EP0511465B2 - Electromagnetic agitating method for continuous casting - Google Patents

Abstract

A mould for continuous casting comprises: (i) a mould tube (14) for receiving molten metal (16); (ii) a cooling circuit surrounding the mould tube (14) for cooling it; (iii) an electromagnetic induction coil (32) for provoking a gyratory movement in the molten metal (16) in the mould tube (14) around its axis, this electromagnetic induction coil (32) being vertically displaceable w.r.t. the mould tube (14); and (iv) a cooling circuit (34, 36) for the electromagnetic induction coil (32). The electromagnetic induction coil (32) with its cooling circuit (34, 36) and the mould tube (14) with its cooling circuit form two separate units. The induction coil unit is mounted around the mould tube unit in a manner that enables it to slide axially as a block along the length of the mould tube (14). The method used to adjust the height of the induction coil unit is also claimed. A crane is used to slide the induction coil (32) unit in some vertical guidance shafts (50) along the length of the mould tube (14) and a mechanical system is used to support the induction coil (32) on the guidance shafts (50) in different predetermined vertical positions. A feature of this continuous casting mould is the use of a source of radiation for constant surveillance of the meniscus of the molten metal in the mould.

Description

The present invention relates to an ingot mold with electromagnetic stirring device of an installation continuous casting comprising a mold tube vertical receiving molten metal, as well as a electromagnetic inductor to generate movement gyration of molten metal in the mold tube around the axis thereof.

A device of this kind is known from the document EP-A-0093068. Depending on the quality and nature of the products cast, there are basically two processes different from casting. The open casting process or in free jet is simply to let the liquid metal in the mold tube through a calibrated nozzle with more or less constant flow. The level of the steel meniscus in the mold is controlled by adapting the extraction speed as a function of the extraction and according to the indication of an installation of level measurement based on a radioactive principle. This process is basically used for casting medium quality steel billets, because the casting is performed in contact with air.

To improve the quality of steel, a process is used airtight casting which is casting with submerged nozzles and powders. According to this process, liquid steel is introduced into the mold tube at through a nozzle which plunges into the liquid metal which is in the mold tube. Contact with air and oxygen is prevented by a layer of powder which covers the surface of the metal at the pouring meniscus.

In this case the casting is done at extraction speed constant. The level of the ingot mold steel is controlled by a buffer or a distributor drawer.

For both casting processes it is also known to improve the quality of steel by stirring electromagnetic which must however be adapted to the process of selected casting and the targeted qualities of steel. Thus, for example, in the case of casting free jet billets, the major goal sought by the application of electromagnetic stirring in an ingot mold consists in improving the surface condition of the billets eliminating pitting and slag encrustations. To achieve this, the speed of rotation of the steel in the mold at the meniscus must be very high, hence the importance of the location of the inductor in relation at the meniscus on the surface condition of the billets.

On the other hand, in the case of pouring blooms with submerged nozzle and pouring powder, it is advisable to reduce the rotation speed at the meniscus to avoid as much as possible the entrainment of the powder and reduce wear on the nozzle, while keeping as high a brewing intensity as possible below the meniscus. In other words, for the free jet casting it is preferable that the inductor found in the upper region of the mold tube, whereas for casting with submerged nozzle, it is preferable that the inductor is placed at a lower level. This is the reason why, to take full advantage advantages of brewing electromagnetic in an ingot mold, it is preferable to have of two different facilities to set up each of the two casting processes.

Document DE-A-3819493 describes an ingot mold with electromagnetic stirring device which would allow the implementation of the two casting methods keep on going. This ingot mold includes an inductor which is adjusted like a piston in a separate compartment of the ingot mold cooling box, so to be essentially movable in height by the pressurized coolant. The ingot mold described does not include means for detecting the level of molten metal in the mold tube.

GB-A-2021459 describes an ingot mold with an essentially movable external inductor horizontally with respect to a vertical ingot mold tube.

Document EP-A-0063072 describes an ingot mold with a fixed inductor mounted in a cooling box surrounding the mold tube. A system for detecting the level of molten metal in the tube ingot mold includes a radiation source arranged outside the inductor. A notch in the inductor lets the radiation through avoiding as well as the inductor does not constitute a screen for the radiation.

Document EP-A-0157255 describes an ingot mold with a fixed inductor. This inductor includes coils having housings for receiving a radiation source or a detector forming a system level detection.

The problem underlying the present invention is to develop a simple ingot mold including a height-adjustable inductor and means for detect the level of molten metal in the tube mold.

This problem is solved by an ingot mold according to the first claim.

According to an advantageous embodiment, the tube of ingot mold is surrounded by a first steel tube coaxial which, in turn, is arranged inside a second coaxial tube around which the inductor is mounted, while the annular spaces between the two tubes and between the mold tube and the first tube are crossed by a coolant.

The ingot mold is equipped with a level detector steel in the ingot mold tube, which consists of a cylindrical radiation source mounted inside the second tube and associated with a scintillometer mounted on the opposite side of said second tube.

The radiation source is preferably located inside a cylindrical protective jacket in lead provided with a radial and movable slot around the axis of said source between an angular position in which the slot is directed on the mold tube and an angular garage position in which the slot is directed on a cylindrical lead block extending along said shirt.

The ingot mold which consists of the ingot mold tube, of the inductor and the two tubes can be integral a set of underlying and removable rollers in block with this one.

la figure 1 montre schématiquement une coupe verticale d'un dispositif selon la présente invention illustrant l'inducteur en position pour une coulée en jet libre;

la figure 2 montre une vue analogue à celle de la figure 1, l'inducteur étant en position de coulée avec busette immergée, et

la figure 3 montre schématiquement une coupe horizontale à travers la tube de lingotière et la source de radiation.

Other features and characteristics will emerge from the detailed description of an advantageous embodiment presented below, by way of illustration, with reference to the appended drawings in which:

Figure 1 schematically shows a vertical section of a device according to the present invention illustrating the inductor in position for free jet casting;

FIG. 2 shows a view similar to that of FIG. 1, the inductor being in the casting position with submerged nozzle, and

Figure 3 schematically shows a horizontal section through the ingot mold tube and the radiation source.

Figures 1 and 2 show an ingot mold 10 contained in a metal case 12. The ingot mold 10 comprises basically a vertical ingot mold tube 14 containing liquid metal 16 which is spilled from a tun-dish not shown. The molten metal 16 solidifies gradually in this mold tube and the blank metallic is extracted there by passing through a set 18 of underlying guide and forming rollers metal blanks. According to one embodiment preferred of the invention, the set of rollers 18 is integral of the mold 10 and can be disassembled as a block with it.

The ingot mold tube 14, which is generally consists of a copper tube, is surrounded by a tube coaxial steel 20 which forms with the mold tube a annular cylindrical space 22 in which a coolant for the ingot mold tube 14. A other cylindrical space 24 is delimited around the tube 20 by a second tube 26. This space 24 is closed towards the bottom by an annular plate 28 fixed to the two tubes 20 and 26.

The cooling water enters the circuit by 30 and then in the annular gap 22 between the tube ingot mold 14 and tube 20. This space is very thin to ensure rapid circulation and cooling effective in the ingot mold tube 14. The water from cooling thus goes up along the mold tube to overflow through the top of tube 20 and fill the annular space 24. The cooling water leaves this space 24 by overflow in a pipe vertical not shown arranged along the inner wall of tube 26 and then through a pipe Release.

Around the outer tube 26 is an inductor electromagnetic 32, known per se, to achieve the electromagnetic stirring of metal 16 in the tube ingot mold 14. The electromagnetic device 32 can be made up of one or more inductors.

In accordance with the present invention, the inductor 32 is not fixed, but can be moved vertically between an elevated position according to figure 1 for casting in free jet and a lower position according to FIG. 2 for casting with submerged nozzle. The means of displacement of the inductor 32 can be constituted by any suitable means known per se, for example three vertical threaded rods which support the inductor 32 and which can be rotated synchronously by a suitable motor.

According to a simple and effective embodiment inductor 32 slides vertically in several, for example three guide rods 50, the operation vertical achieved by a crane not shown. In the example shown, the rods 50 are designed to position the inductor 32 in three vertical positions different defined by three radial perforations upper 52 and two lower notches 54.

When the inductor 32 is raised to the position according to figure 1 it can be retained there by engaging manually a claw not shown in the notch upper 54 and wedged using a key not shown engaged through the upper perforation.

In the lower position the inductor 32 rests on the bottom of the mold 10 and can be keyed by the perforation lower 52. If the embodiment illustrated allows a third intermediate position, not shown, it is, of course, possible to predict than two or plan more.

Inductor 32 has a circuit separate cooling, which is symbolized by arrows 34 and 36 for the inlet and outlet of water from cooling.

Another feature of the present invention is monitoring the meniscus level of the liquid metal in the ingot mold tube 14. This monitoring is performed using a radiation source 38. by example a cobalt source, arranged in the upper region of annular space 24 and that is associated with a scintillometer 40 arranged on the opposite side of the ingot mold tube 14. To reduce the risk of radiation personnel, this radiation source 38 is found inside a cylindrical protective jacket 42, as shown in more detail and enlarged in FIG. 3. This protective jacket 42 which can, for example, being made of lead, has a vertical slot 44 for the passage of the rays. This shirt protection 42 can be rotated around a vertical axis between an operating position shown in FIG. 3, in which the slot 44 is directed on the mold tube 14 and a garage position, not shown in which the slot 44 is directed against a vertical block absorption 46. Thanks to this arrangement, an operator can carry out work on the mold tube 16 without being exposed to radiation from source 38, these radiation being absorbed by the protective block 46.

The actual level measurement will not be explained in more detail since the use a radiation source for measuring a level is known per se.

Claims (8)

1. Ingot mould of a continuous casting plant comprising

   an ingot mould tube (14) receiving a molten metal (16),

   an outer tube (26) surrounding the ingot mould tube (14), a cooling circuit defined between the outer tube (26) and the ingot mould tube (14);

   an electromagnetic inductor (32) to create a gyratory motion of the molten metal (16) in the ingot mould tube (14) around the axis of the latter, the said electromagnetic inductor (32) being capable of being displaced vertically with respect to the ingot mould tube (14), and

   a separate cooling circuit (34,36) for the electromagnetic inductor (32);

   characterised by

   a level-detector to detect the level of the metal in the ingot mould tube (14);

   the said level-detector comprising a source of radiation (38) located between the said outer tube (26) and the ingot mould tube (14), and

   the electromagnetic inductor (32) forming with its cooling circuit (34,36) a stirring unit which is located outside the said outer tube (26) such that it can be vertically displaced en bloc along the said outer tube (26) by a displacement unit.
2. Ingot mould for continuous casting according to Claim 1, characterised in that the said level-detector comprises a scintillation counter (40), the said source of radiation (38) being located on one side of the ingot mould tube (14), and the said scintillation counter (40) being located on the opposite side of the ingot mould tube (14).
3. Ingot mould for continuous casting according to Claim 1 or 2, characterised

   in that an inner tube (20) surrounds the ingot mould tube (14) and forms with the latter a first annular space (22) defining a first cross-section of flow for a cooling liquid,

   in that the said outer tube (26) surrounds the said inner tube (20) and forms with the latter a second annular space (24) defining a second cross-section of flow for a cooling liquid,

   in that the said first cross-section of flow is much smaller than the said second cross-section of flow, and

   in that the said source of radiation (38) is located in the said second annular space (24).
4. Ingot mould according to Claim 1, 2 or 3, characterised in that the source of radiation (38) is equipped with a cylindrical protective jacket (42) absorbing the radioactive radiation, and

   in that this protective jacket (42) has a longitudinal slit (44) for the passage of the energy emitted by the source of radiation (38).
5. Ingot mould according to Claim 4, characterised in that the said cylindrical protective jacket (42) is mounted in the said cooling circuit so that it can be rotated around the longitudinal axis of the source of radiation between a first position, in which the said longitudinal slit (44) is directed towards the ingot mould tube (14), and a second position, in which the said longitudinal slit (44) is directed towards an absorption block (46).
6. Ingot mould according to any one of Claims 1 to 5, characterised by vertical threaded rods supporting the inductor.
7. Ingot mould according to any one of Claims 1 to 5, characterised by vertical guide rods (50) for the inductor.
8. Ingot mould according to Claim 7, characterised by means for supporting the inductor (32) in different predetermined vertical positions on the said vertical guide rods (50).

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