Abstract
An air cap for a spray gun, in particular a paint spray gun, having at least one central opening, which is delimited by a mouth, and two horns, each having at least one inner and one outer horn air duct and one inner and one outer horn air opening. The spacing between the front end of the central opening and an axis which perpendicularly intersects the central axis of the central opening and runs through the center of an inner horn air opening is between 0.6 mm and 2.6 mm. The spray pattern generated by the air cap has a longer core region and a steeper transition of the layer thickness between the external region and the core region, compared to conventional air caps leading to improvement in coating quality. A nozzle assembly and a spray gun, in particular a paint spray gun, can have an air cap having the above properties.
Claims
1. An air cap for a spray gun comprising: a central opening defined by a peripheral rim, the peripheral rim having a conical external face; and two horns arranged on opposite sides of the central opening, each of the two horns having an inner air duct disposed in proximity to the central opening and extending inwardly from the respective horn toward the central opening and an outer air duct disposed further from the central opening than the inner air duct and extending inwardly from the respective horn toward the central opening; wherein a space between a front end of the central opening and a point B at which a line extending from an axis of one of the inner air ducts perpendicularly intersects an axis of the central opening measures between 2.4 mm and 2.6 mm and an angle between the axis of the one of the inner air ducts and the axis of the central opening measures between 57 and 60.
2. The air cap according to claim 1, wherein a space between the front end of the central opening and a point C at which a line extending from an axis of one of the outer air ducts perpendicularly intersects the axis of the central opening measures between 6.0 mm and 6.6 mm.
3. The air cap according to claim 2, wherein the space between the front end of the central opening and the point C measures between 6.2 mm and 6.4 mm.
4. The air cap according to claim 1, wherein an angle between an axis of one of the outer air ducts and the axis of the central opening measures between 78 and 82.
5. The air cap according to claim 4, wherein the angle between the axis of the one of the outer air ducts and the axis of the central opening measures between 79 and 80.5.
6. The air cap according to claim 5, wherein the angle between the axis of the one of the outer air ducts and the axis of the central opening is a spot bore angle of the one of the outer air ducts and the angle between the axis of the one of the inner air ducts and the axis of the central opening is a spot bore angle of the inner air duct.
7. The air cap according to claim 6, wherein a ratio of the spot bore angle of the one of the outer air ducts to the spot bore angle of the one of the inner air ducts is between 1.2 and 1.6.
8. The air cap according to claim 1, wherein a space between one of the inner air ducts and one of the outer air ducts along the axis of the central opening measures between 3.3 mm and 5.8 mm.
9. The air cap according to claim 8, wherein the space between the one of the inner air ducts and the one of the outer air ducts along the axis of the central opening measures between 3.4 mm and 4.2 mm.
10. The air cap according to claim 1, wherein an internal diameter of at least one of the two inner air ducts measures between 1.1 mm and 1.3 mm.
11. The air cap according to claim 10, wherein the internal diameter of the at least one of the two inner air ducts is 1.2 mm.
12. The air cap according to claim 1, wherein an internal diameter of at least one of the two outer air ducts measures between 1.4 mm and 1.6 mm.
13. The air cap according to claim 12, wherein the internal diameter of the at least one of the two outer air ducts is 1.5 mm.
14. The air cap according to claim 1, wherein the space between the front end of the central opening and the point B at which the line extending from the axis of the one of the inner air ducts perpendicularly intersects the axis of the central opening is a spot bore height of the one of the inner air ducts and an internal diameter of the one of the inner air ducts measures between 1.1 mm and 1.3 mm.
15. The air cap according to claim 14, wherein a ratio of the spot bore height of the one of the inner air ducts to the internal diameter of the one of the inner air ducts is between 1.7 and 2.4.
16. The air cap according to claim 2, wherein the space between the front end of the central opening and the point C at which the line extending from the axis of the one of the outer air ducts perpendicularly intersects the axis of the central opening is a spot bore height of the one of the outer air ducts and an internal diameter of the one of the outer air ducts measures between 1.4 mm and 1.6 mm.
17. The air cap according to claim 16, wherein a ratio of the spot bore height of the one of the outer air ducts to the internal diameter of the one of the outer air ducts is between 3.8 and 4.5.
18. The air cap according to claim 1, wherein a front face of the air cap includes six control openings disposed in groups of three in a shape of a triangle on opposite sides of the central opening, a tip of each triangle aligned in a direction of the inner or outer air ducts.
19. The air cap according to claim 18, wherein the control openings have an angle of between 8 and 12 in relation to the axis of the central opening.
20. The air cap according to claim 1, wherein a front face of the air cap includes four control openings disposed in groups of two on opposite sides of the central opening, the groups aligned in a direction of the inner or outer air ducts.
21. The air cap according to claim 1, wherein an internal diameter of the central opening measures between 3.5 mm and 3.7 mm.
22. The air cap according to claim 1, wherein the conical external face of the peripheral rim of the central opening has an angle of between 25 and 35 in relation to the axis of the central opening.
23. The air cap according to claim 1, wherein an axis of at least one of the two inner air ducts and an axis of at least one of the two outer air ducts intersect at a point along the axis of the central opening.
24. The air cap according to claim 23, wherein a space between the front end of the central opening and the point of intersection of the axis of the at least one inner air duct and the axis of the at least one outer air duct measures between 7.5 mm and 8.5 mm.
25. An air cap for a spray gun comprising: a central opening defined by a peripheral rim, the peripheral rim having a conical external face; and two horns arranged on opposite sides of the central opening, each of the two horns having an inner air duct disposed in proximity to the central opening and extending inwardly from the respective horn toward the central opening and an outer air duct disposed further from the central opening than the inner air duct and extending inwardly from the respective horn toward the central opening; wherein a space between a front end of the central opening and a point B at which a line extending from an axis of one of the inner air ducts perpendicularly intersects an axis of the central opening is a spot bore height of the one of the inner air ducts and measures between 2.4 mm and 2.6 mm and an angle between the axis of the one of the inner air ducts and the axis of the central opening measures between 57 and 60; and wherein a space between the front end of the central opening and a point C at which a line extending from an axis of one of the outer air ducts perpendicularly intersects the axis of the central opening is a spot bore height of the one of the outer air ducts and measures between 6.2 mm and 6.4 mm and an angle between the axis of the one of the outer air ducts and the axis of the central opening measures between 78 and 82.
26. The air cap according to claim 25, wherein a ratio of the spot bore height of the one of the outer air ducts to the spot bore height of the one of the inner air ducts is between 2.0 and 3.0.
27. A nozzle assembly for a spray gun comprising the air cap according to claim 1.
28. A spray gun comprising the nozzle assembly according to claim 27.
29. A spray gun comprising the air cap according to claim 1.
30. A spray gun comprising the air cap according to claim 25.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The disclosure will be explained in more detail hereunder in an exemplary manner by means of the drawings in which:
(2) FIG. 1 shows an exemplary embodiment of an air cap according to the disclosure in section;
(3) FIG. 2 shows a plan view of an exemplary embodiment of an air cap according to the disclosure;
(4) FIG. 3 schematically shows the structure of a spray pattern of a standard air cap and of a spray pattern of an exemplary embodiment of the air cap according to the disclosure, together with the profile of the layer thickness of the spray pattern across the length of the spray pattern.
DETAILED DESCRIPTION
(5) FIG. 1 shows an exemplary embodiment of an air cap 1 according to the disclosure, having two horns 3 into each of which one horn air infeed duct 5, each having a horn infeed duct central axis 6 is incorporated. FIG. 1 does not show the actual size ratios of an air cap according to the disclosure but is to be understood to be only a schematic illustration. The air cap 1 has a central opening 7 having a central axis 9 which is delimited by a mouth 11 having a conical external face. The horn air infeed ducts 5 opening into inner horn air ducts 15 having inner horn air openings 15a, and into outer horn air ducts 17 having outer horn air openings 17a. Those horn air ducts or horn air openings, respectively, that are disposed so as to be closer to the central opening 7 are referred to as inner horn air ducts 15 and inner horn air openings 15a; those horn air ducts or horn air openings, respectively, that are located so as to be more remote from the central opening 7 are referred to as outer horn air ducts 17 and outer horn air openings 17a. The angle at which the inner horn air ducts 15 are incorporated into the horns 3 in relation to the central axis 9 of the central opening 7 differs from the angle at which the outer horn air ducts 17 are incorporated into the horns 3 in relation to the central axis 9 of the central opening 7. The angles of the inner horn air ducts 15 each are substantially identical, as are the angles of the outer horn air ducts 17. The angles of the inner horn air ducts 15 are smaller than the angles of the outer horn air ducts 17. It is only for the sake of clarity that only one angle and one angle each are illustrated on opposite sides of the central axis 9 in FIG. 1.
(6) In the present exemplary embodiment, the central axes 16, 18 of all four horn air ducts 15, 17 meet at a point D which lies on the central axis 9 of the central opening 7. The point C marks the spot bore height of the outer horn air ducts 17, the point B marking the spot bore height of the inner horn air ducts 15. The spot bore height of an inner horn air duct 15 is the spacing between the front end A of the central opening 7 in the air cap 7 and an axis 21 which perpendicularly intersects the central axis 9 of the central opening 7 and runs through the centre of the inner horn air opening 15a. The spot bore height of an outer horn air duct 17 is the spacing between the front end A of the central opening 7 in the air cap 1 and an axis 23 which perpendicularly intersects the central axis 9 of the central opening 7 and runs through the centre of the outer horn air duct 17a. In the present exemplary embodiment, the spot bore height of the two inner horn air ducts 15 is in each case identical, as is the spot bore height of the two outer horn air ducts 17.
(7) The central axes 6 of the horn air infeed ducts 5 in relation to the central axis 9 are slightly inclined, that is to say that the horn air infeed ducts 5 are incorporated into the air cap 1 in a slightly oblique manner. The reason is that the horn air ducts 15, 17 are to be designed to be as long as possible so as to achieve guiding of the horn air for as long as possible, which is why the horn air infeed ducts 5 should be disposed in the air cap 1 so as to be as far out as possible, whereas at the same time the external wall of the air cap 1 in this region, by virtue of a groove 13 in the air cap 1, would become too thin if the horn air infeed ducts 5 were to be incorporated into the air cap 1 as far out as possible in parallel with the central axis 9. By way of the inclined horn air infeed ducts 5 there is an adequate wall thickness also in the region of the groove 13, with an adequate length of the horn air ducts 15, 17. The groove 13 which is preferably designed in an encircling manner serves for receiving a locking ring (not shown in FIG. 1) by means of which the air cap 1 may be secured in an annular air nozzle (likewise not shown in FIG. 1). The bearing face 19 of the air cap 1 herein bears on an internal wall of the annular air nozzle, an external wall of the annular air nozzle bearing on the locking ring in the groove 13. The external diameter of the air cap 1 in the contact region between the air cap 1 and the annular air nozzle is somewhat smaller than the internal diameter of the annular air nozzle. On account thereof, the air cap 1 is fixed in the annular air nozzle in all directions, wherein a rotation of the air cap 1 about the central axis 9 is still possible as long as the annular air nozzle has not yet been tightened on the spray gun.
(8) Control openings 25 are disposed in the region next to the mouth 11 that delimits the central opening 7. Only two control openings 25 which are disposed on the sectional line through the air cap 1 can be seen in FIG. 1. The control openings 25 reach through the front wall of the air cap 1 up to an internal region 27. The internal region may be formed from various conical and cylindrical faces. In the assembled state of the spray gun, the paint nozzle (not shown in FIG. 1) which may be screwed into the gun body is located in the internal region 27. The front end of the paint nozzle, or a small front plug of the paint nozzle, herein is disposed in the region of the central opening 7, conjointly with the central opening 7 forming an annular gap. The paint nozzle may at least partially reach into the central opening 7; the front end may be recessed in relation to the central opening 7, may be flush with the front end A of the central opening 7, or may project beyond the front end A of the central opening 7. Air from compressed-air ducts in the gun body flows by way of an annular air distributor into the internal region 27 of the air cap 1 and into the horn air infeed ducts 5. The proportion of air that is infed to the internal region 27 of the air cap 1, and the proportion of air that flows into the horn air infeed ducts 5, may be controlled by way of a round/wide jet regulator in the spray gun; this is furthermore influenced by the size and the design of the compressed-air ducts. The atomizing air, that is to say the air that exits from the internal region 27 of the air cap 1 out of the central opening 7, or out of the annular gap described above, respectively, suctions the material to be sprayed from the paint nozzle, atomizes said material to be sprayed, and conveys the paint mist in the direction of the object to be coated. The air from the internal region 27 of the air cap 1 simultaneously flows through the control openings 25. That part of the air that is infed to the horn air infeed ducts 5 and horn air ducts 15, 17 flows out of the horn air openings 15a, 17a in the direction of the spray jet, acts laterally on the latter, and forms the actual conical jet into an elliptic wide jet. Prior thereto, the so-called horn air that flows out of the horn air openings 15a, 17a is hit by the so-called control air that flows out of the control openings 25, is spread, that is to say widened, is damped and deflected. The control air furthermore contributes towards atomizing the medium to be sprayed, and conveys the paint mist away from the air cap 1, in particular from the region 29 that is adjacent to the mouth 11, thus reducing contamination of this region.
(9) As can be seen in FIG. 1, the region 29 directly next to the mouth 11 that delimits the central opening 7 is inclined. On account thereof, the front end of the mouth 11 may be offset further forward from the adjacent region 29, so as to further reduce any contamination of the region 29, without extending the air cap 1 in length towards the front. Furthermore, an inflow of ambient air towards the outflow region of the atomizing air is facilitated on account of which undesirable turbulences in the region of the spray jet are prevented, as has already been mentioned here above.
(10) FIG. 2 shows a plan view onto the exemplary embodiment of an air cap 1 according to the disclosure, as shown in the section in FIG. 1. FIG. 1 shows the exemplary embodiment sectioned along the symmetry axis 31 as illustrated in FIG. 2. It can be seen in FIG. 2 that the air cap 1 has in each case three control openings 25, 26 which are disposed on two mutually opposite sides of the central opening 7. In each case three control openings 25, 26 are disposed in the form of a triangle, wherein a tip of the triangle is aligned in the direction of the horn air openings 15a, 17a. This means that in each case one of the control openings, presently the control openings 25, are in line with the horn air openings 15a, 17a, and an imaginary line between the two neighbouring control openings 26 is perpendicular to the symmetry axis 31. In another exemplary embodiment, described here above, in which the spot bore height of the inner horn air ducts is further depressed, in each case two control openings are disposed on two mutually opposite sides of the central opening 7 in the air cap 1. Herein, all four control openings are in line with the horn air openings, preferably on a symmetry axis, in a manner corresponding to the symmetry axis 31 of the air cap 1. The centre of the central opening 7 preferably also lies on the symmetry axis 31, and on a further symmetry axis 35 that is perpendicular to the symmetry axis 31, as is illustrated in FIG. 2.
(11) The region 29 next to the central opening 7, or next to the mouth 11 that delimits the central opening 7, respectively, differs from that region 33 that in FIG. 2 is shown above and below the region 29. The region 33 is conically designed in such a manner that the height of the air cap 1 decreases towards the outside, so as to enable the inflow of ambient air towards the flow region of the spray jet. The region 29 is inclined in an opposite manner, that is to say that there exists a slight depression about the mouth 11 that delimits the central opening 7, the mouth 11 being offset therefrom, on account of which a contamination of the region 29 is reduced.
(12) FIG. 3, in the upper part, schematically shows the structure of a spray pattern 43 of a standard air cap, and of a spray pattern of an exemplary embodiment of the air cap according to the disclosure, and in the lower part, shows the profile of the layer thickness of the spray pattern across the length of the spray pattern.
(13) The spray pattern 43 illustrated in FIG. 3 has an external region 37 and a core region 39. The spray pattern that is drawn using solid lines is the spray pattern that has been established by way of an exemplary embodiment of the air cap according to the disclosure, respectively of a spray gun which is equipped with an exemplary embodiment of the air cap according to the disclosure. The core region 41, illustrated using dotted lines in FIG. 3, shows the core region of a spray pattern that has been established by way of an air cap according to the prior art, respectively of an air gun which is equipped with an air cap according to the prior at. The external shape of the external region of the spray pattern corresponds approximately to the external shape of the external region 37 of the spray pattern that has been established by way of an exemplary embodiment of the air cap according to the disclosure, respectively of a spray gun which is equipped with an exemplary embodiment of the air cap according to the disclosure. For this reason, the external boundary of the external region of the spray pattern of an air cap according to the prior art has not been separately plotted in FIG. 3. It can be seen from the spray pattern 43 that the spray pattern of an air cap according to the disclosure in comparison to a spray pattern of an air cap according to the prior art has a longer core region, the overall length of the spray pattern however being approximately identical. As has already been mentioned here above, the boundaries of the internal and external regions are not sharply delimited but are fluid.
(14) A diagram 45 which shows a layer thickness profile in m over a measuring position in mm is illustrated in the lower part of FIG. 3. The auxiliary lines 47 show which measuring point in the diagram 45 is to be allocated to which point in the spray pattern 43. The diagram 47 shows measured data from a spraying experiment which have been carried out using a SATAjet 5000 RP having a standard air cap, that is to say an air cap according to the prior art, referred to in the diagram and hereunder as a standard nozzle, and using a SATAjet 5000 RP having an exemplary embodiment of the air cap according to the disclosure, referred to in the diagram and hereunder as a new nozzle. The layer thickness profile of the spray pattern that has been generated by way of the standard nozzle is illustrated as a dotted line 49 in the diagram, the layer thickness profile of the spray pattern that has been generated by way of the new nozzle appearing a solid line 50. The profile of the graphs is illustrated in a smoothed manner in FIG. 3. The spraying experiment was carried out at an entry pressure at the gun of 2 bar (29 psi), and at a spraying distance of 190 mm from the substrate, in the present case from a vertical sheet-metal panel. A painting robot moved the spray gun at a speed of 150 mm per second at a constant spraying distance in a direction perpendicular to the longitudinal axis of the wide jet generated. The wide jet was vertically aligned, the spray gun being moved from the left to the right. A bi-component solvent-based clear lacquer was sprayed. The material throughput of the paint nozzle corresponded to that of a 1.3 nozzle.
(15) A horizontal stripe was generated in the course of the spraying experiment, wherein the layer thickness of the spray pattern was measured in the vertical direction in a central region of the stripe. The measuring position 0 mm in the diagram 45 corresponds to the position of the central axis 9 of the central opening 7 in the air cap 1 of FIG. 1, in front of the substrate to be coated, in the present case the vertical sheet-metal panel. The central axis 9 is perpendicular to the substrate. The negative range of the X-axis of the diagram 45 shows the layer thickness profile of the spray pattern along a first direction, proceeding from the measuring position 0 towards the outside, for example towards the top, the positive range showing the layer thickness profile of the spray pattern along the opposite direction, proceeding from the measuring position 0 towards the outside, for example towards the bottom. The layer thickness of the spray pattern was thus measured across a length or height, respectively, of approx. 550 mm.
(16) It can be seen in the diagram 45 that the zero point of the layer thickness in the case of the standard nozzle as well as in the case of the new nozzle lies at the outer end of the spray pattern, at the left end in FIG. 3, at the same measuring position of approx. 275 m. However, the layer thickness of the spray pattern that has been generated by way of the new nozzle soon increases more rapidly than is the case with the layer thickness of the spray pattern that has been generated by way of the standard air nozzle. The core region in the case of the new nozzle commences already sooner, that is to say further outside in the spray pattern, than is the case with the standard nozzle. The plateau, that is to say the region of the spray pattern having a roughly identical layer thickness, is wider in the case of the new nozzle than in the case of the standard nozzle. However, it can be seen that the plateau in the case of the new nozzle is at a lower level than is the case with the plateau of the standard nozzle. This means that the layer thickness in the core region of the new nozzle is less than in the core region of the standard nozzle. This is a consequence of the wider plateau, that is to say of the longer core region, at the same material throughput and the same application rate of efficiency. Nevertheless, coatings of a higher quality may be generated using the air cap according to the present disclosure than is possible using air caps according to the prior art.
(17) It is finally to be pointed out that the exemplary embodiments described only describe a limited selection of potential embodiments and thus do not represent any limitation of the present disclosure.
