FR2531596A1 - MULTI-LAYER INDUCTION CYLINDRICAL COIL EQUIPPED WITH A COOLING SYSTEM - Google Patents

Abstract

TO INCREASE THE EFFICIENCY OF CYLINDRICAL INDUCTION COILS INTENDED TO HEAT A METAL SUBSTANCE, AN INDUCTION COIL WITH SEVERAL LAYERS OF WHICH THE CONDUCTOR 50 CONSISTS OF TWO ELECTRICALLY INSULATED 50A, 50B CONDUCTOR PROFILES IS USED ON ONE OF THE OTHER, PARTLY OVERLAPPING AND IDENTICAL ACHIEVEMENTS. THESE PROFILES ARE SOLIDARIZED BY A WALL BANDAGE 52. EACH PROFILE HAS A COOLING CHANNEL 51A; 51B FOR QUICK AND UNIFORM COOLING OF THE COIL WINDINGS. THE USE OF SUCH A CONDUCTOR GIVES THE INDUCTION COIL A COMPACT CONSTRUCTION.

Description

MULTI-LAYER INDUCTION CYLINDRICAL COIL

  PROVIDED WITH A COOLING SYSTEM To The present invention relates to a coil

  cylindrical induction with several turns or layers

  born in the heating or in the fusion of a metallic substance placed in its internal space, and equipped with a cooling system of at least one of its conductors. An induction coil of this type is known, for example, from Report No. 4 of Division I Ia of the VII th Congress of the International Union of Electrothermics, entitled "The Theory of Multi-Layered Windings for Induction Heating and their Application to a I MW, 50 Hz, Longitudinal Flux Billet Heater "and written by Io G Harvey It is stated in this report that multi-layer induction coils allow a better degree of efficiency than single-layer induction coils However, in multi-layer coils, the cooling of

  conductors raise a difficulty In the inductor coil

  known, cooling takes place from the outside,

  that is to say that the isolated windings of this coil are spaced apart from each other in the axial direction and in the direction

  radial, and that the entire coil or several bo-

  partial bines are in a watertight tank and provided with respective water intake and drainage connections The water circulating in the intermediate spaces between the conductors is supposed to provide cooling

wish.

  In view of the fact that the cooling must be as uniform as possible, the known induction coil is however disadvantageous, because it is hardly possible, from the point of view of circulation techniques, to uniformly cool each zone of the coil This coil can show local overheating, which can destroy the insulation of the coil In addition, the insulation can be damaged in the long term under the action of cooling water, which involves the risk of discharges between the windings, and therefore of a deterioration = reel of the coil Another disadvantage lies in the fact that the cosine phi is relatively low because of the

  large spacing caused technically by cooling

  between the workpiece and the internal face of the

  coil As a result of this relative cooling system

  Completely complicated, repairs can only be carried out with great difficulty. Disassembly of the coil requires

time.

  The object of the invention is to provide an induction coil of the aforementioned type, which has a simple embodiment and is distinguished by a good degree of efficiency.

  According to the invention, in an information coil

  duction of the aforementioned type, this object is achieved by the fact that the cooling system is produced in the form of a cooling channel which crosses the conductor in the longitudinal direction It has been known per se for a long time to equip the conductor with an induction coil of a hollow channel preferably passing through a liquid coolant Nevertheless, in induction coils with several layers of the type concerned by this specification, it has hitherto been assumed that the radial thickness of the conductors must not exceed 3 mm For example, on page 9 of the aforementioned report, it is stated that one could also use internally cooled conductors instead of external cooling using a reservoir waterproof

  water, but that the use of such a coil is

  however excluded in most cases of application, due to the fact that the radial thickness of the conductors must not exceed 3 mm In the above-mentioned reference, it is further explained that such a use is not profitable, because that conductors cooled from the inside and having such a small cross-section are expensive, and that the cooling can only be imperfect because of the low water flow rate We know that, in a coili the losses by stray currents increase when the 'thickness of the conductors increases In accordance with the invention, the radial thickness of the conductors exceeds 3 mm Preferably, it is expected that the radial thickness of these conductors is between 7.5 mm and 8.5 mm Although the losses by stray currents which occur in conductors of such a thickness are not negligible, it has however surprisingly turned out that the compact embodiment of the induction coil, due to the

  cooling according to the invention, allows to obtain globa-

  relatively high degree of efficiency, which

  more than compensates for losses by parallel currents

  sites caused by the large thickness of the conductors.

  The induction coil according to the invention allows

  to wrap the conduits directly on top of each other

  isolated factors, which means that the overall dimensions of the

  coil are relatively modest The cosine phi is relati-

  This is very high since the distance between the workpiece and the inner side of the coil is very small. The degree of efficiency of an induction coil of the type in question also depends, in addition to other factors, on this called the percentage of copper This percentage of copper provides an indication of the extent to which the area of the coil section is effectively filled by the copper conductor The more the percentage of copper approaches the value 1, the better are the power factor and the electrical efficiency of the coil In the coil according to the invention, the percentage of copper is very close to the value 1, at least in the direction

radial of said coil.

  Compared to known single-layer coils, the degree of efficiency achieved is notably improved With respect in particular to known induction coils with several layers of the type presented above, the coil of the invention can be produced more compact, therefore presenting smaller external dimensions The risk of local overheating and possible discharges occurring between the conductors is excluded Since it is not necessary to provide

  a special water tank for the coolant, -

  the coil can, if necessary, be repaired quickly.

  Another notable advantage of the invention consists in

  in that pre-existing heating installations by -

  induction can be fitted without any particular complexity

  multi-layer induction coils according to the invention.

  With the "external cooling" known and described above, this rapid and inexpensive transformation of existing installations is not possible As already mentioned above, the measures proposed by the invention result in a degree of relatively good efficiency Nevertheless, it would be desirable to further increase this degree of efficiency

  by further elimination of losses by parallel currents

  sites To this end, in accordance with the invention, the conductor is produced in the form of a multiple conductor composed of several conductive profiles and in particular in the form

  of a double conductor comprising two conductive profiles.

  The realization in the form of a multiple conductor provided with an electrical insulation placed between the conductors largely avoids the generation of losses by currents

  interference during operation of the induction coil.

  In a particular embodiment of the in-

  It should be noted that the double conductor has a substantially rectangular or oval section; and that the

  conductive profiles each comprising a cooling channel

  respective respective at least partially overlap and are electrically isolated from each other in the overlap region As in known conductors, the cross section of the conductors composed of several conductor profiles is preferably approximately rectangular, which allows to obtain a compact coil winding According to

  the above description, it is certainly possible in principle

  to manufacture the entire section of the conductor from solid copper and to incorporate a circulation channel therein, but, according to the above-mentioned improvement, it is more favorable for the conductor channel to have a relatively large section, just as in the massive embodiment of this conductor, said conductor however having a lower height, however. When two conductors of this type are combined,

  the thinnest areas of the conductor thus formed overlap

  vauchent, which allows to obtain a substantially rectangular section overall -Although the conductive profile therefore only has essentially a thickness of 3 mm to 4 mm, the channel has a relatively large section, which guarantees sufficient cooling In this particular embodiment of the conductor comprising conductive profiles which overlap at least partially, the advantage

in autonomous protection.

  The proposed overlap of conductive profiles, intended to reduce losses by stray currents and to

  optimize the degree of yield, can be achieved in different ways

  different ways In one embodiment of the information

  note, it is expected that the two conductor profiles will

  briqu into each other like a comb by their faces distant from the respective cooling channel, and

  whether they are made in particular with a groove or a tongue

  elastic lookout This embodiment makes it possible to obtain,

  in addition to the desired partial overlap of the profiles -conduc-

  good cohesion of these two profiles.

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  The invention further provides that the two conductive profiles are of symmetrical embodiments and jointly form a substantially rectangular or oval section. When assembled, these two symmetrical conductive profiles advantageously complement each other to form a rectangle. In one possible embodiment of the symmetrical conductive profiles, these profiles are wedge-shaped, the cooling channel being provided in

  the end of each profile away from the corner point.

  In a type of embodiment which is appreciably more favorable from the point of view of production techniques, it is intended that

  the conductive profiles have on one side a stepped shape.

  In a preferred development of the invention which is characterized by very low losses by parasitic currents, the conductive profiles comprise a region which surrounds the cooling channel according to approximately the

  3/4 of an annular disc 'and to which an end member

  pointed mite is connected in such a way that two profiles

  offset from each other-from 1800 form a rectan- surface

  gular substantially closed In this type of embodiment according to the invention, the section is comparable to two figures

  "9" juxtaposed, one of which is shot from 1800.

  Of course, the two profiles of a driver can

  basically be electrically interconnected from no

  wears what a way but the conductive profiles of a

  conductors are however preferably connected in parallel.

  To take optimal advantage of the conductive profile according to the invention in an induction coil, the winding of this coil must be such that it is

  actually possible - to obtain a compact realization.

  This is in particular guaranteed when the coil has a winding produced as described in the Applicant's patent application filed on the same date as this memo. According to this document, the present invention provides that the conductor (s) of the coil form one or more coil segments each consisting of two coil spirals which, with several turns or layers, are juxtaposed and wound in opposite directions, the S internal winding layers of the two spirals being connected

  -one to the other, preferably by a transition body-

  extending obliquely to the plane of said spirals.

  Such a coil winding is well suited for relatively thick and wide conductor profiles, since the particular type of this winding does not require

  no marked bends or bends.

  It turned out that, in order to be able to obtain a reduction

  tion of stray current losses, the conductor has at least on one of its short sides, a rounded section, preferably semicircular Thanks to this characteristic according to which the conductor is rounded in a semicircle of

  preferably on its two short sides, it is possible to improve

  improve electrical efficiency by around 10%.

  The invention will now be described in more detail by way of non-limiting examples, with reference to the appended drawing in which: FIG. 1 is a fragmentary side elevation of an arrangement of induction coil FIGS. 2 A to 2 C are respective cross sections of a coil conductor equipped with a channel

cooling -

  Figure 3 is a transerval section of a conductive profile pierced with a cooling channel; Figure 4 is a cross section of two conductive profiles assembled to form a coil conductor; and Figures 5 to 7 are cross sections showing different embodiments of conductors

of coils.

  Figure 1 partially illustrates a cylindrical coil.

  that of induction with several turns or layers, which is used to heat a metal part 1 to be machined, displaced in the internal space of said coil The part of the induction coil illustrated in the drawing consists of a segment 2 of coil which in turn comprises two coil spirals 3 and 4 wound in opposite directions Five layers

  in total are provided in the example of a

  Lization shown The two internal winding layers of the spirals 3 and 4 are in direct connection with a transition member 5 This member 5 extends obliquely with respect to

at the plane of the two spirals 3 and 4.

  The ends extended towards the top of the layers

  of external windings are mutually offset, i.e.

  say that they leave the plane of the drawing - or enter this plane The electrical connection is ensured by connection terminals 6 and 7 Sleeves 8 and 9 for connection to a water circulation system are at the ends

of the coil conductors.

  The induction coil is formed as a whole of several segments 2 which are very close to each other. It should be explained below, with reference to FIGS. 2 to 7, different forms of realization of coil conductors (hereinafter referred to as "conductors") which are used for each coil spiral-described in

the support of figure 1.

  Figure 2A shows a very simple and inexpensive embodiment of a conductor This conductor

  consists of solid copper in which a channel of-

  cooling 21 is developed according to a known and conventional process for this purpose In a manner known per se, with a view to mutually isolating the windings from the coil, the conductor 20 can be surrounded by a wound band 22 electrically insulating The height of the conductor 20 measures 8.5 mm and its width is 40 mm During operation g of the induction coil, the cooling channel 21 is traversed by water, so that the windings

  -individual of the coil are cooled in a suf-

  fisante and uniform While in this example of realization

  tion, the small side of the conductor, 20 illustrated on the right on

  the drawing is flattened> the left side of this conductor pre-

  feels a semicircular section This rounding of the conductor section helps to reduce losses by

stray currents.

  Figures 2S and 2C show other embodiments of a conductor according to the invention and, relative

  to the conductor 20 according to FIG. 2 A, these examples of realization

  sation are distinguished by the fact that the section of said conductor is substantially rounded in a semicircle on the two short sides A conductor 20 ′ shown on the

  Figure 25 has a sensitive cooling channel 21 '

  ment oval which-is arranged symmetrically with respect to = the section of said conductor 'In a conductor 20 "according to Figure 2 C, a cooling channel 21" is located in the left half of the conductor section In the other examples of realization of the invention which will

  described below, at least one of the short sides of the pipe

  the tor is also preferably rounded in a semicircle in order to keep the losses by stray currents as low as possible Experiments carried out with a six-layer coil comprising a conductor whose cross section

  measured 8.5 mm x 23 mm revealed that the electrical performance

  was 0.52 with a conductor of perfect cross section

  rectangular, while this yield was 0.57

  with a conductor whose short sides were rounded.

  In the presence of a cylindrical coil with several layers produced in accordance with FIG. 1, the conductor according to FIGS. 2 A to 2 C makes it possible to obtain a relatively large yield However, because of the relatively large radial thickness (8.5 mm), there are still significant losses by stray currents, which can be reduced very considerably when using

  do they conduct according to figures 3 3 7.

  FIG. 3 illustrates a conductive profile 30 comprising a cooling channel 31 Two profiles 30 of this type, offset from one another by 180 in accordance with FIG. 4, are grouped together to form a conductor 40 These two conductive profiles are secured by an electrically insulating wrapped bandage 42 The two profiles are separated from each other by an intermediate layer 43

electrically insulating.

  Figure 5 shows an alternative embodiment which

  will be preferred to prevent losses by stray currents.

  Unlike the embodiment of Figure 4, which is of substantially rectangular section, the section is approximately oval in the embodiment according to

  FIG. 5 A conductor, 50 comprises two conductive profiles

  tors 50 a and 50 b which are mutually offset by 180 and

  which have a largely closed section in their condition

  Illustrated tion These two conductive pro-wires are separated electrically from each other by an insulating intermediate layer 53 It appears from the drawing that these two profiles 50 a

  and 50 b are perfectly identical and arranged symmetrically-

  is lying. The conductive profile 50 a has for example a region 54 which surrounds a cooling channel 51 a along approximately 3/4 of an annular disc, and to which is

  connects a member 55 This member 55 is of thick

  roughly equal to half that of the whole conductor 50 To allow its adaptation to the circular area of the profile 50 b, the end of the member 55 remote from the cooling channel 51 a is curved at a point at 53 Le profile cooling channel 50 b

bears the reference 51 b.

  The two conductive profiles 50 a and 50 b are

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  It is secured by a wrapped bandage 52 As can be seen in the drawing, the thickness of one of the overlapping profiles 50 a and 50 b is in no place greater than half the thickness of the conductor 50 This guarantees high efficiency of the induction coil due to low losses

  by stray currents occurring in the conductor.

  In the embodiment according to FIG. 6,

  two conductive profiles 60 a and 60 b with identical configurations

  ticks, having cooling channels 6 la and 6 Bb and secured by a wound bandage 62, are brought together in a conductor 60 An insulating layer 63 separates one of

  the other these two profiles 60 a and 60 b.

  According to FIG. 7, a conductor 70 is formed by two conductive profiles 70 a and 70 b which overlap one another like a comb. Profile 70 a has a groove 76 into which an elastic tongue penetrates. 77 of the profile 70 b, an insulating layer 73 being interposed between these two complementary parts. Thanks to this embodiment of the conductive profiles provided with a groove and a tongue.

  elastic, good cohesion of these profiles is ensured.

  This cohesion is further reinforced by a wound bandage 72. The invention was tested on a test device in which a conductor was used according to FIG. 5 The induction coil consisted in the total of fifteen coils

  Partials of the type described above with regard to Figure 1.

  Consequently, in the presence of six winding layers, the number of windings for each partial coil was twelve.The length of the coil measured 720 mm for a diameter of this coil of 210 mm, the conductor had a radial thickness of 8, 5 mm and an axial width of 46 mm Using the induction coil thus produced, a hollow block of copper cooled by water and having a diameter and a length of 165 mm and 650 mm, respectively, has kept warm at a temperature of 120 C. The electrical power was 122 k W In the cooling channel of each conductive profile, the cooling water flow rate was 0.2 m 3 / h A measurement of the water temperature revealed on the inlet side a value of 9.30 C and on the outlet side a value of 19.20 C The current intensity was 1.165 A, the winding voltage was

  3.35 V and the electrical resistance was 1.70 x -10,352.

  The power loss of the entire coil was found to be 34.77 k W and the cosine phi was

  0.175 It results from the parameters indicated an electrical efficiency

  0.715 rating By way of comparison, it will be indicated that, with single-layer induction coils and with internal cooling, an electrical efficiency is achieved

about 0.425.

  The invention is not limited to the exemplary embodiments

  tions described above It is also possible to use other conductive profiles which satisfy the requirement for low losses by parasitic currents. For example, as a variant of the embodiment according to FIG. 7, provision may be made for providing several grooves and elastic tabs on the two conductive profiles, which makes it possible to reduce losses by stray currents The conductors formed

  by several conductor profiles should not be necessary

  obviously made in the form of double conductors, but

  three or more than three profiles can also be flush

  seem to form a single conductor However, in such embodiments, it must be taken into account that the individual conductor profiles are not identical, so that different conductor profiles must be available for the production of a

  driver, which increases the cost of the entire installation.

  The induction coil according to the invention can be used not only for heating a metallic substance, but it is also possible to use this

coil in melting furnaces.

  It goes without saying that many modifications can be made to the coil described and shown,

  without departing from the scope of the invention.

Claims (10)

  1 Cylindrical induction coil with several turns or layers, intended for heating or melting a metallic substance placed in its internal space, and equipped with a cooling system of at least one of its conductors, coil characterized in that the cooling system is designed as a cooling channel (21; 31; 51 a, 51 b; 61 a, 61 b) which passes through the conductor (20; 30; 40; 50; 60; 703 in the direction longitudinal.   2 induction coil according to claim 1,   characterized by the fact that the radial thickness of the conduits   teurs is between 7.5 mm and 8.5 mm.   3 induction coil according to one of claims   1 and 2, characterized in that the conductor is produced in the form of a multiple conductor composed of several conductive profiles, in particular in the form of a double conductor (40; 50; 60; 70) comprising two   conductive profiles (30; 50 a, 50 b; BO 60 a, 80 b: 70 a, 70 b).   4 induction coil according to claim-3; characterized in that the double conductor has a substantially rectangular or oval section; and by the fact that the conductive profiles (30; 50 a, 50 b, 60 a, 60 b) each comprising a respective cooling channel   (31; 51 a, 51 b; B 1 a, 61 b) overlap at least partially-   and are electrically isolated from each other in the ' overlap area.   Induction coil according to one of the claims   3 and 4, characterized in that the two conductive profiles overlap one another like a comb by their faces remote from the respective cooling channel; and are in particular produced with a groove (76 ) or an elastic tongue (77).   B Induction coil according to one of claims   3 and 4, characterized in that the two conductive profiles are of symmetrical embodiments and jointly form a substantially rectangular or oval section. 7 Induction coil according to any one of   Claims 1 to 6, characterized in that the   conductive profiles (60 a, 60 b) are wedge-shaped, the cooling channel (61 a; 61 b) being provided in   the end of each profile away from the corner point.   8 Induction coil according to any one of   Claims 3 to 6, characterized in that the   conductive profiles have a stepped shape on one side 9 Induction coil according to any one of the   Claims 3 to 6, characterized in that the   conductive profiles (50 a, 50 b) have a region (541 which surrounds the cooling channel (51 a; 51-b) along approximately 3/4 of an annular disc and to which a frame (55) at the end point is connected in such a way that two profiles offset from each other by 1800 form a   substantially closed rectangular or oval surface.   Induction coil according to any one of   Claims 1 to 9, characterized in that the profiles   conductors of a conductor are connected in parallel.   11 Induction coil according to any one of   Claims 1 to 10, characterized in that the or   the conductors of this coil form one or more segments (2 l of coil each consisting of two coil spirals (3,4) which, with several turns or layers, are juxtaposed and -wound-in opposite directions, the layers of internal winding of the two spirals (3, 4) being connected to each other, preferably by a transition member (5) extending obliquely to the plane of said coil spirals.   12 Induction coil according to any one of   Claims 1 to 11, characterized in that the   conductor has, at least on one of its short sides,   a rounded section, preferably semi-circular.