DE20308021U1 - Suspended feed of fibres to paper press flows through channel with sidewall lining structure exploiting the Lotus effect - Google Patents

Abstract

In a paper or carton-making process a feed of suspended fibres is transported along a channel to a press. The channel sidewalls are esp. lined with a coating whose surface structure causes a Lotus effect interaction between the moving fibres and sidewalls. The stainless steel sidewall lining has an irregular surface structure, revealed by electron microscopic inspection, which minimises friction between the moving fibres and sidewalls. The structured lining is applied as a foil or paint.

Description

Conveying element for transporting a suspension stream

Technical background

The invention relates to a web-shaped conveying element, as used in particular in paper or cardboard production machines for transporting a suspension stream.

The surface quality of the surfaces touched by the suspension, especially in the machines of interest here for the production of fiber webs, in particular paper and cardboard machines, decisively determines the physical properties such as conveying speed across the entire width of the conveyor track and homogeneity of the suspension flow.

It is already state of the art, for example, to design the inner walls of material feed systems, such as those used in paper and cardboard machines, with defined low surface roughness in order to avoid deposits of fibers, fine materials, etc. from the conveyed suspension.

It is often an essential requirement for the conveying system in material feed systems of machines for the production of fiber webs to ensure that the profile of the suspension distributed onto the wire section is as uniform as possible across the width of the machine, i.e. the composition and conveying speed of the suspension should be essentially independent of the position of the volume element in question on the conveying element.

Without additional measures, this will not be achieved, especially in the edge areas of a conveyor track that is provided with side walls, the fa-

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The amount of hydrogen in the contact areas with the side walls is lower than that in the other mid-latitude areas. The reason for this is the friction between the suspension and the side walls, which is caused by the roughness of the surface of the side walls and the deposits that settle there.

In new systems, this can be compensated for by over-dimensioning the wet working width (conveyor width) in relation to the working width (removal of the fiber web for further processing) so that sufficiently wide edge pieces can be removed at the transition from the screen to the press section.

However, these options are not available in existing systems with narrower conveyor elements, so that the result is a reduction in the quality of the final product (fiber web) due to weight deviations at the edges.

State of the art

There has therefore been no lack of temptation to minimize the friction between the suspension and the side walls of the conveyor element, which is recognized as the cause of these effects, by, for example, making openings in the side walls in order to accelerate the edge flows by selectively removing or feeding in partial quantities and thereby achieving a homogeneous profile of the suspension across the entire width. For this purpose, it is also known to arrange flow channels in the edge area of headboxes in order to also accelerate the edge flows.

The disadvantage of these previously known processes, however, is that these additional measures are only optimized for certain suspensions, but with changing material densities or flow velocities,

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Often other conditions arise, so that the desired compensation of the undesirable "edge effect" is only incompletely achieved.

Description of the invention

It is therefore an object of the invention to further develop the edge regions of a web-shaped conveyor element which guide the suspension, such as a material feed system in machines in the paper and cardboard industry, in such a way that the friction is significantly reduced without additional equipment expenditure and thus an almost uniform outflow of the suspension over the entire outlet width can be achieved.

According to the invention, this object is achieved by the features of claim 1.

The basic idea of the invention is a surface structuring of the edge areas, as referred to in the literature as the "lotus effect". In this lotus effect, as defined for example in DE 101 38 036, elevations extend over the surface at periodic intervals, which are connected by ridges, the effect of which is to influence the physical properties in the boundary area/contact area between this surface and the liquids or suspensions flowing past.

The use of this known effect in suspension-carrying components, in particular in feeding systems for the production of fiber webs, in particular paper and cardboard machines and there especially in the headboxes and side barriers attached to them, enables the desired reduction in friction and thus a "homogenization" of the flowing suspension with regard to the flow velocity and the material composition over the entire conveying width.

The surface structure can be realized in different ways, either the entire component can be provided with a corresponding embossing, but it is also possible to provide overlays of various types and materials that are connected to the side borders.

Short description of the drawings

An embodiment of a conveying element according to the invention is explained in more detail with reference to drawings, in which:

Fig.1 : a schematic perspective view of a conveyor track
Fig. 2: a first flow profile in the conveyor path of Figure 1, and
Fig. 3: a second flow profile in the conveyor path of Figure 1.
Description of an implementation example

Figure 1 shows a perspective schematic representation of a section of a headbox consisting of a longer web with a base area 10, two side parts 11 and 12, and an upper part 30 which carry a suspension stream 20.

In Figures 1 (state of the art) and 2 (according to the invention), the speed profile of the suspension flow 20 is indicated, whereby the length of the arrows V is a measure of the speed; it can be seen that due to the friction between the suspension flow 20 and the edge regions 11 and 12, the transport speed V is lower there than over the middle regions of the conveyor track. Consequently, different material properties are formed in the edge regions because the volume elements conveyed there "remain behind" compared to the middle region of the conveyor track, which ultimately leads to the usable width AB of the headbox being smaller than

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the conveyor width AN, since the undesirable edge areas must be separated or eliminated before further processing, e.g. before the headbox of a paper machine.

Figure 2 shows the movement of a front line A-A after times T1, T2, T3, T4; it can be seen that a profile B-B is established due to the inhibition of the edge areas by the friction on the side parts 11,12.

By profiling the edge regions of both the side parts 11, 12 or, if appropriate, also to a controlled extent of the base part 10 and/or the cover part 30 according to the invention, improvements can be achieved here, which are shown schematically in Figure 3, where the friction effects in the side regions of the suspension flow 20 are significantly lower (profile B*-B') and thus the usable width AB is only slightly smaller than the conveying width AN.

A similarly positive effect is to be expected for the blade structure in the z-direction with a more uniform layer structure at the outlet/outlet gap.

The type of surface structure can, for example, be as in the above-mentioned DE 101 38 036, but other implementations that achieve the lotus effect are also conceivable.

To achieve this, the suspension-carrying parts 10, 11, 12, 30 can be covered in whole or in part, for example, with a type of varnish that has the surface characteristics required to achieve the lotus effect, but it is also possible to provide supports with these surface characteristics as separate parts such as foils or coverings, which are firmly connected to the side parts 11, 12 and, if necessary, also to the base part 10, which then serve as a support.

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Alternatively, the components themselves can of course also have a corresponding surface embossed on them, for example if they are made of stainless steel.

It is of course also possible to carry out different combinations of these implementations, depending on the given cost and the desired technical effect.

Claims (5)

1. Web-shaped conveyor element for transporting a suspension flow, in particular in machines for paper or cardboard production, characterized in that at least some of the surfaces ( 10 , 11 , 12 , 20 ) in contact with the suspension, in particular the edge elements ( 11 , 12 ) for laterally limiting the suspension flow ( 20 ), have a surface structure for producing the lotus effect. 2. Conveying element according to claim 1, characterized in that the surface structure is formed directly from the material (e.g. stainless steel) of the conveying element. 3. Conveyor element according to claim 1, characterized in that the surface structure is designed as a covering, e.g. as a film, which serves as a covering material on the conveyor element serving as a carrier and is connected to it. 4. Conveying element according to claim 3, characterized in that the support material forms the surface structure when it is applied, e.g. as a varnish. 5. Conveying element according to claim 1, characterized in that the suspension-contacting surfaces are formed by the headbox of a paper or board machine.