Electrostatic Powder Coating Apparatus

Abstract

An electrostatic powder coating apparatus for coating the surfaces of articles with pulverulent materials having a quick and efficient material change feature such that said apparatus is adapted for selectively spraying materials having different characteristics wherein the change from one material to another can be accomplished without extensive purging of the system, said apparatus including a spray gun, a powder supply means adapted to be removably connected to the inlet of said spray gun, and a control means adapted to be connected to a switching means on said gun for controlling the supply of pulverulent materials to said gun.

Description

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates generally to an electrostatic spray gun for electrostatically coating pulverulent materials onto an article to be coated. More specifically, the present invention relates to an improved electrostatic powder coating apparatus having a material changing means by which the type of pulverulent materials sprayed from the gun can be easily and efficiently changed without the normal purging of the entire system.

One of the problems with both electrostatic liquid and powder coating apparatus of the past was the time consuming and inefficient process of changing the system from the spraying of a material having one characteristic to the spraying of a material having another. With respect to the electrostatic coating of powder materials, the present methods for changing a spray gun system from the spraying of one color to that of another involves the cleaning of the entire system by purging the powder line and the spray gun with an air flow through the supply line and the gun followed by an air blow-off. This procedure still was often not sufficient due to the very adherent nature of the powder being deposited.

In contrast to the electrostatic color coating guns of the past, the present invention provides an improved spray gun and an improved spray gun system in which the type of pulverulent material being sprayed can be easily and efficiently changed to another without the necessity of purging the entire system as in the past.

More specifically, the present invention includes a hand spray gun having an improved nozzle assembly including an ionization cone designed to be quickly and easily removed from the front portion of the spray gun to be cleaned when a color change is desired and then reinserted into the front portion of the gun. The specific structure on the ionization cone includes a probe extending from one end of the cone to the other, a cone body with a plurality of fins surrounding the rearward end of the probe for retaining the ionization cone within the spray gun, an ionization ring mounted on the fin portions for electrically connecting a high voltage source with the probe, and a conical deflector positioned at the forward end of the probe in a position such that a portion of the probe extends outwardly from an exterior surface of the conical member and such that the conical member is spaced from the cone body. When the high voltage source is actuated, the probe is elevated to a potential substantially greater than the potential of the article to be coated and an electrostatic field is set up between the article to be coated and each of the portion of the probe extending through the mechanical member and the portion of the probe located between the mechanical member and the cone body. It has been found that a structure of this sort affords the desired deposition and wrap-around of the pulverulent materials onto the article to be coated while requiring a much smaller voltage than spray guns of the past.

More specifically, the present invention provides for a quick and efficient material change system by which the spray gun can be selectively adapted for the spraying of several different type of pulverulent materials. The material change system includes, for each different material, a supply unit including a pair of members, one of which is adapted for conveying the pulverulent materials from the powder supply to the spray gun and the other of which is to transmit the "on-off" signal of the trigger movement of the gun to an appropriate relay switch for actuating both the high voltage power source and the powder supply system associated with the particular material to be sprayed. Additionally, the member conveying the pulverulent materials from the powder supply to the gun includes a relatively rigid tube designed to be inserted within the material passage of the gun and to extend substantially through the entire passage thereby minimizing the portion of the material passage and the supply line of the gun which has to be purged. Means is also provided for tightly securing the powder conveying member to the spray gun when that securement is desired.

Accordingly, it is an object of the present invention to provide an electrostatic powder coating apparatus having a quick and efficient material change means adapted for changing from a material having one characteristic to a material having a different characteristic without extensive purging of the system.

Another object of the present invention is to provide an electrostatic powder coating apparatus in which the charging and deflecting means is easily removed and cleaned when a material having a different characteristic is desired to be coated.

Another object of the present invention is to provide an electrostatic powder coating apparatus adapted for an efficient material change having a means associated with each different material for disposition within the material passage of the gun to thereby reduce the length of said passage which must be purged when a material change is effected.

A further object of the present invention is to provide an electrostatic powder coating apparatus in which a control means associated with each different material is adapted to be selectively connected with the spray gun for controlling the supply of that particular material from the powder supply to the spray gun.

These and other objects of the present invention will become apparent by referring to the preferred embodiment, the drawings, and the appended claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevated view partially in section showing the improved spray gun of the present invention.

FIG. 2 is a detailed exploded perspective view partially in section of the nozzle portion of the spray gun.

FIG. 3 is a sectional view of FIG. 1 as viewed from line 3--3.

FIG. 4 is a schematic representation of an electrostatic powder coating apparatus.

FIG. 5 is an elevated view partially in section of the control switch.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1 of the preferred embodiment, the electrostatic powder coating gun 10 of the present invention includes generally a barrel portion 11, a nozzle portion 15 located near the front of the barrel portion 11, a handle 12, a trigger 14 and a means located near the rear portion of the gun 10 for supplying high voltage and pulverulent materials to the gun 10.

More specifically, the barrel portion 11 of the gun 10 encloses a generally cylindrical material passage 18 extending longitudinally through the spray gun 10 and through the entire barrel portion 11, and a generally cylindrical high voltage chamber 19 extending longitudinally through part of the barrel portion 11. In the preferred embodiment, substantially all of the barrel portion 11, and especially those portions of the barrel 11 which enclose the material passage 18 and high voltage chamber 19, are constructed from a molded polyethylene which is electrically non-conductive.

The high voltage chamber 19 is separated from the material passage 18 by a molded polyethylene wall 20 and is disposed within the barrel 11 in a position which is substantially parallel to the passage 18. The chamber 19 extends forwardly through the barrel 11 to a forward barrel portion 21 and rearwardly through the barrel 11 to and through a metal rear portion of the gun 22. At its front end, the chamber 19 houses a 150-megohm resistor 24, the rear end of which is electrically connected to a high voltage cable 25 housed in the rearward portion of the chamber 19. The resistor 24 and the cable 25 are electrically connected by a stress relief cap 26 which includes a compression spring 28 biasing the resistor 24 toward the forward end of the chamber 19. The rearward portion of the high voltage cable 25 is electrically connected by an appropriate fitting to the ungrounded terminal of a high voltage source indicated schematically by the reference numeral 30. The other terminal of the high voltage source 30 is electrically grounded.

Located in the forward portion of the chamber 19 is an electrically conductive set screw 31 threadedly extending through the wall 20 to thereby electrically connect the resistor 24 with a contact or ring member 32 disposed within the material passage 18 and which will be more fully described below. Directly above the set screw 31 is a plug 34 which is threadedly received by a portion of the barrel and which can readily be removed for adjustment or removal of the set screw 31.

The nozzle portion 15 located near the forward end of the barrel 11 generally includes a pattern control sleeve or cylindrical member 36 telescopically mounted over a portion of the forward end of the barrel 11 and adapted for axially sliding movement along the forward portion of the barrel 11. The sleeve 36, constructed of an electrically non-conductive material such as a linear synthetic polyamide, commonly sold under the trademark Nylon, includes a relatively cylindrical interior surface 38 substantially conforming in diameter to the exterior surface of the forward end of the barrel 11, a forward end portion 39 which, when the sleeve 36 is moved to an extended position, is disposed at a position spaced forwardly from the forward end of the passage 18, a rearward end portion 40, and a set screw 41 extending through the body of the sleeve 36 for a limited distance to engage the longitudinal channel 42 which is formed in a portion of the exterior surface of the barrel 11. As shown by the broken line 33, the sleeve 36 can be moved to a plurality of extended positions in which the forward end 39 is forwardly spaced from the forward end of the passage 18. When in a retracted position, the forward end 39 does not extend forward of the forward end of said passage 18. When the screw 41 engages the channel 42, the axial movement of the sleeve 36 is limited as a result of the screw 41 engaging the shoulder portions of the channel 42. In this manner, the sleeve 36 cannot inadvertently be moved to an extent that the sleeve is removed from the barrel 11. Also, the screw 41 can be tightened against the inner surface of the channel 42 when the sleeve 36 is in a desired position to thereby retain the sleeve 36 in that position.

As also shown in FIG. 1, the forwardmost interior surface of the passage 18 is curved or flared outwardly. This flaring, in combination with the axially movable sleeve 36 and the deflecting member 44, which will be described in more detail below, causes the pulverulent materials passing through the passage 18 to be formed into a desired spray pattern.

Referring now to FIG. 2, an elongated ionization member 37 disposed within the passage 18 includes a probe or electrode 45, a deflecting member 44, a body member 46 and a ring member 32. The probe 45 extends the entire length of the ionization member 37. At its rearward end 48, the probe 45 is electrically connected to the ring member 32 by a conducting wire 49. At its forwardmost end, the probe 45 passes through the deflecting member 44 and extends past the concave surface 59 of the deflector 44. The portion of the probe 45 extending past the surface 59 serves as an ionization point or needle 50 causing an electrostatic field to be set up between the point 50 and the article to be coated 13 when the point 50 and the article 13 are maintained at substantially different electrical potentials.

The generally cylindrical body member 46 surrounds a substantial portion of the probe 45 and extends from the rearward end 48 of the probe 45 to a point 51 near the forward end of the probe 45. In the preferred embodiment, the location of the point 51 is substantially even with the forward end of the passage 18 when the member 37 is operatively disposed within the passage 18.

A plurality of fins 52 integrally formed with the rearward portion of the body member 46 are spaced about the circumference of the member 46 and extend upwardly therefrom such that the diameter of the exterior fin surfaces is slightly larger than the interior diameter of the material passage 18 so that the ionization member 37 may be retained within the passage 18. As better seen in FIG. 3, the plurality of fins 52 are equally spaced about the circumference of the body member 46 and extend radially outwardly therefrom.

Referring now to both FIGS. 2 and 3, a ring member 32 is mounted to a portion of the fins 52 at a position which is spaced forwardly from the rearward end 48 of the probe. Referring specifically to FIG. 3, the mounting of the ring in this manner provides a plurality of passages 54 through which the pulverulent materials may pass as they are conveyed through the passage 18.

The ring member 32 is constructed of an electrically conductive material and is electrically connected to the resistor 24 (FIG. 1) by the set screw 31. When the ionization member 37 is inserted into the forward end of the passage 18, the ring 32 engages the set screw 31, thereby electrically connecting the ring 32 with the screw 31, and also preventing further inward movement of the ionization member 37. The member 37 is then retained in this position by the plurality of fins 52 which are force fitted against the interior surface of the passage 18. Because the member 37 is secured within the passage 18 due to the flexible and somewhat resilient nature of the fins 52, the member 37 can easily be removed, cleaned and replaced when such cleaning is desired. This is often the case when the gun or the system is changed from spraying a pulverulent material having one characteristic to a pulverulent material having another.

The deflecting member 44 through which the forward portion of the probe 45 passes is generally conical in shape and includes a cylindrical surface 56, a tapered or conical surface 55 extending from the surface 56 and tapered inwardly toward the body member 46, a tapered surface 58 extending from a cylindrical portion 57 of the member 44 inwardly away from the body member 46, a shoulder portion 60 connecting the surface 56 with the surface 58, and a concave surface 59 which is perpendicular to the longitudinal axis of the probe 45 and which is the forwardmost surface of the deflector 44. The body member 46, the fins 52 and the deflecting member 44 are all constructed of non-conductive material such as a linear synthetic polyamide commonly sold under the trademark Nylon.

As best shown in FIG. 2, the tapered surface 55 tapers inwardly toward the body member 46 and terminates at a point which is spaced from the forwardmost point 51 of the body 46. This provides for a portion 61 of the electrically conductive probe 45 to be directly exposed to the pulverulent materials being discharged from the end of the material passage 18. It is believed that an electrostatic field is set up between the portion 61 and the grounded article 13 to thereby supercharge or precharge the pulverulent materials being emitted from the passage 18, thereby causing greater wrap-around and better deposition of the particles onto the article 13 with a substantially lower voltage.

As shown in FIG. 2, the forwardmost portion of the probe 45, the ionization point 50, extends for a distance past the concave surface 59. A difference in electrical potential between the point 50 and the article 13 causes an electrostatic field to be formed between the point 50 and the grounded article 13 to thereby additionally charge the pulverulent materials emitted from the material passage 18 and direct those charged particles toward and onto the article 13. It should be noted that in the preferred embodiment the forwardmost point of the needle 50 does not extend past the edge formed between the tapered surface 58 and the concave surface 59, but rather is shielded within the concave portion formed by the surface 59. This shielding prevents pulverulent materials which have been precharged by the portion 61 from being repelled by the needle 50 which contains charges of identical polarity to the charges then carried by the pulverulent particles and also limits undesired contact with the point 50. It is believed that this shielding results in a more efficient system which can provide the same wrap-around and same deposition with a much lower voltage.

Referring again to FIG. 1, the rearward portion of the gun 10 of the present invention can be seen as including a metal portion 22, a handle 12 extending downwardly from the rear portion 22, a trigger 14 pivotally connected to the gun at the pivot 62, and a hook 64 by which the gun 10 can be hung when it is not in use. Extending through the material passage 18 is a relatively rigid, electrically non-conductive tube 65 for conveying pulverulent materials through the passage 18. As shown in the preferred embodiment, the tube 65 extends through a substantial portion of the passage 18 with its forward end 66 terminating at a point which is spaced rearwardly of the set screw 31. The rearward end 68 of the tube 65 includes a portion containing a plurality of circumferential ribs 69 which are adapted for attachment of the end 68 to a flexible tube 70 of the type normally used for transporting pulverulent materials in an electrostatic spraying system.

The tube 65, although relatively rigid when compared to the hose 70, is not so rigid that it cannot be bent slightly, and is generally cylindrical having an external diameter slightly smaller than the internal diameter of the material passage 18. With this construction, the tube 65, with the flexible hose 70 attached to its rearward end, can be easily inserted into and removed from the material passage 18 when such insertion or removal is desired. When the tube 65 has been inserted into the passage 18, it is held tightly in place by the fitting 71 which contains internal threads for engagement with a corresponding externally threaded member 72 integrally formed with the gun body 10. A set screw 67 may also be contained in the gun wall and adapted to aid in retaining the tube 65 within the passage 18.

The specific structure of the embodiment shown in FIG. 1, due to the fact that the tube 65 and hose 70 are easily and quickly removable from the gun, allows several such tubes and hoses, each associated with a pulverulent material with a different characteristic, to be selectively used with the gun. This permits the spray gun of the present invention to be changed from the spraying of a pulverulent material having one characteristic to the spraying of a pulverulent material having another with little inconvenience to the operator. This feature will be discussed in more detail below.

Also shown in FIG. 1 is the means 74 for selectively actuating both the powder supply 75, which includes a plurality of powder supply units, and the high voltage source 30. This means includes an "on-off" control switch 76 which, when in the "on" position, electrically connects a ground terminal with a male jack 80. This ground terminal (not shown) enters the gun together with the high voltage cable. When the switch is in the "off" position, the aforementioned ground terminal and the male jack 80 are not electrically connected. The control switch 76, in turn, is controlled by movement of the trigger 14 toward or away from the handle 12 respectively. When the trigger 14 is moved toward the handle 12, a spring-loaded shaft 78 is moved inwardly, thereby turning the control switch 76 to an "on" position and connecting the male jack 80 with the grounded terminal. When the trigger 14 is released, the spring-loaded shaft 78 moves away from the handle 12, thereby turning the control switch to an "off" position and disconnecting the male jack 80 from the grounded terminal. The shaft 78 is centered and retained in the gun handle 12 by the fitting 79.

The switch 76 is secured to the gun handle 12 by the jam nut 82. A cylindrical sleeve member 81, which is integrally formed with the gun handle 12 surrounds the jack 80 and a portion of the switch 76 to shield the jack 80 from any sudden jar which could be caused, for example, by dropping the gun. Also shown in FIG. 1 is a cord 84 containing a single conducting wire and having one end which includes a female jack 85 adapted to engage and connect with the male jack 80. When the female jack 85 and the male jack 80 are engaged, the wire within the cord 84 and the grounded terminal (not shown) are electrically connected. The female jack 85 is retained in engagement with the male jack 80 by the resilient nature of the female jack 85. Although it is specifically shown in FIG. 1, the cord 84 extends from the male jack 80 to a relay switch contained in the powder supply 75, which, when energized, actuates both the powder supply 75 and the high voltage source 30.

The preferred embodiment further includes a supply unit having a plurality of flexible hoses 70 (a - c) and a plurality of cords 84 (a - c) associated respectively with each of the hoses 70 (a - c). All of the hoses 70 (a - c) and the cords 84 (a - c) have one end connected with a powder supply means 75 and the other end adapted for selective engagement with the material passage 18 and the male jack 80 respectively by appropriate connections. In this respect, each of hoses 70 (a - c) includes a fitting 71 (a - c) respectively corresponding to the fitting 71 for engagement with the threaded member 72, and a relatively rigid tube 65 (a - c) respectively corresponding to the tube 65 for insertion into the chamber 18. Also, each of the cords 84 (a - c) includes a female jack corresponding to the female jack 85 adapted to engage the male jack 80. Each of the tubes 70 (a - c) are held to the corresponding cord 84 (a - c) respectively by a clamp 88 so that corresponding pairs of hoses 70 (a - c) and cords 84 (a - c) will be connected with the gun 10 together.

Each of the pairs of hoses 70 (a - c) and cords 84 (a - c) is associated with a pulverulent material having a different characteristic which can be selectively engaged with the gun 10 when a material with a particular characteristic is desired. For example, the hose 70a, the tube 65a and the cord 84a are all associated with a material having a certain characteristic and when it is desired to coat this particular material onto the article 13, the tube 65a with the hose 70a attached is inserted into the material passage 18 and the fitting 71a is tightened over the fitting 72. Likewise, the cord 84a is connected with the male jack 80. When a material having a different characteristic is desired to be coated onto the article, the tube 65a, the hose 70a and cord 84a are removed, and the hose, tube and cord associated with that different material are connected with the material passage 18 and the male jack 80 in a similar manner. Although the pulverulent materials with different characteristics commonly would be materials having different colors, the different characteristics could be differences in materials also such as vinyl, polyester, or cellulose-acetate-butyrate.

Each of the cords 84 (a - c) shown in FIG. 1 like the cord 84, is electrically connected to a relay switch which, when energized, actuates the high voltage source 30 and that portion of the powder supply 75 with which the cord 84 (a - c) is associated. For example, if the hose 70a and the cord 84a are each associated with certain pulverulent material and each are connected to the gun 10 as above described, depression of the trigger 14 will cause the circuit to be completed between the grounded terminal and the conducting wire within the cord 84a to energize a relay switch. When this relay switch is energized, the high voltage source 30 and that portion of the powder supply 75 associated with the cord 84a and hose 70a is actuated. When the trigger 14 is released, the circuit between the grounded terminal and the wire within the cord 84a is open and the relay switch is deenergized, thereby turning off the power source 30 and the powder supply 75.

When a material having a different characteristic is desired to be coated onto the article 13, the hose 70a and the cord 84a are disengaged from the gun 10, the ionization member 37 taken out and cleaned by compressed air and then replaced, and one of the other hoses 70 (b, c) and cords 84 (b, c) associated with a material having the desired characteristic are connected to the gun 10.

An alternative embodiment of the powder coating apparatus of the present invention is shown in FIG. 4. In FIG. 4, reference numerals similar to those in FIG. 1 correspond to components which are identical to those of FIG. 1. FIG. 4 is a schematic representation showing the spray gun 10, the power source 30 for supply a high voltage to the ionization member of the gun, and a powder supply 75 for supplying pulverulent material to the gun 10. This alternative embodiment includes a relay switch 89, which when energized actuated both the power source 30 and an air supply 90. The air supply 90 includes a flexible air hose 91 which is adapted to be removably connected to one of a plurality of ribbed air inlet tubes 92 and 92 (a - c). The hoses 70 and 70 (a - c) are adapted for removable connection to the gun 10 for supplying powder thereto.

As shown in FIG. 5, the switch 95 includes a pair of terminals 96 and 97. One of the terminals 96 is electrically connected to a grounded terminal while the other 97 is electrically connected to the cord 94. The switch 95 is controlled by the movement of the trigger 14 and the spring mounted shaft 78 which is biased forwardly by the compression spring 99. When the trigger 14 is depressed, the switch 95 is turned to an "on" position thereby electrically connecting the cord 94 with the terminal 96 and thereby the grounded terminal (not shown). When the trigger 14 is released, the switch is in an "off" position and the cord 94 and the grounded terminal are not electrically connected. A cylindrical member 98 surrounds the terminals 96 and 97 to prevent undesired contact with the terminals.

Referring again to FIG. 4, when the trigger 14 is depressed, a signal is transmitted from the gun 10 to the relay switch 89 via the cord 94. This signal energizes both the power source 30 and the air supply 90. When the trigger 14 is released, the relay switch 89 is deenergized thereby turning off the power source 30 and the air supply 90.

When a material having a different characteristic is desired to be sprayed, the hose 70 is removed from the gun 10 and the hose 91 removed from the air inlet tube 92. Then, the hose 70 (a - c) associated with the material having the desired characteristic is connected to the gun 10 and the hose 91 is connected to the corresponding air inlet 92 (a - c).

Although the description of the present invention has been quite specific, it is understood by the application that there may be many alternative embodiments of the present invention which can be constructed without deviating from the spirit of the invention. Consequently, the scope of the present invention should be dictated by the appended claims rather than by the description of the preferred embodiment.

Claims

We claim:

1. An electrostatic powder coating apparatus for selectively electrostatically coating the surfaces of articles with pulverulent materials having a desired particular characteristic comprising:

an electrostatic powder coating spray gun having a gun body containing a passage, said passage having an inlet for receiving pulverulent materials and a discharge for discharging said pulverulent materials toward the article to be coated, said spray gun further having

a powder supply connecting means for connecting a powder supply conduit with the inlet of said passage,

a switch means including a second connecting means for the connection of a control wire,

a powder supply conduit adapted for removable connection to said powder supply connecting means and adapted to supply pulverulent material having a particular desired characteristic to the inlet of said passage, and

a control means for controlling the supply of said pulverulent material to the inlet of said passage including a control wire whereby said switch means controls the supply of pulverulent materials having the desired particular characteristic to the inlet of said passage.

2. The electrostatic powder coating apparatus of claim 1 wherein said passage is a longitudinal passage.

3. The electrostatic powder coating apparatus of claim 1 having a plurality of powder supply units each having a powder supply conduit adapted for removable connection to said powder supply connecting means and adapted to supply pulverulent material having a particular characteristic to said passage, each of said powder supply units also having an air supply connection means for selective connection with an air supply.

4. The electrostatic powder coating apparatus of claim 2 wherein said supply conduit includes a relatively rigid tube portion adapted to be disposed within said longitudinal passage.

5. The electrostatic powder coating apparatus of claim 3 wherein said supply conduit includes a rigid tube portion adapted to be inserted into the inlet of said longitudinal passage and extend through said longitudinal passage to a point immediately to the rear of said elongated charging and deflecting means.

6. The electrostatic powder coating apparatus of claim 1 wherein said switch means includes a trigger pivotally secured to said spray gun and wherein said second connecting means includes a male jack.

7. The electrostatic powder coating apparatus of claim 6 having a rigid sleeve means surrounding said male jack for preventing undesired contact with said male jack.

8. The electrostatic powder coating apparatus of claim 1 wherein said switch means is an electrical switch means and wherein said control wire is an electrical control wire.

9. The electrostatic powder coating apparatus of claim 1 having a plurality of powder supply units each having a powder supply conduit adapted for removable connection to said powder supply connecting means and adapted to supply pulverulent material having a particular desired characteristic to said passage, each of said powder supply units also having a control means for controlling the supply of pulverulent material to said passage including a control wire adapted for removable connection to said second connecting means.

10. The electrostatic powder coating apparatus of claim 9 wherein each of said powder supply conduits includes a relatively rigid tube portion adapted to be disposed within said passage.

11. The electrostatic powder coating system of claim 9 wherein said switch means is an electrical switch means and wherein said control wire is an electrical control wire.

12. The electrostatic powder coating apparatus of claim 9 having means for connecting the supply conduit and control means of each supply unit such that when one of said supply conduits is connected to said powder supply connecting means, its respective control wire will be connected to said second connecting means.

13. The electrostatic powder coating apparatus of claim 12 wherein each of said powder supply conduits includes a relatively rigid tube portion adapted to be disposed within said passage and wherein said switch means is an electrical switch means and wherein said control wire is an electrical control wire.

14. The electrostatic powder coating apparatus of claim 13 having a means including a threaded fixture for rigidly securing said powder supply conduit to said gun.