GB988408A - Improvements in or relating to electrostatic spray coating - Google Patents

Abstract

988,408. Electrostatic spray coating apparatus. N. R. WALLIS. Dec. 6, 1963 [Dec. 8, 1962], No. 46418/62. Heading B2F. Electrostatic spray coating apparatus includes a container for a supply of electrically conductive coating material, a rotatable atomizing head for converting the material to its finely divided form, means for maintaining an electrostatic field between the head and an article to be coated, a pipeline connecting the head and container and means for interrupting the electrical path constituted by the coating material in the pipeline without interrupting the supply of such material to the head. In the described embodiment, Figs. 1, 2, 3, the latter means takes the form of an intermediate container 110, 111 to which coating material is supplied which is determined by the rate of actuation through pipes 31 and 32 in pulses the rate of of automatically operated valves 19 and 20 located in respective material supply lines 4 and 3. Air gaps are thus provided between the discharge orifices of the pipes 31 and 32 and the bottom of the containers 110, 111 and in order to ensure no electrical leakage or flashover the material of the operation barrel 21, mounting block 40 and container member 111 are made of electrical insulating material and the pulse rate is controlled-if necessary means are placed in the container for this purposesuch that the distance between the material in the bottom of the container and the material of any "drop" as it leaves the pipe 31 or 32 is sufficient to prevent flash-over. The gun of Figs. 1, 2 and 3 also includes a rotatable atomizing cup 28 driven by an air motor 33. The high voltage cable 37 is connected to the motor through a resistor 39 and a spring 38. Paint spray coating apparatus is shown in Fig. 8 applied to a booth 15 housing an article 1 to be coated. The gun. 2 (as shown in Figs. 1, 2 and 3) is connected to an electrical control equipment 27, valves 8, 19, 20 and a paint container 13 through a multiple cable 18 which includes an air line 29 for the motor 33, two paint lines 3, 4, a high voltage cable 5 and a trigger control cable 6. The arrangement of the equipment 27 is such that depression of the gun trigger 24 allows air to pass to the motor 33 to rotate the cup 28. Subsequently the valves 19, 20 are opened alternately for short periods about 80 times a minute so that the paint is supplied under pressure to the lines 3 and 4 alternately. When the trigger 24 is released the valves 19 and 20 are held closed first and thereafter the air valve 8 is closed to stop the motor. As soon as the lines 3 and 4 are full of paint, a small quantity thereof will issue from the open end of the pipes 31 and 32 every time the associated valve is open. One paint feed line could be employed the pulse flow of the paint arising from actuation of a cam upon a flexible walled portion of the line between two non-return valves.