| 摘要 |
PURPOSE:To facilitate separation of mandrel from a material tube after reducing in tube manufacturing by hot reducing by providing a pressure oil passage in the mandrel and changing outer diameter by changing the oil pressure. CONSTITUTION:An oil pressure passage 17 is provided in the body 11 of a mandrel to communicate with an oil pressure passage 17, and the oil pressure passage 17 is connected to an oil pressure source. Accordingly, when oil pressure is adjusted, oil pressure acting on inside surface of the shell 14 changes, and the shell 14 is expanded or contracted, and outer diameter of rear part of the mandrel is changed. With outer diameter of the mandrel expanded by making oil pressure inside of the mandrel high, it is inserted into a hole of the cylindrical material to be reduced, and reducing work is made using a die. Then, oil pressure in the mandrel is made low to reduce the diameter of the mandrel. The mandrel is then retreated, and the mandrel is stripped and separated from the reduced material tube.
|
