Magnetic Flux Controllers in Induction Heating and Melting
MAGNETIC FLUX CONTROLLERS are materials other than the copper coil that are used in induction systems to alter the flow of the magnetic field. Magnetic flux controllers used in power supplying components are not considered in this article. Magnetic flux controllers have been in existence since the development of the induction technique. Michael Faraday used two coils of wire wrapped around an iron core in his experiments that led to Faraday’s law of electromagnetic induction, which states that the electromotive force (emf) induced in a circuit is directly proportional to the time rate of change of the magnetic flux through the circuit. After the development of the induction principle, magnetic flux controllers, in the formof stacks of laminated steel, found widespread use in the development of transformers for more efficient transmission of energy (Ref 1, 2). Magnetic cores gained widespread use in the transformer industry because they increased the amount of magnetic flux produced with the same alternating current. The higher the magnetic flux, the higher the emf, which results in an increase in energy transfer efficiency from the primary winding to the secondary winding. Similar to transformers, magnetic cores were used on early furnaces for induction melting (Ref 1, 2). The benefits of magnetic flux controllers vary depending on the application. For induction heating, magnetic flux controllers can provide favorable and unfavorable paths for magnetic flux to flow, resulting in increased heating in desired areas and reduced the heating in undesirable areas, respectively. Magnetic flux controllers are not used in every induction heating application, but their use has increased (Ref 3, 4).
Virtual Prototyping of Induction Heat Treating
The time between a product’s definition and production is constantly shrinking. To meet these requirements, extensive use of virtual prototyping has replaced physical models in the mechanical design process. As a result of this, the induction heat treating process developer will often times not receive a quantity of parts for heat treatment until a few weeks prior to having to deliver samples. This makes it nearly impossible to produce good quality parts on time using a traditional test and trial method. The development focus shifts to “just getting a pattern” rather than developing a robust production process. To meet the modern development requirements, the same methods that have led to significant improvements in the mechanical design process are applied to induction heat treating. Virtual prototyping tools include electromagnetic, thermal and metallurgical finite element analysis along with 3D CAD software. Virtual prototyping allows for the study of a much larger design space in a shorter period of time at lower cost. Final process validation is preformed on real equipment. A case story of an induction heat treating process of wheel hub hardening developed with virtual prototyping is presented. Savings achieved with the virtual tools are discussed.
Modeling Coherent Backscattering Errors in Fiber Optic Gyroscopes for Sources of Arbitrary Line Width
We present a new model of the noise and drift induced by coherent backscattering in a fiber optic gyroscope (FOG) interrogated with a light source of arbitrary temporal coherence. This study is critical to understand whether a FOG driven with a laser instead of a broadband source can attain high sensitivity and stability, which would have the overwhelming benefit of improving the FOG scale factor stability by at least ten-fold and would enable the use of FOGs for inertial navigation of aircrafts. Analytical and numerical solutions bring to light two significant new predictions. First, coherent-backscattering noise can be made negligibly small by utilizing a laser with a very narrow linewidth (less than ~ 20 kHz), although in this regime the drift is high. Second, by using a laser with a broad linewidth (greater than ~ 10 MHz), both the noise and the drift are low enough for aircraft inertial navigation. The dependencies of the noise and drift on fiber loss, loop coupling coefficient, and backscattering coefficient are also presented to define the optimum mode of operation of this new class of FOGs.