CA1071937A - Process and apparatus for atomisation of liquids by electrostatic forces - Google Patents
Process and apparatus for atomisation of liquids by electrostatic forcesInfo
- Publication number
- CA1071937A CA1071937A CA282,788A CA282788A CA1071937A CA 1071937 A CA1071937 A CA 1071937A CA 282788 A CA282788 A CA 282788A CA 1071937 A CA1071937 A CA 1071937A
- Authority
- CA
- Canada
- Prior art keywords
- liquid
- electrode
- field
- spray
- conducting
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/324—Thermal treatment for modifying the properties of semiconductor bodies, e.g. annealing, sintering
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
- B05B5/00—Electrostatic spraying apparatus; Spraying apparatus with means for charging the spray electrically; Apparatus for spraying liquids or other fluent materials by other electric means
- B05B5/025—Discharge apparatus, e.g. electrostatic spray guns
- B05B5/04—Discharge apparatus, e.g. electrostatic spray guns characterised by having rotary outlet or deflecting elements, i.e. spraying being also effected by centrifugal forces
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
- B05B5/00—Electrostatic spraying apparatus; Spraying apparatus with means for charging the spray electrically; Apparatus for spraying liquids or other fluent materials by other electric means
- B05B5/025—Discharge apparatus, e.g. electrostatic spray guns
- B05B5/043—Discharge apparatus, e.g. electrostatic spray guns using induction-charging
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
- B05B5/00—Electrostatic spraying apparatus; Spraying apparatus with means for charging the spray electrically; Apparatus for spraying liquids or other fluent materials by other electric means
- B05B5/025—Discharge apparatus, e.g. electrostatic spray guns
- B05B5/053—Arrangements for supplying power, e.g. charging power
- B05B5/0531—Power generators
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
- B05B5/00—Electrostatic spraying apparatus; Spraying apparatus with means for charging the spray electrically; Apparatus for spraying liquids or other fluent materials by other electric means
- B05B5/025—Discharge apparatus, e.g. electrostatic spray guns
- B05B5/053—Arrangements for supplying power, e.g. charging power
- B05B5/0533—Electrodes specially adapted therefor; Arrangements of electrodes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
- B05B5/00—Electrostatic spraying apparatus; Spraying apparatus with means for charging the spray electrically; Apparatus for spraying liquids or other fluent materials by other electric means
- B05B5/025—Discharge apparatus, e.g. electrostatic spray guns
- B05B5/053—Arrangements for supplying power, e.g. charging power
- B05B5/0533—Electrodes specially adapted therefor; Arrangements of electrodes
- B05B5/0535—Electrodes specially adapted therefor; Arrangements of electrodes at least two electrodes having different potentials being held on the discharge apparatus, one of them being a charging electrode of the corona type located in the spray or close to it, and another being of the non-corona type located outside of the path for the material
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
- B05B5/00—Electrostatic spraying apparatus; Spraying apparatus with means for charging the spray electrically; Apparatus for spraying liquids or other fluent materials by other electric means
- B05B5/16—Arrangements for supplying liquids or other fluent material
- B05B5/1691—Apparatus to be carried on or by a person or with a container fixed to the discharge device
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S43/00—Fishing, trapping, and vermin destroying
- Y10S43/90—Liquid insecticide sprayer
Abstract
ABSTRACT
Electrostatic sprayer comprising an electrically conducting or semi-conducting surface; means for supplying liquid adjacent the surface; and a field adjusting member in close proximity to the surface.
Electrostatic sprayer comprising an electrically conducting or semi-conducting surface; means for supplying liquid adjacent the surface; and a field adjusting member in close proximity to the surface.
Description
~ 10'~9~
This invention relates to the atomisation and electro-deposition of liquids. It has particular but by no means exclusive application to the spraying of crops with pes~icidal compositions and to paint spraying. It also has application in the production of an aerosol dispersoid.
When a liquid is displaced from the locality of an electrically conducting surface at a voltage above or below earth potential the liquid may upon emerging into free space carry a net electrical charge resulting from an exchange of electrical charges with the source of the electrical potential.
This technique can be used to atomise the displaced liquid since the net electric charge in the liquid as the liquid emerges into free space from the locality of the conducting surace counteracts the surface tension orces of the liquid. The amount of electrical charge in the emerging liquid droplets after atomisation is, in part, dependent upon the strength of the electric field at the conducting surface.
There are known devices, particularly used for electro-static paint spraying, wherein the field strength at the conducting surface has been maximised by (i) sharpening an 'edge' of the conducting surface, whlch may, for example, be a rotating sharp-edged disc, adjacent which edge paint is constrained to emerge; (ii) raising the electrical potential of the conducting surface to a high value, generally of ~he , . . .
. .
. . . ,, ~
lO~i93~7 order of 60-100 Kv; and (iii) ensurin~ that the spray-target, which is earthed and is ~hus an earth boundary of the electrostatic field that exists between the conducting surface and the target surface, is sufficiently close to maintain a high field strength at the conducting surface adjacent which the liquid emergas. The conducting surface and the target surface define the main boundaries of the ~lectric field.
A salient feature of such known clevices is that the combination of high voltage and sharp-edged conducting suraces causes breakdown of the surrounding air (by the phenomenon known as corona discharge) The effect of this is that not all of the current supplied to the conducting surface is used to charge the liquid. Thus, corona discharge results in unnecessary current loss and greatly increases the current drawn from the source of high electrical potential.
This has disadvantages. One serious disadvantage is that the power required of the high electrical potential source is too high to be met easily by portable energy sources e.g. torch ! batteries.
Surprisingly, we have now ~ound that i~ a member, hereinafter referred to as a field adjusting member or a ~ield intensifying electrode, is in close pro~imity to ~he conductin~
surface lt enable~ a suficiently high field strength to be created at the conducting surface using a relatively low voltage, of the order of 1-20 ~
19~
KV, to charge the droplets. Thus a high charge density for example, of the order of 10 2 coulombs/kilogram may be placed upon the liquidO This gives rise to a high charge-utilisation efficiency which in turn enables low power sources, such as piezo-electric crystals, torch batteries or solar cells to be utilised as a charge t:ransfer device, and to giue rise to electrostatic atomisation of the liquid.
- Such atomisation requires no mechanical assistance such as an air blast or rotating disc. The combined field due to the voltage on the conducting surface plus the space charge of the atomised liquid itself then enables the droplets to be targeted toward an earthed object, or to form an airborne (aero~ol) cloud.
The field adjusting member may be considered to be a 'dummy target' since it strongly influences the field in the region of liquid atomisation. But, unlike an actual target, it is placed close to the conducting surface thus stre~gthening the field. Surprisingly, we have found that the field adjusting member may easily be placed so that it does not itself become a target for the atomised spray~
The reason for this is not fully understood, bu-t observation shows that, provided ~he liquid's physical characteristics (e.g. resistivity, viscosity) and flow rate are such as to produce ligaments (electrostatically) cf about 1 cm or more, the atomisation will take place in that . , , , , . ,:: ............................... .
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: . . . . , , . .: : ' ' , '' :
1~7~3q part of the electric ~ield where the combined forces of inertia, gravity field, and electrostatic ~ield are directed away from the field adjusting member.
It has been found possible to cause impingement of the spray onto the field adjusting member by placing it downstream of the atomising tip of the ligament. In this case it has been noticed that, with relatively small amounts of impinging liquid, that provided the surface of the field adjustlng member is sufficiently conducting, and earthed, the impinging particles give up their rharge and take up an opposite charge by induction in the electric field. This causes them to re-atomise and not to be retained on the member.
According to the present invention there is provided a process of spraying pesticides which comprises suppl~ing a liquid pesticidal composition to an electrically conducting or semi-conducting surface from which it is atomised by electrostatic forces to form a cloud of electrically charged particles said surace being in close proximity to a field adjusting member at such a potential and so sited relative to the surace that an atomising ield strength is created at the sur~ace using a relatively low voltage and with low current loss, as hereinater deined, while there is subs~antially no tendency or-liquid to be re~ained on the member.
This invention also includes electrostatic spraying ; apparatus suitable for use in the process of the invention .... . .. . .. . . .. ... ...
.' ' , : . .
~193q which comprises a spray head having a conducting or semi-conducting surface which may be, in operation, electrically charged and adjacent which liquid atomises; means for delivering the liquid adjacen~ the surfclce; and a field adjusting member in close proximity to t.he surface and being so sited and maintainable at such a potential relative to the surface that a high field strength may be created at the surface using a relatively low voltage and with low current loss, as hereinafter defined, while there is substantially no tendency for particulate liquid to be retained on the member.
By current loss is meant the applied high voltage.
current drain other than that used in charging the liquid.
Preexably the ield adjustlng member and ~he target . are both at earth potential. However the atomising field may also be created by changing the field ad~usting member and earthing the surface.
By the term 'conducting surface' we mean the sur~ace of a material having a resistivity of the order of 1 ohm cm or less, and by 'semi-conducting surface' we mean the surface material having a resistivity value o between 1 and about 1012 ohm cm. ~y 'insulating material' is meant material having a resistivity of more than 1012 ohm cm.
The conducting or semi~conducting surface adjacent which the liquid atomises may have various shapes. It will ~0~937 often be the end o~ a spray conduit, preferably a con~uit of capillary size, for example, a nozzle aperture, through which in operation the liquid spray emerges.
The conducting surface may also comprise the edges o two concentric tubes which edges define an annular aperture through which liquid emerges. The edges of the tubes may be serrated or fluted. Alternatively, the conducting s~rface may comprise two edges defining a slot, preferàbly of capillary width. The slot may be of rectangular or other formO Atomisation may be effected from the flat surface of a solid conductor or semi-conductor to which liquid has been supplied.
The geometric shape of the 1eld-adjusting member in general follows the shape o~ the conducting or semi-conductlng surface. Where the surface is defined by a nozzle the member may take an annular form with the member encircling the nozzle.
The field adjusting member is generally sited AS close as possible to the conducting surface without corona discharge occurring between them. For example with 20 KV on the conducting surface the field adjusting member is preferably sited not less, and not much more than, about 2 cm away rom it. The field adjusting member may be sited either level with, in front of, or behind the conducting surface from which the liquid atomises.
. . .................... . - .. : . :
.: ..... . . :, . ,, . :
. .. .. . . , , . . :. . .: .
~Oq~93~
In a preferred form OL the invention the field adjusting member has an insulating surface. For example, it may be a thin wire embedded in a body or sheath formed of a plastics material. This enables the distance between the field adjusting member and the conducting surface to be very much smaller than would be obtainable with 'air-gap' insulation only. This results in an enhanced field strength in the locality of the conducting surface.
It is preferred that the field adjusting member be adjustably mounted on the apparatus of the invention so that the spatial relationship between the member and the surface can easily be varied.
We have found that the position and the geometxic shape of the field adjusting member control the angle of the stream of droplets emerging into ree space. When the field adjusting member is behind the emerging spray the angle of the stream is increased, and when it is in front of the emerging spray the angle is decreased.
In addition, we have found that the average size of the atomiqed droplets in general may be controlled by the position o the fleld adjusting rnember in relation to the conducting surface. For example, for a given flow rate of liquid, bringing the field adjusting member closer to the conducting surface results in the droplets generally being of a smaller average si~e.
' '. '.'.:
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., ,: . .. . ~ . ........ : . ,.. ,, . . . . ~ .
., '. . ' . . . , : . , : . . ~ , ' ~7~93~
By controlling the position of the field adjusting member a selected size of droplets may be produced suitable for a particular use. For example, large numbers of small particles (e.g. 20-30 ~) of an insecticide may be preferred for maximum coverage of a target, whereas for a herbicide larger droplets less prone to wind drift: may be required.
This selected droplet size can be maintained not~ithstanding the movement of the target relative to the conducting surface because the field strength created by the field adjusting member outweighs that produced by the target.
We have found also that for a given voltage and a fixed field adjusting member position the droplet slze of a given liquid ls related to throughput.
The apparatus may also comprlse one or more additional field adjusting members to further influence the spray pattern. For example, if in a system comprising a conducting nozzle and an earthed circular field adjusting member around it, a second earthed circular member is placed outside the first, this will broaden the spray swath; and conversely a second earthed circular member of smaller cross-sectional area disposed downstream of the nozzle will narrow the spray swath.
We have found that how well a liquid is atomised depends on the potential on the surface, the position of the field adjusting member, the liquid throughput, and the _ g _ , . .
- .: :, . . : . . . . . .
. - . . ..
.. . . : . : ..
- : . , , :. ...
. ... . . .. : . . . : .
~ 3'7 nature of the liquid. For practical purposes we have found that highly non-polar liquids, e.g. pure hydrocarbon solvents, and highly polar liquids, such as water, do not atomise so well.
Atomisation of a liquid effected by the process or apparatus according to the invention requires no mechanical assistance such as a forced air blast or rotating disc.
However, once the liquid has been atomised and has passed out of the atomising field a forced air blast may ~e used to project the atomised droplets over greater distances to a ;
target, thus for example assisting penetration through foliage.
The use of a charged rotating disc as a surface to atomise liquld is known. Howe~er, such a system with the inclusion of a field adjusting member may operate at less current and at a lower voltage than the known system alone.
Accordingly, in a further and separate feature of the invention there is provided spraying apparatus for use in electrostatically coating a target with electrically charged particulate liquid or producing an aerosol cloud whlch apparatus comprises a conducting or semi-conductin~ rotatable surface whlch rotatable surface may be, in operation, electrically charged and from which the liquid atomises;
means for delivering the liquid to the surface; and a field adjusting member in close proximity to the surface and being -10~193~
so sited and maintainable at such a potential relative to the surface that an atomising field strength is created at the surface using a relatively low voltage, and with low current loss while there is substantially no tendency for particulate liquid to be retained on the member. Preferably the fiel~ adjusting member and the target are at earth potential.
Preferably the field adjusting member is adjustably mounted on the apparatus of the invention.
Atomisation and spraying trajectories are influenced by both inertial and field-effect 'electrostatic' forces.
Surprisingly, it is found that both of these fo~ces combine favourably even at potential diEferences of the order of lO
KV or less, to produce fine atomisation. For example, with air-gap insulation only between the field adjusting member and the conducting surface at a potential difference of about 20 KV, uslng a 3-inch diameter disc rotating at 1,500 revolutions per minute as the conducting surface, a droplet mean diameter of the order of 20-30~ has been observed at a flow rate of l.0 cc per second.
Under certain conditions, for example if the throughput of liquid is high enough, a powerful space-charge may be created between the spray nozzle and its target due to the ~-presence of large numbers of charged particles. This space-charge may be sufficiently large to repel very fine charged . . . , , . . ~ . . -. .
. . . . ~
.. . , . . ~ : ., 1~7P~3~
particles emerging from the nozzle, givins them an appreciable component of velocity in a direction no:rmal to, or even opposite to, the nozzle~target direction. We ha~e termed this effect 'back-spray'.
We have discovered that a suitably placed deflector electrode at a high potential may prevent this 'back spray'.
Accordingly, in yet a further feature of the invention there is provided spraying apparatus comprising spraying apparatus according to the invention as here1nbefore de~ined and further comprising a deflector electrode capable. of receiving a high potential and so sited in relation to the nozzle spray that 'back-spray' is prevented.
The d~flector electrode may be formed of a metal such as steel or aluminlum. When the field ad~ustlng member is o an annular orm the deflector electrode may take the ~orm of a co-axial ring of slightly grea~er diameter than that of the ~ield adjusting member, and disposed s~ightly behind it.
The deflecto~ electrode may be mounted on an insulating support 50 as to be fixed in space and retain charge, A .
disc formed of a plastics material such as "Perspex" may be used for this purpose~
The voltage on the de1ector electrode may be ~et by eithex:
(a) a tapping from the high-voltage source used to charge ~5 the conducting surface of the spraying apparatus, either , *Trade Mark ;~
~ . .
l~
107i~7 directly, or via a potential divider of very high resistance to prevent unwanted power dissipation; or, (b) a separate source of high voltage, which could be of lower power rating since the deflector electrode is not essentially an active device because no power is consumed in its operation.
Typically, when the conducting surface has a voltage of 20 KV, a suitable voltage for the deflector electrode would be 15-20 RV. Also, typically, the total resistance of a suitable potential divider would be of the order of 1011 ohms. Such a resistance can be realised by use of a semi-insulating material of about 2 cm length and o 1 square cm cross-section (any geometric shape) having electrodes placed at the ends of the material, and together with a tappiny electrode suitably set between the ends to obtain the potential division required. Strips of wood, cardboard, and rubber like materials may be used.
In yet a further feature of the invention there is provided spraying apparatus which comprises two or more spraying devices according to the invention mounted on a boom. The boom may be hand-held, or mounted on, or comprising part o~, a tractor or aircra~t. Such devices according to the lnvention are of particular use in multi-row crop spraying, and for the spraying of crops and weeds by tractor or aircrait mounted spra,er.
~ .
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, , .....
Some embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
Figure 1 is an elevational view, schematically illustrating the principal components, of a preferrecL electrostatic spray gun according to the invention;
Figure 2 is a cross~sectional vlew of the gun nozzle as shown in Figure l;
Figure 3 is an underside view of the gun nozzle of Figure 2;
Figure 4 is an electrical circuit diagram o the spray gun :
of Figure l;
Figure 5 is an elevational view, part cut away, schematically illustrating the principal components of a spray pistol according to the invention;
Figure 6 is an electrical circuit diagram of the spray :
pistol of Figure 5;
Figure 7 is a cross-sectional view of a gun nozæle comprising two concentrlc tubes for a spray gun according to the invention;
Figure ~ is an underside view of the gun nozzle of Figure 7;
, .
. .
.. . . .
~07~93~
Figure 9 is a cross-sectional view of a gun noz~le comprising a solid conducting block for a spray gun according to the invention;
Figure 10 shows the spray gun of Figure 1 further comprising a deflector electrode;
Figure 11 is a cross-sectional view o~ the gun.nozzle shown in Figure 10;
Figure 12 is a perspective view of a head of a spraying apparatus according to the invention comprising a linear slit arrangement;
F.igure 13 is a cross-sectional view on the line I-I of Figure 10;
Figure 14 is an underside view in part of the apparatus of Figure 10.
Referring to Figure 1, the electrostatic spray gun comprises a hollow tube 1 formed of a plastics material and providing a firm holding support for other parts of the gun.
Within t~e tube 1 is a bank of sixteen 1~ volt batteries 2 which acts as the electrical energy source. Attached to the ~ side of the tube 1 is a Brandenburg 223P tO-20 KV, 200 microamp) high voltage module 3 connected to the batteries 2 and to a 'ON-OFF' switch 4, and providing a source of high , :- , , - ; ~ , ~ . ... . . .. .. .. .
.
10~193~
electrical potential. The tube l at its forward end has an integral, internally screw-threaded eye 5 adapted to receive a bottle 6 containing liquid to be sprayed. The eye 5 at its lower part holds the upper part of a tubular distributor 7 formed of an insulating plastics material and supporting in its lower end a disc 8 (Figure 2) o~E the same material.
Now, referring more specifically to Figure 2, projecting through the disc 8 are eight metal capillary tubes 9 which form the spray nozzle assembly. The capillary tubes 9 are each soldered to a bare-metal wire 10 which in turn is connected to the high potential terminal of the module 3 vla a high potential cable ll.
Encircling the d1stributor 7 is an inverted dish 12 formed of an insulating plastics material. Supported in the lip of the dish 12 is a metal field-adjusting ring member 13 electrically connected to earth by an earth lead 14. The dish 12 may be moved up and down the distributor 7 but fits sufficiently closely thereon to maintain by rictional engagement any position selected.
To assemble the spray gun or use, the bottle 6, containing liquid to be sprayed, is screwed in~o the eye 5 while the spray gun is inverted from the position shown in Figure l. Inverting the spray gun back to the position shown in Figure l allows the liquid to enter the distributor 7 and to drip out o the capillary tubes 9 under gravity flow.
'.
. ..
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.
.
.. .. , , . , , : . .. .
~, . , ':. : ~ .
10~937 In operation to spray liquid, the spray gun is held by hand at a suitable position along the length of the tube 1.
On turning switch 4 to its 'ON' position/ the capillary tubes 9 become electrically charged to the same polarity and potential as the output generated by the module 3. This results in the liquid emerging from the tubes in an atomised and electrostatically charged form when the gun is inverted to the spraying position.
When the field-adjusting member 13 is earthed, via ` earth lead 14, the electrostatic field at and around the capillary tubes g improves both the atomisation and the spray pattern even when the potential on the spray nozzle assembly is at only, say, 10 to 15 kilovolts (either posltive or negatlve polarity with re9pect to the field adiusting member 13). Furthermore, due to the close proximity of the field adjusting member 13 to the spray nozzle assembly, the current drawn from the source of high potential 3 is mainly ~ ;
that which arises from an exchange of charge between the capillary tubes 9 and the liquid being sprayed, and is thus extremely small.
Typically, the charga density of the atomised liquid is 1 x 10 3 coulomb per lltre. Thus, at a l~quid flow rate of, say 1 x 10 3 litre per second the current drawn from the module 3 is only 1 x 10 6 ampere, indicating an output power of only 1 x 10 3 watt when the high potential is 1 x 103 volts. At this low power, the useful life of the batteries
This invention relates to the atomisation and electro-deposition of liquids. It has particular but by no means exclusive application to the spraying of crops with pes~icidal compositions and to paint spraying. It also has application in the production of an aerosol dispersoid.
When a liquid is displaced from the locality of an electrically conducting surface at a voltage above or below earth potential the liquid may upon emerging into free space carry a net electrical charge resulting from an exchange of electrical charges with the source of the electrical potential.
This technique can be used to atomise the displaced liquid since the net electric charge in the liquid as the liquid emerges into free space from the locality of the conducting surace counteracts the surface tension orces of the liquid. The amount of electrical charge in the emerging liquid droplets after atomisation is, in part, dependent upon the strength of the electric field at the conducting surface.
There are known devices, particularly used for electro-static paint spraying, wherein the field strength at the conducting surface has been maximised by (i) sharpening an 'edge' of the conducting surface, whlch may, for example, be a rotating sharp-edged disc, adjacent which edge paint is constrained to emerge; (ii) raising the electrical potential of the conducting surface to a high value, generally of ~he , . . .
. .
. . . ,, ~
lO~i93~7 order of 60-100 Kv; and (iii) ensurin~ that the spray-target, which is earthed and is ~hus an earth boundary of the electrostatic field that exists between the conducting surface and the target surface, is sufficiently close to maintain a high field strength at the conducting surface adjacent which the liquid emergas. The conducting surface and the target surface define the main boundaries of the ~lectric field.
A salient feature of such known clevices is that the combination of high voltage and sharp-edged conducting suraces causes breakdown of the surrounding air (by the phenomenon known as corona discharge) The effect of this is that not all of the current supplied to the conducting surface is used to charge the liquid. Thus, corona discharge results in unnecessary current loss and greatly increases the current drawn from the source of high electrical potential.
This has disadvantages. One serious disadvantage is that the power required of the high electrical potential source is too high to be met easily by portable energy sources e.g. torch ! batteries.
Surprisingly, we have now ~ound that i~ a member, hereinafter referred to as a field adjusting member or a ~ield intensifying electrode, is in close pro~imity to ~he conductin~
surface lt enable~ a suficiently high field strength to be created at the conducting surface using a relatively low voltage, of the order of 1-20 ~
19~
KV, to charge the droplets. Thus a high charge density for example, of the order of 10 2 coulombs/kilogram may be placed upon the liquidO This gives rise to a high charge-utilisation efficiency which in turn enables low power sources, such as piezo-electric crystals, torch batteries or solar cells to be utilised as a charge t:ransfer device, and to giue rise to electrostatic atomisation of the liquid.
- Such atomisation requires no mechanical assistance such as an air blast or rotating disc. The combined field due to the voltage on the conducting surface plus the space charge of the atomised liquid itself then enables the droplets to be targeted toward an earthed object, or to form an airborne (aero~ol) cloud.
The field adjusting member may be considered to be a 'dummy target' since it strongly influences the field in the region of liquid atomisation. But, unlike an actual target, it is placed close to the conducting surface thus stre~gthening the field. Surprisingly, we have found that the field adjusting member may easily be placed so that it does not itself become a target for the atomised spray~
The reason for this is not fully understood, bu-t observation shows that, provided ~he liquid's physical characteristics (e.g. resistivity, viscosity) and flow rate are such as to produce ligaments (electrostatically) cf about 1 cm or more, the atomisation will take place in that . , , , , . ,:: ............................... .
: , ': :' ,. ., ,:
: . . . . , , . .: : ' ' , '' :
1~7~3q part of the electric ~ield where the combined forces of inertia, gravity field, and electrostatic ~ield are directed away from the field adjusting member.
It has been found possible to cause impingement of the spray onto the field adjusting member by placing it downstream of the atomising tip of the ligament. In this case it has been noticed that, with relatively small amounts of impinging liquid, that provided the surface of the field adjustlng member is sufficiently conducting, and earthed, the impinging particles give up their rharge and take up an opposite charge by induction in the electric field. This causes them to re-atomise and not to be retained on the member.
According to the present invention there is provided a process of spraying pesticides which comprises suppl~ing a liquid pesticidal composition to an electrically conducting or semi-conducting surface from which it is atomised by electrostatic forces to form a cloud of electrically charged particles said surace being in close proximity to a field adjusting member at such a potential and so sited relative to the surace that an atomising ield strength is created at the sur~ace using a relatively low voltage and with low current loss, as hereinater deined, while there is subs~antially no tendency or-liquid to be re~ained on the member.
This invention also includes electrostatic spraying ; apparatus suitable for use in the process of the invention .... . .. . .. . . .. ... ...
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~193q which comprises a spray head having a conducting or semi-conducting surface which may be, in operation, electrically charged and adjacent which liquid atomises; means for delivering the liquid adjacen~ the surfclce; and a field adjusting member in close proximity to t.he surface and being so sited and maintainable at such a potential relative to the surface that a high field strength may be created at the surface using a relatively low voltage and with low current loss, as hereinafter defined, while there is substantially no tendency for particulate liquid to be retained on the member.
By current loss is meant the applied high voltage.
current drain other than that used in charging the liquid.
Preexably the ield adjustlng member and ~he target . are both at earth potential. However the atomising field may also be created by changing the field ad~usting member and earthing the surface.
By the term 'conducting surface' we mean the sur~ace of a material having a resistivity of the order of 1 ohm cm or less, and by 'semi-conducting surface' we mean the surface material having a resistivity value o between 1 and about 1012 ohm cm. ~y 'insulating material' is meant material having a resistivity of more than 1012 ohm cm.
The conducting or semi~conducting surface adjacent which the liquid atomises may have various shapes. It will ~0~937 often be the end o~ a spray conduit, preferably a con~uit of capillary size, for example, a nozzle aperture, through which in operation the liquid spray emerges.
The conducting surface may also comprise the edges o two concentric tubes which edges define an annular aperture through which liquid emerges. The edges of the tubes may be serrated or fluted. Alternatively, the conducting s~rface may comprise two edges defining a slot, preferàbly of capillary width. The slot may be of rectangular or other formO Atomisation may be effected from the flat surface of a solid conductor or semi-conductor to which liquid has been supplied.
The geometric shape of the 1eld-adjusting member in general follows the shape o~ the conducting or semi-conductlng surface. Where the surface is defined by a nozzle the member may take an annular form with the member encircling the nozzle.
The field adjusting member is generally sited AS close as possible to the conducting surface without corona discharge occurring between them. For example with 20 KV on the conducting surface the field adjusting member is preferably sited not less, and not much more than, about 2 cm away rom it. The field adjusting member may be sited either level with, in front of, or behind the conducting surface from which the liquid atomises.
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In a preferred form OL the invention the field adjusting member has an insulating surface. For example, it may be a thin wire embedded in a body or sheath formed of a plastics material. This enables the distance between the field adjusting member and the conducting surface to be very much smaller than would be obtainable with 'air-gap' insulation only. This results in an enhanced field strength in the locality of the conducting surface.
It is preferred that the field adjusting member be adjustably mounted on the apparatus of the invention so that the spatial relationship between the member and the surface can easily be varied.
We have found that the position and the geometxic shape of the field adjusting member control the angle of the stream of droplets emerging into ree space. When the field adjusting member is behind the emerging spray the angle of the stream is increased, and when it is in front of the emerging spray the angle is decreased.
In addition, we have found that the average size of the atomiqed droplets in general may be controlled by the position o the fleld adjusting rnember in relation to the conducting surface. For example, for a given flow rate of liquid, bringing the field adjusting member closer to the conducting surface results in the droplets generally being of a smaller average si~e.
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By controlling the position of the field adjusting member a selected size of droplets may be produced suitable for a particular use. For example, large numbers of small particles (e.g. 20-30 ~) of an insecticide may be preferred for maximum coverage of a target, whereas for a herbicide larger droplets less prone to wind drift: may be required.
This selected droplet size can be maintained not~ithstanding the movement of the target relative to the conducting surface because the field strength created by the field adjusting member outweighs that produced by the target.
We have found also that for a given voltage and a fixed field adjusting member position the droplet slze of a given liquid ls related to throughput.
The apparatus may also comprlse one or more additional field adjusting members to further influence the spray pattern. For example, if in a system comprising a conducting nozzle and an earthed circular field adjusting member around it, a second earthed circular member is placed outside the first, this will broaden the spray swath; and conversely a second earthed circular member of smaller cross-sectional area disposed downstream of the nozzle will narrow the spray swath.
We have found that how well a liquid is atomised depends on the potential on the surface, the position of the field adjusting member, the liquid throughput, and the _ g _ , . .
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~ 3'7 nature of the liquid. For practical purposes we have found that highly non-polar liquids, e.g. pure hydrocarbon solvents, and highly polar liquids, such as water, do not atomise so well.
Atomisation of a liquid effected by the process or apparatus according to the invention requires no mechanical assistance such as a forced air blast or rotating disc.
However, once the liquid has been atomised and has passed out of the atomising field a forced air blast may ~e used to project the atomised droplets over greater distances to a ;
target, thus for example assisting penetration through foliage.
The use of a charged rotating disc as a surface to atomise liquld is known. Howe~er, such a system with the inclusion of a field adjusting member may operate at less current and at a lower voltage than the known system alone.
Accordingly, in a further and separate feature of the invention there is provided spraying apparatus for use in electrostatically coating a target with electrically charged particulate liquid or producing an aerosol cloud whlch apparatus comprises a conducting or semi-conductin~ rotatable surface whlch rotatable surface may be, in operation, electrically charged and from which the liquid atomises;
means for delivering the liquid to the surface; and a field adjusting member in close proximity to the surface and being -10~193~
so sited and maintainable at such a potential relative to the surface that an atomising field strength is created at the surface using a relatively low voltage, and with low current loss while there is substantially no tendency for particulate liquid to be retained on the member. Preferably the fiel~ adjusting member and the target are at earth potential.
Preferably the field adjusting member is adjustably mounted on the apparatus of the invention.
Atomisation and spraying trajectories are influenced by both inertial and field-effect 'electrostatic' forces.
Surprisingly, it is found that both of these fo~ces combine favourably even at potential diEferences of the order of lO
KV or less, to produce fine atomisation. For example, with air-gap insulation only between the field adjusting member and the conducting surface at a potential difference of about 20 KV, uslng a 3-inch diameter disc rotating at 1,500 revolutions per minute as the conducting surface, a droplet mean diameter of the order of 20-30~ has been observed at a flow rate of l.0 cc per second.
Under certain conditions, for example if the throughput of liquid is high enough, a powerful space-charge may be created between the spray nozzle and its target due to the ~-presence of large numbers of charged particles. This space-charge may be sufficiently large to repel very fine charged . . . , , . . ~ . . -. .
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particles emerging from the nozzle, givins them an appreciable component of velocity in a direction no:rmal to, or even opposite to, the nozzle~target direction. We ha~e termed this effect 'back-spray'.
We have discovered that a suitably placed deflector electrode at a high potential may prevent this 'back spray'.
Accordingly, in yet a further feature of the invention there is provided spraying apparatus comprising spraying apparatus according to the invention as here1nbefore de~ined and further comprising a deflector electrode capable. of receiving a high potential and so sited in relation to the nozzle spray that 'back-spray' is prevented.
The d~flector electrode may be formed of a metal such as steel or aluminlum. When the field ad~ustlng member is o an annular orm the deflector electrode may take the ~orm of a co-axial ring of slightly grea~er diameter than that of the ~ield adjusting member, and disposed s~ightly behind it.
The deflecto~ electrode may be mounted on an insulating support 50 as to be fixed in space and retain charge, A .
disc formed of a plastics material such as "Perspex" may be used for this purpose~
The voltage on the de1ector electrode may be ~et by eithex:
(a) a tapping from the high-voltage source used to charge ~5 the conducting surface of the spraying apparatus, either , *Trade Mark ;~
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107i~7 directly, or via a potential divider of very high resistance to prevent unwanted power dissipation; or, (b) a separate source of high voltage, which could be of lower power rating since the deflector electrode is not essentially an active device because no power is consumed in its operation.
Typically, when the conducting surface has a voltage of 20 KV, a suitable voltage for the deflector electrode would be 15-20 RV. Also, typically, the total resistance of a suitable potential divider would be of the order of 1011 ohms. Such a resistance can be realised by use of a semi-insulating material of about 2 cm length and o 1 square cm cross-section (any geometric shape) having electrodes placed at the ends of the material, and together with a tappiny electrode suitably set between the ends to obtain the potential division required. Strips of wood, cardboard, and rubber like materials may be used.
In yet a further feature of the invention there is provided spraying apparatus which comprises two or more spraying devices according to the invention mounted on a boom. The boom may be hand-held, or mounted on, or comprising part o~, a tractor or aircra~t. Such devices according to the lnvention are of particular use in multi-row crop spraying, and for the spraying of crops and weeds by tractor or aircrait mounted spra,er.
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Some embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
Figure 1 is an elevational view, schematically illustrating the principal components, of a preferrecL electrostatic spray gun according to the invention;
Figure 2 is a cross~sectional vlew of the gun nozzle as shown in Figure l;
Figure 3 is an underside view of the gun nozzle of Figure 2;
Figure 4 is an electrical circuit diagram o the spray gun :
of Figure l;
Figure 5 is an elevational view, part cut away, schematically illustrating the principal components of a spray pistol according to the invention;
Figure 6 is an electrical circuit diagram of the spray :
pistol of Figure 5;
Figure 7 is a cross-sectional view of a gun nozæle comprising two concentrlc tubes for a spray gun according to the invention;
Figure ~ is an underside view of the gun nozzle of Figure 7;
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Figure 9 is a cross-sectional view of a gun noz~le comprising a solid conducting block for a spray gun according to the invention;
Figure 10 shows the spray gun of Figure 1 further comprising a deflector electrode;
Figure 11 is a cross-sectional view o~ the gun.nozzle shown in Figure 10;
Figure 12 is a perspective view of a head of a spraying apparatus according to the invention comprising a linear slit arrangement;
F.igure 13 is a cross-sectional view on the line I-I of Figure 10;
Figure 14 is an underside view in part of the apparatus of Figure 10.
Referring to Figure 1, the electrostatic spray gun comprises a hollow tube 1 formed of a plastics material and providing a firm holding support for other parts of the gun.
Within t~e tube 1 is a bank of sixteen 1~ volt batteries 2 which acts as the electrical energy source. Attached to the ~ side of the tube 1 is a Brandenburg 223P tO-20 KV, 200 microamp) high voltage module 3 connected to the batteries 2 and to a 'ON-OFF' switch 4, and providing a source of high , :- , , - ; ~ , ~ . ... . . .. .. .. .
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electrical potential. The tube l at its forward end has an integral, internally screw-threaded eye 5 adapted to receive a bottle 6 containing liquid to be sprayed. The eye 5 at its lower part holds the upper part of a tubular distributor 7 formed of an insulating plastics material and supporting in its lower end a disc 8 (Figure 2) o~E the same material.
Now, referring more specifically to Figure 2, projecting through the disc 8 are eight metal capillary tubes 9 which form the spray nozzle assembly. The capillary tubes 9 are each soldered to a bare-metal wire 10 which in turn is connected to the high potential terminal of the module 3 vla a high potential cable ll.
Encircling the d1stributor 7 is an inverted dish 12 formed of an insulating plastics material. Supported in the lip of the dish 12 is a metal field-adjusting ring member 13 electrically connected to earth by an earth lead 14. The dish 12 may be moved up and down the distributor 7 but fits sufficiently closely thereon to maintain by rictional engagement any position selected.
To assemble the spray gun or use, the bottle 6, containing liquid to be sprayed, is screwed in~o the eye 5 while the spray gun is inverted from the position shown in Figure l. Inverting the spray gun back to the position shown in Figure l allows the liquid to enter the distributor 7 and to drip out o the capillary tubes 9 under gravity flow.
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10~937 In operation to spray liquid, the spray gun is held by hand at a suitable position along the length of the tube 1.
On turning switch 4 to its 'ON' position/ the capillary tubes 9 become electrically charged to the same polarity and potential as the output generated by the module 3. This results in the liquid emerging from the tubes in an atomised and electrostatically charged form when the gun is inverted to the spraying position.
When the field-adjusting member 13 is earthed, via ` earth lead 14, the electrostatic field at and around the capillary tubes g improves both the atomisation and the spray pattern even when the potential on the spray nozzle assembly is at only, say, 10 to 15 kilovolts (either posltive or negatlve polarity with re9pect to the field adiusting member 13). Furthermore, due to the close proximity of the field adjusting member 13 to the spray nozzle assembly, the current drawn from the source of high potential 3 is mainly ~ ;
that which arises from an exchange of charge between the capillary tubes 9 and the liquid being sprayed, and is thus extremely small.
Typically, the charga density of the atomised liquid is 1 x 10 3 coulomb per lltre. Thus, at a l~quid flow rate of, say 1 x 10 3 litre per second the current drawn from the module 3 is only 1 x 10 6 ampere, indicating an output power of only 1 x 10 3 watt when the high potential is 1 x 103 volts. At this low power, the useful life of the batteries
2 used to energise the module 3 may be hundreds of hours.
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To maintain the field adjusting member 13 at low or zero potential, the earth lead 14 must contact actual ground or some other low voltage r high capacitance, body. For portable use of the spray gun shown in Figure l, it is sufficient to trail the earth lead 14 so that it touches or occasionally touches the ground. The spray gun may be used for short periods of time without the earth lead 14 being connected to earth, without noticeably affec,ting the spray characteristics. Even when the earth lead 14 is not electrically earthed at all the spray gun will continue to spray electro-statically, albeit with a deterioration in performance.
By varying the position of the dish 12 along the length of the distributor 7 the position of the field-ad~usting member 13 may be adjusted with respect to the fixed position o the capillary tubes 9 so as to achieve the best spray characteristic in accordance with the potential difference between the field adjusting member 13 and the capillary tubes 9, and other variables such as the electrical resistivity of the liquid.
The specific embodiment described hereinabove was tested with various liquids and various target surfaces.
In a flrst test the spray gun was used to spray an acrylic based paint solution ~resistivity approximately 1 x 107 ohm centimetre) onto a flat surface and onto a section of metal tubing. In both cases, atomisation was ~ 18 -~.
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1~7~37 found to be satisfactory with the well-known electrostatic 'wrap-round' effect being clearly demonstrated.
In a second test conducted outdoors a liquid insecticide formulation (resistivity approximately 5 x 10~ ohm cm) was electrostatically sprayed against a set of earthed vertically placed metal tubes, each o 1 inch diameter, placed in a `downwind line at distances of 1 to 15 metres from the spray gun; the liyuid being atomised at a height o~ about 1 metre above the ground. A comparative test was conducted using a commercially available mechanical atomising device used ~or agricultural spraying wherein atomisation is produced ~rom an uncharged spinning disc.
It was ound that the droplets ~rom the electrostatic spray gun were deposited more unl~ormly on all o~ the metal tubes than those from the mechanical atomiser. The electro-static spray gun again clearly demonstrated a significant 'wrap-round' e~ect. .
In a third test, the second test was repeated but with the 2~3P; 0-20 KV; 200 microamp module 3 (ex. Brandenburg Ltd) being replaced with a 11 KV unit having no regulation or ~e~,dback control and being capable o~ delivering an output of only 1 microamp at about 11 KV.
In this test the liquid was electrostatically atomised and sprayed satis~actorily.
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~ 37 The apparatus shown in Figure l may be used to produce an electrostatically charged aerosol cloud, i.e. a cloud o~
droplets having a mean droplet size of less than 50 microns in diameter and generally in the range of 1-10 ~icrons. The apparatus ol Figure 1 having capillary tubes with an internal ~-diameter of 0.1 mm, and using a liquid having a resistivity approximately 5 x 10 ohm metre at a total flow rate of 0.05 cc/second per eight capillary tubes produces such an aerosol cloud.
A further embodiment o~ the invention is the electrostatic spray hand pistol shown in Figure 5. In this embodiment the source o~ high potential comprises lead zirconate crystals which generate the potential by means of the well-known 'piezoelectric effect'.
The hand pistol shown in Figure 5 comprises a pistol-shaped casing 21 formed of an insulating plastics material, and a metal trigger 22 (shown in Figure 5 in a released position). The upper part of the trigger 22 is shaped to ~orm a cam 23.
Wlthin the handle of the pistol are two lead zirconate crystals 24 (type PZT4, manu~actured by Vernitron Ltd, Southampton, England) having a centre tap connection 25.
The crystals 24 each have an upper face 26 which in operation is acted upon by the cam 23.
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1~7~937 Fitted to the end of the nozzle of the pistol is a distributor 27 formed of an insulating plastics material which holds at its ~nd adjacent the no2zle a disc 28 formed of the same material. Protruding through the disc 28 into the distributor 27 is a feed tube 29, having a tap 30, which is connected to a feed bottle 31 which holds the liquid to be sprayed.
The distributor 27 at its other end has a disc 32 formed of an insulating plastics material through which protrude eight metal capillary tubes 33 which ~orm the spray assembly. The capillary tubes 33 are each soldered to a bare-metal wire 34 which in turn is connected to the centre tap connection 25 via a high potential cable 35 provided within the barrel of the pistol.
lS Encircling the distributor 27 is a cylindrical support 36 formed of an insulating plastics material. The support 36 may be moved along the length of the distributor 27 but fits sufficiently closely thexeon to maintain by frictional engagement any position selected. Embedded in the support 36 is a metal field-adjusting ring member 37 which ls electrically connected to the trigger by an ea~th lead 38.
In operation to spray liquid, the tap 30 is turned on.
This allows liquid to flow under gravity from the feed bottle 31 along the feed tube 29 into the distributor 27 and to emerge dropwise out of the capillary tubes 33.
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laqls~7 On squeezing the trigger, the cam 23 acts on the faces 26. This action compresses the crystals 24 and results in the generation of a potential di~erence/ which is trans-mitted via the cable 35 to the capillary tubes 33. This results in the liquid emerging from the tubes 33 in an atomised and electrostatically charged from.
When the field adjusting member 37 is earthed, via earth lead 38, trigger, and operator, the electrostatic field at and around the capillary tubes 33 improves both the atomisa-tion and the spray pattern.
By varying the position of the support 36 along thelength o~ the distributor 27 the position of the ield-adjusting member 37 may be ~djusted with respect to the ixed position o~
the capillary tubes 33 so as to achieve the best spray charac-teristic in accordance with the potential diference between the field ad~usting member 37 and the capillary tubes 33, and other variabl~s such as the electrical resistivity of the liquid.
; Typically, the crystals 24, when squeezed slowly or five seconds or so, produce a potential difference o about 10 KV, and have suf~icient electrical capacitance to impart at least one microcoulomb to the liquid being atomised during a five second squeeze. If the liquid output rate is about 1 x 10 4 litre per second the charge density o~ the atomised droplets is of the order o 2 x 10 3 coulombs per litre, In a spray test using this speci~ic embodiment the resultant spray exhibited satisfactory atomisation and 'wrap-round' when a target tube was earthed and held at a distance of about 0.5 metre.
The pistol illustrated may readily be modified by .
10~1~3~
means of a mechanical connection between the trigger 22 and a valve in the feed tube 29, so arranged that pressure of the trigger opens ~he valve and release closes it. In this way liquid only passes through the nozzle 33 when ~hey are charged.
Alternative gun nozzles which may be substituted for the nozzle of Figure 2 in the gun of Figure l are shown in Figures 7-9.
The nozzle shown in Figures 7 and 8 comprises a hollow steel cylinder 39 having a uniorm bore and a lower half of reduced external diameter. The cylinder 39 at its ùpper part is held by frictional engagement within the tubular dis-tributor 7 of Figure l and connected via the metal wire lO and cable ll to the hiyh pokential terminal of the modul~ 3~ At its lo~er part cylinder 39 is closed by seal 40 and has four holes 41 of capillary size extending radially offthe cylinder ~ -- wall.
An outer seal cylinder 42 at its upper part embraces an intermediate part of the cylinder 39 and is held by frictional engagement thereon. At its lower part cylinder 42 Aefines, with the lower part of cylinder 39, an annular cavity 43. The holes 41 connect the cavity 43 with the inside of cylinder 39.
Encircling the distributor 7 is the dish 12 sup-porting the field-adjusting ring member 13.
In use, turning the switch 4 to its 'OM' position, cylinders 39 and 42 become electrically charged. Liquid passing through distributor 7 passes out of holes 41 into cavity 43 and emerges thereform in an atomised and electrosta-tically charged form.
The nozzle shown in Figure 9 comprises a solid steel "
- ~3 , 107~937 cylinder 44 held at its upper part by frictional engagement with the distributor 7 o Figure 1. The cylinder 44 has a central axial bore 45 running almost the length of the cylinder and terminating at a transverse bore 46 in the lower part of the cylinder. The cylinder 44 is connected to the module 3 via the metal wire 10 and cable 11~ The lo~er part of the cylinder terminates as a solid disc 47 having a bottom surface 48~
In use, when cylinder 44 becomes electrically charged, liquid from distributor 7 passes through bores 45 and 46 and flows around disc 47 to surface 48 from which it is atomised.
If the flow rate o liquid out of bore 46 is suffi-ciently reduced atomisation o the liquid may occur from the surfaces ad~acent the two ~xits of bore 46.
The embodirnent shown in Figures 10 and 11 comprises the spray gun of Figure 1 fitted with a deflector electrode system to prevent 'back-spray'.
As shown in Figures 10 and 11 a disc 51 formed of an insulating material embraces the distributor 7 at its mid-section and is held thereon by rictional engagement. Partly embedded in the lower su~face of the disc 51 is a deflector electrode 52.
in the ~orm of a steel ring. The deflec~or electrode 52 is connected, via a high voltage cable 53, to a tapping 54 of a potential divider 55. The divider 55 comprises a resistor o 101 ohms, connected at one end to the high potential cable 11 and at its other end to the earth lead 14. The high reSistan~Q
of divider 55 minimises current drain from the high voltage source 3, and serves as a current limiter in the event of a short circuit occurring at the deflector electrode 52.
In operation, with switch 4 in the 'ON' position the de1ector electrode 52 receives a high potential from the 1~7~937 potential divider 55. Suitable adjustment of the tapping 54 may give any desired potential be-tween zero volts and the poten~
tial of the source 3. A typical voltage on the deflector electrode 52 would be 14 KV.
The position of the deflector electrode 52 in relation to the field adjusting member 13 and the spray nozzles 9 may be selected by moving the disc 51 along the length of ~he distri-butor 7.
Liquid emerging from the nozzles 9 is atomised and directed by the combined electric field forces set up no~ only by the high voltage on the nozzles 9 and the local low potential ' - :-of the field adjusting member 13 but also by the high potential on the deflector electrode 52.
Reerring to Figures 12 - 14, the head o the spraying apparatus comprises a rectangular body 61 formed of an insu-lating plastics material and having a rectangular chamber 62. : ' Along the length of its lower face, the body 61 has an integ- . ' rally formed upstanding projection 63 having a longitudinal slit 64 which connects with chamber 62. The upper face of the body 61 has an aperture 65, adapted to receive (by means not shown) a liquid to be sprayed, and which communicates with chamher 62.
The,slit 64 is divided by a conducting surface formed o a thin metal sheet 66 connected to a source o high potential (not shown)~ Held by supports 67 adjacent the projection 63 is an earthed metal wire 68 enclosed in a sheath 69 formed of an ;
insulating plastics material. ",., In operation with the high potential applied to the metal sheet 66, liquid to be sprayed e~ters the chamber 52, via ' the aperture 65. It emerges from the slit 64 where it is atomised adjacent the metal sheet 66. The wire 68 acts as a . .
~q~937 field-adjusting member on both sides of the metal sheet 66.
Because it has an insulated protective surface the metal wires 68 can be disposed closer to the metal sheath 66 than if it were not so insulated, and also with a greatly reduced risk o~ arcing.
In an alternative embodiment the conducting surface may comprise a metal wire.
In a further embodLment utilising ~he linear slit arrangement a multiplicity of wire or metal sheet conducting sur-faces in parallel and disposed between a multiplicity of such sheathed wire field adjusting members is used. Such an arrange-ment allows of an increase in the volume of liquid to be sprayed.
The various~devices descrihed are particularly use~ul in the process of the invention, that is to say, in spraying liquid pesticides. They may easily be made portable and self-contained, being conveniently powdered by low output power sources such as dry cells r piezoelectric sources or photoelectric sources. The devices may readily be used for many other pur-poses where atomisation and deposition (e.g. paint spraying, lacquering), or atomisation alone, are required. The process of the inventionhas particular advantages over known methods of spraying liquid pesticides because it can give a more even coat-ing of pesticldes on foliage. Electrostatic forces direct the spray particle to their target, reducing drift, and enable leaves to be coated an both sides. Liquid pesticidal compositions sprayed by the process of the invention may be for example insec-ticides, fungicides and herbicides. Typically they are in the form of solutions or dispersions of a pesticide in a p~sticidally inert organic diluent (e.g. a liquid hydrocarbon) but it is also possible to spray liquid pesticides substantially undiluted~
Because deposition is uniform, drift is minimised, and low flow-- . ... : . . , ; . , ... . . , . :
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rates can be used, the process is particularly suitable for applying pesticides undiluted or in hig~ly concentrated formulations (ultra low volume spraying).
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To maintain the field adjusting member 13 at low or zero potential, the earth lead 14 must contact actual ground or some other low voltage r high capacitance, body. For portable use of the spray gun shown in Figure l, it is sufficient to trail the earth lead 14 so that it touches or occasionally touches the ground. The spray gun may be used for short periods of time without the earth lead 14 being connected to earth, without noticeably affec,ting the spray characteristics. Even when the earth lead 14 is not electrically earthed at all the spray gun will continue to spray electro-statically, albeit with a deterioration in performance.
By varying the position of the dish 12 along the length of the distributor 7 the position of the field-ad~usting member 13 may be adjusted with respect to the fixed position o the capillary tubes 9 so as to achieve the best spray characteristic in accordance with the potential difference between the field adjusting member 13 and the capillary tubes 9, and other variables such as the electrical resistivity of the liquid.
The specific embodiment described hereinabove was tested with various liquids and various target surfaces.
In a flrst test the spray gun was used to spray an acrylic based paint solution ~resistivity approximately 1 x 107 ohm centimetre) onto a flat surface and onto a section of metal tubing. In both cases, atomisation was ~ 18 -~.
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1~7~37 found to be satisfactory with the well-known electrostatic 'wrap-round' effect being clearly demonstrated.
In a second test conducted outdoors a liquid insecticide formulation (resistivity approximately 5 x 10~ ohm cm) was electrostatically sprayed against a set of earthed vertically placed metal tubes, each o 1 inch diameter, placed in a `downwind line at distances of 1 to 15 metres from the spray gun; the liyuid being atomised at a height o~ about 1 metre above the ground. A comparative test was conducted using a commercially available mechanical atomising device used ~or agricultural spraying wherein atomisation is produced ~rom an uncharged spinning disc.
It was ound that the droplets ~rom the electrostatic spray gun were deposited more unl~ormly on all o~ the metal tubes than those from the mechanical atomiser. The electro-static spray gun again clearly demonstrated a significant 'wrap-round' e~ect. .
In a third test, the second test was repeated but with the 2~3P; 0-20 KV; 200 microamp module 3 (ex. Brandenburg Ltd) being replaced with a 11 KV unit having no regulation or ~e~,dback control and being capable o~ delivering an output of only 1 microamp at about 11 KV.
In this test the liquid was electrostatically atomised and sprayed satis~actorily.
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.. , . . : - . , , ~ .
~ 37 The apparatus shown in Figure l may be used to produce an electrostatically charged aerosol cloud, i.e. a cloud o~
droplets having a mean droplet size of less than 50 microns in diameter and generally in the range of 1-10 ~icrons. The apparatus ol Figure 1 having capillary tubes with an internal ~-diameter of 0.1 mm, and using a liquid having a resistivity approximately 5 x 10 ohm metre at a total flow rate of 0.05 cc/second per eight capillary tubes produces such an aerosol cloud.
A further embodiment o~ the invention is the electrostatic spray hand pistol shown in Figure 5. In this embodiment the source o~ high potential comprises lead zirconate crystals which generate the potential by means of the well-known 'piezoelectric effect'.
The hand pistol shown in Figure 5 comprises a pistol-shaped casing 21 formed of an insulating plastics material, and a metal trigger 22 (shown in Figure 5 in a released position). The upper part of the trigger 22 is shaped to ~orm a cam 23.
Wlthin the handle of the pistol are two lead zirconate crystals 24 (type PZT4, manu~actured by Vernitron Ltd, Southampton, England) having a centre tap connection 25.
The crystals 24 each have an upper face 26 which in operation is acted upon by the cam 23.
.. . :, .
., .: ; . . .: . -. .
' : . . ' ': ' ,' :' .
1~7~937 Fitted to the end of the nozzle of the pistol is a distributor 27 formed of an insulating plastics material which holds at its ~nd adjacent the no2zle a disc 28 formed of the same material. Protruding through the disc 28 into the distributor 27 is a feed tube 29, having a tap 30, which is connected to a feed bottle 31 which holds the liquid to be sprayed.
The distributor 27 at its other end has a disc 32 formed of an insulating plastics material through which protrude eight metal capillary tubes 33 which ~orm the spray assembly. The capillary tubes 33 are each soldered to a bare-metal wire 34 which in turn is connected to the centre tap connection 25 via a high potential cable 35 provided within the barrel of the pistol.
lS Encircling the distributor 27 is a cylindrical support 36 formed of an insulating plastics material. The support 36 may be moved along the length of the distributor 27 but fits sufficiently closely thexeon to maintain by frictional engagement any position selected. Embedded in the support 36 is a metal field-adjusting ring member 37 which ls electrically connected to the trigger by an ea~th lead 38.
In operation to spray liquid, the tap 30 is turned on.
This allows liquid to flow under gravity from the feed bottle 31 along the feed tube 29 into the distributor 27 and to emerge dropwise out of the capillary tubes 33.
,. ~ .. . . .
.
'. ' . ''' ' ', '," "' .'~' ', ' '"'', - ~, :. . :~ , . . .. :
laqls~7 On squeezing the trigger, the cam 23 acts on the faces 26. This action compresses the crystals 24 and results in the generation of a potential di~erence/ which is trans-mitted via the cable 35 to the capillary tubes 33. This results in the liquid emerging from the tubes 33 in an atomised and electrostatically charged from.
When the field adjusting member 37 is earthed, via earth lead 38, trigger, and operator, the electrostatic field at and around the capillary tubes 33 improves both the atomisa-tion and the spray pattern.
By varying the position of the support 36 along thelength o~ the distributor 27 the position of the ield-adjusting member 37 may be ~djusted with respect to the ixed position o~
the capillary tubes 33 so as to achieve the best spray charac-teristic in accordance with the potential diference between the field ad~usting member 37 and the capillary tubes 33, and other variabl~s such as the electrical resistivity of the liquid.
; Typically, the crystals 24, when squeezed slowly or five seconds or so, produce a potential difference o about 10 KV, and have suf~icient electrical capacitance to impart at least one microcoulomb to the liquid being atomised during a five second squeeze. If the liquid output rate is about 1 x 10 4 litre per second the charge density o~ the atomised droplets is of the order o 2 x 10 3 coulombs per litre, In a spray test using this speci~ic embodiment the resultant spray exhibited satisfactory atomisation and 'wrap-round' when a target tube was earthed and held at a distance of about 0.5 metre.
The pistol illustrated may readily be modified by .
10~1~3~
means of a mechanical connection between the trigger 22 and a valve in the feed tube 29, so arranged that pressure of the trigger opens ~he valve and release closes it. In this way liquid only passes through the nozzle 33 when ~hey are charged.
Alternative gun nozzles which may be substituted for the nozzle of Figure 2 in the gun of Figure l are shown in Figures 7-9.
The nozzle shown in Figures 7 and 8 comprises a hollow steel cylinder 39 having a uniorm bore and a lower half of reduced external diameter. The cylinder 39 at its ùpper part is held by frictional engagement within the tubular dis-tributor 7 of Figure l and connected via the metal wire lO and cable ll to the hiyh pokential terminal of the modul~ 3~ At its lo~er part cylinder 39 is closed by seal 40 and has four holes 41 of capillary size extending radially offthe cylinder ~ -- wall.
An outer seal cylinder 42 at its upper part embraces an intermediate part of the cylinder 39 and is held by frictional engagement thereon. At its lower part cylinder 42 Aefines, with the lower part of cylinder 39, an annular cavity 43. The holes 41 connect the cavity 43 with the inside of cylinder 39.
Encircling the distributor 7 is the dish 12 sup-porting the field-adjusting ring member 13.
In use, turning the switch 4 to its 'OM' position, cylinders 39 and 42 become electrically charged. Liquid passing through distributor 7 passes out of holes 41 into cavity 43 and emerges thereform in an atomised and electrosta-tically charged form.
The nozzle shown in Figure 9 comprises a solid steel "
- ~3 , 107~937 cylinder 44 held at its upper part by frictional engagement with the distributor 7 o Figure 1. The cylinder 44 has a central axial bore 45 running almost the length of the cylinder and terminating at a transverse bore 46 in the lower part of the cylinder. The cylinder 44 is connected to the module 3 via the metal wire 10 and cable 11~ The lo~er part of the cylinder terminates as a solid disc 47 having a bottom surface 48~
In use, when cylinder 44 becomes electrically charged, liquid from distributor 7 passes through bores 45 and 46 and flows around disc 47 to surface 48 from which it is atomised.
If the flow rate o liquid out of bore 46 is suffi-ciently reduced atomisation o the liquid may occur from the surfaces ad~acent the two ~xits of bore 46.
The embodirnent shown in Figures 10 and 11 comprises the spray gun of Figure 1 fitted with a deflector electrode system to prevent 'back-spray'.
As shown in Figures 10 and 11 a disc 51 formed of an insulating material embraces the distributor 7 at its mid-section and is held thereon by rictional engagement. Partly embedded in the lower su~face of the disc 51 is a deflector electrode 52.
in the ~orm of a steel ring. The deflec~or electrode 52 is connected, via a high voltage cable 53, to a tapping 54 of a potential divider 55. The divider 55 comprises a resistor o 101 ohms, connected at one end to the high potential cable 11 and at its other end to the earth lead 14. The high reSistan~Q
of divider 55 minimises current drain from the high voltage source 3, and serves as a current limiter in the event of a short circuit occurring at the deflector electrode 52.
In operation, with switch 4 in the 'ON' position the de1ector electrode 52 receives a high potential from the 1~7~937 potential divider 55. Suitable adjustment of the tapping 54 may give any desired potential be-tween zero volts and the poten~
tial of the source 3. A typical voltage on the deflector electrode 52 would be 14 KV.
The position of the deflector electrode 52 in relation to the field adjusting member 13 and the spray nozzles 9 may be selected by moving the disc 51 along the length of ~he distri-butor 7.
Liquid emerging from the nozzles 9 is atomised and directed by the combined electric field forces set up no~ only by the high voltage on the nozzles 9 and the local low potential ' - :-of the field adjusting member 13 but also by the high potential on the deflector electrode 52.
Reerring to Figures 12 - 14, the head o the spraying apparatus comprises a rectangular body 61 formed of an insu-lating plastics material and having a rectangular chamber 62. : ' Along the length of its lower face, the body 61 has an integ- . ' rally formed upstanding projection 63 having a longitudinal slit 64 which connects with chamber 62. The upper face of the body 61 has an aperture 65, adapted to receive (by means not shown) a liquid to be sprayed, and which communicates with chamher 62.
The,slit 64 is divided by a conducting surface formed o a thin metal sheet 66 connected to a source o high potential (not shown)~ Held by supports 67 adjacent the projection 63 is an earthed metal wire 68 enclosed in a sheath 69 formed of an ;
insulating plastics material. ",., In operation with the high potential applied to the metal sheet 66, liquid to be sprayed e~ters the chamber 52, via ' the aperture 65. It emerges from the slit 64 where it is atomised adjacent the metal sheet 66. The wire 68 acts as a . .
~q~937 field-adjusting member on both sides of the metal sheet 66.
Because it has an insulated protective surface the metal wires 68 can be disposed closer to the metal sheath 66 than if it were not so insulated, and also with a greatly reduced risk o~ arcing.
In an alternative embodiment the conducting surface may comprise a metal wire.
In a further embodLment utilising ~he linear slit arrangement a multiplicity of wire or metal sheet conducting sur-faces in parallel and disposed between a multiplicity of such sheathed wire field adjusting members is used. Such an arrange-ment allows of an increase in the volume of liquid to be sprayed.
The various~devices descrihed are particularly use~ul in the process of the invention, that is to say, in spraying liquid pesticides. They may easily be made portable and self-contained, being conveniently powdered by low output power sources such as dry cells r piezoelectric sources or photoelectric sources. The devices may readily be used for many other pur-poses where atomisation and deposition (e.g. paint spraying, lacquering), or atomisation alone, are required. The process of the inventionhas particular advantages over known methods of spraying liquid pesticides because it can give a more even coat-ing of pesticldes on foliage. Electrostatic forces direct the spray particle to their target, reducing drift, and enable leaves to be coated an both sides. Liquid pesticidal compositions sprayed by the process of the invention may be for example insec-ticides, fungicides and herbicides. Typically they are in the form of solutions or dispersions of a pesticide in a p~sticidally inert organic diluent (e.g. a liquid hydrocarbon) but it is also possible to spray liquid pesticides substantially undiluted~
Because deposition is uniform, drift is minimised, and low flow-- . ... : . . , ; . , ... . . , . :
1~193~ .
rates can be used, the process is particularly suitable for applying pesticides undiluted or in hig~ly concentrated formulations (ultra low volume spraying).
"i ` ' ' ' ' ........ ..
Claims (23)
1. A process of spraying pesticides which comprises supplying a liquid pesticidal composition to an electrically conducting or semi-conducting surface adjacent a field intensifying electrode, the electrode being at such a potential and so sited relative to the surface that an atomising field strength is created at the surface so that the liquid is atomised at least preponderantly by electrostatic forces substantially without corona discharge to form electrically charged particles which are projected away from the electrode.
2. A process of spraying pesticides as claimed in Claim 1 in which the size of the particles is controlled by control of the field strength at the surface.
3. A process of spraying pesticides as claimed in Claim 2 in which the field strength is controlled by varying the distance of the field intensifying electrode from the surface.
4. A process as claimed in Claim 1, 2 or 3 in which the field intensifying electrode is at earth potential.
5. A process as claimed in Claim 1, 2, or 3 in which the liquid pesticidal composition is a solution or dispersion of a pesticide in a pesticidally inert organic diluent.
6. Electrostatic spraying apparatus suitable for use in the process of Claim 1 which comprises a spray head having a conducting or semi-conducting surface; means for electrically charging the spray-head surface to a potential of the order of 1-20 kilovolts; means for delivering spray liquid to the surface;
a field intensifying electrode mounted adjacent to the surface;
and means for connecting the field intensifying electrode to earth; the electrode being so sited relative to the surface that when the surface is charged, the electrostatic field thereat causes liquid thereon to atomise without substantial corona discharge to form electrically charged particles which are projected past the electrode.
a field intensifying electrode mounted adjacent to the surface;
and means for connecting the field intensifying electrode to earth; the electrode being so sited relative to the surface that when the surface is charged, the electrostatic field thereat causes liquid thereon to atomise without substantial corona discharge to form electrically charged particles which are projected past the electrode.
7. Apparatus as claimed in Claim 6 in which the field intensifying electrode is adjustably mounted on the apparatus so that the distance between the electrode and the surface can be varied, thereby varying the field strength at the surface.
8. Apparatus as claimed in Claim 6 in which the field intensifying electrode is sited as close as possible to the surface without discharge occurring between them.
9. Apparatus as claimed in Claim 6 in which the field intensifying electrode is covered with an insulating material.
10. Apparatus as claimed in Claim 6 in which the field intensifying electrode is sited level with the surface.
11. Apparatus as claimed in Claim 6 in which the field intensifying electrode is sited forward of the surface.
12. Apparatus as claimed in Claim 6 in which the surface forms at least part of one or more orifices for the omission of liquid.
13. Apparatus as claimed in Claim 12 in which the surface comprises the edges of two concentric tubes which define an annular orifice for the emission of liquid.
14. Apparatus as claimed in Claim 12 in which the surface comprises at least one of two substantially parallel edges defining a slot-shaped orifice for the emission of liquid.
15. Apparatus as claimed in Claim 6 which further comprises a further field adjusting member by which the spray pattern may be controlled.
16. Apparatus as claimed in Claim 6 which further comprises a deflector electrode operably capable of maintaining a high potential of the same sign as the atomised liquid, and as sited between the field intensifying electrode and the body of the apparatus as to prevent 'back spray'.
17. Spraying apparatus comprising at least two or more spraying devices as claimed in Claim 6 mounted on a boom.
18 Spraying apparatus as claimed in Claim 17 in which the boom is mounted on a powdered vehicle such as a tractor or an aircraft.
19. A portable, self-contained electrostatic spray gun suitable for use in the process of Claim 1 which comprises a reservoir for containing liquid to be sprayed; a spray-head having a conducting or semi-conducting surface adjacent which liquid may aromise; means for delivering the liquid from the reservoir for atomisation adjacent to the surface; a field intensifying electrode in close proximity to the surface; means for connecting the field intensifying electrode to earth; and a power source adapted to charge the spray-head surface to a potential of the order of 1-20 kilovolts; the electrode being so sited relative to the surface that when the surface is charged, the electro-static field thereat causes liquid thereon to atomise without substantial corona discharge to form a cloud of electrically charged particles which are projected past the electrode.
20. An electrostatic spray gun as claimed in Claim 19 wherein the power source is one or more dry cells.
21. An electrostatic spray gun as claimed in Claim 19 wherein the power source is piezoelectric.
22. An electrostatic spray gun as claimed in Claim 19 wherein the power source is photoelectric.
23. An electrostatic spray gun as claimed in Claim 19 wherein the distance of the field intensifying electrode from the surface is variable thereby to determine and control the droplet size of the atomised liquid.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB29539/76A GB1569707A (en) | 1976-07-15 | 1976-07-15 | Atomisation of liquids |
| GB718677 | 1977-02-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1071937A true CA1071937A (en) | 1980-02-19 |
Family
ID=26241259
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA282,788A Expired CA1071937A (en) | 1976-07-15 | 1977-07-15 | Process and apparatus for atomisation of liquids by electrostatic forces |
Country Status (31)
| Country | Link |
|---|---|
| US (3) | US4356528A (en) |
| JP (1) | JPS5817668B2 (en) |
| AR (1) | AR218258A1 (en) |
| AU (1) | AU521016B2 (en) |
| BG (1) | BG28834A3 (en) |
| BR (1) | BR7704627A (en) |
| CA (1) | CA1071937A (en) |
| CH (1) | CH624589A5 (en) |
| CS (1) | CS233702B2 (en) |
| DE (1) | DE2731712C2 (en) |
| DK (1) | DK152340C (en) |
| EG (1) | EG13161A (en) |
| ES (1) | ES460785A1 (en) |
| FR (1) | FR2358207A1 (en) |
| GR (1) | GR61997B (en) |
| HK (1) | HK68183A (en) |
| HU (1) | HU182865B (en) |
| IE (1) | IE45426B1 (en) |
| IL (1) | IL52496A (en) |
| IT (1) | IT1082126B (en) |
| KE (1) | KE3317A (en) |
| MX (1) | MX145381A (en) |
| NL (1) | NL186065C (en) |
| NZ (1) | NZ184555A (en) |
| OA (1) | OA05708A (en) |
| PH (1) | PH16577A (en) |
| PT (1) | PT66771B (en) |
| RO (1) | RO75479A (en) |
| SG (1) | SG47883G (en) |
| TR (1) | TR20081A (en) |
| YU (1) | YU42153B (en) |
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| US4401274A (en) * | 1980-03-20 | 1983-08-30 | Imperial Chemical Industries Plc | Containers for use in electrostatic spraying |
| US6302331B1 (en) | 1999-04-23 | 2001-10-16 | Battelle Pulmonary Therapeutics, Inc. | Directionally controlled EHD aerosol sprayer |
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