EP2460591B1 - Nozzle head and rotary atomiser with same - Google Patents

Description

The invention relates to a nozzle head for a rotary atomizer for applying a coating material to an object with
a rotatable about an axis of rotation bell cup having an outflow surface, which coating material can be supplied in such a way that coating material is thrown away from the bell cup.

Moreover, the invention relates to a rotary atomizer for applying a coating material to an article with a nozzle head.

Rotary atomizers equipped with a nozzle head of the type mentioned above are used, for example, in the automotive industry to paint objects such as parts of vehicle bodies, or to coat with a protective material.

The bell cup serves to atomize the coating material, for which it is rotated about its axis of rotation in operation with very high rotational speeds of 10,000 to 100,000 U min ^-1.

The rotating bell cup is supplied with the selected coating material. Due to centrifugal forces, which act on the coating material, it is driven on the bell cup as a film to the outside, until it reaches a radially outer spoiler lip of the bell cup. There, such high centrifugal forces act on the coating material that it is thrown tangentially in the form of fine coating material droplets.

This produces droplets of different sizes, which extend over a relatively large size range. Larger droplets are thrown radially further outward than smaller droplets. With nozzle heads and rotary atomizers of the type mentioned so a relatively wide spray is generated, which is conical in the ideal case and has a relatively large cone angle.

In order to focus this spray onto an object to be coated, known rotary atomizers operate, for example, electrostatically. In this case, the coating material to be applied is charged, whereas the object to be coated is grounded. In this case, an electric field is formed between the rotary atomizer and the object, through which the charged coating material is applied to the object in a directionally directed manner. However, this only works with electrically conductive objects.
Alternatively or in addition to the electrostatic operation steering air devices have established in known rotary atomizers. With these, a usually annular shaping air flow is directed onto the spray jet in such a way that it is bundled and the droplets of different sizes are directed directed onto the object to be coated. In some cases, however, strong steering air flows are necessary for this purpose, the generation of which is relatively complicated.

Such rotary atomizers are for example off WO 2005/110611 A1 and US 5 984 993 A known.

WO 2005/110611 A1 discloses a rotary atomizer with a nozzle head comprising a bell cup. In one embodiment, a guide vane means in the form of a circumferential ring is provided, which forms an annular gap surrounding the bell cup, via which a working fluid in the form of compressed air can be blown onto the coating material.

US 5 984 993 A discloses a nozzle head for a rotary atomizer, wherein between a bell cup and a guide ring partially surrounding this, a chamber is formed, via which a cleaning agent on the Bell plate can be dispensed. Within this chamber, in one embodiment, there is a protrusion that results in a taper of the flow path to restrict the cleaning agent supply. This is followed again by a cross-sectional widening of the flow path.

It is an object of the invention to achieve in a nozzle head and a rotary atomizer of the type mentioned with the least possible construction effort that the spray generated is focused on an object.

This object is achieved with a nozzle head of the type mentioned in that
on the bell cup a rotationally symmetrical to the axis of rotation Laval ring nozzle is formed with a dispensing annular gap, from which a working fluid is blown onto the ejected from the bell cup coating material.

In the case of a Laval nozzle, the passage cross-section for a working fluid flowing through initially narrows and then widens again in the direction of an outlet opening. As a result, the working fluid flowing through can be greatly accelerated without the need for further measures.

As explained above, the coating material thrown away from the bell cup is in the form of droplets of different sizes. If the working fluid, usually air, now exits the dispensing annular gap at a greatly accelerated rate and strikes the larger droplets, these are broken up by the air blast into a plurality of smaller droplets and the spray jet homogenized thereby based on the droplet size. Since smaller droplets are not thrown so far radially outward as on the other hand larger droplets, the resulting spray is compared to the spray, which is generated without the Laval ring nozzle, focused and thereby focused on the object to be coated.

It is particularly advantageous if the outer circumferential surface of the bell cup is surrounded by a rotationally symmetrical to the axis of rotation lateral surface of a guide body, which forms the Laval ring nozzle with the outer circumferential surface of the bell cup. In this way, the outer circumferential surface of the Bell plates are used as the flow surface of the Laval ring nozzle.

A Laval ring nozzle can be formed particularly well if the outer surface of the bell cup forms a frustoconical surface.

In particular, in this case, it is advantageous if between the outer circumferential surface of the bell cup and the lateral surface of the guide body, a conical annular channel is formed, wherein the lateral surface has a pointing in the direction of the outer surface of the bell cup rotationally symmetrical elevation, which dictates the narrowest point of the annular channel.

When the outer surface of the bell cup or the lateral surface of the guide body carries vanes, which are arranged so that upon rotation of the bell cup working fluid, which is located between the outer surface of the bell cup and the lateral surface of the guide body, is conveyed to the dispensing annular gap of the Laval ring nozzle , This can be sucked working fluid from a reservoir to the Laval ring nozzle. An additional conveyor for the working fluid can then be dispensed with.

It is particularly effective in this case when the guide body has at least one through-channel, via which fluid can flow from the environment into the annular channel. In this case, no external source for the working fluid longer necessary, but rather serves the ambient atmosphere of the rotary atomizer or the nozzle head.

It is favorable if the passage cross section of the Laval annular nozzle is adjustable at least at its narrowest point. As a result, the final speed of the working fluid can be adjusted which flows out of the Laval ring nozzle.

This can be achieved in an advantageous manner in that the relative position of the bell cup and the guide body relative to each other based on the axis thereof is adjustable. Preferably, the guide body can be moved relative to the bell cup in the axial direction and fixed in different axial positions.

With regard to the rotary atomizer of the type mentioned above, the above-mentioned object is achieved accordingly that the nozzle head is designed according to one of claims 1 to 7.

Figur 1

einen Axialschnitt eines Düsenkopfes eines Rotationszerstäubers, bei dem eine Laval-Ringdüse ausgebildet ist, entlang der Schnittlinie I-I in Figur 2;

Figur 2

einen Schnitt des Düsenkopfes von Figur 1 entlang der dortigen Schnittlinie II-II;

Figur 3

einen der Figur 1 entsprechenden Schnitt, bei dem die Wirkung eines durch die Laval-Ringdüse erzeugten Luftstroms veranschaulicht ist.

An embodiment of the invention will be explained in more detail with reference to the drawings. In these show:

FIG. 1

an axial section of a nozzle head of a rotary atomizer, in which a Laval ring nozzle is formed, along the section line II in FIG. 2 ;

FIG. 2

a section of the nozzle head of FIG. 1 along the section line II-II;

FIG. 3

one of the FIG. 1 corresponding section, in which the effect of an air flow generated by the Laval ring nozzle is illustrated.

In FIG. 1 2 is a total of a rotary atomizer, of which only a head section 4 with a nozzle head 6 is shown. By means of the rotary atomizer 2 paint can be applied to a not specifically shown item.

The nozzle head 6 comprises a rotationally symmetrical bell cup 8. This is formed in the presently described embodiment in total as a hollow truncated cone 10 with a circumferential wall 12 and has a frusto-conical inner surface 14 and a frusto-conical outer surface 16. The bell cup 8 may also have deviating geometries, as they are known per se in bell plates from the prior art.

The bell cup 8 is rotatable at high speed about its axis of rotation 18, to which the rotary atomizer 2 comprises a drive means 20 which in the FIGS. 1 and 3 is illustrated only schematically. The bell cup 8 can be driven for example by means of an electric motor or pneumatically. The bell cup 8 rotates in operation at a rotational speed of 10,000 to 100,000 min ^-1 about its axis of rotation 18th

The bell cup 8 is supported by the free end of a bell 8 to the coaxial hollow shaft 22 which is coupled to the drive means 20 and which defines a Lackzuführkanal 24 in the longitudinal direction, which can be fed from a paint reservoir, not shown.

The hollow shaft 22 terminates in a perpendicular to the axis of rotation 18 extending mounting flange 26, via which it is connected to the bell cup 8. For this purpose, the bell cup 8 comprises a mounting plate 26 of the hollow shaft 22 complementary annular plate 28 having a central discharge opening 30, in which the Lackzuführkanal 24 opens into the hollow shaft 22.

The bell cup 8 further comprises, in a manner known per se, a baffle plate 32 extending from the ring plate 28 is worn. The baffle plate 32 extends perpendicular to the axis of rotation 18 of the bell cup 8 and is arranged at a small distance from the annular plate 28 in the interior of the bell cup 8. The baffle plate 32 extends radially outward until just before the inner circumferential surface 14 of the bell cup 8, which serves as a frustoconical outflow surface 34. The outer diameter of this outflow surface 34 increases accordingly in the direction of the hollow shaft 22 away. At the end remote from the hollow shaft 22, the outflow surface 34 terminates in a peripheral tear-off edge 36.

The outer circumferential surface 16 of the bell cup 8 is surrounded by an inner circumferential surface 38, which is rotationally symmetrical to the outer lateral surface 16, of a guide body designed as a conical guide sleeve 40, which is arranged coaxially with the bell cup 8. The guide sleeve 40 has a free end edge 42, which is arranged radially adjacent to the outer circumferential surface 16 of the bell cup 8, so that there is a dispensing annular gap 44 is formed.

Seen in the direction of the free end edge 42 to the inside, the inner circumferential surface 38 of the guide sleeve 40 has a collection forming, in the direction of the outer circumferential surface 16 of the bell cup 8 to arched portion 46, which merges into a conical portion 48 which, while maintaining a distance runs parallel to the outer circumferential surface 16 of the bell cup 8. The conical section 48 then opens into a hollow cylindrical support 50 with a constant cross section, which surrounds the hollow shaft 22 and serves to fix the guide sleeve 40 on the rotary atomizer 2.

The guide sleeve 40 is mounted stationary relative to the rotatable bell cup 8 with respect to a rotation, but can be displaced in the axial direction and fixed in relation to the bell cup 8 different axial positions become.

Overall, an annular channel 52 is formed between the outer circumferential surface 16 of the bell cup 8 and the inner circumferential surface 38 of the guide sleeve 40, the narrowest point 54 is predetermined by the survey 46.

The inner circumferential surface 38 of the guide sleeve 40 coaxial with the bell cup 8 form in this way with the outer lateral surface 16 of the bell cup 8 a Laval annular nozzle 56 which comprises the dispensing annular gap 44, from which a working fluid is blown onto the coating material thrown away from the bell cup 8. In this case, the inner lateral surface 38 of the guide sleeve 40 is a first flow surface and the outer lateral surface 16 of the bell cup 8 has a second flow surface of the Laval annular nozzle 56 which lie opposite one another.

In general terms, a rotationally symmetrical Laval annular nozzle 56 is thus formed on the bell cup 8, which comprises the dispensing annular gap 44, from which a working fluid can be blown onto the coating material thrown away from the bell cup 8.

As the working fluid air is used in the present embodiment. For this purpose, in the conical portion 48 of the guide sleeve 40 in an area adjacent to the cylinder portion 50 in the circumferential direction more passage channels 58 are incorporated, via which the annular channel 52 can communicate with the surrounding the nozzle head 6 atmosphere.

In addition, the bell cup 8 carries on its outer circumferential surface 16 in the circumferential direction uniformly distributed vanes 60. These have such a geometry and are arranged so that air sucked from the annular channel 52 and in Direction to the discharge gap 44 is promoted when the bell cup 8 rotates in the operation of the rotary atomizer 2. In the annular channel 52, a negative pressure is formed, whereby the air surrounding the nozzle head 6, is sucked through the passageways 58 into the annular channel 52 and thus serves as a working fluid.

The rotary atomizer 2 described above now works as follows:
During operation of the rotary atomizer 10, the bell cup 8 is rotated about its axis of rotation 18 by means of the drive device 20 and the paint feed channel 24 in the hollow shaft 22 is fed with lacquer.

In the process, lacquer first emerges from the dispensing opening 30 in the annular plate 28 of the rotating bell cup 8 and strikes its impact plate 32. This lacquer, due to the rotation of the bell cup 8, arrives as a lacquer film to its inside outflow surface 34 and further forward to its tear-off edge 36 where the paint film is thrown in the form of paint droplets. This produces droplets of different sizes, which extend over a relatively large area. This droplet formation is in FIG. 3 illustrated with larger droplets 62 and smaller droplets 64 shown.

Through the guide vanes 60 on the outer circumferential surface 16 of the rotating bell cup 8, air is simultaneously blown out of the dispensing annular gap 44 onto the droplets 62, 64 thrown away by the spoiler 36. This air has due to the formed Laval ring nozzle 56 such a high exit velocity, that at the discharge gap 44, a pressure surge on the paint droplets 62 and 64 is exercised, the in FIG. 3 in the reference character 66 is indicated. This Pressure surge 66 causes the larger droplets 62 to split into a plurality of smaller droplets 64. This is in FIG. 3 indicated by the small arrows 68.

In the smaller droplets 64 per se, no appreciable influence of the pressure surge is recorded. Overall, thus the average size of the ejected from the tear-off edge 36 of the bell cup 8 paint droplets is unified.

There are thus at least less large and thus heavier droplets 64 present, which are carried by centrifugal forces further radially outward than smaller and thus lighter paint droplets 62nd

In this way, the diameter of the paint mist generated by the nozzle head 6 is smaller than without the Laval ring nozzle 56 and the paint mist is focused on the object to be painted.

As mentioned above, the guide sleeve 40 can be axially displaced relative to the bell cup 8 and fixed relative to the bell cup 8 and its outer circumferential surface 16 in different axial positions. In this way, the passage cross section of the narrowest point 54 of the annular channel 52 of the Laval ring nozzle 56 can be adjusted.

When the guide sleeve 40 is moved back relative to the bell cup 8, the passage cross section increases at the narrowest point 54 of the annular channel 52 of the Laval ring nozzle 56. The passage cross section of the annular channel 52 in the region of the conical portion 48 of the guide sleeve 40 increases accordingly. The velocity of the air exiting the discharge slot 44 of the Laval annular nozzle 56 and the pressure surge thereon on the droplets 64 is then reduced.

On the other hand, when the guide sleeve 40 is displaced forward relative to the bell cup 8, the passage cross section decreases at the narrowest point 54 of the annular channel 52 of the Laval ring nozzle 56. The passage cross section of the annular channel 52 in the region of the conical portion 48 of the guide sleeve 40 decreases accordingly , The velocity of the air exiting the discharge slot 44 of the Laval annular nozzle 56 and the pressure surge thereon on the droplets 64 is then increased.

It is therefore always at least a portion of the outer circumferential surface 16 of the bell cup 8 surrounded by at least a portion of the inner circumferential surface 38 of the guide sleeve 40.

In a modification, the guide vanes 60 may also be provided on the inner circumferential surface 38 of the guide sleeve 40 instead of on the outer circumferential surface 16 of the bell cup 8. Although the vanes 60 are then stationary, the desired effect is achieved due to the high rotational speed of the bell cup 8.

In a further modification, the annular channel 52 of the Laval ring nozzle 56 can also be supplied with compressed air from a compressed air source via a compressed air line, which then serves as working fluid. Optionally, the guide vanes 60 can be dispensed with in this case.

In a further modification, the Laval ring nozzle 56 may also be provided as a separate component, which surrounds the bell cup 8 accordingly. In this case, the outer circumferential surface 16 of the bell cup 8 does not form the second flow surface of the Laval annular nozzle; rather, this is then provided by the separate component.

Claims (9)

1. Nozzle head for a rotary atomizer for applying a coating material to an object, having a bell cup (8) that can be rotated about an axis of rotation (18) and has a discharge surface (34), to which coating material can be fed in such a way that coating material is thrown off the bell cup (8) ;
   characterized in that
   a Laval ring nozzle (56) which is rotationally symmetrical with respect to the axis of rotation (18) is formed on the bell cup (8) and has a discharge ring gap (44), from which a working fluid can be blown onto the coating material thrown off the bell cup (8).
2. Nozzle head according to Claim 1, characterized in that the outer circumferential surface (16) of the bell pump (8) is surrounded by a circumferential surface (38) of a guide body (40) which is rotationally symmetrical with respect to the axis of rotation (18) and which forms the Laval ring nozzle (56) with the outer circumferential surface (16) of the bell cup (8).
3. Nozzle head according to Claim 2, characterized in that the outer circumferential surface (16) of the bell cup (8) forms a frustoconical surface.
4. Nozzle head according to Claim 2 or 3, characterized in that between the outer circumferential surface (16) of the bell cup (8) and the circumferential surface (38) of the guide body (40) there is formed an annular channel (52), wherein the circumferential surface (38) has a rotationally symmetrical elevation (46) which points in the direction of the outer circumferential surface (16) of the bell cup (8) and which predefines the narrowest point (54) of the annular channel (52).
5. Nozzle head according to one of Claims 2 to 4, characterized in that the outer circumferential surface (16) of the bell cup (8) or the circumferential surface (38) of the guide body (40) bears guide vanes (60), which are configured in such a way that, during the rotation of the bell cup (8), working fluid which is located between the outer circumferential surface (16) of the bell cup (8) and the circumferential surface (38) of the guide body (40) is conveyed to the discharge ring gap (44) of the Laval ring nozzle (56) .
6. Nozzle head according to one of Claims 2 to 5, characterized in that the guide body (40) has at least one passage channel (58), via which fluid from the surroundings can flow into the annular channel (52).
7. Nozzle head according to one of Claims 1 to 6, characterized in that the passage cross section of the Laval ring nozzle (56) is adjustable at least at its narrowest point (54).
8. Nozzle head according to Claim 7 with reference back to Claim 2, characterized in that the relative position of the bell cup (8) and the guide body (40) is adjustable with respect to one another in relation to the axis (18) thereof.
9. Rotary atomizer for applying a coating material to an object, having a nozzle head (6),
   characterized in that
   the nozzle head (6) is formed in accordance with one of Claims 1 to 8.

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