Apparatus is disclosed for resistively damping capacitively stored energy in electrostatic spray guns, wherein a fluid spray valve incorporates an electrode for carrying high electrostatic voltage, the electrode terminating in the spray valve and the spray valve having a conductor contacting the electrode and extending externally thereof. A resistive element at least partially encloses the spray valve and electrically contacts the conductor, permitting electrical conductivity while also permitting axial sliding movement of the spray valve inside of the resistive element.
The nozzle assembly of an electrostatic spray gun has an adapter which is made of an electrically insulating material and has a front surface facing in the direction of propagation of material issuing from the orifice of the nozzle. The adapter has a frustoconical extension which surrounds the orifice and whose external surface defines with the front surface of the adapter an annular space for the tips of electrodes which ionize air flowing toward the spray of material that issues from the orifice. The locations of the tips of electrodes (preferably very close to the front surface of the adapter) and the inclination of the external surface of the frustoconical extension determine the location of contact of ionized air with the spray. The tips of the electrodes are shielded from mechanical damage by being located in the annular space.
A fluid stud and resistor design for electrostatic spray guns has a fluid passage which is shaped like a cloverleaf in cross section. By providing this cross-sectional shape, the resistor is allowed to reside in one wall of the fluid stud and run, nearly, the complete length of the stud, thereby providing an increased effective resistor length, thus reducing flash-over and providing a smaller contact wire, thereby reducing capacitance. The design of the fluid needle and electrode is provided so as to reduce the length of the electrode wire, thereby reducing capacitance and allowing an increased diameter wire for increased durability.
A spray gun is designed for mounting on the end of a robot arm. The construction of the gun is provided such that nearly all of the main components with the exception of the spray head itself are located in a main body to which is mounted a pivotal spray head assembly which may pivot approximately 90.degree. to either side of the normal straight-ahead position. The power supply and power generating units are located in the main body. The electrostatic power supply connection to the spray head enters the spray head shaft on the opposite side from the fluid supply entry. The fluid control valve may be located in the spray head shaft.
