FR2530167A1 - Method and installation for protecting a liquid metal runner. - Google Patents

Abstract

The invention concerns the protection of a liquid metal runner flowing between an upper reservoir and a lower container. According to this method, at least one liquified inert gas is injected above and in the proximity of the surface of the liquid metal contained in the lower container and/or at least one inert gas is injected in the liquid metal through the bottom or the sides of the said container. The invention applies to the protection of liquid metal runners, in particular between ladle and distributor, between ladle and ingot mould, between ladle and ladle and between converter (or furnace) and ladle.

Description

 The invention relates to the protection of a jet of liquid metal flowing between an upper reservoir and a lower receptacle.

 Some methods previously used to protect a molten metal casting stream consist of pouring liquefied inert gas into the upper part of said jet. For example, French Patent No. 2,403,852, in the name of the Applicant, describes a process according to which the liquefied inert gas is delivered around the jet by a generally toroidal device arranged under the upper reservoir.

This system is not always satisfactory; indeed, the creation of an inert atmosphere on the entire path of the jet can. sometimes take a certain time: there is then air entrainment by the flowing metal, especially at the level of the impact of the jet on. the metal bath; this air entrained in the bath reacts with the metal causing the dissolution of nitrogen and the formation of oxide inclusions.

 To overcome these drawbacks, the applicant has recently developed a method, described in patent application No. 81.21855, of November 23, 1981, according to which is created around the casting stream and over the entire height of the latter, an ascending gas protective sheath formed from at least one gas substantially inert with respect to the metal. More specifically, this ascending protective sheath is formed by injecting the inert gas around the impact zone of said jet and confining said inert gas above the surface of the liquid metal and around the base of said jet by means of a sleeve, open at both ends, surrounding the base of said jet and partially immersed in the liquid metal.

 Thus, the shielding gas confined around the jet and heated to high temperature is subjected to an upward force which allows the formation of a protective gaseous sheath along the jet of metal circulating against the current and thus opposing any air entrainment by the flowing metal.

 The subject of the present invention is a new method for creating an ascending protective sheath of this type.

 the process according to the invention is characterized in that at least one liquefied inert gas is injected above and in the vicinity of the surface of the liquid metal contained in the lower receptacle and / or an inert gas is injected into the metal liquid from the bottom or walls of said receptacle.

According to a first embodiment of the invention, the injection of a liquefied inert gas above and in the vicinity of the surface of the liquid metal is carried out by injection of said gas inside the sheath and slightly below the upper opening of said sheath. The liquefied gas protective layer thus formed on the liquid metal surface vaporizes and generates inside the barrel a gaseous atmosphere which escapes through the upper liner of the latter. For this atmosphere to be considered as inert with respect to the metal, it must contain less than 5% oxygen. This is why, according to the invention, the injection rate D of the gas is regulated. inert liquefied so that the value of V2 (V2 and T2 being the velocity and the temperature at T 2 that the ascending gaseous atmosphere formed reaches the upper opening of the sheath) corresponds to one. oxygen content of said atmosphere less than 5%, according to the equation
V2 = 1 IL If D (1),
7 = 1 2 1 G
2 60.103 21 TS in which: - 1 is the boiling temperature of the liquefied inert gas, expri
in degrees K - S1 and S2 are the sections of the upper and lower openings
sheath
PL and 2 G are the densities of the inert gas at the
quide and in the gaseous state 2 2 V2 is expressed in mZs, T2 in degrees K and D in liters / min / m2
According to a second embodiment of the invention, the
or the walls of an inert gas in the molten metal by the molten receptacle below the jet impingement zone also causes the formation, above the bath surface and inside the water furnace, 4 'an upward gas protective sheath that escapes through the upper opening of the latter. In addition, the injection of the inert gas into the liquid metal causes a stirring of said metal which prevents parasitic solidification, promotes coalescence of the inclusions and therefore subsequent decantation of the latter, and allows a purge effect, that is to say the desorption of the gases dissolved in the bath. In order for the gaseous atmosphere formed to be considered as being inert with respect to said metal, the injection rate D of the inert gas in the liquid metal is adjusted so that the value of
V2 corresponds to an oxygen content of said atmosphere in
T2 below -5%, depending on the equation
V2 = 1 1 S1 T. D (2), 3600 T1 S2 PG 410 in which V2, T2, T1, Sn, S2,! L and 2 G are the same parameters as in equation (1) above, T is the temperature of the metal liquid expressed in degrees K and D is expressed in m3jhour.

nécessaire pour que la teneur en oxygène de l'atmosphère soit inférieure à 5 % ; et, compte tenu des paramètres relatifs à l'azote (T1 PIX BG) et des dimensions du fourreau utilisé (sections S1 et on on règle le débit D de l'azote injecté selon l'équation (1) ou (2). Si le gaz inerte utilisé est de l'argon, on détermine expérimentalement la valeur V2 qui doit être supérieure à 1-,7 . tO mZs/K
T2 et on règle le débit D de l'argon injecté selon l'équation (1) ou (2).For example, if the inert gas used is nitrogen, the value is determined experimentally.

necessary for the oxygen content of the atmosphere to be less than 5%; and, taking into account the nitrogen parameters (T1 PIX BG) and the dimensions of the sleeve used (S1 sections), and the flow rate D of the nitrogen injected according to equation (1) or (2) is adjusted. the inert gas used is argon, the value V2 is determined experimentally, which must be greater than 1, 7, t0 mZs / K
T2 and the flow rate D of the injected argon is adjusted according to equation (1) or (2).

 According to a third embodiment of the invention, both the iniection of a liquefied inert gas above and in the vicinity of the surface of the liquid metal and the injection of an inert gas into the metal are carried out. liquid from the bottom or walls of the lower receptacle. the liquefied inert gas and the inert gas injected into the liquid metal are either of the same nature or of a different nature.

This produces both the ascending gas atmosphere which prevents any air entrainment by the casting jet and stirring of the metal bath. In addition, according to this embodiment, the amount of total gas necessary to form the ascending gas sheath is less than that required when the gas is injected - only above the surface of the liquid metal.

 According to an alternative embodiment of the invention, the protection of the jet of liquid metal is completed immediately at its outlet from the bottom of the upper reservoir, creating a gaseous protection atmosphere formed from at least one substantially inert gas. with respect to said metal, said atmosphere enveloping a shutter device mounted externally on the bottom of said upper reservoir, comprising a fixed plate and a moving element comprising a movable plate applied against said fixed plate and a metal support integral with said movable plate for at least one nozzle which can come into communication with the flow hole of the liquid metal. More specifically, the inert gaseous atmosphere formed is more particularly opposed to any infiltration of air into the gap between the fixed plate and the movable plate as well as in the junction zone between the movable plate and the nozzle or nozzles and also protects the jet of the m He was just out of a bush.

This protection of the liquid metal jet, immediately to
its outlet of the upper reservoir advantageously completes the protection of said jet over its entire height by the upward gas sheath; indeed, the jet of liquid metal can thus cause, when it flows, only inert gas in the sleeve surrounding its base.

 Another subject of the invention is a liquid metal transfer installation implementing the method in question, which comprises an upper reservoir and a lower receptacle provided with an internal refractory lining and a sheath made of refractory material, open at both ends, the upper opening of said sheath being located below the outlet of the upper reservoir, the end 1rtérieure said sheath being located at a distance - from the bottom of the lower receptacle while the upper end of said sheath protrudes widely above the edge of said lower receptacle.This installation comprises means for injecting a liquefied inert gas inside said sleeve and slightly below the upper opening of said sleeve and / or means for injecting at least one inert gas. by the bottom or walls of the lower receptacle.

The features and advantages of the invention will be better understood on reading the following description made with reference to the appended drawings in which - FIG. 1 is a partial diagrammatic section of a first embodiment.
of an installation according to the invention - FIG. 2 is a partial schematic section of a second
embodiment of an installation according to the invention - FIG. 3 is a partial section along line III - III of FIG.
FIG. 2 - FIG. 4 is a partial section in the same plane as FIG.
Figure 3, but representing another variant of the second mode of
embodiment of an installation according to the invention - FIG. 5 is a partial diagrammatic section of a third
embodiment of an installation according to the invention - FIGS. 6, 7, 8 and 9 are diagrammatic representations
partially in section of four embodiments of the dispo
protective device of the casting stream at its outlet from the reservoir
périeur ..

According to the embodiment shown in FIG. 1, an upper reservoir (1) contains molten metal which, after passing through a plate shutter device (2) mounted externally on the bottom of the reservoir (1), flows under form of a jet J and arrives in a lower receptacle (3). the walls and the bottom of this receptacle (3) are formed of an outer armor (4), an intermediate sand filling (5) and an inner refractory lining (6). A -fourreau (7) refractory material, open at both ends and partially immersed in the bath (8) of liquid metal contained in the receptacle (3), is disposed around the jet J.This sheath (7) comprises two parts (9) and (10): the upper part (9) - protrudes substantially above the upper edges of the receptacle (3); it is in the form of a truncated pyramid having four walls (9a, 9b, 9c, 9d); two opposite walls (9a and 9b) of this upper part (-, bear on two opposite upper edges of the receptacle (3), the lower part (10) consists of two vertical plates (1Ca, 1cob) in line with the parts ( 9c and 9d) of the part (9), i-Prgées in the bath of liquid metal (8) .the sheath (7) PSt arranged so that its axis coincides substantially with the jet J. The lower opening of the sheath ( 7) has a section S1 and the upper opening a section
A tank of liquefied inert gas (11) is connected by a conduit (12) with a valve (13) to a phase separator (14) which, via a flow control valve (15) , supplies with liquefied gas an injection tube (16) with calibrated orifice (17); this injection tube (16) opens slightly below the upper opening of the sleeve (7)
The operation of the installation shown in the figure is as follows. The liquefied inert gas coming from the tank (11) is injected into the upper part (9) of the sheath (7) with the aid of the injection tube (16). ) which discharges this liquefied inert gas directly onto the surface of the liquid metal bath (8) contained in the receptacle (3). the liquefied inert gas thus poured forms, by caulking, a liquid layer on the part of the surface of the bath (8) which is between the plates (10a) and (lob) and vaporizes by creating an ascending gas sheath which, at initially, flushes the air which was contained in the sheath (7) and then opposes any entry of air possibly supplied by the casting jet J.

Given the tightened upward shape of the portion (9) of the sheath (7), this protective sheath ascending flows along the arrows X, towards the casting stream. The injection rate D of the inert gas is adjusted by means of the valve (15), as explained above, in such a way that the speed-to-temperature ratio of the atmosphere formed in the sleeve corresponds to an oxygen content of this atmosphere of less than 5.

 Two examples of implementation of the method using the installation shown in FIG. 1 are given below.

 Example 1

 The inert gas used is nitrogen.

It is desired that the atmosphere formed in the sleeve has an oxygen content of less than 2. The corresponding value V 2 is determined experimentally, ie T2

The nitrogen parameters are as follows
T1 = 77 0K
= 808 kg / m3
4,6 =
kg / m
The sheath used has dimensions such that S1 = 1.8.

Equation (1) can then be written as follows 7. 10-4 1 1. = 1.8. 808. D
60.103 77 4.6
It is therefore necessary to inject the liquefied nitrogen at the inlet of the sheath at a flow rate D> 101 / min / m.

 Example 2

 The inert gas used is argon.

It is desired that the atmosphere formed in the sheath has an oxygen content of less than 1%. Qn determines experimentally the corresponding value V2, ie T2

Argon parameters are as follows
T1 = 87 0K
KL - 1400 kg / m3 = 5.85 kg / m
The same sheath as in Example 1 is used; we
S1 therefore has: S2 = 1, 8.

S2
Equation (1) is written as follows
4 10-4 = 1. 1. 1.8. 1400. D.

60.103 87 - 5.85
It is therefore necessary to inject the liquefied argon at the inlet of the sheath at a flow rate D ≥ 4.73 l / min / m 2.

 According to the embodiment shown in FIGS. 2 and 3, an upper reservoir (21) contains molten metal which, after having passed through a plate shutter device (22), flows in the form of. jet J and arrives in an inferior receptacle (23).

The walls and the bottom of this receptacle (23) are formed of an outer shell (24), an Intermediate sand packing (25) and an internal refractory lining (26). Unfurable (27), open at both ends and partially immersed in the bath (28) of liquid metal contained in the receptacle (23), is disposed around the jet J. This sleeve (27) has two parts (29) and ( 30), the upper part (29) is in the form of a truncated pyramid comprising four walls (29a, 29b, 29c, 29d), two opposite walls (29a and 29b) of this part (29) bear on two opposite upper edges of the receptacle (23) .The lower part (30) consists of two vertical plates (30a) and (3Ob), in line with the parts (29c) and (29d) of the part (29), immersed in the metal bath The sleeve (27) is arranged in such a way that its axis substantially coincides with the jet J.

 In the portion of the internal refractory lining (26) which is below the sleeve (27) are incorporated porous elements (31). These porous elements (31) are connected by pipes (32) placed in the intermediate sand lining (25) and connected to a distributor (33) itself connected to a source (34) of inert gas under pressure.

 The operation of this installation is as follows: the inert gas from the source (34) is injected into the liquid metal bath (28), around the impact zone of the detector J, via the porous elements (31). ). The gas escapes in bubbles which burst on the surface of the bath (28) and form an ascending gas column which is channeled by the sleeve (27), and more particularly by the upper part (29) of said sleeve according to the arrows F .

 According to the variant embodiment shown in FIG. 4, metal nozzles (35) are incorporated in the internal refractory lining (25) of the bottom of the receptacle (23). These nozzles (35) are connected (in the same way as the porous elements ( 31) of Figures 2 and 3) to a source of pressurized inert gas (34) via tubing (32). All the elements of this installation (with the exception of nozzles (35) which replace the porous elements (31)) are identical and bear the same references as those of the installation shown in FIGS. 2 and 3; and the operation is the same.

 According to the embodiment shown in FIG. 5, an upper reservoir (41) contains molten metal which, after having passed through a plate shutter device (42), flows in the form of a jet J and arrives in a lower receptacle (43). The walls and bottom of this receptacle are formed of an outer shell (44), an intermediate sand pack (45) and an inner refractory lining (46). A sheath (47), partially immersed in the baip (48) .de liquid metal contained in the receptacle (43), is disposed around the jet J. This sheath (47) has two upper parts (49) and lower (50) A liquefied inert gas tank (51) is connected by a conduit (52) with a valve (53) to a phase separator (54) which, via a control valve (55) the flow, supplies a liquefied gas injection tube (56) with calibrated orifice (57); this tube (56) opens slightly below the upper opening of the sleeve (47).

 Porous elements (58) are incorporated in the portion of the inner refractory lining (46) which is below the sheath (47).

These porous elements (58) are connected by tubings (59) placed in the intermediate sand lining (45) and connected to a source of inert gas under pressure (not shown in the figure). Of course, the porous elements (sus) could be replaced by metal nozzles.

The operation of the installation of FIG. 5 is as follows: the liquefied inert gas coming from the tank (51) is injected into the upper part (49) of the sheath (47) using the injection tube (56). which discharges this liquefied inert gas directly onto the bath surface (48). Simultaneously, a pressurized inert gas is injected directly into the bath (48) via the porous elements.
Two examples of implementation of the method are given below with the aid of the installation provided in FIG.

 Example 3

 The inert gas used is argon. It is desired to obtain the same results as those of Example 2 described above and we work under the same conditions.

 The argon gas is injected into the liquid metal bath at a rate of 20 m / hour. This amount of argon gas is, according to equation (2), equivalent from the point of view efficiency of inerting to 0.41 liters / min. liquid argon. At the inlet of the sheath 2 liquefied argon is then simultaneously injected at a rate of 4.32 l × min / m 2.

 The gain on the total quantity of gas injected is 0.14 l / min / m 2 relative to Example 2.

 Example 4

 The inert liquid gas used is nitrogen and the gas injected into the liquid metal bath is argon. We want to obtain the same results as those of Example 1 described above and we work under the same conditions.

 Argon gas is then injected into the bath of liquid metal at a rate of 20 m 3 / hour. Simultaneously, liquid nitrogen is injected at the inlet of the sheath at a rate of 9.15 l / min / m.

 Figure 6 shows the plate shutter device (2) (or (22) or (42)) mounted externally on the bottom of the upper reservoir ((or (21) -or (41)). type known and described in application No. 80.19.837 of September 15, 1980 in the name of the applicant.It comprises a fixed plate (60) and a movable plate (.61) applied against each other, the movable plate (61 ) being rotatably mounted and carrying two nozzles (62), the plates (60) and (61) and the nozzles (62) are made of a refractory material, for example impregnated alumina, and the movable plate (61) is provided with a toothed wheel (36), drivable by a pinion (37) connected to a motor (not shown in the figure).

The plate (60) is traversed by an orifice (63), placed in line with the taphole (5d)) which is formed in the refractory lining (65) and the outer metal shell (66) constituting the bottom of the tank (1). The moving plate is crossed
by two passages (67). Each nozzle (62) is traversed by an internal channel (68) and permanently mounted (for example by a bayonet system) on the movable plate (61) via a
metal support (69) so that its channel (68) is in alignment with the corresponding passage (67) .By rotating the plate (61), therefore, one or other of the nozzles (62) in communication with the taphole (64).
A metal case (70) is sealingly mounted on the bottom of the container (1) and substantially completely envelops the closure device (2) - an opening (71) is provided at the bottom
lower portion of the housing (70) for the passage of the nozzles. A
conduit (72), connected to a source of inert gas under pressure (not shown in the figure), opens into the housing (70).

The inert gas introduced through the conduit (72) spreads
the housing (70) and escapes through the opening (71). This inert gas thus forms an atmosphere which protects the device (2) against the atmospheric air, and more particularly the gap between the plates (60) and (61) and the junction zone between the nozzles.
(62) and the plate (61), as well as the jet of liquid metal at its outlet of one of the nozzles (62).

Fig. 7 shows a plate shutter device
(2) identical to that of Figure 6 (the same references were
assigned to the same elements), but which has, in addition, a spring means (73) for holding the plates (60) and (61) against each other. A housing (70) identical to that of Figure 6 envelops the device (2). The spring means (73) has a countertop-shaped abutment (74) open at its end
lower and secured to the plate (61) via the
metal support (69), a piston-shaped bearing (75)
integral with the plate (60) and a spring (76) interposed between the abutment (74) and the part (75) .A conduit (77) connected to a source of
inert gas under pressure (not shown in the figure), opens
in the abutment (74) after passing through the housing (70) by an ori
fice (78) provided for this purpose. So, the inert gas brought in by the con
duit (77) cools the spring means (73), then spreads in the housing (70) playing its role of protection for the device (2) and escapes through the opening (71).

FIG. 8 represents a plate shutter device
(2) identical to that of Figure 6 (the same references have been affeetées the same elements), but-which comprises, in addition, two spring means (80) to maintain the plates (60) and (61) l against each other. The spring means (80) comprise a stop (81) in the form of an inverted cup open at its lower end and integral with the plate (61) via the metal support (69), a support piece (82) ) in the form of a piston integral with the plate (60) and a spring (83) interposed between the stop (81) and the part (82) .A conduit (84), connected to a source of compressed air, opens into the stop (81).

A metal ferrule (85) is disposed concentrically to the movable plate (61); it is secured, at its upper end (86), to the fixed plate (60) and its lower end
(87) stops near the top (88) of the spring means (80). A conduit (89), connected to a source of inert gas under pressure, opens into the ferrule (85). The shell (85) has an opening (not shown in the figure) for the passage of the drive pinion (not shown in the figure) of the movable plate (61).

 A protective metal plate (90), provided with openings (91), is fixed to the support (69) (for example by keying), at a distance and below said support (69). A duct (92), connected to a source of inert gas under pressure (not shown in the figure), is fixed to the support (69) (for example by welding) and opens into the space defined by the movable plate (61) and the protection plate (90).

 The operation of the installation of Figure 8 is as follows; a garnerte is injected through the conduit (89) into the shell (85); this inert gas is spreading in the gap space.

finished by the shell (85) and thus protects the gap between the plates (60) and (51) and the junction area between the nozzles
(62) and the plate (61); it then flows through the openings (91).

 Simultaneously, an inert gas is injected through the conduit (92); this inert gas spreads in the space between the metal support (69) and the protection plate (90), then flows through the openings (91) thus protecting the jet of liquid metal at its outlet from one of the In addition, the spring means (80) are cooled by injection of compressed air through the conduits (84).

 FIG. 9 represents a plate shutter device (2) comprising two spring means (80), identical to that of FIG. 8 (the same references have been assigned to the same elements).

A metal ferrule (95) concentric with the movable plate (61) is secured at its upper end (96) to the fixed plate (60) and its lower end (97) stops in the vicinity of. the upper portion (88) of the spring means (80). The shell (95) has an opening (not shown in the figure) for the passage of the drive pinion (not shown in the figure) of the movable plate (61).

 A protective metal plate (98), provided with openings (99), is secured to the support (69) (for example by keying), at a distance and below said support (69). A first duct (100), connected to a source of inert gas under pressure (not shown in the figure), is fixed to the support (69) (for example by welding) and opens into the space defined by the movable plate ( 61) and the protection plate (98). A second duct (101), connected to a source of inert gas under pressure (not shown in the figure), passes through the plate (98) through a hole (102) provided for this purpose, and the support (69) through an orifice (103), and opens into the gap (104) between the support (69) and the movable plate (61) .This duct (101) is flexible from a certain moment so as not to impede the movement of the mobile equipment.

 The operation of the installation of Figure 9 is as follows: an inert gas is injected through the conduit (101) in the gap (104); this inert gas spreads in the gap (104), then in the space defined by the shell (95) and thus protects the junction zone between the nozzles (62) and the plate (61) and the gap - between the plates (60) and (61); it then flows through the openings (99). Simultaneously, an inert gas is injected through the conduit (100); this inert gas spreads in the space between the metal support (69) and the protection plate (98), then flows through the openings (ac) thus protecting the jet of liquid metal at its outlet from one of the In addition, the spring means (SO) are cooled by injecting compressed air through the conduits (84).

 In all the embodiments of the invention, either a gas substantially inert with respect to the liquid metal such as nitrogen or argon or a mixture of inert gases is used.

 The invention applies to the protection of all castings of metals, vertical or parabolic, in particular between pocket and tundish, between pocket and mold, between pocket and pocket, between converter (or furnace) and pocket.

Claims (16)

 1. A method of protecting a jet of liquid metal flowing between an upper reservoir and a lower receptacle which is formed around said jet and over the entire height of the latter an ascending gas protective sheath formed at from at least one gas substantially inert with respect to said metal, by injecting said inert gas around the impact zone of said jet and confining said inert gas above the surface of the liquid metal and around the base of said jet by means of a sleeve, open at both ends, surrounding the base of said jet and partially immersed in said liquid metal, characterized in that at least one liquefied inert gas is injected above and close to the surface of the liquid metal contained in the lower receptacle and a gas-shielding atmosphere is created for the liquid metal jet, immediately at its outlet from the zone of the upper reservoir, said atmosphere being formed from a gas substantially inert with respect to said metal and enveloping a shutter device, mounted externally on the bottom of said upper reservoir, comprising a fixed plate and a moving element comprising a movable plate applied against said fixed plate and a support metal integral with said movable plate for at least one nozzle that can come into communication with the flow hole of the liquid metal.  2. Method according to revendicatien 1, characterized in that is injected at least one inert gas into the liquid metal through the bottom of the lower receptacle.  3. Method according to one of claims 1 or 2, characterized in that the liquefied inert gas is injected inside the sheath and slightly below the upper opening of said sheath and / or the inert gas in the liquid metal through the bottom of said receptacle, at a rate such that the ascending gaseous atmosphere formed has in said sheath an oxygen content of less than 5%.  4. Process according to one of claims 1 to 3, characterized in that the inert gas having a boiling point and densities PL in the liquid state and ss # G in the gaseous state, the sheath of containment having a lower opening of section S1 and an upper opening of section S2, and the ascending gas atmosphere reaching said opening - greater than a speed V2 and a temperature T2, the value of V2 being  T2 representative of the oxygen content of said ascending 2 gas atmosphere and being related to the flow rate D of the liquefied inert gas injected inside the sheath by the relation  V2 = 1. 1 S1. #L .D,  T2 60.10 T1 S2 #G one adjusts said rate D so that said value of V2  T2 corresponds to an oxygen content of said atmosphere 2 of less than 5%.  5. Method according to one of claims 1 to 3, characterized in that the inert gas having a boiling temperature T1 and density #L to the liquid state and #G to  It is gaseous, the containment sheath having a lower opening of section 51 and an upper opening of section S2, the temperature of the liquid metal being X, and the ascending gaseous atmosphere reaching said opening greater than a speed V2. and at a temperature T21, the value of V2 being representative of the T oxygen content of said gaseous atmosphere and being related to the flow rate D of the inert gas injected into the liquid metal by the rela tion: V2 1 1 S1 f D, T  I S ~~~~~~ -  T2 3600 T1 S2 # G 410 is adjusted said flow D so that. said value of V2 corresponds to an oxygen content of said atmosphere T2 less than 5%.  6. Method according to one of claims 4 or 5, characterized in that the liquefied inert gas and / cu the inert gas injected into the liquid metal is nitrogen and in that the die is adjusted.  V2 bit II of said gas so that VS> 3.5. 10-4 m / s / K.  2  7. Method according to one of claims 4 or 5, characterized in that the liquefied inert gas and / or the inert gas injected into the liquid metal is argon and in that the flow rate D is adjusted. said gas so that

 8. A liquid metal transfer plant implementing the method according to one of claims 1 to 7, comprising an upper reservoir (1) and a lower receptacle (3) provided with an internal refractory lining, and a sheath ( 7) made of refractory material, open at both ends, the upper opening of said sleeve (7) being located below the outlet of the upper reservoir (1), the lower end of said sleeve (7) being located at a distance from the bottom of the lower receptacle (3) while the upper end of said sheath (7) protrudes widely above the edge of said lower receptacle (3), characterized in that it comprises means for injecting an inert gas liquefied within said sheath and slightly below the upper opening of said sheath and means for creating a gaseous shielding atmosphere formed from at least one inert gas for a shutter device (2) externally on the bottom of the upper reservoir (1), comprising a fixed plate (60) and a moving element comprising a movable plate (61) applied against said fixed plate and a metal support (69) integral with said movable plate (61) for at least one nozzle (62) engageable with the flow hole of the liquid metal.  9. Installation according to claim 8, characterized in that it comprises means for injecting at least one inert gas through the bottom of the lower receptacle.  10. Installation according to one of claims 8 or 9, characterized in that the injection means of a liquefied inert gas li are constituted by at least one injection tube (-16) provided with a calibrated orifice ( 17) opening slightly below the upper aperture of said sleeve (7) and connected, via flow rate adjusters, to a source of liquefied gas (11).  11. Installation according to claims 8 to 10, terérisée in that the means for injecting an inert gas through the bottom of the lower receptacle are constituted by metal nozzles (35) passing through the refractory lining (26) of said receptacle and connected to a source of inert gas under pressure (34).  12.- Installation according to one of claims 8 to 10, characterized in that the means for injecting an inert gas through the bottom of the lower receptacle are constituted by porous or permeable elements (31) incorporated ati refractory lining ( 26) of said receptacle and connected to a source of inert gas under pressure (34).  13. Installation according to one of claims8 to 12, characterized in that it comprises a metal housing (70) sealingly attached to the bottom of the upper reservoir (1), surrounding the shutter device (2) provided with a at least one opening (71) and having an inert gas supply duct (72).  14. Installation according to claim 13, wherein the shutter device (2) comprises at least one spring means (73) for holding the moving element against the fixed plate (60), characterized in that the supply duct inert gas (77) opens into the spring means.  15. Installation according to one of claims 8 to 12, wherein the shutter device (2) comprises at least one spring means (80) for holding the moving element against the fixed plate (60Y, characterized in that it comprises - a ferrule (85), concentric with the movable plate (61), whose  upper part is secured to the fixed plate (60) and  the lower part stops near the top  said spring means (80), said ferrule (85) being provided with  a conduit for supplying an inert gas (89), a metal protection plate (90) secured to the support  metallic (69), at a distance and below said metal support  (69) and provided with at least one opening (91), and - a second conduit for supplying an inert gas (92) integral with the  metal support (69) and opening into the space defined by  said protection plate and the moving equipment.  16. Installation according to one of claims 8 to 12, wherein the shutter device (2) comprises at least one spring means (80) for holding the moving element against the fixed plate (60), characterized in that it comprises - a ferrule (95), concentric with the movable plate (61), whose  upper part is secured to the fixed plate (60) and  the lower part stops near the top  said spring means (80); a first inert gas supply conduit (101) passing through the  metal support (69) and opening on the edge of the interstice  between said metal support (69) and the movable plate (61), - a metal protection plate (98) secured to the support  metallic (69), at a distance and below said metal support  (69) and provided with at least one opening (99) and - a second conduit for supplying an inert gas (100) integral with the  metal support (69) and opening into the space defined by  said protection plate and the moving equipment.