SK634487A3 - Device for electrostatic spraying - Google Patents

Abstract

An apparatus is disclosed suitable for electrostatic spraying from fixed wing aircraft. The apparatus includes a linear electrostatic spraying nozzle 2, supported from the aircraft by brackets 8, and electrodes 4 placed near the nozzle's spraying edge 16 to intensify the electric field strength at the spraying edge sufficiently to produce ligaments of the liquid from the spraying edge. In order that the airstream due to the aircraft's movement does not destroy the ligaments, the sprayhead and the electrodes are positioned so that part of the airstream flows between them. The spray head and the electrodes are so shaped and positioned that when directed to spray in substantially the same direction as the airstream, a turbulence free wake is left in the region of the ligaments. The liquid reaches the edges by passing across a slot 18 from a distribution gallery 44, a conducting or semiconducting surface 20 being arranged within the slot. <IMAGE>

Description

Electrostatic spraying equipment

Technical field

The invention relates to a device for electrostatic spraying of liquids.

BACKGROUND OF THE INVENTION

One advantage of electrostatic spraying is that charged spray particles tend to coat the sprayed target. This may be of particular use in, for example, agricultural spraying, since in this case the spraying will cover not only the outer or upper surface, as is usually the case with conventional spraying, but also both sides of the leaves and plants. Another feature of electrostatic spraying is the fact that the spray target attracts spray particles, so that losses due to wind entrainment are reduced. Most or most of the spray rate will achieve the intended goal. In this way, the total amount of spray required and thus the cost of spraying are reduced, and for this reason, the spraying is also more environmentally friendly.

An electrostatic spray device is known which comprises a spray head, a spray edge, an electrically conductive or semiconductive surface and means for supplying spray liquid to the spray edge through said surface, an electrode some distance from said edge and a high voltage source for applying a high voltage between the surface and the electrode such that when sprayed with liquid, the power of the electric field at the spraying edge is increased to such an extent that the liquid is sprayed from the edge predominantly by electrostatic forces in the form of rays which disintegrate into electrically charged droplets.

One of the devices belonging to said type of device is described in British Pat. 1,569,707th

The advantage of this device is that the liquid rays disintegrate into drops having a very narrow spectrum of diameters. This is very advantageous because if a drop of a certain size is capable of transmitting a lethal dose of insecticidal spray, too small drops are actually ineffective, but in larger drops a larger amount of insecticide is required to reach the same number of sites containing the lethal amount of the composition.

In order to treat large areas, the spraying can be carried out by air. Although electrostatic spraying has been proposed in this way, e.g. 186 353, the problem of air flow behind the aircraft has not been solved yet. The use of a fixed wing aircraft for spraying creates an air flow behind the aircraft with respect to its movement, and this air flow is further amplified by the propeller flow to reach a speed of 110 km / h. The problem created by this air flow is that the turbulence around the electrostatic spray head interferes with the formation of rays and thus disrupts the desired drop diameter spectrum or even prevents spraying.

SUMMARY OF THE INVENTION

The solution to the above problems is the wide type of spraying device that for spraying into the air stream the spraying head has a wing profile, the trailing edge of which forms the spraying edge. The spray head and the electrode are spaced from each other and the air flow passes therebetween.

(A wing profile is used herein to mean a profile corresponding to the shape of the profile used in aircraft wings.)

Accordingly, the present invention relates to an electrostatic fluid spraying device comprising an edge sprayer having an electrically conductive or semiconductive surface, means for delivering spray fluid to the spraying edge through an electrically conductive or semi-conductive surface, an electrode remote from the spray head and a high source source. a voltage designed to generate a high voltage between the electrically conductive or semiconductive surface and the electrode. The principle of the invention is that the sprinkler head has a sash profile, the trailing edge of which forms a sprinkling edge, with an airflow gap between the sprinkler head and the electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the device according to the invention is described by way of example with reference to the accompanying drawings.

In FIG. 1 and 2 show the overall arrangement of a device according to the invention on a light aircraft.

In FIG. 3 is a cross-sectional view of a device according to the invention.

•

In FIG. 3a and 3b show details of the embodiment of FIG. Third

In FIG. 4 is a rear view of another embodiment of the device according to the invention.

In FIG. 5 shows a liquid supply in the embodiment of FIG. Third

In FIG. 6 shows an electrical circuit in the embodiment of FIG. Third

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 and 2, the spray head 2a is shown. The position of the spray head 2 is chosen such that the spray head 2 is located in the air without turbulence and is positioned substantially parallel to the air flow, so that the spray does not end to a greater extent on the aircraft stabilizer. Spray head

2. is mounted on arms 6 (see FIG. 1) connected to brackets 8 (FIG. 3) at intervals of approximately 0.5 m.

The spray head 2 shown in FIG. 3 has a wing profile (which is symmetrical in FIG.) At the edge of which is a linear nozzle. The body of the spray head 2 consists of a front end 12 usually formed of insulating material and a nozzle assembly 14 of semi-insulating material. The nozzle assembly 14 comprises two portions 14a and 14b. which are connected together via a spacer, so as to form a slot 18 defined by the thickness of the spacer just before the spraying edge 16.

In use, the agrochemical liquid is fed through the slot 18 through the conductive or semiconductive surface 20 and through the outer surface 21 to the spraying edge kdeέ »where it is splashed. The spraying edge 16 is disposed between two opposing electrodes h.

The electrodes 4 consist of a core 22 of a conductive material which is protected by a cover 24, partly of a semi-insulating material 26 and partly of an insulating material 2. The insulating part of the material 28 of the cover 24 is of glass reinforced plastic. Poloizolačná housing part 24, the tube 25 of a material with a resistivity of the order 10 to 10 ^{x xo} *, preferably 5 x 10 to 5 x ^xx 10 ohm-cm ^x3 Examples of suitable materials for this use include certain types of glass and phenol-formaldehyde-paper-based combination materials. The core 22 is made of iron or carbon granules. The tube 25 is connected to the insulating material 28 with an epoxy filler or glue 23.

The conductive or semiconductive surface 20 is connected by a supply line not shown with one of the outputs of the high voltage generator 50 or 52 (FIG. 6). The electrode cores 22 are connected by another pair of conductors to another output of the high voltage generator, so that in use a high voltage difference, for example 10 to 35 kV, is maintained between the surface 20 and the electrode core 22. Different voltage values can be used. It can be assumed that the target is substantially on the ground potential, in this case either the cores 22 of the electrodes 4 or the surface 20 on the ground potential may be located, as will be explained below. It is also possible to keep the cores 22 at a potential with a value between the potential of the surface 20 and the target. In a preferred embodiment, the surface potential 20 is maintained at ± 35 kv and the electrode potential at ± 17.5 kV. The electrodes thus have the potential of polarity similar to that of the spray droplets. Once dropped behind the electrodes, they are repelled by the electrodes. If the electrodes are at ground potential, there may be a tendency for droplets to be drawn back to the electrodes, especially at high flow rates.

Various circuit arrangements can be used to obtain the voltage required on the cores 22 and on the surface 20. On the

52r ££ FIG. 6, each generator shown has outputs. It is also possible to arrange the circuit so that the potential for the electrode cores 22 is taken from the voltage divider using a single output generator.

The spraying edge 16 is sharp to such an extent that, in combination with the core distance 22, it allows spraying at a relatively low high voltage. In use, the electric field is defined by the semi-insulating material 26 of the electrode housing 21 and the liquid that has reached the spray edge 16. Assuming that the surface 20 has a positive potential relative to the electrode cores 22? a negative charge is removed from the liquid by contact with the conductive or semiconductive surface 20 and a positive charge remains in the liquid. The presence of the electrodes 4 intensifies the electric field at the liquid-air boundary at the spraying edge 16 so that the liquid is sprayed in the form of rays along the spraying edge 16.

The liquid now has a positive charge due to the negative charge being dissipated by the conductive or semiconductive surface 20 so that some positive charge remains in the liquid. This charge in the liquid causes internal repulsive electrostatic forces which overcome the surface tension resistance and create liquid cones at certain distances apart along the spraying edge 16 from the top of each cone a liquid jet is formed. , which arise from the passage of a liquid jet through the flowing air, the decay of a liquid jet into droplets (charged) with a small size dispersion. The mutual repulsion between the droplets causes the spray to extend in a direction transverse to the direction of the beam. The number of rays that are formed depends on the flow rate of the liquid and the intensity of the electric field, as well as other factors such as the resistivity and the viscosity of the liquid. With the stability of all other values, voltage control and flow rate, the number of rays can also be controlled, which also allows the drop size to be controlled to minimize their dispersion.

If the conductive or semiconductive surface 20 is separated from the spraying edge 16, the distance to one another must be carefully selected with respect to the resistivity of the liquid. It has been shown that spraying does not occur if, at a given distance, the resistivity of the liquid is too high or vice versa, at a given resistivity, the distance is too large. A possible explanation for this phenomenon may be that the liquid not only receives charge when passing through the conductive or semiconductive surface 20, but the charge is also discharged from the liquid by the liquid at the spraying edge 16. The resistance on this path must not be large enough field to a value that no longer causes atomization. Thus, the distance between the spraying edge 16 and the conductive or semiconductive surface 20 must be sufficiently small to be able to utilize a specific fluid resistance. It has been shown that a suitable position can also be found for spraying a liquid with a slight resistance in the range of 10 ^e to 10 ^xo ohm.cm.

Since the electrical conductors are connected to the core 22, the surface of the body 24 does not have the same potential. The surface potential will be lowest on the semi-insulating material 26 near the core 22 and here the electric field is concentrated between the spraying edge 16 and the electrodes 4. In order to determine the maximum electrical stress between the spraying edge 16 and the electrode body 4 The discharge between the particles which are close to each other is the core 22 and the cover arranged and positioned so as to be as close as possible to the sprayer head 2 and the sprayer edge 16.

It is important that the area close to the spraying edge 16 where the liquid rays are formed is substantially free of air flow directed transversely to the direction of the jet. Such an air stream could prevent the formation of rays. For this purpose, the spray head 2 is mounted so that it lies in the direction of the air flow and the bearing surfaces are arranged so as not to cause turbulent flow. It is also important that droplets cannot be deposited on the electrodes 4 behind the spraying edge 16. For this purpose, the electrode bodies 4 deviate from each other towards their rear edges, thereby creating an expanding passage. For this reason, the air flow slows as it passes through this passage, creating an environment in which it is difficult to completely eliminate turbulence. However, it is possible to achieve sufficiently low turbulence for the formation of steady rays by electrostatic forces. In practice, an angle of 10-15 ° with respect to the main direction of the air flow is used, since there is still no turbulent flow in this range. This allows spraying during normal summer.

At high spray velocity and / or high potential difference between surface 20 and core 22, spray droplets b tend to pollute the electrodes - This tendency can be reduced by the airflow across the spray edge 16 which will assist the removal of the droplets from the electrodes more quickly than possible. through the air stream.

In the arrangement shown in FIG. 3, it has been found that forward movement of the aircraft causes sufficient air flow to remove the droplets before they can contaminate the electrodes. Too much air flow can cause shear of air and liquid on the surface 21 so that liquid can be entrained before it reaches the spraying edge 16 However, this phenomenon can be avoided by appropriately shaping the electrode support surfaces.0. An amplification of the air flow may be desirable if spray drops begin to settle on the electrodes. This may occur, in particular, when large electrodes with sufficient strength. Suitable support surfaces for current delivery are shown in FIG. These surfaces are substantially cut in cross-section on the side facing away from the spraying edge 16 and thus allow a favorable air flow through the space between these surfaces and between the spray head 2 at the expense of external flow. In this arrangement, the position of the cores 23 of the electrodes M allows air flow in the direction of the liquid rays without a larger transverse component, so that at the same time it protects the spray head from overloading.

Without air flow between the electrodes 4 and the spraying edge 16 if the conductive or semiconducting surface 20 had ground potential and the electrodes 4 had a high positive or negative voltage, most of the drops would settle on the electrodes. air flow, spraying can be carried out even under the above circumstances. A sufficient flow of non-turbulent air can protect the electrodes M again in this case.

The front end 12 of the spray head consists of two parts of the surface layer 12a and of the I-shaped section 12b. Both parts are made of glass-reinforced plastic. The surface layer 12a and the section 12b are screwed together to form a cavity 38 through which the inlet pipes and conductors (not shown) that conduct the liquid and the high voltage to the nozzle pass. The nozzle assembly 14 corresponds to the outer shape of the front end 12 so as to form a support surface section. The nozzle assembly 14 has a protrusion 40 along its entire length which corresponds to the gap between the tubes of section 12b. The inlet ducts and conductors can be inserted between the section 12b and the projection 40, and then the whole assembly can be inserted into the front and removed again if necessary. The fluid supply tube is connected to the manifold 44 within the nozzle assembly 14b. The distribution channel 44 supplies liquid to be sprayed from the projection 40 to the slot 18.

sprinkler headsVulo As is clear from fig. 2, are not horizontal, but their slope corresponds to the slope of the aircraft wings. During spraying, the liquid is fed from the metering pump under positive pressure. If the aircraft reaches the end of the parcel that is being sprayed and turned, the spraying should be interrupted before the next strip of the designated parcel is sprayed after turning. In the event that one slot 18 extends over the entire length of the spray head, the liquid could flow to the lower end of the slot and the upper end may remain empty. This would cause a slight lag before restarting the pump and starting the actual spraying, which could cause the undefined section of the plot not to be affected by the spraying. This problem can be overcome by dividing the slot 18 into short independent sections, each of which would supply liquids separately and short enough to keep the capillarity at full load with normal aircraft movements normally during spraying and associated with its rotation.

In FIG. 5 is a spray head made in standard length. Eight sections 14.1 to 14.8 of the nozzle assembly 14 are shown schematically. Each section comprises three separate sections 18 of the slot 18, which are separated by separators in the spacer insert forming the slot 18.

Liquid is supplied to each section 18 through a separate tube and a separate distribution channel 44. A single closure 46 is provided between the supply tube and the distribution channel 44 to prevent liquid from flowing from one section of the distribution channel 44 to the other. Each section 14.1 to 14.8 of the nozzle assembly 14 comprises three insulated sections of the slot 18 and the distribution channel 44 into which liquid is supplied from the common inlet 41 via the one-way valve 48 and the flow regulator 4 '.

Problems arise with the use of one-way closures to separate the individual sections of the distribution channel 44 and the slot 18 in the sense that some types of solvents used for pesticides are highly aggressive against most elastomeric materials. ^One- way closures, in which the elastomeric materials are not used, usually require high pressures to maintain them in the closed position. This may result in the closure not opening at low pressure and to vary the flow rate between the individual closure at a certain pressure. These facts are not very serious in the case of the shutters 43 which are connected to the flow regulator 42. However, no regulator is connected to the shutters 40. This problem can be overcome by using PTFE-O-ring closures as a seal.

Because there is no direct connection, it is sometimes difficult to maintain a reference voltage with respect to the earth's surface. The solution for this case has been described in European patent specification no. After application to the device according to the invention, the circuit shown in FIG. Third

As shown in FIG. 6, the aircraft carries two electrode sprayhead assemblies 1a, 43 &apos;, &quot; Ah &quot; These parts are mounted on each side of the aircraft as shown in FIG. 2. The apparatus comprises two high voltage generators 52, 52 powered by batteries 54. Each generator two outputs corresponding to ground 5, 60, 60. Both of these outputs are connected to an aircraft frame 61. The output 62 of generator 50 s -35 kV is connected to the sprayer surface 20a. Title 2a. The output 64 of the 17.5 kV generator 50 is coupled to the mating electrodes 4a. Similarly, an output of +35 kV is coupled to the sprayer surface 20b of the head 2b and an output of +17.5 kV is coupled to the associated electrodes 4b. The generators 50 and 52 are preferably fixed at the front end of the corresponding spray heads to avoid the need for high voltage conductors to the spray heads and only external low voltage conductors are required.

The atomized liquid emerging from the spray head 2h carries a positive charge. The liquid exiting the sprayer j of the head 2a is negatively charged. During spraying, positive current from generator 52 to ground flows through outlet 66, conductive or semiconducting surface 20b of spray head 2b with liquid exiting spray head Without the connection between ground 58 and 60, the current cannot in any way flow back to generator 52 from ground ( for example, postre1.

ku). Thus, a negative charge is generated on the generator 54.

This charge generation at the generator 52 reduces the voltage at the electrode 4a by the conductive or semiconducting surface 20b relative to the electrode 4b, thereby reducing the atomization field and reducing the charge of the spray liquid. For this reason, the droplet size increases and the spraying quality deteriorates. The generator 50 will be affected similarly.

In practical use, if one of the generators 50 or 52 delivers more current than the other, a charge is generated on the generators. The polarity of this charge is such that it reduces the atomizing field on the spray head supplied by the generator delivering a larger amount of current. In this way, the spray quality of the associated spray head is reduced and, on the other hand, the atomization field on the spray head, controlled by the second generator, is increased. Thus, the spray quality on this head is higher and the current increases until equalization.

In an alternative arrangement, the slot 18 may be located directly on the spraying edge 16. Although two spraying edges could be formed in this way, since the slot has two sides, in fact there is only an electrostatic effect on only one edge. That is, only one set of liquid rays is formed. If the electrostatic effect were to occur at two edges, rays would form on both sides of the slit. However, it has to be considered that the spray liquid has a relatively high conductivity and thus, in use, bridges the gap.

In a further embodiment, more than one slot 18 may be used to deliver fluid to a single spray edge.

Claims (5)

PATENT CLAIMS An apparatus for electrostatic spraying of liquids having a spraying head with a spraying edge having an electrically conductive or semiconducting surface and means for supplying sprayed liquid to the spraying edge through an electrically conductive or semiconducting surface, an electrode remote from the spraying head and a high voltage source to generate a high voltage voltage between the electrically conductive or semiconductive surface and the electrode, characterized in that the spray head (2) has a sash profile, the trailing edge of which forms a spray edge (16) by the head, and between the spray ( 2) and the electrode (4) is an airflow gap. t Ý Apparatus according to claim 1, characterized in that the spray head has a symmetrical sash profile. according to claim 2, the tip of the spraying edge (16) is located 2>. m that 3. Device on both sides of the electrode (4). m that one 4th 2. The method according to claims 1 to 3, characterized in that the sash profile. Device according to the claims that each electrode (4) (24) at least partially from a semiconductor with a resistance of 5 x 10 ¹¹ to 5 x 10 10 ^and ohm 5th claim 5, characterized in that the core (22) and cover (24) are at the spray head (2) and post6. Apparatus according to the spray edge (16), wherein at least a portion of the housing (24) nearest the spray edge (16) is of semiconducting material. 7th core and cover 8th by (4) they are Apparatus according to claim 6, characterized in that (22) are compressed sawdust or graphite granules (24) have a leaf profile. Device according to claims 1 to 7, characterized in that the spraying edge (16) and the electrode or electrodes are linear. 1/5