GB2061456A - Pressure Rollers - Google Patents

Abstract

A hollow pressure roller (11) for use in treating flexible sheet material such as paper, surrounds a stationary shaft (12) with an intervening gap, and the shaft is allowed to bend under load, the roller shape being controlled by providing two parallel fluid seals (13) between the shaft and the roller, angularly spaced around the shaft axis, and supplying pressure fluid to the gap on one side of the roller axis. Each seal comprises a rocking element (30) pivotally engaging the shaft, and having an edge (32) engaging the internal surface of the roller, and means (34) providing a seal between the element and the shaft. Each rocking element is so formed that the resultant pressure forces either pass through the rocking axis or are balanced on opposite sides of the axis, thus reducing the bearing force (S) on the roller. Each rocking element is urged to engage the roller by a controlled force (Q) provided by fluid pressure or springs. <IMAGE>

Description

SPECIFICATION Pressure Rollers This invention relates to hollow pressure rollers as used in the pressure treatment of webs or strips of material, for example in calendering paper.

Such pressure rollers are often subject to very considerable loading, which can cause the roller itself to distort and lose its true cylindrical profile.

This has undesirable effects on the web being treated. One method of correcting the situation is to shape the pressure roller initially out of true so that under the heavily applied load the effective part of its surface then becomes truly cylindrical.

A great disadvantage of this is that the specially modified shape can only be suitable for one particular set of conditions. Also, the production of such a shaped roller is most expensive.

Another known solution is to mount the hollow pressure roller on an internal shaft with a gap between the two. Lip seals formed at opposite sides of the shaft engage the internal surface of the roller and liquid under pressure is supplied to the gap above or below the seals according to the path of the web. This pressure tends to hold the pressure roller equally supported along its length so that a true cylindrical roller can be used and its shape will be maintained. The internal shaft being supported only at opposite ends will tend to bend, but this is a relatively minor problem.

In such internal pressure support systems it has been proposed to use lip seals which include an L-shaped rocking member and a leaf spring fixed to the body of the shaft and bearing on the short radial flange of the L. A disadvantage of this is that the radial force exerted between the rocking seal and the inner surface of the roller depends largely on the fluid pressure in the gap.

This is most undesirable. It is preferred that there should be a controlled slow fluid leakage through the gap, but it is also desirable that the frictional forces at the seal should be reduced as much as possible. Also, in the previous system referred to any wear at the rubbing lip of the seal caused a change in geometry and the spring force urging the seal against the pressure roller also varied from this geometry change.

It is an object of the invention accordingly to provide an improved sealing arrangement in such a pressure roller, which will reduce or eliminate at least some of the existing disadvantages.

The invention is particularly applicable to the type of hollow pressure roller which is mounted on an internal shaft with an intervening gap and including two seals at angularly spaced positions around the axis, each seal including a rocking element extending parallel with the axis and having a pivoted or rocking connection with the shaft, a part connected thereto engaging the internal surface of the roller, and a fluid pressure seal between the element and the shaft.

From one aspect the invention consists in a pressure roller of the type referred to in which the parts are so designed that a substantial part of the forces applied to the rocking element pass effectively through the pivotal axis or are at least partly balanced on opposite sides of the axis.

From another aspect the invention consists in a pressure roller of the type referred to in which the rocking element is urged towards the internal surface of the roller by an elongted flexible pressure conduit to which a pressure fluid is supplied from an external source.

From yet another aspect the invention consists in a pressure roller of the type referred to in which the rocking element has an exposed pressure face on which the pressure fluid in the gap reacts, which is substantially concentric with the pivotal axis of the element, or has a plurality of sloping facets tangential to such a concentric cylinder.

Conveniently the seal between the rocking element and shaft includes a strip or flap, or spring, which also engages the concentric surface.

The rocking element may be of various different cross-sectional shapes, but is preferably of T-shape or L-shape.

Preferably the rocking element is urged towards the inner surface of the pressure roller by a plurality of of small hydraulic rams.

Thus, the invention enables the resultant force caused by the hydraulic pressure loading and spring seal to be reduced or eliminated, so that the applied load at the actual seal contact line can then be controlled and adjusted independently.

The invention may be performed in various ways and one specific embodiment with several possible modifications will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a sectional side elevation through a hollow pressure roller of the general type to which the invention applies, and Figure 1A is a crosssection, Figure 2 is a similar sectional side elevation illustrating the bending of the central shaft under pressure, Figure 3 is a fragmentary sectional end elevation through an existing form of seal, Figure 4 is a similar sectional end elevation through one form of seal according to the invention, Figure 5 is a similar cross-section through the preferred form of seal according to the invention, Figure 6 is a similar view illustrating the seal of Figure 5 in position on the central shaft, Figure 7 is a view similar to Figure 6 illustrating another embodiment, Figures 8, 9, 10, 11, 12 and 13, are similar sectional end views illustrating further possible modifications.

Referring to the hollow pressure roll assembly illustrated in Figures 1 and 2, the hollow pressure roll 11, which may be of considerable length, is mounted over a central solid shaft 12 with selfaligning bearings 1 5 and part spherical supports 16 at each end. An axially extending seal 13 is provided along each side of the central shaft to engage the internal surface of the pressure roller, as shown in Figure 1A. Also, annular end pressure seals 14 are provided at each end of the shaft engaging the roller, thus forming a part cylindrical pressure chamber above or below the seals into which pressure fluid can be directed via a pressure conduit within the shaft itself.

Figure 2 illustrates the situation which occurs when a web (not illustrated) is in position around the upper part of the pressure roller 11 and the reaction of other pressure rollers above applies a heavy downward pressure loading illustrated by P. Hydraulic pressure admitted through the centre of the shaft 12 may be arranged to apply a substantially equal pressure loading p below the upper part of the pressure roller. This reduces or eliminates any tendency for the upper part of the roller to distort under the applied external load.

The hydraulic pressure reacts on the central shaft and causes this to distort away from the pressure roller, as shown in exaggerated form in Figure 2.

The applied external load is resisted and sustained by the supports 16. Since the central shaft will deform it will be appreciated that the line of each seal 13, as seen in Figure 2, will no longer be straight and the seal must accommodate this small deviation.

Figure 3 illustrates an existing form of seal as used for this purpose. A rocking L-shaped seal element 20 has one limb retained in a groove 21 in the central shaft 12 and the other limb 22 engages the internal surface 23 of the pressure roller 1 The element is urged in an anticlockwise direction by a leaf spring 24 whose tip applies a downward force R' on the upper limb of the element. This leaf spring being held in position in a groove in the shaft by a fixing block or wedge 25. The leaf spring 24 runs the whole length of the seal and itself acts as a fluid pressure seal between the element 20 and the shaft 12.

In this construction it will be seen that the pressure p of the hydraulic fluid in the gap 26 between the shaft and roller acts downwards on the limb 22 and also on the flexible leaf spring 24 and the resultant force creates an anti-clockwise moment T' which causes the tip of the limb 22 to bear against the roller surface 23 with an applied force S. It is desirable that there should be a controlled slow leakage of oil past this sealing position, but the flow rate should be limited and it is also most desirable that the frictional resistancce should be minimised since it causes wastage of considerable horsepower in driving the roller. A disadvantage of this known sealing arrangement is that the applied sealing force S depends largely on the hydraulic pressure fluid p and if large hydraulic pressures are necessary the applied force S can become excessive.Likewise, the spring reaction force R' also creates a component force on the seal which cannot be adjusted to suit different conditions.

In the form of seal according to the invention illustrated diagrammatically in Figure 4, the sealing element 30 is of T cross-section with an upstanding limb 31 having a point at its lower end which fits in a groove in the central shaft and acts as a fulcrum. The cross flange of the T has one limb 32 extending towards the inner surface of the pressure roller and another flange 33 extending in the opposite direction. A leaf spring 34 bears down on the upper face of the cross flange. This construction has the valuable advantage that the hydraulic pressure forces acting downwards on the rocking element and the leaf spring can be at least partly balanced on either side of the centre-line 35.In the arrangement illustrated, the vertical force on the seal element produced by the leaf spring 34 is offset slightly to one side of the centre-line 35, but it may be positioned on the centere-line if desired. To rock the element 30 towards the face of the pressure roller an independent controlled force 0 is then applied to the limb 30 by an appropriate control means, thus creating a sealing force S which can be independent of the applied pressure loading.

Figure 5 illustrates the preferred form of seal according to the invention in which the rocking element of the seal has a limb 40 with a lower end 41 located in a groove 42 of the central shaft, to act as a pivot of fulcrum, and an upper limb 43 with an upper surface 44 which is part cylindrical and concentric with the pivot axis afforded by the parts 41,42. The applied fluid pressure p thus acts on the limb 43 producing a resultant which passes directly through the pivotal axis. Hence it provides substantially no resultant force at the seal S. The leaf spring seal 46 also engages this part cylindrical surface 44 and produces a reaction R which when the seal is stationary also passes through the same pivotal axis and likewise creates no reaction at S. To urge the seal into engagement with the roller surface an independently controller adjustable force 0 is applied to the limb 40.

It will be appreciated that in theory the crosssectional shape of the sealing element is immaterial provided that its upper surface 44 is concentric with its pivotal axis. The element may, for example, be a solid cylindrical sector.

Figure 6 illustrates a seal of the type illustrated in Figure 5, positioned on a shaft 12 to engage the internal surface of the pressure roller 11. Here the controlled force 0 is applied by a series of small hydraulic pressure rams 47 spaced along the length of the shaft, and each supplied with pressure fluid via radial passages 48 from a lengthwise manifold 49. The leaf spring seal 46 is held in position by a fixed strip 45 bolted in position.

Figure 7 illustrates another slight modification of the same construction. Here the rocking seal element 50 is of T-shape, but the upper surface 51 is part cylindrical and concentric with the pivot axis 52, thus affording the same advantages as previously mentioned with reference to Figure 5.

In this arrangement the seal element is urged towards the pressure roller by a series of miniature hydraulic rams 53, supplied from a manifold 54 which is closed by a cover strip 55, which also acts as a clamp for the leaf spring seal 56. In other respects the construction is similar to that of Figure 6.

The embodiment illustrated in Figure 8 is in some respects similar to that of Figure 4. The sealing element is formed from two separate strips 61,62 secured by bolts 63 which clamp the upper edge of a flexible leaf spring support 66 whose lower end is anchored to the shaft by an anchorage strip 67 secured by bolts 69. A flexible sealing strip 64 is also clamped between the two parts 61,62 and wrapped around a curved profile on the shaft and fixed by studs 65. The hydraulic pressure forces on the assembly act downwards on the strip 61, and on the seal 64.The face F of the sealing strip 61 has two inclined facets which are so arranged relative to the pivot point P of spring 66 that the hydraulic pressure forces exert both a clockwise turning moment and a counterbalancing anticlockwise moment, thus reducing or eliminating a pressure-dependent force at the contract line between the strips 61 and the pressure roller.

The embodiment of Figure 9 is in basic principle similar to that of Figure 8, but the construction is simplified. The sealing element 71 is a one-piece extrusion and the flexible supporting strip 74 is located as a simple press-fit in a groove in the shaft. The sealing strip 72 is bonded to the element 71 and fixed to the shaft by a wedge block 73.

In the embodiment of Figure 10 the sealing element 81 is of T cross-section, as illustrated in Figure 4, and the sealing strip 82 is held in position by a wedge block 83 secured by bolts 84.

In the embodiment of Figure 11, the rocking seal element 91 has oppositely sloping upper faces which largely resemble the counterbalancing T profile of Figure 4 combined with the force eliminating effect of Figure 5 due to the reaction forces passing close to the pivot p. A leaf spring 93 bears on the seal element, the spring being located by a clamping strip 94, secured by set screws 96. In addition, there is an auxiliary bellows seal 92 between the sealing element and a groove in the central shaft.

In the diagrammatic illustration of Figure 12, the rocking seal element 101 has a flange F' extending towards the pressure roll and a further flange F2, which provides a bearing seat engaging a resilient flexible pressure tube 102. The assembly is held in place by a series of studs 103.

Pressure fluid to the tube 102 is supplied via a passage or manifold 104. By appropriate dimensions of the flanges F',F2, the pressure reaction of the fluid in the gap above the seal can be arranged to pass through the fulcrum p thus eliminating any component at the seal 101. The sealing force is thus controlled independently by the flexible pressure tube 102.

In the embodiment of Figure 13, the rocking seal element 110 has a T cross-section thus counter-balancing the applied pressure forces above and a rear flange on this element is secured to a loading strip or seal 112 lying within an elongated groove in the shaft, which also acts as a hydraulic pressure chamber 114 to control and adjust the loading at the pressure line 111.

Thus it will be appreciated that all these embodiments of the invention reduce or eliminate the forces at the contact line of the seal created by the hydraulic pressure in the gap and the spring and seal forces acting on the seal element.

The main sealing load can thus be controlled independently and, in particular, can be held at a low level consistent with the need for limiting the escape of oil past the seal.

The invention also has the valuable advantage that the loading forces applied at the two seals can be different. It will be appreciated that if both seals are inserted in the same upright attitude, one will act as a leading edge seal, and the other as a trailing edge seal. The dynamic conditions will be different and it may be of advantage to apply different loading. For this purpose, of course, independent fluid pressure supply lines will be needed within the central shaft to each set of miniature hydraulic rams, or graded mechanical springs may be used instead.

Claims (8)

Claims

1. A hollow pressure roller mounted on an internal shaft with an intervening gap, and including two axially extending fluid seals at angularly spaced positions around the axis, each seal including a rocking element extending parallel with the axis and having a pivoted or rocking connection with the shaft, a part connected to each rocking element engaging the internal surface of the roller, a fluid pressure seal between each element and the shaft, and means for introducing fluid under pressure into the gap between the roller and the shaft, the arrangement being such that a substantial part of the fluid pressure forces applied to each rocking element pass effectively through its pivotal axis or are at least partly balanced on opposite sides of the said pivotal axis.

2. A hollow pressure roller according to claim 1, in which each rocking element has an exposed pressure face on which the pressure fluid in the gap reacts, and which is substantially concentric with the pivotal axis of the element, or has a plurality of sloping facets tangential to such a concentric cylindrical surface.

3. A hollow pressure roller according to claim 2, in which the seal between the rocking element and shaft includes a strip or flap, or spring, which also engages the concentric surface of the element.

4. A pressure roller according to claim 1, or claim 2, or claim 3, in which the rocking element is of generally T-shape or L-shape in crosssection.

5. A pressure roller according to any of the preceding claims, in which the rocking element is urged towards the internal surface of the pressure roller by a plurality of spaced hydraulic rams.

6. A hollow pressure roller according to any of the preceding claims, in which at least one of the rocking sealing elements is urged towards the internal surface of the roller by means of one or more axially spaced springs cooperating with the internal shaft.

7. A hollow pressure roller mounted on an internal shaft with an intervening gap, and including two axially extending fluid seals at angularly spaced positions around the axis, each seal including a rocking element extending parallel with the axis and having a pivoted or rocking connection with the shaft, a part connected to each rocking element engaging the internal surface of the roller, a fluid pressure seal between each element and the shaft, and means for introducing fluid under pressure into the gap between the roller and the shaft, in which the rocking element is urged towards the internal surface of the roller by an axially extending elongated flexible pressure conduit within the roller, to which pressure fluid is supplied from an external source.

8. A hollow pressure roller substantially in any of the forms described herein with reference to the accompanying drawings.