Induction heating apparatus

Abstract: The present invention intends to provide an induction heating apparatus in which a coil or coils can be opened without making use of a contactor and a reliability is improved. One continuous electric current passageway is formed of a first coil section 110, a second coil section 120, a connecting conductor 130 and a second connecting conductor 140. By feeding electric power to this electric current passageway and making an object to be heated pass through a space at the central portion of the coils, the object to be heated can be subjected to induction heating. A gap is provided between the connecting conductor 130 and the connecting conductor 140, or provision is made such that the respective connecting conductors 130 and 140 can be opened and closed, and thereby the object to be heated is carried into the space at the central portion of the coils and carried out therefrom through the gap or the opened space.

Description: BACKGROUND OF THE INVENTION: Field of the Invention: The present invention relates to an induction heating apparatus, and more particularly, to a structure of an induction heating coil in an induction heating apparatus adapted for continuous heating of a conduction object to be heated and starts from AT-A-365 027. Description of the Prior Art: One example of a continuous induction heating apparatus for a plated steel sheet in the prior art is shown in Figs. 5 and 6. As shown in Fig. 5, a plated steel sheet 1 is continuously carried into an induction heating apparatus 3 as guided by guide members 2. Within the induction heating apparatus 3 is equipped a solenoid type induction heating coil 4 as shown in Fig. 6. The plated steel sheet 1 is conveyed as surrounded helically by the induction heating coil 4, in other words, under the condition where the plated steel sheet 1 penetrates through a central space of the induction heating coil 4. The induction heating coil 4 has a heat-insulating dielectric material applied to its outermost layer, and by making an electric current pass through the induction heating coil 4, the plated steel sheet can be inductively heated. An electric power to be fed to the induction heating coil 4 is determined depending upon an extent of temperature rise and a production rate (a steel sheet conveying speed) required for the plated steel sheet 1 chosen as an object to be heated. Since the plated steel sheet 1 is carried in while it is penetrating the space at central portion of the induction heating coil 4, when a leading end portion of the plated steel sheet 1 is to be carried into the heating apparatus 3, a leading wire is connected to the leading end of the plated steel sheet, then at first this leading wire is made to penetrate the induction heating coil 4 to be carried in, and provision is made such that subsequently the plated steel sheet 1 is made to penetrate the induction heating coil 4 to be carried in. The heating apparatus 3 in the prior art shown in Figs. 5 and 6 had the following shortcomings: (1) Because of the fact that a solenoid type induction heating coil 4 is employed, at the time of initial carrying-in, a leading wire must be used, and so, labor is necessitated for initial carrying-in or carrying-out of the plated steel sheet 1 into or from the heating apparatus 3. (2) Since the induction heating coil 4 has a closed structure (spiral shape), among heat-insulating dielectric materials applied to the coil 4, maintenance and inspection of heat-insulating material on the side of the inner surface of the coil (on the surface facing the plated steel sheet 1) are impossible. Therefore, an induction heating apparatus having overcome the above-mentioned shortcomings (1) and (2) has been developed. Outline of one example of the apparatus will be explained with reference to Fig. 7. In this heating apparatus 10, while a solenoid type of coil 11 is employed, a conductor 11a forming a part of the coil 11 is formed to be separable. A plurality of conductors 11a can be opened and closed by means of a revolving mechanism, and at the time of closure, the opposite ends of the conductors 11a are connected via knife-edge type of contactors 12 to the other portions of the coil 11 to form a loop. When the loop is kept formed, electric power is fed from a power supply section 13 to the coil 11, also an object to be heated is made to pass through a space at the central portion of the coil 11, and thereby induction heating can be effected. It is to be noted that the contactor 12 is made to have a sufficient connector capacity for allowing passage of a high-frequency current through the coil 11 without any trouble. In this heating apparatus 10, when an object to be heated is made to pass through the apparatus for the first time, the conductors 11a are opened up to the positions depicted by dotted lines in Fig. 7, then the heating apparatus 10 is moved while the object to be heated is kept stationary, and the object to be heated is set in the space at the central portion of the coil passing through the opened portion of the coil. In addition, if the conductors 11a are kept opened, inspection of the inner surface side of the coil 11 can be carried out easily. However, the heating apparatus shown in Fig. 7 involved the following shortcomings: 1 ○ Since a heavy current (1000 - 2000A) at a high frequency (about 10KHz) flows through the contactors 12, roughening of the contact surfaces at the time of opening and closing is liable to occur. In addition, as the contactors 12 are necessitated twice as many as the number of turns of the coil 11, there is a fear that miscentering may occur when a plurality of contactors 12 open and close. From such reasons, a reliability would be lowered if it is used for a long period. 2 ○ As the contactors 12 and a mechanism for opening and closing the contactors 12 are necessary, rise of costs is brought about. The patent specification AT-A-365 027 discloses an induction heating apparatus including a plurality of double-windings. The windings are arranged side by side and are formed in such a way that the single winding is open at the top side. Thus, a steel wire, for example, can be introduced into the windings easily. Furthermore, the patent specification FR-A-1 202 085 discloses an induction heating apparatus comprising a plurality of windings. The windings are arranged side by side and are each provided with a flexible portion. The flexible portions form a small part of the respective windings and they are also placed at the same position with respect to the heating apparatus (for example at the bottom of the heating apparatus). Opposite to the flexible portions there is provided a contactor which contacts the corresponding windings. The contactor can be opened and closed in order to introduce objects into the heating apparatus for heat treatment. In the state, when the contactor is open, the windings are interrupted physically and no current is flowing therethrough. Documents US-A-3731040 and WO92/15182 disclose induction heating apparatuses having two coils for applying a magnetical field vertical to the main axis of a longitudinal object to be heated. In order to improve the carrying-in and carrying-out of objects, these apparatuses provide flexible portions or loops for power supply of the two coils. The manner of operation of the apparatuses due to their special coil structure, however, has the disadvantage of a non-uniform heating over the width of the object. SUMMARY OF THE INVENTION: It is therefore one object of the present invention to provide an improved induction heating apparatus in which an object to be heated can be simply carried in and carried out of a coil without interrupting an electric current loop nor making use of contactors. According to the present invention, there is provided an induction heating apparatus as set out in claim 1. Further favourable embodiments are defined in the subclaims. In the above-featured induction heating apparatus according to the present invention, as shown in Fig. 1(a), an electric current fed from a high-frequency power supply 60 via a coil feeder section 70 flows through the route of [a coil in the first coil section 110] → [a first connecting conductor 130] → [a coil in the second coil section 120] → [a second connecting conductor 140] → [a coil in the first coil section] → ..... and then returns to the high-frequency power supply via the coil feeder section 70. At this time, induction heating can be effected by making an object to be heated pass through the space in the central portion of the coil. More particularly, the respective coils in the first coil section 110 generate magnetic fields directed in the same direction to heat the object to be heated, and the respective coils in the second coil section 120 generate magnetic fields directed in the same direction to heat the object to be heated. Owing to the fact that a gap is formed between the first connecting conductor 130 and the second connecting conductor 140 or the gap distance therebetween can be varied, an object to be heated can be set within the coil or it can be taken out of the coil through the gap. At the time of current feed when induction heating is being effected, by reducing the gap distance between the first connecting conductor 130 and the second connecting conductor 140, the impedance at the connecting conductor portion is made small, hence a voltage drop at this portion becomes negligibly small, and so, degradation of a heating performance can be made very little. As shown in Fig. 1(b), the first coil section 110 can be made to have a one turn coil, and the second coil section 120 also can be made to have a one turn coil. According to the present invention, as a result of the above-mentioned construction and operation, one can obtain the advantages that since the apparatus is not of opening/closing type necessarily associated with loop-interruption, a contactor becomes unnecessary, a reliability becomes high, and a cost is lowered; that because a gap is formed in the coil or a coil is formed in an openable and closeable structure, a workability upon carry-in and carry-out of an object to be heated is greatly improved, and also maintenance and inspection of an inner surface of a coil become easy; and that owing to the fact that the direction of the current flowing through the first connecting conductor and the direction of the current flowing through the second connecting conductor are opposite to each other and the first and second connecting conductors are opposed to each other with a gap as small as possible held therebetween, lowering of a heating efficiency due to increase of an impedance caused by the gap is negligibly small. The above-mentioned and other objects, features and advantages of the present invention will become more apparent by reference to the following description of preferred embodiments of the present invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS: In the accompanying drawings: Fig. 1 is a schematic view showing a general concept of the present invention; Fig. 2 is a schematic view showing a construction of an induction heating apparatus; Fig. 3 is a schematic view showing a construction of a preferred embodiment of the present invention; Fig. 4 is a schematic view showing a construction of another preferred embodiment of the present invention; Fig. 5 is a schematic view showing a construction of one example of an induction heating apparatus in the prior art; Fig. 6 is a perspective view showing an induction heating coil in the prior art; and Fig. 7 is a perspective view showing an induction heating apparatus in the prior art. DESCRIPTION OF THE PREFERRED EMBODIMENTS: In the following, a number of preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Fig. 2 shows the principle coil and conductor arrangement of an induction heating apparatus 100 according to the present invention. As shown in this figure, an upper coil section 110 is formed in a 3-turn coil consisting of coils 111, 112 and 113 each forming a single-turn coil, and the respective coils 111, 112 and 113 are interrupted at one location. On the other hand, a lower coil section 120 is formed in a 3-turn coil consisting of coils 121, 122 and 123 each forming a single-turn coil, and the respective coils 121, 122 and 123 are interrupted at one location. One interrupted ends (on the front side as viewed in Fig. 2) of the coils 111, 112 and 113 and one interrupted ends of the coils 121, 122 and 123 are electrically connected via connecting conductors 131, 132 and 133, respectively. Also, the other interrupted ends (on the rear side as viewed in Fig. 2) of the coils 111, 112 and 113 and the other interrupted ends of the coils 121, 122 and 123 are electrically connected via connecting conductors 141, 142 and 143 (the conductor 142 is not seen in Fig. 2), respectively. One continuous electric current passageway is formed by the above-mentioned coils 111, 112, 113, 121, 122 and 123 and connecting conductors 131, 132, 133, 141, 142 and 143. Between the connecting conductors 131, 132 and 133 and the connecting conductors 141, 142 and 143 are respectively formed gaps G having a predetermined gap length. The length of the gap G is chosen to be a minimum length (20 - 30 mm) necessitated for allowing an object to be heated (plated steel sheet) 50 to pass therethrough. In the figure, the left end side of the coil sections 110 and 120 is coupled to a moving apparatus not shown. In order to accommodate an object 50 to be heated such as a plated steel sheet in the space at the central portion of the coil, under the condition where the object 50 to be heated is kept stationary, the induction heating apparatus 100 is moved rightwards as viewed in the figure, and by making the object 50 to be heated pass through the gaps G, the object 50 to be heated is advanced up to the space at the central portion of the coil. If the state shown in Fig. 2 has been realized, induction heating of the object 50 to be heated can be achieved by feeding electric power from the high-frequency power supply 60. In order to extract the object 50 to be heated from the space at the central portion of the coil, the induction heating apparatus 100 is moved leftwards as viewed in the figure, and the object 50 to be heated is removed by making it pass through the gaps G. If the object 50 to be heated is kept removed, maintenance and inspection of the coil can be carried out in a simple manner. In the above-described induction heating apparatus (Fig. 2), gaps G serving as spaces for passing a sheet are formed. However, although only a little, due to these gaps G an impedance of a coil is increased, resulting in degradation of a heating performance. When it is required to remove such influence, a preferred embodiment (Fig. 3) or another preferred embodiment (Fig. 4) of the present invention as described in the following are employed. It is to be noted that the degradation of a heating performance due to the gaps G would depend upon a length of the gaps G, a length of the connecting conductors, an area surrounded by one turn of the coil, and the like. In Figs. 3 and 4, component parts achieving the same functions as those in Fig. 2 are given like reference numerals, and further explanation thereof will be omitted. Fig. 3(a) is a perspective view showing the preferred embodiment, and Fig. 3(b) is a plan view of the same embodiment. In an induction heating apparatus 200 according to the preferred embodiment, each of coils 111, 112 and 113 is provided with a flexible conductor portion 210 made of a multi-layer copper belt or the like, and each of coils 121, 122 and 123 is provided with a flexible conductor portion 220 made of a multi-layer copper belt or the like. The flexible conductor portion 210 or 220 forms a part of the coil and can flex. In this induction heating apparatus 200, the coil can be opened and closed by making use of the flexible conductor portions 210 and 220 as movable fulcrums, and when the coil closes, the connecting conductors 131, 132 and 133 are opposed to the connecting conductors 141, 142 and 143, respectively, with insulators 230 interposed therebetween. When an object 50 to be heated is set, the coil is opened so that the object 50 to be heated can pass through the opening. Consequently, the object 50 to be heated can be easily set as passing through the opened portion. Also, if the coil is kept opened, maintenance and inspection of the coil can be achieved easily. On the other hand, upon heating, the coil is closed, and the object 50 to be heated can be inductively heated by feeding electric power from a high-frequency power supply 60. Since the thickness of the insulators 230 is as very thin as about 1 - 2 mm, at the time of heating, degradation of a heating performance occurring at the gaps due to the insulators 230 is negligibly small. One practical example of mounting of an induction heating apparatus according to the preferred embodiment onto a machine frame is shown in Fig. 3(c). Fig. 3(c) is a plan view showing a coil and a frame for mounting the coil, in which one side portions of coils 111, 112, 113, 121, 122 and 123 are mounted to a frame 70 via support metals 73 and reinforcement members 74 (in Fig. 4(c), only the coil 111 at the uppermost level is shown). The other side portion of the same coil is coupled to a pneumatic cylinder 72 mounted to the frame 70, and a vertically extending opening 71 is formed in the frame 70 at the portion where the connecting conductors 131 and 141, the connecting conductors 132 and 142 and the connecting conductors 133 and 143 project (in Fig. 3(c), only the connecting conductors 131 and 141 for the uppermost coil 111 are shown). As shown in Fig. 3(b), the connecting conductor 141 can be arbitrarily opened and closed with respect to the connecting conductor 131 within the opening 71 by actuating the pneumatic cylinder 72, and also it can be easily achieved to set an object to be heated (plated steel sheet) within the coil and to extract it from the coil by making it pass through the opening 71. Fig. 4(a) is a perspective view showing the other preferred embodiment, and Fig. 4(b) is a plan view of the same embodiment. In an induction heating apparatus 300 according to the other preferred embodiment, each of coils 111, 112 and 113 is provided with a slider 310, while each of coils 121, 122 and 123 is provided with a slider 320, and provision is made such that one parts 111a, 112a and 113a of the coils 111, 112 and 113 and the connecting conductors 141, 142 and 143 can be opened and closed with respect to the connecting conductors 131, 132 and 133 by making use of the sliders 310 and 320 as movable fulcrums. When they are closed, the connecting conductors 131, 132 and 133 are opposed to the connecting conductors 141, 142 and 143 via thin (1 - 2 mm) insulators 330. In this other preferred embodiment also, similarly to the preferred embodiment, by holding the coil in an opened state, setting of an object to be heated as well as maintenance and inspection of the coil can be carried out easily, and by switching to a closed state, degradation of a heating performance becomes negligibly small. It is preferable to fabricate the coils in the above-described embodiments by making use of hollow rectangular materials and to circulate coolant water through their inner space so as to perform cooling of the coil. As will be obvious from the detailed description of the preferred embodiments of the present invention above, according to the present invention, the following effects and advantages are obtained: (1) Since the apparatus is not of opening/closing type necessarily associated with loop-interruption, a contactor becomes unnecessary, a reliability becomes high, and a cost is lowered. (2) Because a gap is formed in the coil or a coil is formed in an openable and closeable structure, a workability upon carry-in and carry-out of an object to be heated is greatly improved. Also, maintenance and inspection of an inner surface of a coil become easy. (3) Owing to the fact that the direction of the current flowing through the first connecting conductor and the direction of the current flowing through the second connecting conductor are opposite to each other and the first and second connecting conductors are opposed to each other with a gap as small as possible held therebetween, lowering of a heating efficiency due to increase of an impedance caused by the gap is negligibly small. While a principle of the present invention has been described above in connection to a number of preferred embodiments of the invention, it is intended that all matter contained in the above description and illustrated in the accompanying drawings shall be interpreted to be illustrative and not in a limiting sense.

Claims: An induction heating apparatus including a first coil section (110) having at least one turn of coil each of which is interrupted at one location, and a second coil section (120) having at least one turn of coil each of which is interrupted at one location; wherein one interrupted end of the coil in said first coil section and one interrupted end of the coil in said second coil section are electrically connected via at least one first connecting conductor (131, 132, 133), the other interrupted end of the coil in said first coil section and the other interrupted end of the coil in said second coil section are electrically connected via at least one second connecting conductor (141, 142, 143), thereby one continuous electric current passageway is formed by said coils and said connecting conductors, characterized by a flexible portion (210 or 310) forming part of each turn of said coil so as to make a gap distance between said first connecting conductor (131, 132, 133) and said second connecting conductor (141, 142, 143) variable, wherein, after closing the coils, the gap between the connecting conductors is held as small as possible, with an insulator (230, 330) interposed there between. An induction heating apparatus as claimed in claim 1, characterized in that said flexible portion is a flexible conductor section (210) forming a part of said coil. An induction heating apparatus as claimed in claim 1, characterized in that said flexible portion is a slider (310) for opening and closing one connecting conductor and a part of the coil connected to the same connecting conductor with respect to the other connecting conductor.

Inventors: EGUCHI TAKATOSHI, HANAMOTO MIKIO, KATAYAMA KEIICHI, KATO MITSUO, MIHARA KAZUMASA, TSURUSAKI KAZUYA, EGUCHI, TAKATOSHI, HANAMOTO, MIKIO, KATAYAMA, KEIICHI, KATO, MITSUO, MIHARA, KAZUMASA, TSURUSAKI, KAZUYA, Eguchi, Takatoshi, c/o Eguchi High Frequency Co., Hanamoto, Mikio, c/o Hiroshima Res. &amp; Dev.Center, Katayama, Keiichi, c/o Hiroshima Res. &amp; Dev.Center, Kato, Mitsuo, c/o Hiroshima Res. &amp; Dev.Center, MIHARA, KAZUMASA, HIROSHIMA MACHINERY WORKS, Tsurusaki, Kazuya, c/o Hiroshima Res. &amp; Dev.Center
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1992
Main classification: H05B6
IPC codes: H05B6