Abstract:
An improved immersible oxygen probe for molten metals has a gas permeable body including an immersion end and a support end adapted for being supported by a lance. An oxygen cell and a thermocouple are supported in the immersion end of the body. An unobstructed gas flow passageway is provided through the gas permeable bodies and through the probe body from the immersion end to the support/connector end whereby gases released from the molten metal and sensor body during immersion readily pass through the probe and can escape from within the probe. Thus rapid analysis of the molten metal with improved accuracy within a few seconds after immersion is achieved.

Description:
This application claims priority benefits of International Patent Application No. PCT/US09/41859 filed 28 Apr. 2009. 
     FIELD OF THE INVENTION 
     This invention relates to immersible probes for measuring and sampling selected characteristics of molten metal, especially molten iron or steel. The probes are used to measure the temperature and oxygen content of a molten metal and in accordance with some embodiments, are provided with a sample mold so that they may be used to retrieve, simultaneously with those measurements, a representative, high quality sample of the metal for chemical or spectrographic analysis. The probes of this invention can combine all of said devices in a single probe but may include two or even a single measuring device, if desired. 
     BACKGROUND OF THE INVENTION 
     Immersible oxygen and temperature measuring probes, usually supported for immersion by a molten metal consumable, ablative paperboard tube attached to a sensor and covering and protecting a support pipe or lance that carries the sensor electrical leads. Such lances have been used for at least half a century. In recent decades the probes have often contained a stabilized zirconia oxygen cell and a platinum-rhodium immersible thermocouple. Some such probes have included a sand filling but have included one or more gas impermeable components such as ceramics, plastics, potting cements, silicones or the like in their designs believed to be necessary to protect the measuring devices from unwanted exposure to heat, pressure, hot gases and hot gas movements. Such gas-contact preventing components were heretofore thought to be a necessary protective feature of the oxygen and temperature measurement systems in view of the high temperature melts involved, typically 3000° F. or 1700° C., even though immersion times are limited to about 10 seconds. 
     Notwithstanding the long history of use of thermocouple and oxygen probes, which sometimes include a metal sampling mold, such probes have heretofore sometimes been subject to fluctuating readings and thus are unable to consistently provide the quick, accurate, repeatable oxygen content and temperature readings required for today&#39;s demanding manufacturing processes. The interruption, pressurization and restraint of the movement of even trace amounts of combustion products or moisture emanating from paperboard or from coatings or materials used in the probe or gases dissolved in the melt and existing in the probe often result in errors in the readings, often causing the need for retesting thereby interrupting and increasing production time and therefore increasing production costs. To date, combination immersion testing, sampling and oxygen content determining devices have been found to perform with inadequate speed and inconsistent accuracy. In light of these shortcomings, a need has continued to exist for improved probes and testing devices. 
     SUMMARY OF THE INVENTION 
     The present invention provides improved metallurgical immersible measuring devices by utilizing gas permeable design and components and wherein the measuring devices and related components are preferably all baked together into a gas permeable baked sand-resin structure. Additional features also emphasize increased venting of the devices and elimination of gas flow blockages and pressure surges which may interfere with reading accuracy in previous devices. Test devices in accordance with the invention are able to provide accurate readings in parts per million within seconds after immersion. Gases can flow into or out of the probe virtually instantaneously, even through the immersion, measuring end thereof, so that pressure surges are eliminated that could otherwise adversely affect the accuracy of the readings. 
     Utilizing the pressure of hot gases escaping from the melt, the probe bodies provided by the invention perform in a manner similar to a vented chimney. While it will be understood that the stabilized zirconia oxygen cells commonly used depend on electron transfer and themselves are entirely gas impermeable and gas tight, the configuration of the probe is constructed from gas permeable materials and/or voids or open spaces internal to the gas permeable body that allow a free gas flow throughout and through the probes. Thus internal probe temperatures arrive at an equilibrium nearly instantaneously and internal pressure variations or surges are eliminated in gas containing parts. 
     Briefly, the invention provides an improved immersible oxygen probe for molten metals having a gas permeable body portion including an immersion end and a support end adapted for being supported by a lance. The immersion end is preferably devoid of gas impermeable components with the exception of the measuring devices used, themselves, and a temporary capping system. The latter includes a combustible outer cap and inner fusible metal caps. Measuring devices, usually, an oxygen cell and a thermocouple are supported exclusively by the gas permeable body. The probe includes the testing devices in the immersion end for reading the oxygen content and temperature of the molten metal bath. An unobstructed gas flow passageway is provided through the gas permeable vehicle body and through voids, if any, in the probe body for gas flow from the immersion end to the support/connector end whereby gases released from the molten metal and probe during the immersion of the immersion end can easily escape from within said probe. Thus rapid analysis of the molten metal within a few seconds after immersion is achieved providing consistent nonfluctuating readings of temperature and oxygen content. 
     The probe according to the invention includes a gas permeable body which preferably is of an annular shape formed of baked sand-resin or other particulate material that can be formed into a gas permeable body. In one preferred embodiment, the permeable body is provided with a protruding shoulder adjacent to the immersion end with the annular shape otherwise adapted to fit within a supporting paperboard sleeve. The shoulder serves as a stop member for abutment by an end of a paperboard sleeve. In a preferred embodiment, the support end is also provided with either a reduced diameter continuation of the annular body, or with a separate gas permeable body in the event that a metal sampling mold is included within the probe. In accordance with alternate embodiments, a protruding gas permeable shoulder is not used, but alternative means are provided to act as a stop and gas tight seal for the supporting ablative sleeves. 
     The sand-resin material may include 2 weight % or more of a resin (approximately 5 weight % resin in a preferred embodiment) and approximately 5 weight % ferric oxide. The ferric oxide can alleviate any unwanted RF interference during use of the probe. In accordance with preferred embodiments, no coating nor metal plating is used on the interior of any metal caps used in the vicinity of or in the immersion end of the probe in order to avoid any possible unwanted distortion of the data provided by the probe. It is also preferred that there be no holes or openings in any metal caps used. 
     In order to avoid the formation of a residual metal ring after the melting of the metal caps, it is preferable to use an irregularly shaped edge or protruding pins are used on the portions of the caps that become embedded in the sand-resin body. Metal capping systems are mounted without cement and with the irregular shaping or pins at the sand contact area which will avoid formation of round shapes or rings existing after the capping system has melted. A ground means consisting of a single point rather than a ring or other structure is greatly preferred. 
     In versions that include a sample mold, necessary quick release of the mold and sample from the probe body is enhanced by use of spaces or voids in the sand-resin body or use of a sand-resin blend near the connector end that produces a readily frangible material, for example by reducing the amount of resin in the blend. Likewise, metal clips on the mold body are not preferred and are avoided if possible. Release of the mold can also be facilitated by use a larger particle size resin-sand. Any other particulate or fibrous material that is uniformly sized, high temperature, inorganic, gas permeable and moldable may be used. It is important that the exterior and interior of the immersion end of the probe body be free of any cements, sealing compounds, combustibles, moisture and adhesives, all of which might impede the free gas flow into and through and throughout the probe. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal sectional view of a measuring probe of the invention of a type including an oxygen sensor and a thermocouple showing a pair of supporting/venting loose fitting paperboard tubes adapted to be supported by a lance; 
         FIG. 2  is a longitudinal sectional view of a measuring probe of the invention of a type including a sampling mold in addition to an oxygen sensor and thermocouple; 
         FIG. 3  is a longitudinal sectional view of the probe of  FIG. 2  shown from a different viewing angle offset at right angles from  FIG. 2 ; 
         FIG. 4  is an end view (not to scale) showing the immersion sensor end of the probe of  FIGS. 2 and 3  with cap  17  removed; 
         FIG. 5  is a perspective view of an alternative cap having an irregular scalloped end surface that avoids formation of metal rings when melted during immersion of the probe; 
         FIG. 6  is a longitudinal view of a probe in accordance with another alternative embodiment with a temporary cap partly cut away, illustrating gas flow into, through and out of the gas permeable probe body; 
         FIG. 7  is a longitudinal sectional view of a probe of  FIG. 6 ; and, 
         FIG. 7A  is an enlarged view of the connector/venting area of the probe of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     In accordance with the embodiment of the invention shown in  FIG. 1 , probe  10  includes a first gas permeable sand-resin, generally cylindrically shaped body  12  formed of a baked gas permeable sand-resin mixture. As shown the baked sand-resin body  12  has a stem portion  13  of a size adapted to fit within the interior of paperboard sleeve  18  and a radially raised or enlarged portion  11  which serves as a stop for the immersion end of paperboard sleeve  18 . The abutting surfaces of the sand body and the end surface of the paperboard sleeve  18  should be totally sealed gas tight. Thus a ceramic cement  21  or the like is used between these abutting surfaces. The end surface  45  is abutted by the end of smaller tube  20  but it is not adhered thereto. Any other sand body contact with the paper tubes  18  or  20  internal to the tubes should not be gas tight. Tubes  18  and  20  are loosely fitted in order to allow gas flow therebetween. The embodiment of  FIG. 1  (as well as  FIG. 6-7 ) is used in instances wherein only the oxygen content and temperature of the melt is to be determined. 
     In  FIG. 1  and all figures except  FIG. 5  that show the tip portion  14  of an oxygen measuring cell, usually a stabilized zirconia oxygen cell can be seen in the drawings together with a quartz U-tube loop portion  16  of a thermocouple assembly and Pt/Rh wires which are welded to conductors  24  and  26  and directly encased in the sand body and connected to monitoring instrumentation. A small ceramic basket  19  also supports the quartz loop  16 . The welds are the thermocouple cold junctions  99  and  100  and are best shown in  FIG. 7 . They are not shielded, but instead enclosed in the well vented sand body in accordance with the present invention. The outer surface (internal to the sand body) of the zirconia oxygen cell  14  (also see  FIG. 3 ) internal to the gas permeable sand is totally exposed in all areas to the sand-resin body  12 . The smaller diameter paper tube or sleeve  20  is adapted to be supported by the immersion end of a support pipe or lance of standard configuration. The inner, smaller tube  20  has an outer diameter about the same as that of a reduced diameter end portion  13 ,  45  of probe body  12 . 
     A slot or slots  22 , best seen in  FIG. 1  are provided in the distal end of the sleeve  20  to allow escape of gases from the interior area of sleeve  18  into the interior of the smaller diameter sleeve  20  from whence the gases can escape to the atmosphere either directly or between the loosely fitting tubes, lance or support pipes. As previously noted, sleeve  20  fits loosely within the interior of larger sleeve  18  to facilitate escape of gases. Sleeves  18  and  20  can be stapled together,  23 , to stabilize the assembly. Also a gas vented 360 degree interrupted circle of adhesive  31 ,  FIG. 1 , may be applied around the perimeter of tubes  18  and  20  at the proximal end of tube  18  to allow venting through this area. A metallic connector tube  32  is attached to a steel ground rod or wire  34  that extends into the immersible tip portion of the device as shown. The heavy structural ground rod may be pointed in the area exposed to the molten metal to ensure a fine single point grounding and to avoid possible ground rod dilution and contamination of the sample. In order to further enable venting of gases, one or more openings  48  are provided through the connector and ground tube  32 . See  FIG. 1 . Tube  32  may have a diameter of about ⅜ inch (1 cm). 
     The unvented connector system used and well vented as shown in  FIG. 1  is commonly known and defined as a ⅜ inch pipe sized connector system. The vented connector system used in  FIGS. 2 ,  3 ,  6 ,  7 , and  7   a  are commonly known and defined as a ¾ inch pipe size connector system. A metal sample mold  28 , formed by halves  51  and  52 , having a immersible fused quartz sample mold filling tube  29  covered by a small metal cap  53  is included in the embodiment  40  of  FIGS. 2 ,  3  and  4 . As most clearly shown in  FIG. 2 , sample mold  28  is of a conventional two-part clam-shell configuration common in the art which includes halves  51  and  52  and a quartz fill tube  29  through which the molten metal can enter during immersion. A steel clamp  27  may be used, if preferred, to hold the two mold halves together. Quartz tube  29  may be provided with a fusible steel cap  53 . Also seen in  FIGS. 2 and 3  is ground rod or wire  34  which, as in the case of probe  10  of  FIG. 1 , ensures that the electrical potential of tube  36  is grounded at single point relative to the molten metal bath when it is contacted by the rod  34 . Mold  28  and ground rod  34 , swage  59  and metal ring  36  provide a prebaking structural integrity to the probe prior to the baking of the sand body. 
     Thus greater physical strength is provided to the mold combination of  FIGS. 2 and 3  to better withstand the forces necessary to submerge the probe deeply into a dense metal melt. Since the sensor combination with sample mold  28  displaces a greater volume of the melt, a greater immersion force is required. In order to obtain excellent metal samples a substantially instantaneous evacuation of gases from within the mold is required so that the molten metal can enter the mold in the brief time available. 
     The single point ground rod or wire  34  may be exposed as in  FIG. 2  or may be located in any area that is preferred at the surface of the immersion sensor that will be exposed to the molten metal. Also see ground wire  96 ,  FIG. 7 , for another alternate example of ground point exposure. 
     The venting of the immersion sand sensor system through the paper tubes and connector system is substantially completely gas permeable, instantaneous, with no detectable back pressure. 
     As also best seen in  FIGS. 2 &amp; 3 , oxygen cell  14  utilizes a circuit formed by the ground rod  34  and a positive lead  24  of the thermocouple U-tube  16 , to which a positive lead  25  for the oxygen cell is swaged at junction  59 , so that only three leads are thus necessary to enable operation of the thermocouple  16  and the oxygen sensor  14 . As seen, the immersion tip is covered by a consumable slag repelling paper cover  50  which covers the fusible metal end cap  17 . Cap  17  preferably has no openings in it and the measuring components, sampling tube inlet  29  and ground  34  thus can be covered and protected until immersion. Cap  17  is preferably formed from non-galvanized steel so that, for example, the presence of zinc vapors in the areas of the oxygen cell are avoided. A thin metal cap with only outer surface corrosion protection can be used. Metal caps  17  or  65  are preferably mounted without cement and are provided with irregular shaping such as scallops  63 ,  64  at the sand-resin contact area of cap  65  as seen in  FIG. 5  or alternatively with pins  60 ,  62  as shown on cap  17  in  FIGS. 1 ,  2 ,  3  and  7 . This results in avoidance of the formation of a residual ring remaining after the molten metal exposed capping system has melted which could cause electrical interference with the sensor measurement signals when used in induction or electric melting furnaces or electric reheating ladles. Metal rings are thus avoided except in the connector end or area. The connector ends are provided with mating electrical connectors of known design, except for the venting, for providing means for transmitting data from the testing devices of the probe to remote electronic monitoring equipment. 
     The embodiments of  FIGS. 2 and 3  are intended for use with a pair of paperboard tubes  18  and  20  similar to those shown in  FIG. 1 . The gas permeable body  42 , having a stem portion  43  and provided with a projecting shoulder  41  which, in similar fashion to the embodiment of  FIG. 1 , serves to limit the distal movement of tube  18  to which it is adhered forming a gas tight seal. Stem  43  is adapted to closely fit within the tube  18  and the proximal end  45  of the separate permeable sand-resin body  30  may serve as a stop for the smaller tube  20  which is preferably also provided with a slot  22  (seen in  FIG. 1 ) to provide optimal gas escape from within the probe body into a supporting lance or directly to the atmosphere. Alternatively, a connector  78  supports the end of body  30  as illustrated in  FIGS. 2 and 3 . Connector  78 , which may be formed of a ceramic material, is provided with a shoulder  79  to which tube  20  may be abutted but preferably not adhered at the abutment. The distal end of the outermost tube  18  is adhered gas tight to its abutting surface but, to preserve venting, the inner tube  20  is not adhered gas tight to any of the sand body embodiments of the invention illustrated herein. 
     In the embodiments of  FIG. 1  and of  FIGS. 2 and 3  which utilize two supporting tubes  18  and  20 , several alternative avenues are provided for the flow of gases out of the probe body. Unlike previous devices, the described devices allow the greatest amounts of gases entering the probe body to enter through the most deeply immersed distal end of the probe, adjacent to the measuring instruments, temperature and oxygen which both, of course, have components that are necessarily not gas permeable. The gases are then able to flow between the probe body and the larger tube  18  as well as between the tubes  18  and  20  into the area of slots  22 . In the embodiment of  FIG. 1 , gases can also flow through a ceramic fiber filter  84  and around the plastic electrical connector  89 . Connector  89  is loosely secured by small projections, often referred to as “nubs” in the interior of tube  32 . In the embodiment of  FIG. 1 , gases also exit through metal tube  32 , through filter  84  and around plastic electrical connector  89  into the space between tube  20  and the supporting lance (not shown) and into the atmosphere. In the embodiment of  FIGS. 2 and 3  a similar venting path is also available. In the embodiments, such as  FIG. 1  and  FIGS. 2 and 3 , that have two paperboard tubes  18  and  20 , gases also vent from between the two tubes out through intermittent openings in adhesive of junction  31 . In the case of  FIGS. 2 and 3 , the outer diameter of mold  30  is less than the inner diameter of tube  18  in order to allow free venting in the space between them as well as through the gas permeable probe bodies  12  and  30 . 
     The probes of this invention  10 ,  40  and  70  are formed by assembling all of the illustrated components in a mold together and vibrated with a baking sand-resin mixture used to form each of the gas permeable parts  12 ,  30 ,  42  &amp;  72 . Each such assembly is then baked at approximately 500° F. (260° C.) in order to form the gas permeable sand-resin body with the other components baked in situ and held together in place by the resultant strong porous body. Foundry sand having a particle size of about 50 to 100 mesh, as desired may be used. Sand-resin material comprises approximately 5 weight % resin and approximately 5 weight % ferric oxide has been found suitable with especially preferred uniform particle sizes of 70 to 90 mesh, but other sized particles can be substituted so long as the desired gas permeability, strength and sample release is provided. The sand-resin material may include 2 weight % or more of a resin (approximately 5 weight % resin in a preferred embodiment) and preferably approximately 5 weight % ferric oxide. The ferric oxide can alleviate any unwanted RF interference during use of the probe. In accordance with preferred embodiments, no coating nor metal plating is used on any metal caps used in the vicinity of or in the immersion end of the probe in order to avoid any unwanted distortion of the data provided by the probe. It is also preferred that there be no holes or openings in any metal caps used. While sand-resin mixtures are greatly preferred formation of the permeable probe bodies of the invention, it will be understood by those skilled in the art that other materials can be substituted, for example, resin blends with sized inorganic gas permeable materials or comminuted particles of inorganic materials other than sand. 
     The sand-resin materials preferably used in forming the probes of this invention are commercially available from various foundry sand suppliers and are variously referred to as “resin sand” or “binder coated sand.” Due to sand being the main ingredient of the probe bodies of this invention, however, they are referred to herein as “sand-resin” compositions. Numerous resin binders are used in the foundries. Some of these are low temperature curing systems which could be utilized. However, it is greatly preferred that curing of the probe bodies of the invention be conducted at elevated temperatures of at least 350° F. (176.67° C.), and preferably 500° F. (260° C.) in order that a minimum amount of volatile residues (i.e. volatile at highly elevated temperatures of molten steel) remain in the bodies after curing. Examples of suitable resin systems are epoxide, epoxide novolac, furane, amine-hardened resins and thermosetting resins such various urea formaldehyde systems. Such materials will be selected by those skilled in the art based on characteristics of gas permeable bodies produced by curing of the same. 
     Referring to  FIG. 4 , there is shown an end view (not to scale) of the probe of  FIGS. 2 and 3 . It has been found necessary, in the case of each of the embodiments of the invention, that no part of the stabilized zirconia oxygen cell  14  be closer to the quartz thermocouple tube loop  16  than 0.2375 inch (0.60 cm). 
     Referring to  FIGS. 6-7 , there is seen another alternative probe  70  of the invention in which the gas permeable probe body  72  does not include an outwardly extending flange such as  11  of  FIG. 1 , or of  41  of  FIGS. 2 and 3 , but instead has a generally smooth profile. The immersion tip profile may be varied as desired, for example, cylindrical square or oval rather than the tapered shape illustrated. Gas flow into and out of the probe  70  is symbolized by arrows  80 . Unlike previous probes, gases are able to flow into the distal, immersion end surfaces of the probe body as indicated by arrows  80 . Thus, gases from the melt flow into, through and throughout the described probe bodies. In this modified embodiment of  FIGS. 6 and 7 , a shorter and thinner ground wire  96  is provided. 
     A ceramic connector base  78  is provided with a shoulder  79  which serves as a gas impermeable stop against which an end of a supporting paperboard tube of type  18  of appropriate length and diameter can be adhered. These parts may be supported in a plastic outer connector  82 . This connector has a plurality of openings  93  (see  FIG. 7A ) which allow gas flow out of the probe through the open interior  91  of connector  82  and out of slots  90 . The openings  93  and structure of connector  82  also retain a fibrous filter layer  84  that forms a filter for trapping impurities carried by the gases. As shown in  FIGS. 7 and 7A , a plastic or elastomeric gasket or O-ring  86  prevents impurities from entering associated electrical components. Thus moisture or other contaminants containing gases such as tars, sand particles, etc., are prevented from moving through the venting system formed by the probe. Channels  90  are in the form of two or more intermittent openings around the circumference of the proximal end of connector  82 . The plastic or elastomeric O-ring gasket  86  does not interfere with the air flow channels  90  which allow escape of gases from the probe body, but serves to seal the end of any subsequently attached connector in which electrical components are contained thereby protecting them from poor performance or damage which could be caused by entrance of contaminants. The fibrous filter layer  84  may be formed of refractory fibers, such as tightly packed high alumina fibers, and has been found to protect the connector systems and electrical components from damage caused by gas borne volatiles, contaminants and moisture. 
     As best seen in  FIG. 7 , probe  70  incorporates a ground wire  96 . The smaller diameter wire provides added likelihood that a single point ground results upon immersion of the probe. Also best seen in  FIG. 7  are additional details of probe  70 . See, for example, pins  60  and  62  of cap  17 . Also shown is a temporary combustible paper cap  50 . Details of thermocouple connectors  92  and  94  are also seen as are plastic clip thermocouple assembly fixture  115  which serves to secure the thermocouple quartz tube and lead wires  24  and  26  during manipulation of the probe assembly. The porous baked probe body  72  enables flow of gases into and through the probe  70  upon immersion into the melt. The proximal ends of connecting wires  24  and  26  are adapted to interconnect with connector leads of known design. Internal wires in the probe may be bare if separated or selectively insulated in areas to prevent shorting. 
     Additional details of the internal configuration and wiring of the measuring devices can also be best seen in  FIG. 7 . Wires  26  and  24  are formed with flattened ends  92  and  94 . Welds  99  and  100  secure thermocouple lead wires  97  and  98 , respectively, at the cold junctions of thermocouple assembly. The base of quartz U-tube  16  is sealed by heat resistant sealants  101  and  103  in order to protect the interior of the U-tube from the entry of contaminants during baking of the sand-resin body  72 . It will be noted that, in a radical departure from previous devices, that the thermocouple cold junction areas and leads  97 ,  98 , leads  92 ,  94  and welds  99  and  100  along with the other described internal electrical parts are all not shielded, are unprotected and thus are exposed and open to changes in gas pressure and therefore to the resultant gas flows.