size press

Abstract: The invention concerns a device in a size press comprising a nip formed by press rolls, through which nip the paper or board web is passed. The press rolls are provided with coating devices (23) for the spreading of films of coating agent onto the faces of said rolls. The coating devices (23) are mounted on applicator beams (20) transverse to the machine direction, which applicator beams are supported pivotally on the frame of the size press or on the loading arms of the displaceable roll and which applicator beams are provided with pivot cylinders, by whose means the applicator beams (20) can be opened and closed in relation to the rolls corresponding to them. The applicator beams (20) are provided with catches (27,47), which are arranged to be supported directly or indirectly on the bearings of the rolls that correspond to them when said applicator beams are being closed by means of the pivot cylinders. At least one of the applicator beams (20) of the size press is provided with catches (27,47) placed at each end of the applicator beam (20) and positioned in accordance with the position of the applicator beam (20), said catches being attached to the applicator beam (20) by means of articulated joints and said catches being interconnected mechanically.

Description: The invention concerns a size press comprising a nip formed by press rolls, through which nip the paper or board web is passed and in which size press the first press roll is mounted by means of bearings permanently on the frame of the size press, whereas the other press roll is mounted on the frame of the size press by means of its bearings as displaceable by the intermediate of loading arms or equivalent, and in which size press the press rolls are provided with coating devices for the spreading of films of coating agent onto the faces of said rolls, said coating devices being mounted on applicator beams transverse to the machine direction, which applicator beams are supported pivotally on the frame of the size press or on the loading arms of the displaceable roll and which applicator beams are provided with pivot cylinders, by whose means the applicator beams can be opened and closed in relation to the rolls corresponding to them, and which applicator beams are provided with catches, which are arranged to be supported directly or indirectly on the bearings of the rolls that correspond to them when said applicator beams are being closed by means of the pivot cylinders. It is a usual construction of modern size presses that the size press comprises a pair of rolls which form a nip, the paper or board web being passed through said nip. The coating agent, such as a size or pigment coating, is applied as a film onto the faces of the rolls by means of application devices, and in the roll nip the coating agent is transferred onto the web to be coated. Normally, one roll in the pair of rolls is mounted on the frame of the size press permanently by means of bearings, whereas the other roll is mounted on the frame displaceably, e.g., by means of pivot arms, which permit opening of the nip and loading of the rolls against one another so as to produce the desired nip pressure. The size-press construction described above involves a problem, which is manifested in particular in connection with replacement of the rolls. In particular, when the fixed roll is replaced the new roll is not always positioned optimally on the frame of the size press, but it remains slightly inclined. When the nip is closed, the displaceable roll is positioned in a way corresponding to the fixed roll to produce a uniform nip pressure. Thus, the displaceable roll is also positioned as inclined in a way corresponding to the fixed roll. The application devices of the rolls are normally mounted on an applicator beam parallel to the faces of the rolls, which beam is linked pivotally on the frame of the size press or on the loading arm of the displaceable roll. The applicator beam is normally provided with pivot cylinders, by whose means the beam and the coating device mounted on the beam are "closed" against the corresponding roll. However, the construction of the applicator beam is very rigid, for which reason it cannot always be positioned, by means of its pivot cylinders, in the way corresponding to the positions of the rolls. An applicator beam is, as a rule, provided with mechanical catches, which, when the beam is closed, rest against catch faces formed on the bearing housings of the roll. If the roll has been positioned in a highly inclined position, on closing of the beam a situation may arise in which the catch placed at one side of the beam only reaches contact with the bearing housing of the roll, whereas a gap remains between the catch placed at the opposite side and the catch face formed on the bearing housing. Even if the coating member of the coating device could be placed correctly against the roll face, by means of its loading hose, the pivot cylinders of the applicator beam usually produce an error in the nip pressure, which error is increased linearly in the transverse direction of the machine. This has again had a highly detrimental effect on the coating result. Hydraulic catches have also been applied in applicator beams of size presses. In their simplest form, they consist of a hydraulic cylinder whose length can be adjusted, i.e. of a "jack", by whose means, by adjusting its length, both ends of the applicator beam can be made to rest against the catch faces formed on the bearing housings of the roll. The drawbacks related to such a solution are, however, similar to those of the mechanical catches described above, i.e. the regulation is difficult, because the two catches must be adjusted separately. The support forces of both of the catches would have to be adjusted equal in order that the pivot cylinders of the applicator beam should not produce an error in the nip pressure. More "advanced" hydraulic catches always involve complicated control and regulation circuits, which are also expensive. Also, hydraulic systems always involve a risk of leakage. The object of the present invention is to provide a solution by whose means the above drawbacks related to the prior art are avoided and by whose means, therefore, an improved coating result is obtained. In view of achieving this, the invention is mainly characterized in that at least one of the applicator beams of the size press is provided with catches placed at each end of the applicator beam and positioned in accordance with the position of the applicator beam, said catches being attached to the applicator beam by means of articulated joints and said catches being interconnected mechanically. It is the most important advantage of the invention as compared with the prior art that, when a device in accordance with the invention is used, the load of the size nip in the size press, i.e. the nip pressure, can be made uniform and controlled, in which case the thickness of the layer of coating agent on the paper or board web to be coated can be made as desired across the width of the web. In comparison with hydraulic systems, a further advantage of the invention is low cost and simplicity. The further advantages and characteristic features of the invention come out from the following detailed description of the invention. In the following, the invention will be described by way of example with reference to the figures in the accompanying drawing. Figure 1 is a fully schematic side view of a size press. Figure 2 is a schematic top view of a size press showing, with exaggeration, inclined positioning of the rolls and the resulting error in the nip pressure. Figure 3 is an enlarged detail of Fig. 1, illustrating the construction of the catches on the applicator beam. Figure 4 corresponds to Fig. 3, viewed in the direction A. Figure 5 is a further enlarged detail of Fig. 4. Figure 6 shows a construction alternative to that shown in Fig. 4. Thus, Fig. 1 is a schematic illustration of a size press, which is denoted generally with the reference numeral 10. The press rolls 12,14 in the size press 10 form a nip N with one another, through which nip the paper or board web W is passed. In the solution as shown in Fig. 1, the web W is passed into the nip N over a guide roll 19. The bearing 13 of the first press roll 12 is mounted on the frame 11 of the size press permanently, and, in a corresponding way, the bearing 15 of the second press roll 14 is mounted on a loading arm 16, which is fitted on the frame 11 of the size press pivotally by means of an articulated joint 18. Between the frame 11 and the loading arm 16, loading cylinders are fitted 17, by whose means the nip N can be opened and closed and by whose means the loading pressure between the rolls 12,14, i.e. the nip pressure, can be adjusted to the desired level. Each roll 12,14 in the size press 10 is provided with a coating device 23,23a of its own, by means of which coating device a film of coating agent is applied to the face of the respective roll 12,14, said film being transferred onto the web W in the roll nip N. Each of the coating devices 23,23a is mounted on an applicator beam 20,20a transverse to the machine direction. In the embodiment of Fig. 1, the applicator beam 20a of the first press roll 12 is mounted pivotally, by means of an articulated joint 21a, on holders 24a fixed to the frame 11 of the size press, and further, between said applicator beam 20a and the frame 11 of the size press, pivot cylinders 22a are fitted, by whose means the applicator beam 20a can be opened and closed in relation to the roll 12. In a corresponding way, the coating device 23 of the second press roll 14 is mounted on an applicator beam 20 transverse to the machine direction, which beam is, by means of an articulated joint 21, mounted pivotally on holders 24 fixed to the loading arm 16. Between the applicator beam 20 and the loading arm 16, pivot cylinders 22 are fitted, by whose means the applicator beam 20 can be opened and closed in relation to the second press roll 14. When replacements of rolls have to be carried out in a size press as shown in Fig. 1, it is highly probable that especially the first roll, i.e. the fixed press roll 12, is not positioned exactly in the optimal, transverse position but becomes slightly inclined. Attempts have been made to illustrate this situation by means of the schematic Fig. 2, in which, true enough, the inclination of the first press roll 12 has been exaggerated considerably. When the first press roll 12 is inclined in the way shown in Fig. 2, the second press roll 14 is, of course, also positioned as similarly inclined when the nip N is closed by means of the loading cylinders 17. Thus, from both loading cylinders 17, equal forces are transmitted to the nip N, whereby the forces produced by the loading cylinders 17 produce a uniform nip pressure, i.e. a uniform distribution of loading pressure, in the nip N, which pressure is denoted in Fig. 2 with the reference p₁. Now, however, in a case in which the applicator beam 20 is linked on the frame 11 of the size press, the applicator beam 20 cannot be positioned in a similar way diagonally when it is closed by means of the pivot cylinders 22. This comes in particular from the high rigidity of the applicator beam 20. If the applicator beam 20 is provided with conventional mechanical catches 40,41, when the beam 20 is closed, one catch 41 is loaded against the catch face formed on the bearing 15 of the press roll, whereas, in the worst case, a gap c remains between the catch 40 placed at the opposite side of the machine and the catch face on the bearing 15. In such a case, the force produced by the pivot cylinder 22 at the end next to the gap C of the applicator beam 20 is transferred as a torque along the beam 20 to the other end of the beam and from there further to the loading arm 16, thus increasing the nip force by the amount P₂. In a corresponding way, at the end next to the gap C, the force produced by the pivot cylinder 22 lowers the nip force by the amount P₃. In Fig. 2, attempts have been made to illustrate the transfer of the forces by the dashed lines. Again, this has the consequence that the pressure distribution p₂ produced by the pivot cylinders 22 of the applicator beam 20 in the nip N is not even, but, for example, linearly changing, as is illustrated in Fig. 2. Thus, the nip pressure is, at one edge of the nip N, substantially higher than at the opposite edge. This has a considerably detrimental effect on the coating result. According to the invention, the above problem has been eliminated by means of the arrangement illustrated in Figs. 3 and 4. Figs. 3 and 4 illustrate the support arrangement of the applicator beam 20 of the displaceable roll 14, i.e. of the roll mounted on the loading arm 16, of the size press, but a fully equivalent arrangement can also be accomplished on the applicator beam 20a at the side of the fixed roll 12. As was already described above, the applicator beam 20 is mounted pivotally, by means of the articulated joint 21, on the holders 24,44. By means of the pivot cylinders 22, the applicator beam 20 and the coating device 23 fitted on it can pivoted between the coating position, i.e. the closed position, shown in Fig. 3 and the open position. On the wall 26 of the applicator beam 20 facing the roll 14, in the area of each end of the applicator beam 20 in the direction of width of the machine, lever-shaped catches 27,47 in accordance with the invention are fitted, which are linked to said wall 26 of the applicator beam by means of articulated joints 28,48 so that said lever-shaped catches 27,47 can pivot around said articulated joints 28,48. At the first end of each lever-shaped catch 27,47, a cam 29,49 has been formed, which rests against the support 25,45 fitted on each holder 24,44 when the applicator beam 20 is in the closed position. Thus, by the intermediate of the holders 24,44 and the loading arm 16, the position of said supports 25,45 is fixed in relation to the bearing 15 of the roll 14. At the second end of each catch 27,47, i.e. at the opposite side of the articulated joint 28,48 with respect to the cam 29,49, a connecting link 30,50 is fitted, by whose means the catches 27,47 are interconnected by means of a pulling member 35, which is a rigid connecting rod in the embodiment of Fig. 4. One possible mode of linkage of the connecting link 30 with the catch lever 27 is illustrated in Fig. 5. In this embodiment, like in Fig. 4, it is shown that the articulation shaft of the connecting link 30 with respect to the catch lever 27 is parallel to the pivot shaft of the articulated joint 28. Into each connecting link 30,50, a through hole has been formed, which is perpendicular to the pivot shaft. Into the hole, an inside thread has been formed, and, in a corresponding way, threaded parts 36,56 have been formed on the connecting rod 35 at the connecting links 30,50. The threaded parts 36,56 are of opposite handedness, so that, in a situation as shown in Fig. 4, when the connecting rod 35 is rotated in one direction, the connecting links 30,50 can be made to approach one another while the catch levers 27,47 rotate around their articulated joints 28,48. In a corresponding way, when the connecting rod 35 is rotated in the opposite direction, the connecting links 30,50 move apart from one another. By means of this arrangement, by simply rotating the connecting rod 35, the pre-stress of the catches 27,47 of the applicator beam 20 can be adjusted. As is well known, the construction of the applicator beam 20 is very rigid with respect to rotation. Thus, in conventional solutions of support, it is easy to end up in a situation as shown in Fig. 2, in which the contact is lost between the machine frame and one catch of the applicator beam 20. In the solution in accordance with the invention, it is, however, possible to equalize the support forces produced by the pivot cylinders 22, because the catches 27,47 placed at each end of the applicator beam 20 are interconnected by means of articulated joints in the way in accordance with the invention. Then, if the roll 14 has been placed diagonally as shown in Fig. 2, when the application beam 20 is being closed, a situation arises in which the cam 49 of the second catch 47 meets the support 45 on the holder 44 first. When this happens, the second catch 47 pivots around its articulated joint 48 and, at the same time, by the intermediate of the connecting rod 35, turns the first catch 27 so that the cam 29 of the first catch moves closer to the support 25 provided on the holder 24 and finally into contact with the support 25. After the closing of the applicator beam 20 has been completed, both of the catches 27,47 are in contact with the supports 25,45 with a substantially equal support force, in which case the support forces produced by the pivot cylinders 22 are equal at each end of the applicator beam 20. Thus, when the pivoting movement of the applicator beam has been completed, the beam receives its adjusted position in relation to the roll 14. The kinetic energy of the pivoting movement of the applicator beam 20 is absorbed by means of shock absorbers, but it is also possible to arrange the shock absorption on the connecting rod 35 itself. Fig. 4A shows an alternative to the solution of Fig. 4. In the embodiment of Fig. 4A, the applicator beam is denoted with the reference numeral 20' and the coating device with the numeral 23'. In the embodiment of Fig. 4A, the lever-shaped catches 27',47' are mounted, as compared with the situation of Fig. 4, as mirror images in relation to the vertical axes running through the articulated joints 28',48', in which case the intermediate member 35' acts as the member that receives the compression force. The reference numerals 24',44' refer to the holders, and the reference numerals 30',50' to the connecting links. The threaded parts of the intermediate member 35' are denoted with the references 36',56', the cams of the catches 27',47' with the references 29',49', and the supports on the holders 24',44' with the references 25',45'. The reference 26' refers to the wall of the applicator beam 20'. In the embodiment of Fig. 4A, the member 35' that receives the compression force can be substituted for by a pulling member, such as a wire (not shown), which interconnects the connecting links (30',50') and passes, e.g., over reversing pulleys, which are placed outside the connecting links 30',50' in the direction of width of the applicator beam 20'. Fig. 6 shows a further embodiment alternative to the solution shown in Fig. 4. In Fig. 6, the dashed lines and the references 27'' and 47'' represent the catch ends next to the connecting links. The connecting links are denoted in the figure with the references 30'' and 50''. The solution as shown in Fig. 6 differs from Fig. 4 in the respect that, in Fig. 6, the connecting rod 35 as shown in Fig. 4 has been substituted for by a wire 35'' or by an equivalent flexible pulling member. Moreover, as is shown in the figure, at one end of the pulling member 35'', a length-adjusting device 37'' has been fitted, by whose means it is possible to carry out necessary regulation of the pre-stressing. Thus, as regards its principle of operation, the solution of Fig. 6 is similar to the embodiment shown in Fig. 4. Above, the invention has been described by way of example with reference to the figures in the accompanying drawing. The invention is, however, not confined to the exemplifying embodiments illustrated in the figures alone, but various embodiments of the invention may show variation within the scope of the inventive idea defined in the accompanying patent claims.

Claims: A size press comprising a nip (N) formed by press rolls (12,14), through which nip the paper or board web (W) is passed and in which size press the first press roll (12) is mounted by means of bearings (13) permanently on the frame (11) of the size press, whereas the other press roll (14) is mounted on the frame (11) of the size press by means of its bearings (15) as displaceable by the intermediate of loading arms (16) or equivalent, and in which size press the press rolls (12,14) are provided with coating devices (23,23a) for the spreading of films of coating agent onto the faces of said rolls said coating devices (23,23a) being mounted on applicator beams (20,20a) parallel to the faces of said rolls, which applicator beams are supported pivotally on the frame (11) of the size press or on the loading arms (16) of the displaceable roll (14) and which applicator beams are provided with pivot cylinders (22,22a), by whose means the applicator beams (20,20a) can be opened and closed in relation to the rolls (12,14) corresponding to them, and which applicator beams (20,20a) are provided with catches (27,47), which are arranged to be supported directly or indirectly on the bearings (13,15) of the rolls (12,14) that correspond to them when said applicator beams are being closed by means of the pivot cylinders (22,22a), characterized in that at least one of the applicator beams (20) of the size press is provided with catches (27,47) placed at each end of the applicator beam (20) and positioned in accordance with the position of the applicator beam (20), said catches being attached to the applicator beam (20) by means of articulated joints and said catches being interconnected mechanically. A size press as claimed in claim 1, characterized in that the catches (27,47) comprise levers linked with the applicator beam (20) by means of an articulated joint (28,48), at one end of which levers a cam (29,49) has been formed, which is arranged, during closing of the applicator beam (20), to be supported against a support (25,45), which is in rigid connection with the bearing (15) of the roll (14), and which levers are interconnected by their opposite end, with respect to the articulated joint (28,48), by means of an intermediate member (35,35',35''). A size press as claimed in claim 1 or 2, characterized in that the intermediate member (35,35',35'') is connected to the lever-shaped catches (27,47) by means of connecting links (30,50), whose pivot shafts are parallel to the articulated joints (28,48) of the catches (27,47) and form a quadrangle of articulated joints. A size press as claimed in any of the preceding claims, characterized in that the intermediate member (35,35',35'') is adjustable so that, by means of adjustment of the intermediate member, it is possible to change the relative distance between the connecting links (30,50) of the lever-shaped catches (27,47). A size press as claimed in any of the preceding claims, characterized in that the intermediate member is a connecting rod (35,35'), which is, in the areas of the connecting links (30,50;30',50') of the catches, provided with threaded parts (36,56; 36',56') so that the first and the second threaded parts are of opposite handedness, and that, in a corresponding way, the connecting links (30,50;30',50') are provided with holes with inside threads, whose axial direction is perpendicular to the pivot shafts of the connecting links (30,50;30',50'), whereby, when the connecting rod (35;35') is rotated in one direction, the connecting links (30,50;30',50') of the catches (27,47;27',47') are arranged to approach each other, and when the rod is rotated in the opposite direction, to move apart from each other. A size press as claimed in any of the preceding claims, characterized in that the intermediate member is a pulling member (35;35''). A size press as claimed in any of the claims 1 to 5, characterized in that the intermediate member is a member (35') that receives compression force. A size press as claimed in any of the claims 1 to 4 or 6, characterized in that the pulling member is a wire (35'') or an equivalent flexible member, which is provided with a length-adjusting device (37'') so as to change the relative distance between the connecting links (30'',50'') of the catches.

Inventors: ROUSU ARI, SALO MARKKU, ROUSU, ARI, SALO, MARKKU
Applicants: VALMET PAPER MACHINERY INC, VALMET PAPER MACHINERY INC.
Application year: 1993
Main classification: D21H23
IPC codes: D21H23