Coated electrical steel sheet for the fabrication of magnetic ciruits

摘要

A steel sheet for use in the laminations of a magnetic circuit comprises less than 6.5 wt.% Si and less than 3% Al, and its two sides are coated with different insulating varnishes, each based on at least one organic resin and one of them also containing at least one mineral filler and possibly at least one inorganic polymer. Also claimed are magnetic circuits built up of laminations cut from such coated steel sheets, the steel containing, in addition to the Si and Al, less than 0.010% C, less than 0.010% N, less than 2% Mn, less than 0.25% P and possible small amounts of Sn, Sb, Cu, Cr, Ni and B. One side of the sheet is coated with a varnish containing at least one resin from the group polyester, epoxy, phenol and acrylic and the other side with varnish containing at least one acrylic resin associated with at least one phenol resin. Each varnish may also include a hardening agent from the aminoplast family, an inorganic polymer such as silicone resin or a polyphosphate associated with chromic or phosphoric acid and a mineral which may be a pigment. The mineral may comprise over 60 wt.% of the varnish and may comprise at least one metal sulphate, sulphide, silicate, carbonate or oxide and carbon, particularly barium sulphate, zinc sulphide, aluminium silicate and titanium oxide. The steel may be 0.5 mm thick and the varnish coating 3 microns thick.