Suction roll

Abstract: The invention relates to a suction roll (10) comprising a turbulence suppression apparatus (16) located at least in the vicinity of the end of a suction pipe (15) of the suction roll. The turbulence suppression apparatus comprises at least one plate element, whose surface (E) is essentially in the direction of the radius (R) of the roll (10′). The turbulence suppression apparatus (16) is fitted relative to the end of the suction-pipe (15) in such a way that the turbulence of air sucked in the suction phase is prevented and that the underpressure is thus maintained in the desired, approximately constant value on the inner surface of the roll shell along the entire roll width and the quantity of suction air in the desired, ap­ proximately constant value through the perforation (14) of the roll shell.

Description: The invention relates to a suction roll comprising a roll shell rotated on journals and which roll shell comprises a perforation, wherein several holes are led through the roll shell, whereby the suction is directed to the internal space of the roll shell and air is sucked through the perforation to press the paper web toward the outer surface of the roll shell and which suction roll comprises an internal space of the roll shell, to which underpressure is directed directly from a suction pipe connected to one of the journals of the roll through which air is sucked, the interior of the suction roll having essentially no suction box or a corresponding device arrangement. An earlier patent application FI 881106 by the applicant describes a suction roll solution, in which the paper web is pressed toward a lower drying cylinder. The application is based on the idea that the paper web is supported by a suc-tion roll which does not comprise a suction box inside the roll. In accordance with the above-mentioned invention, the suction roll construction has been formed in such a way that the suction roll comprises a perforation and a separate recess at the ends of the perforation, preferably a groove, through which underpressure is distributed within a larger area on the roll surface for achieving a suitable suction force over the paper web. By dimensioning the holes appropriately in accordance with the invention, a sufficient holding-down force can be achieved without having to place a suction box or another corresponding arrangement inside the suction roll. The object of the present invention is to improve the above-mentioned suction roll construction. When air is removed from a rotating cylinder with a perforated shell and a hollow interior via a hollow shaft or a suction pipe, a turbulence arises inside the cylinder, which causes a high air resistance and thus makes the exit of air from the cylinder more difficult. This detrimental turbulence is caused by a so-called angular-momentum phenomenon. Said turbulence produces a pressure loss, which is dependent on the rotational speed of the cylinder. In practice, this implies that the higher the circumferential speed of the suction roll is, the less the roll's suction device is able to remove air from the interior of the roll, whereby the air flow through the perforation of the roll shell remains insufficient. The object of the invention is, therefore, to provide a suction roll without a suction box or the like, wherein the occurrence of turbulence within the roll is prevented. The object of the invention is thus a suction roll solution, by means of which a large quantity of air can be removed efficiently through the suction-roll perforation without the occurrence of a detrimental turbulence in the construction and the resultant pressure loss. The invention is based on a solution, in which a plate-like structural part preventing the air turbulence and rotating with the roll has been formed inside the construction and in the vicinity of the suction pipe. This structural part is disposed radially in such a way that the air flow starting tangentially from the circumference of the inner surface of the cylinder perpendicularly contacts the surface of the turbulence suppression plate. The occurrence of a detrimental turbulence can thus be efficiently prevented by using such a turbulence suppression plate. The suction roll in accordance with the invention is mainly characterized in that the suction roll comprises a turbulence suppression apparatus located at least in the vicinity of the end of the suction pipe of the suction roll, the apparatus comprising at least one plate element, whose plane is substantially parallel to a plane defined by the rotational axis and the radius of the roll, and which turbulence suppression apparatus is fitted relative to the end of the suction-pipe in such a way that the turbulence of air sucked in the suction phase is prevented and that the underpressure is thus maintained in the desired, approximately constant value on the inner surface of the roll shell along the entire roll width and the quantity of suction air in the desired, approximately constant value through the perforation of the roll shell. The invention will next be described with reference to certain preferred embodiments of the invention, which are shown in the figures of the enclosed drawings and to which the invention is not solely intended to be limited. Fig. 1A is a cross-sectional view of the suction roll according to the invention. Fig. 1B is a section I-I of Fig. 1A. Fig. 1C illustrates the cross-sectional flow areas of the roll grooving and perforation and their relationship to each other. Fig. 2 shows the quantity of suction air as a function of the circumferential speed. The case f A1 is an alternative comprising no turbulence suppression, and the case f B1 shows a suction roll with the inventive turbulence suppression apparatus. Fig. 3 shows the underpressure of the suction pipe as a function of the circumferential speed. The case f A2 is functional curve corresponding to a case, in which no turbulence suppression apparatus has been used, and the case f B2 is a functional curve with a turbulence suppression apparatus. Fig. 4A-4C show in more detail the first preferred embodiment of the turbulence suppression apparatus. Fig. 4B shows the solution of Fig 4A seen from the direction of the arrow K₁ of Fig. 4A. Fig. 4C shows the embodiment as an axonometric view. Fig. 5A-5C show the second preferred embodiment of the inventive turbulence suppression apparatus. Fig. 5B is a view of Fig. 5A seen from the direction of the arrow K₂. In Fig. 5C, the embodiment is shown axonometrically. Fig. 6A-6C show the third preferred embodiment of the inventive turbulence suppression apparatus. Fig. 6B is a view of Fig. 6A seen from the direction of the arrow K₃. In Fig. 6C, the embodiment is shown axonometrically. Fig. 1A shows a suction roll 10 according to the invention. The suction roll 10 comprises a roll shell 11. The roll shell 11 is mounted to rotate on journals 12a and 12b, which are connected to the roll shell 11 via end flanges 13a and 13b. The roll shell 11 comprises a perforation 14. Several holes 14a are led through the roll shell 11. The perforation 14 comprises a hole section 14a extending up to a groove or recess 14b. Air is sucked (arrow L₁) through the holes 14a of the roll shell 11 to the interior C of the suction roll 10, and the paper web W can be pressed against the felt by means of underpressure and through it against the outer surface of the roll shell 11. A suction pipe 15 is connected to the journal 12a and the journal 12a is conveniently a hollow shaft or at least comprises an arrangement, through which air is sucked. The holding-down of the web is thus achieved by means of the suction roll 10 containing no suction box. The perforation 14a, 14b is dimensioned so that the air flow through the perforation remains within controlled limits at all points on the roll-shell surface. The suction roll 10 of Fig. 1 comprises an inventive turbulence suppression apparatus 16, preferably a plate-like part rotating with the roll 10 and fixed thereto. The turbulence suppression apparatus 16 is located in the vicinity of the suction pipe 15 and contains a plate surface (E). Fig. 1B shows a section I-I of Fig. 1A. The figure further includes a drying fabric H and a paper web W. By means of the suction L₁ is achieved a holding-down force F that keeps the web W on the felt H and the roll 10. Fig. 1C illustrates the cross-sectional hole area A o of the holes 14a and the cross-sectional flow area A₁ of the groove 14b. The ratio of the total cross-sectional flow area (A o ) of the holes of the cylinder 10 to the total cross-sectional flow area (A₁) is within the range of 1:10 - 1:150 and most preferably within the range of 1:50 - 1:110. The cylinder or the roll 10 comprises such a perforation 14 that the flow Q through the holes 14a to the interior C of the cylinder 10 is within the range of 500-1500 m³/m h, wherein "m" refers to the width meter of the cylinder and h = 1 hour. Fig. 2 shows the quantity of suction air through the perforation as a function of the circumferential speed. The curve f A1 represents a suction roll solution with no inventive turbulence suppression apparatus 16. It can be seen in the figure that when the circumferential speed increases, the quantity of suction air considerably decreases. By means of the curve f B1 , the figure shows a corresponding case with an inventive turbulence suppression apparatus 16. It can be seen in the figure that when the circumferential speed increases, the quantity of suction air remains approximately constant, which is the object of the invention. Fig. 3 shows correspondingly the underpressure of the suction pipe 15 as a function of the circumferential speed of the roll 10. The curve f A2 represents an apparatus with no turbulence suppression. The figure shows that as the cimcumferential speed increases, the underpressure of the suction pipe considerably increases at the same time. If an inventive turbulence suppression apparatus 16 corresponding to the curve f B2 is utilized, the underpressure of the suction pipe 15 remains approximately constant as a function of the circumferential speed. Fig. 4A-4C show in more detail the first preferred embodiment of the inventive turbulence suppression apparatus. In accordance with Fig. 4A-4C, the turbulence suppression apparatus 16 comprises plate elements 17a and 17b, which are disposed approximately in the radial direction of the roll and connected by a plate element 17c. The cross-sectional profile of the construction is thus a U-profile. The entire construction is fastened by means of a radial diagonal plate element 18, whose plate levels 18a are located essentially in the direction of the radius R of the rotational axis of the roll shell and so that the plate 18 is adapted to pass via the rotational axis X. The plate profile formed of the plate elements 17 is open at its ends, and an air flow in accordance with the arrow L₁ is thus allowed from the ends of the U-profile into the profile and further via the suction pipe 15 out of the interior C of the roll 10. Fig. 4C shows axonometrically the turbulence suppression apparatus of Fig. 4A and 4B, and the arrow L₁ indicates the passage of the air flow. Fig. 5A-5C show the second preferred embodiment of the inventive turbulence suppression apparatus. The apparatus comprises a turbulence suppression apparatus 16 formed of a circular plate element 19, which is fastened to the roll by means of at least one radial plate element 20. The figure represents a solution, in which the circular plate 19 is fastened by means of two cross plate elements 20a and 20b to the end of the roll shell, to its end flange 13a near the suction pipe 15. The dimensions of the circular plate 19 are such that a sufficient flow gap remains between the circular plate and the inner surface 11' of the roll shell, via which gap the air flow can further pass to the suction pipe 15. In the figure, D₃ refers to the diameter of the circular plate. D₃ is approximately 0.9 x diameter D₁ of roll-shell interior. The width L of the fastering plates 20a, 20b is ca. 0.5 x diameter D₂ of suction pipe 15. Fig. 5C shows the passage of the air flow in the turbulence suppression apparatus of Fig. 5A, 5B. Fig. 6A-6C show the third preferred embodiment of the inventive turbulence suppression apparatus 16. In the embodiment of the figure, the turbulence suppression apparatus 16 is formed only of a plate element 21 disposed in the radial direction of the suction roll 10. The plate 21 is located in the immediate vicinity of the end of the suction pipe 15 and fitted centrally on the axis X of the suction roll 10. The plate 21 covers the entire diameter length D₁ of the suction roll 10. In the embodiment of the figure, the width l of the plate 21 is ca. (1-1.5) x D₂ (suction-pipe diameter). Fig. 6C shows the turbulence-free passage of the air flow (arrow L₁) via the perforation 14 of the roll shell 11 to the suction pipe 15, as the plate 21 effectively prevents the turbulence of the air flow.

Claims: A suction roll (10) comprising a roll shell (11) rotated on journals (12a and 12b) and which roll shell (11) comprises a perforation (14), wherein several holes (14a) are led through the roll shell (11), whereby the suction is directed to the internal space (C) of the roll shell (11) and air is sucked through the perforation (14) to press the paper web toward the outer surface of the roll shell, and which suction roll (10) comprises an internal space (C) of the roll shell (11), to which underpressure is directed directly from a suction pipe (15) connected to one of the journals (12a) of the roll (10) through which air is sucked, the interior (C) of the suction roll (10) having essentially no suction box or a corresponding device arrangement, characterized in that the suction roll (10) comprises a turbulence suppression apparatus (16) located at least in the vicinity of the end of the suction pipe (15) of the suction roll, the apparatus comprising at least one plate element, whose plane (E) is substantially parallel to a plane defined by the rotational axis (X) and the radius (R) of the roll (10), and which turbulence suppression apparatus (16) is fitted relative to the end of the suction-pipe (15) in such a way that the turbulence of air sucked in the suction phase is prevented and that the underpressure is thus maintained in the desired, approximately constant value on the inner surface of the roll shell along the entire roll width and the quantity of suction air in the desired, approximately constant value through the perforation (14) of the roll shell. A suction roll according to claim 1, characterized in that said at least one plate element (21) is fitted to the suction pipe end of the suction roll and has its plane (E) essentially located in said defined plane and essentially so that the air sucked through the perforation (14) of the roll, when it begins to flow tangentially to the circumference of the roll shell, contacts essentially perpendicularly the surface (E) of the plate (21), whereby turbulence is effectively prevented. A suction roll according to claim 1, characterized in that the turbulence suppression apparatus (16) is comprised of two of said plate elements (17a,17b), which are connected by a third plate element (17c), to form a U-profile, the air flow being led inside the profile through its ends and further to the suction pipe (15). A suction roll according to claim 3, characterized in that the U-profile construction comprises a further plate element (18), whose plane is essentially included in said defined plane. A suction roll according to claim 1, characterized in that to said at least one plate element (20) is connected a circular plate (19), whose plane is located essentially in a radial plane of the suction roll, and which circular plate element (19) is fitted relative to the inner surface (11') of the suction roll in such a way that a sufficient gap remains for supplying air from between the upper part of the plate element (19) and the inner surface (11') of the roll shell to the suction pipe (15). A suction roll according to claim 1, characterized in that the perforation (14) comprises grooves (14b) connected with holes (14a) extending through the roll shell, whereby the ratio of the total cross-sectional flow area (A o ) of the holes to the total cross-sectional flow area of the grooves is within the range of 1:10 - 1:150 and most preferably within the range of 1:50 - 1:110 and the air flow through the perforation (14) is within the range of 500-1500 m³/m h.

Inventors: ILVESPAEAE HEIKKI, KUHASALO ANTTI, VIITANEN OLAVI, ILVESPAEAE, HEIKKI, KUHASALO, ANTTI, VIITANEN, OLAVI, Ilvespää, Heikki
Applicants: VALMET PAPER MACHINERY INC, VALMET PAPER MACHINERY INC.
Application year: 1990
Main classification: D21F3
IPC codes: D21F3