GB1599895A

GB1599895A - Device for homogenization of a particle filled fluid stream

Info

Publication number: GB1599895A
Application number: GB40275/77A
Authority: GB
Original assignee: Mahler A L
Current assignee: Mahler A L
Priority date: 1977-09-28
Filing date: 1977-09-28
Publication date: 1981-10-07
Also published as: FR2404458A1; DE2842156A1; JPS5457776A

Description

(54) DEVICE FOR HOMOGENIZATION OF A PARTICLE FILLED FLUID STREAM (71) I, ARNOLD LOUIS MAHLER, a Dutch subject, of Prins Bernhardlaan 48, Heelsum, the Netherlands, do hereby declare the invention for which I pray that a patent may be granted to me and the method by which it is to be performed to be par ticularly described in and by the following statement: The invention is related to a device for the homogenisation of a particle-carrying fluid steram, such as a fluid stream carrying fibres.

A fibre web obtained with the conventional devices for laying non-woven random webs shows irregularities in its appearance. In these irregularities can be distinguished those which fluctuate in the longitudinal direction of the web and those which fluctuate transversely.

A first type of irregularity normally shows a relatively slow fluctuation and depends mainly on the regularity of the feed introduced into a card. A second type of irregularity is usually characterised by sudden variations that occur dose to each other and appear as heavy and light bands extending next to each other in the longitudinal direction of the web, and these mainly depend on the flock form of the material with which the card is fed and on the combing characteristics of the card.

The invention aims at reduction or suppression of the second type of fluctuation by providing a more uniform distribution of the fibres over the cross section in a fluid stream and consequently in the case of fibres in the subsequently laid fibre web. The invention is, however, applicable to other forms of particles than fibres and for purposes other than laying non-woven webs.

According to the invention, there is provided a device for the homogenisation of a particle-carrying fluid stream, such as a fluid stream carrying fibres, comprising a duct terminating at a rectangular exit end, and having at least one mixing station intermediate the length of the duct for rearranging the flow, whereat inner baffles are adapted to divide the flow into parts that each occupy a respective portion of the duct cross-section of gradually changing shape in such manner that on completion of their passage through the mixing station respective half-parts of the flow or respective half-parts of each of a plurality of portions of the flow each occupy a cross-sectional area of twice the transverse width occupied by that half-part of the flow immediately preceding said mixing station, and the or each pair of said double-width half-part flows are disposed one above the other.

By use of the device according to the invention a mixing action can be performed on the particle-carrying flow over its whole width in such a manner that a more uniform distribution of the particles, in particular fibres, filaments or flocks, is obtained.

For more thorough mixing it is preferred that there are several mixing stations in succession.

To increase the effect obtained tby several successive mixing stations it is preferred, that there is a progressive subdivision of the fluid flow reaching each successive station into a greater number of portions that are to have their respective half parts guided to be disposed one above the other.

To obtain a simple device, it is possible, that said subdivision follows geometrically progressive increase at successive stations.

To fulfil these requirements, it is preferred that the duct has a rectangular cross-sectional shape that changes in size progressively.

In certain circumstances it will be desired to change the linear speed of the particles in flow direction. To obtain this it is possible that the above-indicated changes in size will predominantly relate to the height of the channel and may develop proportionally or exponentially with respect to the duct length.

To avoid local clogging or adherence of particles to the surfaces of the duct, it is preferred, that the internal surfaces of the duct are polished and have rounded edges, strictly needed in case of fibre-carrying fluid streams, and the duct is made conductive material to neutralize electrostatic charges.

The baffles may comprise laterally extending baffle plates having vertically extending supports, and to disturb the fluid flow through the device as little as possible and to obtain the desired mixing effect as indicated above, it is preferred that the supports have a streamlined shape in the flow direction-the purpose of which is to co-operate by dynamic suction with the action of their neighbouring baffle plates, to reshape respective parts of the fluid flow.

The particles in the fluid stream may, for example, comprise either short paper-making fibres or textile staple fibres or continuous filaments or yarns or mixtures thereof. Said fibre, filament and/or yarn laden fluid stream can be subsequently conducted to a device known per se for the formation of a nonwoven web by the particles.

It may be mentioned that a device according to the invention can also be used with a fibre-flock filled stream and/or with a fluid carrying non-fibrous particles. It also is possible for a device according to the invention to be arranged to co-operate with other flow regulating devices known in the art for use in the feed flow to the headboxes of single wire or of doublewire paper machine systems.

In the accompanying drawings an example of a device according to the invention is schematically shown.

Fig. 1 shows the device in longitudinal section.

Fig. 2 shows a top view with the duct upper wall removed.

Fig. 3 and Fig. 4 show a side view of one baffle element in cross section and a top view of same respectively.

Figs. 5-7 show perspective views of further baffle elements.

The device will be described for a fibre filled fluid flow.

As indicated above the illustrated device is so arranged that a particle-carrying flow, which has a flat rectangular cross-sectional shape, is divided (vertically) at each "station", so that one half of the flow is forced to flow "over" the other, while in the same time the divided flows are each spread out laterally. In this way different parts of the flow which originally moved next to each other as a unity, become rearranged one above the other and are united again maintaining the same total width as the original flow. Each half of the flow is extended width-wise to become a flow that occupies half the local height and having twice the width that it did originally.

This reshaping of the parts of the flow is realised by means of guiding baffles in a duct through which the flow passes.

The same principle of rearrangement may be repeated several times at respective stations spaced along the length of the duct as needed.

In doing so, it will be possible to divide the two kinds of flow (which are going to be directed over each other) into two partial flows.

In Fig. 1 a lengthwise cross section of duct 11 is shown schematically. Baffle plates 1 that are drawn in full lines are mounted upon the bottom wall 2 and baffle plates 3 drawn in dotted lines depend from top wall 4. Note that the side edges 5 and 6 of the baffle plates do not touch each other.

In the present example the baffles are arranged to form three progressively finer mixing stations A, B and C. In Fig. 2 is shown how the widths of the individual baffles changes in the succeeding stations.

Here it can also be observed that the baffles at the side walls of the channel 11 are designed as half-width units. This is constructionally advantageous because by means of the supports mentioned in the following paragraphs. This ensures a smooth flow without backward rotating eddies and it also presents an evident advantage for the levelling co-operation of the succeeding stations by the creation of an extra spreading and mixing action upon the sideways rotating eddies that emerge from the preceding baffle edges.

For the baffle plates to operate adequately and at the same time be mounted firmly, they are supported by steamline shaped elements which the placed between each baffle plate and the top or bottom wall from which it diverges. This is shown in the following Figs. 3 to 7.

Fig. 3 is a cross section, looking sideways: baffle plate 1 diverges away from wall 2 and is held by support 7. Fig. 4 is a top view of the same, and Figs. 5 and 6 show this in perspective. In Fig. 7 a duct side wall bordering half-width baffle 8 is shown with baffle plate 1 and stream line support 7.

The supports have an important effect with respect to the control of the fluid stream.

They generate a slight local depression in the flow-which is levelled out by the flow over the neighbouring baffles. It is mainly by virtue of this that the widthwise flatteningout and evenly spreading action is realised.

It is self-evident that the duct surfaces exposed to the flow should be highly polished and that at least the baffle plates, the supports and the bottom and top plates are advantageously constructed in metal (for stiffness and to minimise static electrical effects).

Generally speaking it will be clear that a flow homogenising system such as that described above is not only useful for a fibre web forming machine, but also for other systems where a particle-laden flow is to be mixed and made more uniform in a broad channel.

Claims

WHAT I CLAIM IS:-

1 A device for the homogensation of a particle-carrying fluid stream, such as a fluid stream carrying fibres, comprising a duct terminating at a rectangular exit end, and having at least one mixing station intermediate the length of the duct for rearranging the flow, whereat inner baffles are adapted to divide the flow into parts that each occupy a respective portion of the duct cross-section of gradually changing shape in such manner that on completion of their passage through the mixing station respective half-parts of the flow or respective half-parts of each of a plurality of portions of the flow each occupy a cross-sectional area of twice the transverse width occupied by that half-part of the flow immediately preceding said mixing station, and the or each pair of said doublewidth half-part flows are disposed one above the other.

2. A device according to claim 1, wherein there are several mixing stations in series along the duct

3. A device according to claim 2, wherein the rearranged flow occupies a rectangular cross-section at the end of each mixing station and successive mixing stations are arranged to treat the incoming flow in an increasing number of said portions each of which is rearranged as two half-parts disposed one above the other.

4. A device according to claim 3, wherein said successive mixing stations produce a geometrically progressive increase of the total number of said half-parts.

5. A device according to any one of the preceding claims, wherein the duct has a rectangular cross-sectional form of changing size along the length of the duct.

6. A duct according to claim 5 wherein said changes of size wholly or predominantly relate to the height of the duct cross-section.

7. A device according to claim 6, wherein said changes of size progress proportionally or exponentially with respect to the channel length.

8. A device according to any one of the preceding claims, wherein the internal surfaces of the duct are polished and have rounded edges, and the material is electrically con ductive to minimise electrostatic charges in the duct.

9. A device according to any one of the preceding claims, wherein the baffles com prise baffle plates respectively forming upper or lower boundaries for said part flows at the or each mixing station, and supports that extend upwardly or downwardly from said baffle plates, said supports having a streamline shape in the flow direction so as to co-operate by dynamic suction with the action of the neighbouring baffle plate or plates to reshape the fluid flow therepast.

10. A device according to any one of the preceding claims, arranged for use with a fluid stream carrying paper-making fibres or flocks or textile staple fibres or continuous filaments or yarns or mixtures thereof.

11. A device according to any one of claims 1 to 9, arranged for use with a fluid stream carrying fibre flock.

12. A device according to any one of claims 1 to 9 arranged for use with a fluid stream carrying non-fibrous particles.

13. A device according to any one of claims 1 to 9, in combination with at least one other flow regulating device for use in the supply of material to the headbox of a single wire or a double wire paper machine system.

14. A device for the homogensation of a particle-carrying fluid stream, constructed and arranged for use and operation substantially as described herein with reference to the accompanying drawings.