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Eldec’s low-frequency technology ensures higher process reliability

  • 01-Feb-2019
  • Articles|Technical Articles

By using low-frequency generators for induction heating, the entire process benefits from shorter cycle times and higher reproducibility.
Faster, more precise, more efficient - this is the basis on which induction heating has conquered many areas of application. The process reveals its typical strengths, such as easy process integration, high productivity and low energy consumption, for example, in heating processes applied prior to welding and joining, in hardening of bonding agents or in preheating when impregnating with resin. The experts at EMAG eldec know these advantages inside out: For more than 30 years, this company has been developing high-quality and robust generators for induction heating. The specialists are currently expanding their portfolio with low-frequency technology (LF). Concrete application examples make this very clear: The entire process benefits from shorter cycle times and higher reproducibility.
Welding and joining processes are particularly challenging for car manufacturing, since tremendous unit volumes must be machined within a minimal cycle time and without any unacceptable changes to the material structure - this is why induction heating often is an indispensable component of the interlinked overall process. Technology helps to quickly bring the component to the temperature required for the process. The main process starts immediately thereafter. However, this must not lead to any overheating of the component, which would result in loss of hardness, oxidation or unacceptable deformation. 
LF technology wins in trials
The advantages that EMAG eldec LF generators (low frequency) provide in this context are illustrated by a current application example from the eldec technology center: The goal here was to heat up a simple corona (similar to a gear) to a temperature of at least 200°C and no more than 370°C - and this with the shortest possible cycle time and highest possible process reliability. To achieve this, the experts used a numerical calculation to comparatively analyse the induction heating with a low frequency as well as with a typical medium frequency. 
The results were clear:
  • When using a low frequency of 2 kHz and a process time of five seconds, the desired heating pattern of at least 200°C appears throughout the corona (see Figure). 
  • If a medium frequency of 12.5 kHz is used, the admissible maximum temperature must be increased to 420°C. Otherwise, the minimum temperature of 200°C will not be reached throughout the corona within the targeted five seconds. However, the higher maximum temperature is not admissible.
  • As an alternative, the process time can also be increased when medium frequencies are used. This will nevertheless require a heating time of 8.5 seconds to achieve the desired temperature distribution (without exceeding the maximum temperature).
Faster heating within the volume
“We use numerical calculations to design processes faster and more accurately as would be possible when proceeding by trial and error—in other words, start by building an inductor, testing it, redesigning it and so on. The results also translate very well into practice from a qualitative standpoint and in this respect they make the advantages that the LF technology provides very clear,” explained Dirk Schlesselmann, Deputy Head of Application Technology Research and Development at eldec.
He added, “The lower frequencies heat up the inside of the volume faster because the magnetic field penetrates into the component. This is why we can significantly reduce the cycle time compared to when using medium frequencies. Moreover, it’s easier to remain within the desired temperature process window and the risk of overheating recedes. Not least, the occurring temperature gradients are smaller. And, in the end, this means that the risk of cracks forming on the component is smaller.” With that in mind, the induction specialists at EMAG eldec already offer a wide range of generators with LF technology (power output: 50 to 500 kW, frequency range: 2 to 8 kHz). 
Their potential areas of application are tremendous: The technology offers great benefits to applications, such as preheating prior to welding gear wheels, joining of stators in electric motor housings, impregnating stators or annealing after hardening, for instance. “In principle, it can make sense wherever heating within the volume should be performed at low cycle times. However, our LF generators not only ensure faster processes, but also operate with higher process reliability. The devices also score points with their cutting-edge technology. They use the robust and well-established IGBT transistor technology, have an efficiency of more than 90 percent and their energy is precisely measured out. We also want to bring these benefits to the LF segment of the market in a targeted manner as of today,” said Schlesselmann.

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