Patent Publication Number: US-7913937-B2

Title: Descaling spray nozzle assembly

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to spray nozzle assemblies, and more particularly, to descaling spray nozzle assemblies operable for directing a wide thin-line high-pressure liquid discharge for penetrating and removing scale from steel in steel manufacturing operations. 
     BACKGROUND OF THE INVENTION 
     Descaling spray nozzle assemblies are extensively used in steel processing for directing a wide thin line high pressure spray onto the surface of steel slabs for penetrating and removing iron oxide scale buildup on the surfaces prior to rolling and subsequent processing of the steel. In such spraying systems, it is desirable that the high pressure liquid discharge be as thin as possible for effecting maximum impact pressure and penetration of the scale. It also is desirable that the distribution of the liquid discharge be uniform across the width of the spray pattern. Heretofore, the liquid distribution often is unevenly reduced toward the opposed ends of the discharging spray pattern, which reduces impact forces and adversely affects the uniformity of the spray penetration and scale removal. 
     Such descaling spray nozzle assemblies typically comprise a tubular body, sometimes referred to as a high impact attachment tube, formed with a liquid flow passageway that tapers inwardly in a downstream direction for accelerating the liquid flow, a strainer affixed to an upstream end of the tubular body for straining particulate matter and scale from recycled steel mill water typically used in such descaling processing, and a carbon insert spray tip mounted at downstream end of the tubular body having an elongated liquid discharge orifice for forming and directing a flat spray discharge pattern. High pressure liquid directed through the strainer can incur considerable turbulence, which in turn can adversely affect the uniformity and impact force of the discharging spray. 
     For reducing turbulence and straightening the liquid flow stream through the high impact attachment tube prior to passage through the spray tip, it is known to provide a vane having a plurality of radial vane elements immediately downstream of the strainer, which effectively defines a plurality of circumferentially-spaced laminar flow passages. Since such vane can only have a limited number of radial vane elements, such as on the order of five, it sometimes is incapable of adequately moderating highly turbulent flow streams, such as from turbulence incurred by high pressure liquid entering the strainer in a radial direction and then abruptly changing direction for passage through the strainer and high impact attachment tube. Efforts to provide such a vane with a greater number of radial vane elements have not been acceptable because the additional vanes result in a corresponding reduction in size of the laminar flow passageways, which restricts fluid passage, creates undesirable pressure drops, and in fact increases turbulence. 
     Such descaling spray nozzle assemblies also are relatively expensive to manufacture, since the components must be precisely formed and assembled in order to achieve acceptable performance. Indeed, without precise radial orientation of the elongated spray tip discharge orifice with respect to the radial vane elements of the liquid straightening vane, the uniformity of the discharging spray pattern again can be adversely affected. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a descaling spraying system having spray nozzle assemblies operable for more efficient and reliable uniform removal of scale from steel slabs. 
     Another object is to provide a descaling spray nozzle assembly as characterized above which has a liquid straightening vane section for more affectively reducing turbulence in the liquid flow stream through the nozzle for enhanced thin line high-pressure impact on a scaled surface. 
     A further object is to provide a descaling spray nozzle assembly of the foregoing type in which the vane section further facilitates improved uniformity in the liquid distribution for more uniform impact and scale removal. 
     Still another object is to provide a descaling spray nozzle assembly of the above kind that has a liquid straightening vane section with greater numbers of radial vane elements than heretofore possible without restricting liquid flow or causing undesirable pressure losses or increased turbulence. 
     Yet a further object is to provide a descaling spray nozzle assembly which lends itself to more economical manufacturer and assembly. A related object is to provide is to provide such a descaling nozzle assembly in which the spray tip and liquid straightening vane section may be assembled without special orientation of the elongated discharge orifice of the spray tip with respect to the radial vane elements. 
     Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic end elevational view of an illustrative descaling spraying system having spray nozzle assemblies in accordance with the invention; 
         FIG. 2  is an enlarged fragmentary section of one of the descaling spray nozzle assemblies of the illustrative spraying systems; 
         FIG. 3  is an enlarged downstream end view of the illustrated spray nozzle assembly taken in the plane of line  3 - 3  in  FIG. 2 ; 
         FIG. 4  is an enlarged longitudinal section of the tungsten carbide insert spray tip of the illustrated spray nozzle assembly; 
         FIG. 5  is an enlarged longitudinal section of the illustrated spray nozzle assembly, taken in the plane of line  5 - 5  in  FIG. 2 ; 
         FIG. 6  is an upstream end view of the liquid inlet strainer of the illustrated spray nozzle assembly, taken in the plane of line  6 - 6  of  FIG. 5 ; 
         FIG. 7  is an transverse section of the spray nozzle assembly through a liquid straightening vane thereof, taken in the plane of line  7 - 7  in  FIG. 5 ; and 
         FIG. 8  is an enlarged and exploded fragmentary view depicting the axial alignment and spacing members of the pair of vanes of the illustrated spray nozzle assembly. 
     
    
    
     While the invention is susceptible of various modifications and alternative constructions, a certain illustrative embodiment thereof has been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific form disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now more particularly to the drawings, there is shown an illustrative descaling spraying system  10  having a plurality of spray nozzle assemblies  11  in accordance with the invention for directing a high pressure liquid spray on opposed sides of a moving steel slab  12  in a steel manufacturing operation. The spraying system  10  in this case comprises upper and lower liquid supply headers  14   a ,  14   b , typically supplied with mill water that is recycled in the steel manufacturing facility. These spray nozzle assemblies  11  are mounted in laterally-spaced relation along the respective header  14   a ,  14   b  such that a plurality of flat, thin-line spray patterns  13  penetrate and remove scale across the entire width of the steel slab  12 . Spray nozzle assemblies  11  in this case are supported in depending fashion from the upper liquid supply header  14   a  for directing liquid spray onto an upper side of the moving slab  12  and the spray nozzle assemblies  11  are supported in upwardly extending relation to the lower liquid supply header  14   b  for directing spray patterns across the underside of the slab  12 . Each spray nozzle assembly  11  is supported by its respective header  14   a ,  14   b  with an upstream end within the header for receiving supply liquid from the header and a downstream end disposed outside the header in facing relation to the moving slab  12 . Since each of the spray nozzle assemblies  11  are of similar construction, only one need be described herein in detail. 
     The spray nozzle assemblies  11  each comprise an elongated high impact attachment tube  15  appropriately supported within a wall  16  of the header  14   a ,  14   b , a strainer  18  mounted at an upstream end of the high impact attachment tube  15  through which supply water from the header enters the spray nozzle assembly, a tungsten carbide insert spray tip  19  mounted at a downstream end of the high impact attachment tube  15  formed with an elongated discharge orifice  20  for discharging and directing a flat spray pattern, and a spray tip retainer  21  for securing the spray tip  19  in mounted position. The strainer  18  in this case has an elongated, generally cup shaped configuration which is threaded onto the upstream end of the high impact attachment tube  15 , and the spray tip retainer  21  is threaded onto a downstream end of the high impact attachment tube  15  with an inwardly directed annular lip  22  retaining the spray tip  19  in abutting relation against a downstream end of the high impact attachment tube  15 . 
     The spray nozzle assembly  11  in this case is supported within the header by means of a cylindrical adapter  23  secured within a radial opening in the header by a weldment  17 . The adapter  23  in this instance has an externally threaded lower end against which a radial flange  21   a  of the spray tip retainer  21  is retained by an internally threaded retaining ring  24 . 
     For accelerating liquid during passage through the spray nozzle assembly, the high impact attachment tube  15  is formed with a liquid flow passage  25  which tapers inwardly in a downstream direction. In the illustrated embodiment, the liquid flow passage  25  includes a first relatively short tapered section  26  angled about 12° to the longitudinal axis of the high impact attachment tube  15 , a relatively longer more gradual tapered section  28  angled at about 5° to the longitudinal axis of the high impact attachment tube, and entry section  29  immediately upstream of the spray tip  19 . It will be understood by one skilled in the art that the high impact attachment tube  15  may be integrally formed as shown in the illustrated embodiment, or may comprise multiple longitudinally connected components for ease of manufacture 
     The tungsten carbide insert spray tip  19  in this case is formed with an inlet passage section  32  that communicates between the high impact attachment tube passageway  25  and the discharge orifice  20  through a radiused entry passage section  34 . The elongated discharge orifice  20  in this instance is defined by a cylindrical groove or cut  35  extending transversely across the end of the spray tip  19  in intersecting relation with the entry passage section  34 . 
     For straining small particulate matter that might exist in the recycled mill water directed through the headers  14   a ,  14   b  from the flow stream entering the spray nozzle assembly  11 , the strainer  18  is formed with a plurality of elongated slits  38  circumferentially about the strainer communicating through a cylindrical sidewall  39  of the strainer and partially into the upstream end  39   a  thereof. The supply water primarily enters the strainer  18  in a radial direction through the elongated slits  38  and must make a 90° change in directional movement, causing turbulence in the liquid, as it is directed toward the inwardly tapered passageway  25  of the high impact attachment tube  15  prior to direction from the spray tip  19 . Turbulence in the high pressure liquid flow stream directed to the spray tip  19 , as indicated above, can adversely affect the liquid discharge, particularly by increasing the transverse thickness of the thin line spray pattern, which reduces the liquid impact force and penetration, and by altering the liquid distribution, particularly at opposite ends of the wide spray pattern, which can result in uneven liquid penetration and scale removal. 
     In accordance with an important aspect of the invention, the spray nozzle assembly has a multi-stage liquid straightening vane section which more affectively reduces liquid turbulence prior to direction from the spray tip, with resultant improved control in tightness of the thin, flat spray pattern and uniformity in liquid distribution throughout the spray pattern. More particularly, the vane section comprises a plurality of liquid straightening vanes each having a plurality of radial vane elements, with the radial vane elements of one vane being circumferentially offset with respect to an immediately upstream vane for multi-stage redirection and straightening of the liquid passing through the high impact attachment tube. To this end, in the illustrated embodiment, a vane section  40  is provided that comprises two identical vanes  41   a ,  41   b  each having five radial vane elements  42   a ,  42   b  extending from a center of the respective vane for defining five respective circumferentially-spaced laminar flow passageways  44   a ,  44   b.    
     In keeping with the invention, the radial vane elements  42   b  of the downstream vane  41   b  are circumferentially offset from the radial vane elements  42   a  of the upstream vane  41   a  such that the five laminar flow streams exiting the laminar flow passages  44   a  of the upstream vane  41   a  must change direction in a controlled staged manner upon entering the laminar passages  44   b  of the downstream vane  41   b . In the illustrated embodiment, the radial vane elements  42   b  of the downstream vane  41   b  are offset circumferentially 36° with respect to the vane elements  41   a  of the upstream vane  41   a , when viewed in an axial direction, so as to be aligned midway through the laminar passageways  44   a  of the upstream vane  41   a . It will be understood that the vane section  40  could comprise more than two vanes  41   a ,  41   b , and in that case, the radial vane elements of the successive vanes could be offset circumferentially smaller distances for effecting the staged longitudinal direction of the liquid. 
     In further carrying out the invention, the vanes  41   a ,  41   b  of the multi-stage vane section  40  are longitudinally spaced apart for defining a transition flow passage  48  between the vanes  41   a ,  41   b  of the two stages. In the illustrated embodiment, the multi-stage vanes  41   a ,  41   b  are axially spaced for defining a transition flow passageway  48  between the outlet ends of the laminar flow passageways  44   a  of the upstream vane  41   b  and the inlet ends of the laminar passageways  44   b  of the downstream vane  41   b . In this case, the vanes  41   a ,  41   b  each have equal longitudinal lengths L and are separated by an axial gap distance D which defines the length of the transition flow passageway  48  between the vanes  41   a ,  41   b . In the preferred embodiment, the gap distance D is less than one-half the axial length L of the vanes, and less than 25 percent of the distance K between the inlet end of the upstream vane  41   a  and the outlet end of the downstream vane  41   b . In an operative embodiment of the invention, the vanes each have an axial length L of 10 mm with a gap distance D of 4 mm. between the vanes. 
     In further keeping with the invention, the vanes  41   a ,  41   b  have axially extending alignment and spacing members  43   a ,  43   b  for axially spacing and circumferentially aligning the vanes  41   a ,  41   b  with respect to each other as an incident to mounting in the high impact attachment tube  15 . In the illustrated embodiment, the upstream vane  41   a  has an axially extending alignment and spacing member or lug  43   a  extending in a downstream direction and the downstream vane  41   b  has an alignment and spacing member or lug  43   b  extending from its upstream end. The alignment and spacing members  43   a , 43   b  each are formed with a cross slot which defines a respective locking and alignment key  48   a , 48   b  and recess  49   a , 49   b  for interlocking engagement between the vanes  41   a , 41   b . The locking keys  48   a , 48   b  each have a respective end face  50   a , 50   b  for abutting relation with the recess  49   a , 49   b  of the adjacent vane for establishing the longitudinal spacing therebetween and an alignment face  51   a , 51   b  in an axial plane for establishing a pre-determined circumferential orientation of the vanes  41   a , 41   b  with respect to each other. 
     The multi-stage vane section  40  has unexpectedly been found to improve spray performance characteristics of the discharging flat spray pattern. The discharging spray has a more controlled narrow transverse thickness T ( FIG. 3 ) for higher pressure impact and penetration into the scale surfaces of steel slabs. The liquid distribution also is substantially uniform across the entire width of the thin line spray for enhanced uniform removal of scale from the slab. While the theory of operation is not completely understood, it is believed that the improved straightening and turbulence suppression of the multi-stage vane section  40  is effected by the liquid being controlled by the greater number of radial vane elements  42   a ,  42   b  of the plurality of vanes  41   a ,  41   b . In the illustrated embodiment, for example, the liquid is controlled and redirected by 10 radial vane elements  42   a ,  42   b . By virtue of the staging of the vanes  41   a ,  41   b , however, the greater multiplicity of radial vane elements neither unduly restrict the laminar flow passageways  44   a ,  44   b , nor imparts turbulence or substantial pressure losses in the flow stream, which would otherwise occur utilizing a single vane having ten radial vane elements which by necessity would result in closer circumferential spacing of the radial vane elements. 
     It has further been found that the spray nozzle assembly of the present invention enables more economical manufacture with reduced tolerance requirements. In prior descaling nozzles it has been found that tolerance variations in formation of the spray tip discharge orifice, the other components of the spray nozzle assembly, or in orientation the positioning of the elongated spray tip orifice  20  with respect to the laminar flow passageways, could influence the spray performance. The spray nozzle assembly of the present invention enables greater tolerance variations and random orientation of the elongated spray tip discharge orifice with respect to the laminar flow passageways without altering the liquid distribution or thin line impact of the discharging spray.