INDEXING AIR CAP

Abstract: An indexing air cap is described comprising an air cap (8), mounted to be adjustably rotatable on the spraygun body (1), a baffle (10) having a recess (12) and a seal (11) of low density plastics material, such as polyethylene, being located between the baffle (10) and the spraygun body (1). The baffle (10) and the seal (11) having a plurality of holes (16) passing axially through them and being spaced radially from each other. A pin (17) passing through an aligned set of the holes (16) in the baffle and seal to connect with a blind hole (18) in and lock them to the spraygun body (1). Rotation of the air cap (8) through a predetermined angle of 90 DEG indexes the air spray cap to control the radial position and targeting of the spray pattern of the fluid being sprayed.

Description: INDEXING AIR CAP This invention relates to an indexing air cap for automatic sprayguns. Automatic sprayguns are increasingly being used in spray booths to spray e.g. paint on the bodywork of motor vehicles. The accuracy of mounting the spraygun on a robot has become critical as the centre of the area to be sprayed must be located within 2 mm to 5 mm of the centre axis of the spraygun nozzle when repositioning the spraygun. Existing automatic sprayguns have the disadvantage that when the air cap is removed, replacement can cause the centre of the spray pattern to diverge from its previous centre point resulting in an uneven disposition of material known as "banding" when the gun follows the predetermined movement path of a machine or robot. Manually operated sprayguns do not have the same disadvantage as the positioning of the spraygun is made by the eye of an experienced operator which prevents this problem. An aim of the present invention is to overcome or mitigate the above mentioned disadvantage of automatic sprayguns. According to one aspect of the present invention there is provided an automatic spraygun comprising an air cap adjustably secured on the sprayhead of the automatic spraygun, a baffle located on the body of the spraygun and a seal of low density plastics material located between the baffle and the body, wherein the air cap is located in angular increments relative to the spraygun ensuring replacement within accurately predetermined limits. Preferably the air cap is located in angular increments of 90°. In a preferred construction the seal is made of polyethylene and has inner and outer sealing beads. According to a second aspect of the present invention there is provided an automatic spraygun with a centrally located aperture passing laterally of the longitudinal axis of the spraygun, a mounting stud passing through the aperture and extending from each side of the spraygun to engage apertures in a mounting fixture, wherein the mounting stud has at least two collars located on a screw-threaded bolt, a plurality of bevelled washers being interposed between the collars such that tightening of the screw-threaded bolt expands the washers within the aperture to adjustably secure the mounting stud to the spraygun. Conveniently, there are three collars on the screw threaded bolt with two sets of bevelled washers between two outer collars and a central collar. Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a longitudinal cross-section of an automatic spraygun according to the present invention; Fig. 2 is a fragmentary axial cross-section of an air cap and indexing assembly on an enlarged scale; Fig. 3 is a front elevation of the seal; Fig. 4 is an axial section of the seal taken along the line 4-4 in Fig. 3; and Fig. 5 is a section taken along the line 5-5 of Fig. 1 with the addition of the mounting stud and mounting fixture. The spraygun illustrated in Fig. 1 comprises a body 1 within which are mounted conventional mechanisms as described in our co-pending Application No. 8914130.3 to control the flow of air to a nozzle 2. The fluid to be sprayed via the nozzle is metered by a needle 3 the fine adjustment of which is controlled by the control knob 4. Air is supplied to the gun via the inlet 5 passing along a series of passages within the gun body to an air cap (shown in Fig. 2) . The control mechanism operating the needle 3 is sealed from the air flow path by 'Shamban' double delta seals 6 and is urged to the forward position by stainless steel helical springs 7 and 8. The air cap indexing assembly according to the present invention is shown on an enlarged scale in Figs. 2 to 4 and comprises an air cap 8 (see Fig. 2) mounted to rotate on the spraygun body 1 having a recess 9. A baffle 10 made of metal axially aligned and non- rotatable on the body 1 with the interposition of a seal 11 mounted on the baffle 10 and seated in a recess 12 in the rear face of the baffle and in the recess 9 of the body. The seal is shown in detail in Figs. 3 and 4 and comprises a central aperture 13 and inner and outer beads 14 and 15. Radially arranged between the beads 14 and 15 are a plurality of holes 16 which are so spaced from one another to allow air to transfer evenly from annular chamber la in the sprayhead to annular chamber 10a in the baffle 10. A pin 17 is located in one of the aligned holes in the baffle and seal where it locates in a blind hole 18 in the gun body 1. This pin locates the baffles and seal relative to one another and fixes them in the desired arcuate position relative to the gun body. The air cap 8 is mounted on the baffle 10 and has horn shaped projections 19 through which is supplied to shape the fluid to be sprayed. The orientation of the air cap 8 controls the position of the pattern of the spray area of the fluid. The air cap is located to the baffle 10 by a pin 20 and is secured to the baffle 10 by a screw-threaded collar 21. This location allows the air cap to be indexed at 90° intervals producing a repeatable and a precise targeting of the centre of the spray pattern within 2 mm to 5 mm of the previous setting. As the automatic sprayguns are operated remotely on robot mechanisms, the spraygun has to be critically adjusted relative to the surface to be sprayed. To facilitate this adjustment, the spraygun body 1 has an aperture 22 (see Figs. 1 and 5) passing transversely of the longitudinal axis of the spraygun about the centre of the spraygun. A mounting stud 23 is adjustably secured in the aperture 22 and extends from each side of the gun body where it is located in a mounting fixture 24, shown in dotted line in Fig. 5. The mounting stud 23 comprises a central screw-threaded bolt 25 with three spaced collars, a central collar 26 and two outer collars 27 and 28. Located on the bolt 25 are a plurality of bevelled washers 29 positioned between the central and outer collars, so that by tightening-up a nut 30 against the outer collars the bevelled washers are expanded in diameter to adjustably lock the mounting stud 23 within the aperture 22. The automatic spraygun can thus be precisely adjusted about the axis of the mounting stud to position the direction of the spray nozzle. The mounting fixture has a pin 31 which locates in a hole 32 drilled in the bottom of the spraygun body 1 to precisely locate the lateral position of the spraygun relative to the mounting fixture 24.

Claims: CLAIMS: 1. An automatic spraygun comprising an air cap (8) adjustably secured on the sprayhead of the automatic spraygun, a baffle (10) located on the body (1) of the spraygun and a seal of low density plastics material located between the baffle (10) and the body (1),characterised in that the air cap (8) is located in angular increments relative to the spraygun ensuring replacement within accurately predetermined limits. 2. A spraygun as claimed in Claim 1, characterised in that the air cap (8) is located in angular increments of 90°. 3. A spraygun as claimed in Claim 1 or 2, characterised in that the baffle (10) is made of metal. 4. A spraygun as claimed in any preceding claim, characterised in that the seal (11) is made of polyethylene and has a central aperture (13) with inner (14) and outer (15) radial beads on both faces. 5. A spraygun as claimed in any preceding claim, characterised in that the air cap (8) is located to the baffle (10) by a pin (17) and is adjustably secured thereto by a screw-threaded collar (21) so that the air cap (8) can be indexed to change the radial position of the spray pattern of the fluid being sprayed. 6. An automatic spraygun with a centrally located aperture (22) passing laterally of the longtiudinal axis of the spraygun (1), a mounting stud (23) passing through the aperture and extending from each side of the spraygun to engage apertures in a mounting fixture (24) , characterised in that the mounting stud (23) has at least two collars (26, 27) located on a screw-threaded bolt (25), a plurality of bevelled washers (29) being interposed between the collars (26, 27) such that tightening of the screw-threaded bolt (25) expands the wahsers (29) radially within the aperture (22) to adjustably secure the mounting stud (23) to the spraygun (1). 7. A spraygun as claimed in Claim 6, characterised in that there are three collars (26, 27, 28) on the screw- threaded bolt (25) with two sets of bevelled washers (29) between the two outer collars (27, 28) and a central collar (26). 8. A spraygun as claimed in any preceding claim, characterised in that the spraygun (1) is located relative to a mounting fixture (24) by a pin (31) located in a hole (32) in the bottom of the spraygun body (1).

Inventors: BATE ANTHONY JOHN, SMITH ROWLAND CHARLES, BATE, ANTHONY, JOHN, SMITH, ROWLAND, CHARLES
Applicants: ITW LTD, ITW LIMITED
Application year: 1991
Main classification: B05B7
IPC codes: B05B7, B05B13, B05B15