Improved paint spray nozzle

Abstract: An improved spray nozzle for use with air atomizable liquids has a spray pattern created by an atomizing nozzle; this spray pattern may be adjusted from a circular pattern to a flat pattern or alternatively to an open oval, the open end facing in preselected directions, the adjustments being capable of occurring during the continuous operation of the nozzle.

Description: The invention relates to an improved paint spray gun and nozzle for adjusting the spray pattern using low pressure and high volume air for atomizing the paint and controlling the spray pattern. Spray guns and nozzles, especially those used with spray painting systems, atomize the liquid paint by means of atomizing air which enters the nozzle area via a chamber which surrounds a fluid nozzle. The atomizing air is then impinged on the end of the chamber and exits via a central aperture located at the end of the chamber. The paint is atomized by the accelerating burst of forward motion of this air as it exits the nozzle via the aperture. The initial conventional pattern of the atomized liquid and air mixture in cross-section is a circle because the exit aperture is circular. The term "pattern" as used herein describes a cross-section of the atomized cloud of paint droplets in a plane perpendicular to the direction of the spray from the fluid nozzle. When the compressed air source for a spray painting apparatus utilizes a high volume, low pressure compressor, it is conventional for the air exit nozzle on the spray painting gun to have a central aperture which is considerably larger than the circumscribed liquid nozzle. Therefore, the large amount of air utilized in a conventional nozzle is due to the relative size of the central aperture compared to that of the liquid nozzle. This excess air, air beyond that required to atomize the liquid properly, constitutes an energy waste as well as a pollution problem. The excess air is a pollution problem since the air in a paint system will tend to carry the paint solvent. The more air that is used, the more dilute the solvent, and the more air that must be processed for the removal of solvents. Therefore, there is a need for an improved spray nozzle which more efficiently utilizes the air that it actually receives from the air source. The pattern of a spray nozzle is conventionally adjusted by impinging additional air jets into the original circular pattern at a location beyond the outlet aperture. A standard design may include two oppositely directed jets which produce a flat or oval pattern, and if those jets are very powerful it produces a flat fan type spray pattern which is many times wider than it is high. However, in production line spraying, there are needs for other than such flat or oval patterns, especially when spray painting the reverse sides of objects or spray painting in an out-of position way and also the traditional problem of painting the insides of angular surfaces. Therefore, there is also a need for improved pattern control in spray nozzle systems and the ability to adjust the pattern to other than flat or oval pattern. It would additionally be desirable if such adjustments of modification of the pattern could be achieved without the necessity of changing the nozzle in use. Another problem with spray guns is that the air from the compressor is hot and tends to heat metal parts in the flow path to an extent that hand held spray guns may burn the operator or at least make his hand most uncomfortable. A spray gun involving passages for pattern-adjusting air as well as atomizing air is disclosed in U.S. Patent 1,910,673 (Bramsen). These passages are formed in a casting. According to the present invention the spray gun comprises a body with a handle and spray-directing sections and passages therethrough for the flow of atomizing and pattern-adjusting air, and for the liquid, an atomizing chamber connected to the passage for atomizing air and having an exit aperture for atomised spray and a converging frusto-conical surface approaching the aperture, a nozzle for said liquid mounted concentrically with the exit aperture, the frusto-conical surface approaching the aperture and the exterior surface of the nozzle functioning to direct the atomizing air, a trigger for controlling the flow of the liquid, and the gun body comprises separate body parts detachably clamped together. Each body part forms part of both air passages and together they provide a structure for receiving air and liquid supply connections. The spray gun of the invention is characterized by the use of high volume (about 0.1415-1.698 m³ per minute) low pressure (less than about 6.89x10⁴ N/m² gauge) air in conjunction with a body comprising separate body parts detachably clamped together. The improved spray gun according to this invention includes an atomizing chamber with a central aperture for the exit of atomized liquid spray. The chamber has a converging frusto-conical surface approaching the aperture that acts to direct and streamline the atomizing air. A fluid nozzle is mounted concentrically with the aperture and the exterior surface is structured to further direct atomizing air through the aperture in streamline flow as opposed to turbulent flow. The spray gun of the present invention preferably includes a pattern adjusting plug valve which adjusts air flow to the pattern adjusting nozzles which may be directed at the atomized liquid spray. The shell of the gun be molded from a resin in two mirror image halves which are bolted together. The resin will serve as an insulator because it is a poor heat conductor. Preferred embodiments of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is an elevational view of a paint spray assembly utilizing a nozzle according to the present invention; Figure 2 is a right hand side elevational view of the gun of Figure 1; Figure 3 is a cross-sectional view taken along line 3-3 of the gun of Figure 1; Figure 4 is a cross-sectional view taken along line 4-4 of the gun of Figure 2; Figure 5 is a cross-sectional view taken along line 5-5 of the gun of Figure 4; Figure 6 is an elevational view of a first alternative form of gun supplied by a source of high pressure air; Figure 7 is a sectional view similar to Figure 4 but illustrating the alternative form of gun shown in Figure 6; Figure 8 is a sectional view taken along line 8-8 of Figure 7; and Figure 9 is a sectional view taken along line 9-9 of Figure 6. With reference to the drawings, Figure 1 shows a paint spray gun 10 which utilizes a nozzle 12 according to the present invention. Any conventional spray painting gun has a pistol grip type handle on the body 10 and can optionally have a hook assembly 13 for hanging the gun after work has been completed or for temporary storage. An air supply fitting 14 provides a connection to a source 15 of low pressure, constant high volume compressed air to the spray painting assembly. Within the body of the spray gun 10 the air supply is directed along a path to an air chamber adjacent a paint nozzle as will be explained subsequently. The paint gun body 10 also has a trigger assembly 20 which is held in its closed position by a spring 22 in the base of the handle. Additionally a pull rod 24 is moved by the trigger assembly, pull rod 24 serving to adjust the flow rate of paint to the nozzle tip while paint supply fitting 26 provides direct access to the supply of paint 27. On the forward end of the body 10 is a nozzle or air cap 28 having a pair of forwardly projecting ears 30, best seen in Figure 4. The cap 28 is mounted in operative position on body 10 and secured in place by a collar 32 threadedly engaging external threads 34 on the body. Turning now to Figure 4, within the concave nozzle ear faces are pattern adjusting orifices 44, 46, 48, 50 in fluid communication with an air chamber 57. Figure 2 shows the right-hand side elevational view of the gun of Figure 1. A knob 54 may be rotated to adjust the compression of spring 22 as desired. A plug valve 56 may be adjusted manually to control the flow of air to pattern adjusting ears 30 as will be explained in more detail subsequently. Line 58 is the split between the two halves forming the body of gun 10. The body of the gun itself is formed of two molded pieces which are mirror images of each other. The pieces are formed from Ryton brand resin, polyphenylene sulfide, in the preferred embodiment but other suitable resins may be used. Any appropriate resin should be a low conductor of heat to protect the hand of an operator from heat in the compressed air from the turbine (up to 82°C (180°F.)). Additionally, the resin should be easy to mold into the illustrated shape and solvent proof to prevent deterioration from paint solvents or airborne solvents in the atomized air. A cross-section of the spray nozzle assembly is shown in Figure 4. In this view atomizing air chamber 52 serves as a plenum chamber and is shown with liquid nozzle valve 58 penetrating it, atomizing air chamber 52 having a central aperture 59 located at its outlet end. It will be noted that the central aperture 59 has an upstream converging frusto-conical shaped surface 60. Preferably the frusto-conical shaped surface 60 has a slope not corresponding to the converging conical end of liquid nozzle valve 58, that is, the angle subtended by the cone shaped surface 58 is less than the angle formed by surface 60. The reason is to have better control of the flow pattern. As best seen in Figure 4, air moves from fitting 14 through the handle 62 into chamber 57 by flowing through plug valve 56. A barrier 64 divides the air passage from fitting 14 and handle 62 into two paths 66 and 68. Flow through path 66 is regulated by plug valve 56. Valve 56 may be rotated from full open to full closed position. The full open position will allow air to flow from the gun through orifices 44, 46, 48 and 50 to compress the paint spray from aperture 59 and form a flat fan shaped spray pattern. The full closed position will result in a circular spray pattern. Note the diamond shaped opening 70 of Figure 5 through plug valve 56. It receives air from the oval shaped duct 66 and allows for easy hand manipulation of valve 56 to adjust the orifice flow with only a small angle of rotation. Conventional O-rings around the plug valve minimize air leaks. Alternatively, the duct 66 may be diamond shaped and the opening 70 could be oval in cross-section. Flow through path 68 leads through opening 72 in a radial flange around nozzle 58, upstream of plenum chamber 52. Flow into plenum chamber 52 dampens flow turbulence to insure laminar flow of air through aperture 59. Laminar flow is desirable because it maintains a more uniform spray pattern at greater distances from aperture 59. Note should be taken of the relatively large flow paths 66 and 68 (about 6.35 mm x 12.7 mm oval cross-section for each, see Figure 3)(0.25 in. x 0.5 in.) and the relatively gently curving path. This is necessary because of the desirability for high volume (about 0.1415 - 1.698 m³/min) (about 5-60 cubic feet per minute (cfm)) and relatively low pressure (less than about 6.89 x 10⁴ N/m²) (less than about 10 pounds per square inch gauge (psig)). Conventional compressor pressures are in the range 21 x 10⁴ - 55 x 10⁴ N/m² (30-80 psig). It is because of the low pressure utilized and the design of the interior of the gun that the gun may be formed of two molded resin halves held together by a plurality of screw combinations 74, best illustrated in Figure 3. With conventional air pressures the gun would leak like a sieve because it would bulge outwardly. Note the mating tongue-in-groove structure 75 in Figure 3 to help minimize leaks. An alternative embodiment of the gun is illustrated in Figures 6 and 7. The difference is that the gun 10 is supplied from a conventional source of high pressure air. A combination filter and pressure reducer valve 76 is designed to receive air at a pressure in the range 21 x 10⁴ - 55 x 10⁴ N/m² (30-80 psig) and 0.85 - 1.7 m³/min (30-60 standard cfm) and deliver the same 0.85 - 1.7 m³/min (30-60 standard cfm) at less than 6.89 x 10⁴ N/m² (10 psig). Figure 9 shows the internal structure of filter-valve 76 and includes a filter 78 inside a sediment bowl 80. Air will pass through the filter and any liquid droplets or solid particles will be retained in bowl 80. A T-handle 82 allows the operator to adjust the outlet pressure as desired. A drain valve 84 allows liquid to be drained from the bowl 80 periodically. Appropriate seals and connecting thimbles and screw threads are illustrated but not specifically described because their function appears self-evident. Another difference illustrated in Figure 7 is the trigger mechanism 90. In Figure 4 the flow of air is continuous, the only adjustment possible from fitting 14 to cap 28 is the plug valve 56 controlling flow through duct 66. In Figure 4 the trigger assembly serves only to open and close the needle valve to stop, start, and adjust the flow of paint from source 27. In the embodiment of Figure 7 the trigger assembly 90 is designed to open and close a port 92 in the handle by a rod 94 which works against a spring 96. In operation in Figure 7 an operator will squeeze the trigger 90 to depress springs 22 and 96. Note that blocking plate 98 which blocks port 92 is the first to move to initiate air flow to the nozzle area through duct 68 prior to the time the trigger engages the abutment 100 on rod 24. Thereby air will begin flowing from the nozzle before paint flow starts. Whether or not air flows through duct 66 when plate 98 opens port 92 is separately controlled by plug valve 56.

Claims: A spray gun for use with an air-atomizable liquid, comprising a body (10) with a handle and spray-directing sections and passages (66, 68) therethrough for the flow of atomizing and pattern-adjusting air, and for the liquid, an atomizing chamber (52) connected to the passage for atomizing air (68) and having an exit aperture (59) for atomized spray and a converging frusto-conical surface approaching the aperture, a nozzle (58) for said liquid mounted concentrically with the exit aperture (59), the frusto-conical surface approaching the aperture (59) and the exterior surface of the nozzle (58) functioning to direct the atomizing air, a trigger (20, 24) for controlling the flow of the liquid, characterized in that the body (10) comprises separate body parts detachably clamped together, each forming part of both air passages (66, 68), and together providing structure for receiving air and liquid supply connections (14, 26). The spray gun according to Claim 1, characterized by said body parts having a mating tongue-in-groove structure (75) to help minimize leaks when said body parts are clamped together. A spray gun according to any one of the preceding claims, characterized by the fact that the two, air passages, (66, 68) extend from a single inlet passage, all of said passages occupying substantially the entire space provided by the separate body parts within the handle section of the gun. A spray gun according to claim 3, characterized by the provision of a control valve (54) in the handle section of the gun for the passage (66) for the pattern-adjusting air. A spray gun according to any one of the preceding claims, characterized by the fact that there are no air passages other than those (68, 66) formed by the two body parts. A spray gun according to anyone of the preceding claims, characterized by the use of high volume (about .15-1.8 m³ per minute) low pressure (less than about 7g per m² gauge) air in conjunction with a body comprising separate body parts detachably clamped together. A spray gun according to any one of the preceding claims, characterized by the fact that the trigger (90, Fig. 7) not only controls the flow of liquid but also the flow of air. A spray gun according to any one of the preceding claims, characterized by the fact that the parts of the passages (68, 66, 72, 58) are two body parts which are mirror images of each other. A spray gun according to any one of the preceding claims, characterized by the fact that the body parts are made of thermoplastic resin.

Inventors: HUFGARD JOHN W, HUFGARD, JOHN W.
Applicants: ACCUSPRAY INC, ACCUSPRAY, INC.
Application year: 1989
Main classification: B05B7
IPC codes: B05B7