Improvements in or relating to methods of applying a coating to a body of material

摘要

A method of producing an electrically insulating coating on a body, e.g. rolled electrical capacitors, comprises electrically charging the body and a powdered insulating substance in opposite senses whilst in an unheated state, bringing the charged body and powder close to each other so that the powder particles are deposited on and adhere to the body, preventing ionization occurring in the atmosphere where the body and powder are brought into proximity so that the powder particles will adhere to any electrically-insulating surface of the body and thereafter melting the powder on the body to form the coating. Ionization of the atmosphere may be prevented by having a low charging voltage or by charging the powder at a distance from the article. The powder, which may be charged negatively may be an epoxy resin, phenol-aldehyde resin, polyethylene, polyamide, polyacrylate, glass and enamel. To prevent cracks appearing in the coating the melting of the powder may be carried out in a two-staged process or the body may be impregnated, e.g. with a mixture of 60% hardwax, 30% ozokerite and 10% polyisobutylene, before being coated. If parts of the body are not to be coated the body may be masked or the powder may be removed from these parts, e.g. by a brush, before melting the powder. As shown in Fig. 1, a charged body 3 is coated by allowing the oppositely charged powder 2 to fall through sieve 1. In Fig. 2 bodies 3 are passed on a conveyer belt 5 travelling vertically between vibrating hoppers 7. The powder dropping past the bodies 3 is recirculated to hoppers 7. The bodies are then passed between strips of velvet or plush 8 and suction brushes 9 to remove powder adhering to the current supply leads. The bodies are earthed by sliding contacts 10. In Fig. 3 powder 22 dropped from hopper 15 on to conveyer belt 11 consisting of an upper layer of insulating material and lower layer of metal, is charged by spray electrodes 17 and attracted to bodies 16. Any powder remaining on belt 11 is removed by brushes 18 and recirculated. An earthed electrode 20 is in sliding contact with the belt 11. In Fig. 4 powder from storage means 22 is dropped on to a rotating p earthed circular metal plate 21, charged by needle-like electrodes 23 and attracted by bodies 27 on conveyer belt 26. A pair of brushes 25 prevent the widening of the ring of powder 24. The plate 21 may be replaced by a drum as shown in Fig. 5.