Abstract
The efficiency of novel superconducting direct current (DC) induction heaters can be up to 80-90%. This is much higher than the 40-50% of conventional alternating current induction heaters. Induction heaters are used to preheat aluminum billets in extrusion pressing. Such devices use a driving motor to rotate the billet. A peak in the electromagnetic torque appears at low rotation speeds (of the motor). Therefore, this peak electromagnetic torque is of particular interest when designing the driving system, which is one of the main challenges for megawatt-class superconducting DC induction heaters. In this paper, the peak electromagnetic torque characteristics of different sized billets were analyzed. A numerical 3D finite element method model was built to analyze the peak electromagnetic torque and resistive heating power behavior of aluminum billets. The results obtained from simulations and experiments match well. The effect of the following five relative parameters, on electromagnetic torque and resistive heating power, were studied: billet diameter, billet length, magnetic flux density, billet material, and electrical conductivity. The peak electromagnetic torque increases nonlinearly with increasing billet diameter, up to 640 mm. The time elapsed between the peak to stable torque decreases nonlinearly with increasing magnetic flux density. The effects of billet material (copper, titanium alloy and stainless steel) on torque were analyzed and compared. These results are likely to guide more cost-effective and practical designs for the billet driving system of superconducting DC induction heaters.
Highlights
Induction heating has been widely used to preheat aluminum billets in extrusion pressing [1]–[3]
Our peak electromagnetic torque characteristics results are useful for industrial applications of superconducting direct current (DC) induction heaters
They may guide more cost-effective, practical and reliable driving system designs, to rotate aluminum billets heated by superconducting DC induction heaters
Summary
Induction heating has been widely used to preheat aluminum billets in extrusion pressing [1]–[3]. Our peak electromagnetic torque characteristics results are useful for industrial applications of superconducting DC induction heaters They may guide more cost-effective, practical and reliable driving system designs, to rotate aluminum billets heated by superconducting DC induction heaters. When an aluminum billet is heated in the superconducting DC magnet, the billet is rotated in a static transverse magnetic field, to induce an eddy current, and is heated by Joule loss. At the stable rotational speed of 350 rpm, when the actual heating process occurs, both the electromagnetic torque and resistive heating power increase with heating time. For resistive heating power they are 197 kW and 210 kW at 240 rpm, respectively
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