CA1148720A - Method of continuously casting metal - Google Patents
Method of continuously casting metalInfo
- Publication number
- CA1148720A CA1148720A CA000332754A CA332754A CA1148720A CA 1148720 A CA1148720 A CA 1148720A CA 000332754 A CA000332754 A CA 000332754A CA 332754 A CA332754 A CA 332754A CA 1148720 A CA1148720 A CA 1148720A
- Authority
- CA
- Canada
- Prior art keywords
- strand
- phase
- coil
- thrust forces
- cast
- 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
- 238000000034 method Methods 0.000 title claims abstract description 27
- 229910052751 metal Inorganic materials 0.000 title claims abstract description 18
- 239000002184 metal Substances 0.000 title claims abstract description 18
- 238000005266 casting Methods 0.000 title claims abstract description 12
- 239000007788 liquid Substances 0.000 claims abstract description 18
- 238000009749 continuous casting Methods 0.000 claims abstract description 14
- 230000005672 electromagnetic field Effects 0.000 claims abstract description 11
- 238000003756 stirring Methods 0.000 claims description 8
- 150000002739 metals Chemical class 0.000 claims description 4
- 230000006872 improvement Effects 0.000 claims description 3
- 230000001939 inductive effect Effects 0.000 claims description 2
- 239000013078 crystal Substances 0.000 abstract description 12
- 238000005204 segregation Methods 0.000 abstract description 12
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 8
- 239000005864 Sulphur Substances 0.000 description 8
- 238000001000 micrograph Methods 0.000 description 7
- 229910000831 Steel Inorganic materials 0.000 description 6
- 239000000155 melt Substances 0.000 description 6
- 239000010959 steel Substances 0.000 description 6
- 230000000694 effects Effects 0.000 description 4
- 238000009434 installation Methods 0.000 description 4
- 238000004804 winding Methods 0.000 description 4
- 210000001787 dendrite Anatomy 0.000 description 3
- 238000010276 construction Methods 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 239000011572 manganese Substances 0.000 description 2
- 238000004445 quantitative analysis Methods 0.000 description 2
- 238000007711 solidification Methods 0.000 description 2
- 230000008023 solidification Effects 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910001208 Crucible steel Inorganic materials 0.000 description 1
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical group [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 230000006735 deficit Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000005284 excitation Effects 0.000 description 1
- BHEPBYXIRTUNPN-UHFFFAOYSA-N hydridophosphorus(.) (triplet) Chemical compound [PH] BHEPBYXIRTUNPN-UHFFFAOYSA-N 0.000 description 1
- 229910001338 liquidmetal Inorganic materials 0.000 description 1
- 239000000696 magnetic material Substances 0.000 description 1
- 238000003760 magnetic stirring Methods 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000005499 meniscus Effects 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 239000007921 spray Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 238000009827 uniform distribution Methods 0.000 description 1
- 239000011800 void material Substances 0.000 description 1
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
- B22D11/12—Accessories for subsequent treating or working cast stock in situ
- B22D11/122—Accessories for subsequent treating or working cast stock in situ using magnetic fields
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Continuous Casting (AREA)
- Mixers With Rotating Receptacles And Mixers With Vibration Mechanisms (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE:
A method for the continuous casting of metal, wherein, in order to improve the crystal or grain structure and to reduce the drawbacks of positive and negative segregation, a turbulent flow is produced with the aid of differently intensive thrust forces acting upon the molten metal in the liquid core of the strand or casting. The thrust forces are produced by means of at least one electromagnetic field.
A method for the continuous casting of metal, wherein, in order to improve the crystal or grain structure and to reduce the drawbacks of positive and negative segregation, a turbulent flow is produced with the aid of differently intensive thrust forces acting upon the molten metal in the liquid core of the strand or casting. The thrust forces are produced by means of at least one electromagnetic field.
Description
~L~ 48720 The present invention relates to a new and improved method for the continuous casting of metal, w~nerein the melt or molten metal is cast in a mold, the formed strand having a liquid core is withdrawn, guided and further cooled, and by means of at least one stirrer, inducing electromagnetic fields in the strand, there is produced a turbulent flow in the liquid core.
During the continuous casting of metals, especially steel, it is known to the art to obtain, by m~gnetic stirring of the melt or molten metal in the liquid core, an improvement in the quality of the cast material by producing a more or less pronounced turbulent flow. These improvements in the quality of the casting have been obtained by different methods which apply thrust forces to the melt. In many instances there have been employed traveling magnetic fields for producing the thrust forces.
Contained within the steel are alloying and accompany-ing elements, such as carbon (C), silicon (Si), manganese (Mn), phosphorous (P), sulphur (S) and 90 forth , wllich, upon solidi-fication, can lead to ssgregations, especially center segre-gations. Such segregations, and equally the crystal structure, are dependent, as is known, among other things, upon the degree of sup3rheating. Due to the electromagnetic stirring and the turbulent flow which is thus produced, it is intended to prevent such segregations. The solidified structure should be affected - in such a manner that there is obtained as large as possible zone of compact or dense, equiaxed crystal structure. However, it has been found that owing to the local, pronounced movement of the melt the solid-liquid interface or solidification front is influenced such that there are formed so-called white bands. Theso white bands constitute negative ssgregations which impair the quality of the cast product.
' 1 ~
~1~8720 A^cording to a state-of-the-art method there are produced, by means of an electromagnetic traveling field, thrust forces in the direction of the lengthwlse axis of the strand, the magnets extending about the strand bein~ arranged between roll pairs up to the end of the liquid core or pool. The flow formed along the liquid core produces the desired region of non-columnar structure and prevents the formation of decisive segregations, especially center segregation and wllite bands.
This prior art arrangement, by virtue of the multiplicity of employed magnets, requires much too much space, hinders cooling of the stran~ and is much too complicated.
In accordance with another known technique for fabricating slab sections, attempts have been made to eliminate these white bands in that, by m~ans of electromagnetic traveling fields, generated by two magnets located opposite one another at the lengthwise sides of the cast strand, thrust forces are produced at the liquid steel. These thrust forces should be effective transversely with respect to the lengthwise axis of the strand, in order to obtain a gentle impact of the metal flow at the solidified strand wall, so that the deflected flow is maintained within a certain region. This limited effective zone produces an insufficient zone of compact, equiaxed crystal structure. Moreover, it has been found that with this method the white bands only can be unsatisfactorily eliminated, so that by virtue of this drawback there cannot be obtained any optimum cast product, something which has a negative effect in terms of the quality of, for instance, the rolled product.
Therefore, with the foregoing in mind, it is a primary object of the present invention to provide an improved method of continuously casting metals in a manner not afficted with the aforementioned drawbacks and shortcomin~s of the prior art proposals.
~87ZO
Still another and more specific object of the present invention aims at providing a continuous casting method which produces an adeq~ate zone of co.mpact or dense, equiaxed crystal structure.
Yet a further significant object is to provide a continuous casting method wherein the cast m~terial is low in segregations, especially center segregations and white bands.
A further object is to provide a continuous casting m~thod, employing electromagnetic stirrer principles, having extremely small space requirements for generating the magnetic stirring effect.
Now in order to implement these and still further obj2cts of the invention, wl~ich will become more readily apparent as the description proceeds, the method contemplates producing a turbulent flow by different thrust forces acting : upon the melt and generated by asymmetrical conditions prevail-~ ing in the phases of the fields.
: Tests carried out with a traveling magnetic field which is effective transversely with respect to the strand, and wherein the polyphase system producin~ the traveling field has identical windings in the coils and such coils carry the same current intensity, have shown that m.icrographs of the cast product exhibit w~lite bands and a wide zone of dendrites., thereby resulting in insufficient quality of the cast steel.
However, and as has been surprisingly found in accordance with the teachings of the present invention, with different thrust forces acting upon the mo~ten metal within the traveling field, there is then produced such a turbulent flow that, p.ractically no white bands app~ared in the micrograph and, furthermore, notwithstanding higher superheating temperature there is obtained the desired zone of compact or dense, e~uiaxed crystal structure without any significant center , . . - :
segregation. This effect is beneficially realized notwith-standing the quite modest space requirements which prevail for producing the traveling magnetic field.
According to a further feature of the invention, in order to produce the different thrust forces in a most simple manner, it is possible to have different current intensities flow through the coil of one phase in relation to the coil of at least one other phase of the electromagnetic field.
Accordin~ to a further aspect of the invention, the different thrust forces which are effective at the molten metal can be realized by having a current flow throu~h the coil of the one phase w~ich is approximately 10% to 25% higher than the current flowing through the coil of at least one other p~ase.
An advantageous effect of the method of the invention can be obtained if the differently effective thrust forces are produced transversely of or along the strand. The term "along the strand" m~ans in the lengthwise direction of the strand and is intended to embrace both the case where such thrust forces act essentially parallel to the lengthwise side of the strand or lengthwise and at an inclination to the lengthwise axis of the strand.
The invention will be better understood and objects other than those set forth above, will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:
Figure 1 illustrates an arrangement for producing a traveling maqnetic field for performing the metho~ in a curved or arc-type casting installation, Figure 2 is a micrograph of one-half of the cross-section of a slab whose liquid core has been stirred with a r ~ 487120 traveling magnetic field effective transversely with respect to the strand;
Figure 3 is a graph showing the distribution of r sulphur along the position of the slab marked by the line III of Figure 2;
Figure 4*is a micrograph of one-half of the cross-section of a slab whose liquid core has been stirred according to the teachings of the invention, Figure 5 is a graph showing the distribution of sulphur in the slab section of Figure 4, taken substantially along the line V-V thereof; and Figure 6 is a schematic circuit diagram of a two- !
phase-traveling magnetic field.
Describing now the drawings, it is to be understood that only enough of the construction of a continuous casting installation has been shown therein in order to enable those skilled in the art to readily understand the underlying prin-ciples and concepts of the invention. Turning attention now to Figure 1, reference numeral 1 designates a standard cooled, curved and oscillating mold for continuously casting a slab.
The liquid metal, here assumed to be steel, is supplied into the oscillating mold 1 by means of a conventional and therefore not particularly illustrated pouring or casting vessel, such as a tundish, with the aid of a pouring or casting tube which extends into the mold 1, as is well known in the technology.
The cast strand or casting 2 having a liquid core 3 and formed in the continous casting mold 1, is guided and supported along a curved strand guide arrangement or roller apron means 4 with the aid of rolls 5. The curved strand guide arrangement 4 follows the continuous casting mold 1 and has a radius which ?
is here assumed to amount to for instance 10 meters. Between the rolls 5 there are arranged standard spray nozzles 6 or the first sheet of drawing.
, -` -~ ~13720 - like for further cooling the continuously cast strand 2. By means of a conventional straightening and withdrawal unit or machine 7 the strand 2 is withdrawn out of the continuous casting mold l and straightened.
An electromagnetic stirrer lO, further details of which have been shown in Figure 6, is arranged below the lower end of the continuous casting mold l at a spacing of about 5 meters therefrom and at the inner side of the strand guide arrangement 5. Between the electromagnets or magnets lO' (Figure 6) of the electromagnetic stirrer lO and the inside of the continuously cast strand 2 there are arranged rolls 5' formed of an anti-magnetic material, for instance stainless steel. The rolls 5' have been omitted as a matter of convenience in illustration from the showing of Figure 6. In the polyphase stirrer system under discussion the electromagnets lO' are operating in a two-phase mode. But, however, also other polyphase electromagnets can be used, i.e. polyphase electromagnetic stirrers working with a greater number of phases can be employed, as will be readily evident to those skilled in the electronics art. The different thrust forces which are produced by the electromagnetic stirring action are effective transversely with respect to the lengthwise axis of the cast strand 2. Yet, these thrust forces also can be effective in the direction of the strand lengthwise axis.
The slabs which were cast at the described continuous casting installation had, by way of example and not limitation, a sectional shape of 1550 mm by 270 mm. The withdrawal speed amounted to about 0.55 m/min. Both phases i.e. the phase coils had applied thereto a potential of 200 volts and a frequency of 2 Hz and carried approximately 1000 amperes. Figure 2 is a micrograph of steel cast at a superheated temperature of 29C and containing 0.15% by weight C, 0.025~ by weight S
and other ac_ompanying el ments, there being employed a ~87ZO
conventional stirring technique. The micrograph shows a relatively thin marginal zone 20 having predominantly equiaxed structure. Following the zone 20 is a zone 21 having columnar structure with dendrites oriented towards the center. Following the zone 21 is a zone 22 containing an equiaxed crystal structure, which is brighter and constituting a white band. This band can consist of one section, as generally indicated by reference character 22, or can be subdivided into a number of bands 23, 24 and 25. Following the zone 22 is a zone 26 having compact, equiaxed crystal structure and which merges into the center segregation 27.
Figure 3 shows in graphic form the results of the quantitative analysis of the sulphur content along the line II-II of the slab micrograph of Figure 2. Along the ordinate there has been plotted the sulphur content in percent and along the abscissa the slab thickness. From this graph it will be recognized that the sulphur content in the white band (zone 23, 24, 25) has been appreciably reduced.
Figure 4 shows a micrograph of one-half of the cross-section of a slab which has been stirred according to theinventive method. The shape of the slab cross-section, steel quality, withdrawal speed, direction of the thrust forces, voltage and frequency were the same as described above in conjunction with the slab produced according to Figure 2 which emplo~ed conventional electromagnetic stirring principles.
The superheating temperature here amounted to approximately 43C. The intensity of the excitation current, for the coil 31,33 (Figure 6) of the one phase amounted to about 1000 amperes and for the coil 32, 34 of th~ other phase to about 830 amperes.
Hence, it will be recognized that one phase or phase coil has flowing therethrough a current which is approximately 20% higher than the current flowing through the other plase or phase coil, ~87~0 i.e., the phases of the electromagnetic fields are asymmetri-cally powered or supplied. In the ~icrograph of Figure 5, portraying a slab produced according to the teachings of the invention, there again will be recognized a zone 31 having predominantly equiaxed structure. Following this zone 31 is a zone 32 having dendrites oriented towards the center of the slab. However, this zone exhibits at the lateral ed~e an equiaxed crystal structure. A weakly formed zone 33 having a crystal structure, which does not exhibit any orientation, follows the zone 32. The center of the slab has a zone 34 possessing a likewise equiaxed crystal structure, which however is finer and more compact than that of the slab Figure 2.
Figure 5 shows the results of the quantitative analysis of the sulphur content along the line V-V of the slab of Figure 4 produced with the inventive electromagnetic stirring principles. From an analysis of such slab it will be seen that upon stirring the liquid core according to the inventive method, with the thus produced turbulent flow, there is obtained a relatively uniform distribution of the sulphur and there no longer occur, for the most part, both the positive center segregation and also the negative segregation in the zone 32, so that insignificant white bands are present.
The compact, equiaxed crystal structure and the inconsequential white bands, upon rollin~ the sl~b, afforded appreciably better properties for the rolled product, notwith-standing the fact that less space was required for the stirrer equipment to produce the turbulent flow.
In Figure 6 there is schematically shown one possibi-lity of designing the electromagnetic stirrer 10. Here there is shown a four part iron core, generally designated by reference character 30. Each part is provided with the coil windings 31, 32, 33, 34. The coil windings 31, 33 of the one phase coil form the firs-t phase and the coil windings 32, 34 of the other coil form the second phase. They are connected such that a traveling magnetic field, directed transversely with respect to the lengthwise direction of the strand, is formed in the liquid core 3.
In the exemplary embodiment under discussion the different thrust forces are produced, for instance, by having the coils 31, 33 and 32, 34 carry different current intensities.
As should be clearly understood, however, these ~ifferent thrust forces also can be produced in a different way,for instance in that there are used different geometric construction of the phases, i.e., for instance a different number of turns in each of the coils. Instead of a traveling magnetic field which is effective from one side of the strand, it is possible to have an additional traveling magnetic field act at the other side of the strand. The turbulent flow also can be effective within the mold itself, wnerein, however, the flo~ of the molten metal therein is advantageously maintained such that it does not affect the meniscus or bath level, in order to ~void impairment of the surface quality of the cast strand. In the case of strands having long liquid cores or sumps it is possible to have more than one traveling magnetic field effective in the lengthwise direction of the strand. The inventive method can be employed with all types of continuous casting installations having open-ended or throughpass molds.
It is of course to be understood that the two-phase system herein ~escribed is but exemplary. Obviously, other polyphase systems generating traveling or even rotating magnetic fields can be used in accordance with the teachings of the - present invention, so as to provide asymmetrical phases for producing the desired thrust forces and, in turn, the beneficial turbulent flow of the melt.
While there are shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto, but may be otherwise variously embodied and practiced within the scope of the follow-ing claims.
' .
During the continuous casting of metals, especially steel, it is known to the art to obtain, by m~gnetic stirring of the melt or molten metal in the liquid core, an improvement in the quality of the cast material by producing a more or less pronounced turbulent flow. These improvements in the quality of the casting have been obtained by different methods which apply thrust forces to the melt. In many instances there have been employed traveling magnetic fields for producing the thrust forces.
Contained within the steel are alloying and accompany-ing elements, such as carbon (C), silicon (Si), manganese (Mn), phosphorous (P), sulphur (S) and 90 forth , wllich, upon solidi-fication, can lead to ssgregations, especially center segre-gations. Such segregations, and equally the crystal structure, are dependent, as is known, among other things, upon the degree of sup3rheating. Due to the electromagnetic stirring and the turbulent flow which is thus produced, it is intended to prevent such segregations. The solidified structure should be affected - in such a manner that there is obtained as large as possible zone of compact or dense, equiaxed crystal structure. However, it has been found that owing to the local, pronounced movement of the melt the solid-liquid interface or solidification front is influenced such that there are formed so-called white bands. Theso white bands constitute negative ssgregations which impair the quality of the cast product.
' 1 ~
~1~8720 A^cording to a state-of-the-art method there are produced, by means of an electromagnetic traveling field, thrust forces in the direction of the lengthwlse axis of the strand, the magnets extending about the strand bein~ arranged between roll pairs up to the end of the liquid core or pool. The flow formed along the liquid core produces the desired region of non-columnar structure and prevents the formation of decisive segregations, especially center segregation and wllite bands.
This prior art arrangement, by virtue of the multiplicity of employed magnets, requires much too much space, hinders cooling of the stran~ and is much too complicated.
In accordance with another known technique for fabricating slab sections, attempts have been made to eliminate these white bands in that, by m~ans of electromagnetic traveling fields, generated by two magnets located opposite one another at the lengthwise sides of the cast strand, thrust forces are produced at the liquid steel. These thrust forces should be effective transversely with respect to the lengthwise axis of the strand, in order to obtain a gentle impact of the metal flow at the solidified strand wall, so that the deflected flow is maintained within a certain region. This limited effective zone produces an insufficient zone of compact, equiaxed crystal structure. Moreover, it has been found that with this method the white bands only can be unsatisfactorily eliminated, so that by virtue of this drawback there cannot be obtained any optimum cast product, something which has a negative effect in terms of the quality of, for instance, the rolled product.
Therefore, with the foregoing in mind, it is a primary object of the present invention to provide an improved method of continuously casting metals in a manner not afficted with the aforementioned drawbacks and shortcomin~s of the prior art proposals.
~87ZO
Still another and more specific object of the present invention aims at providing a continuous casting method which produces an adeq~ate zone of co.mpact or dense, equiaxed crystal structure.
Yet a further significant object is to provide a continuous casting method wherein the cast m~terial is low in segregations, especially center segregations and white bands.
A further object is to provide a continuous casting m~thod, employing electromagnetic stirrer principles, having extremely small space requirements for generating the magnetic stirring effect.
Now in order to implement these and still further obj2cts of the invention, wl~ich will become more readily apparent as the description proceeds, the method contemplates producing a turbulent flow by different thrust forces acting : upon the melt and generated by asymmetrical conditions prevail-~ ing in the phases of the fields.
: Tests carried out with a traveling magnetic field which is effective transversely with respect to the strand, and wherein the polyphase system producin~ the traveling field has identical windings in the coils and such coils carry the same current intensity, have shown that m.icrographs of the cast product exhibit w~lite bands and a wide zone of dendrites., thereby resulting in insufficient quality of the cast steel.
However, and as has been surprisingly found in accordance with the teachings of the present invention, with different thrust forces acting upon the mo~ten metal within the traveling field, there is then produced such a turbulent flow that, p.ractically no white bands app~ared in the micrograph and, furthermore, notwithstanding higher superheating temperature there is obtained the desired zone of compact or dense, e~uiaxed crystal structure without any significant center , . . - :
segregation. This effect is beneficially realized notwith-standing the quite modest space requirements which prevail for producing the traveling magnetic field.
According to a further feature of the invention, in order to produce the different thrust forces in a most simple manner, it is possible to have different current intensities flow through the coil of one phase in relation to the coil of at least one other phase of the electromagnetic field.
Accordin~ to a further aspect of the invention, the different thrust forces which are effective at the molten metal can be realized by having a current flow throu~h the coil of the one phase w~ich is approximately 10% to 25% higher than the current flowing through the coil of at least one other p~ase.
An advantageous effect of the method of the invention can be obtained if the differently effective thrust forces are produced transversely of or along the strand. The term "along the strand" m~ans in the lengthwise direction of the strand and is intended to embrace both the case where such thrust forces act essentially parallel to the lengthwise side of the strand or lengthwise and at an inclination to the lengthwise axis of the strand.
The invention will be better understood and objects other than those set forth above, will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:
Figure 1 illustrates an arrangement for producing a traveling maqnetic field for performing the metho~ in a curved or arc-type casting installation, Figure 2 is a micrograph of one-half of the cross-section of a slab whose liquid core has been stirred with a r ~ 487120 traveling magnetic field effective transversely with respect to the strand;
Figure 3 is a graph showing the distribution of r sulphur along the position of the slab marked by the line III of Figure 2;
Figure 4*is a micrograph of one-half of the cross-section of a slab whose liquid core has been stirred according to the teachings of the invention, Figure 5 is a graph showing the distribution of sulphur in the slab section of Figure 4, taken substantially along the line V-V thereof; and Figure 6 is a schematic circuit diagram of a two- !
phase-traveling magnetic field.
Describing now the drawings, it is to be understood that only enough of the construction of a continuous casting installation has been shown therein in order to enable those skilled in the art to readily understand the underlying prin-ciples and concepts of the invention. Turning attention now to Figure 1, reference numeral 1 designates a standard cooled, curved and oscillating mold for continuously casting a slab.
The liquid metal, here assumed to be steel, is supplied into the oscillating mold 1 by means of a conventional and therefore not particularly illustrated pouring or casting vessel, such as a tundish, with the aid of a pouring or casting tube which extends into the mold 1, as is well known in the technology.
The cast strand or casting 2 having a liquid core 3 and formed in the continous casting mold 1, is guided and supported along a curved strand guide arrangement or roller apron means 4 with the aid of rolls 5. The curved strand guide arrangement 4 follows the continuous casting mold 1 and has a radius which ?
is here assumed to amount to for instance 10 meters. Between the rolls 5 there are arranged standard spray nozzles 6 or the first sheet of drawing.
, -` -~ ~13720 - like for further cooling the continuously cast strand 2. By means of a conventional straightening and withdrawal unit or machine 7 the strand 2 is withdrawn out of the continuous casting mold l and straightened.
An electromagnetic stirrer lO, further details of which have been shown in Figure 6, is arranged below the lower end of the continuous casting mold l at a spacing of about 5 meters therefrom and at the inner side of the strand guide arrangement 5. Between the electromagnets or magnets lO' (Figure 6) of the electromagnetic stirrer lO and the inside of the continuously cast strand 2 there are arranged rolls 5' formed of an anti-magnetic material, for instance stainless steel. The rolls 5' have been omitted as a matter of convenience in illustration from the showing of Figure 6. In the polyphase stirrer system under discussion the electromagnets lO' are operating in a two-phase mode. But, however, also other polyphase electromagnets can be used, i.e. polyphase electromagnetic stirrers working with a greater number of phases can be employed, as will be readily evident to those skilled in the electronics art. The different thrust forces which are produced by the electromagnetic stirring action are effective transversely with respect to the lengthwise axis of the cast strand 2. Yet, these thrust forces also can be effective in the direction of the strand lengthwise axis.
The slabs which were cast at the described continuous casting installation had, by way of example and not limitation, a sectional shape of 1550 mm by 270 mm. The withdrawal speed amounted to about 0.55 m/min. Both phases i.e. the phase coils had applied thereto a potential of 200 volts and a frequency of 2 Hz and carried approximately 1000 amperes. Figure 2 is a micrograph of steel cast at a superheated temperature of 29C and containing 0.15% by weight C, 0.025~ by weight S
and other ac_ompanying el ments, there being employed a ~87ZO
conventional stirring technique. The micrograph shows a relatively thin marginal zone 20 having predominantly equiaxed structure. Following the zone 20 is a zone 21 having columnar structure with dendrites oriented towards the center. Following the zone 21 is a zone 22 containing an equiaxed crystal structure, which is brighter and constituting a white band. This band can consist of one section, as generally indicated by reference character 22, or can be subdivided into a number of bands 23, 24 and 25. Following the zone 22 is a zone 26 having compact, equiaxed crystal structure and which merges into the center segregation 27.
Figure 3 shows in graphic form the results of the quantitative analysis of the sulphur content along the line II-II of the slab micrograph of Figure 2. Along the ordinate there has been plotted the sulphur content in percent and along the abscissa the slab thickness. From this graph it will be recognized that the sulphur content in the white band (zone 23, 24, 25) has been appreciably reduced.
Figure 4 shows a micrograph of one-half of the cross-section of a slab which has been stirred according to theinventive method. The shape of the slab cross-section, steel quality, withdrawal speed, direction of the thrust forces, voltage and frequency were the same as described above in conjunction with the slab produced according to Figure 2 which emplo~ed conventional electromagnetic stirring principles.
The superheating temperature here amounted to approximately 43C. The intensity of the excitation current, for the coil 31,33 (Figure 6) of the one phase amounted to about 1000 amperes and for the coil 32, 34 of th~ other phase to about 830 amperes.
Hence, it will be recognized that one phase or phase coil has flowing therethrough a current which is approximately 20% higher than the current flowing through the other plase or phase coil, ~87~0 i.e., the phases of the electromagnetic fields are asymmetri-cally powered or supplied. In the ~icrograph of Figure 5, portraying a slab produced according to the teachings of the invention, there again will be recognized a zone 31 having predominantly equiaxed structure. Following this zone 31 is a zone 32 having dendrites oriented towards the center of the slab. However, this zone exhibits at the lateral ed~e an equiaxed crystal structure. A weakly formed zone 33 having a crystal structure, which does not exhibit any orientation, follows the zone 32. The center of the slab has a zone 34 possessing a likewise equiaxed crystal structure, which however is finer and more compact than that of the slab Figure 2.
Figure 5 shows the results of the quantitative analysis of the sulphur content along the line V-V of the slab of Figure 4 produced with the inventive electromagnetic stirring principles. From an analysis of such slab it will be seen that upon stirring the liquid core according to the inventive method, with the thus produced turbulent flow, there is obtained a relatively uniform distribution of the sulphur and there no longer occur, for the most part, both the positive center segregation and also the negative segregation in the zone 32, so that insignificant white bands are present.
The compact, equiaxed crystal structure and the inconsequential white bands, upon rollin~ the sl~b, afforded appreciably better properties for the rolled product, notwith-standing the fact that less space was required for the stirrer equipment to produce the turbulent flow.
In Figure 6 there is schematically shown one possibi-lity of designing the electromagnetic stirrer 10. Here there is shown a four part iron core, generally designated by reference character 30. Each part is provided with the coil windings 31, 32, 33, 34. The coil windings 31, 33 of the one phase coil form the firs-t phase and the coil windings 32, 34 of the other coil form the second phase. They are connected such that a traveling magnetic field, directed transversely with respect to the lengthwise direction of the strand, is formed in the liquid core 3.
In the exemplary embodiment under discussion the different thrust forces are produced, for instance, by having the coils 31, 33 and 32, 34 carry different current intensities.
As should be clearly understood, however, these ~ifferent thrust forces also can be produced in a different way,for instance in that there are used different geometric construction of the phases, i.e., for instance a different number of turns in each of the coils. Instead of a traveling magnetic field which is effective from one side of the strand, it is possible to have an additional traveling magnetic field act at the other side of the strand. The turbulent flow also can be effective within the mold itself, wnerein, however, the flo~ of the molten metal therein is advantageously maintained such that it does not affect the meniscus or bath level, in order to ~void impairment of the surface quality of the cast strand. In the case of strands having long liquid cores or sumps it is possible to have more than one traveling magnetic field effective in the lengthwise direction of the strand. The inventive method can be employed with all types of continuous casting installations having open-ended or throughpass molds.
It is of course to be understood that the two-phase system herein ~escribed is but exemplary. Obviously, other polyphase systems generating traveling or even rotating magnetic fields can be used in accordance with the teachings of the - present invention, so as to provide asymmetrical phases for producing the desired thrust forces and, in turn, the beneficial turbulent flow of the melt.
While there are shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto, but may be otherwise variously embodied and practiced within the scope of the follow-ing claims.
' .
Claims (11)
1. In a method for the continuous casting of metals, wherein the molten metal is cast into a mold to form a strand, the formed strand having a liquid core is withdrawn from the mold, guided and further cooled, and there is produced by at least one stirrer, inducing electromagnetic fields in the strand, a turbulent flow in the liquid core of the strand, the improve-ment which comprises the steps of:
generating the turbulent flow by means of differently effective thrust forces acting upon the molten metal and influenced by asymmetry in the phases of the electromagnetic fields.
generating the turbulent flow by means of differently effective thrust forces acting upon the molten metal and influenced by asymmetry in the phases of the electromagnetic fields.
2. The method as defined in claim 1, wherein:
said asymmetrical phases are provided by having a coil of one phase carry a current intensity which differs from the current intensity flowing through another coil of at least one other phase of the electromagnetic fields.
said asymmetrical phases are provided by having a coil of one phase carry a current intensity which differs from the current intensity flowing through another coil of at least one other phase of the electromagnetic fields.
3. The method as defined in claim 2, wherein:
the coil of one phase has a current flowing there-through which is higher, by about 10% to 25%, than the current flowing through the coil of the other phase.
the coil of one phase has a current flowing there-through which is higher, by about 10% to 25%, than the current flowing through the coil of the other phase.
4. The method as defined in claim 1, further including the steps of:
generating the differently effective thrust forces in a direction essentially -transverse to the lengthwise direction of the cast strand.
generating the differently effective thrust forces in a direction essentially -transverse to the lengthwise direction of the cast strand.
5. The method as defined in claim 1, further including the steps of:
generating the differently effective thrust forces essentially along the lengthwise axis of the cast strand.
generating the differently effective thrust forces essentially along the lengthwise axis of the cast strand.
6. A method of continuously casting metals, comprising the steps of:
casting a molten metal into a continuous casting mold to form a strand; and generating at least one traveling electromagnetic field in the continuously cast strand by means of asymmetrical phases in order to produce a turbulent flow in the liquid core of the cast strand for electromagnetic stirring thereof.
casting a molten metal into a continuous casting mold to form a strand; and generating at least one traveling electromagnetic field in the continuously cast strand by means of asymmetrical phases in order to produce a turbulent flow in the liquid core of the cast strand for electromagnetic stirring thereof.
7. The method as defined in claim 6, wherein:
said asymmetrical phases are provided by having a coil of one phase producing the electromagnetic field carry a current intensity which differs from the current intensity flowing through another coil of at least one other phase of the electromagnetic field.
said asymmetrical phases are provided by having a coil of one phase producing the electromagnetic field carry a current intensity which differs from the current intensity flowing through another coil of at least one other phase of the electromagnetic field.
8. The method as defined in claim 7, wherein:
the coil of one phase has a current flowing there-through which is higher, by about 10% to 25%, than the current flowing through the coil of the other phase.
the coil of one phase has a current flowing there-through which is higher, by about 10% to 25%, than the current flowing through the coil of the other phase.
9. The method as defined in claim 6, further including the steps of:
generating by means of said electromagnetic field differently effective thrust forces acting upon the metal of the liquid core of the cast strand.
generating by means of said electromagnetic field differently effective thrust forces acting upon the metal of the liquid core of the cast strand.
10. The method as defined in claim 9, wherein:
said differently effective thrust forces act in a direction essentially transverse to the length-wise direction of the cast strand.
said differently effective thrust forces act in a direction essentially transverse to the length-wise direction of the cast strand.
11. The method as defined in claim 9, wherein:
the differently effective thrust forces act essentially along the lengthwise axis of the cast strand.
the differently effective thrust forces act essentially along the lengthwise axis of the cast strand.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CH813478A CH632172A5 (en) | 1978-07-28 | 1978-07-28 | Method for the continuous casting of steel |
| CH8134/78-0 | 1978-07-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1148720A true CA1148720A (en) | 1983-06-28 |
Family
ID=4335680
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000332754A Expired CA1148720A (en) | 1978-07-28 | 1979-07-27 | Method of continuously casting metal |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5946701B2 (en) |
| CA (1) | CA1148720A (en) |
| CH (1) | CH632172A5 (en) |
| IN (1) | IN150067B (en) |
| ZA (1) | ZA793776B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH04148854A (en) * | 1990-10-12 | 1992-05-21 | Mitsubishi Electric Corp | Surface-defect detecting apparatus |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5440242Y2 (en) * | 1976-08-03 | 1979-11-28 | ||
| SE410940C (en) * | 1978-04-05 | 1986-01-27 | Asea Ab | METHOD OF CHARACTERIZATION BY STRING |
-
1978
- 1978-07-28 CH CH813478A patent/CH632172A5/en not_active IP Right Cessation
-
1979
- 1979-03-01 IN IN189/CAL/79A patent/IN150067B/en unknown
- 1979-07-24 ZA ZA00793776A patent/ZA793776B/en unknown
- 1979-07-27 JP JP54095963A patent/JPS5946701B2/en not_active Expired
- 1979-07-27 CA CA000332754A patent/CA1148720A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| IN150067B (en) | 1982-07-10 |
| ZA793776B (en) | 1980-07-30 |
| JPS5519500A (en) | 1980-02-12 |
| CH632172A5 (en) | 1982-09-30 |
| JPS5946701B2 (en) | 1984-11-14 |
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