GB1265671A - - Google Patents

Abstract

1,265,671. Extruding. R. CHADWICK, and O. E. FLETCHER. 2 Feb., 1970 [15 Feb., 1969], No. 8325/69. Heading B3P. [Also in Division G3] In a process of hot extrusion of metals, e.g. aluminium alloy, the speed at which the metal billet 14 is forced through a die 16 by an hydraulic ram 10 is varied in order to ensure that the extruded metal emerges from the die at a constant predetermined optimum temperature, the friction between the die and metal billet inducing heat particularly in the extruded metal which is likely to be at a higher temperature than the rest of the billet. There is a maximum temperature, e.g. 460‹ C. above which the quality of the metal is affected (e.g. grain coarsening, surface cracking). The billet is preferably pre-heated before extrusion, e.g. to 440‹ C. Allowing for loss in heat before extrusion of say 20‹ C. then the permissable max. generated heat would be 40‹ C. The extruded metal temperature is sensed continuously by a radiation pyrometer 28 the initial reading of which is corrected by comparison with a more accurate temperature recorded by a contact pyrometer 23. Pyrometer 23 has sensing prods (e.g. thermocouples) which become embedded in the leading end portion of the extruded metal and tend to damage the metal, the affected portion of which has to be discarded. The contact pyrometer is therefore used for initial calibration only or may be used intermittently during the extrusion cycle and is mounted on a carriage 20 for movement along the direction of the extrusion and at right angles thereto. The corrected temperature value is compared with a predetermined value which may be the permissible maximum and the difference value is used to automatically control the hydraulic fluid supply to the hydraulic press. Alternatively the fluid supply may be varied manually to adjust the extrusion speed until the difference is zero. The extruded metal may be cooled in a.water bath or spray after it emerges from the die.