Abrasive-band grinding device for rolls and a method for the control of an abrasive-band grinding device in the grinding of the faces of crowned rolls

Abstract: The invention concerns an abrasive-band grinding device (10) for rolls, comprising an abrasive band (11), which is rotated by means of a motor (13). The abrasive band (11) is pressed against the face (T') of the roll (T) to be ground. The abrasive-band grinding device (10) for rolls comprises guide pulleys (12a 1 ,12a 2 ) for the abrasive band (11) and, between said guide pulleys, a contact pulley (15) which has been mounted to revolve. The contact pulley (15), by whose means the abrasive band (11) is pressed against the face to be ground, is controlled by means of an actuator (16), preferably a motor (16), so that the contact pulley (15) can be inclined in compliance with the roll face (T') to be ground.

Description: The invention concerns an abrasive-band grinding device for crowned rolls as per the preamble of claim 1. Such a device is known from WO-A- 94 123 15. The grinding of crowned rolls for paper machines is a particularly difficult and demanding process. The diameter of large so-called Yankee cylinders can be up to 5 metres, in which case correcting or finishing grinding of the crowned shape requires particular operations in order that a satisfactory surface quality could be achieved. From the prior art, the use of an abrasive-band grinding device in the grinding of the faces of crowned rolls is known. In abrasive-band grinding devices, the band is driven from the output of a motor by means of a drive pulley. The band is fitted to run over two reversing pulleys, and a separate backup pulley, i.e. a so-called contact pulley, is fitted between said reversing pulleys. The contact pulley is fitted to form a back stop when the abrasive band is pressed at said backup pulley against the face to be ground. The use of an abrasive band is highly advantageous especially in large-scale grinding work, as compared, for example, with the use of a grindstone. The wear of the grindstone must be monitored constantly, for along with the wear of the stone the control parameters and the geometry of the device are also changed, whereas this does not occur in the case of a band, because the band can always be kept in contact with the crowned face to be ground. Also, by means of a band, it is possible to grind without a grinding fluid, whereas a stone operates best when a grinding fluid is used. With respect to the prior art, reference is made to document WO 94 12315 which describes a grinding device comprising a frame with three pairs of supports in star array, transportably supported on foot sections on a base, i.e. cylinders. A band grinder is secured to the frame and comprises a pivotable arm bearing a bracket for a contact disc. Between the bracket and the base there is a support comprising a guide rule to guide the contact disc precisely. In a conventional prior-art grinding process, the grinding device is passed in the direction parallel to the axis of the crowned roll, and the guide rails of the grinding device are placed as parallel to the axis of the crowned roll. The band or the grinding means is fed, in said solution, perpendicularly to said axial direction of the roll. The device is transferred after each grinding cycle further in the axial direction of the roll to be ground. In such a case, the grinding result becomes serrated. It has been possible to avoid a serrated grinding result by means of a second prior-art solution, in which the grinding device has been fitted to follow a certain pattern. The guides have been shaped curved in compliance with the crown form. A drawback of the device is the long time taken by changing of the settings of the device. In the present patent application, a novel solution is suggested for increasing the precision of grinding. In the solution, no separate guides are needed, but the solution is based on positive control of the backup or contact pulley. The backup pulley is inclined by means of a motor device along with the progress of grinding. Also, in the solution, the contact pulley is always shifted so that the radius of the contact pulley at the grinding point always passes through the geometric axis of rotation of the crowned roll. Thus, in the grinding process, both the inclination of the contact pulley and the position of said pulley in relation to the roll face are regulated. Both regulations are carried out under microprocessor control by means of separate motors, preferably electric stepping motors. In advance, it has been possible to program the desired crown form of the face to be crowned in the microprocessor. The device in accordance with the invention is defined in claim 1. The dependent claims describe advantageous embodiments of the invention. The invention will be described in the following with reference to some preferred embodiments of the invention illustrated in the figures in the accompanying drawings, the invention being, yet, not supposed to be confined to said embodiments alone. Figure 1A illustrates a prior-art method of grinding. Figure 1B shows the so-called contact pulley of Fig. 1A in an enlarged scale. Figure 2A illustrates an improvement over the prior-art. In Fig. 2A, it is suggested that the contact pulley be inclined, and said inclining is carried out by means of a control passed from a microprocessor or equivalent to an actuator, preferably a motor. Figure 2B is a side view of an abrasive-band grinding device in accordance with the invention in the grinding of a Yankee cylinder with a crowned face. Figure 3A is a side view of the device in accordance with the invention. Figure 3B is a top view of the device shown in Fig. 3A, and Figure 3C is a sectional view taken along the line I-I in Fig. 3A. Figure 4A is an axonometric separate illustration of an inclinable backup pulley for use in the invention. Figure 4B shows the equipment viewed in the direction of the arrow k 1 in Fig. 4A. Figure 4C is an illustration of principle of the inclining of the frame R 1 by means of a second actuator 17. In Fig. 1A, conventional prior-art grinding is illustrated. The feed is carried out stepwise, in which case "waves" corresponding to the pitch remain in the ground face, in which connection a contact, for example, with a doctor is not formed uniformly across the whole face. Also, the grinding process itself is slower, because on the crowned face just a narrow portion of the grinding pulley contacts the face at a time. When a crowned face is ground in the classical way, a detrimental stepwise profile is always produced, which allows a gap passable by a fibre to remain between a doctor and the roll face. Also, the grinding speed remains low because of the narrow contact face. With the present standard grinding machines most commonly used, this problem cannot be solved directly. The stepwise grinding result has been eliminated by means of various additional machining methods, which include honing by means of oscillating grindstones and, in later years, so-called superfinish grinding. In order to reduce the step formation, the contact pulley or disk has also been ground slanting, alternatingly in each direction. Besides on the surface quality, the emphasis in Yankee grinding is almost always also on the time taken by the work. Said auxiliary methods are slow and expensive to use. From the prior art, a tangential grinding device is also known, which is based on a mechanically bent guide. The drawback of this device is a "fixed" crown curve (bar), which is, true enough, adjustable, but said adjusting is, however, excessively slow when at the working site. The device was originally designed for the grinding of a certain Yankee cylinder, so that the crown curve was adjusted ready at the factory for the values of the cylinder concerned. Fig. 1B illustrates the prior-art solution, i.e. that shown in Fig. 1A, at the location of the contact pulley. Fig. 2A illustrates the grinding device in accordance with the invention. Its PC-controlled contact pulley 15 is fitted against the abrasive band 11. By means of the inclining motor 16 of the PC-controlled contact pulley 15, the abrasive band 11 is pressed into contact with the face T' to be ground on the roll T. The roll T is rotated during grinding. The contact pulley 15 is inclined actively by means of the motor 16 so as to comply with the desired crown form of the roll T face T' to be ground. The roll T is rotated during grinding. Thus, in the PC-controlled abrasive-band grinding device for crowned rolls and cylinders, the grinding line or grinding area of the abrasive band 11 is controlled by inclining the contact pulley 15. The control takes place, for example, by means of the program of the microprocessor (PC) by acting upon the inclinable actuator 16, preferably a stepping motor, which inclines the pulley 15 and, through said actuator, upon the ball-screw 18 and so further upon the contact pulley 15. The grinding face of the abrasive band 11 can be made to reach contact with the tangent of the desired crown curve at the grinding point. It is an advantage of the PC control, for example, compared with a bent guide that the crown values of the program can be altered quickly in the desired way on the site if the conditions change. This is a significant advantage in particular in the grinding of coated Yankee cylinders, in which case the crown curve must be programmed in accordance with the face and not in accordance with the theoretical curve proper. Further, the device is suitable for the sledges of ordinary grinding machines already in use, in which case no new special guides have to be acquired. It is estimated that, with this device, the grinding time becomes remarkably shorter, as compared with the current prior-art solutions, mainly because the grinding can be carried out with full capacity across the entire area of the mantle face. Fig. 2B is a side view of the grinding device 10 in accordance with the invention in the grinding of the roll T. Fig. 3A is a side view of the grinding device 10. The roll T, which has a crowned face T', is rotated by means of a motor, and at the same time the abrasive band 11 of the abrasive-band grinding device 10 is moved (direction S 1 ) by means of the motor 13 and pressed against the face to be ground by means of the contact pulley 15. The drive pulley 13b placed on the output shaft 13a of the motor 13 is fitted to move the abrasive band 11. The abrasive band 11 is passed over the band guide pulleys 12a 1 and 12a 2 . The guide pulleys 12a 1 ,12a 2 are fitted to revolve freely. Between the band guide pulleys 12a 1 and 12a 2 , inside the band loop 11, there is the backup or contact pulley 15 on its frame R 1 . The equipment comprises means by which the contact pulley 15 can be made to be positioned so at each point to be ground that the radius of the contact pulley 15 at the point to be ground is fitted to pass through the axis O of rotation of the roll T to be ground (Fig. 2B). In the construction in accordance with the invention, the contact pulley 15 comprises a displaceable frame R 1 , which is shifted by means of an actuator, preferably a motor 16, so that the radius of the contact pulley 15 at the grinding point always runs through the geometric axis O of rotation of the cylinder to be ground (in Fig. 2B). Inside the band loop of the abrasive band 11, the contact pulley 15 can be displaced and inclined so that the face of the contact pulley 15 at the grinding point is parallel to the tangent of the crown curve and that the radius of the contact pulley 15 at the grinding point additionally passes through the axis O of rotation of the roll T to be ground. The contact pulley 15 is inclined by means of the motor 16 on the frame R 1 . Further, there is a second motor 17, by whose means the contact pulley 15 can be displaced towards the roll T to be ground or apart from said roll. In this way the radius of the contact pulley 15 can be made to pass through the axis O of rotation of the roll T to be ground. Fig. 3B shows the device in accordance with the invention viewed from the top (in the direction of the arrow k 1 in Fig. 3A). The abrasive band 11 of the grinding device 10 is passed as a closed loop over the guide pulleys 12a 1 ,12a 2 and over the drive pulley 13b of the motor 13 and over the contact pulley 15. Thus, the motor 13 is fitted to rotate the drive pulley 13b placed on its output shaft 13a and, thus, to move the band 11, which is passed over the drive pulley 13b and over the guide pulleys 12a 1 and 12a 2 . Between the guide pulleys 12a 1 and 12a 2 there is a backup or contact pulley 15. The contact pulley 15 can be inclined in accordance with the invention by means of an actuator 16. The actuator 16 that inclines the backup or contact pulley 15 is preferably a motor, favourably an electric motor, and most appropriately a stepping motor. The contact pulley 15 is further connected with a frame R 1 , which can be pivoted around the articulation point E 1 by means of a motor 17, which is fitted between the base frame R 2 and the contact-pulley frame R 1 . Further, the drive pulley 13b with its motor 13 can be shifted by an actuator 18, so that the abrasive band 11 passing over the drive pulley 13b can be tightened by means of the actuator 18. Thus, the motor 13 is articulated to pivot around the articulation point E 2 by means of the actuator 18. Fig. 3C is a sectional view taken along the line I-I in Fig. 3A. The contact pulley 15 can be inclined by means of an actuator 16, preferably a motor. The motor 16 operates a spindle 18, which is in engagement with a frame 19. The frame 19 is linked to pivot around the link and bearing points 30a,30b (FIG. 4B) on the frame R 1 . The contact pulley 15 is mounted to revolve freely on the bearings 20 on the frame 19. The motor 16 for inclining the contact pulley 15 is placed so that the spindle 18 displaced by the inclining motor 16 is perpendicular to the sense of rotation S 1 of the band. Similarly, the motor 17 that inclines the frame R 1 on which the contact pulley 15 is placed is fitted to pivot the frame R 1 in a plane parallel to the plane of the loop of rotation of the band 11. Fig. 4A is a separate illustration showing the bearing system of the inclination of the contact pulley 15. The abrasive band 11 has been passed over the reversing pulleys or rolls 12a 1 ,12a 2 and over the PC-controlled contact pulley 15 between them. As is shown in Fig. 4B, in connection with the backup or contact pulley 15, on the frame 19, there are articulation points, preferably bearings 30a and 30b, and the contact pulley 15 can be inclined around the pivot shaft f 1 between said bearings. The frame 19 passing around the contact pulley 15 is coupled with a motor 16 by means of the spindle 18. In accordance with the invention, the motor 16 is preferably an electric motor and most appropriately a stepping motor, and the spindle device 18 is preferably a ball-screw. The contact pulley 15 is mounted to revolve freely on the bearing/bearings 20 on the frame 19. Between the frame 19 and the frame R 1 , there are the bearings 30a and 30b. The spindle 18 is mounted from the articulation point 50 on the arm 1 of the frame 19. Preferably, the actuator 16 is also mounted by means of a bearing in relation to the frame R 1 . In this way, a little movement of pivoting is permitted for the actuator 16. The guide pulleys 12a 1 ,12a 2 , which have been mounted to revolve freely, are placed on the frame R 1 . The embodiment shown in Fig. 4C illustrates pivoting of the frame R 1 around the articulated joint E 1 by means of the actuator 17, preferably a stepping motor. Now the contact pulley 15 can be positioned so that its radius at the grinding point always passes through the central axis O of the roll T to be ground and rotated (Fig. 2B). The contact pulley 15 is controlled so that it always complies with the desired shape of the face of the roll to be ground. The control of the actuator 16, preferably a motor 16, is carried out based on the control coming from the microprocessor (PC), and, similarly, the control of the second actuator 17, preferably a motor and most appropriately a stepping motor, is carried out based on the control coming from the microprocessor (PC). Said controls may have been formed so that a certain face shape has been programmed in advance in the microprocessor, in which case, when the grinding makes progress, the program gives the set values corresponding to the grinding position to the actuators 16 and 17. The direction of the grinding line or area is affected under positive control by means of the contact pulley 15 by controlling the abrasive band 11 by means of the contact pulley 15. So the contact pulley is inclined by means of a motor 16, and its position in relation to the roll to be ground is also regulated by means of a second actuator 17. The inclining of the abrasive band 11 takes place by inclining the contact pulley 15. The contact pulley 15 is inclined around a shaft f 1 , which is perpendicular to the plane that passes through the central axis O of the roll T to be ground and through the axis of rotation of the contact pulley 15. The motors 16 and 17 can be controlled at the same time. The control of the motors 16 and 17 can come from the PC through a program fed in advance into the PC, or also manually. By means of the program, the set values given to the motors 16 and 17 are changed along with the progress made by the grinding.

Claims: An abrasive-band grinding device (10) for crowned rolls, comprising an abrasive band (11), which is rotated by means of a motor (13) and which is pressed against the face (T') of the roll (T) to be ground, and which abrasive-band grinding device (10) for rolls comprises guide pulleys (12a 1 ,12a 2 ) for the abrasive band (11) and, between said guide pulleys, a contact pulley (15) which is mounted to revolve freely on support of bearings (20) on a first frame (19), said first frame being mounted to pivot on support of bearings (30a, 30b) on a second frame (R 1) between a base frame (R 2 ) of the device and the second frame (R 1 ) connected with the contact pulley (15), there is a second actuator (17), by whose means the second frame (R 1 ) is inclined in relation to the base frame (R 2 ) around an articulation point (E 1 ), in which case the contact pulley (15) can be positioned by means of the second actuator (17) towards the face (T') to be ground of the crowned roll (T) or away from said roll face characterized in that the contact pulley (15) by whose means the abrasive band (11) is pressed against the face to be ground, is arranged to be controlled by means of an actuator (16), preferably a motor (16), so that the contact pulley (15) can be moved in compliance with the roll face (T') to be ground, and that the motor (16) that moves the contact pulley (15) by inclining it is placed between the first frame (19) and the second frame (R 1 ) and is connected to said first frame (19) by means of a spindle (18), said motor (16) receiving its control from a microprocessor (PC). An abrasive-band grinding device as claimed in claim 1, characterized in that the motor (16) is arranged to displace the spindle (18) along a linear path. An abrasive-band grinding device as claimed in claim 2, characterized in that the motor (16) is arranged to displace the spindle (18) which is a ball-screw device. An abrasive-band grinding device as claimed in any of the preceding claims, characterized in that the motor (16) has been linked from its body to the second frame (R 1 ), and, similarly, its driven spindle (18) is linked on the first frame (19). An abrasive-band grinding device as claimed in claim 1, characterized in that the second actuator (17) is preferably a motor and most appropriately a stepping motor.

Inventors: HELLMAN BJARNE, PARVIAINEN SEPPO, HELLMAN, BJARNE, PARVIAINEN, SEPPO
Applicants: METSO PAPER INC, METSO PAPER, INC.
Application year: 1998
Main classification: B24B5
IPC codes: B24B5, B24B21, B24B41