GB2201907A - Atomising disc - Google Patents

Abstract

An atomising disc, suitable for spraying a liquid agrochemical composition, has discrete delivery points 11 at its periphery, the points being of different radii from the centre of rotation 13. Spinning disc sprayers produce a spray footprint in the form of a narrow annulus. As this is moved along it produces a swath which, although covering the full width of the annulus, is greatly concentrated in two narrow bands at the edge of the swath. The present disc helps to fill in the centre of the footprint, thus producing a more even swath. <IMAGE>

Description

ATOMISING DISC This invention relates to an atomising disc for a centrifugal spraying device. In a centrifugal sprayer the liquid to be sprayed is fed to the central region of an atomising disc rotating at a relatively high speed. Under the action of centrifugal force, the liquid is transported from the central region of the disc to the periphery thereof whereat it is thrown off the disc as droplets or as a sheet or as liagments: the sheet or ligaments then break up into droplets.

One application for a centrifugal spraying device is for applying a liquid agrochemical composition, e.g. a fertilizer, growth regulator, and/or pesticide composition, to the land or to crops growing thereon.

Such a centrifugal sprayer may be a hand-held device or it may be mounted on a tractor or on a vehicle adapted to be propelled by a tractor.

For such applications it has been.proposed, e.g. in GB 2026904, to employ a disc whose periphery has a toothed configuration so as to define points from.which the liquid is thrown off the disc. By using such a toothed configuration, the liquid is thrown off the disc as ligaments rather than as a sheet: this generally leads to a relatively uniform spray droplet size.

A similar effect can be achieved by providing a plurality of discrete passages round the periphery of the disc and from the outer ends of which the liquid is thrown off the disc. In the following description the outer ends of such teeth or passages or other discrete points from which the liquid is thrown off the disc are termed delivery points and the distance of any such delivery point from the rotational axis of the disc is termed the delivery radius. If such a centrifugal sprayer is held in a fixed position, the spray pattern is a relatively narrow annulus: for example a typical hand-held sprayer gives an annular spray pattern of 1.2m outside diameter and 1.lem inside diameter. By moving the sprayer in a line relative to the land, a swath of land or crop can be covered by the spray.

However, because of the annular nature of the spray pattern1 the swath produced when the device is moved in a line is non-uniform: a greater concentration of spray is applied to the edge regions of the swath than to the centre thereof. This is often undesirable as such nonuniform application of agrochemicals can lead to overand/or under- treated areas of the crop or land.

We have devised a form of atomising disc wherein the width of the annulus of the spray pattern is significantly increased.

Accordingly the present invention provides an atomising disc for use in a centrifugal spraying device, said disc having a plurality of discrete delivery points around its periphery and said disc being provided with means for mounting the disc for rotation about an axis prependicular to the central region of the disc, characterised in that the disc has delivery points of at least two differing radii.

The disc preferably has at least 4, and in particular at least 8, delivery points: most preferably there are 10-24 delivery points. The ratio of the longest delivery radius to the shortest delivery radius is preferably at least 1.3 and in particular at least 1.8. Preferably that ratio is below 3.

The spray pattern annulus size given by any particular delivery point depends on the delivery radius of that point. Thus if there are two delivery radii, two annuli will be formed: in some cases these annuli will overlap to give a single broader annulus: in other cases, with two delivery radii, the spray pattern will have two distinct, concentric, annuli. To obtain a broad annular spray pattern it is preferred that there are at least three delivery radii. As explained hereinafter, in some cases it is possible to arrange for the delivery point to be regularly disposed around the periphery of the disc, e.g. alternating short/long or short/long/long, if two radii or alternating short/medium/long, short/long/medium, short/medium/long/long, or short/long/medium/long etc. if three radii.However it is preferred that the delivery points describe, in plan, a single- or multi- limb spiral with each limb of the spiral having at least three delivery points. It will be appreciated that in a disc having 3n delivery points (where n is an integer) of 3 differing radii arranged in an alternating short/medium/long configuration, the delivery points describe such a spiral having n limbs.

It is not essential that each delivery point has a radius differing from that of its neighbour: thus some or all of the delivery points may be arranged in pairs or threes of equal radius: where the delivery points describe a spiral the latter may terminate with several delivery points of the same radius.

In the case of a spiral configuration the delivery points may describe a single limb, single turn spiral, a two limb, half turn spiral, or a three limb, third turn spiral etc. Preferably they describe no more than a four limb, quater turn spiral: in particular a single limb single turn spiral is preferred.

In one form of the invention the delivery points are co-planar, i.e. they all lie in the same plane perpendicular to the axis of rotation: in this case it is necessary that the delivery points describe a spiral as aforesaid and the rotational direction of the disc corresponds to the decreasing radius of the spiral: i.e.

when rotating so that a second delivery point succeeds the angular position occupied by a first delivery point adjacent the second delivery point, except at the ends of the spiral, the second delivery point has a radius greater than that of the first delivery point.

Accordingly the present invention also provides a centrifugal sprayer including an atomising disc having a spiral configuration as aforesaid, means for causing rotation of said disc in the direction of decreasing radius of the spiral, and means for feeding liquid to be sprayed to the central region of said disc.

In the case of an atomising disc having co-planar delivery points, rotation in the specified direction is necessary so that the liquid thrown off the shortest radius delivery point does not impinge against the adjacent longest radius delivery point. It will be appreciated that this problem, and hence the need for the specified rotational direction, may not arise if the delivery points do not lie in the same plane: thus the disc may be arranged such that the height of the delivery points above the central region of the disc increases, or decreases, with the delivery radii. In such an arrangement, a spiral configuration, although preferred, is not necessary. Thus there may be alternating short and long delivery points with the height of the latter above the central region of the disc greater than that of the short delivery points. In this case it is also necessary, to avoid impingement of the liquid thrown off the short delivery points that the body of the disc leading to the long delivery points does not obstruct the path of the liquid thrown off the short delivery points.

While with a spiral, co-planar, delivery point configuration and the specified direction of rotation this impingement problem is avoided, there is a risk that if a second delivery point has too great a radius relative to an adjacent first delivery point, the liquid thrown off that first delivery point will impinge on the disc body adjacent that second delivery point. It is to minimise the risk of such impingement that a gradual progression of delivery radii, a single limb, single turn, spiral, and the upper limit on the ratio between the greatest and smallest delivery radii, are preferred.

Preferably the disc is provided with means to divide the liquid flowing outwardly, under the action of centrifugal force, over the central region of the disc into separate streams and to lead each stream to an associated delivery point.

In one form of the invention the means effecting flow division are such that the liquid is divided substantially equally so that each delivery point is supplied with liquid at the same rate. Thus the flow division means may comprise a plurality of channels, one for each delivery point with the entrances to said channels subtending equal angles at the axis of rotation. For example the channel entrances may be of equal width and are positioned on the circumference of a circle concentric with the axis of rotation.

In one form of the invention the angular displacement of the delivery points is uniform. In this case, if the supply of liquid to each delivery point is uniform, then, since the liquid thrown from the longer delivery points is generally thrown a greater distance from the disc than liquid thrown from the shorter delivery points, there may be a tendency for the central region of the swath to receive higher concentrations of liquid than the outer regions. This can therefore compensate for the otherwise higher concentration of liquid applied to the outer regions of the swath by virtue of the annular spray pattern. However in some cases this may give over compensation: in that case it is preferred that more liquid is fed to the longer delivery points, e.g. by arranging that the flow division is non-uniform.This may be achieved by making the angular displacement of the channel entrances to the longer delivery points greater than that of the channel entrances to the shorter delivery points.

Alternatively the angular displacement of the delivery points themselves may progressively decrease as the delivery radius increases: thus as the delivery radii increase the angular displacement between adjacent delivery points decreases. In this case it is preferred that the equal flow division is effected so that each delivery point receives liquid at substantially the same rate.

It is preferred that the radii and angular displacement of the delivery points is such that the ratio between the radius of any delivery point and the radius of an adjacent, shorter, delivery point is not greater than the secant of the angle between the two delivery points.

The invention is illustrated by reference to the accompanying drawings wherein Figures 1,3,5 and 6 are plan views of four alternative discs; Figures 2,4 and 7 are sections along the lines A-A, B-B and C-C of Figures 1,3 and 6 respectively.

Figure 8 is an elevation of a crop sprayer incorporating an atomising disc according to the invention.

In Figures 1 and 2 the disc has a 12 point single limb single turn spiral configuration. Each delivery point is the tip of a tooth 11: the radii of the teeth form an arithmetic progression, i.e. each succeeding tooth is longer than the preceding tooth by a constant amount so that the ratio of the longest tooth radius to that of the shortest is about 2.7 5. The teeth are equiangularly disposed, i.e. the angles between adjacent teeth each equal 301.

The disc has a flat interior surface 12 but the thickness of the disc is increased at the positions of the shorter teeth so as to counterbalance it. The disc is provided with a bore 13 by which it can be mounted on a shaft and so rotated.

The central region 14 of the disc is unobstructed so that liquid fed thereto can flow outwards evenly.

Parrallel sided channels 15 feed the liquid from the central region 14 towards the teeth 11 and so act as flow dividers. Each channel 15 terminates in lip 16 and a Vgroove 17 to the tip of the tooth associated with that channel. Since the angles subtended by the entrances 18 of the channels 15 are equal, substantially equal amounts of liquid will be fed to each tooth.

In the embodiment of Figures 3 and 4 a 15 delivery point disc is shown having a single limb single turn configuration. In this disc however the delivery points are not equiangularly disposed: instead the angles between successive delivery points decrease by 2 as the radii of the delivery points increase. Thus there are in effect progressively more "longer" delivery points. Again the lengths of the radii form an arithmetic progression such that the ratio of the longest to shortest radius is about 1.8.

In this embodiment the delivery points are bores 19 through the outer wall 20 of the disc. At the position of each bore 19, a small rib 21 is formed on the external surface of the disc outer wall so that the liquid will leave the disc rather than flow along the outer surface thereof. Although the delivery points are not equiangularly disposed, the entrances 18 of the feed channels 15 are disposed equiangularly so that substantially equal amounts of liquid is fed to each delivery point. In this embodiment the feed channels 15 taper towards the delivery points.

In the embodiment of Figure 5, a ten delivery point disc is shown in which the delivery points define a two limb, half turn spiral. In this embodiment the delivery radii form a geometric progression with each radius being about 1.1 times the length of its predecessor (except in the case of the first delivery point in each limb). The ratio of the longest to shortest radii is-thus about 1.46.

The delivery points, which are of the type described above in relation to Figures 3 and 4, are disposed equiangularly. However the entrances 18 to the feed channel 15, which taper towards the delivery points 19, subtend increasing angles at the rotational axis as the delivery radii increase: in this embodiment these angles increase by 40 from one channel entrance to the next. By this means the longer channels are fed with more liquid than the shorter channels.

The discs of Figures 1 to 5 all have their delivery points in the same plane perpendicular to the rotational axis. It is therefore necessary, to avoid impingement of liquid thrown from the shortest delivery point on to that portion 22 of the outer surface of the disc between the shortest and longest delivery points, that the discs are rotated anti-clockwise, i.e. in the direction of decreasing radius.

In the embodiment of Figures 6 and 7 however the delivery points are not co-planar: The shortest delivery point is at a level sufficiently below the portion 22 of the disc surface between the longest and shortest delivery points that such impingement is avoided: this disc can therefore be mounted for clockwise or anti-clockwise rotation.

In this embodiment the delivery points again form a 10 point, 2 limb, half turn spiral. The points are teeth 11 disposed equiangularly and the lengths of the delivery radii form an arithmetic progression. The feed channels 15 taper towards the delivery points 11 and the base 23 of the feed channels 15 is inclined upwards towards the tips of the teeth 11. ln this embodiment the entrances 18 to the feed channels 15 are disposed equiangularly.

In Figure 8 there is shown a rotating disc crop sprayer. The apparatus comprises a handle portion 24 to which is attached a lance 25. At the end of lance 25 remote from handle 24 is a spraying head 26 in which an electric motor is housed. Attached to the motor shaft is the atomising disc 27 in accordance with the invention.

The crop sprayer is intended to be used with a "knapsack" arrangement for the liquid to be sprayed: the liquid is fed from the "knapsack" reservoir, not shown, to the handle 24 via a flexible tube 28. The liquid is fed from tube 28, through tubes in the handle 24 and the lance 25 to the spray head so that it is supplied to the central region of the atomising disc. A valve controlled by knob 29 is provided in the handle 24 to vary the rate at which liquid is supplied to the atomising disc.

Also provided in handle 24 are batteries to power the motor: a control 30 is provided to vary the voltage supplied to the motor so that its rotational speed can be varied.

Th an example using a crop sprayer of the type shown in Figure 8 fitted with a disc similar to that of Figure 1, a pesticide formulation was sprayed at a rate of 50 ml/min using a rotational speed of 3000 rpm with the disc 27 40 cm above the ground.

The disc employed had 16 teeth arranged in a single limb, single turn spiral. The teeth radii increased in an arithmetic progression from 12.5 mm to 25 mm and were spaced equiangularly. The feed channels 15 were parrallel sided of width 2 mm and had their entrances 18 disposed equiangularly. The height of each lip 16 at its lowest point was 2 mm and the length of V-grooves 17 was 4 mm.

The maximum depth of the v-grooves was 2 mm. Using this disc under these conditions, the spray pattern was an annulus of internal diameter 32 cm and external diameter 112 cm.

Claims (8)

What we claim is

1. An atomising disc for use in a centrifugal spraying device, said disc having a plurality of discrete delivery points around its periphery and said disc being provided with means for mounting the disc for rotation about an axis perpendicular to the central region of the disc, characterised in that the disc has delivery points of at least two differing radii.

2. An atomising disc as claimed in claim 1, having at least four delivery points.

3. An atomising disc as claimed in claim 1 or 2, wherein the ratio of the longest delivery radius to the shortest delivery radius is at least 1.3

4. An atomising disc as claimed in claim 3 wherein the ratio is from 1.8 to 3.

5. An atomising disc as claimed in any preceding claim in which the delivery points lie on a single or multi link spiral, each limb of the spiral containing at least three delivery points.

6. An atomising disc as claimed in claim 4 wherein the delivery points are co-planar.

7. Centrifugal spraying apparatus, including an atomising disc as claimed in any of claims 1 to 4.

8. Centrifugal spraying apparatus including an atomising disc as claimed in claim 5, means arranged to rotate the disc in the direction of decreasing radius of the spiral, and means for feeding liquid to be sprayed to a central region of the disc.