| 摘要 |
PROBLEM TO BE SOLVED: To provide an overclad tube having extremely little warpage. SOLUTION: After a handle front end 22 is inserted into the internal cavity of a tube 10, a silica pin 30 is inserted therein and the relative terminal of a handle is fixed by a knob 40, by which the tube is perpendicularly hung down. Next, the tube/handle assembly parts are kept at a temperature suitable for removing all of the remaining impurities and generally, the temperature of the assembly parts is raised by passing the parts through the hot region of a furnace, by which the entire part of the tube is fired and thereafter the furnace is heated generally to a sintering temperature. The tube is then passed through the hot region and is returned by pulling up (ascending sintering). The handle front end and the tube around the same are deformed by the high temperature but the handle front end is applied with force and has a tendency to be deformed in the array symmetrically perpendicularly to the tube which maintains perpendicularity by the occurrence of the warpage. The deformation at the front end considerably lowers the induction of the warpage in the tube.
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