CA1163796A - Electrostatic spray gun discharge protection improvement - Google Patents
Electrostatic spray gun discharge protection improvementInfo
- Publication number
- CA1163796A CA1163796A CA000377283A CA377283A CA1163796A CA 1163796 A CA1163796 A CA 1163796A CA 000377283 A CA000377283 A CA 000377283A CA 377283 A CA377283 A CA 377283A CA 1163796 A CA1163796 A CA 1163796A
- Authority
- CA
- Canada
- Prior art keywords
- spray gun
- sleeve
- high voltage
- cable
- ring
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
- B05B5/00—Electrostatic spraying apparatus; Spraying apparatus with means for charging the spray electrically; Apparatus for spraying liquids or other fluent materials by other electric means
- B05B5/025—Discharge apparatus, e.g. electrostatic spray guns
- B05B5/053—Arrangements for supplying power, e.g. charging power
Landscapes
- Electrostatic Spraying Apparatus (AREA)
Abstract
ELECTROSTATIC SPRAY GUN
DISCHARGE PROTECTION IMPROVEMENT
ABSTRACT OF THE DISCLOSURE
Apparatus is disclosed for electrostatic paint spray guns of the typed utilizing high voltage ionizing in assisting coating applications, the apparatus having O-ring air seals positioned adjacent high voltage conductor contact points in the spray gun body, such seals isolating air gaps between conductors and thereby eliminating electrical discharges through the air gaps.
DISCHARGE PROTECTION IMPROVEMENT
ABSTRACT OF THE DISCLOSURE
Apparatus is disclosed for electrostatic paint spray guns of the typed utilizing high voltage ionizing in assisting coating applications, the apparatus having O-ring air seals positioned adjacent high voltage conductor contact points in the spray gun body, such seals isolating air gaps between conductors and thereby eliminating electrical discharges through the air gaps.
Description
~163~9~
~ackground of the Invention The present invention relates to electrostatic spray guns, particularly spray guns utilized in the painting industry for creating an ionizing zone proximate a paint spray tip in a spray gun, the ionizing zone being created by electrostatic high voltages delivered by means of high voltage cable attached to the spray gun and electrical conductors embedded in the spray gun body.
In the prior art it has been customary to deliver /O high voltage to a spray gun by a heavy cable having a conductive wire surrounded by suitable dielectric plastic having good insulation quaLities, and enclosing the plastic insulator with a metallic grounding sheath.
The cable is typically connected to a metal portion of the spray gun handle and good electrical contact is made between the metallic cable sheath and the handle itself to assure that the spray gun handle will be held at ground potential. The central portion of the cable, consisting of the plastic insulator and internal wire is ~ typically extended a considerable distance into the spray gun body, and the cable conductor is brought into electrical contact with a large resistance located in the spray gun body. The other end of the resistance is typically electrically connected by means of various contacting mechanisms to an ionizing needle whicn projects forward of the spray gun. Such a construction is shown in U.S. Patent No. 4,182,490, issued January 8, 1980, which is fairly typical of the prior art.
The portion of the high voltage cable extending into the spray gun body is usually quite long, on the order of 6 - 12 inches, so as to space the exposed inner cable conductor as far as possible from the metal portion of the spray gun handle to prevent voltage arcing. As a ~ 1 63 ~
urther defense against arcing it is common to snugly enclose the spr~y gun cable inside a plastic sleeve insulator which is also inserted into the spray gun body. This reduces the air gap surrounding the cable and further lessens the tendency for electrical arcing.
As a further precaution against arcing it is common to pack the inside of the sleeve with a high dielectric grease material to attempt to fill all air voids in the space between the sleeve and the conductor it encloses.
Such an approach is disclosed in U.S. Patent No.
3,815,820, issued June 11, 1974 and U.S. Patent No.
3,459,374, issued August 5, 1969. It has therefore been well recognized that potentially serious electrical arcing problems can occur inside the spray gun body between any exposed conductor and the grounded metal handle o~ ~he gun.
Since the construction of any high voltage electrostatic spray gun necessarily involves the utilization of components having inherent capacitance, there is the further and additional problem of protecting against voltage discharge between capacitance elements and grounded elements, or between capacitance elements and any conductive path within the spray gun at a different voltage potential. Any air gap within the spray gun body represents a potential discharge path, and it is therefore desirable to reduce as far as is practicable all such air gaps. However, since such spray guns necessarily are constructed from components which are removably replaceable, and replacement must necessarily require some dimensional tolerances between components and the spray gun body, it is impossible to completely eliminate all air gaps within the spray gun and its internal components. Various approaches, some of which have been described above, have been utilized to solve these problems.
~63l9~
Summary of the Invention The present invention provides a novel and simple solution to many of the problems described in the preceding paragraphs, wnile permitting replaceable components to be utilized inside a spray gun body without requiring critical dimensional tolerances to ensure tight fits between the respective components, and without requiring the use of messy greases and other materials to attempt to pack the voids within the spray /0 gun body. According to the primary teachings of the present invention a plastic sleeve member is fitted over the high voltage cable and other conductive elements within the spray gun body, in a body passage suitably sized to accept such sleeve. The sleeve has annular grooves formed therein at points adjacent exposed conductor contact points and an O-ring seal is seated in each of these grooves to create an air seal between the tube and the concentric adjacent component. Such O-ring seals are placed at two or more critical locations where ao exposed conductors are located, and thereby eliminate completely any air gap between such exposed conductor contacts and other conductive elements. The elimination of these air gaps thereby eliminates potential electrical discharge paths without the necessity of utilizing any of the disadvantageous solutions suggested by the prior art. Further, such air gaps and potential discharge paths are eliminated while permitting the use of fitted components having conventional and relatively loosely fitted dimensional tolerances.
It is therefore a primary object of the present invention to provide an apparatus for eliminating potential voltage discharge paths through air gaps in electrostatic spray guns.
~163,9~
It is another object of the present invention to provide elimination of voltage discharge paths through the use of conventionally sized and dimensioned components.
It is a further object of the present invention to provide an apparatus for eliminating voltage discharge paths within a spray gun without requiring special packing procedures utilizing greases and other materials.
Brief Description of the Drawings The foregoing and other objects of the invention will become apparent from the attached specification and from the appended drawings, in which:
FIG. 1 shows a side cross-sectional view of an electrostatic spray gun incorporating the present invention; and FIG. 2 shows an expanded partial cross-sectional view of a portion of FIG. 1.
Description of the Preferred Embodiment ao Referring first to FIG. 1, there is shown in side cross-sectional view an electrostatic spray gun of the type generally known as a "automatic" spray gun. Spray guns may be generally classified as either "automatic"
or "manual", wherein automatic spray guns are intended for affixing to a support mechanism adjacent a conveyor line and are automatically actuated by remote controls for applying spray in sequence with the arrival of articles along the conveyor line. Manual spray guns typically have a handle for grasping by an individual, qO and a built-in trigger mechanism for actuating the spray gun under manual operation. Spray gun 10, being an automatic spray gun, is actuated by means of air pressure applied from a remote source through inlet 3 to actuate air cylinder 28 and thereby retract valve rod 26. The retraction of valve rod 26 causes paint valve 163~6 20 to become lifted from its seat, and thereby opens passage 22 to the flow of paint via inlet 12 and passage 14. Paint is thus emitted from the spray gun through the nozzle 24.
A high voltage cable 30 is attached to spray gun 10 by means of a suitable cable connection 33 in the metal portion 46 of the spray gun body. Cable 30 has a braided metal layer which serves as a groundiny sheath, and which is clamped between body part 46 and the cable IO connector ~3 according to conventional techniques.
Cable 30 has all inner dielectric insulator 42 which encloses high voltage conductor 43 and extends into body part 46. Body part 48 is preferably made from plastic insulation material such as nylon or other similar material an-i is threadably clamped against body part 46 by means of locknut 50. A passage in body part 4~ is in alignment with a similar passaye in body part 46 when ]ocknut 50 is attached. Plastic tube 44 extends through the aligned passages in body parts 48 and 46, and ~O encloses cable insulator 42 and a high valued resistance 32. Resistance 32 has a conductive end contact at 52 and 54 for making good electrical contact at its respective ends. Cable conductor 43 electrically contacts resistor contact point 52, and conductive member 34 electrically contacts resistor contact 54. A
threaded conductor segment 36 contacts conductor segment 34 and needle 40, which passes through nozzle 24 to make the electrical contact.
Tubular sleeve 44 has an external annular groove 58 O (see FIG. 2) proximate one end thereof, and an internal annular groove 60 proximate the other end thereof.
Annular grooves 58 and 60 respectively accept O-rings of resilient material such as rubber. For example, O-ring 55 is a rubber O-ring sized to snugly fit in groove 58;
O-ring 57 is a conventional rubber O-ring sized to fit ~3~9~
within groove 60. Since one O-ring 55 fits over the outside of tube 44 and the other O-ring 57 fits along tne inside of tube 44, tne two O-rings are not of identlcal sizes. For example, in a preferred embodiment of the apparatus the inside diameter of the passage drilled through spray gun parts 46 and 44 is 0.56 inches. Tubular sleeve 44 has an outside diameter of 0.54 inches and an inside diameter of 0.31 inches.
Grooves 58 and 60 are machined to a depth of about .004 /O inches and a width of about .09 inches. 0-ring 55 has a nominal inside diameter of 7/16 inch and an outside diameter of 9/16 inch; while O-ring 57 has a nominal inside diameter of 1/4 inch and an outside diameter of 3/8 inch. The foregoing selection of O-rings and part sizes provides optimum compression of the O-rings when placed in position, and ensures an adequate air seal between the respective sides of the O-rings.
In o~eration, when high voltage of the order of S0 -100 kilovolts is applied to high voltage cable 30, a a O corresponding high voltage potential is found at contact points 52 and 54. The high voltage potential at contact point 54 is effectively isolated from potential discharge along the air gap between tubular insulator 44 and gun body part 48 by means of O-ring 55. The high voltage potential at contact point 52 is effectively insulate~ from a potential electric discharge through the air space along the inside of tubular sleeve 44 and cable insulator 42 by means of O-ring 57. In both cases, the potential electrostatic discharge could otherwise occur between the high voltage point and metal gun body part 46, which is nominally at ground potential. However in both cases the discharge path is eliminated because of the effective air seal provided by the respective O-rings.
1 ~ 63 ~ 9~
The present invention may be embodied in other specific forms without departing from the spirit or essential attributes ther~of, and it is therefore desired that the present embodiment be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.
~ackground of the Invention The present invention relates to electrostatic spray guns, particularly spray guns utilized in the painting industry for creating an ionizing zone proximate a paint spray tip in a spray gun, the ionizing zone being created by electrostatic high voltages delivered by means of high voltage cable attached to the spray gun and electrical conductors embedded in the spray gun body.
In the prior art it has been customary to deliver /O high voltage to a spray gun by a heavy cable having a conductive wire surrounded by suitable dielectric plastic having good insulation quaLities, and enclosing the plastic insulator with a metallic grounding sheath.
The cable is typically connected to a metal portion of the spray gun handle and good electrical contact is made between the metallic cable sheath and the handle itself to assure that the spray gun handle will be held at ground potential. The central portion of the cable, consisting of the plastic insulator and internal wire is ~ typically extended a considerable distance into the spray gun body, and the cable conductor is brought into electrical contact with a large resistance located in the spray gun body. The other end of the resistance is typically electrically connected by means of various contacting mechanisms to an ionizing needle whicn projects forward of the spray gun. Such a construction is shown in U.S. Patent No. 4,182,490, issued January 8, 1980, which is fairly typical of the prior art.
The portion of the high voltage cable extending into the spray gun body is usually quite long, on the order of 6 - 12 inches, so as to space the exposed inner cable conductor as far as possible from the metal portion of the spray gun handle to prevent voltage arcing. As a ~ 1 63 ~
urther defense against arcing it is common to snugly enclose the spr~y gun cable inside a plastic sleeve insulator which is also inserted into the spray gun body. This reduces the air gap surrounding the cable and further lessens the tendency for electrical arcing.
As a further precaution against arcing it is common to pack the inside of the sleeve with a high dielectric grease material to attempt to fill all air voids in the space between the sleeve and the conductor it encloses.
Such an approach is disclosed in U.S. Patent No.
3,815,820, issued June 11, 1974 and U.S. Patent No.
3,459,374, issued August 5, 1969. It has therefore been well recognized that potentially serious electrical arcing problems can occur inside the spray gun body between any exposed conductor and the grounded metal handle o~ ~he gun.
Since the construction of any high voltage electrostatic spray gun necessarily involves the utilization of components having inherent capacitance, there is the further and additional problem of protecting against voltage discharge between capacitance elements and grounded elements, or between capacitance elements and any conductive path within the spray gun at a different voltage potential. Any air gap within the spray gun body represents a potential discharge path, and it is therefore desirable to reduce as far as is practicable all such air gaps. However, since such spray guns necessarily are constructed from components which are removably replaceable, and replacement must necessarily require some dimensional tolerances between components and the spray gun body, it is impossible to completely eliminate all air gaps within the spray gun and its internal components. Various approaches, some of which have been described above, have been utilized to solve these problems.
~63l9~
Summary of the Invention The present invention provides a novel and simple solution to many of the problems described in the preceding paragraphs, wnile permitting replaceable components to be utilized inside a spray gun body without requiring critical dimensional tolerances to ensure tight fits between the respective components, and without requiring the use of messy greases and other materials to attempt to pack the voids within the spray /0 gun body. According to the primary teachings of the present invention a plastic sleeve member is fitted over the high voltage cable and other conductive elements within the spray gun body, in a body passage suitably sized to accept such sleeve. The sleeve has annular grooves formed therein at points adjacent exposed conductor contact points and an O-ring seal is seated in each of these grooves to create an air seal between the tube and the concentric adjacent component. Such O-ring seals are placed at two or more critical locations where ao exposed conductors are located, and thereby eliminate completely any air gap between such exposed conductor contacts and other conductive elements. The elimination of these air gaps thereby eliminates potential electrical discharge paths without the necessity of utilizing any of the disadvantageous solutions suggested by the prior art. Further, such air gaps and potential discharge paths are eliminated while permitting the use of fitted components having conventional and relatively loosely fitted dimensional tolerances.
It is therefore a primary object of the present invention to provide an apparatus for eliminating potential voltage discharge paths through air gaps in electrostatic spray guns.
~163,9~
It is another object of the present invention to provide elimination of voltage discharge paths through the use of conventionally sized and dimensioned components.
It is a further object of the present invention to provide an apparatus for eliminating voltage discharge paths within a spray gun without requiring special packing procedures utilizing greases and other materials.
Brief Description of the Drawings The foregoing and other objects of the invention will become apparent from the attached specification and from the appended drawings, in which:
FIG. 1 shows a side cross-sectional view of an electrostatic spray gun incorporating the present invention; and FIG. 2 shows an expanded partial cross-sectional view of a portion of FIG. 1.
Description of the Preferred Embodiment ao Referring first to FIG. 1, there is shown in side cross-sectional view an electrostatic spray gun of the type generally known as a "automatic" spray gun. Spray guns may be generally classified as either "automatic"
or "manual", wherein automatic spray guns are intended for affixing to a support mechanism adjacent a conveyor line and are automatically actuated by remote controls for applying spray in sequence with the arrival of articles along the conveyor line. Manual spray guns typically have a handle for grasping by an individual, qO and a built-in trigger mechanism for actuating the spray gun under manual operation. Spray gun 10, being an automatic spray gun, is actuated by means of air pressure applied from a remote source through inlet 3 to actuate air cylinder 28 and thereby retract valve rod 26. The retraction of valve rod 26 causes paint valve 163~6 20 to become lifted from its seat, and thereby opens passage 22 to the flow of paint via inlet 12 and passage 14. Paint is thus emitted from the spray gun through the nozzle 24.
A high voltage cable 30 is attached to spray gun 10 by means of a suitable cable connection 33 in the metal portion 46 of the spray gun body. Cable 30 has a braided metal layer which serves as a groundiny sheath, and which is clamped between body part 46 and the cable IO connector ~3 according to conventional techniques.
Cable 30 has all inner dielectric insulator 42 which encloses high voltage conductor 43 and extends into body part 46. Body part 48 is preferably made from plastic insulation material such as nylon or other similar material an-i is threadably clamped against body part 46 by means of locknut 50. A passage in body part 4~ is in alignment with a similar passaye in body part 46 when ]ocknut 50 is attached. Plastic tube 44 extends through the aligned passages in body parts 48 and 46, and ~O encloses cable insulator 42 and a high valued resistance 32. Resistance 32 has a conductive end contact at 52 and 54 for making good electrical contact at its respective ends. Cable conductor 43 electrically contacts resistor contact point 52, and conductive member 34 electrically contacts resistor contact 54. A
threaded conductor segment 36 contacts conductor segment 34 and needle 40, which passes through nozzle 24 to make the electrical contact.
Tubular sleeve 44 has an external annular groove 58 O (see FIG. 2) proximate one end thereof, and an internal annular groove 60 proximate the other end thereof.
Annular grooves 58 and 60 respectively accept O-rings of resilient material such as rubber. For example, O-ring 55 is a rubber O-ring sized to snugly fit in groove 58;
O-ring 57 is a conventional rubber O-ring sized to fit ~3~9~
within groove 60. Since one O-ring 55 fits over the outside of tube 44 and the other O-ring 57 fits along tne inside of tube 44, tne two O-rings are not of identlcal sizes. For example, in a preferred embodiment of the apparatus the inside diameter of the passage drilled through spray gun parts 46 and 44 is 0.56 inches. Tubular sleeve 44 has an outside diameter of 0.54 inches and an inside diameter of 0.31 inches.
Grooves 58 and 60 are machined to a depth of about .004 /O inches and a width of about .09 inches. 0-ring 55 has a nominal inside diameter of 7/16 inch and an outside diameter of 9/16 inch; while O-ring 57 has a nominal inside diameter of 1/4 inch and an outside diameter of 3/8 inch. The foregoing selection of O-rings and part sizes provides optimum compression of the O-rings when placed in position, and ensures an adequate air seal between the respective sides of the O-rings.
In o~eration, when high voltage of the order of S0 -100 kilovolts is applied to high voltage cable 30, a a O corresponding high voltage potential is found at contact points 52 and 54. The high voltage potential at contact point 54 is effectively isolated from potential discharge along the air gap between tubular insulator 44 and gun body part 48 by means of O-ring 55. The high voltage potential at contact point 52 is effectively insulate~ from a potential electric discharge through the air space along the inside of tubular sleeve 44 and cable insulator 42 by means of O-ring 57. In both cases, the potential electrostatic discharge could otherwise occur between the high voltage point and metal gun body part 46, which is nominally at ground potential. However in both cases the discharge path is eliminated because of the effective air seal provided by the respective O-rings.
1 ~ 63 ~ 9~
The present invention may be embodied in other specific forms without departing from the spirit or essential attributes ther~of, and it is therefore desired that the present embodiment be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.
Claims (5)
1. In an electrostatic spray gun of the type having high voltage cable connected to the gun and having an internal electrical contact point between the cable conductor and another electrical component;
the improvement comprising:
an insulating sleeve concentrically positioned around said internal cable and said other electrical component, said sleeve having an internal annular groove proximate one end and an external annular groove proximate the other end;
an O-ring seated in each of said respective annular grooves, said O-rings sized for air sealing fit between said sleeve and the respective concentric adjacent component.
the improvement comprising:
an insulating sleeve concentrically positioned around said internal cable and said other electrical component, said sleeve having an internal annular groove proximate one end and an external annular groove proximate the other end;
an O-ring seated in each of said respective annular grooves, said O-rings sized for air sealing fit between said sleeve and the respective concentric adjacent component.
2. The improvement of claim 1, wherein said external annular groove and O-ring is placed at the innermost end of said sleeve in said spray gun.
3. The improvement of claim 2, wherein said O-rings are constructed of resilient and compressible material.
4. An electrostatic spray gun having a high voltage cable attached to the spray gun and having internal electrical connections to couple said cable to a forward electrode, comprising:
a) a passage in said spray gun between said high voltage cable attachment and said electrode;
b) an electrically insulating sleeve in said passage, the inside of said sleeve adapted to accept a resistance and an end of said high voltage cable; said sleeve having an external annular groove proximate the sleeve end enclosing said resistance, and an internal annular groove proximate the sleeve end enclosing said high voltage cable;
c) an O-ring fitted in each of said annular grooves, said one O-ring in air sealing relation between said sleeve and said passage, and said other O-ring in air sealing relation between said sleeve and said high voltage cable.
a) a passage in said spray gun between said high voltage cable attachment and said electrode;
b) an electrically insulating sleeve in said passage, the inside of said sleeve adapted to accept a resistance and an end of said high voltage cable; said sleeve having an external annular groove proximate the sleeve end enclosing said resistance, and an internal annular groove proximate the sleeve end enclosing said high voltage cable;
c) an O-ring fitted in each of said annular grooves, said one O-ring in air sealing relation between said sleeve and said passage, and said other O-ring in air sealing relation between said sleeve and said high voltage cable.
5. The spray gun of claim 4, wherein each of said O-rings is constructed of resilient and compressible material.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US15073980A | 1980-05-19 | 1980-05-19 | |
| US150,739 | 1980-05-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1163796A true CA1163796A (en) | 1984-03-20 |
Family
ID=22535802
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000377283A Expired CA1163796A (en) | 1980-05-19 | 1981-05-11 | Electrostatic spray gun discharge protection improvement |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5710365A (en) |
| CA (1) | CA1163796A (en) |
| DE (1) | DE3119441A1 (en) |
| FR (1) | FR2482480A1 (en) |
| GB (1) | GB2076600A (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS592443U (en) * | 1982-06-30 | 1984-01-09 | トヨタ自動車株式会社 | small electrostatic coating machine |
| JPH0612286B2 (en) * | 1985-11-15 | 1994-02-16 | オ−バル機器工業株式会社 | Automatic zero adjustment circuit |
| JPH0232955U (en) * | 1988-08-19 | 1990-03-01 | ||
| DE19502522A1 (en) * | 1995-01-27 | 1996-08-01 | Gema Volstatic Ag | Spraying device for coating material |
-
1981
- 1981-05-11 CA CA000377283A patent/CA1163796A/en not_active Expired
- 1981-05-15 JP JP7408081A patent/JPS5710365A/en active Pending
- 1981-05-15 GB GB8114887A patent/GB2076600A/en not_active Withdrawn
- 1981-05-15 DE DE19813119441 patent/DE3119441A1/en not_active Withdrawn
- 1981-05-18 FR FR8109838A patent/FR2482480A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| FR2482480A1 (en) | 1981-11-20 |
| DE3119441A1 (en) | 1982-04-22 |
| GB2076600A (en) | 1981-12-02 |
| JPS5710365A (en) | 1982-01-19 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |