WO1998027274A1

WO1998027274A1 - Roll for a paper machine, in particular for a paper drying device, and dryer group for a paper machine

Info

Publication number: WO1998027274A1
Application number: PCT/FI1997/000771
Authority: WO
Inventors: Pekka Saarikivi; Raimo Virta
Original assignee: Valmet Corporation
Priority date: 1996-12-16
Filing date: 1997-12-10
Publication date: 1998-06-25
Also published as: AU5223798A; CA2275324C; DE19782184B4; AT409871B; FI965026A0; DE19782184T1; FI105573B; FI965026A; CA2275324A1; ATA914097A; BR9714037A

Abstract

The invention concerns a roll for a paper machine, which roll (10) comprises an axle (11), on whose support the roll (10) is fitted to revolve, and a surface construction (13), which is connected to the axle by means of support pieces (14). The openness of the surface construction (13) of the roll (10) is preferably higher than 20 %, so that, when the roll (10) revolves, an effect is produced that sucks air inwards into the roll (10), whereby a flow of air through the roll (10) arises. Also, the invention concerns a dryer group, which comprises two contact-drying cylinders and at least one reversing roll (10) and in which dryer group single-wire draw is applied. At least one of the reversing rolls (10) in the dryer group is an open roll (10), whose surface construction (13) has an openness, preferably higher than 20 %, so that the flow of air travelling along with the wire passes through the open surface construction (13) into the interior of the roll (10) and is discharged further out along with the wire as an air flow through the open surface construction (13) of the roll (10).

Description

Roll for a paper machine, in particular for a paper drying device, and dryer group for a paper machine

The invention concerns a roll for a paper machine, in particular for a paper drying device, which roll comprises an axle, on whose support the roll is fitted to revolve, and a surface construction, which is connected to the axle by means of support pieces or equivalent.

Further, the invention concerns a dryer group for a paper machine, which group comprises two contact-drying cylinders and at least one reversing roll and in which dryer group single- wire draw is applied, wherein the paper web to be dried is fitted to run on support of a drying wire, meandering from a drying cylinder onto the reversing roll and further onto a drying cylinder, so that on the contact-drying cylinders the paper web remains between the cylinder face and the drying wire and on the reversing cylinder at the side of the outside curve.

As is known from the prior art, in multi-cylinder dryers of paper machines, twin- wire draw and/ or single-wire draw is/are employed. In twin- wire draw the groups of drying cylinders comprise two wires, which press the web one from above and the other one from below against heated cylinder faces. In twin- wire draw, between the rows of drying cylinders, which are usually horizontal rows, the web has free and unsupported draws, which are susceptible of fluttering, which may cause web breaks, in particular in the stages of drying in which the web is still relatively moist and, therefore, of low strength. This is why, in a number of recent years, ever increasing use has been made of said single-wire draw, in which each group of drying cylinders includes just one drying wire, on whose support the web runs through the whole group so that the drying wire presses the web on the drying cylinders against the heated cylinder faces, whereas on the reversing cylinders or rolls between the drying cylinders the web remains at the side of the outside curve. Thus, in single-wire draw, the drying cylinders are placed outside the wire loop, and the reversing cylinders or rolls inside said loop. In what is called normal groups with single- wire draw, the drying cylinders are placed in the upper row, and the reversing cylinders or rolls are placed in the lower row, and similarly, in what is called inverted groups with single- wire draw, the drying cylinders are placed in the lower row and the reversing cylinders or rolls in the upper row.

In the prior-art drying devices the drying wire and the paper web come from a preceding drying element, for example a contact-drying suction cylinder, onto a reversing suction cylinder or equivalent as a joint straight run, in which case a closing wedge space is formed between the drying wire and the face of the last- mentioned suction cylinder, which wedge space is, in the following, also called inlet nip. The moving drying wire and the face of the suction cylinder tend to induce a pressure in said wedge space. This again produces a difference in pressure acting upon the paper web placed on support of the drying wire, which difference in pressure attempts to separate the paper web from the drying wire and causes problems of runnability, wrinkles, and even web breaks. On the other hand, in order to improve the efficiency of dryer sections, there is a need to use ever more compact dryer sections in which the contact-drying cylinders and said suction cylinders are placed as close to one another as possible. All of these factors, together with the increasing web speeds, increase the problems of pressure in said inlet nip.

As is known from the prior art, in single-wire draw, the transfer of the paper web from a reversing suction cylinder onto a contact-drying cylinder usually takes place so that the web is supported on the wire by means of a field of vacuum produced by a blow box or equivalent. The applicant markets blow boxes with the trade mark UNO-RUN-BLOW-BOX™, and with respect to the principle of operation of said boxes reference is made to the applicant's US Patent No. 4,516,330 and to the corresponding FI Patent No. 65, 460. By means of these solutions the paper web can be passed from a drying cylinder onto a reversing suction cylinder at the paper machine running speeds of < 1600 metres per minute currently in use. In the prior-art solutions, attempts have also been made to eliminate the problem related to the pressure peak in the inlet nip by means of suction in rolls, suction in sectors of rolls, and by means of suction boxes of different types as well as by means of combinations of rolls and suction boxes, by whose means it has, however, not been possible to eliminate the pressure peak formed in the inlet nip.

From the prior art it is known that, in order to hold the web in contact with the face of a reversing cylinder or roll, a vacuum is sufficient that overcomes the force arising from the centrifugal force. This required pressure can be calculated by means of the equation

Pv x U² p =

p = pressure N/sq.m

Pv = basis weight of web kg/sq.m

U = circumferential speed metres per second r = radius of cylinder, metres

Depending on the running speed of the machine and on the weight of the web, the requirement of pressure is of an order of 100...200 Pa. Thus, a problem has been the control of the pressure formed in the inlet nip. It has also been possible to reduce the detrimental pressure by means of grooves and bores on the roll. However, by means of these operations, it has not been possible to provide a substantial solution for the problems arising from the pressure in the inlet nip.

With respect to the prior art related to the present invention, reference can be made to the US Patent No. 3,259,961, in which the cell construction in accordance with the solution described in said patent produces a pressure in the inlet nip, because it comprises walls perpendicular to the movement of rotation. Further, reference can be made, for example, to the applicant's patent publications US-4,202,113, US-4,441,263, FI-93,876, and FI-83,680, in which solutions of the type described above are described, but in which, however, no solution is suggested for the problems arising from the pressure in the inlet nip.

The object of the present invention is further development of the prior art described above and of equivalent technology so that the problems caused by said narrow wedge-shaped inlet nip area in the draw of the web can be largely solved.

The most important object of the invention is to improve the rurmability in single- wire draw so that the formation of detrimental pressure in the inlet nip is solved.

It is a further object of the invention to permit a more compact dryer group in a paper machine.

In view of achieving the objectives stated above and those that will come out later, the roll in accordance with the invention for a paper drying device is mainly characterized in that the openness of the surface construction of the roll is higher than 10 %, preferably higher than 20 % , so that, when the roll revolves, an effect is produced that sucks air inwards into the roll, whereby a flow of air through the roll arises.

On the other hand, the dryer group in accordance with the invention is mainly characterized in that at least one of the reversing rolls in the dryer group is an open roll, whose surface construction has an openness higher than 10 %, preferably higher than 20 %, so that the flow of air travelling along with the wire passes through the open surface construction of the roll into the interior of the roll and is discharged further out along with the wire as an air flow through the open surface construction of the roll.

The construction of the roll in accordance with the invention is open, preferably open as slot-shaped, which prevents formation of pressure in the inlet nip. Both the surface construction and the interior construction of the roll are formed substantially open so that the flow of air carried along with the wire enters into the roll interior and revolves there at a speed slower than the speed of rotation of the roll and departs from the roll interior as an air flow from the outlet nip along with the wire. As the roll revolves, the roll construction produces an intensive inflow of air, in which connection the roll operates similarly to a flow-through blower.

The flow into the roll interior takes place mainly by the effect of the outflow of air produced by centrifugal force in the area of the opening nip. A pocket space, which is opened in a suitable way for the air present in the gaps in the open, in particular slot-like surface construction, produces a blow effect outwards, as a result of which air flows correspondingly into the roll interior from the area of the closing nip. In the roll interior, air flows at a velocity clearly slower than the speed of rotation of the roll, because formation of centrifugal force is prevented by the effect of the inside openness of the roll, in which case the air present in the roll interior does not revolve at the same speed as the roll revolves.

According to a preferred exemplifying embodiment of the invention, the open construction is obtained by means of a plate-like surface construction and by means of a shape open in the interior, in which the openness of the surface construction is higher than 10 % , preferably higher than 20 % .

According to the invention, the roll is used preferably in an area of single-wire draw in a paper machine. The diameter of the roll in accordance with the invention is preferably substantially smaller than the diameters of several prior-art reversing roll and cylinder embodiments, in which case the roll can be placed close to the contact- drying cylinders, and, moreover, it permits a compact arrangement of the dryer group, whereby a very compact dryer section is achieved. The roll in accordance with the invention is also suitable for use as a paper guide roll if the formation of an air layer between the roll face and the paper constitutes a problem. According to the invention, in order to prevent formation of pressure in the area of the pocket space, a blow box or equivalent can also be provided in connection with the roll so as to prevent entrance of air into the pocket space. This can be accomplished by means of a box operating by means of the blow principle or by means of inhibition sealing, for example by means of a passive box by means of whose shape the free face of the roll is divided into two parts, i.e. into an out-blowing part and an in-flowing part.

In the following, the method in accordance with the invention will be described in more detail with reference to the figures in the accompanying drawing, the invention being by no means supposed to be confined to the details of said illustrations.

Figure 1 is a schematic illustration of an exemplifying embodiment of the roll in accordance with the invention, in which the roll is provided with suction.

Figure 2 is a schematic illustration of a further exemplifying embodiment of the roll in accordance with the invention.

Figure 3A illustrates an application of operation of a roll in accordance with the invention.

Figure 3B illustrates a second application of operation of a roll in accordance with the invention, in which, in connection with the roll, a blow box is fitted in the pocket space.

Figure 3C shows a further application of operation of a roll in accordance with the invention, in which a passive box is fitted in connection with the roll in the pocket space.

Figure 4A is a schematic illustration of measurement results related to an arrangement in accordance with the invention and illustrating the vacuum on the wire face without a blow box. Figure 4B is a schematic illustration of measurement results related to an arrangement in accordance with the invention and illustrating the vacuum on the inlet face of the wire underneath a blow box.

Figures 5 A...5B illustrate an embodiment of a roll in accordance with the invention.

Figures 6A...6C illustrate further possibilities for a roll of the invention.

Figure 7 is a schematic illustration of an arrangement for use in connection with a roll in accordance with the invention.

Figure 8 is a schematic illustration of an exemplifying embodiment of a roll in accordance with the invention in an application of operation of same.

As is shown in Fig. 1, the roll 10 in accordance with the invention comprises an axle 11 and axle journals 12. In the exemplifying embodiment of the invention shown in Fig. 1 the roll 10 is provided with suction, and the suction openings that have been formed into the roll 10 axle 11 are denoted with the reference numeral 21. The roll axle 11 is hollow, and the mantle of the axle 11 is denoted with the reference numeral 20, and the suction space in the interior of the axle with the reference numeral 19. Through the end 19A, the suction space 19 of the roll 10 axle 11 communicates with a source of vacuum. According to the invention, the surface construction of the roll has been formed open by composing the mantle part 13 of the roll of plate-like circular annular plates 18, which are placed at a distance from one another, which are open in the middle, and which are interconnected by means of fastening bars 15A,16A,17A passing through the ends of the arms 15, 16, 17 arranged on the support piece 14. Thus, the roll construction 10 is very open, since a space remains between each annular plate 18, in a similar way as an open area 27 remains between the outer circumference of the support pieces 14 and the inner circumference of the annular plates 18. The support pieces 14, by whose means the annular plates 18 are interconnected, are fixed to the axle 11. The volume of the open area 27 is 20...80 %, preferably 40...70 % , of the roll 10 volume. The support pieces 14 are placed at each end of the axle 11 and as appropriately spaced along the length of the roll so that the support bars 15A, 16A,17A attached to the arm parts 15,16,17 of the support pieces 14 extend through all the annular pieces 18, whereby the annular pieces 18 form a roll 10 which has an open surface construction and an open inner construction, and which roll is provided with an axle 11 mainly because of factors of fastening and strength.

The exemplifying embodiment shown in Fig. 2 is similar to that shown in Fig. 1, and the same reference numerals refer to corresponding parts. In this exemplifying embodiment of the invention the roll 10 is, however, not provided with suction, in which case the axle 11 is solid, and Fig. 2 also shows the axle journals 12 at each end of the axle 11.

The diameter D of the roll 10 is 500...1500 mm, preferably 600...1000 mm, and the proportion of the open interior area DS is 20...80 , preferably 40...70 %, of the diameter D of the roll. The openness of the surface construction of the roll 10 is higher than 10 %, preferably higher than 20 %.

Fig. 3 A shows a roll in accordance with the invention in an application of operation in accordance with the invention as a reversing roll in a dryer group with single-wire draw. The paper web W to be dried comes from the drying cylinder 30, whose sense of rotation is indicated by the arrow S, on support of the wire 35 onto the reversing roll 10, and the web is placed at the side of the outside curve and the wire 35 is placed against the reversing roll 10. From the reversing roll 10 the wire 35 and the paper web to be dried are passed onto the next drying cylinder 31. The space T that remains between the cylinders 30,31 and the reversing roll 10 and the wire 35 is called the pocket space. The roll 10 in accordance with the invention has the effect that the air flow Iι that travels along with the wire 35 is sucked intensively into the interior of the roll 10 and is discharged from the other side of the roll 10 as the air flow I₂ out of the roll and flows out of the pocket space T along with the wire 35. Fig. 3B shows an exemplifying embodiment of the invention similar to Fig. 3 A, wherein a blow box 37 has been fitted in the pocket space T, the blowings from said blow box being denoted with the reference P. By means of this arrangement it is achieved that substantially the entire pocket space T is subjected to a vacuum.

Fig. 3C shows an exemplifying embodiment of the invention similar to Fig. 3 A, wherein, in order to make the air flows in the pocket space T more accurate and to subject the pocket space T to a vacuum, a passive box 39 has been provided, by whose means the free face of the roll 10 is divided into two parts, i.e. an in-flowing part and an out-blowing part.

Fig. 4 A is a schematic illustration of test results in a test with an arrangement in accordance with the invention in an installation as shown in Fig. 3 A. The axis Y represents the vacuum, and the axis X represents the distance from the closing nip. The curves 45 and 46 illustrate the vacuum on the wire face. The curve 45 indicated as a solid line illustrates a test result in which the speed was 1500 metres per minute, and the dashed line 46 illustrates a test result at a speed of 1800 metres per minute. As is seen from the curves 45,46, the vacuum becomes higher when the speed becomes higher. Further, the vacuum is higher near the closing nip, which states that the flow takes place into the roll from the nip.

Fig. 4B is a schematic illustration of test results in a test with an arrangement in accordance with the invention in an installation as shown in Fig. 3B. The axis Y represents the vacuum, and the axis X represents the distance from the closing nip. The curves 41,42,43,44 illustrate the vacuum on the inlet face of the wire underneath the blow box. The curve 41,43 drawn as a solid line illustrates a test result in which the speed was 1500 metres per minute, and the dashed line 42,44 illustrates a test result at a speed of 1800 metres per minute. The curves 41 and 42 illustrate a situation in which the blowing of the blow box had not been switched on, and the curves 43 and 44 illustrate a situation in which the blowing of the blow box had been switched on. Fig. 4 shows that the vacuum in the pocket space becomes higher with a higher speed, which is contrary to normal-roll and suction-roll solutions. Figs. 5A...5B show an exemplifying embodiment of the invention in which a roll 10A with an open construction is composed of longitudinal bars or of a net 51, which are interconnected by means of intermediate rings 52 and end rings 53 so that an open surface construction and an intermediate space that remains between the axle 52 and the surface construction of the support roll 54 are achieved.

Figs. 6A...6C are schematic end views of different rolls in accordance with the invention. The roll 10A shown in Fig. 6A is composed of separate disks 57. The roll 10B shown in Fig. 6B is composed of disks 57 lightened by means of openings 58. These disk constructions 57 can be used as the annular plates 18 in the rolls shown in Figs. 1 and 2. The roll 10E shown in Fig. 6C is formed out of a sheet 59 shaped in accordance with the ribbed-pipe principle, and, as is shown in Fig. 7, it can be provided with a folded face 59E. In the embodiments shown in Figs. 5A...6C, the diameter of the roll 10A...10E is 500...1500 mm, preferably 600...1000 mm, and the openness is higher than 10 %, preferably higher than 20 % .

Fig. 8 shows an arrangement corresponding to the exemplifying embodiment shown in Fig. 3B in single- wire draw in a dryer section, and the checkered area indicates the area of vacuum produced in connection with the roll 10 and the pocket space T by the effect of the roll 10 and the blow box 37. As comes out from the figure, underneath the blow box 37 and inside the roll 10, there is the same pressure because of the open construction.

Above, the invention has been described with reference to some preferred exemplify- ing embodiments of same only, the invention being, however, by no means supposed to be strictly confined to the details of said embodiments. Many variations and modifications are possible within the scope of the inventive idea defined in the following patent claims.

Claims

1. A roll for a paper machine, in particular for a paper drying device, which roll (10,10A...10E) comprises an axle (11,52), on whose support the roll (10) is fitted to revolve, and a surface construction (13), which is connected to the axle by means of support pieces (14) or equivalent, characterized in that the openness of the surface construction (13) of the roll (10) is higher than 10 %, preferably higher than 20 %, so that, when the roll (10) revolves, an effect is produced that sucks air inwards into the roll (10), whereby a flow of air through the roll (10) arises.

2. A roll as claimed in claim 1, characterized in that the velocity of the air flow passing through the roll (10) is different from the speed of rotation of the roll (10).

3. A roll as claimed in claim 1 or 2, characterized in that the inside construction of the roll (10) has been formed as an open intermediate space (27), so that the ratio of the length (DS) of the open portion (27) in the interior of the roll (10) in the direction of the diameter (D) of the roll (10) to the diameter (D) of the roll (10) is 1 to 10 ... 1 to 1.5, preferably 1 to 4 ... 1 to 2.

4. A roll as claimed in any of the claims 1 to 3, characterized in that the surface construction (13) of the roll (10) is composed of annular plates (18) placed at a distance from one another, which plates are fixed to the roll (10) axle (11) by means of support bars (15A,16A,17A) fitted in connection with support pieces (14).

5. A roll as claimed in any of the claims 1 to 3, characterized in that the roll (10A) has been formed open so that the surface construction (13) of the roll is composed of substantially round bars (51) extending in the longitudinal direction, which bars are interconnected by means of support rings (52), which are connected to the roll (10) axle (52) by means of end flanges (53).

6. A roll as claimed in any of the preceding claims, characterized in that the annular piece (18) is made of a disk (57) which comprises a lightened portion (58).

7. A roll as claimed in any of the preceding claims, characterized in that the surface construction (13) of the roll (10) is composed of a folded sheet band (59).

8. A roll as claimed in any of the preceding claims, characterized in that the diameter of the roll is 500...1500 mm, preferably 600...1000 mm.

9. A roll as claimed in any of the preceding claims, characterized in that the interior space (19) in the axle (11) of the roll (10) has been arranged as a suction space, so that one end (19A) of the roll (10) axle (11) is connected with a source of vacuum and the mantle (20) of the axle (11) is provided with suction openings (21).

10. A dryer group for a paper machine, which group comprises two contact-drying cylinders (30,31) and at least one reversing roll (10) and in which dryer group single-wire draw is applied, wherein the paper web (W) to be dried is fitted to run on support of a drying wire (35), meandering from a drying cylinder (30) onto the reversing roll (10) and further onto a drying cylinder (31), so that on the contact- drying cylinders (30,31) the paper web (W) remains between the cylinder face and the drying wire (35) and on the reversing cylinder (10) at the side of the outside curve, characterized in that at least one of the reversing rolls (10) in the dryer group is an open roll (10), whose surface construction (13) has an openness higher than 10 %, preferably higher than 20 %, so that the flow of air (I,) travelling along with the wire (35) passes through the open surface construction (13) of the roll (10) into the interior of the roll (10) and is discharged further out along with the wire (35) as an air flow (I₂) through the open surface construction (13) of the roll (10).

11. A dryer group for a paper machine as claimed in claim 10, characterized in that in the dryer group, in the pocket space (T) between the drying cylinders (30,31), the reversing roll (10) and the wire (35), a blow box (37) is fitted, by means of whose blowings (P) substantially the whole of the pocket space (T) is subjected to a vacuum.

12. A dryer group for a paper machine as claimed in claim 10 or 11 , characterized in that in the pocket space (T) a passive box (39) is fitted, by whose means the free face of the roll (10) is divided into an in-flow area and an out-flow area.

13. A dryer group for a paper machine as claimed in any of the claims 10 to 12, characterized in that the ratio of the diameter (DC) of the drying cylinder (30,31) to the diameter of the roll (10) is 1 to 1 ... 4 to 1, preferably 2 to 1 ... 3 to 1.