EP0097610A1 - Method of and installation for emptying metallurgical vessels - Google Patents

Abstract

Method for emptying tilting metallurgical vessels, filled with metal and slag, provided with a tap hole (2) arranged in the side wall. At the latest after the end of metallurgical operations and before the container is tilted, the taphole (2) is sealed with a plug (3) capable of being attacked by the molten mass. Then the container is tilted, and a bubbling gas is introduced around the tap hole in the container through permeable elements (10). The tap hole is closed with a new plug as soon as the first slag elements are identified. The plug (3), which is provided with a suitable recess (14), is retained by friction on a lug pivotally mounted on an arm (4) actuated by a jack (7).

Description

The present invention relates to a method and a device for emptying tilting metallurgical vessels, in particular steelworks converters, comprising a tap hole arranged in the side wall and containing molten metal on which slag is swimming.

When casting metal, particularly steel, in the ladle or in any other transport or processing container, a certain amount of slag generally passes through the tap hole. In fact, at the start of the emptying, when the converter is tilted into the pouring position, the hole first fills with slag before the steel bath completely covers it. During the pouring of the metal, a vortex, called a vortex, forms above the taphole, which causes slag towards the pocket. Towards the end of the casting, before the converter is brought back to its starting position, an additional quantity of slag flows into the ladle. Slag presents a risk of rephosphorization of the steel. On the other hand, due to the high activity of oxygen in the slag, the metallurgical treatment of quenched and semi-quenched steels is then difficult to perform. In addition, the desulphurization of the steel becomes critical.

To avoid the slag entrainment at the start or at the end of the emptying operation of tilting metallurgical vessels, various devices have already been proposed. The best known of these are the shutter valve, the drawer closure and above all the massive float, the section of which is wider than that of the flow orifice and which swims above the mouth of the tap hole. These floats have a density between that of the slag and that of the metal and have the function of closing the tap hole, when practically all the metal has flowed. Since the contours of the tap hole vary continuously due to wear, the use of floats does not lead to convincing results. DE-OS 26 39 712 discloses a taphole closing device comprising a closing body which can be inserted into the poured hole which leaves an annular slot free relative to the wall of the taphole and which contains a pressurized gas line. The closure body has an outer wall which tapers towards the orifice of the pressurized gas line. The slag is forced back into the container under the effect of the gas flow. This device, which is subject to significant wear in large converters, has been improved (see EP 10.082) in that the external lateral surface of the shutter consists of a surface in the form of a spherical cap which , on the side of the mouth, turns into a frusto-conical surface. In a preferred embodiment, the shutter is made of gray cast iron. Both devices have the disadvantage that they require large quantities of gas to seal the taphole. In addition, there are problems of blockage of the mouth of the gas pipe of the shutter.

To reduce the amount of slag entrained by the vortex, known as a vortex, which forms above the tap hole from the start of ladle pouring, it has already been proposed to inject bubbling gas using nozzles inside the metal bath in the immediate vicinity of the tap hole. Unfortunately, the nozzles require, in order to avoid their obstruction, large quantities of gas, not only during the emptying, but also during the whole campaign. This results in pronounced cooling of the molten metal. On the other hand, the nozzles coming into contact with the slag and the liquid metal, have lifetimes much shorter than those of the coating surrounding the crucible. The disappointing results are probably explained by the fact that the gas bubbling from the nozzles does not scatter enough in the vortex and therefore does not manage to counteract its turn action enough ridging and retaining slag.

The object of the present invention is to provide a remedy for the drawbacks described, and to eliminate in a large proportion the entrainment of slag when emptying metallurgical vessels.

This object is achieved by the method according to the invention which is characterized in that it ensures, at the latest after the end of metallurgical operations, the sealed closure of the taphole using a plug capable of being attacked by the molten mass, in that the container is tilted, in that a bubbling gas is introduced around the taphole in the container through permeable elements, in that the closing hole is closed pouring using a new stopper as soon as the first slag elements are found and the container is tilted to the starting position. Preferential embodiments of the invention are described in the subclaims.

The advantages obtained thanks to this invention consist in that a thorough separation of the metal and the slag is carried out, both at the beginning and during and towards the end of the emptying of the crucible. On the crucible side, in the case of a two-phase step with intermediate scrubbing and recovery of the slag from the second blowing phase, savings in lime due to a reduction in the loss of slag. On the container side there is a marked reduction in the rephosphoration of the metal; the yield of ferro-alloys introduced after emptying increases appreciably. In addition, an increase in the resistance of the refractory of the container is observed of approximately 10%.

• La Fig. 1 montre une coupe schématique à travers un dispositif pour vidanger des récipients métallurgiques.
• La Fig. 2 montre une coupe à travers une forme d'exécution du bouchon qui sert à fermer le trou de coulée ainsi que de son support.
• La Fig. 3 montre, vus de l'intérieur du convertisseur, des détails de l'abord du trou de coulée.

The invention is explained in more detail with the aid of drawings, which show, without limitation, a possible embodiment.

• Fig. 1 shows a schematic section through a device for emptying metallurgical vessels.
• Fig. 2 shows a section through an embodiment of the plug which is used to close the tap hole as well as its support.
• Fig. 3 shows, seen from inside the converter, details of the approach to the tap hole.

We can see in Fig. 1 part of a refining crucible 1 whose tap hole 2 is closed by a plug 3. The plug 3 is mounted on an arm 4, which pivots about an axis 5 fixed on the wall of the tap hole . The arm 4 is provided with a stop 6. (The counter-stop mounted on the wall of the converter is not shown). A hydraulic cylinder 7, operable in both directions, acts by means of a rod 8 and a fork 9 on the arm 4. The cylinder 7 can pivot around an axis integral with the wall of the converter. The plug 3 has the shape of a truncated cone, slightly chamfered. The large base of the truncated cone has a cylindrical recess 14 in which is received a lug mounted on the arm 4 (see also Fig. 2). The plug which is held on the lug by friction is preferably made of an inexpensive, easily machinable and relatively soft material such as wood, preferably fir. To improve its high temperature resistance, _'the surface of the plug is advantageously covered with a de- refractory material layer. Two elements 10 permeable to a bubbling agent are located on either side of the tap hole 2 (see FIG. 3). The optimal place where these elements are placed is preferably determined experimentally for each converter. By positioning them about 0.5 m from the axis of the tap hole, we obtained the expected result for our 150-ton converter. Permeable elements suitable for implementing the invention have been described in patents LU 82.552, LU 82.553, LU 82.554. They consist of several neighboring elongated segments, of rectangular section, surrounded by a metal box. On the cold side of the permeable element 10, a distribution chamber 11 is welded to the walls of the box. Conduits 12 connect this chamber 11 to a source 13 of bubbling agent. The bubbling fluid is passed at the interface of the different segments. It follows that the permeable elements 10 create a well distributed flow of fluid.

Instead of using a rigid mounting of the lug on the arm 4, as shown in FIG. 1, one can advantageously opt for a swiveling mounting (see Fig. 2). In this embodiment of the invention, a tube 20 is fixed, onto which a base 16 is welded, on the arm 4. A bolt 18 screwed into a ball joint 15 provided with the stopper lug ensures, by through the spring 17 and the washer 19, the bearing of the ball joint 15 on the base 16. This orientable mounting of the plug 3 on the arm 4 guarantees automatic centering of the plug on the mouth of the tap hole, the contours vary due to wear.

The operation of the device is as follows: During blowing, the jack 7 can be kept in the extended position, as shown in FIG. 1, to ensure that the plug 3 is held in the mouth of the taphole 2. Note that the taphole is preferably always closed, except during the pouring operation. This limits heat loss and avoids the escape of flame and slag during blowing. Before tilting the converter, the jack 7 withdraws the arm 4 until it stops. The plug 3 remains stuck in the tap hole 2. The liquid mass comes into contact with the plug during the tilting and destroys it in a few seconds. At this time the converter is in such a position that only metal is in the immediate vicinity of the tap hole. As a result of the intense and continuous bubbling, caused by the rising of the flow of bubbling gases leaving the permeable elements, a circular area is created above the taphole. This area is slag-free and has virtually no vorex, so the steel can flow without causing significant amounts of slag. A new plug 3 is positioned on the lug of the arm 4. Towards the end of the casting, as soon as the first pieces of slag are observed, or identified with the aid of optical, magnetic sensors, etc. the jack 7 is pressurized and the plug 5 is pressed into the tap hole. The plug has a reduced mass, the closure is therefore quick. As the cap is relatively soft, it can adapt to the contours of the tap hole. To guarantee a hermetic closure, the position of the shutter is preferably adjustable on the axis of the tap hole. It is also noted that since the plug remains stuck respectively held in the taphole between two emptying operations, the use of a second plug is superfluous.

The bubbling agent is usefully a neutral gas such as argon, nitrogen or possibly carbon dioxide. During the campaign, a gas flow of 2-3 Nm ³ / _h eure ensures the permeability of the refractory elements. At the time of the drawdown, the gas flow rate is increased to reach 5-10 Nm ³ / hour. Note here that higher flow rates cause projections, which mix with the slag and which are then entrained with them towards the tap hole. By adjusting the bubbling gas flow rates, an improvement in the ferro-manganese yield ranging from 3 to 7% has been observed for semi-quenched steels, which is equivalent on average to a saving of 0.35 kg / t steel . Similarly, the number of flows with high rephosphorization, on the order of 0.025 XP, decreased by more than half, while those with low rephosphorization, on the order of 0.002% P, easily doubled.

Although the invention has been described and shows the most convincing advantages in relation to a tilting crucible, it can also be used with static metallurgical vessels having a tap hole provided in the bottom. Likewise, the number of permeable elements need not necessarily be taken to be two, and the bubbling gases suitable for implementing the invention are not only argon, nitrogen or carbon dioxide.

Claims (10)

1. Method for emptying tilting metallurgical vessels, in particular steelworks converters, comprising a tap hole arranged in the side wall and containing molten metal on which a layer of slag is swimming, characterized in that at most late after the end of metallurgical operations and before the container is tipped, the tap hole is sealed with a plug capable of being attacked by the molten mass, in that the container is tipped, that a bubbling gas is introduced around the taphole in the container through permeable elements, in that the taphole is closed with a new plug as soon as the first elements are found slag and that the container is tilted to the starting position. 2. Method according to claim 1, characterized in that the plug is introduced into the taphole using a pivoting arm, preferably actuated by a hydraulic cylinder, which ensures the maintenance of the plug in the tap hole during metallurgical operations using said arm and the arm is removed just before the emptying operation. 3. Method according to claim 1, characterized in that a determined quantity of gas is constantly blown, preferably 3 to 3 _Nm 3 / hour, through each permeable element and that this flow is increased, preferably at 5-10 Nm ³ / hour, when pouring the metal out of the container. 4. Device for implementing the method according to one of claims 1 to 3, characterized in that the gas permeable elements comprise at least one elongated segment preferably having a rectangular section and are provided on the cold side with a gas distribution connected via a conduit to a source of bubbling agent and in that said plug is transiently fixed on a pivoting arm actuated by a jack. 5. Device according to claim 4, characterized in that the transient fixing is constituted by a lug which retains the plug, provided with a suitable recess, by friction. 6. Device according to claim 5, characterized in that the stopper lug is mounted in an orientable manner on the pivoting arm. 7. Device according to one of claims 4 or 5, characterized in that the plug in the form of a truncated cone including the small base. is slightly chamfered and the large base of which includes said recess. 8. Device according to claim 7, characterized in that the plug is made of wood, preferably fir and is partially covered by a layer of refractory material. 9. Device according to claim 4, characterized in that it comprises two permeable elements, located on either side of the taphole, preferably at a distance of about 0.5 m from the axis of the taphole . L0. Device according to claim 4, characterized in that the source of bubbling agent is a source of argon, nitrogen or carbon dioxide.

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