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Magnetic Fields and Induced Power in the Induction Heating of Aluminium Billets
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
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 [en]
Induction, heating, billets, coils, magnetic fields
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-123783ISBN: 978-91-7501-810-2 (print)OAI: oai:DiVA.org:kth-123783DiVA: diva2:630122
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
List of papers
1. Improved short coil correction factor for induction heating of billets
Open this publication in new window or tab >>Improved short coil correction factor for induction heating of billets
2012 (English)In: 3rd International Symposium on High Temperature Metallurgical Processing, 2012, 373-382 p.Conference paper, Published 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.

Keyword
Billet, Heating, Induction, Magnetic field, Short coil
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-89169 (URN)10.1002/9781118364987.ch46 (DOI)2-s2.0-84860809974 (Scopus ID)978-111829141-2 (ISBN)
Conference
3rd International Symposium on High-Temperature Metallurgical Processing - TMS 2012 Annual Meeting and Exhibition; Orlando, FL; 11 March 2012 through 15 March 2012
Note

QC 20120803

Available from: 2012-02-14 Created: 2012-02-14 Last updated: 2013-09-11Bibliographically approved
2. Analytical and FEM modeling of aluminum billet induction heating with experimental verification
Open this publication in new window or tab >>Analytical and FEM modeling of aluminum billet induction heating with experimental verification
2012 (English)In: Light Metals 2012, John Wiley & Sons, 2012, 269-275 p.Conference paper, Published paper (Refereed)
Abstract [en]

Induction heating is commonly used in the re-heating of aluminum billets before forging or extrusion. Powerful finite element modeling (FEM) tools are available to assist in the design of such processes; however, such models should be validated by comparison with analytical solutions or experimental results to ensure accuracy. Induction heating experiments have been performed using a number of different coil designs and work piece dimensions at 50 Hz. Aluminum alloys with different electrical conductivities have been used, i.e. 6060 and A356. Process parameters such as: current, power, magnetic field, electrical conductivity, etc. have been measured with high precision instrumentation. Experimental data are presented and compared with equivalent 1D analytical and 2D axial symmetric FEM modeling results. The effect of frequency on the induction heating process is reviewed using the validated analytical and FEM models. Some recommendations are given with respect to appropriate modeling techniques, boundary conditions and numerical mesh sizes.

Place, publisher, year, edition, pages
John Wiley & Sons, 2012
Series
Light Metals (Year), ISSN 0147-0809
Keyword
Ceramic foam filters, CFF, Electromagnetic, Filtration
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-100045 (URN)10.1002/9781118359259.ch47 (DOI)2-s2.0-84958598303 (Scopus ID)978-111829139-9 (ISBN)
Conference
Light Metals 2012 - TMS 2012 Annual Meeting and Exhibition; Orlando, FL; 11 March 2012 through 15 March 2012
Note

QC 20120803

Available from: 2012-08-03 Created: 2012-08-03 Last updated: 2013-09-11Bibliographically approved
3. Empirical Verification of a Short Coil Correction Factor
Open this publication in new window or tab >>Empirical Verification of a Short Coil Correction Factor
(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
Coils, Induction heating, Magnetic fields
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-123782 (URN)
Note

QS 2013

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

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