GB2048139A

GB2048139A - Continuous casting of tubes

Info

Publication number: GB2048139A
Application number: GB7916061A
Authority: GB
Original assignee: Arbed SA
Current assignee: Arcelor Luxembourg SA
Priority date: 1979-05-09
Filing date: 1979-05-09
Publication date: 1980-12-10
Also published as: GB2048139B; NL7904236A

Abstract

An ascending column of liquid metal is rotated, preferably electromagnetically by means of an inductor (6), and the hollow column of liquid metal thus produced is allowed to solidify to form a tube which is continuously extracted by a drive system (11). The thickness of the tube wall is monitored by a device 12 and as a result a microprocessor 13 can alter either the rotational speed, the pressure in a pot 1 forcing metal upwards, or the extraction speed by the system 11. <IMAGE>

Description

SPECIFICATON Method and apparatus for the production of hollow blanks This invention relates to a method and apparatus for the production of hollow blanks, more particularly for the production of steel tubes.

The present invention is based upon a continuous or semi-continuous casting technique wherein a column of molten metal is upwardly extracted and solidified during extraction. In principle, such casting can be effected in two ways. According to a first technique, there is used either an oven, preferably electrical, or a metallurgical pot which contain liquid metal and which are located within a chamber which can be closed in a hermetic manner. The chamber is provided with devices for introducing a gas to increase the pressure inside the chamber, and an upwardly extending conduit up which the metal ascends as a result of the pressure created in order to be solidified in an ingot mould and continuously extracted after solidification.

According to a second technique, the liquid metal is continuously introduced by a conduit into a metallurgical pot which is located in a hermetically sealed chamber and which comprises a second conduit through which the metal is forced as a result of the ferrostatic pressure created, in order to be solidified in an ingot mould and continuously extracted. After there has been sufficient solidification in the ingot mould, extraction of the product takes place. In both cases, this takes place upwardly.

In order to exploit fully the advantages offered through combining the techniques of continuous or semi-continuous casting and upward extraction of the cast products, it is necessary to overcome the problems which arise during solidification of the metal within the ingot mould. These problems are more pronounced when it is desired to produce hollow blanks having walls of uniform thickness.

We have ascertained that upward extraction of hollow products is able to introduce an improvement in quality in terms of reducing the content of impurities in the walls of these products. Nevertheless, this improvement is not sufficiently marked and reproducible, more particularly when it is a question of producing alloyed or inox steel tubes where the absence of impurities is a more exacting criterion than in the case of non-alloyed steel tubes.

According to the present invention, there is provided a method of producing a hollow blank, which comprises causing an ascending column of liquid metal to rotate, and allowing the hollow column of liquid metal thereby produced to solidify.

According to a preferred embodiment, the method provides for the continuous or discontinuous introduction of the liquid metal into a tight receptacle, for the creation of a pressure inside this receptacle sufficient to force the metal towards a continuous casting ingot mould where the metal is progressively solidified, and for the extraction of a hollow blank in an ascensional manner, the method being characterised in that the column of electro-magnetically ascending liquid metal is rotated about the axis of the ingot mould.

Rotation is preferably at its most intense at the point of the ingot mould where the process of solidification of the metal begins.

Rotation of the liquid metal during the process of solidification produces two separate effects, i.e.

a dynamic effect which causes particles of impurities to concentrate at the centre of the rotating metallurgic mass according to the principle of centrifugation, and a geometric effect wherein the edges ot the surface of the metal liquid rise. The dynamic effect, as a result of which impurities in the metal to be solidified are concentrated in the immediate vicinity of the axis of rotation and are prevented from rising, is responsible for the excellent results in terms of impurity contents of the tubes produced in accordance with the method of the invention. The geometric effect results in an accelerated and controllable solidification of the metal whilst assuming the form of the tube.

When continuous upward extraction of a solid blank from an ingot mould is carried out without rotating the liquid metal, a large mass of liquid metal in the form of a solid cylinder must solidify progressively towards the centre, commencing at the walls of the ingot mould. This necessitates intense cooling and precise control of the temperatures of the liquid metal and of the cooler.

In contrast with this, the situation is completely different when the liquid metal is rotated according to the invention. Indeed, it is no longer a question of cooling a mass of liquid metal in the form of a solid cylinder; instead, a collar of metal having a reduced mass solidifies rapidly in a uniform and readily controllable manner, as a result of being raised against the cooled walls of the ingot mould.

The method according to the invention allows the speed at which the hollow blank is extracted to be controlled while varying the rotational speed of the liquid metal. Indeed, a change in the rotational speed of the metal has an immediate effect on the form of the collar of liquid metal which rises against the walls of the ingot mould.

Thus, an increase in the rotational speed results in a collar having a thinner and more pointed form and, as a result of accelerated solidification, provides the possibility of increasing the speed of extraction.

Furthermore, according to the invention, it is possible to regulate and control the wall thickness of the hollow blank by altering both the rotational speed of the liquid metal and the speed of extraction. In this manner it is easy to control the thickness of the hollow blank. For example, it is sufficient to increase the rotational speed in order to make the collar, and hence the wall of the hollow blank, thinner for a given speed of extraction.

The apparatus for implementing the method is composed in a general manner of a container which can be pressurised and which contains a reservoir of liquid metal and also an ascending conduit for evacuating the liquid metal surmounted by an ingot mould followed by appropriate extraction means, and is characterised by the fact that at least one inductor is located around the column of ascending liquid metal close to the point at which solidification begins with a view to causing rotation about the axis of the ingot mould using electromechanical means in the direction of the column of liquid metal to be solidified.

The inductor is preferably placed in the water cooling circuit of the ingot mould and is supplied with a current having a frequency of less than 1 5Hz. Of course, it is equally possible, the construction of the apparatus permitting, to locate the inductor at the level of the refractory conduit to which the ingot mould is connected or around the body of the ingot mould. Similarly, the intensity and the frequency of the supply current of the inductor can be adapted to the desired rotational speed, or the latter can be regulated by altering the above-mentioned parameters.

The ingot mould is preferably composed of copper, copper alloy, non-magnetic iron alloy or graphite.

For a better understanding of the invention, reference will now be made, by way of example, to the accompanying drawings, in which: Figures 1, 2 and 3 are each a cross-sectional view of a mass of molten metal within an ingot mould; and Figure 4 is a schematic view of an apparatus of the invention.

Figure 1 shows the substantially planar surface of a mass of liquid metal at rest, i.e. not rotating.

When the speed of extraction of a hollow blank from such,a mass is varied, whether in order to vary the speed of production or in order to adjust the thickness of the walls of the blank, there results a variation in the thermal conditions in the cooling zone, which can be controlled only with difficulty. Indeed, an increase in the speed of extraction will have to be accompanied by an increase in the cooling intensity in order to increase the speed at which the liquid metal solidifies. Given that the mass of metal to be cooled is relatively great, the response of the system will be slow, so that variations in the speed of extraction will have to be effected slowly. This is particularly disadvantageous when it is desired to adjust the thickness of the walls of the blank rapidly by varying the speed of extraction.

In contrast with this, Figure 2 shows the appearance of the liquid metal when subjected to rotation. It will be seen that a relatively weaker cooling intensity than before will be sufficient to ensure that the metal solidifies. Indeed, rotation of the metal results in the formation of a collar C having a reduced mass, which can be cooled in a more readily controllable manner.

Figure 3 shows the result obtained by increasing the rotational speed relative to Figure 2. This result is that the collar C is thinner and even more pronounced, and in an improvement corresponding to the regulating possibilities.

It is easy to see that any desired variation in production speed or in the wall thickness of the hollow blank can be realised easily and rapidly by adjusting the rotational speed of the liquid metal.

An intensive cooling system for cooling the ingot mould in a variable manner might not be required, without excluding constant cooling in terms of intensity. This characteristic has a favourable effect on the costs of the whole apparatus.

Figure 4 shows a pressure-tight chamber 1 equipped with a conduit 7 through which a gas, preferably inert, can be introduced with the aid of a pump 8, and with a pressure gauge 10. A metallurgical pot 2 is provided inside the chamber 1. This pot 2 receives liquid metal through a supply conduit 3 provided with a valve 9. The container 1 has a discharge conduit 4 which leads to a continuous casting ingot mould 5 cooled by water. The ingot mould 5, which can be an oscillating ingot mould, is provided with an external electromagnetic inductor 6. A drive system 11 serves to extract the hollow blanks.

Devices for controlling the inductor 6, the pump 8 and the gauge 10, connected to a microprocessor 13, can be Provided.

The apparatus has a measuring system 12 which serves to continously determine the thickness of the wall 14 of the hollow blank, and which is connected to the microprocessor 13.

As a result of a programme established in accordance with empirical data obtained during tests, the microprocessor 13 receives from the system 12, signals which it uses to regulate either the delivery rate of the pump 8 or the rotational speed of the inductor 6 or the speed of the extracting system 11.

Claims

1. A method of producing a hollow blank, which comprises causing an ascending column of liquid metal to rotate, and allowing the hollow column of liquid metal thereby produced to solidify.

2. A method according to claim 1, wherein the metal is magnetic and is rotated electromagnetically.

3. A method according to claim 2, wherein the nietal is steel.

4. A method according to any of claims 1 to 3, wherein the column is produced in a conduit, upwardly extending from a pressure-tight container, by the generation of pressure within the container.

5. A method according to any of claims 1 to 4, wherein the speed at which the hollow blank is produced is regulated, and wherein the rotational speed of the liquid metal is varied.

6. A method according to any of claims 1 to 4, wherein the wall thickness of the hollow blank is regulated by varying the speed of production and the rotational speed of the liquid metal.

7. A method according to any of claims 1 to 6, wherein the rotational speed selected is highest at the level at which solidification begins.

8. A method according to claim 1, substantially as hereinbefore described with reference to any of Figures 2 to 4 of the accompanying drawings.

9. A hollow blank when produced by a method according to any of claims 1 to 8.

10. An apparatus for implementing a method according to claim 1, comprising (a) a pressuretight container which can be pressurised an which can contain a reservoir of liquid metal, (b) a conduit upwardly extending from the container, surmounted by an ingot mould and an extracting means, and (c) at least one inductor located around the conduit substantially at the level at which solidification begins.

11. An apparatus according to claim 9, wherein the inductor is housed within the cooling water circuit of the ingot mould.

12. An apparatus according to claims 10 and 11, including means for supplying the inductor with a current having a frequency of less than 15Hz.

13. An apparatus according to any of claims 10 to 12, wherein control elements of the inductor, of the pump and of the gauge for the level of metal in the container are connected to a microprocessor.

14. An apparatus according to claim 13 including a measuring system for determining in a continuous manner the wall thickness of the hollow blank, this measuring system being connected to the microprocessor.

1 5. An apparatus according to claim 10, substantially as hereinbefore described with reference to, and as shown in, Figure 4 of the accompanying drawings.