Hot rolls are needed in paper machines and in paper finishing devices at a number of locations. The most common places for the use of hot rolls are in calenders and presses, as well as in supercalenders. In particular in the calendering process, raised surface temperatures of a chilled roll are utilized to an ever increasing ex- tent for plasticizing paper and for improving the calendering result. The common- est solution for heating a roll has been to introduce the heat into the roll by means of a suitable heat transfer medium, which has conventionally been water. In such arrangements, water has circulated through a separate heating unit into the roll.

With the soft calenders becoming more common, hot oil as a heat transfer me- dium has rapidly become more common. Hot oil is heated in a separate boiler plant, from which it is pumped into the roll.

Patent literature knows several different methods and arrangements for heating rolls. The oldest prior-art solution is one in which a through hole is drilled into the centre of a massive roll, and the heat transfer medium is circulated in said hole.

However, it is an essential drawback of such an arrangement that the distance from the heat transfer medium to the surface of the roll is very large, thus efficient and economical heating cannot be achieved by means of this solution. Another and more advanced solution is one in which the roll comprises a non-revolving displacement body on which a roll shell is revolvingly mounted by means of bearings. In this arrangement, the heat transfer medium, such as water or oil, is passed into the space between the displacement body and the roll shell to heat the

roll shell. One such arrangement is disclosed, for example, in EP Application Publication No. 0 188 238. However, it is an essential drawback of such an ar- rangement that the quantities of liquid to be dealt with are very large. This causes, among other things, that the roll has a very high power consumption. Other heat- able rolls accomplished with a similar construction, in which the displacement body, however, revolves with the roll shell, have been previously described, among other things, in US Patents Nos. 4, 607, 420, 4, 730, 374 and 4, 734, 966, as well as in EP Application Publication No. 0 158 220. In the case of these rolls too the efficiency of heating is rather poor because the heating medium must be heated separately before introduction into the roll.

One prior-art arrangement for heating a roll is one in which a number of through bores extending in the axial direction are provided in the roll, and a heating me- dium is circulated through said bores. Such arrangements have been described previously, among other things, in Canadian Patent No. 1, 223,763, EP Applica- tion Publication No. 0 597 814, and FI Laid-Open Publication No. 88 632. In connection with the prior art described above, for example, US Patent No.

5, 383, 833 describes a solution in which axial bores have been provided in a hol- low roll shell of a roll. Inside the roll shell there is arranged a non-rotatable dis- placement body, which guides the heating medium passed into the roll so as to circulate in the space between the displacement body and the roll shell as well as in the bores formed in the roll shell.

The latest development in the heating of a roll is induction heating of a roll. An inductor may be located either inside or outside a roll. US Patents Nos. 5, 553, 729 and 5, 895, 598 can be mentioned as examples of internal induction heating.

The greatest problems with today's arrangements are associated with the com- plexity, need of service and rather poor efficiency of the systems. Heating meth- ods that use a heating medium involve the essential drawback already mentioned previously, i. e. that the quantities of liquid to be dealt with are very large. A fur-

ther drawback is that in any case the heat transfer medium must always be first heated in some suitable manner, for example, by means of electricity, after which the heat transfer medium is passed into the roll. The efficiency of heating of such rolls is poor and the consumption of power is remarkably high.

The aim of the present invention is to provide a eatable roll in which the effi- ciency of heating of the roll has been improved and in which the shell of the roll can be heated uniformly. With a view to achieving these aims, the roll according to the invention is mainly characterized in that an apparatus for heating the roll shell is a friction-based apparatus which is disposed inside the roll and which is arranged to produce friction work inside the roll shell in an amount that substan- tially corresponds to the consumption of thermal energy caused by a web in con- tact with the roll shell and to the losses of thermal energy from the roll to the sur- roundings.

By means of the invention, several remarkable advantages are obtained as com- pared with the prior art, of which advantages the following ones may be men- tioned in this connection. First of all, it is an essential advantage that the structure of the roll is simple and the efficiency of heating is very high. The energy needed for heating is most advantageously taken from electric motors and transmitted mechanically into the roll. The efficiencies of the electric motor and mechanical power transmission are, as known, very good. In roll replacement situations, it is easier to detach and handle mechanical parts than rotating couplings and liquid hoses. In connection with the roll according to the invention, there is no need to use any troublesome and expensive devices outside the roll. The other advantages and characteristic features of the invention will become clear from the following detailed description of the invention.

In the following, the invention will be described by way of example by means of the examples shown in the figures of the accompanying drawing.

Figure 1 is a longitudinal vertical view of one advantageous embodiment of the roll in accordance with the invention partly in cross section.

Figure 2 shows an alternative embodiment of the roll in accordance with the in- vention as an illustration corresponding to that of Fig. 1.

In Fig. 1, a roll has been generally denoted with the reference numeral 10. The roll 10 comprises a hollow roll shell 11, roll ends 12,13 being attached to the ends of the roll shell. Axle journals 14,15 are further attached to the roll ends 12,13, the roll 10 being mounted from said axle journals by means of bearings 16,17 on the frame of a machine. The axle journals 14,15 may be made of the same material as the roll ends 12,13 and, as shown in Fig. 1, the axle journal 14 of the first roll end 12 is hollow. The roll 10 is further provided with a drive motor 18, which rotates the roll 10 by means of a suitable power transmission member 19. The drive mo- tor 18 is most advantageously an electric motor, which provides the best advan- tages desired to be achieved by the invention. The use of a hydraulic motor may also be contemplated.

A displacement body 20, which is concentric with the roll 10, is disposed inside the roll shell 11. The ends of the displacement body 20 are provided with axle journals 21,22 or with a through-going shaft which is continuous in a corre- sponding manner and from which the displacement body 20 is revolvingly mounted by means of bearings 23,24 inside the roll 10. The axle journal 21 at the first end of the displacement body 20 is, as shown in Fig. 1, so long that it extends through the first roll end 12 and the hollow axle journal 14. The displacement body 20 is further provided with a drive motor 25, which is coupled to the first axle journal 21 to rotate the displacement body 20. The drive motor 25 of the dis- placement body is most advantageously an electric motor, by means of which the desired advantages are best achieved. A hydraulic motor can also be used as the drive motor 25. The roll 10 and the displacement body 20 are thus both provided

with separate drive motors 18,25, in which connection they can be rotated inde- pendently of each other.

The eatable roll according to the invention is intended in particular for a calender roll and the heating of the roll is accomplished such that, in the invention, friction work is produced inside the roll 10 in an amount that substantially corresponds to the consumption of thermal energy caused by paper and to the losses of it to the surroundings. The losses to the surroundings, in particular because of convection, are considerable and can be as much as of the order of 30 % of the power con- sumption of the roll. In more detail, the arrangement according to the invention is accomplished such that the roll 10 and the displacement body 20 mounted by means of bearings inside the roll shell 11 are rotated by means of drive motors 18, 25 at speeds which differ from each other. An intermediate space S between the roll shell 11 and the displacement body 20 is filled with high-viscosity heat trans- fer oil, and said gap is dimensioned such that, when there is a difference in speed between the roll shell 11 and the displacement body 20, heat is generated as a re- sult of the viscous resistance of the heat transfer oil. The amount of the heat that is being generated can be easily controlled by regulating the relative speed, i. e. the speed difference between the roll shell 11 and the displacement body 20. If the displacement body 20 and in particular its outer surface are further shaped in a suitable manner, a strong flow of oil is produced inside the roll 10, which ensures a uniform distribution of heat over the entire roll shell 11. In order to increase the flow, the outer surface of the displacement body 20 can be, for example, rough- ened in a suitable manner or provide with different wings or corresponding shaped members.

Fig. 2 shows another embodiment of the roll according to the invention, which roll in this figure is generally denoted with the reference numeral 110. In this em- bodiment, the roll 110 comprises a hollow roll shell 111, roll ends 112,113 pro- vided with axle journals 114,115 being attached to the ends of the roll shell. The roll 110 is mounted from the axle journals 114,115 by means of bearings 116,

117 on the frame of a machine. In a manner corresponding to Fig. 1, in this em- bodiment too the axle journal 114 of the first roll end 112 is hollow and provided with a through hole. The roll 110 is provided with a drive motor 118, which ro- tates the roll 110 by means of a power transmission member 119. The drive motor 118 is advantageously an electric motor. A hydraulic motor can also be used.

A displacement body 120 is disposed inside the roll shell 111 concentrically with the roll 110. The ends of the displacement body 120 is provided with axle journals 121,122, from which it is revolvingly mounted by means of bearings 123,124 with respect to the roll 110. Instead of the axle journals 121,122 it is also possible to use a continuous shaft passing through the displacement body 120. The axle journal 121 of the first end of the displacement body 120 is so long that it extends through the first roll end 112 of the roll 110 and through the hollow axle journal 114. The displacement body 120 is further provided with a drive motor 125, which is coupled to the first axle journal 121 to rotate the displacement body 120.

As already previously stated, the drive motor 125 is most advantageously an elec- tric motor, even though a hydraulic motor may also be used. In these respects, the embodiment of Fig. 2 corresponds to the illustration of Fig. 1.

In the embodiment of Fig. 2, the roll shell 111 is provided with substantially axial bores 131 extending from one end of the roll shell 111 to the other end thereof.

There are a number of said bores 131 and they are located at regular intervals from one another in the circumferential direction. Further, radial bores 132,133 are formed in the roll shell 111 in the area of both ends of the roll shell 111, said bores extending from the inner surface of the roll shell 111 to the axial bores 131.

Thus, the axial bores 131 are in communication with the interior space of the roll shell 111 in the area of the first end of the roll through the first radial bores 132 and, in a corresponding way, in the area of the second roll end through the second radial bores 133. The outer surface of the displacement body 120 is additionally so shaped or provided with shaped members 135 which, when the displacement body 120 rotates, cause oil to flow in one direction in the axial direction of the roll

in a gap S between the roll shell 111 and the displacement body 120. The illustra- tion of Fig. 2 shows only one shaped member 135 which is spiral in shape. There may also be several shaped members 135, and their shape may differ from that of the illustration of Fig. 2.

When the rotating motions of the displacement body 120 and the roll 110 have a speed difference, the shape of the outer surface of the displacement body 120 causes the oil to flow in the intermediate space S between the displacement body 120 and the roll shell 111. Said flow has in the intermediate space S a velocity component in one direction in the axial direction. Thus, as already stated above, there occurs an axial flow in the intermediate space S. Since the axial bores 131 are in communication with the interior space of the roll shell 111 through the ra- dial bores 132,133, the axial flow occurring in the intermediate space S causes that oil flows through the first radial bores 132 into the axial bores 131, in which the flow thus occurs in the axial direction in a direction opposite to that of the intermediate space S. From the axial bores 131, the oil returns into the intermedi- ate space S through the second radial bores 133 provided in the area of the second end of the roll. This arrangement provides a very uniform distribution of heat over the entire roll shell, because the heating oil flows in the axial direction in two di- rections, on the inner surface of the roll shell 111 in one direction and in the axial bores 131 in the opposite direction.

Above, the invention has been described by way of example with reference to the embodiment examples shown in the figures in the accompanying drawing. How- ever, the invention is not limited only to the examples shown in the figures, but the different embodiments of the invention may vary within the inventive idea defined in the accompanying claims.