Heat transfer in the hot rolling of metals
- PDF / 1,010,447 Bytes
- 9 Pages / 597.28 x 785 pts Page_size
- 57 Downloads / 194 Views
I.
INTRODUCTION
MODERNsteel and aluminum hot-rolling practices call for the achievement of high productivity coupled with the precise control of strip shape and mechanical properties. Accurate knowledge of the heat-transfer coefficient (HTC) in the roll gap is essential to achieving these goals, because the HTC determines the temperature distribution in the rolls and the rolled strip which, in tum, influences the microstructural evolution and ultimately the mechanical properties of the strip, as well as the shape of the rolls and roiled strip. To date, only a few studies have been conducted to measure the HTC between the rolls and workpiece for aluminum rolling. Pietrzyk and Lenard tz~ reported an HTC between 18.5 and 21.5 kW/m 2 ~ in the warm rolling (155 ~ to 210 ~ of commercial-pure aluminum, whereas B.K. Chen et al. I21 reported values of l0 to 50 kW/m 2 ~ for the hot rolling of A1 + 5 pct Mg alloy. In order to study the temperature distribution in the laboratory rolling of AA5083, Timothy et al. c3I employed subsurface thermocouples to obtain a HTC of 15 kW/m 2 ~ Smelser and Thompson I41 reported a single value of 30 kW/m z ~ However, only B.K. Chen et al.t2] have presented, for aluminum rolling, the dependence of the HTC in the roll bite on the variation of roll pressure along the arc of contact, in a similar manner to that reported by W.C. Chen et aL[5] for various grades of steel. Hlady et aL[6] reported an HTC in the roll gap between 100 and 350 kW/m 2 ~ for the hot rolling of the aluminum alloys AA5052 and AA5182. The HTC was calculated from the temperature response of the aluminum samples in the roll gap, which was measured by double-intrinsic thermocouples fastened to the surface of the samples. Furthermore, Hlady et al.[61 observed a slight increase in the HTC with increasing roll pressure. They also noted that at similar rolling pressures, aluminum exhibited an HTC approximately C.O. HLADY, Research Engineer, J.K. BRIMACOMBE, Alcan Chair in Materials Process Engineering and Director, and I.V. SAMARASEKERA and E.B. HAWBOLT, Professors, are with The Centre for Metallurgical Process Engineering and the Department of Metals and Materials Engineering, The University of British Columbia, Vancouver, BC, Canada V6T 1Z4. Manuscript submitted September 15, 1994. METALLURGICALAND MATERIALSTRANSACTIONSB
4 times higher than that of steel. They attributed this difference to the higher flow stress of steel at the roll-workpiece interface, as compared to aluminum. Thus, they concluded that at similar rolling pressures, aluminum asperities deform to a greater extent than steel asperities, thereby enhancing direct metal-metal contact between the roll and workpiece and, therefore, the HTC. Semiatin e t a / . , tn in a series of ring-upsetting tests on AA2024-O, observed increasing heat transfer between the ring and die with increasing applied pressure. They attributed this to an increased smoothening of asperities at the ring surface, thereby bringing the workpiece into better thermal contact with the dies. This conc
Data Loading...
