Patent Publication Number: US-6669112-B2

Title: Air assisted spray system with an improved air cap

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of prior U.S. Provisional Application Serial No. 60/283,001 filed Apr. 11, 2001 and entitled “AIR ASSISTED SPRAY SYSTEM WITH AN IMPROVED AIR CAP”. 
    
    
     BACKGROUND OF INVENTION 
     The present invention relates generally to an air assisted spray system and more particularly, to an improved air cap for an air assisted spray gun system. 
     Spray gun systems for atomizing a pressurized fluid stream with a pressurized gas, such as air, are known in the art. In such systems, the fluid stream is intermixed with pressurized air to breakdown or atomize the fluid stream into very fine particles. The fluid particle breakdown can occur as the fluid is exhausted from an apertured air cap positioned at a nozzle discharge end of the spray gun system. 
     From efficiency and economic operating viewpoints, it is desirable that such particle breakdown be effected using relatively low air flow rates and pressure. Heretofore, this has created problems. In particular, spray tips or air caps which provide efficient and economic operation are generally relatively complex in design, and hence, are relatively expensive to produce. 
     Moreover, air caps are also limited in terms of their versatility. For example, such air caps are typically designed for use with a specific air assisted nozzle body configuration. Accordingly, multiple air caps must be provided for each type of nozzle assembly. The relatively high costs of such air caps, therefore, only exacerbates the problem of readily achieving the goal of providing efficient and effective operation of the spray gun system. 
     The ability to achieve peak air flow volume from the air cap is complicated by numerous considerations. First, during operation of the spray gun system, the pressurized air flow to the air tip can cause back pressure problems within the system. Second, the transition between component parts of the spray gun system, especially at the conjuncture between the air cap and the air passages within the body of the spray gun system can cause turbulence problems, which can adversely affect pressurized air flow to the air cap. The ability to accurately machine discharge orifices or apertures in relatively thin walled parts or sections of parts is also critical for achieving accurate impingement between the pressurized air and the fluid stream exhausted from the air cap. 
     It would therefore be desirable to have an apparatus and system which is relatively inexpensive to manufacture and capable of minimizing back pressure and turbulence within the spray gun system, particularly in the transition area of the air cap and the air flow passages leading from the spray gun system. 
     BRIEF DESCRIPTION OF INVENTION 
     The present invention is directed to an apparatus and system having apertures configured to discharge pressurized gas toward a pressurized fluid to form a oval-spray pattern. 
     An improved air cap for an air-assisted spray nozzle assembly of a spray gun system is provided. The air cap includes a center aperture for accommodating an aperture nozzle or tip from whence a pressurized liquid is sprayed. The air cap further includes a plurality of apertures within the air cap housing that directs a pressurized medium toward the aperture tip for atomizing and shaping the liquid flow spraying from the nozzle. 
     In accordance with one aspect of the present invention, an air cap for an air-assisted spray nozzle assembly includes a body form by a housing having an inner surface which defines a plurality of apertures. The plurality of apertures is configured to pass a pressurized medium, such as air, therethrough. The plurality of apertures includes at least one non-circular orifice through which the pressurized medium passes through. 
     In accordance with another aspect of the present invention, an air cap for a spray nozzle assembly includes a housing having an inlet end engageable to a discharge end of a spray gun, and an outlet end on an opposite side of the inlet end. The outlet end has a plurality of apertures in an inside surface of the outlet end such that at least one of the plurality of apertures has a non-circular boundary on an inside surface of the outlet end. 
     In a further aspect of the present invention, a spray gun system is disclosed. The system includes a gun body adapted to receive a pressurized fluid and discharge the pressurized fluid at a nozzle end. The system also includes a nozzle assembly connected to a nozzle end of the gun body. The nozzle assembly includes an air cap having a pair of non-circular apertures on an inside surface of the air cap. Each of the non-circular apertures are in communication with a plurality of discharge apertures that discharge pressurized gas toward a pressurized fluid to form a generally oval-shaped spray pattern. 
     In yet another aspect of the present invention, an air cap for an air-assisted spray nozzle assembly includes a body having a cylindrical sidewall and an end wall connected to the cylindrical sidewall. The end wall has an inside surface, an outside surface and at least one aperture therein. The inside surface of the end wall has a non-circular opening in fluid communication with the at least one aperture. The outside surface of the end wall has a plurality of openings in fluid communication with the at least one aperture. 
     Various other features, objects and advantages of the present invention will be made apparent from the following detailed description and the drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The drawings illustrate one preferred embodiment presently contemplated for carrying out the invention. 
     In the drawings: 
     FIG. 1 is a side elevational view of a spray gun system. 
     FIG. 2 is an enlarged longitudinal sectional view of a nozzle discharge end of the spray gun system of FIG.  1 . 
     FIG. 3 is an exploded perspective view of the nozzle discharge end of the spray system of FIG.  1 . 
     FIG. 4 is a perspective view of a forward portion of an air cap in accordance with the present invention. 
     FIG. 5 is a perspective view of a rearward portion of the air cap of FIG.  4 . 
     FIG. 6 is a sectional view of a prior art air cap. 
     FIG. 7 is a sectional view taken along line  7 — 7  of FIG.  2 . 
     FIG. 8 is a partial sectional view taken along line  8 — 8  of FIG.  4 . 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, an air assisted spray gun system and spray gun  10  is shown. The spray gun  10  includes a body portion  12 , a depending grip  14 , and an air-assisted spray nozzle assembly or nozzle discharge end  16 . The grip  14  and body portion  12  of the spray gun  10  have internal passages for communicating a medium, such as air, from a pressurized source  18  to the nozzle discharge end  16  of the spray gun  10 . The spray gun  10  further includes a manually operated trigger  20  pivotally connected to the body portion  12  and a valve stem  22 . The trigger  20  is used for selectively controlling the flow of pressurized fluid to be atomized at the nozzle discharge end  16  of the spray gun  10 . While the present invention is described in connection with a particular illustrated spray gun system, it will be readily appreciated that the present invention is equally applicable to other spray gun systems having different configurations. 
     The nozzle discharge end  16  of the spray gun system  10  includes a gun head  24  and an air cap  26 . Connectors  28  and feed lines  29  connect the gun head  24  to a suitable pressurized fluid source  30 , such as a paint or other liquid. The air cap  24  has a pair of air horns  32 ,  34  that are formed to direct a pressurized medium toward an apertured tip  36  of the nozzle assembly  16 , which is configured to discharge the fluid from the pressurized fluid source  30 . That is, the pressurized medium is directed from the air horns  32 ,  34  to atomize and form a spray pattern of a liquid flow stream delivered to and exhausted from the apertured tip  36  into very fine particles in a preferred pattern so as to maximize spray gun efficiency. 
     Turning to FIG. 2, an enlarged longitudinal sectional view of a nozzle discharge end of the spray gun system of FIG. 1 is shown. The gun head  24  is formed with a generally centralized liquid passage  38  which communicates with the pressurized fluid source  30 . The gun head  24  further has a series of longitudinally extending atomizing passages  40  communicating with the internal passages in the body portion  12  of the spray gun  10 . The longitudinally extending passages  40  open at a distal end to an annular chamber  42  in the gun head  24 . 
     In the illustrated embodiment, the gun head liquid passage  38  directs pressurized fluid or paint to a fluid seat assembly  44  connecting to the apertured tip  36  of the spray gun  10 . Seat assembly  44  includes a fluid seat  46  which is supported and extends from the gun head  24 . An upstream end of the fluid seat  46  is configured with an externally threaded cylindrical extension  48  which is threadably coupled within a distal end of the generally centralized liquid passage  38  in the gun head  24 . Between proximal and distal ends thereof, to fluid seat  46  is configured with an enlarged radial flange  50 . Moreover, the fluid seat  46  has a series of longitudinally extending atomizing passages  52  which communicate with and receive a pressurized medium or gas from the annular chamber  42  in the gun head  24 . A seal  54  is entrapped and seals between the fluid seat radial flange  50  and the gun head  24  and is disposed radially outwardly from the annular chamber  42  and inlet ends of each atomizing passage  52  defined by fluid seat  46 . In the exemplary embodiment seal  54  is configured as a conventional elastomeric O-ring seal. 
     In FIG. 2, the fluid seat  46  has a generally centralized, longitudinally extending fluid passage  56  which, at a proximal end, communicates with the fluid passage  38  in the gun head  24  and at the distal end directs pressurized fluid, such as paint to the tip  36  from whence fluid is atomized. A valve  58  is intermediate the proximal and distal ends of passage  56 , and has a spherical valve element  60  which engages and seals against the fluid seat  46 . The elongated linearly displaceable valve stem  22  is operably connected, at one end, to the valve element  60  and is operably connected at an opposite end to the trigger  20  of the spray gun system  10 . 
     Still referring to FIG. 2, the air cap  26  is mounted and held in place by a retaining ring  62 . Toward a rear end of the retaining ring  62 , internal threads  64  are provided for engaging the gun head  24 . At the other end of the retaining ring  62 , an inwardly turned lip  66  on the ring  62  captures and cooperates with a radial step  68  of the air cap  26  thereby releasably affixing and positioning the air cap  26  at the nozzle discharge end  16  of the spray gun system  10 . As illustrated, the retaining ring  62  operably combines with the fluid seat  46  to define a chamber  70  therebetween. As will be appreciated, other means for affixing and positioning the air cap  26  at the nozzle discharge end  16  of the spray gun system  10  would equally suffice without detracting or departing from the spirit and scope of the present invention. 
     The air cap  26  defines a generally centralized axial opening or center aperture  72  for discharging the pressurized fluid and has a first generally cylindrical portion  74  which is axially aligned and generally concentric with a second generally cylindrical portion  76 . Upon assembly of the spray gun system  10 , the first generally cylindrical portion  74  of the opening  72  is sized to fit snugly about and along a lengthwise portion of the fluid seat  46  on a side of the radial flange  50  opposite from the seal  54 . During tightening of the retaining ring  62  to the spray gun  10 , seal  54  is compressed to effect a fluid tight seal between the gun head annular chamber  42  and the inlet end of each atomizing passage  52  defined by fluid seat  46 . The second lengthwise portion  76  of the opening  72  is sized to snugly accommodate the nozzle tip  36  lengthwise therein. The air horns  32 ,  34  of the air cap  26  have a plurality of openings  78  having passages  80 , some of which are non-parallel to one another. 
     FIG. 3 shows an exploded view of the nozzle discharge end  16  of the spray system of FIG.  1 . The feed line  29  and connector  28  are secured to the gun head  24 , which receives the valve stem  22  shown in FIG.  1  through center opening  81  of washer  82 . The O-ring seal  54  seals the seat assembly  44 , having atomizing passages  52  and fluid passage  56  therein, to the gun head  24  to effect the air tight seal. The air cap  26  engages a discharge end  83  of the seat assembly  44  of the spray gun  10 , and has the tip  36  also secured thereto to discharge the pressurized fluid communicated through line  29 . Retaining ring  62  secures the tip  36 , air cap  26 , and seat assembly  44  to the gun head  24  and is configured to assist with controlling the directional flow of the pressurized fluid sprayed from the tip  36 . 
     FIGS. 4 and 5 are perspective views of the front and back of the air cap  26 . The opening  72  is axially aligned with an axis  84  and the first and second cylindrical portions  74 ,  76  respectively. The first cylindrical portion  74  has a different diameter than the diameter of the second cylindrical portion  76  thereby defining a radial wall  86  extending therebetween. The radial wall  86  has an outlet end  87  for discharging the pressurized medium into the air horns  32 ,  34 . The two air horns  32 ,  34  extend outward and away from an outer side of the radial or end wall  86 , in a direction generally parallel to the axis  84 . Preferably, the air horns  32 , 34  are integrally formed to the radial wall  86  of a housing or body  90  of the air cap  26 , and are adapted to receive a plug  92  upon completion of air cap machining. The housing  90  further includes an inlet end  91  engageable to the discharge end  83  of the spray gun  10 , and has the inlet end  91  connected to the outlet end  87 . 
     Each air horn  32 ,  34  is configured with inner and outer walls  94  and  96 , respectively, disposed at different radial distances from the axis  84  of the air cap  26 . Preferably, the inner walls or discharge end  94  of the air horns  32 ,  34  extend in a generally parallel relation relative to each other and, in the illustrated embodiment, in generally parallel relation to the axis  84  of the air cap  26 . The inner walls  94  also include the plurality of discharge openings  78  which are configured to discharge the pressurized medium. As will be appreciated, the radial disposition of wall  94  is defined by the inner diameter of the second cylindrical portion  76  of the opening  72 . Furthermore, the radial disposition of the outer wall  96  is defined by the outer diameter of the housing  90 . Walls  94  and  96  are joined to each other by an end wall  98 . Opposed and generally parallel side walls  100  and  102  span the radial distance between the inner and outer walls  94  and  96 , respectively. 
     The air cap  26  further includes apertures  104 ,  106  and  108 ,  110  disposed at opposed sides of the longitudinal axis  84  between air horns  32 ,  34  of the air cap  26 . Inlet ends of the passages  104 ,  106  and  108 ,  110  open to and receive the pressurized medium from the air chamber  70 . Outlet or distal ends of the fluid passages  104 ,  106  and  108 ,  110  nearest the air horns  32 ,  34  open to and direct a pressurized stream toward the apertured tip  36  during operation of the spray gun  10 . The pressurized streams directed by the fluid passages  104 ,  106  and  108 ,  110  toward the apertured tip  36  provide a cleansing effect to the tip  36  during spray gun operation. 
     Referring specifically to FIG. 5, an inner surface  112  of the housing  90  defines a non-circular orifice  114  of the air cap  26 . Preferably, the air cap has two non-circular orifices  114  that are configured to discharge the pressurized medium through the air horn openings  78 . The air cap also includes a stem  116  connected to the inner surface  112  during the machining process of the air cap  26 . 
     FIGS. 6 and 7 show sectional views of a prior art air cap (FIG. 6) and the cap  26  of the present invention (FIG.  7 ). The prior art circular orifices  118 ,  120  of radial wall  86  of FIG. 6 are aligned along a Y-axis and are symmetrically disposed about an X-axis that equally segments the housing  90 . The orifices  118 ,  120  have a circular inlet for discharging the pressurized medium through the air horn openings  78  of air horns  32 ,  34 . 
     In accordance with the present invention as best shown in FIG. 7, the inner surface  112  of the housing  90  defines a pair of opposed, uniquely configured apertures  122 ,  124  having non-circular boundaries in the radial wall  86 . The non-circular apertures  122 ,  124  are configured to pass a pressurized medium therethrough, and in one embodiment have the pair of apertures  122 ,  124  arranged on opposed sides of longitudinal axis  84 . In another embodiment, the non-circular boundary is an elliptical boundary. The non-circular boundary is defined by an arcuate wall  130  contiguous with the cylindrical sidewall  74 , a pair of opposing sidewalls  132 ,  134  extending inwardly from the cylindrical sidewall  74  and a wall  136  connecting the pair of opposing sidewalls  132 ,  134 . Preferably, the pair of opposing sidewalls  132 ,  134  form a 90° angle at the connections to the cylindrical sidewall  74  and wall  136 . The passages or cavities  80  in the air horn housings  32 ,  34  are in communication with the discharge orifices  126 ,  128 . In the preferred form, the apertures  122 ,  124  longitudinally extend within the air horn housings  32 ,  34 . Each of the apertures  122 ,  124  opens to and receives the pressurized medium from the atomizing passages  52  of the fluid seat  46 . The apertures  122 ,  124  extend longitudinally and preferably parallel to the axis  84  of the air cap  26  until proximate to the end wall  98  of each air horn housing  32 ,  34 . The apertures  122 ,  124  cooperate relative to each other to direct a high volume flow of discharge pattern shaping atomizing medium or air from a respective passage  80  toward each other and toward the nozzle tip  36  at the discharge end  16  of the spray gun  10 . In one embodiment, the apertures  122 ,  124  can have an elliptical-like cross-section or boundary. 
     The apertures  122 ,  124  are configured to communicate with the passages  80  in the air horns  32 ,  34 . The passages  80  exhaust the pressurized medium from the plurality of air horn openings  78 . Preferably, at least one passage is perpendicular to the non-circular apertures  12 ,  124  for each air horn  32 ,  34  to direct the pressurized medium toward an opposing air horn. 
     FIG. 8 is a partial sectional view taken along line  8 — 8  of FIG. 4 showing a perpendicular passage  80  in air horn  34 , which is also perpendicular to the air horn&#39;s inner wall  94 . Preferably, each air horn  32 ,  34  has two parallel passages perpendicular to the discharge orifice of the air horn, and one passage that is non-parallel to the two parallel passages that discharge the pressurized medium or gas toward the fluid to form a generally oval-shaped spray pattern. 
     The unique configuration of the non-circular boundary of the air cap  26  advantageously increases the volume and velocity of atomizing air or pressurized medium exhausted from the air cap  26  thereby allowing for enhanced air impingement relative to the liquid passing from the apertured tip  36 . Accordingly, the efficiency and effectiveness of the spray gun  10  is significantly enhanced with minimum design changes to the spray gun  10  in a cost efficient manner. 
     The unique configuration of the apertures  122 ,  124  within the air cap  26  provide another advantage of significantly reducing air turbulence in the transition area between the fluid seat  46  and the air cap  26 . That is, the cross-sectional or elliptical-like configuration of the discharge orifices  126 ,  128  promotes a smooth flow of atomizing air or medium from the fluid seat  46  to the air horns  32 ,  34  relative to prior art circular geometries. 
     Another advantage of having non-circular apertures is that machining and manufacture of the air cap  26  is easier. With the present invention, the distance or wall thickness separating the inner wall  94  having the plurality of openings  78  and the apertures  122 ,  124  can be maximized by elongating the cross-sectional configuration along the X-axis. As will be appreciated by those skilled in the art, maximizing the thickness of the inner wall  94  facilitates machining of the openings  78  extending from the passages  80  and enhances impingement of the atomized medium against the pressurized fluid sprayed from the nozzle end  16  of the spray gun system  10 . 
     In accordance with one aspect of the present invention, an air cap for an air-assisted spray nozzle assembly or air nozzle includes a body form by a housing having an inner surface which defines a plurality of apertures. The plurality of apertures is configured to pass a pressurized medium or air therethrough. The plurality of apertures includes at least one non-circular orifice in the air cap through which the pressurized medium or air passes through. 
     In accordance with another aspect of the present invention, an air cap for a spray nozzle assembly includes a housing having an inlet end engageable to a discharge or spraying end of a spray gun, and an outlet end on an opposite side of the inlet end. The outlet end has a plurality of apertures in an inside surface of the outlet end such that at least one of the plurality of apertures has a non-circular boundary, such as an elliptical-like boundary, on the inside surface of the outlet end. 
     In a further aspect of the present invention, a spray gun system is disclosed. The spray gun system includes a gun body adapted to receive a pressurized fluid, such as paint, and discharge the pressurized fluid at a nozzle end having an apertured tip. The system also includes a nozzle assembly connected to a nozzle end of the gun body. The nozzle assembly includes an air cap having a pair of non-circular apertures on an inside surface of the air cap. Each of the non-circular apertures are in communication with a plurality of discharge apertures that discharge pressurized gas or a medium toward a pressurized fluid to form a generally oval-shaped spray pattern. 
     In yet another aspect of the present invention, an air cap for an air-assisted spray nozzle assembly of a spray gun includes a body having a cylindrical sidewall and an end wall connected to the cylindrical sidewall. The end wall has an inside surface, an outside surface and at least one aperture therein. The inside surface of the end wall has a non-circular opening in fluid communication with the at least one aperture, and the outside surface of the end wall has a plurality of openings in fluid communication with the at least one aperture. 
     The present invention has been described in terms of the preferred embodiment, and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims.