EP2183944B1 - Induction heater - Google Patents

Abstract

An induction heater for heating metallic billets with a yoke of E-shaped cross-section, on the middle limb of which a superconducting coil is seated, has a well located between the middle limb and each one of the respective two outer limbs. A billet can be heated by being rotated in each one of the two wells.

Description

The invention relates to an induction heater with a DC-powered superconducting coil assembly on a yoke and a method for adjusting the yoke width.

An induction heater is out of the DE 10 2005 061 670.4 known. To heat a billet of an electrically conductive material, the billet is rotated in a shaft between two legs of a cross-sectionally C-shaped yoke. On the yoke sits a DC-powered high-temperature superconducting coil. As high-temperature superconducting (HTSC) Cupratsupraleiter eg YBCO and more generally all superconductors (SL) with a SL transition temperature above the boiling point of liquid nitrogen called. Induction heaters are usually integrated into a production line. Therefore, the induction heater must provide a heated billet within a timed cycle given by the production line.

From the US Pat. No. 5,412,183 A an induction heater with an approximately E-shaped yoke is known, the three legs are formed as pole pieces and arranged in a star shape offset by 120 degrees to inductively heat a workpiece in the space between the pole shoes by sitting on the pole pieces, AC-powered coil assemblies.

From the FR 904 159 A Another induction heater with an E-shaped yoke is known, on the center leg of which a first coil arrangement is seated and whose end legs are aligned with one another. The workpiece to be heated is located between the spaced end faces the yoke of the yoke and is surrounded by a further coil assembly which is AC powered and primarily provides the power for inductive heating of the workpiece.

From the EP 266 470 A1 Another induction heater with an E-shaped yoke is known, the three legs each carry an AC-powered coil assembly to inductively heat the workpiece located in the free space between the legs.

The invention has for its object to provide an induction heater for a per unit time increased billet output and low energy consumption.

This object is achieved by an induction heater with the features of claim 1 and by a method comprising the steps of claim 22. The dependent claims are directed to preferred embodiments.

The induction heater according to claim 1 has a cross-sectionally at least approximately E-shaped yoke of a middle leg between two outer legs, wherein the center leg and the two outer legs are connected by a transverse leg. At least one superconducting coil sits on one of the legs. Between the two outer legs and the middle leg is in each case a shaft in which a billet can be heated by turning in the shaft. Because the induction heater has two shafts, two billets can be heated at the same time. For example, when changing a heated billet against a new, cold billet another billet can be heated in the other shaft. Accordingly, the output of the induction heater increases. The E-shape of the yoke makes it possible to significantly increase the output of heated billets with just one superconducting coil. Usually, the coil is part a coil arrangement, which usually comprises at least the terminals for the coil.

For example, the coil or the coil arrangement can sit on the middle leg. Alternatively, e.g. two coils or coil arrangements on the transverse leg, preferably on both sides of the center leg each have a coil or coil arrangement sitting. Of course, can also sit on the outer thighs ever a coil.

The further developments of the invention described below are not bound to the E-shape of the yoke, in particular not to the number of shafts.

The two outer legs and the middle leg of the yoke are connected by a transverse leg. Preferably, the coil assembly or the coil is pushed to the stop on the transverse leg on the center leg. This allows a compact yoke with a correspondingly short magnetic return, whereby the efficiency of the induction heater is improved.

Preferably, the legs of the yoke made of solid material. Because the coil is DC-powered, can be dispensed with the expensive construction of a yoke made of laminated sheets without having to take eddy current losses caused by eddy currents in the yoke in purchasing. Due to the lack of lamination, which also includes electrical insulation, the magnetic fill factor is increased compared to a lathed variant. This allows either an increase in the magnetic field or a more cost-effective design by using simpler materials at the same magnetic field strength.

The coil assembly preferably has an evacuated chamber in which there is at least one HTS coil. The evacuated chamber allows good thermal insulation of the HTS coil.

The heat insulation is further improved when the HTSC coil is wrapped in several layers of a metal-coated, preferably aluminum-coated foil.

The HTS coil can be held in the chamber by means of plastic bearings.

Thermal insulation between the coil assembly and the open ends of the wells reduces the necessary cooling power for the HTSC coil. Particularly suitable are microporous thermal insulation. A suitable material for thermal insulation is especially calcium silicate.

In addition or as an alternative to the thermal insulation, an infrared reflector reflecting in the direction of the billet can be, for example, a gold-coated ceramic in the ducts. This reduces heat losses. Particularly suitable is a cross-sectionally U-shaped infrared reflector, in the free center of the billet is rotated.

Preference is given to the coil arrangement in each slot an impact protection plate with a high compared to the yoke magnetic resistance, for example made of stainless steel (V2A, V4A, etc.). Should a rotating billet come loose from its mount, then the baffle plate prevents damage to the more expensive and delicate superconducting coil assembly. The impact protection plates can, for example, each sit in two opposing longitudinal grooves in the corresponding shaft.

Preferably, the wells are tapered towards the free ends of the legs, i. the thighs are thickened accordingly. This shortens the air gap between the free ends of the legs in which the billets are rotated. Accordingly, the magnetic resistance is reduced, and the maximum heating power and the efficiency are increased.

The shafts can be closed to the environment by a thermal insulation. For removing and inserting the billets into the shafts, the shafts closing thermal insulation are preferably movable.

Additionally or optionally, the wells may be covered from the environment by non-magnetic protection plates. These guard plates prevent a rotating billet that has detached from its jig from leaving the shaft and damaging or injuring other machine parts or even persons. Of course, the protective plates for opening the shafts are preferably movable.

Preferably, the width of the shafts is adjustable. As a result, the shafts can be adapted to different billet diameter. This can be done for example by moving or pivoting at least a lower part of the outer leg. The lower part of the outer legs can also be segmented in a plane orthogonal to the axis of rotation. For field adaptation in the respective shaft, the segments can be moved or swiveled independently of each other. Alternatively or optionally, the width of the shafts can be adjusted by interchangeably fixed to the legs of the yoke ferromagnetic metal plates.

Such metal plates may have a larger relative magnetic permeability than the yoke. This leads to a concentration of the magnetic flux through the metal plates and thus also through the billet rotated between the metal plates. If particularly large billets are to be heated, the metal plates may also have a lower relative permeability than the yoke, then the metal plates will act as a scatter, accordingly the magnetic flux will be more uniform.

The width of the shafts may increase from the end faces of the yoke towards the middle. These ferromagnetic metal wedges can be exchangeably attached to the legs of the yoke. This geometry of the shafts reduces the stray fields emerging from the shafts at the ends of the yoke, and accordingly the magnetic flux is increased by the billets.

To adjust the width of the wells, either by moving or pivoting parts of the outer leg or by exchanging exchangeably fixed metal plates or wedges, the HTS coil is preferably first switched off. Then then the width of the shafts can be easily changed. The width of the shafts can be changed particularly easily if the yoke is demagnetized after switching off the coil and before changing the width. For this example, a seated on the yoke coil assembly, in particular the superconducting coil assembly can be fed with alternating current. The amperage of the AC supply is less than the rated current with DC supply. Preferably, it is about 10% to 20% of the rated current for DC power.

Fig. 1

eine teilgeschnittene Seitenansicht eines Induk- tionsheizers,

Fig. 2

einen Querschnitt der Magneteinheit des Indukti- onsheizers aus Fig. 1,

Fig. 3

eine Seitenansicht der Magneteinheit des Indukti- onsheizers aus Fig. 1,

Fig. 4

einen Längsschnitt (B/B aus Fig. 3) des Indukti- onsheizers,

Fig. 5

eine weitere Magneteinheit eines Induktionshei- zers,

Fig. 6

eine schematische Ansicht einer weiteren Magnet- einheit von unten, und

Fig. 7 bis Fig. 10

je einen Schnitt durch einen Induktionsheizer.

In the drawing, schematically simplified, an induction heater according to the invention is shown by way of example. It shows:

Fig. 1

a partially cutaway side view of an induction heater,

Fig. 2

a cross-section of the magnet unit of the induction heater off Fig. 1 .

Fig. 3

a side view of the magnet unit of the induction heating Fig. 1 .

Fig. 4

a longitudinal section (B / B off Fig. 3 ) of the induction heater,

Fig. 5

another magnet unit of an induction heater,

Fig. 6

a schematic view of another magnetic unit from below, and

FIGS. 7 to 10

each a section through an induction heater.

The induction heater in Fig. 1 has a two-piece jig 2a, 2b, which holds a billet 10 in a slot of a magnet unit 100. The billet 10 is rotationally driven over a part of the jig 2 a, a gear 3 and a motor 1. By means of the clamping device 2a, 2b, the billet 10 can be raised and lowered as indicated by the corresponding double arrow. In addition, the clamping devices 2a, 2b can also be moved horizontally. This is also indicated by double arrows.

The billet 10 is in a slot 150 1 of a cross-sectionally E-shaped yoke 140, on the center leg of a coil assembly 120 is seated (see. Fig. 2 to Fig. 4 ). The yoke 140 is E-shaped in cross section and has two outer legs 142 1, 142 r are connected via a transverse leg 141 with a center leg 143. Accordingly, between the outer leg 142 1 and the middle leg 143, a downwardly open slot 150 1 and between the outer leg 142 r and the middle leg 143 another likewise downwardly open slot 150 r. The yoke 140 is made of a solid material.

The coil assembly 120 consists of an evacuated chamber 125 in which e.g. liquid nitrogen cooled HTSC coil 121 (cooling and electrical leads not shown). The HTSC coil 121 is housed in a case 122 which is enveloped by a plurality of layers of an AL-evaporated polyester film as heat insulation 123 and fixed with a plastic holder (not shown) in the chamber 125. A good heat insulation 123 is achieved with about 40 to 60 layers of the film, wherein at the edges preferably 10 to 20 further layers.

Below the chamber 125, in each well 150 1, 150 r is an impact protection plate 153. The impact protection plates 153 are made of a non-magnetic material, e.g. Stainless steel, and sitting in opposing longitudinal grooves 152 in its slot 150 1 and 150 r. For mounting the impact protection plates 153 are inserted from one of the end sides of the yoke in the longitudinal grooves 152 and then secured. The impact protection plates 153 protect the coil assembly 120 from damage by a rotating billet 10, which has been released from the clamping device 2a, 2b.

Downwards, a heat insulation 154, here made of calcium silicate boards, immediately adjoins the impact protection plate 153. at. The heat insulation 154 protects, as well as the subsequent cross-sectionally U-shaped infrared reflector 158 of gold-fired ceramic, the coil assembly 120 and the yoke 140 from the heat of the billets 10. In addition, the losses are lower by heat dissipation of the billet to the yoke.

The shafts 150 1, 150 r are at their lower ends by interchangeable attached to the outer legs 142 1, 142 r and the middle leg 143 attached ferromagnetic plates 155, tapered. As a result, the air gap between the legs 142 1, 142 r and 143 of the yoke 140 and the billets 10 is shortened and, correspondingly, the magnetic resistance of the magnet unit 100 is reduced. The plates 155 have a greater magnetic permeability than the yoke 140. Therefore, the plates 155 concentrate the magnetic flux through the billets 10. Compared to an embodiment in which the wells have a constant, the distance between the plates 155 have narrow width the embodiment shown here has the advantage that the wells 1501, 150r are effectively widened upwards, whereby the evacuated chamber 125 correspondingly larger fails and the insulation of the HTSC coil 121 is improved. The replaceable attachment of the plates 155 allows easy mounting of the magnet unit 100 as well as an adaptation of the width of the wells 1501, 150r to the diameter of the billets 10 to be heated.

Down the shafts 150 1, 150 r are closed by a further heat insulation 156. The thermal insulation 156 is located in a channel of three protective plates 157. The protective plates 157 are made of a non-magnetic material, such as stainless steel, and are used to avoid accidents. Should a billet 10 unintentionally detach from the clamping device 2a, 2b during the heating, it can not leave the corresponding shaft 150 1, 150 r, ie neither damage other parts of the system nor injure persons. The thermal insulation 156 and the protective plates 157 are indicated by double arrows, raised and lowered. As a result, the shafts 150 1, 150 r can be opened to bring a billet 10 from below into the corresponding shaft.

The embodiment in Fig. 5 corresponds substantially to the embodiment in FIG Fig. 1 to 4 (Same or similar parts are identified by identical reference numerals), but the lower portions of the two outer legs 142 1 and 142 r are slidable to adjust the width of the shafts 150 1, 150 r of billets 10 with different diameters. The displaceable part of the two outer legs 142 1, 142 r is shown in two positions, wherein the open position is indicated by a hatching directed against the otherwise used for the yoke 140 otherwise hatching.

To adapt the thermal insulation 154 and the infrared reflectors 158 to a modified shaft width, these can be either completely replaced or telescopically adjustable in width (not shown).

The magnet unit 100 in FIG Fig. 6 is substantially similar to the induction heaters of the other figures. Instead of the plates 153 in Fig. 2 and Fig. 5 are metal wedges 155 b on the outer legs 142 1, 142 r and on both sides of the center leg 143 interchangeable and against each other slidably mounted. As a result, the width of the shafts 150 1, 150 r increases from the end faces toward the center. This reduces stray fields emerging from the front and enables field adaptation to form a field profile. By moving the metal wedges 155 b parallel to the axis of rotation, for example, it is possible to set to different materials or geometries. Accordingly, the efficiency of the magnet unit 100, that is, the induction heater is improved. The induction heaters 100 in the FIGS. 7 to 10 are to the induction heater 100 in the Fig. 1 to 4 similar. Therefore, identical reference numerals are used for the same or similar parts and only the differences will be discussed.

The induction heater 100 in Fig. 7 has instead of a coil arrangement on the center leg 143 as in Fig. 1 to 4 1, a coil arrangement 120 on the right outer leg 142 r and a coil arrangement 120 on the left outer leg 142 1 are shown.

The induction heater 100 in Fig. 8 has only one coil assembly which sits on the left outer leg 142 1 and is pushed onto this up to the stop on the transverse leg 141.

The Fig. 9 shows an induction heater 100 with a coil assembly 120 which sits between the left outer leg 142 1 and the middle leg 143 on the transverse leg 141. For mounting a preassembled coil assembly 120, the left outer leg 142 1, unlike shown, disassembled.

Fig. 10 shows an induction heater 100, each with a coil assembly 120 on both sides of the center leg 143, which sits on the transverse leg 141. For mounting a preassembled coil assembly 120, the two outer legs 142 1, 142 r, other than shown, disassembled.

Claims (18)

1. An induction heater, comprising at least one direct-current powered superconducting coil (121) on a yoke (140) for heating billets, characterized in that the yoke (140) comprises a middle leg (143) between two outside legs (142 1, 142 r) on a common transverse leg (141), and one shaft (1501, 150r) for receiving one each of the billets to be heated is each disposed between the middle leg (143) and the two outside legs (1421, 142r).
2. An induction heater according to claim 1, characterized in that the coil (121) is slid up to the stop on the transverse leg (141) on the middle leg (143) of the yoke.
3. An induction heater according to one of the claims 1 or 2, characterized in that at least one leg (141, 142 1, 142 r, 143) of the yoke (140) is made of solid material.
4. An induction heater according to one of the claims 1 to 3, characterized in that the coil is an HTSC-coil (121) in an evacuated chamber (125) of a coil arrangement (120).
5. An induction heater according to claim 4, characterized in that the coil (121) is held by means of plastic bearings in the chamber (125).
6. An induction heater according to one of the claims 1 to 5, characterized in that the coil (121) is encased by several layers of a metallized foil (123).
7. An induction heater according to one of the claims 1 to 6, characterized by thermal insulation (154) between the coil (121) and the open ends of the shafts (150 1, 150 r).
8. An induction heating according to claim 7, characterized in that the thermal insulation (154) is microporous.
9. An induction heater according to claim 7 or 8, characterized in that the thermal insulation (154) is made of calcium silicate.
10. An induction heater according to one of the claims 1 to 9, characterized by a non-magnetic impact-protection plate in each shaft (150 1, 150 r).
11. An induction heater according to claim 10, characterized in that each shaft (150 1, 150 r) has two oppositely disposed longitudinal grooves (152) in which one of the impact-protection plates (153) is sitting.
12. An induction heater according to one of the claims 1 to 11, characterized in that the shafts (150 1, 150 r) taper in the direction of the free ends of the free legs (142 1, 142 r, 143).
13. An induction heater according to one of the claims 1 to 12, characterized in that the shafts (150 1, 150 r) are sealed by means of a thermal insulation (156) against the ambient environment and the thermal insulation sealing the shafts (150 1, 150 r) is movable for opening the shafts (150 1, 150 r).
14. An induction heater according to one of the claims 1 to 13, characterized in that the shafts (150 1, 150 r) are covered against the ambient environment by non-magnetic protective plates (157) and the protective plates (157) are movable for opening the shafts (150 1, 150 r).
15. An induction heater according to one of the claims 1 to 14, characterized in that the width of the shafts (150 1, 150 r) is adjustable.
16. An induction heater according to claim 15, characterized in that the width of the shafts (150 1, 150 r) is adjustable by displacing or swiveling at least parts of the outside legs (141 1, 142 r).
17. An induction heater according to claim 15 or 16, characterized in that the width of the shafts (150 1, 150 r) is adjustable by ferromagnetic metal plates (155) which are fastened in an exchangeable manner to the legs (142 1, 142 r, 143) of the yoke.
18. An induction heater according to claim 17, characterized in that the relative magnetic permeability of the metal plates (155) deviates from that of the yoke (140).

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