GB2093879A

GB2093879A - Headboxes for paper machines

Info

Publication number: GB2093879A
Application number: GB8206036A
Authority: GB
Original assignee: Escher Wyss GmbH
Current assignee: Sulzer Escher Wyss GmbH
Priority date: 1981-03-02
Filing date: 1982-03-02
Publication date: 1982-09-08
Also published as: IT8219902A0; SE8201223L; FI820726L; NL8200647A; DE3107875A1; ES8303577A1; ES509822A0; FR2500860A1; IT1150210B

Abstract

A headbox having distributor channels (2) with step-like widenings (14) opening into a tapering nozzle channel (6) ending in an outlet gap (8) and bounded by plate-shaped lips (5), partitions (4) with flat surfaces being disposed in the nozzle channel (6) and dividing it into regions (7). The different regions (7) can be supplied with different grades of stock. The partitions (4), which project outwards through the outlet gap (8) each comprise a rigid plate (4) connected to a flexible foil (10). <IMAGE>

Description

SPECIFICATION Headboxes for paper machines This invention relates to headboxes for paper machines.

There is described in German OS 28 OO 547 and US-P S 4 221 635 a headbox comprising distributor channels in a plurality of rows each channel having at least one step-like widening, the distributor channels being connected to a tapering nozzle channel ending in an outlet gap bounded by two lip plates having substantially flat surfaces which bound the nozzle channel, each of the plates being movable in a direction parallel with its respective flat surface, at least one partitition having substantially smooth surfaces being disposed in the nozzle channel and dividing it into regions each of which is connected to a different one of the rows of distributor channels, each partition consisting at least partly of a rigid plate rigidly secured in the nozzle channel.In this headbox, the partitions, which are formed by rigid plates, end in the nozzle channel upstream of the outlet gap. This does not matter since all the regions are supplied with the same grade of stock.

If the aforementioned headbox were to be used for producing layered paper, with the regions supplied with different grades of stock it may happen in some cases that some of the fiows from the different regions become undesirably mixed in the zone between the ends of the portions and the outlet gap.

The invention relates to a development of the described headbox with the arm of adapting the stock feed for the production of layered paper and, in the process, substantially preventing the individual layers from mixing before being deposited on to a wire or between two wires.

To this end, the head box according to the invention is characterised in that the different regions are connected via the distributor channels to different stock feed conduits, and the partitions extend outwards from the nozzle channel through the outlet gap.

By means of these features, the regions of the stock feed can be supplied with different grades of stock, thus making use of the advantageous effect of distributor channels having step-like widenings.

One or more partitions extending through the outlet gap prevent individual layers from prematurely mixing. The supply of stock to one region can be interrupted, or one or more regions can be supplied with suspension mixed with air to form foam.

Advantageously, the or each partition includes a flexible foil connected to the rigid plate of the partition so that the flow cross-sections of the individual regions can automatically adapt themselves to the amounts of flow; this adaptation will preferably occur mainly in the region outside the outlet gap.

According to another optional feature, the transition between the rigid plate and the foil is a turbulence-generating step. This simplifies the manner of securing the foil to the rigid plate and also produces advantageous turbulence of the stock, at the transition between the two parts.

The transition between the plate and foil can be inside the nozzle channel. Alternatively, however, the transition between the plate and the foil may be outside the nozzle channel.

If there are a number of partitions the foils can have different lengths. This can be used to control the place where the stock flowing through the individual regions is deposited on to a wire or a previously-formed fibre web or fleece.

In this connection, West German PS 899 896 describes a headbox comprising a partition component in a nozzle channel for producing layered paper. The partition component, however, does not extend all the way across the outlet gap, and there are no distributor channels having steplike widenings. US-PS 3 853 697 described a headbox having in a nozzle channel a partition having a rigid portion and an adjacent flexible portion. As before, however, the partitions do not extend beyond the outlet gap. The are also unsuited for conveying different grades of stock.

The invention may be carried into practice in various ways but two headboxes embodying the invention and a number of modifications to these headboxes will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic section through the first headbox in which the rigid plates extend outwards through the outlet slot of the nozzle channel; Figure 2 is a diagrammatic section to a larger scale of part of a headbox which is similar to that shown in Figure 1 but in which the rigid plates end inside the nozzle channel: and Figures 3 and 4 show to a larger scale two possible constructions of the connection between the foil and the rigid plate which may be substituted for the connections shown in Figures 1 and 2.

Figure 1 shows a headbox comprising a block 1 in which three rows of distributor channels 2 are formed. The channels 2 include upstream portions or bores which extend into larger cross section counterbores or slots 3 between which rigid platelike partitions 4 are secured. Plate-like lips 5 are secured to the block and co-operate to form a tapering nozzle channel 6 divided by the partitions 4 into regions 7. The nozzle channel 6 ends in an outlet gap or throat 8 through which the partitions 4 extend outwards. Flexible foils 10 are attached to the ends of the plate-like partitions 4.

As Figure 1 also shows, the individual rows of channels 2 are connected by pipes 11 to feed conduits 12 secured to a support structure 13.

The distributor channels 2 have step-like widenings 14 between the upstream and downstream portions thereof. Although only one such widening is shown in each channel, a number of widenings can of course be formed one after the other, as described in US-PS 3 527 197. The aforementioned US-PS 4221 635 should be referred to regarding the construction of the block and lips. US-PS 4 198 270 describes how the feed pipes are disposed relative to the individual rows of distributor channels.

The headbox shown in Figure 2 differs from that of Figure 1 in that the plate-like parts 4 end inside the nozzle channel bounded by the lips 5, i.e. in upstream of the outlet throat. As Figure 2 shows, flexible foils 10 are secured in slots 20 in the downstream edges of the plates 4 and co-operate with the plates to form the partitions.

As shown in Figure 2, the ends of the plates 4 are bevelled so that stock from the regions 7 can flow smoothly past them.

In Figure 3, the transition between the rigid plate 4 and the flexible foil 10 is constructed as a turbulence stage 30. To this end, the plate 4 is cut off at right angles. The end region may be of the same thickness as the remainder of the plate as indicated by pecked lines in Figure 2 or can be given a thicker portion 31. In each case, a turbulent region 32 forms at the end of the plate 4, thus producing advantageous turbulence in the stock.

As Figure 2 shows, the partitions can be given different lengths by, for example, providing foils 10 of different lengths L1, L2 to provide stock flow passages of different lengths. It is also possible to attach a flexible foil to one or other or both of the lip plates 5 and one such foil is shown in Figure 2.

Each plate 4 can be rigidly secured in the nozzle channel 6 as in Figure 1. Alternatively at least one of plates 4 can be allowed some freedom of movement, for example by forming the plate with a groove 43 as shown in Figure 2. The groove reduces the rigidity of the plate 4 so that it can be pivotably bent at the groove and adapted to the flow.

Finally, Figure 4 shows a pivot-like connection between a foil 10 and a plate 4. In Figure 4, the foil 10 is given a substantially cylindrical bead 50 which is trapped in a slot 51 in the edge of the plate 4 with sufficient clearance to permit pivotal movement but so that it cannot slide out of the slot.

Foils 10 can be made, for example, of a plastics material or metal or be laminated from a number of materials.

Claims

1. A paper machine headbox comprising distributor channels in a plurality of rows each channel having at least one step-like widening, the distributor channels being connected to a tapering nozzle channel ending in an outlet gap bounded by two lip plates having substantially flat surfaces which bound the nozzle channel, each of the plates being movable in a direction parallel with its respective flat surface, at least one partition having substantially smooth surfaces being disposed in the nozzle channel and dividing it into regions each of which is connected to a different one of the rows of distributor channels, each partition consisting at least partly of a rigid plate rigidly secured in the nozzle channel, the different regions being connected via the distributor channels to different stock feed conduits, and the partitions extending outwards from the nozzle channel through the outlet gap.

2. A headbox as claimed in Claim 1 in which the or each partition includes a flexible foil connected to the rigid plate of the partition.

3. A headbox as claimed in Claim 2 in which the transition between the rigid plate and the foil is a turbulence-generating step.

4. A headbox as claimed in Claim 2 or Claim 3 in which the transition between the rigid plate and the foil is inside the nozzle channel.

5. A headbox as claimed in Claim 2 or Claim 3 or Claim 4 which includes a plurality of partitions of which the foils are of different lengths.

6. A headbox as claimed in Claim 2 or Claim 3 in which the transition between the rigid plate and the foil is outside the nozzle channel.

7. A headbox as claimed in any of Claims 2 to 6 in which the or each foil is secured to its plate by a pivotal connection.

8. A headbox as claimed in any of the preceding claims which includes at least one additional plate movably secured in the nozzle channel.

9. A headbox as claimed in any of the preceding claims which includes a flexible foil connected to at least one of the lips.

10. A headbox substantially as described herein with reference to Figure 1 or Figure 2 of the accompanying drawings.

1 A headbox as claimed in Claim 10 modified substantially as described herein with reference to Figure 3 or Figure 4 of the accompanying drawings.