GB2178509A

GB2178509A - Roller for the treatment of a web of material and its use

Info

Publication number: GB2178509A
Application number: GB08610451A
Authority: GB
Inventors: Hans Dahl; Alfred Christ; Helmuth Lehmann; Wolf-Gunter Stotz; Christoph Link
Original assignee: Sulzer Escher Wyss AG; Escher Wyss AG
Current assignee: Sulzer Escher Wyss AG
Priority date: 1985-06-18
Filing date: 1986-04-29
Publication date: 1987-02-11
Also published as: GB8610451D0; DE3525950A1

Abstract

For the treatment of a web of material, for example for the smoothing of a web of paper, a tubular roller is used, which is heated from the exterior. In order to reduce the flow of heat between the outer surface and the inner side of the shell, where heat-sensitive components may be situated, the roller shell is composed of a plurality of concentric, radial zones 9, 10, 11 in which at least one of the zones, e.g. the central zone, 11 has a lower thermal conductivity than the remainder of the roller shell. This heat-insulating zone may consist of a layer of ceramic material, porcelain or heat-resistant synthetic material, having cavities, e.g. of individual pieces of such material with air- or gas-filled chambers lying therebetween, or of continuous air- or gas-filled grooves or channels, where the latter may be filled by a porous material. <IMAGE>

Description

SPECIFICATION Roller for the treatment of a web of material and its use This invention relates to a roller for the treatment of a web of material, which roller comprises a tubular roller shell, and to the use of such a roller.

In the thermal treatment of webs of material by such rollers, in particular in the smoothing of webs of paper or of cardboard, in the processing of webs of textile material or in the rolling of metal foils, strips or sheets, a temperature of at least 200"C. on the exterior surface of the roller is frequently necessary.

The heat required to heat up the roller surface may be applied from the exterior, e.g. by heating by impinging jets, or in the case of a roller shell which is electrically conductive at least in the outer zone, by eddy current heating. The outer zone of rollers used for the above mentioned purposes must have sufficient hardness and strength for the purpose and, as a rule, must have a smooth surface.

Such rollers are made, for example, of chilled cast iron or of a material with similar properties. Since, however, these materials as a rule have a relatively high thermal conductivity in the range of about 50 W/m.K., the heat which is applied onto the external surface of the roller shell quickly penetrates into the roller shell and heats the entire roller to a similar temperature. In principle, however, a high temperature is only required on the external surface of the roller.

An additional factor which has to be taken into account is that in the interior of the roller shell temperature-sensitive components are frequently provided. For example, in order to treat a web of material efficiently, the rollers are frequently constructed as deflection compensating rollers, in which the roller shell is rotatable about a fixed carrier, and the inner surface of the roller shell is supported by means of suitable support elements against this carrier with a controllable force. These support elements may be supported against the inner surface of the roller shell purely mechanically, magnetically, pneumatically or, in a particularly advantageous manner hydraulically, as described for example in the specification of United States patent No. 3 802 044 or in a number of other patent documents.However, such rollers have critical parts which as a rule are only useable up to temperature of from 100"C. to a maximum of 1500C. these being, for example, bearings, seals, valves or lubricants. With hydrostatic support elements, in addition, a hydraulic pressure medium is necessary, i.e. in the case of water under atmospheric pressure, only temperatures below 100"C. are permissible and even with the conventional pressure oils, temperatures of at the most approximately 140"C. are permissible. The heat transmission in such deflection compensating rollers with hydrostatic sources of support is, in addition, predetermined by the throughput of pressure medium through the bearing pockets of the support elements and cannot be freely varied.

It is therefore necessary to reduce the heat flow penetrating from the outside into the interior of the roller, in order to keep the interior of the roller shell at a different, e.g.

lower temperature, which may not exceed the permitted values.

Similar conditions are present if the treatment of a web of material has to take place at a low temperature, for example below 0 C.

since the respective parts of deflection compensating rollers as a rule only operate efficiently at temperatures above freezing point.

It would be obvious, in order to eliminate these disadvantages, to construct the entire roller from a material with poor thermal conductivity, for example from a ceramic or a porous material. However, such materials can only be worked with difficulty, and it is not feasible to produce rollers for a tenable expenditure with the necessary properties as regards hardness, strength and smoothness.

Attempts have also already been made to provide channels in the roller shell, in which a cooling agent or heating agent circulates and removes the excess thermal energy. In the case of a rotary roller, however, the operation of such a cooling system is very costly in construction and, in addition, is susceptible to breakdown. Furthermore, the flow of heat between the interior and exterior of the roller is indeed reduced, but the energy consumption of heating remains high, unchanged, and may even lie above the values without roller cooling.

In order to eliminate these disadvantages it is proposed in the specification of German Specification DE 33 40 683 to construct a roller shell from an outer and an inner metallic zone with a heat-insulating layer therebetween, e.g. of "Teflon" (Registered Trade Mark) or concrete, so that in fact with an increased temperature of the outside of the roller, the temperature in the interior of the roller shell does not exceed or fall below predetermined operational values. However, it is a disadvantage of such a construction that the heat-insulating intermediate layer has a distinctly lower heat conductivity than the metallic layers.A combination of the three zones which is also stable under the stress of changes in temperature can therefore scarcely be achieved, i.e. in practical operation with a heated outer zone, and the layers easily become detached from each other or are damaged by the stresses which arise.

It is an object of the invention to reduce or eliminate the above mentioned disadvantages of the prior art and to provide a roller for the treatment of a web of material with a heat insulating zone, such that it also withstands the stress of changes in temperature.

According to the present invention, there is provided a roller for the treatment of a web of material, wherein the roller comprises a tubular roller shell which has at least one concentric zone with a lower thermal conductivity than at least one other concentric zone, and wherein the zone with the lower thermal conductivity is formed with cavities.

The cavities may be air- or gas- filled , but a further reduction in the transmission of heat may be achieved if the cavities in the roller shell are filled with a fibrous or porous material, so that the influence or heat radiation and convection is cut out or reduced.

It is particularly favourable to provide between two metallic tubes, heat-insulating intermediate pieces with intermediate air spaces, whereby the intermediate pieces are attached to the inner tube by means of an elastic intermediate layer, in order to compensate for varying thermal expansions of the different zones.

In a preferred embodiment, the roller shell is composed of two concentric parts, in which on the outer side of the inner part grooves or respectively fillets are provided, running in circumferential direction or arranged in spiral form, which on assembly of the two parts form cavities which may be filled with a foam or a fibrous material. The fillets may be aligned radially or else positioned slightly obliquely, in order to be able to take up thermal expansions.

In order to enable the invention to be more readily understood, reference will now be made to the accompanying drawings, which illustrate diagrammatically and by way of example some embodiments thereof, and in which: Figure 1 is an axial section through a roller with a heatinsulating intermediate layer, Figure 2 is an axial section through a roller with a heatinsulating elements and gas chambers, Figure 3 is an axial section through a roller with a heatinsulating elements and a porous filling, Figure 4 is an axial section through a roller with inner circumferential grooves, Figure 5 is a cross-section through a roller with channels filled with gas, Figure 6 is a cross-section through a roller arrangement with heating by impinging jets, and, Figure 7 is a cross-section through a roller arrangement with eddy current heating.

Referring now to Figure 1, there is shown a roller comprising a roller shell 1 rotatably mounted by means of roller bearings 5 about a fixed carrier 2 which is mounted in a stand 4. The inner surface 6 of the roller shell 1 is supported with respect to the carrier 2 by means of a series of radially movable, hydrostatic support elements 3. Between the support elements 3 and the carrier 2 pressure chambers 7 are formed, which are supplied with a suitable pressure medium, e.g. oil, so that the support elements 3 are pressed against the roller shell 1 and bring about a deflection compensation of the roller.Instead of the hydrostatic support elements which are shown, however, support elements of a different construction may also be used, e.g. hydrodynamic support elements, magnetic support elements, or support elements supported pneumatically or mechanically, or by means of elastic forces, or one or more pressure chambers. Also the type of bearing of the support elements on the inner side of the shell may be of different constructions, for example as shown, as a hydrostatic bearing with a bearing pocket 8 supplied with pressure medium on the bearing surface 6, or else as a conventional, hydrodynamic sliding bearing or roller bearing. A direct bearing 5 of the roller shell 1 on the carrier 2 may likewise also be dispensed with, i.e. the roller shell 1 may also be mounted on the carrier only by means of the support elements 3.

In the roller shown in Figure 1, the roller shell 1 is composed of a plurality of concentric zones. The outer zone 9 consists of metal, for example chilled cast iron with a hard, smooth surface and sufficient strength.

By means of a suitable impinging jet heating or eddy current heating, it can easily be heated up to a required temperature of 200 to 250"C. The inner zone 10 of the roller shell is likewise constructed of metal, for example of a steel with high thermal heat expansion. The heat conductivity of the inner and outer zones is of the order of 15 to 50 W/m.K. Between the two zones with good heat-conductive properties, there is provided a heat-insulating zone 11 with substantially lower heat conductivity, which is concentric thereto and is furnished with cavities, in order to reduce the transfer of heat between the outer zone and the inner zone or vice versa. Suitable materials for the intermediate zone are, for example, ceramics or porcelain with a heat conductivity of from 1 to 5 W/m.K. Also, temperatureresistant synthetic material, for example silicon-based or material polyimides, with an even lower heat conductivity in the range of from 0.2 to 0.5 W/m.K. may be used, if a somewhat lower temperature stability can be accepted into the bargain. With a somewhat lower heat input, a metal or another material with particularly low heat conductivity may also be used as the intermediate layer 11.

It is to be observed that instead of providing three zones, a different number of concentric zones may also be expedient. For example, a metallic outer zone or a metallic inner zone can be dispensed with, in so far as circumstances permit, i.e. the outer surface is compatible with the web of material and the inner surface has sufficiently good running properties for the support elements. In any case, one of the concentric zones must have a low heat conductivity.

In the rollers described above, with a plurality of concentric layers of different material, there is the problem that as a rule the different materials display a different thermal expansion. In an embodiment of the invention, therefore at least one of the layers with a high coefficient of thermal expansion is not constructed as a continuous layer, but is constructed as an interrupted zone consisting of separate component parts.

Referring now to Figure 2, there is shown a roller in which the outer metal layer 9 and the inner metal layer 10 are constructed as continuous tubes, whereas the heat-insulating intermediate layer 11 consists of individual pieces 18, which are wedged between the two tubes 9 and 10. Between the individual pieces 18, which may be ceramic or porcelain pieces there are intermediate spaces 12 filled with air or gas, which have excellent heat-insulating properties and a particularly low heat conductivity of approximately 0.03 W/m.K. These pieces may be constructed as individual blocks or as ceramic rings running in the circumferential direction, or as ceramic rods running parallel to the axis of the roller.

The ceramic or procelain intermediate pieces 18 may be attached on the outer side of the inner metal tube 10 by means of elastic intermediate layers 25 of a suitable temperatureresistant elastomer. Thereby the different thermal expansion of the three layers 9, 10 and 11 can be balanced out and compensated for.

The elastic intermediate layer 25 may also be constructed as a continuous shell on the inner metal tube 10.

In order to avoid a transfer of heat taking place by convection or by radiation of heat in the intermediate spaces 12 filled with air or gas, it is advantageous, as shown in Figure 3, to fill up these intermediate spaces by a suitable porous material 13, for example by a foam or by a suitable fibrous material such as rock wool, asbestos or materials with similar properties. At the same time, this example shows that unfavourable effects of different coefficients of thermal expansion for the outer zone 9 and for the inner zone 10 may be avoided by constructing in the inner zone a plurality of rings 10.1, 10.2, 10.3, and 10.4 lying one behind the other in the axial direction, with sealing rings 14 lying therebetween.

Each of these rings 10.1 to 10.4 thereby forms a runner ring for a corresponding support element 3.

Figure 4 shows an embodiment of a roller, in which the heat-insulting intermediate layer is not in the form of a solid, heat-insulating material. Instead of this, the roller shell 1 is made up of an outer tube 9 and an inner tube 10. Annular or helical furrows or grooves 15, running in the circumferential direction, are tapped or milled into the outer surface of the inner tube 10, so that only thin fillets 19 remain. After the formation of these grooves 15, the two tubes 9 and 10 are placed one into the other and are shrunk on to each other, so that the grooves 15 now form good heat-insulating intermediate spaces. In order to improve the effect, the grooves 15 may in turn be filled with porous material. Both tubes 9 and 10 may be constructed of a material such that the problem of differing coefficients of thermal expansion is considerably reduced.

The grooves or furrows may also be provided on the inner side of the external tube 9, whereby the effect is the same. Instead of being directed in the radial direction, the fillets 19 may also be inclined thereto, so as to be able to take up different thermal expansions of the two tubes 9 and 10 through deformation of the fillets.

Figure 5 shows a roller in cross-section where the roller shell 16 consists of a single tube, in which a central zone is formed with a plurality of bores or channels 17 which extend parallel to the axis of the roller and which may be filled with air or with a porous material.

The bores or channels 17 thereby form the heat-insulating zone of the roller shell. Here, too, thermal expansion scarcely plays any part.

Figure 6 shows a roller arrangement for the pressure treatment of a web of material 22 at increased temperature. This arrangement consists of a rotatable roller 23 with a roller tube with heat-insulating intermediate zone, the surface of which is heated by means of impinging jets in an air container 20 by hot air to a desired temperature, for example to 250"C. A counter roller 24 may be constructed as a solid roller or as a tubular roller with or without a heat-insulating intermediate layer. By the force acting on the support elements 3 a pressure treatment is thereby carried out on the web of material 22 at a temperature between 200 and 250"C. The web of material here may be a web of paper and the roller arrangement may serve as a smoothing machine.However, other applications are also possible, such as the pressure treatment of a web of textile material at increased temperature or the rolling of metal foils or strips.

Figure 7 shows another arrangement, in which the heating of the surface of the roller 23 takes place by means of an eddy current heating 21, which is operated at medium frequency in the range for example of between 1 and 5 kHz. In order to be able to use such eddy current heating, the outer zone of the roller 23 must consist of electrically conductive material, i.e. of metal, which as a rule also has good thermal conductivity.

Other methods of heating up the outer surface of the roller are also possible. In the pressure treatment of a web of material at a low temperature, corresponding measures are to be provided to cool the outer surface of the roller, e.g. in order to counteract too intense a heating of the rolling material in the rolling process.

Claims

1. A roller for the treatment of a web of material, wherein the roller comprises a tubular roller shell which has at least one concentric zone with a lower thermal conductivity than at least one other concentric zone, and wherein the zone with the lower thermal conductivity is formed with cavities.

2. A roller as claimed in Claim 1, wherein the zone with lower thermal conductivity is arranged between an outer zone with a higher thermal conductivity and an inner zone also with a higher thermal conductivity.

3. A roller as claimed in Claim 1 or 2, wherein the zone with the lower thermal conductivity has parts of ceramic material, porcelain, heat-resistant synthetic material or the like.

4. A roller as claimed in Claim 3, wherein the zone with lower thermal conductivity is arranged between two zones with higher thermal conductivities and includes heat-insulating pieces which are separated by cavities.

5. A roller as claimed in Claim 4, wherein an elastic intermediate layer is provided between the heat-insulating pieces and the outer surface of the inner zone.

6. A roller as claimed in any one of Claims 1 to 5, wherein the cavities are filled with a porous material.

7. A roller as claimed in Claim 6, wherein the porous material comprises foam, fibrous material or the like.

8. A roller as claimed in Claim 1, wherein the roller comprises outer and inner concentric zones, and wherein grooves are formed on the exterior of the inner zone or the interior of the outer zone to form cavities and a zone of lower thermal conductivity.

9. A roller as claimed in Claim 8, wherein the grooves are separated by fillets inclined against the radial direction.

10. A roller as claimed in Claim 1, wherein the roller comprises a tubular shell formed in a central region with bores or channels extending parallel to the axis of the shell thereby to provide a concentric zone of lower thermal conductivity between the exterior and interior of the shell.

11. A roller as claimed in any one of Claims 1 to 10, wherein the inner-side of the tubular roller shell is supported by support elements against a fixed carrier.

12. A roller as claimed in Claim 11, wherein the support elements are constructed as radially movable, hydraulic support elements, each of which is mounted in a pressure chamber to which pressure medium can be supplied to press the support element against the interior of the roller shell.

13. A roller as claimed in Claim 11, wherein each support element has a hydrostatic bearing surface with at least one bearing pocket which can be supplied with pressure medium and which cooperates with the inner surface of the roller shell.

14. A roller for the treatment of a web of material in accordance with Claim 1 substantially as hereinbefore described with reference to any one of Figures 1 to 7 of the accompanying drawings.

15. The use of the roller claimed in any one of Claims 1 to 14 for the pressure treatment of a web of material at a different temperature from the interior of the roller.

16. The use of the roller as claimed in Claim 13 for the pressure treatment of a web of material at increased temperature, in which the roller shell is heated up to a predetermined temperature and the heated roller exerts a specified amount of applied pressure onto the web of material with a counter pressing element.

17. The use of the roller as claimed in Claim 19 for the smoothing of a web of paper.