FI65461C - FOER FAR INSPECTION AND PAPER MACHINERY FOR STABILIZATION OF PAPER MACHINES - Google Patents

Description

65461

A method and apparatus in a drying section of a paper machine for stabilizing the flow of a paper web

The invention relates to a method for stabilizing the flow of a paper web in a drying section of a paper machine, in which method the paper web is conveyed from one row of drying cylinders to another by supporting the method uses blowing devices to stabilize the flow of the web by a common run or runs between the drying cylinder rows of the web and the drying wire.

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The invention further relates to a device applying the method according to the invention, comprising a support structure in connection with which nozzle boxes, through which air is blown into the common run of the drying wire and the web between the rows of drying cylinders.

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Web breaks in the drying section of high-speed paper machines are an essential factor limiting the speed of the machines. It is an object of the present invention to provide a device which can significantly reduce web breaks due to web flutter and the disadvantages caused by them.

The invention is intended for the so-called for use in connection with a single felt assembly, wherein one or more rolls or cylinders of the drying cylinder group are inside the wire loop implementing the single felt assembly and the other (s) outside. However, if in the following description of tissues the term wire is used, this means all kinds of suitable tissues, such as blankets and various reticulated e.g.

Single felt export per se is a known technique. For example, U.S. Pat. No. 30 796.601 defines a felt flow chart for a single felt. However, it is known that the single felt export method was introduced into commercial use 2 65461 only about 70 years after its invention. The applications of single felt exports have been mainly high-speed machines.

It is known that a thin layer of air follows all moving surfaces.

5 There is no sliding between the air and the moving surface, but the air particles that touch the moving surface travel at the same speed as the surface.

The gap defined by the fabric (felt or wire) and the cylinder surface (cylinder or roll) 10 is called the inlet nip when the fabric enters this shaft and the exit nip when the fabric exits the shaft.

If all the boundary surfaces of the nip are impermeable to air, an air flow opposite to the boundary layers is created between the boundary layers in both the inlet and outlet nips. In this case, there is an overpressure over the tissue in the inlet nipple due to the damming of the boundary layer flows and a negative pressure over the tissue in the outlet nip due to the suction of the boundary layer flows.

When previously known air-permeable fabrics, i.e. wires, are used, the pressure differences across the wire caused by the boundary layer flows cause air flows through the wire.

The first and second drying groups of the paper machine are known to be usually equipped with a so-called with a single tissue export, often implemented with the upper cylinders having a paper web between the fabric and the cylinder and the lower cylinder having the fabric on top of the fabric.

Numerous problems have been encountered in single tissue export due to pressure differences across the tissue caused by boundary layer flows. The air 30 tends to flow from the higher pressure through the smaller wire and thus break the support contact between the fabric and the paper web. The problem areas are the exit nip and the input nip. At both points, the pressure difference across the wire tends to detach the paper web from the wire. Once detachment has occurred, the paper web begins to behave unstably due to air currents in the pockets 35. The detached web often stretches on the lower cylinders due to centrifugal force. The result is bad squats at the entry nip and, in the worst case, a track break.

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To solve the above problems, various sealing structures have been developed to prevent the entry of boundary layer flows following moving surfaces into the nip. For example, patent application DE-OS 2 712 184 discloses a sealing structure for this purpose.

The fluttering of the paper web in the area of the single-wire export is due to the said boundary layer flows and adhesion forces. As stated, the shafts or nips 10 defined by the fabric / web and the cylinder surface create an overpressure or underpressure due to the boundary layer flows, which tends to detach the web from the fabric. In addition, the paper web tends to follow a denser and smoother surface, i.e. the cylinder, under the influence of the adhesion forces, which also tends to contribute to detaching the web from the fabric.

15 It has been found that in the upper nip the web flutter occurs most at the edges while in the lower nip the web flutteres over its entire width. This is because air tends to flow from the sides of the machine to the upper nip where there is a vacuum. If the web is slightly detached from the tissue, the edge of the web will begin to flutter due to transverse airflow. In the lower nip, on the other hand, there is an overpressure and air flows out of the nip to the sides of the machine and through the fabric, whereby the web tends to rise out of the fabric.

As a general observation, web flutter generally begins at its edge areas and such edge flutter can, however, spread over the entire width of the web even so that the web is completely detached from the drying wire and breaks or at least causes a crease in the web.

Applicant's FI patent application 803891 discloses a method and device by which the disadvantages caused by boundary layer flows can be reduced.

30 However, it has been shown that the device described in the above application is not capable of preventing the fluttering of the edges in the upper nip, in particular when the old paper machine has been converted to a single-wire export during modernization. In older machines, the free strokes between the cylinders are very long and they are particularly prone to 35 fluttering.

65461

The object of the present invention is to provide a method and a device which prevents the edges of the web, in particular the upper nip, from fluttering in a paper machine equipped with a single-wire outlet. It is a further object to provide a method and apparatus which facilitates the passage of the end of the paper web 5 through the drying section.

In order to achieve the above and later objects, the method according to the invention is mainly characterized in that air jets are blown against the drying wire and the direction of travel on until.

The device according to the invention, on the other hand, is mainly characterized in that said device comprises nozzle boxes arranged on a support structure, close to both edge regions of the web, having a plurality of nozzle slots on the drying side of the web, the nozzle openings being oriented towards or against the drying wire. the curvature of the part of the bearing surface adjoining the nozzle slots being such that the direction of the jet is opposite to the direction of travel of the drying wire.

With the device according to the invention, its support beam or other similar support member can be set to an optimal position by turning the axes of rotation of the drying cylinders about an axis parallel to it so that the flutter of the web edge areas and the resulting disadvantages can be minimized.

In the following, the invention will be described in detail with reference to the figures of the accompanying drawing, to which the invention is not limited.

Figure 1 shows a part of a drying machine of a paper machine provided with a single wire outlet, which is known per se, in which overpressures or underpressures are created on the nips which release the web from the wire.

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Figures 2A and 2B illustrate the detachment of the web from the wire due to the vacuum and adhesion forces generated in the upper nip.

Figure 3 shows a device according to the invention.

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Figure A shows a section IV-IV of Figure 3 on a larger scale.

In the single-wire outlet according to Fig. 1, the paper web W is on the upper cylinders 10 of the drying section under the wire 12 and on the lower cylinders 11 on the wire 12 10. Due to the boundary layer flows, an overpressure K is created in the upper nip and an overpressure K + in the lower nip. The adverse effects of the overpressure generated in the lower nip K + can be well eliminated by the method and device presented in the above-mentioned FI application 803891. On the other hand, the fluttering of the edge V of the paper web W in the upper nip K, illustrated by Figures 15A and 2B, is not controllable by the method and apparatus presented in the above application, especially with old machines modernized and converted to single wire export.

As shown in Figures 3 and A, the device 20 according to the invention comprises a tubular beam 22 arranged on the side of the drying wire 12 parallel to the axes of rotation of the cylinders 10 and 11 near the conveying wire 12 and the web running between the drying cylinders 10 and 11. The beam 22 is supported at its ends on brackets (not shown) for pivoting about an axis A-A for later reference.

Connected to both ends of the beam 22 are pipes 21a and 21b through which blowing air is supplied to the device 20. The supply of blowing air is indicated by arrows F1 n · In the region of both ends of the beam 22 inside the ends 10 'of the cylinder 10 there are nozzle housings 23a and 23b attached to the beam. These nozzle housings 23a and 23b abut the closed outer side 2A and the closed ends and the inner side 25 with a plurality of parallel nozzle slots 26. The inner surface with the nozzle slots 26 forms the bearing surface 25 of the device according to the invention Nozzle boxes 23a and 23b .

According to the method of the invention, air jets are blown from the nozzle slots 26 against the direction of travel of the web W and the conveying wire 12. The ejection effect of the air jets F 1 discharged from the nozzles 26 compensates at this point on the opposite side of the web W for the negative pressure prevailing in the shaft K and its detrimental effects. Said ejection effect is illustrated by the arrows F2 · As a result, the web W and its edges W 'remain reliably attached to the conveying stream 12 and 5 the crease shown in Fig. 2A does not form.

The blowing method shown in Figs. 3 and 4 is able to eliminate fluttering of the edge W 'of the web W even when the conditions are favorable for fluttering, such as with old machines in which the free strokes between the blades 10 and 11 of the drying cylinder-10 are long.

It is essential for the operation of the method according to the invention that the blow extends all the way to the contact line B of the web W and the upper cylinder 10.

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The best direction of the air jets discharging from the nozzle openings 26 depends on e.g. machine speed and many other local factors.

Therefore, the angle α between the bearing surface 25 of the blowing members and the wire 12 at is arranged to be changed even during the run, and thus the best direction of the jets F1 can be found for each driving speed and driving conditions.

An important advantage of the invention is that the method and device according to the invention do not cause the edges of the web W to dry out, since the blowing air jets F 1 discharged from the nozzles 26 do not meet the paper web W itself.

If necessary, the method according to the invention is also intended to facilitate the threading of the web, because the edge strip remains attached to the wire 12 due to the method 30. The method can also be used only for heading, whereby the required blowing air can be taken from the compressed air network via reduction valves. Once the web W has been turned on to full width, the blowing is turned off. The use of compressed air as pu-hold air simplifies equipment.

As stated above, the above-mentioned angle α can also be adjusted during the run and thus find the optimal angle α for fluttering and minimizing web breaks. In general, the most preferred angle α is in the range of 5 ° to 15 °.

As shown in Fig. 4, at the front edge of the bearing surface 25 there is a certain small clearance 5 independent of the turning angle α to the transport wire 12. At the clearance Δ, the amount of the clearance Δ is preferably between 10 and 25 mm.

The width L of the nozzle openings is preferably in the range 300-600 mm. One nozzle box has nozzle slots 26, e.g. 2 ... 10 pieces, preferably about 3 ... 6 pieces.

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As shown in Fig. 4, the bearing surface 25 of the blowing device extends substantially half the length of the common run of the drying wire 12 and the web W. In practice, the length of the bearing surface 25 of the nozzle boxes 23a, 23b is generally between 30 and 60% of said free space between the webs 12 and 15 of the drying wire. The nozzle slots 26 are oriented so that the blowing direction of the jets is opposite to the direction of travel of the drying wire. The orientation of the jets can also be realized by using foil nozzles, whereby the curved part of the bearing surface adjoining the nozzle openings causes the jet to turn opposite to the direction of travel of the drying wire 20. The geometry and properties of the foil nozzles are explained in the applicant's FI patent application No. 781375. Em. the patent application discloses a nozzle for applying a vacuum gas flow to be dried or supported to a web or the like. Said nozzle comprises a nozzle housing, the second side of which has a nozzle slot bounded on the one hand by a flow front plate and on the other hand by a wall which continues as a curved flow guide surface and further as a part forming a bearing surface. Said nozzle slot is located in the direction of gas flow before the plane of the inlet edge of the curved guide surface. The ratio of the width of the nozzle gap to the radius of curvature of the guide surface 30 in question has been chosen at the gas flow rates present so that the gas flow separates from the curved guide surface substantially before its trailing edge.

The devices according to the invention are arranged in connection with said wedge spaces 35 in a row of upper cylinders of the drying section for all upper cylinders 10, at least at the beginning of the drying section, where the web is weaker. If necessary, the devices 20 according to the invention can be placed in connection with all 8 65461 vacuum wedge spaces in which the web is on the K side of said wedge space.

The devices according to the invention can well be used with the devices disclosed in the applicant's FI-5 patent application No. 803891.

The following are claims within the scope of which the various details of the invention may vary within the scope of the inventive idea.

Claims (12)

A method for stabilizing the flow of a paper web in a drying section of a paper machine, wherein the paper web (W) is conveyed from one row of drying cylinders (10, 11) to another by supporting a drying wire (12) or a similar fabric so that the second drying cylinder row 5 has a drying wire and a cylinder surface. the web passes on the outer surface of the drying wire, and the method uses blowing devices to stabilize the passage of the web by common runs between the drying cylinder rows of the web and the drying wire (12), characterized in that in the regions of both edges (W) on the side of the wire (12), air jets (F 1) are blown against the direction of travel of the drying wire and the web, and said air jets (F 2) are applied to the drying wire (12) by a wedge 15 (K 1) between the drying cylinder (10) ) at least the baseline of said wedge (K-) (B). A method according to claim 1, characterized in that said air jets (Fp), which are blown from several successive nozzle slots, eject (F1) and at this point compensate for the negative pressure in the wedge space (K-) on the opposite side of the web (W). ) and its edges (V) on the transport wire (12). A method according to claim 1 or 2, characterized in that the blowing range provided by said air jets (Fp) extends to about 30 to 60% of the length of the free flow between the drying drying rows (10, 11) of the drying wire (12) and the web (W). Method according to any one of claims 1 to 3, characterized in that said air jets (F 1) are provided and applied to the drying wire (12) by foil nozzles whose nozzle gap is located in the gas flow direction before the inlet edge plane of said curved guide surface. the ratio of the radius of curvature of the guide surface 35 at the gas flow rates present is selected so that the gas flow detaches from the curved guide surface substantially before its trailing edge. Method according to one of Claims 1 to 4, characterized in that said air jets are blown from a plurality of successive nozzle slots (26) and that the angle (c0) between the nozzle support surface (25) and the drying wire (12) is preferably adjusted during driving. to minimize flutter of the web (W) and that said adjustment is performed by rotating the blower around an axis (AA) near the plane of the drying wire (12), which axis is parallel to the axes of rotation of the drying cylinders (10, 11). Apparatus for carrying out the method according to any one of claims 1 to 5, comprising a support structure (22) with nozzle boxes (23a, 23b) through which the drying wire (12) and the web (W) are connected between the drying cylinders (10, 11). ) is subjected to air blowing, characterized in that said device comprises nozzle boxes (23a, 23b) 20 arranged on both support regions of the web (W) and supported on the support structure (22), with a plurality of nozzle boxes (25) on the drying wire side (25). nozzle slots (26) having an orientation toward the drying wire (12) opposite to its direction of travel, or curvature of a portion of the bearing surface (25) adjacent to the nozzle slots (26) such that the jet orientation is opposite to the direction of travel of the drying wire (12). Device according to claim 6, characterized in that said support structure (22) is an elongate beam (22) extending along the entire width of the web (W) parallel to the axes of rotation of the drying cylinders (10, 11) and supported at both ends for pivoting the drying cylinders (10). 11) about an axis parallel to the axes of rotation (AA), and that said beam (22) is directed by nozzle boxes (23a, 23b) near the edges (W) of the web (W) with a closed outer surface and ends and a bearing surface with nozzle openings (26) 35 ( 25) on the side of the transport wire (12). Device according to Claim 6 or 7, characterized in that the leading edge of the bearing surface (25) with a plurality of successive nozzle slots (26) has a small clearance (Δ) substantially independent of the turning angle (α) of the bearing surface. Device according to any one of claims 6 to 8, characterized in that both ends of said elongate beam (22) are connected to supply air inlet pipes (21a) which communicate with the interior of the nozzle boxes (23a, 23b). 9 65461 Device according to any one of claims 6 to 9, characterized in that said bearing surface (25) has a plurality of substantially evenly spaced parallel nozzle slots (26), the longitudinal direction of which is parallel to the axis of rotation of the transport cylinders. 15 Device according to one of Claims 6 to 10, characterized in that said devices are arranged at all vacuum wedge spaces (K-) in which the paper web (W) runs on the wedge space side at least at the beginning of the drying section. 12 65461