ABSTRACT
Using high-speed rod rolling facilities in the Freiburg laboratory, Lee (Shinokura et al., 1984) carried out a four-pass continuous high-speed rod rolling test to examine the effect of high strain rate, more than 100 (1/s), during rolling on the flow stress and consequently the roll force and torque. Fig ure 5-56 illustrates the schematic of the four-pass continuous high-speed rod rolling facilities before revamping. The roll forces were measured at each stand (pass), and the surface
Figure 4-20 Correlations between rolling speed and material flow round-oval-round pass sequence, (a) Spread and elongation; (b) forward slip and backward slip. Steel: 0.16% C, 0.25% Si, 0.48% Mn, 0.10% Cr. (Courtesy of Dr. G. Goldhahn and Dr. R. Kawalla of the Technical University Bergakademie, Freiberg, Germany.)
temperatures of the workpiece during rolling were measured before the first pass, after the second pass, and after the fourth pass. The finishing rolling speed for this study was set up as 15 m/s. The initial diameter of the specimen was 12 mm, and the diameter of the finally rolled specimen was approximately 8 mm. Figure 5-57 shows the design parameters and roll grooves used in the test. Additional longitudinal drag, generated by different revolutions of single stands, moves the neutral point in one or another direction. Higher drags reduce the spreading; in extreme conditions it disappears completely. In this case, the material flows in one direction only (elongation). Experimental data for this longitudinal drag is described in Figure 5-69.
