Method and Device for Spraying a Liquid or a Suspension

The invention relates to a method for spraying a liquid or suspension by means of centrifuging a spray cone of small droplets from a rotating centrifugal disc, as well as a corresponding spray device with a drive shaft which is activated into a rapid rotation by means of a drive device, at least one centrifugal disc mounted on the drive shaft for operating a spray cone of small droplets, as well as feeding devices for applying of the liquid to be sprayed onto the centrifugal disc.

In known methods and test devices of this type, the direction of the spray cone is influenced by the diameter of the centrifugal disc and its number of rotation. For obtaining a sufficiently fine and uniform droplet size, it is required to drive the centrifugal disc at a very high number of rotations of, for example, 10,000 RPM. Thereby, one can achieve a very uniform droplet size of, for example, 35 u, however the hollow cone which is generated during spraying has a relative large diameter of, for example, 100 to 120 cm which is undesirable for many application purposes.

It is therefore an object of the invention to provide a method for spraying of a liquid or suspension, a corresponding spraying device or a suitable centrifugal disc which obtains in a simple manner the generation of a spray cone of a reduced diameter without impairing the uniformness and fineness of the generated droplet size.

To solve this object of the invention, the aforementioned method is characterized in accordance with the invention by a device and a method in which means and steps are provided for supplying a liquid or a suspension to a centrifugal disc rotatable about an axis of rotation and having an outer annular skirt so that the liquid flows toward and along said outer annular skirt and then off the latter so as to generate a spray cone of small droplets, and for generating during rotation of said centrifugal disc a gas stream directed from inside said spray cone in an axial direction toward said centrifugal disc so as to form a centripetal gas flow extending in a direction transverse to said axial directions and reducing the diameter of said spray cone.

The inventive method and the inventive spray devices enable in a simply, inexpensive manner to substantially reduce the diameter of the generated spray cone with respect to known devices, without impairing the fineness and uniformity of the droplet size.

For example, with a centrifugal disc which has an outside diameter of 5 cm, a spray cone with a diameter of only 25 to 35 cm can be generated, without impairing the fineness and the uniformity of the droplet size. The advantages of the inventive device are particularly accentuated when spraying relative concentrated liquids or suspensions, wherein non-uniformity in the droplet size are particularly disadvantageous on the sprayed articles, due to the non-uniform distribution of the spray good.

The inventive method and the inventive spray devices are particularly suitable when faces of a relative small dimension should be treated, without an undesirable spraying of adjacent areas. For example, this is the case when spraying goods which are mounted on a relative small conveyor belt, whereby the diameter of the spray cone should not exceed the width of the conveyor belt.

In the following, preferred embodiments of the inventive spray device are further explained in conjunction with the appended drawings.

The drawings show:

FIG. 1 a schematic cross section through a spray device and

FIG. 2 a schematic cross section through a modified spray device.

The spray device shown in FIG. 1 is provided with a battery operated drive motor 1 on the drive shaft 2 of which a centrifugal disc 3 is detachably mounted. The centrifugal disc 3 is provided with a substantially radially extending disc segment 4 and at its outer edge obliquely bevelled edge plate 5 whose outer spray edge 6 is shaped in a known manner with fine saw tooth serrations (serration width about 0.5 mm), which is not shown in the drawings for purposes of clarity. A propeller 10 is disposed in the inner chamber of centrifugal disc 3 which is enclosed by the edge plate 5, whereby the propeller is detachably connected with the centrifugal disc 3 and is provided with a plurality of propeller blades 11 which are so shaped an directed that the propeller 10 during its common rotation with the centrifugal disc 3, generates an axial air flow towards the centrifugal disc, so that at the vacuum side of the propeller 10 facing away from the centrifugal disc 3 a vacuum zone 13 is formed.

A supply conduit 7 for the liquid to be sprayed is stationary disposed around drive shaft 2. The liquid which is supplied therethrough is prevented from a radial discharge by the ring plate 18 which is displaced on the centrifugal disc 3 and flows through the throughput opening 8 in the proximity of disc segment 4 to the side of the disc segment 4 facing the propeller 10 from where it is fed under the effect of centrifugal force onto the inner face of the edge plate 5 to the saw tooth like serrated spray edge 6 and then are centrifuged from the acute protruding serrations in form of thin liquid jets which immediately divide into droplets of practically the same size. The centrifuged liquid droplets move radially outward under the influence of the centrifugal force, on the one hand, and simultaneously fall downwardly due to the effect of gravity, so that a hollow spray cone 12 is generated.

Due to the vacuum pressure zone 13 formed on the suction side of the propeller 10 due to its rotation, a pressure drop is generated which generates a substantially inwardly directed flow of air which is present laterally outside of the spray cone. This centripetal flow 17 results in that the diameter of the spray cone 12 is substantially smaller in comparison to conventional devices, without impairing in any way the fineness and the uniformity of the droplet size.

In the modified embodiment illustrated in FIG. 2, a blow wheel 15 is provided on the centrifugal disc 3, instead of propeller 10 at the side facing away from the spray cone which rotates together with the centrifugal disc 3 and accelerates with its blow wheel blades 19 the air disposed therebetween radially outward, whereby air is constantly vacuumed off through a suction opening 14 which communicates with the inner chamber of the spray cone 12, so that a vacuum pressure zone 13 is formed, which again generates a centripetal flow 17 being substantially directed to this vacuum pressure zone, so that a reduction of the diameter of the generated spray cone 12 is obtained.

Throughput conduits 16 are distributed at uniform distances over the circumference, so that the liquid to be sprayed from the supply conduit 7 cannot flow over to the side of the centrifugal disc 3 which faces the inside of the spray cone 12.

In the embodiment illustrated in FIG. 1, the air which is moved by the propeller 10 in the direction to the centrifugal disc 3 is so deflected on the disc segment 4 and the edge plate 5 that it discharges in a direction which is opposite to the prevailing axial direction of the flow in vacuum pressure zone 13 and is gradually deflected inwardly by the pressure drop. For controlling this circulation, gas throughout opening 9 may be provided in the disc segment 4 of the centrifugal disc 3, distributed over its circumference. The gas throughput openings are advantageously so designed by means of an oblique structure of their walls that the liquid to be sprayed is prevented from discharging through the gas throughput openings 9. However, in certain cases it may be desirable, by a corresponding structuring of the gas throughput openings to let a part of the supplied liquid flow over onto the outer face of the centrifugal disc 3. This is particularly true if the centrifugal disc is provided with a second edge plate 5, not shown.

The aforementioned spray device which was explained in conjunction with preferred embodiments can be modified by a person skilled in the art in fifferent efficient ways as long as a rotor is used for generating a vacuum pressure zone 13 within the spray cone 12 and by maintaining a centripetal flow 17. The diameter of the centrifugal disc 3, the design and the dimensions of the edge plate 5, the propeller 10 or the blow wheel 15, as well as the arrangement and the size of the throughput openings 8 and possible gas throughput openings 9 should be efficiently adjusted with respect to the type and the flow characteristics of the liquid or suspension to be sprayed, the desired droplet size and the desired diameter of the spray cone 12. The centrifugal disc is mounted in a conventional manner on the drive shaft by either a clamp screw of by means of a thread.