Method Of Conglomerating Fibers

Abstract

Lignocellulose fibers obtained from wood in a defibrator form conglomerates when held in a state of high turbulence while suspended in air. Globular conglomerates having diameters of 2 to 30 mm., relatively dense outer shells and loose cores are produced continuously in a turbulence zone in dwell times of a few minutes.

Description

This invention relates to a method of combining fibers in conglomerates. More specifically, the invention is concerned with the conglomeration of fibers suspended in a fluid by agitating the suspension so as to produce turbulence in the same.

While it is usually desired to prevent fibers from conglomerating while they are being processed and purified, fiber conglomerates are known to have properties desirable in many applications. The conglomerates are generally of low-bulk density, soft, and yieldably resilient, and may be combined with binders or with other materials to form load-bearing or other construction elements not readily produced from loose fibers with equally desirable results.

It is known to make soft webs, feltlike materials, hard plates and boards, and other shaped bodies from such fiber conglomerates, and to use the conglomerates without or with minor amounts of binders in bulk as insulating materials. Plates having excellent acoustical and thermal insulating properties have been prepared from such fiber conglomerates and plasticized polyvinyl chloride, and other applications have been proposed heretofore.

It is known to combine individual fibers in conglomerates by dispersing or suspending the fibers in a liquid aqueous fluid at very low concentration, and to agitate the suspension to produce mild turbulence, until the desired, generally globular conglomerates are formed. The process is very slow, and it is necessary to agitate the suspension for several hours before conglomerates of useful size are formed.

The suspension must then be filtered to separate the conglomerates from most of the liquid phase, and the fibrous material must be dried to remove the remainder of the water before further processing or storage is possible. The method requires much equipment if a reasonable output rate is to be maintained.

The object of this invention is the provision of a method which permits fibers to be combined in conglomerates at a much faster rate than is possible by the aforedescribed known method, preferably in continuous operation.

Surprisingly, it has been found that many of the shortcomings of the known method can be overcome by replacing the aqueous carrier by a gaseous fluid in which the fibers are suspended, and which is kept in turbulent motion. Rapid conglomeration is achieved when the suspension is confined in a space between upright walls, and turbulence is produced therein by propelling the fibers in a portion of the suspension through the remainder of the suspension in an upwardly extending path spaced from the confining walls.

The velocity at which the fibers are propelled in the aforementioned path should be such as to cause the formation of a turbulent horizontal layer which contains fibers at a density higher than the density of the fibers in all portions of the suspension located below the layer.

When the fibers essentially consist of cellulose or lignocellulose, the preferred fiber material, the upward velocity should be between 2 and 5 meters per second, and best approximately 3 meters per second. The formation of conglomerates is further accelerated if water is sprayed into the space in an amount sufficient to increase the moisture content of the fibers.

The fibers may be propelled upwardly in the aforementioned path by agitator blades which move in the path, or they may be propelled by kinetic energy transmitted thereto by gas injected into the space.

The conglomerates may be given a wide variety of desirable properties by spraying normally solid materials into the processing space in liquid form for deposition on the fibers, removing the fibers from the space, and solidifying the deposited material.

When mechanical agitation is preferred, suitable equipment may include a container and two shafts whose axes extend in a common horizontal direction, and which are spaced from each other in a horizontal direction. Blades project radially from each shaft in the container, at least one blade projecting from each shaft being interposed between the two shafts. The shafts are driven simultaneously in respective directions to cause the interposed blades to move in an upward direction. Fibers are fed to the container adjacent an axially terminal portion of one of the shafts, and conglomerated fibers are discharged from the container adjacent the other axially terminal portion of the shaft.

Other features, additional objects, and many of the attendant advantages of this invention will readily be appreciated as the same becomes better understood by reference to the following detailed description of preferred embodiments when considered in connection with the appended drawing in which:

FIG. 1 illustrates a device for producing fiber conglomerates of the invention in continuous operation, the view being in front elevational section;

FIG. 2 shows the device of FIG. 1 in side elevational section on the line II--II; and

FIG. 3 illustrates a modified device of the invention in a view corresponding to that of FIG. 2.

Referring initially to FIGS. 1 and 2, there is seen an elongated trough 1 whose bottom wall has two cylindrically arcuate sections meeting in a ridge along the longitudinal centerline of the trough. A tall cover 2 is flanged to the horizontal top rim of the trough to enclose a chamber with the same. Openings 3 are provided in the top portion of the cover 2 and normally hold nozzles, omitted from the drawing for the sake of clarity, which permit a liquid to be sprayed into the chamber in a downward direction, as indicated by arrows. A chute 4 is provided at one longitudinal end of the cover 2 for feeding fiber material to the chamber from above. A discharge chute 5 is provided on the transverse end wall of the chamber remote from the feeding chute 4 and closely below the topmost portion of the cover 2.

Agitating equipment installed in the chamber includes two shafts 6 journaled in bearings 11 outside the chamber, passing freely through the end walls of the chamber, and approximately coaxial with the two cylindrical bottom sections respectively. Two groups of diametrical arms project from each shaft and are offset 90.degree. from each other. The arms are distributed on the associated shaft 6 over the entire chamber length in axially spaced relationship, arms of one group alternating with arms of the other group. The free ends of each arm carry blades 7 inclined about 45.degree. to the radial plane in which the arm rotates.

A V-belt pulley 8 on the free end of one of the shafts 6 outside the chamber enclosed by the trough 1 and the cover 2 is connected by a drivebelt to an electric motor 9. Meshing spur gears 10 on the two shafts cause the blades 7 associated with the two shafts to revolve in opposite directions about the axes of the associated shafts, the arrangement being such, as best seen in FIG. 2, that the blades 7 between the shafts 6 move upwardly in a path above the ridge in the bottom wall of the trough 1 in interdigitating relationship, the arms on the two shafts being out of phase by 45.degree..

An opening in the bottom wall of the trough 1 below the discharge chute 5 is covered with a coarse screen 12, and a nonillustrated conveyor leads from the area below the screen 12 to the nonillustrated storage bin from which the feed chute 1 feeds fibers into the chamber.

In the modified device shown in FIG. 3, the mechanical agitation equipment is replaced by pneumatic devices. A trough 1 and cover 2 identical with the corresponding elements described above with reference to FIGS. 1 and 2 constitute the walls of a chamber into which material may be sprayed from above through nonillustrated nozzles set into openings 3 of the cover 2. Partitions arranged along both upright, longitudinal chamber walls enclose a manifold inlet duct 13 which extends over the entire length of the chamber and communicates with the same through closely spaced nozzles 14 distributed over the length of each manifold duct contiguously adjacent the cylindrical bottom wall section or through a corresponding slot. The nozzles 14 direct substantially tangential jets of gas against the associated wall section in a direction toward the central ridge of the bottom wall at which the two streams converge.

An outlet duct is arranged above each manifold duct 13 and is longitudinally coextensive with the same. It is separated from the central main portion of the chamber by a screen 16. Pumps 17 arranged next to the upright longitudinal chamber walls draw air from the chamber through the screens 16 and conduits 15, and return the air under pressure to the manifold ducts 13.

The flow pattern observed in the chamber when the pumps 17 are operated is indicated by arrows in FIG. 3. The two airstreams meeting at the ridge in the chamber bottom mingle and mainly flow upward toward the cover 2 in a straight path until the combined stream is again split and deflected in two opposite lateral directions by the suction in the conduits 15. An area of turbulence thus extends on either side of the vertically rising central stream.

In actual embodiments of the illustrated devices, the chambers bounded by the troughs 1 and covers 2 had each a length of 2 meters, a height of 1 meter and a width of 1.2 meters. Other dimensions are evident from the drawing. They were employed for making globular conglomerates of lignocellulose fibers produced from pine wood on a conventional defibrator. The fibers ranged in length from 1.8 to 4.5 mm., averaging 3.1 mm., and in diameter from 0.014 to 0.046 mm., averaging 0.035 mm. The bulk weight of the fibers was 50 kg./m.sup.3.

The following Examples 1 to 3 illustrate the operation of the apparatus of FIGS. 1 and 2.

EXAMPLE 1

The shafts 6 were rotated at 91 r.p.m. The fibers which contained 8 percent moisture were fed continuously to the chamber at a rate of 10 kg./min. The dwell time in the chamber was 3 minutes, and the 30 kg. of fibers present in the chamber filled the same to approximately one third, the remainder of the chamber being occupied by air.

The blades 7 imparted sufficient upward motion to the fibers to produce a relatively dense layer of fibers in the chamber near the top of the cover 2 which looked somewhat like the surface of a gently boiling, somewhat viscous liquid, such as bubbling pea soup. Turbulence in the top layer of the fiber suspension was intense, and a multiplicity of localized eddies was clearly discernable through an inspection window in the cover 2, not shown in the drawing. The fiber density in the turbulent top layer was much higher than in the lower portion of the chamber.

The turbulent suspension was sprayed through the openings 3 with an aqueous solution of a catalyzed urea formaldehyde precondensate containing 50 percent resin-forming material at a rate of 2 kg. of solution per 10 kg. lignocellulose fibers. Globular fiber conglomerates bonded by partly set urea formaldehyde resin were continuously discharged from the chute 5. They lost their excess moisture quickly while the resin fully set, and thereafter had relatively high crushing strength.

The dried and fully cured conglomerates were employed in bulk for filling cavities in building walls to improve acoustical and thermal insulating properties of the walls. They also could be fed directly from the cute 5 to a press in which they were converted to insulating boards under heat and pressure.

EXAMPLE 2

Electric heaters were attached to the outer walls of the apparatus shown in FIGS. 1 and 2 and supplied with current of a strength sufficient to maintain a temperature of 120.degree. to 130.degree. C. in the chamber. The fibers were preheated to the same temperature before being fed to the chamber through the chute 4, and lost some of their initial moisture content of 8 percent during heating. The blades 7 revolving at 91 r.p.m. caused the conglomeration of a major portion of the individual fibers when they had traveled over about one-half of the axial length of the chamber.

They were sprayed in the longitudinal half of the chamber near the discharge chute 5 with high-vacuum asphalt having a drip point of 85.degree.-95.degree. C. which was sprayed into the chamber at a rate of 9 kg. per 10 kg. of fiber at a temperature of 230.degree. C. and at 15 atmospheres gage pressure.

The globular fiber conglomerates impregnated with the bituminous material which were discharged from the chute 5 were readily converted under moderate pressure to insulating plates of excellent thermal and acoustical properties and impervious to moisture.

EXAMPLE 3

Fibers fed to the chute 4 as described in Example 1 were sprayed through the openings 3 with a latex of styrene butadiene copolymer containing 45 percent solids. The latex was applied at a rate of 2.5 kg. per 10 kg. of lignocellulose fibers.

The fiber conglomerates charged with latex which were obtained in this manner were resilient and could be further processed for form continuous webs or plates similar in their properties to commercial floor covering material prepared from fiber felt and polyvinyl chloride.

The operation of the pneumatic apparatus shown in FIG. 3 is illustrated by Examples 4 to 7.

EXAMPLE 4

Defibrator stock of the type described above and still containing 40 percent moisture was fed to the chamber at a rate of 10 kg./min. while air was injected from the nozzles 14 at a velocity of 50 m./sec. and at a rate of 20 m..sup.3 /sec. A turbulent, relatively dense fiber layer formed in the upper portion of the chamber, and most fibers were converted, mainly in the dense layer, to globular conglomerates of relatively low mechanical strength. Those fibers which traveled through the chamber without forming conglomerates ultimately dropped through the screen 12 and were returned to the chute 4.

After drying, they were sufficiently coherent for use as bulk insulating material that could be poured into cavities in guiding walls and the like.

EXAMPLE 5

The fibrous material received from the defibrator with a moisture content of 40 percent was predried to 8 percent moisture, and was thereafter subjected to intensive turbulence in the apparatus of FIG. 3 by means of air injected in the manner described in Example 4.

The globular fiber conglomerates discharged from the chute 5 were even looser than those obtained in Example 4. They were ready for use as a bulk insulating material having thermal and acoustical properties far superior to those of the starting material.

EXAMPLE 6

The procedure of Example 5 was modified by spraying water droplets fine enough to form a fog on the turbulent fiber material in the chamber through the openings 3 at a rate of 3 kg. water per 10 kg. fibers. The mechanical strength of the conglomerates so obtained was superior to that of the material produced in the method of Examples 4 and 5.

EXAMPLE 7

The method of Example 6 was further modified by replacing the water sprayed through the openings 3 by an equal weight of an aqueous solution containing 70 g. sodium pentachlorophenate per kilogram water. The sodium pentachlorophenate not only provided protection against insects and fungi, but the globular fiber conglomerates so produced were stronger than those obtained from the procedures of Examples 4 to 6, though not as strong as the conglomerates bonded with synthetic resin (Example 1).

Defibrator stock obtained from soft wood without the use of chemicals is the cheapest fibrous material available to us at this time. It is preferred for this reason and has been described with reference to all Examples. However, pure cellulose fibers, fibers of animal origin, synthetic fibers, and fiber mixtures have been converted to globular conglomerates within a few minutes as described above.

It is believed that the fibers are partly interlocked in lumps as they move at different speeds, and partly in opposite directions in the generally rising stream above the rib in the trough bottom, and that the loosely cohering groups of fibers so produced assume the globular shape in the intensely turbulent zones. Lignocellulose fibers, such as those produced from wood on a defibrator, have been found to be superior to most other fibers in their ability of aggregating or interlocking with each other. Their resiliency is high, and the conglomerates formed have thus desirable properties for use as principal ingredients or fillers in compositions for use in construction work.

Moisture present in the conglomeration zone has been found to hasten the formation of the globular bodies from cellulose, lignocellulose, and chemically related fibers. The water need not necessarily be present in the liquid form, and steam has been used successfully. The water is believed to be effective by its surface tension and by the bonding effect of its hydroxyl groups. The small amount of water which is preferably employed is readily removed during a short air-drying period or by hot pressing of the conglomerates.

The normally solid bonding and impregnating agents described in Examples 1, 2, 3, and 7 are merely illustrative of the materials which may be employed for modifying the mechanical and other properties of the fiber balls, and other materials will readily come to mind which are suitable for application while in a liquid state, in the form of their melts or solutions, and which can thereafter be made to solidify by lowering their temperature or by evaporating a solvent. Water-repellent, flame-retarding, and pest-control agents have been applied in the manner obvious from Example 7.

Bonding agents based on polymers other than ureaformaldehyde resin or styrene-butadiene copolymer have been used to produce basically fibrous balls whose properties could readily be predicted from the nature of the synthetic material. Plasticized polyvinyl chloride has been employed in preparing globular conglomerates of the invention which were thereafter converted to floor covering sheets by hot pressing. The ratio of fibers to resin and the pressure employed during pressing may be varied to adapt the ultimate product to the intended use. Phenolic resins have been sprayed on lignocellulose fibers in a procedure similar to that of Example 1, and the resin was fully cured on the globular bodies discharged from the chute 5 while the material was converted to storing plates under high pressure. Such plates have been found to resist weathering well and to be suitable for wall shingles and the like. The fiber conglomerations of the invention have also been mixed with plaster and with cement as fillers in the production of prefabricated boards and plates capable of carrying loads in building constructions.

The fiber conglomerates when produced without additives other than water or other volatile liquids have a globular shell whose fiber density is higher than that of the interior or core. When impregnating agents are applied to the fibrous material at a stage in which the shell has been formed, relatively little of the impregnating material reaches the core. The procedure described in Example 2 is therefore preferred when the fiber balls are intended to be bonded to each other by means of thermoplastic material in a subsequent hot pressing operation. The penetration of the conglomerates by the bituminous material sprayed into the chamber can be controlled precisely by selecting the temperature prevailing in the chamber and the temperature of the sprayed material.

While not specifically illustrated, it will be understood that bonding of lignocellulose fiber conglomerates in a hot-pressing operation can be accomplished by admixing minor amounts of thermoplastic synthetic fibers to the defibrator stock either prior to entry into the chamber or in the chamber itself.

When streams of gas are employed for suspending the fibers and for generating turbulence in the suspension, impregnating agents may be admixed to the gas outside the chamber in an obvious manner, rather than introduced into the chamber itself. Gases other than air may be employed if so desired.

The relatively dense, turbulent fiber layer which is thought to be essential for the rapid formation of globular fiber conglomerates in the method of the invention is readily observed, and other process variables have to be adjusted accordingly. The specific conditions of agitation described above have been found satisfactory for a chamber of the illustrated shape and the described dimensions when processing lignocellulose defibrator stock. The necessary modifications for operation under other conditions have to be determined experimentally.

The angle between the driving surfaces of the blades 7 and a radial plane may have to be reduced to as little as 5.degree., and the blades illustrated in FIGS. 1 and 2 are adjustable over this range by means of nonillustrated threaded studs, nuts, and slots employed for fastening the blades to the diametrical arms in a basically conventional manner. The dwell time of the fibrous material in the chamber is closely related to the blade angle and to the rotary speed of the shafts 6.

Under otherwise unchanged conditions, the dwell time, and particularly the time spent by the fibers in the turbulent, dense, top layer determines the diameter of the fiber balls formed which is readily varied between 2 and 30 mm., being approximately 15 mm. in the material produced in Examples 1 to 7.

The oblique position of the blades 7 also has been found to cause individual fibers to turn about their longitudinal axes while they are being propelled upwardly in the central zone of the chamber. Rapid conglomeration of fibers is thought to be due to this turning movement.

In the apparatus illustrated in FIGS. 1 and 2, the desired turbulent fiber layer is formed at circumferential blade velocities of approximately 2 to 5 meters per second. At rotary speeds too low to result in a circumferential velocity of 2 m./sec., an effective turbulent layer is not formed. At blade velocities higher than 5 m./sec., conglomerates formed by turbulence tend to be broken up by the blades or by collision with other conglomerates traveling at the same velocity as the blade circumference. Most rapid conglomeration is normally achieved at a blade velocity of about 3 m./sec.

In the pneumatic agitation system shown in FIG. 3, the amount of air supplied, the cross section and direction of the nozzles 14 are adjusted in such a manner that the fibers move upwardly in the central chamber zone at a velocity similar to that achieved in the mechanical system, that is, at 2 to 5 meters per second, and preferably at about 3 meters per second.

Claims

What is claimed is:

1. A method of combining individual fibers in conglomerates which comprises:

a. suspending said fibers in a gaseous fluid;

b. confining the suspension so formed in a space between upright walls;

c. propelling the fibers in a portion of said suspension through the remainder of said suspension in an upwardly extending path spaced from said walls until turbulence is produced in said suspension; and

d. maintaining said propelling and said turbulence until said conglomerates are formed.

2. A method as set forth in claim 1, the fibers in said portion of said suspension being propelled in said path at a velocity sufficient to cause the formation of a turbulent horizontal layer containing said fibers at a density higher than the density of said fibers in all portions of said suspension located below said layer.

3. A method as set forth in claim 1, said fibers essentially consisting of cellulose or lignocellulose.

4. A method as set forth in claim 3, the fibers in said portion of said suspension being propelled in said path at a velocity of 2 to 5 meters per second.

5. A method as set forth in claim 4, said velocity being approximately 3 meters per second.

6. A method as set forth in claim 3, spraying water into said space in an amount sufficient to increase the moisture content of said fibers in said space.

7. A method as set forth in claim 1, the fibers in said portion of said suspension being propelled by agitator blades moving in said path.

8. A method as set forth in claim 1, the fibers in said portion of said suspension being propelled in said path by kinetic energy transmitted thereto by gas injected into said space.

9. A method as set forth in claim 1, spraying a normally solid material into said space in liquid form for deposition on said fibers, removing the fibers carrying the deposited material from said space, and solidifying said material.