Abstract:
A purge plug containing a refractory material is configured to be inserted in the bottom of a ladle for introducing purging gas through a heat of molten metal in the ladle. The purge plug houses a retention chamber for holding the lead content of lead-containing molten steel alloys that leaches into, or infiltrates into, the purge plug. The purging gas supply tube is provided with a portion that protrudes into the retention chamber, thereby preventing the lead content of lead-containing molten steel alloys from entering and blocking the purging gas supply tube.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    (1) Field of the Invention 
         [0002]    The invention relates to a purge plug, containing a refractory material, configured to be inserted in the bottom of a ladle for introducing purging gas through a heat of molten metal in the ladle. 
         [0003]    (2) Description of the Related Art 
         [0004]    The steel manufacturing process makes use of a vessel, called a ladle, which is lined with a refractory material to contain the molten steel. A purge plug is a device, installed in a passage through the exterior of the ladle, which is configured to introduce gas into the interior of the ladle. The plug may incorporate pores or passages to permit gas flow. The function of the purge plug is to provide gas stirring of the molten metal, thereby promoting thermal and chemical homogenization. The purging gas may also modify the heat (molten contents of the ladle). Stirring is normally accomplished by percolating argon or nitrogen gas through the purge plug in the bottom of the ladle. Typically, a purge plug has the shape of a truncated ceramic cone (frustum) and is enclosed in a sheet-metal casing. 
         [0005]    In a typical configuration, the purge plug is replaceably mounted in a housing block installed in the bottom of the ladle. In the ladle, various high-temperature processes are carried out in which the purge plug is crucial. The purge plug is worn heavily during the process in its uppermost portion, which is directed towards the heat, and regularly has to be replaced by a new purge plug when its height has shrunk to a minimum permissible level. 
         [0006]    Porous purge plugs are known in the art. These plugs are gas-permeable but do not allow the passage of molten steel. High gas pressure is necessary to obtain adequate gas flow, and the porosity leads to increased wear of the plug. 
         [0007]    Purge plugs with directional porosity allow increased gas flow through the plug. Such a plug can be made more compact, but is prone to a greater risk of steel in the purge plug ducts that provide the directional porosity. 
         [0008]    Purge plugs may contain slots or gaps formed by casting rather than ducts. This design allows increased gas flow, but does not entirely eliminate the possibility of steel infiltration. 
         [0009]    A successful purge plug exhibits a high degree of durability, satisfactory gas permeability and avoidance of infiltration of steel in the gaps of the purge plug. In practice, these three properties must be compromised. 
         [0010]    For certain steel grades (Free Machining Grades) lead is added to the steel, and this lead may settle to the bottom of the ladle and penetrate through the purge plug into the piping attached to the bottom of the purge plug. Accumulation of solidified lead in this piping restricts, and may completely block, the flow of gas through the purge plug 
         [0011]    An attempt to solve this problem makes use of a lead catcher placed in the purge plug pipe by connecting a tee to the purge plug piping. The tee is arranged so that one opening has a horizontal axis and two openings have a vertical axis. The inert gas flows horizontally into the tee and then turns in the tee to flow up into the purge plug. The lead catcher is attached to the bottom of the tee. Lead drips vertically down into the tee into the lead catcher which is a larger diameter sealed pipe. In the event the lead catcher becomes filled with lead it is replaced. If, however, a safety mechanism is used, it is usually installed directly below the plug and, in this case, the lead catcher is unable to protect the safety mechanism. Lead in the safety mechanism prevents it from operating, and the lead in the mechanism must be melted out and the mechanism changed to restore proper operation. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    Accordingly, the present invention is directed to a purge plug designed to prevent liquid lead from entering piping or any safety mechanism beneath the plug. The plug is formed with a body, an end cap disposed below the body, and a collection volume disposed above the end cap and within the body of the plug. A metal can surrounds the plug radially. A gas pipe extends through the end cap and protrudes into the collection volume. The protrusion of the gas pipe permits the collection of lead in the bottom of the collection volume and prevents the lead from flowing into the gas pipe. In some configurations of the plug, refractory surrounds the collection volume radially to provide support for the plug within the can, or is present at the bottom end of the collection volume to support the end cap. 
         [0013]    When the ladle is laid down, the liquid lead flows from the bottom end of the collection volume and may be aspirated from the plug by the gas pressure of natural gas or of an inert gas flowing through the gas pipe during testing in the ladle makeup area. The plug of the present invention may thus exhibit self-cleansing properties. 
         [0014]    The size and geometry of the collection volume, the extent of protrusion of the gas pipe into the collection volume and the diameter of the gas pipe may be modified to optimize lead collection, account for the lead content of a particular grade of steel, or account for ladle volume. The collection volume may, for example, be cylindrical, have the form of a rectangular prism, have the form of two cylinders with common axes with the cylinder with the smaller radius disposed above, and joined with, the cylinder with the larger radius, or have the form of a joined cylinder and rectangular prism. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0015]      FIG. 1  is a section drawing showing a purge plug of the prior art in combination with a lead trap of the prior art; 
           [0016]      FIG. 2  is a section drawing showing a purge plug of the present invention; and 
           [0017]      FIG. 3  is a section drawing showing a purge plug of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    Purge plugs are formed from refractory materials, and generally take the form of a cylinder, truncated cone (frustum) or truncated pyramid (pyramidal frustum).  FIG. 1  shows an assembly incorporating a purge plug  10  of the prior art. The purge plug incorporates a refractory body  12  formed around a longitudinal axis  14  having a feed end  16  and a delivery end  18 . The purge plug has a core  20  that may be composed of a nonporous material, or of a material with directional passages or pores formed in, for example, pressed and fired alumina plates. Optionally housed in core  20  along axis  14  is a wear indicator  22  that, when the plug  10  is viewed from its delivery end  18 , indicates the degree of wear of plug  10  by its presence or absence. Disposed longitudinally around the core are gas delivery structures  24 . These may be, for example, slots, tubes of porous material, or channels between the feed end  16  and the delivery end  18 , or materials containing unidirectional gas passages parallel to axis  14  formed in pressed and fired plates. Refractory body exterior  26  is the portion of refractory body  12  disposed around axis  14  externally to gas delivery structures  24 . Refractory body exterior  26  may be laterally sheathed, partially or entirely, in a metal housing. Feed cap end  28  is disposed on, and covers at least partially, the feed end  16  of purge plug  10 . Feed end cap  28  is configured so that, when it is placed in position on the feed end  16  of purge plug  10 , a plenum  30  is defined between feed cap end  28  and feed end  16 . Feed end cap  28  accommodates gas supply tube  38  so that gas supply tube  38  and plenum  30  are in fluid communication. Gas supply tube  38  passes through tee  40 , to which trap  42  is attached. Tee  40  and trap  42  are configured so that a liquid, such as lead, flowing from plenum  30  into gas supply tube  38  will pass through tee  40  and be retained in trap  42 . 
         [0019]    In operation, the purge plug is installed in a working position by introducing mortar between the lateral face of the purge plug and an interior surface of a block configured to receive the lateral surface, so that gas can be supplied through the feed end of the purge plug and introduced into the interior of a metallurgical vessel at the delivery end of the purge plug. The block is housed within a floor or wall of a metallurgical vessel. In typical installations the block is surrounded by refractory material. Gas is introduced through gas supply tube  38  and flows through feed cap  28  and enters plenum  30 . The gas then flows through gas delivery structures  24  from feed end  16  to delivery end  18  of purge plug  10 , and thence to the interior of a metallurgical vessel. Liquid lead entering the purge plug at delivery end  18 , flowing to feed end  16  and entering gas supply tube  38  may be captured in trap  42 . 
         [0020]      FIG. 2  shows an assembly incorporating a purge plug  110  of the present invention. The purge plug incorporates a refractory body  12  formed around a longitudinal axis  14  having a feed end or lower end  16  and a delivery end or upper end  18 . The purge plug has a core  20  that may be composed of a nonporous material, or of a material with directional passages or pores formed in, for example, pressed and fired alumina plates. Optionally housed in core  20  along axis  14  is a wear indicator  22  that, when the plug  10  is viewed from its delivery end  18 , indicates the degree of wear of plug  10  by its presence or absence. In fluid communication with the feed end  16  and delivery end  18 , and/or disposed longitudinally around the core or the longitudinal axis, are gas delivery structures  24 . These may be, for example, slots, tubes of porous material, channels, or materials containing unidirectional gas passages parallel to axis  14  formed in pressed and fired plates. Refractory body exterior  26  is the portion of refractory body  12  disposed around axis  14  externally to gas delivery structures  24 . Refractory body exterior  26  may be laterally sheathed or enclosed, partially or entirely, in a metal housing. Feed end cap  28  is disposed on, and covers at least partially, the feed end  16  of purge plug  10 . Feed end cap  28  is configured so that, when it is placed in position on the feed end  16  of purge plug  10 , a retention chamber  120  is defined between feed cap end  28  and refractory body  12 . Feed end cap  28  accommodates gas supply tube  38  so that gas supply tube  38  and retention chamber  120  are in fluid communication. Gas supply tube  38  protrudes into retention chamber  120 . Latitudinal volume  124  is the latitudinal extension of retention chamber  120  into refractory body exterior  26 . In selected embodiments of the invention, latitudinal volume  124  is physically and compositionally integral to refractory body exterior  26 . In selected embodiments of the invention, latitudinal volume  124  is a latitudinal extension of retention chamber  120 , and refractory body exterior  26  is attached to feed end cap  28  by a metal housing at least partially enclosing the radial surface of refractory body exterior  26 . The extent of the protrusion of gas supply tube  38  into retention chamber  120  divides retention chamber  120  into two parts. Retention chamber lower portion  132  is the portion of retention chamber  120  below the extent of protrusion of gas supply tube  38  into retention chamber  120 . Retention chamber upper portion  136  is the portion of retention chamber  120  above the extent of protrusion of gas supply tube  38  into retention chamber  120 . Gas supply tube protrusion  128  into retention chamber  120  may be uncapped, may be fitted with a bend or nozzle or may be covered with a ported gas supply tube cap  140 . Ported gas supply tube cap  140  may be configured so that the ports do not face core  20  and would not be in the line of flow of lead if core  20  were constructed of a material permitting the flow of lead. 
         [0021]    Gas supply tube protrusion  128  into retention chamber  120  may be fitted with a bend having an angle from and including 90 degrees to and including 180 degrees, from and including 105 degrees to and including 180 degrees, from and including 120 degrees to and including 180 degrees, or having an angle of 180 degrees. In selected embodiments of the invention, a check valve  141  is placed in gas supply tube  38 . The check valve  141  is disposed or configured so that flow into retention chamber  120  is permitted, but flow from retention chamber  120  into gas supply tube  38  is impeded. This configuration permits the flow of gas through gas supply tube  38  into retention chamber  120 , but impedes the flow of molten material from retention chamber  120  into gas supply tube  38 . 
         [0022]    In operation, the purge plug is installed in a working position by introducing mortar between the lateral face of the purge plug and an interior surface of a block configured to receive the lateral surface, so that gas can be supplied through the feed end of the purge plug and introduced into the interior of a metallurgical vessel at the delivery end of the purge plug. The block is housed within a floor or wall of a metallurgical vessel. In typical installations the block is surrounded by refractory material. Liquid lead entering the purge plug at delivery end  18  and flowing to feed end  16  is prevented from entering gas supply tube  38  by the protruding configuration of gas supply tube  38  within retention chamber  120  and, in certain configurations, by a nozzle or the presence of ported gas supply tube cap  140 . 
         [0023]    Retention chamber  120  is configured to accommodate all lead that will flow into it during the service life of plug  110 . Such a configuration is achieved by adequate extent or length of gas supply tube protrusion  128 , and by adequate retention chamber lower extent  132 . Useful values of gas supply tube protrusion have been found to be at least 3 mm, at least 5 mm, at least 10 mm, at least 15 mm or at least 20 mm. Useful ratios of linear retention chamber lower extent to linear chamber upper extent have been found to be at least 1:1, at least 2:1, at least 3:1 or at least 4:1. Useful ratios of retention chamber volume below the extent of gas supply tube protrusion to retention chamber volume above the extent of gas supply tube protrusion have been found to be at least 1:1, at least 2:1, at least 3:1, or at least 4:1. Useful volumes for the portion of the retention chamber below the extent of gas supply protrusion have been found to be at least 50 cubic centimeters, at least 60 cubic centimeters, at least 75 cubic centimeters, and at least 100 cubic centimeters. 
         [0024]      FIG. 3  shows an assembly incorporating a purge plug  210  of the present invention. The purge plug incorporates a refractory body  12  formed around a longitudinal axis  14  having a feed end or lower end  16  and a delivery end or upper end  18 . The purge plug has a core  20  that may be composed of a nonporous material, or of a material with directional passages or pores formed in, for example, pressed and fired alumina plates. Optionally housed in core  20  along axis  14  is a wear indicator  22  that, when the plug  210  is viewed from its delivery end  18 , indicates the degree of wear of plug  210  by its presence or absence. In fluid communication with the feed end  16  and delivery end  18 , and/or disposed longitudinally around the core or the longitudinal axis, are gas delivery structures  24 . These may be, for example, slots, tubes of porous material, channels, or materials containing unidirectional gas passages parallel to axis  14  formed in pressed and fired plates. Refractory body exterior  26  is the portion of refractory body  12  disposed around axis  14  externally to gas delivery structures  24 . Refractory body exterior  26  may be laterally sheathed or enclosed, partially or entirely, in a metal housing. Feed end cap  28  is disposed on, and covers at least partially, the feed end  16  of purge plug  210 . Feed end cap  28  is configured so that, when it is placed in position on the feed end  16  of purge plug  210 , a retention chamber  120  is defined between feed cap end  28  and refractory body  12 . Feed end cap  28  accommodates gas supply tube  38  so that gas supply tube  38  and retention chamber  120  are in fluid communication. Gas supply tube  38  protrudes into retention chamber  120 . Latitudinal volume  124  is the latitudinal extension of retention chamber  120  into refractory body exterior  26 . In selected embodiments of the invention, latitudinal volume  124  is physically and compositionally integral to refractory body exterior  26 . In selected embodiments of the invention, latitudinal volume  124  is a latitudinal extension of retention chamber  120 , and refractory body exterior  26  is attached to feed end cap  28  by a metal housing at least partially enclosing the radial surface of refractory body exterior  26 . In this embodiment, retention chamber  120  comprises two parts: a cylindrically-shaped retention chamber lower portion  232  with a radius of R, and a cylindrically-shaped retention chamber upper portion  236  with a radius of r. Radius R is greater than radius r. Gas supply tube protrusion  128  protrudes into retention chamber upper portion  236 . Gas supply tube protrusion  128  into retention chamber  120  may be uncapped, may be fitted with a bend, nozzle or crimp, or may be covered with a ported gas supply tube cap  140 . Ported gas supply tube cap  140  may be configured so that the ports do not face core  20  and would not be in the line of flow of lead if core  20  were constructed of a material permitting the flow of lead. 
         [0025]    In various embodiments: 
         [0026]    The invention encompasses a purge plug, comprising a refractory body having a feed end, a delivery end, an exterior and a longitudinal axis, at least one gas delivery structure disposed in fluid communication with the feed end and the delivery end, a retention chamber in fluid communication with the gas delivery structure and located at the feed end of the refractory body, and a gas supply tube in fluid communication with the retention chamber and having a gas supply tube protrusion protruding into the retention chamber. The gas supply tube protrusion has an axis, and the axis of the gas supply tube protrusion is parallel to the longitudinal axis of the refractory body. The gas supply tube protrusion has an axis, and the axis of the gas supply tube protrusion is coaxial to the longitudinal axis of the refractory body. The gas supply tube protrusion terminates in a structure selected from the group consisting of a bend, a crimp, a nozzle and a ported cap. The gas supply tube protrusion terminates in a ported cap, and the planes of the ports of the ported cap are not orthogonal to the longitudinal axis of the refractory body. The gas delivery structures are selected from the group consisting of slots, tubes of porous material, channels, voids formed in castable material, materials containing unidirectional gas passages parallel to the longitudinal axis of the refractory body and formed in pressed and fired plates, and combinations of these structures. The purge plug further comprises a metal housing at least partially enclosing the refractory body exterior. The purge plug further comprises a feed end cap, disposed on the refractory body feed end so as to define the retention chamber between the refractory body and the feed end cap, wherein the feed end cap accommodates the gas supply tube. The extent of the protrusion of the gas supply tube into the retention chamber is at least 3 millimeters, at least 5 millimeters, at least 10 millimeters, at least 15, millimeters, at least 20 millimeters, at least 25 millimeters, or at least 30 millimeters. The gas supply tube has a termination point within the retention chamber, and the ratio of the volume of the retention chamber below the termination point to the volume of the retention chamber above the termination point is at least 1:1, at least 2:1, at least 3:1, or at least 4:1. The retention chamber comprises a cylindrical upper portion having a radius r and a cylindrical lower portion having a radius R, r is less than R, and the gas supply tube protrusion protrudes into the retention chamber cylindrical upper portion. The gas supply tube comprises a check valve. The check valve is disposed or configured so that flow into the retention chamber is permitted, but flow from the retention chamber into the gas supply tube is impeded. 
         [0027]    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.