Patent Application
20220008987
The present disclosure relates to a system, apparatus, and method for a cooling water spray pattern for a direct chill casting mold, and more particularly, to a spiral water spray pattern for a direct chill billet casting mold.
Metal products may be formed in a variety of ways; however numerous forming methods first require an ingot, billet, or other cast part that can serve as the raw material from which a metal end product can be manufactured, such as through rolling or machining, for example. One method of manufacturing an ingot or billet is through a continuous casting process known as direct chill casting, whereby a vertically oriented mold cavity is situated above a platform that translates vertically down a casting pit. A starter block may be situated on the platform and form a bottom of the mold cavity, at least initially, to begin the casting process. Molten metal is poured into the mold cavity whereupon the molten metal cools, typically using a cooling fluid. The platform with the starter block thereon may descend into the casting pit at a predefined speed to allow the metal exiting the mold cavity and descending with the starter block to solidify. The platform continues to be lowered as more molten metal enters the mold cavity, and solid metal exits the mold cavity. This continuous casting process allows metal ingots and billets to be formed according to the profile of the mold cavity and having a length limited only by the casting pit depth and the hydraulically actuated platform moving therein.
The direct chill casting process within the aluminum world refers to the process of semi-continuous casting of aluminum ingots or billets thru and open mold in which the bulk of solidification takes place due to the direct application of cooling water upon the initial forming shell. The initial shell is formed by the heat extraction of the physical mold wall itself, while the remaining solidification is controlled by the cooling water. Over the years there have been many variations in the method of applying the cooling water to the product being cast. These range from continuous water curtains, to water spray holes, to water spray nozzles, and others.
The present disclosure relates to a system, apparatus, and method for a cooling water spray pattern for a direct chill casting mold, and more particularly, to a spiral water spray pattern for a direct chill billet casting mold. Embodiments provided herein include a direct chill casting mold including: a mold body defining a mold cavity there through; and a plurality of spray jets arranged proximate an exit of the mold cavity, where the plurality of spray jets are angled with respect to the mold cavity such that streams of fluid exiting the plurality of spray jets impinge upon a casting exiting the mold cavity at an angle offset from a centerline of the casting. The plurality of spray jets are arranged in a radial pattern around the exit of the mold cavity, and where the plurality of spray jets cooperate to provide a spiral of cooling fluid around the casting as it exits the mold cavity. The plurality of spray jets of some embodiments are angled with respect to the mold cavity such that the streams of fluid exiting the plurality of spray jets experience the Coandă effect around a curvature of the casting exiting the mold cavity.
According to some embodiments, the angle offset from the centerline of the casting comprises a perpendicular rotated angle relative to the casting. The perpendicular rotated angle includes a vertical angle of between about 35 to 45 degrees from perpendicular to the casting. According to some embodiments, the perpendicular rotated angle includes a horizontal angle of between about 20 and 45 degrees from the centerline of the casting. The plurality of spray jets of some embodiments includes a first plurality of spray jets arranged at a first perpendicular rotated angle relative to the casting, the direct chill casting mold further including a second plurality of spray jets, where the second plurality of spray jets are arranged at a second perpendicular angle relative to the casting different than the first perpendicular rotated angle of the first plurality of spray jets. The second perpendicular rotated angle relative to the casting includes a horizontal angle equivalent to the horizontal angle of the first perpendicular rotated angle and a vertical angle different from the first perpendicular rotated angle. The angle offset from a centerline of the casting of some embodiments is less than an angle resulting in a stream of fluid tangential to the casting.
Embodiments provided herein include a method for direct chill casting including: casting a billet from a direct chill casting mold cavity of a direct chill casting mold having a plurality of spray jets; and directing a cooling fluid from the plurality of spray jets to impinge upon the casting exiting the mold cavity at an angle offset from a centerline of the casting. The plurality of spray jets of some embodiments are arranged in a radial pattern around an exit of the mold body, where the plurality of spray jets cooperate to provide a spiral of cooling fluid around the casting as it exits the mold cavity. The plurality of spray jets of some embodiments are angled with respect to the mold cavity such that the streams of fluid exiting the spray jets experience the Coandă effect around a curvature of the casting exiting the mold cavity.
According to some embodiments, the angle offset from the centerline of the casting includes a perpendicular rotated angle relative to the casting. The perpendicular rotated angle includes a vertical angle of between about 35 to 45 degrees from perpendicular to the casting. The perpendicular rotated angle of some embodiments includes a horizontal angle of between about 20 and 45 degrees from the centerline of the casting. The plurality of spray jets includes a first plurality of spray jets arranged at a first perpendicular rotated angle relative to the casting, the direct chill casting mold body further including a second plurality of spray jets, wherein the second plurality of spray jets are arranged at a second perpendicular rotated angle relative to the casting different than the first perpendicular rotated angle of the first plurality of spray jets. According to some embodiments, the second perpendicular rotated angle relative to the casting comprises a horizontal angle equivalent to the horizontal angle of the first perpendicular rotated angle and a vertical angle different from the first perpendicular rotated angle. The angle offset from a centerline of the casting of some embodiments is less than an angle resulting in a stream of fluid tangential to the casting.
Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
Example embodiments of the present disclosure now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the disclosure are shown. Indeed, embodiments may take 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 satisfy applicable legal requirements. Like numbers refer to like elements throughout.
Embodiments of the present disclosure generally relate to a system, apparatus, and method for cooling a billet from a direct chill casting mold, and specifically, to a spiral pattern of cooling fluid used to envelop the billet exiting the casting mold to cool the billet as it descends into the casting pit.
Vertical direct chill casting or continuous casting is a process used to produce ingots or billets that may have a variety of cross-sections shapes and sizes for use in a variety of manufacturing applications. The process of direct chill casting begins with a horizontal mold table or mold frame containing one or more vertically-oriented molds disposed therein. Each of the molds defines a mold cavity, where the mold cavities are initially closed at the bottom with a starter block to seal the bottom of the mold cavity. Molten metal is introduced to each mold cavity through a metal distribution system to fill the mold cavities. As the molten metal proximate the bottom of the mold, adjacent to the starter block solidifies, the starter block is moved vertically downward along a linear path into a casting pit. The movement of the starter block may be caused by a hydraulically-lowered platform to which the starter block is attached. The movement of the starter block vertically downward draws the solidified metal from the mold cavity while additional molten metal is introduced into the mold cavities. Once started, this process moves at a relatively steady-state for a continuous casting process that forms a metal ingot having a profile defined by the mold cavity, and a height defined by the depth to which the platform and starter block are moved.
During the casting process, the mold itself is cooled to encourage solidification of the metal prior to the metal exiting the mold cavity as the starter block is advanced downwardly, and a cooling fluid is introduced to the surface of the metal proximate the exit of the mold cavity as the metal is cast to draw heat from the cast metal ingot and to solidify the molten metal within the now-solidified shell of the ingot. As the starter block is advanced downward, the cooling fluid may be sprayed directly on the ingot to cool the surface and to draw heat from within the core of the ingot.
Of critical importance as the casting process is performed is the cooling of the billet or ingot. Conventionally, direct chill casting cooling was based upon a “water curtain” concept. This typically includes a continuous film or sheet of water surrounding the casting and provided relatively uniform cooling. However, there are several drawbacks. The water film of the water curtain requires s substantial amount of water to maintain the uniformity of the sheet of water. The velocity of the water film is typically relatively low such that efficient heat extraction is limited. Maintaining a truly equal amount of water flow around the entire periphery of the mold is difficult, and the continuous sheet of water prevents the escape of steam which can build up between the continuous sheet of water and contact with the casting. This steam could build in pressure and periodically release in bursts that may disrupt the continuous film of water.
The water curtain has generally been supplanted with a row of water spray holes that direct water to impinge on the surface of the billet. A variety of water hole concepts have been used, with the primary differences being the angle of attack or impingement upon the billet surface. However, the water hole concepts have exclusively focused on water directed straight toward the surface of the billet, toward a central axis of a cylindrical billet. The water hole direct chill cooling concept improved upon the water curtain cooling method for several reasons. The water had an increased velocity through the hoes which increased the efficiency of the cooling effect with lower overall water consumption. Gaps between water holes allowed any steam generation about the impingement point to easily escape. Water flow distribution about the mold periphery was also improved.
While there are benefits of a water jet over a water curtain, there are also shortcomings. It has been established that the more perpendicular the impact, or higher impingement angle of the water stream upon the hot billet surface, the higher the cooling rate. However, the higher the angle (more perpendicular to the surface of the billet), the water stream has a greater tendency to rebound off the surface of the billet, which has a negative effect on the overall cooling efficiency. This is particularly problematic when higher water flows (velocity) are required to compensate for high incoming water temperatures.
The Dualjet water pattern introduced by the Applicant includes two rows of water spray holes with alternating angles of impingement. The primary, or high impact angled holes provide highly efficient cooling. Though due to the high impact angle, the water jets have the tendency to bounce-off, even at lower flow rates. Secondary alternating holes have a lower impingement angle aimed at the water bouncing off of the billet surface, and re-directs the rebounded water together with the water from the secondary holes to the billet surface. This enables very high flow rates and efficient cooling with little water bouncing-off the surface. This Dualjet system provides enhanced cooling technology for improved cooling performance.
While the Dualjet is effective and efficient, Applicant has found an improved method of cooling and solidifying a billet. The alternating jet impingement pattern on the billet surface of the Dualjet may lend to cold spots and warmer areas between the jets. This may lead to a non-uniform solidification front on the surface of the billet. Certain alloys may experience surface cracks from hotter areas, where the shell of the casting is slightly weaker. Further, these warmer areas lend themselves more to casting surface attachments and light intermittent drags. The non-uniform cooling pattern may resemble a herringbone pattern that can be seen on the surface of some billets as shown in
While the Dualjet alternating jet design provides substantial improvements over earlier cooling attempts, embodiments provided herein use an improved water spray cooling pattern. The set of spray jets disclosed herein create a helical, spiral pattern of cooling fluid around a casting. A set of spray jets may include a plurality of water jets with a compound angle of impingement relative to the casting. While conventional cooling jet design includes a jet pointed toward a centerline of the casting extending down into the casting pit, and angled down into the casting pit by a predetermined angle, embodiments described herein include spray jets angled away from the centerline of the casting to a point closer to tangential to the casting. The spray jets may be angled within a range; however, the upper limit of such a range would have the water jet angled just below tangential to the casting, as a tangential spray may not contact the casting and may instead spray off into the casting pit providing no cooling effect. A spray jet angled less than tangential provides an angle of impingement on the casting whereby the Coandă effect occurs, as detailed further below.
Embodiments described herein may include an angle of vertical impingement (angle 155 of
As noted above, a single jet or single impingement water spray pattern is not new. However, the single jet impingement disclosed herein can employ substantially higher water flow rate or velocity than a spray jet pointed toward the central axis of a billet. In direct chill casting, the cooling water flow rate is influenced heavily by the incoming temperature of the cooling water. This temperature can be fairly high in many climates. As the water temperature increases, the water flow rate needs to increase to maintain proper solidification rates. Single jet water spray patterns are susceptible to ‘bounce-off’ of the water jets, which reduces the efficiency of the cooling effect. The Dualjet system was developed to allow for higher water flow rates while maintaining water contact to the billet surface.
According to embodiments described herein with a compound angle of the water jets, angled away from the center axis of the billet and thus not perpendicular to the billet but rather more tangential, the water jet produces a spiral action pattern and allows the cooling fluid or water to ‘hug’ the billet surface and wrap around the billet without bouncing off at higher water flow rates.
As the definition of the Coandă effect outlines, the curvature of the impacted surface and the velocity of the stream are interrelated such that there is a critical angle at which the ‘hugging’ effect of the water no longer exists and the stream separates from the surface. For the application of the Coandă effect relative to the direct chill billet cooling, specific factors influence this critical angle.
The curvature of the billet surface is a function of the compound angles of the water jet impingement stream and the billet diameter itself. These compound angles are in the ‘X-Y’ and ‘X-Z’ planes relative to the billet, as shown in
Embodiments described herein may use a single row of spray jets disposed around the exit of the mold cavity; however, embodiments may optionally incorporate the Dualjet alternating spray jet pattern, whereby two or more rows of spray jets may be disposed around the exit of the mold cavity. In this manner, the spray jets in the two or more rows may be arranged at different angles in each row. The differing angles may be differing in both the vertical angle (down into the casting pit) and the horizontal angle (degree of tangentiality with respect to the casting). Such an embodiment may provide improved cooling efficiency. While two or more rows may aid with catching or deflecting “bounce off” water back toward the casting, embodiments using the spiral pattern water spray as disclosed herein are less susceptible to bounce off, and may further provide a degree of catching the bounce off by virtue of the angled streams of coolant being vertically layered in that water falling from a first coolant stream may be picked up by a stream below in the spiral, helical pattern.
According to another example embodiment described herein for aluminum direct chill casting, individual drilled water spray holes may be substituted with a ‘corrugated’ shaped ring as shown in
An advantage of embodiments described herein is the ability to easily replace the spray pattern as required. Drilled water spray holes may diminish in size over time due to a build-up of hard water deposits. Depending upon the water chemistry at a casting location, this build-up could be relatively slow, while in other locations the build-up may be very fast. Such build-up requires periodic removal from the spray holes to return the cooling performance of the mold to an as-new condition. This may be performed with drills sized according to the original hole diameter. However, this requires careful diligence of the mold technician not to cause irreparable damage by wallowing out the holes which can distort the water pattern.
The spiral cooling fluid pattern as described herein also provides another substantial advantage. When a mold position is plugged off from metal flow due to a bleed-out or other consequence (i.e., when the casing of the casting is not solidified as it exits the mold and the molten metal in the core of the casting pours out, shown in
While the above-described embodiments relate primarily to a round billet casting, embodiments may be used with rectangular or substantially rectangular ingots during casting. Such embodiments may include spray jets arranged as described above along each face of the rectangular ingot. While rounded corners may lead to a Coandă effect around the corners of the ingot, such an effect may not be necessary. Further, the spray jets may be arranged to extend beyond the width of a face of the ingot to ensure coverage of the face with the coolant from the angled spray jets. Such an embodiment would benefit from the angled cascade of coolant from the spray jets along each face thereby improving the cooling efficiency of the casting.
Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that 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 generic and descriptive sense only and not for purposes of limitation.
This application claims priority to U.S. Provisional Patent Application Ser. No. 63/050,391, filed on Jul. 10, 2020, the contents of which are hereby incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63050391 | Jul 2020 | US |
