the step of draining said oxidizing sol¬ ution from said extruder at a location downstream from said impregnation zone and upstream from said outlet.

23. A method as set forth in Claim 21 wherein said reducing agent is taken from the group of sodium hydroxide, ammonium hydroxide, potassium _Q hydroxide and calcium hydroxide.

24. A method as set forth in Claim 21 wherein said oxidizing agent is taken from the group of hydrogen peroxide, hydrogen sulfide, sodium 5 hypochlorite, ammonium sulfate, ammonium sulfide, sulfuric acid, sulfurous acid, hydrochloric acid, calcium chloride, titanium dioxide and ethylene- dinitrilo tetra acetic acid.

0 25. A method as set forth in Claim 21 wherein said mixture is retained in said extruder for a period of about 10 to 90 seconds.

26. A method as set forth in Claim 21 5 including the steps of first preparing said mixture of fibrous material and solvent in a preconditioner and retaining said material in the preconditioner for a period of time in the range of from about five seconds to four minutes. 0

27. A method as set forth in Claim 26, including the step of introducing a reducing agent and water into said preconditioner and subjecting said reducing solution, fibrous material and solvent 5 to intimate mixing.

28. A method of treating a mixture of fibrous material and solvent comprising the steps of: introducing said mixture into the inlet of a barrel of an extruder equipped with an axially rotatable flighted screw and presenting a helical groove about the length thereof; rotating said screw to advance said material through said screw to yield an extruded product; elevating the temperature of said material in said barrel to a range from about 50°F to 500°F; introducing a treating agent into said barrel downstream from said inlet,, advancing said material to an impregnation zone comprising a constriction region and an absorption region; constricting said fibrous material in the presence of said treating agent in said constriction region; decompressing said fibrous material in the presence of said treating agent in said absorption region, said material being advanced through said groove during said counstriction and decompression; and passing said material through an outlet of said extruder.

29. A method of treating a mixture of fibrous material and solvent as set forth in Claim 28, there being a concentration region intermedial said constriction region and said absorption region, and including the step of retaining said fibrous material in a constricted condition prior to decom¬ pression.

30. A method of treating a mixture of fibrous material and solvent as set forth in Claim 28 wherein said material is retained in said extru¬ der for a period of about 10 seconds to about 90 minutes.

31. A method of treating a mixture of fibrous material and solvent as set forth in Claim 28 wherein said fibrous material is advanced through a series of said impregnation zones in the presence of said treating agent.

32. A method of treating a mixture of fibrous material and solvent as set forth in Claim 26 wherein said solvent comprises water.