GB2166670A - Electrostatic sprayers - Google Patents

Abstract

An electrostatic sprayer for agricultural treatment liquids includes a spinner element (2) to disperse a supplied liquid in a spray of droplets and a spray collector (7) to limit the spray to a selected portion, together with means (6) to charge the spray droplets and means (60) to carry a charge to deflect charged droplets. <IMAGE>

Description

SPECIFICATION Electrostatic sprayers This invention relates to electrostatic sprayers such as are used for agricultural treatment liquids.

Treatment liquids for agriculture, which includes horticulture, are herbicides, insecticides and fungicides among others which are most effective when applied in precise quantities to specific locations.

Less accurate techniques waste expensive materials and are unacceptable for environmental and operator health reasons.

Recent proposals for electrostatic sprayers for agricultural and horticultural purposes have used spinner elements such as rapidly rotating cups, dishes and discs to disperse droplets of liquid to which a charge can be applied in a uniform sheet or cone. These devices are effective but care has to be taken in use to maintain a particular attitude of the device for proper operation. This can restrict the usefulness of the device.

It is an object of the invention to provide an electrostatic sprayer which overcomes such restrictions.

According to the invention there is provided an electrostatic sprayer including a spinner element to disperse a supplied liquid in a spray of droplets and a spray collector to limit, in operation, the spray to a selected portion, means to cause the droplets to have electric charge and means to carry a charge te deflect droplets of the spray.

The means to carry a charge to deflect droplets may be a sheet electrode placed to shield the sprayer from the spray.

Preferably collected spray is returned for supply to the spinner.

In one arrangement a spinner in the form of a dish is enclosed around three quarters to one third of its periphery by a trough which collects all but a portion of the spraysheet to provide a flat fan-like dispersion of charged droplets. As a result of this limitation to a fan-like dispersion of droplets a more specific area can be treated with less waste.

Advantageously about half the periphery is enclosed and the spinner is in a vertical plane. This, in operation, produces a charged fan-like dispersion of droplets in a quadrant partly to one side and partly below the spinner. Such a fan will penetrate closely-growing cereal and similar crops. The sheet electrode may have a shape similar to that of the fan-like dispersion of droplets.

Conveniently the collector can be of telescopic or other adjustable form so that the portion of the pe periphery selected can be adjusted in at least one of length and position. The collector may also be adjustable to limit the spray in other than a peripheral direction.

The spray can be charged by inductive direct or other methods.

The sheet electrode may be energised with a polarity appropriate to that on the droplets to bring about the deflection of the droplets away from the sprayer.

According to the invention there is provided a method of spraying electrostatically charged droplets from a sprayer including providing a supply of liquid to be sprayed, causing a spinner element to spin, supplying liquid to the spinner for dispersal as a spray of droplets, collecting spray droplets to limit the spray to a selected portion, charging spray droplets with an electric charge, maintaining an electric field to deflect droplets of the spray away from the sprayer.

Preferably the selected spray portion is a fan-like spray in a vertical plane to below a horizontal level.

Embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure 1 shows a crosssectional elevation of a sprayer, with direct charging, according to the invention, Figure 2 shows a crosssectional elevation of a sprayer, with inductive charging, according to the invention. Figures 2a and 2b showing details, Figure 3 shows in schematic form the form of sprayfan produced by a sprayer according to the invention.

Figure 4 shows charts of results of tests of sprayers according to the invention.

Figure 1 shows a crosssectional elevation of an electrically driven electrostatic sprayer. A spinner element 2 some 140 millimetres in diameter is supported to be revolved in vertical plane by a suitable electric motor 9 which is supported in a housing 5.

Housing 5 can be arranged for handheld use on a suitable shaft, which can also be a batteryholder, or for mounting on a spray boom for vehicle use.

These aspects are wellknown in the art and are not further described. A proprietary sprayer which provides these mechanical features is the Technoma Giro jet (R.T.M.) Serial Number 525.

The spinner 2 is partly cowled by a collector 7. A flinger 3 is provided on the spinner shaft to protect the motor from the entry of spray liquid. The collector, in the present embodiment, extends around the spinner from approximately 5 o'clock to 11 o'clock, when the open face of the spinner is taken as a clock face for reference purposes. Each end of the collector, one of which is seen at 71, is cut at an appropriate angle to conform to the path of spray droplets.

The action of the collector 7 is to limit the arc of the spinner periphery over which spray droplets are dispersed (arrow B) in operation. Elsewhere around the spinner periphery the droplets of spray are collected by the collector.

In the present embodiment the collected droplets are returned to a liquid supply for immediate reuse. This feature is clearly convenient and economic in most cases but in some cases may not be appropriate and the collected droplets may be retained in a suitable container.

As shown in Figure 1 collector 7 and housing 5 together form a volume 8 to which collected droplets flow and in which lip 81 retains the accumulated liquid, as in a sump. A suitable conduit, such as flexible tube 10, extends from volume 8 to a pump 1 and then to a liquid-holding tank 12, which is also refilled with liquid to be sprayed from time to time. This tank is preferably closed against spillage but need not be pressurised or pressure-tight.

A further pump 13 forces liquid from the tank 12 through further conduit, as indicated by arrows A, to a nozzle 4 which directs liquid to be sprayed into the centre of spinner 2 for dispersal as spray droplets when spinner 2 is driven by motor 9 at some 500 to 5000 R.P.M. or other suitable speed or range of speeds. A connection for an electrical supply to motor 9 is shown at 91. The supply may be controlled to vary the speed of the motor.

An electrode 60 is mounted behind the plane of the spinner 2. This electrode, which can also be seen in Figure 3, is conveniently of sheet form and of the same general shape as the spray fan extending to a distance which provides sufficient shielding of the sprayer without being unwieldy. The electrode can be of a metal sheet 65 with an insulating coating 64 of plastics or like material, an electrical connection, via terminal 63, to the sheet being provided. The electrode can have other forms of construction which can carry charge to deflect the spray and are strong enough to maintain their shape in use, for example a metal film can be encapsulated between plastic layers. Even a metal mesh or metal rods or like elements, with an insulating coat, may be effective in some cases.

The electrode 60 is placed about 25 mm behind the spray in this embodiment but a closer (down to 5 mm) or more remote spacing is possible and the best position may have to be found by experiment.

The spray is charged by an electrostatic supply provided by high voltage generator 61 which has a connection 62 to a suitable source of electrical energy, for example to dry cells in the handheld device mentioned above or the vehicle supply (12 V or 24 Vdc usually) for the vehicle-borne devices.

Suitable generators are well known in the art. Generator output voltages in the range 5 KV to 30 KV have been found suitable for this embodiment but other values may be selected as appropriate for other embodiments.

In this embodiment the spray is charged directly and the polarity of the charge on the droplets is the same as that of the high voltage applied at the sprayer. The directly-charged droplets are then moved to the target partly by their momentum and partly by the potential difference between the droplets and and "earthy" target vegetation.

The high voltage supply from the generator 61 is carried over a suitably insulated conductor 6 to an electrode 68, in this embodiment of a needle-like form, held close to the liquid-spreading surface of spinner 2. This surface itself carries a metal lining 11 as an electrode. This lining 11 is, in operation, connected by the conductive spray liquid to the liquid in the supply tank 12. This tank is thus at high potential.

The electrode 68 can be in the form of a brush rubbing on the spinner but this may increase the drag on the motor driving the spinner. The electrode 68 can be in contact with the spray liquid for example by being in or forming nozzle 4 but this is likely to be a less effective method of charge transfer. For the direct form of charging electrode lining 11 may be extended by at least one projection 20 to just beyond the edge of the spinner. This can enhance the transfer of charge.

A connection is also provided between generator 61 and the deflector 60, as indicated by arrow D, to the terminal at 63 on the deflector to cause the metal part 65 to have the same charge polarity as the charged droplets and deflect these away from the sprayer.

Figure 2 shows another embodiment in which the charging action is inductive, not direct as in Figure 1. Components similar to those in Figure 1 have similar references and will not be described again. The deflector 60 is similar but has a different electrical connection as explained below.

To achieve inductive charging spinner 21 has an electrode 24 in the form of a metal ring mounted in the spinner by pillars 23 to be close to the edge of the spinner. Three pillars are suitable and the pillars are required to be insulators at the voltages used and not be permanently affected by the spray liquid to become conductive. The electrode 24 may be a plastic ring 22 carrying a metallised coating 26 on the outer surface, as shown in Figure 2a. The metallising preferably does not reach the periphery, for example being covered by an insulating coating or plastics body 27. In another version, Figure 2b, a plastics body 28 almost completely encloses a metal body 29 leaving only a narrow groove towards the inner edge of body 29 to provide access for an electrode 66. Conveniently the metal body, or metallising, is about 10 millimetres wide and centred on the edge of the spinner.The overall thickness is preferably about 1 millimetre.

An electrode 66, of needle form, is supported close to electrode ring 24 but not in contact and energises ring 24 via the ionised gap between the needle and the ring when the high voltage supply is applied.

The supply has to provide both positive and negative polarities in this inductive charging embodiment. One polarity is connected to electrode 66, the other, as indicated by arrow E, to electrode 60 via terminal 63. The total potential difference is between 2 KV and 10 KV. Above 10 KV breakdown can occur with inductive charging. Conveniently supplies of t 1 KV to + 5 Kv can be used although unequal values are also possible. The ionised gap is preferably 1 to 2 millimetres with a maximum of about 5 millimetres.

In operation spray-liquid supplied, as before, from nozzle 4 is spread across spinner 21 by the rotation of the spinner to form droplets at the edge of the disc. These droplets acquire charge by induction in the vicinity of electrode 24 for dispersal (arrow C) as a charged spray of polarity opposite to that applied at electrode 66. The liquid is earthed, if sufficiently conductive, via the earth on the tank 12. If the liquid is not sufficiently conductive a conductive, earthed coating on the face of spinner 21 is needed. The deflector has the opposite polarity to the droplets and thus repels them away from the sprayer.

Either polarity arrangement can be chosen, i.e. a negative polarity electrode ring producing positive polarity drops and a positive polarity deflector or vice versa. The spray liquid can be at earth potential in this arrangement and this is very useful for safety reasons. For electrical reasons the spray liquid is preferably held at earth potential at the spinner.

For the direct charging technique again either polarity can be used. The spray liquid will be at a high potential.

In a variant of this embodiment (not shown) the electrode 24 may be a metal ring. The electrode is of generally similar size to the jacketed electrode.

In the jacketed electrode however less metal may be used, with a reduction in the overall weight of the items to be driven by motor 9. In any case the metal or metal film is centred on the sharp lip of spinner 21, i.e. 5 mm on either side.

Suitable materials for the various components will be apparent to those skilled in the art. Light weight, freedom from liquid absorption and electrical insulation requirements suggest plastics materials, which in mass-production can be produced cheaply in complex forms by moulding. Metal may be needed for electrodes although metal-plated plastic is often appropriate here. Other materials may be appropriate in special situations such as aggressive liquids. The surface of electrode 24 nearer the spinner is preferably insulated to reduce breakdown in the narrow gap to the spinner.

Various modifications can be made for special requirements. For example with spray liquids of poor conductivity an earth can be applied via nozzle 4, when the high voltage is applied elsewhere, to maximise the potential difference used to charge the droplets. The projection 20 is believed to encourage charge transfer by forming a virtual electrode as it rotates isolated with the spinner.

The deflector electrode greatly reduces the problem of the aprayer being wetted by charged droplets which wetting is both chemically undesirable and can cause problems with the electrostatic equipment.

Electric drive is generally convenient but compressed air may be suitable. The high voltage is conveniently generated by semi-conductor based inverters or similar devices but piezo-electric sources for the inductive system, or even rotary machines, which could be compressed-air driven, may be used to produce a self-contained equipment.

The shape of spray fan produced is outlined in Figure 3, which show schematic front and side views of the sprayer in operation. Again the reference numerals of Figure 1 have been used where appropriate. The front view shows that a vertical sheet of droplets, S, with an included angle of approximately 90 is produced. This sheet is almost wholly in the plane of the spinner. By tilting the sprayer the sheet can be varied between the horizontal S" and the vertical S via positions S' and S", which positions are particularly useful for small plants.

By varying the position of collector 7 around the spinner (not shown) or by varying the extent of the collector around the periphery the position or included angle can be varied. Thus a vertical spinner could produce a spray fan which is sideways and in a substantially vertical plane. The device could also be introduced into the crop rows to spray up into the crop.

Furthermore the collector 7 can be made to be adjustable, for example by having telescoping parts, sliding over one another, so that an operator can set a required spray fan at will. A particularly useful arrangement is to have the sliding parts operable to define two apertures arranged so that a spray fan is produced on both sides of the sprayer.

When the two fans are in a vertical plane they are usable on row crops, and bush fruit such as blackcurrants, to aid penetration.

Figure 4 represents the results of comparative tests on sprayers according to the present invention and on existing electrostatic design.

The tests were conducted on a field of mature cereal crop plants (spring barley) represented in Figure 4 by a diagrammatic plant P having leaves at "flag" (F) "top"(T) "middle" (M) and "bottom" (B) positions. The plants were about 50 mm apart in rows 100 mm apart. Each plant could have several stems. The overall height of the plants is about 800 millimetres. The performance of the sprayers is assessed by measuring the deposit of sprayed active material (in micrograms) per unit of plant material, foliage and head (in grams).

In Figure 4 the bar chart 41 is for an existing electrostatic design generally as described in UK Published Application 2119678A and the bar chart 42 for a sprayer according to the invention as exemplified by the embodiment in Figure 1 and the bar chart 43 for the embodiment in Figure 2.

The test conditions were a spray rate of 4 litres of spray per hectare with a spinner speed of 4500 rpm with the centre line of the sprayer at a distance of 300 mm from the top of the plant P. The voltage was 30 KV for chart 41, 30 KV for chart 42 and + 2 KV for chart 43.

Comparing charts 41 and 42 the sprayer of Figure 1 does not greatly alter the deposit on the flag part F although there is a useful increase. However as a proportion of the flag deposit the deposit on the top, T, and middle, M, leaves is significantly increased from some 7% to 10% and 1.5% to 3.5% respectively. The absolute amount is more than doubled for the middle leaf, where the weight of the plant material is concentrated. This is a clear improvement in application of spray to parts of the plant which the earlier electrostatic sprayer could not reach.

When the inductive charge technique of Figure 2 is applied (chart 43) a further improvement is noted. Although the deposit on the "flag" is reduced to around half of that in charts 41 and 42 the proportion on the top and middle leaves rises significantly to some 27% and 10% of the flag deposit and again to absolutely higher deposits. As the "flag" leaves are only a very small fraction of the total weight of the plant then, despite the very high dosage in micrograms/gram, only a very small fraction of the chemical is on the flag.

By way of comparison a conventional hydraulic sprayer would achieve smaller levels of deposit on the top leaves, similar levels on the middle leaves, and higher levels on the bottom leaves but only with a higher overall consumption of liquid which is wasted on the soil. Tests indicate that more than five times the amount of liquid, and as much as three times the amount of chemical, would be needed. A rate of 30 litreslhectare can be cut to 5 to 10 litreslhectare.

These results show that by restricting the spray to only a portion of the normal pattern much better penetration into the crop is possible when the crop has a dense canopy, such as cereal plants. It is believed that this is because the restricted spray can be directed in a substantially vertical plane to penetrate the crop where there is less resistance to entry between the plants. Also the momentum of drops leaving the sprayer head can be greater than those settling under gravity from a horizontal spinner.

The above embodiments are specifically described by way of examples of the techniques provided by the invention to achieve more efficient spraying of agricultural and horticultural treatment liquids in particular onto "difficult" crops.

Claims (15)

1. An electrostatic sprayer for agricultural treatment liquids including a spinner element to disperse a supplied liquid in a spray of droplets and a spray collector to limit, in operation, the spray to at least one selected portion, means to cause the droplets to have electric charge and means to carry a charge to deflect charged droplets of the spray.

2. A sprayer according to Claim 1 in which the means to carry a charge to deflect droplets is a sheet electrode placed to shield the sprayer from the spray.

3. A sprayer according to Claim 1 in which the collector limits the spray to a flat fan-like dispersion of charged droplets in a vertical plane, partly to one side and partly below the spinner.

4. A sprayer according to Claim 3 in which the means to carry a charge to deflect droplets is a sheet electrode of a shape similar to that of the fan-like dispersion of droplets.

5. A sprayer according to Claim 1 in which the collector is of telescopic or other adjustable form so that the portion or portions of the spray selected can be adjusted in at least one of number, length and position around the spinner.

6. A sprayer according to Claim 1 in which the spray is charged by inductive, direct or other methods.

7. A sprayer according to Claim 2 in which the sheet electrode is energised with a polarity appropriate to that on the droplets to bring about the deflection of the droplets away from the sprayer.

8. A sprayer according to Claim 1 in which the means to carry charge to deflect charged droplets includes a conductor and an insulating coat.

9. A sprayer according to Claim in in which the spinner has a spray charging electrode of a conductive surface to the spinner.

10. A sprayer according to Claim 9 in which the conductive surface has an extension over the edge of the spinner.

11. A sprayer according to Claim 1 in which the spinner has a spray charging electrode of a metal or metallised or other conductive body supported close to a droplet dispersing edge of the spinner.

12. A sprayer according to Claim 11 in which the electrode has an insulating support or covering.

13. A sprayer according to claim 9 or Claim 11 including a further spray charging electrode of a needle close to the spinner electrode.

14. A method of spraying electrostatically charged droplets from a sprayer including providing a supply of liquid to be sprayed, causing a spinner element to spin, applying said liquid to the spinner for dispersal as a spray of droplets, collecting spray droplets to limit the spray to at least one selected portion, charging spray droplets with an electric charge and maintaining an electric field to deflect charged droplets of the spray away from the sprayer.

15. An electrostatically charged sprayer for agricultural treatment liquids substantially as herein described with reference to the accompanying drawings.