US3421693A - Pneumatic atomizer for spraying liquids - Google Patents

Description

Jan. 14, 1969 R. P. FRASER PNEUMATIC momma FOR srnume man-ms Sheet Filed Sept. 25, 1964 Jan. 14, 1969 R. P. FRASER 3,421, -.'93

PNEUMATIC ATOMIZER FOR SPRAYING LIQUIDS Filed Sept. 25, 1964 Sheet 2 of 4 H910 51b 37a 31a Jan. 14, 1969 R. P. FRASER 3,421,693

PNEUMATIC ATOMIZER FOR SPRAYING LIQUIDS Filed Sept. 25, 1964 Sheet 3 of 4 I7 5 x 15 2 I3b j V l 11- Jan. 11, 1969 R. P. FRASER 3,421,693

PNEUMATIC ATOMIZER FOR SPRAYING LIQUIDS Filed Sept. 25, 1964 v Sheet 4 of 1 United States Patent 3,421,693 PNEUMATIC ATOMIZER FOR SPRAYING LIQUIDS Reginald Percy Fraser, Surrey, England, assignor to Societe Anonyme de Machines Electrostatiques, Paris, France, a corporation of France Filed Sept. 25, 1964, Ser. No. 399,322 Claims priority, application Great Britain, Sept. 27, 1963,

38,172/63 US. Cl. 239-15 5 Claims Int. Cl. B05b 5/02,- B05b 7/04; B05b 1/26 ABSTRACT OF THE DISCLOSURE The present invention relates to a pneumatic atomizer for spraying liquids, which is particularly intended for the spray-coating of objects with finely divided liquid particles, for example with paint.

According to the present invention, a pneumatic atomizer for spraying liquids comprises a chamber to which a liquid to be sprayed and a gas are fed, each through a separate inlet or inlets, at such a velocity and in such a manner that they impact to at least partially atomize the liquid, and at least one outlet from the chamber through which passes the atomized liquid particles entrained in a gas stream, and means for imparting an electrostatic charge to said particles.

The liquid and gas may be fed into the chamber as o-p posed jets or streams, or the jets or streams may be at an angle to each other.

The chamber may be of various forms, for example cylindrical, having the liquids and gas fed through separate inlets in its side walls and having the outlet from the chamber at one end. Alternatively the chamber may be of annular form and provided in one of its side walls with one or more inlets for the liquid to be sprayed and in its other side wall with one or more inlets for the gas. Preferably a plurality of inlets, eg, for the liquid to be sprayed, may be provided in the inner wall of the annular chamber and a number of inlets, e.g. for the gas may be provided in the outer wall of the chamber, an inlet for the gas being arranged opposite each inlet for the liquid. Further gas inlets, not necessarily opposed to the liquid inlets, may also be provided. It is of course possible to feed the gas to the inlets in the inner wall and the liquid to the inlets in the outer wall.

The outlet or ioutlets from the chamber may comprise one or more orifices, each in the form of a narrow passage which communicates directly with the chamber. Alternatively the outlet or outlets from the chamber may comprise one or more passages which lead to a further chamber defining or terminating in an outlet nozzle orifice.

The electrostatic charge may be applied to the particles to be sprayed by applying a high DC. potential to the chamber or alternatively by applying this potential to the passage or passages through which the liquid to be sprayed is fed to the chamber, whereby this liquid is charged before it enters the chamber and is atomized. Yet again the charge maybe applied to the atomized particles after they leave the chamber.

In practice, the gas will generally be air although the "ice use of other gases is of course within the scope of the invention.

In order that the invention may be more fully understood, reference will now be made to the accompanying drawings, in which:

FIGURES 1 to 7 are simplified cross-sectional diagrams of different embodiments of spraying apparatus according to this invention, and

FIGURES 8 to 13 are cross-sectional views through practical embodiments of spraying heads according to the invention.

Referring to FIGURE 1, the spraying apparatus comprises a body 1, made of insulating material, in which is formed a generally cylindrical chamber 2. Diametrically opposite passages 3 and 4 are provided which provide inlets intoopposite sides of the chamber. A gas, for example, air is fed through the passage 3 at high velocity and a liquid to be sprayed, for example paint, is fed through the passage 4. The gas and liquid enter the chamber as opposed jets or streams and are impacted or mixed together, whereby the liquid is atomized and then passes out of the chamber entrained in a gas stream through the outlet orifice 5. The atomized liquid particles are charged electrostatically by means of a high D.C. potential applied to the chamber through a conductor 6 connected to the wall of the chamber opposite the outlet 5. This potential initially charges the thin liquid coating which forms on the wall of the chamber and then the atomized particles.

FIGURE 2 shows a further embodiment wherein the outlet 5 from the chamber 2 leads to a further chamber 7 which in turn leads to an outlet orifice 8 arranged in line with the outlet 5. The further chamber 7 enables further mixing of the gas and liquid and further atomization to take place. The embodiment of FIGURE 3 differs from the embodiment of FIGURE 2. in that the outlet orifice 8 is disposed in the side wall of the chamber 7 at right angles to outlet 5 instead of being axially aligned with the outlet 5, as in the embodiment of FIGURE 2.

In the embodiment of FIGURE 4, the outlet from the chamber 2 comprises a passage 5a which meets a crosspassage 8a forming the outlet orifice. These passages meet at an intermediate point along their length and the blind end portions 512 and 8b form vibration cavities improving the: atomization of the particles.

FIGURE 5 shows a further embodiment wherein the supply passage 4 for the liquid to be sprayed is at right angles to the passage 3 feeding the gas to the chamber 2 and the outlet orifice 5 is axially aligned with the passage 4. In addition the high voltage conductor 6 by means of which the electrostatic charge is applied to the liquid particles extends through the passage 4.

FIGURE 6 shows an embodiment wherein the outlet from the chamber 2 comprises three passages 5a, 5b, 5c, inclined at an angle to each other. The high voltage conductor 6 extends through the passage 4.

In all of the above embodiments it will be understood that more than one inlet passage to the chamber may be provided both for the gas and for the liquid to be sprayed.

FIGURE 7 shows an embodiment having a chamber 2a of annular form. The passage 4 for the liquid to be sprayed divides into two branches 4a which enter the inner wall of the annular chamber 2a at diametrically opposite points. Two passages 3 for the gas are provided in the outer wall of the annular chamber opposite to the passages 4 for the liquid. If desired more than two radially arranged inlets 4a for the liquid may be provided with a corresponding number of inlets 3 for the gas arranged opposite them. Additional gas inlets may also be provided, so that the number of gas inlets is greater than the number of liquid inlets. The conductor 6 for electrostatically charging the liquid to be sprayed is connected to the wall of the passage 4 upstream of the chamber. A plurality of outlet passages 5 are provided from the annular chamber, and are disposed at regular intervals on a circular path so as to communicate with the upper wall of the chamber.

FIGURE 8 shows a practical embodiment of spray head comprising a body portion 10 on the upper end of which is secured a retaining cap 11 by means of the screwthreaded connection 12 between these two parts. The body portion is hollow and contains a stem 13 which has an enlarged head portion 13a whose periphery seats on a rebate 14 at the upper end of the body portion. The enlarged head portion 13a is provided with an annular chamber 15 having four equally spaced inlet passages 16 in its inner Wall for the liquid to be sprayed, and four equally spaced inlet passages 17 in its outer wall for the inlet of gas. Each passage 16 is arranged opposite to a passage 17. The passages 16 communicate with a central bore 18 extending axially along the stem and through which the liquid to be sprayed passes. The passages 17 communicate with axially directed holes 19 which in turn communicate with the space 20 between the interior of the body 10 and the outside of the stem 13. The gas is supplied to this space 20, and hence to the chamber 15 through the holes 19 and passages 17, by means of the inlet connection 21. On top of the enlarged head portion 13:: rests a disc member 22 provided with six equally spaced passages 23 therethrough constituting the outlet passages from the annular chamber. A sealing member 24 such as an O ring may be interposed between the disc member 22 and the outer part 13b of the enlarged head of the stem. This outer part 13b is of reduced height to facilitate the formation-and the cleaning of the passages 17. The disc member 22 is surmounted by a nozzle member 25 provided with an outlet nozzle orifice 26 in the form of a slot and containing a further chamber 27 with which the outlet passages 23 communicate. The various parts are held assembled by means of the retaining cap 11. The stem 13, disc member 22 and nozzle member 25 can be made of insulating materials or ceramic. The body 10 and retaining cap 11 are also made of an insulating material.

The central bore 18 is provided with a conducting lining formed by a metal tube 28 to which the high DC. potential is applied through the Wire 6 to electrostatically charge the coating material.

In operation the liquid and gas to be sprayed are fed respectively through the passages 16 and 17 and are mixed, atomized and electrostatically charged in the chamber 15 and then pass through the outlet passages 23 into the further chamber 27 where further atomization takes place and from thence through the outlet nozzle slot 26 as a divergent or bats wing shape of spray.

Referring now to FIGURE 9, wherein corresponding parts bear the same references as in FIGURE 8, the spray head again comprises a body portion 10, a retaining cap 11, and a central stem 13 having an enlarged head portion 13a in which an annular chamber 15 is formed and provided with passages 16 and 17 respectively for the application of the liquid to be sprayed and the gas to the chamber, as in the previous embodiment. However in this embodiment, instead of providing a disc member 22, a nozzle member 30 is positioned on top of the enlarged head 13a of the stern, and is provided with a plurality of outlet orifices in the form of narrow passageways 31 which are inclined outwardly with respect to the axis of the stem 13 and through which atomized liquid to be sprayed passes directly from the annular chamber 15. Six such outlet orifices 31 may be provided spaced equally from each other. Each orifice may have a diameter of about 0.022 inch and be inclined at about 19 with respect to the longitudinal axis of the spray head. In an alternative embodiment, shown in FIGURE 10, the nozzle member 30 is provided with two rings of outlet orifices,

the inner ring 31a comprising three or more equally spaced holes inclined at 10 to the axis of the spray head, whilst the outer ring 31b comprises three or more equally spaced holes inclined at 35 to the axis of the spray head. The holes may have a diameter of about 0.018 inch.

Referring now to the embodiment of FIGURE 11, wherein corresponding parts have again been given the same reference numerals as in the embodiments of FIG- URES 8 and 9, a domed nozzle member 32 is mounted on top of the enlarged head 13a of the stem and contains an annular chamber 15a which, together with the annular chamber 15 in the enlarged head 13a of the stem, forms an overall annular chamber of much greater axial extent. A plurality of inclined outlet orifices in the form of narrow passages 33 are provided around the tip of the member 32 which projects forwardly from the retaining cap 11 of the spray head. Sixteen such outlet orifices may be provided, equally spaced around the member 32, each having a diameter of about 0.02 inch and being inclined at 60 with respect to the longitudinal axis of the spray head.

FIGURE 12 shows a further embodiment of spraying head which is of basically similar form to that shown in FIGURE 11 and wherein corresponding parts have the same reference numerals. In this embodiment however, the domed nozzle member 32 is also provided with a central passage 34 which has a larger diameter than the narrow passages 33. A valve 35 with a head 37 is slidably arranged within the central bores 18 and 18a through which passes the liquid to be sprayed. The end 36 of this valve adjacent the nozzle member 32 is tapered to form a pintle and fits within the central passage 34 to close it. The pintle valve is made of metal and has the high DC. potential applied to it through the wire 6 for the purpose of electrostatically charging the coating material.

The pintle valve is movable axially from the position shown, in which the passage 34 is closed by the end 36, to positions in which the pintle end 36 is withdrawn from the passage 34 and the entrance to the passage is open to some extent. The annular outlet 38 from the passage 18 closes as the pintle end 36 is withdrawn from the passage 34.

When in the position shown in the drawings in which the central passage 34 is closed by the end 36 of the pintle and the outlet 38 is fully open, the liquid pressure in the chamber 18a is higher than the pressure in the annular chamber 15 and the device operates in the same manner as the embodiment of FIGURE 11 to spray the liquid through the passages 33.

As the end of the pintle valve is retracted from the central passage 34 to a position in which both the central passage and the annular outlet 38 are open, the supply of liquid through the outlet 38 is restricted, and the air pressure in passages 19 and through holes 17 becomes greater than the pressure of the liquid in chamber 18a. Thus the atomised liquid ceases to flow from passages 33 and atomised liquid passes from the chamber 18a around the pintle through the central passage 34 and air only issues from the outer passages 33. The atomised liquid in the passage 34 is electrostatically charged by the pointed end 36 of the pintle.

FIGURE 13 shows a further embodiment wherein the charging of the particles is accomplished by a corona dis charge from an annular electrode adjacent the passages 33. The construction is somewhat similar to the embodiment of FIGURE 12 except that the central passage 34 is omitted from the nozzle member 32 and the pintle is removed from the valve 35. In this embodiment the stem 13 is made of metal and the nozzle member 32 is surrounded by a metal sleeve 39, having a sharp edge 40 projecting from the surface of the nozzle member and which is in contact with the stem 13. The latter is in turn connected to a source of DC. charging potential by the wire 6 so that the liquid issuing from the passages 33 is charged from the edge 40. The amount of liquid which is mixed with the air for spraying from the nozzle through the passages 33 is controlled by the pressures and respective diameters of the liquid holes 16 and the air holes 17, and the liquid can be shut off completely by the valve 35.

It will be appreciated that the particular number and arrangement of passages and outlet orifices shown in the various embodiments are given by way of example only and that many other arrangements are possible. The number of outlet orifices and the pattern in which they are arranged is important for determining the coverage of the outlet spray from the spray head as well as the spray pattern.

In all of the embodiments of FIGURES 8 to 13 the diameter of the enlarged head portion 13a may lie between 0.5 to 2 inches.

The volumetric proportion of the gas with respect to the liquid to be sprayed may be about 60 to 1 in the final spray in the embodiments of FIGURES 8 to 11 but can be variable in the embodiments of FIGURES l2 and 13. The gas velocity fed to the mixing chamber may be between 200 and 1000 feet per second and the liquid velocity of the order of 100 feet per second. The velocity of the spray issuing from the nozzle device may also be between 200 and 1000 feet per second depending upon the respective pressure drops to the mixing chamber and from the mixing chamber to the atmosphere. The device functions as an internal mixing atomizer and up to 90% atomization of the liquid material can occur within the mixing chamber or chambers. A thin liquid coating or film is formed on the wall of the chamber or chambers and on the outlet orifices. This coating or film is atomized by electrostatic force at the outlet edges of the holes or passages from which the spray emerges.

The high DC. potential may be produced by means of an electrostatic generator, as is manufactured by Societe Anonyme de Machines Electrostatiques, 21 Rue Jean- Mace, Grenoble, France, for example, and may produce an output of around 100 kilovolts.

It is however possible to achieve atomization by means of the spraying devices according to the invention without the use of electrostatic force and therefore the application of a DC. potential to the spray head is not essential. i

The constructions of spray head herein described are easy to manufacture and assemble. They can also readily be disassembled for cleaning purposes.

It will be understod that the embodiments herein described and the dimensions are only given byway of example. The ratio of the dimensions of the outlet orifices to the dimensions of the passages entering the internal mixing chamber or chambers are such as to produce the required pressure drops internally within the mixing chamber and from inside to atmosphere.

I claim:

1. In apparatus for spraying liquids, in combination, means defining a substantially enclosed chamber having a cylindrical portion and a pair of end walls, said chamber including a plurality of oppositely disposed inlet orifices in said cylindrical portion and an outlet orifice in one of said end walls, first conduit means for introducing liquid into said chamber through one of said inlet orifices, second conduit means for introducing atomizing gas under controlled velocity and pressure into said chamber through another of said inlet orifices, said gas interacting with the liquid within said chamber to at least partially atomize said liquid during the time the liquid is in said chamber, and nozzle means communicating with the outlet orifice of said chamber for receiving the atomized liquid particles entrained in a stream of said gas and for discharging the same from the apparatus.

2. Apparatus for spraying liquids comprising, in combination, means defining a substantially enclosed chamber having a plurality of inlet orifices and an outlet orifice, first conduit means for introducing liquid into said chamber through one of said inlet orifices, second conduit means for introducing atomizing gas under controlled velocity and pressure into said chamber through another of said inlet orifices, said gas interacting with the liquid within said chamber to at least partially atomize said liquid during the time the liquid is in said chamber, nozzle means communicating with the outlet orifice of said chamber for receiving the atomized liquid particles entrained in a stream of said gas and for discharging the same from the apparatus, and means for imparting an electrostatic charge to said liquid, said inlet orifices being positioned in oppositely disposed relationship with each other, said liquid and said gas being introduced into said chamber in the form of opposed jets of fluid.

3. Atomizing apparatus for spraying liquids comprising, in combination, means defining a substantially enclosed annular chamber having a pair of cylindrical side walls and a pair of end walls, said chamber including a plurality of inlet orifices respectively disposed in said side walls and an outlet orifice in one of said end walls, first conduit means for introducing liquid into said chamber through one of said inlet orifices, second conduit means for introducing atomizing gas under controlled velocity and pressure into said chamber through another of said inlet orifices, said gas interacting with the liquid within said chamber to at least partially atomize said liquid during the time the liquid is in said chamber, nozzle means communicating with the outlet orifice of said chamber for receiving the atomized liquid particles entrained in a stream of said gas and for discharging the same from apparatus, and means for imparting an electrostatic charge to said liquid prior to its discharge from said nozzle means, said one inlet orifice being disposed in one of said cylindrical side walls and said another inlet orifice is disposed in the other cylindrical side wall in opposed relationship with said one inlet orifice, said liquid and said gas being introduced into said chamber in the form of opposed jets of fluid.

4. Apparatus for spraying liquids comprising, in combination, means defining a substantially enclosed mixing chamber having a plurality of inlet orifices and an outlet orifice, first conduit means for introducing liquid into said mixing chamber through one of said inlet orifices, second conduit means for introducing atomizing gas under controlled velocity and pressure into said mixing chamber through another of said inlet orifices, said gas interacting with the liquid within said mixing chamber to at least partially atomize said liquid during the time the liquid is in said mixing chamber, means defining an outlet chamber having a dischar-ge orifice, passage means interconnecting the outlet orifice of said mixing chamber with said outlet chamber for leading the atomized liquid particles thereto, said outlet chamber being enlarged with respect to said passage means, nozzle means communicating with the discharge orifice of said outlet chamber for receiving the atomized liquid particles entrained in a stream of said gas and for discharging the same from the apparatus, and means for imparting an electrostatic charge to said liquid.

5. Electrostatic apparatus for spraying liquids comprising, in combination, means including a stem member having an enlarged head portion, said head portion defining an annular chamber having a plurality of inlet orifices, plate means mounted on said head portion for substantially enclosing said chamber, said plate means including an outlet orifice communicating with said chamber, first conduit means for introducing liquid into said chamber through one of said inlet orifices, second conduit means for introducing atomizing gas under controlled velocity and pressure into said chamber through another of said inlet orifices, said gas interacting with the liquid within said chamber to at least partially atomize said liquid during the time the liquid is in said chamber, nozzle means communicating with said outlet orifice for receiving the atomized liquid particles entrained in a stream of said gas and for discharging the same from the apparatus, and means for imparting an electrostatic 7 8 charge to said liquid prior to its discharge from said 3,131,131 4/1964 Wehner 23915 nozzle means. 3,284,009 11/ 19-66 Stull et a1. 239427 References Cited v UNITED STATES PATENTS EVERETT W. KIRBY, Przmary' Exammer. 1,688,827 10/1928 Nelson 239-427 5 US. Cl. X.R. 2,887,275 5/1959 Dixon et a1 239427 239-434, 545 3,129,112 4/1964 Marvin 239-15

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