GB2144609A

GB2144609A - Variable width inductor for induction heating

Info

Publication number: GB2144609A
Application number: GB08320899A
Authority: GB
Inventors: Robert Charles James Ireson
Original assignee: Davy McKee AG
Current assignee: Davy McKee AG
Priority date: 1983-08-03
Filing date: 1983-08-03
Publication date: 1985-03-06
Also published as: GB8320899D0; GB2144609B

Abstract

An induct or element for a transverse flux induction heater has a variable width core and a coil winding 13 surrounding a part of the core. The core consists of a first core section 11 and at least one 15, and preferably more 17, further sections, each of which is displaceable between a first position in which it is at the side of the first core section 11 to increase the core width and a second position in which it does not have a part surrounded by the coil winding 13 and thereby the width of the core is reduced. <IMAGE>

Description

SPECIFICATION Variable width inductor This invention relates to an inductorelementfora transverse flux induction heater.

Transverse flux induction heaters consist essential ly of a pair ofinductor elements positioned on opposite sides of a metal strip to be heated. Each element consists of a magnetic core and a coil winding and, when the coil winding is energised, the magnetic - core carries much ofthe magneticfluxwhich is generated and causes it to pass transverselyth rough the metal strip, thereby causing eddy currents to be setup inthe strip andto heatthe srtip.

It is knownforan inductorelementtoconsistofan E-shaped core with a coil winding surrounding the central limb and, to enable the effective width of the element to be adjustable, it is known for magnetic pole pieces, referred to as flux modifiers, to be movably mounted on the end faces of the three limbs of the core and, by adjusting the position of the modifiers, the effective width of the core is adjusted.

Itwill be appreciatedthatonlya limited amount of width modification can be brought about by using flux modifiers, and it is an object of the present invention to provide an inductor element which has a wide range of effective core width.

According to the present invention, an inductor element for a transverse flux induction heater com prises a coil winding and a magnetic core, said core comprising a first section having a part surrounded by the coil winding and at least one further core section displaceable between a first position, in which it is at the side of the first section and has a part surrounded by the coil winding to thereby increasethe effective width of the core, and a second position, in which the further core section is not adjacent the first section, the part is not surrounded by the coil winding and the further core section does not significantly modify the pattern of the flux generated when the coil winding is energised.

It is intended that, in the second position ofthe further core section, the core section is sufficiently far away from the coil winding for it not to modify the pattern of the flux generated when the coil winding is energised. There is always the possibility, however, that, even when thefurthercoresection is displaced from the first section, itwill still slightly modify the pattern of the flux generated, and so itwill be appreciated that the term "significantly" used above with the reference to the modification ofthe flux pattern takes this into account.

They may be two further sections positioned on opposite sides of the first section, 50 that either or both of the further sections can be brought into use to adiustthe effective width of the core.

There may be a plurality of further core sections positioned on one side ofthe first core section and thesefurther core sections are independently displacable between thefirst and second positions, so as to alterthe effective width ofthe core, and the further core sections are brought into their first position progressively, beginning with the section nearest to the first core section and working outwardly from the first core section.

When the or each further core section is in its first position, where it serves to adjustthe width of the core, the or each section is urged into abutting relation with the first core section, to thereby decrease the reluctance ofthe magnetic path provided by the core.

In orderthatthe invention may be more readily understood, it will now be described, byway of example only, with reference to the accompanying drawings, in which Figure lisa perspective view of a known inductor element, Figure 2 shows diagrammatically howthe effective width of the core of the element shown in Figure 1 can be adjusted between small limits, Figure 3 is a perspective view of an inductor element in accordance with the present invention, and Figure 4 shows diagrammatically howthe width of the magnetic core can be progressively varied.

A transverse flux induction heater which is suitable for heating metal strip comprises a pair of inductor elements spaced apart and the metal strip is passed in the direction of its length through the space between the two elements. Usually, the two elements are identical with one element facing the other. In Figure lithe lower one of a pair of inductor elements is illustrated. The element comprises an E-shaped magnetic core 1 and a generally flattened coil winding 3 surrounds the centre one 5 of the three limbs of the core. When the coil winding is energised, magnetic flux is passed through the core and the metal strip which isto be heated.On the end face of each of the limbs, there is positioned a pair of magnetic bodies 7 which are displaceable to a limited extent towards and away from each other on the end face. The position of these bodies serves to modifytheflux pattern generatedwhen the coil isenergisedandthese bodies are termed flux modifiers, sincetheytend to modify the effective width of the magnetic core and, thus, the flux pattern which is set up when the winding is energised.

Figure 2 shows howthe width of the core can be modified. In the upper figure, the flux modifiers are inboard of the outside edges of the cores and the lowerfigure shows the flux modifiers displaced away from each other so that they each overlap the lateral edges of the core. In the upper figure, the effective width ofthe core is a minimum and in the lowerfigure the effective width of the core is a maximum. The amount of adjustment between the minimum and maximum values is rather limited.

Referring nowto Figure 3, an inductorelementfora transverse flux induction heater comprises a magnetic core which is made up of a number of sections which enables the effective width of the core to be varied The drawings originally filed were informal and the print here reproduced is taken from a later filed formal copy.

The claims were filed later than the filing date within the period prescribed by Rule 25(1,6 of the Patents Rules 1982.

over a wide range. The core consists of a fixed first section 11 of E-shaped form and a flattened coil winding 13 surrounds the centre limb ofthe core 11.

The opening defined by the coil is considerablywider than the width of the magnetic core 11.

To one side of the magnetic core 11, there is a further E-shaped core t5. Onthe otherside ofthe core 11 ,there are a number, saythree, E-shaped cores 17 arranged side-by-side. Each ofthefurthercores 15,17 is mounted on a pair offluid operable piston-cylinder devices 19, whereby the further core sections can be raised and lowered independently of each other. At each end of the core, there is a pair of rams 21 which serve to urge the core sections which are in use into side-by-side abutting relation. Each of the core sections is of E-form and the centre limb of each section can be introduced into, and movedfrom,the opening defined by the coil winding 13.Thefurther core section ISis shown in Figure 3 displaced into its first position, where it is side-by-side with the core section 11,and it has a part within the opening defined by the coil winding 13. In addition, as shown in Figure 3, the nearest one ofthefurther core sections 17 tithe section 11 is in its first position, where it is adjacent the core section 11, and the rains 21 act against the outside walls of the core section 15 and the core section 17 which is in use to urge them into abutment with the section 11. On the end face of each of the limbs,there is a pairofflux modifiers 23which are displaceable between an inboard position and a position as shown where they overlie the outer edges ofthecore.

In the arrangement shown, the width of the core section 11 is approximately 850 mm, the width of the section 15 is approximately 400 mm, and the width of each of the sections 17 is approximately 100 mm. As shown in Figure4, an effective coil width of between 800 and 900 mm can be obtained by employing the core section 11 onlyandtheflux modifiers 23. By introducing the core section 17 which is closestto the section 11 into the operating position, the effective width of the core is between 900 and 1000 mm.By progressively introducing the other core sections 17, an effective corewidthof between 1100 and 1200 mm can be obtained. lfthese further core sections 17 are removed to their lowered position where they do not have a part surrounded bythe coil winding 13, and where the core section does not significantly modify the pattern of the flux generated when the coil winding is energised, the effective width of the core can be between 1200 and 7300 mm by introducing the further core section 15 into the first position in which it serves to modify the width ofthe core. The maximum effective width which can be obtained is between 1500 and 1600 mm where all thefurthercore sections are brought into effective use. As seen clearly in Figure 4, when a core section is introduced or removed, the flux modifiers are adjusted to their correct and nominal position, and the inductor is moved transversetyto align centrally with the strip.

The widthsofthe main core section 11 and the retractable sections 15 and 17 are selected such that a particular range of widths can be achieved with the minimum numberofsections.

It will be appreciated that, in the figures, only one inductor element is shown, whereas, for a transverse flux induction heater, two such elements are required, theelementsfacing each otherand being spaced apart bya distance which permits the metal strip to pass between them.

Claims

1. An inductor element for a transverse flux induction heater comprising a coil winding and a magnetic core, said core comprising a first core section having a part surrounded by the coil winding and at least one further core section which is displaceable between a first position, in which it is at the side of the first section and has a part surrounded bythe coil winding to thereby increase the effective width ofthe core, and a second position, in which said part ofthefurther core section is not surrounded by the coil winding thereby reducing the effective width ofthe core and thefurther core section does not significantly affect the pattern of the magnetic flux generated when the coil winding is energised.

2. An inductorelemertasclaimed in claim 1, wherein a plurality of further core sections are positioned on one side of the first core section, said further core sections being brought into their first position progressively, beginning with the section nearesttothefirst core section, and moving outwardly from thefirstcore section in orderto increase the effective width of the core.

3. An inductor element as claimed in claim 1 or 2, in which the or each further core section hasmeansfor displacing it between its first and second positions.

4. An inductor element as claimed in any preceding claim, including meansfor urging the first core section and the or each further core section, when it is in its first position, into side-by-side contacting relation with the or each core section adjacent thereto.

5. An inductor element as claimed in any preced ingclaim, in which the first core section andtheor each further core section is E-shaped and the part of each core section which issurrounded by the coil winding is the centre one of the three stub-limbs of the core section.

6. An inductor element as claimed in claim 5, in which each stub-limb of the core carries a pair of magnetic flux modifiers which are movable relative to the stub-limb between an inboard position and a position in which they overlie the outer edges of the limb to thereby modify the effective width of the core.

7. An inductor element substantially as hereinbefore described with reference to Figures 3 and 4 of the accompanying drawings.

8. Atransverseflux induction heater including a pair of inductor elements each as claimed in any preceding claim.