| 摘要 |
PROBLEM TO BE SOLVED: To obviate the occurrence of cracks and fissures in an evaporation source assembly, such as a crucible, even in the stage of the initial period of heating of magnetic material with an apparatus for production of magnetic recording media. SOLUTION: A material 11b to be inductively heated is disposed between the refractory crucible 11a and high-frequency induction heating coil 12 constituting the evaporation source assembly 11. The relationship between the coefficientαc of thermal expansion of the refractory crucible 11a and the coefficientαi of thermal expansion of the material 11b to be inductively heated is specified toαc>αi. In heating by the high-frequency induction heating coil 12, the material 11b to be inductively heated is heated as well together with the magnetic material 10 in the crucible 11a, by which the crucible 11a is heated from both of the inner and outer sides and the occurrence of the cracks and fissures by the difference in the thermal expansion may be prevented. Further, the crucible 11a expands more largely than the material 11b to be inductively heated and, therefore, even if the inside and outside diameters are changed by the thermal expansion upon rising of the temperature of the crucible 11a to high temperature, the inside and outside diameters change to the direction where the spacing between the crucible 11a and the material 11b to be inductively heated is reduced and there is no more spacing. Since the circumference of the crucible 11a is protected by the material 11b to be inductively heated, its mechanical strength is improved and the occurrence of the fissure by the thermal expansion may be prevented.
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