WO1991010767A1

WO1991010767A1 - An arrangement for mixing pulp fibres and particulate material

Info

Publication number: WO1991010767A1
Application number: PCT/SE1991/000017
Authority: WO
Inventors: Mikael Svensson; Susan Mattsson; Dag Gundersen
Original assignee: Mölnlycke AB
Priority date: 1990-01-11
Filing date: 1991-01-10
Publication date: 1991-07-25
Also published as: SE9000098L; SE9000098D0; AU7144591A; SE465434B

Abstract

The present invention relates to an arrangement for mixing together pulp fibres and particulate material, in which a layer (2) of pulp fibres is moved, with the aid of a conveyor (1), past a particle material feed means (3), from which a metered flow of particulate material is delivered to the pulp fibre layer passing the feed means (3). According to the invention one rotatable mixing wheel (5) is arranged downstream of the particulate-material feed means. The mixing wheel includes a plurality of parts (7') which project out-wardly from the wheel periphery and which extend to a given depth in the pulp fibre layer during rotation of the wheel.

Description

An arrangement for mixing pulp fibres and particulate material

The present invention relates to arrangement for mixing together pulp fibres and particulate material, in which a layer of pulp fibre, with the aid of a conveyor means, is moved past a particulate material supply means from which a metered flow of particulate material is delivered to the pulp fibre layer as it passes said means.

In recent times it has become more and more usual to use highly absorbent material in absorbent bodies or pads for diapers, incontinence guards or the like. A highly absorbent material is characterized by being capable of absorbing quantities of liquid several times greater than its own intrinsic weight. Despite the large absorption potential of such materials, their use in absorbent pads have not resulted in an increase, in absorption capacity which even closely approaches the theoretical potential of the highly absorbent mate¬ rials. One reason for this is thought to be the occur¬ rence of so-called gel blocking, i.e. that part of the highly absorbent material which is first wetted by the liquid discharge forms a gel when absorbing liquid, this gel being liquid impervious and preventing or blocking the dispersion of liquid to other parts of the highly absorbent material. The risk that gel blocking will occur is relatively high when the highly absorbent material applied to a layer is in particle form.

It is previously known to mix highly absorbent par¬ ticles homogenously in an absorbent pad of fluff fib¬ res. The admixture of highly absorbent particles with fluff is described in U.S. Patent Specifications 3 670 731 and 4 610 678. According to these known mixing methods, highly absorbent particles are added to the fluff flow prior to the fluff being air-laid in separate moulds to form separate absorbent pads, or to being deposited on a wire to form a continuous web of absorbent material.

The admixture of particles with the fluff flow suffers several drawbacks, however. Because of variations in the infeed flow, it is necessary in practice to deliver an excess of materials to the moulds or the wire, this excess or surplus later being recycled for reuse. This excess includes highly absorbent particles which tend to fasten on machine elements to form deposits thereon. Another drawback is that highly absorbent particles are also added to the recycled material, causing the pro¬ portion of highly absorbent particles in the finished absorbent material to vary in an uncontrolled fashion.

From a working environmental aspect, it is important to have strict control over the highly absorbent partic¬ les. This can be achieved by restricting the spreading of highly absorbent particles in the manufacturing arrangement.

The present invention is intended to eliminate the aforesaid drawbacks and to prevent the occurrence of gel blocking in absorbent pads or bodies which include highly absorbent materials, by controlled mixing of the highly absorbent particulate material and pulp fibres. The invention also relates to a device with which different mixing patterns can be achieved readily.

To this end, an arrangement for admixing pulp fibres and particulate material in which a layer of pulp fibres is moved, with the aid of a conveyor, past a particulate material supply means from which a metered flow of particulate material is supplied to the pulp fibre layer passing said supply means is characterized in that at least one rotatable mixing wheel is arranged downstream of the particulate material supply means, and in that the mixing wheel comprises a plurality of parts which project out from the wheel periphery and which penetrate to a given depth in the pulp fibre layer as the wheel rotates. Because the mixing wheel produces controlled mixing of particulate material with pulp fibres, it is ensured that all particles of highly absorbent material will obtain sufficient space to swell freely when taking-up liquid, without inhibiting the dispersion of liquid to other highly absorbent particles.

Another advantage afforded by the inventive arrangement is that varying mixing patterns of particulate material in fluff.pulp can be readily achieved, by changing the mixing wheel.

Exemplifying embodiments of the invention will now be described with reference to the accompanying drawings, in which

Figure 1 illustrates schematically and in side view one embodiment of an inventive arrangement, Figure 2 is a side view of a mixing element forming part of the mixing wheel illustrated in Figure l, Figure 3 is a highly schematic rear view of a mixing element according to Figure 2,

Figures 4 and 5 are front views and side views respec¬ tively of a second embodiment of an inventive mixing wheel, and Figures 6 and 7 are respective front and side views of a third embodiment of an inventive mixing wheel.

The arrangement illustrated in Figure 1 includes a con- ventional forming drum 1 on the peripheral surface of which a fibre layer 2 has been formed with the aid of a fluffer (not shown) this fibre layer being held on the drum by the suction effect produced by subpressure generated in the interior of the drum 1. The drum 1 is rotated in the direction shown by the arrow A. An even stream of highly absorbent particulate material 4 is delivered onto the fibre layer 2 by means of a feed roller 3.

Arranged downstream of the feed roller 3 is a mixing wheel 5 which comprises a transverse hub 6 on which a plurality of mixing elements 7 are mounted sequentially in the cross direction. The mixing wheel is driven for rotation in some suitable manner, for instance with the aid of a motor M and a belt transmission means, as illustrated schematically in Figure 1. The mixing wheel 5 rotates in the direction shown by the arrow B.

The illustrated arrangement also includes a further fluffer 8 which is intended to apply a layer of pulp fibres on top of the layer of particles and pulp fibres mutually mixed by the mixing wheel.

Figure 2 is a side view of a mixing element 7. This element has substantially a C-shape and narrows from the tip or point of the C at which it is intended to be secured to the hub to the opposite tip of the C. The broad end of the element 7 is configured with an aper¬ ture 9 by means of which it can be fitted onto the hub 6. In order to enable the elements 7 to be non-rotatably attached to the hub 6, the hub is provi¬ ded with a transversal spline or rib and the recess 9 is provided with four grooves 10 whose shape is com¬ plementary to the hub spline or rib and which are displaced 90° from one another. Mutually sequential mixing elements are fitted onto the hub while being separated by an insert and displaced through 90° relative to one another.

The outer ends 11, 11', of the parts 7" of the mixing element 7 extending from the periphery are also bent transversely in one direction or the other and prefer¬ ably at different distances from the free tips or points of the mixing elements 7, as illustrated schema- tically in Figures 2 and 3 in broken lines for the ends ll'. The mixing elements will thus operate in a plough¬ like manner at mutually different depths or levels in the layer of pulp fibres and particles and therewith mix together the layer constituents. The mixing wheel 5 rotates much more quickly than the mat forming drum 1, and the peripheral speed of the mixing wheel 5 is 5-10 times greater than the peripheral speed of the mat forming drum 1.

The depth to which the mixing elements 7 penetrate into the mat fibre layer 2, 4 is preferably adjustable in some suitable manner, for instance by movably support¬ ing the hub 6 above the periphery of the mat forming drum 1.

In the embodiment illustrated in Figures 1-3, the free, pointed ends 11, 11' of the stirring or mixing elements are bent to an angle of 45° relative to a vertical plane. Naturally, other bending angles are conceivable, and it is also conceivable to bend,the mixing elements to mutually different angles. The number of mixing elements fitted onto the hub is totally dependent on the width of the layer of pulp fibres and particulate material. Preferably, if possible, the number of mixing elements bent in one direction on the hub will equal the number of mixing elements bent in the other direc¬ tion on said hub.

Thus, the aforesaid embodiment provides arrangement which will prevent gel blocking, by mixing highly absorbent particles and pulp fibres with the aid of the mixing wheel 5. This wheel is constructed from simple components and its cost of manufacture is therefore relatively low.

Figures 4 and 5 illustrate a second embodiment of a mixing wheel 12 which can be used as a substitute for the mixing wheel 5 of the Figure l embodiment. This wheel 12 also comprises a hub 13 which has a large number of mixing elements 14 fitted thereon.

The main distinguishing feature between the mixing wheel 12 and the mixing wheel 6 of the Figure l embodi¬ ment is that the mixing elements of the wheel 12 have a different configuration and are displaced relative to one another through an angle of 15° . As will be seen from Figure 5, each mixing element includes six peri¬ pherally projecting spike-shaped parts 15, which are disposed in uniform relationship around the periphery of the mixing element 14.

This mixing wheel 12 can be driven at the same rota¬ tional speed as the mat forming drum 1, and can thus be driven by the same motor as that which drives said drum without needing to provide transmission mechanism herefor. In this case, however, because of the high peripheral speed of the mat forming drum, the layer of pulp fibres and particulate material will move more quickly than the spike-shaped parts 15 of the mixing elements 14.

The spike-shaped parts 15 projecting down into said layer will act as stream dividers and the material streams will be divided into two streams which pass on either side of each such part 15, therewith imparting to the material stream small, laterally acting force components and forming a furrow in the material stream behind each said part 15. Particles fall from the surface down onto the bottom of these furrows. Since the parts 15 move up and down in the passing material layer, due to rotation of the wheel 12, the bottom of the furrow thus formed will also move up and down and the individual particles falling into the furrow will therefore be uniformly distributed vertically. When the mutually sequential mixing elements 14 on the hub 13 lie sufficiently close to one another, the local, lateral displacements in the material layer caused by the parts 15 will interfere with one another, so that the particles present in the furrows will be displaced laterally relative to one another, in addition to in the vertical direction.

When, on the other hand, there is chosen a transmission which causes the mixing wheel to rotate at a high speed or when rotation of the mixing wheel is effected with the aid of a separate motor, so that the mixing ele¬ ments 4 will move much more quickly than the material stream, these elements will also act in a plough-like manner and form furrows in which particles of highly absorbent material will fall. Since some of these particles will be pressed to one side by following mixing elements, the particles are also displaced laterally in this case. Experiments have shown that an acceptable admixture of particles with the fibre pulp can be achieved when the ratio of the speed of the mixing elements and the speed of the mat forming drum is as small as two. When this ratio is increased, the fibres and particles will be mixed progressively more homogenously, and laboratory tests have shown that a practically homogenous mixture is obtained within the active range of the mixing elements when the ratio is above 100.

The number of parts 15 wheel project from each mixing element 14 is selected so that at least one part 15 will always be located within the material layer when wishing to achieve uniform distribution of particles in the fibre pulp. On the other hand, when desiring uni¬ form particle distribution, this can be readily achieved by positioning the projecting parts non- uniformly around the periphery of the mixing elements and/or by arranging the mixing elements at mutually different distances therebetween.

Figures 6 and 7 illustrate a third embodiment of a mixing wheel. The mixing wheel 16 of this variant differs from the mixing wheel 12, in that the outwardly projecting parts 17 of each mixing element 18 on the mixing wheel 16 are of mutually different lengths around their circumferences, and in that the elements are angularly displaced relative to one another, so as to form in the cross-direction mutually parallel rows of projecting parts 17 of mutually different lengths. This enables further variation to be obtained in the depth extensions between the furrows formed in the cross-direction.

All of the mixing wheels described hitherto are con¬ structed of a hub having mutually identical mixing elements fitted thereon, and the described variations in the depths of the furrows in the longitudinal and transverse directions have been achieved by displacing these elements angularly in relation to one another and by arranging said elements at different distances apart on said hub. It is possible, of course, to provide further variations in the furrow-depth pattern, by using non-similar mixing elements, e.g. elements with which the outwardly projecting parts have mutually different lengths, a different number of outwardly projecting parts, and different distribution of said projecting parts around the periphery. From the aspect of manufacture, however, it is more advantageous from the cost aspect to use mutually identical elements, since this enables one and the same tool to be used in manufacture.

The construction of the mixing wheel with a hub and separate mixing elements which can be fitted thereto is advantageous from the aspect of maintenance, since this facilitates cleaning of the mixing wheel and since damage to one mixing element will not mean that the whole mixing wheel must be replaced. However, it is conceivable to form the hub and mixing elements as a single, integrated unit.

The invention thus provides a pulp fibre and particu- late-material mixing device of simple construction which enables mixing to be varied in the longitudinal, transversal and depth directions with the aid of simple means. It will be understood that the described embodiments can be modified in many ways within the scope of the invention. For instance, the straight mixing elements of the second embodiment may be curved or bent and may also be inclined to the movement direction of the material. Furthermore, the rotational speed of the mixing wheels may also be variable, so as to vary the time sequence of the up and down movement of the mixing elements. It will also be understood that more than one mixing wheel can be included in the inventive device and that these wheels may be arranged so as to be alternatively active, thereby enabling the mixing pattern to be changed at high speeds.

Claims

1. An arrangement for mixing pulp fibres and particu¬ late material, in which a layer (2) of pulp fibres is moved, with the aid of a conveyor (l) past a particle- material feed means (3) from which a metered low of particulate material (4) is delivered to the pulp fibre layer passing said means, c h a r a c t e r i z e d in that at least one rotatable mixing wheel (5, 12, 16) is arranged downstream of the particulate- material feed means; and in that said mixing wheel includes a plurality of parts (7', 15, 17) which pro¬ ject from the periphery of said wheel and which extend to a given depth in the pulp fibre layer during rotation of the wheel.

2. An arrangement according to Claim 1, c h a r a c ¬ t e r i z e d in that the mixing wheel (5, 12, 16) includes a hub (6, 13) and a plurality of mixing ele- ments (7, 14, 18) having one or more outwardly project¬ ing parts (7', 15, 17), said elements being rotational- ly rigid on the hub and readily removed therefrom.

3. An arrangement according to Claim 2, c h a r a c - t e r i z e d in that the mixing elements (7, 14, 17) are attached to the hub (6, 13) by means of a spline joint.

4. An arrangement according to any one of Claims 1-3, c h a r a c t e r i z e d in that the outwardly pro¬ jecting parts (7', 15) of mutually adjacent mixing elements (7, 14) are displaced angularly in relation to one another.

5. An arrangement according to any one of Claims 1-4, c h a r a c t e r i z e d in that the outwardly pro¬ jecting parts (7', 15, 17) of the mixing elements (7, 14, 16) are curved or bent transversely in relation to the direction of movement of the conveyor (1).

6. An arrangement according to any one of the preceding claims, c h a r a c t e r i z e d in that the outward¬ ly projecting parts of mutually adjacent mixing ele- ments have mutually different lengths.

7. An arrangement according to any one of the preceding claims with mixing elements having several outwardly projecting parts, c h a r a c t e r i z e d in that the outwardly projecting parts (17) of each mixing element (18) have mutually different lengths.

8. An arrangement according to any one of the preceding claims, c h a ra c t e r i z e d in that the mixing elements (7) have an essentially C-shape and narrow from the tip or point intended to be fastened to the hub (6) down to the opposite tips or points.

9. An arrangement according to any one of the preceding claims, c h a r a c t e r i z e d in that the mixing wheel (5, 12, 16) is driven by a variable speed motor (M).