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Empirical Verification of a Short Coil Correction Factor
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The magnetic field produced in the air-gap by any particular 'short coil' at a fixed current, is affected by a highly complex interaction of the coil and work piece geometries and changes in frequency. A frequency modified semi-empirical short coil correction factor, based upon the formula published by Vaughan and Williamson in 1945, is presented and experimentally verified. This new equation is shown to predict the total system reactive power and the average magnetic flux at the surface of the work piece with typical differences of less than 2% at 50 Hz AC and to accurately predict work piece heating rates typically within 5% for aluminum billets at 50 Hz to 500 kHz AC. The work piece real and reactive powers, and total system reactive power are compared with both analytic and 2D axial symmetric FEM model solutions, as a function of operating frequencies from 50 Hz to 500 kHz. Measured flux density is compared to FEM and analytical predictions at 50 Hz.

Keyword [en]
Coils, Induction heating, Magnetic fields
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-123782OAI: oai:DiVA.org:kth-123782DiVA: diva2:630111
Note

QS 2013

Available from: 2013-06-18 Created: 2013-06-18 Last updated: 2013-06-18Bibliographically 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.
Keyword
Induction, heating, billets, coils, magnetic fields
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-123783 (URN)978-91-7501-810-2 (ISBN)
Presentation
2013-06-11, Sal D41, Lindstedtsvägen 17, KTH, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 20130618

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

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CiteExportLink to record
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Output format
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