APPARATUS FOR THE ENHANCEMENT OF NON-METALLIC PARTICLE REMOVAL FROM LIQUID METAL FLOWING THROUGH A VESSEL

Abstract

A purifying device for removing impurities from liquid metal present in a vessel includes a baffle including a first surface and a second surface disposed opposite the first surface. A vent channel is formed between the first surface and the second surface, the vent channel having a proximal end and a distal end opposite the proximal end, the vent channel configured to receive a stream of gas at the proximal end and vent at least some of the stream of gas at the distal end. At least one first vent hole is arranged on the first surface and extending into the vent channel, and at least one second vent hole arranged on the second surface and extending into the vent channel. A passage for liquid metal flow is disposed within the baffle, the passage having a proximal surface and a distal surface, where the distal surface is disposed adjacent to the proximal end of the vent channel.

Claims

1. A purifying device for removing impurities from liquid metal present in a vessel, comprising: a baffle including a first surface and a second surface disposed opposite the first surface; a vent channel formed between the first surface and the second surface, the vent channel having a proximal end and a distal end opposite the proximal end, the vent channel configured to receive a stream of gas at the proximal end and vent at least some of the stream of gas at the distal end; at least one first vent hole, arranged on one of the first surface or the second surface, the at least one first vent hole extending into the vent channel; and a passage for liquid metal flow, the passage having a proximal surface and a distal surface, where the distal surface is disposed adjacent to the proximal end of the vent channel.

2. The purifying device according to claim 1, wherein the baffle further comprises a gas supply channel including an input port for receiving a gas, an output port for outputting the gas, and conduit connecting the input port to the output port, wherein the output port is disposed at the proximal surface of the passage.

3. The purifying device according to claim 1, further comprising a porous element disposed at the proximal surface of the passage.

4. The purifying device according to claim 3, wherein the porous element is fluidically coupled to the output port of the gas channel.

5. The purifying device according to claim 3, wherein the porous element spans an entire width of the passage.

6. The purifying device according to claim 1, further comprising at least one second vent hole arranged opposite the at least one first vent hole on the other of the first surface or the second surface.

7. The purifying device according to claim 1, wherein the distal end of the vent channel opens to the ambient environment above a free surface of the liquid metal.

8. The purifying device according to claim 1, wherein the at least one first vent hole comprises a plurality of first vent holes, and the at least one second vent hole comprises a plurality of second vent holes, wherein the plurality of first vent holes are arranged along a first plane and the plurality of second vent holes are arranged along a second plane.

9. The purifying device according to claim 1, further comprising a divider wall arranged within the vent channel, the divider wall splitting the vent channel into two separate channels.

10. The purifying device according to claim 9, wherein the dividing wall spans between the proximal end and the distal end of the vent channel.

11. The purifying device according to claim 1, wherein the passage for liquid metal flow spans an entire width of the proximal end of the vent channel.

12. A tundish, comprising: a floor; a wall attached to the floor, wherein the wall and the floor define a container; the purifying device according to claim 1 arranged with the container.

13. The tundish according to claim 12, wherein the wall comprises a first side wall and a second sidewall arranged opposite the first sidewall, the first and second sidewalls attached to the floor; and a first end wall and a second end wall arranged opposite the first end wall, the first end wall and second end wall attached to the floor and to respective ends of the first and second sidewalls to define a container.

14. The tundish according to claim 12, further comprising: an inlet for receiving liquid metal into the tundish; and an outlet for dispensing liquid metal from the tundish, wherein the purifying device is disposed between the inlet and outlet.

15. The tundish according to claim 12, wherein the tundish has a predetermined maximum level for liquid metal, and the distal end of the vent channel extends above the predetermined maximum level for liquid metal.

16. The tundish according to claim 12, wherein the purifying device spans an entire width of the container between a floor of the container and a maximum liquid metal level of the container.

17. A method for removing impurities from liquid metal present in a vessel, the liquid metal covered by a top layer floating on a free surface of the liquid metal, the vessel including a baffle defining a first vessel section and a second vessel section, the baffle having a passage for liquid metal flow arranged proximate to a floor of the vessel and fluidically coupling the first vessel section to the second vessel section, the method comprising: subjecting liquid metal flowing within the passage to a stream of gas; receiving at least some of the stream of gas and a portion of the liquid metal flowing within the passage at a vent channel disposed within the baffle, the vent channel guiding gas and liquid metal toward the top layer, expelling the liquid metal received by the vent channel out of the vent channel prior to the liquid metal reaching the top layer; and venting the gas received by the vent channel out of the vent channel.

18. The method according to claim 17, wherein the top layer comprises of at least one of flux or slag.

19. The method according to claim 17, wherein venting comprises guiding the stream of gas through a portion of the top layer that is constrained within the vent channel.

20. The method according to claim 17, wherein receiving comprises using a vent channel having a first vent section and a second vent section adjacent to and isolated from the first vent section.

21. The method according to claim 17, wherein expelling comprises laterally expelling the liquid metal from the vent channel.

22. The method according to claim 17, wherein expelling further comprises creating a clockwise flow of liquid metal in the second vessel section, the clockwise flow beginning at the floor adjacent to the passage for liquid metal flow, moving adjacent to the baffle and toward the top layer, and then returning toward the floor.

23. The method according to claim 17, wherein venting the gas received by the vent channel out of the vent channel comprises venting the gas over the top layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] 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:

[0036] FIG. 1 is a side sectional view of a tundish that includes an exemplary vent channel in accordance with the present invention.

[0037] FIGS. 2A-2C are top, front and side views of an exemplary baffle having a vent channel in accordance with one embodiment of the invention.

[0038] FIGS. 3A-3C are top, front and side views of an exemplary baffle having a vent channel in accordance with another embodiment of the invention.

[0039] FIG. 4 is a flow chart illustrating exemplary steps of a method in accordance with the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

[0040] Various aspects now will be described more fully hereinafter. Such aspects may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art.

[0041] The word about when immediately preceding a numerical value means a range of plus or minus 10% of that value, e.g., about 50 means 45 to 55, about 25,000 means 22,500 to 27,500, etc., unless the context of the disclosure indicates otherwise, or is inconsistent with such an interpretation. For example, in a list of numerical values such as about 49, about 50, about 55, about 50 means a range extending to less than half the interval(s) between the preceding and subsequent values, e.g., more than 49.5 to less than 52.5. Furthermore, the phrases less than about a value or greater than about a value should be understood in view of the definition of the term about provided herein.

[0042] In accordance with the present invention, a purifying device is disclosed that can be placed within a vessel, such as a tundish, the purifying device operative to remove impurities from liquid steel present in the container. The purifying device according to the invention utilizes gas purging, where a majority of gas bubbles released into the liquid steel are confined within a vent channel that releases the gas into the ambient environment. In this manner, the effusion of the mixing energy introduced to the tundish by the gas-bubbling of the liquid steel is constrained.

[0043] With reference to FIG. 1, illustrated is side sectional view of an exemplary tundish 100 to which aspects of the invention may be applied. The tundish 100 includes two side walls (not shown), two end walls 102a, 102b and a bottom wall 104 joined together to define a container volume 106. The tundish 100 includes an outer shell 108 formed from steel or other metal, a backing lining 110 attached to the outer shell 108, and a working lining 112 attached to the backing lining 110. The backing lining 110 and working lining 112 are formed from conventional refractory materials that are insulative and resistant to the liquid steel and flux/slag.

[0044] The tundish 100 also includes a ladle shroud 114 having an inlet 114a for receiving an inflow of liquid steel and an outlet 114b for providing the liquid steel received at the input 114a to the container volume 106. The inlet 114a is arranged above a maximum liquid steel level of the tundish 100, and in the exemplary embodiment of FIG. 1 the inlet 114a extends above a top surface of the end and side walls of the tundish 100, while the outlet 114b is arranged below a nominal liquid steel level of the tundish 100. The tundish 100 further includes an outlet nozzle 116 for the outflow of liquid steel from the tundish 100, the outlet nozzle 116 having an inlet port 116a for receiving an outflow of liquid steel from the tundish 100 and an outlet port 116b for directing liquid steel received at the inlet port 116a to another tundish and/or casting mold (not shown). Both the ladle shroud 114 and the outlet 116 include a refractory material capable of withstanding high temperatures encountered during a metal-making process. In FIG. 1, the exemplary tundish 100 is shown filled with liquid steel 118 having a slag and/or flux layer 120 that floats on a top surface of the liquid steel 118.

[0045] Arranged in the tundish 100 is a purifying device 130 in accordance with an embodiment of the invention, the purifying device 130 spanning between side walls of the tundish 100 so as to divide the tundish 100 into a first tundish section 100a and a second tundish section 100b. The purifying device 130 spans the tundish 100 at a location between the ladle shroud 114 (the position of liquid entry) and the outlet nozzle 116 such that the liquid steel exiting the tundish downstream of the purifying device will have passed therethrough. While the purifying device 130 is shown to be centrally located in the tundish, such location is merely exemplary and the purifying device 130 may be located at other locations within the tundish 100 between the ladle shroud 114 and the outlet nozzle 116.

[0046] With continued reference to FIG. 1 and additional reference to FIGS. 2A-2C, the exemplary purifying device 130 is in the form of a baffle 132 having a first surface 132a and a second surface 132b disposed opposite the first surface 132a. The baffle 132 may be formed from a relatively non-porous refractory element 134 and a porous refractory element 136 disposed within a lower region of the baffle (near a bottom wall 104 of the tundish 100). Since virtually all refractory materials have some degree of porosity, a non-porous refractory is understood to have significantly lower gas permeability than a porous refractory element. The porous refractory element 136 may span an entire width of the tundish 100, or span only a portion of the tundish width.

[0047] The purifying device 130 further includes a means for providing gas to the porous refractory element 136, such as a gas supply channel 138. In the exemplary embodiment of FIG. 1, the gas supply channel 138 is in the form of a pipe having an input port for receiving a gas, an output port for outputting the gas, and conduit connecting the input port to the output port. The gas supply channel 138 extends out from a top surface of the baffle 132 to enable easy connection to a gas source (not shown). The conduit portion of the gas supply channel 138 enters the baffle 132, e.g., between walls of the baffle 132, and the output port of the gas supply channel is directed to the a region just beneath the porous refractory element 136 such that the input port, conduit and output port of the gas supply channel 138 are fluidically coupled to the porous refractory element 136. As will be appreciated, other configurations for communicating gas to the porous refractory element 136 are possible. For example, the gas supply pipe 138 may be formed within the tundish 100, and an outlet of the gas supply pipe 138 may be arranged beneath the baffle 132 at a location adjacent to the porous refractory element 136.

[0048] Formed in a lower region of the baffle 132 is a lower opening 140 (also referred to as a passage) arranged near a floor of the tundish 100 (e.g., immediately adjacent to the bottom wall 104 or slightly above the bottom wall 104). The lower opening 140, which in the exemplary embodiment has a width that spans between the first surface 132a and the second surface 132b, is in the form of a through-hole that fluidically couples the first tundish section 100a to the second tundish section 100b to enable the flow of liquid steel from the first tundish section 100a to the second tundish section 100b. A length of the lower opening 140 preferably corresponds to a length of the porous refractory element 136. For example, if the porous refractory element 136 spans the entire width of the tundish 100 along a floor of the tundish (i.e., between side walls that are not shown in FIG. 1), then the lower opening 140 may have a length that spans the entire width of the tundish 100.

[0049] An upstream portion of the lower opening 140 is located on the side of the baffle 132 towards the flow incoming to the tundish from the ladle shroud 114, while the downstream side of said lower opening is located on the side of the baffle 132 towards the flow exiting the tundish via the outlet nozzle 116. A vent channel 142 is disposed within the baffle 132 between the first surface 132a and the second surface 132b, the vent channel 142 having a proximal end 142a and a distal end 142b opposite the proximal end. The proximal end 142a of the vent channel 142 opens into the lower opening 140, while the distal end 142b opens to the ambient environment above a free surface of the liquid steel (above a predetermined maximum level of liquid steel in the tundish 100). Thus, the vent channel 142 fluidically couples the lower opening 140 to the ambient environment. Both the lower opening 140 and vent channel 142 are disposed relative to the porous refractory element 136 such that a stream of gas emitted by the porous refractory element 136 forms a gas curtain that passes vertically along the lower opening 140 and into the proximal end 142a of the vent channel 142. The vent channel 142 guides the stream of gas upwards toward a surface of the liquid steel and at least some of the gas is emitted at the distal end of the vent channel 142.

[0050] The baffle 132 includes a first lateral vent hole 144a arranged on the first surface 132a of the baffle 132, and second lateral vent hole 144b arranged on the second surface 132b of the baffle 132, where both the first and second vent holes 144a, 144b extend into the vent channel 142. In one embodiment, there are multiple first vent holes 144a arranged on the first surface 132a and/or multiple second vent holes 144b arranged on the second surface 132b. At least some of the first vent holes 144a may be arranged directly opposite a respective second vent hole 144b. Alternatively, or additionally, at least some of the first vent holes 144a may be offset from a respective second vent hole 144b, e.g., a first vent hole 144a is arranged vertically and/or horizontally offset from a respective second vent hole 144b. While vent holes 144a, 144b are shown on both sides 132a, 132b of the baffle 132, in some embodiments one or more vent holes may be arranged only on one side of the baffle 132. The slag and/or flux layer 120, in addition to floating upon the liquid steel on each side of the baffle 132, also floats upon the liquid steel that is formed within the vent channel 142 of the present invention.

[0051] In operation, liquid steel 118 is provided to the tundish 100 through the ladle shroud 114, and the liquid steel level within the tundish 100 rises to a nominal level. An inert, or low reactivity, purge-gas is provided to the porous refractory element 136 via the gas supply channel 138 and the outlet nozzle 116 is opened to permit the liquid steel 118 to flow out of the tundish 100. The porous refractory element 136 releases the gas, in the form of gas bubbles, from an upper surface of the porous refractory element 136 that contacts the liquid steel 118. The released gas is dispersed into the liquid steel 118 within the lower opening 140 as the liquid steel 118 flows therethrough. Buoyancy force causes a majority of the gas bubbles emitted from the porous refractory element 136 to rapidly rise upward into the vent channel 142 located above the opening 140.

[0052] An upstream gas trajectory 150a and a downstream gas trajectory 150b are depicted in FIG. 1. A generally rising, turbulent, flow of bubbly liquid steel is formed between the upstream and downstream trajectories 150a, 150b and thus within a vent channel 142. Purge-gas bubbles are principally evolved from the bubbly liquid steel and flow into the flux/slag layer 120 floating within the vent channel 142. The purge-gas evolved from the floating flux/slag layer 120 is confined within an uppermost portion of the vent channel 142, to be then released by passing out the top of the vent channel 142, expelling ambient air and/or other gases from this region so as to protect the liquid steel from reoxidation.

[0053] The flux/slag layer 120 within a vent channel 142 is not readily pushed laterally away from the bubbly region, as the vent channel 142 is substantially filled with bubbly liquid steel 118, and the flux/slag layer 120 is confined within the vent channel 142. Thus, disruption and thinning of the flux/slag layer 120 within the vent channel 142 is highly diminished or eliminated, as compared to the flux and/or slag layer disruption and thinning occurring with conventional purifying devices.

[0054] The liquid steel rising upward in the vent channel 142 is released from the vent channel 142 through the lateral vent holes 144a, 144b, which pierce the vent channel walls below the normal location the floating flux/slag layer 120, thereby reducing dynamic pressure at the flux/slag/liquid steel interface. In this way, turbulent interactions between the rising bubbly liquid in the vent channel 142, gas evolved from the bubbly liquid, and the flux layer 120 in the vent channel 142, are controlled. Thus, the lateral vent holes 144a, 144b provide an additional means to diminish disruption of the flux layer 120.

[0055] The purifying device 130 influences the downstream liquid steel flow in the tundish 100 to adopt a desirable flow pattern and flow behavior. The solid-line arrows of FIG. 1 depict certain noteworthy liquid flows, while the dotted-line arrows depict certain noteworthy gas flows, developed in a tundish equipped with an embodiment of the invention. As can be seen in FIG. 1, the bulk of the liquid steel 118 that has passed through the purifying device 130 calmly flows upward and beneath the downstream layer of floating flux/slag 120, and then the flow quiescently descends toward a tundish outlet nozzle 116.

[0056] In contrast to the purifying device 130 in accordance with the invention, conventional gas-purging devices do not confine the majority of the gas bubbles released into the liquid steel within a vent channel, and therefore the conventional gas purging devices do not constrain the effusion of the mixing energy introduced to the tundish by the gas-bubbling of the liquid steel. For this reason, conventional tundish gas-purging devices induce an extensive, more wide-spread, stirring energy into the liquid steel that has potentially harmful effects, such as short-circuit flows, flux/slag entrainment, and steel reoxidation. Using a purifying device in accordance with the invention, the mixing energy and turbulent stirring induced by gas-purging is largely confined within the apparatus so as to avoid harmful effects on liquid steel flow behavior and liquid steel quality.

[0057] Moving now to FIGS. 3A-3C, illustrated is a purification device 130 in accordance with another embodiment of the invention. FIGS. 3A-3C illustrates top, front, and side views, respectively, of the purification device 130. The purification device 130 of FIGS. 3A-3C is substantially the same as the purification device 130 of FIGS. 2A-2C and therefore only the differences are discussed here. In contrast to the purification device 130, the purification device 130 includes two vent channels 146a, 146b. These two vent channels 146a, 146b are separated by a vent divider 300 that is part of the non-porous element 134. The vent channel divider 300 provides additional mechanical strength and stiffness to the purification device 130, and functions to further constrain disruption, lateral displacement, and thinning, of the floating flux/slag layer within a vent channel, particularly at elevated purge-gas flowrates.

[0058] A wide variety of shapes and sizes of tundish vessels are in use in order to suit particular casting operating conditions. Many alternate embodiments of the purification device 130, 130 are possible to best befit these vessels and conditions. Alternate embodiments may include vent holes only on the downstream side, or only on the upstream side, of the purification device 130, 130 in order to best influence liquid steel flow behavior in a particular application, or for the same reason an alternate embodiment may include no vent holes. Alternate embodiments may include multiple (i.e., three or more) vent channels to ensure strength and stiffness of the purification device 130, 130, as well as to even more highly constrain disruptions of the flux/slag layer, better confine the purge-gas flow evolving from the top of each flow channel, and thereby better protect the turbulent liquid steel in a channel from reoxidation. Also, an alternate embodiment could comprise two or more lower openings in combination with two or more means to supply purge gas to two or more porous elements in order to best span a large tundish vessel.

[0059] Moving to FIG. 4, illustrated is a flow chart disclosing an exemplary method 400 for removing impurities from liquid steel 118 present in a vessel, the liquid steel covered by a top layer 120 floating on a free surface of the liquid steel. In the context of the method, the vessel includes purifying device 130, 130 having a baffle 132 that defines a first vessel section and a second vessel section, the baffle having a passage 140 for liquid steel flow arranged proximate to a floor of the vessel and fluidically coupling the first vessel section to the second vessel section.

[0060] Beginning at step 402, molten metal 118 is provided to an input section (a first tundish section 100a) of the vessel, e.g., a tundish 100, the input section fluidically coupled to an output section (a second volume 100b) of the tundish. Such molten metal may be provided to the tundish via a ladle shroud 114 as is conventional. A flux/slag layer 120 is formed over the molten metal 118 as indicated at step 404, such flux/slag layer formed via conventional means.

[0061] Next at step 406 the molten metal flows from the first tundish section to the second tundish section through a lower opening 140 (e.g., a passage) formed in a baffle 132 of the purifying device 130, 130 according to the invention, where the molten metal 118 is subjected to a stream of gas 150a, 150b as the molten metal 118 moves to the second tundish section. At step 408 at least some of the stream of gas 150a. 150b and a portion of the liquid steel 118 flowing within the passage 140 is received at a vent channel 142 disposed within the baffle 132, the vent channel 142 guiding the received gas and liquid steel toward the top layer 120 as indicated at step 410. As the column of liquid steel 118 and gas 150a. 150b travel upward through the vent channel 142, the liquid steel 118 is expelled from the vent channel 142 prior to the liquid steel 118 reaching the top layer 120 as indicated at step 412. For example, as the liquid steel 118 travels upward in the vent channel 142 it is laterally expelled through vent holes 144a, 144b. Such lateral expelling of the liquid steel 118 creates a clockwise flow of liquid steel in the second vessel section, the clockwise flow beginning at the floor adjacent to the lower opening 140, moving adjacent to the baffle 132 and toward the top layer 120, and then returning toward the floor near the outlet nozzle 116. Additionally, and as indicated at step 414, the gas received by the vent channel 142 is released out of the vent channel 142 above the top layer 120. More specifically, the stream of gas is guided through a portion of the top layer 120 that is constrained within the vent channel 142 (e.g., the gas is vented over the top layer).

[0062] The purification method is advantageous in that it minimizes disturbance to the top layer 120, which reduces the risk of oxidation. Also, the method provides a beneficial flow of the liquid steel in the second tundish section prior to flowing out of the tundish.

[0063] The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purposes of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. 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.