Patent Publication Number: US-2018045581-A1

Title: Apparatus and methods for continuous temperature measurement in molten metals

Description:
RELATED APPLICATION 
     This application claims priority to Indian application No. 190/KOL/2015 titled, “Porous Heat Insulating Bed in a Probe for Continuous Temperature Measurement in Molten Steel Tundish,” filed on Feb. 18, 2015, which is incorporated by reference in its entirety. 
     FIELD OF INVENTION 
     The technology relates to metal manufacturing, and to temperature probes for continuously measuring molten metals in vessels. 
     BACKGROUND 
     The manufacturing of metals can involve several stages of handling molten metal. Metal compositions may be melted in a first vessel and transferred to one or more vessels during a metal manufacturing process. For example, a metal composition may be first heated in a furnace, and transferred by a ladle to a caster or tundish from which it may be poured into molds. At each stage of a metal manufacturing process, the temperature of the melt may be held at a target temperature for a period of time. Appreciable temperature deviations from a target temperature may adversely affect the quality of the final metal product. Accordingly, it is desirable to monitor, as accurately as possible, a temperature of the molten metal through the metal manufacturing process. 
     Several types of temperature measurement techniques have been developed for measuring high temperatures of molten metals. One approach is to use thermoelectric devices, e.g., thermocouples. Some measurements with thermocouples may involve fixing a thermocouple probe at the end of a long lance, and dipping the thermocouple probe into the molten metal to measure the temperature of the metal melt. This is conventionally done in an intermittent fashion. Disadvantages with intermittent measurement of temperature is that the manufacturing process may be interrupted for the measurement, and there may be substantial time intervals between the measurements so that close process control of the melt temperature may not be possible. Additionally, the thermocouple probes may only be used once or a few times before they become damaged and inaccurate or inoperable. 
     Optical-pyrometry-based techniques have been developed for measuring the temperature of liquid metals. Such techniques can provide faster measurements of melt temperatures. Conventional optical measurements comprise piercing an optical probe, mounted on a lance, through a layer of slag covering the metal. Again, these measurements are intermittent, and the slag and measurement technique leads to high wear and a short lifetime of the probe. 
     SUMMARY 
     A temperature probe for molten metal is described that can be installed in a vessel wall and used for continuous temperature measurements of molten metals. Embodiments of the temperature probe may be used for multiple batches of molten metal. To reduce wear of the temperature probe, a porous bed of material may be included at an end of a chamber of the probe that houses a thermocouple. The porous bed permits venting of gases that would otherwise accelerate degradation of the temperature probe. The probe is arranged in a way to facilitate assembly of the probe and installation of the porous bed of material. 
     Some embodiments relate to a temperature probe for measuring temperature of molten metal. The temperature probe may comprise an outer refractory sheath having a central bore extending from a first end of the refractory sheath toward a distal end of the refractory sheath, a thermocouple sensor mounted within the central bore, getter material filling a first region of the central bore around the thermocouple sensor, and a porous bed filling a second region of the central bore at the first end of the refractory sheath. 
     In some aspects, a temperature probe may further comprise a connector assembly and a separator tube arranged to support the thermocouple sensor within the central bore, and include one or more retaining plates attaching the connector assembly to the refractory sheath. In some implementations, the porous bed and the one or more retaining plates are configured to vent gases from the central bore. Additionally, or alternatively, a porosity of the porous bed is at least 40%. In some cases, a first retaining plate of the one or more retaining plates is tack welded to the connector assembly. The tack welding may allow escape of gases from the porous bed. In some aspects, one of the one or more retaining plates is cemented to the outer refractory sheath and the cement does not seal gases within the central bore. 
     In some implementations, a connector assembly of a temperature probe comprises a connector tube, a connector formed from two connector halves mounted within the connector tube, and a first cold junction contact and a second cold junction contact mounted within the connector. In some aspects, a temperature probe further comprises a protector tube covering the thermocouple sensor and at least a portion of the separator tube. An end of the separator tube and an end of the connector tube may be held within the connector. In some cases, the connector tube does not extend into the porous bed. 
     In one or more of the foregoing configurations, a temperature probe is further configured to be inserted into a wall of a vessel that holds molten metal. The various aspects, features, and implementations may be included in any suitable combination, and the temperature probe may be used in one of the following methods. According to some embodiments, a method of measuring temperatures of molten metal may comprise acts of installing a temperature probe in a wall of a vessel, applying an electrical current through a thermocouple sensor within the probe, and venting gases from an interior of the probe when operating the probe at temperatures over 200 degrees Celsius. 
     In some aspects, the venting may comprise venting gases through a porous bed located at a head of the probe. In some implementations, a method may further comprise reducing carbon monoxide with a getter material internal to the probe. 
     A temperature probe of one or more of the foregoing configurations may be fabricated using a method of assembling a temperature probe. The method of assembly may comprise acts of cementing a sheath retaining plate to a protective refractory sheath, subsequently inserting a thermocouple sensor and protector tube into a central bore of the refractory sheath, wherein the protector tube is connected to a connector tube of a connector assembly, subsequently adding getter material to fill a first portion of the central bore, subsequently adding a porous material to the central bore to form a porous bed at a head of the refractory sheath, and securing the connector assembly to the sheath retaining plate. 
     In some aspects, the act of securing does not trap gases within the central bore of the refractory sheath. According to some implementations, the act of securing comprises tack welding. In some aspects, the act of cementing does not trap gases within the central bore of the refractory sheath. According to some implementations, a method of assembly may further comprise assembling the connector assembly by placing the protector tube into a first half of a connector, placing a first cold-junction contact and a second cold-junction contact into the first half of the connector, placing a second half of the connector over the first half of the connector, and inserting the first and second halves of the connector into the connector tube 
     The foregoing and other aspects, embodiments, and features of the present teachings can be more fully understood from the following description in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The skilled artisan will understand that the figures, described herein, are for illustration purposes only. It is to be understood that in some instances various aspects of the embodiments may be shown exaggerated or enlarged to facilitate an understanding of the embodiments. In the drawings, like reference characters generally refer to like features, functionally similar and/or structurally similar elements throughout the various figures. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the teachings. The drawings are not intended to limit the scope of the present teachings in any way. 
         FIG. 1  depicts a vessel containing a molten metal wherein a temperature probe is mounted in the vessel wall, according to some embodiments; 
         FIG. 2  depicts components of a temperature probe for molten metals, according to some embodiments; 
         FIG. 3  depicts a retaining plate for a temperature probe, according to some embodiments; 
         FIG. 4  is a perspective view that depicts a connector for a temperature probe, according to some embodiments; and 
         FIG. 5  is a flow diagram depicting steps associated with a method for manufacturing a temperature probe, according to some embodiments. 
     
    
    
     The features and advantages of the embodiments will become more apparent from the detailed description set forth below when taken in conjunction with the drawings. 
     DETAILED DESCRIPTION 
     During the manufacture of metals, it can be beneficial to monitor the temperature of molten metal throughout the manufacturing process, e.g., during the initial heating of a metal composition in a furnace, during transfer in a ladle, and during the casting process. Accurate knowledge of the liquid metal temperature can improve the quality of the end product as well as the productivity of the metal plant. For example, in some steel manufacturing processes, a melt may be raised to a temperature of about 1650° C. and maintained at that temperature two within about ±5° C. for a period of time. At a later stage, e.g., in a tundish or caster, the melt may be maintained at a temperature between about 1520° C. to about 1550° C., depending on the metal composition, with a tolerance of ±1° C. For some metal manufacturing systems, unnecessarily high temperatures can consume a few megawatts of power for each degree Celsius, leading to a waste of energy and money. Excess heating can further result in using excess alloys, excessive refractory wear, and also metal loss. Less heating can result in insufficient processing of metals, which can result in rejection of the whole batch. Temperature errors in a casting process can ruin the ability to cast the metal, resulting in a unusable batch that must be reprocessed. 
     Measurement of liquid metal temperatures has been performed conventionally with single-use, dip-type immersion probes containing a thermocouple sensor. Continuously measuring temperature in molten metal using probes with thermocouples has been performed previously with limited success. Examples of high-temperature probes can be found in U.S. Pat. No. 5,388,908 and in U.S. Pat. No. 5,209,571, both of which are incorporated herein by reference. An example of a high-temperature probe designed for continuous temperature measurements in a metal melt is described in U.S. Pat. No. 8,071,012, which is incorporated herein by reference. 
     The inventor has found that such conventional temperature probes can be unreliable and degrade more quickly than desired (e.g., within one or a few “runs” or “batches” of metal melts where temperature is monitored continuously), and therefore need replacement at a higher frequency and cost than desired. The inventor has recognized and appreciated that conventional probe designs are not optimally suited for continuous temperature measurements in a vessel or tundish during steel manufacturing. In such measurements, the probe may be mounted to extend through a wall of the vessel, and the temperature of the probes “cold junction” can increase significantly during use. Stresses associated with thermal expansion can fatigue electrical connections at the cold junction, for example. As a result, temperature measurements may become erratic and unreliable, or the probe may simply malfunction. 
     The inventor has further recognized and appreciated that degradation of a high-temperature probe may occur due to trapped gases (which may include corrosive gases) at the interior of the probe that degrade the thermocouple junction and/or crack a protective sheath of the probe or a protective tube housing the probe&#39;s thermocouple sensor. One reason for the failure of a temperature probe during continuous temperature measurements is the entrapped gases such as N 2 , O 2 , CO, CO 2 , SiO, water vapor etc. that expand during use and cause cracks to develop in a tube housing the thermocouple and/or in an outer protective sheath of the probe. The inventor has recognized and appreciated that despite best precautions, it is impossible to completely eliminate in-situ generation of some gases within the probe, such as CO, CO 2 , SiO, and water vapor, at the very high temperatures associated with metal melts. 
     Previous probe designs have employed “getter” material at the interior of the probe to reduce corrosive gases. In conventional designs, the getter material may be sealed in the probe using a refractory cement. However, the inventor has recognized and appreciated that the cementing process can introduce moisture into the probe that can expand during use to cause failure of the probe. U.S. patent publication No. 2007/0053405 describes a pressed or extruded getter tube that is installed in a probe, and that is retained with a contact piece. However, the contact piece is retained in the probe&#39;s sheath near the cold junction with cement. The inventor has recognized and appreciated that the extrusion adds a processing step to the manufacture of the probe, as well as introduces organics and other compounds in the probe which might liquefy or gasify and form harmful gases, degrade probe components, and influence temperature measurements during use at very high temperatures. Additionally, the cement used to retain the contact piece can still introduce water vapor to the interior of the probe upon assembly. 
     Embodiments of temperature probes described herein include improvements in the construction of temperature probes that may be used in very high-temperature environments (e.g., at temperatures in excess of 500° C.). Some embodiments relate to, but are not limited to, probes that house thermocouple-type sensors, which may be used in molten metal temperature measurement applications. The improved temperature probes may be used for measuring temperatures continuously in metal melts and vessels, for example. According to some embodiments, the probes include an insulating and porous bed installed near the cold junction of the probe that permits venting of high-temperature gases from the interior of the probe that would otherwise accelerate degradation of the probe. In some implementations, the probes do not include organics or other materials at the interior of the probe that may liquefy or gasify at low-temperatures (e.g., below about 200° C.). For example, getter material may be added as a powder to the probes interior, and need not be solidified in an extra processing step with a binder containing organics. Additionally, the probe is assembled in such a way that vapor from curing cement is not trapped within a core of the probe. Durability and reliability of the temperature probes are improved so that the associated measurement system may be useful for measuring temperature continuously in high-temperature and very-high-temperature melts for prolonged periods. The embodied probes can provide greater accuracy of temperature monitoring during a metal manufacturing process, for example. 
     A temperature sensing probe  150  of the present embodiments may be mounted through a side wall of a vessel  110  (e.g., a tundish) for steel melts as depicted in  FIG. 1 , for example. The probe  150  may be secured in place by one or more well blocks (not shown individually) and an embedding mortar mix. The well block or blocks may form a portion of an inner lining  105  of the vessel and include a hole into which the probe  150  fits and extends through to the interior of the vessel  110 . The mortar mix may be used to secure the probe to the well block(s) and prevent any leakage of molten metal through the lining to the vessel wall  107  or exterior of the vessel. When filled with molten metal  120 , slag  130  may form over the molten metal. The molten metal may comprise any composition used in the manufacture of commercial or specialized metals. 
     The vessel  110  may be a vessel of a furnace (e.g., an arc furnace) that is used to heat a metal composition, a ladle, a tundish, or a mold in which liquid metal is cooled. In some embodiments, the vessel  110  comprises a outer shell  107 , which may be formed of metal, and an inner lining  105 , which may be formed of refractory material (e.g., refractory blocks or refractory concrete). 
     In some embodiments, the temperature probe  150  may be adapted to be readily removed from the vessel and replaced with a new probe. For example, the temperature probe may be configured to be inserted into a receptacle that allows the probe to extend through the wall of the vessel. The probe may be configured to be fastened to the outer shell  107  with screws or a locking mechanism that can be undone when replacing the temperature probe. The probe may be replaced between batches of metal melts, when the vessel  110  has been emptied. 
     When mounted in the vessel, a “head” of the probe that includes the probe&#39;s cold junction may extend outside the vessel  110 , as depicted in  FIG. 1 . One or more retaining plates may be installed around the probe&#39;s head to secure the probe to the vessel wall  107 . The probe&#39;s cold junction may project out from the vessel wall  107 , and include a connector assembly to which a cable  160  with mating connector or a wireless data acquisition or data transmission system (not shown) is attached. According to some embodiments, the probe&#39;s thermocouple sensor is located within an interior portion of the probe that projects into the interior of the vessel, and the temperature of the molten metal may be sensed continuously as the metal is processed. A thermocouple signal representative of a temperature of the molten metal  120  may be transferred through the cable  160  or the wireless system to an external device where the signal may be recorded and/or processed to determine a temperature of the melt. 
     In further detail and referring now to  FIG. 2 , a temperature probe  150  may comprise a noble metal thermocouple sensor  250  (sometimes referred to as a “hot junction”) located at a distal end  202  of the probe. The sensor may be protected from the very high temperature of the metal melt by an outer refractory sheath  205  and one or more refractory tubes  210 ,  212 . Getter material  207  may be installed in powder form between the outer refractory sheath  205  and the one or more protective tubes to reduce corrosive gases that may enter to the interior of the probe. The head of the temperature probe  150  may include a porous bed  215 , a connector  230  for the probe&#39;s cold junction and associated hardware to attach the connector, refractory tubes, and thermocouple sensor to the probes refractory sheath  205 . 
     In some embodiments, the thermocouple sensor  250  may comprise dissimilar metals or metal compositions that are welded together, e.g., using a tungsten inert gas (TIG) weld. One or more metal compositions of the thermocouple sensor  250  may include platinum. One or more metal compositions may additionally include rhodium. A thermocouple assembly may comprise two long conductive leads that extend from the head of the temperature probe to the thermocouple sensor  250 . An end of a first thermocouple lead  252  may connect to a first contact  242  of the cold junction (e.g., via a TIG weld, or any other suitable method to provide electrical connection). An end of a second thermocouple lead may connect to a second contact  240  of the cold junction. In operation, electrical current may be applied across the thermocouple sensor  250  via the cold junction contacts  240 ,  242 , and a resistance to the current flow may depend upon the temperature of the thermocouple sensor  250 . A measurement of voltage across the sensor may be used to determine a temperature of the molten metal, for example. 
     In some implementations, the thermocouple leads may be housed within a separator tube  212 . The separator tube may be a double-bore tube, having two separated holes running interior along the length of an otherwise solid rod. The two leads of the thermocouple may run separately through the two holes between the thermocouple sensor  250  and the cold junction connectors  240 ,  242 . The two bores may separate and electrically isolate the two long conductive leads of the thermocouple sensor. According to some embodiments, the separator tube may be formed from one or more refractory materials. For example, the separator tube  212  may be formed from any combination of the following materials: silicon oxide (e.g., SiO 2 ), aluminum oxide (e.g., Al 2 O 3 ), magnesium oxide (e.g., MgO), and zirconium oxide (e.g., ZrO 2 ). 
     In some implementations, the separator tube and thermocouple sensor may be encased along a majority of the length of the separator tube  212  by a single-bore, closed-end refractory “protector” tube  210 . In some embodiments, only an end portion of the separator tube at which the thermocouple sensor  250  is located may be encased by the protector tube  210 . The protector tube may shield the thermocouple sensor  250 , and yet allow thermal conduction of heat to the sensor for temperature measurement. The protector tube may be dense and substantially prevent any mass transfer and significantly reduce the transport of harmful gases to the sensor  250 , thus prolonging the life of the thermocouple. For example, a partial pressure of harmful gases within the protector tube may be less than one-tenth the level of harmful gases immediately outside the protector tube when the temperature probe  150  is in use. According to some embodiments, the protector tube  210  may be formed from one or more refractory materials. For example, the protector tube may be formed from any combination of the following materials: silicon oxide (e.g., SiO 2 ), aluminum oxide (e.g., Al 2 O 3 ), magnesium oxide (e.g., MgO), and zirconium oxide (e.g., ZrO 2 ). 
     The thermocouple sensor  250  and its long leads, the separator tube  212 , and the protector tube may be assembled into a central bore of a closed-end outer protective sheath  205 . The outer sheath may be formed from a combination of the following refractory oxides (silicon oxide (e.g., SiO 2 ), aluminum oxide (e.g., Al 2 O 3 ), magnesium oxide (e.g., MgO), and zirconium oxide (e.g., ZrO 2 )), and further include a thermally conducting material (e.g., graphite, silicon carbide, etc.) in the mixture. In some embodiments, the sheath  205  may comprise any one or combination of: zirconia, partially stabilized magnesia, partially stabilized calcia, partially stabilized scandia, partially stabilized yttria, stabilized zirconia, alumina, graphite, spinel, and boron nitride. At least a portion of the outer sheath near the thermocouple sensor  250  may directly contact the molten metal when in use, allowing for heat conduction to the sensor due to the sheath&#39;s thermally conductive property. The outer sheath  205  may be dense to substantially prevent any mass transfer through its walls, and may significantly reduce the transport of gases through its walls. 
     In some implementations, the sheath  205  includes an outer glaze coating (not shown), which inhibits adhesion of metal to the sheath, reduces erosion, and prolongs the life of the probe  150  during pre-heating of the vessel into which the probe is installed. The glaze coating may comprise zinc borosilicate frits and a clay which may be applied over the sheath and fired to form the coating. The coating may be applied from a solution (e.g., sprayed or painted onto the outer sheath surface) and then the sheath may be fired at over 1100° C. to harden the coating. The hardened coating may have a thickness between about 10 microns and about 100 microns. The coating may reduce oxidation of graphite in the outer sheath during a preheating stage of the tundish 
     According to some embodiments, the sheath  205  may taper in diameter from the cold junction to the distal end  202 , as depicted in  FIG. 2 , though it may have other forms in other embodiments. The length of the sheath may be between 350 mm and 550 mm, according to some embodiments, though it may be shorter or longer in other embodiments. A diameter of the sheath may be between 50 mm and 100 mm, in some implementations, though smaller or larger diameters may be used in other implementations. An inner diameter of the sheath may be between 20 mm and 60 mm. The tapering or form of the sheath  205  may be configured to match a mating taper or receptacle in a refractory block or blocks of a vessel  110 , so that the probe registers consistently to a location when installed in a vessel. For example, the probe may insert and be stopped by the mating hole, such that the thermocouple sensor  250  locates to an approximately consistent distance from the vessel&#39;s lining  105  at the interior of the vessel. This can assure that the temperature of different batches of metal melts are measured at approximately the same distance into the melt with different probes, so that the quality of the produced metal is consistent. 
     In some embodiments, one or more refractory blocks may be provided with a temperature probe  150 . A refractory block may be made of any suitable material (e.g., any one or combination of: alumina, magnesium oxide, magnesia carbon, and spinel). A block may have a thickness T that is approximately equal to a thickness of refractory blocks or refractory cement that is used in the inner lining  105  of the vessel  110 . A refractory block provided with the temperature probe may be in any suitable shape, and may have a hole, or portion of a hole (e.g., a quarter or half hole formed at an edge of the brick), into which the temperature probe  150  fits. The refractory block may not be attached to the temperature probe, so that the block may be placed in the inner lining  105  of the vessel  110  and the temperature probe inserted through the outer shell  107  and into the hole formed by the block or blocks. 
     In an annular region between the outer protective sheath  205  and the protector tube  210  or double-bore tube  212 , a “getter” material  207  may be added. The getter material may react with any gases that might be present or generated during use of the thermocouple, and help protect the thermocouple sensor. According to some embodiments, the getter material  207  consists predominantly of a refractory metal oxide (e.g., aluminum oxide or magnesium oxide) along with a metal powder (e.g., aluminum powder). The getter material  207  may be in the form of a free-flowing powder that can be poured into the annular region during manufacture of the temperature probe  150 . According to some embodiments, the getter powder is not densely packed and has significant void spaces, which allow space for any thermal expansions during the high-temperature usage of the probe. For example, the getter material may flow back out of the probe if inverted and not retained in the probe. 
     In some embodiments, the getter material  207  partially fills the annular region within the central bore of the sheath  205 , e.g., only part way to the head of the probe within the sheath. In some implementations, the getter material may extend only over a portion of the temperature probe that protrudes into a vessel  110  beyond the refractory lining  105 , when installed in the vessel. For example, if the length of a probe&#39;s sheath  205  is 450 mm, a total thickness of the vessel wall and lining is 150 mm, and a head of the sheath mounts flush with an outer surface of the vessel wall  107 , then the getter material may fill the annular region and stop a distance of approximately 150 mm or less from the head of the sheath. As such, the getter material  207  may be installed at least in a portion of the temperature probe where the sheath directly contacts molten metal. In some embodiments, the getter material may fill between approximately 60% and 90% of the annular region within the central bore of the sheath. 
     Near the cold junction, a bed of porous insulating material  215  may fill a remaining portion of the annular region and extend along the remaining length of the sheath  205  towards the cold junction. A diameter of the central bore in the sheath may increase near the cold junction, as depicted in  FIG. 2 , in some embodiments. In other embodiments, the diameter of the central bore in the sheath may be uniform along the sheath. The porous insulating material  215  may extend up to the cold junction connector assembly, in some embodiments. In some implementations, the porous insulating material  215  may fill between approximately 5% and approximately 40% of the probe&#39;s central bore. The porous insulating material may comprise any material (e.g., aluminum oxide, zirconium oxide, silica, etc.) that can withstand high temperatures (e.g., between about 200° C. and about 500° C.) for a long period of time without significant degradation or substantial loss of porosity. For example, the porous insulating material should not sinter at operating temperatures where the porous bed is located. When installed, the porous insulating should provide an open porosity of at least 40% by volume ratio. In some embodiments, the porosity may be between 40% and 80%. In some cases, the porosity may be between 40% and 60%. A high porosity allows for escape of gases from the probe interior, and includes thermally-insulating gaps to reduce heating of the cold junction. 
     According to some embodiments, a sheath retaining plate  220  may be affixed to an end of the protective sheath  205 . The sheath retaining plate may be formed from any suitable metal (e.g., galvanized steel such as EDD grade steel which is hot dipped galvanized, stainless steel such as 304 or 316 grade, a mild steel composition, etc.) and may be adhered to the head of the sheath with refractory cement, for example. In some implementations, stainless or galvanized steel is preferred for metal components of at the head of the probe to prevent rusting of the components during use. The inventor has recognized and appreciated that rusting of plain steel can occur during high-temperature use and lead to a loosening of the probe&#39;s connector assembly and cold-junction contacts. 
     According to some implementations, the sheath retaining plate  220  may be formed from a stamped or cut plate (depicted in  FIG. 3 ) to form a disc  300  with radial cut-outs  320  and additional cut-outs  330 . A thickness of the plate may be between 1 mm and 3 mm. The radial cut-outs  320  allow the disc to be subsequently drawn to form an inner circular opening (indicated by the dashed line  340 ) with wall extensions that extend approximately 90 degrees from the plate, as indicated in  FIG. 2 . The additional cut-outs  330  may be of any suitable shape, and provide for improved adhesion of the sheath retaining plate  220  to an interior wall of the sheath  205 . 
     The sheath retaining plate  220 , after being formed, may be adhered to the head of the sheath  205  with refractory cement, prior to insertion of the thermocouple sensor and cold-junction connector assembly. The cement may be cured and any associated vapor allowed to escape from the central bore of the sheath prior to assembling remaining components of the probe. In this manner, water vapor may not be trapped in the probes interior during manufacture of the probe. 
     Referring again to  FIG. 2 , the cold junction connector assembly may include several pieces of hardware that attach the thermocouple sensor  250 , separator tube  212 , protector tube  210 , and cold junction contacts  240 ,  242  together and to the outer protective sheath  205 . According to some embodiments, a connector  230  of the connector assembly is formed in two halves. One-half of a connector  230  is depicted in the perspective view of  FIG. 4 . The connector halves may be configured to receive at least the cold junction contacts  240 ,  242  and separator tube  212 , be joined together, and inserted into a connector tube  224 . An inner retaining plate  222  may be attached to the connector tube  224  (e.g., via tack welding) and attached to the sheath retaining plate  220  to secure the thermocouple sensor  250 , separator tube  212 , protector tube  210 , and cold junction assembly to the probe&#39;s outer protective sheath  205 . 
     In some implementations, a single retaining plate may be used to secure the thermocouple sensor  250 , separator tube  212 , protector tube  210 , and cold junction assembly to the probe&#39;s outer protective sheath  205 . For example, the sheath retaining plate may be formed to provide adhesion to the sheath  205  and edges or surfaces for tack welding to the connector tube  224 . There may be one or more holes in the sheath retaining plate to allow filling of the getter material and porous bed material. A cover plate may later be added to retain the porous bed. 
     The connector tube  224  may be formed from any suitable grade of mild steel, which may be galvanized, or stainless steel. The connector tube may have an outer diameter between 10 mm and 30 mm, and may have a wall thickness between 1.5 mm and 4 mm, according to some embodiments. A length of the connector tube may be between 60 mm and 150 mm. The connector tube may extend into the porous bed  215  to improve rigidity of the connector assembly. In some cases, the connector tube may not extend into the porous bed  215  to improve thermal isolation of the connector assembly. Other dimensions for the connector tube may be used in other embodiments. 
     In some embodiments, an inner retaining plate  222  does not form an air tight seal with the connector tube  224  or sheath retaining plate  220  over the porous bed  215 . For example, tack welding may be used at plural separated locations to attach the inner retaining plate. Additionally or alternatively, the inner retaining plate  222  may include one or more holes for venting gas. Accordingly, gases that may accumulate at an interior of the probe may vent through the porous bed  215  to an exterior of the temperature probe when the probe is in use. In some embodiments, one or more holes or porous plugs may extend from the porous bed through the wall of the protective sheath  205  in a region of the sheath that contacts the refractory lining  105  of a vessel  107 , so that gases may vent into the lining region within the vessel wall  107 . In some embodiments, one or more venting holes may be formed through the connector tube  224  to facilitate venting of gases from the porous bed  215 . 
     Referring again to  FIG. 4 , a half of the connector  230  may include a central trench  415  for receiving a tube (e.g., the protective tube  210  and/or the separator tube  212 ). Along the central trench, there may be a groove  417  for receiving a retaining clip  270  (e.g., a spring clip depicted in  FIG. 2 ) that retains the received tube within the connector  230  when the halves of the connector are assembled together. At an end of the central trench  415  there may be a first lead trench  420  and a second lead trench  422  through which leads of the thermocouple may extend to the probe&#39;s cold junction contacts  242 ,  240  (shown in  FIG. 2 ). A connector half may further include a first cold-junction-contact groove  430  and a second cold-junction-contact groove  432  configured to receive the probe&#39;s cold-junction contacts  242 ,  240 . A connector half may further include an opening  440  through which electrical contacts of a mating connector may extend and make electrical contact to the cold-junction contacts  242 ,  240 . 
     According to some embodiments, the connector body  410  may be formed out of any suitable material that can withstand high temperatures. In some implementations, the connector body may be formed from any combination of the following materials: silicon oxide (e.g., SiO 2 ), aluminum oxide (e.g., Al 2 O 3 ), magnesium oxide (e.g., MgO), and zirconium oxide (e.g., ZrO 2 ). The ends of the connector halves may include detents  412  for receiving spring clips  260  that hold the two halves of the connector  230  together. A connector may include a hole  280  into which a pin or spring pin may be inserted. The pin may extend through the walls of the connector tube  224  to secure the assembled connector  230  within the connector tube. 
     In some implementations, the cold-junction contacts  242 ,  240  may be in the form of a ring, though other shapes may be used, and may be formed from any suitable conductive metal (e.g., copper), plated material, or metal composition (e.g., a copper-beryllium alloy). Resilient contacts on a mating connector may make electrical contact with the cold-junction contacts  242 ,  240  when the mating connector is attached to the head of the probe. 
     According to some embodiments, the protective sheath  205  lasts for long durations in molten steel, thus allowing for continuous temperature measurement. The protective sheath can last for durations up to 8 hours in a tundish containing molten steel at temperatures between about 1520° C. to about 1550° C. Since the thermocouple sensor  250 , protector tube  210 , and separator tube  212  themselves are not capable of withstanding the harsh molten metal conditions for a long duration, the probe assemblies of the present embodiments allows the thermocouple sensor to remain operational for greatly extended periods of time. The inventor has used an embodiment of the temperature probe  150  in a tundish for continuous temperature measurements during 28 successive batches of molten steel that were transported through the tundish. 
     Various aspects of a temperature probe  150  include its compatibility with existing hardware and systems in conventional steel plants, so that it may be easily integrated into existing process systems to provide better accuracy and continuous measurements, which can improve the quality of produced steel. 
     Another aspect of an embodied temperature probe is that the porous insulating material  215  provides an improved level of thermal isolation between the cold junction and the getter material  207  and protective sheath  205 , as compared to a solid plug or cement used in conventional probes. This thermal isolation reduces heating of the cold junction, which can improve the accuracy of the measurements and lifetime of the cold junction and probe. Less heating of the probe head can also reduce thermal stresses on and increase the lifetime of connectors, cables, and/or other equipment attached to the probe head. 
     Another aspect of an embodied temperature probe is that the porous bed  215  permits easy escape of gases that would otherwise be entrapped inside the thermocouple assembly and expand on heating of the thermocouple assembly, possibly leading to damage. The gases might originate from assembly of the thermocouple (e.g., water vapor from cement), from low-temperature volatiles within the assembly (e.g., organic binder components), or might originate from other sources, such as burning of carbonaceous compounds on the furnace lining that permeate the sheath  205  at high temperatures. 
     Another aspect of an embodied temperature probe is that potting compound, such as a hydraulically setting cement to seal or embed the getter material, is not needed. This can avoid the entrapment of water vapor or other gaseous components in the interior of the probe that, upon heating, might cause degradation or catastrophic failure of the thermocouple, protector tube, and/or protective sheath. Additionally, elimination of the potting compound to seal the getter material simplifies and accelerates assembly of the probe. 
     Another aspect of an embodied temperature probe is a reduction in the amount of getter material that is needed in the probe compared to conventional probes. In an embodied temperature probe  150 , the getter material extends part way from the thermocouple to the end of the refractory sheath  205 , rather than the full length of the refractory sheath. Since the getter material  207  is more expensive than material for the porous bed  215 , a reduction in getter material can reduce the overall cost of manufacturing the probe. 
     Another aspect of an embodied temperature probe is a simplification of assembly of the various probe components compared to conventional probes. Only one cementing step is needed for structural support (cementing the sheath retaining plate  220  to the head of the outer sheath  205 ). This step can be done at the time of manufacturing the outer sheath, and only involves the two components. The remaining assembly steps for a probe  150  require no cementing for structural support. Thus, once the sheath and sheath retaining plate are prepared, a complete temperature probe may be assembled quickly and be ready for use. The assembly eliminates a waiting period for a potting compound to set before using the probe. In some embodiments, the single cementing step can occur in parallel with other assembly steps of the probe (e.g., preparation and/or assembly of the thermocouple and connector assembly). 
     When placed in operation, a temperature probe  150  may be mounted in a vessel that contains molten metal, for example, and connected to a measurement instrument. An electrical sensing current may be applied by the measurement instrument across the probe&#39;s hot junction (e.g., via a cable  160 ), while a voltage across the hot junction is monitored. As the probe heats, a resistance of the hot junction will change dependent upon the temperature of the hot junction. From measured voltage and/or resistance values and one or more calibration values for the probe, temperatures of the melt may be continuously determined. At very high temperatures, potentially harmful gases such as CO, CO 2 , SiO may be reduced by getter material  207  within the probe. Additionally, potentially harmful gases may be vented from the probe&#39;s interior through the bed of porous material  215 . 
     A method of assembling a temperature probe  150  will now be described in connection with the flow diagram of  FIG. 5 , though the described method is only one example in which assembly may be performed and is not intended to limit the order or number of steps performed. According to some embodiments, a method  500  may comprise attaching (act  510 ) an outer sheath retaining plate  220  to the protective sheath  205 . In some implementations, a formed sheath  205  may be prepped by applying an alumina cement mixture, for example, to the inner wall at the head of the sheath. The formed sheath retaining plate  220  may then be pushed into place, so that the plate&#39;s wall extensions contact the cement along the inner wall of the sheath. Excess cement may be spread over the plate&#39;s wall extensions and into cut-outs  330 . This sub-assembly may be then allowed to rest for roughly 3-4 hours to let the surface moisture of the cement dry out. In some embodiments, the sub-assembly may be placed in an oven at 150° C. for about 24 hours to cure (act  515 ) the cement. In some embodiments, after removal from the oven, a flame treatment may be applied to the head of the sheath to permanently harden the cement and remove any traces of moisture that might remain. 
     A method  500  of assembling a temperature probe may further include assembling (act  520 ) a thermocouple in a separator tube  212 . According to some embodiments, thermocouple leads are inserted into the double-bore separator tube  212  and cut to a suitable length. The thermocouple sensor may be made by joining the thermocouple leads with a TIG weld. The sensor&#39;s hot junction may then be cleaned (e.g., using acetone) and the leads pulled back, so that the hot junction rests on a bridge at the end of the double-bore tube between the two bores. 
     In some implementations, a single-bore protector tube may be installed (act  522 ) over the double-bore tube and a small amount of alumina cement, for example, may be applied to the ends of the protector tube as a seal to prevent gases from entering the tubes. The tubes and thermocouple leads may fit closely, so that the interior spaces in the tubes see very little cement surface area. Closely fitting the tubes and thermocouple leads can reduce any amount of water vapor or other gases that might enter into the interior of the tubes from the cement. A split-ring spring clip  270 , for example, may be place over the protector tube  210 . 
     The free ends of the thermocouple leads may be spot welded (act  524 ) to the cold junction contacts  242 ,  240  (e.g., copper-beryllium rings), and the contacts may be inserted into their grooves in a first half of the connector  230 . The tube assembly with thermocouple sensor may be placed (act  530 ) in the central trench  415  of one connector half. The second half of the connector may be assembled over the first half and split-ring spring clips  260  may be placed over the connector&#39;s detents  412 . 
     The connector  230  with separator tube, thermocouple sensor, and protector tube may be assembled (act  535 ) in the connector tube  224 . For example, the connector may be inserted into the connector tube, aligned, and rotated, so that a pin or spring pin can be inserted through a hole in the connector tube and through a pin hole  280  in the connector  230 . 
     The resulting assembly can be positioned (act  540 ) in the central bore of the refractory sheath  205 . A getter material may then be added (act  544 ) into the remaining annular region in the sheath  205  that lies between the sheath&#39;s inner diameter and the outer diameter of the double-bore tube  212  or protector tube  210 . A vibrator may be used to vibrate the assembly and compact the getter powder as it fills the void. The vibration is maintained at a level that does not separate the constituents of the getter material. A predetermined volumetric quantity of getter powder may be selected, so that the getter material fills the void to a predetermined level that is below the head of the sheath. In some embodiments, the sheath  205  and connector tube  224  may be held firmly by a jig to maintain alignment and position of the thermocouple  250  and protector tube  210  within the sheath  205  as the getter material is added. 
     According to some embodiments, alumina balls may be added (act  548 ) to form the porous bed  215  at the head of the temperature probe  150 . The balls may be added to fill the remaining void to approximately the head end of the sheath  205 . In some embodiments, there may be one or more holes through walls of the connector tube  224  that allow the porous bed material to move to the interior of the connector tube. 
     The inner retaining plate  222  may be placed over the connector tube  224  and slid into contact with the sheath retaining plate  220 . Tack welding may be used in some embodiments to secure the inner retaining plate to the connector tube and the sheath retaining plate. In some implementations, the inner retaining plate may include one or more holes to allow venting of gas. The welding of the inner retaining plate provides structural support between the connector tube  224  and the outer sheath  205 . 
     As may be appreciated, the probe components (e.g., connector halves, cold-junction contacts, connector tube, powder getter material, powder porous material) and single cementing step which can be done in parallel or early in the assembly process allows for rapid assembly and use of the temperature probes. 
     In some implementations, an assembled probe may be calibrated by placing it in a known thermal environment and determining a resistance of the thermocouple sensor  250  at one or more temperatures. 
     The technology described herein may be embodied as a method, of which at least one example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments. Additionally, a method may include more acts than those illustrated, in some embodiments, and fewer acts than those illustrated in other embodiments. 
     Having thus described at least one illustrative embodiment of the invention, various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description is by way of example only and is not intended as limiting. The invention is limited only as defined in the following claims and the equivalents thereto.