GB804805A - Improvements in or relating to electrostatic coating installations - Google Patents

Abstract

An electrostatic atomizer of the kind in which liquid is atomized by the high potential electrostatic field established between the atomizer and an oppositely charged article to be coated has a liquid discharge passage leading to a discharge orifice, and one or more wipers are disposed in the passage and are movable to clear the passage of dirt &c. In the embodiment of Fig. 3 the atomizer consists of outer and inner cup-shaped members 71, 72 each having sharp-edged lips 74, 76, and an annular discharge passage 132 leading to a discharge opening is provided between them. Spray liquid is fed to an annulus 130 via a line 35 and a valve 121, and flows therefrom to the passage 132 and opening. Each member 71, 72 has uniformly spaced wiper elements 146, 148, Fig. 1, extending axially along the discharge passage to the outlet which wipe the passage walls when the inner member is oscillated about its axis. A shaft 78 to which member 72 is keyed extends through a boss 104 and is oscillated by a lever 82, Figs. 3 and 7, keyed thereto and having one arm coupled to a piston 154 sliding within an air cylinder 152. A return spring 170 is attached to the other arm of the lever and the lever oscillates between stops 166, 168. The members are urged together axially against a thrust bearing 88 by a spring 94 between the lever and a washer 96. A highvoltage conductor is connected to an opening 120 in a rod 114 attached to a cover 110. Fig. 8 shows an alternative wiper arrangement in which the forward peripheral part of the inner member is helically grooved at 60 and the projections separating the grooves clear the discharge passage when the inner member is oscillated about its axis. An air manifold 52 may surround the outer member by means of which an annular air sheath may be discharged therefrom through a passage 58. The atomizer of Fig. 10 comprises upper and lower disc elements 211, 212, with outer discharge edges 213, 214, a liquid supply opening 222 leading to a passage 220, and an annular outlet. Wipers 226,228 are uniformly disposed around the disc elements, and <PICT:0804805/III/1> <PICT:0804805/III/2> <PICT:0804805/III/3> <PICT:0804805/III/4> <PICT:0804805/III/5> <PICT:0804805/III/6> the upper element is oscillated by an air cylinder 230. The piston rod 232 of the cylinder is slotted and co-operates with an element 234 extending from a shaft 216 of the upper disc. One or more pairs of wiper elements may be extended circumferentially in the embodiments described to obstruct any desired portion of the discharge opening and provide a desired spray pattern. Fig. 9 shows an electrical control system for operating the air motor and hence clearing the atomizer 10 during the periods when the atomizer is located between workpieces 46 passing by on a conveyer 50. During such periods the liquid supply to the atomizer is cut off. A counter or timer 184 operates normally-open contacts 186 in the energizing circuit of a solenoid-operated valve 188, this circuit including normally-open contacts 190 of a photo-electrically operated relay 192. The latter forms part of a control system including a lamp 194 and a light-sensitive cell 196 on opposite sides of the conveyer. With the power supply switch 200 closed the counter or timer 184 eventually closes contacts 186 but the valve 188 will not be operated to permit compressed air to operate the air motor until the atomizer is located between the articles i.e. when contacts 190 are closed by the photo-electric system. A similar valve 208 controls the air supply to a paint-control valve 121 so that paint is only supplied to the atomizer when a workpiece is in the spraying region.