METHOD AND DEVICE FOR CUTTING THE EDGE OF PAPER WEB

Method and device for cutting the edge of paper web

The present invention relates to a method for trimming the edge of a paper web, which is of the type presented in the introductory part of the attached patent claim 1. The present invention also relates to a device for trimming the edge of the paper web, which is characterised by the properties presented in the introductory part of the attached patent claim 5.

A narrow area of the edge is cut away from the formed paper web on the paper machine, whereby the area deviating in quality from the rest of the web is removed by cutting, and at the same time a certain set width is obtained for the web. The trimming is usually carried out with water jets, which are directed towards the surface of the web by means of trim squirts at both edges. The trimming is usually carried out in the wire section on the paper web, which has already formed a cohesive fibre mesh due to water removal.

With the help of pressurised water (10-45 bar) and a narrow jet obtained with trim squirts, a reasonable cut can be achieved. However, the control of the squirts is problematic, as they have to be turned to a certain angle in relation to the plane of the paper. Because of vibrations of the machine, it is problematic to sustain this angle, and likewise the distance between the surface of the web and the nozzle. In addition, adjusting the correct angle demands great precision.

The object of the present invention is to eliminate the above-mentioned disadvantages, and to present a method and a device with which the edge of the paper web can be trimmed with a cleaner cut and better precision, and it is possible to avoid the breaks and rejects caused by inaccuracies of control and disturbances during running. To carry out this object, the method of the present invention is mainly characterised in what is presented in the attached characterising part of patent claim 1. The device according to the invention, on the other hand, is characterised in what is presented in the attached characterising part of the patent claim 5. The edge of the paper web is cut with the help of two jets at an angle to each other, thereby producing a smooth cut as the first jet removes the edge strip and the other jet cleans the trimmed edge immediately afterwards. The jets are formed advantageously with the help of the same element that is moved in the cross direction to the web, in which the nozzles can be arranged in fixed positions thus obtaining jet angles that remain constant. This element is movable in the cross direction to the machine i.e. crosswise to the making direction of the web, for example by arranging the element so as to be movable with the help of a linear guide, whereby the control can be carried out very precisely at the correct point in the lateral direction of the web, either by turning the precision control member manually or by motor-operated means.

With the element movable in the cross direction, it is possible to integrate the nozzles into the same movable element so that they are at precise angular positions in relation to the web and to each other. In this way a precise double trimming of the paper web can be carried out, so that the nozzles are at the exact angles wanted.

The invention is described in more detail with reference to the attached drawings, wherein

Figure 1 shows the nozzle element of the device according to the invention from the side,

Figure 2 shows the same as a horizontal section from above,

Figure 3 shows the element as a cross-section at the first nozzle drill hole,

Figure 4 shows the same as a cross-section at the second nozzle drill hole,

Figure 5 shows the device seen from the making direction, and

Figure 6 depicts one of the trimming methods that can be carried out with the device. Figures 1-4 show the nozzle element 1 of the device according to the invention. The nozzle element is a long-shaped element in the machine direction (making direction) and it has two successive nozzle drill holes in the machine direction, which open to the side of the element that is facing towards the paper web. The drill holes are provided with internal threads, to which the trim squirts to be described later, can be attached. The nozzle drill holes are connected through the drill holes made from the ends of the element in the machine direction to the liquid channel 3, which ends in the centre and through which water is fed to the nozzles. The ends of the drill holes in the machine direction are plugged at the ends, so that the water is directed to the nozzle drill holes. The element 1 can be moved along a straight line of travel, controlled by a linear guide.

The nozzle element 1 is located in the ready-made device so that its longitudinal direction is in the same direction as the making direction, whereby the nozzle drill holes near both its ends are placed in succession in the machine direction. As can be seen in Figures 3 and 4, the nozzle drill holes are not in exactly the same position in the cross direction of the machine and, in addition, their angles are different in relation to the plane of the paper web. The nozzle drill hole of the first nozzle forms a larger angle o to the normal of direction of the nozzle element's linear guide than with the nozzle drill hole of the second nozzle (angle CX.2). The first nozzle drill hole in the making direction is thus at a larger angle of inclination in relation to the normal of the paper web plane than the second nozzle drill hole. The effects of the places and positions of the nozzle drill holes on the orientation of the nozzles and on the trimming of the web, are explained below. In addition, Figure 1 shows how the drill holes and the nozzles in them are directed obliquely (at a small angle of about 15°) to the making direction.

Figure 5 shows a device for trimming the paper web, which comprises the nozzle element 1, described above. Nozzle element 1 is placed crosswise at the end of a bar 2, which is movable in the cross direction to the paper web W and which is directed towards the middle of the paper web from outside the edge of the paper web in such a way that the nozzle element 1 can always be brought to the desired distance from the outer edge of the paper web, thus determining the width of the strip to be removed from the edge of the paper web. Inside the bar, presented with a broken line, there is a liquid channel 3, which branches out inside the nozzle element 1 to form channels in the machine direction, directed towards the nozzle drill holes. The bar 2 is moved in linear guide 4, which is placed outside the edge of the web. Thus the movement takes place directly across the web against the making direction of the web W by means of a suitable mechanism. This can be carried out with a manually turned precision control member 5, but it is also possible to consider a motor-driven linear movement, whereby the nozzle element 1 and correspondingly the nozzles can be placed precisely at the desired position in the lateral direction of the paper web.

As Figure 5 shows, the nozzles themselves, la, lb, are formed by attaching, as direct extensions to the nozzle drill holes, the trim squirts, which actually determine the direction of the liquid jets, and the drill hole running inside them produces a fine, highspeed water jet that can cut the paper web precisely. The trim squirts are thus directed at angles corresponding to the angles of the nozzle drill holes to the normal N of the paper web W and create jets at different angles κl , (X2 , directed at the paper web. The jet angle here means the angle which is the normal N of the paper web at the outer edge of the paper web and widens in the flow direction of the jet. Because the attachment of the trim squirts to the element 1 is rigid, the nozzles la, lb always remain at a constant angle in relation to each other and to the paper web W.

With the help of the fixed element 1, the directions of nozzles la, lb and the liquid jets coming out of them are accurately pre-determined and constant in relation to each other, and the angles remain the same despite vibration and other disturbing factors. When element 1 is moved linearly in the cross direction to the machine, these directions remain the same in relation to the plane of the paper web, when the direction of linear movement remains constant in relation to the plane of the paper web, i.e. the direction of the linear movement and plane of the paper web are at an accurately determined angle in relation to each other. When this angle is 0, i.e. the linear movement and the plane of the paper web are exactly parallel, the distance between the nozzle/nozzles and the surface of the paper web also remains always the same.

The described device can be placed on the wire section at a suitable point before the press section. If the wire in question is a twin wire, in which the formed paper web is directed between two water-permeable wires, the device can be placed in the single- wire area between the separation point of the wires and the press section. There can be a device as described above with two successive nozzles at both edges of the paper web .

With the help of the rigid nozzle element 1, it is possible to eliminate the inaccuracies in the control of the nozzles caused by the machine's vibrations. With the help of an accurate linear movement, the angles can be kept the same irrespective of the positions of the nozzles, and also the distance from the paper web can be kept exactly the same. The linear guide can be attached to the body structure of the machine, in such a way that the above mentioned movements can be implemented.

Figure 6 shows on a larger scale than in depiction of Figure 5, how it is possible to carry out the trimming with successive nozzles la, lb located on the same element 1, at different jet angles αl , 0(2 . The nozzles la, lb are directed from the nozzle element 1 to converge as seen from the machine direction, whereby the jets leaving them in a way intersect at a certain point seen from the machine direction, i.e. their projections in a perpendicular plane against the plane of paper web and the making direction, form two intersecting line segments. The nozzles la, lb are in this case placed at a such distance from the surface of the paper web W that the first jet nozzle la cuts the edge of the web with its jet obliquely directed towards the outer edge of the web at the first jet angle Oil, and removes a certain width of edge strip from the paper web's outer edge. The second jet nozzle lb coming immediately after this, cuts the lower part of the oblique edge produced less obliquely, i.e. at a jet angle of 0(2 , which is smaller than the first one, e.g. 1-3° , advantageously approx. 2° smaller than the first angle. The jet angle αl of the first jet nozzle la may be between e.g. 6-8°, advantageously approx. 7°, and the jet angle (X.2 of the second jet nozzle lb may be between e.g. 4-6°, advantageously approx. 5°.

The present invention is not limited to the embodiments presented, but it can be altered within the scope of the inventive idea presented in the claims. Although the figures show the possibility of moving the nozzle element 1 manually with the help of a linear guide, it can be carried out with the help of a motor, for example, by remote control, and thus the placement of the nozzle element and the functions of the nozzles can be monitored e.g. by television surveillance. Double trimming can be carried out in principle with two successive separate, and separately movable nozzle elements, both of which have a constant jet angle, but the exact orientation of the nozzles and the jets in relation to each other can be best accomplished with one nozzle element, into which both nozzles are integrated. In addition, there may be several different twin nozzle elements, which have different nozzle angles, and when needed, the nozzle element can be replaced with another if it is desirable to change the angle of the jets.

Claims:

1. A method for trimming the edge of the paper web, in which a cutting liquid jet directed to the area of the web's edge is used, characterised in that, the first jet in the machine direction cuts the edge of the paper web (W) obliquely at the first jet angle (( l) with a jet directed towards the outer edge of the web, and the oblique edge thus obtained is cut with a second jet in the machine direction, which is directed less obliquely at the second jet angle (α2 ) to the outer edge of the web.

2. A method according to patent claim 1, characterised in that the liquid jet is directed to the area of the edge from an element (1), movable in the cross direction to the machine, producing a jet angle (αl) that is constant.

3. A method according to claim 1 or 2, characterised in that both liquid jets are directed from the same element (1), moved in the cross direction to the machine.

4. A method according to one of the above-mentioned claims, characterised in that the jet angle (αl) of the first jet is between 6-8°, advantageously approx. 7°, and that the jet angle (α2) of the second jet is between 4-6°, advantageously approx. 5°.

5. A device for trimming the edge of the paper web, which comprises a jet nozzle to create a liquid jet to trim the web, characterised in that the device has, at the same edge of the web, in the machine direction, a first jet nozzle (la) and a second jet nozzle (lb) placed successively, which nozzles are placed in the cross direction to the machine at separate points and are directed at different angles (αl , α2) in relation to each other.

6. A device according to claim 5, characterised in that at least one of the nozzles is formed in the element (1) movable in the machine's cross direction), so that its orientation in relation to the element (1) is constant.

7. A device according to patent claim 5 or 6, characterised in that both nozzles (la, lb) are placed on the same element (1) movable in the machine's cross direction. 8. A device according to patent claim 7, characterised in that the orientations of both nozzles (la, lb) in relation to the element (1) are constant.

9. A device according to any of the claims 5-8, characterised in that the nozzles (la, lb) are directed so that they converge as seen from the machine direction.

10. A device according to any of the claims 5-9, characterised in that it comprises a bar (2) moving in the machine's cross direction, inside which there is a liquid channel (3) for bringing the cutting liquid, and at the end of the bar (2) an element (1) comprising one or more nozzles ( 1 a, lb).

11. A device according to claim 9, characterised in that the bar (2) is arranged to be movable in a linear guide (4).

12. A device according to the claim 10 or 11, characterised in that the nozzle (la, lb) is formed with the help of a drill hole made in the element (1), which drill hole is connected to the liquid channel (3), and to which is connected a trim squirt projecting from the element (1) and determining the direction of the jet.