Patent Application
20090206528
The present invention relates generally to refractory linings for metallurgical vessels, and more particularly to a lining bottom for such vessels. The invention is particularly applicable for use in ladles used in handling molten steel, and will be described with particular reference thereto. It will, of course, be appreciated that the present invention has application in other types of metallurgical vessels for handling molten metal.
In the manufacture of steel, molten steel is poured from a metallurgical furnace into a ladle. In pouring the liquid metal from the metallurgical furnace, there is typically some carryover of slag from the furnace into the ladle. The molten steel may also undergo further refinement in the ladle. In this respect, various slag-forming constituents may be added to the liquid steel in the ladle to aid in the refinement process. Thus, the ladle will typically contain molten steel with a layer of slag floating on top of the steel.
The molten steel typically is cast, i.e., drained, from the ladle through a well block in a bottom of the ladle. A slide gate or stopper rod serves to open a channel through which the liquid metal exits the ladle. During the casting process, slag particles can become entrained in the stream of liquid steel exiting the ladle. Entrainment can be caused by vortexing, i.e., swirling, in the vicinity of the well block. Vortexing may occur once the level of the liquid metal in the ladle drops to a critical level. The level of steel in the ladle will eventually drop to a point where slag may also be pulled directly into the stream of liquid steel exiting the ladle, even in the absence of vortexing. The slag particles cause contamination of the liquid metal thereby causing the resulting steel to be of lower quality.
To avoid contamination of the steel by slag, casting is generally terminated before the level of liquid metal in the ladle reaches the critical level at which slag may be entrained. This results in a certain amount of liquid metal being left in the ladle. This residual liquid metal represents lost production, and is referred to as a “decrease in yield.” To increase yield, steelmakers endeavor to allow the level of the liquid steel in the ladle to fall to as low a level as possible before stopping the casting operation.
The present invention provides a ladle bottom that increases the yield of slag-free steel from a steel-making ladle and reduces the entrainment of slag into the stream of liquid metal.
In accordance with the present invention, there is provided a refractory bottom for a metallurgical vessel comprised of a bottom lining having a bottom surface that is dimensioned to overlay a bottom of a metallurgical vessel and an upper surface. The upper surface is comprised of a plurality of discrete sections that include an uppermost section, an intermediate section and a lowermost section. Each section has an upper surface at a discrete elevation such that the upper surface of the uppermost section has a highest elevation and the upper surface of the lowermost section has a lowest elevation. The upper surface of the uppermost section, the intermediate section and the lowermost section comprise a series of successive stepped sections that define a stepped path from the uppermost section downward to the lowermost section. Each successive section of the upper surface is lower than a preceding section. An opening extends through the lowermost section of the bottom lining to allow a molten metal to drain from the vessel.
In accordance with another aspect of the present invention, there is provided a refractory bottom for a metallurgical vessel comprised of a bottom lining. The bottom lining has an upper surface comprised of an uppermost section, an intermediate section and a lowermost section. The sections define a path from the uppermost section to the lowermost section. The path is comprised of successive stepped sections. Each section defines a step in the path and each successive step is lower than a preceding step. An opening extends through the lowermost section of the bottom lining to allow molten metal to drain from a metallurgical vessel.
An advantage of the present invention is the provision of a refractory bottom lining for a ladle used in a steel making process
Another advantage of the present invention is the provision of a refractory bottom lining, as described above that aids in the flow of molten metal in the ladle as the molten metal is drained from the ladle.
Another advantage of the present invention is the provision of a bottom lining, as described above that is designed to minimize the amount of slag entrained in the molten metal as the molten metal is drained from the ladle.
A still further advantage of the present invention is the provision of a bottom lining, as described above that captures slag on sections of the bottom lining as the molten metal is drained from the ladle.
Still another advantage of the present invention is the provision of a bottom lining, as described above that reduces the volume of molten metal remaining in the ladle when the flow of molten metal from the ladle ceases.
Still another advantage of the present invention is the provision of a bottom lining, as described above that increases a yield of molten metal by allowing more slag-free, molten metal to be drained from the ladle.
These and other advantages will become apparent from the following description of a preferred embodiment taken together with the accompanying drawings and the appended claims.
The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail in the specification and illustrated in the accompanying drawings which form a part hereof, and wherein:
Referring now to the drawings wherein the showings are for the purposes of illustrating preferred embodiments of the invention only and not for the purposes of limiting the same, the present invention relates generally to a refractory lining for a metallurgical vessel. The invention is particularly applicable to a steel ladle used in handling molten steel, and will be described in particular reference thereto. It will be appreciated from a further reading of the specification, that the invention is not limited to a steel ladle, but may find advantageous application for linings used in other types of metallurgical vessels handling molten metal.
A bottom lining 30 (best seen in
Bottom lining 30 is dimensioned to cover and rest upon bottom 14 of shell 12. In the embodiment shown, bottom lining 30 is essentially oblong in shape, and is dimensioned to have a lower surface 38. Lower surface 38 is dimensioned to match oblong bottom 14 of shell 12. A V-shaped slot 34, best seen in
Referring now to
In the embodiment shown, bottom lining 30 is formed by molding sections 42, 44, 46, 48, 52, 54, 56, 58 using a single mold (not shown) or using conventionally known forms (not shown). For the method wherein bottom lining 30 is formed in a single mold, a bottom of the mold is dimensioned to match upper surface 36. In this respect, when a refractory material is poured into the mold, upper surface 36 of bottom lining 30 is formed in the bottom of the mold. Bottom lining 30 is then removed from the mold and inverted such that upper surface 36 of bottom lining 30 faces upward. For the method of forming bottom lining 30 using conventional forms, lowermost section 58 is formed first. Conventionally known forms are then used to aid in forming the remaining sections 42, 44, 46, 48, 52, 54, 56 of bottom lining 30 starting with intermediate section 56, then intermediate section 54 and so forth.
Refractory material, used to form bottom lining 30, is selected based upon the desired operating characteristics and performance parameters of bottom lining 30. Various high-temperature refractory castables may find advantageous application in the present invention. In the embodiment of the present invention wherein bottom lining 30 is a monolithic, refractory slab, a low-moisture, high alumina castable, manufactured and sold by North American Refractories Co. under the trade designations D-CAST 85 GOLD or HP-CAST ULTRA is used. Castables having 80% alumina content or higher are preferred. In an embodiment wherein bottom lining 30 is comprised of refractory bricks, an alumina-magnesia-carbon brick, manufactured and sold by North American Refractories Co, under the trade designations COMANCHE FA or COMANCHE FA MX may be used.
Spaced-apart lifting pin assemblies 74 are embedded within bottom lining 30, as best seen in
U.S. Pat. No. 6,673,306 entitled “Refractory Lining For Metallurgical Vessel” and U.S. Pat. No. 6,787,098 entitled “Refractory Lining For Metallurgical Vessel,” which are expressly incorporated herein by reference, describe bottom linings for ladles that are pre-formed.
As best seen in
The present invention shall now be described with respect to assembling bottom lining 30 into ladle 10. Bottom lining 30 may be fabricated, as described above, at a location remote from a place where ladle 10 is used to cast molten steel. It is also contemplated that bottom lining 30 may be fabricated at a mill. Whether bottom lining 30 is formed at a remote location or at a mill, bottom lining 30 is then placed within bottom 14 of ladle 10 using spaced-apart lifting assemblies 74. As shown in
The present invention shall now be described with respect to a steel casting operation using ladle 10. Referring now to
As the level of the molten metal continues to decrease, a point is reached wherein the level of the molten metal in the ladle is equal to the elevation of surface 44a of intermediate section 44. As the level of the molten metal continues to decrease, the slag above surface 44a of intermediate section 44 begins to adhere, i.e., is retained, on surface 44a of intermediate section 44. In this respect, as molten metal continues to drain out of ladle 10, slag has a tendency to adhere and be retained on surfaces 46a, 48a, 52a, 54a, 56a, 58a in a similar manner as described above for surface 42a of uppermost section 42. In other words, as the molten metal is drained from ladle 10, the level of the molten metal in ladle 10 decreases such that slag is first retained on surface 42a of uppermost section 42, then slag is retained on surface 44a of intermediate section 44, then slag is retained on surface 46a of intermediate section 46, and so forth until slag is retained on surface 58a of lowermost section 58. Bottom lining 30 is designed such that as molten metal is drained from ladle 10, slag adheres to and is retained on successive stepped surfaces, namely surfaces 42a, 44a, 46a, 52a, 54a, 56a, 58a, as the level of the molten metal in ladle 10 decreases.
The casting of the molten metal from ladle 10 is preferably stopped before slag above well block 66 is entrained into the stream of molten metal exiting ladle 10. In this respect, the casting of molten metal from ladle 10 may be stopped when the level of the molten metal in ladle 10 is between surface 42a of uppermost section 42 and surface 58a of lowermost section 58.
The present invention therefore provides a stepped bottom lining that collects, i.e., retains, slag on an upper surface of the bottom lining, thereby reducing the amount of slag that may exit the ladle when the molten metal is drained from the ladle. The present invention also provides a stepped bottom lining that can improve yield by reducing the amount of residual molten metal remaining in a ladle at the end of a casting process.
Referring now to another aspect of the present invention, it is generally known that the draining of molten metal from ladle 10 may also cause a vortex, i.e., a swirling motion, to form in the molten steel above well block 66 once the level of molten metal in ladle 10 reaches a critical level. This vortex can cause the slag floating on the molten metal to be entrained into the molten metal exiting the ladle 10. In the northern hemisphere, when fluid drains from a tank, a vortex forms within the tank causing the fluid to rotate in a clockwise direction. Bottom lining 30 of the present invention is designed to facilitate flow of the molten metal in ladle 10 in a counter-clockwise direction to retard the formation of the vortex in ladle 10. In this respect, as molten metal is drained from ladle 10 and the level of the molten metal in ladle 10 decreases, successive sections 42, 44, 46, 48, 52, 54, 56, 58 of upper surface 36 are exposed. At one point the level of the molten metal in ladle 10 is between surface 42a of uppermost section 42 and surface 44a of intermediate section 44. As the level of the molten metal continues to decrease, molten metal above surface 44a of intermediate section 44 flows toward a surface at a lower elevation, i.e., surface 46a of intermediate section 46. In this respect, the molten metal above intermediate section 44 flows in a counter-clockwise direction towards intermediate section 46. This flow of molten metal, beneath the slag layer, is repeated for each successive section 46, 48, 52, 54, 56. The molten metal flows from successive sections 42, 44, 46, 48, 52, 54, 56 of upper surface 36 along a path “B-B” in a counter-clockwise direction. In this respect, bottom lining 30 is designed so that exposure of successive sections 42, 44, 46, 48, 52, 54, 56, 58 of upper surface 36, creates flow of molten metal in a counter-clockwise direction. It is believed that the flow of molten metal in the counter-clockwise direction, created by exposure of successive stepped sections 42, 44, 46, 48, 52, 54, 56, 58, retards the formation of the vortex in the molten metal in ladle 10 above well block 66. Retarding the formation of the vortex in the molten metal reduces the likelihood of slag floating on the molten metal being entrained into metal exiting through well block 66. The present invention, therefore, also provides a stepped bottom lining that retards the formation of a vortex in molten metal in a ladle by creating a flow opposite to the natural flow of the molten metal in the ladle. It is believed that this counter flow reduces the amount of slag that may exit the ladle when the molten metal is drained from ladle.
Referring now to
Well block 66 is placed in bottom lining 130 after bottom lining 130 is placed in ladle 10. Well block 66 is placed in bottom lining 130 below surface 158a of lowermost section 158 such that a recess 61 is formed therein, as best seen in
The present invention shall now be described with respect to a steel casting operation using bottom lining 130 in ladle 10. The casting of steel using bottom lining 130 in ladle 10 is similar in most respects to casting steel using bottom lining 30 in ladle 10. In the second embodiment, the slag adheres to surfaces 142a, 144a, 146a, 158a instead of surfaces 42a, 44a, 46a, 48a, 52a, 54a, 56a, 58a, as described above for the first embodiment. In addition, as molten metal drains from ladle 10, the molten metal above upper surface 136 and beneath the slag layer flows from successive sections 142, 144, 146, 158 of upper surface 136 along a path “D-D” in a counter-clockwise direction. In this respect, bottom lining 130 is designed so that exposure of four (4) successive sections 142, 144, 146, 158 of upper surface 136, creates flow of molten metal in a counter-clockwise direction. The first embodiment, as described above, includes six (6) successive sections that are exposed to create flow of molten metal in a counter-clockwise direction.
Referring now to
Well block 66 is positioned within bottom lining 230 after bottom lining 230 is placed in ladle 10. Well block 66 is placed in bottom lining 230 below surface 258a of lowermost section 258 such that a recess 61 is formed therein, as best seen in
The present invention shall now be described with respect to a steel casting operation using bottom lining 230 in ladle 10. As described above, a slag layer typically floats on top of the molten metal in ladle 10. As the molten metal in ladle 10 is cast from ladle 10, the level of the molten metal decreases and a portion of the slag floating on the molten metal adheres to and is retained on surface 242a of uppermost section 242. As molten metal continues to drain out of ladle 10, slag has a tendency to adhere to and be retained on surfaces 246a, 248a, 258a. In other words, as the molten metal is drained from ladle 10, the level of the molten metal in ladle 10 decreases such that slag is first retained on surface 242a of uppermost section 242, then slag is retained on surface 244a of intermediate section 244, then slag is retained on surface 246a of intermediate section 246 until slag is retained on surface 258a of lowermost section 258. Bottom lining 230 is designed such that as molten metal is drained from ladle 10, slag adheres to and is retained on successive stepped sections, namely uppermost section 242, intermediate sections 244, 246 and lowermost section 258, as the level of the molten metal in ladle 10 decreases.
Similar to the first embodiment, as the level of molten metal decreases, the molten metal above upper surface 236 and beneath the slag layer, flows from successive sections 242, 244, 246, 258 of upper surface 236 along a path “E-E.” In this respect, bottom lining 230 is designed so that exposure of successive stepped sections 242, 244, 246, 258 causes molten metal to flow in a direction along the path “E-E.”
Referring now to
In the embodiment shown, impact pad 331 is a rectangular member typically comprised of a cast, refractory material. In another embodiment (not shown), impact pad 331 is comprised of a plurality of tightly packed high-density and high-temperature refractory bricks or a combination of a cast, refractory material and refractory bricks. In the embodiment shown, impact pad 331 is embedded in bottom lining 330.
The casting of molten metal from ladle 10 containing bottom lining 330 is similar, in most respects, to casting molten metal from ladle 10 containing bottom lining 230. In the embodiment wherein bottom lining 330 is disposed in ladle 10, as molten metal is drained from ladle 10, the level of the molten metal decreases. As the level of the molten metal decreases, a point is reached wherein the level of the molten metal in ladle 10 is equal to the level of surface 331a of impact pad 331. At this point, the slag layer floating on the molten metal engages surface 331a of impact pad 331 such that the slag adheres to surface 331a of impact pad 331. As the level of the molten metal continues to decrease, slag adheres to successive sections 242, 244, 246, 258, as described above for bottom lining 230.
As the level of the molten metal in ladle 10 decreases, molten metal above surface 331a of impact pad 331 flows towards surface 242a of uppermost section 242 or towards surface 244a of intermediate section 244. As the molten metal continues to drain out of ladle 10, the molten metal above surface 336 flows to successive stepped sections 246, 258, as described above for bottom lining 230. The molten metal flows from successive stepped surfaces 331a, 242a, 244a, 246a, 258a of upper surface 336 along L-shape paths “F-F.” In this respect, bottom lining 330 is designed so that exposure of successive surfaces 331a, 242a, 246a, 258a, creates flow of molten metal towards well block 66 along paths “F-F.”
Referring now to
Bottom lining 430 has an upper portion comprised of an uppermost section 442, an intermediate section 444 and a lowermost section 458. In this respect, bottom lining 430 has one (1) intermediate section 444 whereas bottom lining 230 has two (2) intermediate sections 244, 246. Uppermost section 442 has an upper surface 442a, intermediate section 444 has an upper surface 444a and lowermost section 458 has an upper surface 458a. In the embodiment shown, surfaces 442a, 444a, 458a each generally slope downwardly towards well block 66, as best seen in
The operation of casting steel from ladle 10 having bottom lining 430 is similar to casting steel from ladle 10 having bottom lining 230 and shall not be described in detail. Bottom lining 430 is designed to have an upper surface 436 such that the flow of molten metal along path “G-G” (as shown in
It should be understood that a bottom lining, according to the present invention, may assume other shapes and configurations without deviating from the present invention. For example, bottom linings, 30, 130, 230, 330, 430 each show sections of upper surfaces 36, 136, 236, 336, 436 that are generally planar. It is also contemplated that upper surfaces 36, 136, 236, 336, 436 may have sections that are non-planar, e.g., convex-shaped or concave-shaped to facilitate a desired flow of metal within ladle 10. Furthermore, in an alternative embodiment of the present invention all or at least a portion of the refractory cast material of bottom lining 30, 130, 230, 330, 430 may be substituted with refractory bricks. It should be further appreciated that each embodiment of the bottom lining described above may be modified to incorporate one or more features of the other embodiments. For example,
Other modifications and alterations will occur to others upon their reading and understanding of the specification. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.
