Patent GB-645612-A (GB)
Title: Method and apparatus for coating articles by electrostatic deposition
IPC: B05B5/08
Filed: 1946-01-23
Abstract: 645,612. Electrostatic precipitation. RANSBURG, H. J., RANSBURG, H. G., RANSBURG, H. P., and RANSBURG, E. M., (trading as RANSBURG CO., H. J.). Jan. 23, 1946, No. 2301. Convention date, Feb. 3, 1945. [Class 39 (i)] A method of coating articles by electrostatic deposition comprises conveying articles 10, Fig. 2, along a generally L-shaped path, maintaining a high potential difference between the articles 10 and an ionizing electrode 15, and energizing a gun 14 for spraying finelydivided coating material through the " finish " coating zone, i.e. the region around the leg of the L-shaped path adjacent the gun 14, towards the pre-coating zone around the other leg of the L-shaped path. The electrode 15 comprises a series of frames 15a across which a series of 0.010 inch diameter wires 15b are stretched, the wires 15b being spaced apart by about twothirds of the distance of the electrode plane from the surface of the articles 10. The frames 15a and wires 15b extend on both sides and underneath the articles 10 so as to form an approximately U-shaped structure. The voltage source 16 is a half-wave over-controlled, limited current rectifier capable of converting normal line voltage to pulsating high voltage direct current. The coating operation takes place in a booth 13 of non-conducting material which is closed at the sides, top, and bottom; a fan 19 draws air in at the finish coating- zone " and expels it out of the opening 12, this air flow aiding the deposition. A pair of removably mounted spring guide-plates 23 placed in the entrance opening for the articles prevents any lateral swinging thereof. On entering the precoating zone, the articles 10 supported from hooks 26, Fig. 4, are rotated at a speed of one to one and a half revs./foot of linear movement by a spinner 28 which engages a shoe 32, on idler wheel 29 being in contact with a pressure bar 30a, Fig. 2, to ensure contact between the members 28, 32, and to prevent lateral swinging of the articles 10. When the articles 10 enter the " finish " coating zone their rate of rotation is speeded up to four to six revs./foot of linear movement by means of an endless moving belt 33 engaging the spinner 28, a second pressure bar 30 being provided with which the idler wheel 29 engages. The conveyer 27 and endless belt 33 are enclosed in a shield 25. The idler wheel 29 and a sleeve 29a is arranged to lock over a splice in the shank 26 of the hooks; when the wheel 29 is raised the lower portion of the hook may be readily removed for cleaning. In the precoating operation any particles of coating material which pass between the articles 10 in the precoating zone are repelled by the electrode section at the further side thereof from the gun 14 so as to return towards the articles; thus there is very little loss of coating material from the region of the electrostatic field. The spray gun 14, conveyer 27, ventilating fan 19 and voltage supply for the electrode 15 are all controlled from a single panel, Figs. 3, 7 (not shown). Various safety devices, such as limit switches, warning lights, &c., are described, and the whole booth is enclosed in a grounded fence, Figs. 3, 7 (not shown). Specification 645,629 is referred to.