Ordinarily, tubular rolls of paper machines are mounted or journalled from the ends of the roll mantle by means of rolling-contact bearings on the roll axle. Such a traditional mode of journalling has its advantages, for example, the fact that the Journalling can be accomplished quite simply and so far its cost has been considered to be relatively reasonable. However, this traditional mode of journalling in which the roll mantle is journalled by its ends in a fixed manner on the axle, is not suitable for all applications in paper machines. Indeed, in quite a number of situations, e.g., in variable-crown rolls which are in nip contact with a back-up roll, the roll mantle must be able to move in the radial direction in relation to the roll axle, which is hindered by the traditional end-journalling method. In addition to the fact that, by means of the crown variation means in a variable-crown roll, attempts are made to shape the roll mantle in the desired manner in particular for regulation of, the profile of linear load, the roll ends must also be able to move in the radial direction in relation to the roll axle in order that the profile of linear load may also be controlled in the end areas of the roll. Besides the properties of profile regulation in the end areas of the roll, regulation of the loading in the end areas of the roll also affects the control of the temperatures in the end areas.
For this reason, rolls have also been developed in which the entire roll mantle can move in the direction of the load radially in relation to the roll axle. One such roll is described in the assignee's European Patent No. 0 332 594 of earlier date, in which the end bearings of a variable-crown roll are not mounted directly on the central axle of the roll. Rather, the bearings are arranged on separate annular parts which can move radially in relation to the roll axle. The variable-crown roll in accordance with this publication is a nip roll, and the radial movement of the roll mantle is restricted to the direction of the nip plane. The movement has been accomplished so that, between the annular parts and the roll axle, hydraulic power units are arranged. These hydraulic power units shift the end bearings by means of hydraulic pressure medium effective therein relative to the nip, i.e., toward the nip or away from the nip. A principal objective of this embodiment is the opening and closing the nip. There are also a great number of other rolls of Similar type which produce a substantially similar operation, accomplished with a somewhat different technique.
The use of rolling-contact bearings in a roll also produces considerable drawbacks and/or problems for the manufacture and operation of a roll. It is one particular drawback that the rolling-contact bearings require respective machining of the roll mantle. The wear of the bearings may also produce problems and, further, the rolling-contact bearings impose their limitations in respect of the fluid used in the roll. For example, the following properties can be considered to be drawbacks of the traditional mode of journalling.
1. Limitations of speed: Even at present, the speeds of rotation of the rolls exceed the highest permitted speeds specified by bearing manufacturers.
2. Accuracy of rotation: Further improvement of the accuracy of rotation of an assembled roll with the prior art technology is very difficult. In a traditional roll, even if all the components (bearings, bearing housings, outer face of the mantle) are machined as precisely as possible, the errors are summed up in an assembled roll.
The arrangement of the journalling of the roll mantle by means of glide bearings is also known in the prior art. Such rolls with glide bearings are described, for example, in U.S. Pat. Nos. 5,060,357 and 5,111,563. In the roll in accordance with U.S. Pat. No. 5,060,357, the roll mantle is provided with rolling-contact bearings arranged in the areas of its end pieces, which bearings are arranged on separate annular parts of a type similar to those mentioned in the above-referenced EP Patent No. 0 332 594. The roll is meant to be a nip roll, and its roll mantle can move in the direction of the nip plane in relation to the roll axle, for example, for the purpose of opening and closing the nip. The lateral support of the roll mantle, i.e., the support in the direction transverse to the nip plane, is arranged by means of a complicated construction of glide bearings, by whose means the movement of the roll mantle can be made to take place exactly in the direction of the nip plane. One drawback of this construction is expressly the complexity of the construction, among other things with a number of glide faces and articulated joint arrangements, for which reason its reliability in operation, the controllability, and the dependability of the construction are not considered very good.
In U.S. Pat. No. 5,111,563, an arrangement of support of a roll with glide bearings in the lateral direction is described, which arrangement is simpler than the construction of U.S. Pat. No. 5,060,357 mentioned earlier. In this arrangement, the arrangement of the glide bearings in the lateral direction has, however, been accomplished by means of an arrangement of articulated joints by whose means linear movement of the roll mantle in the direction of the nip plane cannot be produced.
In particular in nip rolls, it is important to be able to produce a linear movement, for example, for the following reasons. If the diameter of the rolls (either the roll with glide bearings or the back-up roll) is changed, the nip point is shifted if the roll mantle does not move along a linear path. If the axle of a variable-crown roll is placed at different levels at the opposite ends, without a linear movement, the rolls that form the nip are placed crosswise. This again produces axial forces, wear of the bearings, felts, etc, changes the structure of the felt, produces picking of the felt, etc., all of which factors have a substantially deteriorating effect on the runnability and on the quality of the paper. A further considerable problem is the passing of so-called fiber "clods" into the nip. If the roll mantle does not perform a linear movement, there is the risk that the force produced by the "clods" has an effect that opens the nip, as a result of which the construction may be broken.