GB2058246A - Rotatable body with magnetic device to counteract deflection - Google Patents

Abstract

A rotatable body (3) such as a calender roll shell is supported on a shaft (2). The shaft forms a magnetic body and carries electrical coils (12) which are wound to provide pole faces (13). The pole faces of each circumferential ring of pole faces have the same polarity as one another while the polarities of the rings of pole faces alternate in the axial direction. The magnetic field from the pole faces counteracts deflection in the roll shell with a minimum of eddy currents. The axis of the roll shell may be above the axis of the shaft. In an alternative arrangement (Fig. 5) rotating body (3') is surrounded by a horse-shoe shaped stationary magnetic body (2'). <IMAGE>

Description

SPECIFICATION Rotatable body with magnetic device to counteract deflection The invention is concerned with a device for counteracting the deflection of a body, such as a calender roll, consisting at least partially of magnetizable material and rotating about an axis, by means of a magnet body having pole faces with an airgap between the pole faces and the rotating body.

Bodies which rotate about an axis, e.g. calender rolls, sag because of their own weight and otherwise deflect through the application pressure of adjacent rotating bodies or respectively upper rolls. In the case of long and heavy calender rolls or similar pressure rolls, by which a rolled or smoothed material, e.g. paper, foils or textiles are to be pressed to a uniform thickness across the whole width of roll, this deflection may be so large that uniform treatment of the rolled or smoothed material cannot be guaranteed across the width of the roll. As a result of the deflection the application pressure against the rolled or smoothed material may be greater in the middle of the rolls than at the two ends of the rolls; the rolled or smoothed material will accordingly be thinner in the middle of the rolls than at the ends of the rolls.

In order to achieve across the whole width of the roll uniform application pressure and hence uniform thickness of the rolled or smoothed material, the practice is known in the case of calender rolls of generating a field of hydraulic pressure between the shell of the rotating roll and a non-rotatable supporting shaft which passes through it. But this leads only to satisfactory results if the speed of rotation of the roll is low, whereas, in the case of an increase in the speed of rotation, the field of pressure between the shaft and the roll shell becomes disturbed by the viscosity of the hydraulic liquid so that counteraction of the deflection is no longer possible to a satisfactory degree.

It has further been proposed in the case of calender rolls having a roll shell and a stationary supporting shaft passing through the roll shell, to counteract sag by fitting to the underside of the stationary shaft discrete individual magnets spaced in the axial direction, which raise the roll shell towards the shaft. But when the roll shell rotates, high eddy current losses arise from this, which partially cancel the magnetic force of equalization and in addition lead to an uncontrolled heating up of the roll shell.

In the case of supporting magnets for the magnetic support of a shaft it has further been proposed to provide a magnet body which in the circumferential direction carries electromagnets the pole faces of which exhibit in the circumferential direction alternating polarity. (SKF Technische Information No. 299 of the 12th April 1977.) In principle such a support would also be suitable for the equalization of sag of rotating bodies like calender rolls. But in this case in the case of a rotation of the corresponding magnetically supported bearing part a field reversal corresponding with the alternating polarity of the pole faces in the circumferential direction constantly occurs, which again leads to eddy current losses. These eddy current losses may however be reduced by a laminated iron return path but not wholly cancelled out.

The object of the invention is to create a device for the magnetic counteraction of deflection which is simply constructed and works at high efficiency and low eddy current losses without disturbance of the rotating body and also may be employed successfully at high speeds of rotation.

This problem is solved in accordance with the invention by an assembly comprising a rotatable body consisting at least partially of magnetizable material and a device for counteracting deflection in the body, the device comprising a magnet body having pole faces with an airgap between the pole faces and the rotating body, characterized in that the pole faces of the magnet body extending in the circumferential direction of the rotating body have the same polarity over their whole extent, and the pole faces lying adjacent to one another in the axial of the rotating body have opposite polarities.

As mentioned above, magnetic bearings are indeed known but the device of an assembly in accordance with the invention is distinguished in that no change of pole takes place in the circumferential direction. The pole faces preferably extend in the circumferential direction over a circumferential angle which is as large as possible, so that upon rotation of the rotating body, no field reversal occurs. Only relatively low eddy currents are induced, whereby the rotating body is also not heated up in an unchecked manner. The device thus works with considerably lower losses than a device for the magnetic counteraction of deflection having, say, alternating polarity of the magnet poles in the circumferential direction.

The magnet body preferably has a core and excitable electrical coils wound on the core. In this case, depending upon the extent of the windings in the circumferential direction, the pole faces extend over a certain circumferential angle which is as large as possible. The pole faces of the same polarity in one circumferential direction are preferably split up into a number of sections so that round the whole circumference, say, three pole faces each of 1 200 circumferential extent are provided by the windings.In this case one pole face may be arranged symmetrically about the vertical plane at the underside of the magnet body so that the magnets so formed serve essentially as carrying-magnets for the rotating body which is to be supported; the other two sections of pole face then serving essentially as side or equalizing magnets by which deflections of the rotating body by, say, pressure loading may be counteracted. If the rotating body is a calender roll in which the roll shell is supported rotatably on a stationary supporting shaft, the supporting shaft may be made as the magnet body by forming annular grooves in the shaft in the circumferential direction the annular grooves being connected together by cross grooves to correspond with the sections of the individual pole faces. Then in the usual way the coils for the electromagnets are inserted in these grooves.If as mentioned above, the pole faces of the magnet body are divided up in the circumferential direction into sections, so that each pole face is embraced by a winding, the windings of the individual coils can be held at the points of contact by means of a coil end mounting of magnetic material, so that even at this point the pole face is not interrupted.

For exact regulation of the counteraction of the deflection, it is advantageous if the coils of the magnet body can be controlled i.e. energised independently of one another. This also applies to the coils by which the individual pole faces are formed in the circumferential direction. The coils lying side by side in the direction axiallv of the magnet body may be combined into groups which can then be separately energised. If the axis of rotation of the rotating body and the centreline of the magnet body can be made to coincide by virtue of the counteraction of potential deflection, there exists over the whole circumference of the rotating body a constant airgap.In general in the case of separate control of the individual coils of the electromagnets the coils of the carrying magnets at the bottom must be excited more strongly than those at the top which serve essentially for prevention of deformation and maintenance of the field.

But the production of a constant airgap for the equalization of the sag at the underside of the rotating body may also be assisted if the centreline of the magnet body and the axis of the rotation of the rotating body do not coincide but are supported to be eccentric by a small amount, that is, so that the axis of rotation of the rotating body lies in the vertical direction above the centreline of the magnet body. In the case of magnetic equalization of sag the airgap between the magnet body and the rotating body is then smaller at the bottom than at the top. In this case the carrying magnets and the other side- and guidance-magnets may be excited at the same strength.Since the attraction at the same fiux is proportional to the reciprocal value of the square of the airgap, there results an upwardly directed attraction with simultaneously low eddy current losses in the rotating body.

It is common to the features of the invention mentioned hitherto, that either no eddy currents are induced in the rotating body or any eddy currents are very low. In spite of all that the possibility is also provided of inducing eddy currents in the rotating body in a controlled manner in order to bring it up to a desired temperature which is to be maintained. This may be done, e.g., by different excitations of the individual windings in the circumferential direction, associated with the pole faces, whereby a controlled build-up of field and reduction of field is achieved during the rotation of the rotating body and this is employed primarily for the heating of the rotating body.Another possibility consists in temporarily giving the coils of the magnet body lying in one circumferential direction opposite polarity, so that a change of pole is effected in the circumferential direction and thereby also a controlled field reversal upon rotation.

Furthermore in the coil end mountings already mentioned, which serve for bridging over the pole faces associated in the circumferential direction with the individual coil sections, a gap of a certain size may be provided so that now the individual pole faces are separated from one another.

Controlled eddy currents are also thus induced in the rotating body which lead to controlled heating up. Feeding of the coils with alternating current is suitable for this purpose too. Obviously the possibilities which have been mentioned may also be combined. In this way a simple adjustable heating of the rotating body can be achieved.

Two embodiments of the invention are explained in greater detail with the aid of the accompanying drawings, in which: Figure 1 is a diagrammatic longitudinal section through a calender roll having a device for the prevention of deflection in accordance with the invention; Figure 2 is a section taken on the line Il-Il in Figure 1; Figure 3 is a schematic diagram of the electrical connections for the device; Figure 4 is diagrammatic perspective view of the supporting shaft of the calender roll, fitted with electrical coils; and, Figure 5 is a diagrammatic cross-section through the-second embodiment.

As shown in the drawings, a calender roll 1 consists of a stationary supporting shaft 2 surrounded by a roll shell 3. The stationary shaft 2 is held at both ends in bed blocks 4, whilst the roll shell 3 is supported to be able to rotate on the shaft by means of suitable bearings, e.g., roller bearings 5. The supporting shaft and the roll shell are respectively produced from suitable steel.

The axis of rotation 6 of the roll shell 3 indicated in Figure 2 does not coincide with the longitudinal centreline 7 of the stationary supporting shaft, but lies vertically above it by a small amount. Through this eccentric position of the supporting shaft and roll shell there exists between them a circumferential gap 8 which in the lower region of the calender roll is narrower than in the upper region.

Annular grooves 9 of shallow depth are provided in the circumferential direction in the stationary supporting shaft 2. At angular spacings of respectively 1 20C there are cross-grooves 10 of shallow depth running between adjacent annular grooves in the axial direction of the supporting shaft, which in each case connects together two adjacent annular grooves. One of these groups of cross-grooves 10, runs at the top of the supporting shaft 2 whilst a second group of crossgrooves 102, at the front in Figure 1, runs along the length of the shaft at an angular spacing of soo from the vertical plane and a third group of cross-grooves 103 runs behind, likewise at an angular spacing of 600 on the other side of the vertical plane (Figure 2).Windings 11 of coils 12 are inserted into the annular and cross-grooves 9 and 10 respectively, that is, so that the windings of one coil lie in two adjacent annular grooves and two adjacent cross-grooves. Pole faces 1 3 are thus formed between these annular and crossgrooves, and run in the direction circumferentially of the supporting shaft.The coils the windings of which run in the annular grooves 9 between the groups of the front and rear cross-grooves 102 and 1 03 respectively, are designated below as carrying coils 121, whilst the coils the windings of which run in the annular grooves between the front group of cross-grooves 102 and the top group of cross-grooves 10, are designated as front sidecoils 122 and the coils the windings of which run between the annular grooves and the top group of cross-grooves 10, and the rear group of crossgrooves 1 03 are designated as rear side-coils 123; the associated pole faces are designated by 13 132,133.

The arrangement of the coils on the supporting shaft 2 is illustrated diagrammatically in Figure 4.

The carrying and side-coils are supplied with voltage via the stationary supporting shaft by appropriate leads being laid, e.g., in a groove 22 as is indicated for the carrying coils 12,.

The windings in the annular grooves 9 are covered over by a slot binding 1 4 of magnetically permeable material whereas in the cross-grooves coil end mountings 1 5 of U-shaped cross-section of magnetic material are inserted and bolted to the supporting shaft 2. The surface of the coil end mountings is fitted flush with the surface of the supporting shaft 2.

The carrying and side-coils 121,122and123 respectively, which lie in one circumferential direction are supplied with energy in such a way that the associated pole faces exhibit the same polarity and the groups of carrying and side-coils adjacent in the axial direction exhibit collectively pole faces of opposite polarity. In Figure 1 the pole faces between the two first annular grooves at the lefthand end of the supporting roller are designated as South poles S, whilst the adjacent pole faces are designated as a North poles N. The pole face group following next in the axial direction is again a South pole so that in the direction axially of the supporting shaft South and North poles exist alternately, and extend in each case over the whole circumference of the supporting shaft.

As shown schematically in Figure 3 the carrying coils for the carrying magnets are distributed in groups which can be controlled separately from one another, that is, in this case in five groups GT to Gut5, where each group exhibits four coils. The coil groups are supplied in each case with d.c.

voltage via carrying-magnet regulators 16, the carrying magnet regulators being connected to a 380V threephase alternating current main. The front and rear side-coils can be controlled respectively via their own side-magnet regulators 17, these side-magnets regulators being likewise connected to the same main. Obviously it is also possible to combine the side-coils appropriately in more groups and to control these individually. The carrying-magnet regulators 1 6 and side-magnet regulators 1 7 for the normal state of service deliver a d.c. voltage to the coils of the magnets, which is adjusted across the individual coil groups distributed in the axial direction in each case in such a way that the same or the deliberately desired thickness of the rolled or smoothed material is produced across the whole width.At the same time possible deformations of the roll shell by pressure loadings, etc., are equalized by the side magnet regulators. Further the carrying and side-coiis may also be arranged and controlled in such a way that the roller bearing 5 between the roll shell and the supporting shaft becomes unloaded. The roll shell may thus even be supported on the supporting shaft floating freely, in which case the roller bearing 5 is then no longer necessary.

Since the supporting shaft also sags by its own weight and further becomes loaded by an attraction with the magnets switched on, the shaft or the inner shell of the roll may be made as a paraboloid of rotation having a concave contour, as illustrated in dotted line at 21 in Figure 3. When the magnets are switched on there results thereby between the shaft and the roll shell at the bottom a straight constant airgap over the whole length of roll.

As indicated in Figure 2 the mountings 1 5 of Ushaped cross-section may also be made in two pieces as is indicated for a coil end mounting 1 5'.

A gap thereby remains between the individual parts of the coil end mounting, by which the pole faces of coils adjacent in the circumferential direction are interrupted. Upon turning of the roll shell eddy currents become induced in the latter, and may result in heating up of the roll shell.

Heating up of the roll shell and regulation of the roll temperature may further be produced by the measures mentioned above, by the carrying and side-coils being either excited at different strengths, made of different polarity, or supplied via the magnet regulators with alternating current.

In Figure 5 a further embodiment is illustrated diagrammatically. Here the rotating body 3' is embraced in a horseshoe-shape by the stationary magnet body 2', in which case the coils 1 21t, 122', 123' for the generation of the carrying and side forces are laid in grooves in the inner face of the magnet body. In this case the top coils in the drawing are designated as carrying coils 1 2,'. The kind and arrangement of the coils in the magnet body and also the principle of operation match the first embodiment described above, so that a more detailed description here is superfluous.

Claims (23)

1. An assembly comprising a rotatable body consisting at least partially of magnetizable material and a device for counteracting deflection in the body, the device comprising a magnet body having pole faces with an airgap between the pole faces and the rotating body, characterized in that the pole faces of the magnet body extending in the circumferential direction of the rotating body have the same polarity over their whole extent, and the pole faces lying adjacent to one another in the axial of the rotating body have opposite polarities.

2. An assembly according to claim 1, characterized in that the magnet body consists of a core and excitable electrical coils wound on the cove.

3. An assembly according to claim 1 or claim 2, characterized in that the magnet body passes through the rotating body with an airgap between the magnet body and the rotating body.

4. An assembly according to claim 1 or claim 2, characterized in that the magnet body wholly or partially embraces the rotating body in the circumferential direction.

5. An assembly according to any one of the preceding claims, characterized in that the rotating body is supported rotatably by the magnet body.

6. An assembly according to any one of the preceding claims, characterized in that the poles faces are formed in the circumferential direction of the magnet body by a number of sections which are bridged over magnetically by inserts.

7. An assembly according to any one of the preceding claims, characterized in that the magnet body has annular grooves running in the circumferential direction and cross-grooves interconnecting the annular grooves, for accommodating electrical coils.

8. An assembly according to claim 7, characterized in that the electrical coils accommodated in the annular and cross-grooves for the pole faces running in the circumferential direction are composed respectively of a number of individual coils adjacent to one another in the circumferential direction.

9. An assembly according to claim 8, characterized in that the adjacent coils of each pole face run over part of their wound length in a common cross-groove.

10. An assembly according to claim 9, characterized in that coil end mountings are inserted in the cross-grooves between the annular grooves, and receive the coil ends of two coils which are adjacent to one another in the circumferential direction.

11. An assembly according to any one of claims 7 to 10, characterized in that three individual coils are provided for each pole face in the circumferential direction, a first carrying coil being arranged symmetrically with respect to the plane of deflection and the other coils being arranged adjacent to, and one on each side of, the first coil.

12. An assembly according to any one of claims 7 to 11, characterized in that in each case coils which are adjacent in the axial direction of the magnet body are combined into coil groups which are arranged to be energised independently of one another.

13. An assembly according to any one of claims 7 to 12, characterized in that the individual coils or coil groups arranged in the circumferential direction are arranged to be energised independently of one another.

14. An assembly according at least to claim 11, characterized in that at least the side-coils or sidecoil groups are arranged to be energised together and independently of the carrying-coils or carrying coil groups respectively.

15. An assembly according to any one of claims 7 to 14, characterized in that the coils which are associated with pole faces adjacent to one another in the axial direction of the magnet body are arranged to be energised independently of one another.

1 6. An assembly according at least to claim 6, characterized in that the inserts which bridge over the sections of pole face in the circumferential direction are interrupted and separate the sections of pole face in the circumferential direction.

17. An assembly according at least to claim 8, characterized in that for heating up the rotating body the coils associated with each circumferential pole face are arranged to be energised differently.

18. An assembly according to c!aim 17, characterized in that at least some of the coils are arranged to be supplied with alternating voltage.

1 9. An assembly according to claim 17 or claim 18, characterized in that the coils lying in the circumferential direction of the magnet body may alternatively be energised so that the associated sections of pole face have different polarities in the circumferential direction.

20. An assembly according to any one of the preceding claims, characterized in that the magnet body has an axis which is eccentric to the axis of rotation of the rotating body.

21. An assembly according to claim 20, characterized in that the axis of rotation of the rotating body lies in its plane of deflection above the axis of the magnet body.

22. An assembly according to any one of the preceding claims, characterized in that one of the opposed faces of the magnet body and of the rotating body is made as a concave paraboloid of rotation in such a way that, in use when the deflection has been counteracted magnetically, a constant airgap exists between the magnet body and the rotating body in the vicinity of the pole faces.

23. An assembly according to claim 1, substantially as described with reference to either one of the examples illustrated in the accompanying drawings.