Heating device used for production of shutter for a disk cassette

A heating device for production of a shutter made of synthetic resin and shaped into a U-form in section, the heating device being used for heating a pair of corner portions of the shutter to extinguish residual stresses that exist in the corner portions that are formed where a connecting portion of the shutter connects a pair of shutter plates that cover the respective upper surface and the lower surface of the case so as to be able to open and close a head insertion opening provided in at least one of the upper surface and the lower surface of the case, wherein the heating device comprises:

• support means for fixedly supporting the free ends of a pair of shutter plate in a vertical position wherein the free ends, which are in opposed relation to the respective ends that have been already connected to a connecting portion of the shutter, are in contact with each other at a distal position of each free end,
• fixed heating means accommodated for receiving and contacting only a pair of corner portions of the shutter that have been fixedly supported by said support means, in order to heat said corner portions to a predetermined temperature;
• temperature setting means for setting said predetermined temperature;
• and
• heating-duration setting means for setting a heating duration by said heating means,
• wherein said heating means has a pair of heating surfaces that connect to form a predetermined acute angle with each other,
• wherein the temperature setting means sets a predetermined temperature which is coincident with a softening temperature of the synthetic resin, and
• wherein the support means presses the free ends of the shutter plates together so that the shutter plates form an acute angle.