Fluid atomizing system and method

In accordance with certain embodiments, a spray coating device includes a body and a spray formation head coupled to the body. The spray formation head has a fluid delivery mechanism comprising a pintle, a sleeve disposed about the pintle, and a throat between the pintle and the sleeve, wherein the throat decreases in cross-section at least partially lengthwise through the fluid delivery mechanism toward a fluid exit between the pintle and the sleeve. The spray formation head also has a pneumatic atomization mechanism disposed adjacent the fluid delivery mechanism, wherein the pneumatic atomization mechanism comprises a plurality of pneumatic orifices.

BACKGROUND OF THE INVENTION

The present technique relates generally to spray systems and, more particularly, to industrial spray coating systems. The present technique specifically provides a system and method for improving atomization in a spray coating device by internally inducing fluid breakup.

Spray coating devices are used to apply a spray coating to a wide variety of produce types and materials, such as wood and metal. The spray coating fluids used for each different industrial application may have much different fluid characteristics and desired coating properties. For example, wood coating fluids/stains are generally viscous fluids, which may have significant particulate/ligaments throughout the fluid/stain. Existing spray coating devices, such as air atomizing spray guns, are often unable to breakup the foregoing particulate/ligaments. The resulting spray coating has an undesirably inconsistent appearance, which may be characterized by mottling and various other inconsistencies in textures, colors, and overall appearance. In air atomizing spray guns operating at relatively low air pressures, such as below 10 psi, the foregoing coating inconsistencies are particularly apparent.

Accordingly, a technique is needed for internally inducing fluid breakup to enhance subsequent atomization at a spray formation section of a spray coating device.

SUMMARY OF THE INVENTION

In accordance with certain embodiments, a spray coating device includes a body and a spray formation head coupled to the body. The spray formation head has a fluid delivery mechanism comprising a pintle, a sleeve disposed about the pintle, and a throat between the pintle and the sleeve, wherein the throat decreases in cross-section at least partially lengthwise through the fluid delivery mechanism toward a fluid exit between the pintle and the sleeve. The spray formation head also has a pneumatic atomization mechanism disposed adjacent the fluid delivery mechanism, wherein the pneumatic atomization mechanism comprises a plurality of pneumatic orifices.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

As discussed in detail below, the present technique provides a refined spray for coating and other spray applications by internally inducing breakup of fluid passing through a spray coating device. This internal breakup is achieved by passing the fluid through one or more varying geometry passages, which may comprises sharp turns, abrupt expansions or contractions, or other mixture-inducing flow paths. For example, certain embodiments of the spray coating device may have a fluid delivery tip assembly, which has a sleeve disposed about a pintle to form a converging flow path. This converging flow path extends to a spray formation exit of the spray coating device. Thus, the converging flow path accelerates the fluid flow, thereby enhancing fluid atomization at the spray formation exit. For example, the increased fluid velocity may induce vortex shedding, fluid atomization, droplet distribution and uniformity, and so forth. Moreover, some embodiments of the fluid delivery tip assembly have helical channels to induce rotation of the fluid exiting at the spray formation exit of the spray coating device. Thus, the spray exhibits a vortical motion, which further enhances the spray. For example, the pintle and/or the sleeve may have a plurality of helical channels, which can have a variety of angles, sizes, and so forth. The present technique also may optimize the foregoing fluid breakup and atomization by varying the fluid velocities, degree of convergence and rotation, and other characteristics of the spray coating device.

FIG. 1is a flow chart illustrating an exemplary spray coating system10, which comprises a spray coating device12for applying a desired coating to a target object14. The illustrated spray coating device12may comprise an air atomizer, a rotary atomizer, an electrostatic atomizer, or any other suitable spray formation mechanism. As discussed in further detail below with reference toFIGS. 4-7, the spray coating device12also has a unique fluid delivery tip assembly204in accordance with certain embodiments of the present technique. The spray coating device12may be coupled to a variety of supply and control systems, such as a fluid supply16, an air supply18, and a control system20. The control system20facilitates control of the fluid and air supplies16and18and ensures that the spray coating device12provides an acceptable quality spray coating on the target object14. For example, the control system20may include an automation controller22, a positioning controller24, a fluid supply controller26, an air supply controller28, a computer system30, and a user interface32.

The control system20also may be coupled to one or more positioning mechanisms34and36. For example, the positioning mechanism34facilitates movement of the target object14relative to the spray coating device12. The positioning mechanism36is coupled to the spray coating device12, such that the spray coating device12can be moved relative to the target object14. Also, the system10can include a plurality of the spray coating devices12coupled to positioning mechanisms36, thereby providing improved coverage of the target object14. Accordingly, the spray coating system10can provide a computer-controlled mixture of coating fluid, fluid and air flow rates, and spray pattern/coverage over the target object. Depending on the particular application, the positioning mechanisms34and36may include a robotic arm, conveyor belts, and other suitable positioning mechanisms.

FIG. 2is a flow chart of an exemplary spray coating process100for applying a desired spray coating to the target object14. As illustrated, the process100proceeds by identifying the target object14for application of the desired fluid (block102). The process100then proceeds by selecting the desired fluid40for application to a spray surface of the target object14(block104). A user may then proceed to configure the spray coating device12for the identified target object14and selected fluid40(block106). As the user engages the spray coating device12, the process100then proceeds to create an atomized spray of the selected fluid40(block108). The user may then apply a coating of the atomized spray over the desired surface of the target object14(block110). The process100then proceeds to cure/dry the coating applied over the desired surface (block112). If an additional coating of the selected fluid40is desired by the user at query block114, then the process100proceeds through blocks108,110, and112to provide another coating of the selected fluid40. If the user does not desire an additional coating of the selected fluid at query block114, then the process100proceeds to query block116to determine whether a coating of a new fluid is desired by the user. If the user desires a coating of a new fluid at query block116, then the process100proceeds through blocks104-114using a new selected fluid for the spray coating. If the user does not desire a coating of a new fluid at query block116, then the process100is finished at block118.

FIG. 3is a cross-sectional side view illustrating an exemplary embodiment of the spray coating device12. As illustrated, the spray coating device12comprises a spray tip assembly200coupled to a body202. The spray tip assembly200includes a fluid delivery tip assembly204, which may be removably inserted into a receptacle206of the body202. For example, a plurality of different types of spray coating devices may be configured to receive and use the fluid delivery tip assembly204. The spray tip assembly200also includes a spray formation assembly208coupled to the fluid delivery tip assembly204. The spray formation assembly208may include a variety of spray formation mechanisms, such as air, rotary, and electrostatic atomization mechanisms. However, the illustrated spray formation assembly208comprises an air atomization cap210, which is removably secured to the body202via a retaining nut212. The air atomization cap210includes a variety of air atomization orifices, such as a central atomization orifice214disposed about a fluid tip exit216from the fluid delivery tip assembly204. The air atomization cap210also may have one or more spray shaping orifices, such as spray shaping orifices218,220,222, and224, which force the spray to form a desired spray pattern (e.g., a flat spray). The spray formation assembly208also may comprise a variety of other atomization mechanisms to provide a desired spray pattern and droplet distribution.

The body202of the spray coating device12includes a variety of controls and supply mechanisms for the spray tip assembly200. As illustrated, the body202includes a fluid delivery assembly226having a fluid passage228extending from a fluid inlet coupling230to the fluid delivery tip assembly204. The fluid delivery assembly226also comprises a fluid valve assembly232to control fluid flow through the fluid passage228and to the fluid delivery tip assembly204. The illustrated fluid valve assembly232has a needle valve234extending movably through the body202between the fluid delivery tip assembly204and a fluid valve adjuster236. The fluid valve adjuster236is rotatably adjustable against a spring238disposed between a rear section240of the needle valve234and an internal portion242of the fluid valve adjuster236. The needle valve234is also coupled to a trigger244, such that the needle valve234may be moved inwardly away from the fluid delivery tip assembly204as the trigger244is rotated counter clockwise about a pivot joint246. However, any suitable inwardly or outwardly openable valve assembly may be used within the scope of the present technique. The fluid valve assembly232also may include a variety of packing and seal assemblies, such as packing assembly248, disposed between the needle valve234and the body202.

An air supply assembly250is also disposed in the body202to facilitate atomization at the spray formation assembly208. The illustrated air supply assembly250extends from an air inlet coupling252to the air atomization cap210via air passages254and256. The air supply assembly250also includes a variety of seal assemblies, air valve assemblies, and air valve adjusters to maintain and regulate the air pressure and flow through the spray coating device12. For example, the illustrated air supply assembly250includes an air valve assembly258coupled to the trigger244, such that rotation of the trigger244about the pivot joint246opens the air valve assembly258to allow air flow from the air passage254to the air passage256. The air supply assembly250also includes an air valve adjustor260coupled to a needle262, such that the needle262is movable via rotation of the air valve adjustor260to regulate the air flow to the air atomization cap210. As illustrated, the trigger244is coupled to both the fluid valve assembly232and the air valve assembly258, such that fluid and air simultaneously flow to the spray tip assembly200as the trigger244is pulled toward a handle264of the body202. Once engaged, the spray coating device12produces an atomized spray with a desired spray pattern and droplet distribution. Again, the illustrated spray coating device12is only an exemplary device of the present technique. Any suitable type or configuration of a spraying device may benefit from the unique fluid mixing, particulate breakup, and refined atomization aspects of the present technique.

FIG. 4is a partial cross-sectional view of the spray tip assembly200of the spray coating device12ofFIG. 3in accordance with certain embodiments of the present technique. As illustrated, the needle262of the air supply assembly250and the needle valve234of the fluid valve assembly232are both open, such that air and fluid passes through the spray tip assembly200as indicated by the arrows. Turning first to the air supply assembly250, the air flows through air passage256about the needle262as indicated by arrow270. The air then flows from the body202and into a central air passage272in the air atomization cap210, as indicated by arrows274. The central air passage272then splits into outer and inner air passages276and278, such that the air flows as indicated by arrows280and282, respectively. The outer passages276then connect with the spray shaping orifices218,220,222, and224, such that the air flows inwardly toward a longitudinal axis284of the spray tip assembly200. These spray shaping airflows are illustrated by arrows286,288,290, and292. The inner passages278surround the fluid delivery tip assembly204and extend to the central atomization orifices214, which are positioned adjacent the fluid tip exit216of the fluid delivery tip assembly204. These central atomization orifices214eject air atomizing flows inwardly toward the longitudinal axis284, as indicated by arrows294. These air flows286,288,290,292, and294are all directed toward a fluid flow296ejected from the fluid tip exit216of the fluid delivery tip assembly204. In operation, these air flows286,288,290,292, and294facilitate fluid atomization to form a spray and, also, shape the spray into a desired pattern (e.g., flat, rectangular, oval, etc.).

Turning to the fluid flow in the spray tip assembly200, the fluid delivery tip assembly204includes an annular casing or sleeve300disposed about central member or pintle302, as illustrated byFIGS. 4 and 5. The illustrated pintle302includes a central fluid passage or preliminary chamber304, which leads to one or more restricted passageways or supply holes306. These supply holes306can have a variety of geometries, angles, numbers, and configurations (e.g., symmetrical or non-symmetrical) to adjust the velocity, direction, and flow rate of the fluid flowing through the fluid delivery tip assembly204. For example, in certain embodiments, the pintle302may include six supply holes306disposed symmetrically about the longitudinal axis284of the spray tip assembly200. In operation, when the need valve234is open, a desired fluid (e.g., paint) flows through fluid passage228about the needle valve234of the fluid valve assembly232, as indicated by arrows308. The fluid then flows into the central fluid passage or preliminary chamber304of the pintle302, as indicated by arrow310. As indicated by arrow312, the supply holes306then direct the fluid flow from the preliminary chamber304into a secondary chamber or throat314.

The illustrated throat314ofFIGS. 4 and 5is disposed between the sleeve300and the pintle302. In the illustrated embodiment, the geometry of the throat314substantially diverges and converges toward the fluid tip exit216of the fluid delivery tip assembly204. In operation, these diverging and converging flow pathways induce fluid mixing and breakup prior to primary air atomization by the air orifices214,218,220,222, and224of the air atomization cap210. For example, successive diverging and converging flow passages can induce velocity changes in the fluid flow, thereby inducing fluid mixing, turbulence, and breakup of particulate in the fluid.

In the illustrated embodiment ofFIGS. 4 and 5, the diverging and converging geometries of the throat314are defined by the pintle302and by the sleeve300. The illustrated sleeve300defines the outer boundaries of the throat314. For example, the illustrated sleeve300includes a first annular interior316, a second annular interior318, and a converging interior320that is angled inwardly from the first annular interior316to the second annular interior318. Thus, the first annular interior316has a relatively larger diameter than the second annular interior318. In alternative embodiments, one or more of the sleeve interiors316,318, and320may have a non-circular geometry (e.g., square, polygonal, etc.). Furthermore, some embodiments of the sleeve interiors316,318, and320may have a non-annular geometry, such as a plurality of separate passages rather than a single annular geometry.

The illustrated pintle302defines the inner boundaries of the throat314. As illustrated, a forward portion or tip section322of the pintle302includes an annular section324, a diverging annular section or conic tip portion326, and a converging annular section328extending from the annular section324280to the conic tip portion326. In other words, with reference to the longitudinal axis284, the annular section324has a substantially constant diameter, the conic tip portion326is angled outwardly from the longitudinal axis284toward the fluid tip exit216, and the converging annular section328is angled inwardly from the annular section324to the tonic tip portion326. Again, other embodiments of the tip section322of the pintle302can have a variety of constant, inwardly angled, or outwardly angled sections, which define the inner boundaries of the throat314.

As assembled inFIGS. 4 and 5, the sleeve300and pintle302have the sleeve interiors316, the320, and318surrounding the pintle sections324,328, and326, thereby defining an annular passage330, substantially restricted/unrestricted passages332and334, and a progressively converging annular passage336, respectively. In other words, the annular passage330has a relatively constant flow area, which in certain embodiments may be relatively larger than a flow area of the preliminary chamber304. In turn, the restricted passage332abruptly converges or decreases the flow area where the leading end of the pintle section328meets the trailing end of the sleeve interior320. Next, the pintle section328expands or increases the flow area relative to the sleeve interior318. Finally the pintle section326contracts or decreases the flow area relative to the sleeve interior318. As a benefit of these increasing and decreasing flow areas, the fluid delivery tip assembly204causes decreases and increases in the fluid flow velocity and, also, abrupt and gradual changes in fluid flow directions. Therefore, the fluid delivery tip assembly214enhances fluid mixing and fluid breakup (e.g., more viscous fluids or particulate), and may induce turbulent flow.

Regarding the fluid flow through the throat314, the illustrated arrows338,340, and342indicate fluid flow pathways through the annular passage330, through the substantially restricted/unrestricted passages332and334, and through the progressively converging annular passage336, respectively. At the fluid tip exit216, the fluid flows out to form a sheet or cone of fluid as indicated by arrow344. Simultaneously, the air flows286,288,290,292, and294from the air cap210coincide with the fluid sheet or cone344, thereby atomizing the fluid and shaping a desired formation of the spray. In addition, as illustrated inFIG. 5, a tip346of the pintle302extends beyond the fluid tip exit216by a distance348, which advantageously induces vortex shedding to further enhance the fluid breakup and atomization. Moreover, at the fluid tip exit216, the increased fluid velocity attributed to the progressively converging annular passage336of the throat314further increases the velocity differential between the exiting fluid344and the environmental air. This increased velocity further enhances the vortex shedding and, also, substantially reduces back flow into the fluid delivery tip assembly204.

FIGS. 6 and 7illustrate the pintle302having an alternative tip section350in accordance with certain embodiments of the present technique. Turning first toFIG. 6, a cross-sectional view of the pintle302illustrates the alternative tip section350having a plurality of helical fluid channels352in accordance with certain embodiments of the present technique. As illustrated, the helical fluid channels352are disposed about the conic tip section326. In operation, these helical fluid channels352induce rotational motion or vortical fluid flow of the converging/accelerating fluid flow passing through the converging annular passage336. When the fluid delivery tip assembly204ejects this fluid at the fluid tip exit216(seeFIGS. 4 and 5), these helical fluid channels352cause the spray to exhibit rotation or vortical motion, thereby enhancing fluid atomization, mixing, and droplet distribution and uniformity. These helical fluid channels352may have any suitable angle, geometry, configuration, and orientation within the scope of the present technique. For example, some embodiments of the helical fluid channels352may include four, six, eight, or ten symmetrical channels, which may have an angle of 15, 30, 45, or 60 degrees.FIG. 7is a front view of one embodiment of the pintle section350ofFIG. 6having eight of the helical fluid channels352, wherein the channels352have a rectangular cross-section. In addition, certain embodiments of the helical fluid channels may extend along the other sections324and328of the pintle tip section350. Moreover, alternative embodiments can have helical channels disposed on one or more of the sleeve interiors316,318, and320.