Domed air cap

Abstract: A spray gun (10) comprising a longitudinal axis, a fluid nozzle (12) and an air cap (14) characterised by: said nozzle comprising a frustoconical outer surface (12b); and said air cap comprising a domed curving inner surface (14b, 14c).

Description: BACKGROUND OF THE INVENTION Spray guns using air spray method of atomisation along with its HVLP variant have been known for a number of years. While such application devices are generally capable of producing an excellent finish, there is always room for improvement. Such guns are produced by any number of manufacturers including Graco Inc., the assignee of the instant invention. US Patent No. 5152460A entitled "Spray Gun Nozzle Head", discloses a spray gun nozzle head for atomising a liquid using a flowing pressurised gas. The spray gun nozzle head comprises a central nozzle for supplying the liquid and a cap for supplying pressurised gas. The nozzle (30) has a substantially frustoconical outer surface and the cap (32) has a domed curving inner surface. US Patent No. 2930532A entitled "Spray Gun Nozzle" discloses a spray gun for spraying a coating material and a catalyst simultaneously. The spray gun comprises a nozzle portion (21) coupled to a head portion (15). German Patent No. 714294 discloses a gun for spraying paint by means of compressed air. The spray gun comprises a nozzle (2) through which paint is delivered and an air cap (1) for providing compressed air. The nozzle (2) comprises a frustoconical outer surface and the air cap (1) comprises a domed curving inner surface. SUMMARY OF THE INVENTION It is an object of the invention according to claim 1 to improve such known spray guns. This object is achieved by means of the combination of features forming claim 1. The invention according to claim 1 is concentrated at the front end of such an air spray of HVLP gun and in particular details the relationship between the exterior of the fluid nozzle and the inside of the air cap. In particular, the fluid nozzle has a generally frustoconical outer surface which forms an included angle of substantially 50°. The inside of the air passage at its rearward end has an included angle of substantially 20° and then curves gently to the point where it is adjacent to the front of the air cap. 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. A BRIEF DESCRIPTION OF THE DRAWINGS FIG 1 is a cross-sectional view of the front end of the spray gun of the instant invention. FIG 2 is a cross-sectional view of the air cap of the instant invention. FIG 3 is a detailed cross-sectional view of the air cap of the instant invention. FIG 4 is a front view of the front end of the air cap of the instant invention. DESCRIPTION OF THE PREFERRED EMBODIMENT The instant invention generally shown in Fig 1 and generally designated 10 is comprised of a fluid nozzle 12 having a front end 12a which extends to the front end of the air cap 14. Air cap 14 has an opening 14a therein through which nozzle front end 12a extends. Nozzle surface 12b has an angle substantially 25° relative to the longitudinal axis of the spray gun or total angle of substantially 50°. Spray gun 16 also includes a needle 18. The inside surface of air cap 14 forms a rounded dome 14b which merges from being nearly parallel to the longitudinal axis at its rearward end 14c (an included angle of 20°) to opening 14a. In one version of the preferred embodiment (for particular size nozzle/cap combination), the diameter of the dome at its rearward end 14c is 19.05mm (0.750") and tapers at the aforesaid 20° included angle to a point where it intersects with the dome having a radius of 9.14mm (0.360"). Opening 14a has a diameter of substantially 5.3mm (0.210") for use with nozzle orifice of 1.07mm - 1.4mm (0.042'' - 0.055"). Utilisation of this construction insures maximum air flow and enhanced atomisation while utilising a given amount of air input pressure and volume. It is contemplated that various changes and modifications may be made to the spray gun without departing from the scope of the invention as defined by the following claims.

Claims: An air spray gun (10) comprising a longitudinal axis, a fluid nozzle (12) and an air cap (14) having a pair of air horns, said air spray gun (10) said fluid nozzle (12) comprising a frustoconical outer surface (12b), and said air cap (14) comprising a domed curving inner surface (14b, 14c) having a rearward end (14c) and a forward end (14b) with a nozzle opening (14a) therein, said inner surface (14b, 14c) forming an annular opening between said fluid nozzle (12) and said air cap (14), said annular opening generally decreasing in width between said rearward end (14c) and said forward end (14b) characterised in that said outer surface (12b) has an angle of substantially 25° relative to said longitudinal axis, a front end (12a) of said fluid nozzle (12) extends through the nozzle opening (14a) of said air cap (14), the rearward end (14c) has an included angle of substantially 20°, and in that said inner surface (14b, 14c) has a curve radius of substantially 9.14mm (0.360").

Inventors: FLOER KEN C, SWEAZY JOHN D, FLOER, KEN C., SWEAZY, JOHN D.
Applicants: GRACO INC, GRACO INC.
Application year: 1998
Main classification: B05B7
IPC codes: B05B7