Multiple charging electrodes

[0001] This invention relates to electrode configurations and potential sources for coating delivery devices (hereinafter sometimes referred to as spray guns or pistols).

Background of the invention [0002] Various types of spray guns are known. These are, for example, automatic and manual spray guns, shown and described in the following patents and published applications: US 2006/0081729; US 2003/0006322; U.S. Patent 7,296,760; US 7,296,759; US 7,292,322; US 7,247 205; US 7 217 442; US 7,166,164;

US 7,143,963; US 7,128,277; US 6,955,724; US 6,951,309; US 6,929,698; US 6,916,023;

US 6,877,681; US 6,854 672; US 6 817 553; US 6 796 519; US 6,790, 285; US 6,776,362;

US 6,758,425; US RE 38,526; US 6,712,292; US 6,698,670; US 6,679,193; US 6,669 112;

US 6 572 029; US 6 460 787; US 6,402 058; US Patent RE 36,378; US 6,27616; US 6,189,809; US 6,179,223; US 5 836 517; US 5 829 679; US 5,803, 313; US Patent RE 35,769; US 5 639 027; US 5 618 001; US 5 582 350; US 5 553 788; US 5,400, 971; US 5 395 054; US D 349 559; US 5,351,887; US 5,332,159; US 5,332,156; US 5,330 108;

US 5 303 865; US 5,299,740; US 5,289 974; US 5,284,301; US 5,284,299; US 5,236,129;

US 5,209,405; US 5,209,365; US 5 178 330; US 5,119,992; US 5,118,080; US 5 180 104;

US D 325 241; US 5,090,623; US 5,074,466; US 5,064,119; US 5 054 687; US 5,039,019;

US D 318 712; US 5,022,590; US 4,993,645; US 4,934,607; US 4,934,603; US 4,927,079;

US 4,921,172; US 4,911,367; US D 305 453; US D 305 452; US D 305 057; US D 303 139; US 4,844,342; US 4,819,879; US 4,770 117; US 4,766,096; US 4,759,502; US 4,747,546; US 4,702,420; US 4,613,082; US 4,606 501; US 4,522,438; US D 287 266; US 4,535,357; US 4,521,131; US 4,513,913; US 4,483,483; US 4,453,670; US 4,437,614; US 4,433,812; US 4,401,268; US 4,361,283; US D 270 368; US D 270 367; US D 270 180; US D 270 179; US RE 30 968; US 4 331 298; US 4,289,278; US 4,285,446; US 4,266,721; US 4,248,386; US 4,214,709; US 4,174,071; US 4,174,070; US 4,171,100; US 4,169,545; US 4,165,022; US D 252 097; US 4,133,483; US 4 116 364; US 4,114,564; US 4 105 164; US 4 081 904; US 4 066 041; US 4 037 561; US 4 030 857; US 4 020 393; US 4 002 777; US 4 001 935; US 3 990 609; US 3,964,683; US 3,940,061; US 3 169 883; and US 3,169,882. These are also the disclosures in WO 2005/014177 and WO 01/85353. There are also Ransburg REA 3, REA 4, REA 70, REM and M-90 pistol models, all available from ITW Ransburg, 320 Phillips Avenue, Toledo, Ohio, 43612-1493.

[0003] The above list is not intended to provide a full overview of all the relevant prior art that has been developed, nor is it stated that there is no other significant prior art than that listed or that the prior art

- 2 listed on this list is a material for determining patentability. Nor should any such interpretation be made.

Disclosure of the Invention [0004] US-A-4228961 discloses a device for feeding a coating material, the device comprising at least two electrodes for coupling to at least one high potential source such that the at least two electrodes are held substantially at two different high potentials, and therefore an electric field exists between these at least two electrodes.

[0005] According to the present invention, such a device is characterized in that each of the at least two electrodes comprises a corridor passing through it, ensuring compressed gas flow through the at least one of the at least two electrodes.

[0006] For example, the voltage divider is coupled to at least one high potential source. The at least two electrodes are coupled at different points of the voltage divider to maintain the at least two electrodes at substantially two different high potentials.

[0007] Alternatively, two high potential sources have high potential output ports, providing two different high potentials. Each high potential output is coupled to an appropriate one of at least two electrodes.

[0008] For example, the at least two electrodes are coupled to a common source of compressed gas.

[0009] Alternatively, the at least two electrodes are coupled to respective of at least two compressed gas sources.

[0010] For example, the device is selected from the group consisting of pneumatic atomizers, pneumatically assisted hydraulic atomizers, high pressure, low pressure pneumatic atomizers (HVLP) and hydraulic atomizers.

[0011] Alternatively, the device comprises a device for feeding a powder coating material (hereinafter sometimes referred to as coating powder or powder).

Brief Description of the Drawing [0012] This invention can best be understood with reference to the following detailed description and the accompanying drawing in which the invention is illustrated. In the drawing:

Fig. 1 is a very schematic side view of a system constructed according to the invention;

Fig. 2 is a very schematic representation of an alternative detail shown in Fig. 1;

<td>Fig. 3 is very much shown in Fig. 1;</td><td>schematic</td><td>performance</td><td>alternative</td><td>detail</td>

<td>Fig. 4 is very shown in Fig. 1;</td><td>schematic and</td><td>performance</td><td>alternative</td><td>detail</td>

<td>Fig. 5 is very much shown in Fig. 1.</td><td>schematic</td><td>performance</td><td>alternative</td><td>detail</td>

Detailed Description of Exemplary Embodiments [0013] Fig. 1 shows a coating delivery system 10, comprising a coating feeding device or a gun 12. The device 12 illustratively is a hand-held spray gun, however it should be understood that this invention can equally well be applied to so-called automatic spray guns. In addition, when the depicted pistol 12 is a hydraulic pistol, this invention may equally well be applied to pneumatic (hereinafter sometimes referred to as air), pneumatically assisted hydraulic (hereinafter sometimes referred to as AAA) or high-volume low-pressure pneumatic pistols (hereinafter hereinafter sometimes referred to as HVLP in this document). In addition, this invention can equally well be applied to coating delivery devices for administering coating powders. The gun 12 includes a nozzle 14 through which the coating material from the source 16 is fed, when controlled by the valve 18. The source 16 can be a source of liquid coating material or a source of coating powder such as for example a fluidized bed. The position of the needle of the valve 18 is in turn controlled by the position of the trigger 20 of the gun 12. In manual guns, trigger position 20 is controlled by the operator's hand. In automatic guns, trigger position 20 is typically controlled by a process controller such as, for example, the AllenBradley controller.

[0014] The coating material fed through the nozzle 14 is charged by two or more electrodes 22-1, ..., 22-n, of which only two are shown in the drawing. The 22-1, ..., 22-n electrodes are in the form of hollow needles or small-sized tubes. Various large (usually negative) electrostatic potentials are coupled from a large size source (sources) of 24-1, ..., 24-m, to 22-1, ..., 22-n electrodes. Yes, the electric field (s) occur (occur) not only between each electrode 22-1, ..., 22 on objects 26 (hereinafter sometimes referred to as targets), which are to be coated with the coating material fed through the nozzle 14, but also between the electrodes 22-1, ..., 22-n. In addition, compressed gas, for example air, is supplied from a source of compressed gas 29, for example via a valve 30 controlled by the position of the drain 20, to the base of each of the electrodes 22-1, ..., 22-n. Thus, when the coating material flows through the nozzle 14, the compressed gas flows through the electrodes 22-1, ..., 22-n. This helps to keep electrodes 22-1, ..., 22-n relatively free from the coating material. This promotes charge flow from 22-1, ..., 22-n electrodes to the coating material when it is fed, which in turn improves conveying efficiency

- 4 coating materials for targets 26, when they are placed, for coating, in front of the gun 12, for example on a grounded conveyor 32.

[0015] This 24-1, ..., 24-m high potential source (s) need not (must) be separate power sources. Instead, they may be provided with a common source supplying a voltage divider 36 having an impedance with₁ and with₂that can be provided in the gun body 12, or can be provided in the power supply, or can be a separate voltage divider with which the power supply and the 22-1, ..., 22-n electrodes are coupled. This generalized impedance voltage divider 36 is shown in Fig. 2. The voltage divider may, for example, take the form of a resistive voltage divider 36 'as shown in Fig. 3. It may also take the form of a 36 "capacitive voltage divider as shown in Fig. 4, with the restriction that the electrical capacities must be small enough that the divider cannot store such a large charge Q = CV to cause hazardous working conditions in the coating environment.

[0016] It should also be understood that although resistors and capacitors of different voltage dividers 36, 36 ', 36 "are shown as separate elements, one or more of them may be an element, for example a resistor or capacitor, which are already included in the gun 12 for other known purposes, such as, for example, a portion of a high voltage rectifier and duplicator, typically Cockcroft-Walton duplicators, sometimes referred to as cascades.

[0017] In addition, it should be understood that while the compressed gas sources for the electrode bases 22-1, ..., 22-n were shown as originating from a common source 28 of the compressed gas, electrodes 22-1, ..., 22 -n can be supplied from two or more sources 28-1, ..., 28-p, via appropriate valves 30-1, ..., 30-p, controlled by trigger 20. This is shown in Fig. 5. Also in Fig. 5, tubular electrodes are shown having outer ends cut at an angle of about 30 °. Typically, the angle of such a chamfer should not be less than about 30 °, because the ends of the pipes become "hot spots" for discharging electrostatic potential.

Anna Stenzel Patent Attorney