EP2255904B1

EP2255904B1 - Refractory purging porous block assembly

Info

Publication number: EP2255904B1
Application number: EP20090161298
Authority: EP
Inventors: Alexander Kozlov; Norbert Reichert; Patrick Tassot
Original assignee: Calderys France SAS
Current assignee: Calderys France SAS
Priority date: 2009-05-27
Filing date: 2009-05-27
Publication date: 2014-11-26
Anticipated expiration: 2029-05-27
Also published as: TWM402294U; EP2255904A1; WO2010136519A1

Description

The invention relates to a refractory purging porous block assembly which may typically be used at a sink outlet of a tundish in the steel industry.
A tundish contains liquid metal that is intended for example to be poured in a mould. The metal flows out of the tundish by effect of gravity through a sink outlet which is typically located on a lower side on the bottom of the tundish.
A number of undesirable effects may occur when the metal flows through the sink.
A first effect is due to the temperature decrease in the flowing metal. In melted steel, i.e. liquid steel, the temperature decrease causes a self-de-oxidation and consequently a non negligible quantity of endogen type inclusions is formed inside the volume of liquid steel. The endogen type inclusions that flow into the mould may lead to a decrease in quality of the moulded product.
A second effect is due to convective flow of liquid metal along the walls of the tundish. The convective flow causes a wear of the wall accompanied by the release of exogene type non-metallic inclusions in the volume of liquid metal. The exogene type inclusions may have an adverse effect on the moulded product and must therefore be eliminated as much as possible before the liquid metal flows into the mould.
A third effect is linked to the sink outlet itself wherein the liquid metal flowing out through the sink outlet experiences a vortex movement. The endogene type inclusions and exogene type inclusions caught in the vortex movement obtain an increasing kinetic energy and are therefore more difficult to dissociate and extract from the volume of liquid metal.
It is desirable that as many inclusions as possible are extracted from the liquid metal volume before they flow through the sink outlet and become impurities in the moulded product.
A fourth effect is the cluttering of the sink outlet. A part of the inclusions will naturally rise through the volume of liquid metal and gather in a layer of slag that floats on the surface of the liquid metal. The slag may be caught in the flow of liquid metal, especially when the liquid metal experiences vortex movement, and subsequently led to the sink outlet. This again may degrade the quality of the moulded product but in addition causes a clogging of the sink outlet.
It is known to prevent the slag from reaching the sink outlet and therewith avoid clogging it. This may be achieved by blowing gas from all around the borders of the sink outlet.
European patent application published under EP 0 282 824 A2 discloses a device in which the sink outlet of the tundish is completely surrounded by gas permeable refractory elements which are embedded in the lining of the tundish. Gas-dispensing means provide the gas permeable elements with gas, which then bubbles through the liquid metal. The permeable refractory elements are separated from the sink outlet hole through which the liquid metal flows by elements of non permeable refractory material. The document further states:-

that the flow of bubbles creates a curtain around the sink outlet hole,
that the area inside the curtain, i.e., the area above the sink outlet hole is free of slag, and
that the liquid metal flows without slag inclusions.

As the quantity of slag to keep away from the sink outlet hole increases, the rate of gas injection is increased. Although EP 0 282 824 A2 mentions the existence of a vortex it also states that the injection of gas in not intended to stop the vortex but rather to act on the slag. However EP 0 282 824 A2 is not concerned about addressing the extraction of endogene type or exogene type of inclusion. Further, EP 2 025 431 A1 discloses a device for metal refining, in which the tuyere is placed axially to a flow of effluent metal and bubbles of rare gas are directed to outlet inclusions to refinery slag. However, the device disclosed in D1 is for use with pony ladies.

SUMMARY OF INVENTION

In a first aspect the invention provides a refractory purging porous block assembly for use at a sink outlet of a tundish. The assembly comprises a main body comprising a first material, a bore hole extending from a top side of the main body to a bottom side of the main body, whereby the top side is towards the tundish when the refractory purging porous block is connected with the sink outlet, the bore hole being delimited by an internal peripheral surface of the main body between the top side and the bottom side, the main body further comprising an outer peripheral surface between the top side and the bottom side, wherein the first material has a first permeability. The assembly further comprises a groove made on the top side of the main body, the groove surrounding the bore hole, and a porous body comprising a second material and fitting inside the groove to surround the bore hole, wherein the second material has a second permeability, the second permeability being of higher value than the first permeability. The assembly further comprises a gas supply conduit formed in the main body and allowing gas to flow from an opening on the outer peripheral surface of the main body to the groove, wherein the assembly is characterised in that the groove has a circular cross-section.
In a first preferred embodiment the refractory purging porous block assembly further comprises a first gas supply groove formed in a wall of the groove and surrounding the bore hole, whereby the gas supply conduit is formed between the opening on the outer peripheral surface and the first gas supply groove.
In a second preferred embodiment the refractory purging porous block assembly further comprises a second gas supply groove formed in a wall of the porous body and surrounding the bore hole, whereby the gas supply conduit is formed between the opening on the outer peripheral surface and the second gas supply groove.
In a third preferred embodiment of the refractory purging porous block assembly, the main body comprises a first part which comprises the first material, the first part being delimited towards the bore hole by the internal peripheral surface, and a second part which comprises a third material, the second part being delimited towards the bore hole by the first part, and in a direction pointing away from the bore hole by the outer peripheral surface, wherein the third material has a third permeability and the third permeability is of lower value than the second permeability.
In a fourth preferred embodiment the refractory purging block assembly is shaped as a hollow truncated cone, the extremity of the hollow truncated cone having the largest surface being on the bottom side of the main body.
In a fifth preferred embodiment of the refractory purging block assembly, the bore hole has a top surface section at the top side and a bottom surface section at the bottom side, the top surface section being of smaller size than the bottom surface section.
In a sixth preferred embodiment of the refractory purging block assembly, the first material is a first dense refractory material that has an open porosity less than 30% measured after the EN1402 norm, and has a gas permeability by argon less than 10 Nanoperm, and the second material is a porous refractory material that has an open porosity more than 30% measured after the EN1402 norm, and has a gas permeability by argon higher than 10 Nanoperm.
In a seventh preferred embodiment of the refractory purging block assembly, the first material and / or the second material comprises one or more of the following: alumina, alumina-spinel, alumina carbon.
In a second aspect, the refractory porous purging block assembly is connected to a sink outlet of a tundish for metal treatment.
In a third aspect, the invention provides a method for producing a refractory purging porous block assembly, the assembly being for use at a sink outlet of a tundish. The method comprises the steps of preparing a first mould for a main body comprising a bore hole extending from a top side of the main body to a bottom side of the main body, whereby the top side is the side of the main body intended to be oriented towards the tundish when the refractory purging porous block assembly is connected with the sink outlet, the bore hole being delimited by an internal peripheral surface of the main body between the top side and the bottom side, the main body further comprising an outer peripheral surface between the top side and the bottom side, and the main body further comprising a groove with a circular cross-section made on the top side of the main body and surrounding the bore hole. The method further comprises casting at least a first material into the first mould, the first material having a first permeability, to obtain the main body, forming a gas supply conduit in the main body connecting an opening on the outer peripheral surface to the groove, and heating the main body at a determined temperature in order to harden the first material. The method further comprises providing a porous body that is shaped to surround the bore hole, whereby the porous body comprises a second material, and the second material has a second permeability that is of higher value than the first permeability, and whereby the porous body completely fills the groove in the sense that the porous body is in contact with a first wall of the groove delimiting the groove from the porous body towards the bore hole, and the porous body is in contact with a second wall of the groove delimiting the groove from the porous body in a direction away from the bore hole, the contact between the first wall and the porous body, and between the second wall and the porous body respectively extending all around the bore hole, the groove further including a lower wall of the groove located towards the bottom side between the first wall and the second wall. The method further comprises positioning the porous body in the groove.
In an eighth preferred embodiment of the method, the preparing of a first mould further is further specified in that in the groove of the main body, in the lower wall, a first concave gas supply groove is included, that extends to surround the bore hole, and the forming of the gas supply conduit in the main body is to connect the opening on the outer peripheral surface to the first gas supply groove.
In a ninth preferred embodiment of the inventive method, the positioning in the groove of the porous body involves casting at least the second material into the groove, and the method further comprises secondly heating the porous body at the determined temperature in order to harden the second material.
In a fourth aspect the invention provides a method for producing a refractory purging porous block assembly, the assembly being for use at a sink outlet of a tundish, whereby the method comprises the steps of preparing a second mould for a porous body, the mould being shaped to contain the porous body, whereby the porous body is shaped as a first elongated shaft which is hollow and which has a circular cross-section, casting at least a second material into the second mould to obtain the porous body, whereby the second material has a second permeability, and heating the porous body at a determined temperature in order to harden the second material. The method further comprises preparing a third mould for a second part of the main body, which has the shape of a second elongated hollow shaft delimited on the longitudinal lateral side by an outer peripheral surface, the outer peripheral surface extending between a top side of the second shaft and a bottom side of the second shaft, whereby the top side is towards the tundish when the refractory purging nozzle is connected with the sink outlet, and the bottom side is opposite from the top side, and the second part of the main body comprises a hole connecting the top side and the bottom side, whereby the second part of the main body is delimited towards the hole by a profiled surface, and the profiled surface comprises a notch extending all around the hole, the notch further extending from the top side and having a shape to accommodate the porous body. The method further comprises casting at least a third material into the third mould to obtain the second part of the main body, whereby the third material has a third permeability and the third permeability is of lower value than the second permeability, forming a gas supply conduit in the second part of the main body connecting an opening on the outer peripheral surface to the notch, and heating the second part of the main body at the determined temperature to harden the third material. The method further comprises fitting the porous body into the notch, providing a third elongated shaft that is delimited on a first longitudinal lateral side by a first outer peripheral surface, and the third elongated shaft defining inside the hole a fourth mould between the first peripheral surface, the porous body, a part of the profiled surface distinct from the notch, the top side and the bottom side, whereby the fourth mould is shaped to fit a first part of the main body, inserting said third elongated shaft into the hole of the second part, casting at least a first material into the fourth mould to obtain the first part of the main body, and heating the first part of the main body at the determined temperature in order to harden the first material.
In a tenth preferred embodiment of the method according to the fourth aspect, the step of preparing the third mould for the second part of the main body further forms, in a lower part of the notch opposite to the top side, a first concave gas supply groove that extends to surround the hole, and the forming of the gas supply conduit in the second part of the main body is to connect the outer peripheral surface to the first gas supply groove.
In an eleventh preferred embodiment of the method according to the fourth aspect, the step of preparing the second mould for the porous body further forms in an extremity of the porous body intended to be oriented to the bottom side when the porous body is fitted into the notch, a second concave gas supply groove that extends around the hole when the porous body is fitted into the notch.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be better understood in the light of examples of preferred embodiments described hereunder and with reference to Figures, whereby

Fig. 1: contains a schematic representation of an example refractory purging porous block assembly according to the invention, and inserted into a sink outlet of a tundish;
Fig. 2: contains a schematic view of an example refractory purging porous block assembly according to the invention;
Fig. 3: contains a schematic view from a top of an example refractory purging porous block assembly according to the invention;
Fig. 4: contains a schematic view of a further example embodiment of the inventive refractory purging porous block;
Figs. 5A to Fig. 5C: show magnified schematic views of example gas supply conduits as can be found in a refractory porous block of the invention;
Fig. 6: illustrates in a flow chart an example embodiment of a method for producing a refractory purging porous block assembly according to the invention;
Fig. 7: shows various part of a first mould in an example embodiment according to the invention;
Fig. 8: shows a detail of the first mould according to the invention;
Fig. 9: shows a further detail of the first mould according to the invention;
Fig. 10: shows the first mould of Fig. 7 filled with a first material according to the invention;
Figs. 11 and 12: show different views of the main body according to an example embodiment of the invention;
Figs. 13 and 14: show different views of the main body after an opening is formed in the main body for a gas supply conduit according to the invention;
Fig. 15: shows a main body with a groove that is filed by a porous body according to an example embodiment of the invention;
Fig. 16: shows a mould for preparing a porous body according to an example embodiment of the invention;
Fig. 17: shows the mould of Fig. 16 containing a porous body cast therein according to the invention;
Fig. 18: shows a porous body according to an embodiment of the invention;
Fig. 19: illustrates in a flow chart a further example embodiment of a method for producing a refractory purging porous block assembly according to the invention;
Fig. 20: shows an example of a second part of the main body in a mould according to an embodiment of the invention;
Fig. 21: shows the second part of the main body from Fig. 20 including a porous body fitted therein;
Fig. 22: shows the second part of the main body from Fig. 21 with an elongated shaft positioned to form a fourth mould for a first part of the main body according to an example embodiment of the invention;
Fig. 23: shows the assembly of Fig. 22 after the first part of the main body has been cast according to an example embodiment of the invention.

DESCRIPTION OF EXAMPLE EMBODIMENTS

The inventors found through experimentation and calculations that it is possible to extract the endogene and exogene type of inclusions from the liquid metal by blowing bubbles of an inert gas through the volume of liquid metal. The surface of inert gas in contact with the inclusions causes the inclusions to be transported to the upper surface of the liquid metal as the bubbles rise through the liquid metal liquid. The transported inclusions then gather in the layer of slag.
The efficiency of extraction is dependent on the total specific surface of the bubbles of inert gas created through the bubbles in the liquid metal. The total specific surface in turn depends on the number of bubbles, i.e., the rate of gas flow, and the size of the bubbles.
The rate of gas flow through the liquid metal will in the present invention typically be higher than in devices known from prior art, the latter devices only aiming at keeping the slag out of the sink outlet. Although the gas flow can be set at values as high at 1500 l/min. using the invention, this is generally not necessary and even not desirable. A typical rate of gas flow during the treatment may lies between 20 and 400 l/min.
A diameter of the gas bubbles, i.e, the size of the gas bubbles must also be optimised to obtain the highest possible exposed surface of gas in the liquid metal. The inventors achieved best results for bubbles having a diameter less than or equal to 5 mm. The diameter of the bubbles may be influenced by the choice of material and the pressure of the gas passing through pores of the material. For example, relatively speaking a material with a lower porosity, i.e., a material having smaller grains will produce smaller bubbles than a material with a higher porosity, i.e., a material having coarser grains.
Fig. 1 contains a schematic representation of an example refractory purging porous block assembly 100 in a lateral vertical section, inserted into a sink outlet 101 formed in a lining 102 of a tundish (only partly shown in Fig. 1). Liquid metal (not shown in Fig. 1) contained in the tundish may flow through a bore hole 103 as indicated by an arrow 104.
Fig. 2 contains a schematic and more detailed view of the refractory purging porous block assembly 100 which comprises a main body 200, a groove 201 and a porous body 202.
The main body 201 comprises a first material and has the bore hole 103 that extends from a top side 203 of the main body to a bottom side 204 of the main body. The bore hole 103 is delimited by an internal peripheral surface 205 of the main body between the top side 203 and the bottom side 204. The main body further has an outer peripheral surface 206 extending between the top side 203 and the bottom side 205.
The groove 201 is made on the top side 203 of the main body and surrounds the bore hole 103. This will be better seen in Fig. 3.
The porous body 202 comprises a second material and is shaped to fit inside the groove 201 in a manner that the porous body also surrounds the bore hole 103.
The porous body 202 completely fills the groove 201 in the sense that it is in contact with a first wall 214 of the groove 201 delimiting the groove 201 from the porous body towards the bore hole 103, and with a second wall 215 of the groove 201 delimiting the groove 201 from the porous body in a direction away from the bore hole 103. The contact between the first wall 214 and the porous body, and between the second wall 215 and the porous body respectively extends all around the bore hole.
In one example embodiment the porous body 202 may be obtained by casting of the second material into the groove 201. In this one example the second material of the porous body 202 is generally directly in contact with the first wall 214 and the second wall 215.
In a further example embodiment the porous body 202 may be produced separately from the main body 200 and then be mortared into the groove 201. In this further example embodiment a dense mortar joint may participate in establishing the contact between the first wall 214 and the porous body, and between the second wall 215 and the porous body.
The first material has a first permeability. The second material has a second permeability which is of higher value than the first permeability.
A gas supply conduit 207 is formed in the main body and allows gas to flow from an opening 208 on the outer surface peripheral surface 206 to the groove 201.
In the example embodiment of Fig. 2, the refractory purging porous block has a main body 200 cast as a single massive piece. The refractory purging porous block is in overall shaped as a hollow truncated cone, i.e., an upper surface section at the top side 203 defines a disk having a smaller size than a lower surface section at the bottom side 204. Hence a diameter 209 of the upper surface section is smaller than a diameter 210 of the lower surface section. The truncated cone shape is particularly advantageous to position the purging porous block at the sink outlet. Nevertheless other shapes are possible and comprised in the scope of the invention.
The first material qualifies as a non-permeable material in the sense that it substantially avoids gas passing through. It may preferably consist of a relatively dense and castable material.
The second material qualifies as a permeable material in the sense that it allows gas to pass through the porous body 202.
The second material making up the porous body 202 may be of similar nature as the first material with the difference that a value of the second permeability is higher than a value of the first permeability. This can for example be realized by selecting a grain size of the second material and a distribution of the grain size inside the material to obtain a desired permeability to gas.
Preferably the grain size in the second material, and hence the permeability of the second material is adjusted in a compromise to also achieve a determined mechanical resistance. The grain size and distribution inside the material may be adjusted for example to obtain a porosity in a range from 30% up to 70%.
Hence preferably the second material is a porous refractory material that has an open porosity of more than 30% measured after the EN1402 norm, and a gas permeability by argon higher than 10 Nanoperm (10^-9.cm²). It will be understood that the overall permeability of the porous body is dependent from the size of the porous body, but also from the temperature and the type of gas used.
The second material may be of castable nature in a manner that the porous body is obtainable through casting of such second material.
Preferably the first material is a dense material, i.e., a refractory material that has an open porosity less than 30% measured after the EN1402 norm, and a gas permeability by argon less than 10 Nanoperm (10^-9.cm²). It will be understood that the overall permeability of the main body 200 is dependent from the size of the main body, but also from the temperature and the type of gas used.
The first material making up the main body 200, and / or the second material making up the porous body 202 may for example be constituted from alumina, alumina-spinel, alumina carbon or other basic materials well known from a person skilled in the art.
Although the first material and the second material have different permeabilities, it is possible to manufacture both with similar mechanical resistance to wear.
In the example embodiment of Fig. 2, the bore hole 103 has a top surface section with diameter 211 at the top side 203, the top surface having a smaller size than a bottom surface section with diameter 212 at the bottom side 204. Nevertheless other shapes and sizes are possible for the bore hole and comprised in the scope of the invention.
It is generally desirable that the main body 200 has an inner wall 216 delimited by the internal peripheral surface 205 and the first wall 214, that will be as thin as possible in order to have the flow of gas from the porous body 202 as close as possible from the bore hole 103 and prevent a vortex movement in the liquid metal flowing through the bore hole 103. However for practical reasons related to the mechanical resistance of the material used for the main body 200, there is a minimal wall thickness for the inner wall 216 that will be able to confer a sufficient mechanical strength and resistance to strains and mechanical wear imposed upon the purging porous block assembly 100. The present inventors have been able to achieve a wall thickness of about 10 mm. Nevertheless, the value of 10 mm is an example value only, and a person skilled in the art will understand that smaller values or larger values may be used while remaining in the scope of the invention. The present inventors have also found that it is preferable to have a wall thickness less than 100 mm. Again this value of 100 mm is an example for preferable embodiments only but it is understood that higher values may well be used while remaining in the scope of the invention.
Fig. 3 contains a view in direction of axis 213 of Fig. 2 of the refractory purging porous block assembly 100. In this particular example, the main body 200 at the top side 203 defines an inner concentric ring 300 and an outer concentric ring 301. The porous body 202 defines a middle concentric ring 302 fitted between the inner concentric ring 300 and the outer concentric ring 303.
Fig. 3 further illustrates boundaries of the bore hole 103 and the main body 200, i.e.,

the top surface section of the bore hole as a first circle 303,
the bottom surface section of the bore hole as a second circle 304 in a dotted line,
the upper surface section at the top side 203 of the main body as a third circle 305, and
the lower surface section at the bottom side 204 of the main body as a fourth circle 306.

The view contained in Fig. 3 shows the main body 200 and the porous body 202 as being symmetric to the axis 213. However, it will be understood that this embodiment is an example only and that in different embodiments, different shapes may be used around 213 including shapes that do not exhibit any symmetry through axis 213.
When the refractory purging porous block 100 is in use with a tundish containing liquid metal, an inert gas such as Argon may be injected through the gas supply conduit 207. The gas circulates through the whole porous body 202 and exits into the liquid metal as bubbles. The refractory purging porous block assembly according to the invention enables a flow of bubbles all around the sink outlet, i.e., substantially axially to the flow of liquid metal through the sink outlet.
An flow of inert gas through liquid metal generally allows to extract non-metallic inclusions out of the liquid metal. The inclusions adhere to bubbles of inert gas and are transported by the latter to form a layer of slag at the surface of the liquid metal.
The flow of gas bubbles from around the sink outlet is an effective means to reduce any vortex movement of the liquid metal flowing towards or out off the sink outlet, and to reduce the kinetic energy of non-metallic inclusions therein.
At the same time, due to the reduced kinetic energy and the effect of adherence with non-metallic inclusion, a large relative amount of the latter inclusions are extracted towards the layer of slag by means of the gas bubbles.
The flow of inert gas, and thus the amount of gas entering the liquid metal is adjusted in such a manner that gas bubbles are not allowed to flow through the sink outlet with the liquid metal, and no gas hence reaches any mould into which the liquid metal is to be cast.
The flow of inert gas such as Argon through the liquid metal further allows to prevent endogene inclusions from passing through the sink outlet. Such endogene inclusions result from the temperature decrease in the flowing metal, which causes a self-de-oxidation and consequently a non negligible quantity of endogen type inclusions is formed inside the volume of liquid steel.
A further advantage of blowing inert gas through the liquid metal just before it crystallizes is the lowering of hydrogen content to relatively low values, and the at least partly removal of Nitrogen according to the Sieverts law.
The bubbles of Argon contain neither hydrogen nor nitrogen, and therefore have the effect of a vacuum chamber on hydrogen and nitrogen which are included in the liquid metal.
The lowering of the hydrogen content is particularly efficient because hydrogen has a relatively high speed of diffusion and a lower likeliness to enter any chemical bonds than nitrogen.
On the contrary the extent of diffusion for nitrogen is lower than that for hydrogen. This property of nitrogen together with its' affinity to enter chemical bonds with at least a number of metals render its extraction by means of argon gas bubbles very difficult.
Empirical measurements in liquid metal treated with the inventive refractory purging porous block have shown that the hydrogen content can be reduced at least by 30% and at most by 40%. Concerning nitrogen the content of this can be reduced at least by 0,5ppm at most by 10,5ppm.
Further measurements have been made to show the effect of the inventive refractory purging porous block on macro structure defects in the obtained metal product.

In a first series of measurements, 13 ladles of liquid metal were investigated without any injection of Argon. A ladle includes introducing liquid metal in the tundish and having the liquid metal flow through the sink outlet to be crystallised. The crystallized metal is then measured in its macro structure to detect defects such as central porosity, axial chemical irregularity, liquid strips and splits, and peripheral punctual contamination. The obtained results are displayed in Table 1, wherein the first column contains the macro structural defect, the second column contains numbers of ladles that resulted outside a determined limit of tolerance and the third column contains number of ladles inside the determined limit of tolerance. The determined limit of tolerance was set according to a internal standard and is not further defined here. It is understood that the tolerance is specific to each particular macro structure. At the outcome of the first series of 13 measurements, it appeared that 6 from 13 ladles, i.e., 46,1% were defect because of being outside of the limits of tolerance. The details are in the following Table 1:

TABLE 1:

observed defects for 13 ladles without injection of Argon
Macro structure	Ladles
	Outside limit of tolerance	Inside limit of tolerance
Central porosity		13 (100%)
Axial chemical irregularity		13 (100%)
Liquid strips, splits	5 (38,5%)	8 (61,5%)
Peripheral punctual contamination	4 (30,8%)	9 (69,2%)

In a second series of measurements, 6 ladles were investigated with injection of Argon by means of the inventive refractory purging porous block assembly. At the outcome of the second series of 6 measurements, it appeared that was 2 from 6 ladles, , i.e., 33% were defect because of being outside of the limits of tolerance. The details of the obtained results are displayed in Table 2:

TABLE 2:

observed defects for 6 ladles with Argon injection
Macro structure	Ladles
	Outside limit of tolerance	Inside limit of tolerance
Central porosity	1 (16,7%)	5 (83,3)
Axial chemical irregularity		6 (100%)
Liquid strips, splits	1 (16,7%)	5 (83,3%)
Peripheral punctual contamination		6 (100%)

It could be concluded that between the first series of measurements and the second series of measurements there was an overall improvement of 12,8% of the ladles that are inside the limits of tolerance due to injection of argon with the inventive refractory purging porous block assembly.
3 ladles among the 6 ladles in the series of measurements evaluated in Table 2 were investigated in more detail. The ladles in the series of Table 2 were of course subjected to Argon injection by means of the inventive refractory purging porous block assembly.

The following Table 3 contains results again for measurement of macro structural defects in the crystallised metal such as central porosity, axial chemical irregularity, liquid strips and splits, and peripheral punctual contamination. The first column contains the macro structural defect, the second column contains maximum levels of tolerance in a unit not further explicated here but as used in certain metal melting facilities, and the third to fifth column contain measurement results in the same unit as for the second column for the 1^st, 2^nd and 3^rd ladle respectively.

TABLE 3:

values for defects in 3 ladles with Argon injection

Macro structure	Maximum level of tolerance	Values for Ladles (same unit as in 2^nd column)
		1^st	2^nd	3^rd
	(arbitrary unit)
Central porosity	<= 3	1	1	1
Axial chemical irregularity	<= 3	1,5	1,5	1
Liquid strips, splits	<= 2	1,5	0,5	0,5
Peripheral punctual contamination	<= 2	0,5	0,5	0,5

The results in Table 3 show that for all macro structure defects, the values measured in the Argon treated ladle lies below the set maximum value.
The following Table 4 contains measurement of contamination with non-metallic particles for the same ladles as discussed in Table 3. The measurements concern quantitative detection of round oxides, flat oxides, deformable oxides, brittle silicates, non-deformable silicates and sulphides. Each ladle was subjected to 2 samples, the latter each of which was subjected to the quantitative detection.

The first column in Table 4 contains the reference to the ladle concerned (same ladles as in Table 3), the second column contains the sample concerned for the respective ladle, the 3^rd to 8^th column contain measurement values of quantities of non metallic particles in the samples. The unit used is arbitrary and not further explicated here but the same as the unit used in the last line of Table 4 which exhibits maximum levels of tolerance according to a standard in certain metal melting facilities. The foremost last line in Table 4 shows averages of values over all samples.

TABLE 4:

quantities of non-metallic particles in ladles 1-3 under Argon treatment
		Content of non-metallic particles (arbitrary unit)
Ladle Nr	Sample Nr	Round oxides	Flat oxide	Deformable oxides	Brittle silicates	Non-deformabl oxides	Sulphides
1^st	1	0,5	0	0	0	3	3
	2	0,5	0	0	0	3	3
2^nd	1	0,5	0	0	0	2,5	2
	2	0,5	0	0	0	3,5	3
3^rd	1	0,5	0	0	0	2,5	2
	2	0,5	0	0	0	2,5	2
Average		0,5	0	0	0	2,83	2,5
Tolerance		<=4,5	<= 4,5	<= 4,5	<= 4,5	<= 5	<= 4,5

The values shown in Table 4 illustrate that the Argon treatment induces quantities of non-metallic particles that lie under the set value of tolerance.
Fig. 4 contains a further example embodiment of the inventive refractory purging porous block in a schematic illustration.
The main body 200 of the refractory purging porous block 400 comprises a first part 401 and a second part 402.
The first part 401 of the main body is delimited towards the bore hole 103 by the internal peripheral surface 205.
The second part 402 is delimited towards the bore hole 103 by the first part 401, and in a direction pointing away from the bore hole 103 by the outer peripheral surface 206.
The first part 401 may comprise the first material.
The second part 402 may comprise a third material having a third permeability. A value of the third permeability is lower than the permeability of the second material.
The use of the first part 401 and the second part 402 allows an increased flexibility in the design of the refractory purging porous block in that different mechanical properties or refractory properties may be chosen for the first part surrounding the bore hole 103 and the second part surrounding the first part.
Fig. 4 further illustrates the porous body 202 fitted inside the groove 201 and the gas supply conduit 207 formed in the main body, which allows gas to flow from the opening 208 on the outer surface peripheral surface 206 to the groove 201. The gas conduit 207 leads to a first gas supply groove 403 which is formed in the wall of the groove 201 and surrounds the bore hole 103. Hence gas injected through the gas supply conduit 207 may efficiently be distributed around the whole circumference of the porous body 202.
Fig. 5A shows a magnified view of the gas supply conduit 207 of Fig. 4. The first gas supply groove 403 is formed in the wall of the groove 201. A second gas supply groove 404 is formed in the porous body 202 across from the first gas supply groove 403. The second gas supply groove surrounds the bore hole while remaining across from the first gas supply groove 403. The first gas supply groove 403 and the second gas supply groove 404 constitute a pipe that allows to provide gas around the whole circumference of the porous body 202.
Fig. 5B shows a further embodiment of a mouth of the gas supply conduit 207 towards the porous body 202 comprising the first gas supply groove 403 only.
Fig. 5C shows a still further embodiment of the mouth of the gas supply conduit 207 towards the porous body 202 comprising the second gas supply groove 404 only.
It is understood that the embodiments of the first and second gas supply grooves shown in Figs. 5A-C are examples only and that the cross section of the grooves may vary while remaining in the scope of the invention. Furthermore the first and second gas supply grooves may be used in different embodiments of the refractory porous block than the one shown in Fig. 4.
An example embodiment of a method for producing a refractory purging porous block assembly of the type shown in Fig. 2, according to the invention will now be described.
Fig. 6 illustrates in a flow chart different steps involved in producing the refractory purging porous block assembly. As previously explained the assembly is for use at a sink outlet of a tundish.
The method comprises initially preparing a first mould for a main body as shown in box 600. The first mould is shaped such that it may contain the main body. Figs. 7 to 9 illustrate various parts of the first mould which is built up to obtain the main body comprising the bore hole extending from the top side of the main body to the bottom side of the main body. Fig. 7 shows the various parts assembled with a view on a side that will become the top side of the main body. Fig. 8 shows a ring that is used to shape the groove in the mould. Fig. 9 shows an elongated part of the mould that is used to shape the bore hole in the mould.
The main body is then cast using the first mould by casting with at least the first material as illustrated by box 601. Fig. 10 illustrates the first mould filled with at least the first material. Figs 11 and 12 illustrate different views at various angles of the cast main body which still has the elongated part of the mould in the bore hole.
The gas supply conduit is then formed in the main body to connect an opening on the outer peripheral surface of the main body with the groove as illustrated by box 602. Fig. 13 shows the main body that has an opening on the outer peripheral surface located towards the bottom side of the main body. Fig. 14 shows the main body at a different angle than in Fig. 13 in a manner that allows to see a lower wall of the groove in which the gas supply conduit emerges.
The main body may then be heated at a determined temperature as shown by box 603 to allow the first material making up the main body to harden.
Finally, as illustrated by box 604, the porous body is positioned in the groove. Fig. 15 shows the main body with the main groove filled by the porous body.
The first mould may in a preferred embodiment be prepared such that it produces in the groove of the main body, in the lower wall thereof, the first gas supply groove. In this case the first gas supply groove is preferably filled with a filling material before the porous body is positioned in the groove. This is particularly advantageous if the porous body is cast directly in the groove since the filling material allows maintaining the first supply groove free of the second material used to cast the porous body. Once the porous body is cast, the main body and the porous body are heated at the determined temperature to harden the second material. While the determined temperature is reached, the filling material clears the first gas supply groove. In case the second gas supply groove in the porous body is desired, together with the first gas supply groove such as illustrated in Fig. 5A or without the first gas supply groove such as illustrated in Fig. 5C, before casting the porous body into the groove, a ring of filling material is formed on the filled first gas supply groove or the lower wall of the groove depending on the case, whereby the ring surrounds the bore hole, and the ring forms a convex shape on the bottom wall. The porous body is then cast, and while the main body and the porous body are heated to the determined temperature, the filling material clears the second gas supply groove.
Alternatively, in case a readily produced porous body is positioned into the groove, the filling material may not be required in the first gas supply groove. In this preferred embodiment the readily produced porous body may be mortared using the dense mortar which forms a joint between the porous body and the main body.
Fig. 16 illustrates an example of a mould for preparing and casting a readily produced porous body. The mould of Fig. 16 is shown disassembled to visualise its constituents including a disk which is shaped to form the second gas supply groove in the porous body, two halves of outer moulds that when assembled form an outer wall of a cylinder delimiting the porous body, and a cylinder shaped part that is designed to be axially centred on the disk and to delimit an inner wall of the porous body.
Fig. 17 illustrates the mould of Fig. 16 in an assembled manner but with the cylinder shaped part removed after the porous body has been cast.
Fig. 18 shows the porous body extracted from the mould with a view on a side on which the second gas supply groove is formed.
Fig. 19 illustrates in a flow chart different steps involved in a further example method for producing the refractory purging porous block assembly. Again the assembly is for use at a sink outlet of a tundish. The further method may be used to obtain a purging block assembly of a type shown in Fig. 4.
As illustrated by box 1900, the method involves preparing a second mould for casting the porous body, whereby the second mould is shaped to contain the porous body. The porous body is intended to be shaped as a first elongated shaft which is hollow. The second mould may for example be of the type shown in Figs. 16-17 and the resulting porous body resulting there from as shown in Figs. 17-18.
At least the second material is then cast into the second mould to obtain the porous body as shown in box 1901. The porous body is thereafter heated to the determined temperature in order to harden the second material as shown in box 1902.
In box 1903, a third mould is prepared for the second part of the main body. The second part of the main body has the shape of a second elongated hollow shaft delimited on the longitudinal lateral side by the outer peripheral surface, the latter extending between a top side of the second shaft and a bottom side of the second shaft. The top side is towards the tundish when the refractory purging porous block assembly is connected with the sink outlet, and the bottom side is opposite from the top side. The second part of the main body further comprises a hole connecting the top side and the bottom side, whereby the second part of the main body is delimited towards the hole by a profiled surface. The profiled surface comprises a notch extending all around the hole, the notch further extending from the top side and having a shape to accommodate the porous body.
In box 1904, at least the third material is cast into the third mould to obtain the second part of the main body.
In box 1905, the gas supply conduit is formed in the second part of the main body to connect an opening on the outer peripheral surface to the notch.
Fig. 20 illustrates an example of the second part of the main body after it has been cast and the gas supply conduit formed, whereby the second part is still fitted inside a part of the third mould surrounding the outer peripheral surface.
Coming back to Fig. 19, box 1906 illustrates a step of heating the second part of the main body at the determined temperature to harden the third material.
In box 1907 the porous body is fitted into the notch. This is also illustrated in Fig. 21, where the porous body of Fig. 18 is fitted into the notch of the second part of the main body from Fig. 20.
In a further step represented in box 1908, a third elongated shaft is inserted into the hole of the second part. The third elongated shaft is delimited on a first longitudinal lateral side by a first outer peripheral surface. Once inserted into the hole, the third elongated shaft defines inside the hole a fourth mould between the first peripheral surface and the porous body, and a part of the profiled surface distinct from the notch, and the topside and the bottom side. The fourth mould is shaped to fit a first part of the main body. Fig. 22 illustrates the assembly shown in Fig. 21 with an example of the third elongated shaft inserted inside the hole to form the fourth mould.
Finally, in steps from boxes 1909 and 1910, at least the first material is cast into the fourth mould to obtain the first part of the main body, and the latter is heated at the determined temperature in order to harden the first material.
Fig. 23 illustrates the assembly of Fig. 22 after the first part of the main body has been cast. The fourth mould is partly disassembled due to the fact that the third elongated shaft is removed in Fig. 23.
Preferably, the fitting of the porous body involves mortaring the porous body into the notch using a dense mortar to form a joint between the porous body and notch of the profiled surface. The joint in this case extends all around the hole.
Further preferably, the preparing of the third mould for the second part of the main body takes into account in a lower part of the notch, located opposite to the top side, the first concave gas supply groove that extends to surround the hole, similar to the groove 403 illustrated in Figs. 5A and 5B. In this case the step of forming the gas supply conduit in the second part of the main body is to connect the outer peripheral surface to the first gas supply groove.
Still further preferably, the preparing of the second mould for the porous body further takes into account in an extremity of the porous body intended to be oriented to the bottom side when the porous body is fitted into the notch, the second supply groove that extends around the hole when the porous body is fitted into the notch. The second supply groove is similar to the groove 404 illustrated in Figs. 5A and 5C.

100: refractory purging porous block assembly
101: sink outlet
103: bore hole
200: main body
201: groove
202: porous body
203: top side (of the main body)
204: bottom side (of the main body)
205: internal peripheral surface (of the main body)
206: outer peripheral surface (of the main body)
207: gas supply conduit
208: opening
211: top surface section
212: bottom surface section
214: first (inner) wall of the groove
215: second (outer) wall of the groove
217: lower wall of the groove
218: third elongated shaft
400: refractory purging porous block assembly
401: first part (of the main body)
402: second part (of the main body)
403: first (concave) gas supply groove
404: second gas supply groove

600: preparing a first mould
601: casting at least a first material
602: forming a gas supply conduit
603: heating the main body
604: positioning the porous body in the groove
1900: preparing a second mould
1901: casting at least a second material
1902: heating the porous body
1903: preparing a third mould
1904: casting a third material
1905: forming a gas supply conduit
1906: heating the second part of the main body
1907: fitting the porous body
1908: inserting an elongated shaft
1909: casting a first material
1910: heating the first part

Claims

A refractory purging porous block assembly (100, 400) for use at a sink outlet (101) of a tundish, the assembly comprising
a main body (200) comprising a first material, a bore hole (103) extending from a top side (203) of the main body (200) to a bottom side (204) of the main body (200), whereby the top side (203) is towards the tundish when the refractory purging porous block is connected with the sink outlet (101), the bore hole (103) being delimited by an internal peripheral surface (205) of the main body (200) between the top side (203) and the bottom side (204), the main body (200) further comprising an outer peripheral surface (206) between the top side (203) and the bottom side (204), wherein the first material has a first permeability,
a groove (201) made on the top side (203) of the main body (200), the groove (201) surrounding the bore hole (103),
a porous body (202) comprising a second material and fitting inside the groove (201) to surround the bore hole (103), wherein the second material has a second permeability, the second permeability being of higher value than the first permeability,
a gas supply conduit (207) formed in the main body (200) and allowing gas to flow from an opening (208) on the outer peripheral surface (206) of the main body (200) to the groove (201);
characterised in that the groove (201) has a circular cross-section.
The refractory purging porous block assembly (100, 400) of claim 1, further comprising
a first gas supply groove (403) formed in a wall of the groove (201) and surrounding the bore hole (103),
whereby the gas supply conduit (207) is formed between the opening (208) on the outer peripheral surface (206) and the first gas supply groove (403).
The refractory purging porous block assembly (100, 400) according to any one of claims 1 or 2, further comprising
a second gas supply groove (404) formed in a wall of the porous body (202) and surrounding the bore hole (103),
whereby the gas supply conduit (207) is formed between the opening (208) on the outer peripheral surface (206) and the second gas supply groove (404).
The refractory purging porous block assembly (100, 400) of any one of claims 1 to 3 wherein the main body (200) comprises a first part (401) which comprises the first material, the first part (401) being delimited towards the bore hole (103) by the internal peripheral surface (205), and a second part (402) which comprises a third material, the second part being delimited towards the bore hole (103) by the first part (401), and in a direction pointing away from the bore hole (103) by the outer peripheral surface (206), wherein the third material has a third permeability and the third permeability is of lower value than the second permeability.
The refractory purging porous block assembly (100, 400) according to any one of claim 1 to 4, wherein the refractory purging porous block assembly (100, 400) is shaped as a hollow truncated cone, the extremity of the hollow truncated cone having the largest surface being on the bottom side (204) of the main body (200).
The refractory purging porous block assembly (100, 400) according to any one of claims 1 to 5, wherein the bore hole has a top surface section at the top side and a bottom surface section at the bottom side, the top surface section being of smaller size than the bottom surface section.
The refractory purging porous block assembly (100, 400) of any of claims 1 to 6, wherein
the first material is a first dense refractory material that has an open porosity less than 30% measured after the EN1402 norm, and has a gas permeability by argon less than 10 Nanoperm, and
the second material is a porous refractory material that has an open porosity more than 30% measured after the EN1402 norm, and has a gas permeability by argon higher than 10 Nanoperm.
The refractory purging porous block assembly (100, 400) of any of claims 1 to 7, wherein the first material and / or the second material comprises one or more of the following: alumina, alumina-spinel, alumina carbon.
The refractory porous purging block assembly (100, 400) of any of claims 1 to 8, connected to a sink outlet of a tundish for metal treatment.
A method for producing a refractory purging porous block assembly (100, 400), the assembly being for use at a sink outlet (101) of a tundish, the method comprising the steps of
preparing (600) a first mould for a main body (200) comprising a bore hole (103) extending from a top side (203) of the main body (200) to a bottom side (204) of the main body (200), whereby the top side (203) is the side of the main body (200) intended to be oriented towards the tundish when the refractory purging porous block assembly (100, 400) is connected with the sink outlet (101), the bore hole (103) being delimited by an internal peripheral surface (205) of the main body (200) between the top side (203) and the bottom side (204), the main body (200) further comprising an outer peripheral surface (206) between the top side (203) and the bottom side (204), and the main body (200) further comprising a groove (201) with a circular cross-section made on the top side (203) of the main body (200) and surrounding the bore hole (103),
casting (601) at least a first material into the first mould, the first material having a first permeability, to obtain the main body (200),
forming (602) a gas supply conduit (207) in the main body (200) connecting an opening (208) on the outer peripheral surface (206) to the groove (201),
heating (603) the main body (200) at a determined temperature in order to harden the first material,
providing a porous body (202) that is shaped to surround the bore hole (103), whereby the porous body (202) comprises a second material, and the second material has a second permeability that is of higher value than the first permeability, and whereby the porous body (202) completely fills the groove (201) in the sense that the porous body (202) is in contact with a first wall (214) of the groove delimiting the groove (201) from the porous body (202) towards the bore hole (103), and the porous body (200) is in contact with a second wall (215) of the groove delimiting the groove (201) from the porous body (202) in a direction away from the bore hole (103), the contact between the first wall (214) and the porous body (202), and between the second wall (215) and the porous body (202) respectively extending all around the bore hole (103), the groove (201) further including a lower wall (217) of the groove (201) located towards the bottom side between the first wall (214) and the second wall (215); and
positioning (604) the porous body (202) in the groove (201).
The method of claim 10, wherein the preparing (600) of a first mould is further specified in that in the groove (201) of the main body (200), in the lower wall (217), a first concave gas supply groove (403) is included, that extends to surround the bore hole (103), and the forming of the gas supply conduit (207) in the main body (200) is to connect the opening (208) on the outer peripheral surface (206) to the first gas supply groove (403).
The method according to any one of claims 10 or 11, wherein the positioning (604) in the groove (201) of the porous body (200) involves casting at least the second material into the groove (201), and the method further comprises secondly heating the porous body (201) at the determined temperature in order to harden the second material.
A method for producing a refractory purging porous block assembly (100, 400), the assembly being for use at a sink outlet (101) of a tundish, comprising the steps of
preparing (1900) a second mould for a porous body (200), the mould being shaped to contain the porous body (202), whereby the porous body (202) is shaped as a first elongated shaft which is hollow and which has a circular cross-section,
casting (1901) at least a second material into the second mould to obtain the porous body (202), whereby the second material has a second permeability,
heating (1902) the porous body (202) at a determined temperature in order to harden the second material,
preparing (1903) a third mould for a second part (402) of the main body (200), which has the shape of a second elongated hollow shaft delimited on the longitudinal lateral side by an outer peripheral surface (206), the outer peripheral surface (206) extending between a top side (203) of the second shaft and a bottom side (204) of the second shaft, whereby the top side (203) is towards the tundish when the refractory purging nozzle is connected with the sink outlet (101), and the bottom side (204) is opposite from the top side (203), and the second part (402) of the main body (200) comprises a hole connecting the top side (203) and the bottom side (204), whereby the second part (402) of the main body (200) is delimited towards the hole by a profiled surface, and the profiled surface comprises a notch extending all around the hole, the notch further extending from the top side (203) and having a shape to accommodate the porous body (201),
casting (1904) at least a third material into the third mould to obtain the second part (402) of the main body (200), whereby the third material has a third permeability and the third permeability is of lower value than the second permeability,
forming (1905) a gas supply conduit (207) in the second part (402) of the main body (200) connecting an opening (208) on the outer peripheral surface (206) to the notch,
heating (1906) the second part (402) of the main body (200) at the determined temperature to harden the third material,
fitting (1907) the porous body (202) into the notch,
providing a third elongated shaft (281) that is delimited on a first longitudinal lateral side by a first outer peripheral surface (205), and the third elongated shaft (2818) defining inside the hole a fourth mould between the first peripheral surface (205), the porous body (202), a part of the profiled surface distinct from the notch, the top side (203) and the bottom side (204), whereby the fourth mould is shaped to fit a first part (401) of the main body (200),
inserting (1908) said third elongated shaft (218) into the hole of the second part (402),
casting (1909) at least a first material into the fourth mould to obtain the first part (401) of the main body (200),
heating (1910) the first part (410) of the main body (200) at the determined temperature in order to harden the first material.
The method according to claim 13, whereby the step of preparing (1903) the third mould for the second part (402) of the main body (200) further forms, in a lower part of the notch opposite to the top side (203), a first concave gas supply groove (403) that extends to surround the hole, and the forming (1905) of the gas supply conduit (207) in the second part (402) of the main body (200) is to connect the outer peripheral surface (206) to the first gas supply groove (403).
The method according to any one of claims 13 or 14, whereby the step of preparing (1900) the second mould for the porous body (202) further forms, in an extremity of the porous body (202) intended to be oriented to the bottom side when the porous body (202) is fitted into the notch, a second concave gas supply groove (404) that extends around the hole when the porous body (202) is fitted into the notch.