GB2041161A - Rollers - Google Patents

Abstract

The invention relates to a roller for paper machines, of the kind having a rotatable hollow casing 1 supported by at least one pressure shoe 10 acting against the casing and at least one piston 5 projecting into the latter and braced against a cross-beam 2. The invention is characterised in that the piston 5 is located spherically via annular sealing surfaces 4a against the cross-beam 2, and that in the space between the piston 5, the cross-beam 2 and the sealing surface 4a a pressure acts which considerably reduces or cancels out the pressure of the piston on the sealing surface. Oil may be fed to the space via a duct 3 and to pockets 15 of the shoe 10 via capillaries 4. Preferably, an intermediate ring 4 is fitted between the piston 5 and the cross-beam 2 and may be displaced spherically relative to the piston and linearly relative to the cross-beam 2 in a plane approximately perpendicular to the pressing direction of the piston. <IMAGE>

Description

SPECIFICATION A roller, especially a pressing roller for paper machines The invention relates to a roller, especially a pressing roller for paper machines, of the kind having a rotatable hollow casing and a supporting device which supports the casing and has at least one pressure shoe acting against the casing and at least one piston projecting into the latter and supported against a crossbeam.

For a number of years, in order to achieve the desired distribution of pressure in the gap between two rotating rollers, devices to influence the uniformity of the supporting of a roller casing over its lengths via supporting means provided inside the latter which are held in turn by a cross-beam which does not rotate with it have been used. By means of such arrangements it is possible to eliminate bowing of the roller casing under load, and even to compensate for the bowing under load of a counter-roller, and to achieve uniform pressing across the width which is independent of line pressure. There are also arrangements which make possible variously strong pressure across the width, using individual hydraulic cylinders.However, since the cross-beam bends under the loading of the hydraulic cylinder, and also since a shifting of the cross-beam relative to the casing perpendicular to the pressing line may arise, the known rollers of this kind are constructed so that the pistons are braced against the casing via a cylindrical pressure surface, and are located in their angular position and are spherically movable in the hydraulic cylinder (German Laid-Open Patent Specification No.

22 30 139), or else a universal joint is provided between the piston which moves in a straight line and the bearing part (German Laid-Open Patent Specification No. 22 45 597).

The first of these constructions (German Laid-Open Patent Specification No. 22 30 139) has the disadvantage that the seals on the piston are detrimentally stressed by the additional spherical movement, so that their working life is shortened in an undesirable way, which reduces the accuracy of the pressure and may result in frequent stoppage for maintenance.

The second design (German Laid-Open Patent Specification No. 22 45 597) with the universal joint requires hydraulic venting of the universal joint to prevent excessive friction. However, this device is crude, and results in an undesirable weakening of the cross-beam and this in a limitation of the line pressure and a loss of adjustability for thebowing of the roller.

An object of the present invention is to provide an internal support between the stationary cross-beam and the rotating casing of a roller, which may be adjusted to give a variously strong effect across the width, but has a maximum working life, precision and reliability in operation and avoids the disadvantages of the designs known hitherto.

According to this invention a roller of the kind referred to hereinbefore is characterised in that the pistons are located against the cross-beam spherically adjustable via annular sealing surfaces and that a pressure which considerably reduces or cancels out the pressure of the piston on the sealing surface acts in the space between the piston, the crossbeam and the sealing surface. The main concept of the invention thus consists in separating the functions of pressing and of spherically movability, and in providing optimally designed and arranged elements.

In this instance, pressure shoes which are adapted to the contour of the inner surface of the roller are provided on their radially inner face with cylindrical bores in which pistons slide which are in turn located against the cross-beam spherically-adjustable on annular sealing surfaces and a pressure is applied between the cross-beam, the piston and the sealing surface which considerably reduces or cancels out the pressure of the piston on the spherical annular sealing surface.

By this means it is ensured that the piston seals slide cylindrically and thus with little wear, and a tilting movement of the pressure shoe for the purpose of compensating any inclination between the roller casing and the cross-beam can be carried out with little friction and free from wear.

This ensures troublefree, longterm operation without problems or wear.

The application of pressure on the roller casing via individual shoes across its width entails the problem of local differences. In order to eliminate these, a further concept makes provision for several pistons arranged axially adjacent to each other on the crossbeam to act on a common elongated pressure shoe in the form of a bar which, although it has so little inherent rigidity that it readily adapts across its width to the contour of the cylinder, is still rigid enough to prevent a stronger bowing of the bar between two pistons. The surface of the pressure shoe which faces radially outwards is directed against the casing as a cylindrical supporting surface.

Due to the bowing of the cross-beam, the piston distance varies slightly so that the pistons might jam in the cylinders when there were strong bowing of the cross-beam, if they were rigidly located on the cross-beam.

For this reason, and also to widen the required production tolerances, provision is also made for constructing the spherical surface which supports the piston leak-tight as the upper face of a ring which can slide in turn in a sealing plane approximately perpen dicular to the direction of the piston force, relative to the cross-beam. A pressure prevails inside the ring which corresponds approximately to that in the cylinder, and the ring surfaces loaded with this pressure both opposite the piston and also opposite the crossbeam are approximately the same size as the piston surface, preferably about 0.7 to 1.2 times as large as the latter.

According to another concept, the pressure shoe is prevented from becoming displaced in the roller direction not by the piston itself but by appropriate guide surfaces in the crossbeam. This means that the sliding surfaces between the piston and the cylinder are relieved and protected from excessive one-sided rubbing. The working life of the seal is increased thereby.

A further concept provides for the pistons to be linked to the cross-beam, with or without intermediate provision of a free, displaceable ring, so that, although they may be adjusted perpendicular to the axis and angularly, they cannot lift up radially from the cross-beam on the other face. The articulated connection provides only enough play to make possible easy movement within the required range, but no substantial lack of sealing at the sealing surface can arise.

In one modified embodiment, the substantially cylindrical, radially outer surface of the pressure shoe is constructed as a sliding bearing.

Lubrication of the sliding surface can be effected by oil introduced directly into the casing, or by pressure oil which reaches the sliding surface from the sylinders loaded with oil via ducts in the pressure shoe.

According to another concept of the invention, however, provision is also made for the pressure shoe to act against the roller casing as a hydrostatic bearing. For this purpose, in the cylindrical surface facing the casing it has oil pockets which are connected via capillaries with the interior of the cylinder arranged below. The pockets are arranged so that the shoe positions itself in a known way, selfcentred on the surface of the roller casing.

It is also advantageous to load individual cylinders or groups of cylinders with pressure which can be adjusted independently of the other cylinders. By this means, the shape of the bowing of the casing may be caried according to requirements.

In order to keep oil consumption at a minimum, provision is also made to incorporate elastic seals, such as O-ring seals, for example, between the piston and the support ring, and between the support ring and the crossbeam. In order that the invention may be readily understood, various embodiments of roller in accordance therewith will now be described, with reference to the accompanying drawings, in which: Figure 1 is a partial cross-section through a roller with round support elements distributed across the width.

Figure 2 is a partial cross-section through a roller with round pistons and elongated pressure shoes which extend over several pistons.

Figure 3 is a partial longitudinal section through the pressure roller shown in Fig. 2.

Figure 4 is another longitudinal section through a roller with pressure shoes as in Fig.

2 and 3. Only half the roller is shown.

Fig. 1 shows a rotatable roller casing 1 and a stationary cross-beam 2, which passes through the roller casing 1 and is supported on either side against a machine frame or rocking levers. A fluid pressure medium is supplied from outside the roller through a bore 3. This is preferably oil, and will be called such in the following text.

The oil flows through a spherical intermediate ring 4 which rests on the cross-beam 2 via a lower, planar sealing surface, and positions a piston 5 located above it via its spherical upper sealing surface 4a. The piston 5 and the intermediate ring 4 are linked to the crossbeam 2 via a screw 6 in such a way that although the piston 5 can move easily spherically relative to the intermediate ring 4, lifting from the cross-beam 2 is prevented. Sealing rings 7 and 8 prevent the uncontrolled escape of oil in the gaps in the sealing surfaces between the cross-beam 2, the intermediate ring 4 and the piston 5. Piston rings 9 prevent oil from escaping between the piston 5 and a pressure cylinder constructed as a pressure shoe 10. The pressure oil passes from the bore 3 through ducts 11 and 12 to arrive in a pressure chamber 13, and presses the shoe 10 against the casing 1.A small amount of oil is fed via capillaries into bearing pockets 1 5 in the shoe 10. The pressure medium in the bearing pockets 1 5 forms a friction-free bearing and centres the pressure shoe 10.

The surface of the pressure shoe 10 which is in the shape of a cylindrical section and faces the roller casing 1 contains, for example, three or four bearing pockets 1 5 arranged centre-symmetrical with the cylinder axis, each of each is fed with pressure oil via a capillary 14. The surface of the bearing pockets directed towards the roller casing is larger than the surface of the piston 5 in the pressure chamber 1 5. Accordingly, the pressure shoe 10 is lifted hydrostatically from the roller casing 1 as soon as a sufficiently high oil pressure has arisen in the pockets 1 5. A gap is created between the casing 1 and the pressure shoe 10 through which oil flows continuously. This oil is conducted out again from the roller via return ducts which are not shown, and is supplied through the ducts 3 again via a pressure-raising pump.

In Fig. 2 the elements described in Fig. 1, or elements with a corresponding function, are identified again with the same numbers.

However, in Fig. 2 provision is made for the holding of the pressure shoe 10 against displacement relative to the cross-beam 2 perpendicular to the pressure direction not to be effected via the intermediate ring 4 but directly against the cross-beam, on surface 1 6.

The intermediate ring 4 can be displaced against the cross-beam 2.

The pressure shoe 10 may extend across the entire length of the roller as a continuous bar, or it may be divided up into smaller subsections each supported by several pressure pistons 5 (Figs. 2 to 4), down to a single shoe 10 to each pressure piston 5 (Fig. 1). In the embodiment shown in Fig. 2, the pressure shoe 10 is constructed elongated and extends parallel to the axis of the roller. In Figs. 2 and 3 the cross-beam 2 has a continous longitudinal groove for accommodating the elements 4, 5 and 10. Unlike this, in the embodiment shown in Fig. 1 the pressure shoe 10 seated on a single piston 5 has a round cross-section and it has an extension of the cross-section in the pressure contact zone at the pockets 1 5.

Fig. 3 is a longitudinal section through the arrangement shown in Fig. 2, along the section line Ill-Ill. In this case again, parts analogous to those in Figs. 1 and 2 are designated with the same numbers. The oil return is effected via ducts 1 7 in the pressure shoe 10 and through hollow chambers 1 8 in return flow ducts 1 9.

In Fig. 4 the elements already described in Figs. 1 and 2 are again designated with the same numbers. Identically drawn depiction means the same numbers apply. The pressure shoe 10 is not shown detailed, and smaller details which are shown in Figs. 2 and 3 are not shown.

The roller in Fig. 4 contains a plurality of elongated pressure shoes 10 arranged adjacent to each other, which are each pressed on by several pistons 5 via the oil pressure in the chambers 13.

The roller casing 1 is connected rotatably at its ends to the cross-beam 2 via roller bearings 20. The lateral closing of the bearing chamber is effected by covers 21 which contain sealing rings 22 which seal by rubbing against the cross-beam 2 via an elastic sealing lip. The cross-beam 2 is supported pivotably in the bearing block 24 via a spherical bearing ring 23. Positioning devices which are not shown, disposed between the cross-beam 2 and the bearing block 24, determine the relative angular position between the crossbeam 2 and the bearing block 24. The roller casing 1 is either driven by a counter-roller or by a web running over it. or in a known way via a toothed gear or via the central ring of a three-ring roller bearing.

The pressure oil is introduced into the pressure elements 4, 5, 10 via a collecting line 25 and branch lines 3. The roller shown in Fig. 4 has only one common pressure source for all the pressure elements. However, it is often expedient to connect the pressure elements in groups across the width to individually adjustable pressure sources. The pressure-less, leaked oil is swept off the pressure shoes 10 and passes through the ducts 1 9 into the return line 26.

Claims (11)

1. A roller, especially a pressing roller for paper machines, of the kind having a rotatable hollow casing and a supporting arrangement which supports the casing and has at least one pressure shoe acting against the casing and at least one piston projecting into the latter and braced against a cross-beam, characterised in that the piston is located spherically adjustable via annular sealing surfaces against the cross-beam, and that in the space between the piston, the cross-beam and the sealing surface a pressure acts which considerably reduces or cancels out the pressure of the piston on the sealing surface.

2. A roller according to Claim 1, characterised in that several pressing shoes are combined to form a pressing bar extending over a plurality of pistons.

3. A roller according to Claim 1 or 2, characterised in that an intermediate ring is fitted between the piston and the cross-beam and may be displaced spherically on one side opposite the piston and on the other side opposite the cross-beam in a plane approximately perpendicular to the pressing direction of the piston.

4. A roller according to one of Claims 1 to 3, characterised in that the pressure shoes or the pressing bars are held against displacement in the circumferential direction of the roller by guide surfaces provided on the crossbeam.

5. A roller according to one of Claims 1 to 4, characterised in that the piston or pistons are articulated on the cross-beam spherically movable, but cannot lift off therefrom.

6. A roller according to one of Claims 1 to 5, characterised in that the pressure shoes or pressure bars are constructed as sliding bearings opposite the casing.

7. A roller according to one of Claims 1 to 5, characterised in that the pressure shoes or pressure bars are constructed as self-locating hydrostatic elements.

8. A roller according to one of Claims 1 to 7, characterised in that the pressure chambers above and below the piston are each fluidconnected to external pressure sources via ducts in the cross-beam.

9. A roller according to Claim 8, characterised in that individual pressure chambers or groups of pressure chambers may be loaded with pressure which can be adjusted as re quires.

10. A roller according to one of Claims 1 to 9 characterised in that the sealing surfaces contain elastic sealing elements.

11. A pressing roller for paper machines constructed, arranged and adapted for use substantially as hereinbefore described with reference to Figs. 1, 2 and 3, or 4 of the accompanying drawings.