WO1997045686A1

WO1997045686A1 - Continuous dryer with permanent magnets

Info

Publication number: WO1997045686A1
Application number: PCT/IB1997/000644
Authority: WO
Inventors: Gregory E. Elias
Original assignee: Railfix NV
Current assignee: Railfix NV
Priority date: 1996-05-29
Filing date: 1997-05-28
Publication date: 1997-12-04
Anticipated expiration: 1998-11-29
Also published as: CA2254764A1; ITMI961079A1; IT1282752B1; ITMI961079A0; AU2786397A; NO985374D0; NO985374L; EP0901600A1; JP2000511270A

Abstract

Dryer, in particular for continuous sheet materials, comprising at least a surface which gives heat to the material (9) to be dried, formed by a metal plate or drum (7) heated by eddy currents induced by a rotating cylinder (1) arranged in proximity to such plate and outwardly covered with a plurality of permanent magnets (5). Thanks to this induction heating system, the dryer according to the present invention no longer needs conventional heating units, usually electrical resistance units or steaming units, which are complicated and hard to control.

Description

"CONTINUOUS DRYER WITH PERMANENT MAGNETS"

DESCRIPTION

The present invention relates to a continuous dryer with permanent magnets, and in particular to a dryer for continuous sheet materials, wherein the drying heat is produced by eddy currents (also named Foucault currents) induced in a plate or a metal drum by a rotating cylinder comprising a plurality of permanent magnets.

Continuous 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. The continuous running dryers are particularly used in the textile and paper industries for drying textiles and printed sheets respectively. In the known dryers, the material to be dried is heated by means of conduction, convection or radiation. Each of the three kinds of dryers must be provided with a unit, for instance an electric unit or a steaming unit, which supplies a specific amount of thermal energy suitable for quickly drying, without overheating, the treated material, which is often flammable. Therefore, the known dryers are quite complicated, need a non-stop maintenance and further consume a remarkable amount of energy. Object of the present invention is therefore to provide a dryer free from such drawbacks, namely a dryer of simple manufacture wherein the supply of thermal energy to the material to be dried is easily adjustable. Such an object is achieved by a dryer having the characteristics disclosed in claim 1.

Thanks to the heat produced by magnetic induction in the dryer according to the present invention, the conventional heating units, complicated and hard to control, are no longer necessary. Thus both the use and the maintenance are remarkably improved with respect to conventional 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 an embodiment of the dryer according to the present invention;

- Fig. 2 shows a cross- sectional schematic view of the dryer in Fig. 1;

- Fig. 3 shows a cross-sectional schematic view of a second embodiment of the dryer according to the present invention; - Fig. 4 shows a front schematic view of an embodiment of the dryer magnetic cylinder; and

- Fig. 5 shows a front schematic view of a second embodiment of the diyer magnetic cylinder.

Referring to Fig. 1 and Fig. 2, it can be seen that, according to an embodiment of the present invention, the dryer comprises a cylinder 1, preferably made of ferromagnetic steel, on whose bases two shafts 2,2\ rotatably mounted on two roller bearings 3,3', are fastened, coaxially with the cylinder. One of the two shafts is keyed to a motor 4 whose rotation speed can be adjusted by known control means (not shown in figure). A plurality of permanent magnets 5, preferably parallelepiped-shaped, which are characterized by a high magnetic induction and a high residual coercive force, as e.g. the neodymium permanent magnets, is arranged on the outer surface of rotating cylinder 1, regularly spaced and with alternate polarities. 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 an uniform magnetic field of high intensity is obtained around rotating cylinder 1. Permanent magnets 5 are preferably separated each other by an insulating material layer 6.

A drum 7 of electroconductive material, preferably aluminium, rotatably mounted on shafts 2,2' by means of a pluraUty of rollers 8. is coaxially arranged on the outside of rotating cylinder 1. The inner surface of drum 7 is suitably arranged at a minimum distance from 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 made of a continuous paper sheet, a continuous piece of fabric or another winded material, turns round drum 7 for about a half of its cylindrical development.

One of the two edges of drum 7, preferably that on the opposite side from motor 4, is provided with a toothing 10 engaged in a toothed wheel I I . Such toothed wheel 1 1 is keyed on the hub of a oleodynamic pump 12 connected in series by an hydraulic circuit 13 to an oil tank 14 and to a throttle valve 15 for the oil flow. Said circuit further comprises a safety-valve 16, parallel connected to valve 15, acting to compensate sudden pressure changes, if any, within hydraulic circuit 13.

During the use, cylinder 1 together with magnets 5 is set in rotation at a constant speed by motor 4, thus producing a rotating magnetic field. Thanks to the magnetic force induced by magnets 5 according to Lenz law, drum 7 rotates in the same direction of rotation as cylinder 1, dragging along the material 9 to be dried By operating on valve 15 it is possible to adjust the oil flow within hydraulic circuit 13 and, accordingly, the energy necessary to the working of pump 12, driven by toothed wheel 1 1 engaged in toothing 10 of drum 7. By opening or closing valve 15 it is thus possible to adjust the braking action of hydraulic circuit 13 on the rotation speed of drum 7 according to the rotation speed of cylinder 1, wherefore such drum warms up owing to the eddy currents induced by the rotating magnetic field produced by the relative rotation of cylinder 1.

By acting on motor 4 and on valve 15 it is possible to control the rotation speed of cylinder 1 and drum 7 respectively, thereby adjusting very precisely the thermal energy supply to the material to be dried. Furthermore, such supply may be kept constant irrespective of the forward speed of the material 9 to be dried. In fact, should even be necessary to decrease or increase the forward speed of the material 9 owing to external causes, it would still be possible to adjust the heat provided thereto by decreasing or increasing the rotation speed of cyhnder 1. By using a braking system of the above-mentioned type it is possible to precisely set how much magnetic energy is turned into movement and how much into heat, and this makes the optimization of the dryer efficiency possible.

Referring to Fig. 3, it can be seen that in another embodiment of the dryer according to the present invention the heating surface comprises, instead of a drum. a plane sheet 7, also preferably made of alumhiium, horizontally arranged in a tangent position with respect to cylinder 1. This type of dryer is much more simple from a technical viewpoint than the preferred embodiment, but the adjustment of the amount of heat supplied to the material to be dried can be done only by adjusting at the same time the rotation speed of cylinder 1 and the forward speed of such material, wherefore the drying operation is no longer independent from this latter parameter. hi another embodiment of the dryer according to the present invention, it is possible to arrange the permanent magnets on the rotating cylinder not hi the manner above-disclosed and shown in Fig. 4, namely regularly spaced and with alternate polarities, but in another manner, e.g. in horizontal lines and with alternate polarities, as shown in Fig. 5, provided that in any case the magnetic field produced by the magnets is variable during the rotation of cyhnder 1.

Claims

1. Continuous dryer comprising at least a surface which gives heat to the material (9) to be dried, characterized in that such surface comprises a metal plate (7) heated by eddy currents induced by a rotating cylinder ( 1) arranged in proximity to such plate and outwardly covered with a plurality of permanent magnets (5).

2. Dryer according to the previous claim, characterized in that the permanent magnets (5) are arranged on the outer surface of the rotating cylinder ( 1 ) regularly spaced and with alternate polarities.

3. Dryer according to claim 1, characterized in that the permanent magnets (5 ) are arranged on the outer surface of the rotating cylinder ( 1 ) in horizontal lines with alternate polarities.

4. Dryer according to any of the previous claims, characterized in that the permanent magnets (5) are separated each other by an insulating material (6).

5. Dryer according to any of the previous claims, characterized in that the rotating cylinder ( 1) is driven by a variable speed motor (4).

6. Dryer according to any of the previous claims, characterized in that the metal plate (7) is plane.

7. Dryer according to the previous claim, characterized in that such metal plate (7) is arranged horizontally and tangentially to the rotating cylinder ( 1 ).

8. Dryer according to any of the claims 1 to 5, characterized in that the metal plate (7) is curved so as to form a drum coaxially arranged around the rotating cylinder ( 1 ).

9. Dryer according to the previous claim, characterized in that such drum (7) can rotate owing to the magnetic induction produced by the magnets (5), the rotation speed of the drum (7) being adjusted by braking means.

10. Dryer according to the previous claim, characterized in that one of the outer edges of the drum (7) is provided with a toothing ( 10) engaged in a toothed wheel ( 1 1 ) connected to such braking means.

1 1. Dryer according to the previous claim, characterized in that such braking means comprise an oleodynamic pump ( 12) connected in series by an hydrauhc circuit ( 13) to an oil tank ( 14) and to a throttle valve ( 15) for the flow.

12. Dryer according to the previous claim, characterized hi that such circuit ( 13) comprises a safety-valve ( 16) parallel connected to the throttle valve ( 15).

13. Dryer according to any of the previous claims, characterized in that the permanent magnets (5) are made of a material comprising neodymium.