GB2121260A

GB2121260A - Transverse flux induction heater

Info

Publication number: GB2121260A
Application number: GB08315061A
Authority: GB
Inventors: Robert Charles James Ireson
Original assignee: Davy McKee AG
Current assignee: Davy McKee AG
Priority date: 1982-06-02
Filing date: 1983-06-01
Publication date: 1983-12-14
Also published as: GB8315061D0

Abstract

A transverse flux induction heater suitable for heating metal strip (1) moving in the direction of its length has a multiplicity of C-shaped magnetic cores (3, 3') arranged in pairs with their limbs (5) substantially aligned and with one core (3') of each pair positioned below the strip path and the other core (3) of each pair above the strip path. The cores are arranged in at least one row (7, 8) extending transverse of the direction of movement of the strip and the cores in the or each row have an electrical conductor (9, 9') extending transverse to the direction of movement of the strip and passing through the opening between the limbs of each core. Some of the cores in the or each row are displaceable towards and away from the path in order to adjust the heating effected on the metal strip when an alternating current is passed along the conductor. <IMAGE>

Description

SPECIFICATION Transverse flux induction heater This invention relates to a transverse flux induction heater which is suitable for heating metal strip while the strip is moving in the direction of its length.

If a coil of wire is wound around an electrically conductive workpiece, and it is energised with alternating current, the resultant magnetic flux causes induced currents to circulate within the workpiece and thereby generate heat. However, when the workpiece is a flat strip or plate, insufficient magnetic flux is intercepted to induce a useful amount of heat and effective heating is only possible if very high frequencies are used. To avoid the necessity of employing very high frequencies, transverse flux heating is employed and this comprises arranging induction coils so that magnetic flux between the coils passes through the strip substantially perpendicular to its faces. This causes induced currents to circulate in the plane of the strip to bring about heating of the strip.Uniform heating is achieved when the strip is moved through the heater to run the heat patterns together with every part of the strip eventually receiving an equal amount of energy.

According to the present invention, a transverse flux induction heater, suitable for heating metal strip moving in the direction of its length, comprises a multiplicity of C-shaped magnetic cores arranged in pairs with their limbs substantially aligned and with one core of each pair positioned below the strip path and the other core of each pair above the strip path, the cores on each side of the strip path being arranged in at least one row extending transverse to the direction of movement of the strip and the cores in the or each row having an electrical conductor extending transverse to the direction of movement of the strip and passing through the opening between the limbs of each core and the cores being mounted such that at least some of the cores in the or each row are displaceable towards and away from the path.

In use, when an alternating current is passed through the conductor, magnetic flux is generated and this passes through the strip substantially normal to its thickness. The induced currents which circulate in the strip may produce nonuniform heating across the width of the strip if all the cores are equidistant from the surface of the strip and, consequently, to bring about uniform heating, it is desirable that at least some of the cores can be moved towards and away from the strip in order to adjust the heating effect produced by the cores. Particularly at the edges of the strip the C-cores may need to be positioned further away from the strip than those cores which are at the central portion of the strip.

Preferably, the cores are arranged in a plurality of rows with the cores in adjacent rows being arranged such that the cores in one row are aligned with the spaces between the cores in the other row. With this arrangement, if a heating pattern produced by the cores in one row does not extend completely across the width of the strip but leaves regions between the cores which are not adequately heated, then the cores in the second row are positioned relative to these regions such that these regions are heated by the cores in the second row.

To further adjust the heating pattern, the cores in each row may be movably mounted so that they are displaceable relative to one another in the direction transverse to the direction of movement of the strip.

When the cores are arranged in a multiplicity of rows, then the corresponding cores in each of the rows may be connected together so that these cores may be moved together. The cores may be connected together by a copper bar provided with a water cooling facility.

In order that the invention may be more readily understood, it will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of the upper part of a transverse induction heater in accordance with the present invention.

Figure 2 shows the heat pattern set up in strip material when the strip is stationary, Figure 3 is a perspective view showing cores in different rows connected together, and Figure 4 is an end view of the induction heater.

A transverse flux induction heater for heating metal strip as it is moved in the direction of its length is very useful in processes for annealing, paint curing and the like. A typical transverse flux heating process is a very rapid heating stage in which the moving strip is brought up to a closely controlled temperature in the time taken for it to traverse the length of the induction heater. After annealing, the strip may be quenched. A heater suitable for this purpose is shown in the accompanying figures and in Figure 1 a length of metal strip moving in the direction of its length is indicated by reference 1. On one side of the strip there is a multiplicity of C-shaped laminated magnetic cores 3, each arranged with its two limbs 5 projecting towards the adjacent surface of the strip. The cores are arranged in rows extending transverse to the direction of movement of the strip.The cores in each row, say those constituting the row 7, are spaced apart with the opening between the limbs 5 of the cores extending transverse to the direction of movement of the strip. The cores in the adjacent row, 8, are positioned relative to one another so as to be aligned with the spaces between the cores in the row 7. A heavy current electrical conductor 9 passes through the space between the limbs of each of the cores. The conductor is thus arranged in serpentine manner passing through the cores in successive rows.

The same number of magnetic cores 3', as is shown in Figure 1, are positioned below the strip path, and the cores above and below the strip are arranged in pairs with the limbs of the cores of each pair being substantially aligned. The heavy current electrical conductor 9 also passes through the spaces between the limbs of the cores positioned below the strip, or a second conductor 9' may be used with the cores below the strip. For each pair of cores, the direction of current flow in the two conductors passing between their limbs must be the same.

Figure 2 represents the heat pattern which would develop in the strip if the heater was used with the strip stationary. The regions indicated by dotted lines show the heated areas between the limbs of each pair of cores and it can be seen that the heated regions in the row 7 have spaces between them but that the heated regions in the row 8 overlie the spaces in the row 7 so that, when the strip is moved in the direction of its length, heating is applied across the entire width of the strip.

The corresponding cores in each of the rows may be connected together by a copper bar 11, as shown in Figure 3. A hollow tube 1 3 is positioned on the upper edge of the bar 11 and, by passing cooling water through the tube, the bar 11 and the C-cores can be cooled. The cores which are connected together by one copper bar can be moved together in order to adjust the heating pattern across the width of the strip.

As shown in Figure 4, the cores 15 and 17, which are positioned at the edges of the strip, and the other cores connected to them, can be positioned further away from the strip than those cores which are positioned more centrally of the strip. In this way, any overheating of the edges of the strip which might occur can be avoided.

Furthermore, those cores which are connected together by a copper 11 can be moved sideways relative to the adjacent cores as a unit in order to modify the heating pattern. In this way, the heating applied to the strip material can be arranged to be substantially uniform across the entire width of the strip.

Claims

1. A transverse induction heater, suitable for heating metal strip moving in the direction of its length, comprising a multiplicity of C-shaped magnetic cores arranged in pairs with their limbs substantially aligned and with one core of each pair positioned below the strip path and the other core of each pair above the strip path, the cores on each side of the strip path being arranged in at least one row extending transverse to the direction of movement of the strip and the cores in the or each row having an electrical conductor extending transverse to the direciton of movement of the strip and passing through the opening between the limbs of each core and the cores being mounted such that at least some of the cores in the or each row are displaceabie towards and away from the path.

2. A transverse flux induction heater as claimed in claim 1 wherein the cores are arranged in a plurality of rows with the cores in adjacent rows being arranged such that the cores in one row are positioned in alignment with the space between the cores in the adjacent row.

3. A transverse flux induction heater as claimed in claim 1 or 2, wherein the cores in each row are movably mounted so that they are displaceable relative to one another in the direction transverse to the direction of movement of the strip.

4. A transverse flux induction heater as claimed in claim 2, in which the corresponding cores in each of the rows are connected together so that these cores may be moved together.

5. A transverse flux induction heater as claimed in claim 4, wherein the cores are connected together by a conductive bar provided with a water cooling facility.

6. A transverse flux induction heater as hereinbefore described with reference to the accompanying drawings.