WO1990010514A1

WO1990010514A1 - Atomizing devices and methods for spray casting

Info

Publication number: WO1990010514A1
Application number: PCT/US1989/005394
Authority: WO
Inventors: George J. Muench; Brian G. Lewis; Sankaranarayanan Ashok; William Gary Watson; Harvey P. Cheskis; Thomas J. Mellilo
Original assignee: Olin Corporation
Priority date: 1989-03-13
Filing date: 1989-12-01
Publication date: 1990-09-20
Also published as: AU4663389A; CA2005145A1

Abstract

A molten metal spray-depositing apparatus for atomizing a stream of molten metal into metal particles in a divergent spray pattern of higher mass density at an upstream leading peripheral portion of the spray pattern, relative to the direction of movement of a substrate, than either of a center region or downstream trailing peripheral region of the pattern. The atomizer (34) may generate one-side sheer force for breaking up its metal stream. Alternatively, the atomizing device may be in the form of an annulus (35, 50, 64, 80, 100, 120, 140, 160) of varying configurations with plenum chambers and outlets so arranged that a divergent conical spray pattern is produced having central axes inclined with respect to the vertical axes of the molten metal stream in a direction downstream of the moving substrate upon which the spray material is deposited. An alternative form of the spray depositing apparatus employs a magnetic fuel-generating nozzle (234, 248) which eliminates the use of gas. Other forms of a gasless nozzle (334, 336) have a configuration for confining and imparting mechanically an angular momentum to the molten stream to break it up.

Description

ATOMIZING DEVICES AND METHODS FOR SPRAY CASTING

The present invention generally relates to the spray-deposited production of a product on a moving substrate and, more particularly, is concerned with devices for gas-atomizing a molten metal stream to produce a spray of metal particles providing an improved distribution of temperature through the deposit cross-section and reduced bottom surface porosity in the deposit.

The present invention also generally relates to metal particle spray-deposited production of a product and, more particularly, is concerned with a magnetic field-generating nozzle for atomizing a molten metal stream into a spray of metal particles. The present invention also generally relates to metal particle spray-deposited production of a product and, more particularly, is concerned with an ejection nozzle for imposing a high angular momentum on a molten metal stream to cause break-up of the stream into a spray of metal particles.

A commercial process for production of spray-deposited, shaped preforms in a wide range of alloys has been developed by Osprey Metals Ltd. of West Glamorgan, United Kingdom. The Osprey process, as it is generally known, is disclosed in detail in U.K. Pat. Nos. 1,379,261 and 1,472,939 and U.S. Pat, Nos. 3,826,301 and 3,909,921 and in publications entitled "The Osprey Preform Process" by R.W. Evans et al. Powder Metallurgy, Vol. 28, No. 1 (1985), pages 13-20 and "The Osprey Process for the

Production of Spray-Deposited Roll, Disc, Tube and Billet Preforms" by A.G. Leatham et al. Modern Developments in Powder Metallurgy, Vols. 15-17 (1985), pages 157-173. The Osprey process is essentially a rapid solidification technique for the direct conversion of liquid metal into shaped preforms by means of an integrated gas-atomizing/spray-depositing operation. In the Osprey process, a controlled stream of molten metal is poured into a gas-atomizing device where it is impacted by high-velocity jets of gas, usually nitrogen or argon. The resulting spray of metal particles is directed onto a "collector" where the hot particles re-coalesce to form a highly dense preform. The collector is fixed to a mechanism which is programmed to perform a sequence of movements within the spray, so that the desired preform shape can be generated. The preform can then be further processed, normally by hot-working, to form a semi-finished or finished product.¹

The Osprey process has also been proposed for producing strip or plate or spray-coated strip or plate, as disclosed in U.S. Patent No. 3,775,156 and European Pat. Appln. No. 225,080. For producing these products, a substrate or collector, such as a flat substrate or an endless belt, is moved continuously through the spray to receive a deposit of uniform thickness across its width. Heretofore, extensive porosity typically has been observed in a spray-deposited preform at the bottom thereof being its side in contact with the substrate or collector. This well known phenomenon, normally undesirable, is a particular problem in a thin gauge product, such as strip or tube, since the porous region may comprise a significant percentage of the product thickness. The porosity is thought to occur when the initial deposit layer is cooled too rapidly by the substrate, providing insufficient liquid to feed the inherent interstices between splatted droplets.

In the production of strip by the Osprey process, a gas-atomizing device is typically used. As disclosed in the above-cited U.S. Patent No.' 3,775,156 and European Pat. Appln. No. 225,080, the gas-atomizing device can be a symmetrical arrangement of jets or, alternatively, a single annular-shaped gas opening or annulus, surrounding the stream of molten metal. The gas-atomizing device converts the molten metal stream into a divergent spray cone of molten metal particles. The bottom surface porosity of the strip originates from the low mass density of particles in the leading region of the spray cone.

Insufficient atomized particles are supplied in Jthis region of the spray to maintain sufficient liquid to fill voids even when the center region of the spray is optimally producing high density interior structure in the deposit.

One approach of the prior art for eliminating these problems is preheating the substrate to minimize or reduce the rate of heat transfer from the initial deposit to the substrate so that some fraction liquid is always available to feed voids created during the spray deposition process. However, it is often difficult to effectively preheat a substrate in a commercial spray deposit system because of the cooling effects of the high velocity recirculating atomizing gas. Further, preheating a substrate increases the potential for the deposit sticking to the substrate. Therefore, a need exists for an alternative approach to elimination of the porosity problem particularly in thin gauge product produced by the above-described Osprey spray- deposition process. The present invention provides a gas atomizing device designed to satisfy the aforementioned needs. The gas-atomizing device generates a spray cone of metal particles having an improved, more uniform, distribution of temperature through the deposit cross-section and reduced bottom surface porosity in the deposit.

The gas-atomizing device according to one aspect of the present invention produces a divergent spray cone whose central axis projects angularly away from the central axis of the vertical stream in a direction downstream of the moving-substrate. The leading edge of the spray cone has less distance to travel to the substrate whereby hotter particles reach the substrate during the initial deposit. Additionally, as a result of gravity, more molten metal particles will segregate to the bottom, or leading region, of the spray cone. On the other hand, the prior art gas-atomizing device produces a divergent spray cone whose central axis projects coincident with the central axis of the vertical stream with more of the molten particles located centrally in the middle of the spray cone. Hence, the gas-atomizing device of the present invention provides a higher fraction of liquid in the initial deposits and closer to the substrate than the prior art gas-atomizing device, thus promoting improved temperature distribution through the cross-section of the deposit and minimal porosity in the bottom surface of the deposit. According to one specific form of the present invention, an asymmetrical gas-atomizing device and method is provided which is designed to satisfy the aforementioned needs. The asymmetrical gas-atomizing device generates one-sided shear forces for breaking up a molten metal stream into a spray cone of metal particles having an improved, more uniform, distribution of temperature through the deposit cross-section and reduced bottom surface porosity in the deposit.

The gas-atomizing device of the present invention asymmetrically, relative to the central axis of the molten metal stream, impacts and breaks up the stream from one side of the stream. By comparison, the prior art gas-atomizing_.device symmetrically, relative to the central axis of the molten metal stream, impacts and breaks up the stream from all sides or directions about the stream.

The asymmetrical gas-atomizing device of the present invention thus produces a divergent spray cone whose central axis projects angularly away from the central axis of the vertical stream. As a result of gravity, more molten metal particles will segregate to the bottom, or leading region, of the spray cone.

In the Osprey process, the gas-atomizing jets break up the molten metal stream and produce the spray of metal particles by impact from high pressure gas flows. It is thought that the ultrasonic shock wave of these gas flows is responsible for disrupting the melt stream and causing droplet or particle formation. A problem with this technique is the amount of gas necessary to cause droplet formation. This great quantity of gas requires expensive gas handling equipment. Furthermore, gas flows away from the melt stream carry away small droplets of metal. These small particles in the exhaust gas reduce process yield and remove what are potentially the most useful component. Additionally, the gas may result in porosity in the final product.

Therefore, a need exists for an alternative approach for producing break-up of the molten metal stream into a particle spray which avoids the problems associated with gas atomization.

The present invention provides a magnetic field-generating atomizing nozzle designed to satisfy the aforementioned needs. Magnetic field generated by the nozzle of the present invention are used to destabilize the molten metal stream so as ^ o cause atomization thereof. The magnetic driving field generated by the magnetic atomizing nozzle generates eddy currents which produce an induced field in the metal stream opposing the driving field and creating a torque which causes the stream to break up upon exiting the driving field.

The advantages of non-gaseous magnetic field atomization are both economic (no gas costs) and technical (no loss of fine particles via entrapment in the gas flow and elimination of the porosity in the final product due to the use of gas) . Further, since magnetic interactions with liquid metal sheets are geometrically favored the construction of a slotted nozzle for magnetically atomizing the melt stream would preclude the need to oscillate/process conventional gas-atomizing nozzles to optimize coverage and compaction. In accordance with this aspect of the present invention, there are two configurations of the magnetic atomizing nozzle for generating two generic magnetic field geometries. In one configuration, the nozzle utilizes a pair of spaced magnetic poles, such as provided by Helmholtz coils, for generating a transverse magnetic field geometry across the stream. In the other configuration, the nozzle employs a solenoid for generating a solenoidal magnetic field geometry generally parallel to the stream.

Preferably, the magnetic field of each geometry is a high frequency AC field since better coupling between the field and stream occurs and more eddy currents are induced at higher frequency.

Further, in accordance with the aspect of the present invention, the two generic magnetic field geometries generated by the two nozzle configurations can be used in tandem. Also, variations on either field geometry can be obtained by choosing pole geometry and/or winding patterns.

Some techniques of centrifugal atomization have been used in the prior art to produce particles or droplets of molten metal. These techniques include rotating consumable electrodes and rotating molten metal receiving cups. It has been found that rotation speeds of several thousand RPM are sufficient to create the desired particles. However, there are drawbacks associated with each of these prior art techniques. Feedstock must be in the form of solid cylinders to be used as consumable electrodes. In principle, a melt stream can be used to fill a rotating cup. However, splashing of the melt stream during pouring into the rotating cup can be a significant problem. Further, low throughput is a drawback with both techniques.

Therefore, a need exists for an alternative approach for producing break-up of the molten metal stream into a particle spray which avoids the problems associated with gas atomization and the drawbacks of prior art centrifugal atomization techniques. The present invention according to this aspect of the invention provides an ejection nozzle designed to satisfy the aforementioned needs. The ejection nozzle of the present invention mechanically imposes a high angular momentum on a molten metal stream to cause break-up of the stream into a spray of metal particles. .Higher throughput can.be expected from using the ejection nozzle of the present invention than from using the prior art centrifugal atomization techniques. In accordance with this aspect of the present invention, there are two basic versions of the ejection nozzle. In one version the nozzle is stationary, whereas in the other version the nozzle rotates. The ejection nozzles have different configurations and modes of operation.

More particularly, the stationary ejection nozzle has a flow orifice with internal angular elements, such as spiral grooves, which engage the moving molten metal stream to impart angular momentum to the melt stream and produce stream break-up. The rotating ejection nozzle has a flow channel which engages the moving molten stream and causes it to rotate with the nozzle as it passes there through, rendering the stream unstable and subject to break-up when it leaves the rotating nozzle. The engagement between the flow channel of the nozzle and the melt stream can be augmented by internal elements, such as notches or serrations. The internal elements at the orifice of the nozzle may be chosen as to provide an appropriate shape to the exiting mold stream, i.e.; small streamlets. Furthermore, the rotating ejection nozzle can be driven by any suitable mechanism, including either mechanical or pneumatic means.

Also, in accordance with this aspect of the present invention, the two nozzles can be combined to impart angular momentum and accomplish melt stream break-up. For example, a stationary grooved nozzle can be used to feed a rotating nozzle.

Thus, the concept underlying this aspect of the present invention, being applicable to both the stationary and rotating nozzles, is to impart high angular momentum to the melt stream while confined within the nozzle so that the melt stream, upon exiting the nozzle orifice, will decompose into a spray of particles as the metal moves radially due to rotational inertia. The size of the particles will be a function of the magnitude of the angular momentum and the surface tension of the metal.

These and other features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention. In the course of the following detailed description, reference will be made to the attached drawings in which:

Fig. 1 is a schematic view, partly in section, of a prior art spray-deposition apparatus for producing a product on a moving substrate, such as in thin gauge strip form.

Fig. 2 is a fragmentary schematic elevational view, partly in section, of one modified form of the spray-deposition apparatus employing an asymmetrical gas-atomizing device in accordance with the present invention.

Fig. 3 is a graph comparing the respective temperature distributions across the spray cones produced by the prior art symmetrical gas-atomizing device and the asymmetrical gas-atomizing device of the present invention.

Fig. 4 is a fragmentary schematic elevational view, of another modified form of the spray-deposition apparatus employing the gas-atomizing device of the present invention.

Figure 5 is a fragmentary schematic elevational view, partly in section, of another modified form of the spray-deposition apparatus employing a gas-atomizing device in accordance with the present invention.

Figure 6 is a graph comparing the respective temperature distributions across the spray cones produced by the prior art gas-atomizing device and the gas-atomizing devices of the present invention.

Figures 7-9 are fragmentary schematic elevational views, partly in section, of further embodiments of a gas-atomizing device of the present invention. Figure 9A is a horizontal sectional view of the embodiment shown in Figure 9 taken along the lines 9A-9A of Figure 9.

Figure 10 is a fragmentary schematic elevational view, partly in section, of a further embodiment of a gas-atomizing device of the present invention.

Figure 10A is a horizontal sectional view of the embodiment of Figure 10 taken along the lines 10A-10A of Figure 10.

Figure 11 is a fragmentary schematic elevational view, partly in section, of yet another embodiment of a gas-atomizing device of the present invention. Figure 12 is a fragmentary schematic elevational view, partly in section, of yet another embodiment of a gas-atomizing device of the present invention.

Figure 13 is a fragmentary schematic elevational view, partly in section, of yet a further embodiment of the present invention.

Figure 13A is a horizontal sectional view of the embodiment shown in Figure 13 taken along the lines 13A-13A of Figure 13, and Fig. 14 is a fragmentary schematic view, partly in section, of one modified form of the spray-deposition apparatus employing a first configuration of a magnetic atomizing nozzle for generating a first magnetic field geometry in accordance with the present invention.

Fig. 15 is a fragmentary schematic view, partly in section, of another modified form of the spray-deposition apparatus employing a second configuration of a magnetic atomizing nozzle for generating a second magnetic field geometry in accordance with the present invention.

Fig. 16 is a fragmentary schematic view, partly in section, of still another modified form of the spray-deposition apparatus employing a tandem arrangement of the first and second nozzle configurations.

Fig. 17 is a fragmentary schematic view, partly in section, of one modified form of the spray-deposition apparatus employing a first version of an angular momentum generating ejection nozzle in accordance with the present invention.

Fig. 18 is a fragmentary schematic view, partly in section, of another modified form of the spray-deposition apparatus employing a second version of an angular momentum generating ejection nozzle in accordance with the present invention.

Fig. 19 is a schematic view, partly in section, of the second nozzle version having a mechanical mechanism coupled thereto for driving the rotation of the nozzle.

Fig. 20 is a schematic view, partly in section, of the second nozzle version having a pneumatic mechanism coupled thereto for driving the rotation of the nozzle.

Fig. 21 is a fragmentary schematic view, partly in section, of still another modified form of the spray-deposition apparatus employing a combination of the first and second nozzle versions.

Referring now to the drawings, and particularly to Fig. 1, there is schematically illustrated a prior art spray-deposition apparatus. generally designated by the numeral 10, being adapted for continuous formation of products. An example of a product A is a thin gauge metal strip. One example of a suitable metal B is a copper alloy. The spray-deposition apparatus 10 employs a tundish 12 in which the metal B is held in molten form. The tundish 12 receives the molten metal B from a tiltable melt furnace 14, via a transfer launder 16, and has a bottom nozzle 18 through which the molten metal B issues in a stream C downwardly from the tundish 12.

Also, a gas-atomizing device 20 employed by the apparatus 10 is positioned below the tundish bottom nozzle 18 within a spray chamber 22 of the apparatus 10. The atomizing device 20 is supplied with a gas, such as nitrogen, under pressure from any suitable source. The gas-atomizing device 20 which surrounds the molten metal stream C has a plurality of jets 20A symmetrically positioned about the stream c. The atomizing gas is thereby impacted or impinged on the stream from all sides and directions about the stream so as to convert the stream into a spray D of atomized molten metal particles, broadcasting downwardly from the atomizing device 20 in the form of a divergent conical pattern. If desired, the atomizing device 20 can be moved transversely in side-to-side fashion for more uniformly distributing the molten metal particles.

Further, a continuous substrate system 24 employed by the apparatus 10 extends into the spray chamber 22 in generally horizontal fashion and in spaced relation below the gas atomizing device 20. The substrate system 24 includes drive means in the form of a pair of spaced rolls 26, an endless substrate 28 in the form of a flexible belt entrained about and extending between the spaced rolls 26, and support means in the form of a series of rollers 30 which underlie and support an upper run 32 of the endless substrate 28. The substrate 28 is composed of a suitable material, such as stainless steel. An area 32A of the substrate upper run 32 directly underlies the divergent pattern of spray D for receiving thereon a deposit E of the atomized metal particles to form the metal strip product A. The atomizing gas flowing from the atomizing device 20 is much cooler than the solidus temperature of the molten metal B in^'the stream C. Thus, the impingement of atomizing gas on the spray particles during flight and subsequently upon receipt on the substrate 28 extracts heat therefrom, resulting in lowering of the temperature of the metal deposit E below the solidus temperature of the metal B to form the solid strip F which is carried from the spray chamber 22 by the substrate 28 from which it is removed by a suitable mechanism (not shown) . A fraction of the particles overspray the substrate 28, solidify and fall to the bottom of the spray chamber 22 where they along with the atomizing gas flow from the chamber via an exhaust port 22A.

The mass density and temperature distribution or profile of the gas-atomized metal of the prior art divergent pattern of spray D is bell-shaped across the pattern. Typically, as shown in the graph (A) of Fig. 3, the center region D(C) of the prior art divergent spray pattern D is of higher temperature (and also of higher mass density) than the periphery or outer fringe regions of the spray pattern D(L) and D(T) . Because of the divergent configuration of the prior art spray pattern D and orientation of the substrate 28 relative thereto, the particles in the outer fringe regions thereof have to move through a greater distance to reach the horizontal substrate than particles in the center region thereof.

The porosity problem observed in the bottom surface of the strip F derives from the cooler, low mass density outer fringe regions of the prior art spray pattern D. In effect, this low mass density fringe region supplies .insufficient atomized particles to maintain sufficient liquid to fill voids even when the center region of the spray pattern D is optimized and is producing high density interior structure in the deposit E.

The overall result is a generally non-uniform temperature distribution through the cross-section of the deposit E. Particularly, referring to Figure 3, the inner portion of the deposit E formed by the leading region D(L) of the pattern D, being adjacent the cool substrate 28 and at a mass density and temperature corresponding to the left end of the graph (A) in Fig. 3, is cooler and lower in density than the intermediate portion of the deposit E formed by the center of the pattern D. The intermediate deposit portion, at a mass density and temperature corresponding to the middle D(C) of the graph (A), is also protected from gas impingement and thus remains hotter and more liquid tending to trap bubbles of gas. On the other hand, the outer portion of the deposit E formed by the trailing region D(T) of the spray portion D is at a mass density and temperature corresponding to the right end D(T) of the graph (A) . Like the inner portion of the deposit E, the outer deposit portion is cooler and less dense than the intermediate portion due to being composed of particles which have travel further before deposit and which make up the fringe of the spray cone. Also, the outer portion of the deposit E is cooler because it is subject to gas impingement. To overcome the above problem, the present invention involves modifying the configuration of the prior art symmetrical gas-atomizing device 20 of Fig. 1 to that of the improved asymmetrical gas-atomizing device 34 of Fig. 2. Instead of the plurality of jets 20A arranged in the prior art annular configuration about the molten metal -stream C, now one or more jets 34A are provided only at one side of the molten metal stream C and disposed at an inclined angle relative to the center axis of the stream. Such modification in the atomizing device configuration will bring about a change of the prior art spray pattern D to a spray pattern G of gas-atomized metal particles having a temperature (and also a comparable mass density) distribution or profile resembling that of graph (B) of Fig. 3.

Hence, the one-sided shear forces generated by the asymmetrically-positioned jet 34A produce a spray cone G providing a higher fraction of liquid in the initial deposits, thus promoting minimal porosity. Such temperature and mass density distribution of the gas-atomized metal particles in the spray cone G will result in an improved, more uniform, distribution of temperature through the cross-section of the deposit H and reduced bottom surface porosity in the deposit. The asymmetrical gas-atomizing device of the present invention thus produces divergent spray pattern G whose central axis I projects angularly away from the central axis of the vertical stream. As a result of gravity, with the asymmetrical gas-atomizing device 34 more molten metal particles will segregate to the bottom, or leading peripheral region G(L), of the spray cone or pattern G, resulting in the higher fraction of liquid in the initial deposits and closer to the substrate than in the center and trailing peripheral regions G(C), G(T) of the spray pattern G and also than with the prior art symmetrical gas-atomizing device 20, as represented by the left end of the graph (B) compared to the center and right end thereof in Fig. 3.

The upper run 32 of the substrate 28 can have an orientation relative to the spray pattern G as depicted in either Fig. 2 or Fig. 4. In either orientation, due to the higher density and temperature of metal particles in the leading region of the spray cone G a more uniform temperature distribution is achieved through inner, intermediate

I and outer cross-sectional portions of the deposit H and a reduction of porosity is achieved in the inner portion of the deposit.

More particularly, in the arrangement shown in Figure 2, the deposit-receiving area 32A of the substrate upper run 32 is orientated in a linear, inclined configuration relative to a horizontal plane, with the substrate moving in an upwardly direction as indicated by the arrow in Figure 2. The central axis I of the divergent spray pattern G is inclined with respect to the vertical as shown and may be normal to the deposit-receiving area 32A. With this arrangement, the distance required for the leading and trailing regions of the spray pattern G to reach the substrate may be about the same. However, the larger, more molten droplets will tend to segregate to the bottom edge of the pattern (the leading edge) thereby providing a higher fraction of liquid in the initial deposits.

In the arrangement shown in Figure 4, the deposit-receiving area of the substrate 28 is orientated in a linear horizontal configuration and moves in a direction indicated by the arrow. The central axis I of the divergent spray pattern G is inclined with respect to the vertical as shown. This arrangement results in the leading edge or region of the spray pattern G being closer to the substrate 28 than the trailing edge. With this arrangement there is a shorter distance for the hotter particles to reach the substrate 28 during the initial phase of the deposits thereby further increasing the relative fraction of liquid in the initial deposit.

With the configuration set forth herein, the leading, center and trailing_ι portions of the spray pattern are placed one on top of the other on the moving substrate to form, respectively, the bottom, intermediate and upper portions of the deposit H to form the strip J. The bottom portion of the deposit is disposed closest to, and the upper portion farthest from, the substrate, with the intermediate position therebetween. The higher fraction of particles in the leading edge of the spray and the shortened distance of travel to the upstream portion of the substrate area 32A makes more and higher temperature particles available, providing a higher fraction liquid in the inner portion of the deposit H thus promoting minimal porosity. Additionally, it has been found that with an asymmetrical gas-atomizing device of the type described herein, the porosity of the individual particles of the spray pattern have less gas porosity than particles produced with the prior art symmetrical gas-atomizing device. As a result, the overall gas porosity bf the deposit throughout its cross section is substantially reduced or eliminated. The present invention also involves modifying the configuration of the prior art gas-atomizing device 20 of Figure 1 to that of the improved gas-atomizing devices shown in Figures 5 and 7-13. Referring to Figure 5, one embodiment of a gas-atomizing device constructed in accordance to this invention comprises a circular annulus 35 having an annular plenum chamber 36 therein. The annulus 35 has an annular opening 38 therethrough having an axis 40, coincident with the axis of the annulus 35, and through which the molten stream C passes. Elongated outlets 42 are provided at the bottom of the annulus 35 which communicate with the plenum chamber 36. Each of the outlets 42 has an axis which is inclined inwardly toward the center line 40 of the annular opening 38. It is to be understood that there are a plurality of such outlets 42 on the planar bottom surface 44 of the annulus 35 spaced circumferentially around the axis 40 of the annular opening 38 at equal radial distance from the axis 40. The angle of inclination of the axes of all the elongated outlets 42 with respect to the planar bottom surface 44 of the annulus 35 is the same. The bottom surface 44 is perpendicular to the axis 40 of the annulus 40. The axis 40 of the annulus 35 is tilted with respect to the vertical axis 46 of the molten stream as shown such that the outlets 42a upstream of the molten stream C in respect to the moving substrate 28 are closer to the molten stream C flowing through the annular opening 38 than the outlets 42b downstream of the molten stream C. As a result, the atomizing gas exerts higher shear forces on the upstream side of the molten stream C. With this arrangement, the stream C of molten metal is atomized into a spray of molten droplets having a divergent, conical, spray pattern G which has a central axes I inclined with respect to the central axis 46 of the molten stream C in a direction downstream of the deposit receiving area of moving substrate 28. As shown in Figure 5, the deposit receiving area of the substrate 28 is orientated in a linear horizontal configuration and moves in a direction indicated by the arrow. With the central axes I of the divergent spray pattern G being inclined with respect to the vertical as shown, the arrangement results in the leading edge or region G(L) of the spray pattern G having less distance to travel to the substrate 28 than the trailing edge G(T) . Thus, there is a shorter distance for the hotter particles to reach the substrate 28 during the initial phase of the deposits thereby tending to increase the relative fraction of liquid in the initial deposit. Additionally, with the spray pattern G such that its central axis I is inclined with respect to the vertical, the larger more molten droplets would tend to segregate to the leading edge of the deposit, thereby providing a higher fraction of liquid in the initial deposits. The spray pattern produced in accordance with the aspect of the present invention has a temperature (and also a comparable mass density) distribution or profile resembling that of graph (B) of Figure 6. The temperature and the mass density of the leading edge G(L) of the spray pattern is greater. As a result, the substrate will first receive the desirable spray which provides a higher fraction of liquid in the initial deposits, thus promoting minimal porosity. The temperature and mass density distribution of the gas-atomizing metal particles in the spray cone G will result in an improved, more uniform, distribution of temperature through the cross-section of the deposit H and reduced bottom surface porosity in the deposit. Other embodiments of a gas atomizer constructed in accordance with the present invention and providing a spray pattern of the type shown in Figure 5 and having the advantages as discussed in connection therewith are shown in Figures 7-13.

Referring to Figure 7, the embodiment shown therein includes an annulus 50 which is generally circular in horizontal cross-section and which contains a plenum chamber 52 which receives the atomizing gas. The annulus 50 is provided with a central annular opening 54 through which the molten stream C passes. The axis 56 of the annular opening 54, which is also the axis of the annulus 50, is coincident with the vertical axis of the molten stream C. As will be noted, the bottom surface of the annulus 50 is tapered defining a planar surface 58 inclined at an angle with respect to the horizontal in a direction extending downwardly toward the upstream portion of the moving substrate 28. The bottom surface 58 of the annulus 50 is provided with elongated outlets 60 extending therefrom and in communication with the plenum chamber 52. Each of the outlets 60 has an axis inclined with respect to the bottom surface 58 in a direction whereby the axes all intersect at a point below the annulus 50. The angles of inclination of the axes of the outlets 60 with respect to the bottom surface 58 of the annulus 50 are equal. There are a plurality of such outlets 60 on the bottom surface spaced around the axis 56.

With the arrangement shown in Figure 7, the outlets 60a on the upstream side of the axis 56 of the molten stream C are closer to, and at a greater angle with respect to, the molten stream C than the outlets 60b on the downstream side. This arrangement results in higher shearing forces being applied to the molten stream C on the upstream side. This produces a conical divergent spray pattern G similar to that produced by the device in Figure 5 in which the central axis I of the spray pattern G is inclined with respect to the vertical axis of the molten stream C in a direction downstream of the moving substrate 28. In the embodiment shown in Figure 8, the gas atomizing device comprises a circular annulus 64 which includes an annular plenum chamber 66 therein for reception of the atomizing gas. A central annular opening 68 having a vertical axis 70, coincident with the axis of the annulus 64, is provided in the annulus 64 through which the molten stream C passess. Elongated outlets 72, which are in communication with the plenum chamber 66, extend from the bottom surface 74 of the annulus 64. Each outlet 72 has an axis extending at an angle inclined with respect to the horizontal bottom surface 74 such that all outlets are pointing downwardly and toward each other. The angle of inclination of the axes of all the outlets 72 with respect to the bottom surface 74 is the same. There are a plurality of outlets 72 on the bottom surface 74 spaced around the axis 70 and equidistant therefrom.

The annulus 64 is positioned such that its axis 70 is offset with respect to the axis 76 of the molten stream C in a horizontal direction downstream of the moving substrate 28. With this arrangement, the upstream outlets 72a are closer to the flowing molten stream C than the downstream outlets 72b, thus providing higher shear forces against the upstream side of the molten stream C. This produces the divergent spray pattern G as shown having a central axis I inclined with respect to the vertical axis 76 of the molten stream C in a direction downstream of the moving substrate.

In the embodiment shown in Figures 9 and 9A, the gas atomizing device comprises an annulus 80 which is elongated in a horizontal plane in a downstream direction relative to the moving substrate 28. As in the other embodiments, the annulus 80 includes an annular plenum chamber 82 which receives the atomizing gas. The annulus 80 is provided with an annular circular opening 84 through which the molten stream C passes and which has an axis 86 which is coincident with the vertical axis of the molten stream C.

The elongation of the annulus 80 in the horizontal direction is achieved by constructing the portion on the upstream side thereof such that it has an outer side surface 88 forming an arc of a circle in horizontal cross-section. The downstream portion thereof has an outer surface 90 which in a horizontal cross section is generally parabolic. The bottom surface 92 of the annulus 80 is provided with elongated outlets 94 which are inclined with respect to the bottom surface 92 such that their axes incline downwardly and toward each other at the same angle with respect to the horizontal bottom surface 92. The outlets 94a on the upstream side of the axis 86 of the annular opening 84 are arranged in a circular pattern. The outlets 94b on the down stream side, which is the downstream side of a plane passing through the axis 86 of the annular opening 84 and extending perpendicular to* he direction of movement -.of the substrate 28, follow the general outline of the parabola and thus, are increasingly further away from the axis 86 of the annular opening 84. With this arrangement, the outlets 94a on the upstream side of the annulus 80 are closer to the molten stream C flowing through the annular opening and produce higher shear forces against the molten stream C on the upstream side thereof resulting in the divergent spray pattern G with the inclined central axis I as shown.

Referring to Figures 10 and 10A, the gas atomizing device of this embodiment comprises a circular annulus 100 similar to that shown in Figure 5. It includes a plenum chamber 102 which receives the atomizing gas. An annular opening 104 through which the molten stream C passes has an axis 106 which, in this case, is coincident with the vertical axis of the molten stream C. A plurality of elongated outlets 108 extend from the bottom surface 110 of the annulus 100 and are in communication with the plenum chamber 102. The outlets 108 are equally spaced around the axis 106 and are radially equidistant therefrom. The outlets 108 each have an axis which inclines at equal angles from the horizontal bottom surface 110 in a direction converging toward each other.

As shown in Figure 10A, the plenum chamber 102 is divided into two separate sections 102a and 102b by means of a solid divider 112. The line of division extends in a plane which passes through the axis 106 of the central opening 104 and is perpendicular to the direction of movement of the substrate 28. This arrangement forms a first plenum chamber section 102a upstream of the axis 106 in relation to the movement of the substrate 28 and a second plenum chamber section 102b downstream of the axis 106 in relation to the first chamber section 102a. With this arrangement, relatively high pressure atomizing gas is admitted to the upstream plenum chamber section 102a and relatively low pressure atomizing gas is admitted to the downstream chamber section 102b. The high pressure atomizing gas exiting from the outlets 108a in communication with the plenum chamber section 102a on the upstream side of the annulus 100 will be at a relatively higher pressure than the gas exiting from the downstream outlets 108b which are in communication with the low pressure chamber section 102b. This will produce a higher shearing force against the upstream side of the molten stream C providing the divergent spray pattern G having an inclined central axis I as shown. As an alternative to providing high and low pressure gas to the two separate plenum chamber sections 102a and 102b, the two sections may be separated by a semipermeable membrane and the 5 atomizing gas admitted only to the upstream chamber section 120a. The semipermeable membrane will permit the gas to flow to the downstream chamber section 102b, but such gas will be at a lower pressure. Thus the gas exiting from the upstream outlets 108a will

10 be at a higher pressure than the gas exiting from the downstram outlets 108b resulting in the same spray pattern G as produced with the dual supply of gas at different pressures.

In the embodiment shown in Figure 11, the

15 gas atomizing device is an annulus 120, circular in cross-section, and provided with an annular plenum chamber 122. An annular opening 124 extends through the annulus 120 having a vertical axis 126 coincident with the axis of the molten stream C. A plurality of

20. elongated outlets 128 are provided on the horizontal bottom surface 130 of the annulus 120 spaced circumferentially thereon at equidistances from the axis 126. In this embodiment, the axes of the outlets 128a on the upstream side of the axis 126

25 have an angle of inclination with respect to the horizontal bottom surface 130 of the annulus of a lesser degree than the axes of the outlets 128b on the downstream side of the axis 126. With this arrangement, the upstream outlets 128a direct the 0 atomizing gas to the stream of.molten metal before the gas emanating from the downstream outlets and at a sharper angle, providing the spray pattern G as shown having an inclined axis I. In the embodiment shown in Figure 12, the gas atomizing device is an annulus 140 having an annular plenum chamber 142 and a central annular opening 144 therethrough. The annular opening 144 5 has a vertical axis 146 coincident with the axis of the molten stream C. A plurality of elongated outlets 148 are provided on the horizontal bottom surface 150 of the annulus 140 symmetrically spaced around the axis 146 at an equidistance therefrom.

10. The axes of the outlets 148 are inclined at equal angles with respect to the bottom surface 150 so that the axes converge at a point below the annulus 140. In this particular case, the outlets 148b on the downstream side of the vertical axis 146 have an

15 opening which diverges outwardly along its axis in an outwardly direction as shown. The upstream outlets 148a have openings with a constant or converging diameter which is less than the largest diameter of the openings of the outlets 148b in the downstream

2Q side. With this arrangement, the pressure of the gas after it exits from the downstream outlets 148b will be less than that of the gas exiting from the upstream outlets 148a thereby providing the spray pattern G with an inclined central axis I.

25 Figures 13 and 13A show yet another embodiment in which the gas atomizing device is in the form of a circular annulus 160 provided with an annular plenum chamber 162. An annular opening 164 through which the molten stream C passes is provided

30 in the annulus 160 and has a vertical axis 166 coincident with the vertical axis of the molten stream C. Elongated outlets 168 are provided in the horizontal bottom surface 170 of the annulus 160. The axes of the outlets 168 are inclined at equal angles with respect to the horizontal bottom surface 170 so that they converge below the annulus 160.

In the embodiment shown in Figures 13 and 13A, the outlets 168 are circumferentially spaced around the bottom surface at equal radial distances from the axis 166 of the opening 164. In this particular case, there are a greater number of outlets 168 on the upstream side of the axis 166 as compared with the downstream side. This increases the volume of gas acting on the molten stream on the upstream side thereof, which produces the spray pattern G having the inclined central axis I.

Each of the gas-atomizing devices as shown in Figures 5-13 produces a divergent spray pattern G whose central axis I projects angularly away from the central axis of the vertical stream in a direction downstream of the moving substrate 28. As a result of gravity, with the gas-atomizing devices of the present invention more molten metal particles will segregate to the bottom, or leading peripheral region G(L), of the spray cone or pattern G, resulting in the higher fraction of liquid in the initial deposits and closer to the substrate than in the center and trailing peripheral regions G(C), G(T) of the spray pattern G and also than with the prior art symmetrical gas-atomizing device 20, as represented by the left end of the graph (B) compared to the center and right end thereof in Fig. 6. Additionally, the arrangement of the present invention results in the leading edge or upstream region G(L) of the spray pattern G being closer to the substrate 28 than the trailing edge G(T) . With this arrangement there is a shorter distance -for the hotter particles to reach the substrate 28 during the initial phase of the deposits thereby further increasing the relative fraction of liquid in the initial deposit.

With the configuration of the spray pattern G as set forth herein, the leading, center and trailing portions of the spray pattern are placed one on top of the other on the moving substrate to form, respectively, the bottom, intermediate and upper portions of the deposit H to form the strip. See Figure 5. The bottom portion of the deposit is disposed closest to, and the upper portion farthest from, the substrate, with the intermediate position therebetween. The higher fraction of particles in the leading edge of the spray and the shortened distance of travel to the upstream portion of the deposit receiving area of the substrate 28 makes more and higher temperature particles available, providing a higher fraction liquid in the inner portion of the deposit H thus promoting minimal porosity.

A problem that may arise using the prior art technique of gas atomization to convert the molten metal stream C into the metal particle spray D is the large amount of gas necessary to cause droplet or particle formation. This great quantity of gas requires expensive gas handling equipment. Furthermore, gas flows away from the melt stream carry away small droplets of metal. These small particles in the exhaust gas reduce process yield and remove what are potentially the most useful component. One solution to this problem according to another aspect of the present invention is to employ a magnetic field-generating device instead of the spray atomizer 20 for atomizing or breaking up the ⁵ molten metal stream C into the metal particle spray D. The magnetic driving field generated by the magnetic atomizing device generates eddy currents in the melt stream C which produce an induced field in the stream opposing the driving field and creating a

10 torque which causes the stream to break up upon exiting the driving field.

Referring now to Figs. 14 and 15, in accordance with the present invention there are schematically illustrated two different

15 configurations of the device for generating two generic magnetic field geometries which each impose a body force, e.g., a torque, on the molten metal stream C to cause break-up of the stream into the spray D of metal particles. In the one configuration

20 of Fig. 5, the device is a magnetic atomizing nozzle 234 which utilizes a pair of spaced magnetic poles 236, 238. For example, the poles 236, 238 are defined by Helmholtz coils 240, 242 supported by a nozzle body 244 and located at a pair of opposite

25 sides of the body. The nozzle body 244 has an orifice 246 which receives the stream C therethrough and the coils 240, 242 located at opposite sides of the orifice 246 generate a magnetic field M. between the poles 236, 238 of transverse geometry

30. extending across the stream C and body orifice 246.

In the other configuration of Fig. 15, the device is a magnetic atomizing nozzle 248 which has a body 250 with an orifice 252 the same as the nozzle 234. The nozzle 248 employs a solenoid coil 254 supported by the body 250 in surrounding relation to the orifice 252 for generating a magnetic field M₂ of solenoidal geometry extending parallel to the 5 stream C and through the body orifice 252.

The break-up mechanism of the two fields M- and M₂ is that of a body force which breaks (negatively accelerates) the melt stream. Any field shape which permits the melt stream to start from a Q zero field region and enter a region with a magnetic field will do this somewhat. Since the melt stream is moving, even a static field will work minimally.

The important difference between the ₅ transverse and solenoidal field M. and M_ is in orientation of induced eddy currents. The eddy currents will produce an induced field which opposes the driving field. Thus, a transverse driving field M- will produce eddy currents whose normal is Q perpendicular to the melt stream. This is probably somewhat inefficient for coupling between the field and stream but will result in some torque. The solenoidal driving field M_ will produce eddy currents whose normal is along the melt stream. This 5 will probably produce the better coupling of the two basic geometries.

Preferably, the magnetic field of each geometry is a high frequency AC field since better coupling between the field and stream occurs and more Q eddy currents are induced at higher frequency. As mentioned above, a static magnetic field will cause some breaking action since the melt stream is moving. However since power (and coupling) are fuήctions of frequency, it is more helpful to achieving the objective of stream break-up to deliver an AC field.

For a high delivered power, it is necessary to run at a high frequency. Similarly more eddy currents are induced at higher frequency. Finally, coupling of an electromagnetic wave to a conductor is a function of electromagnetic frequency and conductor size/geometry. However, the desired process has a large distribution in both size and geometry. It starts with a large infinite cylinder and winds up with small spheres. To provide for efficient use of the electromagnetic field, it may be useful to chirp (pulse) the frequency of the signal.

Variations on either field geometry can be obtained by choosing pole geometry and/or winding patterns. Also, as seen in Fig. 16, the two generic magnetic field geometries M, , M« generated by the configurations of the two nozzles 234, 248 can be used in tandem.

Another solution presented by the present invention is to employ an angular momentum generating device instead of the spray atomizer 20 for breaking up the molten metal stream C. Referring now to Figs. 17 and 18, in accordance with the present invention there are schematically illustrated two different versions of the device for mechanically imposing a high angular momentum on the molten metal stream C to cause break-up of the stream into the spray D of metal particles. In the one version of Fig. 17, the device is a stationary injection nozzle 334. In the other version of Fig. 18, the device is a rotating injection nozzle 336. The ejection nozzles 334, 336 have different configurations and modes of operation. More particularly, as can be seen in Fig. 17, the stationary ejection nozzle 334 has a body 338 with a flow channel 340 extending therethrough. Preferably, the channel 340 gradually expands in 5 diameter from a top entry end 340A to a bottom exit end 340B thereof. The body 338 has a plurality of internal angular elements 342, such as spiral grooves, which communicate with the channel 340. The elements 342 engage the moving molten metal stream C 0 and mechanically impart angular momentum thereto as it passes through the orifice 340. The angular momentum so imparted renders the rotating stream C unstable and produces its break-up into the molten metal spray D upon exiting the orifice 340. 5 As shown in Fig. 18, the rotating ejection nozzle 336 has a body 344 with a flow channel 346 extending therethrough. As in the case of the stationary ejection nozzle 334, the channel 346 of the rotating ejection nozzle 336 preferably gradually Q expands in diameter from a top entry end 346A to a bottom exit end 346B thereof. The body 344 has a plurality of internal elements 348, such as notches or serrations, which communicate with the channel 346. The internal elements 348 engage the moving 5 molten stream and mechanically impart angular momentum to it by causing it to rotate with the nozzle 336 as it passes through the channel 346. The angular momentum so imparted renders the stream unstable and causes it to break-up into the molten 0 metal spray D when it leaves the rotating nozzle 336.

Furthermore, the rotating ejection nozzle 336 can be driven by any suitable mechanism. In Fig. 19, a mechanical drive mechanism 350 is illustrated. The mechanical drive mechanism 350 includes a drive chain 352 coupled between a drive sprocket (not shown) and a driven sprocket 354 attached on the exterior of the nozzle 336 for driving the rotation of the nozzle 336. In Fig. 20, a pneumatic drive mechanism 356 is shown. The pneumatic drive mechanism 356 includes an air flow conduit 358 providing a pressurized flow of air for rotatably driving a plurality of impeller blades 360 attached on the exterior of the nozzle 336 and thereby driving rotation of the nozzle.

Turning to Fig. 21, also in accordance with the present invention, the two ejection nozzle 334, 336 can be combined to impart angular momentum and accomplish melt stream break-up. For example, the two nozzles 334, 336 can be disposed in a tandem relation with one above the other. In this case, the top entry 346A of the flow channel 346 of the rotating nozzle 336 would have a diameter substantially equal to the diameter of the bottom exit end 340B of the flow channel 340 of the stationary nozzle 334. The bottom exit end 346B of the flow channel 346 of the rotating nozzle 336 may have a diameter substanially the same as, or larger than, the diameter of the top entry end 346A.

Thus, the concept underlying this aspect of the present invention, being applicable to both the stationary and rotating nozzles 334, 336, is to impart high angular momentum to the melt stream while confined in passing through the flow channel in the nozzle so that the melt stream, when later unconfined upon exiting the nozzle orifice, will decompose into a spray of particles as the metal moves radially due to rotational inertia. The size of the particles will be a function of the magnitude of the angular momentum and the surface tension of the metal. In the case of the rotating nozzle 336, as the melt stream flows through the nozzle, the metal will pick up an angular velocity equal to that of the nozzle. Thus, when the metal stream exits the rotating nozzle, it will be unstable and break up. The velocity vector of the particles will be a function of the linear momentum and angular momentum of the stream C. A gas stream may be used to adjust the velocity vector of the particles and/or to remove heat from the particles. The imparting of angular momentum to the stream and subsequent breakup thereof is assisted by the configuration of the nozzle orifice, i.e., the gradually expanding orifice and the notches or serrations. In the case of the stationary .nozzle 334, as the melt stream flows through the nozzle, the internal grooves will impart angular momentum to the melt stream much like rifling spins a bullet. The rate of spin is the product of the pitch of the grooves and the velocity of the melt stream. For pitches on the order of 1 rev/cm and melt stream velocities on the order of 1 m/sec, the stream rotation will be 6000 rpm. The stationary nozzle 334 provides a mechanically simpler scheme than the rotating nozzle 336 to obtain a high angular momentum stream. However, a disadvantage of the stationary nozzle 334 is that it is impossible to control stream velocity and rotation independently without changing nozzles. As mentioned above, the combination of the two rotation techniques is possible. For example, the stationary nozzle 334 could be used to feed the rotating nozzle 336. This combination would permit more control over stream conditions, but at the cost of additional mechanical complexity.

Claims

What is Claimed:

1. In a molten metal gas-atomizing spray-depositing apparatus, the combination characterized by:

(a) means for producing a stream of molten metal; and

(b) means for asymmetrically atomizing the molten metal stream into a divergent spray pattern of metal particles having a central region and leading and trailing peripheral regions on opposite sides of the center region such that the metal particles in the spray pattern at said leading peripheral region are of higher mass density than at said center and trailing peripheral regions.

2. The apparatus as recited in Claim 1, characterized in that said asymmetrical atomizing means includes at least one gas-atomizing jet disposed at one side of the molten metal stream.

3. The apparatus as recited in Claim 2, characterized in that said jet is disposed at an inclined angle relative to a center axis of the molten metal stream for producing the spray pattern having a central axis projecting angularly away from the center axis of the stream.

4. The apparatus as recited in Claim 1, characterized in that said atomizing means is disposed relative to the molten metal stream for producing asymmetrical shear forces against one side of the stream.

5. The apparatus as recited in Claim 1, further -characterized by:

(c) means movable along an endless path and in a direction generally normal to a central axis of said spray pattern for receiving a deposit of the metal particles in said spray pattern to form a product on said movable means.

6. The apparatus as recited in Claim 1, further characterized by:

(c) means movable along an endless path and in a direction generally inclined to a central axis of said spray pattern for receiving a deposit of the metal particles in said spray pattern to form a product on.said movable means.

7. The apparatus as recited in Claim 1, further characterized by:

(c) means movable along an endless path and having an area thereon for receiving a deposit of the metal particles, said deposit-receiving area of said movable means being oriented relative to said spray pattern to initially receive the metal particles of higher mass density in said leading peripheral portion thereof whereby a bottom surface of the deposit has reduced porosity.

8. In a molten metal gas-atomizing spray-depositing apparatus, the combination characterized by:

(a) means for producing a stream of molten metal;

(b) means for asymmetrically gas-atomizing the molten metal stream into a divergent spray pattern of metal particles having a central region and leading and trailing peripheral regions on opposite sides of the center region such that the metal particles in the spray pattern at said leading peripheral region are of higher mass density than at said center and trailing peripheral regions, said asymmetrical atomizing means including at least one gas-atomizing jet disposed at one side only of the molten metal stream; and

(c) means movable along an endless path and having an area thereon for receiving a deposit of the metal particles in said spray pattern thereof, said deposit-receiving area of said movable means being oriented relative to said spray pattern to initially receive the metal particles of higher mass density in said leading peripheral portion thereof whereby a bottom surface of the deposit -has reduced porosity.

9. The apparatus as recited in Claim 8, characterized in that said jet is disposed at an inclined angle relative to a center axis of the molten metal stream for producing the spray pattern having a central axis projecting angularly away from the center axis of the stream.

10. The apparatus as recited in Claim 8, characterized in that said atomizing means is disposed relative to the molten metal stream for producing asymmetrical shear forces against one side of the stream.

11. The apparatus as recited in Claim 8, characterized in that said movable means is movable along the endless path in a direction generally normal to central axis of said spray pattern.

12. The apparatus as recited in Claim 8, characterized in that said movable means is movable along the endless path in a direction generally inclined to a central axis of said spray pattern.

13. In a molten metal gas-atomizing spray-depositing method, the combination comprising the steps of:

(a) producing a stream of molten metal; and

(b) asymmetrically atomizing the molten metal stream into a divergent spray pattern of metal particles having a central region and leading and trailing peripheral regions on opposite sides of the center region such that the metal particles in the spray pattern at said leading peripheral region are of higher mass density than at said center and trailing peripheral regions.

14. The method as recited in Claim 13, characterized in that said atomizing includes producing asymmetrical shear forces against one side of the stream.

15. The method as recited in Claim 14, characterized in that said atomizing includes directing the shear forces at an inclined angle to a center axis of the molten metal stream.

16. The method as recited in Claim 13, further comprising the step of: (c) moving a substrate along an endless path and relative to said spray pattern for receiving a deposit of the metal particles in said spray pattern to form a product on said substrate, said substrate being oriented relative to said spray pattern to initially receive the metal particles of higher mass density in said leading peripheral portion thereof whereby a bottom surface of the deposit has reduced porosity.

17. The method as recited in Claim 16, characterized in that said substrate is moved in a direction generally normal to a central axis of said spray pattern.

18. The method as recited in Claim 16, characterized in that said substrate is moved in a direction generally inclined to a central axis of said spray pattern.

19. The method of claim 18 characterized in that said substrate is moved in a direction normal to the center axis of the molten stream.

20 In a molten metal gas-atomizing spray-deposition apparatus, the combination characterized by:

(a) means for producing a stream of molten metal;

(b) a gas atomizer for converting said stream of molten metal into a divergent spray pattern, said gas atomizer including an annulus through which said stream of metal flows, said annulus having a plenum chamber therein for receiving pressurized atomizing gas,

(c) outlets in said annulus communicating with said plenum chamber and spaced around the stream of molten metal metal, and (d) a substrate moving in a given direction and having a spray deposit receiving area in a plane substantially perpendicular to the axis of the stream of the molten metal passing through said annulus, the arrangement of said outlets and manifold being such that the central axis of the divergent spray pattern produced by the atomizing gas acting upon the molten stream is inclined with respect to the moving substrate in a direction downstream of the moving substrate.

21. The apparatus of claim 20 characterized in that the inclination of the central axis of the spray pattern is such that the upstream portion of the spray pattern travels a lesser distance to the substrate than the downstream portion.

22. The apparatus of claim 20 characterized in that the pressure of the atomizing gas exiting from the outlets positioned upstream of the axis of the molten stream in respect of the moving substrate is higher than the pressure of the gas exiting from the outlets positioned downstream thereof.

23. The apparatus of claim 20 characterized in that the axes of said outlets positioned upstream of said molten stream in respect to said moving substrate have a greater angle with respect to the axis of the molten stream than the axes of the outlets positioned downstream.

24. The apparatus of claim 20 characterized in that the exit of said outlets positioned upstream of said molten stream in respect to said moving substrate are closer to said molten stream than the outlets downstream thereof.

25. The apparatus of claim 20 characterized in that said annulus has a central axis, said outlets being spaced around and at equidistances from said central axis, said axis of said annulus being tilted with respect to the axis of said molten stream such that the upstream portion of the annulus in respect to the moving substrate is positioned closer to said substrate.

26. The apparatus of claim 25 characterized in that said annulus includes a planar bottom surface perpendicular to said central axis, said outlets being positioned on said bottom surface and having axes equally inclined with respect to said bottom surface.

27. The apparatus of claim 26 characterized in that said annulus is circular in a cross-section perpendicular to its central axis.

28. The apparatus of claim 20 characterized in that said annulus has a central axis coincident with the axis of said molten stream, said annulus including a planar bottom surface, said outlets being positioned on said bottom surface, said bottom surface being inclined downwardly with respect to a plane perpendicular to said central axis in a direction upstream of said moving substrate.

29. The apparatus of claim 28 characterized in that said annulus is circular in a cross section perpendicular to said central axis.

30. The apparatus of claim 20 characterized in that said annulus has a central axis, said outlets being spaced around and at equidistances from said central axis, said central axis being offset with respect to the axis of said molten stream passing through said annulus in a direction downstream in respect to the moving substrate.

31. The apparatus of claim 30 characterized in that said annulus includes a planar bottom surface perpendicular to said central axis, said outlets being positioned on said bottom surface and having axes equally inclined with respect to said bottom surface.

32. The apparatus of claim 20 characterized in that said annulus has an opening therethrough for the passage of said molten stream, said opening having an axis coincident with the axis of said molten stream, said annulus being elongated from said axis of said opening in a direction downstream in respect to said moving substrate.

33. The apparatus of claim 32 characterized in that said outlets on the downstream side of said opening in respect to said moving substrate are at progressively greater distances from said axis of said opening in a downstream direction than the outlets on the upstream side are from the axis of the central opening.

34. The apparatus of claim 33 characterized in that said outlets on said upstream side are positioned equidistant from the axis of said opening.

35. The apparatus of claim 33 characterized in that said annulus includes a planar bottom surface perpendicular to said central axis, said outlets being positioned on said bottom surface and having axes equally inclined with respect to said bottom surface.

36. The apparatus of claim 20 characterized in that said annulus has a central axis coincident with the axis of said molten metal flowing therethrough, said plenum chamber being divided into two sections, one section being upstream of said central axis in respect to said moving substrate, and the other section being downstream with respect to said central axis, a first set of outlets positioned on said annulus upstream of said central axis and communicating with said one section of said plenum chamber, a second set of outlets on said annulus on the downstream side of said central axis in communication with said other section, and means for admitting a higher pressure atomizing gas to said one section of said plenum chamber than to the other section.

37. The apparatus of claim 36 characterized in that said annulus includes a planar bottom surface perpendicular to said central axis, said outlets being positioned on said bottom surface and having axes equally inclined with respect to said bottom surface.

38. The apparatus of claim 20 characterized in that said annulus has a central axis coincident with the axis of said molten metal flowing therethrough, said plenum chamber being divided into two sections by a semipermeable membrane, one section being upstream of said central axis in respect to said moving substrate, and the other section being downstream with respect to said central axis, a first set of outlets positioned on said annulus upstream of said central axis and communicating with said one section of said plenum chamber, a second set of outlets on said annulus on the downstream side of said central axis in communication with said other section, and means for admitting atomizing gas to said one section of said plenum chamber.

39. The apparatus of claim 38 characterized in that said annulus includes a planar bottom surface perpendicular to said central axis, said outlets being positioned on said bottom surface and having axes equally inclined with respect to said bottom surface.

40. The apparatus of claim 20 characterized in that said annulus has a central axis coincident with the axis of said molten stream passing therethrough and a planar bottom surface perpendicular to said central axis, said outlets being positioned on said bottom surface and each having an axis, the axes of said outlets positioned upstream of said molten stream in respect to said moving substrate having a greater angle with respect to said axis of said molten metal than the axes of said outlets positioned downstream.

41. The apparatus of claim 20 characterized in that said annulus has a central axis coincident with the axis of said molten stream passing therethrough, said outlets being spaced around and at equidistances from said central axis, the openings of said outlets on the downstream side of said central axis in respect to said substrate having elongated openings diverging outwardly along their axes in an outward direction, the outlets on the upstream side having a diameter less than the largest diameter of the openings in the outlets on the downstream side whereby the gas exiting from said outlets with the larger openings is at a lower pressure than the gas exiting from the other outlets.

42. The apparatus of claim 41 characterized in that said annulus includes a planar bottom surface perpendicular to said central axis, said outlets being positioned on said bottom surface and having axes equally inclined with respect to said bottom surface.

43. The apparatus of claim 20 characterized in that said annulus has a central axis coincident with the axis of said molten metal passing therethrough, said annulus having a greater number of outlets on the upstream side of the central axis in respect to the moving substrate as on the downstream side.

44. The apparatus of claim 43 characterized in that said outlets are spaced equidistant from said central axis.

45. The apparatus of claim 44 characterized in that said annulus includes a planar bottom surface perpendicular to said central axis, said outlets being positioned on said bottom surface and having axes equally inclined with respect to said bottom surface.

46. In a molten metal spray-depositing apparatus, the combination characterized by:

(a) means for producing a stream of molten metal; and (b) means for generating a magnetic field in a predetermined geometry relative to the molten metal stream to induce a torque in the stream which results in atomizing of the molten metal of the stream into a spray of metal particles when the stream exits said field.

47. The apparatus as recited in Claim 46, characterized in that magnetic field of said predetermined geometry is a high frequency AC field.

48. The apparatus as recited in Claim 46, characterized in that said magnetic field-generating means is a magnetic atomizing nozzle.

49. The apparatus as recited in Claim 48, characterized in that said magnetic atomizing nozzle has a configuration utilizing a pair of spaced magnetic poles for generating a transverse magnetic field geometry.

50. The apparatus as recited in Claim 49, characterized in that said nozzle has a body with an orifice for receiving the stream therethrough, said pair of poles of said nozzle being defined by Helmholtz coils supported by said body at opposite sides of said orifice.

51. The apparatus as recited in Claim 48, characterized in that said magnetic atomizing nozzle has a configuration utilizing a solenoid coil for generating a solenoidal magnetic field geometry.

52. The apparatus as recited in Claim 51, characterized in that said nozzle has a body with an orifice for receiving the stream therethrough, said solenoid coil being supported by said body and surrounding said orifice.

53. The apparatus as recited in Claim 46, characterized in that said magnetic field-generating means is a pair of magnetic atomizing nozzles arranged in tandem one above the other for generating magnetic fields of different predetermined geometries.

54. The apparatus as recited in Claim 53, characterized in that magnetic field of each geometry is a high frequency AC field.

55. The apparatus as recited in Claim 53, characterized in that one of said magnetic atomizing nozzles has a configuration utilizing a pair of spaced magnetic poles for generating a transverse magnetic field geomety.

56. The apparatus as recited in Claim 55, characterized in that said one nozzle has a body with an orifice for receiving the stream therethrough, said pair of poles of said nozzle being defined by Helmholtz coils supported by said body at opposite sides of said orifice.

57. The apparatus as recited in Claim 53, characterized in that the other of said magnetic atomizing nozzles has a configuration utilizing a solenoid coil for generating a solenoidal magnetic field geometry.

58. The apparatus as recited in Claim 57, characterized in that said other nozzle has a body with an orifice for receiving the stream therethrough, said solenoid coil being supported by said body and surrounding said orifice.

59. In a molten metal spray-depositing apparatus, the combination characterized by:

(a) means for producing a stream of molten metal; and (b) a magnetic atomizing nozzle for generating a magnetic field in a predetermined geometry relative to the molten metal stream to induce a torque in the stream which results in atomizing of the molten metal of the stream into a spray of metal particles when the stream exits said field, said magnetic field of said predetermined geometry being a high frequency AC field.

60. The apparatus as recited in Claim 59, characterized in that said magnetic atomizing nozzle has a configuration utilizing a pair of spaced magnetic poles for generating a transverse magnetic field geomety.

61. The apparatus as recited in Claim 60, characterized in that said nozzle has a body with an orifice for receiving the stream therethrough, said pair of poles of said nozzle being defined by Helmholtz coils supported by said body at opposite sides of said orifice.

62. The apparatus as recited in Claim 60, characterized in that said magnetic atomizing nozzle has a configuration utilizing a solenoid coil for generating a solenoidal magnetic field geometry.

63. The apparatus as recited in Claim 62, characterized in that said nozzle has a body with an orifice for receiving the stream therethrough, said solenoid coil being supported by said body and surrounding said orifice.

64. In a molten metal spray-depositing apparatus, the combination characterized by:

(a) means for producing a stream of molten metal; and (b) means defining at least one flow channel for receiving the molten metal stream and having a configuration for confining the stream within said flow channel and mechanically imparting an angular momentum thereto as the stream passes ^" through said channel which renders the stream unstable and produces its break-up into a molten metal spray when the stream becomes unconfined upon exiting said orifice.

65. The apparatus as recited in Claim 64, characterized in that said flow channel defining means is a stationary ejection nozzle having a body with said flow channel extending therethrough.

66. The apparatus as recited in Claim 65, further characterized by: a plurality of internal elements defined on said body which are exposed to the stream within said flow channel for engaging the stream and mechanically imparting the angular momentum thereto as it passes through said channel.

67. The apparatus as recited in Claim 66, characterized in that said angular momentum imparting elements are a plurality of angular grooves defined in said body in communication with said channel.

68. The apparatus as recited in Claim 64, characterized in that said flow channel defining means is a rotating ejection nozzle having a body with said flow channel extending therethrough.

69. The apparatus as recited in Claim 68, further characterized by: a plurality of internal elements defined on said body which are exposed to the stream within said flow channel for engaging the stream and mechanically imparting the angular momentum thereto as it passes through said channel.

70. The apparatus as recited in Claim 69, characterized in that said angular momentum imparting elements are a plurality of notches defined in said body in communication with said channel for engaging the stream and causing it to rotate with said nozzle as it passes through said channel and thereby imparting angular momentum thereto which renders it unstable and produces its break-up into a molten metal spray upon exiting said orifice.

71. The apparatus as recited in Claim 68, further characterized by: means coupled to said rotating ejection nozzle for rotatably driving the same.

72. The apparatus as recited in Claim 71, characterized in that said driving means is a mechanical drive mechanism.

73. The apparatus as recited in Claim 71, characterized in that said driving means is a pneumatic drive mechanism.

74.. The apparatus as recited in Claim 64, characterized in that said channel gradually expands in diameter from an entry end to an exit end thereof.

75. In a molten metal spray-depositing apparatus, the combination characterized by:

(a) means for producing a stream of molten metal; and (b) means defining at least a pair of upper and lower flow channels being disposed in tandem relation one above the other for receiving the molten metal stream and having configurations for confining the stream within said flow channels and mechanically imparting an angular momentum thereto as the stream passes through said channels which renders the stream unstable and produces its break-up into a molten metal spray when the stream becomes unconfined upon exiting said lower one of said orifices.

76. The apparatus as recited in Claim 75, characterized in that said flow channels defining means is a pair of upper and lower ejection nozzles, each having a body with one of said flow channels therethrough.

77. The apparatus as recited in Claim 76, characterized in that said upper ejection nozzle is a stationary nozzle.

78. The apparatus as recited in Claim 76, further characterized by: a plurality of internal elements defined on said body of said upper ejection nozzle which are exposed to the stream within said flow orifice for engaging the stream and mechanically imparting the angular momentum thereto as it passes through said orifice.

79. The apparatus as recited in Claim 78, characterized in that said angular momentum imparting elements in said upper ejection nozzle are a plurality of angular grooves defined in said body in communication with said orifice.

80. The apparatus as recited in Claim 76, characterized in that said lower ejection nozzle is a rotating nozzle.

81. The apparatus as recited in Claim 80, further characterized by: a plurality of internal elements defined on said body of said lower ejection nozzle which are exposed to the stream within said flow channel for engaging the stream and mechanically imparting the angular momentum thereto as it passes through said orifice.

82. The apparatus as recited in Claim 81, characterized in that said angular momentum imparting elements in said lower ejection nozzle are a plurality of notches defined in said body in communication with said channel for engaging the stream and causing it to rotate with said nozzle as it passes through said orifice and thereby imparting angular momentum thereto which renders it unstable and produces its break-up into a molten metal spray upon exiting said lower orifice.

83. The apparatus as recited in Claim 80, further characterized by: means coupled to said rotating ejection nozzle for rotatably driving the same.

84. The apparatus as recited in Claim 83, characterized in that said driving means is a mechanical drive mechanism.

85. The apparatus as recited in Claim 83, characterized in that said driving means is a pneumatic drive mechanism.

86. The apparatus as recited in Claim 75, characterized in that said upper flow channel gradually expands in diameter from an entry end to an exit end thereof.