Textiles: fiber preparation – Assembling – Web forming
Reexamination Certificate
1999-04-22
2001-05-22
Calvert, John J. (Department: 3765)
Textiles: fiber preparation
Assembling
Web forming
C019S296000, C425S082100, C425S083100
Reexamination Certificate
active
06233787
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a forming box to be used by dry forming of a fibrous tissue and encompassing an inlet for introduction of a fibre material which has been splitted up and chosen from amongst synthetic fibres and natural fibres and which is mixed into an airstream, and which forming box contains several revolving rollers, which are provided with radially placed spikes.
Various instruments of this type are known, for instance from the description of European Patent Application 0 159 618. The forming box in such a known plant will frequently be a part of the instrument, which makes an essential limitation for the capacity of the whole instrument.
In respect to the placing of the fibres on the underlying forming wire the forming box is provided with a bottom in form of a net or a sieve in the form of a bottom with a number of openings. In order to promote the passage of the fibres to the bottom of the forming box in the intention of achieving an increase of capacity the application of various mechanical elements has been proposed in form of wings and rollers or other scraping or brushing devices, which in an active way lead the fibres to the bottom of the forming box. Although such mechanical devices do give an increase of the capacity attempts have been made through many years to increase the capacity further.
The elaboration of meshes or openings in the bottom of the forming box has been decided from the fibres, which are used for the preparation of the fibrous tissue. There has primarily been some talk of using cellulose fibres in the manufacturing of paper products or nappy products. Thus, there has been a limitation of the length of the applied fibres. In practice it has thus not been possible to use fibres of lengths of more than 18 mm. This has simultaneously implied that there has been a limitation in the type of products that can be manufactured with such an instrument.
SUMMARY OF THE INVENTION
It is the aim of the present invention to show an instrument of the type mentioned in the beginning, which remedies the drawbacks by the known technique, because there is achieved a substantially bigger capacity and the possibility of application of long fibres for the forming of the fibrous tissue.
According to the present invention this is achieved by a forming box, which is unique by having an open bottom for the releasing of fibre material on the forming wire, because the spikes are arranged to partly holding back the fibres against the effect from the suction of the vacuum box.
It has surprisingly been shown that it is possible to manufacture the forming box with an open bottom. The cloud of fibres, which has been formed inside the forming box of single fibres, which are split up and mixed in the air stream, are transferred down onto the underlying wire by application of the rotating spike rollers. In practice it has been revealed that with an instrument according to the invention capacities can be achieved which are 5-6 times bigger than the capacity with corresponding known instruments.
By running the instrument the raw fibres are split up. This can take place in hammer mills or its like. Hereafter the divided fibres which still can contain a few agglomerates are transferred by means of an air stream down onto the system. The air stream is created by means of transport blowers, which are linked with pipes that lead to the forming box. In the forming box the fibres are primarily led in from each side of the forming box and possibly be means of more inlet pipes on each side of the forming box. It is hereby possible to vary the capacity by opening and closing the supply pipes and the supply blowers.
Inside the forming box a cloud of fibres is formed, where the fibres can circulate because of the transport air. The fibres will hereafter be transferred out from the bottom of the forming box and take place on the forming wire, which is moving beneath the forming box. The layer of fibres, which is formed on the forming wire is fixed by means of a vacuum, which is established in the vacuum box, which is under the forming wire in a position opposite to the forming box.
The present invention brings about a forming box with an open bottom, where a partly retention and distribution of fibres is taking place against that suction which is carried out of the vacuum box. This retention and distribution is established by the rotating spike rollers, because the spikes are influencing the fibres. It has hereby surprisingly been shown that a tissue is formed with a very homogeneous thickness on the underlying forming wire. Hence it can be said that the rotating spikes form a movable bottom or active bottom which is to be differentiated from the traditional passive bottoms consisting of a piece of a net or sieve.
The spike rollers will principally have an extension as seen horizontally so that they for practical purposes cover the sectional area of the forming box. However, it has been demonstrated possible to manufacture forming boxes which function satisfactorily, although the spike rollers do not cover the whole sectional area of the forming box.
It is possible to place rollers or axles, on which the spikes are formed with an almost horizontal orientation or with an almost vertical orientation. It is supposed that an orientation with an angle between horizontal and vertical also is possible and can give satisfactory results.
By orienting the rollers or axles horizontally or vertically the spikes will rotate in a vertical plane and a horizontal plane, respectively. This is preferred because of the symmetrically laying down of fibres, so that a tissue with homogeneous thickness is formed over the width of the forming box.
In the present application the term spikes will cover an embodiment with largely thread-formed spikes. However, the issue will also cover plate-formed elements, which also can be designated as wings. Such plate-formed wings will primarily be formed with the expanse placed in a plane orthogonally on the rotation axis of the axle. Alternatively the plates can be formed with a slope or be formed like propellers to bring about an upwards or downwards directed action on the fibre cloud. To facilitate the passage of air to the forming head when wing-formed spikes are applied, the wings can be provided with holes. Such holes can facilitate the passage of air. By appropriate choice of revolving speed and form of holes in the rollers the passage of fibres to such holes can be hindered or limited.
The rotating spike rollers can be placed so that the outer ends of the spikes describe circles that overlap each other or just touch each other. Furthermore, it is possible to vary the intensity of the placing of the spikes in the enveloping direction as well as in the longitudinal direction. By means of these parameters and the number of revolutions for the spike rollers and the air stream it is possible to adjust the capacity of the instrument.
According to the invention the forming box is able to handle very long fibres. The fibre length will not be limited by sizes of meshes, sizes of openings or its similar in the bottom of the forming box. In practice it has therefore been demonstrated possible to handle fibres with lengths of up to 60 mm, and correspondingly it has been demonstrated possible to handle different types of fibres. It is supposed that by further optimisation of the forming box according to the invention it is possible to handle fibres which are even longer. It is thus possible to use the instrument for manufacturing of products which until now not have been possible with a similar type of instrument.
Because of the capacity of the instrument and the possibility of the handling of very long fibres it will be possible advantageously to use the instrument for manufacturing of fibrous layers with a substantial thickness, which for instance can be of the size of order of up to 200-300 mm. It will thus be advantageous to use the instrument for manufacturing of fibrous tissue in form of isolation mats as a new area for air-laid, non-wov
Andersen Carsten
Eriksen Marianne Etlar
Calvert John J.
Creighton Wray James
Narasimhan Meera P.
Welch Gary L.
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