Abstract:
There is claimed a method for depositing fluid material from a linear nozzle in a substantially uniform manner across and along a surface. The method includes directing gaseous medium through said nozzle to provide a gaseous stream at the nozzle exit that entrains fluid material supplied to the nozzle, said gaseous stream being provided with a velocity profile across the nozzle width that compensates for the gaseous medium&#39;s tendency to assume an axisymmetric configuration after leaving the nozzle and before reaching the surface. There is also claimed a nozzle divided into respective side-by-side zones, or preferably chambers, through which a gaseous stream can be delivered in various velocity profiles across the width of said nozzle to compensate for the tendency of this gaseous medium to assume an axisymmetric configuration.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. application Ser. No. 08/915,230, filed on Aug. 20, 1997, now U.S. Pat. No. 5,968,601, the disclosure of which is fully incorporated by reference herein. 
    
    
     This invention was made with Government support under Contract No. DE-FC07-94ID13238 awarded by the Department of Energy. The Government has certain rights in this invention. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to linear nozzles, i.e., nozzles having a straight, elongated opening, and a tailored gas plume exiting the nozzle for the entrainment and deposition of an atomized liquid material carried in the gas plume. 
     Linear nozzles can be used for producing spray formed sheet and plate, particularly aluminum sheet and plate, the nozzles depositing molten metal material on a planar surface and substrate. The substrate supports the molten metal until solidification, and acts as a heat sink in the cooling and solidifying process. Linear nozzles have the advantage of making the sheet at desired widths and at production rates that compete with the traditional breakdown and hot rolling of cast ingots. The molten metal is deposited by entrainment in a flow of a gaseous medium directed through the atomizing nozzle and to the substrate. 
     Linear nozzles can also be used to spray and deposit other atomizable liquid materials, such as coolants, paints, protective coatings or irrigants on the appropriate surfaces. 
     The velocity profile of the gas flow or plume exiting the nozzle determines the deposit profile independently of the configuration of the supply of liquid medium to the nozzle. In addition, it has been determined that a flat, gas plume will become axisymmetric (circular) downstream of the nozzle due to gas entrainment. Entrainment is more pronounced at the ends or edges of the nozzle so that the gas decelerates at a relatively faster rate at the ends or edges of the plume in comparison to rate of deceleration near and at the plume center. This phenomena is shown in FIG. 1 of the accompanying drawings. The result is a gaussian distribution of the liquid material on the substrate, as shown in FIG.  1 . 
     Prior art efforts to overcome the problem has included the use of a plurality of axisymmetric nozzles scanning over the substrate. Other systems have included multiple nozzles to “fill in” low mass areas of the deposited material, while linear nozzles, using single chamber/single pressure schemes have involved changing the physical geometry of the gas exit of the nozzle for the purpose of controlling the distribution of deposited material. None of these efforts have produced the profile and yield properties needed at required production rates. “Yield” refers to the percent recovery of the liquid as a deposit. 
     SUMMARY OF THE INVENTION 
     By tailoring the gas velocity profile across the width of a linear nozzle, compensation for gas entrainment can be provided that ensures a substantially uniform deposit of the liquid material on a substrate. This can be accomplished by dividing the nozzle into compartments and directing gas flow through the respective compartments at conditions that will level or flatten the gas plume to make uniform the velocity of said gas plume at or near the point of liquid material deposition, thereby resulting in a more level or even deposition of said liquid material onto its substrate. The tailored gas configuration actually pushes downstream, or postpones, the natural tendency of a gaseous stream to assume an axisymmetric configuration and the resultant uneven (gaussian) deposit of liquid material on the substrate caused by an axisymmetric gaseous stream. 
     In a preferred embodiment, size of the individual chambers are controlled by partitions. These partitions are individually movable within the body of the nozzle to adjust and tailor the exit width of the gas leaving the compartments. 
     When creating long stretches of aluminum sheet or plate, the substrate can be moved relative to the nozzle at substantial speeds, or vice-versa, the nozzle can be moved, the process (again) providing an flatter, more planar deposit of liquid on the traveling substrate in both crosswise and lengthwise directions of the substrate. In this manner effective control of the gauge of the sheet or plate (after the liquid solidifies) is effected. Similarly, the embodiment can be used to provide an even application of other liquid metals or fluids. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, along with its advantages and objectives, will be better understood from consideration of the following detailed description and the accompanying drawings in which: 
     FIG. 1 is a schematic representation of a prior art linear nozzle, the standard gas stream velocity profile out of the nozzle and the gas stream velocity profile downstream as it approaches a planar substrate to produce a deposit having a generally gaussian distribution of material on said substrate; 
     FIG. 2 is a schematic representation of a more recent art nozzle having an intentionally straightened gas stream velocity profile for minimizing the gaussian distribution of material deposited downstream on a substrate; 
     FIG. 3 shows a tailored gas profile downstream from a preferred linear nozzle according to this invention which gives a level, even or more consistently flatter deposit profile of material on its substrate; 
     FIG. 4 is an isometric exploded schematic representation of an elongated nozzle and plenum that has been partitioned with internal baffles or partitions and suppliable with individual gaseous streams provided under different pressures; 
     FIG. 5 is a reverse view of the nozzle-plenum of FIG. 4 showing the internal baffles or partitions; 
     FIG. 6 is a diagrammatic representation of an apparatus for depositing molten metal, or any other depositable material, on a traveling substrate to make a solid sheet- or plate-like product from the nozzle of FIG. 5; 
     FIG. 7 is a top view of the nozzle plenum of FIG. 5; and 
     FIGS. 8 a  through  8   c  are top views of three representative nozzle, baffle (or partition) and aperture configurations in accordance with this invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings, FIG. 1 shows the effects of the problem with linear gas nozzles  10  in depositing a material  12  on a surface  14 . Because of excessive deceleration of a gas stream  16   a  near the ends of a linear nozzle, the configuration of the gas stream changes from an elongated to an arcuate pattern, as represented by downstream gas pattern  16   b , before reaching the substrate or target surface  14 . This, in turn, causes the gaussian, bell-shaped distribution of the deposited material shown in FIG.  1 . 
     FIG. 2 shows schematically the effects of somewhat straightening, or flattening, the velocity profile of a gas  16   a  exiting a nozzle  10 , resulting in subsequent gas pattern  16   b , for minimizing the gaussian distribution of material  12  being deposited on surface  14 . 
     FIG. 3 shows the preferred velocity profile  116   a  of a gas exiting a linear nozzle  110   a  in accordance with this invention, for achieving the desired subsequent gas pattern  116   b  that results in a more evenly deposited material  112   a  on planar surface  114 . This is effected by a gas velocity pattern that is relatively even but somewhat slower near the edge of the nozzle than the center portions of the nozzle, which are also relatively even except for a slight dip in velocity at the nozzle center. 
     The velocity of a gas stream across the width of a linear nozzle is produced and controlled by the pressure of the gas supplied to the nozzle. By adjusting gas pressure across the nozzle width, the profile, i.e., a gas plume  116   a , can be changed. FIGS. 4 and 5 show a sectionalized, elongated nozzle  110   a  in which gas pressure and velocity can be selectively changed and controlled according to the invention. The lines midway through these depicted nozzles are meant to show that the invention may contain many more chambers than are actually depicted in the accompanying Figures. With respect to the fractionalized nozzle so depicted, gas is supplied thereto by a plurality of conduits  120  connected to a housing structure  122 . The housing structure has an interior  124  that provides an elongated plenum for receiving gas flows from the ends of the conduits connected to the housing. The gases are directed to the conduits from a supply thereof (not shown) under varying pressures to effect the plume  116   a  shown in FIG. 3 of the drawings. In the preferred embodiment shown in FIG. 4, numerals P 1  to P 5  are used to designate five pressures of the gas flow through the five conduits  120  depicted. The gas pressure combination necessary to effect the uniform mass flow of fluid material  112   a  on a planar substrate would have essentially equal pressures near the opposed ends (P 1  and P 5 ) of the linear nozzle, and equal pressures in the middle sections of the nozzle; the two sets of pressures are not equal to each other, however. Rather, the pressure at the ends of the nozzle are lower than the pressures adjacent the middle portion of the nozzle. The result is the velocity profile  116   a  of FIG.  3 . 
     To better control these pressures and the resultant gas velocity profile  116   a  the plenum  124  of housing  122  can be provided with baffles or partitions  126 , as seen in FIG. 5 of the drawings. The partitions extend crosswise of the nozzle and plenum length between elongated walls of housing  122  and the elongated walls of an interior, vertical member  131 . Such partitions may be evenly spaced, or more preferably unevenly spaced apart as better seen in the subsequent views of FIGS. 5 and 7. The partitions provide side-by-side chambers that permit control of the velocity distribution of gas exiting the chambers through an aperture  132  (FIG. 4) discussed in detail hereinafter. Channel member  128  receives the material of deposit  112  in a fluid or molten form in the case of depositing metal on a substrate, for producing sheet and plate. The channel member is best seen in the exploded view of FIG.  4 . Channel member  128  fits inside a built-in sleeve  131  of housing  122 , having a lower narrow neck portion  130  that enters and resides in plenum  124 . The lower end of the channel member has an elongated opening  136  (better shown in FIG.  7 ), and extends to and through an elongated opening  132  provided in a lower face plate  134 . Plate  134  closes the lower face of the plenum and housing around channel end  131  and thereby provides a narrow continuous closed loop aperture  137  (FIG. 7) that is elongated in the length direction of housing  122  and channel member  128 . Such an opening provides a curtain of gas in the configuration of the elongated closed loop of aperture  137  when gas is directed into plenum  124  that is directed from the plenum and towards a surface or substrate  114  (FIG.  6 ). In FIG. 5, the plate is removed from housing  122  to expose partitions  126  and vertical member  131 . 
     As further seen in FIG. 5, the ends of one or more conduits  120  are located between two consecutive partitions  126  to appropriately locate the flow of gas through the side-by-side chambers of plenum  124  and out of the continuous aperture  137 . This “location” of gas flow through the plenum and chambers and out of the continuous aperture  137  in combination with appropriate gas pressures in the chambers provides the ability to tailor the gas plume in a manner that controls the thickness of the material  112  deposited on a substrate. 
     “Tailoring”, in accordance with this invention, can be accomplished by: (a) adjusting the gas pressures through the respective conduits  120 ; or (b) adjustably mounting partitions  126 , which are preferably laterally moveable in the plenum, then securing the partitions in place before the nozzle is used; or (c) variably changing gas aperture slit size  151  on modified plate  150  along the length of the nozzle as shown in FIG. 8C; or (d) combinations of (a), (b) and (c) above. In the more preferred embodiment, combinations (a) and (b) are used. Gas pressures are effected via traditional methods common in many industries. The partitions can be effected, for example, by providing each partition or baffle with a set screw (not shown). To adjust one or more of the partitions, face plate  134  is simply removed from housing  122  and the set screws loosened. The partitions are then manually moved laterally in the plenum to locate the partitions relative to the ends of conduits  120 . The set screws are then tightened and face plate  134  returned and secured to the bottom of housing  122 . 
     In the special case of depositing molten metal supplied to the upper end (entrance) of channel member  128 , the metal exits the lower elongated opening  131  of the member, is atomized by a continuous curtain of gas flow exiting the continuous aperture  136 , which surrounds the flow of metal from opening  139 , and is deposited on a surface  114 . 
     By appropriate partition adjustment, or by knowing and controlling the pressure of the gas flow in conduits  120 , a gas plume  116   a  can be provided that does not assume a circle or arcuate configuration before reaching its substrate surface  114 . In this manner, the gas flow remains linear in its movement to the surface, and entrains the liquid material exiting nozzle opening  139  in a linear manner such that a uniform mass of liquid material is laid down on the surface. If the nozzle extends crosswise over a surface, the liquid material is evenly deposited across the width of the surface. If the nozzle and surface are moved relative to one another, either by moving the nozzle, the surface (as in FIG.  6 ), or both, the deposit of liquid material  112   a  is generally deposited evenly crosswise and lengthwise of a surface  114  when relative movement is maintained substantially constant. In FIG. 6, surface  114  is shown as a solid belt that provides a planar surface upon which molten metal can be deposited and solidified to provide a cast metal sheet or plate product  112   a  of constant gauge (thickness). The length of the cast product  112   a  can be that of the length of belt  114 . Hence “long” sheets of material can be rapidly produced having a desired gauge and width, as determined by the length of opening  139 . Liquid flow rates passing through channel member and the velocity of gas flow through plenum  124  are sufficient to provide a sheet or plate product at rates higher than conventional axisymmetric nozzles. 
     Three representative nozzle and partition (or baffle) configurations are shown in accompanying FIGS. 8 a ,  8   b  and  8   c . In the first of these, FIG. 8 a , partitions  126  are evenly spaced apart. In the second, more preferred embodiment, FIG. 8 b , baffles or partitions  126  are unevenly spaced apart. In FIG. 8 c , the nozzle housing operates at a single gas pressure, P e , with modified plate  150  in place. Within that nozzle configuration, there are no separate chambers but rather side-by-side zones through which varying gas velocities are delivered. Variably sized gas exit slits  151  are shown in plate  150 . 
     The invention described herein has already been tested with water and molten aluminum alloys including 3XXX, 6XXX, 2XXX and 7XXX series (Aluminum Association designations). Such alloys are typically used in the automotive and aerospace industries. On a less preferred basis, this invention can be used to deliver to a substrate a paint coolant protective coating and/or irrigant. Representative examples of said materials include: glycol; other molten metals like copper, tin, lead, zinc, iron, nickel and combinations thereof; epoxy-based coatings; vinyl-based coatings, and/or liquid fertilizers. Any of the materials otherwise sprayed in accordance with traditional atomization processes may also be applied through this nozzle configuration. 
     Those knowledgeable in the art will recognize other means for accomplishing the main goal of this invention, that being to modulate the gas velocity profile downstream of the nozzle through which atomized materials are passed for eventual substrate deposit. This invention also covers the method of operating nozzle zones at substantially the same pressure, P e , but through differently sized gas slits or openings; or by operating the nozzle at both different pressures and opening sizes. 
     Since the exiting gas pressures of this invention are generally greater than atmospheric, these gases expand. This invention exploits the foregoing and thereby actually “tailors” the mass flow of the gas exiting the zones (not necessarily physically partitioned), chambers or physically compartmentalized nozzles. 
     Having described the presently preferred embodiments, it is to be understood that the invention may be otherwise embodied by the scope of the claims appended hereto.