| 摘要 |
PURPOSE:To keep all the processes for a composite extrusion billet in a preheated condition and to prevent air from penetrating between a cover stock and a billet by preheating a casted billet, sculping it to remove the surface layer, passing a preheated cover stock and the billet through a drawing die to make them a composite billet, and indirectly extruding the composite billet. CONSTITUTION:A casted billet 1 is preheated at a working temp. and is removed its surface layer by passing the billet 1 through a sculping die 3. A composite billet 6 is formed by passing both a preheated cover stock 4 and the billet 1 removed its surface layer through a drawing die 5 to cover the surface of the billet 1 with the cover stock 4 under a preheated condition. Then, the composite billet 6 covered with the cover stock 4 under the preheated condition is put in a container 7, is pierced a hole using a piercing mandrel 8, is extruded by an indirect extruder having a die 9, and is formed into a hollow composite extrusion stock 10. Therefore, air penetration due to differential thermal expansion between the billet 1 and the cover stock 4 is prevented and no foreign matter also penetrate between the billet 1 and the cover stock 4 because the cover stock 4 is not necessary to be formed into a cylindrical shape.
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