FI75892C - ANORDNING I TORKPARTIET ELLER I OMRAODET MELLAN PRESS- OCH TORKPARTIET HOS EN PAPPERSMASKIN. - Google Patents

Description

75892 1 Device in the drying section of a paper machine or between the press and sowing section Anordnlng 1 torkpartiet eller 1 omrldet Melian press- och torkpartiet hos en pappersmaskin 5

The invention relates to a device for use in the drying section of a paper machine to prevent phenomena which interfere with the mutual support contact between the web and the fabric, such as squeegee, in particular overpressure and underpressure in the nips defined by the wire and the cylinder. a blow box connected to the blow-producing and suction-producing means, which suction box is provided with at least two nozzle slots 15a or the like transverse to the direction of travel of the web and a bearing surface therebetween.

The invention further relates to a device for use between the spray section of the paper machine and the sift section to improve mutual support contact between the web and the squeegee when guiding the web for the press section 20 to the drying section in support of the drying wire, the apparatus comprising a suction blower and each suction-blowing box is provided with at least two nozzles or the like transverse to the direction of travel of the web and a bearing surface therebetween.

Paper machine speeds have increased steadily in recent years and are now approaching the 1500 m / min limit. In this case, the fluttering and detachment of the web from the backing fabric poses a serious problem for the runnability of the paper machine.

The present invention is particularly applicable to the so-called in the case of a single-wire export, which in this application means a method of exporting a web over heated drum cylinders in which the web passes from one blade row to the other supported by the blasting wool so that against the surface and that the traction between the rows of cylinders passes 2 75892 1 supported by the drying wire. The advantage of this single fabric export is that the web is supported by the drying wire at all times and has no or at least not substantially long free stretches, thus reducing the flutter of the web and the risk of wrinkles and breaks.

5

In addition, the present invention is applied in the area between the press and the wear section, where the web is known to be very weak and prone to breakage. Maintaining mutual support contact between the web and the wire is necessary when passing the web in the support of the drying wire from the pulp section to the drying section.

In the wear parts of paper machines, the gap delimited by the fabric such as the drying wire and the cylinder (cylinder or roll) is called the input pixel when the fabric enters this shaft and the exit nipix when the fabric exits the shaft.

If the limiting surfaces of the lime nip are impermeable to air, an airflow opposite to the boundary layers will be created 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 20 and a negative pressure over the tissue due to the suction of the boundary layer flows. When it is known to use air-permeable fabrics such as wires, the pressure differences across the fabric caused by the boundary layer flows generally cause harmful airflows through the fabric.

25

Many of the previously known pocket ventilation devices for paper machines are based on the pumping effect of open drying cloths. As is known, the first and second drying groups of a paper machine are usually provided with said single-spindle connection, which is often implemented in such a way that the upper-30 cylinders have a paper web between the wire and the cylinder and the lower cylinders on the wire.

There have been a number of problems and drawbacks in the application of single wire export in practice due to pressure differences 35 across the wire caused by boundary layer flows. The air tends to flow from higher to lower pressure through the wire and thus to disengage the support contact between the wire and the paper web. The problematic points are said outlets and inlet nips, where at each point 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 adjacent to the holidays of the drying cylinders. The Irron-5 nut web often stretches on the lower cylinders under the influence of centrifugal force, resulting in wrinkles at the inlet nip and, in the worst case, a line break that causes downtime on the entire paper machine.

To solve the above problems, the prior art includes 10 different sealing structures designed to prevent moving surfaces following the boundary layer air currents from reaching the nip. For example, patent application DE-OS 2 712 184 discloses a sealing structure for this purpose. A limitation of the mechanical seals according to DE-OS 2 712 184 is that they cannot be brought close enough to the moving web or fabric due to the risk of damage to the web and wear of the wire 15. For example, sealing the outlet nip by mechanical means is impossible, as the moving paper web requires a distance of at least 10 mm from the sealing member. In the inlet nipple, it is theoretically possible to place the seal closer to the tissue, but the problem area then shifts to the front side of the seal, where an overpressure caused by the boundary layer flow dam collar then forms.

Prior art solutions also have the disadvantage that the efficiency of mechanical seals decreases over time if the seals 25 are placed so close to the surfaces that wear occurs.

Applicant's F1 patent application No. 803891 discloses a method and apparatus for preventing the formation of overpressures and underpressures which interfere with the support contact of the fabric and the web. The device according to FI application No. 803891 is generally placed close to the line of the cylinder and the wire. The effect of the device on improving the support contact of the wire and the web extends to approx.

200 to 300 mm from the joint line of the wire and the web, which is usually sufficient for modern paper machines in the drying group itself.

35 However, there may be points between the drying groups where the distances between the rollers or cylinders are so long that the 200 to 300 mm support-improving area mentioned above 4 75892 1 is not sufficient, but web detachment and flutter occur.

In the single-wire connection, the support contact between the web and the wire is disturbed not only by the overpressures induced in said nips, the effect of which is quite short, but also by the instability and fluttering of the web-wire assembly between the drying cylinder rows.

The device disclosed in the applicant's FI patent application No. 840856 is intended for the intervals between drying groups, the effect of which improving the mutual support contact between the web and the wire extends a considerably long distance in the direction of web travel from the wire and cylinder junction.

15 When passing a paper web from the press to the drying section, the problem is that the web has to be stretched strongly to control flutter, which leads to a deterioration in quality and causes inconvenience at the end of the machine, for example when coating paper.

Applicant's Finnish patent application No. 830422 discloses a method and a device which allows the web to be passed from the press to the drying section with considerably less stretching than before and without the occurrence of harmful flutter.

However, it has been found that a heavy web together with a poorly air permeable wire requires, under unfavorable conditions, such a negative pressure on the bearing surface of the blower to maintain support contact between the web and the wire that it is not possible to achieve it with reasonable blowing air volumes.

The object of the present invention is to provide a device by means of which the support contact between the web and the wire is maintained even under unfavorable conditions (e.g. heavy web and poorly permeable wire and long supported distance) and which effect can be extended to the desired distance between the wire and the wire. from the junction of the cylinder or roll. In addition, it is an object to provide a device which is not subject to wear and does not cause damage to the moving wire.

In order to achieve the above and later objects, the device according to the invention is essentially characterized in that said nozzle slots are oriented in such a way that the air jets discharged therefrom suck by their ejection by air from said space between the carrier and the wire. between said nozzle openings or the like, and that the distance of the substantially planar carrier surface from the wire at is several times, preferably at least about five times, the width of said nozzle gap.

The invention will now be described in detail with reference to some embodiments of the invention shown in the figures of the accompanying drawing, to which the invention is not limited.

Figures 1A and 1B illustrate the formation of overpressures and underpressures in the gap bounded by the cylinder surface and the air-impermeable wire.

20

Figures 2A and 2B illustrate the air flows through the wire caused by overpressures and underpressures in the case that the wire is permeable to air.

Fig. 3 shows a device according to the invention cut in the direction of travel of the web and placed in a running part in which a single wire export is used.

Figure 4 shows a device according to the invention cut in the direction of travel of the web and placed in the area between the press and the wear part.

30

Figures 5 and 6 show two alternative sections V-V in Figure 3.

When, according to Fig. 1A, the air-permeable wire F 'enters the drying cylinder 10, an overpressure N + is created in the converging shaft of the cylinder 10 and said wire F' bounded by the boundary layer flows T + and K +. Accordingly, according to Fig. 1B, when the air-impermeable wire F 'leaves and separates from the cylinder 10, a negative pressure N- is created in the shaft.

6 75892 1 Figs. 2A and 2B illustrate a situation in which an air-permeable wire F is used. In this case, the mechanism of formation of the overpressure and underpressure gap, i.e. the nip, is similar to Figs. 1A and 1B. The overpressure in the nip N + of Fig. 2A and the negative pressure in the nip N of Fig. 2B tend to discharge substantially through the wire F as flows F1 and resp. F2.

Figure 3 shows a device 20 according to the invention placed in a gap N + delimited by a cylinder 10 and a wire F. The device 20 is formed by a blower suction 21 with at least two nozzle slots 22 and 23 transverse to the direction of travel of the web W and extending over the entire width of the web W, and between them suction openings 24. The air jet E3 discharged from the first nozzle 22 is directed in the direction of travel of the stationary wire F or in the opposite direction to the direction of travel, and the air jet E4 discharged from the second nozzle slot 23 is directed in the circumferential direction of the cylinder 15. Between the nozzles 22 and 23 is a carrier plane 25 which is planar or nearly planar and substantially parallel to the aligned wire F.

According to the invention, the suction openings 24 are also located in the area between the nozzles 22 and 23 20. The distance Tq of the carrier plate 25 from the wire F is considerably greater than the distances of the device 20 and T0 from the wire F or the cylinder 10 at the jets E3 and E4. This ensures that the flow cross-sections of the vacuum space P in connection with the carrier 25 are large enough, so that the flow resistances 25 remain sufficiently small. The length of the carrier surface 25 in the direction of travel of the web W (dimension L) can be freely chosen according to how far the support contact between the web W and the wire F is desired or necessary to improve.

In order to achieve the objects of the invention, it is essential that the distance Tq of the planar or nearly planar carrier 25 from the wire F is several times the width s marked in the figures of said second or both nozzle slots. In most practical applications the distance Tq is at least five times the width s of said nozzle slot 22 or 23. 35 Usually To - nxs, where n is preferably 6-10.

7 75892 1 The width s of the nozzle gap of the blow nozzles 22 and 23 is generally in the range 1 ... 10 mm, preferably approx. 2 ... 5 mm. The size of the suction openings 24 is selected so that the common area of the suction openings 24 is approximately the same as the common area of the blow nozzle slots 22 and 23. The bearing surface length 5 L is usually in the range L * 300 ... 1000 mm.

The air jets E3 and E4 discharged from the nozzle slots 22 and 23 by their ejection effect absorb air from the space between the bearing surface 25 and the wire F, where a vacuum is thus formed. Suction through the suction openings 24 substantially increases this vacuum. When the suction through the openings 24 is active, the main purpose of the air jets E3 and E4 discharging from the nozzle slots 22 and 23 is to prevent leakage air from entering the vacuum state P. Since the wire F is at least somewhat permeable to the air, but the web W is substantially impermeable to the wire. adheres even more firmly, which is advantageous for the stable passage of the web W.

The effect of improving the mutual support contact between the web W and the wire F or other support fabric provided by the device 20 according to the invention extends from the nozzle 22 all the way to the contact wool of the cylinder 10 and the wire F.

Referring to Figures 5 and 6, it is noted that the leakage flow L1 from both opposite edges of the wire F into the vacuum space P between the bearing surface 25 and the wire F tends to reduce the preferably effective vacuum provided by the device 20 according to the invention. Therefore, the leakage flow LI must be kept as small as possible and in any case reasonable. Figures 5 and 6 show in this respect two embodiments of the device 20 according to the invention, by means of which the leakage flow 30 L1 from both edges of the wire F can be substantially reduced or prevented. The vacuum space P of Figure 5 is closed by edge plates 26 which are of suitable plastic which does not damage the wire F, even if contact occurs from time to time. In the embodiment shown in Fig. 6, the leakage flows L1 from the edges of the wire F are blocked by the opposite ejection block E5 coming from the edge nozzle 27.

8 75892 1 According to Fig. 6, the free distance D at the edge nozzles 27 at the edges of the wire F is the same as at the jet E3, i.e. n.

10 ... 20 mm, preferably about 15 mm, so that the wire does not come into contact with the edge nozzles 27.

5

In both the embodiment of Fig. 5 and Fig. 6, the tapered shaft (N +) formed by the cylinder 10 and the wire F is closed at both edges of the wire F by wedge-shaped plates 28 attached to the blow plate 21 shaped to form the shaft N + and shown in Fig. 3.

The output directions of the jets E3 and E4 are chosen so that the curved guide planes 22 'and 23' in connection with the nozzle slots 22 and 23, which operate in the so-called as coanda surfaces, is adapted to guide the jets E3 and E4 15 so that the angle of intersection of the jets with the plane of the wire F and the tangent plane of the cylinder 10 is formed to fit.

Connected to the nozzle box 21 of the device 20 are means known per se, by means of which air is pressurized from the pressure chambers 21A and 21B of the nozzle box 21 while air is sucked from the air chamber 21c of the nozzle box 21. In this case, it is preferred that the nozzle 21 of the suction chamber or chambers 21c is connected to the suction side of the fan 29 of the duct 29i and the pressure chambers 21A and 21B of the same fan palnepuolen passage 29p, the device circulates the same air continually. Depending on the application, air may have to be introduced into the circuit to compensate for leaks or additional heat due to heat loss. In this case, the necessary accessories are not known per se.

Figure 4 shows a device 30 according to the invention placed in the area between the press and the drying part. The web W is detached from the smooth roll 11 of the press part, e.g. from the stone roll, by means of a pick-up roll 12 and a drying wire F passing over it. The web W is fed from the press to the cylinder 10 of the drying section under the support of the device 30 and the wire F. The device 30 is formed by a blow suction box 31 The suction box 31 has blown jugs 31A and 31B at the ends and suction chambers 31C between them. The blow boxes 31A and 31B and the suction blades 31C may be connected to the suction side and the bellows side of the fan 29 as shown in Fig. 3 or by another similar arrangement. The air jet E6 discharged from the first nozzle slot 32 is directed in the circumferential direction of the pick-up roll 12 and the air jet E7 discharged from the second nozzle slot 33 is directed in the direction of travel of the wire F at. Between the nozzles 32 and 33 is a planar carrier 35 which is substantially parallel to the aligned wire F. According to the invention, the suction openings 34 are also located in the area between the nozzles 32 and 33. The distance of the bearing surface 35 from the wire F (dimension T) is considerably greater than the distance of the device from the pick-up roller 12 (dimension Ί ^) and the wire F (dimension T £) at the jets E6 and E7. This ensures that the cross-sections of the pressurized space P in connection with the bearing surface 35 are large enough, so that the flow resistances 15 remain small. The length of the bearing surface 35 in the direction of travel of the web W (dimension L) can be freely selected. If necessary, the device can extend from the pick-up roller 12 all the way to the first drying cylinder 10.

The size of the blow nozzles 32 and 33 and the air openings 34 correspond to the values of the device 20 according to Fig. 3 given above. The operating principle of the device according to Fig. 4 is also exactly the same as that of the device shown in Fig. 3.

As for the ratio Tq to the ratio s of the width s of the nozzle openings 32 and / or 33, the same applies as described above in connection with Figure 3.

Although the nozzle slot 22,23,32,33 has been discussed above, it will be appreciated that in some cases the uniform nozzle slots of the blowing air may be replaced by nozzle sets or other nozzle arrangements and the corresponding suction openings 24,34 may be replaced by uniform slots. When nozzle rel set or the like is used, the width of the nozzle gap means the width of a uniform nozzle gap having an area corresponding to the set of holes.

35 As an example of the efficiency of the suction-blow hob according to our invention, the following measurement result obtained from a paper machine can be mentioned.

10 75 89 2

The vacuum prevailing in the space between the carrying surface of the box and the wire was measured without suction and with suction in operation. In both cases, the blow nozzles were operational.

- vacuum -70 Pa without suction - vacuum -160 Pa with suction in operation.

The following claims set forth within the scope of the inventive idea, the various details of the invention may vary and differ from those set forth above by way of example only.

Claims (10)

75892 11 A device for use in the drying section of a paper machine to prevent phenomena which interfere with the 5 supporting contacts between the web (W) and the fabric such as the drying web (F), in particular overpressures and underpressures in the shafts (N +, N) delimited by the wire (F) and the cylinder (10). -) and which device (20) comprises a suction-blowing box (21) extending substantially over the entire width of the web (W), which is connected to the blowing air-generating and suction-generating means and which s-blowing-box 10 (21) is provided with at least two with a nozzle gap (22, 23) or the like and a bearing surface (25) transverse to the direction of travel of the web (W), characterized in that said nozzle slots (22, 23) are oriented so that air jets (E 1, E 2 ) absorb with their ejection effect the air from the space between said carrier surface (25) and the wire (F), which is thus evacuated, that the device (20) has suction openings (24) between said nozzle slots (22, 23). ai correspond and that the distance (Tq) of the substantially planar carrier surface (25) from the wire (F) at is several times, suitably at least about five times, the width (s) of said nozzle gap (22 20 and / or 23). 1 Claims 2. Apparatus for use between the spray section and the drying section of a paper machine to improve mutual support contact between the web (W) and the drying wire (F) in guiding the web (W) from the press to the drying portion in support of the drying wire (F), the device (30) substantially comprising W) a full-width vacuum blower box (31) connected to the blowing air generating and suction-generating devices, the suction blower box (31) being provided with at least two nozzle-slots (32,33) parallel to the direction of travel of the web (W), or corresponding to the bearing surface (35) between them, characterized in that said nozzle slots (32, 33) are oriented so that the air jets (E 1, E 2) discharged therefrom absorb with their ejection effect the air between said carrier surface (35) and the wire (F). a space in which a vacuum is thus generated, that the device 35 (30) has suction openings (34) or the like between said nozzle slots (32, 33) and that the distance (Tq) of the angular support surface (35) from the wire (F) at several times, suitably at least about five times, the width (s) of said nozzle gap (32 and / or 33). 12 75892 Device according to claim 1 or 2, characterized in that the device comprises blowing chambers (21A, 21B; 31A, 31B) at both ends thereof and a suction chamber (21C; 31C) or chambers therebetween, said blowing chambers (21C; 21A, 21B; 31A, 31B) 5 are in communication with said transverse nozzle slots (22,23; 32,33) or the like and that said nozzle or chamber (21C; 31C) is bounded by a wall opposite the corresponding wire (F), which contributes to forming said substantially planar carrier surface (25) having said suction openings (24, 34) 10 or the like opening into said suction chamber (21C; 31C). Device according to any one of claims 1 to 3, characterized in that said blowing chambers (21A, 21B; 31A, 31B) are connected to blowing air supplying devices and said air chamber or chambers 15 (21C; 31C) are connected by suction devices. 5. The apparatus of claim 4, characterized in that said blasting chamber (21A, 21B; 31A, 31B) is connected to a fan (29) palnepuolen passage (29b), and that said lmukammio (21C; 31C) of 20 or chambers are connected to the same into the suction duct (29i) of the fan (29) (Fig. 3). Device according to any one of claims 1 to 5, characterized in that said nozzle slots (22, 23; 32, 33) have curved guide surfaces (22 ', 23') which act on them. as coanda surfaces, which surfaces are adapted to guide the air jets (E3, E4) so that the angle of attack of the jets with the plane of the wire (F) and with the tangential plane of the cylinder (10) is formed. Device according to any one of claims 1 to 6, characterized in that the vacuum space formed in connection with said carrier surface (25; 35) is closed by edge plates (26), which are preferably plastic, to prevent leakage flows (L 2) from the edges of the wire (F). to prevent or reduce (Figure 5). 35 Device according to one of Claims 1 to 6, characterized in that the leakage currents (L1) leading from the two edges of the wire (F) to the underfloor space generated in connection with said carrier surface 13 75892 1 (25; 35) are prevented or reduced by ejection air jets (E5), directed outwards from the edge nozzles (27) (Fig. 6). Device according to one of Claims 1 to 8, characterized in that the tapered shaft (N +) formed by said cylinder (10) and the wire (F) is closed at both edges by wedge-shaped plates (21) fixed to the blow box (21). 28) shaped to the shape of the shaft (N +). 10 Device according to one of Claims 1 to 9, characterized in that the flow resistances and the power of the air source of said blowing and suction devices are adapted such that the vacuum 15 in the space between the carrier surface (25; 35) and the wire (F) is of the order - 100 Pa ...- 200 Pa. 20 25 30 35 14 7 5 8 9 2