LU82874A1 - PROCESS AND PLANT FOR THE CONTINUOUS MANUFACTURE OF HOLLOW METAL BLANKS - Google Patents

Description

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Method and installation for the continuous production of hollow metal blanks.

The present invention relates to a process for the continuous production of hollow metal blanks, in particular steel tubes, as well as to the installation necessary for carrying out the process.

In order to manufacture seamless tubes, attempts have been made to carry out continuous or at least semi-continuous metal casting operations, accompanied by an upward extraction and which can take place, for example, as follows: An electric furnace or a pocket contains liquid metal and are on their side inside an enclosure which can be closed hermetically. The enclosure includes the accessories necessary for the introduction of a gas, serving to increase the pressure inside the enclosure, as well as an ascending duct through which the metal is evacuated by means of the pressure created, to be solidified in an ingot mold and extracted continuously after solidification.

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Another technique provides for the continuous flow of liquid metal through a conduit inside a pocket which is in a hermetically sealed enclosure and which comprises a second conduit through which the metal is evacuated by ferrostatic pressure. 25 .. tick created, to be solidified in an ingot mold and continuously extracted.

The extraction of the product is done in both cases from above.

30 However, in order to overcome the problems which arise during the solidification of the metal inside the mold and which are even more pronounced when it comes to producing hollow blanks with a uniform wall thickness, the depositor has developed a process which he described in Luxembourg patent no. 79.444 and which provides for continuously or discontinuously bringing liquid metal into a sealed container, creating inside this container sufficient pressure to discharge the metal to a continuous casting mold where the metal is solidified ”- 2 - gradually and ascend a hollow blank. This method also provides that the vein full of ascending liquid metal is electromagnetically rotated around the axis of the mold. The rotation is preferably most intense at the location of the mold where the metal solidification process begins.

This rotation of the liquid metal in the process of solidification produces a dynamic effect which causes a concentration of the particles of impurities in the center of the metallic mass in rotation, according to the "principle of centrifugation, and a geometric effect which consists of a heightening of the edges of the surface of the molten metal.

The dynamic effect is responsible for the excellent results from the point of view of the contents of inclusions of the tubes manufactured according to the method according to the invention, while the geometric effect, which is manifested by an elevation of the edges of the surface of the metal in rotation, results in an accelerated and controllable solidification of the metal taking the form of the tube to be extracted from the mold.

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In fact, it is no longer a question of cooling a mass of liquid metal in the form of a full cylinder, but a metal collar, of a reduced mass, which by being raised against the cooled walls of the mold, solidifies rapidly. , uniformly and easily controllable. This process therefore makes it possible either to adjust the extraction speed of the hollow blank while varying the rotational speed that is printed on the liquid metal, or to adjust and control the wall thickness of the hollow blank by modifying according to the needs and the rotational speed that is printed on the liquid metal and the extraction speed.

In this way it is easy to control the thickness of the hollow blank, since it suffices for example to increase the speed of rotation in order to thin the flange and thereby the wall of the hollow blank for a given extraction speed.

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However, it has been found that it is difficult to produce, even using strong magnetic fields, very deep menisci in the form of paraboloids, the upper parts of which are tangent vertically.

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In addition, it has proved difficult to achieve a constant level in the mold and this due to sealing problems. A constant level is essential to avoid breaking of the blank during extraction and to guarantee a constant thickness of the walls 10 of the blank. The object of the present invention was to provide a method for manufacturing hollow blanks, free from the difficulties described.

This object is achieved by the method according to the invention which provides for forming a vein of liquid metal essentially in the form of a "U", subjecting one of the branches of the vein to the action of rotating electromagnetic fields as well as '' cooling of its external surface, while ensuring that the metal contained in the other branch of the vein remains liquid, continuously extracting solidified metal from the cold branch and feeding the hot branch by a corresponding amount of liquid metal and subjecting the entire vein to a vertical oscillating movement.

The idea on which the present invention is based is to find an original, simple and valid means of ensuring that there is in the region of the blank extraction a constant level. By providing, according to the invention, a metal vein in the shape of a "U", a system of communicating vessels is implemented which makes it possible to avoid the use of pressurizable chambers which bring about problems of -30 tightness and prevent or at least make difficult the maneuvers of vertical oscillation. Indeed, it should be noted that the absence of a possibility of oscillation leads during the extraction to surface defects, due to the momentary rupture of the solidified carcass.

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According to the invention, this problem is avoided by making the entire system oscillate, i.e. oscillate the vein in the shape of a "U" and - 4 - exert a constant tensile force on the blank. Under these conditions, the rotation of the liquid metal in the process of solidification does not only play the role of a means of raising the edges of the level of the metal, but in addition that of a means of repairing during the rupture. of the carcass, by instant supply of additional liquid metal.

According to the invention, the outside surface of the cold branch is cooled essentially in two ways: At the right where it is intended to initiate the solidification of the metal, the latter is cooled by means of a cold surface, in this case by contact with the wall of a water-cooled ingot mold. On the other hand, after the primary cooling by direct contact, secondary cooling is carried out by means of a cooling fluid.

The method according to the invention provides for essentially using 2 distinct electromagnetic fields: In fact it is intended to subject the metal to the place where solidification begins and therefore 20 * to the place where the primary cooling acts, â the action of a primary electromagnetic field, which is created using an inductor supplied with current of a frequency less than 15 Hz.

On the other hand, after the field of action of this primary electromagnetic field, provision is made for a secondary field which acts at the location of the level of liquid metal. We therefore create at the level; of liquid metal a deep meniscus. It is important to emphasize that said meniscus is inside the blank with solid walls, at the outlet of the mold.

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The secondary electromagnetic field is created by an inductor which is supplied with current of frequency of the network, therefore of 50 Hz. This influences favorably the price of the installation, since the inductors with frequency of 50 Hz. Are definitely less expensive than 35 lower frequency inductors.

- 5 -, The installation necessary for the implementation of the method according to the invention consists in particular of a conduit in the shape of a "U", in refractory material, one of the branches of the conduit comprising a cooled ingot mold â water and equipped with a primary electromagnetic-5 tick with a frequency less than 15 Hz above which is a secondary inductor with a frequency of 50 Hz .; said branch further comprising a series of extraction rollers resp. guide and a spraying system by fluid jets, while the other branch, of larger diameter is disposed under a source of liquid metal supply, the entire duct resting on a movable table provided with means vertical oscillation.

According to a preferred embodiment the inductor is placed in the water cooling circuit of the mold.

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The ingot mold is preferably made of copper, copper alloy, non-magnetic alloy cast iron or graphite.

Above the ingot mold there is disposed a lubrication ring 20 making it possible to add a sufficient quantity of rapeseed oil to promote the release of the solidified metal from the ingot mold.

Since the entire installation rests on a table provided with means allowing vertical oscillation, it is understood that it is provided in addition to the extraction rollers resp. guide, means of extraction physically independent of the conduit, eg in the form of an extensible mandrel which is inserted into the cavity of the blank and which exerts a constant pulling force upwards.

30 Other characteristics and advantages will emerge from the description of the drawing in which the flg.l represents a diagrammatic section through a possible embodiment of the installation according to the invention and which has no limiting character.

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There is a refractory conduit in the shape of a "U", the hot branch (1) of which is disposed under a pocket, not shown.

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The diameter of the cold branch is obviously smaller than that of the hot branch (1), because the addition of fresh liquid metal in the branch (1) will affect the level of metal in the cold branch and that the quantity high metal content in branch (1) 5 is likely to mitigate the effects of possibly irregular addition.

The metal which is conveyed to the cold branch is kept in the liquid state by heating means (50), eg by induction, to avoid premature solidification which would be absolutely harmful.

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We distinguish the mold (10) which is surrounded by the primary inductor (20). Due to the thickness of the mold walls, this inductor (20) must be a low frequency inductor, preferably less than 15 Hz. Above the ingot mold (10) is the lubrication ring (5).

As shown in the drawing, the solidification of the metal is initiated at the level of the mold (10); the speed of solidification depends of course on the intensity of cooling, the speed of extraction as well as the speed of rotation that is printed on the liquid metal, the shape of the solidified profile may differ from the shape represented.

The solidified blank (2) leaving the ingot mold still contains liquid metal, the level of which necessarily corresponds to that which is established in the branch (1). It is at this level that the secondary inductor (30) is located, which gives the relatively thin column of liquid metal a rotational movement such that the deep meniscus (4) is formed there. .

There are the rollers (3) for extracting and guiding the blank; the independent extraction means, in the form of a mandrel with extendable head, is not shown.

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The solidified part of the blank is subjected to secondary cooling by a system (40) of jets of a fluid, eg water. There are also the rollers (3) for driving and guiding the solidified blank, while the extraction means produced by a mandrel with an extendable head is not shown.

The assembly rests on a mobile table (0), which is provided with a system allowing vertical oscillation.

The installation may also include a non-re-presented measuring system, which is used for the continuous determination of the thickness of the wall of the hollow blank and. which is connected in turn to a microprocessor.

15 Thanks to a program established according to empirical data, collected during tests, the microprocessor receives from the wall thickness measurement system signals which it uses to adjust the intensity of the primary and secondary cooling. , the speed of rotation of the inductors, the speed of the drive of the extraction system, as well as the flow rate of fresh liquid metal 20 that is added.

Claims (13)

1. Process for the continuous production of hollow metal blanks, in particular steel tubes, characterized in that a vein of liquid metal is formed, essentially in the form of a "U", which is subjects one of the branches of said vein to the action of rotating electromagnetic fields, as well as to a cooling of its external surface while ensuring that the metal contained in the other branch of the vein remains liquid, which one 10 continuously extracts the solidified metal from the cold branch and feeds the hot branch with a corresponding amount of liquid metal, and submits the entire vein to a movement of vertical oscillation. 2. Method according to claim 1, characterized in that a constant extraction force is exerted on the solidified blank. 3. Method according to claims 1 and 2, characterized in that the solidification of the external surface of the vein 20 is initiated by bringing it into contact with a cooled surface and that, following direct contact with said surface, the solidified walls of the blank are cooled by means of a fluid. 4. Method according to claims 1-3, characterized in that one 25. subjects the metal to the level or begins solidification, to the action, of a rotating primary electromagnetic field. "5. Method according to claims 1-4, characterized in that the primary field is a field with a frequency less than 15 Hz. 30 6. Method according to claims 1-5, characterized in that a deep meniscus is created at the level of the liquid metal by providing a rotating secondary electromagnetic field at this location. 7. Method according to claims 1-6, characterized in that the secondary field is a field with a network frequency of 50 Hz. - 9 - 8. Installation for implementing the method according to claims 1-7, characterized in that it consists in particular of a conduit in the shape of a "U", in refractory material, one of the branches of the conduit comprising an ingot mold cooled with water and 5 provided with a primary electromagnetic inductor with a frequency less than 15 Hz, above which is a secondary inductor with a frequency of 50 Hz .; said branch further comprising a series of extraction rollers resp. guide as well as a spraying system by fluid jets, while the other branch, of larger diameter, is arranged under a liquid metal supply source, the entire duct resting on a mobile table provided with; means of vertical oscillation. 9. Installation according to claim 8, characterized in that the primary inductor is placed in the water cooling circuit of the mold. 10.Installation according to claims 8 and 9, characterized in that above the mold there is a lubrication ring ·. 20 · 11.Installation according to claims 8-10, characterized in that it is provided in addition to the extraction rollers resp. guide means, physically independent extraction means from the conduit, eg in the form of an expandable mandrel which fits into the cavity of the blank and which can exert a constant upward pulling force. 12.Installation according to claims 8-11, characterized in that it comprises a continuous measurement system for the thickness of the walls of the blank. 13.Installation according to claims 8-12, characterized in that it comprises a microprocessor which adjusts from the results of measurement of the thickness of the walls, the intensity of the cooling and of the primary and secondary electromagnetic rotation, the speed of the extraction drive, as well as the flow rate of fresh metal added.