US 3767115 A
An electrostatic spray gun assembly used to spray coating materials. Normally, the invention is useable with the type of spray gun commonly referred to as an airless electrostatic spray gun. The primary advantage of this invention over the prior art is its ability to operationally function with low resistive materials or materials with a high percentage of conductive aggregates. This ability is accomplished by completely electrically insulating the charging elements from the coating material passage while in the gun body. Charges are placed on the coating material by an external electrode that sets up an electrostatic field between the gun and the object to be coated. The nozzle cap that holds the electrode and retains the spray tip can be rotated 360 DEG until it reaches a tightened fixed position. Electrical contact with the electrode is maintained by a conductive ring no matter what the final tightened orientation. The ring and its attached electrode can be selectively adjusted to insure proper placement of the charges on the coating material regardless of the final orientation of the electrode, when in its tightened position, or of the spray tip's orientation. The features of this invention are useable with both operator-actuated hand guns and automatic spray guns.
Claims available in
Description (OCR text may contain errors)
Kozinski et al.
ELECTROSTATIC SPRAY GUN APPARATUS  Inventors: David Arthur Kozinski, Palatine;
- Joseph Kozinski, Chicago; Frank M.
Singel, Hillside; Robert G. Smead, Saint Charles, all of Ill.
 Assignee: Graco Inc., Minneapolis, Minn.
 Filed: Dec. 27, 1971  Appl. No.: 212,335
 US. Cl. 239/15  Int. Cl. B05b 5/00, F23d 11/28  Field of Search 239/3, 15
 References Cited UNITED STATES PATENTS 3,248,059 4/1966 Fischer et al. 239/15 3,677,470 7/1972 Probst et al 239/15 3,425,625 2/1969 Probst 239/15 3,253,782 5/1966 Fischer et al. 239/15 3,169,883 2/1965 Juvinall 239/15 3,459,374 8/1969 Probst 239/3 3,625,424 12/1971 Montica.... 239/15 3,693,877 9/1972 Cowan 239/15 3,589,607 6/1971 Wolf et al 239/15 3,613,993 10/1971 Gourdine et al 239/15 Primary ExaminerLloyd L. King Att0rneyPaul L. Sjoquist An electrostatic spray gun assembly used to spray coating materials. Normally, the invention is useable with the type of spray gun commonly referred to as an airless electrostatic spray gun. The primary advantage of this invention over the prior art is its ability to operationally function with low resistive materials or materials with a high percentage of conductive aggregates. This ability is accomplished by completely electrically insulating the charging elements from the coating material passage while in the gun body. Charges are placed on the coating material by an external electrode that sets up an electrostatic field between the gun and the object to be coated. The nozzle cap that holds the electrode and retains the spray tip can be rotated 360 until it reaches a tightened fixed position. Electrical contact with the electrode is maintained by ABSTRACT a conductive ring no matter what the final tightened orientation. The ring and its attached electrode can be selectively adjusted to insure proper placement of the charges on the coating material regardless of the final orientation of the electrode, when in its tightened po- 15 Claims, 5 Drawing Figures ELECTROSTATIC SPRAY GUN APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention:
Generally, this invention relates to coating material spray guns in which an electrostatic charge is applied to the coating particles. More specifically, it is concerned with an airless electrostatic spray gun useable with low resistance paints or coating materials with a high percentage of conductive aggregates.
2. Description of the Prior Art:
Electrostatic spray guns that initially charge at least part of the coating material column within the body of the gun are known. In addition, air atomizing electrostatic spray guns that have their charging electrodes external of the gun and use a portion of the gun as ground potential to create a localized field therebetween are known. Examples of the latter air guns are disclosed in U.S. Pat. Nos. 3,589,607.to Wolf et al, 3,587,967 to David H. Badger, and 3,606,972 to Wolfgang Ferrant. In none of the known prior art devices is an electrostatic spray gun with a completely electrically isolated coating material passage in the gun and a forwardfacing external electrode used to create a zone of ionization between the gun and the object to be coated uti-v lized. This construction greatly reduces the common problem of airless electrostatic guns associated with the tendency to short out the power source for the high po'- tential generator when low resistance paints or conductive aggregates are used in the coating material. In addition, it reduces the capacitance within the gun body by reducing the charged metal mass and thus providing an increased safety factor, especially when incorporated into operator-held hand guns.
SUMMARY OF THE INVENTION The electrostatic spray gun of this invention utilizes an external material charging electrode for setting up an electrostatic field between the gun and the object to be coated. The charging element is in an electrically isolated passage separated from the coatingmaterial encompasses automatic spray guns in which the trigger operating control is other than manual. FIGS. 1 and 2 illustrate the conventional elements of most electrostatic hand spray guns, namely: a longitudinal insulated barrel, a nozzle assembly 2, a handle 3 connected to an electrical ground by cable 4, a trigger 5, and a valve assembly shown generally as 6 in FIG. 2.
The trigger, needle valve, hook 7 used to hang the gun when not in use, and the handle are of conventional design. When trigger 5 is moved in a counterclockwise direction as shown in FIG. 2, it is pivoted at screw pivot 8 which results in coupled insulated shaft 9 of valve assembly 6 being moved to the right as attached U-shaped member 10 is pivoted rearwardly. Shaft 9 as well as spring 11, valve head 12, valve seat 13, and the connections to assembly 14, plus the adjoining structure between valve head 12 and shaft 9 comprise the valve assembly (FIG. 3). Spring 11 normally biases the shaft 9 and its attached valve head 12 into a seating position (left in FIGS. 2 and 3) in valve seat 13 to normally prevent the flow of coating material until trigger 5 is activated to control the movement of electrically non-conductive shaft 9. The assembly 14 (FIG. 2) is constructed to prevent the movement of shaft 9 when control knob 15 is rotated in a clockwise direction as far as possible. Shaft 9 as well as its attached extension 16 and the nut with plate 14a move in unison to the right (FIG.2) when trigger 5 is activated. During this movement, the nut 16a, which is threaded to the internal threads at the end of the horizontal section of passage 18, does not move. By rotating knob 15, member 14a is moved (to the left in FIG. 2) so that the member 10 is clamped by a vise type action between stationary nut 16a and the plate 14a. As trigger 5 is rigidly attached to the U-shaped bracket member 10 (FIG. 1), the clamping of member 10 also prevents the'pivoting of trigger assembly 5 at screw passage while in the body of the gun. The position of I the external electrode and the field it creates relative to the movement of coating material provides an improved electrostatic spray gun useable with low resistive coating materials.
A primary object of this invention is an improved electrostatic spray gun.
An additional object is an improved selectively adjustable electrode in an insulated nozzle assembly.
Still another object is an airless electrostatic spray gun with a reduced electrical capacity that is useable with coating materials having a larger resistivity range than heretofore possible.
FIG. 1 represents an exploded view of the preferred embodiment of our invention.
FIG. 2 shows the gun of FIG. 1 in cross-section along its longitudinal extent.
FIG. 3 shows the frontal portion of the gun of FIG. 2 in an enlarged detailed cross-sectional view.
FIG. 4 is anenlarged cross-sectional view of the nozzle and frontal charging elements.
FIG. 5 is an end view, as viewed from the right in FIG. 4, of the complete enlarged nozzle cap.
FIG. 1 shows the exploded preferred embodiment of our electrostatic spray gun in the form of an operator hand-held gun. As will be apparent, our invention also pivot 8. Knob 15 can thus act as a safety lock nut when properly adjusted.
The body of the gun is indicated generally as 17 in FIG. 2. It is made of an electrically non-conductive insulating material with a high dielectric strength. The body consists of two major subdivisions, namely, the barrel 1 and handle 3. Both the barrel and handle have at least two joined passages therethrough. The first of these passages 18 (FIGS. 2 and 3) is a conduit for the pressurized coating material as it initially enters through the metal butt plate 19 of the handle and then moves around the exterior surface of insulated passage 18 up to normally close valve head 12 and valve seat 13. The second of the passages 20 in barrel 1 and handle 3 is used'to contain the charging elements for the coating material emitted from the gun. It, of course, is not necessary that the barrel and handle house both the coating material passage 18 and charging passage 20. For example, the-charging could be accomplished by a separated wire conductor externally insulated from the gun and other conductors. Such an external conductor could be clamped, or otherwise attached, to the insulated gun body at one or more positions along its length. For example, similar to the clamps shown in Walberg Pat. No. 3,251,551 issued May 17, 1966. Thus, as used in this application, the term barrel means by itself encompasses the case shown in the preferred embodiment where there are two passages bored in a unitary insulating body and also the case where the coating material passage is in the insulated body and the conductor used to charge the coating material is external of the gun body, usually encased in another insulater.
The charging elements are shown generally as 21 in FIG. 1. They consist of several parts, all of which are internal to the gun, in the preferred embodiment, except for the external electrode 22 (see FIGS. 2-4). The electrode 22 is also the first and only element to come in contact with the coating material as there is complete electrical insulation of the two passages 18 and witnin the body and its handle and barrel 1. It is very important to the operation of our invention that this electrical isolation be maintained between the coating material and the conducting elements of the charging means.
At its lower end, the gun charging elements are connectable by an inserted cable 23 in the handle that extends through butt plate 19 and is coupled to the high voltage cable that leads to a power pack with a voltage generating source and AC to DC transformer (not shown). The connecting couplings 24 and cable 23, as well as the voltage generating and transformer, form no part of this invention. They could, of course, assume various configurations and constructions. They function as a source of high DC voltage for the gun electrode 22 which voltage is usually in the range of many kilovolts. A fuller explanation of one type of useable source with a safety circuit can be found in the commonly assigned U.S. Pat. No. 3,641,971, issued Feb. 15, 1972.
The cable 23 extends well into the passage in the insulated gun handle (FIG. 1) and terminates at approximately the point'at which the passage forms an obtuse angle to join with the barrel section of passage 20. At the end of cable 23, a conductive protruding pin 25. (FIG. 1) is inserted which is surrounded by spring 26 as shown in FIGS. 1 and 2. The end of pin 25 and spring 26 contacts a conductive coupling member 27 that is biased by another spring 28 mounted on the end of a resistor 29.
Resistor 29 is an elongated cylindrical type of resistor in the charging passage 20 of the barrel 1. It is rated at a y. s hms 593 i tensed to 1000 megohms. Its function is to reduce the energy in the hand gun to prevent the possibility of the high voltage from becoming a source of ignition. Other types of resistive elements, such as the cable itself, could be used in lieu of this resistor. As is well-known in the electrostatic spray art, such resistors or resistive elements may or may not be employed as safety features when automatic controlled (versus operator controlled) spray guns are utilized.
As best shown in FIG. 1, connected to the front of the resistor 29 in the same passage is a conductive blunt rounded plug 30 with a biasing spring. This plug contacts an adjustable non-conductive screw 31 which is threadly retained by interior threads in the same passage 20 as it angles at a right angle to the section of passage 20 with resistor 29. Insulated threaded plugs 31 and 32 (FIG. 3) are threaded to interior bore threads on right angle intersecting bores of sections of passage 20. This provides for easy removal of plugs 31 and 32 and the conductive elements each retains. For example, by removing plug 31, member 30, resistor 29, spring 28, and coupling conductor 27 may be removed for replacement or adjustment.
A conductive lead or wire 33 is connected at one end to conductive screw 34 and at the other end to an outwardly (left in FIG. 3) spring biased conductive plug 35. This conductive plug member is at the front end of the insulated barrel passage and is outwardly biased to a position where it contacts an annular conductive ring 36 (FIGS. 1 and 3). Conductive ring 36 is maintained in a fixed position to the inner side of a nozzle assembly 2 by means of a second electrically dead locating pin 37a in a second hole that partially extends into nozzle 39.
The nozzle assembly 2 is an insulated rotatable nozzle that can be moved 360 relative to the barrel 1 of the gun body by rotating it on threads of sleeve 38 until it is fixed in a tightened position. Extending through the nozzle assembly is conductive charging element 37 or wire as shown best in FIG. 3. This charging element is fixed to ring 36 and inserted in a tight but removable manner in the nozzle assembly and rotatable therewith. The extended exterior portion of conductive element 37 forms the electrode 22. This electrode 22 ends in a free point charging tip. Electrode 22 is angled outwardly pointing away from the gun barrel 1 and towards the extended axial center line of the coating material passage 18. Material emitted from passage 18 is charged by electrode 22 in the zone of ionization formed at and forward of the nozzle assembly 2.
The nozzle assembly, in addition to the mentioned charging elements and conducting ring 36, has several other members. The insulated non-conductive cylindrical sleeve 38 is threaded at both of its ends to engage interior threads of the barrel 1 and insulated nonconductive nozzle nose cap 39 (FIGS. 3-5) which also has member 37 extending therethrough. By rotating cap 39 on its threads that engage the front complementary threads of cylinder 38, the electrode 22 that is fixed oncap39 can be positioned anywhere within 360 degrees around the center linea xis of passage 18. Two set screws 41, one a steel interior set screw and the other a nylon exterior screw, act to prevent rotation and removal of cylinder 38. When rotated on the threads of cylinder 38 to the tightest position possible, the angular position or orientation of electrode 22 relative to the center line axis of passage 18 is fixed. Usually, this fixed orientation of the electrode is sufficient for most spraying operations. In some cases, the position of the electrode 22 relative to the stream of coating material may be such that the charge placed on the material is of insufficient strength. For example, should the spray tip 40 be rotated to change the spray pattern, the electrode may end up in the flow of the coating material. Normally, this would not be the best location for imparting charges. A position adjacent to and out of the flow of coating material would be better. To correct this electrode orientation problem, the nozzle 39 has set about apart (FIGS. 4 and 5) from the first through hole 43 at least one additional second through hole 42. By removing charging member 37 and its attached ring 36 and electrically dead locating pin 37a (FIGS. 3 and 4), the electrode 22 may be positioned in this second through hole 42 to insure a satisfactory charge on the particles. These two holes have been found to be satisfactory for just about every spraying pattern to obtain a sufficient charge. Should more holes at the same or different angles be desired for positioning the removable electrode, such could obviously be provided.
FIG. 4 shows the charging element 37 and locating member 37a in position in hole 43 with the dotted lines of hole 42 illustrating the alternate positioning hole about 90 apart. In the FIG. 5 end view, the conductive ring 36 and its charging attachments 37 and 37a have been removed from the FIG. 4 view. Also, FIG. 5 is a completed view of the nozzle cap as opposed to the sectional view of FIG. 4. It shows four holes 42, 43, and the two holes for 37a. As previously stated, holes 42 and 43 extend completely through the longitudinal extent of the nozzle cap 39 and holes 37a extend only partially through cap 39 and act as the receivers of the locating pin 37a depending on which hole 42 or 43 is being used for member 37.
It is thus seen an electrically isolated conductive path has been provided within the gun from the point cable 23 enters plate 19 until it exits as external electrode 22. The outwardly biasing action of the spring on member 35 insures a constant electrical path by continuously contacting ring 36. As can be seen from FIG. 3, the pressurized coating material, which is usually a liquid, exerts no direct pressure on cap 39 as long as valve head 12 is seated in seat13. When head 12 is moved to the right in FIGS. 2 and 3, the pressurized coating material comes in contact with the interior bore of spray tip 40. Tip 40 freely sits in a recess on the front of sleeve 38 and it is held therein by nozzle cap 39 as it is threaded on sleeve 38. When the cap 39 is rotated to a loosened position, the spray tip 40 can be rotated to a different angle to change the spray pattern of the coating material as it passes by tip 40. Once selected, the cap 39 is tightened to fix this new orientation of tip 40.
By isolating the coating material column within the gun from the electrical charging element by the use of non-conductive electrically insulated material, the possibility of current using the coating material as a conductive path is minimized. This added advantage becomes more noteworthy as the resistivity of the coating material decreases. For example, with our invention it is possible to spray paints wit a metallic conductive aggregate of about one pound of conductive aggregate to a gallon of coating solution or with a resistivity as low as 0.1 of a megohm resistanceper cubic inch of material fluid used. No known airless electrostatic spray guns can successfully use such coating material without shorting out the power source.
Further, by not charging any metal in the inner portion of the gun, the electrical capacitance build up is maintained at a minimum. This is true because the electrical capacitance of the gun (c) is a physical feature determined by the value of the metallic parts of the gun. By keeping the metallic content of the charging means between safety resistor 29 and electrode 22 to a minimum, the capacitance is also kept at a minimum.
This insures a small build of charge Q by the relationship Q CV.
The thrust of our disclosure has been to low resistive liquid coating materials with or without conductive aggregates, such as metallic pigments like aluminum, carbon black, or electrolytes, in the coating material. It is not limited to such solutions as it can be used with low resistivity pulverant or powder coatings that are sprayed with electrostatic equipment. It is, of course, useable with high resistive paints or coating materials as would be any ordinary electrostatic spray gun.
The terms air and airless as applied to electrostatic spray guns are well-known in the spraying art. The primary difference between these two methods of spraying is the way the coating material is atomized or broken up into small particles. In air spray, an auxiliary source or sources of pressurized air impinges upon the paint spray stream to aid in breaking up the stream into small droplets or particles. These auxiliary air sources sre usually no more than 150 psi. On the other hand, airless sprays do not use auxiliary sources of air to break up the paint but depend on higher pressure being applied to the coating material to atomize the coating material. Usually, at least a minimum pressure of about 100 psi at the guns spray tip is needed depending 1 pt ssharasts istis .qflb s i g matsfi lbs ns sprayed. Working pressures over 5,000 psi at the gun spray tip are known with the typical atomizing working pressure for hand-held airless spray guns being about 2,000 psi. Variations between psi and 5,000 psi range are common for the atomizing working pressure depending on many factors such as the coating material characteristics, the spray pattern desired, the strength of the systems hoses and couplings, the pump used, the spray gun tip used, and, of course, the gun itself. The magnitude of the pressure must be sufficient to atomize the coating material as it passes from the relatively large diameter coating material passage in the spray gun through the small orifice of the spray tip. In powder guns, the air is used as a conveyance for the powder particles that are already broken up. The principles of this invention could be included in all of these three methods; however, the greatest benefits are found in the airless spray systems.
The described preferred embodiment of a hand-held airless electrostatic spray gun useable with liquid coating materials, it will be understood, should not be used to limit or otherwise restrict the scope of our invention which is set forth in the following claims.
1. An electrostatic spray gun for setting up an electrostatic field between the gun and the object to be coated comprising:
a material charging element connectable to a source vof high potential; barrel means made of electrically insulated material; said barrel means having a front end and two passages terminating adjacent said front end;
the first of said passages constituting a material coating conduit and the second of said passages constituting a conduit to contain said material charging element;
said two passages being electrically insulated from each other in said barrel means such that said charging element and coating material do not contact each other;
said charging element terminating at a charging electrode outside of said barrel adjacent said first passage whereby coating material emitted from said barrel is charged to an electrical potential outside of said barrel by said electrode.
2. The gun of claim 1 including a nozzle cap at the front end of said barrel means with at least two holes therethrough spaced from each other and said charging element being removable from said nozzle cap for insertion through either of said at least two holes.
3. An electrostatic spray gun for setting up an electrostatic field between the gun and the object to be coated comprising:
barrel means made of electricaly insulated material;
said barrel means having a front end and two passages terminating adjacent said front end, the first of said barrel passages constituting a material coating conduit;
a material charging element connectable to a source of high potential in the second of said barrel passages and extending through the front end and electrically insulated in the barrel from said first passage; a rotatable coating material passing nozzle assembly mounted on the front end of said barrel with said charging element being mounted in said assembly and extending therethrough and terminating at an electrode; and means for maintaining the electrical contact with said charging element regardless of the angle of rotation of said nozzle assembly and electrode relative to said barrel.
4. The gun of claim 3, wherein said means for maintaining electrical contact comprises a conductive ring mounted on the inner side of said nozzle assembly.
5. The gun of claim 3 wherein said charging electrode extends away from said nozzle assembly to a free tip with said electrode being angled outwardly toward the axial extended center line of the first passage.
6. An electrostatic spray gun for setting up an electrostatic field between the gun and the object to be coated comprising:
a material charging element connectable to a source of high potential;
barrel means made of electrically insulated material;
said barrel means having a front end and two passages terminating adjacent said front end;
the first of said passages constituting a material coating conduit;
a high electrically resistive member having an electrical resistance and being connected to said charging element; v
the second of said passages containing said resistive member and charging element;
said two passages being electrically insulated from each other in said barrel means such that said charging element and resistive member do not contact each other;
said charging element terminating at a charging electrode outside of said barrel adjacent said first passage whereby coating material emitted from said barrel is charged to an electrical potential outside of said barrel by said electrode.
7. The gun of claim 6 wherein valve means are provided in said first passage to control the flow of coating material to said front end; said valve means normally being in a closed position;
and trigger means on said gun manually operable by an operator to move said valve from its closed position.
8. The gun of claim 7, wherein a rotatable nozzle assembly is provided on the front end of said barrel with said charging element extending therethrough until it terminates at its electrode.
9. The gun of claim 6 wherein the resistive member has an electrical resistance in the range of 50 to 1,000 megohms.
10. The gun of claim 6 including a nozzle mounted on the front end of said barrel with at least two holes therethrough to selectively position said charging electrode therein.
11. An airless electrostatic spray gun for setting up an electrostatic field between the gun and the object to be coated comprising:
barrel means with two passages therethrough at least part of which is made of electrically insulated material;
said barrel having a front end;
a nozzle mounted on said front end and rotatable relative to said barrel and having a conductive ring on its inward side;
the first of said two passages being a coating material conduit;
valve means in said first passage to control the movement of coating material therethrough;
trigger means on said gun manually operable to control the movement of said valve;
and charging means comprising an outwardly extending electrode outside of said gun and attached to the front of said nozzle, a first charging element connected to said electrode and extending through said nozzle to said conductive ring, a second charging element in said barrel normally biased to contact said ring, a resistor in the range of 50 to 1,000 megohms in said second passage connected at one end to said second charging element and connectable at the other end to a source of high potential;
whereby coating material emitted through said first passage is charged to an electrical potential after being emitted through said nozzle assembly by said electrode after it leaves the gun.
12. The gun of claim 11 with at least two holes through said nozzle to rem'ovably allow selective insertion of said first charging means therein.
13. A nozzle for an electrostatic spray gun comprising:
an electrically non-conductive nozzle rotatably mountable on the front of an electrostatic spray gun;
an electrical conductive element at least partially within said nozzle, said element having an external forward facing electrode and a conductive member on the nozzle side opposite said electrode for maintaining continuous electrical contact with a source of high potential regardless of the nozzle angle of rotation; and
means for selectively positioning said conductive element at different locations comprising at least two holes through said nozzle extending from adjacent said conductive member to support and guide said external electrode, and to insure a proper charge on the coating material when the nozzle is rotated to a tightened position.
14. The nozzle of claim 13 wherein the means for selectively positioning the conductive element comprises two holes through said nozzle extending from adjacent said conductive member to adjacent said external electrode.
15. The nozzle of claim 14 wherein said conductive member is an annular conductive ring.
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