US3819115A

US3819115A - Electrostatic spray gun

Info

Publication number: US3819115A
Application number: US00340549A
Authority: US
Inventors: C Soderman
Original assignee: Atlas Copco AB
Current assignee: Atlas Copco AB
Priority date: 1972-03-13
Filing date: 1973-03-12
Publication date: 1974-06-25
Anticipated expiration: 1991-06-25
Also published as: DE2312363A1; BE812038A; GB1388787A; SE371942B

Abstract

The powder spray gun comprises a handle, a barrel and a front member screwed to the barrel. The barrel and the front member form a duct through which paint powder is conveyed entrained in the air. An annular electrode and an elongated central body are clamped between the barrel and the front member and a lead for high voltage extends through an axial bore in the barrel and abuts axially against the annular electrode. The duct is annular and the electrode has an annular forward-directed edge that has a clearance to the walls of the duct and is located at a touch protecting distance from the mouth of the duct.

Description

United States Patent 1191 [11] 3,319,115 Soderman [4 June 25, 1974 ELECTROSTATIC SPRAY GUN 3,698,636 10/1972 Szasz 239/15 75 Inventor: Claes Erik Soderman, Skara, Wme

Sweden 3,740,612 6/1973 Gauthier et al 239/15 X [73] Assignee: Atlas Copco Aktiebolag, Nacka,

S d Primary Examiner-M. Henson Wood, Jr. Assistant Examiner-Michael Y. Mar [22] F'led: 1973 Attorney, Agent, or Firm-Flynn & Frishauf [21] Appl. No.: 340,549

[57] ABSTRACT [30] Foreign Application Priority Data The powder spray gun conprisefi a handle, a lgarrel 13, 1972 5 1 3197 72 and a mm member Screwe e barrel- The we] Mar we en I and the front member form a duct through which 52 US. Cl. 239/15 317/3 Pailt Powder is conveyed entrained in the [51] Int. Cl B05 b 5/02 "ular electrode and an elongated central body are [58] Field of Search 239/15 317/2 R 3 clamped between the barrel and the from member and a lead for high voltage extends through an axial bore in the barrel and abuts axially against the annular elec- [56] References Cited trode. The duct is annular and the electrode has an annular forward-directed edge that has a clearance to UNITED STATES PATENTS the walls of the duct and is located at a touch protectgrastznin.i i i distance from the mouth of the duct Oll'l e a 3,688,990 9/1972 Liedberg 239/15 X 17 Claims, 9 Drawing Figures PAliNlEnJuuzslsn SHEEI 1 OF 2 OM m W W4 WM RMWWOW .UWM4 1 1 v PATENTEDJUNZSIHH 1819.115

SHEET 2 BF 2 37 I 5 F/G.4 37 FIG. 5

37 7 FIG. 6

mum;

ELECTROSTATIC SPRAY GUN This invention relates to a powder spray gun having a powder emitting duct, formed of an electrically insulating material, to which the powder is carried as a gas suspension, and an electrode for electrostatically charging.

In prior art guns of this kind, the electrods is usually situated at the end of the mouth of the duct or outside the mouth. By reason of safety, it is not desirable to have an external electrode and attempts have been made to utilize needle electrodes inside the duct. However, such electrodes have proved not to give as good an electrostatic charge to the powder as external electrodes do.

It is an object of the invention to provide a powder spray gun which imparts an effective electrostatic charge to the powder notwithstanding the electrode is well protected.

The invention will be described with reference to the accompanying drawings in which FIG. 1 is a longitudinal section through a handheld powder spray gun according to the invention,

FIGS. 2 and 3 are cross sections along

lines

22 and 33, respectively, in FIG. 1;

FIGS. 4, 6 and 8 are fragmentary longitudinal sections through modified forms of the forward nozzleforming portion of the powder spray gun;

FIGS. 5, 7 and 9 are front views seen as indicated by the arrows 5, 7-7 and 9-9 in FIGS. 4, 6 and 8, respectively.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS The spray gun shownin FIGS. 1-3 comprises a rear metal member 11 mainly comprising a handle, a barrel 12 and a forwardmember 13. The two

members

12, 13 are made of an electrically insulating material, for instance a plastic, and they form an axial duct 14 to which a hose 15 is connected. The duct 14 is supplied with a suspension of paint powder in air or another gas from a non-illustrated suitable source, for instance from an apparatus which provides a fluidized bed of powder.

A deflector device 16 comprises a central and axial tube-like member 17 which by means of two spokes 18 is connected to a ring 19 that abuts a shoulder 20 in the duct 14. The deflector device 16 is also shown in FIG. 4. The ring 19 is held in place by means of an annular metallic electrode 21 which in turn is held in place by means of the forward plastic member 13 which is threaded onto the barrel 12. The rear end of the tubelike member 17 is guided by means of a number of vane-like spokes 22 and the tube-like member 17 forms an inner wall of the duct 14, i.e., it makes the duct annular. A deflector head 23 has a spindle 24 which is screwed into the rear end of the tube-like member 17,

and an annular passage 25 is formed between the spindle 24 and the tube-like member 17.

Passages

26,27 in the spokes 18 end in this passage 25. Preferably, the entire deflector device 16, i.e., also the deflector head 23 and its spindle 24, should be electrically insulating, for instance by being made of a plastic material. The

passages

26,27 in the spokes 18 are connected to a passage 28 in the housing and this passage 28 leads via a control 6 valve 29 in the rear member 11 of the housing to an air valve 30 operated by a trigger 31. The air valve 30 is supplied with compressed air from a non-illustrated hose connected to a fitting 32. A control passage 33 leads from the passage 28 through a control hose 34 to the powder supplying apparatus previously mentioned but not illustrated.

The electrode 21 has a forward-directed annular portion 35 ending in an edge 35a, and it is connected to an insulated electric cable 36 through a protecting impedance 37. The cable 36 is connected to one of the poles of a high voltage source 38 which has its other pole grounded. The handle portion 11 is electrically conducting and grounded through a braided metallic shield of the cable 36.

When the trigger 31 is actuated, the air valve 30 is opened so that there will be an air stream through the passage 28 and the

passages

26,27,25 to the deflector head 23.Simultaneously the control passage 33 is pressurized which on the one hand actuates a nonillustrated switch to start the high voltage source 38 and on the other hand initiates the supply of the powder-air mixture through the hose 15.

Three modified electrodes are shown in the FIGS. 4-5, 6-7 and 8-9, respectively. The deflector device 16 shown in FIG. 1 is shown in FIGS. 4 and 5 but it is not shown in FIGS. 6-9. Suitably, it should be used also in connection with the modified electrodes in FIGS. 6-9 because it improves the touch protection of the electrodes. It has also a positive influence on the charging of the powder and it forms the jet into a powder cloud in response to the adjustment of the control valve 29.

The powder-air mixture streams also on the outside of the edge-forming ring 35 of the electrode 21 shown in FIGS. 6 and 7. The ring 35 is attached to an outer ring 41 by means of four spokes 40, and the outer ring 41 is secured in the duct 14. As distinguished from the other electrodes, the electrode shown in FIGS. 8 and 9 has not a continuous edge butit has a great number of forwardly directed needles 42 which form an annular edge portion 43 with their tips.

The clearance between the

edge portion

35a and 43, respectively, and the outer wall of the duct 14 should be less than the diameter of the edge portion and preferably narrower than half this diameter. However, it should be at least I millimeter and preferably at least about 2 millimeters. What I claim is: l. A powder spray gun having: an annular powder emitting duct having a mouth at the forward end thereof for emitting said powder, the outer and inner walls of which are formed of an electrically insulating material, to which duct the powder is to be carried suspended in a gas, and

an electrode connectable to a source of high voltage, said electrode comprising an annular base secured to the outer wall of the duct and means extending from said annular base and forming an annular forwardly directed edge portion which has a radial clearance to the walls of the duct and is recessed in said duct at a touch-protecting distance from the mouth of the duct, said forwardly directed edge portion being the foremost extending portion of the electrode in the duct.

2. A powder spray gun as defined in claim 1 in which said edge portion is a circular continuous edge.

3. Apowder spray gun as defined in claim 1 in which said extending means comprises a plurality of needles having forwardly directed tips forming together a discontinuous annular forwardly directed edge.

4. A powder spray gun as defined in claim 1 including means located rearwardly of said electrode for imparting a twisting motion to the powder suspension transmitted through the duct.

5. A powder spray gun as defined in claim 1 in which said electrode is axially clamped between a rear body and a forward body which form together the outer wall of said duct.

6. A powder spray gun as defined in claim 5 in which said forward and rear bodies are screwed together.

7. A powder spray gun as defined in claim 5 in which an elongated central body, forming the inner wall of the duct, has a mount which is axially clamped, together with said annular base of the electrode, between said rear and forward bodies forming the outer wall of the duct.

8. A powder spray gun as defined in claim 7 in which said elongated body at its rear end has radial fins for imparting a twisting motion to the powder suspension transmitted through the duct.

9. A powder spray gun as defined in claim 7 in which said elongated body carries a deflector disposed outside of the mouth of the duct.

10. A powder spray gun as defined in claim 5 in which a lead connected to high voltage is located in an axial passage in said rear body and abuts axially against the electrode to apply high voltage thereto.

11. A powder spray gun comprising:

a front and a rear member made of an electrically insulating material and forming a wall of a powder emitting duct, the rear end of said duct being adapted to receive a flow of powder entrained in air,

an annular electrode clamped between said front and rear members, said electrode having a forwardly directed extension comprised of a plurality of forwardly directed needle-shaped elements in said duct, said forwardly directed extension having a clearance to the wall of the duct, and

a lead for high voltage located in an axial passage in said rear member and abutting axially against the electrode to apply high voltage thereto.

12. A powder spray gun comprising:

a barrel of electrically insulating material, an axial duct in said barrel adapted to be supplied with a flow'of powder suspended in a carrier gas,

a cap of electrically insulating material removably attached to said barrel, said cap having a duct forming an extension of said axial duct in the barrel and forming a powder emitting mouth,

an annular electrode connectable to a source of high voltage and having a forwardly directed edge portion which has a radial clearance to the duct of said cap and is recessed in said duct at a touch protecting distance from said mouth, said forwardly directed edge portion being the foremost extending portion of the electrode in the duct, and r a device upstream of said electrode to impart a twisting motion to the powder-gas suspension transmitted through the duct, said device and said electrode being fastened in the duct by being axially clamped between said barrel and said cap.

13. A powder spray gun as defined in claim 12 in which said device is formed of electrically insulating material and has an extension that extends forwardly through the annular electrode to said mouth of the duct.

14. A powder spray gun as defined in claim 12 in which said device is formed of electrically insulating material and comprises a body coaxially located in the d tan l carried by spokes, said body extendirg for wardly through said electroieandsafi riouth, a gas passage leading through one of said spokes and through said central body to provide for a deflecting gas flow substantially transverse to the flow of powder and gas emitted from said mouth, said gas passage being connected to a gas supply passage in said barrel.

15. A powder spray gun as defined in claim 12 in which said edge portion is a circular continuous edge.

16. A powder spray gun as defined in claim 12 in which said extending means comprises a plurality of needles having forwardly directed tips forming together a discontinuous annular forwardly directed edge.

17. A powder spray gun having:

an annular duct defined by an outer and an inner wall of electrically insulating material, said duct forming a powder emitting mouth and being adapted to be supplied with a flow of powder suspended in a carrier gas,

a plurality of forwardly directed electrode points located annularly in the annular duct and recessed in the duct at a given distance from said mouth, and

means for connecting said electrode points to a source of high voltage.

Claims

1. A powder spray gun having: an annular powder emitting duct having a mouth at the forward end thereof for emitting said powder, the outer and inner walls of which are formed of an electrically insulating material, to which duct the powder is to be carried suspended in a gas, and an electrode connectable to a source of high voltage, said electrode comprising an annular base secured to the outer wall of the duct and means extending from said annular base and forming an annular forwardly directed edge portion which has a radial clearance to the walls of the duct and is recessed in said duct at a touch-protecting distance from the mouth of the duct, said forwardly directed edge portion being the foremost extending portion of the electrode in the duct.

3. A powder spray gun as defined in claim 1 in which said extending means comprises a plurality of needles having forwardly directed tips forming together a discontinuous annular forwardly directed edge.

11. A powder spray gun comprising: a front and a rear member made of an electrically insulating material and forming a wall of a powder emitting duct, the rear end of said duct being adapted to receive a flow of powder entrained in air, an annular electrode clamped between said front and rear members, said electrode having a forwardly directed extension comprised of a plurality of forwardly directed needle-shaped elements in said duct, said forwardly directed extension having a clearance to the wall of the duct, and a lead for high voltage located in an axial passage in said rear member and abutting axially against the electrode to apply high voltage thereto.

12. A powder spray gun comprising: a barrel of electrically insulating material, an axial duct in said barrel adapted to be supplied with a flow of powder suspended in a carrier gas, a cap of electrically insulating material removably attached to said barrel, said cap having a duct forming an extension of said axial duct in the barrel and forming a powder emitting mouth, an annular electrode connectable to a source of high voltage and having a forwardly directed edge portion which has a radial clearance to the duct of said cap and is recessed in said duct at a touch protecting distance from said mouth, said forwardly directed edge portion being the foremost extending portion of the electrode in the duct, and a device upstream of said electrode to impart a twisting motion to the powder-gas suspension transmitted through the duct, said device and said electrode being fastened in the duct by being axially clamped between said barrel and said cap.

14. A powder spray gun as defined in claim 12 in which said device is formed of electrically insulating material and comprises a body coaxially located in the duct and carried by spokes, said body exending forwardly through said electrode and said mouth, a gas passage leading through one of said spokes and through said central body to provide for a deflecting gas flow substantially transverse to the flow of powder and gas emitted from said mouth, said gas passage being connected to a gas supply passage in said barrel.

17. A powder spray gun having: an annular duct defined by an outer and an inner wall of electrically insulating material, said duct forming a powder emittIng mouth and being adapted to be supplied with a flow of powder suspended in a carrier gas, a plurality of forwardly directed electrode points located annularly in the annular duct and recessed in the duct at a given distance from said mouth, and means for connecting said electrode points to a source of high voltage.