GB2125660A - Induction coil combined from component coils - Google Patents

Abstract

To provide a compact and easy-to- repair cylindrical multilayered induction coil, a number of component coils embodied as coil segments having two multilayered pancakes are provided, the two pancakes 3, 4 of a segment 2 being wound in opposite directions. The pancakes 3, 4 are interconnected by a bridging element or link or the like 5 which is led out of the plane of the two pancakes. A number of segments 2 can be disposed axially one beside another on a heat-insulating tube 10, each segment 2, which is formed by a coil conductor having an inner cooling duct, forming a separate cooling circuit. <IMAGE>

Description

SPECIFICATION Induction coil combined from component coils The invention relates to a multilayered cylindrical induction coil for heating or melting articles in its interior.

An induction coil of this kind was disclosed in Report No. 4 of Section lla of the Eighth Congree of the Union Internationale d'Electrothermie, entitled "The Theory of Multi-Layered Windings for Induction Heating and their Application to a 1 MW, 50 Hz, Longitudinal Flux Billet Heater", by I.G. Harvey. The Report states how multilayered induction coils can be more efficient than single-layered induction coils.

The iiterature quoted says nothing about particular features of how the coil is wound. If the coil is wound in layers and the coil conductors are of large cross-section, of the kind which must be used in induction coils of this kind, problems arise at the junctions between the various layers, since the conductors experience considerable bending at such places. The problem becomes a very serious nuisance when the coil conductors have an internal cooling duct.

When internally cooled coil conductors are used and the coil is wound in layers, just a single cooling inlet and a single cooling outlet being provided, cooling problems may arise in some circumstances, for the coolant temperature alters very considerably as the coolant flows through the conductor and the cooling varies in different parts of the coil.

Another problem arises with the known induction coils when the coil system has to be repaired, for instance, when internally cooled coil conductors start to leak. In this event the complete coil of the known arrangement must be removed from the conventionally used thermally insulating tube and possibly be completely replaced.

It is the object of the invention to provide an induction coil of the kind mentioned which is compatible with a compact coil winding and ready repairability even though the conductors used are of relatively large cross-section. It is another object of the invention to provide a process enabling the coil according to the invention to be produced without heavy outlay.

According to the invention, therefore, in a multilayered cylindrical induction coil of the kind specified a number of component coils embodied as coil segments having two multilayered pancake windings are provided and the two pancakes of any segment are oppositely wound, the inner layers of both pancakes being interconnected by a bridging element or link or the like which is led out diagonally from the plane of the pancake.

In otherwords, the coil segments embodied by the two pancake windings (pancakes) each form a compact unit in which there is no sharp bending or kinking of the coil conductor. According to a further development of the invention, the two ends of the coil conductor of any coil segment extend radially outwards, starting from the outer turns of the pancakes. This makes for simplicity of the electricity supply connections and, if the coil conductor is internally cooled, of the securing of the coolant connections. Induction coils of virtually any length can be devised with such coil segments and prefabricated component coils can simply be disposed one after another so that a compact induction coil having a high copper factor is provided despite the rapid assembly.The closer this factor is to unity, the better is the performance and the better is the electrical efficiency of the coil. The copper factor of the coil according to the invention is very near unity, at least radially of the coil.

Each individual component coil has its own coolant inlet and outlet. Cooling is substantially uniform axially of the coil, and so heating cannot occur anywhere. The coil, in addition to having a relatively high power factor, has the further advantage that it can be repaired very quickly, for instance, by the replacement of one or more component coils.

The various component coils are very readily accessible and, since they have a separate cooling circuit, the coil according to the invention is very reliable in operation.

According to another feature of the invention, an outer terminal of one pancake of one coil segment is electrically connected to the terminal of the adjacent pancake of the adjacent coil segment. In this way the various segments are electrically connected in series; however, the corresponding ends of the outer layers can be interconnected by a feed line to give a parallel arrangement.

An induction coil whose conductors have an internal cooling duct can be cooled very satisfactorily and uniformly if each segment forms a separate cooling circuit. With this kind of cooling, the various layers of adjacent coil segments are cooled to substantially the same temperature.

In a process for the preparation of a multilayered induction coil according to the invention, starting with the smallest-diameter turn one pancake of one coil segment is wound clockwise and the other pancake of such segment is wound anticlockwise, the inner ends of the wound conductors are led out of the plane of the pancakes, e.g. by being pushed or pulled out, and the inner ends are welded together.

Since the two pancakes may have been moved apart from one another during welding, they are pressed towards one another after welding to give them their assembled shape in which they are disposed ciosely adjacent one another.

In another process for the preparation of a coil according to the invention, starting with the smallest-diameter turn two pancakes are wound in the same direction and the inner ends of the wound conductors are welded together, one pancake having been rotated through 180" relatively to the other.

The latter process may possibly be particularly favourable, to an extent depending upon the winding mechanism, since all the pancakes can be wound in one direction, for instance, clockwise.

In a process according to the invention for preparing a multilayered induction coil without welding of the two inner ends of the coil conductors, the coil conductor of given length for the two pancakes of a coil segment is wound oppositely, starting from the centre of the coil conductor, to form two adjacent pancake windings. In this process the coil conductor has, for instance, its centre placed on a former, whereafter the two ends of the conductor are wound around the former in opposite directions.

An embodiment of the invention will be described in greater detail hereinafter with reference to the drawings wherein: Figure 1 is a side view of a part of an induction coil having a component coil, and Figure 2 is an end view of the induction coil.

Figure 1 shows some of a multilayered cylindrical induction coil, of use for heating a metal article 1 which extends through the coil interior. The coil part shown in Figure 1 comprises a component coil embodied as a coil segment 2. The segment 2 is embodied by two oppositely wound pancake windings or pancakes 3, 4. There are a total of eight layers of turns in the embodiment shown.

The inner two layers of turns of the pancakes 3,4 are directly interconnected by way of a bridging element or link or the like 5, the same extending at an inclination to the plane of the two pancakes 3, 4.

The led-out ends of the outer layers are offset from one another - i.e., offset inwards and outwards from the plane of the illustration. This is clearly apparent in Figure 2. The electrical connections of the component coil are made by way of lugs 6, 7. In this embodiment the coil conductors are hollow conductors having an inner cooling duct. Spigots 8,9 for the entry and exit of water are disposed at the ends of the coil conductors.

An induction coil according to the invention is combined from a number of segments 2. As the chain lines in Figure 1 show, the segments are placed close together one beside another. They extend around a heat-insulating tube 10 through which the article 1 either moves with guidance or by which it is retained. The various component coils can be so rotated relatively to one another that the water connections and the electrical connection lugs are readily accessible, as indicated by chain lines in Figure 2. The distance by which the ends of the outer layers extend radially outwards depends upon the form of electrical and coolant hose connections. In assembly the component coils are first introduced into the oven body, whereafter the heat-insulating tube is pushed into the coil.Alternatively, the heat insulation can take the form of a ceramic compound which is introduced into the permanently mounted coil.

For a series electrical connection the lugs of two adjacent pancakes of different segments are interconnected. For parallel connection corresponding pancakes of the various segments are interconnected.

To produce a segment 2 of the kind shown in Figure 1, in one prcess a pancake is first wound on a former of slightly larger outer diameter than the outer diameter of the tube 10, so that the various layers a, b x are disposed close on top of one another. The end of the innermost turn a is then pushed or pulled out of the plane of the pancake, for instance, into the plane of the illustration given in Figure 2. The led-out end then has welded to it the corresponding led-out end of an oppositely wound pancake so that the two pancakes are then interconnected by the bridging elementS.

This process is used when the two pancakes for a segment are to be welded together without one of the pancakes having to be removed from the former before completion of the segment.

Both pancakes can be wound in the same sense instead of oppositely, in which event one pancake is rotated through 180 before the inner ends of the pancakes are welded together.

In a process in which it is unnecessary to weld the ends of the innermost layer together, a coil conductor of given length has its centre placed tangentially on a former, whereafter the two halves are wound in opposite directions either consecutively or simultaneously. In this process care must be taken either before the winding or during the winding of the innermost layers to ensure that the subsequent bridging element extends at an appropriate inclination to the coil axis.

After completion of the segments a number of them can be placed on a heat-insulating tube, wired up and connected to coolant hoses. Electrical insulation of the coil conductors is provided by insulating bandages on the outside surface of the coil conductor.

Claims (11)

1. A multilayered cylindrical induction coil for heating or melting metal articles in its interior, which comprises a number of component coils embodied as coil segments having two multilayered pancake windings, the two pancakes of any segment being oppositely wound, with the inner layers of both pancakes being interconnected by a bridging element or link or the like which is at an inclination to the plane of the pancake.

2. A coil according to Claim 1, wherein the outer ends of the pancakes are led out radially.

3. A coil according to Claim 2, wherein an outer terminal of one pancake of one coil segment is electrically connected to the terminal of the adjacent pancake of the adjacent coil segment.

4. A coil according to any one of Claims 1 to 3, wherein the coil conductors have an internal cooling duct, each segment forming a separate cooling circuit.

5. A multilayered cylindrical induction coil, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.

6. A method of preparing a multilayered induction coil in accordance with any one of Claims 1 to 5, which method comprises, starting with the smallestdiameter turn, one pancake of one coil segment being wound clockwise and the other pancake of such segment being wound anticlockwise, the inner ends of the wound conductors being led out of the plane of the pancakes, that is, by being pushed or pulled out, and the inner ends welded together.

7. A method of preparing a multilayered induction coil in accordance with any one of Claims 1 to 5, which method comprises, starting with the smallestdiameter turn, two pancakes being wound in the same direction and the inner ends of the wound conductors being welded together, one pancake having been rotated through 180 perpendicularly to the coil axis relatively to the other.

8. A method of preparing a multilayered induction coil in accordance with any one of Claims 1 to 5, which method comprises winding the coil conductor of given length for the two pancakes of a coil segment oppositely, starting from the centre of the coil conductor, to form two adjacent pancake windings.

9. A method of preparing a multilayered induction coil, substantially as hereinbefore described with reference to the accompanying drawings.

10. A multilayered induction coil whenever made by the method of any one of Claims 6 to 9.

11. Any novel feature or combination of features described herein.