FIE L D O F T H E INV E NT ION

This invention relates to spray heads or atomizers, particularly for use in fruit packing machinery.

BAC K G R OU ND O F T H E INV E NTIO N

Spray heads are well-known and are used in many applications to spray fine droplets of a desired material in the form of a mist In the fruit packing industry, it is known to coat fruits with a thin coating of wax prior to packing and storage. The wax gives a glossy look to the fruit and makes it look more appealing. However, no less important than the cosmetic appeal is the fact that the wax coating may also include pesticides, which help prevent insect damage to the fruit during both storage and transport. The type and quantity of pesticide are dictated by the duration for which the fruit is to be stored prior to transportation and the destination, which determines both the duration of the voyage and also local standards, which may prohibit some pesticides and favor others. In any event the presence of pesticides and other chemicals in the wax render uniform coating of the wax essential in order to limit the amount of pesticide to a safe level.

US Patent No. 6,148,989 discloses a fruit polishing machine for individually conveying and rotati ng fruits within individual cavities for each fruit The device includes a continuous conveyor equipped with a repetitive series of axial ly mounted rotating brushes that are shaped to receive the individual pieces. It is also known to employ generally cylindrical brushes that are rotated axially and which are shaped so that when viewed in elevation, the outer contour is wave-like. In such an arrangement, the rotati ng brushes cause the fruit to spi n so that as the fruit passes al ong the conveyor belt between an array of brushes, the whole surface of the fruit makes contact with the brushes and is coated uniformly thereby.

The wax is directed to the brushes by an array of spray heads that are arranged to spray the wax uniformly to the brushes. A fan is located downstream of brushes to dry the wax pri or to the fruit bei ng packaged. T he fan plays no part i n the sprayi ng, this being achieved only by the spray heads, each of which sprays in a generally conical formation having a hollow center. The spray heads are spaced apart from each other by a distance that ensures that the sprays from adjacent spray heads are mutually overlapping whereby the voids are filled and spray uniformity is achieved. The need for overlap between the sprays mandates multiple spray heads to coat the complete surface area within the outer contour described by a single spray head. In effect this almost duplicates the number of spray heads that could be employed if there were no void.

US Patent No. 4,795,095 discloses a rotary atomizer having a general ly circular integrated fan/cone assembly coupled to a hydraulic motor to effect the rotation thereof. Fluid is introduced onto an upper center hub of the cone and flows downward through apertures therein onto an upper, inner smooth portion of the cone and then into the spaced radial grooves therein to exit the cone via teeth on a lower peripheral edge thereof. The fluid is thus formed into small uniform droplets in a relatively turbulence- free zone with the thus formed droplets then directed outwardly into the radial airflow generated above the cone by the curvilinear fan blades for dispersal of the droplets in a generally circular pattern.

In use a plurality of like atomizers are positioned in a spaced manner upon and along the length a spray boom The radially outward displaced droplets from adjacent rotary atomizers are distributed in an overlapping manner to provide a conti nuous, uniform distribution of the droplets over the sprayed area. The droplets from one rotary atomizer thus encounter the air flow from an immediately adjacent atomizer to further agitate the droplets and improve the uniformity of distribution of the droplets.

It would clearly be preferable to provide a spray head where the hollow dead space is avoided and where uniform coverage is achieved from a single spray head without the need for overlap. SU M MA RY O F T H E INV E NT IO N

It is an object of the present invention to provide a spray head, which produces uniform coverage and thus avoids the need for overlap from an adjacent spray head.

This objective is realized in accordance with the invention by a spray head according to claim 1. BRIE F DE SC RI PT ION O F T H E DRAWING S

In order to understand the i nvention and to see how it may be carried out in practice, embodiments will now be described, by way of non-li miting example only, with reference to the accompanying drawings, in which:

F ig. 1 is a front elevation of a spray head according to an embodiment of the invention;

F ig. 2 is a perspective view of the spray head showing its i nternal design;

F ig. 3 is an exploded view of the spray head;

F ig. 4 is a partial section showing further details of the spray head including a fan and peripheral deflector;

F ig. 5 shows a further detail of the peripheral deflector and outlet nozzles;

F ig. 6 shows an enlarged detail of the i nternal deflector;

F ig. 7 shows the deflector separated from the hub;

F ig. 8 is a partial section of the spray head showing a detail of the liquid inlets and thei r f I ui d coupl i ng to the peri pheral def I ector;

F i g. 9 i s a front el evati on showi ng angul ar di mensi ons of the def I ector;

F ig. 10 shows schemati cal ly the effect of the fan to render the spray uniform;

F ig. 11 is a pictorial representation of the fan blades; and

F igs. 12a to 12d are different elevations of the fan blades showing dimensions. DETAIL E D DE SC RIPTION O F E M BODIM E NTS

In the following description of some embodiments, identical components that appear in more than one figure or that share similar functionality will be referenced by identical reference symbols.

Referring to the figures there is shown a spray head 10, comprising a hub 11 supporting a downwardly tapered skirt 12 having an inner surface 13 of circular cross- section. A tapered deflector 14 of circular cross-section is coupled to a motor 16 shown schematically in Fig. 8 for rotation at high speed within the inner surface of the tapered skirt 12. The motor accommodated inside the hub may be electrically or hydraulically operated. A plurality of nozzles 15 are disposed in the deflector 14 and are configured to direct material toward an inner surface of the deflector 14. As best seen in Fig. 6 the deflector 14 comprises a plurality of mutually abutting V-shaped ridges 17 that break the material into droplets that are deflected radially outwards as a spray cloud.

As best seen in Figs. 4 and 8, the deflector 14 is coaxial with the skirt 12 but of smaller diameter and is supported by the hub 11 so as to leave a radial gap 18 between an outer surface of the def I ector 14 and an i nner surface of the ski it

A fan 20 which may be an axial fan projects downward from and is attached to the deflector 14 and has fan blades 21 that are configured to rotate with the deflector 14 beneath an outer rim 23 of the tapered skirt 12. This generates suction that draws droplets deflected radially outwards by the deflector 14 back toward an axial center 24 of the spray head 10. By such means, the central void that is characteristic of hitherto- proposed atomizers is avoided and the spray head 10 sprays a uniform spray over its complete area of coverage. This avoids the need to mount pairs of laterally spray heads in overlapping relationship as discussed above. Wax material in the form of a fairly viscous liquid is injected into at least one inlet 26 shown in Fig. 8 where it is deposited inside a hollow chamber 27. As seen in Figs. 3 and 4, the hub 11 includes a hollow bore 25 through which ambient air is sucked by the fan 20 thereby assisting in forcing the wax material through the nozzl es 15 for creati ng the spray.

The deflector 14 includes an annular cap 30 that supports a plurality of angularly spaced apart nozzles 15 that are configured to direct the wax material toward the deflector 14. Typically, the tapered deflector 14 has an apex angle of approximately 80· and rotates at a speed of between 1,500-5,000 rp Wax emerging from the nozzles is urged substantially horizontally against the inner wall of the deflector by centrifugal force and the droplets thereby created are deflected outwards in a direction parallel to the i nner wal I surfaces of the def I ector.

In one embodiment shown in Fig. 8, the hub 11 includes two fluid inlets 26 each aligned with a respective pair of nozzles 15 for feeding different liquids thereto, thereby spraying a homogenous mixture of the two liquids. Each of the fluid inlets 26 includes a tubular portion that extends through the hub and intersects an internal lower ri m of the hub to form an opening 34 best seen in Figs. 3 and 7, each of which is aligned with a respective nozzle 15. A spacer element 35 shown in Figs. 3 and 8 ensures that the cap 30 of the deflector 14 is slightly displaced from the hub, thus creating a small cylindrical cavity that constitutes the mixing chamber 27 (shown in Fig. 4) between the openings 34 and the nozzles 15 into which air at high pressure is injected through the hoi I ow bore 25 thereby ensuri ng that the different I i qui ds i nj ected i nto the f I ui d i nl ets 26 are well mixed and form a uniform, homogenous spray before being ejected by the nozzles 15.

As shown i n Fig. 3, the fan blades 21 are mounted at the end of a tapered pillar

40 having an axial bore 41 supported by the deflector 14. The tapered pi llar 40 abuts and is supported by a rigid circular plate 42 have angularly spaced apertures 43 through which the nozzles 15 protrude. When assembled, the plate 42 abuts and is retained by the inner surface of the cap 30 of the deflector 14 so that the deflector 14 and the fan blades 21 form a composite unit

Fig. 9 is a sectional elevation showing angular dimensions of the deflector 14 in an embodiment of the invention reduced to practice. It is seen that the walls are inclined inward to the horizontal at angles of 52.5· and 47.5· . It can be shown that with such a geometry, wax emerging from the nozzles is urged substantially horizontally against the inner wall of the deflector by centrifugal force. The ridges 17 break the wax into small droplets which are deflected by the inner wall surfaces of the deflector. If the inner wall surfaces were planar and thus acted like a conventional reflecting surface, a droplet projected horizontally would strike the wall surface at angle of 42.5· to a line normal to the wall surface and, in accordance with the law of reflection would thus emerge at angl e of 85· to the hori zontal toward the centerl i ne 24 of the def I ector. B ut the ri dges 17 prevent this from happening and break the wax into small droplets, which then follows the lines of the ridges so as to emerge outwards in a direction parallel to axes of the ri dges and thus al ong the i nner wal I surfaces of the def I ector.

Fig. 10 shows schematically the effect of the fan to render the spray uniform, it being seen that the fan 20 sucks air from the sides of the spray head thereby urging spray that is radially deflected by the deflector 14 towards the centerline 24, thereby f i 11 i ng the voi d and ensuri ng uniform coverage.

Reference is now made to Figs. 11 and 12 showing details of the fan blades 21, whose design has been found to impact strongly on their effectiveness to provide the correct amount of suction. Fig. 11 is a pictorial representation of the fan blades showing that they project slightly downward from a central hub and that each blade is also axially curved. Figs. 12a to 12d show dimensions in mm of the critical features of the fan blades, it being noted that the diameter of the tapered skirt 12 at its lower rim is 141.30 mm This means that its radius is slightly larger than 70 mm, while the axial length of the fan blades is slightly larger than 55 mm This leaves an annular space surrounding the fan of approximately 15 mm width into which, as is seen in Fig. 9, air flow is fairly unaffected. The fan serves to divert air from outside the peri phery of the tapered skirt 12 into the inner volume of revolution defined by the rotating fan blades, thereby diverting some of the spray that would otherwise be directed radially outwards towards the center.

Fig. 12c shows that the angle of the main part of the blade at the point of connection with central hub is equal to 36.17· . The angle between the blade and a line normal to the axis of rotation is shown as 12.16· . Consequently the angle of the blade relative to the axis of rotation is 102.16· (i.e. 90· + 12.16· ) in order to induce airflow to turn to the center. Fig. 12d shows that the angle of the main part of the blade from the vertical to 5mm from the end of the blade is 7.39· . T he last 5 mm at the end of the blade is straight to achieve stability and avoid vibrations. The curvature of the blade is designed to prevent fatigue and cavitation. The propeller diameter is larger than that of the def I ector so as to cause the ai r at the si des to turn i nwards to the center.

It will be apparent that modifications can be made to the design of the spray head without affecting its overall manner of use. Thus, although two liquid i nlets are provided, it will be understood that a single liquid inlet may suffice or, if desired, more than two may be provided. The description of the above embodiments is not intended to be I i miti ng, the scope of protect! on bei ng provi ded only by the appended cl ai ms.