Patent GB-721711-A (GB)
Title: Improvements in or relating to electrical coils
IPC: H01F41/06
Filed: 1952-08-01
Abstract: 721,711. Coating wire. WESTERN ELECTRIC CO., Inc. Aug. 1, 1952 [Aug. 4, 1951], No. 19525/52. Class 140. [Also in Group XXXV] A bare conductor is coated with a layer of fluid insulating material having finely-divided solid insulating particles dispersed therein, the insulating coating is partially solidified, the coated conductor is wound into a coil while the coating still possesses a degree of fluidity so that adjacent coatings coalesce and the coalesced coatings are hardened to provide a solid or substantially solid matrix in which the turns of the coil are held in insulated spaced relationship. Thermosetting resins (e.g. phenolic or epoxy) or thermoplastic resins (polyamides, polyvinylchloride, polyethylene, butadiene - styrene - acrylonitrile copolymers, butadiene-styrene copolymers, acrylates, polytetrafluoroethylene and polymonochlorotrifluoroethylene) may be used as the insulating material. Silica, aluminium and magnesium silicates, mica, lead chromate, lead titanate, titanium dioxide, zinc oxide, ferric oxide, aluminium oxide, cupric oxide, talc, and cellulose, nylon or other filamentary material may be used as the finely-divided solid filler. The coating may be applied electrophoretically or by a die wipe or roller coating process. The resin composition may be suspended in a liquid, e.g. water, which may be removed by heat, or in a liquid such as divinyl benzene or acrylonitrile which may be allowed to cross-link with the resin. Partial setting of thermosetting materials may be brought about by heating. As shown (Fig. 3) an electrophoretic applicator comprises a cylindrical tube 35 divided by walls 37 and 38 into chambers 40, 34 and 41. The coating material is pumped from a reservoir 31 into the chamber 34 through pipe 32, overflowing through pipes 46 and 47 back to the reservoir. Any coating material flowing through the holes 40 and 44 in the dividing walls flows back to the reservoir through pipes 49, 50 and 51. The wire 1 under constant tension passes through holes 42, 43, 44 and 45. If the particles in the coating dispersion carry a positive charge, the wire may be grounded and the cylinder or tube 35 charged positively from a battery. Similarly when using negatively-charged particles the cylinder may be charged negatively with respect to the wire. Breaking the electrostatic field by a switch results in a length of wire passing uncoated through the applicator and this bare wire may be used for connection to the terminal block of the coil. The coating is partially solidified by heating or cooling according to the nature of the coating and the coated wire wound into a coil on a laterally moving arbor. A jet of hot gas, e.g. nitrogen, at 120 ‹ C. may be directed toward the arbor during the winding to solidify and bond the coatings together. Alternatively a roller coater (Fig. 4) may be used. This comprises a roller 60 formed with a plurality of grooves 61 and mounted for rotation in a housing 63. Excess coating material is removed by a spring-tensioned scraper 64. The roller rotates partly immersed in the coating composition and the wire passes through one of the grooves 61.