Patent Publication Number: US-6216924-B1

Title: Pressure tube

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The subject invention is directed to apparatus for making steel and, more particularly, apparatus for transferring molten steel from a ladle to a mold. 
     2. Description of the Prior Art 
     Various apparatus and processes have been developed for manufacturing steel. In steelmaking operations, it has been found that transferring molten metal to molds presents a step by which slag or other impurities are sometimes introduced. To improve steel quality, various processes for minimizing the introduction of impurities have been developed. 
     Such processes have included pressure casting processes wherein molten metal is transferred through a pressure tube and into a casting. Briefly, in the pressure casting process a ladle of molten metal is placed upright in an open pressure vessel. A refractory lined lid is then placed over the vessel. One end of the pressure tube is inserted through an opening in the lid and submerged in the molten metal. The opposite end of the tube is then connected to the mold. Air is pumped into the vessel to pressurize it. The air pressure on surface of the molten metal forces the metal upwardly through the pressure tube and into the mold. The metal enters the pressure tube through the submerged end of the tube and flows through the tube and into the mold. Since the molten metal flows from a location under the metal surface near the bottom of the ladle, the process tends to avoid the entrainment of slag in the molten metal and results in a high-quality casting. 
     In the prior art, pressure tubes have been made of various materials including alumina graphite, zirconia-alumina, high alumina, high alumina tar impregnated and coked, and muddite. 
     All of these tubes have the disadvantage that their preparation requires final assembly with a metal collar. The collar is bonded to the outside surface of the tube with a castable or mortar. The collar is located adjacent to one end of the pressure tube. The opposite end of the pressure tube is inserted through the lid opening and the pressure tube is passed through the lid opening until the collar engages the pressure vessel lid. The collar is located on the pressure tube such that the collar contacts the pressure vessel lid and one end of the tube is suspended in the molten metal during pressure casting. 
     To assemble the tube and collar, the metal collar is placed over one end of the refractory tube. The tube is secured to the collar by a mortar or castable that is placed between the inside wall of the collar and the outside wall of the refractory tube. After the tube is thus secured to the collar, a second layer of mortar is applied to the outer surface of the tube adjacent to the innermost end of the collar. This second layer of mortar is intended to prevent leakage of air between the collar and the tube while the tube is under pressurized conditions. Air leaks at this location are particularly undesirable because the air can then become entrained in the steel as it enters the mold. If air reaches the mold cavity, the mold is usually seriously damaged or destroyed. At a minimum, this results in degradation of the steel quality. 
     In the prior art, air leaks between the collar and the tube were sometimes caused by slippage between the collar and the tube that resulted in cracks in the mortar. Accordingly, various structures were employed to strengthen the engagement between the collar and the pressure tube. For example, in some cases circular grooves were cut in the external surface of the tube so that the castable or mortar could flow into these grooves to better engage the tube. In another example, the tube was provided with a circular groove and a steel retaining ring that was partially received in the groove extended from the tube to provide a circular flange around the tube. This also was found to improve the engagement between the collar and the tube. 
     Notwithstanding such improved designs, a persistent problem with the use of such collars has been that they potentially allowed passage of air through mortar cracks or seams between the pressure tube and the collar. This also created a potential for air to become entrained in the steel and carried into the mold. Moreover, the prior art process for assembling collars to the refractory tubes required substantial labor, time and space to complete. All of these requirements significantly added to the overall cost of the pressure casting process. 
     Thus, there was a need in the prior art for an improved design for pressure tubes that would further reduce the likelihood that a pathway between the collar and the refractory tube would develop and entrained air would enter the mold. Preferably, an improved design could also substantially reduce requirements for time, labor and space that were associated with the collar assembly process. 
     SUMMARY OF THE INVENTION 
     In accordance with the subject invention, a pressure cast tube includes a tube body that defines an internal passageway between an intake end and a mold end. The tube body has a larger diameter at longitudinal positions adjacent to the mold end than at longitudinal positions adjacent to the intake end. The tube body also incorporates a flange ring that is located adjacent to the mold end and that extends laterally outward from the rest of the tube body. A shell is secured to the flange ring and a contact ring is connected to the shell. 
     Preferably, the shell that is secured to the flange ring includes an annular band that is secured to the circumferential surface of the flange ring and an upper ring that is connected to one edge of the annular band. The contact ring is secured to an edge of the annular band that is opposite from the edge that is connected to the upper ring. 
     More preferably, the circumferential surface of the flange ring is separated from the lateral surface of the tube body by an upper annular surface and by a lower annular surface. 
     Other details, objectives and advantages of the subject invention will become apparent to those skilled in the art as description of a presently preferred embodiment proceeds. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the subject invention is shown in the accompanying drawings wherein: 
     FIG. 1 is an elevational section of a pressure tube in accordance with the subject invention; 
     FIG. 2 is an enlarged view of the top portion of the pressure tube shown in FIG. 1; 
     FIG. 3 is a top plan view of the complete pressure tube shown in FIG. 1; 
     FIG. 4 is an isometric view of the top portion of the pressure tube of FIGS. 1-3 with portions thereof broken away to better disclose the structure thereof; and 
     FIG. 5 is an elevational section of the pressure tube of FIGS. 1-4 mounted in a typical pressure vessel. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in FIGS. 1-4, a pressure tube as herein disclosed includes a tube body that has a central tube section or region  10  with an intake tube section or tapered region  12  on one end and a flared tube section or region  14  on the other end. 
     Central region  10  is in the general shape of a right circular cylinder with an outer circumferential surface  16  that is spaced at a substantially constant radius from a longitudinal center axis  18 . Central region  10  has a first or upper end or boundary  20  and a second or lower end  22 . Central region also includes an internal passageway  24  that is defined by an internal cylindrical surface  26 . Internal cylindrical surface  26  is located at a substantially constant radius from longitudinal axis  18  such that the wall thickness  28  between outer surface  16  and inner surface  26  is substantially constant over the longitudinal locations or positions of the central region  10 . 
     Tapered region  12  is an intake tube section that is defined between an intake end or distal end face  30  and a connection end face  32 . Tapered region  12  has an internal cylindrical surface  34  that defines an internal passageway  36 . Tapered region  12  is aligned on longitudinal axis  18  and is secured to central region  10  such that connection end face  32  is in opposition to lower end  22 . Internal passageway  36  is in communication with internal passageway  24  and internal surface  34  is located at substantially the same radius from center axis  18  as internal surface  26 . Also, at the longitudinal position on tapered region  12  that is adjacent to connection end face  32 , the outer surface  38  of tapered region  12  is located at substantially the same radius from longitudinal axis  18  as circumferential surface  16  so that wall thickness  40  of tapered region  12  is substantially the same as wall thickness  28  of central region  10 . 
     At locations along longitudinal axis  18  closer to distal end face  30 , outer surface  38  is located at a shorter radius from axis  18  such that tapered region  12  decreases in diameter along longitudinal axis  18  in the direction toward distal end face  30 . Internal surface  34  is located at a substantially constant radius throughout the length of tapered region  12  so that wall thickness  40  diminishes in the direction toward distal end face  30 . Preferably, central region  10  is secured to tapered region  12  by threaded member  42 . 
     Flared region  14  has a mold end face  44 . Flared region  14  joins central region  10  at boundary  20 . Flared region  14  is in longitudinal alignment with longitudinal axis  18 . Flared region  14  monolithically joins central region  10  at boundary  20 . Flared region  14  includes an internal cylindrical surface  48  and an outer circumferential surface  50 . Internal cylindrical surface  48  is at substantially constant radius from axis  18  at positions of flared region  14  along longitudinal axis  18  and defines an internal passageway  52  that is in communication with passageway  24  of central region  10 . A portion of flared region  14  in the region near mold end face  44  is comprised of a layer of alumina-graphite  52   a . Layer  52   a  is hardened by boron carbide so that it is resistant to physical damage caused by impacts from the molds  52   b  (FIG. 5) as they are joined to the pressure tube or removed from the pressure tube. 
     In the portion of flared section  14  that is adjacent to boundary  20 , outer surface  50  is substantially the same radius from axis  18  as circumferential surface  16  of central region  10 . Also internal surface  48  is substantially the same radius from axis  18  as internal surface  26  of central region  10 . Accordingly, the wall thickness  52   b  of the portion of flared region  14  adjacent to boundary  20  is substantially the same as wall thickness  28  of central region  10 . 
     However, the lateral or radial location of outer surface  50  increases at longitudinal positions of flared region  14  in the direction from boundary  20  toward mold end face  44  such that wall thickness  52   b  of flared region  14  is greater at longitudinal positions that are closer to mold end face  44  in comparison to other longitudinal positions. Thus, flared region  14  generally defines a fustrum  53  wherein the base  53   a  of the fustrum is closer to the mold end face  44  than the top  53   b  of the fustrum. 
     Additionally, flared tube section  14  includes a flange ring  54  that is an integral portion of said flared tube section  14 . Flange ring  54  extends radially from outer surface  50  at a longitudinal position that is adjacent to the mold end face  44  of flared section  14 . Thus, flange ring  54  is located between mold end face  44  and the base  53   a  of the fustrum  53 . 
     In the preferred embodiment, flange ring  54  includes an outer circumferential surface such as radial surface  56  and two lateral sides  58  and  60  that extend between radial surface  56  and outer surface  50  of flared region  14 . Thus, radial surface  56  extends laterally beyond the base  53   a  of fustrum  53  to form a lateral side  58  therebetween. 
     The pressure tube herein disclosed further includes a steel shell  64  that is secured to flange ring  54 . Steel shell  64  includes an outer or annular band  66  that is secured to the boundary surface or radial surface  56  of flange ring  54 . Annular band  66  has an upper lateral or side edge  68  and a lower lateral or side edge  70 . Shell  64  further includes an upper ring  72  having an outer perimeter  74 . Upper ring  72  is connected to upper side edge  68  of annular band  66  along perimeter  74 . 
     A contact ring  76  has an outer perimeter edge or surface  78  and an inner annular edge or inner radial surface  80 . Inner radial surface  80  is located laterally outward from the surface  50  of tube section  14  and from base  53   a  of fustrum  53 . Radial face  58  includes an annular recess  82  that receives contact ring  76 . Annular recess  82  is defined by lateral surface  82   a  and a circular or radial edge  84  that opposes inner annular edge or inner radial surface  80  of contact ring  76  when contact ring  76  is received in annular recess  82 . The depth of annular recess  82  is determined by the longitudinal width of radial edge  84  and is substantially equal to the thickness of contact ring  76  such that the annular portion  85   a  of radial face  58  that is defined between circular edge  84  and base  53   a  of fustrum  53  is substantially coplanar with face  86  of contact ring  76 . Contact ring  76  is connected to the lower side edge  70  of annular band  66  at outer perimeter surface  78 . 
     Referring to FIG. 5, when the pressure tube is inserted through the lid  85  of the pressure vessel, contact ring  76  engages a steel flange  86  in the lid of the pressure vessel. This creates a pressure seal between contact ring  76  and lid  85 . In addition, steel flange  86  also engages the annular portion  85 a of radial face  58  that is defined between circular edge  84  and base  53   a  to provide a metal-to-refractory seal. This metal-to-refractory seal has been found to be tighter than the metal-to-metal seals known in the prior art. 
     Also in contrast to pressure tubes known in the prior art, the surfaces of flared region  14  that are exposed to the internal pressures in the pressure vessel define a monolithic body that has no seams or joints that could be penetrated or eroded by internal gases or vapors inside the pressure vessel. The pressure tube herein disclosed does not have a steel collar or steel clading that forms a steel-alumina-graphite interface that is exposed to the internal pressure of the pressure vessel. Instead, a continuous glaze-protected surface of alumina-graphite is presented to pressure conditions. This continuous surface has been found to be more resistant to oxidation so that the pressure tube herein disclosed is found to be more durable than prior art pressure tubes. 
     While a presently preferred embodiment of the subject invention has been shown and described herein, other various embodiments are also included within the scope of the following claims.