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Improved short coil correction factor for induction heating of billets
Norwegian University of Science and Technology, Trondheim, Norway .
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
2012 (English)In: 3rd International Symposium on High Temperature Metallurgical Processing, 2012, 373-382 p.Conference paper (Refereed)
Abstract [en]

To determine the heating rate of billets using 'short coils', an appropriate correction factor must be applied to the theoretical relationship. In 1945, Vaughan and Williamson published a semi-empirically modified Nagaoka coefficient applicable for moderate frequency induction heating processes (10 kHz). Recently it was demonstrated that the method of Vaughan and Williamson gives <10% error in the estimated power when heating aluminum billets at 50 Hz. In the present study, experiments have been conducted on aluminum billets in order to verify an empirical frequency corrected 'short coil' equation. Measurements of electrical conductivity (<± 0.5%), current (± 1%), heat (± 1-3%), and magnetic flux density (± 1-2%) have been performed. The results are compared with 1D analytical calculations, and 2D axial symmetric FEM modeling using COMSOL 4.2®. The frequency corrected equation has proven to provide accurate predictions of power (<4% error) within the frequency range 50 Hz to 500 kHz.

Place, publisher, year, edition, pages
2012. 373-382 p.
Keyword [en]
Billet, Heating, Induction, Magnetic field, Short coil
National Category
Materials Engineering
URN: urn:nbn:se:kth:diva-89169DOI: 10.1002/9781118364987.ch46ScopusID: 2-s2.0-84860809974ISBN: 978-111829141-2OAI: diva2:502771
3rd International Symposium on High-Temperature Metallurgical Processing - TMS 2012 Annual Meeting and Exhibition; Orlando, FL; 11 March 2012 through 15 March 2012

QC 20120803

Available from: 2012-02-14 Created: 2012-02-14 Last updated: 2013-09-11Bibliographically approved
In thesis
1. Magnetic Fields and Induced Power in the Induction Heating of Aluminium Billets
Open this publication in new window or tab >>Magnetic Fields and Induced Power in the Induction Heating of Aluminium Billets
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Induction heating is a common industrial process used for the reheating of billets before extrusion or forging. In this work the influence of the coil and work piece geometry, the effect of the electrical properties of the work piece, and the coil current and frequency, on the magnetic flux density and resulting work piece heating rates were studied. A combination of 1D analytical solutions, 2D axial symmetric finite element modelling and precise measurements has been used.

Dozens of heating and magnetic field experiments have been conducted, with steadily increasing sophistication and measurement accuracy. The development of the experimental techniques will be described in the ‘cover’ and related to the later results published in the supplements. Experimental results are compared to predictions obtained from analytical and numerical models. The published measurements obtained for the billet heating experiments consisted of: billet electrical conductivity with <0.5% error, applied currents with <1% error, magnetic flux densities with 1-2% error, calorifically determined heating rates with <2% error and electrical reactive power with <~2% error. 2 D axial symmetric finite element models were obtained, which describe the measured results with less than a 2% difference (i.e. an ‘error’ of the same magnitude as the measurement uncertainty). Heating and reactive power results predicted by the FEM model are in excellent agreement with analytical solutions from 50 Hz to 500 kHz (differences from <1% to 6%).

A modified 1D short coil correction factor is presented which accounts for the interaction of the coil and work piece geometry, electrical properties and operating frequency, on the average magnetic flux density of the coil/work piece air-gap and the resulting heating rate. Using this factor, the average magnetic flux density in the air-gap can be estimated analytically within 2-3% and the heating rates of billets of known electrical properties can be estimated, with typical errors on the order of 5%.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xii, 57 p.
Induction, heating, billets, coils, magnetic fields
National Category
Materials Engineering
urn:nbn:se:kth:diva-123783 (URN)978-91-7501-810-2 (ISBN)
2013-06-11, Sal D41, Lindstedtsvägen 17, KTH, Stockholm, 14:00 (English)

QC 20130618

Available from: 2013-06-18 Created: 2013-06-18 Last updated: 2013-06-18Bibliographically approved

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Kennedy, Mark W.Aune, Ragnhild E.
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