US3408985A - Electrostatic spray coating apparatus - Google Patents

Description

Nov. 5, 1968 .1. SEDLACSIK, JR 3,408,935

ELECTROSTATIC SPRAY COATING APPARATUS Filed Nov. 7, 1966 5 Sheets-Sheet l FIG.

INVENTOR. uomv 5E0; 4651K, we,

ATTORNEY Nov. 5, 1968 J. SEDLACSIK, JR

ELECTROSTATIC SPRAY COATING APPARATUS 3 Sheets-Sheet 2 Filed Nov. 7, 1966 Nov. 5, 1968 J. SEDLACSIK, JR 3,403,935

ELECTROSTATIC SPRAY COATING APPARATUS Filed Nov. 7, 1966 T5 Sheets-Sheet 5 w WW F I G I I. INVENTOR.

4T'TORNE ,uoliN ssomcsm, JR.

United States Patent 3,408,985 ELECTROSTATIC SPRAY COATING APPARATUS John Sedlacsik, Jr., Garfield, N.J., assignor to Interplanetary Research & Development Corp., Garfield, N..I., a corporation of New Jersey Filed Nov. 7, 1966, Ser. No. 592,560 9 Claims. (Cl. 118629) ABSTRACT OF THE DISCLOSURE An air spray gun, for use in an electrostatic spray coating system, wherein liquid coating material is fed through the body of the gun to a forward atomizing area and atomizing air under pressure is also fed through the gun body to atomize the coating material at said atomizing area. The atomized coating material is directed to leave the front of the gun in a substantially radical direction and a further supply of air under pressure is fed through the body of the gun and directed to form a shroud about the atomized spray exitingfrom the gun to control the pattern thereof. Internal vanes within the gun body impart a swirling motion to the atomizing air and shroud air to decrease the forward velocity thereof.

This invention relates to improvements in spray guns of the type used to spray paint or other coating materials, and more particularly to a spray gun employing air under pressure for atomizing the coating material, which gun is especially adapted for use in an electrostatic spray coating system.

Electrostatic spray coating systems are presently in wide use for the mass production coating of various articles with a layer of paint or other coating material. In these systems an electrostatic field is employed to charge an atomize spray of coating material and deposit the spray particles on the articles with little loss or waste of the coating material.

The earlier types of electrostatic spray coating systems incorporated air atomizer spray guns which directed a spray of coating material into the electrostatic field. Such systems were subject to disadvantages inherent in the operation of the guns themselves, since conventionally the atomizing air is in the form of a high velocity stream which is directed in a forward direction to impinge upon and atomize the coating material, so that the atomized spray is propelled forwardly from the gun with considerable velocity. As a result, a substantial portion of the paint spray would be propelled rapidly through the field without being attracted to the article to be coated. In addition, the size of the spray pattern produced by guns of this type is relatively small, so that an array of guns is required to coat large objects.

' Rotary centrifugal atomizers and systems employing electrostatic forces to atomize liquids have more recently been employed, these systems producing wider spray patterns, and creating atomized sprays without objectionable forward velocity. However, such atomizer means are expensive, and include bearings and other moving parts which require costly maintenance and interruption of the coating operation. In addition, systems depending upon atomization by electrostatic forces are incapable of handling certain types of coating materials, such as waterbase paints, and frequently require touch up operations to coat recesses and depressed areas in the articles to be coated.

Accordingly, an object of the present invention isto provide a spray gun for use in an electrostatic paint spraying system in which the paint is atomized by air thereby to provide a gun which may be utilized in conjunction with the spraying of any type of paint.

Another object of the present invention is to provide a "ice spray gun in which the pattern produced by the paint issuing therefrom is controlled by a shroud of air, thereby to provide a wider paint pattern than can be obtained from spray guns of the electrostatic atomization type.

A further object of the present invention is to provide a spray gun for use in an electrostatic paint spraying system which is more economical to produce and more versatile in its use than spray guns of the electrostatic atomization variety. 1

In furtherance of the above objects, the present invention comprises a spray head which is provided with a paint passage connected with a paint source. Also provided in the spray head is an atomizing passage having .an inlet end connected to a source of compressed air, and a discharge end. The paint passage terminates in the atomizing passage so that the paint is atomized and carried to the discharge end of the passage by the air. A control: or shroud air passage is similarly provided in the spray head and is connected to a source of compressed air. The outlet end of the control passage is positioned to direct the control fluid into the atomized stream and at an angle with respect thereto to produce a resultant desired spray pattern. Accordingly, the paint is atomized and controlled solely by air streams. Additionally, means are provided to control the velocity of the air streams thereby to obtain efficient use of the present spray gun.

As an additional feature of the present invention provision is also made to apply an electrostatic field between the gun and the article which is to be coated to electrostatically paint the article. However, the electric field does not encompass the orifice through which the paint spray is dispensed so that the paint particles are dispersed and spread out thereby to produce a wider pattern than was obtainable heretofore in electrostatic paint spraying systerns.

Other objects and advantages of the present invention will become more apparent from a consideration of the following detailed description when taken in conjunction with the accompanying drawings, in which:

. FIG. 1 is a side elevational view of a paint spraying system utilizing a spray gun constructed in accordance with the present invention;

FIG. 2 is a side elevational view, partially in diagrammatic form, of a modified paint spraying system;

FIG. 3 is a sectional view of the spray gun shown in FIG. 1 taken along line 3-3 thereof, to an enlarged scale and with parts broken away;

FIG. 4 is a side elevational view, partially broken away and shown in section, of the base element of the spray gun shown in FIG. 3;

FIG. 5 is a front end elevational view of the base element of the gun;

FIG. 6 is a side elevational view, partially broken away and shown in section, of the fluid director element of the gun;

FIG. 7 is a front end elevational view of the fluid director element:

FIGS. 8, 9 and 10 are side elevational views, partially broken away and shown in section, respectively of the shroud fluid control element, velocity control element, and tip element of the gun shown in FIG. 3; and

FIG. 11 is a side elevational view partially broken away and shown in section, of the outer sleeve and electrode ring of the gun.

In the description which follows, the operation of the spray gun of the present invention is described as utilized to coat an article with a layer of paint. However, this illustration is by way of example only and is not to be inerpreted as being a limitation on the present invention. That is, the spray gun of the present invention may be used to spray any type of fluent coating material, including power, on an article.

7; Referring 'detail to "the drawings, the parts of the v spray gun of the present invention are shown in assembled form in FIG. 3 and are shown individually in FIGS. 4 through 11. Thus the spray gun, designated generally by reference numeral 10, may be seen to include generally a base member 12, a fluid distributor member 14, an air shroud control member 16, an atomizer air velocity control member 18, a tip member 20, and an outer sleeve 22.

The base member 12, shown in FIGS. 4 and 5, comprises a cylindrical metal body having a rear portion 24 and a forward portion 26 of slightly larger diameter than said rear portion and defining a shoulder 28 therebetween. The front end of the forward portion 26 is inwardly bevelled at 27. The rear portion 24 is sized to be snugly receivedwithin and mounted upon one end of a hollow insulating sleeve 30 forming a portion of the spray gun mount as will be presently described. The outer surface of the insulating sleeve 30 is flush with the outer surface of the base forward portion 26, as shown in FIG. 4, the end of sleeve.30 abutting the shoulder 28 and being secured to the base member 12-by screws 32.

Extending inwardly from the front surface of the base forward portion 26 is a large cylindrical bore 34 provided with threading 36. The bore 34 communicates with an intermediate bore 38 of smaller diameter, which in turn communicates with a bore 40 of still smaller diameter. The bores 34, 38 and 40 are co-axial. As shown in FIGS. 3 and 4, a bevelled shoulder 42 is formed between bores 34 and 38, for purposes which will be explained hereinafter.

A fluid passage 44 communicates with and extends radially from the bore 40, terminating in an enlarged threaded portion 48 which receives the threaded nipple 46 of a fluid inlet conduit. Threadedly received on a right angle portion of the nipple 46 is a nut 50 which connects a fluid conduit tube52 to the nipple 46 and through the latter to bore 40. The tube 52 is supplied with paint or other fluent coating material under pressure from a reservoir, pump or other source (not shown).

In a similar manner, a radial conduit 54 in the base forward portion 26 communicates through longitudinal bore 55 with the intermediate bore 38, while radial conduit 56 communicates through longitudinal bore 57 with the bore 34, as shown in FIG. 5. The conduit 54 communicates with a threaded nipple 58 which is connected by nut 66 (FIG. 1) to a tubular conduit 62 supplied with air under pressure by a source of atomizer air (not shown). The conduit 56 communicates with a threaded nipple which is connected by a nut 68 to a tubular conduit 64 supplied with air under pressure by a source of shroud air (not shown).

Also threadedly received in the forward portion 26 of the base 12, is a screw 70 (FIGS. 3 and 4) which maintain's an electrical connector 72 in contact with the base 12. A lead 74 connects the connector 72 to one terminal 76 of a power supply 78 (FIG. 1), the other terminal of which is grounded by a lead 80. The power supply 78 is operative to apply a high potential between the gun 10 and ground.

The fluid director member 14 is received within the bores 34, 28 and 40 of base 12, and it is operable to direct the air and coating material entering the conduits 44, 54 and 56 from the respective sources to separate paths within the gun 10. The member 14, as shown in FIGS. 3, 6 and 7, includes an inner portion 82, an intermediate portion 84 and an outerportion 86 of progressively increasing diameter. The front end of the portion 82 is externally threaded at 88 over a section of its length and two axially spaced O-rings 90 are provided in appropriate grooves adjacent the rear end of said portion 82. The portions 82, 84 and 86 are stepped at both ends of the fluid director member 14.

The intermediate portion 84 has external threading 92 at its front end, while the outer portion 86 has a threaded circumferential surface 94. A bevelled surface 96 is formed between the rear ends of the portions 84 and 86, which is complementary to the bevel 42 between bores 34 and 38 of base member 12.

As shown in FIG. 3, the fluid director member 14 is mounted on base member 12 by inserting the rear end of inner portion 82 within the bore 40 and turning the outer threading 94 along the internal threading 36 of base 12 util the bevelled surface 96 engages the bevel 42. In this mounted position, the rear edge of the fluid director inner portion 82 is spaced from the end of bore 40 to define a chamber therewith. The fluid director member 14 is provided with a central through bore 97 which extends longitudinallytthrough the inner-portion 82, so that paint or other coating material entering the bore 40 through the radial passage '44, passes through the bore 97 and exits at the front thereof, as indicated by the arrows 98 in FIG. 3, The O -rings 90 "arecompressed against the wall of bore 40 to provide a seal therewith. i In the mounted position of the fluid director member 14, the rear edge of the intermediate fluid director portion 84 is spaced from the rear wall of bore 38 to define an annular circulation chamber for the atomizing air which enters through bore 55. Provided in the intermediate portion 84 are a plurality of circumferentially spaced through bores 100, the axes of which lie on acircle coaxial with the central bore 97. The bores 100 provide an exit for the atomizing air circulating in the aforementioned annular chamber, as indicated by the arrow 102 in FIG. 3. The outer fluid director member portion 86 is provided with a hexagonally-shaped forward section 104, as shown in FIG. 7, so that it may be grasped by a wrench or a similar tool to facilitate the turning of the fluid director member relative to base 12 with the respective screw threads in meshed engagement. I

In the mounted position of the fluid director member 14, the rear edge of the outer portion 86 is also spaced from the' rear end of the bore 34 to define an annular circulation chamber for the shroud air which enters through bore 57. Provided in the outer portion 84 are a plurality of circumferentially spaced through bores 106. The axes of the bores 106 lie on a circle which is coaxial with the central bore 97. The bores 106 provide an exit for the shroud air which circulates about the aforesaid chamber. 7

The atomizing air velocity control member 18 FIGS. 3 and 9) is provided with a central bore 108, one end 'of which extends to the rear edge of the member and the other end of which is closed. The rear portion of the bore 108 is enlarged'and is provided with threads 110 which are sized to mesh with the externallythreaded section 88 of the member 14. The member 18 is thus screw mounted on the forward end of the member 14, as shown in FIG. 3, so that the bore 108 communicates with and acts as an extension of the central bore 97 of the fluid director member 14, to provide a paint passage. The paint exits from the bore 108 through a plurality of circumferentially spaced passages 112 each of which is inclined forwardly and upwardly in the member 18 and each of which communicates with the bore 108at a point spaced rearwardly of the blind end of said bore. The member 18 is formed with a cylindrical portion of enlarged diameter just rearwardly of the mouths of the passages 112, and which enlarged cylindrical portion is cut a plurality of arcuate slots 113 forming therebetween a plurality of circumferentially spaced arcuate vanes 114. These vanes 114 serve to impart a rotary motion to air passing therethrough, as will be explained in. greater detail.

Extending forwardly from the front wall of the member 18 is an externally threaded section 116 of reduced diameter. Additionally, the outer rear edge 118 of the member 18 is bevelled inwardly so that the member 18 does not impede the flow of atomizing air exiting from the bores 100. v

Received on the threaded portion 92 of the fluid director member 14 is a lock nut 120 (FIG. 3). The nut 120 may be turned to an adjusted position on the threaded portion 92 to regulate the spray pattern as will be presently described. 1

I The shroud air control member 16 is shown in FIGS. 3-and 8 as comprising a cylindrical body having a central through longitudinal bore 122 terminating at its rear end in an-internally threaded portion 124. .This threaded portion 124 is sized to be mounted on the threaded section 92 of member 14. Thus, the member 16 may be screwed upon member 14 until it engages the lock nut 120, the latter halting further rearward movement there of, and the position of the nut 120 therefore determining the mounted-position of the member 16. I

When the shroud air control member 16 is mounted on the fluid director member 14, the member 16 encloses the mountedvelocity control member l8, as shown in FIG.' 3. The bore 122 of member 16 is sized to fit snugly but slidably over'the vanes 114 of member 18. The wall of bore 122 is spaced from the remaining outer surface of member 18 to define an annular atomizing air passage 126 therebetween. The passage 126 communicates with the bores 100 in member 14. The vanes 114 are located directly in the path of the air flowing through annular passage 126. Thus the air will flow through the arcuate slots 113 located between said vanes 114 and will impinge upon the latter, causing the air to swirl, and leave the passage 126 in a rotary movement, thereby to decrease the forward velocity of the atomizing air. The front end of the bore 122 is flared outwardly as indicated at 128 to facilitate the emergence of the atomized paint, liquid or powder. v

The member 16 is formed with a cylindrical portion of enlarged diameter on its outer surface intermediate the ends thereof. This enlarged portion is provided with spaced arcuate slots 129 defining therebetween a plurality of raised, circumferentially spaced, arcuate vanes 130. These vanes 130 are operable to impart a rotary path of travel to the shroud air, and decrease the forward velocity thereof, in a manner similar to the action of the vanes 114 upon the atomizing air.

The tip member 20 is provided with a centrally positioned sharp pointed end 132 which tapers rearwardly and outwardly to a circular base 134. Extending rearwarding from the rear surface of base 134 is an annular wall 136 which tapers slightly inwardly toward its axis. The wall 136 has a threaded inner surface 138 which is sized for screw mounting on the threaded forward section 116 of the-member 18. The tip member 20 and the flared portion 128 of member 16 define therebetween an atomized paint orifice 140 through which the atomized paint exists, as indicated by arrow 142 in FIG. 3.

As shown in FIGS. 3 and 11, the sleeve 22 is provided with a central bore 144, the diameter of which is only slightly in excess of the diameter of the vaned portion of the member 16 so that said bore 144 makes a snug slidable fit over the vanes 130. The bore 144 has an internally-threaded rear portion 146 sized to receive a section of the externally-threaded portion 94 of the member 14. The rear edge of the sleeve 22 abuts the front edge of the base 12 to maintain the sleeve 22 in properly mounted position. Provided on the outer surface of the sleeve 22 is a knurled or roughed section 151 (FIG. 11) which may be grasped by the operator to facilitate threading of the sleeve 22 on the threaded portion 94 of the director member 14. y

The wall defining the 'bore 144 is spaced from the outer surface of the member 16 to define an annular shroud air passage 148 therewith. The front portion 150 of the bore 144 is of slightly smaller diameter than the remainder of the bore so that the passage 148 is slightly constricted over the length of the portion 150'.

The annular passage 148 communicates with the plurality of bores 106 in member 14, so that the shroud air exiting from the bores 106 traverses the passage 148 The air impinges on the curved vanes 130, which are di rectly in the path of movement ofthe'shro'ud air,'to cause the shroud air'to swirl and thereby to decrease the forward velocity of the shroud air in amanner similar to that utilized to decrease the velocity of the atomizing air. The shroudair then exits-through -the'constricted portion 150 of the passage 148, as indicated bythe arrow 151 in FIG. 3.

Three circumferentially spaced ribs 152 extend radially and forwardly from the outer surface of the sleeve 22' and at their ends support a ring 154 which is coaxial with the sleeve 22. The ring 154-mounts a plurality of circurnferentially spaced'needle like electrodes 156 'which extend forwardly and outwardly therefrom, as shown in FIG. 3. All the elements comprising the gun 10 are fabricated from a conducting metal with the exception of the insulating sleeve 30. Accordingly, when an electric charge is applied to the gun 10, the chargedparticles will concentrate at the points of the needle electrodes156 and the pointed end 132 of the tipmember 20 in accordance with classical electrostatic principles. v I

It should be noted that the size of orifice 140 is determined by the distance between the members 20' and 16. While most of the parts of gun 10 are adapted to interfit in abutting relationship, the mounted position of the member 16 is adjustable and is determined by the position of the lock nut on the threaded portion 92. Hence, by initially turning the lock nut 120 forwardly or rearwardly, the mounted position of member 16 may also be adjusted forwardly or rearwardly relative to the tip member 20. Accordingly, the width of the orifice may be selectively decreased or increased in accordance with the initial setting of lock nut-120.

The spray gun 10 is particularly advantageous when used as part of an electrostatic paint spraying system such as illustrated in FIG. 1. Additionally, FIG. 1 illustrates the effect of the shroud air and the electrostatic field-in the control of the paint pattern.

Thus the gun 10 is supported on a stand designated generally by the numeral 157. The stand 157 includes a base 158 and an upstanding rod 160. Slidable on the rod 160 is a clamp 162 which may be affixed in place by a set screw 164. A stub shaft 166 extends laterally from the clamp 162 and mounts a clamp sleeve 168 on the end thereof. Slidably received in the sleeve 168 is a rod 170 which terminates in a gun mount 172, the rod 170 being held in adjusted position by a set screw 174.

In operation, the lead 74 is electrically connected to the power supply 78, as noted above. Additionally, the conduit pipes 52, 62 and 64 are respectively connected to the paint source, the atomizing air source and the shroud air source. It is to be understood that the paint and air are supplied to the gun 10 under various pressures which are individually controllable.

The article which is to be spray coated is designatedby the numeral 176 in FIG. 1. The article 176 is suspended from a grounded metal loop 178 by a hook 180 which is connected to the article. Hence, the article 176 is also maintained at ground potential. In practice, the loop 178 comprises a section of a travelling conveyor system which moves a plurality of article 176 past the spray gun 10 for successive spray coating.

The paint feed to gun 10 passes through the paint passage defined by the bores 97 and 108 and through the passages 112 into the atomizing air passage 126. Simultaneously with the movement of the paint through the gun 10, the atomizing air traverses the bores 100 and passage 126 and impinges on the curved vanes 114 which cause the atomizing air to swirl and travel in a spiral path and therefore decrease in forward velocity. While the forward or longitudinal velocity of the air is reduced, the velocity of movement in a spiral direction is sufficient to atomize efiiciently the paint emerging from the passages 7 112. The atomizedpaint 'then exits from the gun 10 through the orifice 140.

It is tobe noted that any type of paint or other liquid coating material may be atomized by the above-described procedure. Hence, the gun of the present invention is extremely versatile in its use as it is not limited to paints which can be readily atomized by electrostatic forces as in some coating systems.

As the atomized paint particles leave the orifice 140 under the propelling force of the atomizing air fed through passage 126, they exit from the gun 10 in radial directions, that is in directions, perpendicular to the axis of said gun 10. If the shroud air supply and high voltage supply, were not in operation, the paint particles would form a radial pattern about the forward end of the gun 10 as indicatedby the broken line 182 in FIG. "1. This is in contrast to conventional air spray guns in which the atomized particles are propelled forwardly with considerable velocity in line with the axis of the gun by the force of the atomizing air.

Operation ofthe shroud air supply causes an annular stream of shroud air to traverse the passage 148 and impinge on the arcuate vanes 130 which cause the shroud airto swirl and decrease in forward velocity. The swirling stream of shroud air exits through the annular orifice at the mouth of the constricted passage 150 in a longitudinal, forwardly directed path. The forwardly-directed shroud air then engages and envelopes the stream of atomized paint and propelling atomizing air to deflect the latter from its radial direction as indicated by the arrows 142 and 151 in FIG. 3, which show the resultant angular direction of the combined shroud air and paint spray.

By regulating the pressure of the atomizing air supplied to the gun, the size of the paint particles can be controlled within a wide range from a very fine spray to a coarser spray as desired. The radially-dispersed paint spray provided by the atomizing air also advantageously provides a much larger paint pattern than is possible with conventional air guns in which the atomizing air emerges in a forward longitudinal direction. By regulating the pressure of the shroud air supplied to the gun 10, the paint pattern can be readily adjusted in area to suit the particular coating requirements, over a wide range. Thus, by controlling the size of the spray pattern as it issues from the gun 10, by means other than the electrostatic forces employed, not only may a larger spray pattern be obtained, but the pattern may be controlled in size to a very considerable extent.

When the power supply 78 is energized to supply an operating voltage to gun 10, which is preferably in the vicinity of 100,000 volts, all of the metallic elements constituting the gun will assume this voltage. However, the needle-like electrodes 156 and the tip point 132 will carry the greater concentration of electrical charge since they constitute points with the smallest radius of curvature. Thus a high potential difference will exist between the gun 10 and the grounded articles 176 to be coated, creating an electrostatic field into which the atomized spray from the gun 10 is discharged. The pointed electrodes 156 and 132 serve as the charging electrodes of this electrostatic field, so that the highest potential gradient line or the electrostatic field extends from the electrodes 156 to the pointed tip 132, as indicated by the dotted line 184 in FIG. 1.

The potential gradient line 184 shows that the spray outlet orifice 140 is shielded from the electrostatic field so that the area of paint atomization and ejection from the gun is remote from the areas of highest field concentration and the paint atomization is unaffected by the electrostatic forces of the system. Further the mass of the gun body is also shielded from the electrostatic field so that it does not tend to attract the atomized spray particles.

Since the charging electrodes 156 and 132 of the electrostatic field are sharply pointed, they function in the usual manner to ionize the molecules of air within the electrostatic field'created. As-the atomized paint spray enters the electrostatic field,.the paint. particlesacquire electrical charges from this ionized air and are attracted toward the grounded article176 to be coated; the latter being at ground potential and at the opposite polarity.

Since the spray discharge orifice is shieldedfrom the electrostatic field, the atomized paint particles emerging from the gun 10 are permitted to disperse in an expanding pattern prior to their entry into the electrostatic field. This may be distinguished from electrostatic atomization systems in which paint is atomized by electro static forces and thus is located within the field andis highly charged at its point of atomization. Thus, ;-by utilizing the gun 10, the operator may obtain a larger paint pattern which is initially controlled by the shroud air in the manner previously described.

As. the atomized paint particles spread out andente the electrostatic field, they acquire a net electrical charge as described above, and the spray is attracted to the grounded article 176 by electrostatic forces, producing a paint pattern such as indicated by the solid lines 186 in FIG. 1. 1

It will be obvious that the resultant direction of ,the paint particles leaving the gun 10 will be determined by the velocities of the shroud air and the atomized paint air mixture. Thus, the decrease in the forward velocity of the shroud air by the vanes 130 permits better control of the resulting paint pattern. Moreover, by increasing the intensity of the shroud air flow, a smaller paint spray pattern, such as shown by the broken lines 188 in FIG. 1, may be obtained. Alternatively, the resultant paint spray pattern may be determined by selectively controlling the atomizing air flow. v

Accordingly, a spray gun for use in an electrostatic paint spraying system has been provided which may be used in conjunction with paints having any type of base and which produces a paint spray pattern which is substantially wider than similar spray guns used heretofore.

FIG. 2 diagrammatically illustrates a modified electrostatic paint spraying system utilizing the gun 10 of the present invention. In this system the gun 10 is isolated from the high voltage power supply. The electrostatic field is produced between a wire grid 190 which is connected to the power supply 78 by the lead 74, and the grounded article 176. The grid 190 is located at one side of and spaced from the forward end portion of the gun 10. The paint particles entering the field between the grid 190 and the article 176 are similarly charged by ionic bombardment and they are attracted to the grounded article to coat the same. Under these circumstances, the gun 10 will acquire a floating voltage due to its location within the electrostatic field created by the grid 190, and some concentration of electrical charge will occur at the pointed tip 132. It will be understood that in this situation, the gun 10 may be grounded, permitting it to be safely handled during the painting operation.

Other modified electrostatic paint spraying systems employing the gun 10 will be apparent to those skilled in the art. The wire grid 190 of FIG. 2 may be replaced by a ring structure similar to the ring 154 and electrodes 156 of FIG. 1, which ring may be mounted by insulating arms on the body of gun 10 or upon the insulating sleeve 30. The ring would thus be connected to the high power supply and the gun 10 would be insulated from the high potential applied to the electrodes 156.

In another embodiment, a hand gun may be provided in which the application of the atomizing and shroud airs, the flow of paint, and the application of high potential may be controlled by a trigger mechanism positioned on the gun. In this application the gun may be grounded, charged or floating similarly to the systems disclosed above.

While preferred embodiments of the invention have been shown and described herein, it will be obvious that numerous omissions, changes and additions may be made 9 in such embodiments without departing from the spirit and scope of the invention.

What is claimed is:

1. A device for spraying coating material on an object comprising a spray head, a coating material source, an atomizing fluid source, and a control fluid source; said spray head including a coating material passage in said head connected with said source of coating material, an atomizing passage in said head having an inlet opening and a discharge opening, means for connecting said inlet opening with said atomizing fluid source so that said atomizing fluid flows through said atomizing passage from said inlet opening to said discharge opening, exit means at the end of said coating material passage for directing said coating material into the path of said atomizing fluid, whereby said coating fluid is atomized and carried to said discharge opening of said atomizing passage and discharged therefrom, and a control fluid passage in said head having an inlet end connected with said control fluid source and an outlet end adjacent to the discharge opening of said atomizing passage, said outlet end of said control fluid passage being positioned to direct said control fluid into the atomized coating fluid exiting from said discharge opening at an angle to the path of flow of the atomized coating fluid to control the pattern of the atomized coating fluid.

2. A device for spraying coating material as in claim 1, and first velocity control means in said atomizing passage positioned upstream of said exit means for decreasing the velocity of said atomizing fluid to facilitate the atomization of said coating material.

3. A device for spraying coating material as in claim 2, in which said first velocity control means comprises a plurality of curved vanes in the path of flow of said atomizing fluid, said vanes being shaped to decrease the forward velocity of said atomizing fluid and to impart a swirling motion to said atomizing fluid.

4. A device for spraying coating material as in claim 2, and second velocity control means in said control fluid passage for decreasing the forward velocity of said control fluid to control the resulting pattern of the atomized coating material.

5. A device for spraying coating material according to claim 4, in which said second velocity control means comprises a plurality of curved vanes in the path of flow of said control fluid, said vanes being sized and positioned to impart a swirling motion to said control fluid, whereby said control fluid traverses a helical path upon leaving the outlet end of said control fluid passage to control the dispersion of said atomized coating material.

6. A device for spraying coating material in accordance with claim 1, and discharge control means for varying said discharge opening of said atomizing passage to control the rate of discharge of the atomized coating material.

7. A device for spraying coating material as in claim 6, in which said discharge control means includes a first member in said spray head having a threaded section, a tubular member threadedly received on said threaded section, said tubular member including a portion spaced from said first member to define said atomizing fluid passage, said first member including a radially extending section, said tubular member terminating in spaced relation to said radially extending section to define said discharge opening therebetween, whereby rotation of said tubular member on said threaded section causes axial movement of said tubular member to vary the width of said discharge opening, and lock means on said threaded section for locking said tubular member in a preselected position to maintain said discharge opening at a predetermined width.

8. A device for spraying coating material on an object as in claim 1, and means for creating an electrostatic field between said spray head and an object to be coated including electrode means mounted on said spray head, and a source of high potential having its opposite terminals connected to said electrode means and said object, whereby the atomized coating fluid enters said field and is electrostatically deposited on the object.

9. A device for spraying coating material on an object as in claim 8, in which said electrode means includes a first electrode mounted on and surrounding said spray head, said first electrode being spaced rearwardly of said discharge opening, a second electrode positioned at the front of said spray head forwardly of said discharge opening, whereby the highest potential gradient line of said electrostatic field extends from said first electrode to said second electrode in spaced relation to said discharge opening when said source of potential is connected between the object and said electrode means.

References Cited UNITED STATES PATENTS 2,993,468 7/1961 Zmuda et al. 23915 XR 3,059,613 10/1962 Nakaya l18629 XR 3,163,362 12/1964 McFee 239405 XR 3,263,127 7/ 1966 Point et al. 239-3 XR 3,296,015 1/1967 Juvinall et al. 239-15 XR 3,326,182 6/1967 Inoue 239-15 XR PETER FELDMAN, Primary Examiner.

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