WO1993021378A1

WO1993021378A1 - Paper machine fabric

Info

Publication number: WO1993021378A1
Application number: PCT/FI1993/000126
Authority: WO
Inventors: Antti Palokangas
Original assignee: Tamfelt Oy Ab
Priority date: 1992-04-10
Filing date: 1993-03-30
Publication date: 1993-10-28
Also published as: IT1260641B; FR2691178B1; FI90362B; BE1006316A3; ITTO930235A0; AU3754993A; FR2691178A1; FI921604A0; ITTO930235A1

Abstract

A paper machine fabric (1) having a metal indicator element (4) attached to its edge in addition to normal fabric threads (2, 3). The indicator element (4) may be a thread (4) interwoven in the fabric or bonded to it e.g. by an extrusion material (5) of the edge. It may also consist of metal particles mixed in the extrusion material (5) or of a metal coating formed on the edge of the paper machine fabric.

Description

Paper machine fabric

The invention relates to a paper machine fabric having at least one fabric layer comprising lengthwise and crosswise threads.

Paper machine fabrics, such as wires and felts, are used in different types of machines producing a weblike product from a fibre suspension, such as paper machines, cardboard machines, and the like, which will be referred to by the name paper machine in this patent application and claims. The fabric, such as a wire or felt, is produced by weaving from various suitable mono- filament or multifilament threads typically of a synthetic material, such as polyester, polyamide, etc., into an endless bandlike product. At the inlet end of the paper machine, i.e. at the wet end, the fibre suspension is fed on a wire to form a web. At the terminal end, i.e. in the press and drying sections, felts are used in which fluffy material has been attached to the woven fabric portion or the fabric has been filled in some other way so as to achieve a felt into which water can be removed from the web when the web is compressed in the press section for drying it before final drying by heat. When in use, paper machine fabrics rotate around various rolls at a rate equal to that of the web. Depending on the texture of the fabric and the shape and position of the rolls, the fabric generally tends to move in the axial direction of the rolls, that is, in the transverse direction of the web towards the edge. To prevent this, controllable and adjustable rolls have been developed for guiding the passage of the fabrics. The position of the rolls is adjusted by sensing the edge of the fabric, and when the fabric tends to be displaced from a desired position in one direction or the other, the roll is adjusted so that it causes the fabric to be displaced in the opposite direction.

As is well-known, the position of the edge is measured either by mechanical sensing means touching the edge or by using air jets in different ways. A problem therewith is that the mechanical sensing means exert a continuous mechanical strain on the edge, which wears it down and finally causes damage. Air jet arrangements in turn are difficult to effect, and they increase the consumption of air and cause noise problems. Attempts have also been made to measure the position of the edge by photocells but the problem therewith is that they are contaminated relatively rapidly during use, which requires regular cleaning and, nevertheless, reliable operation cannot be achieved.

In the prior art, the measuring has been per¬ formed on conventional paper machine fabrics, which requires methods and arrangements of the type described above. The object of the present invention is to provide a paper machine fabric which enables the measurement of the position of the edge to be performed simply and reliably without the problems caused by contamination and wear while the fabric is, however, easy and simple to produce. The paper machine fabric according to the invention is characterized in that an indicator element of a material different from that of the paper machine fabric is provided in the edge of the paper machine fabric over the entire length thereof, the position of the indicator element being measurable without contact so as to detect the position of the edge of the paper machine fabric in the transverse direction of the paper machine and to adjust the position of the paper machine fabric in the transverse direction of the paper machine during the operation of the machine. The basic idea of the invention is that an indicator element made of a suitable material, such as electrically conductive and/or magnetizable metal thread or metal material is provided in the edge of the paper machine fabric. The identifier is either woven within the fabric, or as in the preferred embodiment of the invention, mixed in a filler material provided in the edge of the fabric. Alternatively, the edge of the paper machine fabric can be coated with the indicator element. Thus the edge can be detected e.g. by means of inductive pick-off means, by dielectricity measurements, or by some other suitable measuring technique, such as micro¬ wave or radiation measurements. The position of the edge can thereby be measured simply and easily by using measuring elements not in contact with the edge and not liable to contamination and a measuring technique independent of the propagation of light or the amount of water contained in the fabric. An advantage of the invention is that a reliably detectable edge portion in the paper machine fabric can be made suitable for various measurements and is very easy to mount or attach to the fabric at the production stage. At the same time, if required, the material used, such as magnetizable metal, can be covered by the filler material provided in the edge of the fabric so as to protect it from chemical influences.

The invention will be described more closely in the attached drawings, in which

Figure 1 is a schematic cross-sectional view of the edge of a paper machine fabric according to the invention during measurement;

Figure 2 is a schematic partial sectional top view of the edge of the paper machine fabric of Figure 1; Figures 3a and 3b are a schematic cross- sectional and a schematic top view, respectively, of the edge of another embodiment of the paper machine fabric according to the invention; Figures 4a and 4b are a schematic cross- sectional and a schematic top view, respectively, of the edge of a third embodiment of the paper machine fabric according to the invention;

Figures 5a and 5b are a schematic cross- sectional and a. schematic top view, respectively, of the edge of a fourth embodiment of the paper machine fabric according to the invention;

Figures 6a to 6d illustrate schematically the edge of a fifth embodiment of the paper machine fabric according to the invention in cross-section and from the top; and

Figures 7a and 7b are schematic top views illustrating the edge of two further embodiments of the paper machine fabric according to the invention. Figure 1 shows a paper machine fabric 1 woven from lengthwise and crosswise threads 2 and 3. The weave of a paper machine fabric of this type is known per se and there exist a great number of different applications and embodiments, all of which are applicable in accord- ance with the invention. Figure 1 further shows an edge portion la of the paper machine fabric within which there is a thread-like indicator element 4 preferably made of an electrically conductive material. The thread i.e. the indicator element 4 may be of acid resistant or stainless steel or of some other suitable metal. As the indicator element is thread-like, it can be woven so as to form an integral part of the weave structure of the paper machine fabric simultaneously with the threads 2 and 3. Furthermore, the thread 4 is covered by filler material 5 in the edge of the paper machine fabric. The filler material forms a firm continuous edge area in the paper machine fabric while it covers the thread 4 on all sides so that it will not come into contact with water or other chemical materials employed in the paper production process, being thus protected from any chemical influences. Measuring elements 6a and 6b are provided on both sides of the edge of the paper machine fabric 1. The elements 6a and 6b may be inductive pickoff means whereby the induction field between the elements changes when the edge of the paper machine fabric and the thread 4 protrude between them. Essential is that the measurement can be made withou- contact, which eliminates mechanical abrasion and wear. The measurement can nevertheless be performed accurate- ly, which in turn enables accurate adjustment.

Inductive pickoff means can be realized in several different ways, and the measuring of the field created by them and the respective adjustment are performed accordingly. Preferably, the measurement and the adjustment are performed so that when the edge of the paper machine fabric approaches the pickoff means, the resulting change in the induction field is allowable up to a predetermined limit. When the limit is exceeded, the adjustment is performed in a manner known per se by adjustment and control equipment so that a sideward displacement of the fabric ceases. Correspondingly, if the fabric starts to be displaced in the opposite direction and the induction field changes in another direction, the control is reversed, so that the position of the fabric remains substantially constant.

Figure 2 shows the situation of Figure 1 from the top with the edge of the paper machine fabric 1 partially cut open. As appears from the figure, the thread 4 is interwoven in the fabric in parallel with the other fabric threads in the longitudinal direction. Figures 3a and 3b show another embodiment of the paper machine fabric according to the invention utilizing a thread or a thread-like indicator element in cross-section and from the top, respectively. It employs a separate thread which is positioned in a wavelike manner close to the edge of the paper machine fabric before the edge area is filled with an extrusion material. As appears from Figure 3a, the thread is positioned on one surface of the paper machine fabric, and the filler material, i.e. the extrusion material 5 covers i:he thread and bonds it to the paper machine fabric. As appears from Figure 3b, the thread 4 forms a wavelike pattern close to the edge of the paper machine fabric. Figures 4a and 4b show a third application based on the use of a thread-like indicator element, in which several threads are positioned substantially straight side by side upon the edge of the paper machine fabric and bonded to it by the extrusion material. In the embodiment shown in Figures 4a and 4b, there are three threads, but the number of the threads may vary.

Similarly, the threads 4 need not be absolutely straight if only they are substantially parallel with the edge.

Figures 5a and 5b show a fourth embodiment of the invention, in which the indicator element is formed by mixing metal particles 14 of e.g. acid resistant or stainless steel or other suitable metal material in the extrusion or filler material 5 so that they form a substantially uniform zone of metal particles over the entire length of the edge of the paper machine fabric. This structure is also easily detectable by various inductive, microwave or dielectricity measurements. The structure is also easy to manufacture as it is made simply by mixing preferably electrically conductive or magnetizable metal particles in the extrusion material in a desired ratio. In place of the filler material having metal particles mixed therein, the filler material may consist of some other electrically conductive material, such as electrically conductive rubber material or suitable electrically conductive plastic material without metal particles, or if required, metal particles may be added. Correspondingly, electrically conductive rubber or plastic material can be fed into the filler material or applied to its surface so that it acts as the indicator element.

Figures 6a to 6d show a fifth embodiment of the paper machine fabric according to the invention, where the edge of the paper machine fabric is coated by bonding metal 24 by spraying or by vacuum deposition or in some other way to the outer surface of the paper machine fabric in its edge area. Referring to Figures 6a and 6b, Figure 6a is a cross-sectional view in which the metal coating 24 is formed on the surface of the extrusion material, and Figure 6c shows similarly a cross-sectional view in which the metal layer 24 is formed on the surface of the paper machine fabric without extrusion material. Figures 6b and 6d show the structures of Figures 6a and 6c from the top. It appears that the metal coating 24 covers the edge of the paper machine fabric, thus forming an easily detectable indicator element.

Figure 7a and 7b show two embodiments in which the indicator element comprises metal bodies or metal- containing parts positioned at predetermined intervals. As the paper machine fabric may move at rates up to and above 2,000 m/min, the measuring elements are able to detect the indicator element even in this case. Figure 7a shows an embodiment in which metal rivets or the like metal bodies 34 are attached to the edge of the fabric at suitable intervals. These metal bodies 34 are then covered with a filler material for keeping them in position and for protecting them. In Figure 7b, metal particles 44 are mixed in the filler material at suitable intervals whereas filler material as such without metal particles is fed otherwise.

In the embodiments of Figures 5a to 6d, a single measuring element is used. This method is based on the measurement of eddy currents or the like, and so a single measuring element is sufficient; no transmitter -receiver pair is required. A typical feature of eddy current measurement is that the eddy current losses increase as the distance between the measuring element and the metal indicator element decreases. Furthermore, the sensitivity of this way of measuring increases if the metal material has a high conductivity, such as aluminium.

The invention has been described above and shown in the attached drawings by way of example. The metal indicator element, i.e. the indicator element formed in the edge of the paper machine fabric from a metal thread, metal particles or a metal coating, can be realized in many different ways. The measuring of the position of the edge of the paper machine fabric by utilizing the indicator element and the control and adjustment of the sideward displacement of the fabric in a manner known per se can be effected by various measuring methods by utilizing prior art control and adjustment techniques based on the use of the measuring results. The paper machine fabric according to the invention can be produced by interweaving the thread(s) acting as the indicator element in the fabric or by bonding them in some other way, e.g. by the extrusion material fed to the edge area. In place of various particles and crosswise threads it is also possible to use pieces of thread positioned in the transverse direction of the paper machine, even though they are more difficult to mount at the edge of the paper machine fabric. Even though the indicator element is provided at one edge of the paper machine fabric only in the above specification and in the drawings, it is equally possible to provide such an element at both edges, which, however, is not necessary in practice. Furthermore, the metal acting as the indicator element may be in the form of a continuous thread or an indicator element structure extending over the entire length of the fabric, or indicator element portions of predetermined length may be provided at suitable intervals as the fabric moves at such a high rate that even a change caused by metal material zones provided at-predetermined intervals can be detected and utilized by the measuring elements. The indicator element material may be magnetized in advance so that it is more easily detectable by certain ways of measuring. This, however, is not necessary and magnetism need not be used in the measuring.

Claims

Claims :

1. Paper machine fabric with at least one fabric layer comprising lengthwise and crosswise threads (2, 3), c h a r a c t e r i z e d in that an indicator element (4) of a material different from that of the paper machine fabric (1) is provided in the edge of the paper machine fabric over the entire length thereof, the position of the indicator element (4) being measurable without contact so as to detect the position of the edge of the paper machine fabric (1) in the transverse direction of the paper machine and to adjust the position of the paper machine fabric (1) in the transverse direction of the paper machine during the operation of the machine.

2. Paper machine fabric according to claim 1, c h a r a c t e r i z e d in that the indicator element (4) is formed by attaching at least one metal thread (4) to the edge portion of the paper machine fabric in the longitudinal direction of the fabric.

3. Paper machine fabric according to claim 2, c h a r a c t e r i z e d in that each thread (4) is woven in the edge of the paper machine fabric (1) during the normal weaving process.

4. Paper machine fabric according to claim 2, c h a r a c t e r i z e d in that each thread (4) is positioned on the surface of the paper machine fabric (1) and that the threads (4) are bonded to the paper machine fabric (1) with a filler material (5) by means of which the edge of the paper machine fabric (1) is made continuous and solid.

5. Paper machine fabric according to any of claims 1 to 4, c h a r a c t e r i z e d in that the indicator element (4) is protected from various chemical influences by the filler material (5) applied to the edge of the paper machine fabric.

6. Paper machine fabric according to claim 1, c h a r a c t e r i z e d in that the indicator element is formed by mixing metal particles (14, 44) or grains (34) in the filler material (5) applied to the edge of the paper machine fabric (1).

7. Paper machine fabric according to claim 1, c h a r a c t e r i z e d in that the indicator element (4) is formed by coating the edge of the paper machine fabric (1) with a metal layer (24).

8. Paper machine fabric according to claim 7, c h a r a c t e r i z e d in that the metal layer (24) is formed on the surface of the filler material (5) of the paper machine fabric (1).

9. Paper machine fabric according to claim 7, c h a r a c t e r i z e d in that the metal layer (24) is formed on the surface of the fabric layer (2, 3) of the paper machine fabric (1) without any separate edge filler material.

10. Paper machine fabric according to any of the preceding claims, c h a r a c t e r i z e d in that the metal material used as an indicator element is magnetizable.

11. Paper machine fabric according to any of the preceding claims, c h a r a c t e r i z e d in that the metal material forming the indicator element is substantially continuous over the entire length of the edge of the paper machine fabric.

12. Paper machine fabric according to any of claims 1 to 10, c h a r a c t e r i z e d in that the indicator element is formed by several successive indicator element portions positioned at substantially predetermined intervals.

13. Paper machine fabric according to claim 1, c h a r a c t e r i z e d in that the indicator element is made of electrically conductive plastic or rubber material.

14. Paper machine fabric according to claim 13, c h a r a c t e r i z e d in that the edge filler material is of electrically conductive rubber or plastic material.