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Title:
A METHOD AND AN APPARATUS FOR GRINDING A ROLL
Document Type and Number:
WIPO Patent Application WO/2011/083206
Kind Code:
A1
Abstract:
A method for grinding a roll, in which method a roll (2; 25) in a paper or paper- board machine or a corresponding machine for processing a fibrous web is ground by a grinding device (1; 15) installed in the machine, and in which method an abrasive tool (12; 16) of the grinding device (1; 15) is fed against the surface of the roll (2; 25) by a feeding device (11 ) controlled by a control device. In the method according to the invention, the abrasive tool (12; 16) is fed against the surface of the roll (2; 25) at a speed which is lower than the speed of change in the distance between the abrasive tool (12; 16) and the surface of the roll (2; 25) in the radial direction of the roll (2; 25) when the roll (2; 25) is rotating, as well as in such a way that the abrasive tool (12; 16) first grinds only the peak points of deviations in circularity of the roll (2; 25) and then gradually larger and larger areas as the grinding proceeds and the deviations in the circularity decrease. The invention also relates to an apparatus according to the method of the invention.

Inventors:
KOIRIKIVI KARI (FI)
SYRJAENEN TEPPO (FI)
Application Number:
FI2011/050005
Publication Date:
July 14, 2011
Filing Date:
January 05, 2011
Export Citation:
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Assignee:
WINTECH OY (FI)
KOIRIKIVI KARI (FI)
SYRJAENEN TEPPO (FI)
International Classes:
B24B5/04; B24B5/36; B24B49/04; D21G9/00
Foreign References:
US6645349B12003-11-11
US3552066A1971-01-05
Attorney, Agent or Firm:
TAMPEREEN PATENTTITOIMISTO OY (Hermiankatu 1 B, Tampere, FI-33720, FI)
Download PDF:
Claims:
Claims:

1. A method for grinding a roll, in which method a roll (2; 25) in a paper or paperboard machine or a corresponding machine for processing a fibrous web is ground by a grinding device (1 ; 15) installed in the machine, and in which method an abrasive tool (12; 16) of the grinding device (1 ; 15) is fed against the surface of the roll (2; 25) by a feeding device (11 ; 26) controlled by a control device, characterized in that the abrasive tool (12; 16) is fed against the surface of the roll (2; 25) at a speed that is lower than the speed of change in the distance between the abrasive tool (12; 16) and the surface of the roll (2; 25) in the radial direction of the roll (2; 25) when the roll (2; 25) is rotating, and that the abrasive tool (12; 16) is fed against the surface of the roll (2; 25) in such a way that the abrasive tool (12; 16) first grinds only the peak points of deviations in the circularity of the roll (2; 25) and then gradually larger and larger areas as the grinding proceeds and the deviations in the circularity reduce.

2. The method according to claim 1 , characterized in that the grinding device (1 ; 15) is moved primarily back and forth in the direction of the axis of rotation of the roll (2, 25) during the grinding.

3. The method according to claim 1 or 2, characterized in that the contact force between the abrasive tool (12; 16) and the roll (2; 25) is determined during the grinding.

4. The method according to claim 3, characterized in that the movement of feeding of the abrasive tool (12; 16) is controlled in such a way that the aim is to keep the contact force primarily constant at different points of the roll (2; 25) in its width direction during the grinding.

5. An apparatus for grinding a roll (2; 25), the apparatus comprising a grinding device (1 ; 15) installed in a paper or paperboard machine or a corresponding machine for processing a fibrous web, and comprising an abrasive tool (12, 16) as well as a feeding device (11 , 26) controlled by a control device, for feeding the abrasive tool (12; 16) against the surface of the roll (2, 25), characterized in that the feeding speed of the abrasive tool in the feed- ing device (11 ; 26) is lower than the speed of change in the distance between the abrasive tool and the surface of the roll (2; 25) in the radial direction of the roll (2; 25) when the roll (2; 25) is rotating, and that the abrasive tool ( 2; 16) is arranged to be fed against the surface of the roll (2; 25) in such a way that the abrasive tool (12; 16) first grinds only the peak points of deviations in the circularity of the roll (2; 25) and then gradually larger and larger areas as the grinding proceeds and the deviations in the circularity reduce.

6. The apparatus according to claim 5, characterized in that the feeding device (11 ; 26) is a feeding device for feeding the abrasive tool at a constant speed against the surface of the roll (2, 25).

7. The apparatus according to claim 6, characterized in that the feeding device (11 ; 26) is a pneumatic-hydraulic actuator (11 ) generating a linear motion.

8. The apparatus according to claim 6, characterized in that the feeding device (11 ; 26) is a hydraulic-hydraulic actuator (26) generating a linear motion.

9. The apparatus according to any of the claims 5 to 8, characterized in that the apparatus comprises a guide beam (3) installed in a paper or paperboard machine or a corresponding machine for processing a fibrous web, primarily in the direction of the axis of rotation of the roll (2; 25) and having a length of at least the width of the roll (2; 25), on which guide beam (1 , 15) the grinding device (1 ; 15) is mounted to be movable in the longitudinal direction of the beam.

10. The apparatus according to any of the claims 5 to 9, characterized in that the apparatus comprises means for determining the contact force between the abrasive tool (12; 16) and the roll (2; 25).

11. The apparatus according to claim 10, characterized in that a control device is provided for controlling the feeding motion of the feeding device (11 ; 26) on the basis of the contact force.

12. The apparatus according to any of the claims 5 to 11 , characterized in that the abrasive tool (12; 16) is an abrasive band (12) coiled on two coils, which band can be transferred during the grinding from the first coil (10a) to the second coil (10b) via a contact wheel (10d) that presses the abrasive band (12) against the surface of the roll (2).

13. The apparatus according to any of the claims 5 to 11 , characterized in that the abrasive tool is at least an endless abrasive belt (16) passing via at least one guide roll and a contact wheel (17) that presses the abrasive belt against the surface of the roll (2; 25).

14. The apparatus according to any of the claims 5 to 11 , characterized in that the abrasive tool (12; 16) is an abrasive stone. 15. The apparatus according to any of the claims 5 to 11 , characterized in that the abrasive tool (12; 6) is a hydraulically damped spring.

Description:
A METHOD AND AN APPARATUS FOR GRINDING A ROLL

The invention relates to a method according to the preamble of claim 1 and an apparatus according to the preamble of claim 5.

In paper and paperboard machines or corresponding machines for processing a fibrous web, the circularity of rolls used for guiding or processing the fibrous web changes as a result of their wear. Thus, various deviations in shape and circularity appear, including, for example, the so-called barring phenomenon. In the machines, the barring causes increasing vibration, the noise level increases, and finally a mark is visible in the quality of the paper or paperboard (particularly the surface). The barring also shortens the service life of the roll coating significantly, because the roll must be ground notably before the normal grinding interval.

The barring and other deviations in the shape and circularity of the rolls are removed from the rolls by grinding. The normal recommended grinding interval may be, for example, 2000 hours, but because of the barring, the grinding interval may be reduced to only about 200 hours. Experience has proven that it is impossible to remove barring by means of grinding machines installed in paper or paperboard machines or other machines of prior art for processing a fibrous web, for which reason the grinding to remove the barring must be performed in a separate roll grinding machine; in other words, the grinding of rolls requires that the production is stopped for at least the time needed for replacing the worn-out rolls. Replacing the rolls more often than normally, because of the barring, naturally reduces the degree of utilization of the paper or paperboard machine compared with the situation in which the grinding interval of the rolls would be close to the normal recommendation. Consequently, a grinding interval that is shorter than normal can be consid- ered to cause significant losses of revenue to, for example, a paper or paperboard factory.

Deviations in the shape and circularity of rolls, requiring repair grinding, are normally in the order of 0.03 to 0.06 mm, when the normal tolerance standard for the circularity of rolls is usually <0.02 mm. More frequent repair grinding in a roll grinding machine than normal will shorten the service life of the roll coating. Providing a roll with a new coating is an expensive investment. For example in a paper machine, providing a single calender roll with a new coating may cost about EUR 100,000. Consequently, the shorter grinding interval of rolls, caused by barring, also increases the maintenance costs of paper and paperboard machines to a significant extent.

It is an aim of the invention to introduce a new kind of a method for grinding rolls, to eliminate the above-mentioned drawbacks involved in the methods of grinding the rolls of a paper or paperboard machine or a corresponding machine of prior art for processing a fibrous web. In particular, it is an aim of the invention to introduce a method whereby the deviations in the shape and circularity, such as barring, of rolls in a paper or paperboard machine or a corresponding machine for processing a fibrous web can be eliminated without removing the rolls from the machine and bringing them to a separate roll grinding machine, and whereby the grinding can be performed in such a way that the rolls do not need to be coated as often as when grinding methods of prior art are applied. Another aim of the invention is to introduce an apparatus according to the method of the invention. The inventive idea of the method and the apparatus according to the invention is that the grinding device used is a grinding device to be installed in a paper or paperboard machine or a corresponding machine for processing a fibrous web, in which device the movement of an abrasive tool in the radial direction of the roll is controlled by applying such a feed motion in which the speed of the feed motion is lower than the speed of the surface of the roll in the radial direction when the roll is rotating. Thus, particularly at the early stages of grinding, the abrasive tool does not have time to touch the valley points formed in the surface of the roll, wherein, at first, it only diminishes the peak points/areas protruding in the radial direction of the roll with respect to the valley points. Thanks to this, during the grinding, deviations in the shape and circularity, such as barring, can be removed from the roll better than before and with significantly less grinding. Yet another inventive idea is to control the feeding of the abrasive tool of the grinding device by adjusting the feed motion of the abrasive tool on the basis of the force effective between the abrasive tool and the roll. Normally, the quantity of material removed by the abrasive tool from the roll coating to be ground is only about 0.01 mm during a single grinding motion in the axial direction of the roll, wherein the forces effective on the abrasive tool are small with respect to the rigidity of the structures. A typical deviation in the circularity of the roll coating, caused by barring, is about 0.03 to 0.05 mm per roll circumference. For this reason, elastic deformation of the grinding device and its mounting structures as well as other factors possibly adding to the inaccuracy of the feeding always remain so small that they do not cause inaccuracy in the grinding. Moreover, the contact force between the abrasive tool and the surface of the roll can be kept constant in different parts of the roll in its width direction, which makes it possible, among other things, to use grinding in the machine for processing the fibrous web instead of grinding in a separate roll grinding machine.

To put it more precisely, the method and apparatus according to the invention are characterized in what will be presented in the claims.

The method according to the invention has the advantage that the roll does not need to be removed from its place and thus, for example, the production of the paper and cardboard machine does not need to be stopped each time merely for the reason of repair grinding caused by a deviation in the shape or circularity exceeding the tolerance of circularity of the roll. In other words, thanks to the invention, the above-mentioned extra grinding times in the roll grinding machine are reduced and the degree of utilization of the machines is increased in this respect. Nevertheless, if necessary, the same roll can be ground several times when it is in the machine, because the grinding can be used only to remove the deviations in the shape or circularity of the roll; that is, the desired result can be achieved at a single grinding time with much less grinding than before. Thanks to the lesser degree of grinding than before, the rolls do not need to be coated as often as when the methods of prior art are applied for eliminating the deviations in the shape and circularity of the rolls. Furthermore, compared with roll grinding devices of prior art to be installed in paper or paperboard machines or other machines for processing a fibrous web, the apparatus according to the method of the invention is less expensive in its costs, because there is no need to install an expensive and complex system of measuring the shape and circularity of the roll, thanks to a novel method of adjusting the abrasive tool. Consequently, thanks to this method, savings are achieved not only in the costs caused by production stoppages but also in the costs of coating and grinding of the rolls, wherein the savings . together with the improvement in productivity, achieved by the method, increase, for example, the profitability of production in a paper or paperboard factory to a very significant extent.

By the method and the apparatus according to the invention, it is also possible to eliminate the dynamic deviation of rolls in sizing and coating stations when the rolls are installed in the machine and when they rotate at the normal processing speed. This improves the quality of the coated paper or paperboard. Particularly significant advantages are also achieved when the method is applied in backing rolls of coating stations, because in them, even an average deviation of some hundredths of a millimetre in the radial direction will cause problems in the process of coating the fibrous web, and by the apparatus according to the method of the invention, these deviations can be corrected in the above-mentioned way when the rolls are installed in the machine and when they are rotated at a rotating speed corresponding to the normal running speed of the process. In general, when grinding a roll by the method of the invention, the rotating speed of the roll is several times greater than when applying roll grinding methods of prior art. In the method of the invention, the grinding speed is typically 300 to 1000 m/min, whereas it is only about 30 to 50 m/min when conventional methods of prior art are applied.

In the following, the invention will be described in more detail with reference to the appended drawings, in which

Fig. 1 shows a grinding device of the apparatus according to the invention, and the roll to be ground by it, seen in a slanted view from above;

Fig. 2 shows the grinding device of Fig. 1 and the roll to be ground by it, seen from the side;

Fig. 3 shows a principle diagram of a pneumatic-hydraulic actuator used as a feeding device for the grinding device of Figs. 1 and 2; Fig. 4 shows another grinding device according to the invention, and a roll to be ground by it, seen in a slanted view from above; Fig. 5 shows the grinding device of Fig. 3 and the roll to be ground by it, seen from the side; and shows a principle diagram of a hydraulic-hydraulic actuator used as a feeding device for the grinding device of Figs. 4 and 5.

In an embodiment of the method according to the invention, for grinding a roll 2, a grinding device 1 shown in Figs. 1 and 2 is used, which has been installed in a guide beam 3 mounted in the frame of a paper or paperboard machine (not shown in the figure) or a corresponding machine for processing a fibrous web, in parallel with the longitudinal axis of a roll 2 for processing the fibrous web. It should be noted that the deviations in the shape and circularity in the contour of the surface of the roll 2 shown in Figs. 1 and 2 have been exaggerated to point out the principles of operation of the apparatus shown in these figures.

In this embodiment, the guide beam 3 mounted adjacent to the roll 2 in the machine for processing a fibrous web, has a triangular cross-section. The guide beam 3 is mounted in the frame of the machine by means of an adjusting shaft 4 provided therein and rotatable by means of a worm gear at one end of the guide beam 3. The adjusting shaft protrudes from the guide beam at its both ends. Thus, the guide beam 3 and the grinding device 1 mounted on it can be rotated with respect to the central axis extending in the longitudinal direction of the guide beam 3. Thanks to this structure, the guide beam 3 and the grinding device 1 mounted on rails 5 therein can be set in a desired position with respect to the roll 2. In this case (as shown in Figs. 1 and 2), the position of the guide beam 3 is set in such a way with respect to the roll 2 that that side of the guide beam 3, on which the grinding device 1 has been installed, is uppermost, and that the abrasive band of the grinding device 1 touches the roll 2 slightly above the point where the horizontal plane extending through the central axis of the roll and the surface of the roll intersect.

In this case, the grinding device 1 is a device applying the so-called super- finish grinding method; that is, the grinding is band grinding with a double ended abrasive band. The grinding device 1 comprises a frame 7 mounted at its lower part to the rails 5 on the guide beam 3, to be movable in the longitudinal direction of the guide beam 3 by means of linear bearings 8. The rear of the lower part of the frame 7 is further provided with a transfer device 9 driven by an electronic motor and connected to a gear rack 6 on the rear side of the rails 5 of the guide beam 3, for moving the frame 7 in a controlled manner at a steady adjustable speed back and forth in the axial direction of the roll during the grinding. In this case, the actual grinding is performed by an aggregate which comprises two coils 10a and 10b for abrasive band, con- nected to the upper part of the frame 7 and rotatable by, for example, an electronic motor; a feeding device 11 ; as well as an abrasive band 12 movable from the first coil 10a to the second coil 10b by means of a feeding machine 11 and guided via a guide roll 10c, a contact wheel 10d and a guide roll 10e. As shown in Fig. 2, the contact wheel 10d has a clearly larger diameter than the guide rolls 10c and 10e and it thus forms the point where the abrasive band 12 passing via the contact wheel touches the outer surface of the roll 2 during the grinding.

In this case, the feeding device 11 of the grinding device 1 is a double-acting pneumatic-hydraulic actuator, where a piston 14 fitted in a cylinder 13 is moved by pressurized air supplied into a chamber 13a for pressurized medium in the cylinder 13 in such a way that the speed of motion of the piston 14 is limited by a hydraulic limiter for the speed of motion. Figure 3 shows the principle diagram of the pneumatic-hydraulic actuator used as the feeding device in this embodiment. In this embodiment, the limiting of the speed of motion is implemented in such a way that the outflow of hydraulic fluid from the chamber 13b for pressurized medium in the cylinder 13 of the feeding device 11 is limited by a controllable throttle valve 13c. Thus, the speed of motion of the piston 14 of the feeding device 11 and of the guide rolls 10c and 10e as well as of the contact wheel 10d connected to it, that is, the feeding speed of the abrasive band 12 in the radial direction of the roll 2, can be limited by adjusting the controllable throttle valve 13c as desired. The pressurized air to be supplied into the chamber 13a for pressurized air in the cylinder 13 can be taken, for example, from the system of pressurized air of the factory, or produced by a separate air compressor. The transfer of energy (electricity and pressurized air) into the movable grinding device can be implemented, for example, by arrangements of hoses and cables known as such and allowing the linear movement.

The grinding device 1 is controlled by a control device (not shown in the figures) controlling the actuators of the grinding device, provided with the control electronics known as such and required for these functions, for controlling the pressurized air valve of the pneumatic-hydraulic actuator used as the feeding device 11 and the electronically controlled hydraulic throttle valve limiting the speed of the feed motion, in the grinding machine, as well as for controlling the electronic motor of the transfer device 9 moving the grinding device in the width direction of the roll and the electronic motors (or only a single motor) rotating the coils 10a and 10b for the abrasive band. In this case, the controlling is performed manually, and therefore, the control device comprises the necessary manual controls (for example, potentiometers) for adjusting the speed of motion of the abrasive band from the coil 10a to the coil 10b, the speed of motion of the grinding device in the width direction of the guide beam, as well as the feeding force and the feeding speed of the feeding device (that is, the maximum speed of motion of the contact wheel 10d and the abrasive band 12 pressed against the roll 2 in the radial direction of the roll, when the roll 2 does not prevent the free movement of these).

During grinding, the grinding device 1 is moved at a constant speed from the first end to the second end of the roll and back, and the abrasive band 12 is fed against the surface of the roll 2 to be ground, by moving the contact wheel 10d mounted at the end of the piston rod of the feeding device 11 and the guide rolls 10c and 10e by a constant contact force and at a limited feeding speed against the surface of the roll 2. The traversing motion of the grinding device 1 takes place at a constant speed and in such a way that the grinding time at each point of the roll is equal as exactly as possible. The contact force is controlled by adjusting the pressure of the pressurized air to be supplied to the pneumatic-hydraulic actuator used as the feeding device in such a way that it constantly remains as close as possible to a predetermined setting value that corresponds to the set value of the constant contact force between the abrasive tool and the surface of the roll. At the ends of the roll 2, the feeding force is adjusted to be slightly lower so that the roll is not ground more in the vicinity of its ends, due to the reversal of the direction of movement in the width direction of the roll. Furthermore, during the grinding, the abrasive band 12 coiled on the first coil 10a is slowly transferred onto the second coil 10b. Thus, new abrasive band is continuously transferred from the first coil 10a to the point of contact between the abrasive band 12 and the roll 2 to be ground. The used abrasive band 12 is coiled onto the second coil 10b.

By limiting the feeding speed of the feeding device 11 , it is possible to limit the feeding speed of the abrasive band 12 at the contact wheel 10d, for example, in such a way that it is not greater than 0.05 mm/s when the peripheral speed of the roll to be ground is 500 to 1000 m/min. Thus, the speed of motion (feeding speed) of the abrasive band 12 in the radial direction of the roll 2 is always lower than the speed of motion of the outer surface of the roll 2 in the radial direction of the roll, caused by a deviation in the shape and/or circularity exceeding the tolerance of <0.02 mm in the shape of the roll, when the roll is in rotation. This means that the abrasive band 12 does not have time to move into the valley points of the shape deviations in the roll 2 during the grinding, at least when the deviations in the shape and/or circularity are beyond the above-mentioned tolerance standard. Normally, the grinding belt moves at the valley points only a few millimetres in the radial direction of the roll, but the length of the motion is substantially affected by the peripheral speed of the roll to be ground and the variation in the shape deviations of the roll surface, for which reason the length of the motion varies to some extent. As a result, the abrasive band 12 of the grinding device 1 first grinds only the peak points of the deviations in the shape and circularity of the roll 2 and then gradually larger and larger areas as the grinding proceeds and the deviations in shape are reduced. Thanks to such an operation, the deviations in the shape and circularity (such as barring) of the roll 2 are removed from the roll 2 by less grinding than in the methods of prior art. At the final stage of the grinding, the abrasive band 12 touches the roll 2 on at least nearly the whole extent of its perimeter. In many cases, however, the grinding is continued until the abrasive band touches the roll on its whole perimeter, wherein the shape of the roll is no longer changed. Thus, all the deviations in the shape and circularity of the roll 2, at least those beyond the circularity tolerance (for example <0.02 mm), have been eliminated. This situation, the target of the grinding, can be verified by measuring the shape and circularity of the roll 2 (for example, by means of a dial indicator). Evidence on the sufficiency of the grinding can also be obtained by monitoring the changes in the force or pressure effective on the contact wheel 10d during the grinding. Normally, the thickness of the material layer removed from the surface of the roll during one grinding operation is in the order of 30 to 100 pm.

An essential feature in view of the functionality of the method is the fact that the uniformity of the grinding at different points in the width direction of the roll 2 is secured by keeping the contact force between the contact wheel 10d and the surface of the roll 2 as constant as possible all the time when the grinding device 1 moves in the width direction of the roll 2. This makes sure that the deflection or vibration of the guide wheel 3 caused for example by the grinding forces, or, among other things, deviations in the alignment between the guide beam 3 and the central axis of the roll 2, caused by possible inaccuracy of the installation, will not cause variation in the amount to be ground or in the diameter of the roll 2 at different points of the roll in its width direction, because due to the adjustment based on a constant force, the contact wheel 10d always moves automatically closer to the roll 2 at those points where its fastening structures are farther away from the roll than the other areas. In this context, it should be noted that due to such feeding control, the feeding speed (in the direction of the surface of the roll) is in many cases, during normal grinding, lower than the maximum value set for it. At an early stage of the peak point after a valley in the roll 2, the feeding speed may also be negative, because the feeding force between the roll and the abrasive band 12, which should be kept as constant as possible, would otherwise be exceeded. The maximum value of the feeding speed is normally achieved only at a valley in the shape of the surface of the roll, wherein the abrasive band does not touch the surface of the roll. After the grinding, the apparatus (the guide beam 3 with the respective grinding device 1 and the control device) can be removed from the machine for processing the fibrous belt, and transferred and connected to another roll to be ground, in the same machine or in a different machine. Naturally, the apparatus may also be installed permanently in said machine, for grinding said roll only. Thus, after the grinding, the grinding device 1 remains in its place to wait for the next grinding of the same roll 2. A suitable grinding interval for rolls can be determined for each roll or for each machine. The grinding interval can be determined, for example, by manual measure- ments/monitoring, empirically, or on the basis of data obtained from a condition monitoring system possibly provided in the machine.

Figures 4 and 5 show another apparatus according to the method of the invention. The structure of the grinding device 15 shown in Figs. 4 and 5 dif- fers from the embodiment of Figs. 1 and 2 structurally and functionally, due to the fact that in this case, the abrasive tool used in the grinding device 15 is an endless abrasive band 16 installed as a belt around a contact wheel 17 and a tension pulley 18. Also, the guide beam 19 shown in Figs. 3 and 4, by means of which the grinding device 15 is installed in a paper or paperboard machine or in another machine for processing a fibrous web, is slightly different from the application of Figs. 1 and 2. As shown in the figures, the guide beam 19 consists of a framed structure formed of tubular beams or the like, and for example, it cannot be rotated around its longitudinal axis, but it is installed ready in a position suitable with respect to the roll 25 to be ground. However, the guide beam can also be made rotatable in this embodiment. Such a grinding method is used primarily in the grinding of drying cylinders.

In this case, the grinding device 15 is installed in a feeding carriage 21 movable on rails 20 on top of the guide beam 19 in the longitudinal direction of the guide beam 19 in such a way that the grinding device can be moved at a constant speed back and forth in the width direction of the roll 25 to be ground, during the grinding. The feeding carriage 21 comprises guides 22 which are transverse to the rails of the guide beam, the grinding device 15 being supported by the guides 22 to be movable in the direction transverse to the rails 20 of the guide beams (in the feeding direction). In this embodiment, the moving of the grinding device 21 in the direction of the feeding motion along the guides 22 (that is, the coarse adjustment of the grinding device 15 in the direction of the feeding motion) is implemented by a transfer device driven by an electronic motor (not shown in the figures), wherein the electronic motor rotates a gear wheel moving along a gear rack by means of reduction gear (for example, a worm gear). Furthermore, a hydraulic-hydraulic actuator is provided between this transfer device and the grinding device 15, to generate the actual feeding motion. The transfer device driven by an electronic motor can also be replaced by, for example, a pneumatic cylinder or a hydraulic cylinder.

In the embodiment shown in Figs. 4 and 5, the contact wheel 17 of the grinding device 15 is mounted on the shaft of the electronic motor 23 rotating the same. The frame structures of the electronic motor 23 are provided with a supporting beam 24 extending from its top upwards, a tension pulley 18 being installed at the end of the supporting beam 24 to be adjustable in the longitudinal direction of the supporting beam 24 so that the tension of the abrasive band 16 installed around the contact wheel 17 and the tension pulley can be adjusted to be suitable. . In this case, the grinding device 15 and thereby the abrasive band 16 used as the abrasive tool therein are fed against the roll 25 to be ground, by a hydraulic-hydraulic actuator 26 used as the feeding device (although the pneumatic-hydraulic actuator of the above-mentioned kind could also be used in this embodiment as well). For this reason, the fixed end of the actuator 26 used as the feeding device is mounted to the transfer device fixed to the feeding carriage 21 in such a way that its movable end is connected to the grinding device 15 mounted on the guides 22 of the feeding carriage 21 to be movable in a direction transverse to the guide beam 19; that is, to an aggregate consisting of the electric motor 23, the contact wheel 17, the supporting beam 24, the tension pulley 18, and the abrasive band 16. Figure 6 shows a principle diagram of the hydraulic-hydraulic actuator used as the feeding device. Also in this case, the actuators of the apparatus are controlled by a control device in which the setting values are adjusted manually. When grinding the roll 25 by the grinding device 15 shown in Figs. 4 and 5, the grinding device 15 is moved against the roll 25 to be ground in such a way that the contact wheel 17 and the abrasive band 16 around it touch the surface of the roll 25. At the beginning of the grinding, the grinding device 15 is moved along the guide beam 19 in the width direction of the roll 25 to its first end. In the same way as in the preceding embodiment, during the grinding, the grinding device 15 is pressed by the feeding device, or in this case the hydraulic-hydraulic actuator 26, with a set constant force and at a limited feeding speed, against the surface of the roll 25, and simultaneously the grinding device 15 is moved from the first end of the roll 25 towards its second end. After the abrasive band 16 of the grinding device 15 has reached the second end of the roll 25, the direction of movement is reversed. The speed of motion of the movable end of the hydraulic-hydraulic actuator 26 used as the feeding device is set so that the feeding speed of the contact wheel 17 is lower than the speed of motion of the surface of the roll 25 caused by defects in the shape and/or circularity of the roll 25 in the radial direction of the roll, when the roll 25 rotates at a rotating speed typical of it. Thus, according to the method of the invention, also the grinding device 15 shown in Figs. 3 and 4 removes material first, at the early stages of the grinding, from only those points which are farthest away from the centre of the roll 25 (or which are so-called peak points), and when the grinding proceeds, larger and larger such areas, until at the final stage of the grinding (when the deviations in the shape and circularity of the roll are clearly within the allowed tolerance), the abrasive band 16 of the grinding device touches the roll 25 at least on its almost whole perimeter. Normally, however, the grinding is continued in practice until the surface of the roll has been ground on its whole perimeter.

The method according to the invention for grinding the roll can be imple- mented in a way that is, in many respects, different from the example embodiments presented above. The implementation of the steps of the method can be affected, among other things, by the type of the machine in question for processing the fibrous web, and the step of processing the fibrous web where the rolls are intended to be ground. The method according to the invention is suitable not only for the grinding of various rolls, but also, among other things, for cleaning the surface and correcting deviations in the shape of drying cylinders and so-called Yankee cylinders. Thus, the removal of the material may be several millimetres per the diameter of the roll. Furthermore, the method according to the invention can also be applied in the cleaning and shape grinding of plastic belts in long-nip presses (belt presses) as well as belts in metal belt calenders. It is an advantage of the method that the grinding of such a belt can be performed, for example, in a paper or paperboard machine without removing the belt to be ground.

Also, with respect to the apparatus, many implementations deviating from the structural and functional arrangements presented in the example embodiments above are possible. For example, the feeding motion of the grinding machine according to the method of the invention can be generated in the simplest way by using, for example, a constant force spring equipped with a hydraulic limiter for the speed of motion, instead of a pneumatic-hydraulic or hydraulic-hydraulic actuator. In principle, any actuators that generate a suitable linear motion can be applied as the feeding device, by which the speed of the feeding motion generated can be limited so that it is lower than the speed of motion of the outer surface of the roll to be ground in the radial direction of the roll when the roll is rotating (at a predetermined speed of rotation), and which generate a feeding force whose magnitude can be adjusted to have a constant maximum value. In some embodiments, the adjustment of the feeding force can also be implemented by utilizing the measurement of the contact force between the abrasive tool and the surface of the roll. It should further be noted that experience has shown that the grinding result is usually better, if the speed of rotation of the roll and thereby the peripheral speed of the surface of the roll is sufficiently high in relation to the feeding speed. However, these are dependent on each other, according to the principle described above. This is because the suitable speed of rotation of the roll depends, according to experience, for example on the diame- ter of the roll and on the material of the surface layer of the roll and on other structural properties of the roll.

In the above-presented example applications, the control device of the grinding device is used for controlling the actuators of the device and thereby the setting values manually, without any measurement devices for continuously measuring the circularity of the roll before the grinding and/or the final result of the grinding, and back couplings formed of these. Alternatively, the control can also be implemented in a more automated manner. Thus, the control device comprises a programmable data processing device, in which the desired setting values of the grinding device can be input on the basis of the size and material data as well as, for example, the rotating speed of the roll to be ground. Thus, the predetermined setting values may be, among other things, the feeding force, the feeding speed and the speed of motion of the abrasive band (in a superfinish type device, from one coil to another), as well as the positional angle of the guide beam and the speed of motion of the grinding device 1 in the width direction of the roll to be ground. Even in such an application, it is not necessary to use continuous measurement of the grinding result, but the predetermined setting values can be determined on the basis of indirect control values, such as the pressure of pressurized air or hydraulic fluid. Nevertheless, in some applications, it is possible to use measurement devices which indicate the final grinding result and/or the above-mentioned values that affect the grinding indirectly, and the measurement results obtained from them, in addition to or instead of these control values in the control of the grinding device. It is also obvious that the method according to the invention is not limited to only those grinding devices which have been described in the example embodiments presented above. In principle, it is possible to use, as the grinding device, any grinding device suitable for grinding the rolls of a paper or paperboard machine or a corresponding machine for processing a fibrous web, in which device the abrasive tool that grinds the surface of the roll is fed against the surface of the roll by the above-described principle. Thus, instead of the grinding devices presented above, it would be possible to apply, for example, a grinding device equipped with a rotating abrasive stone or a stationary abrasive shoe. Also in other respects not mentioned herein, the method and the apparatus according to the invention should not be limited to the example embodiments presented above, but various embodiments of the invention can be formed within the scope of the inventive idea defined in the claims.