INORGANIC BINDERS FOR C CORES

Cores are constructed by applying a thin glassy layer to magnetic steel strip and winding the composite until the required build-up is attained. The final laminar bond between adjacent glassy layers is accomplished by heat treatment at the softening temperature of the glass. The hot-winding method for obtaining the laminar bond did not eliminate the need for stress relief annealing. The cold-winding method proposed is just as effective in obtaining the laminar bond, providing the softening temperature of the glass coincides with the requisite stress relief annealing temperature. A viscosity of approximately 10 to the 8th power poises at 810 C is required for glassy binders used in cold-wound cores. For a stress-free core, the binder is also required to match the thermal expansivity of the magnetic material. The coefficient of thermal expansion for grain-oriented silicon steel is approximately 13.5 x 10 to the 6th power. The difficulty in obtaining a glass composition which would satisfy both high viscosity and high thermal expansivity is discussed. The system, Na2O.xRO2.3-xSiO2 where R is Zr or Ti and Rb2O-CaO-SiO2, are being studied for the development of a suitable binder. The importance of surface condition of the magnetic material and binder slip consistency is discussed. Author