Method and doctor construction for removing water out of perforations in a suction roll

Abstract: The invention concerns a method and a device for removing water out of the perforations in a suction roll, in which method a doctor blade (11) is brought into contact with the face (T₁′) of the suction roll (T). The doctor blade (11) is mounted with its slat face (C) in such an angular position in relation to the face (T₁′) of the suction roll (T₁) that the angle between the face plane (C) of the doctor blade and the tangential direction of the face of the suction roll, when the tangent is drawn at the contact point between the tip of the doctor blade and the face of the suction roll, is within a range of 2... 10°. In the method, water is removed by means of the inletside surface plane (D) of the doctor blade, the inlet side being seen in the sense of rotation of the suction roll, and the water is allowed to flow smoothly over the doctor blade out of contact with the construction. In the method, according to the invention, water is removed additionally by means of a suction effect out of the area (V) between the slat face (C) of the doctor blade and the suction roll, negative pressure being produced in said space (V). The negative pressure produces flow of water out of the perforations or grooves (F) in the suction roll.

Description: The invention concerns a doctor for a suction roll in a paper machine. In prior art, in connection with a suction roll placed against a granite roll, doctor solutions are known in which a doctor is fitted to remove water that has remained in the perforations in the suction roll out of said perforations. However, the prior-art solutions are not sufficiently efficient. It follows from this that, out of the perforations in the suction roll, water still moves back into the felt and, thus, wetting of the felt occurs. In the invention, attempts have been made to find a solution for the above problem. In the invention, it has been realized to form a doctor solution in which an optimal angle remains between the doctor blade and the face of the suction roll. In the invention, the angle between the doctor blade and the tangent of the face of the suction roll has been made such that a negative pressure is produced in the space, whereby, by the effect of the negative pressure, the operation of the doctor blade is made more efficient, and any water that may have remained in the perforations in the suction roll is removed out of said perforations. In the invention, it has been realized to fit the doctor blade and the suction roll in such a way in relation to one another that the range of the angle a between the face plane of the doctor blade and the tangential direction of the suction roll in the area of the outlet side of the doctor blade is 2...10°. If the range of the angle is larger or smaller than said number of degrees, the desired suction effect is not produced. Thus, in the invention, it has been highly important to make the support and regulation arrangement of the doctor blade such that, e.g., said angle can be adjusted. The frame of the doctor blade is fitted to be pivotal on an articulation point, and it has been fitted so that it can be set against the suction roll by means of the force produced by a loading hose. The doctor blade itself, its frame part, is attached to a fixed base frame resiliently so that the doctor blade can be made to comply with the face form of the suction roll in all directions of width. According to the invention, a plastic rib is used as the doctor blade. The method in accordance with the invention for removing water out of a suction roll is mainly characterized in that the doctor blade is mounted with its slat face in such an angular position in relation to the face of the suction roll that the angle between the face plane of the doctor blade and the tangential direction of the face of the suction roll, when the tangent is drawn at the contact point between the tip of the doctor blade and the face of the suction roll, is within a range of 2...10°, whereby, in the method, water is removed by means of the inlet-side face plane of the doctor blade, the inlet side being seen in the direction of rotation of the suction roll, and the water is allowed to flow smoothly over the doctor blade out of contact with the construction, and whereby, in the method, according to the invention, water is removed additionally by means of a suction effect out of the area between the slat face of the doctor blade and the suction roll, negative pressure being produced in said space and the negative pressure producing flow of water out of the perforations or grooves in the suction roll. The doctor blade in accordance with the invention, which is to be placed against the suction roll, is mainly characterized in that the doctor construction comprises a slat-shaped doctor blade, which comprises a slat face, at which the angle between the face plane of said slat face and the tangential direction of the face of the suction roll which is jointly operative with the doctor blade is within a range of 2...10°, whereby an area of negative pressure is formed by means of the doctor blade in accordance with the invention between the face of the doctor blade and the face of the suction roll, water being removed by means of the negative pressure efficiently out of the perforations and/or grooves in the suction roll. The invention will be described in the following with reference to some preferred embodiments of the invention illustrated below in the figures in the accompanying drawings, the invention being, however, not supposed to be confined to said embodiments alone. Figure 1 is a schematic illustration of the area involving the solution in accordance with the invention. Figure 2 is a side view of a doctor in accordance with the invention. Figure 3 is a sectional view taken along the line I-I in Fig. 2. Figure 4 is an axonometric view of a doctor blade. Fig. 1 shows a doctor construction 10 in accordance with the invention as fitted in its object of use. The doctor construction 10 is fitted in connection with a suction roll jointly operative with a granite roll in the area of the outlet side of a nip N. The senses of rotation of the rolls are indicated by arrows. In a corresponding way, the run of the felt H is denoted with the arrow L₁, and the run of the paper web with the arrow L₂. The doctor construction 10 is fitted to remove water from the outlet side of the nip N between the suction roll T₁ and the granite roll T₂, and in particular the doctor 10 is fitted to remove water out of the perforations in the suction roll. Before the doctor construction 10, water is also removed out of the space placed ahead of the doctor blade 11 as the front edge D of the doctor blade 11 guides the flow of the drain water into the sewer system M in the way indicated by the arrow E₁. However, according to the invention, the active effect of the doctor blade is produced by the fact that it has been realized to regulate the angle between the face C of the doctor blade and the face of the suction roll to the range of 2...10°, whereby in the space V between the face plane C of the doctor blade and the face plane T₁' of the roll T₁ a negative pressure is formed (in Fig. 2), which absorbs water efficiently out of the perforations in the suction roll. Fig. 2 is a more detailed illustration of the doctor construction. Between the suction roll T₁ and the face C of the doctor blade 11 in the doctor construction 10, a space V remains, in which a negative pressure is formed, which absorbs water efficiently out of the perforations F in the suction roll T₁. According to the invention, the angle α between the face C of the doctor blade 11 and the tangent of the face T₁' of the suction roll jointly operative with the doctor blade in the area of the outlet side from the contact point between the suction roll and the doctor blade 11, seen in the sense of rotation of the suction roll, is in the range of 2...10°. Said range of degrees is optimal, an in said range an active suction effect is achieved, in which case, in the way illustrated in Fig. 2, the water is absorbed out of the perforations F and falls down into the drain trough K. The slanting blade face D above the doctor blade 11 also collects flowing water and guides said water over the doctor blade construction to be passed, in the way indicated by the arrow E₁, into the drain trough and further out of contact with the constructions. As is shown in the figure, the doctor blade 11 is an oblong construction, which is preferably made of plastic and which is attached to the blade frame 12 by means of its holder 11a. Advantageously, a T-rail fastening, a dovetail joint, or an equivalent mode of joining is employed, in which case, when a grasping threading 11b is grasped by means of a tool, the doctor blade 11 can be pulled apart from the blade frame 12. A lock screw 11c prevents falling off of the doctor blade out of a counter-holder 12a fitted on the blade frame 12. The blade frame 12 is fitted to pivot on support of the articulation point 13, and said pivoting is produced by displacing a loading piece 14 by means of loading hoses 15. A deformation is produced in the loading hoses by passing compressed air into the loading hoses through a hose 16. The doctor is opened "by its own weight" when the pressure is discharged from the loading hoses. The articulated joint 13 is placed in the base frame 17, on which the loading-hose means are also fitted. In a corresponding way, the whole constructional solution is fixed to the frame part 18 placed underneath by means of screw devices 19. The basic frame 17 is loaded by means of screw devices 20 while the screw is guided by means of the threading in the bracket 20'. Thus, by means of the screw device 20, the desired transverse deflection is obtained for the base frame 17 and for its articulation points 13, said deformation being transferred further through the blade frame 12 to the blade 11 itself. Thus, the shape of the tip of the blade 11 can be made to comply with the transverse profile and the crown form of the suction roll across the entire width of the suction roll. Said circumstance is essential if a negative pressure of the correct magnitude is to be provided in the space V between the doctor blade 11 and the face T₁' of the suction roll T₁. In the figure, the counter-screw is denoted with the reference numeral 21. The counter-screw can be displaced in the bracket 22 and locked by means of a screw 23 in the desired position. Thus, by means of the counter-screw 21, an extreme position can be set for the pivoting of the blade frame 12. By means of a protective shield 24, any splash water and water that flows from the upper face of the blade 11 are passed into the drain system and sewer system M. Fig. 3 is a sectional view taken along the line I-I in Fig. 2. By means of the screw devices 20, the base frame 17 is given the desired transverse shape. The base frame 17 is attached to the frame part 18 by means of screws 19 fitted into screw openings 25a provided in gaps 25 open from the side. The gaps make it possible that the base frame 17 and, thereby, the blade 11 can be deflected, when tensioned by the loading screws 19, into the shape corresponding to the desired crown form. Fig. 4 is an axonometric view of a doctor blade 11 made of plastic. By grasping the grasping threading 11b by means of a tool, the doctor blade is passed in the transverse direction out of the counter-holder 12a of the blade frame 12.

Claims: Method for removing water out of the perforations in a suction roll, wherein a doctor blade (11) is brought into contact with the face (T₁') of the suction roll (T), characterized in that the doctor blade (11) is mounted with its slat face (C) in such an angular position in relation to the face (T₁') of the suction roll (T₁) that the angle between the face plane (C) of the doctor blade and the tangential direction of the face of the suction roll, when the tangent is drawn at the contact point between the tip of the doctor blade and the face of the suction roll, is within a range of 2...10°, whereby, in the method, water is removed by means of the inlet-side face plane (D) of the doctor blade, the inlet side being seen in the direction of rotation of the suction roll, and the water is allowed to flow smoothly over the doctor blade out of contact with the construction, and whereby, in the method, according to the invention, water is removed additionally by means of a suction effect out of the area (V) between the slat face (C) of the doctor blade and the suction roll, negative pressure being produced in said space (V) and the negative pressure producing flow of water out of the perforations or grooves (F) in the suction roll. Method as claimed in claim 1, characterized in that, in the method, the position of the doctor blade is adjusted by pivoting the frame (12) of the doctor blade on an articulation point (13) by means of a loading-hose device (14,15,16), and that, in the method, the doctor blade (11) is adjusted so that its tip is precisely in compliance with the face shape of the suction roll (T) operating against the doctor blade by, by means of a screw device (20,20'), bringing the base frame (17) of the doctor blade to the desired shape by tensioning the frame (17) by means of the screw devices (20). Doctor construction (10), by whose means water is removed out of the perforations and/or grooves in a suction roll (T₁), characterized in that the doctor construction comprises a slat-shaped doctor blade (11), which comprises a slat face (C), at which the angle between the face plane of said slat face (C) and the tangential direction of the face (T₁') of the suction roll (T₁) which is jointly operative with the doctor blade is within a range of 2...10°, whereby an area (V) of negative pressure is formed by means of the doctor blade in accordance with the invention between the face (C) of the doctor blade (11) and the face of the suction roll, water being removed by means of the negative pressure efficiently out of the perforations and/or grooves in the suction roll. Doctor construction (10) as claimed in any of the preceding claims, characterized in that the doctor construction comprises a blade frame (12) and therein an articulation point (13), and that there are loading means (14,15), preferably a loading hose, whereby, by acting upon the loading means, the blade frame (12) is brought into a position wherein the oblong, slat-shaped doctor blade (11), which is attached to the blade frame (12), is positioned against the face (T₁') of the suction roll (T₁). Doctor construction as claimed in the preceding claim, characterized in that the articulation point (13) is placed in the base frame (17), which comprises gaps (25) in the transverse direction, the equipment comprising loading means, preferably screws (20), by whose means the base frame (17) is fitted to be deflectable so that, at all points, the doctor blade complies with the crown form of the suction roll (T₁) and, thus, is placed against the face (T₁') of the suction roll (T₁). Doctor construction as claimed in the preceding claim, characterized in that the construction comprises a screw (14), by whose means the base frame (17) can be attached to the stationary frame part (18) placed underneath, while the screws are fitted in the end holes (25a) in the gaps (25), whereby, by means of the arrangement, a bending in the transverse direction can be carried out reliably while the base frame (17) is, nevertheless, kept in tight contact with the stationary frame part (18) placed underneath. Doctor construction as claimed in the preceding claim, characterized in that the doctor construction comprises a collecting trough (K) in the base frame, into which trough the water that has been gathered out of the perforations and/or grooves (F) in the suction roll by the effect of suction is passed preferably by the effect of the force of gravity. Doctor construction as claimed in any of the preceding claims , characterized in that the doctor construction comprises a counter-screw (21), whereby, by acting upon the loading hose (14), the blade frame (12) is brought into contact with the counter-screw (21) and whereby, by turning the counter-screw (21), the blade frame (12) and the doctor blade (11) attached to same can be positioned further so that a correct angular position is obtained between the doctor blade (11) and the suction roll (T).

Inventors: KIVIMAA JUHA, SUVANTO LAURI, KIVIMAA, JUHA, SUVANTO, LAURI
Applicants: VALMET PAPER MACHINERY INC, VALMET PAPER MACHINERY INC.
Application year: 1991
Main classification: D21F3
IPC codes: D21F3, D21G3