CA1180532A - Tundish plate for stream shaped control - Google Patents
Tundish plate for stream shaped controlInfo
- Publication number
- CA1180532A CA1180532A CA000411316A CA411316A CA1180532A CA 1180532 A CA1180532 A CA 1180532A CA 000411316 A CA000411316 A CA 000411316A CA 411316 A CA411316 A CA 411316A CA 1180532 A CA1180532 A CA 1180532A
- Authority
- CA
- Canada
- Prior art keywords
- nozzle
- plate
- tundish
- well
- holes
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/10—Supplying or treating molten metal
- B22D11/11—Treating the molten metal
- B22D11/116—Refining the metal
- B22D11/119—Refining the metal by filtering
Abstract
ABSTRACT
There is provided a continuous casting apparatus and process, in which molten metal in a tundish passes into a nozzle well and toward a nozzle at the bottom of the well. During the passage of the molten metal from the tundish to the nozzle, it passes through a plate having a plurality of holes and located above the nozzle, thereby to promote laminar flow below the plate. From the well, the molten metal is passed through the nozzle to form a stream entering a continuous casting mold. The presence of the plate promotes a relatively tight, non-flaring downstream flow from the nozzle, and prevents the formation of a vortex in the tundish which would entrain slag into the stream.
There is provided a continuous casting apparatus and process, in which molten metal in a tundish passes into a nozzle well and toward a nozzle at the bottom of the well. During the passage of the molten metal from the tundish to the nozzle, it passes through a plate having a plurality of holes and located above the nozzle, thereby to promote laminar flow below the plate. From the well, the molten metal is passed through the nozzle to form a stream entering a continuous casting mold. The presence of the plate promotes a relatively tight, non-flaring downstream flow from the nozzle, and prevents the formation of a vortex in the tundish which would entrain slag into the stream.
Description
~ .
ii32 TUNDISH PLATE FOR STREAM S~APE CONTROL
~ n .... . . _ This invention relates generally to the casting industry, and has to do particularly with an improvement applicable to tundishes for use in the continuous casting of steelO
BACKGROUND OF THIS INVENTION
.
In the continuous casting of steel, especially billet casting, the shape of the tundish stream has a strong effect on the surface quality of the billet, the internal quality of the billet, and caster performance.
A tundish stream that swirls or breaks up into droplets between the tundish and the mold will entrain more air and lead to increased slag patches on the surface of the billet and inclusions in the interior of the billet.
Either of these could cause increased quality rejects.
In addition, increased slag quantities on the billets leads to higher breakout frequency. The slag patches reduc~ heat transfer in the mold, causing thinner shells which are unable to support the weight of the liquid steel core. Such breakouts reduce productivity and increase maintenance costs.
In addition, a wildly swirling tundish stream can cause further casting difficulties, particularly on smaller billet sizes. The metal can hit either the mold wall or the top of the mold and solidify, requiring termination of the cast, and again resulting in reduced productivity and increased maintenance costs. Swirling of the stream can cccur under a variety of operating conditions. It is strongly affected by any action which causes mo~ement in the liquid above the tundish nozzle For example, when the ladle nozzle is opened fully to bring up the level in the tundish, the tundish streams swirl appreciabl~, especially the stream closest to the steel entry point in the tundish. This swirling tends to be worse when the liquid level in the tundish is higherO
Another problem in continuous casting is the entrainment of slag. At lower tundish levels, especially under very quiet tundish conditions (the same type that gives very good stream shape), vortexes form above the nozzle and entrain slag into the casting stream. This can give either large surface slag patches on the billets, large internal inclusions, or in some cases a change in steel chemistry by reversion of elements in the slag ~e.g., MnO reverting to Mn in the steel).
Ceramic shrouds have been developed in order to 1~ contain the metal stream to ensure that it hits the desired area in the mold. However, ceramic shrouds have several disadvantages. They do not allow access to the casting stream (for shut off or lancing in the case of blockage), they are difficult to install, their use is restricted to the larg~r billet sizes (because of clearance between outside and the mold wall), and special startup practices are often required to clear the skull that forms on the outside and can bridge the gap between shroud and mold wall. In addition, such shrouds make it 25 more difficult to control the level of steel in the mold.
Other systems are available to prevent or restrict stream oxidation. ~11 of these involve the use of an inert gas around the casting stream. All reqllire equipment fitted on the mold or tundish to feed or 30 contain the gas around the tundish stream and, as such, interfere to some extent with access to the stream.
~lso, because gas is involved, air flow in this area (often used to remove fumes) must be controlled.
Devices are known which reduce vortexing and 35 slag entrainment, these being gas-purged porous nozzles.
However, their use tends to produce worse stream shape.
GENER~L D~SCRIPTION OF THIS INVENTIO~
In view of the foregoing discussionl it is apparent that it would be desirable to achieve a streamlined shape for a -~undish stream, without swirllng or break-up/ while at the same time reducing vortexing and slag entrainment in the tundish. By reducing swirl and break-up, stream oxidation will be restricted.
Tt is therefore an aspect of this invention to provide a device for use with a tundish, and a process utilizing this device, which will produce a tight, smooth tundish stream that enters the mold in a small area and reduces breakout fre~uency in the billet.
A further aspect of this invention is to obtain a minimum of reoxidation in the stream or by air carried into the steel where the stream hits.
A still further aspect of this invention is to reduce the amount of slag entrained in the casting stream hy vortexing in the tundish.
In general terms, this invention consists in providing a plate with a number of holes or perforations, the plate being positioned in the path of the molten metal as it moves from the tundish to the nozzle at the bottom of a nozzle well. Preferably, the plate is located at the top of each nozzle well.
From tests reported below in this specification, it can be concluded genèrally that the plate acts as a kind of barrier separating the liquid conditions in the tundish from those in the well. Its presence inhibits the formation of a tundish vortex under quiet tundish conditions, and shields the well from disturbance under agitated tundish conditions. As the liquid metal passes through the holes of the plate, some slight agitation immediately below the plate can be expected to occur, but such agitation appears to settle into laminar flow as the liquid nears the nozzle.
More particularly, this invention provides a continuous casting process for metal, including several steps. The molten m~tal is teemed into a tundish, and then passed into a nozzle well and toward a nozzle at the bottom of the well~ During its passage from the tundish to the nozzle, the molten metal is passed through a perforated plate located above the nozzle, thereby to promote laminar flow below the plate. Finally, Erom the well, the molten metal is passed through the nozzle to form a stream entering a contlnuous casting ~old.
This invention further provides a perforated plate for use with an apparatus for the continuous casting of metal. The apparatus comprises a tundish having at least one nozzle well with a nozzle at the bottom of the well, and a continuous casting mold into which molten metal can stream from the nozzle. The perforated plate is positioned in the pa-th of molten metal passing from the tundish to the nozzle, but is spaced above the nozzle, whereby the molten metal must pass through the plate perforations to reach the nozzle.
In a preferred embodiment, the plate has at least six holes and is located substantially at the top of the well. The plate must retain its strength and erosion resistance at molten metal temperatures.
GENERAL DESCRIPTION OF THE DR~WINGS
__ - Five embodiments of this invention are illustrated in the accompanying drawings, in which like numerals denote like parts throughout the several views, and in which:
Figure 1 is a sectional view through a tundish and continuous casting mold with the plate of this 25 invention in place;
Figure la is a partial sectional view through a tundish without a plate, showing a vortex in the liquid steel;
Figures 2 through 6 show five preferred 30 embodiments of this invention;
Figures 7 through 9 show configurations which were also tested; and Figure 10 is a section through a conventional wafer nozzle.
Attention is first directed to Figure 1, which shows a tundish 10 having side walls 12, end walls 13 and 14, a bottom wall 16, a well 18, and a nozzle 20 at the bottom of the well 18. The tundish contains molten steel (or other molten metal) 22 up to a level identified by the numeral 24, and a layer of slag 26 i9 located above the level 24. In some situations, the slag layer may be thin ox non-e~istent. The inside wall 29 of the well 18 defines a well chamber through which the molten metal passes in moving from the tundish to the nozzle 20.
Located below the well ]8 is a con-tinuous casting mold 30 having cooling chamber 32 for cooling water or the like. As can be seen in Figure l, a stream 33 carries molten steel dcwnwardly from the nozzle 20 to the mold 30.
In the continuous casting process, the billet 36 is formed on a continuous basis, and continuously moves downwardly from the mold 30. As it does so, it gradually solidifies from the outside inwardly, so that the solidified side "wall'~ of the billet gradually thickens as it moves downward from the mold 30. The gradually thickening wall is identified by the numeral 38 in Figure l.
ii32 TUNDISH PLATE FOR STREAM S~APE CONTROL
~ n .... . . _ This invention relates generally to the casting industry, and has to do particularly with an improvement applicable to tundishes for use in the continuous casting of steelO
BACKGROUND OF THIS INVENTION
.
In the continuous casting of steel, especially billet casting, the shape of the tundish stream has a strong effect on the surface quality of the billet, the internal quality of the billet, and caster performance.
A tundish stream that swirls or breaks up into droplets between the tundish and the mold will entrain more air and lead to increased slag patches on the surface of the billet and inclusions in the interior of the billet.
Either of these could cause increased quality rejects.
In addition, increased slag quantities on the billets leads to higher breakout frequency. The slag patches reduc~ heat transfer in the mold, causing thinner shells which are unable to support the weight of the liquid steel core. Such breakouts reduce productivity and increase maintenance costs.
In addition, a wildly swirling tundish stream can cause further casting difficulties, particularly on smaller billet sizes. The metal can hit either the mold wall or the top of the mold and solidify, requiring termination of the cast, and again resulting in reduced productivity and increased maintenance costs. Swirling of the stream can cccur under a variety of operating conditions. It is strongly affected by any action which causes mo~ement in the liquid above the tundish nozzle For example, when the ladle nozzle is opened fully to bring up the level in the tundish, the tundish streams swirl appreciabl~, especially the stream closest to the steel entry point in the tundish. This swirling tends to be worse when the liquid level in the tundish is higherO
Another problem in continuous casting is the entrainment of slag. At lower tundish levels, especially under very quiet tundish conditions (the same type that gives very good stream shape), vortexes form above the nozzle and entrain slag into the casting stream. This can give either large surface slag patches on the billets, large internal inclusions, or in some cases a change in steel chemistry by reversion of elements in the slag ~e.g., MnO reverting to Mn in the steel).
Ceramic shrouds have been developed in order to 1~ contain the metal stream to ensure that it hits the desired area in the mold. However, ceramic shrouds have several disadvantages. They do not allow access to the casting stream (for shut off or lancing in the case of blockage), they are difficult to install, their use is restricted to the larg~r billet sizes (because of clearance between outside and the mold wall), and special startup practices are often required to clear the skull that forms on the outside and can bridge the gap between shroud and mold wall. In addition, such shrouds make it 25 more difficult to control the level of steel in the mold.
Other systems are available to prevent or restrict stream oxidation. ~11 of these involve the use of an inert gas around the casting stream. All reqllire equipment fitted on the mold or tundish to feed or 30 contain the gas around the tundish stream and, as such, interfere to some extent with access to the stream.
~lso, because gas is involved, air flow in this area (often used to remove fumes) must be controlled.
Devices are known which reduce vortexing and 35 slag entrainment, these being gas-purged porous nozzles.
However, their use tends to produce worse stream shape.
GENER~L D~SCRIPTION OF THIS INVENTIO~
In view of the foregoing discussionl it is apparent that it would be desirable to achieve a streamlined shape for a -~undish stream, without swirllng or break-up/ while at the same time reducing vortexing and slag entrainment in the tundish. By reducing swirl and break-up, stream oxidation will be restricted.
Tt is therefore an aspect of this invention to provide a device for use with a tundish, and a process utilizing this device, which will produce a tight, smooth tundish stream that enters the mold in a small area and reduces breakout fre~uency in the billet.
A further aspect of this invention is to obtain a minimum of reoxidation in the stream or by air carried into the steel where the stream hits.
A still further aspect of this invention is to reduce the amount of slag entrained in the casting stream hy vortexing in the tundish.
In general terms, this invention consists in providing a plate with a number of holes or perforations, the plate being positioned in the path of the molten metal as it moves from the tundish to the nozzle at the bottom of a nozzle well. Preferably, the plate is located at the top of each nozzle well.
From tests reported below in this specification, it can be concluded genèrally that the plate acts as a kind of barrier separating the liquid conditions in the tundish from those in the well. Its presence inhibits the formation of a tundish vortex under quiet tundish conditions, and shields the well from disturbance under agitated tundish conditions. As the liquid metal passes through the holes of the plate, some slight agitation immediately below the plate can be expected to occur, but such agitation appears to settle into laminar flow as the liquid nears the nozzle.
More particularly, this invention provides a continuous casting process for metal, including several steps. The molten m~tal is teemed into a tundish, and then passed into a nozzle well and toward a nozzle at the bottom of the well~ During its passage from the tundish to the nozzle, the molten metal is passed through a perforated plate located above the nozzle, thereby to promote laminar flow below the plate. Finally, Erom the well, the molten metal is passed through the nozzle to form a stream entering a contlnuous casting ~old.
This invention further provides a perforated plate for use with an apparatus for the continuous casting of metal. The apparatus comprises a tundish having at least one nozzle well with a nozzle at the bottom of the well, and a continuous casting mold into which molten metal can stream from the nozzle. The perforated plate is positioned in the pa-th of molten metal passing from the tundish to the nozzle, but is spaced above the nozzle, whereby the molten metal must pass through the plate perforations to reach the nozzle.
In a preferred embodiment, the plate has at least six holes and is located substantially at the top of the well. The plate must retain its strength and erosion resistance at molten metal temperatures.
GENERAL DESCRIPTION OF THE DR~WINGS
__ - Five embodiments of this invention are illustrated in the accompanying drawings, in which like numerals denote like parts throughout the several views, and in which:
Figure 1 is a sectional view through a tundish and continuous casting mold with the plate of this 25 invention in place;
Figure la is a partial sectional view through a tundish without a plate, showing a vortex in the liquid steel;
Figures 2 through 6 show five preferred 30 embodiments of this invention;
Figures 7 through 9 show configurations which were also tested; and Figure 10 is a section through a conventional wafer nozzle.
Attention is first directed to Figure 1, which shows a tundish 10 having side walls 12, end walls 13 and 14, a bottom wall 16, a well 18, and a nozzle 20 at the bottom of the well 18. The tundish contains molten steel (or other molten metal) 22 up to a level identified by the numeral 24, and a layer of slag 26 i9 located above the level 24. In some situations, the slag layer may be thin ox non-e~istent. The inside wall 29 of the well 18 defines a well chamber through which the molten metal passes in moving from the tundish to the nozzle 20.
Located below the well ]8 is a con-tinuous casting mold 30 having cooling chamber 32 for cooling water or the like. As can be seen in Figure l, a stream 33 carries molten steel dcwnwardly from the nozzle 20 to the mold 30.
In the continuous casting process, the billet 36 is formed on a continuous basis, and continuously moves downwardly from the mold 30. As it does so, it gradually solidifies from the outside inwardly, so that the solidified side "wall'~ of the billet gradually thickens as it moves downward from the mold 30. The gradually thickening wall is identified by the numeral 38 in Figure l.
2~ Dissolved in the steel are elements (deoxidizers) designed to combine with the oxygen which comes out of soiution as the steel solidifies. With a swirling or broken up stream, these elements will combine with the oxygen in the air that is either around the stream or entrained in the mold as the stream penetrates, leading to excessive quantities of slag (e.g., MnO, SiO2, etc.). This slag can either float to the top of the steel in the mold and form a layer 40 or be entrapped iIl the solidifying steel shell. The layer of slag on the top of the steel can lead to either breakout problems or surface quality problems as it solidifies against the continuous casting mold. The slag entrapped in the solidifying steel shell leads to worsened internal quality.
Attention is now directed to Figure la, which illustrates two of the typical problems encountered with the continuous casting process for steel. In Figure la, it is seen that the stream 33a tends to flare outwardly as it descends, thus entraining air into the sleel and leading to the problems discussed earlier.
Within the tundish 10 in Figure la, the steel 22 has begun ko form a vorte~ 42 above the nozzle 20, and as a result of ~his vortex slag in the slag layer 26 is being drawn downwardly and into the steel strearn 33a.
It should be pointed out that these two problems, while illustrated simultaneously in Figure la, do not necessarily occur together in prior art processes.
Returning to Figure 1, it will be seen that, in accordance with this invention, a plate 44 having a plurality of holes 46 is provided in the path or steel moving from the tundish to the nozzle 20~ More particularly, the plate 4~ is located substantially flush with the bottom of the tundish 10, and at the top of the chamber defined by the internal wall 29 of the tundish well 18.
TEST DAT~
In order to evaluate the following plate conditions with a view to determining the characteristics o~ an optimum perforated plate, a program of water model simulation tests was carried out at the University of Alberta. It is well understood that water model simulations can provide useful data from the evaluation of systems designed for other liquids. By using a full size model, the Reynolds number and Froud number are substantially the same for the two systems. The key term in these expressions is kinematic viscosity (absolute viscosity , density). The kinematic viscosity of steel and water is about the same. Since the viscosity of most liquid metals is close to that of liquid st~el, any metals whose density is similar to steel (e.g., copper, tin, zinc, etc.) should also show the improvement noted for wate~.
Figures 2 through 9 illustrate various plate configurations which were tested. The main plate characteristics under investigation were the following:
lo Plate Location ~. Plate Thickness 3O Hole diameters 4i Nu~ber of Holes 5. Hole arrays Some of the testlng involved wafer noz~les~ for which a word of explanation is in order.
Attempts in the past to use strong deoxidizers such as aluminum have led to nozzle blockage problems. A
wafer nozzle (seen in axial section in Figure 10) will pour aluminum deoxidized steels but gives much poorer stream shape than regular nozzles. This leads to a worsened condition with respect to slag formation because of the high affinity of aluminum for oxygen. It was decided to test a wafer nozzle in combination with different hole arrays, hole diameters and plate thicknesses for a perforated plate, to determine whether the combination could improve the flow characteristics out of a wafer nozzle.
` In selecting which plate configurations were to be evaluated, certain factors were kept in mind.
Firstly, shop practice required the plates to have a centre hole which is 1 1/8 inch diameter or larger.
Also, because of possible stren~th limitatior.s in the proposed plate material, as few holes as possible should be used. The spacing of holes could well be critical to the life of the perforated plate in practice. In addition, the plate would be more likely to be 1~ inch thick in practice, especially if it were intended to extend the existing fibre liner board over th~ nozzle well. Finally, it was decided to evaluate the performance of the plate when located some distance down into the nozzle well, as well as at the top of the well.
In the material below, each of the investigated characteristics are dealt with in separate sections, and at the end of each, appropriate conclusions are drawn.
A. Effect of Plate Location in the No _ le_30x For these tes-ts it was necessary to reduce the number or holes in the plates so that, in all plate locations, all holes would function.
Four different hole arrays were evaluated, and the plates were placed both flush with the bottom of the tundish, and about 4 inches (10 cm) below the bottom of the tundish. The observations follow.
a~ Fou_ 1 inch _oles, ~ inch plate It was observed that the four hole confiyuration yielded ~very poor flow conditions downstream of the nozzle. Conditions were worse at a tundish head of 42 cm, and were also worse when the plate was placed 4 inches closer to the nozzle. The hole array was that shown in Figure 7.
b) Five 1 inch holes, ~_ inch plate The hole array for this test was that shown in Figure 8. For this test, it was observed that the flow was quite erratic with the flow conditions worse at a tundish head of 42 cm, and also worse with the plate placed 4 inches down into the nozzle well.
c) Six I inch holes with hole plugged, ~" plate This test used the pla~e shown in Figure 9. The plate had a circular six hole array, with the centre hole plugged. It was observed that the flow downstream of the nozzle was poorer with the plate placed 4 inches closer to the nozzle, and also that the flow was more erratic at a tundish head of 42 cm.
In comparing the two different five hole arrays lone including a centre hole), it would appear that, with the plates flush with the bottom of the tundish, the flow conditions were somewhat improved with the array having no hole in the centre. A second comparison was made between a six hole array as illustrated in Figure and the six hole array illustrated in Figure
Attention is now directed to Figure la, which illustrates two of the typical problems encountered with the continuous casting process for steel. In Figure la, it is seen that the stream 33a tends to flare outwardly as it descends, thus entraining air into the sleel and leading to the problems discussed earlier.
Within the tundish 10 in Figure la, the steel 22 has begun ko form a vorte~ 42 above the nozzle 20, and as a result of ~his vortex slag in the slag layer 26 is being drawn downwardly and into the steel strearn 33a.
It should be pointed out that these two problems, while illustrated simultaneously in Figure la, do not necessarily occur together in prior art processes.
Returning to Figure 1, it will be seen that, in accordance with this invention, a plate 44 having a plurality of holes 46 is provided in the path or steel moving from the tundish to the nozzle 20~ More particularly, the plate 4~ is located substantially flush with the bottom of the tundish 10, and at the top of the chamber defined by the internal wall 29 of the tundish well 18.
TEST DAT~
In order to evaluate the following plate conditions with a view to determining the characteristics o~ an optimum perforated plate, a program of water model simulation tests was carried out at the University of Alberta. It is well understood that water model simulations can provide useful data from the evaluation of systems designed for other liquids. By using a full size model, the Reynolds number and Froud number are substantially the same for the two systems. The key term in these expressions is kinematic viscosity (absolute viscosity , density). The kinematic viscosity of steel and water is about the same. Since the viscosity of most liquid metals is close to that of liquid st~el, any metals whose density is similar to steel (e.g., copper, tin, zinc, etc.) should also show the improvement noted for wate~.
Figures 2 through 9 illustrate various plate configurations which were tested. The main plate characteristics under investigation were the following:
lo Plate Location ~. Plate Thickness 3O Hole diameters 4i Nu~ber of Holes 5. Hole arrays Some of the testlng involved wafer noz~les~ for which a word of explanation is in order.
Attempts in the past to use strong deoxidizers such as aluminum have led to nozzle blockage problems. A
wafer nozzle (seen in axial section in Figure 10) will pour aluminum deoxidized steels but gives much poorer stream shape than regular nozzles. This leads to a worsened condition with respect to slag formation because of the high affinity of aluminum for oxygen. It was decided to test a wafer nozzle in combination with different hole arrays, hole diameters and plate thicknesses for a perforated plate, to determine whether the combination could improve the flow characteristics out of a wafer nozzle.
` In selecting which plate configurations were to be evaluated, certain factors were kept in mind.
Firstly, shop practice required the plates to have a centre hole which is 1 1/8 inch diameter or larger.
Also, because of possible stren~th limitatior.s in the proposed plate material, as few holes as possible should be used. The spacing of holes could well be critical to the life of the perforated plate in practice. In addition, the plate would be more likely to be 1~ inch thick in practice, especially if it were intended to extend the existing fibre liner board over th~ nozzle well. Finally, it was decided to evaluate the performance of the plate when located some distance down into the nozzle well, as well as at the top of the well.
In the material below, each of the investigated characteristics are dealt with in separate sections, and at the end of each, appropriate conclusions are drawn.
A. Effect of Plate Location in the No _ le_30x For these tes-ts it was necessary to reduce the number or holes in the plates so that, in all plate locations, all holes would function.
Four different hole arrays were evaluated, and the plates were placed both flush with the bottom of the tundish, and about 4 inches (10 cm) below the bottom of the tundish. The observations follow.
a~ Fou_ 1 inch _oles, ~ inch plate It was observed that the four hole confiyuration yielded ~very poor flow conditions downstream of the nozzle. Conditions were worse at a tundish head of 42 cm, and were also worse when the plate was placed 4 inches closer to the nozzle. The hole array was that shown in Figure 7.
b) Five 1 inch holes, ~_ inch plate The hole array for this test was that shown in Figure 8. For this test, it was observed that the flow was quite erratic with the flow conditions worse at a tundish head of 42 cm, and also worse with the plate placed 4 inches down into the nozzle well.
c) Six I inch holes with hole plugged, ~" plate This test used the pla~e shown in Figure 9. The plate had a circular six hole array, with the centre hole plugged. It was observed that the flow downstream of the nozzle was poorer with the plate placed 4 inches closer to the nozzle, and also that the flow was more erratic at a tundish head of 42 cm.
In comparing the two different five hole arrays lone including a centre hole), it would appear that, with the plates flush with the bottom of the tundish, the flow conditions were somewhat improved with the array having no hole in the centre. A second comparison was made between a six hole array as illustrated in Figure and the six hole array illustrated in Figure
3~ Here again it was seen that the plate with no centre hole showed some improvement in downstream flow conditions.
d) Si~ l inch holes and eEfect of plate location It was noted that the downstream flow conditions worsened when the plate was placed closer to the nozzle. However, the si~ hole plate exhibited better downstream flow conditions than the five hol.e plate, although none of these flow conditions could be considered ideal, nor were they as good as were achieved wi.th the use of more holes.
Conclusions The placing of the perforated plate in the nozzle well below the bottom of the tundish tended to produce poor downstream flow conditions out of the nozzle~
Four, five and even sl~ hole plate configurations produced poorer downstream flow conditions than plates with a greater number of holes.
For a five hole plate, the downstream flow conditions were somewhat improved if there was no centre hole in the array. Also, for six l-inch holes, the downstream flow conditions were better when the plate had no centre hole. It would be expected that the presence or absence of the centre hole would have less of an effect as the number of holes in the plate increased.
B. Effect of Plate Thickness For this evaluation, plate thicknesses of 2, 1~, 1 and ~ inches were tested using 6, 7 and 9 one-inch diameter holes. These plate configurations are shown in Figures 3, 4 and 5.
a~ Six hole plate, circular array, no centre hole At a 16 cm tundish head, the flow characteristics of the stream out of the nozzle all appeared about the same regardless of which plate thickness was used.
The streams appeared to be somewhat ragged but none was wildly splaying. The density and penetration of the air buhbles all appeared to be the same. Thus~
at a 16 cm tundish head the effect of plate thickness in the range from 0~5 inches to 2 inches appeared to be insignificant.
At the 42 cm tundlsh head~ there was an increase in erratic flow patterns for all pla-te thicknesses evaluated with perhaps less turbulence noted for the ~ and l inch plates than for the other two thicker plates. Changing the plate thickness did not seem to alter the depth of bubble penetration into the mold box.
b) Se~en hole plate, circular array, with centre hole Using a l~ cm tundish head, the flow out of the nozæles for plate thicknesses of l, l~ and 2 inches was more laminar in appearance than observed with the use of ~ inch plate. The depth of bubble penetration appeared to be least with the l~ inch plate, but was also most dense for this plate.
With a 42 cm tundish head, there did not seem to be any difference in flow conditions regardless of which plate thickness was used.
c) Nirle hole plate, square array with centre hole At a l~ cm tundish head the nine hole plate array yielded improved downstream flow conditions over those obser~ed for the six or seven hole arrays evaluated above. For the nine hole array (Figure 5), -the l~ inch plate appeared to give the least density o bubbles in the mold box. The laminar appearance of the streams out of the nozzle was unaffected by plate thickness in the range of O.S inches to inches.
At a 42 cm tundish head, there was noted a slightly more laminar-like stream with a l inch plate than with the others, but generally all streams appeared to be tight and laminar in appearance. The depth of penetration of bubbles in the mold box was about the same for all plate thicknesses with possibly less density of bubbles observed with the use of a 1~ inch plate thickness.
l l.
Conclusions Generally, the plate thickness appeared to have less influence on the downstream flow characteristlcs than did the number of holes used in the array. The results appear to indicate that a nine hole array is clearly superior to the seven or six hole arrays evaluated.
The density of bubbles in the mold bo~es was less at a 16 cm tundish head than at a 42 cm tundish head.
The efect of plate thickness, although difficult to evaluate, showed that a ~ inch plate produced poorer results at a 16 cm tundish head for a seven hole plate array, and 1~ inch and 2 inch plates produced slightly poorer stream shapes with a six hole array at a ~2 cm tundish head. It would appear that the inch plate may not be suitable for all hole arrays whereas the 1~ inch plate may be close to or at the optimum thickness for a number of different hole arrayso C. Effect of Hole Diameter Two different hole arrays, seven and ninej were used to evaluate the effects of hole diame-ters of 1, 1 and 1~ inches. All plates were 1~ inch thick.
a) Seven hole circular array At a 16 cm tundish head, the stream shape out of the nozzle was better for the 1~ or 1~ inch diameier holes than for the l-inch hole size. However, the penetration of air bubbles in the mold boxes was least for the one-inch holes.
For a tundish head of ~2 cm, the stream shape was best for the 1~ inch diameter holes. Also, the depth of penetration was least with the plate having 1 inch holes. The plate configuration is shown in Figure 4.
b) Nine hole square array At a 16 cm tundish head, the str~am shape for the different hole diameters was about the same with possibly more laminar flow ~or the l~ or 1~ inch holes than for the 1 inch holes. The penetration of air bubbles in the mold boxes was least for the l-inch diameter holes and most for the 1~ inch diameter holes.
At a 42 cm tundish head, the stream shape was good for all three hole sizes with slightly better results for the l~ inch hole size. The density of bubbles in the mold boxes was about the same for all three hole sizes evaluated.
Conclusions Generally it appears that while hole size a~fected the stream flow conditions out of the nozzle, the effect was not a pronounced one. ~ole diameter appeared to be a stronger factor with the seven hole array than with the nine hole array. This would be expected in that the percentage increase in hole area would be greater with fewer holes in the plate.
Again~ it appeared that the nine hole array produced more laminar flow conditions than did the seven hole array. The plate with 1~ inch holes appeared to give good downstream flow characteristics.
D. Tests with a Wafer Nozzle Wafer nozzles are well known in the art of steel making, and a typical cross section of a wafer nozzle is shown in Figure 10.
Previous to the making of this invention, a wafer nozzle was tested in a continuous casting process.
30 However, it was found that the flow out of the wafer nozzle, although 22% reduced compared with that of the regular nozzle, had wildly erratic flow characteristics.
Because the wafer nozzle has advantages when used in conjunction with a deoxidation practice, it was desirable 35 to evaluate some of the "better" perforated plates to see whether they could be used to improve the downstream flow conditions out of a wafer nozzle. Three different hole arrays and three hole diameters were evaluated. The 16 l3 hole pla~e was ~ inch ~hick, whereas the other plates were l~ inch thick.
a) Sixteen l-inch diameter hole square array A sixteen one-inch diame-ter hole array as seen in Figure 6 was evaluated with a wafer nozzle and compared with a regular nozzle. At both a 16 and a ~ cm tundish head, the flows out of the nozzles were tight and laminar in appearance. However, the density of air bubbles in -the mold box was considerably less for the wafer nozzle than for the regular nozzle. It has been noted that for the same tundish head, the flow out of the wafer nozzle was about 22~ less than out of a regular nozzle. Therefore a more valid comparison, although still only approximate~ would be to compare the flow out of the wafer nozzle at a head of 42 cm to the flow out of a regular nozzle at 16 cm. When this was done, it was still evident that there was less density of bubbles in the mold box with the wafer nozzle than with the regular noæzle.
b) Nine l-inch hole square array The use of the nine hole plate as seen in Figure 5 improved the flow out of the wafer nozzle. In comparing the wafer nozzle with the regular nozzle, it should be remembered that there was ?2~ less flow out of the wafer nozzle than out of the regular nozzle for the same tundish head. At a 42 cm tundish head there was more penetration in the mold box than at the 16 cm tundish head. ~ven accounting for the differences in flow rates it appeared there was less density of bubbles in the mold box with a wafer nozzle than with a regular nozzle.
c) Seven hole arrav - effect of different hole diameters ~t a 16 cm tundish head, increasing the hole diameter from one to l~ to 1~ inches reduced the density but increased the depth of bubble penetration in the mold box. The flow out of the nozzles appeared to be about the same for all hole sizes evaluated.
~5~
With the tundish at 42 cm the flows out of the nozzles were about equal or all hole diameters but the density of bubbles in the mold box was least for the 1~ inch holes. The depth of penetration of bubbles in the mold box was greatest with the 1~ inch diameter holes.
Conclusions Probably more than with the regular nozzle, the merits of a nine hole array over that of the seven hole array were observed in this set of tests~ The nine hole array in combination with a wafer nozzle produced much less density of air bubbles in the mold box than with the seven hole array. The 1~ and 1 inch hole diameter appeaxed to yield laminar flow lS conditions downstream of the nozzle.
Preferred Materials Tests with plates fabricated from tundish liner boards (a silica refractory material called Profax by its manufacturer) have withstood erosion in the tundish at the steel plant~ Any refractories commonly used in steel teeming systems (e.g. alumina, zirconiaj magnesia, alumina-graphite) could be used.
d) Si~ l inch holes and eEfect of plate location It was noted that the downstream flow conditions worsened when the plate was placed closer to the nozzle. However, the si~ hole plate exhibited better downstream flow conditions than the five hol.e plate, although none of these flow conditions could be considered ideal, nor were they as good as were achieved wi.th the use of more holes.
Conclusions The placing of the perforated plate in the nozzle well below the bottom of the tundish tended to produce poor downstream flow conditions out of the nozzle~
Four, five and even sl~ hole plate configurations produced poorer downstream flow conditions than plates with a greater number of holes.
For a five hole plate, the downstream flow conditions were somewhat improved if there was no centre hole in the array. Also, for six l-inch holes, the downstream flow conditions were better when the plate had no centre hole. It would be expected that the presence or absence of the centre hole would have less of an effect as the number of holes in the plate increased.
B. Effect of Plate Thickness For this evaluation, plate thicknesses of 2, 1~, 1 and ~ inches were tested using 6, 7 and 9 one-inch diameter holes. These plate configurations are shown in Figures 3, 4 and 5.
a~ Six hole plate, circular array, no centre hole At a 16 cm tundish head, the flow characteristics of the stream out of the nozzle all appeared about the same regardless of which plate thickness was used.
The streams appeared to be somewhat ragged but none was wildly splaying. The density and penetration of the air buhbles all appeared to be the same. Thus~
at a 16 cm tundish head the effect of plate thickness in the range from 0~5 inches to 2 inches appeared to be insignificant.
At the 42 cm tundlsh head~ there was an increase in erratic flow patterns for all pla-te thicknesses evaluated with perhaps less turbulence noted for the ~ and l inch plates than for the other two thicker plates. Changing the plate thickness did not seem to alter the depth of bubble penetration into the mold box.
b) Se~en hole plate, circular array, with centre hole Using a l~ cm tundish head, the flow out of the nozæles for plate thicknesses of l, l~ and 2 inches was more laminar in appearance than observed with the use of ~ inch plate. The depth of bubble penetration appeared to be least with the l~ inch plate, but was also most dense for this plate.
With a 42 cm tundish head, there did not seem to be any difference in flow conditions regardless of which plate thickness was used.
c) Nirle hole plate, square array with centre hole At a l~ cm tundish head the nine hole plate array yielded improved downstream flow conditions over those obser~ed for the six or seven hole arrays evaluated above. For the nine hole array (Figure 5), -the l~ inch plate appeared to give the least density o bubbles in the mold box. The laminar appearance of the streams out of the nozzle was unaffected by plate thickness in the range of O.S inches to inches.
At a 42 cm tundish head, there was noted a slightly more laminar-like stream with a l inch plate than with the others, but generally all streams appeared to be tight and laminar in appearance. The depth of penetration of bubbles in the mold box was about the same for all plate thicknesses with possibly less density of bubbles observed with the use of a 1~ inch plate thickness.
l l.
Conclusions Generally, the plate thickness appeared to have less influence on the downstream flow characteristlcs than did the number of holes used in the array. The results appear to indicate that a nine hole array is clearly superior to the seven or six hole arrays evaluated.
The density of bubbles in the mold bo~es was less at a 16 cm tundish head than at a 42 cm tundish head.
The efect of plate thickness, although difficult to evaluate, showed that a ~ inch plate produced poorer results at a 16 cm tundish head for a seven hole plate array, and 1~ inch and 2 inch plates produced slightly poorer stream shapes with a six hole array at a ~2 cm tundish head. It would appear that the inch plate may not be suitable for all hole arrays whereas the 1~ inch plate may be close to or at the optimum thickness for a number of different hole arrayso C. Effect of Hole Diameter Two different hole arrays, seven and ninej were used to evaluate the effects of hole diame-ters of 1, 1 and 1~ inches. All plates were 1~ inch thick.
a) Seven hole circular array At a 16 cm tundish head, the stream shape out of the nozzle was better for the 1~ or 1~ inch diameier holes than for the l-inch hole size. However, the penetration of air bubbles in the mold boxes was least for the one-inch holes.
For a tundish head of ~2 cm, the stream shape was best for the 1~ inch diameter holes. Also, the depth of penetration was least with the plate having 1 inch holes. The plate configuration is shown in Figure 4.
b) Nine hole square array At a 16 cm tundish head, the str~am shape for the different hole diameters was about the same with possibly more laminar flow ~or the l~ or 1~ inch holes than for the 1 inch holes. The penetration of air bubbles in the mold boxes was least for the l-inch diameter holes and most for the 1~ inch diameter holes.
At a 42 cm tundish head, the stream shape was good for all three hole sizes with slightly better results for the l~ inch hole size. The density of bubbles in the mold boxes was about the same for all three hole sizes evaluated.
Conclusions Generally it appears that while hole size a~fected the stream flow conditions out of the nozzle, the effect was not a pronounced one. ~ole diameter appeared to be a stronger factor with the seven hole array than with the nine hole array. This would be expected in that the percentage increase in hole area would be greater with fewer holes in the plate.
Again~ it appeared that the nine hole array produced more laminar flow conditions than did the seven hole array. The plate with 1~ inch holes appeared to give good downstream flow characteristics.
D. Tests with a Wafer Nozzle Wafer nozzles are well known in the art of steel making, and a typical cross section of a wafer nozzle is shown in Figure 10.
Previous to the making of this invention, a wafer nozzle was tested in a continuous casting process.
30 However, it was found that the flow out of the wafer nozzle, although 22% reduced compared with that of the regular nozzle, had wildly erratic flow characteristics.
Because the wafer nozzle has advantages when used in conjunction with a deoxidation practice, it was desirable 35 to evaluate some of the "better" perforated plates to see whether they could be used to improve the downstream flow conditions out of a wafer nozzle. Three different hole arrays and three hole diameters were evaluated. The 16 l3 hole pla~e was ~ inch ~hick, whereas the other plates were l~ inch thick.
a) Sixteen l-inch diameter hole square array A sixteen one-inch diame-ter hole array as seen in Figure 6 was evaluated with a wafer nozzle and compared with a regular nozzle. At both a 16 and a ~ cm tundish head, the flows out of the nozzles were tight and laminar in appearance. However, the density of air bubbles in -the mold box was considerably less for the wafer nozzle than for the regular nozzle. It has been noted that for the same tundish head, the flow out of the wafer nozzle was about 22~ less than out of a regular nozzle. Therefore a more valid comparison, although still only approximate~ would be to compare the flow out of the wafer nozzle at a head of 42 cm to the flow out of a regular nozzle at 16 cm. When this was done, it was still evident that there was less density of bubbles in the mold box with the wafer nozzle than with the regular noæzle.
b) Nine l-inch hole square array The use of the nine hole plate as seen in Figure 5 improved the flow out of the wafer nozzle. In comparing the wafer nozzle with the regular nozzle, it should be remembered that there was ?2~ less flow out of the wafer nozzle than out of the regular nozzle for the same tundish head. At a 42 cm tundish head there was more penetration in the mold box than at the 16 cm tundish head. ~ven accounting for the differences in flow rates it appeared there was less density of bubbles in the mold box with a wafer nozzle than with a regular nozzle.
c) Seven hole arrav - effect of different hole diameters ~t a 16 cm tundish head, increasing the hole diameter from one to l~ to 1~ inches reduced the density but increased the depth of bubble penetration in the mold box. The flow out of the nozzles appeared to be about the same for all hole sizes evaluated.
~5~
With the tundish at 42 cm the flows out of the nozzles were about equal or all hole diameters but the density of bubbles in the mold box was least for the 1~ inch holes. The depth of penetration of bubbles in the mold box was greatest with the 1~ inch diameter holes.
Conclusions Probably more than with the regular nozzle, the merits of a nine hole array over that of the seven hole array were observed in this set of tests~ The nine hole array in combination with a wafer nozzle produced much less density of air bubbles in the mold box than with the seven hole array. The 1~ and 1 inch hole diameter appeaxed to yield laminar flow lS conditions downstream of the nozzle.
Preferred Materials Tests with plates fabricated from tundish liner boards (a silica refractory material called Profax by its manufacturer) have withstood erosion in the tundish at the steel plant~ Any refractories commonly used in steel teeming systems (e.g. alumina, zirconiaj magnesia, alumina-graphite) could be used.
Claims (19)
1. A continuous casting process for metal, including the steps:
a) teeming the molten metal into a tundish, b) passing the molten metal into a nozzle well and toward a nozzle at the bottom of the well, c) during its passage from the tundish to the nozzle, passing the molten metal through a plate having a plurality of holes and located above the nozzle, thereby to promote laminar flow below the plate, and d) from the well, passing the molten metal through the nozzle to form a stream entering a continuous casting mold.
a) teeming the molten metal into a tundish, b) passing the molten metal into a nozzle well and toward a nozzle at the bottom of the well, c) during its passage from the tundish to the nozzle, passing the molten metal through a plate having a plurality of holes and located above the nozzle, thereby to promote laminar flow below the plate, and d) from the well, passing the molten metal through the nozzle to form a stream entering a continuous casting mold.
2. The process claimed in claim 1, in which the plate has at least six holes and is located substantially at the top of the well.
3. The process claimed in claim 1, in which the plate has at least seven substantially cylindrical holes of substantially the same diameter, and is located at least about six hole diameters above the nozzle.
4. The process claimed in claim 1, in which the plate has between about six and about ten cylindrical holes of the same diameter, the plate being located above a level which is six hole diameters above the bottom of the well.
5. The process claimed in claim 1, claim 2 or claim 4 in which the plate has at least seven cylindrical holes of which the diameter is between about one inch and about 1?
inches.
inches.
6. The process claimed in claim 1, claim 2 or claim 4, in which the plate thickness is between about ? inch and about 2 inches.
7. The process claimed in claim 1, claim 2 or claim 4, in which the hole size is large enough to prevent freezing of the liquid metal as it first pours through the plate and small enough to promote laminar flow in the well.
8. The process claimed in claim 1, claim 2 or claim 4, in which the metal is steel.
9. For use with an apparatus for the continuous casting of metal:
a tundish having at least one nozzle well with a nozzle at the bottom of the well, and a plate having a plurality of holes and located above the nozzle in a location such that molten metal in the tundish must pass through the holes in the plate to reach the nozzle.
a tundish having at least one nozzle well with a nozzle at the bottom of the well, and a plate having a plurality of holes and located above the nozzle in a location such that molten metal in the tundish must pass through the holes in the plate to reach the nozzle.
10. For use with an apparatus for the continuous casting of metal, the apparatus comprising a tundish having at least one nozzle well with a nozzle at the bottom of the well, and a continuous casting mold into which molten metal can stream from the nozzle:
a plate having a plurality of holes and positioned in the path of molten metal passing from the tundish to the nozzle, but spaced above the nozzle, whereby the molten metal must pass through the holes in the plate to reach the nozzle.
a plate having a plurality of holes and positioned in the path of molten metal passing from the tundish to the nozzle, but spaced above the nozzle, whereby the molten metal must pass through the holes in the plate to reach the nozzle.
11. An apparatus for the continuous casting of metal, comprising:
a tundish having at least one nozzle well with a nozzle at the bottom of the well, a continuous casting mold into which molten metal can stream from the nozzle, and a plate having a plurality of holes and positioned in the path of molten metal passing from the tundish to the nozzle but spaced above the nozzle, whereby the molten metal must pass through the holes in the plate to reach the nozzle.
a tundish having at least one nozzle well with a nozzle at the bottom of the well, a continuous casting mold into which molten metal can stream from the nozzle, and a plate having a plurality of holes and positioned in the path of molten metal passing from the tundish to the nozzle but spaced above the nozzle, whereby the molten metal must pass through the holes in the plate to reach the nozzle.
12. The invention claimed in claim 9, claim 10 or claim 11, in which the plate has at least six holes and is located substantially at the top of the well.
13. The invention claimed in claim 9, claim 10 or claim 11, in which the plate has at least seven substantially cylindrical holes of substantially the same diameter, and is located at least about six hole diameters above the nozzle.
14. The invention claimed in claim 9, claim 10 or claim 11, in which the plate has between about six and about ten cylindrical holes of the same diameter, the plate being located above a level which is six hole diameters above the bottom of the well.
15. The invention claimed in claim 9, claim 10 or claim 11, in which the plate has at least seven cylindrical holes of which the diameter is between about one inch and about 1? inches.
16. The invention claimed in claim 9, claim 10 or claim 11, in which the plate thickness is between about ? inch and about 2 inches.
17. The invention claimed in claim 9, claim 10 or claim 11, in which the hole size is large enough to prevent freezing of the liquid metal as it first pours through the plate and small enough to promote laminar flow in the well.
18. The invention claimed in claim 9, claim 10 or claim 11, in which the metal is steel.
19. The invention claimed in claim 3, claim 10 or claim 11, in which the plate has nine holes in three rows of three each, the plate being located substantially flush with the tundish bottom, the holes being cylindrical and having a diameter of at least 1 inch.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000411316A CA1180532A (en) | 1982-09-13 | 1982-09-13 | Tundish plate for stream shaped control |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000411316A CA1180532A (en) | 1982-09-13 | 1982-09-13 | Tundish plate for stream shaped control |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1180532A true CA1180532A (en) | 1985-01-08 |
Family
ID=4123579
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000411316A Expired CA1180532A (en) | 1982-09-13 | 1982-09-13 | Tundish plate for stream shaped control |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1180532A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4667939A (en) * | 1986-03-26 | 1987-05-26 | Foseco International Limited | Purifying steel |
| US4725310A (en) * | 1986-03-26 | 1988-02-16 | Foseco International Limited | Method of purifying steel |
-
1982
- 1982-09-13 CA CA000411316A patent/CA1180532A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4667939A (en) * | 1986-03-26 | 1987-05-26 | Foseco International Limited | Purifying steel |
| US4725310A (en) * | 1986-03-26 | 1988-02-16 | Foseco International Limited | Method of purifying steel |
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