EP0005609B1

EP0005609B1 - Apparatus for shielding molten metal during teeming

Info

Publication number: EP0005609B1
Application number: EP79300784A
Authority: EP
Inventors: Brian Poole; Philip John Young
Original assignee: Air Products and Chemicals Inc
Current assignee: Air Products and Chemicals Inc
Priority date: 1978-05-09
Filing date: 1979-05-08
Publication date: 1981-05-27
Also published as: EP0005609A1; GB1581201A; CA1135935A; DE2960386D1; ZA792218B

Description

This invention relates to an apparatus for shielding molten metal during teeming.
Figure 1 is a schematic perspective view of an installation for producing metal ingots. The installation, which is generally identified by reference numeral 1, comprises a pit 2, which is typically 24 m long, 3.6 m wide and 3.6 m deep. A plurality of ingot moulds 3 to 10 are disposed in the pit 2 adjacent a plurality of pouring trumpets 11, 12 and 13. A carriage 14 carrying a ladle 15 is arranged to move along the pit 2. The bottom of the ladle 15 is provided with a pouring outlet (not shown). In use, ladle 15 is filled with molten metal and is loweed into position on carriage 14 by a crane. Carriage 14 is then moved along the pit until the pouring outlet is directly above one of the pouring trumpets. A plug is then withdrawn upwardly from the pouring outlet and molten metal passes downwardly through the pouring trumpet and up inside the ingot moulds associated with the pouring trumpet. The operation of pouring molten metal through the bottom of a ladle is known as teeming.
Typically, there is a gap of 25 cm to 30 cm between the bottom of the pouring outlet on the ladle 15 and the top of the pouring trumpet. During teeming air comes into contact with the molten metal entering the trumpet and causes undesirable oxidation to occur.
It has been proposed to reduce oxidation by a number of methods. In one method, the carriage 14 is dispensed with and the ladle 15 is lowered onto the pouring trumpet and held in position during teeming by an overhead crane. This prevents the crane being used for other work during teeming. In another method, a curtain of argon is formed around the molten metal stream by directing jets of argon downwardly from a toroidal nozzle supported around the pouring outlet. Although effective, this method consumes a substantial quantity of argon. In a further method (US-A-3460 725) a tube is mounted on a pivoted lever and the lever can be raised to a position in which its upper end abuts the bottom of the ladle around the pouring spout. A protective gas may be introduced into the tube. However with this method the tube must be sufficiently long for its lower end to extend below the surface of the molten metal received in a tundish.
It is an object of at least preferred embodiments of the present invention to provide an apparatus which, in conjunction with a shielding gas, will inhibit air entering the molten metal during teeming.
According to the present invention there is provided apparatus for shielding a stream of molten metal during teeming, which apparatus comprises a first arm pivotably mounted on a carriage capable of carrying a ladle ; a second arm pivotably mounted on said carriage ; a first cylinder open at both ends connected to said first arm and having one end which, during teeming, is urged against the pouring outlet on the bottom of a ladle mounted on said carriage ; a second cylinder substantially axially aligned with said first cylinder, open at both ends, connected to said second arm, and moveable relative to said first cylinder to vary the total axial length of a passageway defined by said first and second cylinders, and means to introduce a shielding gas into the interior of said cylinders, the arrangement being such that, in use, after the pouring outlet of a ladle is arranged over a pouring trumpet, said arms can be moved so that the passageway defined by said first and second cylinders extends from the pouring outlet on the ladle to the pouring trumpet and shielding gas can be introduced into said passageway via said means to inhibit air coming into contact with .molten metal as it passes through said passageway.
Preferably, means are provided to bias said first cylinder, in use, against the pouring outlet on said ladle. Such means may conveniently comprise a counterweight mounted on said first arm.
Advantageously, said second cylinder is connected to said first cylinder by a flexible support. Such a support may conveniently be defined by chain linking which is preferably of relatively small mesh, e.g. 0.65 mm, and is arranged to prevent molten metal splashes from interfering with said cylinder movement.
Conveniently, a seal, for example an asbestos sleeve, can be mounted on the outside of said first and second cylinders to inhibit loss of shielding gas therebetween. In this connection. for the avoidance of doubt, the term cylinder, as used herein, embraces bodies of all cross-sections, e.g. rectangular, square and polygonal, although bodies of circular cross-section are preferred.
In order to inhibit splashes of molten metal reducing the flow of shielding gas into the inside of the cylinders, the end of the first cylinder, remote from the second cylinder, may conveniently be provided with an inwardly extending lip which, with the inner surface of said first cylinder, defines a cavity opening towards said second cylinder, and wherein said means to introduce a shielding gas into the interior of said cylinders is arranged to introduce shielding gas into the interior of said cylinders via said cavity.
In order to inhibit damage to the pouring trumpets, means are preferably provided so that the carriage is rendered immobile when one or both the first and second cylinders are in such a position that movement of the carriage could result in the cylinder(s) damaging the pouring trumpet(s).
For a better understanding of the invention, reference will now be made, by way of example, to Figures 2 and 3 of the accompanying drawings in which :

Figure 2 is an end elevation of a carriage provided with apparatus in accordance with the present invention positioned for teeming ; and
Figure 3 in a section taken along line III-III of Figure 2.

Referring to Figures 2 and 3, there is shown a carriage 20, which is mounted on rails 21, disposed to either side of a casting pit 52. The carriage 20 is provided with trunnions (not shown) which support a ladle 22 having a pouring outlet 23.
A horizontal shaft 24 is mounted fast on the carriage 20 and acts as a pivot for a first bifurcated arm 25 and a second bifurcated arm 26. A first cylinder 27 is mounted between the bifurcated ends of the first arm 25 and is biased against the pouring outlet 23 on the ladle 22 by counterweight 28. A second cylinder 29 is mounted between the bifurcated ends of the second arm 26 by means of pivotably mounted links, one of which is identified by reference numeral 30.
First arm 25 is provided with a first control arm 31 and second arm 26 is provided with a second control arm 32. As shown in Figure 3, an asbestos seal 33 is disposed around the outer surfaces of the first and second cylinders 27 and 29 respectively and inhibits argon escaping from inside the cylinders whilst permitting axial movement between the said cylinders.
In order to limit movement between the first and second cylinders 27 and 29, a chain link shield 34 is secured to the bottom of first cylinder 27 and the bottom of the second cylinder 29. As will be seen from Figure 3, the chain link shield 34 is funnel shaped and, in use, inhibits molten metal entering the space generally identified by reference numeral 35.
The first cylinder 27 comprises a pair of coaxial walls 36 and 37 which define an annular chamber 38 which communicates with an argon feed pipe 39. The annular chamber 38 is sealed by a bottom flange 40 and an upper flange 41 which supports an asbestos sealing ring 42 and includes a lip 43 which defines, with the wall 37, a cavity 44. Forty 6.25 mm diameter holes 45 are bored through the wall 37 where shown and allow argon to flow from argon feed pipe 39 to the inside of the first and second cylinders 27 and 29 via the annular chamber 38.
In use, carriage 20 is moved along rails 21 until the pouring outlet 23 on ladle 22 is directly above pouring trumpet 46. During this time counterweight 28 biases the seal 42 on first cylinder 27 against the bottom of the ladle 22 circumjacent the pouring outlet 23 and second cylinder 29 is held in a raised position by second control arm 32.
Once in position the operator raises control arm 32. This immediately actuates a switch immobilising carriage 22. The second cylinder 29 moves downwardly until it rests on the top of the pouring trumpet 46.
Once in position argon is introduced through argon feed pipe 39 and flows through pouring trumpet 46 and out of the ingot moulds thereby removing a substantial quantity of air from therein. Teeming is then commenced and the flow of argon is continued until teeming is complete. At the end of teeming the second cylinder 29 is raised to allow a sample of molten metal to be taken for analysis.
If the pouring outlet 23 becomes blocked, first control arm 31 can be raised thereby lowering first cylinder 27 sufficient for the insertion of an oxygen lance.
Whilst argon is the preferred shielding gas it should be understood that other shielding gases may also be used, for example, in certain cases, nitrogen may be acceptable.
Whilst the present invention is particularly intended for use in casting ingots, it is also applicable to continuous casting wherein the molten metal is teemed into a tundish.

Claims

1. Apparatus for shielding molten metal during teeming comprising a first arm (25) pivotably mounted on a carriage (20) for carrying a ladle (22), a second arm (26) pivotably mounted on said carriage (20), a first cylinder (27) open at both ends, connected to said first arm (25) and having one end which, during teeming, is urged against the pouring outlet (23) on the bottom of a ladle (22) mounted on said carriage (20), a second cylinder (29) substantially axially aligned with said first cylinder (27), open at both ends, connected to said second arm (26), and moveable relative to said first cylinder (27) to vary the total axial length of a passageway defined by said first (27) and second (29) cylinders, and means (39) to introduce a shielding gas into the interior of said cylinders, the arrangement being such that, in use, after the pouring outlet (23) of a ladle is arranged over a pouring trumpet (46), said arms (25, 26) can be moved so that the passageway defined by said first and second cylinders (27, 29) extends from the pouring outlet (23) on the ladle to the pouring trumpet (46) and shielding gas can be introduced into said passageway via said means (39) to inhibit air coming into contact with molten metal as it passes through said passageway.

2. Apparatus according to Claim 1, characterized in that it comprises means (28) to bias said first cylinder (27), in use, against the pouring outlet (23) on said ladle.

3. Apparatus according to Claim 1 or 2, characterized in that said second cylinder (29) is connected to said first cylinder (27) by a flexible support (34).

4. Apparatus according to Claim 3, characterized in that said flexible support (34) comprises chain linking which is arranged to prevent molten metal splashes from interfering with said cylinder movement.

5. Apparatus according to any preceding Claim, characterized in that it includes a seal (33) between said first and second cylinders (27, 29) to inhibit loss of shielding gas therebetween.

6. Apparatus according to any preceding Claim, characterized in that said first cylinder (27) is provided with an inwardly extending lip (43) which, with the inner surface of said first cylinder (27), defines a cavity (44) opening towards said second cylinder, and wherein said means to introduce a shielding gas into the interior of said cylinders is arranged to introduce shielding gas into the interior of said cylinders via said cavity (44).

7. Apparatus according to any preceding claim, characterized in that means are provided to render said carriage immobile when one or both the first and second cylinders are in such a position that movement of the carriage could result in the cylinder(s) damaging the pouring trumpet(s).