US3423796A - Defibrator - Google Patents

Description

Jan. 28, 1969 R. NORDSTRAND DEFIBRATOR Sheet Filed July 10. 1967 Jan. 28, 1969 L. R. NORDSTRAND 3,423,796

DEFIBRATOR Filed July 10, 1967 Sheet 2 01 5 Jan. 28,1969 .L. R. NORDSTRAND DEF'IBRATOR sheet a of 5 Filed July 10, 1967 5/ OOOOOOOOO Jan. 28, 1969 L. a NORDSTRAND 3,423,796 DEF'IBRATOR Sheet Filed July 10. 1967 Fi led July 10, 1967 Jan. 28, 1969 L. R. .NORDSTRAND 7 3,423,796

7 DEFIBRATOR FIG] United States Patent 3,423,796 DEFIBRATOR Leif R. Nordstrand, Malmo, Sweden, assignor to M0 Och Domsjo Aktiebolag, Ornskoldsvik, Sweden, a limited company of Sweden Continuation-impart of application Ser. No. 434,761, Feb. 24, 1965. This application July 10, 1967, Ser. No. 658,584 Claims priority, application Netherlands, Feb. 28, 1964,

6402040 US. Cl. 19-156.3 14 Claims Int. Cl. D0lg 11/00, 23/08 ABSTRACT OF THE DISCLGSURE This application is a continuation-in-part of Ser. No. 434,761, filed Feb. 24, 1965, now abandoned.

This invention relates to defibrators, and more particularly to defibrators for tearing a web of cellulose pulp fiber into small pieces, comprising a rotatable tearing device, such as a toothed tearing roll, a support ledge for the pulp web, at substantially zero clearance from the tearing device, and means for feeding the pulp fiber web into the bite between the tearing device, such as the teeth of the roll, and the support ledge. The invention also provides means for distributing the pieces torn from the web on an air-permeable carrier movable in relation to the defibrator and having a suction device for drawing down the particles upon the carrier, in order to form a porous and liquid-absorbent cellulose fiber web on the carrier.

The defibrators employed in earlier machines for the production of porous and liquid-absorbing cellulose fiber webs and sheets were in the form of a hammer mill. However, hammer mills have many serious disadvantages when used for the preparation of cellulose fiber webs. In particular, they are quite bulky, and have a high power consumption, compared with the production of fiber particles per unit of time. Moreover, a hammer mill produces so much dust and noise that as a rule it has to be housed in special quarters.

An apparatus for disintegrating wood pulp board into its component fibers and reassembling the fibers as a soft bat is described in US. Patent No. 3,268,954, to Joa, patented Aug. 30, 1966. In Joas apparatus, the pulp web is passed over a cylindrically rounded breaker plate, preferably in multiple plies, and the fibers are picked from the web by the action of pins projecting radially from a picker drum, which is rotated tangentially with respect to the rounded nose of the breaker plate, to bend the plies of pulp over the nose of the plate, engaging the faces of the successive plies, and moving towards the ends thereof, to discharge the fibers therefrom with a minimum of breakage. The pins have a staggered or random pattern on the drum, so that there is no grooving action on the pulp web, and their clearance from the breaker bar is within the range of 0.002 to 0.005 inch, to obtain optimum picking of the fiber. Because of the substantial clearance between the pins and the breaker plate, a series of small air jets is provided along the nose of the breaker bar, to support the pulp web, and to urge it towards the pins, so as to give the effect of zero clearance between the bar and the pins.

In addition, a segmented backing cylinder is provided, in the path of the material moving with the picking drum pins from the breaker bar. Each segment has pins projecting towards the drum, in offset patterns. If build-up occurs on the pins of the cylinder segments, the pins of the drum strip the accumulated material from the pins of the cylinder. The movement of the drums sets up a substantial vortex movement of air, which aids in carrying pulp fibers through a tangential outlet from the chamber in which the drum operates.

It is also important, according to Joa, that the picking action of the pins always be exercised parallel to the face of the plate, towards the free end thereof, instead of at right angles towards the web. This is said to contribute materially toward the preservation of maximum fiber length.

The Joa apparatus represents the typical compromise that has always been reached when the clearance between the tearing devices of machines of this type has been sought to be minimized as much as possible. It has been recognized that optimum picking of the fibers is obtained at minimum clearance, but on the other hand, minimum clearance is not obtainable except at high manufacturing cost for the machine, and a high degree of wear on the tearing surfaces or devices. It has always been customary to make both tearing devices of the same material, and the Joa machine constitutes no exception to this rule, inasmuch as the picker pins and the breaker bar are both made of metal. Joa puts the tearing devices as close together as he dares, and then makes up the difference in the clearance that is wanting by providing a series of air vents to force the leading ends of the pulp web or webs towards the drum. Joa is satisfied if he can force the pins all the way through the plies, forgetting that when he does so, the pulp web is no longer in contact with the breaker bar, with the result that Joa does not have the advantage of a tearing action in the bite between the pins and the breaker bar. Then he tries to make up for this defect by providing the segmented backing cylinder, bearing a plurality of pins facing towards the drum, Even so, a clearance below 0.002 inch is not suggested or obtained.

In accordance with the instant invention, a defibrator is provided having substantially zero clearance between the tearing device and the supporting ledge for the cellulose pulp fiber web. Substantially zero clearance is achieved by forming the support ledge for the web with a web-supporting surface of plastic material capable of withstanding milling by the tearing device.

The clearance between the tearing device and the websupporting surface is less than 0.01 mm., i.e., substantially zero. In fact, at the start of the operation of the device, when it is first used, the tearing device is preferably in contact with the web-supporting surface. After a certain interval, the duration of which depends upon the wear resistance of the web-supporting surface, the surface is slightly worn, and contact with the tearing device is lost, but the clearance is nonetheless virtually zero, having been adjusted by wear to the point at which the tearing device just barely clears the web-supporting surface. Thereafter, because of the high wear resistance of the plastic material employed for the web-supporting surface, the clearance remains at virtually zero throughout the life of the surface, and in any case is less than 0.01 mm.

As the web-supporting surface, a plastic material having high wear resistance is employed. Thermosetting resins in a hard thermoset stage of polymerization are preferred surface materials. Typical of such resins are phenol-formaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins, polycarbonates, and polyesters. Hard thermoplastic resins also can be employed, such as polytetrafiuoroethylene, polyamides, and polytrifluorochloroethylene. To improve wear resistance, the plastic material can be reinforced by a suitable filler, such as, for instance, a textile fabric or fibrous web material, asbestos fibers, nylon net, glass fibers and mineral silicate fibers, as well a mineral wool and titanium chloride fibers.

The tearing device is normally made of hard durable material such as metal, for example, stainless steel, nickel steel, chrome steel, tungsten carbide-surfaced steel, molybdenum steel, and like materials. The tearing device normally takes the form of a rotatable toothed tearing roll. Teeth have a greater surface area for tearing than pins, and are consequently preferred to pins.

A preferred tearing roll is one provided with teeth that are so arranged that each tooth has its own rotation path, and each path is overlapped by the paths of adjacent teeth. Thus, the teeth of the roll strike all of the web-supporting surface in the initial operation of the device, and wear it uniformly throughout the area of contact, producing substantially zero clearance from end to end of the surface abutting the roll. In this way, the formation of grooves is avoided. Grooves would be undesirable, because they would destroy uniformity and smoothness of contour throughout the tearing surface.

The teeth of a toothed roll can be set in circumferentia'l rows, extending outwardly from the surface of the roll at a 90 angle thereto, or at a lesser angle thereto, as desired. An angular projection makes it possible to arrange the teeth of each row so that each tooth has its own rotation path, and each path is overlapped by the paths of adjacent teeth of the row, simply by adjusting the angle the tooth presents to the surface of the roll. An embodiment of this type is illustrated in FIGURES 1 to 6 of the drawings.

The web-supporting surface is so positioned that it extends substantially along an axial plane of the rotating tearing device, into contact with the teeth or other tearing device. Thus, the pulp web strikes the device head on, between the device and the web-supporting surface, and is drawn into the bite for maximum tearing action. The tearing devices are moved so as to draw the cellulose pulp web down against the web-supporting surface, into the bite between the tearing devices and the surface.

The web-supporting surface can be disposed upon a support ledge, which can be made wholly of or surfaced with the plastic material. It has been found advantageous that the web-supporting surface over which the pulp web is fed into the tearing device, such as the toothed roll, and which faces the device, be rounded. The angle of curvature of the edge is dependent on the flexibility, and thus the moisture content, of the pulp web, and thus should be carefully adapted by trial and error to a given moisture content of the pulp web. It should of course be seen to that the pulp web then always retains this moisture content, or otherwise the rounding of the edge may have to be modified.

To obtain an even and smooth defibration of the cellulose pulp web by means of the tearing device, the pulp web should be fed by a forward movement sulficiently forceful to resist the backward thrust of the pulp web, developed due to its resistance to entering the bite between the web-supporting surface and the tearing device. It is preferred that the feeding means comprise a driven grooved roll, adapted to urge the pulp Web against the web supporting surface, and placed in the vicinity of the tearing device.

The tearing of the cellulose pulp web may generate a considerable amount of heat. Consequently, the tearing device should be provided with cooling means. A totatable toothed roll can be provided with such means by forming it as a hollow roll, provided with an apertured jacket.

Compressed air then can be fed to the interior of the roll for cooling, escaping from the interior of the roll via the apertures of the jacket. The resulting flow of air can be employed to carry the particles produced by the roll from the web to a carrier, on which the particles are laid down to form the cellulosic fiber web that is one desired objective of this type of device. The apparatus employed for preparing such webs is entirely conventional, and forms no part of this invention. A representative example thereof is shown in FIGURES 1 and 7 of the drawings.

The defibrator of the invention is adapted to tear into pieces of cellulosic fiber webs of all types, prepared, for example, from spruce pulp, pine pulp, beech pulp, birch pulp, and other types of coniferous and deciduous wood ulps. Such pulps, as is well known, are normally laid down in the form of rather thick sheets, which are referred to herein as cellulosic pulp webs. These webs are rather stiff, the stiffness depending to some extent upon the moisture content and the fiber size, as well as the process by which the sheet is prepared. The sheet normally has a considerable bending resistance, and this resistance is used to good advantage in the tearing device of the invention. Since the resistance to bending will depend upon resiliency, which in turn is dependent upon moisture content, it will be seen that it is important to adjust the device for tearing pulp web of a given moisture content, and then to maintain this moisture content in the pulp web fed to the device to the greatest extent possible.

A preferred embodiment of the invention is shown in the drawings, in which:

FIGURE 1 is a side elevation, partly in section, of a cellulose fiber Web-forming machine incorporating a defibrator for tearing cellulose pulp webs into particles in accordance with the invention, and laying the particles down on a carrier to form a cellulose fiber sheet.

FIGURE 2 is a detailed view of the defibrator of FIG- URE 1, taken along the lines 2-2 in FIGURE 1.

FIGURE 3 is a section of the defibrator of FIGURE 2, taken along the line 3-3 of FIGURE 2.

FIGURE 4 is a top view of the defibrator of FIGURE 2, showing the arrangement of the teeth on the toothed roll.

FIGURE 5 is an exploded view of the toothed roll, showing the arrangement of the toothed segments, spacers, and end pieces thereof.

FIGURE 5a is a cross-sectional view of a toothed segment of FIGURE 5, taken along the lines 5--5 of FIGURE 5.

FIGURE 6 is an enlarged view of the portion of the toothed roll and the support ledge encircled in the device of FIGURE 2 at the bite therebetween.

FIGURE 7 is a diagrammatic view of another modification of the web-forming machine of the invention, showing a plurality of separators for more uniform distribution of the supply of cellulosic fibers obtained from the defibrator over the carrier.

In the apparatus shoWn in FIGURES 1 to 6, the defibrator is enclosed in a housing 1.- Externally of the housing is mounted an electric motor 2, which rotates a shaft 3 extending from the motor into the housing.

Within the housing, there is afiixed to and mounted on the shaft 3 a hollow toothed roll, the cylindrical hollow barrel 4 of which is provided with a plurality of apertures 4a (see FIGURE 5) extending through the barrel from the interior to the exterior. The roll has a large number of projecting teeth 5, arranged in circumferential rows and carried on a plurality of segments 50, each segment extending circumferentially over of are about the exterior of the roll. These segments are held on the roll as follows.

A ring fastener 51 closely encircling the barrel 4 of the drum is fastened to each of two flanges 52, placed with the smooth surface turned towards the flange, and a sector-indented surface facing inwardly. The flanges 52 are held on the barrel 4 by end plates 6. Two flanges 52, one fastened to each end of the drum, are used (one of the flanges 52 is mounted as the first stage of assembling the toothed roll, and one of the flanges is mounted as the last stage of assembling the toothed roll). Four toothed segments 50 and four segment-formed spacers 53 per row are fastened to the respective ring fasteners 51, in the order mentioned. The spacers 53 are also fastened to the drum barrel 4. The ring fasteners 51 are formed in such a way (best seen in FIGURE 4) that the toothed seg ments 50, fasteners 51, and the spacers 53 have a sloped position, with respect to a concentric circle extending at 90 around the axis of the drum. In this way, ten sets of toothed segments 50 and nine sets of spacer segments 53 are arranged between each set of ring fasteners 51, and fifteen such units 51a are founded on a single drum. The spacers 53 are provided with apertures 4b mating with apertures 4a in the barrel 4. The ring fasteners 51' intermediate each unit are double-faced, that is, they have no plane surface, as do the end ring fasteners 51, but have opposed sector-indented surfaces.

The teeth 5 on each segment 50 are turned at an angle A/ 2 to the concentric circle, about the axis of the drum (see FIGURE 50), so chosen that the toothed segments can effectively mill the pulp web. Each segment 50 is fitted in one of the four sectors 55 on the surface of the fasteners 51, so that each segment is slightly offset, compared to the next succeeding segment constituting the toothed row on the spacer. The depth of each sector a, b, c and 2, taken with the angle A of the teeth on each segment, ensure that no two teeth 5 follow the same rotational path, and that all taken together mill the surface of the web-supporting surface uniformly from end to end. This prevents the cutting of the surface with grooves. The depths of each sector a, b, c, e can be the same or different; in a preferred embodiment, a=b=c=e, and

the angle A is the same for all the teeth on each segment, and on all segments.

The slope of the end pieces 52 is taken with the depths a, b, c, e of the sectors 55 such that each tooth of each segment heads directly into the cellulose pulp web, fed into the bite between the teeth and the web-supporting surface. The clearance d between the teeth and the Websupporting surface (best seen in FIGURE 6) is virtually zero as shown, and in any case is less than 0.01 mm.

The roll barrel 4 also is retained on the shaft 3 in the desired position by means of the end plates 6, which have through flow openings 7.

On the housing 1 there is adjustably mounted a support ledge 8, surfaced with a material 8a that can be worked by the teeth 5 of the roll. The web-supporting surface 8a (shown in FIGURE 4) is of phenol-formaldehyde resin, reinforced with asbestos fabric. The longitudinal edge face 8b of the ledge 8 has been milled by the teeth 5 of the toothed roll, which contacted the ledge initially, when the apparatus was first put into operation. Now, the clearance as shown is substantially zero.

The pulp web 9 to be torn into particles in the bite between the teeth 5 and the web-supporting surface 8a is passed from a supply roll (not shown) in the bite between a grooved feed roll 10 and a grooved roll 11, urging the web 9 against the roll 10. The rolls 10, 11 feed the web over the web-supporting surface 8a on the flat side of the ledge 8 toward the toothed rool. Immediately adjacent the toothed roll there is provided a further driven grooved roll 12 urging the pulp web 9 against the ledge and moving it towards the toothed roll.

In order to seal the housing 1 in the region of the roll 12, a sealing strip 13 secured to the housing 1 trails against the roll 12.

In operation, when the toothed roll rotates in the direction indicated by the arrow in FIGURE 2, and the pulp web 9 is fed against the teeth 5 of the roll, the teeth 5 urge the pulp web against the support ledge 8 at the bite 8b between the ledge surface and the roll, and defibrate it into separate fibrous particles. This defibration is particularly satisfactory because of the rounded contour of the edge formed by that face of the ledge 8 over which the web 9 is fed to the toothed roll, which faces the toothed roll and has been milled thereby, as is seen in FIGURES 2 and 6. As indicated above, the extent of the rounding and moisture content of the pulp web are adjusted by trial and error, for optimum defibration.

As is best seen in FIGURE 1, the housing 1 has a downwardly directed duct 14, the downwardly directed mouth of which opens onto an endless air-permeable mesh carrier. belt 16, which passes over guide and driving rolls 17, 18, 19, 20 and runs across the plate 15. Tensioning roll 18 permits adjustment of the tension on the belt to the desired degree.

In the region below the mouth of the duct 14, the plate 15 is perforated, and beneath it there is disposed a suction box 21, which communicates via conduit 22 with the inlet of a fan 23, the outlet of which communicates through conduits 24, 25, 26, with the interior of the toothed roll in the manner shown in FIGURE 3, thus providing a means for cooling the toothed roll.

In operation, the fan 23 drives air through the ducts 24, 25, 26, into the interior of the toothed roll 4, and thence via the perforations 4a in barrel 4 and the perforations 4b in the spacers 53 into contact with the fibrous particles torn from the pulp web 9 by the teeth 5. The air stream takes up and conveys the torn fibrous particles out the mouth of the duct 14 and towards the carrier belt 16. The fan 23 at the same time draws air through duct 22 from the suction box 21, so that the fibrous particles are drawn down upon the carrier belt 16. The particles collected on the belt are then conveyed beneath the roll 31.

The remove leakage air that has entered the air circulating system, the conduit 24 is equipped with a branch line 27, provided with an adjustable valve 28, venting to the atmosphere.

In the device shown, the cellulose fiber web is laid down on a web of cellulose wadding 29, passed to the carrier belt 16 from a supply roll (not shown) over the roll 20. The web 29 serves as the base support for the mass of fibers laid down on the belt. The web of cellulose wadding 29 has a width slightly more than twice the width of the belt 16. Air is sucked through the web of cellulose wadding during its passage over the plate 15, beneath the duct 14, so that the particles torn from the pulp web 9 by the toothed roll 4 are collected on the surface of the wadding as a porous and liquid-absorbent layer 30 of cellulosic fibers. This layer is carried by the cellulose wadding 29 and the carrier belt 16 out from beneath the duct 14, where the fiber mass is compacted by the pressure roll 31.

In the device shown, the resulting layer of cellulosic fibers is then folded by the folder 32, which raises and folds over the sides of the sheet, interleaving the folds, so that the folded sheet has three plies of cellulose wadding with the layer of cellulosic fibers thereon. The folds are pressed down in the bite between the pressure rolls 33, 34 so as to form a flat composite, which can be divided by cutting into absorbent cores of the desired length for sanitary napkins and diapers.

The apparatus shown in FIGURE 7 is a modification of the apparatus of FIGURES 1 to 6, so as to produce a cellulosic fiber web having different thicknesses at different portions across the width of the web of cellulose wadding. This variation in thickness is achieved by means of the separators 35, which are interposed in the duct 14a directly beneath the toothed roll, and extend cross-wise of the roll, perpendicularly to the axis thereof. These separators divide the duct into three longitudinal sections 36, 37, 38. Sections 36 and 38 are of a considerably greater diameter at the upper portion than the central section 37. The diameters of the sections 36, 37, 38 at their bottom are equal, with the result that a greater proportion of fibers is collected on the wadding 29 at the base of sections 36 and 38 than at the base of section 37. The fibers in these sections are drawn down upon the cellulose wadding web 29 in the same manner as in the apparatus of FIGURES 1 to 6, but in this case, because of the greater proportions of fibers in sections 36 and 38, the mat of fibers laid down on the wadding is considerably thicker in these portions. Consequently, the layer that is laid down on the cellulose wadding is composed of three portions 36a, 37a, 38a, the panels 36a and 38a being of greater depth than the central panel 37a. When this web is folded over, in the folder 32, the top and intermediate layers formed from sections 36a and 38a are considerably thicker than the bottom layer from sections 37a.

It will be evident that the number of partitions 35 and their location in the duct 14a can of course be varied as desired, so as to obtain any desired variation in the thickness and width of the portions of the cellulosic web laid down therefrom on the wadidng. The thickness variation can be arranged very precisely, because the fibers are uniformly broken off from the cellulose pulp web 9, and thus the proportion brought to any portion of the wadding 29 is readily adjusted simply by location of the separators 35 with respect to the toothed roll.

Having regard to the foregoing disclosure, the following is claimed as the inventive and patentable embodiments thereof:

1. A defibrator for tearing a cellulose pulp fiber web into small pieces, comprising, in combination, a rotatable tearing device, a support ledge for the web positioned in a substantially axial plane of the tearing device, said ledge having a plastic web supporting surface adjacent to the tearing device and in milling contact therewith, at a clearance of less than 0.01 mm. therefrom, the surface being formed of a plastic material capable of withstanding such milling contact by the device, to maintain said clearance, and feeding means for feeding the pulp fiber web along said supporting surface and into the milling bite formed between the tearing device and the surface, thereby to tear the web into pieces by the milling action of the tearing device against the surface.

2. A defibrator in accordance with claim 1 in which the tearing device is. a toothed tearing roll.

3. A defibrator in accordance with claim 2 in which the tearing roll is provided with a plurality of teeth arranged in circumferential rows about the roll.

4. A defibrator in accordance with claim 3 in which the teeth in each row are aligned at an angle to the axis of rotation such that each tooth has its own rotation path, and each tooth is disposed relative to the adjacent tooth such that each rotation path is overlapped by the path of the adjacent teeth.

5. A defibrator in accordance with claim 3 in which the teeth are supported on cylindrical segments attached circumferentially about the roll.

6. A defibrator in accordance with claim 5 in which the segments are spaced by corresponding spacer elements, and are offset with respect to each other.

7. A defibrator in accordance with claim 6 in which the segments and spacer elements are sloped at an angle to a concentric circle around the axis of the drum.

8. A defibrator in accordance with claim 7 having four toothed segments per row, and having the teeth set at various angles to the concentric circle so that the path described by the teeth in their rotation with the drum is overlapped by the path of adjacent teeth.

9. A defibrator in accordance with claim 2 in which the roll is hollow and is provided with a plurality of apertures for a cooling flow of air therethrough, and to blow particles of pulp away from the roll.

10. A defibrator in accordance with claim 1 in which the web-supporting surface is made from reinforced plastic material.

11. A defibrator in accordance with claim 1 in which the web-supporting surface and the tearing device are so positioned that the clearance therebetween is substantially zero.

12. A defibrator in accordance with claim 1 in which the rotatable tearing device is made of metal, and the web-supporting surface is made of plastic resistant to wear by the metal tearing device.

13. A defibrator in accordance with claim 1 having a conduit means for collecting and distributing particles torn by the tearing device from the pulp fiber web, provided with one or more separators arranged cross-wise of the tearing device and dividing the fiber-collecting and distributing conduit means into several sections, the crosssectional areas of which are different.

14. A defibrator in accordance with claim 13 in which the fiber-collecting and distributing conduit means feeds the fibers to a carrier web for formation of a layer thereon, and the separators are arranged to feed the fibers in a manner such that the layer laid down on the carrier web has a varying thickness in selected portions corresponding to the location of the separators.

References Cited UNITED STATES PATENTS 1,414,508 5/1922 Garner 19--97 2,676,364 4/1954 Plummer et al l9-l56.4 3,032,830 5/1962 Van Doorn et al 19-202 3,268,954 8/1966 Joa 19-156.3

FOREIGN PATENTS 418,906 2/ 1967 Switzerland.

MERVIN STEIN, Primary Examiner. I. C. WADDEY, JR., Assistant Examiner.

US. Cl. X.R.

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