Roll

FIELD OF INVENTION

The invention relates to a roll according to the preamble of claim 1.

The invention also relates to a method according to the preamble of claim 6.

The invention further relates to a belt calender according to the preamble of claim 11.

PRIOR ART

In web-manufacturing machines, there is a great number of rolls which deflect from the effect of load. The deflection impedes the operation of the machine and, thus, one tries to decrease it. The deflection becomes the greater problem the wider the machine is i.e. the longer the roll becomes. A possibility to decrease the deflection is to extend the diameter of the roll, whereby the roll becomes stiffer. However, extending the roll diameter increases the manufacturing costs of the roll and, at many sites, extending the roll diameter is not possible on the grounds of space. When it is not possible to extend the roll diameter, the roll has to be made stiffer in some other way.

FI patent publication 5002 describes a roll in which there are an outer shell and a hollow or closed inner shaft. In the inner shaft, there is a middle part the outer diameter of which is larger than the outer diameter of the other parts of the inner shaft and the outer shell is combined by shrinking in the middle part of the inner shaft. The outer shell consists of two tubes which have an inner end and an outer end. The inner diameter of the tubes is larger at the point of the inner ends of the tubes compared to the other part of the tube, whereby the wall thickness of the

tubes is thinner at the point of the inner ends of the tubes. The larger inner diameter of the inner ends of the tubes is equal to the outer diameter of the middle part of the inner shaft and the totalled length of the sections having a larger inner diameter of the inner ends in the axial direction is equal to the length of the middle part having a larger outer diameter of the inner shaft in the axial direction. The inner ends of the tubes are welded together so that the middle part of the inner shaft is compressed between the shoulders of the thinned part of the outer shell. In this arrangement, the inner shaft and the outer shell are thus fixedly together. This structure aims at decreasing the deflection of the roll i.e. the roll is made stiffer.

WO publication 01/83884 describes a belt calender in which a metal belt is arranged as an endless loop by means of guide rolls. The metal belt is further arranged to pass through a calendering nip between a loading roll and a counter roll. The counter roll can be a thermo roll or a polymer roll. The loading roll can be a shoe roll or a roll with a hard surface, whereby against the outer shell of the hard- surfaced roll there is a compressible belt in the nip.

Prior-art arrangements have not described a simple way to compensate the deflection of a nip roll in a calender or a press or a belt guide roll in a belt calender. For example, the deflection of the belt guide roll of the belt calender from the centre due to the loading of the belt means that the metal belt is tight on the edges and loose from the centre, whereby the metal belt slides on the surface of the belt guide roll. The sliding of the metal belt on the surface of the belt guide roll wears the thin metal belt, whereby its lifetime will be shortened.

SUMMARY OF INVENTION

The object of the present invention is a roll in which deflection compensation is implemented in a simple way.

The characteristic features of the roll according to the invention are presented in the characterising part of claim 1.

The characteristic features of the method according to the invention are presented in the characterising part of claim 6.

The characteristic features of the belt calender according to the invention are presented in the characterising part of claim 11.

In the roll according to the invention, there is a shaft which consists of a cylindrical middle part and shaft journals at the ends of the middle part. The shaft is ro- tatably supported from its shaft journals to end bearings. The middle part of the shaft is crowned and on top of the middle part of the shaft is fitted a cylindrical shell.

As a result of the crowning of the middle part of the shaft, the roll according to the invention becomes deflection-compensated. In an unloaded situation, the inner surface of the shell is fast on the outer surface of the middle part of the shaft at the centre of the middle part, but at the ends of the middle part there is a small gap between the inner surface of the shell and the outer surface of the middle part of the shaft. When the roll shell is loaded from outside e.g. by another roll, the middle part of the shaft starts to deflect from the centre and, in a certain load, the deflection is of such quantity that the inner surface of the outer shell comes for the whole travel fast on the outer surface of the middle part of the shaft, whereby the outer surface of the shell is straight at the load point. The crowning of the roll can be dimensioned such that the outer surface of the shell becomes straight in desired load conditions.

The belt calender according to the invention comprises at least two belt guide rolls, a metal belt loop guided by the belt guide rolls, and a thermo roll being out- side the metal belt loop, which thermo roll and metal belt form between them an

extended calendering zone. Said at least two belt guide rolls or said thermo roll or both are deflection-compensated rolls.

The invention will next be described by referring to the enclosed figures, without limiting the invention solely to what is shown in the figures.

BRIEF DESCRIPTION OF FIGURES

Fig. 1 shows a roll according to the invention.

Fig. 2 shows a belt calender in which the roll according to the invention can be used in different positions.

DESCRIPTION OF ADVANTAGEOUS EMBODIMENTS

Fig. 1 schematically shows a roll according to the invention. The roll comprises a shaft 12 which consists of a cylindrical middle part 12c and end parts 12a, 12b at both ends of the middle part 12c. The middle part 12c of the shaft 12 is crowned. The end parts 12a, 12b operating as shaft journals are bearing-mounted in end bearings 13 a, 13b. On top of the middle part 12c of the shaft 12 is fitted a cylindrical shell 11 which is supported from its both ends by means of end pieces 20a, 20b to the ends of the middle part 12c of the shaft 12. Each end piece 20a, 20b is fastened with bolts 21b at the ends of the shell 11. Each end piece 20a, 20b is further sealed 31b at the end ofthe shell 11 and the shaft journal 12b. Each end piece 20a, 20b is thus fitted around the shaft journal 12a, 12b so that the fitting allows a small radial movement. The end pieces 20a, 20b move along the shell 11 slightly radially in relation to the shaft journals 12a, 12b in a situation in which an outside load is exerted on the shell 11.

Through the first shaft journal 12a of the shaft 12 is formed a first channel 40 which axially extends to a distance from the second end piece 20b where it di-

verges into several radial channels 41. These radial channels 41 open to a space between the middle part 12c of the shaft 12 and the shell 11. Through the first shaft journal 12a of the shaft 12 is further formed a second channel 50 which surrounds the first channel 40 and which axially extends inside the first end piece 20a at the point of the first shaft journal 12a where it diverges into radial channels 51. Also these radial channels 51 open to the space between the middle part 12c of the shaft 12 and the shell 11. Along the first channel 40, it is possible to feed oil into the space between the middle part 12c of the shaft 12 and the shell 11 close to the second end piece 20b from which the oil is guided along grooves on the outer sur- face of the middle part 12c of the shaft 12 towards the first end piece 20a from which it is guided out of the roll along the second channel 50. The first channel 40 can consist of a tube. Instead of straight or spiral-like grooves formed on the outer surface of the middle part 12c of the shaft 12, it is possible to provide the outer surface of the middle part 12c of the shaft 12 with straight or spiral-like bronze strips. Between the bronze strips, grooves or channels for oil are formed. The crowning of the middle part 12c of the shaft 12 can then be implemented with machining the bronze strips.

As a result of the crowning of the middle part 12c of the shaft 12, the roll according to the invention becomes deflection-compensated. In an unloaded situation, the inner surface of the shell 11 is fast on the outer surface of the middle part 12c of the shaft

12 at the centre of the middle part 12c, but at the ends of the middle part 12c there is a small gap between the inner surface of the shell 11 and the outer surface of the middle part 12c of the shaft. When the roll shell 11 is loaded from outside e.g. by another roll, the middle part 12c of the shaft 12 starts to deflect from the centre and, in a certain load, the deflection is of such quantity that the inner surface of the outer shell 11 comes for the whole travel fast on the outer surface of the middle part 12c of the shaft 12, whereby the outer surface of the shell 11 is straight at the load point.

The crowning of the roll can be dimensioned such that the outer surface of the shell 11 becomes straight in desired load conditions.

The roll illustrated in Fig. 1 can be used as a tliermo roll in a calender. By means of the channel arrangement formed in the inner shaft and the grooves on the outer surface of the middle part of the inner shaft, oil circulation can be arranged in the roll. By using hot oil, the shell of the thermo roll can be heated to a desired temperature. The arrangement according to the invention is not limited solely to a thermo roll but it can be used in a non-heatable roll, in which case the channel arrangement is not required.

Fig. 2 shows a belt calender in which the roll according to the invention can be used in different positions. The applicant markets the belt calender shown in the figure by registered trademark ValZone. The belt calender comprises a metal belt loop 140 which is guided by guide rolls 131, 132, 133. The metal belt 140 rotates a first thermo roll 120 being outside the metal belt loop and forms an extended calendering nip Nl with the first thermo roll 120. The two lowest guide rolls 131, 132 of the metal belt loop 140 are also advantageously thermo rolls by which the metal belt 140 is heated. Inside the metal belt loop 140, a deflection-compensated Sym roll 110 is fitted by which the metal belt 140 is loaded against the thermo roll 120. The web W passes between the outer shell of the first thermo roll 120 and the metal belt 140. With such an arrangement is provided an extremely long calender- ing zone Nl, advantageously about one metre long in the machine direction. Due to long dwell time, high temperature, extensive pre-damping and low nip pressure, the web W becomes plasticised, whereby good smoothness and printability are formed in the web W. Also the flexural rigidity and bulk of the web W remain good. The calendering effect is simultaneously exerted on both surfaces of the web W, due to the hot metal belt 140 on one side of the web W and the hot thermo roll 120 on the opposite side of the web W. The calendering zone Nl is divided into three stages i.e. a pre-processing stage, a compression stage and a finishing stage. Heat transfer in the web W is here very efficient, whereby the web W can be pre-damped to dampness greater than normal before the calender.

In the belt calender according to Fig. 2, the roll according to the invention can be used as the first tliermo roll 120 or as the guide roll 131, 132, 133 of the metal belt 140 of the belt calender. The roll according to the invention can naturally be used in different kinds of belt calenders in similar positions.

The temperature of the first thermo roll 120 of the belt calender and the metal belt 140 shown in Fig. 2 can be kept in the range of 150-200 degrees Celsius due to the long dwell time.

The roll according to the invention can also be used in a press as a second roll of the press nip.

The middle part 12c of the shaft 12 of the roll according to the invention can be hollow or closed.

In the roll according to the invention, small sliding occurs between the outer surface of the middle part of the shaft and the inner surface of the shell but this is not a great problem. The middle part of the shaft and the shell endure such wear well without any great problem arising from it. In a situation in which the roll according to the invention is used as a thermo roll, heating oil passing between the outer surface of the middle part of the shaft and the inner surface of the shell simultaneously lubricates the surfaces so that the wear of the surfaces remains small. In a situation in which the roll according to the invention is not a thermo roll, it is possible to arrange suitable lubrication between the outer surface of the middle part of the shaft and the inner surface of the shell for decreasing the wear of the surfaces.

The roll according to the invention is advantageously manufactured such that the shaft is of cast iron and the shell is of structural steel. The metal belt of the belt calender is advantageously of thin, 0.8 mm thick steel material which endures tensile stress well and the surface properties of which correspond to the surface properties of the thermo roll.

The invention was described above by way of examples with reference to the figures of enclosed drawings. The invention is not, however, limited to what is presented in the figures, but different embodiments of the invention can vary within the scope defined in the enclosed claims.