The invention relates to a process and apparatus for the electrostatic spraying of electrically conductive paint. Paint free of electric charge is intermittently fed from a main supply system to a buffer supply vessel, from which the paint is intermittently fed to a spray paint supply vessel which contains electrically charged paint. The paint in the buffer supply vessel is already electrically charged prior to the replenishing of the spray paint supply vessel from the buffer supply vessel. The paint in the buffer supply vessel is intermittently electrically charged and discharged.
A paint storage vessel is disclosed which is subdivided by flexible insulation into two interior spaces, each connected to its own distribution line and its own paint supply line. The ring main system is connected to the two distribution lines and is effected with the interposition of an electrically insulating change-over mechanism.
A device for feeding an electrically conductive coating material from a supply system to a coating material dispensing device wherein a high electrostatic potential is maintained between the supply system and the device, comprising an intermediate storage container fillable in controlled manner from the supply system to a maximum fill level and connected to the coating material dispensing device by a coating material conduit maintained at substantially the electrostatic potential of the coating material dispensing device, a device provided in the intermediate storage container for breaking up the supply of coating material into the intermediate storage container into electrically separated individual particles, and means for coupling the breakup device to a source of coating material, the breakup device being arranged above the fill level such that, between the breakup device and the interior of the intermediate storage container, a minimum spacing is maintained so that no electrostatic discharge occurs.
A device for insulating the spray liquid source from the high tension voltage of an electrostatic spray system when using an electrically conductive spray liquid. The device comprises a spray gun (13), a supply line (12) which connects the spray gun (13) to a spray liquid reservoir (10) and which includes a vessel (16) containing a barrier forming liquid (17) of low electrical conductivity and a density other than that of the spray liquid. The vessel (16), which is substantially non-conductive is connected at its inlet end (24) to ground potential and at its outlet end (19) to the same high potential as the spray gun (13). An electrode means (22; 25) is provided in the vessel (16) to expose the spray liquid passing through the vessel (16) to at least one intermediate potential for controlling the tension gradient in the barrier forming liquid by limiting and controlling the charging of the spray liquid.
Color change systems for electrostatic coating apparatus are characterized by a dielectric manifold in-line between supplies of different colors of coating materials and a material supply line to the apparatus. To initiate a coating operation, a selected color of material is provided through the manifold to fill the supply line, whereafter the manifold is flushed clean of the material. A high electrostatic charging voltage is then applied to the coating apparatus while the material in the line is supplied to the apparatus for being electrostatically charged and emitted by the apparatus to coat an article. For conductive coating materials, during the coating operation the high charging voltage conducted through the material in the hose is blocked by the nonconductive dielectric manifold and cannot reach and charge the material supplies, so there is no need for a protective enclosure around the supplies of leakage of charging current to the supplies. In one embodiment the color change system is manually operable, and in another it is automatically operable.
A method and apparatus for insulating a spray liquid source from the high tension voltage of an electrostatic spray gun (13) when using an electrically conductive spray liquid. A spray liquid supply line (12) couples the spray liquid source to the spray gun and comprises an insulating device (14) in the form of a closed vessel (16; 26; 36) containing an electrically non-conductive liquid which is not mixable with the spray liquid and which has a density different from that of the spray liquid. A sprinkler nozzle (21; 31; 41) is arranged to disintegrate the spray liquid into separated drops which are transported through the insulating liquid (17; 27; 35) in the closed vessel at least by the influence of the difference in gravity acting on the two liquids. The separated spray liquid drops form a discontinuation of the electrical lead through which the high tension voltage propagates upstream through the supply line. Thereby, the parts of the supply line upstream of the insulating device, which may include a spray liquid feed pump (11) and a spray liquid receptacle (10), are electrically insulated from the high tension voltage. The closed vessel (26; 36) of the insulating device may comprise passages (27, 28; 37, 38) and a pump (30;40) to forcibly circulate the insulating liquid within the passage in the closed vessel such that a movement is superimposed upon the gravity influenced spray liquid transportation movement to increase the spray liquid flow capacity through the insulating device.
