JPS6231267B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the melting, refining and casting of molten metals and alloys, and more particularly to an improved method for the continuous recovery and discharge of molten metal from a rotary furnace through an axial end opening thereof. and equipment.

Rotary furnaces used to melt metal in batches are typically tapped through tapholes located in the walls of the furnace. The furnace rotation is stopped, the taphole is opened by a ram or lance, and the metal is rapidly released into the ladle. In the case of continuous operation, discharge is achieved by overflow on the lip of the axial discharge opening, but the typical discharge rate is affected by changes in the charge replenishment rate and is subject to surges from other sources ( It is also affected by surge). Although some control can be obtained using sophisticated furnace tilting mechanisms, this is cumbersome to use. moreover,
Slag and metal usually eject simultaneously during lip ejection;
Special measures are required for the separation of slag and metal in the discharge lip or after discharge.

The application of controlled suction to siphon metal into an external collection chamber is a conventional technique; for example, closed ladle siphons for recovering molten aluminum from aluminum reduction pots are well known. Although these techniques can fill individual ladles, molds or other batch containers, they are not well suited for continuous operation.

It is therefore a primary object of the present invention to provide a controlled rate through the axial discharge opening from the rotary furnace, essentially independent of changes in the charge replenishment rate or other causes of small changes in the metal level within the furnace. The goal is to achieve continuous recovery of molten metal.

Another object of the invention is to recover the molten metal from the furnace separately from the slag, thereby providing the opportunity for convenient discharge of the slag by separate means.

Another object of the present invention is to limit reoxidation of molten metal due to exposure to external atmosphere during collection, transfer, and discharge from a processing vessel.

Another object of the invention is to provide a method for continuously recovering metal from a furnace, which is particularly suitable for continuous casting directly after the recovery operation.

Another object of the invention is to provide a method for removing dissolved gases from molten metal.

Another object of the invention is to maintain a constant controlled flow rate of ejected metal regardless of surges or periodic disturbances in the furnace charging rate, and at a controlled rate that is varied according to the flow rate of molten metal recovery. Continuous alloy addition allows for precise control of final metal composition.

The invention consists of a combination of the following process steps in a method for continuous melt refining in a rotary furnace in which a charge of liquid metal is contained by being held behind an annular dam of a discharge opening.

(a) maintaining an external metal recovery vessel adjacent to the discharge end of the rotary furnace with a closed chamber as part of the vessel; (b) maintaining negative suction pressure within the closed chamber; (c) the rotary furnace. (d) maintaining a discharge siphon tube inserted into the metal in the furnace and connected to the closed chamber; (d) directing molten metal from the metal bath in the furnace through the siphon tube into the closed chamber at a rate controlled by the magnitude of the suction vacuum; (e) allowing the metal to flow out of the immersion opening in the closed chamber under the action of gravity and at an average rate corresponding to the rate of withdrawal from the furnace via the siphon tube;

The present invention provides continuous recovery at approximately average charging rates by maintaining a controlled and substantially constant suction vacuum within the closed chamber, as well as alloy material and desorption at a constant and controlled rate. Allows for continuous addition of acid, thereby maintaining precise control over the final composition of the casting. Thus,
The present invention solves the control problems caused by intermittent and/or periodic furnace charging, such as from a charging box that is inserted into the furnace and charged periodically.
Surges are overcome by providing measured flow to eliminate and control the amount of alloy addition.

The invention therefore also provides a method in which the charge material is introduced continuously into the charging end of the rotary furnace and the suction vacuum is adjusted to achieve metal recovery at an average rate corresponding to the feed rate of the charge material. , thereby being particularly suitable for maintaining a substantially constant average metal level within the furnace. The method of the invention provides a convenient means of periodically varying the suction pressure and therefore the average metal level above and below this average level, thereby achieving periodic discharge of slag on the annular dam of the discharge opening. . This method can greatly facilitate slag removal, especially when the slag is highly viscous.

The present invention may use either of two different methods of release from a closed collection chamber. In a first method, the collection vessel comprises an open rounder in communication with the closed chamber through a submerged discharge opening, and the metal flows into the rounder at a rate corresponding to the flow rate into the rounder through the submerged opening. It is released by overflowing the partial release lip. In the second method, the closed chamber has a bottom nozzle and the metal is ejected by gravity directly from this nozzle opening. This nozzle is useful for emptying the vessel when the casting is completed and is usually provided with a sliding gate arrangement for opening and closing, which facilitates evacuation of the vessel to begin flow upon start-up.

Various other objects of the method and apparatus of this invention,
Features and advantages will become apparent from the following detailed description in conjunction with the accompanying drawings.

Referring to the drawings, the rotary furnace comprises a body consisting of a cylindrical steel shell with a lining of refractory material 2 and is rotated on a trunnion mounted on a suitable foundation (not shown). The furnace is ignited with gas or oil by a charging end burner 3 which supplies the heat of fusion and a discharge end burner 4 which regulates the temperature before discharge. The furnace charge 5 is fed into the annular charging opening via a charging chute 6 and, in the embodiment shown, directly into the partially molten metal bath. The waste gas is collected in the charging hood 7 and passed through suitable ducts, optionally equipped with heat exchangers and dust collectors. A metal bath 8 extends along the length of the furnace and is usually coated with a layer of slag 9, which can overflow through the annular discharge opening. The annular dam 11 limits the movement of metal between the melting zone near the charge end and the refining zone near the discharge end, thereby helping to stabilize the metal composition within the refining zone prior to discharge.

The metal recovery vessel 12 consists of an outer steel shell having a lining of refractory material and containing a closed chamber 13 . The siphon tube 14 is arranged to extend laterally into the furnace and is bent down at the inlet end to penetrate the slag, with the inlet end immersed in the metal during operation. The siphon tube extends laterally from the furnace at a slight slope to facilitate discharge when the work is completed and is connected at its discharge end into the upper part of the closed chamber. The siphon tube is supported by a suitable flange support 16 for convenient mounting and dismounting, and this joint provides a sealed connection. The siphon tube is generally constructed from a high quality refractory ceramic material, such as fused aluminasilicate, and the molten metal is forced by a suction through a central longitudinal opening and into a sealed chamber 13. The slag is then discharged separately from the furnace, usually by overflowing over the lip of the annular dam 11.

The suction negative pressure required for metal recovery is maintained by a vacuum pump and evacuation system. Manifold 1
7 is equipped with a cooling coil 18 and connects the top of the closed chamber 13 to a receiving tank 19 (condenser), which allows most of the moisture in the gas removed from the dust as well as the metal to be precipitated. This tank is evacuated by a vacuum pump 20 via a valved manifold. The pressure in this system is regulated to a controlled setting by a vacuum controller 21 connected within the tank, which is also equipped with an air bleed valve 22.

In the metal recovery vessel 12, the closed chamber 13 is connected to an open launder via a bottom outlet opening 23.
24, this rounder enables the discharge of molten metal by overflowing the weir-shaped discharge lip 25. In operation, the metal pressure head represented by the difference between the metal level 26 in the chamber and the level 27 in the rounder corresponds to a controlled suction vacuum. According to Bernoulli's theorem, as this difference increases, the rate of metal recovery through the siphon tube 14 also increases. By maintaining a constant suction pressure, a continuous flow of metal is maintained through the siphon tube into the closed chamber, then into the rounder and finally discharged over the lip.

Vacuum is first required to start the flow,
The opening 23 must therefore be temporarily sealed with a refractory plug until a metallic pressure head equivalent to a vacuum is obtained in the chamber 13. Once the pressure head is obtained, the opening is opened and continuous flow begins. Another method of starting flow is to fill the vessel with starting metal by injecting it through the open rounder top before generating a recovery vacuum.

Regarding emptying at the end of work,
The collection container is filled with metal when removal is stopped and must be emptied by tipping. The container may also be provided with a bottom nozzle and a slide gate for emptying as in the device of FIG. used.

There are various forms of equipment and techniques for supporting the retrieval vessel and for inserting, positioning, and retrieving the siphon tube, and these are not shown in detail. The illustrated unit is mounted on a track mounted carriage 28 which rides on wheels 29. The collection vessel itself is located on pivot trunnions on either side of the carriage as part of the cradle, with the pivot point approximately at the center of gravity of the collection vessel. The cradle (not shown) also includes a locking support device for securing the container in the fixed position shown. This configuration is simple and efficient when used with overhead cranes and multiple collection vessel units.

FIG. 2 shows an alternative collection vessel unit and discharge method in which the metal is discharged through a nozzle 30 at the bottom of the chamber instead of overflowing from the rounder. By using a slide gade device 31 to open and close the nozzle, as is commonly used in ladle and continuous casting tundishes today, this configuration has the advantage of convenient closing and sealing to initiate flow by vacuum. and can be shut down and completely emptied while maintaining the recovery unit in the operating position. The relationship between flow rate, nozzle size, siphon tube size and vessel height is adjusted according to Bernoulli's theorem. When initiating discharge, the metal pressure head within the vessel must be increased to approximately correspond to the vacuum applied before opening the nozzle, and thereafter a continuous balanced flow can be maintained. Selection of the diameter of the siphon tube and nozzle opening depends on the desired flow rate and suction pressure used.

Final alloying and deoxidation of the metal can be accomplished in the rounder 24 by lance injection or continuous feeding of sized material, or the metal is discharged into a holding furnace or heating tundish 32 where it is exposed to a suitable chute 33. This is achieved by directly feeding into this container via a. The rate at which alloy material is fed is governed by the metal recovery rate, and in practice:
A controller may be coupled to vary with the amount of suction vacuum within the sealed chamber.

While the preferred embodiments of the rotary furnace metal recovery and discharge method and apparatus have been illustrated and described, many changes and modifications may be made without departing from the spirit and scope of the invention as defined in the claims. It should be understood that this can be done by a trader.

[Brief explanation of the drawing]

FIG. 1 is an elevational view, partially in section, of the apparatus during operation. FIG. 2 is another embodiment of a collection container showing an alternative method of release. 1...Steel shell, 2...Fireproof lining,
3, 4...Burner, 5...Charging material, 6...Chute, 7...Food, 8...Metal bath, 9...Slag, 11...Dam, 12...Metal recovery container, 13
...Sealed room, 14...Cyphon tube, 16...
...Flange support, 17... Manifold, 18...
...cooling coil, 19...tank (condenser),
20... Vacuum pump, 21... Vacuum controller, 22
...Air bleed valve, 23...Bottom opening, 2
4... Rounder, 25... Release lip, 26,2
7...Metal level, 28...Carriage, 29...
Wheel, 30... Nozzle, 31... Slide gate, 32... Tendishu, 33... Shoot.

Claims (1)

Claims: 1. Continuous melting and purification of metal in a rotary furnace 1 in which a charge of liquid metal is contained within the furnace by being held behind an annular dam 11 of a discharge opening at the furnace discharge end. A method comprising: (a) maintaining an external metal recovery vessel 12 adjacent to the discharge end of said rotary furnace 1 and providing a sealed chamber 13 as part of said vessel; (b) inserting into the metal within said rotary furnace 1 (c) applying a suction negative pressure to the sealed chamber 13 from the outside, thereby also venting dissolved gases emanating from the molten metal in the closed chamber as a result of the pressure; (d) pumping the molten metal from the metal bath 8 in the furnace through the opening of the siphon tube 14 controlled by the magnitude of the suction negative pressure; and (e) an average rate corresponding to the rate of withdrawal from the furnace from the submerged openings 23, 30 in the closed chamber 13 under the action of gravity and through the siphon tube. A method for continuous melting and purification of metals, characterized in that the process comprises: flowing the metals at a high rate. 2. The rotary furnace 1 is elongated and includes a melting zone near the charging end and a refining zone near the discharge end, and (a) charge material is continuously but intermittently delivered to the furnace charging end in batches; and (b) adjusting the suction negative to maintain a continuous metal circuit and discharge from the refining zone at an overall average rate approximately corresponding to the average charge rate achieved by the intermittent pumping. 2. The method of claim 1, comprising: adjusting the pressure. 3. The rotary furnace 1 is elongated and includes a melting zone close to the charging end and a refining zone close to the discharge end, and (a) continuously feeding charge material into the charging end of the rotary furnace; and (b) adjusting said suction negative pressure so that metal recovery occurs at an average rate corresponding to the charge feed rate to maintain a substantially constant average metal level within the furnace. The method according to claim 1. 4. The method of claim 1, 2 or 3, further comprising the step of continuously feeding the alloy material into the metal at a rate proportional to the metal recovery rate controlled by the suction negative pressure after discharge. 5. The suction negative pressure is periodically varied above and below said average velocity to periodically raise the metal level in the furnace and lower the metal level to retain the slag substantially completely in the furnace to 5. A method as claimed in any one of claims 1 to 4, further comprising the step of effecting intermittent discharge of slag over the dam. 6 (a) the sealed chamber 1 through the immersion opening 23;
(b) ejecting metal from the rounder 24 by overflowing the ejection lip 25 in the rounder wall at a rate corresponding to the flow rate into the rounder through said immersion opening; The method according to any one of claims 1 to 5, further comprising the step of: 7. The method of claim 1, wherein the submersion opening comprises a nozzle 30 in the bottom of the metal recovery vessel 12 through which metal is ejected directly from the closed chamber 13.