WO1992001835A1

WO1992001835A1 - Method and apparatus for stabilizing the run of a paper web or the like during diagonal cutting

Info

Publication number: WO1992001835A1
Application number: PCT/FI1991/000226
Authority: WO
Inventors: Pekka Hietanen
Original assignee: Tampella Papertech Oy
Priority date: 1990-07-25
Filing date: 1991-07-24
Publication date: 1992-02-06
Also published as: FI903723A0; FI903723A; FI84923C; AU8198191A; DE4191689T; FI84923B; SE9200901L; CA2066582A1; SE9200901D0

Abstract

During the diagonal cutting of a paper web, the tail (W1) for threading of the web (W) is cut out of the web and widened to a full-width web as the cutting member (1) travels in a direction transverse to the web at the free run of the paper web for example in the multi-cylinder dryer section. Associated with the cutting blade (1), there is a carrier surface (2), at the edge of which is a nozzle assembly (3), through which is provided a flow (VA/VB/VC/VD) of gaseous medium directed substantially away from the imagined centre point (2') of the carrier surface. The purpose of the flow is to stabilize the run of the web (W) at the cutting point (C). The carrier surface (2) operating in a reduced pressure owing to said adjustable flows is connected through one or several flow means (5) to a device such as a compressor that produces the gaseous medium, such as air.

Description

Method and apparatus for stabilizing the run of a paper web or the like during diagonal cutting

The present invention relates to a method and apparatus for stabilizing the run of a paper web or the like during diagonal cutting wherein the tail for threading of the web or the like is cut out of the travelling paper web and widened as the cutting member travels in a direction transverse to the web at the free run of the web, for example in a multi-cylinder dryer section, the stabilizing being enhanced by a flow of gaseous medium effected by means of a carrier surface involved with a reduced pressure.

For cutting the tail for threading of the web out of the paper web and for widening this tail by means of a so-called diagonal draw in the multi-cylinder dryer section of a paper machine or the like, use has been made previously of a method which attempts to stabilize the free run of the web in course of cutting by using a counter-blade on the other side of the web together with the cutting blade. This solution causes synchro¬ nizing problems and complicity of the structure. One way of alleviating this problem has been that disclosed for example by Finnish Publication No. 63800 of an examined patent application showing a device on the cutting blade side of the web for creating an air flow parallel to the web at the area of the blade. The air flow induces an increased or reduced pressure at the cutting point for controlling the run of the web. Because the guided air flow before the cutting member in the direction of travel of the web is parallel to the direction of travel of the web, the force components resulting therefrom influencing the web cannot be directed accurately and therefore the device does not provide a fully controllable run of the web at the cutting point. Finnish Patent Application No. 880051 proposes a stabilizing member associated with the cutting blade as a new solution, the member being preferably provided with a suction for effecting a flow from the web towards said member. It cannot be denied that this solution has been proved satisfactory in normal runs in the practice. However, under certain circumstances it has been found out that various devices and tubings used in connection therewith may be partly blocked due to the suction principle used in the above-men¬ tioned method. Hence, there exists a need for an alternative solution based on a blowing principle, especially in view of such difficult circumstances.

The purpose of the invention is to provide an improve¬ ment as far as the above-mentioned drawbacks are concerned. For reaching this goal, the method according to the invention is mainly characterized in that the reduced pressure is created around the cutting member or at least in the area located before the cutting point, seen in the direction of travel of the web, by means of a flow of gaseous medium directed substantial¬ ly away from the carrier surface and_.the cutting member at least during the cutting operation, said flow being generated by means of a flow brought to the edge of the carrier surface. The device according to the invention is characterized in that the device comprises a nozzle assembly at the edge of the carrier surface for effecting a flow of gaseous medium directed away from the carrier surface and the cutting member with the aid of a flow brought to the edge of the carrier surface with the aid of flow means.

Simplicity and operational reliability owing to the utilized nozzle blow and its direction can be mentioned as one of the most important advantages of the present invention. In addition, the cutting member and the carrier surface associated therewith can be constructed to a compact, easily movable construction. By means of the method and device according to the invention, the stabilizing of the paper web can be initiated substantially as early as before the carrier surface and before the associated cutting member because of a nozzle blow that is accomplished before the cutting point, as seen in the direction of travel of the web, and directed opposite to the direction of travel of the paper web. In accordance with the invention, it is also possible to adjust in each particular case the reduced pressure needed between the carrier surface and the paper web by adjusting the partial flows blown from the nozzle devices and/or by adjusting the total flow brought to the carrier surface, said reduced pressure being in the well-known manner dependent on the speed, thickness and surface quality of the web, to mention some examples.

The gaseous medium is most preferably passed to a housing-like construction, wherefro it is passed to the edges of the carrier surface by suitably guiding it. The closed side of the housing construction facing the web can at the same time constitute the well- sealed carrier surface that makes the reduced pressure possible.

The invention is described in the following in more detail with reference to the accompanying drawing, wherein

Fig. 1 shows the location of the apparatus according to the invention in a dryer section,

Fig. 2 shows a cross-section of an advantageous embodiment in accordance with the inven¬ tion, and Fig. 3 shows the embodiment in accordance with the invention as seen in the direction of the web.

Figure 1 shows in side view a part of the rear section of the dryer section of a paper machine, formed by upper cylinders 8 and lower cylinders 9. A web travels in the direction D over the cylinders 8 and 9 along a tortuous path, while it is supported by felts on the cylinders and has a free run between an upper cylinder 8 and a lower cylinder 9 (so-called double guidance) . The felts and the rolls guiding them are not shown herein. A horizontal traversing beam 10 situated perpendicularly to the direction of the travel of the web is mounted in the machine frame. The beam is equipped with a cutting apparatus for the web , mounted movably in the longitudinal direction of the beam. The blade 1 of the apparatus is pivotable into a cutting position where its edge cuts the web . The cutting apparatus is mounted on a carriage travelling in the longitudinal direction of the beam 10, and. as the carriage moves forward and the blade has assumed its cutting position, the web can be widened to a full-width web in the diagonal cutting.

The above-mentioned carriage and the mounting of the apparatus according to the invention is not shown herein, because it comprises a simple construction not to be discussed in conjunction with this invention.

Figures 2 and 3 show one advantageous compact embodi¬ ment of the device in accordance with the invention in schematic sectional and planar views, not showing, for instance, fixing means for mounting the device on the afore-mentioned carriage in more detail. The body of the device is constituted of a housing-like con¬ struction 11, in which is mounted a cutting blade 1 and into which a flow of air is led through a chan- nel 5. The wall of the housing facing the web forms thereby a carrier surface 2 with its outer surface, the carrier surface being situated around the cutting point C substantially parallelly to the web. In the embodiment shown the cutting member 1 is a rotating cutting blade, but it could be also a stationary one. The rotating movement of the cutting blade can be accomplished in the known manner most preferably by means of a driving device driven either by pressurized air or electricity.

In the Figure, the cutting blade is shown in its cutting position where the rotating blade 1 cuts the web W with its edge la at a point denoted by letter C and separates the tail Wl for threading from the rest of the web . The blade rotates in a plane perpendicular to the plane of the web W in the direc¬ tion A against the direction of travel of the web. At the edges of the carrier surface 2 associated with the blade or at least at the edge closest to the cutting edge in the direction of travel of the web or along a part thereof, there is a nozzle assembly 3, the purpose of which is to effect a reduced pressure in the space between the carrier surface 2 surrounding the blade and the web /Wl travelling in this area in order to stabilize the run of the web. The distance of the web to be cut from the blade can be stabilized to a desired value by controlling the nozzle flows which depend in a known manner on the properties of the material to be cut and on the circumstances. The nozzles 3 can be constituted of slits located on the housing 11 at the edges of the carrier surface 2 substantially in a parallel relationship with the plane of the web, that is, of so-called foil nozzles which are so directed that a flow passed through them from the housing 11 creates a fast flow of air which is sufficiently uniform over the direction of width. Also a suitably shaped row of holes having a similar extension can be used for the same purpose.

The flows needed in the embodiment of Figs. 2 and 3 are created by leading an overall flow V of a gaseous medium such as air through one or several flow means 5 from for example a compressor or the like to the inside of the housing-like construction 11 situated at the carrier surface 2. The overall flow is further divided most preferably into partial flows VA, VB, VC, and VD, for example, one for each edge, preferab¬ ly for example by means of guiding means 4 formed in the back part 2' of the carrier surface 2. The partial flows pass further through the nozzle assembly 3 and are directed substantially away from the imagined centre point of the carrier surface 2 and from the blade 1, extending almost parallelly with the plane of the web . The air present in the space between the carrier surface 2 and the corresponding area of the opposite travelling web W/Wl, induced by the flows directed away, is sucked with these flows, causing thus the establishment of the reduced pressure within said space.

The partial flows VA, VB, VC, and VD are directed from the nozzles 3 situated at the edges of the carrier surface 2 against the direction of travel of the web (VA) starting from the nozzles 3 situated before the cutting point, in the direction of travel of the web (VC) starting from the nozzles 3 situated after the cutting point C, as well as transversely to the direction of travel of the web to both sides away from the cutting point C approximately beside the cutting point starting from the nozzles 3 extending in the direction of travel of the web (VB and VD) . The flow VA is of particular importance, because it prevents the entrance of the air flow entrained with the web into the space between the carrier surface 2 and the web .

The magnitude of the negative pressure is in a known manner dependent on the properties of the material to be cut and on the cutting conditions. For controlling and/or closing the partial flows, control and closing means 6 are provided, preferably in association with the guiding means 4 and the nozzle assembly 3. In addition, for ensuring the stability of the process, particularly in changing conditions, in the solution in accordance with the embodiment, it is advisable to place the corresponding closing and control devices 7 also in association with the flow channel 5 feeding the overall flow V divided to separate nozzles. It is thereby possible to make sure that, if for example a part of the nozzle assembly is closed, the inadver¬ tent rise in the flow speed in the active nozzles is prevented by choking the overall flow. The control of the aforementioned control and closing actions can be integrated in a simple manner in the rest of the process automatics, for example by automatically determining the set values of the control and closing devices on basis of other initial values of the process, for example with the aid of a microprocessor, resulting in the simplest possible use of the device.

In practice, the cutting is performed by means of a device which is preferably connected by means of an automatically returnable arm mechanism to the carriage travelling along the traversing beam, by transferring said carriage during the cutting operation on the traversing beam to a desired point in the direction of width of the web, the operating devices 6 and 7 being in association with the nozzle assembly 3 and optionally also those in association with the flow means 5 are set to their set values which depend in the known manner on the process conditions, then the device producing the overall flow, such as a compressor, is activated and the rotating function of the cutter blade 1 is started. After these actions, the device is placed with the help of said arm mechanism in contact with the web for cutting it, during which operation it widens the tail l for threading of the web to a full-width web while it moves in the trans¬ verse direction B. The arm mechanism of the device in accordance with the invention can be simple, for example a mechanism having two positions, because the controllable nozzle flows help to achieve a reduced pressure and a distance between the carrier surface 2 and the web that are suitable for the conditions. After the cutting operation, the overall flow and the rotation of the blade is stopped, whereafter the locking of the position of the arm mechanism, which function is most preferably automated, will be released and the arm will automatically return to its rest position.

The invention is not restricted only to the embodiment shown hereinabove, but it can be modified within the scope of the inventional idea disclosed in the claims. Hence, the nozzle assembly can be, for instance, con- stituted of one or several nozzle means known as such which each are provided with independently controllable and closable flows through their respective flow means. Of course, as disclosed hereinabove, the invention is applicable in conjunction with a rotating cutting blade as well as a stationary one.

Claims

Claims;

1. Method for stabilizing the run of a paper web ( ) or the like during diagonal cutting, wherein the tail (Wl) for threading of the web or the like is cut out of the travelling paper web (W) and widened as the cutting member (1) travels in a direction (B) transverse to the web at the free run of the web, for example in a multi-cylinder dryer section, the stabi- lizing being enhanced by a flow of gaseous medium effected by means of a carrier surface (2) involved with a reduced pressure and situated substantially parallelly to the plane of the web (W) , c h a r a c¬ t e r i z e d in that the reduced pressure is created around the cutting member (1) known as such or at least in the area located before the cutting point (C) , seen in the direction of travel of the web, by means of a flow (VA, VB, VC, VD) of a gaseous medium directed substantially away from the carrier surface (2) and the cutting member (1) at least during the cutting operation, said flow being generated by means of a flow (V) brought to the edge of the carrier surface (2) .

2. Method as claimed in Claim 1, c h a r a c t e r¬ i z e d in that the flow (VA, VB, VC, VD) of a gaseous medium directed away from the carrier sur¬ face (2) is blown substantially parallelly to the plane of the adjacent travelling web (W, Wl) from a nozzle assembly (3) situated at the edge of the carrier surface (2) at a suitable speed (va, vb, vc, vd) in such a manner that a reduced pressure stabilizing the run of the web is generated in the space between the carrier surface (2) and the web (W, Wl) travelling at the corresponding location.

3. Method as claimed in Claim 1 or 2, c h a r a c¬ t e r i z e d in that the flow (V) of a gaseous medium is brought into a housing-like construction (11) associated with the carrier surface (2) using flow means (5) , preferably along a common flow channel.

4. Method as claimed in Claim 3, c h a r a c t e r¬ i z e d in that the amount of the overall flow (V) entering the nozzle assembly (3) is adjusted and/or closed by means of an operating device (7) situated in the flow means (5) .

5. Method as claimed in any of the preceding Claims, c h a r a c t e r i z e d in that the division of the overall flow (V) into partial flows (VA, VB, VC, VD) is adjusted by means of a guiding means (4) situated before the nozzle assembly (3) .

6. Method as claimed in any of the preceding Claims, c h a r a c t e r i z e d in that the partial flows (VA, VB, VC, VD) blown through the nozzle means (3) located at separate edges of the carrier surface (2) are closed and/or their speeds (va, vb, vc, vd) are adjusted separately by means of controll¬ able operating means (6) .

7. Apparatus for stabilizing the run of a paper web (W) or the like during diagonal cutting, wherein the tail (Wl) for threading of the web is cut out of the travelling paper web (W) and widened as the cutting member (1) incorporated in the apparatus travels in a direction (B) transverse to the web, the apparatus being provided for effecting a flow of a gaseous medium stabilizing the web by means of a stabilizing carrier surface (2) involved with a reduced pressure and being associated with the cutting member, c h a r a c t e r i z e d in that at the edge of the carrier surface (2) there is a nozzle assembly (3) for effecting a flow (VA, VB, VC, VD) of gaseous medium, such as air, directed away from the carrier surface (2) and the cutting member (1) with the aid of a flow (V) brought to the edge of the carrier surface (2) with the aid of flow means (5) .

8. Apparatus as claimed in Claim 7, c h a r a c t e r- i z e d in that it comprises a closed housing-like construction (11) associated with the carrier sur¬ face (2) and connected to flow means (5) for introduc¬ ing the flow (V) thereto.

9. Apparatus as claimed in Claim 8, c h a r a c t e r- i z e d in that the nozzle assembly (3) is situated in one of the edges or in several edges of the housing¬ like construction (11) .

10. Apparatus as claimed in one of the preceding Claims 7 to 9, c h a r a c t e r i z e d in that said nozzle assembly (3) comprises a nozzle means known as such which is preferably a uniform slit nozzle, that is, a so-called foil nozzle, or which consists of a row of holes.

11. Apparatus as claimed in Claim 7 or 8, c h a r a c t e r i z e d in that said flow means (5) that is connected to a device producing the gaseous medium, such as to a compressor, comprises an adjusting and closing valve (7) .

12. Apparatus as claimed in Claim 8 or 9, c h a r a c t e r i z e d in that in the housing¬ like construction (11) are provided, preferably for instance by shaping the back-part (2') of the carrier surface (2), guiding means (4) for dividing the overall flow (V) into partial flows, and/or the construction is provided with adjusting and closing devices (6) for adjusting and closing the partial flows (VA, VB, VC, VD) emerging through the nozzle assemblies.