Patent Publication Number: US-2020282412-A1

Title: Passive Electrostatic CO2 Composite Spray Applicator

Description:
PRIORITY CLAIM 
     This application is a divisional continuing patent application of U.S. patent application Ser. No. 15/945,698, filed on Apr. 4, 2018 and issued as U.S. Pat. No. 10,661,287 on May 26, 2020, which claims the benefit of U.S. Provisional Patent Application No. 62/481,575, filed on Apr. 4, 2017, which is incorporated by reference in entirety. 
    
    
     BACKGROUND OF INVENTION 
     The present invention generally relates to spray applicators for forming and projecting a CO 2  Composite Spray (a trademark of CleanLogix LLC). More specifically, the present invention relates to a passive electrostatic spray nozzle and spray applicator assembly employing air, solid carbon dioxide, and additive particles such as organic solvents, coatings, paints, nanoparticles, microabrasives, and lubricants. 
     Use of CO 2  composite sprays for cleaning, cooling and/or lubrication is widely known in the art. For example, CO 2  composite sprays are typically employed during hard machining processes requiring cleaning, selective thermal control, and/or lubrication during turning, precision abrasive grinding, or dicing operations. In these applications, CO 2  composite sprays are employed to extend cutting tool or abrasive wheel life, and to improve productivity, dimensional tolerance, and surface finish. 
     There exist in the art several examples of CO 2  spray applicators which are employed to direct a CO 2  spray onto substrates, work pieces, and the like, in manufacturing or industrial processes. Such examples include U.S. Pat. Nos. 4,389,820, 4,806,171 and 5,725,154. Each of the aforementioned, however, have shortcomings in the application of sprays for cleaning, cooling and lubricating purposes, more especially the formation and application of CO 2  composite sprays beneficial for cooling and lubricating purposes. 
     For example, efficient and effective application of CO 2  composite sprays to machined substrates presents several challenges. When sufficiently high spray velocities are employed to provide enough energy to reach cutting zone surfaces, the majority of the spray tends to deflect from or stream around the cutting zone surfaces rather than impinge upon them. When low velocity sprays are employed, critical surfaces with recesses or complex surfaces cannot be penetrated effectively. For example, during application of CO 2 -based cooling-lubricating sprays it is observed that oil additive agglomerates into very large precipitations during transition from spray nozzles to surfaces. This phenomenon interferes with the even distribution of both CO 2  coolant particles and oil-based lubricant on machined surfaces and causes a large portion of the atomized spray to miss the substrate entirely if positioned at a location too far away from the substrate being machined, wasting a portion of the applied spray. This phenomenon occurs because the lubricating additive, such as an oil, and a cooling component, solid carbon dioxide particles, have certain physicochemical properties which are in complete opposition—namely high melt point and extremely low temperature, respectively. The temperature of the CO 2  particles (i.e., coolant) cause a flowing lubricant additive to solidify or gel prematurely before a uniform particle size and spray distribution can be established within the spray. This phenomenon inhibits uniform and homogenous dispersions. This is particularly the case when the mixing between the CO 2  solid particles and additive particles occurs within the nozzle or near the nozzle tip, resulting in inconsistent spray patterns and chemistry, and the nozzle becoming clogged with frozen and agglomerated oil and additives. 
     The prior art contains several examples of CO 2  spray application techniques for incorporating beneficial additives into a CO 2  composite spray. Examples include the addition of organic solvent additives to enhance spray cleaning performance, lubricant additives to enhance machining performance, and plasma additives to enhance surface modification for adhesive bonding. Examples of prior art in this regard include U.S. Pat. Nos. 5,409,418, 7,451,941, 7,389,941 and 9,352,355. In each of the aforementioned examples, an additive fluid comprising ions, solvent, oil, or a plasma, respectively, is added directly into a centrally disposed CO 2  particle spray using an injection means that is integrated with the CO 2  spray nozzle device, and in some cases include a means for actively charging the additive particles using high voltage and an electrode to enhance additive particle attraction, mixing and atomization. However, as already noted this type of injection scheme introduces constraints for spray additives which are inherently incompatible with the physicochemistry of the CO 2  spray at or near the spray forming nozzle. For example, high spray pressure and velocity, very low temperature, and passive electrostatic charging within the CO 2  particle nozzle body and exit introduce flow and mixing constraints for high melt point oils. High molecular weight natural oils such as soybean and canola oil provide the most superior lubrication qualities for machining applications but will gel or solidify at temperatures much higher than those present within or near the CO 2  particle nozzle exit. Exacerbating this problem is electrostatic fields and charges present during the formation and ejection of CO 2  particles within and from the nozzle. Spray charging using a high voltage electrode or passively charging (tribocharging) the additive and/or CO 2  particles, respectively, electrostatically charges and coalesces the subcooled high melting point oil films into large and sticky gels or masses near or within the nozzle tip which inhibits flow and injection into the CO 2  particle stream. Moreover, these larger additive particle masses once injected into the cold CO 2  particle stream and projected at a target surface inhibit gap penetration during to very low surface area, for example within a cutting zone comprising cutting tool, workpiece and chip crevice. The result is a spray with compositional variance over time—large particle masses with low surface area or a complete lack of lubricating particles. Moreover, the additive injection apparatus and methods of the prior art require an individual additive injection scheme for each CO 2  spray nozzle necessitating more complicated multi-spray configuration schemes in applications requiring larger aerial and radials spray densities for increased application productivity or utility. 
     BRIEF SUMMARY OF INVENTION 
     An apparatus for producing an electrostatically charged and homogeneous CO2 composite spray containing an additive for use on a substrate surface comprising: multiple nozzle electrodes can be positioned axis symmetrically about an additive injection nozzle; said nozzle electrodes can comprise an elongated body with a nozzle tip with a center through hole, and arising from the center through hole, there can be multiple or at least three axisymmetric through ports; the multiple or at least three through ports can form three landing guides  221  or support portions for centering and positioning an adjustable expansion tube assembly; the adjustable expansion tube assembly can comprise a first capillary within a second capillary; the first and the second capillaries can be adjustable within the center through hole; the additive injection nozzle can comprise a through ported and grounded additive injection nozzle body containing an additive delivery tube, and the grounded additive injection nozzle body can flow air to form an air-additive aerosol; whereby CO2 particles are flowed through the adjustable expansion tube assembly to create an electrostatic charge, which is shunted to the three landing guides  221  or support portions to electrostatically charge the nozzle electrodes, and the CO2 particles then mix with air to form air-CO2 aerosol; the electrostatically charged nozzle electrodes and the air-CO2 aerosol can passively charge the air-additive aerosol; the air-additive aerosol and the air-CO2 aerosol combine away from the nozzles to form the electrostatically charged air-additive-CO2 aerosol, which is projected at the substrate surface, whereby the CO2 particles and the additive interact to form the electrostatically charged and homogeneous CO2 composite spray containing an additive mixture in the space between the nozzles and the substrate surface; and the electrostatically charged and homogeneous CO2 composite spray containing an additive can be projected at the substrate surface; the least two nozzle electrodes can be arranged axis symmetrically about the additive injection nozzle; the additive can comprise flowable organic and inorganic liquids and solids; the substrate surface can be a cutting zone; the additive is a machining lubricant. 
     An apparatus for producing an electrostatically charged and homogeneous CO2 composite spray containing an additive for use on a substrate surface comprising: multiple nozzle electrodes positioned axis symmetrically about an additive injection nozzle; said nozzle electrodes comprising an elongated body with a nozzle tip with a center through hole, and arising from the center through hole are multiple axisymmetric through ports; near or proximate to said multiple through ports are landing guides for centering and positioning an adjustable expansion tube assembly; the adjustable expansion tube assembly comprises a first capillary within a second capillary; the first and the second capillaries are adjustable within the center through hole; the additive injection nozzle comprising a through ported and grounded additive injection nozzle body containing an additive delivery tube, and the grounded additive injection nozzle body flows air to form an air-additive aerosol; whereby CO2 particles are flowed through the adjustable expansion tube assembly to create an electrostatic charge, which is shunted to the landing guides to electrostatically charge the nozzle electrodes, and the CO2 particles then mix with air to form air-CO2 aerosol; the electrostatically charged nozzle electrodes and the air-CO2 aerosol passively charge the air-additive aerosol; the air-additive aerosol and the air-CO2 aerosol combine away from the nozzles to form the electrostatically charged air-additive-CO2 aerosol, which is projected at the substrate surface, whereby the CO2 particles and the additive interact to form the electrostatically charged and homogeneous CO2 composite spray containing an additive mixture in the space between the nozzles and the substrate surface; and the electrostatically charged and homogeneous CO2 composite spray containing an additive is projected at the substrate surface. Arising from the center through hole, there can be multiple or at least three axisymmetric through ports; and said multiple or at least three through ports form three landing guides for centering and positioning an adjustable expansion tube assembly; at least two nozzle electrodes are arranged axis symmetrically about the additive injection nozzle; the additive comprises flowable organic and inorganic liquids and solids; the substrate surface is a cutting zone; and the additive is a machining lubricant. 
     A nozzle electrode apparatus for producing an electrostatic field comprising: an elongated body with a nozzle tip with a center through hole, and arising from the center through hole are at least three axisymmetric through ports; said at least three through ports forming three landing guides for positioning an adjustable expansion tube assembly; the adjustable expansion tube assembly comprises a first capillary within a second capillary; the first and the second capillaries are adjustable in position within the through ported center hole; and whereby CO2 particles are flowed through the adjustable expansion tube assembly to create an electrostatic charge, which is shunted to the three landing guides to electrostatically charge the nozzle electrode; the apparatus can be constructed of semi-conductive material or metal; can be between 0.5 and 6.0 inches in length; and can be shunted to earth ground. 
     A method for treating a surface using an apparatus for producing an electrostatically charged and homogeneous CO2 composite spray containing an additive for use on a substrate surface comprising: multiple nozzle electrodes positioned axis symmetrically about an additive injection nozzle; said nozzle electrodes comprising an elongated body with a nozzle tip with a center through hole, and arising from the center through hole are multiple axisymmetric through ports; proximate to said multiple through ports are landing guides for centering and positioning an adjustable expansion tube assembly; the adjustable expansion tube assembly comprises a first capillary within a second capillary; the first and the second capillaries are adjustable within the center through hole; the additive injection nozzle comprising a through ported and grounded additive injection nozzle body containing an additive delivery tube, and the grounded additive injection nozzle body flows air to form an air-additive aerosol; whereby CO2 particles are flowed through the adjustable expansion tube assembly to create an electrostatic charge, which is shunted to the landing guides to electrostatically charge the nozzle electrodes, and the CO2 particles then mix with air to form air-CO2 aerosol; the electrostatically charged nozzle electrodes and the air-CO2 aerosol passively charge the air-additive aerosol; the air-additive aerosol and the air-CO2 aerosol combine away from the nozzles to form the electrostatically charged air-additive-CO2 aerosol, which is projected at the substrate surface, whereby the CO2 particles and the additive interact to form the electrostatically charged and homogeneous CO2 composite spray containing an additive mixture in the space between the nozzles and the substrate surface; and the electrostatically charged and homogeneous CO2 composite spray containing an additive is projected at the substrate surface, comprising the steps: positioning the apparatus at a first position away from the substrate surface; coating the substrate surface with the electrostatically charged and homogeneous CO2 composite spray containing the additive; stopping the coating of the substrate service with the electrostatically charged and homogeneous CO2 composite spray containing the additive; positioning the apparatus to a second position; and removing the additive from substrate surface by applying the electrostatically charged and homogeneous CO2 composite spray without the additive. This method also has the first position is between 6 and 18 inches from the substrate surface; a soak period of between 1 and 600 seconds follows the application of the electrostatically charged and homogeneous CO2 composite spray containing the additive at the first position; the second position is between 0.5 and 6 inches from the substrate surface; the additive comprises flowable organic and inorganic liquids and solids; the substrate surface is a manufactured surface. 
     The present aspect provides an apparatus for producing an electrostatically charged and homogeneous CO 2  composite spray containing an additive. The present invention overcomes the additive mixing and spray projection constraints of the prior art by positioning an additive injection and atomization nozzle into the center of and coaxial with two or more axis-symmetrically positioned and passively charged CO 2  composite spray nozzles. The novel cluster spray arrangement with electrostatic field and velocity driven gradients for mixing additive and CO 2  particles, and induced airflow to assist composite spray propulsion and delivery enables the formation of virtually any variety of CO 2  composite fluid spray compositions. Uniquely, a multi-component CO 2  composite fluid spray of the present invention is formed in space during transit to a target substrate, separated from the CO 2  and additive particle injection means, to eliminate interferences introduced by phase change and direct contact charging phenomenon. Axis-symmetrically clustered CO 2  sprays surrounding a centrally positioned additive spray flow creates adjustable and uniform electrostatic field and velocity gradients. 
     The present invention eliminates constraints imposed by the various physicochemical differences between additive spray chemistry and CO 2  spray chemistry. Any variety of fluid-entrained or flowable microscopic solids, light and viscous liquids, volatile and condensable gases, ionic, aqueous and non-aqueous liquids, and blends of same may be used. Moreover, discrete additives or blends of high boiling liquids, high melt point compounds, nanoparticles, ionic compounds, ionized fluids, ozonized fluids, dispersions, or suspensions may be used. Still moreover, the usefulness of a CO 2  composite spray is extended with the present invention. For example the present invention may be used to apply beneficial surface coatings such as rust prevention agents, primers, and paints immediately following CO 2  composite spray cleaning operations. 
     Another aspect of the present invention is to provide an apparatus and method for providing higher aerial and radial spray densities for a CO 2  composite spray to improve spray process productivity. Advantages of CO 2  composite sprays as compared to conventional CO 2  snow sprays is the ability to adjust CO 2  particle-in-propellant gas concentration, spray pressure, and spray mixture temperature. However, a limitation is low aerial and radial spray densities—spray area—for a CO 2  spray applicator. This limits productivity in many industrial applications and the current technique used to overcome this limitation is to employ multi-ported wide-spray nozzle arrays. However as already discussed, conventional means for adding beneficial additives makes this type of arrangement very complicated and incompatible with high melt point additive chemistries. 
     Another aspect of the present invention is to provide a novel electrical discharge machined (EDM) CO 2  composite spray mixing nozzle apparatus that is used to selectively position an adjustable CO 2  particle injection assembly (i.e., U.S. Pat. No. 9,221,057, FIG. 4B (502)) into a centermost region of a supersonic flow of propellant gas while simultaneously shunting electrostatic charge from the surfaces of the adjustable CO 2  particle injection assembly to create an electrostatically charged spray nozzle. 
     In still another aspect of the present invention, a surface pretreatment coating operation is followed by a precision cleaning operation. In certain cleaning applications surface contamination can be very difficult to remove using a CO 2  composite spray alone. The present invention teaches an exemplary pretreatment process for applying a uniform coat of (preferably) high boiling pretreat agents which first solubilize (or otherwise denature) the complex surface contaminant prior to or simultaneously during spray cleaning with a CO 2  composite spray. 
     Finally, the present invention is useful for forming hybrid CO 2  composite sprays using virtually any additive chemistry that intensifies a particular spray application such as precision cleaning, hard machining, precision abrasive grinding, adhesive bonding, or surface disinfection. The novel CO 2  composite spray applicator of the present invention has been developed to work most efficiently with CO 2  composite spray generation systems developed by the first named inventor. Preferred CO 2  composite spray generation systems for employing the present invention include U.S. Pat. Nos. 5,725,154, 7,451,941, and 9,221,067, and by reference to same are incorporated into the present invention in their entirety. The present invention introduces such refinements. In its preferred embodiments, the present invention has several aspects or facets that can be used independently, although they are preferably employed together to optimize their benefits. All of the foregoing operational principles and advantages of the present invention will be more fully appreciated upon consideration of the following detailed description, with reference to the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an excerpt from prior art U.S. Pat. No. 5,409,418 (FIG. 1) describing a snow spray applicator with coaxial ionized gas additive injection means for use with a conventional CO 2  snow spray system. 
         FIG. 2  is an excerpt from prior art U.S. Pat. No. 7,451,941 (FIG. 5) dense fluid cleaning process and apparatus describing a coaxial spray applicator describing an internal coaxial additive injection means. 
         FIG. 3  is an excerpt from prior art U.S. Pat. No. 7,389,941 (FIG. 2) describing a coaxial spray mixing nozzle using an external Coanda-flow additive injection means for use with exemplary CO 2  composite spray system described under FIG. 2, U.S. Pat. No. 7,451,941. 
         FIGS. 4 a  and 4 b    provide side-by-side photographs comparing an air-CO 2  composite cleaning spray with an air-CO 2 -oil composite machining spray using a prior art Coanda spray apparatus and method of  FIG. 3 . 
         FIGS. 5 a  and 5 b    schematically illustrate basic aspects and functions of exemplary electrostatic field generating CO 2  composite spray nozzles, additive injector nozzle, and axis-symmetric clustering arrangement of same to form a passively charging CO 2  composite spray apparatus. 
         FIGS. 6 a , 6 b , and 6 c    illustrate exemplary axis-symmetric cluster spray nozzle configurations for use with the present invention. 
         FIGS. 7 a  and 7 b    illustrate an arrangement of multiple cluster spray applicators to adjust both aerial and radial spray density. 
         FIG. 8  is a schematic showing the symmetrical electrostatic field established about a centrally disposed floating ground additive injector nozzle and between axis-symmetrically disposed floating charge carrier nozzles. 
         FIG. 9  describes the formation of a composite spray in space comprising passively charged CO 2  particles and additive particles in air, and application to an exemplary substrate. 
         FIGS. 10 a , 10 b , 10 c , 10 d , and 10 e    provide side, back and front, and a sliced isometric view of an exemplary design for a passive electrostatic charge generation CO 2  composite spray nozzle for use with the present invention. 
         FIGS. 11 a , 11 b , and 11 c    provide side, back and front isometric views of an exemplary design for an exemplary atomizing additive injector nozzle for use with the present invention. 
         FIGS. 12 a , 12 b , and 12 c    provide rear, bottom and front facing isometric views of an exemplary design for a 4×1 cluster spray applicator body for axis-symmetrically arranging the CO 2  composite spray nozzles and additive injection nozzle, and means for providing propellant air, CO 2  particles, and additives for using same. 
         FIG. 13  is an isometric view of an exemplary 3D printed handgun assembly using the exemplary spray applicator of  FIG. 12 . 
         FIG. 14  is a photograph of an unheated air-CO 2 -oil composite spray generated using a 4×1 cluster spray nozzle of the present invention. 
         FIG. 15  is an exemplary surface pretreatment and cleaning process using the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is an electrostatic spray application apparatus and method for producing an electrostatically charged and homogeneous CO 2  composite spray mixture containing an additive and simultaneously projecting at a substrate surface. The CO 2  composite spray mixture is formed in the space between CO 2  and additive mixing nozzles and a substrate surface. The CO 2  composite spray mixture is a composite fluid having a variably-controlled aerial and radial spray density comprising pressure- and temperature-regulated propellant gas (i.e., compressed air), CO 2  particles, and additive particles. The invention comprises two or more circumferential and high velocity air streams containing passively charged CO 2  particles which are positioned axis-symmetrically and coaxially about an inner and lower velocity injection air stream containing one or more additives to form a spray cluster. One or more spray clusters may be used to form a larger spray cluster configuration. The axis-symmetrical CO 2  particle-air streams are passively tribocharged during formation and the spray clustering arrangement creates a significant electrostatic field and Coanda air mass flow between and surrounding the coaxial flow streams. Within the spray cluster, the centrally-positioned additive-air stream exerts a small viscous drag and behaves as an anode relative to the circumferential CO 2  particle-air streams behaving as cathodes which causes the charged CO 2  particle-air stream and additive-air stream particles to coalesce in space under the influence of the polarized electrostatic field created within the space between them to form a uniform and hybrid air-CO 2 -additive particle spray stream. Using the present invention, any variety of hybrid air-CO 2 -additive particle spray streams may be created for industrial manufacturing applications such as coating, cleaning, disinfecting, and cooling-lubrication. 
       FIG. 1  is an excerpt from prior art U.S. Pat. No. 5,409,418 (FIG. 1) describing a snow spray applicator with a coaxial ionized gas additive injection means for use with a conventional CO 2  snow spray system. Shown in  FIG. 1 , liquid CO 2  ( 2 ) is supplied though a micrometering valve ( 4 ) which adjustably meters the liquid CO 2  through an internal orifice of a snow spray nozzle ( 6 ) which rapidly expands ( 8 ) to form a very cold CO 2  gas-particle aerosol or snow spray ( 10 ). Surrounding said snow spray nozzle ( 6 ) is affixed an gas ionizing device ( 12 ) which produces a positive or negative high voltage potential through which a gas such as compressed air ( 14 ) is flowed into the ionizer means to produce a coaxial shield or shroud of ionized gas ( 16 ) circumferentially about the expanded snow stream ( 10 ) to form a cleaning spray comprising expanded CO 2  aerosol ( 10 ) and surrounding ionized air sheath ( 16 ), which is selectively projected ( 18 ) at a substrate surface ( 20 ). There are several drawbacks associated with conventional snow sprays such as &#39;418 which have led to the development of a CO 2  composite spray by the first named inventor. These constraints include a very low spray temperature, atmospheric moisture and organic vapor condensation, and excessive CO 2  usage, among others. The ionization scheme of &#39;418 injects ionized gas around a centrally disposed CO 2  snow stream. The centrally disposed CO 2  snow stream is much colder and denser than the circumferential ionized gas stream and is rapidly expanding in an outward direction away from the central spray axis at near-sonic velocity due to sublimation of the CO 2  particles. Although this scheme is useful for preventing external atmosphere from intruding into the centrally-disposed cold snow spray, and particularly near the cold cleaning zone on a substrate being treated by same, this additive injection arrangement hinders the uniform mixing of beneficial electrostatic charge neutralizing ions into the centermost regions of the spray and particularly the contact cleaning zone on the substrate itself. Moreover, the use of a high voltage ionization device on the spray cleaning nozzle is not desirable from a safety perspective and the requirement to utilize a bulky ionizer for each CO 2  spray nozzle increases equipment cost and constrains the development and use of CO 2  processing sprays having very high radial and aerial spray densities. Finally, the injection scheme of &#39;418 cannot be used to inject liquid and solid additives to produce a homogenous CO 2  spray compositions for similar aforementioned constraints such as CO 2  snow spray expansion, flow stream segmentation, and very cold temperatures. 
       FIG. 2  is an excerpt from prior art U.S. Pat. No. 7,451,941 (FIG. 5) dense fluid cleaning process and apparatus describing a coaxial spray applicator describing an internal coaxial additive injection means. Shown in  FIG. 2  is an exemplary coaxial CO 2  composite spray applicator and process developed by the first named inventor. Very different from a conventional snow spray applicator as previously discussed under  FIG. 1 , the basic scheme for producing and projecting a CO 2  Composite Spray (a trademark of CleanLogix LLC) is to combine essential components to form an effective CO 2 -based processing spray: (1) cleaning agent (i.e., microscopic CO 2  particles), (2) CO 2  particle propulsion and spray shielding agent (i.e., heated, ionized, and pressurized air), and (3) optional spray additives (i.e., alcohol, microabrasive particles)—by means of separate spray component generation, control and delivery means, and integration of same using variously designed coaxial spray mixing nozzles. As depicted in  FIG. 2 , the exemplary coaxial CO 2  composite spray applicator comprises three basic elements; a coaxial CO 2  particle delivery capillary tube ( 30 ), which transports microscopic CO 2  particles ( 32 ) generated in-situ, carried within a portion of an outer coaxial propellant gas delivery tube ( 34 ), which transports a pressure-regulated and heated propellant gas ( 36 ); both of which are integrated to a coaxial CO 2 -propellant gas mixing nozzle ( 38 ). In addition to these basic elements, an optional additive injection port ( 40 ) is employed to selectively feed pressure-flowable or pumpable spray cleaning additives such as solvents or microabrasives using an external additive feed tube ( 42 ) which injects the additive directly into the CO 2 -propellant gas mixture ( 44 ) to form an air-CO 2 -additive spray composition ( 46 ), which is then selectively projected ( 48 ) at a substrate surface ( 50 ). The spray generation process and apparatus thus described is detailed in U.S. Pat. No. 7,451,941 and is incorporated into this specification by reference to same. 
     A significant drawback of the exemplary coaxial spray applicator as shown and described under U.S. Pat. No. 7,451,941 (FIG. 2) is rapid internal nozzle clogging and spray aberrations such as sputtering particularly when injecting high melt point additives such as bio-based oils, or any additive that changes phase (i.e., liquid→solid) upon mixing with the CO 2  particles and before dispersion and atomization into fine particles. High velocity and sublimating CO 2  particle streams create passive electrostatic charging (as high as 5 kV or more) and very low mixing temperatures (as low as −109 Deg. F.). The cold CO 2  particles thermally and electrostatically gel the high melt point lubricating oil during injection, forming large agglomerations of frozen CO 2  particles and oil which are not optimal for cooling-lubricating machining sprays. Similarly, injecting low melt point organic solvents such as acetone and methanol directly into the mixing nozzle for precision cleaning applications constrains the formation of small atomized solvent droplets with a uniform distribution of CO 2  particles. A large mass of organic solvent additive serves as a heat sink (and solvent) for the solute CO 2  particles during formation, causing the CO 2  particles to sublimate very quickly in transit to a surface. The result in a very short range cleaning spray containing a very cold atomized spray of liquid solvent absent any appreciable quantity of CO 2  particles. 
       FIG. 3  is an excerpt from prior art U.S. Pat. No. 7,389,941 (FIG. 2) developed by the first named inventor describing a coaxial spray mixing nozzle using an external Coanda-flow additive injection means for use with the exemplary CO 2  composite spray system described under FIG. 2, U.S. Pat. No. 7,451,941. The novel spray nozzle of  FIG. 3  is interchangeable with the coaxial spray nozzle described under  FIG. 2  ( 38 ) and enabled with an exemplary CO 2  composite spray generation system described in U.S. Pat. No. 7,451,941. As shown in  FIG. 3 , CO 2  particles contained within a delivery capillary tube ( 60 ) flowing from an external CO 2  particle generator (not shown but described in detail under U.S. Pat. No. 7,451,941) are fed into and through the central portion of the nozzle, over which flows pressure- and temperature-regulated propellant gas ( 62 ) flowing from an external propellant supply generator (not shown but described in detail under U.S. Pat. No. 7,451,941); all of which are integrated into a Coanda-Coaxial CO 2 -propellant gas-CO 2  particle-additive mixing nozzle ( 64 ). Different from the U.S. Pat. No. 7,451,941 externally fed additive injection and internal coaxial mixing method described under  FIG. 2  ( 42 ), the additive injection feed tube ( 66 ) of U.S. Pat. No. 7,389,941 is carried internally and coaxially with the CO 2  particle feed tube ( 60 ) and is selectively positioned to inject additive ( 68 ) into an adjustable circumferential gap ( 70 ) which mixes and flows with a first portion of the propellant gas ( 62 ) from the nozzle interior and over the exterior surface of the Coanda nozzle surface ( 72 ). The capillary delivery tube ( 60 ) flowing CO 2  particles is selectively positioned to discharge the CO 2  particles near the nozzle exit port ( 74 ) whereupon the CO 2  particles are mixed and propelled with the second portion of propellant gas ( 62 ). The first portion of propellant gas and additive mixture flows over the outer surface the Coanda nozzle towards the nozzle tip ( 76 ), whereupon the propellant gas-additive mixture is injected into the second portion of propellant gas-CO 2  particle mixture exiting the nozzle exit port ( 74 ) to form a CO 2  particle-propellant gas-additive composition ( 78 ) which is projected ( 80 ) at a substrate surface ( 82 ). The Coanda nozzle apparatus thus described is detailed in U.S. Pat. No. 7,389,941 and is enabled by the spray generation process of U.S. Pat. No. 7,451,941 which is incorporated into this specification by reference to same. 
     As with the coaxial mixing nozzle of U.S. Pat. No. 7,451,941 described under  FIG. 2  ( 38 ) with internal additive injection, the Coanda-flow external additive injection method of U.S. Pat. No. 7,389,941 described under  FIG. 3  suffers similar constraints, albeit indirectly so. The external surface of the Coanda nozzle ( 76 ) is charged electrostatically and the surface temperature drops to very low temperatures during spray operation, both of which are caused by the internal expansion and sublimation of cold CO 2  particle-gas spray and mixing with the propellant gas within the nozzle body and near the nozzle exit ( 72 ). A means for mitigating the nozzle freezing effect is to significant increase the propellant gas temperature to offset sublimation cooling. However for machining applications, the propellant gas must not be heated above ambient temperature to preserve CO 2  particles (i.e., coolant) and to amplify the overall cooling capacity and effect of the composite spray. This phenomenon is best illustrated by comparing an air-CO 2  composite spray containing no additive with a spray containing a high melt point additive using the apparatus of  FIG. 3 . 
       FIGS. 4 a  and 4 b    show side-by-side photographs comparing an unheated air-CO 2  composite spray with an unheated air-CO 2 -oil composite spray using the prior art Coanda-Coaxial spray nozzle apparatus and method of  FIG. 3 . As shown in  FIG. 4 a   , an unheated air-CO 2  composite spray exhibits atmospheric ice build-up on the nozzle tip ( 90 ) caused by electrostatic charging and water vapor condensation during spray operation, but overall the composite spray ( 92 ) remains well-formed and stable provided the CO 2  particle injection rate is kept controlled at about 8 lbs./hour (or less) and the propellant pressure is maintained at 70 psi and 70 degrees F. (or higher) to prevent excessive nozzle tip condensation and freezing. Now referring to  FIG. 4 b   , and using these same air-CO 2  particle composite spray conditions as in  FIG. 4 a   , a high melt point bio-based oil is injected through capillary feed tube  FIG. 3  ( 66 ) at approximately 70 ml/hour. As can be seen in  FIG. 4 b   , after a brief period of spray operation the oil additive begins to charge, gel and agglomerate along with atmospheric ice build-up on the entire Coanda injection surface ( 104 ). The build-up is observed as a frozen oily mass ( 106 ) that extends outward from the Coanda nozzle tip  FIG. 4 a    ( 90 ). As this progresses, the nozzle tip build-up ( 106 ) interferes with the central CO 2  composite spray ( 108 ) and results in a cooling-lubricating spray that is unstable and variable, containing inconstant amounts of or no lubricant additive during application to cutting zone ( 110 ) comprising a cutting tool, workpiece, and chip. 
     The generation and projection of a CO 2  spray produces electrostatic charging. This tribocharging phenomenon is caused by contact of high velocity and sublimating CO 2  particles (a dielectric) with surfaces having a different work functions, for example polyetheretherketone (PEEK) delivery capillary tubes and metallic mixing nozzles used to fabricate a CO 2  composite spray applicator. Measures to mitigate electrostatic charge build-up and already discussed herein by reference to the prior art include the injection of ionized gases directly or indirectly into the CO 2  spray as well as nozzle grounding or shunting. However, even with these measures in place the CO 2  particle spray continues to tribocharge as it expands and moves turbulently within the atmosphere during its trajectory to a substrate surface. Moreover, even a relatively charge-neutral CO 2  spray will tribocharge a substrate surface during impingement. As such, it is known to those skilled in the art that the best remedy for mitigating electrostatic charge on the substrate surface during a CO 2  spray treatment is through substrate grounding or shunting means, and through the projection of a separate ionizing fluid or radiation at the substrate during spray treatment. For example, U.S. Pat. No. 9,352,355 co-developed by the first named inventor is an exemplary surface shunting means using an atmospheric plasma (electrically conductive treatment fluid) to contact both the CO 2  composite spray and substrate surface simultaneously during operation. Surface charge build-up is mitigated by draining tribocharge from the contacting surfaces directly into the plasma plume. The &#39;355 apparatus and method is a hybrid treatment process that provides effective surface cleaning and modification while simultaneously controlling electrostatic charging of treatment spray and treated surfaces. 
     In summary, a direct charging method for intensifying the formation of an electrostatically-atomized additive in a CO 2  composite spray is taught by the first named inventor in U.S. Pat. No. 7,389,941 and involves the application of a high voltage (HV) to the flowable additive using a HV power supply and wire. The additive mixture becomes highly charged prior to injection into the Coanda nozzle and subsequent mixing into the tribocharged CO 2  composite spray. Also taught by the first named inventor in U.S. Pat. No. 7,451,941 is an indirect charging method which involves injecting additive directly into the tribocharged CO 2  composite spray as it is being formed to form a passively charged additive in the CO 2  composite spray. However it is evident from the discussion of the prior art, the co-joined constraints by both of these techniques, and particularly when using high melt point additives, are two-fold: (1) uncontrolled phase change of additive due to the very low CO 2  particle-gas mixture temperature (direct body-to-body heat transfer) with (2) premature electrostatic charging or tribocharging (direct body-to-body electrical charge transfer) of additive prior to atomization and condensation phenomenon. As such, the single-piece air-CO 2 -additive mixing nozzle schemes used in the prior art have a significant conflict with regards to the locality of the electrostatic charging, additive injection, and mixing stages of CO 2  composite spray formation. 
     Having thus discussed the prior art in detail, it is apparent that there is a need for an improved CO 2  composite spray application method and apparatus. The following discussion describes aspects of a novel CO 2  composite spray applicator and method for coaxially injecting, atomizing, electrostatically charging, and dispersing virtually any flowable air-additive composition which resolves the aforementioned constraints. The present aspect provides an apparatus for producing an electrostatically charged and homogeneous CO 2  composite spray containing an additive. 
     In a first aspect of the present invention, CO 2  composite spray nozzles are employed as an axis-symmetrically arranged cathode array within which is located an additive injection nozzle behaving as an anode to create a strong ionizing electrostatic field between them in air during spray operation. The CO 2  composite spray nozzle and CO 2  particles are highly charged due to the presence of excess of electrons relative to its surroundings. The additive spray nozzle and atomized particles are oppositely charged with respect to the CO 2  composite spray. The inventors have measured the electrostatic field generated in the air surrounding a CO 2  composite spray mixing nozzle using an Exair Static Meter, Model 7905, available from Exair Corporation, Cincinnati, Ohio. A preferred CO 2  composite spray system for use with the present invention and co-developed by the first named inventor is U.S. Pat. No. 9,221,067 and is incorporated into this specification by reference to same. As depicted in &#39;067 (FIG. 4 a ), an ungrounded coaxial CO 2  composite spray applicator using a single 0.008 inch PEEK capillary throttle (&#39;067, FIG. 4 a  (114)) integrated into a stainless steel supersonic mixing nozzle (&#39;067, FIG. 4 a  (116) was used. The coaxial CO 2  composite spray applicator was operated at a CO 2  throttle capillary pressure of 1200 psi, a propellant pressure of 80 psi, and a propellant temperature of 50 degrees C. Under these CO 2  composite spray conditions, a strong electrostatic field of 5 kV/inch is present at a position within the air gap surrounding and adjacent to said CO 2  spray mixing nozzle at approximately 1 inch away. As such, the CO 2  spray mixing nozzle (i.e., behaving as a cathode) emits a very strong and ionizing electrostatic field in air which can be used to electrostatically charge an adjacent and parallel flowing atmosphere of additive particles (i.e., behaving as an anode) in space separated by a dielectric air gap. The spray atomization, charging, and mixing stages are performed in air and downstream from the CO 2  particle and additive injection nozzles during trajectory to the substrate surface, mitigating spray formation constraints such as freezing, clogging and sputtering present in the prior art using an integrated air-CO 2 -additive mixing nozzle scheme. 
     In another aspect, a cluster nozzle arrangement induces significant and parallel air flow symmetrically about the circumference of the CO 2  composite spray flow field due to the symmetry, multiplicity, and high velocity of the surrounding CO 2  composite sprays. A large inducement of air flow reduces atmospheric drag and extends the effective treatment range (i.e., spray trajectory) of the CO 2  composite spray. 
     In still another aspect of the present invention, the inner additive injection nozzle may use the same source of pressure and temperature regulated propellant gas as the CO 2  spray nozzles but uses a separate coaxial additive feed capillary from a remote additive supply. The mixing nozzle for the additive injector is designed to produce an atomized additive spray having velocity which is less (i.e., higher pressure) than the outer CO 2  spray nozzle array. This enhances incorporation of the atomized (and passively charged) additive particles into the axis-symmetrically arranged CO 2  composite sprays. These and other aspects of the present invention will be best understood by reference to  FIGS. 5 through 14 . 
       FIGS. 5 a  and 5 b    schematically illustrate basic aspects and functions of exemplary electrostatic field generating CO 2  composite spray nozzles, additive injector nozzle, and axis-symmetric clustering arrangement of same to form a passively charging CO 2  composite spray apparatus. Shown in  FIG. 5 a   , three basic components are needed for practicing the present invention. These include a CO 2  composite spray generation system ( 110 ), an additive injection system ( 112 ), and the present invention, a passive electrostatic CO 2  composite spray applicator ( 114 ). The exemplary passive electrostatic CO 2  composite spray applicator ( 114 ) shown in  FIG. 5 a    is fluidly connected to both the CO 2  composite spray generation system ( 110 ) and additive injection system ( 112 ) vis-à-vis flexible and coaxial fluid delivery line and tube assemblies. The CO 2  composite spray delivery assembly comprises a polyetheretherketone (PEEK) capillary tube ( 116 ) providing a pressure- and temperature-regulated supersaturated CO 2  fluid ( 118 ). The additive injection system ( 112 ) provides adjustable volume of additive ( 120 ) vis-à-vis a flexible capillary delivery tube ( 122 ) using a pressure-regulated pump ( 124 ) supplied by an additive feed line ( 126 ) from a reservoir ( 128 ) containing a liquid additive or mixture of additives comprising liquids and solids. The additive delivery tube ( 122 ) contains an optional small grounding wire ( 130 ) which is connected to earth ground ( 132 ) and traverses the entire inside length of the inside of the additive delivery tube ( 122 ). The grounding wire ( 130 ) serves as an electrostatic charge inductor for the additive flowing through the additive delivery tube ( 122 ). The passive electrostatic CO 2  composite spray applicator ( 114 ) contains an array of two or more CO 2  composite spray mixing nozzles ( 134 ) positioned axis-symmetrically about a single additive injection nozzle ( 136 ). The CO 2  composite spray mixing nozzle ( 134 ) combines pressure- and temperature-regulated propellant gas ( 138 ) and micronized CO 2  particles generated in the nozzle ( 134 ) from the supersaturated CO 2  ( 118 ), both fluids provided by the CO 2  composite spray generator ( 110 ), to form a CO 2  composite spray (not shown). The additive injection nozzle ( 136 ) combines the same pressure- and temperature-regulated propellant gas ( 138 ) and additive fluid ( 120 ) to form an atomized additive spray (not shown). Preferred CO 2  composite spray generation systems ( 110 ) for use with the present invention are described in detail under U.S. Pat. Nos. 9,221,067 and 7,451,941, available commercially from CleanLogix LLC, Santa Clarita, Calif., both of which are incorporated into this specification by reference to same. Exemplary additive injection systems ( 112 ) and bio-based metalworking lubricant additives ( 120 ) suitable for use with the present invention are available from ITW ROCOL North America, Glenview, Ill. 
       FIG. 5 b    provides a more detailed description of the exemplary CO 2  composite spray nozzles ( 134 ) and single additive injection nozzle ( 136 ) shown in  FIG. 5 a   . Shown in  FIG. 5 b   , the passive electrostatic CO 2  composite spray applicator ( 114 ) comprises a single additive injection nozzle ( 136 ) positioned centrally between multiple CO 2  composite spray nozzles ( 134 ), all of which is positioned on a face of a cylindrical or tubular spray applicator body ( 140 ). The CO 2  composite spray nozzles ( 134 ) are fabricated from materials which will passively tribocharge when contacted with CO 2  particles, for example metals such as stainless steel will produce a very strong electrostatic field during CO 2  tribocharging. The spray applicator body ( 140 ) may be constructed of various materials including for example stainless steel, aluminum, or polymers such as Delrin®. Moreover, the spray applicator body ( 140 ) may be contained in a 3D-printed applicator housing to provide a means for mounting or handling, and manipulating the spray applicator body ( 140 ) during operation, for example providing mounts for a robot end-effector or providing a handle for manual spray operations. 
     Having described the general features and arrangement of the passive electrostatic CO 2  spray applicator, following is a more detailed description of the CO 2  composite spray nozzles ( 134 ) and additive injection spray nozzle ( 136 ). Referring to the exemplary CO 2  composite spray nozzle ( 134 ), the coaxial CO 2  spray nozzle comprises two components: (1) an outer propellant gas conduit ( 142 ) for flowing pressure- and temperature-controlled propellant gas ( 144 ), and (2) an inner polymeric CO 2  particle conduit ( 146 ) for flowing micronized CO 2  particles ( 148 ). The preferred construction and arrangement of the coaxial CO 2  composite spray nozzle ( 134 ) is described in detail in U.S. Pat. Nos. 9,221,067 and 7,451,941, both of which are incorporated into the present invention by reference to same. 
     Referring to the exemplary additive injection spray nozzle ( 136 ), the coaxial additive spray nozzle comprise three components: (1) an outer propellant gas conduit ( 150 ) for flowing pressure- and temperature-controlled propellant gas ( 144 ), which for this exemplary applicator is the same source as for the CO 2  composite spray nozzle ( 134 ), (2) an inner polymeric additive conduit ( 152 ) for flowing a pressure- and temperature-regulated additive ( 154 ), and (3) an optional metallic grounding wire ( 130 ) which traverses the length of the additive injection tube ( FIG. 5 a   ,  122 ) supplying the additive injection nozzle ( 136 ). Finally, during operation of the exemplary passive electrostatic CO 2  composite spray applicator thus described, CO 2  particle tribocharging within the polymeric CO 2  particle additive conduit ( 146 ) and metallic nozzle ( 142 ) produces an electrostatic field ( 156 ) between the CO 2  spray nozzle ( 134 ) and additive injection spray nozzle ( 136 ). 
       FIGS. 6 a , 6 b , and 6 c    illustrate exemplary axis-symmetric cluster spray nozzle configurations for use with the present invention.  FIG. 6 a    illustrates a 2×1 cluster nozzle arrangement comprising one additive injection nozzle ( 136 ) bounded axis-symmetrically on a common spray applicator body ( 140 ) by two CO 2  composite spray nozzles ( 134 ).  FIG. 6 b    illustrates a 3×1 cluster nozzle arrangement comprising one additive injection nozzle ( 136 ) bounded axis-symmetrically on a common spray applicator body ( 140 ) by three CO 2  composite spray nozzles ( 134 ). Finally,  FIG. 6 c    illustrates an 8×1 cluster nozzle arrangement comprising one additive injection nozzle ( 136 ) bounded axis-symmetrically on a common spray applicator body ( 140 ) by eight CO 2  composite spray nozzles ( 134 ). 
       FIGS. 7 a  and 7 b    illustrate an arrangement of multiple cluster spray applicators to adjust both aerial and radial spray density.  FIG. 7 a    illustrates an axis-symmetric arrangement of seven 8×1 cluster spray nozzles ( 160 ). The individual cluster spray applicators may also be rotated to produce overlapping sprays in both the x axis ( 162 ) and y axis ( 164 ). As shown in  FIG. 7 b   , using multiple cluster spray applicators having different spray nozzle configurations and rotations provides the adjustment of both the radial spray density ( 166 ) and aerial spray density ( 168 ). 
       FIG. 8  is a schematic showing the symmetrical electrostatic field established about a centrally disposed additive injector nozzle and between axis-symmetrically disposed charged carrier nozzles.  FIG. 8  shows a central metallic additive nozzle ( 136 ) producing atomized additive particles ( 170 ) positioned between axis-symmetrically arranged CO 2  composite spray nozzles ( 134 ) producing charged CO 2  composite spray particles ( 172 ), all of which positioned on the face of a spray applicator body ( 140 ). The atomized additive particles ( 170 ) are relatively charge neutral or positive relative to the axis-symmetrical metallic CO 2  spray nozzle ( 134 ) which produces negatively charged CO 2  particles ( 172 ). The result of this arrangement during spray operation is the establishment of an electrostatic field ( 174 ) between the central and outer spray nozzles. The passive electrostatic spray applicator of the present invention comprises an additive injection nozzle ( 136 ) behaving as a central anode and the axis-symmetrically arranged CO 2  composite spray nozzles ( 134 ) behaving as charged cathodes. Electrons are produced by the tribocharging of CO 2  particles between internal capillary and nozzle body surfaces ( 176 ) within the CO 2  spray nozzle ( 134 ). Moreover, the charged CO 2  composite sprays repel each other ( 178 ) due to equal electrostatic charge. Electrostatic repulsion in combination with a higher velocity than the central additive spray maintains the symmetry of the sprays and slightly delays incorporation of the additive until downstream of the cluster spray nozzle array. 
       FIG. 9  describes the formation of a CO 2  composite spray in space comprising passively charged CO 2  particles and additive particles in air, producing an electrostatically charged and homogeneous CO 2  composite spray mixture containing an additive, and application of same to an exemplary substrate. Shown in  FIG. 9 , a basic passive electrostatic CO 2  composite spray cluster nozzle discussed herein is a 2×1 axis-symmetrical arrangement of spray nozzles comprising a centrally-positioned additive injection nozzle ( 136 ) surrounded by two CO 2  composite spray nozzles ( 134 ). Tribocharged CO 2  particles entrained and propelled by a pressure- and temperature-regulated propellant gas stream form an air-CO 2  composite spray ( 180 ), which is projected into space at a velocity (Vc) which is greater than the additive injection spray. The air-CO 2 composite spray ( 180 ) thus formed induces atmospheric air flow ( 182 ) in the space between the CO 2  spray nozzle ( 134 ) and additive injection nozzle ( 136 ), and induces atmospheric air flow ( 184 ) the circumferential space about the cluster spray nozzle applicator. Relatively charge-neutral and atomized additive particles entrained in the same pressure- and temperature-regulated propellant gas stream form an air-additive spray ( 186 ) which is moving at a velocity (Va) less than the CO 2  composite spray. Discussed in more detail under  FIG. 11  and  FIG. 12  herein, the velocity differential between the CO 2  spray nozzles ( 134 ) and additive injection spray nozzle ( 136 ) at an equivalent propellant pressure input is accomplished using different nozzle designs. During spray operation this cluster nozzle arrangement produces both an electrostatic field ( 188 ) and spray velocity ( 190 ) gradient, which results in rapid electrostatic charging and entrainment of additive particles by the CO 2  composite spray to form an air-additive-CO 2  composite spray ( 192 ) downstream from spray applicator. At a distance downstream from the cluster spray applicator nozzles, which is dependent upon propellant pressure input, the air-additive-CO 2  composite sprays mix to form a homogenously charged and additive-dispersed CO 2  composite spray ( 194 ) which is directed ( 196 ) at a substrate surface ( 198 ). The substrate surface ( 198 ) may be earth grounded ( 200 ) or may behave as a relative ground with respect to the highly charged air-additive-CO 2  particle aerosol spray ( 194 ). 
       FIGS. 10 a , 10 b , 10 c , 10 d , and 10 e    provide side, back and front, and a sliced isometric view of an exemplary design for a passive electrostatic charge generation CO 2  composite spray nozzle for use with the present invention. Shown in  FIG. 10 a    (side view), the exemplary CO 2  composite spray nozzle ( 134 ) is a stainless steel coaxial propellant gas-CO 2  particle mixing body having a threaded base ( 210 ) which allows for attachment to axis-symmetric circumferential positions on the spray applicator body ( FIG. 5 b   ,  140 ), a chamfered nozzle exit ( 212 ), and through-ported interior space ( 214 ) for insertion and centering of a PEEK CO 2  particle delivery tube (not shown) bounded by three lobed propellant gas flow channels ( 216 ). The propellant gas flow channels ( 216 ) are produced using electrical discharge machining (EDM) and provide a three-point cradle for centering and securing the PEEK CO 2  particle delivery tube (not shown) surrounding which flows supersonic velocity propellant gas. Shown in  FIG. 10 b    (back view), the threaded base ( 210 ) contains a nozzle sealing face ( 218 ) and interior through-ported space shows the flat cradle base ( 220 ) onto which the PEEK CO 2  particle delivery tube (not shown) slides into position between the intersection of any two EDM propellant flow channels ( 216 ). Finally, shown in  FIG. 10 c    (Front View) the exemplary CO 2  composite spray nozzle contains a center-positioned adjustable expansion tube assembly ( 222 ) (by reference to U.S. Pat. No. 9,221,067 (FIG. 4 b , “Adjustable Expansion Tube Assembly”, (502)), which is cradled between at least three or more center-positioning and shunting bars ( 220 ) created at the intersections between the three EDM propellant flow channels ( 216 ). The exemplary coaxial CO 2  composite spray nozzle thus described produces a flow of air and CO 2  particles having a velocity which is higher than the additive injection spray nozzle. 
       FIG. 10 d    and  FIG. 10 e    provide a more detailed view of the interior design and operational aspects of the CO 2  composite spray nozzle of the present invention.  FIG. 10 d    is a front view of the exemplary CO 2  composite spray nozzle. With reference to U.S. Pat. No. 9,221,067 (FIG. 4B, “Adjustable Expansion Tube Assembly”, (502)) by the first named present inventor, the CO 2  composite spray nozzle of the present invention provides a novel method and apparatus for centering and positioning the referenced adjustable expansion tube assembly ( 222 ) described in &#39;067 (FIG. 4 b ) which injects micronized CO 2  particles into the propellant gas flowing through the EDM propellant channels ( 216 ), and for selectively shunting ( 400 ) and directing the electrostatic charges generated within same. With the shunting circuit ( 402 ) connected to ground ( 404 ), electrostatic charges are directed from the outside surfaces of the adjustable expansion tube assembly ( 222 ) and nozzle surface ( 406 ) along and through the internal EDM shunting bars ( 220 ). Now referring to  FIG. 10 e   , the relatively long and internal EDM shunting bars ( 220 ) have a length between 0.25 inches to 6 inches, or more, and the adjustable expansion tube assembly of  FIG. 10 d    ( 222 ) is selectively positioned within the centermost region of the nozzle body along the traverse ( 408 ) of the EDM shunting bars ( 220 ) from the nozzle tip ( 410 ) to a position within the nozzle cavity ( 412 ). The diameter between the three or more EDM shunting bars ( 220 ) is pre-determined to provide a slip contact fit between the shunting bar land surfaces and the outside surfaces of the adjustable expansion tube assembly of  FIG. 10 d    ( 222 ). The discharge (or injection) position of the adjustable expansion tube assembly ( FIG. 10 d    ( 222 )), and particularly where the micronized CO 2  particles are injected into the supersonic propellant flow channel ( 216 ), is determined based on the development of an optimal spray plume profile for the CO 2  composite spray as determined using U.S. Pat. No. 9,227,215 by the first named inventor of the present invention. Finally, the shunting mechanism described under  FIG. 10 d    is implemented by the selective application of a grounding element ( 414 ) for the nozzle body. If the nozzle connection ( 414 ) is grounded, electrostatic charges flow away from the nozzle body and into earth ground. If the nozzle connection ( 414 ) is ungrounded, electrostatic charges a stored within and drained from the nozzle body tip ( 410 ) into the spray stream. 
       FIGS. 11 a , 11 b , and 11 c    provide side, back and front isometric views of an exemplary design for an exemplary atomizing additive injector nozzle for use with the present invention. Shown in  FIG. 11 a    (side view), the exemplary additive injection spray nozzle ( 136 ) is a stainless steel coaxial propellant gas-additive particle mixing body having a threaded base ( 230 ) which allows for attachment to the centermost position of the spray applicator body ( FIG. 5 b   ,  140 ), a chamfered nozzle exit ( 232 ), and through-ported circular interior space ( 234 ) for insertion of a PEEK additive delivery tube (not shown). With equivalent propellant gas pressure, the circular propellant gas flow channel ( 234 ) of  FIG. 11  flows a lower velocity propellant gas as compared to the EDM propellant flow channels described under  FIG. 10  by virtue of having a larger surface area. Shown in  FIG. 11 b    (back view), the threaded base ( 230 ) contains a nozzle sealing face ( 236 ) and interior through-ported circular space ( 234 ) within which the PEEK additive particle delivery tube (not shown) is somewhat centrally positioned. Finally, shown in  FIG. 11 c    (Front View) the exemplary additive particle spray nozzle contains a somewhat center-positioned and slightly recessed PEEK additive particle delivery tube ( 238 ) about which forms a circular propellant gas flow channel ( 240 ). The exemplary coaxial additive injection nozzle thus described produces a flow of air and additive particles which has a velocity which is less than the CO 2  spray produced by the CO 2  composite spray nozzle described under  FIG. 10 . 
       FIGS. 12 a , 12 b , and 12 c    provide rear, bottom and front facing isometric views of an exemplary design for a 4×1 cluster spray applicator body for axis-symmetrically arranging the CO 2  composite spray nozzles and additive injection nozzle, and means for providing propellant air, CO 2  particles, and additives for using same. Referring to  FIG. 12 a    (Rear View), the rear surface ( 248 ) of the spray applicator body ( 140 ) contains a threaded additive tube inlet port ( 250 ) for inserting and affixing an additive delivery tube, and optional grounding wire contained therein (both not shown), using for example a PEEK nut and ferrule assembly (both not shown). Moreover, the rear surface ( 248 ) of the spray applicator ( 140 ) contains four threaded inlet ports ( 252 ) arranged axis-symmetrically about the additive tube inlet port ( 250 ) for inserting and affixing CO 2  particle delivery tubes using for example PEEK nut and ferrule assemblies (all not shown). The threaded additive inlet port ( 250 ) and four CO 2  particle inlet ports ( 252 ) transition to through-ported circular channels that traverse the entire length of the spray applicator body ( 140 ). Shown in  FIG. 12 b   , the bottom of the spray applicator body ( 140 ) contains a threaded propellant gas inlet port ( 254 ) which is ported through all of the additive ( 250 ) and CO 2  particle ( 252 ) channels which simultaneously provides a common supply of pressure- and temperature-regulated propellant gas to all spray channels containing PEEK additive and CO 2  particle delivery tubes (all not shown). Finally, the front face ( 256 ) of the spray applicator contains a centrally-positioned threaded additive nozzle port ( 258 ) and four axis-symmetrically arranged threaded CO 2  spray nozzle ports ( 260 ) for affixing the exemplary CO 2  composite spray nozzles and additive injection spray nozzle described under  FIG. 10  and  FIG. 11 , respectively. The spray applicator body may be constructed of virtually any material able to withstand the pressures and temperatures commonly used in a CO 2  composite spray application. Exemplary materials of construction include steels, aluminum, and Delrin®. 
       FIG. 13  is an isometric view of an exemplary 3D printed handgun assembly for using the present invention as a manual spray cleaning or coating application tool. Referring to  FIG. 13 , the exemplary spray applicator body of  FIG. 12  shown with additive injection nozzle ( 136 ) and CO 2  composite spray nozzles ( 134 ) protruding through a cylindrical 3D printed ABS plastic shroud ( 270 ) with end-cap ( 272 ) for integrating all of the necessary PEEK additive and CO 2  delivery capillary tubes, all of which is contained in a delivery hose ( 274 ). The exemplary handgun assembly also has a 3D printed ABS handle ( 276 ) which is affixed to the bottom of the shroud ( 270 ) and applicator body contained therein, and contains a through-port for integrating a propellant gas supply hose ( 278 ). 
       FIG. 14  is a photograph of an unheated air-CO 2 -oil composite spray generated using a 4×1 cluster spray nozzle of the present invention. Shown in  FIG. 14 , the cluster spray applicator is operated at a propellant pressure of 80 psi, propellant temperature of 20 Degrees C., an oil additive injection rate of 70 ml/hour, and a CO 2  injection rate of 4 lbs./hour/nozzle. As can be seen in  FIG. 14 , the individual sprays generated by the central additive injection nozzle ( 136 ) and four axis-symmetrical CO 2  composite spray nozzles ( 134 ) remain distinct for a distance of about 2 inches downstream ( 280 ). At about 4 inches downstream ( 282 ), the sprays have completely combined to form a circular and homogenous electrostatically charged air-additive-CO 2  particle spray with a diameter of approximately 1.2 inches. This is shown in an image produced by the impingement of the spray against a pressure test film ( 284 ), the original of which is bright red. Continuous spray operation in testing periods lasting 60 minutes (until liquid CO 2  cylinder supply was exhausted) using the exemplary spray test apparatus shown in  FIG. 14  produced no visible icing, clogging, and oil additive accumulation on any of the CO 2  composite spray nozzles and additive injection nozzle. 
       FIG. 15  is an exemplary surface pretreatment and cleaning process using the present invention. In certain cleaning applications surface contamination can be very difficult to remove, for example following hole drilling titanium, aluminum, and carbon fiber reinforced polymer (CFRP), and stack-ups of same. Conventional hole drilling processes utilize a water-oil emulsion (i.e., coolant). This type of coolant leaves a very tacky surface residue comprising a thin film of oil, water, and surfactant. The present invention can be used to implement a novel pretreatment process that applies a uniform coat of (preferably) high boiling pretreat agent which first solubilizes (or otherwise denatures) the complex surface contaminant prior to or simultaneously during spray cleaning with a CO 2  composite spray. 
     In a first step ( 290 ) of the pretreat-clean process, the cluster spray applicator is positioned to distance from the substrate to be treated of between 6 and 18 inches, whereupon an exemplary eco-friendly, human-safe, and high boiling pretreat additive composition comprising 90% (v:v) volatile methyl siloxane (VMS) and 10% (v:v) 1-hexanol is applied ( 292 ) to the contaminated surface to form a uniform and thin film which penetrates and denatures (or detackifies) the complex surface contaminant. Exemplary cluster spray parameter ranges for the pretreatment step comprise the following:
     CO 2  Injection Rate: 2-4 lbs./hour/nozzle   Additive Injection Rate: 10-200 ml/hour   Propellant Temperature: 20-40 Degrees C.   Propellant Pressure: 30-50 psi   

     This pretreat coating process step is accomplished by positioning the CO 2  composite spray applicator of the present invention away from the contaminated surface to a distance where the CO 2  particle spray is useful for forming and delivering a passive electrostatic composite spray pretreatment coating, but not useful for imposing a surface impingement or cleaning effect so as not to remove the deposited coating. For example, at a distance of about 6 inches (15 cm) or more, the cluster spray applicator of the present invention is very useful for pre-coating a surface because most of the CO 2  particles have sublimated by this point or lack the size and velocity needed to produce an appreciable cleaning (removal) effect. Moreover, CO 2  injection pressure (i.e., CO 2  particle density), propellant pressure, and propellant temperature may be decreased as needed to facilitate the formation and maintenance of a uniform pretreatment coating. 
     Following the surface pre-coating step ( 292 ), and optionally following a dwell period ( 294 ) of between 3 and 600 seconds or more for the surface pretreatment agent to fully penetrate and denature the surface contaminant layer, pretreatment additive injection is stopped and the CO 2  composite spray applicator of the present invention is repositioned ( 296 ) towards the substrate to a distance of between 1 to 6 inches and a spray applicator angle of between 45 and 90 degrees normal to the surface to provide a precision spray cleaning step ( 300 ) to remove the residual pretreatment agent and denatured surface contaminant. Exemplary cluster spray parameter ranges for the spray cleaning step comprise the following:
     CO 2  Injection Rate: 2-8 lbs./hour/nozzle   Additive Injection Rate: 0 ml/hour   Propellant Temperature: 40-60 Degrees C.   Propellant Pressure: 50-120 psi   

     Finally, this novel pretreat-clean process may be performed manually using a handheld spray applicator or automatically using a robot and end-of-arm spray applicator. 
     Suitable additives for use in the present invention include, for example, pure liquids and blends of same derived from hydrocarbons, alcohols, siloxanes, terpenes, and esters. In addition, solid particles such as graphitic nanoparticles and paint pigments may be blended with suitable carrier solvents to form pressure-flowable or pumpable liquid suspensions. Still moreover, ozonated mixtures of liquids and suspensions may be used in the present invention. Finally, additives such as ionized gases may be used in the present invention. 
     The present invention is useful for surface decontamination, surface coating, and precision machining applications to provide a coating, cleaning, disinfection, cooling, pretreatment, preservation, painting, and/or lubricating function. 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the title, headings, terms and phrases used herein are not intended to limit the subject matter or scope; but rather, to provide an understandable description of the invention. The invention is composed of several sub-parts that serve a portion of the total functionality of the invention independently and contribute to system level functionality when combined with other parts of the invention. The terms “CO2” and “CO 2 ” and carbon dioxide are interchangeable. The terms “a” or “an”, as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language). The term coupled, as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically. Any element in a claim that does not explicitly state “means for” performing a specific function, or “step for” performing a specific function, is not be interpreted as a “means” or “step” clause as specified in 35 U.S.C. Sec. 112, Parag. 6. In particular, the use of “step of” in the claims herein is not intended to invoke the provisions of 35 U.S.C. Sec. 112, Parag. 6. 
     Incorporation of Reference: All research papers, publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent appl. was specifically and individually indicated to be incorporated by reference. 
     
       
         
           
               
             
               
                   
               
               
                 U.S. Pat. No. Documents 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 2,052,869 
                 September 1936 
                 Coanda 
               
               
                 2,302,289 
                 November 1942 
                 Bramston-Cook 
               
               
                 2,894,691 
                 July 1959 
                 Sedlacsik 
               
               
                 3,047,208 
                 July 1962 
                 Coanda 
               
               
                 3,117,726 
                 January 1964 
                 Schoberg 
               
               
                 3,628,737 
                 December 1971 
                 Norton 
               
               
                 3,702,519 
                 November 1972 
                 Rice et al. 
               
               
                 3,708,993 
                 January 1973 
                 Hardt et al. 
               
               
                 3,743,186 
                 July 1973 
                 Mocarski 
               
               
                 3,795,367 
                 March 1974 
                 Mocarski 
               
               
                 3,801,020 
                 April 1974 
                 Mocarski 
               
               
                 3,806,039 
                 April 1974 
                 Mocarski 
               
               
                 3,984,054 
                 October 1976 
                 Frochaux 
               
               
                 3,985,302 
                 October 1976 
                 Frochaux 
               
               
                 4,038,786 
                 August 1977 
                 Fong 
               
               
                 4,046,492 
                 September 1977 
                 Inglis 
               
               
                 4,195,780 
                 April 1980 
                 Inglis 
               
               
                 4,336,017 
                 June 1982 
                 Desty 
               
               
                 4,341,347 
                 July 1982 
                 DeVittorio 
               
               
                 4,385,728 
                 May 1983 
                 Inglis et al. 
               
               
                 4,389,820 
                 June 1983 
                 Fong et al. 
               
               
                 4,555,059 
                 November 1985 
                 Collins et al. 
               
               
                 4,703,590 
                 November 1987 
                 Westergaard 
               
               
                 4,707,951 
                 November 1987 
                 Gibot et al. 
               
               
                 4,749,125 
                 June 1988 
                 Escallon et al. 
               
               
                 4,776,515 
                 October 1988 
                 Michalchik 
               
               
                 4,801,086 
                 January 1989 
                 Noakes 
               
               
                 4,806,171 
                 February 1989 
                 Whitlock et al. 
               
               
                 5,056,720 
                 October 1991 
                 Crum et al. 
               
               
                 5,125,979 
                 June 1992 
                 Swain et al. 
               
               
                 5,170,942 
                 December 1992 
                 Spink et al. 
               
               
                 5,222,332 
                 June 1993 
                 Mains, Jr. 
               
               
                 5,312,598 
                 May 1994 
                 Kersey et al. 
               
               
                 5,402,940 
                 April 1995 
                 Haller et al. 
               
               
                 5,409,418 
                 April 1995 
                 Krone-Schmidt et al. 
               
               
                 5,591,412 
                 January 1997 
                 Jones et al. 
               
               
                 5,611,491 
                 March 1997 
                 Bowers 
               
               
                 5,704,554 
                 January 1998 
                 Cooper et al. 
               
               
                 5,725,154 
                 March 1998 
                 Jackson 
               
               
                 5,765,761 
                 June 1998 
                 Law et al. 
               
               
                 5,918,817 
                 July 1999 
                 Kanno et al. 
               
               
                 6,039,269 
                 March 2000 
                 Mandzukic 
               
               
                 6,056,213 
                 May 2000 
                 Ruta et al. 
               
               
                 6,105,886 
                 August 2000 
                 Hollstein et al. 
               
               
                 6,125,787 
                 October 2000 
                 Mochizuki 
               
               
                 6,708,903 
                 March 2004 
                 Kanno 
               
               
                 7,097,717 
                 August 2006 
                 Jung et al. 
               
               
                 7,389,941 
                 June 2008 
                 Jackson 
               
               
                 7,451,941 
                 November 2008 
                 Jackson 
               
               
                 9,352,355 
                 May 2016 
                 Jackson et al. 
               
               
                 9,221,067 
                 December 2015 
                 Jackson et al. 
               
               
                 9,227,215 
                 January 2016 
                 Jackson et al. 
               
               
                 2004/0251327 
                 December 2004 
                 Messerly et al. 
               
               
                 2006/0027679 
                 February 2006 
                 Gratteau 
               
               
                 2006/0071091 
                 April 2006 
                 Ratinik