Patent Application
20070251663
Reference will now be made in detail to the present preferred embodiments of the invention, an example of which is illustrated in the accompanying drawings. The method and corresponding steps of the invention will be described in conjunction with the detailed description of the system. The systems and methods presented herein may be used for casting metals. The present invention is particularly suited for continuous casting of steel and steel alloys.
For purpose of explanation and illustration, and not limitation, a schematic view of an exemplary embodiment of the system made in accordance with the invention is shown in
In accordance with the invention, a system is provided for dynamically controlling the casting of a material. The system is adapted and configured to dynamically cool and solidify a stream of material being cast in accordance with a predefined cooling profile.
For purposes of illustration and not limitation, as embodied herein and as depicted in
After exiting mold 124 within caster 110, slab 140 is guided through a plurality of caster segments 150 from a generally vertical direction to a generally horizontal direction. Slab 140 is guided by a plurality of rollers 160 within the caster segments 150. As slab 140 passes through caster 110, it is also cooled by a cooling means 170. Slab 140 is preferably cooled at a rate sufficiently high to maintain the thickness of the skin of slab 140 to prevent breakout, but sufficiently slow to prevent slab 140 from solidifying too quickly. Preventing overcooling of slab 140 reduces wear and vibration on rollers 160 and other portions of caster 110. When slab 140 has exited the caster 110 at caster exit 114, slab 140 has preferably been cooled to the point that it is solid throughout its cross section. After exiting caster 110, slab 140 is cut into predetermined lengths by a cutting mechanism 300. Each of these elements is discussed in further detail below.
While a horizontal caster 110 is depicted in
It will be understood that caster 110 can be used to continuously cast a variety of materials 10, such as metallic materials. Specifically, caster 110 can be used to cast a wide variety of steel grades, other ferrous and non ferrous materials and the like. Moreover, virtually any mold 124 can be used as are known in the art. Mold 124 can have a cross section of a variety of shapes, including circular, ovoid, rectangular, “I” shaped and the like, as desired. Primary cooling system 130 includes a heat exchanger that is adapted and configured to remove heat from material 10 by way of fluid flow through a plurality of passages formed within or adjacent to tundish 120 and mold 124.
Any suitable number of caster segments 150 can be used. Generally, anywhere between four and eight caster segments can be suitable, depending on the material being cast, and the rate at which it is desired to cool the slab 140. Rollers 160 can be similar to those known in the art of casting. As depicted in
In further accordance with the invention, a cooling means is provided that is adapted and configured to dynamically cool and solidify the strand of material. As discussed herein, there is a long felt and unresolved need in the art for a cooling means including a practical and effective temperature measurement system for accurately measuring the surface temperature of a slab of material while inside of a caster. The present invention provides a plurality of novel solutions for this problem.
For purposes of illustration and not limitation, as depicted in
In accordance with one aspect of the invention, the temperature measurement devices 180 measure the temperature of the slab by way of direct physical contact.
For purposes of illustration and not limitation, as depicted in
In accordance with an alternative embodiment, as depicted in
Alternatively, as depicted in
By way of further example, as depicted in
Roller 382 is rotatably mounted on an axle 384. Roller 382 can be made from a refractory material, such as a ceramic material or other materials, such as silicon carbide or alumina. Axle 384 contains a thermocouple 386 that is operably coupled to a signal line 388 that directs temperature measurements of slab 140 to control system 190. While thermocouple 386 actually measures the temperature inside of axle 384, temperature measurement device 380 is appropriately calibrated to indicate the surface temperature of slab 140 based on the measurement inside of axle 384. A purge gas flow may be applied to the wheel that reduces the error due to convection of water and steam, such as by way of purge gas channel 400a that surrounds beam 390 fed by gas supply line 400. In accordance with one embodiment, the thermocouple 386 is insulated inside of axle 384.
In accordance with a further alternative embodiment, as depicted in
In further accordance with the invention, other embodiments of a temperature measurement device configured and adapted to drag against the surface of slab can also be used.
For purposes of illustration and not limitation, as depicted in
As depicted in
In accordance with another embodiment, as depicted in
In accordance with another embodiment, as depicted in
In accordance with still a further aspect of the invention, the temperature sensing device is configured and adapted to measure the surface temperature of the material without physically contacting the material.
For purposes of illustration and not limitation, as embodied herein and as depicted in
Suitable pyrometers 880 are disclosed in U.S. Patent Publication No. 2005/0247066A1 and U.S. Patent Publication No. 2006/0000219A1 and U.S. Pat. No. 4,521,088, each of which is incorporated by reference herein in its entirety. Pyrometer 880 can be adapted and configured to scan across the surface of slab 140 to obtain a temperature profile across the width of slab 140. In accordance with one embodiment, an active millimeter wave pyrometer can be employed made in accordance with the teachings in U.S. Pat. No. 5,785,426, which is incorporated by reference herein in its entirety. Pyrometer 580 can also be added downstream in the caster 110 at the edge of the slab 140 to measure the surface temperature at the slab edge. Such a construction may be used to detect cracks at the edge of slab 140, since cracking causes sharp changes in the emissivity of the surface of the slab which are detected by the pyrometer.
By way of still further example and as depicted in
By way of further example, the temperature of the surface of slab 140 is measured by measuring the temperature of air proximate the surface of the slab. For purposes of illustration and not limitation, as embodied herein and as depicted in
By way of still further example, as depicted in
Tubular member 1820 may have any suitable dimensions. Generally, it is desired that the gas purge discharged second end 1822 of tubular member 1820 have a sufficiently high velocity to clear debris (e.g., steam and water) from the line of sight of lens 1830. Preferably, the average gas velocity is greater than about 100 feet per second. More preferably, the average gas velocity is greater than about 200 feet per second or more.
It will be further appreciated that the gas purge may be sent down the passage 1826 of member 1820, and/or down one or more supplemental purge lines 1828. Specifically, by using supplemental purge lines 1828 it is possible to eject a high speed flow in the viewing area while minimizing the volume flow rate of the purge gas. Moreover, while a gas purge can still be directed through passage 1826, such a flow can be used to primarily cool the passage and upstream optics and electronics. Such an arrangement also permits the diameter of passage 1826 to be increased to collect additional photons but without significantly increasing the need for a purge gas flow.
In accordance with one embodiment that was tested, the dimensions of the tubular member 1820 was 2 feet long by 0.9 inch inside diameter pipe (¾″ schedule 10 pipe). A single lens 1830 was employed having a two (2) inch focal length to collect radiation passing through passage 1826 and focusing it on the photon sensor 1840. The length of the extension was chosen primarily based on practical considerations of the particular testing application. For example, clearances in the caster 110 may guide the choice of certain dimensions. However, it will be appreciated that tubular member 1820 may be of any suitable length. Generally, a short probe may be more difficult for an installer to reach in and secure. Also, the closer the optics and electronics are to the steel slab 140, the greater is the risk of thermal effects on the electronics. Moreover, if a break out of the molten core of the slab 140 were to occur, it is likely that more damage could occur to the sensor 1800. The purge gas was air supplied from a compressed air source at a line pressure of about 90 pounds per square inch.
In accordance with one embodiment, first end 1822 of conduit 1820 may be cut on an angle to cause the purge gas to blow debris (e.g., soot, water and steam) out of the field of view of lens 1830. Using an extended conduit with a gas purge as described herein has been found to be effective in maintaining a clear radiation path between the slab and the photon sensing device. Specifically, upstream portions of a caster near the mold are the hottest, and the most occluded by steam, water and soot.
However, use of a sensor such as 1800 avoids these problems. Moreover, spacing the photon sensing device portion of the sensor a distance from the slab also has the benefit of exposing the electronics to a less harsh environment.
As further depicted in
As will be appreciated, for any of the embodiments disclosed herein utilizing an optical pyrometer as a device to measure the temperature of slab 140 (including but not limited to sensor 1800), a variety of optical pyrometers may be used. For example, a pyrometer may be used in any suitable region of the spectrum. For example, a pyrometer may be used that is particularly sensitive to the ultraviolet (“UV”) region of the spectrum. In accordance with one embodiment, a UV pyrometer may be used that is sensitive to wavelengths shorter than about 0.5 microns, such as from about 0.35 microns to about 0.45 microns. These wavelengths are relatively high energy wavelengths and are more effective at penetrating the harsh environment of a caster to reach a pyrometer. Moreover, such wavelengths appear to be well suited for measuring the temperature of oxidized steel (about 1700° F.-about 2100° F.), and are less susceptible to error as a result of slag formation on the surface of slab, which is a random occurrence. However, a NIR pyrometer when used with a gas purge as described herein also provides successful results.
Water absorption of photons is a problem because of the water used to spray the surface of slab 140 to cool the slab creates an absorption barrier between the pyrometer and the slab. For example,
Variable emissivity is another problem endue to the slag that forms on the slab surface causing the emissivity to vary significantly. Slag and bare metal vary in emissivity with wavelength and temperature. The emissivity of such oxidized surfaces is typically 0.9 to 0.96. To illustrate the accuracy of UV temperature measurement, a test was run using a piece of carbon steel that was heated on one side using an oxyacetylene torch as depicted in
Moreover, a two color pyrometer may be used to obtain an accurate surface temperature measurement. A two color pyrometer makes measurements in two wavelength regions and electronically takes the ratio of these measurements. A preferred embodiment would have a spectrum covering wavelengths from 300 nm to 500 nm and another spectrum covering 300 nm to 1000 nm, as depicted in
Testing was performed at a steel mill during a continuous casting process. The test employed a temperature sensor similar to sensor 1800 described above including a UV pyrometer to measure the steel temperature. A NIR (near infrared) pyrometer was also mounted at the same location with a tubular member having a gas purge as described herein. Data was examined to compare the accuracy of the spectra obtained from the two pyrometers.
The UV pyrometer utilized silicon photodiodes as photon sensors. Two of the photodiodes were filtered with a color glass filter. This provided a useable spectrum of about 350 nm to 450 nm, well overlapping the UV portion of the electromagnetic spectrum. The NIR pyrometer was a Goodrich production model modified to include a purge line. The NIR pyrometer uses a silicon photodiode that is not filtered. It has a standard silicon responsivity with a peak sensitivity at about 850 nm.
Curve fit equations for each pyrometer in this example can be represented as:
T
1
=A
1(E1g)B1 (1)
T
2
=A
2(E2g)B2 (2)
A and B are curve fit constants and “g” represents the gain needed to make the temperatures T1 and T2 equal (1/emissivity). E1 and E2 are pyrometer outputs. Setting temperatures equal and solving for g:
g=(A1E1B1/(A2E2B2))(1(B2−B1)) (3)
Therefore, the if the gain correction is solved at each data point the corrected temperatures can be solved for at each point. This was plotted in
Still another embodiment of a temperature measurement device 2800 is depicted in
Inside housing 2860, an intermediate electronics compartment 2850 is defined having an electronics board 2852 disposed therein operably coupled to a sensor 2846, such as a photodiode. Electronics board 2852, in turn, is attached to a connector 2880 to direct signals out of device 2800 to a terminal location, such as a computer (not shown). Electronics compartment 2850 is attached at a first end 2854 to end cap 2864 and at a second end 2856 to a sensor housing 2840. First end 2842 of sensor housing 2840 houses a lens 2830 held in place with a clip (not shown) and an o-ring 2845. Sensor 2846 is disposed in a second end 2844 of sensor housing 2840. A plurality of struts or spacers 2848 space housing 2840 from end cap 2862 to define a plurality of gas purge passages 2874. Purge gas is provided through purge inlet 2870 and directed through annular space 2782 defined between wall 2866 and housing 2850, through passages 2874 and through tubular member 2820. Such a gas flow arrangement helps cool the optics and electronics in device 2800. Moreover, as will be appreciated, such an arrangement greatly facilitates maintenance of device 2800. For example, housing 2860 of device 2800 may be disposed outside of the caster and tubular member 2820 may protrude through a wall of the caster. To perform maintenance on the contents of housing 2860, all a technician need do is remove nuts 2868 and pull out the assembly including electronics housing 2850 and sensor housing 2840.
In accordance with another embodiment, as depicted in
Moreover, if desired, an array of electrodes 1282 can be provided with a switching mechanism 1284 to obtain conductivity measurements across different portions of the surface of the slab, such as between electrodes 1282(a) and 1282 (b), or through the slab such as between electrodes 1282(a) and 1282(c). It will be appreciated by those skilled in the art that any suitable number of electrodes can be used and positioned as desired to obtain as many different conductivity measurements and hence, temperature measurements as desired.
In accordance with still another aspect, the temperature of the slab can be sensed using phosphor thermometric techniques. For purposes of illustration and not limitation, as embodied herein, it is possible to measure the temperature of slab 140 by employing one of a variety of thermographic techniques. For example, such surface measurement techniques are described in literature published by Oak Ridge National Laboratory (see http://www.ornl.gov/sci/phosphors/galv.htm). Systems employing such methods to measure the temperature of materials such as a moving substrate are described, for example, in U.S. Pat. No. 6,123,455, U.S. Pat. No. 5,986,272, and U.S. Pat. No. 5,949,539, the disclosure of each of which is incorporated by reference herein in its entirety.
As depicted in
In accordance with an alternative embodiment, if desired, one or more rollers 160 can be coated with a coating that emits light in accordance with its temperature. Suitable coatings include thermographic phosphors and other temperature sensitive coatings. As with the previously described technique, emitted light can be viewed and processed to estimate the temperature of the surface of slab 140.
In accordance with still another aspect, the temperature of the slab can be sensed by measuring heat flux.
For purposes of illustration and not limitation, as embodied herein and as depicted in
In further accordance with the system of the invention, the cooling means includes a coolant delivery system such as nozzles for delivering coolant to the slab. For purposes of illustration and not limitation, as depicted in
The nozzle body 40 further includes a water inlet port 48 to which a water inlet member 50 is secured by a screw-threaded connection, the water inlet member 50 being secured to a water supply line 52.
The nozzle body 40 is formed with a passage 54 in which is located a water orifice member 56 to convey water from the water inlet port 48 to an annular chamber 58 defined around the air orifice member 46. Water from the chamber 58 is able to flow through a cross-slot 46a to a mixing zone 60 where the air flow forms the water into a mist of water droplets, the mist of water droplets being conveyed along the lance 62 and through a spray head 64 to the desired location.
The water orifice body 56 comprises a substantially cylindrical body, part 56a of which is formed with screw-thread formations to allow the water orifice body 56 to be secured within the passage 54 formed in the nozzle body 40. The water orifice body 56 is formed with a through bore 66 shaped to define a region 68 of reduced diameter forming an orifice or restriction to the rate at which water can flow through the orifice body 56. The through bore 66 is closed, at its end remote from the region 68 by an access cap 70 which is securable in position by a screw-threaded connection. The water orifice body 56 further includes a water inlet port 72 defined by a passage perpendicular to, and communicating with, the through bore 66.
In order to minimize or prevent leakage of water between the nozzle body 40 and the water orifice member 56, a deformable sealing washer 74 (made, for example, from copper) is conveniently trapped therebetween.
In use, with the spray nozzle connected to the air and water supply lines 44, 52 as illustrated, water is supplied to the inlet port 48 of the nozzle body 40 to the water orifice member 56 from where it flows along the through bore 66 and through the region 68 to the annular chamber 58. From the annular chamber 58, water is able to flow through the cross-slot 46a to the mixing zone 60 where the action of the air supplied through the air orifice member 46 causes the water to atomize and form a mist of water droplets. The mist of water droplets is carried through the lance 62 to be delivered by the head 64 in the desired location and in the desired pattern.
In the event that a blockage forms in the through bore 66 formed in the water orifice member 56, rather than requiring the nozzle to be totally removed and dismantled, the access cap 70 can be removed from the water orifice body 56, and compressed air supplied to the through bore 66. The action of applying the compressed air will typically clear the blockage thus, once the access cap 70 has been re-secured in position, normal operation of the spray nozzle can continue. In the event that the application of compressed air to the through bore 66 in this manner is unsuccessful in clearing the blockage, then the water orifice body 56 can be removed from the remainder of the spray nozzle to permit cleaning, replacement or servicing thereof again without requiring removal of the complete spray nozzle. After cleaning of the water orifice body 56, it can be returned to its operative position as shown in
A further advantage of the arrangement illustrated in
The arrangement described herein for nozzle 200 may be used in other ways as well. For example, rather than providing an access cap 70 to close the end of the through bore 66, a further inlet line could be connected thereto. One possibility is to connect an additional air line thereto. This has the advantage that, by appropriate control over the pressure of the additional air line, the water supply rate can be changed without having to adjust its supply pressure. Further, the water is, at least partially, atomized prior to reaching the mixing zone 60, thereby permitting the nozzle to be used in the formation of a spray of reduced droplet size compared to typical arrangements.
The nozzle may be modified to orientate the water inlet port 72 such that it is tangential to the through bore 66, thereby imparting a swirling motion to the water, as shown in
In further accordance with the invention, a control system is provided operably coupled to the cooling means and the temperature sensing means. The control system is adapted and configured to control the cooling system to cool the material as it passes through the caster. For purposes of illustration and not limitation, as embodied herein and as depicted in
Temperature measuring device 180 is operably coupled to control system 190. In operation, the amount of cooling fluid provided by way of nozzles 200 is controlled by operating one or more valves, for example, in a valve manifold 196, if desired, in order to achieve a desired surface temperature of slab 140 at a given point in caster I 10.
In accordance with one embodiment of the invention, a predetermined cooling profile is provided for the material being cast.
For purposes of illustration and not limitation, the predetermined cooling profile can be similar to an actual cooling profile, particularly where a system made in accordance with the invention is provided as a retrofit to an existing caster. An example of actual cooling profiles for steel are depicted in
Specifically, the cooling curve depicted in
“Heat Transfer and Solidification Modeling in the Continuous Casting of Multi-Component Steels,” Hardin and Beckerman, HTD-Vol. 347, National Heat Transfer Conference, Volume 9, ASME 1997, pp. 9-20.
“A Transient Simulation and Dynamic Spray Cooling Control Model for Continuous Steel Casting,” Hardin, Liu, Kapoor and Beckerman, Metallurgical and Materials Transactions B, Vol. 34B, June 2003, pp. 297-306.
“Development of a Model for Transient Simulation and Control of a Continuous Steel Slab Caster,” Hardin, Liu and Beckerman, Materials Processing in the Computer Age III, Edited by V. R. Voller and H. Henein, The Minerals, Metals & Materials Society, 2000, pp. 61-74.
Each of the above-referenced publications is incorporated by reference herein in its entirety. Thus, when using a system made in accordance with the invention that is provided in the form of a retrofit kit, for example, the system can be used to operate the caster to closely operate within its design range. However, a system made in accordance with the invention can facilitate design of new, efficient casters that take maximum advantage of the benefits accorded by the invention.
Thus, in accordance with another embodiment of the invention, an ideal cooling curve can be provided that is intended for use with a new caster, as opposed to a caster that is retrofitted with a system made in accordance with the invention. Such an ideal cooling curve is optimized based on the caster design to take maximum advantage of the benefits of active feedback temperature control provided by the invention.
Accordingly, the temperature of the slab is preferably reduced in accordance with a predetermined curve such as ideal cooling curve. Cooling the metal in accordance with such an ideal profile can provide many advantages. These advantages include, among other things, raising yield due to lower defects in the material, and a higher overall consistency of the material produced. Again, it will be understood that the curve will be generated empirically and used as a reference point by the system of the invention to cool steel.
In operation, as depicted in
Accordingly, if desired, a real time mosaic of the surface temperature of slab 140 can be compiled and continuously updated to continuously evaluate whether sufficient coolant is being supplied to slab by the cooling means 170.
In addition, by performing active feedback control as described herein, the caster can be operated at its maximum practical speed while minimizing the chances of a breakout. For example, if the temperature is being monitored continuously, it is possible to detect the presence of overheated areas. This could be accomplished, for example through the use of smart logic in the computer program causing an alarm when there is a sharp temperature rise in the metal surface temperature. Reaction to a break out could be quicker due to the active link of the temperature sensing device and the smart logic of the computer program.
Mitigating steps can also be taken, including compensating for excessive temperature and/or temperature spikes by increasing the fluid flow in those regions of the slab upstream of the temperature detection point. If desired, such cooling can also be applied downstream of the detection point in order to properly cool the slab to the extent that the slab should have been cooled when the temperature rise was detected. Moreover, temperature sensing devices 180 can be positioned strategically inside caster 110 in a manner to accurately predict the cooling fluid flows in time for the cooling system to react to changing conditions of temperature. The control system 190 is adapted and configured to maintain the temperature across the face of the slab 140 as evenly as possible near the optimum temperature.
In accordance with still another aspect of the invention, caster speed control can be employed to control the surface temperature of the material. For purposes of illustration and not limitation, as embodied herein, the logic of the computer program that operates control system 190 may be written to include caster speed control as another method to help keep the metal surface temperature controlled properly. In employing this approach, direct temperature feedback can be utilized from temperature sensors 180 to control the speed. Thus, if it is desired to run caster 110 at a slower speed, the rate of coolant can be decreased to match the slow down in the casting speed. This can be done by monitoring the surface temperature and the output of the mill. If it is desired to operate caster 110 more slowly less coolant would be provided. Conversely, if it is known that there is sufficient operating margin for operating safely at higher casting speeds, the rate of coolant flow can be selectively increased resulting in an increase of the casting process.
In accordance with another aspect of the invention, the control system 190 can be adapted and configured to revert from a state in which it performs active feedback control as described herein to a fail-safe condition wherein cooling is performed in accordance with a predetermined fluid control algorithm. Such predetermined algorithms are well known in the art, and generally represent how casting machines are currently controlled. Providing such a fail safe mechanism can be useful if the active feedback system malfunctions. Without a backup system in place, it would be necessary to shut down the mill, which is costly. By providing a default setting, the caster can continue to operate, saving a great deal of time and money since production can continue. It may also be desirable to default to such a fail safe setting if it is desired to run diagnostics on the active feedback system. When the active feedback system is repaired and/or when such diagnostics have been completed, the system can be configured to resume active feedback control.
The system, method and machine readable program described herein can be provided with a new caster delivered from a manufacturer. Alternatively, if desired, the system, method and machine readable program described herein can be provided in the form of a retrofit kit for an existing caster.
All statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.
Block diagrams and other representations of circuitry herein represent conceptual views of illustrative circuitry and software embodying the principles of the invention. Thus the functions of the various elements shown in the Figures may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software, as appropriate. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared. The functions of those various elements may be implemented by, for example, digital signal processor (DSP) hardware, network processor, application specific integrated circuit (ASIC), field programmable gate array (FPGA), read-only memory (ROM) for storing software, random access memory (RAM), and non-volatile storage. Other hardware, conventional and/or custom, may also be included.
Similarly, it will be appreciated that the system flows described herein represent various processes which may be substantially represented in computer-readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown. Moreover, the various processes can be understood as representing not only processing and/or other functions but, alternatively, as blocks of program code that carry out such processing or functions.
The methods and systems of the present invention, as described above and shown in the drawings, provide for a casting system with superior properties including increased yield and reliability. It will be apparent to those skilled in the art that various modifications and variations can be made in the device and method of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention include modifications and variations that are within the scope of the appended claims and their equivalents.
This application claims the benefit of priority of U.S. Provisional Application Ser. No. 60/796,074 filed Apr. 28, 2006. This application is related to U.S. patent application Ser. No. 11/709,070 filed Feb. 21, 2007. Each of these applications is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60796074 | Apr 2006 | US |
