US3508713A - Mechanical defibration - Google Patents

Description

April 1970 G. P. HUPPKE 3,508,713

MECHANICAL DEFIBRATION Filed Feb. 15, 1968 5 Sheets-Sheet l FIBER CLUMPS AIR DEFIBRATOR I f CYCLONE SEPARATOR AIR BLOWER #PRODUCT F i G.

F I G. 5.

INVENTOR.

GLEN P. HUPPKE April 28, 1970 G. P. HUPPK-E 3,508,713

MECHANICAL DEFIBRATION Filed Feb. 13. 1968 3 Sheets-Sheet 2 GLEN P. HUPPKE April 28, 1970 G. P. HUPPKE 3,503,713

MECHANICAL DEFIBRATION Filed Feb. 15, 1968 3 Sheets-Sheet 5 F l G. 3

F l G. 4.

INVENTOR.

GLEN P. HUPPKE United States Patent 3,508,713 MECHANICAL DEFIBRATION Glen P. Huppke, Beaver Falls, N.Y. 13305 Filed Feb. 13, 1968, Ser. No. 705,037 Int. Cl. B02c 13/10 U.S. Cl. 24119 7 Claims ABSTRACT OF THE DISCLOSURE Mechanical defibration in which small clumps of fibers, while suspended in a gaseous annular layer, are impacted and split by sharp points closely spaced on a rotor, are thrown centrifugally against spiral baffies located on the interior of a stationary surrounding shell, and rebound from the bafiles into repeated contact with the points, whereby the clumps are reduced to individual fibers without substantial fiber shortening.

FIELD OF THE INVENTION This invention relates to a method of mechanical defibration of small clumps of fibers of the type in which the fiber-to-fiber bond is considerably weaker than the fibers themselves, such as Wood splinters, pieces of rags and cloth cuttings. By defibration is mean separation of the individual fibers from one another without substantial reduction of length of the fibers in the fiber clumps of the charging stock.

DESCRIPTION OF THE PRIOR ART Processes for the mechanical reduction of fibrous materials of the character described may be divided into three principal types, (1) wet milling, (2) dry milling and (3) centrifugal reduction. In the wet milling processes, the charging stock is acted upon while suspended in a relatively large proportion of water or other liquid, so as to form a slurry. The refining methods commonly used in paper pulp manufacture, as in the well known Jordan machines, are of this type. Although fiber separation is accomplished without substantial reduction of fiber length, these wet milling processes suffer from the disadvantages that they are slow and their power consumption is high.

In dry milling, pieces of fibrous material, often relatively large, are subjected to the action of tools such as grindstones, hammers, knives or saw teeth, while the pieces are restrained from moving away from the milling tools either completely, as by an anvil, or largely, as when the pieces are packed more or less tightly in a confining channel. Such dry milling methods are not suitable for defibration because, when applied to relatively small clumps of fiber, size reduction takes place about as much by snapping the fibers as by splitting them apart. Excessive dust and extremely small fines are apt to be produced.

The present invention belongs to the third class, centrifugal reduction, in which the charging stock is acted upon by centrifugal force while dry or moist without excess water being present. In prior processes of this type, it has been customary to bat the charging stock by means of rotating blades or fingers against a hard wall, thereby, in effect, relying on what may be called centrifugal smashing as opposed to the centrifugal point splitting of the present invention. When centrifugal smashing is used with woody materials, true defibration is not obtainable, but, instead, the fibers are left interconnected although they are opened up or spread (see Respess U.S. Patent 1,897,620, Feb. 14, 1933).

SUMMARY OF THE INVENTION Small clumps of fibers of such character that the fiberto-fiber bond is considerably weaker than the fibers themselves, are defibrated by repeatedly subjecting them while suspended in an annular layer of air or other gas flowing from an inlet end to an outlet end, to the impact of sharp points moving in circular paths, such as saw teeth mounted on a rotor. Because of the relative weakness of the fiberto-fiber bond, the energy required to split the clumps is less than that required to snap the fibers. By virtue of the gaseous suspension, the fiber clumps, before impact, are moving not only longitudinally toward the outlet but also circumferentially in the same general direction as the points and, after impact, are free to move away from the points, thereby limiting the energy applied to the clumps by the points to a value less than that required to snap the fibers. The necessary repeated actions are obtained by rebounding the clumps back toward the points from baffies arranged on the interior of a stator surrounding the rotor. To improve the rebounding action and to minimize smashing of the fibers on the bafiles, the bafiies are preferably triangular in cross-section and resilient. In order to achieve optimum defibration, the baffles should be spirally arranged in such manner that the angular relationship between the circular paths of the points and the surfaces of the bafiles tends to direct the rebounding clumps, particularly the heavier ones, against the longitudinal fiow of the annular gaseous layer. An important feature of the invention is a particular method of continuously cleaning the sharp points during operation by 'jets of steam or other gas.

BRIEF DESCRIPTION OF DRAWINGS FIGURE 1 is a diagrammatic view of an apparatus for carrying out the method of this invention.

FIGURE 2 is a side elevation of the' defibrator of FIGURE 1, parts being broken away to show the interior.

FIGURE 3 is an end elevation of the defibrator looking at the inlet end, the left end of FIGURE 2.

FIGURE 4 is a cross-section taken on the line 44 of FIGURE 2, looking toward the inlet end.

FIGURE 5 is a detail view taken on the line 5-5 of FIGURE 4, showing a preferred manner of mounting a band of saw teeth on the outer surface of the rotor of the defibrator.

FIGURE 6 is a diagrammatic view, on a reduced scale, of the inside of the rear vertical half of the stator of the defibrator, showing the spiral arrangement of the baffles.

DETAILED DESCRIPTION OF DRAWINGS Referring to FIGURE 1, air and charging stock in the form of fiber clumps are introduced into the inlet of the blower 10, which may be of a conventional centrifugal type, driven by an electric motor (not shown). The resulting mixture is discharged from the outlet of blower 10 into the defibrator 11. The mixture is introduced into the inlet chamber 12 of defibrator 11, passes through the defibrating chamber 13 and into the outlet chamber 14. The mixture passes from outlet chamber 14 to a separator 15, which may conveniently be of the well known cyclone type, with the defibrated product being discharged at the bottom and the separated air at the top. A suitable construction of defibrator 11 is shown in the other figures of the drawing, and the principal steps of the method of this invention are carried out in defibrating chamber 13.

Referring particularly to FIGURES 2, 3 and 4, defibrator 11 comprises a base 20 on which are mounted at each end standards 21 each carrying a bearing 22 supporting the shaft 23. On one end of shaft 23 is mounted a pulley 24 by means of which, through a belt and motor (not shown), the shaft may be rotated in a clockwise direction looking at the inlet end of the defibrator, as shown in FIGURE 3. To shaft 23 are secured the toothed rotor 25 forming the inner surface of defibrating chamber 13 and, at either end of rotor 25, four radial fan blades 26, which are located, respectively, in inlet chamber 12 and outlet chamber 14. The chambers 12 and 14 may be sheet metal housing, constructed identically except that the inlet conduit 27 is preferably located at the top of inlet chamber 12 and the outlet conduit 28 at the bottom of outlet chamber 14, both being preferably tangentially arranged, as best shown in FIGURE 3.

The toothed rotor 25 may be constructed precisely the same as the main cylinder of a shredder, a machine widely used in the textile industry for shredding or opening various kinds of rags, clips, yarn or fabric waste. These cylinders are obtainable on the open market in sizes up to five feet in diameter and six feet long. In a pilot defibrator for practicing the method of this invention, I have successfully used as the rotor, a cylinder of this type one foot in diameter and three feet long. The speed of rotation should be the maximum safe rotational speed, and I have used 1400 rpm. The specific values given below relate to that pilot machine. Of course, other factors being equal, the larger the rotor, the greater the capacity of the defibrator. I believe that a defibrator with a rotor two feet in diameter and six feet long would be eminently suitable for the commercial practice of this invention.

Such cylinders are spirally grooved, with the groove having various numbers of turns per inch, and a direction of wind the same as the intended direction of rotation. Wire clothing is inserted in the groove and secured therein, as by swaging. Such wire clothing is frequently called garnett wire and is illustrated in FIGURE 5. It consists of a wire 29 having saw teeth 30 along one edge, and may have 14 turns per inch. The teeth have three angles, known as the working angle, tooth angle and rake angle, which together total 90. I have found suitable values for these angles to be 40 for the working angle, 25 for the tooth angle and 25 for the rake angle. Suitable dimensions for the teeth are 0.020" wide at their bases, tapered to a thickness of 0.006" or less at their tips, with a tooth height of 0.125", and seven teeth per inch of wire. The teeth must point in the direction of rotation of the rotor, as appears in FIGURE 4. In a shredding machine, the main cylinder cooperates with a plurality of smaller, similarly toothed rolls but, according to this invention, the toothed rotor 25 cooperates with a stator 31 which, with the rotor, defines the annular defibrating chamber 13.

The stator 31 defines the outer surface of defibrating chamber 13 and is supported by a framework secured to the base 20, as by welding. That framework comprises two end plates 32, a longitudinal lower bar 33 and a longitudinal upper bar 34. The stator 31 is shown as being formed of two removable, vertical half- shells 35 and 36, an internal view of the rear half-shell 36 being shown in FIGURE 6. Each half-shell is attached to and supported by a subframe including lower and upper flanges 37 and 38, respectively, which are bolted to the lower and upper bars 33 and 34, as best shown in FIG- URE 4. Each subframe additionally includes semiannular end plates 39 and ribs 40, and the latter may be reinformed midway between the flanges 37 and 38 by tie rods 41 (see FIGURES 2 and 4). It will be observed that this construction permits the stator 31 to be installed and removed without disturbing the rest of the defibrator, and also permits the half- shells 35, 36 to be made of light weight, bendable sheets, such as steel or aluminum of, say, 20 gauge, for convenience in installing the battles 42 and repairing them if necessary.

Together, the half- shells 35, 36 are slightly frustoconical in shape, so that, with the cylindrical rotor 25, the annular defibrating chamber 13 continuously and uniformly decreases in thickness from the inlet end to the outlet end of the defibrator. The thickness of annular chamber 13 may conveniently be such that the clearance between baffies 42 and teeth 30 ranges from /2" at the inlet end to at the outlet end. The baflies 42 are preferably made of strips of resilient material such as rubber, spirally arranged as shown in FIGURE 6. The rubber strip material may conveniently have the crosssectional shape of an equilateral triangle with a height of A". Conveniently, baffles 42 may be cemented, for example with an epoxy resin, to the inner surfaces of the sheets that are to form the half-shells, while the sheets are in a flat condition. In that condition, baffles 42 will be straight, and the straight rubber strips will assume a spiral shape when the sheets are bent to the required frusto-conical shape. The rubber strips may be disposed on the fiat sheets at an angle of 45, which will give the baffles a spiral angle of 45 to the longitudinal axis of the defibrator when the sheets are bent to their final shape. The baflles are preferably equally spaced apart and, conveniently, there may be a total of 27 baffles, as shown in FIGURE 6, for a three-foot long rotor.

It is highly desirable and, from a commercial standpoint, probably necessary, to clean the teeth 30 continuously during operation of the defibrator. For this purpose, I have successfully employed steam jets directed to impinge on the backs of the teeth, as shown in FIG- URE 4. A suitable apparatus is shown in FIGURES 2 and 4 and comprises jet tube 45 provided along its length with a row of apertures 46 and mounted for axial reciprocation in saddle blocks 47. The apertures 46 slant 30 from the vertical in the direction of rotation of the rotor 25, and may be 0.020" in diameter. The portion of tube 45 carrying apertures 46 projects into a space provided between the lower edges of the half- shells 35, 36. One end of jet tube 45 is provided with steam through a hose 48. The steam is preferably dry so as not to add too much moisture to the charging stock. The other end of tube 45 is closed by cap 49 that is connected to the reciprocating mechanism 50 (FIGURE 2), which may be a hydraulic cylinder and piston serving to reciprocate tube 45 through a distance of, say, five inches at a rate of three strokes per minute. The stroke should be longer than the distance between adjacent apertures 46, so

that all teeth are swept by the cleaning jets. I have found that, using this mechanism and method, the teeth are practically as clean at the end of a run as at its beginning, whereas the teeth are apt to become clogged if no cleaning jets are employed.

OPERATION My method of defibration is applicable to any fiber clumps of appropriate size of a material such that the fiber-to-fiber bond is weaker than the fibers themselves. The fiber clumps must be sufi'iciently small so that they can enter defibrating chamber 13 without clogging. Using the pilot difibrator described above, I have successfully obtained substantially defibration without substantial reduction of fiber length, of Wood splinters averaging /2 long along the grain and roughly A" square; diced rags approximately 4" square and smaller; and blue denim cuttings with an average size of 1" square. The Wood chips of commerce average 1" in length along the grain and 1" x 2" in cross-section. For defibration by this invention, such wood chips may readily be reduced by conventional hammer milling to splinters of the size described above, which splinters constitute a highly satisfactory charging stock. The substantially completely defibrated product is useful in paper manufacture and for many other purposes.

The capacity of blower 10 should be sufficiently high to carry the fiber clumps of the charging stock into the defibrator in suspension in air. With the described pilot defibrator, I have found a blower capacity of 700 cubic feet per minute to be sufiicient. Room temperature air is ordinarily entirely satisfactory but, if desired, steam may be admitted into blower 10' along with the air to humidify the charging stock. It is advantageous for the charging stock to have a water content when it enters the defibrator of about 25% if operated at room temperature and about 15% if the charging stock is preheated. Other gases than air could be used as a suspending medium for the fiber clumps, and could be recovered and recycled from the cyclone separator but, with ordinary charging stocks, there is no advantage in going to this additional expense.

Each tooth 30 of rotor 25 constitutes a sharp point revolving in a circular path. When a point strikes a fiber clump, the point splits the clump along and between fibers, and does not tend to break the fibers, because the energy of impact is limited by the freedom of the clump to move away from the point, and because, with charging stocks of the character contemplated, the fiber-to-fiber bond is considerably weaker than the fibers themselves. As a result, the clump is reduced in size by what we may call centrifugal point splitting, without substantial fiber shortening.

At the same time that this splitting takes place, the clump splits are thrown centrifugally outward against stator 31. The air stream flows circumferentially around and longitudinally through defibrating chamber 13, so that the layer of air whirls spirally. Because of the velocity of this layer of air, the impact of a point against a clump does not drive the clump splits radially outward. Instead, the direction of movement of a centrifugally thrown clump split is inclined somewhat from the point toward the exit of chamber 13, and the smaller the clump split the greater this inclination will be, because the air stream has a greater effect on a light fragment than on a heavy one.

In the absence of bafifles, a clump split will rebound from the smooth stator shell in such manner as to land back on the rotor at a point considerably nearer the exit than that which it had just left. Accordingly, even relatively heavy clump fragments pass through the defibrator rather rapidly, and emerge without having been fully defibrated. Indeed, with a stator having a smooth inner wall, very little defibration of wood splinters is obtained, of the order of a few percent. Much the same situation exists with longitudinal baffles, although in that case the yield of defibrated product is somewhat increased, up to around In either of these cases, it is necessary to separate the defibrated product from the remaining fiber clumps at the end of a pass through the defibrator, which fiber clumps will be of a smaller size than initially, and rerun the separated clumps through the defibrator a number of times until substantially complete defibration is obtained. This procedure not only increases the power consumption and time required, but such a separating step is not practicable commercially, although it can be performed in the laboratory.

With the spiral baffles of this invention, substantially 100% defibration is obtainable in a single pass through the defibrator. In order to accomplish this, the baflles must cross the circular paths of the tooth points at an angle such that, when a clump split is centrifugally thrown against a baflle, it rebounds back toward the rotor in a direction against the longitudinal flow of the annular air layer through defibrating chamber 13. The heavier the clump split, the more pronounced this backward rebounding will be. Very light separated fibers are carried along by the air stream toward the outlet, but the heavier splits have sufficient momentum to carry them back to the rotor at a point that may even be further toward the inlet end than the point at which it just previously left the rotor. If it were not for the air stream whirling spirally around and through defibrating chamber 13, the angle of rebound would, of course, be exactly equal to the angle of incidence but, in practice, both angles are affected by the velocity of the air layer. With the chosen method of operation, the net result is that relatively large fiber clumps are retained in defibrating chamber 13 until they are completely defibrated,

6 whereas wholly separated fibers are carried rapidly along to the exit.

The spiral angle of the battles is not critical, and I have found from 25 to 60 to produce satisfactory results, depending somewhat upon the nature of the charging stock and the velocity of the air stream. The recommended 45 angle is, however, suitable with all of the charging stocks specifically mentioned above, and give complete defibration in a single pass with all of them. It is not essential that the batfles follow a true and uniform spiral course, but this is the simplest and most eifective way of obtaining the desired angular crossing of the point paths by the baffle surfaces.

It is by no mean essential that the baflies be triangular in shape and they could be square or rectangular, although I have found that the triangular cross-section gives the best results. Nor is it essential that the baflies be resilient and I have successfully used rigid steel bafifles although, once again, resilient baflles are preferable.

As stated above, it is highly desirable that my point splitting defibration method be carried out in conjunction with the tooth cleaning method above described. With out the cleaning steam jets, tiny bits of fiber tend to cling to the teeth and eventually clog them.

The fan blades in the inlet chamber 12 serve to break up any agglomerates of the charging stock and generally help to supply sufficient turbulence to keep the feed mixture well dispersed as it enters defibrating chamber 13. The fan blades in outlet chamber 14 are less important, but they do help to maintain a turbulent mixture and prevent possible settling out or clogging between defibrating chamber 13 and cyclone separator 15.

Having thus described my invention in the best mode known to me, what I claim is:

1. The method of separating fiber clumps into their constituent fibers, the fiber clumps being of such character that the bond between the fibers is weaker than the fibers themselves, which comprises producing a gaseous stream, introducing said fiber clumps into said gaseous stream and suspending them therein, causing the resulting mixture to flow through a constricted zone in the form of a thin, annular layer, causing said annular layer to rotate circumferentially during its flow toward the outlet end of said zone, impacting said fiber clumps while suspended in said zone by sharp points located adjacent the inner margin of said layer, said points extending in the general direction of a fixed circular path and moving along that path in the direction of said circumferential rotation of said annular layer, whereby said fiber clumps are driven centrifugally toward the outer margin of said layer, rebounding said fiber clumps back toward said points from deflecting surfaces located adjacent said outer margin and across said circular point paths, the angular relationship between the path of said points and said surfaces being such that the direction of rebound is opposed to the direction of longitudinal flow of said annular layer, repeating such impacting and rebounding along said zone, whereby said fiber clumps are mechanically defibrated without substantial fiber breakage, and separating the defibrated product from the gaseou stream beyond the outlet end of said zone.

2. The method as claimed in claim 1 in which said deflecting surfaces cross said circular point paths at an angle in the neighborhood of forty-five degrees.

3. The method as claimed in claim 2 in which said deflecting surfaces are resilient.

4. The method as claimed in claim 1 in which said points are shaped like saw teeth and are arranged in a close spiral.

5. The method as claimed in claim 1 in which said points are arranged along a close spiral and said deflecting surfaces are each located along an open spiral with respect to the longitudinal axis of said gaseous layer, in such manner that aid deflecting surfaces cross said 7 circular point paths at an angle in the neighborhood of forty-five degrees.

6. The method as claimed in claim 1 in which relatively small jets of gas are introduced into said annular layer in the general direction of circumferential rotation thereof and in such manner as to impinge on the rear sides of said sharp points as they travel in their fixed circular paths, thereby tending to keep said point free of accumulations of fibers.

7. The method as claimed in claim 6 in which said gaseous jets are oscillated back and forth through a short distance in the direction of the longitudinal axis of said annular layer.

References Cited UNITED STATES PATENTS 1,458,387 6/1923 Boul'ne 2415 2,024,424 12/1935 Bryson 24128 2,684,206 7/1954 Zettel 241-4 X 2,838,246 6/1958 Adorno 2414 X 3,221,999 12/1965 Curnpston 241255 X US. Cl. X.R.

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