System, apparatus and method for direct chill casting exhaust

Abstract

A system, apparatus and method for venting a direct chill casting mold by venting excess casting gas from the top of the casting and retaining oxides during a direct chill casting process is provided herein. The method of venting casting gas from a direct chill casting mold comprises: supplying molten metal to the direct chill casting mold through a transition plate; supplying casting gas through a casting surface of the direct chill casting mold; venting the casting gas from a gas pocket in the transition plate, wherein venting the casting gas from the gas pocket in the transition plate is performed in response to the pressure of the casting gas in the gas pocket reaching a predetermined pressure.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 073,523, filed on September 2, 2020, the contents of which are hereby incorporated by reference in their entirety. Technical Field

[0003] The present disclosure relates to a system, apparatus and method for venting a direct chill casting mold, and more particularly, venting excess casting gases from the top of the casting and retaining oxides during a direct chill casting process. Background Art

[0004] Metal products are formed in various ways; however, many forming methods first require ingots, billets or other castings, which can be used as raw materials, and metal end products can be made from the raw materials, such as by rolling, extrusion or machining. One method of making ingots or billets is by a continuous casting process called direct chill casting, whereby a vertically oriented mold cavity is located above a platform that translates vertically downward to a casting pit. A starter block can be located on the platform and at least initially forms the bottom of the mold cavity to start the casting process. Molten metal is poured into the mold cavity, and the molten metal is then typically cooled using a cooling fluid. The platform with the starter block on it descends into the casting pit at a predefined speed to allow the metal to leave the mold cavity and descend with the starter block to solidify. As more molten metal enters the mold cavity and solid metal leaves the mold cavity, the platform continues to descend. This continuous casting process allows metal ingots and billets to be formed according to the contour of the mold cavity and have a length limited only by the depth of the casting pit and the hydraulically actuated platform that moves therein. Summary of the invention

[0005] The present disclosure relates to a system, apparatus, and method for venting a direct cooling gas buffer casting hot top ingot mold, and more specifically, venting excess casting gas from the top of the casting and retaining oxides during a direct chill casting process. The various embodiments provided herein include a transition plate for a direct chill casting mold, the transition plate comprising: a top surface; a bottom surface, wherein a casting gas pocket is defined at a periphery of the bottom surface; and one or more vent holes, the one or more vent holes being defined within the casting gas pocket. The transition plate of the example embodiment includes a lip extending around the periphery of the transition plate and separated from the bottom surface by a gas pocket surface. The one or more vent holes of the example embodiment are defined in the gas pocket surface.

[0006] According to an example embodiment of the transition plate, when the transition plate is positioned on the mold, the lip is raised relative to the bottom surface, wherein the casting gas pocket is formed at the periphery of the transition plate by the lip and the gas pocket surface, wherein the vents are positioned closer to the bottom surface than the lip. According to an example embodiment, in response to the formation of bubbles in the casting gas pocket, the plurality of vents are configured to allow casting gas to be exhausted before the casting gas reaches the bottom surface of the transition plate. The gas pocket surface of an example embodiment comprises a chamfered surface relative to the bottom surface, wherein the one or more vents are defined in the chamfered surface. The plurality of vents of an example embodiment comprises a mesh of material that is permeable to gas and impermeable to molten metal. The plurality of vents of an example embodiment vent to atmospheric pressure. The plurality of vents of an example embodiment are associated with a valve, wherein the valve allows the plurality of vents to vent to atmospheric pressure in response to the pressure in the casting gas pocket satisfying a predetermined value. According to an example embodiment, the transition plate comprises a lip, wherein the casting gas pocket is defined between the lip and the bottom surface.

[0007] Various embodiments provided herein include a method of exhausting casting gas from a direct chill casting mold, the method comprising: supplying molten metal to the direct chill casting mold through a transition plate; supplying casting gas through a casting surface of the direct chill casting mold; and exhausting the casting gas from a gas pocket in the transition plate, wherein exhausting the casting gas from the gas pocket in the transition plate is performed in response to the pressure of the casting gas in the gas pocket reaching a predetermined pressure. The predetermined pressure of the example embodiment is determined based on the metal static head pressure of the molten metal supplied to the direct chill casting mold. The method of the example embodiment further includes: supplying pressure to a plurality of exhaust holes in the transition plate to prevent molten metal from flowing through the exhaust holes; and reducing or removing pressure to the plurality of exhaust holes to allow exhaust of casting gas.

[0008] Various embodiments provided herein include a system for venting a direct chill casting mold, the system including: a direct chill casting mold; a sleeve through which molten metal is supplied to the direct chill casting mold; a transition plate attached to the direct chill casting mold and into which the sleeve is received, wherein the transition plate includes a gas passage and a plurality of vent holes disposed therein, wherein casting gas is vented through the gas passage in the transition plate in response to molten metal filling the direct chill casting mold. The transition plate of an example embodiment includes a top surface and a bottom surface, wherein the casting gas pocket is defined at a periphery of the bottom surface.

[0009] According to the system of an example embodiment, the transition plate includes a lip, wherein the lip extends around the perimeter of the transition plate and is separated from the bottom surface by a gas pocket surface. The one or more exhaust holes of the example embodiment are defined in the gas pocket surface. When the transition plate is positioned on the mold, the lip of the transition plate of the example embodiment is raised relative to the bottom surface, wherein the casting gas pocket is formed at the perimeter of the transition plate by the lip and the gas pocket surface, and wherein the exhaust holes are positioned closer to the bottom surface than the lip. According to an example embodiment, in response to the formation of bubbles in the casting gas pocket, the plurality of exhaust holes are configured to allow casting gas to be exhausted before the casting gas reaches the bottom surface of the transition plate. The gas pocket surface of the example embodiment includes a chamfered surface relative to the bottom surface, wherein the one or more exhaust holes are defined in the chamfered surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Having thus generally described the invention, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and in which:

[0011] FIG. 1 shows an exemplary embodiment of a direct chill casting mold according to the prior art;

[0012] Figure 2 An example of the initial stage of direct chill casting or continuous casting according to an exemplary embodiment of the present disclosure is shown;

[0013] Figure 3 An example embodiment after an initial stage of direct chill casting according to an example embodiment of the present disclosure is shown;

[0014] Figure 4 An example embodiment of steady-state direct chill casting according to an example embodiment of the present disclosure is presented;

[0015] Figure 5 Air gap casting of a billet according to an example embodiment of the present disclosure is demonstrated;

[0016] Figure 6 shows a casting gas pocket configuration in a transition plate according to an example embodiment of the present disclosure;

[0017] Figure 7 An exhaust hole defined within a casting gas pocket is shown according to an example embodiment of the present disclosure;

[0018] Figure 8 is a flow chart of a method for exhausting casting gas from a direct chill casting mold according to an example embodiment of the present disclosure; and

[0019] Fig. 9 A transition plate including oxide banks according to an example embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0020] Example embodiments of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which some but not all embodiments of the present disclosure are shown. Indeed, the embodiments described herein take many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that the present disclosure will satisfy applicable legal requirements. Throughout the text, the same reference numerals refer to the same elements.

[0021] Various embodiments of the present disclosure are generally directed to a system, apparatus, and method for venting a direct chill casting mold, and more particularly, venting excess casting gases from the top of the casting and retaining oxides during a direct chill casting process.

[0022] Vertical direct chill casting or continuous casting is a process for producing ingots or billets with various cross-sectional shapes and sizes for use in various manufacturing applications. The process of direct chill casting begins with a horizontal mold table or mold frame containing one or more vertically oriented molds placed therein. Each mold in the mold defines a mold cavity, wherein the mold cavity is initially closed at the bottom with a starter block to seal the bottom of the mold cavity. Molten metal is introduced into each mold cavity by a metal distribution system to fill the mold cavity. When the molten metal near the bottom of the mold, adjacent to the starter block, solidifies, the starter block moves vertically downward into the casting pit along a linear path. The movement of the starter block is caused by a hydraulically lowered platform to which the starter block is attached. The vertical downward movement of the starter block extracts the solidified metal from the mold cavity while introducing additional molten metal into the mold cavity. Once started, the process moves in a relatively steady state for a continuous casting process to form an ingot of metal having a profile defined by the mold cavity and a height defined by the depth to which the platform and starter block move.

[0023] During the casting process, as the starter block is advanced downward, the mold itself is cooled to promote solidification of the metal before it leaves the mold cavity, and cooling fluid is introduced to the metal surface near the mold cavity exit as the metal is cast to extract heat from the cast metal ingot and solidify the molten metal within the now solidified outer shell of the ingot. As the starter block is advanced downward, the cooling fluid is sprayed directly on the ingot to cool the surface and extract heat from within the core of the ingot.

[0024] Fig. 1 depicts a general illustration of a cross section of a direct chill casting mold 100 during a continuous casting process. The mold shown can be used for, for example, a round billet or a substantially rectangular ingot. The cooling water spray pattern as described herein is primarily for casting a round billet. However, each embodiment can potentially be used for a substantially rectangular ingot, especially when the corner of the ingot has a certain degree of curvature. As shown, a continuous casting mold 105 forms a mold cavity, and a casting 110 is formed by the mold cavity. The casting process begins with a starter block 115 sealing or substantially filling the bottom of the mold cavity against the mold wall of the continuous casting mold 105. When the platform 120 moves downward along arrow 145 into the casting pit and the casting begins to solidify at its edge in the mold wall of the continuous casting mold 105, the casting 110 leaves the mold cavity. Metal flows from a casting trough 125, for example, through a sleeve 130 into the mold cavity, and the casting trough in some embodiments includes a heat reservoir or reservoir fed from a furnace. As shown, the sleeve 130 is partially immersed in the molten metal pool 135 to avoid metal oxidation that would occur when feeding from above the molten metal pool 135. Solidified metal 140 forms a shaped casting, such as an ingot. The flow through the sleeve 130 is controlled in the pouring trough 125, such as by a tapered plug mounted in an orifice, which connects the cavity of the pouring trough 125 with the flow channel through the sleeve 130. Conventionally, the pouring trough 125, the sleeve 130 and the mold cavity / mold wall of the continuous casting mold 105 are maintained in a fixed relationship from the beginning of the casting operation to the end of the casting operation. As the platform 120 continues to descend into the casting pit along arrow 145, the metal flow through the sleeve 130 continues. When the casting operation is about to end, whether because the platform is at the bottom of its travel, the metal supply is insufficient, or the casting has reached finished size, the flow of metal through the sleeve 130 is stopped and the sleeve assembled on the trough is removed from the molten metal pool 135 to allow the molten pool to solidify and complete the casting.

[0025] Figure 2 An example embodiment of a hot top casting method according to the present disclosure of a direct chill casting process comprising a continuous casting mold 105, a trough 125, and a sleeve 130 for supplying molten metal from the trough to the cavity of the mold is shown. Figure 2The illustrated embodiment of includes a starting position in which the tip of the sleeve 130 or sleeve is positioned close to the starter block 115 supported by the platform 120. The starter block 115 is positioned on top of the platform 120 and aligned to cooperate with the mold 105, thereby sealing the mold cavity and preventing the molten metal 107 from leaking from between the continuous casting mold 105 and the starter block 115. The sleeve 130 or sleeve is received in a transition plate 200, which is securely attached to the top of the mold 105, such as by threaded engagement. The transition plate 200 of the exemplary embodiment is fixed to the mold 105 by a metal ring that is threaded into a circular opening at the top of the billet mold 105 to securely fix the transition plate to the mold. The mold 105 of the exemplary embodiment is constructed of a metal such as aluminum, while the sleeve 130 and the transition plate 200 are typically formed of a refractory material that is resistant to heat.

[0026] Figure 2 The start of casting is shown with the starter block 115 aligned with the continuous casting mold 105. Figure 3 As the casting begins, as shown in FIG. 1 , the platform 120 is lowered with the starter block 115 as the molten metal flows from the trough 125 through the sleeve 130 and solidifies on the starter block 115 and at the bottom of the mold cavity forming the casting 140. In this way, as the starter block 115 is lowered away from the continuous casting mold 105, a continuous casting mold 105 is formed. Figure 4 The casting is shown as 140. Figure 4 The operating phase or steady state portion of the casting process is shown wherein the plateau 120 descends at a nearly constant rate while the cast part 140 grows accordingly. Figure 2 Also shown is a spray nozzle 150, which will be described in more detail below, wherein the spray nozzle provides a coolant or cooling fluid to the casting surface.

[0027] Using a transition plate 200 Figure 2-Figure 4 Although effective, the direct chill casting of the hot top casting method also has disadvantages. Specifically, excess casting gas and oxides are trapped between the surface of the molten metal 107 and the transition plate 200.

[0028] According to the example embodiments described herein, Figure 5As shown, the billet mold casting technique for hot top direct chill casting of aluminum employs a graphite casting surface 210 on which the initial solidification of the billet being cast occurs. The permeable graphite material allows both casting gas and casting lubricant to flow to the casting surface which creates a gas-slip casting condition, the casting surface comprising an air gap 220 between the molten metal 107 solidifying in the mold cavity and the graphite casting surface 210. The casting lubricant reduces friction on the casting surface 210 to prevent adhesion and tearing of the freshly solidified shell of the casting 140. The casting gas flow further helps to reduce this friction while at the same time providing a gas film between the casting surface and the billet shell, which reduces heat transfer from the molten aluminum to the casting surface. When the proper balance is achieved, the introduction of gas and oil produces an as-cast billet with a very smooth surface and a very narrow shell thickness compared to conventionally cast billets. The water or coolant flowing from the coolant chamber 155 to the spray nozzle 150 impinges on the outer shell of the casting 140 and continues to flow down the side of the casting, as shown at 145, to further cool the casting.

[0029] The amount of casting lubricant used during casting is directly related to the surface area of ​​the billet. Balancing the amount of casting gas introduced through the casting surface is difficult. Due to the inherent shrinkage that occurs during the solidification process, the outer shell of the billet shrinks slightly away from the casting surface 210 and allows gas to escape from the lower part of the mold cavity. However, the density of the casting gas is substantially lower than that of the molten metal, so that any excess casting gas that cannot escape from the lower part of the mold tends to rise upward within the mold cavity and pass upward through the molten metal above the mold in the pouring trough 125 or "hot top" design of the casting system. In addition, the air-entrapment recesses or pockets of the exemplary embodiment are manufactured into the transition plate 200 or graphite casting ring that forms the casting surface 210, which captures gas in the pockets 230 at the corners of the mold cavity, where the flowing liquid metal turns from a horizontal trajectory to a vertical trajectory at the corners of the mold cavity and goes down along the casting surface.

[0030] Figure 6 A cross-sectional view of a portion of the mold 105 is shown containing a transition plate 200 secured to the mold by threaded turns 205. Also shown are the graphite casting surface 210 and the pockets 230 in the corners that capture the rising casting gases. When the proper balance is reached, the continuous stream of casting gas fills the pockets 230 and as the pressure increases to a point where the pressure matches the metallostatic pressure of the metal in the slot 125 described above, the gas flows downward through the air gap 220 without bubbling in the sleeve 130. Bubbling in the molten metal should be reduced or prevented in order to prevent the entrainment of oxide films into the metal above the mold which are then pulled down into the solidifying ingot. These oxide films are considered 'inclusions' which have the potential to create defects in subsequent downstream processed components.

[0031] The gas pocket 230 in the direct chill casting system described herein is the area where the transition plate 200 intersects the casting surface 210. This area is where the molten aluminum flows outward from the metal feed port in the sleeve 130 toward the mold wall and then changes direction and flows downward to begin to form a solidifying shell. Figure 2-Figure 5 In the hot top casting configuration shown, the metallostatic pressure of the head of liquid metal above the mold attempts to force the metal to completely fill this area and form the pocket 230, and the accumulated gas pressure combines with the alloy and strength of the oxide to form a critical radius commonly referred to as the 'meniscus' radius. To aid in the formation of the meniscus radius and contain the trapped gas, a recess is manufactured into the transition plate at the casting surface interface in accordance with example embodiments described herein.

[0032] The gas pocket 230 of the example embodiment is designed so that the width remains close to the natural meniscus radius formed. The depth of the pocket 230 of the example embodiment is kept to a minimum in order to reduce the overall volume of the pocket. The edges of the pocket 230 of the example embodiment are smoothed to reduce the tendency of the oxide layer to tear as it moves along the hot metal surface and transitions to the pocket and meniscus radius. During casting using the hot top method of direct chill casting described herein, a dynamic undulating or pulsating action is formed at the pocket 230 area. Due to the continued inflow of casting gas, the size of the gas bubble in the pocket increases and the pressure also increases until the gas bubble can force its way down between the mold wall and the casting along the air gap 220 and escape from the bottom of the mold cavity. This increase in the volume of the gas bubble forces the metal back up through the sleeve or sleeve 130, so that when the gas pressure is released and the gas escapes, the metal liquid level decreases. Rocking or swaying harmonics may be generated with the mold positioned directly across the metal delivery flow channel of the slot 125. This periodic undulation of the meniscus should be reduced or kept to a minimum to prevent the formation of surge laps with accompanying microstructural anomalies in the solidifying billet shell that typically show up as meniscus marks. These meniscus marks directly affect the total shell zone width, and when too significant, thicker shell zones are undesirable for downstream processing.

[0033] A secondary reason for reducing or keeping metal heave to a minimum is that as the size of the bubbles in the pockets 230 increases, the bubbles extend beyond the edges of the pockets 230 onto the hot metal face adjacent the transition plate 200. As excess casting gas is released along the air gap 220 and the bubbles shrink, the action causes the oxide layer to open across the edges of the pockets. When this occurs, the oxide layer is often torn apart, which can result in metal clinging to the pocket edges with random, non-uniform oxide release on the billet surface.

[0034] In the worst case of an example embodiment of hot top casting, the casting gas flow rate is too great for the natural release of gas downward and outward through the bottom of the mold cavity, and the excess gas overflows over the edge of the sleeve 130 opening and releases bubbles in the melt above the mold. This sudden escape of gas causes the gas pocket to collapse violently and the liquid metal completely fills the area. This event has several undesirable results that lead to poor billet surface quality. For example, the results include a large amount of heavy oxide release that produces a non-uniform billet surface appearance. When the protective oxide layer has been destroyed and the liquid metal contacts these surfaces, the possibility of folding these heavy oxides below the surface into the solidified shell increases, and the possibility of attaching to the transition plate pocket 230 area or the graphite casting surface 210 increases. The collapse of the meniscus and exposure to liquid metal increases the possibility of metal infiltration into any small gap at the transition plate to the graphite casting ring interface or into any type of excess gas exhaust scheme. Metal adhesion may lead to billet scrapping and potential seepage. The temperature of the casting surface rises momentarily during the release of gas from pocket collapse, which can lead to increased combustion of casting lubricants and possible production of varnish, another potential aluminum attachment point leading to surface defects.

[0035] In addition to the above problems, the casting gas that bubbles in the sleeve 130 entrains the oxide film in the melt as the oxygen in the casting bubbles is stripped and reacts with the molten aluminum to form these oxide films. The surface problems caused by these oxides and the movement of the casting gas reduce the quality of the billet. It is desirable to eliminate the foaming casting gas in the melt during the entire casting process to prevent the formation of inclusions. According to the exemplary embodiments described herein, each embodiment reduces or eliminates the casting gas that bubbles in the sleeve 130 and the molten metal to prevent the entrainment of the oxide film. Eliminating any foaming is a balancing act between allowing sufficient flow rate of the casting gas applied to the mold to maintain the air gap 220 casting conditions and limiting the flow rate of the escaping gas to travel down along the air gap interface and flow out through the lower part of the mold instead of upward through the molten metal delivery system. The correct amount of casting gas is directly related to the thermal conditions of the casting surface. Colder casting conditions generally require higher casting gas flow rates than hotter casting conditions because colder conditions cause the billet to solidify more on the casting surface and most of the casting gas escapes from the bottom of the mold.

[0036] Hotter casting conditions cause the solidification front to move further down the casting surface, allowing the casting gas to more effectively maintain the air gap 220. These conditions also reduce the ability of the gas to escape from the bottom of the mold, thereby bubbling in the sleeve 130. This situation poses a challenge because many casting operations go through a significantly changing metal temperature range from the beginning of casting to the end of casting, making it more difficult to optimize the casting gas flow rate to maintain the air gap 220 with minimal melt sloshing and without bubbling in the sleeve 130. However, even when the melt temperature is stable, the casting gas flow rate window remains relatively narrow to maintain the highest billet surface quality without losing the air gap 220, generating surge laps or bubbling. Losing the air gap 220 produces a billet of poorer quality than a billet with surge laps, and may cause the entire billet to be scrapped. In addition, losing the air gap for any period of time may overheat the casting surface and burn the casting oil, thereby blocking the holes of the graphite casting surface 210, thereby preventing gas flow, and requiring the mold to be removed and the graphite casting ring to be replaced.

[0037] The various embodiments described herein include the ability to widen the window of casting gas flow rates without creating any bubbling issues as described above, which increases the robustness of the casting. As described herein, the venting of excess casting gas enables operation at higher casting gas flow rates, which ensures that the air gap 220 is maintained under chilled casting conditions while not allowing bubbling under hotter conditions.

[0038] According to this article and Figure 7 , a cross-section of a portion of a transition plate 200 is depicted and described herein with reference to the example embodiment shown in FIG. The transition plate of the illustrated embodiment includes a top surface 238 and a bottom surface 248. The transition plate 200 further includes an edge 242 extending around the circumference of the transition plate, wherein the edge of the illustrated embodiment includes a lip 244. When the transition plate 200 is in place in the casting mold 105, the lip 244 seals the top of the casting cavity against the mold. The lip 244 of the example embodiment is shown as being raised relative to the bottom surface 248 of the transition plate 200. The raised position of the lip 244 relative to the bottom surface 248 of the transition plate 200 creates a casting gas pocket 230. The lip 244 is joined to the bottom surface 248 of the transition plate by a gas pocket surface. Figure 7 The gas pocket surface (240) of the illustrated embodiment is beveled or chamfered, but various embodiments include rounded or curved surfaces.

[0039] As shown, the transition plate 200 includes vent holes 250 in a plurality of vent holes around the circumference of the transition plate in the area of ​​the pocket 230. The holes (the diameter of the example embodiment of the holes is 0.5 mm) are located along the slope of the gas pocket surface 240 of the recess of the gas pocket 230 in the transition plate. The vent holes 250 vent to the vent channel 260 to allow the casting gas to escape from the casting mold 105. As the gas pocket bubble grows due to the high gas flow rate, the edge of the bubble causes the meniscus 245 to move downward along the inclined surface of the pocket in the direction of arrow 255, thereby preparing to break through the edge of the pocket and bubble in the melt. However, when the leading edge of the expanding bubble in the pocket 230 reaches the vent hole 250 on the slope of the gas pocket surface 240, the gas pocket self-vents the excess gas. This type of system includes an orifice through which the gas escapes, and the orifice is small enough that the metal cannot penetrate the orifice due to the surface tension of the molten metal.

[0040] In another example embodiment, the exhaust hole 250 and / or the exhaust channel 260 are filled with a porous material that can be penetrated by gas but not by molten metal. Such a material includes a fiber mesh material similar to a filter element. The exhaust hole 250 of the example embodiment is filled with a porous material that provides a certain degree of resistance to air flow, so that the exhaust hole is optionally positioned in various positions in the recess 230, so that when the gas pressure in the recess reaches a sufficient pressure, the gas leaks through the exhaust hole without requiring the bubble to break through a specific position before exhausting.

[0041] While passive venting is employed as described in the above embodiments, active venting of the gap of the example embodiments provides an alternative system that can be configured by the user. This example embodiment of active venting includes a floating needle valve and valve seat arrangement designed to rupture at a specific gas pressure in the pocket 230 of the transition plate 200. The pressure of the example embodiment is selected to be a predetermined pressure that approximately matches the metal static head pressure of the metal level above the mold. As the size and resultant pressure of the bubble in the pocket increases, the needle rises from its valve seat and excess casting gas escapes, thereby preventing gas bubbling in the sleeve 130. This pressure relief valve 265 of the example embodiment is housed within the channel 260 of the transition plate 200, as shown in FIG. Figure 7As shown. The pressure relief valve 265 of the example is calibrated to a predefined pressure, which is determined to be a pressure below which the casting gas does not bubble through the molten metal and above which the casting gas escapes in an undesirable path. In addition, various pressure relief systems can be used for active venting of the gap to allow or prevent gas from flowing out of the gas pocket 230 during casting. Although the exhaust of the casting gas from the gas pocket 230 can be carried out at atmospheric pressure or the ambient pressure of the casting environment, the exhaust of the gas from the gas pocket of the example embodiment can also be regulated by pressure control to increase the amount of gas exhausted by reducing the pressure or increasing the pressure to keep the exhaust port open when necessary.

[0042] Although the exhaust of the gas pocket of the above-mentioned embodiment is realized by the exhaust hole in the gas pocket as described above, the embodiment optionally adopts the gas path in the transition plate to guide the gas when the gas escapes from the gas pocket along the defined gas path. The embodiment includes the engraved path in the transition plate 200 and other refractory components such as the sleeve 130 to guide the gas along the path between the refractory tank shell and the liquid metal, so that it is not actually formed to float in the sleeve 130, thereby generating a real bubble with entrained oxide. Another example embodiment of making a path for gas escape is to make a chimney, which allows the gas to bubble toward the metal flow and enter the mold from the metal flow. Although an oxide film may be produced in this embodiment, the oxide film will not be entrained in the casting billet. The concept of exhausting excess casting gas can realize a much wider window for the casting gas flow rate to facilitate multi-strand operation (casting multiple billets at the same time), thereby reducing meniscus pulsation and eliminating bubbling in the melt.

[0043] Figure 8 1 is a flow chart of a method for exhausting casting gas from a direct chill casting mold. As shown, molten metal is supplied to the direct chill casting mold through a transition plate, as shown at 310. Such molten metal of the exemplary embodiment is supplied through a slot (e.g., slot 125) and a sleeve (e.g., sleeve 130). Casting gas is supplied through a casting surface of the mold, as shown at 320. For example, casting gas is supplied through a casting surface 220 of a graphite casting ring, as shown at 320. Figure 2-Figure 6 The casting gas is exhausted from the gas pocket in the transition plate, as shown at 330. The transition plate includes a gas pocket to receive the casting gas, and as the pressure increases, the casting gas is exhausted through the above-mentioned mechanism.

[0044] The blocks of the flowchart support a combination of means for performing the specified functions and a combination of operations for performing the specified functions. It should also be understood that one or more blocks of the flowchart and a combination of blocks in the flowchart can be implemented by various aspects of exhausting casting gas from a direct chill casting mold as described above.

[0045] In some embodiments, some of the operations described above may be modified or further amplified. In addition, in some embodiments, additional optional operations are included. Modifications, additions, or amplifications to the operations described above of the example embodiments are performed in any order and in any combination to facilitate the exhaust of casting gases as described herein.

[0046] In another embodiment, a valve system is used to pressurize the vents during the metal filling phase of the casting. Metal overflowing into the mold may become turbulent, which may force liquid metal into small vents or porous media, effectively blocking the ability to exhaust excess casting gas. Applying a positive flow of gas through the exhaust system helps alleviate this problem of metal penetration. Once the mold is filled with metal and the starter block begins to descend into the casting pit, the valve system switches from a forward flow into the mold cavity to a free flow discharge of the gas pocket. This valve system can be a separately controlled and operated process, or it can be incorporated into an existing casting gas supply port in the mold itself and use a varying casting gas pressure to shuttle between applying a forward flow and exhausting excess gas. This is useful not only to help prevent metal penetration during mold filling, but also to prevent the vents from being blocked when the casting operator applies a release agent coating to the hot metal face of the transition plate 200 between castings.

[0047] Transition plate oxide bank

[0048] A further embodiment of the transition plate comprises a transition plate 'oxide bank', wherein in the case of hot top billet casting, the term 'oxide bank' refers to the undercut recess in the transition plate from the sleeve 130 or sleeve area towards the die hole. The use of oxide banks creates a situation where most of the oxide on the billet head is trapped and cannot fall off and roll onto the surface of the as-cast billet. The hot metal face is greatly reduced and, therefore, the oxide layer is much thinner and tends to remain fluid to flow outward and roll over the meniscus and onto the surface of the as-cast billet. This result makes the surface of the billet very uniform in appearance and prevents random heavy oxide release or 'patch' from breaking off and disturbing the appearance of the billet during casting. The narrow hot metal face also helps to eliminate the need to 'bump' the mold with high gas flow rates to release heavy oxides formed by cascading metal during mold filling.

[0049] Fig. 9Two transition plates 200 are shown, with the transition plate on the right being conventional and including a pocket 230 around the perimeter where the transition plate engages the die cavity. The transition plate 200 on the left includes a pocket 230 around the perimeter, but also includes an undercut 270 that is not present in the surface 280 of a conventional transition plate. The undercut provides an area where the sleeve 130 will be located below the bottom surface of the undercut, thereby providing an oxide bank, because the oxide on top of the molten metal will remain within the undercut, while the clean molten metal will flow below the undercut, passing the pocket 230 and transitioning down the side of the casting.

[0050] Applicants have found that the optimum undercut in the transition plate of the exemplary embodiment is about twelve millimeters deep to reliably retain the oxide as the metal head gently bulges up and down as the meniscus is slightly pulled due to the air gap casting conditions. The hot metal face is typically maintained at about twelve to twenty millimeters. This distance is a compromise that helps prevent bubbles formed at the meniscus from breaking over the edge of the oxide bank and preventing blistering in the sleeve opening, while also helping to limit the time the oxide must 'grow' in thickness and strength before rolling over the meniscus.

[0051] Many modifications and other embodiments of the invention set forth herein will occur to those skilled in the art having the benefit of the teachings presented in the foregoing description and the associated drawings. Therefore, it should be understood that the invention is not limited to the specific embodiments disclosed, and modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a general and descriptive sense only and not for purposes of limitation.

Claims

1. A transition plate (200) for engaging a direct chill casting mold (105), the transition plate comprising: top surface (238); bottom surface (248); an inclined gas pocket surface (240); an edge (242) including a lip (244) extending around a perimeter of the transition plate (200), wherein the lip (244) is joined to the bottom surface (248) via the beveled gas pocket surface (240); wherein the lip (244) is configured to seal the top of the casting cavity of the direct chill casting mold (105); and wherein when the transition plate (200) intersects the casting surface (210) of the direct chill casting mold (105), a casting gas pocket (230) is formed at the periphery of the transition plate (200) by the lip edge (244) and the inclined gas pocket surface (240); and One or more vent holes (250) located around the circumference of the transition plate (200) and along the beveled gas pocket surface (240) are configured to vent the casting gas pocket.

2. A transition plate according to claim 1, wherein when the transition plate is positioned on the direct chill casting mold (105), the lip (244) is raised relative to the bottom surface (248), wherein the raised position of the lip (244) forms the casting gas pocket (230), and wherein the one or more exhaust holes (250) are positioned closer to the bottom surface (248) than to the lip (244).

3. The transition plate of claim 2, wherein in response to bubbles forming in the casting gas pocket (230), the one or more vent holes (250) are configured to allow casting gas to be vented before the casting gas reaches the bottom surface (248) of the transition plate.

4. The transition plate of claim 2, wherein the beveled gas pocket surface (240) comprises a chamfered surface relative to the bottom surface (248), wherein the one or more exhaust holes are defined in the chamfered surface.

5. The transition plate of claim 1, wherein the one or more vent holes (250) comprise a mesh of material that is permeable to gas but impermeable to molten metal.

6. The transition plate of claim 1, wherein the one or more vent holes (250) vent to atmospheric pressure.

7. The transition plate of claim 1, wherein the one or more vent holes (250) are associated with a valve (265), wherein the valve allows the one or more vent holes to vent to atmospheric pressure in response to the pressure in the casting gas pocket (230) satisfying a predetermined value.

8. A method for exhausting casting gas from a direct chill casting mold (105), the method comprising: supplying molten metal (107) to the direct chill casting mold (105) through a transition plate (200), wherein the transition plate has a beveled gas pocket surface (240) and an edge (242), the edge (242) including a lip (244), the lip extending around the periphery of the transition plate (200), the lip (244) being joined to a bottom surface (248) through the beveled gas pocket surface (240), the lip sealing the top of the casting cavity of the direct chill casting mold (105); and the transition plate (200) intersects with the casting surface (210) of the direct chill casting mold (105) so that a casting gas pocket (230) is formed by the lip (244) and the beveled gas pocket surface (240); supplying casting gas through a casting surface (210) of the direct chill casting mold; and exhausting the casting gas from the casting gas pocket (230) in the transition plate, wherein the casting gas is exhausted through one or more exhaust holes (250) positioned around the circumference of the transition plate and along the gas pocket surface (240) of the slope, and, Wherein exhausting the casting gas from the casting gas pocket in the transition plate is performed in response to a pressure of the casting gas in the casting gas pocket reaching a predetermined pressure.

9. The method of claim 8, wherein the predetermined pressure is determined based on a metal static head pressure of the molten metal (107) supplied to the direct chill casting mold (105).

10. The method according to claim 8, further comprising: supplying pressure to one or more vent holes (250) in the transition plate (200) to prevent molten metal from flowing through the one or more vent holes; as well as The pressure to the one or more vents is reduced or removed to allow the casting gases to vent.

11. A system for venting a direct chill casting mold, the system comprising: Direct chill casting mold (105); a sleeve (130) through which molten metal (107) is supplied to the direct chill casting mold; as well as The transition plate (200) of claim 1, wherein the transition plate (200) is attached to the direct chill casting mold and the sleeve is received in the transition plate, and The one or more exhaust holes (250) are configured to exhaust casting gases in response to molten metal filling the direct chill casting mold.

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