FI73260C - Method and apparatus for electromagnetic heating of a roll, in particular a calender roll is used in the manufacture of paper or any other web-shaped product - Google Patents

Description

73260

Method and apparatus for electromagnetically heating a roll, in particular a calender roll, used in the manufacture of a paper or other web-like product

The invention relates to a method for electromagnetically heating a roll used in the manufacture of paper or other web-like product, in particular a calender roll, by induction heating, in which a variable magnetic flux the magnetic flux is applied to the roll shell by a magnetic shoe device having a plurality of sub-cores side by side.

The invention further relates to a paper machine roll device for carrying out the method according to the invention, in particular to a paper machine calender having a roll shell rotatable about its central axis, a magnetic actuator having a plurality of cores and an electromagnetic coil or coils having an iron core magnetized with alternating current.

With regard to the state of the art related to the invention, reference is made as examples to Finnish patent applications Nos. 812697, 820733, 821838 and 824281. FI patent application 812697 discloses an electromagnetically heated calender roll, in which a plurality of magnets are arranged in axially adjacent blocks which leave at least the outer circumferential working area free, in which each block or group of blocks at least one 2 73260 1 temperature sensor is used, which indicates the measured value corresponding to the actual temperature of the outer surface of the roll shell in different, axially separate locations and with control circuitry that changes the setpoints based on the measured values and a predetermined roll shell temperature profile 5 .

According to FI patent application 824281 (applicant Valmet Oy), the calender roll is inductively heated using eddy currents and the eddy current heating is applied only to the surface layer of the roll 10 of ferromagnetic material relative to the roll only from the outside. According to this application, an annular thermal insulation layer of magnetically non-conductive material is provided on the roll body, and said layer has an outer sheath of magnetically conductive ferromagnetic material having a wall thickness as low as possible under mechanical loads. This arrangement aims to apply the heating only to the surface layer of the roll shell in order to improve the heating efficiency and to speed up the adjustment of the temperature profile. Em. however, the arrangement according to the patent application is mechanically quite difficult and expensive to implement.

20

It is an object of the present invention to achieve some of the same objects as in the above-mentioned FI patent application 824281. It is a further object of the present invention to provide a method and apparatus for controlling and rapidly adjusting heating bleaching in the axial direction of a calender roll 25. .

As is known, changes in the temperature profile of the calender roll affect the ralna to be calendered for two periods. Firstly, the temperature 30 directly affects the surface properties of the web to be calendered and secondly the diameter of the calender roll changes to some extent as a function of temperature and these diameter changes affect the natural ones! to the pressure profile of the calendering nip and thereby to the thickness profile of the web to be calendered.

35 In order to achieve the above and later objects, the invention is mainly characterized in that the size of the air gap between the end face of said sub-cores located outside the roll shell and the outer surface of the roll shell that a sufficiently small penetration depth of the heating effect 5 is obtained (formula 3).

The device according to the invention, in turn, is mainly characterized in that the sub-cores of the magnetizing device are each individually arranged in the radial plane of the roll to adjust their position , with which said magnetic spool or coils are supplied with electricity of a suitable frequency.

The invention will now be described in detail with reference to some embodiments of the invention shown in the figures of the accompanying drawing, to which the invention is not limited.

Figure 1 schematically shows a first embodiment of a heating device 25 according to the invention.

Figure 2 schematically shows a second embodiment of a heating device according to the invention.

Fig. 3 shows in more detail an embodiment of the invention corresponding to Fig. 2 as seen in the machine direction.

Figure 4 shows a section V-V in Figure 3.

Fig. 5 shows a block diagram of the power supply part of the heating device according to the invention and of the control system possibly included in the device.

4,73260

The calender roll 10 shown in Figures 1, 2, 3 and 4 is either a machine calender roll or a supercalender roll. Roll 10 is known per se as part of a calender stack formed by calendar rolls. The roll 10 has a smooth and hard surface and has, as shown in Fig. 4, a cylindrical sheath 5 made of a suitable ferromagnetic material selected taking into account the strength properties of the roll and the inductive and electromagnetic heating according to the invention. The roller 10 is mounted to rotate about its central axis K-K by means of its ends 11 and shaft pins 12. The shaft pins 12 have bearings 13 which are fitted in bearing housing housings 14. The bearing housings are attached to a roll support frame 16 which rests on a base 15. In Figures 3 and 4, the roll 10 is the lowest roll of the calender stack and, as is known per se, forms a calendering nip with a counter roll (not shown) through which the paper or board web to be calendered (not shown) passes.

15

The interior 10a of the roll 10 shown in Fig. 4 can be fitted with deflection compensation or control devices known per se, which leave a lot of space due to the invention, since the interior 10a of the roll 10 does not need to use liquid or other similar heating devices, but not excluded by the present invention. for use in connection with

According to the invention, the roll 10 is arranged to be inductively and electromagnetically heated by eddy currents so that the temperature of the surface 25 'of the roll 10 is raised to a considerably high, generally above 100 ° C, by means of this heating. In order to carry out the inductive heating, iron core sub-cores 20 ^, 202--20 ^ are arranged on the other side of the roll in the same horizontal row. These sub-cores form a magnetic shoe device 20, which further comprises a magnetizing coil 30 or, with each sub-core, its own coil 30 (30) (Fig. 1). As shown in Fig. 4, the inductive heating is performed non-contact so that a small air gap 40a, 40b, 40c is left between the iron core and the surface 10 'of the roll 10, through which the magnetic fluxes of the iron core close through the roll 10 jacket, causing a heating effect there.

Figure 1 shows each sub-core 20 ^ .. 20 ^ having its own magnetizing coil 30 ^ .30 ^. Another preferred embodiment of the invention is according to Fig. 2 73260, in which all sub-cores 20 ^ .. 20N (N = 16) have a common magnetizing coil 30, which according to Fig. 2 has two turns.

According to Figures 3 and A, the magnetic spindle 30 of the iron core 20 has only one turn, which is generally most mechanically and electrically feasible. According to Figures 3 and 4, the sub-cores 20p.20 ^ are E-shaped in the projection of Figure 4 and have side branches 21a, 21b and a central branch 21c, between which grooves are left for the magnetic spindle 30.

According to the invention, each sub-core is individually arranged in a displacement in the radial plane of the roll 10 for adjusting the size of the air gap and at the same time the heating power. For this purpose, each sub-core is fastened with screws 24 to a vertical arm 23 articulated via a horizontal arm 26 to a side flange 17 of the body 16 by a shaft pin 25. An eccentric 28 is fixed to the lower end 15 of the vertical arm 27 rotatable about the axis C by a stepper motor 29 ) so that the arm 23 pivots about its articulated shaft 25 (arrow A in Fig. 4), whereby the air gap changes. The air gap A can usually vary, for example, between 1 ... 30 mm. The transplantation of sub-hearts can, of course, be arranged by other mechanisms as well.

An important feature of the device solution according to Figures 3 and 4 is that the single-turn excitation coil 30 or loop is arranged fixedly on its support arms 31. The arms 31 are fastened with screws 32 to the end 17 of the body 25. The parallel branches of the coil 30 are of said electrically insulating material e.g. on Teflon arms 31 and with sufficient clearance in the grooves between the magnetic core branches 21a, 21b and 21c so that even if the coil 30 is fixed, the position of the sub-cores is adjusted according to the invention.

30

In Figure 3, the end of the coil 30 is indicated by the reference 30 '. The coil or magnetic loop 30 is made of a copper tube with a sufficient cross-section, through which a circulation of cooling water is arranged, which is illustrated in Figure 3 by arrows and Wout · The use of a copper tube is advantageous in that when using relatively high frequencies and then —------- J. __ 6 73260 conductive material becomes most efficiently used. The wall thickness of said copper pipe is e.g. approx.

Figure 4 shows the tension springs 27 attached to the vertical arm 23, which 5 hold the partial cores stably in place and the dimension Δ of the air gap stable. The stepper motor 29 and the eccentric 28 are arranged in such a way that the sub-cores 20 ^ cannot at any time contact the surface 10 'of the roll 10.

With respect to the electrotechnical background of the invention, the following is stated. When a variable magnetic field is provided in the electrically conductive material, eddy current and hysteresis losses are generated in the material, and the material heats up. The power of the eddy currents (P) depends on the strength of the magnetic field (B) and the frequency of change of the magnetic field (f) as follows 15 P = B2- f2 (1)

The variable magnetic field generated by the roller 30 is closed between the end face of the iron core and the air gaps 40a, 40b and 40c through the jacket of the roller 10.

This magnetic field induces eddy currents in the surface layer of the roll shell 10 which, due to the high resistance of the roll shell 10, generate heat. The distribution of the induced eddy currents in the jacket 10 in the radial direction x of the roll follows the law I = I e “x / ^ (2) xo 25 I is the current density at depth x from the roll jacket surface 10 ', I vir-X o the bead density on the jacket 10 surface 10' and the penetration depth . The penetration depth is defined as the depth at which the current density has dropped to 1 / e of the surface current density 1 ^. The penetration depth gives the expression 30 ------ * _ 1 T / 10 p m m 6 · - V — fi - ÖT (3) j) is the resistivity of the substance, f is the frequency of the excitation current and jji. the relative permeability of the substance.

35 7 73260

The expression shows that as the frequency increases, the penetration depth decreases. When steel is heated, both electrical conductivity and permeability decrease as the temperature increases.

The invention generally uses heating powers of the order of 4.3 to 8.4 kW / m. As is known, the smaller the air gap Δ, the larger part of the electrical power supplied to the device through the coil 30 is transferred to the heated roll shell 10.

Ίq Figure 5 shows a block diagram of an arrangement and a power supply according to the invention. Power is taken from a 50 Hz three-phase network (3 x 380 W). Rectifier 33 converts alternating current to direct current, which is converted in frequency to suit the purposes of the invention with a power electronics-based inverter known per se. The frequency f applied in the invention is in the range 0.5..50 kHz, preferably 1..30 kHz. This power, which is characterized as the biscuit frequency in induction heating, is passed through a matching transformer 35 and a capacitor 36 to a supply line 37, with which a magnetic actuator 30 is supplied. The voltage U at the terminals 30 "of the coil 30 is generally in the range U = 100 ... 400 V. Cooling water is supplied to the coil 30 and possibly to the supply line 37 20, the supply devices of which are illustrated in Figure 3 by block 38 and supply pipes 39.

However, it is not necessary to adjust the position of the sub-cores 20 ^ 20 of the iron core 20 by the automatic closed control system 25 shown schematically in Fig. 5. The control motors are the above-mentioned step motors 29, which receive their control signal Sj from the control system 23. The control system is controlled by a sensor device. 41, which is e.g. a temperature measuring device for measuring the actual values of the roll surface temperatures Τ ^, Τ ^ 30 at several different points in the axial direction K to K of the roll 10 and / or if the roll 10 is used for thickness calibration, a series of measurement signals describing the thickness profile of the web to be calibrated. If the control system 42 includes a setpoint unit with which the temperature profile along the K-K axis of the roll 10 can be set as desired in each case.

35 8 73260

The following are claims within the scope of which the various details of the invention may vary within the scope of the inventive idea.

Claims (12)

1 N A method for electromagnetically heating a roll used in the manufacture of a paper or other web-like product, in particular a calender roll, by induction heating, the method comprising contacting the roll jacket (10) non-contact via a magnetic shoe device (20) via air gaps (40a, 40b, 40c). eddy currents in the casing (10) which, due to the resistance of the roll casing (10), generate heat, which magnetic flux is applied to the roll casing 10 (10) by a magnetic shoe device (20) with several sub-cores (20 ^ .. 20 ^) side by side, characterized in that the size (Δ) of the air gap between the end face of said sub-cores located outside the roll shell (10) and the outer surface (10f) of the roll shell (10) is adjusted to control the axial (K - K) distribution of the heating effect roll 15 and that the core core magnetization current frequency (f ) at such a high frequency that a sufficiently low fever is produced penetration depth of the effect (formula 3). 1 Claims Method according to claim 1, characterized in that said air gap (Δ) is adjusted in the range 1 ... 30 mm. Method according to Claim 1 or 2, characterized in that the frequency (f) of the excitation current is in the range f = 0.5 to 50 kHz, preferably approximately 1 to 30 kHz. 25 Method according to one of Claims 1 to 3, characterized in that each sub-core (20 ^ .. 20 ^) is provided with its own magnetizing coil (30, .. 30.,) (Fig. 1). Method according to one of Claims 1 to 3, characterized in that all the parallel sub-cores (20 to 20 μm) are magnetized by a common magnetic exciter (10) with about 1 to 5 turns. Paper machine roll device for carrying out the method according to one of Claims 1 to 5, in particular for a paper machine calendar, the roll device having a roll shell (10) arranged to rotate about its biscuit axis (K-K) and a magnetizing device (10 ') arranged near its outer surface (10'). 20) with a plurality of sub-cores (20 ^ .. 20 ^) and an electromagnetic coil (30) or coils (30 ^ .. 30 ^) with which the iron core is magnetized by alternating current (f), characterized in that the magnetizing device (20 ) the sub-cores (20 ^ .. 20 ^) are each separately arranged in the radial plane of the roll (10) to be adjusted in position to adjust the size of the air gap (Δ) between the sub-cores and the outer surface (10 ') 10 near their end faces and thereby in the axial direction of the roll (K to K) and that the device further comprises power supply devices (33, 34, 35, 36, 37) with said magnetic spool (30) or coils (30 ^ .. 30 ^) for supplying a suitable rear electricity (f). Device according to Claim 6, characterized in that the sub-cores (20, 20) of the magnetizing device (20) are each arranged on support arms (23, 26) which are articulated to the body part (17) 20 of the device by horizontal articulated shafts (25). and that the device further comprises adjusting motors (29) with each of the sub-cores (20 ^ .. 20 ^) arranged to be adjustable in position in the radial plane of the roll (10) for changing said air gap (Δ). Device according to claim 7, characterized in that the sub-cores are substantially E-shaped in the axial direction (K-K) of the roll (10) and comprise side branches (21a, 21b) and a central branch (21c) between which the groove spaces are magnetically operated (10). ) and whose end faces delimit the magnetizing air gaps (40a, 40b, 40c) with the outer surface (10 ') of the roll shell (10) (Fig. 4). Device according to one of Claims 6 to 8, characterized in that the magnetic dust coil (10) is arranged fixedly on the support arms (31) or the like and that the magnetic dust coil (10) passes with sufficient insulating clearance between the branches (21a, 21b, 21c) of the core cores. ). and 73260 9 73260 Device according to one of Claims 6 to 9, characterized in that the magnetizing coil (10) is made of a copper tube inside which a cooling water flow (W ^ n - ^ out ^ *) is arranged. Device according to any one of claims 6 to 10, characterized in that the members supporting the partial cores (20 ^ .20 ^) are vertical two-arm lever arms fixed at their center by horizontal articulated shafts (25) to the device body (17) and that said vertical arms (23) ), the lever arm-10 part opposite to the sub-cores has adjusting motors (29), which preferably turn said arms (23) by means of an eccentric (28) or the like. Device according to one of Claims 6 to 11, characterized in that the device comprises a closed control system (41, 42, 29) with a control unit (42) which controls the sub-cores (20 ^ .. 20N) by means of control signals (S ^ - S). ) and that the device further comprises a sensor device (41), such as a temperature measuring device and / or a calender roll thickness profile measuring device, and that the control system includes a setpoint unit (not shown) for setting the axis (K - K) of the roll (10). ) to the desired temperature profile. 25 30 35 12 73260