Apparatus for producing fibrous mats

Abstract

Apparatus is disclosed for producing a fibrous structure or a nonwoven fabric from pulp fibers. This apparatus includes a special form of disintegrator element designed to eliminate a "fan action" in the air fiber mixture which would otherwise cause fibers to flock into clots tending to plug up the openings in a cylindrical separating wall which cooperates with the disintegrator. This separating wall has foramens or openings uniformly distributed substantially over its entire circumferential areas for sifting separated fibers at a maximum rate of production.

Description

This invention relates to apparatus for producing a fibrous mat or felt from shredded pulp fibers, and has for its object the provision of fibrous mats of exceptionally high quality at a rapid rate.

By the term fibrous mat is meant a fibrous web structure suitable for the production of various nonwoven fabric products such as for example covering materials for nursing pads and disposable diapers, paper towels, dusters and the like.

Heretofore, apparatus have been proposed for disintegrating undispersed pulp fibers or flocks into individually separated fibers. Such apparatus have incorporated a rotary disintegrator cooperating with a foraminous wall to sift disintegrated fibers therethrough. One typical example of such prior-art apparatus is disclosed in British Pat. No. 668,216 wherein the fibers of fiber bundles are separated by a disintegrator of a paddle construction cooperating with a foraminous wall. This known apparatus has the disadvantage that the operating speed of the disintegrator is necessarily limited on account of its paddle construction and any attempts to increase this speed would often result in the development of a so-called "fan action" within the dispersing chamber which causes an eddy air current tending to flock the fibers into clots and which further creates an air blow from the openings of the foraminous wall directed towards and tending to interfere with the matforming action of fibers on a wire conveyor, resulting in poor mat formation.

Another prior-art example is typically shown in U.S. Pat. No. 2,940,135 wherein the disintegrator is comprised of annularly arranged brush units. The apparatus disclosed therein has the difficulties that the tips of the brushes are prone to deform and wear so that its disintegrating ability declines with time and that it is burdened by timely rejection of such twisted and curled fiber clots formed between the brushes and the separating wall which are difficult to be further disintegrated.

The present inventors have made exhaustive studies of the art with a view to eliminating the above-noted difficulties encountered with the prior-art devices, and have developed an improved apparatus of the form and construction hereinafter described which is capable of manufacturing fibrous mats of a desired quality (in which elementary fibers are uniformly distributed without surface imperfections) at increased rate of production and which in particular will reduce the fan action to absolute minimum and prevent the formation of objectionable fiber flocks.

According to the present invention, there is provided apparatus which comprises an elongate cylindrical separating wall having sifting openings uniformly distributed substantially over its entire circumferential areas, a rotary shaft journalled in said wall, a disintegrating means rotatably mounted on said shaft and operatively associated with said separating wall for disintegrating undispersed fiber flocks into finely dispersed elementary fibers, a casing disposed in surrounding relation to said separating wall and defining therewith an annular dispersing chamber having a downwardly directed fiber outlet for dispersed fibers, said casing being provided in opposite sides thereof with an elongate aperture communicating with the atmosphere for introducing a volume of air into the air chamber in order to reduce centrifugal fiber flocculation by reseparating said fibers, said chamber increasing in its volume progressively towards said fiber outlet or the distance between the casing and the separating wall increasing progressively towards said fiber outlet, so as to maintain a constant velocity of air throughout all regions of the chamber, a damper provided at the upper end of said dispersing chamber for regulating the volumetric ratio of air to fibers within said chamber, a moving endless wire conveyor underlying said fiber outlet for the deposition thereon of dispersed fibers, a main suction box of the same dimension as said fiber outlet for withdrawing dispersed fibers onto said wire conveyor, and an auxiliary suction box annexed to said main suction box for maintaining a suction air current across said wire conveyor immediately at the forward end of said fiber outlet.

A preferred form of apparatus according to the invention will now be described by way of example and with reference to the accompanying drawings in which:

FIG. 1 is a schematic view utilized to explain the overall aspects of the apparatus embodying the invention;

FIG. 2 is a sectional elevational view of the principal operating parts of the apparatus according to the invention;

FIG. 3 is a longitudinally sectional, elevational view of part of FIG. 2;

FIG. 4 is an enlarged plan view of a disintegrator element or blade runner employed in accordance with the invention;

FIG. 5 is an enlarged fragmentary plan view of a separating wall employed in accordance with the invention;

FIG. 6 is an enlarged sectional, elevational view of a preferred form of blade runner shown as operatively associated with the separating wall;

FIG. 7 is a plan view of a main suction box and an auxiliary suction box annexed therewith; and

FIG. 8 is a side elevation of FIG. 7.

Designated at the reference numeral 10 in FIGS. 1 and 2 is a duct for delivering undispersed pulp fibers from a shredding unit (not shown) to a disintegrator unit generally designated at 100. The duct 10 flares widthwise in the vicinity of an inlet 11 substantially to full width of a perforated separating wall later described, and is connected to this wall as shown in FIG. 2.

The disintegrator unit 100 which constitutes an outstanding feature of the present invention is essentially comprised of a plurality of disintegrating elements or blade runners 101 operatively associated with an elongate cylindrical separating wall 102 hereinafter described. A preferred form of blade runner 101, as better shown in FIG. 4, has an annular core portion 103 defining a circular hole 104 for insertion through a horizontally mounted rotary shaft 110 and two triangular blade portions 105 extending symmetrically on opposite sides of the core 103. Each blade runner 101 should be relatively thin, or about 1 - 5 millimeters thick, preferably 3 millimeters thick. The triangular portion 105 in particular should be as light in weight and tapered off as sharply as strengthwise tolerable with a view to maintaining a high critical number of revolutions for a relatively long shaft or rotor on which the blade runners are mounted. For this purpose, a light metal such as aluminum may be advantageously used for these blade runners 101. To further reduce the weight of the blade runner, there are provided therein punchedout holes 140. Also importantly, the blade runner 101 should be flat and rectilinear in its entire plane so as to minimize the resistance to air during its rotation within a dispersing chamber 114. Blade runners with curved or otherwise distorted plane are prone to produce a fan action in the air stream which would lead to the formation of undesirable fiber clots or nodules as experienced with the conventional paddle or brush type disintegrators and consequently to imperfections in a finished mat.

A number of these blade runners 101 are superimposed one upon another axially at random angles substantially to full length of the separating wall 102 and are thus fixedly mounted on the rotary shaft or rotor 110. Importantly, the blade runners 101 should be stacked one upon another with their triangular portions 105 oriented in random directions, not in such alternately uniform angular relation as will form a spiral arrangement or a screw-thread contour which would tend to align the air stream in an axial direction and swerve the fibers towards an end of the wall 102. The rotor 110 is driven by a motor (not shown) at a high speed commensurate for example with a yield of 40 grams per square meter of fibrous mat deposited on a 2,600 millimeters wide depositing wire conveyor, later described, travelling at 300 meters per minute. The speed of the rotor 110, hence of blade runners 101, may be further regulated so as to obtain yields in the range of from 20 to 200 grams per square meter at a travel speed of 100 - 300 meters per minute of the depositing conveyor.

The elongated cylindrical separating wall 102 is preferably 1.5 - 3 millimeters thick and is provided with foramens or openings 112 uniformly distributed substantially over its entire circumferential areas except an inlet portion through which untreated fibers are fed. The separating wall being thus provided with a maximum of operating areas will advantageously permit of a rate of fiber separation and distribution far greater than ever achieved by any prior-art devices. The openings 112 are preferably 3 - 5 millimeters in diameter, most preferably 4.5 millimeters in diameter and spaced by a distance S of preferably 4.5 - 7 millimeters, most preferably 6.5 millimeters. It has now been found that the total area of openings 112 or their occupancy in the separating wall 102 is preferably in the range of 30 - 50%. Greater foraminous area would fail to sift separated fibers through the wall and would allow undispersed fiber flocks to escape therethrough. Conversely, smaller foraminous area would prevent separated fibers from passing through the wall. The sifting operation of the wall 102 is related to the peripheral speed of the blade runners 101 and to the diameter of the openings 112. For the above-specified diameters of openings 112, the peripheral speed of the blade runners 101 should be preferably 60 - 80 meters per second. Lower peripheral speeds would give very little sifting action and allow fiber flocks to slip out through the opening 112. Conversely, higher peripheral speeds would invite increased fan action.

The separating wall 102 is elongated to be about 2,000 millimeters long according to one illustrated embodiment of the invention and should importantly be devoid of any interposed ribs or supports because these supports tend to disturb the fiber-carrying air stream and cause flock formation.

The blade runners 101 have their tips disposed in close proximity to the inner face of the separating wall 102, and the manner in which they cooperate with this separating wall is illustrated in FIG. 6, from which it will be understood that a "breathing action" takes place in the air current moving circumferentially closely along the inner face of the separating wall as each blade runner rotates in close approach to the wall. More specifically, a circumferential movement of each blade runner in a counterclockwise direction develops a positive pressure at the region (a) forward of the runner and a negative pressure at the region (b) rearward of the runner, with the results that the openings 112 at the region (a) exhale the air which entrains dispersed fibers immediately upon separation and moves them out through the openings of the wall, while the air current at the region (b) is inhaled and directed inwardly towards the blade runners. This breathing action of the openings 112 serves to eliminate the tendency of fibers being entrapped and plugging up the openings. In such instance, flocks or fibers that have not been separated to elementary fibers are caught by the tips of the blade runners or carried on the air current over past the openings without being sifted therethrough and are thus drawn back inwardly of the wall. This is because the flocks have greater inertia as against their air-resistance than separated individual fibers. Unseparated fibers or flocks are therefore continued to rotate with the moving air current or with the rotating blade runners until they are completely disintegrated into individually separated fibers on impinging contact with the blades of the runners 101 and also with the peripheral edges 112a of the openings 112 in the wall that function as stationary blades.

Designated at 113 is an outer casing surrounding the separating wall 102 and defining therewith an annular dispersing chamber 114 in which separated fibers are dispersed in controlled volumes of air. The casing 113 is provided with an elongate slit or aperture 115 communicating with the atmosphere and extending axially on opposite sides thereof. This aperture can be multiplied if necessary and is provided for maintaining a constant supply of atmospheric air with which to militate against the tendency of dispersed fibers being collected and flocked at the lower portions of the inner wall of the casing 113 and thus reduce centrifugal flocculation.

For similar purposes and for diluting the air/fiber mixture in the dispersing chamber 114, there are provided air intakes 116 and dampers 117, 117' associated therewith for introducing such volumes of air as are required to maintain a desired volumetric ratio of air to fibers and at the same time providing an air current to sweep the fibers off the upper portions of the inner wall of the casing 113. The dispersed fibers screened through the separating wall 102 are thus prevented from flocking together in the dispersing chamber 114 by these sweeping air layers established along the inner wall of the casing 113. In order to further ensure that fibers are prevented from becoming agglomerated into flocks within the dispersing chamber 114, it is to be noted that the diameter of this casing is greater progressively towards a fibers outlet 118 or that the distance between the casing 113 and the aeparating wall 102 increases progressively towards the fiber outlet 118 so as to maintain a constant velocity of air throughout all regions of the chamber 114. To this end, there is also provided more fresh air at the counter-flow area, or the right half section as viewed in FIG. 1, of the dispersing chamber 114 than at the forward-flow area, or the left half section of the dispersing chamber 114. Thus, the dampers 117' on the side of the casing where the air flows in a direction reverse to the rotation of the blade runners 101 should be held open wider than those dampers 117 positioned where the air flows in a direction forward to the rotation of the blade runners.

The casing 113 including both ends thereof is advantageously made of a transparent or translucent synthetic resin such as for example vinyl chloride and acrylic resins. The casing being transparent can be utilized to advantage for inspecting the conditions of fiber-entraining air currents within the dispersing chamber 114 so as to readily adjust the dampers 117, 117' and aperture 115 as desired. Another important advantage of the casing being made of the above exemplified plastic materials is that it has a mirror-like smooth contact surface and does not reach the dew point as easily as does any metal and can be charged equipotentially with separated fibers sifted from the wall 102 so that the fibers are prevented from being statically collected at the inner wall of the casing 113.

The casing 113 is provided with a downwardly directed outlet or deposit opening 118 elongated substantially to full length of the casing for depositing dispersed, separated fibers therethrough onto a moving endless wire conveyor 119.

Designated at 120 is a main suction box opening to full dimension of the outlet 118 and situated a predetermined distance apart from the bottom of the separating wall 102. The distance (h) between the lowermost end of the separating wall 102 and the depositing surface of the wire conveyor 119 on the suction plane of the main suction box 120 should be in the range of from 150 to 300 millimeters. Smaller distance will communicate the wind produced by rotating blade runners 101 to a mat forming plane of the wire conveyor and mar the mat formation. Conversely, greater distance will cause large eddy currents tending to deteriorate the surface finish of the resulting mat through flocculation of individual fibers which then form on its surface.

The main suction box 120 is partitioned widthwise as at 121 into a plurality of sections each of which is provided with a damper 122 to be operated independently from the other sections as shown in FIG. 7. Each damper 122 is attached with a handle 123, as shown in FIG. 8, which may be manipulated to regulate the weight of a fibrous web or mat formed on the moving wire conveyor.

Annexed with the main suction box 120 at a position upstream of the run of the wire conveyor is an auxiliary suction box 124 which is adapted to maintain a suction air current thereat to eliminate the tendency of the formed mat being disturbed by a draught of air occuring immediately adjacent the forward end of the outlet 113 upon departure of the wire conveyor therefrom.

The fibrous mat or felt deposited on the wire conveyor 119 is transferred as by a suction pickup roll 130 onto a further processing stage where the mat is finished in the known manner.

Having thus described the invention, it will be understood that various changes and modifications may be made in the specific form and construction herein above advanced, without departing from the scope of the appended claims. As for example, the blade runner 101 may be configured like a cross having four symmetric triangular blade portions or, a spacer may be inserted between adjacent blade runners.

Claims

What is claimed is:

1. Apparatus for producing fibrous mats which comprises: an elongate cylindrical separating wall having sifting openings uniformly distributed over substantially its entire circumferential areas except a full width inlet portion through which untreated fibers are fed; a rotary shaft; a dispersing means mounted on said shaft for rotation therewith and operatively associated with said separating wall for dispersing fiber flocks into elementary fibers; a casing disposed in surrounding relation to said separating wall and defining therewith an annular dispersing chamber having a downwardly directed fiber outlet for dispersed fibers, said casing being provided with full width air intake openings at the upper end thereof and, said casing being further provided in opposite sides thereof with an elongate aperture communicating with the atmosphere for introducing a controlled volume of air into said chamber, said chamber between the casing and the separating wall widening progressively towards said fiber outlet so as to maintain a constant velocity of air throughout all regions of said chamber; a damper provided at the upper end of said dispersing chamber in operative association with said air intake openings for regulating the volumertic ratio of air to fibers within said chamber; and a moving endless wire conveyor and suction means underlying said fiber outlet for the deposition thereon of dispersed fibers.

2. Apparatus for producing fibrous mats which comprises: an elongate cylindrical separating wall having sifting openings uniformly distributed over substantially its entire circumferential areas; except a full width inlet portion through which untreated fibers are fed; a rotary shaft; a dispersing means mounted on said shaft for rotation therewith and operatively associated with said separating wall for dispersing fiber flocks into elementary fibers; a casing disposed in surrounding relation to said separating wall and defining therewith an annular dispersing chamber having a downwardly directed fiber outlet for dispersed fibers, said casing being provided with full width air intake openings at the upper end thereof and, said casing being further provided in opposite sides thereof with an elongate aperture communicating with the atmosphere for introducing a controlled volume of air into said chamber, said chamber between the casing and the separating wall widening progressively towards said fiber outlet so as to maintain a constant velocity of air throughout all regions of said chamber; a damper provided at the upper end of said dispersing chamber in operative association with said air intake openings for regulating the volumetric ratio of air to fibers within said chamber; and a moving endless wire conveyor underlying said fiber outlet for the deposition thereon of dispersed fibers; a main suction box for withdrawing dispersed fibers onto said wire conveyor; and an auxiliary suction box annexed to said main suction box for maintaining a suction air current across said wire conveyor immediately at the forward end of said fiber outlet.

3. Apparatus as defined in claim 1 wherein said dispersing means comprises a plurality of relatively thin blade runners superimposed one upon another at random angles and radially extending in close proximity to the inner face of said separating wall.

4. Apparatus as defined in claim 1 wherein said casing is made of a transparent plastic material.

5. Apparatus as defined in claim 3 wherein at least one blade runner is comprised of an annular core portion and substantially triangular blade portions extending symmetrically on opposite sides of said core portion.

6. Apparatus as defined in claim 3 wherein said blade runner has a uniform thickness of the order of 1 - 5 millimeters.

7. Apparatus as defined in claim 2 wherein said main suction box is provided with dampers for controlling the weight of fibers deposited on the wire conveyor.

8. Apparatus as defined in claim 1 wherein the distance between the lowermost end of said separating wall and the upper surface of said wire conveyor is between 150 to 300 millimeters.

9. Apparatus for producing fibrous mats which comprises: an elongate cylindrical separating wall and a fiber inlet portion therein extending across the full width thereof, said separating wall having sifting openings uniformly distributed over substantially its entire circumstantial areas other than the inlet portion; a rotary shaft journalled internally of said wall; fiber dispersing means particularly designed for minimizing fan action mounted on said shaft for rotation therewith and operatively associatd with said separating wall for dispersing fiber flocks into finely separated elementary fibers, said dispersing means comprising a plurality of thin blade runners of uniform thickness each having an annular core portion and sharply triangular blade portion extending symetrically on opposite sides thereof for minimizing resistance to air, said runners being superimposed one upon another along said shaft at random angles and radially extending in close proximity to the inner face of said separating wall; a generally cylindrical casing disposed in surrounding relation to said separating wall and defining therebetween an annular dispersing chamber having a downwardly directed fiber outlet for dispersed fibers, said casing being provided with full width air intake openings at the upper end thereof and said casing being further provided in opposite sides thereof with elongate aperatures, said intake openings and elongate aperatures communicating with the atmosphere for introducing a controlled volume of air into said chamber across its full width, the casing and separating wall being separated from one another by a chamber which increases progressively in width from the air intake openings towards said fiber outlet so as to maintain a constant velocity of air throughout all regions of said chamber; damper means in operative association with said air intake openings for regulating the volumetric ratio of air to fibers within said chamber; moving endless wire conveyor means underlying said fiber outlet for the deposition thereon of dispersed fibers; and suction means beneath said wire conveyor means and disposed adjacent the fiber outlet for withdrawing dispersed fibers onto said wire conveyor.