Induction heating is commonly used to heat cylindrical workpieces and rectangular shaped parts including RCS (round-corner-square) billets and bars, blooms, slabs, and plates. The uniformity specifications may include maximum tolerable thermal gradients, such as surface-to-core, end-to-end, and side-to-side. A nonuniformly heated billet (over-heated and under-heated areas) can cause problems at subsequent process stages. Depending on the application, different coil designs having various power levels and frequencies are used to uniformly heat the product.
The edges of RCS billets can be nonuniformly heated depending on heating process parameters. The transverse electromagnetic edge effect and thermal edge effect are primarily responsible for temperature nonuniformity within the transverse cross section of the RSC billets, including edge/corner regions. Experience gained on previous jobs and the ability to model induction processes provide a comfort zone when designing new induction bar and billet heating systems. The combination of advanced modeling software and a sophisticated engineering background enables manufacturers of induction heating machinery to quickly determine process details that could be costly, time-consuming, and in some cases, extremely difficult, if not impossible, to determine experimentally.
To illustrate, the figure shows two-dimensional temperature profiles representing the dynamics of induction heating the top-right cross section (1/4 of the part) of a 4-in. (0.1-m) RCS carbon steel bar using a frequency of 500 Hz. Appreciable temperature gradients may occur within the bar cross section. It is important to have a clear understanding of the magnitude of these gradients during the initial and intermediate heating stages (particularly the initial stage) to prevent cracking.
• V. Rudnev, D. Loveless, et al., Handbook of Induction Heating, Marcel Dekker, NY, 2003.
• V. Rudnev, Successful induction heating of RCS billets, Forge, July, p15-18, 2008.