Patent Application
20070145651
The invention relates to a submerged sensor adapted for use in a metallurgical vessel and, more specifically, to a submerged temperature sensor located in a tundish for continuous casting.
The ability to continuously monitor the status of molten metal in a metallurgical vessel is highly desirable for both economic and quality reasons. Accurate monitoring can, for example, greatly reduce energy consumption caused by overheating. Other benefits of continuously monitoring molten metal conditions include the ability to measure high temperature phase changes, chemical reactions, and other related phenomena.
Certain problems exist when measuring conditions of molten metal within a metallurgical vessel. These problems include extremely aggressive slags, thermal shock, violent turbulence from material additions, argon stirring, splashing and skulling, and difficulties in fixing the sensor in the vessel.
Sensors are typically encased in a protective assembly. Sensors include chemical sensors, such as oxygen sensors, and temperature sensors, such as thermocouples. Thermocouples for measuring molten metal temperatures have been described in, for example, U.S. Pat. No. 4,749,416. Such prior art arrangements permanently fix the thermocouple in a sidewall or bottom of the vessel. Alternatively, thermocouples may include a moveable protective assembly as described in U.S. Pat. No. 4,721,533, U.S. Pat. No. 4,746,534, U.S. Pat. No. 5,071,258 and U.S. Pat. No. 6,139,180. Movable protective assemblies typically insert the thermocouple through a floating slag layer into a bath of molten metal. Slag is very corrosive and a thermocouple protective assembly, which is in contact with slag, must combine good thermal conductivity and the ability to withstand chemical attack by the slag layer. A minimum one hundred-hour service life is desired.
Refractory materials with good thermal conductivity typically include carbon, Unfortunately, carbon detracts from slag corrosion resistance and may lead to premature failure after as few as ten hours of operation. Premature failure can also occur due to wire fracture, “emf drift,” and high temperature chemical reactions. Carbon in the protective assembly may accentuate such failures by participating in chemical reactions damaging to the sensor. Encasing the thermocouple inside a refractory metal sheath within the protective assembly has been effective at reducing undesirable chemical reactions. Unfortunately, such metal sheaths are expensive and are not entirely effective. Even a few milligrams of contaminants are sufficient to destroy the thermocouple by fracturing the wire, particularly along grain boundaries, or causing emf drift as a result of reaction product around the thermocouple.
As a further complication, an operator is often interested in the status of the molten metal actually exiting the vessel. In continuous casting, metal exists the vessel through a bottom outlet. The prior art is deficient in that the sensor is typically located near the surface of the molten metal bath. The sensor records, therefore, only near the surface and not near the outlet. Gradients in the vessel ensure that measurements near the surface of the bath are unlikely to be identical with measurements near the outlet. For example, the temperature near the top of a bath will often differ substantially from the temperature at the outlet. Sensors used in the prior art can be lengthened to extend closer to the outlet but this increases both the buoyant and inertial forces acting on the sensor. High buoyancy or inertial forces can cause dangerous conditions if control over the sensor is lost. The sensor may then eject violently from the bath. Additionally, a long sensor is more costly and more subject to premature failure.
A further deficiency of a prior art sensor descending through the surface of the bath is the need for an external support. The external support is highly inconvenient and subject to damage by heat rising from the molten metal and by collision with surrounding structures or equipment during movement of the vessel. The external support must not obstruct vessel movement. Consequently, the support must be placed so as not to obstruct movement or it must be disconnected, repositioned and reconnected each time the vessel is moved. The obstructive nature of the external support often leads to damage of the sensor or the external support.
A need exists for a sensor that is easy to install and operate while permitting measurement near the outlet of a metallurgical vessel. Preferably, the sensor should avoid high buoyancy and inertial forces. The sensor should be unaffected by slag corrosion, and should not interfere with movement of the metallurgical vessel. Preferably, an external support is unnecessary. The sensor should not include refractory materials that deleteriously affect the sensor.
The present invention describes a submerged sensor for use in a metallurgical vessel, such as a tundish. The sensor is positioned so that in use it is below a surface of a molten metal bath within the vessel. The sensor conveniently extends through the vessel wall and protrudes into the volume of the vessel. A terminal end of the sensor is encased in a protective assembly. A refractory material may surround the protective assembly.
An object of the invention is to provide a metallurgical vessel with a sensor that either has no buoyancy in a metal bath or resists the buoyancy force without an external support to secure the sensor. The absence of an external support eliminates the possibility of breakage of the support during movement of the vessel, and permits movement of the vessel without manipulation, repositioning, connecting or disconnecting of an external support. A second object of the invention is to provide a sensor suitable for measuring the lower portion of the metal bath where an outlet for the metallurgical vessel is typically located. Another object of the invention is to position the sensor away from the corrosive effects of slag. A further object is to provide a vessel with a sensor that projects into the molten metal, thereby altering and controlling the pattern of metal flow in the vessel.
In one embodiment, the sensor may be a temperature sensor, such as a thermocouple. The temperature sensor can be simple, easy to install and remove, and is preferably disposable. The sensor permits continuous temperature measurement of molten metal in a vessel. In a second embodiment, the sensor is placed adjacent to an outlet of the vessel, such as that used in continuous casting, so that the sensor actually measures the outflow from the vessel. In another embodiment, the sensor may be placed along the walls of the vessel or within dams, weirs or baffles inside the volume of the vessel.
In still another embodiment, the protective assembly of the invention can be shaped so as to control the pattern of molten metal flow in the vessel or measure more accurately molten metal exiting the vessel. The invention can combine the functionality required for flow pattern modification such as provided by a tundish with a dam, impact pad or baffle, with the functionality required for molten metal temperature measurement. This combination reduces cost and complexity of the tundish.
Other advantages of the invention include the need for a relatively short protective assembly, thereby reducing cost, and a configuration that imparts substantially only compressive forces on the assembly, which forces a ceramic assembly most easily resists.
a shows a side view of a metallurgical vessel with a sensor of the present invention.
b shows a top view of the metallurgical vessel of
c shows a side view of a sensor of the present invention.
a shows a top view of a vessel with a sensor that projects into the volume of the vessel.
b shows a cross-section of the projecting sensor of
In the continuous casting of metal, an upstream metal flow 11 from an upstream vessel (not shown) enters a pouring tube 6 and then into the metallurgical vessel as an incoming flow 12. The pouring tube typically discharges the incoming stream 12 below the top surface 9 of the bath 8. A nozzle 7 defines an outlet through the bottom of the vessel 3 and enables molten metal to drain from the vessel. An accelerating flow 14 accelerates to the entrance of the nozzle 7. An outflow 13 leaves the metallurgical vessel 3 through a nozzle 7. The highest velocities of molten metal flow in the metallurgical vessel are typically found in two areas; near the exit end of the pouring tube 6 as illustrated by the incoming flow 12 and at the point where the accelerating flow 14 enters the nozzle 7.
A sensor entering the molten metal bath through the top surface must be affixed to some external support to remain immersed and in place. The external support must fix the sensor position despite both inertial and buoyancy forces. Inertial forces are induced by molten metal flow in the bath. Buoyancy forces arise because the sensor is typically substantially less dense than the molten metal it displaces. Generally, the buoyancy force is much greater than the inertial forces.
As shown in
Desirably, a sensor measures an outflow from a vessel. The prior art is deficient in that sensors are inserted into the top of the bath, whereas the molten metal is exiting from the bottom of the bath.
a shows the vessel 3 having a bottom 32 defining a hole 33 for the sensor assembly. The vessel may be any type of metallurgical vessel but is commonly a tundish or other vessel which, during operation, a substantial volume of the vessel outflows over a relevant time period. The sensor assembly extends through hole 33. Conveniently, the protective assembly 1 rests on the inner surface 34 of the bottom 32. A protective sleeve 31 may be used to protect the sensor from damage. Preferably, a refractory material 35 surrounds the protective assembly 1. The refractory material may comprise one or more refractory compositions, including castable or vibratable materials. More preferably, the refractory material 35 adheres to the protective assembly I and to the inner surface 34. Conveniently, the refractory material may also be used beneath the protective assembly 1 in order to fill the hole 33 and reduce the likelihood of an escape of molten metal through the hole 33. The refractory material may also stabilize the protective assembly 1 against inertial forces resulting from molten metal flow.
A vessel of the invention may be made-up in accordance with the above description before movement of the vessel into operating position. After service, the vessel can be moved out of operating position. Residual metal can be dumped from the tundish. After casting, and typically during or after dumping residual metal, the sensor is discarded or recovered. The vessel is then again made ready for service.
The sensor of the invention exposes substantially upward facing or substantially vertical surfaces to the molten metal. Such upward or vertical surfaces are subject to little or no buoyancy forces. In fact, the molten metal exerts mainly compressive forces on the protective assembly. Refractory ceramic materials, which typically comprise the protective assembly, are strongest under compression, so the sensor assembly needs no external support.
Placement of the sensor at the bottom of the vessel also permits conditions in the lower portion of the vessel especially of the outflow to be measured more conveniently. The sensor assembly may be placed close to the nozzle 7. Unlike prior art that extend through the top surface of the molten metal bath, placement near the nozzle does not require lengthening the sensor. Inertial forces are not increased and the amount of material required to make the sensor assembly is unchanged.
Referring to
a and 4b show a second embodiment of the invention.
Obviously, numerous modifications and variations of the present invention are possible. It is, therefore, to be understood that within the scope of the following claims, the invention may be practiced otherwise than as specifically described.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US04/05249 | 2/20/2004 | WO | 4/27/2006 |
| Number | Date | Country | |
|---|---|---|---|
| 60448805 | Feb 2003 | US |
