DE2727142A1 - METHOD OF REFINING MOLTEN METAL - Google Patents

Description

PATENT Attorney DIPL.-INC. GERHARD SCHWAN

OFFICE: βΟΟΟ MUNICH M · ELiENSTRASSE »2 /.72/142

L-863O-3-G

UNION CARBIDE CORPORATION
Park Avenue, New York, NY 1OO17, V.St.A.

Process for refining molten metal

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TELEPHONE: OlU / tOllOlf · CABLE: ELECTRlCPATiNT MUNICH

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The invention is concerned with refining molten metal, and more particularly relates to a method to remove dissolved gases and non-metallic contaminants from molten metal without emitting corrosive or environmentally harmful gases and vapors will.

Before casting, molten metal contains numerous impurities which, if not removed, lead to high scrap losses during casting or during casting the products made from these metals result in poor quality. The primarily troublesome contaminants are dissolved gases and suspended gases non-metallic particles such as metal oxides and refractory particles.

The invention is based on the object of creating a method for refining metal with a refining gas, in which dissolved gases and other non-metallic contaminants from the metal in a continuous process Procedure and at high metal throughput rates.

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A method of removing dissolved gases and non-metallic gases Impurities from a molten metal made up of magnesium, copper, zinc, tin and lead Group of metals is essential according to the invention characterized in that the molten metal is introduced into a refining zone and above the surface of the molten bath a protective gas atmosphere with a higher than atmospheric pressure is maintained, whereby prevents air and moisture from penetrating this zone and preventing the molten metal from coming into contact with it will; that a refining gas in the form of discrete bubbles is introduced into the melt below its surface will; that the molten metal in the refining zone is set in motion so that in the molten metal with reference to the entry points of the gas bubbles in the melt such a flow course is formed that the introduced into the melt gas bubbles substantially radially outward with respect to the Entry points of the gas bubbles are transported, whereby the residence time of the gas bubbles in the melt is extended and the gas bubbles with substantially all of the molten metal in the refining zone be brought into intimate contact; that the spent refining gas and the dissolved gases released from the metal are drawn off, while the other non-metallic impurities in a layer of slag on the surface of the molten metal is collected and separated

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be, and that the refined molten metal from is discharged from the refining zone.

The term "refining gas" is intended to include gases conventionally used in the refining of magnesium, copper, zinc, tin and lead. These refining gases What is common is that they are inert to the molten metal to be refined. It is preferred to use argon and nitrogen or mixtures of these gases, although other inert gases of the periodic system can also be used here. More suitable Refining gases are hydrogen and carbon monoxide or Mixtures of these gases with one another or with the inert gases of the periodic table. It is understood that hydrogen and Carbon monoxide can be used in cases where they do not react with the molten metal, but with gaseous ones Impurities, such as oxygen, come into reaction. Other reactive gases can also be used similar properties are used, for example sulfur hexafluoride, chlorine and halogenated hydrocarbons. A specific refining gas is selected in usually on the basis of the characteristics of what is to be refined in each individual case Metal. In the present case, the term “metal” is intended to encompass both the pure metal and its alloys.

The invention is described below on the basis of preferred exemplary embodiments in connection with the drawings

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purifies. Show it:

Fig. 1 is a perspective view of a present

gas injection device to be used,

FIG. 2 shows a section of the device according to FIG. 1,

3 shows a schematic representation in section

a preferred apparatus for refining a metal stream in a continuous one Process, as well

4 and 5 show a section and a plan view of a further preferred embodiment of a Facility dedicated to refining molten metal accordingly the method according to the invention is suitable.

The gas injection device used for the method according to the invention is characterized by the fact that it is able to flow gas into molten metal at high flow rates to be introduced in the form of separate gas bubbles and a high degree of gas dispersion within the melt reach. During the operation of the device, currents are generated in the metal in the vicinity of the injection device, which cause the gas bubbles formed along

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a resulting flow vector directed radially outward and one with reference to FIG the vertical axis of the injector has a downward component. These flow distributions are beneficial in several ways. First of all, move or stir the whole substantially perpendicularly Melt is taken care of, a flow directed downwards along the injection device in conjunction with the rotating blades causes the gas to be subdivided into small discrete gas bubbles. The fact that the gas bubbles from the Introduction point are transported away quickly into the melt, there will also be a union of bubbles in the zone prevented, in which the gas bubble concentration is highest. Furthermore, the length of stay is well distributed Gas bubbles prolonged in the melt because the gas bubbles after their formation are not directly under the influence of the The buoyancy force rises to the surface of the bath.

Another factor that should be used to maximize the subdivision of the gas in small bubbles and thus leads to a large interface between metal and gas, the preheating of the gas before it enters the melt. For this preheating is provided by passing the gas through a passage extending the length of the device immersed in the hot molten bath. In this way the initially cold gas becomes through contact with the hot, heat-conducting walls of the gas passage

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heated so that the gas expands before it is broken into gas bubbles. Consequently the number of for one predetermined volume of gas generated bubbles significantly increased; thermal growth of the small bubbles within the melt is essentially prevented.

If a refining gas is blown into molten metal with the aid of the injection device, this leads to a surprising improvement in the efficiency of the refining process. It just becomes possible to use the metal at degassing at a high throughput rate; the vigorous stirring effect caused by the device rather, in connection with the large gas / metal contact surface of the well-distributed gas bubbles, it also ensures effective removal of solid, particulate impurities that are suspended in the melt.

The gas injection device shown in Figs. 1 and 2 has a rotor 1 which is equipped with vertical blades 2 and with the help of a motor, for example a compressed air or electric motor, not shown, is driven via a shaft 3. The shaft 3, which does not come into contact with the melt during normal operation, can be made of steel, while the The remaining parts of the arrangement are preferably constructed from a refractory material, for example from commercially available graphite or silicon carbide, d. H. Materials,

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which are inert to the metal at the operating temperatures that occur. The shaft 3 is shielded from the molten metal by means of a sleeve 4 which is attached to a Stator 5 is firmly attached. The abutting inner surfaces 6 and 7 of the sleeve 4 or stator 5 and the adjoining outer surfaces 8 and 9 of the shaft 3 or rotor 1 form an annular axial passage 10 for the gas to be injected.

Several vertical channels 11 are incorporated into the stator 5. The stator 5 and the rotor 1 cause a during operation upper and a lower stream of molten metal in the area of the injection device, as indicated by arrows and 13. The upper flow 13 has an im substantial main downward velocity vector, d. H. it runs coaxially to the axis of rotation of the rotor 1, whereby the molten metal flows through the channels 11 of the stator 5 is driven through. The lower, more localized flow indicated by the arrows 12 forms extends from below the rotor 1 and is directed essentially upwards and perpendicular to the axis of rotation of the rotor 1. The resulting Flow is indicated by arrows 14, which indicate that the molten metal by means of the rotating Wing 2 is strongly driven away radially outward and downward from the rotor 1. The resulting flow distribution leads to a well-distributed and uniform dis-

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persion of the gas and a sweeping movement of the molten metal within the treatment vessel.

A refining gas indicated by an arrow 15 is indicated with Introduced into the annular passage 10 at a predetermined pressure and predetermined flow rate. The gas fills the Bell-shaped space 16, which forms a continuation of the passage 10 and surrounds the neck 17 of the rotor 1. There the gas is supplied at a pressure above that in the molten metal in the indicated by arrow 18 If the prevailing pressure is high, the gas space 16 prevents molten metal from passing through the gas passage flows back and comes into contact with the metallic shaft 3 of the gas injection device. The neck 17 includes the shaft 3 and is made of a material resistant to the molten metal, around the shaft 3 to protect against undesired influence by the molten metal. As can be seen from Fig. 2, transmit the torque from the shaft 3 to the rotor 1 via a carrier 21 provided with vanes, which on the Shaft 3 is screwed on. The driver 21 is inserted into a recess 23 of the rotor 1 during the assembly of the device, the shape of which corresponds to that of the driver 21. Then the recess 23 is sealed by the neck 17 is screwed into a thread 24 in the rotor 1 and cemented.

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The refining gas 15 need not necessarily be introduced via the annular passage 10. Corresponding In a modified embodiment, a hollow shaft can be provided, with a passage 19 in the axial direction extends through the shaft 3, which is further provided with a plurality of bores 20 for connection with the Passage 10 and the gas space 16 provide. The indicated by the arrows 15 and 25 gas can in this way on the Passage 10 or passage 19 or both of these passages are supplied.

It is essential that the indicated by the arrows 15 and 25, entering the injection device during the Passing through the passage 1O or the passage 19 as well as the gas space 16 is preheated by being with the sleeve 4 and the shaft 3 comes into contact, which are essentially at the temperature of the melt. The preheated gas is forced between the blades of the rotor 1 where it becomes small discrete by hitting the wings 2 and by the stream of metal sweeping past the wings Bubbles is broken up. As a result of the forced circulation of the metal in the area of the injection device, the gas bubbles that are formed are quickly distributed in a direction that is in the substantially coincides with the main flow velocity vector indicated by the arrows 14. The initial path of the gas bubbles corresponds to the direction of the arrows 14 until the buoyancy predominates and causes the

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Gas bubbles rise to the surface of the melt.

On the beneficial effects of the forced circulation of the metal To include the injection device that an effective mechanism for the formation of small gas bubbles obtained it becomes that the bubbles are prevented from associating with each other because the small gas bubbles are essentially be distributed at the moment of their formation, that an effective circulation of the metal takes place and that the residence time of the gas bubbles in the melt is greater than the retention time that would be obtained if the gas bubbles were hit only the buoyancy would act ..

The refining process described can be discontinuous or carried out continuously using the refiner illustrated in FIG. 3. the Refining device has a cast iron vessel 31, this by means of a conventional heating device, which can be accommodated within a room 32, at the working temperature is held and is protected against heat loss by means of a fireproof outer jacket 33. The inside the vessel 31 is provided with a lining 34 made of graphite or other refractory materials which against molten metal and non-metallic impurities are inert and can be expected to occur. The vessel 31 is equipped with a cover 36, which rests on flanges 39. Between the flanges

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39 and the cover 36, which are screwed on or onto others Can be attached manner, a gas-tight seal is provided, so that when the device is in operation none Air can penetrate. A gas injection device 35, for example of the type illustrated in FIG. 1, is at the Cover 36 attached and is held by this.

Refining gas indicated by an arrow 37 is blown into the molten metal 38 by means of the gas injection device 35. After the melt material has passed through, the gas collects in the head space 43 and forms over there the melt has an inert gas layer. The gas then exits in countercurrent to the incoming metal stream via metal inlet 40. The free cross-sectional area of the gas passage and thus the pressure prevailing in the arrangement are regulated by means of a flap 49 arranged in the inlet 40. The inert gas in the Head space 43 prevents air from entering the vessel.

The metal 38 is introduced into the refiner through the metal inlet 40. Be inside the vessel uniformly distributed small bubbles of inert gas are blown into the metal 38. In addition, the molten metal is kept moving under the action of the rotating gas injector 35. Dissolved in the melt Gases diffuse into the inert gas bubbles and are carried away by them when the bubbles pass through the melt

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climb up to surface 42 of the weld pool. The size The surface of the finely dispersed gas bubbles is also used as an effective means of transporting the suspended, non-metallic particles to that on the surface 42 of the molten pool located slag layer 48 transported, from where they can be removed by deslagging. Oie in that The main flow distribution formed by molten metal is indicated schematically by arrows 50. By the By circulating the metal in the vessel, fresh metal is constantly brought into contact with the gas bubbles emerging from the room emerge between the rotor and the stator of the gas injection device.

The refined molten metal exits the refining vessel via an outlet 44 formed in wall 45 below surface 42 of the molten pool. That Metal then passes through a shaft 46 and leaves the assembly via a drainage channel 47 to from there to one To reach the pouring station. A conventional filter medium can be provided in the shaft 46, for example Chunks of graphite or refractory material.

The deslagging of the surface 42 of the molten bath can be achieved by a suitable construction of the refining vessel or by this occur that the influx of metal to the refining vessel is interrupted while continuing to supply inert gas 37 via the gas injection device 35, so that the

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Slag layer 48 is pushed into the inlet channel 40, from where it can be eliminated by mechanical means. Instead, the bath surface 42 can also by means of a hand-operated tool passed through the inlet chute 40 or one not illustrated Opening of the cover 36 is introduced through into the vessel 31.

The refining process does not need to be carried out in accordance with FIG. 3 in to be carried out in a single refining zone. Instead, the vessel can have multiple refining chambers or zones that contain the molten metal runs through in sequence. Figures 4 and 5 show such a modified embodiment.

The refining vessel illustrated in FIGS. 4 and 5 55 is made of a refractory material that is inert to the molten metal. The vessel is with Protected against heat loss with the help of well-insulating materials. If necessary, the vessel can also with electrical heating elements not shown may be equipped to compensate for heat losses. The refining vessel 55 has a cover 56 that attaches to the vessel 55 is attached gas-tight and only a metal inlet channel 57 leaves free. Gas injection devices 59 and 6O, which are constructed in accordance with FIG. 1, and the associated drives 61 and 62 are held by the cover 56. Arrow

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le 75 indicate the inert gas entering the gas injection devices 59 and 6O via the respective inlet openings entry.

The refining vessel 55 is for use in continuous Operation determined, d. H. molten metal becomes continuously introduced into the vessel 55 via the inlet channel 57, the metal is constantly moving and blowing in the bath refined of gas via injectors 59 and 60, and the refined metal is refined via the gutter 58 continuously withdrawn from the vessel. As can be seen from Fig. 5, the refining vessel 55 is provided with two refining zones 63 and 64, which are separated from one another by an intermediate wall 65. The metal arrives first to the refining zone 63, where it is set in motion and contacted with an inert gas which is introduced via the gas injection device 59. The metal leaves the refining zone 63 partly by flowing over the upper edge of the intermediate wall 65 and partly through Passages 66 formed in the intermediate wall 65 therethrough. The metal is in the second refining zone 64 further refined, where it is similarly set in motion and contacted with inert gas, the is introduced by means of the gas injection device 60. The metal leaves the refining zone 64 by passing through the lower Partition 67 flows away and enters an outlet pipe 68. The outlet pipe 68 is made of a refractory material

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material, for example graphite or silicon carbide, made and diverts the refined molten metal from the Refining zone 64 to an outlet chute 69 from where it leaves the refining vessel via the gutter 58.

The refining gas introduced into the arrangement flows through the molten metal and collects in the head space 74 the molten bath and leaves the refining vessel 55 through the inlet channel 57 through above and in countercurrent the incoming molten metal. The one in the refining vessel 55 prevailing pressure can be adjusted by a seated in the inlet channel 57, hinged flap 73 by the free cross-sectional area of the gas passage in the inlet channel 57 is changed. In this way, in addition to the static seal formed by the cover 56 provided a dynamic gas seal for the refining vessel by keeping the refining vessel 55 at a pressure slightly above atmospheric pressure prevent air from entering the refining vessel.

A decisive advantage of the method described is that an adjustment can easily be made in this way can that the refining gas requirements for different metals are met. Also, the refining speed can can be adapted to a wide range of casting speeds. The specific refining gas requirement that is generally expressed as the gas volume at normal

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temperature and normal pressure per unit weight of the metal to be treated is a function of the composition of the alloy and the required degree of purity of the finished product. The metal flow rate through the refining device can be determined by the casting speed, ie by the type of casting machines used and the number of blocks that are to be cast from the refined metal at the same time. The following examples show a simple way of adjusting the working conditions of the arrangement depending on the particular alloy to be refined and the desired degree of refining.

First, the flow rate of the refining gas per gas injection device is calculated from the following formula:

V-Wx C / N (1)

V ■ flow rate of the refining gas through the device in Ndm / min; W = metal flow rate or refining rate in kg / min;

C = specific refining gas requirement in Ndm / min; N - number of gas injectors in the system.

The specific refining gas requirement C is determined experimentally or initially estimated on the basis of the refining gas quantities required for refining the metal in question

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conventionally used.

After the required gas flow rate for the injection device has been determined, the rotor speed is set according to the following formula:

R = (762O + 673 V + 21O8 r ² ) / d (2)

R = speed of the rotor in rpm;

V = gas flow rate through the device, calculated according to formula (1), in Ndm / min;

r = ratio of the smallest cross-sectional dimension the refining zone in the area of the rotor to the rotor diameter (calculated using the same Units); for example, in the refining device of FIG. 5, the smallest cross-sectional dimension of the refining zone 63 is the smaller of the two dimensions indicated by arrows 70 and 71;

d = rotor diameter in mm.

This formula gives an approximation of the speed of rotation of the rotor that will ensure satisfactory dispersion of the refining gas and ensures good agitation of the metal bath under most working conditions. The formula shows that the rotor speed increases with increasing refining gas flow rates must be increased. The establishment

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however, it can also work at considerably lower speeds than those resulting from this formula. The optimal speed depends primarily on the desired degree of refining.

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Claims (12)

Expectations 1. Process for refining molten metal from the group of metals comprising magnesium, copper, zinc, tin and lead, characterized in that the molten metal introduced into a refining zone and a protective gas atmosphere with a pressure higher than atmospheric pressure above the surface of the molten bath is maintained, thereby preventing the melt from coming into contact with air or atmospheric moisture will; that a submerged in the molten bath gas injection device is provided, which has a shaft at the lower At the end, a rotor provided with blades is fixedly attached, a stationary sleeve encompassing the shaft and a passage extending the length of the gas sparger over the refining gas sent and discharged into the molten metal; that refining gas under one for blowing in Sufficient pressure is introduced into the top of the passage and prior to dividing into the melt Gas bubbles are preheated by contact with the hot walls of the passage and expanded so far that a thermal growth of the bubbles in the melt is substantially prevented; that the preheated refining gas on the blades of the rotor of the gas injection device 709851/1206
ORIGINAL INSPECTED 2727U2 aligns and is divided into discrete gas bubbles by the vane rotor is driven at sufficient speed to produce such a in the molten metal Form flow path that the gas bubbles are substantially radially outward and with respect to their entry points into the melt downward component transported into the melt and under Removal of dissolved gases and essentially all non-metallic contaminants from the melt with essentially the total amount of molten metal in the refining zone Be brought into contact; that consumes refining gas and the dissolved gases released from the metal while other non-metallic impurities are drawn off in a layer of slag on the surface of the molten metal are collected and that the refined molten metal is collected from the refining zone is discharged. 2. The method according to claim 1, characterized in that argon is used as the refining gas. 3. The method according to claim 1, characterized in that nitrogen is used as the refining gas. 4. The method according to claim 1, characterized in that a mixture of argon and nitrogen is used as the refining gas 709851/1206 -r- 2727U2 is used. 5. The method according to claim 1, characterized in that the passage from the outer surface of the shaft and the inner surface the stationary sleeve is formed. 6. The method according to claim 1, characterized in that the passage extends in the axial direction through the shaft . 7. A method for refining molten metal from the group of metals comprising magnesium, copper, zinc, zinc and lead, characterized in that the molten metal is introduced into a refining vessel having at least one refining zone and a protective gas atmosphere with a higher level above the surface of the molten bath maintained than atmospheric pressure, thereby preventing the melt from contacting air or atmospheric moisture; that in the refining vessel at least one gas injection device is provided which is immersed in the molten bath and which has a shaft at the lower end of which a rotor provided with blades is fixedly attached, a stationary sleeve encompassing the shaft and a passage extending over the length of the gas injection device sent the refining gas and into the melting 709851/1206 U- liquid metal is discharged; that refining gas under a pressure sufficient to be blown into the melt in the upper end of the passage in a Flow rate of V = W C / N is initiated, where
V = gas flow rate through each injection device in Ndm / min; W = molten metal inflow into the refining vessel in kg / min; C = specific refining gas requirement in Ndm / kg metal; N = number of gas injectors in the refining vessel; that the refining gas is divided into discrete gas bubbles by rotating the vane rotor at sufficient speed is driven to form such a flow path in the molten metal that the gas bubbles essentially radially outwards and with a component directed downwards with respect to their entry points into the melt, with the elimination of dissolved components Gases and essentially all non-metallic impurities from the melt are transported into the latter will; that the spent refining gas and the dissolved gases released from the metal are withdrawn while other non-metallic impurities are in a layer of slag on the surface of the molten metal are collected, and that 709851/1206 .ßr- 2727U2 S the refined molten metal is discharged from the refining vessel. 8. The method according to claim 7, characterized in that the gas injection device is driven at a speed which results approximately from the following formula: R = (7620 + 673 V + 2108 r ² ) / d whereby R = speed of the rotor in rpm; V = gas flow rate in the injection device in Ndm / min; r = ratio of the smallest cross-sectional dimension of the Refining zone to the diameter of the rotor (dimensionless) and d = rotor diameter in mm. 9. The method according to claim 7 ', characterized in that argon is used as the refining gas. 10. The method according to claim 7, characterized in that nitrogen is used as the refining gas. 11. Process for Refining Molten Metal from the group of metals comprising magnesium, copper, zinc, tin and lead, characterized in that the molten metal is fed into a refining zone 709851/1206 2727U2 and above the surface of the weld pool a Protective gas atmosphere with a higher than atmospheric pressure is maintained, whereby a contact of the Melting with air or atmospheric moisture is prevented; that a refining gas is introduced into the melt below its surface, which before the Subdividing into gas bubbles is preheated and expanded so far that a thermal growth of the bubbles in the melt is essentially prevented; that this Refining gas is divided into discrete gas bubbles and in the molten metal such a flow course is formed that the refining gas bubbles are transported essentially radially outward and with a component directed downward with respect to their entry points into the melt into the melt and below Elimination of dissolved gases and essentially all non-metallic impurities from the melt with essentially the total amount of the in the refining zone located molten metal are brought into intimate contact; that the used refining gas that contains the dissolved gases released by the metal, is withdrawn while other non-metallic impurities in a layer of slag on the surface of the molten metal are collected and that the refined molten metal is discharged from the refining zone. 709851/1206 -I- 2727U2 12. The method according to claim 11, characterized in that argon, nitrogen or mixtures of these are used as the refining gas both gases can be used. 709851/1206