EP1703018B1 - Device and method for the heating of rollers - Google Patents

Abstract

The roller (1) is equipped both with peripheral longitudinal bores (2) and an external heat exchanger. The latter forms a closed circuit with the bores in the roller. Both carry a recirculating, thermal-control fluid. The heat exchanger is an inductor (3) with hollow electrical conductors (5). The fluid is recirculated through both the bores and the conductors. The conductors form an inductive loop (4), and all have the same clearance from the roller surface. A magnetic yoke (6) surrounds the loop. The inductor has an E-shaped cross section, the conductors being located between the limbs. A valve is included in the fluid circuit, and a heat exchanger can be connected to it. The conductor is copper or aluminum. Of two rollers in the calendar, one is electrically heated, the other is heated by thermal fluid. The ratio of internal and external heating is controlled by altering the recirculation flowrate and/or by bypassing. The inductor is designed for operation at above 200[deg]C. The roller is under programmable control. An independent claim is included for the corresponding method of controlling the roller temperature.

Description

The invention relates to a device according to the preamble of claim 1 and a method according to the preamble of claim 10.

Such devices and methods (see, eg DE 103 06 040 A1 ) are used for the direct electrical heating of rolls, in particular one or more rolls used in a calender for the calibration, densification and / or smoothing of paper webs.

The currently most widespread method for heating rolls for the treatment and / or production of webs under the action of elevated temperatures in the nip utilizes the convective heat transfer from a liquid or vaporous heat transfer medium to the roll. For this purpose, it is known to provide the roller with peripheral, parallel to the roll axis bores through which the heat transfer medium is pumped by pumping in the circuit between the roller and a heat exchanger. In this case, the heat transfer medium in the heat exchanger absorbs heat, whereby its temperature increases by a certain value. This amount of heat is released into the peripheral bores to the roller, wherein the temperature of the heat transfer medium decreases by the corresponding value again to heat in the following passage through the heat exchanger again to the flow temperature. In non-stationary operation, the flow temperature gradually increases with the heating of the roller and finally reaches its end value when the stationary operating value of the roll temperature has been set in the roll gap.

As long as the roller is not ready. This unavoidable time required for the heating of the roll is primarily determined not by the heat-related characteristics of the roll alone, but above all by temperature gradients which, during the heating process, depend on the location and duration of their occurrence in the roll because of the roll produced by them mechanical stresses in the roll material may not exceed certain permissible limits. As a result, in particular the difference between the flow temperature of the heat transfer medium and the roller temperature in the peripheral bores and thus inevitably also limited to the transferable to the roller heat output. This results in a minimum value of the heating time, which can not be exceeded and depends solely on the structural properties of the roller and the method of heat transfer. In this case, the allowable heat transfer performance can be well below the nominal value for which the heating system is designed with a view to continuous operation.

A roller used in a calender conventional design represents a hollow cylinder made of cast steel with a wall thickness in the range of 100-200 mm and an outer diameter in the range of 300 -1600 mm. The peripheral holes lie on a pitch circle whose diameter is 90-150 mm is smaller than the outer diameter of the roller, wherein the typical diameter of the peripheral bores 20 - 38 mm. The smallest distance of the peripheral bores is thus 35 mm from the outer and 35-135 mm from the inner shell surface of the roller.

During the heating process, a radial temperature profile sets in, the maximum at the peripheral holes and the minimum values at the lie on both lateral surfaces of the roller. As a result, the thermal expansion of the roll material in the region of the peripheral bores is greater than at the roll surfaces. As a result, tensile stresses are caused in the surface region of the roller, while corresponding compressive stresses occur in the region of the peripheral bores. If the temperature gradient from the peripheral bores towards the roll surfaces during the heating process exceeds the permissible value for the roll material, the shear and tensile stresses generated in this way lead to a destruction of the roll. Because of the smaller distance of the peripheral bores to the outer surface of the roll, this region is particularly affected by such a danger of too rapid heating. Even in other non-stationary thermal states of the roller this is threatened by destruction by internal stresses, if the temperature of the outer roller surface - even temporarily - drops too far below the temperature inside the roll shell.

In order to improve the thermal transient performance of such a roll and for faster and reliable adjustment to other nip temperatures or to be achieved web qualities, a method for controlling the temperature of a roller is known, which in addition to inner also uses external heating means. These are such heating means, such as an induction coil, an infrared radiator or a fan heater, which are arranged radially above the roller and with the aid of which the heat can be transmitted directly to the outer roller surface. This can safely achieve significantly higher heating rates at the roll surface than with an internal heater alone.

If, for example, a roll is to be adjusted during operation from a higher to a lower nip temperature, this is done according to the known method in such a way that, while maintaining the higher nip temperature First, the temperature of the heat carrier in the peripheral bores is reduced by corresponding reduction in the performance of the heat exchanger in the vicinity of the setting in stationary operation at the lower roll nip temperature value, at the same time the heat transferred from the external heating means to the outer roll surface heating power is increased accordingly. If the temperature of the heat carrier in the peripheral bores has reached its desired value, the nip temperature can be lowered very rapidly by a corresponding reduction in the output of the outer heating means to the lower value without exceeding the permissible temperature gradient.

The disadvantage of this method is that it requires two independently controllable heat sources and a complex control loop. The inductive heating to be preferred because of the magnitude of the required power of the external heating means is also liable, with calender rolls of the above dimensions, for the lack of a very low power factor on the order of cos φ = 0.1, which gives rise to thermal efficiencies can be raised only with elaborate Induerkorkonstruktionen over a value of η _th = 0.5. This means that in a conventional system for inductive heating of a calender roll, a power loss approximately the same amount must be removed by cooling from the system, as useful heat output is transferred to the roller.

In the DE 33 40 683 A1 a thermo roll with an outer inductive heating for use in a calender is described, which consists of three coaxial, radially and tangentially material and non-positively connected hollow cylinders. The inner hollow cylinder represents the body of a conventional calender roll made of cast steel. The radially above arranged hollow cylinder consists of a magnetically non-conductive, electrically insulating and particularly temperature-resistant Material, preferably Teflon and has a wall thickness of 10-100 mm. The outer hollow cylinder is made of ferromagnetic material and should have a wall thickness of 1 - 50mm. The middle hollow cylinder separates the outer thermally as well as magnetically and electrically from the inner, mechanically bearing cylinder. Thermally, magnetically and electrically active is thus alone the outer cylinder, in which the magnetic field of radially overlying stationary arranged inductor propagates and thereby induced eddy currents flow, whereby the heat output from the inductor is transmitted to the roller.

This can be achieved that relatively high heat outputs can be transferred to the roller without exceeding allowable temperature gradients. This allows much shorter heating times or correspondingly faster thermal compensation or setting operations. In addition, it can be achieved with sufficiently low wall thickness of the outer cylinder and choice of suitable ferromagnetic material, a significant improvement in the power factor and the thermal efficiency of the inductive roller heating. However, it is questionable whether the requirements of its flexural rigidity in combination with the other two coaxial cylinders of the calender roll can be met with the required low wall thicknesses of the outer cylinder. A commercial execution of such a roller is not yet known.

The invention is therefore based on the object, an apparatus and a method for heating a roller of the type mentioned above, in particular for use in a calender form such that it is possible, the process-technically unusable portion of the delivered power from the AC power source To press on values below 10%, and which also allows to dispense with a special temperature control, without thereby fully exploiting the short-term power reserves available the AC source to the risk that allowable limits of the temperature gradient in stationary or non-stationary operation of the roller are exceeded.

The object is achieved in a device according to the invention characterized in that the outer temperature control means comprises at least one heat exchanger which forms a closed circuit for the temperature control with the peripheral bores of the roller. As a result, it can be achieved that the waste heat generated by the outer temperature control means, for example in electrical conductors, is transferred convectively to a temperature control medium which simultaneously effects a temperature control of the roll from the peripheral bores.

It has proved to be advantageous if the outer temperature control means is an inductor having a conductor formed as a waveguide, and that the tempering medium is guided in a circuit both through the bores of the roller and through the hollow conductor.

Advantageously, the current conductors may be formed into an inductor loop such that they all have the same distance from the surface of the roller.

According to the invention, the inductor may comprise the inductor loop and a magnetic yoke.

Conveniently, the inductor may be formed in cross-section E-shaped, wherein the current conductors are arranged between the legs.

The temperature control circuit can be regulated if a valve is arranged in the circuit of the temperature control medium.

Excess heat can be dissipated easily if a heat exchanger can be connected in the circulation of the temperature control medium.

The outer tempering performance and thus also the ratio of the two tempering powers to each other can be influenced in a simple manner if the inductor is assigned an adjusting device for the air gap between the inductor and the roller.

Advantageously, the conductors can be made of copper and / or aluminum.

The object is also achieved by the method according to claim 10.

It has proved to be advantageous if the operating temperature of a trained as a temperature control inductor by the amount above the nip temperature, for the convective transport of its resulting in the inductive heat transfer current heat to the walls of the peripheral bores of the roller and from there by heat conduction the surface of the roller is required.

It has proven to be advantageous if the air gap between inductor and roller for adjusting the temperature control is variable.

Advantageously, the ratio of the proportions of the outer and inner temperature to each other during operation of the roller can be influenced by changing the circulation rate of the temperature.

According to the invention, excess heat can be dissipated via a heat exchanger arranged in a branch of the temperature control medium circuit located as a bypass to the peripheral bores.

Conveniently, in a calender with at least two rolls, one can be heated convectively with an inductor, while the other can be heated convectively via the tempering medium.

Advantageously, the inductor may be associated with the roller, through the peripheral bores of the tempering medium is circulated.

For the inductive heat transfer of the outer temperature control, a further heat transfer can occur by radiation when the inductor for operating temperatures of about 200 ° C is designed.

According to the invention, the convective heat transfer can be influenced by changing the circulation rate of the temperature control medium.

A complex temperature control is not required when a roller is associated with a programmable logic controller that adjusts all occurring stationary and non-stationary operating conditions such that process-optimal parameters are achieved with high reliability.

Figur 1

einen Querschnitt durch eine Thermowalze mit Induktor im Bereich des aktiven Walzenballens,

Figur 2

eine Seitenansicht der Thermowalze mit Induktor gemäß Figur 1 im Verbund mit einem Wärmetauscher,

Figur 3

eine Thermowalze nach Figur 2 im Walzengerüst eines Kalanders.

The invention will be explained in more detail with reference to an embodiment shown in the drawing. Show it:

FIG. 1

a cross section through a thermo roll with inductor in the field of active roll bale,

FIG. 2

a side view of the thermo roll with inductor according to FIG. 1 in combination with a heat exchanger,

FIG. 3

a thermo roll after FIG. 2 in the rolling mill of a calender.

In the FIG. 1 a roller 1 with peripheral holes 2 and at least one outer, arranged radially above the roller 1 inductor 3 is shown, which consists of an inductor 4-shaped conductors 5 and the inductor loop 4 enclosing magnetic yoke 6, the surface of the roller 1 a distance has as air gap 7. The current conductors 5 are formed as waveguides, which preferably consist of copper or aluminum. In the tubular cavity of the conductor 5 and in the peripheral bores 2 of the roller 1 is a liquid or vaporous temperature control medium, for example water or mineral oil.

Again FIG. 2 can be seen in the in FIG. 1 shown in cross-section roller 1 with inductor 3 is shown in side view, the peripheral holes 2 and the tubular cavities of the conductor 5 via a rotary inlet 8 of the roller 1 and fittings 9, which are located on formed as a hollow sections power supply lines 10 of the inductor loop 4 means Circulation pump 11 interconnected to a closed flow circuit. In this circuit thus formed, the temperature control medium is constantly exchanged between inductor 3 and roller 1.

Between circulating pump 11 and rotary inlet 8, a heat exchanger 12 is bypassed via a valve 13, which is connected via T-pieces to the rotary inlet 8 with the peripheral bores 2.

If a current is now sent through the current conductors 5 of the inductor 3, the inductor loop 4 heats up. This current heat is now transferred to the flowing in the cavities of the profiles of the conductor 5 tempering and transported with this in the peripheral holes 2 of the roller 1. There, the current heat of the inductor 3 is convectively transmitted from the temperature control to the roller 1, so that it heats up from the inside.

At the same time heating power from the inductor 3 is transmitted inductively and at sufficiently high temperature by heat radiation to a surface layer located directly on the surface of the roller 1, whereby the roller 1 additionally heats up from the outside.

wird bei den üblichen Induktorkonstruktionen im Wesentlichen durch den Wirkstrom im Verhältnis zum Blindstrom des Induktors bestimmt.The ratio a _H of external heating power N _a to internal heating power N _i $${\mathrm{a}}_{\mathrm{H}}={\mathrm{N}}_{\mathrm{a}}/{\mathrm{N}}_{\mathrm{i}}$$

is determined in the usual Induktorkonstruktionen essentially by the active current in relation to the reactive current of the inductor.

worin N_a der Anteil der induktiv übertragenen und an der Oberfläche der Walze 1 erzeugten äußeren Heizleistung, N_i der Anteil der in den Stromleitern 5 des Induktors 3 durch den Induktorstrom hervorgerufenen und in die Walze konvektiv übertragenen Heizleistung, R_w der wirksame ohmsche Widerstand der elektromagnetisch aktiven Randschicht am äußeren Walzenmantel, R_s der wirksame ohmsche Widerstand der Induktorschleife 4 einschließlich der Stromzuleitungen 10 und ϕ der Phasenwinkel zwischen Speisestrom und Speisespannung an den Klemmen der Wechselstromquelle sind. Der Ausdruck cos ϕ wird als Leistungsfaktor bezeichnet und stellt das Verhältnis der Wirkleistung zu dem Produkt aus Speisestrom und Speisespannung, der so genannten Scheinleistung der Wechselstromquelle, dar.The reactive current is the component of the inductor current, which is required for the generation of the magnetic field of the inductor 3 in order to be able to effect with the help of the inductive transmission of the heating power to the extent necessary. For the actual generation of the heating power in the roll 1 itself, essentially only the active current component of the inductor current is authoritative, whereas the current heat in the current conductors 5 of the inductor 3 and the corresponding heating power is caused by both components of the inductor current. Thus, the larger the reactive current component becomes in relation to the effective current component of the inductor current, the stronger the effect in the current conductors 5 of the inductor Heating power over the self-produced in the roll 1 in appearance. This relationship can be represented in a formula as follows: $${\mathrm{N}}_{\mathrm{a}}/{\mathrm{N}}_{\mathrm{i}}={\mathrm{R}}_{\mathrm{w}}/{\mathrm{R}}_{\mathrm{s}}\cdot {\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\phi }$$

wherein N _{a is} the proportion of the inductively transmitted and generated on the surface of the roller 1 outer heating power, N _i, the proportion of induced in the conductors 5 of the inductor 3 by the inductor and convectively transferred to the roller heating power, R _w the effective ohmic resistance Electromagnetically active surface layer on the outer roll shell, R _{s are} the effective ohmic resistance of the inductor loop 4 including the power supply lines 10 and φ the phase angle between the supply current and supply voltage to the terminals of the AC power source. The term cos φ is referred to as a power factor and represents the ratio of the active power to the product of the supply current and supply voltage, the so-called apparent power of the AC power source.

The higher the degree of magnetic coupling between the inductor 3 and the roller 1, the larger the power factor cos φ becomes. If, for example, the proportion of the internal heating power decreases to a certain extent, the degree of magnetic coupling between inductor 3 and roller 1 must be correspondingly increased, and vice versa.

Such variations of the magnetic coupling can be achieved in the present example by adjusting the air gap 7 between the magnetic yoke 6 and the roller 1, wherein a decrease in the air gap 7 causes an increase in the degree of magnetic coupling. In this way, it is possible by simply moving the magnetic yoke 6 in the direction of the surface normal of the roller 1, in a limited by the Induktorkonstruktion upwards Range to adjust the heating power ratio a _H continuously during operation of the calender.

A further, but not stepless adjustment of the heating power ratio a _H is possible in that the ohmic resistance of the inductor loop 4 is changed. This can be achieved, for example, by increasing or decreasing the number of parallel, current conductors 5 of the inductor loop 4 through which the alternating current source is switched on or off. To avoid the expense of circuit breakers, this measure is preferably carried out in the de-energized state of the inductor 3. This ensures that the range limits for the continuous adjustment of a _H are shifted upwards or downwards accordingly. If, for example, when changing over a roll 1 to a lower operating temperature without interruption of operation with the least possible transition-related reject length of the web, a value of a _{H is} required which is above the set limit value of the inductor design, the excess internal heating power is temporarily dissipated via the heat exchanger 12. By closing the valve 13, the heat exchanger 12 after setting the new operating temperature of the flow circuit of the circulation pump 11 is disconnected.

If, due to the inductor design, a necessary value of a _H can not be achieved even in stationary heating operation, then the excess current heat output of the inductor 3 can optionally be used to heat a second roll in the calender.

Such a calender is in FIG. 3 shown. In a rolling stand, pressure rollers 14 are arranged together with two rollers 1 and 15. Both rolls 1 and 15 have a structure according to the FIGS. 1 and 2 However, the roller 15 is not associated with an inductor 3. About the valve 16, the rollers 1 and 15 are connected in parallel at their rotary inlets 8, so that in the inductor 3 on the Roller 1 heated heat transfer medium behind the pump 11 to the two rollers 1 and 15 divides and merges the two partial streams after passing through the peripheral holes 2 and transfer of internal heat to the rollers 1 and 15 at the outputs of the rotary entrances 8 and re-heating the Heat transfer medium in the inductor loop 4 are pressed on the connector 9 in the hollow sections of the conductor 5.

Does the roller 15 as in FIG. 3 via no further heat source, so requires a heating operation in conjunction with the roller 1 with approximately the same flow velocities of Temperiermediums that the operating overtemperature of this roller 1 on the incoming web approximately by the amount that is caused by the outer heater, higher than the operating overtemperature of Roller 15 is. In this case, the outer heating of a roller 1 can be used to produce and control a process-technically necessary temperature difference to the other roller 15.

If, on the other hand, the operating overtemperatures of both rolls are to be the same or can be set independently of each other, this is achieved by equipping the roll 15 with an inductor 3 according to the invention.

In special cases, it may be advantageous or necessary to heat the roll 1 only inductively. If this involves optional operating states to be set, then the inner, convective heating of this roller can be switched off by closing the valve 17. Otherwise, it is advantageous to use as roller 1 a much cheaper roller without peripheral holes. The current heat output of the inductor 3 is then fully converted into heating power of the roller 15. By moving the magnetic yoke 6 and / or by connecting or disconnecting current conductors 5 of the inductor loop 4, it can be adjusted to the limits given by the inductor design. Should the current heat output of the inductor 3 is greater than the heating power required for the production of the required operating temperature of the roller 15, the excess power is dissipated by opening the valve 13 to the heat exchanger.

The device according to the invention and the method make it possible to convectively transfer the heat output generated by the current flow directly outside the roll, which is generated primarily in the current conductors of the inductor and in its power supply and discharge lines, to a temperature control medium, and in that this temperature control medium flows in is circulated in a closed circuit, and that in this closed circuit, the peripheral holes 2 of a roller 1 or 15 are inserted / turned on, and that the temperature control medium between said current-carrying conductors 5 and the peripheral bores 2 of the roller 1 is circulated, and that the Inductor 3 is preferably associated with the roller 1, through the peripheral bores 2, the temperature control medium is circulated.

It is thereby achieved that the thermal power generated in the inductor 3 and its Stromzu- - and discharges is no longer lost to the system of roller heating due to the necessary to maintain the permissible operating temperature of the inductor 3 cooling, but by means of heat transfer via the temperature control and the peripheral bores 2 unrestricted for the internal heating of the roller 1 can be used.

The operating temperature of the inductor 3 must be by the amount above the nip temperature, which is required for the convective transport of its resulting in the inductive heat transfer current heat to the walls of the peripheral holes 2 of the roll 1 and from there by heat conduction to the roll surface.

Serves an inductor 3 both the outer heating of a roller 1 by inductive transmission of heat output and the inner heating of the same roller 1 by the inventive use of its current heat, so this is related to the nip temperature overtemperature of the inductor 3 at each unchanged conditions of the convective Heat transport in the heat transfer circuit and in the nip a measure of the proportion of the current heat output of the inductor 3 and thus the inner heater to the total transferred to the roller 1 heating power.

This proportion is greater, the greater the reactive power demand of the inductor 3 for the generation of the magnetic field required for the inductive transmission of heating power. A measure of this is the phase shift φ between current and voltage at the terminals of the AC power source. A large phase shift φ and a correspondingly low value of the so-called power factor cos φ means a high reactive current demand and a correspondingly large proportion of the current heat output of the inductor or the internal, convective in comparison to the outside, inductive heating.

According to the invention, it is possible, by varying the power factor cos φ, to set the ratio of the proportions of external and internal heating to one another continuously at constant heating power and correspondingly to the requirements of optimum roller operation. This can be achieved, for example, by correspondingly changing the magnetic coupling of the inductor 3 to the roll 1, the power factor cos φ increasing as the magnetic coupling of the inductor 3 to the roll 1 becomes narrower. In this case, the distance of the inductor 3 to the roller 1 or when using a ferromagnetic magnetic yoke 6 for field concentration, the distance of the pole pieces of this magnetic yoke 6 from the roller 1 to reduce accordingly. On the other hand, an increase of these distances leads to a reduction of the power factor cos φ and a the corresponding increase in the internal, convective portion of the roller heating.

If the inductor 3 is designed for operating temperatures of, for example, more than 200.degree. C., the heat transfer by radiation, as the decisive component of the external heating, is added to the inductive one. One possibility for adjusting the ratio of the proportions of external and internal heating to each other during operation of the roll 1, the invention provides in this case so that the convective heat transfer is influenced by changing the circulation rate of the temperature control medium accordingly. If, for example, the proportion of the external heating is to be increased by amplifying the heat radiation emitted by the inductor 3, this can be achieved very rapidly by reducing the circulation rate of the temperature control medium and a corresponding, immediately occurring temperature jump of the inductor 3.

On the other hand, for optimum and safe operation, it may be necessary to reduce the overall heating capacity as the proportion of external heating increases. This can be achieved by a corresponding reduction of the inductor current while increasing the power factor cos φ, as long as it remains below its maximum value predetermined by the design of the inductor 3. If this is no longer the case, it is provided for a further reduction of the heating power to dissipate the excess heat from the heating system of the roll 1 via a heat exchanger 12 which is arranged in a branch of the heat transfer medium circuit located in the bypass to the peripheral bores 2. Since this is usually a temporary, the setting of a changed steady-state operating state serving operation, thereby the thermal efficiency of the roller heating is not permanently affected.

The heat output generated in the inductor 3 and its Stromzu- and -ableitungen can be supplied to the same, inductively surface-heated roller 1, but also another roller 15 in the calender for temperature control.

With the procedures according to the invention can be made in a sufficiently wide range each stationary or even temporarily required heating state with the setting of a corresponding ratio of internal and external heating. Thus, the method according to the invention for tempering a roller offers the possibility to operate a roller 1 with a programmable logic controller and thus adjust all occurring stationary and non-stationary operating conditions so that process-optimal parameters are achieved with high reliability without requiring a complex Temperature control is required.

The usual thermal power densities on roll surfaces are in stationary operation at 20 - 35 kW / m ² .

However, more modern multinip inline calenders require up to 50 kW / m ² for sufficient heat transfer to the web in stationary operation. In some special cases 60 kW / m ^{2 are} needed for optimal process conditions. In order to realize roller 1, 15 with such heat outputs, one is still reliant on special, particularly high-quality roller materials in order to master the extreme thermal stresses that are caused by the temperature gradient required for the heat transfer.

With the aid of the method according to the invention, the temperature gradients and thermal stresses in the roll body of high-performance calenders can now also be reduced to conventional values, so that cost-effective and more readily available materials can be used even in the borderline cases occurring hitherto.

For heating powers above 20 kW / m ² , this is to be expected by the sole heating of the rollers from the inside, by means of the peripheral bores, with a significant Barringanregung by the peripheral holes. The excitation and damage image frequency corresponds to the number or an integral part of the number of peripheral bores or the pass-system group number. In most cases, the barring damages are formed on the middle or bending compensating rolls, which are based on an elastic plastic material. The then achieved service life is then very low. By erfindungsmäß Außeninduktivbeheizung this disadvantage is completely eliminated.

In addition, the new method for heating rollers offers the advantageous possibility to use in a calender with multiple thermo rolls, the current heat of the inductor 3 of a roll 1 for the convective heating of another roller 15 in the same mill stand and so with an additional control variable for a optimal energy management to achieve a previously unachieved thermal efficiency not only for a roll 1, but for the calender altogether.

By means of the device according to the invention, heating of a roll 1, in particular of a calender roll, by means of an alternating current source and an inductor 3 arranged outside the roll 1 is achieved and achieves a thermal efficiency of the electric heating of η _th ≥ 0.9. This makes it possible to use the overload capacity of the AC power source unrestricted for the heating of the roll 1 or a very fast setting of the process-technically required roll gap temperature.

For radial and axial temperature compensation and -gleichmäßigung in the roller 1 and the most bolted journal, the roller 1 with communicating, equipped with completed heat pipes. The heat pipes (heat pipes) can be formed for example by peripheral holes 2, which protrude into the journal and individually, or communicating with each other, sealed. Trained as heat pipes hollows are filled with a suitable boiling liquid, which causes a homogenization of the roll and pin temperature or even heating or cooling.

LIST OF REFERENCE NUMBERS

1.

roller

Second

peripheral bore

Third

inductor

4th

lnduktorschleife

5th

conductor

6th

yoke

7th

air gap

8th.

rotary Joint

9th

connector

10

power supply

11

circulating pump

12

heat exchangers

13

Valve

14

printing rollers

15

roller

16

Valve

17

Valve

s

magnetic air gap

N _a

external heating power

N _i

internal heating power

a _H

Heating power ratio = N _a / N _i

R _w

effective ohmic resistance of the electromagnetically active surface layer on the outer roll shell

R _s

effective ohmic resistance of the inductor loop

φ

phase angle

η _th

thermal efficiency

Claims (19)

1. A device for controlling the temperature of a roller (1) which is provided with peripheral holes (2) through which a temperature-control medium is passed, comprising an external temperature-control means assigned to the roller (1) and acting thereon from outside, characterised in that the external temperature-control means comprises at least one heat exchanger which with the peripheral holes (2) of the roller (1) forms a closed circuit for the temperature-control medium.
2. The device according to claim 1, characterised in that the outer temperature-control means is an inductor which has current conductors (5) configured as hollow conductors as the heat exchanger and that the temperature-control medium is guided in a circuit both through the peripheral holes (2) in the roller (1) and also through the current conductors (5) configured as hollow conductors.
3. The device according to claim 2, characterised in that the current conductors (5) are formed into an inductor loop (5) and that all the current conductors (5) are at the same distance from the surface of the roller (1).
4. The device according to claim 3, characterised in that the inductor (3) has a magnetic yoke (6) surrounding the inductor loop (4).
5. The device according to any one of claims 2 to 4, characterised in that the inductor (3) is configured with an E-shaped cross-section wherein current conductors (5) are arranged between the legs.
6. The device according to any one of claims 1 to 5, characterised in that a valve (17) is disposed in the circuit of the temperature-control medium.
7. The device according to any one of claims 1 to 6, characterised in that a heat exchanger (12) can be switched in the circuit of the temperature-control medium.
8. The device according to any one of claims 2 to 7, characterised in that an adjusting device for the air gap (7) between the inductor (3) and roller (1) is assigned to the inductor (3).
9. The device according to any one of claims 2 to 8, characterised in that the current conductors (5) are made of copper and/or aluminium.
10. A method for controlling the temperature of rollers (1) via peripheral holes (2) through which a temperature-control medium is passed, and by means of at least one external temperature-control means assigned to the roller (1) and acting thereon from outside, characterised in that the external temperature-control means comprises current conductors (5) configured as hollow conductors through which the temperature-control medium is passed, wherein temperature-control power generated by the current conductor (5) is transmitted convectively to the temperature control medium and this temperature-control medium is circulated in a closed circuit with the peripheral holes (2).
11. The method according to claim 10, characterised in that the operating temperature of an inductor (3) configured as a temperature-control means lies above the roll gap temperature by the amount required for the convective transport of its Joule heat generated during the inductive heat transfer to the walls of the peripheral holes (2) of the roller (1) and from there by heat conduction to the surface of the roller (1).
12. The method according to claim 10 or 11, characterised in that the air gap (7) between an inductor (3) configured as a temperature-control means and the roller (1) can be varied to adjust the temperature-control power.
13. The method according to any one of claims 10 to 12, characterised in that the ratio of the fraction of external and internal temperature control to one another during running of the roller (1) can be influenced by varying the circulation rate of the temperature-control medium.
14. The method according to any one of claims 10 to 13, characterised in that the excess heat can be removed via a heat exchanger (12) located in a branch of the heat transfer circuit located as a bypass to the peripheral holes (2).
15. The method according to claims 10 to 14, characterised in that in a calender comprising at least two rollers (1) one can be heated directly with an inductor (2) whilst the other can be heated convectively via the temperature control medium.
16. The method according to claim 15, characterised in that the inductor (3) is assigned to the roller (1) through the peripheral holes (2) whereof the temperature control medium is circulated.
17. The method according to any one of claims 11, 12, 15 or 16, characterised in that the inductor (3) is designed for operating temperature above 200°C.
18. The method according to any one of claims 10 to 17, characterised in that the convective heat transfer is influenced by varying the circulation rate of the temperature-control medium.
19. The method according to any one of claims 10 to 18, characterised in that a memory-programmed controller is assigned to one roller (1), which sets all arising stationary and non-stationary operating states in such a manner that process-technically optimum parameters are achieved with high operating safety.

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