CA1296861C - Continuous casting molds - Google Patents
Continuous casting moldsInfo
- Publication number
- CA1296861C CA1296861C CA000551077A CA551077A CA1296861C CA 1296861 C CA1296861 C CA 1296861C CA 000551077 A CA000551077 A CA 000551077A CA 551077 A CA551077 A CA 551077A CA 1296861 C CA1296861 C CA 1296861C
- Authority
- CA
- Canada
- Prior art keywords
- mold
- metal
- thermal barrier
- interior surface
- molten metal
- 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 - Lifetime
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
-
- 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
- B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
- B22D11/045—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds for horizontal casting
-
- 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
- B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
- B22D11/045—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds for horizontal casting
- B22D11/047—Means for joining tundish to mould
-
- 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
- B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
- B22D11/045—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds for horizontal casting
- B22D11/047—Means for joining tundish to mould
- B22D11/0475—Means for joining tundish to mould characterised by use of a break ring
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Continuous Casting (AREA)
Abstract
CONTINUOUS CASTING MOLDS
Abstract of the Disclosure Molds suitable for the continous horizontal casting of ferrous metals have integral thermal barrier layers extending over at least that portion of the end of the mold adjacent to the interior surface of the mold that defines the shape of the casting. The thermal barrier layer eliminates the need for a break ring and can provide stock material of enhanced quality and appearance. Moreover, the mold can be provided in a near net shape configuration to the ultimately desired stock.
Abstract of the Disclosure Molds suitable for the continous horizontal casting of ferrous metals have integral thermal barrier layers extending over at least that portion of the end of the mold adjacent to the interior surface of the mold that defines the shape of the casting. The thermal barrier layer eliminates the need for a break ring and can provide stock material of enhanced quality and appearance. Moreover, the mold can be provided in a near net shape configuration to the ultimately desired stock.
Description
,.. " ~ 97~
CONTINUOUS CASTING MOLDS
This invention relates to molds for the continuous, horizontal casting of metallic materials and processes for using the molds.
Back~ound to the InYention Metals, e.g., steel, nickel, iron, etc., are ormed into shaped articles through a variety of techniques. The continuous casting of molten metal is a particularly advantageous means to form metal into forms useful for further processing. In these continuous casting processes, the molten metal is passed through a mold which shapes the metal and in which solidification commences. Generally, the continuous casting processes fall into one of two classes, a vertical casting process or a horizontal casting process.
In a vertical casting process, the molten metal is poured, through the force of gravity, into a mold. The formed stock then passes downward and is redirected by rollers to a horiæontal orientation for subsequent handling snd processing. While vertical casting processes find commercial application, noticeable drawbacks are the hei8ht at which the casting operation must occur and the energy and equipment that must be used to reorient the continuous stock from the mold.
The horizontal casting process offers an alternative. In this process, molten metal in a tundish is passed through a lower portion of the tundish nnd into a horizontally-oriented mold in which the solidification of the ~tock commences. The stock is withdrawn from the mold, usually with an oscillating pulling to facilitate the movement of the stock in the mold.
Since the operation is horizontal, ~he capital requirements and operational .
problems associated with the vertical casting processes are not incurred.
While the horizontal continuous casting of metals can provide advan-tages, other considerations must be taken into account. For example, a sub-stantially fluid-tight seal must exist between the tundish and the mold to prevent undue leakage of the molten me~al. Further, the mold, which is nor-mally a fluid ~e.g., waterj cooled mold composed of a metal of high heat conductivity such as a copper-based metal, is at a substantially lower temper-ature than the metal in the tundish. Consequently, not only must coefficients of thermal expansion be accommodated, but also, other problems can occur.
For instance, molten metal may pass into any crevices between the tundish and mold and solidify, and these solids can cause scoring of the surface of the stock and may even induce structural weaknesses in the stock. Also, ~hipping of the solid may occur and pass into the stock being produced, resulting in damage and imperfections in the stock as well as the mold.
In order to overcome these problems, the common practice has been to tightly fit the mold with a break ring. The break ring typically fits in the interior of the mold at its inlet end and forms a ring of smaller internal dimensions than the interior perimeter of the mold. The break ring is formed of a low heat conductivity ceramic having a relatively smooth surface.
Generally, the break ring is composed of boron nitride. The break ring must be carefully machined to close tolerances to fit the dimensions of the mold.
~ he break ring serves to provide insulation between the tundish opening (or nozzle) and the mold, and aids in defining where the skin solidification of the stock occurs. Hence, the metal may be molten when it contacts the break ring and commences solidification as it approaches or contacts the mold. Thus, problems with leakage of molten metal into crevices with subse-quent solidification can be virtually avoided. However, the oscillating .~','~. '' ' ' ,, .' ' ~3 movement of the stock as it is pulled from the mold, together with the smaller cross-section opening formed by the break ring and the large cross-section opening of the mold can lead to the formation of what is termed as witness marks, that is, marks coinciding with the pushing of solidified metal surface back into the molten metal flowing from the break ring. Moreover, with start-up or shut-down of the continuous casting apparatus, thermal gradients and differentials in expansion can lead to the damage of the break ring and adversely affect the quality of the stock.
As mentioned above, break rings must be carefully machined to fit the mold. Because of the tight tolerances that must be met in fitting the break ring to the mold and the machining costs, molds are usually of limited con-figurations such as circular, square or rectangular in cross section. Long, narrow molds, for instance, can result in a bowing or breaking in use of the break ring and untoward seepage of molten metal. Hence, the size and cross-sectional configuration of the stock are limited to, e.g., billets, blooms and the like, and significant energy must be expended to work the stock into the sought shape such as an I-beam or plate material.
Accordingly, a need has existed to provide continuous horizontal casting processes which provide acceptable quality metal stock without the diffi-culties attendant with the machining and fitting of break rings into molds.
It would be further desirable to provide processes in which witness marks were reduced in size, if not eliminated, to enhance the appearance and strength of the stock. Moreover, the ability to produce near net shape stock by continuous horizontal casting would be particularly desirable.
Summary_of the Invention By ~his invention molds for the continuous horizontal casting of ferrous metals are provided which do not depend upon the fit~ing of a separate break ring into a mold, yet are able to provide acceptable quality stock. In aspects of this invention, the molds can provide stock with reduced, and sometimes substantially eliminated, witness mark effects. In other aspects of this invention, molds can be readily provided that are suitable for the continuous horizontal casting of near net shape stock which is of acceptable ~uality.
In accordance with this invention, the mold comprises an interior surface, an end surface adapted to contact a nozzle through which molten metal passes and on at least that portion of the end surface adjacent to the interior surface, an integral thermal barrier of sufficient thickness to maintain the metal first contacting the thermal barrier substantially molten. The thermal barrier may comprise any suitably applied ceramic thermal barrier coating that is able to withstand the high temperatures associated with the molten metal and is not chemically attacked by the molten metal.
The coating may provide a cross-section substantially the same as that of the mold and can thereby minimize the de8ree of formation of witness marks.
Moreover, since the coating is integral with the mold, the cross-section configuration of the mold need not be limited to those which are operable with separate break rings.
The metal being formed may be ferrous metal, e.g., steel or iron, or may be non-ferrous such as nickel. Generally, the processes of this invention are most advantageous when handling hi&h temperature metals.
~-Ic~ De~ go f the Drawin ~
Figure 1 is a schematic, longitudinal cross-sectional depiction of a .
--5~ 8 tundish having a noz~le and a mold.
Figure 2 is a schematic, longitudinal cross-sectional depiction of the entry portion of a horizontal casting mold with a break ring.
~ igures 3, 4, and 5 are schematic, longitudinal cross-section depictions of the entry portioh of three horizontal casting molds in accordance with this invention.
Description Continuous casting molds are typically fabricated from a relatively high conductivity metal such as a copper-based metal. The mold is cooled with cooling fluid such as water to remove heat from the mold and provide the casting of the ferrous stock~ The mold has an internal cross-sectional configuration approaching that of the extruded stock. Generally, the cross-section is approximately regular through the length of the mold in the direction of the flow of the steel. One end of the mold is adapted to abut the nozzle from the tundish. For the sake of convenience, this end will be termed the end plate for the purposes herein. The end plate may extend in a plane substantially perpendicular to the axis of the mold or may have another suitable configuration for con~act with the nozzle of the tundish.
In any event, the contact should be substantially f~uid-tight in order to prevent undue leakage of the molten metal be~ween the nozzle and the mold.
`At least that portion of the end plate adjacent to the interior surface of the mold is pro~ided with an integral thermal barrier. The thermal barrier may be ceramic and often is comprised of a refractory oxide. Preferably, the thermal barrier is substantially inert to the molten metal. Typical refractory oxides include alumina, silica, zirconia (especially yttrium-stabilized zirconia), magnesia, chromia and mixtures and compounds .
thereof. Other ceramics include silicon nitride, zirconium nitride, titanium carbide, titanium nitride and the like.
The integral thermal barrier may be applied by any suitable technique that provides adequate adherence to the mold including under the tempera-tures and stresses that exist in the casting operation. Particularly use-ful techniques include the thermal spray processes in which the powder to form the coating is contacted under temperature and velocity with the surface to be coated. Exemplary of these processes are the plasma torch coating, detonation gun, hypersonic combustion spray, and flame spray coating processes.
Undercoats and/or gradient coa~ings may also find application in assist-ing to provide the strength and thermal shock resistance re~uired for the thermal barrier. Undercoats include the MCrAlY-type undercoats in which M is at least one of cobalt, nickel and iron. Often the undercoat is 25 to 200 microns in thickness. This class of undercoats provides desirable adherence to the mold, including the copper-based materials used in fabricat-ing the mold, and in the over-layer of ceramic material. The ceramic material ; may be formed in different layers or may be formed as a continuous gradient of differing compositions to mitigate the effects of differentials in thermal expansion snd thermal shock. As can be well appreciated, the materials of the molds, such as copper and copper-based metals, are often characterized by relatively large coefficients of thermal expansion wherein ceramics generally have much lower coefficients of thermal expansion. By varying the composition of the overlay ~rom one which contains a portion of the ceramic and a portion of a material that has both good bonding and a higher coefficient of ~hermal expansion at the interior to one which consists essen-tially of the ceramic at the exterior surface that contacts the molten metal, :;
, - , - - - - . ~.......................................... . .
- - - , .. ..
-~ ~29~
beneficial properties can be obtained including resistance to cracking or chipping of the thermal barrier. Clearly, any cracking or chipping can result in the molten metal solidifying and adversely affecting the quality of the stock.
With respect to Figure 1 ~undish 100 contains molten metal 102. The tundish is generally filled in a batch operation with molten metal, The tundish may be heated externally to assure that the metal remains molten and is usually fabricated from refractory such as zirconia brick. The tundish ` ~ is provided with nozzle 104 through which the molten metal passes. The nozzle is also usually fabricated from refractory such as zirconia brick. Zirconia brick can be porous and fragile; however9 it is not generally considered to be suitable for the area immediately adjacent the mold. In a conventional, continuous horizontal casting apparatus, the break ring would be positioned between the mold and nozzle.
The mold 106 is shown in schematic cross-section. The mold cooling channels are not shown. The heat transfer to the coolant occurs at the periphery of mold at the area generally designated as lOô. Positioned between nozzle 104 at the interior surface 110 of mold 106 is thermal barrier 112. The partially solidified stock 114 is withdrawn from mold 106 and is passed to a series of rollers 116 (only one depicted), some of which are driven to pull the stock from the mold and pass it to further processing.
The driven rollers are typically operated such that the stock oscillates in the mold. Alternate methods of gripping the stock and moving are also used e.g., jaws which grab the stock and move it.
Figure 2 schematically depicts a portion of a mold using a conventional break rin8. With reference to the drawing, mold 200 shuts nozzle 202 of : ~ .
. . .
the tundish. Break ring 204 is positioned between the nozzle and the in-terior surface 206 of the mold. Molten metal 208 passes through the nozzle and break ring and thereafter fills the cross-section of the mold de~ined by the interior surface 206 of the mold. Solidification of the surface of the molten metal (skin formation) usually occurs at a point on the downstream face of the break ring and on the interior surface of the mold which is desig-nated as zone 210. The oscillation of the stock pushes the skin back into molten metal and causes the irregularities referred to as witness marks.
Figure 3 depicts a portion of mold 300 which is in accordance with this invention. Mold 300 has interior surface 302 and end plate 304 which has placed thereon thermal barrier 306. In this embodiment of the invention, the thermal barrier is exclusively on the end plate and the thermal barrier smoothly meets interior surface 302 and extends the cross-section of the mold.
The thickness of the thermal barrier is sufficient that the molten metal passing between nozzle 308 and the abutting surface of the thermal barrier does not solidify. Molten metal which does seep into the crevice can, however, solidify well within the crevice without undue adverse effect. The portion of the thermal barrier contacting the nozzle 308 can be machined to fit snugly against the nozzle or may be left in a roughened state, especially when a ceramic cement is used to secure the thermal barrier to the nozzle.
The differential in temperature between the nozzle and the mold may nften be 500C. or more. Accordingly, the thickness of the thermal barrier -ust be sufficient to prevent significant cooling of the contact region between the molten metal, ~he thermal barrier and the nozzle. Often, the thlckness of the thermal barrier is at least about 250 microns, say, at least ..
::~
, . . .
8~
about 500 microns, and often is in the range of about 700 to 1500 or 2000 microns.
As can be seen in Figure 3, the thermal barrier extends over at least a portion of the end plate of the mold. By integrally securing the thermal barrier to the end plate9 strength is provided to the thermal barrier to enable it to withstand the forces associated with the flowing molten metal, as well as provide enhanced thermal shock resistance. For instance, the thermal barrier provides thermal insulation not only in a radial direction toward the molten metal flsw, but also in an axial direction.
The solidification (formation of skin) of the molten metal can occur while the molten metal is in contact with the internal surface 310 of the thermal barrier. This is possible since the thermal barrier is integral with the mold and hence molten metal cannot seep between the thermal barrier and the mold as is possible when using a break ring. With a smooth contour between the thermal barrier and the internal surface of the mold, the for-mation of witness marks due to the oscillating of the stock from the mold generally does not occur with the same severity as those formed when using a break ring.
Many of the materials that we applied as thermal barriers can readily be machined. Since the machining can be done when the thermal barrier is integral with the mold, it is much more easily conducted than the machining of a break rin~. The machining can also produce a very smooth surface (less than 50 microinches, rms), which enhances the ability to provide a high quality stock with minimum imperfections.
~ Flgure 4 illustrates another embodiment o~ the invention in which the ;~ thermal barrier 406 on mold 400 is thicker at its interior edge 410. The ' . ' .:, end plate, 404 of the mold shown, is beveled as it approaches the interior surface 402 of the mold~
Figl~re 5 illustra~es yet another embodiment of the invention in which the thermal barrier 506 not only extends over a portion of the end plate 504 of the mold 500, but also extends radially inwardly from interior sur~ace 502 of the mold. As depicted, nozzle 308 abuts with the thermal barrier proximate to the flow of molten metal and a portion of end plate 504.
The strength and integrity provided by the thermal barrier extending over the end plate of the mold enhances the ability of the portion of the thermal barrier extending into the cavity of the mold to withstand the stress-es of the flowing molten metal and reduce the risk of chipping.
The interior surface 510 of the thermal barrier is shown as being con-toured and ~apering into the interior surface 502 of the mold. Since the thermal barrier is integral with the interior surface 502, the deleterious effects of which could be caused by molten metal seeping between the com-ponents do not occur. Moreover, the contour at least partially replaces the void space characteristics of the break ring design of Figure 2, and can result in attentuated witness marks.
As can be seen from the foregoing discussion, the thermal barrier may constitute a wide ~ariety of configurations provided that the thermal barrier extends over at least that portion of the end plate of the mold which is adJacent the interior surface of the mold. The end plate of the mold, for instance, may be tapered or otherwise configured to provide more thermal ~barrier adjacent the interior surface of the mold, such as by beveling, rout-ing, providing indentations or the like.
Since the thermal barrier is integral with the mold, the transverse :: .
., ' ' ~ '' ' . . ' .
~, . . . .
~2~;8~
cross-section of the mold may be in virtually any shape limited by the abili-ty to provide proper cooling to ~he flow of molten metal in the mold and the ability to apply (and machine, if necessary3 the thermal barrier. Hence, near net shape horizontal castings can be produced with substantial reduction in capital and operating costs required to reform a conventional billet or bloom into the desired ultimate shape such as I-beam, plates, sheets, and the like.
Moreover, since the thermal barrier can be applied by a coating tech-nique, molds czn be readily repaired. Further 7 since using thermal barrier materials also exhibit abrasion resistance, by coating a portion of the in-terior surface of the mold, such as in Figure 5, the useful life of the mold may be enhanced.
A copper mold for the horizontal casting of steel is coated in accord-ance with this invention on the end plate, or flange face, using an undercoat of Co-Ni-Cr~ Y and an overcoat of yttria stabilized zirconia. The throat of the copper mold is about 4" long with a cross-section of 5-1/4" x 7" with the corners having approximately a 1/8" radius. The total flange face is about 10-15/16" x 9-3/16" (with the throat centered in the flange face) and corners with about a 2" radius. The periphery of the flange face has a 7/16"
wide lip about 3/8" deep to contain a zirconia block used as a nozzle for pouring steel. Four separate molds are prepared. In all cases, the copper is first grit-blasted using 60 mesh alumina grit and then plasma sprayed with an undercoat of nominally 32Ni-21Cr-8Al-0.5Y-Bal Co, all in weight per-~ent, to a thickness of 0.003 to 0.005 inches~ Over this metallic undercoat a zirconia coating consisting of ZrO,-7 wt.~ Y~O, is applied.
In one of the molds the substrate is ground to a sharp corner prior ., ,' ~ . ' ' ' ' . .
~ \
~fi~
to grit blasting and undercoa~ing and then oversprayed with a total thickness of 0.020-0.025 inches of zirconia. The edge of the zirconia coating at the in~erior surface of the mold has a slight radius since some curvature is inherent i~ the coating process. In another mold the copper at the flange face is ground to a radius of about 0.050 inches before grit blasting and undercoating and subsequently coated at a 90 angle of impingement to a total coating thickness of about 0.515 inches. A portion of this segment is then ground to a total zirconia coating thickness of 0.024 inches, still leaving a small radius of curvature on the coated corner. In a third mold, the sub-strate is ground to a corner radius of about 0.050 inches prior to coating and subsequently coated at an angle of impingement slightly less than 90 to form a lip on the corner. The total zirconia coating thickness is about 0.128 inches. A small portion of this segment is subsequently ground to a total coating thickness of 0.0227 inches leaving a very sharp corner and a slightly negative angle of zirconia Oll the corner. An advantage of this configuration may be a somewhat better bond at the corner. In the fourth mold, the coper substrate is left with a sharp, round corner and about 0.121 inches of zirconi is applied. A portion of this segment is subsequently ground to a thickness of 0.057 inches leaving a very sharp corner on the zirconia. This remaining thickness of zirconia should be equivalent5 thermally, to that which is currently used on conventional boron nitride break rings. The entire flange face could be ground to a uni~orm coating thickness.
The above-described molds having a thermal barrier are employed for the continuous horizontal casting of steel.
' ' ' .
CONTINUOUS CASTING MOLDS
This invention relates to molds for the continuous, horizontal casting of metallic materials and processes for using the molds.
Back~ound to the InYention Metals, e.g., steel, nickel, iron, etc., are ormed into shaped articles through a variety of techniques. The continuous casting of molten metal is a particularly advantageous means to form metal into forms useful for further processing. In these continuous casting processes, the molten metal is passed through a mold which shapes the metal and in which solidification commences. Generally, the continuous casting processes fall into one of two classes, a vertical casting process or a horizontal casting process.
In a vertical casting process, the molten metal is poured, through the force of gravity, into a mold. The formed stock then passes downward and is redirected by rollers to a horiæontal orientation for subsequent handling snd processing. While vertical casting processes find commercial application, noticeable drawbacks are the hei8ht at which the casting operation must occur and the energy and equipment that must be used to reorient the continuous stock from the mold.
The horizontal casting process offers an alternative. In this process, molten metal in a tundish is passed through a lower portion of the tundish nnd into a horizontally-oriented mold in which the solidification of the ~tock commences. The stock is withdrawn from the mold, usually with an oscillating pulling to facilitate the movement of the stock in the mold.
Since the operation is horizontal, ~he capital requirements and operational .
problems associated with the vertical casting processes are not incurred.
While the horizontal continuous casting of metals can provide advan-tages, other considerations must be taken into account. For example, a sub-stantially fluid-tight seal must exist between the tundish and the mold to prevent undue leakage of the molten me~al. Further, the mold, which is nor-mally a fluid ~e.g., waterj cooled mold composed of a metal of high heat conductivity such as a copper-based metal, is at a substantially lower temper-ature than the metal in the tundish. Consequently, not only must coefficients of thermal expansion be accommodated, but also, other problems can occur.
For instance, molten metal may pass into any crevices between the tundish and mold and solidify, and these solids can cause scoring of the surface of the stock and may even induce structural weaknesses in the stock. Also, ~hipping of the solid may occur and pass into the stock being produced, resulting in damage and imperfections in the stock as well as the mold.
In order to overcome these problems, the common practice has been to tightly fit the mold with a break ring. The break ring typically fits in the interior of the mold at its inlet end and forms a ring of smaller internal dimensions than the interior perimeter of the mold. The break ring is formed of a low heat conductivity ceramic having a relatively smooth surface.
Generally, the break ring is composed of boron nitride. The break ring must be carefully machined to close tolerances to fit the dimensions of the mold.
~ he break ring serves to provide insulation between the tundish opening (or nozzle) and the mold, and aids in defining where the skin solidification of the stock occurs. Hence, the metal may be molten when it contacts the break ring and commences solidification as it approaches or contacts the mold. Thus, problems with leakage of molten metal into crevices with subse-quent solidification can be virtually avoided. However, the oscillating .~','~. '' ' ' ,, .' ' ~3 movement of the stock as it is pulled from the mold, together with the smaller cross-section opening formed by the break ring and the large cross-section opening of the mold can lead to the formation of what is termed as witness marks, that is, marks coinciding with the pushing of solidified metal surface back into the molten metal flowing from the break ring. Moreover, with start-up or shut-down of the continuous casting apparatus, thermal gradients and differentials in expansion can lead to the damage of the break ring and adversely affect the quality of the stock.
As mentioned above, break rings must be carefully machined to fit the mold. Because of the tight tolerances that must be met in fitting the break ring to the mold and the machining costs, molds are usually of limited con-figurations such as circular, square or rectangular in cross section. Long, narrow molds, for instance, can result in a bowing or breaking in use of the break ring and untoward seepage of molten metal. Hence, the size and cross-sectional configuration of the stock are limited to, e.g., billets, blooms and the like, and significant energy must be expended to work the stock into the sought shape such as an I-beam or plate material.
Accordingly, a need has existed to provide continuous horizontal casting processes which provide acceptable quality metal stock without the diffi-culties attendant with the machining and fitting of break rings into molds.
It would be further desirable to provide processes in which witness marks were reduced in size, if not eliminated, to enhance the appearance and strength of the stock. Moreover, the ability to produce near net shape stock by continuous horizontal casting would be particularly desirable.
Summary_of the Invention By ~his invention molds for the continuous horizontal casting of ferrous metals are provided which do not depend upon the fit~ing of a separate break ring into a mold, yet are able to provide acceptable quality stock. In aspects of this invention, the molds can provide stock with reduced, and sometimes substantially eliminated, witness mark effects. In other aspects of this invention, molds can be readily provided that are suitable for the continuous horizontal casting of near net shape stock which is of acceptable ~uality.
In accordance with this invention, the mold comprises an interior surface, an end surface adapted to contact a nozzle through which molten metal passes and on at least that portion of the end surface adjacent to the interior surface, an integral thermal barrier of sufficient thickness to maintain the metal first contacting the thermal barrier substantially molten. The thermal barrier may comprise any suitably applied ceramic thermal barrier coating that is able to withstand the high temperatures associated with the molten metal and is not chemically attacked by the molten metal.
The coating may provide a cross-section substantially the same as that of the mold and can thereby minimize the de8ree of formation of witness marks.
Moreover, since the coating is integral with the mold, the cross-section configuration of the mold need not be limited to those which are operable with separate break rings.
The metal being formed may be ferrous metal, e.g., steel or iron, or may be non-ferrous such as nickel. Generally, the processes of this invention are most advantageous when handling hi&h temperature metals.
~-Ic~ De~ go f the Drawin ~
Figure 1 is a schematic, longitudinal cross-sectional depiction of a .
--5~ 8 tundish having a noz~le and a mold.
Figure 2 is a schematic, longitudinal cross-sectional depiction of the entry portion of a horizontal casting mold with a break ring.
~ igures 3, 4, and 5 are schematic, longitudinal cross-section depictions of the entry portioh of three horizontal casting molds in accordance with this invention.
Description Continuous casting molds are typically fabricated from a relatively high conductivity metal such as a copper-based metal. The mold is cooled with cooling fluid such as water to remove heat from the mold and provide the casting of the ferrous stock~ The mold has an internal cross-sectional configuration approaching that of the extruded stock. Generally, the cross-section is approximately regular through the length of the mold in the direction of the flow of the steel. One end of the mold is adapted to abut the nozzle from the tundish. For the sake of convenience, this end will be termed the end plate for the purposes herein. The end plate may extend in a plane substantially perpendicular to the axis of the mold or may have another suitable configuration for con~act with the nozzle of the tundish.
In any event, the contact should be substantially f~uid-tight in order to prevent undue leakage of the molten metal be~ween the nozzle and the mold.
`At least that portion of the end plate adjacent to the interior surface of the mold is pro~ided with an integral thermal barrier. The thermal barrier may be ceramic and often is comprised of a refractory oxide. Preferably, the thermal barrier is substantially inert to the molten metal. Typical refractory oxides include alumina, silica, zirconia (especially yttrium-stabilized zirconia), magnesia, chromia and mixtures and compounds .
thereof. Other ceramics include silicon nitride, zirconium nitride, titanium carbide, titanium nitride and the like.
The integral thermal barrier may be applied by any suitable technique that provides adequate adherence to the mold including under the tempera-tures and stresses that exist in the casting operation. Particularly use-ful techniques include the thermal spray processes in which the powder to form the coating is contacted under temperature and velocity with the surface to be coated. Exemplary of these processes are the plasma torch coating, detonation gun, hypersonic combustion spray, and flame spray coating processes.
Undercoats and/or gradient coa~ings may also find application in assist-ing to provide the strength and thermal shock resistance re~uired for the thermal barrier. Undercoats include the MCrAlY-type undercoats in which M is at least one of cobalt, nickel and iron. Often the undercoat is 25 to 200 microns in thickness. This class of undercoats provides desirable adherence to the mold, including the copper-based materials used in fabricat-ing the mold, and in the over-layer of ceramic material. The ceramic material ; may be formed in different layers or may be formed as a continuous gradient of differing compositions to mitigate the effects of differentials in thermal expansion snd thermal shock. As can be well appreciated, the materials of the molds, such as copper and copper-based metals, are often characterized by relatively large coefficients of thermal expansion wherein ceramics generally have much lower coefficients of thermal expansion. By varying the composition of the overlay ~rom one which contains a portion of the ceramic and a portion of a material that has both good bonding and a higher coefficient of ~hermal expansion at the interior to one which consists essen-tially of the ceramic at the exterior surface that contacts the molten metal, :;
, - , - - - - . ~.......................................... . .
- - - , .. ..
-~ ~29~
beneficial properties can be obtained including resistance to cracking or chipping of the thermal barrier. Clearly, any cracking or chipping can result in the molten metal solidifying and adversely affecting the quality of the stock.
With respect to Figure 1 ~undish 100 contains molten metal 102. The tundish is generally filled in a batch operation with molten metal, The tundish may be heated externally to assure that the metal remains molten and is usually fabricated from refractory such as zirconia brick. The tundish ` ~ is provided with nozzle 104 through which the molten metal passes. The nozzle is also usually fabricated from refractory such as zirconia brick. Zirconia brick can be porous and fragile; however9 it is not generally considered to be suitable for the area immediately adjacent the mold. In a conventional, continuous horizontal casting apparatus, the break ring would be positioned between the mold and nozzle.
The mold 106 is shown in schematic cross-section. The mold cooling channels are not shown. The heat transfer to the coolant occurs at the periphery of mold at the area generally designated as lOô. Positioned between nozzle 104 at the interior surface 110 of mold 106 is thermal barrier 112. The partially solidified stock 114 is withdrawn from mold 106 and is passed to a series of rollers 116 (only one depicted), some of which are driven to pull the stock from the mold and pass it to further processing.
The driven rollers are typically operated such that the stock oscillates in the mold. Alternate methods of gripping the stock and moving are also used e.g., jaws which grab the stock and move it.
Figure 2 schematically depicts a portion of a mold using a conventional break rin8. With reference to the drawing, mold 200 shuts nozzle 202 of : ~ .
. . .
the tundish. Break ring 204 is positioned between the nozzle and the in-terior surface 206 of the mold. Molten metal 208 passes through the nozzle and break ring and thereafter fills the cross-section of the mold de~ined by the interior surface 206 of the mold. Solidification of the surface of the molten metal (skin formation) usually occurs at a point on the downstream face of the break ring and on the interior surface of the mold which is desig-nated as zone 210. The oscillation of the stock pushes the skin back into molten metal and causes the irregularities referred to as witness marks.
Figure 3 depicts a portion of mold 300 which is in accordance with this invention. Mold 300 has interior surface 302 and end plate 304 which has placed thereon thermal barrier 306. In this embodiment of the invention, the thermal barrier is exclusively on the end plate and the thermal barrier smoothly meets interior surface 302 and extends the cross-section of the mold.
The thickness of the thermal barrier is sufficient that the molten metal passing between nozzle 308 and the abutting surface of the thermal barrier does not solidify. Molten metal which does seep into the crevice can, however, solidify well within the crevice without undue adverse effect. The portion of the thermal barrier contacting the nozzle 308 can be machined to fit snugly against the nozzle or may be left in a roughened state, especially when a ceramic cement is used to secure the thermal barrier to the nozzle.
The differential in temperature between the nozzle and the mold may nften be 500C. or more. Accordingly, the thickness of the thermal barrier -ust be sufficient to prevent significant cooling of the contact region between the molten metal, ~he thermal barrier and the nozzle. Often, the thlckness of the thermal barrier is at least about 250 microns, say, at least ..
::~
, . . .
8~
about 500 microns, and often is in the range of about 700 to 1500 or 2000 microns.
As can be seen in Figure 3, the thermal barrier extends over at least a portion of the end plate of the mold. By integrally securing the thermal barrier to the end plate9 strength is provided to the thermal barrier to enable it to withstand the forces associated with the flowing molten metal, as well as provide enhanced thermal shock resistance. For instance, the thermal barrier provides thermal insulation not only in a radial direction toward the molten metal flsw, but also in an axial direction.
The solidification (formation of skin) of the molten metal can occur while the molten metal is in contact with the internal surface 310 of the thermal barrier. This is possible since the thermal barrier is integral with the mold and hence molten metal cannot seep between the thermal barrier and the mold as is possible when using a break ring. With a smooth contour between the thermal barrier and the internal surface of the mold, the for-mation of witness marks due to the oscillating of the stock from the mold generally does not occur with the same severity as those formed when using a break ring.
Many of the materials that we applied as thermal barriers can readily be machined. Since the machining can be done when the thermal barrier is integral with the mold, it is much more easily conducted than the machining of a break rin~. The machining can also produce a very smooth surface (less than 50 microinches, rms), which enhances the ability to provide a high quality stock with minimum imperfections.
~ Flgure 4 illustrates another embodiment o~ the invention in which the ;~ thermal barrier 406 on mold 400 is thicker at its interior edge 410. The ' . ' .:, end plate, 404 of the mold shown, is beveled as it approaches the interior surface 402 of the mold~
Figl~re 5 illustra~es yet another embodiment of the invention in which the thermal barrier 506 not only extends over a portion of the end plate 504 of the mold 500, but also extends radially inwardly from interior sur~ace 502 of the mold. As depicted, nozzle 308 abuts with the thermal barrier proximate to the flow of molten metal and a portion of end plate 504.
The strength and integrity provided by the thermal barrier extending over the end plate of the mold enhances the ability of the portion of the thermal barrier extending into the cavity of the mold to withstand the stress-es of the flowing molten metal and reduce the risk of chipping.
The interior surface 510 of the thermal barrier is shown as being con-toured and ~apering into the interior surface 502 of the mold. Since the thermal barrier is integral with the interior surface 502, the deleterious effects of which could be caused by molten metal seeping between the com-ponents do not occur. Moreover, the contour at least partially replaces the void space characteristics of the break ring design of Figure 2, and can result in attentuated witness marks.
As can be seen from the foregoing discussion, the thermal barrier may constitute a wide ~ariety of configurations provided that the thermal barrier extends over at least that portion of the end plate of the mold which is adJacent the interior surface of the mold. The end plate of the mold, for instance, may be tapered or otherwise configured to provide more thermal ~barrier adjacent the interior surface of the mold, such as by beveling, rout-ing, providing indentations or the like.
Since the thermal barrier is integral with the mold, the transverse :: .
., ' ' ~ '' ' . . ' .
~, . . . .
~2~;8~
cross-section of the mold may be in virtually any shape limited by the abili-ty to provide proper cooling to ~he flow of molten metal in the mold and the ability to apply (and machine, if necessary3 the thermal barrier. Hence, near net shape horizontal castings can be produced with substantial reduction in capital and operating costs required to reform a conventional billet or bloom into the desired ultimate shape such as I-beam, plates, sheets, and the like.
Moreover, since the thermal barrier can be applied by a coating tech-nique, molds czn be readily repaired. Further 7 since using thermal barrier materials also exhibit abrasion resistance, by coating a portion of the in-terior surface of the mold, such as in Figure 5, the useful life of the mold may be enhanced.
A copper mold for the horizontal casting of steel is coated in accord-ance with this invention on the end plate, or flange face, using an undercoat of Co-Ni-Cr~ Y and an overcoat of yttria stabilized zirconia. The throat of the copper mold is about 4" long with a cross-section of 5-1/4" x 7" with the corners having approximately a 1/8" radius. The total flange face is about 10-15/16" x 9-3/16" (with the throat centered in the flange face) and corners with about a 2" radius. The periphery of the flange face has a 7/16"
wide lip about 3/8" deep to contain a zirconia block used as a nozzle for pouring steel. Four separate molds are prepared. In all cases, the copper is first grit-blasted using 60 mesh alumina grit and then plasma sprayed with an undercoat of nominally 32Ni-21Cr-8Al-0.5Y-Bal Co, all in weight per-~ent, to a thickness of 0.003 to 0.005 inches~ Over this metallic undercoat a zirconia coating consisting of ZrO,-7 wt.~ Y~O, is applied.
In one of the molds the substrate is ground to a sharp corner prior ., ,' ~ . ' ' ' ' . .
~ \
~fi~
to grit blasting and undercoa~ing and then oversprayed with a total thickness of 0.020-0.025 inches of zirconia. The edge of the zirconia coating at the in~erior surface of the mold has a slight radius since some curvature is inherent i~ the coating process. In another mold the copper at the flange face is ground to a radius of about 0.050 inches before grit blasting and undercoating and subsequently coated at a 90 angle of impingement to a total coating thickness of about 0.515 inches. A portion of this segment is then ground to a total zirconia coating thickness of 0.024 inches, still leaving a small radius of curvature on the coated corner. In a third mold, the sub-strate is ground to a corner radius of about 0.050 inches prior to coating and subsequently coated at an angle of impingement slightly less than 90 to form a lip on the corner. The total zirconia coating thickness is about 0.128 inches. A small portion of this segment is subsequently ground to a total coating thickness of 0.0227 inches leaving a very sharp corner and a slightly negative angle of zirconia Oll the corner. An advantage of this configuration may be a somewhat better bond at the corner. In the fourth mold, the coper substrate is left with a sharp, round corner and about 0.121 inches of zirconi is applied. A portion of this segment is subsequently ground to a thickness of 0.057 inches leaving a very sharp corner on the zirconia. This remaining thickness of zirconia should be equivalent5 thermally, to that which is currently used on conventional boron nitride break rings. The entire flange face could be ground to a uni~orm coating thickness.
The above-described molds having a thermal barrier are employed for the continuous horizontal casting of steel.
' ' ' .
Claims (19)
1. Apparatus for the horizontal continuous casting of molten metal comprising: a tundish for receiving molten metal, a nozzle outlet through which the molten material is discharged from said tundish and a mold for engaging said nozzle outlet wherein said mold has an interior surface, an end plate and a thermally sprayed barrier coating at least partially separating said end plate from said tundish with said coating being composed of a refractory oxide and having an internal surface extending from the interior surface of the mold for directly contacting the molten metal before the molten metal contacts the mold.
2. The mold of claim 1 wherein the thickness of the thermal barrier coating is at least about 250 microns.
3. The mold of claim 2 wherein an undercoat is provided between the refractory oxide and the mold.
4. The mold of claim 3 wherein the mold is comprised of copper-based metal.
5. The mold of claim 4 wherein the undercoat comprises MCrAlY, wherein M is at least one of nickel, cobalt and iron.
6. The mold of claim 5 wherein the refractory oxide for the thermal barrier coating comprises at least one of zirconia, yttrium-stabilized zirconia, magnesia, silica, alumina and compounds thereof.
7. The mold of claim 6 wherein the thermal barrier coating extends only on the end plate of the mod and defines an edge which smoothly extends from the interior surface of the mold.
8. The mold of claim 7 wherein the end plate is beveled adjacent to the interior surface of the mold.
9. The mold of claim 6 wherein the barrier coating overlaps the portion of the interior surface of the mold adjacent the end plate.
10. The mold of claim 9 wherein the barrier coating is contoured to taper to the interior surface of the mold.
11. The mold of claim 1 having a cross-section of a near net shape of an ultimate stock.
12. The mold of claim 1 having a cross-section of an I-beam
13. The mold of claim 1 having a cross-section of a plate.
14. A process for the continuous horizontal casting of metal using a mold of claim 1.
15. A process for the continuous horizontal casting of metal using a mold of claim 11.
16. A process for the continuous horizontal casting of metal using a mold of claim 12.
17. A process for the continuous horizontal casting of metal using a mold of claim 13.
18. A process for the continuous horizontal casting of metal using a mold of claim 14.
19. The mold of claim 2 wherein the thermal barrier comprises a graded or multiple coated structure combining refractory oxide with varying portions of metal to enhance thermal shock stability.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US91909586A | 1986-10-15 | 1986-10-15 | |
| US919,095 | 1986-10-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1296861C true CA1296861C (en) | 1992-03-10 |
Family
ID=25441500
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000551077A Expired - Lifetime CA1296861C (en) | 1986-10-15 | 1987-10-15 | Continuous casting molds |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0265174A3 (en) |
| JP (1) | JPS63157741A (en) |
| KR (1) | KR880004873A (en) |
| CA (1) | CA1296861C (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0355940A3 (en) * | 1988-06-27 | 1991-10-30 | Chaparral Steel Company | Continuous casting mold with removable insert |
| JPH02180752A (en) * | 1988-12-28 | 1990-07-13 | Kawasaki Refract Co Ltd | Tundish nozzle for continuous casting |
| US5039477A (en) * | 1989-06-02 | 1991-08-13 | Sugitani Kinzoku Kogyo Kabushiki Kaisha | Powdered metal spray coating material |
| FR2705592A3 (en) * | 1993-05-26 | 1994-12-02 | Lorraine Laminage | Method of coating a continuous-casting tundish by spraying refractory material through a flame, and the tundish and its coating resulting from implementation of this method |
| DE102007002806A1 (en) | 2007-01-18 | 2008-07-24 | Sms Demag Ag | Mold with coating |
| DE102008017432A1 (en) * | 2008-04-03 | 2009-10-08 | Kme Germany Ag & Co. Kg | mold |
| CN103447493B (en) * | 2013-09-05 | 2015-06-17 | 东北大学 | Control method of soft-reduction depressed region of wide and thick plate continuous casting blank |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| BE754315A (en) * | 1969-08-05 | 1971-01-18 | Hajduk Stan | WATER-COOLED CONTINUOUS CASTING LINGOTIER |
| DE2604478A1 (en) * | 1976-02-05 | 1977-08-11 | Peter Gloerfeld | Horizontal continuous casting plant - using thermal insulation to prevent heat from furnace reaching cooler surrounding the mould |
| GB1570348A (en) * | 1977-04-28 | 1980-07-02 | British Steel Corp | Coated graphite dies |
| JPS53135826A (en) * | 1977-04-30 | 1978-11-27 | Sumitomo Metal Ind | Continuous casting method |
| JPS55128349A (en) * | 1979-03-26 | 1980-10-04 | Kobe Steel Ltd | Continuous casting method for nickel, cobalt or titanium base alloy |
| GB8401976D0 (en) * | 1984-01-25 | 1984-02-29 | Imi Refiners Ltd | Casting apparatus |
| JPS60221151A (en) * | 1984-04-18 | 1985-11-05 | Kawasaki Steel Corp | Continuous casting mold and formation of thermally sprayed film on inside surface of mold |
| JPS6149752A (en) * | 1984-08-17 | 1986-03-11 | Kobe Steel Ltd | Horizontal continuous casting refractories for decreasing cold shut depth |
| US4744406A (en) * | 1986-10-30 | 1988-05-17 | Chaparral Steel Company | Horizontal continuous casting apparatus with break ring formed integral with mold |
-
1987
- 1987-10-15 JP JP62258485A patent/JPS63157741A/en active Pending
- 1987-10-15 CA CA000551077A patent/CA1296861C/en not_active Expired - Lifetime
- 1987-10-15 KR KR870011587A patent/KR880004873A/en not_active Application Discontinuation
- 1987-10-15 EP EP87309112A patent/EP0265174A3/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| JPS63157741A (en) | 1988-06-30 |
| EP0265174A3 (en) | 1989-06-14 |
| EP0265174A2 (en) | 1988-04-27 |
| KR880004873A (en) | 1988-06-27 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| AU684081B2 (en) | Nozzle for continuous caster | |
| JPH02502706A (en) | Immersion pouring nozzle for metallurgical vessels | |
| CA1296861C (en) | Continuous casting molds | |
| CA1227032A (en) | Composite refractory product | |
| CA1220606A (en) | Refractory coating of edge-dam blocks for the purpose of preventing longitudinal bands of sinkage in the product of a continuous casting machine | |
| EP0448773B1 (en) | Continuous caster mold and continuous casting process | |
| EP0946778B1 (en) | Coating of continuous casting machine components | |
| CA1323745C (en) | Continuous casting mold with removable insert | |
| JP3265239B2 (en) | Immersion nozzle for continuous casting | |
| WO2004002654A1 (en) | Coatings for articles used with molten metal | |
| EP0355940A2 (en) | Continuous casting mold with removable insert | |
| JPH0330461B2 (en) | ||
| US4744406A (en) | Horizontal continuous casting apparatus with break ring formed integral with mold | |
| CN1484558A (en) | Method for operating a strip casting machine and jacket ring for a casting roll used to carry out said method | |
| JPS609553A (en) | Stopping down type continuous casting machine | |
| JP2698186B2 (en) | Manufacturing method of casting nozzle member | |
| JPS62118948A (en) | Continuous casting mold with high-temperature head | |
| US6176298B1 (en) | Continuous casting mould | |
| JPH0661596B2 (en) | Metal continuous casting equipment | |
| CA1196465A (en) | Apparatus and method for continuous casting of metallic strands at exceptionally high speeds using oscillating mold assembly | |
| JPH08267183A (en) | Casting mold for continuous casting | |
| JPS6243655Y2 (en) | ||
| Penlington et al. | Material requirements for narrow neck press and blow plungers within the glass container industry | |
| Triquet et al. | Method for the Continuous Casting of Metal Strands | |
| DR Thornton BSc | Moulds for Continuous Casting |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |