GB2255638A

GB2255638A - Sampling and analysing molten metal

Info

Publication number: GB2255638A
Application number: GB9208467A
Authority: GB
Inventors: Simon William Bateson; Sara Elizabeth Leadbetter; Anthony Paul Redman; Steven Gordon Robinson; Jonathan Simms; David Peter Jackaman
Original assignee: Davy McKee AG
Current assignee: Davy McKee AG
Priority date: 1991-04-22
Filing date: 1992-04-16
Publication date: 1992-11-11
Also published as: GB9208467D0; GB9108534D0

Abstract

A probe is dipped into the molten metal and some of the molten metal flows into the probe chamber (3). When molten metal has been collected in the chamber the probe is withdrawn and oxygen is introduced (13) into the chamber to bring about oxidation of the metal. The gases of oxidation are removed (15) and analysed. <IMAGE>

Description

PROBE STRUCTURE FOR THE ANALYSIS OF MOLTEN METAL This invention relates to a method of analysing a quantity of molten metal and to a probe structure for collecting a sample of molten metal to be analysed.

It is often necessary to chemically analyse molten metal to discover its composition or impurities in it before or during an industrial process. This analysis must be completed as quickly as possible in order to save valuable process time and/or process reagents. There are several known ways of analysing a sample of molten metal once it has been collected and the speed of such techniques usually depends upon the arrangements to collect the sample and then transport it to the site where the analysis takes place.

Clearly, it is important that the analysis be carried out as quickly as possible and both the time taken to obtain a sample and the time taken to analyse a sample are critical.

According to a first aspect of the present invention, in a method of analysing a quantity of molten metal, a probe structure is dipped into a mass of the molten metal to collect in a chamber of the probe a sample comprising a quantity of the molten metal and, after the chamber has been closed and the probe withdrawn from the mass of molten metal, oxygen is introduced into the chamber to bring about oxidation of the sample and the gases of oxidisation are withdrawn from the chamber and are analysed.

By obtaining in the chamber a sample of the molten metal and then oxidising the sample in the closed chamber, the gases of oxidation will give an accurate indication of at least some of the constituents of the molten metal. There are a number of well known methods of analysing a gas to determine its constituents.

According to a second aspect of the present invention, a probe structure for collecting a sample of molten metal includes a probe tip arranged to be dipped into a mass of molten metal, said tip comprising a body defining a chamber, the chamber having at least one molten metal entry port which canb be closed off when a quantity of molten metal has entered the chamber through the port, means for introducing oxygen into the chamber to bring about oxidation of the sample of molten metal in the chamber, and a gas exit tube from the chamber.

In one embodiment of the invention, the tip comprises a body defining a chamber which extends to a molten metal entry port at the outer end of the body, a refractory crucible displaceable within the chamber, means for limiting the displacement of the crucible with respect to the body in the direction away from the port and the crucible having an underside capable of closing off the port after the crucible has been filled with molten metal through the port. With this arrangement, when the tip of the probe structure is dipped into the molten metal, the molten metal flows through the entry port into the chamber causing the crucible to rise up within the chamber. When the crucible is restrained in its vertical movement within the chamber, the molten metal flows into and fills the crucible.The probe structure is then withdrawn from the mass of molten metal, allowing the excess metal to drain back to the chamber through the port but with the crucible retaining the predetermined quantity of molten metal. As the crucible is lowered relative to the wall of the chamber, the crucible closes the port at the lower end of ti body to close the chamber with the crucible containing a predetermined quantity of molten metal within it.

In order that the invention may be more readily understood, it will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a section through a tip of a probe structure in accordance with one embodiment of the present invention; Figures 2A - 2F indicate successive steps in the process of the present invention employing the probe structure shown in Figure 1; Figure 3 is a section through a tip of a probe structure in accordance with a second embodiment of the invention; Figure 4 is a perspective view of part of the probe structure shown in Figure 3; Figure 5 is a plan of the tip of a probe structure in accordance with a still further embodiment of the invention; Figure 6 is a section on the line A-A of Figure 5;; Figures 7 and 8 are sectional views of probe structures in accordance with still further embodiments of the invention; and Figure 9 is a diagrammatic sectional side elevation of another embodiment of the invention.

A vessel containing a mass of molten metal, such as a ladle, converter vessel or the like has a small quantity of the molten metal removed from it in the form of a sample for chemical analysis. In order to obtain the sample, an elongate probe structure is employed with a tip at one end of the probe structure.

The tip is dipped into, and withdrawn from, the vessel to draw out a quantity of the molten metal.

Referring to Figure 1, a probe structure has a tip at one end which is arranged to be dipped into a mass of molten metal in order to obtain a sample of the molten metal. The tip structure comprises a generally cylindrical refractory body 1 which defines a chamber 3. The refractory body is contained within an outer tube 4 which may be of cardboard. At the lower outer end of the body 1 the wall thickness is increased to define a port 5 which extends from the chamber 3. At a position away from the port 5 there is a refractory disc 7 which seals off the upper end of the chamber 3.

Within the chamber 3 there is an open topped refractory crucible 9, the underside of which is shaped to rest upon the widened wall thickness defining the port 5 so that the underside 11 of the crucible can close off the port. An oxygen lance 13 extends through the disc 7 into the chamber and, similarly, a gas exit tube 15 leads from the chamber through the disc. The tube contains a filter 16 to remove solid particles from the gas generated in the chamber. Within the chamber 3 there are upper stops 17 projecting inwardly from the side wall of the body to prevent the displaceable crucible from moving relative to the body upwardly beyond the stops. A protective fusible cap 19 closes off the outer end of the port 5.

The manner in which the probe structure shown in Figure 1 is used to obtain a sample of molten metal will now be described with reference to Figures 2A 2F. The probe structure is shown in Figure 2A with the tip about to be dipped into a mass of molten metal 25 contained in a vessel (not shown). As the tip of the probe is introduced through the layer of slag on the surface of the metal, the protective cap quickly melts and molten metal beneath the slag flows through the port 5 into the chamber 3. As the probe is dipped further into the molten metal, the crucible floats on the surface of the hot metal in the chamber 3. (See Figure 2B). As the tip is dipped further into the molten metal, upward movement of the crucible continues until it engages the upper stops 17 and, as the probe is lowered further, molten metal overflows into and fills the crucible. (See Figure 2C).

Figure 2D shows that, when the probe structure is raised, the crucible containing a predetermined quantity of molten metal falls within the chamber and comes to rest with its underside 11 closing off the port 5. Excess molten metal in the chamber has previously drained back through the port as the probe is raised.

Figure 2E shows the probe raised sufficiently for the crucible to be clear of the molten metal and the chamber is closed at its lower end by the crucible and it contains a predetermined quantity of the molten metal within the crucible.

Finally, as shown in Figure 2F, the oxygen lance 13 is lowered and a quantity of oxygen introduced into the chamber to permit the small sample of the molten metal in the crucible to be oxidised. The gaseous products of oxidation escape from the chamber through the exit tube 15 where they are collected for chemical analysis. Non-gaseous products of oxidation are retained within the probe. Extremely high temperatures are reached as the high purity oxygen is blown on to the molten metal in the crucible and usually complete combustion of the impurities in the metal sample results. The gases of combustion which flow through the exit tube are, as mentioned above, analysed by any convenient method.

Referring now to the embodiment shown in Figures 3 and 4, the tip of the probe comprises a hollow refractory tube 25 having a plate 27 across its outer end and an internal refractory disc 29 at a position spaced along the length of the tube from the outer end. The tube with the plate and disc together define a chamber 31. A cylindrical guide tube 33 is fixed within the chamber adjacent to the plate 27. The guide tube is open at its end adjacent the plate 27 and, at its opposite end, it has a number of slots 35 in its side wall and inwardly extending projections 37.

An open topped refractory crucible 39 is slidable within the guide tube 33. The movement of the crucible is limited at one end by the projections 37 and at the outer end of the tube where the crucible rests on the plate 27 and a projection on the underside of the crucible closes off an opening 41 in the plate. A fusible plug 43 is fitted on the outside of the opening on the plate 27.

The use of the probe shown in Figures 3 and 4 is similar to that of the probe shown in Figure 1 in that, when the tip of the probe is dipped into the mass of molten metal, the protective cap 43 melts allowing molten metal below the slag to flow through the opening 41 into the chamber 31 causing the crucible to rise until it engages the stops 37. Molten metal then flows through the openings 35 to fill the crucible. As the probe is withdrawn, the crucible falls with the falling level of the metal until it reaches the bottom of the chamber and the underside of the crucible closes off the opening 41. The oxygen lance 45 and gas exit tube 47 project through the disc 29.

The embodiment shown in Figures 5 and 6 comprises a fixed outer shell 48 having a generally cylindrical bore 49. Within the bore 49 there is an inner cylindrical shell 50 which defines a chamber 51.

The shell 50 is rotatable within the shell 48 by means of a connecting rod 52 which extends through an internal lateral wall 53 of the outer shell 48.

The inner shell has a pair of openings 54 in its side wall which can be aligned with corresponding openings 56 in the side wall of the shell 48. In a similar manner, a pair of openings 58 in the top wall of the inner shell can be aligned with appropriate openings 60 in the lateral wall 53. The oxygen lance is connected to one of the openings 60 in the lateral wail 53 and the gas exit tube is connected to the other opening 60.

In use, the tip is dipped into the mass of molten metal with the inner shell rotated with respect to the outer shell so that the openings 54, 56 are not in communication. When the openings are below the level of the slag, the connecting rod 52 is rotated to rotate the inner shell to align the openings 54, 56 to allow molten metal to allow enter into the chamber 51.

The connecting rod 52 then rotates the inner shell to close off the openings 54, 56 and, in doing so, it connects the openings 58 with the openings 60 in the lateral wall. Oxygen is introduced into the chamber through the lance and causes the sample to be oxidised.

The gases of oxidation leave through the exit tube.

In the embodiments shown in Figures 7 and 8, the refractory body 62 is closed at its outer end 63 and defines a chamber 65 having side wall(s) and an upper wall 66. A pair of openings 68 in the upper wall lead to the oxygen lance and the gas exit tube, respectively. At least one opening 70 is formed in the side wall of the body 62. The body is surrounded by a tubular sleeve 72, the outer end of which rests on a flange 74 projecting from the outer end of the body.

In the Figure 7 arrangement, the tip is dipped into the molten metal with the outer sleeve closing off the opening(s) 70 in the side wall(s).

When the tip is well below the slag on the surface of the molten metal, the outer sleeve 72 is raised by any convenient means to permit molten metal to flow through the opening(s) 70 into the chamber 65. The sleeve is then lowered to close off the opening(s) and the tip is pulied back through the slag to bring a predetermined quantity of molten metal out of the container.

In the Figure 8 arrangement, the refractory outer sleeve 72 is movable relative to the body 62 which defines the chamber and, as the probe structure is lowered into the body of molten metal, the outer sleeve floats up to open the opening 70 in the side walls of the chamber. Metal now flows into the chamber and, when the probe is withdrawn, the outer sleeve 72 moves back to its position resting on the flange 74 thereby closing the chamber to retain the metal sample inside the chamber.

In both these embodiments the combustionoxidising process is as described heretofore.

Referring to Figure 9, a hollow refractory tip 90 has a bottom wall 91 with an opening 92 in it.

A refractory tube 93 has a substantially elongate portion 94 and a U-shaped portion 95. The elongate portion extends substantially vertically through the opening 92 and into the chamber 96 defined by the tip 90. The U-shaped portion may be integral with, or connected to, the portion 94 and is located beneath the chamber. A lateral wall 97 closes off the upper end of the chamber and an oxygen inlet pipe 98 and a gas outlet pipe 99 project through the wall 97 into communication with the chamber.

In use, the tip is dipped into the molten metal and the metal flows through the U-shaped portion 95 and the elongate portion 94 of the tube into the chamber. As the tip is withdrawn from the molten metal, the molten metal in the chamber which is above the level of the top of the tube 94 drains back through the tube leaving a predetermined quantity of molten metal 100 in the chamber. A quantity of molten metal 101 is trapped in the U-shaped tube and this solidifies to close off the tube and, hence, the entrance to the chamber. When the tube has been sealed by the solidification of the molten metal, oxygen is introduced into the chamber to oxidise the molten metal and the gases produced leave the chamber through the gas tube 99.

In all embodiments of the invention, an analysis based on any method for analysing the gaseous discharge may be employed.

While the apparatus and process of the present invention are particularly suitable for determining the quantity of sulphur present in a quantity of molten metal, an analysis for any element forming gaseous products of oxidation is possible.

Claims

Claims:

1. A method of analysing a quantity of molten metal in which a probe structure is dipped into a mass of the molten metal to collect in a chamber of the probe a sample comprising a quantity of the molten metal and, after the chamber has been closed and the probe withdrawn from the mass of molten metal, oxygen is introduced into the chamber to bring about oxidation of the sample and the gases of oxidisation are withdrawn from the chamber and are analysed.

2. A method as claimed in claim 1, in which the action of withdrawing the probe structure from the mass of molten metal closes the chamber.

3. A method as claimed in claim 1 or claim 2, in which a predetermined quantity of molten metal is collected in a refractory crucible in the chamber.

4. A method as claimed in claim 3, in which the step of dipping the probe structure into the mass of molten metal causes the molten metal to raise the crucible in the chamber to open a port through which molten metal enters the chamber, the upward movement of the crucible is limited to allow molten retal to flow into the crucible and the probe structure is withdrawn from the molten metal allowing the crucible to close off the port.

5. A method as claimed in claim 2, in which a solidified portion of the molten metal closes the chamber.

6. A method as claimed in any preceding claim, in which the analysis of the gases of oxidation is based on chemical or physical properties of the gases.

7. A method of analysing a quantity of molten metal substantially as hereinbefore described with reference to the drawings.

8. A probe structure for collecting a sample of molten metal includes a probe tip arranged to be dipped into a mass ot molten metal, said tip comprising a body defining a chamber, the chamber having at least one molten metal entry port which can be closed off when a quantity of molten metal has entered the chamber through the port, means for introducing oxygen into the chamber to bring about oxidation of the sample of molten metal in the chamber, and a gas exit tube from the chamber.

9. A probe structure as claimed in claim 8, in which a refractory crucible for receiving the predetermined quantity of molten metal is located in the chamber and the crucible serves to close off the entry port.

10. A probe structure as claimed in claim 9, in which the entry port is at the outer end of the tip, and the crucible is such that its underside is capable of closing off the entry port, and means are provided in the chamber for limiting movement of the crucible in the direction away from the entry port to a position in which molten metal can flow from the chamber into the crucible.

11. A probe structure as claimed in claim 10, in which the means for limiting movement of the crucible comprise projections incorporated in the side of the body and projecting into the chamber.

12. A probe structure as claimed in claim 8, in which the body defines a cylindrical chamber, a cylindrical shell is rotatable within the chamber, and, in at least one angular position of the shell, an opening in the wall of the shell is aligned with an entry port in the wall of the body to permit molten metal to enter into the shell, and, in a different angular position of the shell, the opening in the wall of the shell is closed and the oxygen introducing means and the gas exit tube are in communication with the interior of the shell.

13. A probe structure as claimed in claim 8, in which an entry port into the chamber is in a side wall of the body, a removable sleeve extends around the side wall of the body to close off said entry port, and means are provided to raise and lower the sleeve to open and close the entry port.

14. A probe structure as claimed in claim 13, in which the action of dipping the probe into and out of a mass of molten metal causes the sleeve to move vertically with respect to the body to open and close the entry port, respectively.

15. A probe structure as claimed in claim 8, in which the molten metal entry port is at the outer end of the tip and includes a substantially vertical tube, the upper end of which projects into the chamber.

16. A probe structure as claimed in claim 15, in which said substantially vertical tube is connected to, or forms part of, a U-shaped tube arranged such that the action of withdrawing the probe from the mass of molten metal causes molten metal to be retained in the tube and to solidify to close off the tube.

17. A probe structure for collecting a sample of molten metal substantially as hereinbefore described with reference to the drawings.