Patent Publication Number: US-9409191-B2

Title: Internal mixing spray gun

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/675,504, entitled “INTERNAL MIXING SPRAY GUN”, filed Nov. 13, 2012, which is a continuation of U.S. patent application Ser. No. 12/502,527, entitled “INTERNAL MIXING SPRAY GUN”, filed Jul. 14, 2009, now U.S. Pat. No. 8,322,632. Each of the foregoing applications is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     The invention relates generally to an internal mixing spray gun and, more specifically, to a system for effectively mixing multiple materials having substantially different viscosities and flow rates. 
     In many applications, two or more base materials are mixed together to achieve a material composition. The base materials may include different liquids, solids, or some combination thereof. The characteristics of the material composition may depend significantly on the uniformity of mixing of the two or more base materials. For example, if a resin and a catalyst are not adequately mixed together, then the material composition may be weak due to uncured portions of the resin. Unfortunately, existing systems often fail to adequately mix such base materials together, thereby reducing the quality of the final product. 
     BRIEF DESCRIPTION 
     A system, in certain embodiments, includes a spray device including a first liquid passage configured to flow a first liquid in a generally downstream direction toward a spray tip. The spray device also includes a second liquid passage configured to flow a second liquid in a generally upstream direction such that the second liquid impinges upon the first liquid at an outlet to the second liquid passage. The upstream direction is substantially opposite from the downstream direction. 
    
    
     
       DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is a diagram illustrating an exemplary spray coating system in accordance with certain embodiments of the present technique; 
         FIG. 2  is a flow chart illustrating an exemplary spray coating process in accordance with certain embodiments of the present technique; 
         FIG. 3  is a right side view of an exemplary spray coating device in accordance with certain embodiments of the present technique; 
         FIG. 4  is a left side view of the spray coating device, as shown in  FIG. 3 , in accordance with certain embodiments of the present technique; 
         FIG. 5  is a cross-sectional bottom view of the spray coating device, taken along line  5 - 5  of  FIG. 4 , in accordance with certain embodiments of the present technique; 
         FIG. 6  is a perspective view of a valve body, as shown in  FIG. 5 , in accordance with certain embodiments of the present technique; 
         FIG. 7  is a front view of the valve body, as shown in  FIG. 5 , in accordance with certain embodiments of the present technique; 
         FIG. 8  is a cross-sectional side view of the valve body, taken along line  8 - 8  of  FIG. 7 , in accordance with certain embodiments of the present technique; 
         FIG. 9  is a perspective view of a mixing baffle, as shown in  FIG. 5 , in accordance with certain embodiments of the present technique; 
         FIG. 10  is a cross-sectional bottom view of the mixing baffle, taken along line  10 - 10  of  FIG. 9 , in accordance with certain embodiments of the present technique; 
         FIG. 11  is a perspective view of an alternative embodiment of the valve body shown in  FIG. 6  in accordance with certain embodiments of the present technique; and 
         FIG. 12  is a cross-sectional front view of the spray coating device, taken along line  12 - 12  of  FIG. 4 , in accordance with certain embodiments of the present technique. 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Any examples of operating parameters and/or environmental conditions are not exclusive of other parameters/conditions of the disclosed embodiments. 
     Spray guns configured to mix plural components may be employed to apply a wide variety of materials, such as multi-component paints, urethane foam, epoxy resin, and polyester or vinylester resin. For example, polyester or vinylester resin is typically utilized in the manufacture of fiberglass reinforced plastic (FRP) parts, such as boat hulls, bathtubs and shower stalls. The process of producing an FRP part generally includes applying sheets of fiberglass (e.g., chopped strand mat, woven roving, etc.) to a mold, and then spraying a combination of a resin and a catalyst onto the fiberglass. Once the resin and catalyst are mixed, the resin beings to set, ultimately forming the plastic element of the FRP composite structure. 
     As discussed below, the disclosed spray guns are configured to internally mix multiple materials, such as the resin and catalyst, prior to spraying. The disclosed embodiments are configured to provide significant internal mixing to produce a substantially homogeneous mixture, even with different materials (e.g., resin and catalyst) having significantly different viscosities and flows rates. For example, an example of a catalyst for polyester resins includes Methyl Ethyl Ketone Peroxide (MEKP). The viscosity of MEKP may be approximately 10 times lower than the viscosity of the resin. Furthermore, only 1% to 3% of MEKP by volume may be utilized to catalyze polyester resins. Despite the significant differences in viscosity and flow rate, the disclosed embodiments of spray guns are configured to provide significant internal mixing in a compact space (e.g., short length) of the spray guns, rather than requiring long mixing sections. Thus, the disclosed spray guns may be compact, easily maneuverable, and highly efficient at mixing multiple materials. As a result, the disclosed spray guns reduce waste and increase quality of the mixture applied to a target object, e.g., increased strength of the FRP part. 
     Embodiments of the present disclosure may facilitate effective mixing of multiple materials having substantially different flow rates and viscosities within a spray gun. In certain embodiments, a spray gun includes a first liquid passage configured to flow a first liquid in a generally downstream direction toward a spray tip. The spray gun also includes a second liquid passage extending within the first liquid passage and configured to flow a second liquid in a generally upstream direction, substantially opposite from the downstream direction, such that the second liquid impinges upon the first liquid at an outlet to the second liquid passage. The impingement of the second liquid upon the first liquid establishes a region of turbulent flow that serves to mix the first liquid with the second liquid. Further embodiments include multiple mixing baffles positioned downstream from the outlet to the second liquid passage. In such embodiments, each mixing baffle includes at least one set of converging passages configured to direct liquid flows toward one another. As one liquid flow impinges another, a turbulent flow is established that serves to further mix the first liquid and the second liquid. In certain configurations, the at least one set of converging passages of a first mixing baffle is circumferential offset from the at least one set of converging passages of another mixing baffle. This circumferential offset forces the liquid flow to follow a tortuous path through the baffles, thereby further mixing the first and second liquids. The combination of these features may result in effective mixing of the first liquid and the second liquid despite significant differences in flow rate and viscosity. 
       FIG. 1  is a flow chart illustrating an exemplary spray coating system  10 , which comprises a spray coating device  12  for applying a desired coating to a target object  14 . The spray coating device  12  may be coupled to a variety of supply and control systems, such as a liquid supply  16 , an air supply  18 , and a control system  20 . The control system  20  facilitates control of the liquid and air supplies  16  and  18  and ensures that the spray coating device  12  provides an acceptable quality spray coating on the target object  14 . For example, the control system  20  may include an automation system  22 , a positioning system  24 , a liquid supply controller  26 , an air supply controller  28 , a computer system  30 , and a user interface  32 . The control system  20  also may be coupled to a positioning system  34 , which facilitates movement of the target object  14  relative to the spray coating device  12 . Accordingly, the spray coating system  10  may provide a computer-controlled mixture of coating liquid, liquid and air flow rates, and spray pattern. Moreover, the positioning system  34  may include a robotic arm controlled by the control system  20 , such that the spray coating device  12  covers the entire surface of the target object  14  in a uniform and efficient manner. 
     The spray coating system  10  of  FIG. 1  is applicable to a wide variety of applications, liquids, target objects, and types/configurations of the spray coating device  12 . In the present embodiment, the spray coating device  12  is configured to internally mix multiple liquids prior to spraying. In such an embodiment, a user may select a first desired liquid  40  from a plurality of different first coating liquids  42 , and a second desired liquid  44  from a plurality of different second coating liquids  44 . For example, the first coating liquid may be a resin and the second coating liquid may be a catalyst configured to cure the resin. In such a configuration, the first coating liquid may include polyester, vinylester, or epoxy resin, and the second coating liquid may include Methyl Ethyl Ketone Peroxide (MEKP) or an Aliphatic Amine adduct, for example. Certain embodiments may include unique features configured to facilitate effective mixing of the first desired liquid  40  and the second desired liquid  44  despite significant differences in flow rate and viscosity. The user also may select a desired object  36  from a variety of different objects  38 , such as different material and product types. For example, the target object may include fiberglass sheets disposed within a mold such that spraying a combination of resin and catalyst onto the target forms a fiberglass reinforced plastic (FRP) part after the resin has cured. As discussed in further detail below, the spray coating device  12  also may comprise a variety of different components and spray formation mechanisms to accommodate the target object  14  and liquid supply  16  selected by the user. For example, the spray coating device  12  may comprise an air atomizer, a rotary atomizer, an electrostatic atomizer, or any other suitable spray formation mechanism. 
       FIG. 2  is a flow chart of an exemplary spray coating process  100  for applying a desired spray coating to the target object  14 . As illustrated, the process  100  proceeds by identifying the target object  14  for application of the desired liquids, as represented by block  102 . The process  100  then proceeds by selecting the desired liquids for application to a spray surface of the target object  14 . Specifically, a user selects a first liquid  40 , as represented by block  104 , and then selects a second liquid  44 , as represented by block  105 . As will be appreciated, the second liquid  44  may be selected based on the selection of the first liquid  40 . For example, if the first desired liquid  40  is a resin, the second desired liquid  44  may be a catalyst configured to effectively cure the selected resin. As discussed in detail below, certain embodiments may include unique features configured to facilitate effective mixing of the first desired liquid  40  and the second desired liquid  44  despite significant differences in flow rate and viscosity. A user may then proceed to configure the spray coating device  12  for the identified target object  14  and selected liquids, as represented by block  106 . As the user engages the spray coating device  12 , the process  100  then proceeds to create a spray of the selected liquids, as represented by block  108 . The user may then apply a coating of the spray over the desired surface of the target object  14 , as represented by block  110 . Next, as represented by block  112 , the process  100  proceeds to cure/dry the coating applied over the desired surface. If an additional coating of the selected liquids is desired by the user at query block  114 , then the process  100  proceeds through blocks  108 ,  110 , and  112  to provide another coating of the selected liquids. If the user does not desire an additional coating of the selected liquids at query block  114 , then the process  100  proceeds to query block  116  to determine whether a coating of new liquids is desired by the user. If the user desires a coating of new liquids at query block  116 , then the process  100  proceeds through blocks  104 - 114  using new selected liquids for the spray coating. If the user does not desire a coating of new liquids at query block  116 , then the process  100  is finished at block  118 . 
       FIG. 3  is a right side view of an exemplary embodiment of the spray coating device  12 . As illustrated, the spray coating device  12  includes a body  202  configured to receive and mix multiple liquids prior to spraying. The spray coating device  12  also includes a nozzle assembly  204 . As discussed in detail below, the nozzle assembly  204  includes a static mixer configured to provide additional mixing of the liquids. The nozzle assembly  204  also includes a discharge orifice or spray tip  205  that ultimately directs the liquids toward the target  14 . The illustrated spray tip  205  includes two converging exit orifices configured to direct streams of liquid toward one another. This type of spray tip  205  may be described as an impingement tip, and provides a relatively coarse spray pattern. Such a spray pattern may be well suited for applications involving spraying resin and catalyst to form FRP parts. Alternative embodiments may include different spray tips  205 , such as atomizer tips for applying gel coats, or the like. Furthermore, the nozzle assembly  204  of the present embodiment is configured to be removable from the body  202  such that a particular nozzle assembly  204  may be selected for a specific application. 
     The spray coating device  12  also includes connectors and conduits configured to deliver a first liquid and a second liquid into the body  202 . Specifically,  FIG. 3  shows the second liquid conduit  206  and the second liquid inlet  208 . In the present configuration, the second liquid may be a catalyst configured to cure a resin (i.e., first liquid). For example, in certain embodiments, the first liquid is a polyester resin and the second liquid is MEKP. In such configurations, the second liquid conduit  206  may be configured to flow approximately 1% to 3% of the volume of the first liquid conduit, thereby establishing a volumetric ratio of resin and catalyst within a mixing portion of the body  202  to achieve proper curing. 
     The spray coating device  12  further includes a trigger  210  configured to regulate the flow of the first and second liquids into the body  202 . Specifically, the trigger  210  is rotationally coupled to the body  202  at a pivot point  212 . The trigger  210  is also coupled to needle valves that control the flow of the first and second liquids. As illustrated, the trigger  210  includes a mount  214 . A shaft  216  coupled to the second liquid needle valve (i.e.,  301  of  FIG. 5 ) extends through an opening within the mount  214 . A fastener  218  is secured to an opposite end of the shaft  216  from the needle valve. As the trigger  210  is rotated in a direction  211  about the pivot point  212 , the mount  214  contacts the fastener  218 . Further rotation of the trigger  210  moves the shaft  216  in a direction  213  via contact between the mount  214  and the fastener  218 . Movement of the shaft  216  opens the second liquid needle valve and initiates flow of the second liquid into a mixing portion of the body  202 . As discussed in detail below, the mixing portion includes an assembly configured to flow the second liquid in a substantially upstream direction  221  relative to the downstream flow  219  of the first liquid. Impingement of the second liquid upon the first liquid may establish a turbulent flow that enhances mixing of the two liquids. Furthermore, mixing baffles employing circumferentially offset converging passages may be positioned downstream from the outlet of the second liquid to further facilitate mixing. The combination of these features may result in effective mixing of the first liquid and the second liquid despite significant differences in flow rate and viscosity. 
       FIG. 4  is a left side view of the spray coating device  12  shown in  FIG. 3 . As illustrated, a first liquid conduit  220  including a first liquid inlet  222  extends into the body  202 . As previously discussed, the first liquid conduit  220  is configured to flow a significantly higher volume of liquid into the body  202  than the second liquid conduit  206 . Similar to the arrangement described above with regard to the second liquid, the trigger  210  is configured to regulate the flow of first liquid into the spray coating device  12 . Specifically, a shaft  224  is disposed through the trigger  210  and coupled to a fastener  226 . As the trigger  210  rotates in the direction  211  about the pivot point  212 , contact between the trigger  210  and the fastener  226  causes the shaft  224  to move in the direction  213  away from the body  202 . Because the shaft  224  is coupled to a needle valve (i.e.,  329  of  FIG. 5 ) within the body  202 , movement of the shaft  224  in the direction  213  causes the needle valve to open, thereby facilitating a flow of first liquid into the mixing portion of the body  202 . 
       FIG. 4  also illustrates a liquid flushing system  228  configured to flow a solvent through the spray coating device  12 . Because the spray coating device  12  is configured to receive and mix a resin and a catalyst, any liquid remaining in the body  202  after use may begin to set and eventually cure. Therefore, the liquid flushing system  228  is configured to flow a solvent through the mixing portion of the body  202  after spraying of the liquids is complete to substantially remove the liquids from the spray coating device  12 . Specifically, the liquid flushing system  228  includes an inlet  230  and an activation switch  232 . As discussed in detail below, depression of the activation switch  232  engages a flow of solvent through the inlet  230  into the body  202 . The solvent is configured to dissolve and remove residual liquids from the spray coating device  12  to substantially reduce or eliminate the possibility that resin may cure within the body  202  and interfere with operation of the spray coating device  12 . 
       FIG. 5  is a cross-sectional bottom view of the spray coating device  12 , taken along line  5 - 5  of  FIG. 4 . As previously discussed, the shaft  216  is coupled to a needle valve  301  configured to regulate the flow of second liquid into the mixing portion of the body  202 . Specifically, the shaft  216  is coupled to a compression spring  302  configured to bias the needle valve  301  into a closed position. A secondary shaft  304  extends between the shaft  216  and a plunger  306 . While in the closed position, the plunger  306  blocks the flow of second liquid from an inlet  308 , which is coupled to the second liquid conduit  206 . Specifically, the plunger  306  is disposed within an orifice  310  contoured to correspond to the shape of the plunger  306 , thereby forming a seal when the needle valve  301  is in the closed position. As the trigger  210  rotates about the pivot  212 , contact between the mount  214  and the fastener  218  causes the shaft  216  to move away from the body  202  and compress the spring  302 . As the spring  302  compresses, coupling between the shaft  216  and the secondary shaft  304  causes the plunger  306  to exit the orifice  310 , thereby facilitating liquid flow from the inlet  308  through orifice  310 . 
     The second liquid then flows through a conduit  312  to a mixing portion  313  of the body  202 . The second liquid first enters an annular recess or cavity  314  disposed within the mixing portion  313 . The annular cavity  314  serves to distribute the second liquid substantially evenly about the circumference of a valve body  315 . The second liquid then enters the valve body  315  via conduits  316  extending radially through the valve body  315  between the cavity  314  and a central chamber  318 . A check valve  319  is disposed adjacent to the central chamber  318  and serves to block the flow of first liquid into the central chamber  318 . As illustrated, the check valve  319  includes a shaft  320 , a retainer  322 , and a compression spring  324 , each being disposed within a central opening or cavity  326 . The second liquid flows from the central chamber  318  through a gap between the retainer  322  and the central cavity  326 , and then through a space between the shaft  320  and the central cavity  326  (i.e., adjacent to the compression spring  324 ). While in a closed position, the check valve  319  blocks the flow of the second liquid. Specifically, a head  327  of the shaft  320  is biased against the valve body  315  by the compression spring  324 , thereby restricting the flow of second liquid. 
     As discussed in detail below, a mixing chamber  328  is disposed adjacent to the head  327  and contains the first liquid. The check valve  319  is configured to open when the liquid pressure of the second liquid is greater than the liquid pressure of the first liquid plus an addition pressure sufficient to overcome the spring bias of the check valve  319 . For example, in certain configurations, the liquid pressure of the second liquid is approximately 300 psi and the liquid pressure of the first liquid is approximately 200 psi. In such configurations, the pressure sufficient to overcome the spring bias may be less than 100 psi. Therefore, when the second liquid enters the central cavity  326 , the liquid pressure may be sufficient to open the check valve  319  and facilitate mixing of the second liquid with the first liquid in the mixing chamber  328 . Furthermore, because the pressure of the second liquid is greater than the pressure of the first liquid, the mixture will not flow back through the check valve  319 . If the pressure of the second liquid drops below the pressure of the first liquid (plus the pressure sufficient to overcome the spring bias), the check valve will close, thereby blocking the flow of the first liquid into the central cavity  326 . This configuration substantially reduces or eliminates the possibility of liquid mixing within the flow path of the second liquid. 
     Similar to the arrangement described above with respect to the second liquid flow path, flow of the first liquid is regulated by a needle valve  329 . Specifically, the shaft  224  is coupled to a compression spring  330  configured to bias the needle valve  329  into a closed position. A secondary shaft  332  extends between the shaft  224  and a plunger  334 . While in the closed position, the plunger  334  blocks the flow of first liquid from an inlet  336 , which is coupled to the first liquid conduit  220 . As illustrated, the plunger  334  is disposed within an orifice  338  contoured to correspond to the shape of the plunger  334 , thereby forming a seal when the needle valve  329  is in the closed position. As the trigger  210  rotates about the pivot  212 , contact between the trigger  210  and the fastener  226  causes the shaft  224  to compress the spring  330 . As the spring  330  compresses, coupling between the shaft  224  and the secondary shaft  332  causes the plunger  334  to exit the orifice  338 , thereby facilitating liquid flow from the inlet  336  through orifice  338 . 
     With the needle valve  329  in the open position, the first liquid flows in a generally downstream direction  219  from the orifice  338  to the nozzle assembly  204 . Specifically, the first liquid flows from the orifice  338  into the mixing chamber  328 . As previously discussed, the second liquid flows into the mixing chamber  328  in a generally upstream direction  221 , substantially opposite from the downstream direction  219  (e.g., approximately 180 degrees relative to one another). In the present embodiment, the second liquid enters the mixing chamber  328  through a substantially annular orifice formed by the gap between the head  327  of the check valve shaft  320  and the valve body  315 . The annular orifice is configured to provide a generally even distribution of second liquid into the first liquid present in the mixing chamber  328 . Because the first liquid is flowing in a generally downstream direction  219  and the second liquid is flowing in a generally upstream direction  221 , interaction between the liquids induces a turbulent flow within the mixing chamber  328 , thereby effectively mixing the first liquid with the second liquid. 
     As previously discussed, the liquid pressure of the second liquid exiting the check valve  319  is greater than the pressure of the first liquid within the mixing chamber  328 . Therefore, flow of the mixed liquid is blocked from entering the central opening  326 . As a result, the liquid mixture is directed in a generally downstream direction  219  into the mixing portion  313  of the body, i.e., between the valve body  315  and an inner surface of the mixing portion  313 . The liquid then passes through a first mixing baffle  340 . As discussed in detail below, the first mixing baffle  340  includes multiple sets of converging passages, each set configured to direct liquid flows toward one another. As one liquid flow impinges another, a turbulent flow is established that serves to further mix the first liquid and the second liquid. The liquid mixture then flows through a second mixing baffle  342  similar to the first mixing baffle  340  to further mix the liquids. In certain configurations, the converging passages of the first baffle  340  are circumferential offset (i.e., shifted along a circumferential direction  347 ) from the converging passages of the second baffle  342 . This circumferential offset forces the liquid flow to follow a tortuous path through the baffles  340  and  342 , thereby further mixing the first and second liquids. 
     After passing through the baffles  340  and  342 , the mixed liquid continues to flow in the downstream direction  219 . Specifically, the liquid passes through flow passages within a downstream section  344  of the valve body  315 . The flow then passes through a passage  346  downstream of the valve body  315  and enters a static mixer  348  within the nozzle assembly  204 . The static mixer  348  includes a series of turning vanes, each configured to split the flow in half and rotate each half approximately 90 degrees. The splitting and turning motion serves to further mix the liquid. The present configuration includes four turning vanes. However, alternative configurations may employ more or fewer vanes. For example, certain configurations may include 0, 1, 2, 3, 4, 5, 6, 7, 8, or more vanes in the static mixer  348 . After passing through the static mixer  348 , the liquid exits the spray tip  205 . The mixing features within the spray coating device  12  serve to effectively mix the first liquid with the second liquid despite significant differences in flow rate and viscosity. Furthermore, the combination of impinging flow and the mixing baffles establish a well-mixed liquid within a shorter distance than spray coating devices that only employ static mixers, thereby resulting in a shorter, lighter and less cumbersome spray coating device  12 . 
       FIG. 6  is a perspective view of the valve body  315  shown in  FIG. 5 . As previously discussed, the valve body  315  includes the first baffle  340 , the second baffle  342 , and the downstream section  344 .  FIG. 6  also illustrates another perspective of the conduit  316  configured to transfer the second liquid from the annular cavity  314  to the central opening  326 , and the check valve shaft  320  configured to block the flow of first liquid into the central opening  326 . As discussed in detail below, each baffle  340  and  342  includes at least one set of converging passages  402  configured to direct liquid flows toward one another in the downstream direction  219 . The present embodiment includes two sets of two converging passages  402 . Alternative embodiments may include more or fewer sets of passages and/or more or fewer passages  402  per set. For example, certain embodiments may include 1, 2, 3, 4, 5, 6, 7, 8, or more sets of converging passages. Further embodiments may include 2, 3, 4, 5, 6, 7, 8, or more passages  402  within each set. Because of the converging arrangement, liquid exiting one passage of a set is directed toward liquid exiting another passage of the set. The impingement of the two or more liquid streams establishes a turbulent flow that facilitates additional mixing of the first liquid with the second liquid. 
     The configuration of the second baffle  342  may be substantially similar to the configuration of the first baffle  340 . However, in certain embodiments, the second baffle  342  is rotated about a longitudinal axis of the valve body  315 , thereby establishing a circumferential offset between the passages  402 . In such embodiments, liquid exiting the passages  402  of the first baffle  340  impinges upon an upstream surface of the second baffle  342 , thereby establishing a turbulent flow that facilitates liquid mixing. In addition, the offset forces the liquid to flow in the circumferential direction  347  between the first baffle  340  and the second baffle  342 , thereby establishing a tortuous flow path. As will be appreciated, the more tortuous the flow path, the greater the mixing effectiveness. For example, in certain configurations, a set of passages within the first baffle  340  may be rotated at least approximately 20, 45, 60, 80, 100, 120, 140, 160, 180, or more degrees relative to a set of passages within the second baffle  342 . 
     As illustrated, the valve body  315  also includes a pair of o-rings  404  configured to establish a seal between the valve body  315  and the inner surface of the mixing portion  313 . Specifically, the o-rings are positioned on opposite longitudinal sides of the liquid conduits  316 . In this configuration, the o-rings  404  serve to substantially maintain a barrier between the second liquid entering the conduits  316  and the mixed liquid passing through the baffles  340  and  342 . The valve body  315  also includes a flange  406  configured to position the valve body  315  within the mixing portion  313  of the body  202 . Furthermore, as illustrated, each baffle  340  and  342  includes a flange  408  configured to establish a gap between the baffles  340  and  342 . This gap facilitates mixing of the liquid exiting the first baffle  340  before flowing into the second baffle  342 . Consequently, the flanges  408  facilitate axial stacking (i.e., along an axial direction  343 ) of baffles within the valve body  315 . For example, while two baffles  340  and  342  are employed in the present embodiment, alternative embodiments may include more or fewer baffles, such as 1, 2, 3, 4, 5, 6, 7, 8, or more baffles. 
       FIG. 7  is a front view of the valve body  315 , illustrating flow passages  410  within the downstream portion  344 . The flow passages  410  enable the mixed liquid to flow from the baffles  340  and  342  to the downstream passage  346 . As illustrated, a gap between the flow passages  410  facilitates placement of the conduits  316 , such that the second liquid may flow into the central opening  326  without contacting the downstream flow of the mixed liquid. The present embodiment includes  10  circular passages  410 . Alternative embodiments may include passages  410  of different shapes, such as elliptical, square, or polygonal, for example. Further embodiments may include more or fewer passages. For example, certain embodiments may include more than 1, 2, 4, 6, 8, 10, 12, 14, 16, or more passages  410 . Furthermore, a fastener  412  is coupled to the downstream end of the valve body  315 . The fastener  412  serves to separate the flow of second liquid within the central opening  326  from the mixed liquid flowing through the passages  410 . 
       FIG. 8  is a cross-sectional side view of the valve body  315 , taken along line  8 - 8  of  FIG. 7 . As illustrated, the flow passages  410  extend along the entire longitudinal extent of the downstream portion  344  of the valve body  315 . Therefore, the passages  410  serve to facilitate liquid flow from the baffles  340  and  342  to the downstream passage  346 . In addition,  FIG. 8  illustrates the spacing provided by the flanges  408 . Specifically, the flange  408  of the second baffle  342  establishes an axial gap  409  between the first baffle  340  and the second baffle  342  in the axial direction  343 . The axial gap  409  provides a space for liquid from the converging passages of the first baffle  340  to intersect and mix prior to flowing into the second baffle  342 . Because each baffle includes a flange  408 , additional baffles may be axially stacked either upstream or downstream from the illustrated baffles  340  and  342 , while providing an axial gap  409  between baffles for liquid mixing. 
       FIG. 9  is a perspective view of the mixing baffle  340 . As previously discussed, the baffle  340  includes two sets of flow passages, where each set includes two passages  402 . As illustrated, the sets of flow passages are positioned approximately 180 degrees apart along the circumference of the baffle  340 . The flow passages  402  within each set converge in the downstream direction  219 . Specifically, each flow passage includes an inlet  414  and an outlet  416 . Because the inlets  414  are spaced farther apart than the outlets  416 , flows through the passages  402  are directed toward one another. As the two flows intersect, a turbulent flow is established, thereby facilitating mixing of the liquids. As previously discussed, the number of sets, the circumferential position of the sets and the number of passages  402  within each set may vary in alternative embodiments. 
     In the present embodiment, the converging flow passages  402  are configured to direct liquid flows toward one another substantially within a plane parallel to the axial direction  343 . In alternative embodiments, the converging flow passages  402  may be rotated in the radial direction  345  and/or the circumferential direction  347  such that impingement of one liquid upon another establishes a swirling liquid flow. This swirling flow may facilitate additional mixing of the first and second liquids. 
       FIG. 10  is a cross-sectional bottom view of the mixing baffle  340 , taken along line  10 - 10  of  FIG. 9 . As illustrated, the flow passages  402  converge toward an axial center line  418 . Specifically, each passage  402  forms an angle  420  with respect to the center line  418 . In the present embodiment, the angle  420  is approximately 45 degrees. Therefore, the passages are oriented approximately 90 degrees relative to one another. In alternative embodiments, the angle  420  may be approximately between 5 to 85, 10 to 80, 15 to 75, 20 to 70, 25 to 65, 30 to 60, 35 to 55, 40 to 50, or about 45 degrees. By further example, the angle  420  may be greater than approximately 0, 10, 22.5, 30, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or more degrees. As appreciated, larger angles  420  may facilitate enhanced mixing between the first and second liquids. However, a length  421  of the baffle  340  may be increased to accommodate the larger angles  420 , thereby increasing the length of the spray coating device  12 . Therefore, an angle  420  may be particularly selected to both provide effective mixing of the liquids while limiting the spray coating device length. In the present embodiment, liquid flows from the passage outlets  416  flow in a direction  422  and impinge one another, as illustrated. As previously discussed, this impingement facilitates enhanced mixing of the first and second liquids despite differences in flow rate and viscosity. 
       FIG. 11  is a perspective view of an alternative embodiment of the valve body  315 . Specifically, the alternative configuration is adapted for mixing liquids that include abrasives. For example, certain resins include a mineral filler such as calcium sulfate or alumina trihydrate in concentrations ranging from approximately 10% to 50%. While these mineral fillers provide enhanced qualities to certain FRP parts, their abrasive nature causes significant wear to various internal components of the spray coating device  12 . For example, the mixing baffles  340  and  342  are particularly sensitive to such abrasive fillers. Therefore, an alternative valve body  315  including a different baffle configuration may be utilized when spraying resins that include mineral fillers. Furthermore, the valve body  315 , and associated baffles, may be constructed from a harder material, such as precipitation hardened stainless steel, tungsten carbide, etc., to reduce wear. 
     As illustrated, the first baffle  340  is replaced with an alternative first baffle  502 , and the second baffle  342  is replaced with an alternative second baffle  504 . The first baffle  502  includes a U-shaped recess  506 , and the second baffle  504  includes a U-shaped recess  508 , positioned approximately 180 degrees from the recess  506  about the circumference of the second baffle  504 . As the liquid flow reaches the valve body  315 , the liquid is directed through the recess  506 . The liquid flow then impinges upon an upstream surface of the second baffle  504 , thereby establishing a turbulent flow that facilitates liquid mixing. The liquid is then forced to flow approximately 180 degrees in the circumferential direction  347  to pass through the recess  508 . The position of the recesses  506  and  508  establish a tortuous flow path that serves to further mix the first liquid and the second liquid. Because the liquid is not directed through small converging passages, wear on the baffles  502  and  504  may be reduced, thereby extending the useful life of the valve body  315 . 
     While the recess  508  is circumferentially offset approximately 180 degrees in the present embodiment, alternative embodiments may have different degrees of offset. For example, certain configurations may include a circumferential offset greater than approximately 20, 40, 60, 80, 100, 120, 140, 160, or more degrees. Further embodiments may include multiple recesses within each baffle  502  and  504 , such as 2, 3, 4, 5, 6, or more. Yet further embodiments may include additional baffles to provide additional mixing of the liquids. This configuration may provide effective mixing of the first and second liquids despite the absence of converging flow passages present in the previously described embodiment. 
       FIG. 12  is a cross-sectional front view of the spray coating device  12 , taken along line  12 - 12  of  FIG. 4 , illustrating the liquid flushing system  228 . As previously discussed, the liquid flushing system  228  is configured to flow a solvent through areas of the spray coating device  12  where the first liquid is present. This process significantly reduces or eliminates the possibility that resin or other material may cure within the spray coating device  12 , thereby interfering with its operation. The liquid flushing system  228  includes an activation switch  232 , a shaft  602 , and a compression spring  604 . The liquid flushing system  228  is activated by depressing the switch  232 , thereby compressing the spring  604  and driving the shaft  602  to move in a direction  606 . Movement of the shaft  602  establishes a flow path from the solvent inlet  230  through an annular cavity  608  and an orifice  610  in the liquid flushing system  228  to a first conduit  612 . The solvent then flows through a second conduit  614  into the mixing chamber  328 . From the mixing chamber  328 , the solvent flows in the downstream direction  219  through each of the previously described elements and exits the spray tip  205 . In this manner, each element that contacts the first liquid is exposed to the solvent such that the first liquid is flushed from the spray coating device  12 . As previously discussed, the present embodiment facilitates effective mixing of liquids within a shorter distance than configurations which do not employ a counter flow arrangement and mixing baffles. Therefore, less solvent may be utilized to flush the spray coating device  12 , thereby reducing operational costs. Furthermore, because the mixing chamber  328  is positioned directly adjacent to the first liquid needle valve  329 , flushing resin from additional areas within the body  202  is obviated. 
     While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.