Continuous-annealing method for producing a flexible, curved, soft magnetic amorphous alloy ribbon

A method has been developed for continuous annealing of an amorphous alloy ribbon moving forward at several meters per second, giving a curved shape to the ribbon that remains flexible afterward and can be easily wound into a toroidal core with excellent soft magnetic properties. A heat pulse was applied by a compact system on a Metglas 2605HB1 ribbon moving forward at 5 m/s to initiate a thermal treatment at 460 °C, near crystallization onset. The treatment duration was less than 0.1 s, and the heating and cooling rates were above 10 000 °C/s, which helped preserve most of the alloy as-cast ductility state. Such high temperature rates were achieved by forcing a static contact between the moving ribbon and a temperature-controlled roller. A tensile stress and a series of bending configurations were applied on the moving ribbon during the treatment to induce the development of magnetic anisotropy and to obtain the desired natural curvature radius. The core losses at 60 Hz of a toroidal test core wound with the resulting ribbon are lower than the specific values reported by the alloy manufacturer. This method can be implemented at the casting plant for supplying a low-cost, ready-to-use ribbon, easy to handle and cut, for mass production of toroidal cores for distribution transformer kernels (core and coil only), pulse power cores, etc.