EP0223722A1 - Device and process for the low-pressure injection of pulverulent additives into a stream of molten metal - Google Patents

Abstract

The invention relates to a device for continuous injection under low pressure of a powder additive into a stream of molten metal.

It successively comprises, from top to bottom:
- an upper compartment (5), for the entry of molten metal,
- A treatment chamber (7), connected to the upper compartment by a calibrated inlet orifice (8), and into which opens, on the one hand a tube (9) connected to a device for injecting powdery additive under gas pressure and, on the other hand, at least one conduit (11) for evacuating gases, smoke and any grime,
- at least one buffer compartment (6) cooperating with a means for adjusting the output flow rate of the treated metal,
a means for collecting the treated metal, for example a mold or a pocket.

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a device and a method for continuous injection, under low pressure and protected from air, of a powder additive into a stream of molten metal. This pulverulent additive is directed by carrier gas into the jet of molten metal, this gas possibly creating a protective atmosphere. The present invention applies particularly to the case where the additive must be added to the liquid metal in small proportion, in a very homogeneous manner and, for example, immediately before casting.

STATE OF THE ART

It is known to inject powdered additives into a molten metal either for the purpose of treating the metal, such as deoxidation or desulfurization, or modification of structure, or to introduce an alloying element.

These injections are generally carried out by means of a lance immersed in a pocket containing the molten metal, the pulverulent additive being entrained by a stream of inert gas under a pressure sufficient to counterbalance the hydrostatic pressure of the liquid metal. But this mode of injection is discontinuous.

When it is desired to carry out the continuous treatment of a stream of liquid metal, an effort is made to pour a controlled jet of powdered additive onto the metal pouring jet. This operation is delicate to use and imprecise because, in practice, the jet of liquid metal and the jet of powdered additive tend to move relative to each other. In addition, an often large proportion of the additive does not penetrate the metal stream, especially if the additive is in very fine powder. If, on the contrary, the additive is in large grains, it does not dissolve quickly enough. For example, in the case of the injection of inoculant into the jet of liquid metal at the entrance to the mold in order to inoculate lamellar or spheroidal graphite cast irons, the finest particles diffuse, causing possible pollution of the mold sand and flotation on the mold cup.

Inoculant grains that are too large are not dissolved quickly enough and may cause inclusions in the parts.

To solve this problem, the so-called "cored wire" technique has been devised which is gradually unwound in the casting jet. But this technique is not adaptable to all cases, it is more expensive than direct injection of powder additive and less flexible to use for the use of many additives of different types.

OBJECT OF THE INVENTION

The object of the present invention is a device for continuous and controlled introduction, into a stream of liquid metal, of a predetermined proportion of powdered additive, under pressure, out of direct contact with the atmosphere and, if necessary, under a protective atmosphere, with a yield close to 100% and, in all cases greater than 85%. Another object of the same invention is a method of introducing additive into a stream of liquid metal using the above device.

The device is characterized in that it comprises successively, from top to bottom:
- an upper compartment, for the entry of molten metal,
- a treatment chamber, connected to the upper compartment by a calibrated inlet orifice and into which opens, on the one hand a tube connected to a device for injecting powder additive under low gas pressure, and, on the other share, at least one gas, smoke and dirt evacuation pipe,
- at least one buffer compartment, associated, in its lower part, with a calibrated outlet orifice, possibly separated from said buffer compartment,
- a means of collecting the treated metal.

The method, which implements the device according to the invention, comprises the following successive steps:
- the molten metal is introduced into the upper compartment while maintaining the level between an optimal level and a maximum level,
the pulverulent additive is injected into the mixing chamber in a stream of carrier gas under low pressure and the injection speed is adjusted so as to introduce a weight of additive predetermined per kg of metal to be treated,
the level of molten metal in the lower compartment is maintained between the optimal level and the maximum level by acting on the rate of introduction and on the level of molten metal in the upper compartment,
- the molten metal to be treated is recovered at the outlet of the lower orifice.

DESCRIPTION OF THE FIGURES

• . La figure 1 représente, en coupe verticale, le dispositif proprement dit dans lequel s'effectue l'injection de l'additif sans le métal liquide.
• . La figure 2 représente en coupe l'ensemble d'un appareillage industriel comportant, en plus, un distributeur-doseur d'additif pulvérulent qui ne fait pas partie lui-même de l'invention, mais qui est donné à titre d'exemple de mise en oeuvre.
• . La figure 3 représente, en coupe verticale, une variante de dispositif proprement dit dans lequel le dispositif est placé directement sur un moule de coulée.
• . La figure 4 représente, en coupe verticale, une variante du dispositif proprement dit dans lequel 2 injections successives dans le métal liqui­de d'additifs pulvérulents différents peuvent être réalisées grâce à la présence de deux compartiments-tampons.
• . La figure 5 représente, en coupe verticale, une variante du dispositif de la figure 1 (applicable également aux figures 3 et 4) dans lequel un compartiment siphon a été prévu pour retenir totalement les crasses rési­duelles non évacuées par l'orifice prévu à cet effet.

Figures 1 to 5 illustrate the invention.

• . FIG. 1 represents, in vertical section, the device proper in which the injection of the additive is carried out without the liquid metal.
• . FIG. 2 shows in section the whole of an industrial apparatus comprising, in addition, a dispenser-doser of powdery additive which is not itself part of the invention, but which is given by way of example of Implementation.
• . FIG. 3 represents, in vertical section, a variant of the device proper in which the device is placed directly on a casting mold.
• . FIG. 4 represents, in vertical section, a variant of the device proper in which 2 successive injections into the liquid metal of different powdery additives can be carried out thanks to the presence of two buffer compartments.
• . FIG. 5 represents, in vertical section, a variant of the device of FIG. 1 (also applicable to FIGS. 3 and 4) in which a siphon compartment has been provided to completely retain the residual grime not discharged through the orifice provided for this purpose .

The device which has the general shape of an hourglass comprises an outer metal casing (1) and an inner lining (2) heat-insulating and refractory whose nature is adapted to the metal (or alloy) to be treated. In what follows, we will designate by "metal" any molten metal product, not alloyed or alloyed, subjected to the injection of additive, and by "additive" any powdery product (whatever its nature and its effects on the metal) injected into the metal. The term "pulverulent product" is taken here in the sense of product in more or less fine powder and / or in small grains whose size can reach several millimeters, the limit being fixed by the possibilities of entrainment of the product in a current gas at low pressure.

The device is provided, at its upper part, with an inlet (3) for the metal to be treated, and, at its lower part, in the case in FIG. 1, with a calibrated orifice (4) for leaving the treated metal. It has three separate compartments, but communicating with each other: an upper compartment (5) into which the metal to be treated comes either directly from a processing furnace or from a holding furnace, or from an intermediate storage pocket , a buffer compartment (6) which opens through the calibrated orifice (4) onto an intermediate storage container or onto a ladle and, finally, a treatment chamber (7), located in the upper part of the compartment- buffer (6).

The treatment chamber (7) communicates with the inlet compartment (5) which surmounts it by a calibrated inlet orifice (8) whose role will be explained below. The powder additive is injected into the metal through the tube (9), in a stream of pressurized gas, which shatters on the sheet of liquid metal flowing in the central zone (10) of the treatment chamber. A lateral duct (11) allows the evacuation to the atmosphere of the protective gas and of any reaction gases, smoke or grime, so that the reaction chamber remains at a pressure slightly higher than atmospheric pressure. One can also provide (fig. 3) two conduits (11), an upper conduit (11A) for the evacuation of gases, vapors and fumes, and a lower conduit (11B) for the evacuation of dross.

The stream of metal mixed with the pulverulent additive then flows into the buffer compartment (6) where the dissolution of the additive and the reactions between the metal and the additive are eventually completed.

To allow this dissolution and these reactions time to complete and to allow the separation of dross that may form, we de ends the passage section of the outlet (4), that is to say, the speed of the metal exit from the buffer compartment (6) so that this compartment (6) remains constantly filled of liquid metal to a level at least equal to about half the height and, preferably, at least equal to about two-thirds of the height (level N1), without however exceeding a maximum level (N2) located lower than the lower hole (11B) for removing any dirt.

This is a key point of the invention. In fact, by maintaining a metal flywheel in the buffer compartment (6), both the mixing and the reaction between the additive and the metal are ensured (therefore a yield of use of the additive close to 100%) and the dirt (12) which may form is left to collect on the surface of the metal, to be eventually released by the orifice (11B).

• a) alimenter le compartiment supérieur (5) en métal à traiter à une vitesse telle qu'il se maintienne à un niveau proche du niveau optimal N3, et relativement constant.
• b) qu'il y ait, entre la section de passage de l'orifice calibré d'en­trée (8) et celle de l'orifice calibré (4) une relation telle que, compte tenu de la viscosité du métal fondu et de la pression métallostatique, le niveau du métal dans le compartiment-tampon (6) se maintienne entre les limites fixées.
  Dans le cas de la figure 1, lorsque la coulée est achevée, le compartiment (6) se vide en totalité, de telle sorte que les crasses se retrouvent en surface de la poche réceptrice (non représentée).

For these conditions to be met, you must:

• a) supplying the upper compartment (5) with metal to be treated at a speed such that it remains at a level close to the optimal level N3, and relatively constant.
• b) there is, between the passage section of the calibrated inlet orifice (8) and that of the calibrated orifice (4), such that, taking into account the viscosity of the molten metal and the metallostatic pressure, the level of the metal in the buffer compartment (6) is maintained between the fixed limits.
  In the case of FIG. 1, when the pouring is completed, the compartment (6) is completely emptied, so that the dross ends up on the surface of the receiving pocket (not shown).

The controlled supply of powder additive can be carried out by any means known to those skilled in the art. Figure 2 shows schematically a particularly well suited device which essentially comprises a reservoir of powder additive (20), a feed screw (21) passing through the lower part (22) of the reservoir (20), a motor (23) at high speed regulated and variable ensuring by means of a reducer (24) the drive of the screw (21) whose flow rate in powder additive is proportional to the speed of rotation, and a supply (25) in dried and deoiled compressed air, or in neutral gas (for example nitrogen or argon) which drives the additive to the injector (26) which also acts as a non-return device, then to the introduction pipe ( 9), supplied with pressurized gas through the pipe (27). The reservoir (20) has two probes for measuring the level of the powdery additive (28).

FIG. 3 represents, in vertical section, a first variant of the invention, according to which the device is placed directly on a casting mold (30) of which only the inlet is shown. The calibrated outlet orifice is no longer arranged at the base of the lower compartment: it is included in the mold and it is constituted by the smallest cross section of the attack system (set of conduits bringing the metal from the inlet from the mold to the feed channels of the mold cavities) and, for example, in the figurative case, by the descent of the load (31) or by the attacks (32) of the parts to be molded.

In this case, when the casting is completed, the compartment (6) is completely emptied, so that any grime is found on the surface of the mold cup without risk to the internal health of the parts.

FIG. 4 represents, in vertical section, a second variant according to which two successive injections of pulverulent additives in the liquid metal can be carried out thanks to the placing in series of two buffer compartments, an intermediate (6A), a lower (6B) , each having its own inlet (9) (9 ') of powdered additives, its orifices (11A) and (11B) for evacuating gases and dross and its treatment chamber (7) (7'), and its calibrated inlet ports (8) and (8 ').

FIG. 5 represents a third variant of the invention, consisting of the addition to the lower part of the buffer compartment (6) of a siphon (35) making it possible to completely retain the dirt not discharged through the orifice (11B) . The siphon can be adapted as well to the case of FIG. 1 and, in this case, it is the calibrated orifice (4), disposed at the base of the buffer compartment (6) which regulates the speed of exit of the metal, than in FIG. 5 where the buffer compartment (6) or (6B) does not have a calibrated outlet orifice. This role is then played by the section of outlet (36) of the siphon which is, for this, suitably calibrated.

The maintenance of the metal level in the lower compartment (6) can, if necessary, be measured and, if necessary regulated, by placing a certain number of level probes (13) in the wall of this compartment and by controlling the speed. metal introduction into the upper compartment. On the other hand, the flow rate of the powdery additive can be controlled by the flow rate of the liquid metal entering the reaction chamber through the calibrated orifice (8) from the measurement of the level in the upper compartment (5) by means probes (14) for example.

The drawing of the mixing chamber (7) is given as an example of embodiment and does not constitute a limitation of the invention. Those skilled in the art can optimize this design according to the nature of the metal treated (reactivity, viscosity) and the nature of the additive (powder in more or less fine grains, more or less reactive) so as to create , for example, swirling effects or effects of dispersion of the metal current, for example by adapting the shape of the orifice (8) or by interposing an obstacle such as (15) on this current at the exit of the orifice (8) or by any other equivalent means.

To facilitate maintenance and cleaning, the device, object of the invention, can be produced in two parts, separated by a plane passing through the vertical axis AA and perpendicular to the tube (9) for arrival of the powdery product. , and which are maintained, during casting, in contiguous and tight relation by clamps or hydraulic cylinders, in known manner, according to the dimensions of the device.

APPLICATION EXAMPLES Example 1.

est de 87 %.An experimental treatment device was constructed, according to the invention, in accordance with the diagram in FIG. 1, for the treatment of nodulization of spheroidal graphite cast iron by addition of a ferrosilicomagnesium in small grains containing 5.7% of magnesium.
The entry compartment (5) has an inverted pyramid shape. The section inlet is 250 x 250 mm and the height h₁ of the orifice (8) to the top of the inlet compartment (5) is 250 mm.
The orifice (8) has a section of 1200 mm² of rectangular shape 10 x 120 mm. The lower compartment is cylindrical with a diameter of 150 mm and a height h2 of 270 mm between the calibrated outlet hole (4) and the dirt discharge orifice (11B).
The outlet orifice (4) has a diameter of 40 mm, that is to say a passage section of 1257 mm², to be compared to the 1200 mm² of the orifice (8).
The ferrosilicomagnesium additive is injected through the tube (9) with a weight flow of 90 g / second. The carrier gas used is nitrogen at a pressure of 0.06 MPa. The flow rate of liquid pig iron is 10 kg / second, which corresponds to an addition of 0.9% by weight of FeSiMg to 5.7% of magnesium, ie 0.051% of Mg added. The device is supplied with liquid iron by an induction furnace, the treated cast iron being recovered in a 500 kg receiving pocket placed under the treatment device.
The magnesium incorporation yield defined by the relation:

is 87%.

Example 2.

A second experimental treatment device was constructed, according to the invention, in accordance with the diagram in FIG. 3, with a view to carrying out in a single operation the treatment of nodulization and inoculation of spheroidal graphite cast iron.

This device is placed directly on a mold made of furan sand. The total weight of the poured cluster is 55 kg. The casting has a minimum thickness of 5 mm.
The entry compartment (5) has an inverted pyramid shape. The inlet section is 250 x 250 mm and the height of the opening to the top of the inlet compartment (5) is 250 mm.
The orifice (8) has a section of 600 mm² of rectangular shape 6 x 100 mm. The lower compartment is cylindrical with a diameter of 150 mm and a height of 220 mm between the laying plane (34) on the mold (30), and the dirt discharge orifice (11B).
The weight flow rate in the mold is of the order of 5 kg / sec. This flow rate is adjusted by giving the load lowering channel a calibrated section.
The treatment product is a mixed product comprising 95% of FeSiMg with 5.7% of magnesium and 5% of an inoculating ferrosilicon containing, inter alia, 1% of Bismuth and 0.5% of Rare Earths, according to our French patent. FR 2,511,044 (= US 4,432,793).
The mixed product with a particle size of 0.2 to 1 mm is injected through the tube (9) with a weight flow rate of 45 g / second, which corresponds to 0.049% of Mg added. The cast iron thus treated has for final analysis:
C = 3.74 Si = 2.46 Mn = 0.12 P = 0.043 S = 0.004 Mg = 0.037
The casting has a perfectly nodular structure in a totally ferritic matrix free of carbides.
The Mg incorporation yield in this case is 85%.

BENEFITS PROVIDED BY THE INVENTION

Compared with currently used or known systems, the invention has the following advantages:
- yield of incorporation of the additive close to 100%,
- constant rate of addition of the additive during the entire casting period, which avoids manual weighing operations of the liquid metal and the additive,
- possibility of using very fine particles of additives with excellent performance and without risk of loss and pollution of the workshop atmosphere and molding sands.

The invention can also be applied to simultaneous treatments of nodulization and inoculation, as described in Example 2, for spheroidal graphite cast irons; the levels of additives required to obtain the correct characteristics for these cast irons are often 50% lower than conventional nodulization and bag inoculation processes.

The method and the device can on the other hand and without limitation, apply:
- to the vermiculization treatment of cast irons,
- to the recarburization treatment of the fonts,
- the continuous desulfurization treatment of cast irons,
- to the desulfurization and denitriding treatment of steels,
- microadditions in steels (such as boron) or in cast irons (such as vanadium, titanium ...)
- various degassing and refining treatments of light alloys.

The arrangement of the device allows the immediate introduction of the treated metal into the mold (s) (fig. 3) which limits the risk of the effect of certain volatile, oxidizable additives or fleeting action (germination) vanishing. ).

Finally, the device, as just described, in its different variants, also allows the injection of a reactive gas or liquid, with or without associated transport of powdery additive, for example to produce degassing of aluminum by injection of a chloreazote mixture.

Claims (13)

1. Device for continuous injection under low pressure of a powdery additive into a stream of molten metal, characterized in that it successively comprises, from top to bottom:
- an upper compartment (5), for the entry of molten metal,
- A treatment chamber (7), connected to the upper compartment by a calibrated inlet orifice (8), and into which opens, on the one hand a tube (9) connected to a device for injecting powdery additive under gas pressure and, on the other hand, at least one conduit (11) for evacuating gases, smoke and any grime,
- at least one buffer compartment (6) cooperating with a means for adjusting the output flow rate of the treated metal,
- a means of collecting the treated metal. 2. Device according to claim 1, characterized in that it comprises two buffer compartments superposed in series, an intermediate compartment (6A) and a lower compartment (6B), each comprising a treatment chamber (7), (7 '), a calibrated inlet orifice (8) (8 ') and at least one gas, smoke and dirt evacuation duct. 3. Device according to claims 1 or 2, characterized in that the treatment chamber comprises two discharge conduits, an upper conduit (11A) for gases and fumes, and a lower conduit (11B) for the evacuation of dross . 4. Device according to claims 1, 2 or 3, characterized in that it comprises at the base of the buffer compartment (6) or of the lower buffer compartment (6A) a siphon (35) for retaining dirt. 5. Device according to any one of claims 1 to 4, characterized in that the means for adjusting the output flow rate of the treated metal consists of a calibrated orifice disposed on the path of the treated metal. 6. Device according to claim 5, characterized in that the calibrated orifice (4) is arranged at the base of the buffer compartment (6) or of the compartment lower (6A). 7. Device according to claim 5, characterized in that the calibrated orifice is integrated into the collecting means of the treated metal. 8. Device according to claim 5, characterized in that the calibrated orifice is integrated into the siphon (35). 9. Device according to any one of claims 1 to 8, characterized in that it comprises means such as (13) (14) for measuring the level of molten metal in the lower compartment (6) and / or in the upper compartment (5). 10. Device according to claim 9, characterized in that it comprises means for controlling the arrival of molten metal in the upper compartment (5) at the level of the molten metal in the lower compartment (6). 11. Device according to any one of claims 1 to 10, characterized in that it consists of two parts separated by a plane passing through the vertical axis and perpendicular to / to the inlet orifices of the powdery additives (9). 12. A method of continuous injection of a powder additive into a stream of molten metal, using the device according to any one of claims 1 to 11, characterized in that:
- the molten metal is introduced into the upper compartment (5) by adjusting the flow rate so as to maintain the level between an optimal level N3 and a maximum level N4
- is injected into the mixing chamber (s) (7) (7 '), by the tube (s) (9) (9'), in a stream of pressurized carrier gas, the additive (s) including the injection rate is adjusted so as to introduce a predetermined additive weight per kg of metal to be treated,
the level or levels are maintained in the buffer compartment (s) (6) (6 ′) between the optimal level N1 and the maximum level N2 by acting on the rate of introduction of the metal into the upper compartment (5),
- The treated metal is collected at the outlet of the buffer compartment (6) or of the lower buffer compartment (6B). 13. Application of the device according to one of claims 1 to 11, for the treatment of molten metals, ferrous or non-ferrous, characterized in that one injects, by the tube (9) a gas, a vapor or a liquid reactive.

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