WO2008040843A1

WO2008040843A1 - A lamella of a headbox of a paper machine or the like

Info

Publication number: WO2008040843A1
Application number: PCT/FI2007/050508
Authority: WO
Inventors: Marko Maja; Janne Lappi
Original assignee: Metso Paper, Inc.
Priority date: 2006-10-05
Filing date: 2007-09-24
Publication date: 2008-04-10
Also published as: FI20065639A0; FI20065639L

Abstract

The invention relates to a lamella of a headbox of a paper machine or the like, which is located in a slice channel (15) of the headbox (10). The lamella (16) comprises carbon nanotubes.

Description

A lamella of a headbox of a paper machine or the like

The invention relates to a lamella of a headbox of a paper machine or the like according to the preamble of claim 1. A paper machine or the like refers to paper, board or tissue machines.

As known from prior art, lamellae have been used in the slice channels of head- boxes, i.e., lamellae the purpose of which is to lower the tensile strength ratio of a paper, board or tissue web due to increased turbulence output. By means of the lamellae, the scale of created turbulence is also decreased, because through the lamellae are provided: small channel height because the slice channel is divided into layers in the vertical direction; increased boundary-layer turbulence because the lamellae increase wall area; and a thin trailing end because a small change in area is provided over the lamella tip and small swirls caused by the trailing end of the lamella; and, furthermore, the mixing of flows coming from different rows of the turbulence generator is prevented by means of the lamellae. Lamellae used in headboxes vibrate a little in use as a result of headbox flow in certain conditions. A problem in using the lamella technique is that the vibration of the lamella forms a standing wave on the tip of the lamella, which causes to the web very regular streakiness locked in the cross-directional i.e. CD direction which appears in the final structure e.g. as basis weight or fibre-orientation striation, thus weakening the end use properties of the product. The strength of the created phenomenon depends on the structure of the lamellae and the running parameters. A streaked/striated structure in the web is directly connected to cross-directional periodicity in the mean speed profile observed in water measurements. This, again, was proven to be caused by the flow structure interaction in which the turbulence and the periodic swirl detachment from the trailing edge of the lamella create in suitable conditions an excitation which makes the structure vibrate. Due to the effect of the created vibration mode, the detachment of the flow further strengthens in certain cross-directional positions and is damped in others, because of which a secondary flow structure, which forms streaks in the fibre flow, is created after the lamella.

One has not been able to solve this problem satisfactorily with arrangements known from prior art, but has been obliged to make a compromise between the streakiness and some other property of the end-product, whereby one has not been able to improve this property so much as it would principally have been possible.

A disadvantage of lamellae known from prior art is also the wear and tear of the lamella tip caused by the undulation of the lamella tip and the flow. In known composite lamellae, the thin tip area undulates and wears easily and, after the tip has worn, it gets easily dirty thus further increasing the streakiness in the web. It is known from prior art to manufacture lamellae of so-called prepreg (pre- impregnated) fabrics which are semi-finished products in which reinforcements have been pre-impregnated with resin which hardens in heat and is usually based on thermosetting plastic. Prepreg fabrics are characterised by two-stage hardening: in the semi-finished product, resin is in a partially hardened solid state from which it can be finally hardened by means of heat. Typically, the prepreg fabrics are piled in the manufacturing phase in a mould in a desired direction usually by hand, whereby the thickness of the product and the prepregs to be used define the number of layers. After positioning the prepregs, the mould is closed, air is removed either with a vacuum bag or in an autoclave and the matrix plastic is hardened by heating the mould or the autoclave. However, the prepreg fabrics are not cost-effectively available as thin as required in order for the thin tip area of the lamella to be manufactured directly by the inexpensive mould technique. On the other hand, a brittle lamella tip produced by prepreg structure as thin as required from the viewpoint of the flow structure is susceptible to mechanical damages. Thus, it has been necessary to machine the lamella tip for obtaining the desired shape and dimensions of the tip. This, however, will break the fibre structure and the outer surfaces of the lamella will remain open, the reinforcement fibres can hang loose from the surface, the surface will become porous and, furthermore, an area collecting dirt will possibly be created in the tip.

As regards prior art, reference is made to published application WO 03/062527 which describes an arrangement to be used in connection with a paper machine headbox for controlling stock flow by means of a film matrix by feeding to the film matrix a voltage signal the frequency/amplitude of which is regulated. By means of the film matrix, turbulence or vibration is produced to the stock flow which vibration damps the pressure variation of the stock flow. This known arrangement is problematic in that the film matrix wears from the effect of the pulp- suspension flow and the arrangement is complex and expensive.

As regards prior art, reference is also made to published application DE 10249820 which describes an arrangement to be used in connection with a paper or board machine headbox in which arrangement for affecting the fibre orientation of the fibre-pulp suspension at least one geometric change is arranged in the area of the slice channel. A disadvantage of this known arrangement is still that this does not prevent the vibration of the lamella tip.

An object of the invention is to provide a lamella of a headbox of a paper machine or the like, in which problems related to the undulation and wear of the lamella have been eliminated or at least minimised.

An object of the invention is also to provide a lamella of a headbox of a paper machine or the like, in which generation of streakiness in the web has been eliminated or at least minimised.

To achieve the above-mentioned objects and those that come out later, a headbox lamella according to the invention is mainly characterised by what is presented in the characterising part of claim 1. According to the invention in connection with the headbox of a paper machine or the like, carbon nanotubes are utilised in the lamella, whereby the wear of the lamella tip, the streakiness of the web caused by it and the possible soiling of the worn tip part are avoided.

Carbon nanotubes are tubular, three-dimensional structures consisting of combinations of carbon molecules. The diameter of the tube is typically a few nanometres while its length can be several, even dozens of millimetres. There are both single-walled (diameter 2—4 nm) and multi-walled (diameter 5-10 nm) carbon nanotubes. A multi-walled tube consists of several nested single-walled tubes. The wear resistance characteristics of carbon nanotubes are based on an extremely high aspect ratio.

In connection with the invention, carbon nanotubes in connection with the lamella are located advantageously in the machined area of the lamella tip or completely on the outer surface of the lamella or in its desired sub-area.

According to an advantageous embodiment of the invention, carbon nanotubes are chemically bonded in matrix plastic, thermosetting plastic or thermoplastic, e.g. epoxy, vinyl ester or polyurethane. In this advantageous embodiment of the invention, a prepreg fabric, which comprises matrix comprising chemically bonded carbon nanotubes, is located on the neutral axis of the lamella structure, whereby the fabric comprising nanotubes can be processed in the area of the lamella tip, whereby in the area requiring machining there is more impact ductile and more wear enduring matrix plastic for reinforcing the structure and preventing wear and soiling. Advantageously, matrix plastic includes a few percentages, 1-5%, of carbon nanotubes.

According to a second advantageous embodiment of the invention, separate reinforcements and separate matrix plastic are used in the manufacturing process, whereby better possibilities of customising the matrix plastic are obtained. According to a third advantageous embodiment of the invention, the carbon nano- tubes are chemically bonded in a coating, a thermosetting plastic or a thermoplastic based coating, e.g. epoxy, vinyl ester or polyurethane varnish, by means of which the machined tip of the lamella or the outer surfaces of the lamella is coated substantially completely or in a desired area.

Advantages achieved with the invention are based on the covalent bonding between the carbon nanotubes and the matrix and on the good adhesion of the coating, which features reinforce, stiffen and toughen the structure.

The invention can be applied in connection with different types of lamella/wedge structures, e.g. according to pivoted and fixedly fastened lamella structures. Advantageously, the shape of the lamella/wedge is wedge-shapedly narrowing in the flow direction. The invention is applicable to be used in connection with different types of paper machines and the like, also comprising board and tissue machines. The invention is especially well applicable to be used in connection with paper machines or the like utilising a multilayering process. The arrangement according to the invention is thus applicable for the structure of turbulence and separation lamellae. The lamella can be fastened in the structures of the headbox fixedly or by means of a pivot.

The invention will now be described with reference to exemplifying embodiments of the figures of the accompanying drawing, to which the invention is, however, by no means intended to be narrowly defined.

Fig. 1 schematically shows a headbox structure in connection with which the invention is applicable.

Fig. 2 schematically shows an embodiment of the invention. Fig. 3 schematically shows another embodiment of the invention.

Fig. 1 schematically shows a headbox 10 which comprises a stock inlet header 1 1 , after which in the flow direction of the pulp suspension there is a tube bank 12 which comprises flow pipes from which the flow is guided to an intermediate chamber 13. From the intermediate chamber 13, the flow is further guided to a turbulence generator 14 and via its turbulence pipes to a slice channel 15 and further onto a forming wire (not shown). According to Fig. 1 , from the inlet header 1 1 the stock flow is guided via an input plate 1 IA to the tube bank 12. After the input plate HA, there is a divider plate 19. Both the input plate HA and the divider plate 19 comprise channels 22 in vertical and horizontal rows. The channels 22 of the divider plate 19 join channels 23 of the tube bank 12 in corresponding positions. A dilution flow, which is advantageously clean or fibre-containing water, is guided into the pulp flow from a dilution liquid inlet header 20 by means of a channel 24 through the channel of the input plate HA to valves 25 in different width positions of the paper-machine/board-machine headbox for adjusting the basis weight profile of the web. From each valve 25, the dilution flow can be guided to the channel 22 in the divider plate 19. The stock flow is further guided to the intermediate chamber 13. From the intermediate chamber 13, the stock flow is guided to the turbulence generator 14 and further to the slice channel 15 of the headbox. The slice channel 15 of the headbox 10 comprises lamellae/wedges 16 which extend over the width of the slice channel 15 of the headbox 10. According to the invention, the lamellae 16 comprise carbon nanotubes located in connection with the lamella 16. Advantageously, the carbon nanotubes are located in the tip area of the lamella 16 or all over on the surface of the lamella 16.

Fig. 2 shows an exemplifying embodiment of the invention which depicts a lamella 16 located in the slice channel 15 of the headbox 10, into connection with the tip of which is located a prepreg fabric including carbon nanotubes, which fabric is located on the neutral axis X of the structure. Fig. 3 shows an exemplifying embodiment of the invention in which the tip area of the lamella 16 is coated with a coating which comprises carbon nanotubes. The lamella 16 can also be completely coated with a coating comprising carbon nanotubes.

In the foregoing the invention has been described only by referring to some of its advantageous embodiments, to the details of which the invention is, however, by no means intended to be narrowly confined.

Claims

1. A lamella of a headbox of a paper machine or the like, which is located in a slice channel (15) of the headbox (10), characterised in that the lamella (16) comprises carbon nanotubes.

2. A lamella according to claim 1, characterised in that the carbon nanotubes are chemically bonded into matrix plastic and a prepreg fabric consisting of it is located on the neutral axis (X) of the structure of the lamella (16).

3. A lamella according to claim 1, characterised in that the carbon nanotubes are chemically bonded into the matrix plastic and that the structure comprises separate fibre reinforcements and matrix plastic.

4. A lamella according to claim 2 or 3, characterised in that the matrix plastic is of thermosetting plastic or thermoplastic.

5. A lamella according to any one of claims 2-4, characterised in that the matrix plastic is of epoxy.

6. A lamella according to claim 1 , characterised in that the carbon nanotubes are chemically bonded into a coating which is located on the outer surface of the lamella (16).

7. A lamella according to claim 6, characterised in that the coating is of thermosetting plastic or thermoplastic based coating.

8. A lamella according to any one of claims 6 or 7, characterised in that the coating is of epoxy varnish.

9. A lamella according to any one of claims 1-8, characterised in that the carbon nanotubes are located in the tip area of the lamella (16).

10. A lamella according to any one of claims 1-9, characterised in that the carbon nanotubes are located on the outer surfaces of the lamella (16).