GB2268103A

GB2268103A - Apparatus for heating molten metal in a ladle including a vacuum container having a cover for receiving the ladle

Info

Publication number: GB2268103A
Application number: GB9313377A
Authority: GB
Inventors: Michio Kawasaki
Original assignee: Fuji Electric Co Ltd
Current assignee: Fuji Electric Co Ltd
Priority date: 1989-11-09
Filing date: 1993-06-29
Publication date: 1994-01-05
Also published as: GB9313378D0; GB9313377D0; GB2267666A

Description

2268103 APPARATUS FOR HEATING MOLTEN METAL IN A LADLE The present

invention relates to an apparatus for heating in a ladle molten metal, to be poured into a mould.

In the case where the temperature of molten metal in a ladle to be poured into a mould falls so that the fluidity of the molten metal becomes less fluid than is required for proper moulding procedures, the molten metal in the ladle may be returned to a melting furnace to be remelted. However, the remelting of cooled or the solidified metal is undesirable because oil considerable energy losses incurred.

Therefore, an induction heating apparatus has been developed for ladle in which first cores are attached to a ladle adapted to be mounted on a supporting tray, to which second cores and a coil are fixed, to maintain the molten metal in the ladle adequately fluid at all times. Such as apparatus is conventional and disclosed in Japanese Patent Unexamined Publication No Sho-63-137521.

Figure 6 of the accompanying drawings is a sectional view of the conventional apparatus. A ladle 1 includes metal shell body 2 made of a non-magnetic material such as stainless steel, and a refractory heatinsulating material 3 spread on the inside of the metal shell 2. Hanging rods 5,5 are linked to trunnion shafts 4,4 projecting from opposite sides of the metal shell 2. A driven wheel 6 for inclining the ladle is mounted to one trunnion shaft 4. First cores 8a and 8b, arranged in pairs circumferentially at intervals of a predetermined pitch are attached to the outer circumferential portion 3a and the outer bottom portion 3b of the refractory heat-insulating material 3. Second cores 11, corresponding in number and pitch to the first cores 8a and 8b,.are fixed on a tray 10 which is fixed on a floor 2 9 for mounting the ladle 1 from above. A supporting member 12 for engaging the bottom portion of the ladle 1 and a stopper 13 for positioning the ladle 1 circumferentially are provided in the tray 10 so that the f irst cores' 8a and 8b in each pair can be aligned with and face the magnetic pole portions ila and lib provided at the opposite ends of a corresponding one of the second cores 11 when the ladle is put on the tray 10. Further, a coil 14 is wound on the second cores 11.

When the coil 14 is energised to excite the second cores 11, an alternating magnetic field 16 is produced in molten metal 15 in the ladle 1 through the first cores 8a and 8b to effect induction heating of the molten metal 15 to maintain the molten metal 15 in a suitably fluid state.

In the aforementioned conventional apparatus, the second cores 11 and the coil 14 for producing heating energy, together with power cables and water-cooled pipings (not shown), are fixed to the tray 10 side. Accordingly, the conventional apparatus has an advantage in that the structure for providing those try related members can be simplified and the ladle 1 containing the molten metal 15 can be moved freely by hanging rods 5 or can be inclined by trunnion shafts 4.

However, the L-shaped configuration of the second cores 11 makes it difficult to produce the second cores 11. If the height of the magnetic pole portion lib of each second core 11 and the height of the stopper 13 cannot be established accurately, the magnetic pole portion lib may collide with a corresponding first core 8b in the bottom portion 3b of the ladle 1, causing breakage or the gap between the magnetic pole portion lib and the first core 8b to be unacceptably large. This latter condition results increase of reluctance, increase of energy loss 3 and abnormal heating of the ladle periphery.

The present invention has been made in view of the above circumstances and has as an object to provide an apparatus for heating molten metal in a ladle having ladle mounted first cores co-operable with second cores and coil means mounted on supporting tray adapted to received the ladle and which facilitates containment of the ladle and tray or the ladle by itself in a vacuum chamber.

Addition objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realised and attained by means of the instrumentalities and combinations particularly pointed our in the appended claims.

According to the present invention there is provided an apparatus for heating molten metal comprising:

a ladle for holding said molten metal and provided with a refractory heatinsulating material; first cores arranged in pairs and attached to the outer circumference of said refractory heat-insulating material of said ladle; a tray for mounting said ladle; second cores attached to said tray and having magnetic pole portions at both ends of said respective second cores so as to face said first cores; a coil for exciting said second cores; and 4 a vacuum container having a cover capable of being opened and closed for receiving said ladle.

Embodiments of the invention may include forms of sensing and positioning mechanisms so that when the ladle is mounted in the tray, alignment and proximity of poles on the second cores with the first core paired are ensured. Additionally, exemplary embodiments of the invention may include a provision for insulating the coil on the second core both physically and thermally through the provision of circumferential spaced axial shock bars of non magnetic metal, such as stainless steel, and filling the space between the shock bars with thermal insulating material. Alternatively, the thermal insulation of the coils onthe second core from the hot ladle may be achieved byeither gaseou. s or liquid cooling system.

while the radial facing arrangement of the magnetic pole portions with the pairs of first cores at the outer circumferential portions of the ladle facilitates placement of the ladle in the tray containing the second cores and coil, an enhancement of this feature is accomplished by an embodiment having movable magnetic pole portions on the second cores. In this embodiment, the magnetic pole portions may be pivoted or otherwise moved radially away from the ladle as it is being placed on the tray and then returned to an operative inductive heating position with respect to the second cores, under pressure, when the ladle is fully in place. Either one,or the other or both of the first core and magnetic pole configurations may be modified to enhance the inductive efficiency of the heating system.

The accompanying drawings, which are incorporated in and constitute a part of this specification illustrate embodiments of the invention and, together with the description, serve to explain the objects, advantages and principles of the invention. In the drawings, Figure 1 is a fragmentary cross section illustrating an apparatus for heating molten metal; Figures 2(a) and 2(b) are axial cross sections showing relative positions of the ladle and the second cores depicted in Figure 1; Figures 2(c) and 2(d) are radial cross sectional views -showing relative positions of the ladle and the second cores of Figure 1; Figure 3 is a sectional view of one embodiment of a vacuum container in accordance with an embodiment of the invention; Figure 4 is a sectional view of an alternative vacuum container embodiment; Figure 5 is a sectional view of a further alternative embodiment of a vacuum container; and Figure 6 is a sectional view of the conventional apparatus.

Reference will now be made in detail to the present exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

In Figure 1, the ladle 1 is composed of a metal shell 2 and a refractory heat-insulating material 3. The refractory heat-insulating material 3 has a bottom portion.3b and a cylinder portion 3a. The ladle 1 is 6 moved and inclined by trunnion shafts and hanging rods for supporting them in a manner described previously with respect to Figure 6. Poles 8a and 8x in each pair of first cores attached to the ladle 1 are oriented to face radially in the cylinder portion 3a. A second core lly, having magnetic pole portions lia and iix facing the poles 8a and 8b, respectively, is substantially of elongated C-shaped configuration. The second core lly is provided with a heat coil 14 and is fixed onto a tray (not shown). The.trunnion shafts the hanging rods and the tray (not shown) are arranged in the same manner as in the conventional apparatus.

In the aforementioned structure, the poles 8a and 8x in each pair of the first cores are attached in the cylinder portion 3a of the ladle 1. Accordingly, the poles Sa and 8x in each pair of the first cores are arranged to.face the second core lly through a radial gap, and when the ladle 1 is lowered to be placed on the tray, they present no obstruction to the relative positioning in the vertical or axial direction. Accordingly, not only is collision of the magnetic pole portions lla and llx prevented, but also excessive enlargement of the gap is prevented. Because of the elongated C-shaped configuration of the second core lly, the magnetic pole portions lla and lib project slightly radially at opposite ends. In short, the shape of the second core is simplified to avoid the wasteful L-shaped magnetic circuit of the prior art. The metal shell 2 may be circumferentially jointed through one or more insulating plates to thereby prevent heating caused by a current induced circumferentially.

The first cores may be arranged in pairs vertically and the coil may be arranged so as to be wound on the ladle. Alternatively, the first cores may be arranged in pairs circumferentially and the coil may be arranged so as to 7 be wound on the second cores.

The relative positional relationship between the first and second cores in the apparatus in Figure 1 is shown in Figures 2(a) through 2(d). In Figure 2(a), the first cores 8a and 8x have a downward bias with respect to the second core lly. In Figure 2(b), the first cores 8a and 8x have an upward bias with respect to the second core lly. Consequently, magnetic flux leaks into the portions of the metal shell 2 designated by the mark X to overheat those portions. In Figure 2(c), the first cores 8a and 8x are circumferentially inclined by 6, so that the same phenomenon occurs in the portions designated by the mark X in the circumferential direction. In Figure 2(d), the first cores 8a and 8x are eccentrically moved by 6, so that reluctance in the larger gap side increases. Consequently, the larger gap side is overheated because of the leakage into the metal shell 2. on the contrary, the smaller gap side may be broken because of mechanical contact.

Figures 3 through 5 show embodiments in which the ladle is placed in a vacuum container and subjected to a metallurgical treatment such as a vacuum degas treatment. In Figure 3, not only the ladle 1 is contained in a vacuum container 67 having a cover 66 but also the second core lly having the coil 14 is within the vacuum container 67. In Figure 4, the second core lly having the coil is placed on the outside of a vacuum container 68, so that the coil in air is free from corona discharge produced in a vacuum. Accordingly, a high voltage can be utilised with no necessity of a large-size electric circuit.

In Figure 5, the vacuum container 69 has a special shape and also serves as the metal shell of the ladle. Covers 70a and,70x made of a nonmagnetic material and provided 8 to keep the first cores 8a and 8x in a vacuum are formed, by welding or the like, over the first cores 8a and 8x piercing the vacuum container 69.

The foregoing description of preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible within the scope of the invention as defined in the appended claims. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilise the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.

The readers attention is directed towards our copending British Patent Application No 9024377.5 (Serial No 2238496) from which this application was divided, and which claims an apparatus for heating molten metal comprising:

a ladle for holding said molten metal and provided with a refractory heatinsulating material; first cores arranged in pairs and attached to the outer circumference of said refractory heat-insulating material of said ladle; a tray capable of mounting said ladle; second cores attached to said tray and having magnetic pole portions at both ends of said respective second cores so as to face said first cores; and 9 a coil for exciting said second cores; wherein said magnetic pole portions and said pairs of first cores are arranged to face each other radially at the outer circumferential portions of said ladle.

Claims

1. An apparatus for heating molten metal comprising:

a ladle for holding said molten metal and provided with a refractory heatinsulating material; first cores arranged in pairs and attached to the outer circumference of said refractory heat-insulating material of said ladle; a tray for mounting said ladle; second cores attached to said tray and having magnetic-pole portions at both ends of said respective second cores so as to face said first cores; a coil for exciting said second cores; and a vacuum container having a cover capable of being opened and closed for receiving said ladle.

2. An apparatus for heating molten metal as claimed in Claim 1, wherein said second cores together with said coil are receivable in said vacuum container.

3. An apparatus for heating molten metal as claimed in Claim 1, wherein said second cores together with said coil are located out of said vacuum container.

4. An apparatus for heating molten metal as claimed in Claim 1, wherein said vacuum container serves as a metal shell constituting an outer block of said ladle.