US 3111266 A
Description (OCR text may contain errors)
Nov. 19, 1963 I E. A. A. AXELSON EI'AL 3,111,266
SPRAY PAINTING GUN FOR ELECTROSTATICSPRAY PAINTING Filed Nov. 21, 1960 5 Sheets-Sheet 1 FIGJ Nov. 19, 1963 E. A. A. AXELSON ETAL 3,111,266
SPRAY PAINTING GUN FOR ELECTROSTATIC SPRAY PAINTING Filed Nov. 21, 1960 5 Sheets-Sheet 2 Nov. 19, 1963 E. A. A. AXELSON ETAL 3,111,266
SPRAY PAINTING GUN FOR ELECTROSTATIC SPRAY PAINTING Filed Nov. 21, 1960 5 Sheets-Sheet 3 Fl 6.2a
19, 1963 E. A. A. AXELSON ETAL 3,111,266
SPRAY PAINTING GUN FOR ELECTROSTATIC SPRAY PAINTING Filed Nov. 21, 1960 5 Sheets-Sheet 4 Nov. 19, 1963 E. A. A. AXELSON ETAL SPRAY PAINTING GUN FOR ELECTROSTATIC SPRAY PAINTING 5 Sheets-Sheet 5 Filed Nov. 21, 1960 United States Patent 3,111,266 SPRAY PAINTING GUN FGR ELEiITRGSI'ATEC SPRAY PAINTING Eslril Anders August Axelson, Stockholm, and Lars Anders Gustaf Gyliintler, Solleutuna, Sweden, assign- 0:5 to Svenslta Maslsinaktieholaget Greiif, a Swedish joint-stock company Filed Nov. 21, 196i}, Ser. No. 79,711 Claims priority, application Sweden Nov. 20, 1959 5 Claims. (Cl. 239-45) This invention relates to a device for electrostatic spray painting.
It is previously known to use for electrostatic spray painting a conventional spray painting gun in order to effect a fine division of paint. The fine division of the paint is effected by means of compressed air which also blows the finely divided paint through an electrode into an electrostatic field, in which field owing to the electrostatic forces the paint particles are more or less attracted to the grounded article to be sprayed.
For this purpose, spray painting guns having a circular spray field are used.
In connection with the aforesaid spraying into an electrostatic field, the particles should be divided as finely as possible and should have such a low rate of efilux that their kinetic energy will not be of such a magnitude which prevents the paint particles from being attracted by the electrostatic field. Even if in previously known methods the lowest possible air pressure for atomizing the paint were to be applied and the viscosity of the paint were to be reduced to such an extent that the paint is almost as thin as water, it nevertheless would be necessary to apply such a high pressure that the rate of flow of the atomized paint particles would be relatively high, with the result that a great portion of the paint particles would not be taken along by the electrostatic field but are sprayed past the same.
It is further known to use for electrostatic spray painting a conventional spray painting gun in order to effect a fine division of the paint which paint is blown by the compressed air which is applied :to provide the fine division of the paint through, or parallel with, an electrode charged with negative high-voltage direct current of about 100,000 v. into an electrostatic field, in which field the paint owing to the electrostatic forces is more or less attracted to the grounded article to be sprayed. It is further known to connect the nozzle of the gun directly to a high-voltage, preferably negative and direct current, of about 100,000 v. and to place on spray nozzle spraying directly (toward the article to be painted so-called electrodes which, owing to their sharp edges or points and owing to the so-called corona efiect, ionize the paint sprayed out, so that the paint is influenced by the electrostatic effect and is applied onto the article which is to be coated with paint and which represents the positive pole.
The spray gun according to the invention eliminates the above drawbacks by providing a lengthening piece or delivery tube connected to the gun nozzle through which the air-atomized paint is sprayed with a substantially circular spray field which leaves the gun preferably at right angles to the geometrical axis of the spray nozzle. The delivery tube is surrounded by an air tube which is connected to a compressed air source and opens directly 3,1 l 1,26% Patented Nov. 19, 1963 behind the nozzle, so that the adjustable air flow leaving the tube deflects the circular spray field in the forward direction.
An air stream directed into the tube is made adjustable by means of a special valve making it possible to adjustably deflect the circular spray field in the forward direction. Owing to the circular shape of the spray field, the atomization can be carried out with high air pressure enabling the use of considerably thicker paints than heretofore possible. After the atomization, the finely divided paint particles are pressed forward by means of the air stream following behind, so that by adjusting the air stream the paint particles can be caused to enter the electrostatic field at very low speed, in which field the particles are carried forward so that they are attracted by the article to be sprayed. In this manner, the paint losses are very low compared with previously known devices.
According to another embodiment of the invention, the aforesaid drawbacks are overcome in that a spray gun of known construction is used in which the paint is atomized by compressed air substantially circularly and perpendicularly to the desired spraying direction, and which according to the invention is suspended, for example, on porcelain insulators or provided with an insulated handle, and which is connected to a high-voltage direct-current source of about 100,000 v., preferably with negative potential, said spray gain according to the invention being provided with a spaced tube, for example of metal, surrounding the atomizing nozzle of the gun, the mouth of said tube preferably having a knife-sharp edge and being disposed directly behind the mouth of the atomizing nozzle as described above.
At such a high voltage, the electrons flowing out of the tube and passing said sharp edge efiect a negative ionization of the paint flowing in front of said sharp edge. When a lower atomizing pressure is applied, the paint panticles are deflected electrostatically by about ninety degrees into the direction of the article to be coated with paint, which article represents the positive pole whereon, consequently, the paint particles will deposit.
When the article to be painted has depressions into which the electrostatically transferred paint does not penetrate, owing to the fact that the electrostatic attraction force is reduced or screened off by the depressions, it is necessary to increase the speed of the particles toward the article to be painted beyond the speed effected by the electrostatic force alone, in order to force the particles into said depressions. In such a case, a certain quantity of compressed air from a compressed air source is delivered via a control valve and, for example, via a rubber hose into said tube directed to the article to be painted. Said compressed air, when passing the sharp edge of the tube mouth, is ionized and, owing to its energy of motion increases at the same time the speed of the paint particles and deflects the same so that they penetrate into the de pressions. Said deflecting ionizing air stream which at the same time contributes to an additional charge of the paint particles, is also required when higher atomizing pressures are needed, for example, when high spraying capacity and paint feed is required or when the painting is carried out with thick paints, because in such cases the electrostatic deflecting force is not sufiicient to effect a satisfactory result. In order to increase the ionization 3 and, consequently, the attracting force for the paint particles, one or a plurality of additional ionizing electrodes may be spaced around the air tube-electrode which, preferably, should also be provided with sharp edges or points and also may have long and narrow, square or other Ehitpes in order to efiect a suitable shape of the spray The invention will be described in detail in the following, reference being had to the accompanying drawings wherein:
FIG. 1 shows in a schematic manner an apparatus wherein no electric charge occurs on the spray guns, but which is provided with a special discharge electrode between the guns and the article to be sprayed;
FIG. 2 is a side view, partially in section, of a spray painting gun for electrostatic spray painting according to the invention;
FIG. 2a shows the gun provided with needle-like members;
FIG. 3 shows schematically an apparatus corresponding to that of FIG. 1, but wherein the gun is the discharge electrode, and
FIG. 4 shows a side view according to FIG. 2, but with the spray gun designed according to the embodiment in FIG. 3.
Referring to FIGS. 1 and 2, a spray painting chamber 1 is provided with a paint separating filter 2 and a suction fan 3. The spray painting chamber comprises in its interior a supporting bar 4 carrying the article 5 to be spray painted. Said article 5 is grounded by means of a wire 6. From the ceiling 7 of the chamber 1 is suspended a cable 8 which carries before the article in insulated state an electrode frame 9 which is connected to a negative direct-current voltage.
In front of said frame 9 there are provided three substantially conventional painting guns 10 directed towards the article 5. Each of said guns 10 has a lengthening piece 11 between the body '12 of the spray gun and a spray nozzle 13 for a circular spray field. Around said lengthening piece :11 is spaced an air tube connected by a sleeve 14 to a compressed air source (not shown), said tube 15 opening directly behind the mouth 16 of the spray nozzle 13.
The air atomized paint is discharged from mouth 16 of spray nozzle 13. Lengthening piece 11 conducts paint and compressed air for atomizing the paint in known manner.
The air tube 15 is provided with a control valve 17 for adjusting the speed of the air stream.
In its front portion, said tube 15 has three centering screws 18 for centering the air tube around the lengthening piece 11 of the nozzle.
In the embodiment according to FIGS. 3 and 4, a spray painting chamber 101 comprises a paint separating filter 102 with a suction fan 163. A supporting bar 143 4 carries the article *105 to be spray painted, which article is grounded by a Wire 106. In the ceiling 107 is secured an insulator 108 to which is attached an electric line 110 carrying the spray paint gun 109, to which line 110 highvoltage current is delivered through the wire 111. In this figure is also shown the manner in which the atomized paint particles travel towards the article 115 to be painted.
FIG. 4 shows a spray painting gun according to the invention, the gun being provided with a lengthening piece 112 between the body 113 of the gun and the nozzle 114. Around the lengthening piece 112 there is arranged in concentric manner a tube .115 which via a sleeve 116 is conconnected to a compressed air source (not shown), said sleeve being provided with a valve 117 for adjusting the air delivery. Said air tube 115 opens directly behind the mouth of the spray nozzle 114 and has at its end a sharp edge 119 for the outflow of the electrons.
The air atomized paint is discharged from the mouth of the spray nozzle 114. Lengthening piece 112 conducts 1 paint and compressed air for atomizing the paint in known manner.
The spray gun is provided with an additional tubular member 113 disposed concentrically with said tube 115, said member 118 having such a diameter that between said tube and the member 113 is formed a space for increased outfiow of electrons, for which purpose the forwardly directed end of said member 118 is provided with a sharp edge.
The electrodes which are described above may, of course, be designed in any other manner for achieving the same effect. For example, the electrodes may have pointed ends or the like, or they may consist of a plurality of tubes or pins arranged equi-distantly on a peripheral line around the air tube 115, said tubes or pins having sharp points or edges and being electrically connected to the air tube by means of spokes or in another manner.
Even said additional electrodes may be provided for compressed air supply.
What we claim is:
1. A spray gun for spray painting comprising nozzle means having a longitudinal axis and an opening for discharging a continuous disk-like spray of gas-atomized paint through said opening in a plane substantially perpendicular to said axis, air blower means surrounding said nozzle means and located proximate said opening and behind the same, said air blower means being adapted for connection to a source of compressed air to blow the latter in an axial direction against said spray of gas-atomized paint to deflect the same in a forward direction substantially parallel to said axis, and discharge electrode means located behind the opening of the nozzle means for ionizing the gas-atomized paint as the latter is discharged from said nozzle means such that an object to be sprayed which is of opposite charge to that of said paint spray is etfective to attract the paint spray theretowards whereby said gas-atomized paint is directed towards said object under the action of both said air blower means and electrostatic attraction both of which are independent of the atomizing of the paint prior to the discharge of the latter through the opening of the nozzle means.
2. A spray gun as claimed in claim 1, wherein the air blower means includes a compressed air tube coaxially supported with respect to said nozzle means, the compressed air tube having an end of sharp edge behind the opening of the nozzle means which constitutes in part the discharge electrode means, the gun being adapted for connection to one of the poles of a high-voltage, directcurrent source, said gun being insulated from the other pole, said sharp edge enabling the outflow of electrons to ionize the paint spray.
3. A spray gun for spray painting comprising a nozzle having a longitudinal axis and an annular opening lying substantially in a plane perpendicular to said axis for discharging a continuous disk-like spray of gas-atomized paint through said opening and substantially in said plane, a tube surrounding said nozzle in coaxial manner and having an opening behind the nozzle opening, and adjacent thereto, said tube being adapted for connection to a source of compressed air to blow the latter through the tube opening towards said spray of gas-atomized paint to deflect the same in entirety in a forward direction substantially parallel to said axis, and discharge electrode means located behind the nozzle for ionizing the gas-atomized paint as the latter is discharged from said nozzle such that an object to be sprayed which is of opposite charge to that of said spray is effective to attract the paint spray theretowards whereby said gas-atomized paint is directed towards said object under the action of both the compressed air discharge from the tube opening and electrostatic attraction both of which are independent of the atomizing of the paint prior to the discharge thereof through the opening of the nozzle.
4. A spray gun as claimed in claim 3 wherein said discharge electrode means includes an edge portion of point shape on said tube facing the opening of the nozzle and therebehind, and means for charging said edge portion with ne ative high voltage direct current.
5. A spray gun as claimed in claim 3 wherein said discharge electrode means includes a plurality of needle-like members on said tube facing the opening of the nozzle and therebehind and means for charging said needlelike members with negative high voltage direct current.
2,302,289 Bramston-Cook Nov. 17, 1942 6 Eodle et al. May 4, Starkey et a1 Aug. 3, Sedlacsik June 14, Hild May 15, Ransburg Oct. 15, Sediacsik July 14, France Nov. 3, Gauthier Feb. 23, Burr et a1 Nov. 8, Sedlacsik Dec. 27, Tarpley et a1 July 25, Sedlacsik Sept. 19,