GB2143153A

GB2143153A - Spraying

Info

Publication number: GB2143153A
Application number: GB08417052A
Authority: GB
Inventors: Alan Bloomfield
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1983-07-12
Filing date: 1984-07-04
Publication date: 1985-02-06
Also published as: GB2143153B; GB8417052D0

Abstract

A liquid spraying apparatus including an electrostatic spray head 5, a container 4 for spraying liquid, a high voltage source 13 and a manually driven blower 2, all mounted on a support adapted for mounting on the back of an operator. The spray head suitably includes a nozzle, which is connected to the high voltage source so as to charge liquid from the container conductively, and a field intensifying electrode. The spray head is located within an air duct at an outlet of the blower so that atomised liquid emerging from the spray head is directed on to a target by a current of air from the blower. The operator is able to operate the blower with one hand whilst directing spraying liquid on to the target with the other hand. The blower is driven by a crank handle 10, (or a lever or reciprocating mechanism) through a gear train and flywheel. <IMAGE>

Description

SPECIFICATION Electrostatic spraying system This invention relates to electrostatic spraying systems in which the transport of the spray to the target is assisted by a current of air.

It is known to spray crops for example with mist-blowers which generate a powerful blast of air to shear liquid into droplets and carry them to the crop. Such devices require engine-driven blowers which present serious service problems in many areas.

It is also known to disperse powders or dusts by means of hand driven devices which have many advantages in terms of lightness, simplicity and cost. It has not been considered practicable to use such hand-driven devices in the spraying of liquids however because of the additional power needed to atomise the liquid into a spray.

We have now found that by using an electrostatic spraying process it is possible to produce a portable manually driven device capable of air assisted liquid spraying.

According to the invention a liquid spraying apparatus comprises an electrostatic spray head adapted to atomise liquid supplied thereto, and a manually drivable means for producing a directed current of air, the spray head being located within or adjacent to the current of air so that atomised liquid from the spray head is directed by the current at a target to be sprayed.

The electrostatic spray head preferably comprises an electrically chargeable surface which, in use, contacts the liquid and applies charge thereto conductively. In this case, the spray head may further comprise a field intensifying electrode adjacent to the chargeable surface and maintainable in use at earth potential or at a potential which is relatively low compared with the chargeable surface.

Alternatively, the spray head may comprise an electrically chargeable surface which, in use, is spaced from the liquid and applies charge thereto inductively.

The device of the present invention is especially useful in the spraying of agricultural chemicals such as pesticides.

The invention will now be described, by way of example, with reference to the accompanying drawing which shows a perspective view of an apparatus according to the invention designed for mounting on the back of a spray operator.

Referring to the drawing the apparatus comprises a back-support 1 to which is attached a blower 2 driven by manual driving means 3.

Support 1 also carries containers of pesticide 4 intended for spraying crops via electrostatic spray head 5 mounted in an air duct 6 from the blower 2. The back-support 1 is provided with straps 7 for securement to the back of a spray operator in use.

The blower 2 comprises a fan of 1 70 mm diameter with 1 2 die-cast magnesium alloy blades. Intake 8 and outlet 9 are approximately 89 mm and 60 mm in diameter respectively. A fan blade tip speed of 8.9 metres/sec is achieved at 1000 rpm giving a theoretical muzzle velocity of approximately the same figure and a volume output of 1.4 cubic metres/min.

Driving means 3 comprises a crank-handle (lever or reciprocating mechanisms may also be used) 10 driving the blower 2 through a conventional drive-train (details not shown) giving an overall gear ratio of 40:1. Thus in use at a typical cranking speed of 50 rpm, a fan speed of 2000 rpm is obtained. Variation in gear ratio is obtainable via a simple gear box and optimum ease of use for a given operator or operating conditions is obtained through the incorporation of a fly wheel in the driving mechanism.

The air outlet 9 of the blower 2 is extended by an air duct 6 in the form of a flexible hose terminating in an air exit nozzle 11 within which is mounted electrostatic spray head 5.

The spray head 5 is of the type described in our UK Patent No. 1 569707 having an annular nozzle of conducting or semi-conducting material and an earthed field adjusting or intensifying electrode adjacent to the nozzle.

Liquid pesticide is supplied to spray head 5 from container 4 via conduit 1 2 which also comprises an insulated electrical lead conveying a voltage of the order of 20-30 kv to the spray head from a battery-powered high voltage source 1 3. High voltage may alternatively be produced by a generator driven by the driving means 3.

In use for the spraying of crops, the operator secures the apparatus to his back using straps 7 and makes the necessary electrical and liquid connector to the sprayhead 5.

Liquid emerging from the spray head 5 is charged conductively by contact with the surface of the nozzle, which is connected to the high voltage source 13. The presence of the field intensifying electrode enables a sufficiently high field strength to be created at the nozzle surface to produce electrostatic atomisation of the liquid whilst using a relatively low voltage source.

Fan 2 is driven by crank-handle 10 with one hand whilst the air nozzle 11 is directed at the crops to be sprayed with the other. It is found in practice that an operator can drive the crank-handle at 40-50 rpm for 1 5 minutes or more without excessive fatigue.

The spray head 5 is located within or adjacent to the current of air from the blower 2 so that atomised liquid from the spray head is directed towards a target to be sprayed.

Typical air speeds have been found to be in the range of 10-20 metres per second at the air nozzle 11 falling to around 2 metres per second at a distance of 2.5 metres from the nozzle. Typical air volumes were found to be around 2 cubic metres per second.

Air velocity at the nozzle could be increased from approximately 10 metres/sec to 32.0 metres/sec by restricting the nozzle diameter and increasing cranking speed.

It was found in general that the use of somewhat higher cranking speeds with a fly wheel resulted in less operator effort.

It will thus be seen that the apparatus of the present invention provides a simple, robust and low-maintenance way of obtaining air-assisted liquid spraying.

It will be appreciated that the spray head 5, above, can be replaced by a spray head in which an electrode connected to a high voltage source is spaced from liquid emerging from a nozzle and applies charge to the liquid by an inductive process.

Claims

1. A liquid spraying apparatus comprising an electrostatic spray head adapted to atomise liquid supplied thereto, and a manually drivable means for producing a directed current of air, the spray head being located within or adjacent to the current of air so that atomised liquid from the spray head is directed by the current at a target to be sprayed.

2. Apparatus as claimed in claim 1, in which the electrostatic spray head comprises an elecrically chargeable surface which, in use, contacts the liquid and applies charge thereto conductively.

3. Apparatus as claimed in claim 2, in which the spray head further comprises a field intensifying electrode adjacent to the chargeable surface and maintainable in use at earth potential or at a potential which is relatively low compared with the chargeable surface.

4. A liquid spraying apparatus as claimed in claim 1, in which the electrostatic spray head comprises an electrically chargeable surface which, in use, is spaced from the liquid and applies charge thereto inductively.

5. A liquid spraying apparatus constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated in, the accompany drawing.