PURPOSE:To make it possible to automatically pull out an airtight plug in a baking process on a painting line from a water draine hole by a method wherein the title actuator is formed by combining a ferro-magnetic body having a Curie temperature, which is higher by 0-50 deg.C than its working temperature, and a permanent magnet having a Curie temperature higher than that of the ferromagnetic body. CONSTITUTION:The title actuator consists of the ferromagnetic body 3, having a Curie point (Tc) higher by 0-50 deg.C than its working temperature, and a permanent magnet 4 having a Tc higher than the ferromagnetic body 3. It is desirable that the Tc of the permanent magnet is higher by 200 deg.C or above than the Tc of the ferromagnetic body 3. As a result, the ferromagnetic body 3 is magnetized by the permanent magnet 4 at the room temperature or below, the entire body of the ferromagnetic member 3 is attached to the lower surface of the body, and an airtightly plugged state is accomplished. Subsequently, the body is carried into a baking process, and when the entire body is heated up to the temperature in the vicinity of the Tc of the ferromagnetic body 3, the ferromagnetic body 3 loses its magnetization. As a result, the attracting force with the body is reduced, and the plug body is pulled out from a water draine hole by its own weight.
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