WO2001094868A1

WO2001094868A1 - Continuous dryer with permanent magnets having adjustability of the transverse temperature profile

Info

Publication number: WO2001094868A1
Application number: PCT/IT2001/000287
Authority: WO
Inventors: Danilo Molteni
Original assignee: Sgm Gantry S.P.A.
Priority date: 2000-06-06
Filing date: 2001-06-05
Publication date: 2001-12-13
Also published as: IT1317809B1; ITMI20001256A0; AU2001274491A1; ITMI20001256A1

Abstract

A continuous dryer comprises a cylinder (1) externally covered with a plurality of permanent magnets (5) and a rotating drum (7) of electroconductive material arranged coaxially outside said cylinder (1), as well as means for locally changing along the drum (7) the intensity of the magnetic flux passing therethrough by moving magnetically active adjusting members with respect to the cylinder (1). Said adjusting members may be the same permanent magnets (5) made radially mobile with respect to the cylinder (1) or a plurality of magnetic dipoles (10) and/or blocks (12, 12') of ferromagnetic material arranged outside the drum (7) and mobile in the radial and/or circumferential direction.

Description

"CONTLNUOUS DRYER WITH PERMANENT MAGNETS HAVING ADJUSTABILITY OF THE TRANSVERSE TEMPERATURE PROFILE"

The present invention relates to a continuous dryer with permanent magnets, and in particular to a dryer provided with a system for adjusting the temperature profile in the direction transverse with respect to the direction of movement of the continuous sheet material which is being dried.

Continuous running dryers are known to comprise one or more heating metal surfaces, generally plane or cylindrical, which give heat to the material to be dried, driven on said surfaces. Continuous running dryers are particularly used in the textile and paper industries for drying textiles or printed sheets respectively.

In dryers with permanent magnets, the heat required for the drying is produced by parasitic currents (also called Foucalt's currents) induced in a metal plate or drum by a rotating cylinder comprising a plurality of permanent magnets. For a more detailed description of such a kind of dryer reference can be made to

Italian patent n.1.282.752.

A problem of this type of treatment stems from the unevenness in the transverse direction of the moisture content of the material being treated. The conventional solution for eliminating this unevenness is to moisten the less moist areas, detected through suitable sensors, so as to obtain a uniformly moist material.

However this solution has the drawback of increasing the moisture content of the material, thus resulting in a greater consumption of energy for the subsequent drying. Therefore it would be preferable to partially dry the more moist areas so as to reduce the overall energy consumption for the drying. To this purpose there are known electromagnetic dryers which use a plurality of water-cooled variable frequency induction coils. Each coil can be controlled individually, with a mirrimum transverse resolution in the order of 50-75 mm, and thus allows to adjust the dryer temperature in the corresponding area within a wide range (e.g. from 70°C to 160°C) according to the detected moisture level. However the use of induction coils involves a lower degree of efficiency with respect to permanent magnets and most of all much higher manufacturing and operating costs. In other words, this type of known dryers are quite complicated, require continuous maintenance and also use a considerable amount of energy.

Therefore the object of the present invention is to provide a dryer which is free from said drawbacks, i.e. a dryer which combines the simplicity and efficiency of permanent magnets heating with the capacity of controlling the transverse temperature profile of coil dryers.

This object is achieved by means of a dryer having the characteristics disclosed in claim 1. Other advantageous features are disclosed in the dependent claims.

The main advantage of the present dryer is exactly that of replacing the conventional temperature profile adjusting systems, which are complicated and difficult to control, with a much simpler, cheaper and more reliable system. In this way both operation and maintenance are greatly improved with respect to prior art dryers.

Further advantages and characteristics of the dryer according to the present invention will be evident to those skilled in the art from the following detailed description of some embodiments thereof with reference to the attached drawings wherein:

- Fig.1 shows a longitudinal section schematic view of a first embodiment of the dryer; - Fig.2 shows a cross-sectional schematic view of the dryer in Fig. 1 with various adjustment solutions;

- Fig.3 shows a front schematic view of the magnetic cylinder of said dryer;

- Fig.4 shows a cross-sectional schematic view of a second embodiment of the dryer with various adjustment solutions; - Fig.5 shows a front schematic view of the magnetic cylinder of the dryer in Fig.4; and

- Fig.6 shows a longitudinal section of an enlarged detail of a modification applied to the first embodiment of Fig.1.

Referring to Figs.1-3, it can be seen that a first embodiment of the dryer comprises a cylinder 1, preferably made of ferromagnetic steel, on whose outer surface there is arranged a plurality of permanent magnets 5, regularly spaced and with alternate polarities. These magnets 5 are preferably parallelepiped-shaped and characterized by a high magnetic induction and a high residual coercive force, e.g. neodymium permanent magnets.

The "chequered" arrangement of permanent magnets 5, clearly visible in Fig.3, causes the flux lines arising from a magnet to go back in the adjacent magnets and to be thus all linked together. By this arrangement a. uniform magnetic field of high intensity is obtained around cylinder 1. The permanent magnets 5 are preferably separated from each other by a layer of insulating material 6. ,

Outside cylinder 1 there is coaxially arranged a drum 7 of electroconductive material, preferably aluminum, on whose bases there are secured, aligned with the drum, two shafts 2, 2' rotatably mounted on two roller bearings 3, 3'. One of the two shafts is keyed to a motor 4 whose speed of rotation can be adjusted through known control means (not shown in the figure).

The inner surface of drum 7 is arranged at a very small distance from the permanent magnets 5 so that the whole drum 7 is immersed, without remarkable dispersions, in the magnetic field produced by magnets 5. The material 9 to be dried, usually consisting of a continuous paper sheet, a continuous piece of fabric or other wound material, travels around drum 7 for about a half of its cylindrical development. In operation, cylinder 1 together with magnets 5 stands still while drum 7 is rotated at a constant speed by motor 4, whereby said drum heats up due to the parasitic currents induced by the rotating magnetic field generated- by the relative rotation of cylinder 1. By changing the rotation speed of drum 7 it is possible to adjust very precisely the total thermal energy supply to the material 9 to be dried yet still with an even distribution along drum 7, i.e. in the transverse direction of the material being treated.

In order to achieve the object of being able to change the transverse temperature profile it is necessary to change locally along short lengths (e.g. 50- 100 mm) the reluctance of the magnetic circuit so as to change consequently the flux intensity and therefore the local heating.

A first possibility (not shown) is that of making magnets 5 mobile so that they can be moved away from drum 7 in the areas where it is necessary to reduce the temperature of the latter. Obviously, this solution is applicable only when cylinder 1 has a size sufficient to receive therein the mechanisms for moving magnets 5.

Other external solutions are illustrated in figures 1 and 2, essentially based on the use of other magnetically active adjusting members. These members may consist of dipoles 10 with permanent magnets and/or blocks 11, 12 of ferromagnetic, preferably, or diamagnetic or paramagnetic material, as long as it is not nonmagnetic material.

In the view of Fig.1 there is illustrated a series of dipoles 10 longitudinally aligned and arranged with alternate polarities opposite with respect to magnets 5, the distance between said dipoles 10 and the corresponding magnets 5 being adjustable (X-Y). In this way, by moving the external dipole 10 closer or farther in the corresponding area there is obtained respectively an increase or decrease of the magnetic flux passing through drum 7 and consequently of the local temperature. A similar change in the intensity of the local magnetic flux, though over a smaller adjustment range, can also be achieved by means of the ferromagnetic blocks 11, 12.

In a first instance blocks 11 are mounted on cylinder 1 in magnetically neutral areas between magnets 5, and the. series of dipoles 10 is aligned with said blocks 11 rather than with magnets 5. In a second instance dipoles 10 are replaced by a series of external blocks 12 aligned along.magnets 5.

As shown in Fig.2, it should be noted that the movement of dipoles 10 and blocks 12 may take place either in the radial or circumferential direction, this latter movement being indicated by angles +α and - . From a practical point of view the above-described solutions are operationally equivalent, but the use of blocks 11 or 12 reduces the adjustment range due to the obvious reduction in the available change of flux. As a mere indication it can be considered that the maximum change achieved in the supply of thermal energy is of 20% with dipoles 10 and 10% with blocks 11 or 12. Clearly it is possible to increase the amplitude of the adjustment range by using multiple rows of dipoles and/or blocks.

In another embodiment of the dryer it is possible to arrange the permanent magnets 5 on cylinder 1 not in the above-described pattern illustrated in Fig.3 (i.e. regularly spaced and with alternate polarities) but rather in longitudinal rows of the same polarity and in alternate rows, as illustrated in Fig.5, as long as the magnetic field generated by magnets 5 is variable during the rotation of drum 7. This different arrangement of magnets 5 obviously implies a corresponding adaptation of the adjusting members 10', 11' and 12', always keeping in mind the possibility (not shown) of making magnets 5 mobile so as to move them away from drum 7.

In this case the above-mentioned members will extend circumferentially rather than longitudinally, as shown in Fig.4, but for the rest the functionality is the same as in the first embodiment described above. In particular, the movement of dipoles 10' and blocks 12' may take place either in the radial or circumferential direction, as indicated by angles +β and -β.

Figure 6 shows how the presence of ribs 13 separating the different adjustment areas into which drum 7 is longimdinally divided can be used to increase the inertia of the thermal exchange between said areas. In practice, drum 7 has a greater thickness at the border of said areas, so that the difference of thermal flow caused by the movement of the corresponding adjusting member (e.g. external dipole 10) propagates more slowly to the adjacent areas of the drum.

Claims

CLATMS

1. Continuous dryer comprising a cylinder (1) externally covered with a plurality of permanent magnets (5) and a rotating drum (7) of

5 electroconductive material arranged coaxially outside said cylinder (1) so that the inner surface of said drum (7) is located close to said permanent magnets (5), characterized in that it includes means for locally changing along said drum (7) the intensity of the magnetic flux passing therethrough by moving magnetically active adjusting members with respect to the 10 cylinder (1).

2. Dryer according to claim 1, characterized in that said adjusting members are the same permanent magnets (5) made radially mobile with respect to the cylinder (1).

3. Dryer according to claim 1,^" characterized in that said means achieve the 15 movement of the adjusting members in the radial and/or circumferential direction with respect to the cylinder (1).

4. Dryer according to claim 3, characterized in that said adjusting members consist of a plurality of magnetic dipoles (10, 10') arranged outside the drum

(7). 20 5. Dryer according to one or more of the preceding claims, characterized in that said adjusting members consist of a plurality of blocks (12, 12') of ferromagnetic material arranged outside the drum (7).

6. Dryer according to one or more of the preceding claims, characterized in that it includes ferromagnetic blocks (11, 11') mounted on the cylinder (1) in

25 magnetically neutral areas between the magnets (5).

7. Dryer according to one or more of the preceding claims, characterized in that the permanent magnets (5) are arranged on the outer surface of the cylinder (1) regularly spaced and with alternate polarities and the external adjustment dipoles (10) are arranged longitudinally aligned and with alternate polarities

30_{. ^} opposite with respect to the magnets (5).

8. Dryer according to one or more of the preceding claims, characterized in that the permanent magnets (5) are arranged on the outer surface of the cylinder (1) in longitudinal rows of the same polarity and in alternate rows and the external adjustment dipoles (10') extend circumferentially between two^' adjacent rows with polarities opposite with respect to the magnets (5).

9. Dryer according to claims 4 and 6, characterized in that the external adjustment dipoles (10, 10') are arranged aligned along the ferromagnetic blocks (11, 11 ') arranged on the cylinder (1).

10. Dryer according to one or more of the preceding claims, characterized in that the drum (7) has a greater thickness at the border between transverse adjustment areas so as to obtain separating ribs (13) between said areas.