| 摘要 |
In the treatment of a fusible rod by the passage of a molten zone through the rod while one end is maintained stationary and the other end is rotated, formation of the molten zone is effected while a torque is applied to the first mentioned end and the second mentioned end is held stationary. Rotation of the first mentioned end takes place on formation of the molten zone and is used to detect such formation. Rotation may be delayed by the use of an oil damping device. The torque may be produced by a spring or by <PICT:0907478/III/1> <PICT:0907478/III/2> the coaction of a current-carrying coil and a permanent magnet. Solidification of the molten zone may be detected by rotation of the first mentioned end. As shown in Fig. 1 a rod holder 9 depends into a vacuum vessel 2 from a rotatable mounting in a cap 3 and is engaged by a magnetic clutch with an inverted U-shaped member 13 which is rotatably mounted on cap 3. The magnetic clutch is constituted by a pair of soft iron armatures 11 forming part of holder 9 and a pair of bar magnets 12 forming part of member 13. A torque is produced by a coil 20 and a permanent magnet 19 in member 13 and is transmitted by the magnetic clutch to holder 9. Formation of the molten zone, the lower holder (not shown) being stationary, causes rotation of the holder 9 and member 13 until a pin 24 on member 13 contacts a stop 23 on cap 3. Such a contact may produce an electrical signal. A second stop 23 enables to and fro movement a number of times to provide a delay before the signal is given. Initial delay may be provided by an oil damping device comprising vanes 17 attached to member 13 and rotating in an oil bath 3A. Solidification of the molten zone while the lower holder is being rotated breaks the magnetic clutch and causes rotation of the holder 9 only, thereby bringing one of the soft iron armatures adjacent a bar magnet 28 (Fig. 2) which moves so as to produce a signal or disconnect a circuit. |
