GB955647A - Improvements in electrostatic spray coating apparatus - Google Patents

Abstract

955,647. Spray-producers. ATLAS COPCO A.B. Feb. 4, 1963 [Feb. 16, 1962], No. 4480/63. Heading B2F. In an electrostatic spray coating gun having pressurized air and liquid inlets 13 and 14, Fig. 1, the jets of air and liquid issuing from nozzles 46 and 40 are directed into a mixing chamber 47 from whence the atomized liquid spray passes to atmosphere through a slot 48 of a nozzle 43. The portions of the gun defining the mixing chamber are electrically conductive and a high tension conductor 53 is connected thereto through forwardly directed opposed insulated conductors 49. The latter carry a secondary electrode 50 in the form of a fine wire disposed transversely and in the path of the jet issuing from the slot 48. An electrically insulated oval ring 51 is located between the conductors 49 to prevent accidental contact between the electrode 50 and the article to be coated. Secondary electrode wires 52 are also carried by the conductors 49. In operation, actuation of a trigger 15 retracts a spindle 17 and its tip 41 to a preadjusted extent, as defined by the setting of a screw-threaded sleeve 20, whereupon liquid coating material is fed from the inlet 14 through a passage 32 and discharged through the nozzle 40. Simultaneously compressed air is admitted to an annular chamber 33 in the gun via a valve 16 and passes therefrom through passages 34, 35, an annular space 37 and passages 38 to an annular chamber 45, and thence through passages 42 to the nozzle 46 and on to the mixing chamber 47 and the atmosphere. The liquid coating material is atomized in the chamber 47 by the air jet and liquid particles are then projected through the slot 48, which retards the particles and defines the final crosssection of the jet. Simultaneously there takes place in and adjacent the nozzles 40, 46, 43 and the chamber 47 an electrostatic charging and atomizing due to the high potential of the nozzles and the corona discharge caused thereby. Subsequently the spray is acted upon electrostatically by the fields around the secondary wire electrodes 50 and 52. In a modified nozzle arrangement the electrodes 50, 52 and conductors 49 are omitted and the conductor 53 is connected directly to the nozzle 43. The mixing chamber 47 has multiple forwardly directed transverse spray slots which may be arranged in parallel, angular, crosswise or other relation with respect to each other. In yet another nozzle arrangement the body portion 10, Fig. 4, of the gun is of nylon and a metallic nozzle body 62 having a liquid discharge nozzle 68 is screwed thereto. Rotatably arranged and journalled through needle bearings 69 on the body 62 is a metallic spray nozzle 70 which forms an air discharge nozzle 71 around the tip of the nozzle 68. The nozzle 70 incorporates a mixing chamber 72 having a spray slot 83 extending at an angle to the rotational axis of the nozzle 70. Rotation of the nozzle is effected through turbine blading 75 integral therewith, the necessary driving power being obtained by air bled from the air jet supply stream through a passage 78, air discharge from the blading being directed radially through ports 77. This discharge is prevented from influencing the spray pattern of the jet issuing from the nozzles 70 and 71 by a ring 82. The air supply to the nozzle 71 is regulated by a valve 81. This nozzle arrangement enables the spray gun to be used for coating the inner surfaces of tubular articles such as cans.