US 3516608 A
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June 23, 19.70 HDBQWEN ETAL 3,516,608
' ELEcTRosTATIc NozzLE I Filed July 1o, 1968 INVENTORS.
AWORNEK 3,516,608 ELECTROSTATIC NOZZLE Henry D. Bowen, 2200 Charlotte Court, Raleigh, N.C.
27607, and William E. Splinter, 2120 S. 61st St., Lincoln, Nebr. 68506 Filed July 10, 1968, Ser. No. 743,786 Int. Cl. Bb 5/00 U.S. Cl. 239- 12 Claims ABSTRACT 0F THE DISCLOSURE In abstract, a preferred embodiment of this invention is an electrostatic charging nozzle used in conjunction with the application of coatings of liquid and powdered materials.
DESCRIPTION This invention relates to material applicating devices and more particularly to electrostatic charging nozzles for applying materials in both dry powdered and atomized liquid forms.
For many years, electrodes have been placed in particle laden gas streams to electrically charge the particles so that they will be attracted to and deposited on the electrodes. Although the same broad principle is applied in the spray and dust application of paints, insecticides and the like, it is highly desirable to keep the field charging electrodes from becoming coated with any material which would reduce the surface resistivity thereof.
In the use of nozzles for electrostatically charging dust aerosols for agricultural and similar applications, it has been found that under low relative humidity conditions (40% or less) a coating of high resistivity will form on the electrodes, particularly the exterior electrode when this forms the end of the nozzle. The coating thus formed may cause reverse ionization of the electrostatic iield thereby nullifying the charging effect.
To overcome this problem of reverse ionization at low humidities, nozzles have been designed so that the dust aerosol stream impinges off of the electrodes, particularly the outer electrode when it has been necked down, to cause more effective erosion of the deposited material. The advantages obtained by these designs, however, are at least partially off-set by the fact that the particles become discharged upon striking the electrode surfaces and may actually erode with an opposite sign.
Under high humidity conditions dust deposits do not Ibuild up on the electrodes, but a new problem arises. Voltage leakage between the power supply and the electrodes effectively reduces the efficiency of operation of the charging nozzles and can reach the point of complete cessation of charging. It has been noted that a direct short is not necessary to adversely atfect proper operation of the system.
Because of the electrical leakage encountered under high humidity conditions, it has been deemed over the years not to be feasible to use charging nozzles designed for dust aerosols in the application of aqueous atomized sprays. This is a definite disadvantage in view of the fact that many materials for application, chemical properties, and air pollution reasons, preferably come in liquid form.
In recent years, non-wetting materials have been used at least experimentally in coating of leads between the power supply and the electrodes to reduce or eliminate current leakage due to grounding. These experiments have disclosed that no known non-wetting material will effectively prevent leakage from taking place under high humidity conditions created by either the ambient air or blow-back from atomized spray application.
United States Patent Olce 3,516,608 Patented June 23, 1970 The present invention has been developed after much research and study into the above mentioned problems and is designed to overcome the reverse ionization eifect caused by low humidity conditions. It also effectively eliminates current leakages between power supply and electrodes under high humidity conditions created through the use of aqueous sprays or from the ambient air, thus allowing a single nozzle configuration to be used alternately, without extensive modification, for both dusts and sprays.
It is an object, therefore, of the present invention to provide an electrostatic charging nozzle having positive means of preventing deposit build-up on at least one of the electrodes in combination with positive means for preventing leakage in the high voltage line between the power supply and the high voltage electrode.
Another object of the present invention is to provide means for positively eliminating voltage leaks caused by high humidity conditions between the high voltage electrode and the power supply of an electrostatics charging device.
Another object of the present invention is to provide in combination with a voltage leakage preventing means a means for insulating, through the use of a clean air curtain, at least one of the electrodes from the fluid stream being charged.
An additional object of the present invention is to provide a line voltage leak preventing means including a heater having a surface temperature of between 200 to 300 degrees Fahrenheit.
Another object of the present invention is to provide in an electrostatic charging nozzle, a combination of voltage leakage eliminating means, fluid stream from electrode insulating means, and air straightening means for said insulating means.
Other objects and advantages of the present invention will become apparent and obvious from a study of the following description and the accompanying drawings which are merely illustrative of the present invention.
In the drawings:
FIG. 1 is a partially cutaway, side elevational view of a preferred embodiment of the electrostatic charging nozzle of the present invention;
FIG. 2 is an end elevational View of such nozzle;
FIG. 3 is a side elevational View of a modified heater unit for said invention; and
FIG. 4 is a side elevational view of a modification thereof.
With further reference to the drawings, an electrostatic charging nozzle indicated generally at 11 is formed of an elongated, generally cylindrical housing 12 which is open at its discharge end 13.
The end 14 of housing 12 opposite discharge end 13 is enclosed with a clean air inlet conduit 15 communicatively constructed thereinto.
Sealingly mounted through inlet end 14 and extending longitudinally in spaced relation to cylindrical housing 12 to a point inwardly of the ring shaped outer electrode 16 is fluid inlet conduit 17.
Adjacent the outlet end 18 of fluid conduit 17 are a series of baffle-like air straighteners 19 which also act as spacers and mounting supports between housing 12 and said conduit.
A second electrode 20` has its end centrally disposed in the discharge end 13 of housing 12 so that the outer electrode 16 is spaced an equidistance thereabout. A multiplicity of small wire-like probes 21 are included on the tip 0f the central electrode 20 to increase the corona etfect during the charging process.
Fixedly secured to a portion of housing 12 is an insulator mounting block 23 upon which is Xedly mounted a heating unit indicated generally at 24. This unit is composed of an electrical lead 25 which is operatively connected to a power source (not shown) at one end and is operatively connected to heating element 26 at the other end. A heating surface 27 surrounds the heating element and is so adjusted relative thereto that a temperature of between 200 and 30() degrees Fahrenheit may be maintained during operation of the nozzle as humidity conditions require.
From electrode 20, electrode lead 22 curves outwardly from the discharge end 13 of housing 12 toward heating unit 24. This lead then passes either around the heating surface 27 as disclosed in FIGS. l and 2 or through the heating unit as disclosed in FIG. 3. In any event, once central electrode lead 22 has passed around or through the heating unit 24, such lead with its conducting wire 28 passes on to a high voltage source (not shown).
OPERATION In actual operation of the nozzle of the present invention, the heater unit 24 is activated in the usual manner for electrical heating devices so that element 26 will heat surface 27 to a temperature of between 200 and 300 degrees Fahrenheit. From the high voltage power supply (not shown), a potential difference of between 10 kv. and l kv. is established between the central electrode 20 and the outer electrode 16. It should be noted that although in the past most electrostatic nozzles using the general electrode arrangement of the present invention have applied the high potential (either positive or negative) to the central electrode, it has been determined by applicants that the center electrode needs only to be at a different potential than the outer electrode and the magnitude or sign of either is unimportant other than the possible consideration of safety and design. This, of course, indicates that either or both electrodes in the charging system may be at a potential other than ground.
Once the heating unit is at proper operating temperature and the potential difference is established between the electrodes, clean air is introduced into the nozzle through conduit 15. Due to the spaced relation between fluid conduit 17 and housing 12, this clean air completely surrounds said last mentioned conduit and after passing through the air straighteners 19 forms a boundary layer or air curtain along the interior edge of outer electrode 16. The uid to be charged is introduced into the nozzle through fluid conduit 17 and passes out of the nozzle through the center of the air curtain which insulates such uid ow from contact with the outer electrode. Through initial experimentation, it has been found that better insulating qualities are obtained when the velocity of the air curtain is higher than that of the fluid. As the fluid passes through the area of the electrodes, the difference in potential between the outer electrode 16 and the inner or central electrode 20 places a charge on the individual dust particles or spray particles, as the case may be, so that when the same leaves the nozzle they will be attracted to nearby surfaces which are not be treated or coated.
Often enough moisture is in the air to cause leakage of current in the electrode lead 22 regardless of where the power supply is actually located. In addition, use of the aqueous sprays allows depostiion of spring droplets as the electrode leads, also leading to current leakage. This, of course, is because water is a good conductor and a small amount of moisture on the insulation of a lead will allow some bleeding of current. Even the slightest leakage will have a dettinite effect on the effectiveness of charging. In the present invention, however, regardless of the amount of moisture which strikes lead 22, such leakage is etfectively stopped and prevented from passing back along the exterior of such lead since heater 24 is of a suicient temperature to maintain the insulating 4 properties of the portion of said lead adjacent the heater unit.
Although not dealt with in great detail, the present invention may obviously be used with nozzles employing both of the well known electrostatic charging principles. The same solution overcomes both the problems encountered in using the pair of spaced electrodes creating an ionized eld as well as the problems encountered in using the single electrode of the inductive method when a conducting Huid acts to create the desired electrical potential differential. This solution disclosed by applicants invention, among other things, allows maintenance of proper active and passive electrode conditions in ionized eld charging and also allows proper passive condition to be maintained during induction charging as is known by ones skilled in the art to be necessary for proper operation.
In view of the above, it is obvious that the present invention has the advantage of providing an electrostatic charging nozzle which does not allow insulating dust build-up on electrodes due to low humidity conditions and is not affected by voltage variations due to leakage under high humidity conditions. The present invention also has the advantage of being simple in construction, inexpensive to manufacture and yet sturdy in structure and capable of long, constant operation under adverse conditions.
The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the spirit and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.
What is claimed is:
1. In an electrostatic charging nozzle having a conduit through which a fluid stream to be charged passes, an outer electrode spaced adjacent the outlet end of said conduit, a second electrode disposed in the fluid stream adjacent said outlet end, means for creating an electrical potential differential between said electrodes, and electrically conductive lead means connecting said last mentioned means to at least one of said electrodes, the improvement comprising: a stream of air directed between the outer electrode and said fluid stream whereby material from said last mentioned stream will be prevented from building up on said outer electrode; and heater means disposed adjacent at least a portion of said lead means whereby current leakage caused by moisture on said lead will be effectively blocked.
2. The nozzle of claim 1 wherein the heater means maintain said lead at a temperature of between 200 and 300 degrees Fahrenheit.
3. The nozzle of claim 1 wherein the velocity of the air stream is greater than the velocity of the `fluid stream.
`4. The nozzle of claim 1 wherein the iluid stream is a dust aerosol.
5. The nozzle of claim 1 wherein the fluid stream is an atomized spray.
6. An electrostatic charging means comprising: at least one electrode; a high voltage power supply means; electrically conductive lead means connecting said electrode to said power supply means; and means for heating at least a portion of said lead means whereby said portion may be maintained in a dry condition to prevent electrical current leakage.
7. The charging means of claim 6 wherein the heating means maintains at least a portion of said lead means at la temperature of between 200 and 300 degrees Fahreneit.
8. A means for electrostatically charging a fluid stream comprising: at least two spaced electrodes, at least one of which is disposed outside of said stream; a high voltage power supply means; electrically conductive lead 6 means connecting at least one of said electrodes of said 121. The charging means of claim 8 wherein the fluid power means; means for heating at least a portion of said stream is an atomized spray. lead means whereby said portion may be maintained in a dry condtiion to prevent electrical current leakage there- References Cited along; and an air stream means disposed between said r UNITED STATES PATENTS iluld stream and at least one of sald electrodes whereby 0 build-ups of material from said uid stream may be 3195264 7/1965 Ward Z39-15 prevented on said last mentioned electrode. 312121211 10/1965 Bennett 239-15 9. The charging means of claim 8 wherein the heating means maintains said lead means at a temperature of be- EVERETT W KIRBY Prlmary Examiner tween 200 and 300 degrees Fahrenheit. l0 G, A CHURCH, Assistant Examiner 10. The charging means of claim 8 wherein the velocity of the air stream is greater than the velocity of the U.S. C1. X.R. uid stream. 239-3, 118, 135
11. The charging means of claim 8 wherein the fluid 15 stream is a dust aerosol.