INDUCTION HEATING APPARATUS

Abstract: Apparatus for induction heating of billet-shaped blanks (10) of electrically well conductive and non-magnetic metal, in particular aluminium or copper, comprising a winding (21) adapted to surround the blank completely or partially, to be supplied with electric alternating current (8) and to be cooled (22) at least during the heating of the blank (10). The winding has turns comprising superconducting material and is enclosed by a thermally insulating chamber (33). The cooling (22) is adapted to maintain the winding at a temperature in the range 30-90 DEG K, and the frequency of the alternating current (8) is adapted to be in the range of common mains frequencies.

Description: INDUCTION HEATING APPARATUS This invention relates to an apparatus for induction heating of billet-shaped blanks of electrically well conductive and non-magnetic metal, in particular aluminium or copper, comprising a winding adapted to surround the blank completely or partially, to be supplied with electric alternating current from a power supply and to be cooled by means of a cooling system at least during the heating of the blan . A known and typical arrangement for such induction heating is shown in Fig. l in a simplified and schematic manner. There is shown a workpiece or blank 100 and a cut- through winding 101 which is adapted to be supplied with alternating current as shown. Moreover, with dashed lines there is illustrated at least partially how a generated magnetic field passes through the blank 100 for the heating thereo . When the material in blanks of interest is an electrically well conductive and non-magnetic metal, such as aluminium and copper, the prior art induction heating devices have a low efficiency, namely a maximum of about 50%. In other words about one half of supplied electric power will get lost in the windings. Moreover induction heating of aluminium and copper blanks, including the so- called billets, is characterized by a high capacity per unit volume. In typical installations there is the question of capacities of 500 k . Accordingly, within this field there is a strong desire of obtaining improvements for the purpose of energy economy and resource savings. An additional factor of interest in this context is that the blanks concerned of aluminium or copper exist in the form of extrusion billets, which have a relatively elongate shape and are usually solid. Thus, these are per se with respect to their main shape, well suited for induction heating. An actual example of induction heating may be found in US patent 5,781,581. This primarily relates to a chamber ("soaking pit") for cooling and re-heating of parts having just been cast. In this case the material apparently is steel. The parts are placed in the chamber, which is adapted to be evacuated. There are mounted radiation screens or the like in order to prevent heat from escaping and getting lost. In the case of a need for re-heating, induction effect is employed, or as an alternative direct heating by providing for a current flow through the blank or workpiece . The frequency range in induction heating is stated to be in the range of 100-1000 Hz. These frequencies indicate that there is here the question of a magnetic material (steel) that is to be treated. In the patent specification and as a subordinate feature there is included a short reference to superconduction as a possible effect of interest. Another example of prior art having a certain interest in this connection, is US patent 5,391,863. Superconduction is not mentioned in this patent specification, that otherwise has a content coresponding to some degree to the first paragraph of the present description. In this connection there is reason to note that superconductors have been known for a long time and also at least from more than 10 years ago based on cooling with liquid nitrogen. The present invention comprises an advantageous utilization of superconductors, as will appear from the following description. In an arrangement for induction heating of solid, cylindrical billets as illustrated in Fig. 1, the efficiency is determined by the following formula: where p v and p b are the resistivities of the material in the winding and the blank or billet, respectively, and μ b is the relative permeability of the billet material. Whereas the permeability of iron is of the order of magnitude of 1000, it is approximately equal to 1 for non-magnetic materials such as aluminium and copper. This means that iron is substantially more favourable with respect to the efficiency in such induction heating. When the blank or billet consists of a non-magnetic material with very good electrical conductivity, as for example aluminium or copper, the efficiency will be about 50%, since the resistivities for a traditional copper winding and the blank material respectively, are approximately equal. In other words the value of the root expression in the formula above, will be approximately equal to 1. Thus, one half of supplied electric power will be consumed in the induction winding and one half will be transferred to the blank. Substantial improvements in the above relationships will be obtained according to the invention in an apparatus for induction heating as referred to at the beginning of this description, in that the winding has turns comprising superconducting material and is surrounded by a thermally insulated chamber, that the cooling system is adapted to keep the winding at a temperature in the range of 30-90°K, and that the frequency of the alternating current is adapted to be within the range of common mains frequencies. In an advantageous embodiment of the apparatus according to the invention, the cooling in the cooling system takes place with liquid nitrogen or helium gas being brought to circulates in cavities or cooling channels adjacent to the winding inside the thermally insulated chamber. Nitrogen has a boiling point of 77°K at normal atmospheric pressure and in actual practice it can be appropriate to keep the winding temperature 10-12° lower than this boiling point, when liquid nitrogen is used. On the other hand there will often in practice be a somewhat higher temperature in the actual winding than the temperature of the cooling medium. When using nitrogen at 77°K the winding temperature therefore may be at 90°K. A winding temperature of 60°K will be optimal in many instances. Suitable temperatures in this connection will to a significant degree depend upon the materials employed in the winding, in particular the superconducting materials. When helium is used, the temperature range should be between 40° and 60°K. Below 40°K the cooling costs will be significantly increased. In another possible embodiment there is according to the invention, provided a jacket of well heat conducting, but electrically insulating material being in thermal contact with the winding, and being cooled by means of a cooling unit which is a part of the cooling circuit of the cooling system. The embodiments just referred to show that windings comprising superconductors require quite different design solutions from what is tranditionally found in electric induction heating. Usual structures with copper conductors involve hollow conductors, so that cooling water can circulate through the hollow conductors in the winding. With the low (cryogene) temperatures being of interest according to the invention, there will be the question of quite different solutions for the cooling. Accordingly, the thermal insulation will also be more significant. Moreover, it is a feature of interest that certain types of superconducting threads have anisotrope properties in so far as the losses depend upon the direction of the magnetic field in the winding. A substantial advantage with respect to efficiency consists therein that this will increase from about 50% to 90-95%. This of course is very significant and shows that there is here the case of a new solution having a high practical value for the industry. In the following description the invention will be explained more closely with reference to the drawings, showing somewhat schematically and simplified various embodiments being possible in practice. Fig. 1 shows (as already mentioned) a typical known arrangement for induction heating, Fig. 2 in cross sectional view shows the main features of an embodiment of the apparatus according to the invention, Fig. 3 in partial cross section similar to Fig. 2 shows somewhat more in detail some structural features of an apparatus according to the invention, Fig. 4 in partial axial section shows an embodiment corresponding to the one in Fig. 3, Fig. 5 shows the main features of another embodiment as a whole, and in axial cross section, Fig. 6 shows in enlargement and more in detail a cross section of an apparatus as in Fig. 5, Fig. 7 shows a further enlarged and more detailed, partial axial cross section of an embodiment as in Fig. 5 and Fig. 6, Fig. 8 and Fig. 9 serve to illustrate a modification of the magnetic field at an end portion of an induction heating apparatus, Fig. 10 in cross sectional view shows an advantageous assembly of conductor elements into conductor groups being employed for the winding or windings in an induction heating apparatus, Fig. 11 schematically shows the construction of a complete winding in a layered manner according to a common method of winding, taking as a basis conductor groups consisting of conductor elements as for example shown in Fig. 10, and Fig. 12 schematically shows in a similar way how a complete winding can be built up in the form of "pancake" or package-like winding parts. Centrally in the apparatus of Fig. 2 there is inserted a workpiece or blank 10 to be heated by induction effect. The blank 10 is supported by two tube-shaped rails 10A and 10B which can be made of non-magnetic steel. Radially innermost the induction heater shown here, has a lining 10C of non-magnetic steel, so that there is formed an airgap 10 between the blank 10 and the surrounding induction heating apparatus. An essential element therein is an induction winding 1 which according to the invention comprises superconductors. Thus, the winding is surrounded by thermal insulation layers which together constitute a thermally insulated chamber 3. The composite wall that constitutes the chamber 3 lies between the above inner lining 10A and an outer, protective layer 7D of for example glas fiber reinforced epoxy material. In addition to the outer layer 7D corresponding layers 7A and 7C can cover the winding 1, and a layer 7B delimits an insulation layer 6B radially inwards. Advantageously the insulation 6A and the insulation 6B at the outside of the winding 1 can be so-called superinsu- lation consisting of several layers of metallized polymer foils in vacuum. Inside the superinsulation 6A there is a layer 9B of temperature resistant thermal insulation and then again inside this a layer 9A of refractory ceramics, typically in the form of aluminium silicate or the like. It is obvious that the above examples of specific materials employed in the construction of the thermally insulated chamber 3, can be replaced by other materials having corresponding properties. It is not shown in Fig. 2 how alternating current is supplied to winding 1, nor how the winding comprises superconducting ribbons in a bath of supercooled liquid nitrogen. This cooling serves to maintain the winding at a temperature in the range of 30-90°K, possibly limited to 40- 77°K. The frequency of the alternating current applied, is adapted to be in the range of common mains frequencies. For the required cooling of winding 1 to (cryogene) temperatures there are also alternatives to liquid nitrogen, namely in the first place helium gas. The cooling medium is brought to circulate in the form of a bath as mentioned, adjacent to the winding 1 within the thermally insulated chamber 3. During operation of such an apparatus the cooling normally in practice will be effected all the time, and not only during the actual heating of a blank. The cooling effect therefore will be more or less necessary all the time because there will continuously be present a certain, small leakage of heat into the apparatus from the surroundings . In the embodiment of the apparatus as a whole, as it is illustrated in Fig. 5 in axial cross section, elements as referred to above in connection with Fig. 2 are found again, i.e.: blank 10, a winding 21 and a surrounding chamber 33 for the thermal insulation of the winding. 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Hi s; 0 Φ fu tr μ- HJ rt Cu rt M hi 3 a a Φ rt μ- ft O μ- ft o * LΠ Ω φ 3 - X u rt μ- ; rt Φ M fu μ- φ rr tr M o ft rt a en 0 Ω μ- a a u en Φ - Ω o hi Cu 3 LQ μ- 3 •ti φ μ- M 3 φ Φ ft μ- φ Φ •ti cu a Φ LQ hi hi o Hi ^ rt φ Ω ft o fu Cu ft rt 3 Ω M LΠ •ti Φ a μ- a hi Ω 0 M LQ 0 to en a ft Φ tr C μ- Hi 3 Ω tr μ- Ω μ- > Cu o M Ω LQ LQ g rt a M M μ- μ- a en rt μ- H Φ M M 3 r Ω rt Φ 3 H •ti M tr H Φ Φ • φ μ- ft CU a a a Cu Cu 3 μ- cu μ- CU LQ tr Cu fu Hj LQ 0 M μ- 0 rt 3 ft •ti ft 0 μ- rr ft a Ω LQ cu rt ? H{ W rt Ω 3 en Φ 3 < μ- φ u μ- a a - rt •fl 3 tr) o ft r M M Φ ^ tr ϊ*r Cu H en μ- Φ o a hi Cu LQ 0 μ- 0 rt a a "< u Φ M o Cu rt rt rt 3 LQ hi tr r rt rt M en en en φ φ Φ n en LQ •< LO ω t to H o o LΠ O tr Hi 3 en Cu h o rt u 1 Cu en Ω Φ X rt rt Φ μ- cu Φ en Hi 3 Cu to td φ 3 3 Cu Ω •ti > 3 μ- 3 3 X μ- . tr μ- μ- tr 3 3 X o 0 tr X 3 •ti M •ti Hi φ M 3 φ M fu X μ- φ Ω rr φ ft tr μ- φ Φ LQ tr LQ o •ti ii rt Hi Cu rt Hi •ti Φ φ O Cu 3 μ- en Φ rt r μ- hi 3 Ω M φ l_l. fu M H . M • < Φ HI Φ ft hi r Φ M fu 3 Ω g 3 3 rt μ- Ω Φ Φ fu Ω Φ 0 rt ft en Φ M ft rt 3 Cu Φ HI Φ 3 en fu 3 3 ii φ μ- en μ- fu ft rt hi Hi M 3 rt hi H tr μ- Ω M Cu CO 3 VO - H Ω 3 en ft rr ft Φ φ 3 Hi en H 3 tr φ H| μ- μ- M H M Hi ft 3 φ Ω H{ rt ^ M μ- LQ ? - tr 0 rt μ- rt μ- tr Φ 3 3 rt μ- 3 Hi tr μ- M en μ- Cu CU ^ 3 fu fu μ- en fu φ Φ μ- en 3 rt μ- φ 3 O tr u φ ft Ω rt en Ω •ti 0 φ 3 φ Ω M M rt rt 3 rt φ M ft ft Hi 3 Φ tr H Hi Ul ft M 3 φ M en Φ M u •it Hj 3 3 μ- u Φ rt μ- μ- LQ Φ Hi Ω Ii φ en rt Φ o Φ φ 3 o M Φ 3 • H 1 M M 3 rt M 0 •ti X tr 0 3 M cu Hi 3 rt 0 en φ μ- H| en μ- l-h Ω en μ- μ- ^ o Ω H M ^ 3 Hi 3 Cu M h HI rt Φ 3 LQ ■ : ft Φ M . 0 3 φ Ω Φ Cu •ti M Hi rt en 3 3 Φ H o X ^ 0 Φ μ- rt tr ^ 0 Φ Ω Cu tr μ- 3 3 φ M φ o φ Hi ft 3 Φ 3 μ- Cu 0 ft < rt Φ fu rt •ti 3 Ω Ω rt O rt rt Φ rt X 3 Hi tr ft Ω 3 Ω HI en cu M μ- ft en M 3 rr Hi μ- Φ hi Hj en μ- tr Φ ft cu tr tr Hi μ- tr μ- Hi μ- fu rt en rt en X 3 hi Cu μ- M ft tr Hi Hj μ- μ- 3 φ H| μ- < cu Φ μ- 0 ft φ 3 •rl HI Φ en Cu μ- rr • μ- μ- Φ φ •ti X cn Φ fu ^ rt ft cu rt en en rt 3 μ- Hi Φ cn 3 μ- ft μ- 0 M < hi O 3 cu 3 Ω o μ- rt t M h( M μ- μ- φ M O 3 φ μ- LQ rr cr Φ 3 en u Hi μ- LQ 3 ft 3 Ω φ Cu H M Ω rt H cu en cu to φ rt 3 3 • en M φ μ- Φ •ti Ω LQ cu 3 - o 0 M rt rr Φ φ rt M < Φ LQ LQ tr cu φ en ϋ φ Hj g M M X H ft LQ rt rt H| ^ Φ Φ tr ft ft μ- M rt Φ o Cu hi Ω φ rt M o en 3 O Φ tr Cu μ- vo tr X ii ft M Φ μ- Ω o > tr hh hi 3 rt rt Cu μ- φ Cu ft X en " fu μ- 3 cu to Φ tr tr Φ Φ H| CU 3 3 Φ cu φ Cu tr o 3 3 3 3 en en LΠ P rt μ- H Ω en M H fu Φ φ en H tr 3 X φ 3 Cu en 0 Hi 3 Cu rt Φ φ LQ φ M 3 tr - Hi 3 Hj φ •ti tr *< φ μ- Ω LQ 3 Φ en μ- ^ hh Ω 3 φ to fu M σ LQ 0 h Φ Cu φ 3 O Φ 3 3 rt tr 3 rt rt μ- μ- hh tr 3 3 μ- o tr rr M Ω φ Ω h μ- en LQ fu 3 en 3 rt ft μ- Φ Φ o X 3 3 Φ o LQ Cu LQ Hj fu tr en φ Ω -J Hi cu Φ O •ti a en •ti ft Φ Φ en μ- 0 rt fu h Hi X LQ 3 3 3 0 •ti Φ 3 •n M 3 Φ ii μ- Cu 3 3 Ω μ- fu hi rt M hi 3 Ω 3 Φ μ- rt Cu φ o hi 1 hi V 3 μ- ft rt M rt rt o 3 Hi 3 H LQ - o Ω ft tr 3 o 3 Φ X Ω 3 3 ti ft en 0 hi o LQ tr M μ- 3" < LQ μ- en H 3 M en u Φ 3 Cu HI rt Cu fu rt ft rt μ- td < O rt • Ω cu Φ Ω Φ μ- LQ X X en Hi 0 rr 3 fu rr hi μ- rt 3 M tr en rt 3 1 μ- 3 O rt ft ft Φ 3 O fu tr tr μ- μ- X cu Ω LQ Φ Ω tr •ti M Φ rt tr LQ -J ft Cu tr CO 3 hh φ Φ 3 hi hh 3 Φ μ- ft Φ φ rt rt Φ 3 Φ 3 Φ M > < H| tr to Φ O φ LQ Φ •ti rt Cu μ- M ft ft φ ft 3 Ω φ M tr Φ μ- rt hh HI Φ 3 Φ co rt ft 3 Cu o tr •ti φ φ en rt tr Hi ft rt φ 0 rt rt μ- Φ en Cu ^ en 0 Hi Φ H 3 3 μ- •ϋ M 3 Cu •ti tr H rt φ ft tr 3 μ- tr Cu Φ tr rt M hi to fu 0 3^ r Φ ft Φ cn HI ft φ 3 o en φ to tr HI ft Ω Φ Φ 3 Ω Φ rt M μ- Φ Hi M o CO g •*. HJ 0 μ- LQ 3 φ 3 ^ Hi tr μ- Φ o LQ Cu r hf ft en o rt * ft :> φ μ- en Ω CU rt rt Ω ft rt o ft fu tn ft rt 3 hi Φ LQ tr 3 CO fu 3 en LQ rt φ hi μ- en o μ- μ- g μ- X μ- en 3 0 •ti Φ 3 3 Φ Cu Φ rt Cu M LQ X td •ti 3 ^ en 3 ft LQ - u u H Φ 0 u Ω Ω 0 Φ ft Φ rt 3 rt tr ft 3 φ fu 3 μ- Cu Φ • Cu tr LQ H Cu 3 rt LQ l_J. O Φ •ti 3 en rt 3 Φ ft O fu ft 3 fu M Ω μ- hf cn rt 0 ft rt M Hi 3 tr Hi 3 3 en H Φ X μ- Cu ii rt μ- μ- 3 M Ω 3 •ti j Φ vo tr M > U μ- en o Φ Cu en rt O 3 μ- 0 Ω LQ μ- 0 X rt 3 ft 0 0 rt Ω hi CU Φ φ 3 en Hi 3 rt Cu rt <! rt M hh 3 Cu Hi μ- μ- μ- μ- Ω hi i en tr O rt μ- en fu en en 3 en Hi Φ en μ- tr μ- en M Hi Φ M 3 en o 3 Hi 0 ft μ- φ Φ O 3 fυ Hi φ en o Hi 0 X 3 Φ 3 Φ ft X μ- rt ~ r ft 3 3 0 3 μ- LQ H M M tr O φ φ HI rt o HI μ- ft μ- X en φ tr μ- φ μ- tr μ- Hi Cu tr ft 3 fu Φ μ- φ en •ti tr H Φ tr 3 3 3 •ti Cu H Φ 3 M Ω s; φ 3 φ M 0 3 3 LQ 3 en rt 3 tr φ u 3 3 ft •ti M u M Hi 3 ft ft tr LQ en M X en Ω M »^ ft fu LQ Cu μ- Cu μ- ft o rt ft 0 μ- 0 •fl u 3 rt O en μ- hh μ- Cu 3 ^ μ- r rt *< HJ en 3 en 3 φ 3 ft 3 ii μ- μ- μ- Φ Hi 0 3 3 μ- μ- Ω •ti to M ft . μ- X φ 3 μ- φ LQ LQ rt rt μ- μ- LQ r LQ 3 cn hi rt tr LQ cn φ tr •ti H rt en Φ 3 μ- 3 μ- φ μ- N ft hi X tr 3 Hi μ- • Φ 0 3 CU tr ι_ι. M fu . μ- tr LQ cn tr rr en ft 3 Φ φ Cu Φ • ^ to o ft rt Cu Φ Φ to ft H 3 o o Φ rr tr μ- ft o φ hi •*. μ- H 3 CO Hi rt hh HI Ω μ> • Cu S LQ X Hi 0 3 3 ft μ- 3 o μ- μ- r rt 0 3 μ- en Q LQ X o Cu g •ti 3 Φ Φ H 3 hi en H H 3 3 φ LQ M ft en ^ en Φ 3 ft ft O Φ elements 11 and 12 in Fig. 5, a corresponding influence on the magnetic field pattern at the ends of winding 21 can be obtained by appropriate variation of the winding structure, in particular at the end portions of the winding. Fig. 10 in cross section and much enlarged shows a favourable composition of conductors for providing the winding in an apparatus according to the invention. A very suitable form of conductor elements with an incorporated superconducting material is based on elements 43A,B,C,D,E in Fig. 10. These conductor elements are clearly ribbon-shaped with a quite small thickness compared to the width. Such conductor elements each comprises a high number of thin superconducting ribbons or filaments 40 as shown for conductor element 43A, whereby each conductor element has typical dimensions of 4 x 0,2 mm and can carry a couple of tens of amperes of alternating current. The material in each conductor element 43A-E is in addition to the superconducting filaments 40, substantially silver. Conductor elements 43A-E are electrically insulated from each other, for example by having a ceramic coating on the surface or by having thin, insulating foils interleaved between the conductor elements. Such a foil 49 is indicated in Fig. 10 for conductor element 43C. In Fig. 10 five of these conductor elements are assembled into a conductor group 45 with a common outer insulation 50. Such a conductor group then forms the turns in windings as previously described. The conductor group can comprise a variable number of conductor elements, since a number of elements equal to five as shown in the example of Fig. 10, obviously is not limiting. Typically the number of conductor elements may vary from two to eight depending of, inter alia, which voltage level is to be used for operating the induction apparatus . Figs. 11 and 12 illustrate two different winding methods based on a conductor in the form of conductor groups of the same structure as conductor group 45 in Fig. 10, but having only three ribbon-shaped conductor elements. Thus, in Fig. 11 there is shown a conductor group 65 with three conductor elements 63A, 63B and 63C. These are indicated each to ω to to H μ> LΠ o LΠ o LΠ o LΠ Ω g Ω hj fu tr tr ft rt rt en Ω tr X hh LQ μ- X Cu X rt X μ- LQ hi M •ti tr M Ω rt M r en X Ω H X O cu 3 Φ ft φ u μ- tr tr tr o φ μ- μ- Hi 3 μ- fu tr μ- 3 hi φ Cu hi Φ Cu o tr μ- tr *. μ- O H μ- 3 3 hi en l_I. rr < g Φ Φ o g μ- 3 LQ o Ω rt X ^ φ M 0 en * : o rt •<; 3 Φ φ φ - 3 3 rt ft ^ h{ •ti CU X Φ Φ Hi μ- X •ti 3 ft 3 3 0 tr tr M rt 3 •ti φ < X Φ ft en ft < μ- tr 3 Φ φ Ω Φ 3 Φ Hi 3 M LQ μ- H| •ti Hi 0 •ti en tr •ti φ H μ- Φ Hi 3 en μ- rt ^ μ- φ cn Ω •ti 3 Ω Φ Φ rt en tr Φ 3 φ en •ti tr •fl M 0 3 tr Φ Ω en ft Φ Ω 3 3 tr > 3 3 μ- rt o rt rt 3 3 ii μ- • ; •ti rt •ti LQ 0 cu μ- Φ en •ti fu rt φ 3 Cu rr tr ti LQ rt Ω rt O en μ- rt cu 0 u Ω Φ M en hi rt LQ en φ < μ- Hi O en en 0 en rt φ Cu μ- o en H| en rt < Ω 3 3 tr 3 0 Cu H rf * CU Ω • μ- μ- Hi Φ 3 Φ rr rt Hj φ tr φ 3 M o 3 μ- O φ •ti 0 en fu Ω 3 X Ω » tr > rt tr cn tr Ω ft en O tr μ- Λ Φ ft Cu 3 en μ- 0 tr M fu 3 •ti en CD en μ- φ Φ φ μ- H M O fu μ- 3 rt O Φ M LQ 3 Hi *< fu μ- 3 hi μ- rt ^ Ω ft O > ;v rt 3 ft μ- -0 ft 3 to en Φ 3 3 M rt tr ii M hi φ en μ- en φ M ft ft M tr ? 3 en M cu Φ μ- ft Cu *» LQ tr • ft μ- rt tr Φ M 3 o 3 Cu tr Hi Φ μ- rt μ- μ- u Ω μ- en rt μ- en φ Hi td μ- μ- 0 3 Φ ft en Φ u fu en 3 rt 3 tr td 3 Hi < tr rt en rt LQ rt rt O en o 3 3 μ- • HI 3 cn X Ω Λ 3 X 3 ^ rt •ti Φ o X fu φ μ- Φ μ- tr φ 0 μ- 3 H| rr LQ ft Cu cu o 3 3 rt 3 Cu μ- Ω μ- Φ hi en u 3 Cu tr 3 ft ft φ X φ hi O μ- tr Φ • φ en 3 3 cu Hi fu o Cu M 3 0 3 Cu hi Cu 3 3 Hi Φ 3 3 Ω en μ- HI •ti 3 3 en •ti φ LQ ft 3 Cu O HI M 3 ft •ti en rt Cu ft 3 φ Φ hi Φ rt ft ) O 3 φ P LQ rt cu rt H tr <! φ Ω μ- rt 3 en Ω cu ft μ- •ti - Φ Hi rt M Φ Hi O M 3 X ft hi Hi rt cu Ω tr tr • ^ φ 3 o 3 μ- rt ft O 3 3 3 Hj ft φ rt 3 φ μ- μ- - ft μ- μ- fu rt O Cu tr 3 ? φ 3 hi φ LΠ 3 ft M en φ X μ- 3 Ω LQ o Cu - tr u 3 3 3 tr tr a r 3 H| 3 en μ- rt cu en en CU 3 ft μ- M H| μ- cn ft μ- rt •ti en H| Φ M Φ Ω μ- Φ u Ω tr LQ Φ 0 •ϋ cn μ- LQ l-h - μ- M rt fu a Ω 3 M rt 3 3 0 Hi X 0 3 0 Cu • rt rt hi en Cu Φ μ- ft HI Ω Cu en Ω M H Ω •ti hi H μ- Hi tr ft •ti rt hi 3 Φ X Ω O hi en •J tr X M H Ω φ hh tr Φ rt rt rt Cu 3 μ- rt φ tr fu O φ Cu 0 0 en •ti 0 • o tr Hj Φ H tr •ti LΠ O μ- M X en o M φ 0 μ- ii 3 HI tr tr O ft φ Φ rt H hi rt M en O 3 3 μ- en rt o Cu X 3 • <: μ- rt 3 μ- Hi en H| 3 cu ft hi Φ 3 hi Cu M Φ φ Φ M μ- μ- Hi LQ X 3 3 μ, LQ •ti X 3 CU 3 ft 3 ft 3 rt φ •ti LQ rt Φ rt 3 Φ rr φ tr ft o rt 3 u μ- ft iQ π H| φ X 3 Ω 3 μ- M ft O 3 - Φ LQ μ- en 3 rt μ- φ Ω 3 H| φ X ^ X μ- rt o r O Ω μ- Cu ft fu 3 fu μ- Hi Ω rt μ- Ω hi rt o rt Cu o M Φ φ Cu M Cu o μ- O rt Φ rt tr μ- 3 rt M Ω ^ rt LQ H| 3 rt tr •ti en μ- 0 tr 3 td 3 φ 3 3 Φ 3 rt hi 3 3 ir 1 ft tr 3 H •ti M O Φ rt LQ LQ μ- o φ Cu 3 φ - Ω Φ 3 tr rt en Ω •ti tr LQ Φ Φ fu tr rt 3 • tr -J Φ Φ 3 hi Ω tr μ- •ti O 0 3 Cu Φ Φ cn •ti rt M φ rt μ- hi 3 M Φ Hι O tr 3 Φ vo g HI •ti 3 cu ? Cu Ω ~ Ω Hi 3 3 3 Φ 0 H| Φ H| M 3 en fu o φ Φ > 5" Φ LQ X Cu en fu O Φ 3 Cu ft rt μ- X en μ- Φ u Cu μ- en - 3 ^ Ω hi rt Ω rt 3 hh O ft HI hi Hi μ- LQ φ M X 3 rt en Φ ft en 3 μ- μ- Ω μ- M 3 ^ rt H{ 3 φ 0 g tr H| rt Φ O ft μ- rt 3 o cu Φ ft M tr ft tr •ti Ω rt - LQ rt rt CU M φ en Φ tr en en r ft hj φ Φ μ- -o μ- Hi μ- fu • 3 μ- o 3 M ^ φ 3 Φ φ rt Cu tr tr μ- M M Ω •ti Hi Φ rt φ tr Φ en ► ϋ 3 Cu O co LQ g g en •it M o Hi Ω Ω μ- 3 φ en fu μ- o 3 rt o en φ φ ii M LQ en M 3 > tr rt Φ Φ M rt en ft μ- 3 μ- Φ rt en rt o rt O en 3 3 Ω en hi en Ω M 3 3 ft ) Φ rt μ- en tr tr 3 rt C μ- ?r 3 tr 0 Cu μ- 3 Cu Ω o rt μ- φ r 0 u Ω 0 Ω rt ft Hi N fu 0 φ rt Φ Ω X Hi Φ en ft ^ H 3 <! LQ 3 rt en Φ H 3 hi Ω ft tr 3 ^ h 0 en Ω Φ tr 3 φ 3 3 Hj tr μ- tt Φ 0 μ- φ φ rt Φ H| tr μ- Cu Φ •ti u Cu Φ ft φ hi 3 rt O φ Ω ft 0 ft Hj Ω μ- 3 > Ω X Ω Ω rt Φ M 0 H( cu 3 Ω M rt M H| 3 hi 0 ft hj X ft HI μ- O rt rt •ti ft rt μ- Cu cu tr M " ^ o Φ rt μ- tr Φ μ- Φ Hi Φ Ω 3 3 . — , ft μ- μ- 3 r 3 3 tr cu μ- fu μ- 3 M rt hi Φ μ- • rt l-h 3 M hi 3 ft Ω 0 fu rt 0 Ω M μ- 3 3 Hi tr fu LQ 3 μ- cu Ω 3 3 0 ft M φ Φ 3 3 tr rt rt u Ω hi LQ o 3 o hh rt rt 0 3 ft ft Φ u •ϋ td Φ cn 3 r LQ ft 3 μ- Φ ft Φ φ ft φ μ- tr H| 0 Φ Cu 3 rt H| tr 0 X LQ μ- μ- r •ti LQ Ω Cu 3 ft 3 3 Ω Φ 3 ft tr rt 3 M Φ ft Φ Hj φ 3 < O M Hi r hi μ- LQ φ o LQ μ- Ω rr cu X Cu fu ft φ φ Cu Hj LQ tr Hi rr LQ μ- rt O μ- Φ rt Φ fu rf hh 3 o en en μ- rt •ti Ω en 3 rt rt en Ω • : - HI Φ tr LQ 3 0 ft tr μ- 3 0 & en Ω td •ti •ti 3 3 tr Cu 3 Ω o X vo ft Φ 0 Cu hi o μ- 3 rt φ 3 •ti 3 3 •ti tr rt Cu Cu rt ft tr i ft Φ Ω Hi •ti rt Φ - μ- Hi rt 3 X rt 0 en rt 3 fu tr H| LQ μ- cu Cu Cu tr Hi 3 tr 3 φ μ- μ- μ- Hi 0 o X Φ 0 tr •ti μ- Ω 3 rt tr M φ φ μ- Hi X hi μ- en Φ rt Ω μ- Ω μ- LQ 3 tr rt Φ en H| μ- 3 3 r Φ en 3 tr •ti φ •A 3 φ μ- rt 3 en CU cn rt 3 • LQ Φ ^ 3 en rt 0 . ft μ- en μ- cu ft cu >? 0 LQ en rt μ- tr rt μ- 3 LQ hi rt M Φ ii μ> cu rt 0 tr tr H 3 LQ Φ tr rt μ> en M φ 3 LQ Φ 0 φ turns of the winding and the arrangement of the winding as whole, as this can be more or less subdivided or sectioned. Among other things it can be appropriate to provide for adaption of the winding for three-phase operation.

Claims: C l a i s 1. Apparatus for induction heating of billet -shaped blanks (10) of electrically well conductive and non-magnetic metal, in particular aluminium or copper, comprising a winding (1,21) adapted to surround the blank (10) completely or partially, to be supplied with electric alternating current (8) from a power supply, and to be cooled by means of a cooling system (5,22) at least during the heating of the blank (10) , c h a r a c t e r i z e d in that the winding (1,21) has turns comprising superconducting material (40) and is surrounded by a thermally insulating chamber (3,33), that the cooling system (5,22) is adapted to maintain the winding at a temperature in the range of 30-90°K, and that the frequency of the alternating current (8) is adapted to be in a range of common mains frequencies. 2. Apparatus according to claim 1, c h a r a c t e r i z e d in that the cooling in the cooling system takes place with liquid nitrogen or helium gas being brought to circulate in cavities (5) or cooling channels adjacent to the winding (1) inside the thermally insulating chamber (3). 3. Apparatus according to claim 1, c h a r a c t e r i z e d in that a jacket (22) of well heat conducting, but electrically insulating material, being in thermal contact with the winding (21) and being cooled by means of a cooling unit (23) which is a part of the cooling circuit of the cooling system. 4. Apparatus according to claim 3 , c h a r a c t e r i z e d in that the jacket (22) is located substantially radially inside the winding (21) and preferably constitutes a substantial supporting element for the winding (21) . 5. Apparatus according to claim 3 or 4 , c h a r a c t e r i z e d in that the jacket (22) is thermally connected to at least one rod-like cooling head (26A,B) penetrating a wall of the thermally insulated chamber (33), preferably with a cooling head (26A,B) at either end of the winding (21) , and that the cooling unit (23) has fluid communication (23A,23B) with each cooling head. 6. Apparatus according to any one of claims 1-5, c h a r a c t e r i z e d by means (11,12) adapted to at least partially extend the magnetic field resulting from the winding (21) , more axially outwards at the ends of the winding (21) . 7. Apparatus according to claim 6, c h a r a c t e r i z e d in that said means comprise elements (11,12) of ferromagnetic material located at the ends of the winding (21) . 8. Apparatus according to any one of claims 1-7, c h a r a c t e r i z e d in that the cooling system (5,22) is adapted to maintain the winding at a temperature in the range of 40-77°K. 9. Apparatus according to any one of claims 1-8, c h a r a c t e r i z e d in that the superconducting material (40) in the windings (21,45) is incorporated in a ribbon- shaped conductor element (43A) having a substantially larger width than tickness. (Fig. 10) . 10. Apparatus according to claim 9, c h a r a c t e r i z e d in that a number of ribbon- shaped conductor elements (43A-E, 63A-C) are assembled into a conductor group (45,65,75) being incorporated in the winding. (Fig. 10, 11, 12) . 11. Apparatus according to claim 10, c h a r a c t e r i z e d in that one or more conductor groups (45,75) is/are wound into a plurality of flat, package-like parts (24 , A, B, C, 44A,B, C, 74A, B) having a substantially larger diameter than axial dimension, and that the position in the conductor group is transposed (79) between axially adjacent package-like winding parts. (Fig. 12) . 12. Apparatus according to claim 10 or 11, c h a r a c t e r i z e d in that each ribbon-shaped conductor element (43B) is electrically insulated (49) in relation to the adjacent conductor elements (43A,43C), and that each conductor group (45,65,75) is electrically insulated (50) . (Fig. 10) . 13. Apparatus according to claim 11 or 12, c h a r a c t e r i z e d in that between the package-like winding parts (44A,B,C) there are provided rod-shaped or disc-shaped separating elements (48A,B,C) of thermally well conducting, but electrically insulating material. (Fig. 7).

Inventors: RUNDE MAGNE EYSTEIN, RUNDE, MAGNE, EYSTEIN
Applicants: RUNDE MAGNE EYSTEIN, SINTEF ENERGIFORSKNING AS, RUNDE, MAGNE, EYSTEIN
Application year: 2000
Main classification: H05B6
IPC codes: H05B6