US 3635400 A
A method and apparatus for spraying paint and similar coatings. In one form the paint is sprayed at low pressure from a flat fan nozzle. A flat fan of air impinges upon the fan of paint at an angle of from 30 DEG -70 DEG . The air atomizes the paint to form a soft spray with low-forward velocity. In another form of the method, two fans of paint are projected toward one another at an angle and an air fan is directed along the bisector toward the zone of intersection. The air fan atomizes both streams of paint. An electrode can be placed in the air stream to ionize the air stream which in turn charges the paint particles. The width of the paint spray pattern is varied by varying the included angle of the air fan.
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Description (OCR text may contain errors)
Waited atet 3,635,400 Nerd et a1. 5] Jun. 1%, 1972 541 PAINT SPRAYING METHOD AND [57 ABSTRACT APPARATUS Inventors: Eric T. Nor-d, Oberlin; Samuel R. Rosen,
Lorain; Don R. Scarbrough, E1yria; Burton J. Vllngl, Amherst, all of Ohio; PeterW. Runstadier, JB, Hanover, NH.
 Assignee: Nordson Corporation, Amherst, Ohio  Filed: Mar. 27, 1970  Appl. No.: 23,227
 [1.5. CI. ..239/15, 239/422  lint. Cl. ...B05b 5/00, F23d 11/28  Field ofSearch.... .....239/422, 3,15, 543, 544
 References Cited UNITED STATES PATENTS 1,881,345 10/1932 Beatty et a1 ..239/422 3,049,092 8/1962 Sedlacsik et al. 239/15 X 2,302,289 11/1942 Cook 239/15 X 3,067,949 12/1962 Sigvardsson et a1. ..239/l5 3,169,882 2/1965 Juvinall et a1 ..239/3 X 3,540,653 11/1970 Fabre ..239/3 X Primary Examiner-Lloyd L. King AttorneyWood, Herron & Evans A method and apparatus for spraying paint and similar coatings. in one form the paint is sprayed at low pressure from a flat fan nozzle. A flat fan of air impinges upon the fan of paint at an angle of from 30-70. The air atomizes the paint to form a soft spray with low-forward velocity. In another form of the method, two fans of paint are projected toward one another at an angle and an air fan is directed along the bisector toward the zone of intersection. The air fan atomizes both streams of paint. An electrode can be placed in the air stream to ionize the air stream which in turn charges the paint particles. The width of the paint spray pattern is varied by varying the included angle of the air fan.
A spray gun is disclosed having two tubular paint nozzles for projecting two fan-shaped fans of paint. An air nozzle is mounted between the paint nozzles for projecting a fan of air against the paint fans to atomize the paint. The air nozzle is adjustable to provide air fans of difierent angles for varying the width of the paint spray pattern. An electrode is disposed in the air nozzle for ionizing the air stream. This electrode is energized through a resistor and flexible cable. The cable is spring-urged toward the resistor so that when the resistor is removed, the cable shifts causing a safety switch to open deenergizing the gun. When a nozzle mounting member is removed, the cable and surrounding tube are shifted forwardly to automatically close a valve to seal off the air and electrical conduits. Removable caps are provided on the ends of the tubular paint nozzles for facilitating cleaning of the nozzles.
20 Claims, 19 Drawing Figures PATENTED M 1912 7 "3.635 400 SHEET 1 OF 7 17/153 r700 flff PATENTEDJAN18I972 3, 35
SHEET 3 OF 7 I NVENTOIL PATEMTED JAM 8 I372 SHEET 5 UF 7 PAINT SPRAYKNG METHOD AND APPTUS BACKGROUND OF THE INVENTION This invention relates to methods and apparatus of spraying paints, lacquers and similar coating materials and is particularly directed to a novel method and apparatus for effecting air atomization of the paint and for electrostatically charging the paint if desired so that the electrostatic field forces can be utilized to increase the effectiveness of paint deposition.
In the past there have evolved two distinct types of paint spraying equipment. The first type can be characterized as airiess" spraying equipment. In an airless type of spraying apparatus, a paint stream is forced through an orifice under a relatively high pressure, for example, a pressure of the order of BOO-1,000 pounds. As the paint is propelled through the small orifice it is broken up, or atomized, into very fine droplets. The paint spray formed from the gun moves at a relatively low velocity toward the article to be painted. In many cases the paint spraying operation is carried out in the presence of a high-voltage electrostatic field in which the work to be coated is kept at, or close to, ground potential while the atomized paint particles are charged to a relatively high potential. These particles are then urged toward the work by the forces of the electrostatic field.
This type of system has the recognized advantage of providing a very high deposition efficiency, i.e., a large portion of the paint spray emitted from the gun is effectively deposited on the article to be coated. On the other hand, in some installations the airless spray-type apparatus has certain inherent shortcomings. One such objectionable characteristic is that the system requires a paint supply system operated at a relatively high pressure. As a result, it is not feasible to disconnect a gun from one high-pressure paint line and quickly connect it to another high-pressure paint line when, for example, it is desired to change the color of coating being sprayed.
The second general type of spray equipment does not require a high-pressure paint source. This second type of spray system, which is known as air spray equipment, relies upon a stream of air to break up the paint into particle size suitable for spraying. In conventional air spray equipment, the paint is extruded from a nozzle in a generally rodlike form and is subjected to a high-pressure blast of air. In a typical air spray installation, the air pressure at the gun is under a pressure of approximately the order of 75 pounds per square inch. The air is used in large quantifies; for example, it is common practice to utilize an airflow of 14 or 15 standard cubic feet of air per minute to carry out atomization.
Air spray systems of this type do present certain advantages in that they can be utilized to atomize particularly difficult types of paint and can more readily be provided with quick disconnect couplings to the paint line since the paint line is maintained at a relatively low pressure of, for example, 50 psi. At the same time, however, prior art paint spray guns are subject to several disadvantages.
In the first place, the large quantity of high-velocity air used to atomize the paint together with the airflow it induces causes a substantial portion of the paint spray to be carried past the workpiece and wasted even when an electrostatic charge is applied to the paint. Moreover, the rapidly moving air has a high kinetic energy which causes it to bounce back or rebound from the surface being coated carrying with it entrained paint particles. Consequently, an appreciable portion of the paint which is directed toward the workpiece is wasted due to rebound.
Another inherent disadvantage of conventional air spray equipment is the problem of ventilation. Specifically, because of the high volume of air emitted by each spray gun, and in many installations there are several guns operating simultaneously, a ventilation system must be provided having a high capacity'for capture of paint particles entrained in the large mass of high-speed air, for example, capture velocities of 150 feet per minute.
Also, because of paint entrained in the large amount of overspray and rebound, water curtains or other types of filters must be provided for preventing sizable quantities of paint from escaping and polluting the atmosphere.
SUMMARY OF THE INVENTION The principal object of the present invention is to provide a novel method and apparatus for spraying paint in whichrelatively small quantities of air at a relatively low pressure are utilized to atomize the paint in a very effective manner so that the resultant paint spray is a soft, finely divided spray not unlike that which could heretofore be produced only by an airless gun.
At the same time, the present method and apparatus are effective to retain the advantages inherent in any air-type of spray gun, i.e., the ability to atomize various difiicult types of coating material and the facile interconnectability to various paint lines so that the spray gun can be converted quickly from spraying one color or type of coating to another.
More particularly, the present invenu'on is predicated in part upon the concept of spraying paint by emitting a thin, flat fan-shaped stream of paint from one nozzle and a fan-shaped stream of air from a second nozzle. The paint fan in most cases is initially in the form of a continuous sheet. However, the fan can be in the form of a thin, substantially planar discontinuous spray; for example, one which is already partially atomized. The fan-shaped stream of paint and air impinge upon one another at a substantial angle of from approximately 3070. The air thus exerts an optimum shearing force upon the paint fan and breaks the paint down into small particles of a low mean particle size with substantially no particles of an objectionably large size.
This invention is further predicated in part upon the empirical discovery and determination of various physical relationships and values of certain parameters which make it possible to obtain an atomization suitable for fine finishing purposes utilizing as one starting component a low-pressure fan of paint. A flat stream of paint from any presently known form of fan nozzle operated at low pressure is inherently in a very difficult form to atomize into small particles with the uniformity required for producing satisfactory painted surfaces.
The difficulties involved are due to the fact that the paint stream is not a uniformly thin flat sheet. Rather, the sheet in cross section is somewhat like a dumbbell with a thin center web and two enlarged portions, one at each edge. These enlarged portions are in fact longitudinal beads or streamers." These two streamers are several times the thickness of the central web portion and tend to remain integral and resist atomization even when the rest of the sheet is broken up into particles. It will readily be appreciated that no matter how finely most of the paint is atomized, if the streamers are not broken up into particles of generally the same fineness, the quality of the applied coating will suffer and may well become totally unacceptable. The present paint spray method is effective to cause effective breakup of all parts of the paint stream, including the streamers, into small particles while using only a relatively small quantity of air.
In accordance with flie present invention, the air stream is projected under a relatively low pressure, for example, of the order of 9 to 45 pounds per square inch at the gun, while the paint is sprayed under a low pressure of, for example from 30-80 pounds per square inch. This method of atomization is so effective that the quantity of air required to deposit a relatively large quantity of paint, for example, 22-25 fluid ounces per minute of a typical baking enamel, is approximately 7-8 standard cubic feet per minute. As a result of this small volume of low-pressure air and the fine atomization of the paint, the resultant spray is in the nature of a soft spray, or slowly moving fog, having a low forward velocity.
One of the principal advantages of this method of spraying is that it results in a substantially higher deposition efficiency than conventional air spraying methods. There is substantially less paint waste due to overspray and rebound which is minimized or practically eliminated.
Another advantage of the present spray method is that the relatively small quantity of air involved and the smaller quantity of paint entrapped in the exhausted air greatly simplifies the problem of ventilation and prevention of atmospheric contamination.
Another object of the present invention is to provide a novel method for readily changing the width of the paint spray pattern. This aspect of the present invention is predicated upon our determination that the width of the paint spray can be controlled by changing the included angle of the air fan without in any way changing the paint fan.
In accordance with the present invention, the air fan is selectively emitted from one of a series of nozzle openings constructed so that the nozzle openings not only simultaneously produce air fans of difi'erent included angles, but also produce air fans which behave much as though they are emitted from a point pressure source, the distance from the nozzle opening of which is varied in an inverse relationship to the angular size of the nozzle opening. By virtue of this relationship, the height of the air fan along its line of impingement with the paint stream is maintained substantially constant so that all portions of the paint stream are effectively atomized with a minimum air usage.
In addition to the method concepts disclosed above, the present invention also comprehends a preferred spray painting method utilizing in part the method described. More particularly, in the preferred method a fan of air is in effect enveloped between two fans of paint. The fans of paint are directed toward each other with the air fan bisecting the angle so that it impinges upon both paint streams in substantially the same zone. This method results in an even better atomization than the single spray method, apparently due to the fact that in order to escape, a major portion of the air must pass through one or the other paint streams or through the paint particles being separated from the streams. Thus, the kinetic energy of the air is more effectively utilized to shear the paint and cause its breakup into particles of a small mean particle size.
The present two-paint stream method of spraying is also particularly advantageous when employed in conjunction with the present novel method of electrostatic charging. More particularly, in accordance with the present charging method, the paint is not charged directly or by an electrode in close proximity to the paint stream. Rather, it is our concept to ionize the air fan prior to its impingement upon the paint streams by passing the air fan through a corona discharge surrounding an electrode at a high potential. As explained above, the air fan then impinges upon the paint streams and causes the atomization of the paint streams.
The ions present in this air stream have a high mobility and are subjected to the forces of the surrounding electrostatic field. Specifically, these ions, which are charged and exist in a field of high potential, move toward the paint streams and fog of paint droplets existing in regions of a lower potential. The ions attach themselves to the paint particles which are of substantially lower mobility. These charged paint particles are propelled forward by the air stream and under the additional influence of the electrostatic field forces are brought into contact with the surface to be coated which is normally maintained at ground potential.
We have determined that the two-paint stream method results in substantially more effective charging of paint particles than the one-spray method and believe that this is due to the fact that the ions are to a large degree surrounded by .the paint streams and particles and do not have a free path to one side of the paint as is the case when only a single paint spray is utilized.
The present method of charging paint is not only advantageous because of its high efficiency, but is further advantageous because the entire paint supply system, including the tube supplying paint to the gun, the paint pump and the paint reservoir, or tank, remain at or near ground potential.
in contrast, in prior art electrostatic spraying systems, particularly when a conductive paint or coating, such as one of the metallic-containing finishes utilized in the automobile industry, is used, the entire paint system became charged to the same order of potential as the electrode, e.g., 75,000 volts. This necessitated careful insulation of the entire paint system including the paint reservoir. in the event of insulation failure, for example in the paint supply tube, the high potential present could, and not infrequently did, result in fires, electrical shock hazards, and other operational difiiculties. All of these problems are completely eliminated by the present charging method in which no charge is applied directly to the paint either by an electrode in contact with the paint or by an electrode in close proximity to the paint stream.
In addition to the method aspects of the present invention, the invention is directed to the provision of a novel spray gun for carrying out the method. More particularly, the present spray gun includes a handle, a forwardly extending barrel and a nozzle assembly mounted at the forward end of the barrel.
The nozzle assembly comprises two tubular paint nozzles effective to direct thin flat fan-shaped paint sheets toward the axis of the gun, and an air nozzle mounted between the paint nozzles and efi'ective to direct a flat fan-shaped stream of air along the axis of the gun toward the zone of intersection of the two paint fans. In accordance with the present invention the air nozzle and paint nozzles are located so that the distance of the air nozzle from the zone of air-paint impingement is only a fraction of the distance of the paint nozzles from the zone of air-paint impingement. As a result, the velocity of the air issuing from the nozzle is attenuated only minimally prior to its impingement with the paint fans. Each of the paint fans and air fan meet at a substantial angle of the order of 30 to 70. As a result, the air fan exerts an optimum shearing force on the paint fans and breaks up both fans simultaneously into a spray of particles of small mean particle size free from inordinately large particles.
One of the advantages of the present gun is that it is quite compact and maneuverable. Despite the fact that the gun utilizes three separate nozzles it is as small and easy to handle as previous spray guns of the air or airless type.
It is another objective of the present invention to provide a spray gun incorporating paint charging means of a substantially increased efficiency. In fact, the present electrostatic charging system is so efiicient that when operated at 50,000 volts or even less, it provides the same deposition efficiency as is attained using a conventional electrostatic charging mechanism operating at a potential of 75,000 volts.
More particularly, in accordance with the present invention the gun includes an electrode mounted within the center air nozzle in alignment with the nozzle discharge opening. This electrode is effective to establish a corona through which the air passes prior to its discharge from the nozzle. As the air passes through the corona the gas molecules are ionized and dust particles charged. These charged particles move under the electrostatic field forces toward the paint which is at a low potential and are subsequently deposited on the low-mobility paint particles.
As indicated above, one of the principal advantages of this invention is that the paint stream itself does not become charged so that there is at most a negligible charge buildup in any portion of the paint supply system.
Another objective of the present invention is to provide a charging circuit which is substantially safer to use than the prior art. More particularly, in many conventional prior art charging systems the charging electrode projects forwardly from the end of the spray gun. This high-potential electrode is thus in an exposed position in which it can be touched accidentally by a workman or can be shorted by accidental contact with a grounded conductor. In contrast, the electrode of the present invention is buried within the air nozzle where it is effectively shielded from any contact with either the person using the gun or a grounded surface.
The present gun also embodies a second important safety feature which automatically prevents the application of a high potential to the gun in the event that the current-limiting safety resistor is left out. More particularly, it is common practice to provide a resistor in series with the electrode and the cable connecting the power pack to the gun. When a spray gun is overhauled, the resistor is often removed and at times a workman may neglect to replace it when reassembling the gun. When such a resistor is omitted the full potential from the power pack can be capacitively discharged across the void and applied to the gun electrode. In such a case, if a gun is brought too close to a grounded article, a spark may occur which might cause an ignition of the paint material or cause a painful electrical shock to the operator.
In accordance with the present invention, this is prevented by a novel safety switch arrangement in which the main power is automatically cut off whenever the resistor is removed from the gun.
Another objective of the present invention is to provide a construction in which the air and electrical conduits are automatically sealed off when the gun is disassembled by removing the nozzle assembly. In accordance with the present invention, this is accomplished by providing a valve seat at the forward end of the air and electrical conduit in the gun barrel and by providing a shiftable sleeve having a valve-closing plug at its forward end. When the gun is disassembled, this sleeve is spring-urged to the valve closing position to seal off the entrance to the air and electrical conduit. In so moving, it also cuts off the power supply.
A still further objective of the present invention is to provide a novel form of air nozzle for selectively varying the air spray to change the size of the paint spray pattern.
In a preferred form of nozzle, the angle of air spray is changed by selectively emitting the air through one of a series of openings in a nozzle plug. The plug is provided with internal arcuate surfaces of different radiiadjacent to each nozzle opening. We have made the empirical discovery and determination that air projected from such a nozzle appears to have somewhat the same properties as air emitted from a point source which is displaced from the nozzle opening a distance correlated with the radius of the internal nozzle surface.
To obtain a fan spray having a smaller included angle, the plug is shifted to present an opening in which the radius of this internal surface is greater so that a smaller segment of its periphery is cut away. This results in an air fan of smaller included angle and at the same time results in a shifting of the point source away from the nozzle opening. The net effect, as far as matching the width of the paint fans, is thus similar to shifting the nozzle away from the paint film. As a result, although its angle is smaller, the height of the air fan along the line of impingement of the paint film remains unchanged. Consequently, neither a large portion of the air stream is wasted by passing outside the confines of the paint film, nor are portions of the film improperly atomized due to the fact that they are not impinged upon by the air stream. At the same time the distance the air has to travel to reach the zone of impingement is minimized.
These and other objects and advantages of our invention will be more readily apparent from a consideration of the following detailed description of the drawings illustrating the principles involved in the present method of paint spraying and a preferred form of apparatus for carrying out the method.
DESCRIPTION OF Til-IE DRAWINGS FIG. I is a diagrammatic view of a paint spray system embodying the present invention.
FIG. 2 is a semidiagrammatic elevational view of a paint spray issuing under relatively low pressure from a fan nozzle.
FIG. 3 is a cross-sectional view of the paint spray taken along line 33 of FIG. 2.
FIG. 3A is a diagrammatic view plotting the preferred distribution of mass flow rate from an air nozzle used to atomize a paint spray film.
FIG. 41 is an enlarged top plan view of a portion of the paint spray film shown in FIG. 2 illustrating the manner in which the paint spray tilm decreases in thickness as it travels away from the nonle.
FIG. 5 is a diagrammatic view showing the cooperative relationship between a paint spray nozzle and an air spray nozzle in carrying out the present paint spray method.
FIG. 6 is a semidiagrammatic view taken along line 66 of FIG. 5.
FIG. 7 is a diagrammatic view showing the relationship of two paint nozzles and an air nozzle to carry out a preferred method of paint spraying in accordance with the present in vention.
FIG. 8 is a view taken along line fi-8 of FIG. 7.
1 FIG. 9 is a longitudinal sectional view of a preferred form of spray gun constructed in accordance with the present invention.
FIG. I0 is an enlarged cross-sectional view taken along line 10-10 of FIG. 9 and with portions rotated for purposes of clarity.
FIG. 1 l is a view taken along line lll I of FIG. 10.
FIG. HA is a front elevational view of the air nozzle plug.
FIG. 12 is a cross-sectional view taken along line 12-I2 of FIG. 10.
FIG. 13 is a cross-sectional view taken along line 13l3 of FIG. 10.
FIG. 14 is a cross-sectional view taken along line l414 of FIG. 10.
FIG. 15 is a semidiagrammatic view showing the relationship of the air nozzle and paint film to a target.
FIG. 16 is a diagrammatic view similar to FIG. 15 showing the manner in which the air nozzle opening and spacing from the paint film are varied to decrease the width of paint spray.
FIG. 17 is a schematic circuit diagram of the safety circuit.
SYSTEM FIG. I shows a paint spray system I0 for spraying paints and other coatings in accordance with this invention. As is well recognized in the art, coating systems of the general type shown are utilized to apply coatings to many different types of products, such as automobile parts, furniture, containers, and the like. The coating materials utilized include not only paints, but also enamels, lacquers, stains, varnishes, emulsions, waxes, adhesives, and the like. In the following description the word paint" will be used in a very generic sense to encompass all of these various types of coating materials.
In almost all instances, it is desirable that the paint or other finish be applied in a smooth, even coating with the particles deposited on the workpiece being of a small and relatively uniform size. Paint systems for carrying out the present process include a spray gun II which is supplied with paint by means of a pump 12 which feeds paint under pressure to the gun from a paint supply tank I3 through a paint tube I4. (Alternatively pump 312 can be eliminated and tank 13 pressurized). The gun is also supplied with air under pressure from a conventional compressor or other air pressure source. The air is applied to the gun through an air tube I5.
As is well known in the art, when spraying some types of products, for example, the interiors of deep tubular structures, it is desirable to operate the system as a straight air spray system without applying any electrostatic field. However, in spraying other types of articles, it is desirable to charge the paint particles so that the deposition of the particles is aided by the presence of a high-electrostatic field. In such instances, the article being sprayed is normallymaintained at ground potential so that the electrostatically charged paint particles move toward the article under the influence of the electrostatic field forces and a high percentage of them are effectively deposited on the article to be painted.
The present system can be operated either as a straight air spray gun or as an electrostatic air spray gun. In the event that the gun i1 is to be operated as an electrostatic unit, it is connected to a power pack, or source of DC voltage, 16. The power pack is connected to the gun through an electrical cable 17.
Gun 11 may either be a hand-held gun or can be an automatic gun mounted on a suitable support normally positioned adjacent to a conveyor line by means of which the articles to be sprayed are moved past the gun. In either case, and particularly in the case of hand-held guns, it is desirable that the gun itself be compact and maneuverable. With either form of gun the paint particles are atomized by a low-pressure stream of air and are projected forwardly from the gun in a soft spray of fine particles. A typical spray pattern of the present system travels only about one-half of the travel of a conventional air spray gun operated under the same conditions.
PAINT SPRAYING METHOD In order to understand various ramifications of the present paint spraying process, it is desirable to consider the nature of a fan-shaped paint spray film as it is sprayed from a nozzle under relatively low air pressure. The pattern of a typical paint film I8 is illustrated in FIG. 2. The film is being emitted from a nozzle of the flat fan spray-type. Such nozzles are conventionally utilized in airless spray guns and one form is disclosed in Bede US. Pat. No. 2,754,228. Another form of fan spray nozzle is disclosed in detail below. The paint film shown in FIG. 2 is being sprayed under a relatively low pressure, for example, a pressure of the order of 40-50 p.s.i. as opposed to the normal pressure used in airless spray guns of the order of 3001 ,000 p.s.i.
As shown in FIGS. 2-4, the paint film is discharged from the orifice in a generally fan-shaped pattern with the upper and lower edges of the film diverging. The angle of divergence of these upper and lower edges gradually decreases. The film is not uniform in cross section. Rather, for a short distance as it leaves the nozzle 20, the film includes a central, relatively uniform web 21 and two edge enlargements, or streamers 22 and 23. These beadlike streamers run along the upper and lower edges of the fan and are substantially thicker than the central web portion 21.
When low hydraulic pressures are used, such a film of viscous coating material remains relatively stable for a distance of perhaps one to several inches after it leaves the nozzle. However, at the end of this stable region the film begins to form transverse ripples, or waves, 24. As the sheet becomes more, more and more unstable, the waves 24 eventually disintegrate into ligaments and droplets 25. However, the streamers persist and strongly resist disintegration.
In addition to these characteristics, the thickness of the film decreases progressively as the film leaves the nozzle. This decrease in film thickness is generally inversely proportional to the distance from the nozzle so that the most rapid diminution of sheet thickness occurs in the first fraction of an inch (e.g., one-quarter inch) of sheet travel from the nozzle and from that point on the rate of diminution is substantially smaller.
The broadest aspect of the present paint spraying method is illustrated in FIGS. and 6. Essentially, we have determined that very fine paint atomization characterized by low mean particle size and freedom from random large particles can be obtained by spraying a fan-shaped film of paint 27 under relatively low pressure, for example, a pressure of the order of 3080 p.s.i., from a nozzle 28 and impinging this fan-shaped paint spray with a fan-shaped stream of air 30 emitted under a very low pressure of the order of 9-45 p.s.i. by an air nozzle 31. When the air stream impinges upon the paint fan, it exerts a strong shearing force on the film and effectively atomizes all portions of the paint stream, including the streamers 32 and 33. The paint stream is deflected and continues outwardly as a soft spray pattern, or fog, 34 of suitably atomized paint particlcs.
In accordance with the present method, the paint is struck by a relatively small volume of air at a relatively high velocity. We have empirically determined that optimum atomization of particles for paint spraying is obtained when the angle x between the paint spray film and the air spray is made between approximately 30 and 70. The line of impingement 35 between the air stream and paint stream is spaced far enough from the nozzle so that the paint stream has undergone a greater portion of the attenuation of its thickness. At the same time, the line of impingement 35 against a stream of the type shown in FIG. 2 should occur within the region in which the paint film is substantially planar, i.e., before the transverse waves 24 would commence in the absence of an air stream.
Next, the length L, of the path of travel from the air male 31 to the line of impingement 35 should be only a fraction of the corresponding length L of the paint film from the paint nozzle 28 to the line of impingement 35. We have empirically determined that the preferred range of ratio of L /L is from one-sixth to three-fourths. In one preferred embodiment, the
actual length of paint film L is approximately three-eighths to three-fourths inch, while the actual length of air film L is approximately one-eighth to three-eighths inch. The air stream is slightly wider (from edge-to-edge) along the line of impingement 35 of the paint film than is the paint film. This facilitates breaking up and effective atomization of the streamers 32 and 33 which is essential to obtaining a good quality paint spray.
To further improve the atomization of the streamers, the air spray itself is made nonuniform with the air stream having higher mass flow rates adjacent its edges, in the areas of the stream which impinge upon streamers 22 and 23. This is shown diagrammatically in FIG. 3A in which the mass flow rate of the air is shown as being substantially greater in the areas 36 and 37 in which the air stream impinges upon the streamers 22 and 23 than in the central area 38 of the air stream which impinges upon the thin web portion 21 of the paint film.
In practice, this nonuniform air stream can be obtained by emitting air from a thin slot which is not of rectangular configuration, but rather is wider adjacent to the ends. In many cases, however, the use of such a specially configurated nozzle is not necessary since we have found that the use of a flat fan nozzle made with a rectangular gash gives a sufficiently heavy edged airflow to atomize the heavy edges of the paint sheets.
In carrying out the present process, paint can be applied at a high rate without adversely afiecting the highly effective atomization achieved. Moreover, this fine and uniform atomization is achieved while utilizing only a relatively low amount of air in relation to the quantity of paint. For example, on one typical operation an acrylic enamel having a viscosity of 22 seconds as measured by a Zahn No. 2 cup at room temperature was sprayed at a rate of 22 fluid ounces per minute. The paint pressure was approximately 40 p.s.i. and the air pressure was 20 p.s.i. at the gun. The airflow was at the rate of 8 standard cubic feet per minute so that the ratio of air-topaint was 0.36 standard cubic feet of air per fluid ounce of paint sprayed per minute. Conventional air spray guns utilize an air-to-paint ratio approximately twice this large and an air pressure of approximately 75 p.s.i. Consequently, the total energy of the air utilized in the present process is only a small fraction of that required in a conventional air gun. This same relatively low ratio of air volume-to-paint is utilized in the present method through the entire range of viscosities of coating materials which are normally applied using the present method.
For example, a very viscous vinyl coating having a viscosity of 40 seconds as measured on a Zahn No. 2 cup at room temperature was deposited at the rate of 17.2 fluid ounces per minute. The paint pressure was 45 p.s.i. and the air pressure was 26 p.s.i. at the gun. The volume of air employed was 9.5 standard cubic feet per minute. Thus, the ratio of air to ounces of paint was 0.55 standard cubic feet of air per minute pe fluid ounce of paint per minute.
As another example, a stain having a very low viscosity of 16.5 seconds as measured on a Zahn No. 2 cup at room temperature was applied at a rate of 24 fluid ounces per minute. Again, the paint pressure was 45 p.s.i. and theair pressure was 9 p.s.i. at the gun. The amount of air employed to atomize this stain was 4.5 standard cubic feet per minute or approximately 0.18 standard cubic feet of air per minute per fluid ounce paint per minute. In each of the above two examples, the air utilized by a conventional spray gun was approximately twice the amount utilized in the present spray gun.
An even more advantageous version of the present paint spraying process is disclosed in FIGS. 7 and 8. In this preferred method of spraying paint, two substantially identical fanshaped sprays of paint 40 and 41 are emitted from fan spray nozzles 42 and 43. A single fan of air 44 is emitted from an air nozzle 45. The fan of air 44 is disposed so that it bisects the angle formed by the two planar fans of paint 40 and All. The two fan streams of paint converge and are impinged by the air stream M in an area indicated generally at 47. Both paint streams are broken up into a fine mist, or fog, of generally uniform paint particles as indicated in FIG. 8. In fact, the atomization is even more efficient than in the embodiment disclosed in FIGS. and 6 since the air stream is in effect trapped between the two fluid streams and its energy is more effectively utilized in breaking up the paint into minute droplets.
The same parameters described above in connection with the method illustrated in FIGS. 5 and 6 are also applicable to the method disclosed in FIGS. 7 and 8. More particularly, the angles Y and Y between the paint and air streams are in the range of from approximately 30 to approximately 70. The paint pressure is from 30 to 80 p.s.i., while the air pressure is from 9 to 45 p.s.i. at the gun. The ratio of the length of air travel L,, from the nozzle to the zone of impingement compared to the length of paint travel from the nozzle to the zone of impingement is approximately in the range of one-sixth to three-fourths. Also, the actual length of paint travel L is of the range of approximately three-eighths to three-fourths inch, while the actual length of air film travel L is approximately one-eighth to three-eighths inch. Furthermore, the ratio of volume of air to quantity of paint applied is the same as that described above. This ratio is in the range of from 0.2 to 0.6 standard cubic feet of air per fluid ounce of paint.
The process described above can also be employed to effect a simultaneous atomizing, mixing and spraying of two different liquids for coating. More particularly, it has been determined that one type of liquid can be sprayed from one nozzle and a different type of liquid can be sprayed from the second nozzle with the result that the coating deposited on the work is of a uniform blend of the two coating liquids.
The process of atomization described thus far can be employed by itself to cause effective application of paint or a similar coating to a product. However, the atomization process can also be utilized in connection with a paint charging step to electrostaticaily spray paint. In accordance with the present invention, this charging operation is effected by utilizing the atomizing air as a charge carrier for transferring charges to the paint particles.
As is shown in FIG. 7, an electrode 50 is disposed in the air stream preferably within the air nozzle 45. This electrode is connected to a source of high DC potential, for example, a potential of the order of 50 kv. It will, of course, be understood that the potential applied to the electrode 50 can be greater or less than this figure, depending upon such variables as the characteristics, e.g., resistivity of the paint being applied, nature of the article being coated, distance of the gun from the article, etc.
The potential applied to electrode 50 causes a corona discharge to be formed surrounding the tip of the electrode. The. air stream passes through this corona on its path through the nozzle andas a result large numbers of ions are formed in the stream. These ions, i.e., ionized gas molecules have relatively high mobility and move primarily under the influence of the electrostatic field toward the coating material at a relatively low potential. In practice, the ions thus move toward the paint which is at a low potential and ultimately attach themselves to the atomized paint particles.
The two paint stream method illustrated in FIGS. Iv and 8 results in an improved charging efficiency over the one paint stream method shown in FIG. 5. One possible explanation for this is that the paint streams envelope the air stream, i.e., are disposed on both sides of it. Consequently, the ions must pass through a paint stream or a fog of paint particles in order to reach a ground surface. In this travel there is a high likelihood that they will attach themselves to one of the paint particles. In contrast, in the one paint stream method of FIG. 5, the ions can escape to a grounded surface without passing either through a paint stream or a fog of particles, e.g., as shown in FIG. 5 the charged ions could be attracted to a grounded surface and move off to the right without ever contacting the paint.
In any event, empirical tests have shown that the two paint fan electrostatic paint spraying method of FIGS. 7 and 8 as compared to the one paint fan method of FIG. 5 (even when the air stream of the one paint fan method is ionized).
Another important facet of the present spraying method involves the control of the width of the spray pattern. More particularly, it will be appreciated that articles being sprayed vary in physical dimensions so that in order to minimize overspray, it is ofien desirable to alter the size of the paint spray pattern produced by the gun. The novel manner in which this is accomplished in the present invention is diagrammatically shown in FIGS. 15 and 16.
FIG. 15 shows a paint spray directed against a target 55. The actual pattern 56 of spray has a width W which in actual practice would be slightly longer than the target 55. We have empirically determined that the width of the spray pattern can be varied by changing the included angle S of the air stream without changing the width of the paint stream.
As shown in FIG. 15, a fan-shaped sheet of air 57 is emitted from a nozzle 58. The air impinges upon a fan-shaped film of paint 60. It will be appreciated that this film of paint may be a single film which is projected at an angle to the air fan as shown in FIGS. 5 and 6, or may in fact be constituted by two paint films as shown in FIGS. 7 and 8.
In either event, the air is projected from the nozzle in a fanshaped stream which is shown as having upper and lower edges 61 and 62 including an angle S such that the air stream just intercepts the entire section of the film against which the air stream impinges. Again, it will be appreciated that in actual practice the angle S would be slightly greater than that shown so that the air stream passes slightly above and below the film. (This exact relationship is not shown, however, to simplify the present explanation.)
In practice, the spacing between the paint film 60 andthe target 55 remains substantially constant. Accordingly, when it is desired to spray a smaller target 55, as shown in FIG. 16, it is desirable to produce a paint pattern 56' having a smaller width W' without requiring shifting of the gun. In accordance with the present invention, this change in the spray pattern is accomplished by projecting the air fan at a smaller angle S. It will be appreciated that if the angle of the air fan in FIG. 15 were reduced with no further change, the air stream would intersect only a portion of the paint film 60. This would result in substantially unatomized, or coarsely atomized, paint and, hence, a defective finish.
In accordance with the present method, this difficulty is avoided and the paint pattern width is varied without affecting the uniform atomization of all of the paint. Specifically, the size of the paint pattern is altered by making two changes in the air fan. In the first place, the included angle of the air stream is reduced from the angle S-to the angle S. In the second place, the internal configuration of the nozzle opening is changed so that the apparent focal point, or pressure source point, P of the air stream is shifted away from the nozzle opening and away from the paint film to a more remote point as indicated by F.
More particularly, as shown in FIG. 15, it is apparent that the nozzle opening is formed by the intersection of two segments of circular arcs, an external are 63 and an internal arc 64. In this example, the arcs are disposed relative to one another so that the nozzle opening encompasses approximately l80 of the inner are 64. This nozzle functions as though the air emanates from a point source P disposed relatively close to the nozzle opening.
The changed nozzle opening, as shown in FIG. 16, is also formed by the intersection of outer arc 63' and inner arc 64'. In this case, the radius of the outer arc 63' is the same as that of are 63. However, the radius of the inner arc 64 is appreciably greater than the are 64. As a result, the nozzle opening intersects a much smaller portion of the inner arc 64'. This nozzle functions as though the air emanates from a point pressure source I spaced an appreciable distance from the nozzle opening and from film sheet 60'.
As a result of these concomitant changes, i.e., lessening the included angle of the air fan while at the same time shifting the apparent focal point or apparent point source of the air stream away from the nozzle and paint film, the height of the air fan at its point of intersection with the film remains constant. Consequently, by changing the air fan in this manner without changing any other aspect of the operation of the gun, for example, the paint pressure or paint sheet size, the paint pattern can be compacted or enlarged. A preferred form of nozzle construction for effecting these changes in a simple manner is illustrated in FIGS. -14, and the details of construction of this nozzle are explained below.
SPRAY GUN The details of construction of a preferred form of spray gun for carrying out the present method of paint spraying are shown in F168. 9-14. As there shown, the spray gun 11 comprises a hollow handle portion 66, a barrel or extension portion 67 formed of a suitable insulating material and mounted forwardly of the handle and a nozzle assembly 68 mounted on the forward end of barrel 67.
The nozzle assembly 68 includes two paint nozzles 70 and 71 effective to project flat fan-shaped sprays of paint toward the center line of the gun as indicated by dotted lines 72 and 73. The gun further includes an air nozzle 74 effective to project a fan-shaped stream of air forwardly along the axis of the gun toward the area of intersection of the paint streams as indicated by line 75. Additionally, the gun includes an electrostatic charging circuit including a needle electrode 76 for charging the atomizing air and ultimately causing a charge to be applied to the atomized paint particles.
Operation of the gun is controlled by a single trigger 77 which is effective to control flow of paint through a paint valve 78, flow of air through air valve 80, and application of electric potential to electrode 76 through actuation of switches 81 and 82. The trigger functions to first open air valve 80, then open paint valve 78 and finally close switch 81. When the trigger is released this sequence is reversed.
More particularly, handle 66 is formed of a suitable conduc- Live material, such as aluminum or the like. The handle is hollow and is configurated to form a hand grip portion 83, a forwardly extending stock portion 84 and a suspension hook portion 85. A transverse flange is formed at the forward end of the stock for abutment with a mating flange on the barrel. The barrel and stock flanges are bolted together in a conventional manner. Hand grip portion 83 is provided adjacent its lower end with an opening 86 for receiving the combined air and electrical input fitting 87.
Air is introduced to the gun through an air tube which surrounds electrical cable 17, there being an annular space between the tube wall and cable for passage of air from the compressor to the inlet fitting of the gun. The hollow interior of the gun is sealed at the cable entrance in any suitable manner, such as by means of an Oring 90 compressed between a shoulder in the gun housing and a threaded cap member 91. Air passes through an inlet passageway 92 formed in the handle and enters a valve chamber 93 of air valve 80.
This valve includes a reciprocating stem member 94 having an extension 95 disposed for abutment with trigger member 77. An intermediate portion of the stern carries an O-ring 96 or similar packing member disposed between spaced shoulder 97. The inner end of the stem carries a tapered plug 98 adapted to engage a tapered seat to seal off the air flow. When the trigger is depressed, plug 98 is shifted against the force of spring 99 from engagement with seat 100 and air is free to flow into internal chamber 101 in the gun handle.
This chamber communicates with a longitudinal bore 102 in the stock and a continuation of this bore 103 formed in the barrel member. This chamber surrounds a sleeve 104 which is formed of insulating material and is supported in mounting spiders 105 and 106. The forward end of bore 103 communicates with a longitudinal bore 107 formed in nozzle support member 108 which carries the paint and air nozzles. Nozzle support member 108 is preferably formed of an insulating material such as Delrin. Support member 108 is mounted on the front end of barrel member 67 by means of a threaded cap 109 which is coupled to the mounting member by a retaining ring 119 titted in opposed grooves in the cap and mounting member. Cap 109 engages threaded extension 129 on the barrel.
Support member 108 is provided with a circular plugreceiving opening 110. This opening 110 houses a generally cylindrical air nozzle plug 111 which is preferably made of a plastic material, e.g., Delrin. Nozzle plug 111 includes an annular peripheral wall 112 having an arcuate inlet opening 113 which communicates with a vertical central chamber 1 14. The lower end of the plug is closed by a solid circular wall 115, while the top of the plug is closed by a cap 116 which is press fit or otherwise secured to the top of the plug. The cap seals off the upper end of chamber 114 and includes an outwardly extending peripheral flange 117 having a transverse slot 118 for rotating the cap and plug member.
The peripheral wall of the plug member opposite entrance slot 113 is provided with three parallel spaced, rectangular openings 120, 121 and 122. The plug can be rotated to selectively align any one of these openings with front opening 123 in member 108. The selection of the particular nozzle opening 120, 121 and 122 disposed in registry with front opening 123 of the stationary support member 108 provides the means for varying the air stream to vary the paint spray pattern in the manner shown diagrammatically in FIGS. 15 and 16.
More particularly, opening is effective to provide the widest angle of air spray fan and, hence, the widest paint spray pattern. Similarly, opening 121 is effective to provide the narrowest air spray fan and, hence, the narrowest paint spray pattern. Noule opening 122 is effective to provide an air spray fan and paint spray pattern of intermediate size.
It will be noted that nozzle opening 120 is formed by a semicylindrical internal cut 124 formed in peripheral wall 112, the axis of cut 124 being horizontal. This cut is intersected by a segmental disclike cut 125 oriented in a vertical plane and extending inwardly from the outer periphery of wall 112 internally along a radius of the plug member.
In one preferred embodiment of the plug member, the disclike cut 125 has a 0.375-inch radius with a center located 0.178 inch outwardly from the periphery of the plug wall. Intemal cut 124 has a 7/64-inch radius located inwardly 0.169 inch from the periphery of the plug. This nozzle opening has been found effective to emit a fan-shaped stream of air having an included angle of approximately 94. Hydraulically, this nozzle opening functions generally as though there were a point source of gas pressure located at point P1 approximately one-fourth inch inwardly from the periphery of the plug member.
Slot 121 is formed by an internal semicylindrical cut 126 formed in peripheral wall 112 along a horizontal axis. Cut 126 is intersected by a horizontal disclike cut 127. Disclike cut 127 extends radially inwardly from the outer periphery of wall 112. In one preferred embodiment of plug, the disclike cut 127 has a 0.375-inch radius with the center located 0.2l9 inch outwardly from the periphery of the plug wall.
internal cut 126 has a radius of 0.203 inch with the center of the cut being located 0.263 inch from the periphery of the plug. This nozzle opening has been found to emit a fan-shaped stream of air having an included angle of approximately 36. This nozzle functions generally as though the air emitted from it emanated from a point source P3 disposed substantially further from the peripheral wall than point P1 (e.g., approximately four times as far).
in order to maintain the volume of air emitted from nozzle openings 120 and 121 substantially equal, the width of nozzle opening 121 is made slightly narrower than the width of nozzle opening 120 so that the cross-sectional area of the opening is constant. Thus, in one preferred embodiment, the width of nozzle opening 120 is made equal to 0.074 inch, while the width of nozzle opening 121 is made equal to 0.065 inch.
The third, or intermediate size, nozzle opening 122 is similarly formed, i.e., this nozzle opening is formed from asegment of a cylindrically internal cut 128 intersected by a vertical disclike cut 130, disclike cut 130 extending inwardly along a radius from the outer peripheral wall 112. In one preferred embodiment, the cut 130 has a 0.375-inch radius with a center located 0.168 inch from the periphery of the plug. Inner cut 123 has a radius of 0.156 inch located 0.216 inch from the periphery of the disc. This nozzle opening emits a fan-shaped stream of air having an included angle of approximately 64. Air is emitted from this nozzle in generally the same manner as though the air flowed from a point source P2 located of the order of twice the distance from the periphery of the plug as point P1. In this preferred embodiment the pressure of the air applied to the gun is relatively low, for example, of the order of 9-45 psi. at the gun. The exit velocity of the air is approximately sonic.'The distance, in the preferred gun, of air travel L to the point of impingement of the air and paint streams is approximately three-sixteenths inch.
Paint is supplied to the gun from pump 12 through tube 14. This tube is coupled to the gun through fitting 131 which communicates with a longitudinal paint passage 132 formed in extension member 67. Passage 132 communicates with the seat area 133 of paint valve 78. This seat area is engaged by a spherical head 134 of valve stem member 135. This valve stem member reciprocates longitudinally to shift the head 134 toward and away from the seat member and is spring-urged toward the seat by means of a compression spring 136.
The valve is adapted to be opened by pressure on trigger 77. When the trigger is pivoted toward the handle member about pivot pin 137 which supports the upper end of the trigger, the trigger engages a shoulder 138 secured to stem 135, forcing the stem rearwardly to open the paint valve. With paint valve 78 open, paint is free to flow through longitudinal conduit 140 into annular passageway 141 and from this passageway into axial angulated bores 1 12 and 143 formed in nozzle support member 108. These bores communicate with paint nozzle assemblies 70 and 71.
More particularly, bores 142 and 143 are aligned with 1111818 1 M and 145 in cylindrical members 1416 and 1417. Each of these cylinders is formed with an internal passageway 148 and a seat 150 for a check valve formed by ball member 151. Each of the balls 151 is spring-urged against the seat by means of a spring 152 bearing against a thrust washer 153 mounted within a chamber 156 in cylindrical members 116, 1417. Each of the chambers opens into an axial passageway 155 communicating with an axial bore 156 in tubular nozzle member 157. Each of the nozzle members is preferably formed of a suitable plastic material, such as Delrin.
The fluid discharge passageway in each of the nozzles is formed by a V-shaped cut 158 extending inwardly from a periphery of the wall to approximately the centerline of the tube. Each of the V-shaped cuts 153 includes a rearward wall 160 and a forward wall 161. As shown in FIG. 10, each nozzle 157 is angulated, or tilted, slightly outwardly relative to the axis of passageway 155. This tilting enables the nozzle to direct the paint stream at the desired angle relative to the air fan.
More particularly, each nozzle 157 is effective to emit a thin substantially planar fan-shaped stream of paint at an angle of approximately 60 to the axis of bore which is parallel to the axis of the gun. Consequently, this fan-shaped paint stream is impinged by the fan-shaped air stream at approximately the same angle, i.e., at approximately 60. In this preferred embodiment, the length of paint travel L from the nozzle to the I zone of impingement of the paint and air streams is approximately five-eighths inch.
In accordance with the present invention, the ends of axial bores 156 in each of the nozzle tubes 157 is closed by a springlosded plug 159. These plugs are secured to angulated spring members 162 in any suitable manner; for example, as shown in FIG. 10, plug 159 passes through a small bore in a portion of arm 162 and has an overturned head .163 effective to clamp the plug to the arm. Both plugs 159 and spring members 162 are preferably formed of a suitable plastic material. Arms 162 include a transverse section 164 and a foot portion 165 which is mounted upon the support member 108 in any suitable manner, such as by means of bolts 166.
Each of the spring members 162 also includes an overturned flange portion 167 by means of which the spring arm can be pulled outwardly to disengage the plug from the seat formed in the end of the associated tube member 157. In normal operation, the spring force is sufficient to maintain the plug in sealing engagement with the end of the tube 157 How ever, in the event that the nozzle should become clogged, the
passage can readily be cleared by grasping flange portion 163 to pull the spring arm and plug outwardly, opening the end of the tube. Trigger 77 is then depressed to cause paint to be discharged from the end of the tube removing whatever impediment had accumulated in the tube section.
The electrical input to the gun is preferably through a highresistance cable 17. The details of construction of one preferred form of cable are disclosed in Rosen US. Pat. No. 3,348,186. The remote end of this cable is connected to a power pack 16 effective to develop a high DC potential, for example, 50,000 volts. Cable 17 enters the gun through the interior of fitting 87 and passes upwardly through a hollow section 170 of the handle. The cable is flexible and is bent rearwardly around shoulder 171 at the junction of the hand grip portion 83 and the stock portion 84 toward the rear wall 172 of the stock. The cable is then bent forwardly and is inserted into insulating sleeve 104, the cable being loosely received in the sleeve so that it is free to move relative thereto. The forward end of the cable is provided with a contact button 173 disposed for mating contact with a similar contact button 174 provided on the rear end of cylindrical resistor 175.
This resistor is preferably sealed in the end of sleeve 104 and has an electrical resistance of the order of 75 megohms. The forward end of resistor 175 is in electrical contact with a bolt 176 passing inwardly through a cap member 177 enclosing the forward end of sleeve 104.
The head 180 of bolt 176 is engaged by a contact spring 178 which is compressed between the head of the bolt and a head 181 formed on electrode 76. Electrode 76 is in the form of an elongated pin supported in axial aiignment with the air nozzle by means of a cruciform insulating member 182. This cruciform insulating member includes a central bore 183 into which the pin is press fit. The cruciform member is rigidly mounted in the central opening 107 in support member 105.
Electrode '76 extends forwardly through entrance opening 113 in the air nonle member and extends forwardly to a position just inside the peripheral wall 112 carrying the three nozzle openings 120, 121, and 122. In normal operation, this electrode is charged to a suitable potential of the order, for example, of 40,000 volts. A corona is established surrounding the tip of the electrode. The stream of air flowing through the nozzle surrounds the electrode and passes through the corona prior to the time it is discharged from the nozzle opening. As the air passes through the corona gasmolecules are ionized and dust particles are charged. These ions and charged particles move forwardly under the influence of the electrostatic field forces toward a lower potential region of the field constituted by the paint films and atomized particles. There the charges attach themselves to the paint particles to form the charged paint spray.
One of the advantages of this paint charging device is that the paint supply in conduit 14 does not become charged so that the entire paint supply system, including tube 14, pump 12 and the paint supply tank 13, remain at or very near ground potential. In fact, in the embodiment shown the paint supply system is grounded through needle 135 and handle member 66 which is conventionally grounded in use. This greatly simplifies the problem of insulating the paint supply system and eliminates the dangers common in many prior art systems due to charge accumulation in the paint supply system.
In addition to the elements described above, the electrical charging circuit includes a safety circuit for preventing application of power to the cable in the event that resistor 175 is removed from the gun and the gun reassembled without replacing the resistor.
More particularly, as is best shown in FIG. 9, the cable 17 forms a rearwardly extending resilient bend 190 adjacent to rear wall 172 of the stock. An actuating arm 191 is pivoted about pin 192 in the stock portion of the gun and is interposed between cable bend 190 and rear wall 172. This arm includes a forwardly extending link portion 189 which is attached to one end of tension spring 193, the other end of the spring being secured to a stationary bracket 194.
Bracket 194 carries snap-action microswitches 81 and 82. Microswitch 82 is normally closed, while microswitch 81 is normally open. A spring arm 195 is disposed for engagement with actuating plunger 196 of microswitch 82. This spring arm is adapted to be shifted with link 189, for example, by engagement with a shoulder 197 carried by the link.
So long as the cable 17 is positioned rearwardly as shown in FIG. 9, plunger 1% is not depressed and switch 82 remains closed. In normal operation of the gun, the cable is held in this position against forward movement by the presence of resistor 175. However, if resistor 175 and sleeve 104 are not present in the gun, spring 193 acting upon arm 191 forces the cable forwardly within conduit 103. This forward movement of arm 191 causes arm 195 to open switch 82.
As is shown in FIG. 17, switch 82 is connected in series with switch 81 and a coil 198 of relay 200. Switch 81 is normally open switch adapted to be closed upon actuation of trigger 77. More particularly, microswitch 81 includes an actuating plunger 201 adapted to be engaged by a spring arm 202. This arm in turn is positioned for contact with a head 203 formed on the continuation of stem member 135.
When trigger 77 is depressed, the stem and its extension are shifted rearwardly so that head 203 bends spring arm 202, closing microswitch 81. When both microswitch 81 and 82 are closed, relay 200 is energized to complete a circuit to power pack 16. This power pack is then effective to apply a potential to cable 17 and, hence, to electrode 76.
The safety circuit just described is also effective to prevent application of power to the cable when the nozzle assembly is removed from the gun. More particularly, as is shown in FIG. 9, tube 104 is supported in the surrounding bores in the stock member and barrel by means of low friction spiders 105 and 106. The tube is normally retained in its retracted position shown in FIG. 9 by the abutment of spider 182 with the end of cap member 177. However, when the nozzle mounting member 108 is removed by unthreading cap 109 from the threaded extension 129 on the barrel member, the restraint on forward movement of the sleeve is removed. The sleeve is then shifted forwardly under the influence of spring 193 acting on the cable member.
As the cable member is shifted to the left, arm 191 is shifted forwardly causing arm 195 to open switch 82 preventing energization of the power pack and thereby preventing application of potential to cable 17. At the same time, forward movement of sleeve 104 is effective to provide a second function in that it automatically seals the air chamber and end of the resistor or electrical conduit from contamination. More particularly, as best shown in FIGS. 9 and 10, the forward end of cap 177 is tapered to form a seat 204. This seat is effective to engage a mating tapered seat 205 formed in the barrel 67 when sleeve 104 is shifted forwardly, i.e., to the left in FIG. 10.
When the nozzle is reassembled, spider 182 engages cap 177 forcing the cap away from the seat 205 to reopen the air conduit. At the same time, the cable 17 is shifted rearwardly so that bend causes am 191 to pivot, thereby reclosing switch 82 to permit reenergization of the power pack and cable 17 when trigger 77 is depressed.
The construction of the gun as described above also incorporates two additional safety features. In the first place, switches 81 and 82 and the other electrical contacts such as those between the cable and resistor occur in an enclosed or pressurized explosiveproof chamber. Moreover, this chamber is continuously purged to remove any accumulated gases by the flow of the air utilized to atomize the paint.
From the foregoing disclosure of the general principles of the present invention and the above description of a preferred embodiment, those skilled in the art will readily comprehend various modifications to which this invention is susceptible.
For example, while the air fan and paint fan streams have been described as being substantially planar, it is contemplated that the paint fans may be slightly arcuate, i.e., in the form of thin bowed sheets. Moreover, if a gun is to be utilized for atomizing, mixing and spraying two different liquids by spraying one liquid from one nozzle and another liquid from the other nozzle, it is apparent that a separate supply line must be provided for each nozzle. This can readily be accomplished by essentially duplicating the liquid supply system shovm while eliminating the conduit which now interconnects the two nozzles. Also while air has been described as the atomizing gas, it will be appreciated that in some particular installations other gases could be employed. Accordingly, the term air" as used in the following claims should be interpreted as including other gases as well.
Accordingly, we desire to be limited only by the scope of the following claims in which it is to be understood that the term paint is used in the generic sense to cover finish coatings of the type described above and in which the term gun is used generically to cover either a hand spray gun or a mechanically supported control spray device.
Having described our invention, we claim:
1. A paint spray gun, said gun comprising,
a handle portion,
a barrel portion extending forwardly of said handle portion, said handle portion being hollow and having an air passageway therethrough,
an air conduit within said barrel portion in communication with the air passageway in said handle,
a paint conduit in said barrel portion,
a paint nozzle in communication with said paint conduit,
an air nozzle in communication with said air conduit,
an electrode for causing said paint particles to become electrostatically charged,
means for applying a potential to said electrode,
said means comprising a cable, said cable entering said gun through said handle and including a bent portion being disposed within said stock and a forwardly extending portion disposed within said barrel, a resistor in abutment with the end of said cable and extending forwardly thereof, said resistor providing an electrical interconnection between said cable and said electrode, spring means urging said cable toward said resistor, a switch effective to control the voltage applied to said cable, said switch being disposed for actuation to deenergize said cable when said cable is shifted forwardly under the influence of said spring upon removal of said resistor.
2. The paint spray gun of claim 1 in which a sleeve is slidably disposed in said air conduit and said resistor and said cable are disposed within said sleeve, a mounting member is disposed on the end of said barrel for supporting said air nozzle, said paint nozzle and said electrode, said mounting member carrying means for restraining forward movement of said sleeve, whereby when said mounting member is removed said cable moves forwardly and said switch is actuated to deenergize said cable.
3. The paint spray gun of claim 2 in which said barrel is configurated to form a seat and the forward end of said sleeve is configurated to form a plug, whereby when said mounting member is removed said sleeve moves forwardly and said plug engages said seat to seal said air conduit.
4. The spray gun of claim 1 in which said switch is disposed within the air passageway in the handle, said air conduit constitutes an explosive proof chamber.
5. The spray gun of claim 1 further comprising a second switch for controlling energization of said cable,
a trigger for actuating said second switch, said first named switch and second switch being disposed within said air passageway, said air passageway constituting an explosive proof chamber.
6. A paint spray gun for use in a system including a source of compressed air and a source of paint,
said gun having a barrel portion,
an air conduit through said barrel portion, means for connecting said air conduit to said source of compressed air,
a paint conduit through said barrel portion, means for connecting said paint conduit to said source of paint,
a flat fan air nozzle in fluid connection with said air conduit,
a flat fan-type paint nozzle,
means supporting said air nozzle and said paint nozzle on said barrel,
said air nozzle and said paint nozzle being in fluid communication with said air conduit and said paint conduit respectively,
said air nozzle being effective to project a flat fan of air forwardly of said gun,
said paint nozzle being effective to project flat fan of paint forwardly of said gun which intersects said flat fan of air in a zone spaced forwardly of said gun,
means for ionizing said air in an area rearwardly of said zone in which said air fan impinges upon said paint fan,
whereby the air fan is effective to atomize said paint and to charge said paint to form a charged paint spray.
7. The paint spray gun of claim 6 in which said means for ionizing said air comprises an electrode disposed within said air nozzle.
8. The paint spray gun of claim 6 in which the paint nozzle is disposed so that the flat fan of paint intersects the stream of air at an angle of from 30 to 70v 9. The paint spray gun of claim 6 in which the air and paint nozzles are disposed so that the length of air travel of the air fan from the nozzle to the zone of air-paint impingement is from one-sixth to three-fourths the length of travel of the paint fan from the paint nozzle to the zone of air-paint impingement.
110. The paint spray gun of claim 6 in which the air and paint nozzles are disposed so that the air fan travels a distance of approximately one-eighth to three-eighths inch from the air nozzle to the point of air-paint impingement.
ill. The paint spray gun of claim 6 in which the air and paint nozzles are disposed so that the paint fan travels from approximately three-eighths to three-fourths inch from the paint noz zle to the zone of air-paint impingement.
112. The paint spray gun of claim 6 in which said air nozzle comprises a housing having a cylindrical chamber formed therein and an elongated exit slot and an entrance opening communicating with said chamber, a shiftable plug disposed within said chamber, said shiftable plug including a plurality of nozzle slots formed therein, each said nozzle slot being effective to limit a fan of air having a different included angle, a
central bore communicating with said nozzle slots and an inlet opening communicating with said bore, said plug being shiftableto selectively align any of said exit slots with the slot in said housing, and an electrode extends inwardly through the entrance opemng in said housing and the inlet opening of said plug, said electrode being disposed in alignment with the exit slot of said chamber and the nozzle slot of said plug in rem'stry therewith.
13. A paint spray gun for use in a system including a source of compressed air and a source of paint,
said gun having a barrel portion,
an air conduit through said barrel portion, means for connecting said air conduit to said source of compressed air,
a paint conduit through said barrel portion, means for connecting said paint conduit to said source of paint,
a flat fan air nozzle in fluid connection with said air conduit,
a pair of flat fan-type paint noules,
means supporting said air nozzle and said paint nozzles on said barrel,
said air nozzle and said paint nozzles being in fluid communication with said air conduit and said paint conduit respectively,
said air nozzle being effective to project a flat fan of air forwardly of said gun,
said paint nozzles being efiective to project flat fans of paint forwardly of said gun which intersect said flat fan of air in a zone spaced forwardly of said gun, means for ionizing said air in an area rearwardly of said zone in which said air fan impinges upon said paint fans, whereby the air fan is effective to atomize said paint and to charge said paint to form a charged paint spray.
14. The paint spray gun of claim 13 in which the paint nozzles are disposed so that the flat fans of paint intersect the stream of air at an angle of from 30 to 70.
15. The paint spray gun of claim 14 in which the air and paint nozzles are disposed so that the air fan is disposed substantially on the bisector of the angle between said paint fans.
16. The paint spray gun of claim 13 in which the air and paint nozzles are disposed so that the length of air travel of the air fan from the nozzle to the zone of air-paint impingement is from one-sixth to three-fourths the length of travel of the paint fans from the paint nozzles to the zone of air-paint impingement.
17. The paint spray gun of claim 13 in which the air and paint nozzles are disposed so that the air fan travels a distance of approximately one-eighth to three-eighths inch from the air nozzle to the point of air-paint impingement.
18. The paint spray gun of claim 13 in which the air and paint nozzles are disposed so that each paint fan travels from approximately three-eighths to three-fourths inch from the paint nozzle to the zone of air-paint impingement.
19. The paint spray gun of claim 13 in which said means for ionizing said air comprises an electrode disposed within said air nozzle.
20. The paint spray gun of claim 13 in which said air nozzle comprises a housing having a cylindrical chamber formed therein and an elongated exit slot and an entrance opening communicating with said chamber, a shiftable plug disposed within said chamber, said shiftable plug including a plurality of nozzle slots formed therein, each said nozzle slot being effective to limit a fan of air having a different included angle, a central bore communicating with said nozzle slots and an inlet opening communicating with said bore, said plug being shiftable to selectively align any of said exit slots with the slot in said housing, and an electrode extends inwardly through the entrance opening in said housing and the inlet opening of said plug, said electrode being disposed in alignment with the exit slot of said chamber and the nozzle slot of said plug in registry therewith.