REMOTE ENERGY SOURCE FOR AN ELECTROSTATIC PAINT APPLICATOR
BACKGROUND OF THE INVENTION According to a painting method that is frequently used in commercial operations, atomized paint is electrostatically charged at a high voltage in relation to the workpiece being painted. The electrostatic charge causes the atomized paint to be taken to the work piece, which causes it to consider the efficiency to move the paint, as well as to reduce the labor costs as well as the materials, and that environmental problems are reduced. In a commercial painting operation-; • The workpiece is placed in a spray booth before painting it. A low-voltage power source, a hose that carries compressed air, and a hose that carries paint are con- gressed from the outside with the cab and with the spray gun. Characteristically, the gun includes an oscillator and a voltage multiplying circuit, so that the low voltage increases at a very high direct current voltage, to charge the paint as it is atomized. The high voltage can reach, for example, 100 ki-lovatios, or more. In certain applications, it is not possible to use a conventional spray booth because of the size of the workpiece to be atomized. For example, an airplane would not fit in a conventional spray booth. In this case, the hangar of the airplane will be converted into the spray booth, to confine in it an excess of atomization of the paint and its emanations. Since the paint may include flammable volatile organic compounds (VOC's) as solvents, the hangar is considered a hazardous site, and extreme care must be taken to prevent sparks that could ignite the vapors of VOCs. A conventional source of low voltage energy, connected with an electrostatic spray gun, does not meet certain safety standards to operate in risky locations. The switches, as well as the potentiometers and other co-connectors and circuit connections, pose the danger of sparking. A method to comply with safety standards in hazardous locations is to place the low voltage source directly in the spray gun. As shown in the US patents t.219,665 and < * .290,091, the spray gun can be projected from an internal generator that is driven by an air turbine to generate a low voltage, without it being necessary to install electrical connections with the spray gun, in which a conventional network is used of multiplying circuits and voltage rectifiers, in order that the low voltage becomes a high direct current voltage to charge the paint. During the operation, the turbine shares the air with the atomization air that is supplied to the spray gun. The turbine air must escape from the gun after use. In some applications, the above may cause problems due to dust agitation. Likewise, the turbine and the internal generator cause the weight of the spray gun to be considerably increased, which must be borne by the operator during atomization. Like airplanes that are large and large, the time spent on your paint can go on for a long time, and the additional weight can cause the operator to tire quickly. Due to the rotating movement of the turbine inside the atomizing gun, the vibrations are transmitted to the marjgo of this one. The operator feels these vibrations when using the gun. The price of a gun equipped with a turbine and an Ixiternoß generator is extremely high. As a result, the maintenance of spray guns is very expensive, since each gun must include a turbine and a generator. SUMMARY OF THE INVENTION According to the invention, an energy source that includes an electric generator and a grid of rggulation and low voltage energy control circuits, is mounted in a sealed, explosion-proof box, which meets the safety standards that apply to risky sites. The low-voltage power source is suitable to be located in a spray booth, as well as in a hangar in which an airplane is being painted with a paint containing flammable solvents. The generator has a motor shaft that extends through the box, from which it protrudes. An air-powered turbine is attached to the casing and connected in such a way as to rotate the outgoing shaft of the turbine. The network of low voltage power circuits includes a voltage regulator and a potentiometer. The potentiometer has a shaft that extends through the box to manually fi x the voltage output level. The passage of the flame and the distance of separation ® the flame, at the height of the axes of the nerador and of the potentiometer, are established in such a way that they comply with the norms referring to the explosion test. The turbine does not share the air source with the atomizing pistols. The power source is located in an area where the exhaust air has no effect on the atomization area. With the rotating turbine and generator not placed in the spray gun, no vibrations are transmitted to the hand of the gun operator. In addition, the spray gun will have to be much lighter than the guns containing one and an air generator, and for the user it will be less expensive to maintain replacement guns, since it is not necessary to buy a turbine and a generator with every gun. In Bonsequence, an object of the invention is to provide an improved, distant energy generator for electrostatic paint applications; said generator satisfies the safety requirements so that it can be operated in dangerous places. Other objects and advantages of the invention will become apparent from the following d > Detailed description of the invention and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view, in perspective, of a manual electrostatic atomizing gun connected to a remote source of energy, according to the invention. Figure 2 is a fragmentary view, in cross-section, through the generator box and the circuit network, intended for the remote source of energy. Figure 3 is an enlarged fragmentary view, in partial section, of a connector that serves to secure a transmission cable in the atomizing electrostatic painting and the figure is an outline of the circuit network that is used to rectify and regulate the voltage that is applied to the electrostatic atomizing gun. DETAILED DESCRIPTION OF THE INVENTION Referring first to Figure 1, there is shown a low voltage power source 10, designed according to the invention and connected with an electrostatic manual spray gun 11. The gun 11 has three external connections: an insulated low-voltage cable 12, connected to the power source 10, a hose for carrying air compressed 13 and a hose that conducts the paint lk. The hose carrying compressed air is connected to a conventional source (not shown) of pressurized air, for example, an air compressor or a compressed air line. Pipe I hose connects to a pre-sanitized paint tank. When an operator presses a trigger 15 of the atomizing gun 11, an inner ßire valve (not shown) opens to initiate a stream of atomizing air toward a nozzle assembly 15; next, an inner paint valve (not shown) is opened to initiate the passage of the paint to the nozzle assembly 16. The wire 12 applies a low direct voltage to the atomizing gun 11. The voltage may be, for example, at a regulated level between 0 and 10 volts of direct current. This voltage is applied to the input of a conventional high voltage power source (not shown) disposed in the spray gun 11. The high voltage power source includes an oscillator that converts the direct current input voltage into an alternating current voltage of a higher level. The AC voltage is then applied to a diode and capacitor network that multiplies and converts the voltage into a direct current voltage of a very high level, as is well known in the art. The actual level of high voltage depends on the level of the input voltage. If you adjust the level of the direct current voltage applied to cable 12, the high voltage level is also adjusted. Referring to Figures 1 and 2, the power source 10 includes a compressed air motor or turbine 17, which is mounted on a shell 18 of an explosion-proof box 19 by means of a variety of legs or clamps 20. In the energy source 10 being illustrated, three spaced clamps 20 are shown, which insulate the turbine 17 from the box 19 so that the noise decreases. The box 19 includes a central tubular portion 21, which has opposite threaded ends 22 and 23. The cap 18 is screwed into the threaded end 22, and the cap 2U is screwed into the threaded end 23.. The threaded ends 22 and 23 of the tubular portion of the casing 21 can be threaded therein, as shown, or threaded on the outside to mount the cassettes 16 and 2U. The box 19 delimits a closed inner chamber 25, in which an electric generator 26 is located. The generator 26 is mounted on the capacitor 18, it is provided with a motor shaft that extends through an opening 26 made in the cap 16 and has a protruding end 29. The illustrated generator mounted on the cap 18 emits a variety of screws 30. However, for those skilled in the art, other techniques for mounting the generator 26 on the cap 18 will be apparent. Preferably, the generator shaft 27 is aligned with a shaft of the case 19. The air turbine 17 has a drive shaft 31. The air turbine 17 is mounted on the cap 18, so that its motor shaft 31 is aligned with the protruding end t% of the motor shaft 27. The axes 27 and 31 are connected, together, with a coupling 32, of so that when the axis of the turbine 31 rotates, it also rotates the axis of the generator 29, to cause the generator 26 to produce electrical energy. It should be noted that the electrical performance of the generator 26 varies according to the speed at which it is driven by the turbine 17. Preferably, the generator 26 produces AC electric power. Both the frequency and the voltage of ßsiida vary depending on the speed of the turbine. The output of generator 26 is applied, by means of wires 33, to circuitry 3k, which regulates and conditions the output to produce a constant level of low voltage, for example, a voltage constant between 0 and 10 volts . A potentiometer 35 may be used so that the level of the solid voltage is adjusted within the range, in order to adjust the level of the high voltage generated in the atomizing piston 11. The potentiometer 35 has a shaft 36 extending through the an aber- tura 37 practiced in the capacete 2. On shaft 36 a knob J8 is provided to facilitate adjustment of the voltage. The low voltage electrical cable 12 has a threaded connector 39 which is coupled with an opening O of the cap 2, A flexible device that attenuates the deformation l is placed on the cable 12 in the vicinity of the connector 39. Multiple insulated wires, 50 and 51, which start from the cable 12, are fastened to the circuit assembly 1 by means of an extreme pin. In the connector 39, the cable is sealed encap-sulphedol in order to form a gas tight connection, and to comply with the standards relating to the explosion test. Box 19 has an explosion-proof structure. The walls of the eyebrow 19 are constructed fyertes enough to withstand an internal explosion, in the case that they ignite the vapors or the materials contained in the chamber of the box 25. Preferably, the box 19 is manufactured in such a way that can meet safety standards, such as those developed by Factory Mutual Research. It has been determined that an equipment enclosed in a box is explosion proof "if the box is capable of: a) resisting the explosion of a specified gas or a vapor-in-the-air atmosphere; b) prevent the ignition of a specified gas or a vapor-in-the-air atmosphere that gnaws the enclosure, due to sparks, flashes or internal explosions and c) operate at a temperature that does not ignite the surrounding surrounding atmosphere. In order to comply with these standards, the walls of the box 19 must be strong enough. Debp couples a minimum number of threads in cases where threaded connections are made, such as when the caps 16 and are fastened to the tubular portion 21, and when the cable connector 39 engages with the cap 2. In addition to a minimum resistance of the box, the passage of the flame must have a minimum length, and not more than a maximum space of separation of the passage of the flame in all spaces of separation, openings and joints of the box. The "passage of the flame" is defined as the place where corresponding surfaces of two parts of an enclosure will be found, which prevent an internal explosion from being transmitted to the atmosphere surrounding the enclosure. The "flame gap" refers to the distance between the corresponding surfaces of a joint, measured perpendicular to the surfaces. In the case of circular surfaces, this space is defined as the difference between the two diameters, or as a game or diametrical tolerance. The expression "flame pitch length" ß defines as the shortest path from the interior to the exterior of an enclosure, along the surface of a joint. Regarding a determined interior volume of the enclosure, and the type of the joint, the relationship that is established between the length of the aso of the flame and the space of separation of the passage of the flame must be defined, so that they comply with the norms concerning the explosion test. For example, regarding the volume or capacity of an enclosure between 96 and IWb ce (from 6 to 120 cubic inches), if the length of the flame passage along an axis varies from 2.5¿ * cm to 3.99 cm ( from 1 inch to 1.57 inches), the gap of separation of the flame passage must not be greater than 0.02 cm (O.DOT of an inch). That's how it can be »-
play or diametrical tolerance not greater than 0.02 cm (0.008 inch) around the axis of the generator 27, as it passes through the shell 16, provided that the parameters relating to the volume of the box and the minimum length of the box are met. passage of the flame, which allows the axis of the geperadbr 27 to pass through the aperture of the cap 18, without resorting to any seal, while avoiding the risk of a spark occurring inside the chamber from the box 25 that can inflame the surrounding atmosphere. Analogously, within the axis of the potentiometer 36, and of the opening 37 of the cap 2, a suitable hitch of the flame leg and a suitable length of the flame passage, to allow rotation of the shaft 36, to the Once the regulations regarding the explosion test are met. Referring to FIGS. 1 and 3, the voltage cable 12 has an end connector that plugs into a M5 U5 of the atomizing gun 11. The connector presets a cylindrical end 6 that terminates in an Ul pin that engages with a plug. matching plug (not shown) disposed in the spray gun 11. The cylindrical end 6 slides into an opening (not shown) cut into the handle of the gun 5, and is obtained in the ring seal at 0, í * 8. A deformation attenuator 3 surrounds the cable 12 and is connected to the connector kk. Inside the cylindrical end k & , two wires of low «tightening 50, which come from cable 12, connect with pin l. In addition, the cable 12 contains a third wire 51 which is connected to a terminal of a small reed switch 52. A second terminal located at the switch 58 is connected to one of the low voltage wires 50. A magnet (which is not sample) is placed on the handle of the spray gun to make the switch work when the connector is fully seated in the handle of the gun 5. Thus, the wire 51 carries a signal that indicates when the connector it is, or is not, properly connected with the spray gun 11. The figure is an assembly diagram that serves as a model for the 3k circuit. The voltage produced by the generator 26 is applied, via the wireB 33, to a rectifier 53 that converts the voltBje of alternating current into a direct current voltage. Next, the direct current voltage is applied to a voltage regulator 5"which establishes a constant output voltage of low p-level. The potentiometer 35 is connected to the voltage regulator 5 * to set the level of the output voltage and, in turn, to select a high voltage level to charge the paint that is discharged from the spray gun 11. Preferably , a voltage clamp 55 is placed between the voltage regulator 5k and the cable 12 to limit the maximum output of the circuit 3í, in order to protect the oscillator and the set of voltage multiplying circuits, contained in the ato signal. -mlzacidn, against any risk of excessive voltage occurring in the event that the voltage regulator 5 ** fails. The wire 51, which comes from the foil switch 52 contained in the connector of the jack k, connects to the voltage regulator 5U to inhibit the appearance of an output voltage, when the connector k is removed from its settlement, correct or not, on the handle of the komi atomizer gun. Therefore, any risk of a spark arising from a loose connection between the cable 12 and the spray gun 11 is eliminated. The remote source of energy 10, described above, offers several advantages with respect to a source driven by a force motor that is located in the atomizing gun. First of all, the weight of the gun decreases considerably, which reduces possible fatigue of the hand, wrist and arm of the operator. It also lowers the cost of the gun and the replacement guns. In addition, the vibrations produced by the rotation of the air turbine 17 and the generator 26 are isolated from the gun 11 and are not transmitted to the operator's hand. However, remote power source 10 results from adequate UBO on risky sites; for example, paint spray booths and airplane hangars, during atomization, and without increasing the danger of an explosion occurring. It should be noted that it is possible to make various modifications and changes to the preferred embodiment described above, of a power source intended for an electrostatic paint picker, without deviating from the scope of the following