Flame Hardening and Induction Heating: What are The Differences?

17 June 2016

In the foundry, blazing hot furnaces melt metal and produce castings, parts that are imbued with crude properties. It is then down to special alloy-refining facilities to alter those material characteristics, to intelligently manipulate key microcrystalline properties within the alloy so that the metal suits its application. Of these newly injected features, hardness and durability rank very high, perhaps because these are the features we all associate with a toughened metal. Anyway, regardless of these musings, let’s take a look at two of the easily identifiable hardening techniques, the processes we know as flame hardening and induction heating.

  • Induction Heating – An alternating current case hardens metal parts. Placed in the heart of a mammoth copper coil, the part experiences the effects of a rapidly reversing magnetic field. Induction currents then flow in the part, which causes the component to heat until it reaches its transformative temperature range. Suspended at this point, the generated heat surface-hardens the metal. Case hardened depth depends on the period of time the part is held at its transformative temperature and the frequency of the alternating current applied. The Lower the frequency the deeper the heat penetration.
  • Flame Hardening – This hardening method employs a highly energetic flame, a torch-like nimbus of fire that congregates on the exterior of the product. Indeed, intense flames that exhibit such intense output can only be achieved by applying an oxy-acetylene torch or a similarly combustible gas. Unlike the induction method, there’s a certain amount of leeway to be found. The flame head can be stationary or mobile, for example, and there’s an option to integrate a quench stage.
    Key Differences between Flame Hardening and Induction Heating Method

Both of these fine engineering processes yield excellently finished metal components, parts that have been case hardened to enhance the mechanical properties of the product. Still, there are differences to be found, and we should clarify those contrasting features. First of all, the induction process is a whole-unit one, a technique that uniformly case hardens a subject part. Conversely, flame hardening relies on convection and conduction, two influences that are hard to associate with uniform distribution. Similarly, the reliability factor of the induction method favours automation and mass production. Of course, these comparisons aren’t all characterized by a one-sided battle. The flame hardening and induction heating contest sides with the flame when cost is a factor, plus a focused flame can selectively case harden complex geometrical profiles.

Singled out as a mass production champion, the induction hardening mechanism is typically preferred, but the flame still has its place as a cost-effective and versatile hardening solution.

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