Patent Publication Number: US-6708900-B1

Title: HVLP spray gun

Description:
This application is a C-I-P of U.S. application Ser. No. 60/243,095, filed Oct. 25, 2000. 
    
    
     TECHNICAL FIELD 
     1. Background Art 
     HVLP (high volume low pressure) paint spray guns have recently become increasingly popular for providing a high quality finish with good transfer efficiency. 
     2. Disclosure of the Invention 
     It is therefore an object of this invention to provide an HVLP spray gun which is easy to use, versatile, provides a high quality finish, and high transfer efficiency. 
     The spray gun of the instant invention is provided with a long needle guide nay relatively light spraying which enables the gun to have a very low trigger force. The surface on which the nozzle rests and is screwed into is located at the forward most end of the gun body (once the air cap and retaining ring are removed) thereby allowing the nozzle to be easily gripped and mounted or removed from the gun by hand without the need for any tools. 
     As with most air spray and HVLP guns, an air line extends downwardly out of the gun body to a tube which in turn attaches to a fitting on the top of the paint cup. Located on the inner side of this fitting on the paint cup (inside the paint container) is a polyurethane molded duckbill valve which serves as a check valve to prevent the flow of paint up into the air valve. Such a valve is a substantial improvement on the check valves of prior art devices which tend to become clogged with paint and which are more expensive to manufacture. 
     An air adjustment valve assembly has two parts—a total airflow adjustment valve and a spray pattern adjustment valve. The total flow valve adjusts exactly what it says—the amount of airflow into the gun for atomizing and spray pattern adjustment while the spray pattern adjustment valve adjusts only the width for the spray pattern. While this is referred to as a spray pattern adjustment, this adjustment is also commonly referred to as fan air or shaping air. The air valve assembly slides into the back of the gun, which enables it to be removed without the need for tools. 
     On the air cap, a 55° angle between the center hole (the centerline of the gun) and the side holes provides the best spray pattern with a chamfer on the center hole reduces the amount of large droplets at the side of the spray pattern and allows a uniform spray pattern. A radius of 0.015 inches on the front edge of the nozzle allows air to smoothly interface with the liquid flow stream resulting in an improved uniform droplet sized distribution on the spray pattern. Five lengths of nozzles for five different fluid sets allow the gun to use the same air cap with different flows. The nozzle housing is provided with nine 0.1718″ holes and eight 0.156″ holes to allow air to pass into the air cap. 
     In the gun body, airflow is divided into two streams by utilizing two separate holes. A 0.35″×0.70″ hole with a 48° angle provides air to the air cap center hole for atomization. While the 0.800″ hole and a 1.32″ slot introduces air to the side holes on the air cap providing fan air. 
    
    
     These and other objects and advantages of the invention will appear more fully from the following description made in conjunction with the accompanying drawings wherein like reference characters refer to the same or similar parts throughout the several views. 
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a side cross-section view showing the spray gun of the instant invention. 
     FIG. 2 is a perspective view of the duck bill valve of the instant invention. 
     FIG. 3 is a cross-sectional view taken along line  3 — 3  of FIG.  2 . 
     FIG. 4 is a perspective view showing the air valve assembly of the instant invention. 
     FIG. 5 is a partially cutaway view of the air valve also shown in FIG.  4 . 
     FIG. 6 is the cross-sectional view of the air cap of the instant invention. 
     FIG. 7 is the cross-sectional view of the fluid nozzle of the instant invention. 
     FIG. 8 is a side view of the nozzle also shown in FIG.  7 . 
     FIG. 9 is a cross-sectional view of the nozzle housing of the instant invention. 
     FIG. 10 is a front view showing the air holes in the nozzle housing of FIG.  9 . 
     FIG. 11 is a cross-sectional view of the gun body of the instant invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The instant invention generally designated  10  is shown in FIG.  1  and is comprised of a gun body  12 , a nozzle housing  14 , a nozzle  16 , an air cap  18 , and a retaining ring  20 . 
     Body  12  has an air inlet chamber  12   a  in the handle which extends upwardly to an opening  12   b  which extends into distribution air chamber  12   c.    
     FIG. 1 also shows a tube  22  extending downwardly from body  12  to a fitting  24  located on the top of spray cup  26 . Located on the inner end of fitting  24  is a duckbill valve  28 , which is shown in more detail in FIGS. 2 and 3. Duckbill valve  28  is formed from a polyurethane molding material having a hardness in the durometer range of 40 to 50. Air pressure applied to duckbill valve  28  will tend to force open slit  28   a  in the end thereof, allowing air to enter spray cup  26 . When pressurized air is removed from the inside of valve  28 , the valve closes and thus prevents fluid from passing upwardly out of spray cup  26  into gun body  12 . 
     Turning to FIG. 4, the air valve assembly  30  is comprised of a total air valve  32  having sealing and body engaging portion  32   a  and a valve portion  32   b  which are rotatably mounted on a shaft  34   a  of pattern air valve  34  which is further comprised of a handle portion  34   b  and a sealing portion  34   c  having a friction portion  34   d.  Assembly  30  is inserted into a generally cylindrical passageway  12   d  in handle  12  because both portions of valve assembly  30  have frictional engagements (elements  32   a  and  34   d  respectively) each can be operated independently of the other in spite of the fact that one is rotatably mounted on the other. In particular, the pattern handle  34   b  may be used to rotate valve element  34   c  so as to selectively open and close passage  12   e  in body  12 . Similarly, handle element  32   c  on total air valve  32  may be used to rotate valve portion  32   b  to selectively open and close aperture  12   b  in body  12 . Assembly  30  is merely frictionally engaged in body  12  so that merely by pulling rearward on the assembly, the operator may remove and clean and/or replace valve assembly  30 . 
     As can be seen in FIG. 6, the angle between the centerline CL of the spray gun  10  and the pattern air holes  18   a  and  18   b  in air cap  18  is desirably 55° for best performance. 
     The nozzle generally designated  16  in FIGS. 7 and 8 is designed so as to allow different fluid set (needle and nozzle) combinations to provide different flow rates in conjunction with the same air cap. These dimensions are indicated in FIG.  7  and the various combinations are set forth below: 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                 a 
                 b 
                 c 
                 d 
                 e 
               
               
                   
               
             
            
               
                 .032 
                 .075 
                 .590 
                 .200 
                 .470 
               
               
                 .051 
                 .095 
                 .590 
                 .200 
                 .470 
               
               
                 .071 
                 .120 
                 .565 
                 .190 
                 .436 
               
               
                 .087 
                 .135 
                 .570 
                 .180 
                 .429 
               
               
                 .098 
                 .145 
                 .565 
                 .175 
                 .420 
               
               
                   
               
            
           
         
       
     
     FIGS. 9 and 10 show the nozzle housing  14  of the instant invention and in particular the hole arrangement (nine 0.1718″ holes and eight 0.156″ holes) which allows substantial airflow to the air cap in front of the gun with the hole arrangement as set forth. 
     FIG. 11 shows the gun body  12  which has a first aperture  12   b  for metering of total airflow through the gun allows air to flow through the nozzle housing and around the outside of the nozzle and the inside of the air cap as well as pattern air aperture  12   e  which may be selectively included by valve element  34   c  to selectively adjust the amount of pattern or fan or shaping air provided in the front of spray gun  10 . 
     It is contemplated that various changes and modifications may be made to the spray gun without departing from the spirit and scope of the invention as defined by the following claims.