Patent Application
20210154730
The present invention relates to a system, apparatus, and method for continuous casting of metal, and more particularly, to reduce macrosegregation through a mechanism for controlling the position of a spout tip or diffuser during the casting process to maintain the spout tip or diffuser near the solidification front, location of transition between liquid metal and solid metal in the cast part.
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. One method of manufacturing an ingot or billet is through a semi-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 starting 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 starting block thereon may descend into the casting pit at a predefined speed to allow the metal exiting the mold cavity and descending with the starting 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 distribution of metal within the mold cavity and within the still-molten region of a cast part exiting the mold cavity is complex with changing temperature profiles and gradients throughout the casting process. Solidification physics exhibits the formation of macrosegregation whereby the cast part may have a non-uniform chemical composition across a dimension of the cast part. Macrosegregation formed from casting process is irreversible during processing of the cast part, such that it is imperative to minimize macrosegregation during the casting process.
Embodiments of the present invention generally relate to an apparatus and method for continuous casting of metal, and more particularly, to reduce macrosegregation through a mechanism for controlling the position of a spout tip or diffuser during the casting process to maintain the spout tip or diffuser near the solidification front, location of transition between liquid metal and solid metal in the cast part. Embodiments may provide an apparatus for liquid distribution into a mold cavity, the apparatus including: a mold frame supporting a mold defining a mold cavity; a liquid diffuser; and an actuator configured to move at least one of the mold frame and the liquid diffuser relative to one another, wherein the actuator is configured to move at least one of the mold frame and the liquid diffuser relative to one another in response to a signal from at least one sensor. The liquid diffuser may include a tip and define a liquid passageway there through, where the at least one sensor may include a thermocouple disposed proximate the tip of the diffuser.
According to some embodiments, the actuator includes a linear actuator, where an axis is defined through the mold cavity along which a cast part may be drawn, and the actuator is configured to move at least one of the mold frame and the liquid diffuser relative to one another along the axis. The liquid may include metal, where the tip of the liquid diffuser may be submerged in a pool of liquid metal in the mold cavity, where the relative movement between the mold frame and the liquid diffuser may result in movement of the liquid diffuser within the pool of liquid metal. The linear actuator, responsive to the signal from the thermocouple, may be configured to maintain the tip of the liquid diffuser in the pool of liquid metal at a position corresponding to a predefined temperature range of the liquid metal.
The actuator of some embodiments, responsive to the signal from the thermocouple, may be configured to maintain the tip of the liquid diffuser in a region of the pool of liquid metal near a metal coherency point during a casting operation. Embodiments may include a controller, where the controller may be configured to control the actuator and the relative position between the mold frame and the liquid diffuser where the position between the mold frame and the liquid diffuser may be established based, at least in part, on the signal from the thermocouple and at least one property of a liquid dispensed by the diffuser. The at least one property of a liquid may include a liquidus temperature of the liquid being dispensed at a given pressure.
Embodiments of the present invention may provide a method including: receiving an indication of a material to be cast in a mold cavity; establishing from the indication of the material type, a temperature profile of the material type; dispensing the material in liquid form through a diffuser into the cavity of the mold; detecting a temperature of a tip of the diffuser within the cavity of the mold; and moving at least one of the diffuser or the mold relative to the other responsive to the tip of the diffuser to maintain the tip of the diffuser within a pool of the material in liquid form based on a predefined temperature range associated with the temperature profile. Embodiments may include controlling a flow of the material through the diffuser in response to one or more properties of the pool of material.
Methods of example embodiments may optionally include: determining, based on material type, an initial position of the diffuser relative to the cavity of the mold; and moving at least one of the diffuser or the mold relative to the other to the initial position before dispensing material through the diffuser. Methods may include moving at least one of the diffuser or the mold relative to the other from the initial position to a secondary position based on an algorithm associated with the material type after the material has started to be dispensed from the diffuser and casting is occurring at a steady state. Methods may optionally include moving at least one of the diffuser or the direct chill mold relative to the other from the secondary position to a tertiary position based on the algorithm associated with the material type in response to an indication that the casting is ending. The mold may be a direct chill mold including a starting block where the method may include moving the starting block relative to the mold cavity and the diffuser.
Embodiments described herein may provide an apparatus including: a frame; at least one mold cavity attached to the frame, the mold cavity defining an axis along which a material cast in the mold exits the mold in a continuous casting process; and a frame support, where the frame is attached to the frame support by an actuator configured to move the frame and the mold cavity relative to the support arm along an axis parallel to the axis defined by the mold cavity. The actuator may include at least one of a worm gear, a linear actuator, a hydraulic piston, or a ball screw. The apparatus may include a casting liquid distribution diffuser, where the casting liquid distribution diffuser is held fixed relative to the frame support, and where the actuator is configured to move the mold cavity relative to the casting liquid distribution diffuser.
According to some embodiments, the apparatus may include a thermocouple attached to the casting liquid distribution diffuser, where the actuator moves the frame relative to the casting liquid distribution diffuser responsive to a signal from the thermocouple. Embodiments may include a controller, where the controller is configured to cause the actuator to move the frame relative to the casting liquid distribution diffuser responsive to the signal from the thermocouple according to a temperature profile of a casting liquid dispensed from the casting liquid distribution diffuser.
Embodiments of an apparatus may include a memory configured to store a plurality of profiles, each profile including a casting material and a mold configuration, and a controller configured to move the frame and the mold cavity relative to the support arm based on a selected profile between at least two different positions during a casting operation. Embodiments may include a diffuser for dispensing liquid into the mold cavity, and a thermocouple on the diffuser, where the controller is configured to adjust the selected profile and change the position of the frame and the mold cavity relative to the support arm in response to a signal received from the thermocouple.
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:
Exemplary embodiments of the present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, the invention may 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 satisfy applicable legal requirements. Like numbers refer to like elements throughout.
Embodiments of the present invention generally relate to a method, apparatus, and system for metal distribution in a continuous casting mold cavity. Embodiments described herein may be particularly beneficial in vertical direct chill casting; however, embodiments may be used in a variety of different casting applications. Vertical direct chill casting is a process used to produce ingots or billets that may have small or large cross sections for use in a variety of manufacturing applications. The process of vertical direct chill casting begins with a horizontal table containing one or more vertically-oriented mold cavities disposed therein. Each of the mold cavities is initially closed at the bottom with a starting block to seal 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 starting block solidifies, the starting block is moved vertically downward along a linear path. The movement of the starting block may be caused by a hydraulically-lowered platform to which the starting block is attached. The movement of the starting 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 speed for a semi-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 starting block are moved.
During the casting process, coolant may be sprayed proximate the exit of the mold cavity to encourage solidification of the metal shell as the metal exits the mold cavity and the starting block is advanced downward. The cooling fluid is introduced to the surface of the metal from proximate the mold cavity as it 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 starting block is advanced downward, the cooling fluid may be sprayed directly on the ingot to cool.
The direct chill casting process enables ingots to be cast of a wide variety of sizes and lengths, along with various profile shapes. While circular billet and rectangular ingot are most common, other profile shapes are possible.
Various complexities exist in the casting of metal parts, particularly in vertical direct chill continuous casting, including the manner in which metal is distributed within a mold cavity. Metal alloys generally include elements in addition to a pure metal component. These elements are ideally evenly combined in solution to provide a consistent metal alloy composition throughout a metal object, such as an ingot or billet. When in solid form, the elements are in fixed concentrations that do not migrate.
Due to a combination of effects from solute redistribution and shrinkage during solidification of a metal alloy from a liquid, thermal-solutal convection, dendrite fragmentation, and grain migration along a solidification front, where the liquid turns solid, may produce a variation in chemistry from the outer surface of an ingot or billet to a center of the ingot or billet. This variation in chemistry is known as macrosegregation. This macrosegregation is undesirable as the chemistry variation between portions of the metal can lead to unsatisfactory properties affecting the quality of materials produced from the ingot or billet.
Embodiments of the present invention provide a method, apparatus, and system to minimize macrosegregation and improve the quality and consistency of a cast metal object, such as an ingot or billet. Embodiments described herein provide a unique metal distribution system developed to allow feeding of liquid metal near the metal coherency point to solidus region (colloquially known as the “mushy zone”) of a metal object, such as an ingot or billet, as the object is cast and throughout the entire casting process. The boundary region between 100% liquid and the coherency point temperature (the point at which solidification begins to occur through crystalline structure, grains start to coalesce to develop strength) is commonly referred to as the “slurry zone”. Embodiments described herein reduce the accumulation of fragmented grains at the ingot center through metal distribution in the sump to reduce macrosegregation. An automated system may move the mold frame (including the mold cavity or cavities) relative to the metal distribution spout to maintain the spout at the correct metal depth (constant at solidification front) from the start-up phase of the casting to the end phase of the casting. A thermocouple disposed proximate the tip of the spout, which may be integrated with the spout, may provide feedback to a controller to determine the appropriate position of the mold cavity and the pool of molten metal therein relative to the spout tip. This appropriate position may vary depending upon the material being cast as temperature profiles may vary substantially among different alloys or metals.
Systems of example embodiments may include a range of unique metal diffusers/distributors, described further below, to provide the optimum metal flow during distribution in the sump and control algorithms to create the optimal flow conditions for manipulating the typical metal flow field and reduce macrosegregation.
Typical metal distribution systems for a casting mold include a spout and ceramic cloth metal distribution bag that feeds metal just under the surface of the liquid metal in direct chill molds due to the typical fixed constraints of the spout and mold position necessary for the start-up phase of casting. For any direct chill cast ingot, regardless of shape, feeding molten metal from a location near the surface (e.g., within about six inches of the surface), as with the traditional spout and ceramic cloth distribution bag system, may result in some degree of macrosegregation. Incoming metal is swept at its highest rate along the solidification front (e.g., at coherency temperature) towards the center of the ingot fragmenting first forming grains which are solute lean and dumping them at the bottom of the sump. This results in negative segregation formation in the center of the ingot in direct chill casting. Embodiments described herein provide a metal distribution system with automated control for feeding the metal from the distributor within the sump bottom region to decrease the speed in the natural convection cells and reduce the accumulation of solute lean grains at the sump location, thereby reducing macrosegregation.
Using the method illustrated in
According to an example embodiment, the spout 130 may include one or more thermocouples to determine temperature of the spout 130 at one or more locations along its length, and in particular at the tip of the spout 130 where the metal exits the spout 130 from the trough 125. The thermocouple may determine the temperature of the liquid metal at the location of the spout 130 tip in the sump. Embodiments described herein may include metal distributors or diffusers at the spout 130 tip, which may be configured to include one or more thermocouples to provide a temperature of the metal flowing through the diffuser/distributor and/or the temperature of the metal around the diffuser/distributor in the sump. Temperature feedback from proximate the tip of the spout 130 or the attached diffuser may enable active control of the position of the spout or diffuser within the pool of molten metal to adjust to changes in metal temperature, oxide generation, or other casting conditions that may require unplanned movement of the mold 105 relative to the spout 130 to appropriately position the tip of the spout or the diffuser within the sump (e.g., the area of transition between the molten metal and the solid metal). The spout 130 of example embodiments is of a length that can accommodate such positional changes within the pool of molten metal to enable positioning of the tip proximate the sump as deemed desirable.
The spout 130 of example embodiments may be outfitted with specially defined diffusers at the tip of the spout to reduce metal splash at the cast start and to optimize metal distribution during the casting process. These diffusers could be separate parts assembled on the spout 130. The geometry of such diffusers could be triangular, rectangular, or other irregular shapes to accommodate different sizes of cast parts and molten liquid feeding directions and speeds. These diffusers can be made of any known refractory materials such as fiberglass cloth, fiber reinforced ceramics, or one of the various types of thermal ceramics or elevated temperature super alloys. Example embodiments of such diffusers are illustrated and described below.
According to example embodiments described herein, a casting specification may be entered into a programmable logic controller to control the position of a mold frame (otherwise known as a “mold table”) to which one or more molds may be attached. The programmable logic controller is used according to example embodiments to control the position of the mold frame (and the molds held therein) with respect to the spout. While the example embodiment of
At the start of a cast, the mold 105 and mold frame may be positioned low enough relative to the spout 130 to clear the metal distributor spout 130.
As the casting process nears the end of the casting run, the sump becomes more shallow, and the mold shifts down having the relative effect of raising the spout relative to the mold. The spout tip position in the molten pool rises considerably at the end of the casting process relative to the sump as the mold and cylinder are lowered. Pouring of the metal is ceased and the spout is withdrawn to allow the molten metal to solidify.
A special control algorithm is determined that is unique for each alloy and cast part size combination. The algorithm may link the typical heat balance with the spout positioning requirements to ensure that the spout/distributor remains close to the coherency point temperature at the bottom of the sump of a cast product for the duration of the cast. An example illustration of the control algorithm is illustrated in
While control algorithms may be developed for each alloy and cast part size, the thermocouple of the tip of the spout/diffuser may provide feedback of temperatures not anticipated during a standard or ideal casting operation, or to confirm operation is proceeding as anticipated. In such an embodiment, the control algorithm may use the temperature feedback from the spout tip to adjust the position of the spout relative to the sump as necessary, and to locate the spout tip appropriately given the temperature anomalies observed. This may provide a reliable consistency of material across the cross section of the material, even when casting conditions are not ideal or if there is an issue encountered during casting that can be rectified by repositioning of the mold and sump relative to the spout location.
The spout 130 and spout tip described herein and illustrated above provide a spout with no specific geometric characteristics, embodiments described herein may include diffusers at the tip of the spout to promote desired metal flow within the sump. Different metal alloys and different casting sizes may have different properties which benefit from distinct metal flow patterns in the sump.
In addition to different shapes, the profile, diffuser orifices (openings) and size of the diffusers may be altered as desired to achieve optimum flow of metal within the sump.
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 is a continuation of and claims priority to U.S. patent application Ser. No. 15/701,536, filed on Sep. 12, 2017, the contents of which are hereby incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15701536 | Sep 2017 | US |
| Child | 17142810 | US |
