| 摘要 |
<p>PURPOSE:To obtain a duct with dove-tail grooves which keep firmly an insulative-lining on the inner surface of the duct by lining the duct with insulator, after the dove-tail grooves are fomed on the inner circumferential surface of the duct by electrospark machining. CONSTITUTION:A columnar electrode 4 is arranged on the upper part of a duct 1 such that the central axis of the electrode is coincident with the axis of the duct, and vertical movement of the electrode is made movable by a movement-mechanism. Eight protrusion 4a for forming grooves having trapezoidol-form are arranged along the axial direction on the peripheral surface of the electrode 4, and extend in the axial direction. The width of the protrusion section increases gradually in the direction from the electrode-periphery to the outer side. In this apparatus, firstly the electrode 4 is inserted into the duct 1. Simultaneously, electrical discharge between the electrode and the duct is caused to occur, and dove-tail grooves 1b correponding to the groove forming protrusions 4a and extending in the axial direction, are formed on the inner surface of the duct 1. Next, when the insulator lining 2 has been prepared on the internal surface of the duct 1, the lining duct with dove-tail grooves 1b may be obtained, and the dove-tail grooves are used for holding the insulator 2 and extend in the direction of the tube axis.</p> |
