GB655763A - Improvements in or relating to the electrophoretic coating of articles of electrically conducting material - Google Patents

Abstract

655,763. Coating articles electrophoretically; electric cables. SPRAGUE ELECTRIC CO. Feb. 28, 1948, Nos. 6289 and 6290. Convention dates, Jan. 15, 1943, and Aug. 2, 1943. [Classes 36 and 41] [Also in Group VIII] A method of coating articles of electricallyconducting material with insulating material comprises forming a suspension in a liquid medium of finely-divided particles of refractory insulating material, modifying the suspension to make it more flexible and adherent by including in it at least one of a group of substances consisting of water-soluble silicates, zinc oxide, ground mica, and synthetic resins, and electrophoretically depositing a coating from the modified suspension on to the article. To provide a denser deposit the electrolyte may contain a densifying agent which has monovalent cations and polyvalent anions such as a water-soluble silicate, a phosphate, carbonate or ferrocyanide. When the modifying agent is a soluble silicate the subsequent coating may be heated to convert the silicate into a water-insoluble reaction product, or alternatively the coating may be immersed in a solution of a metal salt, such as lead acetate and then heated to form a silicate cement. Mica may be used as its own modifying agent and as a modifying agent for other refractories. The coated conductor is made more flexible by having its pores impregnated with resinous material, preferably by electrophoretic deposition. In the arrangement shown in Fig. 1, a wire 15 is fed to a cell 10 containing a suspension of refractory material together with a modifying and a densifying agent. The container 10 forms one electrode, the wire being the anode and connected to a source of current 22 by a brush 21 and mandrel 17. The coated wire is heated in an oven 11 and is then passed into a cell 12 where the pores of the coating are electrophoretically impregnated with a resinous material. The impregnated coating is baked or polymerized in an oven 13. In a modification shown in Fig. 3, the coating cell 53 has an inlet duct 55 and an outlet duct 56 for the wire, the duct 56 preferably made of copper, functioning as the cathode. The coated wire passes through an oven 60 in three stages, wherein the removal of moisture and solvents and subsequent baking and sintering of the coating may be controlled. The wire then passes into a copper trough 63 containing a solution 4 of ammonium hydroxide which penetrates the porous refractory coating and makes electrical connection between the wire and a source of current 65 connected to the trough 63. Ammonium hydroxide may also be used for cleaning the wire surface before it is coated. The wire passes from the trough to an impregnating cell 67 and hence to an oven 70 also in three stages. The wire may be passed through a further impregnating cell in which the coating voltage is higher than that used in the cell 67 to ensure breakdown and subsequent coating of weak spots in the coating. The coated wires may be used not only for carrying electric current but may also be used in the manufacture of screens, fences, wire gauze, or glass substitutes, in the latter case being formed into a screen the interstices of which are filled with a plastic composition.