DE2207310A1 - Electrostatic spray device - Google Patents

Description

I ¹ ATEUTAMVVSUTe

DR. E. WIEGAND DIPL-IMG. VV. NO ONE 2207310

DR. M. KÖHLER DIPL.-ING. C. GERNHARDT

MUNICH KAMBURG

TELFON: 395314 2000 H AMB U RG 50, ä% Zi t

TELEGRAMS: KAEPATEHT KONIGSTRASS E 23

24 997/71 20 / Yes

Bansburg Electro-Coating Corp.
Indianapolis, Indiana (V.St.JU)

Electrostatic spray device .:

The invention relates generally to a low voltage electrostatic spray device that is electrostatic charged particles sprayed, and in particular on a low voltage electrostatic spray device in which Liquid particles are formed in a passage of the

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Air jet from the side walls of the passage and one
Electrode associated with the sidewalls of the passageway cooperatively be directed away.

The electrostatic spray device according to the invention is primarily for use in electrostatic
Attachment or application of liquid particles to the surfaces of objects or objects at a particle-attracting potential is provided, thereby creating surfaces with a layer of liquid particles and

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wise to a substantially uniform "or continuous To create a film of the coating of liquid particles.

Various systems are commercially available that use electrostatic principles to prevent settling or disintegration. Precipitation of liquid particles on a coating to be coated Object to help. These systems differ differ in various respects from one another, namely in terms of the means and procedures that are used to make to atomize the liquid particles and the atomized Electrostatically charge liquid particles.

A first electrostatic spray system is known as the Ransburg process No. 1 known which is a known air atomizing spray gun au3 metal is used to form uncharged liquid3 particles. A separate grille made of charged wires is used to give the atomized liquid particles an electrostatic charge To give. In this system there is a high intensity electrical level between the grid of charged wires and the area of the object to be coated. The electric field creates a multitude of atmospheric Ions of the same electrical polarity as that of the lattice. The atmospheric ions are heading towards directed to the surface of the object at earth potential. The liquid particles are released through the spray gun formed and brought into or moved into the ion cloud, where they are electrostatically charged by ion bombardment will. The charged liquid particles are directed towards the surface of the object in response to it the effect of the charge carried by the liquid particles, the electric field and the earthed surface of the object attracted and deposited on the surface.

There are a number of other systems which are similar to Ransburg Method No. 1 in that the electrostatic charging of the liquid particle through ionic

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"Bombardment is achieved. The systems with era before are identical from each other with regard to the. Arrangement or position of the ionizing electrode in relation to which the liquid particles forming facility and the surface of the object to be coated.

In another system, the Liansburg Procedure No. 2, becomes a HochspanmmgnauaetEf eld and electrical charging field between the surface of the object to be coated and set up an exposed body of the fluid materiala, which is formed on an atomizer that has an extremely thin edge portion. The exposed body of the liquid material is formed so that it is common with the elongated thin edge portion of the atomizer reaching out or expanding. Dan electric Field has a high gradient on the extended edge of the liquid. The electric field forms the extended one Edge of the liquid into a number of liquid ends or -Tops that protrude outwards. Each of these ends is highly charged and therefore is a strong electrical one Impact force exists between the main body of liquid and the liquid at the ends. The other way round is one strong electrical connections between the liquid present at the ends and face of the object which is at a particle-attracting potential. Hence, a small portion of the liquid at each of the ends is helped with the surface tension forces to escape the liquid. The small part of the liquid is called a charged in the electric field Particles are drawn into the surface of the object, which is attracted to a particle Potential is to be discontinued.

Another system for the electrostatic charging of liquid particles includes a spray gun, which is in the is made essentially of dielectric material, and employs a wire-like electrode supported by a

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Liquid opening protrudes. The electrode charges through air atomized particles through bombardment with atmospheric ions generated at the tip of the electrode will. The atmospheric ions are concentrated in the immediate vicinity of the tip of the electrode. The ion bombardment of the atomized liquid particles charges the Liquid particles even more completely. The wire-like one Electrode also creates an electrostatic field which extends from its tip to the surface of the object or object to be coated. The electrostatic field helps in conveying or propelling the settling of the charged liquid particles on the surface of the object or object. To the necessary To generate atmospheric ions, the wire-like electrode is connected to a DC voltage source, which is capable of an unloaded output voltage of up to approximately 65 kV with a short circuit current at the electrode of up to about 225 microamps. It is evident that the stresses are of such magnitude Create security problems. Furthermore, the voltage source that is necessary to generate such high voltages is bulky and expensive. In the event that the electrostatic spray device is to be operated by hand, this is Tension cable, which is necessary to deliver such high tensions to the device, stiff and heavy and prevents or accordingly hinders the free manipulation of the spray device and causes operator fatigue. Each of the above electrostatic devices and systems has a high degree of technological and economical Success achieved. Each of the devices uses a large size voltage, each device is different each different from the other devices in the magnitude of the charge imparted to the liquid particles The facility differs from the other facilities in the types of fluid materials used by each of the

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Facilities can be sprayed economically, and Each facility differs from the other facilities in terms of general size, weight and the ability to adapt to a special purpose.

It is therefore a desirable goal to have an electrostatic spray device which sprays a wide variety of different types of liquid materials without regard to the physical and electrical characteristics of such liquid materials; which is light in weight and easy to maneuver; which does not subject the operator to dangerous shocks or blows or discharges to earthed surfaces while working; the particles of such size "is that they have a high charge in comparison za the mass of the particles have, so that the electrostatic settling at a relatively high efficiency occurs. Usually, liquid particles, which have a high charge to mass ratio, easier to To attract a surface and to deposit it on a surface of an object having an attractive potential as liquid particles having a low charge-to-mass ratio, therefore, in most cases, the composition of the liquid material and its density are determined by the intended use For a particle of a given size and density, maximizing the charge-to-mass ratio of the particle is a matter of maximizing the charge carried by the particle Generation of highly charged particles possesses while it has the other desired characteristics.

According to the invention is an electrostatic spray device created with a relatively jealous tension, which is able to give very high electrostatic charges to atomized liquid particles. The spray device has a non-ionizing electrode that is

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located within and at a distance from the end of a passage which is formed within a liner, barrel or drum. Inside the passageways and in the immediate vicinity of the electrode is the end of a fluid supply arranged. Means for applying a high intensity electric field is between the End of the liquid supply and the electrode switched. The side walls or side walls of the passage, with the exception of the electrode part, are or is preferably made of a dielectric material to thereby provide the electric field at the end of the liquid delivery focus. The electrode and the side walls of the passage are essentially continuously cleared by a stream of air which removes the particles from the passageway carries out. Freeing the electrode and the sidewalls of the passageway with a stream of air reduces this Noteworthy are the number of liquid particles which are otherwise on the electrode and the side walls of the passage were accumulating. If liquid particles are allowed to separate to any appreciable degree Accumulating either on the electrode or on the sidewalls of the passageway could result in undesirably large droplets of liquid from such an accumulation form · The presence of undesirably large droplets in one Spray jet or mist of charged liquid particles tends to give the coating that is usually desired on or on the surface of an object or object worsen and becomes the charge-hate ratio that is generated on such particles »also reduce · In addition, the arrangement of the electrode In allows immediate« close proximity to the end of the liquid supply and at a different from the potential of the electrode Potential and the formation of the sidewalls of the via mainly from one of the electrical materials the use of a low voltage source to power a box

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high intensity at the end or ends formed on the surface of the liquid flow is or are.

The electrical gradient, as high as practical, that between the electrode and the ends the flow of liquid is maintained in the passage creates a high intensity electrostatic field at each end. The liquid particles that result from the Liquid ends are formed, have a high charge and are from the spray device through the Air jet moves forward and away from the surfaces of objects or items that are on a particle attracting potential are kept attracted. The air jet also preferably aids in the atomization of particles from the liquid ends in the passage where the liquid ends unite within a range of a few ten thousandths of an inch or less from the electrode. The spray device has none exposed or external metallic electrode, eliminating the possibility of touching the metallic electrode by an operator or the contacting of the electrode with surfaces of objects or objects that are suitable to absorb or to absorb the charged liquid particles is reduced take over. The internal arrangement of the electrode within the spray device increases that associated with the spray device Safety.

In accordance with the invention there is also provided an electrostatic spray apparatus which uses DC input voltages to the electrode of about 10 kV or less, and preferably about 7 kV or less and a low one Value of input currents of about 20 microamps or less, and preferably around 10 to x 5 microamps or less. The use of a low input voltage value and a low input current

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for the spray device allows a remarkable reduction in the size and weight of the power source, which is used to create the required field intensity to adequately target the liquid particles load. It is emphasized that the physical size of the energy source is such as to permit it to either inside the handle of the electrostatic spray device or on the operator if desired, can be arranged. Placing the power source within the spray device or on the operator increases portability, ease of handling, and availability of such a device remarkable. It is emphasized, however, that if the operating conditions and / or controls so require, the energy source of the spray device is arranged separately from the point at which the spraying is to be carried out can be.

The invention is explained below with reference to the drawing, for example.

Fig. 1 shows a scheraatic representation of the electrostatic Spray device according to the invention, within which the energy source is preferably arranged.

Fig. 2 is an enlarged side partial cross-sectional view of the forward end portion of a barrel; which is intended to be used with the spray device shown in FIG. 3 is an enlarged side view showing the

Shows the spray device according to FIG. 1, which has an electrode surrounding the sprayed material. 4 is an enlarged, partial cross-sectional side view of the front end of a Laufes showing a further embodiment of a spray device according to the invention. Fig. 1 shows an electrostatic spray device

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or an electrostatic spray gun according to the invention, generally indicated by the reference numeral 10 is. The spray gun 10 has a tubular device or barrel 11, a handle 12, which protrudes from the barrel 11 at an angle, and a trigger 17. The handle 12 can be a convenient battery powered DC power source (not shown) capable of is, up to about 10 kV to a metallic arranged within the barrel 11 of the spray gun 10 Supply electrode.

Leads 13 and 14 protrude from the lower end of the handle 12 of the spray gun 10. the Line 13 connects the gun to an air source 15> capable of delivering appropriate volumes of air to the spray gun 10 for releasing charged particles to deliver the liquid from the gun. The line 14 connects the spray gun 10 to a container 16, which contains a liquid material that is capable of atomizing, loading and applying onto the surface of an object or object is to be deposited. The liquid contained in the container 16 can, for example be a functional liquid that can be atomized, such as paint, coating material, Varnish, emulsions or the like, which, if necessary, with an appropriate conductive solvent or mixtures are dissolved from solvents that are chemically compatible with the liquid to be sprayed, Preferred solvents are ketones, alcohols, ethers and the like. However, it is emphasized that not all of the Solvents in the chemical groups mentioned above are chemically compatible with all of the liquid materials mentioned, but contain'all the groups of the solvents mentioned special solvents within each group, for example with color are compatible.

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The trigger 17, which is pivotably supported by the barrel 11 of the spray gun 10, controls the delivery of air and liquid to the gun and those to the metallic electrode in any one appropriate known manner applied voltage. Because this control mechanism is known from some May be shape, many of which are conventionally used, is for the purpose of illustrating the more clearly inventive part of the spray gun 10, this control mechanism has been omitted. Preferably they are exposed external components of the spray gun, such as the handle 12 and the trigger 17, which are made of conductive Materials such as are made of metal, electrically grounded or connected to earth.

FIG. 2 shows a side enlarged partial cross-sectional view of the front end of a barrel 11 according to FIG the invention. The barrel 11 has an essentially tubular jacket or a tubular housing 18, on which an inwardly protruding radial flange 19 is integrally formed at its foremost end is appropriate. The flange 19 provides an opening 20 through which a spray jet or sprayed material is propelled or expelled from electrostatically charged liquid particles (not shown). The case 18 is of any suitable conductive material such as metal or the like, or of any dielectric Material such as acetal resin and the like. In the event that the housing is made of a conductive Material is made, it is preferably earthed or connected to earth.

An outer tube or tube 25 and an inner tube 26 are arranged inside the barrel 11. The tubes 25 and 26 are preferably concentric and both of any suitable dielectric Made of material which is the highest

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associated with tensions loved by the energy source Stresses without breakthrough accompanying eiBii or can withstand breakage of the material A useful insulating material for the pipes 25 and 26 is acetal resin, epoxy, glass-filled epoxy, glass-filled nylon, or polyamide, and the like.

The tube 26 has an axially movable "dome-shaped" cap 27 at its foremost end. the Cap 27 is preferably made of a dielectric material such as acetal resin. The rear Surface 29 of cap 27 is arranged substantially parallel to and spaced from one end 32 of tube 26. The surface 29 and the end 32 are substantially to the exposed surface of the metallic Electrode / 31 arranged vertically. The end 32 of the tube 26 and the rear surface 29 of the cap 27 work together to form an annular discharge opening through which a stream of liquid exits. The liquid stream flows by applying sufficient pressure to the liquid in the container 16 in the area near the peripheral edge of the ring of the rear surface 29 of the cap 27 «Air moving through an annular passage 21 passing through forming the structural cooperative layer existing between tube 25 and tube 26, assists in reshaping the liquid into numerous liquid ends near the radial extent the rear surface 29 of the cap 27 and carries the atomized liquid from the ends through the opening forward through.

The surface 29 of the cap 27 is preferably axially movable in relation to the end 32, thereby creating an opening 30 to provide with a variable annular opening to thereby regulate or control the To help liquid flow from the liquid container 16 to the liquid ends. As in Fig. 2

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shown, the rear surface 29 of the cap 27 is assigned a larger diameter than the diameter of the adjacent tube 26 «The operation of the pistol with such dimensions or dimensions causes the periphery of the rear surface 29 of the cap 27 to create an annular edge 28 in which Near the liquid ends are formed.

It has been observed that the degree to which the rear surface 29 of the cap 27 radially extends beyond the end 32 of the tube 26, as well is significant in order to charge the liquid particles effectively. The optimal difference between such Dimensions depend, among other things, on the distribution of the jet of air to the atomization process and the resistance of the liquid to dust and load. For example, fluid levels in the range of about 1.6 megaohm-cm to about 13 megaohm-cra more charge, when the rear surface 29 of the cap 27 one by approximately 5 to 8 percent greater radial extension than that Has radial extension of the end 32 of the tube 26. The increase in the difference in the radial dimension of the rear surface 29 over the radial dimension of end 32 by about 10 percent or more appears to reduce the atomization characteristics Not dangerous to affect the liquid, however, the loading of the liquid particles is considerably reduced. It will emphasizes that the differences in radial extension change as the conductivity of the liquid changes differs from the above. For example, if the spec. .Resistance of the liquid is 1.5 megaohm-cm or less, the optimal charge of the liquid particles occurs when the radial extension of the rear surface 29 of the cap 27 and the radial extension of the end 32 of the

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Tube 26 are essentially the same.

Another important dimensional dependency is the distance between the edge 20 of the cap 27 and the electrode · 31 · The optimal distance for good charging of the liquid particles is around 0.025 to 0.063 cm (0.010 to 0.025 inches), and preferably by about 0.038 to 0.051 cm (0.015 to 0.020 inches). The enlarging this distance in excess of 0.063 cm (0.025 inch) reduces the amount of liquid particles released from the Run 11 delivered, carried cargo remarkable.

The annular electrode 31 having an axial length embedded in the tube 25 as shown in FIG. The leading edge of the electrode 31 is adjacent, but distant to the rear, to the opening 23 of the tube 25 arranged. The electrode '. 31 can be through a current limiting resistor 41 connected to the DC power source 22 of an appropriate ohmic resistor.

The ohmic tfert of the current limiting resistor changes depending on the magnitude of the voltage appearing at the output terminal of the power source. · For example, a DC voltage source that provides an output of approximately 4,000 V requires a current limiting resistor, which has an ohmic value of approximately 50 to 60 megohms to the short circuit current to about 70 to 80 microamps while using a source that has an output voltage of about 10 kV requires a current limiting resistor with an ohmic tfert of approximately 125 to 140 megohms in order to achieve the Limit short circuit current to approximately 70 to 80 microamps. The energy source 22 can be located within the spray gun 10 or on the operator of the spray gun. Optionally, the resistor 41 can be removed can be arranged, and the electrode 31 'can be connected to the power source 22 can be connected directly. The voltage supplied to the electrode 31 by the power source 22 is generated a high intensity electric field that is

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between the electrode 31 and the end of the annular Opening 30 extending liquid present, the. The annular edge 28 of the dome-shaped cap is adjacent.

The structure of the cap 27 is important. The construction of the cap 27 should be chosen so as to avoid the expulsion of the Liquid particles from the spray gun 10 to the surface of the object that is on one of the particles attractive potential is to be prevented or impaired. The construction of the dome-shaped cap 27 allows that the air-liquid particle mixture expands into an area of an increasing volume, to thereby align the liquid particles from the electrode 31 and the side walls of the tube 25 to help away. In the vicinity of the side walls of the tube 25 there appears sufficient turbulence and reduction of the Pressure to prevent the vast majority of particles from accumulating on them. Reducing the Air pressure near the side walls of tube 25 attracts most of the particles, if any, are deposited on these, away from the side walls before a dangerous build-up occurs on them.

The distance between electrode 31 and the edge of cap 27 is a fraction of an inch. The distance between electrode 31 and edge 28 is preferably on the order of about 0.051 cm (0.020 inches) or less. The distance between electrode 31 and the outer surface of tube 26 is preferably on the order of 0.076 cm (0.030 inches). An electrostatic field of sufficient strength to provide the liquid particles with a high charge-to-mass ratio extends to the ends of the liquid delivered by the stream near the edge 28. The electrostatic field is preferably generated by a direct current voltage of approximately 10 kV or less

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preferably around 3 to 7 kV are applied to the electrode 31, and the ends of the liquid flow are grounded by a head 2k which is connected to the liquid column in the hollow interior 3 ^ of the tube 26. The mean linear voltage gradient associated with a 0.051 cm (0.020 inch) distance between electrode / 31 at about 4,000 volts and the ends of the liquid at about earth potential is about 80 kV / cm (200 kV / inch). It can be seen that the liquid particles formed from the liquid ends near the edge 28 are formed in an area of very high electric field strength. Since the material forming the opening 30 is dielectric, the electric field lines tend to constrict or to be concentrated at the conductive liquid ends, whereby a very effective charge of the liquid particles is generated. The materials forming the opening 30 should be non-conductive, otherwise the charging efficiency of the device is substantially reduced.

The highly charged liquid particles that are moved out of the opening 23 through the opening 20, are attracted to the surfaces (not shown) of the objects or objects that are on one of the particles attractive potential, preferably earth or earth potential.

The aforementioned and the following dimensions and parameters have been mentioned to facilitate the operation of the to explain the barrel shown in Fig. 2 with the spray gun shown in Fig. 1. Such dimensions, dimensions and Parameters are not mentioned for the purpose of limitation, but only for explanation. It is emphasized that the dimensions of the components that make up the barrel over a considerable range with respect to one another can vary.

The opening 20, which is provided in the flange 19,

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is approximately 1.9 cm (0.75 inches) in diameter. The opening 23 formed in the tube 25 is spaced rearwardly from the opening 20 by approximately 0.9 cm (0.35 inches). The opening 23 is approximately 1.17 cm (0.46 inches) in diameter. The dome shaped cap 27 has a diameter of about 1.07 cm (0.42 inches) at the edge 28 and is tapered by about 30 °. The axial length of the cap 27 from the rear surface 29 to the foremost tip is approximately 0.9 cm (0.36 inches). That
Tube 26 has an outside diameter of about 1.02 cm (0.4 inch) and its end 32 is about 0.038 cm
(0.015 inch) from the rear surface 29 of the cap 27. Accordingly, it can be seen that the opening 30,
formed by the cooperative relationship between rear surface 29 and end 32 has an axial width of about 0.038 (0.015 inches). The axial width of the opening 30 can, if desired,
by rotating the threaded end 33 of the cap 27 into or out of a hub 35 which is cooperatively associated with the tube 26.

A test liquid consisting essentially of about 1,500 ml of boiled linseed oil, about 900 ml of VM&P (Varnish Makers & Painters) Naptha, about 900 ml
η - butyl alcohol and about 350 ml of methyl alcohol makes about 3.8 liters (one gallon) of a sprayable
Liquid with a resistivity of approximately 6.5 megaohms - cm. The test liquid comes out of the opening

30 with flow rates of about 150 to about 540 ml / min under measuring or calibration pressures of about 2.0 to 2.4 absolute atmospheres (20 p.p.sq.inch) flow calmly.

The DC input voltages applied to the electrode

31 are between 4 kV to 7 kV and preferably by 4 kV. The inlet air pressure to the sprayer 10 is approximately 3.4 atmospheres (35 p.p.sq.inches) at

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a flow rate of approximately 200 l / min (7 cub. ft. p. min.). The input current coming from the earth connection the voltage source to earth or to the earth point flows in the range of approximately 7.8 microamps at a test medium flow rate of approximately 150 ml / min up to about 14.0 microamps at one Test media flow rate of approximately 540 ml / min.

The current that flows between the surface just covered with charged liquid particles and the earth or the earth point is in a range of approximately 8.5 microamps at a test medium flow rate from about 150 ml / min up to about 32 microamps at a test medium flow rate of about 540 ml / min.

As a result of the fact that the liquid particles are in an area of concentrated high strength are formed, carry the liquid particles that are emitted or moved away by the barrel of the spray gun, a high charge-to-mass ratio, where the polarity of the charge carried by the particles corresponds to the polarity * the electrode 31 is opposite. It can be seen that a cloud of charged liquid particles is present in the space between the front part of the spray gun 10 and that located at a particle-attracting potential Area is created. Such a cloud creates a space charge effect, which when those charged are deposited Particles near the area to be coated help.

It is emphasized that the size of the individual liquid particles is determined by various factors, including iron, the flow rate of the liquid and air to the gun, the components of the liquid and the like mean particle size should be in the range of about 125 µm or less, and preferably about 50 µm or less

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to obtain quality color coatings.

The barrel 11 shown in Fig. 2 can be modified according to the invention to the extent that it is an appropriate one Has means for dividing or splitting the air jet into two separate and closed air flows, wherein the one of the air currents is used to keep the surface of the electrode 31 clear to the required To achieve cleaning action, and the other the air currents is adjustable so that it more or less distribution of the atomization of the particles from the Ends of the liquid flow at the edge 28 of the rear surface 29 of the cap 27 creates.

The charged spray particles that enter the space between the spray device 10 and the surface of an object are moved forward, which is on one of the spray attracting potential, carry a polarity that of the The polarity of the electrode 31 is opposite and exert a space charge effect, creating an electrostatic Field is generated that extends to the surface of the object and that during the electrostatic deposition or depositing the charged particles in close proximity to the surface of such an object helps. If desired, the electrostatic settling effect can be achieved by providing the spray device with a das Sprayed surrounding electrode 40, as shown in FIG. 3, are enlarged, which are at a settling potential in Relation to the surface of the object located on earth or on earth potential is kept. Such a that Sprayed surrounding electrode 40 acts to reduce the inclination of the spray of the charged coating material particles to reduce expanding when exiting the orifice of the spray device, thereby controlling the control via the resulting spray oyster on the surface of the object to facilitate. In addition, the electrode 40 surrounding the spray causes the electrode 31 from

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the high potential of the charged; / oil of the liquid particles is shielded, which is one of the polarity of the Electrode 31 have opposite polarity. The spray-repellent electrode is made of any suitable one metallic material, such as steel or the like, or made of dielectric material, v; o the surface charge on this is induced by the spray cloud.

4 shows a further embodiment according to the invention. The barrel 11 has a substantially tubular housing 18 or a tubular jacket. The housing 18 has at its front End a radial flange. The flange 19 forms an opening 20 through which a spray jet (not shown) Electrically charged liquid particles from the spray gun 10 is emitted or dispensed.

A substantially concentric outer tube 51 and an inner tube 52 are within the housing 18 and are components of the barrel 11. The tube 51 and the tube 52 are preferably connected to the housing 18 formed coaxially and made of any suitable dielectric material capable of the to withstand stresses associated with high stresses without breakthrough or breakage of the material. Appropriate dielectric materials include acetal resin, epoxy, glass filled Epoxy and glass-filled nylon or polyamide. The tube 51 has a one-piece, inwardly protruding A fixed size flange 58 having a substantially circular particle emitting aperture 53 having.

The tube 52 has a reduced outer diameter 60 at its end. The reduced outer diameter 60 of tube 52 and flange 58 of tube 51 cooperate to provide an annular opening 54 create from which an air jet emerges or flows out. The annular opening 54 is with the air source

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connected by an annular passage 62, which by the structural cooperation between the tubes 51 and 52 is created. The tube 52 has a passage 55, which ends in an opening 56. One under low Pressurized fluid flow exits port 56 while the spray gun 10 is working. The coating material, flowing through passage 55 of tube 52 is preferably electrically grounded or through a head 63 connected to ground which is in contact with the liquid in the passage 55 but backwards in a short distance from the opening 56 is arranged.

An annular metallic electrode 57 of greater axial length is embedded in the tube 51 and spaced rearwardly from the opening 53 as shown in FIG. The electrode 57 can be made of any convenient conductive material such as alloys or copper. The electrode 57 is preferably connected to the energy source 22 in the spray device 10 or on the operator through a current limiting resistor 61 of an appropriate ohmic value. It is emphasized that the electrode 57 is arranged within the tube 51 and thus within the barrel 11 so that it cannot come into contact with any object to be coated and not with an operator, therefore the current limiting resistor can be omitted. However, good safety practice may dictate the use of a current limiting resistor of the appropriate ohmic value connected in series between electrode 57 and the output terminal of power source 22.

The voltage applied to the annular electrode 57 by the power source 22 across the current limiting resistor 61, generates a high intensity electrostatic field that extends from the annular air discharge port 54 to the grounded or grounded end of the liquid at opening 56.

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Delivering pressurized air to passage 62 at flow rates up to about 200 l / min (7 cfpm,) and at flow pressures up to about 4.4 absolute atmospheres (50 ppsq.i.) and flowing the liquid The opening 56 at a flow rate of up to about 280 ml / min under a ^{1 <J} eßpressure of up to about absolute atmospheres (5 ppsq.i.) allows a spray jet of liquid particles with a high electrostatic charge to exit from the opening 23. The air flow flowing in the annular passage 62 and between the annular electrode 57 and the part 60 of the tube 52 causes the liquid flow, the normal cross-section of which is that of the opening 56, to expand and transform into discrete end portions at which the field is concentrated . In addition, this air flow is used to direct the liquid particles away from the inner wall of the tube 51 and from the electrode 57. The jet of air contributes to the atomization of the liquid particles from the end portions of the liquid emerging from the opening 56. ICs are noted that the airflow passes through an enlarged area 64 and then through a reduced area 65 before exiting the annular opening 54. This allows the air flow to accelerate in its velocity immediately before expanding into the area adjacent to the opening 26, thereby ensuring that there is a high velocity air flow between the outer edge of the opening 56 and the electrode 57.

The diameter of the opening 56 of the tube 52 and the The distance between the electrode 57 and the outer surface 60 of the tube 52 are each a small fraction of one Centimeters (inch). For example, the separation distance between the electrode 57 and the outer surface 60 is of tube 52 on the order of approximately

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0.09 cm (0.035 inch). The diameter of the opening 56 is on the order of about 0.15 cm (0.06 inch). The axial extension of the electrode 57 is of the order of magnitude 0.64 cm (0.25 inch).

The electrode 57 is connected to a source of direct current voltage, which is about 10 kV or less and preferably by 3 kV to 7 kV at its output terminal. Assuming that a separation distance of approximately 0.177 cm (0.05 inch) between the outer edge of the portion surrounding opening 56 and the electrode is present and a voltage of approximately 4 kV is impressed on the electrode 57, the mean voltage gradient is across the annular opening 5 ^ approximately 29 kV / cm (73 kV / inch). It is noted that at the liquid ends a high intensity electrostatic field is present. As a result of the fact that the liquid particles Formed in an area of high field strength, the liquid particles carry the spray gun 10, a high charge-to-mass ratio and a charge of opposite polarity to the polarity of the electrode 57.

The aforementioned and following dimensions and parameters are for the purpose of explaining the operation of the barrel of the spray gun shown in FIG. 4 in FIG. Such dimensions and parameters are not intended to Purposes of limitation, but for illustrative purposes only. The dimensions of the components of the Runs can vary over a considerable range in relation to one another.

The opening 53 is approximately 0.43 cm (0.17 inch) in diameter. The opening 56 is rearward in one Distance of about 0.36 cm (0.14 inch) from the foremost extension of electrode 57 and about 0.46 cm (0.18 inch) arranged from the foremost extent of the opening 53. The opening 56 is approximately 0.152 cm in diameter

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(0.06 inch). The annular opening 54 has a radial extension of about 0.089 cm (0.035 inch).

A test liquid or medium consisting essentially of approximately 1,500 ml of boiled linseed oil, approximately 900 ml from Wl & P (Varnish Makers & Painters) Naptha, about 900 ml of n-butyl alcohol, about 300 ml of methyl alcohol and about 30 ml of diethylamine, gives about 3.81 (1 gallon) of the liquid. The resistivity of the test agent is approximately 1.6 kegaohms / cm. The test agent becomes out of the opening 56 at a flow velocity from about 50 to 280 ml / min at a pressure of about 1.07 to 1.34 absolute atmospheres (1 to 5 p.p.sq.i «) let flow.

The inlet air pressure of the air jet to the barrel 11 is approximately 3 »0 absolute atmospheres (30 p.p.sq.i,) at a flow rate of approximately 85 l / min (3 c.f.p.m,). The DC input voltage, supplied to electrode 57 is approximately 4 kV, the input current going into the circuit appears from the earth connection of the voltage source to earth or to the earth point, moves in the range of approximately 3.4 microamps at a test medium flow rate of about 50 ml / min up to about 8.2 microamps at a test media flow rate of approximately 280 ml / min. The liquid particle flow or output current between the surface on which the liquid particles are knocked down, and the earth or the earth point flows, moves by approximately 2.8 microamps at a test medium flow rate of about 50 ml / min up to about 7.6 microamps at a test medium flow rate of 280 ml / min,

Increase the air pressure applied to the barrel shown in Figure 4 to approximately 4.4 atmospheres absolute (50 p.p.s.i.) results in an input current that is derived from the earth potential of the voltage source to earth or to

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the earth point, which is in the range of about 3 Kikroamps at a test medium flow rate of approximately 50 ml / min up to about 3.6 microamps at one Test average flow rate of approximately 260 ml / min emotional. The liquid particle stream or output stream, that between the surface on which the liquid particles are just being deposited and the earth or the Earth Point flows is in the range of approximately 2.5 microamps at a test mean flow rate from about 50 ml / min up to about 13.5 microamps at a test medium flow rate of about 280 ml / min.

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Claims (12)

Claims Low voltage electrostatic spray gun characterized by a barrel (11) having a passage (21) which ends in an opening (23), a dielectric means on / ironing device (25-27) for shaping liquid into a stream or flow comprising a plurality of liquid particles supplying ends or end portions in the passage (21) which are iia spaced from the opening (23) are arranged, an electrode device (31) delimited in the passage (21) and arranged in the immediate vicinity of the liquid ends, which together with the liquid flow with a device for generating a potential difference between the electrode device (31) and the liquid ends and an electric field between them with a high potential gradient at the liquid ends, the dielectric means at Concentrating the electric field at the liquid ends to make the liquid particles electrostatic to load, help, and thereby means in the barrel (11) for aligning one in the atomization of Liquid particles helping air jet along the passage (21) and to carry away the charged from the Liquid sends formed liquid particles from the side walls of the passage (21) and the electrode means (31). 2. Spray device according to claim 1, characterized in that the liquid is in the form of a column is arranged, which has a substantially perpendicular axis to the electrode device (31). 3. Spray gun according to one of claims 1 or 2, characterized in that the device (25-27) to form the stream or flow into a column 209836/085 7 a cap (27) spaced from the open end (32) of a tube (26) and forms an opening (30) from which the liquid flow is discharged at an angle to the electrode (31) is, and that the cap (27) has a radial extension which is slightly larger than the radial extension of the tube (26) is. 4. Spray gun according to one of claims 1 to 3, characterized in that the part of the passage (21), which is located in front of the cap (27) and which extends away from the cap (27), an expanding Has volume. 5. Spray gun according to one of claims 1 to 5, characterized in that the electrode device (31) is annular and that the means (25-27) for shaping the liquid into a column is a column having an axis substantially concentric to the axis of the annular electrode (31). 6. Electrostatic low-voltage spray device, characterized by.eine barrel (11) ;. through a passage (21) in the barrel (11) which ends in an opening (23) at the foremost end of the barrel (11), a device (25-27) for generating a flow of liquid with liquid particle-forming end portions in the Passage (21) behind the opening (23), electrode devices (31) in the passage (21), behind the opening (23) and in close proximity to the liquid end parts, one with the electrode device- (31) and Means connected to the flow of liquid for generating an electric field with a high gradient at the end parts of the liquid with the electric field concentrated at the end parts, and by means for directing a jet of air or a flow of air through the passage (21) between the electrode device (31) and the liquid end 209836/0857 Teilon for the electrostatic emission of charged liquid particles generally away from the side walls (2.5 »26) of the passage (21) and out of the opening (23) of the front end of the barrel (11). 7. Apparatus according to claim 6, characterized in that the device for generating the liquid flow made of a dielectric material sv / ecks concentration of the electric field at the liquid ends is made. 8. Device according to one of claims 6 or 7 _f, characterized in that the voltage applied to the electrode device (31) has a value which avoids corona discharge. 9. A method for producing a cloud of electrostatically charged liquid particles, characterized by creating a flow of liquid having a plurality of end portions in a passageway and spaced apart from one end of the passage, by creating an electric field with a high potential gradient the liquid end portions creating a potential difference between an electrode means in the passage and behind the opening and the liquid end parts, by forming charged liquid particles from the liquid end parts, by directing a jet of air through the passage, by carrying away the charged ones from the liquid ends liquid coating material particles formed from the sidewalls of the passageway and the electrode means away and out of the open end of the passageway and electrostatically by forming a cloud charged liquid particles. 10. The method according to claim 9, characterized in that that the cloud of charged liquid particles has a different polarity from the electrode device Has polarity. 11, method according to one of claims 9 or 10, 209836/0857 characterized in that the liquid is a paint having a resistivity of about 15 megaohm-cm or less. 12. The method according to any one of claims 9 to 11, characterized in that the air flow during atomization the liquid particles from the liquid parts helps. 209836/0857 Blank page