GB1208203A - Determining the piercability of seamless metal tubes - Google Patents

Abstract

1,208,203. Rolling tubes. NIPPON KOKAN K.K. 1 April, 1968 [30 March, 1967], No. 15560/68. Heading B3M. [Also in Division Gl] A Mannessman-type piercer apparatus for making metal tubes, Fig. 3, comprises conical rollers 1, 2 rotating in the same direction and drawing through the roll pinch a billet 4 of hot metal. The rotation of the rollers in combination with the effect of the piercer 3 causes the billet to exit from between the rollers as a tube (rotating forging). In order satisfactorily to test the piercability of a billet it is necessary to test the billet without using the piercer or plug 3, but previously in such tests it has been the practice to run the rollers at a speed the machine would have had were a plug actually in use. With the plug out of use however the delivery rate of the tube is greater than when the plug is in use as the plug resists delivery thus resulting in an increase in the rotating forging effect which is a loosening of the structure of the billet core portion due to the rollers alone. In order to test for this forging effect alone the axis of the rollers at the billet entry side must be varied to give the same delivery speed to the billet in the absence of the plug 3 as when using the plug and the reduction ratio (i.e. the percentage reduction of cross-sectional area after working) imposed by the rolls must be varied as the billet passes through. The billet must then be examined to detect the starting point 12 of internal rupture. The reduction ratio at that point should then be found and not exceeded at the subsequent piercing operation so that tubes having excellent internal finish may be obtained. In operation a tapered billet is used as the test piece, Fig. 5, and is inserted in the roller gap without the plug 3, the taper of the billet giving a variation in the reduction ratio as the billet passes through because the variable billet diameter is converted to a fixed diameter after reduction. In other words the billet in Fig. 5, which is of uniform cross section, has that uniformity produced by passing a tapered billet through the rolls to give various reduction ratios, and the point 12, at which internal rupture starts, is the 15% reduction ratio point which in operation should not therefore be exceeded.