GB2045551A - Apparatus for electroslag re- melting of consumable electrodes - Google Patents

Abstract

Electrode holders 6, 7 hold at least two consumable electrodes 8, 9 connected to different terminals 17, 18 of an a.c. power source 3. The mould 2 and the bottom plate 1 are electrically connected to each other and, through rectifiers 19, 20, to the a.c. power source 3, the rectifiers 19, 20 being connected to the same terminals 17, 18 of the a.c. power source 3 as the electrode holders 6, 7. The rectifiers 19, 20 are so connected into the circuit as to provide a flow of only direct current through the bottom plate 1 and mould 2 towards the a.c. source 3 through the rectifiers 19, 20. This is said to prevent mould destruction by spark discharge and to improve ingot quality. <IMAGE>

Description

SPECIFICATION Apparatus for electroslag remelting of consumable electrodes This invention relates to apparatus for the electroslag remelting of consumable electrodes.

The present invention provides apparatus for the electroslag remelting of consumable electrodes, comprising a bottom plate and a mould electrically connected to each other and to an a.c. power source, electrode holders adapted to hold at least two consumable electrodes to be introduced into the mould and connected to different terminals of the a.c.

power source, rectifiers connected to the same terminals of the a.c. power source and to said bottom plate and to the mould to provide for a flow of only direct current through the mould and the bottom plate towards the a.c.

power source through said rectifiers.

The mould walls are not subjected to destruction by spark discharge, and such objectionable elements as sulphur, oxygen, and hydrogen are constantly removed from the metal pool. This, in turn, improves the quality of the ingot produced.

There may be modifications of the apparatus for the electroslag remelting of consumable electrodes which are powered either from a single-phase or three-phase a.c. power source.

When using a three-phase a.c. delta connected power source with the electrode holders connected thereto, the bottom plate and the mould may be connected to the phase terminals of the power source through at least three rectifiers.

When using a three-phase a.c. star connected power source with the electrode holders connected thereto, it is advisable to use an electrode holder for an additional electrode connected to the zero terminal of the three-phase a.c. power source and to connect the bottom plate and the mould through rectifiers both to the phase terminals and to the zero terminal of the power source.

The invention will be described further, by way of example, with reference to the accompanying drawings, wherein: Figure 1 diagrammatically shows apparatus for the electroslag remelting of consumable electrodes; Figure 2 diagrammatically shows a modification of the apparatus, wherein a three-phase a.c. delta connected power source is used; Figure 3 diagrammatically shows another modification of the apparatus, wherein a three-phase a.c. star connected power source is used; and Figure 4 shows, in horizontal section, a preferred arrangement of comsumable electrodes within the mould of the apparatus shown in Fig. 3.

As shown in Fig. 1, apparatus for the electroslag remelting of consumable electrodes comprises a bottom plate 1 over which a mould 2 is placed, and an a.c. power source 3. The bottom plate 1 is electrically connected to the mould 2 through a lead 4 or directly through their bearing surfaces in the contact area in the case when the mould 2 rests on the bottom plate 1 during the whole process of remelting. The mould 2 is formed with a cooling jacket 5. Mounted above the mould 2 are electrode holders 6 and 7 for holding at least two consumable electrodes 8 and 9. The electrode holders 6 and 7 and the mould 2 are secured by brackets 10 and 11 to a vertical column 12. The brackets 10 and 11 are mounted on the vertical column 1 2 for progressive motion in the vertical direction.

The a.c. power source 3 is a transformer whose primary winding 1 3 has terminals 14 and 1 5 adapted to be connected to a supply circuit. A secondary winding 1 6 of the transformer has terminals 1 7 and 1 8. The electrode holders 6 and 7 are connected to respective terminals of the a.c. power source 3.

In particular, the electrode holder 6 is connected to the terminal 1 8 and the electrode holder 7 to the terminal 1 7 of the transformer secondary winding 16. The bottom plate 1 and the mould 2 are electrically connected to the a.c. power source 3 through rectifiers 1 9 and 20 which, in their turn, are connected to the terminals 1 7 and 18, respectively, of the transformer secondary winding 1 6. The rectifiers 1 9 and 20 are connected in parallel to the a.c. power source 3 through leads 21 and 22, and connected to the bottom plate 1 through a lead 23. The rectifiers 1 9 and 20 are controllable.

The example illustrates an embodiment of the apparatus wherein a single-phase a.c.

power source is used.

There may be other modifications of the apparatus when it is used with a three-phase a.c. power source. In particular, there are possible schemes of the apparatus connection in star or delta configuration. Thus, Fig. 2 shows a modification of the apparatus, wherein a three-phase a.c. delta connected power source is used. As illustrated in this Figure, the three-phase a.c. power source 3 is a transformer provided with windings 24, 25, and 26. The ends of the windings 24, 25, 26 are interconnected in series into a closed triangle. The transformer has three terminals 27, 28, 29. An electrode holder 30 is connected to the terminal 29, an electrode holder 31 is connected to the terminal 28, and an electrode holder 32 is connected to the terminal 27.The bottom plate 1 and the mould 2 are connected to the phase terminals 27, 28, 29 of the power source 3 through at least three rectifiers 33, 34, 35. As shown in the diagram, the rectifiers 33, 34, 35 are connected to the three-phase a.c. power source 3 in parallel to the electrode holders 30, 31, 32. In particular, the rectifier 33 is connected to the terminal 29, the rectifier 34 is connected to the terminal 28, and the rectifer 35 is connected to the terminal 27. The rectifiers 33, 34, 35 are connected to the bottom plate 1 through the lead 23.

When a three-phase a.c. star connected power source 3 is used, as illustrated in Fig.

3, the power source 3 is provided with windings 36, 37, 38, each having one end thereof connected to a zero terminal 39. The other end of the winding 36 is connected to the terminal 40, that of the winding 37 to the terminal 41, and that of the winding 38 to the terminal 42. Electrode holders 43, 44, 45 of consumable electrodes 46, 47, 48 are connected to the phase terminals 42, 41, 40, respectively, of ;he three-phase a.c. power source 3. In this case the apparatus is provided with an electrode holder 49 for an additional electrode 50 which may be either consumable or non-consumable. The electrode holder 49 is connected to the zero terminal 39 of the three-phase a.c. power source 3.

The bottom plate 1 is connected through rectifiers 51, 52, 53 to the phase terminals 40, 41, 42 of the three-phase a.c. power source 3, and through the rectifier 54 to the zero terminal 39. Similar to the foregoing embodiments, the rectifiers 51, 52, 53, 54 are connected to the terminals in parallel, while their outputs are connected to the bottom plate 1 through the common lead 23.

The additional electrode 50 may be of any type, in particular, it may be a composite electrode, as shown in Fig. 3, or a conventional consumable electrode, similar to the electrodes 46, 47, 48. In the latter case, it is advisable to position the electrode holder 49 of the additional electrode 50 above the central portion of the mould 2, as shown in Fig.

4, and to arrange the electrode holders 43, 44, 45 of the consumable electrodes 46, 47, 48 above the periphery of the mould 2.

The apparatus shown in Fig. 1 operates in the following manner. Upon pouring liquid conductive slag into the mould 2, current is supplied from the a.c. power source 3 to the electrode holders 6 and 7. Alternating current flows through the electrodes and the slag pool. Under the action of the heat liberated in the slag pool owing to alternating current passing therethrough, the consumable electrodes 8 and 9 start melting, thus forming a metal pool which gradually crystallizes into an ingot.

During one half-cycle, current flows through the following circuits: electrode 9 - slag electrode 8; electrode 9 - slag - mould 2 rectifier 20; electrode 9 - slag - metal pool ingot - bottom plate 1 - rectifier 20. During the other half-cycle current flows through the circuits: electrode 8 - slag - electrode 9; electrode 8 - slag - mould 2 - rectifier 19; electrode 8 - slag - metal pool - ingot bottom plate 1 - rectifier 1 9. During both half-cycles current flows through the mould 2, the ingot being cast, and the bottom plate 1 only in one direction due to the connection of the rectifiers 1 9 and 20 into the circuit, thus preventing the mould walls from being damaged by spark discharge.

As the height of the ingot increases owing to the crystallization of the molten metal of the consumable electrodes 8 and 9, the mould 2 and the electrode holders 6 and 7 are progressively moved towards each other by changing the position of the brackets 10 and 11 on the vertical column 1 2. In so doing, the ends of the consumable electrodes 8 and 9 are continuously kept within the slag pool. In the process of the electroslag remelting of consumable electrodes, a constant direction of current flow on the slag - metal interface provides favourable conditions for cathode electrochemical reactions which result in removal of sulphur, oxygen, and hydrogen, anion discharge of these impurities occurring both during the first and the second halfcycles, i.e. practically all the time.

Also important is the fact that if the melting of the electrodes is unbalanced, the mode of electrical connection of the mould 2 and bottom plate 1 favours spontaneous elimination of the unbalance, for a higher current flows through the electrode which is more deeply immersed in the slag pool. It is possible to control the melting rate of the electrodes by changing the resistance in the circuits of the rectifiers 1 9 and 20.

The modifications of the apparatus shown in Figs. 2 and 3 of the drawings operate in a similar manner.

Claims (4)

1. Apparatus for the electroslag remelting of consumable electrode, comprising a bottom plate and a mould electrically connected to each other, electrode holders adapted to hold at least two consumable electrodes, means for electrically connecting the electrode holders to respective terminals of an a.c. power source, and rectifiers electrically connected to the same terminals and to the bottom plate so as to provide for a flow of only direct current through the bottom plate and the mould towards the a.c. power source through the rectifiers.

2. Apparatus as claimed in claim 1, wherein the power source is a three-phase a.c.

delta connected power source, the bottom plate and the mould being connected to the phase terminals of the a.c. power source through at least three rectifiers.

3. Apparatus as claimed in claim 1, wherein the power source is a three-phase a.c.

star connected power source, the apparatus including an electrode holder for holding an additional electrode electrically connected to the zero terminal of the three-phase a.c.

power source, the bottom plate and the mould being connected through rectifiers both to the phase terminals and to the zero terminal of the three-phase a.c. power source.

4. Apparatus for the electroslag remelting of consumable electrodes, substantially as described herein with reference to, and as shown in, Fig. 1, Fig. 2, or Fig. 3 and 4 of the accompanying drawings.