| 摘要 |
PURPOSE:To prevent a deformation of a mandrel so that an influence is not exerted on a stroke of a moving frame, by detecting a bend of the mandrel on the rear face of a mandrel supporting frame by utilizing the conductivity between the mandrel, and a conductive plate in the rear of the mandrel supporting frame. CONSTITUTION:In a position of a rear face supporting plate 103 of a mandrel supporting frame, a mandrel 10 is held in the center position of a mandrel passing hole by a guide bush 106 and an O-ring 107. When an abnormal force is applied to the mandrel 10, and the guide bush 106 is deflected in the diameter direction against the elasticity of the O-ring 107, a bend is generated in the mandrel 10, and the mandrel 10 comes into contact in a mandrel passing hole 110 of a conductive plate 109 provided in the rear of the supporting plate 103. By this contact, a current flows to an electric conduction detector from a power source, and the bend of the mandrel 10 is detected. At this time point, the mandrel 10 does not reach a permanent deformation, therefore, the permanent deformation of the mandrel 10 is prevented by suspending the tube expansion.
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